JP4060363B2 - Production of polymer monofilaments or yarns coated with heat stable metals - Google Patents

Description

The present invention is completely and substantially uniform made of a plurality of polymer monofilaments coated with electroless nickel and optionally with a metal electroplated onto the nickel. The invention relates to the production of metal-coated polymer monofilaments or yarns. More specifically, the present invention relates to a method for activating the surface of a polymer monofilament that is subsequently coated with electroless plated nickel.
Until the present invention, metal coatings are plated on polymer monofilament or multifilament yarns to form heat stable composite products and / or from monofilaments or yarns with low or moderate frictional forces. It was difficult to plate a metal coating that did not come off easily. It has been proposed to coat polymer fibers with electrolessly plated copper and then with electroplated copper. However, when exposed to a cycling test, these coatings are unstable, crack and lose metal adhesion.
In order to provide a commercially effective method for metal coating yarns, a continuous method must be provided rather than a batch method. In such a process, the monofilament yarn to be treated is unwound from a feed storage reel, passed through an appropriate chemical treatment stage, and then stored on the take-up reel. Unfortunately, in currently available yarn processing means, the monofilament located inside the yarn is not coated or is poorly coated so that the metal coating on the monofilament is non-uniform. Non-uniformly coated yarns have undesirable, non-uniform conductivity. In many applications, such as for shielding outer layers for cables, non-uniform metal outer layers are unacceptable.
It was extremely difficult to plate electroless nickel uniformly and completely on the surface of monofilaments in a bundle of multifilament yarns by wet chemical electroless methods. Various types of prewoven fabrics are coated with electroless metal, primarily electroless copper, for use as electromagnetic interference (EMI) control and shielding. However, electroless copper appears to have adequate adhesion to the surface of individual monofilament polymers in prewoven fabrics, but for reasons that are not fully understood, exposure to high temperatures or humidity It will not maintain its adherence after exposure to. This problem can be alleviated by using electroless nickel that forms strong polymer bonds to various functional groups on the surface of the polymer treated by the method of the present invention. The resulting nickel coated filament is resistant to disintegrative exposure to thermal cycling and humidity.
In the method for plating electroless metal on the surface of a polymer, it is generally necessary to treat the surface so that it accepts a catalyst for electroless metal plating. U.S. Pat. No. 5,302,415 describes a method for electroless metallization of various aramid fibers using copper, nickel, silver, or cobalt. The published method uses an 80-90% sulfuric acid solution to modify the surface of aramid fibers. The modification is achieved by controlled fiber disintegration as a result of depolymerization and provides a place for the deposition of sensitizers that promote electroless metal plating. However, since aramid fibers will be dissolved or disintegrated in acid, they can only be contacted with this strong sulfuric acid solution for a very short time. Electroless copper plating specifically produces a coarse coating that lacks adhesion, ductility and bending durability as required by the cable shield application in question. Furthermore, the all-electroless copper composition requires the addition of another metal layer on each monofilament to shield the copper exposed to prolonged oxidation. Nickel plating by the conventional phosphite-reduced electroless nickel process specifically results in a coating having a conductivity of less than 15% of copper. Due to the oxidation of these nickel methods, phosphorous acid in nickel-phosphite alloys, these coatings form a much more stable surface, generally for applications involving high corrosion resistance. Liked. However, they are extremely resistant and difficult to clean. Therefore, it is difficult to electroplate other metals onto these nickel-phosphorous acid layers, especially when the surface to be coated is on polymer filaments. Thus, all-electroless nickel, based on conventional phosphite reduction chemistry, is not very suitable for the purpose of achieving a metallized fiber coating with high conductivity, in terms of weight / thickness.
Accordingly, it would be desirable to provide a method for making a polymer-coated polymer yarn that is completely and substantially uniform. Furthermore, it would be desirable to provide such a fully coated yarn that can have high conductivity in terms of weight / thickness. It would also be desirable to provide a method that includes an activation step on the surface of the polymer that does not substantially disrupt the polymer monofilament or yarn. It would also be desirable to provide a metal coated yarn that can be formed by a continuous reel-to-reel method. Such a method would allow commercial production of fully and substantially uniformly metal-coated yarns that could be used in a variety of environments such as EMI shielding. Let's go.
Summary of invention
The present invention is a method for modifying the surface of a polymer monofilament to render the surface water wettable, wherein the surface is sulfuric acid or a strong acid derivative of sulfuric acid having a concentration of 75 to 85 weight percent, And an aqueous activating solution comprising a surfactant and a time sufficient to render the surface water wettable, but not to the extent that substantial mechanical disruption of the monofilament occurs. And a method of contacting at a temperature.
