CA1311351C - Highly absorbent nonwoven fabric made by hydroentanglement - Google Patents

Abstract

ABSTRACT

A strong, highly absorbent hard finished nonwoven toweling fabric consisting of wood pulp and textile fibers essentially free from added binders is prepared by forming a wet-laid web of a blend of fibers containing 30 to 80 weight percent wood pulp and 20 to 70 weight percent staple length fibers and subjecting the fibers in the wet-laid web to hydroentanglement.
The fabric may be embossed or unembossed, apertured or essentially nonapertured, and may be made lint resistant or water repellant or both. The fabric may be converted into pads or towels having medical and surgical applications, or into household cloths, food service wipes, industrial machinery wipes or the like.

Description

t 31 1 351 HIGHI,y ~NONWOVE~7 FABRIC M~DE BY HYDROENTANGLEMENT

This invention relates to highly absorbent hydroentangled nonwoven fabrics containing wood pulp 5 and textile length fibers, and to methods of their preparation. In one of its more specific aspects, the present invention relates to a uni~ue apertured or nonapertured composite fabric consisting essentially of a relatively high proportion of wood pulp intimately 10 entangled with synthetic staple fibers. In another of its more specific aspects, a non-apertured, strong, highly absorbent fabric suitable for use as disposable surgical toweling is produced by blending wood pulp and staple synthetic polymer fibers, dispersing the blend 15 of fibers in an aqueous carrier, forming a wet-laid web of blended fibers, subjecting the wet-laid web to the action of high pressure fluid jets, drying the web, and subjecting the dried web to embossment with matched dies.

Composite webs made up of various combinations of fibers are known in the prior art. Nonwoven fabrics in which staple length textile fibers are hydroentangled with continuous f ilaments are disclosed in U.S.
25 3,494,821 and 4,144,370. In U.S. 3,917,785, staple rayon fibers are blended with wood pulp, supported on an impermeable patterned support, and subjected to the force of water from jets to hydroentangle the fibers and form an apertured fabric. In U.S. Patents Nos.
30 3,917,785 and 4,442,161, a layer of textile fibers, which may be mixed with wood pulp, is supported on a foraminous screen and hydroentangled by means of . . .

- 2 ~ 3 5 t hydraulic jets to form a non-woven fabric.

Nonwoven fibrous webs comprising mixtures of wood pulp and synthetic fibers have high moisture absorption capabilities and may be inexpensively produced by conventional papermaking procedures. However, such products also tend to have relatively low wet strength properties and lack sufficient strength for many applications, for example, for use as surgical towels, household cloths, food service wipes and industrial machinery wipes. The strength of such products may be improved by including a bonding agent in the fiber furnish or by application of an adhesive binder to the formed web. While the strength characteristics of the lS web are improved by use of an adhesive binder, such as a synthetic resin latex, the liquid absorption capability of the web is correspondingly decreased.

We have now discovered that a high strength, nonwoven highly absorbent fabric having visual and clothlike hand characteristics of a woven towel and superior moisture absorption may be produced from a homogeneous blend of 30 to 80 weight percent wood pulp and ~0 to 70 weight percent long synthetic fibers by forming first a wet laid web or blanket of the fibers in the desired relative proportions and subjecting the wet laid web to hydroentanglement with sufficient energy to form a relatively dense, cohesive, uniform fabric. In a preferred embodiment, this fabric is then embossed at room temperature between two matched, interpenetrating dies. In one specific embodiment of this invention, a wet laid web of wood pulp and staple synthetic staple fibers is formed in known manner, dried, and, subjected to hydraulic entanglement. As a specific example, wet-laid webs having a to~al basis weight of 3 to 5 ounces per square yard made up of 50 to 75 weight percent wood pulp and 25 to 50 weight percent polyester fibers hydroentangled at an energy output of the order of 10,000 KPa produces a strong nonwoven fabric having superior water absorption qualities as compared with woven cotton huckaback towels and,when embossed as disclosed herein, comparable hand characteristics with clothlike softness and texture.

The nonwoven fabrics of this invention containing a substantial proportion of wood pulp are strong when wet and highly absorbent, and do not require stabilization 15 with a latex adhesive. The staple length fiber may be produced by known methods from any of various synthetic resins including polyolefins, nylons, polyesters, and the like; polyester fibers are preferred.

