CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Application Serial No. 12/568,818 filed

September 29, 2009, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a method of manufacturing an aerosol container, specifically a pressurized paint formulation. The invention also relates to the final composition of the manufactured aerosol container. In particular, my invention involves significantly reducing or eliminating the amount hydrocarbon propellant typically used in the manufacturing process and to use compressed ambient air to achieved the desired pressure for product discharge.

Aerosol containers are ubiquitous and are used to deliver of great number of products from paint to air fresheners by delivering such products in a convenient spray or atomized stream. Regardless of the specific product to be delivered, one common ingredient of these aerosol containers is a propellant that acts as a carrier to dispense the product. Because the propellants are highly volatile, the container is pressurized to keep the propellant as a liquid. In the case of a spray paint container, these propellants are typically hydrocarbons that must be injected into the container under high pressure during manufacturing. The liquid propellant is typically mixed with the liquid product to be dispensed, such as a paint formulation. When the user pushes or activates the container valve, the liquid propellant is flashed (vaporized) through a spray nozzle or tip carrying with it the liquid product as atomized droplets. Although hydrocarbon propellants provide a convenient delivery vehicle for dispensing spray products, they add a significant cost to the manufacture of aerosol containers and the flashed gaseous hydrocarbons can potentially have a negative impact on the environment. Accordingly, reducing the amount of hydrocarbon propellant required for a given product formulation is cost effective and good for the environment.

SUMMARY OF THE INVENTION

The present invention provides a method of preparing an aerosol container where the amount of hydrocarbon propellant is significantly reduced or eliminated by substituting compressed ambient air. Although the following description is specific to the manufacture of spray paint containers, my invention could also be adapted to for any type of aerosol product where oxygen would not have a deleterious effect on the product to be dispensed. Specifically, my invention concerns a method of filling an aerosol container where an empty container at ambient pressure is supplied to a filling line and a liquid paint mixture and an appropriate agitator device are added to the interior of the container. An aerosol one way check valve is then added to the top of the container and crimped into place using methods well known in the art of manufacturing aerosol containers. The container is then positioned within a charge head assembly where a reduced amount of propellant is injected through the check value under pressure. By "reduced amount of propellant" I mean that the normal volume of propellant typically added to a specific product formulation is reduced by about 1 vol.% to about 99 vol.%, and in some cases all of the propellant is replaced by compressed air.

The container is then injected with compressed ambient air through the check valve in an amount equal to the difference between the reduced amount of propellant and the normal amount of propellant or an amount that is sufficient to deliver substantially all of the product initially contained within the container. By "normal amount of propellant" I mean the volumetric amount of propellant typically used for a given product formulation. Preferably, the amount of compressed air added to the container results in a volumetric ratio of compressed air to propellant is approximately 50:50 and more preferably in the range of from about 20 to 80. Since typical aerosol containers can only be pressurized to about 70 psig to about 120 psig, the added compressed air will not liquefy and will remain as a gas. Because commonly used propellants act as a solvent they will reduce the viscosity of the paint formulation. If air is used to replace propellant, the resulting viscosity will be too high to atomize the paint. But if a solvent is used to replace the propellant it will reduce the viscosity of the paint formulation and allow it to atomize properly and spray in a well defined line. Preferably, an exempted solvent is used because these are sometimes not considered a Volatile Organic Compound, which are typically blamed for air pollution and contributing to the greenhouse effect and the depletion of the ozone layer. Acetone is an example of such an exempted solvent. As such, replacing the propellant, which is considered to be a VOC, with an exempt solvent, the resulting package will have less VOCs and is thus more environmentally friendly.

Depending on the product formulation, we have found that it is sometimes necessary to reduce the viscosity of the liquid product. In the case of paint formulations for example, we have found that reducing the viscosity from 83 seconds to 18 seconds as measured on a Zahn #2 cup allows replacement of 100% propellant with compressed air while at the same time maintaining an acceptable spray pattern of the final paint product.

Once the compressed air has been added, a spray tip or nozzle is attached to the valve followed by a cap and the container is ready for use. Any filling equipment known to the art of aerosol container manufacturing can be used to practice my invention provided a charge head assembly is available to add the compressed ambient air to the container after the addition of the reduced amount of hydrocarbon propellant.

