CN107405909B

CN107405909B - Mold release film

Info

Publication number: CN107405909B
Application number: CN201680014045.1A
Authority: CN
Inventors: 神田俊宏; 铃木太朗
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2015-03-28
Filing date: 2016-02-15
Publication date: 2020-03-03
Anticipated expiration: 2036-02-15
Also published as: TW201703966A; JP2016187866A; WO2016158037A1; KR20170100012A; JP6536123B2; TWI686281B; CN107405909A; KR102050747B1

Abstract

The invention provides a mold release film which has excellent visibility after heat treatment and little foreign matter generation. The release film is formed by sequentially laminating a first primer layer, a second primer layer and a release layer containing a curable silicone resin on a substrate comprising a biaxially stretched polyester film, wherein the surface resistivity of the release layer is less than 1 x 10¹²Ω。

Description

Mold release film

Technical Field

The present invention relates to a mold release film, and particularly to a mold release film having an effect of excellent visibility after heat treatment and little generation of foreign matter.

Background

Biaxially stretched polyester films are excellent in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, and the like, and for example, release films comprising a biaxially stretched polyester film as a base material and a release layer comprising a silicone resin or the like as a main component are used in many fields.

However, a release film in which a release layer containing a silicone resin as a main component is provided on a biaxially stretched polyester film is characterized in that static electricity is easily generated and charged. For example, when peeling off from an adherend such as an adhesive, peeling electrification may occur, and as a result, not only a defect due to adhesion or entanglement of foreign matter or the like but also a serious defect such as damage to a nearby electronic component due to electrostatic obstruction and product failure may occur in a processing site. Therefore, antistatic measures by only the equipment in the production process are not necessarily sufficient, and antistatic treatment of the release film itself is strongly required in the present situation.

In order to suppress such charging, various release films have been proposed. For example, patent document 1 proposes an antistatic release agent. However, the release film coated with such a release material is not sufficient because the release from the adhesive is heavy.

Patent document 2 proposes providing an antistatic layer on the surface of the base film opposite to the release layer. However, the release film having an antistatic layer on the back surface thereof exhibits a certain effect on electrification when the release film wound in a roll is unwound, but the release surface does not have antistatic properties, and therefore, there still remains a problem that the effect thereof is insufficient or there is no effect of suppressing electrification upon peeling the release film from an adherend.

On the other hand, in many applications, the release film is exposed to high temperatures. For example, the heat when the pressure-sensitive adhesive composition is applied to the release layer and dried, or the step of heating the adherend in a state where the release film is attached.

In the step of coating and drying the adhesive, heat of about 100 to 180 ℃ may be applied. However, as a problem of the polyester film, if the film is exposed to such a high temperature treatment, oligomers (low molecular weight components of the polyester, particularly cyclic trimer) contained in the film are precipitated from the inside of the film. The oligomer thus precipitated penetrates the release layer and is crystallized inside the adhesive layer to become a foreign substance, thereby causing a problem of hindering the appearance inspection.

Therefore, a release film using a biaxially stretched polyester film as a base material may not have sufficient characteristics to withstand use depending on the application.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2003-226838

Patent document 2: japanese laid-open patent publication No. 2002-67019

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a mold release film having an effect of excellent visibility particularly after heat treatment and little generation of foreign matter. Means for solving the technical problem

The present inventors have conducted extensive studies on the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by providing a polyester film substrate, a specific primer layer, and a release layer in this order, and have completed the present invention.

That is, the gist of the present invention is a release film characterized in that: the release film comprises a biaxially stretched polyester film and, laminated on a substrate, a first primer layer, a second primer layer and a release layer comprising a curable silicone resin, wherein the surface resistivity of the release layer is less than 1 x 10¹²Ω。

ADVANTAGEOUS EFFECTS OF INVENTION

The laminated polyester film of the present invention can suppress the precipitation of oligomers from the film even when treated at high temperature for a long time, and therefore can provide a product having an excellent appearance without generating foreign matter on the surface of the release layer, and has a high industrial value.

Detailed Description

The base film of the release film of the present invention contains polyester. The polyester is produced by melt polycondensation of a dicarboxylic acid such as phthalic acid, isophthalic acid, 2, 6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, 4' -diphenyldicarboxylic acid, or 1, 4-cyclohexyldicarboxylic acid, or an ester thereof, and a diol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1, 4-butanediol, neopentyl glycol, or 1, 4-cyclohexanedimethanol. The polyester composed of these acid component and diol component can be produced by any conventional method.

For example, the following method is employed: the ester exchange reaction between the lower alcohol ester of the aromatic dicarboxylic acid and the diol, or the direct esterification of the aromatic dicarboxylic acid and the diol to substantially form a bisdiol ester of the aromatic dicarboxylic acid or an oligomer thereof, followed by polycondensation by heating under reduced pressure. The aliphatic dicarboxylic acid may be copolymerized depending on the purpose.

The polyester of the present invention is typically polyethylene terephthalate, polyethylene 2, 6-naphthalate, and 1, 4-cyclohexanedimethanol terephthalate, and may be a polyester obtained by copolymerizing the above acid component and diol component, or may contain other components and additives as required.

The polyester film of the present invention is a single-layer or multi-layer structure. In the case of a multilayer structure, the surface layer and the inner layer, or both the surface layer and the layers, may be made of different polyesters according to the purpose.

In addition, when the additive is added to the film, the additive may be added to a single layer film or may be added to only a part of the layers of the multilayer film. For example, by forming the film in a 3-layer structure and adding particles to one or both outer layers without adding particles to the inner layer, both slipperiness and transparency can be further achieved.

