US 3318240 A
Description (OCR text may contain errors)
United States Patent 3,318,240 MATRIX MAT FOR PLASTIC PRINTING PLATE Winfred Doyle Boggess, Indianapolis, Ind., assignor to The Beveridge Paper Company, Indianapolis, Ind., a corporation of Indiana No Drawing. Filed Feb. 21, 1966, Ser. No. 528,806 5 Claims. (Cl. 101401.2)
The present invention relates to a process of preparing a stereotype matrix mat for use in the preparation of plastic printing plates and further relates to the matrix mat having improved surf-ace properties when prepared by said process. This invention is based in part on the subject matter disclosed in Ser. No. 355,098, filed Mar. 26, 1964, and now abandoned.
It is standard practice in the newspaper publishing industry to print newspapers from metal printing plates formed of lead alloy. However, relatively recently it has been found that improved printing plates can be manufactured using thermoplastic resins in place of lead alloy. Such thermoplastic resin printing plates are more desirable than the lead alloy plates because of the lighter weight of the plastic and the sharper definition in printed word and illustration that can be achieved with plastic.
In general, the above mentioned lead alloy plates are conventionally cast by the use of stereotype mats each of which consist of a relatively thick sheet of felted cellulose fibers which may be composed of rag stock, cotton linters, wood fibers produced by chemical pulping processes, or the like. The stereotype mat itself is usually prepared by forming an aqueous slurry of the fibers in the wet machine or a paper making machine. The slurry is felted out in the form of a web on the screen of the wet machine and the Web is wound until a multiplicity of layers has been built up to form a sheet or mat of the desired thickness. for example, powdered clay, silicate or talc, is mixed with the fibers in the wet machine and is, therefore, incorporated with the fibers in the body of the final sheet or mat.
The resulting sheet is then removed from the roll and is dried and compressed to a thickness suitable for a stereotype mat, usually in the range of .026 to .070 inch. As the compressing operation is in process, the surface of the mat, which is to receive the impression and against which the printing plate is to be cast, is calendered in order to provide a dense smooth surface with as few projecting fibers as possible. In contrast, the opposite surface of the mat is made porous by retaining said opposite surface against a porous uneven surface such as a woven fabric belt. In this manner, the opposite surface of the mat becomes porous and irregular and easily permits the passage of moisture. The impression-receiving surface of the mat is herein called the face and the opposite surface is herein called the back.
After a matrix mat has been manufactured according to the above process, it has a certain amount of moisture therein depending in part upon the requirements of the customer. If the customer or newspaper plant is desirous of using a stereotype mat having high shrinkage properties, the mat may contain moisture as high as 35% by weight. On the other hand, if low shrinkage properties are desired, for example, in the situation of multi-colored printing wherein the various colors must register with one another, the moisture content of the mat may be relatively low such as, for example, 12% by weight. At any rate, in its moistened, and thus plastic condition, the stereotype mat is pressed down against the form or pattern which may be an assembly of linotype characters, electrotypes, etc. arranged in the desired final configuration of the printed newspaper page. The relatively damp matrix mat is then formed into a semi-circular shape by mounting Usually, a filler such as,
3,318,240 Patented May 9, 1967 upon a semi-circular element and is hardened and dried out in the shape by the application of drying heat thereto in an apparatus known as a scorcher.
It is important that the moisture escape rapidly from the matrix without the matrix rupturing by reason of the formation of steam within the mat. Because the back of the mat is relatively porous and irregular as described above, the moisture can readily escape from the back so that no rupturing occurs.
After the mat has been dried and hardened in the relatively rigid condition as above described, the face containing the impression is adapted to impart an accurate reproduction to the printing plate which is cast against the mat. conventionally, the reproduction is made by casting the molten alloy metal against the face of the mat in a casting box and subsequently allowing the metal to cool and solidify. As mentioned, the dry mat is curved to a semi-circular shape in order to form the printing plate in a similarly curved shape for the reason that most printing is done by means of cylindrical presses.
