JP2011233444A - Double side release film for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a release film with high dimensional accuracy for forming a green sheet used as an electrolyte of a solid oxide fuel cell (SOFC).SOLUTION: A release film is used for forming a green sheet utilized as an electrolyte of a solid oxide fuel cell. The release film includes release layers on both sides of a biaxially oriented polyester film, and is a polyester release film of which heat shrinkage when heating for 30 minutes at 100°C is within -0.2 to 0.2% in every film directions.

Description

  The present invention relates to a release film, and more specifically, is used to form a green sheet used as an electrolyte of a solid oxide fuel cell (hereinafter sometimes abbreviated as SOFC (Solid Oxide Fuel Cell)). It relates to a release film.

  2. Description of the Related Art Conventionally, release films based on polyester films are used for green sheet molding, for example, in various ceramic release applications such as ceramic multilayer capacitors and ceramic substrates. In recent years, a process for producing a solid electrolyte for use in SOFC via green sheet molding has also been studied. Patent Documents 1 and 2 give examples of using films as carrier films.

  Fuel cells are attracting attention as clean energy systems that generate electricity by supplying hydrogen and oxygen in the air and reacting them, and do not generate harmful gases. In addition, the operating temperature is as high as about 1000 ° C., internal reforming of the raw material gas is possible, and there is an advantage that natural gas or carbon monoxide or carbon monoxide can be used as a hydrogen source. Furthermore, since the operating temperature is high and the utility value of waste heat is high, the overall efficiency is high and the amount of carbon dioxide generated can be suppressed.

  Further, since SOFC is a solid electrolyte, SOFC has no problem of electrolyte dissipation, has a simple structure, and can be expected to have a long life. Since SOFC has a high output density and does not require a reformer, it can be expected to be compact and highly efficient.

  The solid electrolyte is obtained by applying a ceramic slurry composed of ceramic particles having ionic conductivity (for example, zirconia-based particles), a binder, an additive, and the like, and then drying the solvent to form a sheet.

  On the other hand, since SOFC has a high operating temperature, usable materials are limited. In addition, it takes time to start. Therefore, studies are underway to lower the operating temperature. However, since the internal resistance of the electrode / electrolyte increases when the operating temperature of the fuel cell decreases, Patent Documents 3 to 6 disclose that the ion conductive material has sufficient ion conductivity even when the electrolyte is made thinner and the operating temperature is lowered. In addition, search for electrode materials having high catalytic activity has been conducted.

  In the manufacture of solid electrolyte membranes, for the purpose of reducing the internal resistance of fuel cells, the thinning of green sheets and the development of materials with high ionic conductivity are being studied. There is a need for moldable release films. In particular, as described in Patent Document 7, there is a need for a release film having releasability on both sides, which prevents blocking on the back surface and film breakage due thereto.

  However, in the step of heating and drying the green sheet applied to the polyester release film, there is a problem that the release film shrinks by heating, causing deformation and peeling of the green sheet.

JP-A-10-29205 JP 2001-205607 A JP 2002-358976 A JP 2003-263994 A JP 2003-346816 A JP 2004-200125 A JP 2009-54362 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is a release film having a small thermal shrinkage during heat drying for forming a green sheet used as an electrolyte of a solid oxide fuel cell. It is to provide.

  As a result of intensive studies in view of the above situation, the present inventor has found that the above-described problems can be easily solved by using a release film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is a release film used for forming a green sheet used as an electrolyte of a solid oxide fuel cell, and the release film is released on both sides of a biaxially oriented polyester film. Polyester mold release, characterized in that the film has a mold layer, and the heat shrinkage rate when heated at 100 ° C. for 30 minutes is in the range of −0.2 to 0.2% in any direction of the film Be on film.

  If the release film of the present invention is used for forming a green sheet used for an electrolyte of a solid oxide fuel cell, the internal resistance of the fuel cell can be lowered by thinning the solid electrolyte membrane, and the high fuel cell This can contribute to output.

