Method for manufacturing a floor or wall panel

Abstract

A method for making a floor or wall panel has a foamed polymer core. A foamable polymer powder is foamed between two conveyor belts in the forming zone of a steel belt press. The sum of the thicknesses of the two conveyor belts and the total thickness of the layers at the entrance of the steel belt press is less than or equal to the opening of the steel belt press at the entrance of the steel belt press. The sum of the thicknesses of the two conveyor belts and the total thickness of the substrate at the outlet of the steel belt press is equal to the opening of the steel belt press at the outlet of the steel belt press and greater than the sum of the thicknesses of the two conveyor belts and the total thickness of the layers at the entrance of the steel belt press.

Claims

1. A method for making a floor or wall panel comprising a foamed polymer core, said method comprising providing a double belt press comprising two conveyor belts defined by an upper conveyor belt and a lower conveyor belt, the upper and lower conveyor belts being formed from polymeric material, the upper and lower conveyor belts forming a product gap therebetween; the method further comprising a steel belt press defining a forming zone by an opening formed between an upper steel belt and a lower steel belt; wherein the upper and lower conveyor belts extend between said upper and lower steel belts with said product gap formed in between; wherein at least two layers of the polymer powder comprising at least one layer of foamable polymer powder are provided on the lower conveyor belt, wherein said at least one layer of foamable polymer powder is foamed at least partially into a substrate between the upper and lower conveyor belts of the double belt press in the forming zone of the steel belt press, wherein a sum of thicknesses of the two conveyor belts and a total thickness of the layers at an entrance of the steel belt press is less than or equal to the opening of the steel belt press at the entrance of the steel belt press, and wherein the sum of the thicknesses of the upper and lower conveyor belts and the total thickness of the substrate formed at an outlet of the steel belt press is equal to the opening of the steel belt press at the outlet of the steel belt press and is greater than the sum of the thicknesses of the upper and lower conveyor belts and the total thickness of the layers at the entrance of the steel belt press.

2. The method of claim 1, wherein said double belt press comprises the following successive zones: (i) a spreading zone for spreading the at least one layer of foamable polymer powder on the lower of the two conveyor belts; (ii) a heating zone for heating the at least one layer of foamable polymer powder; (iii) said forming zone; (iv) a cooling zone for cooling the substrate formed; said method further comprising heating the layers in the heating zone, then transforming the at least two layers of polymer powder in the forming zone into a polymer substrate comprising a foamed layer of polymer, and cooling the foamed polymer substrate in the cooling zone; wherein the foamable polymer powder foams at least partially in the forming zone, the sum of the thicknesses of the two conveyor belts and the total thickness of the layers at the entrance of the steel belt press is less than or equal to the opening of the steel belt press at the entrance of the steel belt press, and wherein the sum of the thicknesses of the two conveyor belts and the total thickness of the substrate at the outlet of the steel belt press is equal to the opening of the steel belt press at the outlet of the steel belt press and is greater than the sum of the thicknesses of the two conveyor belts and the total thickness of the layers at the entrance of the steel belt press.

3. The method of claim 2, wherein after the cooling zone, a decorative layer and/or a wearing layer are/is applied on the formed substrate.

4. The method of claim 3, wherein a coating is applied on the wearing layer.

5. The method of claim 3, wherein the decorative layer and/or the wearing layer is applied by thermal laminating.

6. The method of claim 2, wherein the foaming of the at least one layer of foamable polymer powder starts in the heating zone.

7. The method of claim 1, wherein the opening of the steel belt press at the entrance of the steel belt press is identical to the opening of the steel belt press at the outlet of the steel belt press.

8. The method of claim 1, wherein the forming zone comprises a pair of press rolls and/or an S-bend roll, which is positioned before the steel belt press.

9. The method of claim 1, wherein the steel belt press is an isochoric steel belt press.

10. The method of claim 1, wherein the steel belt press is an isobaric steel belt press.

11. The method of claim 1, wherein said at least one layer of foamable polymer powder is a layer of foamable PVC powder.

12. The method of claim 1, wherein the at least two layers of polymer powder are one or more layers of PVC powder.

13. The method of claim 1, wherein the at least one layer of foamable polymer powder foams chemically.

14. The method of claim 1, wherein the at least one layer of foamable polymer powder foams by expansion of one or more fillers.

15. The method of claim 1, wherein the foaming of the at least one layer of foamable polymer powder starts or continues in the forming zone.

16. The method of claim 1, wherein during transforming, the steel belt press is used to heat the layers of polymer.

17. The method of claim 1, wherein during transforming, the steel belt press is used to cool the layers of polymer.

18. The method of claim 1, wherein the layer of foamable polymer powder is the first layer of polymer powder that is spread on the lower conveyor belt.

19. The method of claim 1, wherein the layer of foamable polymer powder is the second or further layer of polymer powder that is spread on the lower conveyor belt.

20. The method of claim 19, wherein the layer of foamable polymer powder is the last layer of polymer powder that is spread on the lower conveyor belt.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For better illustration of the features of the invention, some preferred embodiments are described hereunder, as examples without any limiting character, with reference to the appended drawings, in which:

(2) FIG. 1 is a schematic representation of a production process according to the invention;

(3) FIG. 2 is an alternative schematic representation of a production process according to the invention;

(4) FIG. 3 shows schematic representations of cross sections of the layered structure and substrate at different positions through the production process.

