Patented Oct. 29, 1946 2,410,078 UNITED STATES. PATENT OFFICE 2,410,078 UNIFIED FIBROUS FABRIC Waldo Kellgren, St. Paul, Minn., assignor to Minnesota Mining 8; Manufacturing Company, ,St. Paul, Minn., a corporation of Delaware No Drawing. Application August 3, 1940, Serial No. 351,232 . 6 Claims. 1 (Cl. 117-155) 2 .This invention relates to ?exible uni?ed ?brous cause vulcanization without deteriorating the fabrics, and method of making, wherein a felted rubber (and often the resin) to such an extent as or woven porous fabric (such as a paper or cloth) to make the fabric “punky” and weaker than it would be if no vulcanization had been attempted. More intensive heating caused resiniflcatiton of the rubber and made the fabric sti? and brittle. Such prior attempts included the use with sulfur of an accelerating agent and an activator, in an attempt to overcome the difficulty, but without success. It had, therefore, been assumed for some years that vulcanization of rubber-resin impreg-‘ is uni?ed by saturation or sizing with a non-hy groscopic water-insoluble rubber-resin composi tion, vulcanized in situ in a particular manner, which binds the ?bres together and toughens the fabric, and at the same time imparts other desir able characteristics, but without making the back ing undesirably stiff. _ , ll Uni?ed fabrics made in accordance with this invention may be used for various purposes, such as a backing for adhesive tape,,as electrical tape, nated fabrics was not feasible and offered no com mercial promise. I have discovered‘ a technique of vulcanization as a base for arti?cial leather, as a liner, etc. . The control of elasticity, so that stretchable 16 which goes contrary to expectations and makes sheet materials are possible ranging from those possible successful vulcanization, and in a prac that are inelastic to those that are highly elastic, tical manner which is of commercial value be is an important feature. By variation of the vul cause the attendant bene?ts more than warrant canizing technique, a wide variation of constit the additional expense of such treatment of the uent proportions can be used to effectuate a wide 20 fabric. variation in properties to secure products of dif My discovery is that of producing vulcanization fering types for various uses. , by the use of a self-vulcanizing organic accelera Other objects, advantages and features'of the . tor, by which is meant that type of organic ac invention will be apparent from the following fur celerator which gives a good cure (in the presence ther description. ' 25 of an activator, such as zinc oxide) to sulfur-free The unifying composition which I employ is primarily composed of a ?uxed blend of broken down rubber, admixed compatible resin which in rubber stocks. The preferred kind is represented by the thiuram polysul?de accelerators, illus trated by “Tetrone-A" (dipentamethylene-thi creases ‘the cementing action upon the fibres of uram-tetrasul?de) and “Tuads” (tetramethyl the fabric to bind them ?rmly, a special type of 30 thiuram-disul?de) . These accelerators liberate vulcanizing agentv and an‘ activator thereof. A a nascent form of sulfur during the vulcanization reinforcing pigment may be included to increase , process, which form of sulfur immediately com-' cohesiveness and tensile strength, but is not es bines with the rubber and, for some reason not sential. Various modifying agents may also be known to me, produces vulcanization with use of included, such as ?llers, plasticizers, softeners, 35 temperature-time combinations which do not ad versely affect the rubber-resin combination. In anti-oxidants, etc. After impregnation or sizing stead of such vulcanization producing an impreg of the fabric with the foregoing composition dis nated paper or cloth which is weaker and “punky" persed in a volatile vehicle, the fabric is suitably or still.’ and brittle, as in past attempts, the uni?ed heated to drive off the vehicle and vulcanize the rubber. It may then be coated on one or both 40 fabric has substantially as good ?exibility and has improved tensile strength, as compared with sides with such further coatings as are desired. ' fabric impregnated with the same rubber-resin The successful vulcanization of a ?uxed blend composition but with no vulcanization thereof. of broken-down rubber and resin distributed be By “broken-down" rubber, I mean rubber which tween paper or cloth ?bres, so as to obtain im proved results as compared with a uni?ed fabric 45 has been acted upon so that the “nerve” is re in which the rubber-resin impregnant is not vul duced and the rubber made less elastic, more plastic, and more penetrative. This can be ac canized, has heretofore not been achieved to the complished by mechanical working in the pres best of my knowledge. Prior