  The raw material polyester used in the polyester film of the present invention may be a homopolyester or a copolyester. When using a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. On the other hand, when a copolymer polyester is used, it is preferably a copolymer containing 30 mol% or less of the third component. Examples of the dicarboxylic acid component of the copolyester include one or two of isophthalic acid, terephthalic acid phthalate, 2,6-naphthalenedicarboxylic acid, adipic acid sebacic acid, and oxycarboxylic acid (for example, P-oxybenzoic acid). Examples of the glycol component include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

  In any case, the polyester referred to in the present invention is usually 70 mol% or more, preferably 90 mol% or more of polyethylene terephthalate having ethylene terephthalate units, or polyethylene-2,6-naphthalate having ethylene-2,6-naphthalate units. Refers to a polyester that is the like.

  It is preferable to mix | blend particle | grains in the polyester film in this invention with the main objective of providing slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.
The average particle size of the particles used is preferably in the range of 0.1 to 5 μm, more preferably in the range of 0.5 to 5 μm. If the average particle size is less than 0.1 μm, the particles tend to aggregate and the dispersibility tends to be insufficient. On the other hand, if it exceeds 5 μm, the surface roughness of the film becomes too rough, When a release layer is provided in a subsequent process, problems may occur, and the quality of the obtained green sheet may be deteriorated.
Furthermore, the particle content in the polyester is preferably in the range of 0.01 to 5% by weight, more preferably in the range of 0.01 to 3% by weight. When the particle content is less than 0.01% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the particle size of the particles is too large. As in the case, problems may occur in the step of providing the release layer, or the quality of the obtained green sheet may be deteriorated.

  The method for adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, the particles can be added at any stage for producing the polyester, but preferably, the polycondensation reaction may proceed after the esterification stage or after the transesterification reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  The heat shrinkage rate when the release film of the present invention is heated at 100 ° C. for 30 minutes needs to be in the range of −0.2 to 0.2% in any direction of the film. If it is out of the range, the green sheet is deformed, which is not preferable.

  Although the thickness of the polyester film which comprises the release film of this invention will not be specifically limited if it is a range which can be formed into a film, Usually, 9-250 micrometers, Preferably it is the range of 12-188 micrometers.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.

  That is, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the extending | stretching temperature orthogonal to the extending | stretching direction of the 1st step is 130-170 degreeC normally, and a draw ratio is 3.0-7 times normally, Preferably it is 3.5-6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or relaxation within 30% to obtain a biaxially oriented film.

  In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges. The unstretched sheet can be simultaneously biaxially stretched so that the area magnification is 10 to 40 times. Furthermore, it may be stretched again in the longitudinal and / or transverse direction before or after performing the heat treatment, if necessary.

  A so-called coating stretching method (in-line coating) in which the film surface is treated during the above-described polyester film stretching step can be applied. Although it is not limited to the following, for example, in the sequential biaxial stretching, in particular, the first-stage stretching is completed, and the coating treatment can be performed before the second-stage stretching. When a coating layer is provided on a polyester film by the above-described coating stretching method, coating can be performed simultaneously with stretching and the thickness of the coating layer can be reduced according to the stretching ratio, which is suitable as a polyester film. A film can be manufactured.

  In the release film of the present invention, it is practically preferable that the release force on the release surface is within a specific range. That is, in the release film of the present invention, the normal peel strength of at least one release layer is preferably in the range of 400 mN / cm or less, more preferably in the range of 20 to 200 mN / cm. When the normal state peeling force exceeds 400 mN / cm, particularly when the green sheet is thin, there is a problem that the green sheet is difficult to peel off and easily broken when the green sheet is peeled off. On the other hand, when it is less than 20 mN / cm, there may be a problem that the green sheet is partially peeled off from the end of the carrier film during the process.

  The residual adhesive rate of the release film of the present invention is preferably 80% or more, more preferably 85% or more. When the residual adhesive rate is less than 80%, the silicone transfer to the surface of the counterpart green sheet that contacts the release surface of the release film increases, and when the green sheet is used for SOFC, the transferred silicone is oxidized even after firing. There is concern that it will remain as a product and inhibit the normal electrode reaction.

