JP2005059276A - Mold release film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold release film which overcomes various points at issue caused by an oligomer formed at heating. <P>SOLUTION: The mold release film is constituted by laminating a mold release layer at least on one side of a biaxially oriented polyester film comprising a polyester based on 1,4-cyclohexanedicarboxylic acid and 1,4-cyclohexanedimethanol being repeating units and having a melting point of 200°C or above and characterized in that the change quantity of a film haze value after heating at 150°C for one hour is 1% or below. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a release film, and more particularly to a release film suitable for protecting a pressure-sensitive adhesive layer of an optical component such as a polarizing plate or a retardation plate used in a liquid crystal display.

  A polarizing plate and a retardation plate used in a liquid crystal display (hereinafter sometimes abbreviated as LCD) are provided with an adhesive layer on one side, and a release film is used to protect the adhesive layer. Yes. Conventionally, a biaxially oriented polyethylene terephthalate film (hereinafter sometimes abbreviated as a PET film) has been frequently used as the base film of the release film. (For example, see Patent Documents 1 to 3). The reason is considered that the PET film is excellent in the balance between properties such as mechanical strength, heat resistance, chemical resistance, weather resistance, transparency, and electrical insulation and cost.

  However, a low polymerization degree compound (oligomer) called a cyclic trimer is always present in a PET film, and when heated, this cyclic trimer bleeds out and becomes a white powder on the film surface. It is known to appear.

  Further, according to the knowledge of the present inventors, most of the cyclic trimers bleed out from the PET film pass through the release layer laminated on the surface and often reach the release layer surface. is there. In this case, the cyclic trimer is transferred to the pressure-sensitive adhesive layer to which the release layer is bonded, and remains in the pressure-sensitive adhesive layer of the polarizing plate even after the release film is peeled off. For example, when an LCD is produced by pasting this onto a glass substrate, in the worst case, defects in appearance such as a decrease in luminance of the obtained LCD and occurrence of white spots are caused.

  In order to solve the above problem, a method of reducing the amount of oligomer by adding a heat treatment to a PET resin in advance at a temperature of, for example, 200 ° C. for several hours (see, for example, Patent Document 4), a coating containing polyvinyl alcohol on the PET film surface A method of providing a layer (for example, see Patent Document 5) has been proposed.

However, the heat treatment method requires a large energy cost to reduce oligomers, and the method of providing a coating layer containing polyvinyl alcohol is affected by humidity because the coating layer containing polyvinyl alcohol has high water absorption. There is a drawback that the characteristics of the coating film are easily changed.
JP 2002-36476 A JP 2002-40250 A Japanese Patent No. 3320904 JP 2000-108252 A JP 2001-71420 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a release film that overcomes various problems caused by oligomers generated during heating.

  As a result of intensive studies, the present inventor has used a biaxially oriented film made of an aliphatic polyester having a specific composition and physical properties as a release film substrate, and is used for a polarizing plate and a retardation plate. Even when used as a release film for protecting the adhesive layer, the present inventors have found that the occurrence of defects in appearance due to oligomers is extremely reduced, and the present invention has been completed.

  That is, the gist of the present invention is a biaxially oriented polyester film comprising, as repeating units, a polyester having 1,4-cyclohexanedicarboxylic acid and 1,4-cyclohexanedimethanol as main components and a melting point of 200 ° C. or higher. A release layer is laminated on at least one surface, and the change in film haze value after heating at 150 ° C. for 1 hour is 1% or less.

  Hereinafter, the present invention will be described in detail. The biaxially oriented polyester film used for the substrate of the release film of the present invention is not an unstretched film or a film stretched only in a uniaxial direction, but is biaxially stretched sequentially or simultaneously in the longitudinal direction and the width direction, and thereafter It is necessary that the biaxially oriented polyester film is heat-set.

  Moreover, the polyester composition which comprises said biaxially-oriented polyester film needs to be a polycondensate which has as a main component 1, 4- cyclohexane dicarboxylic acid and 1, 4- cyclohexane dimethanol as a repeating unit. is there. The main component as used herein means that the proportion of 1,4-cyclohexanedicarboxylic acid in the dicarboxylic acid component is usually 95 mol% or more, preferably 98 mol% or more, and that of 1,4-cyclohexanedimethanol in the diol component It means that the ratio is usually 95 mol% or more, preferably 98 mol% or more.

