CYCLIC SULFONIUM ZWITTERION-TITANIUM CATALYSTS FOR ALUMINUM PLATING PROCESS
United States Patent 3836385
An improved process for the application of a decomposition catalytic compound to a substrate, in air, prior to electrolessly aluminum plating the substrate by decomposing an aluminum hydride. A cyclic sulfonium zwitterion, a decomposition catalyst and a mutual solvent therefore are admixed; applied to a substrate and polymerized prior to application of the aluminum plate.
US Patent References:
ALUMINUM PLATING PROCESS
Schmidt et al. - August 1969 - 3462288
ALUMINUM PLATING OF SURFACES
Williams - September 1968 - 3464844
METHOD OF FORMING A PINHOLE-FREE ALLOY LAYER ON THE SURFACE OF A BASE MADE OF ALUMINUM OR AN ALUMINUM ALLOY
Nakano - November 1971 - 3619232
ALUMINUM PLATING PROCESS
Schmidt et al. - August 1969 - 3462288
ALUMINUM PLATING OF SURFACES
Williams - September 1968 - 3464844
METHOD OF FORMING A PINHOLE-FREE ALLOY LAYER ON THE SURFACE OF A BASE MADE OF ALUMINUM OR AN ALUMINUM ALLOY
Nakano - November 1971 - 3619232
Inventors:
Schmidt, Donald L. (Midland, MI)
Roberts, Charles B. (Midland, MI)
Roberts, Charles B. (Midland, MI)
Application Number:
05/222984
Publication Date:
09/17/1974
Filing Date:
02/02/1972
View Patent Images:
Export Citation:
Assignee:
The Dow Chemical Company (Midland, MI)
Primary Class:
International Classes:
C23C18/10; C23C18/00
Field of Search:
117/47A,47R,71R,50,16R,13R,13E,126GM 106/1
Primary Examiner:
Van Horn, Charles E.
Assistant Examiner:
Ball, Michael W.
Attorney, Agent or Firm:
Yates, William Selby Robert Jowanovitz Lloyd M. W. S.
Claims:
What is claimed is
1. In a process for the plating of aluminum onto a substrate by contacting the substrate with a decomposition catalytic compound selected from the group consisting of compounds of titanium, zirconium, hafnium, vanadium, niobium, tantalum and mixtures thereof, and then an aluminum hydride, the improvement comprising contacting the substrate with a mixture of (1) a thermally polymerizable monomer consisting of at least one cyclic sulfonium zwitterion of the formula: ##SPC6##
2. The process of claim 1 wherein the contacting step is carried out in an oxygen containing atmosphere.
3. The process of claim 2 wherein the contacting step is carried out in air.
4. The process of claim 1 wherein polymerizing is carried out at a polymerizing temperature within the range of from about 40°C. to about 200°C.
5. The process of claim 1 wherein polymerizing is carried out at a polymerizing temperature within the range of from about 90°C. to about 150°C.
6. The process of claim 1 wherein the substrate is contacted with a solution of the cyclic sulfonium zwitterion monomer and the catalytic compound.
7. The process of claim 1 wherein the zwitterion monomer has an average of at least 1.2 S♁/mer.
8. The process of claim 1 wherein the decomposition catalytic compound is selected from the group consisting of TiCl4. 2[C2 H5)2 O], Ti(OC2 H5)2 Cl2, TiCl2 (i-OC3 H7)2, TiCl2. 2[(C2 H5)2 O], Ti(BH4)3. 2[(C2 H5)2 O], and the chlorides, bromides and iodides of titanium and niobium.
9. The process of claim 1 wherein the decomposition catalytic compound is selected from the group consisting of chlorides, bromides and iodides of titanium and niobium.
10. The process of claim 1 wherein the decomposition catalytic compound is titanium tetrachloride.
11. The process of claim 8 wherein the catalyst contacting step is carried out with the described mixture containing about 0.05 to about 10 weight per cent of the decomposition catalytic compound.
12. The process of claim 11 wherein the decomposition catalytic compound is titanium tetrachloride.
13. The process of claim 11 wherein the mixture includes about one-half to about 70 weight per cent of the cyclic sulfonium zwitterion monomer.
14. The process of claim 13 wherein the decomposition catalytic compound is titanium tetrachloride and polymerizing is carried out at a polymerizing temperature within the range of from about 40°C. to about 200°C.
15. The process of claim 14 wherein polymerizing is carried out at a polymerizing temperature within the range of from about 90°C. to about 150°C.
16. The process of claim 8 wherein the catalyst contacting step is carried out with the described mixture containing about one-half to about 5 weight per cent of the decomposition catalytic compound and about 20 to about 45 per cent of the cyclic sulfonium zwitterion monomer.
17. The process of claim 8 including contacting the aluminum plated surface with the mixture of the components (1), (2) and (3); polymerizing the monomer and then contacting at least a portion of the polymerized surface with an aluminum hydride.
