Field of the Invention

The invention relates to thermally bonded nonwoven fabrics of spunmelt type, containing aliphatic polyesters with an increased efficiency of thermal bonding, resulting in an increased strength of the fabric.

Background Art

Strength or mechanical resistance of a nonwoven fabric is determined particularly by two principal factors. The first factor is given by the fiber itself (polymeric composition and characteristics of its crystallization, type of distribution, thickness of the fiber). As to biopolymers, particularly aliphatic polymers such as polylactic acid (PLA), e.g. a Kimberly Clark patent is known, which was filed in USA and granted under the number US7994078 and which describes suitable mixtures of aliphatic polyesters (combination of multitude of crystalline and amorphous polymers) for achieving a better quality of the fiber and subsequently of the nonwoven fabric. The above-mentioned mixtures can be used in monocomponent fibers or in various combinations in bicomponent fibers, where the use of a more amorphous constituent with a lower melting point on the surface of the fiber is desirable.

The second factor, which fundamentally influences the resulting mechanical properties of a nonwoven fabric, is the mutual bonding of fibers. For purpose of this disclosure, description of thermal bonding will be limited to thermal bonding, in which a part of fibers is melted, wherein the softened or even melted parts of the fibers join and create a bonding area. A very common type of bonding is e.g. by means of a pair of calender rollers, which, in addition to the effect of temperature, makes use of pressure, wherein the protrusions on one or both of the calender rollers provide so-called bonding impressions. Another known method is for example hot-air bonding, in which a hot-air passes through the entire fabric, wherein the bonding points are created at fiber to fiber contact points. Methods of bonding and various advantages are disclosed e.g. in documents W02012130414 or W02017190717, which underline the advantages of various shapes and distributions of bonding impressions, created by a pair of a smooth bonding roller and a roller with protrusions. Hot-air bonding and its advantages is disclosed for example in the document W02020103964 or in the Czech application no. PV 2020-591 (no yet published).

Summary of the Invention

The aim of the invention is an enhancement of the strength of nonwoven fabrics which contain fibers with aliphatic polyesters, this goal being achieved by a nonwoven fabric containing endless fibers and bonding impressions or bonding points, the endless fibers contain at least 80 wt. % of aliphatic polyesters, the endless fibers contain a first component, which makes up at least 55 % of the surface of the fiber, the first component contains at least one aliphatic polyester and at least 0.1 wt. % of an additive, the additive contains an amide group, the additive corresponds to the general formula (i) or (ii) or (iii)

(i) Rl-(CO)-NH ₂

(ii) R1-CO-NH-R2

(iii) Rl-(CO)-NH-R3-NH-(CO)-R2, wherein Rl, R2, R3 are aliphatic hydrocarbon chains.

Preferably a. Rl is an aliphatic hydrocarbon chain having a length of at least 10 carbons, more preferably at least 12 carbons, preferably at least 15 carbons; and/or b. R2 is an aliphatic hydrocarbon chain having a length of at least 10 carbons, more preferably at least 12 carbons, preferably at least 15 carbons; and/or c. R3 is an aliphatic hydrocarbon chain having a length of at least 1 to 7 carbons, preferably 1 to 3 carbons.

Furthermore, it is preferred when a. R1 is an aliphatic hydrocarbon chain having a length of no more than 30 carbons, better yet no more than 25 carbons, preferably no more than 20 carbons; and/or b. R2 is an aliphatic hydrocarbon chain having a length of no more than 30 carbons, better yet no more than 25 carbons, preferably no more than 20 carbons.

Furthermore, it is preferred when a. R1 is a straight aliphatic chain; and/or b. R2 is a straight aliphatic chain; and/or c. R3 is a straight aliphatic chain.

According to a preferred embodiment: a. R1 is a saturated aliphatic chain; and/or b. R2 is a saturated aliphatic chain; and/or c. R3 is a saturated aliphatic chain.

It is furthermore preferred when the first component contains at least 0.15 wt. % of an additive, better yet at least 0.20 wt. % of an additive, preferably at least 0.25 wt. % of an additive.

In a preferred embodiment, the first component contains no more than 10% of an additive, better yet no more than 5% of an additive, preferably no more than 1% of an additive.

The additive is preferably N,N’-ethylenebis(stearamide).

The component makes up preferably at least 70 % of the fiber surface, better yet at least 85 % of the fiber surface, better yet at least 90 % of the fiber surface, preferably at least 95 % of the fiber surface.

Preferably, in a bicomponent fiber of a core-sheath type, the first component forms the sheath.

In another embodiment, the first component constitutes one of the sides in a bicomponent fiber of a side/side type.

The endless fibers contain preferably at least 90 wt. % of polymeric constituents, better yet at least 95 wt. % of polymeric constituents, preferably at least 99 % of polymeric constituents. It is furthermore preferable when the first component contains a mixture of aliphatic polyesters with differing values of heat of cold crystallization.

It is also preferable when the first component contains PLA or combinations of at least two types of PLA with differing values of heat of cold crystallization, eventually when the first component is comprised of PLA and another aliphatic polyester.

In a particularly preferred embodiment, the fibers of the nonwoven fabric contain a second component, wherein the first component has lower melting temperature than the second component.

The second component preferably contains at least one aliphatic polyester, preferably PLA or a mixture of different types of PLA with differing values of heat of cold crystallization.

The above aim is achieve also by a method of production of a nonwoven fabric, which contains following steps: a) preparation of a material for production of endless fibers, the material containing at least 80 wt. % of polymeric constituents, wherein this material contains constituents of a first component of the endless fibers, the first component containing at least one aliphatic polyester and an additive in the amount of at least 0.1 wt. % of the total amount of the first constituent, wherein the additive contains an amide group and corresponds to the general formula (i) or (ii) or (iii)

(i) Rl-(CO)-NH ₂

(ii) Rl-(CO)-NH-R2

(iii) Rl-(CO)-NH-R3-NH-(CO)-R2, b) at least the constituents of the first component are melted and mixed, c) at least the first component is fed to nozzles of a spinneret through which the endless fibers are formed, wherein at least 55 % of the surface is made up by the first component. Subsequently, the fibers formed in such a way are cooled down and drawn and then they are deposited on a moving belt, wherein d) a batt formed in such a way is then thermally bonded.

Preferably, in the step d), the batt is bonded by calendering and/or by using hot air. Definitions

A “bail" is used herein to refer to fiber materials prior to being bonded to each other. A "bait" comprises individual fibers, which are usually unbonded to each other, although a certain amount of pre-bonding between fibers may be performed, and this pre-bonding may occur during or shortly after the lay-down of fibers in a spun-melt process, for example. This pre bonding, however, still permits a substantial number of the fibers to be freely movable such that they can be repositioned. A "batt" may comprise several layers, resulting by depositing fibers from several spinning heads in a spun-melt process, and distributions of a fiber diameter thickness and a porosity in the "sub layers" laid-down from individual heads do not differ significantly. Adjacent layers of fibers need not be separated from each other by sharp transition, individual layers may blend partly in the area around the boundary.

