JP5270927B2 - Laminated film for manufacturing strong acid polymer sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated film for producing a strong acid polymer sheet which is suitable for cast-molding a sheetlike polymer structure such as an electrolyte film made of a polymeric electrolyte, excellent in contamination-proof properties, inexpensive, and excellent in heat resistance. <P>SOLUTION: In the laminated film for producing the strong acid polymer sheet, a laminated polyester film includes a layer (layer A) containing polyethylene terephthalate as a main component and a layer (layer B) containing polyethylene naphthalate as a main component, and a mold release layer containing an olefin copolymer being formed on the layer B. The thickness of the layer B is 0.5-2.5 &mu;m, and the thickness of the mold release layer converted from the maximum wavelength of the reflectance of the surface of the mold release layer is 75-150 nm. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a laminated polyester film suitably used for production of a polymer electrolyte membrane used for a fuel cell or the like.

  In recent years, fuel cells have attracted attention as clean energy sources that do not generate carbon dioxide, nitrogen oxides, and the like from the viewpoint of reducing environmental burden. In particular, solid polymer fuel cells whose ion exchange membranes, which can be said to be the heart of them, are strong acid polymer electrolytes such as perfluorosulfonic acid resins, are actively developed because they are easy to miniaturize and operate at relatively low temperatures. It has been.

  Electrolyte membranes made of this polymer electrolyte, especially electrode membranes in which platinum catalyst-carrying carbon and the like are dispersed in the electrolyte, are formed in a paste-like or ink-like form with a solvent in the formation. It is often formed by casting on a material film. As a release film used here, for example, as described in Patent Document 1, (1) a polyester film coated with silicone, (2) a stretched polypropylene film, (3) a fluororesin film, (4 ) Polyester film laminated with fluororesin is known, but silicone used as a release agent has a risk of contamination, and fluororesin is generally expensive. Regardless of whether it is laminated to a material or coated on another substrate, there are cost restrictions on the release film as a consumer material, and this is not suitable for reducing the cost of electrolyte membranes to be advanced in the future. Polyolefins such as polypropylene or polymers having long-chain alkyl side chains are inexpensive and have a certain releasability, but they are not necessarily releasable. Use is limited.

  Then, the thing etc. which used the polyethylene terephthalate film excellent in heat resistance as the base material and provided the release layer which consists of polyolefin are proposed (patent document 2). However, if the cast molding temperature is increased to improve the electrolyte membrane production rate, etc., the release layer becomes a molten state, so that a channel is temporarily formed and the strong acid electrolyte polymer directly contacts the base polyethylene terephthalate film. The possibility increases and the polyethylene terephthalate film is attacked, which may lead to defects.

JP 2003-285396 A JP 2006-150812 A

  The present invention has been made in view of the above circumstances, and its solution is a mold release suitable for cast molding of a sheet-like polymer structure such as an electrolyte membrane, which simultaneously satisfies non-contamination, low cost, and excellent heat resistance. To provide a film.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by adopting a specific configuration, and the present invention has been completed.

  That is, the gist of the present invention is to provide a copolymer polyolefin on the B layer of a laminated polyester film comprising a layer mainly composed of polyethylene terephthalate (A layer) and a layer mainly composed of polyethylene naphthalate (B layer). It is a film having a release layer to be contained, the thickness of the B layer is 0.5 to 2.5 μm, and the release layer thickness converted from the maximum wavelength of the reflectance of the release layer surface is 75 to 150 nm. It exists in the laminated film for strong acid polymer sheet manufacture characterized by this.

Hereinafter, the present invention will be described in detail.
The polyethylene terephthalate referred to in the present invention refers to a polyester obtained by condensing terephthalic acid and ethylene glycol, and if it is 10 mol% or less, components other than terephthalic acid and ethylene glycol may be copolymerized. Further, other polyesters, polymers, and auxiliaries may be mixed as long as the characteristics are not impaired.

