WO1998005707A1 - Foamable polyvinyl alcohol composition - Google Patents

Foamable polyvinyl alcohol composition Download PDF

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Publication number
WO1998005707A1
WO1998005707A1 PCT/GB1997/002103 GB9702103W WO9805707A1 WO 1998005707 A1 WO1998005707 A1 WO 1998005707A1 GB 9702103 W GB9702103 W GB 9702103W WO 9805707 A1 WO9805707 A1 WO 9805707A1
Authority
WO
WIPO (PCT)
Prior art keywords
polyvinyl alcohol
blend
irradiation
water
extruder
Prior art date
Application number
PCT/GB1997/002103
Other languages
French (fr)
Inventor
Paul Taylor
Original Assignee
Polyval Plc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Polyval Plc filed Critical Polyval Plc
Priority to EP97934649A priority Critical patent/EP0914368A1/en
Priority to AU37791/97A priority patent/AU3779197A/en
Publication of WO1998005707A1 publication Critical patent/WO1998005707A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
    • C08J9/125—Water, e.g. hydrated salts
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/05—Alcohols; Metal alcoholates
    • C08K5/053—Polyhydroxylic alcohols
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
    • C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
    • C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids

Definitions

  • This invention relates to polyvinyl alcohol compositions which are biodegradable and, hence, environmentally friendly alternatives to polystyrene, polyethylene and other synthetic resins.
  • a foamed or expanded product capable of use in the form of individual pieces as loose fill packaging material, insulation and cushioning material, and in the form of sheets and blocks as insulation, particularly in the construction industry.
  • foamed polyvinyl alcohol has been proposed in the past, it has never been practical to product in a large scale, particularly by extrusion techniques of the type used for polyalkylenes.
  • foamed product which does not require formaldehyde in its manufacture
  • compositions having a mol % hydrolysis figure of 74 to 94, e.g. 80 to 90 for a cold water soluble product or 98 to 100, e.g. about 99 for a hot water soluble product with a minor proportion of glycerol and water, optionally with colouring and opacifying agent or the like, the blend being allowed to reach a temperature of at least 100;
  • the polyvinyl alcohol used in step 1 is chosen desirably to be hot water soluble and compostable and thus has a mol % hydrolysis value of at least 98, more particularly a hydroxy content or about 99. It may be desirable to blend two or more polyvinyl alcohol compositions to obtain the correct properties, for example a product within a % mol hydrolysis value of 98% and a viscosity of 56 mPa.s and a product with a mol % hydrolysis value of 99% and a viscosity of 28 mPa.s.
  • the final blend passed to the extruder typically contains from 60% to 70% polyvinyl alcohol, the remaining part (other than colouring or opacifying additives) comprising glycerol and water in the range 2:1 to 3:l preferably about 2.5: 1. Most preferably the blend contains about 65% polyvinyl alcohols, about 25% glycerol, about 10% water and about 0.25% opacifier (such as a finely divided silica or T,O 2 ) with optional colouring agent.
  • polyvinyl alcohol the remaining part (other than colouring or opacifying additives) comprising glycerol and water in the range 2:1 to 3:l preferably about 2.5: 1.
  • Most preferably the blend contains about 65% polyvinyl alcohols, about 25% glycerol, about 10% water and about 0.25% opacifier (such as a finely divided silica or T,O 2 ) with optional colouring agent.
  • the blend should preferably be allowed to reach a temperature of at least 105°C in order to obtain an intimate mixing of the various ingredients which is suitably plasticised and extrudable.
  • a temperature of 25°C to 35°C, e.g. about 30°C is suitable.
  • Extrusion can take place in a general purpose screw extruder having controlled zonal heating to give a temperature profile along the barrel.
  • a typical temperature profile is for the barrel to have four zones in sequence running at 70 to 125, e.g. about 100°C, about 120°C, about 130°C and 125 to 240, e.g. about 130°C, leading to an adapter also running at about 130°C leading to the die which should be operated at a slightly higher temperature, typically 135°C to 140°C.
  • a typical apparatus has a 2: 1 compression and should be operated at maximum screw speed.
  • a typical example of such an extruder is a standard commercially available 38 mm extruder Betol, Luton, England.
  • the inlet for water injection should be at an intermediate point, typically between zones 2 and 3, but possibly at a later stage. There should be sufficient processing time after injection for the water to be intimately mixed with the blend before reaching the die.
  • the die is treated with a PTFE non-stick coating.
  • the die may be of any appropriate geometry depending on the nature of the extrudate required, e.g. a ribbon, rod or film.
