JP2011033815A - Light reflecting sheet and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin-based light reflecting sheet excellent in light reflectibility, lightweight properties, light diffusibility and rigidity, and a method for producing the polyolefin-based light reflecting sheet. <P>SOLUTION: The light reflecting sheet includes a light reflective layer having a polyolefin resin foam including a resin material containing a polyolefin resin, and bubbles. The resin material contains a fibrillating agent. The light reflective layer has stripe irregularities on the surface thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light reflecting sheet and a manufacturing method thereof, and more particularly, to a light reflecting sheet used for a liquid crystal display, a lighting fixture, and the like and a manufacturing method thereof.

  As a conventional light reflecting sheet, a reflection obtained by a method in which particles are contained in a polyester resin as described in Patent Document 1 and an interface between the polyester resin and the particles is peeled off by using a biaxial stretching method to form a void. There is a sheet. In addition, there is a reflective sheet in which bubbles are formed by batch foaming with an inert gas as described in Patent Document 2 and includes fine bubbles with a foaming ratio of 2 times or more. There is also a structure that reflects light by coating silver as a general reflecting member.

  However, in Patent Document 1, the hue change of reflected light due to yellowing of the reflecting sheet due to ultraviolet rays occurs due to use over time, and an attempt is made to apply an ultraviolet stabilizer to the surface of the reflecting sheet in order to improve this. This is also not preferable because the man-hour increases. Similarly, in Patent Document 2, problems due to use over time occur and this is not preferable, and the reflection sheet exhibits specular reflection behavior, and thus cannot reflect light over a wide range. In addition, with this manufacturing method, only thick-walled products can be manufactured, and the recent space-saving requirements for display products cannot be satisfied.

  Patent Document 3 proposes a reflective sheet stretched by containing an olefin resin and particles. Here, yellowing due to ultraviolet rays is improved by using an olefin-based resin, but it is not preferable in terms of light weight because it contains a large amount of particles. Patent Document 4 proposes a reflective sheet obtained by foaming a polyolefin resin. Similar to Patent Document 3, an olefin resin is used, and yellowing due to ultraviolet rays has been improved. However, in order to impart shock absorption, high foaming of 5 times or more is necessary, so that the rigidity of the material, that is, stiffness, has been reduced recently. As the display becomes larger, the assembly property is expected to deteriorate, which is not preferable. Patent Document 5 also proposes a reflection sheet in which a resin is foamed. However, Patent Document 5 describes that a polyolefin-based resin is used, but is very abstract and not reproducible.

Japanese Patent Laid-Open No. 04-296819 JP 2003-145657 A JP 2004-307730 A JP 2008-275729 A JP 2006-195001 A

  An object of the present invention is to provide a polyolefin-based light reflecting sheet excellent in light reflectivity, light weight, light diffusibility, and rigidity, and a method for producing the same.

The present invention (1) is a light reflecting sheet including a light reflecting layer having a polyolefin resin foam containing a resin material containing a polyolefin resin and bubbles.
The resin material contains a fibrillating agent;
The light reflecting layer is a light reflecting sheet characterized in that the surface has streak-like irregularities.

  This invention (2) is a light reflection sheet of the said invention (1) in which the said polyolefin resin contains a polypropylene.

  The invention (3) is the light-reflecting sheet according to the invention (1) or (2), wherein the main component of the polyolefin resin is a melting point of 160 ° C. or higher and an MFR at 2.16 kgf specified by JIS-K7210 is 5 or less. It is.

  The present invention (4) is the light reflecting sheet according to any one of the inventions (1) to (3), wherein the fibrillating agent is a fluorine-containing polymer having a fibril-forming ability.

  The invention (5) is the light reflecting sheet of the invention (4), wherein the fibrillating agent is polytetrafluoroethylene subjected to acrylic modification.

  The present invention (6) is the light reflecting sheet according to any one of the inventions (1) to (5), wherein the fibrillating agent is contained in an amount of 3.5 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin. .

  The present invention (7) is the light reflecting sheet according to any one of the inventions (1) to (6), wherein the unevenness difference in the streaky unevenness is 3 to 10 μm.