In addition, the polyester film of the present invention preferably uses a polyester containing a small amount of oligomer. The amount of the polyester having a small oligomer content is preferably 50% by weight or more of the total polyester when the film has a single-layer structure, and preferably 50% by weight of the surface layer in contact with the primer layer when the film has a multilayer structure. The polyester having a small oligomer content means, for example, a polyester having a cyclic trimer content of 0.7 wt% or less. Particularly preferably, the cyclic trimer content is 0.5 wt% or less. In order to suppress the deposition of the oligomer on the film surface when the polyester film is heated at a high temperature, a favorable effect can be obtained if the amount is 0.7 wt% or less. It is also known that simply reducing the oligomer content does not reduce the amount of deposition in accordance with this, and particularly when heating the film surface with a pressure-sensitive adhesive layer or the like provided thereon, the amount of deposition can be significantly reduced within the range of about 0.5 wt% of the oligomer content.

When the surface layer of the film having a multilayer structure is a polyester having a small oligomer content as described above, the thickness of the surface layer is usually 2 μm or more, preferably 3 μm or more. As the thickness is increased, the precipitation of oligomer is suppressed, and as a result of a test under various conditions in which the release film is subjected to a heating step, it is found that when the thickness of the surface layer is smaller than the above range, a sufficient oligomer precipitation suppression effect may not be obtained.

The polyester film of the present invention may contain particles for the purpose of ensuring the slidability of the film and preventing the occurrence of scratches. Examples of such particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium phosphate, kaolin, talc, alumina, titanium oxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide, organic particles such as crosslinked polymer particles, and calcium oxalate, and precipitated particles in the polyester production process.

The particle size and the content of the particles used are selected depending on the use and purpose of the film, and the average particle size (d50) is usually in the range of 0.01 to 3 μm, preferably 0.02 to 2.5 μm, and more preferably 0.03 to 2 μm. When the average particle size exceeds 3.0. mu.m, the surface roughness of the film becomes excessively rough, and particles are likely to fall off from the film surface. When the average particle size is less than 0.01. mu.m, the surface roughness may be too small to obtain sufficient slipperiness.

The content of the particles is usually in the range of 0.0003 to 1.0 wt%, preferably 0.0005 to 0.5 wt%, based on the polyester layer containing the particles. When the content of the particles is less than 0.0003% by weight, the slipperiness of the film may be insufficient, while when it is added in an amount exceeding 1.0% by weight, the transparency of the film may be insufficient. In addition, in order to particularly ensure transparency, smoothness, and the like of the film, the film may be configured to contain substantially no particles. In addition, various stabilizers, lubricants, antistatic agents, and the like can be appropriately added to the film.

As the film forming method of the film of the present invention, a generally known film forming method can be used. For example, a sheet obtained by melt extrusion is first stretched at 70 to 145 ℃ by a roll stretching method to 2 to 6 times to obtain a uniaxially stretched polyester film, then stretched at 80 to 160 ℃ in a tenter to 2 to 6 times in a direction perpendicular to the previous stretching direction, and then heat-treated at 150 to 250 ℃ for 1 to 600 seconds to obtain a film. Further, at this time, it is preferable to perform a method of performing the relaxation of 0.1 to 20% in the longitudinal direction and/or the transverse direction in the heat-treated region and/or the cooling region at the heat-treated outlet.

The first primer layer of the present invention can be provided by any of so-called off-line coating in which a coating layer is provided on a film obtained by film formation and so-called on-line coating in which a coating layer is provided during film formation. But is preferably provided by an in-line coating method, particularly a coating stretching method in which stretching is performed after coating.

In-line coating is a method of coating in a process of manufacturing a polyester film, and specifically, a method of coating in an arbitrary step of melt-extruding a polyester, biaxially stretching, heat-fixing, and rolling. Generally, the coating is performed on any one of a substantially amorphous unstretched sheet obtained by melting and quenching, a uniaxially stretched film obtained by stretching in the longitudinal direction (longitudinal direction), and a biaxially stretched film before heat-fixing. In particular, as the coating stretching method, a method of stretching in the transverse direction after coating a uniaxially stretched film is excellent. In the above method, since film formation and coating of the coating layer can be performed simultaneously, there is an advantage in production cost, and since stretching is performed after coating, uniform coating is achieved in the film, and thus the characteristics of the coating layer are stable. Further, the polyester film before biaxial stretching is first covered with the resin layer constituting the coating layer, and then the film and the coating layer are simultaneously stretched, whereby the base film and the coating layer are firmly adhered to each other. In the biaxial stretching of the polyester film, the film is stretched in the transverse direction while the film ends are sandwiched by tenter clips, whereby the film is restrained in the longitudinal/width direction, and during thermosetting, high temperature can be applied while maintaining flatness without generating wrinkles and the like. This makes it possible to increase the film formability of the coating layer and to firmly adhere the coating layer to the polyester film because the heat treatment performed after coating can be set to a high temperature that cannot be achieved by other methods. As a polyester film provided with a coating layer, uniformity of the coating layer, improvement of film formability, and adhesion between the coating layer and the film often exhibit preferable characteristics.

In the case of the coating-drawing method, the coating liquid to be used is preferably an aqueous solution or an aqueous dispersion for reasons of handling, working environment and safety, and may contain an organic solvent as long as water is used as a main medium without departing from the scope of the present invention.

The first undercoat layer of the present invention is preferably obtained by applying and drying a coating solution in which the ratio of the crosslinking agent to the total nonvolatile components is 70% by weight or more. In addition, other components may be contained in the coating liquid.

The crosslinking agent as used herein refers to a crosslinkable resin which reacts particularly by heat, and examples thereof include amino resin-based, isocyanate-based, oxazoline-based and epoxy-based resins. Other polymeric crosslinking reactive compounds having reactive groups on the polymer backbone are also included.

In the present invention, the use of an oxazoline-based crosslinking agent is particularly preferable because the precipitation of oligomers from the polyester film is suppressed and the appearance of the primer layer is good.

In particular, when 2 or more kinds of crosslinking agents are used in combination, the effect of suppressing oligomers from being precipitated from the polyester film during heating is high, and therefore, such a combination is preferable. This is presumably because: by the presence of the crosslinking agent having a different reaction rate at the time of forming the undercoat layer, the voids in the undercoat layer are more effectively filled and the oligomer deposition is suppressed.

As a result of examination of various combinations, the effects obtained by using an oxazoline-based resin, an epoxy-based resin, or an amino resin-based resin, an oxazoline-based resin, or an epoxy-based resin in combination are particularly high.

The oxazoline-based crosslinking agent is preferably a polymer having an oxazoline group in the molecule, and can be produced by homopolymerization of an addition polymerizable oxazoline group-containing monomer or polymerization with another monomer. Examples of the addition polymerizable oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline, and mixtures of 1 or 2 or more of these monomers can be used. Among these, 2-isopropenyl-2-oxazoline is preferable because it is industrially easily available, and other monomers may be any monomers as long as they are copolymerizable with the addition-polymerizable oxazoline group-containing monomer.

The oxazoline-based crosslinking agent of the present invention has an oxazoline group content of usually 0.5 to 10mmol/g, preferably 3 to 9mmol/g, and more preferably 5 to 8 mmol/g. Particularly, when 2 or more crosslinking agents are used in combination, a high effect can be obtained by selecting the oxazoline crosslinking agent in the above range.

The epoxy-based crosslinking agent is a compound having an epoxy group in the molecule, and examples thereof include condensates of epichlorohydrin with a hydroxyl group or an amino group of ethylene glycol, polyethylene glycol, glycerin, polyglycerol, bisphenol a, etc., polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like.

Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether; examples of the diepoxy compound include neopentyl glycol diglycidyl ether, 1, 6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether; examples of the monoepoxy compound include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether; examples of the glycidylamine compound include N, N' -tetraglycidol-m-xylylenediamine, 1, 3-bis (N, N-diglycidylamino) cyclohexane, and the like.

Among amino resin-based crosslinking agents, those obtained by methylolating the amino groups of a melamine resin and further methylating a part of the methylol groups thereof are water-soluble and easy to handle, have high reactivity, and can provide a release film excellent in adhesion between an undercoat layer and a substrate film and durability of the undercoat layer.

When the crosslinking component is contained, a component for promoting crosslinking, for example, a crosslinking catalyst can be used in combination.

The coating liquid for providing the first undercoat layer may contain substances other than the above components as necessary. For example, surfactants, other binders, particulates, defoamers, coating modifiers, tackifiers, antioxidants, ultraviolet absorbers, foaming agents, dyes, pigments, and the like. These additives may be used alone, or two or more of them may be used in combination as required.

The thickness of the first primer layer is usually in the range of 0.003 to 1 μm, preferably 0.005 to 0.5 μm, and more preferably 0.01 to 0.2 μm as the thickness of the film on the biaxially stretched polyester film at the end. When the thickness is smaller than this range, the amount of oligomer deposited from the film may not be sufficiently reduced. When the thickness is larger than this range, the first undercoat layer may have problems such as poor appearance and blocking.

Further, the thickness of the first undercoat layer can be confirmed by the following method: the coating film is dyed with a heavy metal such as a ruthenium compound or an osmium compound, the cross section of the coating film is adjusted by an ultrathin section method, and then a plurality of sites are observed on the coating layer on the cross section of the coating film by a transmission electron microscope, and the measured values are averaged.

As a method for applying the coating liquid to the polyester film, for example, a coating technique as shown in "コーティング method" (coating method), published by yazaki, Maki bookshop, 1979, can be used. Specifically, there may be mentioned techniques such as air knife coater, blade coater, bar coater, knife coater, extrusion coater, impregnation coater, reverse roll coater, transfer roll coater, gravure coater, roll coater, cast coater, spray coater, curtain coater, calender coater, extrusion coater, and the like.

In addition, in order to improve the coating property and adhesion of the coating agent to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment, or the like before coating.

The second undercoat layer of the present invention is obtained by applying a coating solution containing a thiophene-based conductive compound and drying the coating solution. The thiophene-based conductive polymer herein preferably refers to a polymer obtained by doping a compound containing thiophene or a thiophene derivative with another anionic compound, or a polymer that is self-doped with an anionic group in a compound containing thiophene or a thiophene derivative. These substances are suitable because they exhibit excellent conductivity.

Examples of the compound (a) include compounds obtained by polymerizing a compound represented by the following formula (1) or (2) in the presence of a polyanion.

In the above formula (1), R¹、R²Each independently represents hydrogen, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or the like.

In the formula (2), n represents an integer of 1 to 4.

Examples of the polyanion include poly (meth) acrylic acid, polymaleic acid, polystyrenesulfonic acid, and polyvinylsulfonic acid.

Further, as a method for producing the polymer, for example, a method shown in japanese patent laid-open No. 7-90060 can be adopted.

