Decorative panel with a synchronised structure and the method of its production

The invention relates to a decorative panel with a synchronised pattern structure and a method of production of decorative panels with a synchronised pattern structure which could be applied as a decorative panel, especially for flooring.

A method of production and a floorboard bearing a relief made, whereby a curable substance is printed over a panel and then a curing agent is printed over a pattern thus created to form a convexity on the pattern over the panel and then a mixture of the curable liquid and the curing agent undergoes curing, is known from European Patent No. EP 2542426. A raised surface with a relief is obtained that reproduces, for example, a wood grain pattern. The process of production of such boards is complex, and their size is restricted by printer dimensions.

A rigid floorboard made of plastic such as PVC having a decorative layer made of plastic and a wear layer made of a transparent polymer material such as PP, PE, PVC, PET, ABS, PC, POM, PMMA, PS, PEEK, PTFE, PVDF, etc., with all layers being bonded by hot pressing at a specified temperature and pressure, is known from patent description US2017144409.

Application WO 2010/023042 relates to a panel whose load-bearing layer comprises a material that is flexible at the operating temperature of the floor, a decorative layer, additional mechanical interlocking mechanisms positioned on at least two edges of the panel, with the said interlocking mechanisms ensuring securing the interlocked state of two floor panels.

Application WO9731775A1 relates to a method of production of decorative laminated panels, whereby the decorations show, for example wood or minerals such as marble or granite, having a structured surface that captures the characteristic features of the pattern. This method is characterised by a decorative paper layer being impregnated with melamine-formaldehyde resin and applied onto the core, whereupon a surface structure is derived on this decorative layer through high-pressure pressing by means of a matrix and during pressing the thermosetting resin is cured, whereby the desired concave -convex structure is rendered. In this process, the matrix is carefully placed on top of the decorative paper before pressing and is separated from the resultant laminate after pressing, whereby the laminate is imparted with a decorative surface structure corresponding to the decor.

The purpose of the invention was a method of production of long decorative panels, especially flooring panels, with a synchronised surface structure, and a decorative panel made with this method.

The decorative panel, especially the flooring panel, according to the invention of not less than 2,110 mm in length, takes the form of a rectangular multilayer laminate, which comprises a core made of plastic, in particular of PVC, a decorative layer and a protective layer, whereas in the other variants of the invention the decorative panel may additionally have:

• a wear layer;

• a sound damping layer; and

• a grooved structure on the underside of the panel.

The outer surface of the decorative panel has a synchronised surface structure in a decor of the decorative layer. In a preferred method of production, the core of the decorative panel is made of PVC; yet it is also possible to use other plastics such as PP, PE, PET, ABS, PC, PU, POM, PMMA, PS, PEEK, PTFE, PVDF and their derivatives and copolymers as well as their mixtures, whereby it is preferable to use polymers with the addition of mineral fillers in the quantity by weight of 60- 90%, optimally 65-80%.

The decorative layer is made of either a printed PVC film or a polymer selected from among the group of PET, PE, PP, PU, PC and PTFE or paper and features a decorative pattern. The thickness of the decorative layer should preferably range from 0.05 to 1 mm and is generally chosen according to the type of the printing technique employed to produce the decorative pattern.

The protective layer is a varnish that protects against scratches or mechanical damages of the surface. The preferred varnish varieties are acrylic and polyurethane varnishes. It is preferable to use the varnish in a quantity ranging from 10 to 200 g/m ² . Once cured, the varnish should have a scratch resistance of > 15 N, preferably > 23 N.

The synchronised structure can be embossed in either the decorative layer or the wear layer or in both layers. Relative to the printing technique employed to make the pattern on the decorative layer, the structure can be embossed in the decorative layer or in the surface of the core. Rotogravure printing allows for the decorative layer to have the thickness of 0.05 to 1 mm and then the structure can be embossed in the decorative layer. In the case of digital printing, the decorative layer can be very thin, i.e. from 0.05-0. 1 mm, wherein the structure is embossed in the surface of the core; in the latter case, it is preferable for the size of the fdler grain in the core to be below 50% than the thickness of the decorative layer.