  The present invention (8) is the light reflecting sheet according to any one of the inventions (1) to (7), wherein the resin material further comprises particles having a high refractive index.

  The present invention (9) is the light reflecting sheet of the invention (8), wherein the resin material contains 3 to 25 parts by weight of the particles with respect to 100 parts by weight of the polyolefin resin.

The present invention (10) includes a melt-dispersing step in which a resin material containing a polyolefin-based resin and a fibrillating agent are charged into an extruder and melted and dispersed;
After the melting step, gas is dissolved in the molten resin material, a gas dissolving step,
After the gas dissolving step, the molten resin material in which the gas is dissolved is extruded to form a sheet while reducing the pressure and foaming, and the polyolefin resin foam forming step of stretching the sheet while winding it,
The manufacturing method of the light reflection sheet containing the light reflection layer containing this.

  This invention (11) is a manufacturing method of the light reflection sheet of the said invention (10) whose said gas is high pressure gas.

  This invention (12) is a manufacturing method of the light reflection sheet of the said invention (11) whose said high pressure gas is nitrogen gas.

  This invention (13) is a manufacturing method of the light reflection sheet of the said invention (11) or (12) whose high pressure gas is a fluid of a supercritical state.

  This invention (14) is a manufacturing method of the light reflection sheet any one of the said invention (10)-(13) in which the said polyolefin resin contains a polypropylene.

  The invention (15) is any one of the inventions (10) to (14), wherein the main component of the polyolefin-based resin is a melting point of 160 ° C. or higher and an MFR at 2.16 kgf as defined in JIS-K7210 is 5 or less. It is a manufacturing method of two light reflection sheets.

  The present invention (16) is the method for producing a light reflecting sheet according to any one of the inventions (10) to (15), wherein the fibrillating agent is polytetrafluoroethylene subjected to acrylic modification.

  The invention (17) is the production of a light reflecting sheet according to any one of the inventions (10) to (16), wherein the fibrillating agent is contained in an amount of 3.5 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin. Is the method.

  According to the present invention (18), any one of the inventions (10) to (17), wherein streaky unevenness is formed on the surface of the light reflecting layer, and the unevenness difference in the streaky unevenness is 3 to 10 μm. It is a manufacturing method of a light reflection sheet.

  The present invention (19) is the method for producing a light reflecting sheet according to any one of the inventions (10) to (18), wherein the resin material further contains particles having a high refractive index.

  This invention (20) is a manufacturing method of the light reflection sheet | seat of the said invention (19) with which resin material contains 3-25 weight part of said particles with respect to 100 weight part of polyolefin resin.

  Here, the meaning of various terms in this specification will be explained. In the present invention, the “sheet” means a flat product having a thickness that is small for the length and width, and includes a plate.

  According to this invention (1), there exists an effect that the polyolefin-type light reflection sheet excellent in light reflectivity, lightness, light diffusibility, and rigidity can be obtained. In particular, since the reflection sheet of the present invention has minute irregularities formed on the surface of the light reflection layer, the angle dependency of light reflection is small. Therefore, even if it sees from all angles, there exists an effect excellent in the diffuse reflectance that the same brightness is obtained.

  According to the present invention (2) and (14), since polypropylene is used as a material, there is an effect that yellowing hardly occurs even in a long-term ultraviolet exposure state. Thereby, when it is used as a reflection plate of a liquid crystal display, there is an effect that the screen becomes clean. In addition, it has heat resistance and little dimensional change due to heat generated from the light source.

  According to the present invention (3) and (15), there is an effect that it is possible to obtain a reflective sheet foamed in a good state without being lost.

  According to the present invention (4), (5), (16), since the fibrillating agent is likely to be fine fibers, there is an effect that it is possible to obtain a reflective sheet with more excellent diffuse reflectivity.

  According to the present invention (6) and (17), since the fibrillating agent is contained in an amount in the above range, streaky irregularities are easily formed on the surface of the reflective sheet. There is an effect that it can be obtained.

  According to this invention (7) and (18), there exists an effect that the reflection sheet which was more excellent in diffuse reflectance can be obtained because an uneven | corrugated difference is a predetermined range.

