CA2281802C

CA2281802C - Cellulose-binding fibres

Info

Publication number: CA2281802C
Application number: CA002281802A
Authority: CA
Inventors: Pia Holm Hansen; Anne Monrad Larsen
Original assignee: FiberVisions AS
Current assignee: FiberVisions AS
Priority date: 1997-04-08
Filing date: 1998-03-31
Publication date: 2005-05-24
Anticipated expiration: 2018-03-31
Also published as: TW436535B; JP3672324B2; DK0973966T3; ID24606A; WO1998045519A1; AU6918298A; DE69808061T2; EP0973966B1; BR9809749A; JP2001518986A; IL131586A; IL131586A0; KR100403057B1; CN1106469C; CA2281802A1; DE69808061D1; KR20010005771A; CN1259178A; EP0973966A1

Abstract

The invention relates to drylaid nonwoven materials comprising bicomponent fibres comprising a low melting polyolefin component and a high melting polyolefin component, the low melting polyolefin component constituting at least a part of the surface of the fibre and comprising a non-grafted polyolefin component and a grafted polyolefin component, wherein the grafted polyolefin component has been grafted with an unsaturated dicarboxylic acid or an anhydride thereof, e.g.
with maleic acid or maleic anhydride. The bicomponent fibres have an excellent bonding affinity for natural fibres such as cellulose pulp fibres and allow the production of airlaid nonwovens with reduced generation of dust during the production process and with improved nonwoven strength properties.

Description

WO 98!45519 PCT/DK98/00131 CELLULOSE-BINDING FIBRES
FIELD OF THE INVENTION
The present invention relates to drylaid nonwoven materials comprising polyolefin bicomponent fibres having excellent bonding affinity for natural fibres such as cellulose fibres.
BACKGROUND OF THE INVENTION
Hygienic absorbent products such as disposable diapers con-tain, in addition to a water-permeable coverstock, a water-impermeable backsheet and one or more layers for distribution of liquid, an absorbent core typically comprising natural fi-tires such as cellulose fluff pulp fibres, synthetic fibres based on e.g. polyolefin and/or polyester and a superabsorb-ent polymer (SAP) material. In absorbent cores of this type, the synthetic fibres, which often are bicomponent fibres of e.g. polypropylene/polyethylene or polyester/polyethylene, are thermobonded to each other to form a supporting network for the core. Ideally, the synthetic fibres should be able to not only bond to each other, but also to the natural fibres and the SAP, so as to result in a core structure which is as strong and coherent as possible, and in which the natural fi-tires and the SAP are locked into place within the structure.
However, the existing synthetic fibres that are used for the production of drylaid, e.g. airlaid, nonwovens suffer from the disadvantage of suboptimal bonding to e.g. cellulose fi-tires. The problem is made worse by the fact that the natural fibres are typically relatively short, e.g. fluff pulp fibres with a length of not more than about 3 mm, as compared to the synthetic fibres, which are normally (although not necessar-ily) considerably longer. As a result, dust problems are cre-ated in the manufacturing process, and the performance of the resulting nonwovens is also suboptimal, since a large propor-.___..v____ __._. ~_ ~._..~.__~ .~_._.._. ~

p I II

2 tion of the natural fibres is not bonded to any of the syn-thetic fibres or otherwise held in place by means of the structure formed by bonding of the synthetic fibres.
It is therefore an object of the present invention to provide a bicomponent synthetic fibre which has an improved bonding affinity for natural fibres such as cellulose fluff pulp fi-bres and which therefore is particularly suitable for the production of drylaid nonwovens comprising a mixture of syn-thetic fibres and natural fibres.
EP 0465203-Bl discloses thermally bonded fibrous wet laid webs containing bicomponent fibres comprising a first compo-nent of polyester, polyamide or polypropylene and a second component of linear low density polyethylene (LLDPE) with a density of 0.88-0.945 g/cc and a grafted high density poly-ethylene (HDPE) with a density of 0.94-0.965 g/cc which has been grafted with malefic acid or malefic anhydride to provide succinic acid or succinic anhydride groups along the HDPE
polymer.
EP 0421734-Bl discloses thermobondable bicomponent fibres composed of two different polyolefins having melting points which differ by at least 20°C, the lower melting polyolefin containing 3-loo by weight of a monoglyceride of a fatty acid of 12 or more carbon atoms incorporated therein. The fibres are reported to be easily processable without the need for an oiling agent to be applied during spinning or drawing.
US 4,950,541 discloses succinic acid and succinic anhydride grafts of linear ethylene polymers obtained by grafting malefic acid or malefic anhydride onto a LDPE (low density polyethylene), LLDPE or HDPE polymer. The grafted polymers are dyeable and can be used e.g. as the sheath component of a bicomponent fibre.
_...T . _.____. . T _

