Hydroentangled airlaid web and products obtained therefrom

Abstract

A water disposable nonwoven web having good MD and CD strength is provided. The nonwoven web is obtained by hydroentangling an airlaid web of no less than 50% by weight of natural cellulose fibers having a fiber length of no more than 3.5 mm and no more than 50% by weight staple fibers having a fiber length of no less than 8.0 mm. The nonwoven web contains no adhesive, binder or thermal bonding fibers. Products containing the disposable nonwoven web meet municipal guidelines for flushability.

Claims

1. A nonwoven web: consisting of defibrated wood pulp and staple fibers of at least one of viscose and lyocell; wherein a content of the defibrated wood pulp is no less than 50% by weight; and a content of staple fibers is no more than 50% by weight; wherein the nonwoven web comprises no binder, adhesive or thermal bonding fiber, a fiber length of the defibrated wood pulp is from 2.5 mm to 3.5 mm, a fiber length of the staple fibers is no less than 8.0 mm, a basis weight of the nonwoven web is from 20 g/m.sup.2 to 100 g/m.sup.2, and a thickness of the nonwoven web when one airlaid web is hydroentangled and dried is from 0.25 mm to 2 mm, and wherein the nonwoven web is obtained by a process comprising: preparing a homogeneous dry mixture of the defibrated wood pulp and the staple fibers; passing the homogeneous dry mixture through a perforated cylinder onto a foraminous carrier to airform the mixture to obtain at least one homogeneous airlaid web; hydroentangling the airlaid web on the foraminous carrier to consolidate the web on at least one side; and drying the hydroentangled web to obtain the nonwoven web; wherein the airforming and hydroentangling are conducted in a continuous operation.

2. The nonwoven web of claim 1, wherein the staple fiber is lyocell, the content of defibrated wood pulp is 75% by weight; and the content of the lyocell is 25% by weight; wherein the basis weight of the nonwoven web is from 40 g/m.sup.2 to 60 g/m.sup.2, a ratio of the wet tensile strength in the machine direction (MD) to the cross machine direction (CD) (MD/CD) is less than 3, a CD wet tensile strength is at least 5 N/5 cm, and the nonwoven web is a flushable product as defined in accordance with the July 2009 edition of EDANA's Guidance Document for Assessing the Flushability of Nonwoven Consumer Products.

3. The nonwoven web according to claim 1, wherein the staple fiber is viscose, the content of defibrated wood pulp is about 50% by weight; and the content of the viscose is about 50% by weight; wherein the basis weight of the nonwoven web is from 40 g/m.sup.2 to 60 g/m.sup.2, a ratio of the wet tensile strength in the machine direction (MD) to the cross machine direction (CD) (MD/CD) is less than 3, and a CD wet tensile strength is at least 12 N/5 cm.

4. A cleaning wipe, comprising: the nonwoven web according to claim 2; and at least one selected from the group consisting of a cleansing agent, a sterilizing agent, a deodorizing agent, a disinfectant, a moisturizing agent and a cosmetic remover.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic drawing of an arrangement of water jets in a hydroentanglement unit according to one embodiment of the invention.

(2) FIG. 2 shows comparative data for dispersible and non-dispersible nonwoven webs according to the invention in comparison to commercially available wipes.

(3) FIG. 3 shows a schematic diagram of the continuous production line of an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) According to the following description, all numerical ranges described include all sub-ranges and all values therebetween unless other wise specified. All weight content values are based on total weight. The following description provides a general description of the present invention and specific preferred embodiments. However, one of ordinary skill will recognize that many variations of the invention may be possible without departing from the gist of the invention. This description and the following Claims are intended to include all such variation.

(5) In a first embodiment, the present invention provides a method for production of a nonwoven web, comprising: preparing a mixture of natural cellulose fibers and staple fibers; airforming the mixture to obtain at least one homogeneous airlaid web; hydroentangling the airlaid web to consolidate the web on at least one side; and drying the hydroentangled web to obtain the nonwoven web; wherein the airforming and hydroentangling is conducted in continuous operation, a content of the natural cellulose fibers in the mixture of fibers is no less than 50% by weight, preferably no less than 60% and most preferably at least 75% by weight. A content of the staple fibers is no more than 50% by weight, preferably no more than 40% and most preferably, no more than 25%. No binder, adhesive or thermal bonding fibers are utilized in the airforming and hydroentangling operations according to the present invention.

(6) The length of the natural cellulose fibers is no more than 3.5 mm, preferably 1.5 mm to 3.5 mm, most preferably 2.5 to 3.5 mm. Any natural cellulose fiber may be employed as the short fiber of the mixture. In one embodiment a wood pulp of the described length may be the short fiber and in a preferred embodiment, a southern pine Kraft may be the natural cellulose fiber. Wood pulp obtained from a sulfite pulping process may additionally be the source of the natural cellulose fibers. Mixtures of natural cellulose fibers may be used. The natural cellulose fibers may be defibrated in hammermills to form a mixture of individual loose fibers.

(7) The staple fibers may be any non-thermoplastic man-made fiber which is no less than 8.0 mm in length, preferably 8.0 to 100 mm, most preferably 8 mm to 25 mm. Preferably the staple fiber is viscose or lyocell. Mixtures of non-thermoplastic fibers may be employed.

(8) The method of forming an air laid web is generally described in U.S. Pat. No. 4,640,810 to Laursen et al. The staple and defibrated natural cellulose fibers are blended to a homogeneous mixture and while supported in an air stream transported to a distributor unit. The distributor unit contains a rotating cylinder or drum that is perforated with holes, slots or other appropriately shaped apertures designed to allow passage of the fibers onto a foraminous carrier. The construction of the drum and configuration and size of the apertures may be varied according to the characteristics of the fiber mixture to be employed and to obtain unique web construction. Under the influence of a combination of any of air flow, mechanical agitation within the drum and suction from beneath the carrier, the fibers are directed through the openings of the perforated drum and form a homogeneous web on the surface of the carrier. The height and degree of matting of the dry web may be varied via control of process variables including fiber content and size, drum aperture size and shape, rate of air flow, degree of suction applied from the bottom of the carrier and carrier speed. Other equipment controls may also be varied to provide unique matting construction.

(9) The width of the web depends upon the type of air former equipment employed and may vary from 1 m to 6 m. Conventional commercial units such as supplied by Dan-Web, Oerlikon and Anpap Oy range from 2 to 5 m in width.

(10) According to the present invention the formed air laid web is directly and continuously transported to a hydroentanglement unit or spunlacing unit, where the airlaid mat is struck with a series of high pressure water jets to mechanically entangle or consolidate the fibers and form the nonwoven web. The jets may be oriented perpendicular to the surface of the carrier or angled to provide unique properties to the web. Jets may be placed to consolidate the web from one side, preferably, the top side or from both the top and bottom side. The pressure of the jets may be from 0.04 bars/kg/h/m to 15 bars/kg/h/m, preferably, 0.1 bars/kg/h/m to 10 bars/kg/h/m, and most preferably 0.3 bars/kg/h/m to 4 bars/kg/h/m.

(11) An embodiment showing an arrangement of jets to consolidate a web from both sides is shown schematically in FIG. 1. As indicated by FIG. 1, the air laid web taken directly from the airformer is passed along a series of carrier belts and exposed to high pressure jets indicated in numerical order. Jets 11, 12 and 13 impinge the top of the web while jets 21 and 22 strike the opposite or bottom side. The schematic jets 11-13, 21-22, 31-33, 41-43 and 51-52 represent banks of jets across the width of the web and the jet banks may be positioned and arranged to impart varying completeness of entanglement across the web. Thus the entanglement may be patterned or random depending on the intended end use of the nonwoven web.

(12) FIG. 3 shows a schematic drawing of an embodiment of a continuous system for preparing the hydroentangled airlaid web. The airforming system is shown as unit (7), wherein the defibrated natural cellulose fibers (1) and staple fibers (2) are homogeneously mixed in supply unit (3) and then transferred into rotating cylinder (4) having perforations (5). The mixture of defibrated natural cellulose fibers and staple fibers pass through the perforations onto the foraminous carrier (6) which transports the airlaid web through the hydroentangling unit (8) as described above. From the unit (8) the consolidated web is dried in drying unit (9).

(13) The drape, softness and comfortable hand of the nonwoven web may be controlled by the energy delivered by the high pressure jets and by the speed of travel of the web through the equipment. According to the present invention by control of both water pressure and speed of web travel through the spunlacing equipment as well as the absence of adhesives, binders or bonding fibers, a nonwoven web having varying degrees of strength, absorbency, softness and thickness may be obtained.

(14) Spunlacing or hydroentanglement units are available from Fleissner GmbH (Germany) and Andritz Perfojet (France).

(15) In one variation of the above basic embodiment, multiple airlaid webs may be prepared and stacked prior to spunlacing so that thicker nonwoven webs may be produced. The respective stacked layers may be of the same fiber composition or may have differing compositions selected for the intended end use of the nonwoven web. In each such possible embodiment, entanglement may be achieved by variation of water jet pressure and speed of travel of the web through the spunlacing unit. No binders, adhesives or bonding fibers are utilized.

(16) Following the spunlacing the wet nonwoven web may be dried and wound for transport and storage. In a further embodiment, prior to drying, the entangled web may be embossed either by a hydroembossing process or by thermal embossing.

(17) The basis weight of the nonwoven web may be from 20 g/m.sup.2 to 100 g/m.sup.2, preferably, 40 g/m.sup.2 to 80 g/m.sup.2 for a nonwoven web of from 0.25 mm to 2 mm in thickness. However, when multiple airlaid webs are stacked, the basis weight and thickness may not be in these ranges. Basis weight may be varied by control of the process variables described for both the airlaying and spunlacing operations and by other process variables conventionally known to one of skill in the present technology.

(18) The nonwoven webs according to the present invention have strength profiles which are more omnidirectional than some conventionally available nonwoven webs. The ratio of the wet tensile strength in the machine direction (MD) to the cross machine direction (CD) is less than 3. As shown in the Table of FIG. 2, the JHI products according to the invention with no adhesive, binder or bonding fibers, have significantly lower basis weights than comparative commercially available wipes, yet have MD and CD tensile strengths of similar value. Such property is especially surprising because a CD wet tensile strength is known to be difficult to obtain in products that meet standard guidelines for flushablity.

(19) In a special preferred embodiment, a flushable product is made according to the present invention with a composition of about 75% by weight defibrated wood pulp fibers having a length of 3.5 mm or less and 25% by weight lyocell having fibers of 8 mm or greater. The airlaid web is hydroentangled at a jet pressure of from 0.35 bars/kg/h/m to 2.1 bars/kg/h/m. The CD wet tensile strength of the nonwoven web is at least 5.0 N/5 cm and the MD/CD ratio is less than 3. This nonwoven web meets the testing standards for flushability as set forth in the July, 2009, edition of EDANA's Guidance Document for Assessing the Flushability of Nonwoven Consumer Products. Importantly, this product passes the municipal sewage pump test, wherein less than 10% of all data points measured over 5 total runs of 60 wipes each can have a power increase of more than 10%, and preferably less than 10% provokes an increase in power of 10%.

(20) In a special aspect this nonwoven web may be useful as a cleaning wipe and may contain at least one selected from the group consisting of a cleansing agent, a sterilizing agent, a deodorizing agent, a disinfectant, a moisturizing agent and a cosmetic remover.

(21) In another special embodiment having higher strength, a nonwoven web is prepared according to the method of the present invention with a mixture of about 50% by weight of defibrated wood pulp fibers having a length of 3.5 mm or less and about 50% by weight viscose having fibers of 8 mm or greater. The airlaid web is hydroentangled at a jet pressure of from 0.3 bars/kg/h/m to 15 bars/kg/h/m, preferably 0.4 bars/kg/h/m to 6 bars/kg/h/m. The CD wet tensile strength of the nonwoven web is at least 12 N/5 cm and the MD/CD ratio is less than 3. Significantly, the linting property of this product is significantly lower than commercial products current used as baby wipes or hard surface cleaning wipes.