attempts have been unsuccessful because the resin and the ?bres have ence of heat and air (oxygen), as by mastication acted in such a way that vulcanization would not 50 on a rubber mill and in a mixer. Oxidation plays a necessary part in the process of breaking down . occur to any appreciable extent under conditions which could be tolerated by the impregnated fab ric. That is, vulcanization depends upon tem perature and time, and no combination of tem perature and time could be found which would 65 and is accompanied by disaggregation and dis ruption of the rubber particles, and probably de~ polymerization or degrading of the rubber mole cules or macro-molecules also occurs. Whatever 2,410,078 3 4 the precise mechanism and nature of the change sistance. “Dextilose” is a manila hemp ?bre paper which has substantially the same length may be, the broken-down rubber permits of se curing thorough impregnation of the porous fab wise and crosswise tensile strength and tear re ' ric so as to obtain a uni?ed fabric that is ?exible or pliant. The degree of breakdown which is nec essary depends upon the porosity of the fabric. A cloth or thin open-mesh paper (as in "Troya sistance. . The rubber is preferably latex crepe, but smoked sheets or reclaimed rubber may be used. Since reclaimed rubber ordinarily contains zinc oxide, a reduction may be made in the added zinc oxide when employed, or the latter may be tissue”) requires only a small degree in compari son with paper towelling. The admixed resin fur ther plasticizes the rubber and decreases the vis 10 omitted. Equivalent vulcanizable synthetic or cosity of solutions thereof and assists in cement arti?cial rubbers and rubber-like resins may be ing the ?bres of the fabric. substituted for all or part of the natural rubber. In order to assist in breaking down the rubber The resin should be compatible with the rubber with the least effort, peptizing agents may be (both before and after vulcanization) so as to employed, as for example R. P. A. No. 1 (zinc form a homogeneous blend and should improve chloride double salt of phenyl hydrazine) or the cementing of the fabric ?bres and make the naphthyl - beta - mercaptan, which apparently rubber more plastic and penetrative. The resin function as oxidation catalysts and aids to de should also be water-insoluble so that the uni?ed polymerization. Only a small amount, as less paper will be resistant to moisture and water than 1% of the rubber, is needed to produce 20 and be non-hygroscopic. The technique of vul marked results. canization permits the use of both solid and The ?brous fabric may be of an'unwoven na ture such as cotton wadding, a felt or paper. ?uid resins. _ Without vulcanization, a ?uid resin Any type of paper or.paper-like sheet may be used so long as it is sufficiently bibulous or porous to permit of penetration by the sizing or im pregnating composition to result in the desired uni?cation, which uni?cation may be of one side would make the impregnant too soft and lacking in cohesive strength, particularly when the rub ber is highly broken down; but vulcanization of the rubber can, in accordance with this inven tion, be used to ?rm up the rubber to the point of securing the desired cohesive strength of the of the paper or throughout. The paper may be impregnant. made in whole or in part from wood, rope or rag 30 In general, the useful range of resin is 25 to ?bres, or from other ?brous material, natural or 400 parts by weight per 100 parts of rubber. The synthetic, such as cellulose acetate, glass, etc. Cellulose paper which has been acetylated may be used. ' ~ Woven fabrics may be used, such as cloth made from threads or ?bres of cotton, wool, hemp, optimum proportion will depend upon the type of product desired, the degree of rubber break down, the proportion of reinforcing pigment which may be used, the degree of vulcanization, the type of resin, the type of fabric, and the cellulose derivatives, “nylon,” glass, etc. An ex presence of modi?ers, etc. The upper limit of resin proportion is determined by the need of ob secure a good uni?ed fabric suitable for use as taining a flexible unified fabric of good strength. an adhesive tape backing or as an electrical tape, 40 If a solid resin is used, too high a proportion is a white broadcloth having an 80 by 144 thread will result in stiffness and brittleness, while too count per square inch. 1 high a proportion of ?uid resin will result in in The paper may be creped, crimped, embossed, adequate cohesiveness which cannot be overcome ample of a cloth-which may be impregnated to‘ molded, or otherwise formed so as to provide by increased vulcanization. rugosities or corrugations, which may be desired 45 Examples of suitable solid resins are rosin (which may be gum rosin or wood