WO2016072472A1

WO2016072472A1 - Reflective film

Info

Publication number: WO2016072472A1
Application number: PCT/JP2015/081219
Authority: WO
Inventors: 康平細井; 金井　慎一郎; 博信多田
Original assignee: 三菱樹脂株式会社
Priority date: 2014-11-07
Filing date: 2015-11-05
Publication date: 2016-05-12
Also published as: CN107076889A; KR20170080578A; JPWO2016072472A1; KR102452766B1; TW201622980A; TWI670178B

Abstract

Provided is a reflective film having a white base material layer, a metal thin film layer, and a protective layer, in that order, the white base material layer being arranged on the side of the surface to be used for reflection, wherein the reflective film is characterized in that when the reflective film is illuminated with light from the white base material layer side, Δb, represented in the following, is at least 1.0% but less than 4.0%, and the reflectance improvement (Δa/Δb) represented by the ratio of Δa, represented in the following, and the aforementioned Δb is 1.3-3.0, whereby the light-reflective film is provided with high levels of reflectance and durability suitable for a reflective member of a liquid crystal display, and has good chromaticity and low cost. Δa: difference of reflectance of light of 450 nm wavelength and light of 750 nm wavelength by white base material layer; Δb: difference of reflectance of light of 450 nm wavelength and light of 750 nm wavelength by reflective film

Description

Reflective film

The present invention relates to a reflective film. More specifically, the present invention relates to a reflection film used for a reflection plate of an electronic device display device such as a liquid crystal display.

Conventionally, as a light reflector used in optical members, liquid crystal displays, lighting fixtures, solar cells, etc., diffused light reflection represented by a white film obtained by dispersing inorganic particles or organic particles in a plastic film. A specular reflection type light reflection film typified by a mirror film obtained by forming a film or a metal reflection layer made of a metal thin film such as aluminum or silver is known.

In liquid crystal display applications, there is a wide range from large ones exceeding 50 inches such as liquid crystal televisions to small ones that are 5 inches or less for mobile applications such as mobile phones. Especially in small displays, screen display devices Thinning of the light reflecting film is required to reduce the size and weight of the device itself, and a highly efficient light reflecting film contributing to power saving of the backlight aimed at extending the life of the battery is eagerly desired. .

Furthermore, mobile applications include mobile phones and in-vehicle displays. These are assumed to be used outdoors, and are also affected by radiant heat from the LED light source. Is required to have high durability even in a high temperature environment. That is, in the above light reflecting film, it is necessary to suppress a reduction in reflectance under high temperature conditions.

JP 2014-178697 A JP 04-239540 JP 2005-031653 A JP2012-35616 JP-A-10-128908 JP 2006-126236 A JP-A-10-193494 WO2005-039872

In order to satisfy these demands, for example, in Patent Document 1, two types of transparent polyester layers having different refractive indexes are adjusted in thickness strictly and alternately laminated to form a multi-layer, thereby extending over a wide wavelength range. Thus, it has been proposed to realize efficient light reflection and further impart durability with an additive or the like. However, an advanced super multi-layer thinning technique is required, resulting in an extremely expensive article.

As a film that is cheaper and has a certain high reflectance, a fine powder filler such as titanium oxide is dispersed in a resin matrix such as polycyclic and aliphatic polyesters and polyolefins, and / or To a suitable base material such as a white film (Patent Documents 2 to 4) in which a resin / air / fine powder filler having a different refractive index is formed in a film by stretching, and a plastic or metal plate, A metal thin film specular reflection film (Patent Document 5 or 6) obtained by forming a metal thin film having a high reflectance such as silver or aluminum by vapor deposition or sputtering is generally known. The white film is excellent in durability and mechanical strength, but the reflectance is not sufficient. Especially when the film is thinned, light leakage becomes remarkable and the reflectance is extremely lowered. On the other hand, although the metal thin film mirror surface film can be expected to have high reflection characteristics even if the film is thinned, it is inferior in durability from the viewpoint that the metal surface is easily deteriorated and from the characteristics of the metal that uniformly reflects all wavelengths. There is a relatively yellowish problem.

Furthermore, a reflection film in which this white film and a specular reflection film are appropriately combined has also been proposed (Patent Document 7 or 8). However, in any of the proposed articles, the reflectance is far from realizing high luminance as required in recent years.

Accordingly, an object of the present invention is to provide a reflective film that has high reflectivity, high brightness, and high durability, and that has a good chromaticity of reflected light (which can suppress the yellowness of the reflected light). There is to provide to.

In order to solve the above-mentioned problems, the present inventors have made a basic study on a silver thin film that is generally expected to have a high reflectivity, and have made extensive studies and have obtained the following knowledge.
(1) For the silver thin film to have a high reflectance, ideally, it is better not to apply a surface coat.
(2) However, the silver thin film gradually undergoes oxidation and sulfidation in the air, causing a significant decrease in reflectance. Therefore, it is necessary to provide a protective layer on the surface of the silver thin film.
(3) On the other hand, when a protective layer is provided on the surface of the silver thin film, the brightness of reflected light is reduced.
(4) Furthermore, even if a protective layer is provided on the surface of the silver thin film, yellowing of chromaticity cannot be sufficiently suppressed.

Based on the above findings, the inventors have studied more vigorously, and as described above, after appropriately combining a highly durable white substrate, a metal thin film layer, and a protective layer, the white substrate side It was found that all the above problems can be overcome by making the reflection surface side and the difference (Δb) in reflectance between two types of light of a predetermined wavelength within a certain range.

