EP2171725A2 - Electrical devices - Google Patents

Abstract

The invention relates to an electrical device, comprising an electrically conductive element and a plastic part in contact with the conductive element, wherein at least a part of the electrically conductive element is made of a silver comprising composition and wherein the plastic part, partially or integrally, is made of polymer composition comprising a semi-aromatic polyamide (X) comprising units derived from aliphatic diamines and dicarboxylic acids, wherein (a) the dicarboxylic acids (A) consist of a mixture of 5-65 mole% aliphatic dicarboxylic acid and/or aromatic dicarboxylic acid other than terephthalic acid (A1) and 35-95 mole % terephthalic acid (A2); (b) the aliphatic diamines (B) consist a mixture of 10-70 mole% of a short chain aliphatic diamine with 2-5 C atoms (B1) and 30-90 mole % of a long chain aliphatic diamine with at least 6 C atoms (B2); and (c) the combined molar amount of terephthalic acid (A2) and the long chain aliphatic diamine (B2) is at least 60 mole %, relative to the total molar amount of the dicarboxylic acids and diamines.

Description

ELECTRICAL DEVICES

The invention relates to electrical devices such as electrical switchgears and switches, for example for use in electrical supply systems, in electronic systems and in the power distribution industry. The invention relates in particular to electrical switchgears and membrane switches comprising a conductive element or conductive layer comprising silver.

While high conductivity and relatively low cost are advantageous properties of silver conductors, a problem intrinsically linked to silver conductors is that of "silver migration." Silver migration is the ionic movement of silver between two adjacent traces. That is, when a silver conductor is exposed to moisture under a bias (5V, for example), dendrites will grow from an exposed silver conductor trace to an adjacent trace. Silver migration inevitably results in a temporary electrical short circuit and thus rendering the circuit inoperative.

Silver migration is a phenomenon seen in many types of products and industries. It occurs in microelectronics, components, PCB assemblies and membrane switches. Silver is a very active metal and is thus highly susceptible to silver migration or dendrite growth. Yet it is also a very cost effective metal for the electronic industry. With the reduction or elimination of lead in electronics, silver is a very attractive choice because of its solderability and conductivity.

Electrical switchgears are known, for example, from EP-0313106-A2, US-2006/0096846-A1 , EP-0385380-A2, and US-2006/0148339-A1. Membrane switches are known, for example, from US4,458,969 and US-4,243,852.

The electrical switchgear of EP-0313106-A2 is in particular for use in the power distribution industry.

US-2006/0096846-A1 describes low-voltage switchgears, and a contact pad designed to be fixed onto a movable contact therein, designed to withstand peak short-circuit currents between 200 and 600 amperes per square millimetre of pad.

EP-0385380-A2 describes a vacuum interrupter. These vacuum interrupters are applied in inductive circuits such as motors, transformers, or reactors.

US-2006/0148339-A1 describes electric plug-in contacts for plug-in connectors and switchgears in electric DC wiring systems operated at a nominal voltage, and in particular plug-in contacts intended for use in automobiles, in which systems electric arcing may occur.

Electrical switchgears typically comprise two contact elements, generally one fixed and one movable, next to several further elements, such as input contacts, spring washers, pivot pins, pivoting elements, and drive means for driving the switch, etcetera, and a housing. The electrical switchgear may also comprise multiple switching contacts as in of EP-0313106-A2. In EP-0313106-A2 the contact elements are also called conductive links. The housing envelopes the contact elements and the further elements. The housing can be formed from two halves, also called modules, and can be cast or moulded from a suitable insulating resin. The housing, or the individual modules, may comprise internal sections, which, when mounted together, divide the internal of the housing into different chambers. The housing and the chambers therein act as isolator and separator for the contact elements and further elements. The contact elements are part of the switching contacts. The housing may comprise further insulating elements, such as linking arms connected to the switching contacts and insulating barrier plates between the switching contacts, as well as between switching contacts of adjacent phases in a multiple switch, as in EP-0313106-A2.

Contact elements, or at least the end parts thereof, which end parts are also called contact pads, are generally made of electrically highly conductive materials, generally metal alloys of highly conductive metals like Cu, Ag and Bi, and arc-proof components , such as Ti, V, Cr, Zr, Mo₁ and W, optionally graphite and /or crushed carbon fibres for antiwelding properties and acceptable erosion resistance. In EP-0313106-A2 a tungsten-copper alloy is used for the conductive links. Also the wall of one or more of the chambers or the outer surface of the wall structure of each module may be screened by a conductive coating applied thereto. As in EP-0313106-A2, the coating may be sprayed on the wall surface, and may, for example, be of metal or of a plastic coating filled with conductive particles such as zinc, aluminium, nickel, silver or carbon.

In US-2006/0096846-A1 silver- or copper-based conducting material, comprising a fraction of refractory particles such as tungsten carbide, tungsten or titanium nitride and a fraction of carbon fibres, is used for the contact pads. In EP-0385380-A2, Ag- Cu-WC (WC = tungsten carbide) contact materials with optimized composition and structure are used. In US-2006/0148339-A1 the main body of the contact elements are made of copper or a copper based alloy. In order to guarantee stable electric contact making properties even in a corrosive atmosphere, a hard gold, silver or tin layer is applied by galvanic deposition.

The presence of electrical faults inside switchgear devices such as electrical switchgear breakers causes opening of their electrical contacts at high speed. This high speed opening is generally accompanied by electric arcs giving rise to large stresses at the level of said contacts more particular at the level of their contact surfaces or zones.

Problems that can occur are the following: tripping in response to a fault current (EP-0313106-A2); silver based contact materials showing an undesirable tendency to erosion and welding, and tending to cause adherence between the contact surfaces and/or migration of material between the contact elements; in particular circuit breakers with miniature size get polluted by metal deposition (US-2006/0096846-A1 ); with Cu-Bi alloys the bismuth (Bi) migrates and agglomerates, and the current chopping value becomes heterogeneous, while for vacuum interrupters it is extremely important that this value is kept very low (EP-0385380-A2); Ag-WC alloys tend to lead to thermal shortage and scattering of the current chopping values (EP-0385380-A2), altering of the contact surface of the contact elements, by corrosion or by migration of components of the main body into the surface layer, thus increasing the contact transfer resistance, consequently heating of the contact elements, and under circumstances even to welding of plug-in contacts so that the latter can no longer be separated (US-2006/0148339-A1). In particular silver is a widely used material for the contact elements or contact pads or surface layers applied thereon, for its high electrical conductivity and good corrosion resistance properties, but it needs to be combined with other materials in particular to compensate for other problems primarily related to the phenomenon of silver migration.