rosin), ester to provide substantial stretchability and the ability to conform to curved or irregular outlines or surfaces. For convenience, all such paper will be referred to hereafter as creped paper. gum, hydrogenated rosin, hydrogenated. ester gum, damar, copal, cumar, "Nevillite resin” (a cyclopara?in polymer), and an oil-soluble heat The unifying composition is distortable and 50 hardenable phenol-aldehyde resin that is set up stretchable and does not impair the aforesaid during heating of the impregnated fabric. Fluid characteristics. The creped paper may be im resins are illustrated by “Hercolyn" (hydrogen pregnated without causing a loss of the initial ated methyl abietate), “Abalyn” (methyl abie stretch of the paper, which'is an important fea tate) and “Vistac” (isobutylene polymer which is ture. The paper may be given either a “dead 65 viscid and sticky). Mixtures of two or more of stretch” or a “live-stretch,” depending upon the degree of rubber breakdown, proportion and kind of ‘other impregnant components, and degree of vulcanization. A creped towelling paper having the resins may be used. ' Rosin is a preferred resin, particularly when employed in conjunction with zinc oxide, in which case the compounding of the impregnant results a stretch of 25% may be used, for example. ‘The 60 in the rosin being “hardened” by the zinc oxide paper may be creped to have a two-way stretch. whereby zinc abietate .is produced and is the A ?at, uncreped paper may be employed where actual resin used in unifying the fabric. While stretchability is not needed or wanted, and this it is preferred to harden the rosin in situ during may be, for example, a. kraft paper. the compounding, it may be hardened in advance Desirable types of especially thin uni?ed paper 65 by treatment with zinc oxide, etc. The amount can be made by using paper stock of a hemp of zinc oxide consumed by the reaction, when ?bre kind. An illustration is “Flexrope,” a 100% carried to completion, is not over about 8 parts rope paper made of reclaimed rope and charac by weight per 100 parts of rosin. Other basic terized by long ?bre length, open texture, high tensile strength and great uniformity. Another 70 oxides may be used in place of or in conjunction with zinc oxide to form insoluble resinates. example is “Troya tissue,” made from new manila Thus a small amount of lime (preferably hy hemp ?bres and characterized by the fact that drated lime) may be incorporated in the mix, the ?bres largely run in one direction, so that tapes can be made having a high lengthwise or a small amount of magnesia. The preferred tensile strength and a high crosswise tear re proportion of rosin to be used in making masking 2,410,078 tape backings and the like is 75 to 175 parts per 100 parts of rubber. the accelerator, making it unnecessary to have free zinc oxide or‘ other activator present when these hardened rosins are present, although in The balance or the rosin is added, care being taken to add slowly to avoid excessive foaming caused by the water evolved from the reaction between rosin and the zinc oxide, ‘and mixing is continued for another hour. The beta-naphthol is added (if used), and the steam turned 0i‘! and cooling water introduced intothe heating Jacket some cases an additional activator may be desir able or useful. of the mixer. The oleum spirits is then added with continued mixing for half an hour, or until Where zinc oxide is used as an activator, the minimum proportion needed is about 5 parts per 100 parts of rubber, and this amount will func tion even though the zinc oxide reacts with rosin the mixture is homogeneous. The resulting solu tion may then be drawn off and stored until to form zinc abietate. together the "Tetrone-A” and rubber and dis solving in the oleum spirits. This procedure facilitates admixture of the vulcanizer with the Both the zinc abietate and the limed rosin ‘(calcium abietate) will function as activators for The vuloanizer solution is prepared by milling ‘ The use of a larger proportion of zinc oxide than may be-required for the foregoing purposes, is generally desirable in order to provide a rein 15 . rubber-resin solution. forcing pigment toincrease the cohesive strength of the impregnant and the tensile strength and The vulcanizer solution is mixed in with the rubber-resin solution just prior to use of the aging properties of the uni?ed fabric, as well as 20 latter for. the fabric treatment, as the composite to provide opaci?cation. The upper useful limit solution starts to gel within a few hours, even at is about 400 parts per 100 parts rubber, and the room temperature. ‘ optimum proportion depends upon the type of The ?brous sheet material may be impregnated tape being made. For a soft, ?exible type of with the impregnating solution in any suitable backing, the proportion should be kept low. In 25 manner that will deposit a sui?cient amount of the case of backings for masking tapes, and like solids within the ?bre structure to produce ade uni?ed paper, the preferred proportion is 50 to quate uni?cation. 