DE1909489C3 - Process for the production of heat-resilient molded parts with low electrical resistance from polymers - Google Patents

Abstract

1,259,774. Coating plastics with metal: electro-plating plastics. RAYCHEM Ltd. Feb.25, 1969 [Feb. 27, 1968], No.9345/68. Headings C7B and C7F. Heat recoverable hollow polymeric articles are coated with metal, e.g. Al by vapour deposition, Ni by decomposition of nickel carbonyl or Cu, Ni, Au, Cr, Cd, Sn or Ag by electrolytic or electrolessplating. The article may be made conductive by including carbon black or a metal filler, and sensitized with chlorides of Pd, Pt or Au. In an example, a cross-linked polyethylene article is immersed in a chromium trioxide-sodium dichromate solution, washed, immersed in a stannous chloride, hydrochloric acid solution, washed, immersed in a palladium chloride solution, and then plated in a copper sulphate, sodium potassium tartrate, sodium hydroxide, formaldehyde solution. Other examples are coating polyethylene with Ag, polyvinylidene fluoride with Cu, after etching in sodium naphthalene, and Neoprene with copper.

Description

The invention relates to a process for the production of molded parts which can be recovered by heat low electrical resistance from polymers.

Materials that have the property of thermal springback, especially shrinkability Heat can be imparted are well known. Examples include polyethylene, Polyvinyl chloride and polyvinylidene fluoride that have been crosslinked, for example, by irradiation, and polytetrafluoroethylene. Examples of these and other materials that are resilient when exposed to heat are described in U.S. Patents 2,027,962 and 3,086,242. These materials can be small Amounts of fillers, e.g. B. Pigments and flame retardants Means included.

For most practical purposes, crosslinked polymers are used. From these materials Manufactured moldings are heated to a temperature above their crystalline melting point, expanded and left to cool under a pressure at which they retain their expanded shape. When these stretched moldings are later heated to their crystal melting point, they will return to theirs original shape, d. H. they are heat-shrinkable.

From DE-ASn 12 54 933, 12 54 934 and 12 49 048 as well as GB-PSn 8 34 744 and 10 45 086 and from the FR-PS 14 96 278 the metallizing of plastics of various types is known. For metal coating Both thermosetting and thermoplastic plastics are used. The metal coating is in generally applied for decorative or electrical purposes and depending on the required surface condition the metal is applied electrically, chemically, by vapor deposition or in a vacuum. Against it is the metal coating of heat-restoring materials or molded parts made from them has not yet been attempted as it would be expected that a metal coating based on a heat recoverable Material is applied that cracks during the dimensional change triggered by heat and / or peeling. On the other hand, for various purposes, for example electrical purposes, it would be quite desirable a metal coating on such heat-restoring materials or molded parts made from them to work; the heat-resilient materials are inherently insulating materials, their more specific Resistance also through admixture of conductive fillers generally not below about 1000 ohm-cm can be lowered without affecting their other useful properties, for example, their flexibility and mechanical strength, are completely destroyed would. A metal coating would be a suitable way of reducing the electrical resistance without impairing the other useful material properties. However, since the surface of the Most molded parts made from heat-shrinkable materials shrink by 50% or more reduced, one had to reckon with an attempt to metallize the molded parts, that a metal film that is too thin will tear or peel off, a thicker metal coating will not tear or peel off, but the shrinkage of the molded part is hindered and thereby reduced. The cracking and peeling of the Coating is undesirable because it adversely affects electrical properties and resistance increases significantly; the obstruction to shrinkage is also undesirable because it is heat-shrinkable Molding straight to the fullest possible extent Shrinkage matters.

The object of the invention is therefore to improve the electrical resistance of molded parts made of heat-resilient Polymers without impairing the other important material properties, in particular the heat recovery, so that the low resistance is retained even after heat recovery has taken place. In other words, the object of the invention is the production of molded parts with low electrical power Resistance made from heat-recovering polymers.

