JP2017062425A - Light reflection film and backlight unit for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light reflection film capable of maintaining high reflectance even when exposed for a certain period of time under high temperature and high humidity.SOLUTION: A light reflection film includes, in this order: a transparent substrate layer (A); a high refractive index layer (B) having a refractive index higher than a refractive index of light of the transparent substrate layer (A) having a wavelength of 570 nm; a low refractive index layer (C) having a refractive index lower than the refractive index of the light of the transparent substrate layer (A) having the wavelength of 570 nm; a metal reflective layer (D); and a protective layer (E). The low refractive index layer (C) is a resin layer, and the protective layer (E) a resin layer containing a sulfur-containing compound.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light reflecting film and a backlight unit for a liquid crystal display device.

  Conventionally, a reflective member having a metal reflective layer (mainly a silver layer) has been used in applications such as a light reflective film of a backlight unit for liquid crystal display devices, a reflective mirror of a projection television or an optical system device, and a reflective member for LED illumination. It has been. These reflecting members are desired to have a high reflectance.

  Especially, the light reflection film used for the backlight unit of a liquid crystal display device has a reflectance of a blue light region (wavelength of 430 to 470 nm) and a reflectance of a visible light region (wavelength of 560 to 600 nm) from the viewpoint of improving the color tone. Is required to be higher. On the other hand, the silver layer has a lower average reflectance in the blue light region than in the visible light region. Therefore, a reflector in which a low refractive index thin film layer (B) mainly composed of silicon oxide and a high refractive index thin film layer (C) are further laminated on a silver layer has been studied (for example, Patent Document 1).

  By the way, the light reflection film of the backlight unit for liquid crystal display devices may be exposed to a high temperature and high humidity environment during use. Accordingly, there is a need for a light reflecting film that can maintain good reflectivity even when exposed to high temperatures and high humidity for a certain period of time, that is, a light reflecting film having high wet heat durability.

Japanese Patent No. 4498273

However, the reflector of Patent Document 1 has a problem that it cannot maintain a high reflectance when exposed to a high temperature and high humidity for a certain period of time. This is presumably because the low refractive index thin film layer mainly composed of SiO ₂ does not have sufficient adhesion to the silver layer and easily transmits moisture. When the backlight unit for a liquid crystal display device including such a reflector is exposed to a high temperature and high humidity for a certain period of time, there is a possibility that the luminance may be lowered.

  This invention is made | formed in view of the said situation, and it aims at providing the light reflection film which can maintain a high reflectance even if it exposes to high temperature and high humidity for a fixed time.

[1] A transparent substrate layer (A), a high refractive index layer (B) having a refractive index higher than the refractive index of light having a wavelength of 570 nm of the transparent substrate layer (A), and the transparent substrate layer ( A) a low refractive index layer (C) having a refractive index lower than the refractive index of light having a wavelength of 570 nm, a metal reflective layer (D), and a protective layer (E) in this order, and the low refractive index layer (C) is a resin layer, and the protective layer (E) is a resin layer containing a sulfur-containing compound.
[2] The light reflecting film according to [1], wherein the metal reflective layer (D) is a thin film mainly composed of silver or an alloy thereof.
[3] The light reflecting film according to [1] or [2], wherein the low refractive index layer (C) further contains a sulfur-containing compound.
[4] The light reflecting film according to any one of [1] to [3], wherein the protective layer (E) further includes fine particles.
[5] The light reflecting film according to any one of [1] to [4], wherein the protective layer (E) further contains a black pigment.
[6] The light reflecting film according to [3], wherein the high refractive index layer (B) is a thin film containing a metal sulfide as a main component.
[7] A backlight unit for a liquid crystal display device comprising a light source and the light reflecting film according to any one of [1] to [6].

  ADVANTAGE OF THE INVENTION According to this invention, even if it exposes to high temperature and high humidity for a fixed time, the light reflection film which can maintain a high reflectance can be provided.

It is a schematic diagram which shows an example of the light reflection film of this invention. It is sectional drawing which shows an example of the liquid crystal display device of this invention.

  The present inventors arrange “a low refractive index layer (C) made of a resin layer” on one surface of the metal reflective layer (D) and “protect a resin layer containing a sulfur-containing compound” on the other surface. It has been found that by arranging the “layer (E)”, it is possible to remarkably reduce a decrease in reflectance when the light reflecting film is exposed to high temperature and high humidity for a certain period of time. The reason for this is not clear, but is considered as follows.

Since the “low refractive index layer (C) made of a resin layer” has higher affinity with the metal reflective layer (D) than the low refractive index layer made of a thin film of SiO ₂ , it has good adhesion. Moreover, since "the protective layer (E) consisting of a resin layer containing a sulfur-containing compound" contains a sulfur-containing compound that easily interacts with the metal reflective layer (D), it has even better adhesion. Therefore, by sandwiching the metal reflective layer (D) between the “low refractive index layer (C) made of a resin layer” and the “protective layer (E) made of a resin layer containing a sulfur-containing compound”, the metal reflective layer ( It is considered that the moisture permeation to D) can be drastically reduced, and the metal atoms of the metal reflection layer (D) can be highly suppressed from being ionized or aggregated by the permeated moisture. As a result, it is possible to obtain a light reflecting film in which the decrease in reflectance is remarkably reduced even when exposed to a high temperature and high humidity for a certain period of time. The present invention has been made based on such findings.

1. Light Reflective Film The light reflective film of the present invention comprises a transparent substrate layer (A), a high refractive index layer (B), a low refractive index layer (C), a metal reflective layer (D), and a protective layer (E ) In this order.

1-1. Transparent substrate layer (A)
The transparent substrate layer (A) has a light transmittance of a certain level or more in order to make light incident from the surface thereof. The refractive index at a wavelength of 570 nm of the transparent base material layer (A) depends on the refractive index of the high refractive index layer (B) and the low refractive index layer (C) as described later, but it is easy to obtain a certain reflectance. For example, it may be 1.7 or less. The transparent substrate layer (A) may be a transparent resin layer that satisfies these physical properties, and is preferably a transparent resin film from the viewpoint of directly forming a high refractive index layer (B).

