US2305741A - Conductive bottom filler material and method of making the same - Google Patents

Description

Patented Dec. 22, 1942 CONDUCTIVE BOTTOM FILLER MATERIAL AND METHOD OF MAKING THE SAME Anthony Siers, Humboldt, Tenn, assignor to ODonnell Shoe Company, Humboldt, Tenn., a corporation of Minnesota No Drawing. Application July 7, 1941, Serial No. 401,399

3 Claims. (Cl. 260-750) The present invention relates to an improved conductive bottom filler material for electrically conductive shoes and to a method whereby the ingredients which cooperate to makeup such filler material are rendered conductive.

More specifically, the invention relates to a method of treating ground cork, leather scraps, asbestos fiber, sawdust and other base material and combining them with a suitable binder material in such a manner as to produce a conductive filler material which is adapted for use in filling in the space existing between the inturned margins of the upper and the inner and outer soles of conductive shoes of the type having conductive outer and inner soles.

Filler material manufactured in accordance with the principles of the present invention, although distinguished from ordinary materials of this nature by possessing a definite degree of conductivity, retains to a marked degree all of the beneficial characteristics of a high grade bottom filler material and is capable of being prepared as an article of manufacture and packaged in bulk in a self-sustaining form capable of being kept indefinitely for such period as required before being used and thereafter molded into a shoe bottom at room temperatures to constitute a tenacious layer meeting all shoemakers requirements.

The principal object of the present invention is to provide an improved filler composition for shoes, together with a method of preparing the same which will not only meet the ordinary conditions required for its ready application to the cavities of shoe bottoms and during the subsequent steps of constructing the shoe, fill the cavity between the inner and outer soles and adhere firmly to the walls of the shoe cavity, impart to the bottom of the finished shoe the permanent flexibility desired without shifting and losing its form and without drying out and becoming brittle with age, but which also will afford a conductive path for static discharges through the shoe from the conductive inner sole to the conductive outsole and from thence to the ground.

A further object of the invention is to provide such a filler material which, although characteristically conductive, is characterized by an absence of metallic particles and which may be used in the shoe for the purpose of establishing electrical contact between the inner and outer soles without necessitating the utilization of metallic inserts and the like.

Yet another object of the invention is to pro- 55 vide a bottom filler material for shoes, which. will retain its conductive properties permanently and which properties remain substantially constant and are not affected either by age, temperature or humidity of the surrounding atmosphere. In other words, according to the present invention, the improved conductive filler material retains its required degree of conductivity even when conditions of humidity are at an absolute minimum, i. e., when the humidity drops to zero.

Other objects and advantages of the invention will appear from the following description.

According to the present invention a degree of conductivity is imparted to the materials going in to make up the bottom filler material base and, after the required degree of conductivity is attained, the base materials are intimately mixed with a conductive binder material, the conductivity of the mixture depending upon and being a factor of the separate conductivities of the binder and the base.

Among the base materials that are found practicable are ground cork, leather scrap, asbestos fiber, and sawdust, all of which in their original state are substantially non-conductive when dry. For the binder material, I prefer to utilize commercial conductive rubber cement. One form of such a conductive rubber cement is known to the trade as Special Carbon P-33 and consists of rubber which is loaded with approximately pure carbon black.

In the treatment of dry cork or other base materials, the pulverized cork or other material is submerged in a solution obtained by dissolving one and one-half pounds of lithium chloride, onehalf pound of calcium chloride and one-half pound of sodium chloride, in suiiicient water to make up a total solution content of one gallon. The solution may be heated, if desired, but little benefit is obtained thereby and consequently, it is preferred that the submersion of the pulverized cork or other material be performed at room temperatures. The materials are allowed to remain in the solution for a period of time not less than six hours and preferably ten hours and thereafter, they are removed and drained and thereafter allowed to partially dry. If desired, the process may be hastened by employing forced drying with or without the use of heat. Where the time factor is not important, no heat or forced drying is resorted to and the ultimate conductivity of the materials is not altered.

After the above treatment of the base material the partially dry cork or other material is thoroughly mixed with commercial conductive cement containing carbon black and to which there has been added a benzol solution of rosin in the proper amount to obtain the required degree of adhesiveness. While according to the present method, rosin is the preferred substance for this purpose, other substances, such as resin obtained from gum, rosin oil, tar, asphalt, dextrin, etc, may be used.

While the specific proportions of the ingredients may be varied, suitable filler material may be obtained by mixing at least six ounces of liquefied wood rosin in the smallest amount of benzol which will assimilate it, thus obtaining a. practically saturated solution of resin in benzol. A suitable consistency may be obtained by dissolving six ounces of the rosin in from one pint to one quart of the benzol.

The mixture is gradually stirred at room temperatures into one gallon of the conductive rubber cement which may be the aforesaid Special Carbon P-33 and after thorough mixture of these materials, a suitable amount of the previously treated ground cork or other base material is added or stirred into the solution. For each gallon of the solution from two to three pounds of the base material is employed. The adhesiveness of the ultimate product may be varied by varying the amount of rosin employed. The less rosin contained in the product, the less will be the degree of adhesiveness. The adhesiveness may also be varied by varying the materials em ployed as for example, utilizing in place of the benzol other substances such as tar, asphalt or the like.

The materials when treated and mixed as above described are thus brought to their final condition and afford an extremely efficient conductive filler material well adapted to perform the functions required of it when utilized in a shoe assembly. The material is freely plastic when applied in a cold condition at room temperatures and makes intimate contact with and adheres uniformly to the walls of the shoe cavity.

After the outer sole has been attached to the shoe and the shoe is finished the composition does not readily deform or shift its position, either spontaneously or under the usual temperatures and pressures to which it is exposed under the weight of the foot. The material retains its conductive properties indefinitely regardless of conditions of temperature and humidity and the extent of this conductivity is in the neighborhood of 100,000 ohms when measured between two test prods placed on opposite sides of a cubic inch molded block of the material.

Finally, the finished product is found to have no appreciable odor over and above the nondisagreeable odor of the rubber cement material and the color thereof is a grayish or brownish black, depending upon the amount and character of the filler material or base.

The invention is not to be limited to the exact method herein set forth or to the specific materials or solutions employed in carrying out the method as various changes in the method and in the ingredients employed are contemplated.

What is claimed is:

1. The method of preparing a bottom filler material for shoes which consists in submerging at room temperatures dry ground cork in a solution of the chlorides of sodium, calcium and lithium and thereafter mixing at room temperatures the cork material with conductive rubber cement containing carbon block and to which there has been added a quantity of benzol.

2. The method of preparing a bottom filler material for shoes, which consists in submerging at room temperatures approximately two and one-half pounds of dry cork in a solution consisting of approximately one and one-half pounds of lithium chloride, one-half pound of calcium chloride and one-half pound of sodium chloride dissolved in sufficient water to make up one gallon of solution, partially drying the material which has previously been submerged, and thereafter mixing the quantity of thus treated cork intimately with approximately one gallon of conductive rubber cement consisting of approximately equal amounts of rubber and pure carbon black to which cement there has been added approximately one quart of a saturated solution of rosin in benzol.

3. The method of preparing a bottom filler material for shoes which consists in submerging dry ground cork in a solution of the chlorides of sodium, calcium and lithium, withdrawing the cork and allowing the same to partially dry, and thereafter mixing at room temperatures the partially dry treated cork material with conductive rubber cement consisting of approximately equal amounts of rubber and pure carbon black to which there has been added a quantity of benzol.

ANTHONY SIERS.