Two-step process for preparing positive temperature coefficient polymer materials
First Claim
1. A process for producing a positive temperature coefficient polymer composition comprising a crystalline polymer and an electrically conductive filler that is present in a predetermined proportion in the composition, the process comprising the steps of:
- blending the crystalline polymer with the electrically conductive filler into a first intimate admixture in proportions wherein the electrically conductive filler is less in the first intimate admixture than the predetermined proportion in the positive temperature coefficient polymer composition;
extruding said first admixture to obtain an extruded pre-mix of crystalline polymer and filler;
allowing the first admixture to solidify, and thereafter admixing the pre-mix with more electrically conductive filler in sufficient quantity to attain the predetermined proportion of filler in the composition, and melting and extruding the resulting mix to form said positive temperature coefficient polymer composition.
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Abstract
Positive temperature coefficient polymer (PTC) materials of high loading with uniformly distributed electrically conductive material are manufactured by first producing an intimate mixture (pre-mix or master batch) of a crystalline polymer (e. g. high density polyethylene) with an electrically conductive filler (e. g. carbon black) in proportions that is less rich in the filler than the final PTC product. The intimate mixture, pre-mix or master batch, is utilized in a subsequent step in a molten liquid form for admixing with more filler material in quantities to produce the desired loading of the filler in the polymer matrix. The resulting the admixture is extruded, shaped and formed by conventional equipment to provide a positive temperature coefficient polymer composition that, when equipped with electrodes, is suitable for forming positive temperature coefficient circuit protecting devices. Positive temperature coefficient polymer composition having electrically conductive filler, usually carbon black in ratios as high as 55 to 60 percent by weight can be obtained by the process.
171 Citations
21 Claims
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1. A process for producing a positive temperature coefficient polymer composition comprising a crystalline polymer and an electrically conductive filler that is present in a predetermined proportion in the composition, the process comprising the steps of:
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blending the crystalline polymer with the electrically conductive filler into a first intimate admixture in proportions wherein the electrically conductive filler is less in the first intimate admixture than the predetermined proportion in the positive temperature coefficient polymer composition;
extruding said first admixture to obtain an extruded pre-mix of crystalline polymer and filler;
allowing the first admixture to solidify, and thereafter admixing the pre-mix with more electrically conductive filler in sufficient quantity to attain the predetermined proportion of filler in the composition, and melting and extruding the resulting mix to form said positive temperature coefficient polymer composition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A process for producing a positive temperature coefficient polymer composition comprising high density polyethylene and electrically conductive carbon black that is present in a predetermined proportion in the composition in the range of approximately 50 to 60 percent by weight, the process comprising the steps of:
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blending high density polyethylene with carbon black into a first intimate admixture in proportions wherein the carbon black is substantially less in the first intimate admixture than the predetermined proportion of carbon black in the positive temperature coefficient polymer composition;
extruding said first admixture to obtain an extruded pre-mix of crystalline polymer and carbon black comprising carbon black in the range of approximately 25 to 45 percent by weight;
allowing the first admixture to solidify, and thereafter admixing the pre-mix with more carbon black in sufficient quantity to attain the predetermined proportion of carbon black in the composition, and melting and extruding the resulting mix to form said positive temperature coefficient polymer composition. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification