TW201303391A - Optical film, optical sheet and liquid crystal display module - Google Patents

Abstract

The purpose of the present invention is to provide an optical film which generates only a small change in phase difference due to external force with excellent optical uniformity property and is capable of displaying precise image, and also provide an optical sheet and a liquid crystal display module using the optical sheet. The optical film has a major component of cyclic olefin copolymer. The optical elasticity coefficient of the optical film is preferred to be smaller than 10×10 -12 /Pa. The average thickness of the optical film in accordance with the present invention is preferred to be larger than 10 <mu>m and smaller than 500 <mu>m. The absolute value of phase difference (Re) of the optical film in accordance with the present invention is preferred to be smaller than 50 nm. The optical sheet of the present invention has a transparent conductive layer, a hard coating layer, a light diffusing layer, or a prism layer on one face of the optical film. The liquid crystal display module of the present invention is provided with the aforementioned optical sheet.

Description

Optical film, optical sheet and liquid crystal display module

The present invention relates to an optical film, an optical sheet, and a liquid crystal display module which are small in phase difference change due to shrinkage stress and excellent in optical uniformity.

The liquid crystal display module (LCD) is widely used as a flat panel display because of its characteristics of thinness, lightness, low power consumption, etc., and is used as a display device for mobile phones, personal digital assistants (PDAs), personal computers, televisions, etc., liquid crystal display modules. The use has expanded year by year. In recent years, there are various characteristics required for a liquid crystal display module depending on the application, and examples thereof include bright (high luminance), easy viewing (wide viewing angle), energy saving, thinness, and large screen. Wait.

The liquid crystal display module generally has a structure in which a liquid crystal display element, various optical sheets, and a backlight are sequentially superposed from one surface side to the back side. Further, the optical sheet used in the liquid crystal display module includes a polarizing plate protective sheet that protects a polarizing plate that holds a liquid crystal cell, and light disposed between the liquid crystal display element and the backlight. A diffusion sheet, a prism sheet, a transparent conductive sheet used as a transparent electrode, or the like.

The optical sheet generally has a layer of a base material and an optically functional layer laminated on the layer of the base material. As the resin constituting the base material layer, a so-called biaxially stretched polyethylene terephthalate (PET) film or polycarbonate which is stretched in two directions intersecting each other is conventionally used (refer to Japan). Patent Publication No. 2010-44146). In addition, as the resin constituting the base material layer of the polarizing plate protective sheet, a cellulose triacetate film or the like which is easily adhered to a polyvinyl alcohol polarizing plate is used (refer to Japanese Laid-Open Patent Publication No. 2006-235341).

However, the biaxially stretched polyethylene terephthalate, polycarbonate, cellulose triacetate or the like which is conventionally used as a resin constituting the base material layer has a large photoelastic coefficient and is caused by an external force such as heat generation of the display. The phase difference changes greatly. As a result, there is a problem that the liquid crystal display module including the optical sheet using the resin in the base material layer is difficult to display an image finely with the large screen and thinning of the liquid crystal display.

Patent Document 1: Japanese Patent Laid-Open Publication No. 2010-44146

Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-235341.

In view of the above problems, an object of the present invention is to provide an optical film, an optical sheet, and a liquid crystal display module using the optical sheet which have a small change in phase difference due to an external force and are excellent in optical uniformity and can display a fine image.

In order to solve the above problems, the optical film of the present invention contains a cycloolefin copolymer as a main component.

The optical film contains a cycloolefin copolymer having a small photoelastic coefficient as a main component. As a result, the optical film can suppress a change in phase difference caused by an external force such as heat generation of the display. Therefore, the optical film is excellent in optical uniformity and can display a fine image.

Preferably, the optical film has a photoelastic coefficient of 10 × 10 ^-12 /Pa or less. Thereby, it is possible to reduce the phase difference change exposed to the high-temperature and high-humidity environment, and it is possible to suppress a decrease in the degree of picture clarity (visibility) and to display a finer image.

It is preferable that the optical film has an average thickness of 10 μm or more and 500 μm or less. When the average thickness of the optical film is less than the above range, characteristics such as strength of the film and prevention of bending property are lowered, and there is a problem that the large screen of the liquid crystal display device cannot be handled. On the other hand, if the average thickness of the optical film is larger than the above range, there is a problem that the brightness of the liquid crystal display device is lowered, and the requirement for thinning of the liquid crystal display device is also violated.

It is preferable that the absolute value of the retardation value (hysteresis value) (Re) of the optical film is 50 nm or less. Thereby, it is possible to suppress the effect of changing the polarization direction of the transmitted light, and it is possible to suppress the disadvantages such as deformation (skew) of the image.

Therefore, an optical sheet having a transparent conductive layer, a hard coat layer, a light diffusion layer or a prism layer on at least one surface of the optical film can improve optical characteristics, heat stability, and the like, and can suppress a phase difference due to an external force. Variety. As a result, the optical sheet can display a fine image, and can promote large-screening and thinning of the liquid crystal display device.

Further, according to the liquid crystal display module having the optical sheet, since the optical sheet has excellent optical characteristics, heat resistance stability, and the like, it is possible to display a fine image and to promote large-screening and thinning of the liquid crystal display device.

Further, the "phase difference value (Re)" in the present invention means a direction of a fast axis (phase advance axis) and a direction of a slow axis (遅 phase axis) which are perpendicular to the crystal axis direction on the plane of the surface of the optical film. For the x direction and the y direction, the thickness of the optical film is d, and the refractive indices in the x direction and the y direction are nx and ny (nx ≠ ny), and the values calculated by Re = (ny - nx) d are used.