DESCRIPTION OF EXAMPLES OF EMBODIMENTS

(5) The present invention is described hereunder making use of specific embodiments.

(6) It should be pointed out that the term comprising, for example as used in the claims, should not be interpreted in a limiting sense, limiting to the elements, features and/or steps following thereafter. The term comprising does not exclude the presence of other elements, features or steps.

(7) Thus, the scope of an expression an object comprising the elements A and B is not limited to an object that only contains the elements A and B. The scope of an expression a method comprising the steps A and B is not limited to a method that only contains the steps A and B.

(8) In the light of the present invention, these expressions only signify that the relevant elements or steps for the invention are the elements or steps A and B.

(9) In the specification following hereunder, reference is made to an embodiment or the embodiment. Such reference signifies that a specific element or feature, described on the basis of this embodiment, is comprised in at least this one embodiment.

(10) The presence of the terms in an embodiment or in the embodiment at various places in this description refers, however, not necessarily to the same embodiment, although it might well refer to one and the same embodiment.

(11) Moreover, the properties or the features may be combined in any suitable manner in one or more embodiments, as would be obvious to a person skilled in the art.

(12) A double belt press for the manufacture of a wall or floor panel according to the methods of the invention is shown in FIG. 1. The double belt press 100 comprises two conveyor belts 102a and 102b between which a product gap is defined. The double belt press 100 comprises the following successive zones: a spreading zone 200 for the spreading of polymer powder 220 on the lower of the two conveyor belts 102b; a heating zone 300 for heating the polymer powder by means of heat sources 310 and 320, on both sides of the conveyor belts. Here, these heat sources are containers filled with heating fluid, which have one side that is pressed against the respective conveyor belt; a forming zone 400 for forming a polymer substrate from the polymer powder, said forming zone comprising a steel belt press 410 that defines an opening between which the two conveyor belts run, with the product gap between them; a cooling zone 500 for cooling the formed substrate by means of cooling elements or cooling sources 510 and 520, on both sides of the conveyor belts. Here, these cooling sources are containers filled with coolant, which have one side that is pressed against the respective conveyor belt.

(13) In this embodiment, the spreading zone comprises three spreading units 240a, 240b and 240c, each for spreading out a layer of micronized PVC powder. A glass-fiber web 120 is applied between each of the layers. This web has a weight per unit area from 30 to 50 g/m.sup.2

(14) The powder that is spread in the first and third unit 240a and 240c is a PVC powder, with as components, besides PVC with K value K50, K57, K60, and optionally being a VC/VA copolymer, stabilizers and additives between 5 and 20 phr, filler, preferably calcium carbonate, between 50 and 300 phr and plasticizers between 0 and 20 phr. phr signifies the number of parts by weight of the product per hundred parts by weight of PVC. This PVC is not foamable.

(15) The powder that is spread in the second unit 240b is foamable PVC powder with composition is a foamable PVC powder, with as components, besides PVC with K value K50, K57, K60, and optionally being a VC/VA copolymer, and ADCA as foam-forming additive or blowing agent, stabilizers and other additives between 5 and 20 phr, filler, preferably calcium carbonate, between 50 and 300 phr and plasticizers between 0 and 20 phr.

(16) The layers of powder may, but need not in a first instance be preheated with IR radiators 280. The lower conveyor belt brings the layered structure with a thickness T1 to the opening of the product gap between the two conveyor belts. This opening has an opening size T2 of about half the thickness T1. The layers of powder are thus densified (and air is expelled from between the granules) by passing the layered structure between the transport rolls. The layered structure of layers of powder is squeezed between the conveyor belts and led through the heating zone 300. The PVC materials and the glass-fiber webs are heated to a temperature between 180 and 240? C. Preferably the activation temperature of the blowing agent is about 20? C. lower than the melting point of the polymer, in this case PVC. The temperature is gradually increased in the direction of passage of the conveyor belt. At the end of the heating zone, the blowing agent will begin to swell and gasify, so that the middle layer of PVC begins to foam.

(17) The swelled product then comes between the steel belts 412a and 412b of the steel belt press 410, an opening being defined between said belts, between which the two conveyor belts pass, with the layered structure in the product gap between them. The two reversing rollers 414a and 414b are configured so that the opening between the steel belts T3 is greater than the thickness of the layered, foaming structure that passes between the rolls and the thickness of the two conveyor belts 102a and 102b. Since foaming still continues, over a short distance in the gap, the layered structure, carried by the lower steel belt 412b, will begin to press against the top steel belt 412a. The steel belt press, which is preferably of isochoric configuration, will generate a back pressure and thus provide the correct thickness of the substrate, which is formed meanwhile. During passage through the opening of this steel belt press, the forming substrate will be cooled considerably, gradually stopping the foaming. For this purpose, the steel belts are cooled by cooling units 416a and 416b. At the level of the reversing rollers 418a and 418b, the substrate will be cool enough so that it no longer changes shape, and the thickness T4 of the substrate and the conveyor belts will be as thick as the opening between the reversing rollers 418a and 418b.