18. The process of claim 16 wherein the decomposition catalytic compound is titanium tetrachloride.
1. In a process for the plating of aluminum onto a substrate by contacting the substrate with a decomposition catalytic compound selected from the group consisting of compounds of titanium, zirconium, hafnium, vanadium, niobium, tantalum and mixtures thereof, and then an aluminum hydride, the improvement comprising contacting the substrate with a mixture of (1) a thermally polymerizable monomer consisting of at least one cyclic sulfonium zwitterion of the formula: ##SPC6##
2. The process of claim 1 wherein the contacting step is carried out in an oxygen containing atmosphere.
3. The process of claim 2 wherein the contacting step is carried out in air.
4. The process of claim 1 wherein polymerizing is carried out at a polymerizing temperature within the range of from about 40°C. to about 200°C.
5. The process of claim 1 wherein polymerizing is carried out at a polymerizing temperature within the range of from about 90°C. to about 150°C.
6. The process of claim 1 wherein the substrate is contacted with a solution of the cyclic sulfonium zwitterion monomer and the catalytic compound.
7. The process of claim 1 wherein the zwitterion monomer has an average of at least 1.2 S♁/mer.
8. The process of claim 1 wherein the decomposition catalytic compound is selected from the group consisting of TiCl4. 2[C2 H5)2 O], Ti(OC2 H5)2 Cl2, TiCl2 (i-OC3 H7)2, TiCl2. 2[(C2 H5)2 O], Ti(BH4)3. 2[(C2 H5)2 O], and the chlorides, bromides and iodides of titanium and niobium.
9. The process of claim 1 wherein the decomposition catalytic compound is selected from the group consisting of chlorides, bromides and iodides of titanium and niobium.
10. The process of claim 1 wherein the decomposition catalytic compound is titanium tetrachloride.
11. The process of claim 8 wherein the catalyst contacting step is carried out with the described mixture containing about 0.05 to about 10 weight per cent of the decomposition catalytic compound.
12. The process of claim 11 wherein the decomposition catalytic compound is titanium tetrachloride.
13. The process of claim 11 wherein the mixture includes about one-half to about 70 weight per cent of the cyclic sulfonium zwitterion monomer.
14. The process of claim 13 wherein the decomposition catalytic compound is titanium tetrachloride and polymerizing is carried out at a polymerizing temperature within the range of from about 40°C. to about 200°C.
15. The process of claim 14 wherein polymerizing is carried out at a polymerizing temperature within the range of from about 90°C. to about 150°C.
16. The process of claim 8 wherein the catalyst contacting step is carried out with the described mixture containing about one-half to about 5 weight per cent of the decomposition catalytic compound and about 20 to about 45 per cent of the cyclic sulfonium zwitterion monomer.
17. The process of claim 8 including contacting the aluminum plated surface with the mixture of the components (1), (2) and (3); polymerizing the monomer and then contacting at least a portion of the polymerized surface with an aluminum hydride.
18. The process of claim 16 wherein the decomposition catalytic compound is titanium tetrachloride.
Description:
BACKGROUND OF THE INVENTION
This invention relates to a nonelectrolytic process for the plating of aluminum on various substrates and more particularly relates to improved catalysis in a relatively low temperature process for the plating of metallic aluminum from an aluminum hydride.
Metallic aluminum has been plated from aluminum hydrides by contacting such hydrides with a substrate at or above the decomposition temperature of the aluminum hydride. It is also known that aluminum hydrides may be used to produce plating of metallic aluminum at temperatures substantially below the usual decomposition temperature of such hydrides by contacting the hydride with certain transistion metal decomposition catalytic compounds. Useful catalytic compounds have been found to be selected from compounds of the metals titanium, zirconium, hafnium, vanadium, niobium and tantalum.
Generally, the entire aluminum plating process has been conducted in a substantially anhydrous, inert atmosphere due to the sensitivity of most aluminum hydrides to the presence of moist air. Also it has been found that certain of the decomposition catalysts rapidly become less effective when catalysis is carried out in atmospheric air rather than in a dry inert atmosphere. It would be desirable to catalyze a substrate under normal atmospheric conditions, relative to air and humidity, without inhibiting the catalyst's efficiency.
It is an object of this invention to provide a method of catalyzing a substrate in air in a process for electrolessly aluminum plating from an aluminum hydride.
It is another object of this invention to provide a method of catalyzing substrates in air whereby the catalyzed substrate is storable in air and the catalytic compound remains suitable to lower the decomposition temperature of an aluminum hydride for a longer time period than was heretofore possible.
Other objects and advantages of this invention will become apparent during the course of the following description.
SUMMARY OF THE INVENTION
An improved process for the plating of aluminum onto a solid substrate has been developed which permits the catalyzation of the substrate in air and then electroless deposition of aluminum onto the substrate by contacting the catalyzed surface with an aluminum hydride. The catalytic compound on the surface effectively reduces the decomposition temperature of the aluminum hydride. Suitable transition metals useful in the catalytic compounds of the described process are titanium, zirconium, hafnium, vanadium, niobium, tantalum and mixtures thereof. Preferably the metals are titanium, zirconium, vanadium and niobium; more preferably the metal is titanium.
