Description

Field of the invention

This invention relates to synthetic sport surfaces, e.g. tennis courts, and, more specifically, to a multi-layer surface comprising an elastic, dampening layer. Background and related art

Many conventional outdoor sport surfaces, e.g. tennis courts, are comprised of asphalt pavement or concrete. However, these surfaces are not elastic and frequently cause injuries. Moreover, the material is degraded by the weather, ageing and other factors.

Natural clay tennis surfaces show a greater degree of elasticity, but they are difficult to install and to maintain, in particular in colder climates.

There also exist a variety of synthetic surfaces for both indoor and outdoor sports. For example, US 20080213538 A1 discloses that urethane foam laminated over a fill layer is used as a synthetic surface of sports grounds. The fill layer comprises a foaming synthetic resin such as foaming polyurethane (PU) having many air bubbles therein. However, a problem with air entrapped systems is that the surface of the synthetic pavement structure is often not uniform as any irregularities in the substrate surface are multiplied by the air-based foam systems. A further problem of foam-based systems is that they are susceptible to adhesion problems to an asphalt or concrete substrate.

US 20080213538 A1 describes the creation of a two-layer padded surface for tennis courts comprising a urethane-based top wear layer applied over a soft poured-in- place polyurethane elastomeric base (cushion) layer. The cushion layer is formulated as solid polyurethane that is relatively soft and that is mixed with SBR rubber granules. The granules are derived from recycled tires. The polyol ("A") component used for generating the polyurethane of the cushion layer comprises 5- 20 wt % castor oil. The use of castor oil in the given percentage range is used in PU generation for increasing the hydrolysis, heat and humidity resistance of the resulting PU.

US 4457120 A1 describes a floor pavement structure suitable for use in a tennis court. It comprises a customer layer made from liquid polyurethane mixed with rubber chips that is applied as foam.

W088/06971 A1 describes a synthetic sporting surface for tennis courts comprising a laminate of porous base layer formed from a matrix of liquid polyurethane mixed with resilient particles. Summary

It is an objective of the present invention to provide an improved floor pavement structure and a method for creating the same as specified in the independent claims. Embodiments of the invention are given in the dependent claims.

Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

In one aspect, the invention relates to a floor pavement structure. The structure comprises a top layer that seals the floor pavement structure and a PU gel layer. The PU gel layer is comprised of a solid and a liquid component between a base material and the top layer. The solid component is polyurethane polymer matrix. The liquid component is a plasticizer.

This may have the advantage that a high shock absorption rate of 20% and more can be achieved. Thus, very good balance of physical properties needed for the performance of a shock absorbing pavement, e.g. sports surfaces, can be achieved over a wide range of temperatures and a wide range of substrate materials. High shock absorption rates are required for many types of sports grounds, in particular tennis courts and running tracks.

It has been observed that the shock absorption rate of a PU polymer matrix soaked with a liquid plasticizer is higher than of a PU foam layer of similar height whose cells are filled with air. Likewise, in order to achieve a desired shock absorption rate, the height of the pavement structure may be reduced as the same absorption effect may be achievable with a lower volume of the shock absorbing material. This may reduce material costs and may be of particular value for indoor applications where spatial and building construction factors may impose a limit to the permissible height of a shock absorbing pavement structure.

In a further advantageous effect, the PU gel may have excellent self-levelling properties: due to the comparably high mass (in comparison to air-filled PU foams), the reaction mixture can penetrate fine cracks in the base material, fill these cracks and thereby smooth and level out any unevenness in the ground. It has been shown that air-filled PU foams often are too light to penetrate small cracks and to smooth uneven patches of the ground. In embodiments where the gel layer is not applied directly on the base material but rather on a primer layer, the improved fluidity and self-levelling properties may still be relevant as the primer layer may be thin and not be able to level out larger cracks and uneven patches.

The floor pavement structure can be, for example, a surfacing system for tennis courts, basketball courts, playgrounds, handball courts, soccer fields, rugby fields, baseball fields, and more. In some embodiments, the floor pavement structure is used as an outdoor pavement structures while in other embodiments it is used as an indoor pavement structure. According to some embodiments, the pavement structure is used as a pavement structure of parks, schools, and private homes. In particular, the floor pavement structure can be a synthetic surface, i.e. a surface that is completely or largely produced by humans rather than natural processes.

The floor pavement structure can be an indoor or outdoor pavement structure that is to be used as sports ground or playing ground. "To be used as sports ground or playing ground" as used herein means that the floor pavement structure is robust against mechanical stress typically imposed on the floor in a ball sports or running sports use case scenario. The PU gel layer is, according to embodiments of the invention, sufficiently thick as to make the whole pavement structure shock- absorbent and elastic, thereby protecting the joints of players.

According to embodiments, the plasticizer is a triglyceride or is comprised of one or more triglycerides by more than 50% of its weight. The triglyceride can be a mixture of multiple different triglycerides.

