DK141636B - Process for producing a fibrous, nonwoven web material with protruding fiber pads. - Google Patents

Description

(11) PRESENTATION 1 U 1 636 DENMARK (51), nt C | 3 D 04 H 13/00 (21) Application No. 141 5/74 (22) Filed on the 14 th. 1974 1¾¾ (23) Lebedsg Mar 14 197 ^ (44) The application made and 1 o «n framiesgelelee published on> ^ · maJ *

DIRECTORATE OF

PATENT AND TRADE MARKET (30) Priority requested from it

Mar. 15-Mar. 1975 # 541699 # US

(71) THE DEXTER CORPORATION, One Elm Street, Windsor Locke, Connecticut, US.

(72) Inventor: Bernard William C onway, 22 Ernest Lane, Holyoke, Massachu® sets # US: James Moran, 10 Surry Circle, Simsbury, Connecticut, US.

(74) Clerk of the case;

International Patent Office. __.

(54) Process for producing a fibrous, nonwoven web material with protruding fiber tufts.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method of producing a fibrous, woven, wet-laid web material having interspersed fiber tufts, which is integral with the ground web and protrudes freely from its surface, wherein a process of suspending a sufficient amount of fibers into an aqueous dispersion medium obtaining a fiber concentration of at least 0.02%, after which the fibers are deposited on a perforated web forming element.

From Danish patent specification 121,602, a method of this kind is known, whereby a fiber web is first manufactured, e.g. by the specified wet laying method, and then the web provides a peat-like surface upon penetration on a porous substrate, thereby drawing fibers out of the web's plane and forming the desired fiber pads. The method is complicated and expensive because of the two successive operations, which require correspondingly different apparatus, and it further has the disadvantage that the needles of the fibers to pull from the web expose the fibers to a strong bending which weakens the fibers. Upon needling, some of the fibers that the needles grasp may be torn loose from the cohesion of the other fibers or even torn, and holes in the web will occur at the places where the fibers are pulled out to form tufts so that the web material as a whole is weakened. Similar disadvantages arise from the technique known from German Patent Specification No. 1,635,555 where a prefabricated nonwoven fiber web is processed with high pressure water jets which pierce the web. Furthermore, this prior art primarily seeks to produce precisely a perforated web, as is also the method known from German Publication No. 1,947,176, in which a fiber slit is squeezed between two double rollers, each consisting of an inner liner for draining water and an outer pattern drum which produces a corresponding pattern of the dewatered web.

The process of the present invention is characterized in that the dispersion medium has a viscosity of at least 3 cps, that each of the web-forming element openings has an area of at least 12 x 10 cm, and that the fiber concentration, viscosity and aperture size are adjusted accordingly. according to the nature, fineness and length of the fibers, that laminar flow is maintained during sec.

the bearing, and that tufts of individual fibers pass through the apertures of the web forming element.

The invention provides the significant advantage that the protruding fiber paws are formed simultaneously with the base web during its dewatering, where the flow of the dispersant through the apertures in the web forming element draws some of the fibers into the apertures. These fibers are thereby oriented substantially perpendicular to the base web, but at the same time retain their adhesion to the fibers in the base web and are not subject to weakening by mechanical machining and heavy bending. The process is simple and quick and can be accomplished with uncomplicated equipment. The laminar flow is important to achieve the fiber orientation of the protruding tufts and to avoid tearing fibers from the base web. The substantially increased area of the apertures, compared to standard Fourdrinier wires, is also essential to enable the fibers to be pulled out to form individual corrugated fiber tufts which provide the desired fullness and grip. The use of a dispersion medium of higher viscosity than water limits the tendency of the dispersed fibers to filter and enables processing of relatively short fibers and / or fibers which are not normally used in wet paper making.

The viscous medium also keeps the fibers slurried during drainage and promotes uniform fiber distribution in the finished web.

In this connection it is noted that from Danish patent specification no.

123,785 and U.S. Patent No. 2,626,214, it is known that the addition of viscosity enhancing agents to the dispersing medium by wet-forming conventional nonwoven fibrous webs may have a beneficial effect on the quality of the dispersion of the fibers and on the interconnection of the fibers.