The improvement comprises contacting the substrate with a mixture of the decomposition catalytic compound; a thermally polymerizable monomer consisting of at least cyclic sulfonium zwitterion of the formula: ##SPC1##
Where R is Cl, Br, or C 1 -C 4 alkyl and a is O-2, each tetramethylenesulfonium group is ortho or para to the phenoxide group, and Z is a bridging group of the formula:
a. --O(C m H 2m )O-- where m is 1-6 and Σ(x+y) = 0-1, or
b. --CH 2 13 where Σ(x+y) = 0-4;
and a mutual solvent for the cyclic sulfonium zwitterion and the catalytic compound. The monomer in contact with the substrate is then polymerized to form, upon drying, a water insoluble polymer-oxygen stable decomposition catalyst coating on the substrate.
The so-catalyzed substrate is then plated with aluminum by contacting at least a portion of the catalyzed surface with an aluminum hydride and decomposing the hydride in contact with the catalyzed surface. This portion of the process is substantially as described in Schmidt et al., U.S. Pat. No. 3,462,288.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cyclic sulfonium zwitterions (CSZ) of Formula I. can be blended with decomposition catalytic compounds in a mutual solvent for the CSZ monomer and catalytic compound at an alkaline pH, preferably about 9.5 to about 11.5, to give stable coating compositions without coagulation or agglomerization. Furthermore, not only are these CSZ compatible with the catalytic compound, but upon curing these compositions form clear, durable films and coatings with the catalyst dispersed throughout the polymer matrix. Such CSZ monomers can be prepared as described in Hatch et al. U.S. Pat. No. 3,636,052, U.S. Pat. No. 3,660,431 and Hatch et al. Belgium Pat. No. 757,583 by reaction of a phenol with a polymethylene sulfoxide and then with base. Although these CSZ monomers are very soluble in polar hydroxylic solvents such as C 1 -C 3 alcohols, they thermally polymerize to give condensation polymers with exceptional water and solvent resistance. Thus excellent coatings with high solvent resistance are obtained by homopolymerization of a cross-linking CSZ monomer having about 1.2-2.5 sulfonium groups per molecule (S♁/mer) or by copolymerizing such a monomer with a chain extending CSZ monomer, the mixed monomers having an average of about 1.2-2.5 S♁/mer.
Particularly suitable herein are the chainextending monotetramethylenesulfonium zwitterion monomers of phenol (IA), tetrahydro-1-(4-hydroxy-3-methylphenyl) thiophenium hydroxide, inner salt (IB), and 2,6-dichlorophenol (IC) and the cross-linking polytetramethylenesulfonium zwitterion monomers of bis(nesorcinol) polymethylene ether (ID) and phenol-formaldehyde novolac resins (IE): ##SPC2##
Preferred cross-linking monomers are the bisresorcinol di-, tri-, and tetramethylene ether sulfonium zwitterions (ID: m = 2-4) and the cyclic zwitterion monomers of a water soluble novolac resin having an average degree of polymerization of about 2-5 and about 1.5-3.0 S♁/mer (IE: Σ(x+y) = 1-4, y = 0.5-2.0).
The cross-linking monomers ID and IE homopolymerize to give smooth hard coatings with excellent adhesion to solid surfaces and high resistance to strong acids and bases, boiling water, and common organic solvents. Copolymers of the chain-extending and cross-linking CSZ monomers also give smooth hard coatings with the solvent resistance increasing with increasing proportion of the cross-linking monomer.
The aforedescribed decomposition catalytic compounds are beneficially employed in this process. For example, such compounds as NbCl 5 , TiCl 4 . 2[(C 2 H 5 ) 2 O], TiCl 4 , TiBr 4 , TiI 4 , Ti(OC 2 H 5 ) 2 Cl 2 , TiCl 2 , (i--OC 3 H 7 ) 2 , TiCl 2 . 2[(C 2 H 5 ) 2 O], Ti(BH 4 ) 3 . 2[(C 2 H 5 ) 2 O] are effective catalytic compounds. Some of the transition metal catalysts defined herein have a more pronounced effect than others in lowering the decomposition temperature of the aluminum hydride. The chlorides, bromides and iodides of titanium and niobium generally seem to be more effective than the other named transition metals and TiCl 4 has been found to be particularly effective in achieving a lower decomposition temperature of the aluminum hydrides and plating of the aluminum thus produced. If the defined catalysts are not employed, undesirable high temperatures are required to produce decomposition of the aluminum hydride.
Various solvents for the CSZ monomer and the decomposition catalysts can be used herein. Suitable solvents include and can be selected from, for example, aliphatic and alicyclic alcohols containing from about one to about nine carbon atoms such as methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, isopropanol, isobutanol, 2-methyl-2-butanol, cyclobutylmethanol, cyclopentanol, cyclohexanol 2-phenylethanol, ethylene glycol and propylene glycol; and glycol ethers such as propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol n-butyl ether, dipropylene glycol methyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol n-butyl ether, tripropylene glycol methyl ether, propylene glycol phenyl ether and ethylene glycol phenyl ether. The solutes are preferably soluble in the selected solvent to the extent of at least about 5 weight per cent and more preferably at least about 30 weight per cent of the CSZ monomer and at least about one-tenth weight per cent and more preferably at least about 1 1/2 weight per cent of the decomposition catalytic compound at 25°C. All weight per cent values herein are based on the total solution weight unless otherwise specified.
