Aqueous coating of silane precursor from epoxy and amino trialkoxysilanes

• US 5,206,285 A
• Filed: 12/21/1990
• Issued: 04/27/1993
• Est. Priority Date: 12/21/1990
• Status: Expired due to Fees

• Current Assignee: Northrop Corporation
• Original Assignee: Northrop Corporation
• Inventors: Castellucci, Nicholas T.
• Primary Examiner(s): Sellers, Robert E.
• Application Number:
  US07/631,562
• Time in Patent Office: 858 Days
• Field of Search: 524/588, 524/266, 523/425, 523/421
• US Class Current: 524/588
• CPC Class Codes: C08G 77/54 Nitrogen-containing linkages C08G77/485 takes precedence
• CPC Class Codes: C09D 183/14 in which at least two but not all the silicon atoms are connected by linkages other than oxygen atoms C09D183/10 takes precedence
• CPC Class Codes: C23C 22/48 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
• CPC Class Codes: C23C 2222/20 Use of solutions containing silanes

Abstract

Process for producing novel water-base coating compositions and for applying such compositions to metal surfaces to render them corrosion-resistant, comprising reacting an epoxy trialkoxy silane with a primary aminotrialkoxy silane in a molar ratio providing one epoxy group for reaction with each primary amino hydrogen to form a hydrolyzable siloxane precursor coating composition which is solubilized, such as by the presence of a volatile organic weak acid and hydrolyzing said precursor compound in situ on a metallic surface to form a silanol precursor compound which is bonded to a metallic surface and is simultaneously cross-linked with itself and/or with external crosslinking agents under dehydration conditions to form a corrosion-resistant conversion coating or bonding coating having exceptional durability.

Claims

1. An aqueous composition for forming coatings having excellent bonding properties for metallic surfaces and capable of rendering said metallic surfaces resistant to corrosion, said aqueous composition comprising:

an aqueous vehicle having solubilized therein a hydrolyzable silane polymer precursor, said silane polymer precursor being formed by anhydrously reacting an epoxy trialkoxy silane with a primary amino trialkoxy silane in relative stoichiometric amounts providing one epoxy group for reaction with each primary amino hydrogen site,

said reaction occurring for a period of approximately twenty-four hours at room temperature and under an inert gas atmosphere,

said aqueous vehicle also comprising an amount of a high vapor pressure organic acid sufficient to provide a pH of between about 4.5 and 6.5 to said aqueous vehicle, whereby said silane polymer precursor is solubilized in said aqueous vehicle; and

,

a silicone-base wetting agent in a concentration of between about 0.05% and 1.00% by weight,

said silane polymer precursor being applicable to a metal surface and hydrolyzable thereon to form a silanol polymer precursor capable of being dehydrated and crosslinked thereon, whereby a corrosion-resistant coating strongly bonded to said metal surface is formed, said high vapor pressure organic acid evaporating during said formation and crosslinking of said silanol polymer precursor.

2. An aqueous composition according to claim 1 in which said epoxy trialkoxy silane has the formula:

##STR9## wherein x is an integer from 1 to 3, y equals three minus x, z is an integer from 1 to 3, and R is an alkyl group having from 1 to 3 carbon atoms.

3. An aqueous composition according to claim 2 in which said epoxy trialkoxy silane comprises 3-glycidoxy propyltrimethoxy silane.

4. An aqueous composition according to claim 1 in which said primary amino trialkoxy silane has the formula:

##STR10## wherein x is an integer from 2 to 3, y is an integer from 1 to 3, z is an integer from 0 to 3, R'"'"' and R" are each alkyl groups having from 1 to 3 carbon atoms, a is an integer from 0 to 1 and b equals 3 minus a.

5. An aqueous composition according to claim 4 in which said primary amino trialkoxy silane comprises N-(2-aminoethyl) 3-aminopropyltrimethoxy silane.

6. An aqueous composition according to claim 1 in which said aqueous vehicle further comprises ethanol.

7. An aqueous composition according to claim 1 in which said aqueous composition further includes one or more additional alkoxy silane crosslinking agents.

8. An aqueous composition according to claim 7 in which said crosslinking agent has the formula:

space="preserve" listing-type="equation">(CH.sub.3 O).sub.3 --Si(CH.sub.2).sub.n --Si(OCH.sub.3).sub.3

wherein n is an integer from 1 to 10.

9. A process for producing an aqueous composition capable of being applied to a metal surface to form a corrosion resistant coating strongly bonded thereto, comprising:

anhydrously reacting an epoxy trialkoxy silane with a primary amino trialkoxy silane in relative stoichiometric amounts providing one epoxy group for reaction with each primary amino hydrogen site, said reaction occurring for a period of approximately twenty-four hours at room temperature and under an inert gas atmosphere, whereby a hydrolyzable silane polymer precursor is formed;

adding said silane polymer precursor to an aqueous vehicle, said aqueous vehicle comprising an amount of a high vapor pressure organic acid sufficient to provide a pH of between about 4.5 and 6.5 to said aqueous vehicle, whereby said silane polymer precursor is solubilized in said aqueous vehicle;

adding a silicone-base wetting agent to said aqueous vehicle in a concentration of between about 0.05% and 1.00% by weight, whereby said aqueous composition is formed,

said solubilized silane polymer precursor being capable of being applied onto said metal surface and hydrolyzed thereon to form a silanol polymer precursor,

said silanol polymer precursor being capable of being dehydrated on said metal surface, whereby said silanol polymer precursor is crosslinked and bonded to said metal surface, whereby further said corrosion-resistant coating strongly bonded to said metal surface is formed,

said high vapor pressure organic acid evaporating during said crosslinking and bonding of said silanol polymer precursor.

10. A process according to claim 9 in which said epoxy trialkoxy silane has the formula:

##STR11## wherein x is an integer from 1 to 3, y equals 3 minus x, z is an integer from 1 to 3, and R is an alkyl group having from 1 to 3 carbon atoms.

11. A process according to claim 10 in which said epoxy trialkoxy silane comprises 3-glycidoxy propyltrimethoxy silane.

12. A process according to claim 9 in which said primary amino trialkoxy silane has the formula:

##STR12## wherein x is an integer from 2 to 3, y is an integer from 1 to 3, z is an integer from 0 to 3, R'"'"' and R" are each alkyl groups having from 1 to 3 carbon atoms, a is an integer from 0 to 1 and b equals 3 minus a.

13. A process according to claim 12 in which said primary amino trialkoxy silane comprises N-(2-aminoethyl)3-aminopropyltrimethoxy silane.

14. A process according to claim 9 in which said reaction is conducted by adding said primary amino trialkoxy silane to an ethanol solution of said epoxy trialkoxy silane.

15. A process according to claim 9 in which said aqueous composition further includes one or more additional alkoxy silane crosslinking agents.

16. A process according to claim 15 in which said crosslinking agent has the formula:

space="preserve" listing-type="equation">(CH.sub.3 O).sub.3 --Si(CH.sub.2).sub.n --Si(OCH.sub.3).sub.3

wherein n is an integer from 1 to 10.