125 parts per 100 parts rubber. A direct saturation method may be used on Other reinforcing pigments may be used. ordinary sheets of low density (high porosity). Dixie clay may be used in about the same way 30 The sheet is passed through theimpregnating solution until thoroughly permeated, and then as zinc oxide. In the case of carbon black, the upper limit of usefulness is generally 50 parts ' ‘between a pair of squeeze rolls to remove unde per 100 parts rubber and it is ordinarily best sired excess from the surface. An alternative not to go above 10 parts. Inert ?llers, such as procedure, where the sheet is denser, is to pre whiting, may be used to a limited extent. These 35 saturate with a diluted solution (obtained by diluting the stock impregnating solution, given materials do not function as activators and zinc oxide or other activator .must be present. in the above examples, some 20-30% by adding additional solvent), so as to obtain thorough v Exmns ‘1' l I penetration, dry, and then proceed with impreg Two batches are compounded, to be united 40 nation with the regular impregnating solution as shortly before paper treatment, having the fol lowing formulae, in parts by weight. described above. _ x I When the sheet is extremely thin and porous, satisfactory results will be obtained by passing Rubber-resin solution - between two horizontal rollers, the lower of which 100 . 45 dips into the impregnating solution, so as to apply the solution directly to one side only. The solu 160 tion will be carried through the sheet by capil 100 Parts Latex crepe Rosin Zinc oxide Beta-naphthol (antioxidant and optional)-.. ' 1 Oleum spirits (volatile petroleum hydrocar larity. The rollers are set so as to remove excess from the upper side of the sheet, but the ‘lower bon solvent of 306°-424° F. boiling range) -_ 20o '50 side which directly receives the solution will be somewhat denser than the other and will bear a _ Vulcanizer solution Parts slight excess. ' When using relatively heavy paper, a conven "Tetrone - A" (dipentamethylene - thiuram ient procedureis to apply a diluted solution to tetrasul?de) _________________________ .. 3 55 one side and thereafter apply the standard solu Latex crepe _ , 3 tion to the reverse side. This order of treat Oleum spirits 24 ment drives out the air before the more concen trated solution is used. A somewhat similar ex The rubber-resin solution is prepared by mill pedient is to float the paper on the surface of ing the rubber and zinc oxide for 30 minutes, at the impregnating solution and then subm‘erge. it about l50°-160° F., and the resultant sheet is before it leaves ‘the impregnating bath. then taken off and placed in an internal mixer It should be observed that variation in the (such as a Baker Perkins Mogul mixer), the heat proportion of solvent will affect the weight of ing jacket of which carries steam at 40 lbs. pres solids incorporated into the ?brous sheet. T00 sure, and which has previously been allowed to warm up. A small proportion of the rosin (say 65 little solvent will make for too high a viscosity for best penetration, and too much will produce 10-25%) is added to make for lubrication and undesirable dilution and not enough solids will a lower power requirement, and the mass. is be left in the sheet. , mixed for about 8-10 hours, or until reduced to Following impregnation, the fabric sheet is a semi-fluid consistency. The rosin may be omitted from this stage of compounding, but with 70 festooned on racks and put through a drying oven to remove the solvent and vulcanize the rubber. an increase in the power requirement; and an even greater proportion, or all, of the rosin may Various time and temperature combinations may be used to produce substantially equivalent re be added, but with a considerable increase in the time required to produce the same degree of sults. An oven treatment involving 12 hours at rubber breakdown. 