Release film

Abstract

To provide a release film which can effectively prevent the occurrence of undesired recesses in a manufactured flexible printed circuit board when used in a hot press for adhering a coverlay film to a flexible circuit board with an exposed circuit. [Solution] The release film of the present invention is a release film having a release layer and a cushion layer, wherein the number of foreign objects having a maximum length of 30 μm or more within a 20 cm × 20 cm area of ​​the cushion layer is less than 20. The cushion layer is preferably made of a material containing a first resin component having a melting point of 60°C or more and 90°C or less, and a second resin component having a melting point that is 10°C or more and 50°C or less higher than the melting point of the first resin component.

Description

[Technical Field]

[0001] The present invention relates to a release film. [Background technology]

[0002] For example, as shown in Patent Document 1, a release film is generally used when forming a flexible printed circuit board by bonding a coverlay film to a flexible circuit board with an exposed circuit by hot pressing, via an adhesive layer provided on the coverlay film.

[0003] After the coverlay film is bonded to the flexible circuit board, the release film is required to be peeled off from the formed flexible printed circuit board with excellent releasability.

[0004] More specifically, when the release film is peeled off from the flexible printed circuit board, it is required that the release film exhibits excellent releasability with respect to the flexible printed circuit board, thereby suppressing the occurrence of creases and breaks in the flexible printed circuit board.

[0005] However, when conventional release films are used, localized depressions are formed in the manufactured flexible printed circuit board when the above-described hot pressing is performed, which can cause a problem of significantly impairing the appearance of the flexible printed circuit board (see Figure 4).

[0006] The occurrence of such recesses can cause users to have serious doubts about the quality of the flexible printed circuit board, and there is also concern that the occurrence of significant recesses may actually have a negative impact on the quality of the flexible printed circuit board. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6470461 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a release film that can effectively prevent the occurrence of undesired recesses in the manufactured flexible printed circuit board when used in a hot press for adhering a coverlay film to a flexible circuit board with exposed circuits. [Means for solving the problem]

[0009] Such objectives are as follows: (1) 12 This is achieved by the present invention described in (1) A release film having a release layer and a cushion layer, the release layer is made of a material containing a polybutylene terephthalate resin, A release film characterized in that the number of foreign objects having a maximum length of 30 μm or more within a 20 cm x 20 cm area of ​​the cushion layer is less than 20.

[0010] (2) The release film according to (1) above, wherein the cushion layer is composed of a material containing a first resin component having a melting point of 60°C or more and 90°C or less, and a second resin component having a melting point that is 10°C or more and 50°C or less higher than the melting point of the first resin component.

[0011] (3) The release film according to (2) above, wherein the content of the first resin component in the cushion layer is X1 [mass%] and the content of the second resin component in the cushion layer is X2 [mass%], satisfies the relationship 0.80≦X2 / X1≦1.45.

[0012] (4) The release film according to (2) or (3) above, wherein the MFR of the first resin component is 2.0 g / 10 min or more and 8.0 g / 10 min or less.

[0013] (5) The release film according to any one of (2) to (4) above, wherein the cushion layer is further made of a material containing a polybutylene terephthalate-based resin as a third resin component.

[0014] (6) The release film according to (5) above, wherein the content of the first resin component in the cushion layer is X1 [mass%] and the content of the third resin component in the cushion layer is X3 [mass%], satisfies the relationship 0.25≦X3 / X1≦0.90.

[0015] (7) The release film according to (5) or (6) above, wherein the content of the second resin component in the cushion layer is X2 [mass%] and the content of the third resin component in the cushion layer is X3 [mass%], the relationship of 0.20≦X3 / X2≦1.10 is satisfied.

[0016] (8) The release film according to any one of (1) to (7), wherein the cushion layer is composed of a material containing at least one of ethylene-methyl methacrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, and ethylene-α-olefin copolymer.

[0017] (9) The release film according to any one of (1) to (8) above, wherein the cushion layer has an average thickness of 10 μm or more and 200 μm or less.

[0018] (10) The release film according to any one of (1) to (9) above, wherein the release layer is provided on both sides of the cushion layer.

[0020] ( 11 The release layer contains polybutylene terephthalate as the polybutylene terephthalate-based resin, and further contains at least one of a polybutylene terephthalate / polytetramethylene glycol block copolymer, and a polybutylene terephthalate copolymer containing terephthalic acid and a dicarboxylic acid component other than terephthalic acid as a constituent monomer. Either (1) or (10) The release film according to claim 1.

[0021] ( 12 ) The above (1) to (3), wherein the average thickness of the release layer is 5 μm or more and 35 μm or less. 11 2. The release film according to claim 1, wherein [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a release film that can effectively prevent the occurrence of undesired recesses in the manufactured flexible printed circuit board when used in a hot press to bond a coverlay film to a flexible circuit board with exposed circuits. [Brief explanation of the drawings]

[0023] [Figure 1] 10A to 10C are longitudinal cross-sectional views illustrating a manufacturing method for manufacturing flexible printed circuit boards in a multi-layer stacked state. [Figure 2] 1A to 1C are vertical cross-sectional views showing steps in a manufacturing method for manufacturing flexible printed circuit boards in a multi-layer stacked state. [Figure 3] 1 is a longitudinal cross-sectional view showing an embodiment of a release film of the present invention. [Figure 4] 1 is a photograph showing undesired recesses that occur on a flexible printed circuit board when the flexible printed circuit board is manufactured using a conventional release film. DETAILED DESCRIPTION OF THE INVENTION

[0024] Preferred embodiments of the present invention will now be described in detail.

[0025]

[0043] In the following, an example will be described in which a flexible printed circuit board is produced in multiple stages using the release film of the present invention, that is, a case in which the release film of the present invention is used for circuit formation. Prior to describing the release film of the present invention, a method for producing a flexible printed circuit board in multiple stages will be described.

[0026] [1] Manufacturing method for flexible printed circuit boards Fig. 1 is a longitudinal cross-sectional view illustrating a manufacturing method for manufacturing a flexible printed circuit board in a multi-layered state, and Fig. 2 is a longitudinal cross-sectional view illustrating each step in the manufacturing method for manufacturing a flexible printed circuit board in a multi-layered state. Note that, for convenience of explanation, the upper side in Fig. 1 and Fig. 2 will be referred to as "top" or "upper side," the lower side as "bottom" or "lower side," the left side as "left," and the right side as "right."