DETAILED DESCRIPTION

As mentioned, the goal of my invention is to significantly reduce the amount of hydrocarbon propellant that is typically used in the manufacture of aerosol spray containers. I am unaware of any filling process that substitutes compressed ambient air for a portion of the hydrocarbon propellant. The particular propellant used in manufacturing aerosol containers will depend on the properties of the liquid product to be dispensed. For spray paint containers, the type of solvent is dependent on whether the paint formulation is water base or solvent based. As used herein "solvent based" refers to a paint formulation soluble in one or more hydrocarbons. When the initial point formulation is water based, then one particularly preferred propellant is dimethyl ether (DME), however, any known water soluble propellant will work. DME is a commercially available liquefiable gas having a boiling point of -23°C. at one atmosphere, and is soluble in water to the extent of about 35% by weight at 24°C. at about 5 atmospheres of pressure. Although any commercially available DME can be used in the present invention, one commercial supplier of DME is DuPont®. Although DME is one preferred type of propellant, other propellants may be used alone or in addition to DME, for example, propane, 152a, carbon dioxide, and nitrous oxide. In those circumstances where the initial paint formulation is solvent based, then an acceptable propellant is propane, however, any known propellant compatible with a solvent based paint formulation will work. Regardless of the chemical make-up of the propellant, the propellant must be able to pressurize the initial paint formulation for delivery to the substrate or surface to be coated once the container is filled and crimped at the point of manufacture of the container. Each particular paint product formulation or recipe will specify a type and quantity of the propellant to be added to the container. My invention is aimed at reducing this "normal" quantity of propellant by any where from about 1 vol.% to about 99 vol.%, in some cases completely replacing allof the propellant, and substituting compressed air as the carrier gas for the product to be dispensed. Preferably, compressed air is added to the container in an amount equal to about 20 psig. The ambient air is compressed by any known means and is preferably delivered to the check value at a pressure in the range of from about 80 psig to about 120 psig.

The amount of compressed air that can be added is also a function of product quality or spray performance. In other words, if too much compressed air is substituted for the propellant there can be a tendency for the paint not to dispense in an acceptable spray pattern. An acceptable spray pattern is one where a 1 inch to 4 inch line can be sprayed with sharp edges and no overspray.

Prior to adding the propellant and then the compressed air, the container is at roughly ambient pressure and will contain ambient air atmospheric pressure. A paint formulation is added to the container along with an agitator device prior to adding the check valve and pressure sealing the container. The paint formulation can be any known to those skilled in the art and preferably includes a clear non-pigmented base or a clear pigmented base or a white/off-white or neutral base. The type or design of aerosol container that can benefit from my invention is not critical to my invention. Preferably a conventional upright spray paint can be used as well as an inverted spray container that is used to mark horizontal surfaces, such as athletic fields, roadways, yards, and the like.

EXAMPLES

For comparison purposes a standard prior art aerosol paint container might be composed of the following:

14.4% Alkyd resin, 21 .6% Calcium Carbonate, 8.6% Titanium Dioxide, 16.6% VM&P, 9.4% Mineral Spirits, and 1 .4% additives, and 28% propellant, which can be a 65% propane, 35% butane blend. This paint had a viscosity of 85 seconds using a Zahn #2 cup (not including the propellant).

A aerosol paint product was made in accordance with the above mentioned recipe by taking a standard 20 ounce aerosol can, placing 353 grams of a paint formulation into the can and crimping the valve onto the can. The valve used was a typical inverted tip valve used for spraying lines on the ground. After the valve was crimped, 137 grams of propellant was added. When this composition was sprayed on the ground, a 1 to 1 ½ inch line was produced.

A second can was prepared, identical to the first can, except instead of adding the propellant the can was pressurized with 90-100 psi of air. When tested, the resulting line was only a ½ inch in width and the paint splattered, yielding a line that did not have crisp edges.

A third can was prepared, again using the same procedure as for the first can, except this time the propellant was replaced by acetone. The viscosity of the paint formulation, after adding the acetone, was reduced from 85 seconds to 26 seconds as measured using a Zahn #2 cup. Once this paint formulation was added to the can and the valve was crimped on the can, the can was pressurized with 90-100 psi of air.

When this paint product was sprayed on the ground, the resulting line was 1 - 1 ½ inch line and was equivalent to the line produced by the first sample,

It should be understood that the embodiments and examples disclosed herein are presented for illustrative purposes only and that many other combinations and articles that embody the methods, formulations and systems will be suggested to persons skilled in the art and, therefore, the invention is to be given its broadest interpretation within the terms of the following claims: