TWI519860B - Optical sheets and backlight units - Google Patents

Description

Optical sheet and backlight unit

The present invention relates to an optical sheet and a backlight unit.

As a transmissive liquid crystal display device, a transflective liquid crystal display device that emits a liquid crystal layer from the back surface is widely used, and a backlight unit such as an edge light type (side light type) or a direct type is mounted on the lower surface side of the liquid crystal layer. As shown in FIG. 3( a ), the edge light type backlight unit 40 generally includes a light source 41 , a light guide plate 42 having a square plate shape, and an end portion disposed along the light source 41 ; The sheet 43 is superposed on the surface side of the light guide plate 42. The optical sheet 43 has a function of diffusing, refracting, or the like of the transmitted light, and (1) is disposed on the surface side of the light guide plate 42 and has a light diffusing sheet 44 mainly having a light diffusing function; and (2) is disposed on the light diffusing sheet 44. The surface side has a cymbal sheet 45 or the like which refracts light toward the normal direction side.

When the function of the backlight unit 40 is described, first, the light incident from the light source 41 to the light guide plate 42 is reflected by the reflection point or the reflection sheet (omitted from the drawing) on the back surface of the light guide plate 42 and the respective side surfaces, from the surface of the light guide plate 42. Shoot out. The light emitted from the light guide plate 42 is incident on the light diffusion sheet 44, is diffused, and is emitted from the surface. The light emitted from the surface of the light-diffusing sheet 44 is incident on the cymbal sheet 45, refracted toward the normal direction side by a plurality of protruding strip-shaped ridge portions formed on the surface, and is further emitted to the liquid crystal layer not shown in the upper figure. The entire face is illuminated.

The light-diffusing sheet 44 disperses the transmitted light substantially uniformly, and the purpose of using the light-diffusing sheet 44 is to make the brightness uniform, the brightness in the front direction, and the like by utilizing the light diffusing property. As shown in FIG. 3(b), the light diffusion sheet 44 includes a base layer 46 made of a synthetic resin, a light diffusion layer 47 laminated on the surface of the base material layer 46, and laminated on the light diffusion layer 47. The adhesion preventing layer 48 on the back surface of the base material layer 46. The adhesion preventing layer 48 prevents the back surface of the light diffusion sheet 44 from adhering (adhesively) to the surface of the light guide plate 42 to cause an interference fringe. The adhesion preventing layer 48 generally has a spherical bead and a binder made of a thermosetting resin covering the beads, and the convex portion protruding from the back side and the light guide plate are prevented from adhering to the light guide plate.

Acrylic beads are generally used as the beads 50 of the adhesion preventing layer 48 (refer to Japanese Laid-Open Patent Publication No. 2011-126274). However, since the beads of the acrylic material are relatively hard, the beads 50 protruding toward the back surface of the adhesive 49 may damage the surface of the light guide plate 42 laminated on the back side of the light diffusion sheet 44. As described above, if the light guide plate 42 is damaged, unevenness in brightness or the like may occur due to the damage.

Prior art literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2011-126274

In order to prevent the above-mentioned disadvantages, a technique of making the material of the adhesion preventing layer such as beads and a binder soft is proposed. However, it has been found that even if the above-described soft beads or the like are used, the surface of the light guide plate is damaged. The inventors of the present invention conducted an intensive study on the cause, and it is considered that if another optical sheet such as a cymbal sheet is disposed on the surface side of the light-diffusing sheet, the convex portion of the bead is pressed due to the load of the optical sheet on the surface side. In the spherical shape of the soft bead, the tip end portion (the top portion on the back surface side) of the contact portion that is in contact with the light guide plate is easily deformed, and therefore the contact area with the light guide plate laminated on the back surface side is changed. Large, and then the friction becomes larger, but it will increase the damage. Further, it is considered that the coating film of the adhesive on the outer surface of the bead which is the contact portion in contact with the light guide plate is peeled off due to the frictional force described above, and the peeling sheet of the adhesive may also cause damage to the light guide plate.

In view of the above-mentioned problems, an object of the present invention is to provide an optical sheet for a liquid crystal display device that can prevent the optical member disposed on the back side of the light diffusion sheet from being damaged, and an optical system using the liquid crystal display device. Film backlight unit.

In order to solve the above problems, the inventors of the present invention have conducted intensive studies and found that by fixing beads having a suitable hardness with a predetermined binder, it is possible to sufficiently exhibit a function of preventing damage to the optical member on the back side.

That is, in order to solve the above problems, the present invention provides an optical sheet for a liquid crystal display device comprising: a transparent substrate layer; and an adhesion preventing layer laminated on the back side of the substrate layer, containing beads and a covering In the binder of the bead, the main component of the bead is a polyamine-based resin, and the binder is composed of a resin composition containing an ultraviolet curable resin as a host polymer.

In the optical sheet for a liquid crystal display device, a bead made of a polyimide material having a relatively soft texture is used as a bead constituting the adhesion preventing layer, and the binder is made of a UV curable resin having a relatively hard texture, thereby being hard. The adhesive film covers the soft beads. Therefore, even if an external force acts on the convex portion of the bead, the optical sheet for a liquid crystal display device can suppress the front end portion (the top portion on the back side) from being crushed, and the convex portion is deformed in a flat manner as a whole. That is, the convex portion is deformed such that the cross section is elliptical. As a result, even if an external force acts on the optical sheet for a liquid crystal display device, the contact area is hard to increase, and the frictional force is hard to increase, and the effect of preventing damage to other optical members on the back side can be remarkably improved.

