SE518438C2 - Method for hydroentangling polymer fibers and hydroentangled fabric comprising polymer fibers - Google Patents

Abstract

The invention relates to a method of bonding polymer fibers into a nonwoven fabric and a nonwoven fabric manufactured with the aid thereof. According to the invention, the polymer fibers are subjected to hydroentangling, the polymer fibers at the moment of hydroentangling being imparted a temperature exceeding the glass transition temperature of the polymer fiber, but being less than its melting point.

Description

25 30 35 40 518 438 2 section size (I = 1td4 / 64 for circular cross section) which depends on the diameter of the fiber. The e-module is thus a material parameter and this is temperature dependent.

A rigid fiber is more difficult to entangle and requires more specific energy (kWh / ton) to be bound than a soft fiber, which in turn limits the range of fibers that are technically and commercially interesting to use for this technology.

Fibers made from thermoplastic polymers such as polypropylene, polyester, polyamide are common in hydroentangling.

The properties of thermoplastic and other synthetic fibers depend on the properties of the polymer or polymers involved and the nature of the process used. Often the properties of the polymer cannot be fully utilized, but a compromise must be made for process technical reasons.

It is typically very difficult to produce a fiber that is very strong and at the same time has a low E-modulus. The strength of Fibem is largely determined by the orientation, length and mutual attractiveness of the molecular chains. The strength of the fiber and the E-module follow the same tendency in such a way that a high fi strength at the same time means a high E-module.

CA 841,938 describes the production of a nonwoven fabric by hydroentangling in which water under high pressure is pressed through a perforated carrier and against a sheet of a bersus suspension to give rise to an entanglement of the fibers.

WO 95/06769 describes a method and an apparatus for effecting a melt bond and possibly a entanglement of fibers in a ervber tissue, e.g. a nonwoven fabric or so-called non-Woven. In this case, a steam jet or a jet of superheated steam is used to both melt and entangle fi brema. In the case where such jets are used as are normally applied in hydroentangling, they must be hot enough to melt a melting component which has been incorporated into the fibrous web. WO 95/06769 thus describes a process in which a certain melting of an constituent melting component is always achieved. This melting component can be either the själva brema itself or an added melting component in the form of powder or granules. No process for pure hydroentangling is described.

US 3,322.5 84 describes a melt bonding method for bonding two plastic fabrics. The described method can also be used to join two layers of plastic fibers, but again a melt bond is meant and thus the temperature used is high enough to melt the threads.

US 5,069,735 describes a method for edge melting of delimited fabrics or fabrics in order to solve the problem that these fabrics normally peel off and are unsuitable for use e.g. during operations. U.S. Pat. steam or superheated steam, keeping the temperature around or just below the melting temperature of the fiber strands.

A problem with hydroentangling is that the constituent fiber components must have a bending stiffness such that the fibers can be entangled within reasonable energy levels. This means a limitation in terms of usable fiber types and means that thin fibers or fibers with a low E-modulus must be used, even if the fibers themselves are not optimal for the deformation of the fiber or for the functional properties of the finished material.

An object of the present invention is to provide a process for producing a ygberty fabric by hydroentangling, where the bending stiffness of the fibear components does not to the same extent as before imply a limitation on the degree of entanglement.

A further object of the present invention is to provide a method which provides a potential compared with current methods which e.g. can be used to manufacture yg fabric with coarse fl bristles, provide lower energy consumption or provide a stronger fabric. Yet another object of the present invention is to provide a yg grade with special properties, such as good mechanical properties, high bulk, m.m.

SUMMARY OF THE INVENTION We have now found that by bringing about a temperature rise at the very moment of entanglement, we can lower the flexural stiffness of the fi brems and achieve a higher degree of entanglement.

We have further found that it is only at the very moment of entanglement that an excessively high E-modulus is a disadvantage and by lowering the E-modulus just at the actual hydroentangling to then allow the E-modulus to return to the original level, a way and a materials that have great advantages over prior art.

In doing so, the dependence on the limitation involved in compromising the properties of strength and rigidity in the fiber manufacturing process decreases.

