Mixture for the Manufacture of Antistatic Floor Coverings and Coatings

Since the introduction of liquid synthetic resins based on epoxide resins, polyurethanes or unsaturated polyesters, which cure through a polyaddition or polymerisation reaction with suitable curing agents and catalysts at room temperature, these plastics have found increased use, inter alia, in the fields of corrosion protection, in the form of chemically resistant coatings and of jointless hard-wearing floor coverings. In particular the liquid, solvent-free, aromatic epoxide resins, in combination with specially formulated liquid curing agents, for example based on polyamine adducts or polyaminoamide resins, have attained great and ever-increasing importance in practice due to the excellent mechanical properties of the cured coated materials, such as compressive strength, flexural strength, adhesion to various substrates, impact strength, abrasion resistance and chemical resistance, in the fields of use mentioned.

To prevent such coverings acquiring an electrostatic charge, electrically conducting, so-called antistatic, coverings, especially for floors, have been developed in recent years. Such special coverings are considered, above all, for areas where there is a severe explosion hazard, such as, for example, in operating theatres of hospitals, in paint shops, in large garages and in the manufacturing areas of chemical concerns. At the present time, special carbon blacks and graphite are predominantly used as the fillers for achieving the requisite electrical conductivity of such coverings. These floors are not popular, because of the black or dark grey surfaces, and in many cases do not meet the aesthetic requirements of the personnel working in the areas concerned. This limitation on the possible selection of colour shade also prevents the broader use of antistatic floor coverings.

It is also known to manufacture antistatic floor coverings using metal particles, such as aluminium flakes or copper filings. Here, the disadvantage is the non-uniform electrical conductivity, which turns out different from case to case. Admittedly, a process is known, from German Auslegeschrift 1,544,968, according to which this disadvantage is avoided; however, in return it is necessary to accept the fact that prior to the application of the plastic layer containing metal an undercoat of good conductivity, for example containing graphite, must be applied. This undercoat must then be cured and dried before the plastic covering can be applied.

It has now been found that using the mixture according to the invention, antistatic floor coverings and coatings can be manufactured which, on the one hand, are colourful or light-coloured, for example coloured in pastel shades and on the other hand have a uniform electrical conductivity of good reproducibility, and at the same time the application of one or more conducting undercoats is no longer required.

The mixture according to the invention is characterised in that it contains a cold-curing liquid synthetic resin combination, an anti-sedimentation agent and 45-70 percent by weight, based on the mixture, of aluminium grit and, optionally, fillers and/or, preferably, pigments. Preferably, the mixture contains 30-45%, especially 37-40%, of resin combination, 3-30%, especially 18-30%, of pigments and 45-65%, especially 50-60%, of aluminium grit. The particles of the aluminium grit are preferably 0.35-1.2 mm long.

Possible synthetic resin combinations are liquid epoxide resins, preferably based on aromatic compounds, or mixtures of resins based on aromatic compounds, such as bisphenol-A diglycidyl ether, with aliphatic epoxide resins, such as polyglycidyl ethers of polyalcohols, for example pentaerythritol, hexanetriol, butanediol or glycerol, in combination with liquid curing agents for these resins. As such curing agents there may be mentioned aliphatic or cycloaliphatic polyamines or their liquid adducts, containing at least one primary amino group, with polyepoxides, and also liquid polyaminoamide resins, that is to say reaction products of fatty acids and polyamines.

Further suitable synthetic resin combinations are those based on polyurethanes, such as, for example, a mixture of liquid polyester resins or polyether resins having a hydroxyl number of between 1.7 and 12% and liquid polyisocyanates, preferably based on diphenylmethane-4,4'-diisocyanate, as the curing agent.

Further suitable synthetic resin combinations are binders based on liquid unsaturated polyester resins, unsaturated monomeric compounds which react therewith, such as, for example, styrene, vinyltoluene or acrylic acid esters, and a peroxide catalyst.

Finally, there may also be mentioned synthetic resin combinations based on acrylate resin, unsaturated monomers reacting therewith, and a peroxide catalyst.

In order to achieve a uniformly distributed conductivity over the entire surface of the coating, the mixture according to the invention contains an anti-sedimentation agent, which prevents sedimentation of the aluminium grit particles away from the surface of the floor covering, which is liquid during application. Without this, after curing, the surface layer which has become enriched in binder would exhibit an excessive electrical resistance. As anti-sedimentation agents it is in principle possible to use thixotropic agents, such as, for example, silicon dioxide ("Aerosil") and montmorillonite ("Bentones"). The use of finely dispersed asbestos, such as, for example, "Sylodex" (of Messrs. Grace Co.), offers the advantage that it need not be dispersed separately but can be dispersed directly together with aluminium grit in the resin, using simple mixing machines, and exhibits a good anti-sedimentation action and good levelling properties.

The mixing according to the invention can be manufactured according to conventional methods. Preferably, various colour pastes, which consist of approx. 50% of pigment -- it being possible to use all known inorganic and numerous organic pigments -- and approx. 50% of resin, are manufactured by grinding on triple-roll mills or dispersing in Cowles dissolvers. These colour pastes are then introduced into a mixing vessel, after which the remainder of the resin is stirred in. Thereafter, the anti-sedimentation agent can be dispersed in the mixture and finally the aluminium grit, preferably of 99.5-99.7% purity and of 0.35-1.2 mm particle size, and, optionally, the additives required to achieve additional properties, such as levelling agents and de-aerating agents, can be stirred in. Separately from this basic mixture, which in commercial products is frequently also referred to as component I, the curing agent, or component II, is supplied in amounts corresponding to the mixing ratio required for optimum curing.

Before use, the two components are thoroughly mixed together, poured out into the surface to be treated and spread uniformly, by means of a serrated trowel, to give a coating of the desired thickness, which can be between 3 and 5 mm. During the process, care must be taken that the aluminium grit is not distributed unevenly by the movement of the serrated trowel, because of the relatively large particle size of the grit. To achieve optimum levelling of the slightly thixotropic liquid mass, a subsequent treatment with a plastic spiked roller is carried out, which permits de-aeration and achieves bubble-free surfaces.

In order to achieve better de-aeration of the liquid mass during laying, and bubble-free surfaces of the coverings, it is possible to add 1-5%, preferably 1.5-2%, of paraffin oil or benzine (boiling range 100.degree.-125.degree. C) into the mixture which has been prepared for laying.

If, as is usually the case, the floor to be laid has a leakage resistance of 10.sup.2 -10.sup.4 ohm, it easily proves possible, using the mixture according to the invention, to manufacture coverings which exhibit the leakage resistance of less than 10.sup.6 ohm required by the DIN specification. In most cases, coverings with a leakage resistance of 10.sup.3 ohm or less are obtained. If the bases to be covered have higher leakage resistances than 10.sup.4 ohm, it is necessary to provide earthed underlays in the form of metal fabrics, metal foils or metal grids.

The coverings described in the examples which follow can readily be cared for by simple cleansing agents, show no conspicuous wear after months of exposure to chemicals, and to the customary traffic in manufacturing areas of chemical concerns, and retain their initial value of the leakage resistance.

In the examples which follow, the components mentioned are mixed with one another.

The following components are mixed with one another:

A floor covering is produced with this mixture.