JP2020060671A - Reflector - Google Patents

Abstract

To provide a reflector which has excellent reflection characteristics, reduces occurrence of luminance unevenness and scratching on a light guide plate when used in a backlight unit, and is adaptable to thinning of a liquid crystal display.SOLUTION: A reflector includes: a resin layer (A) containing a polyolefin resin as a main component resin and organic particles; and a resin layer (B) containing a polyolefin resin. In the reflector, a glass transition point of the organic particles contained in the resin layer (A) is 115°C or higher, and heat capacity (ΔCp) at the glass transition point is 0.21 J/(g*°C) or higher.SELECTED DRAWING: None

Description

  The present invention relates to a reflector. More specifically, the present invention relates to a reflector that can be suitably used as a constituent member of a liquid crystal display, a lighting fixture, a lighting signboard, and the like.

  Reflective materials are used in many fields such as liquid crystal displays, lighting equipment and illuminated signboards. Recently, in the field of liquid crystal displays, the size of devices and the sophistication of display performance have advanced, and it has become necessary to supply as much light to the liquid crystal as possible to improve the performance of the backlight unit. In view of the above, further excellent light reflectivity (also simply referred to as “reflectivity”) is required.

As a reflective material of this type, for example, a reflective film for a liquid crystal display using a white polyester film containing an aromatic polyester resin as a main material is known (see Patent Document 1).
However, when an aromatic polyester resin is used as the material of the reflector, the aromatic ring contained in the molecular chain absorbs ultraviolet rays, so the ultraviolet rays emitted from a light source such as a liquid crystal display device causes the film to deteriorate and yellow. Then, there is a problem that the light reflectivity of the reflective film is lowered.

In addition, by stretching a film formed by adding a filler to polypropylene resin, a minute void is formed in the film to cause light scattering reflection (see Patent Document 2), and a polyolefin resin. A polyolefin resin light reflector having a laminated structure including a base material layer containing a filler and a layer containing a polyolefin resin is also known (see Patent Document 3).
The reflective film using such a polyolefin resin is characterized in that there is little problem of deterioration of the film or yellowing due to ultraviolet rays.

  Further, there is known a biaxially stretched reflective sheet containing a polypropylene resin and at least one resin that is incompatible with the polypropylene resin and having a reduced heat shrinkage rate (see Patent Document 4). This reflective sheet has a feature that it exhibits a higher reflectance than a conventional reflective sheet having the same basis weight and density even if it does not contain a large amount of inorganic powder.

In recent years, liquid crystal displays are required to be thinner, and backlights provided in the liquid crystal displays are also required to be thinner.
When thinning the backlight, it is necessary to thin the members such as the rear housing and the light guide plate. However, when these members are made thin, the mechanical strength of the backlight is reduced, and therefore, for example, when an external force is applied to the display body, the light guide plate and the reflective material come into strong local contact, resulting in uneven brightness and uneven color ( Hereinafter, they are collectively referred to as “luminance unevenness”). Therefore, a backlight used in a thinned liquid crystal display is required to have a reflection material having a brightness unevenness preventing function.
As a means for solving such a problem of uneven brightness, a reflective material in which specific particles are applied to a specific reflective material has been proposed (Patent Document 5).

JP 04-239540 A JP, 11-174213, A JP, 2005-031653, A JP, 2008-158134, A JP, 2005-163986, A

A light guide plate used for a backlight unit of a liquid crystal display has conventionally been made of polymethylmethacrylate (PMMA) resin. However, since it is easy to shape the dot shape (concave shape) necessary for the function of the light guide plate, in recent years, it has been made of a methyl methacrylate / styrene copolymer (hereinafter, also referred to as “MS resin”). The adoption of light guide plates is increasing.
According to the study by the present inventors, the light guide plate made of MS resin has a feature that it is easily deformed as compared with the light guide plate made of PMMA. When the reflective material disclosed in Reference 5 is used in combination with a light guide plate made of MS resin, there is a problem that the reflective material and the light guide plate easily come into contact with each other due to an external force applied to the liquid crystal display main body, which causes excessive contact. It was found that the light guide plate may be scraped and scratched. If the light guide plate is scratched, it causes a product error as a screen error.

  Therefore, it is an object of the present invention to have good reflection characteristics and to reduce the occurrence of uneven brightness and scratches on the light guide plate when used in a backlight unit, which can be applied to thinner liquid crystal displays. To provide a transparent reflector.

  The present invention is a reflector having a resin layer (A) containing a polyolefin resin as a main component resin and organic particles, and a resin layer (B) containing a polyolefin resin, and having a void, wherein The organic particles contained in the layer (A) have a glass transition point of 115 ° C. or higher, and a heat capacity (ΔCp) at the glass transition point of 0.21 J / (g · ° C.) or higher. Suggest a reflector.

  Advantageous Effects of Invention According to the present invention, it is possible to reduce the occurrence of brightness unevenness and scratches on the light guide plate when used in a backlight unit, which has good reflection characteristics, and is compatible with thinning of liquid crystal displays. A reflector can be provided. Therefore, the reflective material proposed by the present invention can be suitably used as a reflective material for liquid crystal display devices such as liquid crystal displays, lighting fixtures or illuminated signboards.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described below, and various modifications can be carried out without departing from the scope of the present invention.

<< Reflective material >>
A reflecting material (referred to as “present reflecting material”) according to an example of an embodiment of the present invention includes a resin layer (A) containing a polyolefin resin as a main component resin and organic particles, and a resin layer containing a polyolefin resin ( B) and having a void.

  In the present invention, the "main component resin" means a resin having the largest mass ratio among the resins constituting each layer, and it is allowed to contain other resins within a range not hindering the function of the main component resin. To do. At this time, the content ratio of the main component resin accounts for 50% by mass or more, preferably 70% by mass or more, and particularly preferably 90% by mass or more (including 100% by mass) of the resin constituting each layer.

<Resin layer (A)>
The resin layer (A) is a layer containing a polyolefin resin as a main component resin and containing organic particles.

  In the configuration of the present reflective material, the arrangement of the resin layer (A) is not limited. For example, as will be described later, it is preferable to dispose as a surface layer of the reflective material, specifically, as a surface layer on the side where the reflection is used. On the other hand, as the arrangement in the backlight member, it is preferable to arrange it on the surface in contact with the light guide plate.

The technical idea of the present invention can be explained as follows. However, the present invention is not limited to the scope of the following technical idea.
In a backlight unit that uses a light guide plate made of PMMA resin that has been used conventionally, when a reflecting material made of a polyolefin resin is used, uneven brightness is less likely to occur. On the other hand, when the backlight unit is made thinner and the light guide plate is made of MS resin, the use of a polyolefin resin reflecting material tends to cause uneven brightness.
According to the present inventors, the causes are (1) the mechanical strength is reduced due to the thinning of the backlight, and the degree of deformation with respect to an external force is increased, and (2) the PMMA resin is convex. The shape of the light guide plate is changed to the concave shape made of MS resin, the contact area with the reflection material is increased, (3) The softness of the light guide plate makes it easier to contact the reflection material, etc. Was given.
It was also found that such a phenomenon was more remarkable in a polyolefin resin-based reflective material that was more flexible (low elastic modulus) than a polyester resin-based reflective material that was relatively rigid (high elastic modulus). did.
Therefore, as a result of a study to suppress uneven brightness in a polyolefin resin-based reflector, a layer containing a polyolefin resin as a main component resin (also referred to as a “polyolefin resin layer”) contains specific organic particles to form a surface layer. It was confirmed that by forming the protrusion, it is possible to suppress excessive contact with the light guide plate and suppress uneven brightness.
On the other hand, simply avoiding excessive contact with the light guide plate by the protrusions of organic particles may cause stress concentration on the protrusions at the time of contact, and the protrusions of the reflective material may scratch the flexible MS resin light guide plate. found. According to the present inventor, by optimizing the organic particles, specifically, by forming the polyolefin resin layer by containing large-sized organic particles having a specific glass transition point and heat capacity, the brightness is improved. The inventors have found that it is possible to suppress unevenness and also suppress scratches on the MS resin light guide plate.

As a method of providing a layer containing large-sized organic particles, a coating method has been mainly used conventionally. However, when the organic particle-containing layer is provided by a coating method, although the surface roughness is increased, problems such as dropout of particles and deterioration of recyclability (self-recyclability) may occur, and peeling from a substrate, Problems such as curling (winding habit) and reduction in manufacturing efficiency may occur.
On the other hand, according to the present invention, by adopting a configuration in which the polyolefin resin layer contains organic particles, there is no need to provide a layer containing organic particles by coating, and it is possible to enjoy further effects. It was For example, since it is possible to adopt a co-extrusion method, it is possible to increase the surface roughness, prevent particles from falling off, and improve recyclability (self-recyclability). The peeling and curling from the substrate can be suppressed, and the production efficiency can be significantly improved. The coating method is not excluded as a method for providing the resin layer (A) in the present invention.

(Polyolefin resin)
The type of the polyolefin resin as the main resin of the resin layer (A) is not limited. For example, polypropylene-based resin such as polypropylene, propylene-ethylene copolymer, propylene / α-olefin copolymer; polyethylene resin such as high-density polyethylene, low-density polyethylene, ethylene / α-olefin copolymer; polymethylpentene, etc. A-olefin resin, cycloolefin resin such as ethylene-cyclic olefin copolymer; at least one selected from olefin elastomers such as ethylene-propylene rubber (EPR) and ethylene-propylene-diene terpolymer (EPDM) The polyolefin resin can be mentioned.
Among these, polypropylene resin, cycloolefin resin, or a combination of both is preferable in view of mechanical properties and flexibility. Among them, it is particularly preferable to use cycloolefin resin as the main component resin. Cycloolefin resin is suitable as a main component resin of the resin layer (A) because it absorbs less visible light and has heat resistance.

The content of the polyolefin resin in the resin layer (A) is not limited and is usually 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more. When the content of the polyolefin resin is at least the above lower limit value, it is possible to impart good flexibility to the present reflecting material, which is preferable.
Further, the upper limit of the content of the polyolefin resin in the resin layer (A) is not limited, and all except the organic particles may be the polyolefin resin. It is preferably 99% by mass or less, more preferably 98% by mass or less, and further preferably 97% by mass or less. When the content of the polyolefin resin is less than or equal to the upper limit value, the breaking resistance, bending resistance, brightness unevenness preventing function, and the like of the present reflecting material become good, which is preferable.
Here, the content of the polyolefin resin means the total amount of all the polyolefin resins in the resin layer (A).

(Cycloolefin resin)
Next, a cycloolefin resin which is particularly preferable as the main component resin of the resin layer (A) will be described.

  The cycloolefin resin is a polymer compound having a carbon-carbon bond in the main chain and having a cyclic hydrocarbon structure in at least a part of the main chain. This cyclic hydrocarbon structure is introduced by using a compound (cycloolefin) having at least one olefinic double bond in the cyclic hydrocarbon structure, as represented by norbornene or tetracyclododecene, as a monomer. To be done.

  The cycloolefin resin is classified into an addition polymer of cycloolefin or a hydrogenated product thereof, an addition polymer of cycloolefin and α-olefin or a hydrogenated product thereof, a ring-opening polymer of cycloolefin or a hydrogenated product thereof. Can also be used as a cycloolefin resin. The cycloolefin resin may be either a cycloolefin homopolymer or a cycloolefin copolymer.

  Specific examples of the cycloolefin resin include cyclopentene, cyclohexene, cyclooctene; monocyclic cycloolefins such as cyclopentadiene and 1,3-cyclohexadiene; bicyclo [2.2.1] hept-2-ene (common name: norbornene ), 5-methyl-bicyclo [2.2.1] hept-2-ene, 5,5-dimethyl-bicyclo [2.2.1] hept-2-ene, 5-ethyl-bicyclo [2.2. 1] hepta-2-ene, 5-butyl-bicyclo [2.2.1] hept-2-ene, 5-ethylidene-bicyclo [2.2.1] hept-2-ene, 5-hexyl-bicyclo [1. 2.2.1] hepta-2-ene, 5-octyl-bicyclo [2.2.1] hept-2-ene, 5-octadecyl-bicyclo [2.2.1] hept-2-ene, 5- Met Den-bicyclo [2.2.1] hept-2-ene, 5-vinyl-bicyclo [2.2.1] hept-2-ene, 5-propenyl-bicyclo [2.2.1] hept-2- Bicyclic cycloolefins such as ene;

Tricyclic cycloolefins such as tricyclo [4.3.0.12,5] deca-3,7-diene (conventional name: dicyclopentadiene);
4-ring cycloolefins such as tetracyclo [4.4.0.12,5.17,10] dodec-3-ene (also simply referred to as tetracyclododecene);
8-cyclopentyl-tetracyclo [4.4.0.12,5.17,10] dodeca-3-ene, tetracyclo [8.4.14,7.01, 10,3,8] pentadeca-5,10, 12,14-tetraene (also referred to as 1,4-methano-1,4,4a, 5,10,10a-hexahydroanthracene); polycyclic cycloolefins such as tetrapenta of cyclopentadiene, and the like. it can.
These cycloolefin resins can be used alone or in combination of two or more as a copolymer.

  Specific examples of the α-olefin copolymerizable with the cycloolefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, and 3 -Ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1- Hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, etc., having 2 to 20 carbon atoms, preferably having 2 to 20 carbon atoms. 2-8 ethylene or alpha-olefin etc. can be mentioned. These α-olefins may be used alone or in combination of two or more.

The cycloolefin resin is a resin containing a cycloolefin component as a main component, preferably 50% by mass or more, and more preferably 60% by mass or more.
At this time, the "main component" means the component having the largest mass ratio among the components constituting the cycloolefin resin, and it is permitted to contain other components within a range not hindering the function of the main component. . At this time, the content ratio of the main component accounts for 50% by mass or more, preferably 70% by mass or more (including 100%) of the components constituting the cycloolefin resin. The same applies to the main components of other resins.

When the cycloolefin resin is a copolymer of a cycloolefin such as norbornene and an α-olefin, the effect of improving the processing performance such as stretching by using the α-olefin as a copolymerization component and the cycloolefin are copolymerized. From the viewpoint of obtaining a good balance between the effect of heat resistance by using the main component of the components, the content ratio of the cycloolefin component in the cycloolefin resin is preferably 60 to 90% by mass, and particularly 65% by mass or more or 80% by mass or more. It is more preferable that the content is not more than mass%.
There is no particular limitation on the method for polymerizing cycloolefin or cycloolefin and α-olefin and the method for hydrogenating the obtained polymer, and the known method can be used.

  The melt flow rate (MFR) of the cycloolefin resin is not limited. For example, the value measured at 230 ° C. and a load of 21.18 N is preferably 0.1 to 20 g / 10 minutes, and more preferably 0.5 g / 10 minutes or more or 10 g / 10 minutes or less.

The cycloolefin resin may be crystalline or amorphous. Among them, it is preferably amorphous.
The glass transition point (Tg) of the cycloolefin resin is not limited. The glass transition point (Tg) of the cycloolefin resin is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, even more preferably 85 ° C. or higher, preferably 170 ° C. or lower, more preferably from the viewpoint of heat resistance. The temperature is 160 ° C or lower, more preferably 150 ° C or lower.
When the glass transition point of the cycloolefin resin is within the above range, the stretchability tends to be good.
Here, the “glass transition point (Tg)” is a value read by a differential scanning calorimeter when the temperature was raised at a temperature rising rate of 10 ° C./min.
In addition, two or more kinds of cycloolefin resins may be combined and mixed to adjust the glass transition point (Tg) of the mixed resin within the above range.

  As the cycloolefin resin, one kind may be used alone, or two or more kinds having different compositions and physical properties may be mixed and used. For example, two or more kinds of cycloolefin resins may be combined and mixed, and the MFR and Tg of the mixed resin may be adjusted within the above range.

The content of the cycloolefin resin in the resin layer (A) is not limited. It is preferably 30% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more. When the content of the cycloolefin resin is at least the lower limit value described above, it is possible to impart good heat resistance to the present reflecting material, which is preferable.
Moreover, the upper limit of the content of the cycloolefin resin in the resin layer (A) is not limited. It is preferably 85% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less.
When the content of the cycloolefin resin is at most the above upper limit value, the breakage resistance, bending resistance, brightness unevenness preventing function and the like of the reflecting material will be good, which is preferable.

  A commercial product can be used as the cycloolefin resin. For example, "Zeonor (registered trademark)" (a hydrogenated product of a ring-opening polymer of a cyclic olefin) manufactured by Zeon Corporation, "Apel (registered trademark)" manufactured by Mitsui Chemicals, Inc. (addition copolymer of ethylene and tetracyclododecene) ), “TOPAS (registered trademark)” (addition copolymer of ethylene and norbornene) manufactured by Polyplastics Co., Ltd., and the like. Among them, "ZEONOR" and "TOPAS" are preferable because they have a low light absorbing action and thus a reflector having high reflection performance can be obtained.

(Other polyolefin resins)
When a cycloolefin resin is used as the polyolefin resin which is the main component resin of the resin layer (A), a polyolefin resin other than the cycloolefin resin (hereinafter referred to as “other polyolefin resin”) is blended to form the resin layer (A). By forming it, the folding resistance and the heat resistance may be further improved in some cases.
Moreover, only the "other polyolefin resin" may be used as the resin layer (A) without using the cycloolefin resin.

The melt flow rate (MFR) of the "other polyolefin resin" is not limited. Above all, in accordance with JIS K7210, a value measured at 230 ° C. and a load of 21.18 N is preferably 0.1 to 20 g / 10 minutes, and more preferably 0.5 g / 10 minutes or more or 10 g / 10 minutes or less. Is more preferable.
When the cycloolefin resin and the "other polyolefin resin" are used in combination, it is preferable to adjust the MFR of the cycloolefin resin within the above range. When the MFRs of both are adjusted in this way, the mechanical properties of the reflecting material tend to be good.

