Key Points:
- Unilever say nonwovens producers should take new ideas straight to the highest level in marketing, avoiding purchasing and R&D functions.
- Mandatory filtration of all transfusion blood will yield a $150MM filter market by 2004.
- P&G ( Pescara ) has put its VPM technology up for licence.
- Eastman's biodegradable copolyester resin costs 8DM/kg and is made in a 15,000 tpa plant in the UK .
- Cheap 1,3 propanediol made at a 70,000 tonne Louisiana plant allows Shell to produce PTT fibres at prices comparable with other major synthetics.
- INDA expects most future growth to be in wipes, filtration and geotextile markets.
- The latest card/thermal bond lines can make cheaper coverstock than spunbond lines.
- The US invested $410MM to make 100,000 tonnes of new needlefelts between 1998 and 2000.
- Reusable industrial wipes constitute a hidden health hazard due to toxic contaminants.
- 50gsm disposable wipe nonwovens have been made on a 1
metre wide high-voltage powder bonding line using 10% powder binder.
B2B Etrade at Lenzing
Heinrich Jakob of Lenzing demonstrated their new website
which allows customers to order fibre, see their contracts, track their
shipments and see invoices with detailed bale data, all being downloadable in
Microsoft Word or Excel format. The site at etrade.Lenzing.com is only available
to customers with a password, and has been set up relatively cheaply with the
help of external consultants. It is separate from their sales order processing
software, the bale data being transferred from the on-line systems to allow
customers to view it. Moisture content, bale weight and bale number are
available on the invoices but as yet, no other quality control information. In
passing, Dr Jakob mentioned that world internet use is growing about 10 times
faster than radio and 3 times faster than television when the technologieswere
compared at similar intervals after introduction. Etrade in Europe was expected
to reach 1600 billion Euros by 2003, 90% of this being B2B. Asked privately if
customers would ever be able to see elements of the on-line QC and sales order
processing systems in real-time, they thought it unlikely.
Storming Fortress Foods
Graham Houlder, Head of Food Packaging at Unilever
BestFoods in Holland reviewed opportunities for nonwovens in the food industry.
While nonwovens were already used in tea bags, coffee filters, salami skins,
absorbent pads, and beverage filtration, Mr Houlder thought there were many more
possibilities if the nonwovens industry played to the market megatrends now
apparent:
• Higher quality
• Improved functionality
• Environmental pressures
• Increased “Naturalness”
• More convenience
• More variety
• Better value
• Improved functionality
• Environmental pressures
• Increased “Naturalness”
• More convenience
• More variety
• Better value
He thought the nonwovens producers should persevere
despite past difficulties and come to the food industry with new ideas, or
better still with “system solutions”, having done their homework and studied the
competition. High quality prototypes and presentations were essential to present
the ideas effectively. Furthermore the nonwovens industry needed to become more
food-friendly with more emphasis on meeting the food approval standards. Longer
range items on his wishlist were:
• Edible fibres and nonwovens for use in coatings, dressings, snacks and spreads. These should be transparent, wettable and use food approved finishes.
• Products with “environmental” or “naturalness” marketing potential. PLA and starch-based polymers, if embraced by the nonwovens industry, will add value in food-contact uses where most waste will, in Europe at least, be destined for the compostable waste stream.
Illustrations included luxury spun-laced teabags for premium teas, Ponds “Cucumber” nonwovens eye-treatment pads, Jif Glass and Window wipes, and Ponds Clear Pore strips.
Asked where in Unilever the nonwovens industry should submit it's ideas, Mr Houlder recommended avoiding the R&D and purchasing functions in favour of “the highest level in marketing.”
• Edible fibres and nonwovens for use in coatings, dressings, snacks and spreads. These should be transparent, wettable and use food approved finishes.
• Products with “environmental” or “naturalness” marketing potential. PLA and starch-based polymers, if embraced by the nonwovens industry, will add value in food-contact uses where most waste will, in Europe at least, be destined for the compostable waste stream.
Illustrations included luxury spun-laced teabags for premium teas, Ponds “Cucumber” nonwovens eye-treatment pads, Jif Glass and Window wipes, and Ponds Clear Pore strips.
Asked where in Unilever the nonwovens industry should submit it's ideas, Mr Houlder recommended avoiding the R&D and purchasing functions in favour of “the highest level in marketing.”
Worldwide Filtration Trends
Lutz Bergmann's presentation on new products and trends
in filtration worldwide mentioned the following:
• Growth in microfibre nonwovens made by electrostatic spinning for respirators, HVAC and cartridge filters
• Replacement of paper filters by synthetics in the automotive sector.
• Replacement of cylindrical bags with pleated configurations in baghouses, allowing the use of a wider range of finer nonwovens and composites. (Durapex™ from PGI was mentioned as a 330 gsm hydroentangled replacement for 500gsm needlefelt which met the EPA-PM2.5 particle emission standards.)
• The mandatory filtration of all transfusion blood yielding a $150MM/annum market by 2004.
• The use of activated carbon in nonwovens to remove gaseous pollution from car and room air.
• PLA filters with improved disposal options.
• High-loft filters using Kosa's Loftguard® xtra fibre.
• Improved expanded PTFE membranes from Daikin ( Japan ) with finer fibres (0.1-0.2 microns) for HEPA/ULPA filters.
• A revival of interest in PP cigarette filters lead by China .
• The use of Evolon® technology for filter materials by Freudenberg.
He anticipates the roll-goods market for filters to double in value to $4MMM worldwide by 2010.
• Growth in microfibre nonwovens made by electrostatic spinning for respirators, HVAC and cartridge filters
• Replacement of paper filters by synthetics in the automotive sector.
• Replacement of cylindrical bags with pleated configurations in baghouses, allowing the use of a wider range of finer nonwovens and composites. (Durapex™ from PGI was mentioned as a 330 gsm hydroentangled replacement for 500gsm needlefelt which met the EPA-PM2.5 particle emission standards.)
• The mandatory filtration of all transfusion blood yielding a $150MM/annum market by 2004.
• The use of activated carbon in nonwovens to remove gaseous pollution from car and room air.
• PLA filters with improved disposal options.
• High-loft filters using Kosa's Loftguard® xtra fibre.
• Improved expanded PTFE membranes from Daikin ( Japan ) with finer fibres (0.1-0.2 microns) for HEPA/ULPA filters.
• A revival of interest in PP cigarette filters lead by China .
• The use of Evolon® technology for filter materials by Freudenberg.
He anticipates the roll-goods market for filters to double in value to $4MMM worldwide by 2010.
Reusables v Disposables Part I: Drapes and Gowns
Andre Germaine of Allegiance Healthcare reported the
conclusions from the EDANA investigation into the relative quality of woven and
nonwoven drapes and gowns. Based on 68 packs of reusables and 50 packs of
disposables sampled from hospital storage in France , England and Wales :
• 56% of the reusables from England and Wales and 89% of those from France had visible faults (foreign body contamination, holes or open seams). The disposables were fault-free.
• Hydrostatic-head testing of the drapes used close to wounds and of the gown fronts and sleeves showed the majority of reusables to be permeable at only 50cms head. But for 2 drapes, all nonwovens exceeded 150cms hydrostatic head, and 80% of the gowns also exceeded this figure.
• 80% of the reusables from England and Wales and 73% from France failed the wet-bacterial penetration test. All the disposable drapes passed, and only 5% of the gown materials failed.
The French Ministry of Health is now recommending disposables for operations around the brain and central nervous system because prions cannot be removed in sterilising. Asked about the relative costs of disposables and reusables Mr Germaine said that many studies now showed that the disposables were the more cost effective. However hospitals rarely know the true cost of their laundries and remain reluctant to accept the layoffs perceived as being necessary to justify the switch to disposables.
