US3905877A

US3905877A - Process for electroplating polyoxymethylene

Info

Publication number: US3905877A
Application number: US443204A
Authority: US
Inventors: Edward Johnson Deyrup
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1974-02-19
Filing date: 1974-02-19
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16

Abstract

An improved process for electroplating polyoxymethylene is provided wherein shaped articles of polyoxymethylene are treated with pyridine preferably by immersion techniques prior to subjecting the shaped article to surface treatment with an acid etching agent.

Description

United States Patent [191 Deyrup [4 1 Sept. 16, 1975 PROCESS FOR ELECTROPLATING 1 POLYOXYMETHYLENE [75] Inventor: Edward Johnson Deyrup, Northeast,

[73] Assignee: E. I. Du Pont de Nemours and 1 Company, Wilmington, Del.

22 Filed: Feb. 19, 1974 21 App1. No.: 443,204

[52] US. Cl. 204/30;' 29/195; 117/47 A;

204/20; 204/32 R; 204/38 E [51] Int. Cl. C25D 5/56 [58] Field of Search 204/20, 30, 38 E;

[56] 1 References Cited UNITED STATES PATENTS 3,414,427 12/1968 Levy 117/47 Primary Examiner-John H. Mack Assistant Examiner-Aaron Weisstuch [5 7] ABSTRACT An improved process for electroplating polyoxymeth' ylene is provided wherein shaped articles of polyoxymethylene are treated with pyridine preferably by immersion techniques prior to subjecting the shaped article to surface treatment with an acid etching agent.

2 Claims, No Drawings PROCESS FOR ELECTROPLATING POLYOXYMETHYLENE FIELD OF THE INVENTION The present invention relates to a process for electroplating shaped structures of polyacetal polymeric material and, more particularly, is directed to a novel improved process for electroplating articles of polyoxymethylene.

BACKGROUND OF THE INVENTION Processes and 'methods for electroplating shaped structures or objects of polyacetal resins such as polyoxymethylene are known. For example, US. Pat. No.

3,5 54,880 discloses a process for electroplating an article of polyoxymethylene which comprises first subjecting the article to a surface preparation treatment by immersing the article in an acid agent such as orthophosphoric acid thereby to etch the surface of the article. The acid-etched article is thereafter treated as by an immersion technique with a basic solution such as sodium hydroxide. The thus treated article is then subjected to the conventional electroplating technique which entails the sequential steps of treating the article with sensitizing agents and activating agents followed by depositing an electroless plating of, for example, copper on the article and thereafter electroplating the article in a conventional electroplating bath. A drawback and continuing problem encountered heretofore as regards the electroplating of polyoxymethylene articles has been the inability to obtain plated articles wherein the metal plating is firmly bonded to the sur face of the plastic article. Oftentimes, the metal coating on the plastic object will exhibit undesirable blistering when the plated plastic object is subjected to a thermal cycle of heating and cooling, and the plastic objects often exhibit undesirable surface cracks which are be lieved to be induced by the acid etchant. The principal object of the present invention is to provide an improved process for electroplating shaped articles and objects of polyacetal resins such as polyoxymethylene that are characterized by more firmly adhered metal coatings and substantially free of the above-mentioned drawbacks.

THE INVENTION According to the present invention there is provided in a process for electroplating a shaped article of polyoxymethylene by the sequential steps of etching the surface of said article with an acid etching agent such as orthophosphoric acid, neutralizing the etched surface of said article with a basic solution such as sodium hydroxide, treating said article with a noble metal catalyst such as palladium, depositing by electroless plating a metal coating such as nickel on said article, and depositing by electroplating a metal coating such as nickel, copper or chrome on said electroless plated article, the improvement which comprises treating said article with pyridine before etching the surface of said article.

DETAILED DESCRIPTION The nature and advantages of the present invention will be more clearly understood by the following more detailed description thereof.

The salient feature of the present invention is the discovery that subjecting polyoxymethylene shaped articles to a treatment with pyridine prior to the conventional pre-treatment with acid etchants and catalysts (for electroless deposition) prior to the electroless plating and the electroplating thereof results in superior plated polyoxymethylene shaped articles characterized by a unique surface topography after etching and a more uniformly etched surface, fewer acid-etchant induced surface cracks, and unexpected and surprising adhesion of the metal coating characterized by superior resistance to blistering of the metal coating.

The improved process of the present invention may be practiced by treating the shaped articles of polyoxymethylene with pyridine. This is preferably done by immersing the polyoxymethylene article in the pyridine. The pyridine utilized for the treatment may be a solution entirely of pyridene or an aqueous solution of pyridine containing up to about 7.5 percent by volume of water.

After the pyridine treatment, the polyoxymethylene article is subjected to a preplate process and an electroplating process similar to that described in the aforementioned U.S. Pat. No. 3,554,880.

The principle and practice of the present invention will now be illustrated by the following Examples which are exemplary only and it is not intended that the invention be limited thereto since modifications in technique and operation will be apparent to anyone skilled in the art. All parts and percentages specified in the Examples are by volume unless otherwise specified.

EXAMPLE Polyoxymethylene resins containing 0.75 percent by weight of nylon stabilizer and 0.125 percent by weight antioxidant (GAO-5 ,2,2 '-methylene-bis-( 4-methyl-6-tbutyl) phenol and having the number average molecu lar weight indicated in Table 1 below were molded by conventional molding techniques at the temperature also indicated in Table 1 into plaques having a planar dimension of 3 inches by 6 inches and a thickness of one-eighth inch.

The plaque samples were immersed for 2 minutes into an alkaline cleaner solution comprising 6 oz. of Metex S1651 (MacDermid, Inc.., Waterbury, Connecticut) per gallon of distilled water maintained at 84C. and thereafter rinsed for 2 minutes with water at room temperature.

The cleaned plaque samples were next immersed for 5 minutes in a solution of 30% pyridine and distilled water maintained at 60C., followed by a l minute rinse with water at room temperature.

The pyridine-treated plaque samples were next immersed for two minutes in a solution of distilled water containing 83% by volume of 85% by weight orthophosphoric acid maintained at 70C., followed by a one minute rinse with water at room temperature.

The acid etched plaque samples were next immersed for 6 minutes in a distilled water solution containing 12% by weight sodium hydroxide maintained at 104C.

The base-neutralized plaque samples were next immersed for 10 minutes in a distilled water solution con taining 1% by volume of acetic acid maintained at C.

The surface treated polyoxymethylene plaque samples were next subjected to electroless nickel plating in the following manner: (1) the plaques were first immersed for 2 minutes in a preactivator bath (maintained at room temperature) consisting of a solution of distilled water containing 1% by volume of MACuplex Preactivator PA-3 (MacDermid, Dermid, Inc., Waterbury, Connecticut), followed by a one minute rinse water at room temperature, (2) the plaques were next immersed for 2 minutes in a palladium activator bath (maintained at room temperature) consisting of a solution of distilled water containing by volume of MACuplex Activator D-34 (MacDermid, Inc., Waterbury, Connecticut) and 20% by volume of HCI, followed by a 1 minute rinse with water at room tempera- 1O ture, (3) the plaques were next immersed for one minute in an accelerator bath (maintained at 50C.) consisting of an aqueous solution of distilled water containing 5% by volume of MACuplex D-45 Accelerator (MacDermid, Inc., Waterbury, Connecticut), followed by a one minute rinse with water at room temperature, (4) the plaques were next electroless plated by immersing the plaques for 10 minutes into a commercially available electroless nickel bath (maintained at 30C.)

consisting of a solution of distilled water containing about 10% by volume of MACuplex J-6O Electroless Ni concentrate (MacDermid, Ine., Waterbury, Connecticut) and about 3% by volume of MACuplex Electroless Ni Reducer J-6l (MacDermid, Inc., Waterbury, Con- The electroplated plaque samples were next repeatedly subjected to the following thermal cycle: l heating to 180F. and holding at that temperature for 1 hour, (2) cooling to room temperature and holding at room temperature for 15 minutes, (3) cooling to -F. and holding at that temperature for 1 hour, and

(4) heating to room temperature and holding at that temperature 15 minutes, and evaluated for blistering after each cycle. The results are reported in Table l below.

For comparative purposes, the foregoing procedure was repeated except that the polyoxymethylene plaque samples were not subjected to the pyridine treatment. The results also are reported in Table 1 below.

In both cases described above, polyoxymethylene plaque samples were evaluated for surface cracks; these samples were prepared in accordance with the procedure described above except that the electroless nickel plating was conducted for 5 minutes instead of' 10 minutes, in order to obtain a thinner layer of electroless nickel to facilitate evaluation for surface cracks. The summation of the length of the cracks induced on the surface of the plaque samples also is presented in Table 1 below under the column ZCL.

TABLE 1 Surface Area Number Average Molding Pyridine Number of Thermal Blistered After ECL, Sample Molecular Weight Temperature, F. Treated Cycles to Blister l5 Cycles, mm

1 33,000 185 No I I .5 372 2 33,000 I85 Yes 15 0 I66 3 33,000 2I() No I 0.2 295 4 33,000 2 I 0 Yes I 5 0 0 5 39,000 I85 No I 50 lst Cycle) 849 6 39,000 I85 Yes 15 0 355 necticut) having a pH of about 9.0 maintained by the appropriate addition of concentrated (28%) ammonium hydroxide.

The electroless nickel plated plaque samples were next electroplated by subjecting the plaques to the sequential steps of the eleetroplate sequence set forth in the table below; the plaques were immersed sequentially into each treating bath of the composition identified in the table below by immersing the plaques under the conditions also set forth in the table:

Electroplate Sequence Temperature Current Density, Time Plate Thickness Step Bath Composition F. Amps/Sq. Ft. (Min.) In.

I 5% H,SO 70 until gas begins to evolve 2 Water Rinse 7O 025 3* Ni Strike (Watts Ni) l35-I40 0-2 2-5 0.1 4 Water Rinse 70 0.2 5 5% H 0.2 6 Water Rinse 70 0.2 7 MacDermid Bright Acid Copper 70 40 I5 0.5 8 Water Rinse 70 0.2 9 5% H SO 1% HCI 70 02 l0 Water Rinse 70 0.2 l l MacDermid Bright Nickel Process No. 30 I40 40 5 0.1 12 Water Rinse 70 0.2

I3 5% H SO 70 0.2 14 Water Rinse 70 0,2 l5 MAC Chrome I I5 I25 2 0.02-0.06

The nickel-strike was deposited by immersing the plaque samples into the Watts type nickel plating bath operating at a current density of about l5 amps/sq. ft. for up to about 2 minutes after which the current density of the hath was l'fliSLftl to about 30 amps/sq. ft.

ing of pyridine and up to about by volume of water before etching the surface of said article.

2. Shaped articles of polyloxymethylene whenever prepared according to the process of claim 1.

Claims

1. In a process for electroplating a shaped article of polyoxymethylene by the sequential steps of etching the surface of said article with an acid etchant, neutralizing the etched surface of said article with a base solution, treating said article with a catalyst for electroless deposition, depositing by electroless plating a metal coating on said article, and depositing by electroplating a metal coating on said article, the improvement which comprises contacting said article with a liquid consisting of pyridine and up to about 75% by volume of water before etching the surface of said article.

2. Shaped articles of polyoxymethylene whenever prepared according to the process of claim 1.