  The polyethylene naphthalate as used in the present invention refers to a polyester in which 2,6-naphthalenedicarboxylic acid and ethylene glycol are condensed, and if it is 10 mol% or less, components other than 2,6-naphthalenedicarboxylic acid and ethylene glycol are present. It may be copolymerized. Further, other polyesters, polymers, and auxiliaries may be mixed as long as the characteristics are not impaired.

  The present invention uses, as a base material, a laminated polyester film including a layer mainly composed of polyethylene terephthalate and a surface layer mainly composed of polyethylene naphthalate. The surface on which the release layer is provided must be a layer mainly composed of polyethylene naphthalate, but the surface on the opposite side is not necessarily a surface layer mainly composed of polyethylene naphthalate.

  The surface on which the release layer is provided is mainly composed of polyethylene naphthalate, which has a relatively high resistance, because strong acid polymers may come into contact through channels that are accidentally formed in the release layer when heated at high temperatures. Must consist of layers.

  Polyethylene naphthalate film may be applied as a base material only from the viewpoint of resistance to strong acid polymer, but polyethylene naphthalate is several times more expensive than polyethylene terephthalate. When using polyethylene terephthalate film manufacturing equipment, it is necessary to cope with the equipment in terms of high-temperature stretching. Therefore, it is not necessarily optimal in terms of cost to apply to a carrier sheet, which is a standard use form.

  In the present invention, the base material is a laminated polyester film in which a polyethylene terephthalate layer is provided with a polyethylene naphthalate surface layer, as a whole, which can be produced in accordance with a polyethylene terephthalate film and also has resistance to a strong acid polymer. To do. However, in this case, since the glass transition temperature of polyethylene terephthalate and polyethylene naphthalate are remarkably different, the stretching process is performed under a temperature condition that is not necessarily optimum for any of the materials.

  The base film of the present invention generally conforms to polyethylene terephthalate, and it is desirable that the stretching conditions also conform to that of polyethylene terephthalate. As a result, the polyethylene naphthalate surface layer is cooled below the glass transition temperature. Since it becomes extending | stretching, the surface layer thickness must be 2.5 micrometers or less from a viewpoint of suppressing the malfunction which arises by cold drawing. On the other hand, from the viewpoint of resistance to strong acid polymer, the thickness of the polyethylene naphthalate surface layer must be 0.5 μm or more. Even if the thickness of the polyethylene naphthalate surface layer is 2.5 μm or less, if the ratio of the polyethylene naphthalate surface layer in the total thickness is too high, uniform stretching becomes difficult. As a guide, the polyethylene naphthalate surface layer is 5% of the total thickness. The following is desirable.

  The release layer of the present invention can be formed by applying a copolymerized polyolefin, preferably polyethylene, on the polyethylene naphthalate surface layer of the base film.

  Polyolefins generally have a low melting point and are inferior in heat resistance, but are excellent in acid resistance, and also have releasability from strong acid polymers, and are therefore suitable as a material constituting the carrier surface of a strong acid polymer sheet production film. However, when a single sheet is used as process paper, the physical properties and productivity of the cast molded product are limited due to heat resistance restrictions, so it is preferable to laminate a polyolefin layer on a heat resistant substrate. is there.

  As a method of laminating a polyolefin layer on a heat resistant substrate, a method of laminating a polyolefin film to a heat resistant substrate using an adhesive, a method of extruding and laminating polyolefin on a heat resistant substrate, a solution or dispersion of polyolefin Examples of the liquid include a method of coating on a heat-resistant substrate, etc., but in the case of having a step of melt-extruding polyolefin, (1) addition of a plasticizer or the like for relaxing high melt viscosity is required. (2) Since it is difficult to form a flat carrier surface with the thickness variation of the extruded polyolefin layer below a certain level, it is suitable for applications that require precision and cleanliness such as electronic parts. Therefore, a release layer is formed by a coating method.