In practice, the CSZ monomer and the decomposition catalytic compound are mixed with and at least partially dissolved in the solvent. It is highly preferably that the CSZ monomer, decomposition catalytic compound and the solvent form a solution; that is, substantially all of the solute dissolves in the solvent to form a substantially homogenous mixture. Mixing of the various components can be carried out simultaneously or in any order by common means known to those skilled in the art. The solution contains sufficient solute to form a catalytic coating on a substrate; such solution desirably contains about 0.05 to about 10 weight per cent of the catalytic compound and about one-half to about 70 weight per cent of the CSZ monomer. More desirably the solution contains about one-half to about 5 weight per cent of the decomposition catalyst and about 20 to about 45 weight per cent of the CSZ monomer.
Conveniently the monomer-decomposition catalyst solution can be prepared by, for example, gradually adding the catalyst to a monomer-solvent solution and simultaneously stirring the solution. If desired the catalyst can first be dissolved in the solvent and then added to the monomer-solvent solution. Preferably such catalyst dissolution is at least initiated at temperatures approximately 80°C. below zero. The technique and equipment used to prepare the monomer-catalyst-solvent solution is not critical and is readily carried out by those skilled in the art.
Substantially any normally solid material, at least partially wetted by the described mixture, is suitable as a substrate herein. For example, metals such as iron, magnesium, brass and copper, polymers such as polyolefins, polyamides and polymeric fluorocarbons, glass, paper, cloth, carbon and graphite, wood, ceramics and the like are all plated with aluminum by the process of this invention. The described catalytic compound containing solution can be applied to the solid substrate by various means such as brushing, dipping, spraying, roll coating, swabbing and the like. The amount of the catalytic compound applied to the substrate can be closely controlled by varying either the thickness of the solution coating applied to the substrate or the concentration of the catalyst in such solution.
The coated substrate is then heated to about 40°C. to about 200°C., and preferably about 90°C. to about 150°C., to volatilize the solvent and convert the monomer irreversibly into the water and solvent resistant coating containing the decomposition catalytic compound. The temperature is suitably selected to polymerize the monomer and not to deleteriously effect the desired properties of the substrate. Such heating can be carried out using commercially available equipment. A controlled inert atmosphere during such heating is satisfactory, but is not required.
The catalyst-polymer coated substrate can be stored in air, without requiring control of the oxygen or moisture content thereof, and still retain an effective decomposition catalytic compound. Preferably the aluminum plate is deposited within about one day and more preferably within about 4 days after polymerization of the monomer on the substrate surface.
The following examples will further illustrate the process of the present invention.
A CSZ of Formula I is prepared as follows: a solution of 38.5 parts (0.15 mole) biscatechol trimethylene ether and 34.4 parts (0.33 mole) tetrahydrothiophene oxide in about 160 parts methanol is treated at 0°C. with anhydrous HCl. A solid bissulfonium chloride is recovered, dissolved in methanol and slurried with a strong base anion-exchange resin in hydroxide form to give a cyclic sulfonium zwitterionic monomer (ID, m = 3). The CSZ monomer is isolated or used as a methanol solution. In aqueous solution the pH is about 10.5-11.5.
Other CSZ monomers of Formula I are prepared similarly from phenol, bisresorcinol ethers, and phenolformaldehyde novolac resins.
EXAMPLE 1
A methanol solution containing 53 weight per cent of the CSZ 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}]bis(tetrahydro thiophenium hydroxide)bis (inner salt) with the formula: ##SPC3##
and 1 1/2 weight per cent TiCl 4 was prepared by mixing the desired proportions of a methanol-monomer solution with a TiCl 4 -methanol solution. The monomer-TiCl 4 solution was then applied to a portion of one surface of a 4 mil thick Mylar film using a wire wound rod to spread the CSZ monomer-catalyst-methanol solution over the surface. The catalyzed film was heated at 85°C. for 5 minutes to polymerize the CSZ monomer. An adherent, water and solvent insoluble polymer with the TiCl 4 catalyst dissolved therein was obtained. The so catalyzed substrate remained in the laboratory air atmosphere for about 5 minutes before being placed in a dry nitrogen atmosphere, immersed in an 0.3 molar aluminum hydride-diethyl ether solution and dried. When the aluminum hydride in contact with the substrate was heated to 100°C. for about 5 minutes a decorative, specular, aluminum plate was deposited only on that portion of the Mylar film treated with the CSZ monomerTiCl 4 -methanol solution.