In the present invention, a particularly preferred embodiment is an embodiment in which n is 2 in the compound of formula (2) and polystyrene sulfonic acid is used as the polyanion.

When these polyanions are acidic, a part or all of them may be neutralized. The base used for neutralization is preferably ammonia, an organic amine, or an alkali metal hydroxide.

The coating liquid for forming the second undercoat layer may contain various components in addition to the above components.

Examples thereof include polyether resins, polyester resins, acrylic resins, polyurethane resins, vinyl resins, epoxy resins, and amide resins. The respective skeleton structures may have a substantially complex structure by copolymerization or the like. Examples of the resin having a composite structure include polyester grafted with an acrylic resin, polyurethane grafted with an acrylic resin, polyester grafted with a vinyl resin, polyurethane grafted with a vinyl resin, and the like. The inclusion of these resins may improve the strength of the obtained coating layer and the adhesion to the substrate film, other primer layer, and release layer. From the viewpoint of stability when mixed with a thiophene-based conductive polymer, and the like, a polyester resin obtained by copolymerizing sulfoisophthalic acid, an acrylic resin using a reactive emulsifier, an acrylic resin using a nonionic emulsifier, a polyurethane resin in which a carboxyl group is introduced into a skeleton using dimethylolpropionic acid, dimethylolbutyric acid, or the like, and the like are easily used.

Further, for example, glycerin, polyglycerol, an alkylene oxide adduct of glycerin or polyglycerol, a polyalkylene oxide, a polysaccharide, a compound having an amino group, and the like may be contained. When these compounds are contained, there may be a case where the effect of improving the transparency and antistatic property of the obtained second undercoat layer is obtained.

For the purpose of further improving the adhesion and slip properties of the undercoat layer, inorganic particles may be contained, and specific examples thereof include silica, alumina, kaolin, calcium carbonate, titanium oxide, barium salt, and the like.

Further, if necessary, a defoaming agent, a coating property improving agent, a thickener, an organic lubricant, organic polymer particles, an antioxidant, an ultraviolet absorber foaming agent, a dye, and the like may be contained.

The organic solvent used may be only one type or two or more types may be appropriately used within a range not exceeding the gist of the present invention for the purpose of improving dispersibility, improving film formability, and the like.

The mixed liquid dispersed with water may be diluted with an organic solvent, such as an alcohol, which can be mixed with water, to form a coating liquid.

The coating amount of the second primer layer of the present invention is usually 0.01 to 1 μm, preferably 0.02 to 0.5 μm, as the thickness of the coating after drying. When the coating amount is less than 0.01. mu.m, antistatic performance may become insufficient or performance may become nonuniform depending on the site. On the other hand, when the thickness exceeds 1 μm, the strength of the coating film is weak and the coating film may be peeled off or the curing of the silicone in the release layer may be inhibited.

Further, the thickness of the second undercoat layer can be confirmed by the following method: the coating film is dyed with a heavy metal such as a ruthenium compound or an osmium compound, the cross section of the coating film is adjusted by an ultrathin section method, and then a plurality of sites are observed on the coating layer on the cross section of the coating film by a transmission electron microscope, and the measured values are averaged.

In the present invention, a method of providing the second undercoat layer can use a coating technique such as that shown in Progainst courage, Maki Booth, 1979, and コーティング (coating method). Specifically, there may be mentioned techniques such as air knife coater, blade coater, bar coater, blade coater, extrusion coater, impregnation coater, reverse roll coater, transfer roll coater, gravure coater, roll-lick coater, cast coater, spray coater, curtain coater, calender coater, and extrusion coater.

In the present invention, the curing conditions for forming the second primer layer on the polyester film are generally 100 ℃ or higher, and the heat treatment is performed on the basis of preferably 3 to 40 seconds at 100 to 200 ℃, and more preferably 3 to 40 seconds at 120 to 160 ℃. If necessary, irradiation with active energy rays such as heat treatment and ultraviolet irradiation may be used in combination. If the heat treatment is not performed at 100 ℃ or higher, the curing of the coating layer is insufficient, and therefore, the antistatic performance and the peeling force of the release layer are undesirably increased.

In the present invention, a release layer containing a curable silicone resin is further provided on the first primer layer and the second primer layer of the biaxially stretched polyester film obtained in the above-described manner. The silicone resin may be a type containing a curable silicone resin as a main component, or a modified silicone type obtained by graft polymerization or the like with an organic resin such as a polyurethane resin, an epoxy resin, an alkyd resin, or the like.

As the type of the curable silicone resin, any type of curing reaction such as addition type, condensation type, ultraviolet curing type, electron beam curing type, solvent-free type, and the like can be used.

Specific examples thereof include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X-62-2461, DKQ 3-202, DKQ 3-203, DKQ 3-204, DKQ 3-205, DKQ 3-210, YSR-3022, TPR-6700, TPR-6720, TPR-6721, SD7220, SD7226, and SD7229, all of which are available from Dow Corning Toray, all of which are available from shin-Etsu chemical industries, Ltd. In addition, a release controlling agent may be used in combination for adjusting the releasability of the release layer.

From the viewpoint that the obtained release layer has excellent release characteristics and does not use an environmental load such as an organotin catalyst, an addition-type curable silicone resin is preferable.

The addition-type curing type organic silicon has the following technical problems: in a layer containing a large amount of nitrogen such as the first undercoat layer of the present invention, the curing reaction tends to be insufficient. When the curing reaction is insufficient, there are problems that the silicone release layer is likely to fall off from the film, or the release properties are unstable. However, by providing the second undercoat layer as in the present invention, such curing inhibition can also be suppressed.

