KR20050091344A - Light diffusion film having excellent electron-wave shielding property - Google Patents

Abstract

The present invention is provided with a light diffusion layer formed by applying a composition consisting of a transparent organic binder and a transparent organic particle on one surface of the base film made of a high transparent plastic, the other side of the base film is an electromagnetic shielding layer formed of a transparent conductive thin film of metal oxide A light diffusion film having a structure in which an electromagnetic wave shielding layer, a base film, and a light diffusing layer are sequentially stacked from the incident direction of light is provided, which can shield electromagnetic waves with excellent brightness without degrading the backlight of the TFT-LCD. It is useful as a light diffusion film for unit.

Description

Light diffusion film having excellent electron-wave shielding property

The present invention relates to a light diffusing film having an electromagnetic shielding function, and more particularly, to a light diffusing film suitable for use in a backlight unit of a thin film transistor liquid crystal module by excellently blocking electromagnetic waves without deteriorating luminance.

With the recent advances in electronic information device technology, high-speed microprocessors and large-capacity memories become possible, and in the fields of home appliances, industrial devices, and medical devices, such devices are becoming lighter, thinner, smaller, and more versatile. It is also possible to drive.

On the other hand, these devices are often sensitive to malfunctions caused by natural phenomena that are difficult to control artificially and minute electromagnetic disturbances caused by external shocks.

In modern society, as many electric and electronic devices are spread in various fields of society, the density of electromagnetic waves increases and the electromagnetic environment becomes poor, so that the equipment installed in the poor electromagnetic environment does not work as its original goal, causing confusion in society or human body. The risk of obstacles is increasing. In other words, such a device may be a source of noise or a victim from other sources in some cases.

To reduce the electromagnetic interference (EMI) problem, first of all, strengthen the immunity for the device to perform its intended operation even in the electromagnetic environment in the presence of the disturbance source, or to prevent the leakage of electromagnetic waves or the inflow into the equipment. Must be blocked.

In particular, the most problematic problem in the real life is the display field. Among the TVs represented by the CRT, this problem has been raised for a long time, and the generation of noise caused by the electromagnetic wave and the harmfulness of the human body have been controversial.

Conventionally, in order to shield such electromagnetic waves, a method of installing safety glasses in front of a TV or a monitor is adopted. In other words, the electromagnetic shielding function by applying a material that shields the electromagnetic wave or mixed in a sheet and installed in the front of the screen. However, due to the color problem of the electromagnetic shielding element, it is difficult to realize a clear image, and in particular, electromagnetic waves have some divergence, and some of the electromagnetic waves can be shielded, but electromagnetic waves of low impedance characteristics have rotational properties. Not only the shielding but also the conductive material has a problem that is permeated.

In the TFT-LCD, which is increasingly used among display media, the problem of electromagnetic waves is emerging as the large screen, low power, and high brightness of LCD displays have emerged as the core of future technology. In particular, the backlight itself is gradually increasing in size, and in particular, the direct type backlights, such as TVs, have been recently researched, and as the size of a backlight unit of 20 inches or more, such as a TV, increases in size, several lamps enter the lamp. The heat and electromagnetic waves generated by the photo affect the image, causing the screen to flicker.

LCD is a non-light emitting device and requires a separate light source. This light source body is called a backlight unit, and the liquid crystal module is made of a backlight unit and a liquid crystal unit. The backlight unit is a device that converts the linear light into surface light. A cold-cathode fluorescent lamp enters the lower side and reflects the light from the lamp to the front. The light guide plate serves to diffuse the reflected light to the front. It consists of a light diffusion film to conceal patterning and diffuse light secondaryly, a prism to increase the brightness of the diffused light in the vertical direction, and a prism protection film to protect the prism angle of the prism and prevent the moiré phenomenon.

The backlight unit is a structure of a backlight unit for a general notebook computer. In addition to the notebook computer, a backlight having a large screen size, such as an LCD monitor and a TV, has recently been exploded in addition to the notebook computer. When the screen size is increased, multiple diffusers, light guide plates, and the like cannot change the linear light to surface light, and brightness is also lowered.

