Process for metalizing fibrous materials

Abstract: Method for the electroless metalizing of fibrous materials, consisting of coating the above-said fibrous materials, before submitting them to the chemical metalizing treatment, with a uniform film of a polymer which is capable of adhering to the fibrous materials, is resistant to the chemical metalizing treatment, and is suitable for receiving metal coatings.

Description: The present invention relates to a process for the metalizing of fibrous materials. It is known that the metalizing of fibrous materials allows said fibrous materials to be endowed with chose electrical, magnetic and thermal properties, which are necessary in order to have finished articles endowed with high-level antistatic characteristics, radio waves reflection factor, electromagnetic radiation shielding effectiveness, heat conductivity, and so forth. The metalizing by a chemical route, possibly followed by an electrochemical metalizing, results to be advantageous as compared to other techniques, such as the vacuum metalizing, or the arc-spray metal coating, in that it allows a higher flexibility to be achieved in the production processes, simultaneously enabling better quality products to be obtained (characterized, e.g., by a higher adhesion strength of the metal to the fibre, a higher wear resistance, a longer useful life, and so forth). Unfortunately, fibrous materials exist, which, either owing to their nature, or due to their structure, are not very fit to the chemical metalizing treatment. As to the nature of the fibre, the drawbacks and difficulties derive either from the insufficient adhesion strength of the metal to the fibre (e.g. in case of polypropylene fibres), or from the sensitivity to the strongly acidic or alcaline metalizing baths (e.g., in case of polyester or cellulosic fibres), or from the lack in homogeneousness of characteristics, as it occurs, e.g., in case of blends of different fibres. As to the structure, the quality of the results is influenced by the degree of structural homogeneousness of the fibrous material. For example, in case of fabrics made from raffias or from high-count threads (20 dtex or more), the weaving interlacings may cause such shielding effects, as to endanger the reactions of surface activation during the electroless treatment step, leading to different values of conductivity from point to point, which, among others, hinder a subsequent galvanic treatment. Another example is concerned with the case of non-woven articles (including waddings, needle-punched felts, dermoporous felts, and so forth), obtained from staple without passing through the thread step, according to dry web production techniques (for example, rando-webber), or wet web production routes (technologies of paper production type). The manufacturing of these articles leads to considerable unevennesses due to the formation step (cloudiness; differences between the upper and lower sides; between the core and the outer surfaces, between the machine direction and the cross direction, and so forth), and to the step of mechanical, chemical or thermal binding (mechanical damaging of the fibres, irregular depositions of adhesive, melting areas, and so forth). Each one of the above cited phenomena has a negative influence on the chemical deposition of the metal on the fibrous surface, causing covering faults, and/or defects due to insufficient adhesion strength, and/or defects due to alterations in the kinetics of growth of the crystalline metal layer. The pre-treatment of surfaces of films or fibres to be submitted to metalizing by an electroless chemical route, by submitting the same surfaces to a graft-polymerization, is known from the prior art. For example, JP-A-79/116,066 discloses the graft-polymerization of maleic anhydride onto a polyethylene or polypropylene film, which are subsequently submitted to a metal (Ni) coating by a chemical route, and later on by an electrolytic process. JP-A-83/196,238 discloses in its turn plastic surfaces activated in order to enhance the adhesion strength of metal layers applied by an electroless chemical route, wherein said activation consists in a graft-polymerization of acrylic acid onto a poly(ethylene terephthalate) film. In both cases, the applied metal layer shows a good mechanical strength and a good adhesion strength, to the contrary of metals applied in the same way, but on non-grafted films. However, these methods suffer from some disadvantages, due to the fact that the surfaces are treated with very reactive chemical agents, such as acrylic acid and maleic anhydride, which cause problems of dangerousness and of toxicity. Another drawback is due to the fact that, inasmuch as the treatment of the surface is a true chemical reaction, the installation of specific equipment, and hence a more complex technology, are required. JP-A-85/239,234 discloses, on the contrary, the treatment of fibrous materials with poly(vinyl alcohol) before said fibrous materials are submitted to an electroless