CA1083895A - Method of electrostatically depositing a coating of flock fibers onto an adhesive coated surface - Google Patents

Abstract

Abstract of the Disclosure A method of electrostatic flocking wherein flock fibers are fed at a controlled rate from a storage hopper through a screen. The fibers fall into a propelling air stream. Said propelling stream carries the fibers to an applicator gun where they are electrostatically charged and, unlike prior art arrangements, are propelled by the air stream and electrostatically deposited on the adhesive coated surface to be flocked.

Description

This invention relates to electrostatic coating methods, and more specifically, to an improved method of electrostatically applying to an adhesive coated surface a coating of highly conductive flock fibers, that is, particles having a length greater than .010 inch and an electrical resistance of from about 5 X 105 to about 1 X 1011 ohms.
These particles are contrasted with dry powder particles for use in electrostatic coating having a length less than about .010 inch and an electrical resistance of greater than about 1 X 1012 ohmsO
A variety of electrostatic coating apparatus and methods are known for applying paint, powders, or flock fibers to a wall or other surface being coated. Typically, electrostatic coating processes may comprise supplying the desired coating material to a hand held applicator gun which has a highly charged electrode or electrodes for electrostatically charging the coating material by setting up an electrostatic field between the gun and the surface of the article being coated. The article is normally groùnded so that the opposite-ly charged coating material is drawn thereto thereby making the coat-ing process fast and highly efficient with little waste or over spray.
The electrostatic field also causes the charged coating material to ~ 20 surround the grounded article, and thereby enable simultaneous coating ; of remote sides of said article. Of course, with liquid paint, the coating material easily sticks to the article. However, with coating materials such as flock fibers, it is necessary to cover the article with an adhesive prior to electrostatic deposition of the flock so that the coating material will adhere to said article.
A major problem in the electrostatic coating industry arises in the supplying of dry, non-liquid coating materials to the applicator gun at a carefully controlled rateO That is, paint in liquid form can be pumped easily ~83~39~

through supply tubing to an applicator gun at a controlled rate, but powders and flock fibers require special handling.
Accordingly, with powders, it has been common pra~tice to entrain the dry powder particles in a moving air stream by means of a so-called fluidic bed~ In such a bed, the particles are spread in a thin layer over a flat surface having a plurality of fine air streams passing upwardly therethrough. This creates a particle cloud above the flat surface, and this cloud is picked up by another moving air stream for transporting to an applicator gun.
Fluidic beds have not been at all satisfactory when used with flock fibers because the fibers undesirably tend to clump or tangle together on the bed and have a greater bulk factor than powders. Another problem encountered in electrostatic flocking processes employing applicator guns is that once flock fibers have been entrained in an air stream, it has been felt to be necessary to separate the fibers from the air stream as they exit the applicator gun. This insures that the flock fibers are propelled toward the article being coated almost solely by the effects of the electrostatic field to obtain a flock coating. That is, the gun is provided with a series of baffles to remove the flock fibers from the transporting air stream once said fibers are charged. This prevents the fibers from being propelled at a high rate of speed toward the article being coated, and prevents the fibers from bouncing off the article Failing to use the propelling action of the transporting air stream limits the distance which the fibers can be projected from the gun. It also limits the directional control of the fibers to the articles to be coated.
And it fails to remove excess fibers that are not captured by -3- !

the adhesi~e film on the article being coated. These f~ctors limit the utility of the gun for coating the remote sides of the article, as well as interior surfaces and cavities, and fail to insure a uniform flock coating on the article.
Some attempts have been maae to provide better control over the supplying of flock fibers to an applicator gun~ See, for example, U S~ patent No. 3,551,178, wherein flock fibers fall through a screen and further through adjustable-size openings for entrainment in a transporting air stream. The air stream carries the entrained fibers to an applicator gun where, according to conventional practice, the fibers are separate~ by baffles from the transporting stream. Thus, the fiber deposition feed rate, the directional control of the charged fibers, and the distance to which the fibers can be projected are all limited.
This process of separating the charged fibers from the transporting air stream thus has the same attendant dis-advantages as the conventional electrostatic flocking process in which excessive quantities of the fibers are dropped from a storage hopper and fall by gravity toward the grounded articles to be coated while said articles are moved between a pair of electrically charged grids. The grids create an ionizing zone through which the fibers fall. A portion of the fibers become electrically charged in the ionizing zone and are thus attracted to the grounded articles. However, the greatest percentage of the fibers fall through the ionizing zone and are not deposited on the articles and/or are loosely physically held as non-adhesively bound fibers in the other fibers which are bound by the adhesive coating.

.. . , ~ .

