KR100949739B1 - Light-Reflection Plate Using Foamed Propylene-Ethylene Copolymer - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light reflector used in a liquid crystal display device, a lighting device, and the like and a manufacturing method thereof. Specifically, the present invention relates to a light reflection plate having excellent economic efficiency, which is prepared by foaming an inert gas such as carbon dioxide on a propylene-ethylene copolymer base material. The light reflector of the present invention has a high diffuse reflectance component among the total reflectance components and shows a high diffuse reflectance of 90% or more in all wavelength ranges of 380 to 800 nm. The light reflector of the present invention not only prevents the loss of light amount due to the addition of a white pigment or the like, which induces the diffuse reflection of light, and also prevents the double cost of placing a metal having a specular reflection component on the back of the reflector. By using a cheaper propylene-ethylene copolymer as a substrate has the advantage of excellent economic efficiency.

Propylene-ethylene copolymer, light reflector, inert gas, foaming, diffuse reflectance

Description

Light-Reflection Plate Using Foamed Propylene-Ethylene Copolymer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light reflector used in a liquid crystal display device, a lighting device, and the like and a manufacturing method thereof. Specifically, the present invention relates to a light reflection plate having excellent economic efficiency, which is prepared by foaming an inert gas such as carbon dioxide on a propylene-ethylene copolymer base material.

The light reflecting plate refers to a plate used for obtaining uniform diffuse reflection in a luminaire using a light source such as a fluorescent lamp or an incandescent lamp. That is, it is used for diffusing and reflecting the light emitted from the light source to have a uniform luminance distribution as a whole. Particularly, a light reflector having a high diffuse reflectance is preferable. Examples of the use of such a light reflecting plate include a reflecting plate of a backlight unit used in a liquid crystal display device, and lighting fixtures such as general fluorescent lamps and incandescent lamps.

In detail, a side light type liquid crystal display generally uses a backlight unit including a reflector, a light guide plate, a diffusion plate, and the like to obtain performance of a surface light source. Each of the plates is stacked and installed in turn, and several lamps are partially installed on the side or the display surface. Actual operation is achieved by the light generated by the lamp being directed through the light guide plate, causing diffuse reflection through the reflector plate, and finally passing through the diffuser plate and exiting the display surface. In this case, since the light reflecting plate requires a high total reflectance and a high diffusing reflectivity, a method of printing a pattern causing diffusion reflection, a method of forming fine irregularities on the diffusion plate, and the like are used. Efforts have been made to produce light reflectors that meet the needs.

For example, there is a light reflection plate using a mirror reflection by coating a deposition film on the surface of a metal such as aluminum. However, such a reflection plate is difficult to diffuse reflection because the mirror reflection component occupies most of the total reflection, there is a problem in that the amount of light directed toward the display surface is lost.

In addition, there have been attempts to increase the diffusion reflectivity by applying a special paint on the surface or anodizing, but there is a limit that does not meet the level required in the field.

In addition, a light reflector made of a film containing a white pigment such as titanium oxide is also used. In this case, it is necessary to increase the amount of the white pigment added to reduce the light transmittance. However, since the white pigment itself absorbs light of a specific wavelength, the amount of light loss increases rapidly as the amount of addition increases, and thus there is a problem that the light reflectance significantly decreases.

On the other hand, a light reflecting plate made of a foamed polyethylene terephthalate (PET) sheet is used, which is suitable as a reflecting plate because the foam bubbles have a high reflectance by causing diffusion reflection, but is currently limited in use due to long production time and high price.

In addition, in Japan, a reflecting plate laminated with a polyester film obtained by dispersing fine particles such as calcium carbonate in addition to a light reflecting plate made of a polyester film containing microbubbles is produced.

In the case of the microparticle-dispersed polyester film, bubbles are formed around the microparticles when they are stretched, so that diffusion reflection occurs through them, but uniform distribution of the microparticles is difficult, resulting in uneven dispersion of the bubbles. It is difficult to expect high diffusion reflectance as the thickness of the film becomes thin and the light transmittance increases. As a result, in order to suppress light transmission, it is necessary to arrange a separate metal plate having mirror reflection performance on the back side of the film, and the effect is halved.

On the other hand, high light reflectance is also required for lampshades such as fluorescent lamps. The reflection of metal materials such as steel sheets and aluminum plates which are generally used for such applications has a problem that the reflected light is dazzling because there are many mirror reflecting components.

