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(11) | EP 1 216 759 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and unit for producing highly abrasion-resistant protective coverings, in particular for floor and work surfaces |
| (57) There are provided a method and unit (1) for producing highly abrasion-resistant
protective coverings, in particular for floor and work surfaces. The method includes
preparing a mixture (3) of a powdered abrasion-resistant substance (4) (e.g. corundum)
evenly dispersed in a polymer resin (5) suitable for subsequent polymerization and/or
cross-linking; applying the mixture (3) to a substantially dry sheet material (7)
(in particular, nonimpregnated paper or a dried preimpregnated material with a low
wet residue); and drying the sheet material (7) coated with the mixture (3). Tests
have shown the covering so formed imparts to the surfaces on which it is applied an
abrasion resistance superior to that obtainable using conventional methods (e.g. in
which the abrasion-resistant powder is applied, pure or dispersed in a resin, to a
wet preimpregnated material). |
[0001] The present invention relates to a method and unit for producing highly abrasion-resistant protective coverings, particularly for floor and work surfaces, but which may also be used for other applications (e.g. walls or furniture).
[0002] As is known, laminated panels are widely used for covering floors, as an alternative to conventional woodblock floors, or for covering walls, furniture, etc., and normally comprise a number of layers of sheet material (e.g. paper or fabric) impregnated with thermosetting polymer resin (e.g. phenolic, urea, melamine resins or mixtures of these) and which are gripped and compressed under heat (consequent polymerization/cross-linking of the resin compacts the layers to form the panel).
[0003] The eventually visible layer is normally patterned to reproduce a given design (e.g. a given wood grain), and the patterned layer is covered with a protective abrasion-resistant covering or so-called "overlay" containing powdered aluminium oxide Al2O3 (corundum) or other abrasion-resistant substances.
[0004] More specifically, as a protective covering, an overlay paper is known to be used, in which corundum particles are incorporated directly, and which is then impregnated with resin, applied on the patterned layer, and hot-pressed. The method of producing powdered corundum paper is extremely expensive and complicated, and fails to ensure uniform particle distribution (essential for good abrasion resistance).
[0005] Alternatively, abrasion-resistant powder is applied to a wet preimpregnated substrate (i.e. impregnated with resin not yet dried or cross-linked) prior to the final pressing. More specifically, in EP-A-329154, pure abrasion-resistant powder is applied directly to the wet preimpregnated substrate; whereas, in DE-A-19814212, abrasion-resistant powder is dispersed in a resin, and the mixture sprayed on to the wet preimpregnated substrate. In both cases, the abrasion-resistant powder is applied to a wet preimpregnated substrate, and neither completely solves the problem of uniform dispersion of the abrasion-resistant powder, so that the resulting laminates are not always satisfactory in terms of abrasion resistance.
[0006] It is an object of the present invention to provide a method of producing highly abrasion-resistant protective coverings, in particular for floor and work surfaces, designed to eliminate the aforementioned drawbacks of known methods, and which at the same time is relatively cheap and easy to implement, and provides for obtaining products with an abrasion resistance superior to that obtained using known methods.
[0008] According to the present invention, there is provided a method and unit for producing highly abrasion-resistant protecting coverings, in particular for floor and work surfaces, as claimed in the accompanying Claims 1 and 14.
[0009] More specifically, the method according to the invention comprises the steps of: a) preparing a mixture of a powdered abrasion-resistant substance dispersed evenly in a first thermosetting polymer resin; b) providing a substantially dry sheet material; c) applying and distributing said mixture evenly on at least one surface of said substantially dry sheet material; d) drying said sheet material coated with said mixture to form a covering incorporating said powdered abrasion-resistant substance.
[0010] Here and hereinafter:
- "thermosetting polymer resin" is intended to mean a polymer system of one or more components, which sets irreversibly by polymerization and/or cross-linking reactions; as is known, depending on the polymer components used, the setting process can be activated, for example, by heat and/or electromagnetic radiation and/or with the aid of catalysts;
- "sheet material" is intended to mean a thin material in the form of a continuous strip or single sheet (e.g. paper, fabric, etc);
- "powdered abrasion-resistant substance" is intended to mean a solid substance in the form of particles (microspheres, granules, crystals, and particles of any sort) and of superior hardness and abrasion resistance (e.g. metal oxides, silicates or ceramics).
