Base film for membrane switch and membrane switch

The present invention relates to a base film for a membrane switch made of a biaxially oriented polyester film containing polyethylene-2,6-naphthalene dicarboxylate as a main component. More specifically, the present invention relates to a base film for a membrane switch having excellent handleability and durability, particularly a base film for a membrane switch suitable for use in an in-vehicle device of an automobile which may be exposed to a high temperature.

The membrane switch is a switch in which contacts (electrodes) facing each other are arranged on opposite surfaces of two base films having spacers interposed therebetween. Then, by pressing the base film, that is, by changing the distance between the base films, switching actions such as conductivity and insulation can be easily performed. In recent years, membrane switches have been widely used as key pads for mobile phones and portable personal computers, and various control panel switches for household electric appliances such as VTRs and microwave ovens.

Since the switching action of the membrane switch is repeated pressing, the base film used is required to have flexibility and deformation resistance. Conventionally, polyethylene terephthalate (hereinafter, may be abbreviated as "PET") film is generally used as a base film for a membrane switch because of its deformation resistance, adhesion to electrodes, adhesion to printing paste, and the like. Has been widely used in.

However, recently, in automobile-related parts (car audio, car air conditioner, car navigation, etc.), the use of membrane switches and remote control switches for operation panels has become widespread. Therefore, the base film of the membrane switch is required to have deformation resistance under high temperature, which cannot be withstood by PET film. For example, it is said that the temperature inside the car reaches about 80 ° C during the daytime in summer, and the temperature inside the car may exceed the glass transition temperature (Tg) of PET. In such an environment, when a PET film is used as a base film for a membrane switch, the PET film is deformed due to a load applied at a high temperature, and the deformation is not eliminated even after the load is removed. The switch malfunctions because it bends.

As a remedy for this, Japanese Patent Publication No. 4-75610 proposes to use a polyethylene naphthalene carboxylate (hereinafter sometimes abbreviated as "PEN") film, which has a higher glass transition temperature than PET film, as the base film. .. That is, in Japanese Patent Publication No. 4-75610, in a membrane switch in which contacts facing each other are arranged on opposite surfaces of two base films, the F-5 value (5% elongation stress) is set as at least one base film. 11kg / mm²That's it, the density is 1.375g / cm³A membrane switch using a biaxially oriented polyethylene naphthalene carboxylate film having the following and a heat shrinkage rate of 1.0% or less when heated at 120 ° C. for 30 minutes is disclosed.

In addition, in Japanese Patent Publication No. 6-4276, the haze increase rate defined by the following formula when heat-treated at 150 ° C for 2 hours Haze increase rate = {(H2-H1) / H1} x 100 (%) (Here, H1 is the haze value before the heat treatment, and H2 is the haze value after the heat treatment.) Is 20% or less, and the heat shrinkage rate at that time is the film forming direction (the direction of travel when the film is continuously formed, and the longitudinal direction, the longitudinal direction, the continuous film forming direction, or the MD direction of the film. For membrane switches made of polyethylene naphthalate, which are 0.5% or less in both the width direction (the direction orthogonal to the film forming direction in the in-plane direction of the film and also referred to as the lateral direction or TD). Polyester films are disclosed.

<p> However, recently, the quality required for the base film for membrane switches has become more stringent, and it has been pointed out that the PEN film also lacks deformation resistance and durability. </p><p> In response to such changes in required quality, Republished No. 99/37466 discloses that the deformation resistance can be improved by subjecting the PEN film to a specific heat treatment. However, in the handling in the processing process of the membrane switch, the heat treatment temperature before and after circuit printing is restricted by the method of the publication. Therefore, there is a demand for a film for a membrane switch base material which is excellent in handleability in a processing process and also has excellent durability. </p>

<p> A first object of the present invention is a membrane that solves the above-mentioned problems of the prior art and has excellent film handleability and durability, and is used in an in-vehicle device of an automobile that may be exposed to a particularly high temperature. The present invention relates to a base film suitable for a switch. A second object of the present invention relates to a base film for a membrane switch, which has excellent workability when punching a film into the shape of a membrane switch. </p><p> Still other objectives and advantages of the present invention will become apparent from the following description. </p><p> According to the present invention, the above-mentioned objects and advantages of the present invention are, firstly, It consists of a biaxially oriented polyester film containing polyethylene-2,6-naphthalenedicarboxylate as the main component, and the film has a refractive index in the range of 1.770 to 1.790 on both surfaces in at least one direction in the film forming direction and the width direction. It is achieved by a base film for a membrane switch in which the difference in refractive index between the two surfaces is 0.015 or less in absolute value. </p><p><u style="single"> Sa</u>Also, according to the present invention, the above object and advantages of the present invention are:<u style="single">2</u>To It is composed of a biaxially oriented polyester film containing polyethylene-2,6-naphthalenedicarboxylate as a main component, and the film has a refractive index of 1.770 to both surfaces in at least one direction of (1) film forming direction and width direction. It is in the range of 1.790, and the difference in refractive index between the two surfaces is 0.015 or less in absolute value, and (2) the melting subpeak temperature measured by a differential scanning calorimeter (DSC) is 220 ° C or more and 250. It is also achieved by a membrane switch substrate film that is less than or equal to ° C and the difference between the melting subpeak temperature on one surface of the film and the melting subpeak temperature on the other surface is less than or equal to 6 ° C in absolute value. .. </p><p> According to the present invention, the above object and advantage of the present invention are:<u style="single">3</u>To The first above<u style="single">Or</u>No.<u style="single">2 of</u>This is achieved by the base film for a membrane switch of the present invention, and a membrane switch composed of a spacer and an electrode.</p>

<p> The base film for a membrane switch of the present invention is excellent in handleability and durability of the film. In particular, it is suitable for membrane switches used in in-vehicle equipment of automobiles that may be exposed to high temperatures. </p>

&lt;Polyethylene-2,6-naphthalene carboxylate&gt; The polymer constituting the biaxially oriented polyester film of the present invention contains polyethylene-2,6-naphthalene dicarboxylate (hereinafter, may be referred to as PEN) as a main component, and may be a copolymer or a mixture. The main term here is that ethylene-2,6-naphthalene carboxylate is 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 95 mol% or more of all repeating units of the polymer. That is, it is sufficient that the original characteristics of the biaxially oriented polyester film of the present invention are not extremely lost, and the permanent deformation resistance when used at a high temperature can be ensured.

In the case of a copolymer, a compound having two ester-forming functional groups in the molecule can be used as the copolymerizing component constituting the copolymer other than the main component ethylene-2,6-naphthalene dicarboxylate. Such compounds include oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecandicarboxylic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, phenylindandicarboxylic acid, 2 , 7-Naphthalenedicarboxylic acid, tetraphosphonedicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid and other dicarboxylic acids can be preferably used. Further, oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid can also be preferably used. Furthermore, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, ethylene oxide adduct of bisphenol sulfe, ethylene oxide adduct of bisphenol A, diethylene glycol, polyethylene oxide glycol, etc. Dihydric alcohols and the like can also be preferably used.

Not only one of these compounds but two or more of these compounds can be used at the same time. Among these compounds, isophthalic acid, terephthalic acid, 4,4'-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid and p-oxybenzoic acid are used as acid components, and trimethylene glycol is used as a glycol component. Hexamethylene glycol Neopentyl glycol and ethylene oxide adducts of bisphenol sulfone are preferred.

Further, the PEN used in the present invention may be one in which a part or all of the terminal hydroxyl group and / or the carboxyl group is blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Further, the PEN used in the present invention is a copolymer of a trifunctional or higher ester-forming compound such as a very small amount of glycerin or pentaerythritol within a range in which a substantially linear polymer can be obtained. You may.