According to the invention, this object is achieved in that at least part of the surface of the molded part which is capable of heat recovery is coated with a thin film of a metal.
In view of the fact that the person skilled in the art could not have foreseen that the metal coating on such molded parts would not crack or break on recovery by heat and in view of the fact that metal coatings are used in plastics to increase the dimensional stability of the coated materials, in particular in high temperatures, to improve (see. G. Müller "Galvanisierung von Kunststoffen", pages 21 and 26), the solution according to the invention must be regarded as surprising, especially since according to the invention, the free dimensional change due to the action of heat during recovery should not be impaired by the metal coating.

The molded parts according to the invention are preferably made from polymers, in particular polyolefins, chemically or by irradiation, for example with high-energy electrons or have been crosslinked by nuclear radiation, e.g. B. from those described in US Pat. No. 3,086,242 Polymers.

The thermally recoverable material can contain one or more fillers or other additives, e.g. B. Contains antioxidants, flame retardants and pigments.

The metal coating should be thin in relation to the thickness of the molded part, and the resilience of Moldings according to the invention with thermal springback should preferably be essentially the same be the same as with the same resilient molded parts,

which are not provided with the metal coating. In most cases, therefore, the molded parts are resilient practically 100% resilient according to the invention, unless this is due to the action of heat resilient material itself is not capable of such a resetting, such. B. polychloroprene, the so it is assumed that in the deformed, resilient state when left standing, a secondary molecular rearrangement experiences and is not fully resettable

The coating is preferably applied to the molded parts in their resilient, e.g., expanded, state applied, but it can also be applied to the molded parts in their original form, wherein the coated moldings are then deformed under the action of heat and pressure and maintained of the pressure to make them resilient.

The metal coating must not crack or peel off when the molded parts are returned. This depends on its adhesive strength on the molded part and on its thickness. However, the best plating method and the maximum thickness in a particular case can easily be determined by experiment.

Any metals used to clad rigid materials and any heretofore to Methods proposed for this purpose are applicable for the purposes of the invention. It is for example possible to coat the materials with aluminum by vacuum evaporation. For example, vapor deposition by thermal decomposition of nickel carbonyl, as described in US Pat. No. 2,881,094, is also possible, however, it can be used for covering molded parts that are already resilient Form are somewhat limited because the materials are vapor-deposited during the coating process must be at relatively high temperatures of 170 ° C, for example.

Metal coatings such as copper, nickel, gold, chromium, cadmium, tin and silver can be electrolytic or be deposited without current.

The electroless deposition method which is particularly favorable generally includes the following Stages:

a) Etching or roughening the surface of the material

Most resilient due to heat materials can be etched properly with a Chromsäureätze (concentrated H2SO ₄ / chromium trioxide solution at a temperature of about 40 ⁰ C). However, chromic acid etching is not possible with polyvinylidene fluoride. Preferably, a sodium-naphthalene complex in tetrahydrofuran is used here at around room temperature. The treatment with the chromic acid etch generally lasts about 15 seconds, while the sodium-naphthalene complex requires a longer exposure time of about 10 minutes.

b) Sensitization of the etched material

This is generally done with a dilute, weakly acidic Sn ⁺ + solution for a period of 1 or 2 minutes at room temperature or slightly above.

c) Inoculating the material

The material is, for example, 1 to 2 minutes with a dilute, weakly acidic solution of a noble metal chloride, z. B. platinum chloride, gold chloride or especially palladium chloride treated

d) plating the material

The plating can be done by removing the material that undergoes treatment steps a), b) and c) has been immersed in a plating solution for 5 to 30 minutes at room temperature or slightly above, the one salt of the one to be applied. Metal contains if

ίο the material can be plated with copper, for example a modified Fehling's solution can be used.

Optionally, the coating can be electroless by a method of the type described above has been applied and generally has a thickness in the range from 2.54 μ to 25.4 μ, by an additional, electrolytically applied layer are thickened. It is also possible to get a good plating through one To achieve electrolysis processes alone.

The molded parts according to the invention which are resilient by the action of heat can, for example, in Shape of plates, tubes (including generally tubular and non-circular shaped parts and / or varying cross-section and / or with one or more closed ends) and in others Molds are made. You can for example by pressing or extrusion from any polymer are produced, previously proposed for the production of molded parts with thermal springback became. Since their electrical properties are not significantly changed after resetting, the resilient molded parts according to the invention are advantageously used in electrical engineering, especially for the shielding and termination of high-voltage cables.

