WO1992006143A1

WO1992006143A1 - Anti-tack compositions and methods

Info

Publication number: WO1992006143A1
Application number: PCT/US1991/007316
Authority: WO
Inventors: Karl W. Merkel
Original assignee: Merkel Karl W
Priority date: 1990-10-03
Filing date: 1991-10-03
Publication date: 1992-04-16

Abstract

Anti-tack compositions and methods employing aqueous dispersions or solutions containing a water-dispersible film-forming polymer as the anti-tack ingredient.

Description

ANTI-TACK COMPOSITIONS AND METHODS

BACKGROUND OF THE INVENTION

Natural rubber is derived from the rubber tree, HEVEA BRAZLIENSIS. It has been determined that natural rubber can be designated chemically cis-polyisoprene. While the rubber tree originated in Brazil, early on it was imported into the Malay Peninsula. At the start of World War II (1941), Maylasia was producing almost all of the natural rubber consumed by industries around the world, an exception being rubber produced from the guyale plant in Mexico. The fall of Malaysia, including the port of Singapore, to the invading Japanese army effectively cut off all supplies of natural rubber to the Allies. In turn, the Allied fleets cut off all shipments of natural rubber to the Axis nations. During the 1920's, there had been a small synthetic rubber industry in the United States based on work carried out under the direction of Father Nieuwland at The University of Notre Dame. Following this work, it was soon recognized that emulsion polymerization systems using free radical polymerization in the presence of a free radical catalyst were capable of producing not only high polymerization rates, but also high molecular weight products. In the next decade, the German government, in an effort to free itself of dependance on foreign rubber sources when war inevitably came, stimulated research into the field of synthetic rubber. The first development from an emulsion polymerization system was a styrene-butadiene copolymer (Buna S) originating in the research laboratories of I.G. Farberindustrie. This research was carried out under the direction of Bock and Tschunker. Shortly thereafter, this same laboratory produced a butadiene-acrylonitrile copolymer (Buna N) , also by using free radical emulsion polymerization techniques. Later, in the United States, Carothers et al _\. Am. Chem. Soc. 53 4203 (1931). produced a rubber-like polymer, chloroprene (polymerized 2-chloro-l,3-butadiene) . During World War II, both the Allies and the European Axis partners relied heavily on Buna S and Buna N to supply their rubber needs. After the end of World War II, the synthetic rubber industry continued as before and several new types of synthetic rubber were developed, including butyl rubber, ethylene-propylene rubber, polybutadiene, polyacrylic rubber and both silicone and fluorocarbon elastomers, to name but a few. It will be understood that the term "rubber" as used herein includes all rubbers, whether of natural or synthetic origin.

Rubber, regardless of its source, must be compounded in order to be useful. The process of compounding enables the compounder to add various chemicals to improve the quality of the rubber or to adapt it for special purposes, A typical rubber compounding operation consists of the steps outlined in the following flow chart, along with the type of machine preferably used in, and the primary objective of, each operation.

Storage To have stock available for further processing including vulcanizing Because of its low glass transition temperature, Tg, uncured (unvulcanized) rubber, including those of either natural or synthetic origin, has a tendency to stick to itself or other substrates at room temperature to produce a solid rubbery mass. (Tg is defined as the temperature at which an amorphous region of a partially-crystalline polymer changes from a viscous rubbery condition to a hard and relatively brittle one) .

