WO1992011096A1

WO1992011096A1 - Method and apparatus for coating materials

Info

Publication number: WO1992011096A1
Application number: PCT/US1991/009435
Authority: WO
Inventors: Bruce K. Redding, Jr.
Original assignee: Redding Bruce K Jr
Priority date: 1990-12-17
Filing date: 1991-12-17
Publication date: 1992-07-09
Also published as: AU9159591A; CN1064422A; MX9102620A; IL100399A0

Abstract

This invention is a process and apparatus for the manufacture of coated materials employing the use of an abrupt pressure change to a solution containing the target material and a liquid carrier medium which helps to propagate the pressure change. The material is coated with an impermeable or semi-impermeable film through the use of abrupt pressure change. Coated materials are formed by applying an abrupt pressure change to a liquid medium in which the target material, which could be a fiber, and coating film are immersed. By controlling the intensity and pressure level of the abrupt pressure changes and time of exposure, the thickness and hardness of the resultant coating can be adjusted. The coated materials can be made with several coating layers to increase strength. The invention also includes a method and apparatus for making coated materials in a continuous process in a fraction of the time required by methods of the prior art, and with greater versatility in the coating process.

Description

METHOD AND APPARATUS FOR COATING MATERIALS

TVrhniral Field

This invention relates to the field of making coated materials.

Background Art Coated materials have many applications including filament coatings for electrical applications, soil resistant clothing materials and anti-static carpet materials.

The prior art describes several liquid-phase methods of coating materials whereby a fiber is passed through a liquid bath containing a coating material in suspension or solution within the liquid carrier medium. The fiber is passed through either in bulk or a singular manner, and becomes coated by the material within the bath. Materials within the bath may become deposited onto the surface of the fiber or be soaked into the frame or structure of the fiber, if the fiber is porous or has interstitial voids. The batch coating process of the prior art has many disadvantages:

1. It is difficult to achieve precise control of the thickness of the coating.

2. Inadequate mixing within the bath frequently produces materials which have coatings which are either too thick or too thin, often beyond the size range suitable for the desired application.

3. Inefficiency in the coating process, in that many materials may have incompletely coated surfaces.

4. The coating process can be very time-consuming. The time required to form the coated materials adds significantly to the cost of their manufacture.

5. The prior art methods of making coated materials are limited as to the coating materials which can be applied to the surface of a given fiber. Moveover, it often happens that the fiber material is reactant to the coating material or to crosslinking agents employed in the liquid carrier medium. There is presently a great demand for coated materials which can be inexpensively manufactured and which are suitable for various industrial applications.

The present invention provides a process and apparatus for making coated materials with hardened and solidified coatings which can be produced in a fraction of the time required by prior art methods. The present invention also permits the accurate adjustment of the thickness of the coating layer.

Disclosure of Invention The process of the present invention comprises the use of abrupt pressure changes to form coated materials. The target material which may be a fiber is introduced into a vessel which contains a coating mixture which is then subjected to high intensity abrupt pressure changes. The abrupt pressure change creates coated material, in many cases almost instantly. The coated material can be withdrawn from the vessel before the next length of material is introduced, or the material may be subjected to repeated applications of abrupt pressure changes causing additional layers of coating to be deposited.

The coated material of the present invention may be formed in a continuous, or quasi-continuous process. Pressure changes may be applied by the action of a piston pressure applicator device which impacts upon a mixture of a liquid carrier medium and a coating material in which the target material is immersed. Abrupt pressure changes as a result of the impact generate a pressure effect through the mixture, leading to a layer of the coating material to be deposited on the immersed material. This pressure treatment leads to faster coating processes, the ability to control the thickness of the coating and the solidification of various coatings into a hardened form over the target material. Higher pressure tends to produce thinner coating layers; lower pressure tends to yield thicker coatings. The pressure treatment can also be used to "repair" coated materials, i.e. to complete the layering of coating material so that the coating has a given minimum thickness. i other variations of the invention, the initially-formed coated materials are recycled through the pressure treatment system one or more times, each with a different coating material, and/or a different intensity of pressure change. In this way, it is possible to produce coated materials having multiple coating layers, with varying thicknesses, and each coating may be composed of a different material. Brief Description nf thq Dra ings

Figure 1 depicts a schematic diagram of the preferred embodiment of an apparatus for applying abrupt pressure changes to a mixture of a target material and a coating mixture to form coated materials. Figures 2 depicts a schematic diagram illustrating the pressure treatment device.

