Abstract:
The spray gun includes a primary port for receiving a primary material such as adhesive or similar materials, for dispensing. The spray gun further includes a secondary port to receive an aerosol-based cleaner which is stored in an aerosol container within the handle of the spray gun. The valves associated with the primary and secondary ports are sequenced such that during ordinary depression of the trigger to apply the primary material, the aerosol-based cleaner is momentarily “poofed” through the nozzle to clean the nozzle prior to the application of the primary material. After the primary material has been applied and the trigger is released, the aerosol-based cleaner is again momentarily “poofed” through the nozzle to clean the nozzle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to a spray gun, such as is used for adhesive or similar materials, wherein a short burst of aerosol product is used to clean the spray gun tip before and after each application. The valve for the adhesive or similar material and the valve for the aerosol cleaner are both activated in sequence by the operation of a single trigger-like device. Additionally, the present invention uses “bag-in-a-can” technology, particularly for packages in excess of one liter, wherein a collapsible container holds the adhesive or similar material and is placed with a relatively rigid container designed to withstand the pressurization of the propellant charged between the collapsible container and the relatively rigid container. 
     2. Description of the Prior Art 
     In the prior art, aerosol products utilize a solvent to create a solvent or suspension that includes the liquified propellant. The early precursors of aerosols were “bombs” of the late nineteenth century which dissolved insecticides in hydrocarbon mixtures. 
     As technology and environmental concerns have progressed, water has become a required ingredient in aerosol products. However, water does not mix easily with propellant agents. Furthermore, film producing agents such as adhesives are designed with close tolerances with respect to miscibility and resistance to shear. 
     Most adhesives are comprised of synthetic polymers. However, in water-based adhesives, these polymers are simply suspended using surfactants. These surfactants are very specific in their functions within the system and are susceptible to swings in temperature, shear, pH or chemical contamination. 
     Additionally, adhesives are designed to create a film which is tacky and resistant to contaminants that may degrade the tacky characteristic. To create an industrial adhesive designed to bond two substrates under varying conditions of exposure to heat, water and solvents, the film must not soften and release its hold on the substrate. Therefore, the surfaces of application equipment, such as a spray gun, exposed to film curing must remain free of adhesive build-up. The prior art has not addressed how to avoid such adhesive build-up using a self-cleaning operation which does not require specific actions by the user which are separate and distinct from the adhesive application process. 
     Moreover, to a limited extent, the use of water-based products in aerosol packages (that is, self-contained, pre-pressurized containers) is known in the prior art for products. Formulations are also known, to a limited extent, which require complete segregation from the propellants (such as “bag-in-a-can”). However, this technology has apparently not been used successfully for an adhesive or in a package larger than one liter. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an adhesive spray gun which remains free of adhesive build-up. 
     It is therefore a further object of the present invention to provide a cleaning operation for an adhesive or similar spray gun wherein the cleaning of the device is integrated into the operation of the device. 
     It is therefore a still further object of the present invention to provide an adhesive spray gun with simple and intuitive controls. 
     It is therefore a still further object of the present invention to utilize “bag-in-a-can” technology wherein the adhesive or similar product is placed within a collapsible bag which is placed within a relatively rigid container and wherein propellant is charged between the relatively rigid container and the collapsible bag. 
     It is therefore a still further object of the present invention to utilize the above technology for containers larger than one liter. 
     These and other objects are attained by using an application gun which is a modified airless applicator which includes a first port for receiving the adhesive or other primary product and a second port for receiving aerosol-based solvent cleaner. The adhesive or other primary product is supplied from a collapsible bag which is placed in a relatively rigid container with propellant charged between the bag and the relatively rigid container. A perforated dip tube is molded to the bag to act as a siphon for the adhesive or other primary product. The aerosol-based solvent cleaner is provided within a small aerosol container attached via a threaded valve stem in the handle of the gun. 
     The trigger assembly is designed to open and close the valves to the first and second ports in sequence whereby the first stage, typically as the trigger assembly is partially depressed, meters a volume of solvent cleaner via the second port directly to the tip. During the second stage, the first port is opened and the adhesive or other primary product is dispensed through the tip for as long as the trigger assembly is held fully depressed. When the trigger assembly is released at the end of the application, the trigger assembly momentarily passes again through the first stage and a second volume of solvent cleaner is metered or “poofed” via the second port to the tip. 
     The apparatus is designed to work virtually simultaneously with the application process and is user-friendly with a reduced need for specific and separate maintenance operations. The apparatus further allows for a portable, self-contained supply of product and an automatic tip cleaning function. The apparatus is scalable, subject to weight and similar concerns. Furthermore, a wide range of products can be dispensed without the addition of ingredients that are hazardous to the user or to the environment. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional side view, partially in phantom, of the spray gun of the present invention, shown at rest with the trigger not depressed. 
     FIG. 2 is a cross-sectional side view of the valve assembly of the spray gun of the present invention, shown at rest with the trigger not depressed. 
     FIG. 3 is a cross-sectional side view of the valve assembly of the spray gun of the present invention, shown with the trigger partially depressed at a mid-point position, so that the aerosol-based cleaner is communicated to the sprayer tip. 
     FIG. 4 is a cross-sectional side view of the valve assembly of the spray gun of the present invention, shown with the trigger depressed beyond the mid-point position but not to the fully depressed position, wherein neither the aerosol-based cleaner nor the adhesive or other product is communicated to the sprayer tip. 
     FIG. 5 is a cross-sectional side view of the valve assembly of the spray gun of the present invention, shown with the trigger fully depressed, wherein the adhesive or other product is communicated to the sprayer tip. 
     FIG. 6 is a cross-sectional view of the source of adhesive or other product wherein a collapsible bag of product is inserted into a relatively rigid container and propellant is charged therebetween. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, one sees that FIG. 1 is a cross-sectional view of the spray gun  10  of the present invention. Spray gun  10  includes spray tip  12  with an aperture  14  therethrough for spraying or dispensing the adhesive or other primary material  200  and for further receiving the aerosol-based cleaner  300 . The interior of tip  12  further includes chamber  16  which receives the primary material  200  to be dispensed or sprayed. Chamber  16  receives the adhesive or other primary material through central passageway  18  which is selectively opened or closed by needle  20  (see FIGS.  2 - 5 ). Needle  20  is integral with support  22  and primary slider  24 . Primary slider  24  reciprocates within primary material chamber  26  as driven by shaft  28  which is adjustably received within threaded aperture  30  of primary slider  24 . Primary material chamber  26  receives the primary material  200 , such as adhesive or other materials to be dispensed or sprayed, via passageway  32  which communicates with primary material threaded port  34 . Primary material threaded port  34  is fastened to hose  102  by internally threaded fastener  104  and thereby receives primary material  200  from pressurized tank  100  (see FIG.  6 ). 
     When needle  20  is inserted into central passageway  18  and support  22  is seated with seat  36  as shown in FIGS. 2,  3  and  4 , primary material  200  is blocked from flowing into chamber  16  and is therefore not dispensed via tip  12 . However, when the reciprocation of primary slider  24  withdraws needle  12  from central passageway  18  and support  22  from seat  36  as shown in FIG. 5, primary material  200  flows around primary slider  24 , through central passageway  18  and is dispensed from tip  12 . 
     Chamber  16  is likewise in communication with lateral channel  40  through which aerosol-based cleaner  300  is received. Lateral channel  40  is likewise in communication with secondary chamber  42  which is in selective communication with secondary valve passageway  44  via opening  46  as controlled by secondary slider  47  which reciprocates within secondary valve passageway and seal  48  which is secured around opening  46 . Circumferential groove  49  is formed near the end  51  of secondary slider  47 . Secondary valve passageway  44  is further in communication with secondary material threaded port  50  via passageway  52 . Secondary material threaded port  50  receives secondary material  300  (that is, the aerosol-based cleaner) via pipe  54  which communicates to chamber  56  in handle  58 . Chamber  56  includes aperture  60  which is in communication with aerosol container  400  which is contained within handle  58  and includes the secondary material  300  (that is, the aerosol-based cleaner). 
     Secondary material  300  is received within secondary valve passageway  44  and accumulates within the interstice formed between secondary slider  47  and the walls of secondary valve passageway  44 . When secondary slider  47  is in the position shown in FIGS. 2,  4  and  5 , secondary slider  47  is firmly engaged within seal  48  and no secondary material  300  is able to flow through mouth  46  past seal  48  and into secondary chamber  42 . However, when secondary slider  47  is retracted sufficiently that circumferential groove  49  aligns with seal  48  as shown in FIG. 3, secondary material  300  is permitted to pass around seal  48  and through mouth  46  into secondary chamber  42 , through lateral channel  40 , chamber  16  and tip  12 . 
     Secondary slider  47  includes longitudinal passageway  53  through which shaft  28  passes. Shaft  28  is secured to tertiary slider  55  which reciprocates within tertiary chamber  57 . Spring  59  within tertiary chamber  57  biases tertiary slider  55  toward the forward position thereby, in the absence of other forces, urging shaft  28  and primary slider  24  to a forward position, thereby inserting needle  20  into central passageway  18 . However, in the position shown in FIGS. 1,  2  and  3  (unlike FIGS.  4  and  5 ), tertiary slider  55  is spaced from wall  61  of tertiary chamber  57 . 
