Terpolymer emulsions

Abstract: Terpolymer emulsions of vinyl acetate, vinyl chloride and ethylene are used in surface coatings, eg. paints, and require certain properties for this application. The dry tensile strength and water uptake properties of such terpolymers is improved by adding monomer with the initiator during the reaction at rates which provide a reservoir of free monomer in the medium.

Description: Field of the invention: This invention relates to terpolymer compositions in emulsion form comprising vinyl acetate, vinyl chloride and ethylene as the principal monomer components. Terpolymer emulsions of this class are usable as bases for surface coatings, for example paints. Background of the invention: Terpolymers of this class are usable in a variety of applications dependent on the ratios of the monomers selected. Utilities include paints and other surface coatings intended for internal and external applications. These terpolymers are required to have certain properties to perform well in these surface coating applications, as an example, the terpolymers must have satisfactory tensile strength, elongation and water uptake. General description: The invention provides a process for the preparation of an emulsion of a terpolymer consisting essentially of Vinyl acetate units 10 to 90 parts by weight preferably 30 to 80 Vinyl chloride units 5 to 50 parts by weight preferably 10 to 40 Ethylene units 5 to 40 parts by weight preferably 10 to 30 and having improved properties of value in its application for surface coatings. The invention provides a process for the preparation of the terpolymer defined from a monomer mixture comprising a vinyl acetate monomer charge, a vinyl chloride monomer charge and an ethylene monomer charge, wherein from 10% to 100% of the monomer charge of vinyl acetate and vinyl chloride is introduced into the reaction vessel with at least 50% of the ethylene charge in the absence of initiator, and the addition of the remainder of the monomer charge and the addition of the initiator system are started together and are continued over a period in parallel at a rate which ensures there is a reservoir of free monomer in the reaction medium. During the major period of the reaction the sum of the concentration of free vinyl acetate and vinyl chloride monomers should be at least 5%, preferably at least 10%, by weight of the total reaction medium. It is believed this process improvement leads to an increase in molecular weight with consequent improvement in tensile strength and reduction in water uptake. Preferably the total ethylene charge is present in the reaction medium before the initiator is added. Although the process is operable and provides an improvement in terpolymer properties without this feature, the presence of the total ethylene charge at the initial stage assists in control of the subsequent polymerisation. Preferably the initial charge prior to addition of polymerisation initiator comprises at least about 20% and up to about 50% of the vinyl acetate and vinyl chloride monomers. There is a general requirement to improve the properties of the terpolymers of the invention to ensure they are suitable for external use and the process modification described provides improvement in the desired properties. Optionally the terpolymer may include minor amounts of monomer components included to provide specific benefits, examples are sodium vinyl sulphonate, acrylic acid, methacrylic acid, acrylamide and hydroxy functional acrylates. Literature: In Australian patent application 88920/82 (& EP-A-76511) (Wacker) there is described the preparation of vinyl chloride/ethylene copolymers in the presence of an inert organic substrance to increase the proportion of ethylene in the comonomer. There is a disclosure of the metering in of vinyl monomers at a time when there is umpolymerised vinyl monomers present, however the concentration of unpolymerised monomers is required to be kept low preferably below 5% by weight of the total dispersion. Additionally the present invention is performed in the absence of inert organic substances. GB 1355012 (Wacker) describes preparation of copolymer emulsions in which the reaction temperature is guided by the addition of the peroxy catalyst component. Example 9 relates to a terpolymer which is prepared with an initial charge of 83% monomers but to this is added initiator before the addition of further monomer. US 4073779 discloses the preparation of a terpolymer consisting of 43% by weight of vinyl chloride, 43% by weight of vinyl acetate and 14% by weight of ethylene. It was prepared in a process wherein 15% by weight of a mixture, of 50% by weight of vinyl chloride, 50% by weight of vinyl acetate were initially charged. This first charge is allowed to polymerise for a period before the remainder of the monomer is added. Other disclosures of terpolymer emulsions are found in GB 1404349 (Air Products) and GB 1544327 (Sumitomo). Example An example of the process and a comparative process will now be given to illustrate but not limit the invention. The terpolymer was produced from a monomer composition of:- Vinyl acetate 960.5 g Vinyl chloride 425 g Ethylene 306 g Comparative process: This process is based on procedures standard in the industry. An aqueous solution with the composition listed below was prepared and loaded into a pressure reactor (3.7 litres capacity). Hydroxy ethyl cellulose 17 g Anionic surfactant (75% aq) 45.4 g Sodium vinyl sulphonate 8.5 g Ferric chloride 0.017 g Distilled water to 52% non-volatile content Formic acid to give pH 3 to 3.5 The reactor was flushed first with nitrogen and then with ethylene. The agitator was then started, the vessel contents heated to 30°C and the whole of the ethylene component introduced into the vessel to give a pressure of 54 bars. 5% by weight of each of the vinyl acetate and vinyl chloride were added at this stage to form an initial monomer charge. Initiator solutions having the compositions A. Sodium persulphate 6.8 g Sodium bicarbonate 5.1 g Distilled water 170 g B. Sodium formaldehyde sulphoxylate 3.4 g Distilled water 170 g had been previously prepared and 10% of each solution added to the vessel containing the 5% monomer charge, the temperature of which was allowed to rise as the initial monomer charge polymerised. 15 minutes after the addition of the initiator solutions, the remaining 95% of the monomer components was added continuously over a period of 4 hours. The addition of the remaining 90% of the initiator solutions was commenced together with the monomer components, but the initiator solutions were added continuously over a period of 5 hours. The temperature was maintained at 60°C during these additions of monomers and initiators with continuing agitation. At the end of the 5 hour period the reaction mass was cooled to ambient temperature while adding final stage initiator solutions C & D over a period of 0.5 hours. C. t-butyl hydroperoxide (10% solution) 5.1 g sodium bicarbonate 1.7 g distilled water 34 g D. Sodium metabisulphite 5.1 g distilled water 34 g Process of invention: The process described previously was modified by introducing 30% of the monomer charge of vinyl acetate and vinyl chloride into the pressure vessel but in the absence of initiator. In the comparative process 5% of the monomer charge was mixed with 10% of the initiator solutions A and B. This step establishes a high concentration of monomer in the reaction medium. The remaining 70% of the monomer charge was then run in continuously over a period of 3.5 hours in parallel with the initiator solutions A and B, the latter were added over a 5 hour period. This mode of utilising the initiator system ensured a reservoir of free monomers existed in the reaction medium. During the major period of the reaction the sum of the concentration of free vinyl acetate and vinyl chloride monomers should be at least 5%, preferably at least 10%, by weight of the total reaction medium. During the continuous addition the temperature was maintained at 60°C. At the end of the 5 hour period the reaction mass was cooled to ambient temperature while adding final stage initiator solutions C and D over a period of 0.5 hours. After completion of the two processes the terpolymer emulsions were tested for maximum tensile strength, elongation at break and water uptake. A continuous film of polymer was prepared by applying a film of emulsion of 0.1 mm thickness to a PTFE coated glass plate and drying the film for 7 days at 20°C. After this period specimens were cut from it for the tests. Tensile strength and Elongation were measured using an Instron tensometer at an extension rate of 50 mm per minute at 20°C. Water uptake was measured as the percentage weight increase of terpolymer film samples after 24 hours immersion in water at 20°C. These results demonstrate the terpolymer prepared by the process of the present invention had improved tensile strength and water uptake.

