KR20070036595A - Light Diffusion Sheet for Backlight Unit - Google Patents

Abstract

The present invention relates to a light diffusing sheet for a backlight unit of a liquid crystal display device, wherein the light diffusing sheet of the present invention having a plurality of hemispherical protrusions having different sizes of photocurable resin on one surface of a transparent substrate has a hemispherical recess on its surface. The metal sheet may be manufactured using a fixed pattern roll, and may not only be excellent in brightness but also increase the diffusibility in the left and right directions, thereby widening the optical viewing angle of the exit surface.

Description

Light Diffusion Sheet for Backlight Unit {LIGHT DIFFUSION SHEET FOR BACKLIGHT UNIT}

1 is a schematic cross-sectional view showing the configuration of a conventional backlight unit,

2 is a schematic cross-sectional view (a) and a top view (b) of a light diffusion sheet according to the present invention,

Figure 3 schematically shows a manufacturing process of the light diffusion sheet according to the present invention.

The present invention relates to a light diffusion sheet used in a backlight unit of a liquid crystal display and a manufacturing method thereof.

A liquid crystal display (LCD) is a kind of light that displays numbers or images by generating contrast by injecting a liquid crystal, which is an intermediate material between a solid and a liquid, between two thin glass plates and changing the arrangement of liquid crystal molecules by the voltage difference between the electrodes on the upper and lower glass plates. It is a device using a switch phenomenon. The passive matrix method and the active matrix method are classified according to the driving method. The passive matrix method includes TN (Twisted Nematic) and STN (Super Twisted Nematic) methods, and the active matrix method includes TFT (Thin Film Transistor) method. LCDs are widely used in electronic products such as electronic clocks, calculators, liquid crystal TVs, and notebook PCs for speed displays and driving systems of automobiles and aircrafts.

The advantages of such LCDs are low power consumption (1/3 of CRT), low operating voltage, and light and thin processability. On the other hand, the LCD has a narrow viewing angle, difficult to implement a large screen, and low temperature operation.

As a core component of the liquid crystal display device, a backlight unit may be used. The backlight unit is used as a dimming device to evenly transmit light to the entire TFT-LCD panel and displays an image with transmitted light.

 Unlike CRT, PDP, and FED, the screen display by LCD cannot be used without a light source because the liquid crystal device itself is non-light-emitting, and the device that functions as a light source on the LCD and illuminates the information display surface uniformly is backlighted. Unit.

Since the backlight unit is used as a light source for a monitor TFT-LCD and a notebook, a function that needs to emit the brightest light with the minimum power is required. In addition, the backlight unit should play a role of changing the light emitted from the light source to the surface light by maintaining the same brightness to every corner of the LCD surface.

As shown in FIG. 1, components of the backlight unit include a lamp as a light source, a reflector for reflecting light emitted from the lamp, a light guide plate for transmitting light, a mold frame (not shown) for tying components, luminance and a viewing angle. It consists of a light diffusion sheet, a panel, etc., which improves the quality.

The backlight unit is a direct method of directly dimming the front surface of the panel by arranging a light source on one side of the panel, and an edge for reflecting / diffusing light on a light guide plate and a reflective sheet by disposing a light source on one side or multiple sides of the panel. ) Is divided into (or side light). Recently, a side light method in which a light source is disposed on at least one side of a liquid crystal display device has been widely used for manufacturing a small electronic device by reducing the weight and thickness of a backlight unit. On the other hand, in recent years, LCDs for TVs use a unit in which a plurality of light sources are disposed under the light source, a light guide plate is disposed thereon, and a diffusion sheet and a prism are stacked thereon.

As a manufacturing method of the light-diffusion sheet used for a backlight unit, the method of apply | coating the binder resin which disperse | distributed the beads on the surface of a base material is proposed (refer Japanese Unexamined-Japanese-Patent No. 5-73602). That is, this manufacturing method provides the light-diffusion sheet | seat of the structure by which the bead containing light-diffusion layer was laminated | stacked on the base material. As the substrate, a film made of polyethylene terephthalate, polyester, polycarbonate synthetic resin, an acrylic resin or a glass material as a bead, and an acrylic or urethane synthetic resin were used as the binder resin. However, in the case of using the beads, there is a problem that a defect occurs on the screen by dropping the beads when cutting the light diffusion sheet.