3 US 4,684,576 discloses the production of blends of grafted HDPE with ungrafted LLDPE or LDPE, the HDPE having been grafted with malefic acid or malefic anhydride to provide suc-cinic acid or succinic anhydride groups along the HDPE poly-mer. The blends are disclosed for use in producing laminate structures.
It has now unexpectedly been found that polyolefin bicompo-nent fibres whose low melting component comprises a non-grafted polyolefin component and a grafted polyolefin compo-nent which has been grafted with an unsaturated dicarboxylic acid or an anhydride thereof have advantageous properties when used in the production of drylaid nonwoven materials, including improved bonding to cellulose pulp fibres and im-proved strength properties in the resulting nonwovens.
BRIEF DISCLOSURE OF THE INVENTION
In one aspect, the present invention relates to a drylaid nonwoven material comprising bicomponent fibres comprising a low melting polyolefin component and a high melting polyole-fin component, wherein the low melting polyolefin component has a melting point at least 4°C lower than the melting point of the high melting polyolefin component, the low melting polyolefin component constituting at least a part of the sur-face of the fibre and comprising a non-grafted polyolefin component and a grafted polyolefin component, wherein the grafted polyolefin component has been grafted with an unsatu-rated dicarboxylic acid or an anhydride thereof.
Another aspect of the invention relates to a method for pro-ducing a drylaid nonwoven material, comprising forming a fi-brous web using dry lay nonwoven equipment, the web compris-ing bicomponent fibres comprising a low melting polyolefin component and a high melting polyolefin component, wherein the low melting polyolefin component has a melting point at ..__..._

4 least 4°C lower than the melting point of the high melting polyolefin component, the low melting polyolefin component constituting at least a part of the surface of the fibre and comprising a non-grafted polyolefin component and a grafted polyolefin component, wherein the grafted polyolefin compo-nent has been grafted with an unsaturated dicarboxylic acid or an anhydride thereof, and bonding the fibrous web to re-sult in the drylaid nonwoven material.
A further aspect of the invention relates to a bicomponent fibre as described above for the production of drylaid non-woven materials.
DETAILED DISCLOSURE OF THE INVENTION
The term "polyolefin component" for the purpose of this in-vention means a polyolefin-containing polymeric material of which the largest part (by weight) consists of homo- or co-polymers of monoolefins such as ethylene, propylene, 1-bu-tene, 9-methyl-1-pentene, etc. Examples of such polymers are isotactic or syndiotactic polypropylene, polyethylenes of different densities, such as high density polyethylene, low density polyethylene and linear low density polyethylene and blends of the same. The polymeric material may be mixed with other non-polyolefin polymers such as polyamide or polyester, provided that polyolefins still constitute the largest part of the composition. The melts used to produce the polyolefin-containing fibres may also contain various conventional fibre additives, such as calcium stearate, antioxidants, process stabilizers, compatibilizers and pigments, including whiten-ers and colourants such as TiOz, etc.
Although the present description will for the sake of sim-plicity generally refer to "fibres", i.e. cut staple fibres, it is to be understood that the present invention will also j be applicable to the production of continuous polyolefin filaments, e.g. spunbonded filaments.
The term "drylaid" nonwoven refers to a nonwoven material

