JP2010089297A - Mold release film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold release film superior in mold releasability, shape followability, and moldability, an adhesive method with the same, and method for manufacturing a circuit board. <P>SOLUTION: The mold release film has a first layer containing syndiotactic polystyrene as a main component, a second layer containing polyolefin-based resin as a main component, and a third layer disposed between these layers and bonding both. The third layer has a copolymer (A) of a polyethylene structural unit and a polystyrene structural unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a release film and a method for producing a circuit board using the release film.

  For example, in a flexible printed circuit board (hereinafter referred to as FPC), a circuit coating film is used to electrically insulate or protect a circuit formed on the surface of an insulating base material such as a polyimide resin film. It is done. The circuit coating film is called a cover lay (hereinafter referred to as CL), and is used by press laminating a heat-resistant resin film on the circuit board surface.

  In general, in the press laminating process, a release film is used between the pressing plate and the product so that the pressing plate can be easily released from the product. For release films used in CL press laminates, in addition to the above release properties, cushioning for applying pressure and heat evenly to the circuit board surface during pressing, and suppressing bleeding of the adhesive from the CL end face To improve the conformity of the mold release film itself to the uneven surface of the circuit board surface and the appearance of the FPC surface after pressing, the mold release film itself must have extensibility when pressed (hereinafter referred to as moldability). It has been.

  As a film having improved release properties and cushioning properties, a release film is proposed in which a layer composed mainly of a polyolefin resin is provided on a layer made of syndiotactic polystyrene (hereinafter referred to as SPS) resin. Yes. However, the adhesion between the SPS-based resin and the olefin-based resin is not good, and when the release film is peeled after pressing, delamination occurs in the release film itself, and one of the release films is formed on the FPC surface. There was a problem that the department remained.

In order to solve this problem, it has been proposed that an adhesive layer containing an SPS resin, a polyolefin resin, and an elastomer resin be interposed between a layer made of an SPS resin and a layer made of a polyolefin resin. However, even with such a release film, it cannot be said that the adhesion between the SPS-based resin layer and the polyolefin-based resin layer is sufficiently improved. As mentioned above, although the example at the time of FPC manufacture was given, the same problem arises also in other manufacturing fields, for example, a processing process like the case where a prepreg and an interlayer adhesive are pasted up.
JP 2004-051688 A

  The present invention provides a release film that is excellent in mold release property, conformal followability, and moldability, an adhesion method using the same, and a circuit board production method.

  The release film according to the present invention includes a first layer mainly composed of syndiotactic polystyrene, a second layer mainly composed of a polyolefin-based resin, and disposed between these layers. A release film having a third layer to be bonded, wherein the third layer has a copolymer (A) of a polyethylene structural unit and a polystyrene structural unit.

  In the release film according to the present invention, the copolymer (A) may have a main chain composed of a polyethylene structural unit bonded to a side chain composed of a polystyrene structural unit.

  In the release film according to the present invention, the weight ratio of the polystyrene structural units in the copolymer (A) may be 5% by weight or more and 15% by weight or less.

  In the release film according to the present invention, the third layer may further contain an SPS resin and / or an olefin resin.

  In the release film according to the present invention, the polyolefin resin that is the main component of the second layer may be polypropylene.

  In the release film according to the present invention, the second layer may further contain syndiotactic polystyrene.

  In the release film according to the present invention, a fourth layer may be further provided on the side of the second layer opposite to the surface on which the first layer is provided.

  In the release film according to the present invention, the fourth layer may be composed mainly of syndiotactic polystyrene, polypropylene, or a mixture thereof.

  An adhesion method according to the present invention is an adhesion method by a hot press in which a release film (F1), an adhesive body (S), an adherend (H), and a release film (F2) are laminated in this order. This is an adhesion method in which at least one of the mold films (F1) or (F2) is the release film.

  The method of manufacturing a circuit board according to the present invention includes a printed wiring board press in which a release film (F1), an overlay film (S1), a printed wiring board (H1), and a release film (F2) are laminated and heated in this order. A circuit board manufacturing method using a laminating method, wherein at least one of the release films (F1) or (F2) is the release film.

