Ultrafine Microfiber Spunbond for Hygiene and Medical Application

EDANA´S 2000 NONWOVENS SYMPOSIUM Ultrafine Microfiber Spunbond for Hygiene and Medical Application

Dieter Groitzsch The Freudenberg Nonwovens Group, Germany

Introduction

Up to now there is no generally accepted definition for micro fibers. But normally the term is linked to the fiber diameter and/or weight/ length of filament in dtex or denier and not with any properties of the fiber. Due to the fact that cross section of fibers is not exclusively circular the diameter should not be used for characterisation of fiber fineness. Most accepted definition for micro fibers seems to be a fiber with 1 dtex in maximum.

This constribution is essentially focused on melt spun endless filament webs based on so called ultra fine resp. ultra super fine microfibers with a level of around 0,09 — 0,13 dtex. It is well known that such ultrafine fibers are not able to be spun out of a spinneret and would not be able to be processed on carding machines. This problem had been overcome in the past by providing conjugate and island in the sea fibers of more than 1 dtex splittable in ultrafine segments by solvents, alkali treatment or - in the last 10 years more a more favorized and from ecological point of view most friendly - high pressure water jets.

By far the most part of conjugate fibers splittable by hydroentanglement are produced in Far East. They are offered as staple fibers for processing on carding machines and so all present microfiber based nonwoven fabrics available on the market are composed of cut fibers, which of course provide disadvantages compared to endless filaments.

Freudenberg has intensively been working since more than 5 years on a research and development programm - internally called Omega-project - to create a new generation of unique nonwoven spunwebs.

In Table I the most important differences in construction of staple fiber and spundbond nonwoven fabrics are put together.

Table I Construction principle of staple fiber and conventional spunbond nonwoven fabrics Fiber Staple fiber nw fabrics Spunbond nw fabrics Fiber length 38 — 90 mm Continuous (endless) Shape of fiber along its lenght Crimped Not crimped Fiber orientation in the fabric at high speed manufacturing In md anisotropic isotropic (random) (md/cd = 1/1 — 2/1) Range of processable fiber fineness 0,8 — 50 dtex 0,5 — 10 dtex (meltblown not included) Fiber forming polymer Whole range available Restricted on melt spinnability

Carded nonwoven fabrics are composed of staple fibers with two dimensional or helical crimp, anisotropically distributed with strong orientation in machine direction whereas conventional spunwebs are constructed of non crimped continuous filaments with more or less isotropic distribution in the fabric. Therefore both types of nonwoven fabrics have got their advantages and disadvantages. In Table II the most relevant characteristics of carded versus conventional spunbond nonwoven fabrics are collected.

Table II Fabric characteristics staple fiber versus spunbond nw fabrics Fabric characteristics Staple fiber nw fabrics Spunbond nw fabrics Mechanical strengths over all low high

in md much higher than in cd no big difference between cd and md Elongation in cd much higher than in md no big difference between cd and md Softness high low Stiffness low high Drapability high low Loftiness high low Resiliancy high low Textile properties over all high low

Summerized over all conventional spunbond nonwoven fabrics provide much higher mechanical strengths in md and cd than carded nonwoven fabrics but because of the non crimped fibers all characteristics derived from such as softness, drapability, loftiness and the like are uncomparably worse than with carded nonwoven fabrics. Expressed somewhat simplified: the non-textile characteristics of conventional spunbonds has been so unfavorable that huge areas of application such as garment industry or upper material for shoes and luggage could not be covered by them. The Omega-project has been focused on an unique new class of nonwovens which combine the benefits of both the carded and the spunbond fabrics in an ideal way. Transferring textile properties into a spunbond grade there are principally two possibilities:

a) evolute crimping during quenching and aerodynamical stretching, enhanced by thermal post treatment b) reduce the fiber fineness down to microfiber denier and of course a combination of both.

