JP2008192406A - Reflecting sheet and surface light source device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a reflecting sheet which is thin, light-weighted, and high in reflectance, and has less deflection by heat, and furthermore, a surface light source device and a liquid crystal display device using it. <P>SOLUTION: The reflecting sheet which includes synthetic pulp and a core-in-sheath structural fiber, in which in the core-in-sheath structural fiber, the core part is composed of an ester based polymer and the sheath part is composed of an ethylene based polymer is provided. Furthermore, the surface light source device made by using such reflecting sheet, and the liquid crystal display device having the surface light source device as a backlight light source means are provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a reflective sheet made of synthetic fiber and synthetic pulp, having high light reflectivity and low heat deflection. Furthermore, the present invention relates to a surface light source device using the reflection sheet and a liquid crystal display device using the surface source device as a backlight unit.

In recent years, many reflective sheets have been used as main components of liquid crystal display devices such as mobile phones, personal computers, and televisions. In particular, it is important that liquid crystal display devices used in mobile phones can be thinned, reduced in power consumption, and reduced in weight, and improvement in display quality of liquid crystal display devices is also desired. Is required to be supplied to the liquid crystal portion. In order to satisfy the above requirements, it is necessary to increase the amount of light supplied from the light source, and the reflection sheet is required to have high reflection efficiency and high luminance.
The backlight unit of the liquid crystal display device includes a method in which a light source is placed directly below the liquid crystal unit and a method in which the light source is placed beside a transparent light guide plate. In the former method, the reflection sheet is arranged so as to reflect the light of the lamp below the liquid crystal unit, and in the latter method, the light guide plate is placed beside the light guide plate and below the light guide plate so as to reflect the light. Placed in.
Conventionally, as a material of the reflective sheet, a metal plate such as aluminum having a metal thin film layer mainly composed of silver, or a metal plate such as aluminum coated with a white pigment, made of white polyethylene terephthalate A sheet is used. Moreover, the thing made from polyolefin is also reported (for example, refer patent document 1).
However, in the above prior art, in order to improve the reflection characteristics as a reflection sheet, it is necessary to increase the thickness of the sheet itself or to make a porous sheet by containing a large amount of an inorganic filler. When the thickness and weight are reduced, the reflection characteristics become inferior, and a reflection sheet that can be reduced in thickness and weight while having sufficient reflection characteristics has not been obtained.
For this reason, a reflection sheet made of fibers has been considered (see, for example, Patent Document 2). As a result, a light weight and high reflectivity were obtained, but the reflective sheet was bent when the temperature was raised by the heat of the light from the lamp at the time of use, and there was a possibility that it was not suitable for long-term use.

JP-A-11-174213 JP 2005-316149 A

  An object of the present invention is to obtain a reflective sheet that is thin, lightweight, has high reflectivity, and is less bent by heat. It is another object of the present invention to obtain a surface light source device and a liquid crystal display device in which light reflection does not change due to heat.

In view of the above problems, the present inventors have conducted intensive studies, and as a result, have found that the reflective sheet preferably contains synthetic pulp and specific core-sheath structure fibers, and have completed the present invention.
[1] A reflective sheet comprising synthetic pulp and core-sheath fiber, wherein the core of the core-sheath fiber is made of an ester polymer and the sheath is made of an ethylene polymer.
[2] The reflective sheet according to [1], wherein the core-sheath structure fiber has an average fiber diameter of 2.2 dtex or less.
[3] The light reflecting sheet according to [1] or [2], wherein the synthetic pulp is 70% by weight or more based on the total amount of the synthetic pulp and the core-sheath structure fiber.
[4] The reflective sheet according to any one of [1] to [3], which has a thickness of 300 to 700 μm.
[5] The reflective sheet according to any one of [1] to [4], which has an ultraviolet absorber layer on at least one surface.
[6] A surface light source device using the reflecting sheet according to any one of [1] to [5].
[7] A liquid crystal display device using the surface light source device according to [6] as backlight light source means.