• 56% of the reusables from England and Wales and 89% of those from France had visible faults (foreign body contamination, holes or open seams). The disposables were fault-free.
• Hydrostatic-head testing of the drapes used close to wounds and of the gown fronts and sleeves showed the majority of reusables to be permeable at only 50cms head. But for 2 drapes, all nonwovens exceeded 150cms hydrostatic head, and 80% of the gowns also exceeded this figure.
• 80% of the reusables from England and Wales and 73% from France failed the wet-bacterial penetration test. All the disposable drapes passed, and only 5% of the gown materials failed.
The French Ministry of Health is now recommending disposables for operations around the brain and central nervous system because prions cannot be removed in sterilising. Asked about the relative costs of disposables and reusables Mr Germaine said that many studies now showed that the disposables were the more cost effective. However hospitals rarely know the true cost of their laundries and remain reluctant to accept the layoffs perceived as being necessary to justify the switch to disposables.
Highly Breathable Monolithic Membranes
Maurizio Marchesini of Procter and Gamble ( Pescara )
thought their proprietary VPM technology allowed the production of monolithic
membranes to outperform the microporous variety on cost and breathability
without the problems of leakage under pressure. The key to these Vapour
Permeable Membranes is the combination of hydrophilic polymers (such as
polyurethanes, block copolyamides and copolyesters) with hydrophilic
plasticisers used at high concentrations (30-70%). The plasticiser improves
breathability dramatically while lowering processing temperatures, viscosity,
modulus, minimum coating thickness and both investment and running costs. 10
micron coats of the new polymer/plasticiser blend are easily achieved with
hot-melt extrusion technology at 2-4 times normal film extrusion speeds. 3-D
shapes are possible via moulding or thermoforming and the polymers can even be
converted into solutions or emulsions for spray application. In answer to
questions, Mr Marchesini said the polymer would be stable for around 6 months
based on accelerated ageing tests, and that the films were weaker than other
monolithic films due to the plasticiser content. Post-treatment strength
improvement techniques had however been discovered and were being patented.
P&G were looking to licence the technology and welcomed approaches from
would-be producers. They may then become a customer for these new materials.
A new biodegradable elastic polyester
Bill Haile of Eastman Chemical Company described the
aliphatic-aromatic copolyester “Eastar Bio”, a PTAT (polytetramethylene
adipate-co-terephthalate) designed to make films and fibres which degrade in an
active composting environment. Its 108 o C melting point and a glass transition
temperature below freezing point makes it similar in processing performance to
low density polyethylene, and it is said to be runnable on LDPE equipment. It
does however have a low modulus, excellent elasticity and a soft handle.
Furthermore the polymer already has food contact approval. It has been spunlaid
on Ason equipment to give a quiet, drapable, semicrystalline elastic spun-bonded
fabric (Sample obtained). It can be melt-blown but here a secondary quench is
needed. In staple form it appears to have most potential as a binder fibre
either in the skin of a bicomponent fibre or as a short cut bonding fibre for
pulp in wet or airlaid structures. In a composting environment nonwovens based
on PTAT pass the 2mm screen test in a timeframe comparable with Kraft paper.
Powder biodegradation (ASTM D 6340-98) results in >95% of the PTAT degrading
to CO 2 and water within 6 months. Commercial film programmes are already in
place, and spunlaid nonwovens and staple fibre programmes are expected to follow
in the next 6 months.
In response to a question, Mr Haile said the polymer would be more expensive than regular polyester. In private conversation his marketing colleague, Mr Bert Heijne said the resin currently sold for 8DM/kg. It was being manufactured at Hartlepool in the UK in a plant capable of 15,000 tonnes/year which was flexible enough to make the variants needed for all the fibre and film applications. A water quench was required to allow melt-blown production.
In response to a question, Mr Haile said the polymer would be more expensive than regular polyester. In private conversation his marketing colleague, Mr Bert Heijne said the resin currently sold for 8DM/kg. It was being manufactured at Hartlepool in the UK in a plant capable of 15,000 tonnes/year which was flexible enough to make the variants needed for all the fibre and film applications. A water quench was required to allow melt-blown production.