The new process for the manufacture of Evolon Fabrics covers both. In order to provide spiral (helical) crimping a fiber with bicomponental side-by-side or eccentric sheath-core configuration and for ultra fine micro fibers a splittable multi-sector pie fiber has to be used. In Figures 1 and 2 the cross sectional views of side-by-side bicomponental fibers are shown whereas 16 segment pie fiber resp. hollow pie fibers are illustrated in Figures 3 and 4. Hollow pie fibers are more preferred for better hydrodynamic splittability and pie fiber without hole for better spinning properties and depositing onto the moving belt to form a nonwoven fabric of uniform structure.

Fig. 1 Fig. 2

For most end uses ultrafine micro fiber denier spunbond is preferred by far. Fig. 3 Fig.4

In-line-production is illustrated schematically in figure 5, starting from polymer granule and ending with the ultrafine microfiber spunbond fabric. Two different polymers are transported by extruders to the spinneret, leaving it as bicomponental endless filaments, which are quenched and stretched by air streams with a very high speed up to sonic velocity. The stretched filaments are finally laid down onto a moving belt to form a nonwoven fabric of uniform structure. As demonstrated later in more detail the fiber distribution is more or less an isotropical one. Mechanical strengths are practically the same in machine and cross direction which might beneficial for most part of applications.

Afterwards the continuous filament web is subjected to an hydro-entanglement and fiber splitting process. Fig. 5

Splitting rate is normally performed in a range of at least 97%. In order to provide such high degree of splitting many parameters had to be checked on their impact and to adapted one to the other. Such parameters are the hole diameter in the spinneret, quenching, rate of stretching and last not least the water pressure which has to be increased up to 400 bar.

Fiber polymer combinations and weight ratios

For splitting in single ultrafine microfibers an incompatibility of both fiber polymers on their interphase is necessary. Suited polymer couples are polyesters (such as PET and PBT ) with polyamides (such as polyamide 6.6 or 6), polyesters with polyolefins and polyamides with polyolefins.

Weight ratio of both fiber polymer components can be varied from 20/80 to 80/20. Within the Evolon ® fabric range the most common used polymer combination by far is PET / PA 6.6 18- Pie-fiber in a weight ratio of 65/35. The lower raw material costs for polyester granule compared to polyamide might be the driving force for the use of a higher part of polyester.

Up to now Freudenbergs investigations had been focused exclusively on rigid polymers and of course they will be extended to thermoplastic elastomers (TPE) of at least one of both components. Unbelievable fabrics features are expected thereby.

Hydrophilic and hydrophobic properties

Evolon ® fabrics can be adjusted hydrophillic or hydrophobic depending on the applications or end uses posed on the nonwoven. In order to provide durable hydrophilic character usually an add-on of a hydrophilic agent to the polyester fiber polymer is preferred to an external application onto the fiber surface by methods such as spraying, padding and the like. Without hydrophilic agent the Evolon PET/PA 6.6 65/35 fabrics are medium up to weak hydrophobic, mainly due to the presence ot one third of polyamide 6.6. An external finishing of the nonwoven fabric after hydroentanglement and splitting - the wet-in-wet method is the best from economical point of view- is necessary in order to attain highest level of hydrophobic performance. Wear comfort properties

Different Evolon grades had been tested by the German Hohenstein Textile-Research Institute. Its laboratory has developed a computerized skin simulator and it is the leading authority on fabric comfort.

Wear comfort is determined by thermal insulation, drying time, water vapor transmission rate wicking properties and the ability to buffer water vapor for short time. It is also influenced by sensorial comfort characteristics such as the wet-cling index and the number of contact points between the fabric and the skin. Most Evolon samples tested at Hohenstein were found to provide very good wear comfort. In Table III the results of all tests conducted at Hohenstein and by the Institue Textile de France (ITF) are compiled. Most samples obtained top rating 1 = very good for total wear comfort. For excellent wear comfort Evolon fabrics have to be adjusted hydrophillic and to pass any mechanical softening treatment.