In the present invention, as a method for providing a release layer on a polyester film, conventionally known coating methods such as reverse roll coating, gravure coating, bar coating, and knife coating (sector blade coat) can be used.

The amount of the release layer of the present invention to be applied is usually 0.01 to 1g/m as a dry coating after the release layer is formed²The range of (1). The coating amount of the release layer can be calculated from the weight concentration and the coating area of the coating material and the amount of the coating material used. When the amount of the coating is less than the above range, the coating may be difficult to obtainWhen the releasability is more than the above range, problems such as blocking may occur.

As described above, the coating amount can also be determined by confirming the thickness of the release layer from the cross section by a transmission electron microscope and dividing the thickness by the specific gravity. In general, the specific gravity of the curable silicone is usually about 0.9 to 1.2. The amount of the release layer having a thickness of 0.1 μm applied was 0.1g/m at a specific gravity of 1²。

The biaxially oriented polyester film used in the present invention preferably has an inclination of an orientation main axis of 12 degrees or less, depending on the method of use. The inclination of the main axis of orientation referred to herein is also referred to as an orientation angle, and means an inclination of the main axis with respect to the width direction or longitudinal direction of the film. In some cases, the method of using the release film is an inspection by a crossed nicols method of polarizing and transmitting light. For example, when a release film is attached to a polarizing plate with an adhesive, the release film is also placed under a cross nicol when the cross nicol method inspection is performed as the inspection of the polarizing plate. In the case of using a release film of a biaxially oriented polyester film having an orientation angle of more than 12 degrees in this inspection step, light leakage is large, and defect detection of foreign matter, scratches, and the like is hindered.

The direction of the orientation main axis in the biaxially oriented polyester film of the present invention can be adjusted by changing the conditions such as the temperature and draw ratio of longitudinal drawing, the temperature and draw ratio of transverse drawing, and relaxation treatment.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the invention does not depart from the gist thereof.

The evaluation methods in examples and comparative examples are as follows.

(1) Method for measuring intrinsic viscosity of polyester:

1g of the polyester was precisely weighed, and 100ml of a mixed solvent of phenol/tetrachloroethane (weight ratio) 50/50 was added to dissolve the polyester, and the measurement was performed at 30 ℃.

(2) The method for measuring the ester-containing cyclic trimer contained in the polyester raw material comprises the following steps:

the polyester raw material was weighed to about 200mg and dissolved in 2ml of a mixed solvent of chloroform/HFIP (hexafluoro-2-isopropane) at a ratio of 3: 2. After the dissolution, 20ml of chloroform was added thereto, and 10ml of methanol was added little by little. Removing the precipitate by filtration, washing the precipitate with a mixed solvent of chloroform/methanol at a ratio of 2: 1, recovering the filtrate and the washing solution, concentrating with an evaporator, and drying and solidifying. The dried condensate was dissolved in 25ml of DMF (dimethylformamide), and the solution was subjected to liquid chromatography ("LC-7A" by Shimadzu corporation) to determine the amount of oligomer in DMF, which was divided by the amount of polyester raw material dissolved in the chloroform/HFIP mixed solvent to obtain the amount of oligomer contained (wt%). The amount of oligomers in DMF was determined by the peak area ratio of the peak area of the standard sample to the peak area of the measurement sample (absolute calibration curve method).

The standard sample was prepared by accurately weighing a pre-fractionated oligomer (cyclic trimer) and dissolving the oligomer in an accurately weighed amount of DMF. The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg/ml.

The conditions of the liquid chromatography are as follows.

Mobile phase A: acetonitrile

A mobile phase B: 2% aqueous acetic acid solution

Column: MCI GEL ODS 1HU manufactured by Mitsubishi chemical "

Column temperature: 40 deg.C

Flow rate: 1 ml/min

Detection wavelength: 254nm

(3) Method for measuring average particle diameter (d 50: μm):

the cumulative (on a weight basis) value of the spherical equivalent distribution measured by a centrifugal sedimentation type particle size distribution measuring apparatus (model SA-CP 3, Shimadzu corporation) was 50% as the average particle size.

(4) Measurement of orientation principal axis direction (orientation angle):

the orientation of the polyester film was observed with a polarizing microscope manufactured by Carl Zeiss, and the orientation angle was measured by inclining the direction of the main orientation axis in the plane of the polyester film by several degrees with respect to the width direction of the polyester film. The measurement was performed on 3 sites in total, the center and both ends of the obtained film, and the value of the maximum orientation angle among the 3 sites was defined as the maximum orientation angle.

(5) Thickness of the coating layer:

the membrane was fixed with embedding resin, the section was cut with a microtome, and the sample was stained with 2% osmic acid at 60 ℃ for 2 hours to adjust. The obtained sample was observed with a transmission electron microscope (JEM 2010, japan electronics) to measure the thickness of the coating layer. The film was measured for 15 sites in total, and the average of 9 points excluding the maximum 3 points and the minimum 3 points was defined as the coating thickness.

(6) Erase test (rub-off test):

after a polyester film sample was left in a room at 23 ℃/50% RH for 30 days, the release surface was rubbed several times with a fingertip, and the state of the release surface was judged according to the following evaluation criteria as a criterion for adhesion.

