JPS6057192B2 - Means comprising an electrode and conductive polymer and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical means in which an electrode is in contact with a conductive polymer composition and a method for making the same.

Conductive polymer compositions are well known. They consist of organic polymers containing finely divided electrically conductive fillers, such as carbon black or particulate metals, dispersed therein. Some of these compositions are so-called PTC (Positive
TemperatureCoefficient (positive temperature coefficient) behavior. The terminology traditionally used to describe PTC behavior is varied and inaccurate. In this specification, "composition exhibiting PTC behavior" and "
The term "C composition" refers to temperatures from -100°C to about 250°C.
a composition having at least one temperature range (hereinafter referred to as a ``critical range'') within a range of about 1 ohm, at the beginning of the temperature range; and within this temperature range the composition has an R of at least 2.5 cm;
0 or at least 10 (preferably both), and preferably "" refers to a composition having an R.o value of at least 6, where R is 14°C. R,oo is the ratio of resistivity at the end and beginning of the range, and R,oo is 1
The ratio of resistivity at the end and beginning of the 00°C range is then R. o is the ratio of the resistivity at the end and the beginning of the 30°C range. The term "PTC element" refers to an element comprising the PTC composition described above. When plotting the logarithm of the resistance of a PTC composition measured between two electrodes in contact with an element versus temperature, it is often, but not always, over a portion of the critical temperature range. In such cases, when a sudden change in slope is observed, the term ``switching temperature'' is used to refer to the temperature at the intersection of the extrapolated substantially linear sections on either side of the section showing the sudden change in slope. ”('4switchingtem-pe
The term "rature'') (usually abbreviated as Ts) is used. The PTC composition in such a PTC element is described herein as having a "useful Ts."
Ts is between 0°C and 175°C, for example between 50°C and 120°C.
Preferably it is between ℃. Conductive polymer compositions, particularly PTC compositions, are useful in electrical means where the composition contacts an electrode, usually a metal electrode.

This type of means comprises extruding or melt extruding a molten polymer composition around or over one or more electrodes, and the conductive polymer in contact with the electrodes. , Tm (where Tm is the temperature at which the conductive polymer composition begins to melt), at a temperature sufficient to (a) reduce the contact resistance between the conductive polymer and the electrode; (b) A manufacturing method characterized by holding for a period shorter than 5 minutes. 12. The manufacturing method according to item 11 above, wherein the time is shorter than 1 minute. 13. The manufacturing method according to item 11 or 12 above, wherein the conductive polymer composition is melted and extruded around the electrode, and then the electrode is heated by resistance heating.

14. A method according to any of paragraphs 11 to 13 above, wherein the conductive polymer composition exhibits PTC behavior and is melt extruded onto two electrodes to form a self-regulating resistance element.

15 electrode and the conductive polymer in contact with it are maintained at a temperature of at least (Tm+20)°C.
The manufacturing method according to any one of Item 14.

16. The manufacturing method according to item 15 above, wherein the temperature is at least (Tm+55)°C.

17(1) a melt-extruded core of a conductive polymer composition exhibiting PTC behavior and comprising carbon black dispersed in a crystalline polymer; at least two longitudinally extending electrodes embedded parallel to each other, and (3) a layer of a protective and insulating composition surrounding the conductive polymer, comprising: (1) a carbon black content ( L1% by weight) is (a) greater than 15%, or (b) less than 15% such that the resistivity (R1 ohm-cm) of the composition satisfies, and (11) the average linearity between any pair of electrodes. Self-regulating strip heater 18 characterized in that the ratio does not exceed 1.2 The average linearity ratio between any pair of electrodes does not exceed 1.10 Detailed description of the invention: The present invention relates to an electrical means in which an electrode is in contact with a conductive polymer composition and a method for producing the same.