Typical 19 "monitor backlights have two lamps on both sides to compensate for brightness. For 20" and larger TVs, several lamps are arranged on the upper surface of the reflecting film to compensate for brightness. It is called. In other words, as the screen size increases, the number of lamps increases and as the number of lamps increases, there are many driving devices for driving the lamps, and heat and electromagnetic waves from the lamps and the driving devices cause problems such as screen shaking.

In order to solve such a problem, a conventional method performed by a module company is to place an electromagnetic shielding film on the lower or upper surface of the light diffusion sheet in the backlight unit structure. In other words, the film formed by depositing metal oxides such as ITO (Indium Tin Oxide) and ATO (Antimonium Tin Oxide) on one or both sides of the transparent substrate film is placed on the lower or upper surface of the light diffusion film. It is a method of suppressing electromagnetic waves from.

However, this method is a technique against thinning because it is equipped with a separate film, it was not preferable in terms of price competitiveness because a separate film is used. In addition, when the electromagnetic shielding film is positioned above or below the light diffusion film, problems such as damaging the lower surface of the light guide plate or the prism film may be caused.

Therefore, there has been an attempt to shield electromagnetic waves by maximizing the antistatic function in the light diffusion layer. Japanese Patent Laid-Open No. 7-84103 discloses a method of improving the antistatic performance by wet coating an acrylate-based material on a light diffusing film. have. Since the light diffusion film coated with the acrylate-based material exhibits a resistance of about 10e7Ω, it does not reach the resistance characteristic of 1,000 Ω or less required for electromagnetic shielding, and thus the electromagnetic shielding ability is hardly exhibited.

Recently, a method of adding an electromagnetic shielding function to some of the components of the light diffusing film has been introduced due to such problems caused when using a separate electromagnetic shielding film.

Japanese Patent Application Laid-Open No. 8-86906 improves the visible light transmittance by placing a thin film oxide such as SiO ₂ between the PET film constituting the light diffusing film and the light diffusing material. However, such a coating is a means for reducing the reflection, thereby improving the transmittance and increasing the adhesion of the light diffusing material to the PET film because it is placed on the surface of the PET film, it does not function as an electromagnetic shielding function.

Korean Patent Publication No. 2002-64244 discloses a light diffusing film having excellent electromagnetic shielding ability, wherein a transparent conductive thin film is formed by physical or chemical vapor deposition with a metal oxide on an upper surface of a diffusing material of the light diffusing film. However, when the metal oxide is deposited on the light diffusion layer, it acts as a diffusion material, and thus the luminance is sharply lowered.

Accordingly, the present inventors have been trying to solve the problem that the luminance is lowered by placing the electromagnetic shielding layer on the diffusion layer of the light diffusion film in manufacturing the light diffusion film having the electromagnetic shielding function, the light diffusion layer on one surface of the base film As a result of applying the electromagnetic shielding layer on the opposite side after applying the coating, it was found that this problem can be solved, thereby completing the present invention.

Accordingly, an object of the present invention is to provide a light diffusing film capable of excellently blocking electromagnetic waves without deteriorating luminance.

The light diffusing film of the present invention for achieving the above object is provided with a light diffusing layer formed by applying a composition consisting of a transparent organic binder and a transparent organic particle on one surface of the base film made of a high transparent plastic, the other side of the base film An electromagnetic wave shielding layer formed of a transparent conductive thin film of a metal oxide is provided, and the electromagnetic wave shielding layer, the base film, and the light diffusing layer are sequentially stacked from the incident direction of light.

The present invention will be described in more detail as follows.

As shown in FIG. 1, a cross-section of the light diffusing film according to the present invention includes a light diffusing layer 1 on one side of the plastic support film 2, and the other side is composed of an electromagnetic wave shielding layer 3. The electromagnetic wave shielding layer 3, the plastic support 2, and the light-diffusion layer 1 are sequentially stacked from this incident direction.

(1) light diffusion layers

The light diffusion layer scatters and reflects the incident light, diffuses the light, and transmits light at the same time, thereby spreading the light through the light guide plate evenly throughout the LCD screen. Therefore, the light diffusion layer uses a resin that has good adhesion with the plastic support and has good compatibility with the particles that play a role of light diffusion. The main resins used are unsaturated polyester, methyl methacrylate, ethyl methacrylate and isobutyl. Methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide Acrylic, urethane, epoxy, melamine, etc., such as glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer or copolymer or terpolymer It is a film of resin by using a curing agent to increase heat resistance, abrasion resistance, and adhesion. Use to harden. At this time, since the resin used is transparent, the light transmittance is high, and in particular, the adhesive force with the base film is important because it constitutes a light diffusion layer. Without adhesive force with the base film, the coating layer may be partially dropped at the edge of the film when cut to a certain inch size in the finished state, and thus may not serve as a light diffusion film.

When the light diffusion film is cut into a single product after production, the foreign matter inspection is usually performed with alcohol, so it must be resistant to alcohol. If there is no resistance to alcohol, it is not preferable because the alcohol volatilized mark after the foreign material inspection remains on the film as it appears on the screen even after the backlight is mounted. In addition, the light diffusion film is used for a long time exposed to the back light and must be stable from heat from the back light. Even if these properties are completely satisfied, they cannot be used as a binder unless the luminance value is high after the binder is used. This is because the display industry is pursuing high brightness products.

To this end, an acrylic polyol and an isocyanate may be used as the binder resin of the light diffusion layer to prepare a light diffusion layer having adhesion to the base film, alcohol resistance, heat resistance, and excellent optical properties.

Particles constituting the light diffusion layer have a difference in refractive index with the resin used, and various organic and inorganic particles are used to increase the light transmittance and the diffusion rate. Typical particles used are methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxy Propyl methacrylate, hydroxy ethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer or copolymer Or multi-layered particles made by forming olefinic particles such as acrylic copolymers such as ternary copolymers, polyethylene, polystyrene, polypropylene, copolymers of acrylic and olefins, and homopolymer particles, and then covering the layers with other monomers. And organic particles. In addition, inorganic particles such as silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and magnesium fluoride are used.

The light diffusivity of the organic particles is superior to the inorganic particles, and thus the organic particles are mainly used in the present invention. The particle size used depends on the thickness of the coating film, but an average particle diameter of 1 to 30 microns is used. In addition, to increase the light diffusion efficiency, a mixture of particles of different sizes may be used. The reason is that when the particles are in close contact with the coating surface, it is advantageous for uniform packing to mix different particle sizes rather than the same particle size.

The particles may be used in an amount of 30 to 400 parts by weight, preferably 50 to 300 parts by weight, per 100 parts by weight of the binder resin.

In addition to such binder resins and particles, an antistatic agent may be used to impart contamination resistance to prevent dust or impurities that may occur when manufacturing a backlight unit using a light diffusing film. Antistatic agents can be used a variety of quaternary amines, anionics, cationics, nonionics, fluorides, etc., if the amount of use is increased, the antistatic properties are good, but the wear resistance is poor and there is a risk of precipitation if used for a long time Therefore, 10 parts by weight or less, preferably 5 parts by weight or less per 100 parts by weight of resin is used.

In addition, since the particles and the antistatic agent may be uniformly dispersed in the resin and the solvent to create a light diffusion layer having a high light diffusion efficiency, it is also possible to use a dispersant for uniform crude liquid. As the dispersant, an acrylic emulsion type, a modified silicone type, a polydimethylsiloxane, or a fluoride type may be used. The amount of the dispersing agent should be used in a small amount, which has a high light transmittance and does not cause surface precipitation after forming a coating film. It is suitably within 5 weight part with respect to 100 weight part of binders.

Additives of such a light diffusion layer should be used within a range that does not reduce the light transmittance of the basic resin.

The solvent may be any solvent capable of dissolving the acrylic polyol and polyisocyanate. In the coating process, a fast-drying solvent and a slow-drying solvent are used for uniform coating.

When dispersing particles, a conventional disperser may be used, and in particular, a milling machine or a homomixer may be used to reduce the dispersing time.

This dispersion is coated on one side of the plastic support. The coating method can be conventional bar coating, reverse coating, gravure coating, comma knife coating, spray coating, etc. You can choose the most appropriate method.

Drying is urethane crosslinking by thermosetting, but in order to achieve evaporation of the solvent and curing of the coating layer, a temperature of 100 ° C or more and 150 ° C or less is preferable. At 100 ° C. or lower, the curing reaction is slow. When the temperature is higher than 150 ° C., the film state becomes poor due to thermal deformation of the base film. The coating thickness of the prepared light diffusion layer coating layer is 5 to 30 microns is suitable.

