Biaxially oriented sealable polyester film

The invention relates to a transparent sealable, coextruded, biaxially oriented polyester film comprising at least one base layer (B) and cover layers (A) and (C) applied to both sides of this base layer. The invention further relates to a process for the production of the film and its use.

Sealable, biaxially oriented polyester films are known in the art. These known in the art films are characterized either by a good sealing behavior or by a good appearance or by an acceptable processing behavior.

In the <b>GB-A 1 465 973</b> describes a coextruded, two-layered polyester film whose one layer of isophthalic acid-containing and terephthalic acid-containing copolyesters and their other layer consists of polyethylene terephthalate. About the sealing behavior of the film can be found in the document no usable information. Due to the lack of pigmentation, the film can not be produced reliably (film can not be wound) and can only be further processed if restricted.

In the <b>EP-A-0 035 835</b> describes a co-extruded sealable polyester film, which are added to improve the winding and processing behavior in the sealing layer particles whose average particle size exceeds the layer thickness of the sealing layer. The particulate additives form surface protrusions which prevent unwanted blocking and sticking of the film to rollers or guides. About the other, non-sealable layer of the film, no details are given for the incorporation of antiblocking agents. It remains unclear whether this layer contains antiblocking agents. By choosing particles with a larger diameter than the sealing layer and the concentrations specified in the examples, the sealing behavior of the film is impaired. Information on the sealing temperature range of the film are not made in the writing. The seal seam strength is measured at 140 ° C and is in a range of 63 to 120 N / m (corresponding to 0.97 to 1.8 N / 15 mm film width).

In the <b>EP-A-0 432 886</b> For example, a coextruded multilayer polyester film is described which has a first surface on which a sealable layer is disposed and a second surface on which an acrylate layer is disposed. The sealable outer layer can also consist of isophthalic acid-containing and terephthalic acid-containing copolyesters. The back coating gives the film improved processing behavior. Information on the seal area of ​​the film are not made in the Scriptures. The seal seam strength is measured at 140 ° C. For a 11 μm thick sealing layer, a seal seam strength of 761.5 N / m (corresponding to 11.4 N / 15 mm film width) is specified. A disadvantage of the back acrylate coating is that this side no longer seals against the sealable top layer. The film is therefore very limited use.

In the <b>EP-A-0 515 096</b> describes a coextruded, multilayer, sealable polyester film containing an additional additive on the sealable layer. The additive can eg contain inorganic particles and is preferably applied in an aqueous layer to the film during their preparation. In this way, the film should retain the good sealing properties and be easy to process. The back side of the film contains only very few particles, which pass mainly through the regranulate into this layer. Information on the sealing temperature range of the film are not made in this document. The seal seam strength is measured at 140 ° C and is more than 200 N / m (corresponding to 3 N / 15 mm film width). For a 3 μm thick sealing layer, a seal seam strength of 275 N / m (corresponding to 4.125 N / 15 mm film width) is specified.

In the <b>WO 98/06575</b> there is described a coextruded, multilayered polyester film containing a sealable overcoat and a non-sealable basecoat. The base layer may be composed of one or more layers, wherein one of the layers is in contact with the sealable layer. The other (outer) layer then forms the second, non-sealable cover layer. The sealable top layer can also consist of isophthalic acid-containing and terephthalic acid-containing copolyesters, which, however, contain no antiblock particles. The film also contains at least one UV absorber, which is added to the base layer in an amount of 0.1 to 10 wt .-%. The base layer of this film is equipped with conventional antiblocking agents. The film is characterized by a good sealability, but does not have the desired processing behavior and has deficits in the optical properties (gloss and haze).

The object of the present invention was therefore to provide a sealable, biaxially oriented polyester film which does not have the disadvantages of the prior art films mentioned and is distinguished, in particular, by an improved sealability and improved processability with otherwise constant or possibly even improved optical properties , In particular, it was an object of the present invention to extend the sealing range of the film to low temperatures and to improve the seal seam strength of the film. In addition, care should be taken that the film can also be processed on high-speed processing machines. In the production of the film should also be ensured that in the film production resulting waste material can be recycled as regenerate in an amount of up to 60 wt .-%, based on the total weight of the film, back to the manufacturing process, without affecting the physical and optical properties of the film are appreciably adversely affected.

The object is achieved by providing a coextruded, biaxially oriented, sealable polyester film having at least one base layer (B), a sealable top layer (A) and another top layer (C) dissolved, wherein the sealable outer layer A has a sealing temperature of at most 110 ° C and a seal strength of at least 1.3 N / 15 mm film width and the topographies of the two outer layers (A) and (C) are characterized by the following features:

Sealable topcoat (A):

<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext>R</mtext></mrow><mrow><mtext>a</mtext></mrow></msub><mtext>Value ≤ 40 nm</mtext></mrow></math><img file="EP1138480A2_D0001.tif" /></maths> Measured gas flow in the range of 300 to 4000 s;

Non-sealable top layer (C):