Table III Type of fabric Target Values; values for reference Evolon type

OP-464 OP-602 OP-608 OP-711 OP-717 Heat insulation Ret 103 m2K/W For Doppelripp-BW-Unter-hemd approx. 28 not measured not measured not measured 42,5 39,3 Water vapour transmission index imt Good sportswear: >0,3 Maschenware sportswear: approx. 0,45 not measured not measured not measured 0,56 0,53 Humanity transport Fi-Value (g/m2 h mbar) Good sportswear: 20-24 22,6 16,8 21,6 15,2 14,6 Wetting Time sec Cotton: 0,5 0,5 128 2,4 >600 >600 Drying time t min Cotton: approx 37 18,0 34,5 21,0 25,0 24,5 Wet Cling Index iK (skin sensoric) Unacceptable >15 All evolution styles provide values of <4 Surface index Io Length and number of Abstandshalter (skin sensoric) Io<3 Textile is too smooth and adheres Io>15 Textile is too rauh and kratzig All evolution fabrics lie between Io=4,8 - 8,2 Number of contact points nk (skin sensoric) nk>1500 Worse, klamm and humid nk>1500 good Evolon fabrics 1 measurement: 1059

4 measurement: 757 - 822 Stiffness S Maschenware < 27

Evolon fabrics without any mechanical post treatment io 37,8 - 50,6 Resumee: mechanical post treatment for softening, such as tumbling is necessary Sensorial wear comfort WCs Measured at Hohenstein Research Institute 1,5 2,1 1,8 3,0 3,2 Total wear comfort WC

1,0 3,5 1,0 1,0 1,0 Type of fabric Target Values; values for reference OP-464 OP-602 OP-608 OP-711 OP-717

Evolon type

Impact of different parameters on final fabric

As already mentioned Evolon fabrics can be adjusted hydrophillic respectively antistatic by an add-on of hydrophilic agent. Mechanical strengths are also depending on fiber forming polymer respectively the polymer combination of the bicomponental fiber and the number of segment within the PIE-fiber. The impact of these parameters on tensile and tear strength of the fabric after hydro entanglement and splitting is illustrated in Fig. 6. PIE 8 fiber comes off the best in this respect. If normal polyethylenterephthalate is replaced 8 by a low pilling type tensile strenght drops down dramatically and tear strenght only moderately. Fabrics composed of PIE 8 provide somewhat higher strengths than PIE 16. Fig. 6

The impact of dope dyeing on tensile strength is shown more detailled in Fig. 7 for fabrics based exclusively on PIE 16. The concentration of the blue dyestuff - varied from 2 to 4 % - exerts a small influence on tensile strength after hydro entanglement and splitting, i.e. the higher the dyestuff concentration the lower the strengths. The negative effect on tensile strength of black dyestuff (4 %) proved to be higher with the blue one.

Fig. 7 The impact of dyestuff concentration on decrease of tear strength is much less severe than on decrease of tensile strength, as illustrated in Fig. 8.

Fig. 8

Of course any changements in mechanical strengths of final nonwoven fabric have got their original cause in the tenacity of the endless filaments . In Fig. 9 tenacities of different filament types are arranged. Comparing results of Fig. 6 with Fig. 9 there is obviously the same trend.

Fig. 9 Dope dyeing is the preferred kind of dyeing for Evolon fabrics based on PIE 16 or PIE 8 bicomponental filaments. Due to the extremly high fiber surface ultra fine microfibers needs much more dyestuff compared to normal fine denier fabrics providing correspondingly much less color fastness after texile dyeing, especially for darker shades.

The fiber surface of a 100 g/m2 fabric composed of 100% polyethylene terephthalate is calculated

for 1,7 dtex with 23,6 m2 for 0,8 dtex with 33,8 m2 for 0,2 dtex with 64,4 m2 for 0,1 dtex with 94,3 m2

In the case PIE-segmented filaments calculation is more difficult because the splitted filaments are triangle like shaped in cross section providing much higher fiber surface compared to fibers with circular cross section.

