Method of producing a polymeric composite film

Composite membrane and manufacturing method thereof

The present invention relates to a polymer film, and particularly to a composite polymer film.

It is known that polymeric films often have poor handling properties, which can cause difficulties in winding the film into high-quality rolls and inefficiently passing through the entire processing process, such as cutting equipment.

A polyester film composition containing a layer of elemental polyester and a layer of copolyester is described in British Patent No. 1465973. Copolyester can be used as a heat-sealable layer. European Patent No. 35835 describes a similar polyester film composition that contains a filler in a copolyester layer with an average particle size greater than the layer thickness. The filler particles make the entire copolyester layer convex and produce a film with good handling properties. In any case, the above-mentioned film will reduce the heat-sealability due to the presence of filler particles having a particle size larger than the thickness of the heat-sealable layer. In addition, the above-mentioned processing properties can only be achieved under certain ratios of heat-sealable layer thickness/filler particle size, so any necessary changes in the thickness of the heat-sealable layer (for example, in different commercial applications) must also be changed Filler particle size. This situation will result in different ranges for different fillers required for different applications. In the copolyester layer, a relatively high concentration of filler is required to obtain the required processing properties, which will cause a sharp drop in optical transparency and an increase in film turbidity.

The inventors have developed a composite membrane that can reduce or substantially eliminate at least one or more of the above-mentioned problems.

Therefore, the present invention provides a composite film, which contains a polymer substrate layer with a heat-sealable layer containing powder additives on at least one surface, and the exposed surface of the heat-sealable layer contains more than 100 powders per square millimeter. The surface protrusions produced by the additives have an average peak height in the range of 5 to 400 nanometers as measured from the average level of the surface of the heat-sealable layer.

The present invention also provides a method for producing a composite film. The composite film includes forming a polymer substrate layer with a heat-sealable layer on at least one surface thereof, and coating powder additives on the exposed surface of the heat-sealable layer. The powder Additives are linked to and/or penetrate into the heat-sealable layer. The exposed surface of the heat-sealable layer contains more than 100 surface protrusions per square millimeter produced by the powder additives, and the surface protrusions are formed by the surface of the heat-sealable layer. The average level measures the average peak height in the range from 5 to 400 nanometers.

The polymeric film composite substrate according to the present invention can be formed from any synthetic, film-forming polymer. Suitable thermoplastic materials include a 1-olefin, such as a simple polymer or copolymer of ethylene, propylene and 1-butene, a polyamide, a polycarbonate and a synthetic linear polyester. The polyester can be Or more dicarboxylic acids or their lower alkyl diesters (up to 6 carbon atoms), for example: terephthalic acid, isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7- Naphthalenedicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, 4,4'-diphenyldicarboxylic acid, hexahydroterephthalic acid or 1,2-p-carboxyphenoxyethane (Optionally with monocarboxylic acid, such as: trimethyl acetic acid), and one or more dihydric alcohols condensation, especially aliphatic dihydric alcohols, such as: ethylene glycol, 1,3-propanediol, 1 , 4-butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol. A polyethylene terephthalate film is particularly good, especially the film can be stretched successively in two mutually perpendicular directions into a biaxial alignment, typically in the temperature range of 70 to 125°, And it is best to heat and condense, typically in the temperature range of 150 to 250°, for example, as described in British Patent 838708.

The substrate may also contain a polyaryl ether or its sulfur analogues, especially a polyaryl ether ketone, polyaryl ether ketone, polyaryl ether ethyl ether ketone, poly aryl ether ethyl ether ketone, or a copolymerObject or its sulfur analogues. Examples of such polymers are described in European Patent-A-1879, European Patent-A-184458 and U.S. Patent-A-4008203. Especially suitable materials are notified by ICI PLC as a registered trademark. "STABAR" is sold. The substrate may contain a poly(arylene sulfide), especially poly-para-sulfide benzene or its copolymers. Mixing of such polymers can also be applied.

Suitable thermosetting resin-based materials include addition polymer resins (such as acrylic, vinyl, bis-maleimide and unsaturated polyester), formaldehyde condensation resins (such as: urea, melamine or Condensate of phenol), cyanate ester, functionalized polyester, polyamide or polyimide.