It has been found that when an attempt is made to prepare a thermoplastic resin casting by using said resin in place of lead alloy in the above described process employing a stereotype matrix, the resin flows into the pores of the mat on the face thereof even though the face is dense and smooth and even though there are no visible projecting fibers. Consequently, after the resin printing plate has hardened, it is always difiicult and frequently impossible, to separate the printing plate from the paper matrix. In the process of separating the plates the loose fibers are picked out and show up on the finished plate as well as on plates which are subsequently made from the same matrix mat. For the above reasons, an important object of the present invention is to provide a process of preparing a stereotype mat having good release properties for use in the preparation of resin printing plates.
Another object of the invention is to provide an improved stereotype mat which has good release properties when used with a resin plate.
Still another object of this invention is the preparing of an improved stereotype mat whereby the release characteristics of the mat are enhanced by plasticizing in a proper manner the polyvinyl alcohol resin with an appropriate plasticizer in order to intimately surround the surface fibers in the face of the mat with the resin to prevent these from being picked out and thus giving, for example, poor half tone images. Moreover, another aspect of this invention is the coating of the polyvinyl alcohol resin treated mat with another coating to obtain improved release in regions of the mat such as sharp crevices and sharp corners of the different letters.
Other objects of the invention will become apparent from the description which follows.
In fulfillment of the above and other objects, this invention provides a process of preparing a stereotype mat comprising mixing a properly plasticized polyvinyl alcohol and water, placing the mixture upon the molding and casting surface of a stereotype mat, and then spreading the mixture uniformly across said molding and casting surface to form a uniform layer of polyvinyl alcohol, said layer containing from about .5 to about 5 pounds of polyvinyl alcohol per 1,000 square feet of said molding and casting surface. Preferably, the water is removed from said mixture both by absorption into the mat and by evaporation.
In order to obtain a matrix mat of reduced pick-out characteristics the polyvinyl alcohol used must be plasticized with the following plasticizers: glycerine, ethylene glycol, p,p-dihydroxy diethyl ether, 1-3 butane diol, or the like. The preferred plasticizer is 1-3 butane diol.
Acceptable properties are obtained when 12.5 parts by weight of plasticizer are used per parts by weight of polyvinyl alcohol in the form of glycerine. Preferred results are obtained when both glycerine and 1-3 butane diol are used as plasticizers. When these plasticizers are mixed with 2 parts by weight glycerine and 1 part by weight l-3 butane diol and 12 /2 parts by weight of this mixture is used per 100 parts by weight of polyvinyl alcohol, the results are much improved over the use of glycerine alone.
In order to further improve the release of the cast resin plates especially in the sharp crevices and corners which may expose loose cellulose fibers an additional coating agent is used. This agent is sold under the trademark Zonyl RP by the Du Pont Chemical Company, Wilmington, Delaware, and reputedly has the chemical description of a polyfluoroalkyl phosphate. Physical properties of Zonyl RP are given in Table I below.
TABLE I. PHYSICAL PROPERTIES OF ZONYL RP Unaffected (Zonyl RP should To freezing be stirred after thawing). To pH changes Unaffected, pH 7.0 and up.
The amount of Zonyl RP used is of from .5 pound to 3.0 pounds per 1,000 square feet of mat surface. A preferred amount is 1 pound 3 ounces per 1,000 square feet of mat surface.
As a consequence of the above treatments a properly prepared matrix mat gixes improved properties such as no pick-out of fibers.
In practicing the process of the present invention, the steretoype mat used preferably includes co-felted cellulose fibers and discrete particles of a filler. The above described spreading operation, whereby the polyvinyl alcohol solution is applied to the mat, is accomplished preferably by means of oscillating brushes in order that the polyvinyl alcohol mixture not only coats the complete surface of the face, but also penetrates into interstices of the mat. A. suitable oscillating brush arrangement for the present purpose might comprise a coating apparatus manufactured by the John Waldron Corporation of New Brunswick, N; 1., Model 1459A. After application of the liquid polyvinyl alcohol mixture, a substantial portion of 'the water is removed therefrom by absorption into the mat and evaporation.
