KR100963106B1 - Light-diffusing sheet and optical sheet for back light unit - Google Patents

Abstract

The present invention relates to a light diffusion sheet for a backlight unit, and more particularly to a light diffusion sheet for a backlight unit to maximize the refractive and diffraction characteristics of the light to improve the brightness and hiding characteristics. To this end, the light diffusion sheet for a backlight unit according to the present invention includes a light diffusion layer coated with a coating liquid containing a base material and a binder resin and particles on at least one surface of the base film, and a binder resin of the light diffusion layer on the light diffusion layer; It characterized in that it comprises a thin film layer coated by mixing at least one binder resin having a different refractive index, preferably, the refractive index of the binder resin to form the thin film layer is 1.30 ~ 1.80, the binder resin of the light diffusion layer It is characterized by being larger than the refractive index.

Base film, binder resin, particle | grains, light-diffusion layer, refractive index

Description

Light diffusion sheet and optical sheet for backlight unit {LIGHT-DIFFUSING SHEET AND OPTICAL SHEET FOR BACK LIGHT UNIT}

The present invention relates to a light diffusion sheet for a backlight unit, and more particularly to a light diffusion sheet for a backlight unit to maximize the refractive and diffraction characteristics of the light to improve the brightness and hiding characteristics.

Generally, the light diffusion sheet for LCD backlight is provided with a linear lamp on one side of the light guide plate used in small size such as car navigation system, mobile phone, PDA, digital camera, portable TV, camcorder, etc. In the SIDE type backlight unit in which the EDGE type backlight unit and one or more lamps are installed and used, the non-uniform light source from the light guide plate is converted into uniform light centered on the front direction of the backlight unit. Even when a large number of cold-cathode fluorescent lamps or flat lamps are installed in the direct type, that is, the backside of the backlight, which is used in TVs or some large-sized monitors, the surface light source of uniform omnidirectional distribution is diffused by diffusing the linearly visible light. Function to switch the center of light distribution to the front direction It comes to have the effect of increasing the brightness of the face.

In order to perform the function of concealment and diffusion in the function of the light diffusion sheet for the LCD backlight and improve the brightness, a method of applying transparent organic resin particles or inorganic particles on a transparent plastic film with a transparent resin binder has been developed (Japanese Patent) Korean Laid-Open Patent Publication No. 7-174909, Korean Laid-Open Publication No. 2000-0027862, and Korean Laid-Open Publication No. 1998-0020430.

However, the conventional techniques as described above do not satisfy the performance of the brightness and hiding function required for a high efficiency backlight.

The present invention has been made to solve the above problems, an object of the present invention is to provide a light diffusion sheet for a backlight unit that can maximize the refraction and diffraction characteristics of the light to excellently improve the brightness and hiding characteristics. .

The object is a light diffusion layer coated with a base film, a coating liquid containing a binder resin and particles on at least one surface of the base film, and a binder resin having a refractive index different from the binder resin of the light diffusion layer on the light diffusion layer. It is achieved by a light diffusion sheet for a backlight unit, characterized in that it comprises a thin film layer applied by mixing at least one.

Here, the refractive index of the binder resin forming the thin film layer is 1.30 to 1.80, characterized in that greater than the refractive index of the binder resin of the light diffusion layer.

Preferably, the particles of the light diffusion layer is a particle having an average particle diameter of 3㎛ ~ 50㎛, characterized in that the single maximum particle size of the particle or one or more mixed particles having an average particle diameter smaller than the particle having the maximum average particle diameter. It is done.

Also preferably, the base film includes an organic diffusion agent in a transparent polycarbonate (PC) film, a polyethylene terephthalate (PET) film or a polyethylene terephthalate (PET) film, and has a haze of 40 to 95% and 50 to 95%. It is characterized in that the internal diffusion film having a transmittance of%.

Also preferably, the light diffusion sheet for the backlight unit may have a haze of 10 to 95% and a transmittance of 50 to 95%.

Also preferably, the thickness of the thin film layer is characterized in that 0.1 ~ 3㎛.

Also preferably, the thickness of the light diffusion layer and the thin film layer is characterized in that less than 150% of the average particle diameter of the particle having the maximum average particle diameter of the light diffusion layer.