  As the "other polyolefin resin", one or two or more of the polyolefin resins exemplified as the main component resin of the resin layer (A) in the above can be used in combination. Among them, polyethylene-based resins and polypropylene-based resins are preferable, and among them, polypropylene-based resins are preferable from the viewpoints of high melting point, excellent heat resistance, and high mechanical properties such as elastic modulus. However, it is not limited to these.

  When the “other polyolefin resin” is a polypropylene resin, the melt flow rate (MFR) is 0.1 to 20 g / 10 minutes as a value measured at 230 ° C. and a load of 21.18 N from the viewpoint of extrusion moldability. It is preferably 0.2 g / 10 minutes or more or 10 g / 10 minutes or less, and more preferably 0.5 g / 10 minutes or more or 5 g / 10 minutes or less.

When a cycloolefin resin and "other polyolefin resin" are used in combination as a resin component constituting the resin layer (A), MFR of the cycloolefin resin ("MFR (CO)") and "other polyolefin resin" Of MFR (“MFR (PO)”) is preferably MFR (CO): MFR (PO) = 1: 0.05 to 1:20, and 1: 0.1 to 1:10. More preferably.
When the relationship between the MFRs of the two is within the above range, the other polyolefin resin is oriented in the cycloolefin resin, and the mechanical properties as the reflecting material tend to be improved, which is preferable.

The content of the "other polyolefin resin" in the resin layer (A) is not limited. When used in combination with a cycloolefin resin, it is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more. Also, the upper limit is not limited. It is preferably 40% by mass or less, more preferably 30% by mass or less, and further preferably 25% by mass or less.
When the content of the "other polyolefin resin" is not less than the lower limit value, it is possible to more effectively suppress the breakage of the resin layer (A) during stretching, and at the same time, to obtain the resin layer (A) and the resin layer (B). It is preferable because the adhesiveness is maintained at a higher level, and if it is at most the above upper limit, the heat resistance and the brightness unevenness preventing function tend to be further improved.

(Organic particles)
The resin layer (A) of the present reflecting material contains organic particles.
Here, the "organic particles" correspond to any particulate matter composed of an organic substance. Resin particles are preferable, and so-called polymer beads, polymer hollow particles and the like can be mentioned.
The type of organic particles as resin particles is not limited, and examples thereof include (meth) acrylate resin particles, styrene resin particles, silicone resin particles, nylon resin particles, polyethylene resin particles, and benzoguanamine resin spherical particles. , Urethane resin spherical particles and the like.
Here, “(meth) acrylate” means acrylate or methacrylate.
These organic particles may be a homopolymer or a copolymer. These may be used alone or in combination of two or more.

  Among these organic particles, (meth) acrylate resin particles are preferable, methyl methacrylate resin particles or butyl methacrylate resin particles are particularly preferable, and methyl methacrylate resin particles are particularly preferable. In these cases, it may be a copolymer containing methyl methacrylate or butyl methacrylate as a main component.

The shape of the organic particles contained in the resin layer (A) is not limited, and may be, for example, a spherical shape, a rod shape, a flat plate shape, a crushed product or an agglomerate having no particular shape, or an amorphous product. Good. Among these, the shape of the organic particles is preferably spherical.
Here, "spherical" does not necessarily mean only a true sphere, but corresponds to a substantially spherical shape visually. Specifically, for example, the cross-sectional shape of particles corresponds to a circle, a substantially circle, an ellipse, a substantially ellipse, a shape surrounded by an arc having a curvature, or the like.

  When the resin layer (A) is located on the outermost layer which is the reflection surface of the reflecting material, spherical organic particles are contained in the resin layer (A) to form protrusions on the surface of the resin layer (A), thereby It is possible to make the height of the protrusions, the size of the protrusions, and the shape of the protrusions relatively uniform, as compared with the case where the protrusions are formed of regular particles. When the heights, sizes, and shapes of the protrusions are uniform as described above, it is possible to further suppress sticking of the reflection film and the light guide plate and further suppress damage to particles.

The organic particles are preferably particles that have been subjected to a crosslinking treatment (referred to as "crosslinked particles"). By being subjected to the crosslinking treatment, it becomes easy to maintain the shape of particles even in a state where a deformation stress is applied in a heated state during extrusion film formation.
Whether or not the organic particles are crosslinked particles can be confirmed, for example, by swelling without being dissolved when the organic particles are immersed in a solvent (good solvent) that is dissolved unless they are crosslinked. In that case, you may heat appropriately. In addition, it can be confirmed by a nuclear magnetic resonance spectrum (NMR), an infrared absorption spectrum (IR), or the like.
The solvent that dissolves unless it is crosslinked (good solvent) varies depending on the resin species constituting the organic particles, but in the case of (meth) acrylate resin particles, for example, acetone, toluene, ethyl acetate, Methyl ethyl ketone etc. can be mentioned.
In order to make the organic particles into crosslinked particles, for example, a compound having a polyfunctional polymerizable group such as divinylbenzene, polyacrylate, pentaerythritol, trimellitic acid may be used as a polymerization raw material.

The glass transition point (Tg) of the organic particles contained in the resin layer (A) is preferably 115 ° C. or higher. By including the organic particles having a Tg of 115 ° C. or higher in the resin layer (A), it is possible to impart a specific hardness to the surface of the reflecting material and suppress uneven brightness. The lower limit of Tg of the organic particles is preferably 118 ° C. or higher, more preferably 121 ° C. or higher for the same reason as above.
The upper limit of Tg of the organic particles is not limited, and is preferably 260 ° C or lower. When the Tg of the organic particles is equal to or less than the above upper limit, it is possible to prevent the hardness of the surface of the reflecting material from becoming excessively high, so that it becomes possible to avoid scraping the MS resin light guide plate. The upper limit of Tg of the organic particles is preferably 240 ° C or lower, more preferably 200 ° C or lower.
Here, the glass transition point (Tg) is a value read when the temperature is raised at a temperature rising rate of 10 ° C./min by a differential scanning calorimeter, and the particles themselves are measured.

As a method of setting the Tg of the organic particles within the above range, when the organic particles are resin particles, the type of resin skeleton (for example, (meth) acrylate skeleton or styrene skeleton) and the type of monomer (by copolymerization In some cases, the type and composition ratio of the monomers are included), and the molecular weight (the degree of crosslinking in the case of crosslinked particles) can be adjusted.
The Tg of the organic particles is usually changed by crosslinking. This is because the molecular motion of the polymer chain is restricted by the cross-linking point.
In the present invention, when the organic particles are crosslinked particles and their Tg is in the above range, it is particularly preferable from the viewpoint of suppressing uneven brightness and suppressing scratching of the light guide plate.

The heat capacity (ΔCp) at the glass transition point of the organic particles contained in the resin layer (A) is preferably 0.21 J / (g · ° C.) or more. By including organic particles having a ΔCp of 0.21 J / (g · ° C.) or more in the resin layer (A), it is possible to prevent the hardness of the surface of the reflecting material from becoming excessively high. It is possible to avoid cutting. For the same reason as above, the lower limit of ΔCp of the organic particles is preferably 0.22 J / (g · ° C.) or more, more preferably 0.24 J / (g · ° C.) or more, and further preferably 0.26 J / ( g · ° C) or higher.
The upper limit of ΔCp of the organic particles is not limited, and is preferably 0.6 J / (g · ° C) or less. When the ΔCp of the organic particles is equal to or less than the above upper limit value, it becomes possible to impart a specific hardness to the surface of the reflective material and suppress uneven brightness. The upper limit of ΔCp of the organic particles is preferably 0.5 J / (g · ° C) or less, more preferably 0.4 J / (g · ° C) or less.
Here, the heat capacity (ΔCp) at the glass transition point is a value read when the temperature was raised at a temperature rising rate of 10 ° C./min by a differential scanning calorimeter, and the particles themselves were measured.
As a method of setting the ΔCp of the organic particles in the above range, when the organic particles are resin particles, the type of resin skeleton (for example, (meth) acrylate skeleton or styrene skeleton), the type of monomer (copolymerization If it is, the type and composition ratio of the monomer is included), and the molecular weight (in the case of crosslinked particles, the degree of crosslinking) can be adjusted. Above all, the influence of the degree of crosslinking is great.

Here, the glass transition point is the temperature at which the polymer material starts micro Brownian motion, and the ΔCp corresponds to the momentum at that time. That is, even if the resins have similar compositions, the value of ΔCp becomes small when the degree of crosslinking is high because the molecular chains are restricted.
Conventionally, when the light guide plate made of PMMA resin was common, it is possible to suppress uneven brightness by using harder crosslinked particles, in other words, resin particles having a high degree of crosslinking. Since the PMMA resin is hard, there was no problem of damaging the light guide plate. However, according to the studies by the present inventors, in a backlight unit using a light guide plate made of MS resin, if the degree of crosslinking of resin particles is too high, the light guide plate may be scratched. It was found that there is an optimum range for.
On the other hand, a high value of ΔCp means that the molecule is not bound and the degree of crosslinking is low. In such a case, scratching of the MS resin light guide plate is suppressed, but the organic particles are deformed in the step of manufacturing the reflecting material (mainly the stretching step), and do not contribute to the surface roughness. There are cases. In such a case, the effect of suppressing the brightness unevenness tends to be reduced, so that not only the lower limit value but also the upper limit value of ΔCp of the organic particles may be set and adjusted within a specific range.