A: no change was observed on the film surface, good

B: the film surface was observed to be rubbed with a finger, and the peeling force was also changed

(7) Adhesive layer optical defect inspection 1:

an adhesive layer was formed by applying an acrylic adhesive COPONYL N-2233 (manufactured by japan synthetic chemicals) to the release surface of the release film so that the thickness after drying became 2 μm. After the release film was attached to the glass plate via the adhesive layer, the plate was heated at 180 ℃ for 10 minutes. Thereafter, the release film was peeled off, and the sheet was adhered to a glass plate, and subjected to aging treatment in an atmosphere of 60 ℃ and 90% RH for 10 days in a state where an adhesive layer was sandwiched between 2 glass plates. After that, foreign substances generated in the adhesive layer were examined under an optical microscope. For the examination, 12 areas of 100mm × 100mm were selected from arbitrary portions of the sample, and the number of foreign substances having a size of 2 μm or more was counted. The total of 12 inspection ranges is determined based on the following criteria, based on the total number of foreign matters in 10 inspection ranges, except for 2 having the largest number of foreign matters.

A: no foreign matter can be seen

B: the number of the foreign matters is more than 1 and less than 3 (which is slightly problematic in practice)

C: the number of the foreign matters is more than 3 (which is a problem in practice)

(8) Adhesive layer optical defect inspection 2:

an adhesive layer was formed by applying an acrylic adhesive COPONYL N-2233 (manufactured by japan synthetic chemicals) to the release surface of the release film so that the thickness after drying became 2 μm. After the release film was attached to the glass plate via the adhesive layer, the plate was heated at 180 ℃ for 30 minutes. Thereafter, the release film was peeled off, and the sheet was adhered to a glass plate, and subjected to aging treatment in an atmosphere of 60 ℃ and 90% RH for 10 days in a state where an adhesive layer was sandwiched between 2 glass plates. After that, foreign substances generated in the adhesive layer were examined under an optical microscope. For the examination, 12 areas of 100mm × 100mm were selected from arbitrary portions of the sample, and the number of foreign substances having a size of 2 μm or more was counted. The total of 12 inspection ranges is determined based on the following criteria, based on the total number of foreign matters in 10 inspection ranges, except for 2 having the largest number of foreign matters.

A: no foreign matter can be seen

(9) Surface resistivity:

a low resistivity meter manufactured by mitsubishi chemical corporation was used: loresta GP MCP-T600, the surface resistivity of the release layer was measured after conditioning the sample at 23 ℃ under a 50% RH measuring atmosphere for 30 minutes. The lower the surface resistivity value is, the more excellent the antistatic effect is, the lower the surface resistivity value is, the less than 1X 10¹²Omega is good and less than 1X 10⁸Omega is said to be very good.

(10) Visual inspection under crossed nicols:

the release film was closely attached to the polarizing plate via an adhesive so that the width direction of the release film was parallel to the orientation axis of the polarizing plate, thereby producing a sample. The release film after adhesion was superposed with an inspection polarizing plate so that the orientation axis was orthogonal to the film width direction, white light was irradiated from the polarizing plate side, and visual inspection was performed through the inspection polarizing plate, and the visual inspection performance under the crossed nicols was evaluated according to the following criteria.

A: has no optical interference and can be inspected

B: with light interference, but capable of inspection

C: has light interference and is difficult to inspect

The references of a and B are the preferred levels in practical use.

The polyesters used in the examples and comparative examples were the following polyesters.

(polyester 1):

100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol are used as raw materials, 0.09 part by weight of magnesium acetate tetrahydrate is used as a catalyst and is placed in a reactor, the reaction starting temperature is set to be 150 ℃, and the reaction temperature is gradually increased with the distillation removal of methanol, so that the reaction temperature is 230 ℃ after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. To the reaction mixture, 0.04 part of ethyl acid phosphate was added, and then 0.04 part of antimony trioxide was added to conduct polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ℃ to 280 ℃. On the other hand, the pressure gradually decreased from the normal pressure to 0.3mmHg finally. After the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 by changing the stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The resulting polyester 1 had an intrinsic viscosity of 0.63 and a content of oligomer (cyclic trimer) of 0.97% by weight.

(polyester 2):

polyester 1 was pre-crystallized at 160 ℃ and then subjected to solid-phase polymerization at 220 ℃ under a nitrogen atmosphere to obtain polyester 2 having an intrinsic viscosity of 0.75 and an oligomer (cyclic trimer) content of 0.46% by weight.

(polyester 3):

polyester 3 was obtained in the same manner as the polyester 1 production method except that 0.04 part of ethyl acid phosphate was added, 1.5 parts of synthetic calcium carbonate particles having an average particle diameter (d50) of 0.8 μm dispersed in ethylene glycol and 0.04 part of antimony trioxide were added, and the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.65. The resulting polyester 3 had an intrinsic viscosity of 0.65 and an oligomer (cyclic trimer) content of 0.91% by weight.

As a composition contained in the coating liquid for providing the first undercoat layer, the following is used.

(C1) The method comprises the following steps Oxazoline group-grafted Polymer Cross-linking agent (EPOCOS manufactured by Nippon touch Ltd.) in acrylic resin the oxazoline group amount was 7.7mmol/g

(C2) The method comprises the following steps Oxazoline group-grafted Polymer Cross-linking agent (EPOCOS manufactured by Nippon touch Ltd.) in acrylic resin the oxazoline group amount was 4.5mmol/g

(C3) The method comprises the following steps Polyglycerol polyglycidyl ether having an epoxy content of 5.5(eq/kg)

(C4) The method comprises the following steps Hexamethoxyhydroxymethylated melamine having an imino/hydroxymethyl/methoxy molar ratio of 1.5/2/2.5

(T1): 2-amino-2-methylpropanol hydrochloride

(B1) The method comprises the following steps A water-soluble acrylic resin having a glass transition point of 44 ℃ obtained by polymerization in the following composition

Methyl methacrylate/isobutyl acrylate/2-hydroxyethyl methacrylate 50/30/10

(B2) The method comprises the following steps An aqueous acrylic resin dispersion having a glass transition point of 50 ℃, an acid value of 14mgKOH and an average particle diameter of 0.05 μm, which is obtained by copolymerizing an alkyl acrylate, an alkyl methacrylate, methacrylic acid and N-methylolacrylamide as main components in the presence of an alkoxypolyethylene glycol methacrylate as a reactive emulsifier.