That is, the present invention is a reflective film having a white base material layer, a metal thin film layer, and a protective layer in this order, and the white base material layer is disposed on the reflective use surface side. On the other hand, when light is irradiated from the white base material layer side, Δb represented below is 1.0% or more and less than 4.0%, and Δa represented by the following and Δb It is a reflective film characterized by having a reflectance improvement degree (Δa / Δb) represented by a ratio of 1.3 or more and 3.0 or less.
Δa: difference between the reflectance of light with a wavelength of 450 nm and the reflectance of light with a wavelength of 750 nm of the white base layer Δb: difference between the reflectance of light with a wavelength of 450 nm and the reflectance of light with a wavelength of 750 nm of the reflective film

According to the present invention, it is possible to provide a light reflecting film having high reflectivity, high luminance and high durability suitable as a reflecting member of a liquid crystal display, and having good chromaticity at low cost.

It is explanatory drawing which shows the layer structure of the reflective film of this invention. FIG. 1A shows a laminated body in which a white base material layer 1, a metal thin film layer 3, and a protective layer 4 are formed in this order. FIG. 1B shows a laminate formed in the order of the white base material layer 1, the intermediate layer 2, the metal thin film layer 3, and the protective layer 4. It is explanatory drawing showing the relationship between the reflectance in 550 nm, and a brightness | luminance. It is explanatory drawing showing the relationship between the difference ((DELTA) b) of the reflectance of 450 nm and 750 nm, and y value.

Hereinafter, a reflective film as an example of an embodiment of the present invention will be described. However, the present invention is not limited to this reflective film.

In addition, as a form which a reflective film can take, it is preferable that it is a film form or a sheet form. In general, "film" refers to a thin flat product that is extremely small compared to its length and width and whose maximum thickness is arbitrarily limited, and is usually supplied in the form of a roll (Japan) Industrial standard JISK6900), and in general, “sheet” refers to a product that is thin by definition in JIS and generally has a thickness that is small instead of length and width. However, since the boundary between the sheet and the film is not clear and it is not necessary to distinguish the two in terms of the present invention, in the present invention, even when the term “film” is used, the term “sheet” is included and the term “sheet” is used. In some cases, “film” is included.

1. Reflective Film As shown in FIG. 1A, the reflective film of the present invention (hereinafter sometimes referred to as the present reflective film) comprises a white base material layer 1, a metal thin film layer 3, and a protective layer 4. In this order, the white base material layer 1 is a reflective film disposed on the reflective use surface side, and when the light is irradiated from the white base material layer 1 side to the reflective film, it is expressed below. Δb is 1.0% or more and less than 4.0%, and the reflectance improvement degree (Δa / Δb) represented by the ratio of Δa and Δb expressed below is 1.3 or more, It is 3.0 or less.
Δa: difference between the reflectance of light with a wavelength of 450 nm and the reflectance of light with a wavelength of 750 nm of the white base layer Δb: difference between the reflectance of light with a wavelength of 450 nm and the reflectance of light with a wavelength of 750 nm of the reflective film

1.1. White base material layer The white base material layer is characterized by containing a thermoplastic resin and a filler. The thermoplastic resin and the filler are not particularly limited. The white base material layer preferably has a reflectance of 95% or more with respect to light having a wavelength of 550 nm. More preferably, it is 96% or more, More preferably, it is 97% or more. When the reflectance at 550 nm is smaller than 95%, the reflectance of the reflective film having a laminated structure does not become a sufficiently high value, and the luminance may be lowered accordingly.

The thermoplastic resin constituting the white base layer is not particularly limited as long as it can maintain reflectivity and excellent durability. Polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acrylic resins, polyimide resins Various thermoplastic resins such as fluorine resins, olefin resins such as polyethylene and polypropylene, and cycloolefin resins can be used. The thermoplastic resins may be used alone or in combination of two or more.

Among the above, for example, when importance is attached to reflection characteristics, production cost, hydrolysis resistance, etc., it is preferable to select a film made of polyolefin. Examples of the polyolefin resin layer include polypropylene resins such as polypropylene and propylene-ethylene copolymers, polyethylene resins such as polyethylene, high density polyethylene and low density polyethylene, and cycloolefin resins such as ethylene-cyclic olefin copolymers. And at least one polyolefin resin selected from olefin-based elastomers such as ethylene-propylene rubber (EPR) and ethylene-propylene-diene terpolymer (EPDM). Among these, polypropylene resin (PP), polyethylene resin (PE), and cycloolefin resin are preferable from the viewpoint of mechanical properties, flexibility, etc. Among them, particularly excellent in heat resistance and mechanical properties such as elastic modulus. From the viewpoint of high, polypropylene resin (PP) and cycloolefin resin (COC, COP) are preferable.
On the other hand, when importance is attached to the rigidity and heat resistance of the film, it is preferable to select a film made of polyester. Among them, aromatic polyester is preferably selected when importance is attached to heat resistance and hydrolysis resistance, and selected from polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, and the like. And at least one kind of polyester resin.

Examples of the filler include inorganic fine powder and organic fine powder. Examples of the inorganic fine powder include calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, zinc oxide, magnesium oxide, calcium oxide, titanium oxide, zinc oxide, alumina, aluminum hydroxide, hydroxyapatite, silica , Mica, talc, kaolin, clay, glass powder, asbestos powder, zeolite, silicate clay and the like. Any of these may be used alone or in admixture of two or more. Among these, considering the difference in refractive index with the thermoplastic resin constituting the reflective sheet, those having a large refractive index are preferred, and the refractive index is 1.6 or more, calcium carbonate, barium sulfate, titanium oxide or oxidized It is particularly preferable to use zinc.

