EP3246461A1

EP3246461A1 - Electrically conductive linoleum-based floor covering

Info

Publication number: EP3246461A1
Application number: EP17169369.0A
Authority: EP
Inventors: Antonella Bartoletti; Ylenia Leonardi
Original assignee: Tarkett GDL SA
Current assignee: Tarkett GDL SA
Priority date: 2016-05-19
Filing date: 2017-05-04
Publication date: 2017-11-22
Also published as: LU93077B1

Abstract

An electrically conductive floor covering comprising a linoleum-based layer arranged on a fabric backing. The linoleum-based layer includes carbon nanotubes in an amount sufficient to achieve a vertical resistance not exceeding 10⁶ Ohm, measured according to EN 1081, method A, version 1998.

Description

Technical Field:

The present invention generally relates to an electrically conductive linoleum-based floor covering and to a process for producing this floor covering.

Background Art:

Due to an increasing interest in sustainability and environmental friendly products, there is a continued demand for resilient floor coverings made with renewable raw materials, in particular for linoleum-based floor coverings.
A linoleum-based floor covering is typically made by calendering a linoleum paste on a fabric backing. A typical linoleum paste is made of: an oxidized vegetable oil, most often an oxidized linseed oil; a natural resin, most often pine rosin; organic fillers, generally wood dust and/or cork dust; mineral fillers, such as e.g. calcium carbonate; and most often pigments for coloring the linoleum paste. The fabric backing is most often made with vegetable fibers, in particular jute fibers, and exceptionally with synthetic or mineral fibers or with a mixture of vegetable and/or synthetic and/or mineral fibers.
It will be noted that a conventional linoleum-based floor covering has a relatively high electrical resistance (the vertical resistance of a conventional linoleum-based floor covering is in the region of 10¹⁰ Ohm, when measured according to EN 1081, method A, version 1998). It follows that people walking over such a conventional linoleum-based floor covering risk to become electrostatically charged. Consequently, such a conventional linoleum-based floor covering cannot be used in rooms in which electrostatic discharges are to be avoided, such as, for example: facilities or laboratories in which flammable liquids, gases or explosives or sensible electronic equipment are used. For such rooms, the floor covering has to be electrically conductive to quickly discharge electrostatic charges from the upper surface of the floor covering to the ground. In accordance with EN 14041, a resilient floor covering is considered to be electrically conductive if its vertical resistance measured according to EN 1081, method A, version 1998, does not exceed 10⁶ Ohm.
It is well known to reduce the vertical resistance of a linoleum-based floor covering through the addition of electrically conductive additives or fillers, in particular carbon black and/or metal powders. The addition of such electrically conductive fillers has however the drawback that large quantities are required to achieve the required electrical conductivity.
DE 3416573 and WO 99/10592 concern linoleum-based floor coverings which allegedly achieve a vertical resistance below 10⁸ Ohm, through addition of different chemical additives in a liquid form, namely at least one cation active compound with a quaternary nitrogen atom, especially a derivative of imidazole, imidazoline or morpholine. There is however no indication in these prior art documents that a vertical resistance lower than 10⁶ Ohm may be achieved. According to WO 99/10592 , a silica, especially a kieselguhr, should additionally be added to the linoleum paste to absorb the liquid chemical additives. It will further be appreciated that these prior art linoleum-based floor coverings have a vertical resistance that is strongly influenced by air humidity.
WO 99/04085 describes a floor covering based on linoleum that is allegedly achieving a vertical resistance below 10⁸ Ohm. The linoleum wear layer has an irregular pattern of differently colored zones, which show different electrical conductivities. Those zones that have a low electrical resistance are formed by linoleum particles containing large quantities of soot or metallic powder and are very darkly colored. Nevertheless, despite a relatively high content of carbon black in the dark zones, it appears impossible to achieve a vertical resistance as low as 10⁶ Ohm.
US 6,831,023 proposes a two-layer linoleum-based floor covering allegedly having a vertical resistance according to EN 1081 of maximum 10⁷ Ohm. The upper surface (i.e. the visible surface) in the installed floor covering is formed by a linoleum-based wear layer, which is arranged on a linoleum-based lower layer. For reducing its conductivity, the linoleum based wear layer contains mainly colorless chemicals, graphitized synthetic fibers or synthetic fibers which are jacketed with epoxy-graphitized material, but also low quantities of carbon black (0.1 to 5 weight %) and/or metal powders (0.1 to 8 weight %). The electrical conductivity of the lower layer is achieved through mixing much higher contents of carbon black (1 to 20 weight %) and metal powder (1.5 to 40 weight %) to the linoleum mass. In the example provided, the composite of the lower layer and wear layer had a vertical resistance R1 (measured in accordance with EN 1081) of 1.9x10⁶ to 3.8x10⁶ Ohm.
It is an object of the present invention to propose an improved linoleum floor covering that has an electrical vertical resistance, measured according to EN 1081, method A, version 1998, below 10⁶ Ohm.