(F1) The method comprises the following steps Silica particles having an average particle diameter of 0.07 μm measured by BET method

(S1): surfactant Surfynol 465 (manufactured by Air Products)

As a composition contained in the coating liquid for providing the second undercoat layer, the following is used.

(A1) The method comprises the following steps A coating material SEPLEGYDA AS-Q01 (manufactured by Shin-Etsu Polymer) containing a thiophene-based conductive Polymer was diluted to a concentration of 10 times to prepare a second undercoat layer coating solution.

Diluting the solvent: methanol/propylene glycol monomethyl ether mixed solvent (mixing ratio 4: 1)

The following were used as compositions for the release layer.

(R1): curing type silicone resin (LTC 303E: manufactured by Dow Corning Toray)

(R2): curing agent (SRX 212: manufactured by Dow Corning Toray)

< example of production of polyester film >

(production example 1):

an unstretched polyethylene terephthalate film having a thickness composition ratio of a layer/B layer/a layer of 3/32/3 was produced by supplying a mixture of polyester 1 and polyester 3 at a weight ratio of 60/40 as a raw material for the layer a and a mixture of polyester 1 alone as a raw material for the layer B to two vent twin screw extruders, heating to 285 ℃ to melt the mixture, and co-extruding the mixture to form two types of three layers (layer a/layer B/layer a) in which the layer a is divided into two outermost layers (skin layers) and the layer B is an intermediate layer, and curing the mixture while cooling by closely contacting the mixture with a mirror cooling drum having a surface temperature of 40 to 50 ℃ by an electrostatic contact method. The film was stretched 2.9 times in the longitudinal direction while passing through a heating roller set at 90 ℃ to form a uniaxially oriented film. Subsequently, the film was introduced into a tenter stretcher, stretched 5.1 times in the width direction at 120 ℃ and further subjected to heat treatment at 210 ℃, and then subjected to relaxation treatment of 5% in the width direction to obtain a biaxially oriented polyethylene terephthalate film having a film thickness of 38 μm.

(production example 2):

an unstretched polyethylene terephthalate film having a thickness composition ratio of a layer/B layer/a layer of 3/32/3 was produced by supplying a mixture of polyester 2 and polyester 3 at a weight ratio of 60/40 as a raw material for the layer a and a mixture of polyester 1 as a raw material for the layer B to two vent twin screw extruders, heating to 285 ℃ to melt the mixture, and co-extruding the mixture to form two types of three layers (layer a/layer B/layer a) in which the layer a is divided into two outermost layers (skin layers) and the layer B is an intermediate layer, and curing the mixture while cooling by close contact with a mirror cooling drum having a surface temperature of 40 to 50 ℃ by an electrostatic contact method. The film was stretched 2.9 times in the longitudinal direction while passing through a heating roller set at 90 ℃ to form a uniaxially oriented film. Subsequently, the film was introduced into a tenter stretcher, stretched 5.1 times in the width direction at 120 ℃ and further subjected to heat treatment at 210 ℃, and then subjected to relaxation treatment of 5% in the width direction to obtain a biaxially oriented polyethylene terephthalate film having a film thickness of 38 μm.

(production example 3):

an unstretched polyethylene terephthalate film having a thickness composition ratio of a layer/B layer/a layer of 3/32/3 was produced by supplying a mixture of polyester 2 and polyester 3 at a weight ratio of 60/40 as a raw material for the layer a and a mixture of polyester 1 as a raw material for the layer B to two vent twin screw extruders, heating to 285 ℃ to melt the mixture, and co-extruding the mixture to form two types of three layers (layer a/layer B/layer a) in which the layer a is divided into two outermost layers (skin layers) and the layer B is an intermediate layer, and curing the mixture while cooling by close contact with a mirror cooling drum having a surface temperature of 40 to 50 ℃ by an electrostatic contact method. The film was stretched 3.4 times in the longitudinal direction while passing through a heating roller set at 90 ℃ to form a uniaxially oriented film. Subsequently, the film was introduced into a tenter stretcher, stretched 4.0 times in the width direction at 120 ℃ and further subjected to heat treatment at 230 ℃ and then subjected to relaxation treatment of 4.5% in the width direction to obtain a biaxially oriented polyethylene terephthalate film having a film thickness of 38 μm.

Example 1:

in the step of production example 1, coating liquids shown in table 1 were applied to one surface of the obtained uniaxially oriented film. Subsequently, the film was introduced into a tenter stretcher, and the coating solution was dried and heat-treated by the heat thereof, and a laminated polyester film in which a first undercoat layer having a thickness shown in table 1 was provided on a biaxially oriented polyethylene terephthalate film having a film thickness of 38 μm was obtained by the same procedure as in production example 1.

The obtained film was further coated with a second undercoat layer coating liquid so that the coating thickness after drying became 0.05 μm, and dried and heat-treated at 120 ℃ for 30 seconds.