In accordance with the present invention, the synthetic textile fibers are blended with wood pulp and formed into a web by a wet-laying process technique as utilized in the paper and nonwovens industries. One or more such composite wet-laid webs are then subjected to 25 hydraulic entanglement producing a uniform spunlaced composite fabric with superior water absorption properties. A preferred method and apparatus for hydraulically entangling the fibers is disclosed in U.S. Patent No. 3,494,821.

Preferably, the composite we~-laid web is produced by a conventional wet-laid papermaking method by dispersing ' . '~

a uniform furnish of wood pulp fibers and staple synthetic fibers onto a foraminous screen of a conventional papermaking machine. V.S. Patent No.
4,081,319 to Conway and U.S. Patent No. 4,200,48~ to Brandon et âl. disclose wet-laying methods which may be used to produce a uniform web of wood pulp and staple fibers. A preferred method of dispersing a mixture of staple fibers and wood pulp is disclosed in u.S.
Patent No. 4,925,528 filed April 6, 1987.

10 While various wood pulps may be incorporated into the finished fabric by the method disclosed herein, those pulps which are characterized by long, flexible fibers of a low coarseness index are preferred. Wood fibers with an average fiber length of three to five 15 millimeters are especially suited for use in the spunlaced fabrics. Western red cedar, redwood and northern softwood kraft pulps, for example, are among the more desirable wood pulps useful in the nonwoven spunlaced fabrics of my invention.

20 Staple fiber length is an important factor affecting the strength and abrasion resistance of the resulting fabric. Staple fibers which are either too short or too long do not entangle as well as those in the range of from about one-quarter inch to about one inch with a 25 diameter range of 0.5 to 3 denier. Staple fibers in the range of one-half inch to seven-eighths inch in length and a diameter in the range of 0.5 to 2.9 denier are preferred for use in the process of this invention.
Shorter staple fiber lengths in the range of from about 30 one-quarter to one-half inch result in lowered tear 'A~, ~ 5 ~ 1311351 strength of the finished product. Tbe staple fiber~
may be round, elliptical, or scalloped oval in cross section.

The wood pulp content of the improved nonwoven web produced in accordance with the present invention may be in the range of from about 30 weight percent to about 80 weight percent. For most applications, a wood pulp content in the range from about 55 weight percent to 65 weight percent is preferred. The higher levels of wood pulp impart increase absorbency of the product, but usually result in some loss of abrasion resistance, and tensile strength.

In carrying out the process of the present invention, the entangling treatment described in the prior art, for example, by the hydroentanglement process disclosed in U.S. Patent No. 3,485,706 to F. J. Evans, or 3,560,326 to Bunting, Jr., et al., may be employed. As known in the art, the product fabric may be patterned by carrying out the hydroentanglement operation on a patterned screen or foraminous support. Nonpatterned products also may be produced by supporting the layer or layers of fibrous material on a smooth supporting surface during the hydroentanglement treatment as disclosed in U.S. Patent No. 3,493,462 to Bunting, Jr., et al.

The basis weight of the finished fabric may range from about 1 ounce per square yard to about 10 ounces per square yard. The lower limit generally defines the minimum weight at which acceptable water absorption and web strength can be attained. The upper limit generally defines the weight above which the water jets are not effective to produce a uniformly entangled web.

The wet-laid web may be -produced on-site and fed 5 directly from the web-forming apparatus to the hydroentanqling apparatus without the need for drying or bondin~ of the web prior to hydroentanglement.
Alternatively, the wet-laid composite web may be produced at a separate site, dried and supplied in 10 rolls to the site of the hydroentanglement device.

The separately formed wet-laid web containing the staple length textile fibers and wood pulp fibers is hydroentangled by water jets while supported on a 15 foraminous screen or belt, preferably one made up of synthetic continuous filaments woven into a screen.
The web is transported on the scree~n under several water jet manifolds of the type described in U.S.
Patent No. 3,485,706. ~he water jets entangle the ~0 discrete staple fibers and wood fibers present in the wet-laid web producing an intimately blended strong absorbent composite fabric. After drying and embossing with matched dies at room temperature, the - resulting fabric is soft and is a suitable material for 25 conversion to surgeon's hand towel~ and other products useful in disposable personal care or health care applications, or as durable, multiple use products.
Food service wipes, domestic hand towels or dish towels, and other utility wipes made up of spunlaced 30 synthetic staple fibers and wood pulp are stronger, more absorbent and generally superior in service to cloth toweling and similar products made up of hydroentangled rayon bonded with latex or those made ~f 7 t31 135~

scrim reinforced cellulose tissue.