It should be noted that what value of ΔCp is suitable from the viewpoint of preventing unevenness in brightness and damage to the light guide plate is greatly influenced by the main resin component of the resin layer (A). In the present invention, the polyolefin resin as the main component resin of the resin layer (A) has a lower elastic modulus than a polyester resin such as polyethylene terephthalate, and therefore has a lower elastic modulus as a reflecting material (so-called “no stiffness” exists). ). Therefore, in the case of a reflecting material containing a polyolefin resin as a main component, it is considered that the difference in the fine characteristics of the organic particles is more remarkably expressed, and in the present invention, the optimization thereof is intended. is there.
From the above, in the present invention, the case where the organic particles are crosslinked particles and the ΔCp thereof is in the above range is particularly preferable from the viewpoint of suppressing uneven brightness and suppressing scratching of the light guide plate.

The average particle size of the organic particles is preferably 15 to 60 μm. When the average particle size of the organic particles is 15 μm or more, it tends to be possible to efficiently form protrusions having a height of 10 μm or more on the surface. On the other hand, when the average particle size of the organic particles is 60 μm or less, the particles tend to be prevented from falling off.
From the above viewpoint, the lower limit of the average particle size of the organic particles is more preferably 17 μm or more, further preferably 20 μm or more. The upper limit of the average particle diameter of the organic particles is more preferably 55 μm or less, further preferably 50 μm or less.

The average particle size of the organic particles can be measured as follows.
The average particle size of the organic particles as a raw material can be measured as an average particle size (D50) obtained from a volume-based particle size distribution measured by a dynamic light scattering method or the like.
The average particle size of the organic particles contained in the resin layer (A) can be determined by observing the surface of the resin layer (A) or the cross section of the present reflective material using an optical microscope or a scanning electron microscope (SEM). It is possible to measure the diameters of a plurality of particles and obtain the average value thereof. In that case, when the cross-sectional shape is elliptical, the average value of the longest diameter and the shortest diameter can be measured as the diameter of each particle.

  The content of the organic particles in the resin layer (A) is preferably 0.5 to 20% by mass, more preferably 1% by mass or more or 10% by mass or less, and 2% by mass or more or 5% by mass or more. It is particularly preferably not more than mass%. If the content of the organic particles is equal to or more than the lower limit, it is preferable because it is possible to more easily give a specific hardness or roughness to the reflecting material surface, and if the content of the organic particles is equal to or less than the upper limit, It is preferable because production can be performed more efficiently without impairing continuous productivity during extrusion film formation.

(Fine powder filler)
The resin layer (A) may contain a fine powder filler other than the organic particles (hereinafter referred to as “fine powder filler”) together with the organic particles.
By containing the fine powder filler in the resin layer (A), light scattering due to the difference in refractive index between the polyolefin resin and the fine powder filler is caused, and in the process of producing the reflective material, the fine powder filler is provided around the fine powder filler. From the light scattering due to the difference in refractive index between the formed cavity and the polyolefin resin, and further due to the light scattering due to the difference in refractive index between the cavity and the fine powder filler formed around the fine powder filler, The reflection characteristics tend to be further improved. In addition, when sufficient light reflectivity can be secured by the resin layer (B), the resin layer (A) does not need to contain the fine powder filler.

  Regarding the type, particle size and surface treatment method of the fine powder filler that can be used in the resin layer (A), the same as those described as the fine powder filler that can be used in the resin layer (B) described later is the same. It can be used, and preferred examples are also the same. Here, the "resin layer (B)" is to be read as "resin layer (A)" in the matters described later as the fine powder filler used for the resin layer (B).

The fine powder filler contained in the resin layer (A) preferably has an average particle size of 0.05 μm or more and 15 μm or less, more preferably 0.1 μm or more or 10 μm or less.
When the average particle size of the fine powder filler is 0.05 μm or more, the dispersibility in the polyolefin resin does not decrease, and thus a more uniform reflecting material can be obtained. Further, when the average particle diameter is 15 μm or less, the interface between the polyolefin resin and the fine powder filler is densely formed, and a highly reflective reflective material can be obtained.

The average particle size of the fine powder filler can be measured as follows.
The average particle size of the fine powder filler as a raw material is determined by the average particle size (D50) obtained from a volume-based particle size distribution measured by a dynamic light scattering method or the like, or by using a centrifugal sedimentation type particle size distribution measuring device. The particle size of 50% of the total (mass basis) in the measured equivalent spherical distribution can be measured as the average particle size (D50).
For the average particle size of the fine powder filler contained in the resin layer (A), an optical microscope or a scanning electron microscope (SEM) is used to observe the surface of the resin layer (A) or the cross section of the present reflective material. The diameter of 10 or more particles can be measured and the average value thereof can be obtained. In that case, in the case of non-spherical particles, the average value of the longest diameter and the shortest diameter can be measured as the diameter of each particle. The same applies to the fine powder filler contained in the resin layer (B) described later, but in that case, the method of observing the cross section of the present reflecting material is preferable.

  When the resin layer (A) contains a fine powder filler, the content of the fine powder filler in the resin layer (A) is not limited. Considering the light reflectivity, mechanical strength, productivity, etc. of the present reflective material, it is preferably 10 to 80% by mass, and particularly 20% by mass or more or 70% by mass or less based on the entire resin layer (A). More preferably, When the content of the fine powder filler is 10% by mass or more, the area of the interface between the resin that constitutes the resin layer (A) and the fine powder filler can be sufficiently secured, and the reflection material provides a higher reflection. It is possible to impart sex. When the content of the fine powder filler is 80% by mass or less, the mechanical strength required for the reflecting material can be more effectively ensured, which is preferable.

(Other ingredients)
The resin layer (A) may further contain components other than the polyolefin resin, the organic particles, and the fine powder filler as “other components”.
As "other components", resin components (including thermoplastic elastomers) other than the above, antioxidants, light stabilizers, heat stabilizers, dispersants, ultraviolet absorbers, optical brighteners, compatibilizers, Fillers other than lubricants and fine powder fillers can be mentioned.

Further, the regenerated raw material generated in the manufacturing process of the present reflective material or the like may be contained in the resin layer (A) as long as the performance of the present reflective material is not impaired.
The content ratio of the regenerated raw material is not limited, and is preferably 1 to 60% by mass, more preferably 10% by mass or more or 50% by mass or less, based on the total mass of the resin layer (A). . If the content is 10% by mass or more, there is a cost merit by using the recycled raw material, and if it is 50% by mass or less, the light reflectivity and mechanical strength required for the reflecting material are not impaired. It is in.

<Resin layer (B)>
The resin layer (B) in the present reflective material is a layer containing a polyolefin resin.
By providing the resin layer (B) together with the resin layer (A), the present reflective material can obtain the following effects (i) to (iii), for example. That is, (i) the resin layer (B) is given light reflectivity and the resin layer (A) is given heat resistance, or (ii) the resin layer (B) is given light reflectivity and the resin layer Rigidity as a reflecting material is imparted to (A), or (iii) light is reflected on the surface of the resin layer (A) and light transmitted through the resin layer (A) is reflected in the resin layer (B). As described above, it is possible to separate functions, and it is possible to obtain more excellent heat resistance and folding resistance together with higher reflection performance.

  The resin layer (B) may contain another resin as long as it contains a polyolefin resin. However, from the viewpoint of enhancing the adhesiveness with the resin layer (A), it is preferable to contain a polyolefin resin as a main component resin.

(Polyolefin resin)
The polyolefin resin used for the resin layer (B) is not limited, and it can be selected and used from those exemplified as the polyolefin resin for the resin layer (A). For example, polypropylene, polypropylene resin such as propylene-ethylene copolymer, high-density polyethylene, low-density polyethylene, polyethylene resin such as ethylene / α-olefin copolymer, cycloolefin resin such as ethylene-cyclic olefin copolymer. And at least one polyolefin resin selected from olefin elastomers such as ethylene-propylene rubber (EPR) and ethylene-propylene-diene terpolymer (EPDM). Among these, polypropylene resin and polyethylene resin are preferable from the viewpoint of mechanical properties and flexibility, and among these, polypropylene (a homopolymer of propylene) is most preferable.

  The polyolefin resin of the resin layer (B) may be a polyolefin resin different from the polyolefin resin which is the main component resin of the resin layer (A). However, from the viewpoint of enhancing the adhesion between the resin layers (A) and (B), it is preferable to use a polyolefin resin containing the same monomer unit as the polyolefin resin which is the main component resin of the resin layer (A).

