JP2002240017A - Mold release film for manufacturing ceramic sheet and film laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold release film capable of uniformly coating on a mold release layer when particularly an aqueous ceramic slurry is used in the case of manufacturing a thin film ceramic laminate and having a mold release layer of a small mold release force when a ceramic sheet is released from the release layer. SOLUTION: In the mold release film for manufacturing the ceramic sheet in the mold release film obtained by forming a mold release layer on at least one surface of a polyester film, an absolute value |A-B| of a difference of a dynamic hardness A of the surface of the ceramic sheet laminated on a surface of the mold release layer of the mold release film and a dynamic hardness B of the surface of the mold release layer is 20 gf/μm2 or less, and a surfactant exists on the surface of the mold release layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a release film having a polyester film as a base and a release layer of the release film for producing a ceramic sheet by applying and drying an aqueous ceramic slurry. And a ceramic sheet layer. More specifically, the present invention relates to a release film for producing a ceramic sheet having a small peeling force and a stable wetting performance with respect to an aqueous ceramic slurry, and a film laminate in which a ceramic sheet layer is laminated on a release layer of the release film.

[0002]

2. Description of the Related Art Ceramic sheets used for dielectrics, piezoelectrics, substrates and the like are formed by a method such as a doctor blade method, a calendar roll method, and an extrusion method. For example, in the case of the doctor blade method, a ceramic powder, a binder, a plasticizer, a ceramic slurry composed of a solvent, etc. is coated on a carrier film so as to have a constant thickness by a doctor blade, dried, solidified, and then dried. The sheet is peeled from the carrier film to produce a ceramic sheet.

[0003] As a carrier film, mechanical strength,
A release film in which a curable silicone compound is provided as a release layer on a biaxially stretched polyethylene terephthalate film, which is advantageous in terms of dimensional stability, heat resistance, price, and the like, is generally used.

In recent years, in order to reduce the size and capacitance of multilayer ceramic capacitors, it has been required to reduce the thickness of ceramic sheets and to stack them in multiple layers. However, as the thickness of the ceramic sheet becomes thinner, a peeling force at the time of peeling the ceramic sheet from the release layer of the release film becomes larger, and a new problem that peel failure occurs frequently occurs. Therefore, a release film having a smaller peeling force than the conventional release film has been required.
General-purpose release films that have been used for conventional labels, etc., have a small peeling force in their applications, but are insufficient in terms of releasability for the production of thin ceramic sheets. There is a demand for a release film having a small force.

However, even if a release film having a small peeling force from a ceramic sheet having a specific composition is designed, the constituent components of the ceramic sheet (the type of ceramic particles, the average primary particle size, the particle dispersibility, or the binder When the type, the content ratio of ceramic particles and binder, etc.) and the thickness of the ceramic sheet change, the peeling force between the ceramic sheet and the release layer of the release film changes. It was necessary to design the composition of the release layer of the release film most suitable for the above.

In recent years, in forming a ceramic sheet, the amount of the organic solvent is reduced in view of cost reduction of a binder, a solvent, etc., generation of fire and odor by the organic solvent, health care of workers, treatment of waste solvent, and the like. It has become necessary to suppress as much as possible, and an aqueous ceramic slurry has been used instead of an organic solvent ceramic slurry.

The aqueous ceramic slurry has poor wettability with the release layer of the release film. Therefore, when a release film provided with a general silicone compound as the release layer is used, the aqueous ceramic slurry is used. When coating is performed, repulsion occurs, and a uniform ceramic sheet cannot be obtained.

In general, when a release layer having a small peeling force is used, wettability with the aqueous ceramic slurry is further deteriorated, and repelling of the aqueous ceramic slurry on the surface of the release layer of the release film is more likely to occur. It will be easier. Therefore, when the aqueous ceramic slurry is coated on the release layer of the release film, it can be uniformly coated, and when the ceramic sheet is released from the release layer, a release film having a small release force is required. ing.

[0009]

That is, an object of the present invention is to solve such a problem and to uniformly coat a release layer in the production of a thin ceramic sheet, especially when an aqueous ceramic slurry is used. To provide a release film having a release layer having a small release force when the ceramic sheet is released from the release layer, and a film laminate in which a ceramic sheet layer is laminated on the release layer of the release film. It is in.