Screen-printable, silver-based PTF (polymer thick film) conductors have been used for over 20 years in the production of low voltage membrane touch switches (MTS) for use in dishwashers, microwave ovens, and washer/dryers.

US4,458,969 describes membrane switches with conductors of silver. A membrane switch typically consists of a bottom layer and a top layer spaced from, but selectively movable into contact with, said bottom layer. Conductors of silver are painted, printed or silk screened onto the bottom layer and the facing surface of the top layer, silver - A -

being employed because of its high electrical conductivity. At least one silver conductive lead terminates at a termination point for connection to an electrical connector. To reduce silver migration, a strip of non-migrating, conductive material applied is over said conductive lead at least in a region adjacent to said termination point and extending a distance beyond the termination point of said conductive lead for receipt of said electrical connector affixed to and in electrical contact with said strip of non-migrating, conductive material at the extended portion thereof.

The known membrane switch from US-4,243,852 has a first silver conductor formed on a flexible membrane and a second silver conductor formed on a substrate, which may also be a flexible membrane. A spacer is positioned between and adhesively secured to the substrate and membrane in such a way that there is an opening in the spacer in register with the first and second conductors. Pressure applied to the membrane moves it toward the substrate through the opening in the spacer to cause electrical contact between the first and second conductors. Means for impeding migration of the silver between the first and second conductors essentially consists of orienting the conductors so as to provide the longest possible path between portions thereof.

To reduce or prevent the occurrence of silver migration in membrane switches also other solutions have been applied, either alone or in combination, each having its limitations: modifying the silver composition with palladium or copper, with cost and conductivity as trade-off; modified silver paste systems with reduced susceptible to silver migration, where curing temperatures and mechanical properties can pose a problem; covering or overprinting the silver traces with a dielectric insulator or inert coating, where due to the nature of process and materials pinholes can occur, which provide avenues for silver migration to propagate; increasing the conductor spacing between traces that have a voltage potential or reducing the voltage; gasketing and sealing to prevent penetration of moisture.

Though the above mentioned process steps have reduced the problem of silver migration, there are situations such as severe environments or design constraint issues where silver migration is still a risk. As in all aspects of electronics, the industry drive to reduce space and reduce costs with increased functionality continually pushes the designers and manufacturers of electrical devices to stretch their technical capabilities. In view of the trends for further miniaturization and increase in the voltages applied, for example to 42 Volts such as in passenger car wiring systems and to prevent current leakage and short circuitry between closely spaced charge carriers, there is need for plastic materials having a high CTI (comparative tracking index), good dielectric properties and retention thereof under severe environmental conditions, i.e. at high humidity and/or elevated temperature, to allow use thereof in electrical devices, such as for the housing for electrical switchgears and the carrier for the conductors in the membrane switches. In view of the said miniaturization there is also a need for materials allowing for thinner wall sections, without the propensity for warpage, while still having sufficient mechanical properties and / or flame retardancy.

CTI is a measure of the resistance of a material to the propagation of arcs (tracks) along its surface under wet conditions. To increase the lifespan of electrical devices and the electrical contacts used therein, such as in electrical switchgears and membrane switches, there is a need for electrical devices with better performance in CTI as in metal migration, in particular silver migration.

The first aim of the present invention is therefore to provide an electrical device, in particular electrical switchgears and membrane switches, which has a reduced silver migration. An additional aim is to provide an electrical device with a reduced propensity to warp and with good mechanical properties at high temperatures which enables greater design freedoms, especially in regard to reduced dimensions and in particular thin walled sections. A further aim is to provide an electronical device with good blister resistance, especially under conditions experienced during silver soldering. A further aim of the present invention is to provide an electrical device comprising a plastic part, in particular a plastic housing, having a high CTI. In addition, the present invention aims to provide an electrical device that has sufficient dielectric strength, mechanical properties and/or flame retardancy for making an electrical device, such as a switchgear..

These aims, either alone or in combination, have been achieved by using a polymer composition for making the plastic part, wherein the polymer composition comprises a semi-aromatic polyamide with composition comprising a semi-aromatic polyamide (X) comprising units derived from aliphatic diamines and dicarboxylic acids, wherein: a) the dicarboxylic acids (A) consist of a mixture of 5-65 mole% aliphatic dicarboxylic acid and optionally aromatic dicarboxylic acid other than terephthalic acid (A1 ) and 35-95 mole % terephthalic acid (A2); b) the aliphatic diamines (B) consist a mixture of 10-70 mole% of a short chain aliphatic diamine with 2-5 C atoms (B1 ) and 30-90 mole % of a long chain aliphatic diamine with at least 6 C atoms (B2); and c) the combined molar amount of terephthalic acid (A2) and the long chain aliphatic diamine (B2) is at least 60 mole %, relative to the total molar amount of the dicarboxylic acids and diamines.

The plastic part is used for an electrical device comprising an electrically conductive element and the plastic part as a substrate for the electrically conductive element, and wherein at least a part of the electrically conductive element is made of a silver comprising composition. The effect of the polymer composition comprising the said semi-aromatic polyamide X in the plastic part, is that silver migration in the electrical device comprising silver containing conductive elements born by or in contact with the plastic part is very low. In addition, the composition exhibits good blister resistance, excellent stiffness at high temperatures and isotropic type behaviour, which results in a low propensity of thin walled components to warp. Furthermore, the CTI and dielectric strength of the plastic part are very high.

For convenience, reference to the term switchgear or switch will be used to include an electrical device comprising an electrically conductive element and the plastic part as a substrate for the electrically conductive element, and wherein at least a part of the electrically conductive element is made of a silver comprising composition.

A plastic material that is typically used as base substrate for membrane switches is polyester. There is not foreseen that a membrane switch with a base substrate made of a polyamide composition as according to the invention can give such a low occurrence of silver migration.

Electrical switchgears with housings made of polyamide compositions are known, such as polyamide compositions comprising PA6, PA66, PA66/6T and PA46, but their use, if any, is limited to non-critical and less-critical situations. Compared to switchgears comprising a housing made of these polyamides, use of the polyamide composition as according to the invention for the housings results in reduced silver migration and greater design freedom to produce thin walled components which do not warp.

In embodiments in which the electrical device includes silver based solder, the polymer composition of the present invention provides enhanced blister resistance compared to other comparable polyamide compositions, such as PA46, PA 6T/66 and PA9T.

Furthermore the composition has a higher CTI than corresponding compositions of, for example PA66 and PA46, and PA66/6T, while the dielectric strength is better retained, compared to corresponding compositions of, for example PA66/6T, under conditions of elevated temperatures and high humidity.

To test the silver migration different test methods can be applied. For example UL 796 specifies test conditions and methods. An industry standard for testing silver migration is IPC F1996-01. ASTM F1996-01 is a test specific to testing for silver migration in membrane switches. The CTI can be determined in accordance with the IEC 112-1979 (3rd edition) procedure.

