Spray Head

Abstract

A sprayhead for a pressurized aerosol dispenser includes an elongated expansion and mixing chamber upstream of the spray-forming nozzle orifice. Controlled expansion of the dispensed product and propellant mixture within the chamber enhances vaporization of the propellant, promotes uniform mixing of the vaporized propellant with the product prior to passage through the spray nozzle, and produces increased flow rates for a given nozzle orifice diameter.

Description

This invention relates to sprayheads for use with pressurized aerosol dispensers for liquid products such as paint, and particularly for "glitter" paints having intermixed solid particles or flakes.

A conventional sprayhead of the pushbutton type generally has a central passageway in a stem leading from the outlet of a spring-loaded valve mounted in the top of an aerosol dispenser. The passageway connects with a cylindrical recess in the side wall of the pushbutton into which a nozzle insert press fits, with the downstream face of the nozzle orifice substantially flush with the exterior surface of the sprayhead. The diameter of the sprayhead passageway and the inside diameter of the nozzle insert upstream of the orifice section are generally of the same order of magnitude, about one-sixteenth inch. The throat diameter at the orifice may range from 0.016 inch to larger than 0.040 inch, depending on the characteristics of the product dispensed. For relatively viscous liquids such as paint, a common orifice diameter is 0.032 inch, for example.

In operation, axial movement of the sprayhead toward the valve causes it to open and allows a mixture of product and propellant to flow through the passageway and out the nozzle orifice in the form of an atomized spray. The pressure and velocity of the outflowing stream are substantially constant from the valve outlet to the nozzle orifice, where the reduced throat diameter causes the velocity to sharply increase and the pressure to correspondingly decrease. Because the flow area of the passageway from valve outlet to nozzle orifice is relatively small as well as substantially uniform, propellant vaporization and product atomization apparently occur primarily in the reduced pressure region of the nozzle orifice, although some initial vaporization and mixing action does occur during flow through the relatively restricted valve port.

As a consequence of confining mixing and atomization to such a localized region adjacent the nozzle outlet, these conventional sprayheads often produce unsatisfactory spray patterns, particularly when used with liquid products having dispersed solid particles or flakes, such as specialty paints containing flakes of metallic, plastic or glass "glitter." The small particles in this type of product apparently serve as nuclei for agglomerations of liquid in relatively large droplets that tend to spatter and collect inside the rim of the dispenser can and to produce an uneven coating on the object being sprayed. These undesirable results intensify as the size of the suspended particles is increased.

Objects of the present invention are to eliminate the spattering problem when spraying liquids having intermixed solid particles, to increase the average particle size that can be sprayed with a nozzle orifice of given diameter, and to increase flow rates for given dispenser pressures and nozzle orifice diameters.

These and other objects are obtained by incorporating an elongated expansion chamber upstream of the nozzle orifice. Dimensions of the expansion chamber are not critical; however, its diameter should be significantly greater than that of the passageway leading from the valve.

The chamber length should be preferably several times its diameter. It has been found that increasing the chamber length, for example, to at least five times its diameter not only improves uniformity of the spray pattern but also, surprisingly, increases the product flow rate for a given nozzle orifice diameter and propellant pressure.

In the drawings,

FIG. 1 is a perspective view of an aerosol dispenser incorporating the sprayhead of the invention.

FIG. 2 is a section view of an embodiment of the invention.

FIG. 3 is a section perpendicular to the view of FIG. 1.

Referring to the figures, sprayhead 10 comprises an approximately cylindrical body 12 having an axial passageway 14 with an inlet 16 through a slot 18 at the end of a stem 20. The outside surface 22 of stem 20 is sized to fit snugly in the outlet of a conventional spring-loaded valve 21 in the top of a pressurized aerosol dispenser 23.

At its downstream end, passageway 14 opens through slot 24 into expansion chamber 26 in tube 28. Tube 28 is made of a deformable plastic material, and its outside diameter is chosen to make an interference fit with the bore 30 of cylindrical recess 32 in the side wall of sprayhead body 12. A conventional flanged nozzle insert 34 having an orifice 36 at its downstream face 38 force fits into the outer end of tube 28 to form the downstream end of expansion chamber 26.

Although sprayhead body 12 and tube 28 are shown as a two-piece assembly in the drawing, the assembly could be molded as a single piece, if desired. The important consideration is that the cross-sectional area of expansion chamber 26 be significantly greater than the cross-sectional areas of both passageway 14 and orifice 36. Furthermore, the length of expansion chamber 26 should be several times its diameter; preferably the length-diameter ratio should be at least five. When the sprayhead is used with a typical domed-top aerosol dispenser of the type shown in FIG. 1, the length of chamber 26 should also be preferably at least enough to insure that the spray is delivered beyond the valve mounting cup 25.

