JP2013133368A - Reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflector having high reflectivity and high rigidity.
A reflector 1 is a porous body having fine bubbles 7 which are closed cells, and is formed of, for example, a resin foam. An unfoamed surface layer 3 is formed on at least one surface of the reflecting plate 1. The surface non-foamed layer 3 is a region where fine bubbles are not present (or are present only minutely compared with the foamed layer 5). If the surface unfoamed layer 3 is too thin, the effect of improving the rigidity is small. Therefore, in order to increase the rigidity of the reflector, the thickness of the unfoamed surface layer is preferably 15 μm or more, and more preferably 20 μm or more.
[Selection] Figure 1

Description

  The present invention is used for a liquid crystal panel or the like, and relates to a reflector for a backlight panel.

  Conventionally, in a liquid crystal display device or the like, a backlight panel that emits light by illuminating light from the back side of a liquid crystal layer is used. There are two types of backlight panels: an edge light method in which light is incident from the side surface of the light guide plate and a direct type in which light is incident from a light source arranged below the liquid crystal layer. In the case of the edge light system, a reflector is installed adjacent to the light guide plate, and in the case of the direct type, a reflector is installed on the back surface of the light source. In any case, in order to increase the light use efficiency, the reflector is required to have a high light reflectance.

  As such a reflection plate, for example, there is a light diffusion reflection sheet using a thermoplastic polyester resin sheet in which closed cells having an average diameter of 50 μm or less are dispersed (Patent Document 1).

JP 2003-121616 A

  On the other hand, with the recent increase in size of liquid crystal panels, not only the reflectance but also the rigidity is required for the reflector. This is because if the rigidity of the reflector is insufficient, the reflector will bend and cause uneven brightness.

  In the case where a foam is used for the reflecting plate, as one method for increasing the rigidity, for example, there is a method for decreasing the expansion ratio of the foam sheet. That is, the rigidity of the reflector is increased by reducing the hole density. However, when the expansion ratio is lowered, the interface between the resin that reflects light and the air is reduced, which causes a problem that the reflectance of the reflector is lowered.

  Moreover, such a foam usually has a thin skin layer (unfoamed layer) formed on the surface layer. The non-foamed layer has higher rigidity than the foamed layer because there are no voids. Therefore, as one method for increasing the rigidity, there is a technique for increasing the rigidity by increasing the thickness of the unfoamed layer. However, if the unfoamed layer is made too thick, light is absorbed by the unfoamed layer, which causes a problem that the reflectance decreases.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a reflector having high reflectivity and high rigidity.

In order to achieve the above-mentioned object, the present invention provides a reflector for a backlight panel made of a thermoplastic resin foam, wherein a surface unfoamed layer is formed on at least one surface of the reflector, and the unfoamed layer The reflector has a thickness of 15 μm or more and a bubble number density of 10 9 / cm ³ or more.

  Moreover, it is a reflector for a backlight panel made of a thermoplastic resin foam, and the surface unfoamed layer formed on the surface of the reflector is formed on at least one surface of the reflector, and the surface unfoamed An intermediate unfoamed layer formed via a foamed layer is formed inside the layer in the thickness direction, the sum of the thicknesses of the surface unfoamed layer and the intermediate unfoamed layer is 15 μm or more, and the surface unfoamed layer The intermediate unfoamed layer is included in a thickness range of 1/6 or less of the total thickness of the reflecting plate from the surface of the reflecting plate on which the surface unfoamed layer is formed. .

  It is desirable that an average cell diameter of the thermoplastic resin foam is 0.1 to 20 μm. It is desirable that the total thickness of the reflecting plate is 0.3 mm or more. It is desirable that the specific gravity of the reflector is 0.7 or less. The thermoplastic resin is preferably a thermoplastic polyester resin, and is preferably a polyethylene terephthalate resin.

According to the present invention, since the thickness of the surface unfoamed layer is 15 to 50 μm, sufficient rigidity can be obtained. If the thickness of the surface unfoamed layer is less than 15 μm, the sheet has insufficient rigidity, and if it exceeds 50 μm, light absorption increases and affects the reflectance. Moreover, since the cell number density of the foamed layer formed in the surface non-foamed layer is 10 ^ 9 to 10 ^ 15 / cm ³ , a high reflectance can be obtained. If the bubble number density is less than 10 ^ 9 / cm ³ , the reflectivity decreases because the number of bubbles is too small, and if it exceeds 10 ^ 15 / cm ³ , light is transmitted, so the reflectivity is also decreased.

