阅读说明：本技术 脱模膜 (Mold release film ) 是由 中尾洋祐 土谷雅弘 宇都航平 于 2014-07-31 设计创作，主要内容包括：本发明的目的在于提供一种脱模膜,其适合于柔性电路基板的制造、且能够在保持脱模性的状态下抑制皱褶的产生。本发明为一种脱模膜,其适合于柔性电路基板的制造,所述脱模膜的表面和背面被粗面化,所述表面的十点平均粗糙度Rz为4μm以上且20μm以下,并且构成所述背面的脱模层的厚度为35μm以上(其中,不包括所述表面的十点平均粗糙度Rz为4μm以上且5μm以下、并且构成所述背面的脱模层的厚度为35μm以上且36μm以下的情况)。(The purpose of the present invention is to provide a release film which is suitable for the production of a flexible circuit board and which can suppress the occurrence of wrinkles while maintaining releasability. The present invention is a release film suitable for manufacturing a flexible circuit board, the surface and the back surface of which are roughened, the ten-point average roughness Rz of the surface is 4 [ mu ] m or more and 20 [ mu ] m or less, and the thickness of a release layer constituting the back surface is 35 [ mu ] m or more (excluding the case where the ten-point average roughness Rz of the surface is 4 [ mu ] m or more and 5 [ mu ] m or less, and the thickness of a release layer constituting the back surface is 35 [ mu ] m or more and 36 [ mu ] m or less).)

1. A mold release film suitable for the production of a flexible circuit board,

the surface and the back surface of the release film are roughened,

a ten-point average roughness Rz of the front surface is 4 μm or more and 20 μm or less, and a thickness of a releasing layer constituting the back surface is 35 μm or more,

wherein the above-mentioned case is excluded in which the ten-point average roughness Rz of the surface is 4 μm or more and 5 μm or less and the thickness of the release layer constituting the back surface is 35 μm or more and 36 μm or less,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers constituting a front surface and a back surface, respectively.

2. The release film of claim 1,

a ten-point average roughness Rz of the front surface is 4 μm or more and 20 μm or less, and a thickness of the release layer constituting the back surface is 37 μm or more, or,

the ten-point average roughness Rz of the front surface is 8 [ mu ] m or more and 15 [ mu ] m or less, and the thickness of the release layer constituting the rear surface is 35 [ mu ] m or more and less than 37 [ mu ] m.

3. The release film of claim 1 or 2,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers constituting a front surface and a back surface, respectively, the release layer constituting the front surface and the release layer constituting the back surface being different resin compositions.

4. The release film of claim 1 or 2,

the ten-point average roughness Rz of the surface is different from that of the back surface.

5. The release film of claim 1 or 2,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers respectively constituting a front surface and a back surface, the ten-point average roughness Rz of the back surface being 1 μm or more and 45 μm or less, the total thickness of the 2 release layers respectively constituting the front surface and the back surface occupying more than half of the thickness of the release film.

6. The release film of claim 1 or 2,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers respectively constituting a front surface and a back surface, the ten-point average roughness Rz of the back surface being 1 μm or more and 45 μm or less, and of the 2 release layers respectively constituting the front surface and the back surface, the release layer constituting the front surface contains a polybutylene terephthalate resin.

7. The release film of claim 1 or 2,

the ten-point average roughness Rz of the back surface is 1 μm or more and 45 μm or less, and the ratio of the glossy surface of the front surface is 35% or more and 85% or less.

8. The release film of claim 1 or 2,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers respectively constituting a front surface and a back surface, a total thickness of the 2 release layers respectively constituting the front surface and the back surface occupying more than half of a thickness of the release film, and of the 2 release layers respectively constituting the front surface and the back surface, the release layer constituting the front surface contains a polybutylene terephthalate resin.

9. The release film of claim 1 or 2,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers respectively constituting a front surface and a back surface, a total thickness of the 2 release layers respectively constituting the front surface and the back surface occupying more than half of a thickness of the release film, and a ratio of a glossy surface of the front surface being 35% or more and 85% or less.

