US3714693A

US3714693A - Inking cover

Info

Publication number: US3714693A
Application number: US00185127A
Authority: US
Inventors: S Peterson
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1971-09-30
Filing date: 1971-09-30
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06

Abstract

An inking cover which has at least a working surface comprised of filled crosslinked poly(epichlorohydrin/ethylene oxide) elastomer plasticized with monomeric ester plasticizer, e.g., tricresyl phosphate, to provide a hardness value of from about 40 to 50 Shore A durometer, contains an amount of microcrystalline wax sufficient to substantially prevent exudation of the plasticizer.

Description

United States Patent 1191 Peterson 14 1 Feb. 6, 1973 1541 HNKING COVER 3,139,826 7/1964 Rainwater ..29 130 x 3,147,698 9/1964 R [75] Inventor: Stanley G. Peterson, St. Paul, Minn. 3.418.935 12/1968 gzf [73] Assignec: Minnesota Mining and Man f 3,475,803 11/1969 Hill ..29/132 ing Company, St. Paul, Minn. Primary Examiner-Alfred R. Guest [22] Filed: Sept. 30, 1971 Attorney-Harold J. Kinney et a]. [21] Appl. No.: 185,127

[57] ABSTRACT 52 U.S. c1 ..29/132 inking cover which has at least a Working surface 51 Int. Cl. ..B21b 31/08 Comprised Of filled cmsslinked [58] Field of Search .....29/132 129.5 130- 101/330 PY(epichlcmhydrin/ethylene Wide) elastome I I3 48 plasticized with monomeric ester plasticizer, e.g., tricresyl phosphate, to provide a hardness value of [56] References Cited from about 40 to 50 Shore A durometer, contains an amount of microcrystalline wax sufficient to substan- N S ES PATENTS tially prevent exudation of the plasticizer.

2,721,601 10/1955 7 Claims, 2 Drawing Figures Spencer ..29/132 UX PAIENIEDFEB 6 I973 3, 714.693

INKING COVER This invention relates to improved inking covers for use in printing equipment.

Inking covers are used on rolls in direct-printing presses for distributing ink from the ink fountain to the printing plate or cylinder, which in turn imprints the ink upon the paper. Such covers are also commonly used on cylinders for distributing ink upon a lithographic plate.

Early inking covers comprised rubbery compositions of hide glue plasticized with glycerin. Although such covers were inexpensive and quite popular, they had to be re-cast or re-surfaced very frequently because of their tendency to change in hardness, crack, and eventually disintegrate during use. Synthetic rubber inking covers, which have almost entirely replaced glueglycerin covers in modern high-speed presses, are more stable but they are inadequate for various reasons; e.g., some polyurethanes have a tendency to depolymerize in use, butadiene/acrylonitrile polymers such as Bu naN harden and crack on exposure to oxygen, and the hardness of plasticized polyvinyl chloride is inversely related to its working temperature.

Crosslinked poly(epichlorohydrin/ethylene oxide) elastomer has a desirable combination of flexibility, oiland solvent-resistance, low compression set, and ozone resistance, but it is difficult to process on conventional processing equipment. Although the addition of reinforcing filler materials to po1y(epichlorohydrin/ethylene oxide) elastomers improves processability, it also makes the rubbery composition too hard.

It is commonly known to add a sufficient quantity of suitable compatible plasticizer to many synthetic rubber compositions to lower the hardness value. Filled poly(epichlorohydrin/ethylene oxide) elastomer can likewise be endowed with a lower hardness value by plasticizing it with monomeric esters such as tricresyl phosphate, dibutyl phthalate, dioctyl adipate, dibutoxyethyl sebacate, dioctyl phthalate, dioctyl sebacate, and the like, which compounds are extremely compatible with this material. Unfortunately, however, these plasticizers exude from the poly(epichlorohydrin/ethylene oxide) compositions, migrating to the working surface of an inking cover made therefrom and causing two serious problems. First, the loss of plasticizer hardens the rubber. Second, the presence of the plasticizer on the working surface of the inking cover makes the surface more hydrophilic and thus seriously impedes its normal operation, especially in lithographic processes. The use of greasy lithographic ink compositions in the presence of water requires that the inking cover maintain a highly hydrophobic surface throughout its useful life.