  • Paniculate material for use in packaging and insulation can be obtained by passing the extruded ribbon through a rotary cutter.
  • the extruded product typically has a cell size of 0.1 mm to 8 mm and a bulk density similar to that of expanded polystyrene.
  • This material can be used for all the purposes where expanded polystyrene is typically useful but possesses the following distinct advantages:
  • the material is anti-static.
  • the product has an excellent conformation memory, being able to regain its original shape after compression better than expanded polystyrene.
  • the material has a much lower fire risk, being less inflammable and producing less toxic fumes when burnt.
  • the material is totally compostable, hot water soluble or cold water soluble as required, and recyclable into adhesives etc. 6. It is possible to add standard fire retardant additives to render the material totally fireproof.
  • the product has excellent insulation properties, typically having a U-value similar to that of other expanded foams.
  • the blend can be modified by supplementing/replacing part of the polyvinyl alcohol with a compatible resin capable of curing under irradiation, e.g. by UV light.
  • a compatible resin capable of curing under irradiation, e.g. by UV light.
  • Typical materials are resins used in the photo-resist field, in particular cinnamic esters such as polyvinyl cinnamate, or alternatively adding an irradiation-activated curing agent for the polyvinyl alcohol, for example an alkaline metal or ammonium dichromate or a proprietary diazo compound.
  • the blend is extruded as described above, cooled and then subjected to irradiation, typically by UV light in an appropriate chamber.
  • irradiation typically by UV light in an appropriate chamber.
  • the time of exposure and the levels of curing material included in the composition will determine the degree of surface cure. If only the surface is required to cure, the composition can be made opaque to UV light by appropriate additives.
  • the product is obtained with a cured outer coating which renders the product completely impermeable. It will be recognised that this is a significant advance over standard polyvinyl alcohol films which have a permeability which is subject to variation with the relative humidity of the surrounding atmosphere. Typical polyvinyl alcohol products tend to be impermeable under dry conditions but permeable under humid conditions. For many applications, this is undesirable.
  • the UV-curing treatment can be applied to a polyvinyl alcohol product, particularly an extruded film, which is not expanded.
  • a polyvinyl alcohol product particularly an extruded film
  • the production is as described above, without the intermediate injection of water.
  • the extruder is run at higher intermediate and final temperatures and the barrel is vented, in order to evaporate much of the water and glycerol before extrusion to prevent bubbles forming in the extrudate, typically at zone temperatures (as defined above) in the region of 140, 190, 230, 210, 210 and 233°C respectively.
  • the product in this case, is a material with an exterior which is impermeable to gases and water, but which is nevertheless biodegradable and hot water soluble once the surface is disrupted, for example by mechanical abrasion or shredding.
  • the UV-curable component typically polyvinyl cinnamate
  • the extruded product may be applied to the extruded product as a spray or dip coating using an aqueous solution and subsequent irradiation.
  • the extruded product could be treated with an active derivative of cinnamic acid, e.g. cinnamoyl chloride in the presence of a base such as pyridine, to esterify the surface.
  • the screw speed should be set at maximum (typically 75 rev. min " ).
  • the temperatures and speed are adjusted for optimum performance depending upon size of machine.
  • the above profile is based on 38 mm extruder (Betol).
  • Example 1 The procedure of Example 1 was repeated, but including the step of spray cooling the extrudate with an aqueous 5% solution of ammonium dichromate and subsequent exposure to UV to produce a surface-cured product which is effectively waterproof but which can be rendered hot water soluble by being shredded or abraded.
  • Polyvinyl cinnamate 50% of Mowiol weight Place all ingredients into a Baker Perkins mixer and run on full speed until the temperature in the chamber reaches 110°C. Transfer the blend to a cooler and cool to 30°C.
  • the Kytron vernier is set at 5.6 with 3: 1 screws.
  • the extruder screw speed is set at 20 rev. min "1 .
  • the adaptor is a 10 mm diameter extruder (Betol, Type BC38).
  • the die may be either sheet or blown film type.

Abstract

Foamed polyvinyl alcohol can be produced by extruding in the presence of water which acts as a blowing agent. The material is rendered waterproof by incorporating UV-curable resin.