  According to the present invention (8), (9), (19), and (20), a reflective sheet with more excellent diffuse reflectance can be obtained by including particles having a high refractive index in the reflective layer. There is an effect.

  According to the present invention (10) to (12), bubbles are formed in the reflection sheet by dissolving the gas and forming the reflection sheet by extrusion molding. Since streaky irregularities are formed by the apexes and valley points of the tensile wrinkles that are caused by variations in strength caused by the inhomogeneity of the film, it is possible to obtain a reflective sheet having excellent diffuse reflectivity.

  According to the present invention (13), by using a supercritical gas, the fluidity of the resin can be improved and finer bubbles can be formed. Obtainable.

FIG. 1 is a cross-sectional view of the reflective sheet of Example 1 in the stretching direction. FIGS. 2A and 2B are diagrams showing the surface states of (a) Example 1 (front surface), (b) Example 1 (back surface), (c) Comparative Example 1, and (d) Comparative Example 2. FIG. FIG. 3 is a diagram showing a change with time of the Δb value of the reflection sheet according to the example and the comparative example. FIG. 4 is a diagram illustrating a change with time of the reflectance of the reflection sheet according to the example and the comparative example. FIG. 5 is a diagram illustrating the reflection characteristics of the reflection sheet according to the first embodiment. FIG. 6 is a diagram showing the reflection characteristics of the reflection sheet according to Comparative Example 1. FIG. 7 is a diagram showing the reflection characteristics of the reflection sheet according to Comparative Example 2.

"Construction"
The light reflecting sheet according to the best mode is a light reflecting sheet including a light reflecting layer having a polyolefin resin foam containing a resin material containing a polyolefin resin and air bubbles, wherein the resin material is a fibrillating agent. And the light reflecting layer has streak-like irregularities on the surface thereof. By containing the fibrillating agent, streaky irregularities appear on the surface, thereby improving diffuse reflectivity. Moreover, the rigidity of a light reflection sheet can be improved by containing a fibrillating agent. For the light reflection layer of the reflection sheet according to the best mode, a polyolefin-based resin that is a material that does not yellow is selected as a material in order to solve the yellowing problem due to ultraviolet rays. Further, the configuration other than the light reflection layer may include a rigid resin layer for assisting assembly.

The light reflecting sheet according to the best mode has streaky irregularities on the surface of the light reflecting layer. Examples of streaky irregularities are shown in FIGS. 2 (a) and 2 (b). FIG. 2 is a diagram showing a result of observing the surface of the reflection sheet with a nanoscale hybrid microscope (VN-8000, manufactured by Keyence Corporation). A nanoscale hybrid microscope is a microscope in which a digital microscope and an AFM are fused.
Here, the streaky irregularities are formed by, for example, apexes and valley points of tensile wrinkles that are generated due to variations in strength caused by material inhomogeneity due to winding tension during sheet forming.

  In addition, it is preferable that the unevenness | corrugation difference of the surface of a light reflection sheet is 3-10 micrometers, it is more preferable that it is 4-10 micrometers, and it is still more preferable that it is 6-10 micrometers. The unevenness difference of at least one surface of the reflection sheet may be within the above range. By setting it as such a range, many irregular reflections arise on the light reflection sheet surface, and the diffusibility of light improves. Here, the unevenness difference is a difference in height between the apex of the highest recess on the surface of the reflection sheet and the valley point of the lowest protrusion. Further, the unevenness difference can be adjusted by adjusting the amount of the fibrillating agent. For example, if the content of the fibrillating agent is increased, the unevenness difference value tends to increase. Conversely, if the content of the fibrillating agent is decreased, the unevenness difference value tends to decrease.

  Bubbles are formed in the light reflection layer, and the specific gravity of the light reflection layer is 0.3 to 0.6, preferably 0.3 to 0.5, and more preferably 0.3 to 0.4. is there. By setting the specific gravity in such a range, not only can the weight be reduced, but a large number of bubbles are formed inside the light reflecting layer, and thus a high reflectance can be obtained. Compared to open cells or semi-communication, the air / resin material interface that reflects light increases, and as a result, high reflectance can be provided.