10. The release film of claim 1 or 2,

the release film includes a multilayer film having 2 release layers and an intermediate layer, the 2 release layers respectively constituting a front surface and a back surface, a glossy surface ratio of the front surface being 35% or more and 85% or less, and of the 2 release layers respectively constituting the front surface and the back surface, the release layer constituting the front surface contains a polybutylene terephthalate resin.

11. A mold release film suitable for the production of a flexible circuit board,

the surface and the back surface of the release film are roughened,

a ten-point average roughness Rz of the front surface is 4 μm or more and 20 μm or less, and a thickness of a releasing layer constituting the back surface is 35 μm or more,

wherein the above-mentioned case is excluded in which the ten-point average roughness Rz of the surface is 4 μm or more and 5 μm or less and the thickness of the release layer constituting the back surface is 35 μm or more and 36 μm or less,

the release film comprises a single layer film comprising only 1 release layer, the 1 release layer comprising a face and a back.

12. The release film of claim 11,

a ten-point average roughness Rz of the front surface is 4 μm or more and 20 μm or less, and a thickness of the release layer constituting the back surface is 37 μm or more, or,

the ten-point average roughness Rz of the front surface is 8 [ mu ] m or more and 15 [ mu ] m or less, and the thickness of the release layer constituting the rear surface is 35 [ mu ] m or more and less than 37 [ mu ] m.

13. The release film of claim 11 or 12,

the release film comprises a single-layer film comprising only 1 release layer, the 1 release layer constituting a front surface and a back surface, the ten-point average roughness Rz of the back surface being 1 [ mu ] m or more and 45 [ mu ] m or less, and the 1 release layer constituting the front surface and the back surface containing a polybutylene terephthalate resin.

14. The release film of claim 11 or 12,

the ten-point average roughness Rz of the back surface is 1 μm or more and 45 μm or less, and the ratio of the glossy surface of the front surface is 35% or more and 85% or less.

15. The release film of claim 11 or 12,

the release film comprises a single-layer film including only 1 release layer, the 1 release layer constituting a front surface and a back surface, a ratio of a glossy surface of the front surface is 35% or more and 85% or less, and the 1 release layer constituting the front surface and the back surface contains a polybutylene terephthalate resin.

Technical Field

The present invention relates to a release film which is suitable for manufacturing a flexible circuit board and can suppress the generation of wrinkles while maintaining releasability.

Background

In the manufacturing process of the flexible circuit board, a cover film is thermally pressure-bonded to a flexible circuit board body on which a copper circuit is formed, using a thermosetting adhesive or a thermosetting adhesive sheet. In this case, a release film is widely used to prevent the cover film from adhering to the hot press plate.

Release films comprising various resins such as methylpentene resins, polyester resins, and syndiotactic polystyrene resins have been proposed (patent documents 1 to 3).

For example, patent document 1 describes a mold release film composed of a laminate containing a polymethylpentene resin. Patent document 2 describes a release film having a thin release layer, a cushion layer, and a sub-release layer, which have a predetermined surface roughness and contain polybutylene terephthalate. Patent document 3 describes a release film having a release layer containing a syndiotactic polystyrene resin and a buffer layer.

In recent years, along with the spread of smart phones, tablet PCs, and the like, flexible circuit boards have been becoming more highly functional and thinner. In addition, automation of manufacturing methods such as a roll-to-roll (RtoR) method is also advancing, and the following problems arise with such automation of manufacturing methods: in the manufacturing process of the flexible circuit board, wrinkles generated in the release film are transferred to the flexible circuit board.

Therefore, there is a demand for a release film that can suppress the generation of wrinkles, but it is difficult to obtain a release film that can suppress the generation of wrinkles while maintaining other required performances (e.g., filling property, mold release property, etc.).

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a release film which is suitable for the production of a flexible circuit board and which can suppress the occurrence of wrinkles while maintaining releasability.

