JP4924861B2 - Light diffusion film - Google Patents

Description

  The present invention relates to a light diffusing film, and more particularly to a light diffusing film used as a component of a backlight unit of a liquid crystal display device.

An example of a general configuration of a liquid crystal display device conventionally provided in a computer, a mobile phone, a digital camera or the like is shown in FIG. The light diffusion film 7 is normally used as one of the components of the backlight unit 2. In general, the light diffusing film 7 is disposed between the light guide plate 5 and the prism sheet 8, and its function is to deflect the outgoing light from the light guide plate 5 toward the prism sheet 8, and to be retroreflected from the prism sheet 8. Is to diffuse the light for reuse.

  Moreover, an example of the cross-sectional structure of a general light-diffusion film is shown in FIG. Generally, the light diffusion film 7 includes a transparent sheet-like base material 10, a light diffusion layer 11 formed on one surface of the base material 10, and a back layer for preventing sticking on the other surface of the base material 10. 12 is provided. The light diffusion layer 11 contains a light diffusion material 13 and a resin binder 14.

  A conventional light diffusion film has a transparent acrylic resin bead formed of a transparent synthetic resin layer in which transparent acrylic resin beads are mixed as a light diffusion material on the surface of a transparent substrate. However, there are some which are composed of beads embedded in the synthetic resin layer and beads partially protruding from the synthetic resin layer (see, for example, Patent Document 1). Moreover, a light diffusing layer is provided on a transparent support, and the light diffusing layer includes a transparent resin and polystyrene spherical particles as a light diffusing material (for example, see Patent Document 2).

  However, the conventional light diffusing film has not been studied as much as the optical characteristics as to the improvement of the surface hardness, and the scratch resistance is insufficient. In the process of cutting out into a shape according to the design, there is a problem that the light diffusion surface is damaged or the projected light diffusion material falls off and the light diffusion surface is easily stained. When a light diffusing film that is scratched or dirty is attached to the backlight unit, it causes defects in the liquid crystal display screen and degrades the quality. Therefore, the processing process includes defects such as scratches and dirt. The light diffusion film cut-out product is excluded and discarded by appearance inspection. Accordingly, insufficient scratch resistance has caused a reduction in the yield of the light diffusing film and reduced productivity.

In recent years, notebook and book computers and information terminal devices for mobile use have become widespread, and liquid crystal display devices installed in these devices have been required to have specifications that can withstand vibrations caused by carrying and moving. . In other words, the light diffusing film, which is a component of the backlight unit of the liquid crystal display device, receives a lot of vibration as it is carried and moved, so that it is scratched by other components and the light diffusing material falls off. As a result, the quality of the liquid crystal display screen may be impaired.
Japanese Utility Model Publication No. 4-042936 Japanese Utility Model Publication No. 4-000810

  An object of the present invention is to provide a light diffusing film that has sufficient light diffusibility, is less likely to be damaged in the processing step, and is less likely to drop off the light diffusing material.

  As a result of extensive research on the combination of a light diffusing material and a resin binder, the present inventor used acrylic urethane resin fine particles as a light diffusing material in the light diffusing layer, and an acrylic monomer having a hydroxyl group as a resin binder. It has been found that by using an acrylic resin contained in the polymerization component crosslinked with polyisocyanate, the scratch resistance of the light diffusion surface of the light diffusion film can be improved, and the present invention has been achieved.

  That is, the present invention is a light diffusing film having a light diffusing layer containing a light diffusing material and a resin binder on at least one surface of a transparent sheet-like substrate, wherein the light diffusing material contains acryl urethane resin fine particles. The resin binder is a light diffusing film obtained by crosslinking an acrylic resin containing an acrylic monomer having a hydroxyl group as a copolymerization component with polyisocyanate.

Since the light diffusing film of the present invention contains an acrylic urethane resin as a light diffusing material and uses an acrylic resin crosslinked with a polyisocyanate having a high surface hardness as a binder resin, the diffusing surface is hardly damaged. Moreover, since the light diffusing material of acrylic urethane resin and the binder resin are firmly bonded via the polyisocyanate, the light diffusing material can be prevented from falling off. Therefore, the yield of the processing step using the light diffusion film can be improved, and the durability can be improved even with respect to vibrations associated with carrying and moving of the device including the liquid crystal display.
On the other hand, acrylic urethane resin particles have almost the same optical characteristics as acrylic resin particles, and therefore can maintain light diffusion characteristics that are not different from conventional ones.