  According to the present invention, it is possible to provide a reflective sheet that can be reduced in thickness and weight while having sufficient reflection characteristics, and that can withstand long-term use with little heat deflection. In particular, if it is used as a reflection sheet incorporated in a liquid crystal display device of a mobile phone or a personal computer, the light reflection state does not change and the screen is bright, so that it can be suitably used.

Hereinafter, the present invention will be specifically described.
Synthetic pulp Various known pulps are used as the synthetic pulp according to the present invention. The synthetic pulp is made of a synthetic resin and has a branched structure and a short fiber length.
Various known resins can be used for the synthetic pulp, but it is preferably made of a thermoplastic resin, and more preferably polyolefin. Examples of the polyolefin include homopolymers of α-olefins having 2 to 6 carbon atoms, or copolymers of these, and other copolymerizable olefins, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, acrylic Preferred examples include copolymers obtained with acid esters, methacrylate esters, vinyl acetate, and the like, and polymers obtained by grafting unsaturated carboxylic acid monomers with peroxides to these homopolymers and copolymers. Particularly preferred are crystalline polymers and copolymers of ethylene, propylene, 1-butene, 3-methyl-1-butene or 4-methyl-1-butene. Specifically, low density polyethylene, linear low density polyethylene and elastomer (ethylene-α-olefin copolymer), medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, ethylene-methacrylic acid copolymer, maleic acid And acid-modified polyethylene with acrylic acid, polypropylene, polybutene, poly-3-methylbutene, poly-4-methylbutene, and mixtures thereof. These polyolefins may be produced by any production method as apparent from the gist of the invention. Among these, melting point 100-175 ° C., density 0.900-0.980 g / cm 3, molecular weight distribution (Mw / Mn) 1.5-3.5, melt flow rate (MFR: ASTM D1238, 190 ° C.) 0.1 The polyethylene is preferably 100 g / 10 min, and more preferably high-density polyethylene from the viewpoint of moderate flexibility and rigidity and easy handling.

  The fiber of the synthetic pulp according to the present invention has an average length length (hereinafter referred to as “average fiber length”) of usually 0.05 to 50 mm, preferably 0.05 to 10 mm, and in particular. Preferably it is 0.1-5 mm. When the average fiber length is within the above range, it can be preferably used as a reflection sheet when mixed with the core-sheath structure fiber.

  In the synthetic pulp fiber according to the present invention, the minimum value of the diameter (hereinafter referred to as “fiber diameter”) is preferably about 0.5 μm, and the maximum value of the fiber diameter is preferably about 50 μm. . When the fiber diameter is within the above range, the reflective sheet can be preferably used when mixed with the core-sheath structure fiber.

Here, the measurement method of the said average fiber length and fiber diameter is demonstrated.
(1) Average fiber length Using an automatic fiber measuring machine (product name: FiberLab-3.5) manufactured by Metso Automation of Finland, the fiber length was measured for 12000 to 13000 fibers, and the fiber length was incremented by 0.05 mm. The value obtained by substituting the number average fiber length and the number of fibers of each class classified in (1) into the following formula is the average fiber length.

Average fiber length (mm) = Σ (Nn × Ln ³ ) / Σ (Nn × Ln ² )
Ln: Number average fiber length of each class (mm)
Nn: Number of fibers of each class Here, the average fiber length Ln of each class is obtained by the following equation.
Ln = ΣL / N
L: Measured fiber length of each individual in one class N: Number of fibers in one class

The number average fiber length is measured as follows.
The measurement is performed by dispersing the fibers in water at a dilute concentration, irradiating the fibers flowing through the capillary with xenon lamp light, collecting a video signal with a CCD (charge coupled device) sensor, and analyzing the image. More specifically, fibers are dispersed in 0.02% by weight of water, and an automatic fiber measuring machine (product name: FiberLab-3.5) manufactured by Metso Automation Co., Ltd., Finland is used. Measure about. Each fiber length is measured in increments of 0.05 mm, and measurement results of both the fiber length and the abundance (%) of fibers corresponding to each fiber length are obtained.