  Examples of transparent resin films include polyester films such as polyethylene terephthalate film and polyethylene naphthalate film, polypropylene film, acrylic film, polycarbonate film, polyimide film, polysulfone film, polyetheretherketone film, cellulose ester film, polycycloolefin System film and the like are included. Among these, a polyethylene terephthalate film and a polypropylene film are preferable from the viewpoint of high heat resistance, strength, and transparency.

  The average transmittance of the transparent substrate layer (A) at a wavelength of 360 to 400 nm is preferably 80% or more, and more preferably 85% or more. The average transmittance of the transparent substrate layer (A) can be measured with a spectrophotometer U-4100 manufactured by Hitachi High-Technologies Corporation.

  The thickness of the transparent substrate layer (A) can be, for example, 10 to 500 μm. When the thickness of the transparent base material layer (A) is 10 μm or more, the moisture barrier property by the transparent base material layer (A) is high, and thus moisture permeation to the metal reflective layer (D) can be sufficiently suppressed. The thickness of the transparent substrate layer (A) is preferably 10 to 300 μm, and more preferably 20 to 150 μm.

1-2. High refractive index layer (B) / Low refractive index layer (C)
The high refractive index layer (B) and the low refractive index layer (C) can function as an increased reflection layer that increases the reflectance of the metal reflective layer (D). The high refractive index layer (B) has a refractive index higher than the refractive index of light having a wavelength of 570 nm of the transparent base material layer (A); the low refractive index layer (C) is the transparent base material layer (A). The refractive index is lower than the refractive index of light having a wavelength of 570 nm. That is, the refractive index of light having a wavelength of 570 nm in the high refractive index layer (B) is higher than the refractive index of light having a wavelength of 570 nm in the low refractive index layer (C).

  The difference in refractive index of light having a wavelength of 570 nm between the high refractive index layer (B) and the low refractive index layer (C) is preferably 0.35 or more from the viewpoint of obtaining a sufficient reflection enhancement effect. 4 or more is more preferable, and 0.5 to 1.10.

In order for the high refractive index layer (B) and the low refractive index layer (C) to function as a reflection increasing layer, the refractive index at a wavelength of 570 nm of the high refractive index layer (B) is n _H , the thickness is d _H , When the refractive index at a wavelength of 570 nm of the low refractive index layer (C) is n _L and the thickness is d _L , it is preferable to satisfy the following expressions (1) and (2) at the same time.
Formula (1): 300 <8d _L · n _L <730 (preferably 350 <8d _L · n _L <600)
Formula (2): 300 <4d _H · n _H <730 (preferably 350 <4d _H · n _H <600)

1-2-1. High refractive index layer (B)
The refractive index n _H of light having a wavelength of 570 nm of the high refractive index layer (B) can be set in consideration of the refractive index difference from the transparent base layer (A) and the low refractive index layer (C). It is preferably 0.85 or more, and more preferably 2.00 or more and 2.70 or less. The refractive index of the high refractive index layer (B) is adjusted mainly by the refractive index of the material contained in the high refractive index layer (B) and the density of the high refractive index layer (D).

The refractive index n _H of the high refractive index layer (B) can be measured by the following method. That is, a high refractive index layer (single layer) having a thickness of 100 nm is vacuum-deposited on a polyethylene terephthalate substrate to obtain a sample for refractive index measurement. The refractive index of light having a wavelength of 570 nm of the obtained sample is measured using a spectroscopic ellipsometer UVSEL manufactured by Horiba.

  Such a high refractive index layer (B) may be an inorganic layer (preferably a thin film) mainly composed of an inorganic material, or a resin layer mainly composed of a resin. Especially, it is preferable that a high refractive index layer (B) is an inorganic substance layer which has an inorganic material as a main component from the point that a high refractive index is easy to be obtained. The inclusion as a main component means that the content with respect to the high refractive index layer (B) is 50% by mass or more.

Examples of the inorganic material constituting the high refractive index layer (B) include metal oxides or metal sulfides. Examples of the metal constituting the metal oxide or metal sulfide include Zn, Ti, Zr, Nb, Ta and In. Examples of metal oxides include TiO ₂ , ITO (indium tin oxide), ZnO, Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , Ti ₃ O ₅ , Ti ₄ O ₇ , Ti ₂ O ₃ and TiO. Is included. Examples of the metal sulfide include ZnS, MnS, and the like.

  Among these, metal sulfides are preferable because the luminance characteristics of the backlight unit using the light reflecting film can be effectively enhanced; zinc sulfide (ZnS) is more preferable because it has a high refractive index and transparency. preferable.

  The content of the metal oxide or metal sulfide is preferably 90 atomic% or more, and more preferably 95 atomic% or more with respect to the high refractive index layer (B).

The thickness _{d H} of the high refractive index layer (B), depending on the wavelength range of light to be enhanced reflection, in terms of increasing the reflection-increasing effect of the example of the wavelength 430~470nm light is preferably 20 to 80 nm,. 30 to More preferably, it is 70 nm.

1-2-2. Low refractive index layer (C)
The refractive index n _L of light having a wavelength of 570 nm of the low refractive index layer (C) is set in consideration of the refractive index difference from the transparent base layer (A) and the high refractive index layer (B). Is preferably 80 or less, and more preferably 1.30 or more and 1.70 or less. The refractive index n _L of the low refractive index layer (C) is mainly adjusted by the refractive index of the material contained in the low refractive index layer (C) and the density of the low refractive index layer (C).

The refractive index n _L of the low refractive index layer (C) is the same as described above except that a low refractive index layer (single layer) having a thickness of 100 nm is formed on a polyethylene terephthalate substrate to obtain a sample for refractive index measurement. Can be measured.

