JP2003327719A - Polyester film for release film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for a release film which, when used as a release film, e.g. in producing a polarizer, enables a high-accuracy inspection by the cross nicol method. <P>SOLUTION: This polyester film has a slope of orientation main axis of 15° or lower and satisfies inequality (1): 2≤Δp/Δn≤7 (wherein Δp and Δn are respectively defined as Δn=nγ-nα and Δp=(nγ+nβ)/2-nα; when the maximum refractive index in the film plane is nγ; the refractive index in the direction crossing the film plane at right angles is nβ; and the refractive index in the thickness direction is nα). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyester film having excellent optical properties, which are important properties in films for liquid crystal display applications, and more particularly to a polyester film suitable for use as a release film for polarizing plates. Is.

[0002]

2. Description of the Related Art In recent years, with the rapid spread of mobile phones and personal computers, there is a demand for a liquid crystal display (LCD) that is thinner and lighter in weight, consumes less power and has higher image quality than a conventional display such as a CRT. The technology is growing remarkably even in the case of large screen LCDs. However, especially TFT type and ST with large screen
N-type LCDs have a high defect rate in the manufacturing process, and it is necessary to reduce the inclusion of foreign matter as one of the measures to improve them. How to reduce foreign matter in the polarizing plate used for LCDs The issue is how important it is. As a defect inspection such as contamination of a polarizing plate with a foreign substance, a visual inspection by a crossed Nicol method is generally used. In this crossed Nicol method, two polarizing plates are made to have their main axes of orientation orthogonal to each other and a release film is sandwiched between them, and if there is a foreign substance or a defect, it appears as a bright spot, so that a visual defect inspection can be performed. However, the polarizing film to be inspected uses a polyester film having a release layer interposed via an adhesive layer. When the optical anisotropy of the release film is remarkable, the crossed Nicols method is used. There is a problem that it becomes an obstacle to the inspection and it becomes easy to overlook foreign substances and defects.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to solve such a problem, and the problem to be solved is, for example, when the film is used as a release film for producing a polarizing plate, a crossed Nicol method. It is intended to provide a polyester film for a release film, which has excellent properties such that an accurate inspection can be performed in the inspection by

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventors have found that the above-mentioned problems can be easily solved by a polyester film having a specific constitution, and completed the present invention. Came to do.

That is, the gist of the present invention resides in a polyester film for a release film, which is characterized in that the inclination of the orientation main axis is 15 degrees or less and the following formula is satisfied. 2 ≦ Δp / Δn ≦ 7 (where Δp and Δn are the maximum refractive index in the plane of the film, nγ, the refractive index in the direction orthogonal thereto, nβ, and the refractive index in the thickness direction, nα, respectively. , Δn = nγ-nα, Δp
= (Nγ + nβ) / 2-nα respectively)

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The polyester in the present invention refers to a polymer containing an ester group obtained by polycondensation of a dicarboxylic acid and a diol or a hydroxycarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, succinic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2,6-naphthalenedicarboxylic acid, 1,4-
Cyclohexanedicarboxylic acid, etc. as the diol,
Ethylene glycol, 1,3-propanediol, 1,6
-Hexanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol,
Examples of hydroxycarboxylic acids such as polyethylene glycol include p-hydroxybenzoic acid and 6-hydroxy-2.
-Naphthoic acid etc. can be illustrated respectively.

Typical examples of such polymers include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. These polymers may be homopolymers,
Moreover, what copolymerized the 3rd component may be sufficient. As the film of the present invention, a biaxially stretched film is preferably used from the viewpoint of excellent strength and dimensional stability, but an unstretched or at least one stretched polyester film can also be used.