The method also allows the monofilament to be coated from at least one supply reel through an electroless nickel bath where the tension on the monofilament in the bath is completely and substantially uniform. By means of contacting the monofilament with an acid and surfactant solution prior to coating with nickel, characterized in that the monofilament is fed to at least one take-up reel low enough to A method for completely and substantially uniformly coating the surface of a polymer monofilament with a conductive electroless nickel-coating is provided.
The present invention includes monofilaments and monofilament yarns coated with a conductive nickel-boron alloy coating.
Brief description of the figure
The figure shows an apparatus suitable for yarn processing according to the present invention.
Detailed Description of the Invention
As a first step in accordance with the practice of the method of the invention, the activity of making the surface of the monofilament in the metal coated yarn easy to adsorb the catalyst to make the surface hydrophilic and to provide electroless nickel plating Contact with aqueous solution. The activated aqueous solution includes an acid such as sulfuric acid or a strong acid derivative of sulfuric acid such as methanesulfonic acid, chlorosulfonic acid, fluorosulfonic acid, and the like, and a surfactant having 8 to 12 carbon atoms. It becomes. Suitable surfactants include fluoroalkyl salts, ethers and esters, polyethoxylated quaternary ammonium salts, sodium alkylbenzoates, polyethoxylated linear alcohols, and the like. Particularly suitable surfactants include perfluoroalkyl sulfonate amines, fluorinated alkyl alkoxylates, fluorinated alkyl esters, fluorinated alkyl carboxylates, and the like. The use of a surfactant allows the use of weaker acid compositions that allow longer contact times with the monofilament without causing substantial disintegration. Increased acceptable contact time allows for increased penetration of the aqueous activated composition into the monofilament inside any yarn being treated.
The surface of the yarn or monofilament is then contacted with a palladium catalyst to provide a catalytic surface for electroless plating of the conductive metal. As used herein, the term “nickel” with respect to an electrolessly applied metal coating refers to a nickel / boron alloy and excludes a nickel / phosphorous alloy. Electroless nickel baths that produce nickel-boron alloy coatings for polymeric monofilaments contain both nickel and boron and a reducing agent.
After the contact step with the activation solution, the metal-coated monofilament is passed through an electroless bath, generally as a yarn, and the nickel is coated completely and substantially uniformly on all monofilament surfaces. Let To the yarn passing through the electroless nickel bath, the nickel coating solution can penetrate into the entire yarn bundle, especially on the surface of the monofilament located inside the yarn bundle. The tension is removed or kept sufficiently low. When the yarn passes through an electroless nickel bath under moderately significant tension, either the monofilament inside the yarn bundle is not coated at all or is incompletely coated so that the metal coating on the monofilament is not uniform It was discovered.
After the electroless nickel coating of the present invention, the nickel coated yarn can be electrolytically coated with an electrolytic metal such as copper or nickel. Electrolytic metal plating also provides that in a reel-to-reel process, the nickel-coated yarn placed in a stirred electrolytic water bath is exposed to little or no tension, allowing the aqueous electrolytic bath to penetrate inside the yarn to be coated. Can be implemented.
When using polyaramid monofilaments as polymer monofilaments or yarns, there is an optimal composite for electrical shielding and signaling applications where low electrical resistance and high strength versus weight combination is an important design objective. can get. Nickel-coated or nickel-electrolytic metal-coated monofilaments or yarns that can be braided or woven serve as an alternative to metal wires. Multi-layer structures are not only their manufacturing method, but also include several improvements over the prior art:
1. (A) a metal-polymer bond with an appropriately treated polymer surface that does not appreciably collapse under exposure to temperature / humidity cycles or soldering temperatures;
(B) an essentially pure nickel substrate,
(1) Metallurgically compatible with later applied electrolytically layers of metals such as copper,
(2) preventing the migration of absorbed moisture or oxygen from the polymer at the interface between the nickel layer and the metal, eg copper layer,
(3) to enable plating by high-speed electroplating of metals such as copper, since thin layers (thickness less than 0.5 microns) are sufficiently conductive;
(C) uniform and complete metallization of each monofilament in the polymer yarn bundle,
The use of amine-borane reduced electroless nickel as the first metallization layer to achieve
2. Due to its dense particulate composition (a) has excellent ductility and bending durability; (b) a layer of electroplated metal, such as an amine, that has greater conductivity per unit weight than electroless copper -Copper on the borane-nickel layer,
3. To provide oxidation / corrosion protection as well as abrasion resistance to copper, one or several electroplating layers of nickel, silver, tin, etc. on the copper layer,
including.