(2) Fiber diameter The fiber diameter is measured by observing one or one fiber with an optical microscope or an electron microscope. Specifically, the maximum value and the minimum value of the fiber diameter are measured as follows.
Maximum value: observed with a Keyence digital HF microscope VH8000 at a magnification of 100 times, randomly selected 100 locations of 10 μm or more, measured the fiber diameter of the selected portion, and made the maximum value of the measured value .
Minimum value: observed with a scanning electron microscope JSM6480 manufactured by JEOL Ltd. at a magnification of 3000 times,
100 portions are randomly selected for a portion of less than 10 μm, and the fiber diameter of the selected portion is measured to obtain the minimum value of the measured values.

  The fiber of the synthetic pulp according to the present invention has a branched structure. Examples of the branched structure include a form as shown in FIG. The branching of the fiber is confirmed by observing with an optical microscope or an electron microscope. FIG. 1 is a photograph obtained by observing a branched fiber assembly of Example 1 described later at 75 times with a digital HF microscope VH8000 manufactured by Keyence Corporation.

Synthetic pulp production method The synthetic pulp according to the present invention can be obtained by various known methods, but it is preferable to use a method of flushing a thermoplastic resin solution in the presence of water and a suspending agent.
Specifically, the raw material resin is dissolved in a solvent capable of dissolving the resin, and a suspending agent and water are added to form an emulsion. As the raw material resin, the above-described polyolefin is preferable, and among them, high-density polyethylene in which the fibers become thinner is preferable. Solvents include saturated hydrocarbons such as butane, pentane, hexane, heptane, octane, and cyclohexane, aromatics such as benzene and toluene, and carbon halides such as methylene chloride, chloroform, and carbon tetrachloride. A material that dissolves the raw material resin and hardly remains in the fiber aggregate obtained by volatilization at the time of flashing is appropriately selected.

  The suspending agent is considered to reduce the interfacial tension of the fibers and improve the contact efficiency between the fungi and the antibacterial agent, and as a result, contribute to the improvement of the antibacterial action. As the suspending agent, hydrophilic polymers such as polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylate, gelatin, tragacanth gum, starch, methylcellulose, carboxymethylcellulose, and the like can be used. A general nonionic surfactant, cationic surfactant or anionic surfactant can be used in combination. Among these, from the viewpoints of productivity, contribution to antibacterial action, etc., a polyvinyl alcohol-based hydrophilic polymer is particularly preferable, and polyvinyl alcohol having a polymerization degree of 200 to 1000 is preferable. The amount of the suspending agent is preferably 0.1 to 5% by mass. In the production process, when the operation is performed such that a part of the added suspending agent is removed, it is appropriately adjusted and added, such as adding more. As a standard of the addition amount, it is 0.1 to 10 parts by mass with respect to 100 parts by mass of the raw material resin. By adding the suspending agent, the emulsion can be stabilized, and fiber cutting after flushing can be stably performed in water.

The flash is to volatilize the solvent by reducing the pressure of the polymer dissolved in the solvent at high pressure. In particular, when a polyolefin solution dispersed in an aqueous medium in the presence of a suspending agent is flushed by a method as described in JP-A-48-44523, the shape of the fibers randomly branched is obtained. A synthetic pulp according to the present invention is obtained. In the flash, the obtained emulsion is heated to 100 to 200 ° C., preferably 130 to 150 ° C., and the pressure is set to 0.1 to 5 MPa, preferably 0.5 to 1.5 MPa. The solvent is vaporized at the same time as flushing out. The decompression condition is preferably a pressure of 1 kPa to 95 kPa, and the ejection destination is preferably an inert atmosphere such as a nitrogen atmosphere. The pressure indicates an absolute pressure.
By flashing as described above, an indefinite-length fiber having a branched structure can be obtained. This fiber is further cut and beaten with a Waring blender, a disc refiner or the like to obtain a desired length. Is preferred. In that case, it is preferable to perform the said cutting | disconnection and beating process as a water slurry of 0.5-5 g / liter density | concentration of a fiber. After drying, it may be opened with a mixer or the like as desired.
According to the method described above, an aggregate of fibers having a branched structure, that is, a synthetic pulp according to the present invention can be preferably produced.

