JP5804141B1 - Release film - Google Patents

Abstract

The present invention provides a release film having an improved balance between stable release properties and followability. A release film having a release layer containing a polyester resin on at least one surface, the crystallinity of the release layer being 10% or more and 50% or less. The loss coefficient (tan δ) at 150 ° C. (measuring method: JISK7244 compliant, tensile mode, temperature rising rate 5 ° C./min, frequency 1 Hz) is 0.02 or more and less than 0.12. [Selection figure] None

Description

  The present invention relates to a release film.

  The release film is used, for example, when a flexible printed circuit board is produced by bonding a coverlay film to a flexible film with an exposed circuit via a coverlay adhesive by a hot press. Conventionally, various studies have been made on improving the releasability and followability of such a release film. Examples of techniques that focus on improving the releasability of the release film and techniques that focus on improving followability include the following.

  Patent Document 1 discloses a polyester-based elastomer layer showing specific values for glass transition temperature and crystallization rate index, crystalline aromatic polyester and 1,4-cyclohexanedimethanol copolymerized polyethylene blended at a specific mass ratio. There is disclosed a release film comprising a polyester layer made of polyester which is made of terephthalate and has specific values for glass transition temperature and heat of crystal fusion.

  Patent Document 2 discloses a release film having a crystalline polyester layer showing specific values for the heat of crystal fusion and the crystallization speed index, and a polyester layer showing specific values for the heat of crystal fusion and the crystallization speed index. ing.

  Patent Document 3 discloses a polyester-based elastomer layer having specific values for a glass transition temperature and a crystallization rate index, a specific crystallization start temperature at a temperature rise, a temperature rise crystallization peak temperature, and a temperature rise crystallization heat amount. A release film having a copolyester layer exhibiting a value is disclosed.

JP 2011-88351 A JP 2011-88352 A JP 2011-245812 A

However, in recent years, the technical level required for various properties of a release film has been increasing. The present inventors have found the following problems regarding conventional release films as described in Patent Documents 1 to 3.
In other words, when trying to improve the followability of the release film, the rigidity of the film decreases, and the resin bites into the gap with the circuit, which tends to reduce the release property. The peelability was likely to be unstable depending on the type. On the other hand, it was found that if the mold release property is improved, the rigidity increases and the embedding property in the circuit decreases, the followability decreases, and a large amount of adhesive flows out.

  Then, this invention provides the release film excellent in the balance of the stable release property and followable | trackability.

  As a result of intensive studies in order to achieve the above-mentioned problems, the present inventors combined a scale of crystallinity of the release layer with a scale of loss factor (tan δ) of the release layer at 150 ° C. The present invention has been completed by finding that it is effective as a design guideline for improving the balance between stable releasability and followability.

According to the present invention,
A release film having a release layer containing a polyester resin on at least one surface,
The release layer has a crystallinity of 10% or more and 50% or less,
A release film having a loss factor (tan δ) at 150 ° C. of the release layer (measurement method: conforming to JISK7244, tensile mode, heating rate 5 ° C./min, frequency 1 Hz) of 0.02 or more and less than 0.12. Provided.

  ADVANTAGE OF THE INVENTION According to this invention, the release film excellent in the balance of the stable release property and followable | trackability can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

<Release film>
In the release film of this embodiment, the crystallinity of the release layer is 10% or more and 50% or less, and the loss coefficient (tan δ) of the release layer at 150 ° C. (measurement method: JISK7244 compliant, tensile mode) Temperature rising rate 5 ° C./min, frequency 1 Hz) is 0.02 or more and less than 0.12. Thereby, the balance of the stable release property and followable | trackability of a release film can be improved. The reason for this is not necessarily clear, but by combining the specific range of crystallinity and tan δ of the release layer at the temperature at which the release film is peeled off at 150 ° C. as a specific range, By controlling the interaction between the mold and the release layer to reduce the impact on the peelability due to the object to be pressed and the press conditions, the embedding property (followability) of the release film can be compared with that of conventional release films. While improving, it is thought that the stable peelability can also be improved.

The crystallinity of the release layer is 10% or more, and preferably 18% or more from the viewpoint of obtaining appropriate release properties. On the other hand, from the viewpoint of obtaining good followability, it is 50% or less, preferably 42% or less.
The crystallinity is the ratio of the crystallized portion to the entire release layer when the crystalline resin is partially crystallized. Such crystallinity can be calculated from the peak intensity ratio between the crystal part and the amorphous part obtained by the X-ray diffraction method.