In the past, various procedures have been used in an effort to prevent the self-sticking of uncured rubber. These procedures have included (1) dusting the freshly compounded rubber with dry inert materials such as mica, vermiculite, clay and other inert extender pigments and the like; (2) applying aqueous soap solutions to the rubber surface either by dipping or spraying or flow coating; or (3) applying aqueous dispersions of clays, particularly organically-modified montmorillonite, which, upon drying, leave a clay-like film on the rubber surface. Several patents have issued embodying one or more of these procedures. For example, Kajima et al, U.S. Patent 3,990,990, claims the use of aromatic sulfonic or sulfuric acids, their salts, condensation products of HCHO and aromatic compounds containing at least one sulfonic acid group, salts of such polymeric products, and salts of the condensation products of HCHO and an aromatic sulfuric acid. The salts are, of course, water-soluble. In a second embodiment of the invention claimed by Kajima et al, an ionic or non-ionic surfactant is also present. Using a different approach, Thene et al, U.S. Patent 3,935,124, discloses the use, as an anti-tack composition, of a water-soluble soap and finely divided kaolin. The soap must be present in sufficient quantity to provide bridging and tieing between the charge sites on the kaolin particles and the rubber so that the kaolin particles adhere to the rubber surface. Viscosity improving and dispersing additives such as sodium polyphosphate may also be present. Thirdly, Ellslager, U.S.Patent 4,306,994, discloses an anti-sticking composition consisting of a film-forming clay such as Bentonite or attapulgite, a surfactant and an additive capable of "inactivating" Ca or Mg ions and, optionally, a defoamer. The surfactant can be ionic or non-ionic and the patent lists illustrative surfactants at Col. 2, line 64 et seq. None of the above procedures have been found to be entirely satisfactory as they do not completely prevent the self-sticking propensities of freshly compounded rubber.

None of the above prior art reveals or teaches the use of a coating of water-dispersible film-forming polymers to prevent the self-sticking of compounded rubber during storage (see step 7 in the above flow chart).

SUMMARY OF THE INVENTION

It is an object of this invention to provide anti-tack compositions which avoid the drawbacks of the prior art anti-tack compositions, and a process for conferring anti-tack properties to surfaces of freshly-compounded rubber which is efficient, easy to utilize and relatively inexpensive.

In fulfillment of the above and other objects, this invention provides anti-tack compositions comprising a water-dispersible film-forming polymer and optionally containing also one or more inert pigments, dispersing agents, surfactants, biocides, defoamers, plasticizers or cross-linking agents. In this specification, the term "water-dispersible" is used throughout to include all polymers which can be dispersed in aqueous media, either as true solutions or as dispersions involving micelle formation. The use of the term "water solution" as used herein is for convenience of expression and does not imply that a true solution, rather than a dispersion, is necessarily present. Thus, this invention covers broadly anti-tack compositions prepared by adding certain polymeric materials to water regardless of whether the final product is a dispersion or true solution or mixtures thereof. This invention also includes the use of the aforesaid compositions to impart anti-tack properties to the surfaces of compounded rubber products.

DESCRIPTION OF THE INVENTION

The water-dispersible film-forming polymers useful in the methods and compositions of this invention preferably have a viscosity range of from about 100 to about 10,000 cps for 2-10% solutions at 25°C. Such water-dispersible film-forming polymers include partially (87-9%) hydrolysed polyvinyl alcohol having a viscosity in the range 3-50 cps, hydroxypropyl cellulose (low viscosity grades), hydroxyethyl cellulose (molecular weight of about 1.3 x 10 ), methylcellulose, polyvinylpyrrolidone (PVP) of K-value 17-96, hydroxyalkyl guar gum, other suitably modified gums, vinyl acetate-ethylene co-polymer, vinyl acetate homopolymer, soy protein or casein powder binders, carboxymethyl cellulose, sodium alginate oligomers, polyacrylic acid polymers, polyethylene oxide polymers, polypropylene oxide polymers, and derivatives of polyethylene oxide and polyproylene polymers, polymeric carbohydrates having a viscosity range of from about 500 about 10000 cps for 5-10% solutions at 25°C.and the like. The above materials can be used singly or in combination.

The above list of useful and readily available water-dispersible film-forming polymers and like materials is for illustrative purposes only and should not be construed as in any way limiting the scope of this invention. As will be apparent to those skilled in the art, there are many other commercially-available substances which could provide dispersions of suitable viscosity when added to a predetermined quantity of water and also that the chemical literature is replete with equivalent substances which might become commercially available sometime in the future.

