FORMULATIONS FOR ELECTROSTATIC SPRAY ON NONCONDUCTIVE SUBSTRATES

Abstract

A conductive substance for the promotion of adhesion of liquid and powder coatings to non-conductive substrates is provided that includes a solvent. A chlorinated polyolefin dispersed is dispersed in the solvent along with conductive nanoparticulate. A process of applying a conductive adhesion promoter to a non-conductive substrate is also provided that includes the application of this conductive adhesion promoter to a non-conductive substrate. The surface resistivity the substrate with a cured, dried film of the conductive adhesion promotor is less than 10.sup.6 Ohm/Square. The conductive adhesion promotor cures and dries at an ambient temperature of 20 C. (1 atm) in 3-8 minutes. A dried film on a non-conductive substrate is also provided that has a cured matrix of chlorinated polyolefin in which conductive particulate is dispersed.

Claims

1. A conductive substance for the promotion of adhesion of liquid and powder coatings to non-conductive substrates, comprising: a solvent; a chlorinated polyolefin dispersed in said solvent; and conductive nanoparticulate dispersed in said solvent.

2. The conductive substance of claim 1 wherein further comprising an adhesion promoter for said chlorinated polyolefin.

3. The conductive substance of claim 1 wherein said conductive nanoparticulate comprises 0.2-0.6 total weight percent of multiwalled carbon nanotubes.

4. The conductive substance of claim 1 wherein conductive nanoparticulate comprises 0.05-0.33 total weight percent of single-walled carbon nanotubes.

5. The conductive substance of claim 1 wherein conductive nanoparticulate comprises up to 4 total weight percent of graphene.

6. The conductive substance of claim 1 further comprising a self crosslinkable polymer.

7. A process of applying a conductive adhesion promoter to a non-conductive substrate, the process comprising: applying the conductive adhesion promoter of claim 1 to treat the non-conductive substrate and make a treated substrate with a surface resistivity of less than 10.sup.6 Ohm/Square; and drying and curing the treated substrate at ambient temperature for 3-8 minutes.

8. The process of claim 7 wherein the non-conductive substrate is at least one of: wood-plastic composite, polycarbonate (PC), Polycarbonate (PC)/acrylonitrile butadiene styrene (ABS), particle board, laminated board, trim board, ceramic tiles, concrete, glass or medium-density fiberboard (MDF).

9. A dried film on a non-conductive substrate, the dried film having a thickness and comprising: a cured matrix of chlorinated polyolefin; and conductive particulate dispersed in said cured matrix.

10. The dried film of claim 9 wherein the thickness is between 4-25 microns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0014] The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0015] FIG. 1A shows an uncoated polycarbonate/ABS composite;

[0016] FIG. 1B shows a polycarbonate/ABS composite coated with a UV curable powder coating in accordance with an embodiment of the invention;

[0017] FIGS. 2A-C shows an uncoated wood-plastic composite (WPC) in front (FIG. 2A), back (FIG. 2B), and side (FIG. 2C) views;

[0018] FIGS. 2D-E shows the wood-plastic composite of FIGS. 2A-C with a partial UV curable powder overcoating over an inventive dried film in accordance with an embodiment of the invention in front (FIG. 2D), back (FIG. 2E), and side (FIG. 2F) views; and

[0019] FIG. 3 illustrates the results of a pull off adhesion test in accordance with an embodiment of the invention.

DESCRIPTION OF THE INVENTION

[0020] The present invention has utility as a substance and treatment for the promotion of adhesion of liquid and powder coatings to plastics, thermoplastic polyolefins, and other non-conductive substrates. Embodiments of the invention provide rapid drying conductive adhesion promoters (CAPs) that improve adhesion of powder and liquid coatings to nonconductive substrates illustratively including acrylonitrile butadiene styrene (ABS), polycarbonate, Noryl GTX, SMC, and polyolefinics, etc. Embodiments of the inventive CAPs improve transfer efficiency by dissipating static charge. The ability of embodiments of the inventive CAP to dry quickly permits application in a continuous/conveyorized production line followed by the application and curing of powder and liquid coatings to the CAP treated substrate. The use of CAPs in the substrate coating process eliminates the need for preheating, plasma treatment and chemical etching of plastic substrates while improving both film appearance and application efficiency. UV curable powder as well as low temperature cure (LTC) powder and liquid coatings can now be electrostatically applied uniformly even in recess areas and faraday cage areas. Embodiments of the inventive CAPs utilize novel conductive materials in conjunction with a polymeric adhesion promoter and at the same time improves flexibility and interfacial adhesion along with anti-static properties.

[0021] In embodiments of the invention, amount of chlorinated material in an adhesion promotor determines the compatibility with various paint systems. Once the chlorinated polyolefin (isotactic polypropylene) is dispersed with conductive nano particles to form the CAP, the CAP associates with plastics and composite substrates via dispersion interaction and thus adheres to the substrate. Chlorinated material and grafted functional groups (maleic-anhydride) add polarity to the CAP which promotes interfacial adhesion to substrate and a powder or liquid top coat.

[0022] The following are some of the benefits of using the inventive CAPs: [0023] CAPs ensure sufficient dissipation of electric charge of negatively or positively charged powder particles applied by electrostatic spray equipment (corona or tribo respectively) as well as promote interfacial adhesion. [0024] CAPs work more efficiently at lower film thickness on non-porous substrates. On porous substrates higher film thickness may be required since some of the material would be absorbed by porous substrate. [0025] CAPs enable successful application of powder coating on various plastic composites (uniformity, film formation, ability to coat recess areas, etc.). [0026] CAPs can significantly increase transfer efficiency of applying liquid or powder coating to plastic composites having a complex geometry.

[0027] It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

[0028] The CPO (chlorinated polyolefin) may be solvent or water based. Conductive nano particulate operative herein illustratively includes graphene, carbon nano tubes (multiwalled as well as single walled), and metallic nanoparticles having a mean particle size of 2 to 200 nm. There may be a need to add a surfactant, a dispersing agent, coalescing agent, deaerator, polyaziridine or carbodiimide type crosslinker and a stabilizer to achieve fine and stable dispersion of carbon nano tubes and/or graphene when using waterbased CPO as well as desired mechanical and physical properties like early hardness, adhesion and chemical properties like Methyl Ethyl Ketone or solvent resistance.

Application of CAP and Powder Coating:

[0029] CAPs (solventborne or waterborne) were applied on substrates including wood-plastic composite, polycarbonate (PC)/ABS, and MDF and polypropylene substrates at 10-25 microns dry film thickness using a high-volume low pressure (HVLP) spay gun at 20 psi air pressure at the nozzle. The treated substrates were dried and cured at ambient temperature of 20 C. (1 atm) for 2-5 minutes for solventborne CAP and 5-8 minutes for waterborne CAP.

[0030] UV curable smooth, white epoxy powder coating was applied using an electrostatic spray gun on substrates coated with CAP. FIG. 1A shows an uncoated polycarbonate/ABS composite, while FIG. 1B shows a polycarbonate/ABS composite coated with a UV curable powder coating. FIGS. 2A-C shows an uncoated wood-plastic composite (WPC), while FIGS. 2D-E shows a wood-plastic composite with UV curable powder overcoating over an inventive dried film on the same WPC substrate shown in FIGS. 2A-C.

[0031] The present invention is further detailed with respect to the following non-limiting examples. These examples are exemplary of specific embodiments of the present invention and not intended to limit the scope of the appended claims. Unless otherwise specified, amounts are provided in total weight percentages.

EXAMPLES

Example 1

[0032] An inventive composition is provided and designated as SB-CAP1 and includes 10-25% CPO. 0.1-0.4% conductive nano particle, 25-65% Xylene and 3-10% Ethyl Benzene.

Example 2

[0033] An inventive composition is provided and designated as WB-CAP1 and includes 10-35% CPO, 0.23-0.4% conductive nano-particle and 25-65% water.