[0027] In this embodiment, the manufacturing method for manufacturing a flexible printed circuit board 200 (hereinafter also referred to as "FPC200") in multiple layers includes a first step of stacking, in multiple layers, a laminate in which a glass cloth 300A, a release film 10A, an FPC200, a release film 10B, and a glass cloth 300B, each of which has a sheet shape, are stacked in this order; a second step of hot-pressing each of the multi-layer laminates to bond a coverlay film 220 (hereinafter also referred to as "CL film 220") to the flexible circuit board 210 in the FPC200; and a third step of releasing the release films 10 (10A, 10B) from the FPC200 to obtain an FPC200 in which the CL film 220 is bonded to the flexible circuit board 210.

[0028] Each step will be explained below in order. [1-1] First step First, a laminate in which a glass cloth 300A, a release film 10A, an FPC 200, a release film 10B, and a glass cloth 300B, each of which has a sheet shape, are stacked in this order is stacked in multiple layers (see Fig. 1 and Fig. 2(a)). Note that the following description will be given of a case in which the laminate is stacked in two layers.

[0029] [1-1-1] Step 1-1 First, three flat thermocompression plates 521 are prepared and arranged so that two gaps are formed in the thickness direction.

[0030] [1-1-2] Step 1-2 Next, sheet-like (film-like) glass cloth 300A, release film 10A, FPC 200, release film 10B, and glass cloth 300B are placed in the two gaps in a stacked state from top to bottom in this order. Note that in this step (step 1-2), the FPC 200 placed in the gap is in a stacked state by stacking the flexible circuit board 210 and the CL film 220, but the flexible circuit board 210 and the CL film 220 are not joined via the adhesive layer 222 provided on the CL film 220.

[0031] As a result, as shown in Figure 1, a laminate in which glass cloth 300A, release film 10A, FPC 200, release film 10B, and glass cloth 300B are stacked in this order between the thermocompression plates 521 is stacked in two layers.

[0032] This step (step 1-2) constitutes a step of placing a release film on the object (FPC 200).

[0033] [1-2] Second step Next, by performing the first step, the multi-layered laminate is heat-pressed, and the CL film 220 is bonded to the flexible circuit board 210 in the FPC 200 (see FIGS. 1 and 2(b)).

[0034] [1-2-1] Step 2-1 First, the thermocompression plate 521 is heated while the glass cloth 300 (300A, 300B) is in contact with the thermocompression plate 521.

[0035] As a result, the heat from the thermocompression plate 521 is transferred to the laminate in which the glass cloth 300A, the release film 10A, the FPC 200, the release film 10B, and the glass cloth 300B are superimposed, and the laminate is heated.

[0036] In this step (step 2-1), the temperature to which the laminate, i.e., the FPC 200 is heated is not particularly limited, but is preferably 100°C or higher and 250°C or lower, and more preferably 150°C or higher and 200°C or lower.

[0037] The heating time for the laminate is not particularly limited, but is preferably set to 40 seconds or more and 5000 seconds or less, and more preferably 200 seconds or more and 4000 seconds or less, which allows the glass cloth 300A, the release film 10A, the FPC 200, the release film 10B, and the glass cloth 300B in the laminate to be heated almost uniformly.

[0038] [1-2-2] Step 2-2 Furthermore, almost simultaneously with the heating of the thermocompression plates 521 in the above step (step 2-1), the thermocompression plates 521 located on the upper side and the thermocompression plates 521 located on the lower side are brought closer together in their thickness direction (press molding method).

[0039] As a result, in the laminate in which the glass cloth 300A, the release film 10A, the FPC 200, the release film 10B, and the glass cloth 300B are stacked, each of which is placed in two gaps formed between the three thermocompression plates 521, the FPC 200 is pressurized through the glass cloths 300A and 300B and the release films 10A and 10B (see Figures 1 and 2(b)).

[0040] As a result, the FPC 200 is heated and pressurized, and the overlapping flexible circuit board 210 and CL film 220 in the FPC 200 are bonded via the adhesive layer 222 provided in the CL film 220. In other words, the coverlay 221 and the flexible circuit board 210 are bonded via the adhesive layer 222. Furthermore, when the FPC 200 is heated and pressurized, that is, when the coverlay 221 and the flexible circuit board 210 are bonded via the adhesive layer 222, the release film 10 is embedded in recesses 223 formed in the coverlay 221. Therefore, it is possible to prevent the adhesive from the adhesive layer 222 from seeping out into the recesses 223 (see FIG. 2(b)).

[0041] In this step (step 2-2), the pressure to which the FPC 200 is pressed is not particularly limited, but is preferably set to 0.1 MPa or more and 20.0 MPa or less, and more preferably 0.5 MPa or more and 15.0 MPa or less.

[0042] The time for which the FPC 200 is pressed is not particularly limited, but is preferably set to 20 seconds or more and 5000 seconds or less, and more preferably 100 seconds or more and 4000 seconds or less.

[0043] By setting the pressure and time for pressing the FPC 200 within the above ranges, the coverlay 221 and the flexible circuit board 210 can be reliably bonded together via the adhesive layer 222 .

[0044] This step (step 2-2) constitutes a step of performing heat pressing on the object (FPC 200) on which the release film 10 is arranged. Furthermore, when the coverlay 221 is made of a material containing a semi-cured thermosetting resin, the coverlay 221 constitutes the surface of the object (FPC 200) on which the release film 10 is arranged. The release film 10 is used by being overlaid on the surface of this coverlay 221 so that the surface on the side of the first release layer 1 described below is in contact with the surface of this coverlay 221. Therefore, the release film 10 can maintain the shape of the coverlay 221 in which the recesses 223 are formed and harden the thermosetting resin, and therefore the coverlay 221 (molded product) can be molded on the flexible circuit board 210 with excellent precision.

[0045] Furthermore, although it is preferable that the heating of the FPC 200 in the previous step (step 2-1) and the pressurization of the FPC 200 in this step (step 2-2) are carried out almost simultaneously, as described above, steps 2-1 and 2-2 may be carried out in that order. However, by carrying out steps 2-1 and 2-2 almost simultaneously, the time required for the second step and therefore for manufacturing the FPC 200 can be shortened.

[0046] [1-3] Third step Next, the release film 10 (10A, 10B) is released from the FPC 200 to obtain the FPC 200 in which the CL film 220 is bonded to the flexible circuit board 210 (see FIG. 2(c)).

[0047] The method for releasing the release film 10 from this FPC 200 is not particularly limited, but for example, a method in which one end of the release film is grasped by hand and then peeled off in a direction of 90° or more and 180° or less is preferably used.

[0048] In addition, if excellent releasability is exhibited between the thermocompression plate 521 and the release film 10 when the release film 10 is peeled off from the FPC 200, the placement of the glass cloth 300 between the thermocompression plate 521 and the release film 10 may be omitted.

[0049] The method for manufacturing the flexible printed circuit board 200 using the release film 10 is completed by the steps described above.

[0050] The release film of the present invention is used as the release film 10 applied to the production of this flexible printed circuit board 200. That is, the release film 10 has a first release layer 1 made of a first thermoplastic resin composition, a cushion layer 3 made of a third thermoplastic resin composition, and a second release layer 2 made of a second thermoplastic resin composition, with the first release layer 1, cushion layer 3, and second release layer 2 laminated in this order, and the release film 10 used has a small number of foreign matters. The release film 10 to which the release film of the present invention is applied will be described below.

[0051] [2] Release film FIG. 3 is a longitudinal sectional view showing an embodiment of the release film of the present invention.

[0052] The release film 10 of the present invention has release layers (first release layer 1, second release layer 2) and a cushion layer 3. The release film 10 is characterized in that the number of foreign objects having a maximum length of 30 μm or more within a 20 cm × 20 cm area of ​​the cushion layer 3 is less than 20.

[0053] This makes it possible to provide a release film 10 that, when used in a heat press for bonding a coverlay film 220 to a flexible circuit board 210 with an exposed circuit, can effectively prevent the formation of undesired recesses in the manufactured flexible printed circuit board (FPC) 200. More specifically, if the cushion layer that constitutes the release film contains many relatively large foreign objects (foreign objects with a maximum length of 30 μm or more), the shapes of the foreign objects are transferred to the manufactured FPC by heat pressing, making it easy for undesired recesses to form, whereas according to the present invention, such transfer is effectively prevented and undesired recesses are less likely to form. As a result, deterioration in the appearance and quality of the FPC can be prevented. The number of foreign particles can be determined, for example, by visually checking the particles and then observing the surface and cross section with a microscope to count only the foreign particles having a long side of 30 μm or more.

[0054] The number of foreign matter particles may be measured in a plurality of randomly selected 20 cm×20 cm areas.

[0055] The foreign matter may be, for example, a lump (particle) of resin, etc. Such foreign matter generally has a higher hardness than other portions of the cushion layer 3 (portions other than the foreign matter).

[0056] The number of foreign objects with a maximum length of 30 μm or more within a 20 cm x 20 cm area of ​​the cushion layer 3 should be less than 20, preferably less than 15, more preferably less than 10, and even more preferably less than 5. This makes the above-mentioned effects more pronounced.

[0057] Each layer constituting this release film 10 will be described below.

[0058] [2-1] Cushion layer First, a description will be given of the cushion layer 3. The cushion layer 3 is disposed as an intermediate layer between the first release layer 1 and the second release layer 2.

[0059] This cushion layer 3 preferably contains at least one type of thermoplastic resin, and more preferably contains multiple types of thermoplastic resin, in order to provide the release film 10 with suitable embedding properties for the recesses 223.

[0060] In particular, it is preferable that the cushion layer 3 is made of a material containing a first resin component having a melting point of 60°C or more and 90°C or less, and a second resin component having a melting point that is 10°C or more and 50°C or less higher than the melting point of the first resin component.

[0061] This makes it possible to more effectively prevent the generation of foreign matter, particularly relatively large foreign matter (for example, foreign matter having a maximum length of 30 μm or more), in the cushion layer 3, and more significantly exhibits the above-mentioned effects. Also, the condition for interlayer strength between the release layer and the cushion layer 3, which will be described later, can be more suitably satisfied. Also, the cushioning properties of the cushion layer 3 can be more easily improved, and the ability to conform to the recesses 223 can be more improved.

[0062] When the content of the first resin component in the cushion layer 3 is X1 [mass %] and the content of the second resin component is X2 [mass %], it is preferable to satisfy the relationship 0.80≦X2 / X1≦1.45, it is more preferable to satisfy the relationship 0.82≦X2 / X1≦1.40, and it is even more preferable to satisfy the relationship 0.84≦X2 / X1≦1.30.

[0063] This makes it possible to more effectively prevent the generation of foreign matter, particularly relatively large foreign matter (for example, foreign matter having a maximum length of 30 μm or more), in the cushion layer 3, and more significantly exhibits the above-mentioned effects. Also, the condition for interlayer strength between the release layer and the cushion layer 3, which will be described later, can be more suitably satisfied. Also, the cushioning properties of the cushion layer 3 can be more easily improved, and the ability to conform to the recesses 223 can be more improved.

[0064] The melting point of the first resin component is 60°C or higher and 90°C or lower, preferably 62°C or higher and 85°C or lower, more preferably 64°C or higher and 80°C or lower, and even more preferably 66°C or higher and 75°C or lower. This makes the above-mentioned effects more pronounced.

[0065] The difference between the melting point of the second resin component and the melting point of the first resin component, i.e., Tm2 - Tm1, where Tm1 is the melting point of the first resin component and Tm2 is the melting point of the second resin component, is 10°C or more and 50°C or less, preferably 12°C or more and 45°C or less, more preferably 14°C or more and 40°C or less, and even more preferably 16°C or more and 35°C or less. This makes the above-mentioned effects more pronounced.

[0066] The first resin component and the second resin component may be, for example, a polyolefin resin.

[0067] The polyolefin resin is not particularly limited, and examples thereof include α-olefin polymers such as polyethylenes such as low-density polyethylene and high-density polyethylene, polypropylene, etc., ethylene-α-olefin copolymers which are copolymers of ethylene with α-olefins other than ethylene, such as propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene, copolymers of ethylene and (meth)acrylic acid (ethylene-(meth)acrylic acid copolymer), copolymers of ethylene and (meth)acrylic acid esters (ethylene-(meth)acrylic acid ester copolymer), copolymers of ethylene and vinyl acetate (ethylene-vinyl acetate copolymer), and the like, and one or more of these can be used in combination.

[0068] Among these, at least one of ethylene-methyl methacrylate copolymer (copolymer of ethylene and methyl methacrylate), ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer (copolymer of ethylene and methyl acrylate), and ethylene-α-olefin copolymer is preferred.

[0069] This makes it possible to more effectively prevent the generation of foreign matter, particularly relatively large foreign matter (for example, foreign matter having a maximum length of 30 μm or more), in the cushion layer 3, and more significantly exhibits the above-mentioned effects. Also, the condition for interlayer strength between the release layer and the cushion layer 3, which will be described later, can be more suitably satisfied. Also, the cushioning properties of the cushion layer 3 can be more easily improved, and the ability to conform to the recesses 223 can be more improved.

[0070] The MFR (melt flow rate) of the first resin component is preferably 2.0 g / 10 min or more and 8.0 g / 10 min or less, more preferably 2.5 g / 10 min or more and 7.5 g / 10 min or less, and even more preferably 3.0 g / 10 min or more and 7.0 g / 10 min or less.

[0071] This makes film-forming properties more stable, keeps the surface roughness of the multi-layered film below a certain value, and suppresses the transfer of surface roughness during pressing.

[0072] In this specification, MFR (melt flow rate) means "melt mass flow rate" and is the melt flow rate measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190°C and a load of 2.16 kgf.

[0073] The cushion layer 3 may contain, in addition to the first and second resin components described above, a third resin component other than these.

[0074] Examples of the third resin component include polyester-based resins and polyamide-based resins, with polyester-based resins being preferred.

[0075] This makes it possible to more effectively prevent the generation of foreign matter, particularly relatively large foreign matter (for example, foreign matter having a maximum length of 30 μm or more), in the cushion layer 3, and more significantly exhibits the above-mentioned effects. Also, the condition for interlayer strength between the release layer and the cushion layer 3, which will be described later, can be more suitably satisfied. Also, the cushioning properties of the cushion layer 3 can be more easily improved, and the ability to conform to the recesses 223 can be more improved.

[0076] Examples of polyester resins include polyethylene terephthalate (PET), polycyclohexane terephthalate (PCT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycyclohexane dimethylene terephthalate, polypropylene terephthalate, and copolymers thereof, and one or more of these can be used in combination.

[0077] Among these, polybutylene terephthalate resins (polybutylene terephthalate or copolymers containing polybutylene terephthalate) are preferred.

[0078] This allows the aforementioned effects to be more pronounced, particularly when the release layer (at least one of the first release layer 1 and the second release layer 2) is made of a material containing a polybutylene terephthalate resin (polybutylene terephthalate or a copolymer containing polybutylene terephthalate).

[0079] When the content of the first resin component in the cushion layer 3 is X1 [mass %] and the content of the third resin component is X3 [mass %], it is preferable to satisfy the relationship 0.25≦X3 / X1≦0.90, it is more preferable to satisfy the relationship 0.26≦X3 / X1≦0.80, and it is even more preferable to satisfy the relationship 0.27≦X3 / X1≦0.70.

[0080] This makes it possible to more effectively prevent the generation of foreign matter, particularly relatively large foreign matter (for example, foreign matter having a maximum length of 30 μm or more), in the cushion layer 3, and more significantly exhibits the above-mentioned effects. Also, the condition for interlayer strength between the release layer and the cushion layer 3, which will be described later, can be more suitably satisfied. Also, the cushioning properties of the cushion layer 3 can be more easily improved, and the ability to conform to the recesses 223 can be more improved.

[0081] When the content of the second resin component in the cushion layer 3 is X2 [mass%] and the content of the third resin component is X3 [mass%], it is preferable to satisfy the relationship 0.20≦X3 / X2≦1.10, it is more preferable to satisfy the relationship 0.22≦X3 / X2≦1.00, and it is even more preferable to satisfy the relationship 0.24≦X3 / X2≦0.80.

[0082] This makes it possible to more effectively prevent the generation of foreign matter, particularly relatively large foreign matter (for example, foreign matter having a maximum length of 30 μm or more), in the cushion layer 3, and more significantly exhibits the above-mentioned effects. Also, the condition for interlayer strength between the release layer and the cushion layer 3, which will be described later, can be more suitably satisfied. Also, the cushioning properties of the cushion layer 3 can be more easily improved, and the ability to conform to the recesses 223 can be more improved.

[0083] The cushion layer 3 may contain components other than those described above. Hereinafter, such components are also referred to as "other components." Examples of such components include a crystal nucleating agent, an antioxidant, a slip agent, an antiblocking agent, an antistatic agent, a colorant, and a stabilizer.

[0084] However, the content of other components in the cushion layer 3 is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0085] The storage modulus E' of the cushion layer 3 at 150°C is preferably 0.1 MPa or more, more preferably 0.5 MPa or more and 150 MPa or less, and even more preferably 1 MPa or more and 100 MPa or less.

[0086] This makes it possible to more appropriately suppress or prevent a portion of the cushion layer 3 from protruding from the edge of the release film 10 and adhering to the FPC 200 when the release film 10 is embedded in the recess 223 in the second step. This therefore makes it possible to more appropriately suppress or prevent contamination of the FPC 200. Furthermore, it becomes easier to peel off the release film 10 in the third step.

[0087] The storage modulus E' of the cushion layer 3 at 150°C can be determined, for example, in accordance with JIS K7244-4 by preparing a cushion layer 3 having a width of 4 mm and a length of 20 mm, and measuring it using a dynamic viscoelasticity measuring device (Hitachi High-Tech Science Corporation, "DMA7100") in tensile mode, at a frequency of 1 Hz, and at a heating rate of 5°C / min.

[0088] The average thickness Tk of the cushion layer 3 is preferably 10 μm or more and 200 μm or less, more preferably 20 μm or more and 180 μm or less, and even more preferably 30 μm or more and 150 μm or less.

[0089] This prevents the release film 10 from becoming thicker than necessary, while making it easier to improve the cushioning properties of the cushion layer 3 and making it possible to improve the ability to conform to the recesses 223.

[0090] [2-2]First release layer Next, the first release layer 1 will be described. The first release layer 1 is laminated on one side of the cushion layer 3. The first release layer 1 forms one surface of the release film .

[0091] The first release layer 1 has flexibility, and in the above-described method for manufacturing a flexible printed circuit board 200 using the release film 10, the release film 10 is superimposed on the CL film 220 of the FPC 200 so that the first release layer 1 comes into contact with the CL film 220. Then, in the second step, when the superimposed flexible circuit board 210 and the CL film 220 are bonded via the adhesive layer 222, the first release layer 1 is pressed into the flexible circuit board 210 and the CL film 220, following the shape of the recess 223 formed by the flexible circuit board 210 and the CL film 220, and functions as a protective (buffer) material that prevents the release film 10 from breaking. Furthermore, in the third step, the first release layer 1 functions as a contact layer for exhibiting excellent releasability of the release film 10 from the CL film 220 (FPC 200).

[0092] Therefore, when the release film 10 is embedded in the recess 223 formed in the FPC 200 in the second step, it is possible to reliably suppress or prevent the adhesive from seeping out from the adhesive layer 222. Furthermore, after the formation of the FPC 200 in the second step in which the flexible circuit board 210 and the CL film 220 are bonded together via the adhesive layer 222 provided on the CL film 220, when the release film 10 is peeled off from the FPC 200 in the third step, it is possible to reliably suppress or prevent the FPC 200 from elongating and breaking.

[0093] The first release layer 1 may be made of any material, but usually contains a thermoplastic resin, and in particular, it is preferable that it contains a polyester-based resin. This makes the above-mentioned effects more pronounced.

[0094] The polyester resin is not particularly limited, but examples thereof include polyethylene terephthalate (PET), polycyclohexane terephthalate (PCT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycyclohexane dimethylene terephthalate, polypropylene terephthalate, and copolymers thereof, and one or more of these can be used in combination.

[0095] Among these, polybutylene terephthalate resins (polybutylene terephthalate or copolymers containing polybutylene terephthalate) are preferred.

[0096] This allows the aforementioned effects to be exhibited more significantly, particularly when the cushion layer 3 is made of a material containing a polybutylene terephthalate-based resin (polybutylene terephthalate or a copolymer containing polybutylene terephthalate).

[0097] The polybutylene terephthalate-based resin may be polybutylene terephthalate or various copolymers containing polybutylene terephthalate. Among these, it is preferable that the polybutylene terephthalate resin further contains at least one of a polybutylene terephthalate / polytetramethylene glycol block copolymer, and a polybutylene terephthalate copolymer containing terephthalic acid and a dicarboxylic acid component other than terephthalic acid as a constituent monomer.

[0098] This allows the aforementioned effects to be exhibited more significantly, particularly when the cushion layer 3 is made of a material containing a polybutylene terephthalate-based resin (polybutylene terephthalate or a copolymer containing polybutylene terephthalate).

[0099] The content of the thermoplastic resin in the first release layer 1 is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. This makes the above-mentioned effects more pronounced.

[0100] In addition to the thermoplastic resin, the first release layer 1 may further contain at least one of inorganic particles and organic particles.

[0101] The inorganic particles are not particularly limited, but examples thereof include aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, alumina, aluminum nitride, aluminum borate whiskers, boron nitride, crystalline silica, amorphous silica, antimony oxide, E-glass, D-glass, S-glass, and the like, and one or more of these can be used in combination.

[0102] The organic particles are not particularly limited, but examples thereof include polystyrene particles, acrylic particles, polyimide particles, polyester particles, silicone particles, polypropylene particles, polyethylene particles, fluororesin particles, and core-shell particles, and one or more of these may be used in combination.

[0103] Furthermore, the inorganic particles and organic particles preferably have an average particle size of 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 20 μm or less.

[0104] This makes it possible to set the surface roughness of the surface of the first release layer 1 opposite to the cushion layer 3 relatively easily within the range described below.

[0105] The average particle size of inorganic particles and organic particles can be determined by measuring the particle size distribution on a volume basis using, for example, a laser diffraction particle size distribution analyzer (e.g., HORIBA LA-500), and the median diameter (D50) can be used.

[0106] When the first release layer 1 has an uneven surface, the 10-point average roughness (Rz) of the surface is preferably 0.1 μm or more and 20.0 μm or less, and more preferably 1.0 μm or more and 10.0 μm or less. This allows the release film 10 to be released from the FPC 200 (flexible circuit board 210) with excellent releasability. The 10-point average roughness (Rz) can be measured in accordance with JIS B 0601-1994.

[0107] The first release layer 1 may contain components other than those described above. Hereinafter, such components are also referred to as "other components." Examples of such components include a nucleating agent, an antioxidant, a slip agent, an antiblocking agent, an antistatic agent, a colorant, and a stabilizer.

[0108] However, the content of other components in the first release layer 1 is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0109] The storage modulus E' of the first release layer 1 at 150° C. is preferably 50 MPa or more, more preferably 50 MPa or more and 1000 MPa or less, and even more preferably 50 MPa or more and 300 MPa or less. This makes the above-mentioned effects more pronounced.

[0110] The storage modulus E' of the first release layer 1 at 150°C can be determined in accordance with JIS K7244-4 by preparing a first release layer 1 having a width of 4 mm and a length of 20 mm, and measuring it using a dynamic viscoelasticity measuring device (Hitachi High-Tech Science Corporation, "DMA7100") in tensile mode, at a frequency of 1 Hz, and at a heating rate of 5°C / min.

[0111] The average thickness T1 of the first release layer 1 is preferably 5 μm or more and 35 μm or less, more preferably 7 μm or more and 30 μm or less, and even more preferably 10 μm or more and 25 μm or less. This makes the above-mentioned effects more pronounced.

[0112] As described above, when the surface of the first release layer 1 opposite the cushion layer 3 has an uneven shape, the thickness of the first release layer 1 is measured at a position including the convex portion in the case of a convex portion, and at a position including the concave portion in the case of a concave portion.

[0113] The surface roughness Rz of the first release layer 1 is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.3 μm or more and 3.0 μm or less, and even more preferably 0.5 μm or more and 1.0 μm or less.

[0114] This makes it possible to more effectively suppress the transfer of the surface roughness of the release film to the substrate while ensuring releasability.

[0115] The surface roughness Rz can be measured by the method described in the example ([5-2]) below.

[0116] [2-3]Second release layer Next, the second release layer 2 will be described. The second release layer 2 is laminated on the other surface of the cushion layer 3, that is, on the surface of the cushion layer 3 opposite to the first release layer 1. The second release layer 2 constitutes the other surface of the release film 10 (the surface opposite to the surface constituted by the outer surface of the second release layer 2).

[0117] The second release layer 2 has flexibility, and in the above-described method for manufacturing a flexible printed circuit board 200 using the release film 10, the release film 10 is superimposed on the CL film 220 of the FPC 200 so that the first release layer 1 comes into contact with the CL film 220, and in the second step of this manufacturing method, when the superimposed flexible circuit board 210 and the CL film 220 are bonded via the adhesive layer 222, the second release layer 2 functions as a layer that transmits the force from the thermocompression plate 521 to the cushion layer 3. Furthermore, in the third step, the second release layer 2 functions as a contact layer for achieving excellent releasability between the glass cloths 300A, 300B and the release film 10.

[0118] Furthermore, in the manufacturing method of flexible printed circuit board 200, second release layer 2 is in contact with thermocompression plate 521 via glass cloths 300A and 300B. Therefore, second release layer 2 also has the function of transmitting heat from thermocompression plate 521 to cushion layer 3 when FPC 200 is hot-pressed in the second step of this manufacturing method.

[0119] The composition and constituents of the second release layer 2 preferably satisfy the same conditions as those described for the composition and constituents of the first release layer 1 in [2-2] above. This provides the same effect as above.

[0120] The storage modulus E' of the second release layer 2 at 150° C. is preferably 50 MPa or more, more preferably 50 MPa or more and 1000 MPa or less, and even more preferably 50 MPa or more and 300 MPa or less. This makes the above-mentioned effects more pronounced.

[0121] The storage modulus E' of the second release layer 2 at 150°C can be determined in accordance with JIS K7244-4 by preparing a second release layer 2 having a width of 4 mm and a length of 20 mm, and measuring it using a dynamic viscoelasticity measuring device (Hitachi High-Tech Science Corporation, "DMA7100") in tensile mode, at a frequency of 1 Hz, and at a heating rate of 5°C / min.

[0122] The average thickness T2 of the second release layer 2 is preferably 5 μm or more and 35 μm or less, more preferably 7 μm or more and 30 μm or less, and even more preferably 10 μm or more and 25 μm or less. This makes the above-mentioned effects more pronounced.

[0123] In addition, if the surface of the second release layer 2 opposite the cushion layer 3 has an uneven shape, the thickness of the second release layer 2 will be measured at a position including the convex part for the convex part, and at a position including the concave part for the concave part.

[0124] Furthermore, the product of the storage modulus E' at 150°C and the average thickness T2 of this second release layer 2 ((storage modulus E' at 150°C) x average thickness T2) is preferably 1000 N / m or more and 5000 N / m or less, and more preferably 1500 N / m or more and 4000 N / m or less. This makes the above-mentioned effects even more pronounced.

[0125] [2-4]Other In the release film 10 having a laminated structure of the first release layer 1, cushion layer 3, and second release layer 2 as described above, the average thickness Tt is preferably 50 μm or more and 180 μm or less, and more preferably 80 μm or more and 150 μm or less.

[0126] In this embodiment, the release film 10 is composed of a laminate in which a first release layer 1, a cushion layer 3, and a second release layer 2 are laminated in this order, but is not limited to this configuration and may be composed of a laminate having, for example, an intermediate layer such as an adhesive layer arranged at least either between the first release layer 1 and the cushion layer 3 or between the second release layer 2 and the cushion layer 3.

[0127] Furthermore, the release film 10 may be one in which the second release layer 2 that comes into contact with the glass cloths 300A, 300B is omitted, as long as excellent releasability can be maintained between the glass cloths 300A, 300B and the release film 10 in the third step.

[0128] In addition, in the release film 10, the interlayer strength between the release layer and the cushion layer 3 is preferably 3.0 N / 25 mm or more, more preferably 4.0 N / 25 mm or more, and even more preferably 5.0 N / 25 mm or more.

[0129] This makes it possible to improve the releasability of the release film 10. More specifically, for example, after the coverlay film is bonded to the flexible circuit board, the release film can be peeled off from the formed flexible printed circuit board with improved releasability. As a result, it is possible to more effectively prevent part of the release film from remaining on the flexible circuit board (for example, the coverlay film on the flexible circuit board).

[0130] The interlayer strength between the release layer and the cushion layer 3 can be determined by holding one end of the first release layer 1 and the cushion layer 3, creating a peel opening between the first release layer 1 and the cushion layer 3, and then using a tensile tester (manufactured by A&D Co., Ltd., "TENSILON RTG-1310"), pulling the first release layer 1 at a speed of 200 mm / min so that the peel angle is 180°, and measuring the peel strength (interlayer strength, N / mm). In the examples described later, values ​​determined using this method are also shown as interlayer strengths.

[0131] Release layers are provided on both sides of the cushion layer 3 shown in Fig. 3. That is, a first release layer 1 is provided on one side of the cushion layer 3, and a second release layer 2 is provided on the other side of the cushion layer 3.

[0132] In this way, by providing the release layers on both sides of the cushion layer 3, the above-mentioned effects can be obtained, and it is possible to more suitably prevent the adhesive that protrudes from the adhesive layer 222 from being inadvertently bonded to the release film 10 (release films 10A, 10B). Furthermore, for example, even when the orientation of the release film 10 is changed, the above-mentioned effects can also be obtained.

[0133] In the release film 10, it is preferable that the above-described relationship in interlayer strength be satisfied between at least one of the two release layers and the cushion layer 3. More specifically, in the method of using the release film 10 as described above, it is preferable that the above-described relationship be satisfied between the release layer on the side that comes into contact with the CL film 220 (first release layer 1 in the configuration shown in FIG. 2) and the cushion layer 3.