  First, the structure of the light diffusion film of the present invention will be described. The light diffusion film of the present invention comprises at least a transparent sheet-like substrate and a light diffusion layer formed on at least one surface of the substrate. Further, if necessary, a back layer having one or more functions of a sticking prevention function, an antistatic function, a scratch prevention function, a function as a second light diffusion layer, and the like is provided on the other surface of the base material. It may be done.

The material for the transparent sheet-like substrate in the present invention is not particularly limited, but a polyethylene terephthalate (PET) film is preferably used from the surface smoothness and mechanical strength. The thickness of the substrate is preferably 10 to 300 μm. When the thickness is less than 10 μm, not only handling becomes difficult, but also curability due to heat shrinkage occurs and workability is remarkably lowered. When it is thicker than 300 μm, the visible light transmittance of the substrate itself is lowered, and the front luminance of the backlight unit is lowered, which is not preferable.
At least one of the surfaces of the transparent sheet-like base material is subjected to an easy adhesion treatment such as applying an easy adhesion treatment layer or applying a corona treatment in order to improve the adhesion to the light diffusion layer. More preferable.

The light diffusion layer in the present invention contains at least a light diffusion material and a resin binder.
About the acrylic urethane resin particle used for the light-diffusion material of the light-diffusion film of this invention, it can be especially used without a restriction | limiting. The shape of the acrylic urethane resin fine particles is preferably a true sphere. The resin fine particles preferably have a volume average particle diameter in the range of 1 to 30 μm. When the average particle diameter is smaller than 1 μm, light that passes through the light diffusion layer is transmitted without being diffused, and the light diffusion effect tends to be reduced. When the average particle diameter exceeds 30 μm, the resin fine particles are likely to fall off, which is likely to cause a defect, and the appearance is likely to lack uniformity with a foreign object feeling.

  Since the acrylic urethane resin fine particles have a high-density cross-linked structure, they are particularly excellent in heat resistance and solvent resistance, and also have high transparency, which is a characteristic of acrylic resins. In the case where the acrylic urethane resin fine particles are used as a light diffusing material, the inventors maintain a haze and transmittance necessary for a light diffusing film and are generally used as a conventional light diffusing material. As compared with resin fine particles such as methacrylate (PMMA), polystyrene, silicone, etc., the inventors have found that the light diffusion layer is less likely to be scratched.

For this reason, the inventors have compared the resin particles such as polymethyl methacrylate, polystyrene, and silicone that are generally used as conventional light diffusing materials while the acrylic urethane resin particles have a high-density crosslinked structure. The light diffusion layer in which the acrylic urethane resin fine particles are dispersed in the resin binder is easily deformed due to the plastic deformation, and the inside is easy to deform due to the plasticity of the acrylic urethane resin fine particles. The structure was protected by a hard resin binder that was three-dimensionally cross-linked.
Further, when acrylic urethane resin fine particles having hydroxyl groups on the surface are used, in the crosslinking reaction of the resin binder, the hydroxyl groups on the surface of the acrylic urethane resin fine particles undergo a crosslinking reaction with the excess polyisocyanate in the resin binder. Since a crosslinked structure is formed also with the resin binder, the crosslinking density as the light diffusion layer is further increased, which is preferable.
For this reason, the acrylic urethane resin particles used as the light diffusing material in the light diffusing film of the present invention are produced from an acrylic monomer having a hydroxyl group, an acrylic monomer having no hydroxyl group, and a raw material compound group having an isocyanate compound. It is preferable to use these raw material compounds, or oligomers or prepolymers formed from these raw material compounds, and those produced using known production processes such as suspension polymerization and emulsion polymerization. It is preferable.

  In order to achieve both transparency and mechanical strength as the chemical composition of the light diffusing material of the present invention, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, normal butyl methacrylate, normal butyl acrylate, isobutyl methacrylate, isobutyl acrylate, etc. One type selected, or two or more types appropriately mixed, the acrylic monomer containing no hydroxyl group is 30 to 85% by mass; one type selected from hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, etc., Or it is preferable that 2 or more types of hydroxyl-containing acrylic monomers are 5-30 mass%, and a modified polyisocyanate compound is 5-40 mass%. As the modified polyisocyanate compound, since there is no weak point that it is easily yellowed by ultraviolet rays, an isocyanurate type trimerized based on hexamethylene diisocyanate, an adduct obtained by adding a polyhydric alcohol to hexamethylene diisocyanate, and the like can be used. preferable.

