US2941466A

US2941466A - Planographic printing platess

Info

Publication number: US2941466A
Application number: US605963A
Authority: US
Inventors: Douglas A Newman; Allan T Schlotzhauer
Original assignee: Columbia Ribbon and Carbon Manufacturing Co Inc
Current assignee: Columbia Ribbon and Carbon Manufacturing Co Inc
Priority date: 1956-08-24
Filing date: 1956-08-24
Publication date: 1960-06-21
Anticipated expiration: 1977-06-21
Also published as: GB945042A

Description

United States Patent O PLAN OGRAPHIC PRINTING PLATES Douglas A. Newman, Glen Cove, and Allan T. Schlotzhauer, Locust Valley, N.Y., assignors to Columbia Ribbon & Carbon Manufacturing Company, Iuc., Glen Cove, N.Y., a corporation of New York No Drawing. Filed Aug. 24, 1956, Ser. N0. 605,963

3 Claims. c1.101-149.z)

This invention relates to planographic printing and especially to planographic printing plates formed by a coating on a flexible fibrous foundation such as paper. in the preparation of plates of this character it has been found that coating compositions including as a film-forming ingredient a hydrophilic binder of the class of carboxymethyl cellulose compounds or compounds of other polysaccharide carboxy ethers, have the hydroph-ilicoleophilic balance to give particularly good printing results. Such coatings are rendered effective as printing surfaces when the film former is insolubilized, either by a reagent included in the coating mixture, or after-applied to the dried coating. The use of certain appropriate reagents for insolubilization, particularly copper, iron, aluminum and chromium compounds, and especially chromium compounds, result in production of outstandingly good printing surfaces when reacted with the film former and aged for short periods, giving under such conditions exceptionally large numbers of good quality copies from the plate. Plates thus prepared and constituted, however, have after prolonged storage sometimes demonstrated a tendency to become overly sensitive so that they pick up ink in the background areas during printing. Apparently this is especially the case when the plates have been stored under conditions of heat together with humidity. As a result the printing quality of plates of the type in question, while uniformly high at the time of manufacture, is not predictable at a later date.

It is an object of the present invention, therefore, to provide coated flexible planographic printing plates of the type heretofore described, but improved in such a way that the tendency to become sensitive to the ink under certain storage conditions is markedly reduced or altogether eliminated.

According to commercial practice, the coatings employed on coated paper planographic printing plates usually include one or more of various fillers to improve their printing and especially their image-retentive properties. The fillers sometimes used for this purpose are china clay, barium sulphate, hydrated alumina, calcium carbonate, zinc oxide, titanium dioxide, fiuorspar, fullers earth and other similar materials.

According to the present invention, it has been discovered that, in coatings of polysaccharide carboxy ether compounds insolubilized with the salts and compounds heretofore mentioned, the presence in particular of an oxide of zinc, titanium, magnesium or calcium, or mixtures of these particular oxides, in the composition in contrast to the other materials currently used as fillers, in some manner not altogether understood at present, has a pronounced inhibiting effect on the tendency of the coatings to become sensitive with age. It is found that, regardless of storage conditions of heat and humidity, the plates which include, as a significant portion of the filler, one or more of the oxides named will be uniformly usable and capable of producing copies of acceptable grade after a period of aging.

The present invention, therefore, is characterized by the presence of an aging sensitization inhibitor in the form 2,4i',466 Patented June 21, 196Q of material selected from the group consisting of the oxides of zinc, titanium, magnesium and calcium and mixtures thereof, as a significant portion of the filler in coat ings of the polysaccharide carboxy ether type, insolubilized by salts or compounds of copper, aluminum, iron and chromium, and especially compounds of chromium.

Other features and advantages will hereinafter appear.

'In practicing the present invention, a flexible paper foundation sheet is preferably treated in a known manner with wet strength-imparting ingredients such as melamine formaldehyde, although this may be dispensed with in the preparation of plates for certain short-run purposes. Likewise, known surface sizings or water-barrier coat-ings may be applied which provide for improved operation under long-run conditions. When such preliminary preparations, if any, are completed, the paper is coated on at least one surface with one or more coats of a planographic surfacing composition.

