US2318322A - Method for producing lacquer or varnish resist - Google Patents

Description

atented May 4, 1943 Mn'rrron- Fort rnonucmc LACQUER uvamnsn RESIST Charlesltdmund Meulendyke, Rochester, N. Y.

'No' Drawing. Application August'l, 1940,

.' Serial No. 351,783

6 Claims.

This invention relates to the preparation of photomechanical printing plates as generally adapted to relief, planographic, and intaglio printing in either monochrome or polychrome.

Reference is made to co-pehding patent application of C. E. Meulendyke,-filed June 7, 1939, Serial No. 277,843. In this invention, a metallic support such as a copper plate electroplated with a nickel layer directly supports a lacquer 'or varnish layer, which in turn supports a colloid layer containing a sensitive silver salt. The emulsion layer after being exposed under a suitable halftone or line negative is'developed and processed into a colloid relief with bared lacquer or varnish areas. The lacquer orvarnish layer is then cut through to form a lacquer or varnishrelief under supports suitable local resists, it has been'gener ally suggested to cut through the lacquer or varnish layer in a simple solventappropriate to the lacquer or varnish. Thus cellulosenitrate or cellulose acetate can be cut throu'ghwith acetone, gum shellac with alcohol, or bitumen with benzol. It has been suggested that such cutting can be aided by gentle rubbing with a pad of cotton woolmoistened with the solvent, or by brushing with a camels hair brush.

In the etching of metal, there is a clean-cutting action at the surface of the metal. In cutting through a lacquer or varnish layer, how ever, we are dealing with colloid phenomena and with conditions of swelling and gel formation which complicate the removal of the lacquer or varnish. In the use of an ordinary varmsh remover, it is recommended to first swell the varnish, then to scrape off the gel formation. For such purposes as in this invention, however, the operation of forming a secondary lacquer resist with clean-cut half-tone dots and clean bared metallic areas in accurate conformity to the dots of the primary resist, presents a delicate operation which cannot be satisfactorily performed by use of the solvent action of the appropriate solvent alone. Excessive swelling and absorption of the solvent and creeping of the absorbed solvent along the interfaceof the primary resist can cause loosening of the bonding between the varnish layer and the primary resist, and especially can cause undercutting of such primary resist before the solvent action has cut the varnish through to form bared metallic areas for subsequent etching, r v

I have found that the cutting through of the lacquer or varnish layer in such a system as described above can be accomplished without the troublesome colloid phenomena of swelling and gel-formation. In other words, I have found that such operation can be carried out under conditions substantially analogous to the etching of metal, such as the etching of copper with ferric chloride. For example, let us take the case of a layer of gum shellac. The appropriate solvent of gum shellac is ethyl alcohol. Gum shellac is readily soluble in ethyl alcohol with the usual concomitants of swelling, diffusion, and gel for-.

mation, which for my purposes I wish to avoid.

I have found that if I add an'equal'volume of glycerine to the alcohol, its solvent action upon the gumshellac layer becomes practically nil; I now take advantage of the fact that gumv shellac and resins in. general are destroyed-in the presence of strong alkalis, that resins ingeneral are soluble in alcohol, and that alcohols in general can dissolve considerable quantities. of strong alk alis such as potassium, sodium and lithium hydroxides.

. I have found that a solution of equal quantitles of ethyl alcohol and glycerine has practically no solvent action on gum shellac but that this same solution saturated with a strong alkali will cutthrough' the shellac in a 'manner analogous to the etching of metal, that is to say,

- the cutting action,takes place in situ at the exposed surface of the shellac where it comes water-free alcohol or water-free glycerine or to mixtures of the same in any proportion. However, after the desired cutting action on the resinous layer has been attained, the system resinous substances.

may be flushed with water to remove residual solvent mixture and any thin film of water-- soluble resinate which may have formed.

