JP2021033171A - Light diffusion sheet - Google Patents

Abstract

To provide a light diffusion sheet exhibiting excellent optical characteristics and good strength characteristics.SOLUTION: A light diffusion sheet includes thermoplastic resin and an inorganic substance at a mass ratio of 70:30 to 10:90. Porosity of the light diffusion sheet is 18% or more and 35% or less, and transmitted scattered light intensity of the light diffusion sheet at a wavelength of 525 nm, within a scattering angle of 35-70 degrees, is 70% or more of transmitted scattered light intensity thereof at a scattering angle of 0 degree.SELECTED DRAWING: Figure 1

Description

The present invention relates to a light diffusing sheet, particularly a light diffusing sheet used as a backlight type component that irradiates light from the back surface of a display object.

Conventionally, a light diffusing sheet (also called a light diffusing film) has been used in a wide range from for lighting to LEDs and various liquid crystal display devices. Among them, the one used for the backlight method has a role of uniformly diffusing and transmitting the light coming from the light source and also having a role of obscuring the shape of the light source when a human looks at the display object. Although LED light sources have come to be used in most of the above-mentioned devices in which a light diffusing sheet is used, since LEDs are point light sources, uniform scattered light is generated while minimizing the loss of light intensity. A capable light diffusion sheet is required (Non-Patent Document 1).

Most of the light diffusing sheets are made by applying a coating liquid containing a light diffusing agent onto a medium (board). For example, Patent Document 1 describes a light-diffusing film in which a paint containing acrylic urethane resin particles and a resin binder is applied as a light-diffusing agent on one side of a polyethylene terephthalate (PET) film, and 93% in Examples. The light transmission before and after is described. This light diffusing film is used in a liquid crystal display device.

As a light scattering sheet in which a light diffusion layer is laminated on a support, Patent Document 2 describes a light scattering film in which a light diffusion layer is formed on the surface of a transparent support having a thickness of twice or more.

A technique for molding a composition containing a light diffusing agent into a sheet or a plate is also disclosed. For example, Patent Document 3 describes a light-diffusing resin plate obtained by mixing two types of light-diffusing agents having different refractive indexes with a methacrylic resin, melt-kneading them with a single-screw extruder, and then molding them. There is. This light diffusing resin plate exhibits a light transmittance of 66 to 79% and is used for a transmissive display or the like.

Patent Document 4 describes a light diffusing agent of fine particles obtained by polymerizing one or more kinds of vinyl-based monomers, and a light diffusing sheet formed by mixing the light diffusing agent with a thermoplastic resin. There is. Microbeads of such polymers have come to be used to balance the concentration, refractive index, and light transmittance of the light diffusing agent. Patent Document 5 discloses a sheet-shaped transparent molded body provided with a transparent light scattering layer containing a resin and brilliant flaky fine particles. The amount of fine particles blended here is small, and the content of the bright flaky fine particles is preferably 0.0001 to 5.0% by mass, and a clear image can be projected on the transparent screen, but diffusion transmission is possible. The object is different from the present invention, for example, the rate is specified to be 50% or less.

As a light diffusing material using an inorganic material, for example, Patent Document 6 describes a panel for a lighting fixture in which 1.0 to 2.5% by weight of calcium carbonate is added to a translucent plastic, which is excellent. It is said that diffusivity and high transmittance can be obtained. Further, Patent Document 7 describes a light diffusing film obtained by applying a coating material containing a binder resin, an inorganic light diffusing agent, and metal oxide nanoparticles to a transparent polymer film. Patent Documents 8 and 9 _{disclose light diffusing members containing ceramic particles composed of MgO and Al 2} O ₃ at a ratio of about 1 part by weight with respect to 100 parts by weight of the resin. The member is described as having good light transmission and excellent light diffusivity. Patent Document 10 describes a light diffusing sheet for a liquid crystal display / backlight, which is made of a polycarbonate sheet containing calcium carbonate and titanium oxide in a total amount of about 8 to 9% by mass with respect to a resin.

The method of manufacturing a light reflector also describes a technique using an inorganic filler. Patent Document 11 describes a light reflector made of a biaxially stretched polyolefin-based resin film containing calcium carbonate. The light reflector is generally multi-layered, contains 3 to 30% by weight of filler, and has an area stretch ratio of 25 to 70 times. In this case, the porosity is stated to be 15-60%, but the true density used in the formula is stated to be approximately equal to the density before stretching, not the density of the material itself. Further, Patent Document 12 is a resin film containing an inorganic and / or organic filler and having pores inside, and is produced by controlling the balance between transmitted light and reflected light by calculating an optical characteristic value. The body is listed. This resin film is also described as having at least two layers of a surface protective layer and a base layer stretched biaxially after being laminated. It is described that the base layer contains a filler of 30% by weight or less and has a porosity of 3 to 15% by a mechanism for obtaining optical characteristics in the base layer. Further, as a method for producing a highly whiteness thin film sheet highly filled with an inorganic substance, Patent Document 13 describes a method in which 60% by weight or more of an inorganic substance powder and a thermoplastic resin are mixed, kneaded, and then stretched. .. The purpose of this technique is to obtain whiteness and opacity that can be used in the paper field, and does not touch on the characteristics of light diffusion at all.

On the other hand, recently, as a global problem, sustainable development has become an important issue, and the problem of marine pollution has become more serious. It has become a major issue.

Japanese Unexamined Patent Publication No. 2007-286166 Japanese Unexamined Patent Publication No. 2005-999281 Japanese Unexamined Patent Publication No. 7-214684 Japanese Unexamined Patent Publication No. 2006-233055 International Publication No. 2016/104112 Pamphlet Japanese Unexamined Patent Publication No. 60-175303 Japanese Unexamined Patent Publication No. 2009-223135 Japanese Unexamined Patent Publication No. 2007-304539 Japanese Unexamined Patent Publication No. 2008-181115 Japanese Unexamined Patent Publication No. 3-78701 Japanese Unexamined Patent Publication No. 2002-31704 Japanese Unexamined Patent Publication No. 2002-258015 Japanese Unexamined Patent Publication No. 2013-10931

LEDs Magazine Japan, March 2018, pp. 10-14

In response to the above-mentioned social situation, the technological development of the present application includes a technology for manufacturing a light diffusion sheet containing a high amount of inorganic substances, especially mineral substances rich in resources, including the purpose of contributing to the construction of a sustainable society. Aiming to establish the above, we worked diligently to solve the problems.

