JP2010175620A - Release film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect defects and foreign matters with high accuracy in visual inspection by a crossed Nicol method, which is one of inspection methods for polarizing plates, and used in the production process of a release film or a release film Provided is a release film that is difficult to scratch within the process.
SOLUTION: The peak count (Pc) of one film surface of a polyester film having an image clarity value of 90% or more is 20 to 40, has a release layer on the film surface, and has a release layer. A release film for a polarizing plate having a peeling force in the range of 10 to 100 mN / cm.
[Selection figure] None

Description

  INDUSTRIAL APPLICABILITY The present invention is excellent in optical characteristics, which is an important characteristic in films for liquid crystal display applications, etc., and can obtain a high degree of accuracy in defect detection in film inspection, and can be suitably used particularly for polarizing plates. The present invention relates to a release film.

  In recent years, with the rapid spread of mobile phones and personal computers, the demand for liquid crystal displays (LCDs) that are thinner, lighter, consume less power, and have higher image quality than the conventional display CRT is growing significantly. There is also a remarkable growth in the technology for increasing the screen size of LCDs. As an example of increasing the screen size of LCD, recently, LCD is used for large TV applications of, for example, 30 inches or more. An LCD with a large screen is often a bright LCD with a large screen by increasing the luminance of a backlight incorporated in the LCD or incorporating a film for improving the luminance into a liquid crystal unit.

  In such a so-called high-brightness type LCD, small bright spots and scratches present in the display are often problematic, and components such as a polarizing plate, a retardation plate or a retardation polarizing plate incorporated in the display However, there is a problem of minute foreign matter and scratches that have not been a problem with conventional low-brightness LCDs.

  For this reason, it is important to improve the inspection accuracy so that it can be recognized as a defect even if foreign matter is mixed or scratched, while preventing foreign matter and scratching in the manufacturing process. It has become to.

  Conventionally, particles are blended into a film to ensure film slipperiness and winding characteristics. In this case, unless the appropriate particle size and blending amount are satisfied, the desired slipping property cannot be ensured or the winding characteristics are deteriorated, leading to a deterioration in productivity. However, when the particle size and blending amount are within the normally used range, as described above, when used as a release film for a polarizing plate, the added particles become bright spots in the foreign substance inspection process, and are used for inspection. It is a problem to cause trouble.

  For example, as a defect inspection of a polarizing plate, a visual inspection by a crossed Nicols method is generally used. Further, for example, for a polarizing plate used for a large TV application of 40 inches or more, an inspection by an automatic particle inspection device using the crossed Nicols method is used. Is also being implemented. The crossed Nicols method is a method in which two polarizing plates are brought into a quenching state with their orientation principal axes orthogonal to each other, and if there are foreign matters or defects, they appear as bright spots, so that a visual defect inspection can be performed.

  Here, the pressure-sensitive adhesive layer is usually provided on the polarizing plate, and a polyester film provided with a release layer is used as the release film for that purpose. When a product having such a configuration is inspected, a crossed Nicols inspection is performed in a state where a release polyester film is sandwiched between two polarizing plates. In general, when a release polyester film is used for this, foreign matter and defects are difficult to see in the crossed Nicols inspection, and it may be easy to miss them.

  Regarding these, it is disclosed that when a polyester film is sandwiched between two polarizing plates, the inspection value is improved when the retardation value is within a certain range (see Patent Document 1). Even if these are used at a level that requires the above, accuracy may be insufficient if inspection is performed to find defects reliably.

JP 2000-338327 A

  The present invention has been made in view of the above circumstances, and its solution is to release a polyester film that can achieve a high degree of accuracy in the inspection of the polarizing plate by the crossed Nicols method and is not easily damaged in the manufacturing process. To provide a film.

  As a result of intensive studies in view of the above problems, the present inventors have found that a release film suitable for a polarizing plate can be obtained according to a release film comprising a polyester film having a specific configuration without impairing excellent film properties. The present invention has been found out and can be completed.