1~83895 The electrostatic flocking method of this invention overcomes the problems and deficiencies of the prior art by providing a controllable method of supplying flock fibers to a transporting air stream while at the same time allowing the transporting stream to help direct the charged flock fibers ; toward the surface of the article being coated and remove the non-adhesively bound fibers from the article.
In accordance with one form of carrying out my inven-tion, I employ an apparatus in which the fibers to be deposited are stored in a hopper having a screen across the bottom thereof.
A brush is spaced slightly above the screen and is controllably rotated to cause the flock fibers to fall through the screen at ; a controlled rate. The fibers fall into a trough having a vibrator thereon which axially aligns the fibers and feeds them into the mouth of a venturi flow tube where they are picked up by a propelling air stream. The propelling stream carries the flock fibers to and through an applicator gun having a plurality of highly charged electrodes carried in a nozzle at the exit end thereof for electrostatically charging said fibers.
The electrostatically charged fibers are projected from the gun nozzle toward the adhesively coated grounded article by the aforesaid propelling air stream. The fibers are deposited in the adhesive film on the article, but the fibers which are not bound into said film are blown away by the air stream and are either exhausted away from the article or are reswirled ' in the ionizing zone between the gun and article so they will be again attracted to and bound to the adhesive film on the article.
Thus, in accordance with a broad aspect of the invention, there is provided a method of electrostatically depositing a coating of flock fibers onto an adhesive coated surface comprising the steps of gravitationally feeding dry ~ _5_ ~V8~895 flock fibers at a controlled rate into a venturi flow tube;
moving a stream of air through said flow tube at a controlled rate for picking up and entraining said fibers in said air stream; directing said air stream and fibers through a sub-stantially continuous flow passage and over electrode means for electrostatically charging said fibers, said air stream and the electrostatic cllarge on said fibers propelling said fibers from said electrode means toward the surface.
The accompanying drawings illustrate the invention.
In such drawings:

'~`.'.:,:
t~

Fig~ 1 is an eleYation ~iew generally illustrating apparatus that can be employed for carrying out the electro-static flockin~ method of this in~ention;
Fig~ 2 is an enlarged elevation view showing apparatus for supplying flock fibers to an applicator gun, with portions thereof broken away;
Fig 3 is an enlarged horizontal section taken on the line 3-3 of Fig. 2;
Fig. 4 is an enlarged sectional view of the applicator gun of Fig. l; and Fix. 5 is an enlarged front view of the applicator gun shown in Fig. 4.
My electrostatic flocking method can be carried out in the apparatus illustrated in Fig. 1, in which there is a storage hopper 12 for storing a supply of flock fibers there-in and having means for delivering these flock fibers at a controlled rate to an applicator gun 14. The fibers have a resistance value of from about 5x105 to about lxlOll ohms, and , the gun 14 is supplied with electrical power from a D.C. high voltage power supply 16 for electrostatically charging said fibers as they exit the gun. The gun is hand held by an operator 22 who directs the spray of flock fibers toward the surface of an article 24 being flocked. The article 24, which is pre-coated with an adhesive film, is electrically grounded (not shown) and an electrostatic field 25 extends between the gun and article so that the positively charged flock fibers 20 are attracted to the article and are fixedly bonded thereto. Conveniently, the electrostatic field forces tend to draw the charged fibers to all sides of the grounded 30 article 24 for coating thereof~ -.

,~.. . .... . .

- 1083fl95 The hopper 12, shown in detail in Figs. 2 and 3, is conveniently covered ~ith a re~ovable lid 27 to permit the refilling thereof. The bottom of said hopper is defined by a pair of inwardly angled walls 28 whose lower ends are disposed in spaced relation to each other and form a fiber discharge opening 29. The walls 28 at opening 29 are each bent inwardly to form a pair of horizontally disposed flanges 30 upon which is removably carried a screen 31.
The fibers are urged through screen 31 by a brush 32 I0 extending across opening 29 immediately above said screen and driven by a motor 37 electrically connected to a control panel 33 mounted on the outside of the hopper. Said panel 33 is connected to a suitable power source not shown.
The fibers fall through the screen 31 by gravity ~' onto an elongated trough 34. A vibrator 35 is mounted on ' the trough 34 and is interconnected through the brush motor 37 to the control panel 33 whereby actuation of the brush 32 will simultaneously cause an actuation of the vibrator 35. The , trough 34 is angled slightly downwardly for feeding the fibers therefrom into a collecting throat 36. Because of the vibratory action imparted to the fibers as they move along the trough, a substantial portion of said fibers will align them-, selves longitudinally as they move along said trough and fallinto the throat 36.
The throat 36 continuously feeds the fibers into th,e mouth of a venturi flow tube 40. The venturi tube 40 i is supplied with a stream of compressed air from an air pump ,' 42, said pump being supplied with power via the control panel, ~, 33. The Yenturi tube 40 entrains the fibers in a propelling - 30 air stream and said fibers are carried in said air stream through ~'' .

