Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
2000-01-26
2003-08-05
Morris, Terrel (Department: 1771)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S146000, C162S157600, C442S408000
Reexamination Certificate
active
06602386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-decomposable fibrous sheet capable of being readily decomposed and dispersed in water flow. More precisely, it relates to a water-decomposable fibrous sheet having high strength in dry and wet but capable of being readily decomposed in water.
2. Description of the Related Art
To wipe the skin of human bodies including the private parts thereof, or to clean toilets and thereabouts, used are cleaning sheets made of paper or non-woven fabric. The cleaning sheets must be decomposable in water so that they could be directly disposed of in toilets after their use. This is because, if hardly water-decomposable cleaning sheets are disposed of in toilets after their use, they will take a lot of time until they are decomposed and dispersed in septic tanks, or will clog the drainpipes around toilets.
For easy and effective use, many disposable cleaning sheets for wiper applications are packaged while being wetted with a detergent chemical or the like, and are put on the market. Such cleaning sheets must have high strength in wet to such a degree that they are well fit for wiping with them containing a detergent chemical or the like, but must well decompose in water after they are disposed of in toilets.
For example, Japanese Patent Publication No. 24636/1995 discloses a water-decomposable cleaning article that comprises a carboxyl group-having, water-soluble binder, a metal ion and an organic solvent. However, the metal ion and the organic solvent irritate the skin.
Japanese Patent Laid-Open No. 292924/1991 discloses a water-decomposable cleaning article of polyvinyl alcohol-containing fibers with an aqueous solution of boric acid infiltrated thereinto; and Japanese Patent Laid-Open No. 198778/1994 discloses a water-decomposable napkin of polyvinyl alcohol-containing non-woven fabric with a borate ion and a bicarbonate ion introduced thereinto. However, polyvinyl alcohol is not resistant to heat, and therefore the wet strength of the water-decomposable cleaning article and the water-decomposable napkin is lowered at 40° C. or higher. Recently, various water-decomposable absorbent articles including sanitary napkins, panty liners, disposable diapers and others have been investigated in the art. In view of their safety, however, the water-decomposable fibrous sheets mentioned above could not be used as the top sheets for those absorbent articles that shall be kept in direct contact with the skin for a long period of time, as they contain a binder and an electrolyte.
On the other hand, Japanese Patent Laid-Open No. 228214/1997 discloses a water-degradable non-woven fabric having a wet strength of from 100 to 800 gf/25 mm as measured according to JIS P-8135, which is produced by mixing fibers having a length of from 4 to 20 mm with pulp followed by entangling them through treatment with high-pressure water jets. Since the constituent fibers are entangled in it, the non-woven fabric disclosed has a bulky feel. However, in producing the non-woven fabric, long fibers are entangled through high-pressure water jet treatment, whereby the non-woven fabric produced could have such a relatively high wet strength. Therefore, according to the technique disclosed, it is difficult to realize well-balanced bulkiness, strength and water-degradability for the non-woven fabric produced, and the non-woven fabric produced is unsuitable to disposal in flush toilets, etc.
SUMMARY OF THE INVENTION
The present invention is to solve the problems in the prior art noted above, and its one object is to provide a water-decomposable fibrous sheet which is well decomposed in water and has high dry strength.
Another object of the invention is to provide a water-decomposable fibrous sheet which has high wet strength to such a degree that it is well usable in wet even though no binder is added thereto.
Still another object of the invention is to provide a water-decomposable fibrous sheet which is safe for its application to the skin.
Specifically, the invention is to provide a water-decomposable fibrous sheet, which comprises from 3% by mass to 100% by mass of fibrillated rayon comprising primary fibers and microfibers extending therefrom, and from 0% by mass to 97% by mass of other fibers having a length of at most 10 mm, and in which the fibrillated rayon has a degree of beating of at most 700 cc; the primary fibers have a length in a range of from 1.8 mm to 10 mm at a peak of mass distribution thereof; and at least the microfibers extending from the primary fibers of the fibrillated rayon are entangled with at least one of other primary fibers, other microfibers extending from the other primary fibers and the other fibers.
The invention is also to provide a water-decomposable fibrous sheet, which comprises from 3% by mass to 100% by mass of fibrillated rayon comprising primary fibers and microfibers extending therefrom, and from 0% by mass to 97% by mass of other fibers having a length of at most 10 mm, and in which the primary fibers have a length in a range of from 1.8 mm to 10 mm at a peak of mass distribution thereof, the microfibers having a length of at most 1 mm account for from 0.1 to 65% by mass of the self-weight of the fibrillated rayon; and at least the microfibers extending from the primary fibers of the fibrillated rayon are entangled with at least one of other primary fibers, other microfibers extending from the other primary fibers and the other fibers.
The water-decomposable fibrous sheets described above are preferably non-woven fabrics subjected to water jetting treatment.
Also, the invention is to provide a water-decomposable fibrous sheet, which comprises from 3% by mass to 100% by mass of fibrillated rayon comprising primary fibers and microfibers extending therefrom, and from 0% by mass to 97% by mass of other fibers having a length of at most 10 mm, and in which the fibrillated rayon has a degree of beating of at most 700 cc; the primary fibers have a length in a range of from 1.8 mm to 10 mm at a peak of mass distribution thereof; and at least the microfibers extending from the primary fibers of the fibrillated rayon are hydrogen bonded with at least one of other primary fibers, other microfibers extending from the other primary fibers and the other fibers.
The invention is also to provide a water-decomposable fibrous sheet, which comprises from 3% by mass to 100% by mass of fibrillated rayon comprising primary fibers and microfibers extending therefrom, and from 0% by mass to 97% by mass of other fibers having a length of at most 10 mm, and in which the primary fibers have a length in a range of from 1.8 mm to 10 mm at a peak of mass distribution thereof; the microfibers having a length of at most 1 mm account for from 0.1 to 65% by mass of the self-weight of the fibrillated rayon; and at least the microfibers extending from the primary fibers of the fibrillated rayon are hydrogen bonded with at least one of other primary fibers, other microfibers extending from the other primary fibers and the other fibers.
The water-decomposable fibrous sheets described above are preferably produced in a paper-making process. In this case, preferably, the fibrillated rayon has a degree of beating of at most 400 cc.
Naturally in dry and even in wet with water, the water-decomposable fibrous sheet of the invention all the time keeps high strength while it is used as a wiper. In addition, when it is immersed in a large amount of water after used, it is readily decomposed. Therefore, after used, it can be disposed of in toilets, etc. What is more, the water-decomposable fibrous sheet of the invention is composed of materials not harmful to human bodies.
More specifically, in the water-decomposable fibrous sheet of the invention, because the microfibers of the fibrillated rayon act to bind the fibers together, well balanced decomposability in water and strength are realized. With the microfibers entangled with or hydrogen bonded with other fibers, the fibrous sheet procures high strength. On the other hand, when kept in
Konishi Takayoshi
Okada Kazuya
Shimizu Jyoji
Takeuchi Naohito
Tanio Toshiyuki
Befumo Jenna-Leigh
Darby & Darby
Morris Terrel
Uni-Charm Corporation
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