As stated above, other ingredients may optionally be present in the aqueous dispersions useful in the compositions and processes of this invention, and containing one or more of the above polymeric materials. These include extender pigments such as the following: calcium carbonate (particle size 0.5-20 mu) , precipitated calcium carbonate (particle size 0.10-0.70 mu) , barium sulfate (particle size 5-15 mu), silica (particle size 0.5-25 mu) , pyrogenic silica (particle size 0.015-0.02 mu) , magnesium silicate (particle size average 1.5 mu) , pyrophyllite (particle size 2.6% on 325 mesh screen), clay (particle size 0.5-10 mu), calcined clays (particle size 0.5-5 mu) , BENTONE gelling agents (prepared by cation exchange reactions between organic bases and Bentonite) , BEN-A-GEL (beneficiated hydrous magnesium silicate), mica extender pigments, (mainly aluminum potassium orthosilicates) and the like.

The compositions useful in the processes of this invention can also include low molecular weight inorganic dispersants such as tripolyphosphate, sodium hexametaphosphate, sodium, potassium or ammonium salts of high molecular weight polyacrylic or methacrylic acids, sodium salts of sulfonated naphthalene-formaldehyde condensates, sodium salts of oligomeric polymers of styrene with maleic or acrylic acids and the like materials.

Among other permissible ingredients which may be present in the compositions of this invention are included one or more anionic, cationic or nonionic surfactants such as ethoxylated alcohols, ethoxylated alkyl phenols, ethoxylated amines and amides, ethoxylated fatty acids-fatty esters and oils, fluorocarbons, glycerol esters, phosphate derivatives, sorbitan derivatives — alcohol sulfates, succinate-sulfo derivatives, ethoxylated alcohol sulfates, sulfated fatty esters, sulfated and sulfonated oils and fatty acids, benzene-toluene-xylene sulfonates, condensed naphthalene sulfonates, dodecyl and tridecyl benzene sulfonates and free fatty acids, petroleum sulfonates, taurates, quaternary ammonium compounds, and a class of chemical compounds formed by a saponification reaction, the soap being a metallic salt of a fatty acid derived either from animal fats and vegetable oils in the form of esters (glycerides) or from petroleum, rosin, etc.

Still further, the compositions of this invention may include a biocide, one or more defoamers and a cross-linking agent. Suitable biocides are potassium dimethyl dithiocarbamate, alkyl amine (lauryl) hydrochloride, triorganotin compounds and amine/organotin, l-(3-chloroallyl)- 3,5,7-triaza-l-azoniaadamantane chloride; suitable .defoamers and cross-linking agents include tetramethyldodecynediol and ethylene glycol on clay, urea, and sodium borate. These and other compounds of similar properties may be added to our novel compositions singly or in combination as with the other optional ingredients mentioned above. The compositions of this invention can be prepared by mixing the respective ingredients, as illustrated in Examples 1-6 below, in a dry blender or other suitable mixing vessel. In such dry blends, the ratio of extender/prime pigment to water-dispersible film-forming polymer can vary from 1-100% b weight of extender/prime pigment to 100-0.1% by weight of polymer, expressed as the %PVC (percent pigment volume concentration) of the composition. The surfactants, dispersants, biocides and cross-linking agents, as set forth above, can be present from about 0.05 to about 15% by weight individually when it is desired to have one or more of these ingredients present in the final composition useful in preventing self-sticking of freshly compounded, uncured rubber.

The amount of one of my novel compositions, prepared as specified above, to be used in my novel anti-tack imparting process will depend on the nature of the particular rubber or elastomer which is to be rendered non-self-sticking by the application thereto of said composition. For example, a rubber or elastomer with a very low Tg (glass transition temperature) will require generally higher dry weight add-on of one of my anti-tack compositions to render it non-tacky. With rubbers or elastomers having high Tg's on the other hand, a worker can use my anti-tack compositions prepared in accordance with this invention at lower dry-weight add-on levels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the compositions and methods of this invention, an anti-tack composition is prepared by adding 97-90 parts by weight of water and 3-10 parts by weight of a dry composition of this invention into a suitable mixing vessel equipped with a stirrer which produces a vortex. Stirring is continued for about 30 min. The resulting composition is then applied to the surface of a freshly-compounded article of rubber or elastomer by dipping, spraying or flow-coating methods until the surface is substantially completely covered with the anti-tack composition. Excess water is removed by air-drying, and its removal can permissibly be hastened by the use of fans.