This uses a method of applying a white pigment, there is a problem that the reflectance is lowered because the pigment itself absorbs light of a specific wavelength as described above. That is, in the case of the light reflector using this method, the reflectance is only 85% or less, and since the diffuse reflectance is low, highly efficient reflecting performance cannot be obtained.

The present invention has been made in order to solve the above problems, do not add a white pigment or the like to increase the diffuse reflection of light, or do not use a method of arranging a metal reflector on the back of the reflector, poly which is a problem in terms of price It is an object of the present invention to provide a light reflecting plate having excellent diffusion reflectance with respect to light in the visible region and producing in a short time by using a relatively inexpensive propylene-ethylene copolymer as a substrate without using an ester system. .

In order to achieve the object as described above, the light reflection plate of the present invention,

60 to 99 weight percent of propylene monomer, and

1 to 40 wt% ethylene monomer

The inert gas is added and foamed to the copolymer obtained by polymerizing the mixture together.

In addition, the light reflection plate of the present invention may further polymerize together by adding 0.1 to 10 parts by weight of butene monomer per 100 parts by weight of the mixture of the propylene monomer and the ethylene monomer.

In addition, the light reflection plate of the present invention may be polymerized by further including 0.1 to 10 parts by weight of ceramic fine particles per 100 parts by weight of the mixture of the propylene monomer and the ethylene monomer.

In addition, the inert gas is preferably selected from the group consisting of carbon dioxide, nitrogen, helium and argon.

In addition, the ceramic fine particles are preferably selected from the group consisting of calcium carbonate (CaCO ₃ ), titanium oxide (TiO ₂ ), talc (Talc) and mixtures thereof.

In addition, the specific gravity of the reflective plate is preferably 0.4 to 0.8.

In addition, the bubble diameter of the inert gas contained in the reflector is preferably 0.7 to 20 ㎛.

In addition, the size of the ceramic fine particles is preferably 0.5 to 10 ㎛.

The light reflector of the present invention has a high diffuse reflectance component among the total reflectance components and shows a high diffuse reflectance of 90% or more in all wavelength ranges of 380 to 800 nm. The light reflector of the present invention not only prevents the loss of light amount due to the addition of a white pigment or the like, which induces the diffuse reflection of light, and also prevents the double cost of placing a metal having a specular reflection component on the back of the reflector. By using a cheaper propylene-ethylene copolymer as a substrate has the advantage of excellent economic efficiency.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the following description there are shown a number of specific details such as specific components, which are provided to help a more comprehensive understanding of the present invention that the present invention may be practiced without these specific details in the art It will be self-evident to those of ordinary knowledge. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The final object of the present invention is to reduce the price of the product by using the propylene-ethylene copolymer as a material, and to produce a high-efficiency reflector having a diffusion reflectance of 90% or more through foaming.

In the case of existing PET foam reflector, the raw material is expensive, and new economical materials have been sought to lower the price of the product. Polypropylene, a crystalline resin such as PET, was a candidate early, but foams using polypropylene had a significantly lower bubble density than conventional foamed PET, making it difficult to increase the diffusion reflectivity to more than 90%.

The present invention was not only economical by introducing a copolymer polymerized together by adding ethylene monomer instead of the conventional polypropylene homopolymer, but also increased the reflectance of the reflectance by 90% or more.

That is, the present invention is a light reflection plate containing fine bubbles having a bubble diameter of 20 μm or less and made of a propylene-ethylene copolymer having a specific gravity of 0.8 or less. The reason for limiting the diameter of the bubble is that when the bubble becomes 20 µm or more, the number of cells per unit volume decreases, so it is difficult to expect high diffusion reflectance as the number of diffuse reflections occurring at the boundary between the polymer and the bubble decreases. to be. The smaller the average bubble diameter, the better the reflection, but the size and density of the bubble is determined by the material of the foam.

In the case of polypropylene, the crystallinity is about 60%, and the crystal plays a role in suppressing excessive growth of the cell. In addition, if the average bubble diameter is smaller than the wavelength of visible light, since the incident light passes through the bubble instead of causing reflection at the interface between the polymer and the bubble, the diameter of the bubble should be at least 700 nm, the wavelength of the visible light.

If the specific gravity of the light reflector exceeds 0.8, it means that the number of bubbles that act as reflections is small, which also adversely affects material cost reduction. That is, as the specific gravity is lowered, the number of bubbles means more, so that the material cost can be reduced by the volume occupied by the bubbles. However, if the specific gravity is less than 0.4, there is a disadvantage in that the mechanical content is significantly reduced due to excessive content ratio of bubbles.

