Nova Patents
US3136637A

Presensitized lithographic light-sensitive sheet construction

Abstract

This record has no abstract on file.

US3136637A, drawing sheet 1
Sheet 1 of 6

Term

Term ended

Expired 9 June 1981, 45.3 years ago.

  1. Priority and filed
  2. Granted
  3. Expired
  4. Today

8 claims: 6 independent, 2 dependent

  1. 1
    Having now described an embodiment of my invention . in a general way the same will now be illustrated, with the aid of the following non-limiting examples. In the examples the concentrations of all coating solutions or compositions are based on weight of material in grams dissolved or dispersed per 100 milliliters of total volume of solution and/or dispersion. Example I A solution is first prepared by dissolving polyvinylformal resin in ethylene chloride solvent to yield approximately an 8 percent solution. A suitable polyvinylformal resin has a polyvinyl alcohol content of from about 7-9 .percent and a polyvinyl acetate content of from about 9.5-13 percent, and a 5 percent ethylene chloride solution thereof has a viscosity of about 40-60 cps. at 20° C. A phthalocyanine pigment, e.g., “Monastral Fast Blue BC” available commercially from the Du Pont Company, is then ball milled into the 8 percent resin solution on the basis of 1 part pigment per 4 parts polyvinylformal resin, by weight. The resulting composition is then diluted with ethylene chloride to a 2½ percent solids concentration, filtered, and transferred to a coating tank. The area around the coating equipment is well vented to exhaust solvent vapors. A continuously formed presensitized plate construction is then coated under subdued light, e.g., yellow light, with the coating composition previously prepared. The presensitized plate construction is manufactured continuously 65 in accordance with the specific example of Jewett and Case Patent No. 2,714,066. Briefly, such lithographic plate structure is prepared by cleaning a smooth-surfaced aluminum sheet, for example with trisodium phosphate followed by treatment with nitric acid solution and rinsing 70 in water. The:sheet is then treated with an aqueous silicate solution and washed clean of any remaining water: soluble materials. An initially water-soluble light-sensitive diazo resin, e.g., a p-diazodiphenylamine-formaldehyde resin, is then coated over the silicate treated surface. 75 3,136,637 ..... . . 5 exposure of the plate, the resin overcoating nevertheless is bonded extremely well to the underlying in situ insolubilized sensitizer. This is further evidenced by the fact that when the image is being processed with a solvent solution for the resin layer, the resin layer breaks away cleanly and sharply at the line of demarcation between the image and non-image areas and is readily removed from the latter. Although I do not know with exactness just why this occurs, and without intending to be limited by any theories, I hypothesize that there is some physical and/or chemical interaction at the interface of the light-sensitive material and the resin overlayer which occurs when the light-sensitive material is exposed. Then when the solvent, which softens the overlayer, is applied it permeates the thin overlayer film and effectively undermines the overlayer in the nonimage areas by the action of the solvent on the unexposed sensitizer. ' It is preferable to incorporate a pigment or dye in the resin overlayer. Thereby the image is rendered visible to the eye as the background is removed during the processing. Further, ! have found that the presence of a pigment seems to facilitate a clean sharp break at the line. of demarcation between the image and non-image areas. Of course, the pigment employed must be such as to transmit the actinic light which must pass through the resin overlayer in order to strike the underlying light' sensitive resin materials. Ordinarily the amount of pigment employed with the resin is maintained at a level sufficient to provide a clear contrast between image and background when the sheet is processed. This amount is usually something less than about 50 percent by weight of the resin, 25 percent being preferred in the printing plates hereof. . In the preceding example, the. coating weight of the pigmented polyvinylformal resin overlayer was about 50 mg./ft. 2 . Although I prefer to maintain a coating weight of from about 50-70 mg./ft. 2 when employing this overlayer composition, satisfactory plate structures can be prepared where the coating weight varies from about 10-120 mg./ft. 2 . In general, thinner coatings tend to diminish somewhat the press life of the plate, while very heavy coatings may yield an inferior image structure. This latter effect arises from the fact that a very heavy film may not fracture sharply and clearly at the line of demarcation between the image and nonimage areas yielding a distorted printing image. In . printing line copies, the perfection of the image structure is not as important as when printing fine half-tones. . Thus, particularly where extremely great press life is desired, it may be desirable to employ somewhat heavier coatings in printing operations involving the former than can be satisfactorily used in half-tone work. On the other hand, I have made successful plates in accordance with the present example where the coating weight of’ the polyvinylformal resin was as low as about 3.6 