DE2948349A1 - PTC DEVICE WITH OXYGEN BARRIERS - Google Patents

Description

DR.-ING. WALTER ABITZ DR. DIETKR F. MORF DIFL.-PHYS. M. GRIi SCHNEIDER Mui .. ... τι.

I -MS I

10 . Nov. ι .bor 19

Ii} * ··). fiii (i K) W bCX ιO M mn! ..- Μ Hö I

m-q-a- v? 'i

I'ii - ;, 7t.i, B ,, .- rbti; il '^ 28 £. O "T * - / \ J

TeU-foii PH: 12 Tti1i - {, r »i] .iii« Ch'-Jiilnriiifi Miiiic ^ ien Tflfx: (O) 52.1W92

96

RAYCHEM CORPORATION Menlo Park, California, V.St.A.

PTC device with oxygen barriers

O 3 Q O? 4 / O>: '"»

965 34 5

The invention relates to electrical devices which Contains conductive polymer PTC elements.

It is known or described in the applicant's earlier patent applications that PTC-conductive polymer compositions ^ i.e. Compositions containing a polymer and comprising conductive particles dispersed therein and having a positive temperature coefficient (PTC) can be used in a wide variety of electrical devices (cf. e.g. J. Pol. Eng. and Sei, 14 (1974), 706, U.S. Patents 3,351,882, 3,858,144, and 3,914,363; DE-OSes 2 543 314.1, 2 755 077.2, 2 755 076.1, 2 821 799-4 and 2 903 442.2 as well as those at the same time as registrations filed with this application, which the US applications Serial No. 965 344 and 965 345 correspond). Such devices often have a jacket from a polymeric material, which electrically isolates the device and also provides physical protection.

According to the invention it has now been found that such Devices have improved electrical stability when the access of oxygen to the PTC element is inhibited will.

The invention relates to an electrical device which comprises

1) a PTC element, which consists of a composition which has PTC behavior with a switching temperature T and which is a polymer and dispersed therein

- 1 *) same applicant

03032W0B1 i

] ': it includes f.ilnye Tr-ilrhcn,

2) at least two electrodes connected to an electrical S t romquell e can be connected and which, when so connected, a current flow through them bring about the PTC-K1 emηπt, and

Barrier 3) an oxygen or -barrier which, when the device is in air at room temperature and normal pressure, the sour material access to the PTC element in such a way h ^f -mmt that the speed with which the

r ο

PTC clement absorbs oxygen, less than 10 cm /

- 7 3

sec / g, preferably less than 4 χ 10 cm / sec / g, especially

- 7 3 special less than 3 χ 10 cm / sec / g, especially less

- 7 3 less than 2 χ 10 cm / sec / g.

1 no-bi. particularly in the case of a device designed to operate to maintain the barrier at elevated temperatures, it is preferred that the barrier remain an effective oxygen barrier at elevated temperatures and thus prevent any excessive change in the resistance of the device. It is therefore preferred that when the resistance of the device at one temperature is TCR n and the resistance of the device at the same temperature after an active aging treatment (as discussed below) is R ™. R _{TA is} 0.5 R _T to 3 R _T> preferably 0.5 R _T to 2 R, with at least one value of T between (T-110) ° C and T, preferably between (T-60) C and T, in particular for all values of T between (T-60) ° C and T, especially for all values of T between (T-110) C and T. The active aging treatment mentioned consists in passing current through the device for a period of t hours,

2 where the current is dimensioned in such a way that the IR heating the performance holds the PTC element at a temperature between T and (T + 50) ° C and t 100 hours, preferably 50 hours, especially 500 hours, especially 1000

965 34 5 $

2 9 A cS 3 4

Hours. For many devices, some or all of these resistance change criteria are met when R " _{A is} 0.5 R _T to 3 R _T , preferably 0.5 R _T to 2 R _T , at T = 25 ° C.

The PTC compositions used according to the invention can be any of the PTC-conductive polymers which are described in the prior applications of the same applicant and in the prior art. The conductive particles preferably comprise carbon black, but other conductive particles such as metal powder, metal oxides, inorganic salts or graphite can also be used. Preferred compositions comprise an organic polymer (the term "polymer" is also intended to include mixtures of polymers) with a crystallinity of at least 10 %, preferably at least 30%, in which a conductive carbon black with a particle size of 20 to 250 millimicrometers is dispersed. The PTC composition can also contain a non-conductive inorganic filler such as zinc oxide, antimony trioxide or clay, and / or an antioxidant (e.g. a sterically hindered phenol such as those described in US Pat. No. 3,986,981 and those of Ciba Geigy under US Pat Trade names "Irganox" produced substances) or any other additive which stabilizes the composition against thermo-oxidative degradation; the proportion of the additive is generally from 0.005 to 10% by weight, for example from 0.01 to 6% by weight, preferably from 0.5 to 4% by weight, based on the weight of the polymer. Some materials that are generally useful as antioxidants for polymers can have an adverse effect on electrical durability, but suitable antioxidants can easily be found through routine experimentation.