The shape of the bubbles formed in the light reflection layer is not particularly limited, but is preferably a shape flattened in parallel with the plane of the reflection sheet. This is formed by stretching the sheet or extruding it, but with this structure, the number of cell walls existing in the thickness direction of the sheet does not change even if it is thinner than the original thickness. Decrease in reflectance is unlikely to occur.
That is, it is preferable that the bubbles formed in the light reflection layer have a cross-sectional shape that is not nearly a perfect circle, but a cell shape that is elliptical or flattened. That is, in the cross section parallel to the (longitudinal) extrusion direction of the reflection sheet, the cell has an elongated shape having a non-circular major axis, and on the other hand, the cell is substantially circular in the cross section orthogonal to the (longitudinal) extrusion direction of the reflection sheet. The average major axis of the non-circular cells (bubbles) in the cross section parallel to the (longitudinal) extrusion direction is preferably 30 to 140 μm, and more preferably 40 to 130 μm. The average minor axis of the cell in the cross section parallel to the (longitudinal) extrusion direction is preferably 10 to 30 μm, and more preferably 15 to 25 μm. The cell diameter was obtained by taking a cross-section of the reflection sheet with an electron microscope, taking the longest diameter in one cell in the cell as the major axis, and the minor axis in the direction perpendicular to the major axis. . Moreover, it calculates | requires by measuring and averaging all the long diameters of the cell which can be confirmed in the photograph.

  When the average cell diameter ratio [the minor axis / major axis of the cell] is determined by observing a cross section of such a cell, it is 0.15 to 0.40, and the reflection sheet has little angle dependency (excellent diffuse reflectance) and Wavelength dependency is reduced. On the other hand, when the average cell diameter ratio is 0.8 to 1.2, since the cell shape is substantially circular, the angle dependency tends to increase during reflection, and in FIG. When entering the range, the reflectance tends to increase rapidly.

  The bubbles formed in the light reflecting layer are preferably closed cells. By being a closed cell, the cell wall increases, the number of reflections increases, and the reflectance increases.

  In addition, 0.15-1.0 mm is suitable for the thickness of a light reflection layer, 0.2-0.8 mm is more suitable, and 0.2-0.65 mm is still more suitable. By setting it in such a range, both the space saving and the weight saving of the recent display panel can be achieved while maintaining the rigidity of the reflection sheet, that is, the workability at the time of assembly.

"component"
In the light reflecting sheet according to the best mode, the resin material contains a fibrillating agent. The fibrillating agent means a substance having the property that the agent itself becomes a fine fiber, before becoming a fine fiber, when it becomes a fine fiber, and after becoming a fine fiber It is a concept that includes things. Although it is not specifically limited with a fine fiber, For example, it is suitable that it is a fiber with an average diameter of 0.01-0.6 micrometer. The fibrillating agent is preferably a fluorine-containing polymer having a fibril forming ability. As the fluorine-containing polymer having fibril-forming ability, a tetrafluoroethylene polymer, particularly a tetrafluoroethylene copolymer obtained by copolymerizing an acrylate, that is, an acrylic-modified polytetrafluoroethylene is preferably used. As described in JP-A-11-29679, this acrylic-modified polytetrafluoroethylene is a dispersion of polytetrafluoroethylene having a particle size of 0.05 to 1.0 μm and polymer particles (polystyrene, polydodecyl methacrylate). Etc.) is mixed with a dispersion liquid, and then the monomer having an ethylenically unsaturated bond, for example, the above-mentioned ethylene, propylene, acrylate, etc. is emulsion-polymerized and then powdered by coagulation or spray drying And a polytetrafluoroethylene mixture prepared. As this polytetrafluoroethylene mixture, those commercially available from Mitsubishi Rayon Co., Ltd. as “methabrene A-3000” and “methabrene A-3800” (trade name) are known. The content of the fluoropolymer having fibril-forming ability is preferably 3.5 to 10 parts with respect to 100 parts by weight of the polyolefin resin. By setting it as the content of the said range, since it becomes easy to form streak unevenness on the surface of a reflective sheet, diffuse reflectance can be improved.

