Field of the Invention

[0001] The Present invention relates to a coating composition. More specifically, the present invention relates to a coating composition for coating rubber articles.

Background of the Invention

[0002] Generally rubber articles more specifically, rubber gloves are extensively used in various fields such as housekeeping, medical, food and the like for seeking protection against infections, contagious diseases, chemicals, solvents, chemotherapy drugs, cuts, bruises, static electricity and the like. Natural rubber gloves and nitrile rubber gloves are majorly used in many applications due to their versatility and affordable cost. Various synthetic materials used for manufacturing the gloves include nitrile latex, carboxylated nitrile latex, polychloroprene latex and polybutadiene latex.

[0003] Though intended protection for a user is a key criterion for the usage of any glove. But, it’s (glove) ease of wearing or donning and comfort while wearing also plays a pivotal role.

[0004] One of the conventional methods for improving donning properties of the glove includes the use of powder-based lubricants. However, it suffers from many drawbacks. The powder is easily dislodged. Further, while using, it (powder based lubricants) increases the chances of contamination and also causing allergies. Presently, powder-free gloves are preferred by users. Another known technique to improve donning properties of gloves is by reducing tackiness and decreasing the coefficient of friction of rubber. This is achieved by chlorination of rubber surfaces. However, chlorination is associated with several disadvantages. It adversely affects the mechanical properties of the gloves material, may render the material brittle and also poses discolouration issues. Coating glove surfaces with various types of materials to introduce a layer with different surface characteristics to reduce surface friction of rubber in order to improve donning properties are known. A wide variety of materials have been used for coating glove surfaces.

[0005] For example, U.S. Patents 4,499,154 and U.S. 4,575,476 teach coating hydrophilic hydrogel materials on an inner surface of the glove. U.S. Patent No. 5,088,125 discloses coating the hand contacting surface of a glove with a blend of anionic polyurethane and other polymeric material. US 2003/0175500 discloses an aqueous coating material with high Tg that employs a (meth) acrylic emulsion polymer for manufacturing powder-free gloves.

[0006] European Patent EP 2581100 describes a method of coating gloves with polyisoprene latex-based coating composition. There exists a need for a polymeric coating material for rubber articles that reduces the coefficient of friction of the rubber surface upon coating, ensures better adhesion without flaking or de-lamination, which matches with elongation properties of the gloves material.

[0007] Therefore there is a need for a coating composition which overcomes from drawbacks of prior art.

Objects of the Invention

[0008] An object of the present invention is to provide a coating composition for coating rubber articles.

[0009] Another object of the present invention is to provide a coating composition for coating rubber articles for reducing the coefficient of friction of the rubber articles. [0010] Further, an object of the present invention is to provide a coating composition for coating rubber articles for providing high surface adhesion for improved binding with a rubber surface of the rubber article and also reducing flaking or de-lamination of the coating. Summary of the invention

[0011] According to the present invention, there is provided with a coating composition for coatings rubber articles. The coating composition includes a hydrophobic polymeric material, water and at least one additive. The hydrophobic polymeric material is in a range between 1% to 10% by weight. The hydrophobic polymeric material is a carboxylated styrene-butadiene latex. The carboxylated styrene-butadiene latex is characterised by a styrene content ranging between 30% to 90% by weight of the carboxylated styrene-butadiene latex, Tg ranging from 0°C to 50 °C.

[0012] Further, the water is in a range between 90% to 99% by weight. The at least one additive is selected from the group that includes a surfactant, a compatibiliser, a cross-linking agent, a lubricating agent, a wetting agent, an anti-blocking agent, an adhesion promoter, a rheology modifier and the like in range between 0.005% to 10% by weight.

[0013] The lubricating agent is selected from a group consisting of silicon emulsion, polydimethylsiloxane, wax emulsion, polyethylene wax, paraffin wax, polyurethane and the like. The anti-blocking agent is selected from a group consisting of polyethylene emulsion, paraffin wax, high-density polyethylene wax, polystyrene and the like. The wetting agent is selected from a group consisting of nonionic surfactants, siloxane, polydimethylsiloxane, modified siloxane, linear dodecylbenzene sulfonate and the like.

