KR101132503B1 - Reflection sheet - Google Patents

Abstract

The present invention relates to a reflective sheet, and more particularly, using a polycarbonate-based resin as a base resin, a base layer containing microbubbles with an average particle diameter of 50 μm or less, and ultraviolet rays formed on one or both sides of the base layer. The inclusion of the barrier layer provides a reflecting sheet having excellent folding properties, high concealability and high reflectance, and excellent weather resistance.

Reflective sheet, polycarbonate resin, supercritical fluid, micro bubbles, UV protection

Description

Reflection Sheet {Reflection sheet}

The present invention relates to a reflective sheet, and more particularly to a reflective sheet for a backlight unit of a liquid crystal display.

Recently, liquid crystal displays, which are used as main components of TVs, desktop computers, notebooks, mobile phones, etc., use a liquid crystal layer of non-light-emitting materials, so a separate light source must be installed, and the side or rear side of the light source reflects the light emitted to the rear part. In order to install the reflective sheet. The reflected light is emitted to the front while passing through a diffusion plate, a light guide plate, a diffusion film, and a brightness improving sheet.

Here, the reflective sheet should have reflectivity to reflect the light of the light source lamp to improve the brightness to the extent that the liquid crystal screen does not flash and concealment so that devices, frames, and the like arranged on the rear surface of the backlight unit are not identified.

Conventionally, as the reflection sheet, a white pigment such as titanium oxide is dispersed in a sheet made of synthetic resin, a metal deposition film is laminated on the surface, and bubbles are dispersed to scatter light in the sheet made of synthetic resin. .

However, when the white pigment is dispersed, the amount of pigment should be increased to suppress the leakage of light to the back side. Since the white pigment absorbs light of a specific wavelength, the amount of the addition increases the light loss and the reflectance is deteriorated. .

In addition, when the metal deposition treatment on the surface, there is a problem that the manufacturing cost is high first, and because the diffuse reflection is difficult to occur, there is a problem that the luminance stain occurs even in the slight distortion of the sheet. In the case of vapor deposition, there is a problem in that high luminance cannot be obtained depending on the type of metal, or weather resistance is insufficient, so that deterioration proceeds quickly, resulting in deterioration of luminance over time.

On the other hand, in order to form a bubble in the sheet | seat made of synthetic resin, the method of extending | stretching or foaming is used.

The "light reflector and light reflector" of Korean Patent No. 200200 is a light reflector in which a UV protective layer is laminated on at least one surface of a substrate to which an inorganic filler is added to a polyolefin resin, which is stretched in an area ratio of 1.5 to 20 times and has a wavelength. A light reflector is disclosed in which a light reflectance of 550 nm is 95%.

Japanese Patent Laid-Open No. 4-239540 discloses a porous film drawn from a polyester film containing 2 to 25% by weight of polyolefin and a porous film drawn from a porous film and a polyester film containing from 5 to 25% of inorganic particles. The white polyester film which laminated | stacked was disclosed. In this case, since the amount of the inorganic particles is small at 5 to 25% by weight, high reflectance cannot be obtained because the reflection of light by the inorganic particles is small and the air dispersion is insufficient.

Japanese Patent Application Laid-Open No. Hei 8-143692 also discloses a white reflective film in which two kinds of polyolefins and polystyrene resins are contained in a polyester resin, but high reflectance cannot be obtained in this case as well.

When a foaming method is used to form bubbles in a sheet of synthetic resin, a method of producing a foam using a chemical foaming agent or a physical foaming agent is known.

In general, the chemical foaming method is a method of mixing a raw material resin and a low molecular weight organic foaming agent which decomposes at a molding temperature to generate a gas, and heating the foaming agent to a temperature above the decomposition temperature of the foaming agent to perform foam molding. In this method, the generation of gas is sensitive to the decomposition temperature, and the decomposition temperature is also easily prepared because a foaming aid is added, and a foam having independent bubbles can be obtained.

The gas foaming method, which is a physical foaming method, is a method in which a low boiling point organic compound such as butane, pentane, and dichlorodifluoromethane is supplied to a place where a resin is melted by a molding machine, kneaded, and then released into a low pressure region to be molded. The low boiling point organic compound used in this method has a feature that a high magnification foam can be obtained because it has excellent solubility because of its affinity for resin and excellent retention.

