Apparatus for coating by electrostatic force

April 17, 1956

T. LINDQUIST

2,742,018

APPARATUS FOR COATING BY ELECTROSTATIC FORCE

Filed Jan. 2, 1952

Sheets-Sheet 1

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April 17, 1956 τ. lindquist 2,742,018

APPARATUS FOR COATING BY ELECTROSTATIC FORCE Filed Jan. 2, 1952 2 Sheets-Sheet 2

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United States Patent Office ^{2&gt;742 018} ; Patented Apr. 17, 1956

2,742,018

APPARATUS FOR COATING BY ELECTROSTATIC FORCE

Theodore Lindquist, Swansea, Mass.

Application January 2,1952, Serial No. 264,428

Claims. (Cl. 118—51)

This invention relates to a method of and apparatus for applying to an adhesively coated surface, a coating comprising particles and more particularly, though not limited to, particles having definite electrostatic axes, that is, axes in line with the direction of flight of such particles when controlled by the attracting and repelling forces of opposed and like electrostatic fields. In the case of particles such as flock which comprises fibers of substantially greater length than thickness, these axes will coincide with length. In the case of sharp particles such axes will pass through the sharpest points where the greatest concentration of electrostatic charges under the influence of such fields occurs. It has for one object to deposit such particles with such axes predominantly perpendicular to the surface to which they are applied, the orientation of the particles and their flight toward the adhesively coated surface being controlled and at least partly produced by electrostatic means. The particles become charged and are orientated and propelled toward the oppositely charged adhesive coated sheet material below by the-discharge or corona from the fiber ends or the sharp points of. the particles, and by the repulsion from neighboring like charged particles and. electrodes.

For a more complete understanding of this invention reference may be had to the accompanying drawings in which— . Figure 1 is a side elevation of a two-stage flocking •machine embodying the invention.

Figure 2 is an end elevation of the same.

Figure 3 is a detail sectional view to an enlarged scale on line 3—3 of Figure 2. 45

Figure 4 is a detail sectional view on line 4—4 of -Figure 3. ·

Figure 5 is a diagrammatic view showing two stages of the apparatus.

Figure 6 is a sectional view on line 6—6 of Figure 5 ⁵⁰to a larger scale, ^T

Figure 7 is a view similar to Figure .5, but showing a five-stage machine.

This invention will be particularly described with relation to a machine for applying flock to adhesively coated ⁵⁵sheet material. This adhesive may be applied in desired areas so that the flock which is propelled thereagainst will adhere to those areas only to which the adhesive has been applied. Thus desired patterns of flock surface may be produced. 60

It is also evident that by applying adhesive to different areas of the sheet material at different times and applying flock of different colors to these separately coated areas, desirable ornamental color pattern effects may be produced, the flock fibers being attached endwise to the coated 65 •surface and thus presenting the desirable appearance •characteristic of plush, or like pile fabric.

It will be understood, however, that any particles which have definite electrostatic axes may be treated in a similar way and be orientated similarly to flock and be pro- 70 jected against an adhesive coated surface to which it is desired to attach such particles. With abrasive particles, the particles will be secured with sharp points outwardly projecting. Should the particles have no electrostatic axes, they may still be propelled by the mechanism but they would not be orientated in any particular manner ⁵ The method and mechanism by which such particles of flock or abrasive materials, or the like, may be so orientated and projected will be understood from a description of the flocking machine shown herein. As shown best in Figures 1 and 2, this machine comprises ^lu a suitable frame 1 having horizontally spaced pulleys 2 and 3 over which is passed a traveling belt supported at its upper stretch 5 by an electro-conductive table 4. The upper stretch 5 of this belt may have supported thereon the base sheet material to which the coating is to be ¹⁵ applied and this base sheet material may have desired areas of its upper face precoated with an adhesive which is in tacky condition when the flock or other coating is to be applied.

_ Above the top stretch 5 of this belt are arranged trans^M verse to the direction of travel of the belt, one or more pairs of electrodes 6. As shown best in Figure 3, these electrodes may well be formed as metal tubes and they may be supported and attached to hangers 7 of insulating material provided at their upper end portions with longi⁰ tudmal slots 8 through which may be extended clamping screws 9. These hangers 7 are thus angularly and axially adjustable on the clamp screws 9, and these screws may be provided with wing nuts 10 to facilitate loosening the

Rn h^an^ers 7 for such adjustment as may from time to time be desired, after which they may be tightened to secure the parts in adjusted position.

Above and between each pair of electrodes 6 there is arranged a downwardly bowed foraminous conductive 35 l m'⁶ 15' Where flock is to be handled, for example, this baffle may comprise a screen or foraminous member which may well be of brass. This lower baffle 15 is shown as carried by a pair of end plates 16 of insulating material having upward extensions 17 slotted as at 18 for the recep!‘^on °f damping bolts 19 each having a wing nut 20 on ^{4 υ} its outer end as shown best in Figure 4.

Above the baffle 15 there is positioned a flock load retainer formed as a conductive baffle 25 which may be constructed like the baffle 15 and likewise be carried by insulating end plates 26 having slots at 27 (see Figure 4) also engaged by the clamping bolts 19. A longitudinal frame member 28 may support the clamp bolts 19 and an insulating washer 29 may be inserted between the supporting plates 16 and 26. The traveling belt 4 may be driven as by a motor 30 which may be suitably connected thereto as through a reduction gear unit 31 and a chain drive 32, and supply hoppers 35 for the flock or other material to be deposited may be positioned above the upper baffles 25. So long as a supply of flock is present on the load retaining baffles 25 flock is fed therefrom Continuously by the electrostatic action and without requiring any mechanical sifting or agitation. The supply hoppers may have suitable means for agitating and sifting down onto the upper baffle plates the particles contained therein and these distributing hoppers may be driven intermittently whenever the load retainer baffles 25 need to be replenished, as through the chain connections 36, 37, and 38 and the clutch 39 from the motor 30. As such supply hoppers and their agitating and feeding means are well known in the art, no detail description thereof is given herein, it being sufficient to state that the flock or other particles are sifted down as desired onto the upper baffles 25. These baffles, the electrodes 6, and the adhesively coated sheet material are electrostatically charged, the relationships of these charges being shown in Figure 5.

