US 3592137 A
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United States Patent Inventor Douglas A. Newman Glen Cove, NJ.
Appl. No. 795,047
Filed Jan. 29, 1969 Patented July 13, 1971 Assignee Columbia Ribbon and Carbon Mnnuheturlng Cm, lne. Glen Cove, NY.
I'LANOGRAPHIC PRINTING PLATES JChIIns, NoDrlvIlnas U.S.CI. .r 101/462, 101/457, ll7/l38.8, 117/155, 260/296, 260/41 Int. Cl B4ln 1/00, B4ln 3/00 FleldotSeu-ch 101/457,
Primary Examiner-Morris Liebman Assistant Examiner-J. l-l. Derrington Attorney-Johnson and Kline ABSTRACT: An improved planographic printing plate based upon a polyvinyl alcohol binder material in the printing layer. The improvement resides in the incorporation of a certain amount of zinc oxide, relative to the amount of polyvinyl aloohol, in order to provide a printing layer which has an excellent hydrophilic-oleophilic balance, excellent ink-drying properties and avoids spreading of the oleophilic images on the plate surface.
PLANOGRAPHIC PRINTING PLATES This invention relates to the art of planographic printing plates of the polyvinyl alcohol type which represent a marked improvement over prior art plates of this type with respect to ink-drying characteristics and resistance to spreading or broading of the oleophilic images applied to the plate surface.
Polyvinyl alcohol plates of the type described in Perkins U.S. Pat. No. 3,055,295 and other patents have enjoyed widespread commercial success for several reasons including their ease of production. Such plates have a self-insolubilizing formulation due to the presence therein of a polyfunctional organic hardener which reacts with the water-soluble polyvinyl alcohol to insolubiliae it and render it more oleophilic. The binder material is a hydrolyzed polyvinyl alcohol and is commercially available as a dilute aqueous solution such as under the trademark Elvanol.
The polyvinyl alcohol planographic compositions also contain colloidal silica and large amounts of clay which assist in providing the required hydrophilic-oleophilic balance. However the most important ingredient is the hardener. Without this material, the polyvinyl alcohol will not insolubilize sufficiently and will not accept or retain oleous images to the required extent.
The problems presented by hardened polyvinyl alcohol plates relate to the slow drying of oleous images typed onto such plate surfaces and the resultant image spread due to the migration of the liquid ink from the images into adjacent areas of the plate surface. By the time the images dry completely, which takes several days, the images are much broader than originally typed.
Attempts to overcome these problems by increasing the amount of hardener and filler provide some improvement by rendering the planographic layer more oleophilic and more porous. However the necessary hydrophilic properties of the layer are disturbed with resultant toning, stop-start characteristics, and the like.
It is the object of the present invention to overcome the inkdrying and image-spread problems of polyvinyl alcohol planographic layers without disturbing the necessary hydrophilic properties to produce plates having excellent stop start characteristics, resistance to toning, quick ink drying and resistance to image-spreading.
These and other objects and advantage of this invention will be clear to those skilled in the art in the light of the present disclosure.
According to the present invention, l have discovered that plates having excellent ink-drying properties and excellent hydrophilic-oleophilic balance can be produced by adding to the planographic composition an amount of zinc oxide powder which is in excess of the amount of polyvinyl alcohol and which is equal to not substantially more than about one-half the amount of clay filler present. It is not clear how the zinc oxide functions to provide the novel and unexpected results obtained. However this specific material, when used in the amount indicated, improves the hydrophilic properties of the planographic layer while at the same time giving it the ability to dry oleous images in a matter of a few minutes whereby image-spreading is prevented.
The novel planographic compositions of the present invention comprise water, polyvinyl alcohol binder material, colloidal silica, hardener or insolubilizing agent, clay and zinc oxide. Other conventional ingredients are also preferably included such as dispersing agents, catalysts, pH adjusting agents, and the like.
