United States Patent 3833174

Electrostatic deposition is utilized to coat surfaces of materials with polystyrene particles. The surfaces are coated with an electrically-conductive adhesive. Then, an electrostatic field is set up between the adhesive surface and an electrode on an applicator which may or may not be connected to a continuous feed machine for polystyrene particles. Polystyrene particles are given an electrical charge when in contact with the electrode and are propelled by the electrostatic field to the adhesive surface.

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International Classes:
B05B5/057; (IPC1-7): B05B13/04; B05B5/02
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Primary Examiner:
Ward Jr., Robert S.
Attorney, Agent or Firm:
Jones, Thomas & Askew
What is claimed is

1. A portable apparatus for electrostatically applying particles to a surface such as a ceiling or the like, comprising:

2. A portable apparatus as set forth in claim 1, wherein said deflector means in constructed of an electrically non-conducting material and is disposed relative to the flow direction of particles admitted through said inlet to deflect particles toward said electrode means.

3. Apparatus as in claim 1, wherein said first and second sides of the trough are generally opposite to each other;

4. Apparatus as in claim 3, further comprising:

This invention relates to a method and apparatus for electrostatically depositing particles onto surfaces of materials. More specifically, this invention relates to a method of giving surfaces of materials, such as those used in walls and ceilings, an aesthetic appearance along with excellent acoustical and insulating qualities by coating the surfaces with polystyrene particles in the form of beads and bead clusters.

It is well-known to use electrostatic deposition, or flocking, in order to deposit various materials onto surfaces which have been coated with an adhesive material. For example, electrostatic deposition has been used to give a surface a velvet-like appearance by coating short fibers of dyed rayon or nylon onto the surface. Such a method is disclosed in U.S. Pat. No. 2,706,963.

Previous attempts to use electrostatic deposition to produce walls and ceilings which are decorative and have good acoustical and insulating qualities have not been successful. A major problem has been the selection of a material that has all the desired properties and which can be deposited by electrostatics. Certain known materials, when present as small particles, are easily coated onto a surface by electrostatic deposition, but coatings of such materials do not have the necessary acoustical and insulating properties. Larger particulate material which has been tried in electrostatic deposition has been unsuccessful because of the difficulty of projecting the material with an electrostatic field. Apparently, projection is not possible because the weight of the particles is too much for the electrostatic field to overcome, especially when the particles are to be coated in an upward direction. Hence, ceilings have been particularly difficult to coat with large particulate material. Another major problem has been the proper selection of an adhesive that will produce a good strong bond between the particulate material and the coated surface without adversely affecting the properties of the particulate material. For example, many adhesive compositions chemically attack the particle surfaces, resulting in a poor adherence of the particles to the surface coated.

Because of the problems encountered, therefore, various methods have been conventionally used in producing surfaces such as walls and ceilings with acceptable acoustical and insulating properties. One method is to cover such surfaces with pre-formed tile or panel material that is made by forming a sheet of asbestos fibers in a binder and making perforations in the surface of the sheet. The asbestos has acceptable insulating properties and the perforations in the tiles or panels provide a measure of acoustical absorption. However, the use of asbestos is expensive, both from the standpoint of manufacturing the tile and panel material and from the standpoint of the labor cost of installation. Another method encompasses air blowing a composition of asbestos fibers and adhesive onto the surfaces to give a textured finish. The major problem in using this method is that the person applying the asbestos fibers and adhesive is subject to harm caused by inhalation of these airblown materials. Still another method utilizes fiberglass batts which are placed behind the surface materials. The disadvantages of using fiberglass batts are that the properties of the outer surfaces of the wall or ceiling are not directly affected, and that the fiberglass can cause severe skin irritation to those persons installing the batts.

It is therefore an object of the present invention to provide a method and apparatus for electrostatically coating surfaces such as walls and ceilings with a material that will give the surfaces a pleasing appearance as well as excellent acoustical and insulating properties.

It is another object of the present invention to provide a surface coated with an adhesive and a particulate material such that the adhesive strongly bonds the particulate material to the surface without adversely affecting the properties of the particulate material.

The stated objects, aspects, and advantages of the present invention will in part be pointed out and in part be apparent from the following description of a disclosed embodiment taken in conjunction with the accompanying drawings in which:

FIG. 1 diagrammatically illustrates the use of a continuous feed machine and applicator in applying polystyrene particles to a ceiling by the method of the present invention.

FIG. 2 is a partially broken-away isometric view of a portable applicator according to a disclosed embodiment of the present invention.