(18) The thickness of the substrate and the conveyor belts at the level of the reversing rollers, i.e. at the outlet of the steel belt press, is preferably between 1.02 and 1.5 times the thickness of the layered, foaming structure and the thickness of the two conveyor belts at the entrance of the steel belt press, preferably between 1.05 and 1.25 times this thickness.

(19) The layered structure of layers of powder is squeezed between the conveyor belts and led through the cooling zone 500. The PVC materials and the glass-fiber webs are cooled to a temperature that makes the substrate suitable for the next production step. The temperature is roughly 100? C.

(20) In a subsequent laminating step 600, a decorative PVC film 610 (which is printed with a decorative pattern) and a transparent PVC wearing layer 620 are first warmed on their underside by IR radiators 630 and 640, and then pressed against the upper surface of the substrate with nip rollers 650.

(21) The PVC decorative film 610 is a printed PVC film with a thickness of between 75 and 120 ?m.

(22) The wearing layer 620 is a transparent PVC film with a thickness of about 150 to 700 ?m.

(23) After the wearing layer, stamping is then carried out with embossing roll 700, after which a PU varnish layer, which is UV-cured, is applied with roll 800 and UV radiator 810.

(24) The product thus obtained can be cut into rigid PVC planks and each plank may be provided with coupling means on two or four of its sides. The cross section of said plank has a layered structure with, from top to bottom, a wearing layer, a decorative layer, a first rigid, unfoamed layer of PVC with density between 1.7 and 2.1 g/cm.sup.3, a first glass-fiber reinforcement, a foamed PVC layer with density in unfoamed form between 1.7 and 2.1 g/cm.sup.3 and a foaming factor from 10 to 100%, a second glass-fiber reinforcement, and a PVC backing layer with density between 1.7 and 2.1 g/cm.sup.3.

(25) A foaming factor from 10 to 100% signifies that the unfoamed density A is reduced by a factor of 1.1 to 2 (being between A/1.1 and A/2).

(26) In an alternative embodiment of the method, as can be seen in FIG. 2, after the heating zone 300 the layers are first compressed by an S-roll 420, before it is supplied to the steel belt press 410.

(27) Cross sections of the layered structure and substrate at different positions through the production process are shown in FIG. 3. Section AA shows the layered structure after the last layer of polymer powder has been spread. The layer of powder 122a is spread by spreading device 240a. The foamable layer of powder 122b is spread by spreading device 240b. The layer of powder 122c is spread by spreading device 240b. Two glass-fiber webs 120 are positioned between the layers of powder. In section AA, the layered structure has a thickness T1. The conveyor belt 102b has a thickness Tb.

(28) On section BB, on the diverting roller 104 of the upper conveyor belt 102a, the opening between the conveyor belts T2 is about half the thickness T1. The layers 122a, 122b and 122c are densified and the air between the granules of the powder is expelled.

(29) After the heating zone 300, at the entrance of the steel belt press at the level of the diverting rollers 414a and 414b (section CC), it is clear that the foamable layer 122b is already partially foamed, but the opening of the steel belt press (T3) is greater than the sum T5 of the thickness of the layered structure plus the thicknesses of the conveyor belts.

(30) Although cooling takes place in the steel belt press, the foaming of layer 122b will continue. At the outlet of the steel belt press, at the level of the diverting rollers 418a and 418b (section DD), the opening of the press, which is still T3 in this embodiment, is equal to the sum (T4) of the thickness of the substrate and the thicknesses of the conveyor belts. It should be noted that the increase in thickness of the sum of the thickness of the substrate and the thicknesses of the conveyor belts between the entrance and the outlet of the steel belt press 410 is due to the foaming of the middle layer of 122b.

(31) The thickness of the substrate and the conveyor belts at the level of the reversing rollers, i.e. at the outlet of the steel belt press, is in this embodiment preferably between 1.02 and 1.25 times the thickness of the layered, foaming structure and the thickness of the two conveyor belts at the entrance of the steel belt press, preferably between 1.05 and 1.25 times this thickness.

(32) The layers 122a and 122b are rigid, dense PVC layers with a density of between 1.7 and 2 g/cm.sup.3. The layer 122b is a rigid, foamed layer (closed cells) PVC layer with a density of between 0.017 and 0.2 g/cm.sup.3.

(33) In another embodiment, rigid, hard PVC is not used for the lower layer 122a, but a more flexible PVC that comprises more than 20 phr of plasticizers.

(34) In an alternative embodiment, micronized powder PVC is not used, but PVC granules, e.g. granules with an essentially cylindrical shape with a diameter between 1 and 3.5 mm, e.g. between 2.8 and 3.2 mm and a height of between 0.5 mm and 1 mm.

(35) It is clear that although the embodiments and/or the materials for the supply of embodiments according to the present invention have been discussed, various changes or modifications may be applied without departing from the scope and/or spirit of the present invention. The present invention is by no means limited to the embodiments described above, but can be implemented according to different variants without departing from the scope of the present invention.