US3538021A - Resistor composition - Google Patents

Description

Nov. 3, 1970 D. E. ACHEY RESISTOR COMPOSITION Filed May 7, 1968 ATTORNEY United States Patent 3,538,021 RESISTOR COMPOSITION David E. Achey, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Continuation-impart of application Ser. No. 670,178,

Sept. 25, 1967. This application May 7, 1968, Ser.

No. 727,281. I

Int. Cl. H01b 1/06; H01t 13/36 US. Cl. 252-506 Claims ABSTRACT OF THE DISCLOSURE An improved resistor composition for use in spark plugs and other electrical devices. The resistor composition contains glass, an inert filler material such as kyanite, carbon black and a Water soluble, charrable carbonaceous polyhydroxy material such as sucrose. The resistance of the resistor composition after it has been placed in the spark plug insulator centerbore and heated is substantially resistant to change when subjected to electrical aging or field use.

This application is a continuation-in-part of application Ser. No. 670,178, filed Sept. 25, 1967, now abandoned.

This invention relates to resistors, and more particularly to glass phase semiconductor resistor compositions suitable for use in resistors and resistor spark plug of the automotive and aviation type.

Resistors are commonly used to suppress the high frequency oscillations present with spark discharge in an ignition system, the oscillations resulting in rapid erosion of the spark plug electrodes and in interference with electronic equipment. Resistor spark plugs are effective in reducing automobile radio frequency interference and are particularly ueful for FM broadcast and shortwave broadcast automobile receivers.

There are two basic types of resistor compositions. One type of monolithic resistor spark plug described in the McDougal et al. Pat. No. 2,459,282 granted J an. 18, 1949, comprises a heterogeneous mixture of conductor material, that is, carbon either alone or in combination with various conducting metals, metal oxides and metal carbides with glass. In this type of resistor the conducting material, such as carbon, exists as a continuous phase and the resistance of the resistor is dependent solely upon the amount of conductor material that is present. The glass serves only to suspend the conductor material in a rigid structure. An example of this type resistor composition consists essentially of 64 weight percent borosilicate glass, 9 weight percent magnesium borate glass, 11 weight percent fiuorspar, 15% beryl and 1% Thermax carbon.

The second basic type of a monolithic resistor spark plug is described in the patent to Counts et al. No. 2,864,884, granted Dec. 16, 1958, and No. 3,235,655 granted Feb. 15, 1966. This type of resistor consists of a semiconductor material with glass and a small amount of reducing agent such as powdered aluminum or carbon. In this type of resistor the semiconductor material exists as a continuous phase and the resistance of the resistor is dependent mainly upon the resistance characteristics of the semiconductor material that is present. In this type of resistor the amount of reducing agent, that is, carbon or powdered aluminum and the like, are added to obtain precision-like control of the resistance of the final product, but the amount of reducing agent added should be 3,538,021 Patented Nov. 3, 1970 small so that it is present in the product in a discontinuous phase and, as a result, does not function as a conductor material but solely as a reducing agent. An example of this type of resistor composition consists essentially of 25 parts barium borate glass, 30 parts filler (mullite), 0.8 part aluminum, 0.8 part Thermax carbon black, 3 parts bentonite and 45 parts of a semiconductor composition containing parts TiO 20 parts SnO 10 parts TA O 4 parts M00 and 40 parts A1 0 The resistors described above operate satisfactorily once their electrical resistance has been stabilized. It is the practice in the art to subject the resistor spark plug to an electrical aging process prior to actual field use in order to completely stabilize the resistance of the resistor. This aging process comprises subjecting the resistor spark plug to an electrical treatment wherein the peak power dissipated in the element is higher than that encountered in the field use. This treatment precludes a gradual and prolonged decrease in resistance and reduces the resistance of the resistor to a value that will remain substantially constant over long periods of use in the field. Resistors require a stabilized resistance of at least 1000 to 2500 ohms to eliminate radio frequency interference. The relationship of the electrical aging process to actual field use is discussed in detail in the Counts et al. Pat. No. 2,864,884. This electrical aging step requires that each resistor spark plug be subjected to this treatment for a period of time which lasts up to 5 seconds. For example, a spark plug having a resistor with a resistance of 200,000 ohms which is subjected to a voltage ranging from 10 to 35,000 volts for a period of time of up to 5 seconds yields a resistor having stabilized resistance of 15,000 ohms. Another example would be to subject a spark plug having a resistor with a resistance of 16,000 ohms to the aging process of 10 to 35,000 volts for a period of time up to 5 seconds to yield a resistor having a stabilized resistance of 3500 ohms. In the large scale production of this type of resistor spark plug having a specified resistance, it is necessary to subject each resistor spark plug to an individual aging process in order to obtain a given stabilized resistance. For example, one resistor spark plug would reach a stabilized resistance of 3500 ohms when subjected to the aging process for three seconds whereas another resistor may require four or five seconds of the aging process to reach a stabilized resistance of 3500 ohms. Since each resistor spark plug must be individually subjected to this aging treatment in order to obtain a specified stabilized resistance, these resistor spark plugs are relatively expensive.

It is the primary object of this invention to provide a resistor composition which forms an electrically stable resistor element which does not have to be subjected to an electrical aging step to have a stable resistance.

These and other objects are accomplished by a resistor composition containing glass, inert filler material, carbon black and a water soluble, charrable polyhydroxy carbonaceous material. The resistor composition in accordance with this invention consists essentially of 20 to weight percent glass, 25 to weight percent inert filler, 0 to 80 weight percent semiconductor, 0 to 3.0 weight percent inorganic binder, 0.1 to 4.0 weight percent carbon black and 0.1 to 4.0 water soluble, charrable polyhydroxy carbon containing material. When a spark plug containing the resistor composition described above is heated and pressed with a terminal screw as is the practice in the art, the resulting fused mass forms a resistor element or seal which has a stabilized resistance. This resistance of this resistor seal does not decrease when subjected to field use or to electrical aging. The water soluble, charrable polyhydroxy carbon containing material has an effect on the resistance aging characteristics of the resistor seal, that is, the resistance tends to go up when the resistor element is subjected to field use or to electrical aging. This is the opposite effect that carbon black has on the resistance of the resistor seal, that is, carbon black causes the resistance to go down when the resistor element is subjected to field use or electrical aging. The concentration of the Water soluble, charrable carbonaceous polyhydroxy material and the carbon black are balanced so that the effects of these two components more or less cancel themselves and the resistance of the resultant resistor seal containing these two materials does not change appreciably when subjected to field use or to electrical aging.

Other objects and advantages of this invention will be apparent from the following detailed description, reference being made to the accompanying drawing where a preferred embodiment of this invention is shown.

'Referring now to the drawing, the spark plug 10 comprises a conventional outer metal shell 12 having a ground electrode 14 welded to the lower end thereof. Positioned within the metal shell 12 and secured in the conventional manner is the insulator 16. The ceramic insulator 16 should preferably be of a high aluminum base material containing upwards of 85% aluminum oxide such, for example, as covered by United States Pat. No. 2,760,875, issued to Karl Schwartzwalder and Helen Blair Barlett. The insulator 16 is formed with a centerbore having a lower portion 18 of relatively small diameter, and an upper portion 20' of larger diameter which are connected by the insulator centerbore ledge 22. Positioned in the lower portion 18' of the insulator centerbore is the center electrode 24. The center electrode 24 has an enlarged head 26 at the upper end thereof which rests on the inner insulator centerbore ledge 22 and a serrated lower end 28 thereof projecting beyond the lower tip of the insulator 16. Positioned in the upper portion 20 of the insulator centenbore is a terminal screw 30. A lower conductive metal-glass seal 32 positioned in the insulator centerbore portion 20 is bonded to the center electrode head 26 and to the inner walls of the ceramic insulator. Positioned in the insulator centerbore portion 20 on top of the metalglass seal 32 is the monolithic resistor element or seal 34 of this invention which will be hereinafter fully described. Positioned on top of the resistor seal 34 in the insulator centerbore is the upper conductive metal-glass seal 36. The conductive metal-glass seal 36 is bonded to the terminal screw 32 and the inner Walls of the ceramic insulator. The conducting metal-glass seals 32 and 36 may be made of any suitable material capable of being bonded to the insulator and to the resistance element and possessing good electrical conductivity. We prefer to use a mixture of glass and conducting material as described and claimed in the Schwartzwalder et al. patents, No. 2,106,- 5 78 granted Jan. 15, 1938, and No. 2,248,415 granted July 8, 1941, and in the copending patent applications Ser. Nos. 563,824 and 563,775. An example of a conducting metal-glass seal is a composition containing 50 parts copper powder, 14 parts zinc powder, 1 part of an organic binder such as hydrogenated cottonseed oil and 35 parts of a borosilicate glass containing 65 weight percent SiO 23 weight percent B weight percent A1 0 and 7 weight percent Na O. The conductive glass seals 32 and 36 together with the resistor seal 34 provides an electrical conductive path from the terminal screw 30 to the center electrode 24.