Within the meaning of this invention, 1 mean 1 to include in the resinous layer any suitable natural gums or resins such as shellac, copal,

dammar, dragon's blood, etc., as well'as artificial resins. Also I intend to include alcohol soluble cellulosic derivatives such as cellulose .-nitrate,

cellulose acetate, etc., used in conjunction with Within the meaning of the term alcohol," I mean to include those alcohols or equivalents solvents capable. of dissolving sufllcient alkali to carry out the operations substantially as herein described. While I suggest glycerine as especially useful-to function in increasing the viscosity of the solution and in v suitably supported resinous layer supporting suitstrain the-solvent action of the-alcohol, suchingredient being present in such proportion that the solvent mixture without presence of the alkali has no appreciable solvent action on the resinous layer but serves rather as vehicle to .bring the alkali into contact with the resin, thus avoiding troublesome colloid phenomenasubstantially as herein described. 1 f

2. The method of producing resinous reliefs or resinous resists by cutting into or through a able local resists with an alcoholic solution made restraining the solvent action of alcohol, I intend to include any suitable ingredient capable of functioning in an analogous manner,

As a correlated part of this invention, I have further'found that the cutting through of the I lacquer or varnish layer in such asystem as described above is facilitated by adding to the appropriate solvent an ingredient which is an etchant of the metallic surface. As a specific example, we 'may take the system of a nickel layer supporting a gum shellac layer which in turn supports suitable local resists. Cupric chloride and ferric chloride which readily etch nickel are easily soluble in alcohol; The cupric chloride and ferric chloride, besides serving as etchants of the metallic surface, increase the viscosity of the solution and act as restrainers I on the solvent action of the alcohol and as inhibitors to prevent the troublesome colloid phe nomena of diffusion, swelling, and gel formation. This etching action at the metallic surface is a superficial one and is very effective in breakingup and removing last traces of resin in areas to be bared and in producing'a cleancut resinous resist forthesubsequen-tetching of the metal.

It will thus be seen that 1- have described processes with all necessary details embodying the principles and attaining the objects and advantages 'of the invention. Since many matters of treatment, manipulation, selection, and pro-. portion of ingredients, successionof steps, and other details :may be variously 'modii'ied'without departing from the principles involved, I do not thus avoiding troublesome 1 colloid 4 substantially as herein described.

strongly alkaline'with caustic alkali and includ ing g'lycerine to increase the viscosity of such solution and to restrain the solvent action of the alcohol, the glyeerine being present in such proportion that the solvent mixture without presence of the alkali has no appreciable solvent action on the resinous layer but serves rather as vehicle to bring the alkaliinto contact with the resin, phenomena 3. The method of producing resinous reliefs or resinous resists by cutting into or through a suitably supported resinous layer supporting suitable local resists with an alcoholic solution saturated with caustic alkali and containing an 'equal volume of glycerine, substantially as herein described.

4. The method of producing resinous resists by cutting through a resinous layer supported on a suitable metallic layer'and supporting suitable local resists with an alcoholic solution including an ingredient which restrains the solvent. action of the alcohol and an ingredient which superiicially etches the metallic surface, thereby loosening and removing last traces of resin in the metallic areas desired to be bared for subsequent etching, substantially as herein described.

intend any limitation to suchdetails excepting so far as set forth in the appended claims.

What is claimed is: I I v 1. The method of producing resinous reliefsor resinous resists by cutting into or through a suitably supported resinous layer supporting suit, able local resists with an alcoholic solution made strongly alkaline and including an ingredient to increase the viscosity of such solution and to re- 5. The method of producing resinous resists by cutting througha resinous layer supported on a suitable metalliclayer and supporting suitable local resists withan alcoholicsolution including cupric chloride as an ingredient to restrainthe 45 solvent action of thefalcohol and to superficially etch the metallic surface" thereby loosening and removing last traces of. resin in the metallic areas desiredto be bared for subsequent etching; substantially'as herein described. 1

V 6. The'method of producing resinous resists by cutting through a resinous layer supported on a,suitab1e"metallic layer and supporting suitable