JP2007307789A - White film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white film capable of being suitably used as a reflecting plate for the surface light source where a hue change is little by an ultraviolet light or high temperature, and deterioration with time of brightness in little even in use for a long time. <P>SOLUTION: The white film comprises an antistatic layer formed from a waterborne coating agent on a polyester film or at least one side thereof. The antistatic layer includes 10 to 50 wt.% of a high polymer type antistatic agent containing a group of a quaternary ammonium salt, and 3 to 15 wt.% of an interfacial active agent of compound having a phenyl group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a white film, and more particularly to a white film suitable as a reflector for a surface light source.

  In recent years, the use of liquid crystal screens has been remarkably expanded, and in addition to conventional notebook personal computers, they have been widely used in stationary personal computers, liquid crystal televisions, mobile phone displays, and various game machines. In particular, in a liquid crystal television, it is desired to increase the brightness and definition of the screen, and to increase the output of the illumination light source and increase the number of light source lamps. Further, in particular, when a direct light source is used in order to obtain high luminance, the light emitted from the light source directly hits the reflecting plate, and thus higher durability is required.

  There are several types of backlights that include a surface light source reflector as an element. For example, as disclosed in Japanese Patent Laid-Open No. 63-62104, an edge light system is widely used in which light from an illumination light source enters from the edge of a light guide plate. In this method, in order to use light more efficiently, a reflector is provided around the light source, and a reflector is used under the light guide plate to efficiently reflect the light diffused from the light guide plate to the liquid crystal screen side. Yes.

In a backlight unit for a large screen such as a liquid crystal television, a direct light system in which a plurality of illuminations are arranged on the back of a liquid crystal element and light is transmitted to the screen side through a light diffusion sheet has been adopted. In this system, a reflecting plate is required to have a high reflecting function, and conventionally, a film added with a pigment or a white film added with an incompatible resin to contain fine bubbles inside has been used.
JP 63-62104 A

  However, conventional white films with added pigments or incompatible resins are difficult to form stably when fine particles are added at a high concentration, and liquid crystal displays are used for a long time. In the meantime, the white film deteriorates and yellowing occurs, which may cause a problem that the light reflection characteristics are lowered, and consequently the brightness of the screen is lowered. Static electricity is inevitable as long as resin is used as a material for the reflector. However, as the liquid crystal screen becomes larger, it is noticeable that dust is attracted due to the charging of the reflective film during and after installation. become.

  The present invention solves the above problems and can stably form a film even if fine particles are added at a high concentration, and there is little change in hue at ultraviolet light or high temperature, and there is little decrease in luminance over time even when used for a long time. It aims at providing the white film which can be used suitably as a reflecting plate for surface light sources.

  That is, the present invention is a white film comprising a polyester film and an antistatic layer formed from a water-based coating on at least one surface thereof, wherein the antistatic layer is a polymer type antistatic material comprising repeating units represented by the following formula: It is a white film characterized by containing 10 to 50% by weight of an agent and 3 to 15% by weight of a surfactant having a phenyl group.

  According to the present invention, it is possible to stably form a film even when fine particles are added at a high concentration, and there is little change in hue at ultraviolet light or high temperature, and there is little decrease in luminance over time even when used for a long time. A white film that can be suitably used as a plate can be provided.

Hereinafter, the present invention will be described in detail.
[Polyester film]
The polyester film is composed of a polyester composition. As the polyester of the polyester composition, a polyester composed of a dicarboxylic acid component and a diol component is used. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid, and sebacic acid. Examples of the diol include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol. Of these polyesters, polyethylene terephthalate is preferred. As the polyester, a copolyester is preferably used. The ratio of the copolymerization component is preferably 1 to 20 mol%, more preferably 2 to 15 mol%, further preferably 3 to 14 mol%, and particularly preferably 5 to 13 mol%, based on the total dicarboxylic acid component. When the copolymerization component is less than 1 mol%, a layer containing a large amount of inorganic particles, for example, 40% by weight or more is not preferable because film formation may not be possible. If the copolymerization component exceeds 20 mol%, it may be a film lacking in thermal dimensional stability or may not be able to be formed into a film.