[0014] The adhesion promoter is selected from a group consisting of siloxane, polydimethylsiloxane, modified siloxane, polyethylene wax, hydroxyl functional copolymer with an acidic group, salt of polymer with an acidic group, chlorinated polyolefin and the like. The rheology modifier is selected from a group consisting of carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, acrylic copolymer, a polyurethane polymer, xanthan gum, urea-modified polyurethane and the like. The pH value of the coating composition ranges from 8 to 9.5.

Detailed Description of the Invention

Definition:

[0015] The terms and phrases as indicated in quotation marks (‘”) in this section are intended to have the meaning ascribed to them in this‘Definitions. ¹ Section applied to them throughout this document, including in the claims, unless indicated otherwise in context. [0016] A‘rubber article’ means natural and synthetic rubber items including physicians examination gloves, surgeons gloves, worker gloves, balloons, tubing, condoms, figure cot, shunt valve, stent and implant ‘phm’ means“parts per hundred monomers ‘phr’ means“parts per hundred rubber “p.b.w” means“parts by weight.”“NVM” means“non-volatile matter.”“TSC” means“Total Solid Content”.

[0017] Throughout this specification the word “comprise”, or variations such as“comprises” or“comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of Elements, integers or steps. The use of the expression“at least” or“at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.

[0018] An embodiment of this invention, illustrating its features, will now be described in detail. The words "comprising, "having, "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. [0019] The terms“first,”“second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms“an” and“a” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. [0020] The disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. [0021] The present invention provides a coating composition for coatings rubber articles. Further, the coating composition reduces the coefficient of friction of the rubber articles. The coating composition provides high surface adhesion for improved binding with a rubber surface of the rubber article and also reduces flaking or de-lamination of the coating.

[0022] The coating composition includes a hydrophobic polymeric material, water and at least one additive. The hydrophobic polymeric material is in a range between 1% to 10% by weight. Preferably, the range can be between 1% to 5% by weight. The hydrophobic polymeric material is a carboxylated styrene- butadiene latex. The carboxylated styrene-butadiene latex is characterised by a styrene content ranging between 30% to 90% by weight of the carboxylated styrene-butadiene latex, Tg (glass transition temperature) ranging from 0 °C to 50 °C.

[0023] The water is in a range between 90% to 99% by weight.

Preferably water can be in a range from 95% to 99%. The at least one additive is selected from the group that includes a surfactant, a compatibiliser, a cross-linking agent, a lubricating agent, a wetting agent, an anti-blocking agent, an adhesion promoter, a rheology modifier and the like in range between 0.005% to 10% by weight.

[0024] The lubricating agent is selected from a group consisting of silicon emulsion, polydimethylsiloxane, wax emulsion, polyethylene wax, paraffin wax, polyurethane and the like. The anti-blocking agent is selected from a group consisting of polyethylene emulsion, paraffin wax, high-density polyethylene wax, polystyrene and the like. The wetting agent is selected from a group consisting of nonionic surfactants, siloxane, polydimethylsiloxane, modified siloxane, linear dodecylbenzene sulfonate and the like.

[0025] The adhesion promoter is selected from a group consisting of siloxane, polydimethylsiloxane, modified siloxane, polyethylene wax, hydroxyl functional copolymer with an acidic group, salt of polymer with an acidic group, chlorinated polyolefin and the like. The rheology modifier is selected from a group consisting of carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, acrylic copolymer, a polyurethane polymer, xanthan gum, urea-modified polyurethane and the like. The pH value of the coating composition ranges from 8 to 9.5.

[0026] Typically, the viscosity of non-diluted base coating composition (TSC= 15% to 25%) ranges from 1000 to 10000 cps as measured by Brookfield viscometer spindle no.3, l2rpm (QC-S-II-08) method at 25 °C temperature. The hydrophobic polymer coating only ensures better compatibility with the rubber substrate but it also results in improved bonding between the coating and the underlying substrate. In another aspect of the present invention, there is provided with the rubber article coated with the coating composition of the present invention on at least one of the surfaces. The coated surface of the rubber article is characterised by the coefficient of friction ranging from 0.1 to 0.6, the percentage of elongation ranging from 500%to 800% (ASTM D 6319).

[0027] The invention will now be described with the following non limiting examples.

EXAMPLES:

[0028] Referring now to table showing tabulation of contents for preparing the coating compositions (A, B & C) in accordance with the present invention. The tabulation in table 1 shows preferred embodiments of the contents for preparing the composition.

Table 1

[0029] The present invention also provides a method for coating rubber articles with the coating compound having contents described in table 1. A ceramic former is configured according to the shape of an article. In the present embodiment, the article is a glove. The ceramic former is pre-heating at about 80 °C for 5-10 min. The ceramic former is dipped in a coagulant solution (a 20% aqueous solution of calcium nitrate) for 5 sec. The ceramic former is dried at about 80 °C for 5 min. The ceramic former is dipping in natural latex compound or Synthetic latex compound for 10 sec. The ceramic former is dried at about 80 °C for 5 min.

[0030] Further, the article surface deposited on the ceramic former is leached at 60-70 °C hot water for 2-3 min followed by imparting beading on the article for easy release. The article surface deposited on the ceramic former is dipped in the coating compound for 5 sec, further dripping out the excess the coating solution from the article surface to achieve a uniform polymer coating surface. The coated article deposited on the ceramic former is subjected to a vulcanisation process at about 100 °C for 25 min to obtain a cured article. The cured article is subjected to a leaching process at about 60-70 °C hot water for 2-3 min. The compound coated article from the ceramic former is stripped from the ceramic former. EXPERIMENTAL RESULTS:

[0031] Table 2 shows tabulation of comparative test data from the measurement of coefficient of friction for uncoated rubber gloves and gloves coated by the coating composition of the present invention comprising a polymer in an amount of 1 % and 2 % respectively.

[0032] Protocols /standards as reference: ASTM D1894

[0033] Name of the equipment: Universal Testing Machine Gotech AI-3000 and COD text fixture

Setting parameter: testing speed 50mm/min.

[0034] The coefficient of friction test: Table 2

[0035] Further, the uncoated glove is subjected to a tensile test. Table 3 shows the tabulation of reading obtained during the tensile test. The tensile test is carried with the following testing equipment.

Mechanical properties checked by ASTM D6319 standard

Sample specifications: Nitrile examination gloves

Shape: Dumbbell shaped the film

Length: 150 mm

Width: 06 mm

Thickness: 0.12 mm Name of the instalment: Dak System Inc make Model no. UTM9052, Serial no. 353/11-12

Table 3

[0036] Further, the uncoated glove is coated with the composition A.

The coated glove is subjected to a tensile test. Table 4 shows the tabulation of tests results of the tensile test conducted on the rubber glove coated with composition A.

Table 4

[0037] Furthermore, an uncoated glove is coated with the composition B. The coated glove is subjected to a tensile test. Table 5 shows the tabulation of tests results of the tensile test conducted on the rubber glove coated with composition B. Table 5

[0038] Furthermore, an uncoated glove is coated with the composition C. The coated glove is subjected to a tensile test. Table 6 shows the tabulation of tests results of the tensile test conducted on the rubber glove coated with composition C.

Table 6

[0039] The present invention has the advantage of providing a coating composition for coatings rubber articles. The composition A, B, C reduces the coefficient of friction of the rubber articles. The composition A, B, C provides high surface adhesion for improved binding with a rubber surface of the rubber article and also does not exhibit flaking or de-lamination of the coating. Also coatings with composition A, B, C don’t affect the mechanical properties of the gloves as evident from the table 4, 5, 6.

[0040] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilise the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the claims of the present invention.