Summary of invention:

An electrically conductive floor covering in accordance with the invention comprises a linoleum-based layer arranged on a fabric backing. The linoleum-based layer includes carbon nanotubes in an amount sufficient to achieve for the electrically conductive floor covering a vertical resistance not exceeding 10⁶ Ohm, wherein the vertical resistance is measured according to EN 1081, method A, version 1998.
Without the carbon nanotubes, the vertical resistance of this floor covering would be higher than 10⁶ Ohm, i.e. the floor covering would not qualify as an electrically conductive floor covering in accordance with EN 14041. The carbon nanotubes in the linoleum-based layer reduce the vertical resistance below 10⁶ Ohm, so that it is for example in the range of 10⁵ to 10⁶ Ohm.
The linoleum-based layer 12 preferably includes between 0.4 and 4.0 weight %, preferably between 0.4 % and 1.8 weight %, and more preferably between 0.4 % and 1.6 weight % of carbon nanotubes, the weight % being defined in relation to the total weight of the linoleum-based layer.
The linoleum-based layer may further include at least one complementary conductive additive other than carbon nanotubes, so that without including the carbon nanotubes, the vertical resistance would be in the range of 10⁶ and 10⁹ Ohm, preferably in the range of 10⁷ and 10⁸ Ohm.
This at least one complementary conductive additive preferably includes a carbon black powder or a metal powder or a mixture of a carbon black powder and a metal powder.
The content of complementary conductive additive(s) other than carbon nanotubes is preferably limited to 10 weight %, more preferably to 5 weight %, the weight % being defined in relation to the total weight of the linoleum-based layer.
In a first embodiment of the electrically conductive floor covering, the carbon nanotubes are uniformly distributed in the linoleum-based layer.
In a preferred embodiment of the electrically conductive floor covering, the linoleum-based layer comprises a multitude of first crumbles in which all or most of the carbon nanotubes are concentrated and which form conductive paths between an upper surface and a lower surface of the linoleum-based layer.
The content of carbon nanotubes in the first crumbles is preferably in the range of 0.8 to 4.0 weight %, and more preferably in the range of 0.8 to 2.0 weight %.
The first crumbles preferably represent between 20% and 60%, more preferably between 30% and 50%, and most preferably between 35% and 45% of the total weight of the linoleum-based layer.
In a further embodiment of the electrically conductive floor covering, the linoleum-based layer further comprises a multitude of second crumbles that contain no carbon nanotubes or less than 0.4 weight % of carbon nanotubes.
The second crumbles may include at least one complementary conductive additive, which preferably includes a carbon black powder or a metal powder or a mixture of a carbon black powder and a metal powder.
The content of the at least one complementary conductive additive in the second crumbles is preferably in the range of 5 to 15 weight %, more preferably in the range of 5 to 10 weight %.
The electrically conductive floor covering may further include an electrically conductive bottom layer, in which at least one conductivity enhancing additive is uniformly distributed, and which forms a lower surface of the linoleum based layer.

Brief description of drawings:

The afore-described and other features, aspects and advantages of the invention will be better understood with regard to the following description of several embodiments of the invention and upon reference to the attached drawings, wherein:

FIG. 1:: is a schematic section illustrating the structure of an embodiment of a floor covering.
FIG. 2:: is a schematic section illustrating the structure of a second embodiment of a floor covering;
FIG. 3:: is a schematic section illustrating the structure of a third embodiment of a floor covering; and
FIG. 4:: is a schematic section illustrating the structure of a fourth embodiment of a floor covering.

