JPS6244254B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to mark transfer sheets, and more particularly to human and machine readable mark transfer sheets. More particularly, the present invention relates to a method of marking an object using this mark transfer sheet. Continuing efforts have been made to develop more satisfactory means for inventory control and checkout operations in supermarkets. These efforts resulted in the Universal Product Code (UPC), represented by a series of bars and spaces. This type of code can be read by diffuse reflection scanning means. Despite the overall effectiveness of this system,
Difficulties have existed in developing satisfactory means for the application of code messages. Traditional graphic arts printing techniques that use two inks for each bar and space are limited by the ink's tendency to spread during application. Additionally, UPC systems require a minimum contrast between the barcode and the background. This is because the code information is read by detecting the diffusely scattered light reflected by the bar and the background. Additionally, some products and mark application devices require preparation of the mark prior to application to the product. Accordingly, there is a continuing need for reliable systems for efficiently and accurately applying UPC code marks to a wide range of substrates. The present invention provides a mark transfer sheet that is particularly well suited for mark applications such as UPC code labels and its use in such mark applications. These transfer sheets, when so used, provide the necessary contrast to this system independent of the reflectivity of the substrate and provide simplicity, accuracy and economy hitherto unavailable. In accordance with the present invention, there is provided a mark transfer sheet comprising an imaging layer on a carrier support, the imaging layer having: (a) a property in the visible spectrum when exposed to radiation; a radiation-sensitive composition capable of forming a colored substance capable of absorbing at least some of the wavelengths of light, which when exposed to radiation produces a detectable difference in diffuse reflection density between the exposed and unexposed portions; (b) pigments capable of diffusely reflecting the wavelengths of light absorbed by the colored substance (which is present in sufficient quantities per square foot);
(c) a radiolucent, colorless polymeric film-forming thermoplastic binder. The present invention further uses these transfer sheets to
radiation by exposing the radiation-sensitive composition to patterned radiation at wavelengths to which it is sensitive to produce a detectable difference in diffuse reflectance density between the exposed and unexposed portions. imparting an image to the sensitive composition, heating the imaged layer to a temperature of about 40° to 220°C such that the outer surface of the layer becomes adhesive; and applying the outer surface of the imaging layer to the imaging layer. On the other hand, it provides a method for marking an object by bringing it into contact with a more adhesive receptive support than the carrier support, and optionally by separating the carrier support. Radiosensitive components that can be used in the present invention include:
Mention may be made of any known composition that is normally colorless and unaffected under normal light conditions, but which becomes colored upon exposure to appropriate electromagnetic radiation.
Particularly satisfactory are those described in US Pat. No. 3,639,762, which is incorporated herein by reference. This patent discloses suitable conventional light conditions and electromagnetic radiation sources for producing colored materials from radiation-sensitive compositions. Such components are substantially colorless. However, the slight color that exists before irradiation can be seen under colored inspection light.
Does not interfere with achieving sufficient contrast between the UPC bar and the space. Typically, such radiation-sensitive components include dye-forming substances, but they may also include further substances to fix the dye image against further color changes. can. These compositions are photoimageable and photofixable, and
They are dry processable in that they require no treatment other than irradiation with two different types of irradiation. Other radiation-sensitive components that may be used are photoimageable heat-fixable systems which are also dry processable in that they require only light and heat and no chemical treatment for image development and fixation. It is. Such a system is shown in detail in US Pat. No. 3,390,995. UV-sensitive ingredients known in the art can also be used in the present invention, including a variety of chemical, thermal or photoactivating (photofixing) agents, and are described in US Pat. No. 3,390,994.
No. 3390995, No. 3390996, No. 3390996, No. 3390995, No. 3390996, No.
It is described in the specifications of No. 3445234, No. 3630736, No. 3615454, and No. 3658543. Reflective pigments that can be used in the present invention must be capable of diffusely reflecting the wavelength of the test beam. In particular, the amount of such pigment is sufficient to at least opaque the surface of the object to be marked. Accordingly, the pigment is present in an amount to provide a coating density of about 0.05 to 0.34 grams per square foot. The maximum pigment concentration should give a substantial difference in diffuse reflection density between exposed and unexposed areas. When measured with a Macbeth reflection densitometer using a visual filter that approximates the sensitivity of the naked eye, the density difference between exposed and unexposed areas is at least
It should be 0.3, which corresponds to easy readability with the naked eye. For substrate opacification, the reflection density of the unexposed areas is typically based on a comparison material, such as a standard magnesium carbonate surface.