mg./ft. 2 while yet providing significant improvement in press life over a corresponding plate wherein the diazo resin image is unreinforced. Significantly, the thickness of a polyvinylformal resin coating having a weight of about 3-4 mg./ft. 2 is in the order of only about one millionth of an inch, i.e., 0.001 mil. A rather heavy coating weight of 120 mg./ft. 2 has . a thickness in the order of about four one-hundred-thousandths of an inch, or 0.04 mil. Thus, in any event the resin overcoatings in the structures hereof are quite thin. While the present example has illustrated the use of polyvinylformal as the resin overlayer, many other organophilic hydrophobic water-insoluble solvent-softenable organic resin compositions are also suitable. These . include various vinyl polymers, such as polyvinylbutyral, polymethylmethacrylate, polystyrene, polyvinylchlorideacetate, polyvinyl acetate, polyethylene;epoxy resins;condensation polymers such as polyester resins exemplified by alkyd resins, polyamide resins, phenolaldehyde resins, urea-aldehyde resins;other polymers such as cel6 lulose acetate butyrate, polyalkylene-polysulfide resins, various organic silicon containing resins, etc. Various rubbery compounds such as Buna-N, Buna-S, neoprene and natural crepe are suitable. Natural occurring res5 inous materials such as shellac can also be used. Various compatible mixtures of the above mentioned and other similar and equivalent resin materials can be used.. The processing solutions to be used in processing the various sheet constructions hereof, after they have been 10 exposed, should have certain characteristics. Preferably the processing solution exerts a slight but not vigorous solvent or swelling action on the overlayer composition, is an active solvent for the unreacted sensitizer, but has little or no effect on the light-reacted sensitizer. Ordi15 narily a mixture of two or more (preferably miscible) liquids is necessary to provide a processing solution having these desired characteristics. However, an operable processing solution can be found for any combination of sensitizer and resin overlayer employed, although some 20 amount of rudimentary experimentation may be necessary. As a general rule, a suitable processing solution can be obtained by combining a first component which . exerts at least a partial solvent or swelling action on the resin composition with a second component, miscible 25 with the first, which is not a solvent for the resin composition, one of the two being a solvent for the unreacted sensitizer. Neither of the two liquids, nor the mixture thereof, should be a solvent for the light-reacted sensitizer. If the first solvent component is an active solvent 30 for the overlayer resin, it should be diluted by the second component to an extent where its solvent action in combination in the mixture is not vigorous. While suitable processing solutions can be obtained as just indicated, other processing solutions, which can be 35 arrived at by judicious selection, may also be suitable. The isopropanol-water processing solution of Example I is such an instance, neither the water nor isopropanol by itself exerting any substantial solvent action on the polyvinylformal resin. 4 θ The following table will further illustrate the solvent from which various resin overcoating compositions are applied, and an appropriate processing solution therefor in a plate construction hereof , containing the diazo resin of Example I. Where indicated in processing solutions, 45 ratios are by volume. 3,136,637 While Example I is directed to a presensitized metalbacked printing 'plate, printing plates having backings other than metal can also be prepared in accordance with the present invention. The following example illustrates a papcr-b.acked plate. 5 ' Example II _ A light-sensitive resin, which is initially soluble in an organic solvent, is first prepared. An aqueous solution of the p-diazodiphenylamine-formaldehyde resin utilized in the plate structure of Example I, and described with 10 specificity in Jewett and Case Patent No. 2,714,066 is added to a chemical equivalent, based on the resin content of the solution, of p-toluenesulfonic acid. By a reaction between the resin and the acid the p-toluenesulfonate salt of the resin is formed and oils out of the aqueous medium 15 as a viscous tar-like resinous material. The reaction product is separated by decanting and washed with water. On standing, it dries to a glassy solid amber-colored state. It readily dissolves in methanol, but is only very slightly soluble in most other common organic solvents and in water;Upon exposure en masse to actinic light it becomes insoluble to methanol and turns slightly blue-green from its initial amber color. When exposed in thin films, the characteristic blue-green color is barely visible or in very thin films is not visible at all. A 2 percent methanol solution of the light-sensitive resinous product just described is prepared. A sample of 45 lb. vegetable parchment, available from the West Carrollton Parchment Company, of West Carrollton, Ohio, is sensitized with the previously formed ’ light-sensitive resin solution by wiping the surface of the parchment with a cotton cloth saturated with the resin solution. The treated surface is then allowed to air-dry. The thus sensitized surface of the parchment is then overcoated by