Means for solving the problems

The present invention is a release film suitable for manufacturing a flexible circuit board, the surface and the back surface of which are roughened, the ten-point average roughness Rz of the surface is 4 [ mu ] m or more and 20 [ mu ] m or less, and the thickness of a release layer constituting the back surface is 35 [ mu ] m or more (excluding the case where the ten-point average roughness Rz of the surface is 4 [ mu ] m or more and 5 [ mu ] m or less, and the thickness of a release layer constituting the back surface is 35 [ mu ] m or more and 36 [ mu ] m or less).

The present invention is described in detail below.

The present inventors have found that if a release film is formed so that both the front surface and the back surface are roughened and the ten-point average roughness Rz of the front surface and the thickness of the release layer constituting the back surface satisfy a predetermined range, the occurrence of wrinkles can be suppressed while maintaining releasability, and have completed the present invention.

The release film of the present invention is suitable for the production of a flexible circuit board.

The surface and the back surface of the release film of the present invention are roughened. The release film of the present invention can suppress the generation of wrinkles while maintaining releasability by roughening not only one surface but also both the front surface and the back surface.

In the present specification, "roughened" means a state in which an uneven shape is formed by, for example, embossing, etching treatment using a chemical or plasma, melt fracture at the time of film formation, or the like. The roughened state can be confirmed by an optical microscope.

In the release film of the present invention, the ten-point average roughness Rz of the front surface is 4 μm or more and 20 μm or less, and the thickness of the release layer constituting the rear surface is 35 μm or more (excluding the case where the ten-point average roughness Rz of the front surface is 4 μm or more and 5 μm or less, and the thickness of the release layer constituting the rear surface is 35 μm or more and 36 μm or less).

By making the ten-point average roughness Rz of the surface and the thickness of the release layer constituting the back surface satisfy the above ranges, the release film of the present invention can suppress the generation of wrinkles while maintaining releasability. When the ten-point average roughness Rz of the surface is less than the above range, wrinkles are generated in the release film in a large amount. When the ten-point average roughness Rz of the surface exceeds the above range, the releasability of the release film is lowered. Further, when the thickness of the release layer constituting the back surface is smaller than the above range, wrinkles are generated in the release film in a large amount. The upper limit of the thickness of the release layer constituting the back surface is not particularly limited, but is preferably 100 μm, and more preferably 50 μm.

From the viewpoint of effectively suppressing the generation of wrinkles while maintaining the mold release property, more preferable are: the ten-point average roughness Rz of the front surface is 4 μm or more and 20 μm or less, and the thickness of the release layer constituting the back surface is 37 μm or more, or the ten-point average roughness Rz of the front surface is 8 μm or more and 15 μm or less, and the thickness of the release layer constituting the back surface is 35 μm or more and less than 37 μm.

In the present specification, "front surface" refers to a surface on the side of the flexible circuit board in the manufacturing process of the flexible circuit board, and "back surface" refers to a surface on the side of the hot press plate in the manufacturing process of the flexible circuit board. However, the release film alone does not have a distinction between the "front surface" and the "back surface", and the surface having the ten-point average roughness Rz satisfying the above range is referred to as the "front surface".

In the present specification, the "ten-point average roughness Rz" is a value obtained by the following expression (1) in which the elevations from the highest crest to the crest having the height of 5 are represented by Yp1, Yp2, Yp3, Yp4, and Yp5, and the elevations from the deepest valley bottom to the valley bottom having the depth of 5 are represented by Yv1, Yv2, Yv3, Yv4, and Yv5, respectively, in the reference length L. The larger the value of the "ten-point average roughness Rz" is, the rougher the surface as a whole, and the smaller the value is, the smoother the surface as a whole. The "ten-point average roughness Rz" can be measured by using a stylus surface roughness measuring machine (for example, SURF TEST SJ-301 manufactured by Mitsutoyo corporation) in accordance with JIS B0601: the method 2001 uses a stylus having a tip radius of 2 μm and a cone angle of 60 ° of a cone, and performs measurement under the conditions of a measurement force of 0.75mN, a cutoff value λ s of 2.5 μm (when the surface roughness of the object to be measured is smaller than the cutoff value, the cutoff value may be adjusted), and a λ c of 0.8 mm.