The triglycerides can comprise, for example, stearin derived from stearic acid, palmitin derived from palmitic acid, linseed oil (rich in di- and tri-unsaturated fatty acid components) and others. According to embodiments, the triglyceride is selected from a group comprising tristearate, tripalmitate, trioleate, trilinoleate, triricinoleate or a mixture of two or more of the foregoing.

A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (tri- + glyceride). The vegetable oil used as the plasticizer may consist of one or more triglycerides or may comprise the one or more Triglycerides are the major component. In triglycerides, the hydroxyl groups of the glycerol join the carboxyl groups of the fatty acid to form ester bonds.

Preferentially, the triglycerides are unsaturated triglycerides, e.g. unsaturated or polyunsaturated triglycerides derived e.g. from linoleic acid). Saturated fats are "saturated" with hydrogen - all available places where hydrogen atoms could be bonded to carbon atoms are occupied. Unsaturated fats have double bonds between some of the carbon atoms, reducing the number of places where hydrogen atoms can bond to carbon atoms. Using unsaturated triglycerides may be

advantageous as these triglycerides have a lower melting point and are more likely to be liquid at low temperatures.

According to embodiments, the plasticizer is a vegetable oil or a mixture of multiple different vegetable oils.

Using vegetable oil(s) as the plasticizer may have the advantage that the plasticizer may be comparatively cheap, may lower the carbon footprint of the product, may be biodegradable and compostable and may be non-toxic. In particular, vegetable oil plasticizers are free of substances such as polycyclic aromatic hydrocarbons (PAHs).

In some embodiments, the vegetable oil is extracted from plant material essentially without introducing chemical modifications. In other embodiments, the vegetable oil is chemically modified, e.g. for increasing the number of unsaturated carbon bonds and/or for adding one or more hydroxyl or amino groups and/or for replacing the glycerol component by another alcohol (in a transesterification reaction,

preferentially for replacing the glycerol by an alcohol comprising more than three carbon atoms in its "backbone"). Thus, in the transesterification reaction, glycerol is replaced by a Polyoxymethylene (POM) resin (also known as acetal, polyacetal and polyformaldehyd). For example, the POM resin can be

methylcyclohexanonformaldehyd resin.

According to embodiments, the plasticizer is a vegetable oil or a mixture of vegetable oils extracted from lin seed, from soy beans, from the seed from the nut of the tung tree (Vernicia fordii) and/or from the castor oil plant (Ricinus communis). In a preferred embodiment, at least one vegetable oil used as the plasticizer comprises at least one functional group in at least one of its fatty acid chains, whereby the functional group is able to react with isocyanate to covalently bind the vegetable oil molecule to the PU-polymer matrix of the gel layer. An example for such a plasticizer comprising one functional OH group in each of its three fatty acid chains is castor oil. Castor oil is a triglyceride ester of three monounsaturated 18 carbon fatty acid molecules, the ricinoleic acid molecules. This fatty acid has at the C-12 atom a hydroxyl function, which makes the reaction with an isocyanate possible. The plasticizer is added to the PU reaction mixture comprising the A- component and B-component before the PU polymerization has started or at least before the PU polymerization has completed.

Thus, at this stage, there exist many free isocyanate molecules which can react with the functional group, thereby generating a complex network of plasticizer molecules covalently bond via one or more of their functionalized groups to one or more PU polymer molecules.

Using a functionalized vegetable oil may be beneficial, as the PU polymerization reaction will create a highly complex network of covalent bonds between plasticizer molecules and PU polymers. Thus, a significant fraction of the plasticizer is immobilized and does not migrate out of the gel layer or in other portions within the gel layer in response to mechanical stress. Nevertheless, the plasticizer is still in liquid state and comprises sufficient elasticity and motility to provide for a gel layer that is highly elastic.

According to embodiments, the vegetable oil used as the plasticizer comprises a mixture of functionalized and non-functionalized oils. In some plant species, the majority of unsaturated fatty acids forming part of the plant's vegetable oil(s) comprises one or more functional groups and the majority of completely saturated fatty acids forming part of a plant oil is free of a functional group that can react with the isocyanate component. Thus, at least the portion of the vegetable oils that exclusively comprise nonfunctionalized fatty acids are not covalently bound to the PU matrix and can move freely within the volume of the one or more PU matrix cells in which they reside. According to preferred embodiments, more than 60%, preferentially more than 90% of the plasticizer molecules added to the PU reaction mixture that forms the gel layer comprises at least one functional group that is able to react with isocyanate.

The three fatty acids are usually different, and many kinds of triglycerides are known. The chain lengths of the fatty acids in naturally occurring triglycerides vary, but most contain 16, 18, or 20 carbon atoms.

