Filler for optical films, and resin composition and optical film using the same.

Abstract

To provide an optical film filler that reduces the inclusion of aggregates and impurities and effectively prevents a decrease in the optical properties of the resulting optical film, as well as an optical film resin composition and optical film using the same. [Solution] The optical film filler of the present invention contains whisker-shaped calcium carbonate particles. Here, the whisker-shaped calcium carbonate particles have a major axis of 5 μm to 50 μm, a minor axis of 0.05 μm to 2 μm, and an aspect ratio of 5 to 50, and contain 0.03% to 0.7% by mass of phosphorus element based on the total mass of the whisker-shaped calcium carbonate particles.

Description

[Technical Field]

[0001] The present invention relates to a filler for optical films, and to a resin composition for optical films and an optical film using the same. [Background technology]

[0002] Thin displays such as liquid crystal displays (LCDs) and organic EL displays are extremely diverse, and there is a demand for larger displays with high resolution and viewing angle compensation for improved visibility. Seamless integration of thin displays is progressing in multi-display setups and large-scale video walls. Liquid crystal display devices operate when light emitted from the backlight unit passes through the light source polarizer, the liquid crystal panel, and the viewing side polarizer in that order. Light emitted from the light source is diffused as it passes through the backlight unit and then incident on the light source polarizer. Therefore, it has been pointed out that the contrast ratio decreases from the front to the side as the light passes through the light source polarizer, the liquid crystal panel, and the viewing side polarizer.

[0003] In the automotive sector, product development is progressing on using thin-screen displays for the entire unit panel that constitutes the main part of the instrument panel, or for the center information display (CID). Automotive interiors mainly use black (dark-colored) materials to prevent reflection of external light, but from a design perspective, seamless (neutral gray) designs are being made to make the boundary between the front panel, which is the outermost surface of the image display area of ​​the thin-screen display, and the surrounding materials (interior, etc.) less visible and to make the presence of the front panel less noticeable.

[0004] Furthermore, thin-screen displays are increasingly being embedded in various home appliances other than televisions and monitors. Examples include embedded displays in furniture, and in the walls, floors, and ceilings of buildings. In addition, as autonomous driving technology develops, various considerations are being made regarding how to utilize the space inside a vehicle. For example, as the proportion of human driving decreases, the interior space of a vehicle may become a space similar to a living room in a house, and the use of light colors such as white or pastel colors, similar to the walls, floors, and ceilings in a house, is being considered for the interior color scheme of vehicles.

[0005] Methods for obtaining and diffusing polarization from natural light include methods utilizing birefringence as a display method that exhibits color changes with viewing angle (see, for example, Patent Documents 1 and 2). One such method is a diffuse reflective film comprising a birefringent continuous polymer phase and a substantially non-birefringent dispersed phase dispersed within the continuous phase. The refractive indices of the continuous phase and the dispersed phase are substantially mismatched along the first of three mutually orthogonal axes (refractive index difference of 0.05 or more), and substantially coincide along the second of three mutually orthogonal axes. Incident light polarized along the mismatched axis, i.e., parallel to that axis, is scattered, resulting in significant diffuse reflection. Incident light polarized along the coincident axis is scattered considerably less and is transmitted substantially spectrally.

[0006] A reflective polarizer that transmits one polarization component and reflects the polarization component perpendicular to it has been developed by 3M and is widely used under the trade name DBEF (see, for example, Patent Document 3). This polarizer has a structure in which hundreds or more layers of two very thin polymer layers (a first polymer layer with birefringence and a second polymer layer without birefringence) are alternately stacked. The refractive index of one direction of the birefringence exhibited by the first polymer layer matches the refractive index of the second polymer layer, but the refractive index in the direction perpendicular to this does not match, thus transmitting one polarization component and reflecting the polarization component perpendicular to it. This method is costly due to the stacking of polymer layers, and a method to reduce costs is needed.

[0007] Furthermore, the following methods have been disclosed that allow for the easy manufacture of optical films that simultaneously satisfy polarization and diffusion functions using inexpensive materials and equipment investment, and that can be directly formed on other optical elements (see, for example, Patent Documents 4-7). Specifically, a method has been proposed in which birefringent fine particles are dispersed in a translucent matrix in a state oriented in a specific direction. A method has been investigated to improve the brightness ratio or visibility on the front and side by including a brightness ratio or visibility improving layer in the viewing-side polarizing plate. The brightness ratio or visibility improving layer has a predetermined embossed or intaglio optical pattern at the interface between the low-refractive-index layer and the high-refractive-index layer, so that when light is transmitted, it is refracted by the pattern and emitted, thereby improving the brightness ratio and visibility. Here, an example is introduced in which needle-shaped crystals of aragonite-based calcium carbonate are used as birefringent fine particles.

[0008] There is a need for an inexpensive optical film that offers high light transmittance, unimpeded visibility, and minimal blurring, even in wide-angle displays or environments with white or light-colored surroundings. One known method for improving light diffusion is to use birefringence. In particular, whisker-shaped calcium carbonate particles of aragonite crystals have a predetermined refractive index relative to their crystal axis. By incorporating and dispersing them in a resin, they can be produced into a film at a lower cost compared to other methods, and are useful because they offer excellent diffusion.

[0009] However, since these whisker-shaped calcium carbonate particles are made from natural calcium carbonate, they may contain aggregates and impurities, and because aragonite crystals are less stable than calcite crystals, there are concerns that they may degrade the optical properties of the resulting optical film. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Special Publication No. 2000-506989 [Patent Document 2] Special Publication No. 2002-502503

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0011] The present invention aims to solve the above problems, and its object is to provide a filler for an optical film in which the incorporation of aggregates and impurities is reduced and the deterioration of the optical properties of the resulting optical film can be effectively prevented, as well as a resin composition for an optical film and an optical film using the same.

Means for Solving the Problems

[0012] The present invention is a filler for an optical film containing whisker-shaped calcium carbonate particles, where the whisker-shaped calcium carbonate particles have a major axis of 5 μm to 50 μm, a minor axis of 0.05 μm to 2 μm, and an aspect ratio of 5 to 50 and contain 0.03% by mass to 0.7% by mass of phosphorus element based on the total mass of the whisker-shaped calcium carbonate particles, and is a filler for an optical film. In one embodiment, the BET specific surface area of the whisker-shaped calcium carbonate particles is 1.5 m

[0013] / g to 6 m / g. 2

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024] <00001In one embodiment, the residue on a 38 μm sieve of the whisker-like calcium carbonate particles is 100 ppm or less.

[0015] In one embodiment, the whisker-like calcium carbonate particles are particles surface-treated with at least one surface treatment agent selected from the group consisting of fatty acids, fatty acid metal salts, surfactants, coupling agents, silanes, esters of polyhydric alcohols, and phosphate esters.

[0016] In one embodiment, the optical film is a film used to form a display device.

[0017] In one embodiment, the optical film is a diffusion polarizer or a retardation film.

[0018] The present invention also provides a resin composition for an optical film, containing a transparent resin matrix and the filler for an optical film.

[0019] In one embodiment, the content of the filler for an optical film is 1 to 50 parts by mass with respect to 100 parts by mass of the transparent resin matrix.

[0020] The present invention also provides an optical film containing the resin composition for an optical film, in which the filler for an optical film is oriented in the transparent resin matrix.

[0021] The present invention also provides a method for manufacturing an optical film, including a step of stretching the resin composition for an optical film in a certain direction.

Advantages of the Invention

[0022] According to the present invention, a filler for an optical film with few impurities and aggregates can be easily obtained. According to the filler of the present invention, an optical film with improved optical properties such as visibility, blurring, and light diffusibility can be efficiently manufactured.

Embodiments for Carrying Out the Invention

[0023] The present invention will be described in detail below.

[0024] 1. Fillers for optical films The optical film filler of the present invention contains whisker-shaped calcium carbonate particles.

[0025] Here, the whisker-shaped calcium carbonate particles contain aragonite and phosphorus to enhance the light diffusivity of the fabricated optical film.

