JP2012137568A - Release polyester film for polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a release film which facilitates detection of failure during inspection, which suppresses dependency on a releasing speed to the minimum when the film is used for optical use, for example, a touch panel, a liquid crystal polarizing plate and a retardation plate, and which solves problems relating to productivity, cost or the like.SOLUTION: The release polyester film for a polarizing plate comprises a polyester film having a silicone-based release layer containing a silicone resin having an alkenyl group and an alkyl group as functional groups, a low molecular weight silicone compound having a molecular weight of 1000 or less, and a platinum-based catalyst. The release layer shows a low-speed peeling force of 10 to 20 mN/cm in a 300 mm/min speed range, and a high-speed peeling force in a 10000 mm/min speed range as 2.5 times or less as the low-speed peeling force. The release film shows a MOR (molecular orientation ratio) value of 1.5 to 3.0.

Description

  The present invention relates to a polyester film for polarizing plates suitable for optical applications.

  In recent years, there has been a demand for a film having a low peel strength in a polarizing plate application or a substrateless double-sided PSA sheet. In the case of using such a release film having a low peel force for adhesive processing, it is possible to process in a high speed range to some extent from the workability in production, but of course to achieve the first low peel force. However, it is very difficult to reduce the fluctuation of the peeling force as much as possible, that is, to reduce the dependence on the peeling speed even if the processing speed is increased while achieving this. If the peeling speed dependency is large, the peeling force becomes large in the peeling process and the adhesive is peeled off together, resulting in problems in workability and productivity.

  In addition, when such a release film having a light peeling force is used with a polarizing plate attached, an inspection by a crossed Nicols method may be performed. In order to facilitate the detection of defects such as foreign matters in the release film bonded during this inspection, proposals have been made to reduce the inclination of the orientation main axis of the biaxially oriented polyester film used for the release film (for example, Patent Documents). 1).

  In the release film for polarizing plates, not only foreign matters adhering to the outside but also foreign matters inside are inspected together with the pressure-sensitive adhesive. Therefore, defect management of foreign matters and the like has become more important than ever. As for the above-described defect detection, when a release polyester film is used for optical applications such as a polarizing plate base material, an optical inspection for finding foreign matter or the like may be performed while the polarizing plate is attached. Therefore, the prescription which enables a polarizing plate test | inspection is needed for the original fabric.

JP 2009-220296 A JP 2003-231214 A JP 2002-361737 A JP 2001-301024 A JP 2009-220296 A JP 2010-13561 A Japanese Patent Laid-Open No. 10-158519

  The present invention has been made in view of the above circumstances, and its solution is to easily detect defects at the time of inspection and is used for optical applications such as touch panels, liquid crystal deflecting plates, phase difference plates, and the like. In order to solve such problems, a release polyester film for polarizing plate having excellent polarization inspection property is provided.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above problem can be easily solved by a polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is a polyester film having a silicone resin release layer containing a silicone resin having an alkenyl group and an alkyl group as a functional group, a low molecular weight silicone compound having a molecular weight of 1000 or less, and a platinum catalyst, The release layer has a low-speed peeling force in the range of 10 to 20 mN / cm at a speed of 300 mm / min, and a high-speed peeling force in the speed range of 10,000 mm / min is 2.5 times or less of the low-speed peeling force. And the release film has a MOR value of 1.5 to 3.0.

  According to the present invention, the release polyester dependency is small, and furthermore, a release polyester film excellent in polarization inspection property can be provided, so that its industrial value is high.

  The polyester film referred to in the present invention is a film obtained by stretching a sheet melt-extruded from an extrusion die according to a so-called extrusion method.

The polyester constituting the film refers to a polymer containing an ester group obtained by polycondensation from dicarboxylic acid and diol or from hydroxycarboxylic acid.
Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and diols include ethylene glycol and 1,4-butane. Examples include diol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and the like, and examples of hydroxycarboxylic acid include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. be able to. Typical examples of such a polymer include polyethylene terephthalate and polyethylene-2,6-naphthalate.

  In the film of the present invention, it is preferable to blend particles mainly for the purpose of imparting slipperiness and preventing the occurrence of scratches in each step. 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, heat-resistant organic particles as 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, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  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. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.1-2 micrometers. When the average particle size is less than 0.01 μm, the slipperiness may not be sufficiently imparted. On the other hand, when the thickness exceeds 3 μm, transparency may be lowered due to the aggregate of the particles when the film is formed, and it is easy to cause breakage, which causes a problem in terms of productivity. There is.

  Furthermore, the content of particles in the polyester 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 a case.

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

  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.

  Although the thickness of the polyester film in this invention will not be specifically limited if it is a range which can be formed into a film as a film, Usually, 10-350 micrometers, Preferably it is the range of 15-100 micrometers.

  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 preferable 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 is 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 90 to 140 ° C., preferably 95 to 120 ° 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 90 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.

  For the production of the polyester film of the present invention, a simultaneous biaxial stretching method can also be employed. 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 90 to 140 ° C., preferably 80 to 110 ° C., and the stretching ratio is as follows. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. 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.

  Although the method in particular of forming a coating layer on the surface of a polyester film is not restrict | limited, The method of apply | coating a coating liquid in the process of manufacturing a polyester film is employ | adopted suitably. Specifically, a method of applying and drying a coating solution on the surface of an unstretched sheet, a method of applying and drying a coating solution on the surface of a uniaxially stretched film, and a method of applying and drying a coating solution on the surface of a biaxially stretched film Etc. Among these, it is economical to apply a coating solution to the surface of an unstretched film or a uniaxially stretched film, and then simultaneously dry and cure the coating layer in the process of heat treatment on the film. Moreover, as a method for forming the coating layer, a method in which some of the above-described coating methods are used in combination can be adopted as necessary. Specifically, a method of applying a first layer on the surface of an unstretched sheet and drying, then stretching in a uniaxial direction, and then applying and drying a second layer can be used. Use the reverse roll coater, gravure coater, rod coater, air doctor coater, etc. shown in “Coating Method” by Yuji Harasaki, Tsuji Shoten, published in 1979, as a method of applying the coating solution to the surface of the polyester film. Can do.

  The coating solution used in the present invention is usually preferably adjusted with water as the main medium from the viewpoint of safety and hygiene. As long as water is the main medium, a small amount of an organic solvent may be contained for the purpose of improving the dispersion in water or improving the film forming performance. The organic solvent is preferably used as long as it dissolves in water when mixed with water, which is the main medium. Alternatively, it may be used in a state where it does not dissolve in water. The organic solvent may be used alone or in combination of two or more as necessary.

  The release layer formed in one outermost layer of the polyester film obtained in the present invention is not particularly limited as long as it contains a material having releasability. Among them, the one containing a curable silicone resin is preferable because the releasability is improved. 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 ray curable type, an electron beam curable type, and a solventless type can be used.

  Examples of the silicone resin having an alkenyl group and an alkyl group as functional groups used in the present invention include the following. First, a curable silicone resin containing an alkenyl group is a diorganopolysiloxane having a trimethylsiloxy group-blocked dimethylsiloxane / methylhexenylsiloxane copolymer (96 mol% dimethylsiloxane unit, 4 mol% methylhexenylsiloxane unit). , Dimethylvinylsiloxy group-blocked dimethylsiloxane / methylhexenylsiloxane copolymer (97 mol% dimethylsiloxane unit, 3 mol% methylhexenylsiloxane unit), dimethylsiloxane / methylhexenyl blocked with dimethylhexenylsiloxy group blocked at both ends of the molecular chain Siloxane copolymers (95 mol% of dimethylsiloxane units and 5 mol% of methylhexenylsiloxane units) can be mentioned. Genpolysiloxanes include trimethylsiloxy group-capped methylhydrogen polysiloxane with both molecular chains, trimethylsiloxy group-capped dimethylsiloxane / methylhydrogensiloxane copolymer with both molecular chains, and dimethylhydrogensiloxy group-capped methylhydro with molecular chains. Genpolysiloxane, dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer having both molecular chain ends.

Examples of the low molecular weight silicone compound having a molecular weight of 1000 or less used in the present invention include the following. That is, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and the like can be mentioned. In addition to the former low molecular weight cyclic siloxane, a molecular chain both ends trimethylsiloxy group-capped dimethylsiloxane oligomer; a molecular chain both ends dimethylhydroxysiloxy group-capped dimethylsiloxane oligomer and the like may be mixed as necessary. These low-molecular cyclic siloxanes are preferably contained in the silicone resin as a migration component in an amount of 0.1 to 5.0% by weight.
The desired light release can be achieved by the presence of low molecular components such as cyclic siloxane.