The polymeric film substrate used to produce the composite film according to the present invention may be unaligned or uniaxially aligned, but is preferably drawn in two mutually perpendicular directions on the film plane to form a biaxially aligned film, so as to achieve one A satisfactory combination of mechanical and physical properties. The simultaneous biaxial alignment can be affected by the stamped thermoplastic polymer tube, which is then quenched, reheated, and then expanded by the internal air pressure to cause the horizontal axis alignment, and then withdraw at a speed that will cause the longitudinal axis alignment. The successive elongation in the process of slight change can be affected by stamping the extruded profile whose thermoplastic base material is flat. The extruded profile is then first elongated in one direction, and then elongated in the other perpendicular direction. Generally speaking, it is better to stretch in the longitudinal direction first, that is, to penetrate the forward direction of the film stretcher, and then stretch in the transverse direction. The elongated substrate film can (and preferably) be spatially stabilized by heating and condensing at a temperature above its glass transition temperature.

The polymeric film substrate of the present invention is intended to be optically transparent. For a film with a thickness of 12 microns, it is preferably less than 3.5% measured in accordance with the standard American Society for Testing and Materials (ASTM) D 1003-61, More preferably, it is less than 1.5%, and most preferably is a wide-angle haze of 0.5%.

The heat-sealable layer should be able to soften the polymer of the heat-sealable layer by heating, and apply pressure that does not soften or melt the polymer of the substrate layer, and form a heat-seal bond with itself or the substrate, or preferably with Both of them form a heat-seal key.

The heat-sealable layer preferably contains a polyester resin, especially one or more dibasic aromatic carboxylic acids, such as terephthalic acid, isophthalic acid and hexahydroterephthalic acid, and one or more glycols, such as ethyl Copolyester resin derived from glycol, diethylene glycol, triethylene glycol and neopentyl glycol. Typical copolyesters that provide satisfactory heat-sealable properties are copolyesters of ethylene terephthalate, especially those with a molar ratio of from 50 to 90 mol% and relatively from 50 to 10 mol% ethyl isophthalate. The preferred copolyester contains from 65 to 85 mol% ethylene terephthalate and 35 to 15 mol% ethylene isophthalate, and especially about 82 mol% ethylene terephthalate Copolyester with about 18 mol% ethylene isophthalate.

On the substrate layer, the formation of the heat-sealable layer can be affected by traditional techniques-for example, by casting the polymer onto the prefabricated substrate layer. However, very easily, the formation of a combined layer (base material and heat-sealable layer) can be affected by co-punching, which is affected by the simultaneous co-punching of individual mold forming layers through the individual holes of the porous mold, and then the composition is still molten Layers, or are preferably affected by the co-punching of a single tube combined by the melt flow of individual polymers in a pipe extending to the mold manifold, and then punched together from the die hole without intermixing streamline flow And produce a combined layer.

The co-stamping layer is elongated to affect the molecular alignment of the substrate, and is preferably heated and coagulated. Generally, the conditions applied to elongate the substrate layer will cause part of the heat-sealable layer to crystallize, so it is heated and condensed at a specific temperature of the surface geometry required to produce the heat-sealable layer under space constraints. Is better. Therefore, by effective thermal condensation at a temperature lower than the crystalline melting temperature of the heat-sealable polymer and at a temperature that allows or causes cooling of the composition, the heat-sealable polymer will substantially maintain a crystalline state. However, by thermally coagulating at a temperature greater than the crystalline melting temperature of the heat-sealing polymer, the heat-sealing polymer will become substantially amorphous. The thermal coagulation of the combined layer comprising a polyester substrate and a copolyester heat-sealable layer can effectively produce a crystalline heat-sealable layer at a temperature ranging from 175 to 200°C, or at a temperature from 200°C. The temperature range to 250°C produces a substantially amorphous heat-sealable layer. A substantially amorphous heat-sealable layer is preferable.

The heat-sealable layer can be arranged on one side or both sides of the substrate layer. The film composition may have a total thickness in the range of 10 to 500 microns and the heat-sealable layer or each heat-sealable layer preferably consists of from 1% to 30% of the total composition thickness. The heat-sealable layer preferably has a thickness of not more than 50 micrometers, more preferably not more than 10 micrometers, and especially from 0.5 to 5 micrometers.