Description

FOAMABLE POLYVINYL ALCOHOL COMPOSITION
This invention relates to polyvinyl alcohol compositions which are biodegradable and, hence, environmentally friendly alternatives to polystyrene, polyethylene and other synthetic resins.
In one aspect of the present invention, a foamed or expanded product is provided, capable of use in the form of individual pieces as loose fill packaging material, insulation and cushioning material, and in the form of sheets and blocks as insulation, particularly in the construction industry. While foamed polyvinyl alcohol has been proposed in the past, it has never been practical to product in a large scale, particularly by extrusion techniques of the type used for polyalkylenes. In particular, there is a need for a foamed product which does not require formaldehyde in its manufacture
We have now devised a process for the production of a foamed polyvinyl alcohol composition comprising the following steps:
1 blending one or more finely divided polyvinyl alcohol formulations, in particular compositions having a mol % hydrolysis figure of 74 to 94, e.g. 80 to 90 for a cold water soluble product or 98 to 100, e.g. about 99 for a hot water soluble product with a minor proportion of glycerol and water, optionally with colouring and opacifying agent or the like, the blend being allowed to reach a temperature of at least 100;
2. passing the blend through a screw extruder and extruding the material at a die temperature of 125 to 240°C, the blend having been saturated with water, either by simultaneously injecting water at an intermediate point in the extruder barrel, or by first soaking the blend in water and then drying the surface before introduction into the extruder. By this method, the water becomes closely absorbed in the blend while it is being treated in the screw barrel under pressure and instantaneously boils on passing the extruder die, thus foaming and expanding the extrudate
The polyvinyl alcohol used in step 1 is chosen desirably to be hot water soluble and compostable and thus has a mol % hydrolysis value of at least 98, more particularly a hydroxy content or about 99. It may be desirable to blend two or more polyvinyl alcohol compositions to obtain the correct properties, for example a product within a % mol hydrolysis value of 98% and a viscosity of 56 mPa.s and a product with a mol % hydrolysis value of 99% and a viscosity of 28 mPa.s.
The final blend passed to the extruder typically contains from 60% to 70% polyvinyl alcohol, the remaining part (other than colouring or opacifying additives) comprising glycerol and water in the range 2:1 to 3:l preferably about 2.5: 1. Most preferably the blend contains about 65% polyvinyl alcohols, about 25% glycerol, about 10% water and about 0.25% opacifier (such as a finely divided silica or T,O2) with optional colouring agent.
The blend should preferably be allowed to reach a temperature of at least 105°C in order to obtain an intimate mixing of the various ingredients which is suitably plasticised and extrudable.
It may be desirable to cool the blend and store it before passing it to the extruder. Typically, a temperature of 25°C to 35°C, e.g. about 30°C is suitable.
Extrusion can take place in a general purpose screw extruder having controlled zonal heating to give a temperature profile along the barrel. A typical temperature profile is for the barrel to have four zones in sequence running at 70 to 125, e.g. about 100°C, about 120°C, about 130°C and 125 to 240, e.g. about 130°C, leading to an adapter also running at about 130°C leading to the die which should be operated at a slightly higher temperature, typically 135°C to 140°C. A typical apparatus has a 2: 1 compression and should be operated at maximum screw speed. A typical example of such an extruder is a standard commercially available 38 mm extruder Betol, Luton, England.
The inlet for water injection should be at an intermediate point, typically between zones 2 and 3, but possibly at a later stage. There should be sufficient processing time after injection for the water to be intimately mixed with the blend before reaching the die.
In a preferred embodiment, the die is treated with a PTFE non-stick coating.
The die may be of any appropriate geometry depending on the nature of the extrudate required, e.g. a ribbon, rod or film. Paniculate material for use in packaging and insulation can be obtained by passing the extruded ribbon through a rotary cutter.
The extruded product typically has a cell size of 0.1 mm to 8 mm and a bulk density similar to that of expanded polystyrene. This material can be used for all the purposes where expanded polystyrene is typically useful but possesses the following distinct advantages:
1. The material is anti-static.
2. It has a higher strength
3. The product has an excellent conformation memory, being able to regain its original shape after compression better than expanded polystyrene.
4. The material has a much lower fire risk, being less inflammable and producing less toxic fumes when burnt.
5. The material is totally compostable, hot water soluble or cold water soluble as required, and recyclable into adhesives etc. 6. It is possible to add standard fire retardant additives to render the material totally fireproof.
