Decorative lighting paper and a method of manufacturing same

Abstract: A decorative lighting paper is provided on which the printed matter can easily be discerned with clarity, no matter whether it is viewed with transmitted light or reflected light. For this purpose, a polyester or polyolefin film is used as a substrate, and at least the one side of the substrate comprises at least a bonding layer and a printing layer of different compositions formed on top of the substrate. The overall opacity of the sheet is 50 to 75%, the brightness measured from the first side is 80% or more, and the luster is 5 to 23%.

Description: The invention relates to decorative lighting paper, from which, when printed on both sides with a desired design, the design thereof can be discerned by using transmitted and/or reflected light. The invention also relates to a method of manufacturing such a paper. A decorative lighting type of sign board is gaining more and more popularity for display purposes. Usually, a light source is placed behind the board, and when turned on in the evening, the transmitted light enables the display or the design to be seen from the front side. A method for manufacturing such devices is disclosed, for example, in Japanese patent 5-229 244 (1993). However, if a semi-transparent paper is simply printed on both sides, the printed information or design is not displayed with much clarity, particularly during daylight hours when the (artificial) light source is extinguished and the sign board is viewed by using reflected light only. In such a case, the display appears much too dark in order to present the desired effect. The aim of the present invention is to resolve the problem described above. In particular, the object underlying the present invention is to provide a decorative lighting paper from which a design printed thereon can be discerned with exceptional clarity, no matter whether viewed with transmitted light or reflected light. A further object of the present invention is to provide a method of manufacturing such a paper. In the following specification, the meaning of some characteristic values is important for the understanding of the invention, and these characteristic values are explained hereinafter. (a) Brightness The values of brightness are measured in accordance with JIS P-8123, according to which the brightness of Hunter is measured by a brightness meter, and the detected value is the indicator of the degree of brightness. The higher the value, the whiter the color. In this context, 100% is theoretically pure white, whereas 0% is theoretically black. (b) Opacity The values of opacity are measured in accordance with JIS P-8138, wherein the opacity is measured with a colour sensor, and the detected value is the indicator of the degree of opacity. The higher the detected value, the more opaque the product. In this context, 100% is theoretically completely opaque, whereas 0% is theoretically transparent. (c) Luster The values of luster are measured in accordance with JIS P-8142 wherein the luster is measured with a luster meter, and the detected value is the indicator of the degree of luster. The higher the detected value, the higher is the luster. In this context, 100% is theoretically a mirror sheen. According to the JIS standard, a value of 15% or less is unsuitable, but in reality a measured value of 15% or less can be specified, because the luster can be measured with good reproducibility. (d) Coefficient of friction The coefficient of friction is measured in accordance with JIS P-8147, wherein the static coefficient of friction and the dynamic coefficient of friction are measured by means of a tensile testing apparatus, for example of the type as manufactured by Toyo Seiki Seisakusho, Ltd., and the measured values are indicative of the ease-of-slip of an ink-receptive layer as described in more detail hereinafter. The coefficient of friction can be expressed as an absolute number, and the smaller the coefficient of friction, the better is the slip. The above object is solved by a material and a method according to claims 1 and 5. Further developments are specified in the subclaims. Assuming a paper bearing a design or printed scene, no matter whether it is observed with transmitted light or reflected light, the printed scene appears more pronouncedly in its representation, the whiter the paper. Therefore, the entire sheet must have a brightness of at least 80%, otherwise the scene printed thereon will not be pronounced satisfactorily. For decorative lighting paper, the degree of light transmission from a light source determines the quality of light and the effectiveness with which the printed matter can be observed on the other side. Therefore, the opacity of the paper is set between 