[0011] Preferably, the thermosetting polymer resins employed according to the present invention are water-base resins selected, for example, from the group comprising melamine, phenolic, urea resins and mixtures of these; and the powdered abrasion-resistant substance is aluminium oxide (Al2O3, corundum).
[0012] It is important that, before the resin and abrasion-resistant substance mixture is applied, the sheet material has a relatively low wet residue of volatile substances, in particular, below approximately 14% by weight (determined in an oven at 160° for 5 minutes).
[0013] The sheet material may be nonimpregnated paper material or preimpregnated so-called "prepreg" sheet material; in which latter case, the method comprises the steps of: i) impregnating said sheet material with a second thermosetting polymer resin; ii) drying said preimpregnated sheet material to cross-link said second thermosetting polymer resin; and, iii) applying and distributing said mixture evenly on at least one surface of the dried said preimpregnated sheet material.
[0014] In this case, too, it is important that, after drying and before applying the resin and abrasion-resistant substance mixture, the dried preimpregnated sheet material has a low wet residue of volatile substances, in particular, of 7 to 14% by weight (determined in an oven at 160° for 5 minutes).
[0015] The thermosetting polymer resin mixed with the abrasion-resistant substance is continuously agitated and kept in preferably turbulent motion, both when preparing the mixture and when applying the mixture to the sheet material, to prevent the powdered abrasion-resistant substance (which has a higher density than the resin in which it is dispersed) from settling, and to ensure it is evenly distributed in the resin when applied to the sheet material. Turbulent motion of the mixture has proved particularly advantageous.
[0016] In a preferred embodiment, the step of applying the resin and abrasion-resistant substance mixture is performed using a dispenser-applicator device comprising a fountain, and at least one applicator roller positioned substantially contacting said first surface of the sheet material along a generating line of contact to transfer said mixture from said fountain to said first surface, whereas, on a second surface, opposite said first surface, of the sheet material and at said generating line of contact, no support for said sheet material is provided.
[0017] The method also comprises a step of recirculating the resin and abrasion-resistant substance mixture, in which said mixture dispensed by said fountain and not deposited on said first surface of the sheet material is recirculated back to said fountain.
[0018] When preparing the resin and abrasion-resistant substance mixture, at least one viscosity-control additive, selected from the group comprising filmogens and preferably capable of thermal three-dimensional cross-linking, may be added to the mixture. Good results have been obtained, for example, using a viscosity regulator of polyvinyl alcohol (PVA), which also keeps the volatile substances in the mixture low (below approximately 5% by weight) and so prevents powder dispersion in the workplace. Once dehydrated, PVA also leaves a film which does not affect the original colour of the paper (or other substrate) on which it is applied.
[0019] An important aspect of the invention is that said step of applying the resin and abrasion-resistant substance mixture and said step of drying the sheet material coated with the mixture are followed by a further step of applying a layer of a third thermosetting polymer resin, which is in turn dried and/or polymerized-cross-linked. This third resin, hereinafter referred to as "protective resin", is also preferably a water-base resin selected, for example, from the group comprising melamine, phenolic, urea resins and mixtures of these. The protective resin may be applied 100% dry or in a wet phase, and may or may not contain various additives, cross-linking-polymerization catalysts, etc. Most preferably, a particle filler (in the form of microspheres, granules, powder, crystals, etc.) of nonabrasive or relatively nonabrasive solid substances (e.g. metal oxides, silicates or ceramics) is dispersed in the protective resin. The function of the protective-resin layer is to prevent wear of the plates (normally chromium-plated) used to hot-press the covering. Applying the protective resin, preferably with a particle filler, prevents the plates from coming into direct contact with the very hard abrasion-resistant substance in the underlying layer, and so protects the plates against relatively rapid wear.
[0020] The protective resin (possibly with a dispersed particle filler) may also be applied using a dispenser-applicator device identical to that used to apply the first thermosetting polymer resin and powdered abrasion-resistant substance mixture.
[0021] The step of applying the resin and abrasion-resistant substance mixture and the step of drying the sheet material coated with the mixture may be performed repeatedly to form respective superimposed cover layers. Likewise, the step of applying the protective resin (with or without the filler) may also be repeated to form respective superimposed layers.
[0022] Both the step of drying the sheet material coated with the resin and abrasion-resistant substance mixture and the step of drying the protective resin may be conducted to only dry the polymer components by more or less drastic removal of the volatile substances, or to produce a complete or only partial polymerization-cross-linking reaction of the polymer components. Depending also on the type of polymer components used, the drying steps may be conducted in a tunnel furnace, or by infrared or ultraviolet lamp or electron beam radiation.
[0023] After the drying step/s, the sheet material coated with the resin and abrasion-resistant substance mixture (and possibly also the protective resin) is ready for use, e.g. for the next (known) hot-pressing step in which the polymerization-cross-linking reaction of the polymer resins may be completed.
[0024] Buffered acid catalysts are preferably added to the resin and abrasion-resistant substance mixture to control the cross-linking reaction. More specifically, the catalysts are such as to bring about the cross-linking reaction, in 100°C boiling water conditions, in about 200 seconds, and at any rate in less than 4 minutes. The sheet material impregnated with the resin and abrasion-resistant substance mixture (and possibly with the protective-resin layer) is pressed to achieve a high degree of cross-linking (the viscosity-control additive is advantageously also a three-dimensional cross-linking agent for enhancing cross-linking, such as PVA).
[0025] The method according to the invention is easy and relatively cheap to implement; the unit implementing it is cheap and easy to produce and operate; and coverings produced using the method and unit according to the invention have proved more resistant to abrasion than similar coverings or panels produced using known methods, as confirmed by comparative tests. More specifically, abrasion tests were conducted (in accordance with proposed European standard pr-EN-13329, not yet in force but already adopted in the industry as a reference standard) of coverings produced according to the invention, and similar coverings produced using conventional methods : the coverings produced according to the invention were classed AC3 (suitable for heavy-duty flooring), as compared with class AC2 for conventional coverings. The method according to the invention is therefore not only easier to implement and more effective than known methods, but also provides for obtaining better results.
[0026] Purely by way of example, excellent results have been obtained using a mixture of melamine resin (supplier: BASF) with a 60% solid content, and powdered corundum (supplier: Baikowsky): the mixture, with a 25-second viscosity in a Ford 4 cup at 20°C and a 65% solid content, was spread on to the sheet material in an amount corresponding to 40 g/m2 of resin and 16 g/m2 of corundum.
[0027] A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:
Figure 1 shows a schematic side view of a unit for producing protective coverings for laminated panels and implementing the method according to the invention;
Figures 2 and 3 show schematic, larger-scale views of variations of a detail of the Figure 1 unit.
[0028] Number 1 in Figure 1 indicates as a whole a unit for producing highly abrasion-resistant protective coverings, in particular for floor and work surfaces.
[0029] Unit 1 comprises preparing means 2 for preparing a mixture 3 containing a powdered abrasion-resistant substance 4 dispersed evenly in a liquid thermosetting polymer resin 5; feed means 6 for feeding a sheet material 7; a dispenser-applicator device 8 for applying mixture 3 on to a first surface 9 of sheet material 7; and drying means 10 downstream from dispenser-applicator device 8.
