FIELD OF THE INVENTION / BACKGROUND

The present invention relates to a latex dipped article with a wave-like textured porous structure and a method for making the article. The wave like textured porous structure can be applied to gloves or any other article which can be dipped in latex. In one embodiment the article can be a glove which can be made by dipping of hand like formers into the latex compound in which contain different compounding chemicals and different chemical treatments to produce a finished glove. When compounding the latex, different chemical ingredients are added to the latex to get the desired properties and to improve the quality of the end product. The latex contains curing agents that are used to cure the rubber, and a latex film is produced. The formers are first coated with the coagulant, preferably calcium nitrate solution, to facilitate the gelling of the latex. Then the formers are dipped into a latex compound to form a thin layer on the surface of the former. The latex gloves go through one or more rinses to leach out the excess calcium and water-soluble materials. The coagulated layer is dried and cured in a heated oven. After the curing process gloves are reversed stripped from the formers and necessary post-treatments are done on the glove surface and packed. Conventionally, the outer surface of the glove is determined by the texture of the glove former whilst the inner surface of the stripped glove is smooth.

The gripping characteristics are an extremely desirable feature of a latex glove, especially NBR latex gloves that provide slip resistance. Natural rubber latex gloves, the outer surface can be textured to obtain better gripping characteristics in different ways either by using the former embossed pattern or post-treatment process such as solvent treatment. Traditionally, nitrile latex gloves, the textured outer surface produced by dipping of textured formers into aqueous latex medium and reversed stripping of the glove. Therefore, the feeling of the textured former reflected the outer surface of the glove. The textured surface can be varied according to the requirements of the glove manufacturer. Diamond, sand patch and honeycomb are patterns that are most commonly used former types. Most of the textured gloves created as a result of former texture provide a better dry grip rather than wet and oil grip.

The grip/friction properties of the nitrile latex gloves are poor in contact with the different environment (dry/wet/oil) and the dexterity of the glove is also less in comparison to natural rubber glove due to the inherited stiffness of nitrile gloves. Hence grip pattern of the nitrile gloves reflected by the former pattern is not always sufficient to produce a better grip. Hence nitrile gloves with a better grip property and with improved dexterity are preferred for industrial applications.

PRIOR ART

US patent 2008/0244809 A1 refers to a latex glove with engineered geometrically-defined surface texture provides improved dry, wet, or oil surface-gripping characteristics made by applying polymeric coagulant coating, applying discrete coagulant particles, dipping the coated former into an aqueous latex emulsion, vulcanizing, stripping and dissolving the discrete coagulant particles in suitable solvent or water to reveal the geometrically designed texture.

US Patent 4,497,072 refers to a porous glove made of fabric material with a foamed resin coating that has sharp projections in the shape of broken bubbles whereby the glove provides tenacious grip and method of making the porous glove. The bubbles in the coated solution were broken by a vacuum pump.

US Patent 8119200B2 refers to a flexible and breathable glove having excellent grip in wet & oil environment which is made by a semi-gelled polymeric coating on an electrolyte treated glove liner substrate, is treated with a foamed solution of a surfactant, tenside or aerosol solution and overcoated with an electrolyte solution.

US Patent 8119200B2 refers to an improved slip and/or skid-resistant surface produces a better grip in grease and oily environment, made by laminating the foam surface to the substrate.

