Method for spunlace production of nonwoven material and nonwoven material

Abstract

The invention relates to a method for producing a nonwoven material by a wet laying process comprising a spunlace step. A fiber dispersion comprising cellulose-based fibers is prepared, and a fibrous web is formed by supplying the fiber dispersion onto a screen. The web is spunlaced in at least one spunlace station, and the spunlaced web is dried to obtain the nonwoven material. A strength composition comprising at least one cationic strength component having functional groups capable of forming covalent bonds with carboxyl and / or hydroxyl groups is added to the fiber dispersion prior to formation of the web. The invention also relates to the nonwoven material obtained.

Description

Technical Field

[0001] This invention relates to a method for producing nonwoven materials using hydroentangling, as described in the preamble of the appended independent claims. The invention also relates to nonwoven materials obtained by the method of this invention. Background Technology

[0002] Nonwoven materials are now used in a wide range of applications, from hygiene products to agriculture and the automotive industry. They are particularly useful for industrial and household cleaning, personal hygiene, beauty, and healthcare. With increasing environmental awareness, both industry professionals and consumers are paying more attention to reducing the environmental impact of nonwoven production and the materials themselves. Due to the large production volumes and wide range of applications, even small improvements in nonwoven manufacturing can have a significant impact.

[0003] Nonwoven fiber webs can be manufactured using a wet web-forming process, in which an aqueous fiber dispersion is deposited onto a screen, through which water is drained, forming a nonwoven fiber web. Due to the random orientation of the fibers, it is desirable that the strength of the nonwoven fiber web be similar in all directions of the plane. Web strength can be increased by web bonding. Web bonding can be achieved mechanically using hydroentangling (also known as jet spinning). In the hydroentangling step, fine, high-pressure water jets are used to mechanically bond the fiber web. These high-pressure water jets cause the fibers in the fiber web to entangle with each other, thereby increasing the strength of the fiber web. The pressure used in the hydroentangling step is proportional to the strength effect achieved, and to improve the effect, the nonwoven fiber web can undergo repeated hydroentangling steps or cycles before the fiber web is dried. The high pressure and multiple cycles required make hydroentangling a very energy-intensive manufacturing step in nonwoven fabrication. For even higher strength, increasing the jet pressure or the number of cycles in the hydroentangling step further increases the energy consumption of the process. However, the strength achievable through hydroentangling is limited: even with repeated hydroentangling cycles or steps or higher jetting pressures, the strength of nonwoven materials cannot be increased beyond a certain maximum.

[0004] The strength of nonwoven materials also depends on their basis weight, meaning that manufacturing low-basis-weight nonwovens with good strength properties can be challenging. The strength of nonwoven materials can be increased by using synthetic petroleum-based polymer fibers in their manufacture. However, the use of petroleum-based polymer fibers can raise concerns about the post-use disposal of nonwoven materials. With increasing regulations and costs associated with handling waste that cannot be recycled, reused, properly sorted, or composted, there is a general desire to minimize the amount of petroleum-based polymers in products. Simultaneously, there is a need to reduce the basis weight of nonwoven materials, as this conserves raw materials.

[0005] Chemical bonding has also been used to improve the strength properties of nonwoven materials. In chemical bonding, a liquid binder is applied to the nonwoven fiber web after it has been formed by impregnation, coating, or spraying.

[0006] There is a need to improve the manufacturing methods of wet-laid nonwoven materials to allow the use of lower pressures and / or fewer cycles in the hydroentangling process without compromising the strength properties of the final nonwoven material. Furthermore, minimizing the amount of fibers (especially polymer fibers) and chemical binders used without impairing the strength properties of the obtained nonwoven material would be economically and environmentally beneficial. Summary of the Invention

[0007] The purpose of this invention is to reduce or even eliminate the aforementioned problems in the prior art.

[0008] The object of this invention is to provide a method for producing nonwoven materials with improved properties, especially strength properties, by using hydroentangling.

[0009] Another object of the present invention is to provide enhanced strength properties for wet-laid nonwoven materials.