For most applications, the average area of the openings in the -4 2 web forming element will conveniently be between 18.75 x 10 cm and / 0 125 x 10 6 cm. It will be appreciated that the openings must not be larger than that they can retain substantially all of the fibers which are drawn into them upon draining of the dispersing medium.

The optimum viscosity of the dispersing medium will usually be between 10 and 300 cps. A high viscosity can adversely affect the drainage of the medium, and if the viscosity is 50 cps or more, it is appropriate that during the deposition of the fiber slurry on one side of the web forming element, a negative pressure is provided on the opposite side of the element.

In a preferred embodiment, the dispersion medium is a waxy solution of a plastic material and the fibers are synthetic fibers having a titer of at least 1.0 dpf (denier per filament) and a length between 0.32 cm and 2.54 cm. Aqueous solutions of high molecular weight polymers are well suited for controlling the viscosity of the dispersant, which should generally be higher at higher titers of the fibrous material.

The optimum value of the fiber concentration will in most cases be in the range of 0.05% to 0.5%, whereby one should generally choose the lowest concentration compatible with flawless release of the finished web from the web forming element.

The invention will now be explained in more detail by way of example and with reference to the schematic drawing, in which FIG. 1 is a process diagram of some of the steps which form part of an embodiment of the method according to the invention; FIG. 2 illustrates the gradual formation of the web material by the method; FIG. 3 is a photograph of the surface of the fabric of the fabric being enlarged approx. ten times, and FIG. 4 is a photograph of a section through the web material at substantially the same magnification as FIG. Third

FIG. 1 illustrates quite schematically the process of slurrying fibers in a dispersed medium with controlled viscosity and depositing the fiber slurry on a perforated, relatively coarse web forming element, thereby forming a fibrous web material with separate fiber tufts projecting from the surface of the web material perpendicular to this as the dispersing medium is drained through the openings in the web forming element.

In FIG. 3 and 4, it is seen that a web material prepared by the method according to the invention has a characteristic surface which differs substantially from known nonwoven materials with floral loops or with a rough surface produced by brushing. Instead, the material has highly concentrated separate fiber webs that protrude outward from the fibrous base web. The free ends of each tot's fibers lie at random and different distances from the base web. Despite this, the tufts have a somewhat tapered appearance with their greatest length at the middle of the tufts. As best seen in FIG. 3, the long tufts tend to assume wave form and to rest loosely on the surface of the base web. Since each tot is composed of many closely related fiber bundles, although each fiber is essentially unidirectional and relatively independent of the other fibers in the tot, the tots have a substantial flexibility, flexibility and softness which provides fullness and absorbency to the web material. Unlike tufts made by perforating a base web, the fibers in the tufts are not substantially bent or scattered, and the tufts do not exhibit a pronounced central empty space or hole. As will be understood from the following explanation, the number of fibers in each tot and the concentration of the tots will vary mainly depending on the process conditions used in the preparation of the web material.

The most important factor in the process is the generation of a suitable fluid flow through the web forming element at the time the fibers are deposited on the element and begin to form into the nonwoven web. It is particularly important to maintain laminar flow through the web forming element, but it is also important that a relatively coarse web forming element is used, e.g. a wire screen or perforated plate having larger apertures and intermediate regions than a standard Fourdrinier wire, and a suitably high viscosity of the fiber dispersion used. Other factors related to the above essential factors will also affect the manufacturing process. Such factors include: the fiber concentration in the dispersion, the underpressure optionally used to remove the dispersing medium, the type and composition of the fibers, and their denier and length.

As a web forming element, sieves or wires made of twisted metal or plastic wires and having wire thicknesses of at least 0.030 cm, preferably within the range of 0.045 to 0.089 cm, can be used to provide drain openings with an average area of approx. 2-60 times the normal area of the openings in a Fourdrinier wire. It is to be understood that the exact nature and size of the wire used will vary depending on the desired product, the nature, denier and length of the fiber, the concentration of the raw material, and the viscosity of the dispersing medium and the size of the underpressure which used during the runway making. The open and coarse wires provide a wavy web shape and wavy tufts, which also affect the finished material's fullness, grip, draping ability and appearance. However, the area of the openings in the wire should not be so large that the fibers in the fiber dispersion are not retained by the wire, and the intermediate solid areas should not be so large as to affect the dewatering of the fiber 5 dispersion. The optimum size is large enough to allow the necessary fluid flow during dewatering and small enough to allow the necessary retention of fibers as the dispersing medium runs rapidly through the wire.

