US3452676A - Heat-sensitive planographic printing plates and processes - Google Patents

Description

y 1, 969 D. A. NEWMAN 3,452,676

HEAT-SENSITIVE PLANOGRAPHICYPRINTING PLATES AND PROCESSES Filed March 16, 1967 0 H ///Z l INVENTOR. fioqylas A. A en ma/i United States Patent US. Cl. l01-462 Claims ABSTRACT OF THE DISCLOSURE Process for producing and imaging novel planographic printing plates which have a self-contained oleophilic imaging material and which are capable of forming oleophilic images thereon under the effects of applied heat, comprising applying to a flexible foundation sheet a coating of heat-sublimable oleophilic material and applying thereover a planographic layer which contains porous filler and is permeable to said sublimable material and rendered oleophilic or ink-receptive thereby.

The present invention relates to both the planographic printing field and the thermographic imaging field. There are presently known two types of heat-sensitive planographic plates having a self-contained oleophilic imaging material. The first type is disclosed in United States Patent No. 2,800,077 and comprises a flexible foundation sheet carrying a porous planographic layer containing within the pores thereof an oleophilic material capable of flow to the surface under the effects of heat or pressure. Such plates have the disadvantage that the planographic layer is not of the conventional type suitable for long run use or for the production of many good copies, and that the plates are pressure-sensitive and contain the oleophilic imaging material adjacent to the hydrophilic planographic surface whereby the plates are quite susceptible to inadvertent imaging during manufacture, processing, han dling and/ or during the printing operation when the plate is brought into pressure contact with the offset roller.

Another type of heat-sensitive plates which does not suffer from the aforementioned disadvantages is disclosed in my earlier United States Patent No. 3,274,929. Such plates comprise a flexible foundation sheet carrying a layer of heat-meltable oleophilic wax composition and having thereover a thin layer of conventional planographic composition which is capable of being penetrated and rendered oleophilic by the wax composition in heated areas. Such plates offer many advantages but are found to be less heat-sensitive than desired. If the images on the original sheet are weak so that they do not generate a large amount of heat on exposure to infrared radiation, the oleophilic wax will not be heated sufliciently high to cause it to melt and flow into and through the planographic layer. Also the duration of heating must be extended to permit the wax to flow through the planographic layer since the oleophilic composition resolidifies almost instantaneously after removal from heat. However, if excess heat is applied, the melted wax flows into adjacent areas of the planographic layer, forming broadened image areas.

It is the primary object of the present invention to provide a heat-sensitive planographic printing plate which is insensitive to pressure and which is very sensitive to 3,452,676 Patented July 1, 1969 heat so that it can be reliably imaged on substantially instantaneous exposure to heat.

It is another object of this invention to provide a heatsensitive planographic printing plate which has a conventional planographic surface layer and is suitable for long runs and yet is exceptionally sensitive to heat.

The present invention resides in the discovery that there are a number of waterinsoluble heat-sublimable materials which are oleophilic and which in sublimed gaseous condition are capable of penetrating a conventional microporous hydrophilic planographic printing layer con- 7 taining conventional porous fillers such as clay, silica and the like.

When such sublimable materials are present beneath such a planographic layer and heat is applied to the plate in image form, the heat causes the underlying oleophilic material to sublime, i.e., to convert directly from a solid to a vapor, whereby the oleophilic vapors permeate and penetrate through the porous planographic layer in the heated areas and condense or resolidify in the planographic layer when the plate is removed from the heat to form oleophilic, ink-receptive images on the planographic surface.

The novel plates of the present invention comprise a flexible foundation sheet which may be a wet-strength paper or plastic film. The latter is preferred in that it is advantageous that the present plates be translucent so that they can be imaged in the so-called reflex thermographic process as well as in the socalled shoot-thru process. However, translucent papers are also suitable for reflex plates.

The accompanying drawings illustrate the structure of the present plates and the imaging thereof.

FIGURE 1 is a diagrammatic cross-section, to an enlarged scale, of a planographic printing plate imaged according to the present invention; and

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of one of the present plates superposed with an imaged original sheet under the influence of infrared radiation in the reflex exposure method, but separated for purposes of illustration.

As shown in FIG. 1, the present plates 10 comprise a flexible foundation sheet 11 carrying a layer 12 of sublimable oleophilic material under a planographic printing layer 13. The planographic layer has a surface 15 which is hydrophilic except in heated areas 14 which have been rendered oleophilic by condensation of the sublimable material.