75 170° F. gives good results. By increasing the 2,410,078 7 temperature to 250° F., a heating period of 3 hours has been found suitable. Such temperature “Hercolyn” (hydrogenated methyl abietate) is used in place of the rosin. Paper or other fabric uni?ed with this composition also hasv a live stretch owing to the proportion of vulcanizer time combinations do not deteriorate the rubber, and result in adequate vulcanization to ?rm up the rubber and make for a de?nite improvement in properties of the uni?ed ?bre. As previously pointed out, this is a, distinguishing feature of used. . . When employing “Tuads’P (tetramethyl-thiu ram-disul?de) in place of “Tetrone-A," a larger my invention. proportion must be used to compensate for the With respect to the foregoing type of formula, fact that each molecule contains only one sulfur little bene?t from vulcanization is obtained with 10 atom available for vulcanization instead of three. less than 1 part “Tetrone-A” per 100 parts rubber and at least 11/2 to 2 parts are needed, in general, Ordinarily an increase of three times the weight used is sufficient to produce the same results. to obtain results de?nitely worth the expense of A wide variety of ?lm-forming materials may be applied to the unified fabric to provide coat evidence that vulcanization occurs when less than 15 ings of various types. Likewise various sheet or 1 part “Tetrone-A” is used, andll/z to 2 parts ?lm materials may be laminated to the uni?ed are generally required to produce a signi?cant fabric. In some cases bonding may be facili~ increase in tensile strength and aging properties. tated by treating the fabric with the rubber In the lower range of vulcanizer proportions, resin composition so that the side which receives broken-down rubber does not regain its nerve suf 20 the coating has no excess of the rubber-resin or ?ciently to prevent the uni?ed fabric (such as is incompletely saturated or does not include the creped paper) from having the dead-stretch rubber-resinQ Thus the rubber-resin unifying characteristic which may be desired. may be applied to one side of the paper without With 6 parts “Tetrone-A’f per 100 parts rubber, penetrating through, and the desired coating is elasticity begins to be‘ obtained to a de?nitely 25 applied to the other side. Or the fabric may recognizable degree and when about 10 parts are have an excess of rubber-resin upon one or both used the uni?ed fabric (such as creped paper) sides to provide a smooth surface and the desired will be quite elastic. By cutting down‘the rosin coating is applied thereto. An illustrative sizing proportion, and also by increasing the zinc oxide which may be applied over the vulcanized rubber (pigment) proportion, a quicker build-up of elas resin is shellac, which may be conveniently ap ticity occurs with increase of vulcanizer propor plied as a 30-50% solution in denatured ethyl tion, and vice versa. alcohol when the web leaves the vulcanizing oven The incorporation of sulfur, with or without and is still hot, and drying of the shellac may be the inclusion of other accelerators than the self speeded by then subjecting the web to force vul-canizing accelerator, may yield desirable re 35 drying for 20 minutes at 140° F. Or a varnish or sults in some cases, as may the inclusion of an resin coating may be applied prior to vulcaniza other accelerator without addition of sulfur, but tionand dried (and set up where a heat-advanc in general none of these expedients has been ing resin is present) during the vulcanizing found to add appreciable value to the basic operation. technique. Uni?ed fabrics may be coated with plasticized 40 Exmns 2 nitrocellulose or methacrylate resin or polyvinyl acetal resin (such as polyvinyl butyral), and em Same formula and procedure as in Example 1 bossed if desired, to make arti?cial leathers. except that 100 parts "Hercolyn" (hydrogenated The uni?ed fabric may be used as a backing methyl abietate) is used in place of the rosin for adhesive tape by coating one or both sides and the proportion of “Tetrone-A" is increased with adhesive to provide an adhesive coating of to 5 parts to compensate for the use of a fluid a type (as desired) which is activatable by water, resin, being combined with 5 parts rubber and 40 solvents or heat, or which may be of the normally parts oleum spirits in making up the vulcanizer tacky and pressure-sensitive type (as one com solution. This example also illustrates a com position for unifying creped paper or other fabric 50 prised of rubber rendered tacky by a resin or vulcanization treatment. That‘is, there is little to make a dead-stretch sheet. _ plasticizer) . Thus a long-aging, waterproof, tough, pres sure-sensitive cloth adhesive tape may Ibe made by impregnating a broadcloth of 80 by 144 thread Exam?“ 3 Rubber-resin solution Parts 55 count per square inch with the rubber-resin uni Latex crepe _ 100 fying composition of Example 1, so as to ?ll the Zinc oxide Rosin 100 100 cloth and provide a slight excess on the back, followed by vulcanization and back-sizing with shellac, after which a pressure-sensitive adhesive Oleum spirits ___________________________ __ 200 60 is applied to the face-side. Among the advantageous features of my inven vulcanizer solution ' tion, the following points may be noted. Parts (a) A wide versatility in properties of treated “'I'etrone-A" ____________________________ __ 10 fabrics may be secured to meet particular needs, Latex crepe _____________________________ __ 10 Oleum spirits 80 05 and wider ranges of proportions and types of components may be used with the rubber, owing Same technique as in Example 1. The higher to the control made possible by vulcanization. vulcanizer proportion makes for an elastic im Thus ?uid resins may be utilized, and a live pregnant so that creped paper or other fabric stretch fabric produced even when the rubber uni?ed with this compositon has a live-stretch. 