The semi-aromatic polyamide X comprised by the plastic connector housing and by the reinforced flame retardant polyamide composition according to the invention, comprises units derived from aliphatic diamines and dicarboxylic acids. The units derived from the dicarboxylic acids can be denoted as A-A units and the units derived from the diamines can be denoted as B-B units. In line therewith the polyamides can be denoted as AABB polymers, corresponding with the classification applied in for example, Nylon Plastic handbook, Ed. M.I. Kohan, Hanser Publishers, Munich, ISBN 1-56990-189-9 (1995), page 5.

The short chain aliphatic diamine (B1 ) is a C2-C5 aliphatic diamine, or a mixture thereof. In other words it has 2-5 carbon (C) atoms. The short chain aliphatic diamine may be, for example, 1 ,2-ethylene diamine, 1 ,3-propanediamine, 1 ,4- butanediamine and 1 ,5-pentane diamine, and mixtures thereof. Preferably, the short chain aliphatic diamine is chosen from the group consisting of 1 ,4-butanediamine, 1 ,5-pentane diamine and mixtures thereof, more preferably 1 ,4-butanediamine.

The long chain aliphatic diamine (B2) is an aliphatic diamine with at least 6 carbon (C) atoms. The long chain aliphatic diamine may be linear, branched and/or alicyclic. The long chain aliphatic diamine may be, for example, 2-methyl-1 ,5- pentanediamine (also known as 2-methylpentamethylene diamine), 1 ,5-hexanediamine, 1 ,6-hexane diamine, 1 ,4-cyclohexanediamine, 1 ,8- octanediamine, 2-methyt-1 ,8- octanediamine, 1 ,9-nonanediamine, trimethylhexamethylene diamine, 1 ,10-decane diamine, 1,11-undecanediamine, 1 ,12-dodecanediamine, m-xylylenediamine and p- xylylenediamine, and any mixture thereof. Preferably, the long chain aliphatic diamine has 6-12 carbon atoms, and suitably is a C8- or C10 diamine. In a preferred embodiment, the long chain diamine consists for 50-100 mole %, more preferably 75- 100 mole% of a diamine having 6 to 9 carbon atoms. This results in materials that have the even better high temperature properties. More preferably, the long chain aliphatic diamine is chosen from the group consisting of 1 ,6-hexane diamine, 2-methyl-1 ,8-octanediamine, 1 ,9- nonanediamine, and mixtures thereof, more preferably 1 ,6-hexane diamine. The advantage of this preferred choice, and in particular of the more preferred choice of 1 ,6- hexane diamine is that the copolyamide has better retention of its properties at high temperature.

The aliphatic dicarboxylic acid may be straight chain, branched chain and/or alicyclic, and the number of carbon atoms therein is not specifically restricted. However, the aliphatic dicarboxylic acid preferably comprises a straight chain or branched chain aliphatic dicarboxylic acid with 4 to 25 carbon atoms, or a mixture thereof, more preferably 6-18 and still more preferably 6-12 carbon atoms. Suitable aliphatic dicarboxylic acid are, for example, adipic acid (C6), 1 ,4-cyclohexane dicarboxylic acid (C8), suberic acid (C8), sebacic acid (C10), dodecanoic acid (C12) or a mixture thereof. Preferably, the aliphatic dicarboxylic acid is a C6-C10 aliphatic dicarboxylic acid, including adipic acid, sebacic acid or a mixture thereof, and more the aliphatic dicarboxylic acid is a C6-C8 aliphatic dicarboxylic acid. Most preferably the aliphatic dicarboxylic acid is adipic acid.

The aromatic dicarboxylic acid may comprise, next to terephthalic acid, other aromatic dicarboxylic acids, for example isophthalic acid and/or naphthalane dicarboxylic acid.

The semi-aromatic polyamide may suitably comprises, next to terephthalic acid, aliphatic dicarboxylic acids or aliphatic dicarboxylic acids and aromatic dicarboxylic acids other than terephthalic acid. Preferably, the amount of the aromatic dicarboxylic acid other than terephthalic acid is less than 50 mole %, more preferably less than 25 mole %, relative to the total molar amount of aliphatic dicarboxylic acid and aromatic dicarboxylic acids other than terephthalic acid (A1 ).

In the semi-aromatic polyamide in the composition according to the invention, the short chain aliphatic diamine (B1 ) makes up for 10-70 mole% and the long chain aliphatic diamine (B2) makes up for the remaining 30-90 mole % of the aliphatic diamine units (B).

Preferably, the molar amount of the short chain aliphatic diamine is at most 60 mole%, more preferably 50 mole%, 40 mole%, or even 35 mole% relative to the molar amount of short chain and long chain diamines. An advantage of the copolyamide with such a lower molar amount of the short chain diamine is that for the copolyamide with a given Tm the silver migration is further reduced.

Also preferably, the molar amount of the short chain aliphatic diamine in the semi-aromatic polyamide is at least 15 mole %, more preferably, at least 20 mole %, relative to the total molar amount of short chain aliphatic diamine and long chain aliphatic diamine.

The aliphatic dicarboxylic acid and, if present, aromatic dicarboxylic acids other than terephthalic acid (A1 ) make up for 5-65 mole% and the terephthalic acid (A2) makes up for the remaining 35-95 mole % of the dicarboxylic acid units (A).

Preferably, the dicarboxylic acids consist for at least 40 mole%, more preferably at least 45 mole%, or even at least 50 mole%, of terephthalic acid. The advantage of an increased amount of terephthalic acid is that the silver migration is further reduced. Also preferably the amount of the aliphatic dicarboxylic acid and optionally aromatic dicarboxylic acids other than terephthalic acid, (A1 ) is at least 10 mole%, more preferably at least 15 mole% of the dicarboxylic acid. This higher amount has the advantage that the composition has a better processability.

In a highly preferably embodiment, the dicarboxylic acids (A) consist of 50-85 mole % of terephthalic acids (A2) and 50-15 mole% of aliphatic dicarboxylic acid and optionally aromatic dicarboxylic acids other than terephthalic acid (A1 ), relative to the molar amount of dicarboxylic acids, and the aliphatic diamines (B) consist of 40-80 mole % long chain diamines (B2) and 60-20 mole % short chain diamines (B1 ), relative to the total molar amount of aliphatic diamines. More preferably, the amount of the aromatic dicarboxylic acid other than terephthalic acid therein, if present at all, is less than 25 mole %, relative to the total molar amount of aliphatic dicarboxylic acid and aromatic dicarboxylic acids other than terephthalic acid (A1 ). This preferred composition gives a better overall balance in silver migration and other properties, including dielectric breakdown strength, processing behaviour and mechanical properties.

