The conference was organised by Filter
Media Consulting in co-operation with EDANA. Lutz Bergmann of Filter Media
Consulting and Peter Meijer of Fiberweb-BBA Nonwovens chaired the sessions. Paul
Dewingaerden of EDANA opened the meeting.
The 2000 Top 10
Karin Bitz, Editor of Nonwovens Industry
Magazine listed the top 10 nonwoven industry events of 2000 in reverse
order as:
• The forging of partnerships in all segments of the industry.
• Globalisation: the roll-goods producers moving into China , Latin America, Eastern Europe and Turkey .
• The growth of the filtration sector, now a $2bn market. INDA's conference and exhibition last year attracted 2400 visitors.
• The growth of internet marketing
• The growth of web-based commerce.
• Expansion at PGI: their link-up with Vateks in Turkey and with Nanhai in China , the $40m investment at North Little Rock in Miratec hydroentanglement technology.
• Expansion at BBA: the Chinese air-lay line, the acquisitions of Snow Filtration and AQF Technologies.
• Air-laid expansions: Buckeye/Walkisoft and their start-up this spring of the 50,000 tonne air-layer.
• Continued ferocious competition, especially in diapers between P&G and K-C.
• The slower growth of established global markets, leading producers to look to the emerging markets.
• The forging of partnerships in all segments of the industry.
• Globalisation: the roll-goods producers moving into China , Latin America, Eastern Europe and Turkey .
• The growth of the filtration sector, now a $2bn market. INDA's conference and exhibition last year attracted 2400 visitors.
• The growth of internet marketing
• The growth of web-based commerce.
• Expansion at PGI: their link-up with Vateks in Turkey and with Nanhai in China , the $40m investment at North Little Rock in Miratec hydroentanglement technology.
• Expansion at BBA: the Chinese air-lay line, the acquisitions of Snow Filtration and AQF Technologies.
• Air-laid expansions: Buckeye/Walkisoft and their start-up this spring of the 50,000 tonne air-layer.
• Continued ferocious competition, especially in diapers between P&G and K-C.
• The slower growth of established global markets, leading producers to look to the emerging markets.
With regard to this last key issue and the increasing
evidence of overcapacity in some technologies she concluded that the discovery
of the next “great new nonwoven application” was now somewhat overdue.
Filters on the Web
Brandon Ost, the CEO of eFiltration Inc
reminded us that despite the 54% plunge in the Nasdaq index, internet
use was still doubling every 100 days and the Web now hosted 100 million
business users. The internet economy accounted for one-fifth of US revenue
generated in the last 6 months and globally accounted for $657 billion in sales
last year. With many more people and companies researching on-line and buying
off-line, e-Commerce sites were already having a much larger influence than was
suggested by the actual sales figures. Could a website be set up to market and
sell industrial filters? Mr Ost clearly thought so. However, the complexity of
the product range and the supply chain, and the need for in-depth product and
application knowledge, coupled with extensive after sales support meant that the
site would be anything but ordinary. EFiltration had helped a small distributor
of industrial air filters to set up a website. Their complete range could be
displayed and the software allowed customers to configure complex products
on-line and order them at “customer-specific” prices. Combined set-up and annual
costs to the filter distributor were around one-third of the costs of a
salesperson. For a large filter maker with thousands of SKU's, the only
practical approach seemed to be to start quickly with a small investment on a
flexible system, which could grow “daily” as new features were required and as
new e-business tools were developed.
Nanofibres?
Michael Wehmann of JM Laboratories Europe
(soon to be renamed to reflect Nordson's ownership) gave the first of
several papers to mention nanofibres. In the quest for ever-finer fibres, JM
were working with Hills Inc on modified melt blowing processes including the use
of splittable bicomponent technology, and on an electro-spinning process in
co-operation with Akron University and NC State. Electro-spinning appeared to be
melt-blowing with a high voltage between the die and collector. They were also
driving down the fibre size obtainable in melt-blowing by optimising
air-plenums, forming boxes and quench air systems. A 120 o (rather than 60 o )
die-tip angle was being used to generate turbulent air-flow at the point of
extrusion, this having been shown to allow finer fibres with any given polymer.
They were also working with the polymer producers to get the cleaner more
consistent resins needed to maintain throughput as fibre size diminished.