The white base material layer may be increased in thickness in consideration of only the reflectance with respect to the above-described light having a wavelength of 550 nm and the brightness of the reflected light. However, in order to meet the recent demand for thinning, it is necessary to make the white base material layer as thin as possible. In addition, in the present invention, as described later, the above-described Δb needs to satisfy a predetermined value as the whole reflective film. In consideration of the above, the thickness of the white base material layer is preferably 40 μm or more and 200 μm or less. The lower limit is more preferably 50 μm or more, further preferably 60 μm or more, particularly preferably 70 μm or more, and the upper limit is more preferably 160 μm or less, still more preferably 140 μm or less, and particularly preferably 120 μm or less. Especially, when the thickness of a white base material layer is 60 micrometers or more, it can be set as the reflective film provided with still higher reflectance. On the other hand, when the thickness of the white base material layer is 140 μm or less, Δa / Δb has a better value, and a reflective film having excellent performance despite being thin can be obtained.

The white base material layer may have voids inside. In the case of having voids, the proportion of voids (void ratio) in the white base material layer is preferably 5% or more, more preferably 10% or more, and particularly preferably 20% or more. . When the porosity is 5% or more, the area of the interface where the filler having a relatively high refractive index in the resin and the air layer having a low refractive index are in direct contact with each other is improved, thereby further improving the reflectance of the white base material layer. Can be improved. On the other hand, from the viewpoint of mechanical strength and durability of the white base material layer, the porosity is preferably 50% or less. A method for forming voids in the white base material layer is known. For example, if a filler is added to the thermoplastic resin constituting the white base material layer to form a base material layer (base material film), the base material layer (base material film) is stretched in at least one axial direction. Good. In order to set the void ratio inside the white base material layer to a desired range, it is preferably stretched 5 times or more in area magnification, and more preferably 7 times or more. Moreover, it is preferable to extend in the biaxial direction.

The reflective film of the present invention has a high brightness even when the thickness of the entire reflective film is thin by providing a white base layer and a metal thin film layer on the side opposite to the reflective surface of the white base layer. Can be obtained. From this point of view, when the thickness ratio of the white base material layer is 70% or more with respect to the total thickness of the present reflective film, sufficient brightness and reflectance can be obtained due to a synergistic effect with the metal thin film layer. From such a viewpoint, the thickness ratio of the white base material layer is more preferably 80% or more, further preferably 90% or more, and more preferably 92.4% or more with respect to the total thickness of the reflective film. Particularly preferred is 93.5% or more. The upper limit is preferably 99.5% or less, more preferably 99% or less, still more preferably 98% or less, particularly preferably 97.4% or less, and most preferably 97.2% or less.

Further, the reflective film of the present invention has a white base material layer and a metal thin film layer provided on the side of the white base material layer opposite to the reflective use surface, thereby transmitting light at 550 nm of the white base material layer. Even when the rate is somewhat high, high luminance can be obtained. If the transmittance of light at 550 nm of the white base material layer is 1.0% or more, sufficient luminance and reflectance can be obtained by a synergistic effect with the metal thin film layer. From such a viewpoint, the transmittance of light at 550 nm of the white base material layer is more preferably 1.0% or more, and further preferably 1.1% or more. The upper limit is preferably 4.0% or less, more preferably 3.8% or less, still more preferably 3.5% or less, and particularly preferably 3.1% or less.

1.2. Metal thin film layer The reflective film of this invention has a metal thin film layer in the back surface side of a white base material layer, ie, the surface on the opposite side to the reflective use surface of a white base material layer. The metal thin film layer can be formed by vapor-depositing a metal, and can be formed by, for example, a vacuum vapor deposition method, an ionization vapor deposition method, a sputtering method, an ion plating method, or the like. The vapor-deposited metal material can be used without particular limitation as long as it has a high reflectivity, but generally silver, aluminum and the like are preferable, and among these, silver is particularly preferable. Alternatively, it is also preferable to use a silver alloy from the viewpoint of corrosion resistance. For example, silver and Cu, Au, Ni, Pd, Pt, Ru, Rh, In, Al, Si, Mn, Zr, Sn, Bi, Ge, Ti, Cr, Mo, V, Nb, Ta, Hf, W, An alloy with one or more kinds selected from the group of Co and Ge can be given. In addition, the metal thin film layer may be a metal single layer product or a laminate product, or a metal oxide single layer product or a laminate product, in which two or more layers of a metal single layer product and a metal oxide single product are laminated. It may be the body. The thickness of the metal thin film layer varies depending on the material forming the layer, the layer forming method, and the like, but is preferably in the range of 10 nm to 300 nm, more preferably in the range of 20 nm to 200 nm, and 40 nm to 150 nm. Is more preferable, and it is particularly preferable to be in the range of 60 nm to 120 nm. If the thickness of the metal thin film layer is 10 nm or more, sufficient reflectance can be obtained. On the other hand, when the thickness of the metal thin film layer exceeds 300 nm, the reflectance is not further improved, and the production efficiency is lowered.

In the present invention, in order to achieve Δb described later, it is also preferable to adjust the ratio of the thickness of the metal thin film layer to the thickness of the white substrate layer. In the reflective film of the present invention, when the thickness of the metal thin film layer is X (μm) and the thickness of the white base material layer is Y (μm), the thickness ratio (X / Y) is 5.0 × 10 ⁻⁵ or more. It is preferably 7.5 × 10 ⁻³ or less. The lower limit is more preferably 1.0 × 10 ⁻⁴ or more, further preferably 5.0 × 10 ⁻⁴ or more, particularly preferably 8.6 × 10 ⁻⁴ or more, and the upper limit is more preferably 5.0 × 10 4. ⁻³ or less, more preferably 3.0 × 10 ⁻³ or less, and particularly preferably 2.0 × 10 ⁻³ or less.