In the light diffusion sheet, the uniformity of light scattering is important in addition to the transmittance and brightness. However, conventionally, the uniformity of scattering has not been studied so much, and for example, the above-mentioned Patent Documents 6 and 7 do not describe the angle dependence of light scattering. In the light diffusing members described in Patent Documents 8 and 9, the light diffusing property, which has been regarded as a drawback of the inorganic light diffusing filler, is enhanced. In particular, in the member described in Patent Document 9, the light diffusing property is determined by the light scattering intensity. It is said that a light scattering intensity of 70% or more was obtained, but its angle dependence has not been investigated. Patent Documents 11 and 12 also do not describe the change in brightness depending on the angle.

The uniformity of light scattering cannot be grasped only by measuring the light scattering intensity and the diffusion transmittance. According to what the present inventors have found this time, in a sheet having a low content of an inorganic substance as in the conventional case, the scattered light intensity becomes uneven depending on the scattering angle, and good light diffusion may not be obtained. .. In the light diffusing sheet described in Patent Document 10, the relative diffused transmitted light amount for each light receiving angle is defined. However, in Patent Document 10, the amount of light at a light receiving angle of 0 ° is set to 100%, and the amount of relative diffused transmitted light at 70 ° is defined as 25% or more, so it is difficult to say that the scattered light intensity is uniform. , There is no technical idea of equalizing scattered light. From the viewpoint of how the scattered light is perceived by the naked eye, it is necessary to suppress the change in intensity depending on the angle of the scattered light within 30%, preferably within 15%. In the sheet-shaped transparent molded body described in Patent Document 5, the incident angle of the light source is changed after the transmitted light intensity in the 0 degree direction is set to 100, and the viewing angle is in the range of the transmitted light intensity of 0.001 or more. It cannot be said that the change due to the angle of is suppressed.

In order to obtain a good light diffusion sheet, the content of inorganic substances and the porosity in the sheet are important. As described above, when the content of the inorganic material is small, the scattered light intensity may become uneven depending on the scattering angle. In fact, the materials described in Patent Documents 5 and 10 do not have uniform scattered light intensity. Patent Documents 6, 8, 9, 11 and 12 do not describe the angle dependence of scattered light, but the content of inorganic substances is small in any of the materials, and even if the scattered light for each angle is measured, it is uniform. It is presumed that the result was inferior in sex.

On the other hand, it has been said that the addition of a large amount of an inorganic substance significantly reduces the mechanical properties and the overall light transmittance (Non-Patent Document 1). As a result of the investigation, there is no example of a sheet containing a high amount of mineral powder and having excellent light transmission performance including scattering characteristics. Patent Document 7 describes a light diffusing film containing 50 to 300 parts by weight of an inorganic light diffusing agent with respect to 100 parts by weight of the resin in the light diffusing layer, but describes the angle dependence of scattered light. Absent. Moreover, in Patent Document 7, the light diffusing layer is coated on the polymer film, and the amount of the inorganic light diffusing agent in the examples is about half that of the resin component, so it cannot be said that the sheet is filled with a large amount of inorganic substances.

Conventionally, the improvement of the optical characteristics of the sheet has been performed by paying attention to the change in the voids inside the sheet due to stretching, and the porosity has also been calculated by regarding the apparent specific gravity before stretching as the true specific gravity (Patent Document 11). However, according to the results of experiments conducted by the present inventors, the light transmittance and elastic modulus were significantly reduced by stretching (see Examples). In the light reflector described in Patent Document 11, the porosity is adjusted by biaxial stretching to improve the reflection characteristics, but the opacity is high and it is not suitable for transmission. The sheet produced by the method described in Patent Document 13 is not intended to diffuse light, but the whiteness and opacity are improved by stretching.

In other documents, for example, Patent Document 7 described above, the porosity itself has not been examined.

An object of the present invention is to provide a light diffusion sheet exhibiting excellent optical characteristics and good intensity characteristics. Specifically, it is an object of the present invention to provide a light diffusion sheet having uniform light scattering property, high light transmission property, and good mechanical strength.

In order to develop a sheet that is highly filled with inorganic substances and has excellent optical properties, the present inventors have made a diligent study from a completely different viewpoint from the conventional one. As a result, they have found that by controlling the blending amount of the inorganic filler and the porosity within a predetermined range, the above-mentioned specific problems can be solved, and excellent optical characteristics and good strength characteristics can be achieved. Was completed.

That is, in the present invention that solves the above problems, in a light diffusion sheet containing a thermoplastic resin and an inorganic substance in a mass ratio of 70:30 to 10:90, the void ratio of the light diffusion sheet is 18% or more and 35% or less. The transmitted scattered light intensity of the light diffusion sheet at a wavelength of 525 nm is 70% or more of the transmitted scattered light intensity at a scattering angle of 0 degrees within a range of a scattering angle of 35 degrees to 70 degrees. It is a light diffusion sheet.

In one aspect of the light diffusion sheet according to the present invention, the light diffusion sheet in which the inorganic substance is a mineral substance powder is shown.

In one aspect of the light diffusion sheet according to the present invention, the light diffusion sheet in which the inorganic substance is heavy calcium carbonate is shown.

In one aspect of the light diffusion sheet according to the present invention, the light diffusion sheet in which the thermoplastic resin is a polyolefin resin is shown.

In one aspect of the light diffusion sheet according to the present invention, the light diffusion sheet in which the inorganic substance is calcium carbonate having an average particle size of 0.7 μm or more and 10.0 μm or less is shown.