In a preferable variant, especially in the case of a decorative panel used as a flooring panel, the panel according to the invention comprises a wear layer placed between the decorative layer and the protective varnish. The wear layer is made of PVC or another polymer selected from among the group of PP, PE, PET, ABS, PC, PU, POM, PMMA, PS, PEEK, PTFE and PVDF. The wear layer should preferably have a thickness of 0.10 - 1.00 mm. It is preferable for the tensile strength of the wear layer to be > 10 MPa, most preferably > 20 MPa, whereas elongation at break should be > 100%, most preferably > 200%.

The decorative panel has the width of 150 to 1,300 mm and depending on its intended use can either come in a straight-edged variety or be fitted with especially shaped coupling elements designed to securely join adjacent panels.

Preferably, at least two opposite edges have a coupling system.

In a preferable variant, the panel, especially used as a flooring panel, is additionally fitted with a soundproofing mat on its underside to increase sound insulation.

In another preferable variant, the panel, especially used as a flooring panel, is additionally fitted with athermal insulation mat on its underside.

In another preferable variant, the panel, especially used as a flooring panel, is additionally fitted with athermal conductive mat on its underside.

In another preferable variant, the panel, especially used as a flooring panel, is additionally fitted with a base surface levelling mat and/or a mechanical impact attenuation mat.

The individual layers that compose the panel are bonded together in a thermal lamination process during which the outer structure of the panel surface is also made.

In the basic variant, the structure is embossed in the decorative layer or in the surface of the core. If the decorative layer is thin, and this is especially the case for digital printing of the decorative pattern, it is preferable for the grain size of the core filler to be maximum 50% of the thickness of the decorative layer, which allows application of the structure with a very high degree of accuracy.

If the panel comprises the wear layer, the structure is embossed in the wear layer, or in both, the wear and decorative layers. The decorative panel used as a flooring panel according to the invention should preferably have the thickness of 2.00 - 8.00 mm, and its density is within range 1,200 - 2,500 kg/m ³ , preferably -2000 kg/m ³ . Furthermore, its hardness is within range 60-80° Shore D, whereby it is preferable that hardness is -70° Shore D.

The second aspect of the invention is the method of production of a decorative panel.

The method of production of the decorative panels according to the invention comprises the following essential steps:

• extrusion of a core ribbon;

• its subsequent shuttling to the packaging -pressure roller (K4) with the successive addition of: o the decorative layer, predominantly in the form of a film; and o the wear layer, predominantly in the form of a film,

• whereby, the core ribbon, together with the decorative and wear layers attached into the surface of the core ribbon, passes through the gap between the two rollers, the pressure roller (K4) and the embossing roller (K5) that has an engraved synchronous structure, and undergoes initial cooling on the roller;

• whereby, the ribbon travels on the receiver conveyor where the ribbon undergoes final cooling and levelling; and

• further, it is divided into respective sections and widths of the finished product.

The process of imprinting the structure in the surface of the panel has two steps. Figure 2 shows the characteristic points of the system, which are described below.

Step 1: wherein the structure in the surface of the ribbon is made by imprinting the structure of the embossing roller into the surface of the panel placed between the pressure and the embossing rollers. As the core ribbon moves between the rollers, the ribbon comes into contact with both rollers simultaneously, with 3 contact points to be distinguished within this zone:

Point 1 : whereupon roller K5 touches the surface of the core ribbon featuring film layers, and the structure is being made. At this point, the ribbon surface reaches the highest temperature;

• Point 2: the minimum distance between the rollers. At this point, owing to the maximum pressure, the process of making the synchronised structure is completed. However, the synchronised structure is still unstable. At the same time, the lamination of the individual layers is completed, and the core ribbon is converted into a panel ribbon; and

• Point 3: the place where the pressure roller is no longer in contact, and the panel ribbon only interfaces with the embossing roller.

Step 2: contact cooling of the surface of the panel ribbon to stabilise the imprinted structure, while indirect cooling of the panel core occurs. During this step, the panel ribbon is in contact with the embossing roller only through its surface, where cooling is most rapid. In contrast, cooling of the core itself proceeds at a slower rate as a result of indirect cooling through the top surface of the ribbon. Contact cooling terminates at Point 4, where direct contact between the roller and the panel ribbon ends.