As another method for producing a light diffusion sheet, there is a technique of forming irregularities on the surface of a substrate by embossing the substrate of a synthetic resin material. The manufacturing method by the embossing process requires the production of a roll mold with embossing of several tens of microns, which leads to difficulty in the process itself, and it is not easy to form irregularities on the surface that exerts the light diffusing effect on the roll. It is difficult to obtain sufficiently, and problems such as light unevenness due to the surface pattern are likely to occur.

In addition, in Japanese Patent Laid-Open No. 2000-193805, after laminating an ultraviolet curable resin on top of a substrate, the resin is pressed onto the surface of the substrate, a curing process is performed, and a light diffusion sheet is manufactured by a release process in which the substrate is peeled off. . This method has the advantage of improving the brightness compared to the case of using a bead, but there is a problem that bubbles in the resin occurs when laminating the UV-curable resin, and because the resin film is used, pattern damage easily occurs, it is difficult to use long, Since the opposite side of the disc is duplicated, it is a factor that lowers the luminance in geometrical structure.

 SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems of the prior art as described above, and to provide a light diffusion sheet for a backlight unit having excellent luminance characteristics and further increasing the diffusivity in the left and right directions to widen the viewing angle of the exit surface. To provide.

In order to achieve the above object, the present invention provides a light diffusing sheet for a backlight unit, characterized in that a photocurable resin layer having a plurality of hemispherical protrusions having different sizes is laminated on one surface of a transparent substrate.

In the present invention, the photocurable resin composition is coated on either the pattern roll A or the transparent base material B on which a metal sheet having a plurality of different hemispherical recesses is fixed on the surface thereof, and the coating surface is coated. Manufacturing the light diffusion sheet for the backlight unit, characterized in that for carrying out the compression-curing process in contact with the other side of the (A) and (B), and then release the transparent base film having a hemispherical convex portion formed from the pattern roll. Provide a method.

Hereinafter, the present invention will be described in more detail.

The light diffusion sheet for a backlight unit according to the present invention is characterized in that hemispherical protrusions having different sizes of photocurable resins are formed on one surface of the transparent substrate.

Figure 2 schematically shows the structure of a light diffusion sheet according to a preferred embodiment of the present invention. According to Fig. 2 (a) (cross-sectional view), the photocurable resin layer in which the several projection part of the hemispherical shape was formed was laminated | stacked on one surface of the polyethylene terephthalate (PET) film which is a transparent base material, and the space between protrusion parts is laminated | stacked here. Silver, both ends of the projections are formed lower than the base surface can form an arc, this structure further improves the brightness. The transparent substrate may be treated with a primer layer prior to forming the protrusions. 2B is a top view showing a state in which the protrusions are randomly distributed on the PET substrate in the light diffusion sheet.

In the present invention, the projections of the photocurable resin formed on the transparent substrate is characterized in that they have different sizes within the size of the range of about 10 to 100 ㎛, preferably 50 to 90 ㎛ range, these different The protrusions of size increase the light diffusing effect and provide the effect of improving the brightness and the haze.

It is preferable that such protrusions occupy 50 to 90% of the total surface area of the sheet. In this case, when the filling rate of the protrusions is less than 50%, the luminance decreases, and when the protrusions are larger than 90%, it is impossible due to technical limitations.

For example, as shown in FIG. 3, the light-diffusion sheet according to the present invention is coated with a photocurable resin composition on a pattern roll on which a metal sheet having a hemispherical recess is fixed to a surface, and cured by laminating a transparent substrate thereon and pressing it. After performing a process, it can manufacture by releasing a transparent base film from a pattern roll.

The photocurable resin composition may be applied onto a pattern roll as described above, or may be coated on a transparent base surface, and then laminated so as to contact the pattern roll to perform a compression curing process.