  The low refractive index layer (C) is a resin layer containing a resin as a main component. The resin constituting the low refractive index layer (C) may be a resin having a refractive index suitable for the low refractive index layer (C). Examples of such resins include acrylic resins, melamine resins, polyvinyl alcohol resins, and celluloses (such as cellulose esters and cellulose ethers). Among these, from the viewpoint of easily adjusting the refractive index, acrylic resins, melamine resins, and mixtures thereof are preferable, and acrylic resins are more preferable. The acrylic resin may be a cross-linked product (cured product) cross-linked with a curing agent such as isocyanate.

  The acrylic resin may be a homopolymer of (meth) acrylic acid ester or a copolymer of (meth) acrylic acid ester and another copolymerizable monomer. The (meth) acrylic acid ester may preferably be methyl methacrylate.

  Examples of copolymer monomers that can be copolymerized with methyl methacrylate include: alkyl methacrylates having 2 to 18 carbon atoms in the alkyl moiety; alkyl acid alkyl esters having 1 to 18 carbon atoms in the alkyl moiety; acrylic acid; Α, β-unsaturated acids such as methacrylic acid; unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid; 2-hydroxymethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3 Hydroxyl group-containing (meth) acrylic acid esters such as hydroxypropyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, diethylene glycol mono (meth) acrylate, dipropylene glycol mono (meth) acrylate; styrene, α-methylstyrene Aromatic vinyl compounds such as acrylo Etc. acrylamide derivatives such Rumoruforin (ACMO) is included. These may be used alone or in combination of two or more. Among these, a hydroxyl group-containing (meth) acrylic acid ester is preferable from the viewpoint of crosslinking with a curing agent to form a crosslinked product (cured product). The proportion of the structural unit derived from the copolymer monomer in the copolymer of methyl methacrylate and another copolymer monomer is preferably 50% by mass or less, and more preferably 30% by mass or less.

  Specific examples of the acrylic resin include poly (methyl methacrylate) (PMMA), poly (methyl methacrylate) copolymer (coPMMA), and the like.

  The weight average molecular weight of resin should just be the extent which can be apply | coated, for example, may be 1000 to 500,000. The weight average molecular weight can be measured by high performance liquid chromatography.

  The content of the resin is preferably 60% by mass or more with respect to the entire low refractive index layer (C). When the resin content is 50% by mass or more, the durability of the metal reflective layer (D) can be sufficiently enhanced. The content of the resin is preferably 70% by mass or more, more preferably 80% by mass or more, and may be 100% by mass with respect to the entire low refractive index layer (C).

  The low refractive index layer (C) preferably further contains a sulfur-containing compound from the viewpoint of enhancing the wet heat durability of the light reflecting film. Since the resin composition containing a sulfur-containing compound has high affinity with the metal (preferably silver) constituting the metal reflective layer (D), the resulting coating film has good adhesion with the metal reflective layer (D). Easy to have.

  Examples of sulfur-containing compounds include thiol group-containing carboxylic acids such as mercaptoacetic acid and mercaptopropionic acid; thiophenols; polythiol compounds such as 1,2-ethanedithiol and 1,3-propanedithiol; 3-mercapto-1,2 Thiol group-containing triazole compounds such as 1,4-triazole and 1-methyl-3-mercapto-1,2,4-triazole; Thiol group-containing benzothiazole compounds such as 2-mercaptobenzothiazole; Thiols such as 2-mercaptobenzimidazole Group-containing benzimidazole compounds; thiol group-containing benzoxazole compounds such as 2-mercaptobenzoxazole; thiazole, thiazoline, thiazolone, thiazolidine, thiazolidone, isothiazole, benzothiazole, 2-N, N-diethylthioben Thiazole compounds such as thiazole, P-dimethylaminobenzallodanine, and 2-mercaptobenzothiazole; thionalides; thiol group-containing silane compounds such as 3-mercaptopropyltrimethoxysilane; polyols (butanediol, hexanediol, trimethylolpropane) , And pentaerythritol, etc.) and a thiol group-containing monocarboxylic acid (thioglycolic acid, mercaptopropionic acid, etc.) and a thiol group-containing carboxylic acid derivative (glycol dimercaptoacetate, butanediol bisthioglycolate (BDTG) ), Trimethylolpropane tristhioglycolate (TMTG), trimethylolpropane tristhiopropionate (TMTP) and pentaerythritol tetrakisthiopropione Thioether-containing alcohol derivatives (dilauryl 3,3-thiodipro) obtained by reacting monoalcohol (lauryl alcohol, myristyl alcohol, etc.) and thioether group-containing polycarboxylic acids (thiodipropionic acid, etc.) Pionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3-thiodipropionate, etc.); sulfur-containing chelate compounds such as sulfurane, persulfuran, etc. Can be mentioned.

  Among them, compounds having a thiol group in the molecule are preferable, and thiol groups such as trimethylolpropane tristhioglycolate (TMTG), trimethylolpropane tristhiopropionate (TMTP), and pentaerythritol tetrakisthiopropionate (PETG). More preferred are carboxylic acid derivatives.

  It is preferable that content of a sulfur containing compound is 0.5-20 mass% with respect to the sum total of resin contained in a low refractive index layer (C). When the content of the sulfur-containing compound is 0.5% by mass or more, the interaction between the metal reflective layer (D) and the low refractive index layer (C) is sufficiently enhanced, so that the wet heat of the metal reflective layer (D) Durability can be increased sufficiently. When the content of the sulfur-containing compound is 20% by mass or less, coloring and a decrease in reflectance due to light absorption of the sulfur-containing compound are unlikely to occur. As for content of a sulfur containing compound, it is more preferable that it is 1-10 mass% with respect to the sum total of resin contained in a low refractive index layer (C).