In accordance with the present invention, the spark plug resistor seal 34 is a dense, fused mass containing glass, inert filler material, carbon, inorganic binder and a water soluble, charrable polyhydroxy carbonaceous material. The composition of the resistor seal 34 of our invention may be formed of the following constituents in the percent by weight noted:

Weight percent Glass 20 to Inert fillerkyanite, Borolon, zirconia, mullite, chromium oxide, and the like 2 5 to Semiconductor material 0 to 80 Carbon black 0.1 to 4.0

The glass used in the spark plug resistor seal 34 may be any conventional .glass commonly used in spark plug seals. Barium borate glasses are preferred although this invention is not limited thereto. An example of a suitable barium borate glass is a composition containing 75 weight percent B 0 and 25% BaO. Another barium borate glass is a composition containing 60 weight percent B 0 32 weight percent BaO, 6 weight percent Na O and 2 weight percent CaO. Another example is a composition containing 60 weight percent B 0 38 weight percent BaO and 2 weight percent Na O. It has been found that the amount of the particulate glass used has no appreciable effect on the resistance of the composition within the limits of 20 to 75 weight percent.

The fluidity of the final resistor composition, as exhibited during the hot pressing operation, is controlled by the presence of a filler which does not react chemically with the other constituents of the resistor composition. These fillers may be selected from the broad group of filler materials commonly used in resistor glass seals. Examples of suitable fillers are kyanite, alumina, zirconia, mullite, Borolon and the like. A preferred filler is a mixture of 25 parts by weight kyanite and 35 parts by weight zirconia. The concentration of the filler is from about 25 to 80 weight percent.

Since the resistor composition is best handled in a granulated form, a binder such as bentonite, a very plastic aluminum silicate, is added to bond the particles together during processing. Inorganic binders such 'as bentonite, as well as other clays, may be used. Organic binders are not recommended for the practice of this invention since it is well known in the art that this type of material causes the resistance of the resistor to be unstable. The concentration of the binder is from 0.0 to 3.0 weight percent.

The concentration of the carbon black in the resistor composition is from about 0.1 to 4.0 weight percent. The carbon black may function as the sole conductor material for resistors of the type described in the McDougal et al. patent, No. 2,459,282 previously referred to, or solely as a reducing agent as in the resistors of the type described in the Counts et al. patent, No. 2,864,884. It is well known as mentioned previously, that spark plug resistor seals containing carbon black have a high resistance, for example 200,000 ohms which, when subjected to a voltage ranging from 10 to 35,000 volts for a period of time of up to 5 seconds, yield a resistor having a stabilized resistance of about 15,000 ohms.

It has been found that water soluble, charrable polyhydroxy carbonaceous materials, such as dextrin, sucrose, methyl cellulose, corn flour, polyvinyl alcohol and glycerine, cause the electrical resistance of a spark plug carbon black-free resistor seal to increase upon being subjected to an electrical aging step or field use. For example, a carbon black-free resistor seal containing 2 weight percent dextrin having an original electrical resistance of ohms increased its resistance to 2.3 million ohms upon being subjected to an electrical aging step. The following table lists the resistance of resistor spark plugs in which the resistor seals contain 2.0 weight percent of a water soluble, charrable polyhydroxy carbonaceous material befor and after being subjected to an electrical aging step for seconds with an electrical voltage of 20,000 to 30,000 volts.

TABLE I Resistor spark plug resistance, ohms Water soluble charrable polyhydroxy carbona- B These resistors contain 35 parts by weight ZrOz, 36 parts by weight barium borate glass, 25 parts by weight kyanite, 2.4 parts by weight bentonite and 2.0 parts by weight carbonaceous material.

All of the water soluble, charrable polyhydroxy carbonaceous materials tested cause the resistance of the resistor seal to increase after the resistor seal was subjected to electrical aging step. The most effective carbonaceous materials impart a low original resistance and a high final resistance.

The water soluble, charrable polyhydroxy carbonaceous material which combines with the carbon black to form a stable resistor resistance is preferably at least 5 weight percent soluble in water. The higher the solubility of the carbonaceous material in water, the greater the eifectiveness. The water soluble polyhydroxy carbonaceous material must also be of the type which chars; that is, upon exposure to elevated temperatures, the material should form a brown or brown-black decomposition product. For maximum effectiveness the carbonaceous material should char to a high degree.

The water soluble, charrable carbonaceous polyhydroxy compounds contain two or more hydroxyl groups. All the sugars are included in this group of compounds. Sugars include the disaccharides, sucrose, lactose, maltose and cellobiose, the trisaccharides, such as raffinose, and the monosaccharides glucose, gulose, mannose, galactose, tallose, allose, altrose, idose, fructose, sorbose, arabinose, xylose, lyxose and ribose. The sugars are preferred compounds in accordance with this invention since they are very soluble in water and char to a high degree.

Hydrolyzed polysaccharides, such as the dextrins, are also included and are also preferred since they are very soluble in water and char to a high degree.

Water hydrolyzable polysaccharides, such as cornstarch, corn flour, liver starch, methylcellulose, hydroxypropomethylcellulose, methylhydroxycellulose and gums are also included in the group of polyhydroxy compounds in accordance with this invention. These water hydrolyzable polysaccharides come in contact with water during the preparation of the resistor seal and are hydrolyzed to a certain extent. The effectiveness of these compounds is determined to a large degree by the extent they are bydrolyzed. The hydrolyzed products thus formed are water soluble and effective in the practice of this invention. For example, methylcellulose and liver starch which are readily hydrolyzed by contact with water are very effective compounds, whereas cornstartch and corn flour are compounds which are less readily hydrolyzed and, as a result are less effective in the practice of this invention.

The water soluble, charrable monomeric aliphatic hydrocarbons containing at least two hydroxyl groups are also included in this invention. Compounds in this group include ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, I-Z-butanediol, l-3-butanediol, l-4-butanediol, 2-3-butanediol, pentamethylene glycol, hexamethylene glycol, glycerol and the like.

The water soluble, charrable polymeric aliphatic hydrocarbons containing at least two hydroxyl groups are also included. Compounds of this type are polyethyleneglycol, copolymers containing polyethyleneglycol, polyvinylalcohol, copolymers containing polyvinalcohol and the like.

It has been found that spark plug resistor seals containing carbon black can be stabilized so that they have a resistance which will not be appreciably affected by electrical aging or by field use if a sufficient quantity of water soluble, charrable polyhydroxy carbonaceous material is incorporated in the resistor seal composition. It is necessary to balance the concentration of the carbon black and the carbonaceous material to obtain a resistor seal which is resistant to aging. The carbon black in the resistor seal composition causes the resistance of the resistor to decrease whereas the water soluble, charrable carbonaceous material causes the resistance of the resistor seal to increase. The carbonaceous material and the carbon black have opposite resistance effects which cancel each other at the proper concentration levels. The concentration of the carbonaceous material ranges from about 0.1 to 4 weight percent. The preferred concentration of the carbonaceous material depends upon the concentration of the semiconductor and/or carbon black concentration as well as on the effectiveness of the particular carbonaceous material.

EXAMPLE l A resistor spark plug having a resistor seal composition containing 35 parts by weight zirconia, 36 parts by weight barium borate glass, 25 parts by weight kyanite, 2.4 parts bentonite, 1.0 part Thermal carbon black and 1.0 part by weight glycerine was made by conventional methods. The resistance of the resistor spark plug after it was made was 4,400 ohms. The resistor spark plug was subjected to an electrical aging step for 5 seconds with a voltage of 20,000 to 30,000 volts. The resistance of the resistor spark plug after the electrical aging step was 4,400 ohms. The resistances of the resistor spark plug before and after the aging step were the same. This indicates that the water soluble, charrable polyhydroxy carbonaceous material, glycerine, was used at a concentration which effectively cancelled or equalled the resistance decrease effect of the carbon black to yield a resistor composition which is electrically stable and which does not have to be subjected to an electrical aging step to have a stable resistance.