Whereas the minimum amount for the long chain aliphatic diamine is 30 mole %, relative to the total molar amount of aliphatic diamines, and the minimum amount for the terephthalic acid is 35 mole %, relative to the molar amount of dicarboxylic acids, the combined molar amount of the terephthalic acid and the long chain aliphatic diamine is at least 60 mole %, relative to the total molar amount of the dicarboxylic acids and diamines. The consequence thereof is that when the relative amount of the long chain aliphatic diamine is the minimal 30 mole %, the relative amount of terephthalic acid is at least 90 mole%. Analogously, when the relative amount of terephthalic acid is the minimal 35 mole %, the relative amount of the long chain aliphatic diamine is at least 85 mole%.

In another highly preferably embodiment, the sum of the molar amount of terephthalic acid (A2) and the long chain aliphatic diamine (B2) is at least 65 mole%, more preferably at least 70 mole% and still more preferably at least 75 mole%, relative to the total molar amount of dicarboxylic acids and diamines. The advantage of the polyamide with the sum of the molar amount of terephthalic acid (A2) and the long chain aliphatic diamine (B2) being higher is that the silver migration is further reduced. Suitably, the said sum is in the range of 70-85 mole %, or even 75-80 mole%, relative to the total molar amount of dicarboxylic acids and diamines.

Next to the A-A-B-B units derived from dicarboxylic acids (AA) and diamines (BB), the polyamide according to the invention may comprise units derived from other components, such as aliphatic aminocarboxylic acids (AB units) and the corresponding cyclic lactams, as well as small amounts of a branching agent and/or chain stoppers.

Preferably, the polyamide according to the invention comprises at most 10 mass %, more preferably at most 8 mass %, and still more preferably at most 5 mass%, relative to the total mass of the polyamide, of units derived from components other than dicarboxylic acids and diamines. Most preferably the polyamide according to the invention does not comprise such other components at all and consists only of A-A-B- B units derived from dicarboxylic acids and diamines. The advantage is a logistically simpler process and better crystalline properties.

Preferably, the semi-aromatic polyamide has a glass transition temperature (Tg) of more than 100⁰C, more preferably at least 110⁰C, or even at least 120⁰C. Preferably the Tg is at most 140⁰C, more preferably at most 130⁰C. Also preferably, the semi-aromatic polyamide has a melt temperature (Tm) of at least 295°C, preferably at least 300⁰C, more preferably at least 310⁰C. Preferably the Tg is at most 340⁰C, more preferably at most 330⁰C. The higher the Tg and also the higher the Tm, the more the silver migration is reduced. An advantage of the Tg and Tm being within these limits is a better balance in silver migration and processing behaviour.

With the term melting point (temperature) is herein understood the temperature, measured according to ASTM D3417-97/D3418-97 by DSC with a heating rate of 10°C/min, falling in the melting range and showing the highest melting rate. With the term glass transition point is herein understood the temperature, measured according to ASTM E 1356-91 by DSC with a heating rate of 10°C/minute and determined as the temperature at the peak of the first derivative (with respect of time) of the parent thermal curve corresponding with the inflection point of the parent thermal curve.

The said semi-aromatic polyamide may have a viscosity varying over a wide range. Surprisingly it has been observed that the said semi-aromatic polyamide may have a relative viscosity as low as 1.6 or even lower while still retaining good mechanical properties even for the reinforced flame retardant composition comprising both reinforcing agent and flame retardant. Normally, polyamides, and in particular semi-aromatic polyamide with such low molecular weight suffer from being very brittle, which property is enhanced when filler materials and flame retardants are comprised. The reinforced flame retardant composition according to the invention shows improved toughness, in comparison with corresponding compositions comprising a semi-aromatic polyamide according to the cited prior art.

Preferably the relative viscosity is at least 1.7, more preferably 1.8 or even 1.9. Retention of mechanical properties is really important for such moulded parts, which is still the case at such a low relative viscosity. Also preferably the relative viscosity is less than 4.0, more preferably less than 3.5 and still more preferably less than 3.0. This lower has relative viscosity the advantage that the flow during moulding is better and moulded parts with thinner elements can be made. It is noted that the values for the relative viscosity relate to the relative viscosity measured in 96% sulphuric acid according to method to ISO 307, fourth edition.

The said semi-aromatic polyamide may also consist of a blend of a semi- aromatic polyamide with a high relative viscosity and one with a low relative viscosity. Suitably, the blend comprises a component with a relative viscosity of at least 1.8, more preferably at least 1.9 and one component with a relative viscosity is of less than 1.7, more preferably less than 1.6. The first component with the relative viscosity of at least 1.9 can have a molecular weight of at least 10,000, while the second component with the relative viscosity of less than 1.6 can have a molecular weight of less than 7,500, preferably less than 5,000, still more preferably less than 2,500. The first and second component may be present in a weight ratio varying over a large range, and preferably in the range of 19 : 1 - 1 : 1 , more preferably 9 : 1 - 3 : 1. The advantage of the presence of the second component with the relative low viscosity is that the moulding behaviour of the polyamide composition is further improved allowing moulding of parts with even thinner wall sections.

The dimensional stability of polymer composition is critical for the manufacture of thin walled components which are not prone to warping. The switchgears of the present invention are able to provide a combination of improved resistance to warping and improved stiffness at high temperatures compared to conventional polyamide compositions suitable for use in electrical devices, such as switchgears. The combination of isotropic type behaviour, characterised by similar coefficients of linear thermal expansion in the direction parallel and normal to polymer flow, and improved stiffness at high temperature is surprising as improvements in mechanical properties, such as stiffness, are typically associated with anisotropic materials, in which enhanced performance has been derived from increased orientation of the material.

The polymer composition in the plastic part comprised by the switchgears and switches according to the invention may comprise the semi-aromatic polyamide X in an amount varying over a wide range. Suitably the amount of the semi- aromatic polyamide is in the range of 25-95 wt.%, more preferably the composition comprises 30-90 wt.%, or even 35-85 wt.%, relative to the total weight of the reinforced polymer composition. In the flame retardant polyamide composition according to the invention, the semi-aromatic polyamide may also be present in an amount varying over a wide range. Due to the flame retardant also being comprised, the relative amount which will generally be lower. Suitably the amount the semi-aromatic polyamide X therein is in the range of 25-80 wt.%, more preferably the composition comprises 25-60 wt.%, or even 30-50 wt.% of the semi-aromatic polyamide.

The polyamide composition suitably comprises an inorganic filler, a fibrous reinforcing agent, a flame retardant, or a CTI improving agent, or any combination thereof.

