JP2014233846A - Mold release film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold release film which is highly excellent in fabricability and inspectability since the mold release film neither increases the peel force even after heated nor develops process failure such as hooking when used as the mold release film which, for example, has necessity of going through a heating step and is used for a tacky adhesive.SOLUTION: The mold release film is obtained by forming a silicone mold release layer on at least one surface of a polyester film. Onium salt is incorporated in the silicone mold release layer. A change quantity of an orientation angle in the film plane is set equal to or smaller than 8 degrees/500 mm.

Description

  The present invention relates to a release film that does not undergo heavy peeling even when subjected to a heating step when using a release film, does not cause process defects such as catching, maintains good peelability, and has good inspectability. is there.

  In recent years, there has been a significant demand for thin-film optical products, and it is necessary to produce products efficiently and stably, and it is extremely important to reduce the possibility of problems occurring in the process.

  In these products, for example, liquid crystal displays, a process of “bonding” is always performed. At this time, the use of an adhesive is indispensable, and a release film is generally used at that time.

  An adhesive is applied on the release film, and is adhered to, for example, a polarizing plate. In the subsequent step, the release film is peeled off when the substrate is further stuck on the polarizing plate. At the time of applying the adhesive, the solvent-based adhesive undergoes a heating process in order to evaporate the solvent and dry it.

  When the release film is generally heated, the release force increases. For this reason, the peel force when heated is important, but a problem arises because the amount of increase in peel force differs depending on various conditions such as heating temperature and time. When a force greater than that assumed at the time of peeling is required, problems such as a decrease in yield occur.

  Furthermore, it may be bonded to these separators to carry out an inspection with optical evaluation. In that case, when an inspection is performed through an optical member having a polarizing action, the inspection visual field may become dark depending on the angle.

  It is known that a separator in which the orientation angle is controlled is advantageous in such polarization inspection.

  A release film in which such an orientation angle is controlled has a disadvantage that the heat shrinkage rate is large, and it is required to reduce the amount of heat to the film as much as possible before use by a customer.

JP 2003-220666 A JP-A-58-213024 Japanese Patent Laid-Open No. 9-12650 Japanese Patent Laid-Open No. 3-115367 JP 2012-255750 A

  The present invention has been made in view of the above circumstances, and the solution to the problem is that the release force after heating does not increase as a release film for an adhesive that undergoes a heating step, and is excellent in workability and inspectability. A release film is provided.

  As a result of intensive investigations in view of the above-mentioned actual situation, the present inventor has found that the above-mentioned problems can be easily solved by a release film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is that the polyester film has a silicone release layer on at least one side, the release layer contains an onium salt, and the change amount of the orientation angle in the film plane is 8 degrees / 500 mm or less. It exists in the release film characterized by.

  Since the present invention does not increase the peel force even when the release film is heated, it is a release film that does not get caught, has excellent workability, and has good inspection properties. Target value is high.

  In the present invention, the polyester film may have a single layer structure or a laminated structure. For example, in addition to the two-layer or three-layer structure, the polyester film may have four or more layers as long as the gist of the present invention is not exceeded. There may be, and it is not specifically limited.

  The polyester used for the polyester film in the present invention may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyester includes polyethylene terephthalate (PET) and the like. On the other hand, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (eg, P-oxybenzoic acid). 1 type or 2 types or more are mentioned, As a glycol component, 1 type or 2 types or more, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4- cyclohexane dimethanol, neopentyl glycol, is mentioned. In any case, the polyester referred to in the present invention refers to a polyester that is usually 60 mol% or more, preferably 80 mol% or more of polyethylene terephthalate or the like which is an ethylene terephthalate unit.

  In the present invention, it is preferable to blend particles in the polyester layer mainly for the purpose of imparting slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, it is possible to use precipitated particles in which a part of a metal compound such as a catalyst is precipitated and finely dispersed during the polyester production process.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.01-1 micrometer. When the average particle diameter is less than 0.01 μm, the particles are likely to aggregate and dispersibility may be insufficient. On the other hand, when the average particle diameter exceeds 3 μm, the surface roughness of the film becomes too rough and Problems occur when a release layer is applied in the process.

