WO2007088217A1

WO2007088217A1 - Method for metallising urea polymers and other polymers

Info

Publication number: WO2007088217A1
Application number: PCT/ES2006/000044
Authority: WO
Inventors: Pedro Abadia Gamon; Juan Carlos Alcorta Rubio
Original assignee: Gabilondo Muguerza, Andres
Priority date: 2006-02-01
Filing date: 2006-02-01
Publication date: 2007-08-09
Also published as: PT2007088217W

Abstract

The invention relates to a method for metallising urea polymers and other polymers by means of a wet electrolytic chemical process, comprising the following steps, in which: (a) the polymeric substrate is mordanted with a mordanting composition containing an acid or a mixture of organic or inorganic acids, (b) a copper layer is chemically deposited on the mordanted polymeric substrate, and (c) a layer of tin or zinc is electrolytically deposited on the layer deposited in step (b). Optionally, the method can also include an additional step involving the electrolytic or chemical deposition of at least one metal layer and/or an additional finishing step, such as an oxidising, lacquering, polishing or oiling step. Said method can be used to obtain a metal layer on the above-mentioned polymeric substrates, which has very good adhesion and a final appearance suitable for use as a decorative finish.

Description

PROCEDURE FOR METALLIZING UREA POLYMERS AND OTHER POLYMERS

FIELD OF THE INVENTION

The present invention relates to the field of urea polymer coatings (urea-formaldehyde or bakelite) and other polymers with a metal layer with good adhesion thereof and with a decorative final appearance. In particular, it refers to a process for metallizing urea polymeric parts and other polymers on an industrial level in a wet way and in a chemical-electrolytic way that essentially comprises the biting of the pieces, the chemical deposition of a layer of copper on the bitten piece and the electrolytic deposition of a layer of tin or zinc on said copper layer. In this way, a metallic layer is obtained on said polymers that has a very good adhesion.

BACKGROUND OF THE INVENTION

The interest of the manufacturers of bakelite pieces in coating them with a metal layer is known to mainly improve their final appearance.

Currently, it is possible to metal coat other types of polymers such as ABS (acrylonitrile butadiene styrene) or polyester industrially. For this, a wet method is used, in a chemical-electrolytic way in which the parts are subjected to the following stages of the total process:

1- Biting using a biting composition based on chromic acid (chromic acid and sulfuric acid in the case of ABS).

2- Washes

3- Neutralized

4- Washes 5- On

6- Treatment with a catalyst composed of tin and palladium salts

7- Washing 8- Treatment with an accelerator

9- Washes

10-Chemical deposition of nickel (in the case of ABS) or copper (in the case of polyester) 11 -Washing 12-Electrolytic deposition of copper from an acidic electrolyte

13-Washing 14-Various finishes with other metals, lacquers, etc.

All the washing processes are necessary to eliminate the remains of liquid from the last concentrate of the pieces, fundamentally so that they do not contaminate the subsequent concentrates since they would deplete them.

In the biting, that is, in the first step of the process, a small attack is made on the surface of the polymer that opens some cavities in which the catalyst can be deposited.

The neutralized serves to eliminate the chromic acid residues of the piece to be metallized. This step is essential to eliminate any trace of hexavalent chromium from the surface of the pieces since it is a poison for the subsequent treatment with catalyst. Generally in the neutralized sulphite-based salts are used, which are responsible for reducing hexavalent chromium to trivalent.

In the activated one simply employs a solution of hydrochloric acid in water. Its function is to make possible barriers drag contamination of previous steps of the process, as well as acidifying the surface of the piece with the same acid of which the catalyst is composed.

A good catalyzing of the surface of the piece is the key to achieve a good chemical deposition of metal. Currently, the most commonly used catalyst is a colloidal solution of palladium chloride and tin (II) chloride in hydrochloric acid. The colloid is 1 to 5 nm and is constituted by an inner core of palladium surrounded externally by spheres of tin (IV) hydroxide. These colloidal particles adhere in the small cavities produced in the biting stage, completely covering the surface of the piece.

To begin the chemical deposition on palladium it is necessary to remove the tin chloride (IV) that surrounds, in the colloid, the palladium core. This step is carried out in the treatment with an accelerator. Typical solutions are composed of chemicals that dissolve and / or complex the tin compounds (II) and (IV). The most common formulations use fluoroboric acid mixed with hydrochloric acid.