[0010] To achieve the purposes presented above and other objectives, the present invention is characterized by the content presented in the characterizing portion of the appended independent claims.

[0011] Some preferred embodiments of the present invention will be described in the other claims.

[0012] Where applicable, the embodiments and advantages mentioned herein relate to all aspects, methods, products, and uses of the invention, although not always specifically mentioned.

[0013] A typical method for producing nonwoven materials according to the present invention via a wet web-forming process including a hydroentangling step includes: -Preparation of fiber dispersions containing cellulose-based fibers. - A fiber web is formed by supplying a fiber dispersion onto a screen. - The fiber web is hydroentangled in at least one hydroentangling station. -Dry the hydroentangled fiber web to obtain a nonwoven material. A strength composition comprising at least one glyoxalized cationic polyacrylamide is added to the fiber dispersion prior to the formation of the fiber web.

[0014] Typical nonwoven materials according to the invention are obtained by the method according to the invention and have a fiber matrix comprising cellulose-based fibers, wherein a strength composition comprising at least glyoxalized cationic polyacrylamide is uniformly distributed in the fiber matrix.

[0015] It has now been surprisingly discovered that by adding a strength composition containing at least glyoxal-modified cationic polyacrylamide to the fiber suspension prior to web formation, the strength properties, particularly wet strength, of the produced nonwoven material can be significantly improved. Without wishing to be bound by any theory, it is assumed that the glyoxal-modified cationic polyacrylamide may be absorbed onto the surface of the anionic fibers, subsequently forming covalent bonds between the carboxyl and / or hydroxyl groups on the fiber surface and the aldehyde groups of the glyoxal-modified cationic polyacrylamide. It is assumed that this bonding between fibers results from the formation of hemiacetals. The wet strength obtained by glyoxal-modified cationic polyacrylamide is temporary, as the bonding between the fibers and the aldehyde groups of the glyoxal-modified cationic polyacrylamide is reversible in the presence of excess water. The temporary wet strength decreases rather rapidly when the fiber web is immersed in water. Quite surprisingly, this temporary wet strength effect can be retained by hydroentangling and is still observed in the produced nonwoven material. Adding the strength composition to the fiber dispersion prior to hydroentangling allows for a reduction in the jetting pressure during the hydroentangling step while maintaining the strength of the resulting nonwoven material. Reducing the jetting pressure provides significant energy savings in the production of nonwoven materials. Improved strength properties obtained by adding the strength composition to the fiber dispersion prior to fiber web formation also enable a reduction in the basis weight of the resulting nonwoven material, further reducing raw material costs.

[0016] Even with improved strength properties, the washability of the produced nonwoven materials remained, or at least at an acceptable level, which was unexpected. Furthermore, there is indication that incorporating strength compositions containing glyoxal-modified cationic polyacrylamide can improve the liquid absorption capacity of the produced nonwoven materials.

[0017] In this context, the term "nonwoven material" should be understood as an engineered fiber assembly, primarily planar, that has been given a designed level of structural integrity, i.e., a measurable level of tensile strength, through the use of a hydroentangling step, and excluding materials obtained by weaving, knitting, or papermaking. The nonwoven material according to the invention is obtained by a wet-laid process, wherein cellulose-based fibers and optionally other fibers are engineered to the level of structural integrity primarily through physical and / or chemical means between fibers, other than hydrogen bonding. The nonwoven material of the invention meets the definitions of ISO Standard 9092 and CEN EN 29092, which came into effect in August 2024.

[0018] This invention relates to the production of nonwoven materials via a wet web-forming process including a hydroentangling step. In the wet web-forming process, an aqueous fiber dispersion is supplied to a screen, and water is discharged through the screen, thereby forming a fibrous nonwoven web on the screen. The manufacture of nonwoven materials using a wet web-forming process is known to those skilled in the art. In at least one hydroentangling station, the formed fiber web is mechanically bonded in the hydroentangling step using pressurized water jets. Preferably, the fiber web is bonded by hydroentangling, causing the fiber web to pass through at least one hydroentangling station multiple times; that is, the hydroentangling step includes multiple hydroentangling cycles. The required number of hydroentangling cycles depends on the nonwoven material to be produced and can be 1-7 cycles, for example, 1-5 cycles. The pressure used in the hydroentangling step can vary in each cycle. According to one embodiment of the invention, the hydroentangling cycle or hydroentangling station can use a fluid pressure in the range of 10-250 bar, preferably 10-60 bar.