Further, the polymer constituting the base film for the membrane switch of the present invention may be a mixture of other organic polymers in addition to PEN. Organic polymers to be mixed with PEN include polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene-4,4'-tetramethylenediphenyldicarboxylate, polyethylene-2,7-naphthalene carboxylate, and polytrimethylene. -2,6-Naphthalene dicarboxylate, polyneopentylene-2,6-naphthalene dicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene dicarboxylate, etc. it can. Among these, polyethylene isophthalate, polytrimethylene terephthalate, polytrimethylene-2,6-naphthalene dicarboxylate, and poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene dicarboxylate are preferable.

Not only one type of organic polymer to be mixed with these PENs, but two or more types may be used in combination. The proportion of the organic polymer mixed with PEN is at most 20 mol%, preferably 10 mol% or less, particularly preferably 5 mol% or less, in repeating units of the polymer. The production of such a mixture can be carried out by a generally known method for producing a polyester composition.

The polyester constituting the base film in the present invention can be obtained by a conventionally known method. For example, after a method of directly obtaining a low polymerization degree polyester by a reaction of a dicarboxylic acid and a glycol, or a method of transesterifying a lower alkyl ester of a dicarboxylic acid and a glycol using a conventionally known transesterification catalyst, a polymerization catalyst is used. The polymerization reaction may be carried out in the presence of.

Examples of the transesterification reaction catalyst include compounds containing sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt, and these may be used alone or in combination of two or more. Examples of the polymerization catalyst include antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds such as germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or partial hydrolyzates thereof, and oxalic acid. Examples include titanium compounds such as titanyl ammonium, titanyl potassium oxalate, and titanium trisacetylacetonate.

When polymerization is carried out via a transesterification reaction, phosphorus compounds such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate and orthophosphorus acid are added for the purpose of inactivating the transesterification catalyst before the polymerization reaction. To. The content of such a phosphorus compound is preferably 20 to 100 ppm by weight in PEN as a phosphorus element from the viewpoint of thermal stability of polyester. The polyester can also be melt-polymerized and then chipped and solid-phase polymerized under heating and reduced pressure or in an inert air stream such as nitrogen.

The intrinsic viscosity of polyester containing PEN as a main component is preferably 0.40 dl / g or more and 0.90 dl / g or less. It is more preferably 0.43 to 0.85 dl / g, and particularly preferably 0.45 to 0.80 dl / g. If the intrinsic viscosity is less than the lower limit, the film becomes brittle and breakage may easily occur during film formation. Further, when the intrinsic viscosity of the film exceeds the upper limit, it is necessary to considerably increase the intrinsic viscosity of the polymer, and the usual synthetic method requires a long time for polymerization, which may deteriorate the productivity. The intrinsic viscosity is a value (unit: dl / g) measured at 35 ° C using o-chlorophenol as a solvent.

&lt;Additives&gt; The film for a membrane switch of the present invention preferably contains a small proportion of inert particles in order to impart slipperiness to the film. Examples of such inert particles include inorganic particles such as spherical silica, porous silica, calcium carbonate, alumina, titanium dioxide, kaolin clay, barium sulfate and zeolite, and organic particles such as silicone resin particles and crosslinked polystyrene particles. Can be done. Inorganic particles are preferably synthetic products rather than natural products because of their uniform particle size and the like. The crystal morphology, hardness, specific gravity, and color of the inorganic particles are not particularly limited, and can be used according to the purpose.

Specific inorganic particles include calcium carbonate, porous silica, spherical silica, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, etc. Examples thereof include titanium oxide, zirconium oxide, and lithium fluoride. Among these, calcium carbonate particles, spherical silica particles, porous silica particles, and plate-shaped aluminum silicate are particularly preferable.

Examples of the organic particles include organic salt particles and crosslinked polymer particles. Examples of such organic salt particles include terephthalate salts such as calcium oxalate, calcium, barium, zinc, manganese, and magnesium. Examples of the crosslinked polymer particles include a single body or a copolymer of a vinyl-based monomer such as divinylbenzene, styrene, acrylic acid, and methacrylic acid. Furthermore, organic particles such as polytetrafluoroethylene, silicone resin, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin are also preferably mentioned. Among these crosslinked polymer particles, silicone resin particles and crosslinked polystyrene particles are particularly preferable.

The particle size of the inert particles added to these films is preferably 0.05 μm or more and 5 μm or less, and more preferably 0.08 μm or more and 3.5 μm or less, for each type of particles. It is particularly preferably 0.10 μm or more and 3 μm or less. The total amount of the inert particles added to the film is preferably 0.05% by weight or more and 3% by weight or less, more preferably 0.08% by weight or more and 2.5% by weight or less, and 0.1% by weight or more and 2.0% by weight. It is particularly preferable that it is less than or equal to%.

The inert particles added to the film may be a single component selected from the above-exemplified examples, or may be a multi-component containing two components or three or more components. Moreover, in the case of a single component, two or more kinds of particles having different average particle diameters may be contained.

The average particle size of the inert particles was measured using a CP-50 type Centrifugal Particle Size Annalyzer manufactured by Shimadzu Corporation, and calculated based on the centrifugal sedimentation curve obtained from the measurement. It is a value obtained by reading the particle size corresponding to 50% by weight from the integrated curve of the particles of each particle size and their abundance (see "Particle Size Measurement Technology", Nikkan Kogyo Shimbun, 1975, pp. 242 to 247).

The base film of the present invention contains calcium carbonate particles having an average particle size of 0.3 μm or more and 0.8 μm or less in an amount of 0.1% by weight or more and 0.4% by weight or less, and / or spherical silica having an average particle size of 0.1 μm or more and 0.6 μm or less. It is particularly preferable to contain 0.03% by weight or more and 0.5% by weight or less of the particles, and / or 0.03% by weight or more and 0.4% by weight or less of silicone particles having an average particle size of 0.1 μm or more and 0.6 μm or less. Further, particles of the same type but different particle sizes may be contained at the same time, and in that case, the content of the entire Inactive particles of the same type may be within the above range.

The base film of the present invention can be blended with a crystal nucleating agent, an antioxidant, a heat stabilizer, a lubricant, a flame retardant, an antistatic agent, a polysiloxane, and the like, depending on the intended use.

The timing of adding the inert particles and other additives is not particularly limited as long as it is at the stage until the polyester containing PEN as the main component is formed into a film. For example, it may be added at the polymerization stage, or at the time of film formation. It may be added. From the viewpoint of uniform dispersion, it is preferable to add inert particles or other additives to ethylene glycol to obtain a master chip by adding a high concentration at the time of polymerization, and to dilute the obtained master chip with an additive-free chip.

&lt;Difference in melting subpeak temperature (Tsm) between front and back surface of base film&gt; The melting subpeak temperature (Tsm) measured by the differential scanning calorimeter (DSC) of the base film of the present invention needs to be 220 ° C. or higher and 250 ° C. or lower. Moreover, the absolute value (| Tsm (front surface)-Tsm (back surface) |) of the difference in melting subpeak temperature (Tsm) between one surface (temporarily "front surface") and the other surface (provisionally "back surface") of the film is , Must be below 6 ° C.

If the melting subpeak temperature is less than the lower limit, minute cracks and burrs are likely to occur on the end face of the film cut into a sheet shape. On the other hand, when the melting subpeak temperature exceeds the upper limit, the toughness of the film is lost and the durability of the switch deteriorates. When the absolute value of the difference in melting subpeak temperature (Tsm) between the front and back surfaces of the film (| Tsm (front surface) -Tsm (back surface) |) exceeds 6 ° C, the end face of the film cut into a sheet is formed. Fine cracks and burrs are likely to occur, and the film is likely to have curl after being wound up and stored as a roll for a while.

The melting subpeak temperature (Tsm) is more preferably 225 ° C or higher and 245 ° C or lower, and particularly preferably 230 ° C or higher and 245 ° C or lower. The absolute value of the difference in melting subpeak temperature (Tsm) between the front surface and the back surface of the film (| Tsm (front surface) -Tsm (back surface) |) is more preferably 5 ° C or less, and particularly preferably 4 ° C or less. Is.