The mechanical properties of the polyamide composition can easily be enhanced by large when the polyamide composition comprises a fibrous reinforcing agent and/or a nano-filler such as a nanoclay. To meet the requirements on flame retardancy, where applicable, the polyamide composition suitably comprises a flame retardant. Even when the polyamide composition comprises fibrous reinforcing agent as well as flame retardant, it is still possible to make a housing design with thin wall sections while still having sufficient mechanical properties.

Reinforcing agents and fillers will often be present in the compositions used in this invention. The inorganic fillers are for example, glass flakes and mineral filler such as glass spheres or micro balloons, clay, kaoline, like calcined kaolin, wollastonite, and talc, and other minerals, and any combination thereof. The amount of inorganic fillers may be varied over a large range, but suitably is in the range of 0 - 25 wt.%, relative to the total weight of the composition.

Typical examples of fibrous reinforcing agents that can be used include glass fibres such as low-alkali E-glass, carbon fibres, potassium titanate fibres, and whiskers, of which glass fibres are preferred. Sizing agents can be used with such reinforcing agents or fillers, if desired. Suitable glass fibres that can be used in preparing the compositions of this invention are commercially available. Suitably the reinforcing agent is present in an amount of 5-50 wt.%, preferably 15-45 wt.%, more preferably 25-40 wt.% relative to the total weight of the composition.

Suitably, the flame retardant system is present in a total amount of 1- 40 wt.%, preferably 5-35 wt.%, relative to the total weight of the composition. Preferably the flame retardant is present in an amount of 5-30 wt.%, more preferably 10-25 wt.%, and the synergist is preferably present in an amount of 0-15 wt.%, more preferably 1-10 wt.%, and still more preferably 5-10 wt.%, relative to the total weight of the composition.

Suitable additives for improving the CTI include, for example, apolar polymers like polyolefines, such as polyethylene and/or ethylene copolymers, inert fillers, like bariumsulphate and metal borates, such as calcium borate and zinc borate, mixed oxides of zinc and boron, zinc sulfide and compressed pulverized talc, or any combination thereof, preferably a mixture of an olefin-based polymer and any one or more of the foregoing inert fillers. The CTI improving additive is suitably be used in a total amount of 0 - 15 wt.%, for example 0.1 - 10 wt.%, and preferably 0.2 - 5 wt.%. Preferred amounts for the inert filler are 1 - 12 wt.% , more preferably 3 to 10, and for the olefin-based polymer 1 to 10 wt.%, more preferably 3 - 8 wt.%. Herein the weight percentages are relative to the total weight of the polymer composition.

Other additives that may be comprised by the inventive composition include inorganic fillers and auxiliary additives used in injection moulding compounds. With auxiliary additives are understood those additives known by the person skilled in the art of making polyamide moulding composition usually comprised in the said polyamide compositions. The amounts of these conventional additives used will typically be as recommended by the manufacturer for obtaining the particular property enhancement for which the additive is employed. Suitable auxiliary additives are, for example, stabilisers, such as UV stabilizers, heat stabilizers and antioxidants, colorants, which includes both pigments and dyes, processing aids, for example nucleating agents, antistatic agents, mould release agents and lubricants, flow improving additives, such as polyamide oligomers, and agents for improving the impact resistance, i.e. impact modifiers. The amount of auxiliary additives may vary over a large range, but suitably is in the range of 0 - 10 wt.%, preferably 0.1 - 5 wt.% relative to the total weight of the composition.

It will be appreciated that the proportions given herein for the specified components, although typical, are nonetheless approximate, as departures from one or more of the foregoing ranges are permissible whenever deemed necessary, appropriate or desirable in any given situation in order to achieve the desired flame retardancy (e.g., passing with at least a UL V-2 rating or passing the glow wire test) and CTI value (preferably at least 500 volts), while retaining the other physical properties required for the intended use of the finished composition. Thus to achieve the optimum combination of flame retardancy, CTI value, and other properties, a few preliminary tests with the materials to be used is usually a desirable way to proceed in any given situation.

An advantage mentioned above of the polyamide composition comprising the said semi-aromatic polyamide X, is a high CTI (comparative tracking index), and likewise a high dielectric strength. Typically CTI values above 400 V are achieved. When formulated with regular glass fibres as reinforcement agents and regular flame retardants, including halogen free flame retardants based on melamine and/or phosphates derivatives, for example melamine polyphosphates, and metal salts of phosphinates, and halogen containing flame retardant systems based on halogen containing polymers like polybromostyrene, and flame retardant synergists, like zinc borate, and leaving out, or limiting additives that reduce the CTI, CTI values of 600 V and above can be reached. Selection of additives that are neutral in respect of the CTI or have a positive effect on the CTI, and avoiding or limiting the amount of additives that have a negative effect on the CTI, can be selected by the person, skilled in the art of making injection moulding products complying with CTI requirements in general, on the basis of general knowledge and routine experiments. The high CTI values, in combination with the good dimensional stability and part integrity can advantageously be used in industrial high voltage bobbins. Preferably, the CTI of flame retardant material according to the invention used herein has a CTI, of at least 500 V, more preferably at least 600 V. The high CTI values make the switchgears highly suitable for higher voltage applications.

The composition may also comprise polymer components such as polymeric flame retardant, and polymers or polymeric components other than the high temperature semi-crystalline semi-aromatic polyamide and the optionally polymeric flamer retardant. These other polymers may comprise, for example, rubbers and thermoplastic polymers. Rubbers suitably include impact modifiers. The thermoplastic polymers may be other polyamides. Preferably, the other polyamide is a semi-crystalline polyamide having a melting temperature which is lower than the melting temperature of high temperature semi- crystalline semi-aromatic polyamide.

The other polymer is preferably present in an amount of less than 25 wt.%, more preferably, if present at all, in an amount of 1-20 wt.%, still more preferably 2- 15 wt.%, and most preferably 5-10 wt.%, relative to the total weight of the composition. The advantage of a lower content of other polymers, and in particular absence of polymers like polyamide-46 and polyamide-6T/66 is that the reduced silver migration and the increased CTI is better retained.

The electrical device according to the invention, comprising the plastic part at least partially made of the polymer composition comprising the semi-aromatic polyamide (X) and optionally one or more further components, and the conductive element at least which is made of a silver comprising composition, and wherein the plastic part is in contact with the conductive element suitably is an electrical switchgear, a membrane switch, a PCB assembly, a vacuum interrupter or a microelectronic component.

The electrical switchgear generally will comprise at least two electrically conductive elements being contact elements, wherein at least one contact element or a part thereof is made of a silver comprising composition, and wherein the plastic part, partially or integrally made of the polymer composition comprising the semi-aromatic polyamide X, is a housing enveloping the said contact elements.

