Patent Description:
A floor screed is used in buildings to level and flatten the underlying concrete layer and in which pipes and cables can be housed. It should have a good thermal conductivity in case it houses ducts for floor heating. A self-leveling screed is a liquid mortar mainly formed from a hydraulic binder such as cement or calcium sulphate, aggregates and different additives; it is supplied on the job site by truck mixer or directly via a transmix distribution system.

Floor screeds based on cement and/or calcium sulphate binders are well known in the art.

Attempts have been made to improve the thermal conductivity of floor screeds by adding expanded graphite, as described in <CIT>. According to <CIT>, an amount of expanded graphite of <NUM>%w to <NUM>%w, based upon the dry weight of the floor screed is added to change the thermal conductivity, the size of the expanded graphite particles being in the range of <NUM> to <NUM>.

<CIT> discloses a composition for preparing gypsum wallboards comprising a binder based on calcium sulphate in combination with expanded graphite with a D<NUM> of <NUM> micron to <NUM>, the graphite being present in <NUM>-<NUM> wt.

It is an object of the present invention to provide compositions suitable for thermally conductive screeds based hydraulic binders, and thermally conductive floor screeds.

The invention further relates to floor screeds and floor heating systems obtained by using compositions according to the invention.

The invention also relates to the use of compositions according to the invention for floor screeds and floor heating systems.

According to a first aspect of the present invention, a floor screed composition is provided, the composition being set out in claim <NUM>.

The weight percentage "X %w" of the expanded graphite means that X gram of expanded graphite is used per <NUM> gram of hydraulic binder.

By the term "hydraulic binder", reference is made to what is usually understood as hydraulic binders, i.e. compounds having the property to hydrate in the presence of water and moisture to gel a solid mechanical According to the invention the hydraulic binder is calcium sulphate.

This calcium sulfate can be beta calcium sulfate and/or alpha calcium sulfate from natural or synthetic origin, or anhydrous calcium sulfate, e.g. anhydrite II or anhydrite III, obtained from sources of synthesis (for example fluoro anhydrite) or natural sources, e.g. by calcining natural or synthetic gypsum (e.g. from the desulfurization FGD gypsum). Examples of suitable calcining processes are classic calcination process or process RocalTM. One may use mixtures of different sources of calcium sulphate. The screed the invention generally meets the requirements of the European standards EN <NUM>-<NUM> (binder) and EN <NUM> (mortar) for calcium sulphate for fluid screed mortars and binders.

Calcium sulphate, usually as anhydride, may comprise at least <NUM>% by weight of calcium sulphate, preferably at least <NUM>% or even significantly <NUM>%.

The screed may further comprise fillers of various kinds (calcareous, siliceous, Silica fume, fly ash can be used in addition to the calcium sulfate.

The used calcium sulphate preferably is anhydride.

The use of expanded graphite leads to higher values of thermal conductivity compared to unexpanded graphite.

If the amount of expanded graphite is above <NUM> weight % with respect to the weight of hydraulic binder, the cost of the formulation for use as a screed is too high, the further addition may not necessarily bring much additional increase of thermal conductivity, and there may be a potential reduction of mechanical performance.

Despite the low dosage of expanded graphite in the composition according to the invention, a thermal conductivity increase is obtained and thermal conductivity values, as measured according to NF EN <NUM>-<NUM>, of at least <NUM> W/m. K, even of <NUM> W/m. K or more, or <NUM> W/m. K or more, e.g. <NUM> W/m. K or more, or even <NUM> W/m. K or more may be obtained. The low amounts of expanded graphite in the composition according to the present invention offers further advantages such as low additional dust generation and the ease of incorporation said graphite without excessive floating in aqueous medium. According to the invention, the composition comprises expanded graphite in an amount of at least <NUM>%w, the %w being based upon the weight of said hydraulic binder.

According to some embodiments, the composition may comprise expanded graphite in an amount of at least <NUM>%w, the %w being based upon the weight of said hydraulic binder.

The floor screed composition according to the present invention comprises expanded graphite preferably in an amount of from <NUM> to <NUM> weight% with respect to the weight of hydraulic binder. Compositions comprising expanded graphite in an amount of from <NUM> to <NUM> weight% with respect to the weight of hydraulic binder are particularly preferred.

The expanded graphite may have a specific BET surface ranging from <NUM> to <NUM><NUM>/g, e.g. about <NUM><NUM>/g.

The expanded graphite may have a bulk density (scott density) ranging from <NUM> to <NUM>/cm<NUM>, about <NUM>/cm<NUM>, measured by ASTM n° E <NUM>-<NUM> T.

According to the invention the expanded graphite has a mean particle size D50, as measured by laser diffraction, ranging from <NUM> to <NUM>.

The expanded graphite may have a mean particle size D50, as measured by laser diffraction, ranging from <NUM> to <NUM>.