0 3 0 0 ? 4 / Π '

965 345 η

The lock is generally such that if the device is exposed to air, the only oxygen that is at least 95% (preferably practically 100%) the surface of the PTC-E] emonts, oxygen is who passed through the barrier. the Lock is preferably made of a material with a Oxygen permeability rate at 25 C from wc-ni-

- 9 - 93

less than 5 x 10 (preferably less than 10) cm (STP) / cm / mm / sec / cm Hg, measured according to ASTM D 14 34-7 5 (STP = normal temperature and pressure). Especially if the device is to work so that the lock at elevated temperature the physical properties of the barrier including its oxygen permeability are maintained elevated temperatures are preferably such that the barrier retains its structural integrity and the device has the desired electrical properties after the aforementioned active aging has occurred. The thickness of the barrier should be sufficient to prevent air admission to the PTC element to the desired extent prevent the formation of pinholes; the thickness is, for example, at least 1 µm and for polymeric materials generally 0.0025 to 0.25 cm, preferably 0.013 to 0.13 cm, in particular 0.025 to 0.075 cm. The barrier preferably protects the device against mechanical damage and therefore preferably exists

made of a material with a Young's modulus greater than

2
7000 kg / cm. When using such a lock it is to avoid any risk that the lock constricts the PTC element and thereby changes the electrical behavior of the device, preferred that the lock of the PTC element through an air gap or a layer of another material with a Young modulus of less

2
than 7000 kg / cm.

-A-

03ÜÜ24 / 0 ':' ■■ '

965 345 ή ^

Suitable materials for the barrier include metals and polymeric compositions based on, for example one or more polymers selected from the group consisting of polyvinylidene chloride, polyvinyl fluoride, polyethylene terephthalate, Rubber hydrochloride, Polychlorotrifluoroethylene, phenol formaldehyde resins, polyamides, Epoxy resins, styrene / acrylonitrile copolymers, polycarbonates, Polystyrene, isobutene / isoprene copolymers, polyethylene, ethylene / tetrafluoroethyl en copolymers, vinylidene fluoride / hexafluoropropylene polymers and fluorine-containing ethylene / propylene copolymers. The continuous surface temperature of the Polymers should preferably exceed T of the PTC element. These polymer compositions can, but should preferably contain conventional additives do not contain any materials that migrate into the PTC element and have a negative impact on its properties would have. - ^

According to a preferred embodiment of the invention the device is a circuit control device and the barrier has the Form of a self-supporting container, through the walls of which the electrodes run (via suitably sealed openings) and inside which the remainder of the device is carried or out of contact with the walls of the container is hung. The container preferably does not contain any oxygen; for example, the container can be evacuated or filled with an inert gas such as argon or nitrogen. Typically, the container consists primarily of Metal, with the electrodes extending through a wall made of a ceramic material or rigid plastic material consists. In another preferred embodiment, the device is a heater or a Circuit control device, and the lock has the form

030024 / Of;

% 5 345 ήή

i'irc-Γ layer of a roly; ner composition, which the The rest of the device surrounds, the volume being enclosed by the layer practically free of cavities. The lock was made of a single material or two or ; ii ': hr consists of materials that are either mixed or used as separate components of the barrier (e.g. a laminate) are present. One or both electrodes can form part of the barrier. The lock should of course do not constitute an electrical connection between the electrodes.

The electrodes generally consist of a metal or some other material with a specific resistance from who. i gcr as 0.1 ohm. cm. Every elec trode can i η ρ hy si kai i se hem Are in contact with the PTC element or in whole or in part be separated from this by an electrically conductive material, for example by a conductive polymer composition, which has a relatively constant watt consumption behavior he. has, i.e. such behavior that no F-TC behavior at temperatures below T des FTC element shows. Optionally, the electrodes can be between the FTC-Elemer.t and a conductive polymer composition be inserted with a relatively constant wattage consumption. Preferably, at least the outer surface is made up of each the electrodes are made of a metal that does not catalyze the build-up of the conductive polymer it contacts. Thus, the electrodes are preferably made of nickel, tin, silver or gold or one of these metals, which on Copper or another metal is applied. If a flat electrode is required, electrodes are used in Form of an expanded metal (expanded metal) or wire mesh preferred. Other electrodes that can be used include solid wire, stranded wire, and braids. When using electrodes made of stranded wire or

o 2:

965 345 j}

other electrodes that contain cavities care must be taken that these cavities do not create a passage for air to penetrate into the device, for example by filling the cavities or by sealing any exposed parts of it. When manufacturing the device, care should be taken to ensure that to keep the contact resistance as low as possible.

