JP5420454B2 - Release film for polarizing plate - Google Patents

Description

  The present invention relates to a release film for a polarizing plate used in a liquid crystal display (hereinafter, sometimes abbreviated as LCD) that has seen remarkable growth in recent years.

  The liquid crystal display device is generally configured by laminating a polarizing plate, a liquid crystal cell, and a polarizing plate from the backlight side. Furthermore, various compensation plates such as a phase difference plate are inserted for the purpose of improving the display mode and the viewing angle. The lamination of the polarizing plate and the retardation plate is usually performed by bonding a polarizing plate with an adhesive layer or a retardation plate with an adhesive layer to an object.

  The polarizing plate has a structure in which a polarizing film is sandwiched with triacetyl cellulose, and usually has a pressure-sensitive adhesive layer for bonding on one side. In addition, since triacetyl cellulose in the polarizing plate is inferior in scratch resistance and moisture resistance, a surface protective film is provided on both sides to prevent damage, moisture, or adhesion of dust during handling or the manufacturing process of the liquid crystal display device. It is done. A surface protective film (protective film) in which a pressure-sensitive adhesive layer is laminated is used on the side opposite to the pressure-sensitive adhesive layer side of the polarizing plate, and a release film in which a release layer is laminated on the pressure-sensitive adhesive layer side (hereinafter referred to as “the protective film”). Unless otherwise specified, the polarizing plate means a surface protective film and a release film disposed on both sides).

  A polarizing plate having a surface protective film and a release film on both sides is usually processed in a roll state, then cut into a sheet state, stacked in units of several tens of sheets, packed, and supplied to a panel manufacturer. The panel manufacturer has a process of peeling the release film from the polarizing plate and bonding it to the liquid crystal cell via an adhesive. In this process, it is desired from the viewpoint of improving productivity to shorten the time required for bonding as much as possible. Yes.

  Usually, the polarizing plates are taken out one by one from the stacked packaging state using a suction device and transferred to the bonding step. The suction device is composed of a suction cup and a shaft that sticks to the release film side of the polarizing plate, and has a mechanism that moves up and down in the thickness direction of the polarizing plate. The polarizing plate is taken out and transferred one by one. The transferred polarizing plate is set on a base having a hole (hereinafter referred to as a polarizing plate setting base) and fixed to the laminating machine by suction from the hole portion. Thereafter, the release film is peeled off, and a polarizing plate is bonded to the liquid crystal cell.

  If two polarizing plates are removed from the stacked polarizing plate, the polarizing plate is peeled off in the subsequent process of peeling off the release film, and the adhesive is not exposed. This causes a problem that the polarizing plate cannot be pasted together, and the laminating machine stops. This greatly increases production loss. In order to prevent this problem, it is important that the polarizing plates are taken out one by one. If the polarizing plates are not curled, the ease of peeling between the stacked polarizing plates will not be stable, and it will be impossible to remove the polarizing plates one by one only by the vertical movement of the suction device. .

  In addition, if the amount of curl and the direction of curl of the polarizing plates are not aligned, there may be a deviation in the positional relationship with the suction device when the polarizing plates are taken out from the stacked polarizing plates one by one. For this reason, the positional relationship between the polarizing plate set base and the polarizing plate is shifted, and adjustment may take time. Furthermore, if the surface of the polarizing plate curled inward is the release film surface or its opposite surface, the suction force is adjusted for each polarizing plate when fixing the polarizing plate to the polarizing plate set base. In some cases, adjustment time may be required, and the bonding production speed decreases.

  As a method of adjusting the curl of the polarizing plate, a method of applying a tension to the release film laminated on the pressure-sensitive adhesive layer side of the polarizing plate and bonding it to the polarizing plate has been reported. A flatness defect such as wrinkles may occur in the mold film. Planarity defects such as wrinkles may cause air bubbles to bite into the pressure-sensitive adhesive surface, and are preferably as small and stable as possible.

  Furthermore, the production amount of release films for liquid crystal polarizing plates has been rapidly increased with the remarkable growth of the LCD market in recent years. In addition, due to the demand for stabilization of panel manufacturers' production, quality is becoming stricter year by year, and efforts are being made to prevent problems such as contamination of foreign substances in the polarizing plate from the polarizing plate manufacturer. In such a background, the release film based on a polyester film has optical characteristics that do not hinder the visual inspection by the general crossed Nicols method as a defect inspection such as contamination of the polarizing plate. Often requested.

