CA1063889A - Substrates coated with platinum black - Google Patents

Abstract

SUBSTRATES COATED WITH PLATINUM BLACK

Abstract of the Disclosure Catalytic reactors consisting of a substrate carrying a surface coating of platinum black are prepared by applying a solution of hexachloroplatinic acid to the surface of the reactor to form a coating and then reducing the hexachloro-platinic acid to form a surface coating of platinum black.

Description

Jl j - 1~ Soft contact lenses can be disinfected and undesirable - ~ microorganisms removed by soaking the lenses in hydrogen Jl peroxide. A readily available aqueous hydrogen peroxide solution ~j ~or this purpose is the 3% aqueous solution of hydrogen peroxide ¦~ sold as hydrogen peroxide U.S.P.
Soft contact lenses are generally formed from certain hydrophilic polymers which may be a homopolymer of hydroxyethyl ~¦ methacrylate (HEMA) cross-linked with ethylene glycol - j~ dimethacrylate (EDMA) or from a polymer obtained by copolymer-izing a mixture of HEMA, some EDMA and methacrylic acid with 1~1 either poly (N-vinylpyrrolidone) or with monomeric N-vinyl-pyrrolidone. The contact lenses produced ~rom the resulting polymeric materials exhibit marked hydrophilic properties and ;1 are quite so~t and ~lexible when ~ully hydrated.
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¦ While these lenses are not actually perforate, they , do have a sufficient degree of molecular porosity to permit water, o~ygen and tear fluids to permeate the lens structure.
~ In order for the cleaning of these lenses to be effective after ~1 they have been worn, it is important that all contaminants be removed from both surfaces and the interior of the lens.
Hydrogen peroxide has been reported to be an effective agent for use with contac~ lenses in order to kill any contaminating microorganisms. As reported in "Soft Contact Lens" published by the C. V. Mosby Co., St. Louis (1972), Page 247~ hydrogen peroxide penetrates the lens in about 30 seconds, oxidizes any mucoprotein that exists on the surEace of the lens and is simultaneously an effective sterilant for any microorganisms present in the eye.
However, before being inserted into the eye the hydrogen peroxide-treated soft contact lens must be rinsed repeatedly in isotonic buffered saline in order to remove any residual hydrogen peroxide. Isotonic buffered saline is an 0.85% by weight solution of sodium chloride buffered to a pH of 6.9 to 7.1, or even 6.8 to 7.2, and preserved with thimerosal 0.001% and disodium edatate 0.1%. Hydrogen peroxide, even in quantities as low as 10 to 20 ppm (parts per million) can be detected in e eye and may cause some irritation of the eye

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in cases o~ particular sensitivity. Some less sensitive eyes can tolerate as high as 60 ppm or more. Repeated soaking and rinsing in isotonic buffered saline as presently practiced, I`, does not always eEfectively remove all of the hydrogen peroxide ~ present because rinsing merely acts to serially dilute the il hydrogen peroxide to a lower concentration. The rinsed soft contact lens can still retain a sufficient concentration of hydrogen peroxide to be irritative to the wearer.
An adequate rinsing regimen poses other problems. Qne of the principal problems is that it requires a considerable period of time and personal atten~ion in order to carry out an adequate rinsing procedure. For an adequate soaking and rinsing sequence it has been found that four separate rinses are required.
Wlth the necessary intermediate soaking an acceptable procedure will take about 30 minutes or more. Another drawback resides in the fact that rinsing proceclures are generally highly subjective and lack reproducibility in that they can ~ary widely in effectiveness ~rom one person to another. Additionally, large volumes of saline solution are necessary to carry out an adequate four-rinse procedure which makes the practice cumber-some and inconvenient.
A simple and convenient method for treating and disin~ecting soft contact lenses with hydrogen peroxide and '''' ~

