Title of Invention

"A METHOD OF METAL DEPOSITION BY A WET CHEMICAL PROCESS ON POROUS SUBSTRATES"

Abstract

A method of metal deposition by a wet chemical process on porous substrates having porosities between 45 and 95% and made from non—conductive synthetic materials comprising the steps of Activating the substrate by bringing it into contact with an activator solution comprising a Pd/Sn solution and selecting the concentration and temperature of the activating solution to allow substantially optimum metallization of the substrate; - Removing the spent activator solution, wet—chemical metallizing the activated substrate by bringing it into contact with a chemical metallizing solution and selecting the concentration and temperature of the metallizing solution to allow substantially optimum metallization of the substrate; - Removing the spent chemical metallizing solution, - Impregnating with washing water and - Removing the washing water, wherein, each of the steps is incorporated into a single station so that the substrate proceeds continuously though each station sequentially.

Full Text

The invention relates to a method of metal deposition on a porous synthetic substrate by a wet chemical process . On the one hand, the porous synthetic substrates in question consist of a plurality of fibres needled, bonded or otherwise joined to one another in an appropriate manner or formed by the walls of open pores communicating with one another. Porous synthetic substrates of this type are used every day in applications relating to filtering, insulation and, amongst others, for catchment or straining purposes. The base materials which may be used for porous Batting, open-pored foams or needled felt are polyolefins, polyaaides, polyester, polyphenylene sulphide or various other polymers. In many technical applications, it is reconunendable to provide finishing by applying a thin metallic film to the electrically non-conductive wall surfaces of the fibres or pores. This can be done either using physical deposition methods such as PVD or CVD or alternatively using wet chemical deposition methods. The invention relates additionally to wet chemical metal deposition on the wall surfaces of fibres or pores of porous substrates. Metal deposition using a wet chemical method generally requires that the surface of the porous synthetic substratefs /ls~Trrstiy conditioned, which may be by etching, roughening by glow discharge, scoring, applying a hydrophilic substance amongst others ,0 (a catalytTcally active compound containing a precious metal is then deposited on the conditioned surfase, for which purpose a Pd/Sn-compound is commonly used although basically silver or platinum compounds could also be usctd, and finally, after removing the activator solution containing the spent catalytically active particles from the pores of the porous substrate, the activated surface of the fibres or pores is brought into contact with a metallizing solution to bring about chemical metallization. The relevant publication as regards ':he prior art is the book " Kunetstoff-Galvanisierung* , Handbucih fur Theorie und Praxis (Leuze Verlag, Saulgau/Wurtt.), for example, or extracts from the German patent specifications cited below, DE 39 25 232 C2, DE 36 31 055 C2, De 40 33 518 C2, De 42 42 443 C2, DE 38 43 903 C2, DE 39 14 726 C2, DE 37 10 895 C2 or DE 36 37 130 C2. The cited prior art discloses methods whereby in order to apply a metal film to webs of conditioned matting, needled felt or open-pored foam, these are impregnated with an activator solution, preferably with a Pd/Sn base and the spent activator solution is then removed from the pores of the porous substrate and finally a chemical metallizing solution is brought into contact with the substrate surface, copper and nickel are the preferred metals used for deposition, although clearly it is possible to apply a film of other metals. If required, the chemically deposited metal film can then be strengthened by galvanisation with the same or another metal. The individual steps of the method, namely - conditioning - activation - removal of the spent activator solution from the pores of the substrate, - chemical metallization, - removal of the spent metallizing solution from the pores of the substrate and - the rinsing process to remove salt or metal residues of the chemical metallizing solution from the pores of the substrate require, because of their essentially different individual functions, different operating or reaction times, which can be summarised as follows: The conditioning process to impart hydrophiLic properties to the fibre or pore walls, by impregnation and leaving to allow a wetting solution to evaporate can take; hours under certain circumstances. > Activation using an acidic, freshly prepared activator solution with a Pd/Sn base requires between 5 and 15 minutes. » Centrifugation of the spent activator solution from the pores of the substrate can take between 15 and 20 minutes depending on porosity. » Coating the activated surfaces of the fibre or pore walls with a film of metal takes 20 to 30 minutes and the rinsing process 2 minutes. The mechanical removal of the individual rinsing washes can in turn take 15 to 20 minutes where the initial substrate has a porosity of from 45 ... 