US3160093A - Planographic printing plate receptive to carbon ribbon imaging - Google Patents

Description

Dec. 8, 1964 R. T. MCCRUM ETAL 3,160,093

PLANOGRAPHIC PRINTING PLATE RECEPTIVE TO CARBON RIBBON IMAGING Filed Nov. 5, '1962 PLANOGRAPHIC COATING OFAN CONVENTIONAL MACHINE HYDROPHILIC ADHESIVE APPLIED CASEIN-CLAY CONTAINING 2T0 5 PARTS PRIME COAT PIGMENT TO I PART ADHESIVE SIZED CELLULOSIC WEB QC 40 TO IOO POUNDS REAM wE|GHT HYDROPHOBIC HIGHLY PIGMENTED POLYMER INVENTORS RUSSELL T MC CRUM ATTORNEYS United States l atent C) "ice 3,160,093 PLANOGRAPHKC PRTNTING PLATE RECEPTIVE T CON RIBBON MAGING Russell T. McCrum, South Portland, Alfred E. Belisle, Westbrook, and Raymond L. Oransky, Portland, Maine, assignors to S. D. Warren Company, Boston, Mass., a corporation of Massachusetts Filed Nov. 5, 1962, Ser. No. 235,480 4 Claims. (Cl. l01-149.2)

This invention relates to an improved paper-base planographic printing plate for duplicating processes where carbon-ribbon imaging is used. It is more particularly concerned with a paper master that satisfactorily meets the rigid requirements encountered in lithographing checks with magnetic inks.

Paper-base planographic printing plates are now commonly employed for lithographic printing. US. Patent 2,534,650 outlines the general properties that paper-base plates must have such as dimensional stability, lack of tone-up, quick starting and the like.

In 1958, the American Bankers Association approved the magnetic ink character recognition (MICR) method for encoding checks with type E-13b font for mechanized check handling systems. It was found, however, that the paper-base plates then avail-able were not suitable for the MICR program. They failed to print the magnetic ink with the accuracy and uniformity that was needed. This is brought out in an article by M. H. Schaifner, Lithographing Magnetic Ink Successfully, National Lithographer, May, 1962.

While other methods of printing such as letter press could be used to encode the checks for the MICR program, the fact that runs are short makes it desirable if not necessary to use the least expensive master and imaging procedure possible. The master also must be easy to work with and reliable. The short runs, in the order of 150 to 300 prints per run, usually 6 up, require a master that will image readily, start quickly, print accurately and uniformly without toning and remain dimensionally stable.

Three types of read-out or sorting machines are currently being used in the MICR program. One type reads the leading edge of the character only, the second observes the entire outline of the character and the third measures the entire magnetic flux or force of the magnetic ink character. It can be appreciated that the definition, register and uniformity of the printed characters are critical. Any toning is unacceptable. Small variations in character position, in letter shape or in magnetic response from check-to-check will cause the checks to be rejected.

The magnetic inks are highly loaded with the magnetic solid, usually ferric oxide in an amount of about 8 Weight percent.

ink. Some slight indentation is required at the time of" impact of the typewriter-key during imaging in order for the master to properly receive the dope from the carbon ribbon. If the identation imparted is too great, however, start-up is slow because several passes are required before the ink will flow into and fill the indented characters When the depressions are filed, the transfer of ink from too deep a cavity is non-uniform in charac- Such highly loaded inks are diflicult to work with. They do not flow well and quite readily cause 3,160,093 Patented Dec. 8, 1964 ter outline. It is the defining of this indentation problem. that is perhaps the essence of this invention.

This is not to say that several other physical and chemical features of the constituents of the planogr-aphic plate such as those that control toning and dimensional stability are not also of considerable importance and need to be controlled within select ranges to secure satisfactory performance. Certainly, however, it is the criticality of the indenting properties or spring-back qualities of the plate that is the principal key to producing satisfactory plates for the MICR program. It is controlling on both the start-up speed and the uniformity of ink deposit given by the plates.

