US 2447379 A
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Patented Aug. 17 1943 FROCESS FOR METALIZING NONMETALLIC ARTICLES Frederick Ross Wenger, Los Angeles, Calif., as- Signor to Focal Company, Downey, Califl, a corporation of California I No Drawing. Application'April 21, 1943, Serial No. 483,948
- 1 Claims. (Cl. inc-47) This invention relates to a process for the metalizationof plastics and other non-metallic substances, such as paper, Celluloid, sheet cork,
fivory, bone, hard rubber, wood, leather, cloth,
horn, pressed Woods, imitation leather, glass,
porcelain products and plastic materials which are not reactive to alcohols, ketones and esters,
and the products resulting therefrom,
It has heretofore been proposed to coat nonmetallic substances with metal, such as silver or copper, but these processes have not been entirely satisfactory due to cost, time consumed in treating the substance to be metalized, and lack ing the non-metallic substance, or article to be metalized, to three baths to be specified hereinafter, and then a platin operation of any Wellknown type now'in use. As one example of cardipped in the following. solution to oxidize the silver deposited on the sheet'i'n the firstdip:
To equal parts of water and denatured ethyl alcohol byv volume add 5 or 10% of alight metal hydroxide, such as sodium hydroxide or potassium hydroxide. The denatured alcohol content of this solution .should. not drop below 50%. When the hydroxide is added, the solution will turn an amber color. The solution should be allowed to age for at least 24h0urs before using. The treated sheet of plastic is now given a thirty second dip in this oxidizing solution at room temperature whereupon the solution oxidizes the silver on the sheet converting it. toeither silver hydroxide or silver oxide. If a. heavier coating is desired thesheet may beleft in thesolution for or 50 seconds. Itis then dried and'is readyfor a reducing bath.
In order to prepare the reducing bath a select- .ed quantity of water is saturated with sulfurdioxide gas to, obtain sulphurous acid,
rying out the novel process, the same will be j' described, merely for the purpose of illustration, .in' connection'with the metalization of plastics cellulose'nitrates, and cellulose acetates and plastics which do not react to alcohols, ketones and;
A plain, clean sheet of cellulose nitrate plastic is first subjected to abath of acetone, denatured alcohol and silver nitrate. This bath or solution is formed by dissolving silver nitrate crystals in, 1 denatured alcohol at a temperature of approximately 15 C'.,'or"slig'h't1y higher, and this mixture is added to acetone. Preferably the bath comprises 50 parts by volume of denatured ethyl alcohol, 50 parts by volume of acetone and silver nitrate crystals of from 5 to 10 parts of the mixture of acetone and alcohol. Nothing is gained by adding more than 10 parts by volume of silver nitrate although if an alcohol of a higher specific gravity is used a greater amount of silver nitrate crystals will be dissolved. The best results have been obtained by using ethyl alcohol in the bath where methyl alcohol or acetone is used as the denaturant. The plastic sheet is dipped into the bath at room temperature, 1. e., approximately 65 F., for thirty seconds and after this dip the article is dried, preferably in a stream of warm air.
After the initial silver dip, the plastic sheet is Sodium sulphite is now added to the sulphurous acid until the reaction of the acid ceases.
.There isthus obtained a saturate solution of so- 1 to c. c. of the stock solutionof sodium bisulphite is added 500 c. c. of water and into this is poured powdered zinc to obtain the following reaction:
This mixture is kept cool as by means of ice or cold water until the reaction between the zinc and the acid of the bisulphite has been completed. A portion of the zinc sulphite is converted into a basic salt and S02, thus set free, is then reduced in turn by the excessive zinc present. A reducing bath thus formed gives fair results if used within a few hours after it is first made but better results silver finish. The strip can then be plated with any suitable material, such as copper, where the required temperature of the plating bath is below the danger point of deterioration of the plastic base.
The-reducing. bath slowly oxidizes and hence must be' kept in a closed container. It has been found that if a small amount of sugar, honey, or glycerine is added, the oxidation will be slowed and the keeping properties improved. It is noted that meta bisulphite should not be used in making the reducing bath because if used sulphides will be formed and the results" willbe unsatisfactory.
When metalizing the other non-metallic substances referred to above, such as rubber, for 'example, it is preferred to make a solution of a cellulose nitrate plastic and acetone to the consistency of light cream. The rubber, Or other article, is dipped into this cream, then dried and processedin accordance with the procedure outlined v above for the cellulose nitrates strip.
'Therejis "thus" provided a novel and simple "niethod for metalizing non-metallic substances *and'one Whichcan be quickly and inexpensively "carried out. and has awi'de variety of uses as will be apparent to those skilled in the art.
Theproduct obtained is durable fWl'iat is claimed is: "1. A process for metalizing non-metallic arti- "cles ofthe class described-which includes the steps" of "subjecting the article to a bath of de- "'n'atured alcohol; acetone and silver nitrate, dry- "ingiand subjecting the article to a bath of'water, denatured alcohol andan alkali metalihydroxide,
' and'd'rylngand subjectingthe article to a reducingbeithof sodium bisulphite andzinc.
2. A process for metalizing non metallic articlesof the class described which includes the steps of treating the article with r a silver nitrate solution, subjecting the treated article to alcohol, metal hydroxide oxidation of the silver deposited thereon -from= the first s01uti0n,-and subjecting to :convert the :oxidized silver to metallic silver.
A process for-metalizing non-"metallic articles of theclass -described which consists in sub- :je ctingethe article toa silver nitrate-denatured alcohol-and an alkali metalhydroxida. drying the article,.i dipping the dried article in abath of sodium bisulphite and. zinc, and r washinguand drying the article.
4. A process for metalizing non-metallic arti cles..of :the class described which includesthe the article toa solution containing zinc sulphite steps of subjecting the article to a silver nitrate denatured alcohol-acetone bath, drying the article and subjecting it to an oxidizing bath of denatured alcohol, water and sodium hydroxide, drying the article and subjecting it to a bath formed by introducing powdered zinc into sodium bisulphite.
5. A process for metalizing a plastic article which consists in dipping the plastic article in a silver nitrate-denatured ethyl alcohol-acetone bath, drying the article, subjecting the dried article to a bath of water, denatured ethyl alcohol and sodium hydroxide, drying the article, dipping the driedarticle in a bath of sodium bisulphite and zinc, and washing and drying the article.
6; Aproc'ess for metalizing a non-metallic arti-.
cle of the class described which includes the steps of subjecting the article to a silver nitrate bath for approximately thirty seconds at room temperature, drying and subjecting thearticle to an oxidizing bath of water, denatured ethyl alcohol and sodium hydroxide at room"temperaturefor approximately thirty seconds, drying the-'article and subjectin the same to a bat-hcontainingzlnc 3 sulphite-for approximately'two minutes at" room temperature. r
7; A process for metalizing a nommetalllcarticle of the class described'whichincludesthe step of subjecting thearticle to a-solu'tion of cellulose nitrate and-acetone having abOnsis'tencyOI'light cream, drying the articlefsubje'ctingthearticle to a bath of denatured'alcoh'ol; ace'tone'and'silver nitrate, drying and "subjecting the "article "to an oxidizing bath of water, denatured alcohol and an alkali metal hydnoxide and drying-andsubjecting the'article to a reducing bath oil zinc and sodium-bisulphita H H V H FREDERICK" R O SS W'EN'GER.
REFERENCES- CITED FOREIGN PATENTS V Country, "Date" "GreatBritain 1915 anc Ju e; 1.9.2