The layer 12 of sublimable oleophilic material may comprise a surface layer on the foundation 11 or, in the case of paper foundations, may comprise an impregnation of the paper surface. It is preferred that the layer 12 is a discrete layer on the surface of the foundation and that it comprises a porous film-forming binder material containing the sublimable material so that the oleophilic vapors can easily escape and penetrate printing layer 13. Layer 12 may be a water-applied layer and may comprise a hydrophilic film-forming binder material and a porous filler and thus be identical to or similar to the planographic layer except for the inclusion of the sublimable oleophilic material. Also suitable are the socalled blushed layers having a porous structure of vinyl resin or cellulosic plastic formed by applying the layer using a mixture of volatile liquids, the less volatile being a nonsolvent for the binder.

The thickness of layer 12 is not critical provided that there is a uniform complete coverage of the foundation sheet. In the case of translucent plates for reflex imaging, the oleophilic layer 12 should not exceed about 7 pounds per ream (500 sheets, 20" x 30") and must be such that neither it nor its foundation absorb infrared radiation to any substantial extent.

Suitable oleophilic sublimable materials for use according to the present invention are those which are at least substantially water-insoluble and sublime at a temperature ranging between about 100 F. and 400 F. Preferably the oleophilic material is stable and does not sublime below about 215 F. The sublimable material should be one which does not absorb substantial amounts of infrared radiation when used to prepare plates for reflex imaging. The sublimable material may be colorless but preferably has at least a faint color so that the oleophilic images on the imaged plate can be proofread and it can be determined in advance whether the plate has been sufliciently well imaged to produce good planographic copies.

The following sublimable materials are preferred but the selection of other suitable oleophilic sublimable materials is a matter of choice which will be obvious to those skilled in the art in the light of the present disclosure: aromatic compounds such as salicyclic acid, acetyl salicylic acid, gallic acid, pyrogallol, hydroxyquinoline, pyrocatechuic acid; dyestuffs such as quinolizarine green, chrysoidine, rhodamine, Du Pont oil dyes such as orange, yellow, brown and red, and the like.

The layer of oleophilic material is applied to the foundation sheet as an impregnation or coating of the sublimable material dissolved or dispersed in a suitable volatile vehicle such as ethyl alcohol, methyl ethyl ketone, ethyl .acetate, toluol, water or the like. When a film-forming binder material is also used, it is preferably used as a solution in a volatile organic solvent and is insoluble in water, and an amount of water is included to form a blushed, porous structure after evaporation thereof. In such cases, the oleophilic material must be one which has a sublimation temperature which is in excess of the evaporation temperature of water and which preferably is at least about 225 F.

The planographic printing layer 13 is a conventional microporous planographic composition containing porous filler and based upon a hydrophilic binder material such as polyvinyl alcohol, carboxymethyl cellulose or other similar hydrophilic film-forming materials. Suitable planographic compositions are illustrated by United States Patents Nos. 3,031,958; 3,055,295 and 3,274,929 mentioned supra.

The coat weight or thickness of the present planographic layer is not very critical since the oleophilic vapors penetrate quickly. The planographic layer should have a weight which is at least suflicient to insure adequate coverage, generally at least about 2 pounds per ream, and may be as high as about 10 pounds per ream. In cases where the plate is translucent for reflex imaging, the coat weight should not exceed about 7 pounds per ream.

The following examples illustrate the production of planographic printing plates according to the present invention.

Example 1 Ingredients Parts by wt. Ethyl cellulose 13 Du Pont Oil Blue A 7 Acetone 70 Water 10 The formed layer has a porosity which not only assists the escape of the sublimed material but also provides for integration and lock-on of the top planographic layer. The following composition is suitable for formation of the planographic layer and is applied so as to have a weight of about 6 pounds per ream after evaporation of the water.

The formed plate is very translucent and is free of materials which absorb substantial amounts of infrared radiation so that it is useful in the reflex thermographic method and can be imaged using an original sheet which is opaque or has images on both sides.

This is done in the manner illustrated by FIG. 2 of the drawings. The plate is positioned together with an imaged original sheet 20 so that the infrared radiationabsorbing original images 21 are against the rear of the film foundation 11 of the plate. The superposed sheets are subjected to exposure to infrared radiation lamps 30, in an exposure device such as a Thermo-Fax or masterfax machine. A brief exposure is suflicient to generate a temperature in excess of about 350 F. in the image areas and cause the Oil Blue in corresponding areas of the layer 12 to sublime and pentrate the porous printing layer 13. On removal from the heat the Oil Blue vapors condense in and on the printing layer to form blue oleophilic image areas 14 on the hydrophilic surface 15.