[0019] After bonding the fiber web by hydroentangling, the hydroentangled fiber web is dried to obtain the final nonwoven material.

[0020] The strength composition of the present invention is added to the aqueous fiber dispersion before the fiber web is formed, i.e., before the fiber dispersion is supplied to the screen and before the fiber web is hydroentangled. Adding the strength composition to the fiber dispersion provides an appropriate contact time between the cationic strength component of the strength composition and the cellulose-based fibers of the fiber dispersion.

[0021] According to the present invention, the cationic strength component comprises at least glyoxalized cationic polyacrylamide. The strength composition thus comprises or consists of glyoxalized cationic polyacrylamide. From a sustainability perspective, the use of glyoxalized cationic polyacrylamide is advantageous because polyacrylamide can be produced according to the principle of biomass balance, where most fossil-based feedstocks are replaced by bio-based and renewable mass-produced balanced feedstocks.

[0022] Glyoxalized cationic polyacrylamide can be obtained by reacting cationic linear polyacrylamide (the base polymer) with glyoxal, thereby obtaining a cationic polyacrylamide polymer with pendant glyoxalized groups. The cationic polyacrylamide used as the base polymer can be a copolymer obtained by polymerizing acrylamide or a primary amine-containing monomer with at least one cationic monomer. The primary amine-containing monomer can be selected from methacrylamide, ethylacrylamide, N-ethylmethacrylamide, N-butylmethacrylamide, or N-ethylmethacrylamide, or any combination thereof. The cationic monomer can be selected from diallyl dimethylammonium chloride (DADMAC), [3-(acrylamido)propyl]trimethylammonium chloride (APTAC), and [3-(methacrylamido)propyl]trimethylammonium chloride (MAPTAC), and any combination thereof. The cationic polyacrylamide used as the base polymer, and the corresponding glyoxalized polyacrylamide, can contain only one type of cationic monomer, or it can contain two or more types of cationic monomers. Preferably, the cationic monomer can be diallyl dimethylammonium chloride (DADMAC).

[0023] This cationic polyacrylamide polymer can be obtained by polymerization of acrylamide or a primary amine-containing monomer with at least 5 mol%, preferably at least 7 mol%, more preferably at least 10 mol%, of at least one cationic monomer as defined above. According to one embodiment of the invention, the cationic polyacrylamide polymer can be obtained by polymerization of acrylamide or a primary amine-containing monomer with 5 mol% to 40 mol%, preferably 7 mol% to 30 mol%, more preferably 10 mol% to 25 mol%, and sometimes 10 mol% to 20 mol%, of at least one cationic monomer as defined above. The percentages are calculated based on the total moles of polymerizable monomers in the polymerization.

[0024] According to one embodiment of the invention, the strength composition may comprise or consist of glyoxalized cationic polyacrylamide having a charge density at pH 4.3 in the range of 0.5-2.5 meq / g or 0.5-2 meq / g, preferably 0.75-1.9 meq / g, more preferably 1-1.8 meq / g. The charge density is measured as described in the experimental section. The defined charge density value ensures effective interaction between the strength composition and the negatively charged groups on the surface of the cellulose-based fibers without interfering with the formation of the nonwoven fiber web.

[0025] The weight-average molecular weight of glyoxal-modified cationic polyacrylamide can be in the range of 100,000-1,000,000 g / mol, preferably 200,000-700,000 g / mol, more preferably 250,000-600,000 g / mol or 250,000-550,000 g / mol. The weight-average molecular weight is determined by size exclusion chromatography calibrated using polyethylene oxide (PEO) standards.