However, the use of such a method increases the cost, and in the case of chemical foams, problems such as discoloration and odor of the foams occur due to decomposition residues of the foams remaining in the foams, and foams manufactured by the physical foaming method are flammable or toxic. It has the potential to cause air pollution problems. In addition, such a method has a limitation in producing a fine bubble to the level that can maximize the reflectance.

In order to solve this problem, US Patent No. 4473665 discloses a manufacturing method for obtaining a foamed molded article uniformly dispersed fine cells having a diameter of 2 ~ 25㎛. In this method, first, the inert gas is impregnated under pressure until it is saturated in the thermoplastic sheet, heated to the glass transition temperature of the thermoplastic resin, and reduced in pressure to form a cell nucleus by supersaturating the gas impregnated in the resin and then cooling the cell. To control its growth. In this way, a fine foam having a large number of cells can be obtained, but since the inert gas has low affinity with the resin, it requires 10 hours to completely impregnate the gas in the resin, which leads to a problem of low productivity.

On the other hand, the reflective sheet is continuously exposed to light from the light emitting device, the polycarbonate-based resin used as the base resin in the present invention is inevitable deterioration of optical properties due to ultraviolet rays when exposed to light. Conventionally, a method of including a light stabilizer in the base resin or adding an ultraviolet absorber to prevent physical property degradation caused by ultraviolet rays was used, but this also has a difficulty in preventing physical property degradation of the reflective sheet.

In addition, due to the positional characteristics of the reflective sheet located at the bottom of the light source, both ends of the reflective sheet are folded in order to efficiently and totally reflect the light source. In this case, when the folding property (hereinafter, referred to as “foldability”) of the reflective sheet is weak, it is simply broken. There is a problem.

Accordingly, the present inventors have completed the present invention by confirming that it is possible to uniformly form a plurality of fine bubbles with excellent productivity and to freely control the bubble diameter, and to provide a high reflectivity reflective sheet having excellent foldability and weather resistance. .

Accordingly, an object of the present invention is to provide a reflective sheet in which a plurality of fine bubbles are uniformly formed with excellent productivity.

In addition, an object of the present invention is to provide a reflective sheet that can provide excellent weather resistance and reflectance and excellent folding properties.

The present invention for achieving the above object is a base layer using a polycarbonate-based resin as a base resin, containing a micro bubble having an average particle diameter of 50㎛ or less; It provides a reflective sheet comprising a UV blocking layer formed on one side or both sides of the base layer.

The UV blocking layer is characterized in that it comprises a photocurable resin, a photoinitiator and a light stabilizer in a ratio of 100: 2 ~ 10: 0.1 ~ 2.0.

The photocurable resin is an acrylic resin, characterized in that at least one selected from urethane acrylate, urethane methacrylate, epoxy acrylate, epoxy noblock acrylate, polyester acrylate and polybutadiene acrylate.

The UV blocking layer is characterized in that the thickness is 1.0 ~ 5.0㎛.

The base layer is characterized by a specific gravity of 0.2 ~ 0.8.

The fine bubbles of the base layer is characterized in that formed by the supercritical fluid foam.

The supercritical fluid is characterized in that the supercritical fluid of N ₂ or CO ₂ .

The base layer is characterized in that it further comprises 40 parts by weight or less of the inorganic filler with respect to 100 parts by weight of the base resin.

The inorganic filler is at least one selected from barium sulfate, calcium sulfate, magnesium sulfate, barium carbonate, calcium carbonate, magnesium chloride, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc oxide, titanium dioxide, alumina, silica, talc, zeolite. It is done.

The inorganic filler is characterized in that the average particle diameter is 10㎛ or less.

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

The reflective sheet of the present invention uses a polycarbonate resin as a base resin as a white synthetic resin capable of foaming. Polycarbonate resin is a plastic having a specific gravity of about 1.2, and has characteristics such as impact resistance, heat resistance, weather resistance, and transparency, and has an impact of about 150 times or more than that of tempered glass, and is excellent in flexibility and processability. Therefore, it is used in various fields as a substitute of acrylic and a plate that is easily broken and deformed, and also has much better folding property than polymethyl methacrylate and polypropylene resin.