[0026] In the optical film filler of the present invention, the phosphorus element contained in the whisker-shaped calcium carbonate particles is an element derived from the material used to obtain the whisker-shaped calcium carbonate particles. The phosphorus element content is 0.03% to 0.7% by mass, preferably 0.1% to 0.6% by mass, and more preferably 0.3% to 0.5% by mass, based on the total mass of the whisker-shaped calcium carbonate particles. Here, the total mass of the whisker-shaped calcium carbonate particles is based on the mass when the particles are calcined at 500°C.

[0027] If the phosphorus content in whisker-shaped calcium carbonate particles falls below 0.03 mass%, the aragonite content in the whisker-shaped calcium carbonate decreases, and the particle size variation increases, which can reduce the light diffusion properties of optical films such as diffuse polarizers obtained using these particles. If the phosphorus content in whisker-shaped calcium carbonate particles exceeds 0.70 mass%, the aragonite content in the whisker-shaped calcium carbonate particles increases, but when dispersed in a transparent resin matrix, the aggregated particles of whisker-shaped calcium carbonate and the by-product calcium phosphate increase the defects in the diffuse polarizer, leading to unevenness in the diffuse polarizer and poor light diffusion properties.

[0028] In the present invention, the aragonite crystal content of the whisker-shaped calcium carbonate particles is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. If the aragonite crystal content of the whisker-shaped calcium carbonate particles is less than 80%, unevenness may be formed in the optical film made using them. The aragonite crystal content contained in the whisker-shaped calcium carbonate particles can be easily calculated from the results obtained using an X-ray diffraction apparatus.

[0029] The content of the aragonite crystals can be adjusted to satisfy the above range by, for example, adjusting the mixing ratio of calcium carbonate and calcium hydroxide used as raw materials, as well as their concentrations, reaction temperature, and the time required for carbonation.

[0030] In the optical film filler of the present invention, the whisker-shaped calcium carbonate particles have the following further characteristics.

[0031] First, the whisker-shaped calcium carbonate particles have a major axis and a minor axis within a predetermined range.

[0032] In the present invention, the major axis of the whisker-shaped calcium carbonate particles is preferably 5 μm to 50 μm, and more preferably 15 μm to 25 μm. On the other hand, the minor axis of the whisker-shaped calcium carbonate particles is preferably 0.05 μm to 2 μm, and more preferably 0.1 μm to 1 μm. By having the major and minor axes of the whisker-shaped calcium carbonate particles within these ranges, the resulting filler can impart good light diffusivity to the optical film when used in the optical film.

[0033] Whisker-shaped calcium carbonate particles that satisfy the above-mentioned ranges for both the major and minor axes can be obtained, for example, by adjusting the mixing ratio of calcium carbonate and calcium hydroxide used as raw materials, their concentrations, reaction temperature, and the time required for carbonation.

[0034] Whisker-shaped calcium carbonate particles also have an aspect ratio within a predetermined range.

[0035] The aspect ratio of the whisker-shaped calcium carbonate particles in this invention is 5 to 50, preferably 10 to 30. Having the aspect ratio of the whisker-shaped calcium carbonate particles within this range allows the resulting optical film filler to exhibit excellent orientation when compounded with a transparent resin matrix, thereby improving the anisotropy and light diffusion properties of the resulting optical film. The aspect ratio of the whisker-shaped calcium carbonate particles can be calculated, for example, through electron microscopy observation.

[0036] When the aspect ratio of whisker-shaped calcium carbonate particles falls below 5, their orientation in the resin composition obtained by blending them into a transparent resin matrix decreases, resulting in low anisotropy in the resulting optical film. When the aspect ratio of whisker-shaped calcium carbonate particles exceeds 50, the resin composition obtained by blending them into a transparent resin matrix deteriorates in processability and surface smoothness, making the resulting optical film more prone to defects.

[0037] It is known that an aspect ratio satisfying the above range can be obtained for whisker-shaped calcium carbonate particles, and for example, by adjusting the stirring force and the time required for carbonation using the method described in Japanese Patent Application Publication No. 3-088714, the said range of aspect ratio can be satisfied.

[0038] Furthermore, the filler for optical films of the present invention may have the following characteristics:

[0039] For example, it is preferable that the whisker-shaped calcium carbonate particles have a BET specific surface area within a predetermined range.

[0040] In other words, the whisker-shaped calcium carbonate particles in the present invention are preferably 1.5 m 2 / g~6m 2 / g, more comfortably 2m 2 / g~4m 2It has a BET specific surface area of ​​ / g. By setting the BET specific surface area of ​​the whisker-shaped calcium carbonate particles within the above range, the particle size of the resulting whisker-shaped calcium carbonate is uniform, and the diffusion effect when used as a filler for optical films can be enhanced. In addition, the presence of fine particles that inhibit dispersion can be reduced, so the resulting optical film can be provided with excellent light diffusion properties.

[0041] The BET specific surface area of ​​the whisker-shaped calcium carbonate particles is 1.5 m². 2 If the BET specific surface area of ​​the whisker-shaped calcium carbonate particles falls below 6 m², the whisker-shaped calcium carbonate particles will contain many large particles, which may result in unevenness in the fabricated optical film and a decrease in light diffusion and transmittance. 2 If the concentration exceeds / g, the proportion of fine particles contained in the whisker-shaped calcium carbonate particles increases, which can worsen the dispersibility and orientation of the resin composition when blended into a transparent resin matrix, potentially leading to an increase in defects in the resulting optical film and a decrease in light diffusion.

[0042] It is known that a BET specific surface area satisfying the above range can be obtained for whisker-shaped calcium carbonate particles. For example, by using the method described in Japanese Patent Application Publication No. 3-088714, the range of the BET specific surface area can be satisfied by adjusting the stirring force applied to the material and the reaction time.

[0043] For example, it is preferable that the whisker-shaped calcium carbonate particles have a sieve residue of 38 μm that meets a predetermined range.

[0044] Generally, whisker-like calcium carbonate contains coarse particles and aggregates in which whiskers are intertwined. Therefore, it is preferable that the whisker-like calcium carbonate particles in the present invention have these coarse particles and aggregates removed by air classification and / or sieving (e.g., vibrating sieve). This classification process is not limited to after the surface treatment of the calcium carbonate particles described later, but may also be performed before the surface treatment as needed.

[0045] In this invention, the sieve residue of whisker-shaped calcium carbonate particles at 38 μm is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 20 ppm or less. If the sieve residue of whisker-shaped calcium carbonate particles at 38 μm is greater than 100 ppm in this invention, the optical film produced using it may have many defects and unevenness on its surface.

[0046] In the present invention, whisker-shaped calcium carbonate particles that satisfy the above range of sieve residue can be obtained, for example, by using the method described in Japanese Patent Application Publication No. 3-088714, for example, by adjusting the stirring force and temperature when producing the particles, and by increasing the reaction time in addition to purifying the lime milk and particles, in order to disperse the particles.

[0047] In the optical film filler of the present invention, the whisker-shaped calcium carbonate particles may be whisker-shaped untreated (for example, untreated) calcium carbonate particles, or they may be obtained by surface-treating whisker-shaped untreated calcium carbonate particles with a surface treatment agent, or a combination thereof.

[0048] Here, whisker-shaped calcium carbonate particles obtained by surface treatment with a predetermined surface treatment agent can be blended into a transparent resin matrix as a filler for optical films and kneaded to improve their affinity with the transparent resin matrix during kneading and molding processes, thereby improving various properties of the resulting resin composition, such as adhesion, dimensional stability, surface smoothness, and processability.

[0049] Examples of such surface treatment agents include fatty acids, fatty acid metal salts, surfactants, coupling agents, silanes, esters of polyhydric alcohols, and phosphate esters, as well as combinations thereof.

[0050] Examples of fatty acids include saturated fatty acids such as caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid; unsaturated fatty acids such as sorbic acid, elaidic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, cetoleic acid, erucic acid, and ricinoleic acid; and combinations thereof. The fatty acid is preferably a mixed acid of stearic acid and palmitic acid because it exhibits excellent reactivity with untreated calcium carbonate particles, the resulting surface-treated particles (surface-treated whisker-shaped calcium carbonate particles) have good stability and dispersibility, and it is readily available and is expected to reduce manufacturing costs.