[0030] In the non-limiting example shown, preparing means 2 comprise two tanks 11, 12 arranged in series and having respective agitators 13, 14; and a feeder 15 (e.g. a screw) for feeding abrasion-resistant substance 4 into tank 11. Tank 12 is connected to dispenser-applicator device 8 by a feed line 16 fitted with a circulating pump 17; a recirculating line 18 feeds part of the mixture 3 drawn from tank 12 back into tank 12; and circulating pump 17 keeps mixture 3 in constant, preferably turbulent, motion between tank 12 and dispenser-applicator device 8. Means 6 for feeding sheet material 7 are known and therefore not described or illustrated in detail for the sake of simplicity. Though reference is made in the present disclosure to a sheet material 7 in the form of a continuously treated strip, it is understood that unit 1 may process individual sheets of sheet material 7. Dispenser-applicator device 8 comprises a fountain 19; and at least one applicator roller 20 positioned substantially contacting first surface 9 of sheet material 7 along a generating line of contact. Supporting means 21, 22 for supporting sheet material 7 and defined, in the example shown, by respective rollers are provided on opposite sides of applicator roller 20 to keep the sheet material suspended; and, at the generating line of contact of applicator roller 20, a second surface 23, opposite first surface 9, of sheet material 7 has no support, so that sheet material 7 simply spans rollers 21 and 22.
[0031] Dispenser-applicator device 8 also comprises agitating means 24 defined, for example, by a powered arm 25 moving inside fountain 19 to continuously agitate and keep the mixture 3 inside fountain 19 in preferably turbulent motion.
[0032] Unit 1 also comprises recirculating means 26 for recirculating mixture 3 from dispenser-applicator device 8 to tank 12, and which comprise a catch tank 27 located beneath dispenser-applicator device 8 and facing second surface 23 of sheet material 7, and a recirculating line 28 connecting catch tank 27 to tank 12 and fitted with a recirculating pump 29. Unit 1 may also comprise finish rollers 30 of any known type downstream from dispenser-applicator device 8 and upstream from drying means 10.
[0033] Figures 2 and 3 show various detailed embodiments of dispenser-applicator device 8. In the Figure 2a embodiment (corresponding to the one in Figure 1), dispenser-applicator device 8 comprises applicator roller 20 and a dispensing roller 31 : applicator roller 20 and dispensing roller 31 are positioned side by side along respective generating lines, are separated by an axial gap through which mixture 3 flows, and together define fountain 19; the mixture 3 from preparing means 2 is fed between applicator roller 20 and dispensing roller 31; applicator roller 20 transferring mixture 3 from fountain 19 to sheet material 7 is positioned contacting surface 9 (the top surface) of sheet material 7; and dispensing roller 31 is detached from sheet material 7. Preferably (though not necessarily), the rotation direction of applicator roller 20 is such that, at the point at which the mixture is applied, applicator roller 20 moves in the opposite direction to sheet material 7. As opposed to being located over sheet material 7 (as in Figure 2a), dispenser-applicator device 8 may obviously be located beneath sheet material 7, as shown in the Figure 2b variation (in which case, surface 9 of the sheet material to which mixture 3 is applied is the bottom surface). Dispensing roller'31 may rotate in the opposite direction to applicator roller 20 (as shown by the continuous arrows in Figures 2a and 2b) or in the same direction (as shown by the dash arrows).
[0034] In the Figure 2c and 2d variations, dispenser-applicator device 8 comprises an applicator roller 20; and two dispensing rollers 31, 32 detached from sheet material 7 and positioned facing each other a small distance apart to define fountain 19. Applicator roller 20 is positioned contacting sheet material 7 and facing dispensing roller 31. Dispensing rollers 31, 32 may, obviously, be positioned otherwise than as shown with respect to applicator roller 20 and sheet material 7. For example, in Figure 2d, dispensing rollers 31, 32 are aligned in a direction substantially parallel to sheet material 7. Dispensing rollers 31, 32 may be rotated in opposite directions (as shown by the continuous arrows in Figures 2c and 2d) or in the same direction (as shown by the dash arrows).
[0035] In the Figure 2e, 2f variations, dispenser-applicator device 8 comprises an applicator roller 20 contacting sheet material 7; and a doctor 33 cooperating in sliding manner with applicator roller 20. In this case, fountain 19 is defined between applicator roller 20 and doctor 33, and the mixture 3 from preparing means 2 is fed between applicator roller 20 and doctor 33.
