Dual curing coating method for substrates with shadow areas

• US 4,699,802 A
• Filed: 04/29/1985
• Issued: 10/13/1987
• Est. Priority Date: 10/03/1983
• Status: Expired due to Term

• Current Assignee: Loctite Corporation (Henkel AG & Co KGaA)
• Original Assignee: Loctite Corporation (Henkel AG & Co KGaA)
• Inventors: Nakos, Steven T., Lin, Samuel Q. S.
• Primary Examiner(s): Marquis, Melvyn I.
• Application Number:
  US06/728,426
• Time in Patent Office: 897 Days
• Field of Search: 526/279, 522/99, 522/39, 522/40, 522/44, 522/46, 522/77, 427/54.1, 528/34
• US Class Current: 427/515
• CPC Class Codes: C08G 77/20 containing silicon bound to unsaturated aliphatic groups C08G77/045 takes precedence
• CPC Class Codes: C08L 83/06 containing silicon bound to oxygen-containing groups C08L83/12 takes precedence
• CPC Class Codes: H05K 3/285 Permanent coating compositions

Abstract

A method of curing a liquid silicone composition to a crosslinked polymer on a substrate having shadow areas no readily accessible to direct UV light, the method comprising:

(a) applying a liquid composition to the substrate in a manner so as to cover both the light accessible and the shadow areas, the composition comprising a radical photoinitiator and a crosslinkable polydihydrocarbylsiloxane prepolymer having a molecular weight of at least 1000, having a plurality of acrylate or methacrylate groups bound thereto and further including a plurality of groups of the formula ##STR1## where R¹ is a hydrolyzable organic group and R² is R¹ or, if R¹ is dialkylamino, R² is R¹ or hydrocarbyl;

(b) irradiation the substrate with UV irradiation sufficient to substantially cure the composition in the areas directly accessible to UV light, and

(c) exposing the composition on the substrate to moisture for sufficient time to cure the composition in the shadow areas. Suitable polydihydrocarbyl siloxanes have the formula: ##STR2## where n is an integer, R¹ is selected from amino, oxime or --OOCR³, R² is R¹ or hydrocarbyl, provided that when R¹ is not amino, R² is the same as R¹, R³ is hydrocarbyl, R⁴ is H or methyl, R⁵ is a organo group having a carbon atom bound to the adjacent silicon atom and R⁶ is a hydrocarbyl group, said prepolymer having a molecular weight of at least 1,000.

Claims

1. A method of curing a liquid silicone composition to a crosslinked polymer on a substrate having shadow areas not readily accessible to direct UV light, the method comprising:

(a) applying a liquid composition to the substrate in a manner so as to cover both the light accessible and the shadow areas, the composition comprising a radical photoinitiator and a crosslinkable polydihydrocarbylsiloxane prepolymer having a molecular weight of at least 1000, having a plurality of acrylate or methacrylate groups bound thereto and further including a plurality of groups of the formula ##STR8## where R¹ is a hydrolyzable organic group and R² is R¹ or, if R¹ is dialkylamino, R² is R¹ or hydrocarbyl;

(b) irradiating the substrate with UV irradiation sufficient to substantially cure the composition in the areas directly accessible to UV light, and

(c) exposing the composition on the substrate to moisture for sufficient time to cure the composition in the shadow areas.

2. The method of claim 1 wherein R¹ is selected from the group consisting of alkoxy, aryloxy, oxime, OOCR³, N,N-dialkylamino, N,N-dialkylaminoxy, N-alkylamido, ##STR9## and --S--C₃ H₆ Si(OCH₃)₃

where R³ is H or hydrocarbyl.

3. The method of claim 1 wherein the composition further comprises a moisture curing catalyst.

4. The method of claim 1 wherein R¹ is selected from the group consisting of alkoxy, oxime and OOCR³ where R³ is H or hydrocarbyl.

5. The method of claim 4 wherein R¹ is selected from the group consisting of methoxy, acetoximino, and acetoxy, and the composition further comprises a moisture curing catalyst.

6. The method of claim 3 wherein the moisture curing catalyst is an orthotitanate catalyst.

7. The method of claim 1 wherein said polyorganosiloxane prepolymer has the formula ##STR10## where n is an integer;

R¹ and R² are as defined in claim 1;

R⁴ is H or methyl;

R⁵ is a divalent organic group having a carbon atom bound to the atom adjacent silicon atom and R⁶ is a hydrocarbyl group.

8. The method of claim 7 wherein R⁵ is selected from the group consisting of alkylene and alkenylene and the R⁶ groups are selected from the group consisting of methyl, phenyl and mixtures thereof.

9. The method of claim 7 where the polyorganosiloxane prepolymer has a molecular weight of at least 10,000.

10. The method of claim 6 where R¹ is amino and the composition is free of moisture curing catalyst.

11. The method of claim 1 wherein said substrate comprises an electronic circuit board having raised components.

16. The method of claim 1 wherein the moisture curing step comprises exposing the composition on the substrate to ambient atmospheric moisture.

12. A polyorganosiloxane prepolymer crosslinkable by moisture of free radical curing mechanisms having the formula:

##STR11## where n is an integer, R¹ is selected from amino, oxime or --OOCR³, R² is R¹ or hydrocarbyl, provided that when R¹ is not amino, R² is the same as R¹, R³ is hydrocarbyl, R⁴ is H or methyl, R⁵ is a organo group having a carbon atom bound to the adjacent silicon atom and R⁶ is a hydrocarbyl group, said propolymer having a molecular weight of at least 1,000.

13. A prepolymer as in claim 12 prepared by condensation of a silane of the formula ##STR12## with a polydihydrocarbylsiloxane having terminal condensable groups and a viscosity between 600 and 50,000 cps.

14. A prepolymer as in claim 13 wherein said polydihydrocarbylsiloxane with terminal condensable groups is a silanol terminated polydimethylsiloxane having a viscosity between about 750 and 25,000 cps.

15. A prepolymer as in claim 12 which is liquid at ambient temperature.