U.S. patent application number 17/705253 was filed with the patent office on 2022-07-07 for method for forming a stress-free multilayer pvc sheet material.
The applicant listed for this patent is KREAFIN GROUP SA, LICOPLAST SA. Invention is credited to Willy D'HONDT, Yves MICHEL.
Application Number | 20220212458 17/705253 |
Document ID | / |
Family ID | |
Filed Date | 2022-07-07 |
United States Patent
Application |
20220212458 |
Kind Code |
A1 |
MICHEL; Yves ; et
al. |
July 7, 2022 |
METHOD FOR FORMING A STRESS-FREE MULTILAYER PVC SHEET MATERIAL
Abstract
A method for forming a multilayer plastic sheet material is
disclosed, where a first polymer mass is melted under pressure and
is passed through an extruder head at a specified discharge rate in
the form of a plastic strand in sheet form that is provided with
one or more layers so that a multilayer plastic strand is formed.
This is passed to two or more rolls of a finishing stand that
processes the multilayer plastic strand into a sheet. After the
plastic strand in sheet form leaves the extruder head, it is first
passed between a top roll and a bottom roll of a roughing stand.
The speed of the rolls of the finishing stand and the rolls of the
roughing stand is synchronized with the discharge rate of the
plastic strand in sheet form from the extruder head, so that the
plastic strand is processed without stress.
Inventors: |
MICHEL; Yves; (Meldert,
BE) ; D'HONDT; Willy; (Deinze, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KREAFIN GROUP SA
LICOPLAST SA |
Luxembourg
Battice |
|
LU
BE |
|
|
Appl. No.: |
17/705253 |
Filed: |
March 25, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16608122 |
Oct 24, 2019 |
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PCT/IB2018/052855 |
Apr 24, 2018 |
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17705253 |
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International
Class: |
B32B 37/02 20060101
B32B037/02; B29C 48/21 20060101 B29C048/21; B29C 48/07 20060101
B29C048/07; B29C 48/00 20060101 B29C048/00; B29C 48/154 20060101
B29C048/154; B29C 48/90 20060101 B29C048/90; B29C 48/92 20060101
B29C048/92; B29C 48/08 20060101 B29C048/08; B32B 27/08 20060101
B32B027/08; B32B 27/30 20060101 B32B027/30; B32B 37/15 20060101
B32B037/15 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2017 |
BE |
BE-2017/5285 |
Claims
1. A multilayer sheet material with an elastic modulus above 1000
N/mm.sup.2 and a specified length and width, wherein said sheet
material comprises a carrier material formed from rigid PVC
provided with one or more layers, wherein after heating to
80.degree. and cooling back to room temperature, the sheet material
has expansion or shrinkage of a maximum of 0.2% on the initial
length and/or width, wherein the carrier material formed from rigid
PVC is provided with a top layer of flexible PVC.
2. The multilayer sheet material of claim 1, wherein the sheet
material comprises a decorative effect formed from a decorative
layer of PVC or the sheet material comprises a decorative effect
formed from a transparent wear layer with a thickness of between
0.1 and 1 mm that is provided with a print.
3. The multilayer sheet material of claim 1, wherein a wear layer
with a thickness of between 0.1 and 1 mm is applied on the
decorative layer.
4. The multilayer sheet material of claim 1, wherein the carrier
material formed from rigid PVC is provided on its underside with a
stabilizing layer of flexible PVC.
5. The multilayer sheet material of claim 4, wherein the
stabilizing layer has the same thickness as the top layer.
6. The multilayer sheet material of claim 1, wherein the carrier
material is further provided with a bottom layer that is fastened
to the carrier material with an adhesive.
7. The multilayer sheet material of claim 6, wherein the adhesive
is an EVA adhesive.
8. The multilayer sheet material of claim 1, wherein the multilayer
sheet material is produced by a method comprising the steps of:
melting, under pressure, a first polymer mass comprising the rigid
PVC and a second polymer mass comprising the flexible PVC and
passing the first and second polymer masses through an extruder
head at a specified discharge rate in the form of a multilayer
plastic strand in sheet form, the top layer of which is formed by
the second polymer mass.