[0026] The strength composition can be added to the fiber dispersion in such amounts that the amount of glyoxalized cationic polyacrylamide is in the range of 0.1-10 kg / ton dry fiber dispersion, preferably 0.3-6 kg / ton dry fiber dispersion, and more preferably 0.5-5 kg / ton dry fiber dispersion.

[0027] In addition to glyoxalized cationic polyacrylamide, the strength composition may also contain one or more other cationic strength components. The other cationic strength components suitable for the method of the present invention contain at least functional groups capable of forming covalent bonds with carboxyl and / or hydroxyl groups. This means that the other cationic strength components can form covalent bonds with the cellulose-based fibers of the fiber dispersion. The other cationic strength components are preferably synthetic polymers. According to one embodiment of the invention, the other cationic strength component is a synthetic cationic polymer having a charge density in the range of 0.5-2.7 meq / g, preferably 0.7-2.5 meq / g, more preferably 1.0-2.3 meq / g. The operating pH range of the synthetic cationic polymer is 4.5-8.5. Within this pH range, the synthetic cationic polymer preferably has a defined charge density. In this way, the other cationic strength components can effectively form covalent bonds with the cellulose-based fibers of the fiber dispersion.

[0028] The amount of the strength composition added can be such that the total amount of glyoxalized cationic polyacrylamide and optionally other cationic strength components is in the range of 0.1-10 kg / ton dry fiber dispersion, preferably 0.3-6 kg / ton dry fiber dispersion, more preferably 0.5-5 kg / ton dry fiber dispersion.

[0029] In addition to glyoxalized polyacrylamide, the cationic strength component may include another cationic strength component having functional groups capable of forming covalent bonds with carboxyl and / or hydroxyl groups, such as polyamidoamine epihaloalcohols. According to a preferred embodiment, this additional cationic strength component is a polyamidoamine epihaloalcohol polymer, preferably a polyamidoamine epichlorohydrin (PAE) polymer. The polyamidoamine epihaloalcohol polymer has a polyamidoamine backbone, obtained through a condensation reaction between a polycarboxylic acid such as adipic acid and a polyamine such as diethylenetriamine. Subsequent reactions of the main chain with the epihaloalcohol, such as epichlorohydrin, produce a crosslinked polymer structure, wherein highly reactive azahexacyclobutaneonium groups are generated along the polyamidoamine main chain. The amount of azahexacyclobutaneonium groups can be controlled, for example, by the epihaloalcohol / amine ratio. The polyamidoamine epihaloalcohol polymer may have a molar ratio of at least 0.8 between the epihaloalcohol and secondary amine groups. In some embodiments, the molar ratio of epihaloalcohol to secondary amine group may be in the range of 0.8-1.5, for example 0.9-1.3 or 0.95-1.2.

[0030] Polyamide amine epihaloalcohol polymers can have a weight-average molecular weight in the range of 150,000–600,000 g / mol, preferably 200,000–500,000 g / mol, more preferably 250,000–450,000 g / mol. The weight-average molecular weight can be measured using SEC / GPC with PEO (polyethylene oxide) calibration as described below. The weight-average molecular weight (MW) was determined by size exclusion chromatography (SEC) using an Agilent 1100 SE chromatographic instrument equipped with an integrated pump, autosampler, and degasser. The eluent was a buffer solution (0.3125 M CH3COOH + 0.3125 M CH3COONa) at a flow rate of 0.5 ml / min at 35°C. Typical sample concentrations were 2–4 mg / ml, with an injection volume of 50 μl. Ethylene glycol (1 mg / ml) was used as a flow marker. The column assembly used consisted of three columns (one TSKgel PWXL guard column and two TSKgel GMPWXL columns). Detection was performed using an Agilent differential refractive index detector (T=35°C). Molecular weight was determined using the Polymer Standards Service for Narrow Molecular Weight Distribution of Poly(ethylene oxide) / Polyethylene glycol, a standard column calibration method.