As described above, the optical film and the optical sheet of the present invention can suppress a change in phase difference due to an external force and improve optical uniformity. Therefore, according to the optical film, the optical sheet, and the liquid crystal display module of the present invention, a fine image can be displayed, and the large-screening and thinning of the liquid crystal display device can be promoted.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The optical film 1 of Fig. 1 has a cycloolefin copolymer as a main component.

Since the optical film 1 needs to transmit light, it needs to be formed to be transparent, particularly colorless and transparent.

The so-called cyclic olefin copolymer used for the optical film 1 means a non-crystalline cyclic olefin-based resin which is a copolymer of a cyclic olefin and an olefin such as ethylene. The cyclic olefin includes a polycyclic cyclic olefin and a monocyclic cyclic olefin. The polycyclic cyclic olefin may, for example, be norbornene, methylnorbornene, dimethylnorbornene, ethylnorbornene, ethylidene norbornene or butylnorbornene. Dicyclopentadiene, dihydrodicyclopentadiene, methyldicyclopentadiene, dimethyldicyclopentadiene, tetracyclododecene, methyltetracyclododecene, dimethyl Dimethyltetracychlododecene, tricyclopentadiene, tetracyclopentadiene, and the like. Further, examples of the monocyclic cyclic olefin include cyclobutene, cyclopentene, cyclooctene, cyclooctadiene, cyclooctanetriene, and cyclododecanetriene.

The optical film 1 may contain other optional components as long as the transparency and the desired strength are not impaired, and it is preferable to contain 90% by mass or more of the cycloolefin copolymer, and more preferably 98% by mass or more of the cycloolefin. Copolymer. Examples of the optional component include ultraviolet absorbers, stabilizers, lubricants, processing aids, plasticizers, impact-resistant additives, phase difference reducing agents, matting agents, antibacterial agents, antifungal agents, and the like. .

The thickness (average thickness) of the optical film 1 is not particularly limited, and is, for example, preferably 10 μm or more and 500 μm or less, more preferably 50 μm or more and 450 μm or less, still more preferably 80 μm or more and 400 μm or less, and still more preferably 90 μm or more and 300 μm or less. It is particularly preferably 100 μm or more and 200 μm or less. When the thickness of the optical film 1 is less than the above range, characteristics such as strength of the optical film 1 and prevention of bendability (deflection prevention property) are lowered, and there is a problem that the large screen of the liquid crystal display device cannot be handled. On the other hand, if the average thickness of the optical film 1 is larger than the above range, there is a problem that the brightness of the liquid crystal display device is lowered, and the requirement for thinning of the liquid crystal display device is also violated.

The photoelastic coefficient of the optical film 1 is not particularly limited, and is, for example, 10 × 10 ^-12 /Pa or less, preferably 9 × 10 ^-12 /Pa or less, and particularly preferably 8 × 10 ^-12 /Pa or less. If the photoelastic coefficient of the optical film 1 is larger than the above range, the change in the phase difference exposed to the high-temperature and high-humidity environment is large, and there is a problem that the degree of sharpness is lowered. On the other hand, if the photoelastic coefficient of the optical film 1 is within the above range, the phase difference change exposed to the high-temperature and high-humidity environment can be reduced, and the deterioration of the image clarity can be suppressed, and a fine image can be displayed.

The absolute value of the retardation value (Re) of the optical film 1 is not particularly limited, and is, for example, 50 nm or less, preferably 15 nm or less, and particularly preferably 5 nm or less. By reducing the retardation value (Re) of the optical film 1, for example, in the case where the optical film 1 is used for a light diffusion sheet, the effect of the light diffusion sheet on the polarization direction of the transmitted light can be suppressed, and the light diffusion can be suppressed. The sheet influences the optimization (optimization) and controllability of the polarized light to the transmission axis direction of the polarizing plate or the like. Further, in the case where the optical film 1 is disposed on the surface of the polarizing plate, it is possible to suppress disadvantages such as image deformation.

As the optical film 1, an optical film having an arithmetic mean surface roughness (Ra) of 0.02 or more and 0.06 or less can be usually used. Further, matt processing can be performed on the optical film 1 as needed. The arithmetic mean surface roughness (Ra) of the optical film 1 subjected to such a matte treatment is preferably 0.07 or more and 2 or less, and more preferably 0.1 or more and 1 or less. By controlling the surface roughness of the optical film 1 within such a range, it is possible to prevent the damage in the treatment after the production of the original film and to improve the usability. Further, in general, when winding the produced original film, it is necessary to perform embossing (knurling processing) on both ends in the width direction of the film to prevent lumping. When the knurling process is performed on the film, since the treated portion at both ends of the film cannot be used, it is necessary to cut the portion and discard it. Further, in the winding operation of the film, masking may be performed with a protective film in order to prevent damage. However, since the arithmetic mean surface roughness of the optical film 1 is within the predetermined range described above, the knurling process can be prevented, and the squashing can be prevented. Therefore, the manufacturing process can be simplified, and both end portions in the film width direction can be used. And no film failure occurs, and long film winding can be performed. Further, since the optical film 1 has an appropriate surface roughness, damage at the time of winding can be effectively suppressed, and the above-described shielding is not required.