The properties to be processed can be achieved when the heat-sealable layer contains more than 100 surface raised peaks per square millimeter, preferably 5000, and more preferably 400 to 2000 per square millimeter, especially It is from 600 to 1500, and especially from 700 to 900 raised peaks. The average height of the raised peaks measured from the average level of the heat-sealable layer surface is in the range of 5 to 400 nanometers, more preferably from 10 to 200 nanometers, especially from 15 to 100 nanometers, and especially from 20 to 60 nanometers. It is preferable that more than 50%, especially more than 70%, and especially more than 90% of the raised peaks have a height within the aforementioned preferable average height range. The shape of the raised peaks can also play an important role in the processing properties of the formed film. The average raised peak preferably has a value greater than 0.8×10^-3The shape (this shape refers to the height of the raised peak (as defined above) divided by the width of the bottom of the peak measured at the average level of the surface of the heat-sealable layer), preferably from 1.0×10^-3To 100×10^-3Range, especially from 1.5×10^-3Up to 20×10^-3Range, and especially in the range from 2×10^-3To 4×10^-3scope.

The number, size and shape of the raised peaks can be determined by any relevant surface analysis technique. Non-contact methods (such as interferometers) are better, for example: Topo-3D (Topo-3D) membrane milling machine (manufactured by Wyko), which will be described in the following In the test method given.

The powder additives used in the heat-sealable layer should be chemically inert to the polyester material of the heat-sealable layer and the additive-producing substances or other additives in the heat-sealable layer, and preferably contain inorganic particles, which Contains any one of natural or synthetic silica, glass beads, calcium borate, calcium carbonate, magnesium carbonate, barium sulfate, calcium silicate, calcium phosphate, aluminum hydroxide, hydrated and calcined forms of aluminum silicate and titanium dioxide or mixture. Other suitable powder additives include polymeric particles of polymers that melt at a temperature higher than the maximum temperature used for the production of the film composition and/or are difficult to mix with heat-sealable polymers. A preferred powder additive contains silica particles, and particularly contains a type of silica commonly known as fuming or coking silica commercially. Fuming silica can be formed by the reaction of silicon tetrachloride in an oxygen flame to form single, round silicon dioxide particles. The above-mentioned particles grow through collision and coalescence to form larger particles, that is, starting particles. When the particles cool and start to solidify, but continue to collide, they adhere but do not coalesce and form solid aggregates, which then continue to collide to form clumps or clots.

The powder filler suitable for the heat-sealable layer of the composite film according to the present invention preferably has a circular cross-section substantially regardless of the selected observation point.

A different filler particle needs to show the vertical and horizontal d₁: D₂(Here d₁With d₂(Respectively the largest and smallest size of the particles) are in the range from 1:1 to 1:0.5, and preferably 1:1 to 1:0.8.

The average particle size of the powder filler (especially silica particles) mixed with the heat-sealable layer is preferably in the range of 0.01 to 0.09 micrometers, preferably 0.02 to 0.08 micrometers, and especially 0.03 to 0.06 micrometers.

The particle size can be measured by an electron microscope, a coulter or a sedimentation analyzer, and the average particle size can be determined by drawing a cumulative distribution curve representing the percentage of particles lower than the selected particle size.

In the case of spherical powder additives, the average particle size is determined by the diameter of the particles. However, many powder additives, especially inorganic particles, are not spherical in shape, and for the purpose of this design description, their average size is determined by the particle size of their largest size.

In a preferred embodiment of the invention, the initial or individual filler particles aggregate to form agglomerates or clumps containing many initial particles. The agglomeration process of the initial filler particles can occur during the actual synthesis of the filler and/or during the film manufacturing process. The average particle size value you want to include here is applied to the initial unaggregated particle size. Preferably, in the heat-sealable layer of the final composite membrane product, the average particle size of the filler clot (such as the clot of starting silica) is in the range from 0.05 to 0.45 microns, preferably 0.08 To 0.4 microns, and especially 0.1 to 0.35 microns.

The powder additives can be added to the heat-sealable polymer before punching, so that the powder additives can be effectively distributed in the entire layer, preferably not more than 10% by weight based on the weight of the heat-sealable polymer, more preferably Ground is not more than 5% by weight of the weight present in the layer. Generally, suitable film treatment properties can be provided by powder additives in an amount not exceeding 3% by weight, and especially in the range of 0.5% to 2.0% by weight of the polymer.