7. The product has excellent insulation properties, typically having a U-value similar to that of other expanded foams.
In a preferred embodiment of the invention, the blend can be modified by supplementing/replacing part of the polyvinyl alcohol with a compatible resin capable of curing under irradiation, e.g. by UV light. Typical materials are resins used in the photo-resist field, in particular cinnamic esters such as polyvinyl cinnamate, or alternatively adding an irradiation-activated curing agent for the polyvinyl alcohol, for example an alkaline metal or ammonium dichromate or a proprietary diazo compound.
In this modification, the blend is extruded as described above, cooled and then subjected to irradiation, typically by UV light in an appropriate chamber. The time of exposure and the levels of curing material included in the composition will determine the degree of surface cure. If only the surface is required to cure, the composition can be made opaque to UV light by appropriate additives.
Thus, in this embodiment, the product is obtained with a cured outer coating which renders the product completely impermeable. It will be recognised that this is a significant advance over standard polyvinyl alcohol films which have a permeability which is subject to variation with the relative humidity of the surrounding atmosphere. Typical polyvinyl alcohol products tend to be impermeable under dry conditions but permeable under humid conditions. For many applications, this is undesirable.
In a further modification of the present invention, the UV-curing treatment can be applied to a polyvinyl alcohol product, particularly an extruded film, which is not expanded. In this case the production is as described above, without the intermediate injection of water. In this case, the extruder is run at higher intermediate and final temperatures and the barrel is vented, in order to evaporate much of the water and glycerol before extrusion to prevent bubbles forming in the extrudate, typically at zone temperatures (as defined above) in the region of 140, 190, 230, 210, 210 and 233°C respectively. The product, in this case, is a material with an exterior which is impermeable to gases and water, but which is nevertheless biodegradable and hot water soluble once the surface is disrupted, for example by mechanical abrasion or shredding.
In an alternative embodiment, the UV-curable component, typically polyvinyl cinnamate, may be applied to the extruded product as a spray or dip coating using an aqueous solution and subsequent irradiation. In a less preferred embodiment, the extruded product could be treated with an active derivative of cinnamic acid, e.g. cinnamoyl chloride in the presence of a base such as pyridine, to esterify the surface.
The following examples illustrate the invention further:
Example 1
Hot Water Soluble Blown Film
Materials
50:50 blend Mowiol® 56-98, 28-99 (Hoechst)
25% Glycerol
10% Water
0.25% Silica R972
Colouring agent (if required)
Place all materials into Baker Perkins Hydisperser (or other similar mixer), mix on full speed until temperature in chamber reaches 109°C. Transfer mix into a cooler and cool until temperature of blend reaches 30°C. Place materials in the hopper of an extruder using 2: 1 compression general purpose screw. The barrel has water injection system at or near zone two for increased foaming properties.
Typical profile:
Zone 1 Zone 2 Zone 3 Zone 4 adapter die
100°C 120°C 130°C 130°C 130°C 135°C
The screw speed should be set at maximum (typically 75 rev. min" ). The temperatures and speed are adjusted for optimum performance depending upon size of machine. The above profile is based on 38 mm extruder (Betol).
Example 2
Waterproof, Hot Water Soluble Blown Film
The procedure of Example 1 was repeated, but including the step of spray cooling the extrudate with an aqueous 5% solution of ammonium dichromate and subsequent exposure to UV to produce a surface-cured product which is effectively waterproof but which can be rendered hot water soluble by being shredded or abraded.
Example 2
Cold Water Soluble/waterproof film
Materials
Mowiol 56-88 (Hoechst)
Glycerol 15% of Mowiol weight
Water 5% of Mowiol weight
Silica R972 0.25% of Mowiol weight
Polyvinyl cinnamate 50% of Mowiol weight Place all ingredients into a Baker Perkins mixer and run on full speed until the temperature in the chamber reaches 110°C. Transfer the blend to a cooler and cool to 30°C.
Place the plasticised composition into the hopper of Kytron Soder twin screw feeder arranged to supply an extruder with a vented barrel and a screw of an appropriate type for polyvinyl alcohol.
Temperature profile from hopper to die (°C)
Zone 1 Zone 2 Zone 3 Zone 4 Adaptor Die
140 190 230 210 210 233
The Kytron vernier is set at 5.6 with 3: 1 screws. The extruder screw speed is set at 20 rev. min"1. The adaptor is a 10 mm diameter extruder (Betol, Type BC38). The die may be either sheet or blown film type.
After film extruded it is cooled in conventional manner and passes through an ultra violet chamber for subsequent exposure. The time of exposure together with relative levels of polyvinyl cinnamate present within the mix will determine the "coating" thickness within the Enpol film.

