JP5871597B2 - Polyester film for optical film - Google Patents

Description

  The present invention relates to a polyester film for an optical film that is suitably used for a liquid crystal display.

  In recent years, the number of liquid crystal display devices whose number has increased rapidly has been focused on a backlight unit that concentrates the light from the light source on the viewer side and serves as a uniform surface light source, and the applied voltage is adjusted for each display pixel. The liquid crystal cell layer unit that displays red, green, and blue light in a controlled amount is roughly divided into two units.

  Among these, the backlight unit has a cold cathode tube using a phosphor having emission characteristics in the red, green, and blue wavelength regions, and a light source such as an LED arranged on the side as viewed from the viewing side, and the light is viewed on the viewing side. A light guide plate that efficiently guides the light to the viewing side, a diffusion film that uniformly disperses the light guided to the viewing side within the display surface, and condenses the light directed toward the side of the display to the viewing side, thereby reducing the brightness of the display It consists of a prism film that improves, and a composite film that consolidates the diffusion and condensing functions into one sheet.

  In a general liquid crystal display, a diffusion film, which is usually called a lower diffusion film, is arranged on a light guide plate, and two prism films are arranged on the diffusion film so that the light collecting directions are vertical and horizontal directions and horizontal directions, respectively. In addition, a backlight unit is configured by disposing a single diffusion film, usually called an upper diffusion film, thereon.

  As described above, when a plurality of optical sheets are used in an overlapped manner, the transparent members may be brought into close contact with each other, thereby causing interference fringes and causing a problem of disturbing the display image.

  On the other hand, studies have been made to suppress the generation of interference fringes by providing a large number of minute spherical protrusions having a protrusion height from the surface of 1 to 7 μm on the opposite surface of the prism sheet on the prism surface side (patent) Reference 1). However, according to the present invention, although the generation of interference fringes can be suppressed, other optical films, light guide plates, and the like that are in contact with the minute projections are damaged, which causes a problem.

  In order to solve this problem, studies have been made to prevent damage due to concentrated weighting by setting the half-value width of the particle size distribution contained in the coating layer to 1 μm or less and suppressing variations in the protrusion amount (Patent Document 2). However, even in this case, if the thickness of the coating layer exceeds the particle diameter, the amount of protrusion varies depending on the arrangement in the thickness direction of the particles in the coating layer, so that damage due to concentrated load cannot be completely prevented. There's a problem.

Japanese Patent Laid-Open No. 10-300908 JP-A-11-133214

  The present invention is intended to solve such problems, and the problem to be solved is that it can be used as an optical film, can suppress the generation of interference fringes, and scratches other optical films that come into contact therewith. An object of the present invention is to provide a polyester film for an optical film that does not occur.

  As a result of intensive studies in view of the above problems, the present inventor can provide a polyester film that is particularly suitable for a polyester film for optical films without impairing excellent film properties, according to a polyester film having a specific configuration. As a result, the present invention has been completed.

That is, the gist of the present invention is a polyester film for an optical film used by laminating an optical functional layer selected from a hard coat layer, a prism layer, a diffusion layer, and a lens layer, and a surface on which the optical functional layer is formed. A polyester film for an optical film having a coating layer containing particles having a pore volume of 1.3 to 2.0 ml / g and an average particle size of 6 to 10 μm on the opposite surface. Exist.

  According to the present invention, there is provided a polyester film for an optical film that can be suitably used as an optical film, can suppress generation of interference fringes, and does not damage other optical films that come into contact therewith. The industrial value of the present invention is high.

  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.

  The polyester in the present invention is a conventionally known method, for example, a method of directly obtaining a low-polymerization degree polyester by reaction of a dicarboxylic acid and a diol, or a lower alkyl ester of a dicarboxylic acid and a diol reacted with a conventionally known transesterification catalyst. Then, it can obtain by the method of performing a polymerization reaction in presence of a polymerization catalyst. As the polymerization catalyst, a known catalyst such as an antimony compound, a germanium compound, or a titanium compound may be used. Preferably, the amount of the antimony compound is reduced to 0 or 100 ppm or less as antimony to reduce film dullness. preferable.

  In the polyester film obtained by the present invention, a weather resistance agent, a light resistance agent, an antistatic agent, a lubricant, a light shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, You may mix | blend coloring agents, such as a stabilizer and dye, a pigment.

  The pore volume of the particles in the coating layer provided on the polyester film needs to be 0.5 to 2.0 ml / g. If it is less than 0.5 ml / g, the deformability of the particles is lost and the structure becomes rigid, and damage to other optical sheets and the like cannot be prevented. On the other hand, if it exceeds 2.0 ml / g, the deformability of the particles becomes too large, and a constant particle size cannot be maintained or a desired projection height cannot be obtained, resulting in generation of interference fringes. Can not be suppressed. The particle size of the particles used is not particularly limited, but is usually in the range of 0.5 to 10 μm.

