KR20040078188A - Reflective film for backlight unit - Google Patents

Abstract

PURPOSE: A reflective film for a back light unit is provided to apply a chemical solution, which distributes more than one kind of inorganic particles to a binder, to a section of a white foam polyester material film, thereby realizing excellent reflectivity and heat resistance. CONSTITUTION: A reflective film(6) consists of a white foam polyester material film layer(11) and a concealing layer(12) which distributes inorganic particles containing titanium oxides to a binder. The concealing layer(12) distributes more than one kind of the inorganic particles to the transparent binder, and applies the distributed particles to a section of a white foam polyester material film which is 50 to 300 micrometers in thickness. Transmissivity of total lights is between 0.1 and 6%.

Description

Reflective film for backlight unit {Reflective film for backlight unit}

The present invention relates to a reflective film for a backlight unit, and more particularly, to a high hiding property including a concealing layer coated with a solution in which one or more inorganic particles including a binder and titanium oxide are dispersed on a cross section of a white foamed polyester base film. , Reflecting film of high reflectivity

Currently, display apparatuses are gradually being enlarged and thinned in the center of the conventional CRT, and have been developed in a dual format such as miniaturized and thinned display apparatuses as personal portable devices such as notebook computers, mobile phones, and PDAs have appeared. All of them have a common goal of thinning, high brightness, and high resolution to reduce product thickness compared to existing devices, and TFT-LCD, PDP, and organic EL are the common targets. Since the TFT-LCD has no light source that emits light by itself, an external light source is required. A backlight was introduced for this.

Recently, as the use of LCD displays has been expanded from monitors for notebook computers to monitors for large desktop computers and TV monitors, large screens, low power consumption, and high brightness of LCD displays are required. The most important problem in responding to these requirements is the large screen, low power, and high brightness of the backlight unit that makes the light source of the LCD display.

Recently, many attempts have been made to eliminate the backlight unit itself. However, due to the basic characteristics of LCDs, it is currently impossible to form a screen without a separate light source, such as a self-luminous EL element.

As shown in FIG. 1, the film structure of a general backlight unit includes a prism protective film 1, a prism 2, a diffusion film 3, a light guide plate 4, a backlight 5, and a reflective film 6. consist of.

In the backlight unit, the reflective film plays a role of emitting light from the horizontal light source lamp on one side or the back of the LCD display to uniform light on the front of the screen and preventing light leakage on the back of the LCD display. The reflective film is located at the rear of the backlight unit to conceal the frame supporting the backlight unit, and at the same time prevents light leakage of the light from the backlight and increases the brightness by reflecting to the front as much as possible.

This reflective film uses a white polyester film with good reflection efficiency as a base film, and serves to conceal the frame by coating a coating film to give concealability to it again, and also conceal the selection of particles and coating thickness. Attempts are being made to impart gender and high brightness.

That is, it is coated with an opaque concealed coating composition using inorganic particles for high reflection and hiding efficiency, and the base film is also used to increase reflection and hiding efficiency by using an opaque white polyester film.

In addition, the trend toward larger LCD monitors and the development of LCD TVs is increasing the number of products that use two or more backlight lamps. Therefore, the film for backlight requires heat resistance and minimum heat deformation. That is, the reflective film is required to have high concealability with low total light transmittance, thermal stability, adhesion strength and mechanical properties of the coated particles with the base film during the vibration test.

Korean Patent Laid-Open Publication No. 2002-0029374 discloses a method of making a reflective article and a substrate using a thermally induced phase separation technique, in which a support having a porous polyolefin structure is disclosed. And a first surface having a surface member for reducing the optical coupling with the polyolefin structure.

In addition, Japanese Patent Laid-Open Nos. 2002-98811, 2002-98808, 2002-138150, 2002-050222, 2001-305321, 2001-228313, 2001-226501 and 2001- In 166115, a reflective film has been developed that is characterized by a specific structure, light content, refractive index of particles, reflectance, total light transmittance, and partial melting temperature.

In Korea, Korean Patent Publication Nos. 2000-061237, 2000-027220, 2000-027218, 2000-027217, 2000-027216, 2000-025873, 2000-025195, 2000 -018676, 2000-018675 and 1997-065608 have developed a white printable film having excellent printability which can be used as a packaging material or paper substitute by copolymerizing polyester and polyolefin resin. Such a white polyester film is suitable as a base material of a reflecting film because its total light transmittance is 10% or less and its reflectance is 85% or more, which is superior to general polyester in terms of concealment and reflectance.

In addition, the technology related to the manufacturing method of the backlight unit for a liquid crystal display using a reflective film such as a reflective film, a reflector, a reflection sheet, and the like, Korean Patent Publication Nos. 2002-047534, 2002-045818, 2002-040601, 2002 Many other technologies have been developed in addition to -034762, 2002-030714, 2001-106393, 2001-063796, and 2001-055378. These techniques only mention how to assemble a reflective article or describe the structure of the final backlight unit.

Accordingly, the present inventors have made efforts to manufacture the above-mentioned highly concealable, high reflectivity reflective film, while transparent or opaque a crude liquid obtained by dispersing one or more inorganic particles containing titanium oxide having a concealment and reflection effect in a binder. As a result of coating the cross section of the white foamed polyester substrate film to produce a reflective film for a backlight unit, it was found that the reflectance was high and the heat resistance was excellent, thereby completing the present invention.

Accordingly, an object of the present invention is to provide a reflective film for a backlight unit having high reflectance and excellent heat resistance.

The reflective film for a backlight unit of the present invention includes a concealed layer coated with a dispersion of titanium oxide or one or more inorganic particles including the same in a transparent binder on a cross section of a 50 to 300 μm-thick white foamed polyester base film. The transmittance is characterized by being 0.1 to 6%.

1 shows a film structure of a backlight unit,

Figure 2 shows a reflective film for a backlight unit of the present invention.

<Description of Drawing>

1: prism protective film 2: prism

3: diffuser film 4: light guide plate

5: backlight 6: reflective film

11: white foamed polyester base film layer

12: Concealed layer in which inorganic particles containing titanium oxide were dispersed in a binder

Hereinafter, the present invention will be described in detail.

The present invention relates to a reflective film for a backlight unit for use in an LCD display comprising a concealed layer coated with a transparent binder of a crude liquid obtained by dispersing inorganic particles in a cross section of a white foamed polyester base film.

As shown in FIG. 2, the reflective film of the present invention is composed of a white foamed polyester base film layer 11 and a concealed layer 12 in which inorganic particles containing titanium oxide are dispersed in a binder.

As a base film used for this invention, the white foam polyester film copolymerized and foamed by 2 or more types of monomers which are not compatible is used. When the white foamed polyester film is used as the base film, a reflective film having a total light transmittance of 6% or less is produced, which is advantageous in terms of concealment.

The thickness of the white foamed polyester film is suitably 50 to 300 µm, and preferably 90 to 250 µm. Only at this thickness it has the processability, handling and heat resistance of the film.

This is because if the thickness of the base film is less than 50 μm, the concealability of the product is lowered. If the thickness of the base film is more than 300 μm, the backlight unit is thickened, making it difficult to thin the product.

The concealment layer of the present invention prevents light emitted from the lamp from leaking to the rear side and at the same time has the effect of reflecting to the front of the backlight unit to increase the brightness of the liquid crystal display. Therefore, the lower the total light transmittance of the concealed layer, the better the concealing effect, and the higher the reflectance, the greater the luminance improvement effect.

Such a concealed layer is obtained by dispersing at least one inorganic particle containing titanium oxide in at least one transparent binder.

In the present invention, in order to improve the concealability of the concealment layer, inorganic particles having no compatibility with an organic binder are used, and thus, the transparent binder should have a strong adhesion to the white polyester film used as the base film. In addition, since the reflective film is mounted adjacent to the backlight, the thermal deformation due to the heat of the lamp should not occur and the basic mechanical properties should be excellent.

Therefore, in the present invention, a white foamed polyester film used as the base film and a resin having good adhesiveness are used, for example, unsaturated polyester, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal Butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, acrylamide, metyrolacrylamide, glycidyl methacrylate Resin, such as an acryl-type, urethane type, an epoxy type, and a melamine type, such as a acrylate, ethyl acrylate, isobutyl acrylate, a normal butyl acrylate, a 2-ethylhexyl acrylate polymer, a copolymer, or a terpolymer is used.

