AU2007100299A4 - Developments Relating to Plastic Sheet Materials - Google Patents

Description

2007 04/13 14:35 FAX +61 3 9543 2711 MORCOM PERNAT I006/017 0

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION INNOVATION PATENT "Developments Relating to Plastic Sheet Materials" The following statement is a full description of this invention, including the best method of performing it known to us: COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:35 FAX +61 3 9543 2711 MOCMPRAIj07/1 MORCON PERNAT [a 007/017 2 DEVELOPMENTS RELATING

TO

PLASTIC SHEET MATERIALS Field of the Invention This invention concerns the use of a particulate additive to the material comprising at o least one surface of a plastic sheet material in order to increase the tendency for sheets of the material to separate from underlying layers of the same sheet material- Background to the Invention Polycarbonate based sheet materials have become increasingly popular as transparent architectural panels because of their combination of durability, clarity and their weatherability and UV stability when appropriate protective layers or additives. are incorporated on the side of the sheet exposed to the weather. The sheeting material is sold with a profiled cross-section and in a flat configuration. Typically the sheet material has a total thickness of 0.7 to 12mm. Commonly it includes a top layer about 50 micron (gin) thick on one of the faces which includes additives to suppress UV light transmission and to improve the weathering resistance characteristics of the sheet material. Thus the sheet material has a layered structure.

When rigid plastic sheeting is stacked together, the individual sheets often tend to stick together so that they are difficult to separate by hand. This can result in damage being caused to one or more sheets of the material as people struggle to separate the sheets and damage the sheets in the process. The problem arises with both flat and profiled plastic sheets.

It is known to add some particulate mineral materials to polycarbonate resin films and to polyc-arbonate rigid sheet materials in order to assist separation of the sheets.

However these additives have all been of particulate mineral which damages the sheet manufacturing equipment.

COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:36 FAX +61 3 9543 2711 MRO ENTIj0/1 MORCOM PERNAT [a 008/017 Conventional manufacturing equipment for flat and profile sheet comprises of an inline assembly of machines. The front end of this assembly is used in common for both flat and profile sheet manufacture and includes a "chill roll stack"' which consists of three highly polished chromed steel rolls through which the extruded polymer's thickness is determined and then cooled. For flat sheet, these rolls require a mirror like polish. But the mineral particles added to the sheet material damage the surface polish, thus rendering the rolls unsuitable for flat sheet production.

When profile sheet is produced, flat sheet from the chill roll stack is directed to an oto inline re-heating oven which thernally softens the cooled flat sheet alter which it passes through profile forming rolls. When flat sheet is produced, the cooled flat sheet either bypasses both the re-heating oven and profile forming rolls or passes through the disabled oven and rolls unaffected.

An aim of the present invention is to provide a sheet and manufacturing process which utilises polymeric particles instead of the mineral particulates. The polymeric particles are "softer" than the previously used mineral particles and do not damage the surface of the rolls. Flat and profile plastic sheet materials made by the process may be easily separated from a stack of like sheets.

Summary of the Invention Accordingly, in one aspect the invention provides a plastic sheet material having a pair of mutually obverse faces at least one of which faces comprises a mixture of polymeric particles sized in the range 1 to 50 micron suspended in a polymeric matrix.

Preferably said polymeric particles are forned of high molecular weight and/or crosslinked polymers synthesized from one or more monomers selected from the group consisting of: styrene; methyl-styrene; acrylonitrile; diene-containing monomers including butadiene; acrylic acid ester or polyester; met-acrylic acid ester or polyester; maleic acid anhydride or ester; vinyl-containing monomer; phthalic acid ester; and tri-mellitic anhydride, acid or ester.

COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:36 FAX +61 3 9543 2711 MORCOM PERNAT 1009/017 O 4 EPreferably said polymeric matrix comprises material selected from the following group: Spolycarbonate (PC) either branched or unbranched, polyethylene-terephthalateglycol (PETG), polyethyleneterephthalate (PET), polymethylmnethacrylate

(PMMA),

0 polyvinylchloride (PVC), and combinations thereof.

ci o The shape of said polymeric particles is preferably spheroidal or ellipsoidal, but may alternatively be angular.

