Antistatic polymer compositions
US RE28070 E
Description (OCR text may contain errors)
United States Patent Oflice Reissued July 9, 1974 28,070 ANTISTATIC POLYMER COMPOSITIONS Gordon D. Brindell, Crystal Lake, Ill., and Leland E. Dannals, Waterbury, Conn., assignors to Uniroyal, Inc., New York, N.Y.
No Drawing. Original No. 3,658,744, dated Apr. 25, 1972, Ser. No. 867,410, Oct. 17, 1969. Application for reissue Oct. 24, 1972, Ser. N 0. 300,045
Int. Cl. 009d /02; D03d 27/00, 27/12 US. Cl. 260-29.7 28 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.
ABSTRACT OF THE DISCLOSURE Polymer compositions are provided which are sufficiently electrically conductive so as to inhibit the build-up of electrostatic charges. The compositions contain an effective amount of an antistatic agent selected from the group consisting of alkali metal salts of organic acids or mixtures thereof with or without at least one polyhydric alcohol.
This invention relates to new polymer compositions having electrically conductive properties such that the compositions are capable of inhibiting the build-up of electrostatic charges. The invention also relates to articles made from and coated with said compositions.
The invention has particular application in the manufacture of carpets, the face of which is made from fibrous textile material which in use normally tends to accumulate a charge of static electricity, the charge being dissipated by the use of the polymer as a carpet backing. In addition, the invention provides methods of using such polymers and articles treated with such polymer compositions.
BACKGROUND OF THE INVENTION The build-up of charges of static electricity by friction on the surface of an article of manufacture or during the process of manufacture of such articles is a well known phenomenon. Elastomeric and plastic materials generally exhibit a considerable tendency to accumulate static electricity upon milling, calendering, extruding or other operations of manufacture. At times, the static electricity build-up may lead to sudden discharge in the form of sparks or flashes; at other times personnel handling such equipment of manufacture may be exposed to electrical shock.
Furthermore, the presence of a static electrical charge on an article during manufacture causes dust particles to adhere, which results in a coarse surface which requires additional costly polishing operation.
The build-up of static electricity also affects finished articles of which housings of vacuum cleaners are one example. The accumulation of static charges on carpet is well known by anyone who has walked on a carpet when the humidity is low.
Several approaches to overcome the build-up of static electrical charges have been proposed, and numerous antistatic agents are commercially available, such as alpha-N- dodecanol-omega-hydroxypoly (oxyethylene) N,N-bis 2- hydroxyethyl) alkylamines, N,N bis(2 hydroxyethyl) dodecanamide, phosphate esters of the condensation prod nets of nonyl phenol and ethylene oxide, n-alkylsulfonates, N-alkyl sarcosines, methyldodecylbenzyltrimethylammonium chloride, glycerolmonostearate, monoand diglycerides lactylated monoand diglycerides, glycols, polyols. In general, fatty alcohols and quaternary ammonium salts seem to dominate the field.
Some of the foregoing antistatic agents are applied to the surface of a finished article or during manufacture of an article. However, such surface treatment usually provides only temporary effectiveness. Other antistatic materials may be compounded directly into the polymeric substrate, but, in many cases, the original physical-mechanical properties of a polymer are detrimentally affected.
Another method proposed to defeat the problem of static electricity has been the incorporation of metallic, e.g. stainless steel, fibers into a polymeric material. However, even this approach has not been satisfactory in comparison to the antistatic agents of the instant invention.
Another consideration as to the feasibility of an antistat is its cost. The antistatic agents of the instant invention are particularly effective and inexpensive.
US. Pat. No. 2,717,842 in the name of vitalis is directed to antistatic treatment of textile materials in fiber, fabric or other form by applying a liquid treating composition (specifically an aqueous solution or dispersion) comprising (1) an antistatic agent which is a soluble inorganic salt that normally is deposited in the form of relatively large crystals upon volatilization of the solvent in which it is dissolved, and (2) a crystal growth-inhibiting agent in an amount, with respect to the said antistatic agent, that is sufficient to inhibit the deposition of such crystals. However, this patent does not suggest the present invention but is limited to the use of inorganic salts in conjunction with crystal growth-inhibiting agents. In contrast, the antistatic salt used in the present invention contains an organic anion derived from carboxylic acids containing 1 to 20 carbon atoms and, more preferably, 1 to 4 carbon atoms, such as formic acid, acetic acid, propionic acid or butyric acid. It will be demonstrated that the alkali metal salts of these anions, when employed in the invention, are superior to other anions, whether organic or inorganic, including many mentioned by Vitalis. Moreover, the present invention discloses the addition of the antistatic agents of the invention to a rubber or plastic in its solid or liquid phase or to the aqueous phase of a polymer latex. These polymers can be the same type as those which have been used for many years in the manufacture of articles, such as rubber soles, plastic housings, or in carpets as a means of securing the tufts of the textile fibrous material which form the carpet face to the primary jute backing, or to form a coating on the lower face of a carpet made by simple mechanical tufting.
British Pat. No. 1,018,349 (Farbenfabriken Bayer) teaches the use of polypropylene glycols (PPG) as antistatic agents in acrylonitrile-butadiene-styrene thermoplastics (ABS), the PPG having an average molecular weight range from about 2000 to 5000. While the foregoing agents are known to provide antistatic effects, we have demonstrated that the alkali metal carboxylates alone or in conjunction with polyols induce unexpected and superior antistatic properties to polymer compositions.
In the copending application of William Earl Wells, Ser. No. 729,441, filed May 15, 1968, lithium chloride is disclosed as an antistat in carpet technology. It does not militate as prior art with respect to this invention since it in no way, suggests that alkali metal carboxylates alone or in combination with polyhydric alcohols, such as glycerine or polyethylene glycols may be employed as an antistat in carpets. Moreover, while lithium chloride provides adequate antistat properties, there are certain disadvantages to its use: (1) carpets made with it tend to pickup an excessive amount of moisture when exposed to high relative humidity; (2) LiCl tends to promote the resinification of the polymer leading to brittleness, and (3) the cost of the chemical is high relative to those of the instant invention.
