Lightsafe masking film

Abstract: A composite, lightsafe masking film is disclosed which comprises a substrate formed of a plastic material, and a lightsafe layer peelably provided over the surface of said substrate. A fluorescent substance is incorporated in the lightsafe layer, or a fluorescent substance-containing layer is provided on the surface of the lightsafe layer or between the lightsafe layer and the substrate, so that a cutting line formed on the lightsafe layer fluoresces under illuminated conditions to form a legible pattern.

Description: This invention relates generally to a lightsafe masking film and, more specifically, to a composite, lightsafe masking film to be used as an original copy having a transparent pattern in a photomechanical reproduction process. One known lightsafe masking film of this type is composed of a plastics film substrate and a peelable, lightsafe layer provided thereon. See, for example, FR-A-2206866. A desired cutting line is made in the lightsafe layer manually or with a suitable automatic cutting device and then the cut portion is removed by peeling, to leave a desired transparent pattern on the masking film. However, a cutting line which is formed by means of a cutting blade or knife having a keen edge is very thin and therefore is difficult to see. Consequently, the peeling operation is laborious and involves considerable difficulties. The present invention has been made to overcome the problem of the conventional lightsafe masking film, and in accordance with a first aspect provides a lightsafe masking film comprising a substrate formed of a plastics material, and a lightsafe layer peelably provided over the surface of said substrate and containing a fluorescent substance, whereby a cutting line made in said lightsafe layer fluoresces under illuminated conditions and thereby becomes more readily visible. In another aspect, the present invention provides a lightsafe masking film comprising a substrate formed of a plastics material, a lightsafe layer peelably provided over said substrate, and a fluorescent layer containing a fluorescent substance and provided between said substrate and said lightsafe layer or over said lightsafe layer, whereby a cutting line made in the lightsafe layer fluoresces under illuminated conditions and thereby becomes more readily visible. The present invention will now be described in detail below. Lightsafe masking film according to the present invention is comprised of a substrate formed of a plastics material having provided thereon a peelable, lightsafe layer. Any plastics material conventionally used as the substrate of known lightsafe masking film can be used for the purpose of the present invention. Transparent plastics films such as polyethylene terephthalate films, polybutylene terephthalate films, polyoxybenzoate films and polycarbonate films may be suitably used as the substrate. Both stretched and unstretched films may be used. The thickness of the film is generally in the range of 20-300 µm. The substrate is overlaid with a peelable, lightsafe layer. The lightsafe layer is generally comprised of (a) a binder such as a synthetic rubber, e.g. a nitrile rubber, or a synthetic resin, e.g. a vinyl chloride/vinylidene chloride copolymer or a vinyl chloride/vinyl acetate copolymer, and (b) a lightsafe or light-shading substance such as a colorant, e.g. an organic or inorganic dye or pigment. The lightsafe substance is preferably so selected as to provide a lightsafe layer capable of preventing the passage of light having wavelength of about 300-550 nm therethrough. Any binder and any lightsafe substance customarily employed in lightsafe layers of known lightsafe masking films may be used for the purpose of the present invention. The lightsafe layer may further contain one or more additives used in conventional masking films, if desired. The lightsafe layer generally has a thickness of 20-50 µm, preferably 25-40 µm. In one embodiment according to the present invention, a fluorescent substance is incorporated into the lightsafe layer. By this expedient, when the lightsafe layer is cut at the time of the formation of a desired transparent pattern on the masking film, the cut line becomes clear and more readily visible under illuminated conditions because of the fluorescence of the fluorescent substance. The formation of the clear fluorescent line along the cutting line is considered to be attributed (a) to an increased intensity of light being absorbed by the fluorescent substance because of irregular reflection on the edge of the cutting line and (b) to an increased density, at the cutting line, of the fluorescent substance exposed to the light. As the fluorescent substance, there may be used a substance capable of absorbing visible or ultraviolet light and of emitting due to fluorescence light with a wavelength in the visible region, preferably a substance capable of absorbing purple, blue or green visible light and of emitting light with a longer wavelength than the absorbed light. Organic or inorganic fluorescent dyes or pigments may be suitably used. Illustrative of suitable fluorescent substances are organic substances such as Uranine-series, Eosine-series, Rhodamine-series, Thioflavine-series, Trypaflavin-series, Auramine-series and coumarin-series flurorescent dyes. The fluorescent substance is preferably used in the form of a fine powder or a paste. The amount of the fluorescent substance in the lightsafe layer is generally in the range of 2-50 % by weight, preferably 5-30 % by weight. The weight ratio of the fluorescent substance to the lightsafe substance is preferably in the range of 5:95 to 80:20, more preferably in the range of 20:80 to 60:40. The masking film of the above embodiment may be obtained by applying a coating composition containing the binder, lightsafe substance, fluorescent substance, etc. over the surface of the substrate, followed by drying the coated layer. In another embodiment according to the present invention, rather than incorporating the fluorescent substance into the lightsafe layer as in the above embodiment, a layer containing such a fluorescent substance is formed as an overcoat layer over the surface of the lightsafe layer or as an undercoat layer between the substrate and the lightsafe layer. In this embodiment, too, when a cuting line is formed in the lightsafe layer at the time of the formation of a transparent pattern on the masking film, the cutting line fluoresces strongly to permit easy recognition thereof, thereby facilitating the succeeding peeling and removing operations. The overcoat or undercoat layer may be composed of a binder, such as used in the lightsafe layer, and the fluorescent substance. The thickness of the undercoat or overcoat layer is generally 0.5-25 µm, preferably 2-20 µm. The overcoat layer may be formed by applying a coating composition containing the fluorescent substance and the binder over the surface of the lightsafe layer. The undercoat layer may be formed by applying a similar coating composition over the surface of the substrate, followed by the formation of the lightsafe layer over the undercoat layer. The following examples will further illustrate the present invention. Example 1 Preparation of Coating Composition : A coating liquid having the composition shown in Table below was prepared: Ingredient Content (part by weight) Lightsafe substance 2 Fluorescent substance 2 Acrylonitrile-butadiene rubber 6 Vinylchloride-vinylidene chloride copolymer 20 Toluene 35 Methyl ethyl ketone 35 Preparation of Masking Film : The above coating composition was applied over the surface of a substrate of polyethylene terephthalate film (thickness: 100 µm) and dried to obtain a lightsafe layer having a thickness of 25 µm. The lightsafe layer was orange in color and was capable of preventing the passage of light with a wavelength of 300-490 nm therethrough. When the lightsafe layer on the substrate was cut with a knife, the cutting line strongly fluoresced and became pink, permitting easy identification of the cutting line. Example 2 A first coating liquid having the same composition as that in Example 1 except that no fluorescent substance was incorporated was prepared and applied in the same manner as in Examle 1 over the surface of a polyethylene terephthalate film substrate, thereby forming a peelable, lightsafe layer having a thickness of 13 µm on the surface of the substrate. Then, a second coating liquid composed of 2 parts by weight of the fluorescent substance used in Example 1, 6 parts by weight of a acrylonitrile-butadiene rubber, 25 parts by weight of a vinyl chloride/vinylidene chloride copolymer, 36 parts by weight of toluene and 36 parts by weight of methyl ethyl ketone, was applied to the surface of the lightsafe layer and dried to form an overcoat layer having a thickness of 12 µm. The resulting masking film was capable of preventing the passage of light with a wavelength of 300-490 nm therethrough. When the lightsafe layer was cut with a knife, the cutting line strongly fluoresced and became pink, permitting easy identification of the cutting line. Example 3 Over a polyethylene terephthalate film substrate, the second coating liquid used in Example 2 was applied in the same manner as that in Example 2 to form an undercoat layer having a thickness of 12 µm. Then the first coating liquid used in Example 2 was applied on the surface of the undercoat layer to form a lightsafe layer having a thickness of 13 µm. The resulting masking film was capable of preventing the passage of light with a wavelength of 300-490 nm therethrough. When the lightsafe layer was cut with a knife, the cutting line strongly fluoresced and became pink, permitting easy identification of the cutting line.