In general, the electrode reaction of a solid oxide fuel cell (SOFC) includes the following reactions.
<Electrode reaction>
(Positive electrode) / Solid electrolyte / (Negative electrode)
H ₂ + O ₂ ⁻ → H ₂ O + 2e ⁻ / Solid electrolyte / O ₂ + 2e ⁻ → O ₂ ⁻
That is, oxygen (O ₂ ) is reduced at the negative electrode, and the generated oxide ions (O ₂ ⁻ ) diffuse in the solid electrolyte and reach the positive electrode. At the positive electrode, hydrogen (H ₂ ) is oxidized and reacts with the diffused oxide ions (O ₂ ⁻ ) to generate water.

  On the other hand, these electrode reactions can be expected to have higher output when the internal resistance of the battery is smaller. In order to reduce the internal resistance of the battery, it is necessary to reduce the thickness of the solid electrolyte, but in that case, if the unevenness formed on the surface of the release film is large, the quality of the obtained solid electrolyte deteriorates, causing problems. Will occur. For this purpose, specifically, the maximum height (Rmax) of the surface of the polyester film constituting the release film in the present invention is preferably 1.5 to 30 μm, more preferably 3 to 20 μm.

  Further, in the polyester film constituting the release film in the present invention, as a method for forming the film surface having the maximum height (Rmax), a particle kneading method, a particle coating method, an embossing method, a sand blasting method, an etching method are used. A method such as an electric discharge machining method can be used. In the present invention, any of the methods described above may be adopted, and there is no particular limitation.

  Next, typical methods will be described in detail, but the present invention is not limited to the following production examples.

  In the process of kneading the polyester film, inorganic fine particles such as titanium oxide, calcium carbonate, silica, and kaolin are added in the course of manufacturing the polyester film, or the precipitated fine particles of the catalyst residue are left in the polyester. This is a method for roughening the film surface.

  The embossing method is a method of roughening the film surface by embossing at a predetermined temperature using an apparatus composed of an embossing roll and a backup roll having a desired uneven shape.

  The particle coating method is a method in which a roughened surface is formed on a film by applying a coating solution having an appropriate viscosity prepared from particles, a binder, and a solvent to the film surface. Examples of the particles include inorganic particles such as silica, alumina, calcium carbonate, and titanium oxide, and organic particles such as silicone resin, fluorine resin, and benzoguanamine resin. Examples of the binder include polyester resins, acrylic resins, polyvinyl butyral resins, polyurethane resins, phenoxy resins, epoxy resins, polyvinyl chloride resins, and compounds containing radical polymerizable double bonds. Examples of the coating apparatus include a gravure coater, a reverse coater, and a wire bar coater. In addition, an antifoamer, a coating property improving agent, a thickener, a particle dispersion stabilizing resin, and the like can be added to the coating solution as necessary.

  The release layer constituting the release film of the present invention is not particularly limited as long as it contains a material having releasability. Among such materials, it is preferable to use a curable silicone resin because release properties are particularly improved. A type having a curable silicone resin as a main component may be used, or a modified silicone type by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used. As the type of the curable silicone resin, any of the curing reaction types such as an addition type, a condensation type, an ultraviolet ray curable type, an electron beam curable type, and a solventless type can be used.

  Specific examples of the curable silicone resin include KS-772, KS-774, KS-775, KS-778, KS-779H, KS-856, X-62-2422, X- manufactured by Shin-Etsu Chemical Co., Ltd. 62-2461, DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, FSQK-2560, FSRK-2560 manufactured by Dow Corning Asia Co., Ltd. YSR-3022, TPR-6700 manufactured by Toshiba Silicone Co., Ltd. , TPR-6720, TPR-6721, SD7220, SD7226, SD7229 manufactured by Toray Dow Corning Co., Ltd., and the like.

  Further, a release control agent may be used in combination in order to adjust the peelability of the release layer.

The coating amount (Si) of the release layer constituting the release film of the present invention is 0.01 to 5 g / m ² , further 0.01 to ² g / m ² , particularly 0.01 to 1 g / m ² . A range is preferred. When the coating amount of the release layer is less than 0.01 g / m ² , the coated surface may lack stability and it may be difficult to obtain a uniform coating film. On the other hand, when the coating amount exceeds 5 g / m ² , the coating film adhesion and curability of the release layer itself may be deteriorated.