The colloidal silica is a material such as commercially available under the trademarks Ludox or Syton 200 and is present in an amount in excess of the polyvinyl alcohol and up to about four times the weight ofthe polyvinyl alcohol. The colloidal silica functions somewhat as a binder, aftlldfitiidhii insoiubilizing agent for the polyvinyl alcohol. However an amount of a different polyfunctional hardener or insolubilizing agent is also required. Aldehyde donors aredpreferred such as methylol ureas and methylol melamtnes an other urea-or melamine-formaldehyde low polymers conventionally-used for this purpose. Glyoxal is less preferred because of its reactivity and instability, and IS preferably used only in combination with another hardener of the aforementioned type. The hardener is present in an amount equal to from about 10 per cent up to about 120 percent of the amount of polyvinyl alcohol, i.e. in a ratio offrom l:l0 up to l .211.
Clay is an essential ingredient of the present compositions and is used in excess of the amount of polyvinyl alcohol in a ratio of from about 3:1 up to about l0: 1.
The zinc oxide is the ingredient which unexpectedly improves the properties of the planographic layer with respect to ink-drying and image-spreading. The zinc oxide, however, must be used in combination with the other ingredients and in the amount indicated. The ration of zinc oxide to polyvinyl alcohol ranges from above lzl up to 5:1. The latter proportion is only possible where the ratio of clay to polyvinyl alcohol is lOzl.
It should be understood that the present plate formulations may be applied over conventional water-barrier layers and/or hydrophilic underlayers which improve the operation and correction properties of the plates. Coatings of this type are conventional in the planographic printing art. Similarly, the flexible foundation sheet may be a plastic film where the plates are intended for use in the thermographic and photographic fields.
The following Examples are given by way of illustration of suitable planographic compositions which can be coated onto a conventional flexible foundation in conventional manner to provide plates having the novel characteristics enumerated.
[Parts by weight] E samples Ingredients:
Polyvinyl alcohol 2. 0 2. 0 2. 0 Sytonmt](40%auue0us)........ 15.0 11.8 15.0 Glyoxal (40? aqueous) 0. 5 1. 5 2. 0 Methyloluted melamine resin 0. 5 0. 6 l. 0 Clay 15. 5 11.5 18. 0 Zinc oxide. 8. 0 4. 0 8. 0 Acetic acid 0. 2 0. 2 0.2 Zine acetate (25% aqueous) 3. 5 4. 0 3. ll Aluminum sulphate (10% aqueous)... 8.0 9. 0 8.0 Butyl alcohol 0.7 0. 5 0. B 'Irisodium pyrophosphate 0. 05 0. 06 0. 06 Water 46. 05 54. 42. 45
Total 100. 00 100.00 100. 00
For comparison purposes, compositions can be produced according to the foregoing Examples in which the total combined amount of clay and zinc oxide is replaced with an equal amount of clay alone or zinc oxide alone. Modified compositions of this type are unsatisfactory in that plates produced therefrom do not have satisfactory stop-go characteristics or ink-drying properties and the images spread or broaden thereon. Similarly, the replacement of clay or zinc oxide with equal amounts of fillers heretofore regarded as equivalent materials, such as barium sulfate, titanium dioxide, calcium oxide, or the like, results in plates which do not have the sub stantially instantaneous ink-drying properties of the present formulations and have poor stop-go characteristics.
1. Planographic printing plate having fast ink-drying properties and resistance to spreading of oleophilic ink images applied to the printing surface thereof which comprises a flexible foundation supporting a hydrophilic planographic printing layer having a hydrophilic-oleophilic balance comprising 1 part by weight of polyvinyl alcohol binder material, a polyfunctional hardening agent reacted with said polyvinyl alcohol to cause its insolubilization, more than 1 part by weight of colloidal silica, from 3 to 10 parts by weight of clay and from more than i to 5 parts by weight of zinc oxide, said zinc oxide being present in a weight not substantially more than about one-half the weight of clay present.
2. Printing plate according to claim 1 in which the hardening agent is present in a weight equal to from (H to 1.2 times the weight of the polyvinyl alcohol.
3. Printing plate according to claim 2 in which the hardening agent comprises an aldehyde resin.