Colored fabrics may be made up from dyed wood pulp, or dyed or pigmented textile staple fibers or both.

The fabric may be sterilized by currently known and commercially available sterilization processes, e.g., gamma irradiation, ethylene oxide gas, steam, and electron beam methods of sterilization.
By proper selection of the entangling screen, the fabric may be given a fine linen like pattern and texture. This fabric also may be post embossed with a matched die pattern at room temperature; the 15 combination of embossing and fine linen like screen pattern imparts a unique appearance, clothlike feel, bulk, softness and texture to the fabric.

Optionally, a small amount of binder may be 20 incorporated in or applied to the surface of the hydroentangled web to improve its abrasion resistance and reduce linting. A low lint count is an important quality of wipes for use in clean rooms. A wide ` variety of latex binders, thermoplastic binder fibers 25 and thermoplastic powders are available as binders or wet strength binders.

Fig. l is a simplified, diagrammatic perspective view o hydroentanglement apparatus illustrating one 30 specific embodiment of a suitable method for making the nonwoven fabric of this invention from one or more wet-laid webs.

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t3~ ~5t Fig. 2 is a bar graph illustratinq the absorption rate of samples, the test results of which are reported in Table I.
. . .
Fig. 3 illustrates graphically the absorbency under load of the samples reported in Table I.

Fig. 4 is a vertical cross-sectional view along the plane 4-4 of Fig. 5 illustrating on an enlarged scale a dry hydroentangled web pressed bPtween the surfaces of matched die embossing rolls.

Fig. 5 is a plan view of an enlarged section of a web embossed in a preferred embossment pattern.
Fig. 6 is a developed cross-sectional view on an enlarged scale illustrating the surfaces of matched dies and their relationship to the web during the embossing process.
Preformed wet-laid webs 11, 12, 13 and 14 made up of an intimate blend of staple fibers and wood pulp are drawn from supply rolls 15, 16, 17 and 18 over guide rolls 21, 22, 23 and 24 by feed rolls 26 and 27 onto a foraminous carrier belt 28. A woven polyester screen formed of a flexible material is suitable as a carrier belt for transporting the wet-laid webs through the hydroentanglement apparatus to form a uniform fabric web 40. The carrier belt 28 is supported on rolls 31, 32, 33 and 34, one or more of which may be driven by suitable means, not illustrated. A pair of rolls 36 and 37 remove the hydroentan~led web fabric 40 from the belt 28 for drying and subsequent embossing treatment.

t 3t t 35t g Several orifice manifolds 41, 42 and 43 are positioned above the belt 28 to discharge small diameter, high velocity jet streams of water onto the wet-laid webs and resulting composite web 40 as it moves from rolls 5 26 and 27 to rolls 36 and 37. Each of the manifolds 41, 42 and 43 is connected with a source of water under pressure through conduits 46, 47 and 48, and each is provided with one row of 0.005 inch diameter orifices spaced on 0.025 inch centers (to provide 40 orifices iO per linear inch) along the lowermost surface of each of the manifolds. The spacing between the orifice outlets of the manifolds and the web directly beneath each manifold is preferably in the range of from about one-quarter inch to abut one-half inch. Water from jets - 15 discharged from the orifices which passes through the web 40 and the screen 28 is removed by vacuum boxes 51~
52 and 53. Although only three manifolds are illustrated, representing three separate pressure stages, as many as fourteen manifolds are preferred, ~0 the first two operating at a manifold pressure of about 200 psig and the remainder at pressures in the range of 400 to 800 psig as described in the specific examples herein.

25 In accordance with this invention, after the hydroentangled web 40 is dried by conventional drying apparatus, not illustrated, the dried web is embossed with matched embossing dies as illustrated in Figs. 4 to 6. An enlarged section of embossed web 40 is 30 illustrated in Fig. 5 in a plan view with an arrow indicating the machine direction of the web. The rows of embossments 4~' are depressed into the upper surface . . .

of the hydroentangled web 40 while alternate rows of embossments 44' are impressed into the web from its opposite side. This type of embossing is known in the art as "perfembossing".

