JP5249107B2 - Biaxially oriented polyester film for optics - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film for optical applications, and in particular, a biaxially oriented polyester film that is excellent in optical properties, which are important properties in films for liquid crystal display applications, and is suitably used as a release film for polarizing plates. It is about.

  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 CRTs, which are conventional displays, is growing significantly. The technology has also grown significantly in increasing the screen size of LCDs.

  Under such circumstances, there is an increasing demand for film properties for release films for optical use such as liquid crystal polarizing plates, displays for cathode ray tubes, PDPs, and the like that are conventionally used.

  As a defect inspection of the polarizing plate, a visual inspection by a crossed Nicols method is common. This crossed Nicol method is a method in which two polarizing plates are perpendicular to their orientation main axes and a release film is sandwiched between them, and if there is a defect, it appears as a bright spot, so that a defect inspection can be visually observed. However, scratches on the film surface become a bright spot in such inspection, and as a result, it becomes a defect, and when the optical anisotropy of the release film is significant, it becomes an obstacle to the inspection of the crossed Nicols method and it is easy to overlook the defect A malfunction occurs. Further, when an adhesive or the like is applied on the film, scratches may be transferred to the surface of the adhesive, resulting in defects in appearance, which may be undesirable in practice.

JP 2003-327719 A

  The present invention is intended to solve such problems, and the problem to be solved is that, for example, when used as a release film for producing a polarizing plate, an accurate inspection can be performed in the inspection by the crossed Nicols method. An object of the present invention is to provide a biaxially oriented polyester film for optical use having such excellent characteristics.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be easily solved by blending specific particles and having a specific structure, and complete the present invention. It came to.

That is, the gist of the present invention is that 0.10 to 1.0% by weight of aluminum oxide particles having an average particle size of 0.02 to 0.09 μm is contained, the orientation angle is 15 degrees or less, and the following formula is satisfied. It exists in the biaxially-oriented polyester film for optics characterized by doing.

2 ≦ ΔP / Δn ≦ 7
(In the above formula, ΔP surface distribution altitude, Δn means birefringence)
Hereinafter, the present invention will be described in detail.

  The polyester referred to in the present invention refers to a polymer containing an ester group obtained by polycondensation from a dicarboxylic acid and a diol or from 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, and the diol includes ethylene. Glycol, 1,3-propanediol, 1,6-hexanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, etc. as hydroxycarboxylic acids Can be exemplified by p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and the like.

  Typical examples of such polymers include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. These polymers may be homopolymers or may be a copolymer of the third component. As the film of the present invention, a biaxially stretched film is preferably used from the viewpoint of excellent strength and dimensional stability.

  The biaxially oriented polyester film for optical use in the present invention comprises aluminum oxide particles having an average particle diameter of 0.01 to 1.0 μm, preferably 0.05 to 1.0 μm, more preferably 0.05 to 0.5 μm. 0.10 to 1.0% by weight, preferably 0.10 to 0.8% by weight, more preferably 0.10 to 0.5% by weight.

  If the average particle diameter of the aluminum oxide particles is smaller than 0.01 μm, the film surface protrusions caused by the aluminum oxide particles do not appear, so that scratches are likely to occur, which is not preferable. On the other hand, when the average particle size is larger than 1.0 μm, protrusions appearing on the film surface become large, and when the film is wound on a roll, the film surface is rubbed and scratches are generated on the film surface.

  When the added amount of aluminum oxide particles is less than 0.10% by weight, the number of protrusions on the film surface due to the aluminum oxide particles is not sufficient, and scratches are likely to occur, which is not preferable. Further, when the addition amount exceeds 1.0% by weight, the particles aggregate and form large protrusions on the film surface. Therefore, when the film is wound on a roll, the film surface is rubbed and scratches are generated on the film surface. Absent.

As an example of aluminum oxide that satisfies these requirements and can be used particularly preferably in the present invention, for example, aluminum oxide by a so-called pyrolysis method can be mentioned. These particles are usually produced by flame hydrolysis using anhydrous aluminum chloride as a raw material, and the particle size is about 10 mμ to 100 mμ. In the present invention, aluminum oxide particles obtained by hydrolysis of alkoxide can also be preferably used. In this case, usually, Al (OC ₃ H ₇ ) or Al (CO ₄ H ₉ ) is used as a starting material, and fine particles having a size of 1 μm or less are obtained by appropriately selecting hydrolysis conditions. Of course, in this case, it is also possible to employ a method in which an acid is added to the synthesized slurry to obtain a transparent sol, and the sol is gelled and then heated to 500 ° C. or more to form a sintered body. Moreover, you may use the aluminum oxide fine powder obtained by another method, ie, adding methyl acetate and ethyl acetate to a sodium aluminate solution, stirring, and obtaining AlOOH, and then heating this.

  In the present invention, it is preferable to use such aluminum oxide particles that are completely dispersed up to the primary particles. However, as long as the surface state of the film is not adversely affected, the aluminum oxide particles may be slightly agglomerated and behave as secondary particles. In this case, however, the apparent average particle size needs to be in the range of 0.01 to 1.0 μm.