In one aspect of the light diffusion sheet according to the present invention, the light diffusion sheet in which the mass ratio of the thermoplastic resin to the inorganic substance is 50:50 to 10:90 is shown.

In one aspect of the light diffusing sheet according to the present invention, it is shown that the light diffusing sheet is a non-stretched sheet.

In one aspect of the light diffusing sheet according to the present invention, a light diffusing sheet having a coat layer provided on the surface of the light diffusing sheet is shown.

According to the present invention, it is possible to obtain a light diffusion sheet exhibiting excellent optical characteristics and good intensity characteristics. The light diffusing sheet of the present invention has appropriate total light transmittance and diffusive transmittance, is excellent in concealment of a light source, and exhibits uniform light diffusivity and light transmittance. Suitable for use in liquid crystal display devices, etc. In addition, it has sufficient mechanical strength and is not easily deformed by an external force, so that it is excellent in practicality. Furthermore, since the light diffusion sheet of the present invention contains a large amount of inorganic substances, it is possible to reduce plastic waste that causes problems such as marine pollution, and it can contribute to the construction of a sustainable society.

It is a figure which shows the change by the scattering angle of the transmitted light intensity in the light diffusion sheet of this invention. It is a measurement result about the light diffusion sheet obtained in Examples 1 to 3 and Comparative Examples 1 and 4 in which the compounding amount of the inorganic filler and the molding condition were changed.

Hereinafter, the present invention will be described in detail based on the embodiments.

The light diffusion sheet of the present invention contains a thermoplastic resin and an inorganic substance in a mass ratio of 70:30 to 10:90, but at the same time, the void ratio is 18% or more and 35% or less, and will be described later. The transmitted scattered light intensity at such a wavelength of 525 nm is 70% or more of the transmitted scattered light intensity at a scattering angle of 0 degrees within a range of a scattering angle of 35 degrees to 70 degrees. In a more preferred embodiment, the light diffusion sheet of the present invention has a void ratio of 18% or more and 35% or less even though it is not stretched, and the transmitted scattered light intensity at a wavelength of 525 nm as described later has a scattering angle. It is characterized in that it is 85% or more of the transmitted scattered light intensity at a scattering angle of 0 degrees in the range of 35 degrees to 70 degrees, and is substantially uniform. Hereinafter, each requirement constituting the light diffusion sheet according to the present invention will be described in detail.

≪Porosity≫
In the light diffusion sheet of the present invention, the porosity is 18% or more and 35% or less. By containing the thermoplastic resin and the inorganic substance in a mass ratio of 70:30 to 10:90 as described above and at the same time setting the void ratio to 18% or more and 35% or less, the total light transmittance and the diffusion transmittance can be increased. A light diffusing sheet showing appropriate and uniform light diffusivity and light transmittance can be obtained. It is not possible to obtain the uniform light diffusing property and light transmissive property required for the light diffusing sheet simply by adding an inorganic substance without providing voids. On the other hand, if the porosity exceeds 35%, the total light transmittance and the diffusion transmittance may be significantly reduced. The porosity is more preferably 20% or more and 30% or less, and particularly preferably 23% or more and 30% or less.

Generally, in a resin film containing an inorganic substance powder, the size of the voids is adjusted by stretching (see, for example, Patent Documents 11 and 12), but when the thermoplastic resin body containing the inorganic substance is stretched, the inorganic particles are nucleated. Since the stretching is carried out, the voids generated are large. According to the findings of the present inventors, in the light diffusion sheet in which the porosity is increased by such stretching, the total light transmittance and the diffusion transmittance are remarkably lowered.

In the light diffusion sheet of the present invention, it is necessary that extremely minute voids are contained in the sheet in the above ratio in quantity. As a result of the studies by the present inventors, it has been found that such desired voids can be generated in the kneading step of the extrusion molding machine. In particular, a remarkable effect can be obtained with a twin-screw extruder. Since the resin body composed of the thermoplastic resin and the mineral substance powder has a high viscosity, air is easily caught in the resin body. When such a resin body passes through the narrowest gap between the two screws of the extruder and between the barrel (cylinder) and the screw in the kneading or melt mixing process, a large shear stress acts on the resin body. At the same time that the resin bodies are dispersed and mixed, it is considered that fine voids are generated by the entrained gas. During the further kneading, a void structure is formed, which can be inferred to have appropriate optical suitability.

The air mixed in the extrusion molding machine is usually removed to the outside of the molding machine by a vent, but a part of the mixed air is caught in the resin body. The idea is that, for example, when 60% by mass of calcium carbonate and 40% by mass of polypropylene resin are kneaded to form a sheet, the calculated value of the density of the produced sheet based on the true specific gravity of both materials is 1.99, but extrusion molding is performed. The specific gravity of the sheet obtained in is proved by the fact that it is generally in the range of 1.4 to 1.7.

Note that the light diffusion sheet of the present invention, when measuring the cup method water absorption by JIS P8140, the often 0.5 m ² · 120 seconds or less. As shown in this result, in the light diffusion sheet of the present invention, most of the voids are discontinuous with respect to the passage of moisture, that is, they are independent voids.

The porosity can be calculated from the density (specific gravity) of the sheet. For example, in a sheet made of polypropylene resin and calcium carbonate, the true specific gravity ρ _o of the mixture can be calculated from the blending amount using the true specific gravities of 0.90 and 2.71, respectively. Based on the ratio of the value to the specific gravity ρ of the actual sheet, the porosity can be calculated according to the following (Equation 1).
Porosity (% by volume) = (1-ρ / ρ _o ) x 100 (Equation 1)
Although the same calculation method is described in Patent Document 11, Patent Document 11 uses the specific gravity of the sheet before stretching as the true specific gravity, which is different from the true specific gravity in the present invention.