For example, »winding clubs« help to reduce electrical stress evenly Cable terminations used. So far, these winding lobes were made of electrically insulating, by the action of heat Resilient materials made with a shield made of electrically conductive Material is seen, for example, in the form of a tape, a film or a varnish and is used to to continue the normal shielding of the cable up to the largest diameter of the winding lobe and thereby reduce the electric field at the end of the shield, creating the possibility of an electric Discharge at the end of the cable is reduced. The application of the shields proposed so far is awkward because the tape, film or paint is in place after the thermal springback of the insulating Shrink cone had to be applied. A suitably shaped article according to however, the invention can be applied in a single operation. This is used electrically insulating polymeric material as a winding lobe and the metal coating as a shield.

It should be noted, however, that the polymeric material itself, by the presence of suitable fillers, e.g. B.

Soot or finely divided metals, can be more or less electrically conductive. Such materials can be used with a metal are coated in the method according to the invention, with very high quality electrical conductive molded parts which can be recovered by the action of heat are obtained, in which small cracks etc. in the Metal plating does not affect the electrical properties, because the current passes through the electrically conductive polymeric material passed over the crack

will. These molded parts are therefore an excellent substitute for the shields proposed so far of wrapping clubs. It was also found that the plating was carried out by electroless deposition and electrolyzing processes it is more reliable and better if the polymeric material itself is electrically conductive

The electrical properties of the molded parts according to the invention can of course vary within a very wide range. For example, the resistance of pipes and plates, etc. between the ends can be in the range of O ₁ Cl to 10 6 ohms / cm, with a resistance of less than 10 ohms / cm both before and after recovery being preferred for many purposes.

example 1

A heat shrinkable, chemically crosslinked flame retardant Made, injection-molded shoe made of polyethylene (with a tubular part of larger inner diameter, which extends over a part with a uniformly decreasing inner diameter in a part of smaller inner diameter passes) in the expanded state according to the following Process with copper clad:

1) The molded body was completely concentrated in a solution of chromium trioxide and sodium dichromate Dipped in sulfuric acid. The temperature of this etching solution was 40% and the immersion time was 15 seconds. Immediately after this etching, the molding was rinsed well in cold distilled water.

2. The molded body was then immersed in a sensitizing solution for 90 seconds at room temperature dipped in the following composition:

Tin (II) chloride
hydrochloric acid

Distilled water,
to fill up

1.3 g
10 ml
250 ml

The shaped body was then rinsed well with distilled water.

3) The sensitization stage was followed by a vaccination process. Here, the shaped body was in a solution of dipped in the following composition:

Palladium chloride
hydrochloric acid

Distilled water,
to fill up

0.05 g
1 ml
1 1

Dimensions of the molded body in the stretched state

Inner diameter (larger) 23.9 mm

Inner diameter (smaller) 153 mm

Wall thickness 1.7 mm

Length 63 mm

Dimensions of the molding after recovery

The solution was at room temperature. The immersion time was 120 seconds. After vaccination, the Molded body rinsed again in distilled water.

4) The molded body was then immersed in a plating solution of the following composition:

Copper sulfate 10 g

Sodium Potassium Tartrate 25 g

Sodium hydroxide 10 g

Formaldehyde solution (37%) 10 ml

Distilled Wa ^ t 1 1
to fill up

Inner diameter (larger) 17.8 mm

Inner diameter (smaller) 7.1 mm

Wall thickness 13 mm

Length 63.5 mm

Resistance of the molded part from the end of 0.16 ohms

over before shrinking

Resistance of the molded part from the end of 0.81 ohms

over after shrinking

Example 2

The heat-shrinkable molded article described in Example 1 was plated with silver. The molded article was subjected to treatments (2) and (3) described in Example 1 and then plated as follows:

a) 5 g of silver nitrate were dissolved in 300 ml of distilled water. A diluted solution became a solution Ammonium hydroxide solution was added until the precipitate initially formed was almost dissolved. The solution was then filtered and made up to 500 ml with distilled water. Then a solution of 1 g of silver nitrate became made in a small amount of water and poured into 500 ml of boiling distilled water. One Solution of 0.83 g of Rochelle salt (sodium potassium tartrate) in a small amount of water was prepared and added to the boiling solution. A gray precipitate formed which was filtered off. The solution was made up to 500 ml.