  Furthermore, the particle content in the polyester layer is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% by weight, the slipperiness of the film is insufficient. On the other hand, when the content exceeds 5% by weight, the transparency of the film is insufficient.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film in the present invention as necessary.

  The thickness of the polyester film constituting the release film of the present invention is not particularly limited as long as it can be formed as a film.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.

  First, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, the extending | stretching temperature orthogonal to the extending | stretching direction of the 1st step is 70-170 degreeC normally, and a draw ratio is 3.0 to 7 times normally, Preferably it is 3.5 to 6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  The simultaneous biaxial stretching method can also be adopted for the production of the polyester film in the present invention. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is as follows: The area magnification is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be employed.

  Furthermore, a so-called coating stretching method (in-line coating) in which the film surface is treated during the above-described polyester film stretching step can be applied. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with stretching and the thickness of the coating layer can be reduced according to the stretching ratio, producing a film suitable as a polyester film. it can.

  In the polyester film constituting the release film in the present invention, the width of change in the orientation angle in the film plane is 8 degrees / 500 mm or less, preferably 5 degrees / 500 mm or less. When the amount of change in the orientation angle exceeds 8 degrees / 500 mm, the transmitted light intensity varies depending on the position of the polarizing plate during the polarizing plate inspection, which becomes an obstacle to the polarizing plate inspection. The amount of change in the orientation angle is the maximum difference among a plurality of orientation angle differences measured at a certain point and 500 mm away from the point in the width direction of the sample film.

  The curable silicone layer constituting the release layer in the present invention must contain an onium salt, and any curing reaction type can be used as long as the curing method is not thermosetting such as ultraviolet curing. .

  In the present invention, the curing conditions for forming the release layer on the polyester film are not particularly limited, and when providing the release layer by off-line coating, usually at 80 to 200 ° C. for 3 to 40 seconds, The heat treatment is preferably performed at 80 to 150 ° C. for 3 to 40 seconds as a guide. Moreover, combined use with heat processing and ultraviolet irradiation is essential. When solventless silicone is used, the heat treatment step may be omitted and only ultraviolet irradiation may be used.

The coating amount (after drying) of the release layer is usually from 0.005 to 1 g / m ² , preferably from 0.005 to 0.5 g / m ² , more preferably from 0.01 to 5 in terms of coatability. The range is 0.2 g / m ² . When the coating amount (after drying) is less than 0.005 g / m ² , the coating property is lacking in stability and it becomes difficult to obtain a uniform coating film. On the other hand, when the coating is thicker than 1 g / m ² , the adhesiveness and curability of the release layer itself are lowered, resulting in an increase in cost.

  In the present invention, conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating and the like can be used as a method for providing a release layer on the polyester film. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  Further, the polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  Onium salt is a general term for salt compounds that are protonated by hydrogenation, and there is no limitation as long as they are. Specific examples include ammonium salts, phosphonium salts, sulfonium salts, fluoronium salts, chloronium salts, bromonium salts, iodonium salts and the like. Particularly preferred onium salts in the present invention are onium salts containing halogen atoms.

  These onium salts release an acid when applied with energy from the outside and become an initiator for curing silicone. For example, silicone having an epoxy group undergoes ring opening upon proton addition from these strong acids, and the addition reaction proceeds.

  As a means for achieving the peeling characteristics in the present invention, an onium salt in the release layer is appropriately selected and the content is appropriately changed. The amount of onium salt in the release layer is not particularly limited, but is preferably in the range of 5% to 0.5%, more preferably in the range of 3% to 1% in terms of the weight fraction after drying. is there. If it is less than 0.5%, sufficient curing does not proceed, and if it exceeds 5%, the acid concentration increases, resulting in danger during production.