(2) plastic support

As the support film, any transparent support surface can be used, and polycarbonate, polypropylene, polyethylene terephthalate, polyethylene, epoxy, and the like are used, and polycarbonate and polyethylene terephthalate are mainly used.

The support used varies depending on whether the composition for light diffusion used is water-soluble or useful, and in the case of oil-soluble composition, a polyester system such as polyethylene terephthalate having excellent mechanical properties and solvent resistance is used. use. Polycarbonate has better overall light transmittance than polyethylene terephthalate and has good adhesion to general polymer resins.However, when the composition is useful, the film surface melts and haze when forming a coating film due to lack of solvent resistance. This appears to be a problem.

Therefore, the polycarbonate film is limited by the composition to be applied because it is necessary to form a coating film with a composition of an alcohol or an aqueous mixed solution. However, water-based or alcohol-based compositions have a high boiling point compared to general solvents, and require a large amount of heat during drying after coating, resulting in a high production cost. In addition, polycarbonate tends to be easily scratched because the hardness of the film surface is weak. In fact, scratches are easily generated by the guide roll or the driving roll when the coating is applied, which causes the diffusion film defects.

Therefore, when using an oil-soluble composition, it is most common to use a polyethylene terephthalate film.

Such a plastic support should have adhesion to the resin to be applied and should not affect the light diffusing layer due to its high light transmittance in itself, and the surface smoothness should be uniform so that there is no variation in luminance.

The thickness of the plastic support is suitably 10 to 1000 microns, preferably 25 to 500 microns. Only at this thickness it has processability and handling as a film, and heat resistance upon mounting. If the thickness is less than 25 microns, there is no workability, and there is a problem such as static electricity when mounting the backlight. The handling property is good at 500 microns or more, but it is not preferable because all parts are thinner.

(3) electromagnetic shielding layer

An electromagnetic shielding layer is formed on one surface of the base film opposite to the surface on which the light diffusion layer is formed, and the electromagnetic shielding layer should be a transparent conductive material.

Transparent conductive materials can be used for both organic and inorganic materials.Inorganic materials can be selected from indium / tin oxide (ITO), ATO (antimony / tin oxide) and various metal oxides. Should have surface resistance less than 1000Ω.

The organic conductive material may be any material having conductivity such as pyrrole, PPV (polyphenylene vinylene), thiophene, and the like, and may be introduced by a dry or wet method.

Such metal oxides are formed into a metal thin film on the opposite side of the light diffusion layer by physical or chemical vapor deposition. The conductive thin film is formed by sputtering, electron beam deposition, ion-plating, spray pyrolysis and CVD. Physical or chemical vapor deposition such as (chemical vapor deposition), and the like.

The thickness of the electromagnetic wave shielding layer thus formed is 10 to 500 nm, preferably 50 to 150 nm.

The transparent thin film must be formed to a thickness of 50 to 150nm to have an antireflection function by the antireflection effect by the thin film of general physics. When the reflection is prevented, the transmittance is increased. The lower layer of the light diffusing film is a portion of the light guide plate through which light is transmitted and exits the front portion. When the reflection is reduced on the lower surface, the luminance is also increased. The surface resistance of the resulting shielding layer is required to have a value of 5000 Ω or less, preferably 1000 Ω or less. This is because the electromagnetic shielding rate is high only at 1000 Ω or less.

In this way, a light diffusion layer made of a transparent organic binder and transparent organic particles is provided on one surface of the plastic support, and a light conductive film having an electromagnetic shielding function can be manufactured by forming a transparent conductive thin film of a metal oxide on the opposite surface.

In the following Examples described in more detail, the examples are used to make the present invention easier to understand, but the present invention is not limited to the following examples.