  The proportion of trans isomer in 1,4-cyclohexanedicarboxylic acid is usually 80 mol% or more, preferably 85 mol% or more, and the proportion of trans isomer in 1,4-cyclohexanedimethanol is usually 60 mol%. % Or more, preferably 65 mol% or more.

  When the composition ratio of the dicarboxylic acid component and the diol component does not satisfy the above range, the resulting polyester has a low melting point, and often does not satisfy the following range defined in the present invention.

  Examples of other dicarboxylic acid components that can be used within the range of the composition ratio of the dicarboxylic acid component and the diol component include cis 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,2-cyclohexane. Aliphatic dicarboxylic acids such as dicarboxylic acid, oxalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, and the like. Other diol components include cis 1,4-cyclohexanedimethanol, 1, Examples include aliphatic diols such as 3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, ethylene glycol, propylene glycol, butanediol, neopentyl glycol, pentanediol, and hexanediol.

  The polyester used in the present invention needs to have a melting point of 200 ° C. or higher, a preferable melting point is 210 ° C. or higher, and its upper limit is usually 245 ° C. When the melting point is less than 200 ° C., the heat resistance of the polyester is insufficient, and the heat setting temperature after biaxial stretching cannot be set high, resulting in an increase in the shrinkage rate of the biaxially oriented film. Therefore, it is not preferable.

  Regarding the degree of polymerization of the polyester, the intrinsic viscosity measured at 30 ° C. with a mixed solvent of phenol-tetrachloroethane (weight ratio 1: 1) is usually 0.55 dl / g or more, preferably 0.65 dl / g or more. is there. By satisfying such conditions, the continuity during film formation and the mechanical strength of the formed film are enhanced. The upper limit of the intrinsic viscosity is usually 1.5 dl / g.

  To the polyester used in the present invention, fine particles that are substantially inert to the polyester can be added in order to impart slipperiness to the film. It is preferable to select fine particles that do not deteriorate the transparency of the polyester film as much as possible.

  Specific examples of the fine particles include particles made of an organic polymer such as a crosslinked polystyrene resin, a crosslinked acrylic resin, and a crosslinked polyester resin, and inorganic particles such as silica, talc, calcium carbonate, and calcium phosphate. In these, the amorphous silica which is the aggregate of primary particles is suitable as a particle which can also have transparency while maintaining the slipperiness of the film. These fine particles may be used alone or in combination of two or more.

  The average particle diameter of the fine particles is usually 0.05 to 4 μm, preferably 0.1 to 3 μm. The amount added to the film is usually 0.005 to 1% by weight, preferably 0.01 to 0.5% by weight. In addition, a predetermined amount of fine particles may be added to the aliphatic polyester from the beginning, or a predetermined amount of particles is prepared by preparing a high-concentration masterbatch and adding and diluting the polyester not containing fine particles. May be used.

  In the present invention, the biaxially oriented polyester film may have a single layer structure in the thickness direction, but may be a coextruded film in which at least two layers, preferably three or more layers are laminated at the time of melt extrusion. In particular, when the laminated structure is 3 layers or more, it has surface layers on both surfaces, and has an intermediate layer between them, but it is possible to add the aforementioned fine particles only to the surface layer and not add fine particles to the intermediate layer, It is preferable in terms of improving slipperiness without deteriorating transparency. However, all the polyesters of each layer constituting these laminated films must satisfy the melting point range described above.

  In addition, a known additive can be added to the biaxially oriented polyester film for a release film of the present invention without departing from the spirit of the invention. Specific examples of the additive include an antioxidant, a heat stabilizer, an antistatic agent, a lubricant, a flame retardant, and the like. Can be used.

  The release film of the present invention needs to have a release layer on at least one side thereof. This release layer needs to contain a component having releasability such as silicone resin, fluororesin, various waxes, aliphatic polyolefins, etc. Among them, a release layer containing silicone resin is generally a release agent. It is preferable because of its excellent properties. When, for example, a silicone resin is used as the release layer of the present invention, the release layer is formed by, for example, applying a coating liquid containing a curable silicone resin to at least one side of a biaxially oriented polyester film, and drying and curing. Can be formed.

