GB2196022A

GB2196022A - Process for the continuous impregnation of nonwoven or needle felt webs with an activating solution for electroless plating

Info

Publication number: GB2196022A
Application number: GB08721008A
Authority: GB
Inventors: Dr Holger Kistrup
Original assignee: Deutsche Automobil GmbH
Current assignee: Deutsche Automobil GmbH
Priority date: 1986-09-12
Filing date: 1987-09-07
Publication date: 1988-04-20
Anticipated expiration: 2007-09-07
Also published as: DE3631055C1; IT1211766B; FR2603903A1; GB2196022B; GB8721008D0; FR2603903B1; IT8748374A0

Abstract

Webs having a thickness between 1 and 10 mm and a porosity between 50% and 97% are continuously impregnated by spraying or immersion with a noble metal containing activating solution for the purpose of subsequent metallisation, in the web being impregnated with the activating solution with a forward feed speed of 1 to 10 m/min and the contact time of the web with fresh activating solution is at most 120 min. Since the further treatment of the impregnated web (rinsing processes etc.) can likewise be carried out with the same speed, the process makes it possible to construct a continuous activating station where, starting from a roll, an activated roll is produced as end product without the continuous operation having to be interrupted even once.

Description

SPECIFICATION Process for the continuous impregnating of nonwoven or needle felt webs with an activating solution The invention relates to a process for the continuous impregnation of nonwoven or needle felt webs with an activating solution.

Nonwovens and needle felts are customarily produced from plastic fibres and consequently are not electroconductive. For certain industrial fields of application, it is of advantage to provide these materials with an electroconductive, i.e, metallic coating. The applying of a metallic coating to the plastic fibres is customarily effected in two steps, namely the depositing of a very thin metallic layer onto the fibre by chemical means and a subsequent reinforcing of this thin metallic film by electroplating. Suitable plastic fibres are polyamide, polyester, polyolefines, polyacrylnitrile or otherwise customary fibre materials. The metals customarily deposited on the fibre of nonwovens and needle felts are copper and nickel, but in-principle a large number of other metals are suitable for deposition, including in particular combinations of metals, where this is of technical interest.

The production of a thin metal layer on the plastic fibre by chemical means is normally only possible after prior activation of the fibres of the nonwoven or needle felt. This activation serves to deposit a catalytically active amount of a substance which has the function of setting in motion or speeding up to industrially usable reaction rates the subsequent chemical metallisation, namely the deposition of a metal from the solution of one of its salts by a chemical reducing agent onto the fibre surface. Suitable catalytically active substances are noble metals or compounds thereof, for example gold, silver, palladium, platinum, rodium, iridium, osmium.For the deposition onto fibre surfaces, preference is given in particular to ionic, colloidal or finely dispersed tin-containing palladium solutions, since the catalytically active palladium particles are particularly highly adherent to the fibre by virtue of tin (in the form of stannic acid).

The activation normally comprises the process of dipping the nonwoven or the needle felt into the activating solution, which customarily consists of a colloidal or ionic palladium solution with-an excess of tin (II) ions as reducing agent in hydrochloric acid (pH 1), further the subsequent hydrolysis-a treatment with an aqueous solution to improve the adherence of the catalytically active particles to the fibre-and finally, if required, individual wash processes which serve to remove residues of the activating solution from the fibre surface. In this process, the uniform impregnating of the needle felts or nonwovens plays a key part.

The activation of nonwovens or needle felts has hitherto taken the form of completely saturating a nonwoven or needle felt web of a certain length, width and thickness in succession with the activating solution, if necessary the hydrolysis solution and the wash liquors, so that all the pores of the nonwoven or needle felt come to be filled with the respective process solution. For the respectively new process solution to be able to penetrate the pores of the needle felt and hence act on the fibre surface it is of course necessary to remove before each new treatment step the previous solution by customary mechanical methods, for example by centrifuging or suction.

The nonwoven or needle felt webs are wound in accordance with the state of the art in spiral form with inter-leaving of a layer of a corrugated separator onto a roller which is thereafter provided with an outer sleeve. The nonwoven or needle felt web thus rolled up is dipped into the activating solution, the spent activating solution is substantially removed from the pores of the web by mechanical means after the dip, and the further rinsing and treatment steps are subsequently carried out in the same manner.

