EP0171807A2

EP0171807A2 - An entangled nonwoven fabric with thermoplastic fibers on its surface and the method of making same

Info

Publication number: EP0171807A2
Application number: EP85110212A
Authority: EP
Inventors: Alfred T. Mays
Original assignee: Chicopee Inc; McNeil PPC Inc
Current assignee: Johnson and Johnson Consumer Inc
Priority date: 1984-08-16
Filing date: 1985-08-14
Publication date: 1986-02-19
Anticipated expiration: 2005-08-14
Also published as: NZ212999A; BR8503891A; EP0171807A3; DE3586931T2; AU4624385A; ZA856209B; DE3586931D1; ATE84083T1; AU576618B2; EP0171807B1

Abstract

There is disclosed an entangled nonwoven fabric having a layer of fusible fibers on one or both surfaces of a relatively thick layer of base fibers. The fusible fibers are either homofil or conjugate fibers having an exposed low melting point component which have a lower melting temperature than the base fibers. The thermoplastic fibers are located on the outer surface of the base fibers either prior to or subsequent to the entangling of the fibers. The mixture of base and thermoplastic fibers are then heated to a temperature to heat fuse the homofil fibers or the low melting point component of the conjugate fibers.

Description

Technical Field of the Invention

This invention relates to a thermal bonded, nonwoven fabric comprising base fibers and thermoplastic fusible fibers such as low melt polyester or conjugate fibers disposed on one or both surfaces thereof, which fusible fibers form thermobonds at temperatures substantially below the melting and softening temperature of the base fibers; and to a method of making said nonwoven fabric.

Background of the Invention

It is well known in the art to form entangled nonwoven fabrics by passing jets of liquid through a loose assemblage of fibers. Such fabrics have been used for a variety of products including towels, wipes, covers for absorbent products, such as disposable diapers, and other similar applications. The strength and durability of entangled fabrics depends on the level or degree of entanglement of the fibers which, in turn, depends on the level of fluid pressure used to entangle the fibers and the total amount of energy used in the entangling process. High fabric strength in an entangled fabric requires very high energy input and, hence, is very expensive. In addition without a large energy input, these fabrics while satisfactory for many uses tend to pill and fray, with the result that there may be linting and fiber loss and lack of durability after repeated uses and machine washing. These undesirable effects are a result of poor surface tie-down of the fibers of the entangled web. Pilling and fraying is most pronounced at the surface of the entangled fabric opposite the surface against which the jets of liquid are applied, and it would be most desirable to tie down the fiber at that surface with greater tenacity to prevent fiber loss.
Prior art attempts to solve the pilling and fraying problems associated with entangled fiber fabrics have primarily centered around the utilization of an extraneous binder to supplement the mechanical bonding resulting from the interfiber frictional engagement attributable to the entanglement process. However, presently available binders suitable for this purpose introduce undesirable properties into the entangled fabric such as harshness and reduced hand and drape. Furthermore, such binders also make the resulting fabrics unsuitable for certain medical and surgical applications, such as for wound dressings. In addition, extraneous binder material will fill the interfiber spaces of a fabric, altering its capillarity and total absorbency.
Fusible fibers have been used for overall reinforcement of an entangled fabric. U.S. Patent No. 3,485,706, in Example 66, describes the formation of a multilayered entangled fabric having a 1.6 oz./yd. center or reinforcing layer containing thermoplastic fibers and two 0.6 oz.,Lyd.² webs of staple length polyethylene terephthalate on either side thereof. The center or reinforcing layer comprises 88 percent continuous filament polyethylene terephthalate fibers and 12 percent of a continuous filament copolymer fiber made of 20 percent polyethylene isophthalate and 80 percent polyethylene isophthalate. After entangling, the fabric has an abrasion resistance (measure in minutes to hole formation) of 1. The fabric is then heated at 230°C for 2 minutes at 200 psi to fuse the copolymer fiber. The resultant fabric has an abrasion resistance of 15 minutes to hole formation. However, this does not relate directly to surface abrasion resistance, and does not indicate good surface tie-down of the fibers, or a lack of pilling and fraying. In addition, from the thermobonding conditions recited, the fusible fiber is totally melted, loosing all fiber identity which alters the initial fibrous structure and results in a harsh feel. U.S. Patent 3,494,821, in Example XIV, discloses an entangled fabric formed from a 1.9 oz./yd.² reinforcing layer of 88 percent continuous filament polyethylene terephthalate fibers and 12 percent continuous filament copolymer fibers of 80 percent polyethylene terephthalate and 20 percent polyethylene isophthalate, and a single 1.5 oz./yd.² layer of staple length polyethylene terephthalate fibers. After entangling, the fabric is heated to 230°C for 20 seconds under 0.5 psi to fuse the copolymer fibers. No abrasion resistance is recited.
In both of the next above cited fabrics, the overall fabric structure and, hence, the performance characteristics are substantially affected by the use of a high percentage of continuous filament fibers in the reinforcing layer, and the initial formation using, but subsequent meeting of a relatively high amount of fusible fibers. Again, though reinforcement and abrasion resistance in terms of minutes to hole formation are shown, there is no recitation of surface tie-down of the fibers and no apparent effort to achieve surface tie-down with a minimum of effect on the overall fabric structure and performance characteristics.
Fusible fibers have also been used as a surface layer for a layer of carded fibers. The Tendersorb surgical dressing sponge manufactured by Kendall has heat fused polyester surface layers surrounding a center ply of carded rayon and polyester fibers. The dressing sponge suffers from undue linting of fibers.