The voids are formed by extrusion molding as described above, but a sheet having a porosity of 18% or more and 35% or less is selected from the sheets having the above ratios of the thermoplastic resin and the inorganic substance, and used as the light diffusion sheet of the present invention. be able to. That is, the specific gravity of the molded sheet is measured, the porosity is calculated according to the above (Equation 1), and a sheet within the range of the present invention can be used as a light diffusion sheet.

The thickness of the light diffusion sheet is also not particularly limited, and can be a desired thickness according to the display device or the like to be configured. The light diffusing sheet of the present invention does not change so much in light transmittance and light scattering characteristics due to the difference in thickness, and exhibits good physical properties in the range of 0.2 to 0.4 mm, which is usually used.

≪Transmission scattered light intensity≫
In the light diffusion sheet of the present invention, the transmitted scattered light intensity at a wavelength of 525 nm is 70% or more of the transmitted scattered light intensity at a scattering angle of 0 degrees within the range of a scattering angle of 35 degrees to 70 degrees, and by finely adjusting the manufacturing conditions. It will be 85% or more. Therefore, the light diffusing sheet of the present invention exhibits uniform light diffusing property and light transmitting property, and is particularly suitable for use in backlight type lighting, LEDs, liquid crystal display devices, and the like.

The light scattering characteristics can be measured by, for example, using a "small simple scattering measuring instrument" Mini-Diff V2 manufactured by Cybernet System Co., Ltd., by the method described on the website of Light Tec. With this device, the scattering intensity can be evaluated for each angle at three wavelengths of 630 nm, 525 nm, and 465 nm, so that the light diffusivity can be examined in more detail. The scattering characteristics of the light diffusion sheet of the present invention were determined to be 70% or more, preferably 85% or more of the transmitted scattered light intensity at a scattering angle of 0 degrees within the range of a scattering angle of 35 degrees to 70 degrees. Since light having a wavelength of 525 nm has a large effect on the human eye, it is defined only by light having a wavelength of 525 nm in the present invention.

Hereinafter, each raw material and a manufacturing method constituting the light diffusion sheet according to the present invention will be described in detail.

≪Thermoplastic resin≫
As the thermoplastic resin used in the light diffusion sheet according to the present invention, it is necessary to select a thermoplastic resin suitable as the thermoplastic resin from the following according to the type of the inorganic substance to be combined, the application of the light diffusion sheet product, the function, and the like. There is. For example, polyolefin resins such as polyethylene resins, polypropylene resins, polymethyl-1-pentene, and ethylene-cyclic olefin copolymers; ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, and ethylene-methacrylic acid copolymers. Functional groups such as polymers, metal salts of ethylene-methacrylic acid copolymers (ionomers), ethylene-acrylic acid alkyl ester copolymers, ethylene-methacrylic acid alkyl ester copolymers, maleic acid-modified polyethylenes, maleic acid-modified polypropylenes, etc. Containing polyolefin resin; polyamide resin such as nylon-6, nylon-6,6, nylon-6,10, nylon-6,12; fragrance of polyethylene terephthalate and its copolymer, polyethylene naphthalate, polybutylene terephthalate, etc. Thermoplastic polyester resins such as aliphatic polyester resins such as group polyester resins, polybutylene succinates and polylactic acid; polycarbonate resins such as aromatic polycarbonates and aliphatic polycarbonates; atactic polystyrenes, syndiotactic polystyrenes, acrylonitriles- Polystyrene-based resins such as styrene (AS) copolymers and acrylonitrile-butadiene-styrene (ABS) copolymers; polyvinyl chloride-based resins such as polyvinyl chloride and vinylidene chloride can be mentioned. In case of selection. Combining two or more types can also be targeted.

Among these thermoplastic resins, it is preferable to use polyolefin-based resins, aromatic polyester-based resins, and aliphatic polyester-based resins, and among them, polyolefin-based resins, from the viewpoint of ease of molding, performance, and economic efficiency.

Examples of the polypropylene-based resin include resins having a propylene component unit of 50% by mass or more, and examples thereof include a propylene homopolymer and a copolymer with another α-olefin copolymerizable with propylene. Other α-olefins that can be copolymerized with propylene include, for example, ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, and 3,4-dimethyl-1-butene. , 1-Heptene, 3-Methyl-1-hexene and other α-olefins having 4 to 10 carbon atoms are exemplified. Propylene homopolymers include any of isotactics, syndiotactics, atactics, hemiisotactics and linear or branched polypropylenes exhibiting varying degrees of stereoregularity. Further, the above-mentioned copolymer may be a random copolymer or a block copolymer, and may be not only a binary copolymer but also a ternary copolymer. Specifically, for example, ethylene-propylene random copolymer, butene-1-propylene random copolymer, ethylene-butene-1-propylene random ternary copolymer, ethylene-propylene block copolymer and the like can be exemplified. .. The other olefin copolymerizable with propylene in the copolymer is 25% by mass or less, particularly 15% by mass, when the total mass of the composition of the inorganic substance and the thermoplastic resin is 100% by mass. It is preferably contained in the following proportions, and the lower limit is preferably 0.3% by mass. Moreover, you may consider these polypropylene-based resins individually or in mixture of 2 or more types.

Examples of the polyethylene-based resin include resins having an ethylene component unit of 50% by mass or more. For example, high-density polyethylene (HDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and linear low. Density polyethylene (LLDPE), ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene 1 copolymer, ethylene-butene 1 copolymer, ethylene-hexene 1 copolymer, ethylene-4 Examples thereof include a methylpentene 1 copolymer, an ethylene-octene 1 copolymer and the like, and a mixture of two or more thereof.

Among the above-mentioned polyolefin resins, polypropylene resins are preferably used when heat resistance or mechanical strength is required.