A “filament” designates an essentially endless fiber, whereas the term “staple fiber” relates to a fiber that has been cut to a defined length. The terms “fiber” and “filaments”, as used herein, are mutually interchangeable.

To express a “fiber diameter” the SI length units - micrometres (pm) or nanometres (nm) are used. The terms “fiber diameter” or “fiber thickness” are interchangeable for the purpose of this document. In the case where the fibers do not have a circular diameter, a fiber diameter corresponding to an equivalent fiber with a circular diameter is considered. The terms “number of grams of fiber per 9000 m” (also titr denier or Tden or den) or “number of grams of fiber per 10000 m” (dTex) are used to express the level of fineness or coarseness of the fiber.

A “monocomponent fiber” designates a fiber, formed by a single polymeric constituent or by a single mixture of polymeric components, as distinguished from a bicomponent or a multicomponent fiber.

A “mixture” or “blend” herein typically refer to polymeric materials contained in a fiber, e.g. when multiple polymers are mixed together. This does not exclude additions of other materials, typically in a smaller amount (for example colorants, process additives, additives for adjusting surface properties etc.). A blend can be used in monocomponent fibers as well as in bicomponent or multicomponent fibers.

A “bicomponent fiber” designates a fiber, the diameter of which comprises two discrete polymeric constituents, two discrete mixtures of polymeric constituents or a discrete polymeric constituent and a discrete mixture of polymeric constituents. A “bicomponent fiber” is covered by a general term “multicomponent fiber”. A cross-section of a bicomponent fiber can be divided into two or more parts, made up by different constituents of any shape or arrangement, including for example a coaxial arrangement, core-sheath arrangement, side-side, “segmented pie” etc. The term “main constituent” describes a constituent, which makes up a larger weight proportion in the fiber.

A “first component” represents a polymer or a mixture of polymers which is a single component in the case of monocomponent fiber and which is one of the components in the case of a multicomponent fiber.

A bicomponent filament having “sheath-core structure” is a filament, the cross-section of which comprises two individual partial cross-sections, each one of them consisting of different polymeric constituent or a different mixture of polymeric constituents, wherein the polymeric constituents or the mixture of polymeric constituents forming the core is surrounded by the polymeric constituent or the mixture of polymeric constituents forming the sheath. For example, the term “C/S 70/30” describes a bicomponent fiber in a core-sheath arrangement, wherein the core makes up 70 wt. % of the fiber and the sheath makes up 30 wt. % of the fiber.

A "nonwoven fabric" is a web or fiber layer produced of directionally or randomly oriented fibers which are first formed into a bait and then consolidated and bonded together by friction, cohesion, adhesion or one or more patterns of bonds and bonding impressions created through localized compression and /or application of pressure, heat, ultrasonic, or heating energy, or a combination thereof. The term does not include fabrics which are woven, knitted, or stitch- bonded with yarns or filaments. The fibers may be of natural or man-made origin and may be staple or continuous filaments or be formed in situ. Commercially available fibers have diameters ranging from about 0.0005 mm to about 0.25 mm and they come in several different forms: short fibers (known as staple, or chopped), continuous single fibers (filaments or monofilaments), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn). Nonwoven fabrics can be formed by many processes including but not limited to melt-blowing, spun-bonding, spun-melting, solvent spinning, electro-spinning, carding, film fibrillation, melt-film fibrillation, air-laying, dry-laying, wet-laying with staple fibers and combinations of these processes as known in the art. The basis weight of nonwoven fabrics is usually expressed in grams per square meter (gsm).

A “spunbond” process is a process of production of nonwoven fabrics which comprises a direct conversion of a polymer to filaments, the conversion being immediately followed by laying thus produced filaments to form a nonwoven batt comprising randomly arranged filaments. This nonwoven batt is subsequently strengthened in such a way that a nonwoven fabric is formed by forming bonds between the fibers. The strengthening process can be carried out in various ways, for example by air-through-bonding, by passing between bonding rollers etc.

“Filament to filament bonds” or “bonding points” refer to bonds which connect usually two filaments in an area, in which the filaments cross each other or locally meet or abut on each other. The bonding points/strengthening bonds may connect more than two filaments or may connect two parts of the same filament. The term “bonding point” thus here represents a connection between two fibers/filaments at a contact point by interconnecting their constituents with a lower melting point (see Fig. IB). In the bonding point, the constituent with a higher melting point is neither damaged nor shaped. In contrast, the term “bonding impression” represents an area, on which a protrusion of a calender roller has acted (see Fig. IV). A bonding impression has a defined area, given by the size of the protrusion of the bonding roller and typically the bonding impression has lower thickness than its surroundings. Typically, during bonding, a significant mechanical pressure arises in the area of the bonding impression, wherein the mechanical pressure can affect the shape of all of the constituents in the area of the bonding impression.

The expressions “bonding roller”, “calender roller” and “roller” are herein mutually interchangeable.

"Hygienic absorbent article" refers herein to devices or aids that absorb and contain body exudates, and, more specifically, refers to devices or aids that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. Absorbent articles may include disposable diapers, training pants, underwear, and adult incontinence undergarments and pads, feminine hygiene pads, breast pads, care mats, bibs, wound dressing products and the like. As used herein, the term "exudates" includes, but is not limited to, urine, blood, vaginal discharges, breast milk, sweat and faecal matter.

With respect to the making of a nonwoven web material and the nonwoven web material itself, "cross direction" (CD) refers to the direction along the web material substantially perpendicular to the direction of forward travel of the web material through the manufacturing line in which the web material is manufactured. With respect to a batt moving through the nip of a pair of calender rollers to form a bonded nonwoven web, the cross direction is perpendicular to the direction of movement through the nip, and parallel to the nip. With respect to the making of a nonwoven web material and the nonwoven web material itself, "machine direction" (MD) refers to the direction along the web material substantially parallel to the direction of forward travel of the web material through manufacturing line in which the web material is manufactured. With respect to a nonwoven batt moving through the nip of a pair of calender rollers to form a bonded nonwoven web, the machine direction is parallel to the direction of movement through the nip and perpendicular to the nip.

The term “aliphatic polyester” represents any biodegradable polymer (homo- as well as copolymer) based on an aliphatic polyester. Examples of biodegradable aliphatic polyesters useful for this invention comprise, without being limited to the following list, for example: polyhydroxy butyrate (PHB), polyhydroxy butyrate-co-valerate (PHBV), polycaprolactone (PCL), polybutylene succinate (PBS, polybutylene succinate-co-adipate (PBS A), polyglycolic acid (PGA), polylactide or polylactic acid (PLA), polybutylene oxalate, polyethylene adipate, polydioxanone (PDO) or polyoxalates (described e.g. in the patent application US20050027081 from 2004) in general. Given the availability and the price, the most preferable is now the polylactide group, particularly PLA and its derivatives.

