The present invention is generally directed to spunbond multicomponent filaments and to nonwoven webs made from the filaments. More particularly, the present invention is directed to incorporating an additive into one of the polymers used to make multicomponent filaments. The additive enhances crimp, allows for finer filaments, improves the integrity of unbonded webs made from the filaments, enhances bonding of the filaments, and produces webs with improved stretch and cloth-like properties. The additive incorporated into the filaments is a butylene-propylene random copolymer.
Nonwoven fabrics are used to make a variety of products which desirably have particular levels of softness, strength, uniformity, liquid handling properties such as absorbency, and other physical properties. Such products include towels, industrial wipers, incontinence products, filter products, infant care products such as baby diapers, absorbent feminine care products, and garments such as medical apparel. These products are often made with multiple layers of nonwoven fabrics to obtain the desired combination of properties. For example, disposable baby diapers made from polymeric nonwoven fabrics may include a soft and porous liner layer which fits next to the baby""s skin, an impervious outer cover layer which is strong and soft, and one or more interior liquid handling layers which are soft, bulky and absorbent.
Nonwoven fabrics such as the foregoing are commonly made by melt spinning thermoplastic materials. Such fabrics are called spunbond materials. Spunbond nonwoven polymeric webs are typically made from thermoplastic materials by extruding the thermoplastic material through a spinneret and drawing the extruded material into filaments with a stream of high velocity air to form a random web on a collecting surface.
Spunbond materials with desirable combinations of physical properties, especially combinations of softness, strength and absorbency, have been produced, but limitations have been encountered. For example, for some applications, polymeric materials such as polypropylene may have a desirable level of strength but not a desirable level of softness. On the other hand, materials such as polyethylene may, in some cases, have a desirable level of softness but not a desirable level of strength.
In an effort to produce nonwoven materials having desirable combinations of physical properties, nonwoven polymeric fabrics made from multicomponent or bicomponent filaments and fibers have been developed. Bicomponent or multicomponent polymeric fibers or filaments include two or more polymeric components which remain distinct. As used herein, filaments mean continuous strands of material and fibers mean cut or discontinuous strands having a definite length. The first and subsequent components of multicomponent filaments are arranged in substantially distinct zones across the cross-section of the filaments and extend continuously along the length of the filaments. Typically, one component exhibits different properties than the other so that the filaments exhibit properties of the two components. For example, one component may be polypropylene which is relatively strong and the other component may be polyethylene which is relatively soft. The end result is a strong yet soft nonwoven fabric.
To increase the bulk or fullness of the bicomponent nonwoven webs for improved fluid management performance or for enhanced xe2x80x9ccloth-likexe2x80x9d feel of the webs, the bicomponent filaments or fibers are often crimped. Bicomponent filaments may be either mechanically crimped or, if the appropriate polymers are used, naturally crimped. As used herein, a naturally crimped filament is a filament that is crimped by activating a latent crimp contained in the filaments. For instance, in one embodiment, filaments can be naturally crimped by subjecting the filaments to a gas, such as a heated gas, after being drawn.
In general, it is far more preferable to construct filaments that can be naturally crimped as opposed to having to crimp the filaments in a separate mechanical process. Difficulties have been experienced in the past, however, in producing filaments that will crimp naturally to the extent required for the particular application. Also, it has been found to be very difficult to produce naturally crimped fine filaments, such as filaments having a linear density of less than 2 denier. Specifically, the draw force used to produce fine filaments usually prevents or removes any meaningful latent crimp that may be contained in the filaments. As such, currently a need exists for a method of producing multicomponent filaments with enhanced natural crimp properties. Also, a need exists for nonwoven webs made from such filaments.
The present invention recognizes and addresses the foregoing disadvantages, and others of prior art constructions and methods.
Accordingly, an object of the present invention is to provide improved nonwoven fabrics and methods for making the same.
Another object of the present invention is to provide nonwoven polymeric fabrics including highly crimped filaments and methods for economically making the same.
A further object of the present invention is to provide a method for controlling the properties of a nonwoven polymeric fabric by varying the degree of crimp of filaments and fibers used to make the fabric.