≪Inorganic substances≫
As the inorganic substance that can be blended in the diffusion sheet according to the present invention, a substance suitable for the production method, the application of the light diffusion sheet product, the function, etc. can be selected from the following substances. For example, carbonates such as calcium, magnesium, aluminum, titanium, zinc, sulfates, silicates, phosphates, borates, oxides, or hydrates thereof, especially powdery ones, can be mentioned. For example, calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, silica, alumina, kaolin clay, talc, mica, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate, sulfate. Examples thereof include aluminum, magnesium sulfate, calcium sulfate, magnesium phosphate, barium sulfate, silica sand, zeolite, diatomaceous soil, cericite, silas, calcium sulfite, potassium titanate, bentonite, graphite, ferrite and the like. These may be synthetic or derived from natural minerals, and they may be considered alone or in combination of two or more.

Further, the shape of the inorganic substance is preferably spherical or close to spherical, but may be in the form of particles, flakes, granules, fibers or the like. Further, it may be obtained by a synthetic method, or may have an indefinite shape obtained by pulverizing a natural mineral.

These inorganic substances are preferably powders of calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, silica, alumina, kaolin clay, talc, aluminum hydroxide, magnesium hydroxide and the like, and calcium carbonate is particularly preferable. Further, the calcium carbonate is either so-called light calcium carbonate prepared by a synthetic method or so-called heavy calcium carbonate obtained by mechanically crushing and _{classifying a natural raw material containing CaCO 3 as a main component such as limestone.} However, from the viewpoint of economy, it is preferable to use a large amount of heavy calcium carbonate.

Here, heavy calcium carbonate is obtained by mechanically crushing and processing natural limestone or the like, and is distinguished from synthetic calcium carbonate produced by a chemical precipitation reaction or the like. The pulverization method includes a dry method and a wet method, but the dry method is preferable from the viewpoint of economy.

Further, in order to enhance the dispersibility or reactivity of the inorganic substance, it is preferable to modify the surface of the inorganic substance powder or the like in advance according to a conventional method. Examples of the surface modification method include a physical method such as plasma treatment and a method of chemically surface-treating the surface with a coupling agent or a surfactant. Examples of the coupling agent include a silane coupling agent and a titanium coupling agent. The surfactant may be anionic, cationic, nonionic or amphoteric, and examples thereof include higher fatty acids, higher fatty acid esters, higher fatty acid amides and higher fatty acid salts.

The average particle size of the inorganic substance powder, particularly calcium carbonate, is preferably 0.7 μm or more and 10.0 μm or less, and more preferably 0.7 μm or more and 6.0 μm or less. Thereby, the total light transmittance of the light diffusion sheet can be set in an appropriate range. The average particle size of the inorganic substance powder described in the present specification refers to a value calculated from the measurement result of the specific surface area by the air permeation method according to JIS M-8511. As the measuring device, for example, a specific surface area measuring device SS-100 manufactured by Shimadzu Corporation can be preferably used.

The light diffusion sheet of the present invention contains the above-mentioned thermoplastic resin and inorganic substance in a mass ratio of 70:30 to 10:90. As will be described later, if the ratio of the inorganic substance to the total mass of the thermoplastic resin and the inorganic substance is less than 30% by mass, the scattered light intensity of the light receiving surface becomes uneven depending on the scattering angle. On the other hand, if the ratio is higher than 90% by mass, molding by extrusion molding becomes difficult. The mass ratio of the light diffusion sheet according to the present invention is preferably 70:30 to 30:70, and more preferably 70:30 to 40:60.

≪Other additives≫
If necessary, other additives can be added to the light diffusion sheet of the present invention. However, it should be noted that the use of additives may adversely affect the kneading action and may bleed out to the surface of the light diffusion sheet and impair the optical properties. Other additives include, for example, processing aids, coupling agents, fluidity improvers, dispersants, antioxidants, UV absorbers, flame retardants, stabilizers, antistatic agents, colorants, foaming agents and the like. is there. These additives may be used alone, or two or more of them may be used in combination. Further, these may be mixed in the kneading step described later, or may be blended in the resin composition in advance before the kneading step.

Of these, the ones considered to be important will be described below with examples, but the present invention is not limited to these.

Processing aids include lubricants such as stearic acid, hydroxystearic acid, composite stearic acid, fatty acid lubricants such as oleic acid, aliphatic alcohol lubricants, stearoamides, oxystearoamides, oleylamides, ercilamides, ricinolamides. Behenamide, methylolamide, methylene bisstearoamide, methylene bisstearobehenamide, higher fatty acid bisamide acid, aliphatic amide lubricants such as complex amide, stearic acid-n-butyl, methyl hydroxystearate, polyhydric alcohol Examples thereof include aliphatic ester-based lubricants such as fatty acid esters, saturated fatty acid esters and ester-based waxes, and fatty acid metal soap-based lubricants such as magnesium stearate.

As the antioxidant, a phosphorus-based antioxidant, a phenol-based antioxidant, and a pentaerythritol-based antioxidant can be used. Phosphorus-based, more specifically, phosphorus-based antioxidant stabilizers such as phosphite ester and phosphoric acid ester are preferably used. Examples of the phosphite ester include phosphorous acid triesters such as triphenylphosphite, trisnonylphenylphosphite, and tris (2,4-di-t-butylphenyl) phosphite, diesters, and monoesters. Can be mentioned.

Examples of the phosphoric acid ester include trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, tris (nonylphenyl) phosphate, 2-ethylphenyldiphenyl phosphate and the like. These phosphorus-based antioxidants may be used alone or in combination of two or more.

Examples of phenolic antioxidants include α-tocopherol, butylhydroxytoluene, cinapyl alcohol, vitamin E, n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2-. t-butyl-6- (3'-t-butyl-5'-methyl-2'-hydroxybenzyl) -4-methylphenylacrylate, 2,6-di-t-butyl-4- (N, N-dimethyl) Aminomethyl) phenol, 3,5-di-t-butyl-4-hydroxybenzylphosphonate diethyl ester, and tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxymethyl] methane Etc. are exemplified, and these can be used alone or in combination of two or more kinds.