  The polyolefin resin is not particularly limited, but it is preferable to use a resin containing a polypropylene material. In addition, the resin material may include other resin materials such as polyethylene and rubber in addition to the polypropylene material. Although it will not specifically limit if it is a polymer material containing a propylene monomer component as a polypropylene material to be used, For example, a polypropylene and a propylene-ethylene copolymer are mentioned. The main component of the polyolefin resin used here is preferably a melting point of 160 ° C. or higher and an MFR of 2.16 kgf as defined in JIS-K7210 of 5 or less, and more preferably 4 or less. It is more preferable that it is 3 or less. The main component of the polyolefin resin is preferably a polypropylene material. In addition, a main component means the component which occupies 85% or more in polyolefin resin.

  Moreover, 60 to 100% is suitable for the crystallization rate of the polypropylene material used here, 60 to 80% is more suitable, and 60 to 70% is still more suitable. By setting it as the said range, it is easy to cool and solidify at the time of foam molding, and the foam of a fine cell can be obtained. The crystallization rate is calculated with reference to the method for measuring the transition temperature of JIS-K7121 plastic. A sample that has been previously melted at 200 ° C. and cooled at a cooling rate of 10 ° C./min is melted at a temperature increase of 10 ° C./min to obtain melting energy. Sample to be evaluated with a crystallinity at melting energy of 100% obtained by similarly measuring a homopolypropylene resin having an MFR of 40 or more evaluated at 230 ° C. and 2.16 kgf specified in JIS-7210 as a comparative material The crystallinity of is calculated. A homopolypropylene resin having an MFR of 40 or more is determined to be saturate because the melting energy is substantially constant, and a material of MFR 40 or more is used as a comparative material.

  Moreover, 90-120 degreeC is suitable for the crystallization temperature (Tc) of polypropylene material, 95-120 degreeC is more suitable, and 100-120 degreeC is still more suitable. By setting it as the said range, it is easy to cool and solidify at the time of foam molding, and the foam of a fine cell can be obtained. The crystallization temperature was evaluated according to JIS-K7121.

  In addition, MFR at 230 degreeC and 2.16kgf prescribed | regulated to JIS-K7210 of a polypropylene material has 0.1-10 suitably, 0.2-5 are more suitable, and 0.3-3 are Further preferred.

  The resin material may contain particles, pigments, antioxidants, foam nucleating agents, lubricants, crystal nucleating materials, and crosslinking agents. Among these, it is more preferable that particles are included. Further, it is particularly preferable that particles having a high refractive index are included among the particles. Here, the high refractive index is not particularly limited, but means that the refractive index is 1.6 to 3.0, for example. Examples of the high refractive index particles include titanium oxide, barium sulfate, and zinc oxide.

  Known pigments can be used as the pigment, and examples include rutile titanium oxide, calcium carbonate, and barium sulfate.

  As the antioxidant, known antioxidants can be used. Examples of the phenolic antioxidant include ADEKA STAB AO-60 manufactured by ADEKA Corporation and Irganox 1010 manufactured by Ciba Japan Co., Ltd.

  As the foam nucleating agent, known foam nucleating agents can be used, and examples thereof include silica and talc.

  A known lubricant can be used as the lubricant. An example is Dynamar FX9613 manufactured by Sumitomo 3M Limited.

  A known crystal nucleating agent can be used as the crystal nucleating agent. Examples thereof include Gelall from Shin Nippon Rika Co., Ltd. and Adeka Stub NA11 from ADEKA Corporation.

  As the crosslinking agent, a known crosslinking agent can be used. An example is triallyl isocyanurate (TAIC).

"composition"
The content of the polyolefin resin material is preferably 30 to 80% by weight, more preferably 40 to 80% by weight, and still more preferably 70 to 80% by weight with respect to the entire light reflecting layer. The content of the polypropylene material is preferably 30 to 80% by weight, more preferably 40 to 80% by weight, and still more preferably 70 to 80% by weight with respect to the entire light reflecting layer. The content of the other polymer material is preferably 0 to 15% by weight, more preferably 0 to 10% by weight, and still more preferably 0.1 to 8% by weight with respect to the entire light reflecting layer. . The content of the high refractive index particles is preferably 3 to 25 parts by weight, more preferably 5 to 20 parts by weight, and 7 to 17 parts by weight with respect to 100 parts by weight of the polyolefin resin. The content of the antioxidant is preferably 0.1 to 0.3% by weight, more preferably 0.1 to 0.25% by weight, and 0.15 to 0% with respect to the entire light reflecting layer. More preferred is 25% by weight. The content of the nucleating agent is preferably 0.1 to 0.5% by weight, more preferably 0.1 to 0.3% by weight, and 0.2% by weight with respect to the entire light reflecting layer. Is more preferred. The content of the crosslinking agent is preferably 0 to 5% by weight, more preferably 0 to 4% by weight, and still more preferably 0.1 to 3% by weight with respect to the entire light reflecting layer.