3 OBJECTS OF THE INVENTION It is thus the object of the invention to provide improved polymer compositions which are sutficiently electrically conductive so as to inhibit the build-up of static electricity thereon or on a surface to which the compositions are applied.
Another object of the invention is to provide articles of manufacture produced from such improved polymer compositions.
Another object is to provide articles of manufacture made of a material which in use tend to accumulate electrostatic charges, said articles having contactably associated therewith a rubber, a plastic or a rubber latex compostion containing a chemical which confers antistatic properties to said article.
A still further object is to provide a composite article of manufacture comprising a fibrous textile material which in use normally tends to accumulate a charge of static electricity, the fibrous material having attached thereto a dried deposit of rubber latex containing a chemical which confers antistatic properties to the article.
The invention also provides a carpet characterized by a backing composition which allows for the dissipation of static electricity built up in the carpet.
As a further object, the invention also provides a method for treating articles which tend to accumulate charges of static electricity and reduce their tendency to build up such charges.
These and other objects will more clearly appear from the following disclosure which illustrates effective composition ranges for rubber latex containing alkali metal carboxylates and a polyol.
GENERAL STATEMENT OF THE INVENTION Stating it broadly, we provide improved polymer compositions which are sufficiently electrically conductive so as to inhibit the build-up of a charge of static electricity themselves per se or on material on which the compositions are deposited. These compositions contain an effective amount of at least one alkali metal carboxylate as antistatic agent such as those selected from the group consisting of alkali metal organic salts of formic acid, acetic acid, propionic acid and butyric acid, that is to say, alkali metal formate, acetate, propionate and butyrate.
We find it advantageous in achieving optimum results that the aforementioned alkali metal organic salt be used together with a polyhydric alcohol.
The antistatic agents of the invention may be directly added to rubbers or plastics in the so-called dry state or they may be dissolved in solution or the aqueous phase of a rubber latex composition. The rubber latex composition containing the dissolved antistatic agents can be used in the manufacture of carpets in the conventional way.
It is possible to achieve the advantages of our invention by employing antistatic agents as additives to polymer compositions applied to the back of carpet made by simple mechanical tufting. However, better results are achieved when the latex composition is used not only as the tufting adhesive but, in addition, is applied in the form of a coating over the entire back of the carpet, with or without a secondary jute backing, since this double use of latex containing our antistat composition provides a better electrical path than the single use.
If desired, further protection against the build-up of a static electrical charge in the carpet can be achieved by providing means to conduct the static electricity to the ground. This may take the form of one or more metallic conductors leading from the bottom of the carpet to a ground or grounds. Such additional protection is especially advantageous in installations in hospitals, etc. where sparks create a fire or explosion hazard. In this connection, the novel polymer compositions of the invention may have use in providing electrically conductive surgical shoe soles for use in operating rooms where sparks must be avoided. Such shoes may, in effect, be cover-alls for regular shoes and made of fabric or cellulosic material having a tendency to build up electrostatic charges in frictional contact with the floor.
On practicing our invention, we can use any conventional polymer composition. Thus, it may be natural rubber of synthetic rubber such as polyisoprenes, polybutadienes, butadiene-styrene copolymers which typically contain from 40 to by weight of combined butadiene and correspondingly from 60 to 5% of combined styrene, butadiene-acrylonitrile copolymers, polychloroprene, polyisobutylene, ethylene-propylene copolymers or ethylenepropylene-diene terpolymers, polyalpha-olefin rubbers, and also plastics, such as polyethylenes, polypropylenes, polystyrene, polyacrylates, styrene-acrylonitrile copolymers, polyacetates, polyethers, phenolformaldehyde copolymers, polyesters, polyvinylchloride, polyamides, polysulfones, acrylonitrile-butadiene-styrene polymers, cellulose or blends of two or more of the above polymers.
These polymers may be in their dry, solution or emulsion (i.e. latex) phase, and they may be of the carboxylated or non-carboxylated type.
The above-mentioned polymers may also be used for foam, sponge or blown and cellular materials.
The polymers are compounded in accordance with techniques well known in the art. Thus, they may be compounded with accelerators, vulcanizing agents, particularly sulfur, ammonium zirconyl carbonate, zinc oxide, fillers, such as calcium carbonate, clay, starch, extender oil or other filler material.
Any material which normally tends to build up a charge (whether positive or negative) of static electricity as a result of friction on its surface for instance as a result of walking (in the case of carpet), can be successfully treated in accordance with our invention. Examples of fibers which give trouble with static build-up are those made from wool, polypropylene, nylon, polyacrylonitrile. The invention is particularly applicable with synthetic or man-made fibers, but can be applied to natural fibers such as wool which is often used in carpets. The invention is applicable to viscose rayon, acetate rayon and other manmade fibers derived from cellulose.
Use of our antistatic agents in a polymer latex carpetbacking composition for static reduction lends itself particularly to use in the case where conductive metal fibers, such as very fine stainless steel fibers of known type, are spun in known manner with the fibrous textile material in the manufacture of the yarns which the carpet face is made. By use of our antistatic agents in latex carpetbacking compositions in conjunction with such conductive metallic fibers in the tufts which constitute the face of the carpet, it is possible to use a greatly reduced proportion of such metal fiber with a correspondingly great reduction in cost of the carpet.
If such synthetic fibers are made from the improved polymer compositions of the instant invention, their tendency to build up an electrical charge will be reduced, thus possibly eliminating the necessity of incorporating metallic fibers.
The amount of alkali metal salt of a carboxylic acid and the amount of polyol or polyether glycol relative to each other and to the polymer or composition solids should be sufficient to achieve the desired antistatic effect in the final product while keeping the cost low and maintaining physical and mechanical properties for good service under a wide range of relative humidity. By physical and mechanical properties is meant such inherent properties as glass transition temperature, crystalline melting point, decomposition temperature, tensile strength, modulus, elongation, hardness, abrasion and tear resistance, adhesive strength, melt, Brookfield, intrinsic and Mooney viscosities, ozone and flame resistance, oil and chemical resistance, solubility, cure rate, compounding ease, etc.