[ mathematical formula 1 ]

Rz＝(|Yp1+Yp2+Yp3+Yp4+Yp5|+|Yv1+Yv2+Yv3+Yv4+Yv5|)/5 (1)

The ranges of the ten-point average roughness Rz of the front surface and the thickness of the release layer constituting the back surface are derived from the "ten-point average roughness Rz of the front surface" and the "thickness of the release layer constituting the back surface" obtained in examples and comparative examples as ranges in which the occurrence of wrinkles can be suppressed while maintaining releasability.

Fig. 1 shows a graph in which "ten-point average roughness Rz of the surface" and "thickness of the release layer constituting the back surface" obtained in examples (several examples are excluded) and comparative examples are plotted. In fig. 1, the ranges of "ten-point average roughness Rz of the surface" and "thickness of the release layer constituting the back surface" defined in the present invention are indicated by oblique lines. However, the upper limit of the "thickness of the release layer constituting the back surface" is not limited to the range indicated by the oblique lines in fig. 1.

Examples of the method of adjusting the ten-point average roughness Rz of the front surface and the thickness of the release layer constituting the back surface so as to satisfy the above range include: and a method in which a resin constituting a release film is extruded by a T-die of an extruder to be molded into a target thickness, and a cooling roll having a pattern formed thereon is pressed against the surface of the obtained resin film to transfer the pattern formed on the surface of the cooling roll to the surface of the resin film.

The method for producing the cooling roll having a patterned surface is not particularly limited, and examples thereof include: and a method of forming a concave pattern on the surface of a smooth roller and then adjusting the roughness of the smooth portion of the roller. The pattern to be processed on the surface of the cooling roll is not particularly limited, and examples thereof include a single-shaped uneven pattern, and uneven patterns of various shapes obtained by superimposing fine unevenness on an uneven pattern due to a large abrasive blasting material.

In the release film of the present invention, the ratio of the glossy surface of the surface is preferably 35% or more and 85% or less. When the ratio of the glossy surface is less than 35%, the releasability of the release film may be lowered. When the ratio of the gloss surface is more than 85%, wrinkles may be formed in the release film.

In the present specification, the "gloss surface ratio" is a value obtained by observing the surface of a release film at 20 times magnification using an optical microscope, measuring the area of a smooth surface in an observation visual field (700 μm × 525 μm), and determining the percentage of the area of the smooth surface in the observation visual field.

The ten-point average roughness Rz of the back surface of the release film of the present invention is not particularly limited, but is preferably 1 to 45 μm, and may be the same as the ten-point average roughness Rz of the front surface. The ratio of the glossy surface of the back surface is not particularly limited, but may be the same as the ratio of the glossy surface of the front surface.

In the multilayer release film of the present invention, it is preferable to subject the front surface and/or the back surface to a release treatment in order to improve the releasability.

The method of the above-mentioned mold release treatment is not particularly limited, and for example, there can be used: a method of applying or spreading a silicone-based or fluorine-based release agent to the front surface and/or the back surface; a known method such as a method of performing heat treatment, friction treatment, or the like. These mold release treatments may be used alone or in combination of 2 or more.

The release film of the present invention is not particularly limited in layer structure as long as it has the above-mentioned front surface and back surface, and may be formed of a multilayer film having 2 release layers constituting the front surface and back surface, respectively, and an intermediate layer, or a single layer film formed of only 1 release layer constituting the front surface and back surface.

When the release film of the present invention is formed of a multilayer film, the resin forming the 2 release layers constituting the front surface and the back surface is not particularly limited, and the release layer constituting the front surface and the release layer constituting the back surface may be composed of the same resin or different resins, but the release layer constituting the front surface preferably contains a crystalline aromatic polyester resin.

The crystalline aromatic polyester resin is not particularly limited, and examples thereof include: polyethylene terephthalate resins, polybutylene terephthalate resins, polyhexamethylene terephthalate resins, polyethylene naphthalate resins, polybutylene terephthalate copolymers, and the like. These crystalline aromatic polyester resins may be used alone, or 2 or more kinds may be used in combination. Among them, polybutylene terephthalate resins are suitably used because they are excellent in non-staining properties and crystallinity.