  As the curable silicone resin, any reactive type such as addition reactive silicone, condensation reactive silicone, ultraviolet ray or electron beam curable silicone can be used.

  As the addition-reactive silicone resin, for example, a polydimethylsiloxane having a vinyl group introduced at the terminal and a hydrogen silane having a -H group at the terminal are reacted using a platinum catalyst to form a three-dimensional crosslinked structure. Can be mentioned.

  As the condensation-reactive silicone resin, for example, polydimethylsiloxanes having —OH groups at the ends, or polydimethylsiloxanes having —OH groups at the ends and hydrogensilanes having —H groups at the ends are used as organotin catalysts. And a condensation reaction to form a three-dimensional crosslinked structure.

  Examples of UV curable silicone resins include those that use the same radical reaction as ordinary silicone rubber crosslinks as the most basic types, those that introduce photopolymerization by introducing unsaturated groups, and those that decompose onium salts with UV light. Examples include those that generate a strong acid and then cleave the epoxy group to crosslink, and those that crosslink by the addition reaction of thiol to vinylsiloxane. Further, an electron beam can be used instead of the ultraviolet rays. An electron beam has stronger energy than ultraviolet rays, and can perform a crosslinking reaction with radicals without using an initiator as in the case of ultraviolet curing.

  In the present invention, as a method of coating the release layer on at least one surface of the biaxially oriented polyester film, a coating solution containing an addition-reactive, condensation-reactive, ultraviolet or electron beam curable silicone resin as a resin component is applied. In addition, a method of heat drying, heat curing, or ultraviolet (or electron beam) curing is preferable. As a coating method, any known coating method can be applied, for example, a roll coating method such as a gravure coating method or a reverse coating method, a bar coating method such as a Mayer bar, a spray coating method, an air knife coating method, or the like. Can be used.

  The coating solution can be dried and cured at the same time. The conditions are preferably a drying temperature of 100 ° C. or higher and a drying time of 30 seconds or longer. When the drying temperature is less than 100 ° C and the drying time is less than 30 seconds, the silicone resin is not completely cured, causing heavy release (insufficient release force) and back transfer (back-off) of the silicone resin layer This is not preferable.

The thickness of the release layer, as a coating amount after drying of cured silicone resin layer, usually 0.01-5 g / m ^2, preferably from 0.05 to 1 g / m ^2. When the coating amount of the silicone resin layer after drying is less than 0.01 g / m ² , the mold release performance tends to decrease, and when it exceeds 5 g / m ² , the adhesion of the release layer itself to the film, curability, etc. May decrease.

  In the present invention, the residual adhesion rate indicating the degree of cure of the release layer is usually 90% in order to suppress the transfer or transfer of silicone to the surface of the pressure-sensitive adhesive layer to be bonded or the transport roll in the production process. Above, preferably 95% or more.

  The amount of change in the film haze value when the release film according to the present invention is heat-treated at 150 ° C. for 1 hour is 1% or less, preferably 0.5% or less, more preferably 0.2% or less. is necessary. When the amount of change in the film haze value exceeds 1%, more oligomers bleed out on the surface of the release layer of the release film. For example, the release film is attached to the pressure-sensitive adhesive layer of a polarizing plate or a retardation plate. When they are combined, the bleed-out oligomer is transferred to the pressure-sensitive adhesive layer and adheres to the polarizing plate and the retardation plate, which causes a decrease in the transparency of the pressure-sensitive adhesive layer and white spot-like defects. This is not preferable.

  The haze value including the release layer of the release film of the present invention is usually 8% or less, preferably 4% or less, more preferably 2% or less. In this case, the lower limit of the film haze value is usually 0.2%. The total light transmittance of the release film of the present invention is usually 80% or more, preferably 85% or more.

  The heat shrinkage rate in the longitudinal direction and the width direction at 130 ° C. of the release film of the present invention is usually 5% or less, preferably 4% or less, more preferably 3% or less. When the thermal shrinkage rate exceeds 5%, there are the following problems. That is, when a member such as a polarizing plate or a retardation plate bonded via an adhesive layer is subjected to, for example, hard coat processing, the release film becomes significantly contracted by heat applied thereto, causing curling, distortion, Problems such as wrinkles and peeling with the pressure-sensitive adhesive layer are caused.