5 produced by a dry process, including airlaid nonwovens, carded nonwovens., etc.
The bicomponent fibres may be of the sheath-core type with the core being located either eccentrically (off-center) or concentrically (substantially in the center), or of the side-by-side type, in iahich each of the two components typically has a semi-circle cross section. Bicomponent fibres having irregular fibre profiles are also contemplated, e.g. an oval, ellipse, delta, star, multilobal, or other irregular cross section, as well as splittable fibres. The bicomponent fibres will typically have a high melting and low melting polyolefin component which comprise, respectively, polypropyl-ene/polyethylene (the polyethylene comprising HDPE, LDPE
and/or LLDPE), high density polyethylene/linear low density polyethylene, polypropylene random copolymer/polyethylene, or polypropylene/polypropylene random copolymer.
In certain cases, e.g. when the two components of the fibres comprise high density polyethylene/linear low density poly-ethylene or polypropylene/polypropylene random copolymer, the difference in melting points the difference in melting points between the two polyolefin components may be quite small, e.g. about 7-8°C and in some cases even as low as about 4-5°C. However, it is generally preferred that the two components have melting points which differ by at least about 20°C, preferably at least about 25°C, more preferably at least about 28°C, e.g, at least about 30°C.
As mentioned above, a presently preferred aspect of the in-vention relates to a drylaid nonwoven material containing

6 polyolefin bicomponent fibres in which the low melting poly-olefin component comprises a non-grafted component and a grafted component, the grafted component having been grafted with an unsaturated dicarboxylic acid or an anhydride thereof. Examples of such acids and anhydrides are malefic acid, malefic anhydride and derivatives thereof such as citra-conic acid, citraconic anhydride and pyrocinchonic anhydride;
fumaric acid and derivatives thereof; unsaturated derivatives of malonic acid such as 3-butene-l,l-dicarboxylic acid, benzylidene malonic acid and isopropylidene malonic acid; and unsaturated derivatives of succinic acid such as itaconic acid and itaconic anhydride.
Malefic acid and malefic anhydride are particularly preferred as the dicarboxylic acid or anhydride thereof. When these compounds are grafted onto a polyolefin chain, the resulting chain is provided with succinic acid or succinic anhydride groups, respectively, grafted onto it. The grafting of the dicarboxylic acid or anhydride thereof onto the polyolefin may be performed in a manner that is known per se, see e.g.
the above-mentioned EP 0465203, US 4,950,541 and US
4, 684, 576.
The weight ratio of grafted polyolefin to non-grafted poly-olefin in the low melting polyolefin component of the bicom-ponent fibres will be within the range of about 1:99 to 50:50, typically about 1.5:98.5 to 30:70, more typically about 2:98 to 20:80, e.g. about 3:97 to 15:85, such as about 5:95 to 10:90.
Within the grafted polyolefin, the content of carboxylic acid or anhydride thereof is typically in the range of about 1-30 (by weight), typically about 2-20~, more typically about 3-150, such as about 5-10°.

7 The weight ratio between the high melting and low melting polyolefin components will be in the range of from 10:90 to 90:10, typically about 20:80 to 80:20, more typically about 30:70 to 70:30, e.g. 35:65 to 65:35.
As mentioned above, drylaid nonwovens according to the inven-tion comprising polyolefin bicomponent fibres and natural fi-bres may be characterised by an improved bonding of the bi-component fibres to the natural fibres as determined by a standardised dust test whose result reflects the quality of the bonding between the two types of fibres. In this stan-dardised test, drylaid nonwoven samples having a base weight of about 85 g/m~ and a thickness of about 1.1 mm are prepared using a line speed of 20 or 40 m/min from a mixture of 25~~ by weight of the synthetic fibres being tested and 75o by weight of a cellulose pulp fibre (e. g. NB 416 from Weyerhauser).
Nonwovens to be tested are generally prepared using a series of different bonding temperatures (e. g. using hot air or cal-ender bonding, typically a hot air oven) in order to optimise the properties of a given nonwoven.
The determination of the dust value of a nonwoven is per-formed as follows. Before the measurement is carried out, the nonwoven samples to be tested are conditioned for at least 12 hours to ensure that all of the samples have been subjected to the same temperature and humidity conditions. Since, as described below, the results are often expressed as a rela-tive value compared to a control, the exact temperature and relative humidity for the conditioning of the samples is not critical, as long as all samples to be compared have been subjected to the same conditions. Ambient temperature and hu-midity conditions may therefore be used. Prior to condition-ing, the nonwovens are cut into individual samples with a size of 12 x 30 cm. After conditioning, a cardboard strip with a width of 5 mm is attached to the short sides of the sample, after which the sample with the attached cardboard

