The present invention relates to elasticaily deform- able seals, and then particularly to packing pieces for cable and/or pipe lead-throughs or bushings, wherein the seals are composed of material which possesses self-lubricating properties. The present invention also relates to such material and also to the use of such seals and materials.

By seals is meant in the present Application mainly articles of deformable materials which are intended to be used in bushings, lead-throughs, throughlets and the like to seal cables, pipes and the like in walls and like structures against the through-passage of water, dust, flames, gas, pressure and explosions, for instance.

A cable or pipe bushing will normally include at least two packing pieces, which are most often comprised of elasticaily defor able material. When installing a bushing, it is necessary to grease or lubricate the packing pieces used in the bushing, partly to impart desired sealing properties to the bushing and partly to facilitate the actual process of installation.

Hitherto, the packing pieces have been greased by hand, the lubricant used to this end being delivered separately in a stick-like form, for instance. The lubricants are typically comprised of conventional greases or fats and lubricating greases such as Vase¬ line, silicone fats, animal fats, etc.

As will be understood, the aforedescribed method of greasing packing pieces is a particularly time-consum¬ ing task. There is also a risk that some parr of the packing piece will be left ungreaseά or will nor. be greased adequately enough, due to the human factor. The dependency on lubricants that are delivered in

separate packages also has a number of drawbacks: The lubricant may be completely used-up before all packing pieces have been greased; it is necessary for the fitter to unpack the lubricant at the same time as he/she is engaged with fitting the actual bushing; and the use of separately packaged lubricants constitutes a load on the environment, etc.

An object of the present invention is to provide seals of the aforesaid kind, particularly seals in the form of packing pieces, which will assist in eliminating the aforesaid problems and drawbacks associated with the known technique, these problems and drawbacks having prevailed for many years.

Another object of the present invention is to provide a material from which the aforesaid seals can be formed, this material also assisting in avoiding the aforesaid drawbacks and problems.

Other objects of the present invention will be appar¬ ent from the following.

The aforesaid objects are achieved partly with the aid of elasticaily deforraable seals in the form of so- called packing pieces or the like which are comprised of a material composition which is based on at least one type of elastomer, said seals being characterized in that there is included in the material composition 1-10 percent by weight, calculated on the total weight of the material composition, of a lubricant which is admixed essentially uniformly in said composition and which is essentially non-combinable with said composi¬ tion and which will thus migrate to the surface of the seal and therewith impart self-lubricating properties to the surface of said sea , and partly with the aid of a material composition for forming said elasticaily ieformable seals, said material composition including at least one type of elastomer and being characterized

in that the composition includes 1-10 percent by weight, calculated on the total weight of the composi¬ tion, of a lubricant which is essentially non-combin- able with the material composition.

By packing pieces is meant in the present application such elements as those which are intended to be fit¬ ted, preferably stationarily, in cable and pipe bush¬ ings or lead-throughs and to contribute therein to- wards a substantial part of the sealing properties of said bushings.

The lubricant used in accordance with the invention is essentially non-combinable with the material composi- tion in which it is mixed, by which is meant that the lubricant and the composition will not together form a stable homogenous mixture because of their mutual chemical and/or physical dissimilarities. Thus, the homogeneity of the mixture will not remain stable over the passage of time. Instead, the mixture will remain essentially fully homogenous from an initial point of time, i.e. from approximately the time at which the material composition was prepared up to roughly the time at which the finished product, for instance a packing piece, has just been obtained, whereafter the composition will pass to a progressively greater inhomogeneous state as a result of the efforts of the two components to separate from one another due to their mutual repelling effect. This can be expressed as the lubricant successively migrating from within the packing piece material up to the surface of said packing piece and onto the surface thereof.

Such migration is generally undesirable (see, for instance, TNC's "Glossary of Plastic and Rubber Terms" (TNC 84) and the term "Migration"), since the migrat¬ ing substance generally tends to impair the quality cf the polymeric material, for instance by lying as a generally white coating on the surface of the material

and therewith impede further working of the material (see, for instance, "Plaster och deras anvandning ino industrin", ( Plastics and their industrial uses) page 62, Klaus Stoeckhert, Forum publ. , Stockholm 1955).

On the other hand, migration is used in accordance with the invention to bring lubricant continuously to the surface of the finished seal, which equates with the expression that the surface of the seal has self- lubricating properties.

According to the present invention, the aforesaid lubricants may be substances which are conventionally added to polymer mixtures in production processes to facilitate ejection of moulded articles from the moulds upon completion of a moulding process and which can be mixed with "chese mixtures to a limited extent, although the main purpose of the lubricants mentioned in the present paten application is to reduce fric- tion between the surface of the product, i.e. a seal, preferably the surface of a packing piece, and another surface, for- instance the surface of a cable, a pipe, another packing piece or some other part of a pipe or cable bushing, by forming a lubricant boundary or interface between said surfaces; in addition, the lubricant contributes towards the sealing properties of the seal.