  Although the thickness of the release film which concerns on this invention is not specifically limited, Usually, 10-100 micrometers, Preferably it is 20-50 micrometers.

  Next, the manufacturing method of the biaxially-oriented polyester film used as the base material of the release film of this invention is demonstrated concretely.

  First, the above-mentioned aliphatic polyester raw material is melt-extruded by an extruder and formed into a sheet, and cooled and solidified by a cooling roll to obtain an unstretched sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and it is preferable to employ an electrostatic application adhesion method and / or a liquid application adhesion method. In the melt line of the extruder, a filter can be installed for the purpose of removing foreign substances and coarse aggregated particles, and a gear pump can be installed to improve the quantitativeness of the extrusion amount. In this melt extrusion, the polyester raw material is heated in advance and crystallized to sufficiently remove moisture, and then it may be put into an extruder and melt extruded, or a biaxial extruder with a vent is used, Undried polyester raw material can be directly fed into an extruder and melt extruded while removing moisture from the vent port. The resin temperature at the time of extrusion is preferably selected from the range of the melting point (Tm) + 15 ° C. to Tm + 50 ° C. of the polyester raw material used.

  In the above melt extrusion, a single-layer sheet can be prepared using one extruder, but a plurality of extruders and a multi-layer multi-manifold die or feed block are used. An unstretched sheet having a multilayer structure can also be obtained by merging and laminating molten polyester, extruding a plurality of sheets from a T-die and solidifying with a cooling roll.

  Next, the obtained unstretched sheet is stretched biaxially and biaxially oriented. For example, in the case of performing longitudinal and lateral sequential biaxial stretching as an example, it is performed as follows. First, the unstretched sheet is stretched in the machine direction by a roll stretching machine. The stretching temperature is usually in the range of glass transition temperature (Tg) to Tg + 40 ° C. of the polyester raw material, and the stretching ratio is usually in the range of 2.0 to 6.0 times, preferably 2.5 to 5.0 times. It is. Next, stretching is performed in the transverse direction. The range of the temperature and magnification of transverse stretching can be selected from the same range as that of longitudinal stretching. Subsequently, heat treatment is performed under tension or relaxation within 30% in the temperature range of the polyester raw material melting point (Tm) -15 ° C. to Tm-60 ° C. to obtain a biaxially oriented film.

  In the above stretching, in addition to a method of stretching to a predetermined ratio by a single stretching operation, a method of dividing the stretching into two or more steps to obtain a predetermined stretching ratio can be used. Also in that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges. Furthermore, you may extend | stretch longitudinally and / or a horizontal direction again before or after performing heat processing as needed.

  For example, the case of carrying out simultaneous longitudinal and transverse biaxial stretching is performed as follows. First, using a tenter type simultaneous biaxial stretching machine, the unstretched sheet is stretched simultaneously vertically and horizontally so that the area magnification is usually 6 to 30 times. The stretching temperature at this time is in the range of the glass transition temperature (Tg) to Tg + 40 ° C. of the polyester raw material, as in the case of sequential biaxial stretching. In particular, for this simultaneous biaxial stretching machine, it is preferable to use a stretching machine that drives a clip by a linear motor method in terms of a high degree of freedom in setting a stretching ratio and a relaxation rate during heat setting. The film formed by simultaneous biaxial stretching is subjected to heat treatment in the same manner as in the case of sequential biaxial stretching, but may be further subjected to relaxation treatment in the longitudinal direction and / or the transverse direction as necessary.

  The surface of the film can be coated as necessary. For example, in-line coating can be performed for the purpose of imparting slipperiness, imparting antistatic properties, and improving adhesion. For example, in the case of sequential biaxial stretching in the film production method described above, for example, after applying a coating liquid mainly containing water at the stage where longitudinal stretching is completed, drying, preheating, and lateral stretching in a tenter In addition, a series of processes for heat setting can be employed.