  As mentioned above, specific examples of silicone resin coatings include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, and X-62-2422 manufactured by Shin-Etsu Chemical Co., Ltd. , X-62-2461, DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, manufactured by Dow Corning Asia Co., Ltd., YSR-3022, TPR-6700, manufactured by Toshiba Silicone Co., Ltd. TPR-6720, TPR-6721, Toray Dow Corning Co., Ltd. LTC300B, LTC303E, LTC310, LTC314, SRX357, BY24-749, SD7333, BY24-179, SP7015, SP7259, SD7220, SD7226, SD7229, etc. . Further, a release control agent may be used in combination to adjust the release property of the release layer. Further, as described above, a silane compound having an amino group may be added to the release layer.

In the present invention, as a method for providing a release layer on the polyester film, a conventionally known coating method such as reverse roll coating, gravure coating, bar coating, doctor blade coating, or the like can be used. The application amount of the release layer in the present invention is usually in the range of 0.01 to 1 g / m ² .

  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, and the polyester film may be subjected to corona treatment, plasma treatment, etc. A surface treatment may be applied.

  Moreover, drying and / or curing (thermal curing, ionizing radiation curing, etc.) of the coating film of the pressure-sensitive adhesive layer or the release layer can be performed individually or simultaneously. When performing simultaneously, it is preferable to carry out at the temperature of 80 degreeC or more. The drying and curing conditions are preferably 80 ° C. or higher and 10 seconds or longer. When the drying temperature is less than 80 ° C. or the curing time is less than 10 seconds, the coating film is not completely cured, and the coating film tends to fall off, which is not preferable.

  In the polyester film in the present invention, a platinum-based catalyst that promotes an addition-type reaction is used to make the release layer clean and strong. As this component, chloroplatinic acid, alcohol solution of chloroplatinic acid, a complex of chloroplatinic acid and olefin, a platinum compound such as a complex of chloroplatinic acid and alkenylsiloxane, platinum black, platinum-supported silica, platinum-supported activated carbon Is exemplified. The platinum-based catalyst content in the release layer is usually 0.3 to 3.0% by weight, preferably 0.5 to 2.0% by weight. When the platinum-based catalyst content in the release layer is lower than 0.3% by weight, there may be problems such as deterioration of the surface condition due to insufficient peeling force and insufficient curing reaction in the coating layer. On the other hand, when the platinum-based catalyst content in the release layer exceeds 3.0% by weight, the cost is increased, and the process becomes defective due to increased reactivity and generation of gel foreign matter. Sometimes.

  In addition, since the addition-type reaction is very reactive, acetylene alcohol may be added as an unreactive inhibitor in some cases. The component is an organic compound having a carbon-carbon triple bond and a hydroxyl group, and preferably 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol and phenylbuty It is a compound selected from the group consisting of nor.

  In the present invention, the peeling force refers to a double-sided pressure-sensitive adhesive tape (“No. 31B” manufactured by Nitto Denko) attached to the release layer surface and left at room temperature for 1 hour, and then the substrate film and the peeling angle of 180 °. The value measured with a tensile tester when the tape is peeled off at the tensile speed. The method for adjusting the specific peeling force in the present invention can be achieved by selecting the composition in the release layer, but other means can also be adopted, mainly the type of release agent for the silicone release layer. Is preferably changed according to the desired peeling force, and furthermore, since the peeling force largely depends on the application amount of the release agent to be used, a method of adjusting the application amount of the release agent is more preferable.

  The value of the peeling force of the release layer in the present invention is in the range of 10 to 20 mN / cm of the low speed peeling force in the 300 mm / min speed range. When the peeling force is less than 10 mN / cm, the peeling force becomes too light, and the problem of peeling easily occurs even in a scene where it is not necessary to peel off. When the peel force exceeds 20 mN / cm, the difference in peel force between the release film with the larger peel force becomes smaller, causing problems in the peel process, and the selection range of the release film with the greater peel force. There are problems such as narrowing.