The term “polar central part” or “central polar part” represents the functional group -(C=0)- NH-, which is the polar centre of the additive molecule. The central polar part can be at the edge of the molecule in the form of -(C=0)-NH ₂ , as in the example of amides (i), or in the centre of the molecule, surrounded by a plurality of aliphatic residues Rl, R2, as in the example of N- substituted amides (ii). In the additive molecule, the central polar part can be contained once or multiple times. The neighbouring central polar parts are then connected by the aliphatic chain R3.

A "bonding protrusion" or "protrusion" is a feature of a bonding roller at its radially outermost portion, surrounded by recessed areas. Relative the rotational axis of the bonding roller, a bonding protrusion has a radially outermost bonding surface with a bonding surface shape and a bonding surface shape area, which generally lies along an outer cylindrical surface with a substantially constant radius from the bonding roller rotational axis; however, protrusions having bonding surfaces of discrete and separate shapes are often small enough relative the radius of the bonding roller that the bonding surface may appear flat/planar; and the bonding surface shape area is closely approximated by a planar area of the same shape. A bonding protrusion may have sides that are perpendicular to the bonding surface, although usually the sides have an angled slope, such that the cross section of the base of a bonding protrusion is larger than its bonding surface. A plurality of bonding protrusions may be arranged on a calender roller in a pattern. The plurality of bonding protrusions has a bonding area per unit surface area of the outer cylindrical surface which can be expressed as a percentage, and is the ratio of the combined total of the bonding shape areas of the protrusions within the unit, to the total surface area of the unit.

Brief Description of Drawings

Fig. 1: Schematic comparison of a section of a fabric bonded using bonding impressions (V) and a fabric bonded using bonding points (B)

Fig. 2 A: SEM image of a bonding impression of a comparative nonwoven fabric according to Example 1

Fig. 2 B: SEM image of a bonding impression of a comparative nonwoven fabric according to the invention according to Example 2

Fig. 3: Schematic layout of a spunmelt-type production line for nonwoven fabrics Fig. 4: Schematic layout for thermal bonding using two heated rollers (calender roller)

Fig. 5A is a top view photo of a nonwoven fabric according to Example 13,

Fig. 5B is a top view photo of a nonwoven fabric according to Example 12,

Fig. 5C is a photo of the cross-section of the nonwoven fabric according to Fig. 5A and Fig. 5D is a photo of the cross-section of the nonwoven fabric according to Fig. 5B.

Exemplifying Embodiments of the Invention

The subject-matter of the invention is a thermally bonded nonwoven textile made of spunmelt- type endless fibers which contains an aliphatic polyester or a mixture of aliphatic polyesters in combination with a non-polymeric additive which alters the dynamics of crystallization of the material in the fibers and enhances the efficiency of the thermal bonding.

Aliphatic polyesters exhibit a characteristic behaviour during thermal bonding. When exposed to a heat flow, a change in the volume of the polymers occurs after absorption of a certain amount of heat (for example in the zone of so-called cold crystallization). This phenomenon is known as shrinkage. Shrinkage is generally regarded as an undesirable phenomenon and there is a clear tendency within the field of art to use an aliphatic polyester with a high portion of amorphous constituent at least on a part of the surface of thermally bonded fibers (aliphatic polyesters with a high portion of amorphous constituent are characterized by a low value of heat of cold crystallization and, typically, they have a lower melting temperature than the crystalline constituents). Without intending to be bound by theory, we believe that a certain degree of exothermal cold crystallization is desirable. In case of a very amorphous polymer, a rapid melting of its surface can take place without heating and softening of the entire fiber, or at least of its entire bonding component. The melted part of the polymer on the surface of the fiber is adhesive and readily sticks to a surface of any of the components of the line. Releasing such a fiber requires higher force than releasing of a fiber freely laid on the belt. When multiple fibers get stuck, the total adhesiveness of the fibrous layer to the belt increases, which can cause tearing of the fibrous layer and an undesirable winding of the fiber belt on an element of the production line.

At the same time, even a relatively low degree of shrinkage can cause problems during production. It is important to be aware that during the production, the batt is located on the moving belt, drum or roller, which do not tend to be perfectly flat. Before consolidation, the nonwoven fabric batt represents a relatively open structure with partially moving fiber parts. Therefore, a fiber or its part, which comes into an immediate vicinity of a protrusion or a depression may easily stick or wind on it even at a first low shrinkage of the material. Similarly to the example above, release requires a higher force and causes a risk of breaking the batt. Such a scenario typically occurs when in contact with a hot roller with protrusions, when the batt passes from one element to another, when n contact with a drum in a drum dryer or a hot air bonding unit etc.

Aliphatic polyesters are available in a varying degree of crystallinity, in other words with varying values of latent heat of cold crystallization, and both described effects can blend into one another, support one another and narrow down process window for thermal bonding of a nonwoven fabric. The described behaviour was observed for example in PLA fibers with a substantially amorphous polymer on the surface of the fiber at temperatures exceeding 140 °C and at the speed of 150 m/min or for example at temperatures exceeding 110 °C at the speed of 7 m/min.

Without intending to be bound by theory, it is believed that the additive altering the dynamics of the crystallization contributes to a more homogeneous softening and to a subsequent melting of the polymer in such a way that a sintering of the fibers or a sintering of the bonding components of the fibers occurs and at the same time the additive shifts the temperature of the start of softening of the aliphatic polyester so that it allows for a proper thermal interconnection of the fiber surfaces. The additive according to the invention represents a non-polymeric organic compound consisting of a central part and one or more non-polar ends. The polar central part is generally compatible with the structure of aliphatic polyesters, whereas the relatively short and with respect to their 3D structure relatively flexible non-polar ends locally affect the dynamic of the crystallization of the polymer. Ends which are too short do not ensure the desired effect and ends which are too long will tend to make clusters and decrease the homogeneity of the mixture in a polar environment of the aliphatic polyester.

According to a preferred embodiment of the invention, the central polar part is made up of a combination of a positive and a negative partial electrical charge on elements of the central part. Preferably the central part contains amides (i) or N-substituted amides (ii), wherein the nitrogen is bonded by a single bond to the carbon of the ketone group C=0 and by a further single bond on a further carbon of a continuing aliphatic chain Rl-(CO)-(NH)-R2.

In the embodiment in accordance with the invention, the additive is made up by a central polar part, formed by a -(CO)-(NH2) and a hydrocarbon residue R1 (i).

In a particularly preferable embodiment, R1 is a straight saturated aliphatic chain containing 10 to 30 carbons, preferably 15 to 25 carbons.

In another embodiment in accordance with the invention, the additive is made up by a central polar part made up by -(CO)-(NH)- and hydrocarbon residues Rl, R2 (ii).