Figures 3 and 4 are illustrations of coating effects on either a fiber or a flat surface.

Detailed Description of the Invention And Best Mode For Carrying Out The Invention

The present invention may be employed to coat fibers and other solid materials. The process of the present invention comprises a method for coating solid materials. The coating may be made with a predetermined thickness and/or with multiple layers.

Table 1 below identifies representative materials which may be used with the method and apparatus of the present invention and are not to be deemed to limit the invention. TABLE 1

Some Fiber Coating Chemicals

Natural Polymers

Carboxymethylcellulose Zein

Cellulose acetate phthalate Nitrocellulose

Ethylcellulose Propylhydroxycellulose

Gelatin Shellac Gum Arabic Succinylated gelatin

Starch Waxes, paraffin

Bark Proteins

Methylcellulose Kraft lignin

Arabinogelactan Natural Rubber

Synthetic Polymers

Polyvinyl alcohol Polyvinylidene chloride

Polyethylene Polyvinyl chloride Polypropylene Polyacrylate

Polystyrene Polyacrylonitrile Polyacrylamide Chlorinated polyethylene Polyether Acetal copolymer Polyester Polyurethane Polyamide Polyvinylpyrrolidone Polyurea resins Poly (p-xylylene) Epoxy resins Polymethyl methacrylate

Ethylene-vinyl acetate copolymer Polyhdroxyetyl methacrylate Polyvinyl acetate

Synthetic Elastomers

Polybutadiene Acrylonitrile Polyisoprene Nitrile Neoprene Butyl rubber Chloroprene Polysiloxane

Styrene-butadiene rubber Hydrin rubber Silicone rubber E&ylene-propylene-diene copolymer Other Chemicals

Amino silanes Phenolic resins Acetate resins Sulphides Methacrylate Latexes Mineral or Vegetable oils Fatty Amines Fatty Acids Lubricants Photo resistant chemicals Teflon Soil resistant coating Thermoplastic resins Anti-static coating

The preferred embodiment of the present invention comprises a means of applying an abrupt high pressure, which is induced in a piston apparatus, to a mixture containing a target material or fiber and coating mixture, to induce that mixture to coat the immersed target material.

The coating may be any material which may be cast into a film or gelatinous state within a liquid carrier medium through interaction with solvents.

The coating mixture or solution may be made by providing a micro- dispersed state through any available means, including batch mixers, static mixing devices, motionless mixers, fiuidization or homogenization equipment.

Figure 1 illustrates a pressure treatment apparatus 1 which may be used to apply a pressure change according to the present invention. Fluid reservoir 8 permits materials to be introduced into the apparatus. Target materials, which may be a fiber 22 as shown or some other form of material, are introduced into reservoir 8 which contains coating mixture 18. In some cases the coating material in the mixture may dissolve in the carrier fluid. In the case of fiber 22, a feed spool 23 may be provided to help direct fiber material 22 through apparatus 1. Apparatus 1 may be a modified pneumatic pump system with a piston device (not shown), which may be air powered. Compressed air enters an optional air treatment system and may be a pressure regulator system 4 leading to the air motor 3 in the rear of the apparatus 1. Upstream from the air regulator 4. Pressure regulator 4 is used to control the pressure level of the air motor 3. The pressure gauge 4A indicates the available pressure. Line oiler 5 is used to provide a fine oil mist to the air flow to keep air motor 3 lubricated. A 1/4 turn air valve 6A is placed along the air flow to control the air volume reaching air motor 3. The 1/4 turn air valve 6A is controlled by a manually operated knob 6C which is placed on a scale 6B. The scale 6B indicates a closed and a fully opened air valve.

When the regulator 4 is appropriately adjusted, the air motor 3 drives the piston forward at high speed and under high pressure. Figure 2 is a detailed diagram of the piston applicator apparatus 1. Piston 2 is driven against a quantity of coating mixture 18 which is contained within compression chamber 17 between inlet valve 9 and outlet valve 10.

In both Figures 1 and 2, a fiber is shown as the target material. The fiber 22 is directed by the inlet spool 23 into the reservoir 8 which contains the coating mixture 18 into the compression chamber 17 of apparatus 1. The piston 2 abruptly impacts, on its downward stroke, the coating mixture 18 within the compression chamber 17, generating an abrupt pressure change to the coating mixture 18 and the target material 22.

The result of this pressure change is a deposition of the coating mixture on the target material's surface, a hardening of the coating mixture on the surface of the target material and, in some cases, an embedding or doping of the solution into the void in the surface of the target material.