JP 2005-49597 A Japanese Patent Publication No. 56-53745 Japanese Patent No. 3570546 Japanese Patent Laid-Open No. 8-294948

  The present invention is intended to solve such problems, the solution is excellent in the handling of the sheet state, visual inspection by the general cross Nicol method as a defect inspection such as contamination of the polarizing plate It is an object of the present invention to provide a film having optical characteristics that do not become an obstacle.

  As a result of intensive studies to solve the above-mentioned problems, 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 a laminated structure composed of at least two or more polyester layers, the intrinsic viscosity difference between the polyester layers constituting both outermost layers is 0.1 to 0.4 dl / g , and the intrinsic viscosity Having a release layer on the surface of the lower polyester layer, and the absolute value of the difference in shrinkage between the film length direction after heat treatment at 160 ° C. for 5 minutes and the direction perpendicular thereto is 0.5% or more. It exists in the release film for polarizing plates characterized.

  According to the polyester film of the present invention, it is possible to obtain a polarizing plate that is excellent in handling in a sheet state, can have a great effect on productivity improvement of a liquid crystal display device, and a visual inspection of the polarizing plate by the crossed Nicols method. Can be provided without impairing the productivity of the polyester film that does not impair the film, and its industrial value is high.

Hereinafter, the present invention will be described in detail.
The polyester film which is the base material of the release film in the present invention needs to have a laminate structure of at least two layers. As long as the gist of the present invention is not exceeded, the number of layers may be three or more, and is not particularly limited. When the polyester film is a single layer, the release film is not curled after being subjected to a heat treatment such as adhesive processing, and thus the effects of the present invention cannot be obtained.

The polyester film which is the substrate of the release film in the present invention has an intrinsic viscosity (unit is dl / g, hereinafter omitted) and is usually 0.4 to 1.0, and constitutes both outermost layers. The intrinsic viscosity difference of the layer is required to be 0.1 to 0.4, preferably 0.1 to 0.3, and more preferably 0.15 to 0.25. When the intrinsic viscosity of the polyester film is lower than 0.4, the polyester film may not be stably stretched. On the other hand, if it is higher than 1.0, in order to obtain a high intrinsic viscosity, the polymerization time of the polyester as the raw material becomes longer, and the unit price of the raw material increases. When the difference in intrinsic viscosity between the two surfaces is smaller than 0.1, when the release film is subjected to adhesive processing and attached to the polarizing plate, the curl of the release film is too small and the polarizing plate cannot be curled in the same direction. On the other hand, if the difference between the intrinsic viscosities on both sides is larger than 0.4, the release film is not preferable because it can not be successfully attached to the polarizing plate because the curl amount becomes too large due to the heat amount during the adhesive processing.

  The absolute value of the difference in shrinkage between the film longitudinal direction (MD) and the direction orthogonal to it (TD) after heat-treating the release film in the present invention at 160 ° C. for 5 minutes must be 0.5% or more. is there. More preferably, it is 1.0% or more. If it is less than 0.5%, it is not clear whether the direction of curl of the release film is along MD or TD, so the direction of curl of the polarizing plate is not stable and is not preferable. Further, the upper limit of the shrinkage difference is not particularly limited as long as it is 0.5% or more. If it exceeds 2.5%, the relaxation by the rail width reduction, which is generally used as a shrinkage rate control method, is too large, so the film is loosened, and the film is rubbed and scratched by the transverse stretcher (tenter). It may happen.

  Further, in the heat shrinkage ratio of the film MD and TD when the polyester film which is the substrate of the release film in the present invention is heat-treated at 160 ° C. for 5 minutes, the heat shrinkage ratio in the large direction is 1.5% or more. Is preferred. When the heat shrinkage is 1.5% or less, the curl amount of the release film after the adhesive processing is small, and the curl amount of the polarizing plate may be only a slight amount.

  The polyester used for the 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. Typical polyester includes polyethylene terephthalate and the like. On the other hand, the dicarboxylic acid component of the copolyester includes isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxybenzoic acid, etc.), etc. 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, 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.

  It is preferable to mix | blend particle | grains in the polyester layer which comprises the polyester film of this invention for the main purpose of provision of 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 manufacturing process of the film raw material.

  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 0.05-5 micrometers normally, Preferably it is the range of 0.05-3 micrometers. If the average particle size is less than 0.05 μm, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, if it exceeds 5 μm, the surface roughness of the film becomes too rough and Problems may occur when various surface functional layers are applied in the process.

  Further, the content of particles 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 may be insufficient. On the other hand, when the content exceeds 5% by weight, the transparency of the film is insufficient. There is.