(i) amides (ii) N-substituted amides

With an acceptable degree of simplification, it can be said that this arrangement of the atoms in the molecule leads to a creation of a partial negative charge on the oxygen and a partial positive charge on the carbon of the keto group or at the adjacent amide nitrogen as well by effect of resonance, and as such is well compatible with polar chains of aliphatic esters, wherein the effect can be further enhanced if the group -(CO)-(NH)- in the core of the additive is repeated in the combination Rl-(CO)-(NH)-R3-(NH)-Rl (iii). The additive molecule can thus contain two or more central polar parts, connected by the aliphatic chain R3. Aliphatic chains Rl, R2 and R3 can be of different lengths.

(i) Rl-(CO)-(NH)-R3-(NH)-R According to a preferred embodiment of the invention, Rl represents an aliphatic hydrocarbon residue having a length of at least 10 carbons, better yet at least 12 carbons, preferably at least 15 carbons.

According to a preferred embodiment of the invention, Rl represents an aliphatic hydrocarbon residue having a length of no more than 30 carbons, better yet no more than 25 carbons. According to a preferred embodiment of the invention, R2 represents an aliphatic hydrocarbon residue having a length of at least 10 carbons, better yet at least 12 carbons, preferably at least 15 carbons.

According to a preferred embodiment of the invention, R2 represents an aliphatic hydrocarbon residue having a length of no more than 30 carbons, better yet no more than 25 carbons.

R3 preferably corresponds to a portion of the polymer between ester bonds. Preferable embodiments are shown in the Table 1 :

Table 1

According to a preferred embodiment of the invention, for use with PLA R3 represents an aliphatic hydrocarbon residue having a length of 1 to 3 carbons, preferably 2 carbons.

According to a preferred embodiment of the invention, R1 and/or R2 and/or R3 is formed by a straight aliphatic chain.

According to a preferred embodiment of the invention, R1 and/or R2 and/or R3 is formed by a saturated aliphatic chain. According to a particularly preferred embodiment of the invention, R1 and/or R2 is a straight saturated aliphatic chain, containing 10 to 30 carbons, more preferably 15 to 25 carbons.

According to a preferred embodiment of the invention, R1 and/or R2 and/or R3 is formed by a straight saturated aliphatic chain.

According to a preferred embodiment of the invention, R1 and R2 are formed by aliphatic saturated straight hydrocarbon residues having the same length. An example of a suitable non-polymeric additive from the group of amides (i) is represented for example by erucamide, behenamide (which is docosanamide) or oleamide (structural formulas are depicted below and described in Table 2). Table 2: description of erucamide, behenamide and ole amide compounds An example of a suitable non-polymeric additive from the group of N-substituted amides is represented by N,N’-ethylenebis(stearamide) known under the abbreviation EBS with the formula C38H76N2O2. The structural formula is depicted below.

N,N’-ethylenebis(stearamide) = EBS EBS is an additive for a nonwoven fabric according to the invention, wherein the hydrophobic residues R1 and R2 are aliphatic saturated straight chains having an identical length, the length being 17 carbons, and R3 is an aliphatic saturated straight chain having a length of 2 carbons.

According to a preferred embodiment of the invention, the nonwoven fabric monocomponent fiber contains at least 0.10 wt. % of a non-polymeric additive, better yet at least 0.20 wt. % of a non-polymeric additive, preferably at least 0.25 wt. % of a non-polymeric additive.

According to a preferred embodiment of the invention, the amount of the non-polymeric additive according to the invention does not exceed 10 %, better yet 5 %, preferably 1 %.

For thermal bonding of a batt into a nonwoven fabric, it may be preferable to use bi- or multicomponent fibers, wherein the first component contains in at least a part of the fiber surface (for example the sheath in a sheath/core combination or one of the sides in a side/side combination) is formed by a material with a lower melting temperature than the other component. During the bonding, primarily a softening of the first component takes place and a bond is formed at contact points of the fiber surfaces with a content of the first component. When using aliphatic polyesters, the first component contains preferably a higher portion of amorphous polyesters than the second component.

According to a preferred embodiment of the invention, the first component covers at least 55 % of the fiber surface, better yet at least 70 % of the fiber surface, better yet at least 85 % of the fiber surface, better yet at least 90 % of the fiber surface, preferably at least 95 % of the fiber surface. According to a preferred embodiment of the invention, the first component contains at least 0.10 wt. % of the non-polymeric additive according to the invention, better yet at least 0.20 wt. % of the non-polymeric additive according to the invention, preferably at least 0.25 wt. % of the non-polymeric additive according to the invention. According to a preferred embodiment of the invention, the amount of the non-polymeric additive according to the invention does not exceed 10 %, better yet 5 %, preferably 1 %.

The behaviour of pure PLA in comparison with a mixture of PLA-EBS was tested using differential scanning calorimetry (DSC). The results are listed in Tables 3 and 4. Table 3: DSC PLA 1 with and without an addition of EBS

The above data for the crystalline-type PLA1 make clear that the presence of the additive did not significantly affect the glass transition temperature, though significant changes are observable in the zone of dynamics of cold crystallization (with respect to the start, end and the amount of heat received) together with the zone melting (decrease of the start of softening by 20 % and shortening of the temperature interval by half).

The zone of cold crystallization was markedly shortened by the addition of EBS (from an interval of 56 °C to an interval of 31 °C) and the amount of exothermic heat decreased as well (from 34 J/g to 21 J/g). Without intending to be bound by theory, it is believed that the change in the dynamics of cold crystallization due to the described non-polymeric additive leads to a decrease in the degree of shrinkage and thus leads to a restriction of the undesired entrapment of the fibers on the production line components. A further increase will likely lead to undesired effects on the production line (risk of entrapment of the fabric and breaking of the batt increases).

A decrease in the temperature of start of melting is another benefit that helps to better interconnect the nonwoven fabric for example in the form of bonding impressions formed by pressure in the case of calender bonding as well as bonding points formed in fiber contact points in the case of hot-air bonding.

Table 4: DSC PLA2 with and without an addition of EBS and other materials

The above data for the amorphous-type PLA2 make clear that in this case, too, the presence of an additive did not affect the glass transition temperature, though it has a significant influence in the zones of cold crystallization and melting temperature. However, the data shown in Table 4 show also that the additives of other polyesters (aromatic PBAT, crystalline aliphatic PLA1) do not interfere with the described desired effect of the additive according to the invention. The zone of cold crystallization was markedly strengthened by the addition of EBS. While the amorphous PLA2 does not exhibit any, a cold crystallization in a similar zone can be observed in both mixtures of polymers (from about 106 °C to about 130 °C), the amount of exothermic heat being also comparable (about 30 J/g). The amount of EBS is herein optimized for achieving the maximum effect during the thermal bonding for a particular type of polymer - without intending to be bound by theory, it was observed that the heats of cold crystallization and the heat of melting get closer to each other in the optimum zone.