  It is desirable that the polyolefin coating liquid does not contain a component that can be an impurity as much as possible from the viewpoint of not deteriorating the cleanness of the strong acid polymer sheet to be formed, and it is desirable to apply the solution rather than the dispersion liquid that requires a surfactant or the like.

  For this reason, it is preferable to use a copolymer polyethylene having a low crystallinity, a relatively high solubility in a solvent, and an excellent releasability from a strong acid polymer as the polyolefin constituting the release layer.

  In the copolymerized polyethylene applied to the release layer, examples of the component copolymerized with polyethylene include α-olefins, particularly propylene, n-butene, n-pentene, and n-hexene. From the viewpoint of ensuring a certain level of solubility, it is recommended that the molar ratio of the copolymerization component be 10 mol% or more.

  As the solvent used in the copolymerized polyethylene coating solution, toluene, xylene and the like having high affinity for polyethylene are suitable. In order to improve wettability and antistatic properties, a small amount of various organic solvents such as alcohol, ketone, and alkane may be mixed.

  As the coating method, conventional methods such as a bar coating method, a gravure coating method, and a reverse roll coating method can be used.

  In the release layer of the present invention, the thickness of the release layer converted from the maximum wavelength of the release surface reflectance is in the range of 75 to 150 nm. If the release layer thickness is less than 75 nm, even the polyethylene naphthalate surface layer, which is relatively excellent in acid resistance, has insufficient acid resistance protection effect due to the release layer, and the substrate surface layer is affected by the strong acid polymer. When the release layer thickness exceeds 150 nm, the peeling force from the strong acid polymer becomes too heavy. Although the appropriate level of peel force varies depending on the peel method and the strength of the strong acid polymer sheet, it cannot be generally stated, but if it exceeds 50 dN / m at 180 ° peel, it generally tends to cause problems in the peel process after forming the strong acid polymer sheet. Therefore, the upper limit guide for the release layer thickness is 150 nm.

  The release layer of the present invention may be cross-linked in order to improve heat resistance. As a crosslinking method, a small amount of a functional group-containing polyolefin that is compatible with the copolymer polyethylene constituting the release layer is blended, and a functional group is introduced into the main chain of the copolymer polyethylene constituting the release layer. And a method of cross-linking this.

  In particular, the method of introducing a hydroxyl group into a copolymer polyethylene main chain and crosslinking it with a polyfunctional isocyanate can provide not only crosslinking between polyolefins but also crosslinking with a hydroxyl group end of a base polyethylene naphthalate. It is particularly recommended because it has the effect of reducing the erosion of the base material by the strong acid polymer.

  According to the film of the present invention, it is suitable for cast molding of a sheet-like polymer structure such as an electrolyte membrane made of a polymer electrolyte, and is excellent in non-contaminating property, and at the same time satisfies low cost and excellent heat resistance. The film for manufacturing a strong acid polymer sheet can be provided, and its industrial value is high.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example. In the examples and comparative examples, “parts” means “parts by weight” as a solid content. The evaluation method used in the present invention is as follows.

(1) Strong acid polymer resistance 2 ml of strong acid polymer dispersion solution Nafion (registered trademark) dispersion solution DE2021 manufactured by DuPont is dropped on the sample release surface, and a wet sheet having a thickness of 10 mil is formed with a baker type applicator. This is immediately dried for 10 minutes in a hot air oven at an atmospheric temperature of 160 ° C. to form a film on the sample release surface. Subsequently, an adhesive tape No. 25 μm thick on the back of the membrane was used. 31B (manufactured by Nitto Denko) was bonded together, and the film was peeled off at 30 m / min. 31B is peeled 180 °. The release surface after peeling off the film is observed with a confocal laser microscope, and the presence or absence of transition traces (dents) having a depth of 0.5 μm or more is confirmed. Good migration resistance to strong acid polymer with no trace of migration.