"Production method"
The method for manufacturing a reflective sheet according to the best mode includes a melt dispersion step, a gas dissolution step, and a foam sheet forming step. Here, an annealing step may optionally be included. Hereinafter, each step will be described in detail.

Melt Dispersion Step In the melt dispersion step, a resin material containing a polyolefin resin and a fibrillating agent are charged into an extruder and melted and dispersed. More specifically, the resin material is put into a single or tandem type extruder (a type in which two extruders are connected), dissolved in the melting zone, and further the fibrillating agent is dispersed. The resin material used in the melting step is preferably a material obtained by melting and mixing the material in advance using a resin mixing machine such as a twin screw extruder, a kneader, or a Banbury mixer.

Gas dissolving step In the gas dissolving step, gas is dissolved in the molten resin material. The gas used here is preferably a high-pressure gas, and more preferably a supercritical gas. Nitrogen gas or carbon dioxide gas, which has been pressurized by a gas supply device from the injection nozzle provided in the vicinity of the melting zone and brought into a supercritical state, is discharged into the extruder and dissolved in the molten material. A gas in a supercritical state is introduced into an extruder and dissolved in a molten resin material to form bubbles in the light reflecting layer in a polyolefin resin foam forming process described later.

  Examples of the supercritical gas used here include supercritical carbon dioxide and supercritical nitrogen. Among these, the cell diameter can be miniaturized by using supercritical nitrogen gas. Further, the pressure of the supercritical gas is preferably 7 MPa or more, more preferably 8 MPa or more, and further preferably 9 MPa or more. In addition, although an upper limit is not specifically limited, For example, it is 20 Mpa or less.

Polyolefin resin foam forming step In the polyolefin resin foam forming step, after the gas dissolving step, the molten resin material in which the gas is dissolved is extruded to reduce the pressure and form a sheet while foaming. Furthermore, it extends | stretches, winding up the said sheet | seat. Microcell (50μm or less) by introducing gas in the resin in the extruder and maintaining it in a high pressure state of 7 MPa or more until it is discharged from the die port and reduced in pressure to foam. Thus, it is possible to obtain a foam having a high expansion ratio of 1.5 to 10 times. As a result, a reflection sheet having a light specific gravity and high reflection efficiency can be produced.

  In order to obtain a light specific gravity microcell foam that can be used as a suitable reflection sheet in a die structure in an extruder, it is important to maintain the exit angle in the die at a constant angle (20 to 30 °).

  Further, the fibrillating agent is fibrillated by stretching while winding the sheet. Further, when the sheet is formed, streak irregularities are formed by the apexes and valley points of the tensile wrinkles formed by the variation in strength caused by the material inhomogeneity due to the winding tension. The streaky irregularities are formed by being oriented in the stretching direction of the sheet.

《Usage and usage》
The reflection sheet according to the best mode is used as a light reflection sheet in a liquid crystal display, a lighting fixture, or the like.

(Example 1) A biaxial extrusion made by Nippon Steel Works with a polyolefin resin composition of 12 parts by weight of titanium oxide and 6 parts by weight of a fibrillating agent in 100 parts by weight of homopolypropylene having an MFR of 2.4 at 230 ° C. and 2.16 kgf After being melted and prepared by a machine and impregnated with supercritical nitrogen gas, the molten material was extruded to form a foamed sheet to produce a light reflecting sheet. The specific gravity of the obtained light reflecting sheet was 0.4 g / cm ³ and the thickness was 400 μm. The foamed cell was a single cell flattened parallel to the plane of the light reflecting sheet, and the major axis of the cell in a cross section perpendicular to the (longitudinal) extrusion direction was 51 μm. On the other hand, the major axis of the cell in the cross section parallel to the (longitudinal) extrusion direction was 119 μm and the minor axis was 22 μm. When the average cell diameter ratio [cell minor axis / major axis] in the cross section parallel to the (longitudinal) extrusion direction was determined, it was 0.18, which was a very elongated and flat cell shape. Moreover, the photograph of the cross section parallel to the (longitudinal) extrusion direction of the light reflection sheet at this time is shown in FIG.