Preferably, the bead has a D hardness of 30 or more and 70 or less. By setting the durometer D hardness of the bead within the above range, the effect of preventing damage to the optical member on the back side can be further improved.

Preferably, the pencil hardness of the back surface of the adhesive is H or more and 2H or less. When the pencil hardness is within the above range, the adhesive which is in contact with the optical member on the back side has a suitable hardness, so that the cover film on the outer side of the bead of the adhesive can be reliably contacted with the optical member on the back side. The adhesive is inhibited from causing damage to the optical member on the back side.

Preferably, the average coating film thickness of the adhesive on the top side of the back side of the bead is 0.1 μm or more and 3 μm or less. By making the thickness of the cover film of the adhesive in the In the above-described range, the optical sheet for a liquid crystal display device can be made to meet the requirements for thinning, and the peeling of the cover film of the adhesive due to the friction with the optical member on the back side can be reliably prevented, and the back side of the peeling sheet can be improved. The optical component causes damage.

Preferably, the beads have an average particle diameter of from 2 μm to 20 μm. When the average particle diameter of the beads is within the above range, the optical sheet for a liquid crystal display device can be made thinner, and the optical member on the back side can be prevented from being damaged, and the function of preventing adhesion can be sufficiently exhibited.

In order to solve the above problems, the present invention provides a backlight unit for a liquid crystal display device comprising the above-described optical sheet for a liquid crystal display device. Thereby, it is possible to appropriately prevent damage to the optical member on the back side of the light diffusion sheet.

Further, in the present invention, the term "surface side" refers to the side of the person who views when assembled on the liquid crystal display device, and the so-called back side refers to the side opposite to the surface side. The average particle diameter refers to the average value of the particle diameters of 30 particles randomly extracted from the particles observed under an electron microscope at a magnification of 1000 times, and the particle diameter is determined by the Feret diameter (the projection is sandwiched by parallel lines in a certain direction) The interval at which the image is defined). The pencil hardness is a pencil scratch value obtained in accordance with Test Method 8.4 of JIS K5400, which is a value measured in a region where no beads are present. The hardness D hardness is a value measured in accordance with JIS K7215. The average thickness of the cover film of the adhesive covering the nylon beads is the thickness of the cover film of the optical diffuser, and the thickness of the cover film of the adhesive which is randomly selected and covered with 10 parts of the nylon beads (from the The average of the distance between the interface of the Dragon Ball and the outer surface is calculated.

As described above, the optical sheet for a liquid crystal display device of the present invention and the backlight unit including the optical sheet for the liquid crystal display device can sufficiently prevent damage to the optical member on the back side of the optical sheet for a liquid crystal display device. Features.

1‧‧‧Light diffuser

2‧‧‧Substrate layer

3‧‧‧Light diffusion layer

4‧‧‧Binder

5‧‧‧Light diffusing agent

6‧‧‧Adhesion prevention layer

7‧‧‧Binder

8‧‧‧ beads

40‧‧‧Backlight unit

41‧‧‧Light source

42‧‧‧Light guide plate

43‧‧‧Optical film

44‧‧‧Light diffuser

45‧‧‧ Picture

46‧‧‧Substrate layer

47‧‧‧Light diffusion layer

48‧‧‧Adhesion prevention layer

49‧‧‧Binder

50‧‧‧ beads

7A‧‧‧ Cover film

D‧‧‧ hardness

H‧‧‧average thickness

Fig. 1 is a cross-sectional view schematically showing a light diffusion sheet according to an embodiment of the present invention.

Fig. 2 is a partial enlarged view of the light diffusing sheet of Fig. 1.

(a) of FIG. 3 is a perspective view schematically showing a general edge light type backlight unit, and (b) of FIG. 3 is a cross-sectional view schematically showing a normal light diffusion sheet.

Hereinafter, as an embodiment of the present invention, an optical sheet used for a back sheet of a liquid crystal display device will be described in detail with reference to a suitable drawing.

Light diffuser

The light diffusion sheet 1 includes a base material layer 2 and an adhesion preventing layer 6 laminated on the back surface side of the base material layer 2. The light diffusion sheet 1 further includes an optical function layer laminated on the surface side of the base material layer 2. In the present embodiment, the optical function layer is a light diffusion layer that diffuses light from the light guide plate.

Substrate layer

The base material layer 2 is made of a transparent synthetic resin that can transmit light. Here, the transparency may be colored transparent or translucent, and in order to increase light transmittance, colorless transparency is preferred. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, and polystyrene. , polyolefin, cellulose acetate, weather resistant vinyl chloride, etc. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending properties is particularly preferable.

The average thickness of the base material layer 2 is not particularly limited, but is preferably 10 μm or more, more preferably 35 μm or more, and still more preferably 50 μm or more. Further, as the average thickness, it is preferably 500 μm or less, more preferably 250 μm or less, still more preferably 188 μm or less. In the case where the average thickness of the base material layer 2 is less than the lower limit, there is a problem that curling occurs when the material for forming the light diffusion layer 3 or the adhesion preventing layer 6 is applied. On the other hand, when the average thickness exceeds the upper limit, the brightness of the liquid crystal display device may be lowered, and the thickness of the backlight unit may be increased to be thinner than the liquid crystal display device. Requirements.

