JPH07220514A - Light diffusion plate manufacturing method - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a method for manufacturing a light diffusion plate having high front luminance and excellent optical performance. [Structure] Photopolymerizable transparent resin layers having different photopolymerization rates are laminated on a support in order of increasing photopolymerization rate to provide a photocurable layer having a multilayer structure of two or more layers, and then regular arrangement and spacing. Is exposed and cured from the side of the photopolymerizable resin layer having a low photopolymerization rate through the negative mask pattern having the above, and the uncured portion is removed by development to form a large number of fine irregularities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a light diffusing plate used for displays, lighting covers and the like.

[0002]

2. Description of the Related Art A light diffusing plate is a backlight unit of a liquid crystal display, a transmissive type, in order to obtain a uniform surface illumination with high front brightness by diffusing light from a point light source or a linear light source and adjusting the emission angle. It is used for a screen, a cover of a lighting device, and the like. Conventionally, the above light diffusion plate,
The surface of an optically transparent thermoplastic resin extruded film or sheet is sandblasted, honing treated, embossed, and press-molded using a mold with fine irregularities on the surface It is manufactured by forming regular or random unevenness.

Examples of the thermoplastic resin extruded film or sheet include metal oxides such as titanium dioxide, silicon dioxide and aluminum oxide; minerals such as mica; metals such as aluminum powder, tin powder, gold powder and silver powder. A material in which a light diffusing substance such as powder is uniformly mixed and dispersed is also used.

Regarding the light diffusing plate having the above-mentioned regular unevenness, for example, a method of adjusting the light ray direction by using a diffusing plate having a prism shape is disclosed in JP-A-61-57902 and JP-A-61-15104. It is disclosed in the publication.

As a method for forming fine irregularities on the light diffusing plate, for example, a method in which a resin softened by heat is pressure-processed by an embossing roll is disclosed in JP-A-56-157319 and JP-A-1-157319. It is disclosed in Japanese Patent No. 316703. Further, a method of pressing a light or thermosetting resin against a mold having a finely textured surface to cure the resin is disclosed in JP-A-63-82401 and JP-A-2-193102. .

[0006] In the method using the embossing roll and the mold described above, it takes time and effort to manufacture a light diffusing plate which gives a fine unevenness on the surface and obtains high front luminance.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above drawbacks, and an object of the present invention is to provide a method for manufacturing a light diffusing plate having high front brightness and excellent optical performance. is there.

[0008]

As the support used in the present invention, a chemically and thermally stable resin or glass plate, sheet, film or the like can be used. A synthetic resin film is preferably used, and examples of the support include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; polyvinyl halides such as polyvinyl chloride and polyvinylidene chloride; polyamides. Resin films such as polycarbonates are mentioned, and biaxially stretched polyethylene terephthalate is particularly preferable.

The support may be used as a light diffusing plate without removing it, and if the photocurable layer is sufficiently thick and can be formed into a sheet by photocuring, the support is used. It can be removed to form a light diffusion plate.

When the support is used as a light diffusion plate without removing the support, a transparent support is used. At that time, an easy adhesion treatment such as an electric discharge treatment may be added to the surface on which the photopolymerizable transparent resin layer is provided, and when the support is removed and used, a mold release treatment may be performed. Good.

The photopolymerizable transparent resin layer used in the present invention may be any one having photopolymerizability and capable of removing the unexposed portion by development, and examples thereof include a photopolymerizable unsaturated compound and a photopolymerization initiator. Examples include agents and linear polymers.

The above-mentioned photopolymerizable unsaturated compound is preferably a photopolymerizable monomer which is liquid at room temperature and can be cured by initiating a polymerization reaction upon irradiation with light of a photopolymerization initiator. As the monomer, polyfunctional (meth) acrylate,
Examples include monofunctional (meth) acrylates.

Examples of the polyfunctional (meth) acrylates include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, nonaethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate,
Tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, nonapropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol penta (meth) Acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tri (meth) acrylate, 2,2-bis [4- (acryloxydiethoxy) phenyl] propane, 2,2-bis [4- (methacryloxydi) Ethoxy)
Phenyl] propane, 3-phenoxy-2-propanoyl acrylate, 1,6-bis [3-acryloxy-2
-Hydroxypropyl] hexyl ether and the like can be mentioned. ,

Examples of the monofunctional (meth) acrylate include methyl (meth) acrylate and benzyl (meth) acrylate.

Examples of photopolymerizable monomers other than the above include urethane and polyester acrylate oligomers.

The above photopolymerizable unsaturated compounds may be used alone or in combination of two or more.