The following table lists the resistance of resistor spark plugs in which the resistor seals contain water soluble, charrable, polyhydroxy carbonaceous materials of Examples 2 through 7 before and after being subjected to an electrical aging step for 5 seconds with an electrical voltage of 20,000 to 30,000 volts.

TABLE II Carbon Water soluble, charblack Spark plug resistor e rable polyhydroxy Conc., c0110., resistance, ohms carbonaceous parts by parts by material weight Weight; Original Final Example N0.:

1 None 1. 3 5, 000,000 50, 000 2 Glycerine 0. 5 1. 3 23, 000 16, 000 3 Polyvinyl alcohol. 0.5 1. 3 4, 000 3, 300 4 Dextrin 0. 5 1. 3 440 660 5 Sucrose 0. 5 1. 3 560 740 6 Methyl cellulose 0. 5 1. 3 640 900 7..-- Corn flour 0.5 1. 3 820 910 8 Sucrose 0. 3 1. 5 b 7, 000 b 7, 000

B Resistors contain 35 parts by weight Z1O2, 36 parts by Weight BaBOa glass, 25 parts by Weight; kyanite and 2.4 parts by Weight bentonite.

b Resistor contains 41 parts by weight ZrOz, 30 parts by Weight BaBOs glass, 25 parts by Weight kyanite and 2.5 parts by Weight bentonite.

Example 2 listed above indicates that a concentration of 0.5 part by weight glycerine was insufficient to balance the resistance decrease effect of the carbon black since the resistance decreased from an original value of 23,000 ohms to 16,000 ohms. Example 3 indicates that the concentration of 0.5 part by weight polyvinyl alcohol, a water soluble, charrable polyhydroxy carbonaceous material, was insufficient to balance the resistance decrease effect of the carbon black. In order to obtain an electrically stable resistor composition with polyvinyl alcohol, it is necessary to use a higher concentration of the polyvinyl alcohol or, in the alternative, a lower concentration of the carbon black.

Examples 4, 5, 6 and 7 indicate that a concentration of 0.5 part by weight dextrin, sucrose, methyl cellulose and corn flour respectively, was too high to balance the resistance decrease effect of the 1.3 parts by weight carbon black. With these four water soluble, charrable polyhydroxy carbonaceous materials, it is necessary to use a concentration less than 0.5 weight percent and/ or to increase the carbon black concentration in order to obtain an electrically stable resistor which would not be affected by an electrical aging step.

Example 5, as previously mentioned, indicates that a concentration of 0.5 part by weight sucrose was too high and to balance the resistance decrease effect of 1.3 parts by weight carbon black. In example 8, a similar composition containing 0.3 part by weight sucrose and 1.5 parts by weight carbon black yielded a spark plug re sistor having a resistance of 7,000 ohms before the electrical aging step and a resistance of 7,000 ohms after the aging step thereby indicating that the resistance of the resistor spark plugs was stable. The resistance decreasing effect of the carbon black was balanced by the resistance increasing effect of the sucrose to provide an electrically stable resistor.

The semiconductor materials that may be used in this spark plug resistor seal are of the type described in the patent to Counts et al., No. 3,235,655 granted Feb. 15, 1966, which describes a semiconductor material formed from the binary metal oxide systems consisting of as well as the semiconductors described in the patent to Counts et al., No. 2,864,884 granted Dec. 16, 1958, Where the semiconductor material comprises titanium oxide, tin oxide, tantalum oxide, vanadium oxide, molybdenum oxide, and tungsten oxide. The concentration of the semiconductor material is from to 80 weight percent. An example showing the stabilizing effect of the water soluble, charrable polyhydroxy carbonaceous material in this type of resistor composition is given below.

EXAMPLE 9 A resistor composition containing 38 parts by weight stannous titanate, 33 parts by weight barium borate glass, 25 parts by weight kyanite, 3 parts by weight bentonite, 1.5 parts by weight Thermax carbon black and 0.5 parts by weight dextrin was prepared and placed in the spark plug insulator centerbore. After the resistor spark plug was completely assembled, the resistance of the spark plug was checked and found to be 1,400 ohms. It was then subjected to an electrical aging process for seconds at 20,000 to 30,000 volts and the resistance of the aged resistor spark plug was 1,000 ohms. In this example the resistance decreased from 1,400 to 1,000 ohms thereby indicating that the concentration of the dextrin should be somewhat higher.