The devices according to the invention include Schaltungsbzw. Circuit control devices, especially that Of the type disclosed in the aforementioned United States patent application Serial No. 965 344 and self-limiting heating devices such as heating tapes.

In a class of devices according to the invention, im general circuit control devices, the PTC element has a relatively small size with a volume of

3 3

e.g. less than 20 cm, often less than 10 cm or even smaller, such as less than 5 cm or 1 cm, and the resistance of the device at 25 C is relatively low and is for example less than 50 ohms, preferably less than 10 ohms, or it is even less and is e.g. less than 1 ohm or 0.5 ohm.

In another class of devices according to the invention, in general heating devices, such as flexible heating tapes, which are to be immersed in liquids, e.g. water bed heaters, the barrier should not only inhibit the access of oxygen to the PTC element, but also in the be substantially impermeable to water or any other liquid in which the device is immersed shall be. If the device has an outer jacket made of a plasticized polymer (e.g. polyvinyl chloride) has, the lock can also serve the

0 3 0 0 2 A / C;.

965 345 jjß

29A8349

Migration of the plasticizer from the jacket into the PTC element to prevent. For a submersible heating tape of this type, the barrier is preferably made of a laminate with a Layer of metal, preferably aluminum, typically with a thickness of 0.0005 to 0.005 cm that is sandwiched between two polystyrene oils or plates (preferably made of Polyester) is embedded and connected to these foils. Each polymer film typically has a thickness of 0.001 to 0.005 cm. The laminate can be wrapped around the other components of the device, making it forms an overlapping shell surrounding these components, and the overlapping parts can be connected to one another be sealed. A preferred method is to make a progressively uberlappei.de winding around an insulated To produce heating tape with a tape laminate of the type described, which has a coating of a heat-activated adhesive (preferably a Hot melt adhesive), and then the arrangement heated to connect the adjacent windings of the tape to each other and to the heating tape. If that If the heating tape has a grounding element (e.g. a stranded wire), the PTC element is preferably both by a conventional one Insulating jacket (e.g. made of a polyurethane) as well as the oxygen and liquid barrier from the Strand separated. The braid can be placed between the insulating jacket urd the oxygen and liquid barrier are installed; however, if you have a taped lock of the If the aforementioned type is used, air can be retained in the interstices of the braid and the performance can be improved affect the heater. The ends of the heating tape should preferably be sealed so that it is ensured that no water and no other Liquid can touch the PTC element.

0 3 0 0 2 A / 0 8 1

345 ήί ±

The invention is illustrated by the attached drawings. From the drawings show:

Figures 1 to 4 devices according to the invention; and

Fig. 5 shows the effect of active aging on the Resistance at 25 C of various according to the invention Devices.

Fig. 1 shows a circuit control device which includes a PTC element 1 in the form of a round disc, which has round mesh electrodes 2 embedded in its opposite sides; Lines 4 are connected to the electrodes 2; and a barrier layer encapsulates the PTC element 1 and the electrodes 2, wherein the lines 4 pass through the layer. The interface between the barrier layer S and the PTC element 1 and the electrodes 2 are free from voids.

2 shows a heating tape with a constant cross section, which has solid wire electrodes 2 embedded in the PTC element 1 which is surrounded by the barrier layer 3. The ends of such a heating tape are preferably of one Oxygen barrier covered; however, it is important that even then, if this precaution is not taken, the absence of voids between the PTC element 1 and the barrier layer 3 and in the electrodes 2 causes only a very limited proportion of the surface of the PTC element is exposed to air. If, on the other hand, there are cavities are present between the jacket and the PTC element or if stranded wire electrodes are used and the ends of the heater are not sealed, even if the jacket is practically impermeable to oxygen air along the length of the PTC element and penetrate a significant proportion of the surface area of the Touch element.

030024/0813

365 345 / \ ζ

Fig. 3 shows a submersible in water heating tape with constant cross-section, which has electrodes 12, the
embedded in the PIC-E] ernent 14, which one such
T value means that the heater retains water in which it is immersed at a suitable elevated temperature (e.g. 65 C). The insulating jacket 16 (which consists, for example, of polyurethane) and gives the KFC element 14 and is itself surrounded by the oxygen and water barrier 22, which is formed in the manner described above by progressively wrapping and joining a tape laminate.
A woven strand earthing element 23 surrounds the barrier 22 and is itself surrounded by the outer insulating jacket 24 (for example made of plasticized polyvinyl chloride).

