Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
  • H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
  • H01C17/065—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thick film techniques, e.g. serigraphy
  • H01C17/06506—Precursor compositions therefor, e.g. pastes, inks, glass frits
  • H01C17/06513—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component
  • H01C17/0652—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component containing carbon or carbides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C10/00—Adjustable resistors
  • H01C10/30—Adjustable resistors the contact sliding along resistive element
  • H01C10/305—Adjustable resistors the contact sliding along resistive element consisting of a thick film
  • H01C10/306—Polymer thick film, i.e. PTF

Definitions

• the invention relates to a resistance paste made of curable, polymeric binder suitable for the production of electrical resistance layers with at least one electrically conductive pigment dispersed therein and with solvents.
• the invention further relates to a resistance layer made from this resistance paste.
• a generic resistance paste is known from DE-OS 31 48 680. US Pat. No. 3,686,139 also describes such resistance pastes and, in each case, resistance layers to be produced therefrom in several examples. In order to improve the abrasion resistance of a resistance layer with regard to a contacting sliding contact, selected curable polymers are proposed as binders for these resistance pastes.
• DE-OS 36 38 130 shows another way of increasing the abrasion resistance in resistance layers. It improves the friction properties by adding additional agents to the resistance paste.
• Binder of the resistance paste pigment to be dispersed is known (EP-OS 0 112 975). These are hard, refractory carrier particles, for example made of aluminum oxide, which are pyrolytically carbonized from the gas phase. With such resistance layers, the contact resistance increases after the carbonization has been abraded by the sliding contact as a result of the dielectric carrier particles. Resistance layers with particles coated with pyrolytic carbon as conductive pigment are also known from DE-AS 28 12 497, additional conductive pigments, such as carbon black, graphite, nickel, etc., being additionally added to the polymeric binder if necessary.
• the properties of polymeric resistance layers are generally to be improved if, instead of the commonly used carbons, e.g. Carbon black or graphite, a special graphite is used.
• the proposed special graphite is produced by chlorination of carbides at higher temperatures.
• glass-like carbon is obtained as a powder with grain sizes below 50 ⁇ m.
• the powdery, glass-like carbon can be used as an abrasive, as a filler to increase the slip resistance of tires, or for the production of ceramic moldings.
• the resistance to abrasion of the resistance layer is for the life of an arrangement consisting of a resistance layer and a sliding contact interacting with the resistance layer an essential feature.
• Non-abrasion-resistant resistance layers lose substance and thereby change their electrical value.
• Rubbed layer influences the contact ability of the sliding contact.
• the abrasion resistance of resistance layers that can be achieved in the prior art is not yet sufficient.
• the object is achieved in that a glass-like carbon is used as the electrically conductive pigment.
• the object is achieved in that the resistance layer is created from one of the proposed resistance pastes.
• the glassy carbon used according to the invention as an electrically conductive pigment has long been known (see "Zeitschrift für Werkstofftechnik", Volume 15, pp. 331-338).
• Glassy carbon is a very special carbon with a highly disoriented, polymeric crosslink structure and with the mechanical properties of glass. Its enormous hardness, comparable to diamond, its smooth and quasi-non-porous surface and its isotropy are outstanding properties that distinguish the glassy carbon from other amorphous or crystalline materials differentiate structured carbons.
• laboratory devices, rotors for turbochargers in automotive engineering or even tools for processing glass are produced from glassy carbon.
• glassy carbon as an electrically conductive pigment of a resistance paste initially appears to be of little use because of the great hardness, the grain size and the poor wettability or dispersibility which were found in the test. If you overcome these concerns and the adversities in preparation and processing, e.g. by considerably increasing the conventional effort, an abrasion-resistant resistance layer is obtained from such pigmented resistance paste. After 250 hours of stress on the resistance layer due to a sliding contact frequenting 40 Hz, no disadvantageous abrasion was discernible. This corresponds to an improvement of around a factor of 100. It has been shown that conventional binders are suitable.
• the glassy carbon Compared to the amorphous carbon as the usual conductive pigment, the glassy carbon has a smooth, non-porous surface.