Finer Meltblown
One of these producers, Borealis Polymers NV (
Belgium ) took up the story, Nancy Noynaert reviewing
the benefits of increasing the melt-flow rate of PP to 1200. In addition to
finer melt-blown fibres, the new pelletised polymer allows improved
electrostatic charging due to reduced peroxide content, better melt, process and
fibre uniformity, longer die life, and FDA appoval. It also allows a given level
of web air-permeability to be achieved with lower process air volumes. The finer
fibres produced were said to allow 95% of all particles below 0.1micron in
diameter to be retained on the melt-blown filter. Ms Noynaert also reviewed the
current market for melt-blown nonwovens. 120,000 tonnes of meltblown were
produced globally last year, 97,000 tonnes of this being PP. Meltblowns were
consumed in filtration (26%) hygiene (46%) and oil sorbents (28%) Europe used
37,500 tonnes in 2000 and was expected to require 50-55,000 tonnes in 2004. Asia
used 18,400 tonnes and the Americas used 47,100 tonnes.
Melt- versus solution-blown implants
Dr Martin Dauner of ITV Denkendorf
compared melt-blowing with solution spinning routes to microfibres, but
only in the context of their use with resorbable fibres for medical implants.
Both technologies use similar equipment, with a solution of polymer replacing
the melt in the case of solution spinning. The dilute solution of polymer is
blown onto the former where it bonds due to incomplete removal of the solvent.
(A J&J electrostatic spraying process was also mentioned: EP 0095940 and GB
2189758.) The melt-blown process used by ITV has 15 holes and is based on an NC
State development. Polymers tested in both processes included poly-l-lactic
acid, the d,l copolymer, and a segmented polyurethane. Poly glycolic acid could
only be meltblown. Fibres and pore sizes tended to be finer and more uniform
with solution spinning. The fact that on average the solvent route gave fibres
about one-tenth of the diameter of the meltblown route was partly due to the
solutions extruded containing only 2-15% of solids. Illustrations not included
in the written text showed the spray-forming of tubular tracheal implants on
shaped mandrels, and the creation of an artificial ear by spray forming the
shape and then growing skin cells on the resulting fabric. Comparisons of MB,
SS, and an Electrostatic Spinning process showed ES with an undefined polymer to
give the finest, most regular fibres (down to 0.01 micron diameter with up to 3x
variation), but the resulting fabrics were not self supporting. Solution
spinning gave fibres down to 0.1 micron with up to 100x variation, while melt
blowing gave down to 1 micron fibres with up to 100x variation. In private
conversation Mr Dauner agreed to forward a selection of the many slides not
included in the written paper. Asked about cellulosics in implants he said the
body could not absorb cellulose and always tried to reject it.
Multi-layered Media and Markets
Kyung-Ju Choi of AAF International (
USA ) described experiments to optimise the filtration performance of
multi-layered media and provided some data on the world air-filtration market
that was not included in the written paper. Multiple layers do not perform as
well as calculated from filtration data on the individual layers. He concluded
that the layers must be separated for best results. With regard to the market he
estimated world air-filter sales to be $826million with the heating, ventilation
and air-conditioning (HVAC) filters accounting for 52% of this. Bag House
filters on industrial processes were the second biggest category with 24%,
automotive was next (cabin-air 6% and engine air 5%). 8% were respirators and
face-masks, 3% vacuum cleaner bags and 2% were ultra and high efficiency
particulate air filters. The USA used 39% of the total, Europe 33% and Asia 23%.
Melt blowing and needling were the growth technologies, wet-lay was declining.
Naturally charged filters
Bernard Drouin of Texel Inc ( Canada )
described how their triboelectric filter (Tribo™) complemented the other routes
to efficient electrostatic removal of submicron particles from air streams.
Particles below 2.5 microns account for very little inhaled mass but represent
99.5% of the total number of particles inhaled. These are hard to filter
conventionally, but can be collected on electrostatically charged surfaces.
Charged fibres can be obtained by induction (extruding polymer in an electric
field) or by corona discharge treatment of a fibrous web or, as anyone who has
worn or walked on synthetic polymers knows, by friction between
triboelectrically dissimilar materials. Texel has discovered and patented a
blend of polypropylene and polymetaphenylene isophthamide fibres (PCJ/CA
9800470) which produces a large and stable permanent electrostatic charge. In
comparison with another well known triboelectric blend (50/50 PP/Modacrylic
fibre) the Tribo™ blend with only 25% of the expensive fibre gave better
particle retention with less decay over time at a 25% lower air resistance.
Nanofibres!
Nigel Walker of Technical Fibre Products
( UK ) gave the Shrikant Awasthi (Hitco Carbon Composites Inc.) paper
on carbon nanofiber-based filter media. TFP has collaborated with Hitco to
produce wet-laid filters from carbon nanofibres bonded to standard chopped
carbon fibre. The nanofibres are unrelated to the recently discovered
“Buckytubes” and are already produced on an “industrial” scale by growing them
in a burning gas (e.g. acetylene) stream. They appear as soot, but at high
magnification they are revealed as a crimped or spiral fibrous structure with
diameters in the 0.1 to 0.2 micron range. When wet laid with regular carbon
fibre they can produce filters with the particle removal efficiency of membranes
but at 35 times the permeability of a PVDF membrane of similar micron rating.
Applications under development include clarifying beers and fruit juices
(replacing diatomaceous earth) and the microfiltration of industrial process and
waste waters.
Bio-soluble glass fibre
Bio-soluble glass fibre
Johns-Manville has developed a glass
fibre which is classed as no more than an irritant in the latest European
air-filter regulations. Foster Harding explained that this has
been achieved by optimising the formulation to increase bio-solubility without
affecting product performance (USP 5945360). High silica and low aluminium oxide
content appear to the key changes. EU biopersistence testing showed that after
rats breathed airborne 902 glass fibres for 5 days, 50% of inhaled fibres longer
than 20 microns cleared in 6.8 days. Since the test threshold between “irritant”
and “carcinogen” is 10 days, the new fibre gets into the irritant category. In
response to questions the new glass fibre was said to be unsuitable for
wet-laying. While finer polyester fibres were challenging glass in some markets,
Mr Harding said that there is little comparable data on the effects of synthetic
fibres in lungs, the crucial “injection” studies never having been done.
Molecular contamination
The semiconductor industry has successfully removed
particulate contamination from clean-rooms by using HEPA/ULPA filters, so
emphasis is now shifting to control of molecular contaminants. Matthew
Middlebrooks of AQF Technologies/BBA Nonwovens ( USA ) listed the
problem molecules as Acids and Bases (electron acceptors and donors),
Condensables (substances which could condense on a clean surface) and Dopants
(elements used to modify the semiconductor properties). AQF's active
carbon-loaded through-air bonded bico-fibre nonwovens were capable of absorbing
examples of all of these substances. Acids were represented by sulphur dioxide
and hydrogen chloride, Bases by ammonia, Condensables by toluene and Dopants by
trimethyl phosphate and boron trifluoride. Acid or base adsorption could be
enhanced by pre-impregnating the carbon with the bases or acids respectively,
although in both cases the condensables and dopants absorption decreased. Longer
term, Mr Middlebrooks foresaw the technology being used to control odours in
cars and in hotel and airport HVAC systems. (Substituting SAP granules for the
carbon would make an excellent absorbent)
Engine filtration
Robert Murphy of Hollingsworth and Vose
( USA ) compared advances in engine filtration, US versus Europe . In
Europe, filter lives were being extended past 60,000km (air) and 30,000km (oil)
as part of the attempt to keep motoring affordable in a high tax, high gas-price
environment. Frequent servicing is however common in the USA and higher
efficiency filters have been developed in preference to longer-lasting ones.
Europe continues to prefer the low cost phenolic resin bonded filters despite
the need for curing and the associated formaldehyde emission. In the USA ,
solvent-based advanced-cure resins already obviate the need for curing, reduce
the time-in-process and protect the users from future capital costs to upgrade
curing ovens for environmental compliance. Mr Murphy argued that the advanced
cure system would inevitably replace the phenolics as environmental regulations
tightened and the increasingly global motor industry demanded identical filters
wherever they were fitted. Other developments to note: the gasketless Japanese
filters that seal through compressed filter-media, and the all-plastic European
Eco oil-filter that can be incinerated whole.
Developing engines to meet ever-reducing emission
targets requires radical redesign of both petrol and diesel engines. For diesel,
a key step is the use of direct fuel injection through a common rail at very
high pressures, and for this the fuel needs to be filtered to remove particles
above 2 microns at very high efficiency. Roberto Forna reported that
Ahlstrom has achieved this by laminating a meltblown polyester nonwoven
upstream of a conventional phenolic coated woodpulp filter paper. The new
composite media holds 5 times the contaminant and has an initial efficiency of
90% for 2 micron particles.
Hot-gas filtration I
Control of particulate emissions from incinerators
involves the use of cyclones, electrostatic precipitators, wet-scrubbers and
fabric filters. Andrew Startin of Madison Filter Ltd. ( UK )
argued that their low-density ceramic fibre cartridge filters offer some
significant benefits over fabric filters where the gas stream is at elevated
temperatures and where consistent low emissions are mandated. Data was provided
from installations of ceramic filters in clinical and chemical waste
incinerators where sodium bicarbonate sorbent was added to the gas stream to
control acids. They were also being tested by Peugeot as filters on diesel
exhausts where the operating temperature was 700-800 0 C.