In the present specification, the term "polybutylene terephthalate resin" includes a copolymer of polybutylene terephthalate and polyether, polyester, or the like, in addition to a resin of polybutylene terephthalate alone.

The polybutylene terephthalate resin is not particularly limited, and those generally used can be used, and specific examples thereof include: block copolymers of polybutylene terephthalate and aliphatic polyethers, block copolymers of polybutylene terephthalate and aliphatic polyesters, and the like. These polybutylene terephthalate resins may be used alone, or 2 or more kinds may be used in combination. Among them, a mixed resin obtained by mixing a polybutylene terephthalate resin with a block copolymer of a polybutylene terephthalate and an aliphatic polyether is preferable from the viewpoint of a balance among heat resistance, mold release properties, followability to irregularities of a flexible circuit board, and the like.

The crystalline aromatic polyester resin preferably has a melt volume flow rate of 30cm from the viewpoint of film forming properties³Less than 10min, more preferably 20cm³Less than 10 min. The melt volume flow rate was measured in accordance with ISO1133 at a measurement temperature of 250 ℃ under a load of 2.16 kg.

Among the above-mentioned crystalline aromatic polyester resins, as commercially available resins, for example, the following can be suitably used: "Pelprene (registered trademark)" (manufactured by Toyo textile Co., Ltd.), "Hytrel (registered trademark)" (manufactured by Toronto Dupont Co., Ltd., "Duranex (registered trademark)" (manufactured by Polyplastics Co., Ltd.), "Novaduran (registered trademark)" (manufactured by Mitsubishi engineering plastics Co., Ltd.), and the like.

When the release film of the present invention is formed of a multilayer film, the thickness of the release layer constituting the back surface is preferably 35 μm or more, and the thickness of the release layer constituting the front surface is preferably 1 μm or more and 20 μm or less.

When the thickness of the release layer constituting the surface is less than 1 μm, wrinkles may be generated in the release film. When the thickness of the release layer constituting the surface is more than 20 μm, the releasability of the release film may be deteriorated. A more preferable lower limit of the thickness of the release layer constituting the surface is 5 μm, and a more preferable upper limit is 18 μm.

The 2 release layers constituting the front and back surfaces may further contain additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and higher fatty acid salts, as long as the effects of the present invention are not impaired.

When the release film of the present invention is formed of a multilayer film, the total thickness of the 2 release layers constituting the front surface and the back surface is preferably greater than half of the thickness of the release film. By making the total thickness of the 2 release layers constituting the front surface and the back surface satisfy the above range, the release film can more effectively suppress the generation of wrinkles.

When the release film of the present invention is formed of a multilayer film, the resin constituting the intermediate layer is not particularly limited, but the intermediate layer preferably contains a polyolefin resin.

The polyolefin resin is not particularly limited, and examples thereof include: a polyethylene resin; a polypropylene resin; ethylene-vinyl acetate copolymers; ethylene-acrylic acid monomer copolymers such as ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-acrylic acid copolymers. These can be used alone, also can be used in combination of more than 2.

The intermediate layer may further contain a resin such as polystyrene, polyvinyl chloride, polyamide, polycarbonate, polysulfone, or polyester, as long as the object of the present invention is not impaired.

The intermediate layer may further contain additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and higher fatty acid salts, as long as the effects of the present invention are not impaired.

The thickness of the intermediate layer is not particularly limited, but the lower limit is preferably 15 μm and the upper limit is preferably 80 μm. When the thickness of the intermediate layer is less than 15 μm, if the resin constituting the intermediate layer is softened during hot press bonding using a release film, a portion where the intermediate layer is not present may be generated, and the flexible circuit board may not be uniformly pressurized. When the thickness of the intermediate layer exceeds 80 μm, wrinkles may be formed in the release film. A more preferable lower limit and a more preferable upper limit of the thickness of the intermediate layer are 30 μm and 65 μm, respectively.

When the release film of the present invention is a single-layer film, the front surface and the back surface are each composed of 1 release layer. The resin constituting the release layer is not particularly limited, but preferably contains a crystalline aromatic polyester resin.

The crystalline aromatic polyester resin is not particularly limited, and the same resins as those contained in the multilayer film are exemplified. In addition, the same resin as the polybutylene terephthalate resin contained in the multilayer film described above can be suitably used.

The release layer constituting the single-layer film may further contain additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and higher fatty acid salts, within a range not to impair the effects of the present invention.

The thickness of the release film of the present invention is not particularly limited, but the upper limit is preferably 300. mu.m, more preferably 200. mu.m, and still more preferably 150. mu.m.

The method for producing the release film of the present invention is not particularly limited, and examples thereof include the following methods: after a multilayer film or a single-layer film having a desired thickness is produced, the surface of the obtained multilayer film or single-layer film is adjusted so that the ten-point average roughness Rz of the surface and the thickness of the release layer constituting the back surface satisfy the above ranges by the above-described method using a cooling roll or the like.

When the release film of the present invention is formed of a multilayer film, the method for producing the multilayer film is not particularly limited, and examples thereof include: a method for producing a film by a water-cooled or air-cooled co-extrusion blow molding method or a co-extrusion T-die method; a method of producing a film serving as one release layer, laminating an intermediate layer on the film by an extrusion lamination method, and then dry-laminating the other release layer; a method of dry laminating a film serving as one release layer, a film serving as an intermediate layer, and a film serving as the other release layer; solvent casting film forming method; hot press molding, and the like. Among these, a method of forming a film by a co-extrusion T-die method is preferable from the viewpoint of excellent control of the thickness of each layer.

The release film of the present invention is suitable for the production of a flexible circuit board. Therefore, the use of the release film of the present invention is not particularly limited, and when a cover film is thermocompression bonded to a flexible circuit board body having a copper circuit formed thereon with a thermosetting adhesive or a thermosetting adhesive sheet, the release film of the present invention is sandwiched between the cover film and a thermocompression plate, whereby the cover film and the thermocompression plate can be prevented from being bonded to each other.

Effects of the invention

According to the present invention, a release film suitable for manufacturing a flexible circuit board and capable of suppressing the generation of wrinkles while maintaining releasability can be provided.

Drawings

Fig. 1 is a graph in which "ten-point average roughness Rz of the surface" and "thickness of the release layer constituting the back surface" obtained in examples (several examples are excluded) and comparative examples are plotted, and ranges of "ten-point average roughness Rz of the surface" and "thickness of the release layer constituting the back surface" defined in the present invention are indicated by oblique lines.

Fig. 2 is an optical micrograph of the surface of the release film having a gloss surface ratio of 38%.

Fig. 3 is an optical micrograph of the surface of the release film having a gloss surface ratio of 42%.

Fig. 4 is an optical micrograph of the surface of the release film having a gloss surface ratio of 72%.

Fig. 5 is an optical micrograph of the surface of the release film having a gloss surface ratio of 82%.

Fig. 6 is an optical micrograph of the surface of the release film having a gloss surface ratio of 77%.

Fig. 7 is an optical micrograph of the surface of the release film with a 0% gloss surface ratio.

Detailed Description

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 38 and comparative examples 1 to 18

Polybutylene terephthalate resin and polypropylene resin were co-extruded by an extruder (GM 30-28 (screw diameter 30mm, L/D28, manufactured by GM Engineering) with a T-die width of 400mm to form a 3-layer resin film in which 2 polybutylene terephthalate resin layers (a release layer constituting the back surface and a release layer constituting the front surface) each having a thickness shown in table 1 or 2 were laminated on the front and back surfaces of a polypropylene resin layer (intermediate layer) having a thickness of 65 μm.

Then, the cooling roll having a pattern formed thereon was pressed against the release surface of the release layer constituting the surface of the obtained 3-layer resin film, and the pattern formed on the surface of the cooling roll was transferred to form irregularities on the release surface, thereby obtaining a release film. The release surface on which the projections and depressions are formed is a front surface, and the other release surface is a back surface. The roughened surface state of the front and back surfaces of the obtained release film was confirmed by an optical microscope, and the ten-point average roughness Rz of the front surface was measured, and the results are shown in table 1. The release films obtained in examples and comparative examples had a ten-point average roughness Rz of the back surface in the range of 1.0 to 3.0. mu.m.