&lt;Refractive index of base film&gt; On each surface of the film of the present invention, the refractive index in at least one direction in the film forming direction and the width direction needs to be 1.770 or more and 1.790 or less. More preferably, it is 1.772 or more and 1.788 or less. In the present invention, unless otherwise specified, the film-forming direction is the traveling direction when the film is continuously formed, and may be referred to as the longitudinal direction, the longitudinal direction, the continuous film-forming direction or the MD direction of the film. Further, in the present invention, the width direction is a direction orthogonal to the film forming direction in the in-plane direction of the film, and may be referred to as a lateral direction or TD. If the refractive index in both the film forming direction and the width direction of the film is less than the lower limit, the durability of the film deteriorates. On the other hand, when the refractive index in both the film forming direction and the width direction of the film exceeds the upper limit, cutting frequently occurs in the film production. Here, the refractive index of the film was measured for each surface of the film using a laser refractometer (measurement wavelength: 633 nm) using the principle of the Abbe refractometer.

&lt;Difference in refractive index between front and back surface of base film&gt; In the base film of the present invention, the refractive index on one surface (temporarily "front surface") and the refraction on the other surface (tentatively "back surface") of the film in at least one direction in which the refractive index is 1.770 or more and 1.790 or less. The absolute value of the difference from the rate (| Refractive index (front side)-Refractive index (back side) |) must be 0.015 or less. It is more preferably 0.013 or less, and particularly preferably 0.011 or less. If the absolute value of the difference in refractive index between the front and back surfaces of the film in at least one direction, where the refractive index is 1.770 or more and 1.790 or less, exceeds 0.015, minute cracks or burrs are likely to occur on the end face of the film cut into a sheet shape. After winding the film and storing it as a roll for a while, the film tends to become curly.

&lt;Refractive index in the width direction of the base film&gt; The refractive index in the width direction on each surface of the base film of the present invention is preferably 1.770 or more and 1.790 or less. More preferably, it is 1.772 or more and 1.788 or less. The refractive index was measured for each surface of the film using a laser refractometer (measurement wavelength: 633 nm) using the principle of the Abbe refractometer. If the refractive index in the width direction of the film is less than the lower limit, the durability of the film may deteriorate.

On the other hand, when the refractive index of the film exceeds the upper limit, the frequency of cutting occurs in the production of the film increases.

&lt;Phosphorus compound and titanium compound contained in the base film&gt; As described above, the base film of the present invention preferably contains a phosphorus compound. Examples of such phosphorus compounds include phosphoric acid, phosphorous acid, phosphonic acid, phosphonate compounds and derivatives thereof, and these may be used alone or in combination of two or more. Among these, as the phosphorus compound, a phosphonate compound represented by the following formula (I) is preferable.<chemistry num="1"><img file="JP4528126B2_D0001.tif" /></chemistry>

Here, in the formula, R¹And R²Is an alkyl group with 1 to 4 carbon atoms, X is -CH₂-Or -CH (Y)-(Y indicates a phenyl group), R¹And R²May be the same or different.

Particularly preferred phosphorus compounds are carbomethoxymethanephosphonic acid, carboethoxymethanephosphonic acid, carbopropoxymethanephosphonic acid, carpoptoxymethanephosphonic acid, carbomethoxy-phosphono-phenylacetic acid, carboethoxy-phosphono-phenylacetic acid, carboprotoxy. -Phosphono-phenylacetic acid and carbobutoxy-phosphono-phenylacetic acid dimethyl ester, diethyl ester, dipropyl ester and dibutyl ester.

In the present invention, the preferred reason for these phosphonate compounds is that the reaction with the titanium compound proceeds relatively slowly as compared with the phosphorus compound usually used as a stabilizer, so that the catalytic activity of the titanium compound during the polycondensation reaction proceeds. This is because the duration of the above is long, and as a result, the amount of the catalyst added to the polyester can be reduced, and even if a large amount of stabilizer is added to the catalyst, the thermal stability of the polyester is not easily impaired.

These phosphorus compounds may be added at any time after the ester exchange reaction is substantially completed, for example, under atmospheric pressure before the polycondensation reaction is started, or under reduced pressure after the polycondensation reaction is started. It may be added at the end of the polycondensation reaction or after the completion of the polycondensation reaction, that is, after the polymer is obtained.

In the present invention, the catalyst used for producing PEN is preferably a titanium compound substantially soluble in PEN for the purpose of reducing foreign substances caused by the catalyst. That is, the amounts of the respective antimony elements and germanium elements derived from the antimony compound or the germanium compound that have been generally used as catalysts are based on the number of moles of the ethylene-2,6-naphthalenedicarboxylate component. It is preferably at most 5 mmol%. When the content of antimony element and germanium element exceeds 5 mmol%, problems such as precipitation of foreign substances caused by these catalysts occur.

The titanium compound is not particularly limited as long as it is soluble in the polymer, and examples of titanium compounds commonly used as polycondensation catalysts for polyesters include titanium acetate and tetra-n-butoxytitanium. Among these, a compound represented by the following formula (II), or a reaction product of a compound represented by the formula (II) and an aromatic polyvalent carboxylic acid represented by the following formula (III) or an anhydride thereof is preferable.<chemistry num="2"><img file="JP4528126B2_D0002.tif" /></chemistry>

Here, R in equation (II)³, R⁴, R⁵, R⁶Indicates an alkyl group and / or a phenyl group having 2 to 10 carbon atoms, respectively.<chemistry num="3"><img file="JP4528126B2_D0003.tif" /></chemistry>

Further, n in the above equation (III) represents an integer of 2 to 4.

The tetraalcoxide titanium represented by the above formula (II) is R.³, R⁴, R⁵, R⁶Is not particularly limited as long as it is an alkyl group and / or a phenyl group having 2 to 10 carbon atoms, respectively. Particularly preferable tetraalcoxide titanium represented by the above formula (II) is tetraisopropoxytitanium, tetrapropoxytitanium, tetra-n-butoxytitanium, tetraethoxytitanium, and tetraphenoxytitanium. Further, as the aromatic multivalent carboxylic acid represented by the above formula (III), phthalic acid, trimellitic acid, hemmellitic acid and pyromellitic acid are preferable. The aromatic multivalent carboxylic acid represented by the general formula (III) may be an anhydride thereof. In order to react the above titanium compound with the aromatic polyvalent carboxylic acid, a part of the aromatic polyvalent carboxylic acid or its anhydride is dissolved in a solvent, and the titanium compound is added dropwise thereto at 0 to 200 ° C. It suffices to react at temperature for 30 minutes or more.

The content of the titanium compound as a catalyst is preferably 4 mmol% or more and 15 mmol% or less as the titanium element, based on the number of moles of the ethylene-2,6-naphthalene dicarboxylate component. It is more preferably 6 mmol% or more and 12 mmol% or less, and particularly preferably 6 mmol% or more and 10 mmol% or less. If the content of the titanium compound is less than the lower limit, the productivity of PEN is lowered, and it is difficult to obtain PEN having a desired molecular weight. On the other hand, if the content of the titanium compound exceeds the upper limit, the thermal stability of the obtained PEN tends to decrease, and therefore, the molecular weight may be significantly reduced during melt extrusion during film production. The content of the titanium compound soluble in PEN referred to here refers to the titanium compound used as the transesterification reaction catalyst and the titanium compound used as the transesterification reaction catalyst in the case of going through the transesterification reaction. Show the total.