Unlike the case of crystalline-type PLA1, a light increase in melting temperature can be observed, the temperature reaching 144-145 °C which is similar to the above-mentioned value of 141 °C. A significant change is present in the melting temperature, where an increase from 1 J/g to 31-34 J/g was observed. Without intending to be bound by theory, it is believed that the above-mentioned increase in the melting temperature retards the melting of the polymer surface, in other words it contributes to the homogenization of melting of the entire component, which allows for the desired sintering of the fibers or their parts during the thermal bonding and reduces the risk of entrapment of the fabric on a production line component and of breaking the fibrous batt.

Without intending to be bound by theory, it is believed that an addition of an aromatic polyester, better yet of a biodegradable aromatic polyester, can be advantageous. Benzene nuclei with their specific distribution of free electrons and a relatively solid spatial structure may enhance crystallization, especially of amorphous parts of polymers, while the non-polymeric additive keeps the crystallization at a desired level.

In a preferred embodiment, addition of an aromatic polyester, preferably of a biodegradable aromatic polyester may be of advantage. According to a preferred embodiment, the addition of the aromatic polyester does not exceed 10 wt. % of the first component, better yet does not exceed 7 wt. % of the first component, preferably does not exceed 5 wt. % of the first component. According to a preferred embodiment of the invention, the biodegradable aromatic polyester is e.g. PBAT (polybutylene adipate terephthalate).

The above-mentioned changes, described using the DSC method are also observable directly on the nonwoven fabric, e.g. in the character of the bonding impressions. For example a SEM photograph of a bonding impression of pure PLA (produced according to the description of Example 1) shows bonding impressions with unsatisfactorily interconnected fibers. The covers of the used bicomponent fibers did not interconnect properly and it rather appears as though they stuck together only with their surfaces or merely by the effect of pressure (Fig. 2 A). Such created connections do not have the necessary strength and the fibers can be disjoined relatively easily. The second photograph represent a PLA bonding impression with a content of 0.3 % of EBS (produced in accordance with the description of Example 2), where a full interconnection of fibers is visible (Fig. 2 B). The nonwoven fabric depicted in this picture exhibits a markedly higher strength and surface resistance against abrasion. During the production of both samples, the same temperature and the same pressure of identical calender rollers was used. When attempting to increase the bonding temperature in the case of pure PLA, the fabric entrapped on the roller, which caused a risk of winding of the fabric belt and interrupting the production process.

Similarly, the above-mentioned changes can be seen in Fig. 5 as well, wherein the SEM photos of the nonwoven fabric, produced according to the description of Examples 12 and 13 on the laboratory production line of the Centre of polymer systems UTB Zlin, are depicted. Herein it is made clear as well that comparative sample without an additive is not properly interconnected. From a top view (5B) it is evident that the bonding impressions bulge out and twirl. The cause is clear form a cross-section view (5D) - the nonwoven fabric is not properly interconnected across its entire thickness and the bonding impressions are present solely on the surface of the fabric. However, when viewing the sample according to the invention (5A and 5C), straight bonding impressions are seen, interconnected across the entire thickness of the fabric in a cross-section. The strength of both samples corresponds to the described structural changes as well, as shown in Table 6.

The spunbond process is based on polymeric melt spinning under a nozzle. The production line (Fig. 3) may comprise one or more spinnerets 1, adapted for the production of spunbond-type fibers. Each of the spinnerets is connected to at least one extruder, into which the required polymeric mixture is fed. The mixture in the extruder is melted and transported into a spinning nozzle 5. A person skilled in the art knows well that in order to obtain fibers of different cross- section shapes and diameters, various configurations of spinning nozzles can be used which can form monocomponent or multicomponent fibers in various configurations (e.g. core/sheath, side/side, islands in the sea etc). Initial fibers 4 of the spunbond type, formed by the spinneret 5, are cooled and drawn in a cooling and drawing chamber 7 using an airflow (the airflow being fed by supply 6 of cooling and drawing air), then they are vibrated in the diffuser 8 and deposited on moving surface 2, which can be a permeable belt. If necessary, the batt can be pre- strengthened by one or more preconsolidation units 9, 10. In the case of using more consecutive spinnerets, the fibers from the second and subsequent spinnerets 1 fall on the batt, formed by preceding spinnerets 1. A different polymeric composition and/or different process settings of the spinnerets 1 (e.g. power, cooling rate and drawing rate) lead to different characteristics of the batt deposited by given spinneret on the bed - various multilayer composites with specific properties can be formed.

A person skilled in the art will as well recognize the possibility of installing one or more spinnerets between the spunbond spinnerets, e.g. a meltblown, an advanced meltblown or a melt fibrillation spinneret, and thus insert typically a barrier layer with a significantly smaller fiber diameter between the spunbond layers. These composites are known as SMS materials.

A batt, formed by all of the used spinnerets comprises individual fibers, between which a mutual solid bond is usually not yet formed, even though the fibers can be bonded in a certain way, whereas this pre-bonding can take place during the deposition of the layer formed by free fibers or shortly after in the preconsolidation units 9, 10 e.g. by using rollers, hot-air, heat radiation etc. However, this preconsolidation still allows a free movement of a substantial quantity of fibers, which may thus be moved. This batt can be bonded thermally (e.g. by using rollers, flow of a hot medium etc.) to form a nonwoven fabric.

The polymeric component or the mixture contained in the fibers of the nonwoven fabric according to the invention can be formed from one or more granulates based on polymer materials such as, in particular, aliphatic polyesters, more specifically e.g. polylactic acid polymer (PLA). According to a preferred embodiment of the invention, the aliphatic polyesters represent at least 80 wt. % of the fiber, better yet at least 90 wt. % of the fiber, better yet at least 95 wt. % of the fiber, preferably at least 99 wt. % of the fiber. It is worth mentioning that the proportion of the polymeric constituents or the proportion of the aliphatic polyesters is calculated from the entire fiber irrespective of whether the fiber is mono- or multicomponent.

According to a preferred embodiment of the invention, one aliphatic polyester represents the base constituent which makes up at least 60 wt. % of the aliphatic polyesters content.

According to a preferred embodiment of the invention, an aliphatic polyester based on polylactide represents the base constituent which makes up at least 60 wt. % of the aliphatic polyesters content. The nonwoven fabric fibers according to the invention may contain other additives such as colour pigments, materials increasing pleasantness of the touch (soft-touch, cotton-touch etc.), process additives etc.

The nonwoven fabric fibers according to the invention can contain further additional materials such as aromatic polyesters, thermoplastic polysaccharides and other materials. These further additional materials are preferably biodegradable. A person skilled in the art will recognize the advantages of the aliphatic polyester mixtures. For example, the advantages of the combination of PLA and PBS in different ratios and crystalline states are explained in a number of prior documents.

The nonwoven fabric fibers according to the invention can contain a mixture of at least two aliphatic polyesters, at least one of which is characterized by a lower value of heat of cold crystallization than the others. A preferable solution according to the invention is represented by a mixture of at least two aliphatic polyesters, at least one of which has a heat of cold crystallization by at least 1 J/g, better yet by at least 2 J/g, preferably by at least 3 J/g lower than at least one another aliphatic polyester in the composition, wherein even chemically identical aliphatic polyester having a differing grade is regarded as another aliphatic polyester.

The nonwoven fabric fibers according to the present invention may contain further additional materials such as e.g. aliphatic polyolefins, e.g. polypropylene or polyethylene, eventually copolymers thereof.

The individual fibers can be monocomponent or bicomponent. Multicomponent fibers comprise particularly bicomponent fibers, for example fibers of the core-sheath type or side-side type. The individual constituents can often be separated into a first component - binding constituent with a lower melting point - and a second component. In the case of aliphatic polyesters, a more amorphous form of polyester can be used as the first component with a lower melting point so that during the thermal bonding, the first component will act as a binder. Fibers of the side-side type or the eccentric core/sheath type may be used with advantage for example in production of highly voluminous materials. The use of suitable polymers in individual constituents of a bicomponent fiber can lead e.g. to so-called self-crimped fibers which significantly increase bulkiness of the nonwoven fabric. It is preferable for the solution according to the invention when the first component with a lower melting point is the above-mentioned mixture containing at least one aliphatic polyester and an additive. A person skilled in the art will easily recognize various other possibilities and advantages of the use of different types of fibers. It is preferable for the solution according to the invention when the difference between the melting temperatures of the first and the second components in a bicomponent fiber is at least 5 °C, better yet at least 10 °C and when the first component with a lower melting temperature makes up at least 55 % of the fiber surface, better yet at least 70 % of the fiber surface, better yet at least 85 % of the fiber surface, better yet at least 90 % of the fiber surface, preferably at least 99 % of the fiber surface.

It is preferable for the solution according to the invention when the first component represents at least 5 wt. % of the fiber, better yet at least 10 wt. % of the fiber, preferably at least 15 wt. % of the fiber.

The solution according to the invention may be implemented as a spunlaid nonwoven fabric mostly containing bicomponent spunbond fibers with a proportion of the first component of at least 5 wt. % of the fiber, the first component making up at least 55 % of the fiber surface.

A fabric prepared in such a way is subjected to a thermal bonding in the bonding unit 3 which can be implemented in various ways - e.g. by using a pair of heated calender rollers 50, 51 or a flow of hot medium (e.g. air).

The solution according to the invention may be preferably realized by using a thermal bonding of a nonwoven fabric by a pair of calender rollers 50, 51. The technological procedure of this type of thermal bonding comprises a step of forming bonds between the fibers which form a batt, during which the fibers unite and interconnect to a certain degree to form a fabric, while at the same time, the mechanical properties, e.g. tensile strength, increase, which can be necessary for the material to maintain a sufficient structural integrity and dimensional stability during subsequent production processes as well as when using the final product. As apparent from Fig. 4, bonding by calendaring can be carried out so that the batt 21a passes through the clearance between a pair of rotating calender rollers 50, 51, which results in a compression and uniting of the fibers to form a nonwoven fabric 21. One or both of the calendaring rollers 50, 51 can be heated such that they support heating, plastic deformation, blending and/or thermal melting/bonding of fibers layer on top of each other during the compression in the clearance between the rollers. The rollers can make up functional parts of the binding mechanism, wherein they are pressed towards one another by a force with a controllable magnitude so that they apply the required compression force/required pressure in the clearance. In some processes, the bonding mechanism may incorporate an ultrasonic source that allows a transmission of the ultrasound vibrations into the fibers, which again generate thermal energy that improves the bonding

A bonding pattern consisting of bonding protrusions and recessed areas can be formed on the outer surface of one or both calender rollers 50, 51 by machining, etching or in other way, which makes the bonding pressure acting on the batt during its passage through the clearance 52 concentrate on the bonding surfaces of the bonding protrusions, whereas it is decreased or significantly limited in the recessed areas. The shapes of bonding surfaces are predetermined. As a result, a nonwoven fabric 21 with a pattern is formed, the pattern consisting of bonding impressions V (see Fig. 1) between the fibers which make up the nonwoven fabric 21 whose shape corresponds to the shape of the bonding impressions arranged in an identical pattern as on the surface of the calender roller 50, 51. The first roller, e.g. roller 51, may have a flat cylindrical surface without a pattern, thus representing a pressure or abutting roller, whereas the second roller 50 may be provided with the above-mentioned pattern and thus may represent a roller which forms a bonding impression in the processed material; the pattern created on the nonwoven fabric by this combination of rollers will then correspond precisely to the pattern on said second roller 50. In some cases, both of the rollers 50, 51 can be provided with patterns, and the patterns may be different. In such a case, a combined pattern is created by the action of these patterns on the nonwoven fabric, such a pattern being disclosed for example in the patent document US 5,370,764.

It is preferable for the solution according to the invention when the total bond area (total area of the bonding impressions) makes up at least 8% of the total area of the nonwoven fabric, preferably at least 11% of the total area of the nonwoven fabric.

It is preferable for the solution according to the invention when the total bond area does not exceed 30% of the total area of the nonwoven fabric, better yet does not exceed 25% of the total area of the nonwoven fabric, preferably it does not exceed 20% of the total area of the nonwoven fabric.

The calender rollers bond the fibers together by using a combination of temperature and pressure. Therefore, it is preferable to set the temperature of the rollers on a temperature closely below the melting temperature of the bonding polymer. The temperature is preferably set so as to be 1-15 °C lower than the melting temperature of the bonding polymer, more preferably 1-10 °C lower than the melting temperature of the bonding polymer. Said bonding temperatures are suitable for sufficiently rapid production lines, markedly lower temperatures are adequate particularly in slow laboratory lines having a belt speed in the range of meters. The recommended limit value of the temperature of rollers corresponds to a production speed of at least 50 m/min.

The solution according to the invention may be preferably implemented by using thermal bonding of a nonwoven fabric with the use of hot medium. Generally, the heat transfer to the batt can take place in various stages of the production process, e.g. immediately after the filaments have been deposited on the belt to preconsolidate the structure, during the thermal activation process, during the bonding process (final consolidation) etc.

Hot liquid enters the surface of the filamentary batt, flows around the filaments, and a part of the heat being transferred by the hot liquid passes to cooler filaments. It is worth mentioning that the creation of filament-to-filament bonds depends also on the local intensity of the fluid resistance pressure, i.e. the filaments may be in mutual contact or cross each other and will not form a bond (bonding point) or will form only a weak bond (bonding point), while the filaments in a more intense contact will form stronger bonds (bonding points) formed by melted polymer with a lower melting temperature. It is preferable for the solution according to the invention when the flow of the hot medium passes through the fabric which results in a heat transfer across the entire volume of the nonwoven fabric.