EXAMPLE 2
Sufficient TiCl 4 was slowly admixed with a methanol solution containing 40 weight percent solute to form a final solution containing about 2 1/2 weight per cent TiCl 4 . The solute consisted of 90 weight per cent of 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}] bis(tetrahydrothiophenium hydroxide)bis(inner salt) and 10 weight per cent tetrahydro-1-(4-hydroxy-3-methylphenyl) thiophenium hydroxide, inner salt. The final solution was first applied to a 3 mil thick Mylar film using a wire wound rod and then polymerized in air for one minute at 104°C. The polymerized-catalyzed surface was placed in a dry nitrogen environment and partially submerged in a 0.5 molar AlH 3 -ether solution, removed from the hydride solution and developed at 140°C. i.e., the AlH 3 decomposed to aluminum. An adherent aluminum plate was obtained on the AlH 3 contacted, catalyzed portion of the substrate.
EXAMPLE 3
A Mylar film was treated substantially as described in Example 2, including an added exposure to a temperature of 140°C. for 10 seconds prior to contacting the polymerized surface with the hydride. An adherent aluminum plate was produced.
EXAMPLE 4
A methanol solution containing 1 1/2 weight per cent TiCl 4 and 37.4 weight per cent of 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}]bis(tetrahydro thiophenium hydroxide)bis(inner salt) was prepared and applied to a 3 mil thick Mylar substrate, polymerized at 104°C. and aluminum plated as described in Example 2. An adherent aluminum coat was developed on the AlH 3 contacted, polymerized portion of the substrate.
EXAMPLE 5
Contacting the catalyzed substrate of Example 4 with a 0.25 molar solution of AlH 3 in ether and developing the hydride at 140°C. provided an aluminum plate on the AlH 3 contacted, catalyzed portion of the substrate.
EXAMPLES 6 and 7
Separate Mylar substrates were treated substantially as described in Examples 4 and 5, including an added exposure to temperature of 140°C. for 10 seconds prior to contacting the polymerized surface with the hydride. The aluminum plate deposited upon the catalyzed surface visually appeared improved over that deposited in Examples 4 and 5.
EXAMPLE 8
A 3 mil Mylar film was coated, as in Example 4, with the methanol solution containing about 63 weight per cent zwitterion. Polymerizing and decomposition of the aluminum hydride were carried out at 104°C. as described in Example 2. A satisfactory aluminum plate was deposited on the catalyzed portion of the film.
EXAMPLE 9
A Mylar film was coated and polymerized to form an adherent layer on the film consisting of 1 1/2 weight per cent TiCl 4 and a cross-linked polymer of the monomer 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}] bis(tetrahydrothiophenium hydroxide)bis(inner salt). The catalyzed surface remained exposed to the laboratory air for a period of 6 days. At least a portion of the catalyzed surface was dipped into a 0.25 molar solution of AlH 3 in ether and exposed to a temperature usually sufficient to decompose the catalyzed AlH 3 . It is believed that no aluminum plate was formed on the Mylar surface as a result of a time related sensitivity of the polymer-catalyst mixture to the laboratory air. It is also believed that removal of a surface portion from the polymer-catalyst mixture would rejuvenate the catalytic coating.
EXAMPLE 10
A 4 mil thick Mylar film is catalyzed and aluminum plated substantially as described in Example 1. The catalyst-polymer coated substrate is exposed to the laboratory air atmosphere for about 24 hours before applying the aluminum plate to the substrate. A decorative, specular, sharply defined aluminum plate is deposited only where the aluminum hydride had contacted the catalyzed surface.
EXAMPLE 11
A methanol solution containing 20 weight per cent solute consisting of 74 1/4 weight per cent of a CSZ with formula: ##SPC4##
where n = 0.5, 24 1/4 weight per cent of tetrahydro-1-(4-hydroxy-3-methylphenyl)thiophenium hydroxide, inner salt with the formula: ##SPC5##
and 1 1/2 weight per cent TiCl 4 is applied to a 4 mil Mylar film by a roll applicator, polymerized at 140°C. for 10 minutes and maintained in air for 3 days before depositing an aluminum plate thereon as described in Example 1. In a similar manner a second coating of the catalyst containing solution is applied to the plated surface and a second aluminum plate deposited in only the area treated with the catalytic solution. The aluminum plate will tenaciously adhere to the substrate and have a shiny, decorative physical appearance.
This invention relates to a nonelectrolytic process for the plating of aluminum on various substrates and more particularly relates to improved catalysis in a relatively low temperature process for the plating of metallic aluminum from an aluminum hydride.
Metallic aluminum has been plated from aluminum hydrides by contacting such hydrides with a substrate at or above the decomposition temperature of the aluminum hydride. It is also known that aluminum hydrides may be used to produce plating of metallic aluminum at temperatures substantially below the usual decomposition temperature of such hydrides by contacting the hydride with certain transistion metal decomposition catalytic compounds. Useful catalytic compounds have been found to be selected from compounds of the metals titanium, zirconium, hafnium, vanadium, niobium and tantalum.
Generally, the entire aluminum plating process has been conducted in a substantially anhydrous, inert atmosphere due to the sensitivity of most aluminum hydrides to the presence of moist air. Also it has been found that certain of the decomposition catalysts rapidly become less effective when catalysis is carried out in atmospheric air rather than in a dry inert atmosphere. It would be desirable to catalyze a substrate under normal atmospheric conditions, relative to air and humidity, without inhibiting the catalyst's efficiency.