  According to the present invention, it is possible to provide a release film that is excellent in releasability, conformability, and moldability. In addition, the release film according to the present invention can be used, for example, in the CL press lamination process of FPC, etc., thereby releasing the release film after pressing, the appearance of the FPC surface, and bleeding of the adhesive from the CL end face. In addition, it is possible to improve the FPC plating workability in the subsequent process.

The best mode for carrying out the invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view illustrating an example of a release film according to the present invention. The release film according to the present invention includes a first layer 1 mainly composed of syndiotactic polystyrene as shown in FIG. A release film having a second layer 2 made of a polyolefin-based resin and a third layer 3 disposed between these layers and adhering both. The third layer 3 is characterized by containing a copolymer (A) of a polyethylene structural unit and a polystyrene structural unit, and the characteristics of the present invention are exhibited by this feature.
Each configuration will be described below.

(First layer)
The first layer of the release film according to the present invention is preferably composed of a resin composition mainly composed of syndiotactic polystyrene (hereinafter referred to as SPS), that is, a resin composition containing most SPS. (Hereinafter, the main component in the present invention refers to the component that is blended most often). SPS is a polystyrene having a syndiotactic structure having stereoregularity in which side chains are alternately located, and is excellent in releasability. Therefore, SPS is suitably used as a release layer for a release film or the like.

  As the resin mainly composed of SPS used as the first layer, SPS may be used as a single substance, but it is a mixture of a rubber-like elastic body or other thermoplastic resin according to required characteristics. It doesn't matter. Specific examples of the rubber-like elastic material include, for example, natural rubber, polybutadiene, polyisoprene, polyisobutylene, neoprene, polysulfide rubber, thiocol rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, styrene-butadiene block copolymer Copolymer (SBR), hydrogenated styrene-butadiene block copolymer (SEB), styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), styrene-isoprene block Copolymer (SIR), hydrogenated styrene-isoprene block copolymer (SEP), styrene-isoprene-styrene block copolymer (SIS), hydrogenated styrene-isoprene-styrene block copolymer (SE) S), or olefin rubber such as ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), linear low density polyethylene elastomer, or butadiene-acrylonitrile-styrene-core shell rubber (ABS), methyl methacrylate-butadiene. -Styrene-core shell rubber (MBS), methyl methacrylate-butyl acrylate-styrene-core shell rubber (MAS), octyl acrylate-butadiene-styrene-core shell rubber (MABS), alkyl acrylate-butadiene-acrylonitrile-styrene-core shell rubber (ABS) Siloxane-containing cores such as butadiene-styrene-core shell rubber (SBR), methyl methacrylate-butyl acrylate-siloxane Particulate elastic material of the core-shell type, such as Erugomu, or they were modified rubber, and the like. Other thermoplastic resins include linear high density polyethylene, linear low density polyethylene, high pressure low density polyethylene, isotactic polypropylene, syndiotactic polypropylene, block polypropylene, random polypropylene, polybutene, 1, Polyolefin resins represented by 2-polybutadiene, 4-methylpentene-1pentene, cyclic polyolefin and copolymers thereof, atactic polystyrene, isotactic polystyrene, high impact polystyrene (HIPS), ABS, AS, styrene -Methacrylic acid copolymer, styrene-methacrylic acid / alkyl ester copolymer, styrene-methacrylic acid / glycidyl ester copolymer, styrene-acrylic acid copolymer, styrene-acrylic acid / alkyl Stele copolymer, styrene-maleic acid copolymer, polystyrene resin represented by styrene-fumaric acid copolymer, polyester resin such as polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyamide 6, polyamide 6, It can be arbitrarily selected from known resins such as polyamide resins such as 6, polyphenylene ether and PPS. In addition, these rubber-like elastic bodies and thermoplastic resins may be used alone or in combination of two or more according to the purpose. Among these, it is particularly preferable to use a hydrogenated styrene-butadiene-styrene block copolymer (SEBS) or a hydrogenated styrene-isoprene-styrene block copolymer (SEPS) from the viewpoint of improving the conformal followability.

  The thickness of the first layer of the release film according to the present invention is preferably 10 μm or more and 100 μm or less, and more preferably 15 μm or more and 50 μm or less. If it is above the lower limit of the above range, resin adhesion to the FPC surface due to breakage of the first layer during peeling can be suppressed. By setting the value within the above range upper limit value, it is possible to obtain suitable conformal followability.