It has now been found, surprisingly, that the addition of small quantities of microcrystalline wax to rubbery compositions of filled plasticized crosslinked poly(epichlorohydrin/ethylene oxide) elastomer will substantially prevent plasticizer exudation from the composition. Crosslinked poly(epichlorohydrin/ethylene oxide) elastomer suitably filled with reinforcing material and plasticized with monomeric ester plasticizer to'provide a desired hardness, e.g., Shore A durometer of about 40-50, and containing from about 0.05 to 5 parts by weight microcrystalline wax per 100 parts elastomer, provides a superior composition for use as an inking cover. lnking covers made of this new composition retain the same degree of hardness throughout their entire useful life. Not only is the wax itself highly resistant to exudation, but also if minute quantities do exude and form a surface film on the inking cover, the hydrophobic nature of the film does not interfere with the covers function.

Microcrystalline waxes are a mixture of solid, mineral-origin hydrocarbons, e.g., precipitated during the de-oiling of petroleum crude oil distillates and fractionally crystallized. They are generally white to pale amber in color, melt at not less than 71C., and have an iodine value of 4.0 or less. Although chemically very similar to common paraffin wax, microcrystalline waxes differ by having a branched hydrocarbon chain in contrast to a straight hydrocarbon chain. Moreover, microcrystalline waxes are tougher, more flexible, and usually higher melting than paraffinic waxes. The microcrystalline waxes that are useful in the present invention have a melting point within the range of about 71C. to about 100C. A list of useful microcrystalline waxes can be found in Chapter 2 of Industrial Waxes by H. Bennett, Chemical Publishing Company, New York (1963).

Oxidized microcrystalline waxes are most preferred in practicing the invention. These waxes are prepared from the residue on the bottom of the tanks in petroleum refining. This residue is extracted with methyl ethyl ketone, chilled, filtered, refined, and oxidized in air in' the presence of a suitable catalyst, e.g., cobalt or magnesium soaps. Useful oxidized microcrystalline waxes for the present invention are sold commercially under the trade name EstaWax, Cardis One, Mycrox- Wax," Petrolite C, C-23, C-36, PE-lOO, R-50, and others.

The poly-(epichlorohydrin/ethylene oxide) elastomers used in the invention are generally prepared by copolymerizing equimolar amounts of epichlorohydrin and ethylene oxide in an inert organic solvent at moderate temperatures (30 to 100C) in the presence of a small amount of a suitably modified organic catalyst to an average molecular weight in excess of 1,000,000, i.e., to a Mooney viscosity (ML4) at 212F. of -120; see US. Pat. Nos. 3,135,705, 3,158,580 and 3,158,581. The resultant amorphons copolymer has chloromethyl side groups which provide the means by which vulcanization or cross-linking is accomplished through reaction with crosslinking reagents.

Effective vulcanizing or crosslinking agents include diamines, imidazolines, ureas, thioureas, and ammonium salts with the chlorine atoms of the chloromethyl side group. Hexamethylene diamine carbamate sold as Diak No. 1, Z-mercaptoimidazoline sold as NA-2, trimethythiourea sold as Thiate E, triethylene tetramine, and piperazine hexahydrate are examples of satisfactory cross-linking agents.

Since the elastomer requires basic conditions to crosslink properly, an acid acceptor-stabilizer is used with the amine crosslinking agent. Useful acid acceptor-stabilizers are lead monoxide (litharge), basic lead carbonate (white lead), dibasic lead phosphite, and lead tetroxide (red lead), with basic lead carbonate and lead tetroxide being preferred.

As previously noted, reinforcing agents such as high structure carbon black are blended with the crosslinked poly(epichlorohydrin/ethylene oxide) elastomers to improve processability. The amounts of such reinforcing material will vary from about 10 to about lOO parts by weight per I parts elastomer, depending upon the particular materials used. Fillers, extenders, pigments, and modifiers, etc. may also be added to the composition as desired to stiffen, reinforce, increase abrasion resistance, or otherwise tailor its properties.

The preferred plasticizers for filled poly(epichlorohydrin/ethylene oxide) copolymer elastomers are such monomeric esters as tricresyl phosphate, dibutyl phthalate, dioctyl sebacate, and similar compounds. These plasticizers are blended into the tiller copolymer in sufficient quantity to obtain the desired lower hardness value. For a vast majority of printing applications, a Shore A hardness in the range of 40-50 is desired. To achieve this hardness, about 20 to 50 parts by weight of the plasticizer per 100 parts of the copolymer is normally used, but this may vary depending on other components which may be added to the composition.

Up to about 35 percent of the monomeric ester plasticizer can be substituted with polyester or polyether plasticizer which does not exude, to partially reduce the rate of plasticizer extraction with certain solvents, e.g., naphtha. A useful polyester plasticizer is an intermediate molecular weight polyester sold as Paraplex G-SO. Plasticizer systems containing more than 35% of such polymeric plasticizers should be avoided because they may result in undesirable swelling of the composition in the presence of solvents commonly used in cleanup or as a component of printing ink.