According to embodiments, the vegetable oil contains a complex mixture of different triglycerides, in particular a mixture of saturated and unsaturated triglycerides. This may be advantageous as vegetable oils comprising a mixture of different

triglycerides melt over a broad range of temperatures. This may provide for a pavement structure whose elasticity is comparatively constant over a wide temperature range.

According to embodiments, more than 50% by weight of the vegetable oil consists of unsaturated triglycerides. In a preferred embodiment, vegetable oils having more than 50% unsaturated fatty acids are used as the plasticizer. A fatty acid comprising at least one unsaturated carbon bond is considered an "unsaturated" carbon acid and a triglyceride comprising at least one unsaturated fatty acid is referred herein as "unsaturated triglyceride". For example, cottonseed oil having typically 52% polyunsaturated fatty acids and 18% monounsaturated fatty acids can be used as the plasticizer. According to another example, soy bean oil comprises about 84% unsaturated, functionalized oils and about 16 % saturated, nonfunctionalized oils. Accordingly, at least 6% of a soy bean oil based plasticizer will not react with isocyanate and will not be immobilized.

In other embodiments, vegetable oils like soy bean oil, linseed oil or castor oil are chemically converted to achieve a higher degree of unsaturation. The unsaturated conversion products are optionally functionalized, i.e., one or more hydroxyl or amino groups are added to the fatty acid chains of the oil. The converted and optionally functionalized vegetable oils are then used as the plasticizer. According to embodiments, about 55% to 65%, e.g., about 60 % by weight of the gel layer consists of the plasticizer; the rest consists of the PU polymer matrix and optional further substances, e.g. additives. According to embodiments, the floor pavement structure further comprises a barrier layer between the gel layer and the top layer. The barrier layer is adapted to prevent the plasticizer from leaving the gel layer in the direction from the base layer to the top layer. Using a barrier layer may be advantageous as the life expectancy of the pavement structure may be increased. The barrier layer may prevent the plasticizer from leaving the gel layer and thus prevent the gel layer from becoming brittle and less elastic. Thus, the shock absorbing properties of the gel layer may be maintained over many years also under extreme conditions like extreme low temperatures in winter and direct sunlight and high temperatures in summer.

Plasticizers can become available for exposure due to migration and abrasion of the polymer matrix since all or some of the plasticizer molecules are not bound to the polymer matrix. Using a barrier layer may have the further advantage of preventing the newly installed pavement structure from smelling of oil. According to embodiments, the barrier layer is a layer of synthetic resin. The barrier layer comprises an amount of more than 40% of a water based acrylic at the moment of applying the layer onto the gel layer. When the water has evaporated from the barrier layer, the acrylic fraction of the barrier layer may exceed 80% by weight of the barrier layer. "Synthetic resins" as used herein are viscous liquids that are capable of hardening permanently. Some are manufactured by esterification or soaping of organic compounds. Some are thermosetting plastics in which the term "resin" is loosely applied to the reactant or product, or both. For example, liquid methyl methacrylate is often used as a synthetic resin while it is in the liquid state, before it polymerizes and "sets". After setting, the resulting PMMA is the "hardened resin", often renamed acrylic glass, or "acrylic" layer. According to some embodiments, the synthetic resin is epoxy resin, PU resin or polyester resin

According to embodiments, the barrier layer comprises a compatibilizer adapted to promote adhesion of the top layer to the gel layer. For example, the top layer can be an acrylic latex layer, a styrolbutadien layer or a layer that is based on a combination of acrylic latex and carboxylated styrolbutadien. The top layer can comprise a significant portion (e.g. more than 40% or even more than 60% of its weight) filling materials such as sand and/or chalk which improve the surface roughness and the grip but which may deteriorate the adhesion to the PU based gel layer. The compatibilizer can be, for example, ethylene glycol which promotes adhesion between acrylate and PU. The ethylene glycol is comprised in the barrier layer in an amount of at least 0.5%, preferentially about 1 % by weight of the barrier layer.

According to embodiments, a pavement structure is a basically planar, multi-layered flooring. In some example implementation, it is a screed, in particular a screed for a sports field or a playground.

According to embodiments, more than 40% by weight of the barrier and the top layer consists of acrylic latex, styrolbutadien or a combination of acrylic latex and carboxylated styrolbutadien. Using a barrier layer that comprises a compatibilizer may be advantageous as the compatibilizer may prevent a delaminization of the gel layer and the top layer. For example, the top layer can be hydrophilic and the gel layer is typically hydrophobic. By using a compatibilizer that is capable of strongly adhering both to hydrophobic and to hydrophilic substances, a delamination of the gel layer and the top layer may be prevented. Thus, the life expectancy of the pavement layer structure may be increased.

According to embodiments, the method further comprises a primer layer between the base material and the gel layer. The primer layer is adapted to promote adhesion of the gel layer to the base material. According to embodiments, the primer layer is a layer of at least one coat of synthetic resin and comprises an acrylic primer. The synthetic resin can be, in particular, an acrylic resin or an epoxy resin polymer.