Fig. 4 is a cross-sectional view, greatly enlarged in scale, of the embossed web of Fig. 5 taken along the plane 4-4 of Fig. 5. As illustrated, the impressions from the bosses or "knuckles" of the embossing tool are 10 spaced apart by a distance greater than the width of the boss. This produces a uniform pattern on both sides of the web.

Fig. 6 is a developed cross-sectional view taken along 15 the plane 6-6 of Fig. 5 illustrating the relationships of ~he web and the embossing dies during the process of embossment. For the purpose of simplification and clarity of illustration, the surfaces of the cylindrical embossing rolls 43 and 45 are shown as flat 20 plates 43 and 45. Fig. 6 is in three sections A-A, B-B, and C-C, corresponding to planes A-A, B-B, and C-C
of Fig. 4. The bosses 42 extending downward from the surface 43 of the upper embossing roll form depressions 42' of Figs. 4 and 5 in the upper surface of web 40 25 while the bosses 44 extending upward from the surface 45 of the lower embossing roll form impressions 44' of Figs. 4 and 5 on the lower surface of web 40.

Steel-to-steel matched embossing rolls marketed by 30 Industrial Engraving Company under the trade designation I-8306 are capable of operation to produce the patterns illustrated in Fig. 5. The embossing roll 43 may be provided with continuous raised lands 46 - 11 - 1 3~ 1 351 interconnecting bosses 42, and embossing roll 45 may be provided with continuous raised lands 4B
interconnecting bosses 44.
..
5 Embossment of the hydroentangled web 40 in this manner improves absorbency and appearance of the finished product and greatly improves the hand of the fabric as demonstrated in Examples 7 and 8, herein below.

In this example, a 2/1 twill, 31 x 25 mesh, polyethylene terephthalate (PET) screen from National 15 Wire Fabric Corporation having a warp diameter of 0.0199 inch and a shute diameter o~ 0.0197 inch with an open area of 22.9 percent and an air permeability of 590 cubic eet per minute is used as the carrier belt for the hyaroentanglement operation.
A wet laid 3.8 oz./s~. yd. (79 lb./ream) web is prepared from a mixture of 60 weight percent long fiber northern softwood kraft pulp and 40 weight percent of 1.5 denier by three-quarter inch polyethylene 25 terephthalate (PET) staple fibers. The web is passed at a speed of 240 ft./min. under water jets from a manifold provided with a row of 0.005 inch diameter orifices spaced 0.025 inch apart extending across the full width of the web. The fibers in the web are 30 hydroentangled by subjecting them to two passes under the rows of water jets operating at a manifold pressure of 200 psig (1380 KPa), four passes at a manifold pressure of 400 psig (2760 KPa), and eiqht passes at a mani~old pressure of 800 psig (5520 KPa).

Properties of the resulting hard finished nonwoven fabric produced in this example are shown in the 5 accornpanying Table I (Specimen A) in comparison with the properties of several commercially available products including the conventional "huck" (huckaback) cotton towels.

TABLE I
SPECIMEN A B ~l) C (2) D (3) B~sis Weight (oz/sq yd) 3.8 3.1 2.25 7.8 Thickness (mils) 35 25 18 57 Grab Tensile (lb) MD Wet 19 6 5 97 CD Wet 19 5 5 82 Grab Elongation (~) MD Wet 90 25 34 34 CD Wet 100 50 26 26 Elmendor~ Tear (g) MD Wet 1600 200 80 4000 CD Wet 1900 220 50 4000 Absorption Capacity (g/g) 6.2 4.2 3.6 3.2 Area C~pacity (g/m ) 850 450 280 936 Wicking Rate (g/g/sec)X 1000 38.7 29.9 26.8 16.8 Bulk Density ~cc/g) 8.2 6.1 5.8 4.8 Flammability (sec) NFPA-702 - MD - 6.5 5.5 4.3 16.8 - CD 7.4 6.5 4.4 25.6 J ~ 25 (1) Sample B is a hydroentangled 100% rayon fiber towel containing a latex binder sold under the trade name J&J Surgisorb, by Johnson & Johnson, New Brunswick, New Jersey.
(2) S~mple C is a scrim reinforced tissue product having two to four plies of wood cellulose tissue rein~orced by an internal web of synthetic fiber sold under the trade name Kaycel by Kimberly Clark Corporation of Neenah, Wisconsin.
(3) Sample D is a generic huckaback woven cotton towel.