Calculation according to a formula not presentated here provides a fiber surface of 264 m2 for a PIE 16 fiber PET/PA 6.6 with weight ratio 65/35 and a fiber fineness of 1,6 dtex. In other words fiber surface of this PIE 16 fiber is increased for approximately12 times after total splitting in 16 segments.

Evolon for medical and hygiene applications

The unique new Evolon fabric range is highly versatile because practically all end-use properties can be steered during the process. For example different grades can be converted to sports- or workwear, shoe linings or window shades, clean room wipes , substrates for tufting or automotive interior components. The fabrics properties, such as outstanding drape, wear comfort and mechanical strengths are comparable to woven or knitted textiles.

First research and development efforts had been focused on such end-uses, requiring durable or at least semi-durable nonwovens fabrics of higher weights.

The Evolon line is planned to go on stream around September of this year. Additional lines will follow in 2002.

Challenge for the next future will be the creation of Evolon fabrics for hygiene and medical market. They will differ from grades for other applications in some respect. Fabrics for such kind of applications do not require extremely high durability because they are normally disposed after single use and do normally not need high fabric weights.

First projects which have already been started are

- a rigid backing substrate for for medical plasters and wound dressings, - an extensible, elastic backing substrate for for medical plasters and wound dressings - an extremly light weight apertured topsheet.

Further projects will follow. The extension of Evolon product range for hygiene/medical market will be of highest priority.

The rigid backing substrate in white and beige has been focused on replacement of a rigid, non extensible woven with weights of around 100 g/m2. Target weight for the Evolon counter part will 80-100 g/m2 too.

For soft, extensible and (at least partially) elastic backing materials for plasters the incomparably high mechanical strenght of Evolon grades allows a reduction of fabric weight down to around 35 g/m2.

Nonwoven fabrics for backing substrates of wound dressings and plasters coated by pressure sensitive adhesives (PSA) based on synthetic polymers, such as polyacrylic esters, are wide spread. But nonwoven fabrics could not compete with woven fabrics if they are PSA coated by natural rubber, providing much higher adhesive power to human skin than polyacrylics or the like and requiring much higher web integrity in order to prevent delamination within the fabric after removal of the plaster.

Evolon proved to be well suited not only in this repect but also with regard to other properties such as softness of the surface and the suede like properties evolved by ultra-fine microfibers.

In Fig. 10 Evolon PIE 16 PET/PA 6.6 post treated by fluorocarbon resin and thermosol disperse dyed in one single step is compared to a neck stretched fabric on the same base. Neck-in stretch was performed between a pair of rollers with different speeds and at room temperature. It can be demonstrated how the orientation of the fiber can be changed from random (isotropic) to machine direction (md) by this process. Elongation at break in md is reduced from 52 to 11 % and in cross direction (cd) increased from 63 to 150 %.

Fig. 10

In Fig. 11 a and b Evolon fabrics before and after neck-in stretching are compared to other nonwoven fabrics carded and binder bonded with different fiber blends and neck stretched polyamide 6 spunbond, also binder bonded, which had been produced at Freudenberg up to dismantling of the polyamide around 8 years ago. Fig. 11a

Fig. 11b

Outlook for Evolon with regard to future medical-hygiene projects

The most part of end uses for hygiene-medical nonwoven fabrics by far can be covered by low weights under 50 g/m2 either for performance or cost reasons.

We have started investigations for such low fabric weights on our pilot plant at present mainly focused on  single use Operating Room (OR) drapes and gowns in a weight range of around 30 - 45 g/m2 and  apertured fabrics for topsheets of baby diapers, diapers for adult incontinence and sanitary napkins in fabric weights of around 10 - 20 g/m2.

