KR100476068B1 - Light-Diffusing Film - Google Patents

Abstract

In a light diffusing film prepared by coating a transparent binder resin solution in which inorganic or organic particles are dispersed as a light diffusing agent on one side of a transparent polymer resin film, the laminating ratio is 10% or less, and the light diffusing agent forming a lamination By allowing the aggregated particle size of to be 50 µm or less, a light diffusing film having excellent luminance characteristics and no black spots is provided.

Description

Light Diffusion Film {Light-Diffusing Film}

The present invention relates to a light diffusing film.

As the industrial fields are diversified, the application fields of polymer resin films are widely used for various packaging, photographic film, condenser, electric insulation material, label, magnetic recording medium, and medical use. It is expanding to the field of image display devices such as screens, plasma display panels and liquid crystal display devices.

In particular, the display method of the image display device, unlike the cathode ray, indirectly displays an image through the light guide plate by reflecting the light generated from the fluorescent plate of the backlight attached to the back of the device to the metal deposition layer or the translucent or opaque white reflector. Due to the lighting method, there is a problem in that an image is not easily seen, and the situation is gradually increasing according to the trend of increasing the size of the image display device.

In order to overcome this problem, a light diffusing film has been developed that can be bonded to the light guide plate to increase luminance by uniformly diffusing light rays.

For example, Japanese Patent Application Laid-Open Nos. Hei 6-67003, Hei 7-174909, Hei 9-127314, U.S. Patent No. 5,706,134, and Japanese Utility Model No. 2,539,491 have been described on one side of a transparent polymer resin film. A light diffusing film coated with a transparent binder resin solution in which inorganic or organic particles are dispersed as a light diffusing agent has been proposed.

At this time, the light diffusing agent includes inorganic and organic type, and the inorganic light diffusing agent includes silica, zirconia, calcium carbonate, barium sulfate, glass, titanium dioxide, and the like, and the organic light diffusing agent includes urethane resin, acrylic resin, vinyl chloride resin, etc. Particulates.

In addition, the particle diameter of the light diffusing agent is mainly used having a particle size of 1 to 50㎛, in order to maximize the density of the light diffusing agent per unit area, particles having different particle sizes are mainly used.

There has also been an attempt to maximize the ratio of the light diffusing agent to the transparent binder resin in order to increase the diffusion transmittance. However, the light diffusing layer formed by this method does not exist independently of each other and the light diffusing agents are coagulated with each other or are stacked on each other.

3 is a cross-sectional view of the light diffusing film according to the prior art, in which the light transmittance of the light passing through the light guide plate P is lowered in the portion L in which the light diffusing agent particles S are laminated as described above. Since the light transmittance is remarkably lowered at the part where the aggregated particles are laminated, there is a limit to the improvement of the brightness uniformity at the front, and it is not suitable for use as a light diffusion film because the black spot part can be easily distinguished by the naked eye.

An object of the present invention is to provide a light diffusing film which improves the problems of the prior art as described above, which is excellent in luminance uniformity, and which has no partial light transmittance and which do not have black spots.

The present invention for achieving the above object is a light diffusing film formed on one side of the substrate (F) made of a transparent polymer resin film is a light diffusing layer composed of an inorganic or organic light diffusing agent (S) and a transparent binder resin (B) ( In D), the ratio of lamination satisfies Equation 1 below, and the aggregated particle size of the light diffusing agent forming lamination satisfies Equation 2 below.

In Equation 1, Sc means the square of the average radius of the light diffusing agent particles.

In Equation 2, Sd means the average particle diameter of the monodisperse light diffusing agent particles.

Among many factors that determine the brightness of the light diffusing film (D) in which a light diffusing layer composed of an inorganic or organic light diffusing agent (S) and a transparent binder resin (B) is formed on one side of the substrate (F) made of a transparent polymer resin film. In particular, the light diffusing agent has the greatest influence on the luminance of the light diffusing layer depending on the dispersion state, type and size.