  Moreover, as an unfoamed layer, it is divided into a surface unfoamed layer and an intermediate unfoamed layer, and the total thickness is 15 to 50 μm, so that high rigidity can be obtained and the surface unfoamed layer is thinned. Therefore, light absorption can be suppressed. Therefore, light can be efficiently reflected in the foamed layer between the surface unfoamed layer and the intermediate unfoamed layer, and a high reflectance can be obtained.

  Moreover, many fine bubbles can be disperse | distributed because the average bubble diameter of a foam shall be 0.1-20 micrometers. Therefore, a high reflectance can be obtained.

  Moreover, if the total thickness of the reflector is 0.3 mm or more, the occurrence of wave wrinkles on the reflector can be suppressed. Moreover, if the specific gravity of a reflecting plate is 0.7 or less, weight reduction can be achieved and material cost can be reduced. In addition, by applying a polyethylene terephthalate resin, which is a thermoplastic polyester resin, as the thermoplastic resin, a reflector having excellent heat resistance and cost can be obtained.

  According to the present invention, it is possible to provide a reflector having high reflectivity and high rigidity.

FIG. 2 is a schematic diagram showing a cross section of a reflector 1. It is an enlarged view of the surface vicinity of the reflecting plate 1, Comprising: The A section enlarged view of FIG. Schematic diagram showing a cross section of the reflector 1a FIG. 4 is an enlarged view of the vicinity of the surface of the reflector 1a, and is an enlarged view of a portion B in FIG. The figure which shows the rigidity measuring apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a reflector 1 for a backlight panel used in a liquid crystal display device or the like, and FIG. 2 is an enlarged view of a portion A in FIG.

  The reflector 1 is a porous body having fine bubbles 7 which are closed cells, and is formed of, for example, a resin foam. More specifically, a thermoplastic resin sheet having fine bubbles or pores having an average cell diameter of 0.1 nm or more and 20 μm or less inside can be suitably used. If the average bubble diameter is 20 μm or less, a large number of fine bubbles can be dispersed, so that the reflectance can be improved.

  Reflecting plate 1 is preferably made of a thermoplastic polyester resin in view of its heat resistance. The thermoplastic polyester resin used in the present invention is not limited, but for example, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate and the like can be appropriately selected. These may be used individually by 1 type, and may mix and use 2 or more types. Among these, polyethylene terephthalate is preferable in terms of availability, economy, heat resistance, and the like.

  In the present invention, a crystallization nucleating agent, a crystallization accelerator, a bubbling nucleating agent, an antioxidant, an antistatic agent are added to the thermoplastic resin sheet before foaming within a range that does not affect the properties of the obtained reflector 1. Agents, UV inhibitors, light stabilizers, fluorescent brighteners, pigments, dyes, compatibilizers, lubricants, reinforcing agents, flame retardants, crosslinking agents, crosslinking aids, plasticizers, thickeners, thickeners, etc. Various additives may be blended. Moreover, you may laminate | stack resin containing the said additive on the obtained reflecting plate, and may coat the coating material containing the said additive. Applying a layer containing a UV inhibitor to at least one surface of the polyester resin foam is sufficient to prevent UV deterioration even when thermoplastic polyester resins or polyester elastomers that are susceptible to UV deterioration are used. Is particularly preferable.

  In addition, as thickness (T1 of FIG. 1) of the reflecting plate 1, it is desirable that it is 0.1 mm or more. If the thickness of the reflecting plate 1 is less than 0.1 mm, the rigidity is low and wrinkles are likely to occur, which is not preferable. From the viewpoint of increasing rigidity, the thickness of the reflector 1 is preferably 0.2 mm or more, and more preferably 0.3 mm or more.

  The specific gravity of the reflector 1 is preferably 0.7 or less, more preferably the specific gravity is less than 0.6, and the specific gravity is more preferably less than 0.5. If the specific gravity is large, the distribution of the fine bubbles 7 is not sufficient, and the effect of the fine bubbles is reduced.