  When the polyester is polyethylene terephthalate, for example, isophthalic acid or 2,6-naphthalenedicarboxylic acid can be used as the copolymer component. Copolyethylene terephthalate obtained by copolymerizing isophthalic acid or 2,6-naphthalenedicarboxylic acid in the range of 1 to 20 mol% is a preferred polyester in the present invention.

  From the viewpoint of light reflection performance and light resistance, the polyester composition preferably contains 40 to 70% by weight, more preferably 43 to 65% by weight, and particularly preferably 45 to 60% by weight of inorganic particles. That is, in the present invention, a white polyester film made of a polyester composition containing 40 to 70% by weight, more preferably 43 to 65% by weight, particularly preferably 45 to 60% by weight of inorganic particles is used. If the inorganic particles are less than 40% by weight, the reflection performance is inferior, and this is not preferable, and if it exceeds 70% by weight, the film formation becomes very unstable and the film may not be formed.

  The average particle diameter of the inorganic particles is preferably 0.1 to 10 μm, more preferably 0.3 to 7 μm, and particularly preferably 0.5 to 5 μm. If it is less than 0.1, the dispersibility is inferior, the particles themselves agglomerate, unevenness in whiteness, and variation in reflectance, which causes the filtration pressure to increase in the process of filtering the molten resin during melt extrusion. It is not preferable. If it exceeds 10 μm, the film is easily broken, which is not preferable.

  Examples of inorganic particles include titanium dioxide, barium sulfate, calcium carbonate, and silicon dioxide. Titanium dioxide is preferably a rutile type. The rutile type has less yellowing after irradiating the polyester film with light for a longer time than the anatase type, and is suitable for suppressing the change in color difference.

  From the viewpoint of improving the reflectance, barium sulfate is particularly preferable as the inorganic particles. Barium sulfate may have a plate-like or spherical particle shape. In particular, rutile-type titanium dioxide is preferably used after being treated with a fatty acid such as stearic acid or a derivative thereof in order to improve dispersibility, since the glossiness of the film can be further improved.

  When rutile titanium dioxide is used, it is preferable to adjust the particle size and remove coarse particles using a purification process before adding to the polyester. As industrial means of the purification process, for example, a jet mill or a ball mill can be applied as a pulverizing means, and as a classification means, for example, dry or wet centrifugation can be applied. Two or more of these means may be combined and purified step by step.

Various methods can be used as a method of incorporating the fine particles into the polyester. The following method can be mentioned as the typical method.
(A) A method of adding before transesterification or esterification reaction at the time of polyester synthesis or adding before the start of polycondensation reaction.
(A) A method of adding to polyester and melt-kneading.
(C) A method of producing master pellets to which a large amount of inert particles are added in the method (a) or (b) above, and kneading these with a polyester not containing an additive to contain a predetermined amount of additive.
(D) A method of using the master pellet of (c) as it is.

  Among these, it is preferable to take the above method (c) or (d). In addition, when using the method of said (a), it is preferable to add to a reaction system as a slurry disperse | distributed to glycol in titanium oxide.

  In order to reduce the number of coarse agglomerated particles, a non-woven filter with an average opening of 10 to 100 μm, preferably an average opening of 15 to 50 μm made of stainless steel fine wire with a wire diameter of 15 μm or less is used as a filter during film formation, and a molten polymer It is preferable to filter and then extrude to form a film.

  The polyester film may be a polyester film that is whitened by stretching a composition of polyester and polyester and an incompatible resin. Examples of incompatible resins include polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, polystyrene resins, polyacrylate resins, polycarbonate resins, and polyacrylonitrile resins. Among these, polyolefin resins such as polypropylene and polymethylpentene having a small critical surface tension are preferable.