  The polyolefin resin used for the resin layer (B) has a melt flow rate (MFR) of 0.1 to 20 g / 10 minutes as a value measured at 230 ° C. and a load of 21.18 N from the viewpoint of extrusion moldability. Is preferable, and more preferably 0.2 g / 10 minutes or more or 10 g / 10 minutes or less, and further preferably 0.5 g / 10 minutes or more or 5 g / 10 minutes or less.

The content of the polyolefin resin in the resin layer (B) is not limited and is preferably 15% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more. When the content of the polyolefin resin is at least the above lower limit, the strength of the resin layer (B) is further maintained, which is preferable.
Further, the upper limit of the content of the polyolefin resin in the resin layer (B) is not limited, and may be composed of only the polyolefin resin, but preferably 90% by mass or less, more preferably 80% by mass or less, and further preferably Is 70% by mass or less.
When the content of the polyolefin resin is not more than the upper limit value, the strength is maintained without lowering the reflectance, which is preferable.

(Fine powder filler)
The resin layer (B) preferably contains a fine powder filler together with the above-mentioned polyolefin resin, from the viewpoint of obtaining further reflection performance.
When the resin layer (B) contains a fine powder filler, incident light is diffusely reflected by the fine powder filler to improve reflection characteristics, and when the resin layer (B) is a stretched body, voids are formed. Can be easily formed.

The fine powder filler contained in the resin layer (B) is not limited, and examples thereof include inorganic fine powder and organic fine powder. The organic fine powder is the same as the organic particles used in the resin layer (A). Among these, it is preferable that the resin layer (B) contains an inorganic fine powder. Further, the inorganic fine powder and the organic fine powder may be used in combination.
Examples of the organic fine powder that can be contained in the resin layer (B) include polymer beads and polymer hollow particles, which can be used alone or in combination of two or more. .

  In addition, as will be described later, the present reflecting material may be a part of the raw material of the resin layer (B) by using the scrap material generated in the manufacturing process of the reflecting material or the like as a recycled raw material. In that case, the organic particles contained in the resin layer (A) are also contained in the resin layer (B).

Examples of the inorganic fine powder include calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, zinc oxide, magnesium oxide, calcium oxide, titanium oxide, aluminum oxide, zinc oxide, alumina, aluminum hydroxide, Examples thereof include hydroxyapatite, silica, magnesium silicate, mica, talc, kaolin, clay, glass powder, asbestos powder, zeolite and silicate clay. These may be used alone or in combination of two or more.
Among these, in consideration of the difference in the refractive index with the resin constituting the resin layer (B), those having a large refractive index are preferable, and calcium carbonate, barium sulfate, titanium oxide or oxide having a refractive index of 1.6 or more. It is particularly preferable to use zinc.

Among them, titanium oxide has a remarkably high refractive index as compared with other inorganic fine powders, and it is possible to remarkably increase the difference in the refractive index with the resin constituting the resin layer (B), so that other fillers are used. Excellent light reflectivity can be obtained with a smaller compounding amount than in the case. Furthermore, by using titanium oxide, high light reflectivity can be obtained even if the thickness of the reflecting material is reduced.
The content of titanium oxide is not limited and is preferably 30% or more of the total mass of the inorganic fine powder. When the organic fine powder and the inorganic fine powder are used in combination as the fine powder filler, 30% or more of the total mass thereof is preferably titanium oxide.
As titanium oxide, for example, commercially available products such as those manufactured by Ishihara Sangyo Co., Ltd., Kemers Co., Ltd., and KRONOS Co., Ltd. can be used.

  In order to improve the dispersibility of these inorganic fine powders in the resin, use is made of inorganic fine powders whose surface has been surface-treated with silicon compounds, polyhydric alcohol compounds, amine compounds, fatty acids, fatty acid esters, etc. You may.

The fine powder filler preferably has an average particle diameter of 0.05 to 15 μm, and more preferably 0.1 μm or more or 10 μm or less. When the average particle size of the fine powder filler is 0.05 μm or more, the dispersibility in the resin forming the resin layer (B) is good, and a more uniform reflector can be obtained. Further, when the average particle size of the fine powder filler is 15 μm or less, the interface between the resin forming the resin layer (B) and the fine powder filler is densely formed, and a reflective material having higher reflectivity is obtained. be able to.
Here, the "average particle size" can be measured by the method described above.

The content of the fine powder filler contained in the resin layer (B) is preferably, with respect to the mass of the entire resin layer (B), in consideration of light reflectivity, mechanical strength, productivity, etc. of the reflecting material. It is 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more. When the content of the fine powder filler is not less than the lower limit value, the area of the interface between the resin forming the resin layer (B) and the fine powder filler can be sufficiently secured, and the reflective material has high reflectivity. Can be given.
The upper limit of the content of the fine powder filler is not limited, and is preferably 80% by mass or less, more preferably 75% by mass or less, and further preferably 70% by mass or less. When the content of the fine powder filler is not more than the above upper limit value, the mechanical strength required for the reflecting material can be more effectively ensured.

(Other ingredients)
The resin layer (B) may further contain components other than the polyolefin resin and the fine powder filler as “other components”.
"Other components" include resin components (including thermoplastic elastomers) other than polyolefin resins, crystal nucleating agents, antioxidants, light stabilizers, heat stabilizers, dispersants, UV absorbers, optical brighteners. , Compatibilizers, lubricants and other additives.

Further, if it does not impair the performance of the resin layer (B), it may contain a regenerated raw material generated in the manufacturing process of the present reflector or the like.
The content ratio of the recycled material is not limited, and is preferably 1 to 60% by mass, more preferably 10% by mass or more or 50% by mass or less, based on the total mass of the resin layer (B). When the content is 10% by mass or more, cost merit is generated by using the recycled raw material, which is preferable. On the other hand, when the content is 50% by mass or less, the light reflectivity and mechanical strength required for the reflecting material are less likely to be impaired, which is preferable.

<Void>
In the present reflective material, any one of the layers has voids to enhance the reflective characteristics.
The void may be included in either the resin layer (A) or the resin layer (B), both of them, or other layers. In the structure including the resin layers (A) and (B) such as the resin layer (A) / the resin layer (B) / the resin layer (A), when the resin layer (A) has a void, the heat resistance and the elastic modulus are increased. When the mechanical properties such as the above deteriorate, it is preferable to provide the above voids only in the resin layer (B). By providing such voids only in the resin layer (B), the heat resistance of the entire film can be increased, and there is no fear that the heat resistance will decrease.
The voids can be formed by preliminarily stretching, preferably biaxially stretching, a fine powder filler contained in the composition forming each layer.

<Reflective material>
(Layer structure)
The present reflective material may have a structure having any other layer as long as it has the resin layer (A) and the resin layer (B). That is, the resin layer (A) or the resin layer (B) may have another layer on the surface thereof, or may be provided between the resin layer (A) and the resin layer (B) such as an adhesive layer. Other layers may be interposed.
The “other layer” also includes a layer provided by coating or vapor deposition.
Further, it may have a configuration having two or more layers of at least one of the resin layer (A) and the resin layer (B). As such a structure, a structure having the resin layer (A) on both surfaces of the resin layer (B), that is, a structure having three layers of "resin layer (A) / resin layer (B) / resin layer (A)" Is preferred.

By laminating the resin layer (A) and the resin layer (B), it becomes possible to separate the functions of each layer, and to improve the reflection performance, heat resistance, folding resistance, uneven brightness, and scratch resistance to the light guide plate. Performance such as reduction can be improved. For example, the resin layer (B) is mainly provided with a role of imparting light reflectivity, and the resin layer (A) has heat resistance as well as reduction of uneven brightness and damage to the light guide plate. It can have a role.
In the above-mentioned various configurations, the resin layer (A) has a role of reducing the occurrence of uneven brightness and scratching of the light guide plate, in addition to heat resistance, from the viewpoint of the surface layer of the present reflective material, particularly the surface used for reflection. It is preferable to arrange it as the outermost layer.

(Form of resin layer (A))
The resin layer (A) may be a layer formed of a sheet body, or may be a layer formed by forming a thin film by extruding or coating a molten resin composition without forming a sheet. . However, in order to respond to the thinning of the liquid crystal display, a sheet body is preferable.
When the resin layer (A) is composed of a sheet body, the sheet body is preferably formed by an extrusion method, and may be an unstretched film or a uniaxially or biaxially stretched film. Above all, a stretched film obtained by stretching at least 1.1 times in a uniaxial direction, particularly a biaxially stretched film is preferable.

(Form of resin layer (B))
The resin layer (B) is preferably a sheet body formed by an extrusion method. When the resin layer (B) is a sheet body, the sheet body may be an unstretched film or a uniaxially or biaxially stretched film. Above all, a stretched film obtained by stretching at least 1.1 times in a uniaxial direction, particularly a biaxially stretched film is preferable.

(Thickness)
The thickness of the present reflective material is not particularly limited. Above all, it is preferably 30 μm to 1500 μm. Considering the handling property in practical use, the thickness of the present reflective material is preferably about 50 to 1000 μm.
For example, a reflective material for liquid crystal display applications preferably has a thickness of 50 to 700 μm, and a reflective material for lighting equipment and illuminated signboard applications preferably has a thickness of 70 to 1000 μm.

