Field of Invention

The present invention relates to a method of forming a conductive layer on a ceramic surface. More particularly, the present invention relates to a method of forming an electrically conductive abrasion and corrosion resistant layer on a dip moulding ceramic former.

Background of Invention

Pinhole and tear detection tests are generally used to identify if miniscule holes termed as pinholes and tears are present on dip moulded latex articles. Common methods of detecting pinhole and tear defects are by using tests such as air leak test and water tight test. These methods utilize random sampling of dip moulded latex articles from the production line, which is disadvantageous as not all of the dip moulded latex articles are tested for defects.

A proposed method for overcoming the above problem is by allowing dip moulded latex articles to be tested while they are still on the former, which would allow for all dip moulded latex articles to be tested. Accordingly, dipping formers with an electrically conductive layer are provided to allow the dip moulded latex articles to be tested while they are still on the dipping formers. While it would be ideal to replace all existing dipping formers on the production line with formers made of electrically conductive material, the cost involved would be prohibitive.

As such, it would be advantageous to provide a method to allow existing dipping ceramic formers to be adapted for use in an online testing apparatus for pinhole and tear detection.

Summary of Invention

The present invention relates to a method of forming an electrically conductive abrasion and corrosion resistant layer on a ceramic former. The method comprises the steps of mixing a metal or a non-metal with a dispersant in a ratio of 1 :1.5-3 by weight to form a paste, applying the paste onto the ceramic former, and firing the ceramic former at a temperature of 850°C-1 100°C for a duration of 1 hour to 4 hours. The metal or non-metal may be in powder form or pellet form.

In an embodiment, the metal is selected from a group consisting of aluminium, copper, gold, iron, nickel, silver, stainless steel, and tin.

In an embodiment, the non-metal is selected from a group consisting of boron nitrate, graphite, titanium diboride, and titanium carbide.

In an embodiment, the powder form of the metal is aluminium powder.

In an embodiment, the pellet form of the metal is aluminium pellet. In an embodiment, the ratio of the metal or the non-metal to the dispersant is 1 :2.5 by weight.

In an embodiment, the paste is stirred using an agitator at a speed of 30-270rpm and left for 8 hours before being applied onto the ceramic former.

In an embodiment, the dispersant is selected from the group consisting of polyethylene glycol, maleic acid-olefin copolymer, sodium-n-alkyl-(C ₁₀ -C ₁₃ ) benzene sulphonate and polyvinyl alcohol.

In an embodiment, the step of applying the paste onto the ceramic former is by spray coating.

In an embodiment, the ceramic former is fired at a temperature of 1000°C for a duration of 4 hours.

In an embodiment, the method further comprises the step of drying the ceramic former at a temperature of 50°C-1 10°C for a duration of 120s-600s before the step of applying the paste onto the ceramic former.

In an embodiment, the ceramic former is dried at a temperature of 80°C for a duration of 180s.

The present invention also relates to a composition comprising a metal or a non-metal selected from a group consisting of aluminium, copper, ceramic, boron nitrate, gold, graphite, iron, nickel, silver, stainless steel, tin, titanium diboride, and titanium carbide and a dispersant selected from a group consisting of polyethylene glycol, maleic acid-olefin copolymer, sodium-n-alkyl-(C ₁₀ -C ₁₃ ) benzene sulphonate and polyvinyl alcohol. The metal and the non-metal are in powder form or pellet form and ratio of metal or non-metal to dispersant is 1 :1 .5-3 by weight.

Brief Description of Drawings

The drawings constitute a part of this specification and include an exemplary or preferred embodiment of the invention, which may be embodied in various forms. It should be understood, however, the disclosed preferred embodiment is merely exemplary of the invention. Therefore, the figures disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention. Figure 1 shows results of an abrasion resistance test performed on a ceramic former having an electrically conductive layer formed using the present invention.

Figure 2 shows results of a corrosion resistance test performed on a ceramic former having an electrically conductive layer formed using the present invention.

Figure 3 shows dispersing times of aluminium powder into a dispersant stirred to form a paste in accordance with a preferred embodiment of the present invention. Detailed Description of Preferred Embodiment

Detailed description of a preferred embodiment of the present invention is disclosed herein. It should be understood, however, that the embodiment is merely exemplary of the present invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claim and for teaching one skilled in the art of the invention. The numerical data or ranges used in the specification are not to be construed as limiting.

Embodiments relate to a method of forming an electrically conductive abrasion and corrosion resistant layer on a ceramic former and a composition for use thereof. The ceramic former may be a newly fabricated former or a former that has already been in use in producing dip moulded latex articles.

In a preferred embodiment, the method comprises the steps of mixing a metal with a dispersant to form a paste. Preferably, the metal is in powder form. Alternatively, the metal may be in pellet form.

Preferably, a metallic powder such as aluminium powder is mixed with a dispersant such as polyethylene glycol at a ratio of 1 :2.5 by weight to form a paste. Alternatively, aluminium pellet may also be mixed with polyethylene glycol at a ratio of 1 :2.5 by weight to form a paste. While a ratio of powder or pellet to dispersant of 1 :2.5 by weight is preferred, ratio of powder or pellet to dispersant may be 1 :1.5 to 1 :3 by weight.