The metal sheet having a hemispherical recess, which is to be fixed on the pattern roll, may be formed by coating a polyethylene resin on a transparent film such as polyester, and then melting a surface of the polyethylene resin to form a plurality of spherical beads having different sizes on the surface. It can be prepared by supplying a bead layer, attaching the bead-containing transparent film to the plate-shaped mold inner wall, and then forming a metal sheet by electroplating on the bead-formed surface, and then releasing it from the bead-containing film. In this case, the metal sheet may be a metal material such as nickel, zinc, tin, and the like, and may further plate chromium (Cr), and the like, and form a thickness of 0.5 to 2.0 mm.

In addition, the metal sheet having the hemispherical concave portion, the metal sheet is formed by electroplating on a film having a plurality of hemispherical protrusions of different sizes formed by the transparent film containing the beads, and then the metal from the film having the hemispherical protrusions Sheets can be made by releasing.

The transparent substrate used in the present invention is not particularly limited as long as it is a material that transmits active energy such as ultraviolet rays, visible rays, and electron beams, and specific examples thereof include flexible polyester resins, acrylic resins, polycarbonate resins, vinyl chloride resins, and poly Methacrylamide type resin etc. are mentioned. In particular, polyesters such as polymethyl methacrylate, polymethyl acrylate and a mixture of polyvinylidene fluoride-based resins, polycarbonate-based resins, polyethylene terephthalates, etc., having a lower refractive index than the refractive index of the pattern portion It is preferable to use resin. 50-200 micrometers is suitable for the thickness of such a transparent base material.

The photocurable resin used in the present invention is not particularly limited as long as it is cured by active energy rays such as ultraviolet rays and electron beams. Specific examples thereof include polyesters, epoxy resins, polyester (meth) acrylates, and epoxy (meth) s. (Meth) acrylate type resins, such as an acrylate and a urethane (meth) acrylate, etc. are mentioned. Of these, (meth) acrylate resins are particularly preferred from the viewpoint of optical properties and the like. The photocurable resin preferably has a refractive index in the range of 1.24 to 1.60.

The photocurable resin composition for producing such a photocurable resin is a polyhydric acrylate and / or a polyhydric methacrylate (hereinafter referred to as polyvalent (meth) acrylate), monoacrylate, and / Or monomethacrylate (hereinafter referred to as mono (meth) acrylate) and a photopolymerization initiator as a main component. Representative polyvalent (meth) acrylates include polyol poly (meth) acrylates, polyester poly (meth) acrylates, epoxy poly (meth) acrylates, urethane (meth) acrylates, or mixtures thereof. . As mono (meth) acrylate, monoalcohol mono (meth) acrylic acid ester, polyol mono (meth) acrylic acid ester, etc. can also be used. In the latter case, when using a metal type, due to the influence of free hydroxyl groups, It is preferable to use it in small quantity in order to reduce mold release difficulty with the metal mold | type considered, and when using a metal mold | die, since it has high polarity also about (meth) acrylic acid and its metal salt, it is good to use it in small quantity.

The coating method may be any method that can be commonly used in the field of the present invention, but preferably, a roll coating method using gravure roll, reverse gravure roll, micro gravure roll, or the like, using mayer bar, die coating, or the like The bar coating method and the coating method using an air knife can be used.

In addition, in the present invention, the photocurable resin composition is preferably coated on a pattern roll or a transparent substrate with a thickness of 5 to 50 μm, and the coating amount is on the size of a hemispherical recess on a metal sheet fixed on the pattern roll. It may vary.

According to a preferred embodiment of the present invention, in order to improve the coating properties and adhesion performance with the photocurable resin on one surface of the transparent substrate, an anchor coat treatment, primer treatment using an organic solvent, or a primer using a water dispersible composition Forming a layer is more effective.

Preferred resins for forming the primer layer are thermosetting polyurethane resins, which are prepared by condensation polymerization of saturated or unsaturated dicarboxylic acids with alkylene glycols having 2 to 8 carbon atoms, and reacting a polyisocyanate with a polyester polyol containing active hydrogen atoms. It is prepared by forming a precursor and reacting the precursor with bisulfite salts of alkali or alkaline earth metals.

At this time, the polyester polyol is saturated or unsaturated dicarboxylic acid, such as succinic acid, adipic acid, sebacic acid, phthalic acid, maleic acid, and ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, neopentyl glycol and hexylene It is prepared by polycondensing alkyleneglycols such as glycol and the like. Examples of the polyisocyanate include 2,4- or 2,6-tolylene diisocyanate, xylene diisocyanate, 4,4-diphenylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate And aliphatic diisocyanate.

In addition, the primer layer further includes conventional inorganic lubricants such as silica, alumina, talc and the like to improve the activity and winding property, and if necessary, antistatic agents, wetting agents, pH adjusting agents, antioxidants, dyes, pigments, slips. Other additives such as agents may be further included within the scope of not impairing the effects of the present invention.

On the other hand, it is preferable that the thickness of the said primer layer is 0.001-1 micrometer, and content of polyurethane in a primer layer is 0.01-0.5 g / m <^2> . If the thickness of the primer layer is less than 0.001 μm, the coating property is poor, whereas if the thickness of the primer layer is more than 1 μm, the adhesion with the laminated or coated polymer resin may be deteriorated.

The light diffusion sheet of the present invention prepared as described above has a level of 80 to 95% of haze, and when the haze is less than 80%, a desired diffusion effect cannot be obtained, and when it exceeds 95%, sufficient luminance cannot be obtained. none. In addition, the preferred light transmittance of the light diffusion sheet according to the present invention is 50 to 75%, when the transmittance is less than 50% can not be obtained high luminance, if it exceeds 75% can not expect the diffusion effect.

Since the light diffusing sheet according to the present invention does not contain beads, it is possible to obtain high luminance compared to the bead containing sheet during light diffusion, and it is not necessary to manufacture a special structure mold as in the embossing method, thereby preventing product defects due to mold damage. In addition, it is possible to significantly reduce the bubble generation problem caused by the method of directly laminating the photocurable resin on the substrate.

Hereinafter, a concrete embodiment of the present invention will be described in more detail. The following examples are merely illustrative to assist in understanding the present invention and are not intended to limit the scope of the present invention.

Example 1

Forming a polyethylene coating layer on a 125 μm-thick polyethylene terephthalate film (manufactured by SH-71 SKC) and applying heat at 120 ° C., spraying glass beads having different diameters in the range of 30 to 60 μm thereon, It was pressed to contain beads on a PET film. The Ni-plated thin film was formed to a thickness of 0.5 to 1.5 mm by electroplating on the PET film to which the glass beads were pressed. The patterned roll was produced by releasing a Ni plating thin film and fixing it on the roll surface.

Refractive index 1.49, UV curable resin (WOW149, WOW Chemical) coated on the surface of the pattern roll with a thickness of 20 ㎛, a transparent PET film coated with a thermosetting polyurethane resin 0.03 ㎛ thickness (SH-71, manufactured by SKC) The step of laminating and then pressing was performed to perform a curing process by an ultraviolet curing lamp while forming a plurality of protrusions made of ultraviolet curable resin on the transparent PET film.

Example 2

The same process as in Example 1 was performed except that an ultraviolet curable resin (A-BPE-10, manufactured by NK ESTER) having a refractive index of 1.52 was used as the photocurable resin.

Example 3

The same process as in Example 1 was performed except that an ultraviolet curable resin (U-06, manufactured by KYOEISHA) having a refractive index of 1.55 was used as the photocurable resin.

Example 4

The same process as in Example 1 was performed except that an ultraviolet curable resin (WOW157, manufactured by Wow Chemical) having a refractive index of 1.57 was used as the photocurable resin.

Example 5

The same process as in Example 1 was carried out except that an ultraviolet curable resin (U-60, manufactured by Shin-Nakamura, Japan) having a refractive index of 1.47 was used as the photocurable resin.

Example 6

The same process as in Example 1 was carried out, except that 90% or more containing in the range of 40 to 90 μm in size was used as the beads.

