US3902974A

US3902974A - Process for metallizing type heads of plastics materials for printing devices

Info

Publication number: US3902974A
Application number: US482039A
Authority: US
Inventors: Gianfranco Bava
Original assignee: Olivetti SpA
Current assignee: Olivetti SpA; TIM SpA
Priority date: 1971-11-12
Filing date: 1974-06-24
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02

Abstract

Process for the metallic coating of type heads made of plastics materials for printing devices in which the surfaces to be metallized are subjected to a series of operations including in succession the stages of a) chemical deposition of a thin conductive metallic layer, b) growth of the said layer by electrodeposition. The growth by electrodeposition comprises a layer of nickel obtained in a special bath which confers to said layer particular qualities of hardness and wear resistance.

Description

United States Patent [191 Bava 1 Sept. 2, 1975 [5 PROCESS FOR METALLIZING TYPE 3.554.880 m9?! Jenkin 117/47 A HEADS 0F PLASTICS MATERIALS FOR 3.567.594 3/l97l Wells 204/20 PRINTING DEVICES Inventor: Gianfranco Bava, Turin. Italy Ing. C. Olivetti 8: C.. S.p.A.. Turin. Italy Filed: June 24. I974 App]. No.: 482,039

Related U.S. Application Data Continuation of Scr. No. 304.288, Nov. 6 abandoned.

Assignee:

U.S. Cl. 204/20; l l7/47 A; 204/40 Int. Cl. C250 5/54; C25D 5/10 Field of Search l 17/47 A; 204/20. 30, 40

References Cited UNITED STATES PATENTS 3/l969 Boggs ct al. ll7/47 A OTHER PUBLICATIONS Modern Electroplating, Edited by Fred Lowenheim. 2nd Edition. (1963). pp. 260-286. 296-303.

' Attorney, Agent. or FirmI. J. Schaefer [57] ABSTRACT nickel obtained in a special bath which confers to said 7 layer particular qualities of hardness and wear resistance.

7 Claims, N0 Drawings PROCESS FOR METALLIZING TYPE HEADS ()F PLASTICS MATERIALS FOR PRINTING DEVIL'ES This is a continuation of application Ser. No. 304.2%8 filed Nov. 6. W72. now abandoned.

The present invention relates to a process for metallizing the plastics materials employed in themaking of type heads for printing devices.

It is known that to produce type heads which are of small mass. for the purpose of obtaining a high positioning speed. and which at the same time are resistant to the wear caused by the frequent impacts to which they are subjected during operation. ,the said type heads can be formed by moulding. complete with all the types or characters. in plastics material. to which the necessary strength and surface hardness are then imparted by suitably metallizing the surfaces thereof.

Particularly suitable among the numerous types of plastics materials which can be cmployed'for this application are the urea resins and the phenolicresins.

Many processes for metallizing the aforesaid types of plastics materials have been proposed and are known in the state of the art. 1

A typical process for metallizing plastics materials which belongs to the state of the art is that in which the surface to be metallized, which is not conductive. un dergoes a preparation treatment to be then covered by a chemical method with a thin metallic coating which forms a low-resistance path for a subsequent increase of the metallization' carried out electrolytically.

The present invention relates to processes of the aforesaid type and in particular those processes in which at least one layer of the'electrolytic growth is constituted by nickel. v

The preparation treatment which precedes the chemical deposition is closely linked with the type of plastics materials to which it is applied and the present invention relates in thisconnection in particular to urea resins and to glass-loaded phenolic resins. The subsequent stages of chemical deposition and electrodeposition described here, on the other hand, have a greater generality of use and can be applied to type heads of plastics materials of any type whatsoever which have undegone a preparation treatment which has imparted to them surface properties similar to those conferred on the urea and phenolic resins by the preparation treaments described herein.

By employing metallic coating processes known in the art. of the type to which reference has been made hereinbefore, metallizations are obtained which..when

subjected to the particular kind of wear produced by repeated and frequent impacts to which type heads in printing devices are subjected, undergo deformations and peeling and have in the main an average life which is not of satisfactory length.

It has been found that the metallic platings of type heads of plastics materials for printing devices, constituted by a plurality of layers, some of which are deposited chemically and other electrolytically, at least one of which is an electrolytic layer of nickel, become much more resistant to deformations and to wear by impact if the said layer of nickel is obtained in a normal Watts bath with a current density betweenland 4 A/dm' at a temperature between 40 and 50C for a' time between minutes and 100 minutes so that is has a hardness between 20 and HRC and a columnar structure.

If. in particular. urea resins or phenolic resins or one of these loaded with fibres or reinforced insome way are employed as plastics materials, thcreare obtained readily reproducible metallizations characterized by optimum adhesion to the plastic and by absence of peelingor'flaking if. prior to the stage of chemical metallic deposition. the surfaces to be metallized undergo a preparation treatment constituted by a mechanical microroughening by sandblasting and immersion in a chemical conditioning bath" ada'pted'to render the acid surfaces. which are in themselves water-repellent. hy-' drophilic. I Onth e surface of the type heads to be metallizd by the process of the invention there is made a thin chemical deposit of a metal which forms the path for the passage of current for'a subsequent electrolytic growth or accretion. "constituted by nickel or copper-nickel. of the said chemical deposit of metal.

The chemical deposit trueand proper is preceded by a stage of prepar'ation' necessary for rendering the surfaces to be metallized hydrophilic and microporous. These properties are useful for giving the metallic layers a high adhesion to the surface of't'heplastic. The special application of the process of the invention to the metallization of typeheads, which are subjected to very frequent impacts against a hammer ora paper cylinder or platen, makes the property of "adhesionof the metallic covering layer to the plastic very important.

because possible creep phenomena would render the life of the head very short. To obtain the desired properties of resistance for this type of use,- it hasbcen found necessary to carry out the stage of surface preparation in two steps, a mechanical microroughening and mcntsknown for this purpose in the art inwhich, for

example, siliceous sand or glass microspheres are em.- ployed. In the particular. embodiment of the invention described here there was employed a mixture of water and aluminium oxide sand with a diameter between 20;]. and 1. in a 30 percent concentration, expelled with a pressure of. between 1 bar and 3 bars for a of between 10 and 3() .seconds. The.diameter of the grains of sand and the force of expulsion are chosen in such manner as not to cause scratches on the type heads, above all on the printingedges of the types which would result in a poor quality of printing.

The chemical conditioning for the urea resins may be carried out-in accordance withone of the many treatments which have been proposed in the art for this purpose, which are adapted to give riseto a surface microporosity of the objects of urea resin andto render this hydrophilicyso as to permitthe adsorption of the solutions producing the chemical metallic deposit. As regards the glass-loaded phenolic resins. on the other hand. the activation energy necessary for obtaining a chemical deposit of metal is such astorender necessary a very high conditioning inorder to obtain optimum adsorption of the catalytic metal in the stage following the conditioning; j v V This high conditioning is obtained by subjecting the surface to be covered first of auto one of the treatments known in the art for rendering the glass-loaded I phenolic resinshydrophilic, thereafter to a chemical attack by immersion in a bath of hydrofluoric acid at room temperature for a time of between 30 seconds and 90 seconds and. finally. to neutralization in an aqueous solution of sodium hydroxide with a concentration of between 5 and percent by weight at a temperature between 65 and 80C for a time of between 3 and 6 minutes.

The chemical deposition takes place by methods well known in the art. according to which there is first de posited on the surface to be metallized a thin layer of a catalytic metal. such as. for example. palladium. which promotes the subsequent deposition of a layer of metal. The chemical deposit may be of any conductor and may be effected by any method adapted to metallise the plastic non-electrolytically. Particuarly suitable for this purpose are. for example. deposits of nickel obtained by means of one of the many methods belonging to the state of the art. Deposits of nickel with a thickness between 0.5 and l,u have been found useful for the process of the invention.

zation of plastics materials. is obtained in an aqueous solution containing Nickel sul hate 150 g/l Nickel chloride I50 g/l Boric acid 30 gjl Hydrochloric acid 8 mill Naphthalene'trisulphonic acid sodium salt 4 g/l at a temperature between and C with a current density between 0.7 and 2 A/drn for a time of between 3 and' 5 minutes.

On the metallic layer obtained in this way there is deposited a second layer of electrolytic nickel which constitutesthc main layer of the metallization. The characteristics of this layer are critical for obtaining the said properties of resistance to wear by impact with particular reference to the impact to which type heads are subjected. I

To this end. the hardness and the structure of the layer of nickel are determinative. In fact. wear tests have been carried out in which a character of a type head of plastics material plated by the process of the invention is printed repeatedly until the quality of printing falls below a certain predetermined standard.

For equality of thickness of the layer of nickel. better results have been given in this type of test by those heads which had gone through the above-described stages and the electrolytic layer of nickel of which. for equality of other characteristics, had a hardness between 20 and 30 HRC and a columnar structure.

