RESIST TO WATER. SOLVENTS AND DILUTED SOLVENTS

BACKGROUND OF THE INVENTION

Personal Protective Equipment's (PPE) are essential to conduct any work in a safer manner which includes gloves, helmets etc. Among PPE, the top priority can be given to chemical protection gloves which protect hands from hazardous chemicals. There are many gloves in the market which are made of natural rubber, acrylonitrile butadiene rubber (NBR), polychloroprene rubber and etc., Natural rubber gloves are generally resistant to polar solvents, nitrile and polychloroprene latex gloves are mostly suitable for oxidizing acids and bases in addition to certain polar and non polar solvents. However, the above stated gloves are not resistant to certain organic solvents, specially ketones, and other special solvents such as chlorinated solvents and amines. In addition, all PVA coated chemical resistant gloves are fabric supported gloves. Though PVA coated gloves provide promising protection against ketones and other organic solvents, they do not resist to water and diluted solvents due to its inherent nature of water solubility. As a result, PVA coated supported gloves should always be prevented from contact with water. In addition, chemical performances of PVA coated gloves are drastically reduced under high humid conditions due to the absorption of atmospheric moisture by the PVA layer and therefore has to be stored in a moisture free environment to retain the chemical performances.

Novelty of this innovation is that the water soluble/hydrophilic PVA layer is chemically modified in such a way to make the layer hydrophobic and as a result less vulnerable to degradation when contact with water. With this new development, it can be used with diluted solvents (i.e. especially ketones and water mixtures) and under high humid conditions.

Most of the PVA coated gloves in the market are fabric supported versions which are bulky and less comfortable. The glove described in this invention is an unsupported glove with a 0.28 mm thickness and with a good flexibility and dexterity with an enhanced protection towards organic solvents which includes aliphatic and aromatic hydrocarbons, chlorinated solvents, amines, ketones, etc and more importantly diluted solvents.

SUMMARY OF THE INVENTION

The present invention relates to an unsupported nitrile glove with a modified PVA layer with a thickness of 20 pm which imparts hydrophobicity to the glove and as a result resistant towards most of harsh chemicals, solvents, diluted solvents, water.

PRIOR ART

Following patents have used additives such as starch, PVA with melamine formaldehyde, boric acid and borate salts to make the PVA layer water insoluble.

Patent US4731266, describes a method of preparing a thin polyvinyl alcohol film which are gelled, non-tacky, bubble-free and resistant to water at ambient temperatures. The main focus of the invention provides composite, hiaxially oriented, impermeable barrier layer coated, thermoplastic hollow shaped articles useful as packaging material, e.g.as packages and bottles for flavored foods and carbon a ted bey er ages .

IIS patent 5649326, describes a flexible hydrophilic coating for ortopaedic casting gloves and method of making such gloves. The lubricous glove is made of a base material having a coating thereon of a hydrophilic lubricant mixed with a substantial portion of the material of the base material. For an example, a natural rubber latex glove may have coated thereon a mixture of natural rubber latex and polyvinyl alcohol in order to provide a lubricous surface. The glove may be itself made of a mixture of the flexible base material and the hydrophilic lubricant example is a natural rubber latex mixed with either polyvinyl alcohol, polyvinyl pyrrollidone or polyethylene oxide and a glove formed from the mixture in order to provide a lubricous glove.

US patent 2012/0055642A1, concerns a paper or board product with an improved tensile strength comprising cellulose fibers, one or more zirconium carbonate compound(s) and water-insoluble polyvinyl alcohol fibers, and a process for manufacturing such a product, comprising the steps of forming a combined aqueous suspension of cellulose fibers and water insoluble polyvinyl alcohol fibers, and pressing it into a paper or board product, or pressing layers of water-insoluble polyvinyl alcohol fibers and cellulose fibers into a product having a sandwich-structure, and treating the product before drying with an aqueous solution of a zirconium carbonate compound by impregnating one or more of the surfaces of the product or the complete product with the solution.

DETAILED DESCRIPTION OF THE INVENTION

The present innovation relates to a latex dipped article, particularly a latex glove with multiple layers comprising PVA. The inner layer is made of nitrile latex while the outer layers have a combination of materials composed of PVA, layered silicates favorably laponite, zirconium carbonate, nano cellulose and pre crosslinked nitrile latex. PVA which is inherently soluble in water was modified with the incorporation of nanocellulose and pre cross linked nitrile latex so that the outer layer made out of PVA will resist against water and will not degrade when exposed to diluted solvents. GLOVE STRUCTURE

The glove is made of elastomeric composite layers where the inner layer is made of nitrile latex and the outer layers are made of poly vinyl alcohol. The glove is made with two objectives, firstly to make a glove that resists water and secondly to make the glove to be used with diluted solvents (targeting acetone/water mixture).

Figurel: Glove structure

OUTER MODIFIED PVA LAYER

The outermost layer of the glove is made of chemically modified PVA composite where the layer will not dissolve in the presence of water or solvent-water mixtures. PVA, an inherent water-soluble material, is chemically modified by adding nano cellulose and pre crosslinked nitrile latex so that the PVA layer will not be soluble in water. The PVA composite is made of fully hydrolized PVA, zirconium carbonate, layered silicate preferably laponite, nano cellulose, colour pigments, anti-foaming agents and pre crosslinked nitrile latex. The nitrile latex is pre cross linked with a carbodiimide cross linker which is a liquid in nature and will prevent formation of holes in the outer PVA layer due to presence of dispersion pieces. Zirconium carbonate helps to increase the degree of crosslinking, by reacting with the OH groups in the PVA and acts as a binder to form strong crosslinks while the layered silicate/laponite helps in film forming. The crosslinks formed between PVA, nanocellulose and zirconium carbonate provides water resistivity by reducing the available OH groups in the outer PVA layer to react with water. This is further improved by pre cross linked nitrile latex present in the composition , which will act as a barrier for solvent molecules to pass through the glove .

The main ingredient PVA provides excellent permeation resistance towards organic solvents which includes aliphatic and aromatic hydrocarbons, chlorinated solvents, amines, and specially ketones like acetone and MEK.

INNER NITRILE LAYER

The inner layer of the glove is made of nitrile (NBR) latex which provides protection for aliphatic hydrocarbons, acids and bases. For the inner layer natural rubber latex, polychloroprene its blends or any other rubbers, SBR, butyl, PVC, and synthetic poly isoprene can be used.

In addition to latex, the inner nitrile layer contains additives such as wetting agents, stabilizers, curing agents, viscosity modifiers and pigments.

GLOVE MAKING PROCESS

The glove is made by dipping process followed for manufacturing of the glove is as follows

Coagulant Dipping

As the initial step hot former is dipped in a coagulant bath (eg calcium nitrate) which will facilitate the nitrile film formation

Nitrile Latex Dipping

The former is then dipped in a nitrile latex which will form a thin layer of nitrile on top of the former and the process is known as film formation or gelation

Leaching

Gloves are leached in water at a temperature of approximately 50 ^° C to remove excess calcium nitrate and water soluble materials in the nitrile latex layer.

Modified PVA layer dip

The leached former is then dipped in the modified PVA , Multiple dips, preferably two dips are given to ensure uniform coating of the modified PVA layer on top of the nitrile latex film

Curing /Vulcanization

One of the key steps in glove manufacturing is the vulcanization process, where the nitrile latex, PVA layers are crosslinked to increase the elasticity and the strength of the final product Stripping

The finished gloves are stripped from the glove formers manually.

CHEMICAL PERMEATION PERFORMANCE OF THE GLOVE

The performance of the glove for chemical permeation is measured according to EN ISO 374-1:2016 and the results are as follows

Table 1 : Chemical resistance of the glove with modified PVA layer

According to Table 1 , level three and two performance values have been achieved for diluted solvents and methanol respectively while maintaining consistent level 6 permeation resistance for other solvents such as acetone, dichlorome thane, diethyl ether and etc.

PERFORMANCE OF THE MODIFIED PVA LAYER TOWARDS WATER

The resistance of the modified PVA layer towards water was compared with the unmodified PVA layer by measuring in two ways, under high humid conditions and with direct exposure to water.

Performance of the modified PVA layer under direct contact with water

The water resistance against direct water contact was measured by exposing known weight of glove pieces prepared separately with modified and unmodified PVA layers for a time period of one and half hours. The obtained results of weight increase were plotted against the exposed time and Figure 1 indicates the respective results. According to the obtained results modified PVA layer has higher resistance towards water absorption compared to unmodified PVA layer.

Figure 1: weight increment of gloves made with modified and unmodified PVA layer after direct contact with water

Performance of the modified PVA layer under high humid conditions

To evaluate the water absorption under high humid conditions, trials were performed with gloves made of modified and unmodified PVA. Gloves with modified and unmodified PVA layers were placed in a humid chamber and the moisture absorption was measured as percentage weight increment for a period of seven days. The obtained results are plotted as below Figure 2 which clearly indicates the modified PVA layer has high resistance towards water absorption under high humid conditions compared to unmodified PVA layer.

Figure 2: percentage weight increment of gloves made with modified and unmodified PVA layer under high humid conditions.