Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present invention relates to a tile-
like ceramic element which is provided on its visible
side with an electrically conductive surface gla~e
which, when the tile-like ceramic element is laid
together with a plurality of such elements to form a
covering for lining walls or floors, communicates
with an electrically diverting substructure to be
provided below the covering. Coverings made of such
tiles are used, for example, as flooring for
operating rooms, laboratories, industrial rooms with
a fire risk such as paint shops, paint factories,
storehouses for inflammable solvents, etc. They have
also started to be used in areas where a noticeable
discharge on persons is to be avoided, for example in
office rooms in which computers and similar
electrical and electronic devices are set up.
Flooring in operating rooms and the like is
required to ensure constant diversion of static
electricity and, at the same time, to prevent current
from flowing off at a dangerous strength when there
is contact between a human body and poorly insulated
current-carrying parts. This generally means that
the flooring must have an electrical resistance in
the range of 104 to 106 ohms.
The flooring made of PVC and other
synthetic materials as used up to now suffers from
the fact that its resistance to organic solvents and
other chemicals leaves much to be desired. Further-
more, such flooring must be connected to the floor by
electrically conductive adhesives which are not
stable for long periods in terms of their
conductivity.
Use has therefore begun to be made of
ceramic floor tiles produced by firing molded
mixtures of stoneware clay or potter's clay and iron
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oxide in an atmosphere customary for firing floor
tiles. German "auslegeschrift" 17 71 361 might be
stated as an example of a method for producing such
electrically semiconductive ceramic floor tiles.
However, the admixture of iron oxides to the ceramic
material causes darkly colored unglazed ceramic
surfaces to be obtained. Furthermore, the band width
of the conductivity of such floor tiles made to be
electrically conductive is insufficient.
In "Baukeramik" 8/84, p. 96, the Villeroy &
Boch Company presents a new grayish-blue conductive
tile with a 15 x 15 cm format, consisting, in the
practical, commercially available embodiment, of a
ceramic tile having an electrically conductive
coating drawn over the side edges. Thus, electricity
can be diverted only via the joint material adjacent
to the edges of such tiles, which generally consists
of material bound with cement made to be electrically
conductive. However, this joint material is subject
to after-contraction so that the electrical contact
with the side edges of the tiles can disappear at
least in part. Furthermore, this joint material is
washed out very quickly in view of the cleaning which
must be performed extremely often in particular in
operating rooms, which also leads to a reduction of
the contact surfaces. Thus, not only does the
leakage resistance vary, the mechanical loading
capacity of ~he tile covering also suffers. Fur-
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thèrmore, when the joint material contracts or is
worn away this gives rise to tiny spaces that may
fill with germs between the tile edges and the joint
material, which is absolutely intolerable in
operating rooms. As the cited publication shows, the
tiles have a relatively small format so that the
on-site transition resistance required by the test
standard (VDE Regulation 0100/5.73 Art. 24) can only
be reached by the joint portion.
The invention is based on the problem of
making the laying of such a flooring utterly
independent of the joint material so that a joint
material can be selected which completely meets all
requirements to be met by such a material in terms of
its scuff resistance, its elasticity and hygienic
properties.
This problem is solved by the invention by
coating at least part of the side of the tile-like
ceramic element facing away from the visible side
with a material having good electrically conductive
properties which communicates with the surface glaze
in electrically conductive fashion.
In accordance with a particular embodiment
of the invention, there is provided a tile-like
ceramic element for attachment to a substructure
having a visible side and a side facing away from the
visible side, comprising: an electrically conductive
surface glaze on the visible side which, when the
tile-like ceramic element is laid with a plurality of
such elements to form a covering for lining walls or
floors, communicates conductively with the
substructure which diverts electricity and is
disposed under the covering, characterized in that at
least part of the side of the tile-like ceramic
element facing away from the visible side is coated
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with a material having good electrically conductive
properties which communicates with the surface glaze
in electrically conductive fashion via a coating on
at least one side edge which corresponds to the
coating on the side facing away from the visible
side; with said coating on said side edge not
extending onto said visible side.
A particular advantage of the inventive
design of the tile-like ceramic element is that the
joint material need no longer be considered as a
diverting element at all. Thus, one can use any
joint material on the basis of epoxy resins, which
are especially well-suited for the particular
application, for example in operating rooms or the
like.