Detailed description of embodiments illustrating the invention

It will be understood that the following description and the drawings to which it refers describe embodiments illustrating, by way of example, the invention. They cover further aspects of the invention but shall not limit the scope, nature or spirit of the claimed subject matter.
Fig. 1 shows a schematic section illustrating the structure of a first embodiment of a linoleum-based electrically conductive floor covering 10. The latter comprises an electrically conductive linoleum-based layer 12 arranged on a fabric backing 14. Electrically conductive here means that the vertical resistance of the linoleum-based layer 12, measured according to EN 1081, method A, version 1998, does not exceed 10⁶ Ohm. In accordance with EN 14041, a resilient floor covering is considered to be electrically conductive if its vertical resistance measured according to EN 1081, method A, version 1998, does not exceed 10⁶ Ohm.
Just as in a conventional linoleum floor covering, the linoleum-based layer 12 is made of a linoleum paste that is a mixture of a linoleum cement (i.e. an oxidized vegetable oil, generally linseed oil, mixed with a natural resin, generally pine rosin), with organic fillers (generally wood dust and/or cork dust), mineral fillers (such as e.g. calcium carbonate), one or more coloring agents and optionally other additives facilitating the production process or providing specific properties to the final floor covering. A typical linoleum paste composition contains e.g., in relation to its total weight: 30-45% of a linoleum cement; 20-45% of organic fillers; 0-10% coloring agents and up to 40% of mineral fillers. In case of an electrically conductive linoleum-based layer 12, the linoleum paste further includes at least one conductivity enhancing additive, which will be described further below.
This linoleum paste is applied onto the fabric backing 14, calendered to its final thickness and thereafter cured to form the linoleum-based layer 12 in the final floor covering. Curing normally takes place in an oven. In the finished floor covering, the thickness of the linoleum-based layer 12 is generally in the range of 1.5 mm to 4.0 mm, more preferably in the range of 1.9 mm to 3.0 mm and most preferably in the range of 2.3 mm to 2.7 mm.
The fabric backing 14 is generally made with natural fibers, in particular jute fibers. However, it is not excluded to use a fabric backing 14 made with synthetic fibers or with a mixture of natural and synthetic fibers. The thickness of the fabric backing 14 is in the range of 0.1 mm to 1.0 mm, more preferably in the range of 0.5 mm to 0.7 mm.
When the electrically conductive linoleum-based floor covering 10 is installed on a floor surface, the fabric backing 14 is soaked with an electrically conductive glue and the floor surface is equipped with grounded copper strips. The electrically conductive glue establishes an electrical contact between the lower surface of the linoleum-based layer 12 and the grounded copper strips. To facilitate and improve the grounding, the lower side of the fabric backing 14, i.e. the side that is facing the floor surface on which the floor covering is to be installed, may further be equipped with electrically conductive strips or an electrically conductive grid. To improve the electrical conductivity of the fabric backing 14, conductive fibers and/or filaments may be incorporated into the fabric backing 14. (When measuring the vertical resistance according to EN 1081, method A, the fabric backing 14 is soaked with a graphitic suspension.)
The top surface of the linoleum-based layer 12 is advantageously protected by an electrically conductive top coating 16.
In accordance with one aspect of the present invention, the linoleum paste used for forming linoleum-based layer 12 includes carbon nanotubes in an amount sufficient to achieve for the linoleum based floor covering a vertical resistance not exceeding 10⁶ Ohm, wherein this vertical resistance is measured according to EN 1081, method A, version 1998. Preferably, this vertical resistance is in the range of 10⁵-10⁶ Ohm. It will be noted that with conventional electrically conductive additives or fillers, the vertical resistance of the linoleum-based floor covering would at best be in the range of 10⁷ to 10⁸ Ohm and without any conductive additives or fillers would even be above 10¹⁰ Ohm.
The linoleum-based layer 12 preferably includes between 0.4 % and 4.0 %, more preferably between 0.4 % and 1.8 %, and most preferably only between 0.4 % and 1.6 % of carbon nanotubes (expressed as a percentage of the total weight of the linoleum-based layer). It will be appreciated that carbon nanotubes do not present any problem during processing of the linoleum paste and-due to the small weight percentages to be added-they considerably facilitate raw material supply. [ARS1]Furthermore, contrary to other conductivity enhancing agents, carbon nanotubes are not affected by humidity (they are indeed water repellant) and they remain stably embedded within the linoleum matrix (no significant migration is observed), so that they warrant a constant conductivity over the whole lifetime of the floor covering.
In the embodiment of FIG. 1, carbon nanotubes are uniformly distributed in the linoleum-based layer 12. To achieve a vertical a resistance not exceeding 10⁶ Ohm (measured according to EN 1081, method A), the content of nanotubes is the range of 1.0% to 4.0 %, preferably in the range of 1.0% to 2.0%. To reduce the quantity of relatively expensive nanotubes to be added to the linoleum paste, at least one complementary conductive additive (other than carbon nanotubes) may be added to the linoleum paste. For example, one may add one or more of such complementary conductive additives to the linoleum paste, to achieve already without carbon nanotubes a vertical resistance of the linoleum-based layer in the range of 10⁶ and 10⁹ Ohm, preferably in the range of 10⁷ and 10⁹ Ohm, and more preferably in the range of 10⁷ and 10⁸ Ohm. A smaller amount of carbon nanotubes will then be required to reduce this vertical resistance finally below 10⁶ Ohm.