In Examples 1 and 8, the electrically stable resistor compositions do not change their resistance upon being subjected to electrical aging or field use. In these resistor seals, the concentration of the water soluble, charrable polyhydroxy carbonaceous materials and carbon black are such that the resistance increasing effect of the water soluble, charrable polyhydroxy carbonaceous material is essentially equal to the resistance decreasing effect of the carbon black. The resistor seals described in Examples 2, 3 and 9 could be made electrically stable by increasing the concentration of the water soluble, charrable polyhydroxy carbonaceous material and/or decreasing the carbon black concentration. In Examples 4 through 7 the concentration of the water soluble, charrable polyhydroxy carbonaceous material was too high and these resistor seals could be made electrically stable by decreasing the concentration of the water soluble material and/ or by increasing the concentration of the carbon black.

The resistor compositions of this invention may be prepared in granular form by first dry mixing the materials and then adding water to make a plastic mass. The plastic mass is then forced through a 20 mesh screen and the resulting granules dried. The dried material is then regranulated through a 28 mesh screen and the material retained between 28 and 100 mesh is used. This sizing procedure has been found to produce granules which are most suitable for uniform volumetric feed in the mass production of resistor spark plugs. Alternatively, the materials may be dry mixed and formed into a free-flowing slip by the addition of water. The slip is then passed into a spray drying tower where the desired agglomerates are formed.

In assembling the spark plug 10, the center electrode 24 is positioned within the centerbore 18 of the insulator 16 and a measured amount of the copper-glass seal material 32 is fed into the bore and rammed in place. Any loose powder is blown out of the insulator to prevent contamination of the resistor element 34. The desired amount of the granulated resistor composition is then placed in the bore and rammed, followed by a measured amount of the powdered copper-glass seal material 36 which is likewise rammed to form the upper seal 36. A terminal screw 30 is then positioned within the bore and the whole assembly is then heated to a temperature which softens the glass and chars the charrable, carbonaceous material, a temperature of 1600- to 1750 being generally satisfactory. A temperature of 1675 with an 18 minute heating cycle and a 6 to 8 minute hold at the aforementioned temperature is preferred with the barium borate glass used in the preferred embodiment. Other temperatures may be employed for glasses which soften at a lower temperature. When the glass is sufficiently softened, pressure is applied to the terminal screw 30 to force it down into the centerbore, thereby depressing the softened materials and causing the upper seal portion 36 to surround and grip the lower end of the terminal screw. By hot pressing in this manner, which is the customary manner in the art, a continuous electrical path is formed through the plugs from the terminal screw 30' to the center electrode 28, the portions intermediate the top of the electrodes and the bottom of the screw being sealed in glass-tight relationship with the walls of the insulator of the metal parts. The thus formed insulator assembly is then assembled in the shell 12 to form plug 10.

The resistor compositions of this invention contain a water soluble, charrable polyhydroxy carbonaceous material which has a resistance increasing effect and is used at a concentration sufficient to counteract or cancel the resistant decrease of the semiconductor and/or carbon black to provide an electrically stable resistor spark plug. The resistor spark plug of this invention does not change its resistance when subjected to field use or an electrical aging step.

While the invention has been described in terms of specific examples, it is to be understood that the scope of the invention is not limited thereto except as defined by the following claims.

What is claimed is:

1. A resistance element for use in a resistor spark plug formed from a composition consisting essentially of 20 to by weight glass, 25 to by Weight inert filler, 0 to 80% by weight semiconductor material, 0.1

to 4% by weight carbon black, to 3.0 weight percent inorganic binder and 0.1 to 4% by weight water soluble, charrable polyhydroxy carbonaceous material, said composition having been heated to a temperature at which said carbonaceous material chars, said carbonaceous material increasing the resistance of said element when subjected to electrical aging and field use, said carbonaceous material being used at a concentration sufficient to substantially cancel the resistance decreasing effect of said carbon black being caused by electrical aging and field use, said resistance element having an electrical resistance substantially resistant to change when subjected to electrical aging and field use.