PREPARATION OF DRY POWDERS

The following specific examples further illustrate the nature and scope of my invention but are to be construed in no way so as to limit that scope. All parts and weights referred to herein are by weight and all viscosities are measured at 25°C, unless otherwise specified. The PVC (Pigment volume concentration) designation is expressed in percent, and is based on the volume of pigment and the volume of the polymer used in the particular example.

EX M L 1 A composition was prepared by thoroughly mixing in a suitable mixer 50.0 g. of calcium carbonate (d=2.71, particle size = 3.0 mu, oil absorption = 15, Hegman grind = 6), 2.0 g. sodium bistridecyl sulfosuccinate, 50.0 g. polymeric carbohydrate (viscosity range 500-7000 cps for a 5-10% solution at 25°C), and 0.2 g. of l-(3chloroallyl)-3,5,7-triaza- 1-azoniaadamantane chloride. PVC » 34.75%, density - 1.88. EXAMPLE 2

By thorough mixing in a suitable mixer, the following composition was prepared containing 75.0 g. of calcium carbonate (d«2.71, particle size = 3.0 mu, oil absorption = 15, Hegman grind = 6), 5.0 g. of a vinyl acetate-ethylene copolymer, 25.0 g. polymeric carbohydrate (viscosity range 500-7000 cps for a 5-10% solution at 25°C, 2.0 g. sodium bistridecyl sulfosuccinate, and 0.2 g. of l-(3-chloroallyl)- 3,5,7-triaza- 1-azoniaadamantane chloride. PVC - 55.68, density « 2.11.

EXAMPLE 3

A composition was prepared by thoroughly mixing in a suitable mixer 50.0 g. of calcium carbonate (d-271, particle size ■ 3.0 mu oil absorption ■ 15, Hegman grind - 6), 47.0 g. polymeric carbohydrate (viscosity range 500-7000 cps for a 5-10% solution at 25°C), 3.0 g. carboxymethylcellulose, 2.0 g. sodium bistridecyl sulfosuccinate and 0.2 g. l-(3-chloroallyl)- 3,5,7-triaza-l-azoniaadamantane chloride. PVC - 34.75, density - 1.88.

EXAMPLE 4

A composition was prepared by mixing in a suitable mixer 66.0 g. calcium carbonate (d=2.71, particle size = 3.0 mu, oil absorption = 15, Hegman grind =6), 2.0 g. polyvinylpyrrolidone LK-30, 30.0 g. polymeric carbohydrate (viscosity range 500-7000 cps for a 5-10% solution at 25°C), 2.0 g. sodium bistridecyl sulfosuccinate and 0.2 g. l-(3-chloroallyl)-3,5,7-triaza- 1-azoniaadamantane chloride. PVC •*•= 52.42, density = 2.11. EXAWPLE 5

A composition was prepared by thoroughly mixing in a suitable mixer 68.0 g. of calcium carbonate (d«2.71, particle size » 3.0 mu, oil absorption = 15, Hegman grind ^•■*^■ 6) 2.0 g. sodium bistridecyl sulfosuccinate, 25.0 g. polymeric carbohydrate (viscosity range 500-7000 cps for a 5-10% solution at 25°C), 5.0 g. hydroxyethyl cellulose and 0.2 g. l-(3-chloroallyl)-3,5,7-triaza-l-azoniaadamantane chloride. PVC - 54.61, density = 2.13.