According to a preferred embodiment, the primer layer is a polyurethane layer that is basically free of the plasticizer and a compatibilizer (as the gel layer comprises a PU matrix, a compatibilizer is not necessary). Preferentially, the A and B components of the primer layer PU are chosen such that the PU is a non-foamed PU that can be sprayed or painted on the ground. The primer layer may improve the adhesion of the PU based gel layer to the ground.

Using a primer layer may have the advantage that the primer will seal and fill in cracks of the base material. According to embodiments, the top layer is an acrylic emulsion comprising pigments and sand.

This may be advantageous as the sand gives the surface of the material the rough feel and touch of a sandy court, e.g. a tennis court, whereby the sand grains are firmly fixed in the hardened acrylic emulsion of the top layer. According to

embodiments, multiple layers of the top layer may be applied. This may increase the amount of sand added to the pavement structure and may increase the surface roughness, grip and robustness of the pavement structure.

According to embodiments, the pavement structure comprises only one or more coatings of the primer layer, the gel layer, the barrier layer and one or more coatings of the top layer. In addition or alternatively, the pavement structure is basically free of any air-filled foams or air-filled layers comprising elastic granules (e.g. rubber granules). This may be advantageous as it has been observed that pavement structures comprising an air-filled layer with elastic granules may be more susceptible to wear and tear by mechanical stress than pavement structures comprising only a gel layer as elastic element. As a given volume of air (e.g. in a PU polymer bubble or in the inter-granule space of a rubber granule layer) is

compressed much stronger by a given pressure than a liquid, e.g. oil, the

mechanical deformation of the PU foam and of any layer contacting the air-filled PU foam layer may be much higher in case the elastic layer comprises air rather than oil. This may result in an increased wear and tear of pavement structures

comprising an air-filled elastic layer rather than oil-filled elastic layer.

The base material can be comprised of e.g. concrete, asphalt, sand, stone, wood, clay or a mixture of two or more of the foregoing.

According to embodiments, the top layer has a height of 0.1 mm - 2 mm, preferably a height of 0.2 mm-1.0 mm, more preferably a height of 0.4 mm - 0.5 mm. According to said or other embodiments, the barrier layer has a height of 5μιτι - 300pm, preferably a height of 20pm-200pm, more preferably a height of 50 pm - 100 pm. This may be advantageous as this layer thickness may successfully prevent the oil in the gel from evaporating and leaving the surface structure in direction of the top layer.

According to said or other embodiments, the gel layer has a height of 1 mm - 4 mm, preferably a height of 1.5 mm - 3.5 mm, more preferably a height of about 2 mm. This may be advantageous as this layer thickness may be sufficient to provide a shock absorption effect required for many types of sports grounds, e.g. a tennis court.

According to said or other embodiments, the primer layer has a height of 5pm- 500pm, preferably a height of 50 pm-300 pm, more preferably a height of 100 pm - 150 pm.

According to embodiments, the gel layer has a height of at least 1 mm, preferably a height of at least 1.5 mm.

According to a further embodiment, the top layer is a polyurethane layer comprising EPDM granules. According to some embodiments, the pavement structure comprising the PL) layer lacks a barrier layer as the PU layer adheres very well to the PU matrix of the gel layer without an additional barrier layer that prevents delamination of the top layer. It has been observed that plasticizer that migrates to the top of the base layer may not only diminish the elasticity of the gel layer, but also increase the risk of a delamination of the top layer. Thus, the use of a barrier layer was observed to prevent delamination of the top layer by preventing migration of the plasticizer. In case a PU layer is used inbetween the gel layer and the top layer, the plasticizer may migrate to the top layer, but is not able to leave the top layer in direction of the upper surface of the layered structure because the top layer can be a sealing layer that prevents water as well as the plasticizer from penetrating and crossing the top layer. Thus, in some embodiments, the top layer directly contacts the gel layer. Preferentially, according to this embodiment, the PU of the top layer is a non-foamed, latex-like layer that acts as a barrier that prevents the plasticizer from leaving the gel layer in direction of the top layer. For example, the EPDM granules can have a diameter in the range of 0.5 mm to 4 mm, preferentially in the range of 0.5 mm to 2.5 mm.

In a further aspect, the invention relates to a method of constructing a floor pavement structure. The method comprises:

- applying a PU reaction mixture comprising a plasticizer on top of a base material;

- letting the applied reaction mixture form a PU gel layer comprising a solid

component and a liquid component, the solid component being polyurethane polymer matrix, the liquid component being the plasticizer; and

- after the formation of the PU gel layer, applying a top layer that seals the floor pavement structure on top of the PU gel layer.

The expression "applying a layer on top of another layer" as used herein does not imply that the applied layer is necessarily directly applied on the other layer. The applied layer can be applied directly on said other layer but can also be applied on a further layer, e.g. the barrier layer, that is on top of the other layer.