<maths id="math0002" num=""><math display="block"><mrow><mtext>COF ≤ 0.5</mtext></mrow></math><img file="EP1138480A2_D0002.tif" /></maths><maths id="math0003" num=""><math display="block"><mrow><msub><mrow><mtext>40 nm ≤ R</mtext></mrow><mrow><mtext>a</mtext></mrow></msub><mtext> ≤ 150 nm</mtext></mrow></math><img file="EP1138480A2_D0003.tif" /></maths> Measured value of gas flow ≤ 140 s;

Number of surveys N_C per mm² Film surface, which are correlated with the respective height h via the following equations:<maths id="math0004" num=""><math display="block"><mrow><msub><mrow><mtext>A</mtext></mrow><mrow><mtext>C1</mtext></mrow></msub><msub><mrow><mtext> - B</mtext></mrow><mrow><mtext>C1</mtext></mrow></msub><msub><mrow><mtext> · Log h / μm &lt;log N</mtext></mrow><mrow><mtext>C</mtext></mrow></msub><msup><mrow><mtext>/ mm</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> &lt;A</mtext></mrow><mrow><mtext>C2</mtext></mrow></msub><msub><mrow><mtext> - B</mtext></mrow><mrow><mtext>C2</mtext></mrow></msub><mtext> · Log h / μm</mtext></mrow></math><img file="EP1138480A2_D0004.tif" /></maths><maths id="math0005" num=""><math display="block"><mrow><mtext>0.01 μm ≤ h ≤ 10 μm</mtext></mrow></math><img file="EP1138480A2_D0005.tif" /></maths>    A_C1 = 0.29 B_C1 = 3.30    A_C2 = 1.84 B_C2 = 2.70.

The subclaims specify preferred embodiments of the invention, which are explained in more detail below.

According to the invention, the film is at least three-layered and then comprises as layers the base layer (B), the sealable cover layer (A) and the non-sealable cover layer (C).

Polymers used for the base and for the topcoat:

Base material:

The base layer (B) of the film is preferably at least 90 wt .-% of a thermoplastic polyester. Suitable for this are polyesters of ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), of ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), of 1,4-bis-hydroxymethyl-cyclohexane and terephthalic acid (= Poly-1,4-cyclohexanedimethylene terephthalate, PCDT) and from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalatbibenzoat, PENBB). Particular preference is given to polyesters which consist of at least 90 mol%, preferably at least 95 mol%, of ethylene glycol and terephthalic acid units or of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols or Dicarboxylic acids, as they can also occur in the layer (A) or in the layer (C).

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH₂)_n-OH, where n is an integer from 3 to 6 (in particular propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol and hexane-1,6-diol) or branched aliphatic Glycols with up to 6 carbon atoms. Of the cycloaliphatic diols, mention may be made of cyclohexanediols (in particular cyclohexane-1,4-diol). Suitable other aromatic diols correspond for example to the formula HO-C₆H₄XC₆H₄-OH, where X is -CH₂-, -C (CH₃)₂-, -C (CF₃)₂-, -O-, -S- or -SO₂- stands. In addition, bisphenols of the formula HO-C₆H₄-C₆H₄-OH well suited.

Other aromatic dicarboxylic acids are preferably benzene dicarboxylic acids, naphthalene dicarboxylic acids, for example naphthalene-1,4- or 1,6-dicarboxylic acid, biphenyl-x, x'-dicarboxylic acids, in particular biphenyl-4,4'-dicarboxylic acid, diphenylacetylene-x, x'-dicarboxylic acids , in particular diphenylacetylene-4,4'-dicarboxylic acid, or stilbene-x, x'-dicarboxylic acids. Of the cycloaliphatic dicarboxylic acids, mention may be made of cyclohexanedicarboxylic acids, in particular cyclohexane-1,4-dicarboxylic acid. Of the aliphatic dicarboxylic acids, the (C₃ to C₁₉Alkanedioic acids are particularly suitable, wherein the alkane moiety may be straight-chain or branched.

The preparation of the polyester can, for example done after the transesterification process. It is based on dicarboxylic acid esters and diols, which are reacted with the usual transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts. The intermediates are then polycondensed in the presence of commonly used polycondensation catalysts, such as antimony trioxide or titanium salts. The preparation can also be carried out by the direct esterification process in the presence of polycondensation catalysts. It starts directly from the dicarboxylic acids and diols.

Sealable topcoat (A):

The sealable top layer (A) applied by coextrusion onto the base layer (B) is based on polyester copolymers and consists essentially of copolyesters which are predominantly composed of isophthalic acid and terephthalic acid units and of ethylene glycol units. The remaining monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols or Dicarboxylic acids, as they may also occur in the base layer. The preferred copolyesters which provide the desired sealing properties are those composed of ethylene terephthalate and ethylene isophthalate units and ethylene glycol units. The proportion of ethylene terephthalate is 40 to 95 mol% and the corresponding proportion of ethylene isophthalate 60 to 5 mol%. Preference is given to copolyesters in which the proportion of ethylene terephthalate is 50 to 90 mol% and the corresponding proportion of ethylene isophthalate 50 to 10 mol%, and very preferred are copolyesters in which the proportion of ethylene terephthalate 60 to 85 mol% and corresponding proportion of ethylene isophthalate 40 to 15 mol%.