  The release film of the present invention has almost no increase in haze due to the generation of oligomers during heating unlike a release film based on a polyethylene terephthalate film. For this reason, for example, when the release film of the present invention is used as a protective film for the pressure-sensitive adhesive layer of a polarizing plate or a phase difference plate, when the release layer is peeled off by performing heat treatment during subsequent various processing Further, it is possible to prevent appearance defects such as an increase in haze of the pressure-sensitive adhesive layer and vitiligo due to oligomer transfer to the pressure-sensitive adhesive layer. Therefore, the industrial value of the present invention is high.

  The release film of the present invention has almost no increase in haze due to the generation of oligomers during heating unlike a release film based on a polyethylene terephthalate film. For this reason, for example, when the release film of the present invention is used as a protective film for the pressure-sensitive adhesive layer of a polarizing plate or a phase difference plate, when the release layer is peeled off by performing heat treatment during subsequent various processing Further, it is possible to prevent appearance defects such as an increase in haze of the pressure-sensitive adhesive layer and vitiligo due to oligomer transfer to the pressure-sensitive adhesive layer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded. In the examples and comparative examples, “parts” means “parts by weight”. The measurement methods used in the following examples are as follows.

1. Polyester melting point (Tm):
Using a thermal differential analyzer (DSC-2920, manufactured by TAInstuments), the temperature was measured at a rate of temperature increase of 20 ° C./min, and the temperature at the top of the endothermic peak accompanying crystal melting was taken as the melting point.

2. Average particle size of fine particles:
The equivalent spherical diameter of the particles at the 50% by weight point of all particles determined by the light scattering method was used as the average particle diameter.

3. Thermal shrinkage at 130 ° C:
In the longitudinal direction (MD) and the width direction (TD) of the film, about 50 mm between the gauge points was accurately measured (L1), and heat treatment was performed in an oven at 130 ° C. for 10 minutes in a tensionless state. Thereafter, the film was cooled, the distance between the marks was measured again accurately (L2), and the change between the marks before and after the heat treatment was calculated by the following formula to obtain a heat shrinkage rate of 130 ° C.

4). Total light transmittance:
Using an integrating sphere turbidimeter (NDH2000 manufactured by Nippon Denshoku Co., Ltd.) based on JIS K 7136 (2000) (equivalent to ISO 14782 1999), the total light transmittance (%) was measured.

5). Haze value:
Using an integrating sphere turbidimeter (NDH2000 manufactured by Nippon Denshoku Co., Ltd.), the haze value (%) was determined according to JIS K 7136 (2000) (equivalent to ISO 14782 1999).

6). Change in film haze value:
In a forced circulation oven, under a nitrogen atmosphere, the release film with the four sides fixed was heat treated at 150 ° C. for 1 hour, then taken out and cooled, and the haze value of the film was measured. The value was compared with the film haze value before heat treatment, and the absolute value of the difference was defined as the amount of change (%) in the haze value of the release film.

7). Residual adhesion rate of release film:
The residual adhesive strength and basic adhesive strength defined below were determined, and the residual adhesive rate (%) was calculated from the following formula. The adhesive strength was measured at 23 ± 2 ° C. and 50 ± 5% RH.

  Residual adhesive force: Adhesive tape (Nitto Denko No. 31B) was reciprocated once with a 2 kg rubber roller on the release layer surface of the sample film, heat-treated at 100 ° C. for 1 hour, and then pressure-bonded. The sample film was peeled off from the adhesive tape, and this adhesive tape was pressure-bonded to the stainless steel plate according to JIS C 2107 (adhesive strength to the stainless steel plate, 180 ° peeling method), and the adhesive force was measured to determine the residual adhesive strength. .

  Basic adhesive strength: Using the same adhesive tape (No. 31B) used for residual adhesive strength, press the adhesive tape on a stainless steel plate according to JIS C 2107, and measure the adhesive strength in the same way. Adhesive strength was assumed.

9. How dirty the adhesive layer is:
In a forced circulation oven, under a nitrogen atmosphere, the release film with the four sides fixed was heat treated at 150 ° C. for 1 hour, and then taken out and cooled. After sticking black vinyl chloride tape (Eslon tape No. 360 manufactured by Sekisui Chemical Co., Ltd.) to the release layer surface of this release film, peel the vinyl chloride tape and visually observe the adhesive layer to record the change. did.