Conductive polymer compositions are well known. They consist of organic polymers containing finely divided conductive fillers such as carbon black or particulate metals dispersed therein. Some of these compositions are so-called PTC (POsitive
TemperatureCOefficient (positive temperature coefficient) behavior. The terminology used in the past to describe PTC behavior is varied and inaccurate. In this specification, compositions exhibiting RPTC behavior and R
The term PTC composition refers to temperature ranges from -100°C to about 250°C.
a composition having at least one temperature range (hereinafter referred to as a critical range) within a range of has resistivity;
Also within this temperature range the composition has an R of at least 2.5, 4
or RlCO of at least 10 (preferably both), and preferably has an RlO value of at least 6, where Rl4 is the resistivity at the end and beginning of the 14°C range. and RlOO is 100
The ratio of resistivity at the end and beginning of the °C range and R3
O is the ratio of resistivity at the end and beginning of the 30°C range. The term RPTC element refers to an element comprising the PTC composition described above. When plotting the logarithm of the resistance of a PTC composition measured between two electrodes in contact with the element versus temperature, it is often found that St is not always sloped over a portion of the critical temperature range. In such cases, one switching temperature reference is used to refer to the temperature at the intersection of the extrapolated substantially linear sections on either side of the section showing the abrupt change in slope. (゜゜switchingtem-Perat
The term ure (usually abbreviated as Ts) is used. PTC compositions in such PTC elements are described herein as having a useful TSJ of 1. Ts is 0
Preferably it is between 50°C and 120°C, for example between 50°C and 120°C. Conductive polymer compositions, particularly PTC compositions, are useful in electrical means where the composition contacts an electrode, usually a metal electrode.

Devices of this type are usually manufactured by a process consisting of extruding or casting a molten polymer composition around or onto one or more electrodes. In known methods, the electrode is not heated prior to contact with the polymeric composition, or is heated to a localized extent, e.g., to a temperature well below the melting point of the composition, e.g., as in conventional wire coating techniques. It can only be heated to temperatures below 65°C. [Temperatures throughout this specification are expressed in degrees Celsius. ] Well-known examples of such means include a generally ribbon-like core of a conductive polymer composition;
It is a flexible strip heater consisting of a pair of longitudinally extending electrodes, generally stranded wires, embedded near the ends of the core, and an outer layer of a protective and insulating composition.
Particularly useful heaters are those whose composition exhibits PTC behavior and are therefore self-regulating. The composition is 1
In the manufacture of such heaters containing less than 5% carbon black, in order to obtain a sufficiently low resistivity, ? According to the prior art, it is necessary to anneal the heater for a long period of time to obtain +5100g10R×45 (where L is the weight percent of carbon black and R is the resistivity in ohm-cm at room temperature). It is taught that A disadvantage of devices consisting of electrodes and conductive polymer compositions in contact with them, especially with strip heaters, is that the longer they are used, the higher their resistance becomes. and the power output will be lower, especially when this is subjected to thermal cycling.

of the contact resistance between the electrode and the carbon black filled rubber,
Differences between instruments can be an obstacle to the comparison of the electrical properties of such instruments and to the accurate measurement of the resistivity of such rubbers, especially at high resistivities and low voltages. known; and it has been suggested that the same is true for other conductive polymer compositions.

Various methods have been proposed to reduce the contact resistance between a rubber filled with carbon black and a test electrode placed in contact with it. A preferred method is to vulcanize the comb while the rubber is in contact with a brass electrode. Other methods include copper-plating, vacuum coating with gold, and using a colloidal solution of graphite between the electrode and the specimen. For more information, see Applied Science Publishers.
published by R. H
NOrman's 1 Conductive Rubber and Plastic C6CONdLlCtiVerRubbera
See Chapter 2 of ndPlastics 8) (197). From this it will become clear that the factors governing the magnitude of such contact resistance are not fully understood. The inventors have found that the lower the initial contact resistance between the electrode and the conductive polymer composition, the lower the increase in total resistance over time. The inventors have also discovered that by placing or maintaining the electrode and polymer together in contact with each other at a temperature above the melting point of the composition, the contact resistance between them is reduced. The term melting point of a composition is used herein to refer to the temperature at which the composition begins to melt.

The amount of time that the electrode and the composition, each at a temperature above the melting point of the composition, need to be in contact with each other to achieve the desired outcome is very short. Times in excess of 5 minutes do not further significantly reduce contact resistance, and times less than 1 minute are often sufficient and are therefore recommended.

In this way, the processing time is, for example, US Pat. No. 3,823,21
The times required by known annealing treatments to reduce the resistivity of compositions, such as those described in No. 7 and No. 3,914,363, are of a completely different order of magnitude. Accordingly, in one aspect, the invention provides a means for producing a means suitable for use in an electrical circuit comprising an electrode and a conductive polymer composition in contact therewith, in which electrical current is passed through the conductive polymer to the electrode. "The method comprises melt extruding a molten thermoplastic conductive polymer composition onto an electrode, the method comprising: (1) when the electrode is contacted with the conductive polymer for the first time;
(2) the electrode and the conductive polymer in contact with it are at a temperature above Tm (Tm is the temperature at which the conductive polymer composition begins to melt); T provides a manufacturing method characterized by holding for a sufficient time to reduce the contact resistance between the coalescence and the electrode.
It is desirable that both p and Te be at least 20°C higher than Tm, especially at least 55°C higher.