The thickness d _L of the low refractive index layer (C) depends on the wavelength range of light to be increased in reflection, but is preferably 10 to 70 nm, for example, in terms of enhancing the effect of increasing the reflection of light having a wavelength of 430 to 470 nm. More preferably, it is 50 nm, and it is still more preferable that it is 20-40 nm.

  When specifying the thickness of the high refractive index layer (B) or the low refractive index layer (C), the composition of the high refractive index layer (B) or the low refractive index layer (C) changes continuously, and the layer interface is clear. It may not be. In such a case, “the maximum refractive index of the entire high refractive index layer (B) and the low refractive index layer (C)” — “of the entire high refractive index layer (B) and the low refractive index layer (C)” When “minimum refractive index” = Δn, the point of the minimum refractive index + Δn / 2 between the two layers can be regarded as “a layer interface between the high refractive index layer (B) and the low refractive index layer (C)”.

  The maximum refractive index and the minimum refractive index in the entire high refractive index layer (B) and low refractive index layer (C) are the atoms in the depth direction of the high refractive index layer (B) and the low refractive index layer (C). The composition can be determined by measuring by XPS and calculating based on the atomic composition. The atomic composition in the depth direction of the high refractive index layer (B) and the low refractive index layer (C) is the atomic composition at each depth while etching from the surface of the light reflecting film to the depth direction using a sputtering method. The ratio is measured with an XPS surface analyzer; the laminated film of the high refractive index layer (B) and the low refractive index layer (C) is cut, and the atomic composition ratio of the cut surface is measured with the XPS surface analyzer. Can be obtained.

1-3. Metal reflective layer (D)
The metal reflective layer (D) has a function of reflecting light. The metal reflection layer (D) contains, as a main component, one or more selected from the group consisting of Al, Ag, Cr, Cu, Ni, Ti, Mg, Rh, Pt, Au, and alloys thereof. Among these, the metal reflective layer (D) preferably contains Al, Ag, or an alloy thereof as a main component, and more preferably contains Ag or an alloy thereof as a main component in that it has a high reflectance. The inclusion as a main component means that the content with respect to the metal reflective layer (D) is 90 atomic% or more.

  The content of Ag or its alloy is preferably 90 atomic% or more, more preferably 99.9 atomic% or more with respect to the metal reflective layer (D).

  The metal reflective layer (D) may further contain other metal other than Ag or an alloy thereof. Examples of other metals include Au, Pd, Sn, Ga, In, Cu, Ti, Bi and alloys thereof, preferably Au and Ag alloys.

  The metal reflective layer (D) is preferably a thin film formed by a vacuum film forming method as will be described later.

  The thickness of the metal reflective layer (D) is preferably 30 to 200 nm from the viewpoint of reflectance. When the thickness of the metal reflective layer (D) is 30 nm or more, it is possible to suppress a decrease in reflectance due to an increase in the ratio of transmitted light. When the thickness of the metal reflective layer (D) is 200 nm or less, an increase in production cost can be suppressed. The thickness of the metal reflective layer (D) is more preferably 30 to 150 nm, and further preferably 80 to 150 nm.

  The surface reflectance of the metal reflective layer (D) is preferably 80% or more, and more preferably 90% or more. The surface reflectance of the metal reflective layer (D) can be measured with a spectrophotometer U-4100 manufactured by Hitachi High-Technologies Corporation.

1-4. Protective layer (E)
The protective layer (E) has a function of suppressing corrosion by suppressing the transmission of moisture and oxygen from the outside to the back surface (the surface opposite to the light incident surface) of the metal reflective layer (D). The protective layer (E) contains a resin and a sulfur-containing compound.

  As the resin contained in the protective layer (E), the same resin as that contained in the low refractive index layer (C) can be used. Of these, the acrylic resins described above are preferred.

  It is preferable that content of resin is 60 mass% or more with respect to the whole protective layer (E). When the resin content is 60% by mass or more, the wet heat durability of the metal reflective layer (D) can be sufficiently enhanced. The content of the resin is preferably 70% by mass or more, and more preferably 80% by mass or more with respect to the entire protective layer (E).

  As the sulfur-containing compound contained in the protective layer (E), the same sulfur-containing compound contained in the low refractive index layer (C) can be used. Especially, the compound which has a thiol group in a molecule | numerator from the point which can suppress corrosion of a metal reflective layer (D) favorably, a trimethylol propane tris thioglycolate (TMTG), a trimethylol propane tris thiopropionate (TMTP) is preferable. And thiol group-containing carboxylic acid derivatives such as pentaerythritol tetrakisthiopropionate (PETG).

  It is preferable that content of a sulfur containing compound is 0.5-20 mass% with respect to the sum total of resin contained in a protective layer (E). When the content of the sulfur-containing compound is 0.5% by mass or more, the wet heat durability of the metal reflective layer (D) can be sufficiently enhanced. When the content of the sulfur-containing compound is 20% by mass or less, it is possible to suppress the occurrence of poor curing or cracking of the protective layer (E). As for content of a sulfur containing compound, it is more preferable that it is 1-10 mass% with respect to the sum total of resin contained in a protective layer (E).

  The protective layer (E) may further contain other components as necessary. Examples of other components include black pigments and fine particles (matting agents).

  In the black pigment, the light transmitted through the pinhole of the metal reflective layer (D) leaks from the back surface of the metal reflective layer (D) (when the product is made into a product, the light transmitted through the pinhole of the metal reflective layer (D) It can have a function of suppressing (leakage into the housing). Examples of such black pigments include carbon black. Content of a black pigment should just be a grade which can absorb the light which leaks from the back surface of a metal reflective layer (D), for example, can be 0.5-10 mass% with respect to the whole protective layer (E).