coating the surface with the pigmented polyvinylformal-ethylene chloride solution described in Example I, at a dry coating weight of about 30 mg./ft. 2 , the thickness of the overcoating being about 0.01 mil. The overcoating is then air dried. Upon exposure of the plate through a transparency as outlined in Example I, followed by processing with the isopropanol-water solution in the manner there described, an image results which is a clear, accurate and definite representation of the original. Upon being mounted on a lithographic press, it is found to print clean clear copies. It will be seen that the light-sensitive material employed in Example II is of different character than the _ water-soluble light-sensitive resin employed in Example I. A particular advantage in the present invention resides in that virtually any initially soluble light-sensitive material, which insolubilizes upon exposure, can be employed in conjunction with the resin overcoatings hereof so long as the latter are capable of being coated on, i.e., not repelled by, the light-sensitive material. The in situ created adhesion between the light-sensitive layer and the resin overlayer, when the former is exposed and insolubilized, appears to occur largely irrespective of the particular type of light-sensitive material employed. Since the resin overlayer provides the printing surface, lightsensitive materials may now be employed in lithographic plates, even though in and of themselves, they inadequately provide a printing image. Stability of the sensitizer can be high so that the base sheet coated therewith is “presensitized,” i.e., the sensitized sheet can be stored for substantial periods of time with the sensitizer remaining stably soluble and light-sensitive. The light-sensitive diazo resins described in the preceding examples are highly stable and serve as preferred sensitizers in the sheet constructions hereof. It is noted that the various processing solutions noted for the various resin overlayer compositions in the preceding table can also be employed for those respective compositions in plate structures containing the sensitizer of the present example. 8 . Although the previous examples have dealt with the lithographic printing art, the present invention has marked utility in fields diverse from the printing field. In many fields of endeavor it is desired to have some pictorial representation or message adhered on a backing sheet or plate. For example, in the preparation of labels, particularly metal labels, templates, registration tags, signs, etc. a message of some sort is applied to a backing. In so-called “printed circuits” a design, often complex and irregular, formed of conductive metal is adhered to a non-conductive backing. Returning momentarily to the printing field, in the preparation of photoengravings for use in letterpress printing, an image of an acidresistant material must be adhered to the surface of the plate. It has long been desired to utilize photographic techniques to bring out a message or pictorial representation on backing structures in the above-mentioned and other fields. However, this has been largely impractical heretofore because the light-sensitive materials which form the image or pictorial representation (the background for such image or representation where the resulting image is negative) have not had suitable physical characteristics for the conditions under which they would be used. By the present invention I am able to provide photographically an image area with any of widely diverse physical qualities appropriately selected with the particular end use in mind. The following examples illustrate a few of these, the next example illustrating the use of my inven30 tion in providing a novel “printed circuit” board. Example III The copper surface of a construction, consisting of a one mil layer of copper adhered to a non-conducting 35 phenolic resin sheet, was cleaned with scouring powder. Said surface was then coated, by dip-coating techniques, with a diazo-p-toluenesulfonate sensitizer resin described in Example II. Upon air drying, a comparatively heavy diazo resin coating resulted which was clearly visible by 40 its slight yellow tinge. Through dip coating, the light sensitized base was then overcoated at a dry weight of 150 mg./ft. 2 with a 10 percent toluene solution of homopolymeric polystyrene, “Styron 666” available from the Dow Chemical Co. The coating was air dried. The 45 board then was exposed through a suitable negative of the circuit layout desired. The resin surface was then wiped and lightly rubbed with a cloth wet with methanol, whereupon the resin overlayer and unreacted diazo sensitizer were removed from the non-image areas, the resin 50 overlayer breaking away cleanly at the lines of demarcation between image and non-image areas. When the resulting sheet was placed in a solution of 40% ferric chloride at 80° C., the copper etched away in the non-image areas from which the polystyrene coating 55 had been removed. However, no undesirable etch of the copper in the image areas, protected by the polystyrene overcoating, occurred. The remaining copper was found to be patterned in the correct form of the original to serve as a printed circuit. On the other hand, when the 60 polystyrene layer is omitted the diazo resin itself does not effectively resist etching in the image