The above object is also achieved by an optical sheet for backlight unit, wherein in the optical sheet for backlight unit, a first binder resin and a second binder resin having different refractive indices are sequentially applied to the uppermost layer of the sheet.

Preferably, the first binder resin and the second binder resin have different refractive indices.

More preferably, the refractive index of the second binder resin is 1.30 to 1.80, characterized in that it is larger than the refractive index of the first binder resin.

According to the present invention, it is possible to maximize the refraction and diffraction characteristics of the light to excellently improve the brightness and hiding characteristics.

Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention. These examples are only presented by way of example only to more specifically describe the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples. .

The present invention relates to a light diffusion sheet used for a backlight unit of an LCD, and more particularly, to a light diffusion sheet used for a thin film transistor liquid crystal display (TFT-LCD) or a super twisted nematic liquid crystal display (STN-LCD). The present invention relates to a light diffusing sheet capable of inducing uniform surface light and obtaining high brightness and clear light image while passing light from linear light emitted from a cold cathode fluorescent lamp located on the side or the back to obtain a clear image of the light.

According to the present invention, in order to implement a high brightness light diffusion sheet, it is preferable to use particles having an average particle diameter of 3 μm to 50 μm in implementing the light diffusion layer on at least one surface of the transparent base film. In order to obtain high luminance characteristics, it is preferable to apply the entire surface of the particles having a large average particle size evenly, and to coat the spherical shape of the particles to protrude outward as much as possible. However, when particles having an average particle diameter of more than 50 μm are used, wet coating is difficult and difficulty in dispersing the coating liquid is preferably 50 μm or less. In addition, in order to increase the diffusion function and hiding power, it is effective that the single maximum particle diameter is one or more mixed particles having an average particle diameter smaller than the particle or the particle having the maximum average particle diameter.

In addition, the base film includes an organic diffusion agent inside a transparent polycarbonate (PC) film, polyethylene terephthalate (PET) film or polyethylene terephthalate (PET) film, and has a haze of 40 to 95% and a transmittance of 50 to 95%. An internal diffusion film having is preferred.

In addition, spherical transparent particles are suitable as the light diffusing agent, organic particles such as acrylic particles, styrene particles, silicon particles, and inorganic particles such as synthetic silica, glass beads, and diamond may be used as the transparent particles. It can be used individually or in mixture of 2 or more types.

In addition, the binder resin used in the light diffusing layer of the light diffusing film should be transparent, such as acrylic, urethane, epoxy, vinyl, polyester, polyamide, etc., such as polymethyl methacrylate or methacrylic acid ester copolymer. It can use individually or in mixture of 2 or more types in resin.

In addition, the binder resin of the thin film layer of the light diffusion sheet for a backlight unit according to the present invention may use the same binder resin as the binder resin used in the light diffusion layer, but different binder resins may be used.

The technical feature of the present invention is that the above-mentioned light diffusing layer is raised from the light diffusing layer below by coating with a thin film a transparent binder resin having a different refractive index than that of the binder resin used for the light diffusing layer, preferably having a high refractive index. By refracting the direction of light once more using the difference in refractive index, the amount of light directed to the front can be increased to achieve higher brightness performance.Reflected and efficiently recycled by reflecting light transmitted in an unnecessary direction, not only brightness but also light efficiency and lamp concealment A light diffusing sheet having high function can be produced.

Here, the refractive index of the binder resin forming the thin film layer is characterized in that 1.30 ~ 1.80, because it is technically difficult to manufacture a binder resin having a refractive index outside the above range.

The light diffusion sheet implementing the light diffusion layer according to the present invention has the basic characteristics of 10-95% haze and 50-95% transmittance, and implements a coating layer of a thin film by using a binder resin having different refractive indices on the light diffusion layer. The physical properties of the final high-brightness light diffusion sheet also have the characteristics of having a haze of 10 to 95% and a transmittance of 50 to 95%.

As a method of manufacturing the light diffusion sheet, various coating methods such as a conventional wet coating method such as a knife coating method, a gravure transfer coating method, a reverse roll coating method, and other deposition methods may be applied.