8 strips is weighed on a laboratory scale with an accuracy of ~0.1 mg. The nonwoven sample to be tested is then fixed with two clamps having a length of 12 cm, each of which is mounted on an arm. The exposed area of the fixed nonwoven is about 310 cm', which is about the size of a piece of A4 paper. One of the arms is stationary, while the other arm is rotatable and is attached to a spring.
The test is performed by rotating the rotatable arm 45°, so that the nonwoven sample goes from a "stretched out" condi-tion to a "relaxed" condition, after which the rotatable arm is released, whereby the action of the spring returns the ro-tatable arm to its original position. The movement of the arm is stopped by the nonwoven sample, which thus is subjected to a small vibration and stretching effect designed to be simi-lar to the conditions a nonwoven roll is subjected to when it is unrolled at the converter, the vibration and stretching resulting in a loss of loose fibres at the fibre surface.
This action is repeated 50 times. The stretching force the sample is subjected to must of course lie within the non-woven's elasticity limit, so that the nonwoven is not sub-stantially deformed or damaged during the test. For the same reason, and taking into consideration that the tensile strength of different nonwovens can vary considerably, the force provided by the spring must obviously be compatible with the nonwoven to be tested, so that the nonwoven is on the one hand returned to its original stretched out position and subjected to a slight vibration and stretching, but is on the other hand not excessively stretched so as to become de-formed or damaged.
After having been subjected to the vibration/stretching ac-tion 50 times, the sample is again weighed, and the differ-ence between the two values is calculated and expressed as mg of dust.

9 PCT/DK98/00131 In this standardised dust test, the result in mg will often be no more than about 15 mg, typically no more than about 10 mg, preferably no more than about 5 mg, more preferably no more than about 4 mg, still more preferably no more than about 3 mg, most preferably no more than about 2 mg. For non-wovens with a particularly good affinity between the syn-thetic fibres and the natural fibres, the result can be as low as abort 1 mg of dust.
An alternative and often preferred way of defining the dust-reducing properties of a given fibre in the standardised dust test is in terms of reduction of the amount of dust (in mg) in a standard nonwoven prepared from fibres of the invention compared to a similar nonwoven prepared from similar fibres without the grafted polyolefin component. In this case, the nonwoven prepared from the fibres of the invention should show a dust reduction of at. least about 40o by weight com-pared to the control nonwoven prepared with the control fi-bres, typically at least about 50o by weight. Preferably, the dust reduction is at least about 600, more preferably at least about 700, and still more preferably at least about 800. For fibres with particularly good cellulose-binding properties, the dust reduction can be as much as about 90=~ or more. Since the dust properties of a given nonwoven can vary greatly depending on factors such as the nature of the bicom-ponent fibres and the nature of the cellulose or other fibres as well as e.g. the particular webforming and bonding proc-ess, it will often be preferred to compare the performance of a given fibre in terms of i.ts dust reduction percentage com-pared to a similar control fibre rather than in terms of an absolute value in mg.
It is furthermore contemplated that the fibres of the inven-tion will also show an improved bonding and fixation of not only cellulosic fibres but also different superabsorbent polymers (SAP) that are commonly used in hygiene absorbent products in the form of particles or fibres. Such SAPS, e.g.
a crosslinked polyacrylic acid salt, are typically used in the form of superabsorbent particles in the absorbent core of e.g. disposable diapers, since they are able to absorb many 5 times their weight in liquid and form a gel that holds onto the liquid upon wetting. Even if the fibres of the invention are not directly bonded to the SAP particles, it is contem-plated that the improved bonding of the fibres of the inven-tion to the cellulosic fibres will result in an improved