[0051] Examples of fatty acid metal salts include saturated fatty acid salts such as potassium laurate, potassium myristate, potassium palmitate, sodium palmitate, barium stearate, calcium stearate, zinc stearate, potassium stearate, cobalt(II) stearate, tin(IV) stearate, sodium stearate, and lead(II) stearate; and unsaturated fatty acid salts such as zinc oleate, potassium oleate, cobalt(II) oleate, sodium oleate, and potassium oleate diethanolamine salt; as well as combinations thereof. Fatty acid metal salts are preferably metal salts (soaps) of mixed acids mainly composed of stearic acid and palmitic acid, because they exhibit excellent reactivity with (untreated) whisker-shaped calcium carbonate particles, the resulting surface-treated particles have good stability and dispersibility, and they are readily available and expected to reduce manufacturing costs.

[0052] Furthermore, the above-mentioned fatty acid metal salt may be obtained by mixing and reacting the fatty acid itself with a compound containing a metal element such as lithium, sodium, potassium, rubidium, beryllium, magnesium, calcium, strontium, barium, zinc, aluminum, lead, cobalt, or tin, or a compound having an acyl group, during or prior to surface treatment of untreated whisker-shaped calcium carbonate particles.

[0053] In one embodiment, surfactants include, for example, polymers of monomers having vinyl groups; partially or completely neutralized thereof with alkali metal salts, ammonium, and / or amines; and combinations thereof. Examples of such monomers include α,β-monoethylenically unsaturated monocarboxylic acids, α,β-monoethylenically unsaturated dicarboxylic acids, alkyl methacrylates, (meth)acrylic ethers having alkoxy groups, (meth)acrylates having cycloxyl groups, α,β-monoethylenically unsaturated hydroxy esters, polyalkylene glycol mono(meth)acrylates, vinyl esters, vinyl aromatics, unsaturated nitriles, unsaturated dicarboxylic acid esters, vinyl ethers, conjugated dienes, linear olefins, cyclic olefins, and sulfo group-containing monomers, and combinations thereof.

[0054] In one embodiment, examples of surfactants include alkyl ether sulfate, alkyl ether phosphoric acid, alkylaryl ether sulfate, alkylaryl ether phosphoric acid, alkyl sulfate ester, alkyl phosphate ester, alkylaryl sulfate, alkylaryl phosphoric acid, alkylamide sulfate ester, alkyl sulfonic acid, alkylbenzene sulfonic acid, α-olefin sulfonic acid, N-acyl sulfonic acid, N-acyl amino acid, alkyl ether carboxylic acid, acylated peptide, aliphatic amine, aliphatic quaternary amine, aromatic quaternary ammonium, betaine, imidazoline derivatives, alkyl ether, alkyl allyl ether, alkyl ester, alkylamine, sorbitan derivative, polycyclic phenyl ether, aliphatic ester, fluoroalkylcarbon acid, perfluoroalkylcarbon acid, and perfluoroalkyl sulfonic acid, as well as combinations thereof.

[0055] For the reasons that the dispersibility and stability of the resulting surface-treated whisker-like calcium carbonate particles can be improved, and that when kneading with a transparent resin matrix to produce an optical film, the affinity with the transparent resin matrix can be improved, and that manufacturing costs can be expected to be reduced, the surfactant should be sulfates such as alkyl ether sulfate, alkylaryl ether sulfate, alkyl sulfate ester, sulfate ether, and sulfate ester; or combinations thereof.

[0056] Examples of coupling agents include silane coupling agents, titanate coupling agents, zirconate coupling agents, and aluminate coupling agents, as well as combinations thereof.

[0057] Here, as silane coupling agents, examples include vinylsilanes, aminosilanes, methacrylic(acrylic)silanes, epoxysilanes, and combinations thereof, because they can improve the dispersibility and stability of the resulting surface-treated whisker-shaped calcium carbonate particles, and when kneaded with a transparent resin matrix as a filler for optical films, they can improve affinity with the transparent resin matrix and are expected to reduce manufacturing costs. More specific examples include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-chloropropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-ureidopropyltriethotoxylsilane, and combinations thereof. When kneading a silane coupling agent with a transparent resin matrix as a filler for optical films, vinylsilane, epoxysilane, or methacrylicsilane are preferred because they improve adhesion to the transparent resin matrix and are expected to reduce manufacturing costs.

[0058] Examples of titanate coupling agents include isopropyltriisostearoyl titanate, isopropyltridodecylbenzenesulfonyl titanate, isopropyltris(dioctyl pyrophosphate) titanate, tetraisopropylbis(dioctyl phosphite) titanate, tetraoctylbis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl) phosphite titanate, bis(dioctyl pyrophosphate) oxyacetate titanate, and bis(dioctyl pyrophosphate) oxyacetate titanate. Examples include dioctyl pyrophosphate ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylate isostearoyl titanate, isopropyl isostearoyl diacrylic titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumylphenyl titanate, isopropyl tri(N-amidoethyl / aminoethyl) titanate, dicumylphenyl oxyacetate titanate, and diisostearoylethylene titanate, as well as combinations thereof. When kneading with a transparent resin matrix as a filler for optical films, isopropyl triisostearoyl titanate is preferred as the titanate coupling agent because it is expected to improve adhesion with the transparent resin matrix and reduce manufacturing costs.

[0059] Examples of aluminate coupling agents include acetalkoxyaluminum diisopropylate.

[0060] Examples of zirconate coupling agents include zirconium dineoalcanola di(3-mercapto)propionat.

[0061] Examples of silanes include chlorosilanes, alkoxysilanes, and combinations thereof.

[0062] Examples of chlorosilanes include methyltrichlorosilane, methyldichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, and trifluoropropyltrichlorosilane, as well as combinations thereof. Methyltrichlorosilane and phenyltrichlorosilane, or combinations thereof, are preferred as chlorosilanes because they can improve the stability of the resulting surface-treated whisker-like calcium carbonate particles.

[0063] Examples of alkoxysilanes include tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, and trifluoropropyltrimethoxysilane, as well as combinations thereof. Methyltrimethoxysilane, phenyltriethoxysilane, and phenyltrimethoxysilane, as well as combinations thereof, are preferred as alkoxysilanes because they can improve the stability of the resulting surface-treated whisker-like calcium carbonate particles.

[0064] Examples of polyhydric alcohol esters include reaction products of polyhydric alcohols such as sorbitol, sorbitan, glycerin, diglycerin, polyglycerin, polyethylene glycol, polypropylene glycol, pentaerythritol, trimethylolpropane, and their ethylene oxide adducts or propylene oxide adducts, with fatty acids having 10 to 22 carbon atoms (for example, saturated fatty acids such as capric acid, myristic acid, palmitic acid, stearic acid, and behenic acid, or esters of unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and erucic acid).

[0065] Specific examples of such polyhydric alcohol esters include sorbitol monostearate, sorbitol monooleate, sorbitol monopalmitate, sorbitol monobehenate, sorbitan monostearate, sorbitan monooleate, sorbitan monopalmitate, sorbitan monobehenate, glycerin monostearate, glycerin monooleate, glycerin monopalmitate, diglycerin monostearate, diglycerin monooleate, diglycerin monopalmitate, diglycerin monobehenate, diglycerin monocaprylate, diglycerin monolaurate, polyglycerin monostearate, polyglycerin monooleate, polyglycerin monopalmitate, and polyglycerin mono Examples of polyhydric alcohol esters include behenates, polyethylene glycol monostearate, polyethylene glycol monooleate, polyethylene glycol monopalmitate, polyethylene glycol monobehenate, pentaerythritol monostearate, pentaerythritol monooleate, pentaerythritol monopalmitate, pentaerythritol monobehenate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, and other monoesters; sesquiesters such as diglycerin sesquistearate (for example, a mixture of monoesters and diesters in a molar ratio of 1:1); diesters; polyesters; and combinations thereof. For the reason that the resulting surface-treated whisker-like calcium carbonate particles exhibit good dispersibility in a transparent resin matrix, the polyhydric alcohol esters are preferably sorbitol monostearate and sorbitol monopalmitate, and combinations thereof.