Non-sealable top layer (C):

For the other, non-sealable outer layer (C) or for any intermediate layers present, it is possible in principle to use the same polymers as described above for the base layer (B).

Sealing and processing properties:

The desired sealing and the desired processing properties of the film according to the invention are obtained from the combination of the properties of the copolyester used for the sealable top layer and the topographies of the sealable top layer (A) and the non-sealable top layer (C).

The maximum sealing temperature of 110 ° C. and the seal seam strength of at least 1.3 N / 15 mm film width is achieved if the copolymers described in more detail above are used for the sealable outer layer (A). The best sealing properties of the film are achieved if no further additives, in particular inorganic or organic fillers, are added to the copolymer. For this case, given a given copolyester, the lowest seal initiation temperature and highest seal seam strengths are obtained. However, in this case, the handling of the film is poor because the surface of the sealable top layer (A) is prone to blocking. The film can hardly be wrapped and is not suitable for further processing on high-speed packaging machines. To improve the handling of the film and the processability, it is necessary to modify the sealable top layer (A). This is best done with the help of suitable antiblocking agents of a selected size, which are added to the sealing layer in a certain amount in such a way that on the one hand minimizes the blocking of the film and on the other hand, the sealing properties are only slightly deteriorated. This desired combination of properties can surprisingly be achieved if the topography of the sealable topcoat (A) is characterized by the following set of parameters: According to the invention, the roughness of the sealable outer layer, expressed by the R_aValue, less than or equal to 40 nm. In the other case, the sealing properties in the context of the present invention are adversely affected.

The measured value of the gas flow should be in the range of 300 to 4000 s according to the invention. At values ​​below 300 s, the sealing properties are negatively influenced in the sense of the present invention, while at values ​​above 4000 s the handling of the film deteriorates.

To further improve the processing performance of the sealable film, the topography of the non-sealable topcoat (C) should be characterized by the following set of parameters:

The friction coefficient (COF) of this side against itself should be less than or equal to 0.5 according to the invention. Otherwise, the winding behavior and the further processing of the film is unsatisfactory.

The roughness of the non-sealable overcoat (C) expressed as its R_aValue, should be greater than or equal to 40 nm and less than or equal to 150 nm. Smaller R_aValues ​​greater than 40 nm have a negative effect on the winding and processing behavior of the film, while larger R_aValues ​​than 150 nm affect the optical properties (gloss, haze) of the film.

According to the invention, the measured value of the gas flow for the cover layer (C) should be in the range below 140 s. Values ​​above 140 s negatively affect the winding and processing behavior of the film.

The number of surveys N per mm² Film surface is correlated with the respective height h via the following equation:<maths id="math0006" num=""><math display="block"><mrow><msup><mrow><mtext>0.29 - 3.30 · log h / μm &lt;log N / mm</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><mtext> &lt;1.84-2.70 · log h / μm</mtext></mrow></math><img file="EP1138480A2_D0006.tif" /></maths> with 0.01 μm ≤ h &lt;10 μm

If the values ​​for N are smaller than the left side of the inequality, the winding and processing behavior of the film is adversely affected, and if the values ​​for N are greater than the right side of the inequality, the gloss and haze become the film negatively affected.

Anti-blocking agent

The base layer (B) may additionally contain conventional additives, such as stabilizers and / or antiblocking agents. The two other layers (A) and (C) may additionally contain conventional additives, such as stabilizers and / or antiblocking agents. The funds are expedient the polymer or the polymer mixture already added before melting. As stabilizers, for example, phosphorus compounds such as phosphoric acid or phosphoric acid esters are used advantageously.

Typical antiblocking agents (also referred to in this context as "pigments") are inorganic and / or organic particles, for example calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, LiF, calcium, Barium, zinc or manganese salts of the dicarboxylic acids used, carbon black, titanium dioxide, kaolin or crosslinked polystyrene or acrylate particles.

As antiblocking agents it is also possible to choose mixtures of two or more different antiblocking agents or mixtures of antiblocking agents of the same composition but different particle size. The particles can be added to the individual layers in the respectively advantageous concentrations, for example as a glycolic dispersion during the polycondensation or via masterbatches during the extrusion.

Preferred particles are SiO₂ in colloidal and chain-like form. These particles are very well integrated into the polymer matrix and produce only slightly vacuoles. Vacuoles generally cause turbidity and are therefore expedient to avoid. The particle diameters of the particles used are in principle not restricted. For the solution of the problem, it has proved to be expedient, particles having an average primary particle diameter of less than 100 nm, preferably less than 60 nm, more preferably less than 50 nm, measured by the Sedigraph method, and / or particles having a mean primary particle diameter of greater than or equal to 1 micron, preferably greater than or equal to 1.5 microns and more preferably greater than or equal to 2 microns to use. However, these particles described last should not have an average particle diameter greater than 5 μm.