  Further, a part of the light diffusing material may contain other organic resin fine particles, inorganic fine particles, or inorganic-organic hybrid material fine particles as long as the advantages of the acrylic urethane resin fine particles are not impaired. For example, containing one kind or two or more kinds of fine particles mentioned from polymethyl methacrylate, polystyrene, silicone, silica, clay, talc, titanium oxide, zinc oxide, etc., as long as they do not inhibit the properties of the light diffusion film. Can be made.

  The organic resin fine particles to be contained as a part of the light diffusing material are preferably silicone resin fine particles, more preferably true spherical silicone resin fine particles having an average particle diameter of 1 to 5 μm. The gaps between the coarse particles that are likely to be projected and formed on the surface are filled, the surface shape of the light diffusion layer is smoothed, and the appearance can be improved.

  The resin binder of the light diffusing film of the present invention is obtained by mixing acrylic resin and polyisocyanate and crosslinking after forming the light diffusing layer.

  The acrylic resin essentially contains at least one acrylic monomer having a hydroxyl group selected from hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and the like, and includes methyl methacrylate, butyl methacrylate, lauryl methacrylate, methyl acrylate, ethyl One kind selected from acrylic monomers such as acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-methylol acrylamide, glycidyl acrylate, glycidyl methacrylate, and styrene, acrylonitrile, Or a copolymer of two or more monomer components That.

  The hydroxyl value of the acrylic resin is preferably 25 to 500. When the hydroxyl value of the solid content is less than 25, the crosslink density is too low, so that the hardness and solvent resistance of the light diffusion layer are likely to decrease. When the hydroxyl value is greater than 500, the crosslink density is too high, so that it becomes brittle, the light diffusing layer is easily cracked and chipped, and the workability during processing tends to be lowered.

  Here, the hydroxyl value generally refers to the number of milligrams of potassium hydroxide required to neutralize acetic acid generated when 1 g of a sample is acetylated. When the acrylic resin as a sample is a varnish (solution), the hydroxyl value is a numerical value converted to a hydroxyl value per 1 g of the solid content of the sample.

  Polyisocyanates include those based on aliphatic isocyanates such as HDI and XDI that can crosslink with the hydroxyl groups of acrylic resins, and those based on aromatic isocyanates such as TDI and MDI. However, polyisocyanates based on aliphatic isocyanates such as HDI (hexamethylene diisocyanate) and XDI (xylene diisocyanate) are preferred because they do not have a weak point that they are easily yellowed by ultraviolet rays. Examples of the modification types in which these isocyanates are polyisocyanates include adduct types obtained by adding polyhydric alcohols to aliphatic isocyanates such as HDI and XDI, isocyanurate types obtained by trimerization based on HDI, and biurets based on HDI. Examples include molds. Among these, an adduct type polyisocyanate obtained by adding a polyhydric alcohol to HDI is particularly preferable because it can easily obtain extremely advantageous mechanical properties in the processing step of the light diffusion film.

The effective NCO content of the polyisocyanate is not particularly limited, but those having an effective NCO content in the solid content of 5 to 40% are usually used.
Here, the effective NCO content is generally the amount of NCO contained in a commercially available polyisocyanate product expressed as a percentage by weight (%). The effective NCO content in the solid content is a numerical value converted to the effective NCO content per solid content of the sample when the polyisocyanate as a sample is a varnish (solution).

The mixing ratio of the acrylic resin and polyisocyanate is determined using the equivalent ratio of isocyanate to hydroxyl group.
The equivalent ratio of the isocyanate in the polyisocyanate to the hydroxyl group in the acrylic resin is preferably 0.7 to 3.0. If the equivalent ratio is less than 0.7, the crosslinking density tends to be low, and the light diffusion layer tends to have insufficient scratch resistance and solvent resistance. When the equivalent ratio is larger than 3.0, crosslinking between polyisocyanate molecules proceeds, and the light diffusion layer tends to become brittle.

  Here, the equivalent ratio of isocyanate to hydroxyl group (NCO / OH) is generally determined by the following formula 1.

