METHOD OF FILLING AEROSOL SPRAY CANS
United States Patent 3835896
A method of filling aerosol spray cans with paint or other marking material so that the can is able to spray marking material in a well-defined stripe having substantially sharp edges. The can is filled with paint, capped with a valve, and pressurized with aerosol propellant in the conventional manner. The valve is then opened to release some of the propellant but substantially no marking material. The time of opening the valve varies depending on the type of marking material in the can, but the time generally is between about 1 to 60 seconds and usually between about 5 to 25 seconds.
US Patent References:
COMBINED PRESSURE FILLING AND DISPENSING CONTROL VALVE FOR AEROSOL CONTAINERS
Venus, Jr. - March 1972 - 3651997
COMBINED PRESSURE FILLING AND DISPENSING CONTROL VALVE FOR AEROSOL CONTAINERS
Venus, Jr. - March 1972 - 3651997
Application Number:
05/320148
Publication Date:
09/17/1974
Filing Date:
01/02/1973
View Patent Images:
Export Citation:
Primary Class:
International Classes:
B65B31/00; B65B1/04; B65B3/04
Field of Search:
141/3,20
Primary Examiner:
Bell Jr., Houston S.
Claims:
I claim
1. A method of preparing an aerosol spray marking can for spraying marking material comprising the steps of:
2. The method of claim 1 in which the opening of the valve means to release the relatively small quantity of propellant occurs for between about 1 and about 60 seconds.
3. The method of claim 1 in which the opening of the valve to release the relatively small quantity of propellant occurs for between about 5 and about 25 seconds.
4. In a method of preparing an aerosol spray paint can for spraying paint comprising the steps of intermittently advancing a can having an open top along a path of can movement, introducing a quantity of paint through the open top of the can at a first station, inserting valve means in the open top of the can at a second station and securing the valve means to the can to close the top of the can, the valve means being moveable between an open position in which the interior of the can communicates with the exterior of the can and a closed position in which the interior of the can is sealed from the exterior of the can, opening the valve means at a third station while introducing a quantity of propellant under pressure through the open valve means into the can and closing the valve means, the improvement characterized by opening the valve means at a fourth station to release a relatively small quantity of propellant but substantially no paint and then closing the valve means so that when the can is later held in a paint-spraying position and the valve means is opened to release the paint, the paint may be sprayed in a uniform, well-defined stripe having substantially sharp edges.
5. The method of claim 4 in which the valve means is opened at the fourth station for between about 1 to about 60 seconds.
6. The method of claim 4 in which the valve means is opened at the fourth station for between about 5 to about 25 seconds.
7. The method of claim 4 in which the fourth station comprises at least two substations, the valve means being opened at each substantion for substantially the same period of time.
8. The method of claim 4 in which the valve is opened at the fourth station of about 15 seconds.
9. The method of claim 4 in which the can is maintained upright as it is moved from the first through the fourth stations, the can not having a dip tube so that substantially no paint is released at the fourth station when the valve is opened.
1. A method of preparing an aerosol spray marking can for spraying marking material comprising the steps of:
2. The method of claim 1 in which the opening of the valve means to release the relatively small quantity of propellant occurs for between about 1 and about 60 seconds.
3. The method of claim 1 in which the opening of the valve to release the relatively small quantity of propellant occurs for between about 5 and about 25 seconds.
4. In a method of preparing an aerosol spray paint can for spraying paint comprising the steps of intermittently advancing a can having an open top along a path of can movement, introducing a quantity of paint through the open top of the can at a first station, inserting valve means in the open top of the can at a second station and securing the valve means to the can to close the top of the can, the valve means being moveable between an open position in which the interior of the can communicates with the exterior of the can and a closed position in which the interior of the can is sealed from the exterior of the can, opening the valve means at a third station while introducing a quantity of propellant under pressure through the open valve means into the can and closing the valve means, the improvement characterized by opening the valve means at a fourth station to release a relatively small quantity of propellant but substantially no paint and then closing the valve means so that when the can is later held in a paint-spraying position and the valve means is opened to release the paint, the paint may be sprayed in a uniform, well-defined stripe having substantially sharp edges.
5. The method of claim 4 in which the valve means is opened at the fourth station for between about 1 to about 60 seconds.
6. The method of claim 4 in which the valve means is opened at the fourth station for between about 5 to about 25 seconds.