In one aspect of the application of the present invention, a composition comprising a bundle of polyaramid monofilament yarns metallized only with amine-borane reduced electroless nickel is provided. These metallized fibers find use as conductive fillers when cut to short lengths to minimize the accumulation of static electricity on the surface of molded plastic parts used in electrical / electronic products. It is. In this embodiment, an ideal metal coating, in the range of 10-20 ohms / ft, unlike nickel-phosphite alloys, while simultaneously providing acceptable conductivity that is essentially unchanged by oxidation, It must adhere to the surface of the polyaramide monofilament with sufficient adhesion to withstand the mechanical wear of the cut as well as the high temperatures experienced in injection molding processes.
Description of preferred embodiments
The surface of the monofilament treated in accordance with the present invention is more complete on all monofilament surfaces that are adhesive and sufficiently conductive to facilitate subsequent electrolytic metal coating on conductive nickel. Formed from a polymer composition that has been further hydrophilized with an activated solution of acid and surfactant, allowing a more uniform electroless nickel coating. Typical suitable polymer compositions for forming monofilaments or yarns are aramids such as poly (p-phenylene terephthalamide), poly (m-phenylene isophthalamide), nylon 6, nylon 66, etc. Polyamides, polyesters, polyimides, polyetherimides, acrylic derivatives, polytetrafluoroethylene, and the like, preferably including aramid because it provides excellent tension per unit weight. Specifically, the yarn has a denier between about 55 and 3,000, and more specifically, between about 55 and 600 in a 10-15 micron diameter monofilament. The monofilament may be solid or hollow.
It has been discovered that surfactants in acid provide more effective penetration of the acid into the yarn than by unmodified acid solutions. Surfactants allow the use of weaker acids, which leads to a decrease in the decay to the monofilament surface. In the case of sulfuric acid used in combination with a surfactant, 75 to 85%, preferably 78 to 83% sulfuric acid can be used, which avoids undesirable monofilament breakdown while activating composition. Significantly increase the yarn contact time with. Increased contact time and the presence of surfactant result in more complete penetration of the activation solution into the interior of the yarn, thereby ensuring a more reliable, complete and substantially uniform electroless Enable metal coating. The surfactant is used at a concentration of the activation solution between about 10 and 1000 ppm, preferably between about 100 and 500 ppm.
The use of surfactants in the activation solution is preferred and produces surprisingly improved products, but acceptable nickel-coated monofilaments can be used alone or in lower alcohols such as methanol or ethanol, or chromic acid. By treating the monofilament with a solution known to improve surface water wettability, such as potassium hydroxide, sodium hydroxide, or other skein compositions used in combination with Can be generated. Monofilaments also can be used in the United States, for example, by immersion for 2 to 60 seconds at 10 to 100 ° C. in 80 to 90 weight percent sulfuric acid, although the fibers may disintegrate somewhat by such immersion. The treatment can be performed by immersion in concentrated sulfuric acid as described in Japanese Patent No. 5,302,415.
Once the surface of the monofilament has been wetted, the surface is contacted with any one of the catalyst systems well known to those skilled in the electroless plating field to provide electroless metal plating. Catalyst combinations that can be used with sensitized surfaces are published in US Pat. Nos. 3,011,920 and 3,562,038. The use of the catalyst is generally carried out for 1 to about 5 minutes, and then the sample is immersed in an acidic solution to remove tin from the surface in a method called acceleration. The sample is then passed through an electroless nickel bath for a period of about 2 to 10 minutes to provide the desired nickel thickness.
Catalyst plating and activation, and subsequent electroless nickel plating, is performed with a thread under zero or sufficiently low tension so that the treatment bath contacts the surface of all monofilaments.
In the figure, a storage roll 10 has wound thereon multifilament yarns 12 and 14. Guide rollers 16 and 18 pull the yarns 14 and 12 from the storage roll 10 and plate the yarns in the bath 20 and onto the endless web 22. The endless web 22 moves around rollers 24 and 26, at least one of which is motorized. The yarns 12 and 14 pass under the guide rollers 28 and 30,
The treated yarns 36 and 38 are removed from the bath 20 by powered rollers 32 and 34. The bath may be a pretreated bath, a catalytic plating or activation bath, or an electroless nickel bath as described above. The powered rollers 32 and 34 and the endless web 22 are operated on the yarns 40 and 42 plated in the bath 20 on the endless web 22 reliably and at a speed with little or no tension. Accordingly, the entire surface of each monofilament in the yarn is contacted with the composition of bath 20.