[0010]

The present invention has solved the above two problems with the following technical concept. The first technical idea is to reduce the absolute value of the dynamic hardness difference between the ceramic sheet at the peeling interface and the release layer of the release film in the peeling step when manufacturing the ceramic sheet, thereby reducing the constituent components of the ceramic sheet. It does not depend on the type of ceramic, the average particle size, the type of binder, the content ratio thereof, or the thickness of the ceramic sheet, and is excellent in releasability. Such a technical idea relating the physical properties of the ceramic sheet and the release layer of the release film is a novel one that cannot be predicted from the prior art.

The second technical idea is that even when the release film has a small release force, the presence of a surfactant on the surface of the release layer of the release film allows the aqueous ceramic slurry to be coated on the release layer surface. There is no repelling of the aqueous ceramic slurry and uniform coating can be achieved.

That is, the present invention relates to a release film formed by forming a release layer on at least one surface of a polyester film, wherein a dynamic hardness A of a ceramic sheet surface laminated on the release layer surface of the release film. The absolute value | AB | of the difference between the dynamic hardness B of the release layer surface and the release layer surface is 20 g.
A release film for producing a ceramic sheet, wherein the release film has a f / μm ² or less and a surfactant is present on the surface of the release layer.

Further, the present invention is a film laminate in which a ceramic sheet layer is laminated on a release layer of the release film.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The polyester constituting the polyester film used as the base material of the present invention is not particularly limited, and those obtained by forming a film of a polyester generally used as a release film base material can be used. It is preferably a crystalline linear saturated polyester composed of a dibasic acid component and a diol component, and examples thereof include polyethylene terephthalate, polyethylene-2-6 naphthalate, and polymethylene terephthalate.

In order to improve the handleability and slipperiness of the film, organic or inorganic fine particles may be blended with the polyester as long as the effects of the present invention are not impaired.
In particular, fine particles having an average particle size of 0.01 to 10 μm are preferably contained at a ratio of 0.005 to 5% by weight based on the total weight of the polyester.

The polyester film used in the present invention comprises:
In particular, a biaxially stretched polyester film is preferable in terms of mechanical strength, dimensional stability, and heat resistance.

The method for producing the polyester film in the present invention is not particularly limited, and a conventionally used method can be used. For example, the polyester is melted by an extruder, extruded from a T-die into a sheet,
It can be obtained by preparing an unstretched sheet by cooling with a rotary cooling drum and then uniaxially or biaxially stretching the unstretched sheet. The uniaxially stretched film is
It can be obtained by uniaxially stretching an unstretched film in the machine direction or the transverse direction. Further, the biaxially stretched film is obtained by a method of sequentially biaxially stretching a uniaxially stretched film in a longitudinal direction or a transverse direction in a transverse direction or a longitudinal direction, or a method of simultaneously biaxially stretching an unstretched film in a longitudinal direction and a transverse direction. I can do it.

In the present invention, the stretching temperature at the time of stretching the polyester film is preferably at least the secondary transition point (Tg) of the polyester and less than the temperature-rise crystallization temperature (TC1). In the case of a biaxially stretched film, the stretching ratio is preferably 1.1 to 8 times, particularly 2 to 6 times in the longitudinal and transverse directions. Further, in order to improve the thermal dimensional stability, the film after biaxial stretching is heat-set at 200 to 240 ° C., and is subjected to a transverse relaxation treatment and / or a longitudinal relaxation treatment at a relaxation rate of 1 to 8%. preferable. The obtained long film is wound into a roll and slit into a desired size.

The thickness of the polyester film used in the present invention may be set according to the purpose of use, and is not particularly limited, but is preferably from 2 to 300 μm, particularly preferably from 10 to 125 μm. preferable.

The release layer of the release film of the present invention requires the presence of a surfactant on the surface of the release layer. By the presence of the surfactant, when the aqueous ceramic slurry is coated on the surface of the release layer, releasability is not inhibited and repelling of the aqueous ceramic slurry can be prevented. When the aqueous ceramic slurry comes into contact with the surfactant present on the surface of the release layer, the surface energy of the surface of the release layer can be increased and the wettability can be improved. That is, the presence of the surfactant on the surface of the release layer can be confirmed by, for example, an increase in surface energy γs. When the surfactant is present on the surface of the release layer, the surface energy γs can be increased to 40 mN / m or more.