After the chemical deposition of nickel (in the case of ABS) or of copper (in the case of polyester), an electrolytic deposition of copper is made from an acidic electrolyte and, finally, the desired finish is applied .

This process of metallization of ABS dates from the decade of the 60s of the last century and to this day the process has remained the same, having perfected only some of the products used in it.

Said process, however, is not valid to metallize the bakelite since the result obtained with it is not satisfactory: a matte, rough appearance finish is achieved and the adhesion of the metal to the polymeric surface is nil.

It is also known that different research centers and companies have made several attempts to metallize Bakelite but have not achieved it satisfactorily. Moreover, on some occasion it has come to see, in some fair, pieces of this polymer apparently well metallized but that had been made at the laboratory level and that did not meet the minimum required adherence, not being possible to manufacture them at the industrial level.

Thus, the need for alternative processes of metallizing bakelite (urea or urea-formaldehyde), and other polymers at the industrial level and with total adhesion continues to exist in the state of the art.

The present inventors have discovered that the replacement of the acid copper bath in the electrolytic deposition by a tin or zinc bath has led to a strong adhesion of the metal layer to the polymeric substrate, superior even to that achieved with the "deposition system nickel chemistry + copper electrolytic deposition "used in the metallization of ABS and to the system" chemical copper deposition + copper electrolytic deposition "used in the metallization of polyester with fiberglass in printed circuits. That is, a synergistic effect is achieved by the combination of a chemical deposition of copper and an electrolytic deposition of tin or zinc.

In addition, the use of a mordanting composition other than the conventional one in which it does not use chromic acid or any other product containing salts of hexavalent chromium, considered highly toxic, ensures the absence of said hazardous health compounds. With the metallization process of the present invention, therefore, pieces made of urea polymers with a metal layer can be coated on an industrial level, achieving a good adhesion thereof and a decorative final appearance. In addition, the process of the invention improves the metallization characteristics of other polymers that, to date, have not been able to metallize industrially.

OBJECT OF THE INVENTION

The object of the present invention, therefore, is to provide a process for metallizing urea polymers and other polymers by chemical-electrolytic wet route with a good final adhesion and a good decorative finish. Said process essentially comprises the biting of the polymeric substrate, the chemical deposition of a copper layer on the mordented polymeric substrate and the electrolytic deposition of a tin or zinc layer on said copper layer.

DESCRIPTION OF THE INVENTION

The present invention provides a process for metallizing urea polymers and other polymers comprising the steps of: (a) biting the polymeric substrate with a biting composition comprising an acid or a mixture of acids, organic and inorganic;

(b) chemical deposition of a layer of copper on the biting polymer substrate; and (c) electrolytic deposition of a tin or zinc layer on the layer deposited in (b).

It involves metallizing urea polymers and other polymers by chemical-electrolytic wet route, achieving a total adhesion of the metal to said polymer and a final appearance suitable for use as a decorative finish. In the context of the invention, the expression "urea polymers and other polymers" refers to urea-formaldehyde polymers and other polymers such as polyurethane, polypropylene, epoxy resins, etc. Likewise, in the context of the invention, the term "polymeric substrate" refers to a piece or article made of said polymers.

In the case of polymers such as nylon or nylon + fiberglass, although the chemical deposition and the electrolytic deposition of the steps (b) and (c) work well, an adequate biting should be studied.

In said process of the invention, a preparation of the polymeric substrate is carried out before the chemical deposition of stage (b), according to the conventional method indicated above, but varying the characteristics of the etching, both of the chemical composition employed and the conditions of work in which it is carried out. Thus, the biting of step (a) of the process of the invention is carried out with a biting composition comprising an acid or a mixture of acids, organic or inorganic, not using chromic acid or any product containing salts in its composition of hexavalent chromium. Likewise, said biting composition may comprise a surfactant, preferably anionic, and a corrosion inhibitor. The surfactant serves to make the attack more uniform, while the inhibitor and organic acid make the attack slower and therefore also more uniform.

The acid concentration can vary according to the temperature and the immersion time used in the biting. In this way, at a higher temperature or longer immersion time, the acid concentration must be lowered to achieve the same effect.

Thus, in a particular embodiment of the process of the invention, Ia Biting composition comprises 1-80% by weight of acid. In a preferred embodiment, the biting composition comprises 40% by weight of acid.