9. The multilayer sheet material of claim 8, wherein the method
further comprises: passing the multilayer plastic strand to two or
more rolls of a calendering device and processing the multilayer
plastic strand into a sheet of defined thickness.
10. The multilayer sheet material of claim 9, wherein the method
further comprises: leading away the sheet of defined thickness via
a transport device to a sawing device to be cut to the desired
length.
11. The multilayer sheet material of claim 10, wherein the method
further comprises: after the plastic strand in sheet form leaves
the extruder head, passing the plastic strand in sheet form between
a top roll and a bottom roll of a pre calendering unit.
12. The multilayer sheet material of claim 11, wherein the speed of
the rolls of the calendering device and the rolls of the pre
calendering unit is synchronized with the discharge rate of the
plastic strand in sheet form from the extruder head.
13. A multilayer sheet material with an elastic modulus above 1000
N/mm.sup.2 and a specified length and width, wherein said sheet
material comprises a carrier material formed from rigid PVC
provided with one or more layers, wherein after heating to
80.degree. and cooling back to room temperature, the sheet material
has expansion or shrinkage of a maximum of 0.2% on the initial
length and/or width, wherein the carrier material formed from rigid
PVC is provided with a top layer of flexible PVC, wherein the
multilayer sheet material is produced by a method comprising the
steps of: melting, under pressure, a first polymer mass comprising
the rigid PVC and a second polymer mass comprising the flexible
PVC.
14. The multilayer sheet material of claim 13, wherein the method
further comprises: passing the first polymer mass through a first
extruder and passing the second polymer mass through a second
extruder, both the first and the second extruders connected to a
multilayer T-die, wherein the passing of both the first and the
second polymer masses is at a specified discharge rate in the form
of a multilayer plastic strand in sheet form, the top layer of
which is formed by the second polymer mass.
15. The multilayer sheet material of claim 14, wherein the method
further comprises: passing the multilayer plastic strand to two or
more rolls of a calendering device and processing the multilayer
plastic strand into a sheet of defined thickness.
16. The multilayer sheet material of claim 15, wherein the method
further comprises: leading away the sheet of defined thickness via
a transport device to a sawing device to be cut to the desired
length.
17. The multilayer sheet material of claim 16, wherein the method
further comprises: after the plastic strand in sheet form leaves
the extruder head, passing the plastic strand in sheet form between
a top roll and a bottom roll of a pre calendering unit.
18. The multilayer sheet material of claim 17, wherein the speed of
the rolls of the calendering device and the rolls of the pre
calendering unit is synchronized with the discharge rate of the
plastic strand in sheet form from the extruder head.
19. The multilayer sheet material of claim 18, wherein the method
further comprises: providing the plastic material with a decorative
effect by a) applying a decorative layer of PVC on the multilayer
plastic strand before the multilayer plastic strand in sheet form
is passed between the top roll and the bottom roll of the pre
calendaring unit, orb) by applying a transparent wear layer with a
thickness of between 0.1 and 1 mm, which is provided with a print,
on the multilayer plastic strand before the multilayer plastic
strand in sheet form is passed between the top roll and the bottom
roll of the pre calendaring unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/608,122, filed Oct. 24, 2019, which is a
National Phase entry of International Application No.
PCT/IB2018/052855 under .sctn. 371 and claims the benefit of
Belgian patent application No. BE-2017/5285, filed Apr. 24, 2017,
each of which is hereby incorporated by reference in its respective
entirety.