Among them, the dispersion state is the most important factor for determining the brightness of the light diffusing layer. If the light diffusing agent is uniformly dispersed and does not exist or aggregates, the light transmittance is significantly reduced by the aggregated particles when the lamination ratio exceeds 10%. .

However, even if the ratio is 10% or less, when the aggregated particle size of the light diffusing agent forming a lamination exceeds 50 µm, there is a problem that light transmission decreases due to the aggregated particle site.

The stacking ratio is 10% or less, and there may be various methods for the aggregated particle size of the light diffusing agent forming the stack to be 50 μm or less.

First, FIG. 1 illustrates a cross-sectional view of a light diffusing film, which is formed of a light diffusing layer that satisfies Equations 1 and 2 by using one monodisperse particle having a uniform size.

In this case, if the coating is applied to maintain the thickness corresponding to the particle diameter of the light diffusing agent, a single light diffusing layer can be obtained, and the average particle diameter (Sd) of the monodisperse light diffusing agent particles used must satisfy Equation 3 below. .

Sd- (Sd × 0.15) ≤ Sd ≤ Sd + (Sd × 0.15)

In addition, in order to maximize the brightness by increasing the density of the light diffusing agent within the range satisfying the object of the present invention, the average particle diameter of the light diffusing agent having a large average particle diameter is Sa, and the average particle diameter of the light diffusing agent having a small average particle diameter is Sb, at the same time satisfying the equation (3), at the same time, two kinds of light diffusing agent having a different average particle size should be mixed to use the following equation (4).

Sa ^1/2 <Sb <Sa

In addition, it is preferable that the mixing ratio of Sa and Sb shall be 10: 90-90: 10.

FIG. 2 is a conceptual diagram of another light diffusing film, illustrating the formation of a light diffusing layer satisfying Equations 1 and 2 by using different types of monodisperse particles satisfying Equations 3 and 4 above.

In this case, the average particle size of the light diffusing agent is preferably 1 to 50 μm, but when less than 1 μm, it is difficult to monodisperse, so that the particles are easily aggregated, and lamination is more than 10%. In this case, monodispersion is easy, but the attraction force between the particles is large, causing a tendency to reaggregate after a single monodispersion, resulting in a problem of low light transmittance.

In the case of using light diffusing agents having different particle sizes satisfying Equations 3 and 4, the coating thickness is suitably about 5 to 25 g / m 2 based on the coating amount.

If the coating amount is less than 5g / ㎡ is too thin, the effect of light diffusion is insignificant, on the contrary, if it exceeds 25g / ㎡, the lamination ratio exceeds 10%, the light transmittance is lowered to have no practical use as a light diffusion plate.

The method of manufacturing the light-diffusion film meeting the above object can be carried out in accordance with a conventional film production method.

First, the light diffusing agent composition comprising the light diffusing agent and the binder resin is dispersed using a conventionally used disperser such as a bead mill using glass or zirconium beads and a roll mill using horizontal or vertical rolls.

At this time, a dispersant containing a modified polysiloxane or polycarboxylic acid may be used in order to make the dispersion better.

The binder resin solution in which the light diffusing agent is uniformly dispersed is applied onto a base film, preferably a polyethylene terephthalate (PET) film, and then dried to form a light diffusing layer.

The method of applying the light diffusing composition to the base film is not particularly limited as long as it is commonly known in the art, and may be adopted according to the material and shape of the base film, for example, an air knife method, A gravure method, a reverse roll method, a spray method, or a blade method can be arbitrarily selected.

After apply | coating a light diffuser to a base film, a coating layer is formed by heating by irradiating hot air, infrared rays, far-infrared rays, etc.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by the examples described below.

<Example 1>

The light-diffusion layer composition having the following composition was applied onto SKC's 100-micron-thick polyethylene terephthalate film (SH31) using a 0.3 mm Meyer Bar at a coating amount of 15 g / m 2, dried at 120 ° C. for 3 minutes, and the lamination ratio was 1.2%. Meanwhile, a light diffusing film having a diameter of 20 µm of agglomerated particles was prepared, and black spots were evaluated and luminance was measured, and the results are shown in Table 1 below.