Both Tp and Te have the ring and ball formula (R1Ng-
And-Ball) softening temperature is often preferred. It is desirable to subject the conductive polymer composition to pressure to help intimately integrate the conductive polymer composition with the electrode. Pressure is generally at least 14kg/C7lf
, preferably at least 21 kg/All, such as 21 to 200 k9/CTl, especially at least 35 k9/CFl
i, for example 35 to 70k9/Clt. The inventors have also discovered that contact resistance can be correlated to the amount of time required to peel the electrode from the polymeric composition.

The invention therefore further provides means comprising an electrode, in particular a stranded wire electrode embedded in the conductive polymer composition, in contact with the conductive polymer composition, the means comprising a wire electrode embedded in the conductive polymer composition; The force P of is at least 1.4 times that of PO. Here, the PO consists of the same electrode in contact with the same conductive polymer composition, and that it is in contact with the conductive polymer composition melting the electrode at a temperature not higher than 24°C and the polymer composition It is the force required to peel off the same electrode from a means manufactured by a method consisting of cooling the object while in contact with the electrode. Peel force P and P. is measured at 21°C as detailed below. Cut a 5.1 cm long linear sample of a heater strip (or other means) containing a 5.1 cm long electrode.

Peel 2.5 cm of polymer from the electrode at one end of the sample. The exposed electrode is lowered through a small hole slightly larger than the electrode in a rigid metal plate held in a horizontal plane. The bare end of the electrode is tightly clamped by a movable clamp below the metal plate, and the other end of the sample is held loosely above the metal plate to keep the electrode vertical. Next, attach the movable fastener 5.
Move vertically downward at 1 cm/min and measure the maximum force required to peel the conductor from the sample. The inventors also found that for strip heaters, which are currently the most widely used means by which electrical current is passed through conductive polymer compositions, contact resistance is a readily measurable quantity as described below. It has also been found that it can be correlated with the linearity ratio (1jnearityrati0). The present invention therefore further provides: (1) a melt-extruded core of a conductive polymer composition exhibiting PTC behavior and comprising carbon black dispersed in a crystalline polymer; (2) said conductive at least two longitudinally extending electrodes embedded parallel to each other in the polymeric composition; and (3) a layer of protective and insulating composition surrounding the conductive polymer; Is the black content (L1 wt%) (a) greater than 15%, or (b) less than 15%, and the resistivity (R1 ohm-cm) of the composition? +510g10R>45 and (11) the average linearity ratio between any pair of electrodes does not exceed 1.2.

The linearity ratio of the strip heater is (9)M? ? … defined as the resistance at 100°C, the resistance measured at 21°C between two electrodes contacted by a probe penetrating the outer coating of the strip heater and the conductive polymer core. Ru.

Since the contact resistance can be ignored at 100V, the closer the linearity ratio is to 1, the smaller the contact resistance becomes. The invention is useful with any type of electrode, such as a metal plate, strip or wire, but with irregular surfaces;
For example, twisted wire electrodes such as those normally used in strip heaters, braided wire electrodes (such as those described in German Patent Application No. 2635000-5) and expanded wire electrodes such as those described in German Patent Publication No. 2655543-1. This is especially true for expandable electrodes.

Preferred stranded wires are silver-coated and nickel-coated copper wires, which are less susceptible to problems such as melting or oxidation than tin-coated or uncoated copper wires. Of course, the latter type of copper wire can also be used without difficulty as long as the operating temperature is not too high. The conductive polymer composition used in the present invention generally contains carbon black as a filler.
It is contained in an amount of about 5% by weight, for example more than 17% by weight or 2% by weight.

In many cases it is preferred that the composition exhibit PTC behavior.
The resistivity of the composition is generally 50,000 ohms at 21°C.
cm, for example 100 to 50,000 ohm cm. For strip heaters designed to be powered by 115 volts or more alternating current, the composition is typically between 2,000 and 50,000 ohm cm, such as between 2,000 and 40,000 ohm cm.
It has a resistivity of cm.