Another object of the present invention is to provide an improved process for naturally crimping multicomponent filaments.
It is another object of the present invention to provide a method for naturally crimping multicomponent filaments by adding to one of the components of the filaments a butylene-propylene copolymer.
Still another object of the present invention is to provide a naturally crimped filament that has a linear density of less than 2 denier.
Another object of the present invention is to provide a bicomponent filament made from polypropylene and polyethylene, wherein a crimp enhancement additive has been added to the polyethylene.
It is still another object of the present invention to provide a process for naturally crimping multicomponent filaments containing polypropylene and polyethylene in which a crimp enhancement additive and reclaimed polymer has been added to the polyethylene.
Another object of the present invention is to provide a crimp enhancement additive that also improves the strength of unbonded webs made from filaments containing the additive.
These and other objects of the present invention are achieved by providing a process for forming a nonwoven web. The process includes the steps of melt spinning multicomponent filaments. The multicomponent filaments include a first polymeric component and a second polymeric component. The first polymeric component has a faster solidification rate than the second polymeric component for providing the filaments with a latent crimp. The second polymeric component contains a crimp enhancement additive that is a butylene-propylene copolymer.
Once melt spun, the multicomponent filaments are drawn and naturally crimped. Thereafter, the multicomponent crimped filaments are formed into a nonwoven web for use in various applications.
In one embodiment, the second polymeric component can include polyethylene. The butylene-propylene copolymer can be added to the second polymeric component in an amount less than about 10% by weight, and particularly from about 0.5% to about 5% by weight. Preferably, the butylene-propylene copolymer is a random copolymer containing less than about 20% by weight butylene, and particularly about 14% by weight butylene.
The first polymeric component, on the other hand, in one preferred embodiment is polypropylene. Other polymers that may be used include nylon, polyester and copolymers of polypropylene, such as a propylene-ethylene copolymer.
In accordance with the present invention, it has been also discovered that the butylene-propylene copolymer also functions as a polymer compatibilizer. In particular, it has been found that the copolymer allows better homogeneous mixing between different polymers. In this regard, the first polymeric component, in accordance with the present invention, can also contain reclaim polymer. Reclaim polymer, as used herein, are polymer scraps that are recycled and added to the filaments. For instance, the reclaim polymer can comprise a mixture of polyethylene, polypropylene, and copolymers of propylene and ethylene, and can be obtained from the trimmed edges of previously formed nonwoven webs. In the past, difficulties were experienced in recycling reclaim polymer, especially bicomponent reclaim polymer, and incorporating them into filaments without adversely affecting the physical properties of the filaments.
These and other objects of the present invention are also achieved by providing a nonwoven web made from spunbond multicomponent, crimped filaments. The multicomponent crimped filaments are made from at least a first polymeric component and a second polymeric component. In particular, the polymeric components are selected such that the first polymeric component has a faster solidification rate than the second polymeric component. In accordance with the present invention, the second polymeric component contains a crimp enhancement additive. Specifically, the crimp enhancement additive is a butylene-propylene random copolymer.
For instance, in one embodiment, the crimped filaments can be bicomponent filaments which include a polypropylene component and a polyethylene component. The butylene-propylene random copolymer can be added to the polyethylene component in an amount up to about 5% by weight. Preferably, the butylene-propylene random copolymer contains about 14% by weight butylene.
Because of the addition of the crimp enhancement additive, the multicomponent filaments can have a very low denier and still be crimped naturally. For instance, the denier of the filaments can be less than 2, and particularly less than about 1.2.
In this regard, the present invention is also directed to a naturally crimped multicomponent filament that includes at least a first polymeric component and a second polymeric component. The first polymeric component can be, for instance, polypropylene. The second polymeric component, on the other hand, can be, for instance, polyethylene and can contain a crimp enhancement additive in an amount sufficient to allow the filaments to be naturally crimped at a denier of less than about 2 and particularly less than about 1.2.
Other objects, features and aspects of the present invention are discussed in greater detail below.