Optical function layer

The light diffusion layer 3 as an optical functional layer is laminated on the surface of the base material layer 2, and the light diffusion layer 3 is formed by applying a coating liquid containing the light diffusing agent 5 and the binder 4 to the surface of the base material layer 2. The light diffusion layer 3 has a binder 4 and a light diffusing agent 5 contained in the binder 4. By including the light diffusing agent 5 in the light diffusing layer 3 as described above, the light transmitted through the light diffusing layer 3 from the back surface side to the surface side can be uniformly diffused. Further, fine unevenness is formed substantially uniformly on the surface of the light diffusion layer 3 by the light diffusing agent 5. Thus, the light can be diffused better by the refraction of the lens having fine irregularities formed on the surface of the light diffusion sheet 1.

The light diffusing agent 5 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, cerium sulfide, magnesium citrate, or a mixture thereof can be used. As a specific material of the organic filler, an acrylic resin, an acrylonitrile resin, a polyurethane, polyvinyl chloride, polystyrene, polyamine, polyacrylonitrile 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 5 is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scaly shape, and a fiber shape. Among them, it is preferable that the light diffusing property is excellent. Spherical beads.

Although the average particle diameter of the light-diffusing agent 5 is not particularly limited, it is preferably 1 μm or more, more preferably 2 μm or more, and still more preferably 5 μm or more. Further, the average particle diameter is preferably 50 μm or less, more preferably 20 μm or less, and still more preferably 15 μm or less. If the average particle diameter of the light diffusing agent 5 is smaller than the lower limit, the unevenness of the surface of the light diffusing layer 3 formed by the light diffusing agent 5 becomes small, and there is a problem that the light diffusing property required as the light diffusing sheet 1 cannot be satisfied. . On the contrary, if the average particle diameter exceeds the upper limit, the thickness of the light diffusion sheet 1 is increased, and uniform diffusion becomes difficult.

The content of the light diffusing agent 5 is preferably 10 parts by mass or more, and more preferably 20 parts by mass or more, as the content of the resin component of the light diffusing agent 5 with respect to 100 parts by mass of the binder 4 . More preferably, it is 50 mass parts or more. In addition, the content is preferably 500 parts by mass or less, more preferably 300 parts by mass or less, still more preferably 200 parts by mass or less. In the case where the content of the light diffusing agent 5 is less than the lower limit, there is a problem that the light diffusing performance is insufficient. On the contrary, if the content of the light diffusing agent 5 exceeds the upper limit, the effect of fixing the light diffusing agent 5 is lowered. In addition, in the case of a so-called upper light-diffusing sheet which is disposed on the surface side of the ruthenium, since high light-diffusing performance is not required, the content of the light-diffusing agent 5 is preferably 10 parts by mass or more and 40 parts by mass or less. More preferably, it is 20 mass parts or more and 30 mass parts or less.

The binder 4 is formed by curing (crosslinking, etc.) the polymer composition containing the base polymer. The light diffusing agent 5 is disposed at substantially equal density on the entire surface of the base material layer 2 by the binder 4. Further, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, an antistatic agent, and an ultraviolet absorber may be appropriately blended in the polymer composition for forming the binder 4. , antioxidants, viscosity modifiers, lubricants, light stabilizers, etc.

The base polymer is not particularly limited, and examples thereof include an acrylic resin, a polyurethane, a polyester, a fluorine resin, a fluorene resin, a polyamide-imine, an epoxy resin, and an ultraviolet curable resin. One type or two or more types of the above polymers may be used in combination. In particular, as the substrate polymer, a polyol which is excellent in processability and can be easily formed into a light-diffusing sheet 1 by a coating method or the like is preferable. Further, from the viewpoint of improving light transmission properties, the base polymer for the adhesive 4 itself is preferably transparent, and particularly preferably colorless and transparent.

The polyhydric alcohol may, for example, be a polyhydric alcohol obtained by polymerizing a monomer component including a hydroxyl group-containing unsaturated monomer, a polyester polyol obtained under conditions in which a hydroxyl group is excessive, and the like, and a single polyhydric alcohol may be used. Two or more kinds of the above polyols may be used in combination.

The hydroxyl group-containing unsaturated monomer may, for example, be (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate or allylic. a hydroxyl group-containing unsaturated monomer such as an alcohol, a high allyl alcohol, a cinnamyl alcohol or a crotyl alcohol; (b) by, for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1 , 4-bis(hydroxymethyl)cyclohexane, phenyl glycidyl ether, glycidyl phthalate, A diol or an epoxy compound such as FM-1 (manufactured by Daicel Chemical Industries, Ltd.) is reacted with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid or itaconic acid. A hydroxyl group-containing unsaturated monomer or the like. The polyol can be produced by polymerizing one or more selected from the above-mentioned hydroxyl group-containing unsaturated monomers.