In a second paper from Madison Filter, Richard
Lydon explained how their new Tuftex™ filters are coated to improve
abrasion resistance and cake release. The polymer coating is supplied on a
release paper and attached to a polyester or polypropylene needlefelt filter
through a nip roll. The polymer reticulates in a controlled manner during curing
to leave a tough porous surface which appeared to be about 50% covered in film.
This nearly doubled the Martindale abrasion resistance and stops any
fibrillation if the substrate was PP. In response to questions the coating would
double the cost of the filter but would more than double its useful life.
It's an ill wind…
Karl Ott of BASF ( Germany ) gave a
remarkably candid account of the “miserable” launch failure of their Basofil™
flame resistant melamine fibre in hot-gas filtration. Having in retrospect
chosen the wrong partner, the first trials on this relatively weak fibre were
conducted on needlefelt bag-house filters without scrim reinforcement and after
a singeing process which had predictably little effect on improving its surface.
Their filter-producing partner turned out to be more interested in establishing
business for his other filters within BASF than developing Basofil™ and while Mr
Ott did not say so, we guessed he failed at this objective also. Convinced of
the merits of Basofil™, made “from a condensation reaction of methylol to form a
3D structure”, BASF reanalysed the market at targeted the customers of the
leading supplier of aramids. Data from recent bag-house trials at Brox
Industries asphalt plant and at LTV steel in the USA showed long filter lives,
low pressure drops and excellent emission values compared with the aramid
controls. In concluding Mr Ott commented that one of the biggest factors in the
successful relaunch was a predictably unfavourable comparison with aramid in the
competitor's brochure. The fact that the market leader found Basofil™ worthy of
comparison with his aramid created intense interest in the new fibre.
Pleated bags
As particle emission regulations tighten the need to fit
more filter area into existing bag-houses increases. Michael Konesky of
Southern Felt Co. Inc. ( USA ) described how their pleated filter
elements - Pleatlox™ - could be retrofitted to older installations to increase
their capacity. In addition to the increased area obtained by pleating the
cylindrical filters, the new bags could be cleaned at lower pressures and
exhibited reduced abrasion damage.
Hot gas filtration II
Holga Blaha of BWF Textil GmbH and Co. KG
( Germany ) reviewed the choices available for removing dust from power
station flue gases. The fibres to consider were acrylic, polyphenylenesulphide,
polyimide and PTFE. However the filter fabrics would need surface treatments
designed to suit the nature of the dust being removed. Singed surfaces were
appropriate for non-agglomerating dusts whereas an agglomerating dust would need
a glazed filter surface. PTFE coating and even impregnation would be needed for
protection against chemicals, sparks and humidity. For instance, their Needlona®
PAN fibre filter impregnated with fluorocarbon would give a 3 year life in a
combined heat and power plant with flue gas desulphurisation after spray
absorbtion whereas the more expensive polyphenylene sulphide felt with a
microporous coating would last for 6 years in the same process.
Surface or in-depth?
Pulse cleaning of bag filters causes a peak in emissions
to atmosphere associated with finesbeing dislodged from the depth of the filter
and the need for a new cake to form on the surface prior to full efficiency
being regained. One solution to this, proposed by Klaus Schumann of
Albany International Inc (France) was to increase surface filtration
(over depth filtration) by laminating a PTFE membrane or microfibre web to the
surface of the needlefelt. Compared with a 1.7 dtex round fibre, a fully-split
16 segment pie-fibre would give 10 times the surface area. Furthermore when the
PA and PES polymers separate they generate a natural electostatic charge.
Filtering fumes
Günter Weitz of Jacob Handte and Co GmbH
( Germany ) showed SEM's of the welding “fume” from laser welding and
cutting of steel. This dust of submicron (~0.2) spheres of metal oxide blinds
almost any filter unit very quickly and can be ignited by sparks from the laser
process. A laser cutter for steel plate can generate about 100 kgs/day of such
dust, so designing filters for these machines represents a real challenge to the
filter producer. The solution employed by Handte involved a PTFE membrane on a
PES bico needlefelt, following a spark-precipitator cyclone. The unit is fully
automatic, self-cleaning, maintenance free and gives long filter lives.
Waste water filters
• Plate and frame filters clothed with textiles were
first developed in 1830 for filtering liquid effluent from the ceramics
industry. Fully automatic versions of these are still the main filter type for
sewage sludge and industrial process and waste waters. Hubertus Schütt
of Junker Filter GmbH reviewed the types of cloths and membranes now
available. He showed how the use of membranes in filter presses now offers the
best solution to industrial waste water cleaning by reference to trials at a
Hoechst AG plant.
Calvin Woodings 14/3/01