Patent GB-751001-A (GB)
Title: Improvements in the manufacture of electric resistance elements
Inventor: CHITTY JOHN ALBERT
IPC: H01B3/40
Filed: 1950-10-19
Abstract: A resistor comprises a resistance element made up of finely divided conductive material (other than metal powder) distributed throughout a heat-polymerized ethoxylene synthetic resin such as is known under the Registered Trade Mark "Araldite".  A film resistor embodying the invention may be made as follows: a mixture of one part by weight of a solution of one or more "Araldite" resins with about one part by weight of a colloidal graphite dispersion is diluted to the required consistency and applied to a glass or other base by spraying. Heattreatment at a maximum temperature of 250 DEG  C. is maintained for two hours. Finally, a protective layer of "Araldite" varnish is applied. The resistance mixture proportions may vary between 25 to 200 parts by weight of colloidal graphite dispersion to 100 parts by weight of resin solution.  Carbon black may wholly or partly replace the colloidal graphite.  A typical resin solution contains two different "Araldites" dissolved in a mixture of diacetone alcohol, toluene, xylene, ethyl acetate and methyl acetate.  The resistance composition may be applied by dipping, painting, stencilling or printing or in the form of a flexible film or backed coating for die-stamping or embossing.  If a spraying process is employed the dispersion of the beam of the spray may be controlled by an electrostatic field or the wetness may be controlled photo-electrically by measuring the degree of specular reflection. Temperature and process period details are given adverting to curing or polymerizing in a lehr or muffle furnace. Infra-red radiation may be employed for the heat-treatment.  The resistance film may be made into a spiral or zig-zag form.  A resistor according to the invention may be produced in three-dimensional form, i.e. without a base, by the normal plastics manufacturing techniques of casting, moulding or extrusion.  Specification 749,621, [Group III], is referred to.ALSO:A resistor comprises a resistance element made up of finely divided conductive material (other than metal powder) distributed throughout a heat-polymerized ethoxylene synthetic resin such as is known under the Registered Trade Mark "Araldite."  The term ethyoxylene resin is used to denote a product obtained by the alkaline reaction of polyhydric phenols with epichlorhydrin or dichlorhydrin.  A film resistor embodying the invention may be made as follows: (1) a composition is prepared comprising a mixture of one part by weight of a solution of one or more "Araldite" resins with about one part by weight of a colloidal graphite dispersion, (2) this prepared composition is then diluted to the required consistency and applied to a glass or other base by spraying, (3) heat-treatment then follows producing complete polymerization and in this a maximum temperature of 250 DEG C. is maintained for two hours, (4) as a final step a protective layer of "Araldite" varnish is applied completely covering the resistor.  The resistance mixture proportions may vary between 25 to 200 parts by weight of colloidal graphite dispersion to 100 parts by weight of resin solution.  Carbon black may wholly or partly replace the colloidal graphite.  The resistance composition may be applied by dipping, painting, stencilling or printing or in the form of a flexible film or backed coating for diestamping or embossing. If a spraying process is employed the dispersion of the beam of the spray may be controlled by an electrostatic field or the wetness may be controlled photo-electrically by measuring the degree of specular reflection.  Temperature and process period details are given adverting to curing or polymerizing in a lehr or muffle furnace. Infra-red radiation may be employed for the heat-treatment.  The resistance film may be made into a spiral or zigzag form.  A resistor according to the invention may be produced in three-dimensional form, i.e., without a base, by the normal plastics manufacturing techniques of casting, moulding or extrusion.  Specification 749,621 is referred to.