Claims: A process for the preparation of a terpolymer emulsion consisting essentially of Vinyl acetate units 10 to 90 parts by weight Vinyl chloride units 5 to 50 parts by weight Ethylene units 5 to 40 parts by weight from a monomer mixture comprising a vinyl acetate monomer charge, a vinyl chloride monomer charge and an ethylene monomer charge, wherein from 10% to 100% of the monomer charge of vinyl acetate and vinyl chloride is introduced into the reaction vessel with at least 50% of the ethylene charge in the absence of initiator, and the addition of the remainder of the monomer charge and the addition of the initiator system are started together and are continued over a period in parallel at a rate which ensures there is a reservoir of free monomer in the reaction medium. A process according to claim 1 wherein the terpolymer consists essentially of Vinyl acetate units 30 to 80 parts by weight Vinyl chloride units 10 to 40 parts by weight Ethylene units 10 to 30 parts by weight A process according to claim 2 wherein the terpolymer consists essentially of Vinyl acetate units 45 to 65 parts by weight Vinyl chloride units 15 to 35 parts by weight Ethylene units 10 to 30 parts by weight A process according to claims 1, 2 or 3 wherein the total ethylene charge is present in the reaction medium before the initiator is added. A process according to any of the preceding claims wherein the initial charge prior to addition of initiator comprises up to 50% of the vinyl acetate and vinyl chloride monomer. A process according to any preceding claim wherein the initial charge prior to addition of initiator comprises at least 20% of the vinyl acetate and vinyl chloride monomers.

Inventors: CLARK NIGEL LESLIE, CLARK, NIGEL LESLIE
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1987
Main classification: C08F218
IPC codes: C08F214, C08F218