JP2010169869A - Polyester film for mold releasing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film allowing a worker to detect a defect, foreign matter or the like with high precision in a visual inspection by a crossed Nicol method which is one of inspection methods for polarizing plate and favorably usable as a mold releasing film hardly scratched in a manufacturing process for the mold releasing film and a process by use of the mold releasing film. <P>SOLUTION: The polyester film for the mold releasing film for polarizing plate has a peak count (Pc) on a surface of at least one film of 20 to 40 and a value of image clarity of 90% or more. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention is a polyester film that is an important property in films for liquid crystal display applications, etc., is excellent in optical properties, and can obtain a high degree of accuracy in defect detection in film inspection, particularly a release film for polarizing plates The present invention relates to a polyester film in which scratches are difficult to enter within the production process (within the film production process and within the release film production process) that is preferably used.

  Polyester films represented by polyethylene terephthalate and polyethylene naphthalate have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc. It is used in applications.

  However, as its uses diversify, the processing conditions and usage conditions of the film diversify, and when used as a release film for polarizing plates, the particle component in the release film becomes a bright spot when inspecting foreign matter, When inspection accuracy decreases, scratches on the release film cause adhesive transfer to the polarizing plate, and if there are scratches on the release film, the surrounding area is compared with other areas when heat-treated As a result, more oligomers are precipitated.

  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, the particles in the polyester film are usually used to ensure the slipperiness and winding characteristics of the film, and the desired slipperiness cannot be ensured unless an appropriate particle size and blending amount are satisfied. Or the winding characteristics deteriorate, and as a result, the productivity deteriorates. 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, which hinders inspection. Is a problem.

  For example, a visual inspection by the crossed Nicols method is common as a defect inspection of the polarizing plate. Further, for example, in a polarizing plate used for a large TV application of 40 inches or more, an automatic particle inspection device using the crossed Nicols method is used. Inspection is also being carried out. 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, when a polyester film is sandwiched between two polarizing plates, an inspection property is improved when the retardation value is within a certain range (see Patent Document 1). Even if these are used at a level where quality is required, accuracy may be insufficient when inspection is performed to find defects reliably.

JP 2000-338327 A

  The present invention has been made in view of the above circumstances, and a solution to the problem is to provide a polyester film for a release film that can achieve a high degree of accuracy in the inspection of a polarizing plate by the crossed Nicols method and is difficult to be scratched in the manufacturing process. It is to provide.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems 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 for a release film for a polarizing plate, wherein the peak count (Pc) of at least one film surface is 20 to 40 and the image clarity value is 90% or more. Exist.

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.

  If the polyester of the present invention is within the range not impairing the gist of the present invention, the weather resistance agent, light resistance agent, antistatic agent, lubricant, light shielding agent, antioxidant, fluorescent whitening agent, matting agent, heat stabilizer , And coloring agents such as dyes and pigments may be blended.

  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 in the polyester film is usually 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. There is a fear.

  Further, the peak count (Pc) on the surface of at least one of the films needs to be in the range of 20 to 40, and more preferably in the range of 23 to 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) of a film exceeds 40, foreign material 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 after the end of the ester exchange reaction and before the start of the polycondensation reaction. The polycondensation 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 more 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.

  The polyester film in the present invention preferably has a variation in orientation angle of 3 degrees / 500 mm or less, more preferably 2 degrees / 500 mm or less, according to a measurement method described later. 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 a so-called in-line coating for treating the film surface during the stretching step as long as it does not exceed the gist of the present invention. 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.

  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.

  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.

  According to the present invention, there is provided a polyester film that is used for a release film such as a polarizing plate and a retardation plate, has as few luminescent spots as possible, can improve foreign matter inspection accuracy, and is hardly 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 under reflected light 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical), 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical), methyl ethyl ketone (MEK) / A release agent comprising 2200 parts of a toluene mixed solvent system was applied to the film so that the coating amount was 0.1 g / mm ² and dried at 170 ° C. for 10 seconds to obtain a release film. The release film is in close contact with the polarizing film via an adhesive so that the width direction of the release film is parallel to the orientation axis of the polarizing film, and a polarizing plate is used. Each member visually observed and evaluated the visual inspection property under reflected light according to the following criteria. In the measurement, an A4 size sample was cut out from a portion corresponding to a position corresponding to 50% of the film width in the film width direction from the end of the obtained polyester 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 substance recognition under crossed Nicols 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical), 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical), methyl ethyl ketone (MEK) / After applying a release agent comprising 2200 parts of a toluene mixed solvent system to one side of a polyester so that the coating amount is 0.1 g / mm ² and drying at 170 ° C. for 10 seconds to obtain a release film The release film was adhered to the polarizing film through a known acrylic pressure-sensitive adhesive so that the width direction of the release film was parallel to the orientation axis of the polarizing film, thereby producing a polarizing plate with the release film. Here, when the polarizing plate was prepared, black metal powder (foreign matter) having a size of 50 μm or more was mixed between the pressure-sensitive adhesive and the polarizing film so as to be 50 / m ² . 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. The amount of scratches is extremely large. 2. The amount of scratches is large. The middle of the amount of scratches 2, 4 4. 4. The amount of scratches is small. Not scratched Among these, 3 or more are areas that can be used practically.

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 raw material for the outermost layer (surface layer) and intermediate layer obtained by mixing the polyester (A) chip and the polyester (B), (C), (D) chip in the proportions shown in Tables 1 and 2 below. 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 was extremely flat in surface shape and deteriorated in 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 the product was not realized.

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

Claims (1)

A polyester film for a release film for a polarizing plate, wherein the peak count (Pc) of at least one film surface is 20 to 40 and the image clarity value is 90% or more.