Preferably, the composition is thermoplastic. However, it may be lightly cross-linked or in the process of cross-linking, as long as it is sufficiently fluid under the contact conditions to become intimately integrated with the electrode. Preferably, the polymer is a crystalline polymer. The strip heaters to which the invention relates typically have two electrodes separated by a distance of 0.15 to 1 cm, but larger separations, such as 2.5 cm or more, can be employed. .

The core of the conductive polymer may be of conventional shape;
Preferably, this has a cross section whose smallest dimension, in particular not more than three times the circular cross section, in particular not more than 1 times, for example not more than 1.1 times. In one preferred embodiment of the invention, the electrode and polymer composition are heated separately before being contacted.

In this embodiment, the composition is preferably melt extruded onto the electrodes, for example by extrusion around a pair of spaced wire electrodes using a cross-head die. The electrode is preheated to a temperature Te which may be above or below the melting temperature T9 of the polymer composition, but generally above (Tp-55) and preferably above (Tp-30). Tp is usually considerably higher than the melting point of the composition, e.g. 30 to 80
The temperature will be high. Of course, neither the electrode nor the composition should be heated to temperatures at which significant oxidation or other degradation occurs. In another embodiment of the invention, the composition is formed in contact with an electrode (without preheating the electrode) and then heated while in contact to a temperature above the melting point of the composition. do.

Care must be taken to ensure effective reduction of contact resistance by this method. Optimal conditions will depend on the electrode and composition, but increasing time, temperature and pressure will facilitate achieving the desired results. Pressure can be applied, for example in a brace or by a pinch roller (NiprO
1Ier). This aspect of the invention provides, for example, that the composition contains more than 15% by weight, such as 1% by weight.
If an annealing treatment is not necessary or desirable when containing more than 7% by weight or 2% by weight of carbon blocks, or what is the carbon black content L and resistivity R at the end of annealing? +510g10
This is particularly useful when only limited annealing is performed so that R>45. One method of heating the electrode and the surrounding composition is to pass a high current through the electrode, thereby generating the desired heat by resistive heating of the electrode.

In another embodiment of the invention, the conductive polymer composition is initially in the form of a shaped article, such as one or more spherules or pellets, and is not shaped in contact with the electrode. and the composition are heated together under pressure, for example in a compression mold.

Especially when the conductive polymer composition exhibits PTC behavior, it is often preferred that the composition be crosslinked in the final product.

Crosslinking can be carried out as a separate step after the treatment to reduce the contact resistance, in which case crosslinking by radiation is preferred. Alternatively, crosslinking can be carried out simultaneously with the above treatment, in which case chemical crosslinking with the aid of crosslinking initiators such as peroxides is preferred. The invention is illustrated by the following examples.

Some of these are comparative examples. The strip heaters in each example were manufactured as described below.

The conductive polymer composition is prepared by blending medium density polyethylene containing an antioxidant with a carbon'' black masterbatch containing an ethylene/ethyl acrylate copolymer to provide a composition containing the indicated weight percent carbon black. The melting point of the composition (i.e., the temperature at which the composition begins to melt) was approximately 100°C, and the temperature at which the composition completed melting was approximately 115°C. The composition is melted onto a pair of silver-coated copper stranded wires through a cross-head die having an orifice at a melting temperature of about 18
Melt extrusion was carried out at 0°C. Each wire has a diameter of 0.08
The wire had a diameter of 1.5 cm and consisted of strands, and the axis of the wire was at a point 0.2 cm away from and on the diameter of the orifice. Before reaching the cross-head die, the wire was
It was preheated by passing through a 60 cm long open tube at 0°C. The temperature of the wire entering the die is 87C in Comparative Examples 1, 4 and 6, where the speed of the wire opening and passing through the die is 21 m/min, and 165C in Examples 2 and 7; In cases 3 and 5, the temperature was 193°C. The extrudate was then provided with an insulating skin by melt extruding a 0.051 cm thick layer of chlorinated polyethylene or ethylene/tetrafluoroethylene copolymer around the extrudate.

The coated extrudate was then irradiated to crosslink the conductive polymer composition. Examples 1-3 These examples, of which Example 1 is a comparative example, illustrate the effect of linearity ratio LR on power output when subjecting the heater to temperature changes.

In each example, the linearity ratio of the heater was measured, then the heater was connected to a 120 volt AC power source and the ambient temperature was varied continuously in 3 minute cycles. That is, 9@
The temperature was raised from -37℃ to 65℃ over the next 9
The temperature was lowered to -37°C over the entire area. The maximum power output of the heater in each cycle was measured initially and from time to time and expressed as the ratio PN of the initial maximum power output.