The flame retardant is not particularly limited, and for example, a halogen-based flame retardant or a non-phosphorus-based halogen-based flame retardant such as a phosphorus-based flame retardant or a metal hydrate can be used. Specific examples of the halogen-based flame retardant include halogenated bisphenol compounds such as halogenated bisphenyl alkane, halogenated bisphenyl ether, halogenated bisphenyl thioether, and halogenated bisphenyl sulfone, brominated bisphenol A, and bromine. Bisphenol-bis (alkyl ether) compounds such as bisphenol S, chlorinated bisphenol A, and chlorinated bisphenol S, and as phosphorus-based flame retardants, tris (diethylphosphinic acid) aluminum, bisphenol A bis (diphenyl phosphate) , Triaryl isopropyl phosphate, cresildi 2,6-xylenyl phosphate, aromatic condensed phosphate, etc., as metal hydrates, for example, aluminum trihydrate, magnesium dihydration, or a combination thereof. Etc. can be exemplified respectively, and these can be used alone or in combination of two or more kinds. It works as a flame-retardant aid and can improve the flame-retardant effect more effectively. Further, for example, antimony oxide such as antimony trioxide and antimony pentoxide, zinc oxide, iron oxide, aluminum oxide, molybdenum oxide, titanium oxide, calcium oxide, magnesium oxide and the like can be used in combination as a flame retardant aid. ..

As the antistatic agent, for example, as an internally added type, a hydroxyl group-containing compound such as fatty acid diethanolamide such as lauryl diethanolamide and stearyl diethanolamide can be used.

As the colorant, any known organic pigment, inorganic pigment or dye can be used. Specifically, organic pigments such as azo-based, anthraquinone-based, phthalocyanine-based, quinacridone-based, isoindolinone-based, geoosazine-based, perinone-based, quinophthalone-based, and perylene-based pigments, and inorganic pigments such as zinc oxide and titanium yellow are used. Can be mentioned.

The porosity of the light diffusion sheet of the present invention can be adjusted by extrusion molding as described above, but in addition, the foaming agent is 0.04 with respect to the total mass of the thermoplastic resin and the inorganic substance, for example. It can also be controlled by adding about 5.00% by mass. As a matter of course, the foaming agent must be one that creates fine voids in the sheet.

As a foaming agent suitable for the object of the present invention, the inventors have determined from many examination results that a carrier resin containing the active ingredient of the foaming agent is suitable for forming a small amount of voids. Crystalline polyolefin resin is considered to be the most suitable carrier resin, and bicarbonate is considered to be the most suitable as the active ingredient.

≪Manufacturing method of light diffusion sheet≫
In the method for producing a light diffusion sheet according to the present invention, a predetermined amount of thermoplastic resin and inorganic substance powder can be mixed, and kneading and gas mixing can simultaneously form a void structure, which simplifies the process and simplifies the process. It greatly contributes to cost reduction. An extrusion molding machine is suitable as a mechanical device for performing this processing, and a twin-screw extrusion molding machine is particularly preferable. A resin composition having a desired void ratio is prepared and then molded into a sheet. Extrusion molding, injection molding, calender molding and the like can be used as the molding method, but extrusion molding by the T-die method or the inflation method is the most suitable. preferable.

In extrusion molding of plastics, raw materials such as thermoplastic resins, inorganic substances and additives are accompanied by volatile substances such as air, moisture and monomers. Here, assuming that all of the above-mentioned concomitant substances are water, and calculating that all of them change into voids, the calculation is as follows. If the composition of the thermoplastic resin and the inorganic substance contains 0.02% by mass of water, 0.01 mmol or more of water molecules are present in ^{1 cm 3.} If all of this foams to form voids, the porosity will be around 20%. For the volatile components in the material and the generation of air bubbles in the extrusion process, refer to "Extrusion Molding Condition Setting and Trouble Countermeasures" (2018) edited by the Technical Information Association.

These concomitant materials are removed outside the molding machine by open venting or vacuum venting, but it is difficult to remove them completely and it is not possible to measure how much they remain during work. After the venting process, strong kneading is performed and dispersion mixing is repeated in the resin body to create a structure of fine voids inside the sheet. In this case, how much gas is mixed in the resin body is determined. Cannot measure. Therefore, the porosity of the extruded product is determined by measuring the specific gravity of the molded sheet from the die at regular intervals in the width direction and evaluating the variation and the average value thereof. It can be said that this is an important point in the technique of the present invention.

When kneading and molding are performed in separate steps, it is also possible to mold with a uniaxial extruder. In this case, it is necessary to sufficiently knead the raw material pellets in the manufacturing process and pay close attention to prevent the raw material pellets from absorbing moisture. The operation of the extrusion molding machine is the same as that of the twin-screw extruder.

≪Coat layer≫
A coat layer may be further added to the light diffusing sheet of the present invention as described above to improve printability. For example, it is also possible to provide an acrylic coating layer on one side or both sides of the sheet to form an inkjet receiving layer. The raw materials used as the coat layer are not particularly limited, and in addition to acrylic paints, epoxy-based and polyester-based paints, paints produced by mixing synthetic resin emulsions with pigments such as kaolin clay and calcium carbonate can be used. .. The present invention also includes a light diffusing sheet provided on the surface of the light diffusing sheet and having a coat layer suitable for various printing methods such as inkjet printing.

In the light diffusion sheet of the present invention, a high amount of an inorganic substance is blended, the porosity is adjusted to an appropriate value, and uniform light scattering property, high light transmission property, and good mechanical strength are exhibited. The light diffusion sheet of the present invention is expected to greatly contribute to the realization of a sustainable society, which has become a global problem, and to help reduce the amount of plastic substances used or switch to non-plastic substances, which has become a social problem. Will be done. Mineral substance powder, which is the main raw material, is abundant as a resource, and it is expected that the energy cost used to produce the light diffusion sheet will be low. The effect of the present invention is also remarkable in this respect.

Hereinafter, the present invention will be described in more detail based on Examples. It should be noted that these examples are specific embodiments and practices in order to facilitate understanding of the concept and scope of the present invention disclosed in the present specification and described in the appended claims. The present invention is described only for the purpose of exemplifying the embodiments, and the present invention is not limited to these examples.

[Examples 1 to 3 and Comparative Example 1]
As a raw material, polypropylene homopolymer (E111G, melt mass florate 0.5 g / 10 minutes, manufactured by Prime Polymer Co., Ltd.) as a thermoplastic resin, and Ryton S-4 (surface-treated calcium carbonate, average particle size) as an inorganic substance powder 6 μm, manufactured by Bihoku Powder Industry Co., Ltd. was used. Both were used in the mixing ratios shown in Table 1, magnesium stearate was added as a lubricant, and the mixture was kneaded at 200 ° C. using a biaxial kneading extruder (φ25 mm, L / D = 41) rotating in the same direction and placed in water. Extruded with strands, cooled and cut to make four types of pellets. When the strands extruded into water were not continuously connected, it was judged that the kneading was insufficient and the surrounding area was discarded and not used in the next step. After drying each pellet prepared in this manner, it is kneaded at 230 ° C. by a uniaxial T-die extrusion molding device (φ20 mm, L / D = 25) with an open vent, extruded from the T-die, and a take-up roll at 80 ° C. is rolled. It was taken up through the sheet and molded into a sheet having a thickness of about 0.3 mm. The densities (specific gravities) of each sheet were 1.01 in Comparative Example 1 and 1.15, 1.43, and 1.62 in Examples 1 to 3, respectively. The results of calculating the porosity from these are shown in Table 1. The density (specific gravity) was measured according to the following JIS standard. For each sheet, physical properties such as thickness, opacity, total light transmittance, haze, diffusion transmittance, and light scattering characteristics were measured under the following conditions.

The basic physical properties of the sheet were measured according to the following JIS standards.
Density: JIS K7112, Basis weight: JIS P8124, Thickness: JIS K7130,
Elastic modulus: JIS K7127: Measured in both the vertical direction (MD) and the horizontal direction (TD),
Whiteness: JIS P8148, Opacity: JIS P8149,
Air permeability: JIS P8117

When a sheet was molded under the same conditions as in Example 2 by using a foaming agent concentrate containing a crystalline polyethylene resin as a carrier resin and a hydrocarbon salt as a pyrolysis type foaming agent, the sheet was formed. The porosity of was 34.5%. This result indicates that the sheet of the present invention can be produced even if a foaming agent is used, if very weak foaming conditions are applied.
Among the optical characteristics, the total light transmittance, the haze value and the diffusion transmittance were measured by JIS K7361-1 and 7136. All of these were performed on both the gloss surface and the matte surface of each sheet, and the average value of the values on both sides was displayed for the haze value.
The light scattering characteristics were evaluated by the relative value of the transmitted scattered light intensity. The transmitted scattered light intensity was measured using a "small simple scattering measuring instrument" Mini-Diff V2 manufactured by Cybernet System Co., Ltd., and a wavelength of 525 nm was used as an incident light source. Based on the measured values at each scattering angle, the relative value for each scattering angle with respect to the transmitted scattered light intensity at a scattering angle of 0 degrees was calculated. In this measurement, the transmitted scattered light intensity was measured not only for the scattering angle in one direction of the sheet but also for the scattering angles in various directions on the same sheet surface, but the scattering angle dependence is the same in all directions. there were. In other words, the transmitted scattered light intensity for each scattering angle at a certain measurement point on the sheet surface was almost uniform in the circular direction.
The evaluation results are shown in Table 1 and FIG.

As is clear from Table 1 and FIG. 1, in the sheet of Comparative Example 1 in which the calcium carbonate content is 20%, the transmitted scattered light intensity decreases remarkably as the scattering angle deviates from 0 degrees, and at 70 degrees, when it is 0 degrees. It was less than 70%. On the other hand, in the sheets of Examples 1 to 3 in which the calcium carbonate content was in the range of 30 to 90%, the difference in the amount of light depending on the angle of light scattering was almost eliminated, and the light scattering characteristics were remarkably improved.

[Examples 4 to 7]
In these examples, the raw materials were directly put into a twin-screw kneading extruder, kneaded, and then formed into a sheet, instead of being pelletized and then formed into a sheet.
A polypropylene homopolymer (E111G, melt mass florate 0.5 g / 10 minutes, manufactured by Prime Polymer Co., Ltd.) was used as the thermoplastic resin, and four types of calcium carbonate having different average particle sizes were used as the inorganic substance powder. A co-rotating twin-screw kneading extruder (φ20 mm, L / D = 44) equipped with an open vent, in which each calcium carbonate is combined with polypropylene resin at a mass ratio of 60:40 and magnesium stearate is added as a lubricant. It was kneaded at 230 ° C., extruded from a T-die, picked up through a take-up roll at 80 ° C., and molded into a sheet having a thickness of about 0.2 mm.
Physical characteristics such as density, opacity, and light transmittance of each sheet were measured in the same manner as in Example 1. The densities of the sheets molded in Examples 4 to 7 were 1.42, 1.43, 1.39, and 1.47, respectively. Table 2 shows typical evaluation results.

As is clear from Table 2, even if the production conditions were changed, the sheets having a porosity in the range of 18 to 33% showed appropriate total light transmittance and diffusion transmittance. The effect of the particle size of the calcium carbonate powder on the total light transmittance of the sheet was not so clear in the range of 6 to 25 μm, and the total light transmittance increased slightly when the average particle size was 2 μm.