What is crucial for the process of imprinting the embossing roller structure in the panel surface is the length of simultaneous contact occurring between the core ribbon and both the pressure roller and the embossing roller, as limited by Points 1 and 3 in Figure 2, and thus the contact duration between the surface of the ribbon and the embossing roller plays a key role. An excessively brief contact will result in the deformation of the imprinted structure due to the excessive plasticity of the layer in which it is imprinted. In turn, an overly prolonged contact may lead to excessively abrupt cooling of the panel surface, making it impossible to accurately impress the structure, which will become too shallow to the embossing roller structure. The correct rendering of the embossing roller structure in the surface of the panel ribbon can be achieved by adjusting such parameters as the temperature of the panel surface at Point 1 (TPI); the temperature of this surface at Point 3 (TPS); the linear speed of the ribbon (v); and most significantly the embossing roller radius (r). The term “plate ribbon” is understood as both the core ribbon with foil layers applied to it in the phase before lamination, i.e. before reaching the Tp ₂ point, as well as the plate ribbon after passing the Tp2 point.

These parameters allow determination of the rate of a temperature drop in the surface of the extruded panel (K). wherein:

K: the plate ribbon surface temperature drop rate [°C/s] ;

TPI: the plate ribbon surface temperature at Point 1 (Step 1) [°C];

TP2: the plate ribbon surface temperature at Point 3 (Step 1) [°C];

V: the linear speed rate of the extruded ribbon [m/s]; r: the embossing roller radius [m] .

Excessively rapid cooling of the core ribbon produces undesirable tensions within the panel, and for this reason, the temperature drop K should be properly adjusted to the thermal properties of the polymer used in the panel for the panel core matrix as well as the properties of the decorative layer and, in particular, the protective layer.

In the method according to the invention, depending on the type of polymer used, the cooling rate K should be in the range of 2. O to 15.0 °C/s in order to achieve a suitable effect of a non-deformed structure. The cooling rate K should correlate with the surface temperature of the panel at Point 1 in the sense that the higher the temperature of the panel at Point 1, the higher the temperature drop.

The values of the surface temperature of the panel at Points 1 and 3 primarily depend on the type of the polymer from which the upper layers of the ribbon are made. For amorphous polymers, the temperature at Point 1 should range from 50 to 90 °C above the softening point of the polymer, whereas for semi-crystalline polymers the value of this parameter should be in the range of 40 to 80 °C.

Adjusting the value of the temperature drop rate in the gap between the pressure roller and the embossing roller within the range of 2.0 - 15.0 °C/s is not advisable by way of decreasing the linear speed rate of the extruded panel as this would require an increase in the temperature of the rollers, thus contributing to the degradation of the material and, consequently, potential product performance properties loss.

The most effective means of ensuring an appropriate value of the parameter K is to change the size of the embossing roller. The larger the roller radius, the longer the contact between the plate ribbon surface and the embossing roller.

In the method according to the invention it has proved to be the case that the corresponding values of the temperature drop for the panels comprising the invention are obtained on the embossing rollers with a radius greater than 0.335 m.

Depending on the value of the temperature drop K for a given panel production process and the rate of the core ribbon speed rate between the rollers, the temperature of the embossing roller should also be adjusted according to the following rule: wherein:

I : the embossing roller temperature [°C];

K: the temperature drop rate of the plate ribbon [°C/s]; t: the duration of the contact between the plate ribbon and the embossing roller between Points 1-3 [s].

Figure 4 is a diagram of the process implemented in a line comprised of two rollers. Roller 11 serves both as the packaging roller and the pressure roller.

In a preferable variant of the invention, the method of production of the decorative panels according to the invention is through processing on an additional packaging roller, whereby the process comprises the following essential steps:

• extrusion of the core ribbon;

• its subsequent shuttling to the packaging roller (K3) with the successive addition of: o the decorative layer, predominantly in the form of a fdm; and o the protective layer, predominantly in the form of a film;

• whereby, the core ribbon, together with the decorative and protective layers attached into the surface of the core ribbon, passes between the two rollers, the pressure roller (K4) and the embossing roller (K5) that has an engraved synchronised structure;

• subsequently, the ribbon travels on the receiver conveyor, where the ribbon undergoes final cooling and levelling; and

• further, it is divided into respective sections and widths of the finished product.