The polycarbonate resin in the present invention includes linear and branched aromatic polycarbonate homopolymers prepared by reacting dihydroxy phenol with phosgene or by reaction of dihydroxy phenol with a carbonate precursor; Polyester copolymers; Or a mixture of one or more thereof.

Herein, the fine bubbles preferably have an average particle diameter of 50 μm or less. When the average particle diameter exceeds 50 mu m, the reflectance decreases because incident light penetrates into the interior of the reflective sheet or the number of diffuse reflections at the bubble interface decreases.

On the other hand, it is preferable that the base layer has a specific gravity of 0.2 to 0.8, and if the specific gravity exceeds 0.8, that is, the bubble ratio decreases and other requirements are satisfied, the absorption of light in the portion of the resin which is not foamed or the transparency of the reflecting sheet are required. The light loss due to light transmission caused by the light is increased, so that the reflectance is lowered. If the specific gravity is less than 0.2, the rigidity is clearly lowered, indicating a problem that shape retention is difficult.

In addition, in order to form microbubbles in the present invention, it is preferable to use a foaming technique using a supercritical fluid, and in particular, microbubbles of 50 µm or less can be formed. More preferably, the supercritical fluid used here is a supercritical fluid of N ₂ or CO ₂ .

The base layer of the present invention may further include an inorganic filler, a light stabilizer or an antioxidant, in the case of adding them, after mixing the base resin with a substance to be added using a tumbler mixer and then using a twin screw extruder The pellets are processed into pellets and fed into an extruder.

Examples of the inorganic fillers for increasing the reflectance include barium sulfate, calcium sulfate, magnesium sulfate, barium carbonate, calcium carbonate, magnesium chloride, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, titanium dioxide, alumina, silica, talc, zeolite, and the like. . In particular, it is preferable to use barium sulfate and calcium carbonate which are excellent in dispersibility and optical properties with polycarbonate. The inorganic filler for increasing the reflectivity is preferably an average particle diameter of 10㎛ or less, the reason is that when the average particle diameter exceeds 10㎛ exhibits a disadvantage that the surface properties are lowered. On the other hand, it is preferable that the addition amount is 40 weight part or less with respect to 100 weight part of base resins, and when it exceeds 40 weight part, there exists a problem that surface characteristic falls similarly.

In addition, the base layer may further include a UV absorber and a UV stabilizer as a light stabilizer. As the ultraviolet absorber, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4 -n-octoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, bis (5-benzoyl-4-hydroxy-2- Benzophenone compounds such as methoxyphenyl) methane and 2,2'-dihydroxy-4-methoxybenzophenone, 2-2'-methylenebis [4- (1,1,3,3-tetramethylbutyl -6- (2H-benzotriazol-2-yl) phenol], 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'- Benzotriazole-based compounds such as di-tert-butylphenyl) -5-chlorobenzotriazole, etc. The content of the ultraviolet absorber is preferably less than 1% by weight.

In addition to the ultraviolet absorber, it is preferable to supplement the ultraviolet stabilizer in order to suppress deterioration of the resin. A hindered amine stabilizer etc. are mentioned as an ultraviolet stabilizer, As an addition amount, less than 1 weight% is suitable with respect to a base resin.

And an antioxidant may be further included in the base layer. As the antioxidant, primary antioxidants such as hindered phenol derivatives and aromatic amine derivatives are effective, but phosphorus derivatives or sulfur derivatives exhibiting effects on high temperature heat resistance. It is preferable to use the secondary antioxidant of together. The primary antioxidant acts as a radical scavenger to destabilize the polymer by deodorizing free radicals generated in the polymer material, and the secondary antioxidant acts as a peroxide decomposer and acts as a secondary antioxidant. will be. The amount of antioxidant added is suitably less than 1% by weight relative to the base resin.

On the other hand, due to the characteristics of the reflective sheet is continuously exposed to light from the light emitting device is inevitable deterioration of optical and mechanical properties due to ultraviolet light, the light stabilizer included in the base layer alone is insufficient to prevent the degradation of the physical properties, and thus In the present invention, a UV blocking layer is formed on one or both surfaces of the base layer of the reflective sheet. The method of forming the UV blocking layer is not particularly limited, but a method of applying the UV blocking layer composition to the surface of the base layer by applying microgravure, gravure, or mayor may be used to irradiate and cure UV rays after drying.