  The fine particles can function as a matting agent that imparts blocking resistance to the light reflecting film. Such fine particles may be inorganic fine particles or resin fine particles. Examples of inorganic fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Of fine particles. Examples of the resin fine particles include fine particles of silicone resin, fluororesin, and acrylic resin. Among these, fine particles of silicon dioxide are preferable. Examples of the fine particles of silicon dioxide include Aerosil 200V and Aerosil R972V.

  The primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm. The fine particles may be contained as secondary aggregates having a particle size of 0.05 to 0.3 μm. Content of microparticles | fine-particles can be about 0.01-1 mass% with respect to the whole protective layer (E).

  The thickness of the protective layer (E) may be a thickness that can sufficiently suppress the permeation of moisture to the metal reflective layer (D), and is preferably 30 to 300 nm, for example. When the thickness of the protective layer (E) is 30 nm or more, moisture permeation to the back surface of the metal reflective layer (D) can be sufficiently suppressed. If the thickness of the protective layer (E) is 300 nm or less, the force of the protective layer (E) to be thermally deformed can be reduced, so the difference in the amount of thermal deformation between the protective layer (E) and the metal reflective layer (D) The resulting metal reflective layer (D) can be prevented from cracking and peeling. The thickness of the protective layer (E) is more preferably 50 to 200 nm.

1-5. Other Layers The light reflecting film of the present invention may further include other layers as long as the effects of the present invention are not impaired. For example, you may further arrange | position another base material layer (F) in the surface on the opposite side to the surface where the metal reflective layer (D) of the protective layer (E) is arrange | positioned. The other base material layer (F) may be transparent or non-transparent, and in the example, the same resin as the above-mentioned transparent base material layer (A) can be used.

1-6. Laminated structure Each of the high refractive index layer (B) and the low refractive index layer (C) contained in the light reflecting film of the present invention may be one or plural. The plurality of high refractive index layers (B) may be the same as or different from each other. The plurality of low refractive index layers (C) may be the same as or different from each other. From the metal reflective layer (D) side, the low refractive index layer (C) and the high refractive index layer (B) may be laminated in total in this order by 2 m layers (m is an integer of 1 or more).

Examples of the laminated structure of the light reflecting film of the present invention include the following aspects. In the following embodiments, A is a transparent substrate layer (A), B is a high refractive index layer (B), C is a low refractive index layer (C), and D is a metal reflective layer (D). Yes, E is a protective layer (E). In the following embodiments, the right side corresponds to the light incident side.
E / D / C / B / A
E / D / C / B / C / B / A
E / D / C / B / C / B / C / B / A

  The repetition number m of “C / B” is, for example, 1 to 10, preferably 1 to 5, more preferably 1 or 2, although it depends on the required reflectance. The low refractive index layer (C) and the high refractive index layer (B) are preferably in contact with each other in terms of sufficiently functioning as a reflection increasing film.

  FIG. 1 is a schematic view showing an example of the light reflecting film of the present invention. The light reflecting film 10 includes a transparent base layer (A) 11, a high refractive index layer (B) 13, a low refractive index layer (C) 15, a metal reflective layer (D) 17, and a protective layer (E) 19. In order. The light incident surface of the light reflecting film 10 is the surface of the transparent base material layer (A) 11.

1-7. Physical properties (average reflectance)
The average reflectance of the light reflecting film of the present invention at a wavelength of 430 nm to 470 nm may be 94% or more, for example. Moreover, it is preferable that average reflectance R1 of wavelength 430nm -470nm of the light reflection film of this invention is higher than average reflectance R2 of wavelength 560nm -600nm. The light reflecting film having such an average reflectance is suitable as a light reflecting film of a backlight unit for a liquid crystal display device, for example.

  The average reflectance of the light reflection film can be measured using a spectrophotometer U-4100 (solid sample measurement system) manufactured by Hitachi High-Technologies Corporation under the condition of an incident angle of 5 °.

  The thickness of the light reflecting film of the present invention can be, for example, 10 to 500 μm, preferably 10 to 300 μm, and more preferably 20 to 150 μm.

2. Method for Producing Light Reflecting Film The light reflecting film of the present invention can be produced by any method. For example, a high refractive index layer (B) and a low refractive index layer (C) on the transparent substrate layer (A). The metal reflective layer (D) and the protective layer (E) can be sequentially laminated.

  The high refractive index layer (B) can be formed by a vacuum film forming method. The vacuum film forming method includes a resistance heating vacuum deposition method, an electron beam heating vacuum deposition method, an ion plating method, an ion beam assisted vacuum deposition method, and a sputtering method. Among these, the vacuum deposition method is more preferable because the film can be formed by roll-to-roll, which is a continuous film forming method.

  The low refractive index layer (C) can be formed by a coating method. Specifically, the low refractive index layer (C) can be formed by applying a resin composition for the low refractive index layer (C) on the high refractive index layer (B) and then drying or curing.

  The resin composition for a low refractive index layer (C) contains the aforementioned resin and a solvent. Any solvent may be used as long as it can disperse the above-mentioned resin satisfactorily. Examples of aprotic solvents include hydrocarbon solvents such as pentane, hexane, cyclohexane and toluene; halogen hydrocarbon solvents such as methylene chloride and trichloroethane; esters such as ethyl acetate and butyl acetate; ketones such as acetone and methyl ethyl ketone And ethers such as dibutyl ether, dioxane, and tetrahydrofuran are included.

  The resin composition for a low refractive index layer (C) may further contain the above-described sulfur-containing compound and curing agent as necessary. Examples of the curing agent include polyisocyanate, melamine compound, epoxy compound and the like. Content of a hardening | curing agent can be about 0.1-15 mass% with respect to the above-mentioned resin.

  The application of the resin composition can be performed by, for example, a gravure coating method, a spin coating method, a bar coating method, or the like. Curing of the coating film of the resin composition may be photocuring or thermosetting, preferably thermosetting.

  The metal reflective layer (D) can be formed by a vacuum film forming method. The vacuum film forming method is preferably a vacuum vapor deposition method as described above.