  In the present invention, the method for providing the coating layer on the polyester film is not particularly limited, and a known method can be adopted. For example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or other coating apparatus as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” can be used. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  In addition, the timing for forming the coating layer is not particularly limited, and an in-line coating method, an offline coating method performed after the polyester film is manufactured, or the like performed in the process of manufacturing the polyester film as the base material, etc. Conceivable.

  Although the thickness of a coating layer is not specifically limited, Usually, it is the range of 0.1-20 micrometers as final dry thickness. When the thickness of the coating layer is less than 0.1 μm, the fixability of the contained particles to the film surface is deteriorated and there is a risk of dropping off. Moreover, when the thickness of a coating layer exceeds 20 micrometers, light transmittance will fall and a brightness | luminance will deteriorate.

  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 4 to 500 μm, preferably 25 to 350 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.

  For example, a 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 provided with an anchor coat layer in order to enhance the adhesion between the coating layer, the prism / diffusion / lens layer, and the polyester film, as long as the effects of the present invention are not impaired. .

  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 The average particle diameter was defined as the particle diameter 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) Pore volume The pore volume of the particles was determined by a nitrogen adsorption method.

(4) Evaluation of scratching occurrence A prism layer is formed by applying an acrylic binder on the surface opposite to the coating layer of the prepared polyester film, and the resulting prism sheet is doubled with the prism surface facing upward. After being installed in the backlight unit and left in a lighting state for 2 hours, the prism surface of the prism sheet placed on the lower side is visually inspected under the reflection of a fluorescent lamp, and the occurrence of scratches is evaluated according to the following classification did.
◎: Scratch occurrence is not visually observed. △: Scratch occurrence is visually observed. X: Scratch occurrence is clearly observed on the entire surface. It is a level that can be done.

(5) Interference fringe generation evaluation A prism layer is formed by applying an acrylic binder on the opposite side of the polyester film coating layer, and the resulting prism sheet is placed on the light guide plate of the backlight unit to light up. The occurrence of interference fringes was visually observed and evaluated according to the following classification.
◎: Generation of interference fringes is not visually observed. Δ: Generation of interference fringes is visually observed. ×: Generation of interference fringes is clearly observed on the entire surface. It is a level that can be used without problems.

(6) Surface roughness of coating layer (Rz)
It measured according to JIS-B-0601-1982 using the surface roughness measuring machine (SE-3F) by Kosaka Laboratory.

Comparative Example 1 :
<Manufacture of polyester>
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.

<Adjustment of aqueous coating agent>
The aqueous coating agent is a mixture obtained by mixing the following compounds a, b, c and d in a weight ratio of 47/20/30/3.
a: Polyester aqueous dispersion obtained by reacting terephthalic acid / isophthalic acid / 5-sodiumsulfoisophthalic acid / ethylene glycol / 1.4-butanediol / diethylene glycol in a molar ratio of 28/20/2/35/10/5, respectively body.
b: Polymer aqueous dispersion obtained by polymerizing methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide at a molar ratio of 45/45/5/5 (emulsifier: anionic surfactant)
c: Melamine-based crosslinking agent (hexamethoxymethyl melamine)
d: An aqueous dispersion of silicon oxide having an average particle size of 0.06 μm

<Manufacture of polyester film>
After the said polyester chip was melt-extruded at 290 degreeC, it was solidified by cooling on the cooling roll which set surface temperature to 40 degreeC using the electrostatic application adhesion method, and the unstretched sheet was obtained. Next, the film was stretched 3.4 times in the machine direction at a film temperature of 81 ° C. using a difference in peripheral speed of the roll, and then an aqueous coating agent was applied to both sides, led to a tenter, and stretched 4.0 times at 120 ° C. in the transverse direction. Then, after heat treatment at 225 ° C., after passing through a cooling zone at 140 ° C., it was relaxed by 2% in the lateral direction to obtain a polyester film having a thickness of 125 μm.

<Formation of coating layer>
The obtained polyester film is wound up into a roll shape, the roll is wound up again, and a 10% dimethoxyethane solution of a polyester resin (Eastek 1200, Tg = 63 ° C .; manufactured by Eastman Chemical Co.) is shown in Tables 1 and 2. The particles as described above were dispersed to 0.5% with respect to the polyester resin, coated with a bar coater (No. 36), and dried to obtain a film having a microprojection layer with a thickness of 5 μm. .

Examples 1-4, Comparative Examples 1-8:
Changes were made as described in Tables 1 and 2 below to obtain films.
The obtained results are summarized in Tables 1 and 2 below.

  In the above table, the film of Comparative Example 2 was a particle that dropped out of the coating layer to become a foreign substance and could not be used for advanced applications.

  The film of the present invention can be suitably used, for example, for an optical film used by laminating an optical functional layer selected from a hard coat layer, a prism layer, a diffusion layer, and a lens layer.

Claims (1)

A polyester film for an optical film used by laminating an optical functional layer selected from a hard coat layer, a prism layer, a diffusing layer, and a lens layer, wherein pores are formed on the surface opposite to the surface on which the optical functional layer is formed. A polyester film for an optical film having a coating layer containing particles having a volume of 1.3 to 2.0 ml / g and an average particle diameter of 6 to 10 μm .