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then removing the hydrogen peroxide from the soft contact lenses , is to immerse the soft contact lenses in an aqueous hydrogen :.
peroxide system which contains a hydrogen peroxide decomposition ~' catalyst. After exposure to 3% aqueous hydrogen peroxide for ~1 about 10 minutes the lenses are effectively disinfected by the j usual standards. Exposure for periods of up to 2 hours without a catalyst present will effectively yield sterilized lenses.
When a hydrogen peroxide decomposition catalyst is then brought into con~act with the sterilizing solution it will decompose the H2O2 in accordance with the following reaction:

2 2 ~ 2H2O + 2[0] ~ O
the harmless reaction products obtained being water and nascent oxygen and the oxygen formed bubbles off as a gas. Since the catalytic decomposition reaction requires about 6 hours to reduce the H2O2 to a satisfactory level, depending on the amount of catalyst, exposed surEace and the geometry of the reaction container, even though the respective reactions are competing~
effective sterilization will have occurred well before ; decomposition of the H2O2 to an inef~ective level has taken place.
A very effective hydrogen peroxide decomposition catalyst is platinum metal where maximum surface for catalytic activity is presented. ~ form of platinum metaL having maximum -- surface area is platinum black as a coating on a suitable ¦ substrate or support. The substrate may be any inert material -~-,'' l ' . l .. 1~
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such as alumina, carbon, stainless steel or a suitable thermoplastic or thermosetting synthetic polymeric material. These synthetic materials can readily be molded into intricate shapes to provide a relatively large surface area in relation to their overall outside dimensions. To provide a controlled, uniform and adherent coating of platinum black of satisfactory catalytic activity on the surfaces of such intricate molded shapes is, however, a difficult technical problem.
We have now found that an adherent and substantially uniform coating of platinum black of accurately controlled thickness may be provided on substrates of varying shape by applying a layer of a solution of hexa-chloroplatinic acid to the surfaces to be coated, removing the solvent from the surface of the substrate and then converting the residual surface layer of hexachloroplatinic acid to platinum black by reduction in a reducing atmosphere, e.g. a reducing atmosphere containing hydrogen. The hexachloro-platinic acid may be applied as an aqueous or organic solvent solution and, most conveniently, may be applied by being sprayed onto the substrate sur-faces. The reduction step is carried out after the solvent has been eva-porated. Accordingly~ the coating and drying steps may be alternated until sufficient hexachloroplatinic acid has been deposited on the substrate to give a platinum black coating of the desired thickness upon reduction.
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10~ 8~3 ¦ l~hile water may be used as the solvent for the ¦i hexachloroplatinic acid in preparing the hexachloroplatinic acid .,. ~j ~I solution for the coating step, use of a volatile solvent is 3~ preferable since it may be evaporated off more readily. Alcohols ~ such as methyl, ethyl, propyl, isopropyl, isobutyl, n~butyl and heptyl alcohol are satisfactory solvents as are other common solvents such as acetone, methylethylketone, methylisobutyl-ketone, ethylacetate, acetonitrile and 1,4-dioxane, or even isopropylamine, and mixtures of these solvents.
Solutions containing 0.1 to 1% by weight of hexachloro-platinic acid may be convenien~ly employed but higher concentra-tions of even 10% or more may be employed. Sufficient hexa-chloroplatinic acid should be deposited on the substrate to yield a coating of platinum black of from about 0.2 to 0.5 mgs per sq. centimeter after reduction.
The spray coating and evaporation of the solvent may conveniently be carried out us:ing a rotable pharmaceutical tablet coating pan. The substrate to be coated may be in the ~ form of molded shapes of the desired configuration which are converted to reactor pellets coated with platinum black by the coating and reducing steps.
The uncoated pellets are charged into the coating pan which is then caused to rotate and while rotating the hexa-¦-chloroplatinic acid solution is sprayed into the pan and onto the . ~ ~ . .
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moving, rotating pellets. By alternately spraying the solution onto the moving pellets and then drying the moving pellets by using a stream of warm air to evaporate the solvent a coating of hexachloroplatinic acid of the desired thickness is built up in stages with an intermediate drying siage in which for example, the coated pellets may be placed in an oven and dried by being heated to a temperature for example of about 50 to 100C, preferably about 95C for from about 1/2 to 2 hours. Thus/ the pellets may be subjected to 20 to 30 cycles of spraying and drying by warm air solvent -~ ;~
evaporation and then oven dried as described above. They may then, i desired, be subjected to an additional 5 to 15 cycles of spraying and warm ~ air drying by solvent evaporation followed by oven drying at 50 to 100C.
; ~ This coating and drying procedure enables one to produce a very adherent platinum black coating of carefully controlled thickness when the hexa-chloroplatinic acid surface coating is then reduced to platinum black.
Reduction of the hexachloroplatinic acid in a hydrogen atmosphere may be carried out under pressure or at atmospheric pressure by flowing a stream of hydrogen gas over the coated pellets. The reduction can be carried out at a temperature of 40 to 100C. Preferably, where a flowing stream of hydrogen is used, the hydrogen is first diluted with an inert gas such as nitrogen before being passed over the coated pellets so that the hydrogen concentration in the mixture is about 0.5 to 5% by ~ . ' `'~` -:,'~. : :,, ; ~ - 7 -~ ;