The complementary conductive additive is for example a carbon black powder or a metal powder or a mixture of a carbon black powder and a metal powder. The content of carbon black and/or metal powder is preferably limited to 15 weight %, more preferably to 10 weight % and most preferably to 5 weight % (expressed as a percentage of the total weight of the linoleum-based layer).
In the floor covering of Fig. 2, the linoleum-based layer 12 comprises a multitude of electrically conductive first crumbles 18 (i.e. small delimited linoleum volumes), in which all or most of said carbon nanotubes are concentrated. These first conductive crumbles 18 are mixed with second crumbles 20, which contain no carbon nanotubes or substantially less carbon nanotubes than the first crumbles 18 (the second crumbles 20 contain preferably less than 0.2 weight % of carbon nanotubes). As seen in Fig. 2, during lamination and calendering, the first highly conductive crumbles 18 contact and fuse together to form conductive paths between the upper surface and the lower surface of the linoleum-based layer 12. The second less conductive crumbles 20 lie in between these conductive paths. The first crumbles 18 charged with carbon nanotubes preferably represent between 20% and 60%, more preferably between 30% and 50%, and most preferably between 35% and 45% of the total weight of the linoleum-based layer 12.
The content of carbon nanotubes in the first crumbles 18 is in the range of 0.8% to 4.0%, preferably in the range of 0.8% to 2.0%, and most preferably in the range 0.8% to 1.6%. The content of carbon nanotubes expressed as a percentage of the total weight of the linoleum-based layer will consequently be lower than 1% and is for example in the range of 0.4% to 0.8%. Hence, only a very small quantity of relatively expensive nanotubes is required for achieving the desired vertical resistance of less than 10⁶ Ohm (measured according to EN 1081, method A, version 1998). It will further be appreciated in this context that concentrating the carbon nanotubes in relatively small sub-volumes of the linoleum-based layer 12 (i.e. in the first crumbles 18) fosters the formation of so-called "ropes", which constitute efficient conductors for electrical charges, so that relatively small amounts of carbon nanotubes are required for making the crumbles 18 conductive. In conclusion, the amount of carbon nanotubes required to make the floor covering of FIG. 2 conductive is much lower than the amount of carbon nanotubes required to make the floor covering of FIG. 1 conductive.
At the lower surface of the linoleum based layer 12, an electrically conductive glue electrically interconnects the first crumbles 18, when the floor covering according to Fig. 2 is installed on a floor surface. The first crumbles 18 may consequently be considered as a multitude of parallel conductors interconnecting the electrically conductive top surface of the floor covering (which is e.g. formed by the electrically conductive top coating 16) to its electrically conductive bottom surface (which is e.g. formed by the fabric backing 14 soaked with the electrically conductive glue).
To produce the floor covering of Fig. 2, following process may e.g. be used. A first linoleum paste contains carbon nanotubes. A second linoleum paste doesn't contain carbon nanotubes. These first and the second linoleum pastes are then reduced to linoleum crumbles. The linoleum crumbles of the first and the second linoleum pastes are intensively mixed, so as to form a mixture of crumbles in which the crumbles from the first linoleum paste (i.e. the crumbles containing carbon nanotubes) are uniformly dispersed. This mixture of crumbles is then used to form the linoleum-based layer 12 on the fabric backing 14. After calendering onto the fabric backing 14, the linoleum crumbles preferably have a length and a width in the range from 3 mm to 25 mm, and a thickness in the range from 0.2 mm to 3 mm, more preferably in the range of 0.5 mm to 2 mm.
The floor covering of Fig. 3 distinguishes over the floor covering of Fig. 2 in that at least part of the second crumbles 20, which contain no carbon nanotubes or substantially less carbon nanotubes than the first crumbles 18, contain in this embodiment at least one complementary conductive additive. Suitable complementary conductive additives include for example a carbon black powder or a metal powder or a mixture of a carbon black powder and a metal powder. The content of complementary conductive additives in the second crumbles 20 is preferably in the range of 5 to 15 weight %, more preferably in the range of 5 to 10 weight %. The fact that in this embodiment the second crumbles 20 achieve an enhanced conductivity with relatively inexpensive complementary conductive additives, allows to reduce the weight % of first crumbles 18, which contain expensive carbon nanotubes, whereby the electrically conductive floor covering becomes less expensive.
The process for producing the floor covering of Fig. 3 is substantially identical to the process for producing the floor covering of Fig. 2, with the difference that the second linoleum paste, which is used for producing the floor covering of Fig. 3, contains the at least one complementary conductive additive mentioned in the preceding paragraph.
The floor covering of Fig. 4 distinguishes over the floor covering of Fig. 3 in that the lower surface of the linoleum based layer 12 is formed by an electrically conductive bottom layer 24, in which at least one conductivity enhancing additive is uniformly distributed. The at least one conductivity enhancing additive is advantageously a less expensive product than carbon nanotubes, such as e.g. carbon black, a metal powder or a mixture of carbon black and a metal powder. The thickness of the electrically conductive bottom layer 24 is generally in the range of 0.3 mm to 1.5 mm.
A skilled person will of course readily understand that the features disclosed with reference to the embodiments of Fig. 1 to Fig. 4, may be the object of further combinations not illustrated in these figures. For example: the embodiments of Fig. 1 or Fig. 2 too may include an electrically conductive bottom layer 24, as described for the embodiment of Fig. 4.