  The coating solution used in the present invention may contain adhesion improvers, light release additives, heavy release agents, antistatic agents, dyes, pigments and the like. These additives may be used alone or in combination of two or more as necessary.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measuring method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Measurement of average particle diameter (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(3) Measurement of glass transition temperature (Tg) of polyester resin Using a DSC-II type measuring device manufactured by PerkinElmer, the sample was heated at a heating rate of 10 ° C./min under a nitrogen gas stream at a rate of 10 ° C./min. The segregation start temperature was defined as Tg.

(4) Measurement of UV irradiation intensity Using UIT-201 manufactured by USHIO, the UV (UV) integrated light intensity was measured through an ultraviolet irradiation device.

(5) Measurement of change amount of orientation angle in film plane of polyester film constituting release film 50 from the center position in the width direction of the sample film toward both ends in the width direction.
The position at every 0 mm and the samples at both ends were cut out, and the amount of change in the orientation angle every 500 mm in the film width direction was determined using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Instruments. When calculating the change amount of the orientation angle including the positions at the extreme ends, if the distance between the sample positions is less than 500 mm, the change amount of the orientation angle every 500 mm is calculated by proportional calculation. Subsequently, a 3 m length was cut out in the longitudinal direction of the film, and a sample was cut out from a total of 7 positions every 500 mm (including both ends) in the longitudinal direction from the center in the film width direction, and the orientation angle was determined. Thus, the change amount of the orientation angle every 500 mm in the width direction and the longitudinal direction was obtained, and the maximum change amount was set as the change amount of the orientation angle of the film. Further, in the measurement, it is important to make the reference axis of the orientation angle the same in all samples, and the reference axis can be arbitrarily determined.
<Criteria>
○: 8 degrees / 500 mm or less ×: 8 degrees / 500 mm or more

(6) Measurement of normal release force (NF) of release film Affixed with one side of double-sided adhesive tape (Nitto Denko “No. 502”) on the surface of the release layer of the sample film, then cut into a size of 50 mm × 300 mm Then, the peel strength after standing at room temperature for 1 hour is measured. For the peeling force, a tensile tester (“Intesco model 2001 type” manufactured by Intesco Co., Ltd.) was used, and 180 ° peeling was performed under a tensile speed of 300 mm / min.

(7) Heat peeling force (HF) measurement After attaching one side of a double-sided pressure-sensitive adhesive tape (Nitto Denko “No. 502”) to the surface of the release layer of the sample film, it was cut into a size of 50 mm × 300 mm, and 100 degrees The peel force after being left in the oven for 1 hour is measured. For the peeling force, a tensile tester (“Intesco model 2001 type” manufactured by Intesco Co., Ltd.) was used, and 180 ° peeling was performed under a tensile speed of 300 mm / min.
<Criteria>
○: When NF / HF ≧ 1 ×: When NF / HF <1

(8) Residual Adhesion Rate Measurement Adhesive tape “No. 31B” (manufactured by Nitto Denko Co., Ltd.) is reciprocated once with a 2 kg rubber roller on the surface of the release layer, and heat treated at 100 ° C. for 1 hour. Next, the pressure-released release film is peeled off, and the adhesive strength F is measured according to the method of JIS-C-2107 (adhesive strength to stainless steel plate, 180 ° peeling method) using an adhesive tape “No. 31B”. . The percentage of F with respect to the adhesive force F0 when the adhesive tape “No. 31B” was directly adhered to and peeled from the stainless steel plate was defined as the residual adhesion rate.
<Criteria>
○: 90% or more △: 70% to 90% ×: 70% or less

(9) Coating film adhesion promotion evaluation of release film (practical property substitution evaluation)
The sample film was left in a constant temperature and humidity chamber at 60 ° C. and 80% RH for 4 weeks, and then the sample film was taken out. Thereafter, the release surface of the sample film was rubbed with a tentacle five times, and the degree of release of the release layer was determined according to the following criteria.
<Criteria>
○: The coating film is not removed △: The coating film is white but not removed ×: The coating film is confirmed to be removed