In the above formula, Iw, In, Aw, and Ao are as follows.
Iw: Mass part in terms of solid content of polyisocyanate In: Effective NCO content in solid content in polyisocyanate Aw: Mass part in terms of solid content of acrylic resin Ao: Hydroxyl value of solid content in acrylic resin

  In the light diffusion film of the present invention, the blending amount of the acrylic urethane resin fine particles relative to the resin binder is preferably 5 to 400 parts by mass with respect to 100 parts by mass of the solid content of the resin binder, although it varies depending on the use of the light diffusion film. . 5 to 200 parts by mass is preferable for small display applications such as mobile phones, and 100 to 400 parts by mass is preferable for medium-sized or more displays such as monitors. When there are few resin fine particles and it is less than 5 mass parts with respect to 100 mass parts of resin binders, the light-diffusion effect tends to become small. On the other hand, when it exceeds 400 parts by mass, the total light transmittance tends to be low, and in any case, the practicality as a light diffusion layer tends to decrease.

  In addition to the above materials, for example, a dispersant, a plasticizer, an antistatic agent, a deterioration preventing agent, and the like may be blended in the light diffusion layer of the light diffusion film of the present invention.

In the light diffusing film of the present invention, the back layer may be omitted, but in many cases, it prevents friction scratches on the surface of the light diffusing film opposite to the light diffusing layer and prevents sticking with the light guide plate. For example, a back layer is provided.
The back layer of the light diffusion film of the present invention contains at least a resin binder. If necessary, a lubricant for preventing sticking, an antistatic agent for suppressing electrostatic charge on the light diffusing film, an ultraviolet absorber, an ultraviolet shielding agent, a light diffusing material, and the like can be contained.
The resin binder contained in the back layer of the light diffusing film of the present invention is not particularly limited as long as the transparency of the light diffusing film is not impaired, but a thermoplastic methacrylic resin, a thermoplastic methacryl-styrene copolymer resin, or It is preferable if the acrylic resin is crosslinked with polyisocyanate.

  As the lubricant, antistatic agent, ultraviolet absorber, ultraviolet shielding agent and the like contained in the back layer, ordinary materials can be used as long as they do not impair the transparency and light diffusibility of the light diffusion film of the present invention.

  When the back layer has a function as the second light diffusion layer, the light diffusion material to be used is not particularly limited, and conventionally used light diffusion materials such as methacrylic resin, polystyrene resin, and silicone resin can be used. .

Next, an example of the manufacturing method of the light-diffusion film in this invention is demonstrated.
In order to produce the light diffusing film of the present invention, a light diffusing layer coating is applied to at least one surface of a transparent sheet-like substrate to form a light diffusing layer. The back layer is formed by applying a back layer coating.

  First, a coating material for a light diffusion layer is prepared by mixing resin fine particles, a resin binder, a solvent, and other additives blended as necessary.

  Furthermore, if necessary, the coating material for the back layer is prepared by mixing necessary raw materials out of a resin binder, a solvent, a lubricant, an antistatic agent, an ultraviolet absorber, an ultraviolet shielding agent, a light diffusing material, and the like.

A light diffusion layer coating is applied to at least one surface of the substrate and dried to form a light diffusion layer. A general coating method can be used as a coating method. For example, coating methods such as blade, knife, cast, dipping, impregnation machine, screen, spin, reverse roll, air doctor, gravure, spray, curtain, extrusion, fountain, kiss, rod, squeeze, forward rotation roll, kiss roll, etc. Available.
A general drying method can be used to dry the coating film. For example, drying methods such as hot air, infrared rays, microwaves, induction heating, ultraviolet ray curing, and electron beam curing can be used.
The thickness of the light diffusion layer is preferably 2 to 25 μm after the coating film is dried. Here, the thickness of the light diffusing layer does not measure the height from the top of the protruding light diffusing material, but measures the height from the sheet-like base material on the surface of the resin binder holding the light diffusing material. Shall.
After drying, if necessary, heat curing is performed at a predetermined temperature and time.

  A back layer is formed as necessary before and after the light diffusion layer forming step. A back layer coating material is applied to the opposite surface of the light diffusion layer and dried. For the coating and drying methods, the same method as that for the light diffusion layer can be used.

The light diffusion film of the present invention produced as described above is particularly useful for use as a light diffusion film constituting a backlight unit for a liquid crystal display device, but is not limited to this application. The present invention can be applied to various uses that require light diffusion light.

Hereinafter, the present invention will be described using examples.

