1. Field of the Invention
The present invention relates to a nonwoven fabric which is used in a disposable diaper, a sanitary napkin or kitchen utensils. More specifically, the present invention relates to a nonwoven fabric which has a solid, soft appearance, looks solid and soft and which can maintain a satisfactory bond strength of fibers, as well as to a process for producing the same.
2. Prior Art
There is a nonwoven fabric having a base weight of at least 15 g/m2 and at most 45 g/m2 which fabric is embossed to have a raised line pattern (embossed pattern). In this nonwoven fabric, fibers on the surface of the fibrous web formed of fluffed fibers are adhered relatively densely by a predetermined method, for example, by heat-welding or entangling, and the adhered portions are recessed. The embossed pattern has been provided through this adhesion.
Since, however, the embossed pattern is formed densely throughout this nonwoven fabric, the difference in height between the recessed portion given through this embossing and the other portion in the nonwoven fabric is small. Accordingly, the surface of the nonwoven fabric is less raised, that is, it has a less solid appearance. Consequently, it does not look soft, nor does it feel soft when one touches it.
Meanwhile, as shown in FIG. 9, in a product in which welded dot portions M are formed in a fibrous web W at a fixed pitch, a specific volume (volume/weight) is relatively large in the portions other than the welded portions M, and it can easily be given a solid appearance.
Nevertheless, in the product shown in FIG. 9, the area of the welded portion M is small, the outer periphery of each welded portion M is short, and the nonwoven fabric is less raised. Therefore, the difference in volume between the welded portion M and the surrounding portion is small, so that the raising of the nonwoven fabric is unsatisfactory. Thus, the pattern is monotonous, lacking variety when it is adhered to, for example, an outer surface of an outer film in a disposable diaper.
Further, a nonwoven fabric shown in FIG. 9 is laminated on the outer surface of the outer film in a disposable diaper or the like, and a resin film of the outer film and the nonwoven fabric are welded; this welded portion has a pattern or a figure. However, in case the nonwoven fabric having welded dot portions M as shown in FIG. 9 is further welded to the resin film, the portions welded to the resin film are overlapped with the welded dot portions M, and the area of the welded portions is larger than the area of the nonwoven fabric. Thus, the line pattern formed by the welded portions M lacks sharpness, and the nonwoven fabric does not look solid. Further, as the resin film and the nonwoven fabric are welded to each other in the welded portions M, these portions feel stiff. Further, when an air-permeable film is used as the resin film and patterned or figured welded portions are formed in the resin film and the nonwoven fabric, the air permeability of the resin film is reduced as a whole.
Besides the conventional nonwoven fabric is formed of an uncolored fibrous web in many cases. Even if it is formed of a colored web, the overall nonwoven fabric has a single color. For this reason, there is not a product which has a color contrast and in which a pattern is expressed upon using a bulkiness of the nonwoven fabric.
The present invention aims to solve the above-mentioned problems associated with the prior art. It is an object of the present invention to provide a nonwoven fabric which makes vivid a line pattern formed with press-welded portions by improving the shape of the press-welded portions, which can be rendered bulky by raising the non-press-welded portions, which looks soft and feels soft when touched with the hand, as well as a process for producing the same.
Another object of the present invention is to provide a nonwoven fabric which can have a pattern or a figure by improving the shape of the press-welded portions, for example, which can have a pattern or a figure in the outer surface when used as an outer sheet of a disposable diaper for babies or little children, which can increase a beautiful appearance and in which the presence or absence of urine in a diaper can visually be observed in the press-welded portions from outside the diaper, as well as a process for producing the same.
Still another object of the present invention is to provide a nonwoven fabric in which the shape of the press-welded portions is improved to make bulky the non-press-welded portions and the press-welded portions can provide a clearer pattern to give a color contrast, as well as a process for producing the same.
The present invention is to provide a nonwoven fabric having partially press-welded portions that are recessed in the surface of a fibrous web, characterized in that the press-welded portions have a continuous line or uncontinuous line (broken line) pattern with a curved or square part, and the portions other than the continuous line or uncontinuous line press-welded portions in the fibrous web have a raised pattern relative to the recess of the press-welded portions.
As the fibrous web which is a material of this nonwoven fabric, the web formed of relatively dense fibers having a base weight of at least 15 g/m2 and at most 45 g/m2 is preferably used. When the specific volume of the press-welded portions is at least 3 cm3/g and at most 10 cm3/g and the specific volume of the non-press-welded portions is at least 10 cm3/g and at most 30 cm3/g, the non-press-welded portions in the fibrous web become bulky, and the boundary between the press-welded portions and the non-press-welded portions make clear and the nonwoven fabric comes to look solid.