According to embodiments, the method further comprises:

- applying a primer layer on the base material;

- optionally, before the primer has dried, applying silica sand or other forms of granules having the size of silica sand on the primer layer for increasing the surface roughness of the primer layer;

- after the primer layer has dried, performing the application of the PU reaction mixture on top of the primer layer.

According to embodiments, the method further comprises applying a barrier layer on top of the gel layer after the applied reaction mixture has finished forming the PU gel layer. In addition, the method comprises applying the top layer on top of the barrier layer after the barrier layer has solidified.

According to embodiments, the plasticizer is a chemical derivative of vegetable oil. The method further comprises generating the plasticizer. According to one embodiment, the plasticizer is generated by chemically increasing the number of unsaturated carbon bonds in the fatty acids of the vegetable oils. This may have the benefit of a reduced melting temperature and liquid state of the plasticizer over a wide temperature range. In addition, or alternatively, the fatty acids in the vegetable oils are chemically functionalized by adding at least one hydroxyl group and/or at least one amino group to at least one of the fatty acid chains of the vegetable oil. This may have the benefit that a significant portion of the plasticizer can be immobilized as it reacts with the isocyanate monomers in the PU reaction mixture that is used for generating the PU polymer matrix of the gel layer.

According to embodiments, the plasticizer is a chemical derivative of a vegetable oil. The method further comprises generating the plasticizer. The generation comprises reacting a plurality of triglyceride molecules in a transesterification reaction into poly- ester molecules, the poly ester molecules respectively comprising at least three fatty acids. In the transesterification reaction the glycerol of the triglyceride molecules is replaced another alcohol backbone having a carbon atom chain that is longer than the carbon atom backbone chain of glycerol. The poly-ester molecules generated in the transesterification reaction are used as the plasticizer or as a component of the plasticizer. For example, octantriol is an alcohol comprising three hydroxyl-groups whose carbon atom backbone (4 carbon atoms) is longer than that of glycerol (3 carbon atoms).

Replacing the glycerol by another alcohol having a longer carbon atom backbone (or "main chain" and being able to bind four or more fatty acids (via ester bonds) may be advantageous as a large, complex oil molecule is generated that may comprise multiple fatty acid side chains which can bind (via one or more

functionalized groups) to the PU matrix. Thus, a highly complex PU-plasticizer polymer structure is generated that immobilizes at least parts of the plasticizer and increases the elasticity of the gel layer. Even in case the number of bound fatty acids per oil molecule remains constant, a prolonged "alcohol backbone" may increase the flexibility of the fatty acids and thus ease the creation of covalent bonds between the functionalized fatty acids and the PU matrix.

A "PU gel" as used herein is an elastic, jelly-like polyurethane material that comprises a liquid. It can be a dilute cross-linked system, which exhibits basically no flow when in the steady-state. By weight, a gel is mostly liquid, yet behaves like a solid due to a three-dimensional cross-linked network of PU polymer cells within the liquid. It is the cross-linking within the fluid that gives a gel its structure (hardness) and contributes to the adhesive stick (tack). Thus, a gel is a dispersion of molecules of a liquid, within a solid network of PU cells in which the solid is the continuous phase and the liquid is the discontinuous phase. The liquid used for providing the gel-like properties of the PU gel layer is a "softening agent". A "softening agent" or "softener" may "soften" the gel, i.e., makes the gel elastic. The softening agent is also referred to as "plasticizer". The gel can consist of a solid three-dimensional network that spans the volume of the whole gel layer and ensnares it through surface tension effects. This internal network structure may result from chemical bonds, i.e., may be caused by the polymerization reaction that creates the PU in an on-site PU polymerization process. According to embodiments, vegetable oils are used as "softening agents" and "plasticizers". The resulting gel is thus an oil-based gel. Both by weight and volume, the gel thus may exhibit densities similar to those of the vegetable oil used for its creation.

Polyurethanes are produced by mixing two or more liquid streams (or "liquid components"), a polyol stream (also referred to as Έ component') and the

isocyanate stream (also referred herein as Ά component'). According to

embodiments, the polyol stream contains catalysts, surfactants, blowing agents and so on. This mixture might also be called a 'resin' or 'resin blend' or 'reaction mixture'. The reaction mixture may further comprise chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers. A "softening agent" or "softener" as used herein is a substance that is added to another substance to increase softness.

A "plasticizer" as used herein is a substance that increases the plasticity or viscosity of a material. Plasticizers for plastics are additives, most commonly phthalate esters in PVC applications giving this material improved flexibility and durability. The wide variety of ester plasticizer that are in production include sebacates, adipates, terephthalates, dibenzoates, gluterates, phthalates, azelates, and other specialty blends. Nevertheless, embodiments of the invention use vegetable oils as

plasticizers. A "vegetable oil" as used herein is a natural, plant-based oil.