1.3. Intermediate Layer In the present invention, the metal thin film layer described above is provided on the back side of the white base material layer. Various methods are mentioned as a method of providing the metal thin film layer on the back surface side of the white base material layer. In particular, as shown in FIG. 1B, the metal thin film layer 3 is preferably provided on the back side of the white base material layer 1 with the intermediate layer 2 interposed therebetween.

1.3.1. Smooth coat layer For example, after a smooth coat layer is provided on the surface of the white base layer, a metal thin film layer is formed on the back side of the white base layer by depositing metal on the surface of the smooth coat layer by sputtering or the like. Can be provided. That is, the white base material layer of the present invention may have a smooth coat layer on the surface on which the metal thin film layer is provided. At this time, the smooth coat layer plays a role of reducing the surface roughness on the side where the metal thin film layer is provided, and further providing an effect of improving the reflectance. From such a viewpoint, the surface roughness (Ra) on the side on which the metal thin film layer is provided when the smooth coating layer is provided on the white base material layer is preferably 1.0 μm or less, and is 0.7 μm or less. Is more preferably 0.4 μm or less.

The smooth coat layer can be a layer mainly composed of various curable resins or a layer mainly composed of an inorganic oxide (such as glass or ceramic). Or it is good also as a layer which consists of a silicon wafer. In particular, various smooth coat layers are provided from the viewpoint that they are easily provided on the surface of the white base material layer and give a certain degree of flexibility to improve the adhesion to the metal thin film layer, and are excellent in handleability. A layer mainly composed of a curable resin is preferable, and a layer mainly composed of at least one of acrylic resin, polyester resin, melamine resin, and urethane resin is particularly preferable. In order not to impair the reflectance and brightness of the present reflective film, the smooth coat layer preferably has a total light transmittance of 80% or more, more preferably 90% or more.
“Mainly” means that 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more of the constituent components of the layer. The smooth coat layer may contain various known additives as long as the effects of the present invention are not impaired in addition to the various cured resins and metal oxides described above.

The thickness of the smooth coat layer is preferably 0.5 μm or more and 10 μm or less. The lower limit of the thickness of the smooth coat layer is more preferably 1 μm or more, and particularly preferably 2 μm or more. When the thickness of the smooth coat layer is too small, the surface of the white base material layer may not be sufficiently smoothed. When the thickness of the smooth coat layer is too large, smoothness may be deteriorated due to coating unevenness and formation unevenness.

1.3.2. Adhesive layer or pressure-sensitive adhesive layer Or a metal thin film layer may be provided on the back side of a white base material layer by laminating a film formed with a metal thin film layer and a white base material layer via an adhesive layer or an adhesive layer. it can.

When laminating a white base material layer and a metal thin film layer via an adhesive layer or an adhesive layer, it is preferable to provide an adhesive layer or an adhesive layer having a total light transmittance of 80% or more. When the total light transmittance of the adhesive layer or the pressure-sensitive adhesive layer is 80% or more, the reflectance and luminance of the reflective film are not impaired. From this viewpoint, the total light transmittance is more preferably 85% or more, and further preferably 90% or more.

The adhesive layer or the adhesive layer in the present invention is a layer provided to ensure adhesion between the white base material layer and the metal thin film layer, and includes any meaning as long as this is satisfied. To do. Examples of the adhesive layer or the adhesive layer include a urethane-based, acrylic-based, rubber-based, silicone-based, polyester-based, polyamide-based, epoxy-based, polyvinyl acetate-based, vinyl alkyl ether-based, and fluorine-based adhesive layer or adhesive layer. Can be mentioned. Especially, what satisfy | fills said desired total light transmittance is preferable, and the adhesion layer containing an acrylic ester adhesive is more preferable.

1.3.3. Air Layer In the present invention, the method of providing the metal thin film layer on the back surface side of the white base material layer is not limited to the form in which the smooth coat layer is provided or the form in which the adhesive layer or the adhesive layer is provided. For example, in the present invention, an air layer may be provided between the white base material layer and the metal thin film layer. The thickness of the air layer is preferably 0.1 μm or more and 100 μm or less, more preferably 0.2 μm or more and 50 μm or less, and particularly preferably 0.5 μm or more and 10 μm or less. The air layer is provided by simply overlapping the metal thin film layer and the white base material layer, or the metal vapor deposition layer and the white base material layer are in the range of 0.1% to 50% of the actual use area of the reflective film. It can be provided by bonding inside. The range is more preferably from 0.1% to 30%, further preferably from 0.1% to 10%. The presence of an air layer between the white base material layer and the metal thin film layer can further improve the luminance and reflectance.

In the present invention, as long as the desired reflectance and Δb are satisfied, a metal thin film layer may be provided directly on the surface of the white base material layer without using the intermediate layer as described above. However, when the intermediate layer as described above is provided, the desired reflectance and Δb can be more easily satisfied.

1.4. Protective layer In order to protect a metal thin film layer, the reflective film of this invention has a protective layer on the back surface side of a metal thin film layer, ie, the opposite side to the reflective use surface of a film. The material forming the protective layer can be used without particular limitation as long as it can prevent corrosion of the metal thin film layer and has good adhesion to the metal thin film layer. A paint made of any one of a plastic resin, a thermosetting resin, an electron beam curable resin, an ultraviolet curable resin, and the like can be used. Specifically, amino resins, amino alkyd resins, acrylic resins, styrene resins, acrylic-styrene copolymers, urea-melamine resins, epoxy resins, fluorine resins, polycarbonates, nitrocellulose, cellulose acetate In addition, resin coatings composed of alkyd resins, rosin-modified maleic acid resins, polyamide resins, or the like, or a mixture thereof can be used. Such a paint can be formed by dispersing the resin in a solvent such as water or a solvent. Moreover, a plasticizer, a stabilizer, and an ultraviolet absorber can be added as necessary. In addition, as a solvent, the thing similar to the solvent normally used for a coating material can be used.