Example 1

90 parts by weight of acrylic polyol (A-814, Aekyung Chemical) and 10 parts by weight of isocyanate (DN950, Aekyung Chemical) were dissolved in 200 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene as solvents and PMMA particles (PB-010, 100 parts by weight of Kolon) was dispersed, and the composition was dispersed for 1 hour at 20,000 revolutions per minute using a Tego disperser, followed by removing bubbles in the crude liquid for 1 hour, and the crude liquid was polyethylene terephthalate film (FCTT, 125 microns, Kolon). Product, a total light transmittance of 92%) was applied using a gravure roll and dried for 30 seconds at 100 ℃ to prepare a film having a thickness of 12㎛.

An electromagnetic wave shielding layer was formed on the opposite side of the film to have a thickness of 100 nm by DC magnetron sputtering to prepare a light diffusing film of the present invention.

Comparative Example 1

90 parts by weight of acrylic polyol (A-814, Aekyung Chemical) and 10 parts by weight of isocyanate (DN950, Aekyung Chemical) were dissolved in 200 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene as solvents and PMMA particles (PB-010, 100 parts by weight of Kolon) was dispersed, and the composition was dispersed for 1 hour at 20,000 revolutions per minute using a Tego disperser, followed by removing bubbles in the crude liquid for 1 hour, and the crude liquid was polyethylene terephthalate film (FCTT, 125 microns, Kolon). Product, a total light transmittance of 92%) was applied using a gravure roll and dried for 30 seconds at 100 ℃ to prepare a film having a thickness of 12㎛.

There was no separate treatment on the opposite side of the film.

Comparative Example 2

An electromagnetic wave shielding layer was formed on a polyethylene terephthalate film (FCTT, 125 microns, manufactured by Kolon, 92% of total light transmittance) so that ITO was 100 nm thick by DC magnetron sputtering. 90 parts by weight of acrylic polyol (A-814, Aekyung Chemical) and 10 parts of isocyanate (DN950, Aekyung Chemical) are dissolved in 200 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene on the upper surface of the electromagnetic shielding layer. After dispersing 100 parts by weight of PMMA particles (PB-010, manufactured by Kolon), the composition was dispersed for 1 hour at 20,000 revolutions per minute using a Tego dispersion machine, and then bubbles were removed from the crude liquid for 1 hour, and the crude liquid was gravure rolled. After the coating on the electromagnetic wave shielding layer was used to dry for 30 seconds at 100 ℃ to prepare a light diffusion film 13㎛ the overall thickness of the coating film.

The brightness, surface resistance, and total light transmittance of the light diffusing films prepared according to the above Examples and Comparative Examples were shown in Table 1 below. Specific evaluation method is as follows.

(1) brightness

After removing the diffusion sheet used for the 17-inch LM170E01 (Korea Heesung Electronics) model, two sheets of diffusion sheets obtained according to the above examples and comparative examples were lifted, and the average value of 13-point luminance was measured using a BM7 (Topcon Japan) luminance meter. Was obtained.

(2) surface resistance

Keithley238 (Keithley Co., Ltd.) surface resistance meter was used to determine the resistance value.

(3) light transmittance

Total light transmittance (TT) was measured using a haze meter NDH2000 spectrophotometer manufactured by Nippon Denshoku.

Example 1 Comparative Example 1 Comparative Example 2 Luminance (cc㎠) 1980 1975 1950 Surface resistance (ohm) 250 2e12 320 Total light transmittance (%) 91 90 88

As described in detail above, the light diffusing film in which the electromagnetic wave shielding layer is laminated on the opposite side of the light diffusing layer according to the present invention can shield electromagnetic waves with excellent brightness without degrading the light diffusion film for the backlight unit of the TFT-LCD. Useful as

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

<Detailed description of the main symbols in the drawing>

1-light diffusion layer 2-plastic support

3-Electromagnetic shielding layer 10-Diffusion film

Claims (3)

A light diffusion layer formed by applying a composition composed of a transparent organic binder and transparent organic particles is provided on one surface of a base film made of a high transparency plastic, and an electromagnetic wave shielding layer formed of a transparent conductive thin film of metal oxide is provided on the other side of the base film. A light diffusion film having a structure in which an electromagnetic wave shielding layer, a base film, and a light diffusion layer are sequentially stacked from an incident direction of light. The light diffusing film of claim 1, wherein the electromagnetic shielding layer formed of the transparent conductive thin film has a thickness of 50 to 150 nm. The light diffusing film of claim 1, wherein the surface resistance is 1000 ohm or less.