The microcrystalline wax additive is blended into the filled plasticized poly(epichlorohydrin/ethylene oxide) elastomer in amount at least sufficient to prevent the plasticizer from exuding from the composition, typically from about 0.5 to about parts by weight microcrystalline wax per 100 parts of filled plasticized elastomer. Generally, as the proportion of plasticizer in the composition increases, the proportion of microcrystalline wax should also be increased. For example, for compositions having a plasticizer content of about 35 parts by weight per 100 parts by weight of poly(epichlorohydrin/ethylene oxide) elastomer, about 1.5 parts by weight of microcrystalline wax substantially prevents exudation of the plasticizer. The addition of more than 5 parts microcrystalline wax per lOO parts elastomer produces no observable improvement in the composition and, in fact, may cause the rubber to lose some of its desired properties, e.g., by decreasing resilience or causing undesirable compression set.

if there is insufficient microcrystalline wax in the filled elastomer composition, the plasticizer will begin to exude. A rapid means of determining whether or not sufficient wax is present is a wettability test. llf the surface contact angle of a drop of'distilled water at 23C. on a smooth flat surface of the cured composition, ex-

' ceeds about 65 it contains a sufficient amount of wax.

If the surface contact angles is less than about 65, the composition surface is undesirably hydrophilic and therefore useless as a lithographic inking cover.

in the preparation of articles of the invention, i.e., inking blankets, sleeves, or rolls, the

poly(epichlorohydrin/ethylene oxide) elastomer is broken down on a rubber mill or other suitable equipment and the reinforcing filler, microcrystalline wax, acid-acceptor stabilizer, plasticizer (added last) and other additives, if used, are added and intimately mixed to provide a dough-like mass. The cross-linking agent is normally added after the plasticizer and other components are blended into the composition to prevent premature crosslinking caused by heat build-up during mixing. Although these polymers may be mixed entirely on a two roll mill, faster mixing is accomplished in a high shear mixing device such as a Banbury mixer, followed by sheeting on a mill. Sticking can be eliminated by incorporating lubricant such as zinc steara te. Mix temperatures are preferably maintained between and C.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing, wherein:

FIG. 1 is a longitudinal plan view of a printing roll incorporating the inking cover of the invention; and

FIG. 2 is a longitudinal cross-section view of a printing roll having a renewed inking surface provided by a sleeve made of the inking cover of the invention.

As shown in FIG. 1, the inking roll surface may be provided by a cylindrical structure 10 comprised of a fairly thick annulus of elastomeric composition mounted on an axial shaft 11. Such a roll can be prepared by molding the above described composition on a suitable shaft, curing the composition, and grinding the surface of the roll to provide a uniform diameter throughout its length.

Alternatively, as shown in FIG. 2, the inking surface may be provided by a relatively thin sleeve 20, comprised of the aforementioned elastomeric compositions and formed by extruding a tubular structure of the above described composition using conventional equipment. The cured sleeve is then applied over core structure 21, which in turn is mounted upon axial shaft 22. Core structure 21 can be either a worn or otherwise useless inking roll body or any convenient structure which has been provided with a uniform diameter throughout its length. The sleeve can be applied to the core-by a variety of known techniques, e.g., by using a compressed air jet to float it over the surface of the core structure, by vacuum expansion, or by other means. In general, the relaxed inner diameter of the sleeve should be at least about 10 percent and preferably 15 percent smaller than the diameter of the core to which it is to be applied.

To better illustrate the invention, the limiting examples are provided.

following non- I. Available as Hydrin 200" 2. Available as NA--22" 3. Available as "Petrolite C-23 The poly(epichlorohydrin/ethylene oxide) elastomer is mixed in a size 3 Banbury high shear mixing device with internal water cooling on both the shell and the mixing rotors, maintaining a mixing temperature of about 120C. After about 1 minute of mixing, the zinc stearate, lead tetroxide and microcrystalline wax are added, with further mixing to provide a homogeneous blend. The carbon black is next added and thoroughly mixed. Finally, the tricresyl phosphate plasticizer is added in two or three increments, with continuous mixing, until a homogeneous blend is again produced.

