WO2004104285A1

WO2004104285A1 - Nonwoven fabric having low fiber density

Info

Publication number: WO2004104285A1
Application number: PCT/KR2003/002782
Authority: WO
Inventors: Jae Hun Shim; Soo Young Lee; Seok Bong Lyu; Tae Yaun Park
Original assignee: Hanjin Printing & Chemical Co., Ltd
Priority date: 2003-05-26
Filing date: 2003-12-19
Publication date: 2004-12-02
Also published as: AU2003289554A1; KR100555178B1; KR20040101887A

Abstract

Disclosed is a nonwoven fabric having a low fiber density, characterized in that a nonwoven fabric is sequentially drawn in a first axis and then in a second axis, thus increasing an open pore ratio and flexibility. That is, a biaxial drawing process of the nonwoven fabric can lead to an increased open pore ratio and flexibility of the nonwoven fabric. Thereby, nonwoven fabric articles having high qualities can be inexpensively provided.

Description

NONWOVEN FABRIC HAVING LOW FIBER DENSITY

Technical Field

The present invention relates to a nonwoven fabric having a low fiber density so as to increase flexibility (softness of the touch) and an open pore ratio.

Background Art

Typically, a nonwoven fabric has been used as a skin- contacting material of a disposable diaper and sanitary napkin, in which the skin-contacting material should have softness of the touch, skin compatibility, air permeability, and moisture absorption. Further, a water- transferring capacity of the nonwoven fabric, required in addition to the above mentioned properties, has relation to a fiber density and an open pore ratio of the nonwoven fabric. Therefore, nonwoven fabric articles having improved softness of the touch and a high open pore ratio are variously exemplified by disposable diapers, disposable sanitary napkins, disposable wet towels, animal matting, etc. In cases where a general nonwoven fabric is employed as the skin-contacting material of disposable diapers or sanitary napkins, it should be improved in softness of the touch and water-transferring capacity (required to transfer a body secretion to an absorbent of the diaper or sanitary napkin) . To improve the water-transferring capacity of the nonwoven fabric, a hydrophilic agent to be coated on the nonwoven fabric has been utilized. However, since a hydrophilic agent is a chemical, it reduces skin compatibility and environmentally-friendly properties of the nonwoven fabric. Hence, in foreign countries, use of a specific hydrophilic agent on the nonwoven fabric is forbidden. In the present invention, use of a nonwoven fabric, which is low in fiber density and high in open pore ratio, results in a reduced use of the hydrophilic agent. This is based on high hydrophilicity and environmentally- friendly properties of the nonwoven fabric of the present invention. Moreover, the nonwoven fabric, which comes into contact with the skin of the user, should be soft to the touch. The reason why the soft nonwoven fabric is expensive is that it makes a favorable impression on a user. Accordingly, the nonwoven fabric of the present invention is regarded as being environmentally-friendly, with economic benefits and marketability.

Disclosure of the Invention

Accordingly, an object of the present invention is to alleviate the problems encountered in the related art, such as low softness of the touch (mainly generated in an embossed nonwoven fabric) , resulting from a hardened fiber texture of an adhesive pattern disposed on a nonwoven fabric and a thermally deformed fiber texture in a space of the nonwoven fabric, with the exception of the patterns, upon manufacturing the nonwoven fabric, and to provide a nonwoven fabric which is lowered in fiber density to increase an open pore ratio and softness of the touch.

Another object of the present invention is to provide a nonwoven fabric having high open pore ratio and high flexibility, manufactured economically.

A further object of the present invention is to provide a nonwoven fabric, which is advantageous in terms of a low fiber density, an increased open pore area, and improved softness of the touch or flexibility, by biaxially drawing a nonwoven fabric, that is, drawing or necking an embossed nonwoven fabric in a first axis to allow a fiber texture of the nonwoven fabric to be tensed in a first axis and then drawing the tensed nonwoven fabric in a second axis. In the present invention, through the biaxial drawing process, a hardened fiber texture of the nonwoven fabric becomes flexible, and a dense texture thereof becomes loose. Further, the biaxial drawing process of the present invention includes either necking a nonwoven fabric in a first axis to rearrange a fiber texture of the nonwoven fabric, followed by drawing the necked nonwoven fabric in a second axis, or drawing a nonwoven fabric in a first axis while preventing a shrinkage in a second axis, thus decreasing a fiber density and increasing an open pore ratio. Yet another object of the present invention is to provide a nonwoven fabric, which has a high open pore ratio so as to be substituted for a conventional water- transferring improver.

Still another object of the present invention is to provide a nonwoven fabric, which has high softness of the touch.