0.4 or less. It is desirable to be able to form a representation that is easily readable by the human eye. For machine readability, the criteria are even more critical to allow interaction of the representation with the scanning device, as described in the UPC regulations. At density levels up to 34% pigment concentration (at which level coverage of the dark substrate is virtually complete), a print contrast signal of 0.36 ( It can be generated using Print Contrast Signal (abbreviation PCS). Successful mechanical scanning requires higher contrast, ie, an optical density contrast of at least 0.7 above the background and a corresponding PCS ratio. Particular materials that can be used as pigments in the present invention include paper, felt, natural and synthetic fibers, plastics, ceramics, and powdered glasses (silica) and inorganic oxide, sulfide, and carbonate powders. Particularly suitable, however, are particulate metal oxide and sulfide pigments, especially those in which the metal is a polyvalent heavy metal having an atomic number of at least 21. Heavy metals are explained in ``Fundamental'' by HG Deming.
Chemistry, 2nd edition (published by John Wiley & Sons). Typical pigments are oxides of antimony and bismuth trioxide, hafnium, zirconium and bismuth dioxide, lead monoxide, tin dioxide, yttrium oxide, zinc, cadmium and mercuric oxide. Suitably colored corresponding sulfides, such as zinc sulfide, can also be used. Particularly preferred are TiO <sub>2</sub> (rutile), ZnO (containing zincite), zinc sulfide containing lithopone (urtozite, sphaarelite, blends), SiO <sub>2</sub> and ZrO <sub>2</sub> . The particular pigment chosen should, of course, be compatible with the radiation-sensitive composition and the coloring material produced therefrom in the mark-forming step by means of radiation. Pigments can be selected to absorb radiation-developed dyes at their surfaces. Acidic oxides can be used in combination with photosensitive components that allow the development of cationic dyes. Most preferably, titanium dioxide and cationic triarylmethane dye-forming components may be used in the coating composition. Colored pigments can often be used for further identification purposes, eg to indicate different groups of goods. However, the color of the pigment should not be so strong as to interfere with the minimum required contrast of the wavelength of the test light. Yellow cadmium sulfide pigments are compatible with the development of red light absorbing dyes, for example. The diffuse reflection provided by different pigments varies depending on their chemical nature and average particle or fiber size. It is known that the scattering of visible light is a function of surface area per gram. Therefore, the smaller the particle size, the greater the visible light scattering power. Pigments having an average particle size of about 0.04-50μ are commercially available and can be used in the present invention. Smaller particles within the abovementioned range are particularly satisfactory. The amount of pigment of a given average particle size and scattering surface area necessary to satisfy the reflection and contrast criteria defined herein can be readily determined by one skilled in the art. Generally smaller amounts of smaller sized pigment particles are required. In order to transfer from a carrier support to a receptive support at a particular transfer temperature, the film-forming thermoplastic binder must be applied to the surface of the receptive support to a greater extent than to the surface of the initial carrier. Must have adhesive properties. The binder should be such that it transmits sufficient radiation to the radiation-sensitive component to produce colored material in a reasonably short period of time and does not unduly inhibit the mark-forming operation. The light absorption properties of the binder should be compatible with those of the radiation-sensitive composition, dyes made therefrom, and pigments. The binder should be capable of transmitting the test colored light corresponding to the absorption color developed by the photosensitive component. Usually it is virtually colorless. Polymeric binders also contribute to dimensional stability. That is, such a binder retains the width and position of the exposed and unexposed areas established during exposure up to the point where the mark can be read by a scanner. Typical thermoplastic polymeric binders that may be used include vinylidene chloride copolymers such as vinylidene chloride/acrylonitrile, vinylidene chloride/methacrylate and vinylidene chloride/vinyl acetate copolymers, ethylene/vinyl acetate copolymers, cellulose ethers. For example, methylcellulose, ethylcellulose and benzylcellulose, cellulose esters such as cellulose acetate, cellulose acetate succinate and cellulose acetate butyrate, synthetic rubbers such as butadiene/acrylonitrile copolymers, and 2-chlorobutadiene-1,
Tripolymers, polyvinyl esters such as polyvinyl acetate/acrylate, polyvinyl acetate/methacrylate and polyvinyl acetate, polyvinyl chloride and copolymers such as polyvinyl chloride/acetate, polyvinyl acetals such as polyvinyl butyral and polyvinyl formal, polyurethanes and polyacrylates and alpha alkyl polys Acrylate esters include, for example, polymethyl methacrylate and polyethyl methacrylate. As will be clear to those skilled in the art, particular binders can be selected for their compatibility with the substrate to which the mark is applied, and this may include additives that modify surface photoselectivity, abrasion resistance, etc. It can be denatured by At least 1 with absorption in the range of 300-420 nm
A type of ultraviolet absorbing compound can be included in the carrier support or in an interlayer between the imageable layer and the support. Many known UV absorbers can be used including benzophenones, benzotriazoles and nickel complexes. Typical ultraviolet absorbers and their preparation are described in the Encyclopedia of Chemical Technology, 2nd Supplement, pages 883-902 (1960), under ``Ultraviolet Absorbers''. In a preferred embodiment, a carrier support with ultraviolet absorption is retained over the markings on the surface of the product for physical protection. The ultraviolet absorption should be sufficient to inhibit further imaging of the radiation-sensitive component through the carrier support. This UV absorption is the same as the UV absorption discussed above.