  The thickness of the resin layer (A) (in the case of two or more layers, the total thickness thereof) is not particularly limited, but is preferably 5 to 100 μm, and more preferably 10 μm or more or 80 μm or less. When the thickness of the resin layer (A) is within the above range, the uneven brightness tends to be suppressed more effectively. Here, the thickness of the resin layer (A) means an average thickness, and is a thickness obtained by averaging the convex portions formed by the organic particles.

  The thickness of the resin layer (B) (the total thickness of two or more layers) is not particularly limited. For example, it is preferably 20 to 1400 μm, and more preferably 50 μm or more or 600 μm or less. When the thickness of the resin layer (B) is within the above range, the reflection characteristics tend to be good.

  In the reflecting material, the thickness ratio of the resin layer (A) and the resin layer (B) is preferably resin layer (A): resin layer (B) = 1: 2 to 1:15. When the thickness ratio of the resin layer (B) to the resin layer (A) is 2 times or more, the reflection characteristics tend to be good, and the flexibility becomes good, so that the bending workability tends to be improved. When the thickness ratio of the resin layer (B) to the resin layer (A) is 15 times or less, the heat resistance tends to be good. In addition, the said thickness ratio means the thickness ratio of the total thickness of each layer, when it is a structure which has two or more resin layers (A) or resin layers (B).

Regarding the resin layer (A), the ratio (Dmax / Dav) of the maximum thickness (Dmax) and the average thickness (Dav) of the resin layer (A) is preferably 1.1 to 4.0, and among them, 1. It is more preferably 2 or more or 3.0 or less.
Since Dmax usually corresponds to a convex portion formed by organic particles, a large value of Dmax / Dav means that a significant convex portion is formed. Therefore, it is preferable that the value of Dmax / Dav is in the optimum range because it is possible to reduce the occurrence of uneven brightness and the damage to the light guide plate.

(Surface roughness Rz)
The surface roughness Rz (maximum height roughness) of the present reflecting material is not particularly limited and is preferably 5 μm or more, more preferably 7 μm or more, and further preferably 8 μm or more. When the surface roughness Rz of the present reflective material is at least the lower limit value described above, it is preferable because the reflection characteristics become better and the uneven brightness tends to be further suppressed.
The upper limit of the surface roughness Rz of the present reflecting material is not limited, but is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. It is preferable that the surface roughness Rz of the present reflective material is equal to or less than the above upper limit value because the possibility of scratches occurring when contacting the light guide plate is further reduced.

Here, the surface of the reflecting material having the surface roughness Rz within the above range may be any of the resin layer (A), the resin layer (B), and other layers. It is preferable that the resin layer (A) is formed on at least one of the surfaces of the reflecting material, and the surface of the resin layer (A) achieves the value of the surface roughness Rz.
The method for adjusting the surface roughness Rz of the surface of the resin layer (A) is optimal depending on the type and blending ratio of the polyolefin resin as the main component resin, the type and blending ratio of organic particles, the stretching conditions when manufacturing the reflecting material, etc. Can be converted.
The measurement of the surface roughness Rz is based on JIS B0601, and more specifically based on the method of Examples described later.

(Surface roughness Ra)
The surface roughness Ra (arithmetic mean roughness) of the present reflecting material is not limited and is preferably 0.5 μm or more, more preferably 0.6 μm or more, and further preferably 0.7 μm or more. When the surface roughness Ra of the present reflective material is at least the lower limit value described above, it is preferable because the reflection characteristics are better and the uneven brightness tends to be more effectively suppressed.
The upper limit of the surface roughness Ra of the reflecting material is not limited, either, and is preferably 3.0 μm or less, more preferably 2.0 μm or less, and further preferably 1.5 μm or less. It is preferable that the surface roughness Ra of the present reflective material is equal to or less than the above-mentioned upper limit value because scratches can be more effectively suppressed during contact with the light guide plate.

  Here, the surface of the reflecting material having the surface roughness Ra within the above range may be any of the resin layer (A), the resin layer (B), and other layers. It is preferable that the resin layer (A) is formed on at least one of the surfaces of the reflecting material, and the surface of the resin layer (A) achieves the value of the surface roughness Ra described above.

  The method for adjusting the surface roughness Ra of the surface of the resin layer (A) is optimal depending on the type and blending ratio of the polyolefin resin as the main component resin, the type and blending ratio of organic particles, the stretching conditions when manufacturing the reflecting material, and the like. Can be converted.

  The measurement of the surface roughness Ra is based on JIS B0601, and more specifically based on the method of Examples described later.

(Reflectance)
The reflective material can have high reflective performance.
There is no restriction on the reflection performance of the present reflective material, and the average reflectance of at least one surface can be 97% or more, further 98% or more, and particularly 99% or more. If the reflective material has such a reflective performance, the screen of a liquid crystal display or the like incorporating the reflective material can realize sufficient brightness.
Here, the “reflectance” means an average reflectance with respect to light having a wavelength of 420 to 700 nm, and a more detailed measuring method will be described in Examples described later.

(Porosity)
The present reflective material preferably has voids in order to enhance the reflection performance.
The presence of voids in the reflecting material can be confirmed, for example, by observing the cross section of the reflecting material with a microscope (electron microscope or optical microscope).
The porosity of the present reflector is not limited. It is preferably 10% or more, more preferably 20% or more, while the upper limit is preferably 90% or less, more preferably 80% or less.
When the porosity of the reflective material is at least the above lower limit, the whitening of the reflective material will proceed sufficiently, so that it tends to have high light reflectivity. If the porosity of the reflective material is equal to or less than the upper limit value, the mechanical strength of the reflective material tends to be suitable.

  The porosity of the resin layer (B) is not limited. It is preferably 20% or more, more preferably 25% or more, further preferably 30% or more, while the upper limit value is preferably 80% or less, more preferably 75% or less, further preferably 70% or less. . If the porosity of the resin layer (B) is at least the above lower limit value, the whitening of the reflecting material will proceed sufficiently, so that it tends to have higher light reflectivity. Further, if the porosity of the resin layer (B) is not more than the upper limit value, the mechanical strength of the reflecting material tends to be more suitable.

  In addition, the porosity of the present reflecting material substantially covers the resin layer (A) and the resin layer (B), and when other layers are provided between these layers, this is also included. On the other hand, when another layer such as a resin plate or a metal plate is provided on the outer surface of the resin layer (A) and the resin layer (B), these layers are not included in the calculation of the porosity of the reflecting material.

The porosity of the reflecting material can be obtained by the following method.
(1) When forming voids by stretching, the density can be determined by the following formula by measuring the density of the reflecting material before and after stretching.
Porosity (%) = {(density of film before stretching-density of film after stretching) / density of film before stretching} × 100
(2) When the density and blending ratio of each raw material are clear, the density without voids can be calculated from the density and blending ratio of each raw material, and can be determined by the following formula.
Porosity (%) = {(density without voids-density of reflecting material) / density without voids} × 100
(3) Further, it is also possible to obtain the density by measuring the density of the reflecting material and then calculating the density after the voids are removed by melting, decompressing, cooling and solidifying the reflecting material.

<Method of manufacturing the present reflective material>
As an example of the method for manufacturing the present reflective material, a reflective material having a three-layer structure of "resin layer (A) / resin layer (B) / resin layer (A)" manufactured by a coextrusion method will be described below.
However, it is not limited to the following manufacturing method. For example, instead of the co-extrusion method, it is possible to form a laminated structure by coating, extrusion laminating, heat fusion, an adhesive or the like.

First, a resin composition A containing a polyolefin resin, organic particles and, if necessary, other additives is prepared. Specifically, after mixing these raw materials with a ribbon blender, a tumbler, a Henschel mixer, etc., using a Banbury mixer, a single-screw or twin-screw extruder, etc., a temperature above the flow initiation temperature of the resin (for example, 220 ° C The resin composition A can be obtained by kneading at ˜270 ° C.).
Further, the resin composition A can be obtained by adding a predetermined amount of each raw material using a separate feeder or the like. Alternatively, a part of the raw material may be used as a master batch and used as a raw material. Alternatively, a resin composition may be prepared in advance by using a part of the raw material, and the resin composition may be obtained by kneading the resin composition with another raw material.

On the other hand, a resin composition B is prepared by blending a polyolefin resin with a fine powder filler, other additives, etc., if necessary. Specifically, after mixing these raw materials with a ribbon blender, a tumbler, a Henschel mixer, etc., a temperature (for example, 190 ° C. to 270 ° C.) higher than the melting point of the resin is used by using a Banbury mixer, a single-screw or twin-screw extruder and the like. The resin composition B can be obtained by kneading at (° C.).
Further, like the resin composition A, it may be produced using a feeder or the like, a part of the raw material may be used as a masterbatch, or a part of the raw material may be used to prepare a resin composition in advance.
When only the polyolefin resin is used for the resin layer (B), it corresponds to the resin composition B without any compounding or the like.

