US3378506A - Elastomeric porous material and method for manufacturing same - Google Patents

Description

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United States Patent 3,378,506 ELASTOMERIC POROUS MATERIAL AND METHOD FOR MANUFACTURING SAME Joseph Rockotf, Dayton, Ohio, assignor to Dayco Corporation, Dayton, Ohio, a corporation of Ohio No Drawing. Filed Oct. 7, 1963, Ser. No. 314,486 11 Claims. (Cl. 260-25) The present invention relates to a porous elastomeric material and to a method for manufacturing the same. More particularly, the invention relates to porous printing members of such a material wherein the pores are microscopic cells or cavities, all of which are interconnected as a result of Which the platen may be made to contain a substantial quantity of fluid, such as a liquid ink, in channeled association with the printing surface. Moreover, the material of the present invention is deformable and resilient as a result of which it may be repeatedly deformed as by being impressed upon or against a surface whereupon it will deposit a coating of the ink upon such surface. These members may be printing rollers used for applying ink to platens and commonly referred to as platen rollers, flat printing plates, or stamp pads.

It is known that porous elastomeric materials can be conveniently employed as printing plates capable of bolding their own ink supply and yielding a coating thereof to a surface upon which printing is desired by bringing the material into contact with the surface. A variety of such porous materials and methods for manufacturing the same are also known and have been successfully used where the quality of the printed image is not critical and where a large number of impressions from one inking of the platen are not required. It has long been recognized, however, that greatly improved printing could be achieved by the utilization of a material having much smaller pores in greater number and more uniformly distributed through and upon the surface of the material than has heretofore been available. While the prior art has disclosed means for obtaining this desired size and distribution of pores in a deformable and resilient material otherwise suitable for printing platens, it has not in such instances achieved any degree of interconnection between pores with the result that the ink storing and delivering capacity of such platens has been seriously More recently, as described in United States Patent No. 2,763,208 to Rockoif et al., an ink storing and delivery material having the desired interconnected and uniformly distributed small pores has been achieved; but this material lacks the requisite resilience and deformability satisfactorily to deposit an ink coating on a printing platen and is repeatedly impressed against surfaces to be printed. Notwithstanding that it is thus unusable as a mechanism to impart a direct printed image to a surface, the Rockoif et al. material has found utility as an inking roller for inindirect printing; i.e., Where the paper to be printed is first deformed by contact with a type-carrying medium such as a credit card and the hard inking roller is passed across the paper whereupon it imparts an ink coating to the raised portion of the paper only. Attempts to modify the material of the Rockoff et al. patent so that it would be deformable have consistently proved unsuccessful and the material has generally been abandoned as a medium for application on platens, notwithstanding its otherwise desirable characteristics. More specifically, all attempts to incorporate softeners or plasticizers in the method and composition of the Rockoff et al. patent have caused the essential ingredients to cake badly during the mixing or blending thereof which in turn has prevented uniform distribution of and has destroyed the interconnecting microporous network in the finished product.

It is accordingly an object of the present invention to provide an improved microporous elastomeric material.

A further object of the invention is to provide such a material wherein the pores or cells are uniformly distributed throughout the material and upon the surface thereof and are interconnecting.

Still another object of the present invention is to provide an interconnecting cellular material capable of storing and transporting a liquid ink supply for use as the platen in a direct printing unit such as a hand stamp.

Still another object of the present invention is to provide a method for the manufacture of such materials and of such printing mechanisms.

These and other objects and advantages which will be apparent from a reading of the following disclosure are achieved in the case of this invention by the use of Factice, as a plasticizer or softener, the same being incorporated in its dry particulate or powdered state along with other particulate and/or powdered ingredients to be employed in manufacturing the highly porous composition. Specifically, the present invention contemplates the admixture of the Factice along the discrete particles of elastomeric material such as unvnlcanized or partially vulcanized rubber or synthetic rubber and, in some cases, a powdered resinous binder for the elastomeric particles. This represents a modification of the prior process in that it is possible to eliminate completely the particulate blowing agent; and it may also be possible to eliminate the resinous binder. When all these ingredients are placed together in a mixer such as a ball mill, for example, thorough and uniform distribution of each throughout the mixture can be accomplished without caking or other premature softening or plasticizing. The thoroughly admixed ingredients are then placd in a confined mold and subjected to sufficient heat to cause vulcanization to take place. The Factice enters into the compound in such a manner that it imparts softness, deformability and resilience to the finished product which have been heretofore unobtaina-ble. The specific Factices found most suitable for the present invention are those having the following specification:

