KR100476067B1 - Light-Diffusing Film - Google Patents

Abstract

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 substrate has a transmittance and haze of the substrate film and heat in the longitudinal and transverse directions. By providing a non-filler transparent polymer resin film having excellent shrinkage ratio, the present invention provides a light diffusion film having excellent luminance characteristics, no decrease in light transmittance, and excellent thermal characteristics.

Description

Light Diffusion Film {Light-Diffusing Film}

The present invention relates to a light diffusing film, and more particularly, to a support used for a light diffusing film.

As the industrial fields are diversified, the application fields of polymer resin films are widely used in various packaging, photographic films, capacitors, electrical insulation materials, labels, magnetic recording media, and medical substrates. Background Art [0002] It has been extended to substrates of image display devices such as projection screens, plasma display panels, liquid crystal display devices, and the like.

Since the substrate used in the light diffusion film is required to have high transparency, a resin film made from a transparent polymer resin such as polyester resin, polyacrylic resin, polystyrene resin and polycarbonate resin has been mainly used.

Among them, polyethylene terephthalate films having high transparency, good mechanical strength, excellent processability, strong durability against light and heat emitted from the backlight unit, and relatively low cost are most frequently used.

However, due to the organic or inorganic particles added to the inside or the surface of polyethylene terephthalate in order to improve the processability and durability, the control of the transparency was bound to follow.

The present invention has been made in view of improving the problems of the prior art as described above, to provide a light diffusing film having excellent luminance characteristics, no decrease in light transmittance, and excellent thermal characteristics.

The present invention for achieving the above object is a light-diffusion film formed on one side of the substrate consisting of a transparent polymer resin film is a light diffusion layer composed of an inorganic or organic light diffusing agent and a transparent binder resin, the substrate is It is characterized in that the transparent polymer resin film of the filler without satisfying the equation (2) and (3).

In this case, T is the transmittance of the base film to light rays having a wavelength of 400 to 900 nm, I is the intensity of light after passing through the base film, and I _o is the intensity of light before passing through the base film.

At this time, T is the transmittance of the base film with respect to the light ray whose wavelength is 400-900 nm, and Td is a diffusion transmittance.

At this time, Ht is a heat shrinkage rate in the longitudinal direction of the base film and Hm is a heat shrinkage rate in the transverse direction of the base film.

The transmittance of the base film should be maintained at 88% or more. When the transmittance is 88% or less, the light transmittance is lowered, so that the luminance cannot be improved.

In order to maintain the transmittance of Equation 1 above 88%, it is essential to control the extinction coefficient, concentration, and thickness, which are factors influencing T value. However, the extinction coefficient becomes constant depending on the material.

The concentration of the base film is influenced by the density of the resin constituting the base material, and ultimately, the concentration of the film can be controlled by adjusting the weight average molecular weight.

The weight average molecular weight of the base resin is preferably 20,000 to 25,000. However, when the weight average molecular weight of the base resin is less than 20,000, there is a problem in that workability and strength are lowered.

Although the concentration of the base film is important, the concentration of the resin itself is important, but since the effect of scattering or absorption caused by impurities present in the base is greater than that of the resin, the film is composed of polyethylene terephthalate alone without the filler. It is preferable.

In addition, the thickness of the film also affects the transmittance. If the thickness of the film is preferably 100 to 200 µm, and the thickness of the film is greater than 200 µm, the handleability is good, but there is a problem that the transparency is poor and the liquid crystal backlight unit is not thinned. If thin, the transparency is excellent, but there is a problem of poor handling.

On the other hand, the haze value is preferably 1.2 or less, but when it is 1.2 or more, the transmittance of the light diffusing film is lowered, which in turn causes a decrease in luminance. In particular, since diffused acid or quenching occurs due to the filler of the base film, the filler needs to be removed.

In particular, the light-diffusion film prepared using the non-filler base film having a transmittance of 88% or more and the haze of 1.2 or less has an advantage of excellent luminance when compared to a conventional base film when two or more sheets are overlapped.

This phenomenon is because the filler present in the substrate has a greater effect on light transmittance reduction when two or more sheets are overlapped than when one sheet is used. In the case of the liquid crystal backlight unit, two light diffusion films are used to improve the brightness. It is important to evaluate superposition optical characteristics because three sheets may be superimposed.