In the above-described process of dipping into the activating solution, the impregnation is relatively rapid and in particular non-uniform.

Depending on how uniformly the activating solution flows along in the channels of the corrugated separator across the entire length and width of the web while impregnating the nonwoven or needle felt web by penetrating in the horizontal direction, the deposition of the catalytically active Pd/Sn particles can give rise to non-uniformities. This non-uniform deposition occurs particularly readily when the nonwovens or needle felts have nominal thickness of 1 to 10 mm and porosities of 50 to 97%. The non-uniformities of the deposition of catalytically active particles on the fibre can come about for example due to air inclusions during impregnating. However, it has also been found that a non-uniform activation can take place in properly filled pores.The consequence of all this is that the chemical metallisation of the nonwoven or needle felt web taking place after the activation starts non-uniformly owing to the non-uniform distribution of the Pd/Sn catalyst particles deposited on the fibre, which frequently leads to non-uniform and consequently also faulty chemical metallisations. It will be readily understood that if electroplating is carried out after the chemical metallisation the fibres will only be electroplatable wherever the chemical metallisation was sufficiently thorough.

This invention seeks to provide a process for a reliable and uniform deposition of cata lytically active particles on the fibres of nonwoven or needle felt webs, so that any chemical metallisation carried out after this activation proceeds uniformly on the whole of the fibres and problem-free uniform electroplating is possible.

According to the present invention there is provided a process for the continuous impregnating of nonwoven or needle felt webs having a thickness between 1 and 10 mm and a porosity between 50% and 97% with a noble metal containing activating solution for the purpose of subsequent metallisation, characterised in that the web is impregnated with the activating solution with a forward feed speed of 1 to 10 m/min and is contacted with fresh activating solution for at most 120 min.

It has been found that for example a very uniform deposition of catalytically active PD-Sn particles from a PdCI2, SnCl2 and hydrochloric acid-containing activating solution on the fibres of nonwovens or needle felts is obtained when the nonwoven or needle felt web is impregnated with the activating solution with a speed of 1 to 10 m/min. This impregnating speed corresponds to the forward feed speed of the need felt web through the impregnating station.

If the impregnating speed of 10 m/min is exceeded there is danger that the needle felt web is left with air inclusions which lead to non-activated fibre. If the impregnating speed is less than 1 m/min, the capillary action can cause activating solution to migrate from previously filled ceils into other cells. However, from this solution the activating constituents have already been completely or substantially depositied by reaction in the other pores, so that, although the newly filled pores are full of a solution, activation is no longer possible for lack of activating particles. Yet, as a consequence of the fact that the pores have been filled with spent activating solution even by contact with fresh activating solution it is no longer possible to obtain any activation in these areas, since the pores are already full of liquid and the diffusion processes are much too slow.

The speed with which the web is impregnated with activating solution also depends on the thickness of the nonwoven or needle felt web. For instance, with relative thick webs a relatively slower speed is advisable than with relatively thin webs. After impregnation of the web with activating solution, contact of the web with further fresh activating solution should ideally be prevented, since the web, when in contact with the activating solution, frees substances, for example from the finish on the web, which have a precipitating effect on- the constituents of the activating solution and thereby reduce the active substance content thereof. The contact of the previously impregnated web with further activating solution should therefore if possible be terminated after at most 120 min.

The impregnating of the web with the activating solution can be effected by pulling the web with a forward feed speed of 1 to 10 m/min through a bath containing the activating solution. For the previously mentioned reasons the residence time of the web in the bath should not be too long. It is particularly advantageous for the residence time of the web in the bath to be as short as possible, i.e, no more than 30 min. It is of particular advantage for the bath to contain only a relatively small amount of activating solution which is replenished with fresh activating solution at the same rate as the solution is carried out of the bath by the impregnated web. Particularly favourable results are obtained when the amount present in the bath corresponds to about 2 to 200 times the amount of activating solution which the web carries out of the solution per minute.