  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 of producing the polymer constituting each layer.

  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 release film of the present invention is not particularly limited as long as it can be formed as a film and can be processed as a release film, but is usually 10 to 100 μm, preferably 15 to 50 μm. Range. When the film thickness is less than 10 μm, the film is not stiff. In addition, when the film thickness exceeds 100 μm, the curling of the film becomes too strong, and curling occurs when the release layer is processed or when the film is formed, which makes handling difficult. is there.

  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.

  That is, 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. Next, the film is stretched in the direction perpendicular to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. is there. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under 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.

  In the present invention, the simultaneous biaxial stretching method can be adopted for the production of the polyester film constituting the release film. 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 stretch ratio. As an area magnification, it 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, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  In the release film of the present invention, the inclination of the orientation main axis is preferably 15 degrees or less, and more preferably 12 degrees or less. Here, the orientation angle is the inclination of the main axis with respect to the film width direction or the vertical direction. When the release film of the present invention is used for a polarizing plate, the direction of vertical polarization of the polarizing plate coincides with the longitudinal direction of the polyester film. In the step of inspecting it by the crossed Nicol method, in order to obtain crossed Nicol, that is, a polarizing plate for inspection is installed in the vertical direction. Therefore, the polarization direction of the polyester film is the longitudinal direction and the width direction perpendicular thereto. In the inspection process, the angle between the polarization direction and the orientation main axis is set to a specific range, so that the accuracy can be maintained at a high level. If the orientation angle is greater than 15 degrees, light leakage tends to increase during the crossed Nicols method.

  Furthermore, what is called an in-line coating which processes the film surface during the extending | stretching process of the above-mentioned polyester film can be given. When a coating layer is provided on a polyester film by in-line coating, coating can be performed simultaneously with stretching, and the thickness of the coating layer can be changed by the stretching ratio, so that a film suitable as a polyester film can be produced. .

  Next, formation of the coating layer in the present invention will be described. The coating layer constituting the release film in the present invention may be provided on the polyester film by the above-mentioned in-line coating, or a so-called off-line coating that is applied outside the system on the film once manufactured may be employed. May be used in combination. In-line coating is preferably used because the production of the laminated polyester film can be inexpensively handled.

  Although in-line coating is not limited to the following, for example, in longitudinal biaxial stretching, particularly longitudinal stretching is completed, and coating treatment can be performed before lateral stretching. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with film formation, and the coating layer can be treated at a high temperature, and a film suitable as a polyester film can be produced.

  Next, formation of the release layer in the present invention will be described.

The release layer of the release film of the present invention needs to be provided on the side of the surface having a low intrinsic viscosity of the polyester film serving as the substrate. When a heat treatment is performed on a polyester film having a difference in intrinsic viscosity on both sides, the polyester film curls so that the surface having a higher intrinsic viscosity is wound inside. Since the effect of the present invention is to control the curling of the polarizing plate by curling due to the amount of heat during the adhesive processing of the release film, if the surface on which the release layer is provided is not determined, the curled surface of the polarizing plate will not be stable not good. If the surface to be curled is stable, the surface on which the release layer is provided can be effective even if the surface has a high intrinsic viscosity. In this case, however, the release film should be curled so that the adhesive side is wound inside after the adhesive processing. Therefore, the adhesive is stuck and the release film cannot be attached to the polarizing plate, which is not preferable.
Further, the release layer constituting the release film in the present invention may be provided on the polyester film in the film production process such as the above-described coating and stretching method (in-line coating), and may be provided on the once produced film. So-called off-line coating, which is applied by the above method, may be employed, and any method may be employed. The coating stretching method (in-line coating) is not limited to the following, but for example, in sequential biaxial stretching, the first stage of stretching may be completed and the coating treatment may be performed before the second stage of stretching. it can. When a release layer is provided on a polyester film by a coating and stretching method, the film can be applied simultaneously with stretching, and the thickness of the release layer can be reduced according to the stretching ratio. Can be manufactured.

  Moreover, it is preferable that the release layer which comprises the release film in this invention contains a curable silicone resin in order to make mold release property favorable. A type having a curable silicone resin as a main component may be used, or a modified silicone type by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used.