  Furthermore, it is necessary that the high speed peeling force in the 10,000 mm / min speed range in consideration of workability is 2.5 times or less of the above low speed peeling force. When the ratio of the peeling force is larger than 2.5 times, the difference in peeling force from the release film having a larger peeling force becomes small, and peeling cannot be performed well in the peeling process, or the whole adhesive is peeled off. Cause a malfunction.

  In the release polyester film for polarizing plate of the present invention, the MOR_C value obtained by measuring the release film with a microwave molecular orientation meter can be reduced in order to reduce the occurrence of foreign matter and light interference colors in the optical inspection of the process. Very important.

  The MOR_C value of the release film of the present invention is 1.5 to 3.0, preferably 1.8 to 2.7, and more preferably 2.1 to 2.4. When the MOR_C value is larger than 3.0, the release layer is not uniform, and in optical inspection, the light interference color is easily visible. When the MOR_C value is smaller than 1.5, there is a problem that the production yield of the release film itself is deteriorated.

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

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

(2) Measurement of average particle size (d50: μm) 50% integrated (weight basis) in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) The value was defined as the average particle size.

(3) Measurement of transmittance of polyester film According to JIS-K7105, the total light transmittance of the polyester film was measured with an integrating sphere turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. Judgment is based on the following criteria.

(4) Measurement of haze (turbidity) of polyester film According to JIS-K7105, the haze of the film was measured with an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd.

(5) Measurement of heat shrinkage rate of polyester film The polyester film was sampled at an arbitrary length L (cm) in the longitudinal direction (hereinafter abbreviated as MD) and the lateral width direction (hereinafter abbreviated as TD). To do. Subsequently, the sample is heated in an oven at 160 ° C. for 5 minutes, and the sample is taken out of the oven and the length l (cm) is measured. This operation is performed three times, and the average value is adopted as the value of the heat shrinkage rate. The heat shrinkage rate can be calculated by the following formula.
Heat shrinkage (%) = {(L−l) / L} × 100

(6) Measurement of catalyst amount in coating layer Using SAICAS, the sample film was obliquely cut to expose the cross section. Then, the amount of catalyst containing platinum contained in the polyester film coating layer was determined using TOF-SIMS (time-of-flight mass spectrometry mass spectrum).

(7) Measurement of amount of catalyst in coating layer Using SAICAS, the sample film was obliquely cut to expose the cross section. Then, the amount of catalyst containing platinum contained in the polyester film coating layer was determined using TOF-SIMS (time-of-flight mass spectrometry mass spectrum).

(8) Evaluation of peeling force (F) of release film After applying one side of a double-sided adhesive tape (Nitto Denko "No. 31B") to the release layer surface of the sample film, cut into a size of 50 mm x 300 mm After that, the peel strength 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 conditions of a tensile speed of 300 mm / min and further 10,000 mm / min. Judgment is based on the following criteria.

<Peeling force at 300 mm / min>
○: Range of 10 to 20 mN / cm ×: Less than 10 mN / cm or greater than 20 mN / cm

<Comparison of peel force at 10,000 mm / min and peel force at 300 mm / min>
Judgment was made based on the value obtained by the following equation.
(10000 mm / min peeling force (mN / cm)) / (300 mm / min peeling force (mN / cm))
○: 2.5 or less ×: More than 2.5

(9) Evaluation of silicone low molecular weight component transferability of release film (XRF)
A surface on which a release layer of a release film is provided under the following measurement conditions by an FP (Fundamental Parameter Method) method using an X-ray fluorescence measurement apparatus (Shimadzu Corporation, model “XRF-1500”). And the amount of silicon element on 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

(10) Evaluation of silicone low molecular weight component transferability of release film Cut sample film into A4 size, and put 75μm thick biaxially stretched PET film (Mitsubishi Resin Co., Ltd .: Diafoil T100-75) on the release surface. Press for 2 hours under conditions of a temperature of 60 ° C. and a pressure of 1 MPa. A 75 μm-thick film pressed against this release surface is used as a migration evaluation film. Similarly, a 75 μm-thick biaxially stretched PET film (same as above) is pressed against an untreated PET film as a reference film. Adhesive tape (“No. 31B” manufactured by Nitto Denko Corporation) is applied to the pressed surface of each film, then cut to a size of 50 mm × 300 mm, and the peel strength after standing for 1 hour at room temperature. It was measured. The peeling force was “Intesco Model 2001” manufactured by Intesco Co., Ltd., and 180 ° peeling was performed under the condition of a tensile speed of 0.3 (m / min).
Transferability evaluation adhesion rate (%) = (Peeling force of transferability evaluation film / Peeling force of reference film) × 100