[0066] Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, tributyl phosphate, 2-ethylhexyl phosphate, butoxyethyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, cresyl di-2,6-xylenyl phosphate, resorcinol diphenol phosphate, various aromatic condensed phosphate esters, 2-chloroethyl, chloropropyl phosphate, dichloropropyl phosphate, tribromoneopentyl phosphate, halogenated condensed phosphate, bis-2-ethylhexyl phosphate, diisodecyl phosphate, 2-methacryloyloxyethyl acid phosphate, diphenyl-2-methacryloyloxyethyl phosphate Examples include trimethyl phosphate, methyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, 2-butylhexyl acid phosphate, isodecyl acid phosphate, monoisodecyl phosphate, triphenyl phosphate, dibutyl hydrogen phosphate, dibutyl hydrogen phosphate, diphenyl phosphorochloride, phenyl phosphorodicidate, polyoxyethylene lauryl ether phosphate, polyoxyalkyl ether phosphate having 12 to 15 alkyl groups, polyoxyethylene alkylphenyl ether phosphate having 12 to 15 alkyl groups, polyoxyethylene dialkylphenyl ether phosphate having 12 to 15 alkyl groups, and nitrilotris (methylenephosphonic acid), as well as combinations thereof. The phosphate esters are preferably trimethyl phosphate and nitrilotris (methylenephosphonic acid), as well as combinations thereof, because they can impart good thermal stability to the mixture of surface-treated whisker-like calcium carbonate particles and the transparent resin matrix.

[0067] The amount of surface treatment agent used varies depending on the type and / or application of the transparent resin matrix in which the resulting optical film filler is used, and is not necessarily limited, but is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 8 parts by mass, per 100 parts by mass of untreated whisker-shaped calcium carbonate particles. If the amount of surface treatment agent used per 100 parts by mass of untreated whisker-shaped calcium carbonate particles is less than 0.01 parts by mass, the effectiveness of the surface treatment agent may not be fully realized for the untreated whisker-shaped calcium carbonate particles. If the amount of surface treatment agent used per 100 parts by mass of untreated whisker-shaped calcium carbonate particles exceeds 10 parts by mass, when an optical film is made by incorporating the resulting surface-treated whisker-shaped calcium carbonate particles into a resin, the optical properties such as light diffusion and transmittance may be significantly reduced.

[0068] The above surface treatment can be carried out by known methods. For example, a wet method may be used in which whisker-shaped calcium carbonate particles are dispersed in a solvent and then surface-treated. Alternatively, a dry method may be used in which whisker-shaped calcium carbonate particles are placed in a mixer such as a Henschel mixer, and a surface treatment agent is added in liquid, emulsion, or solid form under sufficient stirring conditions, and the surface treatment is performed by mixing with or without heating. The wet method is preferred in that it allows for more uniform surface treatment, but the dry method can also be used in order to improve manufacturing efficiency.

[0069] When surface treatment is performed under heating, the surface treatment temperature is preferably such that the components used as the surface treatment agent can react with calcium carbonate. For example, when the dry method described above is employed, the surface treatment temperature is, for example, above the melting point of the surface treatment agent used, preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher. By adopting such a surface treatment temperature, it becomes possible to perform surface treatment on whisker-shaped calcium carbonate particles more uniformly. The surface treatment temperature is also preferably 140°C or lower in order to prevent thermal degradation of the surface treatment agent used.

[0070] After the surface treatment described above, the resulting particles may be powdered through any operation such as desolvation, drying, or grinding.

[0071] In this way, the surface-treated whisker-shaped calcium carbonate particles can be obtained. These whisker-shaped calcium carbonate particles can be used as is as particles constituting the filler for optical films of the present invention.

[0072] The optical film filler of the present invention can also be used to manufacture optical films that constitute various display devices or display displays, such as liquid crystal displays, organic EL displays, LED displays, and plasma displays. For example, the optical film constituting the display display is preferably a diffuse polarizer or a phase difference film because it plays an important role in the display device and higher quality performance is desired.

[0073] 2. Resin compositions for optical films The resin composition for optical films of the present invention contains a transparent resin matrix and the above-mentioned filler for optical films.

[0074] In the resin composition of the present invention, for example, whisker-shaped calcium carbonate particles contained in the above-mentioned birefringent optical film filler are dispersed and oriented in one direction within an isotropic transparent resin matrix. As a result, either the refractive index in the short-axis direction or the refractive index in the long-axis direction of the whisker-shaped calcium carbonate particles substantially matches the refractive index of the transparent resin matrix, thereby exhibiting the property of transmitting a polarization component in one direction of incident light and strongly diffusing a polarization component perpendicular to it.

[0075] Here, we will briefly explain the relationship between the transparent resin matrix and the whisker-shaped calcium carbonate particles constituting the filler for the optical film when an optical film having a flat surface is made using the resin composition for optical films of the present invention.

[0076] Assume that the long axis of the whisker-shaped calcium carbonate particles contained in the optical film is the x-axis, the plane of the optical film (transparent resin matrix) forms the xy-plane, and the thickness direction of the optical film (transparent resin matrix) is the z-axis. Also assume that the refractive indices along each optical axis in this optical film are nx, ny, and nz, and the refractive index of the transparent resin matrix is ​​n0.

[0077] For example, if the refractive index n0 of the transparent resin matrix and the refractive index nx in the long axis direction of the whisker-shaped calcium carbonate particles are substantially the same, and there is a certain difference between the refractive index n0 of the transparent resin matrix and the refractive indices ny and nz in the short axis direction of the whisker-shaped calcium carbonate particles, then the polarization component in the x axis direction of the light incident on this optical film will be transmitted through the film, while the polarization components in the short axis and y axis directions will be diffused by the interface between the whisker-shaped calcium carbonate particles and the transparent resin matrix.

[0078] The light transmitted and diffused through this optical film exhibits oval or linear shapes extending perpendicular to the orientation direction of the whisker-shaped calcium carbonate particles. However, the central part has a large polarization component in the x-axis direction, while the diffused light portions extending from both ends have a large polarization component in the y-axis direction.

[0079] Here, of the refractive indices of the whisker-shaped calcium carbonate particles, ny and nz in the short axis direction cannot be controlled or distinguished in the transparent matrix, so in effect, their average value nw = (ny + nz) / 2 can be considered as the refractive index in the short axis direction. Furthermore, if we redefine the refractive index in the long axis direction of the whisker-shaped calcium carbonate particles as nl = nx, the optical properties of this optical film can be expressed in terms of the relationship between the three refractive indices nl, nw, and n0. That is, if the relationship |nl-n0|<|nw-n0| is satisfied, a large proportion of the polarization component that coincides with the orientation direction of the whisker-shaped calcium carbonate particles is transmitted without diffusion, and if the direction of the inequality is reversed, the amount of linear transmission of the polarization component perpendicular to the orientation direction of the whisker-shaped calcium carbonate particles is large. In the present invention, it is desirable that, for example, the refractive index of the whisker-shaped calcium carbonate particles in one direction and the refractive index of the transparent resin matrix are substantially the same. Substantially the same means that the difference in refractive index between the two is 0.05 or less, preferably 0.03 or less, and more preferably 0.01 or less. Conversely, it is preferable that the difference between the refractive index of the other whisker-shaped calcium carbonate particle and the refractive index of the transparent resin matrix is ​​0.05 or more, preferably 0.1 or more. That is, it is preferable that the relationship expressed as |nl-n0|<0.05<|nw-n0| is satisfied.

[0080] In the above, the long axis of the whisker-shaped calcium carbonate particles is taken as the x-axis, and the refractive index of the whisker-shaped calcium carbonate particles is expressed as (nx,ny,nz). However, in general, the long axis of the whisker-shaped calcium carbonate particles is sometimes taken as c, and the refractive index is expressed as (na,nb,nc). In this case, the relationship between each is (nx,ny,nz)=(nc,na,nb). Furthermore, the aragonite crystals that may be contained in the whisker-shaped calcium carbonate particles have refractive indices of na=1.681, nb=1.685, and nc=1.530, and exhibit characteristic light diffusion properties when compounded in a transparent resin matrix.