Further, the loss coefficient (tan δ) at 150 ° C. of the release layer (measurement method: conforming to JISK7244, tensile mode, temperature rising rate 5 ° C./min, frequency 1 Hz) (hereinafter sometimes simply referred to as “tan δ”). From the viewpoint of obtaining good followability, it is 0.02 or more, preferably 0.075 or more, and more preferably 0.10 or more. On the other hand, from the viewpoint of obtaining stable releasability, it is less than 0.12, and more preferably 0.118 or less.
In the present embodiment, tan δ is defined as follows. That is, tan δ is based on JISK7244, using a dynamic viscoelasticity measuring apparatus (Seiko Instruments, DMS6100), tensile mode, frequency 1 Hz, heating rate 5 ° C./min, minimum tension / compression ratio 49 mN, tension / Measure storage shear modulus (G ′) and loss shear modulus (G ″) from 25 ° C. to 250 ° C. with a compression force gain of 1.0 and initial force amplitude of 49 mN. It is evaluated by calculating.

  From the viewpoint of the balance between followability and releasability, when the crystallinity of the release layer is 18% or more and 25% or less, tan δ is preferably 0.075 or more and 0.115 or less, preferably 0.1 or more. More preferably, it is 0.112 or less. Further, from the viewpoint of improving the stable releasability, when the crystallinity of the release layer is 30% or more and 45% or less, tan δ is preferably 0.075 or more and 0.118 or less. Further, from the viewpoint of reducing the peel strength, when the crystallinity of the release layer is 34% or more and 42% or less, tan δ is preferably 0.075 or more and 0.11 or less, and 0.08 or more and 0.01 or less. It is preferably 1 or less.

Further, the surface 10-point average roughness (Rz) of the release surface of the release layer is preferably 0.5 μm or more from the viewpoint of obtaining stable release properties while ensuring the strength of the release layer. 1.0 μm or more is more preferable, and 1.2 μm or more is more preferable. On the other hand, from the viewpoint of suppressing the transfer of the surface roughness, the surface 10-point average roughness (Rz) is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less.
The surface 10-point average roughness (Rz) can be measured according to JIS-B0601-1994.
In addition, the surface 10-point average roughness (Rz) is a numerical value of a surface (release surface) corresponding to the object to be pressed of the release layer.

The average interval (Sm) of the unevenness of the release surface of the release layer is preferably 180 μm or more, and more preferably 195 μm or more from the viewpoint of obtaining stable release properties while ensuring the strength of the release layer. On the other hand, from the viewpoint of suppressing the transfer of the surface roughness, it is preferably 450 μm or less, and more preferably 345 μm or less.
The average interval (Sm) of the unevenness can be measured according to JIS-B0601-1994.
In addition, the average space | interval (Sm) of an unevenness | corrugation is a numerical value of the surface (release surface) which hits the target object side to be pressed of a release layer.

The arithmetic mean roughness (Ra) of the release surface of the release layer is preferably 0.08 μm or more, and preferably 0.14 μm or more from the viewpoint of obtaining stable release properties while ensuring the strength of the release layer. Is more preferable. On the other hand, from the viewpoint of suppressing the transfer of the surface roughness, it is preferably 3 μm or less, more preferably 1 μm or less, and even more preferably 0.8 μm or less.
The arithmetic average roughness (Ra) can be measured according to JIS-B0601-1994.
In addition, arithmetic mean roughness (Ra) is a numerical value of the surface (release surface) which corresponds to the object side to be pressed of the release layer.

  Further, the peel strength of the release surface of the release layer is preferably as low as possible, but is preferably less than 30 N / 50 mm, and more preferably 25 N / 50 mm or less. For the peel strength, for example, the adhesive surface of the coverlay is bonded to the release surface, heat pressed at 195 ° C. × 2 minutes × 6 MPa, and a tensile tester (Force gauge AD-4932A-50N manufactured by A & D) is used. Thus, the peel force between the release surface and the CL adhesive can be measured at a speed of about 50 mm / second in the 180 ° direction. The measurement of the peeling force is preferably performed immediately after hot pressing.

  The release layer includes a polyester resin. The polyester resin is not particularly limited. For example, polyalkylene terephthalate resins such as polyethylene terephthalate resin (PET), polybutylene terephthalate resin (PBT), polytrimethylene terephthalate resin (PTT), and polyhexamethylene terephthalate resin (PHT). , And other polyester-based copolymer resins copolymerized with other components. These may be used alone or in combination of two or more. Among these, it is preferable to use polybutylene terephthalate resin from the viewpoint of improving the balance between releasability and followability.

  Examples of the component to be copolymerized in the polyester copolymer resin obtained by copolymerizing other components include known acid components, alcohol components, phenol components, derivatives thereof having ester forming ability, polyalkylene glycol components, and the like.

  Known acid components that can be copolymerized include, for example, divalent or higher valent aromatic carboxylic acids having 8 to 22 carbon atoms, divalent or higher valent aliphatic carboxylic acids having 4 to 12 carbon atoms, and 2 Examples thereof include alicyclic carboxylic acids having a carbon number of 8 to 15 or more and those having an ester forming ability. Specific examples of known acid components that can be copolymerized include, for example, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, bis (p-carbodiphenyl) methaneanthracene dicarboxylic acid, and 4-4′-diphenylcarboxylic acid. 1,2-bis (phenoxy) ethane-4,4′-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, maleic acid, trimesic acid, trimellitic acid, pyro Examples thereof include merit acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and derivatives thereof having an ester forming ability. These can be used alone or in combination of two or more.

  Examples of the alcohol component and / or phenol component that can be copolymerized, and derivatives thereof having ester-forming ability include, for example, a dihydric or higher aliphatic alcohol having 2 to 15 carbon atoms and a divalent or higher carbon number of 6 Examples thereof include ˜20 alicyclic alcohols, bivalent or higher aromatic alcohols having 6 to 40 carbon atoms, and phenols and derivatives thereof having ester forming ability. Specifically, ethylene glycol, propanediol, butanediol, hexanediol, decanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediol, 2,2'-bis (4-hydroxyphenyl) propane, 2,2'- Examples thereof include compounds such as bis (4-hydroxycyclohexyl) propane, hydroquinone, glycerin and pentaerythritol, derivatives thereof having ester forming ability, and cyclic esters such as ε-caprolactone.

  Examples of the polyalkylene glycol component that can be copolymerized include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and random or block copolymers thereof, alkylene glycols of bisphenol compounds (polyethylene glycol, polypropylene glycol, poly And modified polyoxyalkylene glycols such as adducts such as tetramethylene glycol and random or block copolymers thereof.

  Among such polyester copolymer resins, a copolymer of a polyester resin material and a polyalkylene glycol component is preferable, more specifically, a copolymer of a polyester resin and polytetramethylene glycol, more specifically, Specifically, a copolymer of polybutylene terephthalate resin and polytetramethylene glycol is preferable. Thereby, an excellent release film can also be obtained from the viewpoint of plating property.

  The content of other components that can be copolymerized (particularly polytetramethylene glycol) is not particularly limited, but is preferably 5% by weight or more and 50% by weight or less of the entire polyester-based copolymer resin, In particular, it is preferably 10% by weight or more and 40% by weight or less. When content is more than the said lower limit, it is possible to improve the followable | trackability to the target object of the said release film. Moreover, when content is below the said upper limit, mold release property can further be improved.

  In addition to the polyester resin, the release layer includes an antioxidant, a slip agent, an antiblocking agent, an antistatic agent, a coloring agent such as a dye and a pigment, an additive such as a stabilizer, a fluororesin, a silicone rubber, and the like. An impact resistance imparting agent, an inorganic filler such as titanium oxide, calcium carbonate, and talc may be included.

  Although the thickness of a mold release layer is not specifically limited, From a viewpoint of improving the embedding property with respect to a molded article, 5 micrometers or more are preferable, 10 micrometers or more are more preferable, and 20 micrometers or more are further more preferable. On the other hand, from the viewpoint of obtaining an appropriate strength, it is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 30 μm or less.

  The release film in the present embodiment may have a release layer containing a polyester resin on at least one surface, and depending on the application, has a release layer containing a polyester resin on both sides of the release film. It is good. In this case, in at least one of the release layers, the crystallinity of the release layer is 10% or more and 50% or less, and the loss coefficient (tan δ) of the release layer at 150 ° C. (measurement method: JISK7244 compliant, tensile mode) The heating rate is 5 ° C./min and the frequency is 1 Hz) may be 0.02 or more and less than 0.12. Moreover, the release film may further have a cushion layer in contact with the release layer. The release film may have a three-layer structure in which a release layer, a cushion layer, and a release layer are laminated in this order. The plurality of release layers may include a polyester resin, may be formed from the same material, may be formed from different materials, and may have different thicknesses. Good.

  The cushion layer imparts cushioning properties to the entire release film by using a resin having flexibility. Thereby, when using the release film, heat and pressure from the press hot plate are easily transmitted to the adherend, and the adhesion and followability between the release film and the adherend can be improved. .

  The cushion layer is not particularly limited, but is an α-olefin polymer such as polyethylene or polypropylene, an α-olefin copolymer or polyether having ethylene, propylene, butene, pentene, hexene, methylpentene or the like as a polymer component. Engineering plastics resins such as sulfone and polyphenylene sulfide may be used, and these may be used alone or in combination. Of these, α-olefin copolymers are preferred. Specifically, copolymers of α-olefins such as ethylene and (meth) acrylic acid esters, copolymers of ethylene and vinyl acetate, copolymers of ethylene and (meth) acrylic acid, and parts thereof Examples thereof include ionic cross-linked products. Furthermore, from the viewpoint of obtaining a good cushion function, an α-olefin- (meth) acrylic acid ester copolymer such as ethylene alone, or polybutylene terephthalate and 1,4-ciclehexanedimethanol copolymer A mixture of polyethylene terephthalate, an α-olefin polymer, and a mixture of an α-olefin- (meth) acrylic acid ester copolymer such as ethylene are preferable. For example, a mixture of ethylene and an ethylene-methyl methacrylate copolymer, polypropylene A mixture of ethylene and an ethylene-methyl methacrylate copolymer is more preferable.

  The cushion layer may further contain a rubber component. Examples of the rubber component include thermoplastic elastomer materials such as styrene-based thermoplastic elastomers such as styrene-butadiene copolymer and styrene-isoprene copolymer, olefin-based thermoplastic elastomers, amide-based elastomers, and polyester-based elastomers, and natural rubber. And rubber materials such as isoprene rubber, chloroprene rubber and silicon rubber.

  In addition, for the cushion layer, antioxidants, slip agents, antiblocking agents, antistatic agents, coloring agents such as dyes and pigments, additives such as stabilizers, impact resistance imparting agents such as fluororesin and silicon rubber, An inorganic filler such as titanium oxide, calcium carbonate, or talc may be included.

  In addition, as a method of forming a cushion layer, well-known methods, such as an air cooling or a water cooling inflation extrusion method and a T-die extrusion method, are mentioned, for example.

  The thickness of the cushion layer is not particularly limited, but is preferably 30 μm or more and 100 μm or less, more preferably 50 μm or more and 90 μm or less, and further preferably 50 μm or more and 70 μm or less. When the thickness of the cushion layer is equal to or more than the above lower limit value, it is possible to suppress a decrease in cushioning properties of the release film. When the thickness of the cushion layer is equal to or less than the above upper limit value, it is possible to suppress a decrease in releasability.

  Further, the release film may have a configuration of four or more layers such as four layers and five layers having an adhesive layer, a gas barrier layer, and the like. In this case, the adhesive layer and the gas barrier layer are not particularly limited, and known ones can be used.

<Method for producing release film>
The production method of the release film in this embodiment is different from the conventional production method, and it is necessary to highly control the production conditions of the release layer. That is, the crystallinity of the release layer is not less than 10% and not more than 50% for the first time by a production method that highly controls various factors according to at least one of the following conditions (1) and (2). It is possible to obtain a release film having a loss factor (tan δ) at 150 ° C. of the layer (measurement method: JISK7244 compliant, tensile mode, temperature rising rate 5 ° C./min, frequency 1 Hz) of 0.02 or more and less than 0.12. it can.
(1) Selection of resin material for forming release layer (2) Annealing conditions

First, (1) selection of a resin material for forming a release layer will be described.
As the polyester resin forming the release layer, a crystalline polyester resin may be selected. Thereby, although the orientation degree of a mold release layer can be controlled, the mold release layer in this embodiment cannot be implement | achieved only by this. Since a crystalline polyester resin has a polar group such as a carboxyl group, the amount of the polar group such as a carboxyl group is preferably highly controlled. By carrying out like this, when carrying out heat press, it can suppress interacting between the material which forms the target object surface which arrange | positions a release film, and the polar group in resin which forms a release layer.