(11) Evaluation of air release resistance of release film A sample film is cut to A4 size, and hung on a string passed into a laboratory (non-clean environment) adjusted to room temperature 23 ° C. and humidity 50% RH for 24 hours. An adhesive tape (“No. 31B” manufactured by Nitto Denko Corporation) was applied to the release surface, then cut to a size of 50 mm × 300 mm, and the peel force (F24) after standing for 1 hour at room temperature was measured. . The peeling force was “Intesco Model 2001” manufactured by Intesco Co., Ltd., and 180 ° peeling was performed under the condition of a tensile speed of 0.3 (m / min).

(12) MOR_C value measurement by microwave molecular orientation meter of polyester film Using a microwave molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd., the MOR_C value was determined from the transmission microwave intensity pattern. Judgment is based on the following criteria.
○: 2.0 to 2.5
Δ: 1.5 to 1.9, or 2.6 to 3.0
X: Lower than 1.5% or higher than 3.0

(13) Practical characteristics <Visual inspection property under crossed Nicols>
Taking the polarizing plate inspection into consideration, the width direction of the release film obtained by applying a release agent on the film and having a dryer temperature of 120 ° C. and a line speed of 30 m / min is parallel to the alignment axis of the polarizing film. In this way, the release film is closely attached to the polarizing film through an adhesive to form a polarizing plate, and the polarizing plate for inspection is superimposed on the attached release film so that the orientation axis is orthogonal to the film width direction. White light was irradiated from the plate side, visually observed from a polarizing plate for inspection, and visual inspection property under crossed Nicols was evaluated according to the following criteria. In the measurement, A4 size samples were cut out from a total of three locations in the center and both ends in the width direction of the obtained film.
"Criteria"
○: Inspection is possible without optical interference. Δ: Optical interference is present but inspection is possible. ×: Optical interference is present and inspection is not possible. ○ and Δ are at a level where there is no problem in actual use.

(14) Release characteristics The release characteristics were evaluated from the situation when the release film was peeled off from the laminated film having the adhesive layer.
○: The release film peels 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 at a high speed. Adhesive adheres to the release film and does not peel off well.

(15) Comprehensive evaluation An evaluation is performed in consideration of all film forming properties, productivity, and inspection characteristics. Judgment is based on the following criteria.
○: Even if it is produced, it can be sufficiently supplied as a product. Δ: Productivity is good and the frequency of defects is low. ×: Productivity is poor. Many troubles occur.

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (a)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, adding tetrabutoxy titanate as a catalyst to the reactor, setting the reaction start temperature to 150 ° C., and gradually increasing the reaction temperature as methanol is distilled off. It was 230 degreeC after 3 hours. After 4 hours, the transesterification reaction was substantially completed, and then a polycondensation reaction was performed for 4 hours.
That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.61 due to a change in the stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester (a) having an intrinsic viscosity of 0.61.

<Method for producing polyester (b)>
In the method for producing polyester (a), after adding ethyl acid phosphate, an ethylene glycol slurry of synthetic calcium carbonate particles having an average particle diameter of 0.8 μm was added so that the content of the particles with respect to polyester was 1% by weight. Obtained polyester (b) using the method similar to the manufacturing method of polyester (a). The obtained polyester (b) had an intrinsic viscosity of 0.60.

<Production of polyester (c)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours.
After 4 hours, the transesterification reaction was substantially terminated. Ethyl acid phosphate was added to the reaction mixture, which was then transferred to a polycondensation tank, and 0.04 part of antimony trioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C.
On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.45 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (c). The intrinsic viscosity of this polyester was 0.45.

<Manufacture of polyester (d)>
The intrinsic viscosity of this polyester chip 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 3 hours to obtain a polyester (d) having an intrinsic viscosity of 0.70.

<Manufacture of polyester (e)>
When producing the polyester (d), solid phase polymerization was performed in a solid phase polymerization tank for 5 hours to obtain a polyester (e) having an intrinsic viscosity of 0.80.