FIELD OF THE DISCLOSURE
[0002] The present invention relates, on the one hand, to a method
for forming a multilayer plastic sheet material for floor and/or
wall panels, wherein a first polymer mass comprising a rigid PVC is
melted under pressure and is forced through an extruder head at a
specified discharge rate in the form of a plastic strand in sheet
form that is provided with one or more layers so that a multilayer
plastic strand is formed, which is propelled towards two or more
rolls of a finishing stand, which processes the multilayer plastic
strand into a sheet of defined thickness, which is then led away
via a transport device to a sawing device to be cut to the desired
length, wherein, after the plastic strand in sheet form leaves the
extruder head, it is first passed between a top roll and a bottom
roll of a roughing stand, wherein the speed of the rolls of the
finishing stand and the rolls of the roughing stand is synchronized
with the discharge rate of the plastic strand in sheet form from
the extruder head, so that said plastic strand is processed without
stress. On the other hand, the present invention relates to a
multilayer sheet material with an elastic modulus (E) above 1000
N/mm.sup.2, preferably between 2000 N/mm.sup.2 and 3000 N/mm.sup.2,
and a specified length and width.
[0003] The present invention relates in particular to a method that
allows a multilayer PVC sheet material to be formed with minimum
possible internal stresses.
BACKGROUND
[0004] The sheet material that is manufactured by said method is in
particular a plastic panel manufactured from PVC, which can be both
a floor panel and a wall panel. The thickness of such panels is
preferably between 2 and 10 mm, in particular between 3 and 8 mm.
The panels that are manufactured as standard preferably have a
width between 5 and 300 cm and a length between 10 and 500 cm.
[0005] The known panels are manufactured by an extrusion process. A
disadvantage of this technique is that stresses are built up in the
finished material. There is consequently a risk of subsequent
development of fine cracks in the material.
[0006] The Japanese patent publications JP 2002 234116A and JP H07
100898A describe a known extrusion process.
SUMMARY
[0007] An aim of embodiments of the present invention is to supply
a method that will allow stress-free manufacture of sheet
material.
[0008] This aim may be achieved by a method for forming a
multilayer plastic sheet material for floor and/or wall panels,
wherein a first polymer mass comprising a rigid PVC is melted under
pressure and is passed through an extruder head at a specified
discharge rate in the form of a plastic strand in sheet form that
is provided with one or more layers so that a multilayer plastic
strand is formed, which is passed to two or more rolls of a
finishing stand, which processes the multilayer plastic strand into
a sheet of defined thickness, which is then led away via a
transport device to a sawing device to be cut to the desired
length, wherein, after the plastic strand in sheet form leaves the
extruder head, it is first passed between a top roll and a bottom
roll of a roughing stand, wherein the speed of the rolls of the
finishing stand and the rolls of the roughing stand is synchronized
with the discharge rate of the plastic strand in sheet form from
the extruder head, so that said plastic strand is processed without
stress, and wherein a second polymer mass comprising a flexible PVC
is melted under pressure and is co-extruded on the first polymer
mass, and then both are passed through the extruder head in the
form of a multilayer plastic strand in sheet form, the top layer of
which is formed by the second polymer mass.
[0009] In a particular embodiment of the method according to the
invention, the second polymer mass comprising a flexible PVC is
melted under pressure and is co-extruded on the underside of the
first polymer mass, and both are then passed through the extruder
head in the form of a multilayer plastic strand in sheet form, this
additional second polymer mass forming a stabilizing layer for the
multilayer sheet material. The stabilizing layer preferably has the
same thickness as the top layer. The stabilizing layer will prevent
warping of the sheet material.
[0010] Preferred embodiments of the method are described in the
dependent claims.
[0011] The present invention in some embodiments further relates to
a multilayer sheet material with an elastic modulus (E) above 1000
N/mm.sup.2, preferably between 2000 N/mm.sup.2 and 3000 N/mm.sup.2
and a specified length and width, wherein said sheet material
comprises a carrier material formed from rigid PVC provided with
one or more layers, wherein the sheet material, after heating to
80.degree. and cooling back to room temperature, has expansion or
shrinkage of max. 0.2% on the initial length and/or width and
wherein the carrier material formed from rigid PVC is provided with
a top layer of flexible PVC. Preferably, after heating to
80.degree. and cooling back to room temperature, the sheet material
has expansion or shrinkage of max. 0.1% on the initial length
and/or width.