SUMMARY OF THE INVENTION

The present invention relates to a latex dipped article with a wave-like textured porous structure on the surface to provide a better grip/friction in different environmental conditions. The wave-like textured porous surface is formed by repeatedly removing the skin of the foam layer followed by deposition of removed skin on the outer surface of the glove by dipping the glove in a distorting solution thereafter gelling, drying and cure the glove to obtain the finished product. As shown in Figure 1, the present invention may provide a wave-like textured porous surface coating on the outer surface of the glove to improve, dry, wet and oil grip while maintaining an improved dexterity of the glove. The present invention provides a wave-like textured porous structure that consists of open-celled porous structure and micro-roughness on the surface of the glove. DETAILED DESCRIPTION OF THE INVENTION

The present invention is a latex dipped article with a wave-like textured porous structure made from foamed latex layer by repeatedly removing the skin of the foam layer followed by deposition of removed skin on the outer surface of the glove and stabilizing/gelling the particles of the latex by immersing the glove in a solution of calcium nitrate before it is dried. This repeatedly removing and deposition of foam skin creates a wave-like surface pattern and open-cell porous structure on the outer surface. The process is completed by drying and thereafter curing the glove. As depicted in Figure 2, this wavy nature with the porous structure of the foam layer provides an excellent wet and oil grip by the absorbing the liquids into the foam structure and with the assistance of micro-roughness of the flat area. Furthermore, wave-like foam layer produces dexterity/flexibility to the glove by stretching and contracting through the porous areas of the wavy pattern. In addition to that, the foam layer provides an insulation property on to the gloves.

The distorting solution used here is a mixture of calcium nitrate and surface-active agent which has an ability of repeatedly removing the skin of the foam layer followed by deposition of removed skin on the outer surface of the glove and stabilize/gelling the foam structure at the same time. With the removal of the skin of the foam layer produce an open-cell porous structure. The water-based or solvent-based calcium nitrate with a surface-active agent can be used as a distorting solution. The water-based calcium nitrate is used in the present invention wherein the useful concentration of calcium nitrate is range from 100-400 g/L. The calcium salt used here is not limited to calcium nitrate; it can be any salt or combination thereof. Distorting solution can create a wave-like porous surface without break down or collapses the foam layer and produce a novel wavy pattern that consists of an open-cell porous structure.

Definitions

Gelling - converting compounded latex to a gel form.

Distorting solution - consists of calcium nitrate and a surface-active agent. The distorting solution used to create a wave-like textured porous surface of the glove.

Coagulation - an agglomeration of dispersing rubber particles to a coherent jelly-like mass. Process steps of the wave-like textured porous clipped article

1. repeatedly removing the skin of the foam layer followed by deposition of removed skin on the outer surface of the glove and stabilize/gelling the foam structure at the same lime

EXAMPLE 1

Step 1. The following coagulant solution is prepared

Formulation 1

Compound By weight

Calcium nitrate 30.0%

Isopropyl alcohol 42.0%

Water 28.0%

The coagulant solution is heated to 55°C. A clean and dry porcelain glove former is heated to around 40°C and the heated former is evenly coated over the surface of the former by immersing in the coagulant solution as prepared according to Formulation 1.

Step 2. The dried, coagulant coated former is dipped into below mention latex compound.

Formulation 2

Compound phr

Latex 100.00

KOH 0.45

Surfactant 0.20

Sulfur 1.30

Activator 4.10

Accelerator 2.20

Dispersion agent 0.20 Anti-forming agent 0.04 Viscosity modifier 0.15 Wax 0.50

The pH is maintained around 10 with adding KOH to the compound. The viscosity of the latex should be controlled around 50 cP at 25°C. (Brookfield viscometer, spindle - 1, rpm - 60).

Step 3. Partially gelled latex film is leached in water

Step 4. The partially gelled or cured latex film is dipped into the below mention foam latex. The forming agent in the formulation 3 used is potassium oleate, but not limited to fatty acid soaps, including polycarboxylic acid soap, alkali metal soap and combination thereof.

Formulation 3

Compound By weight

Latex 100.00

KOH 0.45

Surfactant 0.20

Sulfur 1.30

Activator 4.10

Accelerator 2.20

Forming agent 0.20

Viscosity modifier 0.15

Wax 0.50

The pH of the latex has been adjusted to around 10 with the addition of KOH to the latex before it is formed, and the viscosity of the latex has been adjusted around 150 cP at 25°C. (Brookfield viscometer, spindle - 2, rpm - 6) using viscosity modifier.

