The present invention relates to aerosol adhesive application devices capable of spraying very high solid content aerosols, and, more particularly, very high solid content aerosol adhesives.
In general, aerosol spray cans for a variety of aerosol products include a substance to be sprayed, an optional carrier fluid and a propellant. Typically, the propellant is a composition that pressurizes the can and assists in atomization of the substance being sprayed.
In the past chlorofluorcarbons (CFC""s) were widely used as propellants but these propellants are now banned by international agreement. In response, industry has been seeking ways to reduce the amounts of organic solvents present in adhesive and other aerosol sprays.
A reduction in solvent would also produce other benefits. For Example, as the proportion of solvent present in aerosol adhesive decreases, more of the adhesive composition itself is present in the aerosol. This means fewer spray cans would be necessary to deliver the same amount of adhesive saving on cost and waste management.
Thus, for example, spray can-applied adhesive/solvent mixtures containing 20-25% by weight adhesive compound, also known as very high solid content (VHS) adhesives, have become increasingly desirable in the field of contact adhesives because of their use of smaller proportions of organic solvents. Our copending U.S. patent application Ser. No. 09/126,383, entitled xe2x80x9cVery High Solids Adhesivexe2x80x9d filed Jul. 30, 1998, which is hereby incorporated by reference, discloses such a composition for a VHS adhesive and a method for making the VHS adhesive. The adhesive typically comprises a resin/rubber/solvent mixture. The resins used typically include polyterpene resins, phenolic resins, phenolic modified terpene resins, aliphatic petroleum hydrocarbon resins, and the like. The rubbers used in the adhesive mixtures generally use a blend of polychloroprene synthetic rubbers. A wide range of solvents may be used depending on the composition of the adhesive with which it must be compatible to form a solution. Thus, the solvents used may include, among others, various chlorinated solvents, ketones, aliphatics, aromatics, alcohols, and esters, or even inorganic solvents such as water.
However, it has been found that in practice using VHS adhesives can be quite difficult. For example, in general, as the solid content of the adhesive increases, the viscosity of the adhesive/solvent mixture increases. When using standard nozzles and buttons on typical aerosol spray cans, the increased viscosity causes the spray pattern of adhesive mixture from the can to be uneven. For example, if a standard can, valve, and button (such as variable valve Model #V8-10-118, with a 906 collar and button Model #166-197-1620-white, both provided by Newman-Green of Addison, Ill.) are used to spray a VHS adhesive/solvent mixture having 30 wt % adhesive, such as neoprene, the spray tends to be uneven. That is, the spray pattern will have varying concentrations across the area of application. It is believed that this generally occurs because the button contains a substantially circular shaped exit port through which the VHS adhesive mixture stream passes so that there is limited or no xe2x80x9cfanningxe2x80x9d of the spray; the stream exits in a substantially straight line. Additionally, even if some outward xe2x80x9cfanningxe2x80x9d should occur, the fanning is not controlled and the concentration of the sprayed fluid is not uniform and tends to vary throughout the application area.
Various nozzles for attachment to the spray buttons have been designed to try to overcome the nonuniformity of spray problem. U.S. Pat. No. 4,401,272, issued to Merton et al., on Aug. 30, 1983, and U.S. Pat. No. 4,401,271, issued to Hansen, on Aug. 30, 1983, each disclose nozzles which attach to aerosol spray can buttons. These nozzles do not appear to resolve the issue. For example, the ""272 patent discloses that the nozzle is only capable of spraying mixtures with solid content levels up to 11. 1%, well below typical VHS levels. When such nozzles are used, the spray tends to be more concentrated at the top and bottom of the spray area and less concentrated near the center of the spray area. The ""271 patent provides another attempt at a solution to the xe2x80x9cnonuniformity of sprayxe2x80x9d issue.
As explained above, there is a need for a VHS adhesive/solvent mixture with higher workable solids contents than heretofore known and a device for applying such a mixture substantially uniformly.
The present invention relates to an aerosol spray device, comprising:
a spray can;
a valve mounted to the can;
a button mounted to the valve to control opening and closing of the valve, the button having an exit port in fluid communication with an interior of the can when the valve is open; and
a nozzle, mounted to the exit port of the button, said nozzle including a throughbore having a flow restrictor proximate to the throughbore""s exit end and having a substantially rectangular exit port, the port having at least one pair of opposite walls flaring outward from the flow restrictor at an angle of about 20 to about 75xc2x0, wherein the spray can has an interior and the interior comprises:
(a) propellant; and
(b) an adhesive mixture comprising:
(a) 35 to 70% by weight solvent,
(b) 4 to 30 weight % resin, and
(c) 8 to 40 weight % rubber, based upon the weight of the adhesive mixture, wherein the adhesive mixture has a Brookfield viscosity of from about 50 to 600 cps, and a solids content of at least about 20%.
The present invention provides a very high solids application device which allows substantially more uniform application of the high solids fluid than was previously attainable. Additional aspects of the present invention will become evident upon reviewing the non-limiting embodiments described in the specification and the claims taken in conjunction with the accompanying figures, wherein like numerals designate like elements.