The strength of the fiber can instead be fully optimized.

At the same time, it is possible to choose a. Fibers for the fi grade to be bound based on criteria other than the limitation that the entanglement process entails. In many cases, it is an advantage to have rigid fibers in the pre-bonded fi fabric depending on what the material is to be used for. 10 15 20 25 30 35 40 518 438 4 Fibers that are already relatively well adapted for hydroentangling can be further optimized, which means improved material properties and / or lower energy consumption in the process.

According to the invention there is provided a process for the hydroentangling of polymer fibers with a glass transition temperature (Tg) of 20 - 100 ° C for the production of a nonwoven fabric. The polymer fiber is given, at the moment of hydroentangling, a temperature equal to or exceeding the glass transition temperature of the polymer fiber and below the melting temperature of the polymer fiber.

According to the invention there is further provided a hydroentangled yg fabric comprising polymer fibers with a glass transition temperature (Tg) of 20 - 100 ° C, the polymer fibers in the nonwoven fabric having an E-modulus of 250 cN / tex.

Furthermore, according to the invention, a hydroentangled polymeric fibrous fabric is provided with a bulk mass of 28 cm 3 / g.

Additional embodiments are set out in the accompanying subclaims.

DETAILED DESCRIPTION OF THE INVENTION The polymer fibers according to the invention have a glass transition temperature (Tg) of 20 - 100 ° C. According to the invention, the polymer fiber is heated so that at the moment of entanglement it reaches a temperature above the glass transition temperature (Tg) of the polymer. At this temperature, the mobility of the molecules increases to such an extent that the stiffness is dramatically affected and a lowering of the modulus of elasticity or the E-modulus up to several 10-powers can be obtained.

The mechanical properties of synthetic polymers change dramatically at the glass transition temperature of the polymer. By momentarily heating the desired fiber to the glass transition temperature or just above it during the hydroentangling, the flexural stiffness of the fiber is reduced and the degree of entanglement or entanglement degree in the fi fabric is increased.

Many different types and blends of polymer fibers can be used. Particularly preferred is, according to the invention, a nonwoven fabric which wholly or partly comprises synthetic polymeric fibers, or mixtures of synthetic polymeric fibers. Depending on the purpose of the non-woven fabric, the type of fiber and the degree of incorporation of natural fibers is chosen. The more proportion of synthetic polymer that can be included in the nonwoven fabric, the greater the possibilities.

Examples of fibers that can be used in the material according to the present invention are synthetic staple fibers, synthetic continuous fibers, staple fibers of regenerated cellulose, natural fibers such as plant fibers, pulp fibers or mixtures thereof. Examples of commercially available regenerated cellulose fibers are rayon, viscose and lyocell. Examples of synthetic fibers are fibers of polyester, polylactide, polyamide and polypropylene. The synthetic polymer fibers may comprise partly polymeric fibers made of natural fibers and partly polymeric fibers made of synthetic fibers. Even continuous filaments, such as meltblown and spun bond fibers can be used and further profiled so-called capillary fibers are used. These profiled beams are often very rigid and normally difficult to handle, but can be entangled using the present method. Mixtures of these different fibers can also be used. A typical mixture is 40-50% long, synthetic fibers and the rest cellulose, but all mixtures are applicable. Mass fi brema can be of chemical, mechanical, thermomechanical, chememechanical or chemithermomechanical pulp (CTMP). Mixture of mechanical, thermomechanical, chememechanical or chemithermomechanical pulp fibers gives a material with higher bulk and improved absorption and softness, as described in SE 9500585-6.

According to the invention, thermoplastic, synthetic polymers and in particular semi-crystalline polymers are used in particular. Amorphous polymers can also be used.

The heating of polymer fi bern at the moment of hydroentangling can be done in many different ways. One way to achieve an instantaneous temperature rise in the process is to heat the entangling water to a temperature so that the, children, at the very moment of hydroentangling, reach a temperature above Tg.

Additional ways to heat fi bears can be through IR heating, e.g. by IR irradiation of the fiber web, or alternatively the entangling water.