To achieve the above objects, the present invention provides a nonwoven fabric having a low fiber density, prepared by drawing a nonwoven fabric in a first axis and then in a second axis to allow a fiber texture of the nonwoven fabric to be tensed and then relaxing the drawn nonwoven fabric. In the present invention, the first axis is an X axis or a Y axis, and the second axis is an axis perpendicular to the first axis, as shown in FIG. 2. Further, the present invention provides a nonwoven fabric having a low fiber density, prepared by drawing a nonwoven fabric in a first axis while preventing a shrinkage in a second axis, drawing the nonwoven fabric in the second axis while preventing a shrinkage in the first axis, and then relaxing the drawn nonwoven fabric. Furthermore, the present invention provides a nonwoven fabric having a low fiber density, prepared by necking a nonwoven fabric in a first axis to allow a fiber texture of the nonwoven fabric to be tensed and then relaxing the necked nonwoven fabric in a second axis. In addition, the present invention provides a nonwoven fabric having a low fiber density, prepared by drawing a nonwoven fabric in a first axis while preventing a shrinkage in a second axis and then relaxing the drawn nonwoven fabric.

In such cases, an elongated length of the nonwoven fabric drawn in the first axis is 1-10 times of an original length of the nonwoven fabric, and a width of the nonwoven fabric drawn in the second axis is 0.2-15 times of a width of the nonwoven fabric before the drawing.

The nonwoven fabric, useful in the present invention, has a basic weight of 5-180 g/m², which is selected from the group consisting of polypropylene thermally bonded nonwoven fabrics, polypropylene spun-bonded nonwoven fabrics, polypropylene melt-blown nonwoven fabrics, bicomponent nonwoven fabrics of polypropylene and polyethylene, at least two thermally-bonded laminates of polypropylene melt- blown nonwoven fabrics and polypropylene spun-bonded nonwoven fabrics, polyethylene nonwoven fabrics, nylon nonwoven fabrics, polyester nonwoven fabrics, nonwoven fabrics formed with bicomponent yarns of polypropylene and polyethylene, polypropylene yarns, polyethylene yarns, viscose yarns, polyester yarns, nylon yarns and mixtures thereof, air-laid nonwoven fabrics, airthrough nonwoven fabrics, spunlace nonwoven fabrics, and cotton nonwoven fabrics .

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view showing a non-drawn nonwoven fabric which is subjected to embossing;

FIG. 2 is a plan view showing a biaxial drawing process of a nonwoven fabric, according to the present invention;

FIG. 3 is a photograph showing a thickness comparison of the non-drawn nonwoven fabric and the biaxially drawn nonwoven fabric, according to the present invention;

FIG. 4 is a ^• photograph showing a surface comparison of the non-drawn nonwoven fabric and the biaxially drawn nonwoven fabric, according to the present invention; and FIG. 5 is a view showing a flexibility comparison of the non-drawn nonwoven fabric and the biaxially drawn nonwoven fabric, according to the present invention.

Best Mode for Carrying Out the Invention Hereinafter, a detailed description will be given of the present invention with reference to the appended drawings .

FIG. 1 illustrates a non-drawn nonwoven fabric N on which adhesive patterns P (caused by an embossing treatment) are disposed. As illustrated in FIG. 1, the embossed nonwoven fabric N is in the inflexible state, resulting from a hardened fiber texture of the adhesive patterns P and a thermally-deformed fiber texture (deteriorated in the state of shrunken or meandered) of a space Sf of the nonwoven fabric, with the exception of the patterns P, upon embossing of the nonwoven fabric.

