TITLE: "Self-Curing Composition"
BACKGROUND OF THE INVENTION
The present invention relates to a self curing polymeric composition. In particular, the present invention relates to a self curing polymeric composition for rubber compositions.
Self curing polymeric compositions are known whereby an agent present in the composition reacts at ambient temperature to form a cured or crosslinked polymer. These self curing polymeric compositions have a variety of applications comprising use as waterproof membranes, adhesives, paints and lacquers.
A problem or disadvantage that exists with known self curing polymeric compositions is that under conditions with high humidity and/or low temperature or with poor air movement, the agents present in the composition do not allow at ambient temperature the formation of a cured or crosslinked polymeric product.
Throughout the specification, the term "cured" will include partially cured polymeric products which resist deformation on application of force as applied by a thumb test. The term "cured" will also include fully cured and substantially cured polymeric products.
In particular, self curing polymeric compositions which delay the curing over an extended period of time, for example 24 to 48 hours, suffer from the problem of not curing at ambient temperature to form the cured polymeric product.
SUMMARY OF THE INVENTION
It is an object of the present invention to seek to overcome or, at least, reduce the above stated problems with the prior art.
According to a first aspect of the present invention, there is provided a self curing composition for a polymeric composition comprising
(a) a silicon containing compound or a salt with limited solubility,
(b) an oil, an olefine or a fatty acid; and
(c) a starch, a carbohydrate, a polysaccharide, a cellulose or a gum.
The composition preferably has the oil such that it has a medium saponification number. The oil may be a naphthenic or process oil. The oil may also be in the form of a vegetable oil. The vegetable oils include cottonseed, peanut, rapeseed, sunflower, canola oil and safflower oil
In a preferred form, the starch is a cold water swellable and soluble starch. The starch is preferably in the form of a corn starch.
The composition also preferably includes water.
The silicon containing compound is preferably a halogen containing compound. The silicon containing compound which contains halogen preferably includes fluorine containing and chlorine containing compounds. In particular, the preferred halogen containing silicon compounds include alkali silico halides.
The composition also preferably includes a biocide to provide antifungal properties to the composition.
According to a second aspect of the present invention, there is provided a self curing polymeric composition comprising
(a) a thermoplastic polymer;
(b) a self curing composition comprising a silicon containing compound, an oil and a starch.
According to a third aspect of the present invention, there is provided a method of controlling the curing of a thermoplastic polymer comprising the steps of
a) premixing a starch, an oil and a curing agent in an aqueous solution to form a coated curing agent;
b) adding the coated curing agent to the thermoplastic polymer;
such that thermoplastic polymer will be cured over an extended period of time.
DETAILED DESCRIPTION OF THE INVENTION
The thermoplastic polymer is preferably a polychloroprene polymer, bituminous polymer, asphaltic polymer or any anionic emulsion of a thermoplastic polymer which is unstable in combination with small amounts of a cation.
Other suitable polymers include acrylic resins, polyurethanes, Styrene/Butadiene/Rubber (SBR) resins, polyvinyl acetate resins, synthetic rubber resins and polyethylenes and polyvinyl chloride resins.
In accordance with one embodiment of the present invention, the self curing polymeric composition is a controlled release self curing composition which operates such that curing of the polymer will occur after a predetermined time. The predetermined time is preferably in the range of half an hour to 8 hours.
The self curing composition according to a preferred aspect of the present invention is a composition which when added to a thermoplastic polymer will not immediately cure or cross link the thermoplastic polymer. Rather, the oil, the starch and the silicon containing compound are pre-mixed in a manner so as to allow the curing or cross linking of the thermoplastic polymer to be controlled or delayed over an extended period of time.
It is believed that the starch and oil act to form a coating over the silicon containing compound which is thought to act to cure or cross link the thermoplastic polymer. Since the silicon containing compound is coated with the oil and starch, it is believed that the curing or crosslinking reaction of the
thermoplastic polymer and the curing agent is delayed. The adjustment of the ratios of the oil, starch and the silicon containing compound can control the rate of release of the curing agent to the thermoplastic polymer. However, it is to be understood that the components of the self curing composition may operate in another manner to that just described.
The components in the self curing composition comprising starch, the silicon containing compound and the oil are mixed in such a ratio so as to provide curing or crosslinking of a thermoplastic polymer under conditions of high humidity and/ or low temperature.
A preferred range for the starch is 300 to 450 parts. A further preferred range for the starch is 320 to 420 parts. A still further preferred range is 350 to 400 parts. A yet still further preferred range is 370 to 380 parts.
A preferred range for the silicon containing compound is 200 to 600 parts preferably 200 to 300 parts. A further preferred range for the silicon containing compound is 450 to 550 parts. A still further preferred range is 470 to 530 parts. A yet still further preferred range is 480 to 500 parts.
A preferred range for the oil is 250 to 450 parts. A further preferred range for the oil is 300 to 400 parts. A still further preferred range for the oil is 350 to 390 parts. A yet still further preferred range for the oil is 370 to 380 parts.