In accordance with the present invention, a surface such as a wall or ceiling is coated with an electrically conductive adhesive composition. An electrical lead from a high voltage power source is then connected with the adhesive layer. Another electrical lead exists between the power source and an applicator having an electrode. When the applicator is brought in proximity with the adhesive layer, an electrostatic field is produced. Polystyrene particles are conveyed to the applicator by any suitable technique such as a flexible conduit system. At the applicator, the particles receive an electrostatic charge from the applicator and are then propelled by the electrostatic field toward the adhesive layer of opposite electrical charge. After the adhesive surface has been covered with the polystyrene particles, the adhesive is allowed to dry.

Polystyrene particles are very suitable for electrostatic coating according to the present invention because the polystyrene particles have the ability to accept and retain an electrostatic charge, the ability to be projected by electrostatics, especially in an upward direction, and when present as a built-up layer of beads and bead clusters, the ability to absorb and disperse sound and thermally insulate surfaces. Both the charging and insulative properties of polystyrene particles result from the inability of the particles to conduct both electrical and thermal energy. The ability of polystyrene particles to be electrostatically projected results from the particles being able to accept a large charge combined with their low density. The acoustical properties of polystyrene particles result from the softness which is indicated by a cohesive energy density of 74 cal/cm3. Most other polymeric materials have higher cohesive energy densities, making such materials less suitable acoustically.

The polystyrene particles useful in the present invention can be obtained by various conventional processes. If individual discrete polystyrene beads are to be used, the beads can be obtained by heating polystyrene polymer beads in the presence of a blowing agent such as pentane or other hydrocarbon, in such a manner as to entrap the blowing agent in the beads. The beads thus expand to produce individual expanded beads which are either round, oval, or irregular in shape. If bead clusters are to be used, a similar procedure is used as is used in forming the expanded beads except that the beads are allowed to combine in a mold or extruder with other beads during the expanding step. A conventional continuous polystyrene material is thus formed which is normally used in packaging, insulation, and the like. The polystyrene bead clusters are obtained by pulverizing or breaking up this polystyrene material. The pulverization of the conventional polystyrene materials results in a mixture of discrete beads and bead clusters, or several beads stuck together. For use in the present invention the beads and bead clusters have specific sizes and shapes, depending upon the desired results.

When the polystyrene particles are present as discrete beads in the present invention, the beads preferably have a diameter between 1/32 inch and 6/32 inch, and an especially preferred electrostatic deposition is obtained when round beads having a diameter between 1/32 inch and 3/32 inch are used. The beads with diameters in the range of 1/32 - 3/32 inch produce a very uniform surface and are easily applied with a hand applicator without the use of a continuous forced feed system, whereas the larger beads require the forced feed system to give the beads sufficient initial velocity in order to transfer the beads to the adhesive surface. When the polystyrene particles are present as bead clusters, the clusters should contain from two to ten beads and have a diameter between 2/32 inch and 16/32 inch.

The particular sizes of polystyrene particles selected for use in the present invention depend upon the effects sought. For example, if predominantly small discrete beads of approximately 1/32 inch in diameter are used, a substantially greater portion of the bead surface is covered by adhesive than if larger beads are used. Since relatively little bead surface is exposed, the acoustical effects are less than those obtainable with larger beads. Also, relatively little light diffusion occurs, and because of the thin layer of polystyrene beads, the insulating properties are minimized. However, such a polystyrene bead surface is easy to maintain because of the small amount of dirt accumulation. In contrast, if predominantly large beads (6/32 inch in diameter) or bead clusters are used, better acoustical and light-diffusing effects are obtained because of the greater portion of particle surface exposed beyond the surface of the adhesive. The polystyrene particle layer is thicker and the layer is therefore more insulating. Coupled with the better results obtained using the larger particles is the greater difficulty of maintaining the surface because of dirt accumulation.

The polystyrene particles useful in the present invention can be either round, oval, or irregular in shape when present as discrete beads. The use of round and oval beads results in a surface with a pleasing appearance because the adhesive appears to surround each bead, producing a symmetrical effect. The use of irregular beads and bead clusters gives a slightly better bond between the polystyrene particles and the adhesive than the round or oval beads because these irregular particles have rough or jagged edges which the adhesive can grip. Because most of the electrostatic charge concentrates at the edges, the edges enter the adhesive first, allowing for a deeper penetration into the adhesive layer and a greater bond between the two materials.

The polystyrene particles of the present invention may contain special additives such as light stabilizers, ultraviolet screening agents, flame retardants, and synergistic systems for improving weathering and chemical resistance. Other additives that may be present in the polystyrene particles include colorants, dyes, organic pigments, and metal oxides. All of these additives are conventional for polystyrene and are added during the blowing step in which the polystyrene particles are formed.