Claims: A lightsafe masking film comprising a substrate formed of a plastics material and a lightsafe layer peelably provided over the surface of said substrate, characterized in that said lightsafe layer contains a fluorescent substance, whereby a cutting line made in said lightsafe layer fluoresces under illuminated conditions and thereby becomes more readily visible. A lightsafe masking film as claimed in Claim 1, wherein the content of the fluorescent substance in the lightsafe layer is 2-50% by weight. A lightsafe masking film as claimed in Claim 1 or Claim 2, wherein the lightsafe layer includes a binder, a lightsafe substance and the fluorescent substance. A lightsafe masking film as claimed in Claim 3, wherein the weight ratio of the fluorescent substance to the lightsafe substance is in the range of 5:95 to 80:20. A lightsafe masking film as claimed in any preceding claim, wherein said lightsafe layer has a thickness of 20-50 µm. A lightsafe masking film comprising a substrate formed of a plastics material and a lightsafe layer peelably provided over said substrate, characterized in that a fluorescent layer containing a fluorescent substance is provided between said substrate and said lightsafe layer or over said lightsafe layer, whereby a cutting line made in the lightsafe layer fluoresces under illuminated conditions and thereby becomes more readily visible. A lightsafe masking film as claimed in Claim 6, wherein the fluorescent substance is used in an amount of 2-50% by weight based on the total weight of the lightsafe layer and said fluorescent layer. A lightsafe masking film as claimed in claim 6 or claim 7, wherein the lightsafe layer includes a first binder and a lightsafe substance and the fluorescent layer includes a second binder and said fluorescent substance. A lightsafe masking film as claimed in claim 8, wherein by weight ratio of the fluorescent substance to the lightsafe substance is in the range of 5:95 to 80:20. A lightsafe masking film as claimed in any one of claims 6-9, wherein said lightsafe layer has a thickness of 20-50 µm and said fluorescent layer has a thickness of 0.5-25 µm.

Inventors: HORII YOSHIHARU, MARUYAMA HIROSHI, HORII, YOSHIHARU, MARUYAMA, HIROSHI
Applicants: SOMAR CORP, SOMAR CORPORATION
Application year: 1988
Main classification: G03F1
IPC codes: G03F1