The base film of the present invention preferably contains the above-mentioned titanium compound as a catalyst and a phosphorus compound as a stabilizer at the stage of producing the resin composition. The contents of the titanium compound and the phosphorus compound preferably satisfy the following formulas (1) to (3) in combination with the above-mentioned conditions. 4 Ti 15 ... (1) 0.5 P / Ti 15 ... (2) 15 Ti + P 150 ... (3) In the formulas (1) to (3), Ti is the value (mmol%) obtained by dividing the number of moles of the titanium compound as a titanium element by the number of moles of the ethylene-2,6-naphthalenedicarboxylate component in the composition. Yes, P is a value (mmol%) obtained by dividing the number of moles of the phosphorus compound as a phosphorus element by the number of moles of the ethylene-2,6-naphthalenedicarboxylate component in the composition.

If (P / Ti) is less than the lower limit, the thermal stability of the obtained PEN deteriorates, and heat-deteriorated substances may precipitate near the die slit and contaminate the outlet portion of the slit and the peripheral portion of the die. On the other hand, if (P / Ti) exceeds the upper limit, the reactivity of PEN during polymerization is significantly reduced, and it may be difficult to obtain PEN having a desired molecular weight. A more preferable range of this (P / Ti) is 2 or more and 10 or less.

If (Ti + P) is less than the lower limit, the productivity in the film forming process by the electrostatic application method may decrease, and the uniformity of the film thickness may deteriorate. On the other hand, when (Ti + P) exceeds the upper limit, foreign matter derived from the catalyst is likely to be generated, albeit in a small amount, and foreign matter derived from the catalyst is precipitated near the die slit of the melt extruder during film production, and the film forming direction. It may cause streaky surface defects along the line. A more preferable range of this (Ti + P) is 25 or more and 100 or less.

The PEN in the present invention is an ester-forming derivative of 2,6-naphthalenedicarboxylic acid typified by 2,6-dimethylnaphthalate and ethylene glycol even when 2,6-naphthalenedicarboxylic acid and ethylene glycol are used as raw materials. May be used as a raw material. Among these, a production method via a transesterification reaction in which 80 mol% or more of the total dicarboxylic acid component used as a raw material is 2,6-dimethylnaphthalate is preferable. Among the production methods using 2,6-dimethylnaphthalate as a raw material, at least a part of the titanium compound is added before the start of the transesterification reaction so that the two catalysts, the transesterification reaction catalyst and the polycondensation reaction catalyst, are used in combination. The method is more preferable because the amount of the titanium compound added can be reduced. Further, it is preferable to carry out the transesterification reaction under a pressure of 0.05 MPa or more and 0.20 MPa or less because the amount of the titanium compound added can be further reduced.

&lt;Heat shrinkage rate&gt; When the base film of the present invention is heat-treated at 200 ° C. for 10 minutes, the heat shrinkage in the film-forming direction and the width direction is preferably 0.2% or more and 1.4% or less, and 0.3% or more and 1.3% or less. Is even more preferable. If the heat shrinkage rate after heat treatment at a temperature of 200 ° C for 10 minutes exceeds the upper limit, the dimensional change becomes large, and the flatness of the film may be deteriorated by the preheat treatment before processing into the membrane switch. On the other hand, if the heat shrinkage rate is less than the lower limit, the durability after using the membrane switch may deteriorate.

The difference in heat shrinkage between the film-forming direction and the width direction (heat shrinkage (MD) -heat shrinkage (TD)) when heat-treated at 200 ° C for 10 minutes is not particularly limited, but is flat. In order to prevent deterioration, it is preferable that the difference in heat shrinkage between the film forming direction and the width direction is -1.0% or more and 0.5% or less.

&lt;Thickness of base film&gt; The thickness of the base film for a membrane switch of the present invention is preferably 40 μm or more and 190 μm or less, more preferably 45 μm or more and 175 μm or less, and particularly preferably 50 μm or more and 160 μm or less. If the thickness of the film is less than the lower limit, the durability against repeated pressing may be insufficient. On the other hand, if the thickness of the film exceeds the upper limit, it becomes extremely difficult to bend, which is not preferable for a membrane switch.

The variation in thickness of the film of the present invention at an arbitrary location is preferably 10% or less, more preferably 8% or less, based on the central thickness of the film. The smaller the variation in film thickness, the more stable the membrane switch operates, which is preferable.

&lt;Surface roughness of base film (SRa)&gt; The surface roughness of the base film for a membrane switch of the present invention, that is, the three-dimensional center surface average roughness (SRa) is preferably 10 nm or more and 45 nm or less on at least one surface. It is more preferably 10 nm or more and 40 nm or less, and particularly preferably 12 nm or more and 35 nm or less. If SRa is less than the lower limit, after a large number of sheet-shaped films are stacked, when each film is sequentially fed to the switch manufacturing process, the films do not slip easily and poor feeding may occur. .. On the other hand, if SRa exceeds the upper limit, the films slip too much when a large number of sheet-shaped films are stacked, so that the films may be frequently displaced when they are stacked.

&lt;Density of base film&gt; The density of the base film of the present invention is 1.350 g / cm.³Above 1.376g / cm³The following is preferable. More preferably 1.352 g / cm³More than 1.365g / cm³Below, particularly preferably 1.354 g / cm³More than 1.363g / cm³It is as follows. If the density is less than the lower limit, the durability against repeated pressing may deteriorate. On the other hand, if the upper limit is exceeded, the crystallinity becomes too high and the toughness of the film is lost, so that the processability of the membrane switch may deteriorate. The density of the film is a value measured by the floating-sink method at 25 ° C. in a density gradient tube using an aqueous solution of calcium nitrate as a solvent.

&lt;Coating layer&gt; The base film of the present invention may be provided with a coating layer on at least one side thereof for the purpose of improving easy adhesion to the printing paste.

The coating layer is preferably made of at least one water-soluble or water-dispersible polymer resin selected from polyester resin, urethane resin, acrylic resin, and vinyl resin, and particularly preferably contains both polyester resin and acrylic resin. .. The polyester resin of the coating layer used in the present invention has a glass transition point (Tg) of 0 to 100 ° C, more preferably 10 to 90 ° C. The polyester resin is preferably a water-soluble or dispersible polyester, but may contain a small amount of an organic solvent.

Such a polyester resin comprises the following polybasic acid or an ester-forming derivative thereof and a polyol or an ester-forming derivative thereof. That is, the polybasic acid components include terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, and pyromellitic acid. , Dimeric acid, 5-sodium sulfoisophthalic acid and the like. A copolymerized polyester resin is synthesized using two or more of these acid components. In addition, hydroxycarboxylic acids such as maleic acid, itaconic acid and the like, and p-hydroxybenzoic acid, which are unsaturated polybasic acid components, can be used in a small amount. The polyol components include ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, and poly (ethylene oxide) glycol. , Poly (tetramethylene oxide) glycol, bisphenol A, ethylene oxide or propylene oxide adduct of bisphenol A and the like. The polyester resin used as the coating layer is formed of, for example, these monomers, but is not limited to the above-mentioned monomers.

The acrylic resin of the coating layer used in the present invention has a glass transition point (Tg) of -50 to 50 ° C, more preferably -50 to 25 ° C. The acrylic resin is preferably acrylic that is soluble or dispersible in water, but may contain some organic solvent. Such an acrylic resin can be copolymerized from the following acrylic monomers. The acrylic monomer includes alkyl acrylate and alkyl methacrylate (the alkyl group includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group and cyclohexyl. Groups, etc.); Hydroxy group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether; Contains carboxyl groups such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.) or salts thereof. Alkoxy, methalkoxy, N-alkylacrylamide, N-alkylmethalkoxy, N, N-dialkylacrylamide, N, N-dialkylmethacrylate (alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl) Group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxyacrylamide, N-alkoxymethacrylicamide, N, N-dialkoxyacrylamide, N, N-dialkoxy Methacrylate (alkoxy groups include methoxy group, ethoxy group, butoxy group, isobutoxy group, etc.), acryloylmorpholin, N-methylolacrylamide, N-methylolmethacrylate, N-phenylacrylamide, N-phenylmethacrylate and other amide groups. Contains monomer; Monomers of acid anhydrides such as maleic anhydride, itaconic anhydride; vinyl isocyanate, allylisocyanate, styrene, α-methylstyrene, vinylmethyl ether, vinyl ethyl ether, vinyl trialkoxysilane, alkyl maleic acid monoester, alkyl fumalic acid Monomers such as monoester, alkylitaconic acid monoester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate and butadiene can be mentioned. The acrylic resin used as the coating layer is not limited to those using these monomers.