. ~ 35 It will be evident from the foregoing example that the nonwoven fabric of this invention (Sample A) provides superior absorption capacity as compared with conventional huckaback woven cotton towels (Sample D) and currently available non-woven fabrics represented by Samples B and C. The absorption capacity of Sample A of our nonwoven fabric is twice that of the huck towel, on a weight basis while the nonwoven fabric is approximately 50~ lighter in basis weight. Even at the lower basis weight, the fluid area capacity of the nonwoven fabric (Sample A) compares favorably with that of the huck towel (Sample D).

In these examples, fabrics are produced by forming wet-laid webs of varying fiber compositions and subjecting the ~e~laid webs to the conditions described in Example 1. The forming screen in Examples 2 and 3 is the same as that of Example 1. In Example 4, the forming screen is made up of PET fibers with a warp diameter of 0.024 inch and a shute diameter of 0.028 inch and an air permeability of 555 cfm. The forming screen of Example 5 is made up of PET fibers with a warp diameter of 0.042 inch, and shute diameter of 0.049 inch.

In Examples 2 and 3, the fabric is made up from four layers of preformed and dried wet-laid substrate webs as illustrated in Fig. 1 of the dra~7ings. The PET
component of Examples 2 and 3 is three-quarters inch, 1.5 denier staple fibers; in Examples 4 and 5, the PET
fibers are three-quarters inch by 1.2 denier. In l~t 135t Examples 4 and 5, the fabric is made ~p from two layers of preformed and dried wet-laid substrate webs.

Physical properties of the finished fabrics are shown 5 in Table II. The data from Specimen A of Example 1 are repeated for comparison purposes.

" - 16 - 131 1351 ``
. . .
mAB L E I I
SPECIMEN A E F G H
EXAklPL~ 1 2 3 4 5_ Fiber Composition 5~wt. %) Pulp 60 50 75 60 60 ,' PET 40 50 25 40 40 Forming Screen Mesh (per in) 31x2431x25 31x25 22x23 20~16 Twill 2/1 2/1 2/1 2/1 2/1 Basis Weight 10toz/sq yd) 3.8 3.8 3.8 3.8 3.8 Thickness (mils) 35 27 38 44 48 Peak Grab Tensile Dry(lbs) MD 42.3 25.0 32.0 40.5 41.7 CD 39.6 16.0 22.0 40.7 35.3 15Wet(lbs) MD 19 12.0 14.0 26.5 22.6 CD 19 6.0 10.0 26.4 22.9 Peak Grab Elongation Dry(~) MD 39.3 53.1 47.8 57.3 53.3 CD 48.2 94.5 66.3 62.4 71.7 Dry(%) MD 90 81.9 54.5 79.8 86.7 20CD 100102.6 107.4 85.4 98.9 Slemndor Tear Dry(g) MD 1470 1100 950 1650 1633 Wet(g) MD 1600 1100 950 2733 3800 25 Mullen Burst (p5i) 122 63 68 87 93 Air Permeability (cfm) - 230 98 223 248 Absorptive Capacity (g/g) 6.2 7.2 5.97 7.55 7.57 ~P Y
(g/m ) 850 802 802 866 833 Wicking Rate (g/g/sec)X 1000 38.7 46.6 32.9 20.78 34.45 Flammability (sec) MD 6.5 4.2 5.2 7.6 9.4 NFPA-702 CD 7.4 5.3 5.7 7.4 11.0 - 17 - 13~13~1 A fabric is made up from a wet-laid web composed of 60 weight percent cotton linters and 40 weight percent 5 three-quarter inch by 1.2 denier polyethylene terephthalate (PET)..staple fibers on the forming screen and under the conditions described in Example 1.

Physical properties of the product are listed in Table 10 III.