Example 1
<Preparation process of coating material a for light diffusion layer>
Toluene 278 parts by mass Acrylic urethane resin particles “BC-79” 137 parts by mass [volume average particle diameter of about 6 μm, manufactured by Gifu Shellac Manufacturing Co., Ltd.]
100 parts by mass of acrylic resin solution “Acridic A-801-P” [50% solid content, hydroxyl value 100 of solid content, manufactured by Dainippon Ink & Chemicals, Inc.]
55 parts by mass of polyisocyanate solution “Coronate HL” (solid content 75%, HDI, effective NCO content 17% in solid content, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a light diffusion layer coating material a. At this time, the equivalent ratio of isocyanate to hydroxyl group was 1.9, and the blending amount of the light diffusing material (acrylic urethane resin particles) with respect to 100 parts by mass of the solid content of the resin binder (acrylic resin + polyisocyanate) was 150 parts by mass.

<Preparation process of paint b for back layer>
Toluene 120 parts by mass Acrylic resin “Dianal BR-80” 10 parts by mass [100% solid content, no hydroxyl value, manufactured by Mitsubishi Rayon Co., Ltd.]
0.5 parts by mass of an antistatic agent “Katiogen ES-L-9” [cationic surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.]
Lubricant “Chemisnow MR-10HG” 0.2 part by mass (acrylic resin particles, volume average particle diameter 10 μm, manufactured by Soken Chemical Co., Ltd.)
Among the above materials, the total amount of acrylic resin and 40 parts by mass of toluene are sufficiently dissolved by stirring with a dispersion stirrer, and then the remaining materials are added and stirred and mixed with a dispersion stirrer to obtain a paint b for the back layer. It was.

<Coating / drying / curing process to substrate>
As a substrate, a polyethylene terephthalate (PET) film having a thickness of 100 μm is used, and the light diffusion layer coating material a is applied to one surface of the film so as to have a dry film thickness of 16 μm, followed by drying with hot air to form a light diffusion layer. A dried coating film was obtained. On the other surface, the back layer coating material b was applied so as to have a dry film thickness of 2 μm and dried with hot air to obtain a dry coating film for the back layer. After the application process of the light diffusion layer coating material a and the back coating material b, the light diffusion film was prepared by storing in a constant temperature room at 40 ° C. for 48 hours in order to accelerate the curing reaction.

(Example 2)
<Preparation process of coating material c for light diffusion layer>
Toluene 393 parts by mass Acrylic urethane resin particles “BC-79” 181 parts by mass [volume average particle diameter of about 6 μm, manufactured by Gifu Shellac Manufacturing Co., Ltd.]
100 parts by mass of acrylic resin solution “Dianar LR-1532” [solid content 60%, solid content hydroxyl value 83, manufactured by Mitsubishi Rayon Co., Ltd.]
81 parts by mass of polyisocyanate solution “Coronate HL” (solid content: 75%, HDI, effective NCO content in solid content: 17%, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a light diffusion layer coating material c. At this time, the equivalent ratio of isocyanate to hydroxyl group was 2.8, and the blending amount of the light diffusing material (acrylic urethane resin particles) with respect to 100 parts by mass of the solid content of the resin binder (acrylic resin + polyisocyanate) was 150 parts by mass.

  Hereinafter, a dry coating film was formed on the substrate in the same manner as in Example 1 except that the light diffusion layer coating c was used instead of the light diffusion layer coating a in Example 1, and the light diffusion was performed. A film was prepared.

(Example 3)
<Preparation process of coating material g for light diffusion layer>
Toluene 175 parts by mass Acrylic urethane resin particles “BC-79” 91 parts by mass [volume average particle diameter of about 6 μm, manufactured by Gifu Shellac Manufacturing Co., Ltd.]
100 parts by mass of acrylic resin solution “Acridic A-801-P” [50% solid content, hydroxyl value 100 of solid content, manufactured by Dainippon Ink & Chemicals, Inc.]
Polyisocyanate solution “Coronate HL” 14 parts by mass (solid content: 75%, HDI, effective NCO content in solid content: 17%, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a light diffusion layer coating material g. At this time, the equivalent ratio of isocyanate to hydroxyl group was 0.5, and the blending amount of the light diffusing material (acrylic urethane resin particles) with respect to 100 parts by mass of the solid content of the resin binder (acrylic resin + polyisocyanate) was 150 parts by mass.