Fibres for Coverstock
Ulrich Aunskjaer of Fibervisions a/s Denmark again
promoted their range of fibres, this time using diaper topsheet and acquisition
layers to illustrate the differences. Increased and more durable fibre
hydrophilicity (as represented by the Hy-Repeat III fibre) gave strike through
times below 5 seconds up to the 5 th insult. Bulkier acquisition layers gave
faster acquisition rates in GATS testing.
An old polyester at a new price
Ian Carson of the Shell Coordination Centre ( Belgium )
considered possible nonwovens uses of their Corterra polymer: a polytrimethylene
terephalate or PTT. First prepared by Whinfield and Dickson at Calico Printers
Association in 1941 it has had no real commercial success because of the high
price of the 1,3 propanediol (PDO) which is condensed with terephthalic acid. In
the last 10 years Shell has developed and commercialised a new PDO process and
in 1999 started up a 70,000 tonne plant to make it in Lousiana. PTT polymer is
now available “at a price comparable with other major fibre forming synthetic
polymers” and Shell are looking for applications. Compared with PET polyester it
has slightly lower density (1.35), melting point (228 o C) and T g (45 o C for
the amorphous form). The fibre load-elongation curves however indicate a soft
low-modulus fibre with adequate tenacity(~2.5 gms/denier) and very high
extensibility (~95%). It also has a high elastic recovery and excellent
resilience, carpet test data showing that it is comparable with nylon in this
end-use. In nonwovens it gives very bulky card webs which resist compression,
and soft spunbonds which are resistant to UV and gamma irradiation and to attack
by 5% caustic soda. In hydroentanglement it provides the softness and durability
of nylon with almost the strength of PET, its easier entanglement making up for
its lower fibre strength. A 0.62 intrinsic viscosity version of PTT has been
successfully melt-blown at Tandec, the webs showing less than half the shrinkage
(90 o C/7mins) of PET.
INDA's North American Nonwovens Statistics
Ted Wirtz, President of Inda reviewed current and future
trends in the North American nonwovens industry.
• In 2000, 967,000 tonnes or 21 billion square meters of nonwoven worth $3.8 billion were consumed in North America . 60% by weight and value were disposables.
• Within disposables, the main hygiene and medical markets are mature (2-2.5% annual growth), but wipes, filtration and “others” show 4-5.5% growth.
• In Durables, geotextiles remain the high growth sector with 7%, “Others” coming in second with 6%.
• Hydroentangling and airlaying are the fastest growing technologies (5-7%) with spunlaid (2-3%) showing high growth in area consumption (6-8%) reflecting the downward trend in average basis weight.
• Spunbond remains the most important production technology with 61% by area and 44% by weight.
• Between 1998 and 2000, needlepunching attracted most investment ($410MM for 32 new lines to make around 100,000 tonnes) followed by spunlaid with $252MM for 7 new lines to make 40,000 tonnes. HE attracted $56MM for 6 new lines to make 46,000 tonnes.
• The latest card/bond lines are now capable of making coverstock more cheaply than spunbond.
Overall worldwide growth for the fibre-fabric processes was put at 4% for the next 5 years, and overall growth for the polymer-fabric systems at 7%. Mr Wirtz thought these figures were somewhat conservative and would be inclined to add a further 1% to allow for the many new consumer products now in the pipeline.
• In 2000, 967,000 tonnes or 21 billion square meters of nonwoven worth $3.8 billion were consumed in North America . 60% by weight and value were disposables.
• Within disposables, the main hygiene and medical markets are mature (2-2.5% annual growth), but wipes, filtration and “others” show 4-5.5% growth.
• In Durables, geotextiles remain the high growth sector with 7%, “Others” coming in second with 6%.