Step 5. Partially gelled latex film is dried for 30 sec (maximum) and dipped into the distorting solution as prepared according to formulation 4 to repeatedly remove the skin of the foam layer followed by deposition of removed skin on the outer surface of the glove and stabilize/gelling the foam structure at the same time. The distorting solution comprising calcium nitrate or at least one salt selected from the group consisting of calcium salts or ammonium salts of nitric acid, sulfuric acid, carbonic acid, phosphoric acid , hydrochloric acid or formic acid and a surface-active agent selected from the group consisting of fatty alcohol ethoxylates, alkylphenol ethoxylates (APEs) and fatty acid ethoxylates.

Formulation 4 - Distorting Solution

Compound By weight

Calcium nitrate 25.0%

Octyl phenol ethoxylate 0.4% Water 74.6%

Step 6. The gelled or partially gelled glove is dried for around 30 sec at 25°C and dipped into water heated to 50-60°C to leach out the residual calcium nitrate and other chemicals.

Step 7. The gelled glove product is dried and cured in an oven at 130° C. For approx. 40 minutes.

Step 8. The cured glove is allowed to cool and is then reversed stripped off the former.

Step 9. The finished, cured glove is then turned inside out so that the textured surface is on the outside of the glove.

Compounded latex need to be foamed followed by 24-48 hours of waiting time (maturation time) and stabilized to produce evenly distribution of foam bubbles and bubble sizes with the range of 0.05-2 mm of diameter. The density of the foam compound needs to control over time with the range of 15-45% and the foam layer thickness is governed by the foam density. The foam is generated by either mechanical foaming or chemical foaming. In the present invention, mechanical foaming is preferred.

The viscosity of the compounded latex before it is foamed must be adjusted around 150 cP (Brookfield viscometer, spindle - 1, rpm - 20) at 25°C. Lower the viscosity of un-foamed latex and higher the density of foam latex tends to break down or collapse the foam layer on the glove surface. The maturation time should be considered both of the foam and un-foamed compounds with the range of 24-72 hours.

The porous texture is formed by repeatedly removing the skin of the foam layer followed by deposition of removed skin on the outer surface of the glove and stabilize/gelling the foam layer at the same time. Hence it produces a wavy-like texture and open-cell porous structure on the surface of the glove. The wave-like pattern is created by the porous texture that is formed by repeatedly removing and deposition of the skin of the foam layer when contact with the distorting solution. The crest of the wave pattern is flattened, and trough of the pattern has an open-cell porous structure. The open cell porous structure comprises of cavities are in the range of 10 microns to 1000 microns in diameter. The flat area is micro roughen by the deposition of removed skin layer with the dipping of distorting solution. The length between two adjacent crests of the wave pattern is in a range of 0.1 mm to 10 mm. The wavy pattern is generated perpendicular to the plane of the dipping.

The gap between two crests of wave pattern can be controlled by the dipping speed of formers on to the distorting solution and strength of the distorting solution. The slow speed of dipping can obtain evenly distributed wave pattern and fewer gaps between two adjacent crests of the wave pattern. The preferable former dipping speed can be varied 0.1 -2.0 cm/s to achieve evenly distributed wave pattern on the outer surface of the glove, but it's not limited to the range of 0.1-2.0 cm/s speed. A most preferred and convenient method to control the length between two adjacent crests of the pattern is the dipping speed of formers on to the solution of distorting solution tank.

A pinch grip test is one of the test methods used to test the grip of the glove. In pinch grip test, the force is measured to lift a vertically suspended cylindrical metal bar having a polished surface when it is pulled downwards. The grip force is measured by weights of counterbalance loaded. The maximum load that can withstand without lifting the metal surface is the final results of the test. This test can be performed as same as the dry grip to measure the wet and oil grip of the glove by covering with oil or water layer on the surface of the metal bar and the glove grip surface. A pinch grip test can perform different gloves and can compare the grip.