In addition, it is also possible to use ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, n-propyl methacrylate, Isopropyl acrylate, n-butyl methacrylate, t-butyl methacrylate, ethylhexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyl toluene, 1 -methylstyrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, allyl acetate, diallyl adipate, diallyl itaconate , diethyl maleate, polyvinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N-butoxymethyl acrylamide, diacetone acrylamide, ethylene, One or two or more kinds of ethylenically unsaturated monomers selected from the group consisting of propylene, isoprene and the like are polymerized with the hydroxyl group-containing unsaturated monomer selected from the above (a) and (b) to produce a polyol.

The number average molecular weight of the polyol obtained by polymerizing the monomer component including the hydroxyl group-containing unsaturated monomer is 1,000 or more and 500,000 or less, preferably 5,000 or more and 100,000 or less. Further, the hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 150 or less.

The following (c) and (d) can be produced by reacting a polyol having a larger number of hydroxyl groups than a polybasic acid in a polyhydric alcohol such as propylene glycol, hexanediol, polyethylene glycol or trimethylolpropane. A polyester polyol obtained under conditions of excess hydroxyl groups. (c) is for example Ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, hexanediol, decanediol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, hexanetriol, glycerin, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis(hydroxymethyl) ring a polyhydric alcohol such as alkane, hydroquinone bis(hydroxyethyl ether), tris(hydroxyethyl)isocyanate or benzenedimethanol; (d) is, for example, maleic acid, fumaric acid, succinic acid, adipic acid, hydrazine Diacids such as diacid, azelaic acid, trimellitic acid, terephthalic acid, phthalic acid, and isophthalic acid.

The number average molecular weight of the polyester polyol obtained under conditions in which the hydroxyl group is excessive is 500 or more and 300,000 or less, preferably 2,000 or more and 100,000 or less. Further, the hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and more preferably 20 or more and 150 or less.

The polyol used as the base polymer of the polymer composition is preferably obtained by polymerizing the polyester polyol and the monomer component including the hydroxyl group-containing unsaturated monomer, and having An acrylic polyol such as a (meth)acrylic unit. The weather resistance of the binder 4 which uses a polyester polyol or an acrylic polyol as a base polymer is strong, and it can suppress that the said light-diffusion sheet 1 turns yellow etc.. 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 hydroxyl groups in the polyester polyol and the acrylic polyol is not particularly limited as long as it is two or more per molecule, but if the hydroxyl value in the solid component is 10 or less, cross-linking is possible. The physical properties of the cover film such as the number reduction, the solvent resistance, the water resistance, the heat resistance, and the surface hardness tend to be lowered.

Adhesion prevention layer

The adhesion preventing layer 6 is laminated on the back surface of the base material layer 2, and the beads 8 and the binder 7 covering the beads 8 are provided on the back surface of the base material layer 2. The adhesion preventing layer 6 forms a convex portion by using the beads 8, thereby preventing the light diffusion sheet 1 and the light guide plate on the back side from adhering, and it is possible to suppress unevenness in brightness of the screen of the liquid crystal display device. Further, as shown in FIG. 1, the adhesion preventing layer 6 has the convex portion formed by the presence of the beads 8 and the flat portion in which the beads 8 are not present.

The main component of the beads 8 is a polyamide resin. As the polyamine-based resin, an aliphatic polyamide resin, an aromatic polyamide resin, or the like can be used. Among them, it is preferred to use a suitable aliphatic polyamide resin such as hardness. As the aliphatic polyamine resin, nylon 6, nylon 66, nylon 68, nylon 46, nylon 612, nylon 610, or the like can be used. The beads 8 may contain one or more kinds of the above polyamine-based resins. In addition, the bead 8 may be a nylon copolymer containing a polyamine-based resin as a main component and containing a component other than the polyamine-based resin, or may be a mixed resin containing a resin other than the polyamine-based resin.

The shape of the bead 8 is not particularly limited, and examples thereof include a spherical shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scaly shape, and a fibrous shape, and a spherical shape excellent in adhesion prevention function or the like is preferable.

The hardness D hardness of the beads 8 is preferably 30 or more, and more preferably 40 or more. Further, as the durometer D hardness, it is preferably 70 or less, and more preferably 60 or less. When the hardness D of the bead 8 is less than the lower limit, when the optical sheet such as a cymbal sheet is disposed on the surface side of the light diffusion sheet 1, there is a possibility that the bead 8 is excessively deformed due to the load of the optical sheet. The problem that the adhesive 7 is peeled off from the beads 8. On the other hand, when the hardness D hardness exceeds the upper limit, the function of preventing damage to the light guide plate on the back side of the light diffusion sheet 1 cannot be sufficiently obtained.

The beads 8 may be monodisperse beads or polydisperse beads. Here, the coefficient of variation of the particle diameter of the beads 8 is not particularly limited, and a coefficient of variation of a particle diameter of 0.05 or more and 1 or less is preferably used. The lower limit of the coefficient of variation of the particle diameter of the beads 8 is more preferably 0.1, and the upper limit is more preferably 0.3. If the coefficient of variation of the particle diameter of the beads 8 exceeds the upper limit, there is a problem that an excessive load acts on a part of the protruding beads. On the contrary, if the coefficient of variation is smaller than the lower limit, there is a problem that the cost of the beads used is too high.

Although the average particle diameter X of the beads 8 is not particularly limited, it is preferably 2 μm or more, more preferably 3 μm or more, and still more preferably 4 μm or more. Further, as the average particle diameter X, it is preferably 20 μm. Hereinafter, it is more preferably 10 μm or less, and still more preferably 6 μm or less. By making the average particle diameter X of the beads 8 within the above range, the optical sheet for a liquid crystal display device can be made thinner, and it is possible to effectively prevent damage to the optical member on the back side and to sufficiently prevent adhesion. Features.