In order to obtain a release layer having the above-described characteristics, a resin containing a hydrophobic group in a molecular chain is used as a resin (abbreviated as a release resin) as a main component of the release layer. If not particularly limited, preferably silicone resin,
Fluororesin, and the like. By mixing a surfactant with the release resin or by coating the release resin coating solution on the surfactant layer, a hydrophilic functional group may be present on the surface of the release layer. is necessary.

The release film of the present invention has an absolute value | AB | of the difference between the dynamic hardness A of the ceramic sheet surface laminated on the release layer surface of the release film and the dynamic hardness B of the release layer surface. Should be 20 gf / μm ² or less, and preferably 15 gf / μm ² or less. Particularly preferably, it is 10 gf / μm ² or less.

Absolute value of the difference in dynamic hardness | A-
Exceeds 20 gf / μm ² , the releasability decreases when the ceramic sheet layer is peeled off from the release film to produce a ceramic sheet. Particularly, in the case of a thin ceramic sheet, the ceramic sheet is broken at the time of peeling. In addition, problems such as frequent occurrence of peeling failure and decrease in yield occur.

Absolute value of the difference in dynamic hardness | A-
By setting B | within the above range, the peeling force at the time of manufacturing the ceramic sheet by peeling the ceramic sheet layer from the release film is small, and the ceramic sheet layer can be easily peeled, thereby reducing damage to the ceramic sheet. be able to.

When the ceramic sheet layer is peeled off from the release film to produce a ceramic sheet, the peeling mode changes depending on the hardness of the ceramic sheet, so it is necessary to change the hardness of the release layer surface of the release film.

That is, when the ceramic sheet is hard,
Alternatively, when the thickness of the ceramic sheet is small, the influence of the viscosity of the ceramic sheet layer is hardly observed when the ceramic sheet layer is peeled off. Therefore, it is preferable to increase the hardness of the release layer of the release film.

On the contrary, when the ceramic sheet is soft,
When the ceramic sheet layer is peeled off, the influence of the viscosity of the ceramic layer appears. Therefore, it is preferable that the release layer corresponding thereto has a small hardness. For example, a release layer having excellent chemical peeling power, such as increasing the hydrophobic group content of the release resin, is preferable.

The peeling behavior at the interface between the ceramic sheet and the release film is different from the peeling behavior at the normal interface between the pressure-sensitive adhesive sheet and the release film. That is, in the case of separation at the interface between the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet and the release layer of the release film, the cohesive energy at the interface becomes dominant. On the other hand, in the case of peeling at the interface between the hard ceramic sheet and the release film, when the release layer is hard, deformation of the release layer at the time of peeling is small, and as a result, the peeling force becomes small. When the release layer is soft, the release layer is greatly deformed at the time of peeling, and as a result, the peeling force is increased.

Therefore, it is considered that the peeling behavior between the hard ceramic sheet and the hard release film is governed by the interfacial shear force, not the interfacial peel force as in the peeling of the pressure-sensitive adhesive sheet and the release film. .

Absolute value of the dynamic hardness difference | AB
In order to make | 20 gf / μm ² or less, it is necessary to design the hardness of the release layer of the release film according to the hardness of the ceramic sheet layer.

For example, a ceramic sheet is composed of ceramic particles (barium titanate, alumina, aluminum nitride, etc.) and a binder (acrylic resin, vinyl acetate resin, etc.).
When the content ratio (weight ratio) of the binder to the ceramic particles is large, or when the thickness of the ceramic sheet layer is large, the ceramic sheet when the ceramic sheet layer is laminated on the release film is formed. Hardness decreases. In addition, the dispersibility of the ceramic particles in the ceramic slurry also affects the hardness of the ceramic sheet,
If the dispersibility of the ceramic particles at the time of preparing the ceramic slurry is insufficient, the hardness of the ceramic sheet becomes small.

When the ceramic sheet having a small hardness as described above is peeled, it is necessary to reduce the hardness of the release layer. For example, 1) the content of the hydrophobic group in the release resin is made possible. It can be achieved by, for example, increasing the content as much as possible, 2) reducing the content of the crosslinking group introduced into the release resin, and 3) using a release resin having a linear molecular structure. It is also effective to increase the thickness of the release layer.

When the content ratio (weight ratio) of the binder to the ceramic particles is small, or when the thickness of the ceramic sheet layer is small, the hardness of the ceramic sheet when the ceramic sheet layer is laminated on the release film is as follows. growing.

When peeling a ceramic sheet having a high hardness as described above, it is necessary to increase the hardness of the release layer. For example, it is necessary to adjust the content of the hydrophobic group introduced into the release resin. Although necessary, it can be achieved by increasing the crosslink density of the release resin by a method such as increasing the content of a crosslinking group introduced into the release resin.

If the thickness of the release layer containing a curable silicone resin as a main component is uniform in the plane,
The smaller the thickness, the higher the crosslinking density even at a certain curing energy. Therefore, by making the thickness as small as possible, the hardness of the release layer can be increased. Further, the hardness may be increased by increasing the mechanical strength of the base polyester film.

In the present invention, the thickness of the release layer may be set according to the purpose of use, and is not particularly limited.
It is preferable that the coating amount of the release layer after drying is 0.01 to 0.2 g / m ² . The coating amount of the release layer is 0.01 g / m
^If it is less than ² , the peeling performance tends to decrease. Also,
If it exceeds 0.2 g / m ² , the hardness of the release layer becomes small, so that when the hardness of the ceramic sheet is high, the hardness difference becomes large, and the releasability tends to deteriorate. In addition, it is disadvantageous in terms of productivity, for example, the processing speed cannot be increased.

As a method for applying the coating liquid for the release layer,
Any known coating method can be applied, for example, a known method such as a roll coating method such as a gravure coating method or a reverse coating method, a bar coating method such as a Meyer bar, a spray coating method, and an air knife coating method is applied. can do.

In the present invention, in order to improve the adhesion between the release layer and the polyester film, the surface of the polyester film may be subjected to a pretreatment such as an anchor coat prior to the application of the coating solution for the release layer. good. In order to impart antistatic performance to the release layer, an antistatic layer may be provided on the surface of the polyester film opposite to the release layer prior to the application of the release layer coating solution.

[0039]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The properties and physical properties used in the present invention were measured by the following methods.

(1) Intrinsic Viscosity of Polyester Polyester is dissolved in a mixed solvent of 60% by weight of phenol and 40% by weight of 1,1,2,2-tetrachloroethane, and undissolved solids are removed by a glass filter. ,
It was measured at 30 ° C.

(2) Dynamic hardness Dynamic ultra-fine hardness tester (DUH-2 manufactured by Shimadzu Corporation)
01-202), a triangle cone with a load of 2 gf is pressed against the sample (ceramic sheet surface or release layer surface),
The dynamic hardness after holding for 2 seconds was determined by the following equation. In addition, the measurement was performed 10 times and the average value was used. The measurement of the dynamic hardness on the release layer surface of the release film may be performed on the release film before the ceramic sheet layer is provided, or the release of the ceramic sheet layer after the ceramic sheet layer is provided. It may be performed on a film. Dynamic hardness (gf
/ Μm ² ) = α × P / D ² where P is load (gf),
D is the penetration amount (μm) of the indenter into the sample, and α is a constant (115 ° triangular cone) depending on the shape of the indenter, which is 37.838.

(3) Measurement of Surface Energy γs The contact angle between water and methylene iodide was determined with a contact angle meter (manufactured by Kyowa Interface Chemical Co., Ltd., CA-X type), and the surface energy γs was measured.

(4) Evaluation of Repellency of Aqueous Ceramic Slurry An aqueous ceramic slurry having the following composition was sufficiently dispersed on the release layer surface of the release film, and then coated by a doctor blade method.

(Composition of aqueous ceramic slurry) Barium titanate 100 parts by weight Water-dispersible vinyl acetate resin 10 parts by weight Polycarboxylic acid 1 part by weight Water 20 parts by weight

The aqueous ceramic slurry was prepared according to the following procedure. One part by weight of polycarboxylic acid is mixed with 20 parts by weight of ion-exchanged water, and 100 parts by weight of ceramic particles (barium titanate (BaTiO ₃ ) having an average particle diameter of 0.6 μm, manufactured by Fuji Titanium) are mixed therein. After being dispersed in a ball mill for 24 hours, a binder (water-dispersible vinyl acetate resin,
5 parts by weight of Hoechst Synthetic Co., Ltd.) and further dispersed for 24 hours in a ball mill to obtain a paste-like ceramic slurry. After dispersion, the slurry was left at room temperature and defoamed for 1 hour.

The repellency of the release layer surface after application of the aqueous ceramic slurry was visually evaluated according to the following criteria. ：: Not repelled at all △: Repelled only at the end of the coated surface ×: Repelled over the entire coated surface

(5) Evaluation of Releasability of Ceramic Sheet The above aqueous ceramic slurry was coated on the surface of a release layer so as to have a dry thickness of 10 μm, and dried at 120 ° C. for 10 minutes to obtain a ceramic sheet. This ceramic sheet is cut into a width of 5 cm, a polyester adhesive tape (Nitto 31B, manufactured by Nitto Denko Corporation) is applied to the ceramic sheet layer surface, and a peeling method (peeling rate: 500 mm / min, T-type peeling)
And the ceramic sheet layer was peeled off from the release film, and evaluated by the following criteria. In addition, the test was performed 5 times, and when it was ○, the test was passed.

：: When the entire surface of the ceramic sheet after peeling was visually observed, there was no damage such as pinholes or tears in the ceramic sheet in all five tests. Δ: The entire surface of the ceramic sheet after peeling was visually observed. At this time, when a part of the ceramic sheet was broken even once in five tests. ×: When the entire surface of the ceramic sheet after peeling was visually observed, the ceramic sheet was broken and broken even in one test in five times.

(6) Surface Specific Resistance After the release film was kept at 23 ° C. × 65% RH for 24 hours, the surface specific resistance of the release layer surface was measured with a surface specific resistance measuring device (manufactured by Mitsubishi Industrial Co., Ltd., Hiresta IP). MCP-HT26
0). The applied voltage was 500 V.

Example 1 0.2 parts by weight of cationic polymer antistatic agent (manufactured by Sanyo Chemical Industries, Chemistat 6300H), polyethylene wax (manufactured by Toho Chemical Industries, Hitec E6000)
One part by weight, 50 parts by weight of methanol, and 49.7 parts by weight of water were mixed to prepare a coating solution, which was biaxially stretched polyethylene terephthalate film having a thickness of 50 μm and an intrinsic viscosity of 0.60 dl / g (Toyobo Co., Ltd.) Co., Ltd., E5151)
It is applied to a thickness of 0.04 g / m ² after drying, and dried in a hot air drier at 90 ° C. for 30 seconds to form a long film having an antistatic layer on one side into a roll. Wound up.

Next, the above-mentioned roll was unwound and adjusted by dissolving 1 part by weight of a long-chain alkyl resin (manufactured by YAS Co., Ltd., Piroyl 1050) in 49.5 parts by weight of toluene and 49.5 parts by weight of methyl ethyl ketone. A coating solution having a solid content of 1% by weight is applied with a wire bar on the antistatic layer of the long film having an antistatic layer on one side obtained above,
After drying at 100 ° C. for 30 seconds, the amount of coating after drying is 0.
A long release film having a release layer of 10 g / m ² was wound into a roll.

Also, 1 part by weight of polycarboxylic acid is mixed with 20 parts by weight of ion-exchanged water, and ceramic particles (barium titanate (BaTiO ₃ ) having an average particle size of 0.6 μm, manufactured by Fuji Titanium Co.) are mixed therein. Parts by weight and mix with a ball mill.
After dispersing for 4 hours, 10 parts by weight of a binder (water-dispersible vinyl acetate resin, manufactured by Hoechst Synthetic Co., Ltd.) was mixed, and further dispersed for 24 hours by a ball mill to obtain a paste-like ceramic slurry. After dispersion, the mixture was left at room temperature and defoamed for 1 hour.

The release film roll is unwound, and the surface of the release layer of the release film is coated with the aqueous ceramic slurry using a doctor blade so that the thickness after drying becomes 10 μm. After drying for a minute, a ceramic sheet layer (weight ratio of ceramic particles / binder: 100/5) was provided, and the laminate was wound into a roll. Table 1 shows the obtained results.

Example 2 Silyl isocyanate-based resin (manufactured by Matsumoto Kosho Co., Ltd.
(Orgatic SIC-4123, silyl isocyanate solution / antistatic agent solution / catalyst solution = 100 parts by weight / 5 parts by weight / 5 parts by weight) in isopropyl alcohol so as to have a solid concentration of 3% by weight. With a bar, a biaxially stretched polyethylene terephthalate film (manufactured by Toyobo Co., Ltd.) having a thickness of 50 μm and an intrinsic viscosity of 0.60 dl / g
Was dried at 140 ° C. for 30 seconds, and a long release film having a release layer having a coating amount of 0.10 g / m ² after drying was wound into a roll. Further, the roll film was unwound, a ceramic sheet layer was formed on the release layer surface of the release film in the same manner as in Example 1, and the laminate was wound into a roll. Table 1 shows the obtained results.

Example 3 In Example 1, an addition polymerization reaction type silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KS
830), except that 1 part by weight of a platinum catalyst was added to 100 parts by weight of the silicone resin. Table 1 shows the obtained results.

Comparative Example 1 The procedure of Example 3 was repeated, except that the antistatic layer was not provided, and the coating amount of the release layer after drying was changed to 0.5 g / m ² . Table 1 shows the obtained results.

Comparative Example 2 In Example 3, an addition polymerization reaction type silicone resin (KS830, manufactured by Shin-Etsu Chemical Co., Ltd.) was used without providing an antistatic layer.
Instead of 0.6 parts by weight of an addition polymerization type silicone resin (KS847H, Shin-Etsu Silicone Co., Ltd.) and KS71, a paintable silicone resin (KS71, Shin-Etsu Silicone Co., Ltd.)
8) Same as Example 3 except that 0.4 parts by weight was used. Table 1 shows the obtained results.

[0058]

[Table 1]

In Examples 1 to 3, the dynamic hardness difference | A
−B | is not more than 20 gf / μm ² and the surface energy γ
s was high, and no repelling or poor peeling of the ceramic was observed. On the other hand, in Comparative Example 1, the dynamic hardness difference | AB | exceeded 20 gf / μm ² , the peeling force with the ceramic sheet was large, and the ceramic sheet was broken at the time of peeling. Further, the surface energy γs of the surface of the release layer was low, and repelling was observed at the end of the application surface when the aqueous ceramic slurry was applied. In Comparative Example 2, the dynamic hardness difference | AB | was 20 gf / μm ² or less, and the ceramic was not broken at the time of peeling. When applied to the surface, repelling was observed at the end of the applied surface.

[0060]

Since the release film of the present invention has a small peeling force at the time of peeling, when the ceramic sheet layer obtained by applying and drying the aqueous ceramic slurry is peeled from the release layer,
The ceramic sheet can be peeled from the release layer of the release film with no peeling failure and a moderate force. Further, since the release film of the present invention has good wettability between the aqueous ceramic slurry and the release layer, the aqueous ceramic sheet can be uniformly applied to the surface of the release layer without being repelled. It is suitable as a carrier film for producing a sheet.

Continued on the front page (72) Inventor Harunobu Kuroiwa 2-8-8 Dojimahama, Kita-ku, Osaka-shi, Osaka Toyobo Co., Ltd. F-term (reference) 4F100 AD00C AK41A AR00B BA02 BA03 BA07 BA10A BA10B BA10C BA25B BA25C CA18B GB90 JK12B JK12C JL14B YY00B YY00C 4G052 DA02 DB10

Claims (2)

[Claims] 1. A release film having a release layer formed on at least one surface of a polyester film, wherein a dynamic hardness A of a ceramic sheet surface laminated on the release layer surface of the release film and the release hardness are determined. A release film for producing a ceramic sheet, wherein the absolute value | AB | of the difference from the dynamic hardness B of the mold layer surface is not more than 20 gf / μm ² and a surfactant is present on the surface of the release layer. . 2. A film laminate, wherein a ceramic sheet layer is laminated on a release layer of the release film according to claim 1.