10 structure that in itself serves to ensure that the SAP parti-cles are maintained in the desired location in the absorbent product, whereby the function of the SAP will be improved.
The spinning of the fibres is preferably accomplished using conventional melt spinning (also known as "long spinning"), with spinning and stretching being performed in two separate steps. Alternatively, other means of manufacturing staple fi-bres, in particular "compact spinning", which is a one step operation, may be used to carry out the invention. Methods for the spinning of bicomponent fibres and filaments are well-known in the art. Such methods generally involve extru-sion of the melts to produce filaments, cooling and drawing of the filaments, treatment of the filaments with an appro-priate spin finish to result in desired surface properties, e.g. using a spin finish to provide hydrophilic properties when the fibres are to be used in an absorbent core and/or to provide antistatic properties, stretching the filaments, typically, treating with a second spin finish, texturizing the filaments, drying the filaments and cutting the filaments to result in staple fibres.
As indicated above, the drylaid nonwovens of the present in-vention typically comprise, in addition to the polyolefin bi-component fibres, at least one additional fibrous material, in particular natural fibres or regenerated fibres, e.g.
selected from cellulose fibres, viscose rayon fibres and T

11 Lyocell fibre ~. The cellulose fibres may e.g. be pulp fibres or cotton fib res and are in particular pulp fibres such as CTMP (chemi-thermo-mechanical pulp), sulfite pulp or kraft pulp.
The fibrous web comprising the bicomponent fibres and the ad-ditional fibrous material will typically comprise 5-50$ by weight of the bicomponent fibres and 50-95$ by weight of the additional fibrous material, more typically 10-40$ by weight of the bicomponent fibres and 60-90$ by weight of the addi-tional fibrous material, e.g. 15-25~ by weight of the bicom-ponent fibres and 75-85$ by weight of the additional fibrous material.
EXAMPLES

Trials were run with different polyolefin bicomponent fibres to evaluate their bondability to cellulose pulp fibres.
The cellulose fibres were NB 416 from Weyerhauser. The weight ratio of between the bicomponent fibres and the'cellulose fi-bres was 25:75.
The tested bicomponent fibres had the following composition, fibre No..l being according to the present invention:
l: Core: polypropylene; sheath: loo grafted LLDPE (5$ malefic acid grafted onto 95$ LLDPE), 90$ LLDPE.
Z. Control fibre; core: polypropylene; sheath: 100$ LLDPE.
3. AL-Speci ~ -C from Danaklon A/S; polypropylene core, HDPE
sheath. ~
4. Hercules 449 from Hercules Inc., length 5 mm, fineness 1.5 dtex; polypropylene core/polyethylene sheath.
~ Tr~dem~

12 Bicomponent fibres 1, 2 and 3 all had a fineness of 1.7 dtex, a length of 6 mm and a weight ratio between core and sheath of 35:65.
The fibres were run at a very low speed of 8.33 m/min on an airlaid apparatus (Dan-Web, Denmark), since the primary pur-pose of these trials was to determine the fibres' ability to bond to cellulose. During the trials, an airlaid nonwoven product having a basis weight of 80 g/m2 was aimed at, and the trials were started at the lowest possible bonding tem-perature, after which the temperature in the oven was in-creased in increments of 5 or 10°C.
Results:
The cross direction (CD) dry strength, machine direction (MD) dry strength and MD wet strength were determined an samples produced at different temperatures as indicated below (EDANA
test method No. 20.2-89, tested at a speed of 100 mm/min).
Furthermore, the thickness and the basis weight (g/m2) of each sample was determined, and this information (not listed below) was used to adjust the strength values to result in normalised values that are comparable in spite of minor differences in thickness and base weight of the individual samples tested. The results are shown below.
Tm~t~

13 BondingStrength Strength Strength MD MD, SampleTemp. CD wet No. ~C N/5cm N/5cm N/5cm 1 125 25.9 25.2 25.4 1 130 20.9 20.5 18.3 1 135 23.5 22.4 20.6 1 140 23.1 22.3 20.1 1 145 23.9 22.5 18.0 2 125 17.46 15.43 15.13 2 130 13.63 13.32 11.62 2 135 15.17 15.06 12.66 2 140 16.25 15.72 13.99 2 145 12.77 7.3.08 9.78 2 150 11.28 7Ø77 6.77 2 155 4.15 4.26 2.23 3 130 24.01 23.37 23.59 3 140 19.34 7.8.08 18.57 3 150 15.59 1.6.66 14.92 4 130 7.98 7.78 7.98 4 140 9.23 7.93 8.73 4 150 8.83 8.93 8.83 4 160 4.21 4.31 2.26 4 170 3.24 3.14 1.27 The results of the dust test were as follows (average of 2 trials, except for fibre No. 3, which is the range of results obtained in a larger number of test runs with this fibre):
Fibre number Dust (mg) 1 1.7 2 7.4 4 14.0 Compared to the control PP/PE fibres 2, 3 and 4, fibre 1 ac-cording to the invention gave a significantly improved result in the dust test, the greatly reduced dust generation re-flecting a significantly improved bonding of the bicomponent fibres of the invention to the cellulose fluff pulp fibres.
Observation of the samples by microscope also revealed bond-ing of the bicomponent fibres of the invention to the cellu-CA 02281802 19'99-08-24