The presence of powder additives distributed throughout the heat-sealable layer has an unfavorable effect on the transparency of the composite film. In a preferred embodiment of the present invention, the powder additives are coated on the exposed surface of the heat-sealable layer. It is dispersed in a liquid medium, such as an organic solvent, and is preferably an aqueous dispersant. The liquid medium may optionally contain a plasticizer for the heat-sealable layer. Examples of compounds that may be suitable as plasticizers for the polyester heat-sealable layer include benzaldehyde, benzyl alcohol, methyl salicylate, o-dichlorobenzene, dimethyl phthalate, diethyl oxalate, and disuccinate. Ethyl ester, tetrachloroethane, o-phenylphenol, 1-phenylethanol and dichloromethane. In addition, the powder additives can be applied to the heat-sealable layer by electrostatic deposition in a dry state or by choosing an electrostatically assisted fluidized bed, just like a gas turbid mass. When coating in a dry state, the powder additives can be dispersed throughout the heat-sealable layer, if necessary, to provide a reasonable uniform distribution covering the entire surface.

If necessary, a slight pressure can be applied to the entire powder additive layer to press the particles into the heat-sealable layer. Excess powder additives that have not been bonded or penetrated into the heat-sealable layer can be removed from the surface, for example, by turning the combined film, using air blowing to disperse the particles, or brushing off the particles or washing off the particles. The composite film can be allowed to be cooled or quenched in air to complete the bonding of the particles to the heat-sealable layer, and the cooling or quenching operation can produce effects no matter before or after the excess particles are removed from the surface of the film.

Powder additives can be applied to the aligned film. However, the coating of powder additives before or during the stretching operation can produce better results.

In particular, powder additives should be applied to the film substrate between the two steps (vertical axis or horizontal axis) of the biaxial stretching operation. The result of this coating and elongation is particularly good for the production of a copolyester heat-sealable layer bonded to a linear polyester film substrate, such as a polyethylene terephthalate substrate, preferably first It is stretched and coated by a series of rotating rollers in the direction of the longitudinal axis, and then stretched on the horizontal axis in the micro-changing furnace, preferably followed by heating and condensing. During the heating and coagulation, the film is preferably heated to a temperature greater than the softening point of the heat-sealable layer, so that the powder additive sinks into the polymer layer. Preferably, the powder additive sinks just below the polymer surface layer, so that it is completely immersed within the layer and confined to the surface area of the heat-sealable layer. More than 90%, preferably more than 95% of the particles are preferably within 1 micrometer of the upper part, and more preferably in the 0.5 micron thick part of the upper part of the heat-sealable layer. The result is that most of the particles in the layer have surface bumps, preferably with an average peak height greater than 5 nanometers.

The powder additive composition can be applied to the heat-sealable layer by any suitable conventional coating technique, such as hot dip coating, weld coating, reverse roller coating or notch coating, like an aqueous dispersant or organic solvent solution. . The powder additives are preferably coated on the heat-sealable layer at a concentration ranging from 2 to 15% of the dispersant (preferably in an aqueous medium), more preferably from 4 to 8%.

In a preferred embodiment of the present invention, the composite film will exhibit high optical transparency and low turbidity. For a film with a thickness of 15 microns, it is preferable to have a film measured according to the standard American Society for Testing and Materials D 1003-61. The wide-angle haze of less than 8%, more preferably less than 6%, especially less than 5%, and especially less than 3%. The above-mentioned optical properties can be appropriately achieved by the presence of little or no powder additives in the substrate. The substrate may contain a relatively small amount of filler material, for example, due to the general practice of using re-filming in the film manufacturing process. The optical properties of the composite film are in the polymer of the heat-sealable layer. Before the film is formed, it can be improved by not including any added powder additives, that is, basically all the powder additives present in the heat-sealable layer are The surface is coated with powder additives.

However, in another specific embodiment of the present invention, the composite film is opaque, which is defined as the transmittance density exhibited by a film (Sakura Densitometer; PDA 65 type; transmissive)/film The ratio of thickness (expressed in millimeters) is from 7.5 to 17.5, and especially from 12.0 to 15.0. The opacity of the composite film is preferably achieved by having an opaque substrate layer. The substrate layer is easily opaque by containing an effective amount of the synthetic polymer of the opaque agent. However, in a preferred embodiment of the present invention, the opaque substrate layer is porous, that is, includes a cell-like structure containing at least partially dispersed, closed cells. Therefore, it is preferable to mix an effective amount of an agent capable of producing an opaque and porous substrate layer structure into the substrate polymer. Suitable pore agents that also produce opacity include an incompatible resin filler, a powdered inorganic filler, or a mixture of two or more such fillers.