' ' 1~838~

an air hose 54 to the applicator gun 14.
The mesh of screen 31, rotational speed of the brush 32, and flow rate through the venturi tube 40 are all a function of the type, length, and denier of the parti-cular flock fibers being used. The fibers can have lengths of from a~out ~010 inches to about ~250 inches and weights of from about 1~5 to about 30 denier. With the fiber characteristics falling within these parameters, the screen may have mesh sizes of from about 8 to about 50. Also, with these parameters, the brush 32 can be disposed above screen 31 at distances from about ~25 inches to a position in direct contact with said screen and be rotated at speeds of from about 5 to about 150 revolutions per minute. Also, with the fibers falling within these parameters, the air stream moving through the venturi tube 40 can have a flow rate of from about 2 to about 10 çubic feet per minute. With this flow rate, from about 1 to about 10 ounces per minute of flock fibers can be moved through a hose 54 having a diamter of 5/8 in. The air stream, and thus the fibers entrained therein, has a velocity of from about 2000 to about 5000 feet per minute.
While higher velocities may be employed, generally velocities higher than 5000 feet per minute tend to cause an excessively high percentage of the fibers to be blown past the surface 1 to be coated without being deposited thereon, and can cause fibers bound in the adhesive film on the surface to be blown over into a disoriented pattern.
. While various types of applicator guns can be employed in carrying out my process, the embodiment of the gun 14 as shown generally diagrammatically in Figs. 4 and 5 comprises a -generally cylindrical barrel 56 having a downwardly projecting , 1~83895 handle 72. A longitudinal passage 58 of circular cross-section extends through the barrel forwardly of the handle 72 and terminates at the front end of the barrel in a discharge nozzle 62. The air hose 54 carrying the air-propelled flock fibers 20 is connected by a fitting 60 at the bottom of the handle ~ith a sleeve 61 interconnecting said fitting and the barrel passage 58. In this manner, the flock fibers 20 are carried b~ their propelling air stream into and completely through the applicator gun 14 and are discharged therefrom through the nozzle 62 at the front end thereof.
A second fitting 64 is mounted on the bottom of handle 72 for connecting an electrical conductor 66 thereto.
Said conductor interconnects the applicator gun to the high voltage power supply 16, shown in Fig. 1. The conductor 66 is electrically connected through the gun 14 to a finger-operable low voltage trigger switch 70 mounted in front of the handle 72. The trigger switch 70 is manually operable by the operator 22 to actuate a relay 73 to complete an electrical path to activate the high voltage power supply. The high voltage is supplied from the conductor fitting 64 through a large resistance current limiting resistor 74 to three charging electrodes 76 carried on an inwardly inclined face 61 of the gun nozzle 62. These electrodes, as shown in Fig.
5, are equiangularly spaced about the barrel passage 58 and extend parallel thereto before terminating at the forwardmost extent of the nozzle 62 in the path of the fibers being dis-charged from the gun. When coupled to the power supply 16, the electrodes are charged with a Yoltage of from about 10 kilovolts to about 150 kilovolts to electrostatically induce a charge on the flock fibers 20 as they exit the applicator .

1~83895 gun 14 and to create the electrostatic field 25 bet~een the gun nozzle 62 and the ~rounded article 24 being flocked.
As will ~e understood, the gun components in contact wit~ the high Yoltage components are made of electrically insulating material to protect the operator 22. It is also understood that the gun can be fixedly or reciprocatingly mounted in fixtures and mechanically actuated thereby eliminating the necessity of t~e operator holding the gun. This arrangement is particularly advantageous when it is not necessary to manually manipulate the gun to coat remote or recessed areas of the o~ect being coated.
In the flock coating of certain articles, for instance, the interior walls of cylindrically shaped articles, it is desirable to spread the spray pattern of the flock radially outwardly. To accomplish this, I mount a spider 90 in the nozzle 62 to support a small diameter post 92 as shown in Fig. 4. The post 92 projects axially outwardly from the spider, and a diffuser 94, a cone in the embodiment illust-rated, is removably and slidably carried on said post. When the diffuser 94 is placed on post 92, it will be disposed directly in the center of the air stream propelling the fibers outwardly from the nozzle. Said diffuser will cause the spray pattern of the fibers in the air stream to flare outwardly from the discharge end of said nozzle. As will be understood, the closer the diffuser 94 is moved inwardly on post 92 toward the spider 90, the more spreading effect said diffuser will have upon the spray pattern being discharged from the gun.
The diffuser and its mounting assembly are merely employed to help control the configuration of the spray pattern and not to impart any electrical properties to the flock fibers.