  The protective layer (E) can be formed by a coating method as described above. Specifically, after the resin composition for the protective layer (E) is applied on the metal reflective layer (D), the protective layer (E) is formed by drying or curing. The resin composition for protective layer (E) contains the above-mentioned resin, a sulfur-containing compound, and a solvent, and may further contain a curing agent as necessary. As the solvent and the curing agent, the same ones as described above can be used.

3. Use of Light Reflecting Film The light reflecting film of the present invention can be used as a reflecting member for various uses, for example, a light reflecting film of a backlight unit for a liquid crystal display device, a reflecting mirror of a projection television, a lamp reflector and the like. Especially, the light reflection film of this invention is preferably used as a light reflection film of the backlight unit for liquid crystal display devices from the point which has a favorable reflectance and wet heat durability.

(Backlight unit for liquid crystal display)
The backlight unit for liquid crystal display devices includes a light source and the light reflecting film of the present invention. The light reflecting film of the present invention is disposed so that the transparent base material layer (A) faces the back surface of the light source or the light guide plate (the surface not facing the liquid crystal display panel).

  Examples of the light source include a cold cathode tube (CCFL), a hot cathode tube (HCFL), an external electrode fluorescent tube (EEFL), a flat fluorescent tube (FFL), a light emitting diode element (LED), and an organic electroluminescence element (OLED). Etc. are included. Among these, a cold cathode tube (CCFL) and a light emitting diode element (LED) are preferable.

  The backlight unit for a liquid crystal display device may further include another optical film. Examples of other optical films include light diffusion films and prism films. Examples of the light diffusion film include a diffusion film coated with a filler or a bead-containing binder.

  The backlight unit for a liquid crystal display device may be a direct type backlight unit or a side edge type backlight unit. A side-edge type backlight unit is preferable because it is suitable for a medium / small-sized liquid crystal display device.

  The side-edge type backlight unit includes a light source, a light guide plate disposed adjacent to the light source, and a light reflection film disposed on the back side of the light guide plate, and further includes other optical films as necessary. But you can. An example of the aspect of the side edge type backlight unit includes a backlight unit 40 shown in FIG. 2 described later.

(Liquid crystal display device)
The liquid crystal display device of the present invention includes a liquid crystal display panel and a backlight unit. FIG. 2 is a cross-sectional view showing an example of the liquid crystal display device of the present invention. The figure shows an example in which a side edge type backlight unit is used. As shown in FIG. 2, the liquid crystal display device 20 includes a liquid crystal display panel 30 and a side edge type backlight unit 40.

  The liquid crystal display panel 30 includes a liquid crystal cell 31 and a pair of polarizing plates 33 and 35 sandwiching the liquid crystal cell 31. The display method of the liquid crystal cell 31 is not particularly limited, and may be various display modes such as VA (MVA, PVA) and IPS. Each of the polarizing plates 33 and 35 includes a polarizer and a protective film disposed on at least one surface thereof.

  The side-edge type backlight unit 40 includes a rod-shaped light source 41, a light guide plate 43 disposed so that the side end portion is adjacent to the light source 41, and the light reflecting film 10 disposed on the back side of the light guide plate 43. And a plurality of optical films 45 disposed on the surface side of the light guide plate 43. The light reflecting film 10 is disposed so that the transparent base material layer (A) 11 faces the light guide plate 43.

  The light source 41 is covered with a lamp reflector 42. The plurality of optical films 45 are not limited to the embodiment shown in FIG.

  In the side edge type backlight unit 40, the light emitted from the light source 41 propagates through the light guide plate 43. A part of the light emitted from the light guide plate 43 is reflected by the light reflecting film 10 and emitted to the surface side of the light guide plate 43 (the liquid crystal display panel 30 side). The light emitted to the surface side of the light guide plate 43 is diffused by the light diffusion film 47, refracted by the prism film 49, and incident on the entire surface of the liquid crystal display panel 30.

  The light reflection film 10 can maintain a high reflectance even when exposed to a high temperature and high humidity for a certain period of time. Therefore, the liquid crystal display device 20 including such a light reflecting film 10 can maintain high light utilization efficiency for a long time.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Example 1>
(Preparation of resin composition for low refractive index layer (C-1))
Resin for Low Refractive Index Layer (C-1) by adding Dianal BR-608 (acrylic resin, manufactured by Mitsubishi Rayon Co., Ltd.) as resin to methyl ethyl ketone (MEK) so as to be 3% by mass. A composition was prepared.

(Preparation of resin composition for protective layer (E-1))
After dissolving Dainal BR-608 (acrylic resin, manufactured by Mitsubishi Rayon Co., Ltd.) as a resin in methyl ethyl ketone (MEK) so as to be 3% by mass, trimethylolpropane tristhiopropionate as a sulfur-containing compound (TMTP, manufactured by Sakai Chemical Co., Ltd.) was added so as to be 1% by mass with respect to the dialnal solid content, and mixed to prepare a resin composition for the protective layer (E).

(Production of light reflecting film)
As the transparent substrate layer (A), a transparent polyester film (A4100 manufactured by Toyobo Co., Ltd.) having a thickness of 25 μm was prepared. Zinc sulfide (ZnS) was vacuum-deposited on one surface of the transparent polyester film to form a high refractive index layer (B) having a thickness of 50 nm. Next, the above-prepared resin composition for the low refractive index layer (C-1) was applied on the high refractive index layer (B), and then dried at 90 ° C. for 1 minute, and the low refractive index layer (30 nm thick) ( C) was formed. Subsequently, silver (Ag) was vacuum-deposited on the low refractive index layer (C) to form a metal reflective layer (D) having a thickness of 120 nm. And after apply | coating the prepared resin composition for protective layers (E-1) on a metal reflective layer (D), it was made to dry at 90 degreeC for 1 minute, and a 30 nm-thick protective layer (E) was formed. A light reflecting film was obtained.

<Example 2>
(Preparation of resin composition for low refractive index layer (C-2))
Low refraction in the same manner as in Example 1 except that trimethylolpropane tristhiopropionate (TMTP, manufactured by Sakai Chemical Co., Ltd.) was added as a sulfur-containing compound so as to be 1% by mass with respect to the dialnal solid content. A resin composition for the rate layer (C-2) was prepared.

(Production of light reflecting film)
A light reflecting film was obtained in the same manner as in Example 1 except that the low refractive index layer (C) was formed using the resin composition for the low refractive index layer (C-2).

<Example 3>
(Preparation of resin composition for protective layer (E-2))
Silica fine particles (Aerosil R972V, manufactured by Nippon Aerosil Co., Ltd., primary particle size: 16 nm) were further added as a matting agent so as to be 1% by mass with respect to the solid content (total of the dialnal solid content and the sulfur-containing compound). A resin composition for the protective layer (E-2) was prepared in the same manner as Example 2 except for the above.

(Production of light reflecting film)
A light reflecting film was obtained in the same manner as in Example 1 except that the protective layer (E) was formed using the protective layer (E-2) resin composition.

<Example 4>
(Preparation of resin composition for protective layer (E-3))
Carbon black [manufactured by Mitsubishi Chemical Co., Ltd., product number: MA100] (carbon black concentration in nonvolatile content: 40% by mass) as a black pigment was further added so as to be 1% by mass with respect to the dialnal solid content. Prepared a resin composition for the protective layer (E-3) in the same manner as in Example 3.

(Production of light reflecting film)
A light reflecting film was obtained in the same manner as in Example 2 except that the protective layer (E) was formed using the resin composition for the protective layer (E-3).

<Examples 5 to 8>
A light reflecting film was obtained in the same manner as in Examples 1 to 4 except that the material of the high refractive index layer (B) was changed to niobium oxide (Nb ₂ O ₅ ).

<Comparative Example 1>
(Preparation of resin composition for protective layer (R-1))
After dissolving DIANAL BR-608 (acrylic resin, manufactured by Mitsubishi Rayon Co., Ltd.) as a resin in methyl ethyl ketone (MEK) so as to be 3% by mass, Coronate HX as a curing agent was added to resin solids (DIANOAL). The resin composition for the protective layer (R-1) was prepared by adding the mixture so as to be 1% by mass relative to the solid content).

(Production of light reflecting film)
The low refractive index layer is formed by vacuum deposition of silicon oxide (SiO ₂ ), and the protective layer is formed by using the prepared resin composition for protective layer (R-1) as in Example 1. Similarly, a light reflecting film was obtained.

<Comparative example 2>
A light reflecting film was obtained in the same manner as in Example 1 except that the low refractive index layer was formed by vacuum deposition of silicon oxide (SiO ₂ ).

<Comparative Example 3>
Except that the low refractive index layer was formed by vacuum vapor deposition of silicon oxide (SiO ₂ ) and the protective layer was formed using the protective layer (R-1) resin composition prepared in Comparative Example 1. In the same manner as in Example 5, a light reflecting film was obtained.

<Comparative example 4>
A light reflecting film was obtained in the same manner as in Example 5 except that the low refractive index layer was formed by vacuum deposition of silicon oxide (SiO ₂ ).

<Comparative Example 5>
A transparent polyester film (A4100 manufactured by Toyobo Co., Ltd.) having a thickness of 25 μm was prepared as a transparent substrate layer. Titanium oxide (TiO ₂ ) was vacuum deposited on one surface of the transparent polyester film to form a high refractive index layer having a thickness of 55 nm. Subsequently, silicon oxide (SiO ₂ ) was vacuum-deposited on the high refractive index layer to form a low refractive index layer having a thickness of 48 nm. Next, silver (Ag) was vacuum-deposited on the low refractive index layer to form a metal reflective layer having a thickness of 120 nm. And after apply | coating the resin composition for protective layers (E-1) prepared in Example 1 on a metal reflective layer, it was made to dry at 90 degreeC for 1 minute, a 30 nm-thick protective layer was formed, and light reflection A film was obtained.

<Comparative Example 6>
A transparent polyester film (A4100 manufactured by Toyobo Co., Ltd.) having a thickness of 25 μm was prepared as a transparent substrate layer. Zinc sulfide (ZnS) was vacuum-deposited on one surface of the transparent polyester film to form a high refractive index layer having a thickness of 50 nm. Next, after applying the resin composition for the low refractive index layer (C-1) prepared in Example 1 on the high refractive index layer, the low refractive index layer having a thickness of 30 nm was dried at 90 ° C. for 1 minute. Formed. Next, silver (Ag) was vacuum-deposited on the low refractive index layer to form a metal reflective layer having a thickness of 120 nm. And after apply | coating the resin composition for protective layers (R-1) prepared by the comparative example 1 on a metal reflective layer, it was made to dry at 90 degreeC for 1 minute, a 30 nm-thick protective layer was formed, and light reflection A film was obtained.

<Comparative Example 7>
A transparent polyester film (A4100 manufactured by Toyobo Co., Ltd.) having a thickness of 25 μm was prepared as a transparent substrate layer. Silver (Ag) was vacuum-deposited on one surface of the transparent polyester film to form a metal reflective layer having a thickness of 120 nm. And after apply | coating the resin composition for protective layers (R-1) adjusted by the comparative example 1 on a metal reflective layer, it was made to dry at 90 degreeC for 1 minute, a 30-nm-thick protective layer was formed, and light reflection A film was obtained.

  The average transmittance of the transparent substrate layer (A), the transparent substrate layer (A), the refractive index of the high refractive index layer (B) and the low refractive index layer (C) used in each example / comparative example, Each was measured by the following method.

(1) Average transmittance of transparent base material layer (A) The average transmittance at 360 to 400 nm of the transparent base material layer (A) was measured by a spectrophotometer U-4100 manufactured by Hitachi High-Technologies Corporation. Met.