14 lose fibres. It was also found that fibre 1 gave a bulkier nonwoven compared to fibres 2 and 3 (fibre 4 was not compared in this regard). Furthermore, as shown by the strength values given in the table above, the fibres of the invention re-suited in nonwovens with improved strength and elongation characteristics.

A test of the ability of two different fibres to bind cellu-lose was performed in a test on a commercial airlaid line.
Airlaid nonwovens with a basis weight of about 80 g/m- and a thickness of about 1 mm were produced. The nonwovens con-tained 25o by weight of bicomponent fibres and 75o by weight of cellulose pulp fibres. The bicomponent fibres tested had a fineness of 1.7 dtex and a length of 6 mm. In addition to (control) fibre No. 3 described above, a bicomponent fibre (referred to as No. 5) with the same cellulose-binding addi-tive as in fibre No. 1 but a higher melting polyethylene sheath component (HDPE) was tested. This fibre thus had the following composition:
5: Core: polypropylene; sheath: 10o grafted LLDPE (5o malefic acid grafted onto 95o LLDPE), 90o HDPE.
The individual nonwoven samples were bonded at different tem-peratures with intervals of 3°C in order to ascertain the op-timum bonding temperature for the individual fibres.
It was found that the nonwovens containing bicomponent fibres of the invention (fibre 5) resulted in an improved binding of the cellulose fibres as evidenced by a reduced generation of dust during processing compared to the control fi-bre(quantitative measurements were not performed in this case). Furthermore, the fibres of the invention resulted in ...._.. . T

nonwovens with improved strength characteristics as evidenced by the following test results:
MD tensile strength, dry (N/5 cm) Bonding Fibre Temp. °C Control 5 137 13.96 15.08 140 15.77 19.01 143 ~ 12.56 19.40 146 - 15.41 Tests were performed to illustrate the influence of varying the amount of additive (malefic acid grafted LLDPE with an ac-

15 tine content of 50) in the sheath component.
The bicomponent fibres tested all had a fineness of 1.7 dtex and a length of 6 mm. The core/sheath weight ratio for fibres 6-9 was 35:65, and 50:50 for fibre No. 10. The core was in all cases of polypropylene. Nonwovens were produced on a com-mercial airlaid line using technology from Dan-Web, Denmark, the nonwovens having a basis weight of about 80 g/m', a thickness of about 1 mm, and weight ratio of bicomponent fibres to cellulose fibres of 25:75. Samples with each of the bicomponent fibres were tested at 3 different bonding temperatures, 137, 140 and 143°C.
The sheath composition of the individual fibres was as fol-lows:
6: 5o grafted LLDPE (5o malefic acid grafted onto 95o LLDPE), 95o LLDPE.
7: 5o grafted LLDPE (5o malefic acid grafted onto 95o LLDPE), 95 o HDPE .
8: 10o grafted LLDPE (5° malefic acid grafted onto 95o LLDPE), 9 0 ° HDPE .

16 9: 12.50 grafted LLDPE (5% malefic acid grafted onto 950 LLDPE), 87.50 HDPE.
10. 13° grafted LLDPE (5o malefic acid grafted onto 950 LLDPE ) , 8 7 o HDPE .
As a control, AL-Special-C from Danaklon A/S (polypropylene core, HDPE sheath; No. 3 above), was used.
The wet and dry tensile strength and the elongation of the various nonwovens was tested. As the results below show, the nonwovens containing the fibres of the invention showed a substantially improved dry and wet tensile strength compared to the control nonwovens. In addition, some of the fibres of the invention, notably Nos. 6, 7 and 8, showed elongation values above those of the control fibres, while fibre 10 and to a certain extent fibre 9 showed elongation values lower than for the control fibres. The suboptimal results for fi-bres 9 and 10 in terms of elongation are believed to be re-lated to the fact that some difficulties were experienced in spinning these fibres with a relatively large amount of the grafted component in the sheath. It is believed that with further tests and optimisation of the spinning process and other process parameters, it will be possible to obtain im-proved results for these and other fibres with a relatively large content of the grafted polyolefin component as well.
Tensile strength, dry (N/5 cm) Bonding Fibre No.