  As the type of the curable silicone resin, any of the curing reaction types such as an addition type, a condensation type, an ultraviolet curable type, an electron beam curable type, and a solventless type can be used. Specific examples include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X-62-2461, X manufactured by Shin-Etsu Chemical Co., Ltd. -62-1387, KNS-3051, X-62-1496, KNS320A, KNS316, X-62-1574A / B, X-62-7052, X-62-7028A / B, X-62-7619, X-62 -7213, GE Toshiba Silicones Co., Ltd. YSR-3022, TPR-6700, TPR-6720, TPR-6721, TPR6500, TPR6501, UV9300, UV9425, XS56-A2775, XS56-A2982, UV9430, TPR6600, TPR6604, TPR6605, SM3200, SM3030, Toray Da DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, SRX357, SRX211, SD7220, LTC750A, LTC760A, SP7259, BY24-468C, SP7248S, BY24-452, SP7265S, SP7265S , LTC1000M, LTC1050L, SYLOFF7900, SYLOFF7198, SYLOFF22A, and the like. Further, a release control agent may be used in combination to adjust the release property of the release layer.

  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.

In the present invention, the curing conditions for forming the release layer on the polyester film are not particularly limited. For example, when the release layer is provided by a coating stretching method (inline coating), it is usually 170 to 280. The heat treatment may be performed at a temperature of 3 to 40 seconds, preferably 200 to 280 ° C. for 3 to 40 seconds. On the other hand, when providing a release layer by off-line coating, heat treatment is usually performed at 80 to 200 ° C. for 3 to 40 seconds, preferably 100 to 180 ° C. for 3 to 40 seconds. Moreover, you may use together heat processing and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of the coating extending | stretching method (in-line coating) or offline coating. In addition, a conventionally well-known apparatus and energy source can be used as an energy source for hardening by active energy ray irradiation. The coating amount of the release layer from the viewpoint of coating property, usually 0.005~1g / ^{m 2,} preferably in the range from 0.005 to 0.5 / ^{m 2.} If the coating amount is less than 0.005 g / m ² , the coating property may be less stable and it may be difficult to obtain a uniform coating film. On the other hand, when the coating is thicker than 1 g / m ² , the coating layer adhesion and curability of the release layer itself may be lowered.

  In the present invention, when a release layer is provided on the coating layer, the film may be temporarily wound after the coating layer is provided, and the release layer may be provided again. After the coating layer is provided, the release layer is continuously provided. A mold layer may be provided on the coating layer, and any method may be adopted.

  Regarding the release film in the present invention, a coating layer such as an adhesive layer, an antistatic layer and an oligomer precipitation preventing layer may be provided on the surface where the release layer is not provided, as long as the gist of the present invention is not impaired.

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

  The release force of the release film of the present invention is usually 10 to 100 mN / cm, preferably 10 to 50 mN / cm. If the peeling force is less than 10 mN / cm, the peeling force may become too light and may cause a problem of easy peeling even in a scene where it is not necessary to peel off. On the other hand, if it exceeds 100 mN / cm, the peeling force Becomes too heavy, and the pressure-sensitive adhesive may be deformed when it is peeled off, causing problems in the subsequent steps, or the pressure-sensitive adhesive may adhere to the release film side.

  The residual adhesive rate of the release film of the present invention is preferably 80% or more, and more preferably 90% or more. When the residual adhesion rate is less than 80%, the release layer has high transferability, so the release layer is transferred to the anti-coating surface side of the release film wound in a roll state, or processed in the adhesive processing step. Problems such as transfer of the release layer to the transport roll of the machine may occur. Moreover, the adhesive force of the pressure-sensitive adhesive layer in contact with the release surface may be reduced.

  If the polyester film of the present invention is within a range not impairing the effects of the present invention, foreign matters may be removed by a dry cleaning method after longitudinal stretching and / or lateral stretching in the film forming process. Alternatively, it is preferable to remove foreign matters by a dry or wet cleaning method or a combination of both cleaning methods during a slitting operation and a rewinding operation for adjusting the width and length of the polyester film. The wet cleaning method is preferably a method of peeling and removing foreign substances adhering to the film surface by applying ultrasonic vibration to the cleaning liquid and bringing the liquid into contact with the film surface.

  The polyester film of the present invention can be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate as long as the effects of the present invention are not impaired. Further, an ultraviolet absorber, an antioxidant, a surfactant, a pigment, a fluorescent brightening agent, and the like can be mixed.

  When a release layer is installed on the polyester film of the present invention, the material constituting the release layer is not particularly limited as long as it has releasability, and a type mainly composed of a curable silicone resin may be used. Alternatively, a modified silicone type obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used. Among these, when a curable silicone resin is used as a main component, good releasability is sufficient.