  You may mix | blend an antioxidant and a fluorescent whitening agent with the polyester composition which comprises a polyester film as needed within the range which does not deviate from the scope of the present invention. When a fluorescent brightening agent is blended, the concentration relative to the polyester composition is preferably 0.005 to 2.0% by weight, more preferably 0.01 to 1.0% by weight. If it is less than 0.005% by weight, the reflectance in the wavelength region near 400 nm is not sufficient, and the illuminance is not sufficient when the reflector is used. If it exceeds 2.0% by weight, a specific color of the fluorescent brightening agent appears, which is not preferable. As the fluorescent whitening agent, known fluorescent whitening agents such as OB-1 (manufactured by Eastman), Uvitex-MD (manufactured by Ciba Geigy), and JP-Conc (manufactured by Nippon Chemical Industry Co., Ltd.) can be used.

The white film of the present invention has, for example, a single layer, a two-layer configuration of A layer / B layer, a three-layer configuration of B layer / A layer / B layer, and 4 layers of B layer / A layer / B layer / A layer. A layer structure may be used. In particular, a three-layer structure of B layer / A layer / B layer is preferable because good reflection characteristics can be obtained.
Moreover, you may apply | coat the coating agent which has antioxidant, a fluorescent whitening agent, etc. to the at least single side | surface of a polyester film as needed.

[Antistatic layer]
In the present invention, from the viewpoint of achieving both antistatic performance and durability, a polymeric antistatic agent containing a quaternary ammonium salt group, specifically, a polymeric charging composed of a repeating unit represented by the following formula: An antistatic agent is contained in the antistatic layer in an amount of 10 to 50% by weight.

  If the content is less than 10% by weight, sufficient antistatic properties cannot be obtained. Even if it is added in an amount exceeding 50% by weight, the antistatic effect reaches a saturated state, and a further preventing effect cannot be expected. The molecular weight of the polymer antistatic agent is preferably 200 to 1000, more preferably 300 to 600. If it is less than 200, there is a concern that bleeding out may occur, and if it exceeds 1000, it is not preferable because an increase in the viscosity of the coating material may occur when an antistatic layer is formed by coating.

  In the present invention, the antistatic layer contains 3 to 15% by weight of a surfactant of a compound having a phenyl group. If it is less than 3% by weight, defects in coating are likely to occur, and if it exceeds 15% by weight, sufficient antistatic properties are inhibited, or the antistatic effect after irradiation with ultraviolet light is reduced. The surfactant compound is preferably a polyoxyethylene having a phenyl group. The repeating unit of polyoxyethylene having this phenyl group is preferably 2 to 20, and more preferably 3 to 15.

  As other components of the antistatic layer, known polymer binders and crosslinking agents can be used. For example, a polyester resin or an acrylic resin can be used as the polymer binder. For example, oxazoline can be used as the crosslinking agent.

  The thickness of the antistatic layer is preferably 10 to 60 nm, more preferably 15 to 50 nm, and particularly preferably 20 to 40 nm. If the thickness is less than 10 nm, it is not preferable because the antistatic performance is not exhibited, and if it exceeds 60 nm, a coating defect tends to occur, which is not preferable.

[Production method]
An example of the method for producing the white film of the present invention will be described. A laminated unstretched sheet is produced by a simultaneous multilayer extrusion method using a feed block from a polymer melted from a die. That is, the polymer melt for forming the A layer and the polymer melt for forming the B layer are laminated to form, for example, B layer / A layer / B layer using a feed block, and developed on a die and extruded. carry out. At this time, the polymer laminated by the feed block maintains the laminated form. A multi-manifold die can also be used to form a film, but it is more preferable to use a feed block in terms of increasing the peel strength.