The Zonyl RP solution must be sprayed on the face of the mat,'that -is, over the surface coated by the plasticized polyvinyl alcohol. This spraying is preferably done by airless spray equipment manufactured by Alemite Sales Company, Inc., of Indianapolis, Ind. The Zonyl RP as described in Table I is diluted before spraying in the following proportions: 1 part by weight Zonyl to 2.3 parts by weight water. This mixture is then sprayed on the mat so as to apply about 1 pound 3 ounces of Zonyl RP (as described in Table I) per 1,000 square feet of mat surface.
In one preferred embodiment of the invention, the gly cerine plasticizer was added at a proportion of one part by weight of glycerine to eight parts by weight of polyvinyl alcohol (4% ,by'w'eight in water).
, least 4%.
An aqueous slurry of coniferous alpha pulp fibers is placed in a beater and beaten until the fibers are well separated and there is suitable hydration thereof. A suitable amount of a filler, in this case approximately 30% of powdered silicate, based on the oven dry weight of the fibers, is added to the slurry, and the mass agitated until a thorough, initimate mixture of fiber and filler is obtained. The slurry is then transferred to a wet machine and the mixture of fiber and filler is felted out on the screen in the form of a web and the web transferred to a roll upon which it is wound until a sheet of the desired thickness is obtained. The sheet is then removed from the roll and dried and compressed to the desired thickness, usually between 0.26 and .070 inch, for example, .068 inch. The compression and drying are carrier out with a porous woven fabric sheet against the back of the mat and with a calendering roll operating across the face of the mat, whereby the face is compressed to a relatively dense, smooth, uniform surface, while the back is relatively porous and irregular.
A coating is then applied to the calendered face of the stereotype mat of the following composition:
10 lbs. polyvinyl alcohol 30 gallons of water The polyvinyl alcohol is added to the water and the resulting liquid composition is thoroughly mixed and heated to 180200 F. to provide a fluid liquid.
The composition is applied to the face of the mat by the coating apparatus mentioned above which applies a uniform coating over the surface of the mat. The compotion is applied to the mat in an amount providing one pound of polyvinyl alcohol for each 1,000 square feet of surface of the mat. The mat is then moved beneath the above mentioned oscillating brush arrangement whereby the composition is caused to penetrate into the mat. The water in the composition is caused to evaporate and to be absorbed into the mat. The mat is then re-wet by suitable spraying apparatus until it contains 18% water based on the dry weight of the mat.
The mat is then subjected to the usual molding procedure in'which a printing form containing type and/or illustration is impressed against the face of the mat. The mat takes a deep and sharply defined impression of the form. The mat is then dried in a scorcher and placed in in a a casting box. A thermoplastic resin is cast against the mat according to conventional casting procedure. An exact reproduction of the form is made and the cast plate separates from the stereotype mat with an excessive tendency to adhere. This is demonstrated by the discoloration which the resin causes when it penetrates into the face of the mat.
Throughout the specification, the term polyvinyl alcohol is meant to include a material prepared by hydrolysis of polyvinyl acetate having a solubility in water of at In general, at least 35% of the acetate groups must be hydrolysed from polyvinyl acetate to yield a polyvinyl alcohol having the desired solubility in water. I prefer to use, however, a polyvinyl alcohol which still retains about 5% or so of the original acetate groups, although any polyvinyl alcohol having from about 1 to 5 percent residual acetate groups is fully operative.
Example N0. 2
A stereotype mat is formed in the manner described above in connection with Example No. 1 up to and including the drying and compressing of the mat by a calendering operation to bring the mat to the desired thickness. A coating is then applied to the calendered face of the stereotype mat, said coating including 10 pounds of polyvinyl alcohol mixture and 30 gallons of water. The polyvinyl alcohol mixture is added to the water in the same manner described above with relation to Example No. 1 and the resulting liquid composition is thoroughly mixed and heated to 180-200 F. to provide a fluid liquid.
