Two-step coating process

• US 3,935,330 A
• Filed: 12/08/1971
• Issued: 01/27/1976
• Est. Priority Date: 12/08/1971
• Status: Expired due to Term

• Current Assignee: Union Carbide Corporation (Dow, Inc.)
• Original Assignee: Union Carbide Corporation (Dow, Inc.)
• Inventors: Smith, Oliver W., Carder, Charles H., Trecker, David J.
• Primary Examiner(s): Gwinnell, Harry J.
• Application Number:
  US05/205,855
• Time in Patent Office: 1,511 Days
• Field of Search: 117/93.31, 117/161 ZB, 117/161 LN, 117/161 UC, 117/161 UB, 117/161 UT, 117/119, 117/DIG. 3, 204/159.15, 204/159.19, 260/851, 260/856, 260/837, 96/115 P
• US Class Current: 427/487
• CPC Class Codes: B05D 3/0209 Multistage baking
• CPC Class Codes: B05D 3/067 Curing or cross-linking the coating
• CPC Class Codes: B05D 3/068 using ionising radiations (gamma, X, electrons)
• CPC Class Codes: C08F 222/102 of dialcohols, e.g. ethylene glycol di(meth)acrylate or 1,4-butanediol dimethacrylate
• CPC Class Codes: C08G 59/18 Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
• CPC Class Codes: C08L 33/00 Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 61/20 Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen with aminophenols C08L61/04
• CPC Class Codes: C08L 63/00 Compositions of epoxy resins; Compositions of derivatives of epoxy resins
• CPC Class Codes: C09D 4/00 Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16

Abstract

Coating compositions are cured by initially treating them for a brief period with ionizing or non-ionizing radiation whereby they are partially cured and then completing the cure by a thermal treatment. This two-step process decreases the amount of volatiles escaping into the atmosphere and it also permits the use of compounds not useful in the past and allows significant improvement in film properties such as adhesion to metal. The initial radiation cure can be with electron beam, ultraviolet mercury lamp, plasma arc or other radiation means; the thermal cure is carried out by any heat means.

Claims

1. A method for coating a substrate which comprises the steps of

A. applying a fluid coating composition to said substrate, said fluid coating composition comprising

a. from 0.1 to 50 weight per cent of a thermally curable reactive thermoset crosslinker selected from the group consisting of:

i. a polyfunctional epoxide having at least two oxirane units,

ii. the polyoxirane-containing low molecular weight polymers of (i),

iii. a urea/formaldehyde resin, or

iiii. a melamine/formaldehyde resin,

b. from 0.1 to 50 weight per cent of a radiation and thermally curable reactive solvent selected from the group consisting of;

i. an acrylate or methacrylate of a monofunctional or polyfunctional alcohol, or

ii. an acrylamide or methacrylamide of a monofunctional or polyfunctional amine, said solvent having both at least one vinyl polymerizable double bond and at least one thermally sensitive hydroxyl, carboxyl, amino or oxirane group, and

c. the balance thereof being a radiation sensitive reactive component of the formula ##EQU4## wherein X is hydrogen or methyl;

aryl is phenyl or substituted phenyl;

z has a value of 1 to 4;

when z is 1, Y is monovalent cycloalkyl of 5 to 12 carbon atoms, cycloalkenyl of 5 to 12 carbon atoms, --C_m H_2m H, --C_m H_2m CN, --C_m H_2m Cl, --C_m H_2m NR₂ ", --C_m H_2m COONR₂ ", --C_m H_2m COOCH₂ OCH₂ CH₃, or --(C_p H_2p O)_r C_p H_2p H, when z is greater than 1, Y is --C_q H_2q --, --(C_p H_2p O)_x C_p H_2p --, --(C_y H_2y COO)_x C_y H_2y --, --C_q H_2q^-1 --, or --C_q H_2q^-2 --;

R" is hydrogen or alkyl of 1 to 5 carbon atoms;

m has a value of 1 to 10;

r has a value of 0 to 4;

p has a value of 2 to 4;

q has a value of 2 to 8;

x has a value of 1 to 5; and

y has a value of 2 to 5;

B. subjecting said applied coating composition to ionizing or non-ionizing irradiation to initiate free-radical polymerization of components (b) and (c) and thereafter

C. subjecting the coated article of step (B) to elevated temperature of from 50°

to 250°

C. to thermally cure components (a) and (b) and obtain a solid, dry coating on said substrate.

2. A method for coating a substrate as claimed in claim 1 wherein said coating composition comprises:

a. from 0.1 to 50 weight per cent of a thermally curable reactive thermoset crosslinker selected from the group consisting of;

i. a polyfunctional epoxide having at least two oxirane units,

ii. the polyoxirane-containing low molecular weight polymers of (i),

iii. a urea/formaldehyde resin, or

iiii. a melamine/formaldehyde resin,

b. from 0.1 to 50 weight per cent of a radiation and thermally curable reactive solvent selected from the group consisting of;

i. an acrylate or methacrylate of a monofunctional or polyfunctional alcohol, or

ii. acrylamide or methacrylamide of a monofunctional or polyfunctional amine, said solvent having both at least one vinyl polymerizable double bond and at least one thermally sensitive hydroxyl, carboxyl, amino or oxirane group.

3. A method for coating a substrate as claimed in claim 2 wherein said coating composition additionally contains (c) a radiation sensitive reactive component of the formula:

##EQU5## wherein X is hydrogen or methyl;

aryl is phenyl or substituted phenyl;

z has a value of 1 to 4;

when z is 1, Y is monovalent cycloalkyl of 5 to 12 carbon atoms, cycloalkenyl of 5 to 12 carbon atoms, --C_m H_2m H, --C_m H_2m CN, --C_m H_2m Cl, --C_m H_2m NR₂ ", --C_m H_2m COONR₂ ", --C_m H_2m COOCH₂ OCH₂ CH₃, or --(C_p H_2p O)_r C_p H_2p H, when z is greater than 1, Y is --C_q H_2q --, --(C_p H_2p O)_x C_p H_2p --, --(C_y H_2y COO)_x C_y H_2y --, --C_q H_2q^-1 --, or --C_q H_2q^-2 --;

R" is hydrogen or alkyl of 1 to 5 carbon atoms;

m has a value of 1 to 10;

r has a value of 0 to 4;

p has a value of 2 to 4;

q has a value of 2 to 8;

x has a value of 1 to 5; and

y has a value of 2 to 5.

4. A method for coating a substrate as claimed in claim 1 wherein the irradiation in step (B) is non-ionizing high intensity predominantly continuum light radiation, said non-ionizing high intensity predominantly continuum light radiation having a source intensity of at least 350 watts per square centimeter steradian when integrated throughout the entire spectral range of said continuum light radiation with a positive amount up to 30 per cent of the light radiated having wavelengths shorter than 4,000 Angstroms and at least 70 per cent but less than all of the light radiated having wavelengths longer than 4,000 Angstroms.

5. A method for coating a substrate as claimed in claim 1 wherein the irradiation in step (B) is non-ionizing radiation of from 2500 Angstroms to 4500 Angstroms wavelength range.

6. A method for coating a substrate as claimed in claim 1 wherein the radiation in step (B) is ionizing radiation.

7. A method as claimed in claim 1 wherein component (a) is present at a concentration of from 10 to 30 weight per cent and component (b) is present at a concentration of from 15 to 25 weight per cent.

8. A method for coating a substrate as claimed in claim 1 wherein the thermal curing is carried out under an inert atmosphere.

9. A method as claimed in claim 1 wherein step (B) is carried out under an inert atmosphere.