In another preferable variant of the invention, the method of production of the decorative panels according to the invention the core ribbon is standardised between calenders and, subsequently, packed on a packaging and pressure roller and then the process comprises the following essential steps: extrusion of the core ribbon;

• which is then transported by a system of the dimensioning calenders (KI and K2) that impart its desired thickness;

• then, the core ribbon is transported to the packaging and pressure roller (K4) with the successive addition of: o the decorative layer, predominantly in the form of a fdm; and o the protective layer, predominantly in the form of a film;

• whereby, the core ribbon, together with the decorative and protective layers attached into the surface of the core ribbon, passes through the gap between the two rollers, the pressure roller (K4) and the embossing roller (K5), that has an engraved synchronised structure;

• subsequently, the ribbon travels on the receiver conveyor, where the ribbon undergoes final cooling and levelling; and

• further, it is divided into respective sections and widths of the finished product.

In the most preferable variant of the invention, the method of production of the decorative panels according to the invention comprises the following essential steps:

• extrusion of the core ribbon;

• which is then transported by a system of the dimensioning calenders (KI and K2) that impart the desired thickness;

• then the following is added successively on the next packaging roller (K3): o the decorative layer, predominantly in the form of a film; and o the protective layer, predominantly in the form of film; • whereby, the core ribbon, together with the decorative and protective layers attached into the surface of the core ribbon, passes through the gap between the two rollers, the pressure roller (K4) and the embossing roller (K5), that has an engraved synchronised structure;

• subsequently, the ribbon travels on the receiver conveyor, where the ribbon undergoes final cooling and levelling; and

• further, it is divided into respective sections and widths of the finished product.

An essential parameter of the process is a proper temperature distribution at all steps thereof, with the temperature distribution dependent on the type of the core material used as well as the properties of the individual layers of the decorative panel.

Depending on the type of the core material, different temperature regimes are employed, whereas:

• for amorphous plastics, specifically such as polyvinyl chloride (PVC), polycarbonate (PC), poly(methyl methacrylate) (PMMA), polystyrene (PS), their copolymers and their mixtures, the temperature parameters of the process according to the invention are provided with reference to the softening temperature; and

• for semi-crystalline plastics, specifically such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate) (PET), their copolymers and their mixtures, the temperature parameters of the process according to the invention are provided with reference to the melting temperature.

Figure 1 is a schematic representation of the technological process of how to produce the decorative panels according to the invention on a line composed of five rollers. Figures 4-6 are diagrams showing the technological process of how to produce the decorative panels according to the invention on a line composed of a smaller number of rollers.

The method according to the invention on the line composed of five rollers is implemented under the conditions described below. The polymer mixture, along with fillers and modifiers, is extruded through the extruder die (1), with the die temperature higher by 10 to 100 °C than the softening temperature of the amorphous polymers, whereas in the case of semi -crystalline polymers the die temperature is higher by 10 to 100 °C than the melting temperature.

The extruded core ribbon (2) is fed into the gap between the dimensioning calenders KI and (3, 4), which are designed to ensure that the desired thickness is obtained for the ribbon (2). The temperature of the dimensioning calenders KI and K2 (3, 4) should be thermostated and maintained at a constant level as much as possible, with their temperature lower by 10 to 40 °C than the extruder die temperature measured at the centre of the die.

After the core ribbon is fed through the dimensioning calenders KI and K2 (3, 4), the core ribbon is routed to the next packaging roller K3 (5) where the decorative film (6) which is pressed by a roller (7) and a protective layer film (8) which is pressed by a roller (9) are added in a sequence during the travel of the core ribbon (2) and then the core ribbon (2) is moved by guide rollers (10) to the pressure roller K4 (11) and further to the gap between the rollers, namely the pressure roller K4 (11) and the embossing roller K5 (13). The packaging roller (5) should be thermostated to a temperature equal to the temperature of the rollers (3, 4) or lower, with a difference of no more than 30 °C.

During the travel of the core ribbon (2), together with the decorative (6) and protective (8) films applied, between the packaging roller (5) and the pressure roller (11), the films are heated via a heating device (12) to a temperature higher by 50 to 90 °C than the softening temperature of the amorphous polymers or by 40 to 80 °C than the melting temperature of the semi-crystalline polymers from which the films are made.