In order to achieve the abovementioned properties of the sealable film, it has proven expedient to set the amount of particles in the base layer (B) lower than in the two outer layers (A) and (C). In the case of a three-layer film of the stated type, the amount of particles in the base layer (B) will be between 0 and 0.15% by weight, preferably between 0 and 0.12% by weight, in particular between 0 and 0.10% by weight .-%. The particle diameter of the particles used is in principle not restricted, but particles with an average diameter of greater than or equal to 1 μm are particularly preferred.

In the advantageous form of use, the film consists of three layers, the base layer (B) and cover layers (A) and (C) applied to this base layer on both sides, the cover layer (A) being sealable against itself and against the cover layer (C).

To obtain the mentioned property profile of the film, the cover layer (C) has more pigments (ie higher pigment concentration) than the cover layer (A). The pigment concentration in this second outer layer (C) according to the invention is between 0.1 and 1.0% by weight, advantageously between 0.12 and 0.8% by weight, in particular between 0.15 and 0.6% by weight. %. The other, the cover layer (C) opposite, sealable outer layer (A), however, contains less inert pigments. Namely, the amount of inert particles in the layer (A) is between 0.01 and 0.2% by weight, preferably between 0.015 and 0.15% by weight, in particular between 0.02 and 0.1% by weight. %, all data in wt .-% are based on the total weight of the respective layer.

Optionally, an intermediate layer may be present between the base layer and the cover layers. This in turn may consist of the polymers described for the base layers. In a particularly preferred embodiment, the intermediate layer consists of the polyester used for the base layer. The intermediate layer may also contain the conventional additives described. The thickness of the intermediate layer is generally greater than 0.3 μm and is preferably in the range from 0.5 to 15 μm, in particular in the range from 1.0 to 10 μm, particularly preferably in the range from 1.0 to 5 μm.

In the particularly advantageous three-layer embodiment of the film according to the invention, the thickness of the outer layers (A) and (C) is generally greater than 0.1 μm and is preferably in the range from 0.2 to 4.0 μm, particularly preferably in the range of 0 , 2 to 3.5 microns, in particular in the range of 0.3 to 3 microns and most preferably in the range of 0.3 to 2.5 microns, wherein the outer layers (A) and (C) be the same or versc thick can.

The total thickness of the polyester film of the invention may vary within certain limits. It is 3 to 80 microns, especially 4 to 50 microns, preferably 5 to 30 microns, wherein the layer (B) has a proportion of preferably 5 to 90% of the total thickness.

The polymers for the base layer (B) and the two outer layers (A) and (C) are fed to the production of the film three extruders. Existing foreign bodies or impurities can be removed from the polymer melt before extrusion by suitable filters. The melts are then formed into flat melt films in a multi-layer die and stacked one on top of the other. Subsequently, the multi-layer film is drawn off and solidified with the aid of a cooling roller and optionally further rollers.

Production method:

The invention also relates to a process for the preparation of the polyester film according to the invention by the coextrusion process known per se from the literature.

In this process, the procedure is such that the melts corresponding to the individual layers (A), (B) and (C) of the film are coextruded through a flat die, and the film thus obtained is stripped off on one or more rolls, the film is then biaxially stretched (orientated), the biaxially stretched film is heat-set and, if appropriate, corona or flame-treated on the surface layer intended for the treatment.

The biaxial stretching (orientation) is generally performed sequentially, with the successive biaxial stretching, in which stretching is first longitudinal (in the machine direction) and then transverse (perpendicular to the machine direction), is preferred.

First, as usual in the coextrusion process, the polymer or compresses and liquefies the polymer mixtures for the individual layers in an extruder, wherein the optionally provided as additives additives already in the polymer or may be contained in the polymer mixture. The melts are then pressed simultaneously through a flat die (slot die) and the extruded multilayer melt is drawn off on one or more draw rolls, with the melt cooling and solidifying into a prefilm.

The biaxial stretching is generally carried out sequentially. In this case, the prefilm preferably first in the longitudinal direction (ie in the machine direction, = MD direction) and then in the transverse direction (ie perpendicular to the machine direction, = TD direction) stretched. This leads to a spatial orientation (orientation) of the polymer chains. The stretching in the longitudinal direction can be carried out with the help of two according to the desired stretch ratio different speed rotating rollers. For transverse stretching is generally used a corresponding clip frame in which the film is clamped on both edges and then pulled at elevated temperature to both sides.

The temperature at which the stretching is carried out may vary within a relatively wide range and depends on the desired properties of the film. In general, the longitudinal stretching is carried out at a temperature in the range of 80 to 130 ° C and the transverse extension in the range of 90 to 150 ° C. The longitudinal stretch ratio is generally in the range of 2.5: 1 to 6: 1, preferably 3: 1 to 5.5: 1. The transverse stretch ratio is generally in the range of 3.0: 1 to 5.0: 1, preferably 3.5: 1 to 4.5: 1. Before the transverse stretching, one or both surfaces of the film can be coated in-line according to the known methods. The in-line coating can be used, for example, for improved adhesion of a metal layer or any later to be applied ink, but also for improving the antistatic behavior or the processing behavior.