The pressure shock change is developed as piston 2 is pushed downward by air motor 3. To keep the intensity and power level as high as possible, inlet valve 9 and outlet valve 10 are kept closed for a sufficient period of time to allow the development of an abrupt pressure change within the coating mixture 18, thereby creating a coating film 27 over the target material which is indicated as a coated fiber 26 in both Figures 1 and 2. Examples of liquids which may be used as the liquid carrier mediuπ solvent in the application of the present invention are water, hexane, toluene, cyclohexane, and alcohols.

Li experiments conducted it has also been observed that the abrupt pressure change may be used as part of the hardening process for coated materials, in that the pressure energy produced from the piston's action, through a process known as cavitation, may cause the coating material to become heated through interaction with the ultrasonic transmission. Heat is known as a means to crosslink, solidify or otherwise harden many polymers and coating mixtures which are usable as fiber coating materials. One such example is the use of urea-formaldehyde resins. Cavitation effects may generate enough localized heat energy upon a fiber or other material coated with such heat-reactive polymers to cause such polymers to solidify, thus completing the coating process. In many cases, pressure treatments may be used not only to form coated materials themselves, but to provide an aid in the hardening process of other conventional liquid phase methods of coating.

The fiber 22 is drawn through the compression chamber 17 of the pressure applicator apparatus 1 by a mechanical or electric motor (not shown). Upon exiting apparatus 1, the fiber 22 is coated. The speed of the fiber's flow through apparatus 1, and the intensity of the pressure change determines the thickness of the resultant coating and the degree of solidification for the coating mixture onto the surface of the fiber.

The Figures show a means for drawing a fiber under continuous or semi-continuous motion through the pressure applicator apparatus for the purpose of effecting a coating of the fiber. To effect this coating process, fiber 22 is drawn into compression chamber 17 past inlet valve 9. The valves are then locked as piston 2 is forced into compression chamber 17, generating an abrupt pressure change in the coating mixture 18 in which fiber 22 is immersed. The valves 9 and 10 may be kept closed for additional pressure treatments by repeated cycling of piston 2. Each recycle of piston 2 generates additional pressure changes which act to further solidify the coating mixture onto the fiber's surface, to thin the coating layer or to apply additional coatings onto the original coating layer. In this manner it is possible to use more than one coating mixture to form different shell layers over the target material's surface. Once the fiber is properly coated, with the proper shell layer 27 or multiple shell layers, the coated fiber 26 is drawn from the apparatus 1. Examples of fibers for coating purposes include, but are not limited to:

Clothing fibers

Carpet fibers, with soil, and anti-static coatings Optical or light transmitting fibers Additional target materials may include any material which is inserted between the inlet valve 9 and outlet valve 10 while the coating mixture 18 is subjected to an abrupt pressure change by the action of piston 2. EXAMPLE 1: Starch-Coated Nylon Fiber A nylon fiber is inserted into the compression chamber 17 of apparatus 1. The apparatus consisted of a pneumatic pump, supplied by S.C. Hydraulic Supply Company, and known as model number SC10-500-8-SI. The device contained spring-loaded check valves as illustrated in Figure 2. The tension on the outlet check valve was tightened to alter the normal opening timing sequence. Normally the pump would have drawn a solution into the compression chamber through inlet check valve 9 as the piston 2 is raised. Then, with the downward action of the piston 2, the inlet valve closes and the outlet valve 10 would open, exiting the solution from the pump. With an adjustment of the tension in the spring of the outlet valve 10, the action is altered so that the outlet valve 10 stays closed longer, instead of immediately opening, as piston 2 strikes downward. This helps to generate the required pressure change.

25 grams of Capsul Starch supplied by National Starch Company, is dispersed in a 1 liter glass beaker under mild agitation using an electric stirrer, then heated to 65'C for 30 minutes, forming a coating mixture of the modified starch in water. 50 ml of this solution is thai placed into reservoir 8 and drawn into compression chamber 17 through just two stroke cycles. The fiber, which was sized in a 1/2 inch length, was then removed from the compression chamber and allowed to cool to ambient temperature. A second fiber of the same material and length was placed in another beaker containing 50 ml of the starch/water solution and stirred for one full hour under moderate agitation. The two fibers were then compared for the effectiveness of the coating processes. The pressure-treated fiber had a more even and uniform coating, a harder or more solidified coating forming a shell over its surface than did the stir-coated fiber.

