JPH0961804A - Light diffusing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give flame-retardant property to a film without decreasing optical properties such as luminance, light-diffusing property and chromaticity and environmental characteristics such as moisture resistance and weather resistance by using a phosphate, bromine compd. or chlorinated paraffin flame retardant as a flame retardant. SOLUTION: A flame retardant is added to a light-diffusing layer 10 composed of a light-transmitting resin and light-diffusing fine particles 9 formed on at least one side or both sides of a base film 7. The flame retardant is a phosphate, bromine compd. or chlorinated paraffin and is compounded by 0.5-30 pts.wt. to 100 pts.wt. of the light-diffusing layer. The base film 7 is selected from oriented or non-oriented 50-200μm-thick films of polyethylene terephthalate, cellulose triacetate, polymethyl methacrylate, etc. The film of polyethylene terephthalate or polycarbonate after the treatment to impart flame retardant property is preferably used considering the resistance against light, moisture resistance, etc.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light diffusing film used in a backlight system for a liquid crystal display device.

[0002]

A backlight system for a liquid crystal display device includes a linear light source, which is a fluorescent tube of the backlight, a light guide plate made of a light transmissive material, a light reflector, and a light guide plate serving as a light emitting surface. A light diffusion film placed on the top of the
It is composed of a lens sheet. However, the conventional light diffusing film, particularly the light diffusing film provided with the light diffusing layer in which resin-based light diffusing fine particles are dispersed as the main component, has not been given special consideration to flame retardancy. Therefore, even if the other parts of the liquid crystal display device are made flame-retardant, the backlight as a whole will start burning if it accidentally comes into contact with the flame and will not burn even after the flame is removed. There was a problem of continuing. An object of the present invention is to provide a light diffusing film having flame retardancy in order to solve self-combustibility of a liquid crystal display device.

[0003]

A light diffusing film for a liquid crystal display device of the present invention comprises a light transmissive resin 8 and light diffusing fine particles provided on at least one surface or both surfaces of a base film 7 made of a thermoplastic resin. The light-diffusing layer 10 contains a flame retardant. The light diffusion layer contains 0.5 to 30 parts by weight of a phosphoric acid ester-based compound, a bromine-based compound, or a chlorinated paraffin-based flame retardant in 100 parts by weight of the light diffusion layer. It is a film.

[0004]

2. Description of the Related Art A backlight for a liquid crystal display device is shown in FIG.
The edge light method shown in is often used. The edge light type backlight includes a light guide plate 2 made of a light transmissive material (for example, polymethylmethacrylate), a linear light source 1 made of a cold cathode tube and the like provided at an upper end portion thereof,
A light reflection plate 3 arranged to cover the side surface of the light guide plate 2 and the linear light source 1, a light diffusion film 4 arranged on the side surface of the light guide plate 2 serving as an output light source, a polarizing plate 5, and a lens as necessary. It consists of a sheet.

As shown in FIG. 1, light emitted from a linear light source 1 which is a backlight fluorescent tube is sent to a light diffusion film 4 and diffused by a light guide plate 2 and a reflecting plate 3 behind it. It passes through the polarizing plate 5 and the liquid crystal panel 6.

Conventionally, as shown in FIG. 2 (a), a light diffusing film has a base film 7 made of polyethylene terephthalate, polycarbonate, or the like, on at least one surface thereof,
Light-transmissive resin 8 as a main binder and light-diffusing fine particles 9
2 is provided by coating the light diffusion layer 10 in which
As shown in (b), a concavo-convex pattern layer 11 is formed by embossing or sandblasting on the side of the base film 7 such as polycarbonate or polymethylmethacrylate where the light diffusion layer 10 is not present, or as shown in FIG. ), A mat layer 12 in which an inorganic filler 13 is dispersed in a binder 14 of a mat layer is coated on the side where the light diffusion layer 10 of the base film 7 is not provided, or a resin such as polycarbonate (not shown). In order to form a void by dispersing a light diffusing agent, or a combination of these processing methods has been used.

The light diffusing layers used in the above light diffusing films were all flammable materials and had no fire extinguishing property. In addition, the above light-diffusing film was simply laminated with a light-diffusing layer containing a flame-retardant agent and subjected to flame-retardant processing, but there are problems of transparency, cost, waste pollution, and safety. From the viewpoint, it was not always satisfactory.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 2, a light diffusing film for a liquid crystal display device of the present invention has a light transmitting resin and a light diffusing property provided on at least one surface or both surfaces of a base film 7 made of a thermoplastic resin. Light diffusion layer 10 composed of fine particles 9
It contains a flame retardant. Further, as the flame retardant for the light diffusion layer, a phosphoric acid ester-based, bromine-based compound or chlorinated paraffin-based flame retardant is blended in an amount of 0.5 to 30 parts by weight in 100 parts by weight of the light diffusion layer. It is a light diffusion film for.

In consideration of transparency, light resistance, coatability, etc., the base film of the present invention may be stretched or unstretched with polyethylene terephthalate, cellulose triacetate, polymethylmethacrylate, polycarbonate, methylpentene polymer, polypropylene, polystyrene or the like. It can be appropriately selected from a stretched film of 50 to 200 μm. From the viewpoint of light resistance and moisture resistance, it is desirable to use a grade obtained by subjecting polyethylene terephthalate or polycarbonate to a flame-retardant treatment. Also, in order to prevent Newton's rings from coming into contact with the light guide plate and causing uneven brightness, an uneven pattern layer is formed on the surface of the base film opposite to the surface on which the light diffusion layer is provided by embossing or sandblasting. By providing or by providing a matte coat layer in which an inorganic filler such as calcium carbonate or silica is dispersed and coated in a resin varnish, adhesion with the light guide plate is prevented. Further, it is preferable that the matte coat layer has a function of preventing reflection of light from the substrate.

The light-transmitting resin used for the resin varnish of the light-diffusing layer is a linear polyester, an acrylic resin, a vinyl chloride / vinyl acetate copolymer, a vinyl butyral resin, a polystyrene resin, a polyvinylidene chloride resin, Examples thereof include polyethylene, polypropylene and their copolymers, polyurethane resins, polyamides, polyvinyl acetates, polyvinyl alcohols, epoxy resins, cellulose derivatives, organosiloxane resins, polyimides, polysulfones, and polyarylates. Then, using a simple substance or a copolymer of these resins as a binder or a mixture of two or more kinds including additives such as a plasticizer, a varnish using an organic solvent or water as a medium is prepared. Among these, as the binder, it is easy to control the difference in refractive index between the light-diffusing fine particles, the wettability is good, and the light-diffusing layer formed on the base film has adhesiveness with the base film, light resistance, Polyester, which has excellent scratch resistance and transparency, is desirable.

The flame retardant used for the resin varnish of the light diffusion layer is
It can be selected from phosphorus-based flame retardants, halogen-based flame retardants, chlorine-based flame retardants, aluminum hydroxide, magnesium hydroxide, antimony-based flame retardants and the like. In particular, it has excellent compatibility with the light-transmitting resin that constitutes the light-diffusing layer, and has optical properties such as brightness, light-diffusing property and chromaticity of the light-diffusing film, and environmental properties such as heat resistance, moisture resistance and weather resistance. Phosphate ester-based, bromine-based compounds or chlorinated paraffin-based flame retardants that do not reduce the amount are preferable.

The flame retardant is added in an amount of 0.5 to 30 parts by weight based on 100 parts by weight of the light diffusion layer. If it is less than 0.5 parts by weight with respect to 100 parts by weight of the light diffusion layer, flame retardancy cannot be imparted to the light diffusion film, and if it exceeds 30 parts by weight, the optical diffusion characteristics such as optical characteristics and environmental characteristics. Will be reduced.