In another particular embodiment, the acid of the biting composition of step (a) is an inorganic acid selected from the group consisting of sulfuric, hydrochloric, hydrofluoric, phosphoric, nitric and silicic acid; an organic acid selected from the group consisting of acetic, ascorbic, benzoic, nitrobenzoic, sulfamic, tartaric, citric, formic, lactic and methanesulfonic acid; or a mixture thereof.

In a preferred embodiment, the acid of the biting composition of step (a) is sulfuric acid alone or mixed with an organic acid of those indicated above.

Mixtures of approximately 65-90% by weight of one or more inorganic acids may be used, the remainder being one or more organic acids.

On the other hand, the surfactants used in the biting composition can be anionic surfactants and, in particular, lauryl ether sulfates, and used in a proportion of 0.1-2% by weight. The corrosion inhibitors, on the other hand, can be compounds of the alkyl phosphate esters, lauryl mines and thioureas families, and used in a proportion of 0.1-10% by weight, the rest of the biting composition being water .

In a particular embodiment of the process of the invention, the biting of stage (a) is carried out at a temperature between

0 and 70 ⁰ C, the maximum permissible temperature being 70 ⁰ C. As regards the time of stay of the pieces in the biting composition, this varies depending on the working temperature. Thus, in another particular embodiment of the process of the invention, the residence time of the pieces in the biting composition varies from

2 minutes to 12 hours, the maximum stay time being 24 hours.

Likewise, during this stage of biting you can work with or without agitation of any kind.

After the biting stage (a), the polymeric substrate is subjected to the same stages of the traditional method of plastic metallization, as previously indicated (washing, activated, treatment with a catalyst, washing, treatment with an accelerator, washes), until you reach

The chemical deposition of stage (b).

In the chemical deposition of stage (b), a chemical deposition bath of copper is used (instead of the nickel bath usually used for ABS plating).

In a particular embodiment of the process of the invention, in the chemical deposition of stage (b), the minimum residence time of the polymeric substrate in the copper bath is that necessary to deposit a minimum of 0.2 μm.

In another particular embodiment, in the chemical deposition of stage (b) the maximum working temperature is 60 ⁰ C.

Thus, in said step (b) a copper layer with a thickness of 0.2-40 μm, preferably 6 μm, can be deposited.

Once the polymeric substrate is metallized in the chemical copper bath, a layer of tin or zinc is applied on it by electrolysis. In a preferred embodiment, the layer deposited in stage (c) is a tin layer. In another preferred embodiment, the layer deposited in The step (c) is a layer of zinc.

In a preferred embodiment of the process of the invention, in the electrolytic deposition of stage (c), the minimum deposition time will be necessary to deposit a minimum of 1 μm.

Thus, in said step (c) a layer of tin or zinc with a thickness of 1-40 μm, preferably 20 μm, can be deposited.

The replacement of the acid copper bath, traditionally used in

The electrolytic deposition, by one of tin or zinc, is one of the reasons for achieving the strong adhesion of the metal to the polymer. In addition, as indicated, the tin bath is a process normally used in the sector of metal coatings and has a low cost compared to other baths of other metals. On the other hand, tin bath is preferred over zinc, since it is a nobler metal and gives the polymeric substrate a better final appearance.

The synergistic effect produced by the chemical deposition of copper combined with the electrolytic deposition of tin or zinc has been shown to be very positive in order to achieve good adhesion to the urea polymer and other polymers, as mentioned. The adhesion achieved by this process of the invention is far superior to that achieved by the conventional method of chemical deposition of nickel combined with the electrolytic deposition of copper used in

The metallization of the ABS. Likewise, it is superior to that achieved by the conventional method of chemical deposition of copper combined with the electrolytic deposition of copper that is used in the metallization of polyester with fiberglass in printed circuits.

After the tin or zinc coating of stage (c), it is possible to apply back layers of another metal by any conventional chemical or electrolytic method. Thus, in a particular embodiment, the process further comprises an additional electrolytic or chemical deposition stage of at least one other metallic layer.

In a preferred embodiment, said additional metal layer is a layer of copper, nickel, gold, silver, chromium, zinc, rhodium, or one of its alloys, or mixtures thereof. These alloys include brass and bronze, among others.