The protective layer is obtained by appropriately diluting the above-mentioned paint with a solvent or the like as necessary, for example, by applying a general coating method such as a gravure coating method, a roll coating method, a dip coating method on the entire surface of the metal thin film layer, and drying. It is formed by curing (in the case of a curable resin).

A protective layer can also be formed other than paint coating. Examples of the protective layer forming means for that purpose include film bonding, vapor deposition of other materials, and sputtering. As described above, when the white thin film layer is laminated after forming the metal thin film layer on the surface of the film, the film itself serves as a protective layer.

The thickness of the protective layer is not particularly limited, but is preferably in the range of 0.1 μm to 200 μm. When the thickness of the protective layer is 0.1 μm or more, the surface of the metal thin film layer can be uniformly coated, and the effect of forming the protective layer is sufficiently exhibited. When the film itself serves as a protective layer, the overall thickness of the reflective film can be adjusted according to the application and purpose by adjusting the thickness of the protective layer within such a range.

The protective layer can be colored by adding inorganic or organic fine particles. By coloring the protective layer, slight light leakage from the metal thin film layer can be prevented. Further, it is possible to prevent a mistake that the metal thin film layer is mistakenly used as a reflection use surface, and to suppress glare of the metal thin film layer. Furthermore, this protective layer can be used as a printing layer. From this point of view, the protective layer resin material includes, for example, barium sulfate, barium carbonate, calcium carbonate, gypsum, titanium oxide, silicon oxide, alumina, silica, talc, calcium silicate, magnesium carbonate, carbon black, graphite, copper oxide, and carbon dioxide. Inorganic pigments such as manganese, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, complex oxide black pigment, acrylic, polystyrene Organic resin particles such as polyurethane, amide, polycarbonate, silicone, urea-formalin and melamine, metal powders such as aluminum powder, brass powder and copper powder, ink compositions such as pigments and dyes, etc. Use premixed and dispersed materials. Can. The amount of the inorganic or organic fine particles added is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, based on the solid content of the protective layer.

In the present invention, it is preferred that the back side of the protective layer, that is, the side opposite to the reflective use surface of the film is constituted by a hard coat layer. The hard coat layer can more appropriately prevent peeling of the metal thin film layer, physical damage to the film, and corrosion of the metal thin film layer. Specific examples of the hard coat layer are preferably acrylic resins, urethane resins, melamine resins, epoxy resins, organic silicate compounds, silicone resins, and the like. What is necessary is just to determine the thickness of a hard-coat layer suitably in consideration of the thickness of the whole protective layer.

1.5. Layer structure Examples of the layer structure of the reflective film of the present invention include white base layer / smooth coat layer / metal thin film layer / protective layer, white base layer / adhesive layer or adhesive layer / metal thin film layer / protective layer, white group Examples thereof include a material layer / air layer / metal thin film layer / protective layer, or a white base layer / smooth coat layer / air layer / metal thin film layer / protective layer. However, the white base material layer is disposed on the side irradiated with light. Further, the reflective film of the present invention may further have other layers between these layers, and the white base material layer, the metal thin film layer, the protective layer, and the like are each independently composed of a plurality of layers. May be.

The thickness of the reflective film of the present invention is preferably at least 45 μm, more preferably 50 μm or more, and even more preferably 60 μm or more in order to obtain a desired reflectance. On the other hand, in order to meet the recent demand for thinning, a thinner one is preferable, and the upper limit is preferably 250 μm or less, more preferably 200 μm or less, and further preferably 150 μm or less.

In the present invention, an antioxidant, a light stabilizer, a heat stabilizer, a hydrolysis inhibitor, a lubricant, a dispersant, an ultraviolet absorber, and a white pigment are optionally added to each layer as long as the effects of the present invention are not impaired. , Fluorescent brighteners, and other additives can be blended.

1.6. Characteristics of reflective film 1.6.1. Reflectivity In the reflective film of the present invention, the reflectance of light having a wavelength of 550 nm when irradiated with light from the white base layer side is preferably 98% or more, more preferably 98.5% or more, More preferably, it is 99% or more. As shown in FIG. 2, the reflectance at 550 nm has a correlation with the luminance value of the screen display device when used in a backlight which is a member of a liquid crystal display, for example, and the reflectance at 550 nm is 98% or more. The luminance value of the screen display device is also increased, and sufficient brightness can be imparted to the liquid crystal display. In FIG. 2, the diffuse reflection film and the regular reflection film have different sensitivities in the integrating sphere in the spectroscopic device, and therefore the absolute value of the reflectance between the two cannot be simply compared.

1.6.2. Reflectance difference (Δb)
In the reflective film of the present invention, the difference between the reflectance of light having a wavelength of 450 nm and the reflectance of light having a wavelength of 750 nm is defined as Δb. At this time, Δb needs to be 1.0% or more and less than 4.0%. As shown in FIG. 3, the present inventors have found that the difference (Δb) between the reflectance at 450 nm and the reflectance at 750 nm is correlated with the y value of the chromaticity obtained when the luminance is measured. It was. Here, if the difference between the reflectance at 450 nm and the reflectance at 750 nm is less than 1.0%, the yellowish color becomes too strong from a practical viewpoint. From this viewpoint, the difference in reflectance is more preferably 1.3% or more, and further preferably 1.5% or more. On the other hand, if the upper limit is 4.0% or more, the effect of improving the luminance is hardly recognized. Furthermore, when Δb is 4.0% or more, in the present invention in which the white base material layer and the metal thin film layer are essential, the characteristics of the metal thin film layer are hardly exhibited. That is, there is a possibility that a high reflectance or the like cannot be obtained as a reflective film. From this viewpoint, it is more preferably less than 3.5%, and further preferably less than 3.0%. The y value here is a luminance measurement method to be described later, that is, x and chromaticity coordinates in the CIE color system measured simultaneously with the luminance value when the present reflective film is used for a display backlight. It means y out of y, and in a certain region (x, y: 0.28 to 0.35) of this xy chromaticity coordinate, it means that the larger the value of x and y, the more yellowish it becomes For convenience, the y value is large and small, and it is used for the evaluation of yellowness.