The composition used in the present invention is preferably used in the form of an aqueous coating solution such as an aqueous solution, an aqueous dispersion or an emulsion in order to form a coating film. In order to form a coating film, if necessary, resins other than the above compositions, such as polymers having an oxazoline group, cross-linking agents such as melamine, epoxy and aziridine, antistatic agents, colorants and surfactants. , UV absorbers, lubricants (fillers, waxes), etc. can be added. Such a lubricant can be added as needed for the purpose of improving the slipperiness of the film or improving the blocking resistance.

The solid content concentration of the aqueous coating liquid is usually 20% by weight or less, and more preferably 1 to 10% by weight. If this ratio is less than 1% by weight, the applicability to the polyester film is insufficient, while if the upper limit is exceeded, the stability of the coating agent and the appearance of the coating may be deteriorated.

The coating layer can be firmly provided on the film by applying an aqueous coating solution to an unstretched film or a film that has been uniaxially stretched, and then stretching the film in two or one directions and heat-fixing the film. As the coating method, a roll coating method, a gravure coating method, a roll brushing method, a spray method, an air knife coating method, an impregnation method, a curtain coating method and the like can be used alone or in combination.

&lt;Manufacturing conditions&gt; The base film for a membrane switch of the present invention is a biaxially oriented film containing PEN as a main component. This biaxially oriented film is obtained by a usual method, for example, melting the polymer at a melting point or higher and extruding it from a die slit onto a casting drum whose temperature has been adjusted to around 60 ° C to adhere-cool and solidify it to obtain an unstretched film. This unstretched film can be produced by biaxially stretching in the vertical and horizontal directions, heat-fixing the film, and if necessary, relaxing the unstretched film in the vertical and / or horizontal directions. Film stretching is performed by known roll-type longitudinal stretching machines, infrared-heated longitudinal stretching machines, tenter clip-type transverse stretching machines, multi-stage stretching machines that perform these stretching in multiple stages, tubular stretching machines, oven-type longitudinal stretching machines, etc. It can be carried out using a simultaneous biaxial stretching machine or the like, but is not particularly limited. In the present invention, sequential biaxial stretching or simultaneous biaxial stretching may be used as long as the refractive index in at least one direction of the film formation direction and width direction can be controlled to 1.770 or more and 1.790 or less.

Next, the method for producing the polyester film of the present invention will be described in detail, but the present invention is not necessarily limited thereto.

First, the production by the simultaneous biaxial stretching method will be described. The vertical stretching mechanism of the simultaneous biaxial stretching machine is a conventional screw method in which a clip is placed in the groove of the screw to widen the clip interval, a pantograph method in which the clip spacing is widened using a pantograph, and a linear motor. There is a linear motor system that uses. Compared with the screw method and the pantograph method, the linear motor method is preferable because the film forming speed is faster and the conditions such as the draw ratio can be easily changed. Simultaneous biaxial stretching does not use a longitudinal stretching roller as in sequential biaxial stretching, so it has the advantage of reducing scratches on the film surface. Further, in general, since the unstretched film is stretched at the same time in the vertical direction and the horizontal direction, there is an advantage that the orientation in the vertical direction and the horizontal direction can be controlled more easily than the sequential biaxial stretching. Since these characteristics match the required characteristics of the film for a membrane switch of the present invention, simultaneous biaxial stretching can be adopted in the present invention.

Simultaneous biaxial stretching in the present invention is stretching for simultaneously orienting the film in the vertical and horizontal directions, and the film is conveyed while being gripped by clips at both ends using a simultaneous biaxial stretching machine. An operation of stretching in the vertical direction and the horizontal direction. Of course, it suffices if there is a portion in which the vertical and horizontal stretching are simultaneously stretched in time, and therefore, after the film is first stretched independently in the horizontal or vertical direction, the vertical and horizontal directions are required. Also included in the scope of the present invention is a method of simultaneously stretching and a method of further stretching the film independently in the lateral or longitudinal direction after simultaneous biaxial stretching.

In order to produce the film of the present invention, a film-like melt of PEN which has been melt-extruded at a temperature of, for example, 280 to 330 ° C after containing inert particles in a predetermined PEN has a surface temperature of 30 to 70 ° C. Quench on the surface of the rotary cooling drum set to C to obtain an unstretched film with an intrinsic viscosity of 0.40 to 0.90 dl / g. Drying before melt extrusion is preferably performed at 160 to 190 ° C. for 4 to 7 hours. The ratio of the thickness of the edge to the center of the unstretched film (edge thickness / center thickness) is preferably 1 or more and 10 or less, preferably 1 or more and less than 5, and more preferably 1 or more. , Less than 3. If the thickness ratio is less than 1 or exceeds the upper limit, film tearing or clip detachment occurs frequently, which is not preferable.

Next, this unstretched film is guided to a simultaneous biaxial stretching machine by gripping both ends of the film with clips, heated to 80 to 170 ° C in the preheating zone, and then in one step or two or more steps. Simultaneous biaxial stretching with an area magnification of 9 to 20 times (vertical magnification of 2 to 4.5 times) is performed at 120 to 170 ° C. Further, if necessary, the area may be further biaxially stretched at a temperature range of 140 to 245 ° C, one step or two steps or more, and the area magnification is 2 to 5 times. Subsequently, heat fixing is performed in a temperature range of 190 to 250 ° C. If necessary, heat fixing is performed, or relaxation treatment is performed in the cooling process from heat fixing. As such a relaxation treatment condition, a temperature range of 140 to 240 ° C. is preferable, and the relaxation treatment is performed in the vertical and horizontal directions, preferably in the range of 1 to 10% in each direction. In the case of the film for membrane switch of the present invention, the preheating temperature is preferably about 130 ° C, the stretching temperature is preferably about 145 ° C, and the heat fixing temperature is preferably about 240 ° C. After the relaxation treatment, the film is cooled to room temperature and wound up to obtain the desired simultaneous biaxial film. In the present invention, in order to impart functions such as easy adhesiveness, easy slipperiness, releasability, and antistatic property to the surface of the film, the polyester film is subjected to a step before or after simultaneous biaxial stretching. Coating of the coating on the surface can also be preferably performed.

The film of the present invention can also be produced by ordinary sequential biaxial stretching. As described above, the unstretched film of PEN obtained by a known method is heated to 80 to 170 ° C in the preheating zone, and then 120 to 180 ° C, more preferably 125 to 170 ° C, and particularly preferably 130 to. It is stretched 3.0 to 4.5 times, more preferably 3.2 to 4.2 times in the longitudinal direction at 160 ° C with an infrared heating type longitudinal stretching machine. Further, a roll-type longitudinal stretching machine may be used, and it is preferable to perform the stretching in a plurality of stages in order to stretch the stretch without difficulty in the longitudinal stretching. A desired PEN film can be obtained by longitudinally stretching, laterally stretching, and if necessary, heat-fixing or relaxation treatment.

For lateral stretching, after longitudinal stretching, the temperature is heated to 80 to 150 ° C again in the preheating zone, and then 120 to 180 ° C in the stenter.<u style="single">,side</u>It is preferable to multiply by 3.0 to 4.5 in the direction. More preferred transverse stretching temperatures are in the range of 125-170 ° C, especially 130-160 ° C. The more preferable lateral stretching ratio is 3.3 to 4.2 times. The heat fixation is preferably performed at 195 to 250 ° C for 0.3 to 50 seconds. The more preferred heat-fixing temperature is in the range of 205-245 ° C. Further, it is preferable to perform the thermal relaxation treatment at a temperature of 140 to 240 ° C. in the vertical direction and / or the horizontal direction in a relaxation rate range of 0.5 to 15%. As the stretching in the lateral direction, multi-step stretching may be used, which is divided into a plurality of steps.