[0012] Preferred embodiments of the sheet material according to the
invention are described in the dependent claims.
[0013] To explain the properties of this invention and to indicate
additional advantages and particular features thereof, a more
detailed description of the method and the sheet material according
to the invention is presented below. It should be pointed out that
nothing in the following description is to be interpreted as a
limitation of the protection claimed in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] This description is explained with the aid of the appended
drawings, in which:
[0015] FIG. 1: a schematic representation of a multilayer sheet
material according to the invention;
[0016] FIG. 2: shows schematically a part of the device in which
the method according to the invention is applied;
[0017] FIG. 3: explains the application of a structure in the
wearing layer;
[0018] FIG. 4: shows the transport device along which the formed
multilayer sheet material is led away to a sawing device;
[0019] FIG. 5: shows schematically the application of a bottom
layer against the underside of the sheet material.
DETAILED DESCRIPTION
[0020] A sheet material (1) according to some embodiments of the
present invention is a PVC sheet built up from several layers,
which will preferably be used as a waterproof and low-noise floor
or wall covering.
[0021] As can be seen from FIG. 1, the sheet (1) is built up as
follows: [0022] 1) UV varnish coat (6), about 25 g/m.sup.2; [0023]
2) wearing layer (5); [0024] 3) decorative layer (4) (film) made of
PVC (may optionally also be PP or PE); [0025] 4) flexible PVC layer
(3); [0026] 5) rigid PVC layer (2), which functions as a carrier or
base sheet; [0027] 6) layer of adhesive (7), preferably an EVA
adhesive (other types of adhesive may also be considered); [0028]
7) bottom layer (8), preferably made of a foamed material.
[0029] Obviously sheet materials with some other structure likewise
fall within the scope of protection of this invention, such as for
example a sheet material where a decorative layer (4) is not
present and the decorative effect is provided by providing the
wearing layer (5) (preferably on the underside) with printing or
where the wearing layer is omitted for the wall application and the
decorative effect is applied via the decorative layer (4) or by
direct printing on the flexible PVC layer (3) or on the rigid PVC
layer (2) before applying the UV varnish coat (6).
[0030] The rigid PVC layer (2) of the sheet material may also be
provided on its underside with a flexible PVC layer, which
functions as a stabilization (stabilizing) layer. The stabilizing
layer preferably has the same thickness as the flexible PVC layer
that forms the top layer (3). The stabilizing layer is applied at
the same time as the top layer.
[0031] Through the presence of the stabilizing layer, the sheet
material will be less susceptible to the so-called "bimetal effect"
and the sheet will remain straight and will not warp.
[0032] The various layers from which the sheet is built up may be
manufactured (applied) in a single production process, and if a
structure is also applied in the surface, this may for example be a
wooden or stone structure. The method in an embodiment is described
below, along with the precise points requiring attention in order
to keep it stress-free.
[0033] Step 1: Manufacture of the Carrier Sheet:
[0034] The basis or the core of the sheet (1) is the layer of rigid
PVC (2) provided with a layer (3) of flexible PVC. Both layers are
manufactured by means of a so-called multilayer T-die (9). Said die
is connected to two separate extruders. The main extruder supplies
the material for the rigid PVC layer (2), and a second extruder,
the so-called co-extruder, supplies the material for the flexible
PVC layer (3). The two layers are distributed in the die over a
sheet width with a specified thickness and density.
[0035] A rigid PVC consisting of various components is processed in
the main extruder. Fillers and minerals may also be added via a
mixer on top of the extruder, in order to obtain optimum thermal
stability of the sheet (1). Addition of a chemical blowing agent
provides small air bubbles in the sheet, thus reducing the specific
weight of the sheet. During the extrusion process, the additives
are mixed and melted with the PVC, this melt enters the die at a
specified pressure and temperature and is spread by the "hat-rack"
principle over the full width of the die and with a specified
thickness.
