US2286220A - Cellulose composition material - Google Patents

Description

Patented June 16, 1942 CELLULOSE CODIPOSITION MATERIAL Ralph H. McKee, New York, N. Y.

No Drawing. Application March 4, 1938, Serial No. 193,921

14 Claims. (Cl. 106-473) This invention relates to an improved plasti- 'cizable mixture which is initially moldable, which is especially adapted to take fine imprints and impressions from copy plates and reliefs, and

when hardened or solidified into a film or sheet, is serviceable in the printing, graphic and reproduction arts as a printing plate having printing impressions in the surface thereof. The present application is a continuation-in-part of my prior application Serial No. 559,778, filed August 27, 1931, issued on May 10, 1938, as Patent No. 2,116,- 536.

The plastic material which I have invented possesses such characteristics as make it especially valuable for use in the printing, graphic and reproduction arts. The finished product herein disclosed will take a sharp, clear and accurate impression of surfaces, such as copy reliefs, when the composition is pressed forcibly into contact therewith and allowed to harden and set. In addition, the product does not shrink upon hardening or with age, is free from plastic flow, is substantially non-thermoplastic and accurately and uniformly retains its original surface shape and contour. The product as herein disclosed will not adhere to a dampened or water swollen gelatine copy relief, and, therefore, constitutes and excellent material for printing plates which can be cast from such a copy relief. When fully solidified, the improved product of the present invention is hard, tough, durable and wear resisting and is especially useful and valuable in situations where such a material is desired.

The printing plates are made and cast from my improved composition substantially as follows: Using the screens and photographic apparatus customary in the printing industry, a positive (if intaglio), or negative (if half tone or relief) is taken on a gelatine plate (generally backed with celluloid) impregnated with a chromate salt. Where the light strikes the gelatine it is rendered nearly unswellable by water. The exposed gelatine plate is moistened with water (by immersion or otherwise) for 10 to 30 of cellulosic bases of varying viscosities.

bulk of the viscous liquid composition gradually pushed forward toward the other end of the gelatine plate and the excess of the liquid composition finally pushed out and discarded. The moldable composition is then allowed to harden and set to the final product. The time required for solidification of the composition depends upon the viscosity and air conditions but averages approximately 10 minutes.

The backing sheet with the solidified material immutably adhering thereto constitutes the printing plate and the whole is now stripped from the gelatine relief plate and allowed to com- 1 pletely solidify by exposure to the air for several hours. It is then ready to be put on a roll and rotogravure printing begun. Either half tone or intaglio printing plates may be made by following the above general procedure, using of course the proper type of screen as recognized by those skilled in the art.

I have found that cellulose nitr'ate or cellulose acetate constitutes an excellent base material. A composition which runs approximately 25% of the cellulose ester provides a finished printing material of great hardness and durability. In general the greater the precentage of cellulosic base (considering the solids exclusive of $01- vents) that can conveniently be used without destroying the necessary initial molding plasticity of the product the greater will be the hardness and durability of the finished solidified product. I have found that a composition made from a cellulosic base of low viscosity does not make as hard a materialas a composition made from a cellulosic base of relatively high viscosity, but the hardest material is made from a mixture In order to get a plastic which will flow at the desired rate for molding purposes when a particular solvent is used and to obtain a liquid composition containing total solids of 20% to 35% or more, it is preferable to use a mixture of cellulosic bases of varying viscosities. Such a mixture may comprise part -second cellulose nitrate and part cellulose nitrate of a high viscosity, such as part 4-secorld cellulose nitrate and part LO-second cellulose nitrate. Cellulose acetate also constitutes a valuable cellulosic base material.

I have found that, as a rule, plasticizers, and particularly plasticizers such as camphor, castor oil and the like, have a tendency to decrease the hardness of the finished product. It is necessary, however, to add some plasticizer to the ingredients used in order that the composition be sufficiently plastic for initial molding purposes.

Preferred plasticizers for cellulose nitrate are tricresyl phosphate, triphenyl phosphate, or dibutyl phthalate, and for the cellulose acetate .1 find that triacetin is a satisfactory plasticizer.