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~ '3 J volume. Not only does this use of an inert diluent constitut-e~
~j a safety factor but the inert diluent component also aids in ~3 removing by-product hydrogen chloride from the reactor in which ~l the reduction is carried out.
¦1 In order further to illustrate this invention the ¦ following examples are ~iven:

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t ~1 3 ~l Twenty cylindrically catalytic reactor substrates in j~ the form of shaped pellets 1/2 inch long and 5/8 inch in 3 diameter provided with six peripherally spaced vertical 1/8 inch wide flutes about 1/16 inch deep to provide additional surface area and molded of "Noryl'~polymer are introduced into a small tablet coating pan and~ whiLe the pan is rotating at about 40 r.p.m. a 0.5% by weight solution of H2PtC16 (hexachloroplatinic acid~ in U.S.P. ethyl alcohol is sprayed into the pan until all of the moving reactor pellets are wet. Hot air is then blown into the pan until the ethyl alcohol has evaporated off.
- Alcoholic hexachloroplatinic acid solution is again sprayed into the pan until the reactor pellets are wetted and the alcohol again evaporated off by using a current o hot air. The procedure is repeated until about 30 cc of solution has been sprayed for each 10 reactor pellets present in the coating pan.
The dried hexachloroplatinic acid coating adhering to the surface of the reactor pellets is then converted to platinum black by reduction with gaseous hydrogen. The coated reactor pellets are placed in a closed vessel under about 30 lbs. per sq. in. hydrogen pressure and maintained under this hydrogen atmosphere for about 6 hours at a temperature of 20C to effect the desired reduction.
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Each reactor pellet carries about 4.5 mg by weight of platinum black which is equivalent to about 0.2% by weight of the base material.
~, The polymeric material identified by the trademark ~¦ "Noryl" is marketed by the General Electric Company. This plastic material is a phenylene oxide polymer formed by the oxidative polymerization of 2,6-dimethylphenol in the presence of an amine-basic cupric salt complex as the oxygen-carrying intermediate. These phenylene oxide polymers are more particularly described in U. S. Patent Nos. 3,306,874 and 06,875.