The portion surrounded with the continuous line or uncontinuous line press-welded portions is formed in the above-mentioned non-woven fabric, and the fibrous web in the surrounded portion is preferably raised relative to the recessed press-welded portions.
It is further preferable to form a plurality of press-welded dot portions other than the continuous line or uncontinuous line press-welded portions. In this case, it is advisable that the press-welded dot portions are formed where these portions do not overlap with the continuous line or uncontinuous line press-welded portions of the fibrous web. The continuous line or uncontinuous line press-welded portions are preferably spaced apart from the adjacent press-welded dot portions by at least 1 mm, preferably at least 1 mm and at most 5 mm.
It is still further preferable that the total area of the press-welded dot portions in the nonwoven fabric is the same as, or less than, the total area of the continuous line or uncontinuous line press-welded portions.
It is furthermore preferable to use fibers having a square or uneven cross-section as a starting material of the fibrous web.
It is moreover preferable that a color sheet is overlaid on the reverse surface of the nonwoven fabric and they are adhered so that the color of the color sheet is seen through the press-welded portions of the nonwoven fabric. This procedure gives the sharp color contrast between the recessed press-welded portions of the fibrous web and the bulky portions of the fibrous web and makes clear the pattern drawn by the press-welded portions.
A process for producing a nonwoven fabric in the present invention comprises a step of forming a fibrous web from starting fibers, a step of feeding the fibrous web between a hot roller provided on the surface with curved or square line or uncontinuous line projected portions and a hot roller having a smooth surface, and a step of holding the fibrous web between the hot rollers provided on the surface with the projected portions and the hot roller having the smooth surface, and press-welding the fibers of the fibrous web with the projected portions on the surface of the hot roller to partially recess the fibrous web and form the press-welded portions.
A plurality of dot-shaped projected portions, in addition to the above-mentioned continuous or uncontinuous line projected portions are formed on the surface of the hot roller.
In a method of placing the color sheet under the nonwoven fabric and welding them, a colorless fibrous web is laminated on a dyed or colored thermoplastic sheet, the laminate is fed between the two hot rollers and held therebetween, and the thermoplastic sheet and the fibrous web are press-welded together with the projected portions formed on the surface of the hot roller to give press-welded portions.
In another method, a fibrous web formed of colorless fibers is laminated on a color fibrous web formed of dyed or colored fibers, the laminate of these fibrous webs is fed between the two hot rollers and held therebetween, and the color fibrous web and the colorless fibrous web are partially press-welded with the projected portions formed on the surface of the hot roller to give press-welded portions.
In this nonwoven fabric , the fibrous web is formed of thermoplastic short fibers having a fiber length of at least 30 mm and at most 70 mm, and fed to the hot rollers. When the fibrous web is passed through the hot rollers, it is partially pressed with the projected portions of one hot roller, and heated to give partially press-welded portions. In the present invention, it is assumed that the thermoplastic fibers of the fibrous web are not welded in the portions other than the above-mentioned press-welded portions. However, since the fibrous web may be raised on the portions other than the recesses in the press-welded portions of the fibrous web, the thermoplastic fibers of the fibrous web may be hot-welded in the portions other than the press-welded portions.
The press-welded dot portions formed with the projected portions of the hot roller refer to circular, elliptical or very short line press-welded portions. For example, circular-, elliptical- or very short line-shaped projected portions are formed on the surface of the hot roller at a fixed space. The press-welded dot portions refer to those in which the area of each of these portions is much smaller than that of each of the continuous line or uncontinuous line press-welded portions. The uncontinuous line press-welded portions refer to short line press-welded portions which are spaced apart from each other.
The press-welded portions are not only those recessed in one surface of the nonwoven fabric as shown in FIG. 8, but also those recessed in both surfaces of the nonwoven fabric.
The continuous line or uncontinuous line press-welded portions are formed in the nonwoven fabric of the present invention. The continuous line or uncontinuous line press-welded portions may be straight lines, but preferably curved lines (arcked lines) or square lines. When the continuous line or uncontinuous line press-welded portions are the straight lines, a pattern can be formed by crossing the straight line press-welded portions. When the press-welded portions are the continuous lines or the uncontinuous lines, the surface of the fibrous web is raised in the boundary between the press-welded portions and the non-press-welded portions, and the raised portions become conspicuous as shown in FIG. 3. Consequently, the overall nonwoven fabric becomes bulky and looks solid. It looks or feels soft compared to the conventional nonwoven fabric. In the continuous line or uncontinuous line press-welded portions, the fibers become filmy and transparent or semitransparent. Therefore, the color contrast between these press-welded portions and non-press-welded portions goes sharp. Thus, the continuous line or uncontinuous line press-welded portions look clear; the nonwoven fabric improves in the appearance as compared to the conventional nonwoven fabric.