The striking force of the keys of the typewriters used for imaging vary from day-to-day. It is not practical to keep adjusting them to have the same striking force. The tendency is simply to increase the striking force of all of the keys of a unit if one of the keys is not striking hard enough. It is essential that a planographic plate have some tolerance for or abuse resistance to'excessive striking forces. It is not clear Whether the tolerance of the plate of this invention stems from its ability to resist being indented or from its ability to spring-back after indenta tion, but the end result is that the final amount of identation is about optimum for printing the heavy magnetic inks.

Best results are secured when the ink is transferred from a relatively smooth surface. The amount transferred is uniform in thickness and has good definition. When initially imaged, some embossure can usually be observed on the reverse side of the plate. This embossure will normally disappear or be pressed-out during printing because of the nip pressure between the plate and blanket. It may be that the slow start-ups of conventional plates are in part caused by the resistance of a plate to being pressed-out to a smooth surface. It is believed that in the present invention that the combination of indentation resistarice, spring-back and ability to be pressed-out to some extent accounts for the quick start-up quality of the plate. Evidently the strength of the plate is such that it will image properly even with excessive key forces and yet it is spongy or flexible enough to conform adequately to to the platen of the typewriter and to respond quickly to the nip pressure during printing.

No standard test was available for determining the critical indentation value of a plate and it was necessary to develop for this purpose what is termed for convenience the Indentation test. This test is carried out as follows: The specimen to be tested is imaged with the dash symbol of the E-l3b font using an International Business Machine (ABA) Executive Model typewriter, arljusted to have a striking impulse of 0.01-0.015 lb.-Sec. (#6 pressure) and equipped with an IBM polyethylene ribbon. A mold form is placted around the image thus made on the master with a castable material such as a low melting polyethylene or a wax is poured in to make a negative of the image. The third mark of the dash symbol, the one with the smallest surface area, is then shaved with a microtome mil slices) to determine its height. An average of at least 4 measurements is used. To be suitable for MICR printing the identations of the plate as determined by this test shouldbe under 1 mil and preferably are in the range of 0.2 to 0.8 ofa mil (thousandth of an inch).

This test appears to correlate with measurements of embossure using a Federal Caliper Tester (0.1 mil measments). The caliper is taken on either side of the symbol and at the embossure caused by the'symbol, with the average difierence being determined. The symbol 1 is used in this case. While the magnitude of the measurements of the two tests are different, the degree of difference observed between plates isabout the same.

3. While a short-run paper-base planographic master usually has only two main elements, a cellulosic web body .stock and a pigmented hydrophilic top coating to receive should satisfy the conditions outlined'in the following 5 paragraphs. For convenience the specific ranges for the various properties are summarized in a table presented hereinafter.

The Body Stock (Cellulosic Web) The caliper and density of the cellulosic web should be so selected that the finished plate will have adequate strength and yet enough flexibility to conform to the typewriter platen and to the printing roll. Broadly, a paper having a ream weight of 40 to 100 pounds can be used. A lightly sized sheet, preferably one that has been machine coated to improve its smoothness, is preferred. The Cobb water absorption value of the base sheet is probably its most significant inspection." It is desirable for the web to have some amount of resistance to water uptake but not so much as to prevent proper absorption of and bonding with the latex barrier coating.

. The Pigmented Barrier Coating While the web selected will influence the spring-back qualities of the plate to some extent, it is the tough rubbery nature of the barrier coating that primarily controls springback. It also imparts water resistance to the plate because of its hydrophobic nature and thus helps to as- The preferred barrier coating must be cured at an ele-* vated temperature. It is preferably just dried and calendered before the top coating is applied, and is cured only after the top coating has been applied and dried.- The barrier coating has a Cobb (100 square centimeters,-

120 seconds) of over v0125 before curing and under 0.15 after curing in absence of top coat. Thus it is more of a semi-barrier before curing.

The Top Coating The type of planographic top coating used very materially affects the performances of the master. The top coating has little effect on the indenture and dimensional stability of the plate, but it does control the image letdown, image retention and toning performance of the master. I

Proper imaging of a master is important. With carbon" ribbon imaging using a film type of ribbon such as poly ethylene or acetate, all of the oleaginous dope should be transferred at the area of impact. Improper images must be corrected by hand or discarded. In some instances as many as 50 percent of the masters prepared With con- 1 ventional plates had to be discarded for this reason alone.

As noted before, the high solids content magnetic inks tone readily and cause dirty or dingy backgrounds. The

nature of the film forming hydrophilic binder used to hold the pigment is important in this respect. Its nature should be such, in combination with the pigment, as to allow for sure dimensional stability. The thickness of, the coating and the elastomeric properties have, of course, complementary effects on the springback properties of the master, and one can be increased to some extent as the other is decreased. The amount of latex used and its elastomeric properties must be sutficient to impart the desired springback properties but the coating cannot be so tough as to adversely effect the flexibility or conformity of the plate and cannot be too impervious as blistering during drying may result. If the barrier coating is too soft, even though it be water-proof, blocking may result and the finished plate may be too limp. Latices based on acrylic copolymers were found to be suitable. They can be cross-linked.

on two sides with the same composition and thickness is desirable to ofiset curling. The preferred compositions have a high pigment content, greater than 1.7 parts tol part elastomer. (excluding resin),'which helps to prevent blocking when masters coated on two sides are stacked together.

It should be emphasized that and flexibility of the master as determinedby the base stock and barrier coat are quite important. The printed magnetic ink characters must be in accurate register on the check and any misalignments will result in the checks being rejected by the'sorting machines. Several of the the dimensional stability uniform wetting of non-image areas by the fountain solution and the retention of the water film adequately throughout the length of the run. I 4 1 I There is no appreciable drain-oft" of the adhesive intd -the body stock from the top coating solution because of the barrier coating. If slow drying conditions are used the amount'of adhesive in the composition should be in-' creased to accommodate a slight amount of draifi fit Fast drying is preferred, however, preferably in less than i -minute at air temperatures greater than 300 F. Image let-down from a ribbon and image retention are improved by increasing the clay or pigment content ofthe top coat= ing. Too much pigment results in poor stop and restart performance (toning after a stop without re-wetting the master). It' is preferred to use a hydrophilic adhesive that will give adequate bonding with rapid drying at pig ment to adhesive weight ratios in the range of 2/1 to 5/1 High oil absorption pigments such as precipitated calcium carbonate are preferred. f

Generally speaking, the polyvinyl alcohol-type adhesive's were found to be most suitable but others such as hydroxy ethyl starch and carboxy methyl'cellulose can be used. Whencast, they have the desired hydrophilic but water insoluble nature and have a high pig-ment bonding power so that only a small amount need be used. In addition they bond well directly to the hydrophobic acrylic type barrier coating so that no bridging adhesives are re quired between the top and barrier coatings. When cast as an 8 mil film free of pigment, it is preferred that the adhesive have a tensile strength of at least 7500 p.s.i. and an elongation of at least 260%, both at 20 in./ min., 43% RH. and 23 C. p v

The surface off-the master should be as smooth as possible but should not be too slick. This smoothness can be obtained by several means such as calendering or cast coating. It is preferred to Work with a web that has had a machine-applied prime coat. 1 The barrier coating is then applied, for example by means of a roll coater, dried prior art master's investigated failed-from the standpoint 1 of their dimensional stability because the Web became quately conform to the platen of the typewriter.

i wetted with water and swelled or stretched Others I failed because the web was not'flexible enough to ade---- and cal'endered. This is followed, for example by application of the'top coating by an air knife coater, and drying I with the master thereafter being cured .at air temperature of,'400 to 800 F. for-a few seconds and calendered. Calendering can be carried outbeforecuring if desired; This procedure will produce thesmoothness and uniform-- ity of thickness that are desired.

The drawing attached to and forming a part of the; specification, and the following example williserve to make this invention clear. The drawing illustrates in enlarged cross section the improved planographic plate of this invention.

Referring to the drawing, it can be seen that the pl-anographic master of this invention comprises a sized cellulosic web base-stock machine coated on one side with a conventional prime coat and then coated on both sides with an elastomeric hydrophobic pigmented barrier coating to which a top planographic coating of a pigmented hydrophilic adhesive is directly bonded on one side.

EXAMPLE A paper web was selected of the desired weight and thickness. The furnish for the web was sized and the web was machine coated with a conventional casein-clay prime coating with some urea formaldehyde added.