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~il Reactor pellets are molded of "Noryl" to form a ?
hollow and generally cylindrical shape about 5/16 inch long, the ~7 inner surface carrying three inwardly disposed flutes about 1/16 inch in height and the outer periphery being provided with a series of 12 spaced outwardly extending rounded flutes with three of the flutes, separated by 120 , being about 1/8 inch in height and the remainder about 1/16 inch in height, thus yielding a total exposed reactor pellet surface of about one square inch.
3000 of these reactor pellets are placed in a 16 inch diameter baffled coating pan and the pan is rotated while the reactor pellets are sprayed with a solution of 15 g hexachloro-platinic acid in 1500 ml of S. D. No. 30 ethyl alcohol. The spray cycle consists of an alternate 90 second spray period a~d a 30 second drying period using hot air to evaporate the ethyl alcohol solvent. Approximately 40 cycles are employed to apply about 1000 mL of solution to the 3000 reactor pellets. The coated reactor pellets are then dried in an oven àt 95 C. The dried reactor pellets are then coated with the remaining 500 ml - I of solution by continuing the spraying and drying steps for ~ 20 about another 20 cycles. After the coated reactor pellets are :~ dried at 95C for another 45 minutes they are reduced in a - i hydrogen atmosphere. The reactor pellets are placed in a vessel Il -11_ I
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I 1~3~ 3 ¦ held in a water bath at about 95 C through which nitrogen gas ¦~ is passed while maintaining the pellets at about 44 C and then a gaseous mixture of l to 5% hydrogen in nitrogen is passed ~I through ~he vessel and over the reactor pellets. The internal ~ temperature may rise to as high as 80 C during the reduction.
~ The gaseous reduction is continued for about 24 hours or until - ~ at least 98% of the hexachloroplatinic acid present on the surfaces of the reactor pellets has been reduced to platinum black. After reduction, the reactor pellets are washed ln hot distilled water and are then ready for use.

WE CLAIM: ¦
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Claims (12)

1. Process for the production of a substrate carrying a coating of platinum black which comprises coating the surface of the substrate with a solution of hexachloroplatinic acid, evaporating the solvent and reducing the hexachloroplatinic acid deposited on the surface of the substrate to platinum black by exposing the coating of hexachloroplatinic acid to a reducing atmosphere.

2. Process in accordance with claim 1 in which a plurity of coatings of hexachloroplatinic acid are applied to the substrate before reduction.

3. Process in accordance with claim 1 wherein the reducing atmosphere contains hydrogen.

4. Process in accordance with claim 1 wherein the reducing atmosphere is a mixture of hydrogen and a carrier gas chemically inert toward the hexachloroplatinic acid.

5. Process for the production of a substrate carrying a coating of platinum black which comprises coating the surface of the substrate with a solution of hexachloroplatinic acid by spraying the solution onto the substrate surfaces and then evaporating the solvent from the substrate by passing a current of warm gas over the substrate surfaces, repeating the spraying and evaporating steps until the desired amount of hexachloro-platinic acid has been applied to the substrate and then reducing the hexachloroplatinic acid to platinum black by exposing the coating of hexachloroplatinic acid to a reducing atmosphere.

6. Process in accordance with claim 5 wherein the reduction is carried out in a reducing atmosphere with the coated substrate being heated to an elevated temperature.

7. Process in accordance with claim 6 wherein the reducing atmosphere is hydrogen.

8. Process in accordance with claim 6 wherein the reducing atmosphere is hydrogen in admixture with a chemically inert diluent gas.

9. Process in accordance with claim 5 wherein the coated substrate is dried by being heated to a temperature of from 50 to 100°C prior to being exposed to a reducing atmosphere.

10. Process for the production of a substrate carrying a coating of platinum black which comprises coating the surface of the substrate with a solution of hexachloroplatinic acid by spraying the solution onto the substrate surfaces and then evaporating the solvent from the substrate by passing a current of warm gas over the substrate surfaces, repeating the spraying and evaporating steps until the desired amount of hexachloro-platinic acid has been applied to the substrate, drying the coated substrate by heating the coated substrate to a temperature of from 50 to 100°C and then exposing the coated substrate to a reducing atmosphere comprising hydrogen.

11. Process in accordance with claim 10 wherein the reducing atmosphere comprises hydrogen and an inert carrier gas.

12. Process in accordance with claim 11 wherein the reduction is carried out with the coated substrate at an elevated temperature.