The antistatic agents of the instant invention seem to have only minor effect on the above properties at the desired level of application.
The amounts of alkali metal carboxylate and of polyol, that may be employed here, are best expressed in milligram equivalent units since the antistatic performance of these materials is related to, but not a function only of, the number of ions and the number of hydroxy groups in the various polymer compositions. Milligram equivalent(s) is abbreviated for convenience as meq. and is used hereinafter as defining the formula weight in milligrams, or, in the case of mixtures, the average formula weight in milligrams divided by the functionality. This functionality, in the case of alkali metal carboxylates, is the number of alkali metal ions associated with one molecule of the carboxylate ion, while for polyols, it is the number of hydroxy groups in one molecule. For any particular compound, the number of milliequivalents or number of meq.s, stands for a definite weight of that compound. This definite weight, number of meq.s, is based either on 100 g. of the polymer solids present in the polymer composition, or on 100 g. of the polymer composition solids. Polymer solids is used here to include not only polymer, but also those non-polymeric residual materials that are used in the manufacture of the polymer. Polymer composition solids, or composition solids, include the polymer solids plus any modifying and/ or extending materials such as fillers, oil, carbon black and the like. As will be appreciated, composition solids may comprise polymer alone or polymer plus the aforementioned modifying or extending materials.
The alkali metal carboxylates may be added to the polymer compositions to achieve concentrations of from 1 to 250 meq. per 100 g., preferably 5 to 100 meq. per 100 g. of composition solids.
As has been stated hereinabove, it is preferred to employ polyols in using our antistatic agents in the polymer compositions. The amount of polyol employed may vary from about 0.3 to 450 meq. per 100 g. of composition solids. Preferably, a range of 3 to 300 meq. per 100 g. composition solids may be employed.
The ratio of meq. of alkali metal carboxylates per 100 g. composition solids to meq. of polyols per 100 g. composition solids may range from 50:1 to 1:100 but the preferred range of this ratio is 30:1 to 1:30.
Many alkali metal carboxylates are suitable for the preparation of antistatic polymer compositions. They may be represented by the general formula where M stands for alkali metal such as lithium, sodium and potassium; where n is an integer ranging from 1 to 4; where R is either hydrogen or a mono-, dior polyradical group such as alkyl, cycloalkyl, alkenyl, aryl, aralkyl or alkylaryl having from 1 to 20 carbon atoms, R may also carry one or more substituent groups such as X, -OR, -SR' or -CN where X designates a halide selected from the group consisting of fluorine, chlorine, bromine and iodine; where O, S, C stand for oxygen, sulfur and carbon respectively; and where R represents a hydrocarbon radical, of from 1 to 7 carbon atoms similar to the abovedescribed R. However, the total carbon atoms of R and R should not exceed 20.
Examples for compounds as indicated by the foregoing general formula are potassium formate, lithium acetate, potassium propionate, potassium butyrate, potassium valerate, potassium octanoate, sodium laurate, potassium pentadecanoate, potassium stearate, lithium arachidate; also potassium oxalate, lithium malonate, potassium succinate, sodium adipate, potassium brassylate, potassium pentane-l,1,5-tricarboxylate, sodium 2-propylpentane-l,2, 4-tricarboxylate, potassium 3-hexene-2,2,3,4-tetracarboxylate, also lithium vinylacetate, potassium allylacetate, lithium acrylate, sodium crotonate, also potassium maleate, sodium fumarate, lithium glutaconate, also potassium cyclohexyl formate, lithium benzoate, sodium phenylacetate, potassium naphthylacetate, potassium phthalate and the like. In addition to the foregoing alkali metal salts, it will be appreciated that the salt of rubidium, cesium and francium may also be employed.
Examples for substituted alkali metal carboxylates are potassium monochloroacetate, potassium trichloroacetate, lithium glycolate, potassium cyanoacetate, potassium tartrate, potassium citrate, potassium acetoacetate, potassium diglycolate, potassium thioglycolate, potassium anisate; sodium mandelate and others.
Under polyols are understood hydrocarbon compounds having more than one hydroxy group. Particularly suitable are polyols selected from the group consisting of sorbitol, ethylene glycol, propylene glycol, tetramethylene glycol, glycerine, pentaerythritol, and polyether glycols such as poly(ethylene glycol), poly(propylene glycol). The molecular weight of these polyols may range from 62 (ethylene glycol) to about 5000 for polypropylene glycol and, advantageously, from about 92 to 4000.
The preferred alkali metal carboxylates are those of potassium formate, acetate, propionate and butyrate especially when used in latex polymer compositions.
The additive alkali metal carboxylate may be provided in the form of a solution or dispersion in polyol, e.g. glycerol, which is then compounded into the polymer, the carboxylate salt being derived from carboxylic acids containing l to 20 carbon atoms and, more preferably, from those acids containing 1 to 4 carbon atoms.
DETAILS OF THE INVENTION The method of producting molded, cast or extruded articles is well known. Because the invention is particularly applicable to the manufacture of carpets, and be cause the manufacture of carpets is rather intricate and involves many variables, a detail description will be given insofar as it relates to carpets.
In the manufacture of a tufted carpet, the face yarn is pushed into the primary jute backing and held there by frictional forces. A latex compound is then applied to the back of the primary jute backing with the effect that, upon driving off the water by drying, the tufts are firmly bonded to the jute and the carpet has some dimensional stability. Usually a secondary backing, e.g. another layer of jute with a layer of latex, is applied for improved appearance.
The antistatic compositions of the instant invention are especially suitable not only as a primary (i.e. adhesive) and secondary backing but also as a scrimming" adhesive to bond the tufted primary backing to the secondary backing. The use of said antistatic agents in all three above-mentioned layers is especially effective because it provides a continuous electrical path from each tuft to the entire floor-engaging face of the carpet.
