Patent Application
20200255991
The present invention relates to a fabric, more specifically to a fabric having certain strength and elongation properties.
Synthetic fabric, and especially lightweight fabric, is used in a large variety of applications. By being lightweight, the fabric may be made in a cost-efficient way concerning material usage, material costs, and transportation costs. Further, synthetic fabric enables thin and light composite products.
Applications foreseen within the scope of the present invention include the use of the fabric as a component in baby diapers, closure mechanisms in diapers, adult incontinence products, feminine hygiene products, and in the healthcare industry in general. Said products may all require some degree of stretch or elongation for use. In the following, the use of the fabric as a component in diapers is considered. Nowadays, diapers are commonly made of a synthetic fabric due to the reduced costs and improved properties compared to natural materials. However, diapers need to meet certain requirements concerning feel and strength. The feel is highly important due to the peculiar use, whereas the strength is important due to the wear and handling. Today, diapers are made in different designs, where especially the closure mechanism relies on different techniques depending on the make. For example, the closure mechanism may rely on hook and loop fasteners attaching ears of the diaper onto the waist of said diaper. The ears are the tabs on the side of the diaper having hook and loop fasteners or similar non-permanent fixing to close and adjust the diaper fitting. Typically, the hook and loop fasteners are adjusted according to the size of the user, e.g. through the ears comprising hooks and the waistband comprising a band of loops, whereby the ears may be attached any place on said waistband. In another configuration, the ears are stretchable/flexible (“stretch-ears”), whereby an elastic or recovery effect arise, said recovery effect improving the closure and fit. It should be noted that not all diaper products necessarily comprise fasteners arranged on the waistband (sometimes referred to as the landing zone). Moreover, a waistband may not even be present, but instead be embodied as an integral part of the diaper. In some products, the landing zone may be specifically engineered and may be of another substrate added as a layer to the remaining assemble.
However, stretchable ears impose certain limitations to the fabric being stretched, most importantly its elongation properties. For this reason, different types of fabric have been employed in an attempt to balance the required strength and elongation. A desire exists to replace the types of fabric used nowadays with a fabric comprising optimised strength and elongation properties and preferably accompanied by an improved softness without affecting the cost.
General Description
An object of the present invention is to solve some of the above-mentioned problems. More specifically, the present invention discloses a fabric comprising a plurality of textile fibres, wherein said plurality of fibres comprises fibres that have been selected from two groups of fibres. The first group of fibres comprises multiple fibres having a first average length, and the second group of fibres comprises multiple fibres having a second average length, the first average length being shorter than the second average length. Further, the fibres of the first group of fibres have a first length variance being greater than a second length variance of the fibres of the second group of fibres. Further, the invention relates to a method of making a fabric comprising a plurality of textile fibres, the method comprising selecting fibres from two groups of fibres; a first group of fibres comprising multiple fibres having a first average length and a first length variance, and a second group of fibres comprising multiple fibres having a second average length and a second length variance, where the first average length is shorter than said second average length, and where the first length variance is greater than said second length variance.
Preferably, the fabric is a lightweight fabric. By being a lightweight fabric, comparison is drawn to a fabric of identical use, quality, or function, but where the lightweight fabric is lighter. In the present context, a fabric is considered lightweight if it weighs less than 30 grams per square meter (gsm, g/m2). Preferably, the fabric is a non-woven fabric made from hydroentanglement, also known as spunlacing.
By a plurality of textile fibres is meant that multiple textile fibres are combined in a plurality, where a part of said textile fibres may be identical/indistinguishable within the plurality.