7. The method of claim 4 in which the fourth station comprises at least two substations, the valve means being opened at each substantion for substantially the same period of time.
8. The method of claim 4 in which the valve is opened at the fourth station of about 15 seconds.
9. The method of claim 4 in which the can is maintained upright as it is moved from the first through the fourth stations, the can not having a dip tube so that substantially no paint is released at the fourth station when the valve is opened.
Description:
BACKGROUND
This invention relates to aerosol spray cans, and, more particularly, to aerosol spray cans which are filled with a marking material such as paint and which are intended for use in spraying stripes.
The use of aerosol marking cans to spray stripes on pavement and other surfaces is becoming increasingly common. For example, stripes may be sprayed on a parking lot to designate parking areas, on factory floors to designate walkways, on grass to mark playing fields and boundaries, etc. Such an aerosol can is usually equipped with a conventional aerosol can valve which releases the contents of the can when the valve stem is depressed or moved laterally, and a nozzle which is inserted over the valve stem and which is provided with a slotted or rectangular orifice for spraying the contents of the can in a stripe-shaped pattern. One such nozzle which I have had good results with is described in my co-pending application entitled "Actuator For Aerosol Can Valve," Ser. No. 193,433, filed Oct. 28, 1971.
An aerosol can which is to be used for marking surfaces generally is not provided with a dip tube extending from the valve toward the bottom of the can so that the marking material will be expelled from the can by the propellant when the can is inverted. When the can is upright, the marking material, which is heavier than the propellant, will be located at the bottom of the can, and the propellant will be located above the marking material. When the valve is opened when the can is upright, the propellant will be released, but no marking marking material will be released.
A common problem heretofore experienced with aerosol marking cans is that the marking material will not be sprayed in a well-defined, uniform stripe. Rather, more material will be deposited in the central portion of the strip that is being sprayed when along the edge portions of the strip. Further, the strip will not have sharp, well-defined edges, and marking material will splatter or be sprayed beyond the edges of the stripe that is desired. The result is a somewhat sloppy looking stripe having splattered or feathered edges, and the stripe does not provide a definite boundary or line of demarcation. Further, the marking material might not completely cover the surface, particularly a dark surface, along the edge portions of the stripe because insufficient material has been deposited. These thin edge portions will not only render the surface partially visible but will wear away faster than the central, thicker portion of the stripe.
SUMMARY
The invention solves the foregoing problems by providing a method of filling aerosol marking cans so that the marking material can be sprayed to form a well-defined stripe having sharp edges and a substantially uniform covering of marking material from one edge to the other. The cans are filled in the conventional manner with marking material and aerosol propellant, but after each can is filled, the valve is opened to release a quantity of propellant. The can is positioned when the valve is opened so that little or no marking material is released with the propellant, i.e., if the can is not provided with a dip tube, the can is positioned in an upright manner. I have found that if the valve is held open for between about 1 to about 60 seconds, and usually for between about 5 to about 25 seconds, an amount of propellant, along with, perhaps, other ingredients in the can, is released that enables the can when inverted to spray the marking material in a sharply defined, uniform stripe.
DESCRIPTION OF THE DRAWING
The invention will be explained in conjunction with the accompanying drawing, which is a schematic illustration of the process of filling aerosol cans in accordance with the invention.
DESCRIPTION OF SPECIFIC EMBODIMENT
The invention will be described with reference to a continuous filling process represented in the drawing in which a plurality of cans 10 are advanced in the direction of the arrow A by a conveyor 11. The conveyor moves each can to a plurality of stations 12, 13, 14, and 15, and in the particular embodiment illustrated the conveyor moves intermittently so that each can stops at each station for a discrete period of time.
The first three stations are conventional in aerosol can filling procedures and need not be described in detail. Each of the cans is first advanced to the first or filling station 12 which, in the embodiment illustrated, comprises a pair of filling nozzles 16a and 16b and is maintained stationary below each nozzle for a period of time when the conveyor stops. Each can has a generally cylindrical body 17 and a dome-shaped top 18 which is provided with a central opening 19. The first filling nozzle 16a is connected to a source of liquid marking material such as paint, and the second filling nozzle is connected to a source of methylene chloride. When each can stops below each nozzle of the first station, the nozzle is actuated to allow a predetermined amount of marking material or methylene chloride to flow into the can through the opening.
The can is then advanced to the second station 13 which includes a conventional vacuum crimper tool 21. Before each can reaches the second station, a conventional aerosol valve 22 is placed on the top of the can by the usual valve feeder (not shown). Each valve includes a cap 23 which extends over the edges of the top opening and which supports the valve mechanism and an upwardly extending valve stem 24 which opens the valve when the stem is moved laterally. The vacuum crimper is mounted for vertical reciprocation as indicated by the arrows, and when the can stops at the second station, the tool moves downwardly to the top of the can and crimps the cap about the edges of the top opening to provide a gas-tight seal.
The vacuum crimper tool also includes means for moving the valve stem to open the valve, and after the cap is crimped about the edges of the opening, a vacuum pump or other means for providing a vacuum within the cans withdraws the air within the aerosol can to create a substantial vacuum therein. The valve is then permitted to close as the vacuum crimper tool is retracted to its upper position, and the can is advanced to the third station 14.
The third station includes a nozzle 25 which also is reciprocable between upper and lower positions and which is connected to a supply of aerosol propellant. When the can reaches the third station and the conveyor stops, the nozzle 25 is lowered over the valve stem and moves the valve stem to open the valve. The can is then filled with a predetermined quantity of propellant after which the nozzle 25 is retracted to close the valve and permit the can to be moved to the fourth station 15.
The fourth station 15 includes a reciprocable nozzle 26 similar to the nozzle 25. When the can stops at the fourth station, the nozzle 26 is lowered over the valve stem and moves the valve stem to open the valve. However, the nozzle 26 does not inject anything into the can but merely permits a quantity of the pressurized propellant within the can to be exhausted to the atmosphere. The amount of propellant which is exhausted will depend upon the length of time which the valve is maintained open by the nozzle 26. Since the can is not provided with a dip tube, little or no marking material, which is located in the bottom portion of the can, is released, and substantially only propellant is exhausted. It is believed, however, that some unknown ingredients of the marking material probably do escape with the propellant. The propellants which I have used are colorless, and the material leaving the can at the fourth station is also colorless. If desired, an exhaust tube or the like can be connected to the nozzle 26 to convey the material which is released at the fourth station out of the filling room or to a collecting chamber.
After the can is advanced beyond the fourth station, a spray nozzle 27 can be mounted on the valve stem to permit the contents of the can to be sprayed in a stripe pattern, and the can can then be packaged for shipment.
The particular aerosol propellants which I have used are hydrocarbon propellants, which are blends or mixtures of isobutane and propane. Isobutane is a colorless, easily liquefied gas which is generally shipped as a liquefied gas under its own vapor pressure. The vapor pressure of isobutane is 30.7 psig at 70°F. Propane is a gas at atmospheric pressure and normal temperatures and is colorless in both its gaseous and liquid phases. Propane is also generally shipped as a liquefied gas under its own vapor pressure, which is 110 psig at 70°F. Blends of hydrocarbon propellants are generally identified by the vapor pressure of the blend at 70°F. For example, a 90-10 blend consists of 90 percent isobutane and 10 percent propane, by weight, and this blend has a vapor pressure of 40 psig at 70°F. Blend 84-16 consists of 84 percent isobutane and 16 percent propane by weight, and this blend has a vapor pressure of 46 psig at 70°F.
The marking material which I have used is conventional paint made from resin, pigment, and solvent.
I have found that when aerosol spray cans are filled in the conventional manner by introducing paint and hydrocarbon propellant into the cans in accordance with the procedure described hereinbefore with respect to stations 1 through 3, the cans will not spray a uniform, sharply defined stripe when the can is inverted and the valve is opened, regardless of the type of nozzle that is used. The stripe will have ragged, splattered, or feathered edges, and the amount of paint will not be uniform from one edge to the other, more being deposited in the central portion of the stripe.
The principle of the invention is not completely understood, but I have discovered that if a quantity of propellant is released from the can when the can is held upright so that no paint can be observed in the propellant which is exhausted, the can will spray a sharply defined, uniform stripe when the can is inverted. The length of time during which the valve is maintained open to release the propellant is determined empirically as discussed hereinafter, but an average time is about 15 seconds. It is possible that some of the ingredients of the can besides the propellant, namely, the resin, pigment, and solvent, are released from the can with the propellant, but I have been unable to observe any visible evidence of this. It is also possible that the percentage of the blend of the propellant remaining within the can is changed by virtue of the fact that more or less isobutane than propane is released, but I have no way of making this determination. I do known that if the same end result is attempted to be obtained by using a different percentage blend of propellant or by filling the can with less propellant rather than first filling the can with a predetermined amount of propellant and then releasing some of the propellant, a well-defined, uniform stripe still cannot be obtained.