  It is preferable to remove foreign matters attached to the film surface by dry or wet cleaning at a stage before installing the release layer and by dry cleaning at a later stage. Furthermore, in the previous stage, dry cleaning is performed, and then ultrasonic cleaning is applied to the cleaning liquid, and the liquid is brought into contact with the film surface to remove the foreign substances using a method of peeling and removing the adhered foreign substances on the film surface. Is preferred.

  Types of curable silicone resins include solvent addition type, solvent condensation type, solvent UV curable type, solventless addition type, solventless condensation type, solventless UV curable type, solventless electron beam curable type, etc. But it can also be used.

  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. In the examples and comparative examples, “parts” means “parts by weight”. 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.
When measuring the difference in intrinsic viscosity between the two surfaces, a sample for measurement was collected from both surfaces of the polyester film, and the measurement was performed. In collecting the sample, a SAICAS (Surface and Interface Cutting Analysis System) apparatus manufactured by Daipura Wintes was used.

(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 heat shrinkage rate A sample is cut out on a strip of 15 mm width × 150 mm length in the longitudinal direction from both ends of the film, heat treated for 5 minutes in a 160 ° C. atmosphere under no tension, and the length of the sample before and after that is measured. Thus, the heat shrinkage rate (%) was calculated by the following formula.
Heat shrinkage rate (%) = [(ab) / a] × 100
In the above formula, a means the sample length before heat treatment, and b means the sample length after heat treatment. Further, the difference in shrinkage rate was calculated so as to be positive by subtracting a small value from a value larger than the measurement results at both ends.

(4) Measurement of orientation angle Using a polarization microscope manufactured by Carl Zeiss, observe the orientation of the polyester film, and how many times the direction of the main orientation axis in the polyester film plane is inclined with respect to the width direction of the polyester film. Measured to obtain an orientation angle. This measurement was carried out at a total of three locations on the center and both ends of the obtained film, and the largest orientation angle value among the three locations was taken as the maximum orientation angle.

(5) Application amount measurement of mold release layer Mold release under the following measurement conditions by FP (Fundamental Parameter Method) method using a fluorescent X-ray measurement apparatus (Shimadzu Corporation, model “XRF-1500”). The amount of silicon element on the surface provided with the release layer and the surface without the release layer was measured, and the difference was taken as the amount of silicon element in the release layer. Next, the coating amount (Si) (g / m ² ) as a unit of —SiO (CH ₃ ) ₂ was calculated using the obtained amount of silicon element.

"Measurement condition"
Spectral crystal: PET (pentaerythritol)
2θ: 108.88 °
Tube current: 95 mA
Tube voltage: 40 kv

(6) Evaluation of residual adhesive rate of release film << residual adhesive strength >>
Nitto Denko (manufactured) no. The 31B adhesive tape is subjected to one reciprocating pressure bonding with a 2 kg rubber roller, and heat-treated at 100 ° C. for 1 hour. Next, the sample film was peeled off from the pressure-bonded sample. The adhesive strength of the 31B pressure-sensitive adhesive tape is measured according to the method of JIS-C-2107 (adhesive strength to stainless steel plate, 180 ° peeling method). This is the residual adhesive strength.
《Basic adhesive strength》
Using the same tape (No. 31B) as in the case of residual adhesive force, an adhesive tape is pressure-bonded to a stainless steel plate according to JIS-C-2107, and measurement is performed in the same manner. The value at this time is defined as the basic adhesive strength. Using these measured values, the residual adhesion rate is determined based on the following equation.
Residual adhesion rate (%) = (residual adhesive force / basic adhesive force) × 100
The measurement is performed at 20 ± 2 ° C. and 65 ± 5% RH.

(7) Evaluation of release force of release film After attaching one side of a double-sided adhesive tape (Nitto Denko "No. 502") to the release layer surface of the sample film, it was cut into a size of 50 mm x 300 mm, The peel force after standing for 1 hour at room temperature 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 the condition of a tensile speed of 300 mm / min.

(8) Practical properties <Curl after bonding with polarizing plate>
Using a polyvinyl alcohol (PVA) film (manufactured by Kuraray Co., Ltd., degree of polymerization 2400), after stretching 3 times in the first bath (iodine, KI aqueous solution-30 ° C.), the second bath (boric acid, KI aqueous solution-55). The polarizer was obtained by stretching the total draw ratio up to 6 times. Then, using a PVA adhesive, two protective sheets made of a triacetyl cellulose (TAC) film having a thickness of 80 μm were bonded to both sides of the polarizer to produce a polarizing plate.
Next, an acrylic pressure-sensitive adhesive (product name: BPS-5127, manufactured by Toyo Ink Co., Ltd.) is applied to the release layer of the release film so that the dry thickness is 25 μm, and the hot air circulation dryer at 100 ° C. is used for 2 minutes. After drying, the sample is bonded to the above polarizing plate. At the time of bonding, the release film and the polarizing plate were bonded together as described in the item of visual inspection under crossed Nicols described later. This sample was allowed to stand at 23 ° C. and 65% RH for 24 hours, then cut into a size of 10 cm × 10 cm, placed on a horizontal plate, and the curled state of the test piece was observed to divide it into the following three ranks to curl. Evaluated.
○: The release film is slightly curled so that it is always inside, and the curl degree is always constant and good. Δ: The release film is always curled so that it is inside. The degree of is too small ×: The direction of curl is not stable and varies from sample to sample. In addition, the release film is curled so as to be inward, but curling along the MD or TD of the release film differs from sample to sample and is not stable. O and Δ are levels at which the effect of the present invention can be expected. . × is an unfavorable level that is likely to cause practical problems.

<Visual inspection under crossed Nicols>
A sample is prepared by bringing the release film into close contact with the polarizing plate via an adhesive so that the width direction of the release film is parallel to the orientation axis of the polarizer. Overlay the polarizing plate for inspection on the release film so that the orientation axis is orthogonal to the film width direction, irradiate white light from the polarizing plate side, and visually observe from the polarizing plate for inspection, The visual inspection property under crossed Nicols was evaluated according to the following criteria.
○: Inspection is possible without light interference Δ: Light interference is present but inspection is possible ×: Inspection is difficult due to light interference ○ and Δ are the preferred levels in practical use.

<Release properties>
The release characteristics were evaluated from the situation when the release film was peeled off from the polarizing plate having the adhesive layer.
○: The release film is peeled off cleanly, and the phenomenon that the adhesive adheres to the release layer is not observed. Δ: The release film peels off, but the adhesive adheres to the release layer when peeled off at a high speed. : Adhesive adheres to the release film, or the adhesive strength decreases due to silicone transfer.

<Productivity>
The productivity of the release film was evaluated from cost, film formation stability, and the like.
○: Appropriate cost and sufficient film-forming stability, so good productivity can be obtained. Δ: Cost is appropriate, but there is a problem with film-forming stability. Not

[Production method of polyester]
(Production method of polyester chip A)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct the transesterification reaction, and it takes about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was terminated, and a polyester A having an intrinsic viscosity of 0.63 was obtained by chipping according to a conventional method.

(Production method of polyester chip B)
When manufacturing the said polyester A, 2500 ppm of amorphous silica with an average primary particle diameter of 3.4 micrometers was added, and the polyester B was obtained.

(Production method of polyester chip C)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct the transesterification reaction, and it takes about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 2 hours, the reaction was completed, and a polyester C having an intrinsic viscosity of 0.45 was obtained by converting into chips according to a conventional method.

(Production method of polyester chip D)
When the polyester C was produced, 2500 ppm of amorphous silica having an average primary particle size of 3.4 μm was added to obtain polyester D.

(Production method of polyester chip E)
The intrinsic viscosity of polyester D was increased by a solid phase polycondensation method. After treatment in a preliminary crystallization tank at 170 ° C. in a nitrogen atmosphere for 0.5 hours, the moisture content becomes 0.005% at a temperature of 200 ° C. using a tower dryer that flows an inert gas. Until dried. Thereafter, it was sent to a solid phase polymerization tank and subjected to solid phase polymerization at 240 ° C. for 4 hours to obtain polyester E having an intrinsic viscosity of 0.79.

(Production method of polyester chip F)
When producing polyester E, solid phase polymerization was carried out in a solid phase polymerization tank for 8 hours to obtain polyester F having an intrinsic viscosity of 0.90.

(Manufacturing method of polyester chip G)
When producing polyester E, solid phase polymerization was carried out in a solid phase polymerization tank for 12 hours to obtain polyester G having an intrinsic viscosity of 1.02.

(Production method of polyester chip H)
Polyester D was dried at 180 ° C. for 4 hours in an inert gas atmosphere, melted at 290 ° C. by a melt extruder, extruded into a strand, cooled with water, cut and pelletized to obtain polyester G. The intrinsic viscosity of polyester G was 0.35.

Example 1:
The polyester A, polyester B and polyester E are each dried in an inert gas atmosphere at 180 ° C. for 4 hours, melted at 290 ° C. by a melt extruder, extruded from a die, and surface temperature using an electrostatic application adhesion method. Was cooled and solidified on a cooling roll set at 40 ° C. to obtain an unstretched sheet. When obtaining an unstretched sheet, polyester A was laminated with an intermediate layer, polyester B on one side, and polyester E on the opposite side. The obtained unstretched sheet was first stretched 2.9 times to MD at 90 ° C. and then led to a tenter, and then subjected to sequential biaxial stretching 5.1 times to TD at 120 ° C. Thereafter, heat treatment was performed at 210 ° C. for 10 seconds, and then 5% relaxation was applied in the width direction at 160 ° C. to obtain a polyester film having a thickness of 38 μm. The laminated thickness of polyester B, polyester A, and polyester E was set to 4.6 μm, 28.8 μm, and 4.6 μm in this order. Properties of the obtained polyester film and stretching conditions are shown in Table 1. Next, a release agent comprising the following release agent composition-1 was applied to the polyester B side of the obtained polyester film by a reverse gravure coating method so that the coating amount (after drying) was 0.1 g / m ² , A roll-shaped release film was obtained under conditions of a dryer temperature of 120 ° C. and a line speed of 30 m / min. Table 1 shows the peel strength and residual adhesion rate of the obtained release film.

<< Releasing Agent Composition-1 >>
Curing type silicone resin (KS-847H: manufactured by Shin-Etsu Chemical) 100 parts Curing agent (PL-50T: manufactured by Shin-Etsu Chemical) 1 part MEK / toluene mixed solvent (mixing ratio is 1: 1) 1500 parts

  Next, in accordance with the method for evaluating the curl after bonding with the polarizing plate in the practical characteristics described above to the release layer of the obtained release film, the adhesive processing and the bonding with the polarizing plate were performed. . The curl state of the obtained sample is shown in Table 1. The release film was curled stably so as to be wound inside, and the handling of the sheet-like polarizing plate was also good. Furthermore, a visual inspection was performed under practical characteristics of crossed Nicols. Since the orientation angle of the release film is sufficiently along TD, there was little light leakage and the inspection was easy. The practical properties are shown in Table 1 below.

Example 2:
A polyester film and a release film were obtained in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 1. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, and the handling of the sheet-like polarizing plate was also good. Furthermore, visual inspection under crossed Nicols was easy to inspect with little light leakage. Table 1 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 3:
A polyester film and a release film were obtained in the same manner as in Example 1 except that polyester F and polyester E were used as the surface layer polyester and a release layer was provided on the polyester E side. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, but only a small amount was curled. The handling of the sheet-like polarizing plate was good. Visual inspection under crossed Nicols was easy to inspect with little light leakage. Table 1 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 4:
A polyester film and a release film were obtained in the same manner as in Example 3 except that polyester B was used instead of polyester E. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, and the handling of the sheet-like polarizing plate was also good. Furthermore, visual inspection under crossed Nicols was easy to inspect with little light leakage. Table 1 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 5:
The stretching conditions were changed as shown in Table 1, and a polyester film and a release film were obtained in the same manner as in Example 1 except that a polyester film was obtained from the tenter end side. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, but only a small amount was curled. The handling of the sheet-like polarizing plate was good. In the visual inspection under crossed Nicols, there was much light leakage, and the inspection was not easy. Table 1 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 6:
In Example 5, a polyester film and a release film were obtained in the same manner as in Example 5 except that a polyester film was obtained from the center of the tenter. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, but only a small amount was curled. The handling of the sheet-like polarizing plate was good. In the visual inspection under crossed Nicols, there was little light leakage and the inspection was easy. However, only about 25% of the tenter width had an orientation angle of 15 degrees or less, and the remaining 75% leaked light, and the inspection was not easy as in Example 5. The stretch conditions, polyester film characteristics, release layer characteristics, and practical characteristics are shown in Table 2 below.