Aluminium powder is preferred as the metallic powder to be mixed with the dispersant. It is envisioned that powders of other types of electrically conductive metals may be used. These may include powder form of metals such as copper, gold, iron, nickel, silver, stainless steel, and tin.

Alternatively, non-metallic powders may be used. Examples of non-metallic powders are such as boron nitrate, graphite, titanium diboride, and titanium carbide. Similarly, a non- metallic powder may be mixed with a dispersant such as polyethylene glycol at a ratio of 1 :2.5 by weight to form a paste. A ratio of non-metallic powder to dispersant at 1 :1 .5 to 1 :3 by weight may also be used.

Preferably, the metallic or the non-metallic powder used is available commercially and has a particle size of 1 -75pm. Alternatively, metallic or non-metallic pellets which are commercially available may be used.

Alternatively, pellet form of metals such as copper, gold, iron, nickel, silver, stainless steel, and tin may be used.

Alternatively, pellet form of non-metals such as boron nitrate, graphite, titanium diboride, and titanium carbide may be used.

Preferably, pellets used have sizes ranging from 5 pm to 100 pm. Still preferably, the pellets are in granule, small rounded shapes or other geometrical shapes. Polyethylene glycol is a preferred dispersant to be mixed with the metallic or the non-metallic powder. Alternatively, a maleic acid-olefin copolymer commonly known by the trade name SOKALAN CP9; sodium-n-alkyl-(C ₁₀ -C ₁₃ ) benzene sulphonate which is commonly known by the trade name DISPONIL LBDS; or polyvinyl alcohol may be used as a dispersant.

Preferably, the paste is stirred using an agitator at a speed of 30-270rpm and left for a duration of 8 hours before being applied onto the ceramic former. This allows the metallic or the non-metallic powder or pellet to disperse homogenously into the dispersant. The paste may be stirred using any type of agitator known to a person having ordinary skill in the art. Preferably, an anchor type agitator is used. Still preferably, the paste is mixed to reach a dynamic viscosity within the range of 4000cPs to I OOOOCPS.

Referring to Figure 3, the dispersing time of the aluminium powder into the dispersant is shown. Seven types of agitators which are axial flow agitator, paddle 4-blade agitator, paddle 2-blade (2 layers), propeller agitator, helical agitator, turbine agitator and anchor agitator were used to study the effectiveness of aluminium powder dispersing into the dispersant. Nine different speeds range from 30-270rpm with interval of 30rpm were used for each type of agitator. The results show that the anchor agitator is the most effective (8 hours at 240rpm) and axial flow agitator is the least effective (38.4 hours at 270rpm) in dispersing the aluminium powder into the dispersant. At speeds of 30 rpm, sedimentation is observed in axial flow agitator, paddle 4-blade agitator, paddle 2-blade (2 layers) agitator, propeller agitator and helical agitator. However, it is still possible to stir the paste at 30 rpm using turbine agitator and anchor agitator. While Figure 3 shows dispersing times for aluminium powder only, the results are the same for aluminium pellets.

Preferably, the aluminium-polyethylene glycol paste is loaded into a spray gun with a compressed air pressure of 100000 Pa to 300000 Pa and sprayed onto the ceramic former. Alternatively, the aluminium-polyethylene glycol paste may be applied onto the ceramic former using any suitable means known to a person having ordinary skill in the art.

Preferably, the ceramic former is washed with water and dried in an oven at a temperature of 50°C to 1 10°C for a duration of 120s to 600s before the paste is applied onto the ceramic former. Still preferably, the ceramic former is dried at a temperature of 80°C for a duration of 180s. After the paste is applied onto the ceramic former, the paste is then allowed to cure in an oven. Preferably, the coated ceramic former is fired at a temperature of 850°C to 1 100°C for a duration of 1 hour to 4 hours. Still preferably, the ceramic former is fired at a temperature of 1000°C for a duration of 4 hours.

It is observed that thickness of the electrically conductive abrasion and corrosion resistant layer at 0.1 to 300 MW-cm may be created using this method.

Figure 1 shows results of an abrasion resistance test. In order to test for abrasion resistance, the coated ceramic former is abraded against silicon carbide paper. Up to 10000 cycles of abrasion against silicon carbide paper was performed to simulate real-life conditions. After 10000 cycles of abrading against silicon carbide paper, the aluminium coating still displays electrical conductivity even though a significant area of the aluminium coating has been abraded away. After testing, it is calculated that the coated former has a shelf life of 1 to 3 years.

Figure 2 shows results of a corrosion resistance test. In order to test for corrosion resistance, the coated ceramic former was soaked in corrosive liquids at a temperature of 70°C for a duration of 3 days. The corrosive liquids are the following: nitric acid, chlorine water and alkaline-based cleaning agents. It was observed that the coated formers lost 0.2% of their total weight.

The invention being thus described, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the embodiments as disclosed therein. Such modifications are to be considered as included in the following claims unless the claims by their language expressly state otherwise.