The film used as the substrate of the light diffusing film, as well as the optical properties as described above, the thermal properties should be considered. If the thermal characteristics are not sufficient, curling occurs due to shrinkage or expansion of the light diffusing film due to heat emitted from the light source of the liquid crystal backlight unit, and thus it cannot be used as a light diffusing film.

Therefore, when the heat shrinkage ratio (Hm, Ht) in the longitudinal direction and the transverse direction is 1.0 or less, and the percentage of the heat shrinkage ratio (Ht / Hm) in the transverse direction and the longitudinal direction is 100% to 50%, curling in the light diffusion film This will not happen. On the contrary, if it exceeds 100% or less than 50%, curling occurs due to the difference in balance in the transverse direction and the longitudinal direction, and thus the luminance uniformity of the liquid crystal backlight is lowered.

The method of manufacturing a light diffusing film that meets the above objectives may be carried out according to a conventional film manufacturing method, wherein a binder resin solution in which a light diffusing agent having an average particle size of 1 to 50 μm is uniformly dispersed is polyethylene terephthalate (PET). ) It is obtained by applying onto a base film and then drying to form a light diffusion 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, for example, an air knife method, a gravure method, a reverse roll. It can be used arbitrarily selected from (reverse roll), spray (spray) method or blade (blade) method.

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>

A light diffusing layer composition having the following composition was prepared using a 0.3 mm Mayer bar, and the base film had a transmittance of 88%, a haze of 0.8, a percentage of Ht / Hm of 63.0%, and a filler for light having a wavelength of 400 to 900 nm. On the 100 μm thick polyethylene terephthalate film (SH31) of SKC Co., Ltd., which was applied at a coating amount of 13 g / m 2 and dried at 120 ° C. for 3 minutes, a light diffusion film was prepared. The percentage of heat shrinkage ratio (Ht / Hm) in the longitudinal and longitudinal directions was measured and the results are shown in Table 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.)

20.5 parts by weight of light diffusing agent

(Epostar MA-1010, product of Japan Catalyst)

Solvent 51.2 parts by weight

(MEK: toluene = 1: 1)

<Example 2>

Using the same apparatus and method as in Example 1, but having a transmittance of 89%, haze of 0.8, a percentage of Ht / Hm of 62.4% and containing no filler 100 ㎛ thick polyethylene terephthalate film (SH35 The light diffusing film was prepared by using the same method, and the percentage of thermal shrinkage ratio (Ht / Hm) in one and two superimposed luminance and in the transverse and longitudinal directions was measured, and the results are shown in Table 1 together with Example 1. Indicated.

Comparative Example 1

Using the same device and method as in Example 1, the light diffusion layer composition having the following composition had a transmittance of 84%, a haze of 3.0, a percentage of Ht / Hm of 50.0%, and 0.05% by weight of silica filler. The light diffusing film was prepared by using the polyethylene terephthalate film (SG82) of 100㎛ thickness of the company, by measuring the percentage of thermal shrinkage ratio (Ht / Hm) of one and two superimposed brightness and transverse and longitudinal direction The results are shown in Table 1 together with Example 1.

Comparative Example 2

The same apparatus and method as in Example 1 were used, but 100% thick polyethylene tere of SKC, having a transmittance of 86%, a haze of 1.5, a percentage of Ht / Hm of 55.1%, and 0.03% by weight of titanium dioxide filler It was applied to phthalate film (SH71) and dried to prepare a light diffusing film, and measured the percentage of thermal shrinkage ratio (Ht / Hm) in one and two superimposed brightness and transverse direction and longitudinal direction, and the result It is shown in Table 1 with 1.

28.5 parts by weight of binder resin

(U1753C, manufactured by SK Chemicals)

2.4 parts by weight of curing agent

(Duranate P301-75E, manufactured by Ukhwasung Co., Ltd.)

35.7 parts by weight of light diffusing agent

(Techpolymer MBX-15, product of Epoxy Chemicals)

Solvent 33.4 parts by weight

(MEK: toluene = 1: 1)

Comparative Example 3

The same apparatus and method as in Example 1 were used, except that 100% thick polyethylene terephthalate of SKC, which had a transmittance of 85%, a haze of 1.6, a percentage of Ht / Hm of 40.0%, and 0.03% by weight of silica filler. A light diffusing film was manufactured using the film SH92, and the percentage of thermal shrinkage ratio (Ht / Hm) in one and two superimposed luminance and in the transverse and longitudinal directions was measured, and the result was combined with Example 1. Table 1 shows.