(Second layer)
For the second layer of the release film according to the present invention, a resin having flexibility such as a polyolefin resin is preferably used. This improves the cushioning properties of the entire film, and the pressure and heat from the press hot plate are evenly transmitted to the adherend such as the release layer and the FPC board in the adhesion process such as press lamination, and the release film and the adherence. Adhesion with the body is improved.

  Examples of the polyolefin resin used in the second layer of the release layer film according to the present invention include α-olefin polymers such as polyethylene and polypropylene; ethylene, propylene, butene, pentene, hexene, 4-methyl-1-pentene. Examples include α-olefin copolymers having a resin or the like as a copolymer component, and these may be used alone or in combination. Specific examples of particularly preferable materials from the viewpoints of cushioning properties and conformal followability include polyethylene, polypropylene, ethylene-vinyl acetate copolymer (EVA), and ethylene-methyl methacrylate copolymer (EMMA). Further, syndiotactic polystyrene may be used in combination with the polyolefin resin in order to suppress the resin outflow from the film end face during pressing.

  The thickness of the second layer of the release film according to the present invention is preferably 20 μm or more and 100 μm or less, and more preferably 40 μm or more and 80 μm or less. By setting it to the range lower limit value or more, the cushioning property of the entire film becomes suitable, and the embedding property of the release film in the FPC becomes excellent. Moreover, it becomes possible to suppress the ooze-out of the resin from the film end face by setting it to the upper limit of the above range.

(3rd layer)
The 3rd layer of the release film which concerns on this invention is comprised by the resin composition containing the copolymer (A) which has the principal chain which consists of a polyethylene structural unit, and the side chain which consists of a polystyrene structural unit. In particular, it is preferable to use a copolymer having a polystyrene structural unit weight ratio of 5% by weight to 15% by weight. By setting the weight ratio of the polystyrene structural unit to the range lower limit value or more, the adhesive force with the first layer containing the syndiotactic polystyrene resin as a main component is improved. Moreover, the adhesive force after press lamination with the 2nd layer which has polyolefin-type resin as a main component becomes favorable by setting it as the said range upper limit value or less. Thereby, delamination at the time of peeling from the adherend such as FPC of the release film after press lamination can be suppressed. Specific examples of resins that satisfy such requirements include Modick F502 (polyethylene structural unit component 91.4% by weight, polystyrene structural unit component 8.6% by weight) manufactured by Mitsubishi Chemical Corporation. Further, in order to improve the adhesion with the first layer or the second layer, SPS or an olefin resin may be blended in the third layer.

  Moreover, as a 3rd layer of the release film which concerns on this invention, you may use resin containing the said copolymer (A) by a single layer, and adhesiveness with a 1st layer or a 2nd layer You may use what laminated | stacked the several layer according to improvement and the other objective. As a specific example, the first layer side is a resin layer containing the copolymer (A) and SPS, and the second layer side is a resin containing the copolymer (A) and an olefin resin. The aspect using the resin layer laminated | stacked so that it may become a layer is mentioned. FIG. 2 is a schematic cross-sectional view showing an example of an embodiment in which the third layer has a two-layer structure.

The weight ratio of the polyethylene structural unit to the polystyrene structural unit in the resin used for the adhesive layer was analyzed by NMR and calculated as a relative component ratio using the peak integral value of the ¹ H-NMR spectrum. The analysis method is as follows.
Pretreatment: Several pellets are minced and weighed about 80 mg. Thereafter, a sample weighed in 1 g of the measurement solvent was added, and the sample dissolved by heating at 130 ° C. was used as the measurement sample.
Measuring instrument: JNM-ECA400 superconducting FT-NMR measuring instrument nucleus manufactured by JEOL Ltd .: ¹ H, ¹³ C
Measurement temperature: 125 ° C
Measurement solvent: deuterated 1,2-dichlorobenzene number of integration: 16 times ⁽¹ H), 16384 times ⁽¹³ C)
Repeat latency: 5 seconds ⁽¹ H), 2 seconds ⁽¹³ C)
Reference peak: Peak of the solvent to be measured
¹ H: Set to 7.40 ppm as internal standard
¹³ C: set to 127.70 ppm as internal standard

  The thickness of the third layer of the release film according to the present invention is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less. By setting it to the range lower limit value or more, the interlayer adhesive force of the release film after press lamination becomes suitable, and delamination does not occur at the time of release. Moreover, the amount of the resin oozing out to the film end face can be suppressed by setting it to the upper limit of the above range.