Fig. 4 shows a circuit control device in which the
Lock by a sleeve with generally rectangular
Cross-section is formed and has a metal top 1 and a base sealed therewith. The rifle is with
Filled with nitrogen. The base comprises a metal ring 2,
which has a peripheral sealing gap with which the upper part 1 is sealed, and a disc 4 which is sealed with the ring 2 and is made of glass or an epoxy resin. Needle lines 3 run through the disc and the carrier and are connected to rectangular electrodes between which a PTC element is inserted; the electrodes and the PTC element are shown (only in contours) as shown.

The following examples illustrate the invention; Part- and percentages relate to weight, unless stated otherwise. In each example there are devices manufactured and tested according to the method described below. A PTC composition is made by using the table below

- 10 -

0 3 U Ii "■> A /

965 345 jH

gc-benen ingredients (the weight amounts are given in grams) mixed. The polymers used are commercially available materials which contain a small amount (about 0.5% by weight) of an antioxidant. Mixing is carried out at the river temperature for 5 minutes in a steam-heated Banbury mixer with a water-cooled rotor. The mixture is removed from the mixer, allowed to cool to room temperature and chopped into small pieces. The chopped material is compression-molded at a temperature of 180 ° C. and a pressure of about 70 kg / cm for 5 minutes to form a 0.2 cm thick plate. Round disks with a diameter of 1.9 cm are punched out of the plate. An electrode is created on each side of each disc by pressing a disc 1.9 cm in diameter into it, which has been cut out of an expanded metal mesh consisting of nickel-coated copper. The sample is irradiated at 20 megarads to crosslink the PTC composition. 20 AVG wire leads are connected to the electrodes. As can be seen from the table, the manufacture of the device is completed by surrounding the sample with a barrier as specified in the table. In Example 2, the sample is immersed in the epoxy resin composition, which is then cured at 80 ° C. for 16 hours. In Examples 3 and 5, the sample is heated to 110 ⁰ C, and then immersed in a fluidized bed of the epoxy resin which is then cured for 16 hours at 110 ⁰ C. In example 6, the sample is immersed in the silicone resin, which is then cured at 20 ° C. for 16 hours. In Examples 2, 3, 5 and 6 the barrier layer is 0.025 cm thick.

The electrical durability of the devices after the aforementioned active aging is tested as follows. the Lines of the device are connected to an AC power source

- 11 -

030024/0 8

965 345

connected with variable voltage. The tension of the Power source is held at 1 PO V except when the device is first or again connected to the power source will. In this case the voltage is 30 to 45 V for the first 30 seconds and then becomes within increased to 1? 0 V over a period of 2 minutes. At intervals during aging, the connection of the device to the power source and the device is allowed to cool to room temperature for 30 minutes, after which its resistance is measured at room temperature.

The room temperature resistance of the devices after the aforementioned aging is shown in FIG. One recognises, that the products of Examples 1, 4, 6 and 9i, which do not have barriers according to the invention, have poor electrical properties Have stability, while the products of Examples 2, 3, 5, 7 and 8 according to the invention are excellent Have stability.

The presence of the lock in the devices according to the invention has the additional advantage that when the device is subjected to electrical stress which leads to a breakdown of the PTC composition, the likelihood of an explosive failure or inflammation is considerably reduced.

- 12 -

030024/0 ^

965 345 table

Example 1 23456789

PTC composition

high density polyethylene 699.1 699.1 699.1 741.3 741.3 699.1 699.1 699.1 699.1 Marlex 6003 (Philips Petroleum)

Ethylene / acrylic acid copolymer 873.9 873.9 873.9 925.7 925.7 873.9 873.9 873.9 873.9 EAA-455 (Dow Chemical)

Russ 1391.5 1391.5 1391.5 1358 1358 1391.5 1391.5 1391.5 139L5

Furnex N-765 (City Services)

added antioxidant * 60.5 60.5 60.5 - - 60.5 60.5 60.5 60.5 co block none none

% Epoxy resin (Hysol EE ΌΟ67 HD 7054) -yes
to (oxygen permeability less
* - as 10 " ⁹ )

_o Epoxy resin (REP 35312-40) - yes ______

co (oxygen permeability less
as 10-9)