In the present invention, conventionally known coating methods such as reverse roll coating, gravure coating and bar coating can be used as a method for providing a release layer on the polyester film.
The peeling force of the release film of the present invention is preferably 400 mN / cm or less from the viewpoint of peelability with respect to the green sheet after molding. When the peeling force exceeds 400 mN / cm, there may be a problem that the sheet breaks when the green sheet is peeled off.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measuring method used in the present invention is as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of a sample was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measured at 30 ° C.

(2) Measurement of average particle diameter (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(3) Measurement of maximum height (Rmax) of polyester film Only a reference length (2.5 mm) was extracted from a cross-sectional curve obtained by a surface roughness measuring machine (SE-3F) manufactured by Kosaka Laboratory Ltd. When the extracted part is sandwiched by two straight lines parallel to the average line of the part (hereinafter referred to as the extracted part), the distance between the two straight lines is measured in the direction of the vertical magnification of the cross-sectional curve, and the value is measured in units of micrometers (μm) The maximum height of the extracted part is represented by. The maximum height was expressed as an average value of the maximum heights of the extracted portions obtained from 10 cross-sectional curves obtained from the sample film surface. The radius of the stylus used at this time was 2.0 μm, the load was 30 mg, and the cutoff value was 0.08 mm.

(4) Evaluation of peel strength (F) of release film One side of a double-sided pressure-sensitive adhesive tape (Nitto Denko “No. 502”) was attached to the release layer of the measurement sample, cut into a size of 50 mm × 300 mm, and room temperature The peel force after standing for 1 hour was measured. For the peeling force, a tensile tester (“Intesco model 2001 type” manufactured by Intesco Co., Ltd.) was used, and 180 ° peeling was performed under the condition of a tensile speed of 300 mm / min.

(5) Measurement of coating amount (Si) of release layer Using a fluorescent X-ray measurement apparatus (model “XRF-1500” manufactured by Shimadzu Corporation), the FP (Fundamental Parameter Method) method was performed under the following measurement conditions. The amount of silicon element on the surface of the release film provided with the release layer and the surface without the release layer was measured, and the difference was taken as the amount of silicon element in the release layer. Next, the coating amount (Si) (g / m ² ) as a unit of —SiO (CH ₃ ) ₂ was calculated using the obtained amount of silicon element.
"Measurement condition"
Spectral crystal: PET (pentaerythritol)
2θ: 108.88 °
Tube current: 95 mA
Tube voltage: 40 kv
In the case where no silicon element is present in the release layer, the coating amount is measured by a technique such as cross-sectional observation.

(6) Evaluation of Residual Adhesion Rate of Release Film / Residual Adhesive Strength Nitto Denko (manufactured) No. The 31B adhesive tape is subjected to one reciprocating pressure bonding with a 2 kg rubber roller, and heat-treated at 100 ° C. for 1 hour. Next, the sample film was peeled off from the pressure-bonded sample. The adhesive strength of the 31B adhesive tape was measured according to the method of JIS-C-2107 (adhesive strength to stainless steel plate, 180 ° peeling method), and this was defined as the residual adhesive strength.

・ Basic adhesive strength Using the same tape (No. 31B) as the residual adhesive strength, press the adhesive tape on the stainless steel plate according to JIS-C-2107, and measure in the same way. The value was defined as basic adhesive strength. Using these measured values, the residual adhesion rate was determined based on the following formula.
Residual adhesion rate (%) = (residual adhesive force / basic adhesive force) × 100
The measurement was performed at 20 ± 2 ° C. and 65 ± 5% RH.