When the thickness of the light reflector is thin, the light transmittance generally increases, resulting in a decrease in reflectance. However, the thickness of the light reflecting plate is not particularly limited because the size of the bubble and the specific gravity of the product can be reduced to increase the density of the bubble, thereby reducing the light transmittance and reducing the light reflectance.

The thermoplastic propylene-ethylene copolymer is used for the light reflection plate of the present invention. Propylene-ethylene copolymers include random copolymers, regular copolymers, block copolymers, graft copolymers, and the like. Of these, block copolymers are most preferred.

The weight ratio of the propylene monomer and the ethylene monomer is preferably in the ratio of 60 to 99 wt% of the former and 1 to 40 wt% of the latter in terms of achieving the addition amount of the inert gas, which will be described later, and reaching the desired diffusion reflectance.

The present invention may also copolymerize together, further comprising butenes, more preferably 1-butene monomers, in addition to the two monomers. The addition amount of the butene is preferably 0.1 to 10 parts by weight per 100 parts by weight of the mixture of the propylene monomer and the ethylene monomer in terms of achieving the addition amount of the inert gas to be described later and achieving the desired diffusion reflectance.

The light reflector of the present invention includes a crystallization nucleating agent, a crystallization accelerator, a foaming nucleating agent, an antioxidant, an antistatic agent, an ultraviolet ray preventing agent, a light stabilizer, and a pigment in the propylene-ethylene copolymer before foaming within a range that does not affect the light reflecting properties. , Various additives such as dyes and lubricants can be blended. Of course, it is also possible to mix | blend these additives with the light reflection board after foaming, or to laminate other resin containing these additives.

The method of manufacturing the light reflection plate of the present invention may be both a method using a high temperature liquid, a method using hot air, a method using a plate heater, or a method using an infrared heater. However, since the foaming process by heating using a high temperature liquid requires a post-treatment process, the mass production efficiency is relatively low. In particular, a method using an infrared heater that transmits heat by radiation is simple and has high reflectance.

On the other hand, the light reflection plate of the present invention may further contain ceramic fine particles. The ceramic fine particles may have a function of increasing the reflectance by themselves, but the biggest advantage is that the production cost can be reduced because of the low cost.

Ceramic microparticles capable of performing this function are not particularly limited, and include calcium carbonate (CaCO ₃ ), titanium dioxide (TiO ₂ ), talc (Talc), and the like, and mixtures thereof may be used.

The amount of the ceramic fine particles added is preferably 0.1 to 10 parts by weight per 100 parts by weight of the mixture of the propylene monomer and the ethylene monomer. If the added amount is less than 0.1 part by weight, the effect of cost reduction is insignificant, and if it exceeds 10 parts by weight, not only may cause a decrease in reflectance, but also a serious decrease in mechanical strength of the light reflection plate.

In addition, it is preferable that the size of the ceramic fine particles added is 0.5 to 10 μm. If the size of the ceramic fine particles is less than 0.5 μm, the size of the fine particles is too small to increase the grinding cost, and a lot of loss may occur during the operation. On the contrary, when it exceeds 10 micrometers, a reflectance will fall seriously.

The light reflection plate of the present invention first rolls up a sheet of a thermoplastic propylene-ethylene copolymer and a separator to form a roll, and maintains it for a predetermined time under high pressure conditions to contain an inert gas inside the roll, and at a normal pressure to the sheet It is produced by a method in which foaming proceeds by applying heat.

EMBODIMENT OF THE INVENTION Hereinafter, the method of manufacturing the light reflection board of this invention is demonstrated in detail.

First, a roll rolled by wrapping a thermoplastic propylene-ethylene copolymer sheet and a separator is formed. At this time, the separator used has a gap through which an inert gas can pass freely, and a thickness of 500 μm or less is used. Any material that satisfies the above conditions may be used, and examples thereof include a polypropylene nonwoven fabric.

Thereafter, the formed roll is placed in a high pressure vessel, an inert gas is supplied into the high pressure vessel, and the high pressure vessel is completely sealed. In this process, the thermoplastic propylene-ethylene copolymer sheet contains an inert gas serving as a blowing agent.

The inert gas is preferably selected from the group consisting of carbon dioxide, nitrogen, helium, and argon. Among these, carbon dioxide is more preferable at the point which can contain a large amount in the propylene-ethylene copolymer of this invention.

The penetration pressure of the inert gas is 30 to 70 kg _f / cm ² , it is more preferable to operate at 50 kg _f / cm ² or more. The filling time of the inert gas into the high-pressure vessel is 1 hour or more, but the gas is continuously supplied until it is saturated.

The time and amount of penetration of the inert gas into the propylene saturation into the propylene-ethylene copolymer depend on the type of copolymer to be foamed, the type of inert gas, the penetration pressure, and the thickness of the sheet. Usually, carbon dioxide is used as an inert gas, and when the pressure of carbon dioxide is 70 kg _f / cm ² and the thickness of the sheet is 0.8 mm, it is preferable to set it as 10 hours or more. At this time, the amount of carbon dioxide contained in the resin is 3 to 6% by weight.

The roll is removed from the high pressure vessel, the separator is removed, and foamed by applying heat to a propylene-ethylene copolymer containing an inert gas. At this time, the shorter the time to take out of the high-pressure vessel and to heat the lower the specific gravity of the foamed copolymer.

The heating temperature at the time of foaming is set in a section 5 to 30 ° C. lower than the melting temperature of the copolymer. The heating means includes an oil booth, a hot air blowing furnace, a plate heater, an infrared heater, and the like, and in consideration of process efficiency, it is preferable to use a hot air blowing furnace, a plate heater, or an infrared heater, particularly an infrared heater method.

The foaming conditions in the plate heater are set at a linear speed at which the foaming temperature is 140 ° C. and the foaming time is 30 seconds or more, for example.

Thereafter, cooling is carried out to obtain a light reflection plate made of a thermoplastic expanded propylene-ethylene copolymer.

The shape of the light reflection plate is not limited. The shape of the sheet obtained in the above process can be used as it is as a light reflection plate for enhancing the light diffusion reflectance of a liquid crystal display device or the like. It can also be bent and used as a light reflector for general lighting equipment such as fluorescent lamps. In this case, a heating vacuum molding or the like may be used as the molding method.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described.

Example

Example  And Comparative example  1: density, bubble diameter  And reflectance

Propylene-ethylene block copolymer (Korea emulsification. BP2000) sheet, propylene-ethylene random copolymer (Korea emulsification. RP2400) sheet, propylene-ethylene-butene terpolymer (emulsification. CF3340) sheet and propylene homopolymer (for Oil painting 1088) sheets were prepared. The sheets and the separator (Y & K) were wrapped and wound, and introduced into a pressure tank, and maintained at a pressure of 50 kg _f / cm ² to infiltrate carbon dioxide. The pressure in the pressure tank was removed, passed through a foaming furnace maintained at 150 ° C. by a glycerin oil bath, cooled, and the separator was separated to obtain a light reflector. The density, bubble diameter, and reflectance of each light reflector were measured. The change in density according to the bubble diameter was achieved by adjusting the holding time in the pressure tank and the passage time of the foaming furnace, and the results are shown in Table 1.

As shown in Table 1, the block copolymer had the highest reflectance, followed by random copolymers, propylene-ethylene-butene terpolymers, and the comparative homopolymers achieved reflectivity of 90% or more in any specimen. I couldn't.

Example  And Comparative example  2: density, bubble diameter  And reflectance

The same process as in Example 1 and Comparative Example 1, except for preparing the sheet, 2% by weight of calcium carbonate (CaCO ₃ ), titanium dioxide (TiO ₂ ), or talc (Talc) as ceramic fine particles in each polymer resin The blended specimens were further prepared and the density and reflectance of each specimen were measured. The results are shown in Table 2.

No additives CaCO ₃ (2 wt%) TiO ₂ (2 wt.%) Talc (2% by weight) Density (g / cm ³ ) Reflectance (%) Density (g / cm ³ ) Reflectance (%) Density (g / cm ³ ) Reflectance (%) Density (g / cm ³ ) Reflectance (%) Block copolymer 0.55 99 0.51 101 0.53 99 0.53 97 Random copolymer 0.60 97 0.55 98 0.56 97 0.54 96 Terpolymer 0.60 94 0.54 96 0.55 96 0.54 95 Homopolymer 0.80 88 0.76 92 0.77 87 0.78 87

As shown in Table 2, even when the ceramic fine particles are introduced, the reflectance does not significantly decrease, and in the case of calcium carbonate, the reflectance increases. Through this, it can be seen that the cost can be further reduced by introducing some of the inexpensive ceramic fine particles.