The fabric comprises at least two groups of fibres, whereby it should be understood that said groups comprise different properties. Said properties may be differences in regard to average length, variance, or inherent material properties. A group may comprise a blend of distinguishable fibres, such that fibres made of different materials or properties are blended into a single group. For example, one group may comprise polyester (PES) fibres and polypropylene (PP) fibres blended into a blend. When referring to polyester in this document, it should be understood that polyester is a family covering multiple polymers which may be suitable in the present invention. An example of a polymer being classified as a polyester is polyethylene terephthalate (PET) which is a preferred type of polyester in the present invention. The relative amounts of PES fibres and PP fibres may vary between the groups, just as the average length or length variance may vary between the groups. In the case of a blend, the fibres constituting the blend may have been blended prior to selecting the fibres to constitute the fabric. Thereby, the blend may be provided from external sources, whereby the production line is simplified.
By a first group of fibres comprising multiple fibres having a first average length being shorter than a second average length of fibres within a second group of fibres, is meant that the fibres being part of the first group are on average shorter than the fibres within the second group of fibres. The average may be the mean or more specifically the geometric mean. The maximum length of any given fibre within the first group of fibres, i.e. any fibre contributing to the average length of the fibres in the first group, may be equal to, or shorter than, the average length of fibres within the second group of fibres. In other words, the maximum length of a given fibre within the first group may be said to be limited to the average length of the fibres within the second group.
Thereby, the elongation properties of the fabric is changed in respect of the cross direction of the fabric, whilst maintaining almost unchanged strength in the longitudinal direction at a low basis weight. The elongation properties include a controlled reduction in the cross-directional tensile strength and a corresponding increase in cross-directional elongation, whilst still providing enough cover and longitudinal direction strength for the material to be made and formed in industrial processes. Thus, the extension profile may be said to be engineered when using fibres of different average lengths in a fabric as disclosed. Further, the possibility of controlling the average lengths of fibres through the right selection of groups of fibres provides a possibility of engineering the strength in detail. More specifically, according to the present invention, a weakness is engineered in the cross direction, whereby the maximum elongation length in said cross direction is increased compared to a conventional and comparable fabric not comprising groups of fibres selected according to the invention.
By a cross direction and a longitudinal direction is meant directions relative to the machine preparing the fabric using hydroentanglement. Said directions are relevant since the industrial process of making non-woven fabric using hydroentanglement is conducted on a conveyor belt. When making a non-woven fabric using hydroentanglement, the cards preparing and laying the fibres prior to hydroentanglement are usually in line with the rest of the machinery, i.e. the fibres are laid in a fibrous web on the conveyor belt moving at a given speed into the hydroentanglement section. This fact causes the fibres to be oriented primarily in the longitudinal direction, also known as machine direction, relative to the travelling direction of the conveyor belt. The processes within the card itself may also cause the fibres to be oriented primarily in the longitudinal direction. Thereby, the strength in the longitudinal direction is greater than in the cross direction, said cross direction being perpendicular to the longitudinal direction. Thus, the cross direction may also be named the transverse direction. The longitudinal strength is greater since friction between fibres being oriented primarily in the same direction is greater.
The cross-directional strength of the fabric according to the invention is reduced due to the introduction of a first group of fibres comprising multiple fibres having a first average length being shorter than the second average length of the fibres in the second group of fibres. The difference of fibre lengths within the fabric causes the reduction of cross-directional strength since it is the friction between individual fibres that characterises a non-woven fabric, and a reduced length of a part of the fibres causes said friction to be reduced, in turn causing the strength to be reduced. The specific average lengths used to engineer the desired properties of the fabric according to the invention depend on the end use of said fabric.
In an embodiment, the fibres of the first group of fibres may have a first length variance being greater than a second length variance of the fibres of the second group of fibres. By a first group of fibres comprising multiple fibres having a first average variance being greater than the second average variance of the fibres of the second group of fibres, is meant that from the plurality of fibres constituting the fabric, the fibres being part of the first group of fibres have on average a greater length variance than the length variance of the fibres being part of the second group of the fibres. By variance is meant the statistical term for the expectation of the squared deviation of a random variable from its mean. Instead of variance, the variation may be described through the standard deviation, the standard deviation being the square root of the variance.
The length of the fibres in the first group of fibres and the length of the fibres in the second group of fibres may be normally (Gaussian) distributed. In other words, the length of the fibres may be normally distributed around a mean value, the mean value being the average length of the fibres within the relevant group. In other words, the length of the fibres within each group may constitute a normal distribution. The standard deviation deduced from the normal distribution of the lengths of the fibres of the first group of fibres (i.e. the first normal distribution) may be broader than the standard deviation deduced from the normal distribution of the lengths of the fibres of the second group of fibres (i.e. the second normal distribution). Further, the first and second normal distributions may be separated by more than two standard deviations related to the second normal distribution. Thereby, the mean lengths of the fibres of the first and second group of fibres are significantly separated. In other words, the mean of the normally distributed lengths of the first group of fibres is separated from the mean of the normally distributed lengths of the second group of fibres by at least two standard deviations. It is noted that reducing the variance of a population reduces the width of the corresponding normal distribution. Thus, the first group of fibres may have a broader normal distribution than the normal distribution of the second group. For this reason, it was specified above that the separation of at least two standard deviations is related to the second normal distribution in regard to the standard deviation.
Thereby, a second possibility of engineering the properties, including the strength, of the fabric according to the invention is attained. Further, through a difference in length variances (or a separation of the first and second normal distribution, if the lengths are normally distributed), the at least two groups of fibres are increasingly distinguishable in the fabric.
In an embodiment, the first group of fibres may comprise a blend of polyester (PES) fibres and polypropylene fibres (PP).
The first group of fibres may also be said to be a blend of fibres comprising PES fibres and PP fibres, such that said first group of fibres solely comprises PES fibres and PP fibres. However, fibres made from other materials than PES and PP may be included in the first group as well.
The fibres within the second group of fibres may likewise be embodied in blends.
Thereby, the first group of fibres is ensured to encompass inherent properties of PES and PP.
In an embodiment, the ratio between PES fibres and PP fibres in the first group of fibres is between 1:0 (PES:PP) and 0:1 (PES:PP).
Thereby, the first group of fibres may comprise anything between 100% PES fibres and 0% PP fibres (1:0) and 0% PES fibres and 100% PP fibres (0:1). However, preferred ratios are 1:1 (PES:PP, e.g. 50% PES fibres and 50% PP fibres), or 45% PES fibres and 55% PP fibres, or 20% PES fibres and 80% PP fibres, or purely PP fibres, i.e. 100% PP fibres. Likewise, said preferred ratios further include the corresponding ratios of 45% PP fibres and 55% PES fibres, or 20% PP fibres and 80 PES fibres, or purely PES fibres, i.e. 100% PES fibres.
In an embodiment, the first group of fibres may constitute 50% of the fabric.
Thereby, half of the fabric is composed of fibres belonging to the first group, i.e. half of the fibres constituting the fabric is on average shorter than the other half of fibres. However, other percentages are foreseen within the present invention.
In an embodiment, the second group of fibres within the fabric may comprise 50% PES fibres and 50% PP fibres.
Thereby, the fabric comprises PES fibres and PP fibres in varying ratios and varying average lengths. Thus, the inherent properties of PES and PP are utilised, but the use of different average lengths allows engineering of the elongation properties.
In an embodiment, the fibres of the first group of fibres may have an average length below 30 mm and a length variance above 5 mm.
In an embodiment, the fibres of the second group of fibres may have an average length above 30 mm and a length variance below 5 mm.
Thereby, the average length of fibres within the first group is shorter than the average length of fibres within the second group of fibres. Likewise, the variance in length is greater for the fibres within the first group than for the fibres within the second group.
In an embodiment, the fabric may be a non-woven fabric.
By a non-woven fabric is meant a fabric wherein the individual fibres are bonded together in a random manner, e.g. through entanglement and frictional forces.
In an embodiment, the selection may be made among PES fibres, PET, and PP fibres.