Several tests are ordinarily performed in order to determine performance and quality of carpets. It has been found that the measurement of the force required to remove the secondary backing is a satisfactory method of determining the effectiveness of the latex compound. This test is called ultimate adhesion. The unit of measure is pounds per 3 inch wide strip.
The moisture pick-up of a carpet is determined on samples without secondary backing. The weight gain after exposure to -85% relative humidity (72 F.) is related to the dry weight by a percent figure.
The measurement of the antistatic properties of a carpet usually takes the form of a simulated use test. For instance, the voltage developed by a person walking on a carpet is measured. However, in the present work, back surface resistivity is measured, since the conductivity of the coating compound is of principal concern, and since it has been found that the correlation between this measurement and simulated use tests is very good. A surface resistance of 100 gigohms (1 gigohm=10 ohms) or less is desirable for a conventional carpet.
It may be pointed out that in other articles of manufacture, the general degree of resistivity may vary according to requirements and/or specifications.
As illustrative of polymer compositions that may be compounded according to the invention, for each 100 parts by weight (e.g. grams) of polymer solids, up to about 2500 parts by weight (e.g. grams) of extenders may be employed, e.g. 100 to 1500 parts by weight of extenders. Other ingredients, such as stabilizers, antifoam agents, bactericides, etc. may be added, and enough water to give a total of about 68% solids by weight. Thickeners, usually polyacrylates, are added to establish a viscosity of about 200 to 10,000 cps. The amount of alkali metal carboxylate added is determined on the dry basis of the total solids present. Thus, as stated hereinbefore, for 100 parts by weight (grams) of composition solids present, the amount of alkali metal carboxylate may range from about i to 250 meq. and, more preferably, from about 5 confer antistatic properties on an article is achieved by our antistatic agents, at from 6 to 48 meq., alkali metal carboxylate (potassium formate) and 0 to 114 meq., polyol (glycerine) per 100 g. composition solids. It is to be noted that the upper limit of the meq. ratio of alkali metal carboxylate to polyol (potassium formate to glycerine) is unlimited (1:0) while the lower limit of this ratio, 1:19 does not exceed, in the above table, the actual lower limit of utility.
The effectiveness of the antistatic agents of the instant invention in polymer compositions that have a low polymer content will be demonstrated. The experimental procedure was identical with that given for Table 1, but the percent polymer solids of the composition solids was reduced by increasing the filler. The amounts of antistatic agents were kept constant in relation to the polymer solids so these amounts, in relation to the composition solids, were reduced. The meq. ratio of alkali metal carboxylate (potassium formate) to polyol (glycerine) was kept constant at 122.7. These data are in Table 2.
TABLE 2.SURFACE ELECTRICAL RESISTANCE OF PLOYMER COM POSITIONS ON GLASS Potassium Formats Glycerlne to 100 meq. On the basis of 100 g. composition solids, the polyol if present may range from 0.3 to 450 meq., but preferably 3 to 300 meq.
The efficacy of our antistatic agents will be demon strated with polymer compositions supported on glass. The polymer compositions used here contained polymer solids relative to the composition solids with remaining solid materials consisting of principally calcium carbonate filler with small amounts of tetrapotassium pyrophosphate and acrylate thickeners. These polymer compositions, as liquids, were cast as films on glass plates and dried overnight at room temperature. The films on the glass plates were then oven dried and placed in a glove box at 17% relative humidity and 72 F. After allowing a few days to reach moisture equilibrium, the surface electrical resistance of these films was measured and expressed as megohms per square, that is 10 ohms/ square. Antistatic performance is, of course, improved as the surface resistance becomes smaller. Film strength, adhesion and other attributes were not measured during these tests, but anyone skilled in the art and knowledgeable as to his antistatic requirements and his substrates, would be able to use the results of the following Table l to fabricate a product of remarkable antistatic properties as well as the other required properties.
TABLE 1.-SURFACE ELECTRICAL RESISTANCE OF POLYMER CONPOSITIONS ON GLASS IMPROVEMENT EFFECTED BY THE PRESENCE OF ANTISTATIC AGENTS Meq./l00 g. composition solids 1 Potassium formate to glycerine. I 17% relative humidity at 72 F. megohms/square.
The data of Table 1 shows that extraordinary reduction of surface electrical resistance that is required to The fact that antistatic agents of great utility have been discovered is strongly supported by the data of Table 2. It will be noted that small concentrations of the antistatic materials may be employed to keep the surface electrical resistance low. Good antistatic properties always attend a low surface electrical resistance of an article. Since the filler is the least expensive ingredient of the above polymer composition, lower cost articles having good antistatic properties can be made in accordance with the invention. We wish to point out, furthermore, that the Table 2 results show that the antistatic agents of the invention are elTective from about 9 meq. or less or more than about meq. alkali metal carboxylate (potassium formate) per g. composition solids and on the same basis, from about 24 meq. or less to about 261 meq. or more polyol (glycerine).
As additional supporting evidence that the antistatic agents give outstanding results, tests were conducted with a polymer composition that contained only 9% polymer solids with increasing amounts of the agents. The experimental details are the same as given in Table l. The results given in Table 3 show an astonishing decrease in surface electrical resistance as the amounts of antistatic agents are increased. In fact, the upper limit of effectiveness of these agents in this polymer composition is about 45 meq. potassium formate and 148 meq. glycerine per 100 g. of composition solids.
TABLE 3.RANGE OF EFFECTIVENESS OF THE ANTI- STATIC AGENTS IN POLYMER COMPOSITIONS CON- TAINING 9% POLYMER SOLIDS ON GLASS Meq./l00 g. composition solids Surface electrical It is seen, in the foregoing Table 3, that without antistatic agents, this polymer composition has such high surface electrical resistance that leakage in the system of capacitative discharge causes an apparent reverse current flow. It will be noted that the antistatic agents begin to show effectiveness at levels of 1 meq. potassium formate and 3 meq. glycerine per 100 g. composition solids. Shelf life is an important consideration in polymer compositions containing antistatics, particularly since such compositions may be stored for some time between manufacture and ultimate use. Antistatic agents which cause polymer instability are not commercially desirable.