2. A resistance element as described in claim 1 wherein said water soluble, charrable polyhydroxy carbonaceous material is taken from the group consisting of sugars, hydrolyzed polysaccharides, water hydrolyzable polysaccharides, water soluble, charrable monomeric aliphatic hydrocarbons containing at least two hydroxy groups and Water soluble, charrable polymeric aliphatic hydrocarbons containing at least two hydroxy groups.

3. A resistance element as described in claim 1 wherein said water soluble, charrable polyhydroxy carbonaceous material is a sugar.

4. A resistance element as described in claim 1 wherein said water soluble, charrable polyhydroxy carbonaceous material is dextrin.

5. A resistance element as described in claim 1 wherein said water soluble, charrable polyhydroxy carbonaceous material is methyl cellulose.

6. A resistance element for use in a spark plug formed from a composition consisting essentially of to 35 weight percent glass, 58 to 76 weight percent inert filler, 1 to 2 weight percent carbon black, 2 to 3 weight percent inorganic binder, and 0.1 to 1.0 weight percent water soluble, charrable polyhydroxy carbonaceous material taken from the group consisting of dextrin, sugars and methyl cellulose, said composition having been heated to a temperature at which said carbonaceous material chars, said carbonaceous material increasing the resistance of said element when subjected to electrical aging and field use, said carbonaceous material being used at a concentration sutficient to substantially cancel the resistance decreasing eifect of said carbon black being caused by electrical aging and field use, said resistance element having an electrical resistance substantially resistant to change when subjected to electrical aging and field use.

7. A resistance element for use in a resistor spark plug formed from a composition consisting essentially of 28 to 38 weight percent glass, 30 to Weight percent inert filler material, 33 to 35 weight percent semiconductor material, 1 to 2 weight percent carbon black, 2 to 4 weight per-cent inorganic binder, and 0.5 to 1.5 weight percent Water soluble, charrable polyhydroxy carbonaceous material taken from the group consisting of dextrin, sugars, and methyl cellulose, said composition having been heated to a temperature at which said carbonaceous material chars, said carbonaceous material increasing the resistance of said composition when subjected to electrical aging and field use, said carbonaceous material being used at a concentration sufiicient to substantially cancel the resistance decreasing effect of said carbon black being caused by electrical aging and field use, said resistor composition having electrical resistance substantially resistant to change when subjected to electrical aging and field use.

8. A resistor composition consisting essentially of 20 to percent by weight glass, 25 to percent by Weight inert filler, O to 80 percent by weight semiconductor conductor material, 0.1 to 4 percent by weight carbon black, 0 to 3.0 weight percent inorganic binder, and 0.1 to 4 percent by weight water soluble, charrable polyhydroxy carbonaceous material, said canbonaceous material when charred increasing the resistance of said resistor composition when subjected to electrical aging or field use, said carbonaceous material being used at a concentration sufficient when charred to substantially cancel the resistance decreasing effect of said carbon black being caused by electrical aging and field use, said resistor composition having an electrical resistance in a resistor spark plug substantially resistant to change when subject to electrical aging and field use.

9. A resistor composition as described in claim 8 wherein said water soluble, charrable polyhydroxy carbonaceous material is taken from the group consisting of sugars, hydrolyzed polysaccharides, water hydrolyzable polysaccharides, water soluble, charrable monomeric aliphatic hydrocarbons containing at least two hydroxyl groups and water soluble, charrable polymeric aliphatic hydrocarbons containing at least two hydroxyl groups.

10. A resistance element for use in a resistor spark plug formed from a composition comprising glass, an inert filler material, carbon black and a water soluble, charrable polyhydroxy carbonaceous material, said composition having been heated to a temperature at which said carbonaceous material chars, said carbonaceous material increasing the resistance of said resistance element when subjected to electrical aging and field use, said carbonaceous material being used at a concentration sufficient to substantially cancel the resistance decreasing eflFect of said carbon black being caused by electrical aging and field use, said resistance element having an electrical resistance substantially resistant to change when subjected to elec trical aging and field use.

References Cited UNITED STATES PATENTS 5/1949 Schwartzwalder et a1. 106-47 12/1965 Kesten 252512 DOUGLAS J. DRUMMOND, Primary Examiner

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