Summary of the Invention

In accordance with the present invention, there is provided on one or both surfaces of an entangled fiber web a thin layer of thermoplastic fusible fibers. The major fiber constituent of the fabric of the present invention, hereinafter referred to as "base fibers" includes any fiber that is capable of being formed into an entangled fabric. Examples of such fibers are polyester, nylon, cotton, or other natural or synthetic fibers. Upon subsequent heating, the fusible fibers are thermobonded creating a thermobonded entangled network of fusible fibers and base fibers at the surface of the fabric. This surface network provides a fabric with enhanced surface tie-down of fibers achieved with a relatively low level of entangling in the overall fabric and at little increase in cost, and without substantially effecting the fabric characteristics of the base layer.
Thermoplastic fusible fibers suitable for use in the present invention include polyolefin fibers having a melting temperature in the range of about 163-171°C. The term "polyolefin fibers" as used herein and in the appended claims, refers to manufactured fibers in which the fiber-forming substance is any long chain synthetic polymer comprised of at least 85 percent by weight of ethylene, propylene, or other olefin units, except amorphous (non-crystalline) polyolefins qualifying as rubber. It is, of course, within the scope of this invention to use other thermoplastic fusible fibers so long as they have a thermobonding temperature significantly less than the base fibers. An example of such other thermoplastic fusible fibers is a low melt polyester fiber.
However, while fusible fibers of the type referred to above provide a significant improvement in the fabric to accomplish the desired results, a still further improvement is obtained by using conjugate fibers. When using conjugate fibers, the integrity of the fibers can be maintained through many varieties of heat treatment, which has many obvious advantages. The conjugate fibers have an exposed low melting point component that is melted and fused to adjacent conjugate fibers and base fibers to provide enhanced surface abrasion and reduce the linting, pilling or fraying of the surface fibers.
The base fibers are of staple length and in excess of 1/4 inch in length and normally from about 1/2 inch to about 2 inches or longer in length. Typical base fibers that can be used are polyester and Nylon 6, which have melting temperatures in the range of about 250-288°C and about 213-221°C, respectively, which melting temperatures are significantly greater than the polyolefin fibers referred to above. The denier of the fibers should be such as to allow bending of the fibers and should be on the order of about 1 to 6 denier, with the preferred range being from about 1-1/2 to 3-1/2 denier.
In the method and fabric of the present invention, the fusible fibers may be disposed on one or both surfaces of a layer of base fibers, which layer of fusible fibers can be added either prior or subsequent to the entangling of the base fibers. In subsequent heating, e.g., by hot calendering, the fusible fibers are thermobonded to each other at their _'points of intersection or tangency.
In the most preferred embodiment, a web of base fibers such as polyester is formed with a thin layer of fusible fibers such as sheath/core polyethylene/polyester conjugate fibers on one or both surfaces thereof. The web of base and thermoplastic fibers is then entangled to provide interfiber frictional bonds. Where only one outer surface of the finished fabric is to be strengthened by the addition of fusible fibers, the fusible fibers are disposed on the side opposite to that exposed to the jets during the entanglement process.
If it is desired to increase the strength and durability of both surfaces of the fabric, a layer of conjugate fibers is initially laid down on a conveyor on top of which is located a web of base fibers and an outer layer of conjugate fibers.
This composite web is then passed through a mechanism one or more times where the entanglement of the fibers takes place by the introduction of high pressure columns of fluid, such as water jets, as disclosed in detail in Evans U.S. Patent 3,485,706. Where both outer surfaces are to be reinforced against pilling or fraying, the resulting fabric consists of outer relatively thin layers of mixed conjugate and base fibers and a relatively thick intermediate layer of base fibers. Similarly, if only one of the outer surfaces is to be reinforced, a thin layer of mixed conjugate and base fibers will be disposed on a relatively thick-layer of base fibers.
The entangled fabric is then passed through a heating means, such as a hot air oven, where the low melting point component of the conjugate fibers are melted and bonding occurs at the point of intersection and tangency of the conjugate fibers and the base fibers. With this reinforcing of the outer surfaces by the bonding of the conjugate fibers to each other and to the base fibers, the outer surfaces of the fabric is stronger and pilling and fraying has been substantially decreased if not eliminated, without effecting the basic fabric characteristics, such as absorbency, of the base layer.
While in the preferred embodiment, the conjugate or fusible fibers are introduced before the base fiber web is entangled. However, if the fusible fibers are not entangled into the base layer, it is essential that the fusible fibers and base fibers be selected so as to effect specific adhesion of the fusible fibers to the base fibers following heat treatment. The essence of the invention, in its broadest aspect, is the provision of thermobonded entangled network of fusible fibers and base fibers, on one or both surfaces of the fabric to achieve good surface abrasion and low linting or fraying of surface fibers without substantially effecting the fabric characteristics of the base layer in forming the final fabric.