Ultrafine micro fibers of Evolon fabrics might provide very good barrier properties with low fabric weights. Actually Spunbond-Meltblown-Spunbond fabrics (SMS) based on polypropylene are proved to generate best barrier properties due to the micro fiber meltblown sheet. PP is used for performance (high water repellency) and cost reasons. Disadvantage of this polymer in conjunction with a 3 sheet composite structure is the film like handle missing any textile properties and the non sterilizability with gamma- or beta- irradiation.

Evolon process will have the benefit to apply hydrophobic polymer combinations such as polyethylene terephthalate and polyolefine and the option to put a meltblown sheet on a ultra fine microfiber spunbond or between two of such ultra fine microfiber spunbond layers.

As far as apertured topsheets are concerned we started around 2 years ago a project. The high mechanical strengths, the soft micro fiber surface of Evolon fabrics and the fact that fiber entanglement, splitting in ultrafine microfibers and aperturing are attained in one single step by high pressure water jets are pleading for the Evolon process.

Samples in a weight of 15-17 g/m2 were manufactured on the pilot plant. In order to provide water repellency the polymer combination PET/PA 6,6 weight ratio 65/35 PIE 16 had been replaced by PET/PP weight ratio 78/22 PIE 16.

Apertured topsheets are already used in sanitary napkins. Vacuum perforated plastic films with funnel like holes are wide spread in this field. But also nonwoven/film composites are known.

There are different methods for perforation:

(1) Perforation by heat embossing at temperatures over the melting point of the fiber (2) Perforation by friction calendering between an engraved and a smooth roller (3) Perforation by slitting and extension perpenticular to the slits (4) Perforation by passing male-/female rollers (5) Hot needle perforation and last not least (6) Perforation by water jets onto suitable supporting means such as coarse mesh sreens or perforated drainage drums with projections in order to provide clear holes

In Fig. 12 tensile strength of a 16 g/m2 Evolon fabric based on PET/PP = 78/22, perforated by hydro entanglement is compared with further nonwoven fabrics, manucatured at different methods - carded; carded//meltblown (CM) and spunbond//meltblown (SM) - apertured also either by hydroentanglement or by heat embossing according to method (1). Tensile strenght is again related to 1 g/m2 in order to elaminate the impact of different fabric weights. Fig. 12

Evolon PET/PP (actual fabric weight: 16,7 g/m2) provides specific tensile strength of more than 3 times compared to carded/perforated by melt-embossing, around 5 times compared to PP//PP-SM=10/20, around 3 times compared to PP/PE//PP-SM=10/20, approx. 2,5 times compared to PP//PP-SM=20/20 and 14 times compared to PP/PE//PP-CM=10/20. The tremendous superiority of Evolon cannot be shown more effective than by these numbers.

With the unique new Evolon fabric range and manufacturing process Freudenberg has contributed a further major technological breakthrough to the nonwoven industry. We are in the very beginning with our investigations and are sure that the tremendous benefits of Evolon fabrics will provide a lot of new application and open the hygiene and medical market more and more in future.

This article is published on NT New Textiles, see the contents.

WHAT'S NEW  COMBEAU INDUSTRIES ANNOUNCES THE INSTALLATION OF A NEW HIGH-SPEED, WIDE-WIDTH SLITTER/REWINDER FOR NONWOVEN FABRICS

 SYNTHETICS FINISHING OPENS NEW MEGA-WAREHOUSE AND STORAGE FACILITY IN THE SOUTH

 COMBEAU INDUSTRIES TO INSTALL NEW HIGH-SPEED WIDE- WIDTH NONWOVEN FINISHING LINE

 DEFEND™ FAMILY OF PROTECTIVE FINISHES

COMBEAU INDUSTRIES ANNOUNCES THE INSTALLATION OF A NEW HIGH-SPEED, WIDE-WIDTH SLITTER/REWINDER FOR NONWOVEN FABRICS

HICKORY, NC – According to Ralph Krueger, Vice President for New Product Development, “This is our third slitter/rewinder devoted almost exclusively to the needs of the major nonwoven roll goods producers. It is capable of handling fabric widths out to 180” and roll diameters up to 60” and, as such, will fulfill a growing need in the wide commodity fabric business.” Combeau Industries has recently experienced increased demand for nonwoven slitting and rewinding, which augments it core service businesses, such as chemical coating, saturation, lamination, thermal bonding, needling, calendering, and embossing of woven and nonwoven fabrics.