The content of the beads 8 is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 or less, based on 100 parts by mass of the resin component of the binder 7 . More than the quality. In addition, the content of the beads 8 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less. In the case where the content of the beads 8 is less than the lower limit, the existence ratio of the beads 8 in the adhesion preventing layer 6 is too small, and the function of preventing adhesion to the light guide plate cannot be sufficiently achieved. On the other hand, in the case where the content exceeds the upper limit, there is a problem that although the ratio of the presence of the beads 8 in the adhesion preventing layer 6 is increased, the adhesion preventing function cannot be further improved; since the beads 8 hinder the light diffusion The function of slice 1.

The binder 7 is formed of a resin composition containing an ultraviolet curable resin as a host polymer. The host polymer is not particularly limited, and examples thereof include (a) a radical polymerizable resin such as epoxy acrylate, urethane acrylate or melamine acrylate; and (b) a photoaddition polymerization type polythiol- a polyene resin; (c) a photocationic polymerization resin. Among them, as the host polymer, an ultraviolet curable acrylic resin is preferable.

In addition, a photoinitiator and a diluent may be blended in the resin composition containing the ultraviolet curable resin as a host polymer, and various solvents and antistatic agents for adjusting the viscosity may be appropriately blended. Slip agent, photosensitizer, polymerization inhibitor, antioxidant, dispersant, surfactant, inorganic filler, inorganic pigment, organic pigment, organic dye, light stabilizer, light absorber, leveling agent, defoamer, Rust inhibitors, etc.

The resin composition containing the ultraviolet curable resin as a host polymer preferably contains (a) an alicyclic isocyanate compound, an ester polyol, and a hydroxyl group. a urethane acrylate produced by using an acrylate compound as an essential component; (b) an acrylate-based reactive diluent; and (c) a photoinitiator.

When the alicyclic isocyanate compound, the ester polyol, and the hydroxyl group-containing acrylate compound are present at a temperature of 50 to 120 ° C, if necessary, a urethanization reaction occurs, whereby the (a) can be easily synthesized. Polyurethane acrylate. Even if the urethanization reaction is a reaction in which all components are added at once, the residual component of the polyol component and the isocyanate component after the isocyanate group is temporarily allowed to pass through the synthetic prepolymer may be retained by using a hydroxyl group-containing acrylate compound. The isocyanate group can also be synthesized. Further, a method may be employed in which the residual isocyanate group is reacted with the polyester polyol after the isocyanate group is temporarily left over by synthesizing the hydroxyl group-containing acrylate compound and the isocyanate compound into a prepolymer. The molecular weight of the urethane acrylate synthesized by the above reaction is preferably in the range of 700 to 20,000.

As the alicyclic isocyanate compound, isophorone diisocyanate, hydrogenated xylene diisocyanate, dicyclohexylmethane diisocyanate or the like can be used. Further, an isocyanurate compound, a biuret compound or the like, an aromatic isocyanate compound or an aliphatic isocyanate compound, or a co-isocyanurate compound or the like may be used in combination with the above-mentioned alicyclic isocyanate compound.

As the ester-based polyol, an ester compound of a polyhydric alcohol compound and a polycarboxylic acid compound, a substance synthesized by a ring-opening reaction of a cyclic ester compound and a polyhydric alcohol, or the like can be used. Representative examples of the polyhydric alcohol compound include ethylene glycol, 1,3-propanediol, 1,2-propanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, and 1,3-butane. Alcohol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, 2,2,4-trimethyl-1,3-pentane Alcohol, 3-methyl-1,5-pentanediol, dichloro neopentyl glycol, dibromo neopentyl glycol, neopentyl glycol hydroxypivalate, cyclohexane dimethylol, 1,4 - cyclohexanediol, spirodiol, tricyclodecane dimethylol, hydrogenated bisphenol A, ethylene oxide addition bisphenol A, propylene oxide addition bisphenol A, trimethylolethane, Trimethylolpropane, glycerol, 3-methylpentane-1,3,5-triol, pentaerythritol, two Pentaerythritol, tripentaerythritol, glucose, and the like.

As the carboxylic acid-containing compound, various known carboxylic acids, their acid anhydrides, ester compounds of carboxylic acid compounds and lower alkyl alcohols, and the like can be used. Specific examples of the carboxylic acid-containing compound include maleic acid, fumaric acid, itaconic acid, citraconic acid, tetrahydrophthalic acid, chlorobridge acid, nadic acid, and chloric acid ( Acid), dimer acid, adipic acid, succinic acid, alkenyl succinic acid, azelaic acid, sebacic acid, 2,2,4-trimethyladipate, 1,4-cyclohexanedicarboxylic acid , terephthalic acid, 2-sulfonic acid monosodium terephthalate, 2-sulfonic acid monopotassium terephthalate, isophthalic acid, 5-sulfonic acid isophthalic acid monosodium, 5-sulfonic acid isophthalic acid Di-lower alkyl 5-sulfonate isophthalate mono-lower alkyl ester such as monopotassium dicarboxylate or dimethyl or diethyl ester, or phthalic acid, 4-sulfonic acid phthalic acid, 1,10-decamethylenedicarboxylic acid, hexadiene diacid, oxalic acid, malonic acid, glutaric acid, trimellitic acid, hexahydrophthalic acid, tetrabromophthalic acid, methyl ring A hexenyltricarboxylic acid, or pyromellitic acid, or an acid anhydride thereof, or an alcohol ester compound formed by methanol, ethanol or the like.