As a web forming element, alternatively, a nonwoven or woven web of textile fibers may be used which is embedded in the nonwoven web material formed on the web. Such an arrangement will substantially strengthen the material without compromising its softness.

Some typical examples of woven web forming elements are given in the table on the next page. In general, the size of the orifice area will be proportional to the fiber diameter, since thicker fibers form tufts most efficiently using coarse large-mesh elements. For most applications, a -4 -4 2 average opening area is preferred between approx. 18.75 x 10 and 125 x 10 cm, the size of the area may vary depending on other parameters in the process.

The use of a dispersing medium of higher viscosity than water allows processing of numerous fibers and blends of fibers not heretofore used in wet paper making, including blends of textile stack fibers with fibers having a substantially shorter length. The viscous dispersion medium prevents the formation of fiber clumps in the dispersion and reduces the tendency of the dispersed fibers to filter. In addition, the medium maintains the fibers in their slurry state during drainage and ensures a more uniform fiber distribution in the finished web material, providing better softness, flexibility and draping properties of the fabric produced. At present, only dispersions in which all the fibers are very short hardwood fibers are unusable, and this is primarily due only to the opening areas being too large in relation to the short fibers.

On the other hand, the dispersing medium will allow the use of 100% natural or synthetic papermaking or textile table fibers or suitable mixtures thereof.

Although it is possible to achieve some formation of fiber pads already at a viscosity of approx. 3 centipoise, when other process properties are appropriately controlled, and with certain fibers, a viscosity above 10 centipoise is required to achieve truly good results. A viscosity of 30 centipoise or more gives the best results. In practice, the viscosity can be as high as 250-300 centipoise. However, it will be appreciated that very high viscosities can impair the drainage properties of the web forming element. Other factors affecting viscosity selection are the underpressure available to remove the dispersing medium without bursting the web, the ability to recover the medium, the effect of the residual media remaining in the web, and the economy.

The viscosity controlling material in the dispersing medium may be a natural or synthetic material or mixtures thereof, preferably high molecular weight resins, for example, water-soluble polymers made from polystyrene-6 1A16-3 6 Φ μ cd oj

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As mentioned, the web forming element used and the viscosity of the dispersing medium will depend on other interrelated factors including the nature, denier and length of the fibers. By the method of the invention, web materials of a wide variety of natural, synthetic paper making and textile fibers can be made. Eg. For example, synthetic or artificially made papermaking or textile staple fibers, including rayon, nylon, polyester or vinyl polymer or copolymer fibers, can be used either alone or in combination with natural fibers, e.g. bleached or unbleached kraft paper, manila, hemp, jute and similar papermaking fibers. In addition, inorganic fibers, for example glass, quartz, ceramics, mineral wool, asbestos and similar materials can also be processed by the process of the invention.

The synthetic fibers can vary in both denier and length, although small denier fibers are generally preferred. Fibers from approx. 1 denier per filament (dpf) tilca. 15 dpf and more have been used successfully. For higher denier fibers, it is usually necessary to use a smaller fiber concentration and a slightly viscous dispersing medium. It can be seen that the minimum and maximum denier that can be used will depend on many other relevant factors, including the requirements of the product, the operating condition of the machinery, the opening area of the web forming element, etc.

The length of the synthetic fibers used depends to a large extent on the particular wire used, and will be in a range of approx. 0.31 cm up to several centimeters. The fibers may be of the straight cut type of paper used for papermaking, or the wrinkled or uncrossed textile staple fiber type. Finer denier material preferably has a length of approx. 1.25-1.90 cm or more to give the material more softness while achieving the desired fullness and absorbency. However, mixtures of natural and synthetic papermaking fibers with lengths down to '0.16 cm or less can also be used depending on the particular properties desired by the finished product.

In addition to the length and denier of the fibers, the fiber concentration in the dispersion requires appropriate control. In general, the lowest fiber concentration, which can be combined with a good solution of the finished product from the web forming element, gives the best formation of fiber tufts. Therefore, a fiber concentration in the range of approx. 0.02% - approx. 1.0% is used with a preferred range of approx. 0.05% to 0.5% fiber concentration. In standard laboratory processes, it has been found that a fiber concentration of approx. 0.1% gives uniformly good results.