Next, the core ribbon (2) is fed into the gap between the pressure roller (11) and the embossing roller (13). The maximum size of the gap between the pressure roller (11) and the embossing roller (13) corresponds to the thickness of the core ribbon together with the decorative (6) and protective films (8), wherein it is preferable when determining the gap between these rollers to assume as the thickness of the protective film that the surface of the embossing roller corresponds to the average distance of the outermost points of the embossing roller structure from the roller axis.

After the panel surface with the embossed synchronised structure is cooled to a temperature lower by 10-50 °C than the softening temperature of the amorphous polymers or the melting temperature of the semi-crystalline polymers, which are the materials used to make the upper layers of the product, the ribbon is detached from the embossing roller and is routed to the receiving rollers with the simultaneous switch from contact cooling of the panel surface to its indirect cooling. The temperature of the core itself should remain above the softening temperature of the amorphous polymers or the melting temperature of the semi -crystalline polymers, of which the core is made, allowing it to retain its elasticity, and it undergoes deformation to a flat panel after being transferred to the receiver rollers or belts; thereafter, the panel is further cooled in a flat form by means of indirect cooling.

Satisfying the conditions set out above is preferable to achieve:

• the quality of the structure engraving in the embossed surface;

• the strength of adhesion of the protective and decorative layers to the core; and

• resistance of the finished product to mechanical damage throughout its useful life.

Once the extruded panel has passed through the calender system, it is then transported on the rollers of the cooling table. It is essential that the core temperature of the panel at Point 4, as shown in Figure 2, be higher by 10-40 °C than the softening temperature of the amorphous polymers or the melting temperature of the semi -crystalline polymers of the core material so that the required flatness of the product can be achieved. Furthermore, the surface temperature of the panel upon which the structure of the roller K5 was imprinted should have already cooled below the softening temperature of the amorphous polymers or the melting temperature of the semicrystalline polymers of the decorative and protective layers, thus ensuring that the structure is not deformed. It should be emphasised that an excessively prolonged contact between the surface of the panel and the roller K5 (the embossing roller) may cause excessive cooling of the core of the extruded panel, which, in turn, may hinder achieving flatness of the product on the cooling table. To ensure adequate contact time between the panel surface and the roller K5 without overcooling the panel core, calender systems with a diagonal or horizontal orientation can be used, whereby it is preferable to use diagonal calender systems.

Further transport of the extruded panel along the cooling table is ensured by means of a roller or tracked lashing system. Upon exiting the lashing system, the panel is then formatted to the appropriate size using a saw or guillotine.

In another variant of the invention, an additional layer (15), generally in the form of a fdm, is applied onto the core as a sound damping layer. In general, the sound damping layer is applied on the packaging roller (5) between the decorative layer and the core.

In another variant of the invention, an underlay is applied on the underside of the core ribbon (16).

Figures 3, 3a and 3b show a magnification of Detail A in Figure 1 demonstrating the arrangement of the respective layers of the laminated core ribbon before the lamination process.

In another variant of the invention, the calender (4) can have a grooved structure, thereby allowing for the imprint of the said structure from the underside of the panel core ribbon.

The decorative panels produced by means of the method according to the invention should contain a core made of mixtures based on: • 10-40% by weight, preferably 20-30% by weight, of the thermoplastic material constituting what is known as a polymer matrix, selected from the group of PVC, PC, PMMA, PS, PE, PP, PET and their copolymers as well as their mixtures;

• 60-90% by weight, preferably 70-80% by weight, of the fdlers, in particular glass fibres, polymer fibres especially polypropylene, polyacrylate, Kevlar, nylon and other fillers, metal particles, wood flour, mineral fillers, especially calcium carbonate, talc and mica;

• in addition, they may contain up to 5% by weight of processing aids such as stabilisers, emulsifiers, processing modifiers, impact modifiers and lubricants.