  In addition, as the polyester resin, a polyester resin obtained by solid phase polymerization instead of the polycondensation reaction may be used. The crystallinity of the polyester resin can be controlled by controlling the reaction conditions such as the type of polymerization catalyst, reaction temperature, and reaction time in solid phase polymerization.

  Moreover, you may control the molecular weight of the monomer used when synthesize | combining a polyester resin. By doing so, the orientation of the crystal component in the polymer can be controlled.

  Moreover, you may control the polymerization degree of a polyester resin. By doing so, the balance between the viscosity and elasticity of the release layer itself can be controlled.

Next, (2) annealing treatment conditions will be described.
In order to obtain the release film in the present embodiment, annealing conditions suitable for the resin material for forming the release layer selected as described in (1) above may be adopted. Specifically, it is important to highly control and combine various factors such as processing temperature, processing time, material of the apparatus used for annealing, and surface temperature of the apparatus used for annealing. For example, hot pressing may be performed at a processing temperature of 190 ° C., a processing time of 5 minutes, and 10 MPa.

  Assuming that at least one of the above conditions (1) and (2) is satisfied, the release film may be a known method such as a co-extrusion method, an extrusion lamination method, a dry lamination method, or an inflation method. it can. In addition, when the release film has a multilayer structure, the release layer and the cushion layer may be manufactured separately and then joined by a laminator or the like, but the air-cooled or water-cooled coextrusion inflation method, coextrusion T It is preferable to form a film by a die method. Especially, the method of forming into a film by coextrusion T die method is more preferable at the point which is excellent in the thickness control of each layer. Further, the release layer and the cushion layer may be joined as they are, or may be joined via an adhesive layer.

<Usage of release film>
The release film is used, for example, in a cover lay press laminating process which is one of the manufacturing processes of a flexible printed wiring board. More specifically, the release film is disposed so as to wrap the coverlay film so that the coverlay film adheres to the concavo-convex portion of the circuit pattern when the coverlay film is adhered to the circuit exposed film. At the same time, it is heated and pressurized by a press device. The press apparatus raises the temperature from room temperature to 170 ° C. in 15 minutes from the start of pressurization, then maintains the temperature for 35 minutes, and then cools from 170 ° C. to room temperature over 50 minutes. The pressing pressure at this time is appropriately adjusted at 5 to 15 MPa.

  As mentioned above, although embodiment of this invention was described, these are illustrations of this invention and various structures other than the above are also employable.

  Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to these.

<Example 1>
Using a polybutylene terephthalate resin (PBT) (manufactured by Changchun Petrochemical Co., Ltd., 1100-211X) shown in Table 1, a 30 μm PBT film was formed by an extrusion T-die method, and the PBT film was 10 MPa at 190 ° C. A pressure annealing was applied for 5 minutes to obtain a release layer made of PBT.
From the release layer, polypropylene (Sumitomo Chemical Co., FH1016), modified polyethylene (ethylene-methyl methacrylate copolymer (Sumitomo Chemical Co., WD106)), acid-modified polyethylene (Mitsubishi Chemical Co., F515A) and the PBT. A cushion layer (compounding ratio: polypropylene: ethylene-methyl methacrylate copolymer: acid-modified polyethylene: PBT = 15: 30: 40: 15) and a second release layer made of the PBT are laminated in this order. And it manufactured by heat-pressing the release film which consists of three layers.
The thickness of each layer of the obtained release film was 30 μm for the release layer and the second release layer, and 60 μm for the cushion layer.

<Example 2>
A release film was obtained in the same manner as in Example 1 except that (1100-211H manufactured by Changchun Petrochemical Co., Ltd.) was used as PBT.

<Example 3>
A release film was obtained in the same manner as in Example 1 except that (1100-211M manufactured by Changchun Petrochemical Co., Ltd.) was used as PBT.