The fiber concentration and viscosity of the dispersing medium will also affect the size of the underpressure to be exerted on the underside of the web forming element to provide the desired tooth formation. Although it is possible to operate without suppression under suitable conditions, it is generally preferred to maintain an underpressure on the underside of the web forming element to ensure an adequate fluid flow. However, these parameters will depend not only on the fiber concentration and on the viscosity of the dispersing medium, but also on other factors, including the size of the web forming apertures and the type and length of the fibers used.

Another factor to consider is the desired weight of the material to be produced. It is possible to make a web material with a weight as low as 8.5 g / m. However, such lightweight materials require very fine control of the other factors in the process and the basis weight of most 2 materials is 34 g / m or more.

The formation of the fiber tufts begins simultaneously with the web formation, and it is believed that the tufts are the first to form when the fibers lie on top of the massive sections of the web forming element and are drawn through the intermediate openings due to the flow of liquid through the openings. This is illustrated in FIG.

2. As the web grows in thickness, fibers are deposited both in the tufts and in the ground web until the desired base weight and strength of the web are achieved. If the deposition of fibers was completed already after the actual forming, the fibrous material would have only very little strength and would not have the character of a web and could not be removed from the web forming element. On the other hand, it is found that as soon as the basic weight exceeds approx. 204 g / m, only a few or none of the later deposited fibers will participate in the formation of tufts. Instead, they will simply form a mat on top of the ground web with little or no fiber connection to their tufts.

It is generally found that the best results are obtained by using a dispersant medium with the highest possible viscosity compatible with the operation of the machine, the minimum fiber concentration which can be combined with a good dissolution of the web material from the web forming element and the smallest fiber denier which is acceptable based on the requirements of the product. It has further been found that longer fibers not only produce longer tufts but also help to loosen the web material because a stronger web is produced. It has been found that coarse wires produce better tufts than fine wires and that lower denier fibers provide better toting than higher denier fibers regardless of the length of the fibers.

In this connection, and as mentioned above, fibers with larger denier generally require a coarser wire, higher viscosity and lower fiber concentration than similar fibers of finer denier. Eg. for example, a 1.5 dpf fiber will provide an acceptable product at a viscosity of 50 cps and a fiber concentration of approx. 0.2%, whereas similar results with a 15 dpf fiber material can only be obtained at a viscosity of 150 cps and a concentration of 0.1%. It should also be noted that the lower limit of the basis weight of the web fabric produced will vary with the coarseness of the wire used, so that a lower basis weight material can be obtained with a finer wire than with a coarser wire.

As shown in FIG. 2 only tufts are formed on one side of the base web, but products with tufts on both sides can easily be made by attaching two webs to each other with back to back.

For a better understanding of the invention, the following is explained in greater detail by means of some particular examples.

EXAMPLE I

A fiber dispersing medium having a viscosity of 150 cps was prepared as a 0.15% aqueous solution of a water-soluble polyacrylamide. A sufficient amount of 1.9 cm long, 15 dpf rayon stack fibers was fed to the viscous medium to produce a 0.1% fiber dispersion. The fiber dispersion was poured into a hand mold with a 0.71 x 1.19 mm sieve of twisted bronze wire with an average ^ 2 * "= * hole area of 50.8 x 10 cm and drained by means of a vacuum. fibrous product had a basis weight of 86.7 g / m.

EXAMPLE II

With the general procedure of Example I, a 0.1% fiber dispersion was made from 1.9 cm long, 1.5 denier rayon table fibers dispersed in a 50-cps polyacrylamide solution. The fiber dispersion was poured into a hand mold. with a 1.19 x 1.19 mm regular polyester tissue with an average opening area of approx. 76.25 x 10 cm. The underside of the wire was subjected to vacuum and a nonwoven web material was made at a basis weight of 86 g / m.

EXAMPLE III

The procedure of Example II was repeated using a 0.05% fiber dispersion of 70% 0.95 cm long, 1.5 denier rayon stack fiber and 30% Weyerhauser Kraft in a 25 cps polyacrylamide solution. The finished web material had a basis weight of 81.6 g / m.