In the case of an acrylic binder, in order to improve heat resistance, abrasion resistance, and adhesiveness, it uses the hardening film of a resin using a hardening agent.

In addition, in the present invention, the inorganic particles are used to impart concealment, because the inorganic particles are superior in concealability to the organic particles. As the inorganic particles of the present invention, titanium oxide may be used alone, or inorganic particles selected from aluminum paste, aluminum powder, silicon oxide, aluminum oxide, zirconium oxide, magnesium fluoride, barium sulfate, and calcium carbonate may be mixed with titanium oxide. have.

Inorganic particles used in the concealed layer have a great influence on the reflectance and the total light transmittance according to the refractive index and the light characteristics of the particles themselves. The size of the particles used depends on the thickness of the coating film, but particles of 10 μm or less are preferred.

It is also possible to mix and use different kinds of particles in order to increase the concealment efficiency.These particles may have different transmittance and reflection efficiency depending on the ratio contained in the resin, the coating thickness, and the mixing ratio between particles when two or more kinds of particles are used. Will be different.

Therefore, in order to show high concealment and reflection efficiency, it is preferable to contain 100 to 400 parts by weight of particles with respect to 100 parts by weight of the transparent binder when the coating film thickness is 1 to 50 μm.

When the particle content is less than 100 parts by weight, the total light transmittance is increased, and the concealability is insufficient. When the particle content is more than 400 parts by weight, problems such as particle aggregation and surface protrusion due to excessive particles and fine dispersion occur.

Meanwhile, dispersants for uniform dispersion in dispersing the inorganic particles in the transparent binder include acrylic emulsions, modified silicones, polydimethylsiloxanes, fluorides, and the like. Only a small amount, which is not used, is preferably used within 0.1% to 10% by weight based on 100 parts by weight of the transparent binder.

In addition, the dispersion stabilizer is mixed together to prevent precipitation of particles, and the content thereof is prepared by adding 0.1 to 10 parts by weight based on 100 parts by weight of the binder.

The concealed layer crude liquid thus prepared is applied onto the white foamed polyester film by a comma, knife or gravure coating method, and the thickness of the coating film is preferably 1 to 50 µm.

When the thickness of the coating film is less than 1 μm, the adhesion between the coating layer and the particles decreases, and when the thickness of the coating film is more than 50 μm, the product becomes thicker, and thus it is difficult to mount the backlight unit.

In this case, the amount applied is applied to 50 to 100g per square meter based on the crude liquid, 10 to 50g based on the dry weight after coating may have a suitable optical and mechanical properties as a reflective film.

If the coating amount during the coating is less than 10g / ㎡, there is a lack of concealability, and if the coating amount exceeds 50g / ㎡ occurs a problem that the thickness of the product becomes thick.

As described above, by applying a concealment layer to the white foamed polyester substrate film to produce a reflective film for the backlight unit, the thus prepared reflective film has a total light transmittance of 0.1 to 6% and a haze of 90 to 100%. The reflectivity on the uncoated surface is 85% or more at the wavelength of light of 400 to 700 nm.

Hereinafter, the present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Example 1

5 parts by weight of a dispersant (Disperbyk-161, manufactured by BYK) was dissolved in 500 parts by weight of methyl ethyl ketone in 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and titanium oxide particles having an average particle diameter of 0.5 μm (Dupont) Co., Ltd.) and aluminum particles (manufactured by Kokuda Co., Ltd.) were dispersed in a weight ratio of 20: 1 to disperse 300 parts by weight of inorganic particles to prepare a concealed layer crude liquid.

The concealed layer prepared solution was coated on a 188 μm white foamed polyester base film E60L (manufactured by Toray Corporation) by a gravure coating method to form a concealed layer having a thickness of 25 μm.

The film properties, total light transmittance, and reflectance of the thus prepared reflective film were evaluated in the following manner, and the dimensional stability and heat resistance were evaluated by evaluating optical properties and heat shrinkage, and the results are shown in Table 2 below.