[0134] Although the release film of the present invention has been described above, the present invention is not limited thereto.

[0135] For example, in the above embodiment, the release film of the present invention is described as being applied to a press molding method in which flexible printed circuit boards arranged between thermocompression plates are stacked in one layer, but the number of stacked flexible printed circuit boards is not limited to one layer and may be two or more layers.

[0136] Furthermore, although the release film of the present invention is applied to a case where pressure is applied to a flexible printed circuit board arranged between thermocompression plates by using a press molding method, the present invention is not limited to this, and pressure can be applied to the flexible printed circuit board by using, for example, a roll-to-roll press machine, or can also be applied by using a vacuum pressure molding method. [Example]

[0137] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0138] [3] Preparation of raw materials The following raw materials were prepared for producing the release film:

[0139] Polybutylene terephthalate (manufactured by Mitsubishi Chemical Corporation, "Novaduran 5020") (hereinafter referred to as "hPBT") Polybutylene terephthalate copolymer (manufactured by Mitsubishi Chemical Corporation, "NovaDuran 5505S") (hereinafter referred to as "coPBT") Polybutylene terephthalate copolymer (manufactured by Bell Polyester Products, Inc., "P02220") (hereinafter referred to as "C-coPBT") Polypropylene (Sumitomo Chemical Co., Ltd., "FH1016") (hereinafter referred to as "PP") Low-density polyethylene (Sumitomo Chemical Co., Ltd., "FX352," melting point: 70°C, MFR: 4g / 10min) (hereinafter referred to as "LDPE2") Low-density polyethylene (manufactured by Tosoh Corporation, "360", melting point: 106°C, MFR: 1.6g / 10min) (hereinafter referred to as "LDPE6") Ethylene-vinyl acetate copolymer (manufactured by Mitsui Dow, "EV360", melting point: 77°C, MFR: 2g / 10min) (hereinafter referred to as "EVA") Ethylene-methyl methacrylate copolymer (Sumitomo Chemical Co., Ltd., "WK307", melting point: 80°C, MFR: 7g / 10min) (hereinafter referred to as "EMMA1") Ethylene-methyl methacrylate copolymer (Sumitomo Chemical Co., Ltd., "CM-8014", melting point: 79°C, MFR: 4g / 10min) (hereinafter referred to as "EMMA2") Ethylene-methyl methacrylate copolymer (manufactured by Sumitomo Chemical Co., Ltd., "WH206-F", melting point: 86°C, MFR: 2g / 10min) (hereinafter referred to as "EMMA3") Ethylene-methyl methacrylate copolymer (manufactured by Sumitomo Chemical Co., Ltd., "WH102", melting point: 90°C, MFR: 0.25g / 10min) (hereinafter referred to as "EMMA4")

[0140] [4] Production of release film Example 1 First, a kneaded and pulverized mixture of 70 parts by weight of hPBT and 30 parts by weight of coPBT was prepared as a composition for forming the release layer (first release layer and second release layer), and a kneaded and pulverized mixture of 35 parts by weight of LDPE2, 40 parts by weight of EMMA4, 15 parts by weight of PP, and 10 parts by weight of hPBT was prepared as a composition for forming the cushion layer.

[0141] Next, the composition for forming the release layer was formed into a film by an extrusion T-die method, thereby obtaining a first release layer.

[0142] Next, the first release layer was subjected to the extrusion T-die method using a composition for forming a cushion layer and a composition for forming a release layer, and each was then formed into a film, thereby forming a laminate in which the cushion layer and the second release layer were laminated in this order on the first release layer, thereby obtaining a release film as shown in Figure 3.

[0143] In the obtained release film, the average thickness T1 of the first release layer was 20 μm, the average thickness Tk of the cushion layer was 80 μm, and the average thickness T2 of the second release layer was 20 μm.

[0144] In addition, the number of foreign particles with a maximum length of 30 μm or more within a 20 cm x 20 cm area was determined by visual inspection and then observing the surface and cross section with a microscope and counting only those with a long side of 30 μm or more.The number of foreign particles with a maximum length of 30 μm or more within a 20 cm x 20 cm area was found to be 12.

[0145] The interlayer strength between the first release layer and the cushion layer and the interlayer strength between the second release layer and the cushion layer were both 3.2 N / 25 mm.

[0146] <Examples 2 to 9 and Comparative Examples 1 to 4> A release film was produced in the same manner as in Example 1, except that the compositions for forming the cushion layer and the release layer, meeting the conditions shown in Table 1, were used.

[0147] The release film conditions for each of the examples and comparative examples are summarized in Table 1. The "number of foreign particles" in the table refers to the number of foreign particles with a maximum length of 30 μm or more within a 20 cm × 20 cm area, determined by visually checking the surface and cross-section and then counting only those with a long side of 30 μm or more through observation under a microscope. The unit is "number / 20 cm□." In the table, the unit for melting point is "°C," and the unit for MFR is "g / 10 min." In the table, the "interlayer strength" refers to the interlayer strength between the first release layer and the cushion layer, and the unit is "N / 25 mm."

[0148] [Table 1]

[0149] [5] Evaluation The release films of the above-mentioned Examples and Comparative Examples were evaluated as follows.

[0150] [5-1] Appearance of FPC The release films of each of the examples and comparative examples were each 100 mm x 100 mm in size, and a coverlay film (DuPont's "HXC1220") was attached to a flexible circuit board with the adhesive layer of the coverlay film facing the flexible circuit board to form an FPC (laminate) having irregularities with a pitch of 50 μm, a width of 50 μm, and a height of 18 μm. The release film was then attached to the FPC 200, which was laminated in two layers as shown in FIG. Using a molding press (Kitagawa Seiki Co., Ltd., "KVHCIII"), the sample was heated from room temperature to 180°C over 20 minutes, kept at 180°C for 20 minutes, and cooled from 180°C to room temperature over 20 minutes at a press pressure of 3 MPa. After that, one end of the release film was held and pulled off, and the surface of the flexible circuit board exposed in the recess was visually observed for the presence or absence of transfer of the surface roughness of the release film and the presence or absence of transfer of irregularities due to foreign matter, and evaluated according to the following criteria.

[0151] [Evaluation criteria] ○: No problems with appearance. ×: Significant depressions were observed on the surface of the FPC, and the appearance was poor.