  The unstretched sheet extruded from the die is cooled and solidified by a casting drum to form an unstretched film. This unstretched film is heated by roll heating, infrared heating or the like, and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The stretching temperature is preferably a temperature equal to or higher than the glass transition point (Tg) of the polyester, and more preferably a temperature higher by Tg to 70 ° C. The draw ratio is preferably 2.5 to 4.0 times, more preferably 2.8 to both the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction), although it depends on the required characteristics of the application. 3.9 times. If it is less than 2.5 times, the thickness unevenness of the film is deteriorated, and if it exceeds 4.0 times, breakage tends to occur during film formation, which is not preferable.

  The film after the longitudinal stretching is then coated with an aqueous coating liquid as a component constituting the antistatic layer. This is preferable from the viewpoint of ease of manufacturing. Transverse stretching, heat setting, and heat relaxation are sequentially performed to obtain a biaxially oriented film having an antistatic layer. These processes are performed while the film is running. The transverse stretching process starts from a temperature higher than the glass transition point (Tg) of the polyester. And it is performed while raising the temperature to (5 to 70) ° C. higher than Tg. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone. The transverse stretching ratio is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times, although it depends on the required characteristics of this application. If it is less than 2.5 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.5 times, breakage tends to occur during film formation, which is not preferred.

  The film after transverse stretching is preferably heat-treated at a constant width or a width reduction of 10% or less at a temperature (Tm-10 to 100) while holding both ends to reduce the thermal shrinkage. When the temperature is higher than this, the flatness of the film is deteriorated, and the thickness unevenness becomes large, which is not preferable. On the other hand, if the heat treatment temperature is lower than (Tm-80) ° C., the thermal shrinkage rate may increase. Also, in order to adjust the heat shrinkage in the region below (Tm-10 ~ 100) ° C in the process of returning the film temperature to room temperature after heat setting, both ends of the film being gripped are cut off, and the take-up speed in the film vertical direction Can be adjusted and relaxed in the vertical direction. As a means for relaxing, the speed of the roll group on the tenter exit side is adjusted. As the rate of relaxation, the speed of the roll group is reduced with respect to the film line speed of the tenter, and preferably the speed is reduced by 0.1 to 1.5%, that is, relaxation (hereinafter this value is referred to as the relaxation rate). More preferably, a relaxation rate of 0.2 to 1.2%, more preferably a relaxation rate of 0.3 to 1.0% is performed to adjust the heat shrinkage rate in the longitudinal direction. Further, the width of the film in the horizontal direction can be reduced in the process until both ends are cut off, so that a desired heat shrinkage rate can be obtained.

[Physical properties]
The white film of the present invention thus obtained has a heat shrinkage rate of 85 ° C. of 0.7% or less, more preferably 0.6% or less, and particularly preferably 0.5% or less in two orthogonal directions. Is possible. The thickness of the film after biaxial stretching is preferably 25 to 250 μm, more preferably 30 to 220 μm, and still more preferably 40 to 200 μm. If the thickness is less than 25 μm, the reflectance decreases, and if it exceeds 250 μm, the increase in the reflectance cannot be expected even if the thickness is increased beyond this, which is not preferable.

  The white film obtained by the present invention can achieve 92% or more, more preferably 95% or more, and particularly preferably 97% or more as an average reflectance at a wavelength of 400 to 700 nm as a reflectance of at least one surface. If it is less than 92%, it is not preferable because sufficient screen brightness cannot be obtained.

The white film obtained by the present invention can achieve a surface resistance value of 10 ¹⁴ Ω / □ or less after ultraviolet irradiation. If it exceeds 10 ¹⁴ Ω / □, there is a concern about adhesion of dust due to electrification, which is not preferable.

The white film obtained by the present invention can achieve a hue change ΔE * 5 or less after ultraviolet irradiation. If it exceeds 5, the reflectance is lowered due to yellowing of the white film by ultraviolet rays, which is not preferable. In addition, the ultraviolet irradiation here uses a high-pressure mercury lamp irradiator “Toscuer 401” manufactured by Harrison Toshiba Lighting Co., Ltd. for 3 hours at an intensity of 30 mW / cm ² .

  Hereinafter, the present invention will be described in detail by way of examples. Each characteristic value was measured by the following method.