  Further, the reflectance of the reflector 1 is not limited, but when used as a reflector of a liquid crystal panel, the total reflectance of the reflector 1 is desirably 90% or more. Further, from the viewpoint of energy saving, the reflectance is preferably 95% or more, and more preferably 98% or more.

  As shown in FIG. 2, the surface unfoamed layer 3 is formed on at least one surface of the reflector 1. The surface non-foamed layer 3 is a region where fine bubbles are not present (or are present only minutely compared with the foamed layer 5). If the surface unfoamed layer 3 is too thin, the effect of improving the rigidity is small. Therefore, in order to increase the rigidity of the reflector, the thickness of the unfoamed surface layer (t1 in the figure) is preferably 15 μm or more, and more preferably 20 μm or more.

  Next, the manufacturing method of the reflecting plate 1 is demonstrated. The method for introducing bubbles into the sheet is not limited. For example, a batch foaming method in which a resin sheet is impregnated with gas in a pressure vessel and then heated and foamed, or a thermoplastic resin sheet is extruded from a die of an extruder. There are an extrusion foaming method in which foaming is performed, and a stretching method in which a void is formed at the interface between the filler and the resin by extruding a thermoplastic resin sheet containing a filler and then stretching. Here, the manufacturing method of the reflecting plate 1 by a batch foaming method is shown as an example. In the case of the batch foaming method, there are advantages that the bubbles are more easily refined than the extrusion foaming method, thicker than the stretching method, and easy to reduce the specific gravity.

  In the batch foaming method, first, a thermoplastic resin sheet is produced, and a roll is formed by overlapping and winding the thermoplastic resin 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.

  On the other hand, the thermoplastic resin sheet is preferably unstretched. This is because when the thermoplastic resin sheet is stretched, the gas does not sufficiently permeate into the sheet, and the intended foamed sheet cannot be obtained.

  In the above method, the resin sheet may contain an organic solvent before the roll made of the resin sheet and the separator is held in the pressurized inert gas atmosphere and the resin sheet contains the inert gas. When an organic solvent is contained in the sheet, the crystallinity of the thermoplastic resin 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.

  Next, the obtained roll is put in a high-pressure vessel and held in a pressurized inert gas atmosphere so that the thermoplastic sheet contains an inert gas that becomes 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.

  Next, the roll is taken out from the high-pressure vessel and foamed by heating to a temperature equal to or higher than the softening temperature of the resin sheet under normal pressure 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. In addition, the heating temperature at the time of foaming is set to the melting point or less above the glass transition point of the resin.

  At this time, the surface non-foamed layer 3 is formed on the surface layer of the foam. The surface non-foamed layer 3 is formed, for example, by the gas that has permeated into the inside from the surface of the resin sheet before foaming. By reducing the amount of gas on the surface of the resin sheet, the fine bubbles 7 are not generated in the vicinity of the surface layer of the resin sheet during the subsequent foaming treatment, or the generation amount thereof is reduced. Therefore, in the non-foamed layer 3, the fine bubbles 7 are hardly observed and a solid resin portion is obtained.

  Next, another embodiment of the reflector will be described. FIG. 3 is a cross-sectional view showing a reflector 1a for a backlight panel used in a liquid crystal display device or the like, and FIG. 4 is an enlarged view of a portion B in FIG. In addition, about the structure which show | plays the function similar to the reflecting plate 1 in the reflecting plate 1a, the code | symbol same as FIG. 1, FIG. 2 is attached | subjected and the overlapping description is abbreviate | omitted.

  In the reflecting plate 1a, a surface unfoamed layer 3a and an intermediate unfoamed layer 9 are formed on at least one surface of the reflecting plate 1a. Moreover, the surface non-foamed layer 3b is provided in the other surface of the reflecting plate 1a. The surface unfoamed layers 3 a and 3 b have the same form as the surface unfoamed layer 3. On the other hand, the intermediate unfoamed layer 9 is formed on the inner side in the thickness direction of the surface unfoamed layer 3a via the foamed layer 5a. That is, the surface unfoamed layer 3a, the foamed layer 5a, the intermediate unfoamed layer 9, the foamed layer 5b, and the surface unfoamed layer 3b are formed in order from one surface of the reflector 1a. The intermediate non-foamed layer 9 is a region where the fine bubbles 7 are not present (or are present only minutely compared with the foamed layers 5a and 5b), similarly to the surface unfoamed layer 3.