[0036] As stated, the rotation direction of applicator roller 20 may be such that, at the point at which mixture 3 is applied to sheet material 7, applicator roller 20 moves in the opposite direction to sheet material 7 (as shown in Figure 2). Alternatively, the rotation direction of applicator roller 20 may be such that, at the point at which mixture 3 is applied to sheet material 7, applicator roller 20 moves in the same direction as sheet material 7, as shown in Figure 3 (which shows the same embodiments of dispenser-applicator device 8 as in Figure 2, but with applicator roller 20 rotating in the opposite direction).
[0037] Operation of unit 1 implementing the method according to the invention described above is as follows.
[0038] Abrasion-resistant substance 4 and resin 5 are fed into and mixed and agitated continuously in tank 11 (possibly together with the additives and catalysts mentioned previously); when abrasion-resistant substance 4 is evenly dispersed in resin 5, mixture 3 is drained into tank 12, mixed further, and fed along feed line 16 to fountain 19; and, in the meantime, dry sheet material 7 (which may be a strip of paper or other nonimpregnated material or a dried preimpregnated material) is supplied.
[0039] By means of dispenser-applicator device 8, mixture 3 is applied and spread evenly on surface 9 of sheet material 7; sheet material 7 spread with mixture 3 is then fed to drying means 10 (e.g. an oven) from which emerges a covering 35 comprising a substrate defined by sheet material 7, and a layer of resin 5 incorporating powdered abrasion-resistant substance 4.
[0040] Circulating pump 17, recirculating pump 29, and agitators 13, 14 continuously agitate and keep mixture 3 in preferably turbulent motion to prevent abrasion-resistant substance 4 (which has a higher density than resin 5) from settling.
[0041] Mixture 3 is applied by dispenser-applicator device 8 by means of applicator roller 20, which transfers mixture 3 from fountain 19 to sheet material 7. Any mixture 3 not deposited on sheet material 7 (e.g. dripping from the axial ends of applicator roller 20) is collected in tank 27 and recirculated. Not providing any support for sheet material 7 on the surface 23 side opposite surface 9 prevents mixture 3 from depositing on and impairing operation of a contrast roller or other mechanical member.
1. A method of producing highly abrasion-resistant protective coverings, in particular
for floor and work surfaces; the method being characterized by comprising the steps of: a) preparing a mixture of a powdered abrasion-resistant
substance dispersed evenly in a first thermosetting polymer resin; b) providing a
substantially dry sheet material; c) applying and distributing said mixture evenly
on at least one surface of said substantially dry sheet material; d) drying said sheet
material coated with said mixture to form a covering incorporating said powdered abrasion-resistant
substance.
2. A method as claimed in Claim 1, characterized in that, prior to applying said mixture, said substantially dry sheet material has a wet
residue of volatile substances (determined in an oven at 160° for 5 minutes) of less
than approximately 14% by weight.
3. A method as claimed in Claim 1 or 2, characterized by also comprising, after said step of applying said mixture and said step of drying
said sheet material coated with said mixture, the steps of: applying at least one
layer of a third thermosetting polymer resin to said covering incorporating said powdered
abrasive-resistant substance; and drying said third resin.
4. A method as claimed in Claim 3, characterized in that a particle filler of nonabrasive or relatively nonabrasive solid substances is dispersed
in said third resin.
5. A method as claimed in one of Claims 1 to 4, characterized in that said sheet material is a nonimpregnated paper material.
6. A method as claimed in one of Claims 1 to 4, characterized in that said sheet material is a preimpregnated, so-called "prepreg" sheet material; in which
case, the method comprising the steps of : i) impregnating said sheet material with
a second thermosetting polymer resin; ii) drying said preimpregnated sheet material
to polymerize-cross-link said second thermosetting polymer resin; and, iii) applying
and distributing said mixture evenly on at least one surface of the dried said preimpregnated
sheet material.
7. A method as claimed in Claim 6, characterized in that, after drying and before applying said mixture, said dried preimpregnated sheet material
has a wet residue of volatile substances (determined in an oven at 160° for 5 minutes)
of 7 to 14% by weight.
8. A method as claimed in one of the foregoing Claims, characterized in that said first thermosetting polymer resin is continuously agitated and kept in preferably
turbulent motion during said steps of preparing and applying said mixture.