The cyclic ester compound may, for example, be γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε-caprolactone, substituted ε-caprolactone, or D-gluconic acid-1,4. - lactone, 1,10-phenanthrenecarboxylate (1,10- ), lactones such as 4-pentene-5-lactone and 12-dodelactone. The substituted ε-caprolactone is various ε-monoalkylcaprolactones having an alkyl group having from 1 to 12 carbon atoms, and for example, ε-methylcaprolactone, ε-ethylcaprolactone, ε can be used. - Alkyl caprolactone, ε-dodecyl caprolactone, etc., from a 1-substituted alkyl lactone to an alkyl substituted lactone of 2 to 3.

As the hydroxyl group-containing acrylate compound, a known one can be used, and specific examples thereof include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxyl. Butyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol single (A) Acrylate, pentaerythritol tris(methyl)propene a carboxylic acid ester or a glycidyl methacrylate-(meth)acrylic acid adduct, a hydroxy-containing (meth) acrylate compound, and a ring-opening reaction product of ε-caprolactone and a modified product thereof .

Among the polyester resin-based polyols, polycaprolactone-based polyols are preferable from the viewpoint of adhesion to the base material layer 2, and polyester resin-based polyols having a molecular weight of from 300 to 5,000 are preferable. The alcohol is preferably a polyester resin-based polyol having a functional group number of 3 or more functional groups.

For the purpose of improving the processability of the ultraviolet curable resin composition, that is, the suitability for coating, printing, and the like, and various physical properties, the acrylate-based reactive diluent of (b) is specifically used, and specific examples thereof include: 1) methoxyethylene glycol (meth) acrylate, methoxy polyethylene glycol (meth) acrylate, β-(meth) propylene methoxyethyl hydrogen phthalate, β -(Meth)propylene methoxyethyl hydrosuccinate, nonylphenoxyethyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, phenoxy (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, methoxy polyethylene glycol (meth) acrylate, β-(meth) propylene methoxy propyl hydrogen Phthalate, β-(meth)acryloxypropyl hydrosuccinate, butoxy polyethylene glycol (meth) acrylate, alkyl (meth) acrylate, cyclohexyl (A) Acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2- Hydroxypropyl (meth) acrylate, 2- Hydroxy-3-phenoxypropyl (meth) acrylate, 2-(methyl) propylene oxiranyl ethyl 2-hydroxyethyl phthalate, 3-propenyl methoxy glycerol ( Methyl) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-1-(methyl) propylene methoxy-3-(methyl) propylene oxypropane, polypropylene glycol single (A) Acrylate, polyethylene glycol mono (meth) acrylate, poly ε-caprolactone mono (meth) acrylate, dialkylaminoethyl (meth) acrylate, glycidyl (methyl) Acrylate, mono[2-(methyl)acryloxyethyl]acid phosphate, trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (methyl) ) Acrylate, 2,2,3,4,4,4-hexafluorobutyl (meth) acrylate, perfluorooctylethyl (meth) acrylate, dicyclopentenyloxyalkyl (A Acrylate, dicyclopentenyl (meth) acrylate, tricyclodecenyl (meth) acrylate, tricyclodecenyloxyethyl (meth) acrylate, isobornyloxy a monofunctional polymerizable diluent such as ethyl (meth) acrylate; (2) 2,2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate Methyl) acrylate, ethylene glycol di(meth) acrylate, polyethylene glycol di(meth) acrylate, propylene glycol di(meth) acrylate, polypropylene glycol di(meth) acrylate, 1, 4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerol di(meth)acrylate, neopentyl glycol di(meth)acrylate a di(meth)acrylate of hydroxypivalic acid neopentyl glycol, a di(meth)acrylate of an ethylene oxide adduct of bisphenol A, and a propylene oxide adduct of bisphenol A. (meth) acrylate, di(meth) acrylate of 2,2'-bis(hydroxypropoxyphenyl)propane, 2,2'-di(hydroxyl) Di(meth) acrylate of ethoxylated phenyl) propane, di(meth) acrylate of tricyclodecane dimethylol, 2,2'-bis(glycidyloxyphenyl)propane a bifunctional polymeric diluent such as a (meth)acrylic acid addition; (3) trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate Dipentaerythritol hexa(meth) acrylate, tetramethylol methane tri(meth) acrylate, tetramethylol methane tetra(meth) acrylate, tris(2-hydroxyethyl) isocyanurate Tris(meth)acrylate, tris(meth)acrylate of tris(hydroxypropyl)isocyanurate,tris(meth)acrylate of trimellitic acid, triallyl trimellitic acid A polyfunctional polymerizable diluent such as an ester or triallyl isocyanurate.