  That is, the gist of the present invention is that the peak count (Pc) of one film surface of a polyester film having an image clarity value of 90% or more is 20 to 40, has a release layer on the film surface, It exists in the mold release film for polarizing plates characterized by the peeling force of a mold release layer being the range of 10-100 mN / cm.

Hereinafter, the present invention will be described in detail.
The polyester film referred to in the present invention is a film which is melt-extruded from an extrusion die, and is subjected to stretching and heat treatment as necessary after cooling a molten polyester sheet extruded by a so-called extrusion method.

  The polyester constituting the film of the present invention is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The polyester used may be a homopolyester or a copolyester. In the case of a copolyester, it may be a copolymer containing 30 mol% or less of the third component. The dicarboxylic acid component of the copolymerized polyester is selected from isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and oxycarboxylic acid (for example, P-oxybenzoic acid). The glycol component includes one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

  In the polyester obtained by the present invention, a weathering agent, a light-proofing agent, an antistatic agent, a lubricant, a light-shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, and a heat-stabilizing agent as long as the gist of the invention is not impaired You may mix | blend an agent and coloring agents, such as dye and a pigment.

  Examples of the particles to be blended in the film include silicon oxide, alumina, calcium carbonate, kaolin, titanium oxide, and crosslinked polymer fine powder as described in JP-B-59-5216. These particles may be used alone or in combination of two or more components. The content of the film layer to which these particles are added is usually 1% by weight or less, preferably 0.01 to 1% by weight, and more preferably 0.02 to 0.6% by weight. When the content of the particles is small, the film surface is flattened, and in the film production process, the surface is liable to be scratched or the winding properties tend to be inferior. Further, when the content of the particles exceeds 1% by weight, the degree of roughening of the film surface becomes too large, and the transparency may be impaired.

  The average particle size of the particles contained in the polyester film is usually in the range of 0.02 to 5 μm, preferably 0.1 to 3 μm, more preferably 0.2 to 1.8 μm. When the particle size is less than 0.2 μm, the film surface is flattened and the winding properties in the film production process tend to be inferior. When the particle diameter exceeds 5 μm, when used as a polarizing plate release film, it may become a bright spot and hinder foreign matter inspection.

  On the other hand, in order to improve the transparency of the film, when a laminated film of two or more layers is used, a method of blending particles only in the surface layer is also preferably employed. The surface layer in this case is at least one of the front and back layers, and of course, particles can be blended in both the front and back layers.

  In the present invention, it is necessary that the image clarity value of the film by the measurement method described later is 90% or more. When the image clarity value of the film is less than 90%, when used as a polarizing plate release film, the image is distorted during defect inspection of the polarizing plate with transmitted light, which hinders visual inspection and automatic inspection. .

  Moreover, the peak count (Pc) of one film surface needs to be 20-40, More preferably, it is 23-34. Although the mechanism is unknown, when the peak count (Pc) of the film is less than 20, the film surface is easily damaged in the film manufacturing process and the release film manufacturing process. When used as a polarizing plate release film, the amount of scratches on the surface on which the release layer is provided is preferably small, more preferably no scratches. Moreover, when the peak count (Pc) on the film surface exceeds 40, the foreign substance recognition is inferior. When used as a polarizing plate release film, if the foreign matter recognition is poor, the yield of the polarizing plate is reduced.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction. The condensation reaction may proceed. 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 method of blending dried particles and a polyester raw material using a kneading extruder Etc.

  The polyester used in the present invention may be converted into chips after melt polymerization, and further subjected to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and preferably 0.40 to 0.90 dl / g.

  In the present invention, it may be a film having a structure obtained by coextrusion laminating a polyester having a low oligomer content on the surface of at least one side of a layer composed of a polyester having a normal oligomer content. In the polyester film for release film obtained in the present invention, the effect of preventing bright spots due to oligomer precipitation is obtained, which is particularly preferable.