The self curing composition preferably includes 10 to 50 parts of a biocide. The self curing composition further preferably includes 10 to 30 parts of the biocide. The composition is preferably mixed together in an aqueous solution.
The self curing composition is admixed with a base thermoplastic polymer in such a ratio so as to provide curing or crosslinking of the base thermoplastic polymer under conditions of high humidity and/or low temperature.
A preferred range for the base thermoplastic polymer is 50 to 150 parts. A further preferred range is 70 to 140 parts. A still further preferred range is 80 to 130 parts.
A preferred range for the self curing composition is 5 to 50 parts. A further preferred range is 10 to 40 parts. A still preferred range is 20 to 30 parts.
All parts for the admixture of the self curing composition and the base thermoplastic polymer are given in parts by volume.
A preferred ratio of the self curing composition to the base thermoplastic polymer is 1 to 15. A still preferred ratio is 1.5 to 13. A still further preferred ratio is 2 to 10.
EXAMPLES OF THE INVENTION
The present invention will now be illustrated with reference to the following example.
EXAMPLE 1
A biocide was added to water in a vessel to form an aqueous solution and then stirred so that the biocide was evenly distributed throughout the aqueous solution. A corn starch was then added to the aqueous solution by slow sprinkling at high speed and then followed by stirring at slow speed for approximately one hour.
In a separate formulation, sodium silico fluoride was pre-mixed with canola oil such that a smooth paste is formed. A further quantity of canola oil is mixed with the smooth paste until the paste is uniform in texture.
The pre-mixed formulation of sodium silico fluoride and canola oil is then added to the vessel containing the aqueous solution of biocide and corn starch. The aqueous solution is then stirred at medium speed until a viscous liquid is formed.
The promoter composition is then added to a base material which in this example is a polychloroprene resin. The polychloroprene resin is an anionic resin which is acrylic modified and pigmented with silica flour and suitable iron oxides, titanium oxides and zinc oxides. The base material may also be an anionic bitumen emulsion.
The polymeric composition of the present invention is typically used as a single pack material for forming a waterproofing membrane. The viscous liquid is applied to a surface where the waterproofing composition self cures at a temperature of 5 to 35 degrees Celsius and at 98 per cent relative humidity. However, the polymeric composition may also be used in the form of a spray, a gel or as a brushable composition. After a period of up to 24 hours, the polychloroprene base material has cured to form a waterproof elastomeric rubber product.
A first formulation of the composition used in the example is as follows:
a) 15 to 30 parts of a biocide;
b) 350 to 380 parts of a corn starch;
c) 480 to 520 parts of a sodium silico fluoride;
d) 350 to 375 parts of canola oil.
The balance of the composition is made of water.
A second formulation of the composition used in the example is as follows:
a) 15 to 30 parts of a biocide;
b) 350 to 380 parts of a corn starch;
c) 200 to 300 parts of a sodium silico fluoride;
d) 350 to 375 parts of canola oil.
The balance of the composition is made of water.
The pot life of the self curing composition is 30 to 60 minutes at 35 degrees Celsius and 5 to 6 hours at 20 degrees Celsius.
The cure / set times of the self curing composition were evaluated in the following apparatus. The apparatus provides adverse conditions of high relative humidity of 80 to 98 percent and elevated temperatures of 28 to 40 degrees Celsius. The apparatus has an insulated chest having an internal capacity of 40 litres and a removable insulated clip on lid. A thermostatically controlled immersion heater is provided in a sealed water bath within the inside of the chest. High relative humidity is achieved by use of an open water reservoir which contains warm or hot water depending on the conditions required. The lid of the insulated chest is fitted with a continuous read out thermohygrometer for the monitoring of the environment. Test panels are mounted in either horizontally or vertically in a rack so that there is no direct contact with any water in the bottom of the insulated chest. A circulating fan is optionally provided to provide air movement.
The cure time of the above example is as set out as follows for a coating applied to a dry surface and to a water saturated surface:
Temp/ Relative Humidity Dry surface Water saturated surface.
35 degrees C/ 98% approx. 30 mins approx. 4 hrs.
20 degrees C/50 % approx 15 mins approx. 1.5 hrs
In Figure 1 , there is shown a graph of temperature ( in degrees C) versus relative humidity for polymeric compositions with and without the self curing composition of the present invention.
The parabolic curve as shown by the dash and dot line illustrates the temperature and relative humidity conditions of prior curing compositions.
The broken line with a series of dashes illustrates the temperature and relative humidity conditions of the present invention. As can be seen from figure 1 , the area of gain is shown by the shaded area between the pair of lines.
In use, the self curing composition of the present invention is preferably used with polychloroprene type resins to form waterproof membranes. In waterproofing applications, the self curing composition will self cure within a predetermined time to form a cured or crosslinked elastomeric rubber product which is substantially waterproof. In particular, the self curing composition of the present invention will self cure in conditions at high humidity and low temperature.
Throughout this specification, unless the context requires otherwise, the word "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
It is to be understood that the present invention should not be restricted to the particular embodiments or examples described above. Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention