Non-stick ceramic coating composition and process

Abstract

A method of making a series of new non-stick ceramic coating materials prepared from organic-inorganic hybrid materials, including silica sol, MTMS, FAS and PDMS (Polydimethylsiloxane) using the sol-gel process. The hybrid materials have good mechanical properties and are fashioned into a main ceramic network and good non-stick properties from organic non-stick compounds. The non-stick ceramic coating consists of two layers applied to cookware and for other applications. Methods of preparing a substrate coated with the non-stick ceramic coating are also disclosed.

We claim: 
     
         1 . A method of making a non-stick ceramic coating for a substrate, comprising the steps of:
 making a first component by:
 adding a colloidal silica sol to at least one organoalkoxysilane of chemical formula R x Si(OR′) 4-x , wherein R represents an organic substituent, R′ represents an alkyl group, and 0≦x<4, and a catalyst to effect a condensation reaction; 
 adding a solvent; 
 adding a colorant in particulate form; and, 
 mixing to form a first stable binder solution; 
   making a second component by:
 adding an organoalkoxysilane and a catalyst, said organoalkoxysilane including a minor portion of fluoroalkylalkoxysilane; 
 adding a solvent; 
 mixing to form a second stable binder solution; 
   mixing said first component and said second component, thereby producing a two-component mixture; and,   aging said two-component mixture.   
     
     
         2 . The method of making a non-stick ceramic coating for a substrate according to  claim 1 , wherein said at least one organoalkoxysilane is selected from the group consisting of (a) organoalkoxysilanes wherein x=0 and each R′ is selected independently from the group consisting of methyl and ethyl; (b) organoalkoxysilanes wherein x=1, R is selected from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups, and each R′ is selected independently from the group consisting of methyl and ethyl; (c) organoalkoxysilanes wherein x=2, each R is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups, and each R′ is selected independently from the group consisting of methyl and ethyl; (d) organoalkoxysilanes wherein x=3, each R is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups, and each R′ is selected independently from the group consisting of methyl and ethyl; (e) organoalkoxysilanes wherein R is a substituent selected from the group consisting of (R A R B )N(CH 2 ) n —, (R A R B )NNH(CH 2 ) n —, (R A R B )N(CH 2 ) n [N(H)(CH 2 ) m ] y —, and (R A R B )N(CH 2 ) n [N(H)(CH 2 ) m ] y CH 2 —, where R A  and R B  are independently selected from H, C 1 -C 8  straight-chain, branched chain, and cyclic alkyl groups, or (R A R B N) describes a piperizinyl, piperidinyl, or morpholino ring, n≦3, m≦3, and y≦3, and each R′ is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups; (f) organoalkoxysilanes wherein R is a vinyl group, and each R′ is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups; (g) organoalkoxysilanes wherein R is a 3-glycidoxypropyl group and R′ is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups; (h) organoalkoxysilanes wherein R is a 3-methacryloxypropyl group and each R′ is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups; (i) organoalkoxysilanes wherein R is an alkyl group in which at least one H atom is substituted with a halogen atom and each R′ is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups; (j) organoalkoxysilanes wherein R is an —SH terminated alkyl group, and each R′ is selected independently from the group consisting of straight-chain or branched C 1 -C 8  alkyl groups and aromatic groups; and (k) any combination of above. 
     
     
         3 . The method of making a non-stick ceramic coating for a substrate according to  claim 1 , wherein said organoalkoxysilane is methyltrimethoxysilane. 
     
     
         4 . The method of making a non-stick ceramic coating for a substrate according to  claim 1 , wherein said step of making a second component comprises adding a polysiloxane. 
     
     
         5 . The method of making a non-stick ceramic coating for a substrate according to  claim 4 , wherein said polysiloxane is selected from the group consisting of polysiloxanes and polysiloxane copolymers of the general formula QO—[SiR A R B O] n —SiR A R B OQ, wherein Q is selected from the group consisting of H and organic substituents, and wherein R A  and R B  are independently selected from H, straight-chain alkyl groups, branched-chain alkyl groups, cyclic alkyl groups, aromatic groups, RNHR′NH 2 , C 3 H 5 O(C 2 H 4 ) m (CH 3 C 2 H 3 O) n H, C 3 H 5 O(C 2 H 4 ) m (CH 3 C 2 H 3 O) n R, (CH 2 ) 3 OCH 2 C 2 H 3 O, and (CH 2 ) n CF 3 . 
     
     
         6 . A non-stick ceramic coating composition comprising:
 a colored base layer for bonding to a substrate, said base layer comprising:
 70-85% by weight of a first matrix comprising a condensation product of a silica sol and an alkoxysilane mixture, said alkoxysilane mixture comprising:
 80-95% by weight of at least one organoalkoxysilane of chemical formula R x Si(OR′) 4-x , wherein R represents an organic substituent, R′ represents an alkyl group, and 0≦x<4; and, 
 5-20% of a polysiloxane; and, 
 
 15-30% by weight of a colorant; 
 said colored base layer comprising:
 a lower portion composed principally of (a) said condensation product of said silica sol and said organoalkoxysilane and (b) said colorant; and, 
 a distinct upper portion composed principally of (a) the condensation product of said silica sol and said polysiloxane and (b) said colorant; and, 
 
   a top layer superimposed upon, and bonded to, said base layer, said top layer composed of a second matrix comprising:
 a condensation product of a silica sol and an alkoxysilane mixture, said alkoxysilane mixture comprising:
 80-95% by weight of at least one organoalkoxysilane of chemical formula R x Si(OR′) 4-x , wherein R represents an organic substituent, R′ represents an alkyl group, and 0≦x<4; 
 5-20% by weight of a polysiloxane; and, 
 about 0.3% to about 12% by weight of a fluoroalkylalkoxysilane; 
 
   
       wherein said non-stick ceramic coating composition is prepared by the method according to  claim 1 . 
     
     
         7 . The use of the method of making a non-stick ceramic coating for a substrate according to  claim 1  to prepare the non-stick ceramic coating according to  claim 6 . 
     
     
         8 . A method of coating a substrate with a non-stick ceramic coating comprising the steps of:
 preparing a substrate by:
 removing dust and oil from the substrate surface to be coated; 
 drying the substrate surface; 
 roughening the substrate surface to substantially increase its area; and, 
 cleaning the substrate surface and preheating the substrate surface; 
   coating the substrate surface with a first coating comprising a colored base layer comprising:
 70-85% by weight of a first matrix comprising a condensation product of a silica sol and an alkoxysilane mixture, said alkoxysilane mixture comprising:
 80-95% by weight of at least one organoalkoxysilane of chemical formula R x Si(OR′) 4-x , wherein R represents an organic substituent, R′ represents an alkyl group, and 0≦x<4; and, 
 5-20% of a polysiloxane; and, 
 
 15-30% by weight of a colorant; 
 said colored base layer comprising:
 a lower portion composed principally of (a) said condensation product of said silica sol and said organoalkoxysilane and (b) said colorant; and, 
 a distinct upper portion composed principally of (a) the condensation product of said silica sol and said polysiloxane and (b) said colorant; 
 
   coating the substrate with a second coating comprising a top layer, said top layer composed of a second matrix comprising:
 a condensation product of a silica sol and an alkoxysilane mixture, said alkoxysilane mixture comprising:
 80-95% by weight of at least one organoalkoxysilane of chemical formula R x Si(OR′) 4-x , wherein R represents an organic substituent, R′ represents an alkyl group, and 0≦x<4; 
 5-20% by weight of a polysiloxane; and, 
 about 0.3% to about 12% by weight of a fluoroalkylalkoxysilane; and, 
 
   drying in air.   
     
     
         9 . The method of coating a substrate with a non-stick ceramic coating according to  claim 8 , wherein the coating is sprayed onto the substrate and heated to 120° C. to 300° C. for 10 to 30 minutes. 
     
     
         10 . The method of coating a substrate with a non-stick ceramic coating according to  claim 8 , wherein said fluoroalkylalkoxysilane is present from about 0.3 wt % to about 2 wt %. 
     
     
         11 . The method of coating a substrate with a non-stick ceramic coating according to  claim 8 , wherein said organoalkoxysilane is methyltrimethoxysilane. 
     
     
         12 . The method of coating a substrate with a non-stick ceramic coating according to  claim 8 , wherein at least one component selected from the group consisting of said first component and said second component comprises a condensation product of a mixture comprising from about 30% to about 70% by weight said silica sol and about 2% to about 40% by weight R x Si(OR′) 4-x . 
     
     
         13 . The method of coating a substrate with a non-stick ceramic coating according to  claim 8 , wherein at least one component selected from the group consisting of said first component and said second component additionally comprises a condensation catalyst in an amount of not more than 2 wt %. 
     
     
         14 . The method of coating a substrate with a non-stick ceramic coating according to  claim 8 , wherein at least one component selected from the group consisting of said first component and said second component comprises said solvent in an amount from 10 wt % to 40 wt %. 
     
     
         15 . A non-stick ceramic coated substrate comprising:
 a substrate having a surface to be coated;   a first layer coated on the surface of the substrate to be coated and having an exposed top surface;   a second layer coated on the exposed top of the first layer and having an exposed top surface serving as a non-stick ceramic surface suitable for cooking food;   said first layer comprised of a lower portion in contact with the surface of said substrate and being composed of a colorant and a SiO 2  matrix resulting from the condensation of a colloidal silica sol and an organoalkoxysilane; and the upper portion of the first layer being composed of a SiO 2  matrix resulting from the condensation of a colloidal silica sol and an organoalkoxysilane containing a minor portion of polysiloxane;   said second layer comprised of a SiO 2  matrix resulting from the condensation of a colloidal silica sol and an organoalkoxysilane containing a minor portion of polysiloxane, and a minor portion of fluoroalkylalkoxysilane.   
     
     
         16 . The non-stick ceramic coated substrate according to  claim 15 , wherein said fluoroalkylalkoxysilane is present from about 0.3 wt % to about 2 wt %. 
     
     
         17 . The non-stick ceramic coated substrate according to  claim 15 , wherein said organoalkoxysilane is methyltrimethoxysilane. 
     
     
         18 . The non-stick ceramic coated substrate according to  claim 15 , wherein the silica sol is present in an amount from 30 wt % to about 70 wt %, and the methyltrimethoxysilane is present in an amount from 2 wt % to 40 wt %. 
     
     
         19 . The non-stick ceramic coated substrate according to  claim 15 , wherein at least one layer selected from the group consisting of said first layer and said second layer additionally comprises a condensation catalyst in an amount of not more than 2 wt %. 
     
     
         20 . The non-stick ceramic coated substrate according to  claim 15 , wherein at least one layer selected from the group consisting of said first layer and said second layer comprises a solvent in an amount from 10 wt % to 40 wt %. 
     
     
         21 . A kit for production of a non-stick ceramic coating composition, said kit comprising two solutions provided in separate containers, said two solutions comprising an “A” solution comprising a colorant, 30-70 wt % of a silica sol, 2-40 wt % of organoalkoxysilane of formula R x Si(OR′) 4-x , 0≦x<4, 0-2 wt % of a catalyst, and 10-40 wt % of a solvent, and a “B” solution comprising 75-99 wt % of organoalkoxysilane of formula R x Si(OR′) 4-x , 0≦x<4, 0.3-2 wt % of a fluoroalkylalkoxysilane, 5-20 wt % of a polysiloxane, and 0-3 wt % of a catalyst.