(7) Measurement of heat shrinkage rate Each of the films was cut into strips of 15 mm width × 150 mm length, and 30 in an oven set at 100 ° C. in a non-tensioned state (manufactured by Tajii Corporation: hot air circulating furnace). The heat treatment was performed for 2 minutes at 150 ° C. for 1 minute, the length before and after the heat treatment was measured with a micrometer, and the heat shrinkage rate was determined by the following formula. Among the measurement results of the samples in each direction, the maximum value and the minimum value were obtained.
Heat shrinkage rate (%) = [(ab) / a] × 100
(In the above formula, a and b mean the film length (mm) before and after heating, respectively)

<Manufacture of polyester film>
3 parts of silicon dioxide particles having an average particle diameter of 3.5 μm, polyethylene terephthalate having an intrinsic viscosity of 0.65 were dried at 180 ° C. for 4 hours in an inert gas atmosphere, melted at 290 ° C. by a melt extruder, An unstretched sheet was obtained by extruding from a die and cooling and solidifying on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method. The obtained sheet was stretched 3.5 times in the longitudinal direction at 85 ° C. Next, the film was guided to a tenter and stretched 3.7 times in the transverse direction at 100 ° C., and then heat-set at 230 ° C. to obtain a PET film F1 (Rmax = 4.5 μm) having a thickness of 50 μm.

Example 1:
A release layer composed of silicone resin A1 is provided on one side of the PET film so that the coating amount is 0.1 g / m ² (after drying) on the PET film obtained above, and passed through an oven at 120 ° C. A silicone resin curing reaction was performed. Further, a release layer made of silicone resin A1 is provided on the surface where no release layer is provided so that the coating amount is 0.1 g / m ² (after drying), and the paper is passed through an oven at 120 ° C. Then, the double-sided release film was annealed by passing it through a 150 ° C. oven at a tension of 7 kg / m per unit width of the film, and a normal peel strength of 20 mN / cm on both sides. A release film was obtained.
<< Releasing agent composition >> A1
Curable silicone resin (Shin-Etsu Chemical: X62-5039): 100 parts Curing agent (Shin-Etsu Chemical: CAT-PL-50T): 5 parts

Example 2:
A release layer comprising the same silicone resin A1 as in Example 1 is provided on one side of the same PET film as in Example 1 so that the coating amount is 0.1 g / m ² (after drying), and passed through an oven at 120 ° C. A silicone resin curing reaction is performed using a paper, and a release layer made of silicone resin A1 is provided on the surface where no release layer is provided so that the coating amount is 0.1 g / m ² (after drying). Pass the paper through a 150 ° C oven at a tension of 7 kg / m per unit width of the film, and simultaneously perform the curing reaction of the silicone resin and the annealing treatment of the release film to obtain a double-sided release film with a normal peel strength of 20 mN / cm. Obtained.

Example 3:
In Example 1, a double-sided release film having a normal state peeling force of 400 mN / cm was obtained in the same manner as in Example 1 except that the silicone resin A3 was used instead of the silicone resin A1.
<< Releasing agent composition >> A3
Curable silicone resin (Shin-Etsu Chemical "X-62-5040A"): 40 parts Release control agent (Shin-Etsu Chemical "KS-3800"): 60 parts Curing agent (Shin-Etsu Chemical "PL-5000"): 5 Part

Comparative Example 1:
As in Example 1, after applying silicone resin A1 on both sides and carrying out a curing reaction, annealing was not performed by passing paper through a 150 ° C. oven at a tension of 7 kg / m per unit width of the film. A double-sided release film having a peeling force of 20 mN / cm was obtained.

Comparative Example 2:
As in Example 3, after applying silicone resin A3 on both sides and carrying out a curing reaction, annealing was not performed by passing paper through a 150 ° C. oven at a tension of 7 kg / m per unit width of the film. A double-sided release film having a peeling force of 380 mN / cm was obtained.
The characteristics of each film obtained in the above Examples and Comparative Examples are shown in Table 1 below.

  The film of the present invention can be suitably used as a release film used for forming a green sheet used as a solid electrolyte of a fuel cell.

Claims (1)

A release film used for forming a green sheet used as an electrolyte of a solid oxide fuel cell, the release film is a film having release layers on both sides of a biaxially oriented polyester film, A polyester release film having a heat shrinkage rate in the direction of 0.2 to 0.2% in any direction of the film when heated at 100 ° C. for 30 minutes.