Next, the following release layer coating material was applied in an amount of 0.1g/m after drying²The release film of (1) is coated by the reverse gravure coating method, and then dried and heat-treated at 150 ℃ for 30 seconds to obtain a release film in which a first primer layer, a second primer layer, and a release layer are sequentially stacked on a polyester film.

(R1)100 parts

(R2)1 part

MEK/toluene mixed solvent (mixing ratio 1: 2)1500 parts

Examples 2 to 7, comparative example 1:

in the process of production example 2, coating liquids shown in table 1 were applied to one surface of the obtained uniaxially oriented film. Subsequently, the film was introduced into a tenter stretcher, and the coating solution was dried and heat-treated by the heat thereof, and a laminated polyester film in which a first undercoat layer having a thickness shown in table 1 was provided on a biaxially oriented polyethylene terephthalate film having a film thickness of 38 μm was obtained by the same procedure as in production example 2.

The obtained film was further coated with a second undercoat layer coating liquid so as to have a coating thickness after drying shown in table 2, and dried and heat-treated at 120 ℃ for 30 seconds.

Next, the following release layer coating material was applied in an amount of 0.1g/m after drying²The release film of (1) is obtained by coating the polyester film by the reverse gravure coating method, drying the coating film at 150 ℃ for 30 seconds, and heat-treating the coating film to obtain a release film in which a first primer layer, a second primer layer, and a release layer are sequentially stacked on the polyester film.

(R1)100 parts

(R2)1 part

MEK/toluene mixed solvent (mixing ratio 1: 1)1500 parts

Example 8:

in the step of production example 3, coating liquids shown in table 1 were applied to one surface of the obtained uniaxially oriented film. Subsequently, the film was introduced into a tenter stretcher, and the coating solution was dried and heat-treated by the heat thereof, and a laminated polyester film in which a first undercoat layer having a thickness shown in table 1 was provided on a biaxially oriented polyethylene terephthalate film having a film thickness of 38 μm was obtained by the same procedure as in production example 3.

The obtained film was further coated with a second undercoat layer coating liquid so as to have a coating thickness after drying as shown in table 2, and dried and heat-treated at 120 ℃ for 30 seconds.

Next, the following mold release was performedThe coating weight of the layer coating after drying was 0.1g/m²The release film of (1) is obtained by coating the polyester film by the reverse gravure coating method, drying the coating film at 150 ℃ for 30 seconds, and heat-treating the coating film to obtain a release film in which a first primer layer, a second primer layer, and a release layer are sequentially stacked on the polyester film.

(R1)100 parts

(R2)1 part

MEK/toluene mixed solvent (mixing ratio 1: 1)1500 parts

Comparative example 2:

in the same steps as in examples 2 to 8, a release film was obtained by sequentially laminating a second primer layer and a release layer on a polyester film in the same manner except that the first primer layer was not provided.

Comparative example 3:

in the same steps as in examples 2 to 8, a release film was obtained by sequentially laminating a first primer layer and a release layer on a polyester film in the same manner except that the second primer layer was not provided.

[ Table 1]

The weight ratio in table 1 indicates the weight ratio of nonvolatile components of each component in the coating liquid.

[ Table 2]

Table 3 shows properties of the films obtained in examples and comparative examples.

[ Table 3]

Industrial applicability of the invention

The film of the present invention can be suitably used as a release film for use in applications where foreign matter is generated in an adherend after exposure to high temperature and charging becomes a problem. In addition, the resin composition is also provided with characteristics suitable for the use under crossed Nicol prism inspection.

Claims

1. A release film characterized by:

a release film comprising a base material comprising a biaxially stretched polyester film and, laminated in this order, a first primer layer, a second primer layer and a release layer comprising an addition-molded curable silicone resin,

the first undercoat layer is a layer obtained by applying and drying a coating liquid in which the ratio of a crosslinking agent to the total nonvolatile components is 70% by weight or more, the crosslinking agent being a combination of an oxazoline system and an epoxy system or a combination of an amino resin system, an oxazoline system, and an epoxy system,

the second undercoat layer is a layer obtained by applying a coating liquid containing a thiophene-based conductive compound and drying the coating liquid, and has a thickness of 0.05 to 1 μm,

the surface resistivity of the surface of the release layer is less than 1 × 10¹²Ω，

The release film was evaluated as a in the following adhesive layer optical defect inspection,

an acrylic pressure-sensitive adhesive COPONYL N-2233 was applied to the release surface of a release film so that the thickness after drying became 2 μm, an adhesive layer was provided, the release film was attached to a glass plate via the adhesive layer, the glass plate was heated at 180 ℃ for 10 minutes, then the release film was peeled off, the release film was attached to the glass plate, aging treatment was performed at 60 ℃ and 90% RH for 10 days in a state where the adhesive layer was sandwiched between 2 glass plates, then foreign matters generated in the adhesive layer were examined under an optical microscope, for the examination, 12 areas of 100mm × 100mm were selected from arbitrary portions of the sample, the number of foreign matters having a size of 2 μm or more was counted, and the total number of foreign matters in 10 examination ranges was determined on the basis of the following criteria except for 2 having the largest number of foreign matters among all 12 examination ranges,

a: foreign matter was not visible.

2. The release film of claim 1, wherein:

the polyester film layer constituting the surface of the polyester film which is in contact with the primer layer is a layer having a thickness of 2 μm or more and comprising 50% by weight or more of polyester having an oligomer content of 0.7% by weight or less.

3. The release film of claim 1 or 2, wherein:

the orientation main axis direction of the biaxially oriented polyester film is 12 degrees or less.