Core- sheath structure fiber The core-sheath structure fiber according to the present invention has a core portion made of an ester polymer and a sheath component made of an ethylene polymer. A core-sheath structure fiber is comprised by the core part near the center of a fiber, and the sheath part in the outer side.

  Examples of the ester polymer constituting the core include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and wholly aromatic polyester. Among these, polyethylene terephthalate is preferably used. These ester polymers may be one kind or a mixture of two or more kinds. In addition, various additives, pigments and the like may be included within the range not detracting from the object of the present invention. When the raw material resin of the core is polypropylene, it is not preferable because the heat deflection occurs when it is formed into a reflective sheet.

  Examples of the ethylene polymer constituting the sheath include low density polyethylene, linear low density polyethylene and elastomer (ethylene-α-olefin copolymer), medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, and ethylene-methacrylic acid. Examples thereof include copolymers, acid-modified polyethylene with maleic acid and acrylic acid. Alternatively, a copolymer based on them or a blend with other polymers based on them may be mentioned. The raw material resin of the sheath component is preferably the same type as the thermoplastic resin used for synthetic pulp. This is because, in order to improve the paper strength of the synthetic paper obtained by wet papermaking and reduce fiber dusting, it is preferable to heat-treat the wet papermaking synthetic paper with a hot roll. When the raw material resin for the sheath component and the raw material resin for the synthetic pulp are the same, the fibers are fused together to obtain good physical properties. On the other hand, in the case of different raw materials, the fibers are not fused to each other, so that the raw material fibers are bonded to the heat roll to cause production problems, and the obtained sheet is likely to generate dust. When the raw material resin of synthetic pulp is high-density polyethylene, the fibers are thin and have high reflectivity, which is preferable. High density polyethylene is preferred, and among these, high density polyethylene is preferred. These ethylene polymers may be one kind or two or more kinds may be mixed. In addition, various additives, pigments, and the like may be included as long as the object of the present invention is not impaired.

  Thus, when the core part is an ester polymer and the sheath part is an ethylene polymer, when the heat is applied to obtain the reflection sheet, the core part does not melt but the sheath part melts. Since the core part does not melt, there is little deflection due to the heat of the reflection sheet, and the sheath part melts, so that the fibers adhere firmly. In addition, when heat is applied when using the reflective sheet, the core portion does not expand due to heat, and the bending due to heat is small. When the fiber mixed with the synthetic pulp does not have a core-sheath structure, it is not preferable because the bending due to heat is large.

  There is no restriction | limiting in particular about the cross-sectional shape of a core sheath structure fiber. The cross-sectional shape of the fiber may be a circle or an ellipse, or may be an irregular cross-section such as a polygon. The cross-sectional shape of the core is not particularly limited, and may be circular or elliptical, or may have a modified cross-section such as a polygon.

Moreover, there is no restriction | limiting in particular also about arrangement | positioning of a core and a sheath. The core may be centered or offset from the center (eccentric) with respect to the cross section of the fiber, or a part of the core may protrude from the fiber surface.
The weight ratio of the core portion to the sheath portion of the core-sheath structure fiber is not particularly limited, but is usually about 1: 4 to 4: 1, and usually 1: 1. When there are few core parts, heat-flexibility is inferior, and when there are few sheath parts, adhesive strength may be insufficient.

The average fiber diameter of the core-sheath structure fiber according to the present invention is not preferable if the fiber is too thick, because the reflectance decreases. Therefore, it is preferable that the average fiber diameter is as small as possible in a range where a core-sheath structure can be obtained, and specifically, it is preferably 2.2 dtex or less. The method for measuring the fiber diameter uses the same method as for the synthetic pulp.
The core-sheath structure fiber according to the present invention is a relatively short fiber. The length of the fiber is not particularly limited, but one having a length suitable for wet papermaking by mixing with synthetic pulp is used.