The membrane switch will comprise at least a fist conductor formed on a first substrate and a second conductor formed on a second substrate, wherein at least the first conductor is an electrically conductive element at least a part of which is made of a silver comprising composition, and at least the first substrate is a plastic part, partially or integrally made of the polymer composition comprising the semi-aromatic polyamide X.

The vacuum interrupter according to the invention will comprise at least two electrically conductive elements being contact elements, wherein at least one contact element or a part thereof is made of a silver comprising composition, and wherein the plastic part is a housing enveloping the contact elements.

The invention also relates to the use of the electrical devices in various applications, in particular including the use of an electrical switchgear according to the invention in an electrical supply system, in an electronic system, in a power distribution system, or in an automobile, as well as the use of the membrane switch according to the invention in household appliances, for example dishwashers, microwave ovens, and washers/driers, whereas the vacuum interrupter according to the invention can be used in an inductive circuit, preferably a motor, a transformer, or a reactor. Experimental.

The polyamide compositions used in the preparations of electrical devices were prepared by first preparing the polyamide polymer for Examples 1 to 5 (E-1 to E-5) and comparative examples (CE) A, B, C and F. Comparative examples D and E were commercial flame retardant, glass fiber reinforced polyamide compositions formulated for use in electrical devices such as switchgears.

Polymer preparation

E-1 Polymer : PA-6T/4T/46 (mole ratio 67.5/21.3/11.2)

A mixture of 179.8 g tetramethylene diamine, 347.25 g hexamethylene diamine, 537 g water, 0.36g sodium hypophosphite monohydrate, 72.36 g adipic acid and 653.38 g terephthalic acid was stirred in a 2.5 liter autoclave with heating and with the removal of water by distillation. It is noted that a slight excess of tetramethylene diamine of about 2-4 wt.% has been used, compared to the composition of the calculated polyamide composition, to compensate for the loss of tetramethylene diamine during the preparation of the polyamide. After about 27 minutes a 91 wt.% aqueous salt solution was obtained. In this process the temperature increased from 169°C to 223°C. The polymerisation was effected at increasing temperatures of 210⁰C to 226°C for 21 minutes, during which the pressure rose to 1.3 MPa, after which the autoclave's contents were flashed and the solid product was cooled further under nitrogen. The prepolymer thus obtained was subsequently dried in a drying kiln for several hours heating at 125°C under vacuum and a stream of nitrogen of 0.02 MPa. The dried prepolymer was post-condensed in the solid phase in a metal tube reactor (d= 85mm) for several hours heating at 200⁰C under a stream of nitrogen (2400g/h) and then under a stream of nitrogen/water vapour (3/1 weight ratio, 2400 g/h)) for 2 hours at 225°C and 40 hours at 260⁰C. Then the polymer was cooled to room temperature.

E-2 Polymer: Preparation of PA-6T/4T/46 (mole ratio 75/10/15)

In the same way as for the E-1 Polymer a mixture of 127.09 g tetramethylene diamine , 350.05 g hexamethylene diamine, 487 g water, 0.66 g sodium hypophosphite monohydrate, 91.59 g adipic acid and 567.48 g terephthalic acid was stirred in a 2.5 liter autoclave with heating so-that an 91 wt.% aqueous salt solution was obtained after 22 minutes. In this process the temperature increased from 176°C to 212°C. The polymerisation was effected at increasing temperatures of 220⁰C to 226°C for 22 minutes, during which the pressure rose to 1.4 MPa. The prepolymer thus obtained was subsequently dried in a drying kiln for several hours heating at 125°C and 180⁰C under vacuum and a stream of nitrogen of 0.02 Mpa. The prepolymer was post- condensed in the solid phase in a metal tube reactor (d= 85mm) for several hours heating at 190⁰C and 230⁰C under a stream of nitrogen (2400g/h) and then under a stream of nitrogen/water vapour (3/1 weight ratio, 2400 g/h) for 96 hours at 251⁰C. Then the polymer was cooled to room temperature.

E-3 Polymer: Preparation of PA-6T/56 (mole ratio 85/15) equivalent to PA-6T/5T/66 (mole ratio 70/15/15)

A mixture of 55.3 g of pentamethylene diamine (98 wt.%), 529.7 g aqueous hexamethylene diamine (59.6 wt.%), 360.4 g water, 0.5g sodium hypophosphite monohydrate, 67.2 g adipic acid and 433.04 g terephthalic acid was stirred in a 2.5 litre autoclave with heating and with distillative removal of water. After 35 minutes a 90 wt.% aqueous salt solution was obtained, while the temperature rose from 170⁰C to 212°C. Then the autoclave was closed. The polymerisation was effected at increasing temperatures of 212°C to 250⁰C for 25 minutes. The mixture was stirred at 250⁰C for 15 min, during which the pressure rose to 2.9 MPa₁ after which the autoclave's contents were flashed and the solid product was cooled further under nitrogen. The prepolymer was post- condensed in the solid phase in a metal tube reactor (d= 85mm) for several hours heating at 200⁰C under a stream of nitrogen (2400g/h) and then under a stream of nitrogen/water vapour (3/1 weight ratio, 2400 g/h)) for 2 hours at 230°C and 24 hours at 260⁰C. Then the polymer was cooled to room temperature.

E-4 Polymer: Preparation of PA-6T/5T/56 (mole ratio 75.5/15/9.5)

A mixture of 78.4 g of pentamethylene diamine (98 wt.%), 473.3 g aqueous hexamethylene diamine (59.6 wt.%), 382.56 g water, 0.5g sodium hypophosphite monohydrate, 42.6 g adipic acid and 461.5 g terephthalic acid was stirred in a 2.5 litre autoclave with heating and with distillative removal of water. After 35 minutes a 90 wt.% aqueous salt solution was obtained, while the temperature rose from 170⁰C to 212°C. Then the autoclave was closed. The polymerisation was effected at increasing temperatures of 212°C to 250⁰C for 25 minutes. The mixture was stirred at 250⁰C for 15 min, during which the pressure rose to 2.8 MPa, after which the autoclave's contents were flashed and the solid product was cooled further under nitrogen. The prepolymer was subsequently dried and post-condensed in the solid phase in the same way as the E-1 polymer. Then the polymer was cooled to room temperature.

E-5 Polymer: Preparation of PA-6T/66/56 (mole ratio 76.5/12/11.5)

A mixture of 36.9 g of pentamethylene diamine (98 wt.%), 553.0 g aqueous hexamethylene diamine (59.6 wt.%), 351.2 g water, 0.5 g sodium hypophosphite monohydrate, 105.8 g adipic acid and 391.4 g terephthalic acid was stirred in a 2.5 litre autoclave with heating and with distillative removal of water. After 35 minutes a 90 wt.% aqueous salt solution was obtained, while the temperature rose from 170°C to 212°C. Then the autoclave was closed. The polymerisation was effected at increasing temperatures of 212°C to 250°C for 25 minutes. The mixture was stirred at 250⁰C for 20 min, during which the pressure rose to 2.8 MPa, after which the autoclave's contents were flashed and the solid product was cooled further under nitrogen. The prepolymer was subsequently dried and post-condensed in the solid phase in the same way as the E-1 polymer. Then the polymer was cooled to room temperature.

CE-A Polymer: PA6T/66 (molar ratio 60 / 40)

In the same way as for Polymer I a mixture of 520 g hexamethylene diamine, 537 g water, 0.36g sodium hypophosphite monohydrate, 330 g adipic acid and 420 g terephthalic acid was stirred in a 2.5 litre autoclave with heating so-that an 91 wt.% aqueous salt solution was obtained after 27 minutes. In this process the temperature increased from 169°C to 223°C. The polymerisation was effected at increasing temperatures of 210⁰C to 226°C for 21 minutes, during which the pressure rose to 1.3 MPa. The prepolymer was subsequently dried and post-condensed in the solid phase in the same way as the E-1 Polymer. Then the polymer was cooled to room temperature. CE-B. C Polymer: PA 46

In the same way as for Polymer I a mixture of 430.4 g tetramethylene diamine , 500 g water, 0.33 g sodium hypophosphite monohydrate and 686.8 g adipic acid was stirred in a 2.5 liter autoclave with heating so-that a 90 wt.% aqueous salt solution was obtained after 25 minutes. In this process the temperature increased from 110⁰C to 162°C. The polymerisation was effected at increasing temperatures of 162°C to 204⁰C in during which the pressure rose to 1.3 MPa. The prepolymer was subsequently dried and post-condensed in the solid phase in the same way as for the E-1 polymer. Then the polymer was cooled to room temperature.

Comparative example CE-F: Preparation of PA-6T/5T (mole ratio 56/44)

A mixture of 201.4 g of pentamethylene diamine, 300.8 g hexamethylene diamine , 521.1 g water, 0.65 g sodium hypophosphite monohydrate and 722.18 g terephthalic acid was stirred in a 2.5 litre autoclave with heating and with distillative removal of water. After 27 minutes a 90 wt. % aqueous salt solution was obtained, while the temperature rose from 170⁰C to 211°C. Then the autoclave was closed. The polymerisation was effected at increasing temperatures of 211°C to 250⁰C in 15 minutes. The mixture was stirred at 250⁰C for 29 min, during which the pressure rose to 2.9 MPa₁ after which the autoclave's contents were flashed and the solid product was cooled further under nitrogen. The prepolymer was subsequently dried and post- condensed in the solid phase in the same way as for the E-3 polymer. Then the polymer was cooled to room temperature.

Compound preparation

E-1 to E-5, CE-A to C and CE-F also included the following components:

• Standard glass fibre grades for polyamides;

• Flame retardant: brominated polystyrene (Saytex® HP3010 available from Albermarle);

• Flame retardant synergist: zinc borate (Firebrake® 500 available from Luzenac); and

• Auxiliary additives comprising a release agent and a stabilizing package, Comparative Experiments D and E were based on commercial products: CE-D being Zytel HTNFR52G30BL, a PA6T/66 product from DuPont, and CE-E being Genestar GN2332 BK, a PA9T product from Kururay. Conventional analytical techniques were used to estimate the proportions of brominated polystyrene, sygnergists and auxiliary additives used in these commercial products. Analysis of the PA9T product from Genestar revealed that the polyamide component consisted of PA8T and PA9T in a molar ratio of approximately 20:80.

The compounds of E-1 to E-5, CE-A to C and CE-F were prepared on a Werner & Pfleiderer KSK 4042D extruder set on a 325⁰C flat temperature. All components were dosed into the feed port of the extruder, except for the glass fibers that were dosed separately into the melt via a side feed port. The polymer melt was degassed into strands at the end of the extruder, cooled and chopped into granules. The compounded and commercial compositions are shown in Table 1.

Injection moulding:

The materials described above were pre-dried prior to use in injection moulding, by applying the following conditions: the copolyamides were heated under vacuum of 0.02 Mpa to 80°C and kept at that temperature and pressure for 24 hrs while a stream of nitrogen was passed. The pre-dried materials were injection moulded on an Arburg 5 injection moulding machine with a 22 mm screw diameter and a Campus UL 0.8 mm 2 body injection mould. The temperature of the cylinder wall was set at 345°C, and the temperature of the mould was set at 140⁰C. The Campus UL bars thus obtained were used for further tests.

Table I Compound compositions

Test methods

Aq migration was determined using an industry based test based upon UL 796.

Relative viscosity (RV) was determined in 1 mass % formic acid solution.

Spiral flow was determined on spiral cavity with dimensions 280 x 15 x 1 mm at a temperature 10°C above the melt temperature of semi-aromatic polyamide X at 80 MPa effective injection pressure.

Thermal characterization by DSC:

Melting point (T_m) and glass transition temperature (T_g)were determined with the aid of differential scanning calorimetry (DSC) (2nd run, 10°C/min.) according to ASTM D3417-97 E793-85/794-85.

E-modulus was determined in a tensile test at 23⁰C and 5 mm/min, according to ISO 527.

Impact test (notched-Charpy) was determined at 23⁰C according to ISO 179/1 A.

Water/Humidity absorption tests:

Pre-dried samples (0.8 mm UL bars) were conditioned in a humidifying cabinet or a container of distilled water at a preset temperature and humidity level, the weight increase was monitored over time until the saturation level was reached. The weight increase at saturation level was calculated as a percentage of the starting weight of the pre-dried sample.

Blistering performance under Reflow soldering conditions.

For the blistering performance under reflow soldering conditions a large number of pre-dried samples were conditioned in a humidifying cabinet at a preset temperature and humidity level in the same way as for water absorption test described above. At different time intervals individual samples (in lots of 10) were taken from the cabinet, shortly cooled at ambient conditions to room temperature, put in a reflow oven and subjected to temperature conditions as applied in reflow soldering processes. The temperature profile applied was the following. First the samples were preheated with a heating ramp of average 1.5°C/sec to reach a temperature of 140⁰C after 80 seconds, after which the sample was heated more gradually to reach a temperature of 160⁰C after 210 sec from the start. Then, the sample was heated to 260⁰C with a initial heating ramp of about 6°C/sec to reach a temperature of 220⁰C after 220 sec and a more gradual heating rate of 2 ⁰C / sec to reach a temperature of 260⁰C after 290 sec from the start. After that, the sample was cooled down to 140⁰C in 20 sec. Then the 10 samples were taken from the oven, let cool to room temperature and inspected for the presence of blisters. For each condition period in the humidifying cabinet the percentage of samples that showed occurrence of blistering was rated. The percentage of samples with blisters was recorded.