(2) Refractive index of transparent base material layer (A), high refractive index layer (B) and low refractive index layer (C) (refractive index of transparent base material layer (A))
The refractive index of light having a wavelength of 570 nm of a transparent polyester film having a thickness of 25 μm (A4100, manufactured by Toyobo Co., Ltd.) was 1.68 when measured using a spectroscopic ellipsometer UVSEL manufactured by Horiba.

(Refractive index of high refractive index layer (B) and low refractive index layer (C))
A high refractive index layer (B) having a thickness of 100 nm was vacuum-deposited on a polyethylene terephthalate (PET) substrate having a thickness of 100 μm to obtain a sample 1 for refractive index measurement. Similarly, a low refractive index layer (C) having a thickness of 100 nm was applied and formed on a PET substrate having a thickness of 100 μm to obtain a sample 2 for refractive index measurement. The refractive indexes of light having a wavelength of 570 nm of Samples 1 and 2 were measured using a Horiba spectroscopic ellipsometer UVSEL, respectively.

  Moreover, the brightness | luminance characteristic (after initial stage and wet heat endurance) of the backlight unit using the light reflection film obtained by each Example / comparative example was measured with the following method.

<Luminance>
(initial)
The backlight unit was taken out from the liquid crystal display device (trade name: LC-37GX1W, manufactured by Sharp), and the light reflection film of the backlight unit was replaced with the light reflection film produced above. The light reflecting film was disposed so that the transparent substrate layer (A) was a light incident surface. A luminance meter (product name “CS-2000” manufactured by Konica Minolta Co., Ltd.) is located on the side opposite to the surface on which the light reflecting film of the obtained backlight unit is disposed and at a height of 200 mm from the light reflecting film. ) And measure the tristimulus value Y (luminance) [cd / m ² ] at intervals of 0.6 mm from end to end in the shape of crossing the center of the surface light source device in the vertical direction of the light sources arranged in parallel did. These values were measured at 25 ° C. Also, the larger the luminance value, the better.

(After wet heat durability)
The produced light reflecting film was allowed to stand for 500 hours in an environment of 60 ° C. and 90% RH. Thereafter, the obtained light reflecting film was replaced with the light reflecting film provided in the backlight unit. The light reflecting film was disposed so that the transparent substrate layer (A) was a light incident surface. The tristimulus value Y (luminance) [cd / m ² ] of the obtained backlight unit was measured in the same manner as described above. The obtained luminance after wet heat durability was determined as a relative value to the initial luminance.

The evaluation results of the light reflecting films prepared in Examples 1 to 8 are shown in Table 1; the evaluation results of the light reflecting films prepared in Comparative Examples 1 to 7 are shown in Table 2.

  As shown in Tables 1 and 2, the light reflecting films of Examples 1 to 8 have less reduction in luminance after wet heat durability and better wet heat durability than the light reflecting films of Comparative Examples 1 to 7. I understand that.

Specifically, the light reflective film of Comparative Example ₂ in which the low refractive index layer (C) is SiO ₂ is more lightly reflective than the light reflective films of Examples 1 and 2 in which the low refractive index layer (C) is a resin layer. It shows low wet heat durability. Further, the light reflecting film of Comparative Example 6 in which the protective layer (E) does not contain a sulfur-containing compound has lower wet heat durability than the light reflecting film of Example 1 in which the protective layer (E) contains a sulfur-containing compound. Recognize. From these things, the low-refractive-index layer (C) is a resin layer and the protective layer (E) is a resin layer containing a sulfur-containing compound, so that the wet heat durability of the light reflecting film can be significantly increased. It is shown that it can.

  Further, it can be seen that the lower refractive index layer (C) further contains a sulfur-containing compound, so that the decrease in luminance after wet heat durability can be further reduced (contrast between Examples 1 and 2 and contrast between Examples 5 and 6). ).

  Furthermore, the light diffusing film of Example 3 in which the protective layer (E) further contains a matting agent is more rolled up than the light reflecting film of Example 2 in which the protective layer (E) does not contain a matting agent. It was confirmed that sticking (blocking) between films laminated on each other can be reduced.

10 Light reflecting film 11 Transparent base material layer (A)
13 High refractive index layer (B)
15 Low refractive index layer (C)
17 Metal reflective layer (D)
19 Protective layer (E)
DESCRIPTION OF SYMBOLS 20 Liquid crystal display device 30 Liquid crystal display panel 31 Liquid crystal cell 33, 35 Polarizing plate 40 Side edge type backlight unit 41 Light source 42 Lamp reflector 43 Light guide plate 45 Optical film 47 Light diffusion film 49 Prism film

Claims (7)

A transparent substrate layer (A), a high refractive index layer (B) having a refractive index higher than the refractive index of light having a wavelength of 570 nm of the transparent substrate layer (A), and the transparent substrate layer (A). A low refractive index layer (C) having a refractive index lower than that of light having a wavelength of 570 nm, a metal reflective layer (D), and a protective layer (E) in this order;
The low refractive index layer (C) is a resin layer;
The light reflecting film, wherein the protective layer (E) is a resin layer containing a sulfur-containing compound.   The light reflection film according to claim 1, wherein the metal reflection layer (D) is a thin film mainly composed of silver or an alloy thereof.   The light reflection film according to claim 1 or 2, wherein the low refractive index layer (C) further contains a sulfur-containing compound.   The said protective layer (E) is a light reflection film as described in any one of Claims 1-3 which further contains microparticles | fine-particles.   The said protective layer (E) is a light reflection film as described in any one of Claims 1-4 which further contains a black pigment.   The light reflection film according to claim 3, wherein the high refractive index layer (B) is a thin film containing a metal sulfide as a main component.   The backlight unit for liquid crystal display devices containing a light source and the light reflection film as described in any one of Claims 1-6.