metalizing. Unfortunately, even when this treatment is used, satisfactory results cannot be achieved, in particular as regards the homogeneousness and/or the integrity of the metal coating obtained. The present Applicant has surprisingly found that the above mentioned problems can be overcome resorting to suitable preformed polymers, which are capable of adhering to the fibrous material. The use of such polymers makes it possible as well, the use of highly toxic materials to be avoided, with at the same time very simplified technologies being used. The object of the present invention is therefore a process for the metalizing of fibrous materials by means of a chemical route, which consists in uniformly coating such fibrous materials with a continous, well-anchored film, resistant to the chemical treatments required by the metalizing, said film being constituted by a polymer which is capable of adhering to the fibrous material, and is suitable for receiving metal coatings. The polymers according to the present invention are used as aqueous dispersions, or as solutions or dispersions in organic solvents, but they are preferably used as aqueous dispersions, or anyway water-dilutable dispersion (usually traded at concentrations comprised within the range of from 30 to 60%), which, by simply removing the dispersing medium at room temperature, or at temperatures anyway comprised within the range of from 0°C to 60-70°C, and preferably of from 50°C to 70°C, generate the above said continuous and uniform polymeric films. The polymer concentration in the solutions or dispersions is preferably from 10 to 25 percent by weight of dry polymer. Many water-dispersible synthetic polymers have shown to be suitable for the purposes of the invention; among these, polymers based on either homopolymerized or copolymerized vinyl acetate, vinyl propionate, styrene, α-methyl-styrene, acrylonitrile, ( C₁-C₈ )-alkyl acrylates and methacrylates, butadiene, with or without functional groups of OH, COOH, CN, NH₂ or CONH₂ type - this latter being possibly either methylolated or methoxylated - may be herein cited. Water-dispersed polymers of polyurethane type, anyway constituted, are indicated as well. Of all of the above mentioned polymers, types available from the market exist. The application of said polymers onto the fibrous material is carried out according to the technologies used in the textile industry for using the finishes, such as, e.g., the full-bath impregnation, the tangential-roll impregnation, the spraying, the spreading, followed by the removal of the aqueous medium by drying, possibly preceded by a wringing, or by a removal of the excess of the bath by suction. As to the operative conditions, the use formulations and the application modalities, they are defined from time to time as a function of the fibrous materials treated, of the selected polymer and of the equipment used, according to the criteria well-known to those skilled in the art, so as to produce on the fibres film deposits which are as continuous, uniform and as thin as possible. The uniformity and continuity of the film are in fact essential in order to ensure the protection of the fibres from the metalizing baths, and to guarantee that the deposition of the metal coating takes place in a uniform way on any individual points of the fibrous material. However, the applied amount of polymeric material should be suitably kept as small as possible, in order not to alter more than necessary the characteristics of cohesion, hand and stiffness of the article used as the starting material. Preferably the applied amount of polymeric material is from 5 to 20 percent with respect to the total weight of the final product. The fibrous material used as the metalizing substrate can be constituted by natural, artificial and synthetic fibres (cellulose, polyacrylonitrilic fibres, polyester fibres, polyamidic fibres, polyolefinic fibres, and so forth), practically with no exceptions, including the advanced organic fibres (e.g., the aramidic fibres), as well as the inorganic fibres (e.g., carbon fibres, fiberglass, asbestos). As to the nature of the fibrous material, it can be in the form of practically any types of fabrics, knitted fabrics or non-woven fabrics. In principle, no preliminary treatments of the fibrous substrates are necessary, before the anchoring polymeric material is applied. Usually, verifying the suitability of said polymeric material for the specific sustrate used, so as to be able to select a type capable of securing the desired coating effect, will be enough. The chemical (electroless) metallisation is carried out by means of known techniques. In particular it is possible to employ metallisation baths in which solutions of metal salts, as salts of Ni Cu or Ag are chemically reduced. Examples of suitable salts are copper sulphate, nickel chloride, silver nitrate. It is also possible to carry out the deposition of more than one layer of different metals. The additional layers can be deposited by means of galvanic methods. In this case