In the above-mentioned production method (simultaneous biaxial stretching and sequential biaxial stretching) of the base film for a membrane switch of the present invention, the absolute value of the difference in the melting subpeak temperature (Tsm) between the front surface and the back surface of the film (| Tsm (front surface)- In order to keep Tsm (back side) |) below 6 ° C, it is necessary to check and adjust the temperature at which the upper and lower surfaces of the film are actually heated in the heat-fixing zone. The adjustment here does not mean simply setting the temperature of the upper side and the lower side of the heat fixing zone to the same temperature.

Conventionally, attention has not been paid to the actual heat treatment temperature for heat treatment on each of the front surface and the back surface of the film, and generally only the melting subpeak temperature of the entire film has been discussed. However, in the case of a thick film in which the thickness of the biaxially stretched film is 50 μm or more, the difference in melting subpeak temperature (Tsm) between the front surface and the back surface of the film depends on the handleability and workability in the membrane switch manufacturing process. It was the present invention that found that the above had a great influence and solved the problem.

Further, in the above-mentioned manufacturing method (simultaneous biaxial stretching and sequential biaxial stretching) of the base film for a membrane switch of the present invention, the refractive index in at least one direction in the film forming direction and the width direction of the film is set to 1.770 or more and 1.790 or less. For this purpose, it is preferable to adjust the temperatures of the upper surface and the lower surface of the film in each preheating zone before the longitudinal stretching and the transverse stretching in a well-balanced manner. A good balance here means that the upper surface of the film in the preheating zone and the upper surface of the film in the preheating zone can be stretched reasonably over the entire film thickness, taking into consideration the temperature difference between the upper surface and the lower surface of the film in each stretching zone. It means adjusting the temperature of the lower surface. Therefore, it does not mean that the temperatures above and below the preheating zone are simply set to the same temperature. Conventionally, much attention has not been paid to the temperature of the preheating zone, but especially for thick films in which the thickness of the unstretched film is 700 μm or more or the film thickness after uniaxial stretching is 300 μm or more, the temperature of the preheating zone is large for the subsequent stretching. Affect.

As a guideline for adjusting the temperature difference between the upper side and the lower side of the preheating zone, the temperature difference between the upper surface and the lower surface of the film in the preheating zone is preferably 8 ° C or less, more preferably 6 °. It is C or less, particularly preferably 5 ° C or less. The temperature of the preheating zone is preferably 100 ° C to 160 ° C.

Further, in order to make the absolute value of the difference between the refractive indexes of the front surface and the back surface of the film within a desired range, the heat relaxation treatment temperature in the vertical and / or horizontal directions after heat fixing is set to the upper surface and the lower surface of the film. It is preferable to adjust the temperature difference within 12 ° C, and more preferably to the temperature difference within 7 ° C. For example, when the refractive indexes of the front surface and the back surface of the film are compared, if the heat relaxation treatment temperature on the surface side having a small refractive index is set higher, the difference in the refractive indexes between the front surface and the back surface of the film tends to be small.

The base film for a membrane switch of the present invention thus obtained has excellent performance that is less likely to deteriorate (wet heat deterioration) in a harsh environment (high temperature and high humidity) inside an automobile. Therefore, the film of the present invention is preferably used in an automobile as a film that can withstand the useful life of an automobile. It is considered that the development of the above-mentioned property of being resistant to moist heat deterioration is related to the extreme orientation in at least one direction.

Further, the base film for a membrane switch of the present invention shows excellent deformation recovery after being released from deformation even if it is forcibly deformed for a long time, and is particularly good even at a high temperature of about 80 ° C. Deformation recovery is shown. Therefore, even if the film is embedded in the seat surface of the automobile seat as a base material of the membrane switch and receives the weight of the seated occupant, the deformation of the film is recovered when the occupant leaves the seat, and the switch always functions as a normal switch. Therefore, it is particularly preferably used as a base material for a seating sensor switch for an occupant. That is, as a sensor for detecting that an occupant is seated on the seat in a state where a plurality of seats are embedded inside the seat surface of each seat excluding the driver's seat in the car, and / or when the occupant is seated. The film of the present invention can be preferably used as a base film for a membrane switch used as a sensor for detecting pressure at each position on a surface to detect a seating position. It is considered that the elastic strength of the film extremely oriented in at least one direction is also involved in the occurrence of such deformation recovery.

Hereinafter, the present invention will be described in more detail with reference to examples. In addition, each characteristic value in an Example was measured or evaluated by the following method. Further, the parts and ratios in the examples indicate parts by weight and weight ratios unless otherwise specified. (1) Calculation of the amount of ethylene-2,6-naphthalene carboxylate components (main component mol ratio, copolymer component mol ratio) Measure the film sample solvent (CDCl₃: CF₃After dissolution in COOD = 1: 1), 1H-NMR measurement is performed, and the integral ratio of each obtained signal is calculated. (2) Metal content concentration analysis For titanium and phosphorus atom concentrations, set a dried film sample in a scanning electron microscope (SEM, Hitachi Measuring Instruments Service S570 type) and use an energy dispersive X-ray microanalyzer (XMA, Horiba EMAX-7000) connected to it. Quantitative analysis was performed. (3) Intrinsic viscosity (IV) Intrinsic viscosity (IV) is measured at 35 ° C using o-chlorophenol as a solvent. (4) Film thickness Using a micrometer (trade name "K-402B type" manufactured by Anritsu Co., Ltd.), the film is measured at intervals of 10 cm in the longitudinal direction and the width direction of the film, and the film thickness is measured at 300 points in total. The average value of the obtained film thicknesses at 300 locations is calculated and used as the film thickness.

Furthermore, using an electronic micrometer (trade name "K-312A type" manufactured by Anritsu Co., Ltd.), measurements are made continuously over a length of 2 m in each of the vertical and horizontal directions of the film at a stylus pressure of 30 g and a running speed of 25 mm / sec. Get a thickness chart. The maximum thickness and the minimum thickness are read from this chart, and the variation in thickness is obtained from the following formula together with the above film thickness.

Thickness variation (%) = ((maximum thickness-minimum thickness) / film thickness) x 100 (5) Melting subpeak temperature (Tsm), front and back difference between front and back melting subpeak temperatures From one side (front or back) of the film, sand with sandpaper (# 200) and scrape the film to a thickness of 20% of the original film thickness. A film sample for DSC measurement was taken from the uncut film (back side sample or front side sample), and a differential scanning calorimetry device DSC220 manufactured by Seiko Electronics Co., Ltd. was used, and the temperature rise rate was 20 ° C / min. The sample volume is 10 mg, and the sub-peak temperature is measured under the measurement conditions in a nitrogen stream. (6) Refractive index of film With a laser refractometer using the principle of the Abbe refractometer, prisms are brought into contact with each side of the film to obtain the in-plane direction of the film. That is, a prism coupler (Metricon Model) Using 2010), the refractive indexes in the film forming direction and the width direction (referred to as nMD and nTD, respectively) at a wavelength of 633 nm are measured on the front surface and the back surface of the film, respectively. Find the absolute value of the difference in refractive index between the front and back surfaces in the direction in which the refractive index value is 1.770 or more and 1.790 or less. (7) Heat shrinkage rate The film is held in an oven set at a temperature of 200 ° C for 10 minutes in a non-tensioned state, and the dimensional change before and after the heat treatment is calculated as the heat shrinkage rate by the following formula.