It is also possible to effect the impregnating of the web by spraying with the activating solution, the amount of activating solution being diminished in such a way that the sprayed area of the web is fully impregnated within 1 to 400 sec, whereupon the spraying of this web area is terminated. The spraying is expediently carried out by passing the web with a forward feed speed if 1 to 10 m/min through the spray zone, at the end of the spray zone the pores of the web having to have been completely filled with the activating solution and the residence time of a web section in the spray zone being 1 to 400 sec.In addition to being sprayed from above, where the nonwoven or needle felt web is expediently transported through the spray station in a horizontal position, the activating solution can also be brought into contact with the nonwoven or needle felt web from below, through a perforated floor or through nozzles.

In addition to the dipping or spraying described. the impregnating of the nonwoven or needle felt webs can also be replaced by other impregnating methods known in textile technology. It is merely necessary to ensure that the parameters described for the speed are complied with.

After the web has been impregnated, the excess, spent activating solution is removed from the pores of the web in a manner known per se, for example by squeezing off by means of rolls or by suction. Any subsequent further steps such as wash processes, treatment with a catalytic solution and the like can be in principle be carried out at the same time speeds, although here compliance with certain residence times is not so critical. If a corresponding number of treatment stations are connected in series, it is possible to produce an activated nonwoven or needle felt web in a wholly continuous process, the raw web running as the starting material from a roll or directly from a corresponding manufacturing machine and a fully activated web being present at the end of the treatment.

Example 1 A nonwoven web made of polyethylene and having a thickness of 3.2 mm, a porosity of 92% and a fibre linear density of 1.7 dtex was unwound from a supply roll and pulled with a speed of 3 m/min, by a suitable system of guide rollers, through a bath filled with activating solution. The bath contents were about 5 times the amount of activating solution carried out of the bath per minute. The residence time of a web section in the activating bath was 10 sec. Thereafter the web was freed of spent activating solution and guided with the same speed through further treatment stations such as wash stations, a hydrolysis station etc. In the subsequently performed conventional chemical nickelisation it was found that nickelisation took place everwhere equally rapidly and sufficiently uniformly.

Example 2 A needle felt web made of polypropylene having a thickness of 4.5 mm, a porosity of 95% and a fibre linear density of 2.7 dtex was impregnated in an impregnating station with an activating solution based on PdCl2, SnCI2 and HCI. The needle felt web, which had a width of 50 cm, was pulled off a supply roll, by a system of guide rollers, through an empty tank with a forward feed speed of 2 m/min. Above the tank there was positioned a system of nozzles from which the activating solution was sprayed onto the needle felt web while said web was pulled through the tank.

The amount of activating solution sprayed on was dimensioned in such a way that the pores of the web were completely full of activating solution after exit from the impregnating station. The residence time of a web section in the impregnating station was 90 sec. After exit of the impregnated web from the impregnating station the web was aftertreated and chemically nickelised as in example 1. The nickelisation started uniformly and at virtually the same time in all felt areas, so that after conclusion of chemical nickelisation an extremely uniformly metallised needle felt web was present.

Claims

1. A process for the continuous impregnation of nonwoven or needle felt webs having a thickness between 1 and 10 mm and a porosity between 50% and 97% with a noble metal containing activating solution for the purpose of subsequent metallisation, characterised in that the web is impregnated with the activating solution with a forward feed speed of 1 to 10 m/min and is contacted with fresh activating solution for at most 120 min.

2. A process according to claim 1, wherein the impregnation is carried out by pulling the web through an activating bath with a forward feed speed of 1 to 10 m/min and a residence time in the bath of at most 30 min.

3. A process according to claim 1, wherein the impregnation is effected by spraying the web with the activating solution, the amount of activating solution sprayed on being dimensioned in such a way that the sprayed area of the web is completely impregnated after 1 to 400 sec and the spraying onto this web area is then terminated.

4. A process according to claim 2, wherein the amount of activating solution present in the bath is dimensioned in such a way that it corresponds to 2 to 200 times the amount which is carried out of the bath per minute by impregnating the web and in that the amount carried out is continuously replaced by a corresponding amount of fresh activating solution.

5. A process for the continuous impregnation of nonwoven or needlefelt webs, substantially as described herein with reference to the examples.