JP2009244749A - Light reflective plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light reflective plate that has a superior diffuse reflectance to visible light only with a base without adding a pigment nor particulate for enhancing scattering of light nor disposing another light reflective plate having a metal mirror surface behind it. <P>SOLUTION: The light reflective plate is formed in a sheet shape of a thermoplastic polyester foaming body which includes fine air bubbles of not larger than 50 μm in average air bubble diameter and has a thickness of not less than 100 μm and a relative bulk density of not larger than 0.7, a non-foaming skin layer being on one sheet surface and air bubbles or recesses being exposed on the other sheet surface. The light reflective plate is obtained by, for example, a method of cutting a thermoplastic polyester foaming body sheet 20 including fine air bubbles 18 so that a cut surface 22 orthogonal to the thickness is formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light reflector that is suitably used for a backlight device of a liquid crystal display device, a lighting fixture such as a fluorescent lamp, an incandescent lamp, and an LED.

  In a sidelight type liquid crystal display device, a backlight device having a structure as shown in FIG. 10 is generally used in order to obtain a function as a surface light source. As shown in FIG. 1, a light reflection plate 1, a light guide plate 2, and a light transmission diffusion plate 3 are provided in a stacked manner, and a lamp 4 is provided on these side surfaces. The light from the lamp 4 is guided to the light guide plate 2 and finally emitted to the display surface through the light transmission diffusion plate 3 while repeating diffuse reflection at the interface between the light guide plate 2 and the light reflection plate 1.

  As described above, in order to cause diffuse reflection at the interface between the light guide plate 2 and the light reflection plate 1, the following method is used. For example, a method of printing a pattern that causes diffuse reflection on the lower surface of the light guide plate 2 (a boundary surface with the light reflection plate 1), or another method in which a predetermined pattern is printed between the light guide plate 2 and the light reflection plate 1 These include a method of inserting a film and a method of forming fine irregularities on the lower surface of the light guide plate 2.

  In addition, since the light reflecting plate 1 is required to have a high light reflectance, various materials as described below have been conventionally used. For example, a light reflecting plate in which a metal vapor deposition film is deposited on the surface of a substrate such as metal to form a metal mirror surface is used. However, since the light reflection plate having a metal mirror surface hardly causes diffuse reflection, the amount of light directed toward the display surface is rather reduced.

  A light reflector made of a film containing a white pigment such as titanium oxide is also used. In the light reflecting plate made of this film, it is necessary to increase the amount of pigment added in order to suppress light leakage to the back surface. However, since the white pigment added to the film absorbs light of a specific wavelength, there is a problem that if the amount added is increased, an increase in light loss cannot be ignored and the reflectance is lowered.

  Furthermore, Patent Document 1 discloses a light reflecting plate made of a polyester film having fine bubbles. There is also disclosed a light reflector made of a film obtained by laminating a polyester film containing fine bubbles and another polyester film in which particles of calcium carbonate or silica having no light absorption are dispersed. In this case, the polyester film containing fine bubbles disperses the incompatible polymer in the polyester, and forms voids (bubbles) around the incompatible polymer particles when the polymer is uniaxially or biaxially stretched. It is manufactured by. However, it is difficult to uniformly disperse the incompatible polymer in the polyester. For this reason, the dispersion | distribution of the bubble in polyester also becomes non-uniform | heterogenous, and cannot fully diffuse-reflect light. Moreover, since the stretched film is as thin as less than 200 μm, more light leaks to the back of the film. As a result, it is difficult for the film described in Patent Document 1 to achieve satisfactory reflectance. Therefore, in order to obtain a sufficient reflectance, there is a problem that it is necessary to arrange another light reflecting plate having a metal mirror surface on the back surface of the film.

  Patent Document 2 also discloses a light reflecting plate made of a polyester film containing fine bubbles. However, since the light reflection plate of Patent Document 2 has an unfoamed skin layer on both sides, it is not sufficient when a more excellent diffuse reflectance is obtained.

  Similarly, for example, a shade portion of a lighting fixture may be required to have a high light reflectance. As the light reflecting plate for this application, a plate made of a metal material such as a steel plate or an aluminum plate, or a plate obtained by applying a paint containing a light reflecting pigment on the surface of a plastic injection molded body is used. Among these, when a light reflector made of a metal material is used, the total reflectance of light is sufficiently high, but there is a problem that the reflected light feels dazzling because there is little diffuse reflection. On the other hand, with a light reflection plate in which a coating material containing a light-reflective pigment is applied to the surface of a plastic injection molded body, there is a limit to increasing the thickness of the coating film, and the pigment itself absorbs light. There is a problem that the rate decreases.