To provide a light diffusing layer on the substrate film, a composition prepared by dispersing a flame retardant in a light transmitting resin varnish is used as a slit reverse method, a comma coat method, a three roll reverse coat method, a die coat method. Ordinary coating methods such as the curtain flow coating method and the gravure coating method can be used. The composition is coated and dried by adjusting the viscosity, taking into consideration the desired coat thickness, heat resistance of the base film and the like. The coating amount is preferably 10 to 50 μm (as solid matter), though it depends on the thickness of the substrate film. Further, in order to strengthen the adhesion between the light diffusion layer and the base film, a primer layer may be provided between them, if necessary.

As described above, by using a phosphoric acid ester type, bromine type compound or chlorinated paraffin type flame retardant as the flame retardant, the optical properties such as brightness, light diffusivity and chromaticity of the light diffusion film, It is possible to impart flame retardancy without deteriorating environmental resistance such as humidity resistance and weather resistance. Further, these phosphoric acid ester-based, bromine-based compounds or chlorinated paraffin-based flame retardants have a plasticizing effect on the resin used as the binder, and have the effect of preventing curling of the light diffusion film.

Next, the present invention will be described in more detail with reference to the drawings.

【Example】

(Example 1) In FIG. 2 (c), as a base material film 7, a 100 μm thick biaxially stretched polyethylene terephthalate film (HS type) manufactured by Teijin Limited was coated on one surface with Diffusing layer coating liquid] was comma-coated and dried to form a light diffusing layer 10 having a thickness of 20 μm and comprising light diffusing fine particles 9, a light transmitting resin 8 and a flame retardant. Then, on the other surface of the polyethylene terephthalate film, a two-component reactive resin having the following composition is used as a binder 14
[Coating liquid for mat layer] containing an inorganic filler 13 as a matting agent is coated by a gravure reverse method, dried, and provided with a matting layer 12 having a thickness of 5 μm by aging at 45 ° C. for 48 hours to provide the liquid crystal display of the present invention. A light diffusion film 4 for a device was created. [Coating liquid for light diffusing layer] Light-transmitting resin Polyester Byron # 200 100 parts by weight Toyobo Co., Ltd.-Light-diffusing fine particles Acrylic resin beads Average particle diameter 10 μm 70 parts by weight Sekisui Plastics Co., Ltd. MB50X- 10 ・ Flame retardant Phosphoric acid ester flame retardant 20 parts by weight Asahi Denka Kogyo PFR ・ Solvent Toluene 200 parts by weight Methyl ethyl ketone 200 parts by weight [Coat liquid for mat layer] ・ Polyester Byron # 200 Toyobo Co., Ltd. 30 parts by weight Part-inorganic filler microsilica average particle size 5 μm 1 part by weight-solvent toluene 35 parts by weight methyl ethyl ketone 35 parts by weight-curing agent XEL curing agent (D) 75 parts by weight The Inktec Co., Ltd.-solvent ethyl acetate 25 parts by weight

(Example 2) In FIG. 2 (b), as the base film 7, a surface opposite to the mat surface of a biaxially stretched polyethylene terephthalate film (PS type) having a thickness of 100 μm manufactured by Teijin Ltd. Then, the same [light diffusing layer coating liquid] as in Example 1 was coated by comma coating and dried to provide a light diffusing layer 10 having a thickness of 20 μm, and the light diffusing film 4 for a liquid crystal display device of the present invention was obtained. Created.

Example 3 In FIG. 2 (c), the flame retardant of the coating liquid for the light diffusion layer was replaced by Asahi Denka Kogyo Co., Ltd. instead of 20 parts by weight of the phosphate ester type flame retardant PFR. A light diffusion film 4 for a liquid crystal display device of the present invention was produced in the same manner as in Example 1 except that 40 parts by weight of chlorinated paraffin flame retardant E500 manufactured by Co., Ltd. was used.

(Comparative Example 1) Although not shown, the same procedure as in Example 1 was carried out except that a flame retardant was not added to the coating solution for the light diffusion layer, on the surface opposite to the mat surface of the stretched polyethylene terephthalate film. [Light diffusing layer coating liquid] is provided by comma coating to form a light diffusing layer 10 having a thickness of 20 μm,
A light diffusion film 4 for a liquid crystal display device of a comparative example was created.