As illustrative of the various embodiments of the invention, the following examples are given:
Example I The carpet compound is prepared as described in Steps 1 to 8. The alkali metal carboxylates of Step 5 are identified by name and amount in Table 4 which is a summary of the various tests obtained on the resulting carpet utilizing the improved polymer composition containing 25% polymer solids by weight.
TABLE 4.-ANTISTATIC AGENTS VS. CARPET PROPERTIES Alkali metal carboxylate (65 men. glycerine per 100 g. composition solids also used) A typical carpet coating composition illustrated hereinafter by way of example was compounded by employing the following order of steps:
FORMULATION (1) Synthetic polymer latex, 50% solids, 200 g. (100 g. solids) containing a carboxylated butadiene/styrene polymer of approximately 60% by weight of styrene. A mixture of anionic emulsifiers is used in the manufacture. The pH is 9 plus.
(2) A bactericide, Dowicide G" emulsion (sodium pentachlorophenoxide), 25% solids, 1.0 g. (0.25 g. dry).
(3) Alkylated para-cresol emulsion, 49% solids, 2.1 g. (1.0 g. dry), an antioxidant known as Wing Stay L.
(4) An aqueous solution of tetrapotassium pyrophosphate as stabilizer, 50% solids, 1.5 g. (0.75 g. dry).
(5) Aqueous solutions of the alkali metal carboxylate antistats to in amounts as described in the This example illustrates the various results obtained with alkali metal cations as acetates as compared to the control composition, the surface electrical resistance with lithium acetate being only about A that of the control. (Note Table 5). The potassium salt is particularly advantageous as an antistat as evidenced by the very low value of 15.5 gigohms per square. It also should be noted that the ultimate adhesion of the carpet is not seriously affected by these antistatic agents, and the increase in moisture pick-up is very near to the minimum expected with reduced surface electrical resistance. These data show the reason for our stated preference for potassium as the alkali metal since it seems more eifective to reduce surface electrical resistance. The coating composiiton contained 25% polymer solids by weight.
TABLE 5.ANTISTATIC AGENTS VS. CARPET PROPERTIES Alkali metal earhoxylate (all except control contain men. glyceririieigler 100 g.
composition so Carpet back Carpet Mom/100 g. surface Ultimate percent composition electrical adhesion moistu re Acetate ofsolids resistance 1 cl carpet pick-up Potassium- 20 15. 5 l0 7. 5 Sodium. 24 3,000 9 8.8 Lithium 30 0, 700 9 8. 0 Control (no antistatic agent) i8, 000 ii 5. 0
l 15% relative humidity at 72 F. gigohms/sq. I Pounds/3 inches. 1 80% relative humidity at 72 F.
examples. Polyols and polyether glycols were added with- Example III out previous dilution.
(6) Water in an amount calculated to give 68% solids.
(7) Georgia #10, a powdery calcium carbonate filler or whiting, 300 g. It is added dry, in small increments, to the agitated mixture of ingredients 1 through 6.
(8) Sodium polyacrylate thickener, 10% solids, no more than 30 g. (3 g. dry) but enough to attain 7000- 8000 c.p.s. viscosity (Brookfield viscometer #4 spindle at 10 r.p.m.).
To demonstrate that a great variety of carboxylates may be suitable for the reduction of static electricity in poly- 70 mer compositions, a latex was prepared following the formulation outlined herebefore, and the antistatic agents were added in the usual manner at the levels indicated in Table 6. In all cases, potassium salts were selected. The coating composition contained 25% polymer solids by weight.
TABLE 6.ANTISTATIC AGENTS VS. CARPET PROPERTIES Alkali metal carboxylate (all, except control, contain 65 meq. glycerlne per 100 g.composition solids) Meq./100 g. Carpet back Carpet Carpet percent composition surface elcctriultimate moisture Potassium salt ofsolids cal resistance 1 adhesion l pick-up Formats 24 3. 3 10 5, 3 Acetate.-- 20 15. 5 7. 3 Propionate. 18 15. D s 5, 9 Butyrato. i6 80 9 7, 6 Valerate. 14 260 9 7 2 Oetanoate- 11 B, 380 9 6 Lactato 16 170 13 7 1 Oxalate. 24 170 13 5, 5 Succinate 21 250 10 7, 6 Tartrate 1B 3, 300 15 5, B Citrate 5, 600 15 (i 5 Control 18, 000 ii 5, o
l 15% relative humidity at 72 F. gigohms/sq. 1 Pounds/3 inches. I 80% relative humidity.
Example IV 2O alkali metal (potassium) carboxylates (M) and the polyoi (OH), e.g. glycerine, were each added to the polymer in the latex phase at an 8 parts per hundred parts of polymer solids level. The latex formulation was the same as previously described. The polymer composition was supported on glass and the surface electrical resistances (SER) was determined in megohms/square at 12% relative humidity and 72 F.
TABLE 7.-COMPONENTS OF INSTANT ANTISTATIC AGENTS VS. CARPET P ROPE R'IIES Polyol (all, except control, contain 24 meq. potassium acetate per 100 g. composition solids) Carpet back Carpet Meq./100 3. surface Carpet percent composition electrical ultimate moisture Name solids resistance adhesion pickup! G lycerine 65 l6 l0 7. 8 Ethyleneglycol 65 830 11 6. 5 Polyethylene glycol of 600 molecular weight 7 55 7 7.6 Control 18. 000 11 5. 0
i 15% relative humidity at 72 F. gigohms/sq. Poundsi3 inches. 3 relative humidity at 72 F.