Heat shrinkage% = ((L0-L) / L0) × 100 Here L0 is heat treated distance between the gauge points before the , and L is the distance between the drift points after the heat treatment. (8) 3D center surface average roughness (SRa) Measure with a surface roughness meter (Tokyo Seimitsu product name "Surfcom SE-3CK") according to the method specified in JIS B-0601. That is, the film surface is under the conditions of measurement length (Lx) 1 mm, sampling pitch 2 μm, cutoff 0.25 mm, thickness direction magnification 10,000 times, surface direction magnification 200 times, and number of scanning lines 100 (Ly = 0.2 mm). Measure the protrusion profile of and calculate the surface roughness. (9) Film density The density of the film is measured by the floating and sinking method at 25 ° C. in a density gradient tube using an aqueous solution of calcium nitrate as a solvent. (10) Continuous film forming property of film The film-forming state of the film when the film was continuously formed was observed, and the time until the streak-like unevenness defect that locally occurred in the film-forming direction was measured and evaluated according to the following criteria. The evaluations of and were passed. : Streaky unevenness defects do not occur until 72 hours after the start of film formation. Very good continuous film formation. Δ: Streaky unevenness defects occur between 36 hours and 72 hours after the start of film formation. The continuous film forming property is generally good. X: Streaky unevenness defects occur within 36 hours from the start of film formation. Poor continuous film formation.

(11) Film slipperiness After supplying the film to the tray of the copier with 400 sheets of film cut out to the size of A4 plate stacked, 400 sheets are continuously copied in the same way as copying to an OHP sheet, and the slipperiness in film feeding It was evaluated according to the following criteria. The evaluations of and were passed. : There is no film feed defect, and the slipperiness of the film is extremely good. Δ: Film feed failure occurs 1 to 3 times, but the slipperiness of the film is generally good. ×: Film feed failure occurred 4 times or more, and there was a problem with the slipperiness of the film. (12) Film workability The state of the end face after cutting or punching the film was observed, and the workability was evaluated according to the following criteria. If it was evaluated as or Δ, it could be used as the film of the present invention and was accepted. : After cutting, observe the end face after punching with a microscope at a magnification of 100 times. The end face is straight and undisturbed, and the end face condition is extremely good. Δ: After cutting, observe the end face after punching with a microscope at a magnification of 100 times. Although the end face is partially disturbed, even if the end face is traced with a finger, the unevenness of the end face is not felt, and the end face condition is generally good and there is no problem in practical use. X: When the end face after cutting and punching is traced with a finger, unevenness of the end face is felt and the end face condition is poor. (13) Durability evaluation of membrane switch Repeated ON / OFF test of the membrane switch in an environment of 60 ° C and 65% RH. The load at which the switch is turned on (initial load, for example, 1.5 kg / cm)²) Load and load removal are repeated every 1 minute. This ON / OFF cycle is performed continuously for 360 hours. After the repeated ON / OFF test is completed, remove the load and leave it in an environment of 60 ° C and 65% RH for 30 minutes. After that, apply a load to the switch again and measure the load (post-processing load) that turns the switch on. A sample in which the post-treatment load could maintain 90% or more of the initial load was passed, and the above test was carried out at n = 100 and evaluated according to the following criteria (pass rate). Pass rate% = (number of samples whose processed load is 90% or more of the initial load / number of n) x 100 : The pass rate is 95% or more, and the durability of the switch is extremely good. Δ: The pass rate is 80% or more, and the durability of the switch is generally good. ×: The pass rate is less than 80%, and the durability of the switch is poor.

If the evaluation is or Δ, the film has the durability required for the film of the present invention. (14) Comprehensive evaluation Based on each of the above evaluation results, the overall evaluation is represented by "", "", "", and "×". Those evaluated as "" to "" are passed, and those evaluated as "x" are rejected.

Example 1 Using 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol as transesterification catalysts and 0.03 parts of manganese acetate tetrahydrate, 0.25% by weight of calcium carbonate particles with an average particle size of 0.5 μm as a lubricant, average particle size After adding 0.06% by weight of 0.2 μm spherical silica particles and 0.1% by weight of 0.1 μm average particle size spherical silica particles and causing a transesterification reaction according to a conventional method, 0.042 parts of triethylphosphonoacetate was added. Was added to substantially complete the transesterification reaction.

Then, 0.024 part of antimony trioxide was added, and the polymerization reaction was subsequently carried out by a conventional method at high temperature and high vacuum to obtain a PEN having an intrinsic viscosity of 0.60 dl / g and a Tg of 121 ° C. After drying this PEN polymer at 175 ° C for 5 hours, it is supplied to an extruder, melted at a melting temperature of 300 ° C, extruded from a die slit, and then cooled and solidified on a casting drum set to a surface temperature of 55 ° C. To prepare an unstretched film.

This unstretched film is stretched 3.4 times in the longitudinal direction at 140 ° C. After that, it was biaxially stretched 3.8 times in the lateral direction at 135 ° C, and then immediately after that, the temperature on the upper side of the film was adjusted to 241 ° C and the temperature on the lower side of the film was adjusted to 239 ° C. Heat fixed for seconds. After the heat fixing treatment, a heat relaxation treatment of 1.5% was performed in the lateral direction to obtain a biaxially oriented film having a thickness of 100 μm, which was wound on a roll. Silver paste as a conductive circuit and carbon paste as a printing contact (electrode) are screen-printed on this PEN base film, dried at 140 ° C for 20 minutes to create a switch sheet, and then these two sheets are printed. A film-like styrene-butadiene resin was used as an adhesive for bonding and a spacer for the membrane switch. Table 1 shows the physical characteristics, evaluation results, film-forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Example 2 In Example 1, the same operation was repeated except that the temperature of the upper side of the film in the heat fixing zone was set to 243 ° C and the temperature of the lower side of the film was set to 238 ° C. Table 1 shows the physical properties of the biaxially oriented film, the evaluation results, the film-forming properties, and the evaluation results of the membrane switch.

Example 3 0.011 part of tetra-n-butyl titanate (referred to as "TBT") and 0.25% by weight of calcium carbonate particles with an average particle size of 0.5 μm as a lubricant in a mixture of 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 56 parts of ethylene glycol. , 0.06% by weight of spherical silicone particles with an average particle size of 0.25 μm, and 0.1% by weight of spherical silica particles with an average particle size of 0.1 μm are added to a SUS (stainless) container capable of pressurization reaction. After charging, pressurizing 0.07 MPa and conducting a transesterification reaction while raising the temperature from 140 ° C to 240 ° C, 0.042 parts of triethylphosphonoacetate (denoted as "TEPA") was added to complete the transesterification reaction. I let you.

After that, the reaction product was transferred to a polymerization vessel, the temperature was raised to 290 ° C, and a polycondensation reaction was carried out in a high vacuum of 100 Pa to obtain a PEN having an intrinsic viscosity of 0.62 dl / g and a Tg of 121 ° C. Subsequent drying and film formation of the PEN polymer repeated the same operations as in Example 1. The results are shown in Table 1.

Comparative example 1 In Example 1, the film was formed in the same manner except that the temperature on the upper side of the film in the heat-fixing zone was set to 220 ° C and the temperature on the lower side of the film was set to 217 ° C. The results are shown in Table 1.

Comparative example 2 In Example 1, the film was formed in the same manner except that the temperature on the upper side of the film in the heat-fixing zone was set to 240 ° C and the temperature on the lower side of the film was set to 232 ° C. The results are shown in Table 1.

<tables num="1"><img file="JP4528126B2_D0004.tif" /></tables>

Example 4 Using 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol as transesterification catalysts and 0.03 parts of manganese acetate tetrahydrate, 0.25% by weight of calcium carbonate particles with an average particle size of 0.5 μm as a lubricant, average particle size After adding 0.06% by weight of 0.2 μm spherical silica particles and 0.1% by weight of 0.1 μm average particle size spherical silica particles and causing a transesterification reaction according to a conventional method, 0.042 parts of triethylphosphonoacetate was added. Was added to substantially complete the transesterification reaction.