Any lubricant whatsoever can be used when practicing the present invention, provided that the lubricant is suitable for the purpose intended. For instance, the lubricant may be chosen from different sorts of oils, fats, greases, waxes, monovalent or multivaient amines, amides, esters or alcohols or the like, or combinations thereof. However, the lubricant will preferably have the form of fatty acid amides, partic¬ ularly oleyl amides, for instance of the kind sold commercially by Unichema Che ie BV, Netherlands, under the trade name "UNISLIP 1757".

By "elastomer" is meant in this document primarily polymers of the rubber or thermoplastic elastomer type, such as the types defined in the aforesaid "Glossary of Plastic and Rubber Terms". When practic- ing the present invention, any suitable type of rubber or thermoplastic elastomer whatsoever can be used, although rubber will be preferably used, for instance different types of diene rubber (including among other things butadiene rubber, isoprene rubber, natural rubber, nitrile rubber and styrene rubber), ethylene- propylene rubber, silicone rubber and butyl rubber or the like or combinations thereof. Ethylene-propylene rubber is particularly preferred, and then primarily so-called EPDM rubber, for instance of the kind ob- tainable from the Exxon Chemical Co . , U.S.A., under the trade name "VISTALON 8504".

According to one embodiment of the present invention, the material composition includes about 20-40 percent by weight elastomer, about 5-20 percent by weight filler, about 0.5-5 percent by weight activator, about 0.5-5 percent by weight accelerator and about 0.5-5 percent by weight vulcanizing agent, and has admixed therewith about 1-10 percent by weight lubricant, wherein the remainder of the composition iε comprised of optional additives, such as pH-stabilizing agent, flame retardants, colourants and/or mould release agents up to 100 percent by weight, all percentages being calculated on the total weight of the material composition.

According to one preferred embodiment, the inventive material composition includes about 25-32 percent by weight elastomer, about 10-13 percent by weight fill- er, about 1-3 percent by weight activator, <3 percent by weight accelerator and <2 percent by weight vulcan¬ izing agent, and has mixed therewith about 1-3 percent by weight lubricant, wherein the remainder of the composition is made-up of flame retardant, pH-stabi-

lizing agent, viscosity-reducing process-auxiliary agent, means for enhancing cross-linking between rubber and filler, mould release agent and colourant up to 100 percent by weight, all percentages being calculated on the total weight of the material compo¬ sition.

The present invention is described in more detail below with reference to a working Example. The working Example is solely intended to provide a general illus¬ tration of the invention and shall not be considered to limit the scope of the invention.

Example

The following ingredients and quantities were used in the preparation of an inventive material composition:

EPDM (VISTALGN 8504) 29 kg Whiting 11 kg

Stearine 6 kg

Antimonoxide + aluminium hydroxide.... 39 kg

Magnesium carbonate 5 kg

Zinc oxide 1 kg Tricresyl phosphate 1 kg

Polyethylene (in wax form) .... , 1 kg

Zinc stearate 1 kg

Iron + titanium oxide 1.5 kg

Cyclohexyl benzothiazyle sulfenamide.. 0.5 kg γ-Mercaptopropyltrimethoxysilane 0.5 kg

Dithiodimorpholine 1 kg

Sulphur 1 kg

Oleyl amide (UNISLIP 1757) 1.5 kg

All ingredients, with the exception of sulphur, cyclo¬ hexyl benzothiazyle sulfenamide (CBS) and dithiodimor¬ pholine (DTDM) were introduced into a closed mixture (Inter ixer K5, from Francis Shaw & Co. Ltd., England) and there mixed. The stamp pressure was about 22-27

Pa. The mixture was heated by the mixing process, no external heat being supplied. After about six minutes, the mixture had reached a temperature of about 125°C, whereafter the mixture was emptied onto a rolling mill, flattened, removed, and cooled in the take-off and then placed on a pallet. The mixture was then passed back to the mixture and sulphur, CBS and DTDM were added while mixing. After about five minutes, the mixture had reached a temperature of about 90°C and was emptied onto the rolling mill, flattened, removed and cooled in the take-off and then placed on a pal¬ let. The non-vulcanized rubber slabs were then granu¬ lated to granules in a granulator. The granulate was fed into a carousel press by means of a screw feeder ' and was injected from the press into different tools and shaped into packing pieces under pressure and at a vulcanizing temperature of about 160°C. The finished, self-lubricating packing pieces were removed from the tools after some minutes. After cooling and being cleaned, the packing pieces were ready to be packaged and delivered.

It will be understood that other types of seals and other material compositions than those described are embraced by the scope of the present invention, as will be obvious to all those skilled in this particu¬ lar technical field.