• Hydroentangling and airlaying are the fastest growing technologies (5-7%) with spunlaid (2-3%) showing high growth in area consumption (6-8%) reflecting the downward trend in average basis weight.
• Spunbond remains the most important production technology with 61% by area and 44% by weight.
• Between 1998 and 2000, needlepunching attracted most investment ($410MM for 32 new lines to make around 100,000 tonnes) followed by spunlaid with $252MM for 7 new lines to make 40,000 tonnes. HE attracted $56MM for 6 new lines to make 46,000 tonnes.
• The latest card/bond lines are now capable of making coverstock more cheaply than spunbond.
Overall worldwide growth for the fibre-fabric processes was put at 4% for the next 5 years, and overall growth for the polymer-fabric systems at 7%. Mr Wirtz thought these figures were somewhat conservative and would be inclined to add a further 1% to allow for the many new consumer products now in the pipeline.
HVAC Filters assessed
Dean Arnold of Kimberly-Clark Corp. USA gave a detailed
and highly technical paper comparing standard and electrostatically charged HVAC
filters operating outdoors and indoors in both commercial and residential
environments. They had also been tested using the ASHRAE 52.2 test method in the
laboratory. He concluded that:
• Charged (“electreted”) filters gave much better efficiency over the first 20 days of use due to the charge.
• Longer term performance was entirely explained by the structure of the nonwoven: the electrets having been neutralised.
• Filters prove more efficient indoors than outdoors due to the fibrous lint layer which accumulates wherever clothing and household textiles are used.
• ASHRAE 52.2 Minimum Efficiency Reporting Values (MERV) accurately represented the efficiency in real life use. (However the test dust used is unimodal with an average particle diameter of 10 microns whereas atmospheric dusts are bimodal, with peaks below and above this figure.)
• Charged (“electreted”) filters gave much better efficiency over the first 20 days of use due to the charge.
• Longer term performance was entirely explained by the structure of the nonwoven: the electrets having been neutralised.
• Filters prove more efficient indoors than outdoors due to the fibrous lint layer which accumulates wherever clothing and household textiles are used.
• ASHRAE 52.2 Minimum Efficiency Reporting Values (MERV) accurately represented the efficiency in real life use. (However the test dust used is unimodal with an average particle diameter of 10 microns whereas atmospheric dusts are bimodal, with peaks below and above this figure.)
Reusables v Disposables Part II: Wipes
Berit Gullbranson of SCA Hygiene Products described the
workings of EDANA's wipes interest group, a group of competitors who meet to
discuss common interests in environmental matters, regulatory threats, and the
collective defence of disposables in a reusables-oriented industrial wiping
market. After dabbling with a Life Cycle Assessment of laundered and disposable
products the group decided that this was not the best way of influencing
customers who were convinced the laundry route was the more economical. They
therefore decided to compare product quality and occupational safety rather like
the Drapes and Gowns group had reported earlier.
A comparison of the cleanliness of wipes as received by the user was therefore commissioned from the Swedish Institute of Fibres and Polymers. This showed that the laundered products contained 10 times more metallic residues than the disposables. A further study used TOXICON * and IVEBE ! to establish the health risks associated with this contamination. This concluded that the use of laundered wipes constituted a “hidden health hazard” because the presence of the contamination was not brought to the attention of the user. These conclusion have now been widely reported in the trade press. The group has also tried (unsuccessfully) to change the EU definition of waste to allow discarded disposable wipes to be classed as a recyclable material. With regard to the definition of hazardous waste the group has influenced the EU to prevent all used disposable industrial wipes being classed as hazardous: this classification will in future only be used if certain specific contaminations are present.
A comparison of the cleanliness of wipes as received by the user was therefore commissioned from the Swedish Institute of Fibres and Polymers. This showed that the laundered products contained 10 times more metallic residues than the disposables. A further study used TOXICON * and IVEBE ! to establish the health risks associated with this contamination. This concluded that the use of laundered wipes constituted a “hidden health hazard” because the presence of the contamination was not brought to the attention of the user. These conclusion have now been widely reported in the trade press. The group has also tried (unsuccessfully) to change the EU definition of waste to allow discarded disposable wipes to be classed as a recyclable material. With regard to the definition of hazardous waste the group has influenced the EU to prevent all used disposable industrial wipes being classed as hazardous: this classification will in future only be used if certain specific contaminations are present.
Lamination I
Kay Knorre of Eduard Küsters GmbH ( Germany ) reviewed
the theory and practice of sonic bonding, a cold-bonding technique which uses
vibrations in the ultrasonic region – typically 20KHz – to melt fibre surfaces
by friction arising from vibrating while them under pressure. A piezo-ceramic
converter transforms electrical energy into mechanical oscillations with an
amplitude of ~10 microns. This is too low for practical use so a booster is
employed to double it. This vibration is transmitted through the weld-horn to
the fabric supported on an “anvil” against which it is “hammered”. The anvil is
typically an engraved roller not unlike a calender bowl carrying the pattern to
be embossed onto the fabric. Weld-horns cannot be made much wider than 160mms so
many of them need to operate side-by-side to bond a practical fabric width.
Engineering tolerances for successful operation are stringent. The rolls must be
large in diameter to minimise resonant vibrations, cooled to prevent heat build
up, and run with less than 5 microns deviation in surface position. Bonded areas
up to 10% are possible, and production line speed depends crucially on this
parameter. Examples of practical uses were all in lamination:
• Knitted acrylic and hydroentangled polyester bonded to either side of aluminium foil. (insulation?)
• Vacuum cleaner filters made by bonding paper, melt-blown and nonwovens.
• Polyester/wool needlefelts bonded to aluminium foil.
The complete absence of secondary bonding (between the bonding points) is a unique benefit of the technique.
In response to questions Mr Knorre was unaware of dust accumulating from fibre damage clogging the engraved roller. The system only worked with thermoplastics but one layer of synthetic could be used to stick two layers of natural fibres together. The Küsters lab. Machine will run up to 300 m/min on lightweights, but 60m/min is more typical of heavier (150gsm) laminates with higher bonded area.
• Knitted acrylic and hydroentangled polyester bonded to either side of aluminium foil. (insulation?)
• Vacuum cleaner filters made by bonding paper, melt-blown and nonwovens.
• Polyester/wool needlefelts bonded to aluminium foil.
The complete absence of secondary bonding (between the bonding points) is a unique benefit of the technique.
In response to questions Mr Knorre was unaware of dust accumulating from fibre damage clogging the engraved roller. The system only worked with thermoplastics but one layer of synthetic could be used to stick two layers of natural fibres together. The Küsters lab. Machine will run up to 300 m/min on lightweights, but 60m/min is more typical of heavier (150gsm) laminates with higher bonded area.
Lamination II
Lamination using calenders was the subject of James
Young's (Dupont Central R&D) presentation, although his bio indicated that
his main job was currently inventing new routes to spunlaid nonwovens. The
market for lamination was defined as the “flexible roll-goods market” said to be
a $300 billion business comprising textiles, nonwovens, films and papers.
Lamination of these flexible sheets was a route to a cornucopia of new products:
lamination being defined as “a critical maximum-value-added step that determines
the ultimate end-use properties, production yield, customer satisfaction, and
market acceptance of many new flexible polymeric/fibrous sheets”. The new angle?
After some impressive computer simulations of temperature gradients in calender
nips, Dr Young concluded that uniformity of pressure in the calender nip and
residence time under pressure were key elements of successful lamination. Both
could be improved by using “soft nips”, and a graph of Moisture Vapour
Transmission Rates showed that the soft-nipped laminates gave higher and more
uniform values than conventionally calendered laminates. Furthermore, several
nips were better than one, 4 being recommended for lamination at 60 m/min to
achieve simultaneous productivity and quality benefits. In response to
questions, Dr Young revealed that the soft-nip was achieved by using a
fibre-reinforced silicone rubber sleeve. Asked how durable such a cover would be
in production he admitted it would have a relatively short life. The effect of
soft-nips on Tyvek strength? A 20% reduction c.f hard nips.