Then, 0.024 part of antimony trioxide was added, and the polymerization reaction was subsequently carried out by a conventional method at high temperature and high vacuum to obtain a PEN having an intrinsic viscosity of 0.63 dl / g and a Tg of 121 ° C. After drying this PEN polymer at 175 ° C for 5 hours, it is supplied to an extruder, melted at a melting temperature of 300 ° C, extruded from a die slit, and then cooled and solidified on a casting drum set to a surface temperature of 55 ° C. To prepare an unstretched film.

This unstretched film is led to a preheating zone of 120 ° C before longitudinal stretching, heated so that the temperature difference between the upper surface and the lower surface of the film is within 4 ° C, and then in the longitudinal direction at 145 ° C. Stretch 3.2 times. After that, it is guided to the preheating zone of 130 ° C before lateral stretching, heated so that the temperature difference between the upper surface and the lower surface of the film is within 4 ° C, and then 3.9 times in the lateral direction at 135 ° C. The film was biaxially stretched sequentially, and then the temperature of both the upper and lower surfaces of the film was immediately fixed at 237 ° C for 6 seconds. After the heat fixing treatment, the temperature on the upper side of the film is set to 215 ° C and the temperature on the lower side of the film is set to 218 ° C, and 1.5% heat relaxation treatment is performed in the lateral direction to obtain a biaxially oriented film with a thickness of 100 μm and roll it. I rolled it up.

Silver paste as a conductive circuit and carbon paste as a printing contact (electrode) are screen-printed on this PEN base film, dried at 140 ° C for 20 minutes to create a switch sheet, and then these two sheets are printed. A film-like styrene-butadiene resin was used as an adhesive for bonding and a spacer for the membrane switch. Table 2 shows the physical characteristics, evaluation results, film forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Example 5 In Example 4, the same operation was repeated except that the temperature on the upper side of the film was set to 213 ° C and the temperature on the lower side of the film was set to 221 ° C in the lateral heat relaxation treatment after heat fixing. Table 2 shows the physical characteristics, evaluation results, film forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Example 6 0.011 part of tetra-n-butyl titanate (referred to as "TBT") and 0.25% by weight of calcium carbonate particles with an average particle size of 0.5 μm as a lubricant in a mixture of 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 56 parts of ethylene glycol. , 0.06% by weight of spherical silicone particles with an average particle size of 0.25 μm, and 0.1% by weight of spherical silica particles with an average particle size of 0.1 μm are added to a SUS (stainless) container capable of pressurization reaction. After charging, pressurizing 0.07 MPa and conducting a transesterification reaction while raising the temperature from 140 ° C to 240 ° C, 0.042 parts of triethylphosphonoacetate (denoted as "TEPA") was added to complete the transesterification reaction. I let you.

After that, the reaction product was transferred to a polymerization vessel, the temperature was raised to 290 ° C, and a polycondensation reaction was carried out in a high vacuum of 100 Pa to obtain a PEN having an intrinsic viscosity of 0.61 dl / g and a Tg of 121 ° C. Subsequent drying and film formation of the PEN polymer repeated the same operations as in Example 4. Table 2 shows the physical characteristics, evaluation results, film forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Comparative example 3 In Example 4, the same operation was repeated except that the product was stretched 3.3 times in the vertical direction and then 3.4 times in the horizontal direction. Table 2 shows the physical characteristics, evaluation results, film forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Comparative example 4 In Example 4, the same operation was repeated except that the temperature on the upper side of the film was set to 225 ° C and the temperature on the lower side of the film was set to 211 ° C in the lateral heat relaxation treatment after heat fixing. Table 2 shows the physical characteristics, evaluation results, film forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Comparative example 5 In Example 4, the same operation was repeated except that the product was stretched 3.0 times in the vertical direction and then 4.7 times in the horizontal direction. However, there were many breaks during film formation, and film formation could not be performed continuously for 1 hour or more. Therefore, no evaluation was performed other than the physical characteristics of the film.

<tables num="2"><img file="JP4528126B2_D0005.tif" /></tables>

Example 7 Using 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol as transesterification catalysts and 0.03 parts of manganese acetate tetrahydrate, 0.25% by weight of calcium carbonate particles with an average particle size of 0.5 μm as a lubricant, average particle size After adding 0.06% by weight of 0.2 μm spherical silica particles and 0.1% by weight of 0.1 μm average particle size spherical silica particles and causing a transesterification reaction according to a conventional method, 0.042 parts of triethylphosphonoacetate was added. Was added to substantially complete the transesterification reaction.

Then, 0.024 part of antimony trioxide was added, and the polymerization reaction was subsequently carried out by a conventional method at high temperature and high vacuum to obtain a PEN having an intrinsic viscosity of 0.60 dl / g and a Tg of 121 ° C. After drying this PEN polymer at 175 ° C for 5 hours, it is supplied to an extruder, melted at a melting temperature of 300 ° C, extruded from a die slit, and then cooled and solidified on a casting drum set to a surface temperature of 55 ° C. To prepare an unstretched film.

This unstretched film is led to a preheating zone of 120 ° C before longitudinal stretching, heated so that the temperature difference between the upper surface and the lower surface of the film is within 4 ° C, and then in the longitudinal direction at 145 ° C. Stretch 3.2 times. After that, it is guided to the preheating zone of 130 ° C before lateral stretching, heated so that the temperature difference between the upper surface and the lower surface of the film is within 4 ° C, and then 3.9 times in the lateral direction at 135 ° C. The film was biaxially stretched sequentially, and then immediately heat-fixed in a heat-fixing zone in which the temperature on the upper side of the film was adjusted to 241 ° C and the temperature on the lower side of the film was adjusted to 239 ° C for 6 seconds. After the heat fixing treatment, the temperature on the upper side of the film is set to 215 ° C and the temperature on the lower side of the film is set to 218 ° C, and 1.5% heat relaxation treatment is performed in the lateral direction to obtain a biaxially oriented film with a thickness of 100 μm and roll it. I rolled it up.

Silver paste as a conductive circuit and carbon paste as a printing contact (electrode) are screen-printed on this PEN base film, dried at 140 ° C for 20 minutes to create a switch sheet, and then these two sheets are printed. A film-like styrene-butadiene resin was used as an adhesive for bonding and a spacer for the membrane switch. Table 3 shows the physical characteristics, evaluation results, film-forming properties, and evaluation results of the membrane switch of the obtained biaxially oriented film.

Example 8 In Example 7, the same operation was repeated except that the temperature of the upper side of the film in the heat fixing zone was set to 243 ° C and the temperature of the lower side of the film was set to 238 ° C. Table 1 shows the physical properties of the biaxially oriented film, the evaluation results, the film-forming properties, and the evaluation results of the membrane switch.

Example 9 0.011 part of tetra-n-butyl titanate (referred to as "TBT") and 0.25% by weight of calcium carbonate particles with an average particle size of 0.5 μm as a lubricant in a mixture of 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 56 parts of ethylene glycol. , 0.06% by weight of spherical silicone particles with an average particle size of 0.25 μm, and 0.1% by weight of spherical silica particles with an average particle size of 0.1 μm are added to a SUS (stainless) container capable of pressurization reaction. After charging, pressurizing 0.07 MPa and conducting a transesterification reaction while raising the temperature from 140 ° C to 240 ° C, 0.042 parts of triethylphosphonoacetate (denoted as "TEPA") was added to complete the transesterification reaction. I let you.

After that, the reaction product was transferred to a polymerization vessel, the temperature was raised to 290 ° C, and a polycondensation reaction was carried out in a high vacuum of 100 Pa to obtain a PEN having an intrinsic viscosity of 0.62 dl / g and a Tg of 121 ° C. Subsequent drying and film formation of the PEN polymer repeated the same operations as in Example 7. The results are shown in Table 3.

<tables num="3"><img file="JP4528126B2_D0006.tif" /></tables>