  In this case, a part of aluminum oxide, for example, less than 30% by weight, may be substituted with oxides such as Si, Ti, Fe, Na, and K.

  Further, in the present invention, the particle size distribution of the aluminum oxide particles is not particularly limited, but when the particles are sharper, specifically, the particles having a weight fraction of 75% and 25% when integrated from the smaller particle size. A diameter ratio of 2.0 or less, preferably 1.5 or less is suitably used.

  Further, the shape of these particles is not particularly limited, but those having a lump shape or a shape close to a sphere are preferably used. Specifically, for example, particles having a volume shape defined in Japanese Patent Publication No. 53-14583 are 0.1 to π / 6, preferably 0.2 to π / 6.

Further, the specific surface area is not particularly limited, and can be suitably used up to about 500 m ² / g.

  In the present invention, even if the surface of the aluminum oxide particles is treated with various surface treatment agents such as a silane coupling agent or a titanium coupling agent, the effect is sufficiently exhibited.

  Such biaxially oriented polyester film for optical use includes, in addition to aluminum oxide particles, inert fine particles such as inorganic particles such as silica, calcium carbonate, kaolin, titanium oxide, barium sulfate, zeolite, or silicone resin, crosslinked polystyrene, It is preferable to mix organic particles such as acrylic resin. In this case, the average particle diameter, addition amount, and particle size distribution of the particles to be used are not particularly limited, but the average particle diameter is 0.1 to 4.0 μm, and the addition amount is 0.1 to 2. The dispersion is preferably as small as 0% by weight and the particle size distribution.

Furthermore, the polyester film of the present invention has an orientation angle (sometimes expressed as the inclination of the orientation main axis) of 15 degrees or less and needs to satisfy the following formula. Here, the orientation angle is the inclination of the main axis with respect to the film width direction or the vertical direction.
2 ≦ ΔP / Δn ≦ 7
(In the above formula, ΔP surface distribution altitude, Δn means birefringence)

  When the orientation angle is greater than 15 degrees, light leakage increases during the crossed Nicols method, which is not preferable. Even when ΔP / Δn is less than 2 or greater than 7, light leakage during the crossed Nicols inspection also increases. It is not preferable.

  The film of the present invention preferably has a heat shrinkage of 4% or less when held for 5 minutes in an atmosphere at 180 ° C. When the heat shrinkage rate is larger than 4%, the planarity of the film may be impaired in the heat treatment step in the step of installing the release layer or the step of bonding the release film to the polarizing plate. .

  The polyester film of the present invention may be a single layer film or a multilayer film in which a plurality of layers are laminated as long as the gist of the present invention is not exceeded.

  Hereinafter, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the structure of this invention is satisfied, this invention is not specifically limited to the following illustrations. Polyester chips dried by a known method are supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to melt. 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.

If the polyester film of the present invention is within the range not impairing the effects of the present invention, it may be stretched in the longitudinal direction as necessary to improve the required properties such as antistatic properties, weather resistance and surface hardness. After the completion, so-called in-line coating may be performed in which coating is performed before the entrance of the tenter for transverse stretching and drying is performed in the tenter. 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 offline coating, but is preferably water-based or water-dispersed for in-line coating.
The polyester film of the present invention can be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate as long as the effects of the present invention are not impaired. Further, an ultraviolet absorber, an antioxidant, a surfactant, a pigment, a fluorescent brightening agent, and the like can be mixed.

  When a release layer is installed on the polyester film of the present invention, the material constituting the release layer is not particularly limited as long as it has releasability, and a type mainly composed of a curable silicone resin may be used. Alternatively, a modified silicone type obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used. Among them, when the curable silicone resin is a main component, the release property is good. Types of curable silicone resins include solvent addition type, solvent condensation type, solvent ultraviolet ray curable type, solventless addition type, solventless condensation type, solventless ultraviolet ray curable type, solventless electron beam curable type, etc. Can be used.

According to the present invention, it is possible to carry out an accurate inspection in the inspection of the polarizing plate by the crossed Nicols method, and it is possible to provide a biaxially oriented polyester film for optical applications having excellent characteristics. Target value 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. Various physical properties and characteristics are measured or defined as follows.

(1) Average particle diameter The particle diameter is measured with a microscope, and the particle diameter (diameter) at the point where the volume fraction of the equivalent sphere equivalent is 50% is defined as the average particle diameter.