The polymer composition used in Example 1 contained approximately 26% carbon black.

The polymer compositions used in Examples 2 and 3 contained approximately 22% carbon black. The results obtained are shown in Table 1 below.

Examples 4-7 These examples, summarized in Table 2 below, illustrate the effect of electrode preheating on the straightness ratio and peel strength of the product.

Claims (1)

[Scope of Claims] 1. A method for producing a means suitable for use in an electrical circuit comprising an electrode and a conductive polymer composition in contact therewith, in which an electric current flows through the conductive polymer to the electrode. , the method comprises melt extruding a molten thermoplastic conductive polymer composition onto an electrode, wherein: (1) the electrode is brought to a temperature above 65°C when the electrode is first contacted with the conductive polymer; (2) the electrode and the conductive polymer in contact with the electrode are at a temperature above Tm (Tm is the temperature at which the conductive polymer composition begins to melt), and the contact between the conductive polymer and the electrode A manufacturing method characterized by holding for a sufficient time to reduce resistance. 2. The method of claim 1, wherein the conductive polymer composition exhibits PTC behavior and is melt extruded onto two electrodes to form a self-regulating resistance element. 3 When the electrode is first contacted with the molten conductive polymer, (
The manufacturing method according to item 1 or 2 above, wherein the temperature is higher than Tp-55)°C (where Tp is the temperature of the molten conductive polymer). 4. The manufacturing method according to any one of items 1 to 3 above, wherein the electrode is at a temperature of at least 165°C when it is first brought into contact with the molten conductive polymer. 5 When the electrode is first contacted with the molten conductive polymer, T
The manufacturing method according to any one of the above items 1 to 4, wherein the temperature exceeds m. 6. The manufacturing method according to any one of items 1 to 5 above, wherein the conductive polymer is melted and extruded around the electrode, and then the electrode is heated by resistance heating. 7 After the conductive polymer is melt-extruded around the electrode, the electrode and the conductive polymer in contact with it are
7. The manufacturing method according to any one of the above items 1 to 6, wherein the method is heated so that the temperature exceeds 5 minutes. 8. The manufacturing method according to item 7 above, wherein the time is shorter than 1 minute. 9. The electrode and the conductive polymer in contact with it are maintained at a temperature of at least (Tm + 20) °C.
The manufacturing method described in any of paragraphs. 10. The manufacturing method according to item 9 above, wherein the temperature is at least (Tm+55)°C. 11. A method for producing a means suitable for use in an electrical circuit comprising an electrode and a conductive polymer composition in contact with the electrode, the method comprising:
The method comprises melt extruding a molten thermoplastic conductive polymer composition onto an electrode that is at a temperature below 65° C. when the electrode is first contacted with the conductive polymer; Tm (Tm is
(a) sufficient to reduce the contact resistance between the conductive polymer and the electrode; and (b) )5
A manufacturing method characterized by holding for a time shorter than minutes. 12. The manufacturing method according to item 11 above, wherein the time is shorter than 1 minute. 13. The manufacturing method according to item 11 or 12 above, wherein the conductive polymer composition is melted and extruded around the electrode, and then the electrode is heated by resistance heating. 14. A method according to any of paragraphs 11 to 13 above, wherein the conductive polymer composition exhibits PTC behavior and is melt extruded onto two electrodes to form a self-regulating resistance element. 15. The electrode and the conductive polymer in contact with the electrode are maintained at a temperature of at least (Tm + 20) °C.
The manufacturing method according to any one of items 1 to 14. 16. The manufacturing method according to item 15 above, wherein the temperature is at least (Tm+55)°C. 17 (1) a melt-extruded core of a conductive polymer composition exhibiting PTC behavior and comprising carbon black dispersed in a crystalline polymer; at least two longitudinally extending electrodes embedded parallel to each other; and (3) a layer of a protective and insulating composition surrounding the conductive polymer, comprising: (i) a carbon black content (L); , weight %) is (a) greater than 15%, or (b) less than 15%, and the resistivity (R, ohm-cm) of the composition satisfies 2L+5log_1_0R>45, and (ii) between any electrode pair. Self-regulating strip heater 18 characterized in that the average linearity ratio between any pair of electrodes also does not exceed 1.2. The strip heater according to item 17 above, wherein the average linearity ratio between any pair of electrodes does not exceed 1.10.