Among the acrylate-based reactive diluents, an acrylate compound having a tetrahydroindenyl group which is excellent in curability, adhesion to the surface of the base material layer 2, and the like is particularly preferable. Specifically, examples of such an acrylate compound include tetrahydrofurfuryl acrylate, lactone-modified tetrahydrofurfuryl acrylate, dimer acrylic acid-modified tetrahydrofurfuryl acrylate, and dimer acrylic acid modification. Sex lactone modified tetrahydrofurfuryl acrylate Wait.

Specific examples of the photoinitiator of (c) include 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexylphenyl ketone, and 2,2-dimethoxy-2-phenylbenzene. Ethyl ketone, 2,2-diethoxy-2-phenylacetophenone, alkoxyacetophenone, benzophenone, benzophenone derivative, etc., one of them may be used or a combination thereof may be used. Two or more of them are used. In addition, the amount of the photoinitiator to be added is preferably 0.2 part or more and 30 parts or less, and particularly preferably 2 parts or more and 20 parts or less, per 100 parts of the acrylate resin component.

Further, the polymer composition for forming the binder 7 may be appropriately blended with, for example, a lubricant, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, and the like in addition to the base polymer described above. A leveling agent, an antistatic agent, an antioxidant, a viscosity modifier, and the like.

Further, the average thickness H of the flat portion of the adhesion preventing layer 6 is preferably 0.2 times or more, more preferably 0.3 times or more, and further preferably 0.4 times or more of the average particle diameter of the beads 8. Further, the average thickness H of the flat portion is preferably 1 time or less, more preferably 0.8 times or less, and still more preferably 0.6 times or less the average particle diameter of the beads 8. If the average thickness H of the flat portion of the adhesion preventing layer 6 is smaller than the lower limit, the effect of fixing the beads 8 is lowered. On the other hand, if the average thickness H of the flat portion exceeds the upper limit, there is a problem that it is difficult to form the ridge portion by the beads 8 and the adhesion function is prevented from being lowered.

The average coating film thickness D of the adhesive 7 as the top of the back side of the bead 8 is preferably 0.1 μm or more, more preferably 0.3 μm or more, and still more preferably 0.5 μm or more. Further, the average coating film thickness D of the adhesive 7 as the top portion on the back side of the bead 8 is preferably 3 μm or less, more preferably 2.5 μm or less, and still more preferably 2.0 μm or less. By setting the average coating film thickness D of the adhesive 7 at the top of the back side of the bead 8 within the above range, the thinning of the light-diffusing sheet can be satisfied, and the optical member with the back side can be appropriately prevented. Friction causes the cover film of the adhesive 7 to peel off, and it is possible to improve the prevention of the peeling sheet against the back side The optical component causes damage.

The pencil hardness of the back surface of the binder 7 is preferably H or more and 2H or less. When the pencil hardness is within the above range, since the adhesive 7 in contact with the optical member on the back side has a suitable hardness, when the cover film outside the bead 8 of the adhesive 7 comes into contact with the optical member on the back side, The adhesive 7 can be appropriately suppressed from causing damage to the optical member on the back side.

Method for manufacturing light diffusing sheet

The method for producing the light-diffusing sheet 1 includes an adhesion preventing layer forming step of forming an adhesion preventing layer 6 on the back side of the transparent base material layer 2, and a light diffusion layer forming step of forming a surface side of the base material layer 2 Light diffusion layer 3.

The method for producing the light-diffusing sheet 1 further includes a sheet forming step of forming a sheet constituting the base material layer 2 before the adhesion preventing layer forming step and the light-diffusing layer forming step. The substrate sheet forming step is not particularly limited, and a method of extruding a molten thermoplastic resin from a T-die and then extending the extruded body in the longitudinal direction of the layer and the width direction of the layer may be employed. Thus, a substrate sheet was formed. As a well-known extrusion molding method using a T die, a polishing roll method and a cooling roll method are exemplified. Further, the base material sheet may be subjected to drawing processing, and as a well-known film stretching method, a tubular film biaxial stretching method, a flat film biaxial stretching method, or the like may be mentioned.

The adhesion preventing layer forming step includes a step (a) of preparing a coating liquid for an adhesion preventing layer, a step (b) of applying the coating liquid on the substrate layer 2, and a step of curing the coating liquid after coating. (c).

The preparation step (a) is a step of preparing a coating liquid containing the beads 8 and a binder forming material containing the ultraviolet curable resin as a main component. Here, as the material for forming the beads 8 and the binder, the same material as that described in the structure of the light diffusion sheet 1 can be used. The coating liquid is prepared by mixing the beads 8 in a solvent containing a binder forming material.

The coating step (b) is to apply the coating liquid prepared as described above to the base. The step of the back surface of the material layer 2. The method of applying the coating liquid is not particularly limited, and a known method can be employed. For example, a slit coating method, a roll coating method, a knife coating method, an air knife coating method, a flow coating method, a gravure coating method, or a spray coating method can be used. Or stick coating method.

The curing step (c) is a step of irradiating the coating liquid applied to the back surface of the base material layer 2 with ultraviolet rays to cure the adhesive 7 to form the adhesion preventing layer 6. When the ultraviolet curable resin is used as the binder 7, in the curing step (c), the binder 7 is cured by irradiation of ultraviolet rays. As a method of irradiating the ultraviolet rays, a well-known method can be employed, and for example, a method of using a low-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh pressure mercury lamp, a metal halide lamp, an ultraviolet laser or the like as a light source can be employed.