At this time, the thickness (after coating) of the light diffusing layer and the thin film layer does not exceed 150% of the average particle diameter of the particles having the maximum average particle diameter, thereby obtaining the desirable effect of the uniform coating surface. This is because if the coating degree exceeds 150% of the average particle diameter of the particle having the maximum average particle diameter, it may cause a decrease in luminance due to excessive particle amount per unit area and deterioration of the effect of the lens shape.

In a preferred embodiment of the light diffusion sheet according to the present invention, the thin film layer formed on the light diffusion layer is characterized in that formed in 0.1 ~ 3㎛. If the thickness is less than 0.1 μm, it is difficult to coat. If the thickness exceeds 3 μm, particles formed on the surface of the light diffusion layer may be buried in the binder, and thus the surface of the light diffusion layer may be flat and may not have the characteristics required for the light diffusion sheet. Because.

An application layer having an antistatic function for the purpose of imparting slip properties to the back surface of the light diffusion sheet and the light diffusion layer formed on one surface thereof, increasing hardness for suppressing scratches generated during cutting and assembling operations, and preventing foreign matter from mixing. May be formed.

The light diffusion sheet for the backlight unit manufactured by the present invention is improved in brightness than the conventional light diffusion sheet when mounted on the backlight unit.

In addition, the optical sheet for a backlight unit according to the present invention is characterized in that the first binder resin and the second binder resin having a different refractive index applied to the top layer of the sheet in sequence, the second binder resin than the first binder resin It is preferable to form the upper layer (outer layer). Also preferably, the first binder resin and the second binder resin have different refractive indices. More preferably, the refractive index of the second binder resin is 1.30 to 1.80, which is larger than the refractive index of the first binder resin.

The optical sheet for the backlight unit includes all the technical features of the light diffusion sheet for the backlight unit described above, and is intended for application to other sheets used for the backlight in addition to the light diffusion sheet. Therefore, the optical sheet for backlight unit according to the present invention includes the same technical features applied to the light diffusion sheet for the backlight unit described above will be omitted below.

EXAMPLE

The film having the light diffusing layer used in the following examples, that is, the film having the light diffusing layer coated with the coating liquid containing the binder resin and the particles on the base film having a thickness of 100 μm, all had the same coating liquid (the binder resin refractive index of the light diffusing layer; 1.49 ), A sample having a haze of 88% and a transmittance of 78% was prepared and commonly used (Standard), and a sample according to each binder resin (difference in refractive index) was prepared on the prepared sample. In addition, the sample according to the coating amount was evaluated by using the same binder resin for the evaluation according to the coating amount (coating layer thickness consisting of the light diffusion layer and the thin film layer).

Example 1

A coating liquid having the following composition was applied to the diffusion film on which the light diffusion layer was formed in microgravure to form a thin film layer.

Coating liquid composition

Binder Resin 1 (refractive index: 1.52): 30 wt%

Solvent: 69% by weight

Curing agent and additives: 1% by weight

[Example 2]

A coating liquid having the following composition was applied to the diffusion film on which the light diffusion layer was formed in microgravure to form a thin film layer.

Coating liquid composition

Binder Resin 2 (refractive index: 1.54): 30 wt%

Solvent: 69% by weight

Curing agent and additives: 1% by weight

Example 3

A coating liquid having the following composition was applied to the diffusion film on which the light diffusion layer was formed in microgravure to form a thin film layer.

Coating liquid composition

Binder Resin 3 (refractive index: 1.58): 30 wt%

Solvent: 69% by weight

Curing agent and additives: 1% by weight

Example 4

A coating liquid having the following composition was applied to the diffusion film on which the light diffusion layer was formed in microgravure to form a thin film layer.

Coating liquid composition

Binder Resin 4 (refractive index: 1.64): 30 wt%

Solvent: 69% by weight

Curing agent and additives: 1% by weight

 Example 5

By adjusting the same amount of binder resin as in Example 1, a light diffusion sheet was prepared in which the coating thickness was adjusted.

Coating liquid composition

Binder Resin 1 (refractive index: 1.52): 45 wt%

Solvent: 54% by weight

Curing agent and additives: 1% by weight

Example 6

By adjusting the same amount of binder resin as in Example 1, a light diffusion sheet was prepared in which the coating thickness was adjusted.