Temp . Control 6 7 8 9 10 C

137 8.54 21.58 17.65 16.91 18.68 12.75 140 9.85 18.58 20.98 17.00 17.95 14.40 143 8.53 18.59 19.25 30.63 18.18 16.38 _....__.........T...

17 Elongation, dry (o) Bonding Fibre No.

Temp . Control 6 7 8 9 10 C

137 185.25 190.25 154.50 199.67 174.25 133.50 140 175.00 184.75 188.25 195.67 169.00 119.00 143 178.67 189.25 185.78 184.25 185.75 144.75 Tensile strength, wet (N/5 cm) Bonding Fibre No.

Temp . Control 6 7 8 9 10 C

137 8.24 17.57 15.21 16.03 17.11 9.39 140 9.32 13.64 17 - 13.78 16.31 10.19 143 8.01 15.34 15.2 24.08 17.04 16.31 E1 ion, wet (o) Bonding Fibre No.

Temp . Control 6 7 8 9 10 C

137 175.25 220.75 161.50 179.67 205.25 118.75 140 159.50 194.25 177.75 186.75 189.00 132.50 143 142.50 196.00 179.67 177.00 188.50 123.75 A visual assessment of the dust properties of the nonwovens indicated that all of the tested bicomponent fibres of the invention had an improved bonding to the cellulose fibres compared to the control bicomponent fibres. Fibres 7 and 8 ran particularly well on the production line, and, as the re-sults above show, excellent strength values were also obtained for nonwovens containing these fibres.
The results of the fibres of this example in the dust test were as follows (fibre 10 was not tested):

CA 02281802 19,99-08-24

18 Fibre number Dust (mg) 6 6.6 7 14.9 8 5.8 9 6.7 Control 29.9 It can be concluded from the above that good results were ob-tained with all levels of additive addition, although there appeared to be a tendency for better results with additions of about 5-100.

Claims

1. A drylaid nonwoven material comprising bicomponent fibres each fibre comprising:
A) a high melting polyolefin component; and B) a low melting polyolefin component 1) having a melting point at least 4°C lower than the melting point of said high melting polyolefin component, 2) constituting at least a part of the surface of said bicomponent fibre, and 3) comprising a non-grafted polyolefin component and a grafted polyolefin component a) wherein said grafted polyolefin component has been grafted with an unsaturated dicarboxylic acid or an anhydride thereof.

2. A drylaid nonwoven material according to claim 1 wherein the grafted polyolefin component of the bicomponent fibres has been grafted with a compound selected from the group consisting of: maleic acid, maleic anhydride and derivatives thereof; fumaric acid and derivatives thereof; unsaturated derivatives of malonic acid; and unsaturated derivatives of succinic acid.

3. A drylaid nonwoven material according to claim 2 wherein the grafted polyolefin component of the bicomponent fibres has been grafted with a compound selected from the group consisting of citraconic acid, citraconic anhydride, pyrocinchonic anhydride, 3 butene-1,1-dicarboxylic acid, benzylidene malonic acid, isopropylidene malonic acid, itaconic acid and itaconic anhydride.

4. A drylaid nonwoven material according to claim 2 wherein the grafted polyolefin component of the bicomponent fibres has been grafted with maleic acid or maleic anhydride.

5. A drylaid nonwoven material according to claim 1 wherein the bicomponent fibres are sheath-core fibres in which the lower melting polyolefin component constitutes the sheath and the high melting polyolefin component constitutes the core.

6. A drylaid nonwoven material according to claim 1 which further comprises at least one additional fibrous material.

7. A drylaid nonwoven material according to claim 6 wherein the additional fibrous material is selected from the group consisting of cellulose fibres, viscose fibres and Lyocell fibres.