[0031] Further cationic strength components of this strength composition may include or be composed of a polyamide amine epihalool polymer having a charge density of 1.0 meq / g or higher, preferably 1.2 meq / g or higher, more preferably 1.4 meq / g or higher, and even more preferably 1.5 meq / g or higher, as determined at pH 9.5. The charge density of the polyamide amine epihalool polymer may be ≤2.7 meq / g, preferably ≤2.5 meq / g, more preferably ≤2.3 meq / g, as determined at pH 9.5. The charge density can be determined by titration with a potassium salt of polyvinylsulfuric acid. Mütek PCD-03 is used for endpoint detection.

[0032] The strength composition can be added to the fiber dispersion in an amount such that the amount of an additional cationic strength component (such as a polyamide amine epihalo alcohol polymer) is in the range of 0.1-10 kg / ton dry fiber dispersion, preferably 0.3-6 kg / ton dry fiber dispersion, and more preferably 0.5-5 kg / ton dry fiber dispersion.

[0033] In addition to the strength composition, one or more sizing agents, such as natural and / or synthetic polymers, such as cationic starch, alkenyl ketone dimer (AKD), and / or alkenyl succinic anhydride (ASA), or any combination thereof, may be added to the fiber dispersion prior to the formation of the fiber web. According to a preferred embodiment, the sizing agent is cationic starch. One or more sizing agents may be added before and / or after the addition of the strength composition. The use of one or more sizing agents can further improve the wet strength properties of the resulting nonwoven material, and they can also positively influence the water absorption properties of the resulting nonwoven material.

[0034] According to one aspect of the invention, a strength composition comprising glyoxal-modified cationic polyacrylamide (GPAM) and optionally a polyamide-aminoephidroxyl alcohol (PAE) polymer is used to improve the strength properties of nonwoven webs by hydroentangling. For example, the invention is capable of improving the strength characteristics of nonwoven webs in the transverse direction, meaning that the resulting nonwoven webs can exhibit similar strength characteristics, such as wet and / or dry tensile strength, in both the longitudinal and transverse directions of the fiber web. Similar or identical strength properties in both the longitudinal and transverse directions make the nonwoven material suitable for a wide variety of different applications. According to one embodiment, the nonwoven material may have the following characteristics compared to the same nonwoven material manufactured without any chemical additions to the fiber dispersion: - Increase dry tensile strength by at least 15%, preferably at least 20%, and / or - An increase of at least 30%, preferably 40%, in the wet tensile strength of the material measured in the transverse direction of the machine, and / or - An increase of at least 10%, preferably at least 15%, in wet tensile strength measured from the material in the machine direction.

[0035] According to one embodiment, a typical method for producing nonwoven materials via a wet web-forming process including a hydroentangling step includes: -Preparation of fiber dispersions containing cellulose-based fibers. - A fiber web is formed by supplying a fiber dispersion onto a screen. - The fiber web is hydroentangled in at least one hydroentangling station. -Dry the hydroentangled fiber web to obtain the nonwoven material. Prior to forming the fiber web, a strength composition comprising at least one cationic strength component is added to the fiber dispersion, the cationic strength component having functional groups capable of forming covalent bonds with carboxyl and / or hydroxyl groups.

[0036] The fiber dispersion used in the method of the present invention for preparing nonwoven materials comprises cellulose-based fibers. The fiber dispersion preferably contains 90 wt% to 100 wt%, more preferably 95 wt% to 100 wt% of cellulose-based fibers. According to a preferred embodiment, the fiber dispersion is composed of cellulose-based fibers.

[0037] These cellulose-based fibers may include or be selected from natural cellulose fibers, man-made cellulose fibers, i.e., man-made fibers derived from cellulose, or any mixture thereof.

[0038] Natural cellulose fibers may be selected from wood fibers, such as cork or hardwood fibers; seed fibers, such as cotton, kapok, or milkweed fibers; leaf fibers, such as sisal, banana leaf, or pineapple fibers; bast fibers, such as flax, hemp, jute, or kenaf fibers; or any combination thereof. These natural cellulose fibers may also include cellulose fibers of microbial origin. Natural cellulose fibers may have a fiber length in the range of 0.5–3.5 mm, preferably 1–3 mm.