For the production of a film with very good sealing properties, it has proved favorable if the planar orientation Δp of the film is smaller than Δp = 0.168, but especially smaller than Δp = 0.165. In this case, the strength of the film in the thickness direction is so great that when measuring the seal seam strength, the seal is definitely broken and the film does not tear and tear.

It has been found that the main influencing factors on the planar orientation Δp are the process parameters in the longitudinal stretching and in the transverse extension, as well as the SV value of the raw material used. The process parameters include in particular the stretch ratios in the longitudinal and in the transverse direction (λ_MD and λ_TD), the stretching temperatures in the longitudinal and in the transverse direction (T_MD and T._TD), the film web speed and the type of stretching, in particular that in the longitudinal direction of the machine. For example, with a machine, one obtains a planar orientation of Δp = 0.169 with the parameter set λ_MD = 4.8 and λ_TD = 4.0, the stretching temperatures in the longitudinal and in the transverse direction T_MD = 80 to 118 ° C and T_TD = 80 to 125 ° C, we obtain by increasing the longitudinal stretching temperature to T_MD = 80 to 125 ° C or by increasing the transverse stretching temperature to T_TD = 80 to 135 ° C or by lowering the Längstreckverhältnisses to λ_MD = 4.3 or by lowering the transverse stretching ratio to λ_TD = 3.7 a planar orientation Δp, which lies in the desired range. The film web speed was 340 m / min and the SV value of the material was about 730. In the case of longitudinal stretching, the abovementioned data relate to the so-called N-TEP stretching, which is composed of a low-orientation elongation step (LOE) and a high-orientation stretching step (REP = rapid elongation process). In other drafting systems, the same conditions arise in principle, but the numerical values ​​for the respective process parameters can be slightly different. The indicated temperatures refer to the respective roll temperatures during the longitudinal stretching and to the film temperatures which were measured by means of IR during the transverse stretching.

In the subsequent heat-setting, the film is held at a temperature of 150 to 250 ° C over a period of about 0.1 to 10 s. Subsequently, the film is wound in the usual manner.

Preferably, after biaxial stretching, one or both surfaces of the film are corona- or flame-treated by one of the known methods. The treatment intensity is generally in the range of over 45 mN / m.

To adjust further desired properties, the film can be additionally coated. Typical coatings are adhesion-promoting, antistatic, slip-improving or dehesive-acting layers. It is advisable to apply these additional layers by means of in-line coating by means of aqueous dispersions before the stretching step in the transverse direction to the film.

Advantages of the invention:

The film of the invention is characterized by an excellent sealability, a very good handling and by a very good processing behavior. In the case of the film, the sealable outer layer (A) seals not only against itself (fin sealing) but also against the self-sealable outer layer (C) (lab sealing). In the last-mentioned variant of the lab sealing, the sealing-impinging temperature is merely increased by approx. 10 K shifted upward, the seal seam strength is reduced by not more than 0.3 N / 15 mm film width.

In addition, the gloss and haze of the film could be significantly improved. In addition, it is ensured in the production of the film that the blend material (regenerated) in an amount in the range of 20 to 60 wt .-%, based on the total weight of the film, can be fed back to the extrusion, without affecting the physical properties of the Slide are negatively influenced, especially their visual appearance.

Accordingly, the film is very well suited for use in flexible packaging, especially where its excellent sealing properties and good processability come into full effect. This is especially their use on high-speed packaging machines.

The table below (Table 1) summarizes the most important film properties according to the invention once again at a glance.<tables id="tabl0001" num="0001"><img file="EP1138480A2_D0007.tif" /></tables>

For the characterization of the raw materials and the films, the following measuring methods were used in the context of the present invention:

SV value (standard viscosity)

The standard viscosity SV (DCE) is measured, based on DIN 53726, in dichloroacetic acid.

The intrinsic viscosity (IV) is calculated from the standard viscosity as follows<maths id="math0007" num=""><math display="block"><mrow><msup><mrow><mtext>IV (DCE) = 6.907 x 10</mtext></mrow><mrow><mtext>-4</mtext></mrow></msup><mtext> SV (DCE) + 0.063096</mtext></mrow></math><img file="EP1138480A2_D0008.tif" /></maths>

Determination of the sealing temperature (minimum sealing temperature)

The sealer HSG / ET from Brugger is used to produce heat-sealed samples (sealing seam 20 mm x 100 mm), the film being sealed at different temperatures with the help of two heated sealing jaws at a sealing pressure of 2 bar and a sealing time of 0.5 s. Test strips of 15 mm width were cut from the sealed samples. The T-seam strength was measured as in the determination of the seal strength. The seal initiation temperature is the temperature at which a seal strength of at least 0.5 N / 15 mm is achieved.