(1) coating properties

Observation of the adhesion with the film and the appearance of the coating film (with or without fisheye, pinhole, and cratering) was made by visual observation. If the adhesion with the substrate is good, it is good if it drops a little. If there is at least one dot, the hatch is defective.

(2) Total Light Transmittance (TT) and Turbidity (Haze)

Nippon Denshoku's haze meter NDH2000 and COH300A are used to measure 40 x 40 mm film samples and measure total light transmittance (TT) and haze.

(3) reflectance

Shimzu's UV / Vis / IR spectrometer UV3101-PC mounts a 40 x 40 mm film sample and measures the reflectance for each wavelength.

(4) luminance

After cutting the reflective film to 14.1 inches, it is mounted directly on the 141X4-156, which is 14.1 inches, as a backlight, and the luminance is evaluated using a BM7 luminance meter manufactured by TOPCON.

(5) heat resistance

After leaving for 15 minutes in a hot air dryer at 150 ℃ is evaluated by measuring the rate of dimensional change caused by the shrinkage or expansion of the film.

Example 2

5 parts by weight of a dispersant (Disperbyk-161, manufactured by BYK) was dissolved in 500 parts by weight of methyl ethyl ketone in 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and titanium oxide particles having an average particle diameter of 0.5 μm (Dupont) Co., Ltd.) and aluminum particles (manufactured by Kokuda Co., Ltd.) were dispersed in an amount of 200 parts by weight of the inorganic particles to prepare a concealed layer crude liquid.

The concealed layer prepared solution was coated on a 188 μm white foamed polyester base film E60L (manufactured by Toray Corporation) by a gravure coating method to form a concealed layer having a thickness of 25 μm.

The film properties, total light transmittance, and reflectance of the thus prepared reflective film were evaluated in the following manner, and the dimensional stability and heat resistance were evaluated by evaluating optical properties and heat shrinkage, and the results are shown in Table 2 below.

Example 3

5 parts by weight of a dispersant (Disperbyk-180, manufactured by BYK) was dissolved in 400 parts by weight of methyl ethyl ketone in 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and titanium oxide particles having an average particle diameter of 0.5 μm (Dupont) Co., Ltd.) and aluminum particles (manufactured by Kokuda Co., Ltd.) were dispersed in an amount of 25 parts by weight of inorganic particles to prepare a concealed layer crude liquid.

The concealed layer prepared solution was coated on a 188 μm white foamed polyester base film E60L (manufactured by Toray Corporation) by a gravure coating method to form a concealed layer having a thickness of 30 μm.

The film properties, total light transmittance, and reflectance of the thus prepared reflective film were evaluated in the following manner, and the dimensional stability and heat resistance were evaluated by evaluating optical properties and heat shrinkage, and the results are shown in Table 2 below.

Example 4

5 parts by weight of a dispersant (Disperbyk-180, manufactured by BYK) was dissolved in 500 parts by weight of methyl ethyl ketone in 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and titanium oxide particles having an average particle diameter of 0.8 μm (Dupont) Co., Ltd.) and aluminum particles (manufactured by Kokuda Co., Ltd.) were dispersed in an amount of 250 parts by weight of inorganic particles to prepare a concealed layer crude liquid.

The concealed layer prepared solution was coated on a 188 μm white foamed polyester base film E60L (manufactured by Toray Corporation) by a gravure coating method to form a concealed layer having a thickness of 25 μm.

The total light transmittance and reflectance of the thus prepared reflective film were evaluated by the following method, and the dimensional stability and heat resistance were evaluated by evaluating optical properties and heat shrinkage, and the results are shown in Table 2 below.

Comparative Example 1

5 parts by weight of a dispersant (Disperbyk-161, manufactured by BYK) was dissolved in 500 parts by weight of methyl ethyl ketone in 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and titanium oxide particles having an average particle diameter of 0.5 μm (Dupont) Co., Ltd.) and aluminum particles (manufactured by Kokuda Co., Ltd.) were dispersed in an amount of 250 parts by weight of inorganic particles to prepare a concealed layer crude liquid.

The prepared concealed layer crude solution was coated on a 125 μm transparent polyethylene terephthalate-based film FCTT (manufactured by Kolon Corporation) by a gravure coating method to form a concealed layer having a thickness of 25 μm.