As solvents for the cellulosic base, acetone,

ethyl acetate, butyl acetate, amyl acetate, butyl alcohol and similar well-known solvents in commercial use may be used. To obtain the best results, the solvent which should be used will depend somewhat on the particular cellulose base which is used. If cellulose nitrate is used as the base material, I have found that ethyl acetate and butyl acetate are especially valuable. Very effective results, where cellulose nitrate is used, can be obtained by using a mixture of two solvents, i. e., technical butyl acetate this contains some butyl alcohol) and ethyl acetate. If a material possessing very rapid setting and hardening characteristics is desired, ethyl acetate also serves as an excellent solvent. However, if a material possessing great hardness, sharpness and durability is desired, as for example a material initially moldable to form a printing plate for fine detailed printing, I prefer to use a mixture of butyl acetate and butyl alcohol with a small amount of ethyl acetate added. Pure ethyl acetate is a less desirable solvent where a fine printing form is to be made since the fine imprints and details carried by the copy relief are not so accurately and sharply copied by an initially plastic 'cellulosic composition having ethyl acetate as the sole solvent. Furthermore, ethyl acetate evaporates very quickly with corresponding rapid hardening of the plate. Where quick hardeningis a major consideration, and where exact impressions are not of primary importance, ethyl acetate provides an excellent solvent. Acetone and amyl acetate have proven to be particularly valuable solvents where cellulose acetate is used as a base material.

All the materials should be as free from water as possible. Any appreciable amount of water in the ingredients used greatly decreases the solubility of the cellulosic base. The commercial products mentioned are, however, normally free from water, so that no difficulty is encountered in obtaining materials capable of forming a composition of desired characteristics.

My preferred composition when in liquid form contains 12 to of total solids and 65 to 80% of solvents. The solids comprise preferably cellulose nitrate or acetate, with a small amount of plasticizer added. I have found that a'mixture of cellulose nitrate material of varying viscosities generally produces a harder, tougher and more desirable hardened product. The mixtures of cellulose nitrate should be so selected as to achieve this end. An excellent mixture comprises V second cellulose nitrate approximately 50%, 4 second cellulose nitrate approximately 10%, and 40 second cellulose nitrate approximately 40% Any of these amounts might be increased with corresponding reductions in the others. As plasticizers, I have found triphenyl phosphate or tricresyl phosphate or dibutyl phthalate to be among the best and should be used in small or moderate percentages, of from 1 to 5% of the totalcomposition. As solvents, mixtures of com mercial butyl acetate and ethyl acetate seem to be the best, but amyl acetate may also be used. Commercial butyl acetate generally carries about 20% butyl alcohol, which is not objectionable. A small amount of benzene or similar cheaper solvent may be used to reduce the cost.

The particular portions and ingredients which we have found to be especially valuable may be described as follows:

Example 1 A composition giving a printing plate of great hardness and durability and which will faithfully *copy the finest surface impressions may be made from a mixture comprising 25% by weight of total solids and 75% by weight of solvents. The total solids comprise 20% triphenyl phosphate, 20% 40 second cellulose nitrate, and 60% /2 second cellulose nitrate. The solvent used comprises a mixture of 58% amyl acetate and 42% butyl acetate. Giving the quantities by weight and in total percentages, this composition comprises 15% /2 second cellulose nitrate, 5% 40 .percentages, this composition comprises 10% second cellulose nitrate, 10% 40 second cellulose nitrate, 5% triphenyl phosphate, 43.5% amyl acetate and 31.5% butyl acetate. This composition has a viscosity of 70 seconds (by falling ball test).

Example 3 A composition comprising 25% by weight of solids and 75% by weight of solvents. The solids comprise 5% tricresyl phosphate, 71% second cellulose nitrate, and 24% 40 second cellulose nitrate. The solvent used is ethyl acetate unmixed with any other material. Giving the quantities by weight and in total percentages this composition comprises 17.75% V: second cellulose nitrate, 6% 40 second cellulose nitrate, 1.25% tricresyl phosphate and 75% ethyl acetate. This composition has a viscosity of 39 seconds (by falling ball test).