Seal strength

To determine the seal seam strength, two 15 mm wide film strips were superposed and sealed at 130 ° C., a sealing time of 0.5 s and a sealing pressure of 2 bar (device: Brugger type NDS, one-side heated sealing jaw). The seal strength was determined by the T-Peel method.

friction

The friction was determined according to DIN 53 375. The coefficient of sliding friction was measured 14 days after production.

surface tension

The surface tension was determined by means of the so-called ink method (DIN 53 364).

cloudiness

The haze according to Hölz ​​was determined according to ASTM-D 1003-52, but measured to use the optimum measuring range on four superimposed layers of film and instead of a 4 ° hole aperture a 1 ° slit was used.

shine

The gloss was determined according to DIN 67 530. The reflector value was measured as an optical parameter for the surface of a film. Based on the standards ASTM-D 523-78 and ISO 2813, the angle of incidence was set at 20 ° or 60 °. A light beam strikes the flat test surface under the set angle of incidence and is reflected by it or scattered. The light rays incident on the photoelectronic receiver are displayed as a proportional electrical quantity. The measured value is dimensionless and must be specified with the angle of incidence.

Determination of grain sizes on film surfaces

The size distribution of elevations on film surfaces is determined using a scanning electron microscope and an image analysis system. The scanning electron microscope XL30 CP from Philips is used with an integrated image analysis program AnalySIS from the company Soft-Imaging System.

For these measurements, film samples are placed flat on a sample holder. Subsequently, these are at an angle a with a thin metal layer (eg of silver) obliquely evaporated. Here, a is the angle between the sample surface and the propagation direction of the metal vapor. This oblique evaporation creates a shadow behind the elevation. Since the shadows are not yet electrically conductive, the sample is then still with a second metal (eg Gold) vapor deposited or sputtered with the second coating impinging perpendicularly on the sample surface, thus leaving no shadows on the second coating.

The thus prepared sample surfaces are imaged in a scanning electron microscope (SEM). The shadows of the elevations are visible due to the material contrast of the metals. The sample is oriented in the SEM such that the shadows run parallel to a picture edge. For image acquisition, the following conditions are set on the SEM: secondary electron detector, working distance: 10 mm, acceleration voltage: 10 kV and spot: 4.5. The brightness and contrast are adjusted so that all image information is displayed as gray values ​​and the intensity of the background noise is so small that it is not detected as a shadow. The length of the shadows is measured with the image analyzer. The shadow detection threshold is set to the location where the 2. Derivation of the gray value distribution of the image crosses the zero point. Before shadow detection, the image is smoothed with an NxN filter (size 3, 1 iteration). The setting of a frame ensures that surveys that are not completely displayed in the image are not measured. The magnification, the frame size and the number of evaluated images are selected to be 0.36 mm in total² Film surface are evaluated.

The height of the individual surveys is calculated from the individual shadow lengths with the following relationship:<maths id="math0008" num=""><math display="block"><mrow><mtext>h = (tan α) · L</mtext></mrow></math><img file="EP1138480A2_D0009.tif" /></maths> where h is the height of the elevation, α is the evaporation angle and L is the shadow length. The surveys thus determined are divided into classes to arrive at a frequency distribution. The classification is made in 0.05 mm wide classes between 0 and 1 mm, whereby the smallest class (0 to 0.05 mm) is not used for further evaluations. The diameters (propagation perpendicular to the shadow throwing direction) of the protuberances are similarly classified into 0.2 mm wide classes from 0 to 10 mm, again using the smallest class for further evaluation.

Surface Gas Flow Time

The principle of the measurement method is based on the air flow between a film side and a smooth silicon wafer plate. The air flows from the environment into an evacuated space, wherein the interface between the film and silicon wafer plate serves as a flow resistance.

A round film sample is placed on a silicon wafer plate, in the middle of which a bore ensures connection to the recipient. The recipient is evacuated to a pressure of less than 0.1 mbar. It determines the time in seconds that the air takes to cause a 56 mbar pressure increase in the receiver. Measurement conditions:<tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">measuring surface</entry><entry namest="col2" nameend="col2" align="left">45.1 cm²</entry></row><row><entry namest="col1" nameend="col1" align="left">pressing weight</entry><entry namest="col2" nameend="col2" align="left">1276 G</entry></row><row><entry namest="col1" nameend="col1" align="left">air temperature</entry><entry namest="col2" nameend="col2" align="left">23 ° C</entry></row><row><entry namest="col1" nameend="col1" align="left">humidity</entry><entry namest="col2" nameend="col2" align="left">50 % relative humidity</entry></row><row><entry namest="col1" nameend="col1" align="left">Gas collection volume</entry><entry namest="col2" nameend="col2" align="left">1.2 cm³</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">print interval</entry><entry namest="col2" nameend="col2" align="left">56 mbar</entry></row></tbody></tgroup></table></tables>

Determination of the planar orientation Δp

The determination of the planar orientation is made by measuring the refractive indices with the Abbe refractometer according to the internal operating instruction 24. <tables id="tabl0003" num="0003"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">sample preparation</entry><entry namest="col2" nameend="col2" /></row><row><entry namest="col1" nameend="col1" align="left">Sample size and sample length</entry><entry namest="col2" nameend="col2" align="left">60 up to 100 mm</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">sample width</entry><entry namest="col2" nameend="col2" align="left">corresponds to prism width of 10 mm</entry></row></tbody></tgroup></table></tables>