While the specific charges, whether positive or negative, for each element, are not important, the polarity

3,743,018 relations between the various charged elements is of importance. For example, assuming that the sheet material to which the coating is to be applied is charged positively, the electrodes 6 will be charged negatively, the lower baffle plate 15 will be charged positively and the upper baffle plate 25 will be charged negatively. That is, the material to be coated and the lower baffle plate are charged to the same polarity and the electrodes 6 and the upper baffle 25 are charged in the opposite polarity- . ,

Means for statically charging the various parts, and indicated in Figures 1 and 2 as contained in a casing 50 is well known and may, for example, comprise a type known as “brute force D. C. power.” Another comprises the R. F. or radio frequency apparatus such as are commonly used in projection television. A D. C. power supply designed to deliver, say, 30 kv. with a capacity of 1 milliamp is quite satisfactory. An R. F. type of power supply producing 24½ kv. with a capacity of 200 microamps is also satisfactory. The precise potential provided is not critical, however, but should be sufficient to produce the desired propelling effect and a range of, say, 25 kv. to 45 kv. will ordinarily be found perfectly satisfactory.

Where flock is employed as the coating material, it is important that it be in fairly moist condition, as under these conditions it is more easily electrostatically charged and discharged. A moisture content of, say, 10.5% to 13% is satisfactory. This moisture content may be maintained by storing the flock supply under humid conditions at a temperature of 70° F. and a relative humidity of 65%. Rayon flock under such conditions picks up and retains the desired moisture percentage over night. The amount of moisture determines somewhat the best adjustment of the electrodes 6 and the 35 baffles 15 and 25. Sidewise adjustment of the electrodes 6 varies the volume of flock delivered to the adhesive, and where the flock is to be applied in two or more stages, it is usually found desirable to produce a relatively light coverage at the first stage with increasing 40 volume at each successive point of delivery. Decrease in the gap between the electrodes 6 increases the projecting force exerted on the flock. The best relative positioning for the electrodes 6 and the baffles 15 and 25 is dependent upon the length of the fibers and upon 45 their moisture content and it may be adjusted as the functioning of the apparatus appears to indicate desirable. It will be understood that the various parts, including electrodes and baffles are provided with insulat- ------„------ing mountings so that they may be oppositely charged as 50 statically charging said table and the lower of said bafdescribed.

The effects of the charges on the flock may be understood by an inspection of Figures 5 and 6. Assuming that the various elements are charged as shown, the upper baffles 25 being charged negatively, the lower baf- 5 lies 15 positively, the electrodes 6 negatively,, and the sheet material to be coated positively, the flock material retained by the upper baffles 25 becomes negatively charged and is attracted by the positively charged baffle 15 below. Since the openings through the baffles are much larger than the fibers, the fibers pass through the upper baffles 25 and are forced by electrostatic attraction toward the oppositely charged lower baffles 15. The charged fibers orient themselves lengthwise in their ---------- .... _ __ direction of flight by repulsion from each other. As 05 baffles to one polarity and paid electrodes and the upper the fibers thus projected and orientated lengthwise pass ° a» into the field of the lower baffles 15 their charges become reversed in polarity so that as they pass through the lower baffles they are attracted to and between the pairs of electrodes 6. As these electrodes are charged oppo- 70 sitely to the flock particles but in the same polarity as each other, the particles are driven between them where they again change polarity to negative and are repelled by the negatively charged electrodes 6 and attracted to

Thus the particles are not only projected by gravity, but are also propelled by the reaction of their static charges and the charged parts of the apparatus through the upper and lower baffles, gaining momentum all the time, and between the electrodes 6. They then strike endon against the adhesively coated sheet material and become firmly embedded in the adhesive while arranged in vertical position.

In Figure 5 it will be noted that there are two stages of delivery. It is found, however, that these stages may be increased in number by the interposition of other electrodes as 40 which may be interposed between adjacent edges of the lower baffles 15 as shown in Figure 7, these electrodes 40 being charged with the same polarity as the baffles 15 and the adhesively coated sheet material. The paths of the flock materials are then somewhat as indicated diagrammatically in Figure 7, particles upon the upper baffles 25 being attracted by the electrodes 40, from which they are projected downwardly between these electrodes 40 and the lower baffles 15 in the manner somewhat similar to the manner in which the particles are projected between the adjacent lower electrodes 6. These particles, being then charged with the same polarity as the electrodes 40 are repelled therefrom toward the oppositely charged electrodes 6 and are then changed in polarity and projected against the adhesively coated surface. Thus with the three sets of upper and lower baffles and three pairs of electrodes 6, the number of delivery positions or stages is increased from three to five by the addition of the upper electrodes 40.

It is also desirable to bridge across the upper baffles 25 so that the material supplied by the hoppers does not build up on the electrodes 40, and cover plates 41 for this purpose are illustrated in Figure 8.

I From the foregoing description of certain embodiments of this invention and the method of operation, it should be evident to those skilled in the art that various changes and modifications may be made without departing from the spirit or scope of the invention.