WO1983004195A1

WO1983004195A1 - Epoxy coating powders with wrinkle finishes

Info

Publication number: WO1983004195A1
Application number: PCT/US1983/000814
Authority: WO
Inventors: Dean Schreffler
Original assignee: The Polymer Corporation
Priority date: 1982-05-24
Filing date: 1983-05-24
Publication date: 1983-12-08
Also published as: EP0110968A1

Abstract

An epoxy coating powder applied in a fusion coating process that yields a low gloss, wrinkled finish. The coating composition is a heat reactive epoxy resin in which the wrinkled finish results from the use of methylene disalicylic acid as the curing agent for the epoxy resin. Adjustment of the inclined plate flow alters the appearance of the wrinkle pattern.

Description

Epoxy Coating Powders With Wrinkle Finishes

Technical Field

This invention relates to coatings applied by fusion coating processes and more particularly to epoxy coating powders that yield wrinkled finishes.

Background Art

The coating compositions of this invention are dry, free flowing powders that may be used in fusion coating processes. "Fusion coating processes" are here defined as those coating processes in which coating powders are distributed over a substrate (which may be hot or cold) and heat, supplied from the substrate or an external source, fuses the powders into a continuous film. Examples of fusion coating processes include fluidized bed, electro statis spraying, hot flocking (with or without electro static spray), and cloud chambers. When coating powders are based upon heat curing resins, as is the case of the epoxy resins of this invention, sufficient heat in excess of that required to fuse the powders must be available to cure the coatings and fully develop their physical and chemical properties.

The coating compositions of this invention are distinguished in that when coated onto a substrate, they produce coatings of low gloss with a randomly developed wrinkled surface. Wrinkled surfaces of this type are desired in many applications and are commonly applied to office equipment such as typewriters, staplers, dictating equipment, file cabinets, and the like. In addition to being asthetically pleasing, these finishes have certain utilitarian functions in that they are of low gloss (i.e., not shiny), they do not show scratches, and they hide surface defects of a substrate even when applied in thin films.

Wrinkle finishes conventionally are applied from solvent-based paints, usually using two coats, to establish a compound system in which the surface sets up first. When the rest of the coating sets up, the resulting shrinkages deform the previously set surface and cause a fine wrinkle pattern to develop on the surface of the coating. In co-pending application Serial No. 220,709, filed on December 29, 1980, of common assignee, which application is incorporated herein by reference, it is disclosed that epoxy coating powders can be formulated to provide coatings having low gloss and a randomly developed wrinkle pattern. This is accomplished through the use of a methylene disalicylic acid curing agent. The application teaches that the gel time of the coating powders should be adjusted to be in a range of from about 30 to 70 seconds when measured at 205°C. and the inclined plate flow should be in a range of from about 50 to 80 mm when measured at 150ºC. It has now been found that satisfactory wrinkle finishes can also be obtained outside of these ranges and, more specifically, that the appearance of the wrinkle can be altered by adjusting the inclined plate flow over a range of from about 30 to 130 mm. At the lower end of this range, the wrinkle pattern is tighter and more subdued; whereas, at the upper end of the range, the wrinkle pattern is more open and somewhat more pronounced. It has also been found through thermographic analysis that a two-stage reaction apparently takes place that can be identified by two exothermic peaks. Further, the temperature difference between these peaks effects the wrinkle pattern. For example, when a boron trichloride amine complex is used as a catalyst in combination with the methylene disalicylic acid of this invention, the boron trichloride catalyst provides a characteristic peak at about 152ºC. to 156ºC. and the methylene disalicylic acid provides a second peak in a useful range of about 182°C. to 186°C. It is generally true that the gel time and the inclined plate flow are a direct function of molecular weight and functionality of the epoxy resin. Melt viscosity and the inclined plate flow are also influenced by fillers which generally increase the viscosity depending on the amount used, the particle size, the surface area and the surface chemistry of the fillers. By judiciously balancing the functionality and the molecular weight of the resin in combination with the selection of the curing agent, catalyst system, and fillers, it is well within the skill of a formulating chemist to arrive at a coating powder that has gel times and inclined plate flows that will be useful in the practice of this invention. In the examples that follow, the epoxy resins used are type 3, low viscosity epoxy resins. More specifically, they are epoxies of the epichlorohydrinbisphenol-A type having epoxy equivalent weights of from about 600 to 750, a functionality of about 2, and a Gardner-Holdt viscosity in a range of from about K to L. The catalyst used in the examples is a boron trichloride amine complex. The acid methylene disalicylic/curing agent is used.in approximately stoichiometric quantities. Having defined the above parameters, final adjustment of the gel time and inclined plate flow can be obtained by the selection of the particle size, shape, surface chemistry and amount of fillers, including the pigments, used in the system.

EXAMPLE I

A coating powder was prepared in accordance with this invention by initially blending the following ingredients: Material Phr*

1. Epoxy low viscosity-type 3 100 (Ciba Geigy Aral 9539)

2. Epoxy type 3 with 5% 15 polyalkylacrylate flow promoter

(Shell DRH-203)

3. Methylene Disalicylic Acid 18

(Tenneco)

4. Sparmite (BaSO₄) filler 30 5. Blue pigment 5 Example 1 (continued)

Material Phr*

6. BCl₃ amine catalyst 0.6

*Phr is used herein to designated parts by weight per hundred parts resin.

The above materials were melt-mixed in an extruder and the extrudate chopped and ground to a fine powder that was passed through a 60 mesh screen (U.S. standard).

Precleaned steel test panels (from "Q" Panel Co.) of about 3" x 6" x 0.032" (7.6 cm x 15.2 cm x 0.08 cm) were coated using standard electrostatic spray techniques and baked in an oven at a temperature of about 190ºC. for 10 minutes. There is no great criticality to the time and temperature of the cure and quite generally a useful range with the above formulation is from about 150°C. at 20 minutes to about 200ºC. for 10 minutes.

The coating powder had a gel time of 36 to 60 seconds and an inclined plate flow of 35 to 85 mm. At the lower end of the glass plate flow, a well developed, random finely wrinkled surface was produced; however, the pattern was tighter and more subdued than usually observed with powders having higher glass plate flows.

EXAMPLE II

The following ingredients were mixed, a coating powder was prepared and panels were coated in a manner identical to Example I.

Material Phr*

1. Epoxy low viscosity, type 3 100

2. Methylene Disalicylic Acid 18 (Tenneco)

3. Silicone Oil 0.4 (Mobay Bay Silone 0:1)

4. Fumed Silica 0.1 (DeGussa Aerosil 380) 5. BCl₃ amine catalyst 0.6

(Ciba Geigy XU-213) The difference between this example and Example I is that the gel time was 35 to 55 seconds and the inclined plate flow was 80 to 110 mm. As a result, coatings made with the powder of Example II yielded a coating with a more open and more pronounced wrinkle pattern.

Claims

1. A powdered coating composition adapted to provide a wrinkled finish, comprised of a heat reactive epoxy resin, a curing agent, a catalyst, and fillers, the improvement being that the curing agent is methylene disalicylic acid and the catalyst is a boron trichloride amine complex.

2. A powdered coating composition according to Claim 1 wherein the inclined plate flow is in a range of from about 30 to 130 mm.

3. A powdered coating composition according to

Claim 1 in which the gel time is in a range of from about

30 to 70 seconds.

4. A method for obtaining a wrinkled surface when coating a substrate in fusion coating processes with heat reactive epoxy resins, the improvement comprising the use of methylene disalicylic acid as the curing agent and a boron trichloride amine complex.