Using vegetable oils may have the advantage of using a bio-degradable, non-toxic material.

Brief description of the drawings In the following, embodiments of the invention are explained in greater detail, by way of example only, making reference to the following drawings:

Fig. 1 is a flow chart of a method for constructing a multi-layer pavement

structure according to an embodiment of the invention. Fig. 2 depicts a multi-layer pavement structure according to an embodiment of the invention.

Fig. 3 depicts a multi-layer pavement structure according to a further

embodiment.

Fig. 1 is a flow chart of a method for constructing a pavement structure 200 as depicted, for example, in Fig. 2. In the following, a method for constructing a pavement structure and the corresponding pavement structure will be described together, thereby making reference to figures 1 and 2.

In a first step 102, a person or a machine applies a PU reaction mixture on top of a base material 210, e.g. a concrete floor. The PU reaction mixture comprises a plasticizer 214. The PU reaction mixture is applied directly on the base material or can be applied on a primer layer 208 that was applied on the base material before and has already hardened. The applied reaction mixture is allowed to form in step 104 a PU gel layer 206. The PU gel layer comprises a solid component and a liquid component. The solid component 212 is a matrix of cells made of polyurethane polymers. The liquid component is the plasticizer. For example, a composition of vegetable oils is used as the plasticizer, whereby the composition of the oils is chosen such that the oils remain liquid over a broad temperature range.

Preferentially, the typical temperature range of the geographic region where the pavement structure is constructed is taken into account. For example, the composition of the vegetable oils is chosen such that the fraction of unsaturated oils negatively correlates with the temperature: the lower the temperature, the higher the fraction of unsaturated vegetable oils for ensuring that the oils remain liquid. After the formation of the PU gel layer has completed, a top layer 201 is applied in step 106 on top of the PU gel layer 206. The top layer seals the floor pavement structure on top of the PU gel layer, thereby preventing rain from penetrating the structure 200. Thus, according to embodiments, the top layer is a sealing layer that makes the floor structure water- and other liquid-impenetrable and resistant. Thus, the top layer may protect the floor structure against rain. Optionally, before the primer has dried, silica sand or other forms of granules having the size of silica sand is applied on the primer layer for increasing the surface roughness of the primer layer. After the primer layer has dried, the PL ⁾ reaction mixture is applied on top of the primer layer as described above for embodiments of the invention.

Preferentially, a barrier layer 202 is applied on top of the gel layer when the applied reaction mixture has finished forming the PU gel layer. The application of the top layer comprises: after the barrier layer has solidified, applying the top layer 201 on top of the barrier layer. According to some embodiments, the substances used for generating the pavement structure are provided in the form of a sports surfacing system that can be customized to different temperature ranges, different appearance and different use case scenarios.

For example, the top layer is a 100% acrylic emulsion consisting of pigments and PU polymers that are blended into a highly concentrated form that is highly wear resistant.

A more concrete example of a possible composition of the barrier layer and the top layer is given below.

When the barrier layer has dried and the water (including the water of the acrylic latex solution and of the additives, if any) has evaporated, the barrier layer comprises acrylic latex in an amount of more than 70 % by its weight. It strongly adheres to the polyurethane matrix of the gel layer.

Top layer composition (liquid state) Acrylic latex solution (dry matter: 60%) 22 %

Water 2 %

Chalk 34 %

Thickener (Xanthan Gum) 9 %

Further additives (fungicides, etc.) 4 %

When the top layer has dried and the water has evaporated, the major weight component of the top layer may consist of the filler material (chalk). In particular, in case the top layer comprises sand in addition to chalk, the top layer may comprise sand and chalk in an amount of more than 60 % by its weight. Thus, the fraction of acrylic latex in the top layer is comparatively small. Nevertheless, as the top layer is preferentially applied not directly on the gel layer but rather on the barrier layer with the compatibilizer, it is ensured that the top layer does not delaminate.

The primer layer can comprise, for example, about 65 % of a PL ⁾ prepolymer, about 25% of solvent naphtha (Mixtures of light aromatic hydrocarbons obtained from coal tar or petroleum) and about 0% of Propylene glycol methyl ether acetate (PGMEA, 1 -methoxy-2-propanol acetate) (an adhesive).

For instance, the primer is applied to asphalt, clay or properly prepared concrete.

The generated pavement structured is a resilient, multi-layered application designed to give added comfort and cushioning for an enjoyable playing experience. According to some embodiments (not shown), the pavement structures comprises EPDM (ethylen-propylen-dien) rubber particles application designed to increase shock-absorbing properties of the structure for. Preferentially, the EPDM rubber particles are embedded in a top layer that consists of non-foamed polyurethane that is directly applied onto the gel layer. Before the surfacing system is applied the base material, e.g. concrete or asphalt, needs to be prepared properly, e.g. must be cleaned from dust and moisture.