The UV blocking layer composition is characterized in that it comprises a photocurable resin, a photoinitiator and a light stabilizer in a ratio of 100: 2 ~ 10: 0.1 ~ 2.0. When the content of the photoinitiator is included in less than the above range, it may be difficult to cure the photocurable resin, and when included in the content of the photoinitiator exceeding the above range may cause physical property degradation or discoloration of the photocurable resin. In addition, when the content of the light stabilizer is contained less than the above range, it is not possible to obtain appropriate weather resistance by lowering the light resistance, etc., if it is included beyond the above range may cause a decrease in physical properties of the photocurable resin.

As the photocurable resin, at least one selected from urethane acrylate, urethane methacrylate, epoxy acrylate, epoxy noblock acrylate, polyester acrylate and polybutadiene acrylate is used as the acrylic resin.

As the photoinitiator, benzyl dimethyl ketal, benzoin butyl ether, trimethyl benzophenone, alpha-hydroxy ketone and benzophenone can be used.

The light stabilizer used in the UV blocking layer composition is as described in the base layer.

The UV blocking layer has a thickness of 1.0 to 5.0 μm, and the reflective sheet may have a thickness of 0.5 to 1.5 mm.

If the thickness of the UV blocking layer is less than 1.0㎛ the UV blocking effect is deteriorated and curing of the photocurable resin may not occur properly, if it exceeds 5.0㎛ it is difficult to fulfill the function of the reflective sheet. In addition, when the thickness of the reflective sheet is less than 0.5 mm, there is a disadvantage in that it is difficult to handle during post-processing and inferior in shape retention, and the reflectance is reduced by increasing the amount of light leaking. In addition, when the thickness exceeds 1.5mm, the thickness of the backlight unit becomes thick, which is contrary to the trend of thinning of the liquid crystal display.

Hereinafter, examples of the present invention will be described in more detail, but the scope of the present invention is not limited to these examples.

Compositions and composition ratios of Examples 1 to 3 and Comparative Examples 1 to 16 are shown in Table 1 below.

Supercritical fluid technology, chemical foaming technology and stretching technology of the following base layer manufacturing method and the UV blocking layer is prepared by the following method, respectively.

(1) Supercritical Fluid Technology

0.2 part by weight of a benzophenone ultraviolet absorber and 0.1 part by weight of a phenolic antioxidant were added to 100 parts by weight of a polycarbonate resin having a melt index of 1.2 g / 10 min (250 ° C., 1.2 kg _f ) in an extruder, followed by melting at 270 ° C. Thereafter, about 1% of the N ₂ gas in the supercritical fluid state is introduced, and the supercritical fluid and the base resin introduced using the screw are kneaded under the condition of 220 ° C. Thereafter, the supercritical fluid is made into a foamed state just before extrusion and passed through a pressing roll to form a reflective sheet.

When calcium carbonate having an average particle size of 1.5 µm was added, the polycarbonate resin and the additives were added to the extruder together with calcium carbonate.

(2) chemical foaming technology

100 parts by weight of polycarbonate resin having a melt index of 1.2 g / 10 min (250 ° C., 1.2 kg _f ) and 0.2 parts by weight of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as an organic peroxide. 1 part by weight of divinylbenzene as a monomer and 0.1 part by weight of a phenolic antioxidant were fed to a 65 mm tandem extruder at 50 kg / h, plasticized at 270 ° C. in a first stage extruder (diameter 65 mm), and then isobutane as a blowing agent. 5 parts by weight to 100 parts by weight of the resin was pressed, and then the resin temperature was cooled to 230 ° C. in a second stage extruder and passed through the pressing roll and the guide roll to obtain a sheet having a thickness of 2 mm.

(3) stretching technology

The resin composition was obtained by mixing calcium carbonate and an additive with 100 parts by weight of a polycarbonate resin having a melt index of 1.2 g / 10 min (250 ° C., 1.2 kg _f ). The obtained resin composition was processed into pellets using a twin screw extruder, and then melt-extruded at 270 ° C. using an extruder equipped with a T die to obtain an unstretched sheet. The sheet thus obtained was uniaxially stretched at a draw ratio of 6.5 times between the preheat roll and the stretch roll heated to 130 ° C to obtain a sheet.