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

(3) Refractive index measurement Using an Abbe refractometer manufactured by Atago Optical Co., Ltd., the maximum refractive index nγ in the film plane, the refractive index nβ in the direction perpendicular to it, and the refractive index nα in the thickness direction of the film are measured. Then, Δn and ΔP were obtained by the following formula, and ΔP / Δn was calculated. The refractive index was measured at 23 ° C. using sodium D line. In addition, the refractive index was measured by measuring a total of three locations at the center and both ends of the obtained film, calculating ΔP / Δn at each location, and determining the maximum and minimum values at three points.
Δn = nγ- nβ
ΔP = (nγ + nβ) / 2−nα

(4) Measurement of heat shrinkage rate An oven set to 180 ° C. in a tension-free state by cutting out a sample having a length of 35 mm × 1000 mm in the longitudinal direction and the transverse direction of the film (manufactured by Takai Seisakusho: hot air circulating furnace) The heat treatment for 5 minutes was performed in the sample, the length before and after the heat treatment was measured with a JIS class 1 scale, and the thermal shrinkage was obtained by the following formula.
Heat shrinkage rate (%) = [(ab) / a] × 100
(In the above formula, a is the film length (mm) before heating, and b is the film length (mm) after heating)

(5) Scratch inspection In a dark room, light is applied to the film surface with a fluorescent lamp, and the film surface is visually observed to detect a scratch. The state of the detected scratch is observed with reflected light under a bright room such as a fluorescent lamp.
<Criteria for visual inspection of scratches>
◎: Scratch cannot be detected under dark room ○: Scratch cannot be confirmed under bright room △: Slight scratch can be confirmed under bright room ×: Scratch can be confirmed under bright room In the above criteria, ○ and △ are practical It is a level without any problem.

(6) Visual inspection property under crossed Nicols 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical) using the obtained polyester film, curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical) A release agent consisting of 1 part, 2200 parts of methyl ethyl ketone (MEK) / toluene mixed solvent system was applied so that the coating amount was 0.1 g / mm ² , and dried at 170 ° C. for 10 seconds to release film. On the release film so that the width direction of the release film is parallel to the orientation axis of the polarizing film, and the release film is closely attached to the polarizing film via an adhesive. A polarizing plate for inspection is superimposed on the film so that the orientation axis is orthogonal to the film width direction, white light is irradiated from the polarizing plate side, visually observed from the polarizing plate for inspection, and visual inspection under crossed Nicols. Sex below It was evaluated in accordance with standards. In addition, in the case of a measurement, it evaluated using the film of a total of three places of the center part and both ends of the obtained film, and made the evaluation result which was the most bad the visual inspection property of the film.
<Criteria for visual inspection under crossed Nicols>
○: Inspection is possible without optical interference Δ: Optical interference is possible but inspection is possible ×: Optical interference is possible and inspection is not possible In the above standards, ○ and Δ are levels that have no practical problem.

(7) Planarity inspection after setting release layer 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical) on polyester film, 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical) A release agent comprising 2200 parts of methyl ethyl ketone (MEK) / toluene mixed solvent system was applied 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 flatness of the release film was visually inspected.
◯: Extremely flat and rich in practicality Δ: Slightly lacking in flatness but practical ×: Poor flatness and lack of practicality

Example 1:
(Polyester chip manufacturing method)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct transesterification, and take about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was completed, and chips were obtained according to a conventional method to obtain polyester A. When the polyester A was produced, 15,000 ppm of δ-type aluminum oxide having an average particle size of 0.06 μm was added to obtain polyester B. Moreover, when manufacturing the said polyester A, 10000 ppm of amorphous silica with an average particle diameter of 2.4 micrometers was added, and the polyester C was obtained. Furthermore, when manufacturing the said polyester A, 20000 ppm of calcium carbonate with an average primary particle size of 0.7 micrometer was added, and the polyester D was obtained.

(Manufacture of polyester film)
After feeding the above-mentioned polyester B 20% (content in film 0.30% by weight), polyester C 20%, and polyester A mixed at a ratio of 60% to the extruder and melting at 285 ° C., A non-oriented sheet was obtained by cooling and solidifying on a casting drum cooled to 20 ° C. Next, the film was stretched 2.8 times in the longitudinal direction at 125 ° C. using the difference in the peripheral speed of the roll, and then subjected to a preheating step in the tenter and 4.2 times transverse stretching at 100 ° C. Heat treatment was performed for 10 seconds, and then 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 was a polyester film having no practical scratches, good visual inspection, and high practicality. Furthermore, after the release layer was applied onto the polyester film thus obtained to obtain a release film, the planarity of the release film was examined, and as a result, the planarity was also good.

Examples 2-5:
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 had the results shown in Table 1, and was a highly practical film. Moreover, when the release film was obtained like Example 1 using the polyester film obtained in Examples 2-5, and the planarity of the release film was examined, the planarity 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 2. Although the obtained polyester film had a good scratch appearance, it was a film lacking in practicality because of poor visual inspection.

Comparative Examples 2-7:
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 has the results shown in Table 2, all of which are inferior in scratch inspection or visual inspection property, and inferior in any of the flatness properties when used as a release film, and practical. The film lacked. 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, stable release layer coating could not be performed due to significant shrinkage in the film width direction, and a release film could not be obtained.

  The film of the present invention can be suitably used as an optical film, for example.

Claims (1)

0.10 to 1.0% by weight of aluminum oxide particles having an average particle diameter of 0.02 to 0.09 μm, an orientation angle of 15 degrees or less, and satisfying the following formula: Biaxially oriented polyester film.
2 ≦ ΔP / Δn ≦ 7
(Wherein, [Delta] P Menhai direction of, [Delta] n denotes the birefringence)