SYNTHETICS FINISHING OPENS NEW MEGA-WAREHOUSE AND STORAGE FACILITY IN THE SOUTH

HICKORY, NC – Commission fabric finisher, Synthetics Finishing, Division of TSG Incorporated, has just completed their largest expansion project in the company’s 100-year history. Recently opened is a new 2,400,000 cubic foot warehousing, shipping, and distribution center located on approximately six acres adjacent to its main finishing plant in Hickory, North Carolina.

According to Darryl Grater, Vice President of Southern Operations, ?This facility, our 5th in North Carolina, represents the company’s continuing commitment to the upholstery business and the southern furniture industry in general. For years many of our top customers, including mills, jobbers, and overseas exporters, have complained about the lack of fast, efficient warehousing, cutting, and shipping services available in the south. This installation should finally answer that complaint.”

The high-bay warehousing section of this installation, nearly 40 feet from floor to ceiling, reportedly contains the largest number of fabric storage tubes (all manufactured by Sunoco Products Company) at any single location in the United States. State-of-the-art material handling shuttles operating in seven 185 foot isles are capable of picking and placing individual fabric roles into their own storage locations.

COMBEAU INDUSTRIES TO INSTALL NEW HIGH-SPEED WIDE-WIDTH NONWOVEN FINISHING LINE

HICKORY, NC - Commission nonwoven finisher, Combeau Industries, a division of TSG Incorporated, is in the process of installing a second high-speed wide-width nonwoven finishing line at its North Carolina location. The new equipment is capable of handling fabric widths out to 170” and roll diameters up to 60”.

According to Ralph Krueger, Vice President for New Business Development, “This line should expand our well-known wide-width capabilities beyond low viscosity saturation and spray application of light to medium weight nonwoven webs used primarily in the medical, hygiene, and filtration markets. Utilization of ultra high efficiency drying and curing technology, in addition to a newly developed multi- purpose coating station, should position Combeau perfectly to service ever-growing markets for high add-on single or double sided coating and high-viscosity impregnation, used primarily in nonwovens for roofing, geotextiles, and automotive applications.”

The new finishing line is expected to be fully operational in the second quarter of 2002.

DEFEND™ FAMILY OF PROTECTIVE FINISHES

HICKORY, NC - TSG Incorporated and its commission finishing division, Synthetics Finishing offers its Defend™ family of specially modified protective coatings for furnishing fabrics used mainly in commercial and institutional environments. Defend™ finishes impart a variety of protective features to textiles while still retaining the original textured, fabric-like surface characteristics, breathability and hand.

The Defend™ coating is suitable for use with a multitude of fabric constructions, fibers, and weights. Many “loom state” high style fabrics can be successfully treated with Defend™ to withstand the rigors of the institutional market. Defend™ treated fabrics exhibit enhanced dirt, stain, and abrasion resistance in addition to antimicrobial properties which inhibit the growth of bacteria or fungus.

Defend™ treated fabrics are ideal for use in restaurants and food service areas where maximum abrasion resistance and easy removal of nasty food-born stains are of primary importance. Outdoor upholstery and fabric for medical/incontinent applications require the ultra-high liquid repellency of the Defend™ coating in order to perform adequately. Defend™ finishes have also helped create a whole new generation of “soft” fabric tote products (luggage, golf bags, backpacks, handbags) that display the beauty and design possibilities of real woven fabric while not sacrificing scrubability, scuff resistance and repellency.

Various Defend™ finishes are presently available, each individually tailored to specific styles of fabric and performance requirements. Contact your sales representative for more information.