The method for producing the optical film 1 is not particularly limited. For example, an additive such as a sheet-like raw material of a synthetic resin and a plasticizer can be mixed by a conventionally known mixing method, and a thermoplastic resin composition can be prepared in advance to produce an optical film. For example, the raw material is premixed by a mixer such as a universal mixer, and the obtained mixture is extrusion-kneaded to obtain the thermoplastic resin composition. In this case, the kneading machine used in the extrusion kneading is not particularly limited, and for example, a conventionally known kneading such as an extruder such as a single-screw extruder or a twin-screw extruder or a kneading kneader can be used. machine.

As a method of forming the optical film 1, a known method such as a solution casting method (solution casting method), a melt extrusion method, a calendering method, or a compression molding method can be exemplified. Among them, a solution casting method (solution casting method) or a melt extrusion method is preferred. In this case, the thermoplastic resin composition after pre-extrusion kneading may be used, or other additives such as a synthetic resin and a plasticizer may be dissolved in a solvent to form a uniform mixed solution, and then supplied to a solution casting method (solution). Casting process) or film forming step of melt extrusion.

The solvent to be used in the solution casting method (solution casting method) may, for example, be a chlorine solvent such as chloroform or dichloromethane; an aromatic solvent such as toluene, xylene, benzene or a mixed solvent thereof; methanol Alcohol solvent such as ethanol, isopropanol, n-butanol or 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethyl azine, two Oxane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone (MEK), ethyl acetate, diethyl ether, and the like. Only one of the solvents may be used, or two or more kinds may be used together. As an apparatus for performing a solution casting method (solution casting method), a drum type casting machine, a belt casting machine, a spin coater, etc. are mentioned.

The melt extrusion method may, for example, be a T-die method, a tubular film process or the like. The film forming temperature at the time of melt extrusion is preferably from 150 ° C to 350 ° C, more preferably from 200 ° C to 300 ° C. When the film formation is carried out by the T-die method, the T-die is attached to the front end portion of a known single-screw extruder or twin-screw extruder, and the film which is extruded into a film shape is taken up to obtain a roll shape. membrane. At this time, the temperature of the take-up roll is appropriately adjusted, and by stretching the film in the extrusion direction, the uniaxial stretching step can be obtained. Further, by adding a step of stretching the film in a direction perpendicular to the extrusion direction, sequential biaxial stretching may be added, and simultaneous biaxial stretching or the like may be added.

The optical film 1 may be an unstretched film or a stretched film. In the case of stretching, it may be a uniaxially stretched film or a biaxially stretched film. In the case of a biaxially stretched film, it may be a film obtained by simultaneous biaxial stretching, or may be a film obtained by sequential biaxial stretching. In the case of biaxial stretching, the mechanical strength of the film can be increased, thereby improving the performance of the film.

The stretching temperature in the case where the stretching step is carried out is preferably carried out in the vicinity of the glass transition temperature of the thermoplastic resin composition of the film raw material, specifically, (glass transition temperature -30) ° C - (Glass transition temperature + 100) is carried out at ° C, more preferably (glass transition temperature -20) ° C ~ (glass transition temperature + 80) ° C. If the stretching temperature is lower than (glass transition temperature - 30) ° C, it is not preferable because a sufficient stretching ratio cannot be obtained. If the stretching temperature is higher than (glass transition temperature + 100) ° C, the flow of the resin is caused, and stretching cannot be performed stably, which is not preferable.

The stretching ratio defined by the area ratio is preferably in the range of 1.1 times or more and 25 times or less, and more preferably in the range of 1.3 times or more and 10 times or less. If the draw ratio is less than 1.1 times, the toughness is not promoted accompanying the stretching, which is not preferable. If the draw ratio is more than 25 times, the corresponding effect cannot be obtained even if the draw ratio is increased.

The stretching speed (one direction) is preferably in the range of 10 to 20000%/min, more preferably in the range of 100 to 10000%/min. If the stretching speed (one direction) is less than 10%/min, it takes a long time to obtain a sufficient stretching ratio, resulting in an increase in manufacturing cost, which is not preferable. If the stretching speed (one direction) is higher than 20,000%/min, there is a problem that the stretched film is broken, and the like, which is not preferable. Further, in order to stabilize the optical isotropy and mechanical properties of the optical film 1, heat treatment (annealing) or the like may be performed after the stretching treatment.

The plasticizer is not particularly limited, but preferably has a functional group that can interact with the synthetic resin by hydrogen bonding or the like, so that the optical film 1 does not cause blurring or does not bleed or volatilize from the optical film 1. Examples of the plasticizer are not particularly limited, and examples thereof include a phosphate ester plasticizer, a phthalate plasticizer, a trimellitate plasticizer, and pyromellitic acid. Plasticizer, polyol plasticizer, glycolic acid plasticizer, citric acid ester plasticizer, fatty acid ester plasticizer, carboxylate plasticizer, polyester plasticizer Agents, etc.

The optical film 1 has a cycloolefin copolymer having a small photoelastic coefficient as a main component. As a result, the optical film 1 can suppress a change in phase difference caused by an external force such as heat generation of the display. Therefore, the optical film 1 is excellent in optical uniformity and can display a fine image.

The optical sheet 11 of FIG. 2 includes a base material layer 12 composed of an optical film 1 and a transparent conductive layer 13. The optical sheet 11 is laminated with a transparent conductive layer 13 on one surface of the base material layer 12.

The transparent conductive layer 13 may be formed as an amorphous layer or as a crystalline layer. Further, the transparent conductive layer 13 may also be formed as a layer in which amorphous and crystalline are mixed. The thickness (average thickness) of the transparent conductive layer 13 is not particularly limited, and may be, for example, 10 nm or more and 100 nm or less.