Coefficient of linear thermal expansion was determined in accordance with ISO 11359-1/- 2.

Dielectric constant of the sample (DAM) was determined in accordance with IEC 60250 at a frequency of 3 Ghz at 23⁰C.

Dielectric strength of the sample (DAM) was determined in accordance with IEC 60243-1. Comparative Tracking Index was determined in accordance with IEC 60112.

Heat Deflection Temperature was determined in accordance with ISO 75-1/-2 with a load of 1.8 MPa applied.

All compounds complied with UL-94-V0 for 0.8 mm test bars.

Results

The results of the experimentation are presented in Table 2.

As illustrated in Table 2, the compositions of the present invention overcome the problems associated with soldering electrical devies, such as switchgears, with conventional polyamide compositions by providing a polyamide composition with reduced Ag migration, improved blistering resistance, dimensional stability and mechanical properties at high temperatures, while at least retaining the required processing, electrical and flame retardant properties of conventional compositions.

The compositions of the present invention exhibited reduced Ag migration in comparison to compositions comprising PA 46, PA 6T/66 and PA9T. This result was unexpected, given that Ag migration is known to increase with increased water absorption of the polyamide composition. This observation was consistent to test results of the comparative samples which saw PA9T (CE-E) having the lowest Ag mitration (although still higher than the Ag migration in the compositions of the present invention), while the PA46 compositions (CE-B₁CE-C) exhibited the highest Ag migration levels.

The compositions of the present invention have been found to provide improved blister performance against polyamide compositions suitable for electrical device applications. Compositions under the scope of the present invention were found to comply with the requirements of the JEDEC 2/2a blister test (IPC/JEDEC J-STD-020C July 2004). In contrast, none of the comparative examples were able to comply with this industry standard.

JEDEC level 2 is achieved if no blistering is observed after reflow soldering conditions after conditioning the samples for 168 hrs at 85⁰C and 85% relative humidity. JEDEC level 2a is achieved if no blistering is observed after reflow soldering conditions after conditioning the samples for 696 hrs at 3O⁰C and 60% relative humidity.

Of the comparative examples, CE-E which included a polyamide 9T based composition recorded the best blister performance, although still considerably lower than the compositions within the scope of the present invention. This finding is to be expected, based upon the lower moisture absorption of the CE-E. Indeed, the blister results within the comparative examples reveal a correlation between blister performance and moisture uptake levels.

The teaching that improved blistering performance is to be achieved through producing a more hydrophobic polyamide which absorbs less moisture is also present in US 6,140,459 and WO2006/135841 which discloses improved blister performance in a polyamide composition comprising repeating units derived from dicarboxylic acid monomers comprising terephthalic acid and aliphatic diamines having 10 to 20 carbon atoms (eg. PA10T). Thus, it is surprising that the examples under the scope of the present invention have superior blister performance, compared to conventional polyamides, despite their relatively high water uptake.

For comparison purposes it is noted that in the cited art US 6,140,459 the blistering was tested after 96 hrs conditioning at 40⁰C, 95% RH, and applying peak temperatures up to 250°C. In those tests PA 6T/66 already failed at 240⁰C and PA 6T/D6 did not even pass 210⁰C.

In contrast to comparative examples, the compositions of the present invention exhibit isotropic behaviour, as illustrated by the lower variation in the coefficient of linear thermal expansion (CLTE) between normal and parallel directions of the polymer flow. This low variance results in components which are less prone to warp. This property is becoming increasingly important due to the trend towards a reduction in component wall thicknesses. Similar improvements were also observed in respect to mold shrinkage performance.

Likewise stiffness at high temperature, as measured by the temperature of deflection under load (T_def), is an increasing important parameter to enable thin wall components to mechanically withstand the high temperature environment encountered during the soldering process. The compositions of the present invention exhibit improved stiffness at high temperature, with component parts able to withstand loads to within 11⁰C of their melting point compared to about a 2O⁰C difference between T_m and T_def of the PA 66/6T and PA 9T based compositions.

Borderline pass

Claims

1. Electrical device, comprising an electrically conductive element and a plastic part in contact with the conductive element, wherein at least a part of the electrically conductive element is made of a silver comprising composition and wherein the plastic part, partially or integrally, is made of polymer composition comprising a semi-aromatic polyamide (X) comprising units derived from aliphatic diamines and dicarboxylic acids, wherein: a. the dicarboxylic acids (A) consist of a mixture of 5-65 mole% aliphatic dicarboxylic acid and optionally aromatic dicarboxylic acid other than terephthalic acid (A1) and 35-95 mole % terephthalic acid (A2); b. the aliphatic diamines (B) consist a mixture of 10-70 mole% of a short chain aliphatic diamine with 2-5 C atoms (B1) and 30-90 mole % of a long chain aliphatic diamine with at least 6 C atoms (B2); and c. the combined molar amount of terephthalic acid and the long chain aliphatic diamine is at least 60 mole %, relative to the total molar amount of the dicarboxylic acids and diamines.

2. Electrical device according to claim 1 , wherein polyamide composition comprises an inorganic filler, a fibrous reinforcing agent, a flame retardant or a CTI improving agent, or any combination thereof.

3. Electrical device according to claim 1 or 2, wherein the electrical device is an electrical switchgear, a membrane switch, a PCB assembly, a vacuum interrupter or a microelectronic component.

4. Electrical switchgear according to claim 3, comprising at least two electrically conductive elements being contact elements, wherein at least one contact element or a part thereof is made of a silver comprising composition, and wherein the plastic part, partially or integrally made of the polymer composition comprising the semi-aromatic polyamide X, is a housing enveloping the said contact elements.

5. Membrane switch according to claim 3, wherein the membrane switch comprises a fist conductor formed on a first substrate and a second conductor formed on a second substrate, wherein at least the first conductor is an electrically conductive element at least a part of which is made of a silver comprising composition, and at least the first substrate is a plastic part partially or integrally made of the polymer composition comprising the semi- aromatic polyamide X.

6. Vacuum interrupter according to claim 3, comprising at least two electrically conductive elements being contact elements, wherein at least one contact element or a part thereof is made of a silver comprising composition, and wherein the plastic part is a housing enveloping the contact elements.

7. Use of an electrical switchgear according to claim 6 in an electrical supply system, in an electronic system, in a power distribution system, or in an automobile.

8. Use of a membrane switch according to claim 8 in household appliances, for example dishwashers, microwave ovens, and washers/driers.

9. Use of a vacuum interrupter according to claim 9 in an inductive circuit, preferably a motor, a transformer, or a reactor.