Brief Description of the Drawings

Figure 1 is a schematic side elevation of an apparatus used for carrying out the method of the invention;
Figure 2 is a schematic side elevation of an apparatus used in forming a composite web having a layer of base fibers and a thin top surface of fusible fibers;
Figure 3 is an enlarged illustration of a top plan view of a fabric of the present invention;
Figure 4 is a cross-sectional view of a fabric in which one surface thereof includes thermobonded fusible fibers; and
Figure 5 is a cross-sectional view of a fabric in which both surfaces of the fabric include thermobonded fusible fibers.

Detailed Description of the Invention

Referring first to Figure 1, there is shown an apparatus that can be used to provide a preferred embodiment of the fabric made in accordance with the invention in which the fabric is composed of a web 12 having a layer of base fibers 14 and an outer surface of fusible conjugate fibers 16. The web is supported on a liquid pervious support member such as an endless woven belt 18, which carries the web through an entangling mechanism 20 where a series of high pressure, fine, essentially columnar jets of water 22 impact the web, entangling the fibers. The high pressure water is supplied from manifold 24. The jets are arranged in rows disposed transversely across the path of travel of the belt 18. Preferably, there is a vacuum means 26 pulling a vacuum, e.g, of up to 5 to 10 inches of mercury, beneath the belt 18.
Evans, in U.S. Patent No. 3,485,706, describes a process and apparatus for rearranging/entangling fibrous webs by carrying such webs on a woven belt under a series of high pressure, fine, columnar jets of liquid. Apparatus of the general type disclosed by Evans can be used in the process of this invention, although typically the degree of entanglement contemplated by this invention is much less than that generally preferred by Evans.
The entangled web 28 is then passed through an oven 30 where the fusible conjugate fibers are thermobonded to form a reinforced surface which prevents pilling and fraying thereof.
Specifically, in the embodiment illustrated, a dual rotor mechanism 32 of the type disclosed in Ruffo et al patent 3,768,118 is used to provide a web 12 in which the majority thereof consists of base fibers 14 disposed atop a layer of fusible conjugate fibers 16. The dual rotor mechanism is schematically illustrated, and as will be apparent from a review of the 'l18 patent, it can readily be adjusted to provide the desired web composition. The dual rotor apparatus is fed by cards 34,36 containing fusible conjugate and base fibers 16,14, respectively. The card 35 is used to provide the fusible conjugate fibers 16. The card 36 is used to provide the base fibers 14 such as suitable natural or synthetic fibers.
As previously mentioned, it is preferred to use as fusible fibers conjugate fibers having fiber components with differing melting points. In accordance with the present invention, when a fabric including such conjugate fibers is heated to melt only the low melting point component, the higher melting point fiber component retains its integrity to contribute as a fiber to the finished nonwoven fabric. An example of such conjugate fibers is polyester/ polyethylene conjugate fibers. It is preferred to use sheath/core bicomponent fibers, and even more preferred to employ sheath/core bicomponent fibers with polyethylene as the sheath and polyester as the core, although side-by-side conjugate fibers are also within the purview of the present invention. The fibers usually have a denier within the range of about 1 to about 6, preferably and are in excess of about 1/4 inch in length up to about 3 or 4 inches long.
Preferably the conjugate fibers employ high density polyethylene that has a density of at least about 0.94 and a melt index .("M.I.") by ASTMD-1238(E) (190°C, 2160 gms.) of greater than 1, preferably greater than about 10 and preferably about 20 to about 50. Usually the fibers will be composed of about 40 to 60 weight percent, and preferably 45 to 55 weight percent, polyester, the remainder being polyethylene.
Other conjugate fibers having utility in the present invention are heterofil medium tenacity fibers. Such fibers, which are available from ICI Fibers, Harrogate, North Yorkshire, England, under product codes 3.3/100/V303, 3.3/50/V303, 6.7/50/V302, 13/65/V302, and 13/100/V302 include sheath/core fibers wherein the sheath is a nylon 6 material and the core is a higher melting point nylon 66 material. Such fibers are particularly useful in combination with polyester base fibers. Other medium tenacity heterofil fibers available from ICI Fibers for use in the present invention will include polyester fibers sold under product codes 3.3/50/V544 and 3.3/90/V544. Other suitable sheath/core fibers include fibers having polyethylene or polyethylene terephthalate as a core material and an isophthalic copolymer as the sheath material.