70 has been highly broken-down. Adhesive tape having this type of backing is well (b) The vulcanization improves the tensile adapted for use in coil winding, etc. strength of the uni?ed fabric without rendering it stiff or brittle. To illustrate this point, a 27 EXAMPLE 4 lb. per ream bibulous creped paper was uni?ed Beta-naphthol _________________________ __ 1 Same as Example 3 except that 50 parts of 75 in accordance with Example 1 (the paper being 2,410,078 9 saturated) and had a tensile strength of 5 lbs. before uni?cation and 9 lbs. after uni?cation. When uni?ed in the same-Way but without use of the vulcanization treatment, the tensile strength was '7 lbs. Tests were made on a Schopper tensile tester at a speed of 12 inches per minute, on sam ples of half-inch width. 10 - 2. An article according to claim 1 in which the accelerator is dipentamethylene-thiuram-tetra sul?de. 3. An article according to claim 1 in which the accelerator is tetramethyl-thiuram-disul?de. ' 4. A ?exible sheet comprising an initially por ous ?brous paper impregnated and uni?ed by a highly cohesive composition largely composed of (0) The vulcanization increases the useful life the in situ vulcanized ?uxed blend of broken of the uni?ed fabricby decreasing aging effects. Unified paper retains the desired resistance to 10 down rubber, admixed compatible resin adapted to increase the cementing action upon the ?bres splitting and delamination for a longer period of the paper and present in the proportion of than uni?ed paper which has not been vulcanized. about 25 to 400 parts per 100 parts of rubber, a (d) The vulcanization greatly increases the reinforcing pigment imparting additional co resistance of the uni?ed fabric to prolonged heat ing, which otherwise would lead to embrittle 15 hesiveness, and a self-vulcanizing organic ac celerator of the thiuram polysul?de type, said ment, loss of uni?cation and strength, and dis composition including an activator for the latter, coloration. Thus a uni?ed paper made in accord said uni?ed paper having a greater tensile ance with Example 1, upon exposure to 220° F. strength than untreated paper per se and at for 24 hours, did not become brittle or discolored and there was no destruction of uni?cation 20 least as great as would result without vulcaniza strength. (e) Uni?ed paper may be wound in rolls with tion of the impregnant. 5. A ?exible sheet having a porous ?brous fabric sized or impregnated by a composition de out blocking. Without vulcanization, there is a posited from solution in a volatile organic ve tendency to block so that turns of the roll may weld together unless a liner is employed, for al 25 hicle so as to penetrate and bind the ?bres of the fabric and vulcanized in situ after application, though the rubber-resin impregnant is relatively largely composed of a ?uxed blend of broken non-tacky when absorbed in the paper there is down rubber, admixed resin of the class consist apt to be considerable bonding between contact ing of rosin and derivatives thereof compatible ing surfaces of the uni?ed paper unless this'is 30 with rubber and present in the proportion of at overcome by vulcanization. ’ least about 25 parts per 100 parts rubber and What I claim is as follows, including such range within the range necessary to produce a ?exible of equivalents as the nature of the invention and composition and fabric, a self-vulcanizing or of the prior art permits: ganic accelerator of the thiuram polysul?de type 1. A ?exible sheet comprising an initially por and an activator for the latter. ous ?brous fabric sized or impregnated by a 6. An article according to the preceding claim highly cohesive composition essentially comprised in which the impregnating composition includes of the in situ vulcanized ?uxed blend of broken zinc oxide and said accelerator is largely di— down rubber, admixed compatible resin adapted pentamethylene-thiuram-tetrasul?de present in to increase the cementing action upon the ?bres of the fabric and present in the proportion of 40 the amount of at least 1 part per 100 parts of the rubber. about‘25 to 400 parts per 100 parts of rubber, and WALDO KELLGREN. a self-vulcanizing organic accelerator of the thi uram polysul?de type and an activator therefor.