(10) Foreign matter recognition A sample film is closely attached to a polarizing film through a known acrylic pressure-sensitive adhesive so that the width direction of the sample film is parallel to the alignment axis of the polarizing film, thereby creating a polarizing plate with a release film. did. Here, when producing the polarizing plate, black metal powder (foreign matter) having a size of 50 μm or more was mixed between the pressure-sensitive adhesive and the polarizing film so as to be 50 particles / m 2. A polarizing plate for inspection is superimposed on the polarizing plate release film mixed with the foreign matter thus obtained so that the orientation axis is orthogonal to the width direction of the release film, and white light is irradiated from the polarizing plate side. Ten inspectors visually observed from the polarizing plate for inspection, and evaluated whether the foreign matter mixed between the adhesive and the polarizing film could be found by the following classification. In the measurement, the film was evaluated using a total of three films at the center and both ends of the obtained film, and the result of the point where the visual inspection property was the best was obtained. It was cognitive.
<Criteria>
○: Good foreign body recognition ×: Poor foreign body recognition

(11) Continuous peelability An acrylic pressure-sensitive adhesive having the following composition is applied to a sample, heat-dried, and bonded to a polarizing plate. Each sample is heated for 1 minute and the temperature is increased by 5 degrees from 60 degrees to 100 degrees, and all sample films are continuously peeled off. It was judged whether continuous peeling was possible.
<Acrylic adhesive composition>
(Monomer composition)
2-ethylhexyl acrylate 70% by weight
2-methoxyethyl acrylate 29% by weight
4-hydroxybutyl acrylate 1% by weight
0.1 part of Nippon Polyurethane Coronate L was added to 100 parts by weight of the monomer composition to obtain an acrylic pressure-sensitive adhesive layer forming composition.
<Criteria>
○: Continuous peeling is possible with all sample films ×: Continuous peeling is not possible due to the occurrence of catching on some films

(12) Appearance (practical property substitution evaluation)
A sample film with a width of 1000 mm is irradiated with light of halogen light on the surface of the release layer on which the coating layer is provided, about 10 m in the longitudinal direction, and the release layer is visually observed to appear uneven due to the coating layer. The appearance was judged according to the judgment criteria.
<Criteria>
○: A pattern that looks uneven is not confirmed and is good △: A pattern that appears uneven is slightly confirmed ×: A pattern that appears uneven is clearly confirmed and is not good In the above, it is long Although unevenness has been confirmed with respect to the sample, it is possible to determine whether the unevenness is good or not by a method similar to the above even for a film of about A4 size.

(13) Comprehensive evaluation (practical property substitution evaluation)
Using the release films produced in the Examples and Comparative Examples, the evaluation criteria for the orientation angle, the peelability upon heating, the residual adhesion rate, the adhesion, the continuous peelability, and the coating appearance are comprehensively evaluated according to the following criteria. Went.
<Criteria>
○: practically no problem level, orientation angle, peelability upon heating, residual adhesion rate, adhesion, continuous peelability, and coating appearance are all over Δ ×: practically problematic level, At least one of orientation angle, peelability during heating, residual adhesion rate, adhesion, continuous peelability, and coating appearance is x

The polyester used in the examples and comparative examples was prepared as follows.
<Manufacture of polyester>
Production Example 1 (Polyethylene terephthalate A)
100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate are placed in a reactor, the temperature is raised by heating, methanol is distilled off, transesterification is performed, and 4 hours are required from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, after adding 0.04 part of ethylene glycol slurry ethyl acid phosphate and 0.03 part of antimony trioxide, the temperature reached 280 ° C. and the pressure reached 15 mmHg in 100 minutes. It was 0.3 mmHg.
After 4 hours, the system was returned to atmospheric pressure to obtain polyethylene terephthalate A1 having an intrinsic viscosity of 0.61.

Production Example 2 (Polyethylene terephthalate B)
In Production Example 1, production was carried out in the same manner as in Production Example 1 except that 0.6 part of silica particles having an average particle diameter of 2.5 μm was added, and polyethylene terephthalate B having an intrinsic viscosity of 0.62 was obtained.

Production Example 3 (Production of polyester film F1)
Polyester A was used as a raw material for the intermediate layer, and a mixed raw material of polyester A and polyester B at a ratio of 9: 1 was used as a raw material for the surface layer, and each was supplied to two extruders and melted at 290 ° C., respectively. Then, it coextruded by the layer structure of 2 types 3 layers (surface layer / intermediate layer / surface layer) on the cooling roll set to 40 degreeC, it was made to cool and solidify, and the unstretched sheet was obtained. Next, the film was stretched 2.8 times in the machine direction at a film temperature of 85 ° C. using the roll peripheral speed difference, then led to a tenter, stretched 5.4 times at 120 ° C. in the transverse direction, and heat-treated at 200 ° C. Thereafter, the film was relaxed by 3% in the lateral direction to obtain a transparent polyester film having a thickness of 38 μm (surface layer: 1.9 μm, intermediate layer: 34.2 μm).

Production Example 4 (Production of polyester film F2)
Polyester A was used as a raw material for the intermediate layer, and a mixed raw material of polyester A and polyester B at a ratio of 9: 1 was used as a raw material for the surface layer, and each was supplied to two extruders and melted at 290 ° C., respectively. Then, it coextruded by the layer structure of 2 types 3 layers (surface layer / intermediate layer / surface layer) on the cooling roll set to 40 degreeC, it was made to cool and solidify, and the unstretched sheet was obtained. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85 ° C. using the roll peripheral speed difference, then led to a tenter, stretched 4.0 times at 120 ° C. in the transverse direction, and heat-treated at 230 ° C. Thereafter, the film was relaxed by 4.3% in the lateral direction to obtain a transparent polyester film having a thickness of 38 μm (surface layer: 1.9 μm, intermediate layer: 34.2 μm).

  The release agent (a) used is as shown in Table 2 below.

  The used curing agents / additives (b) are shown in Table 2 below.

  The used adhesion improving agent (c) is as shown in Table 3 below.

Example 1:
<Manufacture of release film>
The following release layer composition (A) was applied off-line by a reverse gravure coating method on a coating layer of a polyester film F1 having a thickness of 38 μm so that the coating amount (after drying) was 0.1 g / m ² . Thereafter, heat treatment was performed at 120 ° C. for 30 seconds, and then irradiation was performed at 200 mJ / cm ² with a high-pressure mercury lamp irradiation apparatus (EUV482A: manufactured by Celitec).

Release layer composition A
UV curable silicone resin (a1) 100 parts Onium salt type curing agent (b1) 1 part MEK / toluene mixed solvent (mixing ratio is 1: 1) 1500 parts

  From the above, the properties of the obtained release film are shown in Table 1.

Examples 2-5 and Comparative Examples 1-4:
A release film was obtained in the same manner as in Example 1 except that the release layer composition was changed as shown in Table 4 below. The characteristics of the release films obtained in the above examples and comparative examples are shown in Table 5 below.

Comparative Examples 5-8:
In Example 1, the release layer composition was changed as shown in Table 1 below, the heat treatment time was set to 150 ° C. for 30 seconds, and production was performed in the same manner as in Example 1 except for the presence or absence of irradiation with a high-pressure mercury lamp. A film was obtained. Table 5 shows the properties of the release films obtained in the comparative examples.

Comparative Example 9:
In Example 1, it manufactured like Example 1 except changing a film type into F2, and the release film was obtained.
Table 5 shows the properties of the release films obtained in the comparative examples.

  About the peeling force of the comparative examples 7 and 8, when a 5N load cell was used, since the peeling force exceeding a measurement limit value was required, it could not be measured.

  The release film of the present invention provides a release film that does not increase the peel strength after heating and is excellent in workability and inspectability.

Claims (2)

A release film comprising a polyester release layer on at least one side of a polyester film, the release layer containing an onium salt, and the amount of change in orientation angle in the film plane is 8 degrees / 500 mm or less. The release film according to claim 1, wherein the release force of the release layer is 1.0 or more in the following formula.
Normal peel force ÷ heat peel force ≧ 1.0