The mixture prepared at an earlier stage, after being dosed into the extruder, undergoes a process of plasticisation under the influence of shear forces inside the plasticising system. Owing to the rotary motion of the screws, the material is transported to the die which forms the material into a ribbon with a pre-set thickness and shape; it is preferable for the thickness to be from 1 to 20 mm, and particularly from 3 to 8 mm. In order to achieve appropriate rheological properties of the polymer alloy, it is desirable for the extruder cylinder and the die to be thermostated at a temperature higher by 10-100 °C, preferably by 40-80 °C than the softening temperature of the amorphous polymers or the melting temperature of the semi -crystalline polymers of the material. It is essential for the plasticising system to have a pressure of 10-40 MPa, preferably 20-30 MPa, during plasticising and for excess moisture and volatile parts to be extracted by means of a vacuum system with a vacuum pressure in the range of -1.0 to -0.5 bar, preferably -1.0 to -0.8 bar. The gap height in the die should be set taking into account the Barns effect expressed by the jet expansion coefficient P, which is the numerical value of the Barns effect as the percentage increase in the width of the fluid jet leaving the channel relative to the width of the channel. Preferably, the parameter is 90-140% at the centre of the die and its value increases towards the edge of the die, where it should be 100-170%. The calenders (3, 4) give the plastic ribbon the right thickness. It is advisable that the gap height between the calenders (3, 4) be less than 90% of the height of the die measured at its centre. Preferably, the lower dimensioning calender K2 (3) should be used for imprinting a grooved structure on the underside of the core ribbon, if the product should have such a structure, in the form of the grids or another structure, which allows efficient material use. In order to maintain the proper rheological properties of the core ribbon and avoid degradation of the polymer, the rollers KI and K2 should be thermostated to a temperature lower by 10-40 °C than the temperature of the die.

It is preferable for the rollers KI and K2 to have the same temperature, but it is possible to apply different temperatures, with the temperature difference between the rollers KI and K2 not exceeding 30 °C.

In the variant of the invention, it is possible to apply a layer of molten plastic on the packaging roller K3 (5), instead of the film of the protective layer, intended to make the protective layer, for example, by means of a doctor blade or spraying.

The use of the pressure rollers (7, 9) makes it possible to remove air bubbles between the layers. All films used for lamination, i.e. the decorative film, the protective film and other types of films, should be obtained from thermoplastic materials such as PVC, PC, PMMA, PS, PE, PP, PET, their copolymers or mixtures. It is preferable to apply films derived from the same polymer as the one used for the polymer matrix of the extruded core. The use of diverse materials may require an additional ingredient to ensure adhesion between the layers of the panel to be produced.

The rollers K4 and K5 are used to make the relevant surface of the panel synchronised with the decorative pattern of the ribbon by imprinting the structure of the roller K5, whereby depending on the type of the panel to be produced, its thickness and temperature, the structure can be imprinted: • in the protective film;

• in the protective, decorative and other films applied; and

• in the protective and decorative films as well as on the core of the extruded panel.

During lamination of the decorative and protective films with the core, their temperature should be 50 to 90 °C higher than the softening temperature if the amorphous polymers are used and 40 to 80 °C higher than the melting temperature if the semi -crystalline polymers are used. If the temperature of the films in the surface of the ribbon is too low, the material will have inadequate plasticity when synchronised structure of the K5 roller is being imprinted. In turn, an excessively high film temperature can result in the deformation of the structure imprinted in the panel surface. To reach the right temperature, a heating system is positioned above the roller K4 (Fig. 1).

The preferable examples of production of a decorative panel according to the invention are further explained below with reference to the figures enclosed, where the respective figures show:

Figure 7, the diagram of the decorative panel;

Figures 8 and 8a, the cross-section of the decorative panel according to Figure 17 in variants for two different decorative layer thicknesses;

Figure 9, the diagram of the decorative panel with the wear layer;

Figure 10, the diagram of the flooring panel with panel coupling elements;

Figures 11 and 1 la, the cross-section of the decorative panel with the decorative and wear layers; and

Figure 12, the cross section of the decorative panel with the damping layer.

To ensure the clarity of the figures, some details shown therein differ in their actual sizes from what is presented in the figure. For instance, the outlines of the synchronised structure in the cross-section figures are enlarged in relation to the real ones. Furthermore, the thicknesses of the decorative, wear and varnish layers are increased to illustrate their mutual positions and to ensure the clarity of the figure.

Figure 7 is a diagram of a partial view showing the outer structure of the decorative panel according to the present invention, composed of a core (21 ), a decorative layer (22) with a pattern, a protective varnish (23) and the position of the structured surface composing a synchronised structure (24).