I can readily determine the length of time that the valve should be held open in the "degassing" step at the fourth station for each type of paint and blend of propellant by testing the spraying ability of the can is the apparatus described in my U.S. Pat. No. 3,700,144, issued Oct. 24, 1972. I have found that approximately 15 seconds is the average optimum degassing time, and when I begin a continuous filling operation, I can arbitrarily adjust the operating mechanism associated with the nozzle at the fourth station so that this nozzle will hold the valve open during the degassing step for 15 seconds. After the first can passes the fourth station and is equipped with a spraying nozzle such as described in my aforementioned patent application Ser. No. 193,433 I will check the stripe obtained from that can by inserting the can in the spraying apparatus described in the patent and operating the apparatus to spray a stripe. The stripe can then be observed, and if the stripe is not satisfactory, the fourth station can be adjusted to release more or less propellant from the second can. If too little propellant is released during the degassing step, the stripe will have more paint along its central portion than its edges, and the edges will be ragged. If too much propellant is released, the central portion of the stripe will be thinner than the edge portions, although the edges will be sharp. The testing procedure is repeated until the optimum degassing time is determined, after which the filling process can be operated continuously. I have found it advantageous, however, to spotcheck a can periodically by inserting the can in the spraying apparatus to check its striping ability.
I have found that the darker the paint which is used, the less degassing time that is required. For example, I use the longest degassing time when the can contains white paint, slightly less when the can contains yellow paint, still less when the can contains red paint, and the least when the can contains black paint. The degassing time for each color may vary from one batch of paint to the next and from one day to the next, and it is impossible to give an optimum degassing time for a particular mixture of paint and propellant. This is the reason for determining the degassing time empirically for each batch. I have found, however, that the optimum degassing time will almost always be between 1 to 60 seconds for a can with an 18 ounce fill and will usually be between about 5 to about 25 seconds.
It is believed that the primary reason for the inability to obtain acceptable stripes relates to the resin in the paint. The resin may react in some way with the hydrocarbon propellant which interferes with the striping ability, and the degassing operation may correct the unfavorable results produced by such reaction. It is possible that air remaining within the can after the vacuum is drawn at the second station also interferes with the striping ability, and the degassing operation might permit this air to escape.
The following specific examples will facilitate an understanding of the invention.
Example I
Four cans were filled using white paint as the marking material, methylene chloride as a solvent-propellant, and an 84-16 blend of isobutane and propane as a propellant. The methylene chloride acts as both a solvent and a propellant since a portion of it may be a gas at the temperatures and pressures involved. The paint contained white pigment, Polynyl "N" resin available from Stresen-Reuter Co., and toluol as solvent. These ingredients were used in the following proportions:
Weight % by Weight ______________________________________ Paint 357 gm. 70% Methylene Chloride 67 gm. 13% Propellant 87 gm. 17% ______________________________________
The first can was degassed at the fourth station for a period of 1 second. When this can was used in the spraying apparatus described in the aforementioned patent, the stripe produced had unacceptably rough or ragged edges, and more paint was sprayed in the middle of the stripe than at the edges.
The second can was degassed for a period of 5 seconds, and when this can was used in the spraying apparatus, a uniform stripe with well-defined sharp edges was produced.
The third can was degassed for a period of 25 seconds, and this can also produced a well-defined uniform stripe with sharp edges.
The fourth can was degassed for a period of 30 seconds, and the stripe produced from this can, while having relatively sharp edges, was not uniform and had less paint deposited in the middle than along the edges.
Other cans filled in the foregoing manner which were degassed for a period ranging between 5 and 25 seconds also produced uniform, well-defined stripes. As the degassing time increased beyond 30 seconds, the nonuniformity of the stripe increased and more paint was deposited along the edge portion of the stripe. Degassing for less than 5 seconds produced stripes having unacceptable ragged edges.