Example 7:
In Example 1, a polyester film was obtained so that each of polyester E and polyester B was 19 μm, and a release film was obtained by providing a release layer on the polyester B side. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, and the handling of the sheet-like polarizing plate was also good. Furthermore, visual inspection under crossed Nicols was easy to inspect with little light leakage. Table 2 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 8:
In Example 7, a polyester film and a release film were obtained in the same manner as in Example 7 except that polyester D was used instead of polyester B. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled stably as if the release film was wound inside, and the handling of the sheet-like polarizing plate was also good. Furthermore, visual inspection under crossed Nicols was easy to inspect with little light leakage. Table 2 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 9:
A polyester film and a release film were obtained in the same manner as in Example 1 except that the stretching conditions were changed as described in Table 3. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curl was curled so that the release film was wound inside, and was stable. There was no problem with the handling of the sheet-like polarizing plate. However, since the relaxation rate in the tenter is too large, the effective width of the product is narrowed and the cost is increased, it is not preferable for production. In the visual inspection under crossed Nicols, there was little light leakage and the inspection was easy. Table 2 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Example 10:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the coating agent composition was changed to the release agent composition-2 shown below.
<< Releasing agent composition-2 >>
Curing type silicone resin (KS-774: manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts Curing agent (PL-4: manufactured by Shin-Etsu Chemical Co., Ltd.) 10 parts MEK / toluene mixed solvent (mixing ratio is 1: 1) 1500 parts Stretching conditions, characteristics of polyester film Table 2 shows the properties and practical properties of the release layer.

Example 11:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the coating agent composition was changed to the release agent composition-3 shown in Table 1 below.
<< Releasing agent composition-3 >>
Curable silicone resin (KS-847H: manufactured by Shin-Etsu Chemical) 100 parts Curing agent (PL-50T: manufactured by Shin-Etsu Chemical) 1 part Polyether-modified silicone oil (KF-351: manufactured by Shin-Etsu Chemical) 8 parts MEK / toluene mixed solvent ( The mixing ratio is 1: 1) 1500 parts The stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics are shown in Table 3 below.

Example 12:
In Example 1, a release film was obtained in the same manner as in Example 1 except that the coating agent composition was changed to the release agent composition-4 shown below.
<< Releasing agent composition-4 >>
Curable silicone resin (KS-723A: manufactured by Shin-Etsu Chemical) 100 parts Curable silicone resin (KS-723B: manufactured by Shin-Etsu Chemical) 5 parts Curing agent (PS-3: manufactured by Shin-Etsu Chemical) 5 parts MEK / toluene mixed solvent (mixed) The ratio is 1: 1) 1500 parts Table 3 shows the stretching conditions, the properties of the polyester film, the properties of the release layer, and the practical properties.

Comparative Example 1:
A polyester film and a release film were obtained in the same manner as in Example 1 except that polyester B was used instead of polyester E in Example 1. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The curling direction was changed depending on the state of the polarizing plate and was not stable, and it was difficult to handle the sheet-like polarizing plate. In the visual inspection under crossed Nicols, there was little light leakage and the inspection was easy. Table 3 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Comparative Example 2:
A polyester film and a release film were obtained in the same manner as in Example 8 except that polyester G was used instead of polyester E in Example 8. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. When pasting to the polarizing plate, the curl of the release film was too large and it was difficult to bond. The curl was curled largely so that the release film was wound inside, and was stable. There was no problem with the handling of the sheet-like polarizing plate. However, the production cost of polyester G is large, which is not preferable for production.
In the visual inspection under crossed Nicols, there was little light leakage and the inspection was easy. Table 3 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Comparative Example 3:
A polyester film and a release film were obtained in the same manner as in Example 1 except that the stretching conditions were changed as described in Table 3. The obtained release film was attached to a polarizing plate in the same manner as in Example 1, and the curling of the polarizing plate was examined. The release film was curled so as to be wound inward, but the curling direction was not stable along the MD of the release film or along the TD. For this reason, it was difficult to handle the sheet-like polarizing plate. In the visual inspection under crossed Nicols, there was little light leakage and the inspection was easy. Table 3 shows the stretching conditions, the characteristics of the polyester film, the characteristics of the release layer, and the practical characteristics.

Comparative Example 4:
In Example 7, an attempt was made to obtain a polyester film using polyester H instead of polyester B. However, the film was broken during stretching, and a polyester film could not be obtained.

  The film of the present invention can be suitably used as a release film for a polarizing plate.

Claims (3)

It is a laminated structure composed of at least two or more polyester layers, the difference in intrinsic viscosity between the polyester layers constituting both outermost layers is 0.1 to 0.4 dl / g , A release layer for a polarizing plate having a release layer, wherein the absolute value of the difference in shrinkage between the film length direction after heat treatment at 160 ° C. for 5 minutes and the direction perpendicular thereto is 0.5% or more the film. The release film for a polarizing plate according to claim 1, wherein the orientation of the orientation main axis is 15 degrees or less. The release film for polarizing plates according to claim 1 or 2, wherein the release layer has a residual adhesion rate of 80% or more and a peel strength in the range of 10 to 100 mN / cm.