EXAMPLE IV

A 0.12% fiber dispersion was made from 1.12 cm long, 1.5 denier rayon stack fibers dispersed in a karaya rubber solution having a viscosity of 40 cps.

141636 ίο

The fiber dispersion was poured into a hand mold with a 1.19 x 1.19 mm polyester wire as in Example II, and the underside of the wire was subjected to vacuum to promote the flow of the dispersing medium. The basic weight of the product was 224.4 g / m2.

EXAMPLE V

A 1.9 cm long, 1.5 denier rayon stack fiber dispersion was prepared in an aqueous solution of a 50 cps polyacrylamide viscosity and charged to the feed container of a papermaking machine at a 0.2% fiber concentration. The machine had a beveled 0.71 x 1.00 mm twisted bronze wire with an average aperture of approx. 44.37 x 10 cm. The dispersion was applied to the papermaking machine without change in viscosity and the drainage was supported by vacuum. The resulting product had a basis weight of 96.9 g / m 2.

This example was repeated with a 1.19 x 1.19 mm regular polyester fabric wire as in Example II and also resulted in a nonwoven web material with well-formed tufts.

EXAMPLE VI

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As an example of the increased viscosity required when using a larger denier and stiffer fibers, the fibers listed below were dispersed in a solution of the indicated viscosity. In each case, a tufted product was produced which had excellent fullness, draping ability and grip in comparison with textile products.

Fiber Denier Length (cm) Wife. viscosity

Glass 9 * 2.54 0.03% 250 cps

Rayon 15.0 dpf 1.9 0.05% 150 cps

Rayon 5.5 dpf 1.25 0.1% 100 cps

Rayon 3.0 dpf 1.25 0.1% 50 cps

Rayon 1.5 dpf 1.25 0.25% 12 cps

Rayon 1.5 dpf 1.9 0.1% 3 cps

H

Diameter in ym.

EXAMPLE VII

The procedure of Example I was repeated using 1.5 denier and 0.48 cm length rayon stack fibers and 3 denier and 3.81 cm length nylon fibers. In both cases, the web fabric produced had the desired properties and the longer nylon fibers produced tufts of substantially greater length than the shorter rayon fibers.

Claims (5)

EXAMPLE VIII The procedure of Example I was repeated using 1.5 denier and 1.9 cm length rayon fibers and a dispersion having a viscosity of 100 cps. The fiber concentration was 0.1% and webs having basis weights ranging from 20.3 to 306 g / m 2 were prepared. Among the numerous applications for nonwoven web materials made according to the invention are disposable articles such as washcloths, dishcloths, towels, facial tissues, sanitary napkins, dressings, robes and other disposable garments. Furthermore, it can be used as filter material, packaging material, for linings and inserts in garments and as substrates in laminate materials, e.g. for lamp shades or upholstery fabric. A method of producing a fibrous, nonwoven, wet-laid web material with spaced apart fiber tufts, which protrudes into the St with the base web and protrudes freely from its surface, by which a sufficient amount of fiber is suspended in an aqueous dispersion medium. obtaining a fiber concentration of at least 0.02%, after which the fibers are deposited on a perforated web forming element, characterized in that the dispersion medium has a viscosity of at least 3 cps, that each of the web forming element openings has an area of at least 12 x 10 4 cm 2 and that fiber concentration, viscosity, and aperture size are so adjusted to each other and to the nature, fineness and length of the fibers, that laminar flow is maintained during deposition and that tufts of individual fibers pass through the apertures in the web forming element. Method according to claim 1, characterized in that the average area of the openings in the web forming element is between 18.75 x 10 4 2 -4 2 cm and 125 x 10 cm. Process according to claim 1 or 2, characterized in that the viscosity of the dispersant is between 10 cps and 300 cps. Method according to claim 3, wherein the viscosity of the dispersant is at least 50 cps, characterized in that during the deposition of the fiber slurry on one side of the web forming element, a negative pressure is provided on the opposite side of the element. Process according to any one of claims 1-4, characterized in that the dispersing medium is an aqueous solution of a plastic material and that the fibers are synthetic fibers having a titer of at least 1.0 dpf and a length between 0.32 cm and 2. 54 cm.