areas. Polystyrene was chosen in the above example because of its insensitivity to water and acid. Similarly, a nonoxygenated resin such as polyvinylchloride or a rubber ®5 composition such as Buna-N or neoprene can be used. In other etch resist applications it might be desirable to use a fusible heat curing resin, such as an epoxy resin, which ’ is cured before etching the plate. In employing a curable . ' resin system care should be taken to select a system which ‘° will not undesirably degradate the light-sensitizer. The next example illustrates the preparation of a metalbacked label in accordance with my invention. Example IV 75 A coating composition was first prepared.by dissolving 3,136, 5 parts by weight of polyethylmethacrylate resin, available from the Du Pont Company as “Lucite 42,” in 100 parts of methyl ethyl ketone following which 1.5 parts of a green phthalocyanine pigment (Du Pont “Monastral Fast Green G Powder”) was milled into the solution. 5 The composition was then coated over the diazo resin surface of a presensitized lithographic plate like that employed in Example I, prepared in accordance with Jewett and Case Patent No. 2,714,066. A dry coating weight of . 135 mg./ft. 2 provided good color depth. After the resin To overlayer had been air dried the sheet was exposed to actinic light through a transparency of the desired message. The image was then processed with a solution of isopropanol-water (2:1 by volume) to yield a reverse green colored image having pleasant contrast with the 15 aluminum. The image showed excellent durability to weathering. Thus sheet constructions containing images of a wide variety of colors can be made, in accordance with the procedures hereof, by incorporation of suitably colored 20 actinic-light transmittable pigments into the resin overlayer. Combinations of such pigments can be used, e.g., where a resulting black color is desired. It is to be noted that the exposure time may vary with the color and type of pigment selected. For example, somewhat longer ex- 25 posure times may be required in the case of yellow and red than with other pigments. My invention is also valuable in proofing color separation negatives preparatory to color lithography. In color printing, color separation negatives are prepared photo- 30 graphically in three or more colors. Each color separation negative is used to prepare a printing plate from which reproductions are printed in sequence using appropriately colored inks. In proofing the color separation negatives by conventional methods, it is necessary 35 to prepare all of the printing plates, to set up the printing press for operation, and then actually to print all of the colors in the proper sequence and registration. All this is necessary to determine whether the original color separation negatives were true and accurate. Such conventional proofing procedures are extremely costly and time consuming. With each correction, one or more new plates has to be prepared and the entire operation repeated until the desired result is achieved. In accordance with my invention, it is possible to complete the color proofing to a degree at least equal to that obtained by conventional proofing procedures without having to prepare a printing plate and without having to run a single reproduction. In so doing, I provide a light-sensitive transparent sheet construction in each of the colors to be printed. Each of the sheets is exposed through its respective color negative and then processed, by which the color in the non-image areas is removed. Respectively colored sheets result, each of which is appropriately colored in its image areas and colorless and transparent in the non-image areas. In proofing it is only necessary to superpose the resulting transparencies in registry on a white background, whereupon an accurate color proof of the original negatives results. The entire proofing procedure can be accomplished in a matter of a few minutes. Should a correction of one or more of the color negatives be desired, after viewing the composite proof, a corrected negative can be prepared, a new proof sheet of the negative exposed and processed and then the composite re-proofed. It is thus unnecessary to prepare the plates, to set up presses and actually to print reproductions until the correctness of the negatives has been verified. In preparing light-sensitive sheet constructions for use in color-proofing, I employ a colorless transparent backing sheet for the light-sensitive layer and resin overcoating, which preferably is dimensionally stable. The overcoating in each sheet contains the same respective pigment, or equivalent thereof, as that contained in the printing ink. The amount of pigment contained per unit 10 area is adjusted to provide the same color-density to be printed from the respective inks. Thus very accurate color proofs result. The following example illustrates the preparation of a color separation proof hereof. Example V In accordance with Palmquist Patent No. 2,786,778, a one mil thick film of biaxially-oriented polyethylene terephthalate (“Mylar”) is vapor coated to provide thereon a thin, invisible hydrophilic treatment or layer of silicon monoxide. The silicon monoxide surface is then coated with the diazo resin solution described in Example Π. The coating weight is quite light so that, upon exposure, no visible blue