For example, when an alkaline aqueous solution is used as the developing solution, the above linear polymer may be one that is soluble or swellable in the alkaline aqueous solution, for example, α, β-unsaturated ethylene having a carboxyl group. It is composed of a copolymer of a base monomer polymer and an α, β-unsaturated ethylene monomer having no carboxyl group.

Examples of the α, β-unsaturated ethylenic monomer having a carboxyl group include (meth) acrylic acid, crotonic acid, maleic acid (anhydride), fumaric acid,
Examples thereof include unsaturated carboxylic acids such as itaconic acid.

Further, α, β-having no carboxyl group
Examples of unsaturated ethylenic monomers include styrene and
o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene,
Styrenes such as 2,4-dimethylstyrene, pn-hexylstyrene, pn-octylstyrene, p-methoxystyrene, p-phenylstyrene and 3,4-dimethylchlorostyrene; such as α-vinylnaphthalene Vinylnaphthalene; ethylene, propylene, butylene or C _{5 to} C ₃₀ and higher α-olefins; vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride; vinyl acetate, vinyl propionate, vinyl butyrate. Vinyl esters such as; methyl (meth) acrylate,
Propyl (meth) acrylate, butyl (meth) acrylate, ithibutyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acrylic acid −
(Meth) acrylic acid esters such as 2-chloroethyl, α-chloro (meth) acrylate, phenyl (meth) acrylate, and dimethylaminoethyl (meth) acrylate; vinyl ethers such as vinyl methyl ether and vinyl ethyl ether. Vinyl ketones such as vinyl methyl ketone and vinyl ethyl ketone; N-vinyl compounds such as N-vinyl pyrrole and N-vinyl indole;
Examples thereof include (meth) acrylonitrile and (meth) acrylic acid amides.

When the weight average molecular weight of the linear polymer is small, so-called cold flow is likely to occur, and when the photopolymerizable transparent resin layer is formed and then wound into a roll and stored, the photopolymerizable transparent resin layer is stored. Wrinkles
When it is large, it becomes difficult to dissolve in a solvent during coating, and the coating viscosity also increases and the coatability decreases, so that it is 20,000 to 3
It is preferably 0,000, more preferably 50,000 to 200,000.

When the amount of the linear polymer added is increased, the developability is deteriorated and it becomes difficult to form the desired unevenness, and when the amount is decreased, the solubility of the photopolymerizable transparent resin layer in an alkaline aqueous solution is decreased, Since the developability decreases, 30 parts by weight to 100 parts by weight of the photopolymerizable unsaturated compound is added.
It is preferable to use 300 parts by weight.

Any photopolymerization initiator may be used as long as it has a property of initiating the polymerization of the photopolymerizable unsaturated compound by an actinic ray such as a visible ray or an ultraviolet ray. , Sulfides such as, for example, sodium methyl dicarbamate sulfide, tetramethyl thiuram monosulfide, diphenyl monosulfide, dibenzothiazoyl monosulfide and disulfide; thioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-diethyl. Thioxanthone derivatives such as thioxanthone; diazo compounds such as hydrazone, azobisisobutyronitrile, benzenediazonium; benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether Aromatics such as benzoleone, benzophenone, dimethylaminobenzophenone, Michler's ketone, benzylanthraquinone, t-butylanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-aminoanthraquinone, 2-chloroanthraquinone, benzyldimethylketal, and methylphenylglyoxylate. Group carbonyl compounds; 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, α-hydroxy-α, α'-dimethyl-acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy Acetophenone derivatives such as acetophenone;
Dialkylaminobenzoic acid esters such as methyl p-dimethylaminobenzoate, ethyl p-dimethylaminobenzoate, butyl p-dimethylaminobenzoate and isopropyl p-diethylaminobenzoate; benzoyl peroxide, di-t-butyl peroxide , Peroxides such as dicumyl peroxide and cumene hydroperoxide; 9-phenylacridine, 9-p-methoxyphenylacridine, 9-acetylaminoacridine,
Acridine derivatives such as benzacridine; 9,10-
Phenazine derivatives such as dimethylbenzphenazine, 9-methylbenzphenazine, 10-methoxybenzphenazine; 4,4 ', 4 "-trimethoxy-2,3-diphenylquinosaline and other quinosaline derivatives; 2,4,5
-Triphenylimidazoyl dimer; halogenated ketones; acylated phosphorus compounds such as acylphosphine oxide and acylphosphonate.

When the amount of the photopolymerization initiator added is small, it takes a long time to cure, and when it is not sufficiently cured, the formation of irregularities is deteriorated, and when the amount is large, the cured photopolymerizable transparent resin layer turns yellow. Therefore, the amount is preferably 0.05 to 10 parts by weight with respect to the photopolymerizable unsaturated compound.