8. A drylaid nonwoven material according to claim 6 wherein the additional fibrous material comprises cellulose fluff pulp fibres.

9. A drylaid nonwoven material according to claim 1 wherein the high melting polyolefin component comprises polypropylene and the low melting polyolefin component comprises at least one polyolefin selected from LLDPE, HDPE and LDPE.

10. A drylaid nonwoven material according to claim 1 wherein the difference in melting points between the low melting component and the high melting component of the bicomponent fibres is at least about 20°C.

11. A drylaid nonwoven material according to claim 1 wherein the high melting polyolefin component comprises a first polypropylene, and the low melting polyolefin component comprises a second polypropylene or a polypropylene copolymer with a melting point at least 5°C lower than the first polypropylene.

12. A method for producing a drylaid nonwoven material, comprising forming a fibrous web using dry lay nonwoven equipment, the web comprising bicomponent fibres each fibre comprising:
A) a high melting polyolefin component; and B) a low melting polyolefin component 1) having a melting point at least 4°C lower than the melting point of said high melting polyolefin component, 2) constituting at least a part of the surface of said bicomponent fibre, and 3) comprising a non-grafted polyolefin component and a grafted polyolefin component a) wherein said grafted polyolefin component has been grafted with an unsaturated dicarboxylic acid or an anhydride thereof, and bonding the fibrous web to result in the drylaid non woven material.

13. A method according to claim 12, wherein the fibrous web further comprises at least one additional fibrous material.

14. A method according to claim 13 wherein the additional fibrous material is selected from the group consisting of cellulose fibres, viscose fibres and Lyocell fibres.

15. A method according to claim 13 wherein the additional fibrous material comprises cellulose fluff pulp fibres.

16. A method according to claim 12 wherein the grafted polyolefin component of the bicomponent fibres has been grafted with a compound selected from the group consisting of: maleic acid, maleic anhydride and derivatives thereof; fumaric acid and derivatives thereof; unsaturated derivatives of malonic acid; and unsaturated derivatives of succinic acid.

17. A method according to claim 16 wherein the grafted polyolefin component of the bicomponent fibres has been grafted with a compound selected from citraconic acid, citraconic anhydride, pyrocinchonic anhydride, 3-butene-1,1-dicarboxylic acid, benzylidene malonic acid, isopropylidene malonic acid, itaconic acid and itaconic anhydride.

18. A method according to claim 16 wherein the grafted polyolefin component of the bicomponent fibres has been grafted with maleic acid or maleic anhydride.

19. A method according to claim 12 wherein the bicomponent fibres are sheath-core fibres in which the lower melting polyolefin component constitutes the sheath and the high melting polyolefin component constitutes the core.

20. A method according to claim 12 wherein the high melting polyolefin component comprises polypropylene and the low melting polyolefin component comprises at least one polyolefin selected from LLDPE, HDPE and LDPE.

21. A method according to claim 12 wherein the difference in melting points between the low melting component and the high melting component of the bicomponent fibres is at least about 20°C.

22. A method according to claim 12 wherein the high melting polyolefin component comprises a first polypropylene and the low melting polyolefin component comprises a second polypropylene or a polypropylene copolymer with a melting point at least 5°C
lower than the first polypropylene.

23. A bicomponent fibre for the production of drylaid nonwoven materials, the fibre comprising:
A) a high melting polyolefin component; and B) a low melting polyolefin component 1) having a melting point at least 4°C lower than the melting point of said high melting polyolefin component, 2) constituting at least a part of the surface of said bicomponent fibre, and 3) comprising a non-grafted polyolefin component and a grafted polyolefin component a) wherein said grafted polyolefin component has been grafted with an unsaturated dicarboxylic acid or an anhydride thereof.

24. A drylaid nonwoven material comprising bicomponent fibres as defined in claim 1 and a natural or regenerated fibrous material, the bicomponent fibres having a bonding affinity to the natural or regenerated fibres such that the nonwoven material shows a dust value in the standardised dust test described herein of less than about 15 mg.

the bicomponent fibres having a bonding affinity to the natural or regenerated fibres such that the nonwoven material shows a dust value in the standardised dust test described herein of not more than about 10 mg.