color will be imparted by the diazo so as to disturb the delicate color balance required in color proofing. Preferably, the amount, of diazo applied is just under that which would impart a visible color effect upon exposure. The diazo surface is then overcoated with a polyvinylformal containing a suitable transparent pigment, in a manner similar to that described in Example I. Since color is of primary importance the pigment loading will be most useful in the range of 30 to 50 percent of total solids in the overlayer. The coating weight required will be dependent upon the color density desired. For use in duplication of 3-color process printing reproductions, reflective optical densities measured through complementary color filters will be in the range of 1.0 to 1.5, and the respective coating weights will be adjusted to attain that range. A coating weight of 60 to 120 mg./ft. 2 ordinarily is an optimum weight depending upon the specific desired color levels. Suitable pigments for use in each of the three color constructions are: cyan, e.g., “Monastral Fast Blue BC,” available from the Du Pont Company;magenta, e.g., “Alkali Resistant Red RT-539-D,” available from the Du Pont Company;and yellow, e.g., “Benzidine Yellow Dye D-2840,” available from the SherwinWilliams Company. ' .. Since a transparent backing is employed on the light40 sensitive sheet hereof a black backing is required behind the light-sensitive sheet during exposure in order to reduce halation in the exposed image. In use, each of the three color sheets is exposed through its corresponding color separation negative. The sheet 45 is then processed, as previously described, with a solution of isopropanol-water in a 2:1 ratio to remove the pigmented overlayer from the non-image areas to leave the latter clear and colorless. Thereby an image is defined which corresponds to the single color proof made 5θ by mounting the proper plate on a press and printing. When the three proofs are superposed in registry on a white background an accurate proof is obtained of the 3-color print which would result from forming printing plates of the negatives and printing from those plates. 55 Oyerlayers which are opaque, i.e., wherein the pigment in the overlayer is opaque, can also be used in structures hereof employing transparent backings. In such construction the sheet is exposed from the reverse side (through the transparent backing sheet). Such a con00 struction is desirable, for example, in providing the black print for proofing 4-color process printing. Carbon black is a suitable opaque pigment in this construction. A construction of the present example coating, opaque black pigment is also useful in preparing a positive 65 transparency from a negative transparency or vice versa without necessity of employing the usual photographic film. Although in the previous examples various specific organic hydrophobic organophilic water-insoluble sol70 vent-softenable resin overlayers have been disclosed, it is to be understood that many of the compositions disclosed in the respective examples can be used in the constructions described in other examples. The selection of the appropriate overlayer composition will be gov75 erned primarily by the final properties desired of the .3,136,( image-areas, as respects the end use to which the exposed and processed sheet structure hereof will be put. Herein, I have provided novel means for providing an accurate pictorial representation or message, on a backing sheet,' wherein the character of the pictorial representa- 5 tion or message, or the background thereof, can be widely varied to suit the particular end use desired of the product. Although the present invention has special significance in connection with metal-backed presensitized lithographic printing plates, it has wide and marked util- iq ity elsewhere.. Herein my invention has been described with the aid of various illustrative examples. However, my intent is not to be limited thereby. Rather, I intend to be limited only by the disclosure taken as a whole, including the appended claims. 15 What I claim is : . 1. A presensitized lithographic sheet comprising a base sheet, a soluble light-sensitive diazo resin sensitizer layer overlying at least , one surface of said sheet in contact therewith, and over and in direct contact with said sensi- 20 tizer layer a thin continuous hard durable abrasionresistant and wear-resistant coating composed predominantly of an organophilic hydrophobic water-insoluble solvent-softenable resinous polymer, said coating having a thickness of at least about 0.001 mil and containing 25 not more than about 50 percent by weight of pigment;said sensitizer layer upon exposure of the sheet to actinic light through a transparency reacting in the exposed areas and becoming insolubilized and firmly bonded to said surface of said base sheet;said abrasion-resistant and 30 wear-resistant coating being isolated from bonding contact with said base sheet and being intimately associated with and . adherently bonded to said sensitizer layer, and further remaining abrasion-resistant and water-insoluble upon subjection thereof to the products evolved by said 35 sensitizer upon exposure of said sheet to actinic light, and being firmly bonded in said exposed areas, while being readily removable with unexposed sensitizer in areas not light-exposed. .