As a method of producing the optical sheet 11, a sputtering method may be exemplified. For example, the sputtering method performs sputtering using a target containing In ₂ O ₃ and SnO ₂ in a mixed gas containing a gas for sputtering and oxygen. As the sputtering method, in addition to the standard magnetron sputtering method using a DC power source, various sputtering methods such as RF (radio frequency) sputtering method and double magnetron sputtering method can be used.

Further, as for the production of the transparent conductive layer 13, a surface modification treatment such as plasma treatment may be performed in an inert gas atmosphere such as argon gas or nitrogen gas as a pretreatment. Further, an undercoat layer may be laminated on one surface of the base material layer 12, and the transparent conductive layer 13 may be formed via the undercoat layer.

Since the optical sheet 11 uses a cyclic olefin copolymer as the base material layer 12, optical characteristics, heat resistance stability, and the like can be improved. This optical sheet 11 can suppress a change in phase difference due to an external force, and can suppress occurrence of display unevenness. Therefore, the optical sheet 11 can display a fine image and can promote large-screening and thinning of the liquid crystal display device.

The optical sheet 21 of FIG. 3 includes a base material layer 12 and a hard coat layer 22 composed of an optical film 1. The optical sheet 21 is laminated with a hard coat layer 22 on one surface of the base material layer 12.

The resin forming the hard coat layer 22 is not particularly limited, and examples thereof include an active energy ray-curable resin. Examples of the active energy ray-curable resin include a polyurethane acrylate resin, a polyester acrylate resin, an epoxy acrylate resin, a polyol acrylate resin, and an epoxy resin. The thickness (average thickness) of the hard coat layer 22 is not particularly limited, and may be, for example, 3 μm or more and 50 μm or less.

The optical sheet 21 can be produced by applying an active energy ray-curable resin to one surface of the base material layer 12 and then drying it. The method of applying the active energy ray-curable resin is not particularly limited as long as it can uniformly apply the active energy ray-curable resin to one surface of the base material layer 12, and examples thereof include a spin coating method, a spray coating method, and a slanting method. Various methods such as a plate coating method, a dip coating method, a bar coating method, a roll coater method, and a screen printing method.

Since the optical sheet 21 uses a cyclic olefin copolymer as the base material layer 12, optical characteristics, heat resistance stability, and the like can be improved. The optical sheet 21 can improve heat resistance stability and the like, and can suppress a change in phase difference due to an external force. Further, since the optical sheet 21 has the hard coat layer 22, the scratch resistance can be improved, and the ease of use can be improved.

The optical sheet 31 of FIG. 4 includes a base material layer 12 and a light diffusion layer 32 composed of an optical film 1. The light diffusion layer 32 is laminated on one surface of the base material layer 12 to form an optical sheet 31.

The light diffusion layer 32 has a minute and random uneven shape on the surface. The light diffusion layer 32 has a function of diffusing transmitted light due to the minute uneven shape of the surface. The uneven shape of the light diffusion layer 32 can be formed by a light diffusing agent dispersed in the binder.

The light diffusing agent for the light diffusion layer 32 is a particle having a property of diffusing light, and is mainly classified into an inorganic filler and an organic filler. Specifically, as the inorganic filler, cerium oxide, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfate, magnesium citrate or a mixture thereof can be used. Further, as a specific material of the organic filler, an acrylic resin, an acrylonitrile resin, a polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamine or the like can be used. Among them, an acrylic resin having high transparency is preferred, and polymethyl methacrylate (PMMA) is particularly preferred. The shape of the light diffusing agent is not particularly limited, and examples thereof include a spherical shape, a spindle shape, a needle shape, a rod shape, a cubic shape, a plate shape, a scaly shape, and a fiber shape. Among them, those having excellent light diffusibility are preferable. Spherical beads.

The lower limit of the average particle diameter of the light diffusing agent is preferably 1 μm, particularly preferably 2 μm, and further preferably 5 μm. On the other hand, the upper limit of the average particle diameter of the light diffusing agent is preferably 50 μm, particularly preferably 20 μm, and further preferably 15 μm. When the average particle diameter of the light-diffusing agent is less than the above range, the unevenness of the surface of the light-diffusing layer 32 formed of the light-diffusing agent becomes small, and there is a problem that the optical sheet 31 cannot satisfy the required light-diffusing performance. On the contrary, if the average particle diameter of the light diffusing agent is larger than the above range, the thickness of the optical sheet 31 is increased and it is difficult to uniformly diffuse.

The lower limit of the amount of the light diffusing agent (100 parts of the base material polymer in the polymer composition as the binder forming material, and the amount of the solid component to be added) is preferably 10 parts, particularly preferably 20 parts, more preferably 50 parts, the upper limit of the compounding amount is preferably 500 parts, particularly preferably 300 parts, further preferably 200 parts. This is because if the amount of the light diffusing agent to be incorporated is less than the above range, the light diffusibility is insufficient. On the other hand, if the amount of the light diffusing agent to be incorporated is larger than the above range, the effect of fixing the light diffusing agent is lowered. In the case where the light-diffusing sheet is a so-called upper light-diffusing sheet disposed on the surface side of the prism sheet, since the light diffusing property is not required, the amount of the light diffusing agent to be incorporated is preferably 10 or more. 40 parts or less, particularly preferably 10 parts or more and 30 parts or less.

The binder is formed by crosslinking and curing the polymer composition containing the polymer of the matrix material. The light diffusing agent is disposed and fixed substantially uniformly on the surface of the base material layer 12 by the binder. Further, in addition to the base material polymer, the polymer composition for forming the binder may be appropriately blended with a fine inorganic filler, a curing agent, an antistatic agent, a plasticizer, a dispersant, various leveling agents, UV absorbers, antioxidants, viscosity modifiers, lubricants, light stabilizers, etc.

The base material polymer is not particularly limited, and examples thereof include an acrylic resin, a polyurethane, a polyester fiber, a fluorine resin, an anthraquinone resin, a polyamide-imine, an epoxy resin, and an ultraviolet curing type. As the resin or the like, one type of the base material polymer or two or more types of the base material polymer may be used in combination. Particularly preferred as the base material polymer is a polyol which is excellent in processability and can be easily formed into a light-diffusing layer 32 by a coating method or the like. Further, from the viewpoint of improving the light transmission performance, the base material polymer itself used in the binder is preferably transparent, and particularly preferably colorless and transparent.

The polyhydric alcohol is preferably a polyester polyol or an acrylic polyol having a (meth)acrylic unit or the like obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer. The polyester polyol or the acrylic polyol as a binder of the base material polymer has good weather resistance, and can suppress yellowing of the light diffusion layer 32. Further, either one of the polyester polyol and the acrylic polyol may be used, or both of them may be used.

Further, the number of the hydroxyl groups in the polyester polyol and the acrylic polyol is not particularly limited as long as it is two or more per molecule, and if the hydroxyl value in the solid component is 10 or less, the number of crosslinking points is decreased. The physical properties of the cover film such as solvent resistance, water resistance, heat resistance, and surface hardness tend to be lowered.

Preferred as the base material polymer is a polyol having a cycloalkyl group. By introducing a cycloalkyl group into a polyol which is a base material polymer forming a binder, the water repellency such as water repellency and water resistance of the binder can be improved, and the bending resistance of the optical sheet 31 under high temperature and high humidity conditions can be improved. , dimensional stability, etc. Further, the basic properties of the coating film such as weather resistance, hardness, satiety, and solvent resistance of the light diffusion layer 32 can be improved. Further, the affinity with the fine inorganic filler having the organic polymer fixed on the surface and the uniform dispersibility of the minute inorganic filler are further improved.

The cycloalkyl group is not particularly limited, and examples thereof include a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecyl group, a cyclodecyl group, a cyclodecyl group, and a ring. Dodecyl, cyclotridecyl, cyclotetradecyl, cyclopentadecyl, cyclohexadecyl, cycloheptadecyl, cyclooctadecyl, and the like.

A polyol having the cycloalkyl group can be obtained by copolymerizing a polymerizable unsaturated monomer having a cycloalkyl group. The polymerizable unsaturated monomer having a cycloalkyl group means a polymerizable unsaturated monomer having at least one cycloalkyl group in the molecule. The polymerizable unsaturated monomer is not particularly limited, and examples thereof include cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, and t-butylcyclohexyl (meth) acrylate. Cyclododecyl (meth) acrylate and the like.

Further, an isocyanate may also be contained as a curing agent in the polymer composition. By containing an isocyanate curing agent in the polymer composition, a stronger crosslinked structure can be obtained, and the physical properties of the coating film of the light diffusion layer 32 can be further improved. The same as the polyfunctional isocyanate compound is used as the isocyanate. Among them, an aliphatic isocyanate capable of preventing yellowing of a cover film is preferable.

In particular, in the case where a polyol is used as the base material polymer, as a curing agent to be incorporated into the polymer composition, hexamethylene diisocyanate, isophorone diisocyanate, and xylene diisocyanate may be used. Any one of two or more kinds of hexamethylene diisocyanate, isophorone diisocyanate, and xylene diisocyanate may be used in combination. When the curing agent is used, since the curing reaction rate of the polymer composition becomes large, even if a cationic antistatic agent which contributes to the dispersion stability of the fine inorganic filler is used as an antistatic agent, it can be sufficiently compensated. The rate of curing reaction due to the cationic antistatic agent is lowered. Further, an increase in the curing reaction rate of the polymer composition contributes to uniform dispersibility of the minute inorganic filler into the binder. As a result, the bending and yellowing of the optical sheet 31 due to heat, ultraviolet rays, or the like can be remarkably suppressed.

Further, an ultraviolet absorber may be contained in the polymer composition. By forming a binder from a polymer composition containing an ultraviolet absorber and imparting a function of cutting ultraviolet rays to the optical sheet 31, it is possible to cut off a small amount of ultraviolet rays emitted from the lamp of the backlight unit, thereby preventing damage of the liquid crystal layer due to ultraviolet rays. .

The ultraviolet absorber is not particularly limited as long as it is a compound which can absorb ultraviolet rays and is efficiently converted into heat energy and is stable to light, and a known ultraviolet absorber can be used. Among them, a salicylic acid-based ultraviolet absorber, a benzophenone-based ultraviolet absorber, a benzophenone having a strong ultraviolet absorbing function, good compatibility with the matrix material polymer, and stable presence in a matrix material polymer is preferable. As the triazole-based ultraviolet absorber and the cyanoacrylate-based ultraviolet absorber, one or two or more selected from the group of ultraviolet absorbers can be used. In addition, as the ultraviolet absorber, a polymer having an ultraviolet absorbing group in a molecular chain (for example, "Udouble UV" series of Japanese catalyst) is also suitably used. By using the polymer having an ultraviolet absorbing group in the molecular chain, the compatibility with the host polymer of the binder is high, and deterioration of the ultraviolet absorbing function due to bleeding of the ultraviolet absorbing agent or the like can be prevented. Further, a polymer having an ultraviolet absorbing group in a molecular chain may be used as a base material polymer of a binder. Further, the polymer having the ultraviolet absorbing group bonded thereto may be used as a base material polymer of the binder, and further the ultraviolet absorbing agent may be contained in the base material polymer to further enhance the ultraviolet absorbing function.