(4) UV blocking layer

On one side or both sides of the base layer prepared as described above, the UV blocking layer composition prepared in the ratio shown in Table 1 was applied with microgravure, dried at 100 ° C., and the ultraviolet rays generated by the mercury lamp were lighted with a light amount of 50 mJ / cm ² . Irradiation for 5 seconds to cure to form a UV blocking layer of various thickness.

In addition, the average particle diameter of the bubble formed in the base layer manufactured as mentioned above is calculated | required by taking the SEM photograph of a cross section, and measuring and averaging the particle diameter of the bubble contained in a fixed cross-sectional area.

Specific gravity is measured by the submerged method, and measurement conditions are carried out at a temperature of 23 ° C. and a relative humidity of 65%. The thickness is obtained using a vernier caliper.

Reflectance is measured in the wavelength range of 380 ~ 780nm by using a spectrophotometer (UV spectrophotometer, Varian) and reflectance of the wavelength of 550nm as a representative value.

Yellowing is a measure of weatherability using the change of yellowness after UV exposure, after 240 hours in a Q-UV accelerated weathering tester equipped with FS-40 313/280 lamp according to ASTM D1925 standard, and then according to ASTM D1003 standard. The amount of change in the YI value before and after exposure is obtained and shown.

Foldability is denoted by 않으면 if it is not broken when the 10 cm × 10 cm specimen is folded at 90 degrees, and × when broken.

division Base layer UV protection layer Reflective Sheet Suzy
(100
Parts by weight) Carbonic acid
calcium UV absorbers Oxidation
Inhibitor Manufacturing method Bubble particle size
(Μm) importance Photocurable resin Photoinitiator Light stabilizer thickness
(Μm) reflectivity
(%) Yellowing Foldability Supercritical fluid Chemical foaming Stretch Example 1 PC 0 0.2 0.1 ○ × × 19 0.6 100 5 One 2 95  6.1 ○ Example 2 PC 10 0.2 0.1 ○ × × 18 0.6 100 5 One 2 98  6.2 ○ Example 3 PC 20 0.2 0.1 ○ × × 20 0.6 100 5 One 2 98  6.1 ○ Example 4 PC 0 0.2 0.1 ○ × × 20 0.6 100 5 0.5 2 95  6.7 ○ Example 5 PC 0 0.2 0.1 ○ × × 18 0.6 100 5 1.5 2 95  5.9 ○ Example 6 PC 0 0.2 0.1 ○ × × 19 0.6 100 5 One 4 95  5.8 ○ Comparative Example 1 PC 0 0.2 0.1 ○ × × 19 0.6 - - - - 95 17.0 ○ Comparative Example 2 PC 10 0.2 0.1 ○ × × 20 0.6 - - - - 98 16.4 ○ Comparative Example 3 PC 20 0.2 0.1 ○ × × 19 0.6 - - - - 98 16.9 ○ Comparative Example 4 PC 0 0.2 0.1 ○ × × 20 0.6 100 5 0.05 2 98 11.7 ○ Comparative Example 5 PC 0 0.2 0.1 ○ × × 20 0.6 100 15 One 2 98 10.0 ○ Comparative Example 6 PC 0 0.2 0.1 ○ × × 19 0.6 100 5 One 0.2 74 12.8 ○ Comparative Example 7 PC 0 0.2 0.1 × ○ × 251 0.4 100 5 One 2 74  6.5 ○ Comparative Example 8 PC 10 0.2 0.1 × ○ × 250 0.4 100 5 One 2 77  6.5 ○ Comparative Example 9 PC 20 0.2 0.1 × ○ × 248 0.4 100 5 One 2 91  6.4 ○ Comparative Example 10 PC 0 0.2 0.1 × × ○ 16 0.5 100 5 One 2 93  6.0 ○ Comparative Example 11 PC 10 0.2 0.1 × × ○ 18 0.5 100 5 One 2 94  6.2 ○ Comparative Example 12 PC 20 0.2 0.1 × × ○ 16 0.5 100 5 One 2 94  6.2 ○ Comparative Example 13 PC 0 0.2 0.1 ○ × × 52 0.5 100 5 One 2 92  6.1 ○ Comparative Example 14 PC 0 0.2 0.1 ○ × × 74 0.4 100 5 One 2 89  6.1 ○ Comparative Example 15 PC 0 0.2 0.1 ○ × × 88 0.2 100 5 One 2 93  6.2 ○ Comparative Example 16 PMMA 20 0.2 0.1 ○ × × 20 0.6 100 5 One 2 97 5.8 × * PC: Polycarbonate (GE company, LEXAN * Resin OQ1020C, MI: 1.2 (250 ℃ / 1.2kgf))
* PMMA: Polymethylmethacrylate (Kuraray, EH)
* UV absorber: Benzophenone UV absorber
* Antioxidant: Phenolic Antioxidant
* Calcium Carbonate: Heavy Calcium Carbonate
* Photocurable resin: Urethane acrylate resin composition (KOLON, KF2121A)
* Photoinitiator: Ketone photoinitiator composition (KOLON, KF2121B)
* Light stabilizer: Hindered amine light stabilizer

As a result of the experiment, it can be seen that in Examples 1 to 6, a reflective sheet having a good high reflectance was obtained, and a slight reflectance synergistic effect was obtained as the amount of calcium carbonate increased. In addition, when compared with Comparative Examples 1 to 3 and the ratio of the UV blocking layer composition and the thickness of the UV blocking layer which do not apply the UV blocking layer compared to Comparative Examples 4 to 6 that do not belong to the scope of the present invention, Example 1 of the present invention It can be seen that the reflective sheets 6 to 6 have excellent weather resistance.

On the other hand, in Comparative Examples 7 to 9 it can be seen that by applying a general chemical foaming method the size of the bubble particle size is relatively large, showing a low reflectance.

Comparative Examples 10 to 12 can be seen that a relatively low reflectance compared to Examples 1 to 3 as a film generated by applying the stretching technology bubbles. This is judged to be due to insufficient bubble dispersion and insufficient thickness.

In Comparative Examples 13 to 15, it can be seen that as the bubble diameter increases, the reflectance decreases.

In Examples 1 to 6 and Comparative Examples 1 to 15, the reflecting sheet was composed of polycarbonate resin, and the folding property was excellent, whereas in Comparative Example 16, the reflecting sheet was composed of polymethyl methacrylate resin, but the folding sheet was excellent. It can be seen that the sex is not excellent.

As described above, the present invention improves the reflectance by forming a plurality of fine bubbles uniformly by applying an extruded foam supercritical fluid technology capable of excellent productivity and freely controlling the diameter of the bubbles to the reflective sheet, thereby improving weather resistance and weather resistance. It is possible to provide a reflecting sheet for a backlight unit having excellent excellent folding properties.

Claims (10)

A base layer using polycarbonate resin as a base resin and containing fine bubbles having an average particle diameter of 50 µm or less; It comprises a UV blocking layer formed on one side or both sides of the base layer, The microbubble of the base layer is a reflective sheet, characterized in that formed by the supercritical fluid foam. The method of claim 1, The UV blocking layer is a reflective sheet comprising a photocurable resin, a photoinitiator and a light stabilizer in a ratio of 100: 2 to 10: 0.1 to 2.0. The method of claim 2, The photocurable resin is an acrylic resin reflecting sheet, characterized in that at least one selected from urethane acrylate, urethane methacrylate, epoxy acrylate, epoxy noblock acrylate, polyester acrylate and polybutadiene acrylate. The method of claim 1, The UV blocking layer is a reflection sheet, characterized in that the thickness is 1.0 ~ 5.0㎛. The method of claim 1, The base layer is a reflection sheet, characterized in that the specific gravity is 0.2 ~ 0.8. delete The method of claim 1, The supercritical fluid is a reflective sheet, characterized in that the supercritical fluid of N ₂ or CO ₂ . The method of claim 1, The base layer is a reflective sheet, characterized in that it further comprises 40 parts by weight or less of the inorganic filler with respect to 100 parts by weight of the base resin. The method of claim 8, The inorganic filler is at least one selected from barium sulfate, calcium sulfate, magnesium sulfate, barium carbonate, calcium carbonate, magnesium chloride, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc oxide, titanium dioxide, alumina, silica, talc, zeolite. Reflective sheet. The method of claim 8, The inorganic filler is a reflective sheet for a backlight unit, characterized in that the average particle diameter is 10㎛ or less.