The molded body was placed in a glass container in the same space as the two described above Solutions were poured. A silver coating had formed after about 1 hour.

Results

Resistances were about the same as copper (0.2 ohms before shrinkage, 0.91 ohms after shrinkage), but the adhesive strength was poor.

Example 3

An irradiated polyvinylidene fluoride heat shrinkable tube was coated with copper as follows Plated: The tube was first placed in a tetrahydrofuran for 10 minutes at room temperature Etched sodium-naphthalene complex, which had been prepared as follows: 10 g of naphthalene were in 100 ml Tetrahydrofuran, which had been dried over sodium, dissolved. After adding 3 g of pure sodium was the mixture was stirred until the complex formation was recognizable by the black coloration of the solution. That The tube was then rinsed in diethyl ether and subjected to treatments (2) to (4) described in Example 1.

The plating solution was at room temperature. The immersion time was 15 minutes. The plated molding was removed from the solution and rinsed well in distilled water. The following results were received:

Results: in the stretched state: Dimensions of the pipe 10 mm Inside diameter 0.076 mm Wall thickness 38.1 mm length

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Dimensions when shrunk:

Inside diameter

Wall thickness

length

End to end resistance

before shrinking
End to end resistance

after shrinking

3.81 mm
0.23 mm
38.1 mm
0.68 ohms

1.8 ohms

Example 4

A heat-shrinkable molded part made of polychloroprene with the same dimensions as in Example 1 and 2 was plated with copper. The treatment was carried out in the same way as for the molding Made of polyethylene in Example 1.

Results:

End to end resistance

before shrinking
after shrinking

0.3 ohms

1.1 ohms

By changing the thickness of the coating, corresponding changes in the shrinkage and in the Resistance can be made.

Example 5

A heat-shrinkable molding of the type described in Example 1 was etched in a mixture of chromic acid and sulfuric acid in the manner described in paragraph (1) of Example 1, rinsed in cold distilled water and dried. The shaped body was placed in a vacuum chamber which contained a centrally arranged tungsten element on which aluminum wire was placed. The pressure in the chamber was lowered to 10- ⁴ mmHg and electrically heating the Wolframelernent. The aluminum evaporated from the wire and deposited on the surfaces of the molded part. After the coating, the molded article was taken out of the chamber and coated with a layer of varnish to protect the aluminum film. The resistance between the

Ends of the coated molding before shrinkage was 3 ohms. After shrinking, this was it Resistance increased to 4.5 ohms.

It is possible to treat a number of molded parts simultaneously in the vacuum chamber.

Example 6

A molded body which had the dimensions mentioned in Example 1 and consists of a heat-shrinkable Electrically conductive polymer composition of the following composition was prepared on the Plated with copper as described in Example 1:

Parts by weight Ethylene-ethyl acrylate copolymer 75 (Ethyl acrylate content 18%) Terpolymer of ethylene, 75 Propylene and cyclopentadiene Conductive soot 160 Magnesium oxide 3 Triallyl cyanurate 10 2,5-dimethyl-2,5-di (tert-butyl- 5 peroxy) hex-3-in p-benzoquinone dioxime 4th

Results

Resistance from end to end 0.16 ohms

before shrinking
End-to-end resistance 1.1 ohms

after shrinking

The electrical properties of the molded parts according to the invention are as resistances between the ends They can also be expressed as the resistance of a surface square, measured across two opposite ones Sides of the square (the resistance thus measured is independent of the Size of the square).

For example, an end-to-end resistance of 10 ohms / cm would result in the Examples of molded parts described correspond to a resistance per square of about 2 ohms.

030 245/21

Claims (4)

Patent claims: 1. Process for the production of heat-resilient foils with little electrical energy Resistance made of polymers, characterized in that at least part of the resilient molded part surface with a thin Film of a metal is coated. 2. The method according to claim 1, characterized in that the molded parts in the expanded Coated condition. 3. The method according to any one of claims 1 or 2, characterized in that the metal coating takes place in a currentless way 4. The method according to any one of claims 1 to 3, characterized in that one essentially Molded parts that can be completely restored to their original shape are coated.