The lower limit of the content of the ultraviolet absorber relative to the base material polymer of the binder is preferably 0.1% by mass, particularly preferably 1% by mass, further preferably 3% by mass, as the content of the ultraviolet absorber. The upper limit is preferably 10% by mass, particularly preferably 8% by mass, and further preferably 5% by mass. This is because if the mass ratio of the ultraviolet absorber to the base material polymer is smaller than the lower limit, the optical sheet 31 cannot effectively exhibit the ultraviolet absorbing function, and if the mass ratio of the ultraviolet absorbing agent is larger than the upper limit, It has a bad influence on the polymer of the base material, resulting in a decrease in the strength and durability of the binder.

Instead of the ultraviolet absorber, a UV stabilizer may be used or a UV stabilizer (including a base material polymer having an ultraviolet stabilizing group bonded to a molecular chain) may be used together with the ultraviolet absorber. The ultraviolet stabilizer can passivate radicals generated by ultraviolet rays, active oxygen, and the like, thereby improving ultraviolet stability, weather resistance, and the like. As the ultraviolet stabilizer, a hindered amine-based ultraviolet stabilizer having high ultraviolet stability is suitably used. Further, by using the ultraviolet absorber together with the ultraviolet stabilizer, it is possible to prevent deterioration due to ultraviolet rays and remarkably improve weather resistance.

Further, an antistatic agent can be kneaded in the polymer composition. By forming a binder from the polymer composition in which the antistatic agent is kneaded, the optical sheet 31 can have an antistatic effect, and it is possible to prevent the occurrence of static electricity due to adsorption of dust and difficulty in overlapping with the prism sheet or the like. Unfavorable situation. Further, if an antistatic agent is applied to the surface, surface stickiness and dirt are generated, but by disposing the antistatic agent in the polymer composition, such drawbacks can be reduced. The antistatic agent is not particularly limited, and examples thereof include an anionic antistatic agent such as an alkyl sulfate or an alkyl phosphate; a cationic antistatic agent such as a quaternary ammonium salt or an imidazoline compound; and a polyethylene glycol system. A nonionic antistatic agent such as polyoxyethylene sorbitan monostearate or ethanol decylamine; a polymer-based antistatic agent such as polyacrylic acid. Among them, a cationic antistatic agent having a relatively good antistatic effect is preferred, and a small amount of addition has an antistatic effect.

Further, the optical sheet 31 may have an adhesion preventing layer (not shown) laminated on the other surface of the base material layer 12. The adhesion preventing layer has a structure in which a small amount of beads are dispersedly dispersed in a binder, and a lower portion of the beads protrudes from the back surface of the bonding agent, thereby preventing the back surface of the optical sheet 31 (with the surface on which the light diffusion layer 32 is laminated) The opposite surface) is inferior to the surface of the light guide plate and the like to cause interference fringes.

The manufacturing method of the optical sheet 31 is exemplified by a manufacturing method including the steps of: (a) producing a composition for a light-diffusing layer by mixing a light-diffusing agent in a composition for forming a binder. And (b) a step of laminating the composition for a light-diffusing layer on the surface of the base material layer 12 and curing it to form the light-diffusing layer 32. The method of laminating the composition for the light-diffusing layer 32 on the base material layer 12 is not particularly limited, and examples thereof include a spin coating method, a spray coating method, a swash plate coating method, a dip coating method, and a bar coating method. Various methods such as roll coater method and screen printing method. Further, when the light diffusion layer 32 is laminated, if necessary, a surface modification treatment such as plasma treatment in an inert gas atmosphere such as argon gas or nitrogen gas may be performed as a pretreatment.

Since the optical sheet 31 uses the cycloolefin copolymer as the base material layer 12, optical characteristics, heat resistance stability, and the like can be improved. The optical sheet 21 can improve heat resistance stability and the like, and can suppress a change in phase difference due to an external force.

Further, in the liquid crystal display device, in order to improve the light use efficiency, the polarization characteristics of the backlight and various optical sheets are designed such that the polarization direction of the incident light (the maximum planar direction of the polarized component of the light) and the liquid crystal display element are The transmission direction of the polarizing plate on the back side (or the reflective polarizing plate on the back side thereof) is uniform. Therefore, by making the absolute value of the phase difference (Re) of the base material layer 12 of the optical sheet 31 50 nm or less, it is preferable that the absolute value of the phase difference (Re) of the base material layer 12 of the optical sheet 31 is 15 nm. In the following, it is particularly preferable that the absolute value of the phase difference (Re) of the base material layer 12 of the optical sheet 31 is 5 nm or less, and the effect of changing the polarization direction of the transmitted light by the optical sheet 31 can be suppressed, and the optical sheet 31 can be suppressed. The influence of the polarization and the controllability on the transmission axis direction of the polarizing plate or the like.