Coating liquid composition

Binder Resin 1 (refractive index: 1.52): 55 wt%

Solvent: 44% by weight

Curing agent and additives: 1% by weight

Example 7

By adjusting the same amount of binder resin as in Example 1, a light diffusion sheet was prepared in which the coating thickness was adjusted.

Coating liquid composition

Binder Resin 1 (refractive index: 1.52): 60 wt%

Solvent: 39% by weight

Curing agent and additives: 1% by weight

[Experimental Example]

The physical properties of the light diffusing sheet prepared according to the above example were measured using the following method.

1.Haze was measured according to ASTM D-1003, and the measuring instrument was NIPPON DENSHOKU KOGYO Co. Ltd. Ltd. Model 1000 was used.

2. The luminance was compared by measuring the front luminance value on the backlight assembly using Topcon's BM-7A measuring device.

3. The shielding force was quantified by defining the front luminance on the backlight assembly at 30 intervals at equal intervals using Topcon's BM-7A measuring device.

[Equation 1]

The values measured based on the experimental example are shown in Table 1 below. Here, "thickness" represents the total thickness of the base film, the light diffusion layer and the thin film layer.

TABLE 1

Properties
Comprehensive Evaluation Haze
(%) Transmittance
(%) After
(Μm) Luminance
(%) Shielding force
(%) Standard 88.23 78.85 110.0 100.0 1.7 Standard Example 1 88.43 77.72 110.1 102.3 1.4 Good Example 2 88.40 76.94 110.1 102.6 1.4 Good Example 3 88.45 75.53 110.1 103.1 1.2 Great Example 4 88.47 73.54 110.1 104.6 1.1 Great Example 5 88.42 77.91 110.1 102.0 1.4 Good Example 6 88.43 78.18 110.2 101.1 1.3 Good Example 7 88.29 79.53 110.3 99.2 1.3 lack

As can be seen in Table 1, it can be seen that the higher the refractive index of the binder resin in Examples 1 to 4, the brightness and shielding performance is improved, as can be seen in Examples 5 to 7 to increase the coating amount of the binder resin It can be seen that the brightness and shielding performance is poor.

As described above, according to the light diffusion sheet according to the present invention, the brightness and shielding performance is improved by coating a thin film of a binder resin having a refractive index higher than that of the binder resin of the light diffusion layer on the light diffusion film on which the light diffusion layer is formed. It can be seen that higher.

Claims (10)

In the light diffusion sheet for the backlight unit, Base film, A light diffusion layer coated with a coating liquid including a binder resin and particles on one surface of the base film; And a thin film layer coated on the light diffusion layer using a binder resin having a refractive index different from that of the binder resin of the light diffusion layer. The method of claim 1, The refractive index of the said binder resin which forms the said thin film layer is 1.30-1.80, It is larger than the refractive index of the binder resin of the said light-diffusion layer, The light-diffusion sheet for backlight units. The method of claim 1, Particles of the light diffusing layer is a particle having an average particle diameter of 3㎛ ~ 50㎛, backlight, characterized in that at least one mixed particle having a single maximum particle diameter of the particle or the average particle diameter smaller than the particle having the maximum average particle diameter Light diffusion sheet for the unit. The method of claim 1, The base film includes an organic diffusion agent in a transparent polycarbonate (PC) film, polyethylene terephthalate (PET) film or polyethylene terephthalate (PET) film, and has a haze of 40 to 95% and a transmittance of 50 to 95%. Light diffusion sheet for a backlight unit, characterized in that the inner diffusion film. The method of claim 1, The light diffusion sheet for the backlight unit is a light diffusion sheet for a backlight unit, characterized in that having a haze of 10 to 95% and transmittance of 50 to 95%. The method of claim 1, The thickness of the thin film layer is a light diffusion sheet for a backlight unit, characterized in that 0.1 ~ 3㎛. delete In the optical sheet for backlight unit, An optical sheet for a backlight unit, wherein a first binder resin and a second binder resin having different refractive indices are sequentially applied to the uppermost layer of the sheet. The method of claim 8, The first binder resin and the second binder resin has a different refractive index, characterized in that the optical sheet for a backlight unit. The method of claim 8, The refractive index of the second binder resin is 1.30 ~ 1.80, it is larger than the refractive index of the first binder resin, the optical sheet for a backlight unit.