all the metals are employable, which can be deposited by galvanic methods such as, in addition to the above cited ones, Sn, Pb, Au. In order to better understand the purpose of the present invention, and to allow it to be practiced, some examples are reported hereinunder for merely illustrative, non-limitative purposes, which show the preparation of fibrous materials metalized by means of the process according to the present invention. Example 1 A non-woven fabric of polyacrylonitrilic fibre, with a weight of 30 g/m² is impregnated with a water-dispersed acrylic resin based on butyl acrylate and acrylonitrile, such as, e.g., CRILAT (R) DR 1467 by ROL, diluted with water down to a concentration of 15% by weight, in the presence of a non-ionic wetting agent (e.g., PoLIROL (R) NF80 by ROL), and is subsequently wrung between two rolls under a pressure of 1-2 bar. The fabric is then dried with air at 60-70°C and is subsequently heated to, and maintained for 1-5 minutes, at the temperature of 120-150°C, in order to attain the cross-linking of the resin. The so-obtained fabric is then sensitized by being dipped for a time of from 5 to 10 minutes in a solution containing 15 g/l of SnCl₂.2H₂O, in the presence of HCl at 2% (pH 1-1.5), is thoroughly rinsed with H₂O and is activated by means of a treatment for a time of from 3 to 5 minutes in a solution containing 0.3 g/l of PdCl₂ in the presence of HCl at 0.2% (pH 2-2.5). After being rinsed with water, the fabric is treated for 30 minutes at room temperature inside a copper bath: this bath contains 5 g/l of CuSO₄.5H₂O, 25 g/l of sodium-potassium tartrate tetrahydrate, 7 g/l of sodium hydroxide, 11 g/l of formaldehyde at 40% and 0,1 g/l of sodium lauryl-sulphate. The pH value of the bath is of about 13. Through the bath, air is bubbled under a pressure of 1 bar. The fabric absorbs about 4 g/m² of copper, and has a resistivity of about 155 Ω/m² (0.1 Ω/sq). The fabric is then submitted for 1-5 minutes to an electrodeposition of nickel inside an electrolytic cell with nickel anodes, at the temperature of 50-70°C, and at a pH of 1.2-1.5, with a current density of 1-5 A/dm². The bath contains 300 g/l of nickel chloride hexahydrate, 30 g/l of boric acid and 0.7 g/l of saccharin. The bath is maintained at an acidic pH value by means of controlled additions of HCl at 15%. The fabric absorbs from 4 to 15 g/m² of nickel, according to the residence time, and to the current density, with a uniform distribution, and a perfect adhesion. The resistivity of the fabric is of 31 - 155 Ω/m² (0.02 - 0.1 Ω/sq). The fabric is endowed with a shielding effectiveness for the electromagnetic radiations of 60-70 dB within the range of frequencies of from 10 kHz to 12 GHz. Example 2 A non-woven fabric of polyacrylonitrilic fibre, of a weight of 40 g/m², is respectively impregnated with an acetovinylic resin, e.g., VINAVIL (R) HC by ROL, diluted with water down to a concentration of 20% by weight, or with a butadiene-acrylonitrile resin, e.g., PERBUNAN (R) NT by BAYER, diluted with water down to a concentration of 20% by weight, in the presence of a non-ionic wetting agent (e.g., POLIROL (R) NF80 by ROL), and is subsequently wrung between two rolls under a pressure of 1 bar. The fabric is then dried with air at 60-70°C, and is subsequently heated to, and maintained at, the temperature of 120-130°C for 2-3 minutes. Both said non-woven fabrics, respectively impregnated with the polyvinylic resin and with the polybutadienic resin were submitted to an electroless copper deposition, and to a subsequent electrocoating with nickel according to modalites analogous to those disclosed in Example 1. They display a resistivity of 31 - 155 Ω/m² (0.02-0.1 Ω/sq), and a shielding effectiveness of 60-70 dB within the range of frquencies of from 10 kHz to 12 GHz. Example 3 A non-woven fabric of polyester fibre, having a weight of 10 g/m², is impregnated with a polyacrylic resin as disclosed in Example 1 and is subsequently submitted to an electroless deposition of copper and to a subsequent electrodeposition of nickel, as disclosed in Example 1. The resistivity is of 155 - 620 Ω/m² (0.1-0.4 Ω/sq), and the shielding effectiveness is of 50-60 dB with the range of frequencies of from 10 kHz to 12 GHz. Example 4 A fabric of polyester fibre, with a weight of 24 g/m², is impregnated with a water-dispersed polyurethanic resin, e.g., PURBINDER (R) DPT or PA 531 (in Foreign Countries, the product is known under the trademark ITALPUR (R) ) by ROL, diluted with water down to a concentration of 20% by weight. The fabric is dried at 60-70°C for 30-40 minutes, then, after being sensitized and activated in the same way as of Example 1, an electroless deposition of copper and a subsequent electrodeposition of nickel are carried out on it, as disclosed in Example 1. The resistivity is of 775 - 1550 Ω/m² (0.5-1 Ω/sq), and the shielding effectiveness is of 45-50 dB at frequencies comprised within the range of from 10 kHz to 12 GHz. Example 5 A fabric of polyester fibre, with a weight of 50 g/m², is