Fibers having a cross-section shown in FIG. 4(A), (B) or (C) may be used as starting fibers of the fibrous web. The fibers having the above-mentioned cross-section reflect light diffusely to increase the whiteness of the fibrous web. Accordingly, the raised portions other than the press-welded portions come to have a clear white color. Meanwhile, the press-welded portions become transparent or semitransparent. Therefore, the contrast between the transparent or semitransparent press-welded portions and the raised white portions other than the press-welded portions is made even clearer.
In the present invention, the continuous line or uncontinuous line press-welded portions are made to have a curved or square shape to be able to provide a predetermined pattern. This pattern is given from the curved (arched) or square shape, or a combination thereof continuous line or uncontinuous line press-welded portions or a combination thereof. This pattern is provided by a figure, a combination of figures, characters, symbols, a combination of characters and symbols, a combination of figures and characters, and a combination of figures and symbols.
As shown in an enlarged view of FIG. 2, when the fibrous web constituting the nonwoven fabric is partially press-welded in the production of the nonwoven fabric, the pattern (or the figure) is expressed from the press-welded portions to give an appearance different from that of the conventional nonwoven fabric shown in FIG. 9. The pattern is expressed from the continuous line or uncontinuous line press-welded portions. The surface of the fibrous web is raised from the continuous line or uncontinuous line press-welded portions, and the nonwoven fabric is bulky, solid and soft visually and tactually. Further, the contrast between the continuous line or uncontinuous line press-welded portions and the non-press-welded portions becomes clear, and the pattern is seen sharply.
Moreover, when a color sheet is adhered to the reverse surface of the nonwoven fabric having the press-welded portions, the color of the color sheet on the reverse surface appears through the transparent or semitransparent press-welded portions, and the sharp color contrast is given between the press-welded portions and the non-press-welded bulky portions. Especially when using fibers having a square or uneven sectional shape in the nonwoven fabric, the non-press-welded portions have a clear white color, making sharp the contrast between the color of the color sheet on the press-welded portions and the white color of the non-press-welded portions.
For example, a colored resin film is used as a color sheet. The colored resin film is adhered to the reverse surface of the nonwoven fabric having the press-welded portions that form the pattern. The nonwoven fabric having the pattern and the colored resin film may be adhered partially or wholly using a hot melt adhesive or another transparent adhesive.
It is also possible that the non-press-welded fibrous web is laminated on the colored thermoplastic resin film, the colored thermoplastic resin film and the fibrous web are press-welded together, and the colored resin film and the fibrous web are press-welded together in the press-welded portions.
When a resin sheet having a light warm color such as pink is used as the colored resin film, the nonwoven fabric looks softer. When using a resin sheet having a color such as light blue, a user can feel clean and fresh.
The nonwoven fabric of the present invention may have only curved or square continuous line or uncontinuous line (broken line) like press-welded portions and be free from press-welded dot portions. However, it is preferable that there are the above-mentioned plural press-welded dot portions besides the continuous line or uncontinuous line press-welded portions.
Further, portions surrounded by the curved or/and square continuous line or uncontinuous line press-welded portions are formed in the above-mentioned pattern. It is advisable that the above-mentioned plural press-welded dot portions are formed inside and outside the surrounded portions.
When the press-welded dot portions are formed inside and outside the surrounded portions other than the continuous line or uncontinuous line press-welded portions that give the pattern as mentioned above, it is possible to increase the tensile strength of the nonwoven fabric in the portions other than the continuous line or uncontinuous line press-welded portions, and also to prevent fluffing of the fibrous web in the portions other than the continuous line or uncontinuous line press-welded portions.
In the present invention, when forming the continuous line or uncontinuous line press-welded portions and the press-welded dot portions, it is advisable that these portions are provided so as not to overlap with each other. That is, as shown in FIG. 2, it is advisable that the press-welded dot portions are formed in spaced apart relationship with the continuous line or uncontinuous line press-welded portions at a fixed space (for example, at least 1 mm and at most 5 mm), and that the press-welded dot portions are formed in both sides of the continuous line or uncontinuous line press-welded portions at the same space. In this construction, the pattern drawn by the continuous line or uncontinuous line press-welded portions does not overlap with the press-welded dot portions, and it tends to become clear.
It is further advisable that the total area of the press-welded dot portions occupied in the nonwoven fabric is the same as, or less than, the total area of the continuous line or uncontinuous line press-welded portions occupied in the nonwoven fabric, whereby the pattern drawn by the continuous line or uncontinuous line press-welded portions is not erased by the press-welded dot portions, making it possible to make clear the pattern.