For the determination of n_MD and n_a (N =_z), the sample to be measured must be cut out of the film, in which the running edge of the sample must coincide exactly with the TD direction. For the determination of n_TD and n_a (N =_z), the sample to be measured must be cut out of the film, at which the running edge of the sample must coincide exactly with the MD direction. The samples are taken from the middle of the film web. Make sure that the Abbe refractometer has a temperature of 23 ° C. On the well cleaned before the measurement lower prism is using a glass rod a little diiodomethane (N = 1.745) or Diiodomethane-bromonaphthalene mixture applied. The refractive index of the mixture must be greater than 1.685. On top of this, the sample cut out in the TD direction is placed first so that the entire prism surface is covered. With the help of a paper tissue, the film is now ironed firmly on the prism, so that the film rests firmly and smoothly. The excess liquid must be sucked off. Thereafter, a little of the measuring liquid is dropped on the film. The second prism is folded down and pressed firmly. Now use the right-hand thumbscrew to turn the display scale until a transition from light to dark in the viewing window is visible in the range 1.62 to 1.68. If the transition from light to dark is not sharp, the colors are merged with the aid of the upper knurled screw so that only one light and one dark zone is visible. The sharp transition line is brought to the crossing point of the two (in the eyepiece) diagonal lines with the aid of the lower knurled screw. The value now displayed in the measuring scale is read and entered in the measuring report. This is the refractive index in the machine direction n_MD, Now the scale with the lower knurled screw is turned so far that the range visible in the eyepiece is between 1.49 and 1.50.

Now the refractive index in n_a or n_z (in the thickness direction of the film) determined. So that the only weakly visible transition is better seen, a polarizing film is placed on the eyepiece. This is to turn until the transition is clearly visible. The same applies as for the determination of n_MD, If the transition from light to dark is not sharp (colored), the colors are merged with the aid of the upper knurled screw so that a sharp transition is visible. This sharp transition line is brought to the crossing point of the two diagonal lines with the help of the lower knurled screw and the value indicated on the scale is read off and entered in the table.

Subsequently, the sample is rotated and the corresponding refractive indices n_MD and n_α (N =_z) of the other surface side and recorded in a corresponding table.

After determining the refractive indices in the MD direction or in the thickness direction, the sample strip cut out in the MD direction is applied and, correspondingly, the refractive indices n_TD and n_a (= n_z) certainly. The strip is turned over and the values ​​for the B side are measured. The values ​​for the A-side and the B-side are combined to mean refractive values. The orientation values ​​are then calculated from the refractive indices according to the following formulas:<maths id="math0009" num=""><math display="block"><mrow><msub><mrow><mtext>Δn = n</mtext></mrow><mrow><mtext>MD</mtext></mrow></msub><msub><mrow><mtext> - n</mtext></mrow><mrow><mtext>TD</mtext></mrow></msub></mrow></math><img file="EP1138480A2_D0010.tif" /></maths><maths id="math0010" num=""><math display="block"><mrow><msub><mrow><mtext>Δp = (n</mtext></mrow><mrow><mtext>MD</mtext></mrow></msub><msub><mrow><mtext> + n</mtext></mrow><mrow><mtext>TD</mtext></mrow></msub><msub><mrow><mtext>) / 2 - n</mtext></mrow><mrow><mtext>z</mtext></mrow></msub></mrow></math><img file="EP1138480A2_D0011.tif" /></maths><maths id="math0011" num=""><math display="block"><mrow><msub><mrow><mtext>n</mtext></mrow><mrow><mtext>av</mtext></mrow></msub><msub><mrow><mtext> = (n</mtext></mrow><mrow><mtext>MD</mtext></mrow></msub><msub><mrow><mtext> + n</mtext></mrow><mrow><mtext>TD</mtext></mrow></msub><msub><mrow><mtext> + n</mtext></mrow><mrow><mtext>z</mtext></mrow></msub><mtext>) / 3</mtext></mrow></math><img file="EP1138480A2_D0012.tif" /></maths>

example 1

Chips of polyethylene terephthalate (prepared via the transesterification process with Mn as transesterification catalyst, Mn concentration: 100 ppm) were dried at a temperature of 150 ° C to a residual moisture of below 100 ppm and fed to the extruder for the base layer (B). Also, chips of polyethylene terephthalate and a filler were fed to the extruder for the non-sealable top layer (C).

In addition, chips were prepared from a linear polyester consisting of an amorphous copolyester with 78 mole percent ethylene terephthalate and 22 mole percent ethylene isophthalate (prepared via the transesterification process with Mn as the transesterification catalyst, Mn concentration: 100 ppm). The copolyester was dried at a temperature of 100 ° C. to a residual moisture content of below 200 ppm and fed to the extruder for the sealable outer layer (A).