Furthermore, other radiant heating can be used as well as heating with microwaves. An additional possibility is to use metal wires. It is suggested that a copper wire be used, which is heated by means of hot air, hot water or another medium or a combination of these.

The hydroentangling can be done on the basis of either a dry-laid or a wet-laid fi berbana. In dry forming, dry fibers are aerated on a wire, after which the fibrous web is subjected to hydroentangling. When wet-laid, a wet or foam-shaped fi berbane is prepared by dispersing the fibers in liquid or alternatively in a foamed liquid containing a foam-forming surfactant and water. An example of a suitable such foaming process is found in SE 940247 0-0. The fiber dispersion is dewatered on a wire and hydroentane glass thereafter. Hydroentangling can be done with conventional equipment.

The hydroentangling of a wet or foam formation fi berbana can either take place in-line, ie. in direct connection with the fiber web being dewatered on the wire, or on a wet-formed sheet which has been dried and rolled up after the forming. Several such sheets can be laminated together by hydroentangling. It is also possible to combine dry forming with wet or foam forming, in such a way that an air-laid web of e.g. synthetic fibers are entangled together with a wet or foam-formed sheet of pulp. 10 15 20 25 30 35 40 518 438 s After the hydroentangling, the material is pressed and dried and rolled up. The finished material can then be converted in a known manner to a suitable format and packaged.

According to one embodiment of the present process, a carrier dispersion is formed of the desired polymer (s). The fiber dispersion is formed on a rotating support, e.g. a wire and once the dispersion has formed it is subjected to a hydroentangling by water jets which strikes the layer of the fiber dispersion and thus entangles or entangles the fibers. At least at the moment of hydroentangling, the polymer fiber is then given a temperature which exceeds Tg for the polymer, but at the same time falls below its melting point. This can be done by the water used to effect the hydroentangling, at least during the hydroentangling itself, being heated to a temperature above Tg for the polymer fiber according to any of the above methods. Examples of energy levels used are 300 - 600 kWh / ton with a water pressure of 80 -120 bar.

The present process is used for polymers with a Tg of 20-100 ° C, preferably 50-100 ° C and more particularly 50-70 ° C. An especially preferred polymer fiber is polylactide (PLA) which has a Tg of 50-70 ° C.

Reported glass conversion temperature for a polymer can vary greatly partly due to the fact that the glass conversion takes place over a temperature range and not at a certain temperature, partly due to the method used to determine the glass conversion temperature.

One method useful in the present invention for determining the glass transition temperature is DSC (Differential Scanning Calorimetry), which measures the change in enthalpy as a function of temperature. At the glass transition temperature, the enthalpy-temperature curve makes a jump and the value at this jump gives the glass transformation temperature.

Another method that is considered more sensitive is DMA (Dynamic Mechanical Analysis). In this method, storage module, loss module, and tanö are measured at a frequency (normally 1Hz) as a function of temperature. At the glass transition temperature, the storage module for an amorphous polymer with several tens of powers changes as the loss module and tanö go through a maximum. With this method, it is also possible to form an idea of how much the module changes at the glass conversion temperature. The glass transition temperatures of most polymers are given in e.g. a manuals well known to those skilled in the art. According to the invention, Tg can be produced from the "Polymer Handbook", authors J. Brandrup and E.H. lmmergut, publisher "Interscience publishers". Tg can also be generated using one of the DSC or DMA methods.

The method according to the invention is particularly suitable for fibers with high flexural stiffness. High flexural stiffness can be achieved either by a high E-modulus value or by a coarse bearing thickness. This means that particularly suitable polymer fibers are either those with a high E-modulus value or polymers with very coarse fibers. Eg. a thin fiber with a high E-modulus value or a thick fi ber with a more moderate or low E-modulus value. Alternatively, those where both the E-module value and thickness are high can also be used. The e-modulus value of a polymer fi ber is expressed in cN / tex.

Measurement of the E-module value for a kan ber can e.g. done by measuring the initial slope in a stress-strain diagram from a tensile test; performed according to Swedish standard SS-EN ISO 5079. An example of equipment that can be used to measure the E-module according to the present invention is a Lenzi g Vibrodyn. With the help of DMA, it is also possible to get an idea of how much the module changes at the glass conversion temperature. The E-modulus value for polymer fi bem is, according to the present invention, the E-modulus value for fi children at room temperature (see SS-EN ISO 5079).

Fibers of all thicknesses can be used, ie. both microfibers, normally thick around 1-2 dtex, and thick around 6-7 dtex. According to a special embodiment, very coarse fibers can be entangled into a bulk fabric with high bulk.

According to the invention, new materials are also produced, ie. new fi certificates made by hydroentangling.

Suitably the polymer has an E-modulus value of 2 cN / tex, especially 250 cN / tex and more preferably 2100 cN / tex. In particular, fi grades of polymers with very high E-modulus values such as 100-2000 cN / tex, especially 500-1500 cN / tex, more especially 200-750 cN / tex and even more especially 250-600 cN / tex can be achieved.

According to one embodiment, the method according to the invention can be used for the production of very strong fi fabrics of fibers with very high E-modulus values, e.g. aromatic polyamides and aromatic polyesters. It is further of particular interest according to the invention to manufacture fibrous fabrics with a high bulk mass.

Using the method, nonwovens with very thick fibers, e.g. 6-7 dtex, manufactured, which can give a yg grade with a very high bulk mass.

By coarse fibers is generally meant fibers 25 dtex and by means of such fibers a material with very high bulk 28 cm 3 / g can be produced according to the present invention. Bulk is expressed as the thickness / basis weight of the material (cm3 / g).

According to the present invention, e.g. nonwoven fabrics with a bulk of 5-15 cm3 / g, especially 8-15 cm3 / g and more especially 10-15 cm3 / g.

An example of a fabric made with the aid of the present invention is a fabric with a very high bulk of 10-15 cm 3 / g, a product which has very good resilience properties. Fibers with a dimension of 25-50 μm were used. Such fibers are p. G.a. its stiffness very difficult to entangle otherwise. Such a material is particularly useful as a spreading layer in diapers, but can be used in many other areas where high bulk and good resilience properties are desired properties, e.g. as a cloth.

It is especially preferred to be able to produce materials of semi-crystalline polymers, with fibers of thick diameter and / or high E-modulus value.

The fabric produced can, due to the lesser dependence on the stiffness of the fiber, give a fabric which consists mainly of 100% polymer polymer or the fiber mixture. Ie. a som ber that does not need to be added plasticizers or other additives that would otherwise be required to handle e.g. a stiff fiber.

The present process for the production of således grades thus involves a method which is less dependent than previous methods on fi children's flexural stiffness and provides, as shown above, various possibilities to utilize the free potential that is created. New materials with new properties can be produced. Eg. For example, a fiber can be optimally stretched before hydroentangling so that it is as stiff as possible and entangled. Examples of suitable such boards are polyester boards and polypropylene boards. By stretching, the breaking strength of a fiber can be increased to impart new properties to the fiber and the fabric produced therefrom, and by means of the present process, such a fiber can be hydroentane glass. A fiber pretreated in this way is often not possible to hydro-entangle with today's known methods.

The present invention relates in particular to a hydroentangled nonwoven fabric comprising polymers with a glass transition temperature (Tg) of 20 - 100 ° C, wherein the polymeric fibers in the fabric are fibers of polyester, polylactide, polyamide or polypropylene, or mixtures thereof and have an E-modulus of 2,500 cN / eg at room temperature. According to one embodiment, the polymer fibers in the har grade have an E-modulus of 500-2000 cN / tex, especially 600-1500 cN / tex.

The meaning of the invention is that fibers with higher stiffness and / or higher coarseness than what is normally used in hydroentangling can be entangled to a high degree of entanglement at reasonable energy levels. Alternatively, fibers with, for hydroentangling, normal stiffness and coarseness can be entangled at a lower energy level or to a higher degree of entanglement.

The process means that fi fabrics containing very coarse fibers can be easily entangled and thereby a material with high bulk and good resilience properties is obtained.