The boron-based bath is plated with a form of nickel that is resistant to oxidation and is sufficiently conductive to facilitate subsequent plating of an electrolytic metal, such as copper, onto the nickel surface. Thus, suitable electroless nickel baths are based on boron rather than those based on phosphorous acid. Suitable boron-based electroless nickel baths are disclosed in US Pat. Nos. 3,062,666; 3,140,188; 3,338,762; 3,531,301; , 537,878; and 3,562,038. Some specific preparations are as follows:
1. Nickel sulfate (NiSO_Four・ 6H₂O) 20.00 g / l
Dimethylamine boronic acid 3.0 g / l
Citric acid 10.0 g / l
Concentrated HCl 25.0 ml / l
Ammonium hydroxide up to pH 7.0
2-mercaptobenzothiazole 0.5-2.0 mg / l
65 ° C
2. Nickel chloride (NiCl₂6H₂O) 16.0 g / l
Dimethylamine borane 3.0g / l
Sodium citrate 18.0 g / l
Glycine 8.0g / l
Bismuth nitrate 20.0mg / l
Thiourea 15.0mg / l
pH 7.0, 65 ° C
Nickel is plated on the receiving surface by electroless plating to form a surface of a conductive nickel coat formed from a nickel-boron alloy rather than a nickel phosphite alloy. In this process, the nickel ions are reduced to nickel metal coated on the monofilament catalyst surface to form a complete and substantially uniform conductive layer. The specific resistivity of the nickel-boron alloy is between about 8 and 15 micro-ohm cm. The specific resistivity of the nickel-low phosphite alloy is 20-50 micro-ohm cm; and for a nickel-high phosphite alloy is 150-250 micro-ohm cm. The electroless layer is thick enough to allow subsequent electroplating of a uniform metal layer such as copper. Generally, the electroless nickel layer is between about 0.1 and 1.0 micrometers thick, but can be thicker if desired.
In one step of the electroplating process, the nickel-coated monofilament can be further coated with an electrolytic metal such as electrolytic copper. In the preferred electroplating stage, the nickel coated yarn is in little or no tension so that the aqueous electroplating bath can penetrate into the entire yarn and contact the surface of all the nickel coated monofilaments. Pass through the electroplating bath. The charge is applied to an electroplating bath to provide an electrolytic metal plating completely and substantially uniformly on all nickel surfaces. The thickness of the electrolytic metal coating can be adjusted by adjusting the time, temperature, and metal concentration of the bath, and by adjusting the amount of charge passing through the bath in a manner well known in the art. it can.
The following examples illustrate the present invention and are not intended to limit it.
Example 1
200 denier (d) para-aramid yarn with 89 monofilaments containing 50 ppm of a 3: 1 mixture of surfactant of perfluorinated alkyl ester and surfactant of perfluorinated alkyl alkoxylate Treated in an activated aqueous solution of 79% sulfuric acid at 40 ° C. for 90 seconds. The para-aramid yarn was a product sold under the trade name “Kevlar” by E.I.du Pont de Nemours and Company. The yarn was then rinsed with water and conveyed by a continuous process on zero or very low tension on a conveying film as shown in the figure. The continuous process involved a series of steps in a series of equipment as shown in the figure, including a solution that provides the catalyst system prior to the electroless nickel plating, final rinse, drying, and winding steps. . First, the monofilament surface is passed through the yarn before passing it through an activated solution of palladium, an ionic, soluble palladium complex sold under the trade name Neoganth 834 by the company Atotech, Inc. A solution of about 5% NaOH was passed through which was made alkaline. This solution contains 0.5% 50% NaOH solution used to adjust the pH to 11.5, 3% Neoganth 834 palladium activator concentrate in 96.5% by volume deionized water. Generated by using. The bath was heated to 50 ° C. for about 2 hours and then cooled to 45 ° C. for use in yarn processing. After the palladium bath, the yarn is passed through two rinsing stations, each rinsing with deionized water for about 1 minute, and then sold under the name “Neoganth WA” by Atotech, Inc. A dimethylamine borane reducing agent solution was passed through. A reducing agent solution was produced by taking 0.5% by weight of Neoganth WA concentrate and diluting it with 99% deionized water containing 0.5% boric acid as pH buffer. This solution was heated to 35 ° C. for use in the reduction of soluble palladium ions to palladium metal, which provides active catalytic sites on the polymer surface to initiate electroless nickel plating. The yarn was transferred directly from the reducing agent solution into an electroless nickel plating bath comprising Niklad 752 sold by MacDermid Corp. This bath was treated at pH 6.6 at 70 ° C. and contained dimethylamine borane as the reducing agent; and was prepared according to the supplier's instructions for the desired percent nickel and reducing agent. The yarn was moved through the bath while being supported on the transport film under very low tension. By vigorous stirring in the bath, complete penetration of the bath into the yarn bundle and uniform metallization of each monofilament could be obtained. Specifically, a 4 minute dwell in this bath resulted in an increase of about 30% by weight of the yarn due to the nickel coating. The coated yarn produced is about 100 ohm / ft. Has the resistance of Additional yarns treated with shorter residence times yielded proportionally less nickel and higher resistance, while longer residence times proportionately with lower resistance, This resulted in higher metal adhesion. The provided cross-sectional analysis showed complete and uniform deposition of nickel around all monofilaments in the yarn bundle.