[0081] Such transparent resin matrices can be made from resins that are isotropic, have high optical transparency, and possess the desired physical strength when molded into an optical film. Furthermore, when the resulting optical film is directly laminated onto a transparent substrate or optical element as described later, the transparent resin matrix used must have high adhesion to the transparent substrate or optical element.

[0082] Resins that can constitute a transparent resin matrix include, for example, thermoplastic resins. Examples of thermoplastic resins include acrylic resins, styrene resins, styrene-acrylic copolymers, polyurethane resins, polyester resins, polycarbonate resins, epoxy resins, cellulose resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, cycloolefin resins, norbornene resins, fluororesins, silicone resins, etc., and these can be used individually or in combination. Alternatively, the resins that can constitute a transparent resin matrix may include, for example, thermosetting resins and photocurable resins, as well as combinations thereof, and may also be hybrid resins of organic and inorganic resins produced using techniques such as the sol-gel method.

[0083] The resin that can constitute the transparent resin matrix may also be an adhesive with a low glass transition temperature (Tg) (mainly an acrylic adhesive), as long as it satisfies the relationship of refractive index with the above-mentioned filler for optical film.

[0084] As for the combination of whisker-shaped calcium carbonate particles and a transparent resin matrix, since the whisker-shaped calcium carbonate may contain aragonite crystals, it is preferable to select a transparent resin matrix for which the refractive index n0 is substantially the same as either n1 or nw. Examples of easily handled transparent resins that can constitute the transparent resin matrix include acrylic resins, polyesters, polyurethane resins, and styrene-acrylic copolymers.

[0085] The content of the optical film filler in the resin composition for optical films of the present invention can be appropriately designed, for example, according to the difference in refractive index between the transparent resin matrix and the filler, but is preferably 1% to 50% by mass, and more preferably 5% to 30% by mass, relative to the total mass of the composition. If the content of the optical film filler is less than 1% by mass, the optical properties of the optical film made from the resulting resin composition may be insufficient. If the content of the optical film filler exceeds 50% by mass, the binding force between the transparent resin matrix in the composition and the filler may decrease, making the filler more prone to detachment.

[0086] The resin composition for optical films of the present invention may also contain an organic solvent, for example, to dissolve a transparent resin matrix and improve the dispersibility and orientation of the filler for optical films within it. The organic solvent is not particularly limited, but examples include ethyl acetate, acetone, methyl ethyl ketone, and toluene, or combinations thereof. Furthermore, in order to improve the coating properties of the resulting resin composition, such as wettability, leveling, and drying properties, other solvents such as butyl acetate, methyl isobutyl ketone, and cyclohexanone may be added as needed, in addition to the above-mentioned organic solvent. The content of the above-mentioned organic solvent and other solvents in the resin composition of this application is not particularly limited, and appropriate amounts can be selected by those skilled in the art.

[0087] Thus, by including an organic solvent and, optionally, other solvents, the resin composition of the present invention can be adjusted to a viscosity suitable for coating onto substrates such as the transparent substrate described later, and the whisker-shaped calcium carbonate particles constituting the filler for optical films can be mixed and dispersed more uniformly within the resin composition.

[0088] The resin composition for optical films of the present invention may also contain other additives as needed. These other additives are not particularly limited, but include, for example, surfactants, coloring dyes, fluorescent dyes, thickeners, leveling agents, and combinations thereof. The content of these other additives in the resin composition of the present application is not particularly limited, and an appropriate amount can be selected by those skilled in the art.

[0089] In the resin composition for optical films of the present invention, the dispersion of the optical film filler into the transparent resin matrix can be carried out using various mixing and stirring devices and dispersion devices such as discpersers, agitators, homogenizers, ball mills, and attritors. In particular, in order to disperse the whisker-shaped calcium carbonate particles constituting the optical film filler while maintaining their shape as much as possible, it is preferable to use a device that can generate strong shear force without using beads for mixing and stirring. It is preferable to degas the prepared resin composition beforehand using a method known to those skilled in the art.

[0090] 3. Optical film The optical film of the present invention is composed of the above-described resin composition for optical films.

[0091] The optical film of the present invention may, for example, have the form of an independent film, or it may have the form of being arranged on a substrate such as a transparent substrate as described later.

[0092] The thickness of the optical film is not particularly limited, but is preferably 5 μm to 100 μm, more preferably 15 μm to 90 μm, and even more preferably 20 μm to 80 μm. If the thickness of the optical film is less than 5 μm, it may not be possible to provide sufficient haze in the entire film or in part, making it difficult to exhibit the desired optical properties. If the thickness of the optical film exceeds 100 μm, the manufacturing process of the film itself becomes complicated, and manufacturing efficiency may decrease.

[0093] The optical film of the present invention may take the form of, for example, a diffuse polarizer, a phase difference film, a reflective film, an anti-reflective film, an orientation film, a diffusion film, a brightness-enhancing film, a light-gathering film, a light-shielding film, a glossy film, an optical protective film, a glossy composite film, or a nano-optical film.

[0094] If the optical film of the present invention is, for example, a diffuse polarizer, the diffuse polarizer can be manufactured by coating the above-mentioned resin composition for optical films in a predetermined direction. Therefore, it is easy to orient the birefringent whisker-shaped calcium carbonate particles, which are components of the filler for optical films, in substantially one direction. Furthermore, since the transparent resin matrix on which the filler for optical films is arranged is isotropic, it has the characteristic that no depolarization occurs in the matrix portion.

[0095] As a result of the whisker-shaped calcium carbonate particles oriented in approximately one direction, polarization components vibrating in the same direction as the orientation (when the refractive index in the major axis direction is approximately the same as the refractive index of the matrix resin) or polarization components vibrating perpendicular to the orientation (when the refractive index in the minor axis direction is approximately the same as the refractive index of the matrix resin) are transmitted, while polarization components vibrating perpendicular to these components (when the refractive index in the major axis direction is approximately the same as the refractive index of the matrix resin) or polarization components vibrating horizontally to these components (when the refractive index in the minor axis direction is approximately the same as the refractive index of the matrix resin) are diffused. Consequently, by changing the orientation of the polarizer so as to transmit the diffused polarization components or not transmit the diffused polarization components, it becomes possible to adjust the width and intensity of the transmitted light from the polarizer to a desired degree.

[0096] The optical film of the present invention can be manufactured by stretching the above-mentioned resin composition for optical films in a certain direction. Such stretching may be performed, for example, by coating the resin composition for optical films onto a substrate and spreading it in a certain direction to form a thin layer, or by stretching pellets composed of the resin composition for optical films in a certain direction. Here, the term "certain direction" as used herein means that the direction in which the resin composition for optical films is stretched is predetermined, and includes, for example, uniaxial, biaxial, and (predetermined) multiaxial directions. On the other hand, when an operator stretches the film in an arbitrary direction, that direction is excluded from the above-mentioned "certain direction".

[0097] Regarding the spreading of the above-mentioned resin composition for optical films, first, we will describe the case in which the resin composition for optical films is coated onto a substrate and then spread into a thin layer to produce an optical film.

[0098] Examples of substrates include transparent substrates, release sheets, metal substrates, ceramic substrates, and various optical elements. When using a transparent substrate, it is preferable that it has high transparency. Such a transparent substrate is preferably one that has a total light transmittance of 80% or more, more preferably 85% or more, and even more preferably 90% or more, in accordance with JIS K 7361-1, and / or a haze value of 3.0 or less, more preferably 1.0 or less, and even more preferably 0.5 or less, in accordance with JIS K7136. Transparent plastic films and glass plates can be used as transparent substrates, but plastic films are preferred because they are thin, light, resistant to breakage, and have excellent productivity. Specific examples of resins that make up such plastic films include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetylcellulose (TAC), polycarbonate (PC), polyarylate, polyimide (PI), aromatic polyamide, polysulfone (PS), polyethersulfone (PES), cellophane, polyethylene (PE), polypropylene (PP), polyvinyl alcohol (PVA), cycloolefin resins, and norbornene-based resins, as well as combinations thereof. The plastic film that makes up the transparent substrate may consist of a single layer made of the above resins, or it may be a laminate of multiple layers.