Example 4 A composition comprising 25% by weight of solids and 75% by weight of solvents. The total solids comprise a mixture of 5% tricresyl phosphate and of cellulose acetate (60% of 15 second cellulose acetate and 40% of 5 second eellulose acetate). The solids above described are dissolved in a mixture of equal proportions of methyl acetate and acetone. Giving the quantitles by weight and in total percentages, this composition comprises 23.75% of cellulose acetate, 1.25% tricresyl phosphate and 75% mixed substantially self sustaining and a mass of the masolvent. The composition as above named has a viscosity of '70 seconds (by falling ball test).

Example 5 A composition comprising total solids 35.6% by weight and solvents 64.4% by weight. The

total solids comprise 5.2% triphenyl phosphate,

8.3% gum dammar, 43.25% second cellulose nitrate, and 43.25% 40 second cellulose nitrate. The solvents used comprise 66.1% butyl acetate, 27.8% ethyl acetate and 6.1% of gum dammar solvents. The solvents for the gum dammar comprise 42% benzene, 9.2% ethyl acetate, 8.1% acetone and 40.7% methyl alcohol. Giving the quantities by weight and in total percentages, this composition comprises 15.4% /2 second cellulose nitrate, 15.4% 40 second cellulose nitrate, 1.9% triphenyl phosphate, 2.9% gum dammar, 42.6% butyl acetate (technical), 1'7 .9% ethyl acetate, and 3.9% gum dammer solvent. This composition has a viscosity of 800 seconds (by falling ball test). It is noted that this material has a high viscosity and if, for certain purposes, it is found too viscous to mold properly, its viscosity can be lowered by adding butyl acetate or ethyl acetate.

Example 6 A composition comprising total solids 20% by weight and 80% by weight of a solvent consisting of tetrachlorethane. The solids comprise 5% of triacetin and 95% of equal amounts of 15 second and 1 second cellulose acetate. Giving the quantities by weight in total percentages, this composition comprises 1% of triacetin, 19% of cellulose acetate and 80% of tetrachlorethane. This composition has a viscosity of 50 seconds (by the falling ball test).

Where the composition is composed of only cellulose nitrate or acetate, a plasticizer and a solvent, it does not matter in what orderthey are mixed. The resulting solution, however, requires some time and stirring before it reaches complete homogeneity. When completely dissolved and mixed, the material should be filtered and is then ready for use.

When a gum or resin'such as gum dammar is used, it is preferable to dissolve the gum in its own solvent and later add this solution to the material above described. The gum solvent which should be selected will depend upon the gum or resin chosen, but in general it will consist of an anhydrous mixture of benzene, methyl alcohol and possibly other solvents, such as.acetone and ethyl acetate. The gum solution is added to the cellulose base solution and the two are mixed by stirring together. The final material is filtered and is then ready for use.

The moldable composition which is to be applied to the gelatine copy relief, as noted above, is very viscous. It has been found that the preferred viscosity is such that the material, while moldable, is not of itself freely flowable (like a spraying or brushing lacquer) but requires a considerable degree of mechanical pressure to force it into the fine macroscopic depressions of the copy relief. On the one hand the 'material should be sufflciently fiowable to be forced into such depressions and on the other" hand must not be so fluid as to freely enter such depressions. In the latter case, as where the material has a high percentage of solvents, subse quent evaporationof the solvent causes shrinkage of the mass during the hardening process, resulting in poor work. The material employed in actual practice is of such viscosity that it is terial placed on a swollen-gelatine sheet would not, within any reasonable time, flow over the sheet. The viscosity characteristics are therefore of salient importance.

The finished material generally is semi-trans- I parent and water colored. It may be found desirable in certain instances to give the materiala distinctive color. I have found, for example, that the material can be colored without harm thereby by adding a coloring material dissolved in asuitable solvent. for example, .01 g. of oil red, or oil orange, or other color, dissolved in 5 cc. of ethyl acetate.