The photopolymerization rate in the present invention means the photocuring reaction rate of a photopolymerizable unsaturated compound, and the photocuring reaction rate is the addition of a photopolymerization initiator added to the photopolymerizable transparent resin layer. The larger the amount, the larger the amount, and the smaller the amount, the smaller the amount.

When the ratio of the photopolymerization rate of the photopolymerizable transparent resin layer having the highest photopolymerization rate to the photopolymerization rate of the photopolymerizable transparent resin layer having the lowest photopolymerization rate used in the present invention becomes smaller, The curing of the joint with the photopolymerizable transparent resin layer is delayed, and the required exposure amount is large, resulting in overexposure, and when it is large, the amount of the photopolymerization initiator is large and the light diffusion plate tends to yellow. Therefore, it is preferably 2 to 20 times, more preferably 4 to 10 times, and the photopolymerizable transparent resin layer having an intermediate photopolymerization rate of these is adjusted as necessary by adjusting the addition amount of the photopolymerization initiator. Created.

The photopolymerizable transparent resin layer is provided with additives such as thermal polymerization inhibitors such as hydroquinone and p-methoxyphenol; stabilizers; UV absorbers; antioxidants; surface modifiers; defoamers. The photopolymerizable unsaturated compound 100 may be added. If the addition amount of these additives is small, there is no effect, and if the addition amount is large, the photopolymerizable transparent resin layer is colored or the light transmittance is lowered. 5 to 0.05 for parts by weight
It is preferable to add parts by weight.

The above-mentioned photopolymerizable transparent resin layer has a light-scattering powder for the purpose of improving the light-diffusing performance and concealing the light-scattering dots formed on the light guide plate usually arranged on the back surface of the light-diffusing plate. A body may be added, and examples of such a light-scattering powder include metal oxides such as divalent titanium, silicon dioxide, and aluminum oxide, minerals such as mica, aluminum powder, tin powder, gold powder, and silver powder. Materials generally used as a light-scattering substance such as metal powder can be used.

When the amount of the light-scattering powder added is large, the light-transmitting property is poor, and the light-diffusing plate is fragile. When the amount is small, light-scattering occurs locally to generate bright spots, and the light-diffusing performance is deteriorated. Photopolymerizable unsaturated compound 100
The amount is preferably 1 to 400 parts by weight, more preferably 10 to 300 parts by weight, based on parts by weight.

To form the photopolymerizable transparent resin layer used in the present invention, for example, the above-mentioned photopolymerizable unsaturated compound,
A photopolymerization initiator and a linear polymer are mixed with a solvent, and the mixture is stirred and dissolved using a commonly used stirrer to obtain a coating solution, such as a roll coating method, a doctor blade method, and a bar coating method. The coating can be carried out by a known method, but the roll coating method is particularly preferably used, and the coating is carried out in this way, and if necessary, the solvent is removed using a dryer to form the layer.

As the solvent used for forming the photopolymerizable transparent resin layer, a commonly used colorless organic solvent can be used. Examples of these organic solvents include methyl ethyl ketone, toluene, methyl isobutyl ketone, cyclohexanone, Examples thereof include ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), butyl acetate, isopropyl alcohol, acetone, anisole, etc., which may be used alone or in combination.

The photocurable layer used in the present invention is applied in order from the photopolymerizable transparent resin layer having the highest photopolymerization rate,
Two or three or more photopolymerizable transparent resin layers having different photopolymerization rates are laminated and formed. As a method of laminating the photopolymerizable transparent resin layer on the photopolymerizable transparent resin layer,
A method of directly coating on the photopolymerizable transparent resin layer; a photopolymerizable transparent resin layer is formed on a separate support in the same manner as above, and superposed so that the photopolymerizable transparent resin layers are in contact with each other, A method of laminating under constant pressure so that air bubbles and the like do not enter, then peeling off the support provided with the photopolymerizable transparent resin layer having a lower photopolymerization rate, and transferring it may be mentioned.

In the above method for transferring the photopolymerizable transparent resin layer, the lamination is preferably carried out at a temperature as low as possible and at a low pressure, and the temperature is preferably 10 to 30 ° C. and the pressure is preferably 3 kg / cm ² or less. .

When the thickness of the photocurable layer is thin, the formation of irregularities is deteriorated, and when it is thick, the thickness of the display plate itself is increased when it is used for a liquid crystal display plate. The thickness of the transparent resin layer is preferably 3 to 200 μm,
5 to 500 μm is preferable.