  The manufacturing method of the polyester raw material used in the following examples is as follows.

<Polyester A>
In a reactor equipped with a stirrer, a distillation tube and a decompression device, 184 parts by weight of 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) (trans isomer 98%), 1,4-cyclohexanedimethanol (1,4 -CHDM) (67% trans isomer) 158 parts by weight, 0.9 part by weight of a 6% by weight butanol solution of Ti (OC ₄ H ₉ ) ₄ was heated to 150 ° C. under a nitrogen stream, and then 1 to 200 ° C. The temperature increased over time. Thereafter, the esterification reaction was carried out by maintaining at 200 ° C. for 1 hour, and then the polycondensation reaction was carried out while gradually raising the pressure in the reactor from 200 ° C. to 250 ° C. over 45 minutes. After polymerization for 2 hours at a reactor internal pressure of 0.1 kPa and a reaction temperature of 250 ° C., the obtained polymer was extracted into water in the form of a strand and then pelletized. The obtained pellet had an intrinsic viscosity (IV) of 0.85 dl / g. The melting point of this polyester was 220 ° C.

<Polyester B>
Amorphous silica with an average particle size of 2.4 μm is dry blended to 0.1% by weight to polyester A, put into a twin screw extruder with a vent, and melt mixed while removing moisture at a vacuum of 1 kPa. Then, it was extruded into a strand shape and cooled in water to prepare a master batch of particles. The intrinsic viscosity of this polymer was 0.76 dl / g. The melting point was 220 ° C.

<Polyester C>
Polyester A is dry blended with 0.1% by weight of divinylbenzene crosslinked polystyrene particles with an average particle size of 1.1μm, put into a twin screw extruder with a vent and melted while removing moisture at a vacuum of 1kPa. The mixture was mixed, extruded into a strand, and cooled in water to form a master batch of particles. The intrinsic viscosity of this polymer was 0.82 dl / g. The melting point was 220 ° C.

<Polyester D>
In the production of polyester A, polymerization was performed in the same manner as in the production of polyester A, except that 1,4-cyclohexanedicarboxylic acid (trans isomer 98%) was used instead of 1,4-cyclohexanedicarboxylic acid (trans isomer 98%). To obtain polyester pellets. The intrinsic viscosity of the obtained pellet was 0.84 dl / g. The melting point of this polyester was 192 ° C.

<Polyester E>
Polyester D is dry blended with amorphous silica having an average particle size of 2.4 μm to a weight of 0.1 wt%, put into a twin screw extruder with a vent, and melt mixed while removing moisture at a vacuum of 1 kPa. Then, it was extruded into a strand shape and cooled in water to prepare a master batch of particles. The intrinsic viscosity of this polymer was 0.76 dl / g. The melting point was 192 ° C.

<Creation of biaxially oriented polyester film>
Polyester A and polyester B were mixed at a weight ratio of 1: 1 and charged into a surface layer extruder. Apart from this, 100% of polyester A was introduced into the extruder for the intermediate layer. Each extruder was a twin screw extruder with a vent, and the resin was extruded at a melting temperature of 250 ° C. while removing moisture from the vent port at a vacuum degree of 1 kPa without drying. Each extruder is equipped with a gear pump and a filter. After passing them through the molten polymer, they are merged and laminated in a feed block and melt extruded from a T-die. An unstretched sheet was prepared. At this time, the thicknesses of both surface layers were the same, and the total thickness of both surface layers was set to 10% of the total thickness. At this time, casting was carried out on a cooling drum at 20 ° C. by applying an electrostatic application adhesion method. The unstretched sheet thus prepared was guided to the longitudinal stretching process.

  First, a roll stretching method was used for longitudinal stretching, preheating to 70 ° C. with a plurality of rolls, and stretching in the longitudinal direction at a stretching ratio of 3.0 times using an IR heater. Next, this uniaxially stretched film was guided to a tenter, preheated at 85 ° C., and then stretched in the width direction at a stretch ratio of 4.0 times. Then, after heat setting at 180 ° C. under tension in the same tenter, a relaxation treatment was performed in the 3% width direction at a temperature of 150 ° C. to obtain a biaxially oriented polyester film having a total thickness of 38 μm.