01 ~Preferably said polymeric particles are formed by a suspension polymerisation process. Alternatively they may be formed by micronising larger particles.

Said polymeric particles preferably comprise in the range 0.05 to 5% by weight of said mixture of polymeric particles in the polymeric matrix. More preferably the polymeric particles comprise in the range 0.1 to even more preferably less than and still more preferably in the range 0.2 to 0.6% by weight of said mixture of polymeric particles in the polymeric matrix.

Said plastic sheet material may be a rigid plastic sheet, preferably having a thickness in the range 0.5 to 10mm. The polymeric particles may be distributed throughout the full thickness of the plastic sheet material, but preferably the polymeric particles are incorporated into a first layer of said polymeric matrix material which is co-extruded onto a second layer comprising a substrate sheet material where said substrate sheet material may or may not be the same as said matrix material. Said plastic sheet material may comprise a relatively thick substrate layer with a relatively thin cap or coating layer thereon. Preferred embodiments have a substrate layer of 0.7 to 1.3mm thick polycarbonate with a coating layer of 0.03 to 0.08mm thick polycarbonate on one side.

The polymeric particles may be incorporated into the outside one of a plurality of layers which are applied with or to an underlying substrate to form the complete plastic sheet material.

COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:37 FAX +61 3 9543 2711 MORCOM PERNAT M010/017 0 0 ci en Said plastic sheet material and/or said coating layer may also contain colorants, thermal stabilisers, weathering stabilisers such as Hindered Amine Light Stabilisers (HALS), ultra-violet light absorbers (UVAs), or combinations thereof The inclusion of the polymeric particles in the matrix means that the surface including the particles is rougher and has a roughened texture due to the particles protruding from the otherwise flat surface. The protruding lumps provide clearance for a small air gap to be formed between the adjacent faces of a stack of sheets and this air gap allows the sheets to be much more readily separated.

Description of a Preferred Embodiment and Other Examples of the Invention In one embodiment of the invention, a two-layer polycarbonate sheet is produced by co-extruding a body layer of 0.8mm thickness together with a cap layer of 0.05mm thickness and passing this through a chill roll stack in conventional polycarbonate sheet manufacturing equipment. Both layers comprise a base material of polycarbonate polymer. The thickness of the body layer can be selected within the range 0.75 to 0.90mm and the thickness of the cap layer selected within the range 0.040 to 0.060mm. For heavier duty applications, the polycarbonate sheet is typically produced with a body layer of 1.1 to 1.3mm thickness and a cap layer in the range of 0.040 to 0.060mm.

The body layer contains:

UVA

HALS

Colorants The cap layer contains:

UVA

HALS

Colorants Optical brightener Polymeric particles 0.00 to 0.60 by weight (typically 0.3%) 0.0 to 0.40 by weight (typically nil) 0.0001 to 1.5 by weight (typically 1 to 2ppm) 2.0 to 8.0 by weight (typically 7%) 0.0 to 0.4 by weight (typically nil) 0.001 to 1.5% by weight (typically 0.003%) 0.0001 to 0.1% by weight (typically 0.01%) 0.05 to 0.8% by weight (typically 0.6%) COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:37 FAX +61 3 9543 2711 MRO ENTI11/1 MORCOM PERNAT R011/017 6 The specific polycarbonate material and quantity of the IJVA, HILLS, colorants and M optical brightener additives listed above as used in the body layer and cap layer vary according to the specific end purpose of the sheet material being made, and are readily selectable according to that purpose by those skilled in the art.

o During manufacture of the polycarbonate sheet, the molten polymer for the body o layer and the differently formulated molten polymer for the cap layer are typically fed from a layered supply. The material to be extruded is drawn from around the o1t interface area. The resultant sheet is uniformly bonded throughout its thickness, even though the composition changes fairly abruptly between the body layer and the cap layer.

The polycarbonate sheet coming out of the extruder's die passes through the 'nip' between two (a first and a second) of the three "chill" rolls, and then wraps around the first roll for approximately 180'. The polymer on the body-layer side of the sheet is then in direct contact with the first roll and cools quickly while the other surflace (on the cap-layer side) stays softer for longer. During that chilling stage, the caplayer side is unrestrained and, as that surface cools, the polymer matrix contracts and the polymeric particles are left standing slightly proud of the surrounding surface of matrix material. They are mainly covered in a thin layer of the base polymer of the matrix so causing each polymeric particle to create a microscopic bump on the surface. After the cooled but still soft sheet has travelled the approximate 180' around said first roll, the sheet transfers to the third roller and cools the cap-layer side which is then in contact with the third roller.