(Fourth layer)
In the release film according to the present invention, a fourth layer can be further provided on the opposite side of the second layer provided with the first layer, thereby releasing the release film and the plate. Can improve the performance. The resin used for the fourth layer is not particularly limited as long as it has good releasability from the metal backing plate, but is mainly composed of a resin mainly composed of SPS, a polypropylene resin, or a mixture thereof. Examples of the resin used as a component. FIG. 3 is a schematic cross-sectional view showing an example of an embodiment in which the fourth layer 4 is provided.

  The thickness of the fourth layer of the release film according to the present invention is preferably 10 μm or more and 100 μm or less. By setting it as more than the said range lower limit, the mold release property from a backing plate becomes suitable, and it can suppress the leaching of the resin to a film end surface by setting it as the said range upper limit or less.

  The fourth layer and the second layer of the release film may be directly laminated, or an adhesive layer for improving the adhesion between them may be provided between these layers. Examples of the adhesive layer in this case include modified polyolefins that are provided with adhesiveness by introducing a functional group into polyolefin, and specifically include modified polyethylene, modified polypropylene, and modified EVA. Moreover, when using resin which has SPS as a main component as a 4th layer, it is preferable to use the copolymer (A) which has the principal chain which consists of the said polyethylene structural unit, and a side chain which consists of a polystyrene structural unit.

(Total thickness of release film)
The thickness of the release film as a whole is usually 70 μm or more and 200 μm or less, preferably 80 μm or more and 150 μm or less in consideration of the strength, flexibility and adhesion of the release film. By setting the thickness within the above range, both the releasability and the conformal followability are suitable. In order to obtain a cushioning property suitable for the entire film, the thickness of the release layer is preferably smaller than the thickness of the cushion layer.

(Manufacturing and usage of release film)
The method for producing the release film of the present invention is not particularly limited, and methods known in the production of multilayer films such as a co-extrusion method, an extrusion lamination method, and a dry lamination method can be used.

  The release film according to the present invention is used as a release film, for example, in a CL press laminating process which is an example of a manufacturing process of FPC. As an example in this case, it is arranged in the order of the pressing plate / cushion paper / release film / CL / FPC / release film / cushion layer / the pressing plate and supplied to the press laminating process.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
(Examples 1-5)
Examples 1 to 5 have a three-layer structure as shown in FIG. Specifically, SPS (Zarek S104 manufactured by Idemitsu Kosan Co., Ltd.) as the first layer, polypropylene resin (Nobrene FH1016 manufactured by Sumitomo Chemical Co., Ltd., hereinafter abbreviated as PP) as the second layer, and polyethylene structure as the third layer A copolymer (A) of units and polystyrene structural units (Modic F502 manufactured by Mitsubishi Chemical Corporation, hereinafter abbreviated as copolymer (A)) was used. These resins were supplied to three extruders, and the extrusion conditions were adjusted so that each layer had the thickness shown in Table 1 with a three-layer die (300 ° C.), and co-extruded to produce a release film.

(Examples 6 and 7)
Examples 6 and 7 have a three-layer structure as shown in FIG. As the second layer, a mixture of PP (Nobrene FH1016 manufactured by Sumitomo Chemical Co., Ltd.) and SPS (Zarek S104 manufactured by Idemitsu Kosan Co., Ltd.) at a ratio shown in Table 1 was used. Except for the resin used for the second layer, a release film was prepared using the same raw materials and production method as in Examples 1-5.

(Example 8)
Example 8 has a three-layer structure as shown in FIG. As the second layer, an ethylene methyl methacrylate resin (Aclift WD105-1, manufactured by Sumitomo Chemical Co., Ltd., hereinafter abbreviated as EMMA) was used. Except for the resin used for the second layer, a release film was prepared using the same raw materials and production method as in Examples 1-5.