Example 2
A hollow, picture-frame rack can be cut from a 1/16 "polyethylene sheet material and the yarn can be wrapped loosely around the rack without clumping the monofilaments together at the folded contact joints on the sides of the rack U-shaped grooves were formed on the top and bottom of the rack so that about 20-25 ft. Yarn treated with the acid surfactant activation solution of Example 1 was wound on the rack and the following: Hand-immersed in the following treatment solutions in sequence: 2 minutes in 5% NaOH pre-immersion solution at pH 11.5 at ambient temperature; 45 ° C. in a palladium catalyst solution available as Actibator 834 from Atotech Corp. Soak in direct deionized water for about 2 minutes; then rinse in deionized water for 1 minute; then soak in Neoganth WA reducing agent for 2 minutes at 30-35 ° C. and then soak in a low phosphite electroless nickel bath This bath is both 190 ml of Niklad 797A (metal concentrate) and 570 ml of Niklad 797B (sodium hypophosphite solution) and deionized water, also available from MacDermid Corp., and 3.8 liters of electroless nickel plating solution The pH was adjusted to 5.0-5.2 with 50% ammonia and the solution was heated to 90 ° C. before dipping the rack containing the yarn sample. Stirred while immersed in the bath for 5 minutes, which resulted in a 33% weight gain of the yarn due to the nickel coating, the final dried yarn being 300 times larger than the coated yarn of Example 1 300 Ohm / ft.
Examples 3 and 4
Examples 1 and 2 were repeated except that the yarn was treated in concentrated sulfuric acid for a much shorter time as taught in US Pat. No. 5,302,415. In order to minimize substantial disintegration of the monofilament, it was necessary to limit the soaking of the yarn in concentrated sulfuric acid to only half the time of soaking in Examples 1 and 2. The coated yarn exhibited an electrical resistance similar to that of Examples 1 and 2.
Example 5
Stirring the metallized yarn obtained by the method of Example 1 with a gas, with a contact rod through which an electric current is passed into the yarn when the nickel-coated yarn enters the plating bath and is discharged. Later, it was electroplated with copper by passing it through a copper sulfate plating bath of electrolytic acid. Nickel-coated yarns can withstand about 5 amps of current before being damaged, with the addition of about 65 wt% copper and 1 ohm / ft. A material with less than resistance was produced. This copper-plated yarn still retained all the good processability, draping and flexibility characteristics of the original starting yarn. This electroplating method provided an equiaxed crystal structure of fine particles on copper.

Claims (11)

A method for continuously coating the surface of an aramid monofilament, the surface comprising an aqueous solution comprising sulfuric acid or a strong acid derivative of sulfuric acid having a concentration of 75 to 85% by weight and a surfactant; In a period and at a temperature that is sufficient to make the surface of the monofilament water-wettable, wherein substantial mechanical collapse of the monofilament does not occur , and the monofilament is Supplying from at least one supply roll to at least one take-up reel through an activation solution and an electroless nickel bath. The method of claim 1 wherein the surfactant is a fluorinated surfactant. The method of claim 1 including the additional step of coating said electroless nickel coating with at least one electrolytic metal. The method of claim 3, wherein the electrolytic metal coating is electrolytic copper, electrolytic nickel, or electrolytic silver. The method of claim 1 wherein the monofilament is solid. The method of claim 1, wherein said monofilament is hollow. The method of claim 1, wherein the monofilament yarn is transported through a process. A method according to claim 3 wherein said monofilament yarn is transported through the process. The method of claim 8, wherein said monofilament is solid. The method of claim 8, wherein said monofilament is hollow. A polymer monofilament coated completely and substantially uniformly with a conductive electroless nickel-boron alloy coating according to the method of paragraph 1.

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