TABL~ III
Example 6 Basis Weight (oz/yd2) 4.9 5 Thickness (mils) 43.6 Peak Grab Tensile Wet(lb) MD 21.3 CD 2~.0 Peak Grab Elongation Wet(%) MD 84.5 10CD 83.1 Elmendorf Tear Wet(g) MD 3100 ~bsorption Capacity (g/g) -- 5.59 Wicking Rate (g/g/sec)X 1000 7.34 ~rea Capacity (g/m2) 85 Flammability (sec) NFP~-702 MD 10.9 20CD 9.2 In the following examples, nonwoven hydroentangled fabrics were produced from wet laid webs,dried and embossed between steel-to-steel matched embossing 25 rolls. The matched steel rolls supplied by Industrial Engraving Co. were-provided with an elongate hexagonal protuberances or knuckles as illustrated in Fig. 4. In these examples, the embossing rolls were adjusted to produce a center float half step perforation pattern as 30illustrated in Fig. 5. The knuckles on each of the embossing rolls have an overall lonyitudinal base dimension in the machine direction of 0.114 inch, a base width in the cross machine direction of 0.030 131 t351 inch, a height of 0.046 inch, a machine direction spacing of 0.029 inch, and a spacing of 0.148 inch in the cross machine direction. The sides of the knuckles have a slope of 3 from the vertical plane or radius of 5 the roll; the slope of the end of a knuckle is 25 relative to the vertical or radius of the roll.

ExamPle 7 In this example, a nonwoven fabric is produced by 10 forming a wet-laid substrate (95 lb./ream) of 60%
Northern softwood kraft and 40% of three-quarter inch by 1.5 denier PET staple fiber. The forming screen in this example is the same as that of Example 1. The web was subjected to two passes under the rows of water 15 jets operating at a manifold pressure of 200 psig (1380) KPa), ~our passes at a manifold pressure of 800 psig (5520 KPa) and 4 passes at 1600 psig (11040 KPa) affecting intimate entanglement of the wood fibers and staple fibers.
The web was then dried and embossed with matched (Industrial Engraving I-8306) steel-to-steel embossing rolls. We used two levels of penetration of either 25 of 50 mils and the rolls were set either at a side 25 contact or center float for both full or half step perforating condition. Absorbent properties of the resulting finished nonwoven fabric produced in this example are shown in Table IV.

-~31 1351 TABLE IV
SPECIMEN J (unembossed) K (embossed) EX~MPLE 6 7 Fiber Composition Pulp (w~ %) 60 60 PET (wt %) 40 40 Basis Weight (oz/sq yd) 4.68 4.75 (g/sq m) 158.9 161.3 Bulk*
(cc/g) 5.0 6.9 Absorptive capacity (g/g~ 4.29 4.69 (g/m ) 682 75 Initial Wicking Rate (g/g/sec)X 1000 5.1 9.8 Absorption Time (sec) *Measured under 7 g/cm2 con~ining pressure.

ExamPle 8 A wet laid web having a basis weight of 3.8 ounces per square yar~, as in Example 1, was prepared and dried and then hydroentangled at a speed of 40 feet per 25 minute under two rows of wAter jet operating at a manifold pressure of ~00 psig, two rows at 900 psig, and one row at 1200 psig followed by two rows at 400 psig on the reverse side of t-he fabric. After drying, the hydroentangled fabric was embossed at 40 feet per 30 minute with the pattern illustrated in Fig. 5 at 50 mils penetration. Properties of the embossed and unembossed webs are set forth in Table V.

TABLE V
SPECIMEN L (unembossed) M (embossed) Basis ~eight (g/~l ) 127 127 (oz/yd2) 3.74 3-74 Dry Bulk (Load = 7 g/cm2) (cc/g) 6.1 10.5 Wet Bulk (Load = 7 g/cm2) (cc/g) 5.8 9.5 Wet Bulk Under Load (cc/g) 4.6 6.4 (Load = 100 g/cm2) Wet Bulk After Load Removal ~cc/g) 5.4 7.8 Wet Bulk Recovery After ~emoval of Load (%) 17 22 Absorption capacity (g/9) 5 6.7 20 Area capacity (g/m2) 635 850 Softness (Loop Test)*

CD ............ 25 5 ; Softness (Sensory)** 65 82 25 Hand Crush (Sensory)** 55 87 *Lower number = softer end product.
**~igher number = softer end product.