9. A method as claimed in one of the foregoing Claims, characterized in that said step of applying said mixture is performed by a dispensing device comprising
a fountain, and at least one applicator roller positioned substantially contacting
said first surface of the sheet material along a generating line of contact to transfer
said mixture from said fountain to said first surface; whereas, on a second surface,
opposite said first surface, of the sheet material and at said generating line of
contact, no support for said sheet material is provided.
10. A method as claimed in the foregoing Claim, characterized by also comprising a step of recirculating said mixture, and in which said mixture dispensed
by said fountain and not deposited on said first surface of the sheet material is
salvaged and fed back to said fountain.
11. A method as claimed in one of the foregoing Claims, characterized in that, during said step of preparing said mixture, at least one viscosity-control additive,
selected from the group comprising filmogens and preferably capable of thermal three-dimensional
cross-linking, is added to said mixture.
12. A method as claimed in one of the foregoing Claims, characterized in that said thermosetting polymer resins are water-base resins selected, for example, from
the group comprising melamine, phenolic, urea resins and mixtures thereof; said powdered
abrasion-resistant substance being aluminium oxide (Al2O3, corundum).
13. A method as claimed in one of the foregoing Claims, characterized in that said steps of applying said mixture and drying said sheet material coated with said
mixture are repeated one or more times to form respective superimposed cover layers.
14. A unit (1) for producing highly abrasion-resistant protective coverings, in particular
for floor and work surfaces; the unit comprising preparing means (2) for preparing
a mixture (3) of a powdered abrasion-resistant substance (4) evenly dispersed in a
thermosetting polymer resin (5); feed means (6) for feeding a substantially dry sheet
material (7); a dispenser-applicator device (8) for applying said mixture on a first
surface (9) of said sheet material; and drying means (10) for drying said sheet material
coated with said mixture, and located downstream from said dispenser-applicator device;
the unit being characterized in that said dispenser-applicator device (8) in turn comprises a fountain (19), and at least
one rotary applicator roller (20) positioned substantially contacting said first surface
(9) of the sheet material along a generating line of contact to transfer said mixture
from said fountain to said first surface; and by also comprising supporting means
(21, 22) located on opposite sides of said applicator roller (20) to keep said sheet
material suspended, so that, at said generating line of contact and at a second surface
(23), opposite said first surface (9), of the sheet material, the sheet material has
no support.
15. A unit as claimed in Claim 14, characterized in that said fountain (19) is defined between said applicator roller (20) and a dispensing
roller (31); said applicator roller (20) and said dispensing roller (31) being positioned
side by side along respective generating lines, and separated from each other by an
axial gap through which said mixture (3) from said preparing means (2) flows.
16. A unit as claimed in Claim 14, characterized in that said fountain (19) is defined between two dispensing rollers (31, 32) detached from
the sheet material (7) and facing each other a small distance apart along respective
generating lines; said applicator roller (20) being positioned facing a first of said
dispensing rollers (31, 32) and separated from said first dispensing roller (31) by
an axial gap through which said mixture (3) flows.
17. A unit as claimed in Claim 14, characterized in that said fountain (19) is defined by a rotary applicator roller (20), and by a doctor
(33); said mixture (3) from said preparing means (2) being fed between said applicator
roller (20) and said doctor (33).
18. A unit as claimed in one of Claims 14 to 17, characterized by comprising agitating means (24) for keeping said mixture (3) agitated and preferably
in turbulent motion in said fountain (19).
19. A unit as claimed in one of Claims 14 to 18, characterized by comprising circulating means (16, 17) for circulating said mixture (3) from said
preparing means (2) to said fountain (19); said circulating means keeping said mixture
in constant preferably turbulent motion between said preparing means and said fountain.
20. A unit as claimed in one of Claims 14 to 19, characterized by comprising recirculating means (26) for recirculating said mixture (3), for collecting
the mixture dispensed by said fountain (19) and not deposited on said first surface
(9) of the sheet material, and for feeding said mixture back to said fountain.