The polymeric particles (beads) included in the cap layer have a melting point higher than the polycarbonate. The beads are softened while they are in the molten polycarbonate but their cross-linked structure causes them to resist permanent distortion when soft, so they maintain their inherent shape during the extrusion process.

COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:37 FAX +61 3 9543 2711 MRO ENTij1/1 NORCOM PERNAT Q012/017 The polymeric particles are too soft to scratch-mar the polished chill rolls, thus enabling both flat and profile sheet to be produced on the sane extrusion line.

While the above described example incorporates the polymeric particles into a thin layer which is applied to an underlying substrate material having no such polymeric particles included in it, the polymeric particles could be incorporated into a single o layer of material which comprises the entire thickness of the sheet material.

Alternatively, the plastic sheet material could be a composite of more than two layers with, for example, an underlying thick substrate to which is applied a thin layer of material containing a colorant and wit a further layer over the top of that containing weathering stabilisers and UV light absorbers plus the polymeric particles which provide the surface roughness required by the present invention.

Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention.

For example in the above description of the preferred embodiment the freshly extruded polycarbonate sheet wraps around the first chill roll with the body layer in contact with the first chill roll. In an alternative embodiment however, it is the cap layer which held in contact with the first chill roll and this produces a sheet where (initially) the polymeric particles in the cap do not create the minute bumps in its surface. However when such sheet material is later formed into a profile, the sheet is softened by heating during the shaping process, and that heating and the subsequent cooling stages can cause the polymeric particles to "rise towards the surface" thus creating the desired surface roughness.

It will be also understood that where the word "comprise", and variations such as "comprise" and "comprising", are used in this specification, unless the context COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:38 FAX +61 3 9543 2711 MORCOM PERNAT [013/017 8 0 0 requires otherwise such use is intended to imply the inclusion of a stated feature or Sfeatures but is not to be taken as excluding the presence of other feature or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the Scommon general knowledge in Australia.

0 0 0 0 ci COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13

Claims (4)

1. 2. A plastic sheet material according to claim 1 wherein said polymeric particles F are formed of high molecular weight and/or cross-linked polymers synthesized from O 10 one or more monomers selected from the group consisting of: styrene, methyl-styrene, acrylonitrile, diene-containing monomers including butadiene; acrylic acid ester or polyester, meth-acrylic acid ester or polyester, maleic acid anhydride or ester, vinyl-containing monomer, phthalic acid ester, and tri-mellitic anhydride, acid or ester; and said polymeric matrix comprises material selected from the group consisting of: polycarbonate (PC) either branched or unbranched, polyethylene-terephthalateglycol (PETG), polyethyleneterephthalate (PET), polymethylmethacrylate (PMMA), polyvinylchloride (PVC), and combinations thereof.
2. 3. A plastic sheet material according to claim 1 or 2 wherein the shape of said polymeric particles is spheroidal or ellipsoidal. COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13 2007 04/13 14:38 FAX +61 3 9543 2711 MORCOM PERNAT [@015/017 1
3. 4. A plastic sheet material according to any one of the previous claims wherein said mixture of polymeric particles in the polymeric matrix comprises in the range 0.05 to 5.0% by weight of said polymeric particles.
4. 5. A plastic sheet material according to any one of the previous claims wherein said plastic sheet material is a rigid sheet, the polymeric particles are incorporated Sinto a first layer of said polymeric matrix material which is formed onto one side of a o second layer comprising a substrate sheet material, said substrate sheet material is a 0 layer of 0.7 to 1.3mm thick polycarbonate, and said first layer is a cap of 0.03 to 0 10 0.08mm thick polycarbonate. Dated this 13th day of April 2007 Kantfield Pty Ltd by their patent attorneys Morcom Perat COMS ID No: SBMI-06980723 Received by IP Australia: Time 14:43 Date 2007-04-13