Figure 8 schematically shows the cross-section of the decorative panel composed of the core (21), the decorative layer (22), with the synchronised structure (24) in the form of indentations (25, 25', 25", 25"") and reliefs (26, 26', 26", 26"") and the protective varnish (23). Due to the thickness of the decorative layer, the synchronised structure (24) is also imprinted in the surface of the core. A pattern-printed decorative layer (22) is made of PVC, PE, PP, PU, PET or paper and features a pattern that is synchronously reproduced as the synchronised structure (24). The core (1) is made of a comparatively tightly filled flexible plastic, in particular PVC or PP, PE, PET, containing the filler.

Figure 8a shows a variant of the decorative panel similar to the one in Figure 8, in which the decorative layer is thick enough for the synchronised structure (24) not to be imprinted in the surface of the core (21).

Figure 9 is a diagram of a partial view showing the synchronised outer structure of the decorative panel according to the present invention, composed of a core (27), a decorative layer (28) with a pattern, a wear layer (29) and a protective varnish (30) as well as the position of the structured surface composing a synchronised structure (31).

Figure 10 is a diagram of a partial view of the decorative panel as a flooring panel, showing the synchronised outer structure of the decorative panel that according to the present invention is composed of a core (32), a decorative layer with a pattern (33), a wear layer (34), a protective varnish (35), a synchronised structure (36) and right (37) and left (38) interlocking elements for coupling adjacent planks. Figure 11 schematically shows a cross-section of the decorative panel containing a core (39), a decorative layer (40), a wear layer (41) with a synchronised structure (42) and a protective varnish layer (43). A core (39) is made of a comparatively tightly fdled flexible plastic, in particular PVC or PP, PE, PET, with a fdler content in the range of 60 to 90%. A pattern-printed decorative layer (40) is made of PVC, PE, PP, PU, PET or paper and features a design that depicts any type of decoration, for instance, wood or stone imitation or any other pattern. This design is synchronously reproduced in the form of a synchronised structure in a wear layer (41) in the form of reliefs (44, 44' 44", 44"') and indentations (45, 45', 45", 45'").

Figure I la shows a variant of the decorative panel similar to the one in Figure 11, in which a wear layer (46) is thin enough for a synchronised structure (47) to be imprinted in a decorative layer (48) as well. A pattern-printed decorative layer (48) is made of PVC, PE, PP, PU or PET and features a pattern synchronously imprinted as a synchronised structure (47) in a wear layer (46) and as reliefs (49, 50) and indentations (51, 52) in a decorative layer (48).

Figure 12 schematically shows a cross-section of the decorative panel composed of a core (39), a decorative layer (40), a wear layer (41) with a synchronised structure (42), a protective varnish layer (43) and, in addition, a damping layer (53). The core (39) is made of a comparatively tightly fdled flexible plastic, in particular PVC or PP, PE and PET, with a fdler content in the range of 60 to 90%. The pattern-printed decorative layer (40) is made of PVC, PE, PP, PU, PET or paper and features a design that depicts any type of decoration, for instance, wood or stone imitation or any other pattern. This design is synchronously reproduced in the form of the synchronised structure in the wear layer (41) in the form of reliefs (44, 44' 44", 44'") and indentations (45, 45', 45", 45'"). The damping layer (53) is made of PE, PS, PU, PP or PET and contributes to the damping of mechanical impacts, noise in the room and/or acts as thermal insulation, thermal or base surface levelling padding.

The method according to the invention allows production of deformation-resistant decorative panels with a length exceeding 2100 mm. The invention is shown on examples.

Example 1

A composite material formulated as a dryblend in a fluid mixer serves to produce the plastic panels with the following composition:

• 29.3% by weight of PVC INOVYN S6745 constituting a polymer matrix with the softening temperature of 130 °C;

• 70.0% by weight of calcium carbonate OMYADOL 15-JA as the filler;

• 0.5% by weight of acrylic processing modifier DL-125G; and

• 0.2% by weight of DEUREX E09 wax.

The dryblend is then fed into the extruder to be plasticised under the conditions in the plasticising system:

• Barrel temperatures: o Zone 1: 170 °C; o Zone 2: 175 °C; o Zone 3: 180 °C; o Zone 4: 185 °C; o Zone 5: 190 °C; and o Zone 6: 195 °C;

• Pressure: 30 MPa; and

• Vacuum pressure: -0.90 bar.