Inking Sleeve Preparation The mixture as prepared above is removed from the Banbury and transferred to a 60-inch rubber mill where it is allowed to mix and cool to a temperature of about 100C. The NA-22" crosslinking agent is added to the mixture and blended therein on the rubber mill. The stock is then fed in strips into the barrel of a Royal No. 2 extruder that has a concentric die arrangement capable of extruding a tubular structure having an inner diameter of 1% inch and an outer diameter of '1 13/16 inch, the extruder barrel being maintained at 45 C and the die at 65C during the extrusion. A 48-inch length of the extrudate is blown with compressed air onto a 1.574-inch diameter 56-inch long highly polished chrome-plated steel mandrel. A 2- mil polyester film liner is placed over the surface of the sleeve to protect the curing stock and to eliminate any sticking or impression of the cure tape. A 24-foot length of nylon cure tape is spirally wrapped under tension over the liner covered sleeve-mandrel combination. Curing is accomplished in an autoclave set at steam pressure of 90 psi for 60 minutes. After curing, the assembly is cooledby running water through the inside of the mandrel, after which the tape and liner are removed. The sleeve is then removed from the mandrel and mounted on a 1.700-inch diameter rubber-covered finishing mandrel, whereon it is ground to a uniform wall thickness of 0. 1 inch.

The sleeve is everted and mounted by a vacuum expanding technique on a core consisting of a worn inking roll for 21 Harris" Model LUM" 25 X 38 lithographic printing press so that a slight overhang on the edge of the core remains, as shown in FIG. 2.

When the sleeve-covered core is mounted on the Harris press and printing tests made with a variety of paper stocks indicate performance superior to the original Buna N rubber roll surface. Clean-up of the glassy smooth surface is accomplished more readily than with the conventional ground surface. After about 3 months of use, 5 days a week, about 12,000 copies per day, under a variety of conditions, there is no evidence of sleeve malperformance, failure, or movement.

A drop of distilled water at 23C applied to the surface of this composition produces a contact angle of 83, indicating the composition surface has a hydrophobic nature making it useful as a lithographic inking cover.

Example 2 Using the procedure outlined in Example 1 an inking cover composition was made from the following ingredients:

ingredients 4. Petronauba D" A drop of distilled water at 23C. applied to the surface of a test sample of the composition produces a contact angle of 87.

Example 3 An inking cover composition was prepared as in Example 1 from the following ingredients:

Ingredients Parts by Weight Poly(epichlorohydrin/ethylene oxide) elastomer 100 Lead tetroxide 5 Zinc stearate 1 Fast extruding furnace carbon black 35 Tricresyl phosphate 35 Microcrystalline wax 1.5 Z-mercaptoimidazoline 2.25

l. Hydrin 200" 2. Be Square 190.195" 3. NA-22" A drop of distilled water at 23C. applied to the surface of a test sample of the composition produces a contact angle of 90. 1

Although the descriptions and examples of the invention are primarily directed toward inking roll covers, it is to be understood that the composition will also provide an equally superior inking blanket. Accordingly the invention broadly covers any shape which will provide an inking surface.

What is claimed is:

1. An inking cover comprised of crosslinked po1y(epichlorohydrin/ethylene oxide) elastomer containing sufficient reinforcing filler to permit processing, plasticizer to provide a hardness value of from about 40 to 50 Shore A durometer, said plasticizer consisting essentially of at least 65% byweight monomeric ester, and an amount of compatible microcrystalline wax sufficient to substantially prevent exudation of the plasticizer.

2. The inking cover of claim 1 wherein said microcrystalline wax is oxidized microcrystalline wax.

3. The inking cover of claim 1 wherein the microcrystalline wax is present in an amount equal to about 0.5 to about 5 parts by weight per parts of said elastomer.

4. The inking cover of claim I wherein said poiyether. monomeric ester is seiected from the groupconsisting The inking cover Of claim 1 wherein said reinforcof tricresyl phosphate, dibutyi phthalate, dioctyl 8 fine! i8 Carbon bla kadipate, dibutoxyethyi sebacate, and dioctyl phthalate. An inking r ha ing a Working surface of the ink- 5. The inking cover of claim 1 wherein up to about 8 9" of ciaim 35 percent by weight of said plasticizer is polyester or Y

Claims

1. An inking cover comprised of crosslinked poly(epichlorohydrin/ethylene oxide) elastomer containing sufficient reinforcing filler to permit processing, plasticizer to provide a hardness value of from about 40 to 50 Shore A durometer, said plasticizer consisting essentiallY of at least 65% by weight monomeric ester, and an amount of compatible microcrystalline wax sufficient to substantially prevent exudation of the plasticizer.

3. The inking cover of claim 1 wherein the microcrystalline wax is present in an amount equal to about 0.5 to about 5 parts by weight per 100 parts of said elastomer.

4. The inking cover of claim 1 wherein said monomeric ester is selected from the group consisting of tricresyl phosphate, dibutyl phthalate, dioctyl adipate, dibutoxyethyl sebacate, and dioctyl phthalate.

5. The inking cover of claim 1 wherein up to about 35 percent by weight of said plasticizer is polyester or polyether.

6. The inking cover of claim 1 wherein said reinforcing filler is carbon black.