Fine Denier Spunlaid Polyester
EMS Inventa Fischer has more than 30 years experience of
making spunbonded nonwoven machines and has now developed a high speed suction
process for the production of sub-denier polyester spunbond. Key elements of the
process are:
• Chips dried to <20ppm water.
• Pigment injection possible
• Pre-filtration down to 10 microns
• Top-loaded spin packs for quick and easy changing
• Air velocities up to 16,000 m/min to allow spin speeds above 6000m/min.
• Air velocity in drawing controlled by suction in the web forming chamber.
• 5-250 gsm weight range defined by conveyor speed.
• 1:1 MD/CD ratio
• Spinning and drawing speed optimisation gives boiling water shrinkage of <3%
• 4.2 g/d tenacity and 60% extension filaments can be made at 6000m/min spinning speed.
Suggested applications for these PET spunbonds were battery separators, filters, backing sheets for underfloor heating, ink-jet printable display media, sound absorbents, optic cable wrap and antistatic fabrics.
• Chips dried to <20ppm water.
• Pigment injection possible
• Pre-filtration down to 10 microns
• Top-loaded spin packs for quick and easy changing
• Air velocities up to 16,000 m/min to allow spin speeds above 6000m/min.
• Air velocity in drawing controlled by suction in the web forming chamber.
• 5-250 gsm weight range defined by conveyor speed.
• 1:1 MD/CD ratio
• Spinning and drawing speed optimisation gives boiling water shrinkage of <3%
• 4.2 g/d tenacity and 60% extension filaments can be made at 6000m/min spinning speed.
Suggested applications for these PET spunbonds were battery separators, filters, backing sheets for underfloor heating, ink-jet printable display media, sound absorbents, optic cable wrap and antistatic fabrics.
High Voltage Powder Bonding
Mrs Caramaro an R&D Engineer from the University of
Lyon described the powder bonding process developed by Fibroline and IFTH * Lyon (EP 1028836 – Feb 2001). The inventive
step appeared to be the use of high voltage to charge the powder particles
allowing them to form a “cloud” which occupies all the spaces in the fibre web
as it passes between the electrodes. Free radicals - as in plasma treatment -
may also be created by the voltage thereby increasing adhesion between powder
and fibre. Webs from 50-2000 gsm can be impregnated with from traces of powder
up to more than 100%. Powder size should be small compared with the inter-fibre
spaces and is typically 50 to 300 microns. Infra red heaters are used to fuse
the powder. Examples of uses given were:
• A 2000 gsm glass mat being impregnated with and bonded by its own weight of PP powder.
• 1200 gsm hemp or kenaf being impregnated and bonded with an epoxy/polyester thermosetting resin powder.
• Manufacture of domestic wipes by impregnating a 50gsm nonwoven web with 10% binder powder.
Powder can be screen-printed into patterns to allow discontinuous “point” bonding. Line speeds depend on product but vary from 3m/min for glass mat up to 40 m/min for light “tissues”. A 1 metre wide pilot plant is now operational in France .
• A 2000 gsm glass mat being impregnated with and bonded by its own weight of PP powder.
• 1200 gsm hemp or kenaf being impregnated and bonded with an epoxy/polyester thermosetting resin powder.
• Manufacture of domestic wipes by impregnating a 50gsm nonwoven web with 10% binder powder.
Powder can be screen-printed into patterns to allow discontinuous “point” bonding. Line speeds depend on product but vary from 3m/min for glass mat up to 40 m/min for light “tissues”. A 1 metre wide pilot plant is now operational in France .
C R Woodings: 12/6/01
* Toxicon
International – a toxicological research organisation
! Instituut Voor
Bedrijsveiligheld – an occupational safety research organisation
* Institut Francais Textile-Habillement, Ecully, Lyon
