US2287766A - Rubber flooring or sheeting - Google Patents

Description

Patented June 30, 1942 RUBBER FLOORING OR, SHEETING Carroll 0. Davis, Belmont, Mass., assignor to 1305- ton Woven Hose & Rubber Company, Cambridge, Mass, a corporation of Massachusetts No Drawing. Application March 15, 1940,

Serial No. 324,121

1 Claim.

This invention relates to rubber material adapted for use as flooring or rubber sheeting and in One aspect consists of rubber sheet material having a novel composition to render it electrocon'ductive together with other desirable characteristics.

A very serious condition exists in operating rooms of hospitals on account of the extremely explosive nature of certain modern anesthetics and the danger of their ignition by electrostatic discharges. Many operating rooms have been equipped With various types of floors having high insulating characteristics. In working and walking about on such floors, surgeons and nurses are likely to accumulate a charge of static electricity, which, on being discharged through contact with another person or article in the room, is often sufficient to ignite any combustible vapor present in the air of the room or in the lungs of the patient. Disastrcus and fatal explosions of this kind have occurred in the past under the conditions described, and not only in operating rooms but in laboratories and factories where explosive mixtures of air and vapor have been formed.

My improved flooring is particularly adapted for use in factories, shops, hospitals, and like places which especially require the features above referred to and hereinafter described. One essential requirement for many of such uses is that the flooring shall be non-productive of sparks which may cause injurious explosions and the improved flooring is constructed to fulfill this requirement to a high degree andat the same time meet the other necessary requirements. These other requirements include a flexibility and resilience providing a quiet and easy treading surface and a flooring sheet capable of being bent and rolled without cracking and resiliently firm and hard to a degree precluding permanent indentation in use. The composition of my improved flooring is furthermore such that other desirable characteristics possessed by known flooring, such as the presenting of an attractive surface appearance, are not lost or sacrificed. The production of an improved flooring embodying a novel combination of these desirable features comprises the primary object of the invention.

The electrical resistivity of the present known commercial fioorlngs is extremely high, running into millions of ohms per centimeter cube. In

contrast to such resistivity characteristics, the present invention contemplates a resistivity of not more than 20,000 ohms per centimeter cube. In practice, it has been found possible to reduce the resistivity of my improved flooring to approximately 1,200 per centimeter cube. It will be apparent that this flooring provides such a grounding for persons and objects in contact with it as immediately to dissipate dangerous static charges that might otherwise exist or be generated by sending or other frictional movement.

While not essential, it is highly desirable to incorporate with the sheet material a ply of metal screen wire such as copper or brass of 12 to 24 mesh or thereabouts. The screen wire acts as a reinforcing element and a rigid skeleton to prevent the sheet material from stretching and buckling. It also greatly improves the conductance of the composite sheet. It is important that the screen wire should not be lacquered but should present a bare uncoated metal for intimate conductive contact with the composition of the rubber sheet material whereby to render the sheet uniformly highly conductive from any point on its surface.

As a result of most careful and extended research, I have discovered that a satisfactory electroconductive rubber or rubber-like sheet material may be compounded of smoked sheet rubher, with advantageous proportions of graphite in flake or powdered form, carbon black, sulfur, activating agent, dispersing agents and antioxidant. One satisfactory formula is as follows:

\ Parts by weight Smoked sheet rubber 23 Graphite 59 Thermax'black 12 Pine tar 2% Zing mrirlp 1f Stearic acid Sulfur it Benzothiazyl disulflde A Mixed polymers of 2,2,4-trimethyi-L2-hydroquinoline V .cube.

mixture of the above formula is calendered, and cured to the desired thickness by the usual steps of, commercial processing, which need no elaboration here, since they are well known and understeed by those skilled in the art. The resulting sheet material does not crack when bent, has sufiicient resilient hardness or firmness to resist indentation during service, and has an electrical resistivity of 1,200 to 2,400 ohms per centimeter j I Parts by weight Smoked sheet rubber 100 Graphite 300 Zinc oxide- Stearic acid Sulfur Paramn wax Benzothiazyl disulfide Vulcanized sheet material produced from this formula does not crack when bent, has sufficient resilient hardness or firmness to resist indentatiorr and a resistivity of 2,000 ohms per centimeter cube. In this formula the stearic ,acid and paraflin wax are bothsoftening ingredients.

I have found that a mixture of graphite and of commercial carbon blacks, such as Thermax and Fumonex, gives higher electrical conductiv- Another satisfactory formula ity than graphite alone, and that these blacks also increase resistance to wear. v

z I have given two typical and satisfactory formulas and from these it will be evident that the proportion by weight of graphite should be at least twice that of rubber and that, whereas the addition of a commercial black is desirable, it is not essential. Furthermore, it is possible, and perhaps advantageous under some conditions, to substitute Neoprene for natural rubber. An illustrative formula using Neoprene is as follows:

enemas Parts by weight Neoprene G 100 Light magnesium oxide 4 Zinc oxide 6 Soy bean oil 10 Mineral oil 10 Stearic acid V2 Paraiiln Graphite (powdered) 200 In general, powdered graphite is preferred for the graphite ingredient of the formula, although flaked graphite may be substituted with setbfactory results if more convenient. In this formula the soy bean oil, mineral oil, stearic acid and paraflln are softening ingredients.

Flooring compounded in accordance with any of the formulas above suggested has a conductivity of an order of magnitude of about 1.0 mho per square foot between the surface of the flooring and the conductive wire screen. Actually flooring has been made with a conductivity as high as 4.0 mhos per square foot between the surface of the flooring and the electrically conductive wire screen. These values refer to floor ing with a layer of rubber approximately 0.06.25 inch on top of the wire screen. In service,

therefore, the material has little or no insulating effect, and accumulation of static charges does not occur to any detectable extent.

.In the following claims the term "rubber ingredient is used to include within its scope natural rubber, artificial or synthetic rubber, and rubber-like materials, such as Neoprene.

1 Having thus disclosed my invention and speclflcally described certain specific embodiments thereof for purposes of illustration, but not by way of limitation, I claim as new and desire to secure by Letters Patent:

A rubber-like electro-conductive flooring sub-I stantially of the following composition processed to a homogeneous mass and shaped in sheet form and vulcanized to provide flooring sufliciently flexible and resilient to form a quiet and easy treading surface and capable of being bent and .rolled without cracking and resiliently firm and hard to a degree precluding permanent indentation in use: r

- Approx. parts by weight CARROLL 0. Davis.