  2. 3
    A presensitized light-sensitive sheet construction comprising an aluminum sheet having a well-bonded treatment on one surface thereof, a soluble light-sensitive 45 diazo resin material over and in contact with said surface treatment, and a thin continuous abrasion-resistant coating composed predominantly of water-insoluble polyvinylformal resin overlying and in contact with said diazo resin layer;said coating of polyvinylformal resin 50 having a thickness of at least about 0.001 mil, being transparent to actinic light, containing not more than about 50 percent by weight of pigment, and being isolated from bonding contact with said aluminum sheet and being intimately associated with and adherently 55 bonded to said diazo resin layer;said coating further remaining abrasion-resistant and water-insoluble upon subjection thereof to the products evolved by said diazo resin upon exposure of said sheet construction to actinic light, said treatment being characterized in that it causes 60 an in situ light-reacted diazo resin firmly to bond to said aluminum sheet.
  3. 5
    A plate suitable for use in planographic printing and related uses comprising an aluminum sheet having on at least one surface thereof an extremely thin layer 70 of the reaction product of said aluminum sheet and an aqueous solution of an alkali metal silicate, providing a permanently hydrophilic surface, a thin coating of a water-soluble light-sensitive diazo resin over and in contact with said hydrophilic surface, and over and in con- .tact with said, diazo, resin coating a thin continuous pigmented coating of water-insoluble polyvinylformal resin in an amount of from about 50-70 mg./ft. 2 , the amount of pigment in said coating not exceeding about 25 percent by weight thereof;said diazo resin being characterized that, upon exposure of the.plate to ultra-violet light through a transparency, it will react in the exposed portions to form an image of water-insoluble, hydrophobic and organophilic material which is tightly bonded to said permanently hydrophilic, surface;said polyvinylformal resin coating being transparent to actinic light, being isolated from bonding contact with said aluminum sheet and being intimately associated with said diazo resin and adherently bonded thereto, and further remaining waterinsoluble and organophilic upon subjection thereof to the products evolved by said diazo resin upon exposure of said plate to actinic light.
  4. 6
    A presensitized lithographic plate comprising a metal base sheet, a soluble light-sensitive diazo resin sensitizer layer overlying at least one surface of said sheet in contact therewith, and over and in direct contact with said sensitizer layer a thin continuous hard durable abrasion-resistant and wear-resistant coating composed predominantly of an organophilic hydrophobic waterinsoluble solvent-softenable resinous polymer, said coating having a thickness of at least about 0.001 mil, being transparent to actinic light and containing not more than about .50 percent by weight of pigment;said sensitizer layer upon exposure of the sheet to actinic light through a transparency reacting in the exposed areas and becoming insolubilized and firmly bonded to said surface of said base sheet;said abrasion-resistant and wear-resistant coating being isolated from bonding contact with said base sheet and being intimately associated with and adherently bonded to said sensitizer layer, and further remaining abrasion-resistant and water-insoluble upon subjection thereof to the products evolved by said sensitizer upon exposure of said plate to actinic light, and being firmly bonded in said exposed areas, while being readily removable with unexposed sensitizer in areas not light exposed. Ί. A presensitized metal lithographic plate comprising an aluminum sheet having on at least one surface thereof an extremely thin layer of the reaction product of said aluminum sheet and an aqueous solution of an alkali metal silicate, providing a permanently hydrophilic surface, a thin coating of a water-soluble lightsensitive diazo resin over and in direct contact with said hydrophilic surface, and over and in contact with said diazo resin a thin continuous hard durable abrasionresistant and wear-resistant coating of an organophilic hydrophobic water-insoluble solvent-softenable resinous polymer, said coating having a thickness of at least about 0.001 mil, being transparent to actinic light and containing not more than about 50 percent by weight of pigment;said diazo resin being characterized in that, upon exposure of the plate to ultraviolet light through a transparency, it will react in the exposed portions to form an image of water-insoluble material which is tightly bonded to said permanently hydrophilic surface;said abrasion-resistant and wear-resistant coating being transparent to actinic light, being isolated from bonding contact with said aluminum sheet and being intimately associated with said diazo resin and adherently bonded thereto, and further remaining abrasion-resistant water-insoluble and organophilic upon subjection thereof to the products evolved by said diazo resin upon exposure of said plate to actinic light, and being firmly bonded in said exposed areas, while being readily removable with uiiexposed sensitizer in areas not light-exposed.