Backlight unit

The light-diffusing sheet 1 having the above-described configuration is used in a conventional backlight unit for a liquid crystal display device (for example, FIG. 3(a)). Specifically, the backlight unit for a liquid crystal display device includes a light guide plate, a light source that irradiates light to an end surface of the light guide plate, and the light diffusion sheet 1 that is disposed to overlap the surface of the light guide plate, and is disposed to overlap the light diffusion sheet 1 Optical sheets such as cymbals and lenticular sheets on the surface side.

advantage

Since the adhesion preventing layer 6 can be prevented from adhering to the light guide plate, the light diffusion sheet 1 is less likely to cause unevenness in brightness. Further, the adhesion preventing layer 6 contains the beads 8 and the binder 7 containing the ultraviolet curable resin as a main component, and the beads 8 are softer than the conventional acrylic beads, so that it is possible to appropriately prevent damage to the light guide plate, and thus it is possible to appropriately Prevent uneven brightness due to damage of the light guide plate.

In particular, since the polyamide 8 resin beads 8 having a relatively soft texture are used, and the binder 7 is a binder made of a relatively hard ultraviolet curable resin, the hard binder film 7 covers the soft beads 8 and As a result, even if an external force is applied to the convex portion of the bead 8, it is possible to suppress only the distal end portion (the top portion on the back side) from being crushed as in the related art, and the convex portion is deformed so as to be flat as a whole, that is, the cross section becomes an ellipse. shape The way the deformation. Therefore, even if an external force acts on the light-diffusing sheet 1, it is difficult to increase the contact area, and it is difficult to increase the frictional force, and the effect of preventing damage to other optical members on the back side can be remarkably improved.

Further, by using an acrylic resin as a main component of the binder 7, the adhesion to the beads 8 is excellent, the beads 8 are hardly detached from the adhesive 7, and the cover film 7a of the adhesive 7 is also difficult to peel off from the beads 8.

Other embodiments

The optical sheet for a liquid crystal display device of the present invention is not limited to the above embodiment, and the design can be appropriately changed within the scope of the present invention. In the above-described embodiment, the so-called lower light diffusion sheet disposed on the surface of the light guide plate has been described. However, the optical sheet for a liquid crystal display device of the present invention may be disposed as a tantalum sheet on the surface side of the tantalum sheet. The so-called upper light diffusion sheet.

Example

The invention will be specifically described below by way of examples, but the invention is not limited to the following examples.

Example 1

A coating liquid obtained by mixing 0.118 g of nylon beads, 15 g of a UV curable resin, 0.481 g of an antistatic agent, and 11 g of a solvent was used to form an adhesion preventing layer, and a light-diffusing sheet was produced. The average particle diameter of the beads was 5 μm. The coating amount of the coating liquid was 2 g/m ² .

The dynamic friction coefficient of the back surface (adhesion preventing layer) of the light-diffusing sheet of Example 1 was measured, and as a result, it was 0.272.

Comparative example 1

As the UV curable resin, the antistatic agent, and the solvent, the same materials as in Example 1 were used, and a coating liquid obtained by mixing them with 0.118 g of polydisperse polyurethane beads was used to form an adhesion preventing layer. The average particle diameter of the polyurethane beads was 7 μm.

The dynamic friction coefficient of the back surface (adhesion preventing layer) of the light-diffusing sheet of Comparative Example 1 was measured, and as a result, it was 0.415.

Since the light diffusion sheet of Comparative Example 1 has a large dynamic friction coefficient, light diffusion When the sheet slides on the surface of the light guide plate, there is a high possibility that the adhesive cover film on the surface of the bead is peeled off. In contrast, the light diffusion sheet of the first embodiment has a small dynamic friction coefficient, and the cover film peeling of the adhesive occurs. The possibility of adverse situations is small.

Industrial applicability

As described above, the optical sheet for a liquid crystal display device, the backlight unit for a liquid crystal display device, and the method for producing an optical sheet for a liquid crystal display device are useful as constituent members of the liquid crystal display device, and particularly can be preferably used. In a transmissive liquid crystal display device.

2‧‧‧Substrate layer

6‧‧‧Adhesion prevention layer

7‧‧‧Binder

8‧‧‧ beads

7A‧‧‧ Cover film

D‧‧‧ hardness

H‧‧‧average thickness

Claims (4)

An optical sheet for a liquid crystal display device comprising: a transparent substrate layer; and an adhesion preventing layer laminated on a back side of the substrate layer, comprising beads and a binder covering the beads; the main component of the beads is a polyamide resin; the binder is composed of a resin composition comprising an ultraviolet curable resin as a host polymer; the beads having an average particle diameter of 2 μm or more and 20 μm or less; and the adhesion preventing layer The thickness is 0.3 times or more and 1 time or less of the average particle diameter of the beads; and the average coating film thickness of the binder at the top of the back side of the beads is 0.1 μm or more and 3 μm or less. The optical sheet for a liquid crystal display device according to claim 1, wherein the bead has a durometer D hardness of 30 or more and 70 or less. The optical sheet for a liquid crystal display device according to claim 1, wherein the pencil hardness of the back surface of the adhesive is H or more and 2H or less. A backlight unit for a liquid crystal display device, comprising the optical sheet for a liquid crystal display device according to any one of claims 1 to 3.