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Two component powder coating system and method for coating a heat sensitive substrate therewith

Inactive Publication Date: 2000-06-20
ROHM & HAAS CHEM LLC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

It is a related object of this invention to provide a method for coating wood without the problems associated with volatile organic solvents.
It is another object of this invention to provide a low temperature process for producing a smooth, low gloss coating on wood.

Problems solved by technology

The curing of powder coatings on heat sensitive materials such as wood, plastic, and the like has been limited by the fact that the extrusion of a mixture of a resin and a low temperature curing agent, i.e., one that is active at 200.degree. F. or less, would cause the coating powder to gel in the extruder because the extrusion typically generates enough heat to raise the temperature to 200.degree. F. or higher.
Such a resin tends to block during storage at normal temperatures.
But that leads to a possible thermosetting of the resin in the extruder.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

examples 1-4

AND CONTROL

Coating powders were made as described above from the following components:

______________________________________ COMPONENTS (A) RESIN (A) (B) WITH RES- (A**) PIG- CATAL- IN CRY- MENT (B*) YST & PIG- STAL- CUR- CAT- PIG- MENT LINE ING AL- MENT ONLY EPOXY AGENT YST ______________________________________ Crystalline Epoxy RSS -- -- 50 -- -- 1407 Epoxy Resin GT-7072 100 100 50 -- -- Imidazole Adduct P-101 2 -- -- -- 100 Acrylate Flow Acid 1.4 1.4 1.4 1.4 -- Benzoin .8 .8 -- .8 -- Pigments .079 .079 -- .079 -- TiO.sub.2 R-902 60 60 -- 60 -- Amine Adduct LMB- -- -- -- 100 -- 5218 UVI 6974 Catalyst* -- -- 2 -- -- ______________________________________ *substantially nonfunctional under these conditions

TABLE 1 ______________________________________ Control 1 2 3 4 Coventional Extrusion ______________________________________ Component A 70 -- 100 -- 100 Component A* -- 70 -- -- -- A** -- -- -- 70 -- Component B 30 30 -- -- -- Component B* -- -- 3 -- -- LMB 5218 adduct -- -- -- 30...

examples 11-15

The coating powders of Examples 9 and 10 were deposited on pre-heated wooden panels by tribocharging guns and post-heated on a flat-line conveyor in an oven heated by IR and convection heating according to the conditions given in Table 5 wherein the results are given also.

TABLE 5 __________________________________________________________________________ Board Line Speed Temperature Line Speed in Actual Temp. Mek Rate 50 Ex. # Powder Substrate of Coating Before Coating Curing Oven Exiting IR Appearance Double Rub Thickness __________________________________________________________________________ 11 Ex. 9 MDF 30 ft / min 290 (.degree.F.) 15 ft / min 290.degree. F. Good #4 5 mils 12 Ex. 9 UV-P* 30 ft / min 280 (.degree.F.) 15 ft / min 300.degree. F. Very good #4-5 5 mils 13 Ex. 9 UV-P* 100 ft / min 290 (.degree.F.) 15 ft / min 290.degree. F. No pinholes #4-5 3+ 14 Ex. 9 MDF Hand spray 280.degree. F. 5 ft / min 280.degree. F. Very slightly yellow -- -- Smooth 15 Ex. 10 MDF 20 ft / min 280.degree. F. 5...

examples 16-18

The coating powder of Example 16 is the same as that of example 1 except for the addition of 0.1 part by weight of an optical brightener to both Components A and B. The coating powder of Example 17 is the same as that of Example 16 except for the addition of 1.0 part by weight of IRGAFOS 168 anti-oxidant to both Components A and B of the powder of Example 16. The coating powder of Example 18 is the same as that of Example 16 except for the addition of 1.0 part of IRGANOX 1425 to both Components A and B of the powder of Example 16. A coating powder of Comparative Example 1 is the same as the powder of Example 16 except for the addition of 1.0 part of IRGANOX 1098 to both Components A and B of the powder of Example 16. The powders of Examples 9 and 16-18, as well as the powder of the Comparative Example were deposited by a hand-operated tribocharging gun on to a surface of a 0.5 inch thick wooden panel whose temperature was about 230.degree.-250.degree. F. and then cured at 300.degree...

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Abstract

[Wood] A heat sensitive substrate is [electrostatically] coated with a thermosetting powder coating system in which a mixture of a self-curing epoxy resin and a catalyst therefore is extruded and pulverized and a low temperature curing agent [are both] a pulverized and the powders are blended with conventional additives to make a coating powder which is deposited on [a wooden] the substrate and heated to cure. The mixture of resin and catalyst does not cure within the extruder but it is made to cure at low temperatures by the separate addition of the curing agent. A small amount of the low temperature curing agent, insufficient to cause substantial curing during extrusion may be used in place of the catalyst.

Description

BACKGROUND OF THE INVENTIONThis invention relates to a two-component powder coating system by which the curing of a coating occurs at a significantly faster rate and / or at a significantly lower temperature and produces an exceptionally smooth surface. This invention also relates to thermally stable powder coating whereby white coatings do not yellow during thermal curing. This invention also relates to the electrostatic coating of metal and, in particular, to the triboelectric coating of wood with a coating powder and low temperature curing of that coating having a pleasing smoothness.Traditionally, coating powders have been made by the extrusion of a mixture of resins and curing agents to obtain a homogeneous mixture and then grinding the extrudate and screening the comminuted product to obtain the desired particle sizes and particle size distribution. The powder is then electrostatically sprayed onto a substrate, traditionally a metal substrate, and cured at temperatures much high...

Claims

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Application Information

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IPC IPC(8): C08G59/68C08G59/18C08G59/00C09D163/00B05D1/06B05D3/02C08G59/50C09D5/03
CPCB05D1/06C09D163/00C08G59/182C08G59/184C08G59/50C08G59/686C09D5/03C08G59/18B05D3/0218B05D3/0227B05D3/0254B05D3/0263Y10T428/31511Y10T428/662
Inventor CORRELL, GLENN D.DALY, ANDREW T.KOZLOWSKI, JOSEPH J.HALEY, RICHARD P.MUTHIAH, JENOHORINKA, PAUL R.REINHEIMER, EUGENE P.
Owner ROHM & HAAS CHEM LLC
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