JP2007261192A - Light-reflective coated metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-reflective coated metal sheet having a uniform light-reflective performance and a high reflectance in the visible light region of a wavelength of 400 to 700 nm and useful as a reflector of an illuminating unit and a back-light reflector or the like of an LCD television. <P>SOLUTION: The light-reflective coated metal sheet coated with a light-reflective coating having a bilayer structure consisting of two or more layers. The outermost surface layer of the light-reflective coating comprises a first light-reflective layer wherein the content of a white pigment substantially composed of anatase type titanium oxide is 30 to 70 mass%, while the lower layer side of the top-most surface layer is composed of a second light-reflective layer wherein the content of the white pigment substantially composed of rutile type titanium dioxide is 30 to 70 mass%, thereby attaining a uniform light-reflective performance and a high reflectance in the visible light region. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coated metal plate excellent in light reflectivity, and in particular, has a uniform and excellent reflectivity for visible light, and is used as a reflector for lighting fixtures or a backlight reflector for liquid crystal televisions. The present invention relates to a useful light-reflective coated metal plate.

  For reflectors of lighting fixtures and backlight reflectors of liquid crystal televisions, reflectors that exhibit high reflectivity in the entire wavelength region of the visible light region (400 to 700 nm) are required from the viewpoint of reducing power consumption and energy efficiency. When a metal plate is applied to these uses, a light-reflecting paint containing titanium oxide having a low absorption of visible light and a high refractive index is applied to the metal plate as a white pigment.

  By the way, there are two types of titanium oxide, a rutile type and an anatase type. Looking at the reflection characteristics of both, rutile type titanium oxide is highly reflective to light having a wavelength of 500 to 700 nm, but is reflective to light having a wavelength of around 400 nm. On the other hand, anatase-type titanium oxide has high reflectivity with respect to light in the vicinity of a wavelength of 400 nm, but low reflectivity with respect to light with a wavelength of 500 to 700 nm. For this reason, it is the rutile type that shows high reflectivity in a wide wavelength region of visible light, and the anatase type is mostly used for lighting reflectors and liquid crystal reflectors indoors and outdoors. Not. In addition, anatase-type titanium oxide has photocatalytic activity, and when this is used as a white pigment, there is a concern that when an organic resin is used as a vehicle component, its photodegradation is promoted. This is considered to be one of the reasons why type titanium oxide is disliked as a white pigment.

  On the other hand, in order to further improve the energy efficiency for lighting, and to respond to the expansion of color and color tone and the improvement of sharpness that are manifested for liquid crystals, there is a demand for further enhancement of the functionality of the light reflector. Under these circumstances, in order to respond to the recent needs for higher functionality, in addition to the improvement in reflectivity, there is no bias in the reflection characteristics, and the reflection characteristics are uniform over the entire visible light region (ie, , The light reflectance in the wavelength region of 400 to 700 nm is generally high and there is no difference in reflectance).

  However, the conventional light-reflective coating using rutile titanium oxide as a white pigment can cope with the improvement in reflectance by increasing the thickness of the coating, but uniform reflection characteristics are obtained in all visible light wavelength regions. In addition, the increase in coating cost due to the thick film is an economic burden.

  Incidentally, Patent Document 1 shows an example in which rutile-type titanium oxide is contained in a coating film as a highly diffuse reflective coating metal plate and applied to a reflective plate for liquid crystal. However, since this coating film has a low reflectance due to light absorption in the vicinity of 400 nm, which is a characteristic of rutile-type titanium oxide, uniform light reflection characteristics cannot be obtained in the entire visible light region. Absorption near 400 nm not only lowers the reflectivity but also prevents blue color development.

  As a remedy for such problems, it is conceivable to simply use a rutile type and anatase type titanium oxide in combination. However, this method can slightly improve the light reflectivity in the vicinity of the wavelength of 400 nm, but cannot provide a significant improvement effect. In the combined use system, the high reflectance near the wavelength of 400 nm, which is a feature of anatase-type titanium oxide, cannot be fully utilized, and not only the effect of improving the light reflectance is insufficient, but also the uniformity of the reflectance is insufficient. .