Asphalt and concrete substrates shall be allowed to cure a minimum of 30 days before application of any coatings. The primer can be applied to 5- day old concrete substrates. The base material shall be clean and dry before the different layers are applied. The surface of the substrate shall be inspected and made sure to be free of grease, oil, dust, dirt and other foreign matter before any coatings are applied.

Preferentially, the surface and air temperatures should be at least 50°F ( 0°C) and rising for applying the individual layers. Once the surface has been thoroughly cleaned and is free of all loose material, dirt, or dust, the court shall be flooded and allowed to drain a minimum of 30 minutes and a maximum of 1 hour. Any area that holds water in depth greater than 1/15 inch shall be outlined and patched with the primer.

According to embodiments, the primer is mixed by pouring the "B" component into the "A" component (B and A components refer to the isocyanate and polyol components of a PU reaction mixture) and mixing using a low speed jiffy mixer (400 to 600 rpm) for 2 minutes. The mixed primer is applied on the base material using a medium nap roller to achieve a total coverage of approximately 0.0 30 gal/yd 2 (0.15 kg/m 2 - 300 ft 2 /gal). Optionally, 40 to 60 mesh silica sand is applied onto the wet primer at the rate of 5 pounds per 100 sq. ft. (0.24 kg/m 2) to create e a rough texture. Allow 5 to 6 hours drying time before proceeding with applying additional layers on top of the primer layer.

According to some embodiments, the polyurethane reaction mixture comprising the liquid plasticizer is applied to a ground in one or more lanes using a vehicle. The polyurethane reaction mixture can be applied directly on the ground or can be applied on top of a primer layer that has been applied previously to seal the ground.

In case multiple lanes of the gel layer are applied, the lanes are arranged adjacent to each other and a side edge of a first lane is in contact with a side edge of an adjacent second lane of the reaction mixture that generates a PU polymer matrix soaked with the plasticizer as the PU gel layer.

According to embodiments, the PU reaction mixture that is applied on top of the base materials (or the primer layer) is generated in a method comprising providing polyurethane reactive components and the plasticizer. The reactive components comprise a isocyanate component and a polyol component.

- mixing the polyurethane reactive components; the reactive components and/or the composition of the plasticizer can chosen in dependence on environmental parameters, e.g. the typical temperature range at the installation site; - mixing the isocyanate component and the polyol component and the liquid plasticizer; for example, a mixing unit of the vehicle can be used for the mixing step,

- applying one or more lanes of the reaction mixture comprising the plasticizer to a ground using an application unit connected to the mixing unit.

Alternatively, the mixing and application can be performed manually.

In case multiple lanes are applied, a side edge of the second lane gets in contact with a side edge of the first lane. The process parameters for mixing the

polyurethane reactive components are determined so that the PU gel layer and its PU polymer matrix of the first lane is not cured before applying the foam of the second lane.

The curing time of the polyurethane (PU) matrix ( may depend on various

conditions: in particular the environmental conditions. For example, high

temperatures, direct sunlight or low relative humidity may accelerate the curing process.

The plasticizer is preferentially incorporated into the cells of the forming PU polymer matrix by whisking the liquid plasticizer into the polyurethane reaction mixture or into one of the components of the reaction mixture, e.g. the polyol component. In an embodiment the cellular polyurethane polymer matrix is generated by the oscillation of a tube or pipe reactor fed with the PU mass and the liquid plasticizer and compression and expansion effects are achieved by the oscillation of the tube. The tube is constructed such that air is prohibited from filling the PU matrix cells.

In an embodiment the used PU formulation comprises an MDI based NCO terminal prepolymer, produced from an isomeric mixture of 2,4'; 4,4' and 2,2' MDI monomer based prepolymer with an NCO content of 1.5- 8 weight % with 2,2 MDI between 1 and 40%. The preferred polyol being either standard or endcapped, activated polyether polyols like polypropylene glycol of the average molecular weight ranging from 100 up to 6000. In a very preferred embodiment, a high molecular weight primary hydroxyl terminated diol of the molecular weight 2000- 4000 with

hydroxylnumbers of 25-60 mg KOH/g is used to produce the NCO terminal prepolymer. As hydroxyl-terminal component a branched castor oil based polyol can be used, which typically is generated by a thermal and enzymatic transesterification process reacting with a ketone resin. Reactivity may be adjusted by using typically suitable metal-organic catalyst like e.g. dibutyltin or dilaurate.

In another embodiment the NCO terminal prepolymer and the OH terminal polyol are chilled at 10 - 25 °C and pumped in a prefixed ratio through a static mixer, transported to a mixing unit - as e.g. the aforementioned oscillating reaction pipe.

To avoid undesired excessive foaming a water-adsorbing additive like a zeolite or any other molecular sieve or desiccant can be used. In an embodiment the desiccant can have a pore size of 3-5 angstrom and is used in the range of 0, 1 - 3 weight % of the polyol weight, in a very preferred embodiment between 0,5 - 2% of the polyol weight.