The desired barrier coating was then applied to both sides of the Web by a roll coater. The amount of clay used to extend the elastomer in the coating was not such as to unduly eifect strength or resiliency of the coating but was greater on a weight basis than the amount of elastomer. The hydrophobic film forming elastomer polymer used in this case was an acrylic copolymer in the form of a latex. This polymer by itself gave a stretchable but tough coating but did have a tendency to block and was not as water resistant as desired. A thermosetting resin was thus incorporated into the barrier coating formulation to react with the acrylic copolymer. The amount used, while fairly high, surprisingly did not offset the rubbery nature of the polymer. The coating was dried and then calendered.

The top coating was applied after drying of the barrier coating. The polyvinyl alcohol used was a very highly hydrolyzed alcohol which can be cast from a colloidal water solution to give a smooth uniform coating. This coating adheres tenaciously to the barrier coating and suppresses the hydrophobic nature of the barrier coating. The top coating was applied by means of an air knife followed by drying in a tunnel dryer. The coatings used in this example were then cured or crosslinked by heating the paper to 400 F. (paper temperature) for 10 seconds in a curing oven.

Inspections of Planographic Plate Constituents Range Example Preferred Paper Base (body stock):

Ream Weight, lbs 52 to 56. Caliper, mils 3.5 to 4 3.8. Cobb water absorption, gms./l00 cm. 0.22 to 0.45 0.35.

(30 seconds). Tear Strength, Elmendori 80 to 90 85. Burst strength, Mullen 35 to 45 40. Machine coatin Pounds adhesive plus pigment] 3 to 4.

ream. Pounds pigment (clay)/adhes1ve 2 to 4 4.

(casein) ream. Barrier Coat (pigmented latex):

Percent total solids 25 to 50 39.9. Pounds solid-applied/side/ream 5 to 10. 7. Weight ratio of pigment to hydro- 0.5 to 5 1.43.

phobic elastomer (plus resin it used). Weight ratio elastomer to resin it used 1 to 4 2.5. Drying conditions:

Air temperature F 180. Time, minutes 15. Oobb* water absorption of coating Below 0.15 0.10.

cured without top coating. Top Coat (planographie coating):

Percent total solids 21. Pounds solids applied/rennin 6. Weight ratio of pigment/binder- 3. Drying conditions:

Temperature, F 280-300. Time, seconds 25. Curing conditions: I

. Air temperature F 400 to 800.--- 600. Time sec. Cobb; water absorption of cured top Under 0.15.- Under 0.15.

coa mg. Indentation Test Value, mils Under 1 0.5.

*TAPPI Standard Test No. T441 M-GO (100 square centimeters, 120 seconds).

6 NOTES 1) The furnish for the paper base of the example consisted of equal parts of long and short wood fibers, modenately beaten and well sized with rosin.

(2) The reactive latex used in the barrier coat of the example was an acrylic latex (Rohm & Haas, Rhoplex HA-12). The resin used was a urea formaldehyde commonly used to impart wet strength to papers (Colab Resin Corp., Colabco #120). Finely divided clay was used as the pigment. The ingredients were mixed by simple stirring.

(3) The binder used in the top coat of the example Was a fine particle size reactive film forming 99.85% hydrolyzed polyvinyl alcohol having a viscosity in 4% aqueous solution of 26 cps. (20 0.). (Air Reduction Chemical Company, Vinol 125.) A clear 8 mil film cast on a glass plate from a solution of the resin has a tensile strength of 9,400 psi. (20 in./min.) and an elongation of 25% (20 in./min.), both at 43% RH. and 23 C. The resin was first dissolved in 9 times its weight of water by heating to 200 F. The pigment used was 1 part of precipitated calcium carbonate to 3 parts of English Coating clay suitably dispersed in water. A

small amount of a melamine formaldehyde solution was used, (American Cyanamid, Parez 611) in the amounts of 12 parts by weight (dry weight) per parts of the polyvinyl alcohol. Also, a water solution of 20 pounds of zinc acetate (dry weight) per 100 parts of the pigment were incorponated into the formulation. The ingredients were blended by simple high speed mixing. Small amounts of anti-foamants were incorporated into thebarrier and top coat formulations.