Example V T ABLE 0 A test was conducted to show that the antistat coating MI meqJ QB. mm I compositions of the invention also improve the electrical cflrbolylam 00 g. 100:; SER conductivity of a carpet face in which the face yarn con- Monocmommmm 15 65 2,930 tains stainless steel fiber. In carrying out the test, the g g 4,530 carpet stock was prepared with a composite wool/ stainless glycolatennj 17 65 -253 Thioglycolate. 15 610 steel yarn, the wool containing 0 2% by weight steel yarn Thiodi Mom 18 65 2. 500 The carpet back face was coated as described hcreiu- 55 i 16, 700.000 before using a coating of the control composition and two formulations of the invention. A secondary jute backing was then applied. The face yarn resistance of the three carpets was measured at 15% relative humidity and the following results were obtained. Example [VI] VII TABLE 8.-EFFEC'I OF ANTISTATIC AGENTS ON FACE SURFACE ELECTRICAL RESXSTANCE OF CARPET MADE WITH WOOL/STAINLESS STEEL YARN Antistatic agents Example VI The following example illustrates the usefulness of substitutcd alkali metal carboxylates as antistatic agents. The
The following example demonstrates the ability of the antistats of the invention to reduce the surface electrical resistance of an elastomeric blend of butadiene-acrylonitrile copolymer with an acrylonitn'le-styrene grafted butadiene-styrene copolymer. The total acrylonitrile (A), butadiene (B) and styrene (S) contents by weight of this clastomeric blend were as follows: about 27% A, 58% B and 15% S.
The above polymer was compounded as indicated in Table 10, the blends being cured at 320 F. for 10 minutes. The surface electrical resistance (SER) measurements were carried out in a dry box at 72 F. and a relative humidity of 7%. A reduction of the SER by a factor of 7 was realized through the addition of the antistatic agents.
Example VIII In order to demonstrate the effectiveness of the antistatic agents in polyalpha-olefin elastomers, an ethylene (66% )-propylene (30% )-ethylidene norbornene (4%) terpolymer (EPDM) was selected. Ethylene-propylene copolymers and terpolymers generally may have an ethylene content from about 40 to 80% and a propylene content of from 60 to 20%. There are several dienes suitable for the preparation of terpolymers such as 1,4-hexadiene, dicyclopentadiene, ethylidene norboruene, tetrahydroindeue, 1,6-octadiene and many other including conjugated dienes such as isoprene. The diene content may range from about to 15%. In most cases, the diene, when present, does not exceed 10% (wt.) of the total polymer and may preferably be as low as 2%. The polymer compositions were cured at 320 F. for 20 minutes.
The surface electrical resistance (SER) measurement data on Table 11 clearly indicate that the novel antistatic agents drastically reduce the tendency of rubbery polyalphaolefins to build up a static electrical charge.
TABLE 11.EFFECTIVENESS 0F ANTISTA'IIC AGENTS IN POLYALPHA-OLEFIN Parts by weight Control Invention EPDM 100 100 1(1) 100 Complex aluminum silicate.- 180 180 180 180 Hydrogenated naphthsnic oil 70 70 70 70 Rutlle type T10 30 30 30 30 Zinc oxide. 5 5 5 5 Stearic acid 1 I I l a a a oy ropy enegyoo Zinc dibutyl dithiearbamate 1.5 1. 5 1. 5 1. s Merceptobenzothiazole" 3. 0 8. 0 3. 0 3. 0 Dtpentylmethylenethimam tet sulfide- 0.4 0.4 0.4 0.4 Sulfur 2.0 2.0 2.0 2.0 j u m a am-[ 3% 8 :3 8
o to ene g co meq. g flEfi jm gohmsjf 31x10 18x10 4 23 'M.W. is molecular Weight.
Example IX In order to evaluate the effectiveness of the antistatic agents in a plastic polymer, a blend of acrylonitrile-butadiene copolymer with a styrene-acrylonitrile-grafted butadiene-styrene copolymer with a total content of about 23% acrylonitrile, 18% butadiene and 59% styrene was made. These polymer blends are known to the trade as AE'S thermoplastics. The antistatic agents potassium formate, glycerine and polypropylene glycol (the latter having an average molecular weight of 3600) were added to the ABS dry thermoplastic at the milliequivalent levels indicated on Table 12. The composition was blended, diced and calendered to a thin sheet. Sheet samples I to V (see below) were then evaluated for their dust attracting power, the accumulation of dust being known to be directly related to the build-up of a static electrical charge on the surface of the sheets. This so-called dust box test was carried out by placing the samples within the test area of an enclosure wherein a motor driven fan circulates dust (is. carbon black) throughout. A visual evaluation was made immediately after the minute test run by comparing the samples of the antistatic compositions (III, IV and V) with a standard containing no antistatic agents (1) and a sample II in which polypropylene glycol (average molecular weight 3,600) was the sole antistatic agent.
TABLE l2.--COMPONENTS OF ANTISTATIC AGENTS VB.
THERMOPLASTIC PROPERTIES COPOLYMER MIX- TUBES 0F BUTADIENE- STYRENE- AND ACRYLONI- TRILE-POLYMERS (ABS) Invention I II III IV V ABS, parts by weight 100 100 100 100 Potassium formate, meq./
100 g Polypropylene glycol, me I 00 g Glycerine, meqJlOO 5.- Dust layer (dustbox test).
Tensile strength, p.s.i 5,450 4, 630 5,360 5, 540 5,120 Flex strength, p.s.i B, 6, 080 7. 620 7, 100 7, B30 Heat deflection temp, F- 200 200 197 199 203 Flex modulusXlO 2. 4 2. 3 2. 1 2. 3 2. 5
The results indicate that the antistatic agents of our invention (III, IV and V) not only induced superior antistatic properties to the thermoplastic polymer but they did so without significant loss of physical properties in comparison to the prior art antistat polypropylene glycol alone (II). This surprising superiority was achieved at a greatly reduced concentration level in terms of milliequivalents of antistatic agents per 100 grams of polymer.
Blends of acrylonitrile butadiene styrene polymers which may be employed in producing formulations utiliz ing the concept of the invention may range in composition by weight of from about 20% to 30% acrylonitrile, about 15% to 65% of buta-diene and the balance essentially styrene ranging from about 10% to 65%.