Next, the resin composition A and the resin composition B thus obtained are dried, if necessary, and then supplied to different extruders and heated to a predetermined temperature or higher to be melted.
The conditions such as extrusion temperature are arbitrary. For example, the extrusion temperature of the resin composition A is preferably 220 ° C to 270 ° C, and the extrusion temperature of the resin composition B is preferably 190 to 270 ° C.

  Then, the melted resin composition A and resin composition B are merged into a T-die for two-kind three-layer, extruded in a laminated form from a slit-shaped discharge port of the T-die, and solidified by adhering to a cooling roll to form a cast sheet. Form.

The cast sheet obtained is preferably stretched in at least one axial direction. By stretching, the interface between the polyolefin resin and the fine powder filler inside the resin layer (B) peels off to form voids, the whitening of the sheet proceeds, and the light reflectivity of the film can be enhanced.
Further, the cast sheet is more preferably stretched biaxially. The voids formed by uniaxial stretching only have a fibrous shape extending in one direction, but by biaxial stretching, the voids are stretched in both vertical and horizontal directions and have a disk shape.
That is, by biaxially stretching, the peeling area at the interface between the polyolefin resin and the fine powder filler inside the resin layer (B) is increased, and the whitening of the sheet is further promoted. As a result, the light reflectivity of the film is improved. It can be further increased. In addition, since biaxial stretching reduces the anisotropy in the shrinking direction of the film, the heat resistance of the film can be improved and the mechanical strength of the film can be increased.

The stretching temperature for stretching the cast sheet is preferably a temperature within the range of not less than the glass transition point (Tg) of the polyolefin resin contained in the resin layer (A) and not more than (Tg + 50 ° C.).
When the stretching temperature is the glass transition point (Tg) or more, the film can be stably carried out without breaking during stretching. Further, if the stretching temperature is (Tg + 50) ° C. or lower, the stretch orientation becomes high, and as a result, the porosity increases, so that a film having high reflectance is easily obtained.

The stretching order of biaxial stretching is not particularly limited, and may be simultaneous biaxial stretching or sequential stretching, for example. After forming the cast sheet in a molten state, it may be stretched in the machine direction (MD) by roll stretching and then stretched in the transverse direction (TD) by tenter stretching, or may be biaxially stretched by tubular stretching or the like. Good.
The stretching ratio in the case of biaxial stretching is not limited. The area magnification is usually 4 times or more, preferably 5 times or more, more preferably 6 times or more, and the upper limit is usually 25 times or less, preferably 20 times or less, more preferably 15 times or less. By setting the area magnification within the above range, it is possible to control the porosity of the reflecting material within an appropriate range and to exhibit excellent reflection performance, which is preferable.
When sequentially performing biaxial stretching, the uniaxial stretching ratio is preferably 1.1 to 5.0 times, more preferably 1.5 to 3.5 times, and the biaxial stretching ratio is It is preferably 1.1 to 5.0 times, more preferably 2.5 to 4.5 times.

After stretching, it is preferable to perform heat setting in order to impart dimensional stability (form stability of voids) to the reflecting material. The processing temperature for heat-fixing the film is preferably 130 to 160 ° C. The processing time required for heat setting is preferably 1 second to 3 minutes.
Further, the stretching equipment and the like are not particularly limited, but it is particularly preferable to perform tenter stretching, which can perform heat setting treatment after stretching.

<Use>
The use of this reflector is not particularly limited. It is useful as a reflection member used in liquid crystal display devices such as liquid crystal displays, lighting fixtures, illuminated signboards, etc. because of its excellent reflection performance.
Generally, a liquid crystal display is composed of a liquid crystal panel, a polarized reflection sheet, a diffusion sheet, a light guide plate, a reflection sheet, a light source, a light source reflector and the like.
This reflecting material can be suitably used as a reflecting material that plays a role of efficiently making the light from the light source enter the liquid crystal panel or the light guide plate, and collects the irradiation light from the light source arranged at the edge part. It can also be suitably used as a light source reflector having a role of making it enter the light guide plate.

The present reflective material is suitable as a reflective material provided in a backlight unit of a liquid crystal display. The use of the present reflective material can reduce the occurrence of uneven brightness and the damage to the light guide plate, so that the material of the light guide plate is not restricted. Therefore, it can be suitably used for a backlight unit equipped with various light guide plates made of polymethylmethacrylate (PMMA) resin, methylmethacrylate / styrene copolymer (MS resin), cycloolefin resin, and the like. It is suitable for a backlight unit including a light guide plate made of MS resin.
Therefore, it is possible to provide a backlight unit including the present reflector and a light guide plate made of polymethylmethacrylate (PMMA) resin, methylmethacrylate / styrene copolymer (MS resin), cycloolefin resin, or the like. .

The present reflective material can also be used as it is as a reflective material having the above-mentioned layer structure.
Further, it can be used as a structure laminated on a metal plate or a resin plate (collectively referred to as “metal plate etc.”), and can be used for the above-mentioned applications, that is, liquid crystal display devices such as liquid crystal displays, lighting fixtures, lighting signboards, etc. It is useful as a reflector as a constituent member.
Therefore, a liquid crystal display device, a lighting fixture, or a lighting signboard can be provided by using the present reflective material as a constituent member.

Examples of the metal plate on which the present reflecting material is laminated include an aluminum plate, a stainless plate, and a galvanized steel plate.
The method of laminating the present reflective material on a metal plate or the like is not particularly limited. For example, a method of using an adhesive, a method of heat fusion, a method of adhering via an adhesive sheet, a method of extrusion coating, etc. can be mentioned.
More specifically, a reflective material such as a metal plate can be bonded by applying an adhesive such as polyester, polyurethane, or epoxy to the surface on the side where the reflective material is bonded.
Then, the coated surface is dried and heated by an infrared heater and a hot-air heating furnace, and while keeping the surface of the metal plate or the like at a predetermined temperature, immediately using a roll laminator, the reflective material is coated and cooled to reflect. You can get the board.

  Further, the present reflective material can be used in various applications other than the above, for example, various industrial materials, packaging materials, optical materials, electrical equipment materials and the like.

<Explanation of terms>
In the present invention, the term “film” includes “sheet”, and the term “sheet” also includes “film”.
In the present invention, “reflection” means reflection of light, and more specifically, reflection of visible light, unless otherwise specified.
In the present invention, when expressed as “X to Y” (X and Y are arbitrary numbers), “preferably larger than X” and “preferably smaller than Y” together with the meaning of “X or more and Y or less” unless otherwise specified. Embraces the meaning of.
When expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and when expressed as “Y or less” (Y is an arbitrary number), Unless otherwise specified, the meaning of "preferably smaller than Y" is included.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples, and various applications are possible without departing from the technical idea of the present invention.

<Measurement and evaluation method>
The measurement methods and evaluation methods of the samples obtained in the examples and comparative examples will be described below.

(Glass transition point (Tg) of organic particles and heat capacity (ΔCp) at the glass transition point)
Using a differential scanning calorimeter (manufactured by Perkin Elmer, model name: Diamond DSC), the glass transition point (change between baseline shifts) when the organic particles were heated to 250 ° C. at a heating rate of 10 ° C./min. The bending point) and the heat capacity at the glass transition point were measured.

(Average particle size of organic particles)
The average particle size of the organic particles in the resin layer (A) was obtained as an average value by observing the resin layer (A) surface of the reflecting material with an optical microscope and measuring the diameter of 10 or more particles.

(Thickness of reflective material)
The thickness of all layers of the reflective material was measured with a film thickness meter. The thickness of each of the resin layer (A) and the resin layer (B) was confirmed by observing the cross section of the reflecting material with an optical microscope.

(Porosity)
The density of the laminated sheet before stretching (unstretched sheet density) and the density of the laminated sheet after stretching (stretched sheet density) were measured, and the void ratio (%) of the reflective material (sample) composed of the laminated sheet was calculated by the following formula. ) Was asked.
Porosity (%) = {(unstretched sheet density-stretched sheet density) / unstretched sheet density} × 100

(Surface roughness)
With the reflecting material (sample) left stationary on a flat surface, Rz and Ra were measured on five randomly selected surfaces, and the average value thereof was used as the maximum height roughness Rz (μm) of the reflecting material (sample). ) And arithmetic mean roughness Ra (μm).
For the measurement, "Surftest SJ-210" manufactured by Mitutoyo Corporation was used, and λc: 0.8 mm and λs: 2.5 mm were measured based on JIS B0601 (2001).

(Average reflectance)
The integrating sphere was attached to a spectrophotometer ("U-3900H" manufactured by Hitachi High-Technologies Corporation), and the reflectance of the reflecting material (sample) when the alumina white plate was set to 100% was 0.5 nm over a wavelength range of 420 to 700 nm. Measured at intervals. The average value of the obtained measured values was calculated and defined as the average reflectance (%).

(Evaluation of sharpness of light guide plate)
On the friction fastness tester (Daiei Kagaku Seiki Seisakusho, Gakushin-type friction tester RT-300), a light guide plate (thickness: about 2 mm) made of MS resin with a concave dot shape and a reflective material (sample) are overlaid. The reflective materials were rubbed 50 times under the conditions of a load of 500 g and a stroke of 100 mm. The state of the surface of the light guide plate after rubbing was observed and judged according to the following criteria.
◯ (good): There was little scraping and there was no problem in practical use.
X (poor): There were many scrapes, and there was a problem in practical use.