[0036] The action of the co-extruder is similar; the material fed
into the co-extruder is a flexible PVC with a specified Shore
hardness. The Shore hardness of the flexible PVC is preferably
between 80 and 100, more particularly between 85 and 95. The
purpose of the flexible PVC layer is on the one hand to guarantee
perfect thermal fusion with the decorative film (see hereunder) and
on the other hand to create a soft feel.
[0037] It is important that the flows of the two layers in the die
advance at the same speed, to avoid stresses and warping of the
sheet during subsequent thermal loading. The lip opening of the die
(where the material is forced out) must be set according to a
specified ratio so that the final thickness of the co-extruded
sheet leaves the die within a specified thickness ratio. If these
speeds are too different over the width of the die, the shrinkage
ratios on cooling of the sheet will be insufficient to be able to
guarantee a good, stable floor.
[0038] Step 2, Pre-Thickness Calibration of Sheet+Pre-Lamination of
Decorative (Film) Layer and Wearing Layer (See FIG. 2)
[0039] Once the melt comes out of the die (9), this melt is
received by two rolls (10, 11) that form part of a roughing stand,
namely a top roll (10) and a bottom roll (11). A specific feature
of these rolls is that they must be maintained at a specified
temperature so that the hot melt leaving the die (9) is not cooled
immediately owing to an excessive temperature difference between
the rolls and the hot melt. A specific composition of silicone
rolls is selected for this purpose.
[0040] The operation of the roughing stand is as follows: [0041] a)
a first pre-calibration in thickness of the melt leaving the T-die
(9), together with the applied decorative layer (4) and wearing
layer (5). The gap between the two rolls (10, 11) must therefore be
very accurate so that the rolls (10, 11) do not press excessively
on the sheet, which is still hot. [0042] b) light pressing of the
decorative layer on the hot sheet. The decorative layer is
preferably a layer of PVC film. This PVC film comes from a roll
produced beforehand. The unwinding of the film takes place over a
number of rolls, the roll RPVC 1 is a roll that measures the stress
constantly on the decorative layer (PVC film) (4) and ensures that
the forces exerted that are necessary for unwinding the PVC film
are always the same, regardless of the diameter of the roll of PVC
film or the film thickness. The roll RPVC 2 is located at a
specified angle. The purpose of this roll is to bring the film
under the wearing layer (5) and between the rolls (10 and 11) of
the roughing stand, in such a way that there is no inclusion of air
between the PVC film (4) on the one hand and the wearing layer (5)
and the extruded PVC sheet. Temperature, stresses, angle and
distance are very important for obtaining a stable process. Of
course, the whole unwinding unit is provided with continuous web
tensioning and web guidance. [0043] c) Applying the wearing layer
(5) on the 3 layers already present: the decorative film, flexible
PVC layer and rigid PVC layer. The wearing layer (5) is also
unwound by a complete unwinding unit provided with web tensioning
and web guidance. However, a number of points have to be taken into
account. [0044] 1) Depending on the thickness of the wearing layer
(5), it must be warmed up to some extent for example by means of IR
radiant heaters (12), to make the whole a bit more flexible but
also to limit the thermal shock when they are laminated together;
the melt emerging from the die (9) has a temperature of about
150.degree., the decorative film (4) is so thin that it reaches
this temperature immediately, but the wearing layer (5) has
thicknesses from 0.1 to 1.0 mm and must therefore be warmed up
somewhat. This is provided by the IRWL radiant heaters (12). [0045]
2) After this preheating, the film passes over a roll stand RWL2
and RWL3, and once again angles, distances and stresses are
extremely important. The aim is that the preheated wearing layer is
entrained almost stress-free by the top roll (10), and an important
aspect is the contact surface or the angle at which the wearing
layer comes into contact with the top roll. [0046] d) Finally, the
top rolls (10 and 11) will press the melt emerging from the die
(9), the PVC decorative film and the wearing layer together. The
gap between the rolls (10, 11) is important. It must be in
proportion to the thickness of the melt emerging from the die and
the thickness of the film and the wearing layer that are to be
pressed together. If there is insufficient contact, air will be
trapped between the different layers. With excessive contact or
excessive squeezing together, creases may form on compressed sheet
that are visible to the naked eye, but mechanical forces will also
develop in the hot state, which will be harmful later, possibly
with negative thermal stability as the sheet cools down. [0047] e)
It is therefore very important that the decorative film and the
wearing layer are unwound with a certain tension, just sufficient
for everything to be fused together without inclusion of air and
without stretching the film and the wearing layer. On the other
hand, it is also important that the melt emerging from the die is
brought stress-free between the top roll and the bottom roll.