(1) Film thickness A film sample was measured for 10-point thickness with an electric micrometer (K-402B manufactured by Anritsu), and the average value was taken as the thickness of the film.

(2) Thickness of each layer A sample is cut into triangles, fixed to an embedded capsule, and then embedded in an epoxy resin. Then, after embedding the sample with a microtome (ULTRACUT-S) into a thin film section having a thickness of 50 nm in parallel with the microtome, the specimen was observed and photographed with a transmission electron microscope at an acceleration voltage of 100 kv. The thickness of each layer was measured and the average thickness was determined.

(3) Reflectance An integrating sphere was attached to a spectrophotometer (Shimadzu Corporation UV-3101PC), and the reflectance when the BaSO ₄ white plate was 100% was measured over 400 to 700 nm. The reflectance was read from the obtained chart at intervals of 2 nm. An average value was determined within the above range.

(4) Ultraviolet irradiation accelerated test Using a high-pressure mercury lamp irradiator “Toscuer 401” manufactured by Harrison Toshiba Lighting Corporation, irradiation was performed at an intensity of 30 mW / cm ^{2 for} 3 hours.

(5) Surface resistance value The surface resistivity on the surface of the antistatic layer is 1 minute at an applied voltage of 100 V under the conditions of a measurement temperature of 23 ° C. and a measurement humidity of 60% RH using a “specific resistance measuring device” manufactured by Takeda Riken. The subsequent surface resistivity (Ω / □) was measured. Moreover, said ultraviolet irradiation acceleration | stimulation test was done and the surface resistance value after irradiation was measured similarly.

(6) Glass transition point (Tg), melting point (Tm)
Using a differential scanning calorimeter (TA Instruments 2100 DSC), the measurement was performed at a heating rate of 20 m / min.

(7) Average particle size of inorganic particles Using an S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., arbitrarily measure 100 particles each before being added to the resin (film) at a magnification of 10,000 times. (In the case of an ellipse, the average particle diameter was determined by (long diameter + short diameter) / 2).

(8) Hue change ΔE *
The above UV irradiation acceleration test is performed, and the hue before processing (L1 *, a1 *, b1 *) and the hue after processing (L2 *, a2 *, b2 *) are measured by a color difference meter (Nippon Denka SZS-Σ90 COLOR). (MEASURING SYSTEM) and the hue change ΔE * was determined by the following formula.
ΔE * = {(L1 * -L2 *) 2 + (a1 * -a2 *) 2 + (b1 * -b2 *) 2} 1/2

(9) Appearance of coating The surface of the coating film was evaluated for omission of coating, defects such as coating stripes by visual observation under a fluorescent lamp. The film was evaluated for a range of 10 m in the longitudinal direction.
○: Neither application omission nor application stripe is visible ×: Application omission or application stripe is visible

(10) Coating thickness The film was fixed with an embedding resin, the section was cut with a microtome, stained with 2% osmic acid at 60 ° C. for 2 hours, and the coating thickness was measured with a transmission electron microscope.

(11) Ingredients Acrylic 1
Product name “RX9008A” manufactured by Nippon Carbide

・ AS1
Copolymer having a structure represented by the following formula: 50 mol% / methyl acrylate 35 mol% / N-methylol acrylamide 15 mol%

・ AS2
Copolymer having a repeating unit having a structure represented by the following formula: 60 mol% / methyl acrylate 35 mol% / acrylic acid 5 mol%

・ AS3
Copolymer made of 95 mol% / methacrylic acid 5 mol% of repeating units having a structure represented by the following formula

・ AS4
Homopolymer consisting of 100 mol% of repeating units having a structure represented by the following formula