• the stability of the electrical values of the resistance layer under the influence of moisture is improved.
• the proportion of vitreous carbon usually varies between 5 and 80 percent by weight, based on the solids content of the binder.
• Various options can be used individually or in combination to increase the microlinearity of the resistance layer to be produced with the paste. For example, it is advantageous to choose the grain size of the glassy carbon below 50 ⁇ m. It is particularly advantageous to use rounded or spherical glassy carbon with a mixed grain size, the average value of which, however, should be less than 30 ⁇ m.
• Other electrically conductive pigments in particular carbon black, graphite, silver, nickel, individually or in combination, can be dispersed in. For resistance areas with a lower, specific conductivity, additional pigmentation of the resistance paste with relatively high-resistance conductive pigments is recommended due to the pigment thinning.
• the resistivity layer to be produced with the paste has a low specific conductivity, filler pigmentation with abrasion-resistant, insulating material can be recommended. This is particularly the case when the proportion of the polymeric binder on the surface of the resistance layer produced is to be small. Titanium dioxide, iron oxide, aluminum oxide, silicon oxide, talc, kaolin, barium sulfate, zinc sulfide and others are suitable as the filler pigment.
• vitreous carbon is carbonized before it is incorporated into the binder, i.e. coated with carbon pyrolytically obtained from the gas phase, it loses its repellent properties and can be wetted and dispersed without problems.
• the electrical resistance layer generated from the resistance paste is abrasion-resistant and increases resistance to environmental influences.
• the finished resistance paste is made up of the following substances: 20 parts by weight of dissolved, fully etherified melamine resin 9 parts by weight of dissolved, saturated polyester resin 10 parts by weight of dissolved, modified esterimide resin 61 parts by weight of glassy carbon 3 parts by weight of an acid catalyst.
• the roughly mixed components of the recipe are dispersed in three passes in a three-roll mill.
• the dispersion is subsequently adjusted to the processing viscosity. This can be achieved, for example, for screen printing processing using butyl carbitol acetate.
• the finished paste which is set for processing, is applied as a film to an electrically insulating and temperature-compatible substrate using a screen printing device.
• the film is cured for 1 hour at 230 ° C.
• the resistance layer according to the invention is then completed. If a different way of processing the resistance paste is considered, eg pouring, drawing, spraying, etc., the processing viscosity must be adjusted to the selected processing.
• a further exemplary embodiment of the invention results in resistance layers which are particularly suitable as a long-life potentiometric sensor in the fuel supply of diesel-powered internal combustion engines.
• Another embodiment leads to resistance layers, for example for elastic substrates with improved electrical homogeneity. 8 parts by weight of phenolic resin 5 parts by weight of epoxy-modified phenolic resin 5 parts by weight of epoxy resin 8.5 parts by weight of isophorones 34.5 parts by weight of glass-like carbon, splinter-shaped, grain size ⁇ 30 ⁇ m 34.5 parts by weight of glassy carbon, spherical, grain size ⁇ 20 ⁇ m 2 parts by weight of flame black 10 parts by weight of methyl ethyl ketone
• curable resins are also suitable as modified or combined as binders for the resistance paste or layer according to the invention.
• Typical resins from this family are, for example, alkyds, epoxies, melamines, polyacrylates, polyesters, polyimides, polyphenols, polyurethanes and others.

Landscapes

• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Adjustable Resistors (AREA)
• Non-Adjustable Resistors (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Conductive Materials (AREA)
• Parts Printed On Printed Circuit Boards (AREA)

Applications Claiming Priority (2)

Publications (3)

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Family Applications (1)

Country Status (6)

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Family Cites Families (16)

• 1989
  • 1989-05-24 DE DE3916921A patent/DE3916921C1/de not_active Expired - Fee Related
• 1990
  • 1990-05-10 ES ES90108782T patent/ES2062159T3/es not_active Expired - Lifetime
  • 1990-05-10 EP EP90108782A patent/EP0399295B1/de not_active Expired - Lifetime
  • 1990-05-10 DE DE59006946T patent/DE59006946D1/de not_active Expired - Lifetime
  • 1990-05-10 AT AT90108782T patent/ATE110878T1/de not_active IP Right Cessation
  • 1990-05-21 US US07/525,701 patent/US5219494A/en not_active Expired - Lifetime
  • 1990-05-23 JP JP2131460A patent/JPH0311602A/ja active Pending

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