The rotary motion of the screws ensures that the gelled material is transported to the die whose temperature reaches 190 °C at its centre and rises to 205 °C at its edges. A thickness of the extruded ribbon of 4.00 mm may only be reached if the height of the mouthpiece gap is 4.40 mm (P = 110%) at the centre of the die and 4.80 mm ( = 120%) at the edges of the die.

Upon exiting the die, the extruded ribbon is transported through a 5 -roller system of calenders with a horizontal -diagonal orientation. The height of the gap between the calanders KI and K2 is 3.55 mm, which corresponds to 81% of the die mouthpiece gap height, measured at the centre of the die. The rollers KI and K2 are thermostated to 180 °C, which is 50 °C higher than the softening temperature of PVC. The surface of the extruded ribbon is topped with a decorative PVC film with the softening temperature of 130 °C and a protective PVC film with the softening temperature of 130 °C through the lamination process performed on the roller K3. The temperature of the roller K3 reaches 180 °C, which is higher by 50 °C than the softening temperature of PVC decorative and protective films. The surface of the extruded ribbon is then heated to 200 °C. The ribbon passes through the gap between the rollers K4 and K5 in order for the synchronised structure of the roller K5 to be imprinted.

The surface temperature of the panel upon detachment from the roller K5 was 110 °C and was lower by 20 °C than the softening temperature of PVC of the decorative and protective films, while the temperature of the core itself was 150 °C and was higher by 20 °C than the softening temperature of PVC of the core ribbon.

Using a ribbon linear speed of 0.03 m/s and the temperature of the roller K5 of 19.5 °C as well as the embossing roller with a radius of 0.43 m, a temperature drop rate of K = 9.8 °C/s was obtained.

Subsequently, the panel was transported on the cooling table rollers by means of a roller lashing cable to the end of the line where it was cut to the appropriate size using a guillotine.

Example 2

A composite material formulated as granulate serves to produce the plastic panels (with the use of a compounding machine) with the following composition:

• 29.0% by weight of PP MOPLEN HP 400R constituting a polymer matrix with the melting temperature of 160 °C

• 70.0% by weight of calcium carbonate OMYADOL 15-JA as the filler; and

• 1.0% by weight of acrylic processing modifier KANE ACE PA310. The mixture is then fed into the extruder to be plasticised under the conditions in the plasticising system:

• Barrel temperature: o Zone 1: 190 °C; o Zone 2: 190 °C; o Zone 3: 195 °C; o Zone 4: 200 °C; o Zone 5: 205 °C; and o Zone 6: 210 °C;

• Pressure: 25 MPa; and

• Vacuum pressure: -0,85 bar.

The rotary motion of the screws ensures that the plasticized material is transported to the die whose temperature reaches 210 °C at its centre and rises to 220 °C at its edges. The thickness of the extruded ribbon of 5.00 mm may only be reached if the height of the mouthpiece gap is 5.70 mm (P = 114%) at the centre of the die and 6.20 mm ( = 124%) at the edges of the die.

Upon exiting the die, the extruded ribbon is transported through a 5 -roller system of the calenders with a horizontal orientation. The height of the gap between the calenders KI and K2 is 4.45 mm, which corresponds to 78% of the die mouthpiece gap height, measured at the centre of the die. The rollers KI and K2 are thermostated to 200 °C, which is 44 °C higher than the melting temperature of PP in the surface of the extruded ribbon. A polypropylene acoustic fdm with the melting temperature of 158 °C, a polypropylene decorative fdm with the melting temperature of 160 °C and a polypropylene protective fdm with the melting temperature of 160 °C were added to the surface of the extruded ribbon on the packaging roll. The temperature of the roller K3 reached 210 °C, which is higher by 54 °C than the melting point of PP in the surface of the ribbon. The surface of the extruded ribbon was then heated to 230 °C. The ribbon passed through the gap between the rollers K4 and K5 in order for the synchronised structure of the roller K5 to be imprinted. The surface temperature of the panel upon detachment from the roller K5 was 140 °C, while the temperature of the core was 190 °C.

Using a ribbon linear speed of 0.04 m/s and the temperature of the roller K5 of 19 °C as well as the embossing roller with a radius of 0.52 m, a temperature drop rate ofK = 9.7 °C/s was obtained.

Subsequently, the panel was transported on the cooling table rollers by means of the tracked lashing mechanism to the end of the line where it was cut to the appropriate size using a saw.