The test gloves are donned by a volunteer tester. The counterbalance loaded with known weights. The tester grips the apparatus to the metal surface using five fingers and the palm. The tester squeezes and holds the apparatus with enough force to hold it motionless without slip. The tester attempts to pull the metal bar towards downwards and determine whether it begins to slip. Additional weights are subsequently added to the apparatus and the above steps are repeated. The maximum weight is recorded at the point of slip. The surface of the metal bar and test glove are covered with water layer and the above steps are repeated. The surface of the metal bar and test glove are covered with oil layer and steps. Above steps are repeated. Above steps are repeated for the gloves that having raised diamond and sand patch grip pattern. The test result of pinch grip test, shown in Table 1, the textured surface prepared in example 1, when handling dry, wet and oily objects, provides exceptional user grip and controlled results.

TABLE 1

Test glove Dry Grip Wet grip Oil grip

(kg) (kg) (kg)

Wave-like porous glove 10.000 10.000 9.350

Conventional raised diamond 8.000 8.005 4.020

Conventional Sand patch 10.000 10.000 3.030

As shown in Table 1, the wave-like porous glove made according to Example 1 exhibits improved wet and oil grip. When compared to conventional gloves, the wave-like porous glove requires the highest grip force to slip the metal bar. According to the test results, the wave-like porous glove shows an excellent oil and wet grip compared to conventional raised diamond and sand patch gloves.

Friction testing is one of the test methods used for a variety of materials from lubricants, to films to determine the frictional characteristics of a material. The coefficient of friction (either static or kinetic) can be determined by the friction tester using the ASTM D 1894 standard.

The major items of the fixture include a 200 g square metal sled wrapped with a 1/8 in (3.2 mm) thick foam pad and a rectangular- shaped metal table with a defined surface finish. A pulley is located at one end of the table which allows the sled, when attached to the crosshead via a nylon or metal tow line to be pulled horizontally along the plate. Test material can be attached to either the sled or the plate or both. The coefficient of friction fixture mounts in the testing system load frame using Instron's Universal Testing Machine with standard type D base grip adapter. The tow line attaches directly to the load cell. The test sample is attached to the surface of the metal table and the sled is placed on top of the test sample.

The kinetic and the static coefficient of friction is measured by ASTM D 1894 standard. This test can be performed as same as the dry condition to measure the friction in wet and oil condition of the glove surface by covering with oil or water layer on the surface of the attached glove on the metal surface. Table 2: Friction Data of latex with different surface texture

As shown in Table 2, the Wave-like textured porous glove made according to Example 1 exhibits improved dry, wet and oil friction. When compared to conventional gloves with different grip patterns, the Wave-like porous glove having the highest value of the coefficient of friction in dry, wet oil environmental conditions.

Example 2

Gloves were prepared in the same manner as in Example 1, except that a knitted polycotton/nylon base liner was put on a hand-shaped former, dipped in a calcium nitrate solution of formulation 1 and dried. Then the hand-shape former was dipped in glove compound of formulation 2, dipped in foam compound of formulation 3, dipped in distorting solution of formulation 4 and heat set at 130° C for 40 minutes and then removed from the former as example 1.

Example 3

Gloves were prepared using the compounds of Formulation 1, 2, 3 and 4 as described in Example 1. First, a knitted nylon/cotton base seamless liner was put on a hand-shaped former and dipped in a calcium nitrate solution of formulation 1, then dried, and palm dipped or full dipped in compound of formulation 2, then partially gelled or cured glove was palm-dipped or full-dipped in a solution of Formulation 3, and then the partially gelled glove was dipped in a solution of formulation 4 and then cured at 130°C for 40 minutes and then removed the glove from the former or gloves can be prepared as in example 3 except the dipping of formulation 2.