1.6.3. Reflectivity improvement degree (Δa / Δb)
Furthermore, in the reflective film of the present invention, the difference between the reflectance of light having a wavelength of 450 nm and the reflectance of light having a wavelength of 750 nm of the white base material layer is defined as Δa. In the present invention, the degree of improvement in reflectance (Δa / Δb) represented by the ratio of Δa and Δb is 1.3 or more and 3.0 or less. Thus, the synergistic effect of the white base material layer and the metal thin film layer can be maximized.
That is, when the (Δa / Δb) is 1.3 or more, a brightness improvement effect by laminating the white base material layer and the metal thin film layer can be sufficiently obtained. From this viewpoint, it is more preferably 1.5 or more, and further preferably 1.8 or more. On the other hand, when the upper limit is 3.0 or less, yellowness is suppressed, and a reflective film with good chromaticity can be obtained. From this viewpoint, it is more preferably 2.8 or less, and further preferably 2.6 or less.

The transmittance of light having a wavelength of 550 nm of the reflective film is preferably less than 1.0%. By setting the total light transmittance to less than 1.0%, the light of the backlight can be reflected efficiently, the luminance can be improved, and the display contrast can also be improved. From this viewpoint, it is more preferably less than 0.5%, further preferably less than 0.3%, and particularly preferably less than 0.1%.

1.6.4. Durability The durability of the present reflective film is determined by calculating the difference in reflectance with respect to light having a wavelength of 550 nm before and after a high temperature treatment held at 80 ° C. for 240 hours in a constant temperature bath. The difference in reflectance is preferably 0.5% or less, more preferably 0.4% or less, and further preferably 0.3% or less. When the difference in reflectance is 0.5% or less, for example, it can be used without a decrease in luminance even under conditions exposed to use in a backlight of a liquid crystal display.

2. Production Method of Reflective Film Hereinafter, the production method of the present reflective film will be described with an example, but is not limited to the following production method.

First, a filler is blended with the thermoplastic resin constituting the white base material layer, and other additives are blended as necessary to prepare a resin composition. Specifically, a filler or the like is added to a thermoplastic resin and mixed with a ribbon blender, tumbler, Henschel mixer, etc., and then kneaded at a temperature equal to or higher than the melting point of the resin using a single screw or twin screw extruder. Thus, a resin composition for each layer can be obtained. Alternatively, a so-called master batch in which a filler or the like is blended with a thermoplastic resin at a high concentration in advance is prepared, and the master batch and the resin are mixed to obtain a resin composition having a desired concentration.

Next, the resin composition for a substrate thus obtained is melted and formed on a film. In general, an inflation molding method or an extrusion molding method using a T die is preferably used as a method of forming on a film. Specifically, after drying the substrate resin composition as necessary, it is supplied to an extruder and heated to a temperature equal to or higher than the melting point of the resin to melt. Or you may supply a resin composition to an extruder, without drying, but when not drying, it is preferable to use a vacuum vent at the time of melt-extrusion. Thereafter, the melted resin composition for a base layer is extruded from a slit-shaped discharge port of a T die, and is solidified on a cooling roll to form a cast sheet.

The white base material layer is preferably stretched at least in a uniaxial direction, and more preferably stretched in a biaxial direction. Stretching can be performed with a roll, a tenter, air inflation, a tubular, a mandrel, or the like. For example, after stretching in the MD direction by a roll, it may be stretched in the TD direction by a tenter, or biaxially stretched by a tubular. Next, a white reflective film can be obtained by performing heat setting as necessary.

Next, if necessary, a resin coating for a smooth coat layer is applied on the white base layer and dried or cured. A metal thin film layer is formed on the smooth coat layer. Then, a reflective film (white base material layer / smooth coat layer / metal thin film layer / protective layer) is obtained by forming a protective layer on the metal thin film layer.

Alternatively, a metal thin film layer is separately formed on the protective layer. Next, a white base material layer and a metal thin film layer are laminated | stacked through an adhesive agent or an adhesive as needed. Alternatively, the metal thin film layer and the white base material layer are simply overlapped, or the metal vapor deposition layer and the white base material layer are bonded within the range of 0.1% to 10% of the actual use area of the reflective film. By laminating through the air layer.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the examples and comparative examples. In addition, the measured value and evaluation which are shown to an Example were performed as shown below.

(Measurement and evaluation method)
1. Reflectance The reflectance of the reflective film is based on the reflectance (100%) calibrated with a standard component plate made of alumina using a spectrophotometer “UV-4000” (trade name) manufactured by Hitachi High-Technologies Corporation. The measurement was performed in the wavelength range of 300 nm to 800 nm (in units of 0.5 nm) under such conditions.

2. Calculation of reflectivity improvement The reflectivity at 450 nm and 750 nm is read by the above reflectivity measurement, Δa is the difference between the reflectivity at 450 nm and the reflectivity at 750 nm of the white base material alone, and Δb is 450 nm of the present reflective film. The reflectance improvement degree (Δa / Δb) of the reflective film was calculated as the difference between the reflectance at 750 nm and the reflectance at 750 nm.

3. Transmittance “Light transmittance of the white base material layer alone” and “Light transmittance of the reflective film as a whole” were measured. Specifically, a spectrophotometer “UV-4000” (trade name) manufactured by Hitachi High-Technologies Corporation is used, and the transmittance calibrated with an alumina standard component plate is used as a reference (100%), and a film is formed in the optical path. By inserting the sample, the transmittance of the film sample in the wavelength range of 300 nm to 800 nm (0.5 nm unit) was measured.

4). Luminance / y value This reflective film sample was used as a reflective film for the backlight unit of a liquid crystal display (Century Co., Ltd. “Plus One” 8 inch, model number: LCD8000V). The y value was measured with a luminance meter (Konica Minolta, Inc., model: CA-2000).

5. Durability The reflectivity of the film sample was measured, and as a high-temperature test, the reflectivity was measured again after being held in a thermostatic bath at 80 ° C. for 240 hours. The difference in reflectance at 550 nm before and after the high temperature test was calculated and evaluated based on the following evaluation criteria.
◎: Reflectance difference at 550 nm before and after the high temperature treatment is within 0.3% ○: Reflectance difference at 550 nm before and after the high temperature treatment is within 0.5% ×: Difference in reflectance at 550 nm before and after the high temperature treatment Over 0.5%

6). Peel strength of silver layer Cello tape (registered trademark, manufactured by Nichiban Co., Ltd., CT405AP-18) was affixed to the coated surface of the film sample by 10 cm and peeled rapidly in the direction of 180 ° to evaluate how the silver layer peeled off.
(Double-circle): The level which a coating layer does not peel at all.
○: Level at which the coat layer hardly peels off and does not cause any problem in actual use ×: Level at which the coat layer peels off significantly

(Example 1)
(White base material layer)
As the white base material layer, a polyolefin white base material (trade name “Lumirex II R20” manufactured by Mitsubishi Plastics, Inc.) having a thickness of 100 μm was used.

(Formation of metal thin film layer)
An electron beam curable acrylic resin and a diluting solvent MIBK are mixed at a mass ratio of 1: 1 as a smooth coat layer on a primer-treated surface of a polyethylene terephthalate film (trade name “Diafoil T600E25”, manufactured by Mitsubishi Plastics, Inc., thickness 25 μm). Then, a resin solution (ink) having a resin solid content ratio adjusted to 50% by mass was coated with a bar coater, dried and cured, and a smooth coating layer having a thickness of 2 μm was formed. A silver thin film layer having a thickness of 120 nm was formed as a metal thin film layer on the surface of the smooth coat layer by sputtering to obtain a silver thin film.

(Production of reflective film)
An acrylic ester-based pressure-sensitive adhesive is applied to the white base layer and dried to form an adhesive layer (thickness 2 μm). The silver thin film surface of the silver thin film is overlapped with the adhesive layer side, and a hand roller Was used to produce a reflective film having a thickness of 129.12 μm. Each evaluation shown above was performed about the produced reflective film. The results are shown in Table 1.

(Example 2)
An electron beam curable acrylic resin, a photoinitiator, and a diluent solvent MIBK are mixed at a mass ratio of 1: 0.03: 1 with respect to the same white base material layer as in Example 1 to obtain a resin solid content ratio of 50. A resin solution (ink) adjusted to mass% was coated with a bar coater, dried and cured to form a smooth coat layer having a thickness of 2 μm. A silver thin film layer having a thickness of 120 nm is formed as a metal thin film layer on the surface of the smooth coat layer by a sputtering method, and a layer similar to the above smooth coat layer is formed as a protective layer on the surface of the silver thin film layer. A reflective film was prepared. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

(Example 3)
A reflective film was produced in the same manner as in Example 1 except that the white base material layer and the silver thin film were simply overlapped to obtain a reflective film having a thickness of 130.12 μm. Among these, the air layer was 3 μm. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

Example 4
Example 3 except that the white base material layer was changed to a polyolefin white base material having a thickness of 70 μm (trade name “Lumirex II R20” manufactured by Mitsubishi Plastics Co., Ltd.), and a reflective film having a thickness of 100.12 μm was obtained. A reflective film was produced in the same manner as described above. Among these, the air layer was 3 μm. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

(Example 5)
Example 2 except that the white base material layer was changed to a polyolefin white base material having a thickness of 80 μm (trade name “Lumirex II R20” manufactured by Mitsubishi Plastics Co., Ltd.) to obtain a reflective film having a thickness of 111.12 μm. A reflective film was produced in the same manner as described above. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

(Example 6)
In Example 5, each evaluation shown above was performed about the reflective film obtained by processing similarly except not depositing a smooth coat layer but direct silver vapor deposition. The results are shown in Table 1.

(Example 7)
A reflective film was produced in the same manner as in Example 5 except that the metal thin film layer was a silver thin film layer having a thickness of 60 nm. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

(Example 8)
In Example 2, an electron beam curable acrylic resin, titanium oxide, a photoinitiator, and a diluent solvent MIBK were further mixed on the protective layer at a mass ratio of 1: 0.3: 0.02: 3 to obtain a resin solid content. The resin solution (ink) whose ratio was adjusted to 50% by mass was coated with a bar coater, dried and cured to provide a hard coat layer having a thickness of 2.0 μm. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

Example 9
A reflective film was produced in the same manner as in Example 3 except that the white base material layer was a polyester white film (trade name “Lumirror E80E” manufactured by Toray Industries, Inc.). Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

(Example 10)
A reflective film was produced in the same manner as in Example 3 except that the metal thin film layer was an aluminum thin film layer having a thickness of 120 nm. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 1.

(Comparative Example 1)
Each evaluation shown above was performed about the polyolefin-type white base material (Mitsubishi resin Co., Ltd. make, brand name "Lumirex II R20") 100-micrometer-thick. The results are shown in Table 2.