[0099] Furthermore, considering the application and productivity, the thickness of the substrate is preferably 1 μm to 5 mm, more preferably 10 to 500 μm, and even more preferably 50 to 200 μm.

[0100] For coating the above-mentioned substrate with the resin composition for optical films, it is preferable to employ a coating method that strongly promotes the flow orientation and shear orientation of the birefringent whisker-shaped calcium carbonate particles in the resulting optical film. This makes it relatively easy to produce an optical film in which the whisker-shaped calcium carbonate particles are oriented so that their long axes are substantially aligned with the coating direction.

[0101] Specific coating methods include coating using coating equipment such as reverse coaters, gap coaters, comma coaters, die coaters, lip coaters, wire bar coaters, dip coaters, microgravure coaters, and roll coaters.

[0102] Furthermore, in the present invention, for example, by using the above-mentioned resin composition for optical films, a diffuse polarizer laminated film can be obtained by directly coating a birefringent whisker-shaped calcium carbonate onto a transparent substrate. In addition, if the resin composition for optical films is applied to a substrate other than a transparent substrate, such as a release sheet, a metal substrate with low adhesive strength, or a ceramic substrate, a single-layer optical film can be obtained by peeling off the coated and dried optical film resin composition.

[0103] Furthermore, in the present invention, in addition to the above, an arbitrary adhesive layer or bonding layer may be provided on the substrate in advance, and the above-mentioned resin composition for optical films may be coated thereon to form an optical film (layer).

[0104] Regarding the stretching of the above-mentioned resin composition for optical films, the following will describe a case in which an optical film is manufactured by stretching pellets made of the resin composition for optical films in a predetermined direction.

[0105] The kneader into which the resin composition for optical film is introduced may be single-screw or twin-screw, and its L / D ratio (where L represents the length of the extruder cylinder and D represents the inner diameter of the cylinder) is preferably selected to be between 15 and 80. This improves the dispersibility of whisker-shaped calcium carbonate particles in the resin composition. In this invention, the resin composition for optical film may be introduced into the kneader in a pre-blended state, consisting of the transparent resin matrix and the filler for optical film. However, in order to maintain the shape of the whisker-shaped calcium carbonate particles, which are components of the filler, as much as possible, it is preferable to introduce the transparent resin matrix and the filler for optical film into the kneader separately, and it is more preferable to introduce the filler for optical film through the vent port of the kneader.

[0106] In this way, pellets composed of a resin composition for optical films are produced.

[0107] Subsequently, the pellets are fed into another film manufacturing extruder equipped with a T-die at its tip, and a roll of film can be obtained by winding up the film extruded from this T-die. At this time, the winding temperature and speed may be controlled to stretch the film in the direction of extrusion (uniaxial stretching), or to stretch it in a direction perpendicular to the direction of extrusion and the extrusion direction (biaxial stretching). The temperature and stretching ratio used in such a stretching process are not particularly limited. Appropriate temperature and stretching ratio can be appropriately selected by those skilled in the art depending on the type and amount of transparent resin matrix constituting the optical film resin composition, the required thickness of the resulting optical film, etc.

[0108] According to the present invention, by varying the type and mixing ratio of the optical film filler and transparent resin matrix used during the above manufacturing process, various optical films with adjusted optical properties such as diffuse polarization can be produced.

[0109] Furthermore, according to the present invention, for example, as a diffusion film for a direct-type backlight using a cold cathode fluorescent lamp among backlights for liquid crystal display devices, it is possible to eliminate and equalize spatial brightness unevenness caused by the shape of the light source through its diffusion function, and to improve brightness through its diffusion polarization function. In addition, by combining multiple optical films of the present invention, it is possible to reduce the number of components and make the film thinner. Furthermore, by arranging them in combination with optical elements selected from light guide plates, light reflecting elements, light diffusing elements, prism elements, polarizing elements, phase difference elements, and viewing angle expanding elements, or by laminating them together, it is expected that the functions of both will be further enhanced, or that functions beyond simple combinations will be exhibited. [Examples]

[0110] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, unless otherwise specified, % means mass%, and parts means parts by mass.

[0111] (Evaluation method) In the following examples and comparative examples, each physical property was obtained using the following methods.

[0112] (A) Aspect ratio of calcium carbonate particles, etc. The aspect ratios of untreated calcium carbonate particles and surface-treated calcium carbonate particles were measured as follows.

[0113] Samples of untreated calcium carbonate particles and surface-treated calcium carbonate particles (whisker-shaped calcium carbonate particles) were examined using an electron microscope (Hitachi, Ltd. Scanning Electron Microscope (SU3500 II)) and the field of view was captured according to the following measurement method. Next, 100 particles were randomly selected from the microscope field of view, and their major axis (maximum diameter) and minor axis (minimum diameter) were measured. The average value of the major axis divided by the minor axis for each particle was calculated. In addition, the average value of the major axis for each particle was calculated, and the average value of the minor axis for each particle was calculated.

[0114] (Measurement method using a scanning electron microscope) Procedure (1): Untreated whisker-shaped calcium carbonate particles suspended in a solvent (distilled water or methanol) or surface-treated whisker-shaped calcium carbonate particles were placed on a sample stage and dried in a drying oven at 110°C. Procedure (2): The dried sample stage was deposited onto platinum (Pt) using ion sputtering. Procedure (3): The sample stage was set up on the scanning electron microscope, and the microscope field of view was photographed at the predetermined magnification.

[0115] (B) Phosphorus content The phosphorus content in surface-treated calcium carbonate particles (whisker-shaped calcium carbonate particles) was measured by preparing samples using an inductively coupled plasma (ICP) emission spectrometer (SPS3500, manufactured by SII Nanotechnology Co., Ltd.) as follows.

[0116] (Measurement method using inductively coupled plasma (ICP) emission spectrometer) Procedure (1): Approximately 1000 mg of untreated whisker-shaped calcium carbonate particles or surface-treated whisker-shaped calcium carbonate particles were weighed into a crucible and calcined in an electric furnace at 500°C for 3 hours. Procedure (2): After firing, transfer the mixture to a 200 mL beaker, add a small amount of distilled water and 7.5 mL of nitric acid, boil it on an electric stove, and then allow the mixture to cool. Procedure (3): Place 100 μL of yttrium standard solution (Y1000) manufactured by Fujifilm Wako Pure Chemical Industries into a 100 mL volumetric flask, add the cooled mixture obtained in Procedure (2) above, and make up to 100 mL with distilled water. Procedure (4): After making up the volume, the sample was filtered through 5C filter paper to obtain a sample for inductively coupled plasma (ICP) emission spectroscopy.

[0117] (C) BET specific surface area The BET specific surface area of ​​untreated whisker-shaped calcium carbonate particles or surface-treated whisker-shaped calcium carbonate particles was measured using the Macsorb BET specific surface area measuring device HM model-1210 manufactured by Mounttech Co., Ltd. as follows.

[0118] (Method for measuring BET specific surface area) Procedure (1): Approximately 300 mg of each whisker-shaped calcium carbonate particle was placed in a dedicated glass cell and set in the measuring device. Procedure (2): As a pretreatment, the samples were heated at 200°C for 10 minutes under a mixed gas atmosphere of nitrogen and helium. Procedure (3): Surface-treated calcium carbonate particles were subjected to low-temperature, low-humidity physical adsorption on a dedicated glass cell under a liquid nitrogen environment, and the BET specific surface area was measured using a single-point method.