EXAMPLE 6

A composition was prepared by thoroughly mixing in a suitable mixer 35.0 g. of polymeric carbohydrate (viscosity range 500-7000 cps for a 5-10% solution at 25°C), 62,0 g. calcium carbonate (d-2.71, particle size 3.0 mu, oil absorption *- 15, Hegman grind * 6), 0.5 g. sodium dioctyl sulfosuccinate, 1.0 g. l-(3-chloroallyl)-3,5,7-triaza-l-azoniaadamantane chloride, 3.0 sodium salt of sulfonated naphthalene- formaldehyde condensate, 0.5 g. tetramethyldodecynediol and ethylene glycol on clay. The physical properties of this composition were: PVC = 48.95, density - 1.95, pH 3.0% sol. -= 7.2-8.5 viscosity, 3% solution, Brookfield # 3/50 rpm « 50-100 cp., 6% solution # 3/50 rpm = 250 - 350 cp.

The dry compositions from Examples 1-6 above were evaluated as anti-tack coatings by first adding 3% by weight of the respective powder compositions into 97% of water under agitation and then mixing these solutions for 30 minutes prior to application to uncured rubber samples. The rubber samples used consisted of SBR/natural rubber, uncured and carbon black filled. These samples were cut into 2 x 2 x 1/4 inch slabs, and were preconditioned in an oven at 100°C for one hour. They were then dipped into the above compositions and dried using a hot air blower, thus simulating plant application conditions. After the samples were dried, a blocking test was performed by placing two composition-treated samples face to face under a weight equivalent of 2-3 psi at ambient temperature for 24 hours. After the 24 hour load-test, the samples were checked for their anti-tack properties. All of the above compositions tested positive for anti-tack properties, i.e., all gave 100% release with no visible sticking. A control set of two slabs of the same uncured rubber, not coated with any of the above compositions, was tested by the same method and had fused into one solid piece of rubber.

Claims

What is claimed is:

1. A method for imparting anti-tack characteristics to the surface of a compounded rubber product which comprises applying to said surface an aqueous anti-tack composition containing as its anti-tack ingredient a water-dispersible film-forming polymer and evaporating the water therefrom, leaving on said rubber surface a substantially continuous layer of -said polymer.

2. A method according to claim 1 in which the water-dispersible film-forming polymer is a polymeric carbohydrate having a viscosity in the range of about 500 to about 10,000 cps for a 2-10% solution at 25°C.

3. In a process for imparting anti-tack characteristics to the surface of an article of compounded rubber comprising the application to said rubber surface of an aqueous dispersion containing an anti-tack ingredient, the improvement which comprises using a water-dispersible film-forming polymer as the anti-tack ingredient.

4. A process according to claim 3 in which the water-soluble/dispersible polymer is a polymeric carbohydrate having a viscosity in the range of about 500 to about 10,000 cps for a 2-10% solution at 25°C.

5. A process according to claim 1 in which the water-dispersible film-forming polymer is selected from the class consisting of partially-hydrolysed polyvinyl alcohol having a viscosity in the range 3-50 cps,, hydroxy C_ ₃alkyl celluloses (low viscosity grades), methyl celluloses, polyvinylpyrrolidone (K value 17-96), hydroxyalkyl guar gum, vinyl acetate-ethylene co-polymer, vinyl acetate homopolymer, carboxymethyl cellulose and polymeric carbohydrate having a viscosity in the range 500-10,000 cps for a 2-10% solution at 25°C.etc.

6. In an anti-tack composition for use in preventing self-sticking of freshly compounded rubber surfaces, the improvement which comprises employing, as the anti-tack ingredient, a water-dispersible film-forming polymer.

7. A composition according to Claim 6 in which the anti-tack ingredient is a polymeric carbohydrate having a viscosity in the range of about 500 to about 10,000 cps for 2-10% solutions at 25°C.

8. An anti-tack composition according to claim 6 optionally containing one or more of the following ingredients: inert pigments, dispersing agents, surfactants, biocides, defoamers, plasticizers and cross-linking agents.