The paper base master of the example is the paper master referred to in the Schaifner article. This master was tested in standard commercial equipment. The imaging equipment used was as described for the Indentation test. The off-set duplicator used was a Multilith Simflomatic Off-set Duplicator, Model 1278. The magnetic ink was Addressograph-Multigraph MBM999. The fountain solution consisted of MBM Repelex, diluted with 7 parts Water.

It was found that there were only two rejects per 1500 checks attributable to the paper master. Satisfactory printing was obtained in all cases with under 10 starting impressions and usually in less than 5. Run lengths 'of over 300 prints were repeatedly made with no loss in quality because of toning, lack of image retention or loss of dimensional stability.

This invention is also suited for manufacturing paperbase phanographic masters for any application where carbon ribbon imaging is used such as in the printing of brochures with ordinary lithographic printing ink.

By ream is meant 500 sheets, 25" x 38". By papercoating-grade pigment is meant any of the conventional pigments or fillers that are conventionally used for coating paper webs. Examples of other hydrophobic filmforming elastomeric binders that can be used in the barrier coating are: styrenebutadiene latex (Dow 512R), vinylidene chloride latex (Dewey and Almy Daran 202),

Butadiene-acrylonitri'le latex, and the like. These can be modified as needed by reaction with a urea formaldehyde or melamine formaldehyde thermosetting resin derived from a dispersion (latex) or solution.

Examples of other hydrophilic, water insoluble filmforming polymers that can be used as the binder in the planographic coating are: modified starches, carboxymethyl cellulose, polyacrylic acids, hydroxy-ethyl cellulose, carboxy-methyl-hydroxy-ethyl cellulose, and the like.

Having described this invention what is sought to be protected by Letters Patent is succinctly set forth in the following claims:

What is claimed is:

1. A process for preparing a flexible lithographic'printing plate for encoding checks with magnetic inks for absorption value on the coated side in the range of 0.22

to 0.45 (100 square centimeters, 30 seconds); applying .a barrier coating to both sides thereof in an amount in the range of to pounds (dry weight) per side per ream of a heat-curable pigmented latex comprising a hydrophobic acrylic elastomer, a minor amount thereon of, a reactive amine-formaldehyde resin and a paper-coating grade mineral pigment, the weight ratio of pigment to elastomer plus resin in said latex being in the range of 0.5 to 5 and the Cobb water absorption (100 square centimeters, 120 seconds) after drying and before curing being greater than 0.25 and after curing being less than 0.15; drying and calendering said coating; applying a top planographic coating directly on said barrier coating on the machine-coated side in an amount in the range of 5 to 8 pounds (dry weight) per ream, said top planographic coating comprising a slurry of an oil absorptive papercoating-grade mineral pigment arid a hydrophilic colloidal polyvinyl alcohol adhesive that dries to a Water insoluble coating having a tensile strength of at least 7500 psi. and an elongation of at least.260% measured as an 8 mil film, the weight ratio of pigment of adhesive being in the range 2/1 to 5/1; rapidly drying said top planographic coating in less than 1 minute at a drying gas temperature greater than 300 F; curing the coated sheet at a temperature of at least 400 F., and thereafter calendering the same, said lithographic printing plate having an In- ,denture Test value in the range of 0.2 to 0.8 of a mil.-

'2. A lithographic printing plate produced by the process "of claim 1.