For this purpose an aqueous suspension or slurry is prepared containing between one and five percent of a film-forming constituent such as carboxymethyl cellulose,

' or other polysaccharide carboxy ether, such as the carboxy ethers of starch, or carboxy ethers of the watersoluble gums containing saccharid units, such as gum arabic, gum tragacanth, mesquite gum, larch gum, etc. In addition, the suspension includes a filler which may be about two tofour times the weight of the binder present. Heretofore this filler has often consisted entirely of china clay or the like, but according to the present invention, at least a certain percent of the filler is composed of an aging sensitization inhibitor in the form of an oxide of zinc, titanium, magnesium or calcium, or a mixture of two or more of these materials. Other ingredients may be included to aid, for example, in the coating operation, or for other special purposes, but the ingredients enumerated are the essentials. The slurry is applied to the paper, for example by a brush coating operation, and allowed to dry.

One example of a coating suspension for this purpose is:

Formula I Ingredients: 7 Parts by weight 5% aqueous dispersion of sodium carboxymethyl cellulose China clay 15 Zinc oxide 5 Glycerine- -n 3 When the coating is substantially dry, the coated surface of the sheet is treated, as by tub sizing, with an aqueous solution of one or more of the metal salts or com pounds heretofore mentioned. For best results a mixture of chlorides or sulfates of aluminum, ferric iron and copper, together with chromium trioxide, are employed as disclosed in the patent to Douglas A. Newman, No. 2,655,864. The preferred formula as shown in said patent is as follows:

Formula II Percent Copper sulphate 3 Aluminum sulphate 1 Ferric chloride Chromium trioxide This treament renders the coating insoluble in water, and the dried coating will then accept and retain imaging material and print copies of high quality when used the plate or master in a planographic printing process.

While the two step treatment of the printing surface is very effective, there has also been discovered a means whereby substantially equivalent printing quality can be achieved using a single coating formula which automatically becomes insoluble on drying, and the present inaga nst:

of the invention is as follows:

.SQ nm a b m h s u ase -5 Water' cc .78 Methanol cc .12 C a :a p .7- Zinc oxide d o 2.5 Glycerine do 1.0 5% ammoniacal coppersnlphate cc 40 Ammonium" dichron a g, Cl. "gra ns-.. 1.0 Ferric ammonium citrate, U. S.P. ;.do 1.5

The slurry of Formula'IIIis applied tothe paper web, as by brush coating, and allowedto a pma asl the application of'heat, to give a coating is water insoluble and provides a planographic printingsurface ofgood quality. j

It can be seen that both the form of the invention exemplified by Formulas I and Hand that exempiified by"Formula HI relate to polysaccharide carboxy ether coatings which are rendered insolublc by a particular group of metal salts or compounds, and including 'especially, although not necessarily,'a compound of chromium. The plates thus constituted may be aged for extended periods, even under adverse conditions ofrhigh temperature and humidity, and may then he successfully imaged and used to print copies of goodquality Q'Ifhe tendency heretofore experienced for the reaction product of insolubilization treating materials such as copper, aluminum or iron salts or chromium compoundsjwith film formers of the polysaccharide carboxy'ether type to become increasingly ink sensitive with prolonged aging, presumably due to sustained subjection to heat and humidity, is found to be effectively inhibitedby the prescnce of the special oxide filler which acts to maintain the originally manufactured vand normally aged condition of the plate surface, free from. unusual ink sensitivity, regardless of the duration and temperature-humidity conditions of storage which the plate may encounter.

' Formula I and Formula III have been presented showing the desensitization inhibitor as zinc oxide and represent the form of the invention at present preferred from the standpoint of cost and availability. Itwill be understood, however, that formulas which differ from these essentially by a substitution of a substantially equal amount of titanium dioxide, magnesium oxide or calcium oxide, or of such of the more complex oxide compounds of these metals, e.g. peroxides or sesquioxides, as are commercially available, or any mixture thereof, are equally good examples of the invention and will provide compositions demonstrating in full the stated advantages.

The proportion of the special oxidefiller which should be included may vary, but it has been found that the use of amounts equivalent to about thirty percent of the weight of the film former present will produce clearly noticeable etfects for the purpose. In most cases it appears that no particular advantage accrues from including amounts in excess of the weight of film forming material although more maybe used if desired without substantial detriment.

-W h ile the invention herein has been described with particular reference to incorporation 0f the special oxide filler directly in the polysaccharide carboxy ether coating mix, it has also been foundthat i-f the' same is included instead in a coating which directly underlies the polysaccharide carboxy ether coating, thelsensitization inhibiting advantagesheretoiore set out will beattained to a substantially equal extent. when the ial oxide filler is thus incorporated, it appearsithat s' ewhat'less than all of the special oxide materialused; is effective. Accordingly the amountto be employed maybe calculatedon the basis of whatamount would give the desired results if placed directly in the surface coating planned, and then preferably using a somewhat increased amount in the undercoating. For this purpose, an increase of between fi-fty percent and one hundred percent above the amount of special oxide filler which would have been used in the surface coating is at present recommended. It .wnrbe' appreciated also thatalportion of thespecial oxide filler may be includedin both coatings if desired with equivalent'beneficial effect. In Iact the m n o th ee px'u file in an f aa nf a printing surface layerc'onsisting of the printing surface coating and the coating, if any, directly underlying it will give a result demonstrating the beneficial'efiect heretofore noted.