An "incompatible resin" refers to a resin that does not melt or substantially does not mix with the base polymer during layer stamping and manufacturing when it encounters the highest temperature. These resins include polyamide and olefin polymers, in particular, a homo- or co-polymer of a mono-α-olefin with up to 6 carbon atoms in the molecule is mixed into the polyester film, or the aforementioned type of polyester is mixed into the poly Olefin film.

Powder inorganic fillers suitable for producing opaque and porous substrate layers include traditional inorganic pigments and fillers, and in particular metal or metal-like oxides, such as alumina, silica and titan, and alkaline metals Salts, such as calcium and barium carbonate and sulfate. Barium sulfate is a particularly preferred filler and can also be used as a pore agent.

Non-porous powder inorganic fillers can also be added to the polymeric substrate layer formed by the film.

Suitable porous and/or non-porous fillers can be homogeneous and mainly consist of a single filler substance or compound, such as titanium dioxide or just barium sulfate. In addition, at least a portion of the filler may be heterogeneous, and the starting filler material is combined with an additional modified composition. For example, the starting filler particles can be treated with a surface modifier, such as pigments, soaps, surfactant binders, or other modifiers that improve or change the degree of compatibility between the filler and the substrate polymer.

The production of a substrate layer with satisfactory opacity, porosity and bleaching requires that the filler should be finely divided, and its average particle size needs to be from 0.1 to 10 microns, while the true particle size of 99.9% of the particles is not More than 30 microns. Preferably, the filler has an average particle size of from 0.1 to 10 microns, and particularly preferably from 0.2 to 0.75 microns. Reducing the particle size can improve the gloss of the substrate.

Preferably, the actual particle size of the filler particles mixed into the substrate layer does not exceed 30 microns. Particles larger than 30 microns can be removed by a sieving process well known in the art. However, the sieving operation has not completely succeeded in eliminating all particles larger than a certain selected size. Therefore, in fact, the size of 99.9% of the particles should not exceed 30 microns. Most preferably 99.9% of the particles should not exceed 20 microns in size.

The opacity/porosity agent mixed into the substrate layer polymer can be affected by traditional techniques-for example: by mixing with polymer-derived monomer reactants before film formation, or by mixing with granular or sheet polymer drying technology Influence.

The amount of filler mixed into the base polymer, especially the amount of barium sulfate, should be no less than 5% nor more than 50% based on the weight of the polymer. Especially when the concentration of the filler is from about 8 to 30%, and especially from 15 to 20% by weight based on the weight of the base layer polymer, a satisfactory degree of opacity and smoothness can be achieved.

Generally, a relatively small amount of other additives can be mixed into the substrate layer, for example: China clay can be mixed in an amount not exceeding 25% to improve porosity, and an optical polishing agent not exceeding 1500ppm can improve the bleaching degree without exceeding 10ppm The amount of dye can improve the color, and these specified concentrations are based on the weight ratio of the base polymer.

In a film composition that typically has a heat-sealable layer thickness in the range of 2 to 4 microns, an aqueous dispersion of silica particles with a starting average particle size of 8% by weight in the range of 30 to 50 nanometers is applied. The surface concentration of the raised peaks that are arranged on the heat-sealable layer to produce the surface of the second substrate is in the range of 700 to 900 per square millimeter, and the average peak height is in the range of 20 to 60 nanometers. This surface provides good processing properties and heat sealing properties. It includes a biaxially aligned and thermosetting polyethylene terephthalate substrate layer and a layer of 70 to 85 mol%/30 to 15 mol% ethylene isophthalate. The film composition of the ester copolyester heat-sealable layer, and the heat-sealable layer is self-tested by the heat-sealable layer, and the static friction coefficient is in the range of 0.50 to 0.65, and the heat-seal strength measured by the free-sealable heat-sealable layer is 200 Up to 1500 Newtons (m)^-1Range representation.