25.4 parts by weight of binder resin

(Niporan 125, product of Nippon Polyurethane Co., Ltd.)

2.9 parts by weight of curing agent

(Cornate HX, Nippon Polyurethane Co., Ltd.)

30.3 parts by weight of a polymethyl methacrylate monodisperse light diffusing agent having an average particle diameter of 10 μm

(MX-1000, product made by Soken)

Solvent 41.4 parts by weight

(MEK: toluene = 1: 1)

<Example 2>

Using the same apparatus and method as in Example 1, except that a light diffusing film having a lamination ratio of 2.7% and agglomerated particle diameter of 25 μm was prepared using the following composition, black spots were evaluated, and luminance was measured. It is shown in Table 1 with 1.

25.4 parts by weight of binder resin

(Niporan 125, product of Nippon Polyurethane Co., Ltd.)

2.9 parts by weight of curing agent

(Cornate HX, Nippon Polyurethane Co., Ltd.)

21.2 parts by weight of a polymethyl methacrylate monodisperse light diffusing agent having an average particle diameter of 10 μm

(MX-1000, product made by Soken)

9.1 parts by weight of a polymethyl methacrylate monodisperse light diffusing agent having an average particle diameter of 5 μm

(MX-500, manufactured by Soken)

Solvent 41.4 parts by weight

(MEK: toluene = 1: 1)

<Example 3>

Using the same apparatus and method as in Example 1, a light diffusing film having a laminated ratio of 0.8 μm and agglomerated particle diameter of 30 μm was prepared with the following composition, and black spots were evaluated and luminance was measured. It is shown in Table 1 with 1.

25.4 parts by weight of binder resin

(Niporan 125, product of Nippon Polyurethane Co., Ltd.)

2.9 parts by weight of curing agent

(Cornate HX, Nippon Polyurethane Co., Ltd.)

30.3 parts by weight of a polymethyl methacrylate monodisperse light diffusing agent having an average particle diameter of 15 μm

(MX-1500, manufactured by Soken)

Solvent 41.4 parts by weight

(MEK: toluene = 1: 1)

Comparative Example 1

Using the same apparatus and method as in Example 1, a light diffusing film having a laminated ratio of 30.2% and agglomerated particle diameter of 90 μm was prepared using the following composition, and black spots were evaluated and luminance was measured. It is shown in Table 1 with 1.

25.4 parts by weight of binder resin

(Niporan 125, product of Nippon Polyurethane Co., Ltd.)

2.9 parts by weight of curing agent

(Cornate HX, Nippon Polyurethane Co., Ltd.)

30.3 parts by weight with a particle size distribution of 0.03 to 26 μm

Polymethylmethacrylate Monodisperse Light Diffusion

(Epostar MA-1010, product of Japan Catalyst)

Solvent 41.4 parts by weight

(MEK: toluene = 1: 1)

Comparative Example 2

Using the same apparatus and method as in Example 1, a light diffusing film having a lamination ratio of 21.5% and agglomerated particle diameter of 81 μm was prepared using the following composition, and black spots were evaluated and luminance was measured. It is shown in Table 1 with 1.

25.4 parts by weight of binder resin

(Niporan 125, product of Nippon Polyurethane Co., Ltd.)

2.9 parts by weight of curing agent

(Cornate HX, Nippon Polyurethane Co., Ltd.)

21.2 parts by weight of a polymethyl methacrylate monodisperse light diffusing agent having an average particle diameter of 15 μm

(MX-1500, manufactured by Soken)

9.1 parts by weight of a polymethyl methacrylate monodisperse light diffusing agent having an average particle diameter of 1.5 μm

(MX-150, product made by Soken)

Solvent 41.4 parts by weight

(MEK: toluene = 1: 1)

<Evaluation method>

-Stacking ratio

On the light guide plate of the liquid crystal backlight unit, two or three light diffusing films were placed on the light guide plate, and the stacking ratio of Equation 1 was calculated by observing with a 500 times optical microscope.