(Comparative Example 2)
Each evaluation shown above was performed about the polyolefin-type white base material (The Mitsubishi Plastics Co., Ltd. make, brand name "Lumirex II R20") 70-micrometer-thick. The results are shown in Table 2.

(Comparative Example 3)
Each evaluation shown above was performed about the polyolefin-type white base material (The Mitsubishi Plastics Co., Ltd. make, brand name "Lumirex II R20") 80-micrometer-thick. The results are shown in Table 2.

(Comparative Example 4)
Each evaluation shown above was performed about the silver thin film single shown in Example 1. FIG. The results are shown in Table 2.

(Comparative Example 5)
A reflective film was produced in the same manner as in Example 2 except that the protective layer was not provided on the silver thin film surface. About the obtained reflective film, each evaluation shown above was performed by making a silver thin film surface into a reflective use surface. The results are shown in Table 2.

(Comparative Example 6)
Example 2 except that the white base material layer was changed to a polyolefin white base material having a thickness of 225 μm (trade name “Lumirex II R20” manufactured by Mitsubishi Plastics Co., Ltd.), and a reflective film having a thickness of 229.12 μm was obtained. A reflective film was produced in the same manner as described above. Each evaluation shown above was performed about the obtained reflective film. The results are shown in Table 2.

(Comparative Example 7)
Each evaluation shown above was performed about the polyolefin-type white base material (Mitsubishi resin Co., Ltd. make, brand name "Lumirex II R20") single thickness of 225 micrometers. The results are shown in Table 2.

(Comparative Example 8)
Each evaluation shown above was performed about the 80-micrometer-thick polyester-type white base material alone in Example 9. The results are shown in Table 2.

(Reference Example 1)
Each of the evaluations described above was performed on an ultra-multilayer reflective film (trade name “ESR-80” manufactured by 3M Co., Ltd.) composed of two types of transparent polyester layers having different refractive indexes. The results are shown in Table 2.

(Simulation test)
As shown in Table 3, the thickness of the white base material layer was changed, and the reflectance at 450 nm, 750 nm, and 550 nm was measured using a ray tracing simulation software (product name: Light Tools). Table 3 shows Δa, Δb, and Δa / Δb values obtained from the reflectance values.

For reference, for Examples 1 to 10, Comparative Examples 1 to 8 and Reference Example 1, FIG. 2 shows the relationship between the reflectance at 550 nm and the luminance, and FIG. 3 shows the relationship between Δb and the y value.

<Discussion>
As is clear from Table 1, the film of each example was good in all of reflectance, luminance, chromaticity (reduction in yellowing), and durability. On the other hand, Comparative Example 1 which is a white base material layer alone and Comparative Example 2 and Comparative Example 3 which are films obtained by thinning the white base layer have low reflectivity, and brightness is accordingly reduced. Moreover, the film of the comparative example 4 which is a silver thin film single was strong yellowish, and its durability was inferior. Furthermore, it was found that in Comparative Example 5 in which a smooth coat layer was provided on the white base material layer, silver was deposited, and the characteristics were evaluated from the surface of the silver thin film layer, the yellowness was extremely strong and the luminance was also lowered.
Further, from Table 3, the values of Δa, Δb, and Δa / Δb of the reflective film of the present invention are suitably changed by appropriately changing the thickness of the white base material layer with respect to the thickness of the specific metal thin film layer. It was found that the reflectance, luminance, and chromaticity (reduction of yellowing) can be improved as a result.

According to the present invention, a reflective film having high reflectivity, high brightness, and high durability, and having reflected light having good chromaticity (which can suppress yellowness of reflected light) is provided at a lower cost. can do. The reflective film according to the present invention can be suitably used as a reflective member of a display device for an electronic device such as a liquid crystal display, for example, as an alternative to a conventional expensive super multilayer reflective film. In this case, good light reflection characteristics can be ensured without redesigning the LED light source and the optical film.

1: White base layer 2: Intermediate layer 3: Metal thin film layer 4: Protective layer

Claims

A reflective film in which a white base material layer, a metal thin film layer, and a protective layer are provided in this order, and the white base material layer is disposed on the reflective use surface side,
In the case where light is irradiated from the white base material layer side to the reflective film,
Δb expressed below is 1.0% or more and less than 4.0%, and the reflectance improvement degree (Δa / Δb) expressed by the ratio of Δa expressed below and Δb is 1 A reflective film characterized in that it is 3 or more and 3.0 or less.
Δa: difference between the reflectance of light with a wavelength of 450 nm and the reflectance of light with a wavelength of 750 nm of the white base layer Δb: difference between the reflectance of light with a wavelength of 450 nm and the reflectance of light with a wavelength of 750 nm of the reflective film
The reflective film according to claim 1, wherein the reflectance of light having a wavelength of 550 nm of the white base material layer is 95% or more.
The reflective film according to claim 1 or 2, wherein the white base material layer has a light transmittance of 1.0% or more at a wavelength of 550 nm.
The reflective film according to any one of claims 1 to 3, wherein a thickness ratio of the white base material layer is 50% or more of a thickness of the reflective film.
The reflective film according to any one of claims 1 to 4, further comprising an adhesive layer or an adhesive layer having a total light transmittance of 80% or more between the white base material layer and the metal thin film layer.
5. The reflective film according to claim 1, further comprising an air layer between the white base material layer and the metal thin film layer.
In the white base material layer, a smooth coat layer is provided on the surface on which the metal thin film layer is provided, and the surface roughness (Ra) on the side of the smooth coat layer on which the metal thin film layer is provided is 300 nm or less. The reflective film according to any one of claims 1 to 6, wherein:
The reflective film according to any one of claims 1 to 7, wherein the protective layer has a thickness of 1 to 200 µm.
An electronic device display device comprising the reflective film according to any one of claims 1 to 8.