50% to 75%. If the opacity is less than 50%, too much light is transmitted, and if the opacity is greater than 75%, not enough light is transmitted. For paper of the same opacity, the higher the content of a masking agent, such as titanium oxide, the higher will be its surface luster. Under reflected light, a display will look too dark, but the brightness can easily be increased by increasing the scattered reflectance, in particular by reducing the luster of the surface layers. Then, when viewed under reflected light in particular, the effect approximates that of one-sided printing. Accordingly, according to the invention, the luster is set between 5 to 23%, preferably 7 to 20%. If the luster is less than 5 to 7%, the colour deepens, but if the luster is higher than 20 to 23%, not enough white is reflected. According to the invention, as means of increasing the scattered reflectance, a blend of different polymers is used, in particular polymers of low mutual compatibility will increase the visible brightness. This can be attributed to the scattering of the light at the boundaries between polymer molecules when an admixture of different polymers in a finely dispersed state is dried and solidified. The same scattered light effect can be obtained by using, for the coating solution, a mixed solvent comprising a solvent in which the polymers are readily soluble, plus a high-boiling solvent in which the polymers are poorly soluble. Paper which has a high scattered reflectance effect is characterized by a low luster and values of a = 0 to 2 and b = 0 to 3,5 when the chromaticness index is measured according to the standard JIS Z-8730 in the Hunter colour system. The film which forms the substrate for a coating should, for reasons of homogeneity and cost considerations, preferably be a transparent or semi-transparent polyester or polyolefin. However, if the surface layers are set to have a scattered reflectance as described above, then an ordinary film will not have an adequate bonding strength with the coated film. In such a case some kind of adhesive treatment underneath the coated film is necessary. This bottom or lower bonding layer should contribute to a portion of the opacity of the paper, and for this purpose preferably an organic or inorganic filler should be mixed in an amount that will not affect the bonding. However, if such a type of paper is used for offset printing, static electricity will cause problems with the feeding and discharge of the paper, necessitating some kind of anti-static treatment. This can be achieved by adding an anti-static agent to the coating, or it can be applied as another top layer after the coating is dried. The first method requires the addition of a large amount of an anti-static agent. Also, for a surface as used in this invention, in which the surface luster has been reduced, to achieve an adequate effect, a larger amount of anti-static agent is required than for a high-luster surface. Most anti-static agents have surface active properties, wherein, if used in large quantities, the surface active agent causes the ink to emulsify, leaving contaminants on the printed scene. Also, for paper of this type of low surface luster, in order to reduce the frictional electrostatic charge, and in order that feeding and discharge of paper will not be impeded by static charge, it is preferable that the surface coefficient of friction is quite low and has a dynamic coefficient of friction of 0,6 or less, preferably 0,5. The surface coefficient of friction can be reduced by adding a lubricating agent to the coating solution for the surface layer, for which the following substances can be used: A polyethylene wax, a stearamide or other amide chemical, zinc stearate or other metallic soap, or similar waxy type substance. The lubricant should comprise 1 to 10% of the total amount of binder, preferably between 2 to 7%. Paper according to the invention, which enables an image printed on both sides to be easily ascertained, no matter whether observed under transparent light or reflected light, must have the following properties: Opacity 50 to 75% Brightness as observed from a first side A ≥ 80% Luster as observed from the first side A 5 to 23%. Morover, in order to achieve these properties, the coating solution is characterized by using the following features: (i) A polymer different from and of low compatibility with the main binder and/or (ii) an additional high-boiling solvent in which the main binder is poorly soluble, wherein the side being viewed with reflected light must be comprised of a surface scattered reflectance layer of low luster and a bonding layer which will adhere to the substrate. The composition of the paper according to the invention and in particular the action and effect