Example 3

[0034] An inventive composition is provided and designated as WB-CAP2 and includes 25-55% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 25-65% water.

Example 4

[0035] An inventive composition is provided and designated as WB-CAP3 and includes 23.5-53.78% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 25-65% water and 1-3% polyaziridine.

Example 5

[0036] An inventive composition is provided and designated as WB-CAP4 and includes 23.5-53.78% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 25-65% water, 1-3% polyaziridine and 1-5% -(3,4-epoxycyclohexyl) ethyltrialkoxysilane.

Example 6

[0037] An inventive composition is provided and designated as WB-CAP5 and includes 23.5-53.78% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 25-65% water and 0.25-4% -(3,4-epoxycyclohexyl) ethyltrialkoxysilane.

Example 7

[0038] An inventive composition is provided and designated as WB-CAP6 and includes 23.5-53.78% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 25-67.34% water and 1-13.3% CPO.

Example 8

[0039] An inventive composition is provided and designated as WB-CAP7 and includes 23.5-53.78% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 15-51.79% water and 1-13.3% CPO.

Example 9

[0040] An inventive composition is provided and designated as WB-CAP8 and includes 23.5-52.33% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 15-51.79% water and 1-13.3% CPO.

Example 10

[0041] An inventive composition is provided and designated as WB-CAP9 and includes 23.5-52.33% self crosslinkable aliphatic polymer, 0.33-0.5% conductive nano-particle, 15-51.79% water and 0.01-5% 2,2,4-Trimethyl-1,3-pentanediol monoisobutyrate.

[0042] Table 3 summarizes the results of crosshatch adhesion test and pull-off adhesion test of WBCAP variations 1-9 described in examples 2-10.

TABLE-US-00003 TABLE 3 ASTM D3359 Crosshatch adhesion (1 mm) and ASTM D4541 Positest AT-A Pull off adhesion test ASTM D4542 Positest pull-off ASTM D3359 Crosshatch adhesion adhesion test (bond strength in test (1 mm crosshatch) pounds per square inch.) WB-CAP Variations Polypropylene Polycarbonate Polypropylene Polycarbonate WB-CAP1 0B 1B 99 177 WB-CAP2 0B 0B NA (coating 134 delaminated) WB-CAP3 0B 0B 334 136 WB-CAP4 0B 0B 214 167 WB-CAP5 0B 0B 229 221 WB-CAP6 5B 5B 390 421 WB-CAP7 5B 5B 365 395 WB-CAP8 2B 5B 358 220 WB-CAP9 2B 5B 251 197

Example 11

Melting and Curing Schedule of UV Curable Powder Coating:

[0043] UV curable powder was melted first at 120 C. for 3-4 minutes and then cured using conveyorized UV oven having medium pressure H-bulb in 2 passes with a total UV dosage of 3,451 mJ/cm.sup.2.

Example 12

[0044] A pull off adhesion test was carried out to determine interfacial adhesion. Multiple adhesion tests with 20 mm dollies were carried out to determine interface of the coating failure and the force/area at which failure happens. Dry film thickness of CAP and cured powder coating was measured using Positector B100, ultrasonic film thickness gauge. Table 4 summarizes the results of the pull off adhesion test.

TABLE-US-00004 TABLE 4 ASTM D4541 Positest AT-A Pull off adhesion test Conduc- DFT DFT of CAP/ CAP/ tivity of Powder Sub- Powder Sub- agent CAP Coating strate coating Type of strate loading (%) () () interface interface failure WPC 0.33 11-25 51 No failure No failure Cohesive, powder coating PC/ 0.33 10-25 45 No failure No failure Cohesive, ABS powder coating

[0045] FIG. 3 illustrates the results of the pull off adhesion test showing cohesive failure of powder coating on wood-plastic composite after positest pull-off adhesion test. As shown in the figure there is cohesive failure of the powder coating, with no adhesive failure at the CAP/substrate or CAP/powder coating interface.

[0046] The foregoing description is illustrative of particular embodiments of the invention but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.