The image surface of the plate is then moistened with a conventional etch and several hundred copies of excellent quality can be made on a planographic printing machine.

The following example illustrates the production of a paper base plate carrying the sublimable material as a surface impregnation.

Example 2 A suitable wet-strength paper stock such as 20 pound kraft paper is coated on one srface with a 5% solution of Du Pont Oil Orange in acetone and the acetone is evaporated to leave a thin continuous film of the orange crystals on and in the paper surface. The treated surface is then coated with 8 pounds per ream of the planographic composition of Example 1 and dried.

This plate is suitable for imaging in the shoot-thru method using a translucent original sheet having images on one side thereof. The original images are positioned closest the radiation source and the planographic layer is in contact with the rear of the original sheet. Brief exposure to infrared radiation is sufficient to generate a temperature in excess of about 300 F. in the image areas to cause the Oil Orange in corresponding areas of layer 12 to sublime and penetrate printing layer 13 and irom orange oleophilic images 14 on the hydrophilic surace 15.

The imaged plate is suitable for the production of several hundred excellent copies in the planographic printmg process.

While the present plates are primarily intended for imaging in infrared radiation thermographic processes of the type illustrated by FIG. 2 of the drawings, it should be understood that they may also be imaged by means of a heated stylus, heated type face or any other means by which sufficient heat can be applied in the form of an image pattern to cause sublimation of the oleophilic material used.

I claim:

1. The process of imaging a heat-sensitive planographic printing plate comprising a flexible foundation sheet supporting a layer containing a water-insoluble oleophilic solid which sublimes at a temperature between about 100 F. and 400 F. and having over said layer a microporous hydrophilic planographic printing layer which is resistant to melting at the sublimation temperature of said oleophilic solid, which comprises the step of applying sufficient heat in the form of an image pattern to said printing plate to cause said oleophilic solid to sublime and permeate said printing layer in the heated areas, and removing said heat to cause at least a portion of said sublimed material to resolidify in the permeated portions of said printing layer and render said portions oleophilic.

2. The process of claim 1 in which the step of applying heat is carried out by superposing the printing plate with an original sheet carrying infrared radiation-absorbing images and applying a sufficient amount of infrared radiation to said images to generate a corresponding heat pattern to sufficient intensity to cause said oleophilic solid to sublime and permeate said planographic printing layer in areas corresponding to the location of said images.

3. The process of claim 1 in which the said oleophilic solid sublimes at a temperaure greater than about 215 F.

4. A heat-sensitive planographic printing plate comprising a flexible foundation sheet supporting a layer containing a water-insoluble oleophilic solid which sublimes at a temperature between about 100 F. and 400 F., and having over said layer a microporous hydrophilic planographic printing layer which is resistant to melting at the sublimation temperature of said oleophilic solid and which is permeable by said oleophilic solid in its sublimed state.

5. A printing plate according to claim 4 in which the layer containing the oleophilic solid is a porous layer which comp-rises a film-forming binder material which is resistant to melting at the sublimation temperature of said oleophilic solid.

6. A printing plate according to claim 4 in which 6 the said oleophilic solid sublimes at a temperature greater than about 215 F.

7. A printing plate according to claim 4 in which the planographic printing layer comprises a hydrophilic binder material and a porous filler.

8. The process of producing a heat-sensitive planographic printing plate which comprises the steps of:

(a) applying to a flexible foundation sheet a layer containing a water-insoluble oleophilic solid which sublimes at a temperature between about F. and 400 F.; and

(b) applying over said layer a microporous hydrophilic planographic printing layer which is resistant to melting at the sublimation temperature of said oleophilic solid and which is permeable by said oleophilic solid in its sublimed state.

9. The process of claim 8 in which the layer containing said oleophilic solid is a porous layer comprising a film-forming binder material which is resistant to melting at the sublimation temperature of said oleophilic solid.

10. The process of claim 8 in which the layers of steps (a) and (b) are applied by means of volatile vehicles which are evaporated to form said layers.

References Cited UNITED STATES PATENTS 2,800,077 7/1957 Marron 101-461 3,060,026 10/1962 Heiart 96-28 3,245,796 5/1966 Metuchen 101-473 X 3,274,929 9/1966 Newman l01462 X ROBERT E. PULFREY, Primary Examiner. FREDERICK FREI, Assistant Examiner.

US. Cl. X.R.

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