Silicone resin (Sylgard 170 A / B) _____j _a ___ (oxygen permeability more
than 50 χ 10 ~ ^y )

sealed metal container ______ y _a __

under vacuum

sealed with argon- ------- yes-

teter metal container

Metal container with a _____ ___- _a

small hole ⁴ ^ ₀

* An oligomer of 4,4'-thiobis (3-methyl-6-tert.-Butylphenol) with a Durchschnittspoly ^ <* ⁴ ^ risationsgrad of 3 to 4, as described in U.S. Patent No. 3,986,981. ^? P °

- 13 - -P-

Claims (16)

Electrical device containing 1) a PTC element, which consists of a composition consists, the PTC behavior with a switching temperature T shows and a macromolecular polymer and comprises conductive particles dispersed therein, and 2) at least two electrodes, which can be connected to a power source and which, if they are connected in such a way that a current flow through the PTC element, characterized in that the device also contains 3) an oxygen barrier, which when the device is in air at room temperature and normal pressure, inhibits the access of air to the PTC element, so that the speed at which the PTC element - 6 "\ Oxygen absorbed, less than 10 cm / sec / g amounts to. 2. Device according to claim 1, characterized in that the speed at which the PTC element is oxygen absorbed, is less than 4 x 10 cm / sec / g. 3. Apparatus according to claim 1 or 2, characterized in that it has a change in resistance, at least when a temperature between (T - 110) ° C and T, of -50 0 3 C &quot;}? - ^ / f &quot;
ORIGINAL INSPECTED 965 345 * up to t? 00% after having undergone an aging treatment was subjected, in which current is passed through the device for 250 hours, the current 2
is sized so that the I "R heating of the device holds the PTC element at a temperature between T and (T _s + 50) ° C. 4. The device according to claim 3, characterized in that it has a change in resistance at all temperatures between T ₅ and (T ₅ - 6O) ⁰ C of -50 to +100% after said aging treatment. 5. The device according to claim 3 or 4, characterized in that it has a change in resistance, at least at a temperature between (T - 110) C and T, of -50 to +200 % , after it has been subjected to an aging treatment in the current is passed through the device for 500 hours, the current 2
is sized so that the IR heating of the device the PTC element at a temperature between T and (T + 50) ° C. 6. The device according to claim 1 to 5 »characterized in that the barrier consists of a material which has an oxygen permeability rate of less than 5 χ 10 ~ ⁹ cm ³ (STP) / cm ² / mm / sec / cmHg (STP = normal temperature and pressure). 7. The device according to claim 6, characterized in that the lock consists of a material which a Oxygen permeability rate less than 10 cm (STP) / cm / mm / sec / cmHg. 8. Apparatus according to claim 6 or 7, characterized in that 0300 2 4/0 P. 965 345 7 net that the lock is 0.0025 to 0.13 cm thick and has at least one layer of an electrically insulating composition, which at least one Polymer includes. 9. The device according to claim 8, characterized in that the barrier comprises a polymer which has a continuous Surface temperature above T of the PTC element owns and is selected from the group polyvinylidene chloride, polyvinyl fluoride, polyethylene terephthalate, Rubber hydrochloride, polychlorotrifluoroethylene, phenol-formaldehyde resins, polyamides, epoxy resins, styrene / Acrylonitrile copolymers, cellulose acetate, butadiene / acrylonitrile copolymers, Polycarbonates, polystyrene, isobutene / isoprene copolymers, polyethylene, ethylene / tetrafluoroethylene copolymers, Vinylidene fluoride / hexafluoropropylene polymers and fluorine-containing ethylene / propylene copolymers. 10. The device according to claim 1 to 9, characterized in that the lock includes a metal. 11. The device according to claim 10 in the form of a Schaltbzw. Circuit control device, characterized in that that the barrier comprises a self-supporting container which is mainly made of metal, wherein the electrodes pass through a wall made of a ceramic or rigid plastic material. 12. The device according to claim 10, characterized in that at least one of the electrodes is part of the barrier forms. 13- device according to claim 1 to 12, characterized in that that the lock has a hermetic seal around it 0 3 0 ^Λ 965 34 5 if KiC-El forms again. 14. The device according to claim 1 to 10 in the form of a Heating tape, characterized in that the barrier is impermeable to water. 15 · Device according to claim 1 to 10 and 14, characterized characterized in that the barrier comprises a laminate which includes a layer of a metal, that is inserted between two polymer films and is bound to these foils. 16. The device according to claim 1 to 1 5, characterized in that that at least one of the electrodes from the PTC element completely or partially through a layer a conductive polymer composition, which shows a relatively constant watt consumption behavior, separated is. 0 3 0 0? A / 0