of items (i) and (ii) will be explained in further detail hereinafter. The substrate must be a homogeneous, smooth and cheap film, for which a polyolefin or polyester is preferable. For decorative lighting paper in particular, in view of the heat usually generated by electric light, a polyester is preferable, and in terms of cost, a polyethylene terephthalate is preferable. Moreover, the substrate should be transparent, but a milky-white film of slight opacity can be used as long as the properties of the finished product are within the scope of the present invention. In order to facilitate the discernibility of the printed matter with either transmitted light or reflected light, the entire surface must be fully coloured, or a portion of the surface must be partially coloured equally on both sides. Otherwise, with ordinary one-siding printing, when viewed with transmitted light, the colour density is inadequate; but if such an inadequate portion is built up, then under reflected light the colour becomes too dense, making the image too dark. The first side or side A must satisfy the properties of the paper according to the invention, and it is comprised of a bonding layer and a printing layer. The purpose of the bonding layer is to bond the surface layer to the substrate, and it consists mainly of a binder that can adhere to both layers. It must be of a thickness to compensate for the brittleness of the surface layer and must be in a range from 0,5 µm to 10 µm, preferably from 1 µm to 5 µm. The same types of binders can be used for the bonding layer as for the printing layer. However, the bonding layer can be of any suitable composition that will provide good bonding between the substrate and the printing layer. The printing layer embodies the main features of the present invention, and because of its brightness and luster, provides the same visual sense as a normal printed product, even if the background light is extinguished and the subject is viewed with reflected light only. Although not confirmed, this is probably attributed to the fact that the scattered reflectance of the light on the front surface secures brightness on the one hand and minimizes the effects by printing on the reverse side on the reflected light on the other hand. Next, the methods of manufacturing paper having the above-indicated properties (i) and (ii) that provide the scattered reflectance layer will be explained in more detail. The surface layer of this layer can be produced to a thickness of 1 to 30 µm, however, in terms of economy and surface strength, a thickness of 2 to 10 µm only is preferable. A. Preparation of light-scattering layers with polymer blends Different polymers of low mutual compatibility are dissolved in a solvent which will totally dissolve all polymers. Such a solution is coated onto a substrate, then dried to produce a finely dispersed polymer blend in which light will scatter at the boundaries between the polymer molecules, and where light absorption is minimal, the brightness is high. An oleophilic resin, used as a finely dispersible binder X will facilitate the absorption of the printing ink, and will also reduce problems of migration to the reverse side and other problems. Also, the addition of a fluorescent whitening agent is effective in increasing the brightness. The main binder in the printing layer of the present invention serves to form the printing layer, affix the filler and other purposes. It can be selected from any general binder resins, but a polyester, polyurethane, acrylic-styrene copolymer, acrylonitrile-styrene copolymer, polyolefin chloride, or similar polymer is preferable. An oleophilic resin used in the present invention can be selected from any publicly-known resin, but preferably one which contains unsaturated double bonds in its molecular structure, such as an ethylene-vinyl acetate copolymer, a styrene-butadiene copolymer, an acrylic-vinyl acetate copolymer, a methylmethacrylate-butadiene copolymer. An ethylene-vinyl acetate copolymer, or a styrene-butadiene copolymer are most preferable. The ratio of main binder to oleophilic resin is preferably in the range of 100:5 to 40, most preferably in the range of 100:5 to 30. A ratio of less than 5 parts oleophilic resin will lower the effectiveness of the polymer blend, but a ratio of more than 40 parts will reduce the strength of the printing layer and increase the viscosity of the coating solution. The ethylene-vinyl acetate copolymer used in the present invention should preferably have a vinyl acetate content in the range from 30 to 50%. Otherwise, if the content is less than 30%, there will be an insufficient number of unsaturated double bonds, thereby reducing the absorption capacity of the copolymer. Hence, the vinyl acetate content is preferably more than 30%, but more preferably more than 40%. On the other hand, a copolymer of a vinyl acetate content of more than 50% will render the final polymer impractical and cannot be used. The substance Evaflex (trademark), manufactured by Dupont-Mitsui Polychemicals Co., Ltd., is a commercially available polymer that has these properties. The styrene-butadiene copolymer used in the present invention should preferably have a butadiene content in the range from 50 to 80%. Otherwise, if the content is less than 50%, there will be an insufficient number of unsaturated double bonds, thereby reducing the absorption capacity of the copolymer. Hence, the butadiene content is preferably more than 50%, but more preferably more than 55%. On the other hand, a butadiene content of more than 80% will render the final polymer impractical and cannot be used. The substance Tufprene (trademark), manufactured by Asahi Chemical Industry Co., Ltd., is a commercially available polymer that has the desired properties. There are no particular restrictions on the fluorescent whitening agent used according to the invention. Specific examples that can be used include the substances Mikephor (trademark), manufactured by Mitsui Toatsu Dyes, Ltd., or Blankophor (trademark), manufactured by Bayer AG. B. Preparation of light-scatterinq layers with high-boiling poor solvents The binder is first dissolved in a good solvent or solvent blend, and then a solvent having a comparatively high boiling point, in which the binder is poorly soluble, is added to the first solution. Upon drying, the polymer will gel before the coated film is formed, and after drying, a white film of low luster will be formed. A very white, low-luster surface layer can be obtained by using this technique and principle. For an ordinary, low-boiling good solvent (A), substances such as ethyl acetate, methyl ethyl ketone, or toluene can be used, while for the high-boiling poor solvent (B), diethylene glycol, ethylene glycol monoethylether, propylene glycol monoethylether, butylene glycol monoethylether, benzyl alcohol, or similar solvents can be used, wherein the ratio of A:B is preferably 3:2 to 5. Any other publicly-known binder, filler, anti-static agent, and other agents can be used for preparing the surface layer coat solution. There are no particular restrictions on the type of filler, but precipitated light calcium carbonate, heavy calcium carbonate, kaolin, talc, satin white, silica, titanium oxide, barium sulfate, alumina trihydrate, or other inorganic filler, or an acrylic-styrene copolymer resin, an urea resin or other organic filler can be used. The reverse face can be the same as the front face, provided that it contains an anti-static agent and a lubricant in order to prevent troubles in the feeding and discharge of the paper, or can have the properties required for offset printing, including simple UV printing. There are no particular restrictions as to the coating method used for preparing the decorative lighting sheets according to the invention, and gravure coating, gravure reverse coating, roll reverse coating, air knife coating, lip coating, or other publicly-known coating methods are suitable. Moreover, there are no particular conditions for drying, but the conditions should preferably be within a range that they will not adversely affect the properties of the coated layer and the substrate. The invention will be explained in more detail with reference to the following practical examples and comparative examples. Example 1 A clear polyethylene terephthalate film having a thickness of 125 µm was stretched along both axes, coated, using a gravure coater, on both sides with a solution of Coating Formulation 1 as described below, then dried. Next, again using a gravure coater, the film was coated on both sides with a solution of Coating Formulation 2, then dried to obtain a decorative lighting sheet. The oleophilic resin used here was a styrene-butadiene copolymer with a butadiene content of 60%. Coating Formulation 1 Substances Parts by weight White, polyester rotogravure ink (Lami-Z XE-White (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 300 Toluene-based solvent blend (Lami-Z Solvent (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 150 Coating Formulation 2 Substances Parts by weight White, polyolefin chloride rotogravure ink (PXAO-White (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 300 Toluene-based solvent blend (PXAO Solvent (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 260 Powdered silica 15 (Mizukasil P-526 (trademark), manufactured by Mizusawa Industrial Chemicals, Ltd.) 15 Anti-static agent (Share-Stat SN (trademark), manufactured by Cyanamid International) 4,5 Styrene-butadiene copolymer (Tufprene 