The optical sheet 41 of FIG. 5 includes a base material layer 12 and a prism layer 42 composed of an optical film 1. The prism sheet is laminated on one surface of the base material layer 12 to form the optical sheet 41, and the plurality of ridge prism portions are formed in a stripe shape to constitute the prism layer.

The prism layer 42 has a function of refracting light toward one side in the normal direction by a plurality of strip prism portions which are formed in stripes on the surface.

Since the prism layer 42 needs to transmit light, it is made of a transparent, particularly colorless, transparent synthetic resin, and one or two or more kinds of resins which are the same as or different from the base material layer 12 can be used. The lower limit of the refractive index of the material constituting the prism layer 42 is preferably 1.3, particularly preferably 1.45, and the upper limit of the refractive index of the material constituting the prism layer 42 is preferably 1.8, and particularly preferably 1.6.

The ridge prism portion has a triangular prism shape. The cross-sectional shape of the ridge prism portion is generally an equilateral right triangle having an apex angle of 90° and a base angle of 45°.

The lower limit of the width (W) of the bottom surface of the ridge prism portion is preferably 10 μm, particularly preferably 30 μm. On the other hand, the upper limit of the width (W) is preferably 1000 μm, particularly preferably 400 μm. This is because if the bottom surface width (W) of the ridge strip prism portion is smaller than the lower limit, it is difficult to form the ridge strip prism portion. Conversely, if the bottom surface width (W) of the ridge strip prism portion is larger than the upper limit, there is a dazzling, Problems such as uneven brightness.

The method for producing the optical sheet 41 is not particularly limited as long as the structure can be formed, and may be a method of separately forming the prism layer 42 after the base material layer 12 is formed, and integrally forming the base material layer 12 and the prism layer 42. The method, specifically, the method of manufacturing the optical sheet 41 includes the following method:

(a) a method of forming the optical sheet 41 by laminating the synthetic resin on a sheet type having a shape opposite to the shape of the surface of the prism layer 42 by peeling off the sheet mold;

(b) an injection molding method in which a molten resin is injected into a mold having a shape opposite to that of the surface of the prism layer 42;

(c) a method of reheating the resin formed into a sheet and sandwiching it between the same mold and the metal plate as described above to pressurize the shape;

(d) an extrusion sheet forming method in which the resin in a molten state is transferred between a roll mold having a shape opposite to the shape of the surface of the prism layer 42 and other rolls on the circumferential surface to transfer the shape;

(e) applying an ultraviolet curable resin to the base material layer 12, and pressing it with a sheet mold, a mold or a roll mold having the same shape as that of the surface of the prism layer 42 as described above, in the uncured ultraviolet ray a method of transferring a shape onto a curable resin and then irradiating the ultraviolet ray to cure the ultraviolet curable resin;

(f) applying a uncured ultraviolet curable resin to a mold or a roll mold having the same shape as that described above and having a shape opposite to the surface of the prism layer 42, and pressing it with the base material layer 12 and a method of curing the ultraviolet curable resin by irradiating ultraviolet rays;

(g) A method of replacing an ultraviolet curable resin with an electron beam curable resin.

Since the optical sheet 41 uses the cycloolefin copolymer as the base material layer 12, optical characteristics, heat resistance stability, and the like can be improved. This optical sheet 41 can improve heat resistance stability and the like, and can suppress a change in phase difference due to an external force.

Further, in the liquid crystal display device, in order to improve the light use efficiency, the polarization characteristics of the backlight and various optical sheets are designed such that the polarization direction of the incident light (the maximum planar direction of the polarized component of the light) and the liquid crystal display element are The transmission direction of the polarizing plate on the back side (or the reflective polarizing plate on the back side thereof) is uniform. Therefore, by setting the absolute value of the phase difference (Re) of the base material layer 12 of the optical sheet 41 to 50 nm or less, preferably 15 nm or less, and particularly preferably 5 nm or less, the optical sheet 41 can be suppressed from transmitting light. The effect of changing the polarization direction can suppress the influence of the light diffusion sheet 41 on the optimization of the transmission axis direction of the polarizing plate or the like and the controllability.

Example

The invention is described in detail below based on the examples, but should not be construed as limiting the invention in light of the examples.

Example 1

A cycloolefin copolymer ("TOPAS 8007" manufactured by Polyplastics Co., Ltd.) was used, and after pre-drying, melt-extrusion was performed on a cooling roll using a single-screw extruder (L/D = 35), and a thickness was made using a take-up device. 100 μm optical film.

Example 2

The optical film produced in Example 1 was subjected to ITO treatment by a sputtering process to prepare an optical sheet (transparent conductive sheet) having a transparent conductive layer on one surface of the optical film.

Example 3

A hard coat agent ("Purple UV-7605B" manufactured by Nippon Synthetic Chemical Co., Ltd.) was applied to the optical film produced in Example 1, and the thickness of the hard coat layer was 5 μm, and it was cured. An optical sheet (hard coat film) having a hard coat layer on one side of the optical film.

Example 4

An optical sheet (light-diffusing sheet) having a light-diffusing layer on one surface of the optical film was produced by applying a coating material in which a light-diffusing agent was applied to the optical film produced in Example 1.

Example 5

The photosensitive curable film ("SR-3000" manufactured by Hitachi Chemical Co., Ltd.) was pressure-bonded to the optical film produced in Example 1, and heated by a roll under reduced pressure in a molding die having a concave-convex pattern formed thereon. By pressurization, a concave-convex pattern was formed on the photosensitive curable film, and the photosensitive curable film was cured by irradiation with ultraviolet rays, and separated from the molding die, and an optical sheet (prism sheet) having a prism layer on one surface of the optical film was produced.