[0152] [5-2] Surface roughness For the first release layer of the release film of each of the above examples and comparative examples, the 10-point average roughness (Rz) of the surface exposed on the side opposite the cushion layer was measured using a surface roughness measuring device (manufactured by Mitutoyo Corporation, "SURFTST SJ-210").

[0153] [5-3] Embeddability of release film The release films of each of the examples and comparative examples were each 100 mm x 100 mm. A 200 μm thick coverlay film (10 sheets of "CMA0525" manufactured by Arisawa Manufacturing Co., Ltd.) with a 4 mm diameter hole was attached to a flexible circuit board to form an FPC 200 (laminate). The release film was then pressed into the two-layer FPC stack shown in Figure 1 using a molding press ("KVHCIII" manufactured by Kitagawa Seiki Co., Ltd.) under the following conditions: temperature was increased from room temperature to 100°C in 20 minutes, held at 100°C for 20 minutes, and cooled from 100°C to room temperature in 20 minutes. The press pressure was 3 MPa. One edge of the release film was then grasped and peeled off, and the embedding height of the release film corresponding to the 4 mm diameter hole was measured. The higher this value, the better the embedding ability.

[0154] [5-4] Release properties of release film The release films of each of the examples and comparative examples were each 100 mm x 100 mm in size. A coverlay film (DuPont, "HXC1220") was attached to a flexible circuit board with the adhesive layer of the coverlay film facing the flexible circuit board to form an FPC (laminate) with irregularities of 50 μm pitch, 50 μm width, and 18 μm height. The release film was then pressed into the two-layer FPC 200, as shown in FIG. 1, using a molding press (Kitagawa Seiki Co., Ltd., "KVHCIII") under the following conditions: the temperature was increased from room temperature to 180°C in 20 minutes, kept at 180°C for 20 minutes, and then cooled from 180°C to room temperature in 20 minutes, with a press pressure of 3 MPa. One edge of the release film was then grasped and peeled off. The ease of peeling (releasability) of the release film was evaluated according to the following criteria.

[0155] [Evaluation criteria] ◯: The release film can be peeled off. ×: When peeling off the release film, peeling is difficult due to fusion between the cushion layers or stretching or breaking of the release film.

[0156] [5-5] Cushion layer overflow The release films of each of the above examples and comparative examples were each cut to a size of 100 mm x 100 mm, and these release films were heated from room temperature to 180°C over 20 minutes using a molding press (Kitagawa Seiki Co., Ltd., "KVHCIII"), kept at 180°C for 20 minutes, and cooled from 180°C to room temperature over 20 minutes, and clamped under conditions of a press pressure of 3 MPa.The maximum distance of the cushion layer that protruded from the release layer of the film was then measured with vernier calipers on each of the four sides, and the average value was calculated.

[0157] The above evaluation results are summarized in Table 2. In the table, the unit for evaluation of surface roughness is "μm", the unit for evaluation of embeddability (maximum exudation amount) is "mm", and the unit for evaluation of cushion layer exudation is "mm".

[0158] [Table 2]

[0159] As shown in Table 2, excellent results were obtained in each of the Examples, whereas satisfactory results were not obtained in each of the Comparative Examples. [Explanation of symbols]

[0160] 1 First release layer 2 Second release layer 3 Cushion layer 10 Release film 10A Release Film 10B Release Film 200 Flexible Printed Circuit Board (FPC) 210 Flexible Circuit Board 220 Coverlay film (CL film) 221 Coverlay 222 Adhesive layer 223 recess 300 Glass Cloth 300A Glass Cloth 300B glass cloth 521 Heat-bonding plate T1 Average thickness of the first release layer T2 Average thickness of the second release layer Tk Average thickness of cushion layer Tt Average thickness of release film

Claims

1. A release film having a release layer and a cushion layer, the release layer is made of a material containing a polybutylene terephthalate resin, A release film characterized in that the number of foreign matter particles having a maximum length of 30 μm or more within a 20 cm x 20 cm area of ​​the cushion layer is less than 20.

2. 2. The release film according to claim 1, wherein the cushion layer is composed of a material containing a first resin component having a melting point of 60°C or higher and 90°C or lower, and a second resin component having a melting point that is 10°C or higher and 50°C or lower than the melting point of the first resin component.

3. 3. The release film according to claim 2, wherein the content of the first resin component in the cushion layer is X1 [mass%] and the content of the second resin component in the cushion layer is X2 [mass%], and the relationship of 0.80≦X2 / X1≦1.45 is satisfied.

4. 4. The release film according to claim 2, wherein the first resin component has an MFR of 2.0 g / 10 min or more and 8.0 g / 10 min or less.

5. 4. The release film according to claim 2, wherein the cushion layer is made of a material further containing a polybutylene terephthalate resin as a third resin component.

6. 6. The release film according to claim 5, wherein the content of the first resin component in the cushion layer is X1 [mass%] and the content of the third resin component in the cushion layer is X3 [mass%], the relationship of 0.25≦X3 / X1≦0.90 is satisfied.

7. 6. The release film according to claim 5, wherein the content of the second resin component in the cushion layer is X2 [mass%] and the content of the third resin component in the cushion layer is X3 [mass%], the relationship of 0.20≦X3 / X2≦1.10 is satisfied.

8. 3. The release film according to claim 1 or 2, wherein the cushion layer is made of a material containing at least one of an ethylene-methyl methacrylate copolymer, an ethylene-vinyl acetate copolymer, an ethylene-methyl acrylate copolymer, and an ethylene-α-olefin copolymer.

9. 3. The release film according to claim 1, wherein the cushion layer has an average thickness of 10 μm or more and 200 μm or less.

10. The release film according to claim 1 or 2, wherein the release layer is provided on both sides of the cushion layer.

11. The release layer is a release film according to claim 1 or 2, which contains polybutylene terephthalate as the polybutylene terephthalate-based resin, and further contains at least one of a polybutylene terephthalate / polytetramethylene glycol block copolymer, and a polybutylene terephthalate copolymer containing terephthalic acid and a dicarboxylic acid component other than terephthalic acid as a constituent monomer.

12. 3. The release film according to claim 1, wherein the average thickness of the release layer is 5 μm or more and 35 μm or less.

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