Other examples of polymer pairs suitable for use in the conjugate fibers of the fabrics of the present invention are copolyester/polyester, nylon/polyester, and nylon 6/polypropylene. The conjugate fibers may comprise side-by-side, or sheath/core polymer configurations.
During the entangling process, the fusible conjugate fibers 16 concentrated on the undersurface of the fabric are mechanically entwined. The base fibers 14 will be primarily entangled with each other, but the fusible conjugate fibers on the outer surface will be entangled with the base fibers and with each other.
The endless belt 18 transfers the entangled web onto conveying mechanisms including belts 38, 40 to the oven 30 where it is subjected to elevated temperatures to melt the low melting point component of the conjugate fibers, which has a lower melting temperature than the high melting point core of the conjugate fibers and the base fibers. Upon cooling and solidification, the fusible fibers 16 fuse to the adjacent fibers to form bonds 38 at points of fiber-to-fiber adjacency.
The web is preferably thermal bonded under conditions of zero pressure, or very light pressure, so that the web is not significantly crushed or compacted during the thermal bonding step. The exact temperatures employed in the thermal bonding step will vary depending upon the weight and bulk density of the web, and upon the dwell time employed in the heated zone. For instance, bonding temperatures within the range from about 130°C to about 180°C have been found to be satisfactory for a web comprised of polyester base fibers and polyethylene/polyester bicomponent fibers of the type described above. Dwell times in the bonding zone will generally vary from about 2 seconds to one minute, and more normally will be from 3 to about 4 seconds. As aforementioned, the important factor in selecting the heating conditions for optimum bonding when using conjugate fibers is to heat only the low melting point component to at least its melting point, but not to such a temperature that the high melting point component of the conjugate fibers or the base fibers could melt. By not melting the high melting point component, or core, the conjugate fibers retain their integrity, whereby the fibrous characteristics of the surface of the fabric is retained. In addition, the stiffness and loss of absorbency that can result from the total melting of fusible fibers, whereby the fibrous structure is destroyed and the remaining interfiber spaces or capillarity of the fabric is filled with the melted thermoplastic material, is avoided.
In the thermal bonding step, the low melting point component of the conjugate fiber entraps some of the base fibers in a thermoplastic mass creating inclusion bonds. The molten material also tends to flow around the fibers, and to preferentially flow to fiber intersections. The molten material also coheres to like molten material on the bicomponent fibers to bond such fibers to one another to form adhesion bonds. Upon cooling, the welds of the fused low melting point component, e.g., polyethylene, solidify, and excellent fiber-to-fiber bonds are thereby formed. Simple exposure to ambient air will ordinarily provide adequate cooling.
The thermal bonding step can be carried out by through-air bonding as illustrated in Figure 1 by the oven 30, or by other means, such as infrared heating, or other types of heating. Through-air bonding .is accomplished by carrying the web on a porous conveyor belt through a zone where hot air is forced through the web. It can be carried through a heated zone between two porous screens or belts, or it can be carried on a rotating drum having a porous surface which is equipped to suck hot air through the web as it is passing around the drum. The exact method of effecting the heating has not been found to be narrowly critical. If desired, the thermal bonding step can be performed by passing the web between heated restraining belts, which apply moderate pressure, or between heated embossing or calendering rolls, which apply heavier pressure. With these latter methods, some compaction and densification of the web takes place. However, application of pressure increase the number of fiber contact points and thermal bonds.
After thermal bonding and cooling to solidify the bonds, the fabric of the invention is collected as on a conventional windup roll 42.
In the illustrated apparatus, the surface of the fabric provided with fusible conjugate fibers is disposed on the side of the web opposite to the jets that provide for the entangling in the entangling mechanism 20. Such a fabric is disclosed and described in Figure 4 therein below.
If it is desired to provide a fabric having a web of thermoplastic fibers on both outer surfaces of the fabric to be formed, this can be accomplished by providing a thin layer of fusible fibers 44 atop web 12 before it reaches the entangler 20.
As specifically illustrated in dotted lines in Figure 1, a card 46 is disposed downstream of the dual rotor mechanism to provide the web of fusible fibers 44 on the web 12. Such a fabric is disclosed and described in Figure 5, herein below.
Another way of producing a fabric having a thin outer surface of fusible fibers disposed on one side of a relatively thick layer of base fibers is shown in Figure 2. In this embodiment, cards 50 and 52 of base fibers and fusible fibers, respectively, are disposed on an endless conveyor 54 similar to the conveyor 18 referred to when discussing the apparatus shown in Figure 1. The seriatim cards 50,52 provide the composite web 56 which is directed through the entangling mechanism 20 and thereafter by way of conveyors 38,46 to calender rolls 58. The fusible fibers disposed on the outer surface of the entangled web 28 are heat fused to each other and preferably to the base fibers to strengthen the surface to prevent pilling or fraying. the bonded web is then wound up on a conventional windup roll 60.
It is to be noted that in the embodiments illustrated, the surface formed with a layer of fusible fibers disposed on one or both sides thereof is entangled before it is introduced into the oven or the nip of the calender rolls. However, while these are the preferred embodiments, the essence of the invention is the provision of a thin layer of fusible fibers located on one or both outer surfaces of a thick layer of entangled base fibers, which fusible fibers are subsequently bonded to each other and to the base fibers to create a thermobonded entangled network of fusible with the broadest aspect of the present invention, it is not essential that the fusible fibers be entangled with the base fibers, and it is within the scope of the invention to introduce the fusible fibers on one or both sides of one base fiber after the web leaves the entangling mechanism, but before it is heated to fuse them to each other and the base fibers.
One example of a fabric of the present invention is made up of 80 percent polyester and 20 percent conjugate fiber. However, depending on the surface strength desired, the fiber content ratio could be as low as 90 percent polyester, 10 percent conjugate fiber, and as high as 10 percent polyester and 90 percent conjugate fiber. The exact weight of the web is not critical, although useful weights have been found within the range of about .8 ounces to about 2 ounces per square yard.
Figure 3 illustrates a preferred embodiment of the fabric of the present invention, wherein sheath/core conjugate fibers 70 have been entangled with base fibers 72 at one surface of the fabric and thermobonded. As shown in Figure 3, the low melting point components or sheaths of the conjugate fibers has been heat fused to each other and to the base fibers of the web to form a thermobonded entangled network to the surface of the fabric. As described above, the low melting point component sheath melts and fuses to the sheath of adjacent conjugate fibers to form adhesion bonds 75. In addition, the low melting point component sheath flows around adjacent base fibers, as at 76, to form inclusion bonds. The remaining core of the conjugate fibers is seen at 78.
Figures 4 and 5 illustrate cross-sections of fabrics made according to the present invention. In Figure 4, a layer of fusible or conjugate fibers 80 have been provided at one surface of, and entangled with, a layer of base fibers 82 and thermobonded. The reinforced surface 84 so formed comprises a thermobonded entangled network of conjugate fibers and base fibers, strengthening the surface of the fabric which substantially effects the fibrous structure of fabric characteristics of the base layer. In Figure 5, a layer of conjugate fibers 80 has been provided at both surfaces of a layer of base fibers 82 and entangled therewith. After heat treatment to thermobond the conjugate fibers to each other and to the base fibers, the fabric is provided with reinforced surfaces 84 and 86, each comprising thermobonded entangled network of conjugate fibers and base fibers. The layer of base fibers remain substantially uneffected by the method and means by which the reinforcing is accomplished.
It is intended to cover by the appended claims all such methods and fabrics that are covered thereby.