Comparative example 1

An optical film having a thickness of 100 μm was produced in the same manner as in Example 1 using a polycarbonate resin ("TARFLON A2200" manufactured by Idemitsu Kosan Co., Ltd.).

Comparative example 2

The optical film produced by the comparative example 1 was subjected to ITO treatment by a sputtering process to produce an optical sheet (transparent conductive sheet) having a transparent conductive layer on one surface of the optical film.

Comparative example 3

The same hard coat agent as in Example 3 was applied onto the optical film produced in Comparative Example 1, and the thickness of the hard coat layer was 5 μm, and it was cured, and a hard coat was formed on one surface of the optical film. Layer of optical sheet (hard coating film).

Comparative example 4

An optical sheet (light-diffusing sheet) having a light-diffusing layer on one surface of the optical film was produced by applying the same light-diffusing agent-like coating material as in Example 4 to the optical film produced in Comparative Example 1.

Comparative Example 5

The optical film produced in Comparative Example 1 was subjected to the same treatment as in Example 5 to prepare an optical sheet (prism sheet) having a prism layer on one surface of the optical film.

The light-diffusing sheet and the prism sheet of the fourth embodiment and the fifth embodiment are used in the backlight unit of the thin liquid crystal display device, and the hard coat film of the third embodiment is used as the polarizing plate protective sheet of the liquid crystal display device, and the liquid crystal is used as the liquid crystal. The transparent electrode of the display device was subjected to a lighting test for 96 hours in a high-temperature, high-humidity bath at 60 ° C and 85% RH using the transparent conductive sheet of Example 2. In the same manner, the light-diffusing sheet and the prism sheet of Comparative Example 4 and Comparative Example 5 were used in the backlight unit of the thin liquid crystal display device, and the hard coat film of Comparative Example 3 was used as the polarizing plate protective sheet of the liquid crystal display device. Further, as the transparent electrode of the liquid crystal display device, the transparent conductive sheet of Comparative Example 2 was used, and a lighting test was performed for 96 hours in a high-temperature and high-humidity bath at 60 ° C and 85% RH. The results are shown in Table 1 below.

Deformation evaluation

The optical sheets of the respective examples and comparative examples were taken out after the lighting test, and the presence or absence of deformation was evaluated by a visual method according to the following criteria.

○: No deformation was observed.

×: Deformation was observed.

Evaluation of the picture surface seen (display evaluation)

The display screen was visually confirmed 96 hours after the lighting test, and the change of the display screen was evaluated according to the following criteria.

○: No change in the display screen was observed.

×: A change in color (whitening) of the display screen was observed.

As shown in Table 1, no deformation was observed in the optical sheets from Example 2 to Example 5, and no blush of the display screen was observed, thereby confirming that the optical sheets of Example 2 to Example 5 were External forces such as heat have sufficient resistance as required. On the other hand, deformation was observed in the optical sheets of Comparative Example 2 to Comparative Example 5, and the display screen was observed to be whitish. Therefore, it was confirmed that the optical sheets of Comparative Example 2 to Comparative Example 5 did not have an external force such as heat generation. Sufficient resistance required.

Industrial applicability

As described above, the optical film and the optical sheet of the present invention have a small change in phase difference due to an external force and are excellent in optical uniformity. Therefore, the optical film, the optical sheet, and the liquid crystal display module of the present invention can display a fine screen and are suitable for promoting large-screening and thinning of the liquid crystal display device.

1. . . Optical film

2. . . Base material layer

11. . . Optical sheet

12. . . Base material layer

13. . . Transparent conductive layer

twenty one. . . Optical sheet

twenty two. . . Hard coating

31. . . Optical sheet

32. . . Light diffusion layer

41. . . Optical sheet

42. . . Prism layer

Fig. 1 is a cross-sectional view showing an optical film according to an embodiment of the present invention.

2 is a cross-sectional view showing an optical sheet having a transparent conductive layer according to an embodiment of the present invention.

Fig. 3 is a cross-sectional view showing an optical sheet having a hard coat layer according to an embodiment of the present invention.

Fig. 4 is a cross-sectional view showing an optical sheet having a light diffusion layer according to an embodiment of the present invention.

Fig. 5 is a cross-sectional view showing an optical sheet having a prism layer according to an embodiment of the present invention.

1. . . Optical film

2. . . Base material layer

Claims (9)

An optical film characterized in that the optical film contains a cycloolefin copolymer as a main component. The optical film of claim 1, wherein the photoelastic coefficient is 10 × 10 ^-12 /Pa or less. The optical film of claim 1 or 2, wherein the average thickness is from 10 μm to 500 μm. The optical film of claim 1, wherein the absolute value of the retardation value (Re) is 50 nm or less. An optical sheet characterized in that the optical sheet has a transparent conductive layer on at least one side of the optical film of claim 1 of the patent application. An optical sheet characterized in that the optical sheet has a hard coat layer on at least one side of the optical film as in the first aspect of the patent application. An optical sheet characterized in that the optical sheet has a light diffusion layer on at least one side of the optical film of claim 1 of the patent application. An optical sheet characterized in that the optical sheet has a prism layer formed on at least one surface of the optical film of the first aspect of the patent application, the prism layer being formed by forming a plurality of ridge prism portions into stripes. A liquid crystal display module characterized by having an optical sheet according to any one of claims 5 to 8.