95%. To the knowledge of the applicant, no practical way has yet been found to link these different steps of the method into a standard, continuous process of metal deposition on porous substrates having initial porosities of from 45 to 95% because of the differing processing times involved. DE 41 06 696 C2 discloses for the purposes of deposition, i.e. for the portion relating to activation, one option for a continuous process. In this case - as is usual - the prior conditioning of the surface of the substrate is incorporated in the process of producing the porous substrate. In accordance with this particular piece of prior art, the webs of porous substrate are continuously activated with a Pd/Sn-solution in what is referred to as a single-step process, which incorporates only impregnation with activator solution and a two-stage drying process in the continuous process of the method. The subsequent chemical metal deposition process is then performed in batches. Apart from the fact that only a proportion of the different steps of the method used for wet chemical metal deposition on webs of porous substrates is performed in one entity, this known method also gives rise to difficulties in respect of the complex, two-stage removal of the spent activator solution from the pores of the substreite because the quantities of air charged with atomised hydrochloric acid applied as part of the process can only be detoxified with great difficulty. with the methods of the prior art, the removal of the spent metallizing solution from the pores and the subsequent washing processes can not simply be incorporated in a continuous process including the entire metal deposition procedure. Furthermore, it is very difficult to control the hot-air drying process in order to avoid the localised migratory effects of catalytically inactive Pda+. If the continuous procedure of the metal deposition is interrupted at all on a batch basis in order to remove mechanically any spent metallizing solution and rinsing washes from the pores of the substrate, other downstream steps, such as finishing the web of metallized substrate or galvanic reinforcement of the metal film, cannot logically be set up as1, part of the continuous process. This necessarily implies increased handling and personnel deployment. Using the cited prior art as a basis, the present invention to provide a method of metal depositi.on on webs of porous substrate made from non-conductive synthetic material, in which the greatest possible proportion of the metal deposition processing chain can be operated or a continuous basis, without interruption. According to the present invention there is provided a method of metal deposition by a wet chemical process on porous substrates having porosities between 4S and 95% made from non-conductive synthetic materials such as needled felts, matting substances or open-pored foams, in which the fibre surfaces or pore walls of the substrates are firstly activated by means of an activator solution containing Pd/Snr the activated surfaces are then metallized with a metallizing solution and then rinsed before the rinsing water is removed, wherein the substrate which is hydrophilic or has been made hydrophilie is fed as a contiguous web in a continuous process through a series of processing stations, at which the metallization steps listed below are effected, at a sane feed rate for all the processing stations: - Impregnation with activator solution with a Pd/Sn base - Removal of the spent activator solution, - Impregnation with chemical metallizing solution, - Removal of the spent chemical metallizing solution, - Impregnation with washing water and - Removal of the washing water, in which, taking account of the length of the respective reaction times within the processing stations and on the basis of the residence time of the substrate in the respective processing station resulting from the feed rate, any shortfall in the conventional reaction times is compensated by selecting parameters relating to the processing fluid, namely concentration and/or temperature, in order to alter the rate of the reaction in such a way as to allow a continuous ttirough-put on the basis of the actual reaction times produced at each of the processing stations and the respective processing periods, and spent processing fluids, namely activator solution, chemical metallizing solution and adherent rinsing water, are removed from the pores of the porous substrate by suction. The task as proposed by the invention resides in the fact that the reaction rates inherent in activation and chemical metallization are adjusted to match cne another by specifically selecting and combining the parameters of the activator and metallizing solutions and this intervening removal of the respective spent reaction solution from the pores of the porous substrate, which, in conjunction, allow the same input rate to be set for the subutrate at all processing stations and hence a continuous operating mode. The invention offers a continuously operated and cost-effective method of chemical metallization, i.e. rwquiring only relatively little control or regulation and operable by a minimum of personnel, which is perfectly feasible in commercial practice. The surprising aspect of the inventicn resides in the fact that standardising the application of the processing solutions to the surface of the fibres or pores as well as across the thickness of the material, namely the activator solution and the metallizing solution, allows reactions of different reaction rates, absorptive activation using activator solutions containing precious metals (Pd/Sn) and chemical metallization (nickel plating, copper plating, amongst others), to be adjusted to match cms another by adjusting parameters relating to concentration, type of substances in solution and temperature, to such a degree in terms of their reaction rates that the web of (substrate can be fed continuously through at most six stations. The mechanical suction process to remove the spent processing solutions can be incorporated in the continuous method simultaneously. For the purposes of the invention, the* substrate to be metallized is fed continuously as a continuous web through a series of individual processing stations, at which the relevant individual treatments are performed ir a sequential order. Surprisingly, the respective processing parameters can be specifically so selected, combined and assimilated for each of the processing stations as to allow continuous processing, whereby a small number of individual processing steps are enough to produce full and effective wet chemical metal deposition. A surprisingly simple and comprehensive method has therefore been found, requiring reduced input: in terms of control and regulation. For the purposes of th« invention, a porous substrate of the type specified above and which is hydrophilic or has had hydrophilic properties ;lmparted to it is fed through the following six stations: - impregnation with activator solution with a Pd/Sn base/ - suction to remove the spent activator solution, - impregnation with chemical metallizing solution, - suction to remove the spent chemical metallizing solution, - impregnation with rinsing water and - suction to remove the rinsing water. These six stations are operated continuously a-c a specific feed-rate for the substrate and the invention is such as to ensure that the activator solution containing !Pd/Sn is not only applied for a uniform length of time across, the surface and the thickness of the substrate, by dint of appropriate factors such as - concentration of the solution complement, - temperature of the activator solution, - type of distribution of the activating solution on the wall surface of the pores or fibre of the porous substrate, but that this reaction time also matches the tiraa required by the chemical metallizing solution to react with the substrate surface to be metallized. The essential factor recognised by the invention is that porous substrates which have been made hydrophilic for the purposes of metal deposition by a wet chemical process can be fed at the same feed-rates through activator stations and through chemical metallization stations such that, surprisingly, the requisite synchronisation of the individual steps can be forced by adjusting the processing parameters at the individual processing stations. The rates of the individual reaction types, such as adsorption, redox reaction of a higher order with accompanying catalytically induced hydrogenation can be just as easily controlled as the inherent residence times so that the respective reaction periods are extended accordingly, Another feature of the invention resides in the fact that the low adherence of the catalytically active particles to the activated substrate surface and the equally low adherence of the excess metallizing solution to the chemically deposited metal skin allow the spent activator solution containing precious metal and the spent chemicnl metallizing solution to be sucked out from the pores of th« substrate 'at the relevant stations without the metal skin being damaged, due for example to outbreaks of dried and broken spangles of metal, which is conducive to a continuous configuration of the entire metallization process within the meaning of the invention. By preference, the reaction time of the chemical metallizing solution is adjusted within the continuous process as a whole by raising the temperature and omitting chelating agents and/or pH stabilisers. In preferred embodiments, the chemical metallizing solution contains no chelating agents, pH regulators, or other agents at all and the chemical metallizing solution is adjusted solely by raising the temperature or applying the correct temperature setting for the reaction rate needed to match the reaction by which the substrate surface is activated with precious metal, in order to metallize the surface of a porous substrate by a wet chemical process, including a necessary washing process, the method of the invention requires only six individual stages within the method, whereby the substrate is fed along continuously, starting from a substrate surface which is hydrophilic or h*s been made hydrophilic through to producing a chemically metallized substrate surface which can then be directly reinforced by galvanisation. The preferred types of activation correspond in theory to those of the prior art, namely activation with colloidal palladium/tin solution (Pd/Sn). In a known manner, chemical metallization often takes the form of nickel plating, which is also a preferred application, in this instance, however, it was observed that a chemical metallizing solution could be obtained by omitting the usual chelating agents or pH regulators and simply by dissolving a nickel salt (chloride hydrate) and a reducing agent (e.g. hypophosphite), which could be heated without detriment (e.g. to approximately 60'C) and thus used for the purposes of the invention to speed up the metallization reaction and hence the likewise speed-adjusted continuous operating mode allowing various types of processing. By preference, the suction power and/cr suction time of the suction system for the