30 With reference to Table 5, it will be observed that embossment improved the dry bulk (measured under 7 g/cm2 confining pressure) of the product was improved by 70 percent. The first value is the bulk of the 13~ 1351 - 2~ -specimen after absorption of water under a load of 7 g/cm2. The second value is determined after placing a load of lO0 g/cm2 on the wet specimen and the final value is determined after removal of the load. The wet 3 5 bulk recovery, reported in percent, is calculated from the wet bulk under load and the wet bulk after removal of the load. The wet bulk recovery of the specimens shows that the embossed specimen has the greater resilience. It can be observed that the absorbency per 10 square meter of the product, related to its resilience, increased by more than 33 percent.

Softness of the specimens was measured by the so-called Loop Method and by a sensory softness test panel. The 15 Loop Test Method is designed for determining the softness of flexible sheet materials by measuring the force required to cause a specimen, which was previously formed into a loop and held in a specimen holder, to buckle. In this test, if the treated 20 specimen re~uires a lower force to bend than untreated specimen, then that specimen is softer. At least five specimens 88.9 mm X 25.4 mm (3.5 in. by 1 in.), in both machine and cross direction are selected ~or testing and the results averaged. These samples (conditioned 25 at 23 degree F and 50~ RH) were tested by the Loop Softness Tester and the result recorded in table V.
The force required to buckle the embossed specimens, for both machine and cross machine directions, is considerably lower than for the unembossed specimens.
30 The softness of this product was also measured by a group of twenty in-house softness panelists. This test result (Table V) also conirmed the results obtained by the Loop Test Method.

As indicated in Table III, embossment of the hydroentangled dry nonwoven web by this method of embossment enhanced the absorption rate and increased the absorption capacity of the web. In addition, the 5 apparent bulk, softness and hand of the product was comparable to that of the huck towel of Example l.

From the foregoing examples, it will be seen that the nonwoven fabric of Example l, Specimen A of Table I, ` 10 compares favorably with that produced in Example 5, particularly with respect to wicking rate, area capacity and absorption capacity.

In the foregoing examples, the Elmendorf tear strength, 15 reported in grams is determined by repeated tests on an Elmendorf tear tester using single ply test strips.
Thickness, reported in mils, is determined with an Aime~ 212.5 lot tester on a single ply of the specimen.
The absorption capacity in Examples 1 to 3 and 6 to 8 is determined by a fluid absorption test method which measures tne ability of a material to absorb as much fluid as it will hold without being flooded. A
25 material sample is placed over a sintered glass porous plate and liquid from a reservoir is allowed to flow through the plate as it is absorbed by the material undergoing test. The weight of the reservoir is recorded before the test and again after the sample no 30longer absorbs additional fluid and has reached its maximum fluid saturation without flooding. The liquid absorption ratio is calculated and reported as the - 24 - 131 13~t amount of ~luid in grams absorbed per gram of the material sample. Liquid absorption ratio is independent of the sample's actual weight.

5 The wicking rate is a method used to determine the time elapsed in seconds for a liquid to travel 6 centimeters along a vertically suspended 2.5 x 10 cm ~est specimen with the lower end in contact with the liquid. The sample weight is recorded before and after the liquid 10 has reached the six centimeter mark. The vertical wicking rate is reported as the ratio of the liquid weight to sample dry weight divided by the time elapsed in seconds (g of liquid/g dry weight of sample/sec).
This ratio is then multiplied by 526. The test is 15 repeated on specimens cut from the material in both the machine direction and the cross direction and the average is reported.

The method for determining absorbency under load or wet 20 resiliency properties of nonwoven fabrics measures the absorbency of the material under load; specifically, it measures the absorbency capacity of the test specimen after successively increasing the load over the sample in 500 gram weight increments. The test is conducted 25 as described above, and absorption capacity is determined in 500 gram increments from 50 grams to 2500 grams load weight.

Area Capacity is a~aerived number indicating the liquid 30 holding capacity of a sample and is expressed in grams per square meter. Area capacity is calculated by multiplying the absorptive capacity of the test material expressed in grams of liquid per gram of material by the basis weight in grams per square meter.