Example II
Four cans were filled as before with yellow paint in accordance with the following formula:
Weight % by Weight ______________________________________ Paint 382 gm. 75% Methylene Chloride 51 gm. 10% Propellant 77 gm. 15% ______________________________________
The yellow paint contained yellow pigment, Marbon VTAC resin available from Thompson Hayward Chemical Co., and toluol.
The four cans were degassed for periods of 1, 5, 25, and 30 seconds, and the stripes produced by these cans were comparable to the stripes produced by the respective cans of Example I. In general it was found that the optimum degassing time for yellow paint was comparable to the optimum degassing time for white paint but perhaps slightly less.
When black paint is used, I have found that a degassing time of as low as 1 second enables the can to produce a good stripe of uniform thickness and sharp edges.
I have also found that the degassing time sometimes varies depending upon the manufacturer of the resins and pigments which are used to produce the paint. For example, acceptable stripes of both white and yellow paint have been obtained by using degassing time as high as 60 seconds or more. Because the reason why the degassing operation permits well-defined stripes to be obtained is unknown, the determination of the optimum degassing time for a particular mixture of ingredients remains essentially empirical, and may vary from one batch of ingredients to the next. However, this determination can be quickly and easily made simply by testing the striping characteristics obtained for several degassing times, and the use of the spraying apparatus described in my patent facilitates these tests. It will be understood, however, that the striping characteristics can also be easily checked manually by holding the can by hand and spraying the contents thereof on a surface.
In the continuous filling operation described in conjunction with the drawing, the conveyor advances intermittently and stops each can at each station for the same period of time. Since the operations performed at the first three stations generally take only a few seconds and the degassing step might take considerably longer, the filling and degassing procedure can be speeded up by composing the fourth station of two or more substations, each substation having a degassing nozzle. For example, if the desired degassing time is ten seconds and the degassing station comprises two substations, a particular can can be degassed for five seconds at the first substation and degassed for an additional five seconds at the second substation. In this way, the time during which the cans remain stationary can be reduced and the filling procedure can be accelerated.
The degassing operation releases only a relatively small quantity of the propellant within the can. For example, with the amounts of ingredients specified in the foregoing examples, the cans can be inverted and the paint can be sprayed for a period of about 7 to 8 minutes. I have found that the degassing operation has no noticeable effect on the ability of the propellant to completely empty the can of paint when the can is inverted.
While in the foregoing specification a detailed description of a specific embodiment of the invention was set forth for the purpose of illustration, it is to be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.
This invention relates to aerosol spray cans, and, more particularly, to aerosol spray cans which are filled with a marking material such as paint and which are intended for use in spraying stripes.
The use of aerosol marking cans to spray stripes on pavement and other surfaces is becoming increasingly common. For example, stripes may be sprayed on a parking lot to designate parking areas, on factory floors to designate walkways, on grass to mark playing fields and boundaries, etc. Such an aerosol can is usually equipped with a conventional aerosol can valve which releases the contents of the can when the valve stem is depressed or moved laterally, and a nozzle which is inserted over the valve stem and which is provided with a slotted or rectangular orifice for spraying the contents of the can in a stripe-shaped pattern. One such nozzle which I have had good results with is described in my co-pending application entitled "Actuator For Aerosol Can Valve," Ser. No. 193,433, filed Oct. 28, 1971.
An aerosol can which is to be used for marking surfaces generally is not provided with a dip tube extending from the valve toward the bottom of the can so that the marking material will be expelled from the can by the propellant when the can is inverted. When the can is upright, the marking material, which is heavier than the propellant, will be located at the bottom of the can, and the propellant will be located above the marking material. When the valve is opened when the can is upright, the propellant will be released, but no marking marking material will be released.
A common problem heretofore experienced with aerosol marking cans is that the marking material will not be sprayed in a well-defined, uniform stripe. Rather, more material will be deposited in the central portion of the strip that is being sprayed when along the edge portions of the strip. Further, the strip will not have sharp, well-defined edges, and marking material will splatter or be sprayed beyond the edges of the stripe that is desired. The result is a somewhat sloppy looking stripe having splattered or feathered edges, and the stripe does not provide a definite boundary or line of demarcation. Further, the marking material might not completely cover the surface, particularly a dark surface, along the edge portions of the stripe because insufficient material has been deposited. These thin edge portions will not only render the surface partially visible but will wear away faster than the central, thicker portion of the stripe.
SUMMARY
The invention solves the foregoing problems by providing a method of filling aerosol marking cans so that the marking material can be sprayed to form a well-defined stripe having sharp edges and a substantially uniform covering of marking material from one edge to the other. The cans are filled in the conventional manner with marking material and aerosol propellant, but after each can is filled, the valve is opened to release a quantity of propellant. The can is positioned when the valve is opened so that little or no marking material is released with the propellant, i.e., if the can is not provided with a dip tube, the can is positioned in an upright manner. I have found that if the valve is held open for between about 1 to about 60 seconds, and usually for between about 5 to about 25 seconds, an amount of propellant, along with, perhaps, other ingredients in the can, is released that enables the can when inverted to spray the marking material in a sharply defined, uniform stripe.
DESCRIPTION OF THE DRAWING
The invention will be explained in conjunction with the accompanying drawing, which is a schematic illustration of the process of filling aerosol cans in accordance with the invention.
DESCRIPTION OF SPECIFIC EMBODIMENT
The invention will be described with reference to a continuous filling process represented in the drawing in which a plurality of cans 10 are advanced in the direction of the arrow A by a conveyor 11. The conveyor moves each can to a plurality of stations 12, 13, 14, and 15, and in the particular embodiment illustrated the conveyor moves intermittently so that each can stops at each station for a discrete period of time.
The first three stations are conventional in aerosol can filling procedures and need not be described in detail. Each of the cans is first advanced to the first or filling station 12 which, in the embodiment illustrated, comprises a pair of filling nozzles 16a and 16b and is maintained stationary below each nozzle for a period of time when the conveyor stops. Each can has a generally cylindrical body 17 and a dome-shaped top 18 which is provided with a central opening 19. The first filling nozzle 16a is connected to a source of liquid marking material such as paint, and the second filling nozzle is connected to a source of methylene chloride. When each can stops below each nozzle of the first station, the nozzle is actuated to allow a predetermined amount of marking material or methylene chloride to flow into the can through the opening.
The can is then advanced to the second station 13 which includes a conventional vacuum crimper tool 21. Before each can reaches the second station, a conventional aerosol valve 22 is placed on the top of the can by the usual valve feeder (not shown). Each valve includes a cap 23 which extends over the edges of the top opening and which supports the valve mechanism and an upwardly extending valve stem 24 which opens the valve when the stem is moved laterally. The vacuum crimper is mounted for vertical reciprocation as indicated by the arrows, and when the can stops at the second station, the tool moves downwardly to the top of the can and crimps the cap about the edges of the top opening to provide a gas-tight seal.
The vacuum crimper tool also includes means for moving the valve stem to open the valve, and after the cap is crimped about the edges of the opening, a vacuum pump or other means for providing a vacuum within the cans withdraws the air within the aerosol can to create a substantial vacuum therein. The valve is then permitted to close as the vacuum crimper tool is retracted to its upper position, and the can is advanced to the third station 14.
The third station includes a nozzle 25 which also is reciprocable between upper and lower positions and which is connected to a supply of aerosol propellant. When the can reaches the third station and the conveyor stops, the nozzle 25 is lowered over the valve stem and moves the valve stem to open the valve. The can is then filled with a predetermined quantity of propellant after which the nozzle 25 is retracted to close the valve and permit the can to be moved to the fourth station 15.
The fourth station 15 includes a reciprocable nozzle 26 similar to the nozzle 25. When the can stops at the fourth station, the nozzle 26 is lowered over the valve stem and moves the valve stem to open the valve. However, the nozzle 26 does not inject anything into the can but merely permits a quantity of the pressurized propellant within the can to be exhausted to the atmosphere. The amount of propellant which is exhausted will depend upon the length of time which the valve is maintained open by the nozzle 26. Since the can is not provided with a dip tube, little or no marking material, which is located in the bottom portion of the can, is released, and substantially only propellant is exhausted. It is believed, however, that some unknown ingredients of the marking material probably do escape with the propellant. The propellants which I have used are colorless, and the material leaving the can at the fourth station is also colorless. If desired, an exhaust tube or the like can be connected to the nozzle 26 to convey the material which is released at the fourth station out of the filling room or to a collecting chamber.
After the can is advanced beyond the fourth station, a spray nozzle 27 can be mounted on the valve stem to permit the contents of the can to be sprayed in a stripe pattern, and the can can then be packaged for shipment.