  5. 7
    8. A presensitized light-sensitive sheet construction comprising a base sheet, a light-sensitive diazo resin sensitizer layer overlying at least one surface of .said sheet in contact therewith, and overlying said sensitizer layer in intimate association therewith an in situ formed thin 3,136,637 continuous abrasion-resistant coating composed predominantly of water-insoluble polyvinylformal resin, said coating having a thickness of at least about 0.001 mil, containing not more than about 50 percent by weight of pigment, and being isolated from bonding contact with said base sheet by said coating of diazo resin, said coating further remaining water-insoluble and organophilic upon subjection thereof to the products evolved by said sensitizer upon exposure of said sheet construction to actinic light;said diazo resin layer, upon exposure of the sheet to actinic light through a transparency, reacting in the exposed areas and becoming insolubilized and firmly bonding said resin coating to said base sheet, the portions of said resin coating in the areas not exposed to light being readily separable from the portions thereof in exposed areas and being removable with the remaining unexposed sensitizer upon mild rubbing with an aqueous solvent solution.
  6. 8
    9. A presensitized light-sensitive sheet construction comprising a dimensionally-stable transparent and colorless base sheet, a stable soluble light-sensitive diazo resin sensitizer layer overlaying at least one surface of said sheet in contact therewith, said sensitizer layer, upon exposure of the sheet to actinic light through a transparency, reacting in the exposed areas and becoming insolubilized and permanently bonded to said surface of said base sheet and being transparent and essentially colorless in said areas, and said sensitizer having thereover and in contact therewith a thin continuous abrasion-resistant coating Of pigmented water-insoluble polyvinylformal resin, the amount of pigment in said coating not exceeding about 25 percent by weight thereof, said coating having a thickness of at least about 0.001 mil, and further remaining water-insoluble and organophilic upon subjection thereof to the products evolved by said diazo resin upon exposure of said sheet construction to actinic light. References Cited in the file of this patent UNITED STATES PATENTS 1,342,590 Lovejoy________________June 8,1920 1,992,965 Rowell________________Mar. 5,1935 2,173,480 Jung__________________Sept. 18,1939 2,311,888 Toland et al.-----------Feb. 23,1943 2,714,066 Jewett et al.------------July 26,1955 2,732,304 Vanselow et al.---------Jan. 24,1956 2,754,279 Hall------------------July 10,1956 2,760,893 Plambeck_____________Aug. 28,1956 2,791,504 Plambeck______________May 7, 1957 2,804,388 Marron et al.----------Aug. 27,1957 FOREIGN PATENTS 371,153 Great Britain___________Apr. 21,1932 740,165 Great Britain____________Nov. 9, 1955 761,493 Great Britain___________Nov. 14, 1956 1,090,398 France________________Oct. 20, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,136,637 June 9, 1964 Gerald W. Larson It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. Column 12, line 1, after continuous” insert — abrasion-resistant --. Signed and sealed this 4th day of May 1965 SEAL) Attest:ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents
Independent claims6