The preferred embodiment according to the invention comprise a bonding process (final consolidation), which is conducted using at least three different consolidating sections. The air flow is substantially perpendicular to the fabric and maintains a uniform temperature and flow rate with small fluctuations.

The first consolidating section preheats the fabric to a temperature nearly below the temperature of the bonding polymer. The temperature is preferably set to be 5-20 °C lower than the melting temperature of the bonding polymer, more preferably the temperature is set to be 5-15 °C than the melting temperature of the bonding polymer, preferably the temperature is set to be 5-10 °C lower than the melting temperature of the bonding polymer. The first consolidating section preferably comprises alternating directions of the heat flow entering the first and the second outer surface of the fabric.

The second consolidating section is set to achieve a narrow range of melting temperature of the polymer composition with a lower melting temperature in such a way to allow a fusion bond to be formed. On the other hand, with respect to the basis weight of the fabric, the size of the fibers and the ratios of the cross-sections of the polymer constituents, the set temperature should not be in a range broader than 5.0 °C below up to at the most 3.0 °C above the melting temperature of the bonding polymer. For example, when the melting temperature is 130 °C, the set temperature should be in the range of 5 °C below the melting temperature of the bonding polymer to a temperature equal to the melting temperature of the bonding polymer, preferably the temperature is set in the range of 4 °C to 1 °C below the melting temperature of the bonding polymer. The second consolidating section preferably comprises alternating directions of the heat flow entering from the first and the second outer surface of the fabric.

The third consolidating section is a cooling section providing a significantly cooler air, preferably at a temperature of 10-40 °C, more preferably 20-30 °C. Ambient air may be used. The cooling section contributes to the solidification of the filaments or at least of the filaments on the surface of the fabric and to a stabilisation of the formed fabric strata structure. Preferably, no additional tension is applied immediately before and during the cooling process. Further cooling can be provided by an additional air flow, a cooling roller etc. The additional cooling is preferably carried out when the temperature of the fabric exiting the third consolidating section does not yet reach the ambient temperature. The fabric should preferably reach ambient temperature, preferably the fabric should reach a temperature of 40-10 °C, more preferably the fabric should reach a temperature of 20-30 °C. For economically advantageous reasons, the process described herein is used to produce bulky, soft, nonwoven fabrics with a low tendency to felting at a high production capacity and a high production speed.

For example, in an embodiment according to the invention, a consolidation device containing 4 drums can be used, the device using the effect of passing hot air. This device enables a process with short idle periods even at high speeds but also with sufficient exposure to the hot air flow and the hot air volume along the maximized path of the fibers, in order to reach a necessary melt flow with a low viscosity for forming fusion bonds in a defined narrow parameter range. In the machine direction, the drums allow for contact angles with the nonwoven fabric of at least 100°, preferably at least 130°, more preferably at least 150°, preferably at least 160°.

The precise parameter settings range for a given device depends on the selected bonding polymer as well as the size of the filaments, filament cross-section and the weight-ratio between the formulations of the polymer constituent.

The device, containing 4 drums, can also allow for an intense, alternating, essentially vertical air flow through the substrate of the nonwoven fabric in a short time. The first pair of drums is set to preheat the fabric structure immediately below the melting temperature of the polymer composition with a low melting temperature. The second pair of drums is set to reach the range of melting temperatures of the polymer composition with a low melting temperature to allow for forming fusion bonds. For the purpose of maintaining the structure of the fabric and to ensure that the fusion bonds are maintained intact, the last drum comprises a hot section and a cooling section along its circumference in the machine direction. It is preferable when the fabric structure, or at least the surface of the fabric structure, is solidified before the release of the fabric from the consolidation device. A separate additional cooling roller with a high flow rate of the cooling air across the fabric is located in the shortest distance possible form the last drum of the consolidation device which makes use of the air-through bonding which finishes the solidification of the fabric with an immediate cooling.

The interconnected nonwoven fabric 21 is in the final stage wound up on a winder 11 In the case where it is necessary to modify the surface characteristics of the nonwoven fabric, e.g. to achieve improved fluid transfer or to increase the fluid drainage capability, a spraying device or a soaking roller is located either between the moving belt and the final consolidation device or between the final consolidation device and the bobbin.

The nonwoven fabric according to the invention may be, if necessary, adjusted in other known ways. For example, a use of a water jet called “hydroengorgement” is known for softening of the nonwoven fabric (described for example in the patent document US 8093163) or “hydro- patterning” which is intended directly for a modification of a nonwoven fabric containing bonding impressions (described in yet unpublished patent application US 63/183,148). The fabric according to the invention can be for example perforated using various methods (overbonding, hot needles, water jet etc.)

The nonwoven fabric according to the invention may be produced having any basis weight. A person skilled in the art will recognize that higher basis weight is generally associated with a higher caliper and an improved touch of the final fabric, although this entails correspondingly higher costs. In contrast, even though a lower basis weight is associated with correspondingly lower costs, at the same time it makes difficult e.g. formation of a covering outer layer of hygienic absorbent products, where a specific level of covering ability or other barrier properties are required. In accordance with this foreknowledge, in such cases a nonwoven fabric according to the invention may be used, having a basis weight of no more than 60 gsm, better yet no more than 40 gsm, better yet no more than 30 gsm, preferably no more than 26 gsm. A person skilled in the art will recognize that to achieve the desired properties it is necessary that the nonwoven fabric according to the invention comprises at least a minimum amount of material. In accordance with this presumption, in such cases a nonwoven fabric according to the invention may be used, having a basis weight of at least 6 gsm, better yet 8 gsm, preferably at least 10 gsm.

In other cases, at least when using the nonwoven fabrics according to the invention to produce articles such as disposable clothing articles, parts of absorbent cores of diapers, wipers or dusters, higher basis weights of no more than 150 gsm, preferably no more than 100 gsm, may be used. The optimum basis weight is determined by various necessities associated with the individual methods of use as well as by material costs.

In the following examples 1-11 of the production of nonwoven fabric, one layer of bicomponent fibers of the core/sheath type having an average thickness of 14-17 microns with a weight ratio of components core:sheath = 80:20 was prepared using a spunbond-type spinneret using a REICOFIL 4 technology at a nozzle output of 220-225 kg/h/m on a pilot line in at STFI (Sachsisches Textilforschunginstitut e. V.). The type of aliphatic polyester used in the individual components and the type and amount of additive is shown in Table 5 for individual examples. The Ingeo type represents products of the company Nature Works and the Lumina type represents products of the company Total Corbion. Examples 1,3 and 9 represent comparative compositions without an addition of the additive according to the invention. The sheaths of Examples 4-8 and 10-11 include PBAT (Polybutylene adipate terephthalate) - an aromatic polyester - in an amount not exceeding 5 wt. % of the component (sheath) in addition to an aliphatic polyester and an additive according to the invention. The batt was thermally bonded using a pair of hot calender roller 50, 51 (flat roller, patterned roller), one of which is provided with an elevated pattern known as gravure U 2888 (by Ungricht) with a total bonding area of 18.1 %. The values of the temperature of the rollers and the compression are also shown in Table 5 and the measured properties of the produced nonwoven fabric are shown in following Table 6.