  Hereinafter, a dry coating film was formed on the substrate in the same manner as in Example 1 except that the light diffusion layer coating g was used instead of the light diffusion layer coating a in Example 1, and light diffusion was performed. A film was prepared.

(Comparative Example 1)
<Preparation process of coating material d for light diffusion layer>
Toluene 278 parts by mass Acrylic resin particles “Chemisnow MR-7HG” 137 parts by mass [volume average particle diameter of about 6 μm, manufactured by Soken Chemical Co., Ltd.]
100 parts by mass of acrylic resin solution “Acridic A-801-P” [50% solid content, hydroxyl value 100 of solid content, manufactured by Dainippon Ink & Chemicals, Inc.]
55 parts by mass of polyisocyanate solution “Coronate HL” (solid content 75%, HDI, effective NCO content 17% in solid content, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a d-coating for the light diffusion layer. At this time, the equivalent ratio of isocyanate to hydroxyl group was 1.9, and the blending amount of the light diffusing material (acrylic resin particles) with respect to 100 parts by mass of the solid content of the resin binder (acrylic resin + polyisocyanate) was 150 parts by mass.

Hereinafter, a dry coating film was formed on the substrate in the same manner as in Example 1 except that the light diffusion layer coating material d was used instead of the light diffusion layer coating material a in Example 1, and light diffusion was performed. A film was prepared.

(Comparative Example 2)
<Preparation process of coating material e for light diffusion layer>
Toluene 278 parts by mass Silicone resin particles “KMP-701” 137 parts by mass [volume average particle diameter of about 3.5 μm, manufactured by Shin-Etsu Silicone Co., Ltd.]
100 parts by mass of acrylic resin solution “Acridic A-801-P” [50% solid content, hydroxyl value 100 of solid content, manufactured by Dainippon Ink & Chemicals, Inc.]
55 parts by mass of polyisocyanate solution “Coronate HL” (solid content 75%, HDI, effective NCO content 17% in solid content, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a light diffusion layer coating material e. At this time, the equivalent ratio of isocyanate to hydroxyl group was 1.9, and the blending amount of the light diffusing material (silicone resin particles) with respect to 100 parts by mass of the solid content of the resin binder (acrylic resin + polyisocyanate) was 150 parts by mass.

  Hereinafter, a dry coating film was formed on the substrate in the same manner as in Example 1 except that the light diffusion layer coating material e was used instead of the light diffusion layer coating material a in Example 1, and light diffusion was performed. A film was prepared.

(Comparative Example 3)
<Preparation process of coating material f for light diffusion layer>
Toluene 278 parts by mass Styrene resin particles “Techpolymer SBX-6” 137 parts by mass [average particle diameter of about 6 μm, manufactured by Sekisui Plastics Co., Ltd.]
100 parts by mass of acrylic resin solution “Acridic A-801-P” [50% solid content, hydroxyl value 100 of solid content, manufactured by Dainippon Ink & Chemicals, Inc.]
55 parts by mass of polyisocyanate solution “Coronate HL” (solid content 75%, HDI, effective NCO content 17% in solid content, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a light diffusion layer coating material f. At this time, the equivalent ratio of isocyanate to hydroxyl group was 1.9, and the blending amount of the light diffusing material (styrene resin particles) with respect to 100 parts by mass of the solid content of the resin binder (acrylic resin + polyisocyanate) was 150 parts by mass.

  Hereinafter, a dry coating film was formed on the substrate in the same manner as in Example 1 except that the light diffusion layer coating material f was used instead of the light diffusion layer coating material a in Example 1, and light diffusion was performed. A film was prepared.

(Comparative Example 4)
<Preparation process of coating material h for light diffusion layer>
Toluene 840 parts by mass Acrylic resin “Dianal BR-80” 100 parts by mass [100% solid content, no hydroxyl value, manufactured by Mitsubishi Rayon Co., Ltd.]
120 parts by mass of acrylic urethane resin particles “BC-79” [volume average particle diameter of about 6 μm, manufactured by Gifu Shellac Manufacturing Co., Ltd.]
Among the above materials, the total amount of acrylic resin and 400 parts by mass of toluene are sufficiently dissolved by stirring with a dispersion stirrer, and then the remaining materials are added and stirred and mixed with a dispersion stirrer to obtain a light diffusion layer coating material. It was. The compounding quantity of the light-diffusion material (acrylic urethane resin particle) with respect to 100 mass parts of solid content of the resin binder (acrylic resin) was 120 mass parts.