In operation, sprayhead 10 is displaced axially by finger pressure on surface 40, the spring-loaded valve 21 opens, and a mixture of liquid product and propellant flows through inlet 18, along passageway 14, and through slot 24 into expansion chamber 26. The abrupt increase in flow area in expansion chamber 26 reduces the flow velocity, and the abrupt change in flow direction induces a swirling flow that promotes intimate mixing of the product and the vaporizing propellant prior to discharge as a fine spray through orifice 36.

Tests have been run to compare the performance of the above-described sprayhead embodiment with an expansion chamber with that of a conventional sprayhead without an expansion chamber and also to determine the effect of chamber length. Product used in the tests was "glitter" paint having intermixed solid particles with maximum dimensions of about 0.008 inch.

Pertinent dimensions of sprayhead 10 were:

Inlet slot 18 0.060 inch wide .times. 0.125 inch long Chamber 26 0.112 inch diameter Orifice 36 0.032 inch diameter

For comparison, tests were run with two different expansion chambers 26 having effective lengths of five-eighths and five-sixteenths inch, respectively. In addition, the sprayhead was tested without an expansion chamber but with nozzle insert 36 pressed directly into recess 32.

By way of illustration, typical test results for the three sprayhead variations described above used with 16-ounce capacity aerosol dispensers taken from a production line are listed below. Spray time in each case was five seconds.

Product Expended __________________________________________________________________________ Sprayhead without expansion chamber 27.7 gm Sprayhead with 5/16 in. expansion chamber 27.8 Sprayhead with 5/8 in. expansion chamber 30.4 __________________________________________________________________________

Substantial variations from test to test preclude a quantitative correlation between chamber length and flow rate, but in every case the amount of product expended was greater with the long chamber than with the short chamber and was greater with the short chamber than with no chamber.

As mentioned above, the size of inlet slot 18 in each of the three test sprayheads was 0.060 inch wide by 0.125 inch long. For comparison, a sprayhead having no expansion chamber and an inlet slot size of 0.060 inch wide by 0.055 inch long expended 21.3 grams in 5 seconds. It is thus clear that the size of inlet slot 18, as would be expected, has a significant effect on flow rate. With respect to uniformity of spray pattern and absence from splatter, however, the incorporation of the expansion chamber of the present invention produced much greater improvement than did changes in size of inlet slot 18.

In both tests with expansion chambers, the spray pattern was more uniform and the "glitter" particles more randomly distributed on the sprayed surface than in the test without an expansion chamber. Moreover, the flow rates--as determined by container weighings before and after equal duration spray bursts--were greater in the tests with an expansion chamber than those without, the difference being especially marked in the tests with the longer chamber. Greater flow rates, of course, permit the operator to obtain desired coverage in a shorter time.

Other embodiments and dimensions will occur to those skilled in the art. For example, the length of tube 28 could be extended to the edge of container 23 or even beyond, if desired. For liquids of different viscosities and having different sized particles intermixed therein, the dimensions of slots 18 and 24 and the size of orifice 36 can be varied accordingly for optimum results.

Although the utility of the sprayhead of the present invention has been described specifically in regard to spraying liquids having intermixed solids, the invention is not limited to such application. Increased flow rates also result when spraying other fluids or fluid mixtures such as immiscible liquids as well as liquids or solids in a gas. For example, the sprayhead produces superior results with enamels and works well even when spraying cosmetic aerosol formulations such as talcum powder. In short, the sprayhead of this invention is applicable to all types of fluids or dry mixes which are capable of being expended from a pressurized aerosol dispenser.

Claims

What is claimed is:

1. In an atomizing sprayhead of the type having a cylindrical body with an axial passageway open at one end for attachment to the valve of a pressurized aerosol spray container, a discharge channel with an axis transversely intersecting the axis of the axial passageway, an expansion chamber formed in the discharge channel, and a coaxial restricted spray forming orifice at the downstream end of the expansion chamber, the improvement wherein:

the expansion chamber has an inlet at its upstream end that is larger in cross-sectional area than the spray forming orifice and a cross-sectional flow area larger than that of the inlet, and the length of said expansion chamber is at least five times its diameter.

2. The sprayhead of claim 1 wherein the length of said expansion chamber is at least approximately five-eighths inch.

3. The sprayhead of claim 2 wherein the inside diameter of said expansion chamber is at least 0.1 inch.

4. The sprayhead of claim 3 wherein the wall of said axial passageway adjacent the open end has a rectangular inlet slot with a longitudinal dimension of approximately one-eighth inch and a lateral dimension of approximately one-sixteenth inch.

5. The sprayhead of claim 4 wherein the spray forming orifice has a diameter of about 0.032 inch.

6. The sprayhead of claim 1 wherein the inlet to the expansion chamber is at least as large as the cross-sectional area of the axial passageway.

7. The sprayhead of claim 6 wherein the upstream end of the expansion chamber intersects the wall of the axial passageway.