The polyester film in the present invention is
It is necessary that the inclination of the orientation main axis (hereinafter abbreviated as orientation angle) is 15 degrees or less and the following formula is satisfied. In addition,
The orientation angle mentioned here is the inclination of the main axis with respect to the film width direction or the longitudinal direction. 2 ≦ Δp / Δn ≦ 7 (where Δp and Δn are the maximum refractive index in the plane of the film, nγ, the refractive index in the direction orthogonal thereto, nβ, and the refractive index in the thickness direction, nα, respectively. , Δn = nγ-nα, Δp
= (Nγ + nβ) / 2-nα respectively) When the orientation angle is larger than 15 degrees, the light leakage becomes large during the crossed Nicols test, which is not preferable, and when Δp / Δn is less than 2 or greater than 7. However, the light leakage during the crossed Nicols inspection is large, which is not preferable.

Further, the polyester film is heated to 180 ° C.
After heat treatment for 10 minutes, the amount of oligomer extracted from dimethylformamide (hereinafter abbreviated as surface OL amount) is preferably 10 (mg / m ² ) or less, and more preferably 1 (mg / m ² ) or less. Is desirable. Surface O
When the amount of L is more than 10 (mg / m ² ), OL is deposited on the film surface in the heating step when the release layer is installed,
In some cases, the release layer installation step may be contaminated or foreign matter may be mixed into the polarizing plate when the release layer is provided and attached to the polarizing plate. Further, the number of foreign matters having a diameter of 30 μm or more present in the polyester film is preferably 4 pieces / m ² or less, and more preferably 1 piece / m ² or less. If the number of foreign substances in the film is more than 4 / m ² , it is difficult to classify the foreign substances in the polarizing plate during the defect inspection of the polarizing plate, and as a result, it is regarded as a defective product and the yield of the polarizing plate is increased. May cause a decline.

Further, the film of the present invention preferably has ab value measured by transmitted light using a color difference meter within a range of -2.0 to 2.0. When the b value is out of this range, in the release film roll having the release layer provided on the polyester film, the color tone of the end face may be extremely yellow or blue, which may cause a problem in practical use. . Further, the film of the present invention preferably has a heat shrinkage ratio of 4% or less when held in an atmosphere of 180 ° C. for 5 minutes. If the heat shrinkage is greater than 4%,
The flatness of the film may be impaired in the step of providing the release layer and the heat treatment step in the step of attaching the release film to the polarizing plate.

A filler is added to the polyester film of the present invention for the purpose of improving workability,
It is preferable to improve the slipperiness of the film, and as the filler to be added, for example, silica, calcium carbonate,
Inorganic particles such as kaolin, titanium oxide, aluminum oxide, barium sulfate, zeolite, or silicone resin,
Examples thereof include organic particles such as crosslinked polystyrene and acrylic resin, which are mixed alone or in a mixture in the film. In this case, the average particle size, the addition amount, and the particle size distribution of the particles used are not particularly limited without departing from the gist of the present invention, but the average particle size is 0.1 to 4.0 μm.
m, and the addition amount is preferably 0.01 to 3.0% by weight. Further, the polyester film of the present invention may be a single-layer film or a multi-layer film in which a plurality of layers are laminated, as long as the gist of the present invention is not exceeded.

The method for producing the film of the present invention will be specifically described below, but as long as the constitution of the present invention is satisfied,
The present invention is not particularly limited to the following examples. The polyester chips dried by a known method are supplied to a melt extrusion device, and heated to a temperature higher than the melting point of each polymer to be melted. Next, the melted polymer is extruded from a die and rapidly cooled and solidified on a rotating cooling drum to a temperature not higher 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 enhance the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid coating adhesion method is preferably adopted.

