Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
1998-12-22
2001-08-07
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S115000, C162S109000, C019S161100, C028S104000, C028S105000, C428S131000, C442S408000
Reexamination Certificate
active
06270623
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for making an apertured nonwoven fabric containing thermoplastic synthetic microfibers and being suitable to be used as a liquid-permeable topsheet in disposable body fluids absorbent articles such as disposable diapers or sanitary napkins.
It is known to form a nonwoven fabric comprising the thermoplastic synthetic fibers having a fineness of 1~10 d with liquid-permeable apertures so as to be used as a topsheet in a body fluids absorbent article. An example of the methods for such nonwoven fabric is disclosed in Japanese Patent Application Disclosure Gazettes (Kokai) Nos. Sho 61-176346 and Sho 62-69867, according to which a card web comprising fibers each having a fineness of 1~10 d and a length of approximately 50 mm is subjected to high velocity water jet streams to form a nonwoven fabric. During this processing by the water jet streams, component fibers of a web are partially reoriented around a plurality of projections formed on a surface of support for the web and thereby the nonwoven fabric is formed with a plurality of liquid-permeable apertures corresponding to the respective projections. It is also known to form these liquid-permeable apertures by feeding the nonwoven fabric to a pair of embossing rolls so that the nonwoven fabric may be pierced by a plurality of needle teeth formed on a peripheral surface of one of these embossing rolls.
However, the conventional method for forming the liquid-permeable topsheet with these apertures is often accompanied with an inconvenience such that, when it is attempted to form the apertures each having a diameter of 0.5~5 mm, individual fibers may often extend from the aperture periphery into this aperture, resulting in the indistinctly contoured aperture. Probably, it is for the reason that the individual fibers can not be smoothly reoriented around each of projections. The smaller a diameter of the aperture and/or larger a basis weight of the nonwoven fabric is, the greater this problem becomes serious. While it is obvious that the individual fibers extending into the aperture lead to a substantial reduction of the aperture's diameter, a degree of such reduction is not necessarily uniform. This makes a proper design of the aperture difficult. Accordingly, it is required for the nonwoven fabric used as the liquid-permeable topsheet to have a sufficiently high formability to facilitate formation of the apertures.
SUMMARY OF THE INVENTION
In view of the problem as has been described above, it is an object of the invention to provide a method for making a nonwoven fabric allowing formation of distinctly contoured apertures to be facilitated.
According to the invention, there is provided a method for making an apertured nonwoven fabric containing thermoplastic synthetic microfibers, the method comprising the steps of:
a. obtaining a wet sheet from slurry containing 0.5~20% by weight of thermoplastic synthetic fibers having a length of 7~30 mm and a fineness of 0.1~0.8 d dispersed in water;
b. placing the wet sheet on a support and then subjecting the wet sheet to high velocity water jet streams of 50~200 kgf/cm
2
for mechanically entangling the fibrous mixture; and
c. during the mechanically entangling of the fibrous mixture, forming any one of the wet sheet and dry sheet obtained from the wet sheet with a plurality of apertures each having a diameter of 0.5~5 mm at a total apertured area ratio of 3~60%.
According to one preferred embodiment of the invention, the method for making the apertured nonwoven fabric includes a step of placing the wet sheet on a support provided on a surface thereof with a plurality of projections each having a desired tip configuration and reorienting the component fibers of the wet sheet around the projections under the effect of the high velocity water jet streams. Alternatively, the method for making the apertured nonwoven fabric includes a step of causing a plurality of projections each having a desired tip configuration to pierce the dry sheet in a thickness direction thereof.
According to still another embodiment of the invention, the thermoplastic synthetic fibers comprise melt blown fibers.
REFERENCES:
patent: 3485706 (1969-12-01), Evans
patent: 0 215684 (1987-03-01), None
patent: 61-176346 (1961-08-01), None
patent: 61-176346 (1986-08-01), None
patent: 62-69867 (1987-03-01), None
Goda Hiroki
Tsuji Tomoko
Baker & Daniels
Halpern Mark
Silverman Stanley S.
Uni-Charm Corporation
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