The Mullen Burst test (ASTM-D3786-802) is used to determine the bursting strength of fabrics and films in 5 a hydraulic diaphragm type bursting tester. The bursting strength i5 .eported in pounds per square inch hydraulic pressure required to rupture a 1.2 inch diameter test specimen by distending it with force applied from one side by a flexible diaphragm of the 10 same ~iameter as that of the specimen.

Grab Tensile and Grab Elongation are measured by ASTM
D1682-64 test method, to determine the load in pounds and elongation in percent at the break point in a 15 constant rate of extension tester.

Flammability is determined by using NFPA Test Method Number 702.

.

Claims (21)

1. A method of making a highly absorbent nonwoven fabric consisting essentially of wood pulp and staple length synthetic fibers which comprises forming a wet-laid web containing a blend of from about 30 to about 80 weight percent wood pulp and 70 to 20 weight percent staple length synthetic fibers basis the dry weight of the fibers, forming a compacted highly absorbent web of entangled fibers by subjecting the fibers in the wet-laid web to hydroentanglement, and drying the hydroentangled web to form said nonwoven fabric.

2. A method as defined in claim 1, wherein the wet-laid web contains 50 to 75 weight percent wood pulp and 25 to 50 weight percent staple length synthetic fibers basis the dry weight of the fibers.

3. A method as defined in claim 1 comprising the further step of embossing the hydroentangled web with a match die pattern at ambient temperature.

4. A method as defined in claim 1 wherein the wet-laid web contains 55 to 65 weight percent wood pulp and 35 to 45 weight percent staple synthetic fibers.

5. A method as defined in claim 1 wherein the length of said staple synthetic fibers is in the range of from about one-half inch (12mm) to about seven-eighths inch (22mm).

6. A method as defined in claim 1 wherein the diameter of the synthetic fiber is in the range of from about .5 to about 3 denier.

7. A method as defined in claim 1 wherein the wet-laid web is subjected to the entanglement action of water jets ejected from 0.005 inch diameter orifices equivalent to at least two passes at a head pressure 200 psig, four passes at 600 psig and eight passes at 800 psig.

8. A method as defined in claim 7 wherein the weight of the nonwoven fabric is in the range of from about three to four ounces per square yard.

9. A method of making a highly absorbent nonwoven fabric consisting essentially of wood pulp and staple synthetic textile fibers free from added binders which comprises laminating a plurality of wet-laid webs each containing a blend of 50 to 75 weight percent wood pulp and 25 to 50 weight percent staple synthetic fibers, and combining said webs into a single compacted highly absorbent web of entangled wood pulp fibers and synthetic fibers by subjecting the laminated webs to hydroentanglement, and drying the hydroentangled web to form a highly absorbent fabric.

10. A highly absorbent nonwoven fabric having a basis weight in the range of three ounces to about eight ounces per square yard free from added binders and consisting essentially of 50 to 75 weight percent wood pulp and 25 to 50 weight percent staple length synthetic fibers uniformly admixed with one another in a wet-laid web and hydroentangled under sufficient energy to form a compact, highly absorbent fabric.

11. A nonwoven fabric according to claim 10 wherein the dry weight ratio of wood pulp to synthetic fibers is in the range of from about 1 to about 3.

12. A nonwoven fabric according to claim 10 wherein the synthetic fiber is a polypropylene fiber.

13. A nonwoven fabric according to claim 10 wherein the synthetic fiber is a nylon fiber.

14. A nonwoven fabric according to claim 10 wherein the synthetic fiber is a polyester fiber.

15. A method of making a nonwoven fabric according to claim 9 wherein the dry weight ratio of wood pulp to synthetic fibers is in the range of from about 1 to about 3.

16. A method of making nonwoven fabric according to claim 9 wherein the synthetic fiber is a polypropylene fiber.

17. A method of making a nonwoven fabric according to claim 9 wherein the synthetic fiber is a nylon fiber.

18. A method of making nonwoven fabric according to claim 9 wherein the synthetic fiber is a polyester fiber.

19. A method of making a nonwoven fabric as defined in claim 9 wherein the dry hydroentangled fabric has a basis weight in the range of from about 3 to about 10 ounces per square yard.

20. A method of making a nonwoven fabric as defined in claim 9 wherein the wet-laid webs are dried prior to lamination.

21. A method of making a nonwoven fabric as defined in claim 20 wherein the wet-laid webs have a basis weight in the range of 1 to 4 ounces per square yard.