A protective layer is preferably laminated on the photocurable layer for the purpose of preventing the inhibition of the photocuring reaction due to oxygen and the like and preventing the contamination of the negative mask. The protective layer is made of polyethylene terephthalate, stretched polypropylene or the like. Provided by laminating a film that is substantially transparent to light, or applying a dilute solution of a resin soluble in a developing solution such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, and polyacrylamide, and drying, If the thickness of the protective layer is increased, the formation of the unevenness is deteriorated due to diffraction, scattering, reflection, etc. of light.
The following is preferable.

The resin layer laminated as the protective layer is developed by removing the protective layer, and the protective layer is formed by applying a resin solution soluble in a developing solution.
A developing solution is sprayed and development is performed while removing the protective layer.

The fine irregularities used in the present invention have a problem that when the distance between the irregularities becomes large, the irregularities are visually recognized when the light diffusing plate is used on the liquid crystal display plate and the image quality deteriorates.
It is preferably 00 μm or less.

The shape of the unevenness is preferably one in which the cross section in the depth or height direction of the unevenness is a substantially triangular shape. For example, triangular pyramids, quadrangular pyramid convex shapes, triangular pyramids, quadrangular pyramid concave shapes, continuous shapes. A prismatic convex shape can be used.

In the above-mentioned continuous prism-shaped or cone-shaped convex, the higher the slope ratio (S) calculated by the following formula, and the closer the apex angle (α) is to 90 °, the higher the frontal luminance becomes. Those having S of 0.3 or more and α of 30 to 150 ° are more preferably used.

S = A / L

In the formula (1), L is a continuous prism-shaped convex, and is a line of intersection between a surface perpendicular to the light diffusing plate and perpendicular to the longitudinal direction of the continuous prism-shaped convex, and the outer surface of the convex. Is the length of the straight line of the slope portion, and in the cone-shaped convex, the intersection of the plane perpendicular to the light diffusing plate and containing the apex and the cone-shaped outer surface. It is the length of the line, and A represents the length of the straight line of the slope portion. ]

The protrusion may have a curved surface near the top or bottom.

To form the above-mentioned fine irregularities, the photocurable layer is exposed to an actinic ray such as an ultraviolet ray through a negative mask having a pattern-like optical density distribution having a regular arrangement or intervals to form the photocurable layer. It is cured by patterning, spraying a developing solution, rinsing the uncured portion with the developing solution, and leaving the insoluble cured portion on the support.

The exposure light source may be any one that can emit actinic rays, and a (super) high pressure mercury lamp, a mercury xenon lamp or the like that emits ultraviolet rays is preferably used.

In the above negative mask, for example, the light transmitting portion is a pattern of lattices, circles, dots, lines, etc.
As long as they are arranged regularly or randomly and convert the intensity of actinic rays into the above-mentioned pattern. Examples of such substances that convert the intensity of actinic rays into the pattern include negative films and chrome. Examples thereof include a dry plate and a metal plate having fine slits.

The developing solution is not particularly limited as long as it can dissolve the uncured photopolymerizable transparent resin layer, but an aqueous solution of sodium carbonate having a concentration of 0.5 to 5% by weight is preferable. There is no particular limitation on the developing device used for the development, and a known device can be used.

[0046]

EXAMPLES Next, examples of the present invention will be described. In the following, "parts" means "parts by weight".

(Example 1) (Preparation of coating solution for photopolymerizable transparent resin layer having high photopolymerization rate) Methyl methacrylate / butyl methacrylate / 2-ethylhexyl acrylate / methacrylic acid copolymer having a weight average molecular weight of 100,000 ( Weight ratio 31: 31: 13: 2
5) 100 parts, urethane acrylate oligomer (manufactured by Shin-Nakamura Chemical; PU-4000) 20 parts, trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical; A-TMP)
T) 80 parts, 2,2-dimethoxy-2-phenylacetophenone (manufactured by Ciba Geigy; Irgacure 651) 6
Part was dissolved in 300 parts of methyl ethyl ketone to prepare a coating solution for a photopolymerizable transparent resin layer having a high photopolymerization rate.

(Preparation of Photopolymerizable Transparent Resin Layer Coating Liquid with Low Photopolymerization Rate) The same procedure as described above except that the content of 2,2-dimethoxy-2-phenylacetophenone was changed from 6 parts to 0.8 parts. A coating liquid for a photopolymerizable transparent resin layer having a low photopolymerization rate was prepared. )

(Formation of Photocured Layer) Thickness of 10 as a support
A polyethylene terephthalate film having a thickness of 0 μm (manufactured by Teijin) was coated with the coating solution for the photopolymerizable transparent resin layer having a high photopolymerization rate by a roll coating method, at 50 ° C. for 1 minute, and then at 100 ° C. for 1 minute. After drying for 1 minute, thickness 80μm
Was provided with a photopolymerizable transparent resin layer.