My compositon material gives a product which is only slightly thermoplastic and hardens first by absorption of the solvent by the backing sheet (if one is used), secondly by precipitation processes when the plastic composition material contacts with the moisture and water carried by the water swollen gelatine copy relief, and finally, by evaporation of the residual solvent through exposure of the material to the air.

As many changes can be made in the steps and ingredients used without departing from the scope of my invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not ina limiting sense.

What I claim is:

1. 'A moldable composition for forming printing plates, comprising a plurality of cellulose acetate materials of differential viscosity, a minor proportion of a plasticizer, the whole being dissolved in an organic solvent, the composition having a viscosity in excess of 10 seconds.

2. A hardenable composition for printing plates and the like, comprising cellulose acetate materials of difierential viscosity, a resinoid, a small quantity of a plasticizer, and a suflicient quantity of a volatile solvent to render the mass workable, the composition having a viscosity in excess of 10 seconds.

3. A hardenable composition for printing plates and the like, comprising cellulose acetate materials of differential viscosity, a relatively small amount of tricresyl phosphate, and a ketonic solvent, the composition having a viscosity in excess of 10 seconds.

4. A moldable composition for forming printing plates comprising a plurality of cellulose acetate materials of differential viscosity and a small amount of a plasticizer dissolved in a volatile solvent, the composition having a viscosity greater than 50 seconds (by falling ball test).

5. A moldable composition for forming printing plates comprising a plurality of cellulose acetate materials of differential viscosity and a small amount of a plasticizer dissolved in a 'volatile solvent, the composition having a viscosity of between 50 and 70 seconds (by falling ball test).

6. A moldable composition for forming printing plates comprising a mixture of cellulose acetates of difierential viscosity, a small amount of a plasticizer comprising an amount not more' than 5% of the cellulose acetate base and a volatile solvent, and having a viscosity of between 50 and '70 seconds (by falling ball test.)

7. A moldable composition for forming printing plates comprising, a plurality of cellulose acetate materials of differential viscosity, a plasticizer added in such minor proportions as not to substantially decrease the hardness of the finished product, the whole being dissolved in an organic solvent, the composition having a viscosity substantially in excess 01 seconds, whereby mechanical pressure is required to force the composition into impressions of the order of those obtained in a sensitized water swollen gelatin copy reliei'.

8. A potentially hardenable composition for the manufacture of printing plates comprising, a major percentage of a plurality of cellulose acetate materials of diflerential viscosity, minor percentages of a suitable plasticizer and a resinoid, and a suiiicient quantityoi volatile solvent to render the mass moldable, the composition having a viscosity in excess of 50 seconds, whereby mechanical pressure is required to force the composition into impressions of the order of those obtained in a sensitized water swollen gelatin copy relief.

9. A hardenable composition for making printing plates comprising, a plurality of cellulose acetate esters of diflerential viscosity,v a resinoid, a small quantity of a plasticizer, and a suflicient quantity of a volatile solvent to render the mass workable, the composition having a viscosity sub- .stantially greater than 10 seconds.

10. An improved printing plate comprising. a

cellulose acetate base and a plasticizer, the cellulose acetate including a plurality of cellulose acetate compositions of diflerent viscosity, the plasticizer comprising an amount not more than 5% 01' the cellulose acetate base.

assaasocomposition having a viscosity in excess oi 10 seconds, the tricresyl phosphate comprising an amount not more than 5% o! the cellulose acetate base.

12. A hardenable composition for making printing plates including, a plurality of cellulose acetates of diflerential viscosity, a minor proportion of tricresyl phosphate, and a sufllcient quantity of a volatile organic solvent to render the mass workable, the composition having a viscosity in excess of '10 seconds.

13. A hardenable composition for making printing plates including, a plurality of cellulose acetates of varying viscosity, 9. minor proportion 01' triacetin, and a sui'iicient quantity of a volatile solvent to render the mass workable, the composition having a viscosity in excess of 10 seconds.

14. A hardenable composition for making printing plates comprising, a plurality of cellulose acetates of differentialviscosity, a small quantity of a plasticizer, and a suillcient quantity of tetrachlorethane to render the mas workable, the composition having a viscosity in excess of 10 seconds.

RALPH H. McKEE.