[Examples 8 to 13, Comparative Examples 2 to 5]
The same operation as in Examples 4 to 7 was performed using a twin-screw extruder having a screw outer diameter of 100 mm. The sheet after extrusion molding was divided into two samples, one without coating and one with coating, and the coated sample was subjected to an acrylic coating treatment effective for improving printability, and a coat layer was provided.
Polypropylene homopolymer (E111G, melt mass florate 0.5 g / 10 minutes, manufactured by Prime Polymer Co., Ltd.) as a thermoplastic resin, and Ryton S-4 (surface-treated calcium carbonate, average particle diameter 6 μm, Bikita) as an inorganic substance powder. (Made by Powder Industry Co., Ltd.) was used. These were used in a mass ratio of 40:60, magnesium stearate was further added as a lubricant, and kneaded at 230 ° C. using a co-rotating twin-screw kneading extruder (φ100 mm, L / D = 44).
During the kneading process, one open vent and one vacuum vent were installed in this equipment, and air, moisture, volatile components, etc. associated with the raw materials were removed from the extruder. Even after the air, moisture, etc. were removed by the vent, some air, etc. remained in the barrel, and these were taken in during kneading and uniformly dispersed in the resin body. The resin body was passed through a gear pump and a screen, extruded from a T-die, and then formed into a sheet having a thickness of about 0.2 to 0.4 mm via a take-up roll at 80 ° C., and the sheet density was measured. In Comparative Examples 2 to 5, the sheet formed as described above was not wound and was directly stretched by a longitudinal stretching treatment utilizing the difference in peripheral speed of the roll (stretching ratio 2 times).
The density was measured each time the sheet was formed, and the results were as follows for the uncoated sheets of Examples 8, 10 and 12 and Comparative Examples 2 and 4, respectively: 1. .48, 1.45, 1.47, 0.91, 0.91.
The physical characteristics of the prepared sheet are shown in Table 3-1 and the optical characteristics are shown in Table 3-2.

As is clear from Tables 3-1 and 2, the sheets of Examples 8 to 13 according to the present invention all have a light transmittance that can be used for a backlight, have good light scattering characteristics, and have an excellent elastic modulus. Was there. Table 4 shows the measured values of Examples 8 and 9 as an example of the light scattering characteristics.
On the other hand, in the sheets of Comparative Examples 2 to 5 in which the porosity greatly exceeded 33%, the total light transmittance and the diffusion transmittance were remarkably lowered. It was clarified that the optical properties of the sheet deteriorated when voids were generated in the sheet by stretching. Table 4 shows the measured values of the light scattering characteristics of Comparative Example 4, and it can be seen that the light scattering characteristics are also inferior to those of the unstretched sheet. In the light reflector of Patent Document 11, the area stretching ratio was 25 to 70 times, and the reflection characteristics were improved on the sheet surface having a large pore ratio, but the optical characteristics of the light diffusion sheet were completely different.

The transmittance measurement result of Comparative Example 4 is shown in FIG. As is clear from FIGS. 1 and 3 to 4, the sheet subjected to the stretching treatment in the manufacturing process generally has high whiteness and opacity, and can be easily distinguished from the non-stretched sheet. It was confirmed that increasing the opacity does not lead to an improvement in the performance of the light diffusion sheet. Further, the sheets of Comparative Examples 2 and 4 which have not been coated have low air permeability (that is, gas easily permeates), suggesting that a large number of communication holes were generated by stretching.
The elastic modulus was also greatly reduced by stretching, and the elastic modulus of the unstretched sheet (Examples 8 to 13) was 1000 MPa or more, whereas the elastic modulus of the stretched sheet (Comparative Examples 2 to 5) was all 1000 MPa or more. It was 600 MPa or less.
In the range of 0.2 to 0.4 mm, which is usually used, the thinner the sheet, the better both transmittances, and the sheets of Examples 8 and 9 having a sheet thickness of 0.2 mm transmit light. The rate and light scattering characteristics were particularly good.

[Example 14, Comparative Examples 6 to 8]
Using the sheet of Example 9, the light transmittance and the hiding property were evaluated and compared with a commercially available backlight film for illumination.
In the market for lighting applications, most light diffusion sheets have a light transmittance of 40% or less, with 38.3% for commercial product A, 38.5% for commercial product B, and 37.8% for commercial product C. there were. The diffusion transmittance was 38.2% for commercial product A, 38.5% for commercial product B, and 37.6% for commercial product C. On the other hand, in the sheet of Example 9 according to the present invention, the total light transmittance was 43.9% and the diffusion transmittance was 43.8%, which were relatively high transmittances.
For the measurement of concealment, for a sample placed at a position X cm away from the light source, when the light source is observed with the naked eye from a place 1.5 m away from the surface of the sample, the shape of the light source cannot be recognized. It was done by measuring. It can be said that the lower the numerical value, that is, the closer the light source and the sample are to the sample as compared with the reference sample, the better the concealment property.
The value of X was 7.0 cm for the sheet of Example 9, 8.5 cm for the commercial product A, 8.5 cm for the commercial product B, and 9.0 cm for the commercial product C. The sheet according to the present invention showed a smaller X value than the commercially available product, and was also good in terms of concealment.

Claims (8)

In a light diffusion sheet containing a thermoplastic resin and an inorganic substance in a mass ratio of 70:30 to 10:90, the light diffusion sheet has a void ratio of 18% or more and 35% or less and a wavelength of 525 nm. The light diffusion sheet is characterized in that the transmitted scattered light intensity of the above is 70% or more of the transmitted scattered light intensity at a scattering angle of 0 degrees within a range of a scattering angle of 35 degrees to 70 degrees. The light diffusion sheet according to claim 1, wherein the inorganic substance is a mineral substance powder. The light diffusion sheet according to claim 2, wherein the inorganic substance is heavy calcium carbonate. The light diffusion sheet according to claim 1, wherein the thermoplastic resin is a polyolefin resin. The light diffusion sheet according to any one of claims 1 to 4, wherein the inorganic substance is calcium carbonate having an average particle size of 0.7 μm or more and 10.0 μm or less. The light diffusion sheet according to any one of claims 1 to 4, wherein the mass ratio of the thermoplastic resin to the inorganic substance is 50:50 to 10:90. The light diffusion sheet according to any one of claims 1 to 6, wherein the light diffusion sheet is a non-stretched sheet. A light diffusion sheet having a coat layer provided on the surface of the light diffusion sheet according to any one of claims 1 to 7.

Images