The film composition according to the present invention is suitable for self-heat-sealing or using traditional heat-sealing equipment and conditions to heat-seal it to other films such as polyethylene terephthalate film. The reason is that the film composition is heated to a certain A substantially amorphous heat-sealable layer will soften and bond to an acceptable surface temperature to form a seal. The heat-sealable layer containing 70 to 85 mol% ethylene terephthalate/30 to 15 mol% ethylene isophthalate is suitable for heat sealing. The film composition according to the present invention is better than 200 Newton·(m) measured by self-sealing with the heat-sealable layer, more preferably more than 300^-1The heat seal strength.

The film composition according to the present invention also has acceptable handling properties, preferably exhibiting a static friction coefficient of less than 1.0, more preferably less than 0.8, and especially less than 0.65.

The modification of the surface of the substrate and/or heat-sealable layer, such as flame treatment, ion bombardment, electron beam treatment, ultraviolet light treatment or preferably corona discharge, can improve any subsequent coating layer (for example: metal plating Layer) adhesion, but may not provide satisfactory adhesion.

By the better treatment of corona discharge, traditional equipment can produce effects in atmospheric air. This equipment uses a high-frequency, high-voltage generator, preferably with 1 to 20 thousand watts at a potential of 1 to 100 thousand volts. The power output. Discharge can be simply achieved by passing the film through the insulating base roller at a preferred speed of 1.0 to 500 meters per minute at the discharge station. The discharge electrode can be placed at a distance of 0.1 to 10.0 mm from the surface of the moving film.

The composite film layer according to the present invention can simply contain any additives traditionally used in the manufacture of polymer films. Therefore, if appropriate, such as dyes, pigments, pore agents, lubricants, antioxidants, anti-adhesives, surfactants, slip agents, gloss improvers, degeneratives, ultraviolet stabilizers, viscosity modifiers and dispersion stabilizers can be combined. The agent is mixed into the substrate and/or the heat-sealable layer.

In this design specification, the following test methods are used to determine certain characteristics of the film composition:

The characteristics of the raised peaks were measured with a Topo-3D master milling machine (manufactured by Weike Corporation). A statistical tip (ie, raised peak) analysis with a cut-off height of 5 nanometers and a critical value greater than 5 nanometers is performed to generate the number of tips or raised peaks. The average height of a raised peak (the height measured from the average level of the surface of the heat-sealable layer) is calculated from the probability graph obtained in nanometers. The height of 50% of all peaks in the graph is below this value . The shape of the raised peak, that is, the height/width, is determined by measuring the height of the raised peak (as defined above) and dividing it by the width of the bottom of the peak measured at the average level of the surface of the heat-sealable layer. Calculate the average height/width value of 10 typical raised peaks.

The heat-seal strength is measured by the self-sealable heat-sealable layer at 140°C for 1 second under a pressure of 103,000 Bascals (15 psi), cooling to room temperature, and measuring the linearity per unit of sealing width The pulling force is the force required to remove the sealing film at a fixed speed of 4.23 mm/sec.

The static friction coefficient of the heat-sealable layer is measured by the inclined plane method based on the American Society for Testing and Materials D 4518-87 test using IPST type (Specialist Engineering, Welwyn, UK).

The wide-angle turbidity is basically based on the American Society for Testing and Materials D 1003-61 test, using the Hazegard XL211 film turbidity meter (BYK Gardner, USA), during the period of light passing through the film, It is determined by the percentage of the transmitted light that deviates from the normal line of the surface of the film by the average amount of radian greater than 2.5°.

The present invention is described with reference to the attached drawings, in which:

Figure 1 is an unillustrated scale, schematic vertical section of a polymer film with a heat-sealable layer directly attached to the first surface of a substrate.

Figure 2 is a similar schematic cross-section of a polymer film with an additional heat-sealable layer attached to the second surface of the substrate.

Referring to Figure 1 in the graph, this film includes a polymer substrate layer (1) with a heat-sealable layer (2) bonded to one of the surfaces (3), and the powder material (4) is located just in the heat-sealable Layer below the surface.

The film of Fig. 2 further includes an additional heat-sealable layer (6), which is bonded to the second surface (5) of the substrate (1). This additional heat-sealable layer (6) also contains a powder substance just below the surface of this layer.

The present invention is further explained with reference to the following examples.