Table 5: Polymer composition and process settings of Examples 1-11

Table 6: Properties of the nonwoven fabric produced according to Examples 1-11 (columns

1-3 from the Table 5 are shown again for better orientation) All examples represent a combination of various differing types of PL A from two different producers with the type with a lower melting temperature always being included in the sheath. The strength of the nonwoven fabric according to the invention always exhibited a significant increase, ranging from an increase of a half (+41 % in Example 2) to a three-fold increase (+200 % in Examples 10 and 11). A varying degree of increase indicates that different commercially available types of polymers are at a varying distance from the desired state, which is achieved using the described additive.

Examples 1 and 2 represent the effect of an additive (in this case EBS) on the strength of a thermally bonded (in this case by calender) nonwoven fabric produced from an aliphatic polyester (in this case PLA). Comparative example 1 represents a composition with 100 % of PLA arranged in the bicomponent fiber such that the constituent with a lower melting point makes up the sheath. Example 2 represents the same polymer composition except that EBS additive is added to the sheath. A marked increase of strength is immediately observed (+41 % in MD and +64 % in CD direction). Fig. 2A, 2B also shows a clear difference in the appearance of the bonding impressions, where the fibers in bonding impression on the nonwoven fabric according to Example 1 look like merely stuck to each other, while the fibers in the bonding impression on the nonwoven fabric according to Example 2 are sintered in the bonding impression and form a significantly stronger unit.

Examples 4-8 and 9-10 show a material with an addition of an aromatic polyester (PBAT) in the sheath, namely in a concentration of about 2 % to almost 5 %. In none of the cases has the addition increased to a value of 5 %. It is clear from the results that the described addition of aromatic polyester does not limit the positive effect of the additive. On the contrary, a possible synergistic effect is shown.

Examples 6 and 7 show a nonwoven fabric according to the invention with a lower basis weight (20 and 15 gsm). Even though standards without an additive for a calculation of the strength increase are not available, a comparison with Example 3 (25 gsm) makes clear that a significant increase in strength must have occurred. The nonwoven fabric according to the invention having a basis weight of 15 gsm (Example 7) has a higher strength than the comparative nonwoven fabric without additives having a basis weight of 25 gsm (Example 3).

The nonwoven fabric in accordance with the invention can be prepared e.g. on a laboratory production line of UTB Zlin University. This laboratory production line with a model label LBS-300 allows for production of monocomponent or bicomponent fibers for nonwoven fabrics of the spunbond or meltblown type. Its extrusion system which consists of two extrusion machines can heat up polymers to temperatures up to 450°C. Fibers for nonwoven spunbond-type fabrics can be produced using a spunbond-type extrusion machine containing 72 orifices (having a diameter of 0.35 mm and a length of 1.4 mm) on a square area of 6x6 cm. There are several possible arrangements of the extrusion tool for processing of bicomponent fibers - core/sheath, components arranged in parallel, segmented pie or islands in the sea. The system is open; in the inlet system, the pressure of the extrusion air is available up to the level of 150 kPa. The filaments can be retrieved in the original state or laid on a belt, moving at a speed in the range of 0.7 to 12 m/min. The final length of the product is 10 cm at the maximum. The total output of the line can be set in the range of 0.02 to 2.70 kg/h. The final basis weight can be set within a range of 30 to 150 g/m ² . The laboratory production line was used for producing layers described in Examples 12-13.

In the following Examples 12-13, one layer of bicomponent fibers was produced, the layer being of the core/sheath type and having an average diameter of 16 microns with a mass ratio of the components core:sheath equal to 80:20 with the output of the nozzle being 0.44 g/min/capillary and the air pressure set to 85 kPa. The core was made up of PL A polymer (type Ingeo 6100D of Nature Works) and the sheath made up of a composition of PLA (type Ingeo 6752 of Nature Works) and an additive. The fibre layer was laid on a moving porous belt and thermally bonded at the speed of 7 m/min using a pair of hot calender rolls 50, 51 (flat roller 102°C, patterned roller 102°C), one of them being provided with a raised oval shaped pattern with a bonding surface of 25% (see Fig. 5).

Example 12 represents a comparative sample, wherein the sheath composition does not contain any additives.

Examples 13 represents a solution in accordance with the invention, wherein the sheath composition contains 0.2% of behenamide.

Both samples were produced with a basis weight of 125 g/m ² .

Table 7: Properties of the produced nonwoven fabric according to Examples 12-13

Behenamide, the selected representative of the amide group (i), exhibits an effect similar to the one observed in EBS. The additive significantly increases the strength of the nonwoven fabric (by 163 % in this case). Fig. 5 depicts SEM photos of Examples 12 and 13, wherein the cause of this increase can be clearly seen. While in Example 12 it is clear that the bonding impressions do not interconnect the fabric properly and across its entire thickness, Example 13 (according to the invention) displays bonding impressions across the entire thickness of the nonwoven fabric (particularly in the cross-sectional view).

Measurement methodology

“Basis weight” of a nonwoven fabric is measured using a measurement methodology in accordance with the standard EN ISO 9073-1 : 1989 (corresponding to a methodology according to WSP130.1). Ten layers of nonwoven fabric are used for the measurement, the size of a sample being 10x10 cm ² .

“Strength and elongation of material” is measured using a standard method ED ANA defined in the specification WSP 110.4.R4 (12), wherein the width of the sample is 50 mm, the distance of jaws is 100 mm, the speed is 100 mm/min and the preloading has a value of 0,1 N.

“Crystallinity”, “(latent) heat of crystallization”, “temperature of cold crystallization”, “heat of melting” and “melting temperature” are measured using the measurement method ASTM D3417 by means of DSC, wherein the rate of temperature change is 10 °C/min in the measured zone of 25-230 °C and with a sample weight of 7.0-7.5 mg.

Industrial applicability

The invention is applicable wherever a nonwoven fabric containing aliphatic polyesters is required - for example in the hygienic industry in the form of various constituents of hygienic products with absorption capabilities (e.g. baby diapers, incontinence products, hygienic products for women, disposable baby changing pads etc.) or in healthcare, e.g. as a part of sponges for treatment of wounds and/or protective garments, surgical cover sheets, underlays and other products made of barrier materials. Another possible application is in industrial applications, e.g. in the form of parts of protective garments, in filtration, insulation, packaging, sound adsorption, shoe industry, automotive industry, furniture industry etc. The invention is preferably applicable particularly in applications, for which renewable resources origin and partial or full biodegradability are required.