A further advantage is that materials can be manufactured at a lower cost, as the manufacturing cost of synthetic fibers is dimension-related and decreases with increased fiber coarse size. Another advantage is that fibers with very high strength can be entangled in a yg fabric with very good mechanical properties, especially high wet strength, without the simultaneous high flexural stiffness of these fibers affecting the degree of entanglement or the energy input in a negative sense. 10 15 '20 25 30 35 40 518 438 9 In summary, it can be said that the present invention creates a potential, not only by expanding the number of current fi coatings regarding polymer and dimension, but also by the possibility of optimizing the constituent fiber components based on other criteria. than to limit the flexural stiffness of children.

This potential can be used for improved material properties (increased bulk, resilience, tensile strength, etc.) or reduced costs in the form of lower energy consumption or lower costs for components.

As mentioned earlier, the fabric may comprise various mixtures of fibers, including mixtures with non-synthetic fibers. The greater the proportion of synthetic polymer fibers that may be included, the greater the possibility of utilizing the free g potential that is achieved. Of course, the fiber fabric also has very different properties depending on the degree of admixture and type of fiber. All in all, the present invention creates great opportunities for optimization and new materials.

The nonwoven fabric made according to the present invention can be used e.g. a. as wiping materials for household or industrial use, such as for large consumers such as workshops, industries, hospitals and other public institutions.

It is also useful as a disposable material in healthcare, e.g. such as surgical gowns, sheets and the like. Furthermore, it can be used for hygiene use, e.g. as a component in absorption products such as bandages, panty liners, diapers, incontinence products, bed sheets, wound dressings, compresses and the like. In particular, this nonwoven fabric made according to the present invention has high wet strength.

Fiber fabrics with a high bulk mass are especially advantageous to be used as e.g. spreading layers in diapers, but also as wiping materials for household use.

Example 1, below, shows that the surfactant strength of fi bern (PLA- fi bem) has been increased by 20-25% by exceeding the Tg temperature during hydroentangling.

This thus gives a potential of 20-25% which can be utilized in different ways. As can be seen from Example 1, a stronger material can be obtained, but the potential can also be used to provide an energy saving and thus a cost saving.

EXAMPLE 1 A foam-shaped fiber dispersion consisting of 60% pulp fiber of chemical sulphate pulp and 40% thermoplastic synthetic fi ber (1.7 dtex, 19 mm) was formed on a rotating wire. The fiber dispersion was hydroentangled from one side at an energy input of 300 kWh / ton.

The experiment was repeated to include 3 different variants (experiments 1, 2 and 3) of polylactide fi ber (with Tg = 50-70 ° C) as thermoplastic synthetic fiber. In each experiment, the hydroentangling was carried out partly with room temperature water (20 ° C) and partly with water heated to 75 ° C. 5 15 518 438 10 For comparison, an experiment (experiment 4) was performed according to the same embodiment with a fi ber of polyethylene terephthalate (Tg = 85 ° C).

The tensile strength in dry and wet conditions (water and surfactant solution) as well as elongation, basis weight, bulk, etc. were measured and the values are reported in Table 1 below.

Tg was measured using a Perkin Elmer DSC 7 and the measurement was performed from room temperature to 50 ° C above the melting point.

The e-module values were obtained as follows. Tensile testing was performed on a Lenzig Vibro pad with a tensile speed of 50 mm / min and a clamping length of 10 mm.

A weight of 100 mg was used to bias fi bern. The E-module was calculated manually by plotting the key to the tensile test curves in the linear range. The values given in the table are the E-module values at room temperature. 518 438 ll NM. wdN Ww Nw WmN ww o fi www www mß Hmm * I WoN: w wo WmN QÉ w fi omv mww oN Fmm v Now v42 YÉ E. vw N.m_ämm m fi www .NE 2 alm Now __: QQ NH Nm QÉ __: ßw conv www oN <~ E m fi a md md SN E ww Wm m3 Wow m »(Jm ms. wa mi» vw E Q. Fm _Nm E oN <5 * N EN _.N_ m.N_ o »w 2 oi: N wow WE mß alm EN E fi N fl w fi v »ï vi vw <5» »Nm oN <\ E _ nwëz. Ašš aš æšë ašzv Cßtzuv EÉB Ešï v83: øxu to. xuuuwwæh fi -fi ußätohm xuwciwcwämh xwwiw fl h fi -wüêfâmwwhß šsm xïxooqh 8.3; hšmömëøh Loëbom É fi wm _: onßw 10 15 20 25 518 438 12 such as strength, elongation and E-modulus.