  Hereinafter, a dry coating film was formed on the substrate in the same manner as in Example 1 except that the light diffusion layer coating material h was used instead of the light diffusion layer coating material a in Example 1, and light diffusion was performed. A film was prepared.

(Evaluation of scratch resistance of light diffusion layer)
Using a surface property tester HEIDON-14D (manufactured by Shinto Kagaku Co., Ltd.), with a stainless steel ball indenter (SUS304, diameter 4.76 mm), while applying the predetermined load shown in Table 1, the moving speed was 60 mm / second. The light diffusion surface was rubbed 50 times. The scratches remaining after rubbing were visually observed. The evaluation results are shown in Table 1. In the table, the evaluation of scratches with respect to a predetermined load was made visually using the following criteria.
○ ... Almost no lines were left on the rubbing trace.
Δ: A slight trace was visible by adjusting the viewing angle.
X: A faint line was formed.
XX: A clear line was formed so that the scratches appeared to shine white.
The evaluation results are shown in Table 1. As can be seen from Table 1, when acrylic urethane resin particles were used, the scratch resistance was the best.

(Evaluation of solvent resistance of light diffusion layer)
A cotton swab moistened with a mixed solvent of toluene: methyl ethyl ketone = 1: 1 was used to rub the light diffusion layer. When rubbed a predetermined number of times shown in Table 1, the following criteria were used for visual evaluation.
○: No change is observed in the light diffusion layer.
Δ: Traces of partial dissolution of the light diffusion layer remained.
X: The light diffusion layer was peeled off and the substrate surface appeared.
The evaluation results are shown in Table 1.

(Evaluation of resin particle shedding)
Using a surface property tester, Souzaland Love Tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), the light diffusion film was fixed so that the light diffusion layer surfaces were rubbed with each other, and the light diffusion surface was rubbed 1000 times with a load of 18N. The light diffusion film rubbed on the lower side after the friction was cut into a 10 mm square, and the falling state of the resin particles on the surface of the light diffusion layer was observed with a microscope. The evaluation results are shown in Table 1. The following criteria were used for evaluation of the resin particle detachability.
○ ... No dropout is observed.
△ ... There are very few dropouts but very few.
× ... Many omission points are easily found.
XX: The resin binder is damaged and drops off frequently.

  As can be seen from Table 1, the light diffusing films of Examples 1 to 3 are superior to the light diffusing films of Comparative Examples 1 to 4 in abrasion resistance. The light diffusion films of Example 1 and Example 2 in which the equivalent ratio curing agent for the hydroxyl group of isocyanate is 0.7 equivalents or more have further improved solvent resistance, and the surface durability of the light diffusion film is further improved. You can see that

It is the exploded view which showed an example of the general structure of a liquid crystal display device. It is sectional drawing which showed an example of the general structure of a light-diffusion film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal module 2 Backlight unit 3 Light source 4 Reflective film 5 Light guide plate 6 Reflective sheet 7 Light diffusion film 8 Prism sheet 9 Protective film 10 Transparent sheet base material 11 Light diffusion layer 12 Back surface layer 13 Light diffusion material 14 Resin binder

Claims (3)

Have a light diffusion layer containing a light diffusing material and a resin binder on at least one surface of a transparent sheet-like substrate, at least a portion of the light diffusing material is partially light diffusion which projects from the light diffusion layer A light diffusing film composed of a material , wherein the light diffusing material contains acrylic urethane resin fine particles, and the resin binder comprises an acrylic resin containing an acrylic monomer having a hydroxyl group as a copolymerization component, polyisocyanate in all SANYO crosslinked, the equivalent ratio hydroxyl value of the acrylic resin is 25 to 500, relative to the hydroxyl group of the isocyanate in the polyisocyanate, a light diffusing film to 0.7 to 3.0 der Rukoto characterized . 2. The optical film according to claim 1, wherein the volume average particle size of the acrylic urethane resin fine particles is 1 to 30 μm, and the thickness of the light diffusion layer is 2 to 25 μm. The other surface of the sheet-like substrate has a back layer containing a resin binder and a light diffusing material, and the resin binder is made of a thermoplastic methacrylic resin, a thermoplastic methacryl-styrene copolymer resin, and an acrylic resin. The light diffusing film according to claim 1 or 2, wherein one selected from the above is crosslinked with polyisocyanate.

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