The polyvinyl alcohol mixture of the present example includes 8 parts by weight of dry Vinol 165 and 1 part by Weight of a mixture including glycerine and 1-3 butane diol at a two to one ratio by weight. Vinol 165 is a polyvinyl alcohol dry powdered product of the Airco Chemical Company, 150 E. 42nd St., New York, N.Y. Vinol 165 is further identified by the fact that it has a viscosity of 55-65 cps., a percent hydrolysis of 997+, a percent volatiles max. of 5.0, a max. ash percentage of 1.0, and a pH of 6-8. In the present example, the compositon is placed upon the face of the mat in an amount providing one pound of polyvinyl alcohol for each 1,000 square feet of surface of the mat. The polyvinyl alcohol is applied to the mat by the use of the above described oscillating brush arrangement. After the water in the composition evaporates and is absorbed .into the mat, the mat is re-wet by suitable spraying apparatus until it contains water based on the dry weight of the 'mat. It will be noted that the above mentioned glycerine and butane diol provide plasticizing action. The use of the above two-component plasticizer makes possible reasonably effective casting and release of liquid thermoplastic resin.
Example N 0. 3
The stereotype mat is formed and treated in exactly the same manner described above in Example No. 2 with the exception that the polyvinyl alcohol mixture consisting of glycerine and of 1-3 butane diol in a 2 to 1 weight ratio is applied to the mat surface in the amount of 2 pounds of polyvinyl alcohol per 1,000 square feet. The resulting mat exhibits the same excellent molding but does show improved release over Example No. 2 when casting liquid thermoplastic resin thus demonstrating that the quantity of coating mixture per 1,000 square feet of mat surface is of prime importance.
Example N0. 4
This example is identical to Example No. 3 except that 5 pounds of polyvinyl alcohol per 1,000 square feet were applied instead of 2 pounds per 1,000 square feet. No appreciable improvement in release is effected.
Example N0. 5
The stereotype mat is formed an-d treated in exactly the same manner described above in Example No. 3. The polyvinyl alcohol and plasticized mixture is applied as above described. The coating is dried by absorption and external infra-red heat. It is then passed through a spraying tunnel where the Zonyl RP is sprayed on the coated side of the mat over the polyvinyl alcohol coating. The Zonyl RP (as described in Table I) is prepared for spraying by dilution with water in the amount of 1 part Zonyl to 2.3 parts of water. The speed of the mat through the spraying tunnel and the volume of Zonyl sprayed must be controlled so as to apply about 1 pound 3 ounces of Zonyl RP (as described in Table I) per 1,000 square feet of mat surface. The diluted Zonyl and the water mixture is then caused to dry by absorption and external heat and the mat then re-wet to 15 to 18% water based on the 'dry weight of the mat. It is then molded and cast in exactly the same way as described in preceding examples. The resulting mat readily separates from the cast plate and exhibits excellent release properties. The method of production described in this example is the present commercial method used by applicants assignee.
Example N0. 6
The stereotype mat is formed and treated in exactly the same manner described above in connection with Example No. 3 with the exception that the polyvinyl alcohol mixture in dry powdered form consisted of 8 parts by weight dry Vinol 350 plus a plasticizer mixture consisting of 1 part by weight of glycerine and of 1-3 butane diol in a 2 to 1 weight ratio. The resulting mat exhibits the same molding and release properties when casting liquid thermoplastic resin as does the mat of Example No. 3. Vinol 350, also a product of Airco Chemical Company, is a polyvinyl alcohol in dry powdered form having a viscosity of 55-65 cps., a percent hydrolysis of 98.0-98.8, a percent max. volatiles of 5.0, a percent ash of 1.0 and a pH of 6-8.
Further examples The following further examples of the invention were carried out in exactly the same fashion as Example No. 3 with the exception that the polyvinyl alcohol was applied to an extent providing 2 pounds of alcohol for each 1,000 square feet of surface and the water in the solution is caused to evaporate and to be absorbed in the mat. Also the mats are re-wet until the mat contained 15 water based on the dry weight of the mat.