  Here, the fibrillating agent used was a tetrafluoroethylene copolymer obtained by copolymerizing acrylate, that is, acrylic-modified polytetrafluoroethylene. Specifically, “Methbrene A-3800” (trade name) from Mitsubishi Rayon Co., Ltd. was used as the polytetrafluoroethylene mixture.

(Comparative example 1) Toray mirror E-60L
When the cell size was measured, the major axis was 11.3 μm and the minor axis was 1.8 μm. Further, the average cell diameter ratio [cell minor axis / major axis] was 0.16.
(Comparative Example 2) Furukawa Electric MC-PET
When the cell size was measured, the major axis was 4.1 μm and the minor axis was 3.8 μm. The average cell diameter ratio (cell minor axis / major axis) was 1.08.
(Comparative Example 3) A reflective sheet was produced under the same conditions as in Example 1 except that only the fibrillating agent was not added.
(Comparative Example 4) A sheet having a foaming ratio of 10 times was prepared using a homopolypropylene having an MFR of 0.5 at 230 ° C. and 2.16 kg without adding titanium oxide or a fibrillating agent.

(Surface analysis)
The surface of the reflective sheet of an Example and a comparative example was measured with the nanoscale hybrid microscope (the Keyence make, VN-8000). The results are shown in FIG. FIGS. 2A and 2B are views showing the state of the front surface (a) and the back surface (b) of the reflective sheet according to Example 1. FIG. FIG. 2C is a diagram showing the surface state of Comparative Example 1. FIG. 2 (d) is a diagram showing the surface state of Comparative Example 2.
(Unevenness difference)
The surface of the reflective sheet of the example and the comparative example was measured in a 200 μm × 200 μm range with a nanoscale hybrid microscope (manufactured by Keyence, VN-8000), and the height of the peak of the highest concave portion and the valley point of the lowest convex portion The difference was measured. In addition, data that deviated from the data that was apparently scratched were excluded. The results are shown in Table 1.
(Diffuse reflectivity)
Wavelength dependence of reflected light from 380 nm to 780 nm while changing the angle from −30 ° to 30 ° with respect to the incident light in increments of 2 ° using an ultraviolet-visible spectrophotometer (V-650 manufactured by JASCO Corporation) Spatial distribution was measured. A case where there is a large change in the difference in reflectance between 0 degree, 30 degrees, and -30 degrees for each wavelength, and the top peak of the reflectance at 0 degree is not constant is denoted as x. The reflectance for each wavelength does not change significantly at 0 degrees, 30 degrees, and -30 degrees, that is, the angle dependence is small. The results are shown in Table 1 and FIGS. When the angle dependency of the sheets of Example 1 and Comparative Examples 1 and 2 was examined, the cell had an elongated shape, and the example having a specific cell size had excellent physical properties with little angle dependency and wavelength dependency. Obtained (FIG. 5).
On the other hand, although the cell has an elongated shape, the comparative example 1 having a very small cell size has little angle dependency, but has wavelength dependency, and as it approaches 780 nm, the reflectivity at 0 angle becomes remarkable and varies. Produce.
Moreover, the comparative example 2 in which the cell has a substantially circular shape is inferior in both angle dependency and wavelength dependency.
(rigidity)
A rectangular test piece of 250 mm × 50 mm is cut out and fixed at 1 cm on one end of the short side. The amount of deflection of the fixed edge and the unfixed edge was evaluated. A state where the end face which is defeated by its own weight and which is not fixed is attached to the ground is defined as x. If the deflection cannot be determined by visual inspection, it is determined that it will not lose its own weight at the time of assembly. The results are shown in Table 1.
(Yellowing resistance)
With a die plastic metal weather (manufactured by Daipura Wintes Co., Ltd.), 75 mW / cm ² , black panel temperature of 63 ° C., humidity of 70%, no rain condition, 0, 2, 4, 6 using a metal halide device The surface of the sample irradiated for 8 or 24 hours was evaluated for reflectance at a wavelength of 555 nm and change in color coordinates (Δb value) with respect to 0 h, that is, the initial sample, using an ultraviolet-visible spectrophotometer manufactured by JASCO Corporation. Note that Spectralon was used as the standard white plate used for the reflectance measurement. The case where there is a large change in the Δb value due to the change over time is taken as x. ◎ indicates that there is almost no change in the Δb value even with a change with time (the Δb value is within 1). The evaluation results are shown in Tables 2 and 3 and FIGS.