Then by coextrusion and subsequent stepwise orientation in the longitudinal and transverse directions, a transparent, three-layer film with ABC structure and a total thickness of 12 microns was prepared. The thickness of the respective outer layers is shown in Table 2.<tables id="tabl0004" num="0004"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Covering layer (A), mixture of:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center">97.0% by weight</entry><entry namest="col2" nameend="col2" align="left">Copolyester with an SV value of 800</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center">3.0% by weight</entry><entry namest="col2" nameend="col2" align="left">Masterbatch of 97.75 wt .-% copolyester (SV value of 800) and 1.0 wt .-% ® Sylobloc 44 H (synthetic SiO₂ from Grace) and 1.25% by weight of ® Aerosil TT 600 (pyrogenic SiO₂ the company Degussa)</entry></row></tbody></tgroup></table></tables><tables id="tabl0005" num="0005"><table frame="all"><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col2" align="left">Base layer (B):</entry></row></thead><tbody valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="center">100.0% by weight</entry><entry namest="col2" nameend="col2" align="left">Polyethylene terephthalate with an SV value of 800</entry></row></tbody></tgroup></table></tables><tables id="tabl0006" num="0006"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Covering layer (C), mixture of:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center">88 Wt .-%</entry><entry namest="col2" nameend="col2" align="left">Polyethylene terephthalate with an SV value of 800</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center">12 Wt .-%</entry><entry namest="col2" nameend="col2" align="left">Masterbatch of 97.75 wt .-% copolyester (SV value of 800) and 1.0 wt .-% Sylobloc 44 H (synthetic SiO₂ from Grace) and 1.25% by weight of Aerosil TT 600 (chain-like SiO₂ the company Degussa)</entry></row></tbody></tgroup></table></tables>

The production conditions in the individual process steps were: <tables id="tabl0007" num="0007"><table frame="all"><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" colsep="0" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">temperatures</entry><entry namest="col3" nameend="col3" align="left">A layer B-layer C layer</entry><entry namest="col4" nameend="col4" align="right">3e + 08 ° C ° C ° C</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">Die width:</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">2.5 mm</entry></row><row><entry namest="col1" nameend="col1" align="left">extrusion</entry><entry namest="col2" nameend="col2" align="left">Temperature of the take-off roll</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">30 ° C</entry></row><row><entry namest="col1" nameend="col1" morerows="1" align="left">longitudinal stretching</entry><entry namest="col2" nameend="col2" align="left">Temperature:</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">80-125 ° C</entry></row><row><entry namest="col2" nameend="col2" align="left">Longitudinal stretching ratio:</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">4.2</entry></row><row><entry namest="col1" nameend="col1" morerows="1" align="left">transverse stretching</entry><entry namest="col2" nameend="col2" align="left">Temperature:</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">80-135 ° C</entry></row><row><entry namest="col2" nameend="col2" align="left">Transverse stretching ratio</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">4</entry></row><row><entry namest="col1" nameend="col1" morerows="1" rowsep="1" align="left">fixation</entry><entry namest="col2" nameend="col2" align="left">Temperature:</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">230 ° C</entry></row><row rowsep="1"><entry namest="col2" nameend="col2" align="left">duration:</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">3 s</entry></row></tbody></tgroup></table></tables>

The film had the required good sealing properties and shows the desired handling and the desired processing behavior. The film structure and the properties of films produced in this way are shown in Tables 2 and 3.

Example 2

In comparison to Example 1, the cover layer thickness of the sealable layer (A) was increased from 1.5 to 2.0 μm with an otherwise identical film structure and identical production method. The sealing properties have improved as a result, in particular, the seal seam strength has become much larger.

Example 3

In comparison to Example 1, a 20 μm thick film was now produced. The cover layer thickness of the sealable layer (A) was 2.5 μm, and that of the non-sealable layer (C) was 2.0 μm. The sealing properties have thereby improved even further, in particular, the seal seam strength has become much larger. The handling of the film has tend to be even better.

Example 4

Compared to Example 3, the copolymer for the sealable top layer (A) was changed. Instead of the amorphous copolyester having 78 mol% of polyethylene terephthalate and 22 mol% of ethylene isophthalate, an amorphous copolyester having 70 mol% of polyethylene terephthalate and 30 mol% of ethylene isophthalate has now been used. The raw material was processed on a twin-screw extruder with degassing, without having to be pre-dried. The cover layer thickness of the sealable layer (A) was again 2.5 μm, and that of the non-sealable layer (C) was 2.0 μm. The sealing properties have improved as a result, in particular, the seal seam strength has become much larger. To achieve good handling and a good processing behavior of the film, the pigment concentration in the two outer layers was slightly increased.

Comparative Example 1

Compared to Example 1, the sealable topcoat (A) has now not been pigmented. Although this has somewhat improved the sealing properties, the handling of the film and the processing behavior have become unacceptably worse.

Comparative Example 2

Compared to Example 1, the sealable topcoat (A) has now been pigmented as high as the non-sealable topcoat (C). The handling and the processing properties of the film have improved by this measure, but the sealing properties have become significantly worse.

Comparative Example 3

Compared to Example 1, the non-sealable outer layer (A) has now been markedly less pigmented. The handling of the film and the processing behavior of the film has become significantly worse.

Comparative Example 4

Example 1 from EP-A-0 035 835 was worked up. The sealing behavior of the film, the handling of the film and the processing behavior of the film is worse than in the inventive examples<tables id="tabl0008" num="0008"><img file="EP1138480A2_D0013.tif" /></tables><tables id="tabl0009" num="0009"><img file="EP1138480A2_D0014.tif" /></tables>