Since the joint material does not play any
part when it comes to diverting electricity, the tile
dimensions can be selected at will. Thus, one can
select an optimum value for the
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relation between the tile area and the joint area in
such wall or floor linings, i.e. reduce the propor-
tional joint area to a minimum.
It is particularly advantageous to use
tile-like elements having a tile thickness of approx.
8 mm and less and dimensions of 60 x 60 cm to 120 x
160 cm. Tile dimensions of 60 x 60 cm correspond
essentially to the conventional grid dimensions,
resulting in particularly easy laying and access
possibilities for connections to be provided on the
floor level.
It may be advantageous for the surface
glaze to communicate in electrically conductive
fashion with the coating on the side facing away from
the visible side via a coating on at least one side
edge, this edge coating being expediently made of the
same material as the coating on the side facing away
from the visible side of the tile-like ceramic
element. In this way, a more intimate connection can
be achieved via this edge coating between the surface
glaze and the coating on the side facing away from
the visible side, for example by drawing the surface
glaze somewhat over the side edge coating. This also
creates the possibility of achieving a better
appearance when the joint material in the joint is
not flush with the surface of the covering.
It is expedient for the surface glaze to
run at the edge directly into the edge coating.
However, it is also possible to provide the edge
coating only locally. The same applies to the
transition between the edge coating and the coating
on the side facing away from the visible side. The
coating need not necessarily cover the entire surface
here; it may suffice for the coating to cover part of
the side facing away from the visible side.
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If a coating material is selected whose
melting point is substantially higher than the
melting point of the surface glaze, the tile-like
ceramic element can be made by a single firing
because the coating on the side facing away from the
visible side only sinters in the temperature range in
which the surface glaze begins to flow, so that the
tile-like ceramic element is prevented from clinging
to or bonding with the means of transport. For if a
material similar to the material of the surface glaze
were used instead of this coating, this material
would flow in the corresponding firing interval and
the side of the tile-like ceramic element facing away
from the visible side would adhere to the means of
transport.
According to a modified embodiment of the
invention, the coating is produced only after the
firing of the tile-like element provided with the
surface glaze by applying a conductive paste or a
conductive varnish, which is then sintered or set by
the effect of heat, or by vacuum metallizing or
plasma spraying a conductive substance. A dipping
process or another suitable coating process may also
be used.
Since the electrical resistance of the
coating is in any case substantially smaller than
that of the surface glaze, only the electrical
resistance of the surface glaze is responsible for
the conductivity of the corresponding tile-like
ceramic element, can thus be precisely adjusted and
is also maintained for a long period of time.
The prior art also includes sritish Patent
No. 1 202 924. In the embodiment according to Fig. 2
of this patent, which is the only one of interest
here, the floor consists of a layer of bituminous
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felt which is laid over a concrete base. The
bituminous felt is bent upwards at the edges. One or
more layers of polyethylene layer material coated
with bitumen are laid over the bituminous felt and
also bent up at the edges. Copper strips are then
laid on this layer material and connected to ground
via at least two resistors. The flooring itself
consists of terrazzo tiles. These terrazzo tiles are
special tiles which have been given the appropriate
conductivity by the incorporation of a corresponding
conductive additive into the mixture before the
production of the tiles. This evidently does not
address either the problem on which the invention is
based or the solution thereto, for it is assumed in
the case of the subject of the invention that the
glaze is to be electrically conductive, the important
thing being that this is independent of the joint
material.
The single figure shows a cross-section of
an embodiment of a tile-like ceramic element
according to the invention.
1 refers to a tile-like ceramic body having
on its side facing away from visible side 2 a coating
3 extending at least partly across this side and
running at the side edge into an edge coating 4
covered at least partly by surface glaze 5 which
extends across the entire visible side 2 of ceramic
body 1. At 6 one can see the joint material which
consists, for example, of an epoxy resin and need not
have any electrical conductivity whatsoever because
electricity can flow off directly into a diverting
element 7 via ~laze 5, edge coating 4 and coating 3
present on the side facing away from the visible
side.
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Surface glaze 5 and coating 3/4 are made of
materials having different conductivity. The
conductivity of coating 3/4 is higher than that of
surface glaze 5. In the case of an electrically
conductive ceramic coating, the melting point of the
coating material is higher than that of the surface
glaze material, so that when ceramic body 1 is fired
the coating material only sinters but does not melt,
so that it cannot stick to the firing base.
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