As can be seen from Table 1, the strength in the dry state is largely not affected at all, which indicates that the fis have regained their original mechanical properties after the instantaneous heat treatment to which they have been subjected.

When tensile tests are performed in water, the fibers will slide more easily towards each other, whereby the degree of mechanical bonding (entanglement) increases somewhat in importance for the mechanical properties of the fabric. Table 1 shows that for all samples the tensile index is slightly higher for the materials that are hydroentangled with hot water.

In tensile testing in surfactant solution, the friction between the fibers is largely eliminated, which means that the degree of entanglement will dominate as an influencing factor for the mechanical properties of the fibrous fabric. As can be seen from Table 1, we see here a clear increase of between 20 and 25% of the tensile index when the material has been hydroentangled in hot water.

The values of the stiffness index, which are largely unchanged (some have increased slightly, some have fallen slightly), show that the type of bond is unchanged. If it were the case that the increase in surfactant strength is due to the blivit bres being thermally bound to each other during the heat treatment, this would also have been shown in a dramatic increase in the stiffness index. However, to achieve a thermal bond with polylactide, significantly higher temperatures are required.

What has been achieved is thus a non-woven fabric where the fibers have their original mechanical values, but where the structure has been changed in such a way that fi brema has reached a higher degree of entanglement.

Claims (14)

518 438/3 PATENT REQUIREMENTS Process for the hydroentangling of polymer fibers for the production of a yg fabric, characterized in that the polymer fiber has a glass transition temperature (Tg) of 20 - 100 ° C, and that at the moment of hydroentangling, the polymers fi bern are given a temperature equal to or exceeding the glass transition temperature ( Tg) for polymer fi bem and falls below the melting temperature of polymer fi bern. Process according to Claim 1, characterized in that the polymer has an E-modulus of 2 50 cN / tex, at room temperature. Process according to Claim 1, characterized in that the polymer has an E-modulus of 2,100 cN / tex, at room temperature. Process according to Claim 3, characterized in that the polymer has an E-modulus of 100 - 2000 cN / tex, in particular 500-1500 cN / tex, more in particular 200-750 cN / tex and even more especially 250-600 cN / tex , at room temperature. Process according to one of Claims 1 to 4, characterized in that the temperature is obtained by means of hot or superheated water. Method according to one of Claims 1 to 4, characterized in that the temperature is obtained by means of IR heat. Method according to one of Claims 1 to 4, characterized in that the temperature is obtained by means of microwaves. Process according to one of the preceding claims, characterized in that the polymer has a glass transition temperature (Tg) of 50-70 ° C. Process according to one of Claims 1 to 8, characterized in that the polymer contained in the polymers comprises polyester, polylactide, polyamide or polypropylene, or mixtures thereof. 10. l0. Hydroentangled glass fabric comprising polymer glass with a glass transition temperature (Tg) of 20 ~ 100 ° C, characterized in that the polymer fibers in the fabric are fibers of polyester, polylactide, polyamide or polypropylene, or mixtures thereof and have an E-modulus of 2,500 cN / tex at room temperature. 518 438/1 / Fibre fabric according to Claim 10, characterized in that the polymers in the fabric have an E-modulus of 500-2000 cN / tex, in particular 600-1500 cN / tex. Fiber fabric according to Claims 10 to 1, characterized in that the polymers in the fabric have a glass transition temperature (Tg) of 50-70 ° C. Fiber fabric according to one of Claims 10 to 12, characterized in that the fabric has a bulk density of 28 cm 3 / g. Fiber fabric according to Claim 13, characterized in that the fabric has a bulk density of 8 to 15 cm 3 / g, in particular 10-15 cm 3 / g.