  The total thickness of the reflection plate 1a (T2 in FIG. 3) is substantially the same as the total thickness of the reflection plate 1 (T1 in FIG. 1). As shown in FIG. 4, the total thickness (t2 + t3 in the figure) of the surface unfoamed layer 3a and the intermediate unfoamed layer 9 is preferably 15 μm or more. That is, the thickness of the surface unfoamed layer 3a may be less than 15 μm.

  Further, the thickness (T3 in the figure) including the foamed layer 5a and the surface unfoamed layer 3a and the intermediate unfoamed layer 9 formed from the surface of the reflector 1a is 1/6 of the total thickness T2 of the reflector 1a. Must be in the following range: This is because if the thickness is out of this range, the reflector has insufficient rigidity. The thickness in which both unfoamed layers are present is preferably 1/7 or less, more preferably 1/8 or less of the total thickness T2 of the reflector 1a.

  In addition, the surface unfoamed layer 3a can increase the surface unfoamed layer by promoting gas desorption from the surface by heating after removing the resin sheet containing the inert gas. At this time, when heated under appropriate conditions, the intermediate unfoamed layer 9 can also be generated due to the effect of thermal crystallization of the resin.

According to the present invention, since the surface unfoamed layer 3 having a predetermined thickness or more is formed on the surface of the reflector 1, rigidity can be ensured and the bubble number density is 10 ^ 9 / cm ³ or more. Therefore, sufficient reflectance can be obtained. Similarly, by providing the intermediate unfoamed layer 9 together with the surface unfoamed layer 3a, the total thickness with the intermediate unfoamed layer 9 is increased even if the thickness of the surface unfoamed layer 3a is reduced. Rigidity can be ensured by setting the thickness at which the foamed layer 3a and the intermediate unfoamed layer 9 are formed to 1/6 or less of the total thickness.

(Measurement evaluation method)
Hereinafter, the present invention will be described in detail by way of examples. Measurement and evaluation were performed by the following methods.

(1) Sheet thickness The thickness at the four corners, four sides of the sample and the center of the sheet was measured with a micrometer, and the average value of a total of nine points was taken as the sheet thickness.

(2) Average bubble diameter It calculated | required according to ASTMD3576-77. An SEM photograph of the cross section of the sheet was taken, a straight line was drawn in the horizontal direction and the vertical direction on the SEM photograph, and the length t of the bubble chord crossed by the straight line was averaged. Assuming that the magnification of the photograph is M, the average bubble diameter d was determined by substituting it into the following equation (d = t / (0.616 × M)).

(3) Specific gravity of the foam The specific gravity of the foam was determined by dividing the density (ρf) of the foam sheet measured by the underwater substitution method by the density of water (ρw).

(4) Bubble number density of foam An electron micrograph of the foam cross section was taken at M magnification. The photographing magnification was adjusted so that 10 or more bubbles were present in the area of area A (cm 2) on the photograph. Next, the number of bubbles in the area of A (cm2) was counted, and this was defined as n. The cell number density N (number / cm 3) at any five locations was determined by the following formula, and the average value was taken as the cell number density of the foam.

(5) Reflectance The reflectance was measured with a spectrophotometer (U-4100, manufactured by Hitachi High-Tech Co., Ltd.) under the condition of a spectral slit of 4 nm and a spectral total reflectance at a light wavelength of 550 nm. The reference used an aluminum oxide white plate (210-0740: manufactured by Hitachi High-Tech Fielding Co., Ltd.), and the measured value was a value relative to the reference.

(5) Sheet Rigidity A test body having a length of 70 mm and a width of 10 mm was cut out from the reflector and measured by the rigidity measuring apparatus 10 shown in FIG. In the stiffness measuring apparatus 10, 5 mm at one end of the test body 15 was fixed with the clamp 11, and a weight 25 of 2.25 g was disposed at the other end. The amount of deflection C at this time was measured, and if the amount of deflection was less than 40 mm, it was determined to be acceptable, and if it was 40 mm or more, it was determined to be unacceptable.