(Evaluation of uneven brightness)
An evaluation model of an edge light type backlight unit was created by using a light guide plate made of MS resin and having a thickness of about 2 mm.
The light guide plate was placed on the reflector (sample), and the edge light was turned on with a weight (2 kg) placed on the light guide plate. A camera installed above the light guide plate was used to confirm whether or not luminance unevenness was generated near the weight, and the judgment was made based on the following criteria.
◯ (good): Brightness was not uneven, and it was suitable as a reflective material for thin backlights and the like.
X (poor): Uneven brightness was generated and it was unsuitable as a reflective material for thin backlights and the like.

<Raw material>
Raw materials used in Examples and Comparative Examples will be described below.
<COP-1>
Amorphous cycloolefin resin (MFR (230 ° C, 21.18N): 1.2g / 10 minutes, Tg: 127 ° C)
<COP-2>
Amorphous cycloolefin resin (MFR (230 ° C, 21.18N): 12g / 10 minutes, Tg: 100 ° C)

<PP-1>
Polypropylene resin ("Novatech PP EG6D" manufactured by Japan Polypro Co., MFR (230 ° C, 21.18N): 1.9 g / 10 minutes)
<PP-2>
Polypropylene resin ("Novatech PP FY6HA" manufactured by Japan Polypro Co., MFR (230 ° C, 21.18N): 2.4 g / 10 minutes)

<Organic particles-1>
Methyl methacrylate-based crosslinked resin particles (Tg: 121.0 ° C., ΔCp: 0.299 J / g · ° C.), average particle diameter (D50): 28 μm)
<Organic particles-2>
Methyl methacrylate cross-linked resin particles (Tg: 128.8 ° C., ΔCp: 0.196 J / (g · ° C.), average particle diameter (D50): 30 μm)

<Titanium oxide>
"KRONOS 2450" manufactured by KRONOS (Rutile type titanium oxide manufactured by a chlorine method and surface-treated with alumina and silica, TiO ₂ content 96.0%, average particle diameter (D50): 0.31 μm)
<Calcium carbonate>
"Softon 3200" manufactured by Bihoku Powder Co., Ltd. (average particle diameter (D50): 0.70 μm)

<Example 1>
(Production of Resin Composition A)
PP-1 pellets and organic particles-1 were mixed at a mass ratio of PP-1 / organic particles-1 = 90: 10, and then pelletized using a twin-screw extruder to obtain PP-1 / organic particles-1. A mixture was obtained. Then, the pellets of COP-1 and COP-2 and the PP-1 / organic particle-1 mixture were mixed at a mass ratio of COP-1 / COP-2 / PP-1 / organic particle-1 mixture = 50: 25: 25. After mixing, it is pelletized using a twin-screw extruder, and as a raw material of the resin layer (A), COP-1 / COP-2 / PP-1 / organic particles-1 = 50: 25: 22.5: 2. A resin composition A having a mass ratio of 5 was produced.

(Production of Resin Composition B)
PP-2 pellets and fine powder filler were mixed at a mass ratio of PP-2: titanium oxide: calcium carbonate = 55: 40: 5, and then pelletized using a twin screw extruder heated at 270 ° C. A resin composition B was prepared as a raw material for the resin layer (B).

(Production of reflective material)
The above resin compositions A and B were respectively fed to the extruders A and B heated stepwise to 250 ° C., melted by the respective extruders, and then merged into a T-die for 2 layers of 3 layers to form a resin. It was extruded into a sheet form so as to have a three-layer constitution of layer (A) / resin layer (B) / resin layer (A), and cooled and solidified to form an unstretched laminated sheet.
The laminated sheet thus obtained is roll-stretched 2.3 times in the machine direction (MD) of the film at a temperature of 142 ° C., and further bi-axially stretched at 141 ° C. by a triple tenter stretching in the orthogonal direction (TD). A reflective material (sample) composed of a laminated sheet having a total thickness of 166 μm was obtained.
The resulting reflective material was measured or evaluated for porosity, surface roughness, average reflectance, light guide plate scraping evaluation, and brightness unevenness evaluation, and the results are shown in Table 2.

<Comparative Example 1>
In the production of the resin composition A, PP-1 pellets and organic particles-2 were mixed in a mass ratio of PP-1 / organic particles-2 = 90: 10, and then pelletized using a twin-screw extruder, After obtaining the PP-1 / organic particle-2 mixture, the COP-1, COP-2 pellets and the PP-1 / organic particle-2 mixture are mixed with COP-1 / COP-2 / PP-1 / organic particle- 2 mixture = 40: 20: 40 by mass ratio, and then pelletized using a twin-screw extruder, and as a raw material of the resin layer (A), COP-1 / COP-2 / PP-1 / organic particles- A reflective material (sample) was obtained in the same manner as in Example 1 except that the resin composition A having a mass ratio of 2 = 40: 20: 36: 4 was prepared. The obtained reflective material (sample) was subjected to the same measurements and evaluations as in Example 1, and the results are shown in Table 2.

<Comparative example 2>
In the production of the resin composition A, the pellets of COP-1 and COP-2 and the PP-1 / organic particle-2 mixture are replaced with COP-1 / COP-2 / PP-1 / organic particle-2 mixture = 50: 25. After mixing in a weight ratio of 25 :, pelletized by using a twin-screw extruder, and used as a raw material of the resin layer (A) in a weight ratio of COP-1 / COP-2 / PP-1 / organic particles-2 = 50: A reflective material (sample) was obtained in the same manner as in Comparative Example 1 except that the resin composition A having a ratio of 25: 22.5: 2.5 was produced. The obtained reflective material (sample) was subjected to the same measurements and evaluations as in Example 1, and the results are shown in Table 2.

<Comparative example 3>
In the production of the resin composition A, PP-1 pellets and organic particles-2 were mixed at a mass ratio of PP-1 / organic particles-2 = 85: 15, and then pelletized using a twin-screw extruder, After obtaining the PP-1 / organic particle-2 mixture, the COP-1, COP-2 pellets and the PP-1 / organic particle-2 mixture are mixed with COP-1 / COP-2 / PP-1 / organic particle- 2 mixture = 50:25:25 by weight, then pelletized by using a twin-screw extruder, and the weight ratio of COP-1 / COP-2 / PP-1 / organic is used as a raw material of the resin layer (A). A reflective material (sample) was obtained in the same manner as in Comparative Example 1 except that the resin composition A in which the particle-2 was 50: 25: 21.25: 3.75 was prepared. The obtained reflective material (sample) was subjected to the same measurements and evaluations as in Example 1, and the results are shown in Table 2.

As is clear from Table 2, in Example 1, organic particles having a glass transition point (Tg) of 115 ° C. or higher and a heat capacity ΔCp at the glass transition point of 0.21 J / (g · ° C.) or higher. Since the resin layer (A) has a high reflectance, uneven brightness is suppressed, and even when MS resin is used as the light guide plate, the light guide plate is not scraped. confirmed.
On the other hand, the reflective materials of Comparative Examples 1 to 3 in which the resin layer (A) contains organic particles having a heat capacity ΔCp at the glass transition point of less than 0.21 J / (g · ° C.) are MS resin light guide plates It was confirmed that there was a problem in practical use.

Claims (12)

A reflective material comprising a resin layer (A) containing a polyolefin resin as a main component resin and organic particles, and a resin layer (B) containing a polyolefin resin, and having voids,
The organic particles contained in the resin layer (A) have a glass transition point of 115 ° C. or higher and a heat capacity (ΔCp) at the glass transition point of 0.21 J / (g · ° C.) or higher. And reflective material.   The reflective material according to claim 1, wherein the organic particles are crosslinked particles.   The reflective material according to claim 1, wherein the organic particles have an average particle diameter of 15 to 60 μm.   The reflecting material according to claim 1, wherein the resin layer (A) contains 0.5 to 20% by mass of the organic particles.   The reflective material according to any one of claims 1 to 4, which has a surface roughness Rz of 5 to 30 µm.   The reflective material according to claim 1, which has a porosity of 10 to 90%.   The reflective material according to any one of claims 1 to 6, wherein the resin layer (A) is arranged as a surface layer.   The reflection material according to any one of claims 1 to 7, wherein the polyolefin resin which is the main component of the resin layer (A) is a polypropylene resin or a cycloolefin resin.   The reflective material according to any one of claims 1 to 8, wherein the resin layer (B) contains a fine powder filler.   A backlight unit comprising the reflector according to claim 1 and a light guide plate made of a methyl methacrylate / styrene copolymer.   The reflective material according to any one of claims 1 to 9, which is used as a constituent member of any one of a liquid crystal display device, a lighting fixture, and a lighting signboard.   A liquid crystal display device, a lighting fixture, or a lighting signboard, which comprises the reflective material according to claim 1 as a constituent member.