List of Reference Signs used in the Figures:

10: linoleum-based electrically conductive floor covering
12: linoleum-based layer
14: fabric backing
16: top coating
18: first crumbles
20: second crumbles
24: electrically conductive bottom layer

Claims

An electrically conductive floor covering (10) comprising a linoleum-based layer (12) arranged on a fabric backing (14) characterized in that said linoleum-based layer (12) includes between 0.4 and 4.0 weight % of carbon nanotubes, said weight % being defined in relation to the total weight of said linoleum-based layer and being sufficient to achieve for said electrically conductive floor covering (10) a vertical resistance not exceeding 10⁶ Ohm, wherein said vertical resistance is measured according to EN 1081, method A, version 1998.
The floor covering as claimed in claim 1, wherein said vertical resistance is in the range of 10⁵ to 10⁶ Ohm.
The floor covering as claimed in claim 1 or 2, wherein said linoleum-based layer 12 includes between 0.4 % and 1.8 weight %, and preferably between 0.4 % and 1.6 weight % of carbon nanotubes, said weight % being defined in relation to the total weight of said linoleum-based layer.
The floor covering as claimed in claim 1, 2 or 3, wherein:
said linoleum-based layer includes at least one complementary conductive additive other than carbon nanotubes.
The floor covering as claimed in claim 4, wherein:
said at least one complementary conductive additive includes a carbon black powder or a metal powder or a mixture of a carbon black powder and a metal powder.
The floor covering as claimed in claim 4 or 5, wherein:
the content of complementary conductive additive other than carbon nanotubes is limited to 10 weight %, more preferably to 5 weight %, said weight % being defined in relation to the total weight of said linoleum-based layer.
The floor covering as claimed in any one of the preceding claims, wherein said carbon nanotubes are uniformly distributed in said linoleum-based layer.
The floor covering as claimed in any one claims 1 to 6, wherein:
said linoleum-based layer comprises a multitude of first crumbles (18) in which all or most of said carbon nanotubes are concentrated and which form conductive paths between the upper surface and the lower surface of said linoleum-based layer (12).
The floor covering as claimed in claim 8, wherein:
the content of carbon nanotubes in said first crumbles (18) is in the range of 0.8 to 4.0 weight %, preferably in the range of 0.8 to 2.0 weight %.
The floor covering as claimed in claim 8 or 9, wherein:
said first crumbles (18) represent between 20% and 60%, preferably between 30% and 50%, and most preferably between 35% and 45% of the total weight of the linoleum-based layer.
The floor covering as claimed in claim 8, 9 or 10, wherein:
said linoleum-based layer comprises a multitude of second crumbles (20) which contain no carbon nanotubes or less than 0.4 weight % of carbon nanotubes.
The floor covering as claimed in claim 11, wherein:
said second crumbles (20) include at least one complementary conductive additive.
The floor covering as claimed in claim 12, wherein:
said at least one complementary conductive additive includes a carbon black powder or a metal powder or a mixture of a carbon black powder and a metal powder.
The floor covering as claimed in claim 12 or 13, wherein:
the content of said at least one complementary conductive additive in the second crumbles (20) is in the range of 5 to 15 weight %, preferably in the range of 5 to 10 weight %.
The floor covering as claimed in any one of the preceding claims, further including:
an electrically conductive bottom layer (24) in which at least one conductivity enhancing additive is uniformly distributed, said electrically conductive bottom layer (24) forming a lower surface of said linoleum based layer (12).