Example 9
Example 9 is an example having a three-layer structure as shown in FIG. As the second layer, polyethylene 1 resin (UBE polyethylene F222NH manufactured by Ube Industries, Ltd., hereinafter abbreviated as PE1) was used. Except for the resin used for the second layer, a release film was prepared using the same raw materials and production method as in Examples 1-5.

(Example 10)
Example 10 has a four-layer structure in which a fourth layer as shown in FIG. 3 is provided. Specifically, in addition to the resin used for the first layer, the resin used for the second layer, and the resin used for the third layer, the resin used for the fourth layer is further changed to SPS (Idemitsu Kosan Co., Ltd.). Zalek S104) was supplied to four extruders and coextruded with a four-layer die (300 ° C.) to prepare a release film. The resins used for the first, second and third are those used in Examples 1 to 5, respectively.

(Examples 11 to 13)
Examples 11 to 13 have a three-layer structure as shown in FIG. Specifically, as the third layer, copolymer (A) (Modic F502, manufactured by Mitsubishi Chemical Corporation) and SPS (Zarek S104, manufactured by Idemitsu Kosan Co., Ltd.) and / or PP (Nobrene FH1016, manufactured by Sumitomo Chemical Co., Ltd.) Were mixed in the proportions shown in Table 1. Except for the resin used for the third layer, a release film was prepared using the same raw materials and production method as in Examples 1-5.

(Example 14)
In Example 14, the third layer as shown in FIG. 2 has a two-layer structure. Specifically, a layer (third layer a) comprising a copolymer (A) (Modic F502 manufactured by Mitsubishi Chemical Corporation) and SPS (Zarek S104 manufactured by Idemitsu Kosan Co., Ltd.), a polyethylene structural unit, and a polystyrene structural unit Copolymer (A) (Modic F502 manufactured by Mitsubishi Chemical Co., Ltd.) and a layer (third layer 3b) made of polypropylene resin (Nobrene FH1016 manufactured by Sumitomo Chemical Co., Ltd.). . For the third layer a and the third layer b, those in which raw materials were mixed at the blending ratio shown in Table 1 were used. Each material used for the first layer, the second layer, the third layer a, and the third layer b is supplied to four extruders, and each layer is shown in Table 2 by a four-layer die (300 ° C.). Extrusion conditions were adjusted so that the thickness shown in FIG. Except for the resin used for the third layer, a release film was prepared using the same raw materials and production method as in Examples 1-5.

(Comparative Examples 1 and 2)
Comparative Example 1 corresponds to Example 4 of Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-051688), and Comparative Example 2 corresponds to Example 7 of the same cited document. As the third layer of Comparative Examples 1 and 2, polyethylene 2 resin (NUC-8042 manufactured by Nihon Unicar, hereinafter abbreviated as PE2), SPS (Zarek S104 manufactured by Idemitsu Kosan Co., Ltd.), styrene-ethylene-butadiene block copolymer 1 (Kuraray Septon 8104, hereinafter abbreviated as SBES1) and styrene-ethylene-butadiene block copolymer 2 (G1650, Showa Shell Sekiyu KK, hereinafter abbreviated as SEBS2) were mixed in the ratios shown in Table 3. A thing was used. Except for the third layer resin, a release film was prepared using the same raw materials and preparation methods as in Examples 1-5.

(Comparative Examples 3-5)
In Comparative Examples 3 to 5, SPS (Zarek S104 manufactured by Idemitsu Kosan Co., Ltd.) as the first layer, PP (Nobrene FH1016 manufactured by Sumitomo Chemical Co., Ltd.) and SPS (Zarek S104 manufactured by Idemitsu Kosan Co., Ltd.) as the second layer Were mixed at the ratio shown in Table 3, and the third layer was not provided. The above SPS and PP were supplied to two extruders, and a two-layer die (300 ° C.) was used to adjust the extrusion conditions so that each layer had the thickness shown in Table 3, and co-extruded to prepare a release film.

(Press evaluation method)
Using this release film, it was pressed by a one-stage press machine in a press configuration in the order of this plate / cushion paper / release film / CL / FPC / release film / cushion paper / plate. In pressing, the temperature was raised to 170 ° C. at a rate of temperature rise of 10 ° C./min under a pressure (5 MPa) condition, and then held for 30 ° C. and then cooled to room temperature. Thereafter, the press samples were evaluated according to the following items and criteria. In addition, the following evaluation is based on the JPCA standard (design guide manual single-sided and double-sided flexible printed wiring version JPCA-DG02) of the Japan Electronic Circuits Association (hereinafter abbreviated as JPCA), and the following items and standards are used. went.