Patent Document 2 describes that a fluorescent agent is added in order to compensate for the light reflectance in the vicinity of a wavelength of 400 nm, which is reduced by light absorption by rutile-type titanium oxide. However, although this method seems to be effective for improving the reflectance, it is difficult to control the reflection characteristics and the uniformity of the reflectance cannot be improved. Moreover, since the fluorescent agent is expensive, its practical application range is naturally limited from the viewpoint of cost.
JP 2002-172735 A JP 2003-73624 A

  The present invention has been made paying attention to the above-described circumstances, and without using a fluorescent agent, improves the light reflectivity in the vicinity of a wavelength of 400 nm, which is a defect of rutile titanium oxide, An object of the present invention is to provide a light-reflecting coated metal plate that exhibits a uniform light reflectance in the wavelength region and has a light reflectance superior to that of a rutile-type titanium oxide-containing single coating film with a similar film thickness.

  The light-reflective coated metal plate according to the present invention that has solved the above problems is a light-reflective coated metal plate coated with a light-reflective coating film having a multilayer structure of two or more layers, The outermost layer of the protective coating film is composed of a first light reflecting layer having a white pigment content of substantially 30 to 70% by mass substantially consisting of only anatase-type titanium oxide, and the lower layer side of the outermost layer is substantially It is characterized in that it is composed of a second light reflecting layer having a white pigment content of 30 to 70% by mass consisting only of rutile titanium oxide.

  In the coated metal plate of the present invention, the characteristics are more effectively exhibited when the thickness of the first light reflecting layer is 10 to 60 μm and the thickness of the second light reflecting layer is 10 μm or more. There is something. Moreover, in this invention, what formed the transparent surface protective film on the light reflective coating film of the said multilayer structure, and improved the durability as a reflective coating film also becomes preferable embodiment.

  According to the present invention, the light reflective coating film formed on the surface of the metal plate is composed of a multilayer coating film having a two or more layer structure containing a white pigment mainly composed of titanium oxide, and the outermost layer side is the first light reflecting layer. As a second light reflecting layer, a reflective layer mainly composed of rutile titanium oxide and having a long wavelength light reflectivity is used as the second light reflecting layer. Thus, it is possible to provide a coated metal plate that efficiently reflects light in the entire wavelength region of visible light and exhibits uniform and excellent light reflection characteristics.

  When light is applied to a coating film containing titanium oxide, light is reflected at the titanium oxide interface due to the difference in the refractive index between the vehicle component (resin) constituting the coating film and titanium oxide, and the resin and titanium oxide are transmitted. Part of the light is absorbed. Therefore, the reflectance increases when light absorption is low, and the reflectance decreases when light absorption increases. In addition, the shorter the wavelength, the greater the amount of attenuation when passing through the coating film, and the light cannot reach deep into the coating film. For example, light having a short wavelength near 400 nm is affected by the reflection characteristics of the outermost layer of the coating film. It is considered easy. On the other hand, since long wavelength light reaches deep inside the coating film, it is considered that it is easily affected by the reflection characteristics inside the coating film at a certain depth.

  Therefore, in order to improve the average reflectance of the coating film as a whole, the inventors have a multilayer structure of two or more layers, and a white pigment that reflects more short-wavelength light is blended on the surface layer side. However, if a white pigment that reflects more of the long-wavelength light that has passed through the surface layer side is added to the lower layer side, the reflectance of the coating film as a whole cannot be increased on average due to their mutual complementation. I thought. And as a result of repeating research to make use of this idea to improve the uniformity of the light reflectance of the entire coating film, the inventors have arrived at the coating film configuration of the present invention.

