Extensible non-woven, method for producing an extensible non-woven and use of same

Abstract

The invention relates to an extensible non-woven, in particular, cover sheet material for a multi-layer laminate comprising hydroentangled staple fibers, where the non-woven contains 5 to 25 wt % of binder fibers made of thermoplastic material, in particular 10-15 wt % of binder fibers, and is in addition to hydroentanglement thermally bonded. Furthermore, the invention relates to an elastic multi-layer laminate for use in an elastic component for personal hygiene products composed of elastic base material covered on one or both sides by cover material, where the cover material is formed from extensible non-woven fabric.

Claims

1. An extensible non-woven bonded by hydroentanglement and thermal processes, wherein the non-woven has a weight range from 15 to 40 g/m.sup.2 and comprises: 10 to 20 wt % of binder fibers of 2.2 dtex/40 mm, wherein binder fibers are formed of a thermoplastic material, 40 to 45 wt % of first staple fibers of 1.3 dtex/40 mm, and 40 to 45 wt % of second staple fibers of 2.2 dtex/40 mm, wherein the first staple fibers and the second staple fibers are thermoplastic fibers, and wherein the binder fibers have a melting point that is at least ten degrees Celsius lower than the first staple fibers and the second staple fibers.

2. The extensible non-woven according to claim 1, wherein the binder fibers are staple fibers.

3. The extensible non-woven according to claim 1, wherein the binder fibers are bi-component fibers comprising a sheath/core structure, wherein a sheath of the sheath/core structure has a melting point that is at least ten degrees Celsius lower than the melting point of a core of the sheath/core structure.

4. A process for producing the extensible non-woven according to claim 1, the process comprising: blending first staple fibers, second staple fibers, and binder fibers, carding the first staple fibers, the second staple fibers, and the binder fibers to produce a non-woven, and performing hydroentanglement and subsequently drying with hot air to remove excess water, wherein the binder fibers are made of the thermoplastic material and activated and thermally consolidated during drying, and wherein the non-woven has a weight range of 15-40 g/m.sup.2 and comprises: 10-20 wt % the binder fibers of 2.2 dtex/40 mm, 40-45 wt % the first staple fibers of 1.3 dtex/40 mm, 40-45 wt % the second staple fibers of 2.2 dtex/40 mm.

5. An elastic multi-layer laminate for use in an elastic component for personal hygiene products composed of elastic base material covered on one or both sides by a cover material, wherein the cover material is formed from the extensible non-woven according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the following, the invention is explained in more detail using embodiments with reference to the appended drawings, where:

(2) FIG. 1 shows the force-elongation behavior of differently produced non-wovens under tensile stress in the machine direction (MD=machine direction), where curves 1-3 represent comparative examples and curves 4 to 5 show examples according to the invention.

(3) FIG. 2 shows the force-elongation behavior of differently produced non-wovens under tensile stress transverse to the machine direction (CD=cross direction). The materials used in the individual curves correspond to the materials of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention is further explained by use of different fiber mixtures, both mixtures according to the invention as well as also comparative mixtures, and process settings. The individual fiber mixtures and their properties are specified in Table 1 below.

(5) The following fiber mixtures were examined in more detail as part of this embodiment:

Sample 1: Comparative Example

(6) hydroentangled (water-jet bonded) non-woven, 25 g/m.sup.2

(7) fiber: 50 wt % polypropylene fibers 1.3 dtex/40 mm and 50 wt % polypropylene fibers 2.2 dtex/40 mm,

(8) water-jet bonded

Sample 2: Comparative Example

(9) thermally bonded non-woven, 25 g/m.sup.2

(10) fiber: 100 wt % bi-component fibers, 2.2 dtex/40 mm, where the sheath is made of polyethylene having a melting point of approx. 128 C. and the core is made of polypropylene having a melting point of approx. 165 C.

(11) hot air bonded

Sample 3: Comparative Example

(12) fiber: 50 wt % bi-component fibers, 2.2 dtex/40 mm, where the sheath is made of polyethylene having a melting point of approx. 128 C. and the core is made of polypropylene having a melting point of approx. 165 C., and 50 wt % polypropylene fibers 1.3 dtex/40 mm
water-jet and hot air bonded

Sample 4: Example According to the Invention

(13) fiber: 45 wt % polypropylene fiber, 1.3 dtex/40 mm, 40 wt % polypropylene fibers 2.2 dtex/40 mm and 15 wt % bi-component fiber, 2.2 dtex/40 mm, where the sheath is made of polyethylene having a melting point of approx. 128 C. and the core is made of polypropylene having a melting point of approx. 165 C.,
water-jet and hot air bonded

Sample 5: Example According to the Invention

(14) fiber: 45 wt % polypropylene fiber, 1.3 dtex/40 mm, 45 wt % polypropylene fibers 2.2 dtex/40 mm and 10 wt % bi-component fiber, 2.2 dtex/40 mm, where the sheath is made of polyethylene having a melting point of approx. 128 C. and the core is made of polypropylene having a melting point of approx. 165 C.,
water-jet and hot air bonded

(15) For the samples containing the bi-component fibers, it must be ensured in the production that the non-woven has for activating or melting the bi-component fibers already been dried in the dryer.

(16) The temperatures in the belt dryer in the first zones are therefore below the activation temperature, so that only drying is preformed and the activation of the bi-component fibers is triggered only in the last part of the dryer, in a region of approx. 30%.

(17) Exemplary temperatures are given below.

(18) Temperature dryer zone 1: 116 C.

(19) Temperature dryer zone 2: 102 C.

(20) Temperature dryer zone 3: 96 C.

(21) Temperature dryer zone 4: 130 C.

(22) In a three-drum dryer, the first two drums are commonly used for drying and the bi-component fibers are in analogy to the belt dryer activated in the last drum.

(23) After production, the individual non-wovens were subjected to the following test methods to obtain the data given in Table 1 below.

(24) In the context of the tests, the term longitudinal, longitudinal direction or MD is used to specify the orientation of a sample in the direction of production of the material or the machine direction, respectively. The terms transverse, cross direction or CD indicate the orientation of the sample transverse to the direction of production of the material. Unless otherwise indicated, a sample width of 50 mm with a clamped length of 100 mm and a peel rate of 500 mm per minute was chosen for the tensile tests to simulate the width of a diaper ear.

(25) Grammage: according to WSP 130.1, specified in g/m.sup.2

(26) Thickness: according to WSP 120.6, determined at gauge pressure 0.5 kPa, specified in mm

(27) Maximum force Fmax longitudinal/transverse: according to WSP 110.4, option A, specified in N/50 mm

(28) Elongation at Fmax longitudinal/transverse: according to WSP 110.4, option A, specified in %

(29) Elongation at 5N longitudinal/transverse: according to WSP 110.4, option A, in %, automatic determination of elongation when reaching a force of 5N in the tensile test

(30) Fiber elongation at fracture: according to ISO 5079, specified in %

(31) Width contraction: it is determined as the ratio of the width B0 of a non-woven web in the unloaded state lying flat on a table to the width B1 of the same non-woven web when the latter is loaded with a tension of 10N. To determine the width under force, a non-woven sample 150 cm long and 20 cm wide is first fixed at the upper end of a test setup such that at least a piece of non-woven 120 cm long can hang down freely. It is there fixed such that the non-woven web is held across the entire width. A mass element is then attached at a distance of 110 cm from the upper clamping and fixed across the entire web width so that a force of 10N/20 cm arises at the non-woven web. Width B1 of the non-woven web is then again determined at a distance of 55 cm from the upper clamp. The width contraction is then obtained according to the following formula:

(32) $\mathrm{width}\mathrm{contraction}\left(\%\right)=100-\left(\frac{B1}{B0}.Math.100\%\right)$

(33) Table 1 in addition to the non-wovens of the invention also shows non-wovens according to prior art, i.e. a purely hydroentangled non-woven and a purely hot air bonded non-woven.

(34) Curve 1 in FIGS. 1 and 2 there schematically shows a conventional force-elongation curve of a hydroentangled bonded non-woven, initially almost linear with the lowest inclination, shortly before reaching the maximum force then with a progressive curve profile.

(35) Curve 2 in FIGS. 1 and 2 shows the typical force-elongation curve of a non-woven purely bonded by way of hot air, i.e. a linear profile with greater inclination until the highest tensile force is reached, followed by a fracture of the sample.

(36) The hydroentangled non-woven, in particular in the transverse direction, see FIG. 2, at the beginning of the force shows less inclination of the curve as compared to the hot air bonded non-wovens shown in curve 2, but which then rises almost exponentially with further elongation. The reason for this is knot formation among the individual fibers in the fiber entanglement points. This effect is positive for usage, since the user likewise perceives this behavior at the diaper ear so that overstretching can during use be prevented.

(37) The fiber entanglements are in a hydroentangled non-woven not rigidly fixed, but are movable within themselves since the fibers are three-dimensionally entangled with each other. The fiber entanglements are there given uniformly over the entire surface of the non-woven. If a mechanical tensile force acts upon a non-woven of this kind, then the fibers entangled with each other can adapt over a wide part of this force without a noticeable increase in force and without the fiber entanglements disintegrating. The structural integrity of the non-woven is not lost.

(38) This movable fiber entanglement points, however, are disadvantageous during the production and the further processing of such non-wovens due to the high sensitivity to tensile forces acting in the longitudinal direction associated therewith. Tensile forces in the longitudinal direction lead to width contractions that in part amount to above 20%, as indicated in Table 1, sample 1.

(39) According to the present invention, binder fibers are used in addition to the hydroentangled staple fibers, whereby the fiber entanglement as well as the unbonded fibers in the fiber composite are fixed such that the resulting non-woven of the invention is, firstly, adapted to the force elongation behavior of non-woven that is only bonded by water jet, and secondly, insensitive to processing influences in the longitudinal direction, i.e. the width contraction of a non-woven according to the invention is marginal.

(40) Since the drying process following the hydroentanglement is not only used to remove excess water, but also serves to activate the binder fibers contained in the fiber mixture and thereby leads to thermal bonding of the non-woven, the method can be performed in a cost-efficient manner because no additional process steps nor temporal elongation of the method are necessary.

(41) Samples 2 to 5 shown in Table 1 each contain different proportions of binder fibers in the fiber mixture.

(42) A non-woven that is thermally bonded consisting purely of binder fibers does exhibit good mechanical resistance to tensile forcesthe width contraction is at 0.8%but the maximum tensile forces and the related elongations, however, are too low. Furthermore, the material is too hard for use in hygiene products.

(43) Due to the admixture of a binder fiber component according to the invention, which results in additional thermal bonding in the drying process of the hydroentanglement, an additional binding mechanism acts upon the non-woven. This results in the normally very extensible structure of a non-woven that is bonded purely by water jet being blocked or locked.

(44) As is evident from the examples of sample 3 and in particular of samples 4 and 5 according to the invention, the melt fiber binding points are relatively brittle for which reason they fracture even with a low mechanical load and accordingly already at elongations between 30-70%.

(45) Due to combining the two bonding methods water jetting and hot air, a superposition from a technological perspective of the force-elongation curves occurs. The mechanical stability of the non-woven in the longitudinal direction and hence its processability is thereby improved without the properties in the transverse elongation in the functional region deteriorating.

(46) The behavior of a respective non-woven containing binder fibers is shown in curves 3 to 5 of FIGS. 1 and 2. It is clear that the curve profile in the lower elongation region can be set via the weight proportion of the binder fibers and adapted according to demands.

(47) Since the strengths in a staple fiber non-woven, regardless of the bonding technology, largely follow the fiber direction, for example, 4.0-4.5/1 fiber orientation MD/CD indicates a similar strength ratio, the admixture of bi-component fibers also acts preferably in the machine run direction, i.e. exactly where more stability in terms of process technology is needed, while the functional properties in the CD direction are not adversely affected.

(48) The functional properties are essentially limited to:

(49) 1. the force/elongation profile in the transverse direction, where an elongation as high as possible is required at a 5 and 10 N/5 cm force

(50) 2. furthermore, final strength of 15N/5 cm are demanded.

(51) As can be seen from Table 1, the comparative example according to sample 3 exhibits a transverse strength of 11N/50 mm, i.e. a transverse strength which corresponds to prior art. The elongation in the transverse direction at 5N force is at 39% insufficient as compared to sample 1. Also the grip is due to the proportion of binder fibers of 50 wt % too hard for the intended purpose of use.

(52) Samples 4 and 5 according to the invention comprise a significantly reduced proportion of binder fibers so that the number of bonding points existing in the non-woven can be significantly reduced. In particular the binder fiber content in sample 4 amounts to 15 wt % and in sample 5 to 10 wt %. Further tests have in this context demonstrated that a binder fiber content of up to 25 wt % yields results that satisfy the desired objectives.

(53) The force-elongation curve of sample 4 is shown in the figures as curve 4. It has in particular shown that the material is with respect to the elongation behavior in the transverse direction, cf. FIG. 2, ideal for the intended use as cover sheet material. In the lower region of the force, almost no force builds up, only toward the end of the elongation force does the force increase rapidly so that the desired stop function is obtained. Sample 4 exhibits an Fmax-elongation in the transverse direction of 200% which corresponds to the level of sample 1 which is only water-jet bonded.

(54) However, increasing the binder fiber content to about 25 wt % is detrimental to the grip, so that this proportion of binder fibers was set as the upper limit.

(55) In sample 5, shown as curve 5 in FIGS. 1 and 2, the proportion of binder fibers was further reduced. The curve closely approximates curve 1, i.e. the sample that is only hydroentangled, so that further reduction of the binding fiber content increasingly corresponds to the purely hydroentangled non-woven. In has in this context shown that a binder fiber content of 5 wt % represents a lower limit for a non-woven according to the invention.

(56) It has with respect to the width contraction at the processing force of approximately 10N in the longitudinal direction shown that sample 4 with a width contraction of 2.4% exhibits very good longitudinal stability without developing an excessive increase with cross elongation. Sample 5 exhibits a width contraction of 5.1%, i.e. a value still being acceptable, and has an F/E curve which almost corresponds to that of sample 1, in particular in relation to the transverse direction.

(57) Non-wovens produced according to the invention, i.e. non-wovens in the weight range of 15-40 g/m.sup.2, containing a content of 5-25 percent by weight of binding fibers and in which hydroentanglement is performed with subsequent thermal bonding by way of hot air, meet requirements a. to h. defined at the outset for extensible cover sheet materials.

(58) Non-wovens thus produced according to the invention are suitable in particular as cover sheet materials for elastic closure systems since they meet all demands of the aforementioned requirement profile over prior art.

(59) TABLE-US-00001 TABLE 1 Sample 1: Sample 2: Sample 4: Sample 4: comparative comparative Sample 3: example example example (prior example (prior comparative acc. to the acc. to the art) art) example invention invention type of water jet thermal water water water bonding jet/thermal jet/thermal jet/thermal content of 0 100 50 15 10 binder fibers (wt %) grammage 25.1 26.4 25.9 25.6 26.4 (g/m.sup.2) thickness 0.56 0.49 0.70 0.48 0.52 (mm) Fmax MD 48 19 72 65 64 (N/50 mm) Fmax CD 17 11 21 20 19 (N/50 mm) width 22.2 0.8 1.4 2.4 5.1 contraction at 1 kg load (%) elongation at 70.0 22 25 51.0 63.5 Fmax MD (%) elongation at 187.0 46.0 115.0 200.0 194.0 Fmax CD (%) elongation at 115 18 39 104 105 5N CD (%) elongation at 10 7.9 1.67 3 6.9 5N MD (%)