These tests have moreover revealed that a galvanic or electrodeposited nickel plating with the characteristics indicated has a more general utility. because it increases the rcsistancc to wear also of type heads made of plastics materials different to urea resins and phenolic resins. but which have in any case undergone a chemical metallic deposition preceded by a stage of surface preparation which gives the said metallic layer a sufficient degree of adhesion to the surface of plastics be light and therefore thin. A good compromise has proved to be to deposit layers of nickel with a thickness between 30 p. and 60 a.

Deposits with these characteristics are obtained by a galvanic process in a Watts bath containing Nickel sulphate Nickel chloride 30-60 g/l Boric acid at a temperature which may vary between 40 and 50C. with a current density between 1 and 4 A/d, and

. for a time of between 25 minutes and 100 minutes.

Baths of the type indicated above frequently give rise to pitted deposits. that is to say having surface inicrocavities caused by the liberation of hydrogen during the galvanic or electrodeposition process which prevents locally the deposit of the nickel.

This drawback is-obviated by the addition of surfaceactive products which bring the surface tension of the bath to values between 40 and 50 dynes/cm. Substances useful for this purpose and compatible with the characteristics required for the layer of nickel are-the alkali metal salts of arylsulphoni'c and alkylaryls'ulphonic acids.

To obtain a better resistance to corrosion and to improve the metallized object aesthetically. the'object metallized in this way may be subjected to electroplating with chromium to obtain a-thickness of chromium between 0.2 a and 0.6 a, by processes well known in the art. such as. for example. that which employs an electroplating bath consisting of an aqueous solution comprising from 380 to 420 g/l of chromic anhydride and from 4.2 to 4.4 g/l of sulphuric acid. with a current density between 20 A/dm and 40 A/dm for a time of between 1 and 3 minutes.

7 A variation in the above-described process consists in making on the chemical deposit of metal an electrode posit constituted by a layer of copper and over this layer of nickel, in which the thickness of the. copper may vary from 30 to 50 percent of the total thickness of the electrodeposit.

A deposit of copper satisfactory for the process of the invention is obtained with a pyrophosphate bath composed of potassium pyrophosphate 320 g/l copper pyrophosphate g/l ammonia 3 g/l with a current density between 0.8 and 2.5 A/dm and a time of between 25 minutes and minutes.

Good results have also been obtained with a deposit from an acid bath.

The deposit of nickel is obtained by a method similar to that already described. in which. however. the duration of the electrodeposition is limited to between and 75 minutes.

EXAMPLE A preferred embodiment ofthe stage of surface preparation of urea resins and glass-loaded phenolic resins will now be described. A sandblasting treatment suitable for both types of resins is obtained with a mixture of water and aluminium oxide sand with grains having a diameter of 1.4. which is expelled with a pressure of 1.5 bars for 15 seconds.

Each of the two resins is then immersed in one of the baths known in the art adapted to render the surface thereof hydrophilic. While. for urea resins. the preparation stage is thus concluded. for glass-loaded phenolic resins there is subsequently carried out an immersion in a bath of hydrofluoric acid for 1 minute at room temperature and then an immersion in an aqueous solution of 10. by weight of sodium hydroxide at a temperature of 80C for 5 minutes.

A preferred embodiment of the electrodeposition of nickel is represented by an electroplating bath constituted by an aqueous solution comprising:

Nickel sulphate 250 g/l Nickel chloride g/l Boric acid 30 g/l with the addition. as anti-pitting agent. of 1.5 cc/l of Antipit N62, a commercial product of Udylite. at a temperature of C with a current density of l A/dm for 90 minutes.

What 1 claim is:

1. In a process for metallizing a type head of plastic material for use in printing devices. the process having the steps of microroughening the surface of the type head and chemically coating the roughened surface with a thin metallic conductive layer. wherein the improvement comprises: clectrodepositing a layer of metal on the coated surface from a first acid bath having a higher acidity than a Watts bath and thereafter electrodepositing a working layer of metal thereon from a Watts bath having a lower acidity than said first acid bath to effect electrochemical accretion of nickel over the layer from the first acid bath and wherein the Watts bath is used at a temperature between 40 and C, with a current density between 1 and 4 A/dm for a time between 25 and 100 min. thereby obtaining a coapproximately 150 gll approximately 150 gll approximately 30 gl 1 approximately 8 ml/l approximately 4 g/l nickel sulphate nickel chloride boric acid hydrochloric acid sodium naphthalentrisulphonate at a temperature between 25 and 30C. with a current density between 0.7 and 2 A/dm'-. for a time between 3 and 5 min.

3. ln a process according to claim 1. wherein said Watts bath for the electrochemical accretion of nickel also includes a surface-active substance chosen from the group of alkali metal salts of arylsulphonic and alkylarylsulphonic acids.