[0039] Man-made cellulose fibers may include regenerated cellulose fibers such as viscose, lyocell, modal, acetate, triacetate, cuprammonium, Ioncell™, Infinna™, or any combination thereof. Man-made cellulose fibers are preferably short fibers. Man-made cellulose fibers may have a fiber length in the range of 3-15 mm, preferably 5-13 mm, more preferably 5-12 mm.

[0040] These cellulose-based fibers (both natural and man-made cellulose fibers) may include virgin fibers, regenerated fibers, or a mixture of virgin and regenerated fibers. The fiber dispersion may also contain only virgin fibers and / or only recycled fibers. The cellulose-based fibers may alternatively or additionally be fibers derived from agricultural waste or residues, or fibers derived from food processing and / or beverage industry waste, such as citrus industry waste.

[0041] According to one embodiment of the invention, the fiber dispersion may comprise 50 wt%-100 wt%, preferably 60 wt%-99 wt%, more preferably 60 wt%-95 wt% of natural cellulose fibers on a dry weight basis. The fiber dispersion may comprise 0 wt%-50 wt%, typically 1 wt%-40 wt%, more typically 5 wt%-40 wt% of synthetic cellulose fibers. The use of the strength composition allows for an increase in the amount of natural cellulose fibers in the fiber dispersion without compromising or reducing the strength properties of the resulting nonwoven material. The increased amount of natural cellulose fibers makes the nonwoven material more sustainable and easier to deposit after use. Furthermore, the natural cellulose fibers absorb moisture / water, thus providing a resulting nonwoven material with advantageous absorption properties.

[0042] In addition to cellulose-based fibers, the fiber dispersion may include synthetic fibers, such as synthetic polymer fibers, carbon fibers, and / or glass fibers. These synthetic polymer fibers may be thermoplastic polymer fibers, such as polyolefin fibers, such as polyethylene fibers, polypropylene fibers; polyamide fibers, such as polyaramid fibers; polyester fibers; polylactic acid fibers; or any mixture thereof. The fiber dispersion typically contains <10 wt%, preferably <5 wt%, more preferably <1 wt% of synthetic fibers. According to one embodiment, the fiber dispersion does not contain synthetic fibers selected from synthetic polymer fibers, carbon fibers, and / or glass fibers, especially synthetic polymer fibers. The addition of the strength composition according to the invention enables the production of nonwoven materials providing sufficient strength properties without the use of synthetic fibers, especially synthetic polymer fibers.

[0043] The nonwoven material of the present invention, obtained by the method according to the present invention, can have a content of 10-260 g / m². 2 Preferred concentration: 30-150 g / m 2 More preferably 40-70 g / m 2 The weight range is specified. The nonwoven material can have, for example, a weight of 30-100 g / m³. 2 Preferred concentration: 45-90 g / m 2 More preferably 50-70 g / m 2Within a certain weight range. Adding strength compositions to fiber dispersions makes it possible to produce nonwoven materials with low basis weights without compromising their strength properties. This saves resources in the form of reduced raw material usage. Products with low basis weights also offer a significant impact on CO2 emissions from product transportation, as more product can be transported with the same amount of emissions.

[0044] This invention relates to the manufacture of nonwoven materials for use as flushable and / or biodegradable wipes. Generally, this invention is applicable to the manufacture of nonwoven materials whose main technical characteristics are strength and decomposition properties. The manufactured nonwoven materials can be used, for example, as personal or industrial wiping products (personal / industrial wipes), household articles (e.g., tablecloths), agricultural products, or geotextiles. The manufactured nonwoven materials can preferably be disposed of after use by flushing, composting, decomposition, recycling, or similar end-of-life methods. Detailed Implementation

[0045] Experimental

[0046] Some embodiments of the invention are described in the following non-limiting examples.

[0047] Measurement of charge density

[0048] The charge density of the glyoxalized polyacrylamide used was determined below.

[0049] Particle charge measurements were performed using the CAS Touch charge analysis system. This titrator can be used to determine the cation / anion ratio and acid / base requirements of aqueous charge systems. The method is based on polyelectrolyte titration, in which the charge of the solution under study is altered. In this case, the adsorption of colloidal particles on the piston and chamber of the device changes, and simultaneously the flow potential changes.