Acetone extract, percent 5 to 30 Ash, percent 2 to 40 Acetone soluble sulfur, percent 0.5 to 2 Specific gravity 1.02 to 1.46 Hardness (Shore A Durometer) 35 to These Factices are vegetable oils which are themselves vulcanized by means of sulfur, sulfur chloride, or other vulcanizing agents to form a composition having a broad range of physical properties ranging from a sticky mass to a dry powder. In the present invention, a vegetable oil such as rapeseed -(co1za) or soya oil vulcanized with sulfur chloride to produce a dry powdery white F actice has been found particularly suitable. Where the oil or the sulfur chloride or both are diluted in a nonvulcanizable oil such as a petroleum spirit or in a similar inert solvent the Factice itself will be quite soft even though it remains in powdered and free-flowing form and is therefore amenable to use according to this invention to provide even softer and more deformable end products. Other specific properties may be achieved or influenced by the incorporation of such dry mineral pigments as cla zinc oxide, or the like along with the vegetable oils in the preparation of the Factice. Depending upon the degree of softening required, from three parts to sixty parts by weight of the Factice may be added to one hundred parts of the elastomeric polymer or rubber hydrocarbon to produce a wide variety of microporous materials suitable for soft rollers, stamp pads, and the like for use in a variety of direct printing operations. Such products will range in hardness from 15 to 50 measured on the Shore A Durometer Scale.

One specific example of the present invention may incorporate a synthetic rubber-like copolymer according to the following recipe:

Parts by weight 40% acrylic nitrile-60% butadiene copolymer 100 Sulfur Vulcanization accelerator 1 Zinc stearate 1 Another typical recipe for a natural rubber to be em- In either of the above basic recipes or in others similar thereto, the rubber or rubber-like material is obtained in particulate form by spray drying a latex of the particular substance or by freezing the latex and grinding it while frozen. The various compounding ingredients such as the vulcanizing agents, accelerators, antioxidants, fillers, and the like may be incorporated in the latex before it is spray dried or ground to particulate form; or since these particles are themselves in powdered form, they may be admixed with the powdered rubber as such along with any resins that may be optionally incorporated as hereinafter described. The powdered rubber particles should be such as to pass through a thirty mesh sieve or screen or smaller, depending upon the size of pores desired in the finished product.

A typical Factice formula of the type referred to above as particularly adaptable to the material and method of the present invention is as follows:

Refined rape oil (colza oil) gallons 33 Heavy carbonate of magnesia pounds 2.25 Petroleum spirits gallons 4 Sulfur chloride pounds 57 As previously stated, the oil or the sulfur chloride, or both, are preferably diluted in the petroleum spirit which because sulfur chloride is readily decomposed by water \should be dried. Upon heating of the above formula to ;from 100 C. to 210 C. while stirring, the oil will vul- -canize and the Factice mass will become rubbery. The Factice, like the principal rubber or rubber-like elastomer, may then be powdered by freezing and grinding or by other known expedients and graded to a particle size substantially equal to that of the principal elastomer.

These powdered ingredients; i.e., the particulate rubber composition and the Factice are then subjected to thorough mixing, preferably on a ball mill for a suflicient length of time uniformly to distribute each of them throughout the mixture. The mixture, still in particle form, is thereupon packed in a mold which is then tightly closed so as to confine the mixture during its subjection to vulcanizing temperatures which in the case of the typical recipes given above are on the order of 300 F., for a period of time on the order of from thirty to sixty minutes. During this time the rubber or synethetic rubber particles become vulcanized together in the form of a loose, porous mass and form the interconnected cellular structure. This structure is often referred to as stereoreticulate, because of the development of a network of pores connected by substantially straight-line passages. Where greater density and finer porosity are desired, the mixture of the various particles may be preformed by compression to a slug or mass conforming generally to the ultimately desired shape before it is placed in the mold and subjected to a similar heat process, while maintaining this pressure. The pressure should be in the order of 1,000 to 5,000 pounds per square inch, the exact pressure dependent upon the specific compound to be used and the desired porosity. Excessive pressures should be avoided, lest the structure be squeezed to the point where the voids are excessively reduced. At the same time, sufiicient pressures must be applied to create a self-supporting structure.