It is an object of this invention to provide a method of catalyzing a substrate in air in a process for electrolessly aluminum plating from an aluminum hydride.
It is another object of this invention to provide a method of catalyzing substrates in air whereby the catalyzed substrate is storable in air and the catalytic compound remains suitable to lower the decomposition temperature of an aluminum hydride for a longer time period than was heretofore possible.
Other objects and advantages of this invention will become apparent during the course of the following description.
SUMMARY OF THE INVENTION
An improved process for the plating of aluminum onto a solid substrate has been developed which permits the catalyzation of the substrate in air and then electroless deposition of aluminum onto the substrate by contacting the catalyzed surface with an aluminum hydride. The catalytic compound on the surface effectively reduces the decomposition temperature of the aluminum hydride. Suitable transition metals useful in the catalytic compounds of the described process are titanium, zirconium, hafnium, vanadium, niobium, tantalum and mixtures thereof. Preferably the metals are titanium, zirconium, vanadium and niobium; more preferably the metal is titanium.
The improvement comprises contacting the substrate with a mixture of the decomposition catalytic compound; a thermally polymerizable monomer consisting of at least cyclic sulfonium zwitterion of the formula: ##SPC1##
Where R is Cl, Br, or C 1 -C 4 alkyl and a is O-2, each tetramethylenesulfonium group is ortho or para to the phenoxide group, and Z is a bridging group of the formula:
a. --O(C m H 2m )O-- where m is 1-6 and Σ(x+y) = 0-1, or
b. --CH 2 13 where Σ(x+y) = 0-4;
and a mutual solvent for the cyclic sulfonium zwitterion and the catalytic compound. The monomer in contact with the substrate is then polymerized to form, upon drying, a water insoluble polymer-oxygen stable decomposition catalyst coating on the substrate.
The so-catalyzed substrate is then plated with aluminum by contacting at least a portion of the catalyzed surface with an aluminum hydride and decomposing the hydride in contact with the catalyzed surface. This portion of the process is substantially as described in Schmidt et al., U.S. Pat. No. 3,462,288.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cyclic sulfonium zwitterions (CSZ) of Formula I. can be blended with decomposition catalytic compounds in a mutual solvent for the CSZ monomer and catalytic compound at an alkaline pH, preferably about 9.5 to about 11.5, to give stable coating compositions without coagulation or agglomerization. Furthermore, not only are these CSZ compatible with the catalytic compound, but upon curing these compositions form clear, durable films and coatings with the catalyst dispersed throughout the polymer matrix. Such CSZ monomers can be prepared as described in Hatch et al. U.S. Pat. No. 3,636,052, U.S. Pat. No. 3,660,431 and Hatch et al. Belgium Pat. No. 757,583 by reaction of a phenol with a polymethylene sulfoxide and then with base. Although these CSZ monomers are very soluble in polar hydroxylic solvents such as C 1 -C 3 alcohols, they thermally polymerize to give condensation polymers with exceptional water and solvent resistance. Thus excellent coatings with high solvent resistance are obtained by homopolymerization of a cross-linking CSZ monomer having about 1.2-2.5 sulfonium groups per molecule (S♁/mer) or by copolymerizing such a monomer with a chain extending CSZ monomer, the mixed monomers having an average of about 1.2-2.5 S♁/mer.
Particularly suitable herein are the chainextending monotetramethylenesulfonium zwitterion monomers of phenol (IA), tetrahydro-1-(4-hydroxy-3-methylphenyl) thiophenium hydroxide, inner salt (IB), and 2,6-dichlorophenol (IC) and the cross-linking polytetramethylenesulfonium zwitterion monomers of bis(nesorcinol) polymethylene ether (ID) and phenol-formaldehyde novolac resins (IE): ##SPC2##
Preferred cross-linking monomers are the bisresorcinol di-, tri-, and tetramethylene ether sulfonium zwitterions (ID: m = 2-4) and the cyclic zwitterion monomers of a water soluble novolac resin having an average degree of polymerization of about 2-5 and about 1.5-3.0 S♁/mer (IE: Σ(x+y) = 1-4, y = 0.5-2.0).
The cross-linking monomers ID and IE homopolymerize to give smooth hard coatings with excellent adhesion to solid surfaces and high resistance to strong acids and bases, boiling water, and common organic solvents. Copolymers of the chain-extending and cross-linking CSZ monomers also give smooth hard coatings with the solvent resistance increasing with increasing proportion of the cross-linking monomer.
The aforedescribed decomposition catalytic compounds are beneficially employed in this process. For example, such compounds as NbCl 5 , TiCl 4 . 2[(C 2 H 5 ) 2 O], TiCl 4 , TiBr 4 , TiI 4 , Ti(OC 2 H 5 ) 2 Cl 2 , TiCl 2 , (i--OC 3 H 7 ) 2 , TiCl 2 . 2[(C 2 H 5 ) 2 O], Ti(BH 4 ) 3 . 2[(C 2 H 5 ) 2 O] are effective catalytic compounds. Some of the transition metal catalysts defined herein have a more pronounced effect than others in lowering the decomposition temperature of the aluminum hydride. The chlorides, bromides and iodides of titanium and niobium generally seem to be more effective than the other named transition metals and TiCl 4 has been found to be particularly effective in achieving a lower decomposition temperature of the aluminum hydrides and plating of the aluminum thus produced. If the defined catalysts are not employed, undesirable high temperatures are required to produce decomposition of the aluminum hydride.
Various solvents for the CSZ monomer and the decomposition catalysts can be used herein. Suitable solvents include and can be selected from, for example, aliphatic and alicyclic alcohols containing from about one to about nine carbon atoms such as methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, isopropanol, isobutanol, 2-methyl-2-butanol, cyclobutylmethanol, cyclopentanol, cyclohexanol 2-phenylethanol, ethylene glycol and propylene glycol; and glycol ethers such as propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol n-butyl ether, dipropylene glycol methyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol n-butyl ether, tripropylene glycol methyl ether, propylene glycol phenyl ether and ethylene glycol phenyl ether. The solutes are preferably soluble in the selected solvent to the extent of at least about 5 weight per cent and more preferably at least about 30 weight per cent of the CSZ monomer and at least about one-tenth weight per cent and more preferably at least about 1 1/2 weight per cent of the decomposition catalytic compound at 25°C. All weight per cent values herein are based on the total solution weight unless otherwise specified.
In practice, the CSZ monomer and the decomposition catalytic compound are mixed with and at least partially dissolved in the solvent. It is highly preferably that the CSZ monomer, decomposition catalytic compound and the solvent form a solution; that is, substantially all of the solute dissolves in the solvent to form a substantially homogenous mixture. Mixing of the various components can be carried out simultaneously or in any order by common means known to those skilled in the art. The solution contains sufficient solute to form a catalytic coating on a substrate; such solution desirably contains about 0.05 to about 10 weight per cent of the catalytic compound and about one-half to about 70 weight per cent of the CSZ monomer. More desirably the solution contains about one-half to about 5 weight per cent of the decomposition catalyst and about 20 to about 45 weight per cent of the CSZ monomer.
Conveniently the monomer-decomposition catalyst solution can be prepared by, for example, gradually adding the catalyst to a monomer-solvent solution and simultaneously stirring the solution. If desired the catalyst can first be dissolved in the solvent and then added to the monomer-solvent solution. Preferably such catalyst dissolution is at least initiated at temperatures approximately 80°C. below zero. The technique and equipment used to prepare the monomer-catalyst-solvent solution is not critical and is readily carried out by those skilled in the art.
Substantially any normally solid material, at least partially wetted by the described mixture, is suitable as a substrate herein. For example, metals such as iron, magnesium, brass and copper, polymers such as polyolefins, polyamides and polymeric fluorocarbons, glass, paper, cloth, carbon and graphite, wood, ceramics and the like are all plated with aluminum by the process of this invention. The described catalytic compound containing solution can be applied to the solid substrate by various means such as brushing, dipping, spraying, roll coating, swabbing and the like. The amount of the catalytic compound applied to the substrate can be closely controlled by varying either the thickness of the solution coating applied to the substrate or the concentration of the catalyst in such solution.
The coated substrate is then heated to about 40°C. to about 200°C., and preferably about 90°C. to about 150°C., to volatilize the solvent and convert the monomer irreversibly into the water and solvent resistant coating containing the decomposition catalytic compound. The temperature is suitably selected to polymerize the monomer and not to deleteriously effect the desired properties of the substrate. Such heating can be carried out using commercially available equipment. A controlled inert atmosphere during such heating is satisfactory, but is not required.
The catalyst-polymer coated substrate can be stored in air, without requiring control of the oxygen or moisture content thereof, and still retain an effective decomposition catalytic compound. Preferably the aluminum plate is deposited within about one day and more preferably within about 4 days after polymerization of the monomer on the substrate surface.
The following examples will further illustrate the process of the present invention.
A CSZ of Formula I is prepared as follows: a solution of 38.5 parts (0.15 mole) biscatechol trimethylene ether and 34.4 parts (0.33 mole) tetrahydrothiophene oxide in about 160 parts methanol is treated at 0°C. with anhydrous HCl. A solid bissulfonium chloride is recovered, dissolved in methanol and slurried with a strong base anion-exchange resin in hydroxide form to give a cyclic sulfonium zwitterionic monomer (ID, m = 3). The CSZ monomer is isolated or used as a methanol solution. In aqueous solution the pH is about 10.5-11.5.
Other CSZ monomers of Formula I are prepared similarly from phenol, bisresorcinol ethers, and phenolformaldehyde novolac resins.
EXAMPLE 1
A methanol solution containing 53 weight per cent of the CSZ 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}]bis(tetrahydro thiophenium hydroxide)bis (inner salt) with the formula: ##SPC3##
and 1 1/2 weight per cent TiCl 4 was prepared by mixing the desired proportions of a methanol-monomer solution with a TiCl 4 -methanol solution. The monomer-TiCl 4 solution was then applied to a portion of one surface of a 4 mil thick Mylar film using a wire wound rod to spread the CSZ monomer-catalyst-methanol solution over the surface. The catalyzed film was heated at 85°C. for 5 minutes to polymerize the CSZ monomer. An adherent, water and solvent insoluble polymer with the TiCl 4 catalyst dissolved therein was obtained. The so catalyzed substrate remained in the laboratory air atmosphere for about 5 minutes before being placed in a dry nitrogen atmosphere, immersed in an 0.3 molar aluminum hydride-diethyl ether solution and dried. When the aluminum hydride in contact with the substrate was heated to 100°C. for about 5 minutes a decorative, specular, aluminum plate was deposited only on that portion of the Mylar film treated with the CSZ monomerTiCl 4 -methanol solution.
EXAMPLE 2
Sufficient TiCl 4 was slowly admixed with a methanol solution containing 40 weight percent solute to form a final solution containing about 2 1/2 weight per cent TiCl 4 . The solute consisted of 90 weight per cent of 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}] bis(tetrahydrothiophenium hydroxide)bis(inner salt) and 10 weight per cent tetrahydro-1-(4-hydroxy-3-methylphenyl) thiophenium hydroxide, inner salt. The final solution was first applied to a 3 mil thick Mylar film using a wire wound rod and then polymerized in air for one minute at 104°C. The polymerized-catalyzed surface was placed in a dry nitrogen environment and partially submerged in a 0.5 molar AlH 3 -ether solution, removed from the hydride solution and developed at 140°C. i.e., the AlH 3 decomposed to aluminum. An adherent aluminum plate was obtained on the AlH 3 contacted, catalyzed portion of the substrate.
EXAMPLE 3
A Mylar film was treated substantially as described in Example 2, including an added exposure to a temperature of 140°C. for 10 seconds prior to contacting the polymerized surface with the hydride. An adherent aluminum plate was produced.
EXAMPLE 4
A methanol solution containing 1 1/2 weight per cent TiCl 4 and 37.4 weight per cent of 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}]bis(tetrahydro thiophenium hydroxide)bis(inner salt) was prepared and applied to a 3 mil thick Mylar substrate, polymerized at 104°C. and aluminum plated as described in Example 2. An adherent aluminum coat was developed on the AlH 3 contacted, polymerized portion of the substrate.
EXAMPLE 5
Contacting the catalyzed substrate of Example 4 with a 0.25 molar solution of AlH 3 in ether and developing the hydride at 140°C. provided an aluminum plate on the AlH 3 contacted, catalyzed portion of the substrate.
EXAMPLES 6 and 7
Separate Mylar substrates were treated substantially as described in Examples 4 and 5, including an added exposure to temperature of 140°C. for 10 seconds prior to contacting the polymerized surface with the hydride. The aluminum plate deposited upon the catalyzed surface visually appeared improved over that deposited in Examples 4 and 5.
EXAMPLE 8
A 3 mil Mylar film was coated, as in Example 4, with the methanol solution containing about 63 weight per cent zwitterion. Polymerizing and decomposition of the aluminum hydride were carried out at 104°C. as described in Example 2. A satisfactory aluminum plate was deposited on the catalyzed portion of the film.
EXAMPLE 9
A Mylar film was coated and polymerized to form an adherent layer on the film consisting of 1 1/2 weight per cent TiCl 4 and a cross-linked polymer of the monomer 1,1'-[ethylenebis{oxy(4-hydroxy-o-phenylene)}] bis(tetrahydrothiophenium hydroxide)bis(inner salt). The catalyzed surface remained exposed to the laboratory air for a period of 6 days. At least a portion of the catalyzed surface was dipped into a 0.25 molar solution of AlH 3 in ether and exposed to a temperature usually sufficient to decompose the catalyzed AlH 3 . It is believed that no aluminum plate was formed on the Mylar surface as a result of a time related sensitivity of the polymer-catalyst mixture to the laboratory air. It is also believed that removal of a surface portion from the polymer-catalyst mixture would rejuvenate the catalytic coating.
EXAMPLE 10
A 4 mil thick Mylar film is catalyzed and aluminum plated substantially as described in Example 1. The catalyst-polymer coated substrate is exposed to the laboratory air atmosphere for about 24 hours before applying the aluminum plate to the substrate. A decorative, specular, sharply defined aluminum plate is deposited only where the aluminum hydride had contacted the catalyzed surface.
EXAMPLE 11
A methanol solution containing 20 weight per cent solute consisting of 74 1/4 weight per cent of a CSZ with formula: ##SPC4##
where n = 0.5, 24 1/4 weight per cent of tetrahydro-1-(4-hydroxy-3-methylphenyl)thiophenium hydroxide, inner salt with the formula: ##SPC5##
and 1 1/2 weight per cent TiCl 4 is applied to a 4 mil Mylar film by a roll applicator, polymerized at 140°C. for 10 minutes and maintained in air for 3 days before depositing an aluminum plate thereon as described in Example 1. In a similar manner a second coating of the catalyst containing solution is applied to the plated surface and a second aluminum plate deposited in only the area treated with the catalytic solution. The aluminum plate will tenaciously adhere to the substrate and have a shiny, decorative physical appearance.