  In the polyester film of the present invention, the variation in the orientation angle in the film plane by the measurement method described later is preferably 3 degrees / 500 mm or less, more preferably 2 degrees / 500 mm or less. When the variation in the orientation angle exceeds 3 degrees / 500 mm, the transmitted light intensity varies depending on the position of the polarizing plate when inspecting the polarizing plate, which may be an obstacle to stable inspection of the polarizing plate.

  The total thickness of the film of the present invention is not particularly limited as long as it can be formed as a film, but is usually in the range of 4 to 100 μm, preferably 9 to 50 μm.

  Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.

  First, the preferable example of the manufacturing method of polyester used by this invention is demonstrated. Here, an example in which polyethylene terephthalate is used as the polyester is shown, but the production conditions differ depending on the polyester used. According to a conventional method, esterification from terephthalic acid and ethylene glycol or transesterification of dimethyl terephthalate and ethylene glycol is carried out, the product is transferred to a polymerization tank, the temperature is increased while reducing the pressure, and finally vacuum is applied. Under heating to 280 ° C., the polymerization reaction proceeds to obtain a polyester.

  The intrinsic viscosity of the polyester used in the present invention is usually in the range of 0.40 to 0.90, preferably 0.45 to 0.80, more preferably 0.50 to 0.70. When the intrinsic viscosity is less than 0.40, the mechanical strength of the film tends to be weakened. When the intrinsic viscosity is more than 0.90, the melt viscosity becomes high, the load on the extruder is increased, and the production cost is increased. Problems may occur.

  Next, for example, the polyester chip obtained as described above and dried by a known method is supplied to a melt-extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. It is preferable to perform ~ 6 times stretching and heat treatment at 150 to 240 ° C for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. Furthermore, it is also possible to perform simultaneous biaxial stretching of the unstretched sheet so that the area magnification is 10 to 40 times.

  The polyester film of the present invention can be subjected to so-called in-line coating for treating the film surface during the stretching step as long as the effects of the present invention are not impaired. Although it is not limited to the following, for example, after the first stage of stretching is completed, before the second stage of stretching, improvement of antistatic property, slipperiness, adhesion, etc., secondary workability improvement, weather resistance, etc. In order to improve the property and surface hardness, a coating treatment with an aqueous solution, an aqueous emulsion, an aqueous slurry, or the like can be performed. Various coatings may be performed by offline coating after film production. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

Next, formation of the release layer will be described.
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 / stretching method (inline coating). Applying so-called off-line coating 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 Corning Corporation 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 in “Coating Method” Tsuji Shoten, Yuji Harasaki, published 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 at 200C, preferably 3 to 40 seconds at 200 to 280C. 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 an 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, in the case of the thick coating beyond 1 g / m ^2, the coating adhesion of the release layer itself, curing and the like may deteriorate.

  In the present invention, when a release layer is provided on the coating layer, the film is temporarily wound after the release layer is provided, and the release layer may be provided again, or after the coating layer is provided, A release 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 peeling force on the surface of the release layer of the release film of the present invention is in the range of 10 to 100 mN / cm, preferably in the range of 10 to 50 mN / cm. When the peel force is less than 10 mN / cm, the peel force becomes too light and easily peels even in the case where it is not necessary to peel. On the other hand, when the peel force exceeds 100 mN / cm, the peel force becomes too heavy and peels. This is not preferable because the pressure-sensitive adhesive is deformed and a problem occurs in a later process or the pressure-sensitive adhesive adheres to the release film side.

  According to the present invention, there is provided a release film used for a release film such as a polarizing plate and a retardation plate, which has as few bright spots as possible, can improve the accuracy of foreign matter inspection, and is less likely to be scratched in the manufacturing process. The industrial value of the present invention is high.

  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 was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measurement was performed at 30 ° C.

(2) Average particle diameter (d50)
The average particle size d50 was defined as the particle size having an integrated volume fraction of 50% in an equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution analyzer (SA-CP3 type) manufactured by Shimadzu Corporation.

(3) Measurement of variation in orientation angle in the film In the width direction of the polyester film, from the center position toward the both ends in the width direction, the sample at every 500 mm and the samples at the extreme ends are cut out, respectively, Oji measuring instruments Using an automatic birefringence meter (KOBRA-21ADH) manufactured by the company, the change in the orientation angle for every 500 mm in the film width direction was determined. When calculating the change in the orientation angle including the positions at the extreme ends, if the distance between the sample positions is less than 500 mm, the change in the orientation angle every 500 mm is calculated by proportional calculation. Subsequently, a 3 m length was cut out in the longitudinal direction of the film, and a sample was cut out from a total of 7 positions every 500 mm (including both ends) in the longitudinal direction from the center in the film width direction, and the orientation angle was determined. Thus, the variation of the orientation angle for every 500 mm in the width direction and the longitudinal direction was obtained, and the maximum variation value was set as the variation of the orientation angle of the film. Further, in the measurement, it is important to make the reference axis of the orientation angle the same in all samples, and the reference axis can be arbitrarily determined.

(4) Measurement of centerline average roughness (Ra) Using a surface roughness measuring machine (SE3500 type) manufactured by Kosaka Laboratory, measurement was performed according to JIS-B0601. The measurement length was 2.5 mm.

(5) Measurement of peak count (Pc) The center line of the film cross-sectional curve obtained at the time of Ra measurement is separated by 0.05 μm at the peak count level (h), above the center line, and above the center line. The total number of counts at a measurement length of 2.5 mm was counted when a peak was counted as one peak when there were two points intersecting with the upper peak count level roughness curve.

(6) Measurement of image clarity value According to JIS-K7105, the image clarity of the film was measured by the transmission method with the image clarity measuring device ICM-1 manufactured by Suga Test Instruments. The value is read with an optical comb of 0.125 mm.

(7) Visual inspection property under reflected light Ten inspectors visually observed the polarizing plate under reflection of a fluorescent lamp, and the visual inspection property under reflected light was evaluated according to the following criteria. In the measurement, an A4 size sample was cut out from a portion corresponding to a position of 50% with respect to the film width in the film width direction from the end of the obtained release film.
<Criteria for visual inspection under reflected light>
(Good inspection) ◎>○>△>×> XX (Inspection failure)
Among the above criteria, those above Δ are levels that can be used without any problem in actual use.

(8) Foreign matter recognition under crossed Nicols When creating a polarizing plate with a release film, 50 metal particles / matter of black metal powder (foreign matter) having a size of 50 μm or more between the adhesive and the polarizing film ² was mixed. A polarizing plate for inspection is superimposed on the polarizing plate release film mixed with the foreign matter thus obtained so that the orientation axis is orthogonal to the width direction of the release film, and white light is irradiated from the polarizing plate side. Ten inspectors visually observed from the polarizing plate for inspection, and evaluated whether the foreign matter mixed between the adhesive and the polarizing film could be found by the following classification. In addition, in the case of a measurement, it evaluated using the film of the center part of the obtained film.
<Foreign substance recognition classification criteria>
(Good foreign body recognition) ◎ ＞ ○ ＞ △ ＞ × (foreign body poor recognition)
Among the above criteria, those above ○ are levels that can be used without any problem in actual use.

(9) Scratch resistance (scratch evaluation)
A sample film slit to 1/2 inch (with the surface on which the release layer is provided as a scraping surface) is rubbed once on a hard chromium fixing pin having a diameter of 6 mm at a tension of 50 g, a winding angle of 135 °, and a running speed of 4 m / sec. About 1000 liters of aluminum was deposited on the rubbing surface of the sample film, and the amount of scratches was visually determined, and divided into the following five stages.
1. 1. The amount of scratches is very large 2. The amount of scratches is large. The middle of the amount of scratches 2, 4 4. 4. Less scratches Not scratched Among these, 3 or more are practically usable areas.