・ Crosslinking agent 1 Oxazoline manufactured by Nippon Shokubai "Epocross WS-700"
・ Cross-linking agent 2 Oxazoline made by Nippon Shokubai "Epocross WS-300"
・ Surfactant 1 manufactured by Kao Polyoxyethylene distyrenated phenyl ether
Product name "Emulgen A90"
・ Surfactant 2 Polyoxyethylene distyrenated phenyl ether made by Kao
Product name "Emulgen A60"
・ Surfactant 3 Polyoxyethylene alkyl ether made by Kao
Product name "Emulgen 1108"
・ Surfactant 4 Kao polyoxyethylene oleyl ether
Product name "Emulgen 420"

[Examples 1 to 8]
As shown in Table 1, particles were added to various polymers (polymers obtained by copolymerizing the components described in the copolymerization component column to the polymers described in the resin type column) and heated to 275 ° C., respectively. A three-layer feed block device (provided that Examples A and B are A / B / A in Examples 7 and 8). In Examples 7 and 8, they were joined using a two-layer feed block device) and formed into a sheet from a die while maintaining the laminated state. Furthermore, this sheet is cooled and solidified with a cooling drum having a surface temperature of 25 ° C. to form an unstretched film, which is heated at the temperature described in Table 2 and stretched in the longitudinal direction (longitudinal direction). Cooled down. Subsequently, in order to provide an antistatic layer on one side of the longitudinally stretched film, coating with an aqueous coating agent (concentration: 1.5% by weight) shown in Table 3 was performed, and then the film was guided to a tenter while holding both ends with clips. In an atmosphere heated to 120 ° C., the film was stretched in the direction perpendicular to the longitudinal direction (lateral direction). In the two-layer films of Examples 7 and 8, coating was performed on the side where the amount of inorganic particles added was large. Thereafter, heat setting was performed in the tenter at the temperature shown in Table 2, longitudinal relaxation and lateral width entered in the temperature range shown in Table 2 were performed, and the mixture was cooled to room temperature to obtain a white film. The physical properties of the obtained white film as a reflector substrate were evaluated. The results are summarized in Table 3.

[Comparative Examples 1 and 2]
The same procedure as in Example 1 was performed except that the conditions were changed as shown in Tables 1 and 2. Table 3 shows the evaluation results.

[Comparative Example 3]
The same procedure as in Example 1 was performed except that the coating was not performed. Table 3 shows the evaluation results.

[Comparative Examples 4 to 7]
The same procedure as in Example 1 was performed except that the conditions were changed as shown in Tables 1 and 2. Table 3 shows the evaluation results.

[Comparative Example 8]
A film roll was prepared without coating with a water-soluble coating, and then a water-insoluble coating was applied as shown below, and the thickness after coating was adjusted to 2500 nm (2.5 μm). . The surface resistance after UV irradiation was high.

下記式に示す構造の化合物 ５部

Water-insoluble coating liquid Toluene / ethyl acetate = 1/1 mixed solution 70 parts Acrylic resin (1-butene / methyl methacrylate / methacrylic acid / butyl acrylate / hydroxyethyl acrylate = 4/47/19/27/3 20 parts 5 parts of a compound having the structure shown below

5 parts of the compound shown in the following formula

  The white film of the present invention can be particularly suitably used as a reflector for a surface light source, particularly as a reflector used for a backlight unit of a liquid crystal display. In addition, back plates for solar cells, base materials for reflectors for internally illuminated signboards, base materials for paper substitutes, that is, cards, labels, stickers, home delivery slips, image paper for video printers, inkjets, barcode printers It can also be used as a base material for receiving sheets used for various printing records such as image receiving paper, posters, maps, dust-free paper, display boards, white boards, thermal transfer, offset printing, telephone cards and IC cards.

Claims (3)

A white film comprising a polyester film and an antistatic layer provided on at least one surface thereof, wherein the antistatic layer contains 10 to 50% by weight of a polymeric antistatic agent composed of a repeating unit represented by the following formula: A white film comprising 3 to 15% by weight of a surfactant having a phenyl group.

  The white film of Claim 1 used as a reflecting plate for surface light sources.   A liquid crystal display device comprising the white film according to claim 2.