Moreover, it is extremely important that the top roll and bottom
roll speeds can be set accurately and separately. The rolls C1, C2
and C3 of the finishing stand, which function as master, are
decisive for the speeds of the top and bottom rolls of the roughing
stand. The latter are now synchronized with the speed of rolls C1,
C2 and C3 with the possibility of setting a certain delta between
the two speeds to prevent the development of stresses. In its turn,
the extrusion speed, with the associated discharge rate of the melt
from the T-die, is also synchronized with the top and bottom rolls
of the roughing stand also taking into account a possible delta on
these speeds, once again to prevent the possible development of
stresses.
[0048] Step 3: Final Calibration of the Thickness and Introduction
of a Structured Surface (Embossing) (See FIG. 3)
[0049] Once the aforementioned layers have been (pre)laminated on
one another, they still need to be fused together, better
calibrated on thickness and the surface must be provided with a
defined embossing structure. This must all be done at specified
temperatures and of course with minimum stresses.
[0050] After the roughing stand, the sheet (1) passes over 2 driven
support rolls (S1 and S2). This interval is needed for carrying out
the following two operations: [0051] 1) Completion of thermal
fusion of all the layers. It is of course important that the
various layers used are compatible (fusible) with each other with
respect to chemical composition. [0052] 2) Softening (warming) the
top layer of the sheet for final impressing of an attractive
surface structure (embossing) with roll C2. Thus, the top part of
the wearing layer (5) is made soft again by means of a second IR
radiant heater (13). The lamps of this radiant heater (13) have a
specific wavelength that only softens the top part of the wearing
layer. It is very important not to heat up the whole wearing layer
again. That is why IR lamps with a specific wavelength are used for
this. The temperature of the surface after the IR radiant heaters
is measured continuously and is kept constant by means of a PID
control system. It is very important at this point to have a
constant surface temperature over the entire surface of the sheet,
for finally producing an embossing structure that is as uniform as
possible in the sheet by means of roll C2.
[0053] Thus, S1 and S2 are only support rolls, there is no top roll
that would compress the sheet thickness.
[0054] Moreover, it is extremely important that after it leaves the
die and during its subsequent path the sheet is not under tension.
In other words this sheet must not be pulled, otherwise excessive
stresses will be created in the sheet. On the other hand it is
necessary to ensure that the sheet also does not sag excessively.
In that case the sheet will be stretched under its own weight and
it is impossible to bring about a stable process. Very good
synchronization with the necessary offset possibilities between on
the one hand the speed of discharge from the T-die and the speed of
all the aforementioned rolls is thus of the utmost importance on
the one hand for obtaining a stable thickness and on the other hand
to produce minimum mechanical stresses in the sheet.
[0055] After the support rolls and heating of the wearing layer
with the IR radiant heaters (13), the sheet goes into the rolls of
the finishing stand (calender). All three rolls have a specific
constant temperature. The middle roll C2 is a structure roll, which
will apply a specified structure (embossing) on the surface of the
sheet (1). The accuracy or the sharpness of this structure depends
on the thickness of the assembled sheet that is passed between the
rolls, but also on the temperature. Once again it is necessary to
find the right conditions between the temperature, pressure and
thickness setting between the rolls. The slightest deviation of
these factors results in a poorer finish.