The particular aerosol propellants which I have used are hydrocarbon propellants, which are blends or mixtures of isobutane and propane. Isobutane is a colorless, easily liquefied gas which is generally shipped as a liquefied gas under its own vapor pressure. The vapor pressure of isobutane is 30.7 psig at 70°F. Propane is a gas at atmospheric pressure and normal temperatures and is colorless in both its gaseous and liquid phases. Propane is also generally shipped as a liquefied gas under its own vapor pressure, which is 110 psig at 70°F. Blends of hydrocarbon propellants are generally identified by the vapor pressure of the blend at 70°F. For example, a 90-10 blend consists of 90 percent isobutane and 10 percent propane, by weight, and this blend has a vapor pressure of 40 psig at 70°F. Blend 84-16 consists of 84 percent isobutane and 16 percent propane by weight, and this blend has a vapor pressure of 46 psig at 70°F.
The marking material which I have used is conventional paint made from resin, pigment, and solvent.
I have found that when aerosol spray cans are filled in the conventional manner by introducing paint and hydrocarbon propellant into the cans in accordance with the procedure described hereinbefore with respect to stations 1 through 3, the cans will not spray a uniform, sharply defined stripe when the can is inverted and the valve is opened, regardless of the type of nozzle that is used. The stripe will have ragged, splattered, or feathered edges, and the amount of paint will not be uniform from one edge to the other, more being deposited in the central portion of the stripe.
The principle of the invention is not completely understood, but I have discovered that if a quantity of propellant is released from the can when the can is held upright so that no paint can be observed in the propellant which is exhausted, the can will spray a sharply defined, uniform stripe when the can is inverted. The length of time during which the valve is maintained open to release the propellant is determined empirically as discussed hereinafter, but an average time is about 15 seconds. It is possible that some of the ingredients of the can besides the propellant, namely, the resin, pigment, and solvent, are released from the can with the propellant, but I have been unable to observe any visible evidence of this. It is also possible that the percentage of the blend of the propellant remaining within the can is changed by virtue of the fact that more or less isobutane than propane is released, but I have no way of making this determination. I do known that if the same end result is attempted to be obtained by using a different percentage blend of propellant or by filling the can with less propellant rather than first filling the can with a predetermined amount of propellant and then releasing some of the propellant, a well-defined, uniform stripe still cannot be obtained.
I can readily determine the length of time that the valve should be held open in the "degassing" step at the fourth station for each type of paint and blend of propellant by testing the spraying ability of the can is the apparatus described in my U.S. Pat. No. 3,700,144, issued Oct. 24, 1972. I have found that approximately 15 seconds is the average optimum degassing time, and when I begin a continuous filling operation, I can arbitrarily adjust the operating mechanism associated with the nozzle at the fourth station so that this nozzle will hold the valve open during the degassing step for 15 seconds. After the first can passes the fourth station and is equipped with a spraying nozzle such as described in my aforementioned patent application Ser. No. 193,433 I will check the stripe obtained from that can by inserting the can in the spraying apparatus described in the patent and operating the apparatus to spray a stripe. The stripe can then be observed, and if the stripe is not satisfactory, the fourth station can be adjusted to release more or less propellant from the second can. If too little propellant is released during the degassing step, the stripe will have more paint along its central portion than its edges, and the edges will be ragged. If too much propellant is released, the central portion of the stripe will be thinner than the edge portions, although the edges will be sharp. The testing procedure is repeated until the optimum degassing time is determined, after which the filling process can be operated continuously. I have found it advantageous, however, to spotcheck a can periodically by inserting the can in the spraying apparatus to check its striping ability.
I have found that the darker the paint which is used, the less degassing time that is required. For example, I use the longest degassing time when the can contains white paint, slightly less when the can contains yellow paint, still less when the can contains red paint, and the least when the can contains black paint. The degassing time for each color may vary from one batch of paint to the next and from one day to the next, and it is impossible to give an optimum degassing time for a particular mixture of paint and propellant. This is the reason for determining the degassing time empirically for each batch. I have found, however, that the optimum degassing time will almost always be between 1 to 60 seconds for a can with an 18 ounce fill and will usually be between about 5 to about 25 seconds.