The adhesives useful in the present invention may be any of the adhesives normally used to adhere polymeric materials to surfaces. Examples of useful adhesives are the silicone polymers, the thermosetting resins such as the aliphatic epoxy compounds, and the thermoplastic resins such as polyethylene and polyvinyl acetate. The adhesive compositions should not contain any components that tend to attack polystyrene, such as the aromatic or chlorinated hydrocarbons. The preferred adhesive for adhering polystyrene particles to surfaces according to the present invention is an adhesive containing predominantly polyvinyl acetate. This adhesive component produces an excellent bond with the polystyrene particles, allowing them to be subjected to light abrasion without harm.

The adhesives must be made electrically conductive to be useful in the present invention. The adhesives contain electrically conductive materials. Suitable additives are powdered aluminum, bronze, iron, copper, or other materials having suitable electrical properties. In order to impart electrical conductivity to the adhesives, between 1 gram and 10 grams of the powdered metal per liter of adhesive has been found to be sufficient.

The adhesive compositions, in addition to the electrically conducting component, can also contain various additives such as dyes, pigments, thickening agents, plasticizers, and fillers.

Substrates which may be electrostatically coated with the polystyrene particles of the present invention include all materials to which the particular adhesive will adhere. Examples of suitable substrate materials include wall and ceiling materials such as plaster, wallboard, cork, fabric-coated panels, and the like.

Considering the applications of coatings according to a specific disclosed embodiment of the present invention, FIG. 1 illustrates the electrostatic deposition of polystyrene particles 10 onto a ceiling 11 which has been coated with an electrically-conductive adhesive 12. A portable applicator 13 supported by a handle 18 is used to deposit the particles. A continuous feed machine 14 with control panel 19 contains a conventional direct-current power source (not shown) and also a conventional system for continuously supplying particles (also not shown). The direct current is supplied to the electrically conductive adhesive 12 through electrical lead 16 and to the applicator 13 through electrical lead 15. Polystyrene particles are fed from the continuous feed machine 14 to the portable applicator 13 through a flexible hose 17.

Applicator 13 (FIG. 2) generally comprises a troughlike housing 22 of electrically insulating material with an opening in the top to form an outlet 23 through which polystyrene particles 10 pass when the particles are acted on by an electrostatic field between electrode 21 and ceiling surface 11 together with electrically conductive adhesive 12. Electrode 21 covers the inside bottom of the applicator 13 approximately below the outlet 23 so that the polystyrene particles 10 can be projected through the outlet 23 without being obstructed. An electrical lead 25 connects the electrode 21 to the electrical power inlet 27 on the housing 22. At the other end of the applicator 13 from the outlet 23 is an inlet 24 on the bottom of housing 22 through which the polystyrene particles 10 are fed into the applicator 13. Located above the inlet 24 on top of housing 22 is a deflector 26 that deflects the polystyrene particles 10 entering the applicator 13 through the inlet 24 and directs the particles in a downward direction and towards the electrode 21.

The direct-current power source and particle supply system contained within the continuous feed machine 14 may be any of those conventionally used in the art of electrodeposition. For example, a direct-current power source which produces a high-voltage (40,000 v) and a low amperage (less than 1 amp) is a suitable supply of electrical current. Suitable supply systems which are capable of feeding particles continuously to the applicator 13 are also well-known to those skilled in the art.

To apply polystyrene particles 10 to the surface of ceiling 11, the surface is first coated with a layer of electrically conductive adhesive 12. Polystyrene particles 10 are placed in the particle supply system of the continuous feed machine 14. The direct-current power source is turned on and the voltage is regulated by using the control panel 19 on the continuous feed machine 14. The applicator 13 is brought to within about eight inches of the ceiling 11 using the applicator handle 18 for support purposes. Continuous supply of polystyrene particles 10 is begun and controlled by control panel 19. The polystyrene particles are fed from the continuous feed machine 14 through flexible hose 17 and into the inlet 24 of applicator 13. The polystyrene particles hit the deflector 26, are deflected downward and towards the electrode 21 where the particles are given an electrical charge, and are then forced through the outlet 23 and onto the ceiling 11 by the electrostatic field that exists between the electrode 21 and the ceiling 11 coated with an electrically conductive adhesive 12. The adhesive 12 is then allowed to air dry.

As previously pointed out, when round polystyrene beads having a diameter between 1/32 inch and 3/32 inch are used, electrostatic deposition is possible with the use of an applicator that is not connected to a continuous feed machine. An applicator similar to the one depicted in FIG. 2 can be used in which the deflector 26 is removed and the inlet 24 is covered. The polystyrene beads are placed in the applicator by any suitable means, such as pouring, and when an electrostatic field is set up between the electrode 21 and the electrically conductive adhesive 12, the beads are attracted onto the adhesive surface. Because of the bead size and light weight, no initial particle velocity such as is produced in the continuous feed machine is necessary to convey the beads to the adhesive surface.

The method and apparatus for electrostatic deposition have been described hereinabove for purposes of illustration and are not intended to define the limits of the present invention, the scope of which is defined by the following claims.