Maximum aggregated particle diameter

On the light guide plate of the liquid crystal backlight unit, two to three light diffusing films were placed on the light guide plate, and the particle size of Equation 2 was calculated by observing with a 500 times optical microscope.

-Sunspot

Two or three light diffusing films were placed on the light guide plate of the liquid crystal backlight unit and magnified 14 times using an optical microscope to observe the presence or absence of black spots with the naked eye.

Good: No spots or dark spots due to lamination

Poor: When spots or dark spots due to lamination are present

Luminance

Two or three light diffusing films were stacked on the light guide plate of the liquid crystal backlight unit, and measured using a luminance meter BM-7 manufactured by TOPCON.

Sa (μm) Sb (μm) Sa and Sb usage ratio Stacking Ratio Aggregated particle size (㎛) black spot Luminance (cd / ㎡) Example 1 10 - 10: 0 1.2 20 Good 1723 Example 2 10 5  7: 3 2.7 25 Good 1720 Example 3 12 - 10: 0 0.8 30 Good 1725 Comparative Example 1 10 - 10: 0 30.2 90 Bad 1683 Comparative Example 2 15 1.5 7: 3 21.5 81 Bad 1694

As can be seen from the results of the present invention, in the case of the light diffusion films (Examples 1 to 3) in which the lamination ratio is 10% or less, and the aggregated particle size of the light diffusing agent forming the lamination is 50 μm or less according to the present invention. It was confirmed that the luminance characteristic was excellent as well as no black spot was generated.

On the other hand, in Comparative Examples 1 and 2 in which aggregation and lamination occur, the luminance characteristics are inferior and black spots are generated, which is not suitable for use in various image display elements.

According to the present invention, a light diffusing layer composed of a light diffusing agent and a binder resin is dispersed so that the light diffusing agent is dispersed in single particles, the lamination ratio is 10% or less, and the aggregated particle size of the light diffusing agent forming a lamination is 50 μm or less. The light diffusing film formed on one side of the substrate is suitable for application to various image display devices because of excellent luminance characteristics and no black spots.

Although the present invention has been described with reference to one embodiment, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible.

1 is a cross-sectional view of a light diffusing film according to an embodiment of the present invention

2 is a cross-sectional view of a light diffusing film according to another embodiment

3 is a cross-sectional view of a light diffusing film by the prior art;

Explanation of symbols on the main parts of the drawings

B: Binder C: Light Diffusion Layer

D: Light Diffusion Film F: Base Film

L: Laminated part S: Light diffuser

Sa: Average particle diameter of light diffusing agent with large average particle diameter

Sb: average particle diameter of the light diffusing agent having a small average particle diameter

Sd: average particle diameter of the light diffusing agent

Claims (3)

In a light diffusing film in which a light diffusing layer composed of an inorganic or organic light diffusing agent and a transparent binder resin is formed on one side of a substrate made of a transparent polymer resin film, the lamination ratio satisfies the following expression (1) and forms lamination: An aggregated particle size of the diffusing agent satisfies Equation 2 below, and the light diffusing agent forming a stack is composed of different types of monodisperse particles satisfying both Equations 3 and 4 below. <Equation 1> <Equation 2> <Equation 3> Sd- (Sd × 0.15) ≤ Sd ≤ Sd + (Sd × 0.15) <Equation 4> Sa ^1/2 <Sb <Sa Sa is the average particle diameter of the light diffusing agent having a large average particle diameter, Sb is the average particle diameter of the light diffusing agent having a small average particle diameter, Sc is the square of the average radius of the light diffusing agent particles, Sd is the Mean average particle diameter. delete The light diffusing film according to claim 1, wherein the light diffusing agent is composed of one kind of monodispersed particles.