The final layer of the required metal will be given according to the desired finish. In some cases it will be necessary to apply several layers. Thus, for example, to give a final finish of brass, chrome, gold or silver, it is necessary to apply a previous layer of nickel.

Likewise, the polymeric substrates thus coated with oxidized, lacquered, waxes, oils or other type of treatment or product that improves the characteristics of the final appearance can be finished. Thus, in another particular embodiment, the process of the invention comprises an additional stage of finishing, preferably of oxidized, lacquered, waxed or oiled.

Briefly, the urea polymeric part (polymeric substrate) is subjected to the following stages of the total process:

1. Biting of the piece: it is carried out by means of a biting composition comprising an acid or a mixture of acids, organic or inorganic, as previously indicated. In particular, said composition is formed by weight of 35% inorganic acid, 5% organic acid, 0.2% ammonium surfactant and 1% inhibitor, the rest being water.

2. Double wash with net water in comment. 3. Activated with 10-20% hydrochloric acid by volume for 30-90 seconds at room temperature.

4. Catalyst A commercial product is used on purpose for this purpose, consisting of a mixture of tin and palladium chlorides in hydrochloric acid. The piece is immersed in it for 5-10 minutes at a temperature between 15 and 35 ⁰ C.

5. Double wash with net water in comment.

6. Accelerator. A commercial product suitable for this purpose, consisting of fluorine salts, is used. The piece is immersed in it for 30-90 seconds at a temperature between 15 and 35 ⁰ C.

7. Double washing with mains water.

8. Chemical deposition of copper. A commercial product suitable for this purpose is used. The pieces are submerged for a minimum of 5 minutes and a maximum of 60, at a temperature between 10 and 60 ⁰ C.

9. Double wash with mains water.

10. Neutralized in 5% sulfuric acid by volume for 30-90 seconds at room temperature.

11. Tin coating, for example, from an acidic pH solution, or zinc coating from an acidic or alkaline solution. With a deposition time to deposit a minimum of 1 μm.

12. Double washing with mains water.

After tinning or galvanizing the piece, any other metal backing can be applied chemically or electrolytically.

Thus, for example, after the tin layer the pieces can be finished with the following finishes: - copper

- nickel - nickel - chrome

- copper - nickel

- nickel - brass

- bronze - radio - black nickel

- bronze

- nickel - black chrome

- matt nickel - chrome

- nickel - silver, etc.

For this, baths normally used in the surface coatings sector are used for this purpose.

Finally, the metallized polymeric piece can be subjected to a final stage of finishing such as oxidized, etched, lacquered, oiled, etc., as previously indicated.

Below is an example of the process of the invention that is set forth for a better understanding of the invention and in no case should it be considered a limitation of its scope.

EXAMPLE 1

Procedure to metallize a polymeric urea piece in an industrial plant Pieces made of urea or bakelite polymer were metallized in an industrial plant, conventional for surface coatings, to which the necessary modifications were made to apply the method of the invention previously described . The pieces used were light switch frames of the following measures: 85 x 85 cm those of one body and 155 x 85 cm those of two bodies. The process applied was as follows:

A mordanting composition was formulated with the following concentrations by weight: 40% sulfuric acid and 5% citric acid. In addition, 0.2% sodium lauryl sulfate was added as an anionic surfactant and 1% thiourea as an inhibitor, the rest was completed with net water. Ia solution was heated to a temperature of between 35 and 40 ⁰ C and immersed therein for 2 hours parts.

Parts were washed thoroughly with running water.

Then, the pieces were immersed for 60 seconds at room temperature in an activated solution formulated at 10% by volume with 35% hydrochloric acid, in net water.

Then, the pieces were immersed for 5 minutes in a tin / palladium catalyst bath at a temperature between 20 and 30 ⁰ C. The bath was composed by volume of 1% of a commercial product suitable for this purpose and 20% of 35% hydrochloric acid, the rest was completed with deionized water.

Parts were washed thoroughly with running water.

The pieces were immersed for 60 seconds in an accelerator bath at room temperature. The bath was composed by volume of 1% of a commercial product suitable for this purpose composed of fluorine salts, as previously indicated and 20% of 35% hydrochloric acid, the rest was completed with network water.

Parts were washed thoroughly with running water. The pieces were immersed in a bath of chemical copper deposition for 30 minutes at a temperature between 35 and 40 ⁰ C. The bath was composed essentially of copper sulfate, formaldehyde as reductant, EDTA as sequestering and soda to adjust pH, all dissolved in deionized water.