Claims

1. An entangled nonwoven fabric having enhanced surface abrasion resistance, said fabric comprising an entangled layer of base fibers having a layer of fusible fibers at a surface thereof, said fusible fibers being thermobonded to each other and to the base fiber at fiber intersections creating a thermobonded, entangled network of said fusible fibers and base fibers of the layer at the surface of the fabric.

2. An entangled nonwoven fabric having enhanced surface abrasion resistance, said fabric comprising an entangled layer of base fibers and fusible fibers, said fusible fibers being concentrated at a surface thereof, and thermobonded to each other at fiber intersections creating a thermobonded entangled network of said fusible fibers, and base fibers at the surface of the layer.

3. A nonwoven fabirc as in Claim 2 wherein said fusible fibers are thermobonded to said base fibers at fiber intersections.

4. An entangled nonwoven product as in Claims 1 or 2 wherein.said fusible fibers are conjugate fibers comprising an exposed low melting point component and a higher melting point component and wherein said low melting point component of said conjugate fibers are thermobonded to each other. -

5. An entangled nonwoven fabric as in Claims 1 or 2 wherein said fusible fibers are polyester.

6. An entangled nonwoven fabric as in Claim 4 wherein said conjugate fibers are sheath/core polyethylene/ polyester fibers.

7. An entangled nonwoven fabric as in Claims 1 or 2 wherein both surfaces of the fabric comprise a fused entangled network of fusible fibers and base fibers.

8. A method of forming a nonwoven fabric comprising the steps of: providing a first fibrous web of base fibers; passing columnar jets of fluid under pressure through said web to entangle fibers of the web; superimposing a thin fibrous layer comprising fusible fibers on said first fibrous entangled web; and heating said fusible fibers to heat fuse said fusible fibers at their fiber intersections to create a thermobonded entangled network of fusible fibers and base fibers at the surface of the fabric.

9. A method as set forth in Claim 8 in which the fusible fibers are conjugate fibers comprising an exposed low melting point component and a high melting point component and the conjugate fibers are heated to a temperature to heat fuse said exposed low melting point component only, whereby the conjugate fibers retain their integrity during fabric formation.

10. A method as set forth in Claims 8 or 9 in which layers of fusible fibers are disposed on both surfaces of the web.of base fibers after the base fibers have been entangled.

11. A method of forming a nonwoven fabric comprising the steps of: providing a fibrous web having a layer of base fibers and a surface layer comprising fusible fibers; passing columnar jets of fluid under pressure through said web to entangle the fibers of the web; and heating said fusible fibers to heat fuse said fusible fibers at their fiber intersections to create a thermobonded entangled network of fusible fibers and base fibers at the surface of the fabric.

12. A method as set forth in Claim 11 wherein columnar jets of fluid are directed at a surface of the web opposite the layer of fusible fibers.

13. A method as set forth in Claim 11 in which the fusible fibers are conjugate fibers comprising an exposed low melting point component and a high melting point component and the conjugate fibers are heated to a temperature to heat fuse said exposed low melting point component only, whereby the conjugate fibers retain their integrity during fabric formation.

14. A method as set forth in Claims 11 or 13 in which layers including fusible fibers are disposed on both surfaces of the web of base fibers before the web is entangled.