912 (trademark), manufactured by Asahi Chemical Industry Co., Ltd.) 12 As shown in Table 1, the decorative lighting sheet obtained thereby is of suitable opacity and sufficient brightness. Example 2 A clear polyethylene therephthalate film having a thickness of 125 µm was stretched along both axes, coated, using a gravure coater, on both sides with a solution of Coating Formulation 3 as described below, then dried. Next, again using a gravure coater, the film was coated on both sides with a solution of Coating Formulation 4, then dried to obtain a decorative lighting sheet. The oleophilic resin used here was styrene-butadiene copolymer with a butadiene content of 60%. Coating Formulation 3 Substances Parts by weight White, polyester rotogravure ink (Multiset E-61 (trademark), manufactured by Toyo Ink Mfg. Co., Ltd.) 300 Toluene-based solvent blend (LP302 Solvent (trademark), manufactured by Toyo Ink Mfg. Co., Ltd.) 150 Coating Formulation 4 Substances Parts by weight White, polyolefin chloride rotogravure ink (PXAO-White (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 300 Styrene-butadiene copolymer (Tufprene 912 (trademark), manufactured by Asahi Chemical Industry Co., Ltd.) 12 Toluene-based solvent blend (PXAO Solvent (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 260 Powdered silica (Mizukasil P-73 (trademark), manufactured by Mizusawa Industrial Chemicals, Ltd.) 12,3 Fluorescent whitening agent (Mikephor YO (trademark), manufactured by Mitsui Toatsu Dyes, Ltd.) 0,3 Anti-static agent (Cyastat SN (trademark), manufactured by Cyanamid International) 4,5 Polyethylene wax (PE Wax, manufactured by Hoechst AG) 4 Glass beads (Microbeads MB-20 (trademark), manufactured by Toshiba-Ballotini Co., Ltd.) 2,5 As shown in Table 1, the decorative lighting sheet obtained thereby is of suitable opacity and gives sufficient brightness. Example 3 A clear, polyethylene terephthalate film having a thickness of 125 µm was stretched along both axes, coated, using a gravure coater, on both sides with a solution of Coating Formulation 1 as described below, then dried. Next, again using a gravure coater, the film was coated on both sides with a solution of Coating Formulation 5 then dried to obtain a decorative lighting sheet. The oleophilic resin used here was an ethylene-vinyl acetate copolymer with a vinyl acetate content of 46%. Coating Formulation 1 Substances Parts by weight White, polyester rotogravure ink (Lami-Z XE-White (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 300 Toluene-based solvent blend (Lami-Z Solvent (trademark), manufactured by Osaka Printing Ink Mfg. Co., Ltd.) 150 Coating Formulation 5 Substances Parts by weight Acrylonitrile-styrene copolymer (Estyrene AS (trademark), manufactured by Nippon Steel Chemical Co., Ltd.) 100 Ethylene-vinyl acetate copolymer (Evaflex 45X (trademark), manufactured by Dupont-Mitsui Polychemicals Co., Ltd.) 19 Toluene-based solvent blend (LP302 Solvent (trademark), manufactured by Toyo Ink Mfg. Co., Ltd.) 376 Ethylene glycol mono-n-butylether (Butyl glycol, manufactured by Nippon Nyukazai Co., Ltd.) 350 Powdered silica (Mizukasil P-526 (trademark), manufactured by Mizusawa Industrial Chemicals, Ltd.) 26,6 Rutile titanium dioxide (Tipaque R-670 (trademark), manufactured by Ishihara Sangyo Kaisha, Ltd.) 66,6 Fluorescent whitening agent (Mikephor YO (trademark), manufactured by Mitsui Toatsu Dyes, Ltd.) 0,2 Anti-static agent (Cyastat SN (trademark), manufactured by Cyanamid International) 6,6 As shown in Table 1, the decorative lighting sheet obtained thereby has a suitable opacity and provides sufficient brightness. Good results were obtained when printing on both sides using a synthetic paper ink (Best SP (trademark), manufactured by T & K Toka Co., Ltd.). Example 4 A clear, polyethylene terephthalate film having a thickness of 125 µm was stretched along both axes, coated, using a gravure coater, on both sides with a solution of Coating Formulation 3 as described below, then dried. Next, again using a gravure coater, the film was coated on both sides with a solution of Coating Formulation 6, then dried to obtain a decorative lighting sheet. The oleophilic resin used here was a styrene-butadiene copolymer with a butadiene content of 60%. Coating Formulation 3 Substances Parts by weight White, polyester rotogravure ink (Multiset E-61 (trademark), manufactured by Toyo Ink Mfg. Co., Ltd. 300 Toluene-based solvent blend (LP302 Solvent (trademark), manufactured by Toyo Ink Mfg. Co., Ltd.) 150 Coating Formulation 6 Substances Parts by weight Acrylonitrile-styrene copolymer (Estyrene AS (trademark), manufactured by Nippon Steel Chemical Co., Ltd.) 100 Styrene-butadiene copolymer (Tufprene 912 (trademark), manufactured by Asahi Chemical Industry Co., Ltd.) 8,4 Toluene-based solvent blend (LP302 Solvent (trademark), manufactured by Toyo Ink Mfg. Co., Ltd.) 340 Propylene glycol monoethylether 350 Powdered silica (Mizukasil P-527 (trademark), manufactured by Mizusawa Industrial Chemicals, Ltd.) 30 Rutile titanium dioxide (Tipaque R-670 (trademark), manufactured by Ishihara Sangyo Kaisha, Ltd.) 45 Fluorescent whitening agent (Mikephor YO (trademark), manufactured by Mitsui Toatsu Dyes, Ltd.) 0,2 Anti-static agent (Surfynol 440 (trademark), manufactured by Nisshin Chemical Industry Co., Ltd.) 20 Polyethylene wax (PE Wax, manufactured by Hoechst AG) 3 As shown in Table 1, the decorative lighting sheet obtained thereby has a suitable opacity and provides a sufficient brightness. Example 5 A clear polyethylene terephthalate film having a thickness of 125 µm was stretched along both axes, coated, using a gravure coater, on both sides with a solution of Coating Formulation 1 as described above, then dried. Next, again using a gravure coater, the film was coated on both sides with a solution of Coating Formulation 7, then dried to obtain a decorative electric lighting sheet. No oleophilic resin was used in this example. Good results were obtained upon printing both sides using a UV ink (Bestcure (trademark), manufactured by T&K Toka Co., Ltd.). Coating Formulation 7 This Coating Formulation 7 was prepared in the same manner Coating Formulation 6, except that the styrene-butadiene copolymer was omitted. Comparative Example 1 The procedures to obtain the sheets were the same as in Example 5, except that the propylene glycol monoethylether was omitted, and the toluene solvent blend content was adjusted to 500 parts. The surface luster was observed, and a product, printed on both sides was prepared in the same manner as in Example 5. However, when using reflected light, the image was too dark and could not be readily discerned. Effectiveness In the paper sheets according to the present invention, the surface brightness and luster are set to be within a specified range, which provides a printing paper having a superior visual discernibility. In particular, an independent and unique whitening technique was used in its preparation which has been judged to be very effective in producing a decorative lighting paper with good visual discernibility both in transmitted and reflected light. The results obtained in connection with the examples and the comparative example described above have been summarized in the attached Table 1 comprising various values obtained by measurement.

Claims: A decorative lighting paper formed from a polyester or polyolefin film, which when printed on both sides yields good visual discernibility in transmitted and/or reflected light, wherein at least a first side or side A of the sheet comprises at least a bonding layer and a printing layer of different compositions on top of the film and wherein the overall opacity of the sheet measured according to JIS P-8138 is 50 to 75 %, the brightness as measured from the first side according to JIS P-8123 is 80 % or more, and the luster measured according to JIS P-8142 is 5 to 23 %. The decorative lighting paper according to claim 1, in which the printing layer of the first side contains a binder X of low compatibility with the main binder, and a fluorescent whitening agent. The decorative lighting paper according to claim 2, in which the binder X is an ethylene vinyl acetate copolymer and/or a styrene-butadiene copolymer. The decorative lighting paper according to any of claims 1 to 3, in which the static coefficient of friction measured according to JIS P-8147 is at maximum 0.9 and the dynamic coefficient of friction measured according to JIS P-8147 is at maximum 0.6, when the front face and the reverse face of two sheets are piled together. A method of manufacturing a decorative lighting paper according to any of claims 1 to 4, wherein a substrate consisting of a polyolefin or polyester is used, wherein a bonding layer is formed on the first side of the substrate, wherein a printing layer is subsequently formed on the bonding layer on the first side of the substrate by using a solvent for the coating formulation which comprises an admixture of a low-boiling solvent in which the main binder is of good solubility, and a high-boiling solvent, in which the main binder is of poor solubility, and wherein the low-boiling solvent and the high-boiling solvent are mixed in a ratio of 3:2 to 5 parts by weight.

Inventors: KIJIMA TOSHIHIRO, NEMOTO KAZUNOBU, KIJIMA, TOSHIHIRO, NEMOTO, KAZUNOBU, Kijima, Toshihiro, c/o Nisshinbo Industries Inc., Nemoto, Kazunobu, c/o Nisshinbo Industries Inc.
Applicants: NISSHIN SPINNING, NISSHINBO INDUSTRIES INC.
Application year: 1995
Main classification: G09F13
IPC codes: B32B27, B41M3, G09F13