Low Temperature Cure Sealant

This invention relates to a vinyl plastisol sealant having excellent adhesion and will have application especially to a vinyl plastisol sealant which may be cured at a relatively low temperature.

A sealant is a coating used to keep moisture and air from a surface which may contain abutments or openings. The sealant is therefore required to be highly adhesive with a high degree of integrity. Such a sealant may be a plastisol, an organosol, a plastigel or an organogel. A plastisol sealant is disclosed in U.S. Pat. No. 3,772,237, incorporated herein by reference. This sealant has two major drawbacks, namely, a high cure temperature (about 340.degree. F.) and a tendency to leak into the top undercoated paint layers during curing. Additionally, the ketone-formaldehyde resin required in the sealant is of scarce availability.

The sealant of this invention utilizes a dispersion resin, a blending resin, a filler, a plasticizer and a silane adhesion promoter like the sealant of U.S. Pat. No. 3,772,237 but has added a solution type resin. The solution resin is a vinyl chloride/vinyl acetate co-polymer dissolved in a plasticizer. The addition of this resin acts with a talc filler to prevent permeation of the paint top coat and removes the need for the ketone-formaldehyde has permitted the use of lower temperatures for curing (approximately 230.degree. F.), thereby saving in energy costs.

Accordingly, it is the object of this invention to provide a composition for a vinyl sealant curable at low temperatures.

Another object is to provide a sealant which will not leak through a top paint coat.

Other objects will become apparent upon reading the following description.

The preferred embodiment described is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is chosen and described in order to best explain the principles of the invention and its application and practical use to thereby enable others skilled in the art to best utilize the invention.

The primary ingredients of the composition include a vinyl co-polymer dispersion resin, a blending resin, a solution type resin, a filler, a plasticizer and an adhesion promoting silane. In addition, the thixiotrope may be added to prevent dripping or sagging of the sealant, and a stabilizer may be added if desired.

The dispersion resin is a commercially available paste resin such as vinyl chloride/vinyl acetate copolymer. The blending resin may be either a vinyl chloride homopolymer or a vinyl chloride/vinyl acetate copolymer. By definition, the blending resin will be of a much larger particle size than the dispersion resin to allow the dispersion resin to disperse within the blending resin forming a base material for the sealant. The ranges of particle size are from 0.5 to 2 microns for the dispersion resin and 10 to 115 microns for the blending resin, as defined in U.S. Pat. No. 3,772,237. Both the dispersion resin and the blending resin must have an inherent viscosity in excess of 0.9 when measured at 30.degree. C. using 2 grams of resin and 100 ml of cyclohexanone. The dispersion resin preferred is PVC-74 from Diamond Shamrock Co. of Cleveland, Ohio. The preferred blending resin homopolymer is VC 260SS from Borden Chemical Co. of Leoninster, Mass. and the co-polymer is MC-85 from Goodyear Chemical of Akron, Ohio.

The solution type resin is a solution grade resin of vinyl chloride/vinyl acetate where the vinyl acetate composes 9-11% of the resin. This must first be dissolved in a plasticizer by agitation at 230.degree. F. A preferred resin is a vinyl chloroide/vinyl acetate co-polymer sold under the designation VC-171C from Borden Chemical Company. The preferred plasticizer is DIDP (diisodecyl phthalate) in a ratio of 1 part resin to 17 parts plasticizer.

The fillers used in this composition may be selected from various alkaline earth metal carbonates such as calcium carbonate, magnesium carbonate and barium carbonate. Other fillers which are available include platy talcs, such as mica talc and dessicant type fillers, such as calcium oxide, calcium chloride, anhydrous calcium sulphates. The dessicant serves to hold moisture from the adhesion promoters. Moisture can cause a premature reaction of the silane adhesion promoter, thereby causing a loss in adhesion of the sealant.

The plasticizers used are preferably selected from phthalate plasticizers having six or more carbons. Although several plasticizers may be utilized, the preferred choice is DIDP (diisodecyl phthalate) as based on its effect on viscosity, viscosity stability and ultimate cure time. Other acceptable plasticizers are DOP (dioctyl phthalate) and DIOP (di iso octyl phthalate).

The adhesion promoters used in this composition are of the silane type. These are characterized by having at least one silicone atom and three hydrolyzable groups, such as alkoxyalkoxy's, having one to three carbon atoms, such as ethoxyethoxy or methoxy ethoxy. The silane adhesion promoters also contain an organo-functional group with at least one primary amino group in which the nitrogen contains at least two hydrogens bonded directly to the nitrogen atom. The nitrogen functionality is present in an organic group which is bonded to the silicone through a silicone-carbon bond. Such silane adhesion promoters are characterized as possessing a single organo-functional group and three hydrolyzable groups such that, when the silane is contacted with moisture contained on a surface or water which is embodied within the sealant formulation, the hydrolyzable groups are converted to silanol groups which in turn condense to form siloxane. When these adhesion promoters are incorporated into a sealant forumlation and the sealant is applied to a substrate, the adhesion promotere migrates to the surface to form a siloxane coating which acts to bond the sealant to the substrate. During the bonding, the sealant is heated to gain fusion.

When the bonding surface is untreated or not primed, the silane will contain only a single amino group. Preferred mono-amino silanes are gamma-aminopropyl (trimethoxy) silane available as A-1130 from Union Carbide Company of New York, N.Y., and delta-amino-n-butyl (trimethoxy) silane. When the bonding surface is treating or primed, a silane with both amino groups is used. Examples of such silanes are N-beta-aminoethyl-gamma aminopropyl (trimethoxy) silane, available as A-1120 from Union Carbide, n-trimethoxysilypropyl diethylene triamine, n-trimethoxysilypropyl, polyethyleneamine and the urea adducts of the aforementioned amino silanes.

The plastisol of this composition may include a stabilizer. The stabilizer may be selected from a standard list for plastisols which includes dibasic lead-, barium-, cadmium-, zinc- or calcium-phosphite. However, the stabilizer must be tested separately to insure it does not cause an adverse effect on adhesion or the rehological properties. The preferred stabilizer is a dibasic lead phosphite such as dyphos.

The sealants are generally applied over various geometric shaped substrates. Thus it is imperative that the sealant not sag when put in place prior to curing. This non-sagging characteristic is accomplished by the use of thixiotrope. Although asbestos is a prime example of a thixiotrope, a calcium-organic thixiotrope predispersed in DOP (dioctyl phthalate) at two parts thixiotrope to one part DOP is preferred. An example of one such thixiotrope is Ircogel #901 from Lubrizol Chemicals of Cleveland, Ohio. This product is chosen because it will give the necessary non-sag characteristics and is readily dispersed in the plastisol.

A working formulation of a preferred embodiment of the composition of this invention is as follows:

The above formulation may be mixed on any adequate mixer which will produce a uniform product without a heat buildup. It is transferred to containers via pumping. The pump must be adequate to move the sealant and not build up excessive heat. It is then applied to the area to be sealed. It may be pumped, troweled, mulled, sprayed or otherwise placed in the desired end shape. At this point the sealant will stay in the shape and in place until fusion upon curing. The curing will occur within a range of 210.degree. F. to 250.degree. F.

Although this invention discusses the use of plastisols, it also will apply to organosols, organogels and plastigels with proper additions familiar to one versed in the manufacture of these compounds.

It is to be understood that the invention is not to be limied to the preceding but may be modified within the scope of the appended claims.