Note: Descriptions are shown in the official language in which they were submitted.
CA 02339264 2001-02-O1
WO 00/07812 PCTI1L99100411
CORRUGATED COEXTRUDED FOAMED POLh'CARBONATE SHEET AND A
METHOD FOR PRODUCTIONI THEREOF
FIELD OF THE INVEN'IfION
The present invention relates to outdoor building materials in general
and to polycarbonate sheet material for roofing and cladding in particular.
BACKGROUND OF THE INVENTION
In the industrial world there is a strong need for outdoor building
materials that will perform for many years in harsh environments. In general,
the
existing materials do not perform as welt as needed by current standards, and
~o therefore substitute materials are in great demand.
The main requirements for outdoor building materials can be
summarized, as follows:
1 ) service temperature of up to 80 - 90°C and down to -30°C
(service
temperature is the temperature range in which the material is stable);
2) UV resistance for 20 - 50 years in extreme radiation conditions (the
ozone hole problem is making this issue more important);
3) corrosion resistance;
4) impact resistance to wind, hail and flying debris;
5) water resistance and water impermeability;
20 6) chemical resistance to airborne chemicals such as acid precipitation;
smoke, dust and soot; resistance to biodegradation;
7) flexibility and resilience: the ability to perform even after suffering
deformations;
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8) fire resistance and fire performance that will not compromise safety
and if possible will improve safety;
9) good heat and sound insulation; and
10) environmentally friendly.
Existing roofing, siding and cladding materials such as wood, steel
sheets, fiberglass, asbestos cement and PVC sheets, suffer from several
disadvantages. For example, wood board is corrosive, water-sensitive, and has
bad fire performance. In addition, wood is not considered environmentally
friendly
and commonly, toxic materials are used to treat prime grade wood against
1o biodegradation and to improve fire resistance.
Steel sheets are very corrosive and react strongly to humid air and
polluted environments. Anti-corrosive coatings used on steel are impact- and
weather-sensitive. Furthermore, steel is not resilient, is not flexible,
suffers from
permanent deformation after strong forces are applied and has a high heat
transfer coefficient and a low insulating coefficient.
Fiberglass sheets are brittle, and have I!ow impact resistance, bad UV
and fire resistance. Also, the use of glass fibers in their productioh and
disposal is
not environmentally sound. Glass fbers are suspected of causing diseases, such
as fibrosis.
2o Asbestos cement sheets are brittle, corrosive and biodegradable {i.e.
fungus growth in the pores causes color change and embrittlement), have low
heat insulation, can cause asbestosis to human beings chronically exposed to
the
asbestos cement and are dangerous in fires, tending to explode and shatter in
extensive heat.
2
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PVC sheets are generally only suitable for use in light colors and in
medium temperature climates. Clear PVC sheets suffer from low impact
resistance and low UV resistance unless special modifiers are used.
Japanese Patent 8,183,054 assigned to JSP Corp. of Japan describes a
flat, foamed polycarbonate sheet. Furthermore, commercially available sheets
of
PC laminated with acrylic are produced by Tsutsunaka Plastic of Tokyo, Japan.
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SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polycarbonate (PC)
sheet material which can be used as an outdoor building material which
overcomes the limitations and disadvantages of existing materials. A system
for
the production of the PC sheet is also provided.
There is provided in accordance with a preferred embodiment of the
present invention a rigid polycarbonate (PC) sheet includinf a foamed PC
layer,
and a second PC layer co-extruded with the foamed PC Payer.
Moreover, in accordance with a preferrE;d embodiment of the present
io invention, the second PC layer includes UV-resistant material.
Furthermore, in accordance with a preferred embodiment of the present
invention, the sheet is one of a group including: a~ flat sheet, a corrugated
sheet
and a mufti-wall sheet.
Additionally, in accordance with a preferred embodiment of the present
invention, the rigid PC sheet further includes a third PC layer co-extruded
with the
foamed PC layer on the side opposite to the second PC layer.
Moreover, in accordance with a preferred embodiment of the present
invention, the third PC layer includes UV-resistant material.
Furthermore, in accordance with a preferred embodiment of the present
2o invention, the rigid PC sheet further includes a third PC layer co-extruded
with the
second PC layer on the side opposite to the foamed PC layer.
Additionally, in accordance with a preferred embodiment of the present
invention, the third PC layer includes UV-resistant material.
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There is provided in accordance with a preferred embodiment of the
present invention a method for production of a rigicl polycarbonate {PC)
sheet, the
method comprising the steps of feeding a first Pt; material into'a first
extrusion
line, foaming the first PC material, feeding a second PC material into a
second
extrusion line, co-extruding the frst PC material and the second PC material
into a
melt, extruding the melt through an extrusion die, and solidifying the melt
into a
rigid sheet. The second PC material forms a Payer on the first PC material.
Moreover, in accordance with a preferred embodiment of the present
invention, the step of foaming includes adding a chemical blowing agent to the
~o first PC material.
Furthermore, in accordance with a preferred embodiment of the present
invention, the step of foaming includes adding a liquid blowing agent to the
first
PC material.
Additionally, in accordance with a preferred embodiment of the present
~s invention, the step of foaming includes injecting liquefied gases at
sufFciently high
pressure into the first PC material.
Moreover, in accordance with a preferred embodiment of the present
invention, the step of foaming includes adding a chemical blowing agent to the
first PC material prior to the first PC material being fed into the first
extrusion line.
2o Furthermore, in accordance with a preferred embodiment of the present
invention, the method includes at feast one additional step of thermoforming
the
rigid sheet. The at feast one additional step of thermoforming is performed on-
line
or off line.
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There is provided in accordance with a preferred embodiment of the
present invention, a sheet material for outdoor building use comprising a
foamed
PC layer, and a second PC layer co-extruded with the foamed PC layer.
Moreover, in accordance with a preferred embodiment of the present
invention, the second PC layer includes UV-resistant material.
Furthermore, in accordance with a preferred embodiment of the present
invention, the sheet is one of a group including: a flat sheet, a corrugated
sheet
and a multi-wall sheet.
Additionaiiy, in accordance with a preferred embodiment of the present
~o invention, the thickness of the foamed PC layer is 1 - 10 millimeters, and
the
thickness of the second PC layer is 25 -100 microns.
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BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood a,nd appreciated more fully
from the following detailed description taken in conjunction with the appended
drawings in which:
s Fig. 1A is a schematic cross-section ilfustr~ation of a flat poiycarbonate
(PC) sheet, according to a preferred embodiment of the present invention;
Fig. 1 B is a schematic cross-section illustration of a corrugated
polycarbonate (PC) sheet, according to a further prE:ferred embodiment of the
present invention;
~o Fig. 2 is a block diagram iliustration of a s~,rstem for the production of
a
polycarbonate (PC) sheet, according to a preferred embodiment of the present
invention;
Fig. 3 is a schematic flowchart of the operation of the system of Fig. 2;
Figs. 4 and 5 are graphs of results of an accelerated weathering test on
a PC sheet, according to a preferred embodiment of the present invention; and
Fig. 6 is a table of results of a heat insulation test on a PC sheet,
according to a preferred embodiment of the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
Reference is naw made to Fig. 1A, which is a schematic illustration of a
cross-section of a flat polycarbonate (PC) sheet 10, according to a preferred
embodiment of the present invention. The p~olycarbonate (PC) sheet 10
comprises a rigid bulk foamed PC sheet 12 and a rigid skin layer 14 of UV
protective PC.
The skin layer 14 is applied via co-extrusion, but it will be apparent to
those skilled in the art that any other suitable method for applying the skin
layer
may be utilized. In a non-limiting example, the skin layer 14 of UV protective
PC
~o has a thickness of 30 microns. In a preferred embodiment, a PC sheet for
outdoor building is preferably composed of a 30-micron layer of UV protective
PC
and a 2-mm layer of foamed PC.
The PC sheet 10 is shown as being flat, having been extruded through a
flat sheet die. It will be appreciated that any shape of sheet may be
produced,
depending on the die used.
Reference is now made to Fig. 1 B, which is a schematic illustration of a
cross-section of a corrugated poiycarbonate sheet. The flat polycarbonate
sheet
10 of Fig. 1 has been thermoformed into a corrugated sheet. The foamed PC
sheet 12 and the skin layer 14 are thermoformed together into a corrugated
sheet.
zo In alternative embodiments, thermoforming may be used to transform the flat
PC
sheet 10 of Fig. 1 into complex or small size articles, such as, but not
limited to,
multi-wall sheets, roof ridges, roof tiles, flashings and accessories.
Fig. 2 is a block diagram illustration of a system for the production of a
polycarbonate (PC) sheet, according to a preferired embodiment of the present
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WO OU/07812 PCT/IL99/004I 1
invention. The system comprises an extruder 20, a co-extruder 22, a flat sheet
extrusion die 24, a therrnoformer 26, an edge trimnner 28, a cross 'cutter 30
and a
stacker 32.
Reference is now made additionally to Fig. 3, which is a schematic
s flowchart of the operation of the system of Fig. 2. In operation, a
pofycarbonate
(t'C) material 34 is fed (step 100) into the extruder 20. In a preferred
embodiment
of the present invention, a foaming agent 36, such as a chemical blowing
agent, is
fed (step 102) with the PC material 34 into the extruder 20. Other foaming
agents
can be used, for example, but not limited to, liquid blowing agents, which are
~o chemicals that decompose at the extrusion temperatures and release a gas
that
causes foaming. In another embodiment, the foarr~ing could be achieved by
using
"physical blowing", which is the injection of water or liquefied gases, such
as, but
not limited to, C02 and N2. In this embodiment, no chemical reaction is used
to
cause the foaming. In a further alternative embodiment, the PC material
already
contains the chemical blowing agent, and the addition of a blowing agent on-
line
can be omitted.
