Day: September 21, 2017

Pvc Sealant Mechanism

Pvc Sealant Mechanism

The present invention relates to polyvinyl chloride plastisol compositions, for example sealant compositions. In the manufacture of automobiles, the automobile body is initially primed with a coating composition to prevent corrosion of the metal. This can be done in a number of ways although generally it is performed by cationic electrodeposition using the auto body as the cathode. Once the automobile body has been primed in this manner, subsequent steps in the assembly are carried out. These steps typically include the use of sealants over the primed automobile body.

The sealants are subsequently topcoated along with the remainder of the body during the final stages of the painting process. Polyvinyl chloride plastisols offer several advantages for use as sealant compositions: a good balance of strength, elongation and toughness, minimal to no volatile organic component and low cost. However, despite these advantageous properties, when used in conjunction with cationically electrodepositable primer compositions in automotive applications, adhesion is poor and yellowing of the topcoat composition results.

Historically, polyaminoamides which are art recognized adhesion promoters, have been utilized in an attempt to deal with the above adhesion problems. These, however, can adversely affect the stability of the plastisol based sealant composition, the cure of the topcoat and in addition, cause more yellowing. There is a need, therefore, for a polyvinyl chloride plastisol based composition which exhibits excellent adhesion to primed metal and is capable of being topcoated with a variety of coating compositions without yellowing of the topcoat.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a plastisol based composition comprising: (a) a copolymer of an aliphatic olefinically unsaturated material and an anhydride containing material; and (b) a polyvinyl chloride plastisol. DETAILED DESCRIPTION OF THE INVENTION The composition of the present invention comprises as one of its principal components a polyvinyl chloride plastisol.

A plastisol is a dispersion of powdered polyvinyl chloride resin in a liquid plasticizer to produce a fluid matrix which may range in viscosity from pourable liquid to a heavy paste. The polyvinyl chloride homopolymers or copolymers are typically produced by emulsion polymerization. Once the polymer is produced and dried, it is dispersed in plasticizer. The choice of plasticizer depends upon many factors including the desired solids viscosity relationship, processing characteristics and the ultimate desired performance properties.

Suitable plasticizers include didecyl phthalate, diisodecyl phthalate, diisononyl phthalate, trimethyl pentanediol isobutyrate, sucrose benzoate, butyl cyclohexyl phthalate, butyl octyl phthalate, isooctyl epoxystearate, dipropylene glycol dibenzoate, di-2-ethylhexyl adipate, diisodecyl adipate, diisodecyl gluterate, dioctyl sebacate and mixtures thereof. Also suitable for use alone or in admixture with the monopolymeric plasticizers are polymeric plasticizers including polymeric benzoates, polymeric adipates, polymeric glutarates, polymeric sebacates, polymeric phthalates and mixtures thereof.

It should be understood that polyvinyl chloride homopolymers or copolymers can be prepared either as functional or non-functional polymers. By functional polyvinyl chloride is meant a homopolymer or copolymer (usually with vinyl acetate) of polyvinyl chloride in which a small amount of comonomer is added which contributes, hydroxyl, carboxyl, anhydride or other side groups to the chain. Examples include carboxyl functional polyvinyl chlorides such as Union Carbide’s VMCA and hydroxyl functional polyvinyl chlorides such as Union Carbide’s VROH.

By non-functional is meant the homopolymer or copolymer without such modification. In one embodiment of the present invention the polyvinyl chloride plastisol is prepared from a mixture of functional and non-functional polyvinyl chloride polymer. Although a brief description of the preparation of vinyl chloride plastisols has been given above, it should be understood that the preparation of these materials is well appreciated by those skilled in the art and further details are not required for practice of the present invention.

If further details are desired, the following references provide a detailed description of the preparation of vinyl chloride plastisols which are suitable for use in the present invention: Plastisols and Organosols, edited by Harold A. Sarvetnick, published by Van Nostrand Reinhold, 1972 and “PVC: Formulation, Compounds and Processing, A Review and Update”, reprint of the Society of Plastic Engineers, 1981. The second principle component of the claimed curable compositions is a copolymer of an aliphatic olefinically unsaturated material and an anhydride containing material.

The aliphatic olefinically unsaturated material can be a linear aliphatic material such as a diene. Suitable dienes include 1,3-dienes containing from 4 to 12 and preferably from 4 to 6 carbon atoms. Typical dienes include 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, isoprene, chloroprene, and piperylene. Other polymerizable monomers such as methyl methacrylate, acrylic acid and styrene can be copolymerized with the dienes. The aliphatic olefinically unsaturated material can also be a normal alpha olefin such as 1-decene, 1-hexene, 1-octene or tetradecene.