<Example 4>
A release film was obtained in the same manner as in Example 1 except that (1100-211D manufactured by Changchun Petrochemical Co., Ltd.) was used as PBT.

<Example 5>
A release film was obtained in the same manner as in Example 1 except that the same PBT as in Example 4 was used and the annealing treatment was not treated.

<Example 6>
A PBT (Mitsubishi Engineering Plastics, 5020) was used as a PBT, and instead of annealing, the entire surface on the release film side of the release film was subjected to friction treatment with wool so that the work energy was 300 KJ. A release film was obtained in the same manner as in Example 1 except that the layer was used.

<Comparative Example 1>
A release film was obtained in the same manner as in Example 1 except that (BT1 manufactured by Toray Industries, Inc., 1201K) was used and the annealing treatment was not treated.

<Comparative Example 2>
As a PBT, a release film was prepared in the same manner as in Example 1 except that 1% by mass of a crystal nucleus material was added to (Toray Industries, Inc., 1201K) and annealed in an oven at 180 ° C. and atmospheric pressure for 1 hour. Obtained.

The following evaluation was performed using the release film obtained by the Example and the comparative example. The results are shown in Table 1.
<Evaluation>
-Crystallinity The crystallinity of the release layer (PBT) was calculated from the peak intensity ratio of the crystal part and the amorphous part obtained by the X-ray diffraction method.

-Loss factor (tan δ) of the release layer at 150 ° C
Based on JISK7244, using a dynamic viscoelasticity measuring device (DMS6100, manufactured by Seiko Instruments Inc.), tension mode, frequency 1 Hz, heating rate 5 ° C./min, minimum tension / compression ratio 49 mN, tension / compression force gain Evaluated by measuring G ″ / G ′ by measuring storage shear modulus (G ′) and loss shear modulus (G ″) from 25 ° C. to 250 ° C. with an initial force amplitude of 49 mN. did.

・ Peel strength (Releasability)
The adhesive surface of CL (CMA type) manufactured by Arisawa Manufacturing Co., Ltd. was bonded to the release surface of the release film, and heat-pressed at 195 ° C. × 2 minutes × 6 MPa, and a tensile tester (Force gauge AD− manufactured by A & D Corporation) was used. 4932A-50N) was used to measure the peel force between the release surface and the CL adhesive at a speed of about 50 mm / sec in the 180 ° direction. The measurement was performed immediately after hot pressing.

・ Followability The adhesive surface of CL (CMA type) manufactured by Arisawa Manufacturing Co., Ltd. was bonded to the release surface of the release film, and after heat-pressing at 195 ° C. × 2 minutes × 6 MPa, the release film was peeled off, The CL surface was measured in accordance with the “7.5.7.2 Wrinkle” of the JPCA standard.
○: Wrinkle occurrence rate less than 1.0% △: Wrinkle occurrence rate 1.0% or more and less than 2.0% ×: Wrinkle occurrence rate 2.0% or more

・ Surface roughness (Ra, Rz, Sm)
The surface of the release surface of the release film was measured for the center n = 3 using “Handy Surf E-35B manufactured by Tokyo Seimitsu Co., Ltd.” according to JIS B0601 (1994).

Claims (6)

A release film having a release layer containing a polyester resin on at least one surface,
The release layer has a crystallinity of 10% or more and 50% or less,
A release film having a loss factor (tan δ) at 150 ° C. (measurement method: conforming to JISK7244, tensile mode, heating rate 5 ° C./min, frequency 1 Hz) of the release layer of 0.02 or more and less than 0.12. The release film according to claim 1,
A release film in which the polyester resin contains a polybutylene terephthalate resin. The release film according to claim 1 or 2,
The mold release film whose average space | interval (Sm) of the unevenness | corrugation of the mold release surface of the said mold release layer is 180 micrometers or more. In the release film as described in any one of Claims 1 thru | or 3,
A release film having a 10-point average roughness (Rz) of a release surface of the release layer of 0.5 μm or more. In the release film as described in any one of Claims 1 thru | or 4,
A release film having a three-layer structure in which the release layer, the cushion layer, and the second release layer are laminated in this order. In the release film as described in any one of Claims 1 thru | or 5,
A release film used by superposing the release surface side of the release layer on the surface of a coverlay film.