     As shown in FIG. 1, trigger  70  is journaled to pivot about pivot point  72  on body  74  of spray gun  10 . Trigger  70  includes boss  76  at a central upward location thereon which drives valve drive shaft  80 . Valve drive shaft  80  is received within aperture  82  in body  74  and is biased by spring  84  within aperture  82  which urges valve drive shaft  80 , in the absence of other forces (such as manual pressure by the user), to the position shown in FIGS. 1 and 2 wherein both primary material  200  and secondary material  300  are blocked from flowing by needle  20  of primary slider  24  and by secondary slider  47 , respectively. 
     Valve drive shaft  80  is attached directly to secondary slider  47  so that secondary slider  47  moves in concert with valve drive shaft  80 . 
     Therefore, when the trigger  70  is slightly depressed, such as would happen momentarily when the user initially depresses the trigger  70  but has not yet fully depressed the trigger  70 , secondary slider  47  moves from the position shown in FIGS. 1 and 2 wherein the movement of secondary material  300  is blocked as described above, to the position shown in FIG. 3 wherein the circumferential groove  49  of secondary slider  47  aligns with seal  48  so that secondary material  300 , such as an aerosol-based cleaner, moves freely past seal  48 . This allows the secondary material  300  to move freely from aerosol container  400  through the route described above to be dispensed through tip  12 . As this configuration happens only momentarily, a “poof” of aerosol cleaner is passed through aperture  14  of tip  12  to clean aperture  14 . During this momentary “poof”, secondary slider  47  has not moved sufficiently for wall  61  of tertiary chamber  57  to have engaged and urged tertiary slider  55  rearward. Therefore, needle  20  stays within central passageway  18  and no primary material  200  is dispensed. 
     As the user continues to depress trigger  70 , the position shown in FIG. 4 is reached wherein circumferential groove  49  of secondary slider  47  is not aligned with seal  48 . End  51  of secondary slider  47  is engaged within seal  48  thereby blocking the flow of secondary material  300  and terminating the “poof”. Secondary slider  47  has still not moved sufficiently for wall  61  of tertiary chamber  57  to have urged tertiary slider  55  rearward. Therefore, needle  20  stays within central passageway  18  and no primary material  200  is dispensed. However, in the position shown in FIG. 4, wall  61  of tertiary chamber  57  abuts tertiary slider  55 , so that further movement of trigger  70  will translate into movement of secondary slider  47  and tertiary slider  55  in concert. 
     This further movement of trigger  70  with the movement of secondary and tertiary sliders  47 ,  55  in concert results in the movement of primary slider  24  via the mechanical communication of shaft  20  thereby resulting in the position shown in FIG. 5 wherein needle  20  is withdrawn from central passageway  18  thereby allowing the flow of primary material  200 . However, end  51  of secondary slider  47  is remains engaged within seal  48  thereby blocking the flow of secondary material  300 . This position is maintained for as long as trigger  70  is fully depressed for the application of primary material  200 . 
     When the user releases trigger  70 , spring  84  forces the valve drive shaft  80  back to the position shown in FIGS. 1 and 2 and spring  59  likewise forces tertiary slider  55  forward whereby needle  20  is inserted into central passageway  18  as shown in FIGS. 1 and 2. However, during this transition, the spray gun  10  passes through the positions of FIGS. 4 and 3, sequentially, thereby resulting in another “poof” of secondary material  300  to clean aperture  14  of tip  12  immediately after the termination of the application of primary material  200 . 
     FIG. 6 illustrates pressurized tank  100  which is relatively rigid. In fact, for industrial purposes, pressurized tank  100  is envisioned to be a steel cylinder (DOT-4BA) designed for propane or refrigerant containment or a similar application. However, for consumer applications, plastic containers (such as PET) may be envisioned. Primary material  200 , such as adhesive or similar materials, is contained within collapsible plastic bag  110  contained within pressurized tank  100 . Bag  110  is made of any material suitable for the separation and containment of the primary material  200 . Polypropylene is envisioned, but those skilled in the art will recognize that a range of equivalent substitutes are available. Bag  110  is preferably slightly oversized. 
     Propellant  500  is charged between pressurized tank  100  and bag  110 . This propellant  500  provides the differential pressure to drive primary material  200  out of bag  110  when the various valves have been suitable opened. 
     A cylinder valve  112  is threaded onto a receiving port  114  of the pressurized tank  100 . Cylinder valve  112  incorporates a quick-release air fitting to allow for easy installation and removal of bags  110 . Perforated dipstick  116  is molded into bag  110  to act as a siphon for primary material  200  and provides a path for primary material  200  to pass through cylinder valve  112 , through hose  102  and into primary material threaded port  34  (see FIGS.  1 - 5 ). 
     Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.