<Creation of release film>
On one side of the above-mentioned biaxially oriented polyester film, an addition-reactive curing release agent having the following composition is applied so that the coating amount after drying / curing is 0.1 g / m ² , followed by drying / curing. A release layer was applied. The properties of this release film are shown in Table 3.

<Creation of biaxially oriented polyester film>
A mixture of polyester A and polyester C in a weight ratio of 1: 1 was used as a raw material. The resin was put into a twin screw extruder with a vent without drying, and melt extrusion was performed at a melt line temperature of 250 ° C. At this time, the vent port is connected to a vacuum line, melt extrusion is performed while removing moisture at a vacuum degree of 1 kPa, and the molten resin is extruded in a sheet form from a T die through a gear pump and a filter. Was cast on a cooling drum at 20 ° C. (single layer). The unstretched sheet thus prepared was longitudinally stretched, laterally stretched and heat-set in exactly the same manner as in Example 1 to obtain a biaxially oriented polyester film having a total thickness of 38 μm.

<Creation of release film>
A release layer was coated on one side of the biaxially oriented polyester film in the same manner as in Example 1. The properties of this release film are shown in Table 3.

<Creation of biaxially oriented polyester film>
The biaxially oriented polyester film having a total thickness of 38 μm prepared in Example 1 was used as it was.

<Creation of release film>
A condensation-reactive curing release agent having the following composition is applied to one side of the above biaxially oriented polyester film so that the coating amount after drying / curing is 0.1 g / m ² and dried / cured. A release layer was applied. The properties of this release film are shown in Table 3.

（比較例１）

(Comparative Example 1)

<Creation of biaxially oriented polyester film>
Polyethylene terephthalate resin pellets (inherent viscosity was 0.64 g / dl) containing 0.05% by weight of amorphous silica having an average particle size of 2.4 μm were put into a surface layer extruder. Separately, polyethylene terephthalate resin pellets (intrinsic viscosity was 0.64 g / dl) containing no fine particles were charged into an extruder for the intermediate layer. And it melt-extruded exactly like Example 1 except having changed the temperature setting of the melt line at the time of melt-extrusion to 285 degreeC, and obtained the unstretched sheet | seat of 3 layers structure. The unstretched sheet thus prepared was guided to the next longitudinal stretching step.

  First, a roll stretching method was used for longitudinal stretching, preheating to 83 ° C. with a plurality of rolls, and further stretching in the longitudinal direction at a stretching ratio of 3.0 times in combination with an IR heater. Next, this uniaxially stretched film was guided to a tenter, preheated at 90 ° C., and then stretched in the width direction at a stretch ratio of 4.0 times. Then, after heat-setting at a temperature of 220 ° C. under tension in the same tenter, a relaxation treatment was performed in the 3% width direction at a temperature of 150 ° C. to obtain a biaxially oriented polyester film having a total thickness of 38 μm.

<Creation of release film>
A release layer was coated on one side of the biaxially oriented polyester film in the same manner as in Example 1. The properties of this release film are shown in Table 3.
(Comparative Example 2)

  As a raw material resin, a mixture of polyester D and polyester E in a weight ratio of 1: 1 was put into a surface layer extruder. Apart from this, 100% of polyester D was put into the extruder for the intermediate layer. And it melt-extruded like Example 1 and obtained the unstretched sheet | seat of the single layer. The unstretched sheet thus prepared was subjected to longitudinal stretching and lateral stretching in exactly the same manner as in Example 1. Then, after heat-setting at 150 ° C. under tension in the same tenter, relaxation treatment was performed in the 3% width direction at a temperature of 130 ° C. to obtain a biaxially oriented polyester film having a total thickness of 38 μm. The film properties are shown in Table 3.

<Creation of release film>
A release layer was coated on one side of the biaxially oriented polyester film in the same manner as in Example 1. The properties of this release film are shown in Table 3.

Claims (1)

  As a repeating unit, a release layer is laminated on at least one side of a biaxially oriented polyester film made of polyester having 1,4-cyclohexanedicarboxylic acid and 1,4-cyclohexanedimethanol as main components and a melting point of 200 ° C. or higher. The release film is characterized in that the amount of change in the film haze value after heating at 150 ° C. for 1 hour is 1% or less.