The film properties, total light transmittance, and reflectance of the thus prepared reflective film were evaluated in the following manner, and the dimensional stability and heat resistance were evaluated by evaluating optical properties and heat shrinkage, and the results are shown in Table 2 below.

Comparative Example 2

5 parts by weight of the dispersant Disperbyk-180 (manufactured by BYK) in 500 parts by weight of methyl ethyl ketone was dissolved in 100 parts by weight of polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and titanium oxide particles (manufactured by DuPont) and aluminum particles were added thereto. 250 parts by weight of inorganic particles obtained by mixing the product (manufactured by Kokuda Co., Ltd.) at a ratio of 20: 1 was prepared to prepare a concealed layer crude liquid.

The prepared concealed layer crude solution was coated on a 125 μm transparent polyethylene terephthalate-based film FCTT (manufactured by Kolon Corporation) by a gravure coating method to form a concealed layer having a thickness of 20 μm.

Comparative Example 3

5 parts by weight of the dispersant Disperbyk-180 (manufactured by BYK) was dissolved in 500 parts by weight of methyl ethyl ketone in 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.), and an organic polymethyl methacrylate having an average particle diameter of 2 μm was added thereto. 250 parts by weight of particles (MPB-HX2 Kolon, Inc.) were dispersed to prepare a concealed layer crude liquid.

The concealed layer prepared solution was coated on a 188 μm white foamed polyester base film E60L (manufactured by Toray Corporation) by a gravure coating method to form a concealed layer having a thickness of 25 μm.

The film properties, total light transmittance, and reflectance of the thus prepared reflective film were evaluated in the following manner, and the dimensional stability and heat resistance were evaluated by evaluating optical properties and heat shrinkage, and the results are shown in Table 2 below.

division Example Comparative example One 2 3 4 One 2 3 Coating property Adhesion Good Good Good Good Good Good Good Exterior Good Good Good Good Good Good Good Optical properties Concealable Good Good Good Good Bad Bad Bad Total light transmittance (%) NDH2000 3.8 2.5 4.0 2.4 27.3 25.2 10.5 COH300A 3.4 2.2 3.6 2.0 26.8 24.8 8.6 Turbidity (%) NDH2000 99.3 99.5 99.0 98.8 99.2 99.2 98.3 COH300A 93.4 93.5 93.3 93.0 93.1 93.6 93.0 Reflectivity (400-700 nm,%) 93-95 94-96 93-95 93-95 88-90 86-88 87-88 Luminance (cd / m ² ) 1720 1735 1710 1720 1710 1700 1702 Heat resistance Dimensional strain (%) 0.5 0.3 0.3 0.5 0.4 0.4 0.3

From the results of Table 2, in the case of using a white foamed polyester film as a base film, Comparative Example 1, Comparative Example 2 and Comparative Example 3 using organic particles instead of inorganic particles containing titanium oxide, high total light transmittance is poor hiding performance The reflectance is 90% or less.

As described in detail above, the reflective film formed by applying a concealed layer in which inorganic particles containing titanium oxide is dispersed on the cross section of the white foamed polyester substrate film has low reflection efficiency and excellent concealability. It has high brightness.

Claims (5)

50-300 μm thick white expanded polyester base film comprising a concealed layer coated by dispersing titanium oxide or one or more inorganic particles including the same in a transparent binder on a cross section, and having a total light transmittance of 0.1 to 6%. Reflective film. The reflective film of claim 1, wherein the inorganic particles are included in an amount of 100 to 400 parts by weight based on 100 parts by weight of the binder. The reflective film for a backlight unit according to claim 1 or 2, wherein the inorganic particles are selected from aluminum paste, aluminum powder, silicon oxide, aluminum oxide, zirconium oxide, magnesium fluoride, barium sulfate and calcium carbonate. The method of claim 1, wherein the coating layer has a coating thickness of 1 to 50㎛ based on the dry thickness, the coating weight is a reflective film for a backlight unit, characterized in that 10 to 50g / ㎡ on the basis of dry weight. The reflective film of claim 1, wherein the manufactured reflective film has a turbidity of 90 to 100% and a reflectance on an uncoated surface of 85% or more at a wavelength of 400 to 700 nm.