  In Patent Document 3, a transparent base material such as glass is used to scatter visible light made of a metal oxide (for example, titanium oxide) having a thickness of 0.3 to 0.8 μm including an infrared transmission film and fine bubbles. A light reflector with a film is described. However, also in this case, since the thickness of the light scattering film is thin, the reflectance is only about 85%, and highly efficient reflection characteristics cannot be obtained.

Japanese Patent Laid-Open No. 4-29565819 Japanese Patent Publication No. 9-1117 JP-A-61-2225709

  The present invention has been made in view of the above-described circumstances, without adding a pigment or fine particles that enhance light scattering properties, or without arranging another light reflecting plate having a metal mirror surface on the back surface. It is simply to provide a light reflector excellent in the diffuse reflectance of visible light.

In order to achieve the above object, the present invention provides the following light reflectors (1) and (2).
(1) It has a sheet shape made of a thermoplastic polyester foam having fine bubbles with an average cell diameter of 50 μm or less, a thickness of 100 μm or more, and a bulk specific gravity of 0.7 or less, and one sheet surface is an unfoamed skin A light reflecting plate comprising a layer, wherein bubbles or recesses are exposed on the other sheet surface.
(2) The light reflecting plate according to (1), wherein the thermoplastic polyester foam is formed into a shape having a concave polyhedral or curved reflecting surface.

  In the light reflecting plate of the present invention, the diffuse reflectance of the surface is improved by exposing bubbles or recesses on one surface. And the light reflection board excellent in the diffuse reflectance can be obtained by making the surface in which this diffuse reflectance improved into a reflective surface.

  Although there is no limitation in the manufacturing method of the light reflecting plate of this invention, it cut | disconnects so that the cut surface orthogonal to a thickness direction may be formed in the thermoplastic polyester foam sheet which has a skin layer on both surfaces in the appropriate position of a thickness direction And a method of removing the skin layer on one surface of the foamed sheet can be suitably employed.

  The light reflecting plate of the present invention is excellent in diffuse reflectance and exhibits high luminance.

  Hereinafter, the present invention will be described in more detail. In the light reflecting plate of the present invention, the average bubble diameter, thickness and bulk specific gravity of the light reflecting plate are defined as described above for the following reasons.

  When the average bubble diameter exceeds 50 μm, the incident light penetrates into the light reflecting plate or the number of irregular reflections at the bubble interface decreases, so that the diffuse reflectance tends to decrease. In particular, when a sheet-like light reflecting plate is used in a backlight device of a liquid crystal display device, the amount of light returning to the surface of the light reflecting plate is reduced due to light loss from the end of the light reflecting plate. descend. The average cell diameter is more preferably 30 μm or less. In addition, since incident light permeate | transmits when an average bubble diameter becomes smaller than the wavelength of visible light, an average bubble diameter needs to be more than the wavelength of visible light at least.

  If the thickness of the light reflecting plate is less than 100 μm, even if the other requirements are satisfied, the light leakage to the back surface of the light reflecting plate increases, and the diffuse reflectance decreases. Moreover, when the thickness of the light reflecting plate is small, the shape retaining property is inferior when the light reflecting plate is molded into a predetermined shape. The thickness of the light reflecting plate is more preferably 400 μm or more.

  If the bulk specific gravity of the light reflector exceeds 0.7, that is, the bubble ratio becomes small, even if other requirements are satisfied, light absorption in the resin portion that is not foamed or light transmission due to the transparency of the light reflector, etc. Since the optical loss increases, the diffuse reflectance decreases. In addition, it is preferable that the bulk specific gravity of a light reflection board is 0.05 or more.

  A thermoplastic polyester resin is used for the light reflecting plate of the present invention. Specific examples of the thermoplastic polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like. Other resins such as polycarbonate may be blended with polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate and the like. Of these resins, polyethylene terephthalate is most preferred.

  In the present invention, the thermoplastic polyester resin before the foaming treatment is added to the crystallization nucleating agent, the crystallization accelerator, the bubbling nucleating agent, the antioxidant, the antistatic agent, and the ultraviolet ray within a range that does not affect the light reflection characteristics. Various additives such as an inhibitor, a light stabilizer, a pigment, a dye, and a lubricant may be blended. Of these additives, the amount of the crystallization nucleating agent added is preferably 5% by weight or less. Moreover, you may apply | coat these additives to the light-reflection board after foaming, or you may laminate other resin containing these additives.