A special PC compound 38 with increased UV resistance properties is
fed (step 104) into the co-extruder 22. ProximatE: the exit of extruder 20,
the UV
protective PC compound 38 is combined (step 7 06) with the PC material 34 into
a
2o melt. This process, known as skin layer UV co-extrusion, is well knoVdn in
the art.
The melt consisting of the PC material 34 and the UV protective PC
compound 38 is forced (step 108} through the fiat sheet extrusion die 24. At
the
exit of the melt from the extrusion die 24, the PC material 34 foams due to
the
expansion of the gas released by the foaming agent 36. The UV protective PC
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compound 38 does not foam. The melt is then solidified (step 110) into a flat
sheet.
The flat sheet can be used as is or can be further thermoformed either
on-line or off line. On-line thermoforming into corrugated sheets and multi-
wall
sheets is the preferred method for sheets for building. Off line thermoforming
of
more complex or small size articles is the preferred method for producing roof
ridges, roof tiles, (lashings and accessories.
If thermoforming is used, the flat sheet is passed (step 112) through the
thermoformer 26. The corrugated (or flat} sheet is trimmed (step 114) by the
~o edge trimmer 28, cut (step 116) to its final size by the cross cutter 30 on-
line and
stacked (step 118) by the stacker 32 on pallets for ahipment.
The properties of a PC sheet comprising foamed PC and a skin layer of
UV protective PC make it suitable for use as an outdoor building material. It
is
well known in the art that PC is resistant to fungus>, microorganisms, humic
acids
1s and termite attack. It is also known that PC is water-resistant and
impermeable.
PC can be colored internally, with no need to paint or coat. PC is suitable
for
contact with food. Furthermore, since no hazardous materials are used in the
production or disposal of PC, and since it is fully recyclable, PC is an
environmentally friendly material. Another advantage of PC is that its service
2o temperature is above 100°C. This is very important for dark colored
building
materials that are subject to strong solar radiation and may heat up to
temperatures of 80 - 90°C. The properties mentioned hereinabove are
described
in L. Bottenbruch, Enqineering Thermot~lastics~ Poiycarbonates Polyacetals,
Polyesters, Cellulose Esters, Carl Hanser Verlag (1996) pp. 177 - 181, 194,
198,
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200, 254 and 259. It is known in the art that PC has good sound insulation
properties.
The skin layer of UV protective PC provides UV and weathering
resistance. An accelerated .weathering test using the QUV Accelerated
Weathering Tester produced by Q-Panel Lab Products of Cleveland, Ohio, USA
was conducted on a PC sheet according to a preferred embodiment of the
present invention. The test exposes materials to alternating cycles of light
and
moisture at controlled elevated temperatures, thereby reproducing the damage
caused by sunlight, rain and dew. The test involved exposing the PC sheet to
UV
io exposure (UVB, 20h radiation, 4h condensation, '45°C), and then
testing tensile
strength at yield (ASTM D-638 - 10 mm/min) and elongation at break (ASTM
D-638 - 10 mmlmin). The results are shown in Figs. 4 and 5, to which reference
are now made, which are graphs of tensile strength (in MPa) and elongation (in
%), respectively, per hours of QUV exposure. The conclusion of the test was
that
zs the PC sheet retains its mechanical properties after 1500 hours of QUV
exposure.
It is welt known that PC, being a plastic, is non-corrosive. Furthermore,
as described in Chemical Resistance - Thermoplastics, 2"d edition, Plastics
Design Library USA, (1994) vol. 1, p. 404, PC is resistant to acid rain and
air
pollution.
Zo According to the Applicant's internal impact tests, the PC sheet of the
present invention is ductile and resilient, as well as resistant to hail and
wind. A
falling bag test according to the AustralianlNe:w Zealand standard, AS/NZS
4040.4:1996 "Design and installation of sheet cool' and cladding I part 3:
plastics",
was conducted on a PC sheet according to a preferred embodiment of the
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present invention. The sandbag did not penetrate i:he PC sheet, and no holes
nor
splinters were formed, leaving the PC sheet intact.
Reference is now made to Fig. 6, which is a table of results of a heat
insulation test conducted by the Standards institution of Israel on a PC sheet
s according to a preferred embodiment of the present invention. The standard
test
(ASTM-C177-85} was conducted on two PC sheet;> of approximately 30x30x3 cm,
and it was found that the PC sheet has good heat insulation due to its foam
structure.
Standard burn tests (ASTM-D 635 - 91 ) were conducted by Warnock
io Hersey fnc. on PC sheets according to a preferred embodiment of the present
invention. The results, that foamed polycarbonate had an average extent of
burn
of 14.8 mm, snow that the PC sheet is fire resistant. Self-venting properties
allow
it to melt and disappear in extreme heat, thereby allowing smoke to escape
from a
burning building, and reducing the likelihood of injuries due to smoke
inhalation.
It will be appreciated by persons skillE~d in the art that the present
invention is not limited to what has been particularly shown and described
hereinabove. Rather the scope of the present invention is defined only by the
claims which follow:
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