<Evaluation method>

-Curl characteristics

After 500 hours of placing the light diffusion film on the light guide plate of the liquid crystal backlight unit, the portion where the edge portion was raised from the light guide plate was measured to maximum, and the curl characteristics were evaluated according to the following criteria.

Good: Max. Climbed part is less than 1mm

Poor: Maximum raised part exceeds 1mm

1 color coordinate (x, y) and luminance

One light diffusing film was placed on the light guide plate of the liquid crystal backlight unit and evaluated using TOPM BM-7.

-2 color coordinates (x, y) and luminance

Using the same measuring apparatus and method as the single color coordinate measurement, two light diffusing films were overlaid and the color coordinates were measured.

-Ht / Hm

After leaving the 2.5cm × 30cm specimen in the longitudinal or transverse direction of the light-diffusion film for 30 minutes at 150 ° C, the transverse length of the initial specimen is called H _mo and the longitudinal length is called H _to , and the specimen after heat shrinkage. When the lateral length of is denoted by H _m and the longitudinal length is denoted by H _t , it is obtained from Equation 4 below.

Transmittance (%) of base material Haze (%) of mention Ht__ × 100Hm Filler content Curl characteristics Color coordinates Luminance (Cd / ㎡) 1 sheet 2 sheets 1 sheet 2 sheets x y x y Example 1 88 0.8 63.0 0.00% Good 0.2913 0.3001 0.2942 0.3010 1715 1860 Example 2 89 0.8 62.4 0.00% Good 0.2915 0.2998 0.2939 0.3011 1720 1863 Comparative Example 1 84 3.0 50.1 0.05% Good 0.2820 0.2871 0.2843 0.2905 1616 1702 Comparative Example 2 86 1.5 55.1 0.03% Good 0.2815 0.2869 0.2840 0.2910 1624 1713 Comparative Example 3 85 1.6 40.2 0.03% Bad 0.2811 0.2852 0.2825 0.2868 1611 1698

As can be seen from the results of the present invention, the light diffusing film has a transmittance of 88% or more, haze of 1.2 or less, and a percentage of heat shrinkage ratio of 50-100 according to the present invention for light having a wavelength of 400-900 nm. In the case of the light diffusing films (Examples 1 to 2) containing no fillers, the luminance characteristics were improved by about 6% due to the increase in the transmittance of the substrate as compared to the case in which the fillers were not included (Comparative Examples 1 to 3). In particular, when the two sheets overlapped was found to be more excellent.

This result is presumably because there is no light loss by the filler present in the substrate. In addition, it can be seen that the higher the heat shrinkage ratio, the better the luminance uniformity of the liquid crystal backlight unit since no curl occurs.

According to the present invention, the light-diffusion film has a transmittance of 88% or more and a haze of 1.2 or less, and a ratio of the thermal contraction ratio in the longitudinal direction and the transverse direction of 50 to 100 for light having a wavelength of 400 to 900 nm. It is excellent in characteristics and thermal characteristics, and is suitable for application to various image display elements.

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.

Claims (3)

In the light diffusion film formed on one side of the substrate made of a transparent polyethylene terephthalate film, the light diffusing layer composed of an inorganic or organic light diffusing agent and a transparent binder resin, the thickness of the substrate is 100 to 200㎛, Light-diffusion film, characterized in that the transparent polymer resin film of the non-filler satisfying the formula (2) and formula (3) <Equation 1> In this case, T is the transmittance of the base film to the light rays having a wavelength of 400 to 900nm, I is the intensity of the light after passing through the base film, I _o is the intensity of the light before not transmitting the base film <Equation 2> In this case, T is the transmittance of the base film to the light rays having a wavelength of 400 to 900nm, Td is the diffusion transmittance <Equation 3> In this case, Ht is the heat shrinkage in the longitudinal direction of the base film and Hm is the heat shrinkage in the transverse direction of the base film delete The light diffusing film according to claim 1, wherein the substrate is a polyethylene terephthalate film having a weight average molecular weight of 20,000 to 25,000.