These data show that our coating compositions reduce dramatically the face yarn electrical resistance, even if the face yarn is a conductive type, so that such carpets with the coating compositions of the invention will exhibit outstanding utility where static electrical discharge must be inhibited.
As will be appreciated, the invention is characterized by many embodiments. For example, the invention provides an antistat additive for compounding with polymers, e.g. rubber latex, the additive comprising a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from 62 to about 5000 containing an alkali metal carboxylate derived from carboxylic acids containing 1 to 20 carbon atoms. Advantageously, the ratio of alkali metal carboxylate to the polyhydric alcohol in terms of equivalent weights may range from about 50:1 to 1:100 and, more advantageously, from about 30:1 to 1:30, the alkali metal carboxylate being preferably selected from the group consisting of alkali metal formate, acetate, propionate and butyrate, the potassium salt being particularly preferred. Thus, a liquid of the foregoing materials can be provided which can then be compounded with a polymer, such as rubber latex. The rubber latex may be an aqueous emulsion or dispersion with which the foregoing formulation is then compounded. A surface can then be coated with the compounded composition which is allowed to dry, the dried coating having then conferred to it electrical conductive properties sufficient to inhibit the build-up of electrostatic charges.
As another embodiment, the invention provides a polymer composition containing alkali metal carboxylate for use in forming products capable of inhibiting the buildup of electrostatic charges thereon. The polymer composition in the broad sense may comprise polymer alone or polymer containing extender material. The polymer solids in the composition may be as low as about 4%. Advantageously, it may range from about 6% to 50% by weight of the composition. In a preferred embodiment, the polymer composition, e.g. rubber latex, contains a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from about 92 to 4000, the alkali metal carboxylate being derived from carboxylic acids containing 1 to 20 carbon atoms. Thus, the polymer composition may contain from about 1 to 250 milliequivalents of alkali metal carboxylate (e.g.
alkali metal formate, acetate, propionate, butyrate, etc.) per 100 grams of polymer solids and any extender present taken on the dry basis, and from about 0.3 to 450 milliequivalents, preferably about 3 to 300, of polyhydric alcohol per 100 grams of polymer and any extender material present. Advantageously, the alkali metal carboxylate and the polyhydric alcohol in the polymer may be controlled over the ratio of about 50:1 to 1:100 on the equivalent weight basis, the ratio of about 30:1 to 1:30 being particularly preferred.
A formulation of the polymer together with the antistat material may be provided in the form of a liquid for the coating of materials or substrates. Thus, one formulation may comprise a liquid rubber latex dispersion or emulsion with or without extender material, which is adapted upon drying of providing an electrical conductive deposit capable of inhibiting the build-up of a charge of static electricity. The amounts of alkali metal carboxylate and polyhydric alcohol employed in the liquid polymer formulation are determined in accordance with the polymer composition taken on the dry basis over the ranges mentioned hereinbefore.
Other embodiments include articles of manufacture produced from the improved polymer composition itself, or the article may be a composite comprising a substrate, e.g. fabric, paper, etc., upon which the improved polymer composition is applied to inhibit the build-up of electrostatic charges thereon.
As has been stated herein, the invention is particularly applicable to the manufacture of carpets comprising tufts of fibrous textile material attached to a backing material having adhesively associated therewith the novel polymer composition of the invention, rubber latex modified according to the invention being particularly preferred.
As another embodiment, the invention provides a method for treating an article of manufacture, e.g. a carpet, which in use exhibits a tendency to accumulate a charge of static electricity by applying to the article the improved polymer composition of the invention.
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.
What is claimed is:
1. A polymer composition for use in products capable of inhibiting the build-up of an electrostatic charge thereon, said composition containing amounts of an alkali metal carboxylate containing 1 to 4 carbon atoms and of a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from about 62 to 5000 effective to inhibit the build-up of said electrostatic charge, and said carboxylate and alcohol being unreacted with each other and present on the surface of said composition.
2. The polymer composition of claim 1, wherein at least about 4% of composition solids constitutes polymer solids, wherein the amount of alkali metal carboxylate ranges from about 1 to 250 milliequivalents per 100 grams of composition solids, and wherein said polyhydric alcohol ranges from about 0.3 to 450 milliequivalents per 100 grams of composition solids.
3. The polymer composition of claim 2, wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol expressed in terms of equivalent weights ranges from about 50:1 to 1:100, and wherein the alkali metal carboxylate is selected from the group consisting of alkali metal formate, acetate, propionate and butyrate.
4. The polymer composition of claim 3, wherein the alkali metal is potassium, and wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol we 16 pressed in term of equivalent weights ranges from about 30:1 to 1:30.
5. A rubber latex composition adapted to form upon drying an electrically conductive deposit capable of inhibting the build-up of a charge of static electricity on material on which said deposit is formed, said latex composition having an alkali metal carboxylate containing 1 to  4 carbon atoms and a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from 62 to about 5000 as the active antistatic agents included in the latex, and said carboxylate and alcohol being unreacted with each other and present on the surface of said deposit.
6. A rubber latex composition as set forth in claim 5, wherein the alkali metal carboxylate is selected from the group consisting of alkali metal formate, acetate, propionate and butyrate, wherein about 6 to 50% of the composition solids constitute latex solids, wherein the amount of alkali metal carboxylate ranges from about 1 to 250 milliequivalents per grams of composition solids and the amount of polyhydric alcohol ranges from about 0.3 to 450 milliequivalents per 100 grams of composition solids.
7. The rubber latex composition of claim 6 wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol expressed in terms of equivalent Weights ranges from about 50:1 to 1:100.
8. The rubber latex composition of claim 7 wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol expressed in terms of equivalent weights ranges from about 30:1 to 1:30.
9. An article of manufacture formed from a polymer composition which in use normally tends to accumulate a charge of static electricity, said polymer having contained therein amounts of an alkali metal carboxylate containing 1 to  4 carbon atoms and a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from 62 to about 5000 effective to inhibit the build-up of a charge of static electricity on said article, and said carboxylate and alcohol being unreacted with each other and present on the surface of said article.