Comparative example

According to a conventional method for producing a light diffusion sheet, 21.4 parts by weight of acridic AA-960-50 (Aekyung Chemical) as a binder and 41.4 parts by weight of n-butyl acetate as a solvent and Brunnock DN-950 (Aekyung Chemical) as a curing agent After dissolving 2.9 parts by weight, 30.3 parts by weight of Techpolymer MBX-15 (Sekisui), a light diffusing agent, was added with stirring to prepare a dispersion. Thereafter, the dispersion liquid prepared above was applied to one surface of a transparent PET film (SH-71, manufactured by SKC Co., Ltd.) coated with a thermosetting polyurethane resin at a thickness of 0.03 μm in a thickness of 10 μm, and then thermally cured at 100 to 120 ° C. To make a light diffusion sheet.

Test Example

Haze, light transmittance and luminance were measured for the light diffusing sheets prepared from Examples 1 to 6 and Comparative Examples, and the results are shown in Table 1 below. In this case, the luminance was measured by using a luminance meter (BM-7) for each sheet and two sheets, respectively, and haze and light transmittance using a hazemeter (NDH 5000, manufactured by Densho Kogyo Co., Ltd.). It was measured by.

From Table 1, it can be seen that the light diffusion sheet of the present invention is generally excellent in terms of haze, light transmittance, and luminance.

Since the light diffusing sheet of the present invention does not contain beads, the luminance is higher than that of the light diffusing sheet, and there is no problem such as foreign matter mixing due to the dropping of beads when the sheet is cut. have.

Claims (17)

A light diffusion sheet for a backlight unit, wherein a photocurable resin layer having a plurality of hemispherical protrusions having different sizes is laminated on one surface of the transparent substrate. The method of claim 1, A light-diffusion sheet, wherein both ends of the hemispherical protrusion are lower than the base surface to form an arc between the protrusion and the protrusion. The method of claim 1, A light diffusing sheet, wherein the protrusion comprises 50 to 90% of the total surface area of the sheet. The method of claim 1, Light diffusion sheet, characterized in that the projections have a size in the range of 10 to 100 ㎛ diameter. The method of claim 4, wherein Light diffusion sheet, characterized in that the projections having a diameter in the range of 40 to 90 ㎛ 90% or more. The method of claim 1, A light diffusion sheet, wherein a primer layer is formed between the transparent substrate and the photocurable resin layer. The method of claim 6, A light diffusion sheet comprising a primer layer comprising polyurethane. The method of claim 1, The photocurable resin is polyester type, epoxy type, and (meth) acrylate type resin, The light-diffusion sheet characterized by the above-mentioned. The method of claim 1, A light diffusion sheet wherein the photocurable resin has a refractive index of 1.42 to 1.60. The method of claim 1, A light diffusion sheet characterized by exhibiting haze in the range of 80 to 95%. The photocurable resin composition is coated on either the pattern roll (A) or the transparent base material (B) having a metal sheet having a plurality of hemispherical recesses of different sizes fixed on the surface thereof, and the coating surface is coated with (A) and ( A method for manufacturing the light-diffusion sheet for a backlight unit according to claim 1, wherein the transparent base film having the hemispherical convex portion is released from the pattern roll after performing a compression hardening process by contacting with the other side of B). The method of claim 11, A metal sheet having a hemispherical recess is formed from a bead-containing film after forming a metal thin film on the bead-containing transparent film, or a metal thin film is formed on a film having a plurality of hemispherical protrusions having different sizes formed on one surface of the transparent substrate. And forming by releasing from the film having protrusions after forming. The method of claim 11, Wherein the metal sheet consists of a nickel or nickel / chromium composite layer. The method of claim 11, The metal sheet has a thickness of 0.5 to 2 mm. The method of claim 11, And wherein the photocurable resin composition comprises a mono (meth) acrylate, a polyvalent (meth) acrylate, and a photopolymerization initiator. The method of claim 11, The photocurable resin composition is coated with a thickness of 5 to 50 ㎛. The method of claim 11, It is used after forming a primer layer in a transparent base film.

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