The floor screed composition usually comprises aggregate, e.g. sand, and may comprise other additives such as plasticizers, anti-foaming agents, fluidizers, superplasticizers and dispersants, SiC, B<NUM>C and/or Al<NUM>O<NUM>.

According to the invention, the expanded graphite is present in an amount less than <NUM> %w, the %w being based upon the weight of said floor screed composition.

This weight percentage "X %w" of the expanded graphite means that X gram of expanded graphite is used per <NUM> gram of the floor screed composition in pourable form, i.e. ready to be used to provide the floor screed on the job site.

The floor screed composition according to the present invention comprises expanded graphite preferably in an amount less than <NUM> %w, the %w being based upon the weight of said floor screed composition. Floor screed comprising expanded graphite in an amount of from <NUM>,<NUM> to <NUM>,<NUM> weight%, such as in the range of <NUM>%w to <NUM>%w with said %w being based upon the weight of said floor screed composition are particularly preferred.

According to some embodiments, the floor screed composition may further comprise an anti foaming agent.

According to some embodiments, the anti foaming agent may be selected from silicone-based antifoaming agents, fatty acids, esters, polypropylene glycols, and combinations thereof.

The amount of anti foaming agent is preferably between <NUM> and <NUM>%w, and more preferred between <NUM> and <NUM>%w, the %w based upon the weight of said hydraulic binder.

According to some embodiments, the floor screed composition may further comprise fluidizing agents and/or dispersants and/or plasticizers and/ or superplasticizers.

The fluidizing agents and/or dispersants and/or plasticizers and/ or superplasticizers may be selected from sulfonated condensation products of formaldehyde and napthalene, sulfonated condensation products of formaldehyde and melamine, comb-branched copolymers having a backbone of acrylic and metacrylic acid, esterified with polycabroxylates or polyoxyalkylenes, such as polyoxyethylenes and combinations thereof.

The total amount of fluidizing agents and/or dispersants and/or plasticizers and/ or superplasticizers are is preferably between <NUM> and <NUM>%w, and more preferred between <NUM> and <NUM>%w, the %w based upon the weight of said hydraulic binder.

When fluidizing agents and/or dispersants and/or plasticizers and/ or superplasticizers are used, and an antifoaming agent is used, the weight ratio anti foaming agent over fluidizing agents and/or dispersants and/or plasticizers and/ or superplasticizers is between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

The floor screed composition is combined and mixed with water to form a suitable floor screed in wet state. After applying the wet floor screed, the screed cures and evaporates part of the water. The floor screed so obtained is in dry state. The weight ration of water/calcium sulphate is preferably between <NUM> and <NUM>, and more preferred between <NUM> and <NUM> such as between <NUM> and <NUM>.

According to a second aspect of the present invention, a floor screed composition according to the first aspect of the invention is used for the manufacture of a floor screed.

According to some embodiments, the floor screed being provided may have a thermal conductivity measured according to NF EN <NUM>-<NUM> of at least <NUM>,<NUM> W/mK.

According to some embodiments, the floor screed composition may further comprise aggregates.

According to a third aspect of the invention, a method to provide a floor screed composition is provided, the method being set out in claim <NUM>.

According to some embodiments, the addition of hydraulic binder and the expanded graphite may be performed in the presence of water.

According to some embodiments, at least part of the expanded graphite may be added to the hydraulic binder packed in a water soluble container.

This container can e.g. be a water soluble bag, e.g. a polyvinyl alcohol based bag.

According to some embodiments, at least part of the expanded graphite may be provided together with the water.

According to some embodiments, at least part of the expanded graphite may be provided together with the hydraulic binder.

The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent or other dependent claims, and/or with features set out in the description above and/or hereinafter as appropriate.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, which illustrate, by way of example, the principles of the invention.

The present invention will be described with respect to particular embodiments.

It is thus to be interpreted as specifying the presence of the stated features, steps or components as referred to, but does not preclude the presence or addition of one or more other features, steps or components, or groups thereof.

Throughout this specification, reference to "one embodiment" or "an embodiment" are made. Such references indicate that a particular feature, described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, though they could. Furthermore, the particular features or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art.

The following products were used for the preparation of the compositions in the examples :.

Table <NUM> summarizes the compositions of the mortars which have been prepared and tested as follows:.

Alter mixing the mortar is poured into two 14x16x4cm moulds.

The results in table <NUM> show that compositions comprising the expanded graphite at the same dosage level expressed in weight % with respect to the binder, give higher thermal conductivities.

Compositions <NUM>, 3a, 3b, 3c, 4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b and 6c are comparative compositions.

Claim 1:
Floor screed composition, said composition comprising a hydraulic binder which is calcium sulphate and expanded graphite, characterized in that the amount of expanded graphite is of at least <NUM>%w and less than <NUM> %w, the %w being based upon the weight of said hydraulic binder, the expanded graphite having a mean particle size D50, as measured by laser diffraction, ranging from <NUM> to <NUM>, wherein the expanded graphite is present in an amount less than <NUM> %w, the %w being based upon the weight of said floor screed composition.