[0119] (D) Method for measuring residue on a 38 μm sieve The 38 μm sieve residue was measured using the following procedure. Procedure (1): 400 g of the whisker-shaped calcium carbonate particle sample was accurately weighed into a glass container using a chemical balance, and 400 mL of dispersion medium and 1600 mL of water were added as needed to form a slurry. Procedure (2): After thoroughly stirring the slurry, transfer it to a test sieve with a nominal size of 38 μm and an inner diameter of 200 mm as specified in JIS Z 8801. While pouring water over the sieve, be careful not to let any leak out, and gently mix with a brush to allow the sample to pass through. Then, lightly sweep the mesh with a brush until the liquid passing through the sieve is completely clear. Procedure (3): The residue was transferred onto a test sieve with an inner diameter of 75 mm and dried in a dryer set to 105°C for at least 30 minutes. Step (4): Transfer the remaining contents to a desiccator and allow to cool for 15 minutes. Procedure (5): The residue was placed on weighing paper, weighed using a chemical balance, and the sieve residue (ppm) was calculated using the following formula: Sieve residue (ppm) = Residue (g) ÷ Sample (g) × 1,000,000

[0120] (Example 1: Preparation of an optical film filler (E1) composed of untreated whisker-shaped calcium carbonate particles) Needle-shaped aragonite-type calcium carbonate having a major axis of 5 μm and a minor axis of 0.5 μm and calcium hydroxide were mixed so that the molar ratio of the two was CaCO3 / Ca(OH)2 = 1 / 5, and water was added to obtain a water slurry having a total concentration of 120 g / L after mixing. Next, phosphoric acid corresponding to 1.0 part by mass was added to 100 parts by mass of the synthesized calcium carbonate to this water slurry. After adjusting the slurry temperature to 50 °C, CO2 gas (as 100% CO2) was blown into the slurry at a flow rate of 1 L / min / kg·Ca(OH)2 while stirring at 360 rpm with respect to 30 L of the slurry to carry out carbonation. Then, by dehydration and drying, whisker-shaped calcium carbonate particles were obtained. The content of phosphorus element in the whisker-shaped calcium carbonate particles is 0.30% by mass, the BET specific surface area is 5.1 m 2 / g, the major axis is 25.0 μm, the minor axis is 0.8 μm, and the aspect ratio is 31. The residue on a 38-μm sieve was 50 ppm. The thus-obtained untreated (not surface-treated) whisker-shaped calcium carbonate particles were designated as a filler (E1) for an optical film hereinafter.

[0121] (Example 2: Preparation of a filler (E2) for an optical film composed of surface-treated whisker-shaped calcium carbonate particles) The amount of phosphoric acid added to the water slurry was changed to 0.33 parts by mass with respect to 100 parts by mass of calcium carbonate, and whisker-shaped calcium carbonate particles were obtained in the same manner as in Example 1.

[0122] 100 parts by mass (3 kg) of the obtained untreated whisker-shaped calcium carbonate particles were charged into a Henschel mixer and stirred while heating the jacket provided outside the mixer. Then, 1.0 part by mass of trimethyl phosphate was added and heated and stirred until the product temperature reached 130 °C to obtain whisker-shaped calcium carbonate particles surface-treated with trimethyl phosphate. The content of phosphorus element in the whisker-shaped calcium carbonate particles is 0.10% by mass, the BET specific surface area is 3.0 m 2The particle size was / g, with a major axis of 25.0 μm, a minor axis of 1.0 μm, and an aspect ratio of 25. The residue on a 38 μm sieve was 20 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as optical film filler (E2).

[0123] (Example 3: Preparation of a filler for optical films (E3) composed of surface-treated whisker-shaped calcium carbonate particles) Whisker-shaped calcium carbonate particles were obtained in the same manner as in Example 1, except that the amount of phosphoric acid added to the aqueous slurry was changed to 0.1 parts by mass per 100 parts by mass of calcium carbonate.

[0124] 100 parts by mass (3 kg) of the obtained untreated whisker-shaped calcium carbonate particles were placed in a Henschel mixer and stirred while heating the jacket provided on the outside of the mixer. Then, 1.0 part by mass of epoxysilane coupling agent was added and the mixture was heated and stirred until the temperature reached 130°C, thereby obtaining whisker-shaped calcium carbonate particles surface-treated with the epoxysilane coupling agent.

[0125] The phosphorus content of these whisker-shaped calcium carbonate particles is 0.03% by mass, and the BET specific surface area is 1.5 m². 2 The particle size was / g, with a major axis of 30.0 μm, a minor axis of 1.5 μm, and an aspect ratio of 20. The residue on a 38 μm sieve was 50 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as optical film filler (E3).

[0126] (Example 4: Preparation of a filler for optical films (E4) composed of surface-treated whisker-shaped calcium carbonate particles) Whisker-shaped calcium carbonate particles were obtained in the same manner as in Example 1, except that the amount of phosphoric acid added to the aqueous slurry was changed to 2.0 parts by mass per 100 parts by mass of calcium carbonate.

[0127] 100 parts by mass (3 kg) of the obtained untreated whisker-shaped calcium carbonate particles were placed in a Henschel mixer and stirred while heating the jacket provided on the outside of the mixer. Then, 1.0 part by mass of vinylsilane coupling agent was added and the mixture was heated and stirred until the temperature reached 130°C, thereby obtaining whisker-shaped calcium carbonate particles surface-treated with vinylsilane coupling agent.

[0128] The phosphorus content of these whisker-shaped calcium carbonate particles is 0.60% by mass, and the BET specific surface area is 6.0 m². 2 The particle size was / g, with a major axis of 20.0 μm, a minor axis of 1.0 μm, and an aspect ratio of 20. The residue on a 38 μm sieve was 110 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as optical film filler (E4).

[0129] (Example 5: Preparation of an optical film filler (E5) composed of surface-treated whisker-shaped calcium carbonate particles) 100 parts by mass (3 kg) of untreated whisker-shaped calcium carbonate particles obtained in Example 1 were placed in a Henschel mixer and stirred while heating the jacket provided on the outside of the mixer. Then, 1.0 part by mass of acrylic silane coupling agent was added and the mixture was heated and stirred until the temperature reached 130°C, thereby obtaining whisker-shaped calcium carbonate particles surface-treated with the acrylic silane coupling agent. The phosphorus content of these whisker-shaped calcium carbonate particles was 0.30% by mass, and the BET specific surface area was 4.0 m². 2 The particle size was / g, with a major axis of 25.0 μm, a minor axis of 0.8 μm, and an aspect ratio of 31. The residue on a 38 μm sieve was 10 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as optical film filler (E5).

[0130] (Example 6: Preparation of an optical film filler (E6) composed of surface-treated whisker-shaped calcium carbonate particles) 100 parts by mass (3 kg) of untreated whisker-shaped calcium carbonate particles obtained in Example 1 were placed in a Henschel mixer and stirred while heating the jacket provided on the outside of the mixer. Then, 1.0 part by mass of trimethoxyvinylsilane was added and the mixture was heated and stirred until the temperature reached 115°C, thereby obtaining whisker-shaped calcium carbonate particles surface-treated with this vinylsilane coupling agent. The phosphorus content of these whisker-shaped calcium carbonate particles was 0.30% by mass, and the BET specific surface area was 4.5 m². 2 The particle size was / g, with a major axis of 15.0 μm, a minor axis of 0.5 μm, and an aspect ratio of 30. The residue on a 38 μm sieve was 50 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as optical film filler (E6).

[0131] (Comparative Example 1: Preparation of a filler for optical films (C1) composed of surface-treated whisker-shaped calcium carbonate particles) Whisker-shaped calcium carbonate particles were obtained in the same manner as in Example 1, except that the amount of phosphoric acid added to the aqueous slurry was changed to 3.0 parts by mass per 100 parts by mass of calcium carbonate.

[0132] 100 parts by mass (3 kg) of the obtained untreated whisker-shaped calcium carbonate particles were placed in a Henschel mixer and stirred while heating the jacket provided on the outside of the mixer. Then, 1.0 part by mass of trimethoxyvinylsilane was added and the mixture was heated and stirred until the temperature reached 130°C, thereby obtaining whisker-shaped calcium carbonate particles surface-treated with a vinylsilane coupling agent.

[0133] The phosphorus content of these whisker-shaped calcium carbonate particles is 0.91% by mass, and the BET specific surface area is 7.0 m². 2 The particle size was / g, with a major axis of 25.0 μm, a minor axis of 1.0 μm, and an aspect ratio of 25. The residue on a 38 μm sieve was 120 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as optical film filler (C1).

[0134] (Comparative Example 2: Preparation of a filler for optical films (C2) composed of surface-treated whisker-shaped calcium carbonate particles) Whisker-shaped calcium carbonate particles were obtained in the same manner as in Example 1, except that the amount of phosphoric acid added to the aqueous slurry was changed to 0.05 parts by mass per 100 parts by mass of calcium carbonate.