Referring to FIG. 2, there is shown a plan view of a non-drawn nonwoven fabric N on which an embossing pattern is disposed. As shown in FIG. 2, the nonwoven fabric N is elongated in a Y axis to obtain a nonwoven fabric Ny. As such, the nonwoven fabric Ny has a 1.1-5 times elongated length with a shrunken width. The 1.1-5 times elongation in the nonwoven fabric Ny results in that a fiber texture of the nonwoven fabric is rearranged according to the drawing process in a Y axis, and simultaneously, fibers thereof are relatively straightened, thereby restoring fiber elasticity. The nonwoven fabric having a fiber texture rearranged by the Y axis drawing is characterized by having a wave pattern elongated in the Y axis centering the adhesive patterns P. Then, the nonwoven fabric Ny is elongated in an X axis, to obtain a nonwoven fabric Nxy. An elongation ratio in the X axis reaches 50-1000% based on a width of the nonwoven fabric before the shrinkage. The biaxially drawn nonwoven fabric Nxy has a low fiber density by allowing a fiber texture thereof to be tensed and then relaxed through a biaxial drawing process. Further, when a nonwoven fabric having a basic weight less than 20 g/m² is heated under strong tension, the nonwoven fabric is necked while reducing a width in an X axis, and thus, has a rearranged fiber texture, as in the above Y axis drawing. Thereafter, such a nonwoven fabric is further drawn in the X axis, whereby the nonwoven fabric may decrease in fiber density. Meanwhile, the wave pattern of FIG. 2 symbolically represents a behavior of the nonwoven fabric . As stated above, the biaxially drawn nonwoven fabric has a low fiber density, and hence, increases in an open pore ratio. In addition, respective fibers of the nonwoven fabric, which are deteriorated by thermal deformation, are relatively straightened, thereby restoring flexibility. In the present invention, the biaxial drawing process of the nonwoven fabric is performed by use of both a first drawing unit in a machine direction (Y axis of FIG. 2) and a second drawing unit in a width direction (X axis of FIG. 2) . The drawing process of the nonwoven fabric in a machine direction (Y axis) is conducted by means of the first drawing unit equipped with feeding rolls and drawing rolls . In this case, the drawing unit may be a drawing unit which allows a transferring rate of the nonwoven fabric by drawing rolls to be faster than that by the feeding rolls, or a necking unit for use in heating the nonwoven fabric to shrink a width thereof. As well, the drawing process in a width direction (X axis of FIG. 2) is carried out by fixing both longitudinal ends of the nonwoven fabric with clips or pins and then drawing the nonwoven fabric in a width direction. Moreover, the biaxially drawing process includes a heating process of the nonwoven fabric.

Turning now to FIG. 3, there are photographs showing a thickness difference of a non-drawn nonwoven fabric Nl and a biaxially drawn nonwoven fabric N2. The nonwoven fabric N2 is thicker than the nonwoven fabric Nl. This means that a dense texture of the non-drawn nonwoven fabric is relaxed upon a biaxially drawing process, and a fiber texture thereof expands in the relaxation state, finally reducing the fiber density. Further, FIG. 4 shows surfaces of a non-drawn nonwoven fabric Nl and a biaxially drawn nonwoven fabric N2. As apparent from FIGS . 3 and 4, the biaxially drawn nonwoven fabric N2 decreases in fiber density, and hence, has high moisture and air permeability, and is softer to the touch. In addition, the biaxially drawn nonwoven fabric N2 comes to be cushiony to the touch, resulting in obtaining properties capable of increasing values of articles, for example, disposable diapers, disposable sanitary napkins, garments, disposable patches, disposable garments, other goods, disposable wet towels, etc.

In addition, such a nonwoven fabric having the above properties is necked to allow a fiber texture thereof to be tensed, and then, the nonwoven fabric drawn in a first axis is further necked in a second axis and relaxed. Thereby, the nonwoven fabric having a low fiber density can be prepared so as to improve an open pore ratio and flexibility.

In the present invention, an inexpensive nonwoven fabric is biaxially drawn to increase softness of the touch, thereby improving qualities of nonwoven fabric articles . Specifically, a polypropylene spun-bonded nonwoven fabric, as the inexpensive nonwoven fabric, is biaxially drawn according to the present invention, therefore obtaining high softness of the touch as in airthrough nonwoven fabrics, spunlace nonwoven fabrics or bicomponent nonwoven fabrics as expensive nonwoven fabrics. Also, while the fiber density of the nonwoven fabric decreases, a water absorption rate thereof becomes faster and an air content therein increases, with high warming properties. In general, a fur piece or a neat textile keeps warm by an air-containing layer therein. In the present invention, the hardened fiber texture of the nonwoven fabric having high density is changed to have low density through a biaxially drawing process . Thereby, while the layer of the nonwoven fabric becomes thicker and a fiber density thereof decreases, the air-containing layer therein expands. After all, warming properties and softness of the touch of the nonwoven fabric increase. Like this, the nonwoven fabric having a low fiber density may be referred to as a nonwoven fabric which is high in thickness and low in basic weight. Thus, since the nonwoven fabric treated to have a low fiber density can _, increase in softness of the touch, cushioning properties, water permeability, air permeability, and warming properties, an inexpensive nonwoven fabric can be variously applied as in expensive nonwoven fabrics .

In this regard, the improved nonwoven fabric has a variety of applications, such as a coverstock (a nonwoven fabric of a disposable diaper in contact with the skin of the user) of disposable diapers, a coverstock of disposable sanitary napkins, waterproof surfaces of disposable diapers and sanitary napkins, disposable wet towels, warming materials of disposable garments and other personal goods, and other products requiring high flexibility and air permeability of nonwoven fabrics. A better understanding of the present invention may be obtained through the following example which is set forth to illustrate, but is not to be construed as the limit of the present invention.

Example 1 A polypropylene spun-bonded nonwoven fabric having a basic weight of 15 g/m² with an embossing pattern of FIG. 1 was heated, and then drawn or necked in a first axis (Y axis) , whereby a width of the nonwoven fabric was reduced to 540 mm, from 1500 mm which was a width before the drawing. Subsequently, the drawn nonwoven fabric was further drawn in a second axis, and thus, the reduced width thereof, 540 mm, was elongated to 1500 mm. That is, a width of the nonwoven fabric drawn in the second axis was elongated to 1500 mm from 540 mm. The properties of the non-drawn nonwoven fabric and the drawn nonwoven fabric are summarized in Table 1, below.

TABLE 1

The thickness change of the nonwoven fabric before and after the drawing process was determined by measuring a thickness of ten nonwoven fabrics. As for flexibility, 10x10 cm nonwoven fabric samples Nl (non-drawn nonwoven fabric) and N2 (biaxially drawn nonwoven fabric) were placed onto a table, after which 5 cm of each nonwoven fabric sample was pulled out of the table, and angles of each nonwoven fabric sample tilting downward due to gravity were measured. In the hydrostatic test, a hydrostatic tester (FX3000, purchased from Tex Test, Switzerland) was used. From the results of Table 1, it can be seen that the biaxially drawn nonwoven fabric decreases in fiber density, and thus, has a lower basic weight and a higher thickness, compared to before being drawn. The increase of the thickness means that an air content in the nonwoven fabric increases, thus improving warming properties, water permeability and air permeability. Also, the non-drawn nonwoven fabric Nl has a tilting angle Al of 45° or less, while the biaxially drawn nonwoven fabric N2 has a tilting angle A2 of 68° or more. Thereby, it appears that the drawn nonwoven fabric has high flexibility.

Industrial Applicability

As described above, the present invention provides a nonwoven fabric having a low fiber density, characterized by performing a biaxial drawing process acting to tense a fiber texture of the nonwoven fabric and to decrease the fiber density of the nonwoven fabric. Through such a biaxial drawing process, the nonwoven fabric having a high open pore ratio and flexibility while being restored in fiber elasticity can be economically manufactured. Therefore, it is possible to inexpensively provide nonwoven fabric articles having high qualities .

Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A nonwoven fabric having a low fiber density, which is prepared by drawing a nonwoven fabric in a first axis and then in a second axis to allow a fiber texture of the nonwoven fabric to be tensed and then relaxing the drawn nonwoven fabric.

2. A nonwoven fabric having a low fiber density, which is prepared by drawing a nonwoven fabric in a first axis while preventing a shrinkage in a second axis perpendicular to the first axis, drawing the nonwoven fabric in the . second axis while preventing a shrinkage in the first axis, and then relaxing the drawn nonwoven fabric .

3. A nonwoven fabric having a low fiber density, which is prepared by necking a nonwoven fabric in a first axis to allow a fiber texture of the nonwoven fabric to be tensed and then relaxing the necked nonwoven fabric in a second axis .

4. A nonwoven fabric having a low fiber density, which is prepared by drawing a nonwoven fabric in a first axis while preventing a shrinkage in a second axis and then relaxing the drawn nonwoven fabric.

5. The nonwoven fabric according to claim 1, 3 or 4, wherein an elongated length of the nonwoven fabric drawn in the first axis is 1-10 times of an original length of the nonwoven fabric, and a width of the nonwoven fabric drawn in the second axis is 0.2-15 times of a width of the nonwoven fabric before the drawing.

6. The nonwoven fabric according to claim 1, 2 , 3 or 4, wherein the nonwoven fabric has a basic weight of 5-180 g/m², which is selected from the group consisting of polypropylene thermally bonded nonwoven fabrics, polypropylene spun-bonded nonwoven fabrics, polypropylene melt-blown nonwoven fabrics, bicomponent nonwoven fabrics of polypropylene and polyethylene, at least two thermally- bonded laminates of polypropylene melt-blown nonwoven fabrics and polypropylene spun-bonded nonwoven fabrics, polyethylene nonwoven fabrics, nylon nonwoven fabrics, polyester nonwoven fabrics, nonwoven fabrics formed with bicomponent yarns of polypropylene and polyethylene, polypropylene yarns, polyethylene yarns, viscose yarns, polyester yarns, nylon yarns and mixtures thereof, air-laid nonwoven fabrics, airthrough nonwoven fabrics, spunlace nonwoven fabrics, and cotton nonwoven fabrics.

7. An article, comprising any one of a disposable diaper, a disposable sanitary napkin and animal matting, a disposable wet towel, a garment, a disposable garment, a disposable working garment, and a sleeping bag, manufactured by use of a nonwoven fabric having a low fiber density while obtaining a high open pore ratio and flexibility through a drawing process .