It is believed that the primary reason for the inability to obtain acceptable stripes relates to the resin in the paint. The resin may react in some way with the hydrocarbon propellant which interferes with the striping ability, and the degassing operation may correct the unfavorable results produced by such reaction. It is possible that air remaining within the can after the vacuum is drawn at the second station also interferes with the striping ability, and the degassing operation might permit this air to escape.
The following specific examples will facilitate an understanding of the invention.
Example I
Four cans were filled using white paint as the marking material, methylene chloride as a solvent-propellant, and an 84-16 blend of isobutane and propane as a propellant. The methylene chloride acts as both a solvent and a propellant since a portion of it may be a gas at the temperatures and pressures involved. The paint contained white pigment, Polynyl "N" resin available from Stresen-Reuter Co., and toluol as solvent. These ingredients were used in the following proportions:
Weight % by Weight ______________________________________ Paint 357 gm. 70% Methylene Chloride 67 gm. 13% Propellant 87 gm. 17% ______________________________________
The first can was degassed at the fourth station for a period of 1 second. When this can was used in the spraying apparatus described in the aforementioned patent, the stripe produced had unacceptably rough or ragged edges, and more paint was sprayed in the middle of the stripe than at the edges.
The second can was degassed for a period of 5 seconds, and when this can was used in the spraying apparatus, a uniform stripe with well-defined sharp edges was produced.
The third can was degassed for a period of 25 seconds, and this can also produced a well-defined uniform stripe with sharp edges.
The fourth can was degassed for a period of 30 seconds, and the stripe produced from this can, while having relatively sharp edges, was not uniform and had less paint deposited in the middle than along the edges.
Other cans filled in the foregoing manner which were degassed for a period ranging between 5 and 25 seconds also produced uniform, well-defined stripes. As the degassing time increased beyond 30 seconds, the nonuniformity of the stripe increased and more paint was deposited along the edge portion of the stripe. Degassing for less than 5 seconds produced stripes having unacceptable ragged edges.
Example II
Four cans were filled as before with yellow paint in accordance with the following formula:
Weight % by Weight ______________________________________ Paint 382 gm. 75% Methylene Chloride 51 gm. 10% Propellant 77 gm. 15% ______________________________________
The yellow paint contained yellow pigment, Marbon VTAC resin available from Thompson Hayward Chemical Co., and toluol.
The four cans were degassed for periods of 1, 5, 25, and 30 seconds, and the stripes produced by these cans were comparable to the stripes produced by the respective cans of Example I. In general it was found that the optimum degassing time for yellow paint was comparable to the optimum degassing time for white paint but perhaps slightly less.
When black paint is used, I have found that a degassing time of as low as 1 second enables the can to produce a good stripe of uniform thickness and sharp edges.
I have also found that the degassing time sometimes varies depending upon the manufacturer of the resins and pigments which are used to produce the paint. For example, acceptable stripes of both white and yellow paint have been obtained by using degassing time as high as 60 seconds or more. Because the reason why the degassing operation permits well-defined stripes to be obtained is unknown, the determination of the optimum degassing time for a particular mixture of ingredients remains essentially empirical, and may vary from one batch of ingredients to the next. However, this determination can be quickly and easily made simply by testing the striping characteristics obtained for several degassing times, and the use of the spraying apparatus described in my patent facilitates these tests. It will be understood, however, that the striping characteristics can also be easily checked manually by holding the can by hand and spraying the contents thereof on a surface.
In the continuous filling operation described in conjunction with the drawing, the conveyor advances intermittently and stops each can at each station for the same period of time. Since the operations performed at the first three stations generally take only a few seconds and the degassing step might take considerably longer, the filling and degassing procedure can be speeded up by composing the fourth station of two or more substations, each substation having a degassing nozzle. For example, if the desired degassing time is ten seconds and the degassing station comprises two substations, a particular can can be degassed for five seconds at the first substation and degassed for an additional five seconds at the second substation. In this way, the time during which the cans remain stationary can be reduced and the filling procedure can be accelerated.
The degassing operation releases only a relatively small quantity of the propellant within the can. For example, with the amounts of ingredients specified in the foregoing examples, the cans can be inverted and the paint can be sprayed for a period of about 7 to 8 minutes. I have found that the degassing operation has no noticeable effect on the ability of the propellant to completely empty the can of paint when the can is inverted.
While in the foregoing specification a detailed description of a specific embodiment of the invention was set forth for the purpose of illustration, it is to be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.