  That is, the light-reflective coated metal plate of the present invention has a light-reflective coating film having a laminated structure composed of two or more layers containing titanium oxide as a white pigment as described above, and is the outermost layer of the reflective coating film. The side is a first light reflecting layer having a white pigment content of substantially 30 to 70 mass consisting essentially of only anatase-type titanium oxide, and the lower layer side of the outermost layer is substantially composed only of rutile-type titanium oxide. It is comprised by the 2nd light reflection layer whose content of a white pigment is 30-70 mass%.

  In the present invention, the use of titanium oxide is defined as the white pigment constituting the light-reflective multilayer coating as described above. This is because titanium oxide has higher light reflectivity and whiteness than other white pigments such as zinc oxide, barium sulfate, calcium carbonate, and cerium oxide, and is suitable as a light reflective white pigment. It depends on Moreover, titanium oxide is classified into anatase type and rutile type according to the crystal structure as described above, and each has different light reflection characteristics, in particular, light reflectivity and absorptance according to wavelength, and the light reflectivity intended in the present invention. This is because it is most suitable for making the light reflection characteristics uniform by making the coating film into multiple layers.

  The reason why the white pigment on the outermost layer side is substantially only anatase-type titanium oxide and the content thereof is set to 30 to 70% by mass is that light in the vicinity of 400 nm, which is a low wavelength region of visible light, is effectively used. The reason for this is to reflect, and if it is less than 30% by mass, the reflectance for light in the low wavelength region becomes insufficient, and the object of the present invention to ensure uniform light reflectance in the entire wavelength region cannot be achieved. The content of anatase-type titanium oxide on the outermost layer side is more preferably 40% by mass or more, and still more preferably 45% by mass or more, in order to more reliably reflect light in the low wavelength region. However, if the content of the anatase-type titanium oxide in the outermost layer is too large, the total reflectivity is lowered and the vehicle component content of the outermost layer coating is insufficient, resulting in coating properties (especially impact resistance and resistance). (Scratchability, durability, etc.) are reduced, so it is preferable to stop at most 70% by mass, more preferably about 65% by mass.

  The thickness of the outermost layer is in the range of 10 μm to 60 μm so that light in the wavelength range from about 450 nm to 700 nm can be sufficiently transmitted while effectively reflecting light having a wavelength in the vicinity of 400 nm. It is good to adjust it to fit. Incidentally, if the thickness of the surface layer is too thin, the reflectance near 400 nm becomes insufficient, and conversely, if the surface layer is too thick, the light reflectance near 400 nm reaches saturation and does not further improve. The light absorptance at 700 nm is increased, the reflectance in the long wavelength region is lowered, and as a result, the light reflectance is also lowered. Therefore, the thickness of the outermost layer portion mainly composed of anatase-type titanium oxide is in the range of 10 to 60 μm, more preferably in the range of 20 to 40 μm.

  The second light reflecting layer formed on the lower layer side of the outermost layer is mainly composed of a white pigment so that sufficient light reflectance can be secured for visible light of 450 to 700 nm transmitted through the outermost layer. The rutile type titanium oxide is used, and its content is in the range of 30 to 70% by mass and a thickness of at least 10 μm is ensured. Incidentally, when the rutile-type titanium oxide content on the lower layer side is less than 30% by mass, it is difficult to obtain sufficient reflectance for the light in the long wavelength region, and due to insufficient reflectance of light in the 450 to 700 nm region, A uniform light reflectance cannot be secured over the entire visible light range.

  The rutile type titanium oxide content on the lower layer side is more preferably 40% by mass or more, and further preferably 45% by mass or more, in order to more reliably reflect light in the low wavelength region. However, if the content of rutile-type titanium oxide in the lower layer side is too large, the light reflectivity is lowered and the vehicle (binder) component content of the lower layer side coating film becomes relatively insufficient, and the coating film characteristics (Especially impact resistance and peel resistance, etc.) are lowered, so it is preferable to stop at most 70% by mass, more preferably about 65% by mass.