Thereby, the fabric benefits from the inherent properties of PES, PET, and PP which may all be considered textile fibres. More specifically, the mentioned textile fibres have a low density compared to other textile fibres. Thereby, more textile fibres may be present in the fabric at a given basis weight. Further, if a given number of fibres is required to make a coherent fibrous web, the resulting fibrous web is lighter than when made from denser fibres.
In an embodiment, PP fibres may constitute at least 50% of said fabric.
Thereby, a majority of the fabric is PP. The amount of PP is essential for sonic bonding the fabric in a possible subsequent step since less energy is required to cause bonding between PP fibres than between PET fibres. Thereby, sonic bonding machinery may be run faster.
In an embodiment, the density of the fibres used within the fabric according to the invention may be between 1.3 dtex and 1.7 dtex.
However, the use of finer (<1.3 dtex) fibres or coarser (>1.7 dtex) fibres are foreseen within the present invention. For example, use of finer or coarser fibres may be envisaged as part of the product engineering in one or more of the groups of fibres. Further, the fibres may comprise varying cross sections. For example, the cross section of the fibres may be round, flat, trilobal, multilobal, triangular, hollow, solid, etc.
Thereby, the low density of the fibres adds to the lightweight properties of the fabric. Further, the low density of the fibres allows the basis weight of the fabric to be reduced in case a fixed number of fibres is needed to form a fabric having the desired strength, opacity, softness, and volume. By density is meant the yarn count expressed in terms of mass per unit length. In the present case, the unit used is dtex which is equal to the number of grams per 10,000 m.
In an embodiment, the basis weight of the fabric may be between 15 gsm and 35 gsm, or between 20 gsm and 30 gsm.
Thereby, the fabric is considered lightweight since fabric weighing below approximately 30 gsm is generally considered lightweight in the industry.
In an embodiment, the fabric may be made using hydroentanglement.
Hydroentanglement is a fabrication technique wherein the individual fibres are entangled using high-pressure water jets. Spunlacing is another word for hydroentanglement. When fabricating a non-woven fabric using hydroentanglement, a plurality of non-entangled individual fibres is arranged in a fibrous web followed by the introduction of multiple high-pressure water jets, said water jets penetrating the fibrous web and causing entanglement and thereby (mutual) physical bonding of the textile fibres. Thereby, the entanglement of textile fibres creates a non-woven fabric. The fibrous web may be formed using at least one card, but may also be formed by other means. Hydroentanglement is commonly employed to non-woven fabric having a relatively low weight due to the limitations set by the use of water jets. A relatively low weight may be less than 100 gsm (grams per square meter, g/m2).
Thereby, benefits, mainly the look and feel, from hydroentanglement are achieved. Further, hydroentanglement provides the possibility of making a fabric lightweight.
In an embodiment, the fabric may be provided with a stretch engine.
In order to use the fabric in diapers, it may be advantageous to equip said diapers with closure mechanisms being flexible. Thereby, the waistband keeping the diaper in place is always tightened around the waist of the user. Similar flexible behaviour may be wanted or needed in other uses as well. By a stretch engine is meant a flexible element capable of extending and recovering without deformation, preferably a type of plastic, such as polyethylene (PE). For example, the stretch engine may be a stretch-film laminated onto the fabric by means of glue or heat application, a stretch adhesive applied to the substrate, or any other element capable of providing a stretch and recovery to the fabric according to the invention. Preferably, the stretch engine is applied to the fabric in an almost relaxed state of said fabric, where a relaxed state is a state wherein no external forces are applied. By being in an almost relaxed state during the application process, it is ensured that the stretch engine and the fabric are smooth and non-deformed. Thereby, when pulling the combined fabric and stretch engine in opposite directions, the stretch engine extends and additionally provides an opposite-directed force aiming to revert the extended stretch engine and fabric to the original relaxed state. Thus, the stretch engine provides a recovery effect to the fabric. In other words, the stretch engine may be regarded a stretch-and-recovery-element. However, in such use, the fabric has to comprise beneficial elongation properties in the cross direction, said beneficial elongation properties including a low modulus at the relevant part of the stress-strain curve compared to the longitudinal direction. The strength of the stretch engine limits the maximum elongation of the fabric, whereby said maximum elongation of the fabric is limited to the maximum elongation of the stretch engine. Therefore, the strength of the fabric should be sufficient to withstand tearing for the entire elongation range set by the stretch engine. Preferable elongation properties and tensile strengths are found in a fabric according to the invention.