10. The article of manufacture of claim 9 wherein at least about 4% of the composition constitutes the polymer, wherein the amount of alkali metal carboxylate ranges from about 1 to 250 milliequivalents per 100 grams by weight of the composition, and wherein the amount of said polyhydric alcohol ranges from about 0.3 to 450 milliequivalents per 100 grams of the composition.
11. The article of manufacture of claim 10 wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol expressed in terms of equivalent weights ranges from about 50:1 to 1:100, and wherein the alkali metal carboxylate is selected from the group consisting of alkali metal formate, acetate, propionate and butyrate.
12. The article of manufacture of claim 11 wherein the alkali metal is potassium, and wherein the ratio of alkali metal carboxylate to polyhydric alcohol expressed in terms of equivalent weights ranges from about 30:1 to 1:30.
13. The composition of claim 1, wherein the polymer is a blend of polymers comprising acrylonitrile, butadiene and styrene.
14. The composition of claim 13, wherein the blend of polymers ranges by weight in composition from about 20% to 30% acrylonitrile, about 15% to 65% butadiene and the balance essentially styrene ranging from about 10% to 65%.
15. The article of manufacture of claim 9 wherein the polymer is a blend of polymers comprising acrylonitrile, butadiene and styrene.
16. The article of manufacture of claim 15, wherein the blend of polymer ranges in composition from about 20% to 30% acrylonitrile, about 15% to 65% butadiene and 1 7 the balance essentially styrene ranging from about 10% to 65%.
17. The composition of claim 1, wherein the polymer is an elastomer selected from the group consisting of ethylene-propylene copolymers and ethylene-propylenediene terpolymers.
18. The composition of claim 17, wherein the elastomer contains by weight 40% to 80% ethylene, to 15% diene and the balance essentially propylene ranging from about 20% to 60%.
19. The article of manufacture of claim 9, wherein the polymer is an elastomer selected from the group consisting of ethylene-propylene copolymers and ethylenepropylene-diene terpolymers.
20. The article of manufacture of claim 19, wherein the elastomer contains by weight about 40% to 80% ethylene, 0 to 15% diene and the balance essentially propylene ranging from about 20% to 60%.
21. In a method for conferring antistatic properties to polymer compositions, the improvement which comprises adding amounts of alkali metal carboxylate containing 1 to  4 carbon atoms and of a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from 62 to about 5000 to said composition eifective to inhibit the build-up of static electricity on said composition when formed into an article, said carboxylate and alcohol being unreacted with each other and present on the surface of said article.
22. The method of claim 21, wherein the alkali metal carboxylate and the polyhydric alcohol are added to a composition containing at least 4% by weight of polymer, wherein the amount of alkali metal carboxylate added range from about 1 to 250 milliequivalents and the amount of polyhydric alcohol ranges from about 0.3 to 450 milliequivalents per 100 grams of composition.
23. The method of claim 22, wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol expressed in terms of equivalent weights ranges from about 50:1 to 1:100, and wherein the alkali metal carboxylate is selected from the group consisting of alkali metal formate, acetate, propionate and butyrate.
24. The method of claim 23, wherein the alkali metal is potassium, and wherein the ratio of the alkali metal carboxylate to the polyhydric alcohol expressed in terms of equivalent weights ranges from about 30:1 to 1:30.
25. The polymer composition of claim 1, wherein the alkali metal carboxylate is a substituted alkali metal cat'- boxylate in which the substituent is selected from the group consisting of X, 0R', SR' and CH; where X designates a halide selected from the group consisting of fluorine, chlorine, bromine and iodine: where 0, S, and C stand for oxygen, sulfur and carbon, respectively: and where R represents a hydrocarbon radical of from 1 to 7 carbon atoms, the total carbon atoms of the carboxylate not exceeding 20.
26. The article of manufacture of claim 1, wherein the alkali metal carboxylate is a substituted alkali metal carboxylate in which the substituent is selected from the group consisting of X, -OR', SR' and -CN; where X designates a halide selected from the group consisting of fluorine, chlorine, bromine and iodine; where O, S, and C stand for oxygen, sulfur and carbon, respectively: and where R represents a hydrocarbon radical of from 1 to 7 carbon atoms, the total carbon atoms of the carboxylate not exceeding 20.
27. A polymer composition selected from the group consisting of acrylonitrile-butadiene-styrene polymer, ethylene-propylene copolymers and ethylene-propylene-diene copolymers capable of inhibiting the build-up of an electrostatic charge, said composition consisting essentially of an alkali metal carboxylate containing I to 20 carbon atoms and of a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from about 62 to 5000 in addition to the polymer in amounts efiective to inhibit the build-up of said electrostatic charge, said carboxylate and alcohol being unreacted with each other and present on the surface of said composition.
28. An article of manufacture formed from a polymer composition selected from the group consisting of acrylonitrile-butadiene-styrene polymer, ethylene-propylene copolymers and ethylene-propylene-diene copolymers which in use normally tends to accumulate a charge of static electricity, said polymer composition consisting essentially of an alkali metal carboxylate containing 1 to 20 carbon atoms and a polyhydric alcohol selected from the group consisting of polyols and polyether glycols of molecular weight ranging from 62 to about 5000 in addition to the polymer in amounts efiective to inhibit the build-up of a charge of static electricity on said article, said carboxylate and alcohol being unreacted with each other and present on the surface of said composition.
References Cited The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.
UNITED STATES PATENTS 3,158,475 4/1964 Cassiers et al. 260-45 2,729,860 l/l956 Balkin et al. 2'6016 3,223,664 12/1965 Coulon 26016 FOREIGN PATENTS 1,064,189 4/ 1967 Great Britain.
CLIFTON B. COSBY, Primary Examiner T. MORRIS, Assistant Examiner US. Cl. X.R.
139391, 399, 425; 161-62, 203, 217, 227, 242, 248, 251, 253, 254, 256; 260-23.7, 29.2 UR, 29.7 T, 29.7 E, 29.7 AT, Digests 16, 19, 20