The pressure-treated fiber, which was locked in place for one stroke of the pump device, which took only two seconds to accomplish, was found to be immediately coated upon removal from the compression chamber. Figure 3B illustrates the product created by this experiment, indicating that the fiber 22 was totally and completely coated, encapsulating the circumference of the fiber. In fact, the leading and trailing edges of the fiber 22 were also coated. EXAMPLE 2; Starch-Coated Nylon Fiber with Multiple Coating Layers The procedure of Example 1 was repeated in all aspects except that the fiber 22 was subjected to repeated pressure treatments as the piston was re¬ cycled for a total of 10 strokes, over a period of approximately 20 seconds.

Upon removal from the compression chamber the pressure coated fiber, again compared to the stir-coated fiber and the fiber made in Example 1, was found to have a thicker coating which had solidified in several individual shell layers 27A and 27B as illustrated in Figure 4B.

EXAMPLE 3: Stpirh-Crø-_ltf Gins The procedure of Example 1 was repeated except that a 1.0 inch glass slide was used instead of the fiber, placed horizontally within the compression chamber of the pump device. This produced a surface coating 27 on the slide 30 of the starch film as illustrated in Figure 3A, with a surface coating 27 on just one side of the glass slide 30. By repositioning the glass slide to a vertical configuration within the compression chamber, a two-sided coating was produced along both faces of the slide, with another coating on the top surface, which was directly under the path of the piston. Figure 3B illustrates the double-face coating provided by the vertical alignment configuration within the compression chamber.

EXAMPLE * Stareh-Coated Glass (two-sided) The procedure of Example 2 was reproduced using the glass slide made in Example 3 instead of the coated fiber, with the glass slide placed horizontally within the compression chamber, producing a coating with two distinct layers as indicated in Figure 4A. Rotating the position of the glass slide to a vertical configuration resulted in a coating of both faces of the slide and the top edge as well, corresponding to the illustration provided in Figure 4B.

Statement of Industrial Utility The present invention may be useful in the application of uniform coatings to fibers and other materials.

Claims

We claim:

1. A method of coating a first material with a second material comprising the steps of preparing a mixture which includes a liquid carrier medium and a first material, immersing the second material in the mixture, and subjecting the mixture to an abrupt pressure change causing the second material to form a coating on the first material.

2. The method of Claim 1, wherein the abrupt pressure change is applied for a period of one second or less.

3. The method of Claim 1 wherein said abrupt pressure change is applied repeatedly.

4. A method of making coated materials, comprising the steps of: a) mixing a material and a coating mixture in a liquid carrier medium, b) agitating the mixture until an initial coating begins to form, and c) applying one or more abrupt pressure changes to the mixture, said changes being applied in a sufficient intensity and for a sufficient time to complete the coating process of the partially formed coated materials.

5. A method and apparatus employing the use of abrupt pressure changes as a hardening aid for coating mixtures applied to the surface of a target material which is intended to become coated by said coating mixture, whereby heat energy generated by abrupt changes in pressure applied to the coating mixture, acts to cause heat-reactive materials within the coating mixture to solidify into a final hardened coating over the surface of the target material.

6. Apparatus for coating materials, comprising: a) means for storing a mixture of materials and coating materials, b) a processing chamber, fluidly connected to the storing means, the processing chamber also being connected to means for generating abrupt pressure changes within said chamber, and c) means for conveying the coated material out of the chamber.

7. An apparatus according to Claim 6 wherein said processing chamber is an internal chamber of a pump, and said pressure change generating means is a piston, impeller, or other similar pumping member, and wherein said chamber is isolated from said storage means and said conveying means by a pair of closed valves

8. An apparatus according to Claim 7 whereby the mixture of materials and coating materials is drawn into and from the processing chamber on a continuous, semi-continuous or batch loading manner.

9. The method of Claim 1, wherein the step of subjecting the mixture to an abrupt pressure change is performed at differing levels of intensity, to obtain different coating thicknesses in the resultant coated material.

10. A method of applying multiple coating layers to a target material comprising the following steps: a) preparing a mixture of coating material in a liquid medium, b) immersing a target material in the coating mixture, c) applying one or more abrupt pressure changes to effect an initial coating of the target material, d) delivering the coated materials made according to steps a, b, and c above into another coating mixture containing a different coating substance from that employed in step a. e) applying one or more subsequent pressure pulses to the second mixture to effect a resultant material which has at least two distinct coating layers, composed of two different coating substances.

11. The method of Claim 10, wherein additional layers of coating substances are placed on a target material by repeating steps d and e.

12. The coated material product made by the method of Claim 1.