In the following, example embodiments are described according to the invention, where
In the following the invention is described in detail through embodiments thereof that should not be thought of as limiting to the scope of the invention.
In an embodiment, at least one side of the fabric 100 is provided with a stretch engine 200. Preferably, said stretch engine 200 is a stretch-film laminated onto a surface of the fabric 100 through glue, heat application, or similar methods for bonding the materials. However, the stretch engine 200 may likewise be an adhesive prodiving similar stretch and recovery properties. The stretch engine 200 is capable of a reversible extension when exposed to opposite-directed external forces, i.e. said stretch engine inherently comprises a recovery effect. When the stretch engine 200 is combined with the fabric 100, said recovery effect ensures that said fabric 100 may return from an elongated state to its relaxed state when no opposite-directed external forces are applied.
A first set of arrows 1a, 1b indicates a first pull in the cross direction C. Said first pull may be said to be opposite-directed external forces, i.e. the pull aims to extend the fabric 100 in the cross direction C. Likewise, a second set of arrows 2a, 2b indicates a second pull in the longitudinal direction L. The combination of fibres within the selection S according to the invention gives the fabric 100 engineered elongation properties, including an altered stress/strain curve, compared to a selection without a selection and combination of fibres as disclosed. Further, said engineered elongation properties include a reduced tensile strength and a greater maximum elongation length which is desired in the intended use of the fabric although other uses are foreseen. Further, the selection S causes the longitudinal tensile strength to be reduced compared to a selection without a selection and combination of fibres as disclosed. The increased maximum elongation length compared to a conventional and comparable fabric may be desired when a highly flexible and stretchable fabric is needed, such as in use in diapers.
It should be understood, that the above-disclosed process of making a fabric according to the invention is not limiting to the scope of the invention. For example, multiple cards may be used each providing different groups of fibres, just as other aspects may vary in production.
Further, it is noticed how the mean M2 of the second normal distribution N1 is lower (see orientation of axis K, said axis denoting the length of fibres within the first and second group of fibres) than the mean M1 of the first normal distribution N1 according to a preferred embodiment of the invention. The nomination of “mean” instead of average length as used above is used in accordance with common nomenclature in statistics.
The separation of the first N1 and second N2 normal distributions may be described through the size of the first standard deviation D1. In an embodiment of the invention, the separation of the two normal distributions may be at least two standard deviations, where said at least two standard deviations are measured using the second standard deviation D2. This minimum separation is indicated using the juxtaposed set of arrows D2′, each of said arrows being equal in size to the second standard deviation D2.
A1 First average length
A2 Second average length
C Cross direction
D1 First standard deviation
D2 Second standard deviation
D2′ Minimum separation
F First group of fibres
K Axis
L Longitudinal direction
M1 Mean of the first normal distribution N1
M2 Mean of the second normal distribution N2
N1 First normal distribution
N2 Second normal distribution
S Selection
V1 First length variance
V1 Second length variance
X Second group of fibres
Z Zoom
1
a First pull
1
b First pull
2
a Second pull
2
b Second pull
10 Diaper
11 Front
12 Back
13 Intermediate section
14 Absorbing pad
15 Ears
16 First attachment means
17 Second attachment means
20 Card
21 Fibrous web
22 Conveyor belt
29 Moving direction of conveyor belt 22
31 Hydroentanglement station
32 Water jets
100 Fabric
111 PES fibres
112 PP fibres
131 First fibres
132 Second fibres
200 Stretch engine
| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2017 70761 | Oct 2017 | DK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2018/057755 | 10/5/2018 | WO | 00 |