[0056] The depth of the structure in the structure rolls is
normally somewhat deeper than the depth of the structure in the
final sheet. The great difficulty in this method of production is
that a structure is impressed in the sheet while it is still almost
completely soft (has not hardened). The sheet can thus be flattened
without much difficulty, which in itself would make the process a
bit easier. However, experience and tests teach us that this then
introduces a very large mechanical load into the sheet, if we form
the sheet and cool it with these introduced stresses, then the
thermal properties that we obtain after cooling are actually very
poor.
[0057] Step 4, stress-free cooling of the sheet on a long roller
table at a specified angle (see FIG. 4)
[0058] This process has already been described in an earlier patent
publication of the patent holder. Here, the sheet will be cooled on
a long roller table that is set up at an angle.
[0059] At the end of this roller table there are two driven pinch
rolls (TR), which ensure that the sheet will advance at a specified
linear speed. The sheet will sag between roll C3 and the first roll
(15) of the roller table. The value or factor of the sag is
measured by measuring sensors. The values of these measurements are
converted and control the peripheral speed of the pinch rolls (TR)
via a PID control system. In this way, the value of the sag of the
sheet (factor X) will always be kept constant and we are able to
state that the sheet is cooled stress-free. Once the sheet comes up
to the level of the pinch rolls it has been cooled to the extent
that it is in the solid state and so is no longer susceptible to
certain mechanical stresses to which it may be subjected in the
further course of the process (sawing off of edge strips, gluing a
sound-absorbing bottom layer, sawing to length).
[0060] If we now examine FIGS. 2, 3 and 4 together, we can state
that the speed of rolls C1, C2 and C3 is decisive (master) in this
process. These therefore have the speed that is selected by the
operator. The rolls before and after these rolls operate
automatically as follower (slave), these therefore adapt, via
synchronization and measurement and offset systems, their
peripheral speed so as to be able to guarantee a complete
production process with a constant tension. Of course, the
discharge rate of the melt from the die (9) must also be constant
for this process to be kept stable overall.
[0061] Step 5, gluing of the bottom layer (see FIG. 5) The bottom
layer (8) is preferably a pre-extruded PS foam layer, which is
glued onto the underside of the sheet (1). The purpose of this
bottom layer is generally known in applications of floating floor
covering.
[0062] The bottom layer comes from a roll, via constant web
guidance and constant web tensioning measured by roll U1, the layer
(8) will be glued to the bottom of our sheet. The layer of adhesive
(7) is applied by means of a special gluing head (slip nozzle). The
bottom layer (8) slips with a specified force over the slip nozzle,
which will apply an amount of glue on the bottom layer; the glue is
heated in a reservoir and forced by gear pumps into the slip nozzle
over a roll system U2 and U3 ensuring a constant area of contact
between the outlet of the slip nozzle (14) and the bottom layer
(8), so that a constant amount of glue will be applied on the
bottom layer. The bottom layer then goes under the pinch rolls TR
and is thus pressed against the sheet, which is produced as
described above.
[0063] The speed of the gear pumps is controlled by the speed of
the pinch rolls TR, thus guaranteeing a constant yield/m.sup.2
glue. Factors such as residual temperature and open times of the
glue must be taken into account.
[0064] Constant web guidance ensures that the bottom layer is or
will always be glued on the sheet at one and the same tension.
[0065] Practically all steps of the production process have now
been completed. After gluing, the sheet is trimmed to width, the
left and right edge strips are removed by means of circular saws,
cutting or cutting-off devices so that we finally obtain a constant
width of the sheet. After removing the edge strips, the sheet will
be reduced to the desired length, preferably by means of a sawing,
cutting or cutting-off device.
[0066] Once the sheet has been reduced to the desired length, it
goes through a brush system to remove all residues from the sawing
operation, and in a last step the sheets are provided with a UV
varnish coat (6). This varnish coat on the one hand provides a matt
finish, and on the other hand this varnish coat is an extra
protection against soiling of the floor.
[0067] The varnish coat is applied using classical rotary
applicators, two layers are applied wet in wet, and after applying
the varnish these are cured by means of UV lamps.
* * * * *