spent processing solutions should be set so that, at the end of suction, a residual moisture of only approximately 3% remains. The present invention relates to a method of metal deposition by a wet chemical process on porous substrates having porosities between 45 and 95% and made from non—conductive synthetic materials comprising the steps of - Activating the substrate by bringing it into contact with an activator solution comprising a Pd/Sn solution and selecting the concentration and temperature of the activating solution to allow substantially optimum metallization of the substrate; - Removing the spent activator solution, - wet—chemical metallizing the activated substrate by bringing it into contact with a chemical metallizing solution and selecting the concentration and temperature of the metallizing solution to allow substantially optimum metallization of the substrate; - Removing the spent chemical metallizing solution, - Impregnating with washing water and - Removing the washing water, wherein, each of the steps is incorporated into a single station so that the substrate proceeds continuously though each station sequentially. The present invention also relates to a coated porous device produced by the method as claimed in any one of the preceding claims. The underlying theory of the invention will be described in the context of an example, although this in no way restricts the applicability of the teaching of the invention. Example A needled felt substrate of polypropylene (PP) with a fibre size of 20 urn, a porosity of 95% and a nominal thickness of 3 m», in a web suitable for processing purposes in which the fibres have been treated to impart hydrophilic properties, was fed continuously at an input rate of 3 m/min. through the following stations: Station 1: Impregnation with fully developed activator solution containing Pd/Sn by specifically metering and topping-up a tank with fresh activator solution in the vicinity of the submersed substrate and feeding the impregnated felt to the next station. Station 2: Removal of the activator solution from the pores of the substrate by suction via nozzles using *i pump. Station 3: Impregnation of the activated substrate with a chemical nickelizing solution containing only dissolved nickel chloride hexahydrate and sodium hypophosphite and heated to a temperature of 60"c before feeding to the next station. Station 4: Removal of the spent metallizing solution from the pores of the substrate by suction via nozzles using a pump. Station 5: Impregnation of the chemically metallized substrate with washing water. station 6: Removal of the water from the metallized and washed substrate by suction. An evenly metallized web of porous needled felt was produced, the metal coating on the fibres of which was ready for galvanisation if required. With corresponding metal deposition processes, it is of course possible to use an identical washing and suction station at stations 5 and 6 if required or, on th«s other hand, to omit the stage at which metallization residues are washed from the pores at stations 5-6 altogether, without departing from the teaching of the invention. WE CLAIM: 1. A method of metal deposition by a wet chemical process on porous substrates having porosities between 45 and 95% and made from non—conductive synthetic materials comprising the steps of Activating the substrate by bringing it into contact with an activator solution comprising a Pd/Sn solution and selecting as hereindescribed the concentration and temperature of the activating solution to allow substantially optimum metallization of the substrate; Removing the spent activator solution, wet—chemical metallizing the activated substrate by bringing it into contact with a chemical metallizing solution and selecting the concentration and temperature of the metallizing solution to allow substantially optimum metallization of the substrate; Removing the spent chemical metallizing solution, Impregnating with washing water and Removing the washing water, characterized in that, each of the steps is incorporated into a single station so that the substrate proceeds continuously though each station sequentially at a specific feed rate. 2. A method as claimed in claim 1, wherein a nickelizing solution is used as the chemical metallizing solution, which consists of a nickel salt in solution and a chemical reducing agent and is heated to a temperature of approximately 600C to accelerate the metallization reaction. 3. A method as claimed in claim 1, wherein the temperature of the activator solution is raised to 30 to 350C in order to accelerate the activation reaction and thus match its rate to that of the metallization reaction. 4. A method as claimed in any one of claim 1, wherein the substrates are nickelized during the chemical metallization. 5. A method of metal deposition by a wet chemical process on porous substrates, substantially as described herein with reference to the example. 6. A coated porous device produced by the method as claimed in any one of the preceding claims.

Documents:

1624-del-1997-abstract.pdf

1624-del-1997-claims.pdf

1624-del-1997-correspondence-others.pdf

1624-del-1997-correspondence-po.pdf

1624-del-1997-description (complete).pdf

1624-del-1997-form-1.pdf

1624-del-1997-form-13.pdf

1624-del-1997-form-19.pdf

1624-del-1997-form-2.pdf

1624-del-1997-form-3.pdf

1624-del-1997-form-4.pdf

1624-del-1997-form-6.pdf

1624-del-1997-gpa.pdf

1624-del-1997-petition-137.pdf

1624-del-1997-petition-138.pdf