Claims

CLAIMS:
1. A process for the production of a foamed polyvinyl alcohol composition comprising the following steps:
a) blending one or more finely divided polyvinyl alcohol formulations, in particular compositions having a mol % hydrolysis figure of 74 to 94, e.g. 80 to 90 for a cold water soluble product or 98 to 100, e.g. about 99 for a hot water soluble product with a minor proportion of glycerol and water, optionally with colouring and opacifying agent or the like, the blend being allowed to reach a temperature of at least 100;
b) passing the blend through a screw extruder and extruding the material at a die temperature of 125 to 240°C, the blend having been saturated with water, either by simultaneously injecting water at an intermediate point in the extruder barrel, or by first soaking the blend in water and then drying the surface before introduction into the extruder.
2. A process according to Claim 1, in which the blend is modified by supplementing/replacing part of the polyvinyl alcohol with a compatible resin capable of curing under irradiation, or alternatively adding an irradiation-activated curing agent for the polyvinyl alcohol, or the UV-curable component or curing agent is applied to the extruded product as a spray or dip coating using an aqueous solution and subsequent irradiation.
3. A process for the production of an extruded polyvinyl alcohol composition in which a blend of polyvinyl alcohol(s) and plasticisers is extruded characterised in that the blend is modified by supplementing/replacing part of the polyvinyl alcohol with a compatible resin capable of curing under irradiation, or alternatively adding an irradiation-activated curing agent for the polyvinyl alcohol or the UV-curable component or curing agent is applied to the extruded product as a spray or dip coating using an aqueous solution and subsequent irradiation.
PCT/GB1997/002103 1996-08-05 1997-08-05 Foamable polyvinyl alcohol composition WO1998005707A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP97934649A EP0914368A1 (en) 1996-08-05 1997-08-05 Foamable polyvinyl alcohol composition
AU37791/97A AU3779197A (en) 1996-08-05 1997-08-05 Foamable polyvinyl alcohol composition

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9616460A GB2316080A (en) 1996-08-05 1996-08-05 Polyvinyl alcohol compositions
GB9616460.3 1996-08-05

Publications (1)

Publication Number Publication Date
WO1998005707A1 true WO1998005707A1 (en) 1998-02-12

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Family Applications (1)

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PCT/GB1997/002103 WO1998005707A1 (en) 1996-08-05 1997-08-05 Foamable polyvinyl alcohol composition

Country Status (5)

Country Link
EP (1) EP0914368A1 (en)
AU (1) AU3779197A (en)
GB (1) GB2316080A (en)
WO (1) WO1998005707A1 (en)
ZA (1) ZA976971B (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2366798A (en) * 2000-09-13 2002-03-20 Procter & Gamble Elastic article
GB2366796A (en) * 2000-09-13 2002-03-20 Procter & Gamble Foam component

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5884736A (en) * 1981-11-14 1983-05-20 Sekisui Plastics Co Ltd Preparation of thermoplastic resin foam
US4874562A (en) * 1986-02-13 1989-10-17 Biomaterials Universe, Inc. Method of molding a polyvinyl alcohol contact lens
US5147344A (en) * 1990-03-10 1992-09-15 Beiersdorf Aktiengesellschaft Hydrogel foams, and a process for their preparation
JPH04295377A (en) * 1991-03-25 1992-10-20 Sumitomo Metal Ind Ltd Golf tee

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4248812A (en) * 1977-07-18 1981-02-03 Japan Exlan Company Limited Process for producing a rush-like structure
US5308879A (en) * 1992-09-07 1994-05-03 Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha Process for preparing biodegradable resin foam
IT1274603B (en) * 1994-08-08 1997-07-18 Novamont Spa BIODEGRADABLE PLASTIC EXPANDED MATERIALS

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5884736A (en) * 1981-11-14 1983-05-20 Sekisui Plastics Co Ltd Preparation of thermoplastic resin foam
US4874562A (en) * 1986-02-13 1989-10-17 Biomaterials Universe, Inc. Method of molding a polyvinyl alcohol contact lens
US5147344A (en) * 1990-03-10 1992-09-15 Beiersdorf Aktiengesellschaft Hydrogel foams, and a process for their preparation
JPH04295377A (en) * 1991-03-25 1992-10-20 Sumitomo Metal Ind Ltd Golf tee

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 007, no. 183 (M - 235) 12 August 1983 (1983-08-12) *
PATENT ABSTRACTS OF JAPAN vol. 017, no. 108 (C - 1032) 5 March 1993 (1993-03-05) *

Also Published As

Publication number Publication date
GB9616460D0 (en) 1996-09-25
AU3779197A (en) 1998-02-25
GB2316080A (en) 1998-02-18
ZA976971B (en) 1998-02-19
EP0914368A1 (en) 1999-05-12

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