  The core-sheath structure fiber can also be obtained by composite spinning, drawing and opening. In that case, a method of spinning with a circular or rectangular composite spinneret having a plurality of spinning holes is generally used. Stretching includes a method using aerodynamic force or a roller, and an independent circular cross-section jet or the like can be used. As the opening method, a method using an air flow or a method of charging using friction or high voltage is generally used. The fiber thus obtained is cut to a cut length of 1 to 25 mm, preferably 3 to 15 mm. Next, using a disaggregator, the obtained fibers are disaggregated in a solution and dispersed as short fibers. If the fibers are uniformly dispersed, papermaking is easy.

Reflective sheet The reflective sheet of the present invention comprises the synthetic pulp and the core-sheath structure fiber. The reflective sheet of the present invention may contain other fibers in addition to the pulp and fibers as long as the object of the present invention is not impaired, or may contain other resins and additives. For example, a light resistance agent or an antistatic agent may be applied or impregnated in the sheet in order to suppress deterioration due to light or to suppress chargeability of the sheet.

  Since the reflection sheet of the present invention has a high reflectance when irradiated with light and is less deflected by heat, it can be used in a long-term surface source device. The reflectance can be measured by, for example, a spectrophotometer U-3010 manufactured by Hitachi High-Technologies Corporation. Deflection by heat, for example, cut out a sample to 20cm x 10cm, affix a double-sided tape on both sides of 10cm, affix to an aluminum plate and heat at 80 ° C for 15 minutes with a hot air dryer, Appearance can be evaluated by visual inspection.

  In the reflective sheet of the present invention, the fibers of the synthetic pulp and the core-sheath structure fibers are mixed, and the fiber portions and the void portions generated between the fibers are in a randomly mixed state. In the synthetic pulp, the fibers are divided into branched shapes, and the tips of the fibers are thin and branched into a large number and entangled with the core-sheath structure fibers. When light is irradiated onto the reflection sheet, the light is reflected and refracted on the surface of the fiber and dispersed in a plurality of directions. Light repeatedly reflects and refracts in a plurality of directions on the fiber surface, and travels straight in the void portion. The more times the light strikes the fiber, the more reflection and refraction occurs.

  Moreover, the reflection sheet of the present invention has little bending when heated. Since the fiber normally expands when heated, when the expanded fiber is made into a sheet, the strength is lowered, and thus bending occurs. Since the ester-based polymer in the core is highly oriented and crystallized in order to stretch when the fiber is produced, there is little expansion due to heat. Thereby, it is considered that the entire core-sheath structure fiber is prevented from expanding, and as a result, the deflection due to heat is small. Moreover, it seems that the core-sheath structure fibers need to be bonded to each other to some extent by heat in order to bend by heat. Moreover, the fact that the fibers of the synthetic pulp are bonded to each other also affects the deflection due to heat.

  The reflective sheet of the present invention has a thickness of usually 300 to 700 μm, preferably 400 to 600 μm. If it is too thick, the flexibility is impaired, and the product cannot be taken out in a roll shape, which may make it difficult to handle. If the thickness is too thin, the light is not reflected and refracted and is transmitted through the reflecting sheet, which is not preferable.

The reflection sheet of the present invention has a basis weight of 150 to 300 g / m ² , preferably 180 to 250 g / m ² . If the basis weight is too small, the amount of light that is transmitted when the reflection sheet is irradiated with light increases, and the reflectance may decrease. In addition, when the basis weight is constant and the thickness of the reflection sheet is reduced, the fibers contact each other and the void portion disappears, and the reflected and refracted light is not dispersed in multiple directions, or is absorbed in that portion and the reflectance is reduced. May decrease.

Production Method of Reflective Sheet The reflective sheet of the present invention can be obtained by various known methods, but can usually be produced as follows.
That is, a synthetic pulp and a core-sheath structure fiber are obtained and mixed, respectively, this is wet-made, dried, and heated to join the fibers to be a sheet.

For paper making, a paper machine is used. What is necessary is just to use what is generally used for a paper machine, and should just select a papermaking density | concentration suitably according to the fabric weight of the target reflective sheet. That is, if the papermaking concentration is low, papermaking with a low weight can be performed, and a uniform papermaking product is obtained by increasing the number of papermaking. If the papermaking concentration is high, papermaking with a high basis weight becomes possible, so it is necessary to select a concentration that matches the production speed.
In addition, it is preferable to add a surfactant, a dispersant, and a thickener as appropriate in the disaggregation step and the paper making step because even more uniform short fiber dispersion or uniform paper making becomes possible.

  The paper-made product is moved on a conveyor and dehydrated, and is heat-treated using a heat treatment apparatus such as a Yankee dryer or a flat calendar. A press roller may be used after heat treatment with a hot air dryer, a suction dryer or the like. In any of these cases, it is generally preferable to carry out at about 100 ° C to 110 ° C.

  Subsequently, the wet paper sheet is heat treated with a calender. This treatment is for heat-bonding the synthetic pulp and the core-sheath fiber, and the heat treatment condition is higher than the melting point of the polymer having the lowest melting point among the polymers constituting the synthetic pulp and the core-sheath fiber. It is preferable to apply a temperature lower than the melting point of the polymer having the highest melting point. When a temperature lower than the melting point of the polymer having the lowest melting point among the polymers constituting the synthetic pulp and the core-sheath structure fiber is applied, the short fibers cannot be thermally bonded, and practical strength cannot be obtained. Further, when a temperature equal to or higher than the melting point of the polymer having the highest melting point is applied, the synthetic pulp and the core-sheath structure fiber are all melted, and the void portion of the sheet disappears, so that the reflectance decreases. Specifically, it is preferably performed at 125 to 136 ° C. If it is this temperature, the polymer of the core part of a core-sheath structure fiber will not melt, but the polymer of a sheath part will melt | dissolve and fibers will adhere | attach easily. The reflective sheet of the present invention can enable adhesion between core-sheath structure fibers or synthetic pulp at a low temperature by using an ethylene polymer for the sheath part of the core-sheath structure fibers.

Applications The surface light source device of the present invention uses the reflection sheet of the present invention. Examples of the surface light source device include a liquid crystal display and a backlight light source for a display body. Particularly, a thin backlight used for a thin panel using an LED or a cold cathode tube as a light source such as a mobile phone or a PDA. A unit.
Moreover, it can be set as the liquid crystal display device which uses the surface light source device using the reflective sheet of this invention as a backlight light source means.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by the said Example. About the obtained reflection sheet, the reflectance and the heat flexibility were measured. The results are shown in Table 1.

Fiber diameter Photographs were taken with an electron microscope, and the diameters of 50 fibers were measured and averaged.
A test piece having a basis weight of 100 × 100 mm was sampled, measured for weight, and calculated per 1 m ² .
Thickness measurement was performed by using a sample used for the basis weight measurement, and measuring n = 9 with a digital thickness meter in conformity with JIS Z1702 to obtain an average value.
Reflectivity A 150φ integrating sphere was installed in a Hitachi auto-recorded spectrophotometer (model U-3010), and the value at a wavelength of 550 nm was measured to obtain the reflectivity.
Thermal flexibility Sample was cut into 20cm x 10cm, double-sided tape was applied to both sides of 10cm on one side of the sample, and it was attached so as not to float on a 3mm aluminum plate, and heated with a hot air dryer at 80C for 15 minutes. At that time, the case that did not bend was marked with ◯, and the case that was bent was marked with ×.