As a support, a 100 μm-thick release-treated polyethylene terephthalate film (manufactured by Teijin) is coated with a coating solution for the photopolymerizable transparent resin layer having a low photopolymerization rate on the release-treated surface. It was coated on the surface by a roll coating method, dried at 50 ° C. for 1 minute and further dried at 100 ° C. for 1 minute, and then a photopolymerizable transparent resin layer having a thickness of 80 μm was provided.

The photopolymerizable transparent resin layer having a high photopolymerization rate and the photopolymerizable transparent resin layer having a low photopolymerization rate were superposed so as to be in contact with each other, and a laminator was used at room temperature to apply a pressing pressure of 2 kg / cm ² and a line speed. The film is uniformly laminated at 0.8 m / min, the support provided with the photopolymerizable transparent resin layer having a low photopolymerization rate is peeled off, and the photopolymerizable transparent resin layer having a low photopolymerization rate is transferred. A polyethylene terephthalate film having a thickness of 6 μm (manufactured by Teijin) as a protective layer is laminated on the above under the same conditions as the above-mentioned laminate to form a protective layer / photocurable layer (photopolymerizable transparent resin layer having a low photopolymerization rate / A laminate having a layer structure of photopolymerizable transparent resin layer / support having a high photopolymerization rate was obtained.

(Formation of Convexity) Contact with the protective layer of the above laminate
Width of 30 μm obtained by chrome plating on a glass plate
The linear mask part and the 30 μm wide linear light transmission part are alternately
Overlay the negative masks that have side-by-side patterns, and
Then, with the mercury xenon lamp, the irradiation dose is 60 and 120.
mJ / cm²To cure the light-transmitting part, and then
Peel off the protective layer and add 1 wt% sodium carbonate aqueous solution at 25 ° C.
Discharge pressure of 1.5 kg / cm using liquid ²Spray for 5 minutes
-Development, dissolve and remove uncured parts to form irregularities, and spread light
A spreading plate was prepared.

(Example 2) In order to prepare a coating solution for the photopolymerizable transparent resin layer having a high photopolymerization rate in Example 1, 2, 2
6 parts of dimethoxy-2-phenylacetophenone
6 parts, and the irradiation amount for forming unevenness is 140 mJ /
A light diffusing plate was produced in the same manner as in Example 1 except that cm ² was used.

(Comparative Example 1) Using a photo-curable layer consisting of only a photo-polymerizable transparent resin layer having a low photo-polymerization rate in Example 1, the irradiation dose was 120, 180, 250 mJ to form the projections.
A light diffusing plate was produced in the same manner as in Example 1 except that the light diffusion plate was set to / cm ² .

Comparative Example 2 The front luminance was measured using only the liquid crystal display plate without using the light diffusing plate.

The light diffusing plates obtained in Examples 1 and 2 and Comparative Example 1 were placed on a backlight for a liquid crystal display plate, and the front luminance was measured. The results are shown in Table 1. As for the front brightness, a light diffusing plate is arranged on the light guide plate of the backlight module for liquid crystal display in which one cold cathode tube is installed so that the continuous direction of the continuous protrusions is parallel to the longitudinal direction of the cold cathode tube. A luminance meter (manufactured by Minolta; LS-100) was installed at a distance of 30 cm and measured.

Further, the convex slope rate and the apex angle of the light diffusing plates obtained in Examples 1 and 2 and Comparative Example 1 were measured from scanning electron micrographs (Hitachi; model S-2300) and shown in Table 1. Indicated.

[0058]

[Table 1]

[0059]

As described above, the method for producing a light diffusing plate of the present invention comprises the steps of laminating photopolymerizable transparent resin layers having different photopolymerization rates on a support in order of increasing photopolymerization rate. Since a small photopolymerizable transparent resin layer is exposed to light and developed to form convex portions, a light diffusing plate having high front brightness can be produced even with a small exposure amount, and also when used as a light diffusing plate together with a support. Prevents peeling of protrusions, for liquid crystal display,
It can be used for lighting covers.

Claims (1)

[Claims] 1. A photopolymerizable transparent resin layer having a different photopolymerization rate is laminated on a support in order of increasing photopolymerization rate to provide a photocurable layer having a multilayer structure of two or more layers, and then a regular arrangement. ,
A method for producing a light diffusing plate, which comprises exposing and curing from a side of a photopolymerizable resin layer having a low photopolymerization rate through a negative mask pattern having a space, and removing an uncured portion by development to form irregularities.