Variations and modifications: may be made within the scope of the claims and portions of the improvementsmay be'used without others. l i 7 We claim:

1. A planographic printing plate comprising a fibrous flexible foundation web; a'p'rinting surface 'coating 'on said'webconsisting essentially of an insoluble {hydrophilic polysaccharide carboxy ether 'film- Iorriiing niaterial insolubilized by reaction with a metal compound selectedfrom the group consisting of coppensaltgiron salts, aluminum salts and chromium compounds which thus reacted has a hydrophilic-oleophilic balance suitable for direct -irnaging use, and which is subje :to becoming excessively ink-sensitive upon subsequent exposure to protracted conditions of abnormal heat and humidity, said coating including an amount of zinc oxide 'suflicient to act as an aging sensitization inhibitor for said insolubilized film former, said amount being equivalent to at least about thirty percent of the weight of'said forming material.

2. A planographic printing plate comprising a fibrous flexible foundation web; a printing surface coatin gon said Web consisting essentially of an insoluble'hydro philic polysaccharide carboxy ether film formin'g material insolubilized by reaction with metal'conipounds consisting of copper, iron and aluminum saltsfand 'a chromium compound and which thus reactedjha sl a hydrophilic-oleophilic balance suitable for direct-imaging use, and which is subject to becoming excessively ink-sensitive upon subsequent exposure to protracted conditions f abnormal heat and humidity, said coating including a quantity of inert filler and a sufiicient amount ofjzinc oxideto act as an aging sensitization inhibitor for said insolubili z ed film former, said amount being equivalenbto at least about thirty percent of the weight of said film forming material.

3. A planographic printing plate comprising a fibrous flexible foundation web; a printing surface coating on said web vconsisting essentially of an insoluble hydrophilictpolysaccharide carboxy ether film torming materi al insolubilized by reaction with m etal compounds consisting of copper, iron and aluminum'salts; and ;a chromium oxide compound and which when-thus reacted has a hydrophilic-oleophilic balance suitable for direct-imaging use, and which is subject to becoming. .excessively ink-sensitive upon subsequent exposureto protracted conditions of abnormal heat and;hum idity, said coating including a filler which is an aging s'ensitization inhibitor, said inhibitor being zinc oxide present in ,an amount equal to at least about thirty percent -oflthe weight-of said'film forming material.

References Cited in the fileof this patent UNITED STA'IES PATENTS 2,542,784 Van Dusen Feb. 20, l 91 2,598,189 Q425 2,635,537 Apr.'2 7, 1953 2,655,864 r 1 r1 2,693,145 Mullen f Nov. 2, 19 5 1 2,778,301 Brinnick et al. Ian. 22, 1957

Claims

1. A PLANOGRAPHIC PRINTING PLATE COMPRISING A FIBROUS FLEXIBLE FOUNDATION WEB, A PRINTING SURFACE COATING ON SAID WEB CONSISTING ESSENTIALLY OF AN INSOLUBLE HYDROPHILIC POLYSACCHARIDE CARBOXY ETHER FILM FORMING MATERIAL INSOLUBILIZED BY REACTION WITH A METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF COPPER SALTS, IRON SALTS, ALUMINUM SALTS AND CHROMIUM COMPOUNDS AND WHICH THUS REACTED HAS A HYDROPHILIC-OLEOPHILIC BALANCE SUITABLE FOR DIRECT-IMAGING USE, AND WHICH IS SUBJECT TO BECOMING EXCESSIVELY INK-SENSITIVE UPON SUBSEQUENT EXPOSURE TO PROTRACTED CONDITIONS OF ABNORMAL HEAT AND HUMIDITY, SAID COATING INCLUDING AN AMOUNT OF ZINC OXIDE SUFFICIENT TO ACT AS AN AGING SENSITIZATION INHIBITOR FOR SAID INSOLUBILIZED FILM FORMER, SAID AMOUNT BEING EQUIVALENT TO AT LEAST ABOUT THIRTY PERCENT OF WEIGHT OF SAID FILM FORMING MATERIAL.