Example  And Comparative example  3: density and reflectance according to foaming method

The same process as in Example 1 and Comparative Example 1, using a hot air dryer (Shinil Engineering, Korea), plate heater (Shinil Engineering, Korea), or infrared heater (Shinil Engineering, Korea) in addition to the glycerin oil bath (bath) After foaming, the density and reflectance of the obtained light reflector were measured. The results are shown in Table 3.

Oil bath When hot air drying Plate heater Infrared heater Process time (seconds) 30 120 20 20 Density (g / cm ³ ) Reflectance (%) Density (g / cm ³ ) Reflectance (%) Density (g / cm ³ ) Reflectance (%) Density (g / cm ³ ) Reflectance (%) Block copolymer 0.55 99 0.64 97 0.53 99 0.50 100 Random copolymer 0.60 97 0.66 96 0.57 98 0.56 98 Terpolymer 0.60 94 0.68 92 0.58 95 0.55 96 Homopolymer 0.80 88 0.83 87 0.79 89 0.77 90

As shown in Table 3 above, the desired reflectance was obtained through appropriate adjustment of the foaming process time. However, the method using the hot air dryer has a disadvantage that the process time is relatively long, and as described above, the method using an oil bath such as glycerin has a disadvantage of requiring an additional process of removing oil. In particular, the method using an infrared heater using radiant heat was not only simple, but also showed a slight increase in reflectance, which was judged to be a more preferable foaming method.

Example  4: size of additive vs . reflectivity

The same procedure as in Example and Comparative Example 2 was performed, but calcium carbonate having different sizes was added in the block copolymer, and the reflectance was measured. The results are shown in FIG. As shown in FIG. 1, it can be seen that the reflectance increases as the size of the calcium carbonate particles decreases.

Example  5: bubble density vs . reflectivity

The same procedure as in Example 1 and Comparative Example 1 was performed, and the reflectance according to the change in bubble density (Micromeritics, USA) was measured using a random copolymer. The results are shown in FIG. 2, and as shown in FIG. 2, the reflectance increases as the bubble density increases.

Example  6: crystal size vs . reflectivity

The same process as in Example 1 and Comparative Example 1 was carried out, and the reflectance according to the change in crystal size was measured using a block copolymer. The results are shown in FIG. 3, and the larger the size of the crystal, the lower the reflectance, which can be explained by the growth of the crystal that suppresses the growth of bubbles.

Although the above has been illustrated and described with respect to the preferred embodiments of the present invention, the present invention is not limited to the specific embodiments described above, those skilled in the art without departing from the gist of the present invention various modifications Of course, implementation is possible. Therefore, the scope of the present invention should not be construed as being limited to the above embodiments, but should be defined by the claims below and equivalents thereof.

1 is a graph showing the reflectance change of the light reflector of the present invention according to the size of the ceramic fine particles.

2 is a graph showing a change in reflectance of the light reflector of the present invention according to the bubble density.

3 is a graph showing the change in reflectance of the light reflector of the present invention according to the size of the polymer crystal.

Claims (8)

60 to 99 weight percent of propylene monomer, and 1 to 40 wt% ethylene monomer Inert gas was added and foamed to the copolymer obtained by polymerizing a mixture of Light reflecting plate, characterized in that the bubble diameter of the foamed inert gas is 0.7 to 20 ㎛. The method according to claim 1, Light reflecting plate, characterized in that the polymerization of together further comprising 0.1 to 10 parts by weight of butene monomer per 100 parts by weight of the mixture of propylene monomer and ethylene monomer. The method according to claim 1, Light reflecting plate, characterized in that the polymerization by further comprising 0.1 to 10 parts by weight of ceramic fine particles per 100 parts by weight of the mixture of the propylene monomer and ethylene monomer. The method according to claim 1, The inert gas is a light reflection plate, characterized in that selected from the group consisting of carbon dioxide, nitrogen, helium and argon. The method according to claim 3, The ceramic fine particle is a light reflection plate, characterized in that selected from the group consisting of calcium carbonate (CaCO ₃ ), titanium oxide (TiO ₂ ), talc (Talc) and mixtures thereof. The method according to any one of claims 1 to 5, Specific gravity of the reflector is a light reflector, characterized in that 0.4 to 0.8. delete The method according to any one of claims 1 to 5, The size of the ceramic fine particles is a light reflection plate, characterized in that 0.5 to 10 ㎛.

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