In certain instances, it may be desired to impart a greater degree of strength and durability to the molded product, particularly in the case of natural rubber compounds. This may be accomplished by incorporating in the mix a natural or synthetic resin, also in powdered form, along with the above-described ingredients. Typical resins include thermosetting resins such as phenol aldehyde or urea aldehyde; thermoplastic resins such as polyvinyl acetate or polyvinyl chloride; or natural resins such as shellac or the like in granular form. These resins may be employed in weight proportions of from five to one hundred parts based upon one hundred parts of the rubber polymer to give the desired results.

In all of the examples and modifications considered above, the addition of the Factice in the range of from three to sixty parts by weight based upon one hundred parts of the rubber or rubber-like polymer yields a relatively soft and deformable product having a hardness of from fifteen to fifty as measured on the Shore A Durometer Scale, the hardness varying inversely as the proportion of the Factice is increased. At the same time, the Factice, even where it is itself compounded with plasticizers or oil so as to be relatively soft and thereby capable of imparting even greater deformability to the finished product, has been found to be such that it does not interfere with the essential uniform distribution of the particles of the rubber, the blowing agent and the other compounding ingredients throughout the mixture to be molded. Because of this thorough and uniform admixture of the ingredients, made possible primarily by the unexpected fact that the addition of Factice in particle form does not interfere with the dry and free-flowing properties of the particle mix, the molded printing roller, plate or pad will have the desired microporosity wherein a large percentage of its volume will be in the form of ink-storing cavities, all of which, by virtue of their interconnection, are in communication with the surface. Because the pores not only within but on the surface of the product are uniformly distributed and may be quite small in size, the impression made thereby will be of fine and uniform quality. As previously stated, while materials having these pore characteristics have been known, none have simultaneously possessed the necessary deformability and resilience to render them suitable for the purposes described.

While the present invention has been described in considerable detail in connection with certain preferred embodiments thereof, it is to be understood that the fore going description has been for purposes of illustration only and does not limit the scope of the invention as it is defined in the subjoined claims.

I claim:

1. A porous product comprised of a mass of powdered rubber and Factice particles bonded together by heating and vulcanizing to cohere said particles to form a resilient stereoreticulate structure, said particles uniformly distributed throughout the mass.

2. A product according to claim 1 wherein said rubber is selected from the group consisting of natural rubber, a butadiene-acrylic nitrile copolymer, and a butadiene-styrene copolymer, polychloroprene.

3. A product according to claim 1 wherein the Factice particles are present within the range of from three parts to sixty parts by weight based upon one hundred parts by weight of the rubber particles.

4. A porous product comprised of a mass of powdered particles bonded together by heating and vulcanizing to cohere said particles to form a resilient stereoreticulate 5 structure, said particles comprising a uniform mixture of rubber, Factice and resin.

5. The product of claim 4 in which said resin is present within the range of five to one hundred oarts by weight per one hundred parts of rubber.

6. The product of claim 5 in which said resin is thermosetting.

7. The product of claim 5 in which said resin is thermoplastic.

8. A method for the manufacture of a deformable and resilient stereoreticulate porous material comprising the steps of finely dividing rubber into particulate free-flowing powdered form, finely dividing a Factice into a particulate powdered form, admixing said rubber and Factice particles and bonding said particles together by heating and vulcanizing the admixture.

9. The method of claim 8 which includes the step of adding resinous particles to said admixture.

10. A method according to claim 8 which includes the step of applying pressure while simultaneously subjecting said admixture to vulcanizing conditions.

11. The method of claim 10 in which said pressure ranges from about 1,000 to 5,000 pounds per square inch.

References Cited UNITED STATES PATENTS 2,680,140 6/1954 Carter 2602.5 2,999,822 9/1961 Pfau et a1. 260-25 OTHER REFERENCES MURRAY TILLMAN, Primary Examiner.

N. F. OBLON, M. FOELAK, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,378,506 April 16, 1968 Joseph Rockoff It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

and insert the same before Column 4, line 66, cancel "and" "polxchloroprene" in line 67, same column 4.

" Signed and sealed this 3rd day of March 1970.

(SEAL) Anam WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents

Claims (1)

1. A POROUS PRODUCT COMPRISED OF A MASS OF POWDERED RUBBER AND FACTICE PARTICLES BONDED TOGETHER BY HEATING AND VULCANIZING TO COHERE SAID PARTICLES TO FORM A RESILIENT STEREORETICULATE STRUCTURE, SAID PARTICLES UNIFORMLY DISTRIBUTED THROUGHOUT THE MASS.