  Moreover, the thickness of the lower layer side should be at least 10 μm or more so that light in a long wavelength region of 450 to 700 nm can be effectively reflected, and there is an upper limit of the thickness particularly from the viewpoint of reflectivity. However, in consideration of economy, it is sufficient up to about 60 μm, more generally up to about 40 μm.

  The particle diameter of the titanium oxide is not particularly limited. However, in order to obtain a higher and more uniform reflectance, regardless of whether it is anatase type or rutile type, 0.1 to 0.4 μm, preferably 0.15 to It is preferable to use one having a uniform particle size within the range of 0.35 μm, more preferably 0.20 to 0.30 μm. Further, these titanium oxides may be those surface-treated with alumina, silica, zirconia, organic matter, or the like in order to improve dispersibility in the binder resin.

  In the present invention, as described above, the content of the anatase type titanium oxide or rutile type titanium oxide contained in the outermost layer and the light reflecting layer on the lower layer side thereof is determined within a specific range, and the remaining components of each layer are substantially the vehicle. Although it is a (binder) component, if necessary, other additives such as white pigments and other extender pigments other than titanium oxide, ultraviolet absorbers, ultraviolet stabilizers, dispersants, viscosity modifiers, etc. may be included. Good.

  In the present invention, as the resin used as the binder, any resin known in the paint field can be used, and examples thereof include polyester resins, polyolefin resins, polyamide resins, fluorine resins, silicone resins, and epoxy resins. It is done. Among these, polyester resins or modified polyester resins (epoxy-modified polyester resins, thermosetting polyester resins such as polyester resins in which a phenol derivative is introduced into the skeleton, or unsaturated polyester resins) are preferable. Is mentioned. Among these, polyester resins are particularly preferable from the viewpoint of bending workability and the like. Moreover, it is also possible to use a crosslinking agent together with the above resin, and preferred examples of the crosslinking agent used for the polyester-based resin include melamine resin and urethane resin. These crosslinking agents can be used alone or in combination of two as required.

  In addition, the type of the metal plate used in the present invention is not particularly limited, and various alloy steel plates such as cold-rolled steel plate, hot-rolled steel plate, or stainless steel plate, and further, electroplated steel plate, hot-dip galvanized steel plate, alloyed melt Various plated steel sheets such as galvanized steel sheet, 5% Al—Zn plated steel sheet, 55% Al—Zn plated steel sheet and Al plated steel sheet, or non-ferrous metal sheets such as Al plate and Cu plate can all be used.

  In order to form the above light-reflective coating film on a metal plate, a coating film-forming coating material containing a binder resin and a white pigment is prepared, and a known coating method such as a roll coater method, a spray method, or a curtain flow coater method is used. Using a bar coating method, a dipping method, or the like, it may be applied to at least two layers on the surface of the metal plate. When the paint for forming a coating film contains a solvent or when the binder resin is of a type in which the binder resin is thermally crosslinked, a baking treatment by heating is performed after coating. As the metal plate, a steel plate or various metal plates can be used, and plating treatment, various known ground treatments, or the like may be performed. Moreover, well-known protective films, such as a clear coating film, may be formed on the light reflective coating film. Similarly, on the lower layer side of the light-reflective coating film, a masking layer containing other white pigment may be provided, or an arbitrary undercoat film layer for improving coating film adhesion may be formed. Of course it is possible.

  The present invention is configured as described above, and a white pigment mainly composed of anatase-type titanium oxide is used on the outermost layer, and a white pigment mainly composed of rutile-type titanium oxide is used on the lower layer side, so that it is visible from 400 nm to 700 nm. It can improve the uniformity of light reflectivity in the light region, improve the stability of quality when used as a reflector of lighting equipment, and often occurs due to non-uniform reflectivity when used as a liquid crystal backlight. The rainbow color change phenomenon can be suppressed, and it can contribute to the quality improvement including the color tone of the liquid crystal screen, the expansion of the color and the improvement of the sharpness.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

In the present invention, when “reflectance” is referred to without particularly limiting the wavelength, the reflectance is measured with a color difference meter Σ90 manufactured by Nippon Denshoku Industries Co., Ltd. every 20 nm between 400 and 700 nm. Means the total reflectance (total R:%) obtained by In the following formula, R (λ) represents the reflectance at the wavelength λ.
(Total) Reflectivity = {[R (400) + R (420) + ... R (660) + R (680)] + [R (420) + R (440) + ... R (680) + R (700)]} × 20 ÷ 2 ÷ (700-400)

Experimental example 1
Apply a light-reflective coating for the lower layer and a light-reflective coating for the upper layer twice each to a 0.8 mm thick electrogalvanized steel sheet so that the dry coating thickness of each layer is 40 μm with a bar coater, Each coating was baked for 120 seconds in a baking furnace so that the ultimate plate temperature was 220 ° C. to form a light-reflective coating film having a two-layer structure. About the coating film of single layer structure, the coating material which comprises each coating film was apply | coated 4 times so that it might become a predetermined | prescribed dry film thickness, and it baked at 220 degreeC for 120 second similarly for every application. Table 1 shows the coating film structure and the laminated structure.

  As a binder resin, a polyester resin (trade name “Byron 29XS” manufactured by Toyobo Co., Ltd.), a melamine resin (trade name “Summar M40-ST” manufactured by Sumitomo Chemical Co., Ltd.) as a crosslinking agent, and as a rutile type titanium oxide, Ishihara The product numbers “CR-50”, “CR-58”, “CR-60” manufactured by Sangyo Co., Ltd. and the product number “A-220” manufactured by Ishihara Sangyo Co., Ltd. are used as the anatase-type titanium oxide, and cyclohexanone and xylene are used as solvents. Mix the binder resin and titanium oxide so that each compounding ratio is achieved, and knead thoroughly with a ball mill. Adjust the solid content with a solvent so that the solid content concentration is 50 to 75%, and then use it for coating. did.

  For each of the obtained light-reflective coated metal plates, the reflectance was measured at a measurement pitch of 20 nm between wavelengths 400 to 700 nm using a spectrophotometer Σ90 manufactured by Nippon Denshoku Industries Co., Ltd., and the maximum value (Rmax) The minimum value (Rmin) and the average value (Rave) were obtained, and the ΔR value (= Rmax−Rmin) was obtained.

  The results are shown in Tables 1-3. The “concentration in the coating film” in the table means the concentration (content ratio) of each component in the dry coating film, and “separation” means that the reflective coating film is separately applied to the upper layer and the lower layer. The coating specification of the present invention is shown, "single" is a single-layer coating using anatase type or rutile type alone, and "mixing" is two types of titanium oxide of anatase type and rutile type. Each single-layer coating film used by mixing is meant.

  As is clear from Tables 1 to 3, in the examples of the present invention in which the outermost layer side coating film and the lower layer side coating film were separately applied to form a multilayer coating film composition, compared with a comparative example of single or mixed coating film specifications. Thus, the total reflectance is high and the vertical difference (ΔR) of the reflectance is small, and a uniform light reflectance is obtained. It should be noted that increasing the total reflectivity (total R) by 1% as a light reflector used in lighting fixtures and liquid crystals is extremely useful in practice and meets the demands of consumers.

Claims (2)

  A light-reflecting coated metal plate coated with a light-reflecting coating film having a multilayer structure of two or more layers, wherein the outermost layer of the light-reflecting coating film is substantially composed of only anatase-type titanium oxide The content of the white pigment consisting essentially of rutile titanium oxide is 30 to 70% by mass on the lower layer side of the outermost layer. A light-reflective coated metal plate, characterized by comprising a second light-reflecting layer.   2. The light-reflecting coated metal plate according to claim 1, wherein the first light reflecting layer has a thickness of 10 to 60 μm, and the second light reflecting layer has a thickness of 10 μm or more.