3. A process for preparing aflexible lithographic printing plate for encoding checks with magnetic inks for MICR processing, comprising: forming a sized cellulosic paper web having a ream weight in the range of 40 to elongation of at least 260% 100 pounds, a Cobb water absorption value on one side in the range of 0.22 to 0.45 (100 square centimeters, 30 seconds) and a Mullen burst strength in the range of 35 to applying a barrier coating to both sides thereof in an amount in the range of 5 to 10 pounds (dry weight) per side per ream ofa heat-curable pigmented latex comprising particles of a synthetic polymer that yields a tough hydrophobic elastomer when cured and a papercoating-grade mineral pigment, the Weight ratio of pigment to synthetic polymer in said latex being in the range of 0.5 to 5 and the Cobb Water absorption square centimeters, seconds) of the coated paper web after drying and before curing being greater than 0.25 and after curing being less than 0.15; drying said coating; applying a top planographic coating directly on said barrier coating on said one side in an amount in the range of 5 to 8 pounds (dry weight) per ream, said top pl anographic coating comprising a slurry of an oil absorptive paper-coating-grade mineral pigment and a hydrophilic colloidal. adhesive'that dries to a Water insoluble coating having a tensile strength of at least 7500 psi. and an (measured as an unpigmented 8 mil film), the Weight ratio of pigment to adhesive therein being in the range of 2/1 to 5/1; rapidly drying said top planographic coating; and curing the coated sheet at a temperature of at least 400 F., said lithographic printing plate having an Indenture Test value in the range of 0.2 to 0.8 of a mil.

4. A lithographic printing plate produced by the process of claim 3. 7

Worthen Dec. 19, 1950 Halpern et a1 Oct. 16, 1956,

Claims (2)

1. A PROCESS FOR PREPARING A FLEXIBLE LITHOGRAPHIC PRINTING PLATE FOR ENCODING CHECKS WITH MAGNETIC INKS FOR MICR PROCESSING, COMPRISING: FORMING A SIZED CELLULOSIC PAPER WEB MACHINE-COATED ON ONE SIDE AND HAVING A REAM WEIGHT IN THE RANGE OF 40 TO 100 POUNDS AND A COBB WATER ABSORPTION VALUE ON THE COATED SIDE IN THE FRANGE OF 0.22 TO 0.45 (100 SQUARE CENTIMETERS, 30 SECONDS); APPLYING A BARRIER COATING TO BOTH SIDES THEREOF IN AN AMOUNT IN THE RANGE OF A HEAT-CURABLE PIGMENTED LATEX COMPRISING A HYDROPHOBIC ACRYLIC ELASTOMER, A MINOR AMOUNT THEREON OF A REACTIVE AMINE-FORMALDEHYDE RESIN AND A PAPER-COATING GRADE MINERAL PIGMENT, THE WEIGHT RATIO OF PIGMENT TO ELASTOMER PLUS RESIN IN SAID LATEX BEING IN THE RANGE OF 0.5 TO 5 AND THE COBB WATER ABSORPTION (100 SQUARE CENTIMETERS, 120 SECONDS) AFTER DRYING AND BEFORE CURING BEING GREATER THAN 0.25 AND AFTER CURING BEING LESS THAN 0.15; DRYING AND CALENDERING SAID COATING; APPLYING A TOP PLANOGRAPHIC COATING DIRECTLY ON SAID BARRIER COATING ON THE MACHINE-COATED SIDE IN AN AMOUNT IN THE RANGE OF 5 TO 8 POUNDS (DRY WEIGHT) PER REAM, SAID TOP PLANOGRAPHIC COATING COMPRISING A SLURRY OF AN OIL ABSORPTIVE PAPERCOATING-GRADE MINERAL PIGMENT AND A HYDROPHILIC COLLOIDAL POLYVINYL ALCOHOL ADHESIVE THAT DRIES TO A WATER INSOLUBLE COATING HAVING A TENSILE STRENGTH OF AT LEAST 7500 P.S.I. AND AN ELONGATION OF AT LEAST 260% MEASURED AS AN 8 MIL FILM, THE WEIGHT RATION OF IGMENT OF ADHESIVE BEING IN THE RANGE 2/1 TO 5/1; RAPIDLY DRYING SAID TOP PLANOGRAPHIC COATING IN LESS THAN 1 MINUTE AT A DRYING GAS TEMPERATURE GREATER THAN 300*F.; CURING THE COATED SHEET AT A TEMPERATURE OF AT LEAST 400*F., AND THEREAFTER CALENDERING THE SAME, SAID LITHOGRAPHIC PRINTING PLATE HAVING AN INDENTURE TEST VALUE IN THE RANGE OF 0.2 TO 0.8 OF A MIL.

2. A LITHOGRAPHIC PRINTING PLATE PRODUCED BY THE PROCESS OF CLAIM 1.

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