  The method for producing the light reflecting plate of the present invention is not particularly limited. However, considering mass productivity, for example, the following method is preferably used. That is, a roll is formed by winding a sheet of thermoplastic polyester and a separator, and the roll is held in a pressurized inert gas atmosphere so that the thermoplastic polyester sheet contains an inert gas, and further inert. It is preferable to use a method in which a thermoplastic polyester sheet containing gas is heated and foamed under normal pressure. In this method, an organic solvent is added to the thermoplastic polyester sheet before the roll comprising the thermoplastic polyester sheet and the separator is held in a pressurized inert gas atmosphere and the thermoplastic polyester sheet contains the inert gas. You may make it contain.

  Hereinafter, the method for producing the light reflecting plate of the present invention will be described in more detail.

  (1) First, a roll is formed by overlapping and winding a thermoplastic polyester sheet and a separator. The separator used here may be any one as long as it has a void through which an inert gas or an organic solvent used as needed freely enters and exits, and the permeation of the inert gas into itself can be ignored. . As the separator, a resin nonwoven fabric or a metal net is particularly suitable. The resin nonwoven fabric is preferably made of polyolefin resin or nylon resin. Moreover, even if it is a nonwoven fabric which consists of a polyester-type resin, if the fiber is extended | stretched and it is difficult for the inert gas to penetrate | permeate, it can be used conveniently. The metal net is generally called a wire cloth, and is preferably a weaving method such as plain weave, twill weave, plain tatami weave, twill tatami weave and the like in which vertical lines and horizontal lines are knitted in a perpendicular direction. Iron, copper, aluminum, titanium, or an alloy thereof can be used as the material, but stainless steel is more preferable in consideration of price and life. On the other hand, the thermoplastic polyester sheet is preferably unstretched. This is because when the thermoplastic polyester sheet is stretched, the gas does not sufficiently permeate into the sheet, and the intended foamed sheet cannot be obtained.

  When an organic solvent is contained in the sheet, the crystallinity of the thermoplastic polyester sheet can be increased to 30% or more. As a result, the rigidity of the sheet is increased and it is difficult for the trace of the separator to remain on the surface of the sheet, and the permeation time of the inert gas can be shortened. Depending on the type of separator, the trace of the separator may not remain on the surface of the sheet, so that the treatment containing the organic solvent is not necessarily required. However, from the viewpoint of shortening the gas permeation time, it is preferable to carry out a treatment containing an organic solvent.

  Organic solvents used to increase the crystallinity of the resin sheet include benzene, toluene, methyl ethyl ketone, ethyl formate, acetone, acetic acid, dioxane, m-cresol, aniline, acrylonitrile, dimethyl phthalate, nitroethane, nitromethane, benzyl alcohol Etc. Of these, acetone is more preferable from the viewpoints of handleability and economy.

  As a method for containing the organic solvent in the roll, a method of immersing the roll in the organic solvent or a method of holding the roll in the vapor of the organic solvent is used. The latter method is superior to the former method in that an organic solvent may be used in a small amount and the additive added to the thermoplastic polyester sheet is hardly eluted.

  In the method of immersing the roll in the organic solvent, it is sufficient that the treatment time is several hours to several tens of hours at room temperature, and the content of the organic solvent in the resin does not increase so much even if the treatment is performed for a longer time. The treatment time when the roll is held in the vapor of the organic solvent to contain the organic solvent varies depending on the type of resin to be foamed and the thickness of the sheet. For example, when a roll made of polyethylene terephthalate is put into a closed container saturated with acetone vapor at room temperature and atmospheric pressure and acetone is infiltrated, if the sheet thickness is 0.6 mm, the processing time is 24 hours or more, 0 .9 mm is sufficient if it is 48 hours or longer. By such treatment, the content of acetone in the resin becomes 4 to 5% by weight.

If the roll is preliminarily containing an organic solvent to increase the crystallization degree of the sheet, it is not necessary to increase the crystallization degree by containing a large amount of inert gas. Can be shortened. For example, when carbon dioxide is permeated into a polyethylene terephthalate sheet at 60 kg / cm ² , if the sheet thickness is 0.6 mm, the permeation time is 1 hour or longer, and if it is 0.9 mm, 2 hours or longer is sufficient.