In the present invention, the sheet thus obtained is preferably biaxially stretched to form a film. Describing the stretching conditions specifically, the unstretched sheet is preferably 2 to 6 at 70 to 145 ° C. in the longitudinal direction.
After stretching twice to form a longitudinally uniaxially stretched film, it is stretched 9 times in the transverse direction.
Stretching 2 to 6 times at 0 to 160 ° C, 150 to 240 ° C
It is preferable to perform the heat treatment for 1 to 600 seconds. Further, in this case, 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 exit of the heat treatment is preferable. Further, it is also possible to add re-longitudinal stretching and re-transverse stretching if necessary. The polyester film of the present invention may be longitudinally stretched, if necessary, in order to improve the required properties such as antistatic property, weather resistance and surface hardness as long as the effects of the present invention are not impaired. After the completion, so-called in-line coating may be carried out in which coating is performed before the entrance of the tenter for transverse stretching and drying in the tenter. Further, various coatings may be performed by off-line coating after the film is manufactured. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based in the case of off-line coating, but is preferably water-based or water-dispersed in the case of in-line coating.

Further, the polyester film of the present invention may be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate as long as the effects of the present invention are not impaired. Further, an ultraviolet absorber, an antioxidant, a surfactant, a pigment, a fluorescent whitening agent and the like can be mixed. When the release layer is provided on the polyester film of the present invention, the material forming the release layer is not particularly limited as long as it has releasability, and may be a type containing a curable silicone resin as a main component. Alternatively, a modified silicone type by graft polymerization with an organic resin such as urethane resin, epoxy resin or alkyd resin may be used. Among them, when the curable silicone resin is the main component, the mold releasability is good. As the type of curable silicone resin, any curing reaction type such as solvent addition type / solvent condensation type / solvent UV curing type, solventless addition type, solventless condensation type, solventless UV curing type, solventless electron beam curing type can be used. Can be used.

[0015]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, various physical properties,
The characteristics are measured or defined as follows.

(1) Measurement of orientation angle The orientation of the polyester film was observed using a polarizing microscope manufactured by Carl Zeiss Co., and the direction of the main orientation axis in the plane of the polyester film was inclined several times with respect to the width direction of the polyester film. The orientation angle was measured to determine the orientation angle. This measurement was carried out at a total of 3 locations on the center and both ends of the obtained film, and the value of the largest orientation angle among the 3 locations was taken as the maximum orientation angle.

(2) Measurement of Refractive Index Using an Abbe type refractometer manufactured by Atago Optical Co., Ltd., the maximum value nγ of the in-plane refractive index, the refractive index nβ in the direction perpendicular thereto,
Further, the refractive index nα of the film in the thickness direction was measured, and Δn and Δp were calculated by the following equations to calculate Δp / Δn. In addition,
The refractive index was measured at 23 ° C. using sodium D line. In addition, the above-mentioned refractive index is measured at a total of 3 places on the center and both ends of the obtained film, and Δp /
Δn was calculated, and the maximum and minimum values of the three points were calculated. Δn = nγ-nα Δp = (nγ + nβ) / 2−nα

(2) Measurement of surface OL amount After heat-treating the polyester film at 180 ° C. for 10 minutes, the polyester film after the heat treatment was folded so that the upper part was opened and the bottom area became 250 cm ² .
Create a square box. When a coating layer is provided, the surface of the coating layer should be on the inside. Then, put 10 ml of DMF in the box made by the above method and leave it for 3 minutes.
Collect F. The recovered DMF was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer in DMF, and this value was divided by the area of the film in contact with DMF to obtain the amount of film surface oligomer (mg / m ² ). And The oligomer amount in DMF was determined from the peak area ratio of the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing the preliminarily collected oligomer (cyclic trimer), and then accurately weighing DM.
It was prepared by dissolving in F. The concentration of the standard sample is 0.001
The range of mg / ml to 0.01 mg / ml is preferred. The conditions of the liquid chromatograph were as follows. Mobile phase A: acetonitrile Mobile phase B: 2% acetic acid aqueous solution column: Mitsubishi Chemical Co., Ltd. MCI GEL ODS
1HU Column temperature: 40 ° C Flow rate: 1 ml / min Detection wavelength: 254 nm

(3) Measurement of the number of foreign substances in the film A polyester film having a width of 700 mm and a length of 10 m (area 7 m ² ) was visually inspected for foreign substances using the crossed Nicols method, and the size of all detected foreign substances was measured. The number of foreign matters having a size of 30 μm or more was counted, and then the number of foreign matters of 30 μm or more per unit area was calculated.

(4) Measurement of b value Using a spectral color difference meter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd., the b value was measured by the transmission method according to the method of JIS Z-8722. (5) Measurement of heat shrinkage rate A sample of 15 mm wide x 150 mm long strip was cut out in the lateral direction of the release film, and the oven was set to 180 ° C in a tensionless state (Tabai Seisakusho: hot air circulation furnace). ), The length before and after the heat treatment was measured with a micrometer, and the heat shrinkage rate was calculated by the following formula. Heat shrinkage rate (%) = [(ab) / a] × 100 (In the above formula, a is the film length before heating (mm), and b is the film length after heating (mm))

(6) Visual inspection property under crossed nicols Using the obtained polyester film, 100 parts of a curable silicone resin ("KS-779H" manufactured by Shin-Etsu Chemical), a curing agent ("CAT-PL-" manufactured by Shin-Etsu Chemical) 8 ") 1 part, methyl ethyl ketone (MEK) / toluene mixed solvent system 2200
Part of the release agent is applied at a coating amount of 0.1 g / mm ² and dried at 170 ° C. for 10 seconds to obtain a release film, after which the release film is polarized in the width direction. The release film is adhered to the polarizing film via an adhesive so that it is parallel to the orientation axis of the film to form a polarizing plate, and the alignment axis is inspected on the release film that has been adhered so that it is orthogonal to the film width direction. Polarizing plates were superposed, white light was irradiated from the polarizing plate side, and visually observed from the polarizing plate for inspection, and the visual inspectability under crossed Nicols was evaluated according to the following criteria.
At the time of measurement, evaluation was carried out using a total of three films at the center and both ends of the obtained film, and the evaluation result which was the worst was taken as the visual inspection property of the film.

<Visual inspection property under crossed Nicols> Criteria: ○: inspection is possible without optical interference Δ: inspection is possible with optical interference X: inspection is not possible due to optical interference Among the above criteria, ○ and △ are It is a level with no practical problems.

(7) Inspection of flatness after installation of release layer 100 parts of curable silicone resin ("KS-779H" manufactured by Shin-Etsu Chemical) on the polyester film, curing agent ("CAT-PL-8" manufactured by Shin-Etsu Chemical) 1 part, a release agent consisting of methyl ethyl ketone (MEK) / toluene mixed solvent system 2200 parts was applied to a coating amount of 0.1 g / mm 2 and dried at 170 ° C. for 10 seconds to form a release film, The flatness of the obtained release film was visually inspected. ◯: Very good flatness and high practicality Δ: Slightly lacking flatness, but practical ×: Poor flatness and poor practicality

Example 1 (Production Method of Polyester Chip) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate were placed in a reactor, heated and heated, and methanol was distilled off to transesterify. And then
About four and a half hours after the start of the reaction, the temperature was raised to 230 ° C., and the transesterification reaction was substantially completed. Then phosphoric acid 0.04
And 0.035 part of antimony trioxide were added, and the mixture was polymerized according to a conventional method. That is, the reaction temperature was gradually raised to 280 ° C., while the pressure was gradually reduced to 0.05 mmHg. After 4 hours, the reaction was completed, and chips were formed into chips having an intrinsic viscosity of 0.6 according to a conventional method.
A polyester A of 5 was obtained. Solid phase polymerization is carried out by a known method using the polyester A, and the intrinsic viscosity is 0.78.
Polyester B was obtained. Further, when producing the polyester A, 10000 ppm of amorphous silica having an average primary particle size of 2.4 μm was added to obtain a polyester C. When the polyester A is manufactured, δ-type aluminum oxide having an average primary particle diameter of 60 nm is added to 20000 p.
pm was added to obtain Polyester D. Further, when producing the polyester A, 20,000 ppm of calcium carbonate having an average primary particle size of 0.7 μm was added to obtain a polyester E.

(Production of Polyester Film) The above polyesters A to E were used as a mixed raw material for layers A and B in the compounding ratios shown in Table 1 below, and each was fed to two extruders at 285 ° C. After melting, casting was performed by cooling the layer A to the outermost layer (surface layer), the layer B as an intermediate layer, and cooling to 20 ° C. in a layer structure of two types and three layers so that the thickness of the layer B was 75% of the total thickness. A non-oriented sheet was obtained by co-extruding on a drum and cooling and solidifying. Then, after stretching 2.8 times in the longitudinal direction at 125 ° C., through a preheating process in a tenter and then transversely stretching 4.2 times at 100 ° C., heat treatment is performed at 205 ° C. for 10 seconds, and thereafter. 20% relaxation was applied in the width direction at 180 ° C. to obtain a polyester film having a width of 2000 mm and a thickness of 38 μm. The obtained film has a good visual inspection property,
It was a highly practical polyester film with a small amount of surface OL and the number of foreign matters. Further, the release layer was applied on the polyester film thus obtained to obtain a release film, and the flatness of the release film was examined. As a result, the flatness was also good.

Example 2 A polyester film was obtained in the same manner as in Example 1, except that the raw material composition and film forming conditions were as shown in Table 1. The obtained polyester films had the results shown in Table 1, and were all highly practical films. Further, when a release film was obtained using the polyester film obtained in Example 2 in the same manner as in Example 1 and the flatness of the release film was inspected, the flatness was also good.

Comparative Example 1 A polyester film was obtained in the same manner as in Example 1 except that the raw material composition and film forming conditions were as shown in Table 1. The obtained polyester film was inferior in visual inspection property and lacked in practicality. Comparative Examples 2 to 5 Polyester films were obtained in the same manner as in Example 1 except that the raw material composition and film forming conditions were as shown in Table 1. The obtained polyester films have the results shown in Table 1, which are inferior in visual inspection property, and surface OL
The film was inferior in practicality because it was inferior in any of the properties such as the amount, the number of foreign matters, the b value, and the flatness of the release film. In Comparative Example 2, when the heat shrinkage ratio was measured, the shrinkage was too large to measure the film length after the heat treatment. Further, even in the step of installing the release layer, the release layer could not be stably coated due to the remarkable shrinkage in the film width direction, and the release film could not be obtained.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

EFFECT OF THE INVENTION According to the present invention, a polyester film for a release film having excellent characteristics can be provided which can be accurately inspected by a crossed Nicol method of a polarizing plate. High value.

Claims (6)

[Claims] 1. A polyester film for a release film, which has an orientation main axis inclination of 15 degrees or less and satisfies the following formula. 2 ≦ Δp / Δn ≦ 7 (where Δp and Δn are the maximum refractive index in the plane of the film, nγ, the refractive index in the direction orthogonal thereto, nβ, and the refractive index in the thickness direction, nα, respectively. , Δn = nγ-nα, Δp
= (Nγ + nβ) / 2-nα respectively) 2. The polyester film for a release film according to claim 1, wherein the amount of the oligomer extracted from the film surface after the heat treatment is 10 (mg / m ² ) or less. 3. The polyester film for a release film according to claim 1, wherein the number of foreign matters having a diameter of 30 μm or more present in the polyester film is 4 pieces / m ² or less. 4. The polyester film for a release film according to claim 1, wherein the b value measured by transmitted light using a color difference meter is in the range of −2.0 to 2.0. 5. The polyester film for a release film according to claim 1, which has a heat shrinkage ratio of 4% or less when held in an atmosphere of 180 ° C. for 5 minutes. 6. A release film having a release layer on one surface of the polyester film according to claim 1.