(2) Peeling force of strong acid polymer sheet (unit: dN / m)
2 ml of strong acid polymer dispersion solution Nafion (registered trademark) dispersion solution DE2021 manufactured by DuPont is dropped on the sample release surface, and a wet sheet having a thickness of 10 mil is formed using a baker type applicator. This is immediately dried for 10 minutes in a hot air oven at an atmospheric temperature of 160 ° C. to form a film on the sample release surface. Subsequently, an adhesive tape No. 50 mm wide on the back of the membrane was used. After bonding 31B (manufactured by Nitto Denko), a release film and a strong acid polymer film are cut into a width of 50 mm according to the size of the adhesive tape. Then, at a peeling speed of 300 mm / min, No. 31B is peeled 180 °. The value obtained by dividing the average peel load measured at that time by the width of 50 mm was taken as the peel force.

(3) Release layer thickness A black vinyl tape (No. 21; manufactured by Nitto Denko) was bonded to the opposite surface of the measurement surface, and a wavelength of 200 to 2000 nm was used using a spectrophotometer (UV-3100PC; manufactured by Shimadzu Corporation). Measure the 5 ° absolute reflectance of the measurement surface in the area. A value obtained by dividing the peak wavelength of the maximum peak on the longest wavelength side among the maximum peaks of reflectance by 3.0 was defined as the release layer thickness. In this conversion, the refractive index of the copolymer polyethylene constituting the release layer is assumed to be 1.5.

(Preparation of copolymerized polyethylene coating solution)
・ Coating liquid A
A mixture of 2-hydroxyethyl methacrylate and peroxide (trade name Perhexa 25; manufactured by Nippon Shokubai Co., Ltd.) (weight ratio 19: 1) is added to ethylene / propylene rubber (trade name EP02P; manufactured by JSR) at 200 ° C. Kneaded to prepare a modified copolymer polyethylene grafted with 1% by weight of 2-hydroxyethyl methacrylate. This modified copolymerized polyethylene was mixed with toluene and stirred at reflux for 5 hours to obtain a solution having a polyolefin concentration of 3% by weight. Immediately before coating, a polyfunctional isocyanate (MYTEC NY718A; manufactured by Mitsubishi Chemical) was added to the solution so as to be 2.9% by weight based on the copolymerized polyethylene to obtain coating solution A.
・ Coating fluid B
99 parts of ethylene / propylene rubber (trade name EP02P; manufactured by JSR) and 1 part of polyolefin polyol (trade name Polytail H; manufactured by Mitsubishi Chemical) are mixed with toluene and stirred at reflux for 5 hours to obtain a solution having a polyolefin concentration of 3% by weight. It was. Immediately before the application, polyfunctional isocyanate (trade name: Mytec NY718A; manufactured by Mitsubishi Chemical) and triethyldiamine (trade name: 1,4-diazabicyclo [2.2.2] octane; manufactured by Wako Pure Chemical Industries, Ltd.) are respectively added to this solution. A coating solution B was prepared by adding 1% by weight with respect to the polyolefin solid content.

(Preparation of polyethylene naphthalate)
100 parts of dimethyl-2,6-naphthalate, 60 parts of ethylene glycol and 0.08 part of magnesium acetate were placed in a reactor to carry out a transesterification reaction. Next, 0.15 part of amorphous silica was added, 0.04 part of ethyl acid phosphate and 0.04 part of antimony trioxide were added, followed by polymerization according to a conventional method, and an intrinsic viscosity of 0.55 dl / g. Polyethylene naphthalate was obtained. Solid phase polymerization was then performed to increase the intrinsic viscosity to 0.60 dl / g.

(Preparation of polyethylene terephthalate)
Polyethylene terephthalate having an intrinsic viscosity of 0.60 dl / g was obtained in the same manner as in the preparation of polyethylene naphthalate except that 100 parts of dimethyl terephthalate was used instead of 100 parts of dimethyl-2,6-naphthalate.