Claims (20)

In a light reflecting sheet including a light reflecting layer having a polyolefin resin foam containing a resin material containing a polyolefin resin and air bubbles,
The resin material contains a fibrillating agent;
The light reflecting layer, wherein the light reflecting layer has streaky irregularities on the surface thereof.   The light reflecting sheet according to claim 1, wherein the polyolefin resin contains polypropylene.   The light reflecting sheet according to claim 1 or 2, wherein the main component of the polyolefin-based resin is a melting point of 160 ° C or higher and an MFR of 2.16 kgf as defined in JIS-K7210 is 5 or less.   The light reflecting sheet according to any one of claims 1 to 3, wherein the fibrillating agent is a fluoropolymer having a fibril forming ability.   The light reflecting sheet according to claim 4, wherein the fibrillating agent is acrylic-modified polytetrafluoroethylene.   The light reflecting sheet according to any one of claims 1 to 5, wherein the fibrillating agent is contained in an amount of 3.5 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin.   The unevenness | corrugation difference in the said streaky unevenness | corrugation is 3-10 micrometers, The light reflection sheet as described in any one of Claims 1-6.   The light reflecting sheet according to any one of claims 1 to 7, wherein the resin material further contains particles having a high refractive index.   The light reflecting sheet according to claim 8, wherein the resin material contains 3 to 25 parts by weight of the particles with respect to 100 parts by weight of the polyolefin resin. A melt dispersion process in which a resin material containing a polyolefin-based resin and a fibrillating agent are charged into an extruder and melted and dispersed;
After the melting step, gas is dissolved in the molten resin material, a gas dissolving step,
After the gas dissolving step, the molten resin material in which the gas is dissolved is extruded to form a sheet while reducing the pressure and foaming, and the polyolefin resin foam forming step of stretching the sheet while winding it,
A method for producing a light reflecting sheet including a light reflecting layer.   The method for producing a light reflecting sheet according to claim 10, wherein the gas is a high-pressure gas.   The method for producing a light reflecting sheet according to claim 11, wherein the high-pressure gas is nitrogen gas.   The method for producing a light reflecting sheet according to claim 11 or 12, wherein the high-pressure gas is a fluid in a supercritical state.   The method for producing a light reflecting sheet according to claim 10, wherein the polyolefin resin contains polypropylene.   The method for producing a light reflecting sheet according to any one of claims 10 to 14, wherein the main component of the polyolefin-based resin is a melting point of 160 ° C or higher and an MFR at 2.16 kgf specified by JIS-K7210 is 5 or less.   The method for producing a light reflecting sheet according to any one of claims 10 to 15, wherein the fibrillating agent is polytetrafluoroethylene subjected to acrylic modification.   The method for producing a light reflecting sheet according to any one of claims 10 to 16, wherein the fibrillating agent is contained in an amount of 3.5 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin.   The method for producing a light reflecting sheet according to any one of claims 10 to 17, wherein streaky irregularities are formed on the surface of the light reflecting layer, and the unevenness difference in the streaky irregularities is 3 to 10 µm.   The method for producing a light reflecting sheet according to any one of claims 10 to 18, wherein the resin material further contains particles having a high refractive index.   The method for producing a light reflecting sheet according to claim 19, wherein the resin material contains 3 to 25 parts by weight of the particles with respect to 100 parts by weight of the polyolefin-based resin.