[0050] Titration is used to determine the zero charge point (i.e., the isoelectric point), where the total charge of the solution passes through zero. The total charge of the sample can be determined based on the consumption of the titrant. The titrant is added in reverse order of the initial addition. Prepare 100 ml samples of each chemical with a solid content of 200 ppm. Titrate the samples with poly(DADMAC) or PES-Na based on the initial potential. Results are expressed in milliequivalents per gram (meq / g).

[0051] Manufacturing of nonwoven materials

[0052] Wet-laid nonwoven fabrics were manufactured using a fiber dispersion comprising wood pulp (GP cellulose) with an average fiber length of 2.8 mm and viscose fiber (1.7 dtex, Kelheim fiber) with a fiber length of 10 mm. The wood pulp was refined by beating to 15 degrees of freedom (SR). The fiber dispersion contained 60 wt% wood pulp and 40 wt% viscose fiber by dry weight.

[0053] Prior to forming the nonwoven fiber web, a strength composition comprising cationic glyoxal-modified polyacrylamide was added to the fiber dispersion along with starch (sizing agent). Details of the chemicals used are given in Table 1, and the amounts added are given in Table 2. Nonwoven material samples were produced by wet web forming using a sheet forming machine (Herman Manufacturing, USA). The target areal density of the nonwoven material was 60 g / m². 2 The fiber web was hydroentangled using a low-pressure profile to demonstrate the synergistic effect of mechanical and chemical bonding. Five hydroentangling processes were performed at a speed of 5 m / min in the Andritz Perfojet unit, with a pressure distribution profile of ↑30 bar ↓30 bar ↑50 bar ↓50 bar ↑50 bar. The resulting nonwoven material samples were then dried in a tension oven at 120°C for 10 minutes.

[0054] Table 1. Chemicals used.

[0055] Table 2. Test protocol and chemical dosage.

[0056] dry fiber

[0057] Testing and Results of Nonwoven Materials

[0058] Before testing, the nonwoven material sample was conditioned for 20 minutes at 23°C and 50% RH (relative humidity).

[0059] The following properties were tested from samples of nonwoven materials using a defined test method / Nonwoven Standard Procedure (NWSP): Wet tensile strength: EDANA–NWSP 1104R0 (20), five parallel measurements Dry tensile strength: EDANA–NWSP 1104R0 (20), five parallel measurements Liquid absorbance capacity (LAC): EDANA–NWSP 0101R0 (20), five parallel measurements Dispersibility: Assessed by disintegration in a drain line test. Place the sheet sample in 1 liter of water and agitate at 100 rpm for 3 hours. Change direction every 45 minutes. Pour the contents through a 12.5 mm sieve, and define the passing level as >50% passing. Perform two parallel measurements.

[0060] The measurement characteristics of the manufactured nonwoven materials are given in Table 3.

[0061] Table 3: Properties of the manufactured nonwoven materials.

[0062] The 0-reference sample was measured only from one direction because the MD and CD properties were expected to be the same (no hydroentanglement).

[0063] The results in Table 3 clearly show that, compared to spunlace treatment with glyoxal-modified polyacrylamide, adding glyoxal-modified polyacrylamide to the fiber dispersion before the formation of the nonwoven web and the spunlace step resulted in a 44% increase in dry tensile strength in the transverse direction. Wet tensile strength was improved without deterioration of washability, which remained at an acceptable level. Compared to spunlace treatment with glyoxal-modified polyacrylamide, adding glyoxal-modified polyacrylamide to the fiber dispersion before the formation of the nonwoven web and the spunlace step resulted in a significant increase in wet tensile strength of up to 92% in the transverse direction and up to 38% in the longitudinal direction. An improvement in the liquid absorption capacity of the produced nonwoven material can also be observed.

[0064] Although certain implementation methods and embodiments have been described in detail above, it will be clearly understood by those skilled in the art that many modifications are possible in the implementation methods and embodiments without departing from their teachings. All such modifications are intended to be included within the scope of the claims of this invention.

Claims

1. A method for producing nonwoven materials using a wet web-forming process, the process including a hydroentangling step, the method comprising: -Preparation of fiber dispersions containing cellulose-based fibers. - A fiber web is formed by supplying the fiber dispersion onto a screen. - The fiber web is hydroentangled in at least one hydroentangling station. - The hydroentangled fiber web is dried to obtain the nonwoven material. A strength composition comprising at least glyoxalized cationic polyacrylamide is added to the fiber dispersion prior to the formation of the fiber web.

2. The method according to claim 1, characterized in that... The cationic strength component includes glyoxalized cationic polyacrylamide having a charge density in the range of 0.5-2.5 meq / g or 0.5-2 meq / g, preferably 0.75-1.9 meq / g, more preferably 1-1.8 meq / g, as measured at pH 4.

3.

3. The method according to claim 1 or 2, characterized in that... The glyoxalized cationic polyacrylamide has a weight-average molecular weight in the range of 100,000-1,000,000 g / mol, preferably 200,000-700,000 g / mol, and more preferably 250,000-550,000 g / mol.

4. The method according to claim 1, 2 or 3, characterized in that... The cationic strength component includes additional cationic strength components having functional groups capable of forming covalent bonds with carboxyl and / or hydroxyl groups, such as polyamide amine epihalo alcohols.

5. The method according to claim 4, characterized in that... The additional cationic strength component includes a polyamide amine epihalo alcohol polymer having a charge density of ≥1.0 meq / g, preferably ≥1.2 meq / g, more preferably ≥1.4 meq / g, and even more preferably ≥1.5 meq / g as measured at pH 9.

5.

6. The method according to any one of claims 1 to 5, characterized in that... The amount of the strength composition added is such that the amount of glyoxalized cationic polyacrylamide is in the range of 0.1-10 kg / ton dry fiber dispersion, preferably 0.3-6 kg / ton dry fiber dispersion, and more preferably 0.5-5 kg / ton dry fiber dispersion.

7. The method according to any one of claims 1 to 6, characterized in that, The method further includes adding at least one sizing agent, such as cationic starch, alkenyl ketone dimer and / or alkenyl succinic anhydride, to the fiber dispersion prior to forming the fiber web.

8. The method according to any one of claims 1 to 7, characterized in that, The fiber dispersion comprises 90 wt% to 100 wt%, preferably 95 wt% to 100 wt%, of cellulose-based fibers.

9. The method according to any one of claims 1 to 8, characterized in that, The cellulose-based fiber is selected from natural cellulose fibers, man-made cellulose fibers, or any mixture thereof.

10. The method according to claim 9, characterized in that, On a dry weight basis, the fiber dispersion comprises 50 wt% to 100 wt%, preferably 60 wt% to 99 wt%, more preferably 60 wt% to 95 wt% of natural cellulose fibers.

11. The method according to any one of claims 1 to 10, characterized in that, The hydroentangling station uses a fluid pressure in the range of 10-250 bar, preferably 10-60 bar.

12. A nonwoven material obtained by the method according to any one of claims 1 to 11, the nonwoven material having a fiber matrix comprising cellulose-based fibers, wherein a strength composition comprising at least glyoxalized cationic polyacrylamide is uniformly distributed in the fiber matrix.

13. The nonwoven material according to claim 12, characterized in that, The nonwoven material has a density of 10-260 g / m³. 2 Preferred concentration: 30-150 g / m 2 More preferably 40-70 g / m 2 Weight within the range.

14. The nonwoven material according to claim 12 or 13, characterized in that, Compared to the same nonwoven material manufactured without any chemical additions to the fiber dispersion, it has - Increase dry tensile strength by at least 15%, preferably at least 20%, and / or - An increase of at least 30%, preferably 40%, in the wet tensile strength measured from the material in the transverse direction of the machine, and / or - An increase of at least 10%, preferably at least 15%, in wet tensile strength measured from the material in the machine direction.

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