(Evaluation item)
Release properties:
For the releasability, the releasability from the FPC of the release film was evaluated. Specifically, the peeled state from the FPC of the release film after CL press lamination was visually evaluated in accordance with “JPCA Standard 7.5.7.1 Surface Adherence”.
The evaluation was performed with the number of evaluation samples set to n = 100, and the number of samples with breaks on the sample surface was less than 5% of the number of evaluation samples.
Those with a tear generation rate of less than 5% were considered acceptable.
◎: Breakage rate less than 3% ○: Breakage rate 3% or more and less than 5% ×: Breakage rate 5% or more

CL adhesive exudation amount:
In accordance with “JPCA Standard 7.5.3.6 Coverlay Adhesive Flow and Covercoat Bleeding”, whether or not there is a seepage of the CL adhesive layer on the circuit board. The amount of oozing out was evaluated. The exudation amount was less than 150 μm as acceptable.
○: Exudation amount less than 150 μm ×: Exudation amount 150 μm or more

Formability:
The moldability was evaluated in accordance with “the air bubbles in 7.5.3.3 of the JPCA standard”. Each code is as follows. A void generation rate of less than 2% was considered acceptable. Evaluation was performed with n = 100 as the number of evaluation samples, and the number of voids confirmed on the sample surface was less than 2% of the number of evaluation samples.
○: Void generation rate of less than 2% ×: Void generation rate of 2% or more

Film edge exudation:
The release film end face oozing length was measured (measured by the length of the resin oozing out from the film 4 direction end face). The exudation length of less than 5 mm was accepted.
○: Bleeding length less than 5 mm ×: Bleeding length of 5 mm or more

The release film according to the present invention is excellent in releasability, conformability, and appearance improvement of the FPC after pressing, and is suitably used as a release film used in the FPC press lamination process.

It is a schematic sectional drawing which shows an example of the release film which concerns on this invention. It is a schematic sectional drawing which shows an example of the release film which concerns on this invention in case a 3rd layer has a 2 layer structure. It is a schematic sectional drawing which shows an example of the release film which concerns on this invention at the time of providing a 4th layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st layer 2 ... 2nd layer 3 ... 3rd layer 3a when it is set as 3rd layer 3a, 3b ... 2 layers 4 ... 4th layer 10, 20, 30 ... Release film

Claims (10)

A first layer based on syndiotactic polystyrene;
A second layer mainly composed of a polyolefin-based resin;
A release film having a third layer disposed between these layers and bonding them together,
A release film in which the third layer has a copolymer (A) of a polyethylene structural unit and a polystyrene structural unit.   The release film according to claim 1, wherein the copolymer (A) has a main chain composed of polyethylene structural units and a side chain composed of polystyrene structural units.   The release film according to claim 1 or 2, wherein a weight ratio of polystyrene structural units in the copolymer (A) is 5 wt% or more and 15 wt% or less.   The release film according to any one of claims 1 to 3, wherein the third layer further contains a syndiotactic polystyrene resin and / or a polyolefin-based resin.   3. The release film according to claim 1, wherein the polyolefin resin that is a main component of the second layer is polypropylene.   The release film according to claim 5, wherein the second layer further comprises syndiotactic polystyrene.   The release film according to claim 1, wherein a fourth layer is further provided on the surface of the second layer opposite to the surface on which the first layer is provided.   The release film according to claim 7, wherein the fourth layer is mainly composed of syndiotactic polystyrene, polypropylene, or a mixture thereof.   An adhesive method using a hot press in which a release film (F1), an adhesive body (S), an adherend (H), and a release film (F2) are laminated in this order, the release film (F1) or (F2) ) At least one is a release film according to any one of claims 1 to 8.   A method for producing a circuit board using a press lamination method for a circuit board in which a release film (F1), an overlay film (S1), a circuit board (H1), and a release film (F2) are laminated in this order and heated and pressed. A method for producing a circuit board, wherein at least one of the release films (F1) or (F2) is a release film according to any one of claims 1 to 8.

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