Example 1:
<Manufacture of polyester film>
As a raw material for the surface layer, 70% by weight of polyester (e) and 30% by weight of polyester (b) are mixed. As a raw material for the intermediate layer, 84% by weight of polyester (a) and 16% by weight of polyester (b) are mixed. Each was supplied to an extruder with a vent and melt-extruded at 290 ° C., and then cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched sheet. Next, the film was stretched 2.8 times in the longitudinal direction at 100 ° C., then subjected to a preheating step in a tenter and subjected to a transverse stretching of 5.1 times at 120 ° C., followed by heat treatment at 220 ° C. for 10 seconds, 4% relaxation was added in the width direction at 180 ° C. to obtain a master roll having a width of 4000 mm. A slit was made from a position of 1400 mm from the end of the master roll, and the core roll was wound up 1000 m to obtain a polyester film. The total thickness of the obtained film was 38 μm (layer constitution: surface layer 4 μm / intermediate layer 30 μm / surface layer 4 μm).

A release agent composed of release agent composition-A shown below was applied to the obtained polyester film by a reverse gravure coating method so that the coating amount (after drying) was 0.12 g / m ² , and the dryer temperature was 120. A roll-shaped release polyester film was obtained under the conditions of ° C and a line speed of 30 m / min. The obtained release polyester film had a release force of 14 mN / cm at a speed of 300 mm / min and a release force of 32 mN / cm at a speed of 10,000 mm / min.

<Releasing agent composition-A>
Curable silicone resin (LTC303E: manufactured by Toray Dow Corning) 20 parts Octamethylcyclotetrasiloxane (LTC303E: manufactured by Toray Dow Corning) 0.5 parts Addition type platinum catalyst (SRX212: manufactured by Toray Dow Corning) 0.16 Parts (0.8 wt%, 79 ppm)
MEK / toluene / n-heptane mixed solvent (mixing ratio is 1: 1: 1)

  For the obtained polyester film, a polarizing plate was prepared by the following method, and the peeling characteristics were evaluated. The obtained release film was peeled off cleanly, and the phenomenon that the adhesive adhered to the release layer was not observed.

<Manufacture of polarizing plate with release film>
The acrylic adhesive shown below is applied to the polarizing plate so that the thickness after drying is 25 μm, and after passing through a 130 ° C. drying oven in 30 seconds, the release film is bonded, and the adhesive is interposed. Thus, a polarizing plate with a release film in which the release film and the polarizing film were adhered to each other was prepared. The laminating direction of the film was performed so that the width direction of the release film was parallel to the orientation axis of the polarizing film.
Acrylic adhesive coating solution Acrylic adhesive (Olivein BPS429-4: manufactured by Toyo Ink) 100 parts Curing agent (BPS8515: manufactured by Toyo Ink) 3 parts MEK / toluene mixed solvent (mixing ratio is 1: 1) 50 parts

Examples 2-7:
In Example 1, it manufactured similarly to Example 1 except changing the draw ratio at the time of polyester film manufacture, film thickness, and changing the release agent application quantity (after drying), and obtained the polyester film. The obtained results are summarized in Table 1 below.

Comparative Examples 1-6:
In Example 1, it manufactured similarly to Example 1 except changing the draw ratio at the time of polyester film manufacture, film thickness, and changing the release agent application quantity (after drying), and obtained the polyester film. The results obtained are summarized in Table 2 below.

  The polyester film of the present invention is a mold release for polarizing plates in optical applications where demand is great, or in the field of substrate-less double-sided pressure-sensitive adhesive sheets, with good productivity, small peeling rate dependency, and excellent polarization inspection properties. It can be suitably used as a polyester film.

Claims (2)

A polyester film having a silicone release layer containing a silicone resin having an alkenyl group and an alkyl group as a functional group, a low molecular weight silicone compound having a molecular weight of 1,000 or less, and a platinum-based catalyst. The MOR of the release film has a low speed peel force in the range of 10-20 mN / cm in the partial speed range, and a high speed peel force in the speed range of 10,000 mm / minute is 2.5 times or less of the low speed peel force. A release polyester film for a polarizing plate having a value of 1.5 to 3.0. The release polyester film for a polarizing plate according to claim 1, wherein the low molecular weight silicone compound in the silicone release layer is a cyclic siloxane.