  Moreover, when a roll-shaped sheet | seat is immersed in the organic solvent, you may rewind a sheet | seat with the separator which prepared the sheet separately before the next process, and may produce a roll newly.

(2) Next, the roll formed as described above is placed in a high-pressure vessel and held in a pressurized inert gas atmosphere so that the thermoplastic polyester sheet contains an inert gas serving as a foaming agent. Examples of the inert gas include helium, nitrogen, carbon dioxide, and argon. Among these, carbon dioxide is preferable because it can be contained in a large amount in the thermoplastic polyester. Penetration pressure of the inert gas is preferably set to 30~70kg / cm ^2, further 50 kg / cm ² or more. The infiltration time of the inert gas is 1 hour or more, and more preferably the gas is infiltrated until it becomes saturated. The gas permeation time and gas permeation amount until saturation is reached vary depending on the type of resin to be foamed, the type of inert gas, the permeation pressure, and the thickness of the sheet. For example, when carbon dioxide is permeated into a polyethylene terephthalate sheet at 60 kg / cm ² , the permeation time is preferably 24 hours or longer if the sheet thickness is 0.6 mm, and 96 hours or longer if 0.9 mm. Under such conditions, the content of carbon dioxide in the resin is 6 to 7% by weight.

  (3) Further, the roll is taken out from the high pressure vessel, and the thermoplastic polyester sheet containing an inert gas is foamed by heating while removing the separator. Under the present circumstances, after taking out from a high pressure container, the bulk specific gravity of the foam obtained can be adjusted by adjusting the time until it makes it foam.

  Specifically, the longer this time, the larger the bulk specific gravity. The heating temperature at the time of foaming is set to be not lower than the melting point and not lower than the glass transition point of the resin. Examples of the heating means include a hot air circulation type foaming furnace, an oil bath, a molten salt bath, and the like, but it is preferable to use a hot air circulation type foaming furnace from the viewpoint of handleability. The foaming conditions in the hot-air circulating foaming furnace are set to a linear velocity such that the foaming temperature is about 240 ° C. and the foaming time is 1 to 5 minutes. Thereafter, the foamed sheet coming out of the furnace is wound up on a thermoforming roll whose temperature is adjusted to 150 ° C. or higher, and cooled to obtain a thermoplastic polyester foam sheet.

  (4) Since the obtained thermoplastic polyester foam sheet has skin layers on both sides, as shown in FIG. 1, the thermoplastic polyester foam sheet 20 having the fine bubbles 18 is positioned at a half position in the thickness direction. The light reflecting plate of the present invention is obtained by a method of cutting so that a cut surface 22 orthogonal to the thickness direction is formed, a method of removing the skin layer on one surface of the foam sheet, or the like.

  On the surface of the light reflector obtained by the method described above, the surface where the bubbles or recesses are exposed is added with pigments and fine particles that enhance light scattering, or another light reflector with a metal mirror is placed on the back. In the wavelength region of 350 to 1200 nm, a diffuse reflectance of 95% or more is exhibited.

  The shape of the light reflecting plate of the present invention is not particularly limited. For example, it can be used as a light reflecting plate for causing a side light of a liquid crystal display device to function as a surface light source in the shape of the sheet obtained by the above method.

  In addition, the sheet obtained as described above is formed into a shape that partially surrounds the periphery of the light source, for example, a shape having a concave multi-surface or a curved reflection surface, so that a light reflection plate for a lighting apparatus. Can be obtained. As this molding method, for example, a press molding machine provided with male and female molds is used, and a method of press molding under a heating condition such that the temperature of the thermoplastic polyester foam sheet is 200 to 240 ° C. is used.

The form of the light reflection plate for a lighting fixture is, for example, as shown in FIG. In FIG. 2, a lamp 13 is attached to the center of a light reflecting plate 11 having a concave and multiple reflecting surface, and the periphery of the lamp 13 is surrounded by the reflecting surface of the light reflecting plate 11.
In this case, the light reflecting plate 11 also serves as a housing. In FIG. 3, a housing 12 is further provided outside the light reflecting plate 11. The reflective surface of the light reflecting plate 11 may be a smooth curved surface.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example and a comparative example, this invention is not limited to the following Example. First, measurement items and evaluation items in Examples and Comparative Examples will be described.
(Bulk specific gravity)
The bulk specific gravity was measured by an underwater substitution method.
(Average bubble diameter)
The average bubble diameter was obtained by taking a SEM photograph of the cross section of the sheet, measuring the diameter of the bubbles contained in the constant cross-sectional area, and averaging the measured bubbles.
(Diffuse reflectance)
The diffuse reflectance was measured in a wavelength range of 350 to 1200 nm with a self-recording spectrophotometer (UV-3101C: manufactured by Shimadzu Corporation). In FIG. 5, the diffuse reflectance of each light reflector is shown as a relative value, assuming that the diffuse reflectance of the white plate made of hard barium sulfate fine powder is 100%.
(Shape retention)
Using the obtained foamed PET sheet, a conical light reflector for a lighting fixture having a diameter of 95 mm and a depth of 45 mm as shown in FIG. 4 was thermoformed by a press molding machine. The obtained light reflection plate was held by hand and force was applied to observe the presence or absence of deformation to evaluate shape retention.

Example 1
Polyethylene terephthalate (PET) sheets (SA-1206 grade, manufactured by Unitika Co., Ltd.) having different thicknesses and an olefin-based nonwoven fabric (FT300 grade, manufactured by Japan Vilene Co., Ltd.) as a separator were prepared. The PET sheet and the olefin-based non-woven fabric were overlapped and wound so that there was no portion where the surfaces of the PET sheet were in contact with each other to produce a roll. The roll was kept in acetone vapor for 48 hours at room temperature and atmospheric pressure and then removed. This roll was put into a high-pressure vessel, and 60 kg / cm ² of carbon dioxide gas was infiltrated for 2 hours. Next, the roll is taken out from the high pressure vessel, and while removing the separator of the olefin-based nonwoven fabric, only the PET sheet is continuously supplied to a hot-air circulating foaming furnace set at 240 ° C. so that the foaming time is 1 minute and foamed. I let you. The thickness of the obtained foamed sheet was 1.0 mm. At this time, the bulk specific gravity of the foam was adjusted by adjusting the time from when the roll was taken out of the high pressure vessel to foaming. Then, the light reflection board was obtained by removing the skin layer of one surface of the obtained foam sheet. The obtained light reflecting plate had a thickness of 0.8 mm, a bulk specific gravity of 0.26, an average bubble diameter of 1 μm, and a good shape retention.

(Comparative Example 1)
A light reflecting plate was produced in the same manner as in Example 1 except that the skin layer on one surface of the obtained foam sheet was not removed. The obtained light reflecting plate had a thickness of 0.8 mm, a bulk specific gravity of 0.28, an average cell diameter of 1 μm, and a good shape retention.

(Comparative Example 2)
UXZ1 (thickness 0.23 mm) manufactured by Teijin DuPont, which is a light reflecting film, was used as the light reflecting plate of Comparative Example 2. UXZ1 is a film biaxially stretched by mixing PET with barium sulfate.

  FIG. 5 shows the diffuse reflectance of the surface (cut surface) where the bubbles or recesses of the light reflecting plate of Example 1 are exposed, and the diffuse reflectance of the surface of the light reflecting plate of Comparative Examples 1 and 2. From FIG. 5, it can be seen that the diffuse reflectance of the surface of the light reflecting plate of the present invention where the bubbles or recesses are exposed is higher than the diffuse reflectance of the light reflecting plates of Comparative Examples 1 and 2.

  Also, the luminance of the surface of the light reflecting plate where the bubbles or recesses are exposed is higher than that of the sheet having skin layers on both sides.

It is typical sectional drawing which shows an example of the manufacturing method of the light reflection board of this invention. It is sectional drawing which shows an example of the light reflection plate for lighting fixtures. It is sectional drawing which shows the other example of the light reflection board for lighting fixtures. It is sectional drawing which shows the light reflection plate for lighting fixtures produced in the Example of this invention. It is a graph which shows the diffuse reflectance of the light reflection board of an Example and a comparative example. It is sectional drawing of the backlight apparatus in a liquid crystal display element of a sidelight system.

Explanation of symbols

11 Light Reflector 12 Housing 13 Lamp 20 Thermoplastic Polyester Foam Sheet 22 Cut Surface

Claims (2)

  It has a sheet shape made of a thermoplastic polyester foam having fine bubbles with an average cell diameter of 50 μm or less, a thickness of 100 μm or more and a bulk specific gravity of 0.7 or less, and one sheet surface has an unfoamed skin layer. And a light reflecting plate, wherein bubbles or recesses are exposed on the other sheet surface.   2. The light reflecting plate according to claim 1, wherein the thermoplastic polyester foam is formed in a shape having a concave polyhedral or curved reflecting surface.

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