Example 1
After adding 2 parts by weight of a polyester elastomer (grade: Hytrel 2551, manufactured by Toray DuPont) to 100 parts by weight of polyethylene terephthalate (grade: SA-1206, manufactured by Unitika, ρs = 1.34), kneading was carried out. The sheet was formed into a sheet of 5 mm thickness × 250 mm width × 60 m length. Next, after heating the said sheet | seat in a 200 degreeC thermostat for 5 second, it put into the pressure vessel, pressurized to 6 MPa with the carbon dioxide gas, and the carbon dioxide gas was osmose | permeated to the resin sheet. The penetration time was 72 hours. After completion of the infiltration, the roll was taken out from the pressure vessel, and while removing the separator, only the resin sheet was supplied to a hot air oven set at a temperature lower than the melting point of the resin and foamed.

The thickness of the obtained foam sheet was 0.75 mm, and the specific gravity was 0.5. The unfoamed layer had a surface unfoamed layer on one side and a thickness of 15 μm. The foam sheet had a cell number density of 10 ^ 12 / cm ³ and a reflectance as high as 100%.

(Example 2)
Only the surface heating condition of the sheet having the same composition as in Example 1 was changed to 180 ° C. for 5 seconds, and the other was obtained under the same conditions as in Example. The thickness of the obtained foamed sheet was 0.74 mm, the surface unfoamed layer and the intermediate unfoamed layer were present, the thicknesses were 10 μm and 15 μm, respectively, and the total thickness of the unfoamed layer was 25 μm . The specific gravity of the sheet was 0.5. The foam sheet had a cell number density of 10 ^ 12 / cm ³ and a reflectance as high as 100%.

(Comparative Example 1)
A sheet having the same composition as in Example 1 was not heated before gas permeation, and a foamed sheet was obtained under the same conditions as in Example. The thickness of the obtained foamed sheet was 0.74 mm, only the surface unfoamed layer was present, the thickness was 5 μm, and the specific gravity of the sheet was 0.5. The foam sheet had a cell number density of 10 ^ 12 / cm ³ and a reflectance of 100%. However, when the rigidity was evaluated, it was a rejected level.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

DESCRIPTION OF SYMBOLS 1 ......... Reflection plates 3, 3a, 3b ......... Surface unfoamed layers 5, 5a, 5b ......... Reflection plate 7 ......... Microbubbles 9 ......... Intermediate unfoamed layer 10 ......... Rigidity measuring device 11 ......... Clamp 15 ......... Test body 17 ......... Weight

Claims (7)

A reflector for a backlight panel made of a foam of a thermoplastic resin, wherein a surface unfoamed layer is formed on at least one surface of the reflector, and the thickness of the unfoamed layer is 15 to 50 μm, A reflector having a bubble number density of 10 ^ 9 to 10 ^ 15 / cm ³ or more in a portion excluding an unfoamed layer. A reflector for a backlight panel made of a foam of a thermoplastic resin, the surface unfoamed layer formed on the surface of the reflector on at least one surface of the reflector, and the surface unfoamed layer An intermediate unfoamed layer formed through a foamed layer is formed in the thickness direction inside, the total thickness of the surface unfoamed layer and the intermediate unfoamed layer is 15 to 50 μm, and the surface unfoamed layer And the intermediate unfoamed layer are included in a thickness range of 1/6 or less of the total thickness of the reflector from the surface of the reflector on which the surface unfoamed layer is formed, and the surface unfoamed layer and the intermediate unfoamed layer reflector, wherein the bubble number density of the portion excluding the foamed layer is 10 ^ 9-10 ^ 15 / cm ³ or more.   3. The reflector according to claim 1, wherein an average cell diameter of the thermoplastic resin foam is 0.1 to 20 μm.   The total thickness of the said reflecting plate is 0.3 mm or more, The reflecting plate in any one of Claims 1-3 characterized by the above-mentioned.   The specific gravity of the said reflecting plate is 0.7 or less, The reflecting plate in any one of Claims 1-4 characterized by the above-mentioned.   The said thermoplastic resin is a thermoplastic polyester-type resin, The reflecting plate in any one of Claims 1-5 characterized by the above-mentioned.   The reflector according to any one of claims 1 to 6, wherein the thermoplastic resin is polyethylene terephthalate.

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