[0135] 100 parts by mass (3 kg) of the obtained untreated whisker-shaped calcium carbonate particles were placed in a Henschel mixer and stirred while heating the jacket provided on the outside of the mixer. Then, 1.0 part by mass of trimethoxyvinylsilane was added and the mixture was heated and stirred until the temperature reached 130°C, thereby obtaining whisker-shaped calcium carbonate particles surface-treated with a vinylsilane coupling agent.

[0136] The phosphorus content of these whisker-shaped calcium carbonate particles is 0.01% by mass, and the BET specific surface area is 1.0 m². 2 The particle size was / g, with a major axis of 30.0 μm, a minor axis of 2.0 μm, and an aspect ratio of 15. The residue on a 38 μm sieve was 50 ppm. The surface-treated whisker-shaped calcium carbonate particles obtained in this manner will be referred to below as (C2) filler for optical films.

[0137] (Examples 7-12 and Comparative Examples 3-4: Preparation and evaluation of laminated films using optical film fillers) An acrylic polyol resin with a refractive index of 1.50, produced by adding an isocyanate-based curing agent, was selected as the transparent resin matrix. An acrylic polyol resin solution was prepared by dissolving it in a mixed solvent of methyl ethyl ketone and ethyl acetate at a total solids concentration of 30%. To 270 parts by mass of this acrylic polyol resin solution, 10 parts by mass of whisker-shaped calcium carbonate particles (E1) to (E6) or (C1) to (C2) prepared in Examples 1 to 6 or Comparative Examples 1 to 2 were added. Furthermore, 40 parts by mass of ethyl acetate was added as a diluent, and the mixture was stirred at 2,000 rpm for 15 minutes to obtain a dispersion of whisker-shaped calcium carbonate particles. To this dispersion, 6 parts by mass of an isocyanate-based curing agent was added and thoroughly mixed to prepare a paint composition.

[0138] This composition was applied in a consistent direction to an 80 μm thick TAC film using an applicator, and dried at 100°C for 3 minutes to produce a laminated film. The thickness of each laminated film was 20 μm.

[0139] Furthermore, for each of the resulting laminated films, the graininess and unevenness of the film surface on the side coated with the composition, as well as the deflection and light diffusion properties of the entire laminated film, were evaluated based on the following evaluation criteria. The results are shown in Table 1.

[0140] (Film grains) The number of particles larger than 50 μm that could be observed was counted and classified based on the following evaluation criteria. ◎: The number of visible granules in an A4-sized booklet was two or less. ○: The number of visible granules in an A4-sized booklet was 3 to 5. △: The number of visible granules in an A4-sized booklet was 6 to 9. ×: There were 10 or more visible granules in the A4-sized booklet.

[0141] (Film unevenness) Ten laminated films were prepared, and the unevenness appearing within the dimensions of an A4 sheet of paper was visually inspected on the laminated film (the film surface on the side coated with the composition), and they were classified based on the following evaluation criteria. ◎: No unevenness could be visually confirmed within the dimensions of an A4 size sheet. ○: Unevenness was visually confirmed in less than 30% of the area within the dimensions of an A4 size sheet. △: Unevenness was visually confirmed in an area (area) of 30% to less than 60% within the dimensions of an A4 size sheet. ×: Unevenness was visually confirmed in more than 60% of the area within the dimensions of an A4 sheet of paper.

[0142] (Polarization) The obtained laminated film was placed parallel to a white sheet of paper on a horizontal table, at a distance of 10 cm, with the coated surface of the composition facing upwards. By perpendicularly shining light from a laser pointer onto the film from above, an elliptical light image, extending perpendicular to the long axis of the whisker-like calcium carbonate, was projected onto the paper. The longest points of the light image projected onto the paper in both the vertical and horizontal directions were measured with calipers, and the ratio of the longest vertical length to the longest horizontal length was calculated as the "magnification ratio of the laser pointer's vertical to horizontal direction," and classified according to the following evaluation criteria. ○: The vertical and horizontal magnification of the laser pointer was 4 or higher. △: The vertical and horizontal magnification of the laser pointer was between 2 and 4. ×: The vertical and horizontal magnification of the laser pointer was less than 2.

[0143] (Light diffusivity) The obtained laminated film was placed parallel to a white sheet of paper on a horizontal table, at a distance of 10 cm, with the coated surface of the composition facing upwards. By perpendicularly shining light from a laser pointer onto the film from above, an elliptical light image, extending perpendicular to the long axis of the whisker-like calcium carbonate, was projected onto the paper. The presence or absence of an outline in the light image projected onto the paper was visually observed and classified according to the following evaluation criteria. ○: The elliptical outline of the light was clearly visible. △: The outline of the elliptical light was blurred. ×: The outlines of the light were lost, and the overall image was faintly blurred.

[0144] [Table 1]

[0145] As shown in Table 1, the laminated films produced in Examples 7 to 12 all exhibited better polarizing and light-diffusing properties compared to the laminated films of Comparative Examples 3 and 4. This confirmed that the whisker-shaped calcium carbonate particles constituting the optical film filler in the laminated films were oriented substantially along the coating direction of the composition. The laminated films produced in Examples 7 to 12 also effectively suppressed the occurrence of granules and unevenness within the film. From this, it can be seen that the laminated films produced in Examples 7 to 12 were all excellent as diffuse polarizer laminated films (optical films).

[0146] (Examples 13-18 and Comparative Examples 5-6: Preparation and evaluation of uniaxially oriented films using optical film fillers) 90 parts by weight of acrylic resin was melt-kneaded at 240°C in a φ25 mm twin-screw extruder (TEX25αIII twin-screw extruder manufactured by Japan Steel Works Ltd.), and pellets were obtained by side-feeding 10 parts by mass of whisker-shaped calcium carbonate particles (E1) to (E6) or (C1) to (C2) prepared in Examples 1 to 6 or Comparative Examples 1 to 2 through a vent port. The obtained pellets were melt-extruded at 260°C in a single-screw extruder equipped with a T-die at the tip (Laboplastmill manufactured by Toyo Seiki Seisakusho Co., Ltd.), and uniaxially stretched to obtain a uniaxially oriented film with a thickness of 20 μm.

[0147] For each of the obtained uniaxially oriented films, the film surface graininess and unevenness, as well as the overall deflection and light diffusion properties of the uniaxially oriented film, were evaluated in the same manner as in Example 7. The results are shown in Table 2.

[0148] [Table 2]

[0149] As shown in Table 2, the uniaxially oriented films obtained in Examples 13-18 all exhibited better polarizing and light-diffusing properties compared to the oriented films of Comparative Examples 5-6. Furthermore, the uniaxially oriented films produced in Examples 13-18 effectively suppressed the occurrence of grains and unevenness within the film. This indicates that the oriented films obtained in Examples 13-18 are all excellent as diffuse polarizer oriented films (optical films). [Industrial applicability]

[0150] The present invention is useful in a wide range of technical fields, for example, related to the field of wide-viewing-angle visibility of displays.

Claims

1. A filler for optical films containing whisker-shaped calcium carbonate particles, These whisker-shaped calcium carbonate particles are Major axis of 15.0 μm to 30.0 μm, Short axis of 0.5 μm to 1.5 μm, and Aspect ratios from 20 to 31 It has, and The product contains 0.03% to 0.6% by mass of phosphorus element based on the total mass of the whisker-shaped calcium carbonate particles. The BET specific surface area of ​​the whisker-shaped calcium carbonate particles is 1.5 m². ２ / g~6m ２ A filler for optical films, with a concentration of / g.

2. The optical film filler according to claim 1, wherein the sieve residue of the whisker-shaped calcium carbonate particles at 38 μm is 100 ppm or less.

3. The optical film filler according to claim 1, wherein the whisker-shaped calcium carbonate particles are particles that have been surface-treated with at least one surface treatment agent selected from the group consisting of fatty acids, fatty acid metal salts, surfactants, coupling agents, silanes, polyhydric alcohol esters, and phosphate esters.

4. The optical film filler according to claim 1, wherein the optical film is a film used to constitute a display device.

5. The optical film filler according to claim 1, wherein the optical film is a diffuse polarizer or a phase difference film.

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