impregnated with a polyacrylic resin, e.g. CRILAT (R) DR 1467 by ROL, according to the same procedure of Example 1. The fabric, after being sensitized with SnCl₂ , and activated with PdCl₂ , according to the same modalities of Example 1, is treated for 15 minutes at 70-80°C in a nickel bath: this bath contains 30 g/l of nickel chloride hexahydrate, 10 g/l of monosodium hypophosphite monohydrate and 35 g/l of hydroxyacetic acid. The pH value of the bath is maintained within the range of from 4 to 5 by means of gradual additions of an NaOH solution at 10%. The fabric absorbs about 8 g/m² of nickel, has a resistivity of about 310 Ω/m² (0.2 Ω/sq), and its shielding effectiveness is of about 55 dB within the range of frequencies of from 10 kHz to 12 GHz. Example 6 A non-woven fiberglass fabric by VETROTEX, having a weight of 450 g/m² , is impregnated with a water-dispersed polyurethanic resin, e.g. , PURBINDER (R) DPT or PA 531 (in Foreign Countries, ITALPUR (R) ) by ROL, diluted with water down to a concentration of 25% by weight. The impregnated article is heated at 60-70°C for 30 minutes, then is submitted to an electroless deposition of copper and to a subsequent electrodeposition of nickel, as disclosed in Example 1. The resistivity is of 155 - 775 Ω/m² (0.1-0.5 Ω/sq), and the shielding effectiveness is of 50-60 dB at frequency values comprised within the range of from 10 kHz to 12 GHz. Example 7 A non-woven fabric od fiberglass, analogous to the one used in Example 6, is impregnated with a polyacrylic resin, e.g., CRILAT (R) DR 1467 by ROL, according to the same modalities disclosed in Example 1. The impregnated article, after being sensitized with SnCl₂ and activated with PdCl₂ , according to the same modalities of Example 1, is submitted to an electroless deposition of nickel, in a bath equal to the one as disclosed in Example 5. The article absorbs about 12 g/m² of nickel, and has a resistivity of about 310 Ω/m² (0.2 Ω/sq). The shielding effectiveness is of about 55 dB within the range of frequencies of from 10 kHz to 12 GHz. Example 8 A fabric of poly-p-phenylene-terephthalamidic fibre (e.g., KEVLAR (R) by DUPONT), with a weight of 80 g/m², is treated with a solution of NaOH at 5% at 40°0 for 10-15 minutes, is washed with water and is impregnated with a polyurethanic resin, e.g., PURBINDER (R) PA 531 by ROL. The fabric is heated at 60-70°C for 40-60 minutes, then, after having been sensitized with SnCl₂ and activated with PdCl₂, according to Example 1, is treated for 30 minutes at 70-80°C in a bath of nickel: this bath contains 30 g/l of nickel chloride hexahydrate, 10 g/l of monosodium hypophosphite monohydrate, 12.6 g/l of sodium citrate dihydrate and 5 g/l of sodium acetate. The pH of the bath in maintained at a value comprised within the range of from 4.5 to 5.5 by means of the addition of suitable amounts of a solution of NaOH at 10%. The fabric absorbs about 16 g/m² of nickel, with a resistivity of about 310 Ω/m² (0.2 Ω/sq). The shielding effectiveness is of about 55 dB at frequencies comprised within the range of from 10 kHz to 12 GHz.

Claims: Method for pretreating fibrous material before metallizing by means of a chemical route, which consists in uniformly coating said material with a continuous film of a polymer, which is based on either homopolymerized or copolymerized vinyl acetate, vinyl proprionate, styrene, α-methyl-styrene, acrylonitrile, (C₁-C₈)-acrylates and methacrylates, butadiene, with or without functional groups of -OH, -COOH, -CN, -NH₂ or -CONH₂ type, or which polymer is a water-dispersed polymer of polyurethanic type , said coating film being formed by applying onto said fibrous material an aqueous dispersion of the polymer or a dispersion or solution thereof in organic solvents. Method according to claim 1 , characterized in that the film is formed by applying onto the fibrous material the polymer and subsequently removing the dispersing medium at a temperature comprised within the range of from 0°C to 70°C, and preferably of from 50°C to 70°C. Method according to claim 2, characterized in that the aqueous, or water-dilutable dispersion of the polymer is applied onto the fibrous material by full-bath impregnation, tangential-roll impregnation, spraying, or spreading. Method according to any of claims from 1 to 3, characterized in that the fibrous material is constituted by natural, artificial or synthetic organic fibres. Method according to any of claims from 1 to 4, wherein the fibrous material is constituted by cellulosic fibres, polyacrylic fibres, polyester fibres, aramidic fibres, polyamidic fibres, polyolefinic fibres. Method according to any of claims from 1 to 4, characterized in that the fibrous material is constituted by inorganic carbon fibres, fiberglass or asbestos fibres.

Inventors: CASOLO GINELLI UBERTO, MASSA VINCENZO, MERLO FABRIZIO, CASOLO GINELLI, UBERTO, MASSA, VINCENZO, MERLO, FABRIZIO
Applicants: TEXMET SPA, TEXMET S.P.A.
Application year: 1989
Main classification: D06Q1
IPC codes: D06M11, D06Q1, D06M15, D06M101, C23C18