This can be provided by the inclusion of absorbers or by choosing a carrier support, such as "Kapton" polyimide film, which has inherent UV absorbing properties. The imageable layer of the structures of the present invention is generally prepared by mixing the components in a solvent. The solvent should be volatile at normal temperatures and pressures. Examples are alcohols and esters, which may be in the amount necessary to achieve dissolution of the radiosensitive component;
aromatic hydrocarbons, ketones and various solvents. The order in which the components are combined is not critical. The solvent facilitates mixing of the components of the radiation-sensitive component, but is later largely removed from the coating by evaporation. It is often advantageous to leave a small amount of solvent residue in the coating applied to the product surface so that the desired degree of color development can be obtained by radiation. Carrier support materials that can be used in this invention vary widely depending on the nature of the imageable layer and the intended use. These may include paper, cloth, cellulose esters such as cellulose acetate, cellulose propionate, and cellulose butyrate, and other plastic compositions and other organic film-forming compositions such as polyimide. The support can contain additives therein or on its surface to facilitate release of the imaged film from the carrier support during transfer. A typical example of such an additive is a silica coating as a roughening agent. Preferred carrier supports are materials commonly used in graphic arts and decorative applications. These range from paper to heavy cardboard;
Examples include polyesters of glycol and terephthalic acid, vinyl polymers and copolymers, polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate and polyvinyl chloride films or sheets. Opaque as well as transparent supports can be used. If exposure of the photosensitive film through a carrier support is desired, a carrier support that is transparent to the active wavelength of light for the color-forming reaction can be used. This will result in a symbol that can be read correctly after transcription. Image reversal is usually overcome by the correct use of photographic negatives when directly exposing the coating. The carrier support should be inert to the contacting photosensitive and binder components of the coating formulation as well as other substances such as solvents and plasticizers that may be present. The formulation for the imageable layer can be applied to the carrier support using spraying or other convenient means. Typical equipment for wet film application can be used, such as nip fed three roll reverse coating heads, gravure coaters, trailing blade coaters, knife over rolls, four roll pan heads and Meyer bar coating heads. Removal of the solvent can be carried out at room temperature, under room temperature vacuum, or by forced air solvent evaporation or at elevated temperatures. Radiant heating should generally not be used to dry compositions containing IR-sensitive ingredients. The dry film thickness of the imageable layer should be 0.2 to 0.8 mil, and preferably about 0.2 to 0.5 mil. Coatings below this are difficult to coat uniformly and often lack sufficient opacity. On the other hand, thicker coatings reduce the detectable difference in diffuse reflection density. After coating the film on the carrier support, the coated surface exhibits a substantially uniform diffuse reflection that is usually attributed to the pigment dispersed in the coating. Formation of the marks requires exposure to appropriate radiation to produce the desired pattern during coating. Depending on the nature of the light source used and the nature of the pattern-forming optics, the exposure time is usually a fraction of the time.
Varies from seconds to minutes. An appropriate UV or IR radiation source is chosen for the radiation-sensitive component used. Although U.S. Pat. No. 3,639,762 describes the selection and use of radiation sources for various light-sensitive mark-forming components, the polymeric binders used in the present invention transmit effective radiation wavelengths. Many combinations are suitable for the present invention.
Preferably for use with the preferred UV sensitive coating compositions described above, from about 200 nm to about
It is a UV light source that provides radiation in the 420 nm range. The optical system used should be capable of forming the specific pattern desired, for example the UPC bar representation. Radiation is focused onto the surface of the imageable layer to mark it with an appropriate representation. After exposure to radiation, the mark and remaining radiation-sensitive component can be fixed by chemical or thermal means best suited to the particular composition used. After imaging in the desired pattern using actinic radiation, the image-containing film is transferred to a receptive support in a manner that promotes adhesion to the receptive support. This can be accomplished by bringing the film into contact with a receptive support and heating it.
Alternatively, the film can be heated before, after, or before and after contact with the receptive support. Heating can be direct, for example by dielectric heating or infrared heating. However, indirect heating, for example by heating the receptive support or both the receptive support and the carrier support, is usually more convenient. The film surface in contact with the carrier support can be kept at a lower temperature and the film surface can be raised to the tack temperature by heating only the receptive support. Tack temperatures typically range from 40°C to 220°C depending on the fabric and transfer film composition. When the adhesive bond of the film to the carrier support is weak, such as the carrier support's commercially available release paper, the adhesion of the film to the receptive support is determined by the thermoplastic binder providing a good bond to the receptive substrate. It occurs when the softening occurs to just enough depth to produce results. Transfer to a receiving support with a release of the carrier support can occur at the tack temperature or upon subsequent cooling to a lower temperature. The pressure applied to the composite should, of course, be sufficient to cause intimate contact between the film layer and the receptive support. After application of the receptive support, the carrier support is generally removed. However, for certain radiation-sensitive component and carrier support combinations, advantages may be realized by keeping the carrier in place. For example, the carrier film can be chosen to have an absorption in the same wavelength range as the radiation-sensitive component of the film layer and thus protect the mark from activating radiation. For example, the "Kapton" polyimide film described in GB 903271 absorbs blue and UV light. Its retention on the final mark surface may therefore eliminate the need for fixatives commonly used in the exposure of radiation-sensitive compositions. The final use of an object marked with a Universal Product Code illuminates the mark with inspection light that is essentially the wavelength of light absorbed by the colored substance and reflected by the pigment, and the wavelength of the inspection light is and reading the information conveyable by the predetermined width and position of the exposed and unexposed portions by diffuse reflection scanning means sensitive to . Universal product code systems typically read code representations by a high speed scanner using a laser light source, such as a red helium-neon laser. However, other sources can be used, such as an incandescent lamp, with an optical filter placed between the inspection light source and the mark it illuminates, or between the mark and the detector of diffusely reflected light. Known diffuse reflection scanning means suitable for use in the present invention include rotary scanners that rotate a very narrowly focused beam of light from a laser, mercury vapor lamp or incandescent lamp at a speed of 1000 revolutions per second or more; These include fixed position photocells that scan marks while moving along a fixed path. In some applications, a newly developed hand-held scanner in the form of a pen or wand can be used to record scanned information directly into a portable cassette for storage prior to entry into a computer system. The transfer sheet of the present invention provides a convenient method for applying labels or other marks to a wide variety of surfaces. These products combine various properties that were previously thought to be incompatible in this type of label. Because of the required pigment concentration, this transfer sheet opaques the surface of the object to be marked. At the same time, this pigment does not opaque the mark itself. The transfer sheet of the invention can optionally be irradiated from the back side for the formation of marks. And the label does not need to be removed from the carrier support before being adhered to a new substrate. The readability of marks imparted to the newly exposed surface of the imageable layer by transfer is particularly unexpected. It is generally expected that opacification of this layer to the extent that it obscures the optionally applied colored surface will also obscure the marks themselves on the final upper surface of the layer. The combinations of the present invention are generally applicable as pigmented coatings to a wide variety of surfaces;
This in turn provides a reflective background and a mark created with less reflective illumination. Use of the mark compositions presented herein produces images with good resolution and better stability compared to previously used mechanical printing system images. The accuracy achievable with the compositions of the invention makes it possible to reduce the size of UPC representations by 25%, as ink spreading problems are avoided. Additionally, the restriction imposed by mechanical printing systems that the bars must be in the printing direction is also eliminated. These factors give greater freedom in packaging design. The transfer sheet of the invention makes it possible to mark independently the color and other optical properties of the surface of the object to be marked. They have mirror-reflective metal can surfaces, light-transparent glass bottles, and dark or highly pigmented surfaces that can have substantially the same color as can be developed by the radiation-sensitive components used in the present method. It is suitable for marking the surface of colored products and reading the representation. No special selection or modification of the product surface is required. The transfer sheets of the invention are particularly well suited for marking film-wrapped products, such as commercially packaged fresh meat, fruits and vegetables, with inscriptions fixing their content and price. The present invention is a UPC
In addition to bar code representations, other representations involving two parts of different reflections and alpha-abbreviation applications can also be used. An advantage of the mark transfer sheet of the present invention is that it provides printer design flexibility with improved performance characteristics of the transfer pattern. For example, the photosensitive substrate of the present invention can be applied to a continuously moving belt, imaged, and transferred to a receptive surface to produce a human/machine readable object such as a glass bottle, metal can, or the like. Other advantages of the present invention occur when the supported imaged photosensitive substrate is adhered to the object that is intended to be marked. This is because the film support can provide protection against environmental effects such as chemical spills, moisture, light, etc. that can be destructive to the integrity of the label. Furthermore, representations so protected cannot be changed, thus providing a higher level of stability. The present invention is illustrated by the following specific examples, in which parts and percentages are by weight unless otherwise indicated. Example 1 A mark composition was prepared by mixing the following ingredients. Binder Cellulose acetate butyrate 10.28g Pigment Rutile type titanium dioxide (manufactured by DuPont “Ti
-Pure"R, titanium dioxide distillate 1.37g Coating solvent Acetone 80.14g Photosensitive component plasticizer N-ethyl-p-toluenesulfonamide (manufactured by Monsanto Co., Ltd. "Santicizer-
3) 2.225g Anion source Dodecylbenzenesulfonic acid (Richonic Acid, manufactured by Richardson)
0.856g Photooxidative leuco dye Tris(N,N-diethylamino-o-tolyl)methane 0.154g Photooxidative component 2,2'-bis(o-chlorophenyl)-4,4',5,5'- Tetrakis (m-
methoxyphenyl)1,2-biimidazole
0.7153g Hydrogen donor Triethanolamine triacetate 1.882g Oxidizing agent Pyrenequinone (1,6- and 1,
8-1:1 mixture of isomers) 0.0061g Oxidized component 9,10phenanthrenequinone
0.10g Plasticizer Polyethylene adduct of o-phenylphenol [average molecular formula C ₆ H ₅ C ₆ H ₄ O
(CH ₂ CH ₂ O) _{2 .23} H] 1.951 g This composition was sprayed onto a commercially available yellow polyimide film as "Kapton" Type H from DuPont. The mark composition was dried to produce a 0.45 mil thick film coating containing 0.1 g of pigment per square foot. This coating made the yellow film opaque and white. A photographic negative of the UPC representation is placed in contact with this coating and has a peak at approximately 365 nm.
A blue-white UPC mark was produced by exposure to UV light (2.75 milliwatts/cm ² ) for 1 minute. When viewed through the polyimide film, this UPC mark consisted of a green-blue line on a yellow background. The carrier film and film coating were temporarily adhered to a black plastic bottle cap by heating the film coating to about 70°C to soften its thermoplastic binder component and contacting it with the bottle cap. The green-blue and yellow UPC mark obscured the black color of the bottle cap and remained unchanged even after several days of exposure to sunlight. This representation has excellent photostability, and it could be successfully read by a red helium-neon laser scanning system at a supermarket checkout counter. Example 2 The general procedure of Example 1 was repeated except that a clear "Mylar" polyester film carrier support was used in place of the polyimide film. Coating a film with a marking composition and exposing it to patterned UV light produces a blue-white UPC.
Marks can now be viewed directly or through film. Marking and protection polyester film carrier support Example 1
When glued to a black bottle cap, a blue-white mark became visible. This representation could be photofixed by exposure to visible light, for example on a supermarket shelf, and this could be read by laser scanning. This mark, which is more susceptible to fading over time than the polyimide film protection mark of Example 1, is particularly useful for marking fast moving perishable items such as bread products. Example 3 A mark composition similar to that described in Example 1 was prepared, except that titanium dioxide pigment was present in the amounts indicated for the five samples listed in the table. Also listed in the table is the amount of pigment per square foot of light sensitive film coating. After exposure as described in Example 1, the values of light background reflectance R _L (%) and dark background reflectance R _D (%) were measured on a Macbeth densitometer and print contrast. UPC Symbol Specification
(May 1973) is determined using the formula PCS=R _L % - R _D %/R _L %.

TABLE Imaged film samples can be adhered to various substrates such as black plastic bottle caps, glass and metal reflective surfaces such as aluminum foil and transparent packaging films and the resulting composites (a) to (d) can be successfully machine scanned. Complex (e) is not successfully machine scannable but can be read by eye. Example 4 (Release coating) A coating of the composition described in Example 3, but with a _TiO2 content of 17%, was applied with a 0035 wire rolling pin onto a release paper [product of Ludlow Paper Co., USA].
Apply at a coating weight of g/ft2. This paper coating has high contrast
Exposure to ultraviolet light through a photographic negative of the UPC representation produces an intense blue-white image. this image
Thermal transfer onto a black printed card used for paint coverage measurements with a reflection density of 2.0. The combination of light-sensitive coating and black card gives a high contrast image with a dark reflection of 4 and a bright reflection of 29 (corresponding to an optical density of 1.3 and 0.5, respectively). By the formula described in Example 3
A PCS of 0.86 is determined. This image can be machine scanned.

Claims (1)

Claims: 1. comprising an imageable layer on a carrier support and which imageable layer (a) when exposed to radiation detects a diffuse reflection density between the exposed and unexposed areas; a radiation-sensitive composition capable of forming a colored substance capable of absorbing at least a portion of the wavelengths of light in the visible spectrum when exposed to radiation, present in an amount sufficient to produce a possible difference; b) a pigment present at a density of about 0.05 to 0.34 grams per square foot capable of diffusely reflecting the wavelength of light absorbed by the colored substance; and (c) forming a radiation-transparent colorless polymeric film. A mark transfer sheet containing a thermoplastic binder. 2. The mark transfer sheet of claim 1, wherein the imageable layer has a thickness of about 0.2 to 0.8 mil. 3. The mark transfer sheet of claim 2, wherein the imageable layer has a thickness of about 0.2 to 0.5 mil. 4. The mark transfer sheet of claim 1, wherein the radiation-sensitive composition produces a colored substance when exposed to ultraviolet light. 5 Colored substances are fixed when exposed to light;
The mark transfer sheet according to item 4 above. 6. The mark transfer sheet according to item 1 above, wherein the pigment is a heavy metal oxide. 7. The transfer sheet according to item 6 above, wherein the pigment consists essentially of _TiO2 . 8. The mark transfer sheet of claim 1, wherein the carrier support exhibits sufficient UV absorption to prevent imaging of the radiation-sensitive component through the carrier support. 9 The thermoplastic binder contains at least about 1% by weight of the
The first one contains a UV ray absorber.
Mark transfer sheet as described in section. 10 (a) on the carrier support: (1) radiation present in an amount sufficient to produce a detectable difference in diffuse reflectance density between the exposed and unexposed portions when exposed to the radiation; a radiation-sensitive composition capable of forming a colored substance capable of absorbing at least a portion of the wavelengths of light in the visible spectrum when exposed to light; (2) present at a density of about 0.05 to 0.34 grams per square foot; and (3) a radiation-transparent, colorless, polymeric film-forming thermoplastic binder. (b) exposing the image layer to patterned radiation at wavelengths to which the radiation-sensitive composition is sensitive to produce a detectable difference in diffuse reflectance density between the exposed and unexposed portions; Approximately 40 to become adhesive
(c) contacting the outer surface of the imageable layer with a receiving support that is more adhesive to the imageable layer than to the carrier support, and optionally (d ) A method of marking an object by separating the carrier support from the imageable layer. 11. The method of paragraph 10, wherein the imageable layer has a thickness of about 0.2 to 0.8 mil. 12. The method of claim 10, wherein the imageable layer has a thickness of about 0.2 to 0.5 mil. 13. The method of paragraph 10, wherein the radiation-sensitive composition produces a colored material upon exposure to ultraviolet radiation. 14. The method of claim 14, wherein the colored substance is fixed by exposure to light. 15. The method according to item 10 above, wherein the pigment is a heavy metal oxide. 16 Said first pigment, wherein the pigment consists essentially of TiO ₂
The method described in item 0.