(Preparation of base polyester film)
・ Polyester film A
Polyethylene naphthalate and polyethylene terephthalate were melted at 300 ° C. by separate twin screw extruders, and then merged in a T die so that polyethylene naphthalate constitutes both surface layers and polyethylene terephthalate constitutes an intermediate layer. The discharge amount of the surface layer / intermediate layer / surface layer was controlled by a gear pump so as to be 1/98/1. This laminated melt was extruded in the form of a sheet from a T-die onto a cast drum and quenched by an electrostatic application cooling method to obtain an amorphous sheet. This amorphous sheet was subjected to longitudinal stretching at 100 ° C. 3.6 times, followed by lateral stretching at 110 ° C. 4.0 times, and finally heat-fixed at 220 ° C. to obtain a polyester film having a thickness of 50 μm. A was obtained.

・ Polyester film B
Polyester film A except that it is not a three-layer structure of polyethylene naphthalate surface layer / polyethylene terephthalate layer / polyethylene naphthalate surface layer, but a two-layer structure of polyethylene naphthalate surface layer / polyethylene terephthalate layer (the discharge ratio is 1/19) Similarly, a polyester film B having a thickness of 50 μm was obtained.

・ Polyester film C
A polyester film C having a thickness was obtained in the same manner as the polyester film A, except that the discharge amount ratio of polyethylene naphthalate surface layer / polyethylene terephthalate layer / polyethylene naphthalate surface layer was set to 1/198/1.

・ Polyester film D
A polyester film was obtained in the same manner as the polyester film A except that the discharge amount of the polyethylene naphthalate surface layer / polyethylene terephthalate layer / polyethylene naphthalate surface layer was changed to 5/40/5. Whitening occurred and could not be applied as a substrate film.

Example 1:
The coating solution A was diluted with toluene at 40 ° C. to a polyolefin concentration of 0.75% by weight on the polyester film A using the Mayer bar # 4, and then heat-treated at 150 ° C. for 5 seconds. The laminated film was obtained by maintaining at a temperature of 48 ° C. for 48 hours.

Example 2:
The coating solution A was diluted with toluene at 40 ° C. to a polyolefin concentration of 1.6% by weight. The coating solution was applied onto the polyester film A using the Mayer bar # 6, and then heat-treated at 150 ° C. for 5 seconds. The laminated film was obtained by maintaining at a temperature of 48 ° C. for 48 hours.

Example 3:
A laminated film was obtained in the same manner as in Example 2 except that the coating liquid A was changed to the coating liquid B.

Example 4:
A laminated film was obtained in the same manner as in Example 1 except that the polyester film B was used instead of the polyester film A.

Comparative Example 1:
The coating solution A was diluted with toluene at 40 ° C. to give a polyolefin concentration of 0.5% by weight on the polyester film A using the Mayer bar # 3, and then heat-treated at 150 ° C. for 5 seconds. The laminated film was obtained by maintaining at a temperature of 48 ° C. for 48 hours.

Comparative Example 2:
The coating liquid A was applied on the polyester film A using the Mayer bar # 7, and then heat-treated at 150 ° C. for 5 seconds and kept at 23 ° C. for 48 hours to obtain a laminated film.

Comparative Example 3:
A laminated film was obtained in the same manner as in Example 1 except that the polyester film C was used instead of the polyester film A.

Comparative Example 4:
A film was obtained in the same manner as in Example 2 except that a polyethylene terephthalate film (trade name Diafoil T100-50S; manufactured by Mitsubishi Chemical Polyester Film Co., Ltd.) was used instead of the polyester film A.

  The film of the present invention can be suitably used, for example, for the production of polymer electrolyte membranes used for fuel cells and the like.

Claims (1)

A film having a release layer containing a copolymerized polyolefin on layer B of a laminated polyester film comprising a layer containing polyethylene terephthalate as a main component (A layer) and a layer containing polyethylene naphthalate as a main component (B layer) A strong acid polymer sheet, wherein the thickness of the B layer is 0.5 to 2.5 μm, and the release layer thickness converted from the maximum wavelength of the reflectance of the release layer surface is 75 to 150 nm Laminated film for manufacturing.