(10) Evaluation of release film peeling force (F) After attaching one side of a double-sided adhesive tape (Nitto Denko “No. 502”) to the surface of the release layer of the sample film, cut into a size of 50 mm × 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 condition of a tensile speed of 300 mm / min.

(11) Release characteristics The release characteristics were evaluated from the situation when the release film was peeled off from the polarizing plate with the release film.
<Releasing properties classification criteria>
○: 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 Among the above criteria, those above Δ are those that can be used without problems in actual use.

Examples 1-3 and Comparative Examples 1-5:
<Manufacture of polyester (A)>
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 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (A). The intrinsic viscosity of this polyester was 0.63.

<Manufacture of 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 the 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 0.63.

<Manufacture of polyester (C)>
In the production method of polyester (B), the additive particles are the same as the production method of polyester (B) except that the synthetic calcium carbonate particles having an average particle diameter of 1.5 μm and the content with respect to the polyester are 1% by weight. Polyester (C) was obtained using the method. The obtained polyester (C) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (D)>
In the method for producing polyester (B), the additive particles are the same as the method for producing polyester (B), except that silica particles having an average particle size of 2.2 μm and the content with respect to polyester are 0.6% by weight. Polyester (C) was obtained using the method. The obtained polyester (C) had an intrinsic viscosity of 0.63.

<Manufacture of film>
A mixed raw material obtained by mixing the polyester (A) chip and the polyester (B), (C), and (D) chips in the proportions shown in Tables 1 and 2 is used as a raw material for the outermost layer (surface layer) and the intermediate layer. Each was supplied to two extruders, 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 the tenter and subjected to transverse stretching of 4.9 times at 120 ° C., followed by heat treatment at 190 ° C. for 10 seconds, 10% relaxation was applied in the width direction at 180 ° C. to obtain a polyester film having a width of 3000 mm. The total thickness of the obtained film was 40 μm, and the thickness of each layer was 4 μm / 32 μm / 4 μm.

  In addition, since the film of Comparative Example 1 had an extremely flat surface shape and deteriorated slipperiness, when the film after stretching and heat treatment was wound into a roll, the film could not be wound well, and the film Scratches occurred on the entire surface, and it was not a product.

<Manufacture of release film>
For films other than Comparative Example 1, a release agent having the following release agent composition was applied by a reverse gravure coating method so that the coating amount (after drying) was 0.1 g / m ² , and the dryer temperature was 120 ° C. A roll-shaped release film was obtained under the conditions of a line speed of 30 m / min.
(Release composition-A)
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

(Release composition-B)
Curing type silicone resin (KS-774: manufactured by Shin-Etsu Chemical) 100 parts Curing agent (PL-4: manufactured by Shin-Etsu Chemical) 10 parts MEK / toluene mixed solvent (mixing ratio is 1: 1) 1500 parts

(Release composition-C)
Curable silicone resin (KS-723A: manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts Curable silicone resin (KS-723B: manufactured by Shin-Etsu Chemical Co., Ltd.) 5 parts Curing agent (PS-3: manufactured by Shin-Etsu Chemical Co., Ltd.) 5 parts MEK / toluene mixed solvent (mixed) The ratio is 1: 1) 1500 parts

<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 was produced. The direction of laminating the films 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

* The film of Comparative Example 1 had an extremely large amount of scratches, and the testability could not be determined.

  The film of the present invention can achieve a high degree of accuracy in various inspection methods for polarizing plates, and can be suitably used as a release film that is less susceptible to scratches in the manufacturing process.

Claims (1)

The peak count (Pc) of one film surface of the polyester film having an image clarity value of 90% or more is 20 to 40, has a release layer on the film surface, and the release force of the release layer is 10 A release film for a polarizing plate, which is in a range of ˜100 mN / cm.