Example N0. 7.Vinol 165 plus glycerine (8 parts by weight of dry polyvinyl alcohol to 1 part by weight glycerine) Example N0. 8.-Vinol 350 plus glycerine (8 parts 'by weight of dry polyvinyl alcohol to 1 part by weight glycerine) Example N0. 9.Vinol plus glycerine (8 parts by weight of dry polyvinyl alcohol to 1 part by weight glycerine) Example N0. 10.-Vinol plus 1-3 butane diol (8 parts by weight dry polyvinyl alcohol to 1 part by weight of 1-3 butane diol) Example N0. 11.Vinol 350 plus 1-3 butane diol (8 parts by weight dry polyvinyl alcohol to 1 part by weight of 1-3 butane diol) Example No. 12.-Vinol 125 plus 1-3 butane diol (8 parts by weight dry polyvinyl alcohol to 1 part by weight of 1-3 butane diol) Each of the above Examples 7-12 produced mats which exhibited excellent molding and release prope'rties which properties when complemented with the Zonyl RP treatment produce resin plates of superior properties.
While the invention has been disclosed and described in some detail in the foregoing description, the same is to be considered illustrative and not restrictive in character, it being understood that only preferred embodiments have been described and that all changes and modifications that come within the spirit of the invention and scope of the claims are also desired to be protected.
The invention claimed is:
1. A process of preparing a stereotype mat for use in the casting of resin printing plates which comprises mixing polyvinyl alcohol, plasticizer and water, said polyvinyl alcohol containing no more than 5% residual acetate groups, placing said mixture upon the molding and casting surface of a stereotype mat, and spreading said mixture uniformly across said surface to form a uniform layer of between .5 and 5 pounds of polyvinyl alcohol per 1,000 square feet of said molding and casting surface, and removing a portion of the water from said polyvinyl alcohol by absorption into said mat; and further treating the surface of said mat with a release improving agent, said release improving agent being a polyfiuoroalkyl phosphate, said polyfiuoroalkyl phosphate being characterized as a clear, light brown liquid having an alcoholic odor, 33% solids, a density of 8.85 lbs./ gal. at 77 F., a viscosity of 10 cps. at 77 .F., a flash point, Tag Open Cup, of 105 F, a pH of 7.0, said polyfiuoroalkyl phosphate being soluble in water in all proportions, slightly soluble in polar solvents and having negligible solubility in non-polar solvents, said polyfiuoroalkyl phosphate being unaffected by aging, freezing and pH changes of 7.0 and up.
2. A process according to claim 1 wherein the surface of said mat is treated with said polyfiuoroalkyl phosphate by depositing on the mat from about .5 pound to 3.0 pounds of said polyfluoroalkyl phosphate per 1,000 square feet of said surface.
3. A process according to claim 2 wherein said polyfiuoroal-kyl phosphate is sprayed onto the surface of said mat.
4. A process according to claim 2 wherein said surface of said mat is treated with said polyfluoroalkyl phosphate by depositing on the matl pound 3 ounces of said polyfluoroalkyl phosphate per 1,000 square feet of mat surface.
5. A stereotype mat comprising co-felted cellulose fibers and discrete particles of a filler, said mat having present at the molding and casting surface thereof a uniform coating of plasticized polyvinyl alcohol, said polyvinyl alcohol containing no more than 5% residual acetate groups, said polyvinyl alcohol coating carrying on its surface fromabout .5 to about 3 pounds per 1,000 square feet of mat'surface of a release improving agent, said release improving agent being a polyfluoroalkyl phosphate characterized as a clear, light brown liquid having an alcoholic od-or, 33% solids, a density of 8.85 lbs./ gal. at 77 F., a viscosity of 10 cps. at 77 F., a flash point,
Tag Open Cup, of 105 F., 'a pH of 7.0, said poly-fluoroalkyl phosphate being soluble in water in all proportions, slightly soluble in polar solvents and having negligible solubility in nonpola'r solvents, said polyfiuoroalkyl phosphate being unaffected by aging, freezing and pH changes of 7.0 and up.
References Cited by the Examiner OTHER REFERENCES Handbook of Plastics, 2nd edition, New York, D. Van Nostrand Company, Incorporated, 1949, pages 569, 570, 724, and 725.
ROBERT E. PUIJFREY, Primary Examiner.
L A. BELL, Assistant Examiner.