,.

.

~83895 Consequently, these components are all formed from an electrically non-conductive material~
In carry~ng out my process, the fibers are fed from the hopper 12 into the trough 34 where a substant~al portion of said fibers are longitudinally aligned and from which they enter the venturi 40. The propelling air stream then carries them to and through the gun 14 where they are electrostatically charged. Said air stream fllrther aligns the fibers so that they are discharged from the gun in an alignèd relationship. The charged fibers are blown from the gun through the electrostatic field 25 by the propelling air stream and are deposited on the fi~m of adhesive on the article 24.
The air stream imparts a sufficient velocity to the fibers 20 that those fibers that are not bound in the adhe~ive film are blown past the article 24 and are captured for subseguent use or are rebounded back into the electro-.l static field 25 and then reattached to the article where they can be captured and bound by the adhesive film. This prevents the fibers that are not bound in the , adhesive film from being physically entangled in the fibers that are aahesively bound and thereby eliminates high density fiber areas which will slough off.
In a specific example of carrying out my process for electrostatically coating automobile sun visoxs with : a flock coating, the visors were coated with an adhesive film and coated with nylon fibers having a length of .040 inches, a weight of 3 denier, and a resistance of ;l lx106 ohms~ These fibers were fed thxough the screen 31 30 which was a 12 mesh screer while the brush 32 was ' , .~ . . .
-.: ~ . ' : ' ~83895 rotating in contact with said screen at 47 revolutions per minute. The fibers were fed to the venturi at the rate of 3 1/3 ounces per minute, while the propelling air moving through said venturi had a flow rate of 3 cubic feet per minute. The fibers were discharged from the gun 14 while its electrodes were maintained at a voltage of 80 kilovolts. Under these operating condi-tions, a highly uniform and dense flock coating was deposited on the fibers.

' ' .
'',' "
., .

' I ! .
.

, ' :
. ,. , ~ , : -.,

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of electrostatically depositing a coating of flock fibers onto an adhesive coated surface, comprising the steps of gravitationally feeding dry flock fibers having lengths of from about .010 to about .250 inch and weights of from about 1.5 to about 30 denier at a controlled rate into a venturi flow tube, moving a propelling air stream through said flow tube at a flow rate of from about 2 to about 10 cubic feet per minute for entrainment therein and movement therewith of said fibers, moving said fibers in said air stream through a substantially continuous flow passage and over electrode means along said flow passage for electrostatically charging said fibers, said air stream and the electrostatic charge on said fibers propelling said fibers from said electrode means to said surface whereby said fibers will be captured in the adhesive on said surface.

2. The method as set forth in claim 1 in which said fibers have resistance values of from about 105x 5 to about 106X 5 ohms.

3. The method as set forth in claim 1 in which said propelling air stream has a velocity of from about 2000 to about 5000 feet per minute.

4. A method of electrostatically depositing a coating of flock fibers onto an adhesive coated surface comprising the steps of gravitationally feeding dry flock fibers at a controlled rate into a venturi flow tube; moving a stream of air through said flow tube at a controlled rate for picking up and entrain-ing said fibers in said air stream; directing said air stream and fibers through a substantially continuous flow passage and over electrode means for electrostatically charging said fibers, said air stream and the electrostatic charge on said fibers propelling said fibers from said electrode means toward the surface.

5. The method as set forth in claim 4 wherein said air stream has a flow rate of from about 2 to about 10 cubic feet per minute, and said fibers have lengths from about .010 to about .250 inches, weights of from about 1.5 to about 30 denier, and resistance values of from about 105x 5 to about 1011x 5 ohms.

6. The method as set forth in claim 4 including the steps of gravitationally feeding said fibers at a controlled rate through a screen into an upwardly open, downwardly angled trough, and vibrating said trough for longitudinally aligning a substantial portion of said fibers and for feeding said fibers from said trough into the venturi flow tube.

7. A method as claimed in claim 4 wherein the electrode means are contained in an electrostatic charging gun.

8. A method as claimed in claim 7 including electrostati-cally charging and aligning said fibers as they exit said gun, said electrode means being mounted on said gun generally parallel to the direction of air and fiber travel through said gun for allowing said air and fibers to travel through said gun substantially uninterrupted.

9. A method as claimed in claim 4, 7 or 8 including axially aligning the flock fibers prior to feeding them into the venturi flow tube.