(Example 1)
A core-sheathed fiber with a core of polyester terephthalate and a sheath of polyethylene (Teijin Fibers Co., Ltd. TJ04EN (fiber diameter 1.2 dtex, fiber length 5 mm) 10% by weight and synthetic pulp (Mitsui Chemicals "SWP") "(Registered trademark) E620) 90% by weight was put in a 2L household mixer, filled with water, and the fiber was opened. This was put into a square paper machine measuring 25cm in length x 25cm in width x 30cm in height, A sheet having a thickness of 650 μm and a basis weight of 210 g / m 2 was obtained, and then this sheet was calendered at 129 ° C. with a calender machine (manufactured by Yuri Roll Machinery Co., Ltd.) to a thickness of 500 μm, and the surface was fluffy The synthetic pulp used was observed with a digital HF microscope VH8000 manufactured by Keyence Corporation at a magnification of 75 times. To become like. Reflectivity of the obtained reflective sheet was 98.5%, heat deflection of evaluation it was good without flexing.

(Examples 2-6, Reference Examples 1-5)
A reflective sheet was obtained in the same manner as in Example except that synthetic pulp, core-sheath fiber and reflective sheet were as shown in Table 1. Their reflectivity and thermal flexibility were evaluated.

(Comparative Example 1)
A reflective sheet was obtained in the same manner as in Example 1 except that no core-sheath fiber was used and only synthetic pulp was used. The reflectance of the obtained reflection sheet was 98.4%, and the evaluation of thermal flexibility was unfavorable because deflection occurred.

(Comparative Example 2)
Example 1 except that 30% by weight of the core-sheath structure fiber having a core of polypropylene and a sheath of polyethylene and 70% by weight of synthetic pulp (“SWP” (registered trademark) E620 manufactured by Mitsui Chemicals) made of high-density polyethylene is used. Thus, a reflection sheet was obtained.
The reflectance of the obtained reflection sheet was 97.4%, and the evaluation of the heat deflection property was unfavorable because the deflection occurred.

(Comparative Example 3)
A reflective sheet was obtained in the same manner as in Comparative Example 2 except that the fiber diameter of the core-sheath fiber was changed to 2.2 dtex.
The reflectance of the obtained reflection sheet was 97.4%, and the evaluation of the heat deflection property was unfavorable because the deflection occurred.

(Comparative Example 4)
Example except that 30% by weight of a core-sheath structure fiber having a core of polyester terephthalate and a sheath of polyethersulfone and 70% by weight of synthetic pulp made of high-density polyethylene (“SWP” (registered trademark) E620 manufactured by Mitsui Chemicals) was used. In the same manner as in Example 1, a reflective sheet was obtained.
The reflectance of the obtained reflection sheet was 98.2%, and the evaluation of the heat deflection property was good with no deflection, but the fibers adhered to the roll when calendered, and the reflection sheet was It was not preferable.

(Comparative Example 5)
A reflective sheet was obtained in the same manner as in Example 1 except that 30% by weight of single fiber made of polyethylene terephthalate and 70% by weight of synthetic pulp made of high-density polyethylene (“SWP” (registered trademark) E620 manufactured by Mitsui Chemicals) were used. .
The reflectance of the obtained reflection sheet was 98.4%, and the evaluation of thermal flexibility was unfavorable because deflection occurred.

It is a microscope picture of the fiber of a synthetic pulp.

Claims (7)

A reflective sheet comprising synthetic pulp and a core-sheath structure fiber, wherein the core part of the core-sheath structure fiber is made of an ester polymer and the sheath part is made of an ethylene polymer. The reflective sheet according to claim 1, wherein the core-sheath structure fiber has an average fiber diameter of 2.2 dtex or less. The reflective sheet according to claim 1 or 2, wherein the synthetic pulp is 70% by weight or more based on the total amount of the synthetic pulp and the core-sheath structure fiber. The reflective sheet according to any one of claims 1 to 3, which has a thickness of 300 to 700 µm. The reflective sheet according to any one of claims 1 to 4, further comprising an ultraviolet absorber layer on at least one surface. A surface light source device using the reflection sheet according to claim 1. A liquid crystal display device using the surface light source device according to claim 6 as backlight light source means.

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