<u style="single">Example 1</u>

Preparation of a film composition comprising a heat-sealable layer containing polyethylene terephthalate as a substrate and a copolyester containing 82 mol% ethylene terephthalate/18 mol% ethylene isophthalate .

The above-mentioned polyester is prepared by a traditional method, comprising ethylene glycol and an acid (ie, terephthalic acid in the case of polyethylene terephthalate, or 82 mol% terephthalic acid in the case of copolyester) With 18 mol% isophthalic acid mixture) direct esterification reaction, followed by polycondensation reaction. After the end of the polycondensation reaction, the polymer is cut into small particles suitable for punching.

The film composition is produced from the above polyester by a single-tube stamping method, in which the poly(ethylene phthalate) stream and the copolyester stream supplied by the separate stamping machine are combined in a tube extending to the manifold of the stamping die And at the same time, it is punched out through the die under the condition of streamline flow and no intermixing. The film composition exposed from the punching die was immediately quenched on a water-cooled rotating metal drum with a polished surface at a temperature of about 90°C, and stretched 3.6 times its original size in the punching direction. This elongated film was then coated on the heat-sealable layer with an aqueous dispersion of silica (Aerosil K330, Degussa) with an average particle size of 40 nanometers at a weight ratio of 8% . The longitudinally elongated film was then stretched to 4.2 times its original size on the horizontal axis at a temperature of 100°C in a micro-changing furnace. The film composition is finally heated and condensed in a micro-surge furnace at a temperature of about 225°C under space constraints.

The resulting film composition consists of a layer of biaxially aligned and heated coagulated polyethylene terephthalate substrate and a layer of amorphous copolyester. The final film thickness is 15 microns, and the copolyester layer is 3 microns thick. Applying the above-mentioned test method to the film, the film will show the following characteristics: (1) The number of raised peaks on the surface of the heat-sealable layer = 700 average height per square millimeter = 25 nanometers average height/width = 2.2× 10^-3(2) Turbidity = 2.7% (3) The coefficient of static friction of the heat-sealable layer = 0.63 (4) The heat-seal strength of the heat-sealable layer = 275 Newton·(m)^-1

<u style="single">Example 2</u>

The process of Example 1 was repeated, but the polyethylene phthalate substrate layer contained 1550 ppm of china clay with an average particle size of 0.8 microns, and the copolyester heat-sealable layer additionally contained 1250 ppm of china clay with an average particle size of 0.8 microns. Applying the above-mentioned test method to the resulting film, the film will show the following characteristics of beads: (1) The number of raised peaks on the surface of the heat-sealable layer = 739 average height per square millimeter = 63 nanometers (2) Turbidity = 6.7% (3) The coefficient of static friction of the heat-sealable layer = 0.56 (4) The heat-seal strength of the heat-sealable layer = 250 Newton·(m)^-1

<u style="single">Example 3</u>

The process of Example 1 was repeated, but the poly(ethylene phthalate) base material layer contained 18% by weight of the polymer based finely cut powdered barium sulfate filler with an average particle size of 0.4 microns. The final film thickness is 250 microns, copolymerized

The ester layer is 40 microns thick. Applying the above-mentioned test method to the resulting film, the film will show the following characteristics: (1) The number of raised peaks on the surface of the heat-sealable layer = 710 average height per square millimeter = 26 nanometers (2) Haze -Not applicable, it is an opaque film (3) The coefficient of static friction of the heat-sealable layer = 0.58 (4) The heat-seal strength of the heat-sealable layer = 1400 Newton·(m)^-1

<u style="single">Example 4</u>

This example is a comparative example, not an example according to the present invention. The process of Example 2 was repeated, but the silica coating step was omitted, and the polyethylene terephthalate substrate layer did not contain china clay filler. The final film thickness is 75 microns, and the copolyester layer is 12 microns thick. Applying the above-mentioned test method to the resulting film, the film will show the following characteristics: (1) The number of raised peaks on the surface of the heat-sealable layer = 26 average height per square millimeter = 26 nanometer average height/width = 0.6×10^-3(2) Turbidity = 0.3% (3) The coefficient of static friction of the heat-sealable layer =&gt; 1.2 (4) The heat-seal strength of the heat-sealable layer = 590 Newton·(m)^-1

The above examples illustrate the improved properties of the film composition according to the present invention.