< evaluation >

The following evaluations were made with respect to the release films obtained in examples 1 to 38 and comparative examples 1 to 18. The results are shown in Table 1 or 2.

(1) Ratio of glossy surface

The surface of the release film was observed under an optical microscope (manufactured by Keyence corporation, laser microscopy VK8710) at 20-fold magnification. The area of the smooth surface in the observation visual field (700. mu. m.times.525 μm) was measured, and the percentage of the area of the smooth surface in the observation visual field was determined, and the obtained value was defined as the gloss surface ratio (%). Fig. 2 to 7 show optical micrographs of the surface of the release film at gloss surface ratios of 38%, 42%, 72%, 82%, 77%, and 0%, respectively.

(2) Evaluation of Properties relating to wrinkle formation (wrinkle resistance)

CCL (20cm × 20cm, polyimide thickness 25 μm, copper foil 35 μm), coating film (20cm × 20cm, polyimide thickness 15 μm, epoxy resin adhesive layer 25 μm) and release film were sequentially laminated from bottom to top, and the resultant was aligned between pressing molds heated at 180 ℃ in advance using a slide-type vacuum thermocompressor (MKP-3000V-WH-ST, manufactured by Mikado Technis Co., Ltd.), and then pressed (about 10 seconds from the start of setting to the actual application of pressure), and 50kg/cm was applied under vacuum conditions²The pressing was performed for 2 minutes, thereby producing a flexible circuit board (FPC) evaluation sample including CCL and a cover film.

Then, the FPC evaluation sample and the release film were taken out, and after the release film was peeled off, the number of wrinkles transferred to the surface of the cover film was measured. The number of wrinkles was 0 and evaluated as "excellent", 1 to 10 as "o", 11 to 20 as "Δ", and 21 or more as "x".

When the number of wrinkles is 20 or less, the release film has sufficient wrinkle resistance as a release film in the production of a flexible circuit board. More preferably, the number of wrinkles is 10 or less.

(3) Evaluation of mold Release Properties

CCL (20 cm. times.20 cm, polyimide thickness 25 μm, copper foil 35 μm), a cover film (20 cm. times.20 cm, polyimide thickness 25 μm, epoxy resin adhesive layer 35 μm) and a release film were sequentially laminated from bottom to top, and the resultant was aligned between pressing molds heated at 180 ℃ in advance using a slide-type vacuum thermocompressor (MKP-3000V-WH-ST, manufactured by Mikado Technis Co., Ltd.), and then pressed (about 10 seconds from the start of setting to the actual application of pressure) at 50kg/cm²The FPC evaluation sample containing CCL and a cover film was prepared by pressing for 2 minutes.

Then, the FPC evaluation sample and the release film were taken out and placed on a table, and the time until the release film was peeled off from the FPC evaluation sample was measured. Specifically, since air enters between the release film and the FPC evaluation sample from the state where the release film is in close contact with the FPC evaluation sample, the color tone seen from the release film side changes, and therefore the time from the time when the FPC evaluation sample and the release film are taken out to the time when the color tone change is completed is taken as the time until the release film is peeled.

The time taken until the release film was peeled off was 30 seconds or less, evaluated as "very excellent", more than 30 seconds and 60 seconds or less was evaluated as "o", and more than 60 seconds and 90 seconds or less was evaluated as "Δ".

When the time taken until the release film is peeled off is 60 seconds or less, it can be said that the release film has sufficient releasability as a release film in the production of a flexible circuit board. More preferably, the time until the release film is peeled is 30 seconds or less.

[ TABLE 1 ]

[ TABLE 2 ]

Is industrially available

According to the present invention, it is possible to provide a release film which is suitable for manufacturing a flexible circuit board and can suppress the occurrence of wrinkles while maintaining releasability.