In order to improve the controlling of the curing time, additional polyurethane forming ingredients may be added to the reaction mixture. The type and the quantity of the polyurethane forming ingredients depends e.g. on measured environmental data or on the type of plasticizer used. The additional polyurethane forming ingredients may include one or more of the following: additives, frothing agents or other known additives for polyurethane floorings.

Preferentially, the components of the PU reaction mixture are chosen such that the generated PU polymer matrix cells more or less completely encapsulate the liquid plasticizer contained in the cells. Thereby, the totality of PU polymer cells largely prevent the plasticizers to escape to other cells or into an inter-cellular space when mechanical pressure is applied on the gel layer.

The produced PU polymer matrix may be stabilized by a silicone high sheer foam stabilizer enhancing cell stabilization at polymer matrix densities (without the plasticizer) of 200- 400 kg/m ³ , preferably100- 600 kg/m ³ . In an embodiment the silicone stabilizer is used at 0,1 % - 4 weight % , preferably between 1 % and 2 %. Furthermore, diverse pigments and fillers can be used like calcium carbonate, bentonite to stabilize the foam further and strengthen its structure.

In an embodiment, the gel layer may render high elastomeric resilience and good damping properties (achieving a shock absorbance of e.g. > 40% at temperatures of 15°C). According to embodiments, the position and/or the speed of a vehicle for applying the foam to the ground may be measured and the process parameters and the type and the quantity of PU gel layer forming ingredients are adjusted depending on the position and the speed of the vehicle.

Figure 3 depicts a pavement structure according to a further embodiment. The pavement layer comprises the layers described already for embodiments of the invention, in particular the embodiments depicted in figure 2. In addition, the pavement structure comprises a further layer 302 referred herein as "structure layer". The structure layer preferentially has a thickness of 100 pm-2500 pm, 400 μιη-1500 pm, 800 pm to 1200 pm, e.g. 1000 pm. The structure layer is located between the gel layer and the top layer or between the gel layer and the barrier layer, if any. The structure layer is a further polyurethane layer. Preferably, the polyurethane in the PL ⁾ layer is a none-foamed or moderately foamed PU layer. For example, the PU of the structure layer can have a density of about 1.0 to 1 .1 g/cm ³ . The structure layer may improve the structural stability of the pavement structure by ensuring that any mechanical pressure is distributed evenly on the gel layer. Thus, the structure layer may prevent the gel layer from being damaged by a high mechanical pressure applied to a single small spot.

According to one embodiment, the plasticizer is a derivative of one or more vegetable oils. For example, the plasticizer can comprise or consist of(mixed) triglyceride molecules comprising three different fatty acid chains: monounsaturated oleic acid, di-unsaturated linoleic acid and tri-unsaturated alpha-linoleic acid. A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other animals, as well as vegetable fat. They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver, and are a major component of human skin oils. The triglyceride can comprise a carbon atom backbone consisting e.g. of three carbon atoms.

Preferably, the backbone comprises four, five or more than 10 carbon atoms. A longer carbon atom backbone may have the advantage that a larger number of fatty acids can be bound to the backbone. Preferably, at least four fatty acid chains are covalently linked to the backbone. Thus, a high-molecular but nevertheless highly flexible macro molecule is provided that can be covalently linked to the PU matrix of only one of its fatty acid chains comprises a functional group, e.g. an -OH or -NH2 group that reacts with the isocyanate component in the PU reaction mixture. Using vegetable oils may have the advantage that many vegetable oils contain a complex mixture of individual triglycerides. Because of this, they melt over a broad range of temperatures. For example, linseed oil can be used as plasticizer. It comprises triply unsaturated a-linolenic acid (51.9-55.2%), saturated acids palmitic acid (about 7%) and stearic acid (3.4-4.6%), monounsaturated oleic acid (18.5- 22.6%), and doubly unsaturated linoleic acid (14.2-17%).

When the polyurethane reaction mixture is generated, the mixture comprises an isocyanate component, a polyol component, and a liquid plasticizer generated as a derivative of one or more vegetable oils described above. At least the isocyanate component and the polyol component react with each other to form a solid component of the gel. Optionally, also functional groups of one or more fatty acid chains of the vegetable oils react with the isocyanate component to form the solid component 212. The solid component is a polyurethane polymer matrix. The liquid plasticizer is comprised in cells of the polyurethane polymer matrix. Depending on the reaction conditions, the majority of the cells may be closed or may be connected with one or more neighboring cells via openings that allow the plasticizer molecules that are not covalently bound to the matrix to migrate from one cell to the next, e.g. in response to mechanical stress exerted on the gel.

List of reference numerals

102 step

104 step

106 step

200 pavement structure

201 top layer

202 barrier layer

206 gel layer

208 primer layer

210 base material

212 solid PU polymer matrix

214 liquid vegetable oil

302 structure layer