4. In a process according to claim 1. wherein an electrolytic layer of chromium of a thickness between 0.2 and 0.6 microns is deposited over said electrolytic nickel layer.

5. In a process according to claim 1. wherein the step of microroughening includes mechanically microroughening by sandblasting and subsequently immersing the surface in an acid chemical conditioning bath adapted to render the surface to be metallized hydrophilic.

6. In a process according to claim 1. wherein the plastic material is glass-loaded phenolic resins and wherein the step of microroughening comprises mechanically microroughening by sandblasting followed by a first immersion in an acid chemical conditioning bath adapted to render the surface to be metallized hydrophilic. a second immersion in a bath of hydrofluoric acid at room temperature for a time of between 30 seconds and 90 seconds. and a third immersion in a neutralizing bath consisting of an aqueous solution of sodium hydroxide with a concentration of between 5 and 10 percent by weight. at a temperature between and C for a time of between 3 and 6 minutes.

7. In a process according to claim I. wherein said first acid bath comprises a nickel chloride. nickel sulfate bath.

' I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,902,974 0 DATED September 2, 1975 INVENTOR(S) Gianfranco Baya It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Q On the first page after [21] appln. No. 482,039" insert -[30] Foreign Application Priority Data November 12, 1971 Italy. .70696-A/7l-.

glgned and Scaled this [SEAL] sixteenth D y of March 1976 Attest:

. k 0 S2133? C. MARSHALL DANN Y K Commissioner oflarents and Trademark;

Claims

1. IN A PROCESS FOR METALLIZING A TYPE HEAD OF PLASTIC MATERIAL FOR USE IN PRINTING DEVICES, THE PROCESS HAVING THE STEPS OF MICROROUGHENING THE SURFACE OF THE TYPE HEAD AND CHEMICALLY COATING THE ROUGHENED SURFACE WITH A THIN METALLIC CONDUCTIVE LAYER, WHEREIN THE IMPROVEMENT COMPRISES: ELECTRODEPOSITING A LAYER OF METAL ON THE COATED SURFACE FROM A FIRST ACID BATH HAVING A HIGHER ACIDITY THAN A WATTS BATH AND THEREAFTER ELECTRODEPOSITING A WORKING LAYER OF METAL THEREON FROM A WATTS BATH HAVING A LOWER ACIDITY THAN SAID FIRST ACID BATH TO EFFECT ELECTROCHEMICAL ACCRETION OF NICKEL OVER THE LAYER FROM THE FIRST ACID BATH AND WHEREIN THE WATTS BATH IS USED AT A TEMPERATURE BETWEEN 40* AND 50*C, WITH A CURRENT DENSITY BETWEEN 1 AND 4 A/DM2 FOR A TIME BETWEEN 25 AND 100 MIN. THEREBY OBTAINING A COLUMNAR STRUCTURE HAVING A SURFACE HARDNESS OF 20 TO 30 HRC AND A THICKNESS OF 30 TO 60 MICRONS RESISTENT TO WEAR AND CREEP.

2. In a process according to claim 1 wherein said layer of metals from said first acid bath is constituted by nickel, and is obtained in an aqueous solution containing: at a temperature between 25* and 30*C, with a current density between 0.7 and 2 A/dm2, for a time between 3 and 5 min.

3. In a process according to claim 1, wherein said Watts bath for the electrochemical accretion of nickel also includes a surface-active substance chosen from the group of alkali metal salts of arylsulphonic and alkylarylsulphonic acids.

4. In a process according to claim 1, wherein an electrolytic layer of chromium of a thickness between 0.2 and 0.6 microns is deposited over said electrolytic nickel layer.

5. In a process according to claim 1, wherein the step of microroughening includes mechanically microroughening by sandblasting and subsequently immersing the surface in an acid chemical conditioning bath adapted to render the surface to be metallized hydrophilic.

6. In a process according to claim 1, wherein the plastic material is glass-loaded phenolic resins and wherein the step of microroughening comprises mechanically microroughening by sandblasting followed by a first immersion in an acid chemical conditioning bath adapted to render the surface to be metallized hydrophilic, a second immersion in a bath of hydrofluoric acid at room temperature for a time of between 30 seconds and 90 seconds, and a third immersion in a neutralizing bath consisting of an aqueous solution of sodium hydroxide with a concentration of between 5 and 10 percent by weight, at a temperature between 65* and 80*C for a time of between 3 and 6 minutes.

7. In a process according to claim 1, wherein said first acid bath comprises a nickel chloride, nickel sulfate bath.