Parts were washed thoroughly with running water.

The pieces were immersed in a neutralizing solution formed with 5% sulfuric acid for 60 seconds and at room temperature.

The pieces were immersed for 20 minutes at a temperature between 20 and 25 ⁰ C in an acid bath tin electrolytic composition by weight 3% of tin sulfate and 15% sulfuric acid, and a range of organic products suitable for this bath in order to make the tin coating bright (polyethylene glycol and benzalacetone).

Parts were washed thoroughly with running water.

After the tin layer, the pieces were finished with the following finishes:

Urea metallic copper oxide: a layer of copper was deposited that was oxidized with a suitable product for it and then gratified to give an old look. After the engraving, the piece was lacquered. The final appearance was bright pink with black trim.

Urea metallized brass oxide: it was deposited from a layer of copper and then another layer of brass that was oxidized with a suitable product for it and then gratified to give an old look. After the engraving, the piece was lacquered. He final appearance was bright yellow with black trim.

Urea metallic silver oxide: a layer of silver was deposited that was oxidized with a suitable product for it and then gratified to give an old look. After the engraving, the piece was lacquered. The final appearance was bright white with black trim.

The final appearance of the pieces was very attractive, suitable for the decorative market.

The adhesion test was also performed, obtaining a total adhesion result. For this, bending tests of the pieces were carried out until they were broken, from the cascade part it was tried, with a knife blade, to separate the metal layer from the base material, which was impossible. The test was also performed according to the UNE-EN ISO 2409 standard of the "Lattice cutting test", obtaining the classification 0, the maximum granted according to this test.

Although reference has been made to a specific embodiment of the invention, it is evident to one skilled in the art that the described process is susceptible of numerous variations and modifications, and that all the mentioned details can be substituted by other technically equivalent ones, without departing from the scope of protection defined by the appended claims.

Claims

1. Method for metallizing urea polymers and other polymers, characterized in that it comprises the steps of: a) biting of the polymeric substrate with a mordanting composition comprising an acid or a mixture of acids, organic or inorganic; b) chemical deposition of a layer of copper on the biting polymer substrate; and c) electrolytic deposition of a layer of tin or zinc on the layer deposited in (b).

2. Method according to claim 1, characterized in that the layer deposited in stage (c) is a tin layer.

3. Method according to claim 1, characterized in that the layer deposited in step (c) is a zinc layer.

4. Method according to claim 1, characterized in that the biting composition of step (a) comprises 1-80% by weight of acid.

5. Method according to claim 4, characterized in that the biting composition of step (a) comprises 40% by weight of acid.

6. Method according to claim 1, characterized in that the acid of the biting composition of step (a) is an inorganic acid selected from the group consisting of sulfuric, hydrochloric, hydrofluoric, phosphoric, nitric and silicic acid; an organic acid selected from the group consisting of acetic, ascorbic, benzoic, nitrobenzoic, sulfamic, tartaric, citric, formic, lactic and methanesulfonic acid; or a mixture thereof.

7. Method according to claim 6, characterized in that the acid of the biting composition of step (a) is sulfuric acid alone or mixed with an organic acid.

8. Method according to claim 1, characterized in that the biting of stage (a) is carried out at a temperature between 0 and 70 ⁰ C, the maximum allowed temperature being 70 ⁰ C.

9. Method according to claim 1, characterized in that in the biting of stage (a) the time of stay of the pieces in the biting composition varies from 2 minutes to 12 hours, the maximum time of stay being 24 hours.

10. Method according to claim 1, characterized in that in the chemical deposition of stage (b) the minimum treatment time in the bath is the one necessary to deposit a minimum of 0.2 μm.

11. Method according to claim 1, characterized in that in the electrolytic deposition of stage (c) the minimum deposition time will be necessary to deposit a minimum of 1 μm.

12. Method according to any one of the preceding claims, characterized in that it comprises an additional electrolytic or chemical deposition stage of at least one other metallic layer.

13. Method according to claim 12, characterized in that the additional metal layer is a layer of copper, nickel, gold, silver, chromium, zinc, radius, or one of its alloys, or mixtures thereof.

14. Method according to any one of the preceding claims, characterized in that it comprises an additional stage of finishing, preferably oxidized, lacquered, waxed or oiled