Table 1 shows the results of evaluation of the optical characteristics and durability tests of the light diffusion films for liquid crystal display devices of Examples 1 to 3 and Comparative Example as follows. Evaluation method * 1 Luminance: Luminance measuring instrument MP-8 manufactured by Topcon Corporation
Using, the average value of the brightness at the position corresponding to the opening of the liquid crystal display is divided into 3 × 3 9 parts is compared. * 2 Light diffusivity: The dot pattern on the back surface of the light guide plate is visually recognized with the dot pattern of the comparative example. * 3 Chromaticity: Using a color computer SM-5 manufactured by Suga Test Instruments Co., Ltd., the chromaticity measured by the transmitted light of a halogen lamp is compared. * 4 High-temperature and high-humidity test: Confirm optical characteristics (luminance, chromaticity, light diffusion), curling, presence or absence of coating layer peeling, and changes in appearance after leaving for 2000 hours under conditions of 60 ° C and 90% relative humidity. . * 5 Light resistance test: Xenon long life weather meter WEL-25AX-HC-BE manufactured by Suga Test Instruments Co., Ltd.
320W / m ² × 500 with xenon lamp by c ・ L
hr = 560,000 KJ / m ² , set temperature 65 ° C., set relative humidity 50%, irradiation area 4.5 cm × 5.5 cm, and the optical characteristics (luminance, chromaticity, Check for light diffusivity), curling, peeling of coating layer, and appearance change. * 6 Curling resistance: The samples after the high temperature and high humidity test and the light resistance test are visually evaluated for curling. (Below margin)

[0020]

[Table 1]

[0021]

INDUSTRIAL APPLICABILITY As described above, the present invention uses a phosphoric acid ester type compound, a bromine type compound or a chlorinated paraffin type flame retardant as the flame retardant, so that the brightness, the light diffusing property and the color of the light diffusion film can be improved. Optical properties such as degree, moisture resistance,
Flame retardancy can be imparted without deteriorating environmental resistance such as weather resistance. Further, these phosphate ester-based, bromine-based compounds or chlorinated paraffin-based flame retardants have a plasticizing effect on the resin used as the binder, and can also prevent curling of the light diffusion film. Therefore, all of the optical properties such as brightness, light diffusivity and chromaticity are at a high level, and temperature, humidity,
UL standard "combustion test 94VTM- for polymer materials" does not cause deterioration of optical characteristics or curls even when exposed to environmental changes such as light irradiation, and self-extinguishes even when contacted with flame. A light diffusing film having a flame retardancy of 2 "or more can be formed, and an excellent effect is obtained as a backlight for a liquid crystal display device.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a cross section of a liquid crystal display device.

FIG. 2 (a) is a schematic sectional view of a light diffusion film according to the present invention. (b) It is a cross-sectional conceptual diagram of the light diffusion film according to Example 2. (c) It is a cross-sectional conceptual diagram of a light diffusion film according to Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Line light source 2 Light guide plate 3 Reflector 4 Light diffusing film 5 Polarizing plate 6 Liquid crystal panel 7 Base film 8 Light transmissive resin in which flame retardant is dispersed 9 Light diffusing fine particles 10 Light diffusing layer 11 Uneven pattern layer 12 of film Coat layer 13 Inorganic filler 14 Mat layer binder

Claims (2)

[Claims] 1. A flame-retardant agent is contained in a light-diffusing layer made of a light-transmitting resin and light-diffusing fine particles provided on at least one side or both sides of a base film made of a thermoplastic resin. Light diffusion film for liquid crystal display devices. 2. The light-diffusing layer contains 0.5 to 30 parts by weight of a phosphoric acid ester-based compound, a bromine-based compound, or a chlorinated paraffin-based flame retardant in 100 parts by weight of the light-diffusing layer. A light diffusing film for a liquid crystal display device according to claim 1.