Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
2000-09-18
2003-04-15
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S141000, C162S146000, C162S149000, C162S158000, C162S177000, C162S181100, C162S181200, C162S183000, C428S152000, C428S154000
Reexamination Certificate
active
06547927
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 of which the decomposability in water measured in wet, the strength at break measured in dry, and the strength at break measured in wet are all good, even though not containing a large amount of an organic solvent.
2. Description of the Related Art
To wipe the skin of human bodies including the private parts thereof, or to clean toilets and thereabouts, fibrous sheets are used as wiper sheets. The strength of the wiper sheets must be enough for wiper applications. In view of easy use and work effectiveness, moreover, many fibrous sheets are used while being previously wetted with a detergent chemical or the like. Therefore, the fibrous sheets must have high strength even in wet to such a degree that they are well fit for wiping with them containing a detergent chemical or the like.
On the other hand, the fibrous sheets of the type are preferably decomposable in water in order that they could be directly flushed in toilets after their use. This is because, if hardly water-decomposable sheets are flushed in toilets or the like, they will take a lot of time until they are decomposed and dispersed in septic tanks, or will clog the drainpipes around toilets, etc.
Accordingly, the fibrous sheets to be used in wet with a detergent chemical or the like infiltrated thereinto must satisfy the two contradictory requirements, one being that they must have high strength even in wet with a detergent chemical or the like infiltrated thereinto to such a degree that they are well fit for wiper applications, and the other being that they must be decomposable in water after flushed in toilets.
Regarding fibrous sheets of the type, Japanese Unexamined Patent Publication (Kokai) No. Heisei 1-168999 discloses a water-dispersible cleaning article of easily water-dispersible paper prepared from a mixture of from 60 to 99% by weight of water-dispersible fibers for paper and from 1 to 40% by weight of water-insoluble carboxymethylated pulp, wherein the paper carries an active substance-containing organic compound applied thereto. However, the cleaning article shall contain a mixture of from 5 to 60% by weight of water and from 40 to 95% by weight of an active substance-containing organic compound (e.g., mono- or polyalcohols, oils, fats, etc.) infiltrated thereinto to an extent of from 0.5 to 5 times the self-weight of the article. As containing a large amount of a skin-irritating compound such as alcohol or the like, the article could not be used for wiping the private parts of babies and infants. In addition, as containing an organic solvent, the cleaning article will damage resin objects if applied thereto.
Japanese Unexamined Patent Publication (Kokai) Nos. Heisei 9-132896 and Heisei 9-132897 disclose water-decomposable sheets which contain water-insoluble or water-swellable carboxymethyl cellulose along with sodium carbonate added thereto. However, the decomposability in water of the water-decomposable sheets is not satisfactory.
Japanese Unexamined Patent Publication (Kokai) No. Heisei 10-310960 discloses a water-decomposable non-woven fabric that comprises regenerated cellulose fibers and wood pulp entangled together. This non-woven fabric contains from 3 to 17% by weight of carboxymethylated fibers in which the carboxyl group accounts for from 10 to 60% of all carboxymethyl groups. When heated, the non-woven fabric loses its ability to decompose in water, since the carboxymethyl groups constituting the carboxymethylated fibers therein bond to each other through hydrogen bonding under heat. In that situation, desired is a fibrous sheet of better decomposability in water.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a fibrous sheet capable of readily decomposing in water and having good dry strength and wet-strength enough for use.
Another object of-the invention is to provide a fibrous sheet suitable to any type of wiper applications.
According to the invention, there is provided a water-decomposable fibrous sheet that comprises water-dispersible fibers and water-insoluble carboxymethyl cellulose, wherein;
the water-insoluble carboxymethyl cellulose has a degree of substitution for etherification (DE) falling between 0.3 and 0.6, and, in the water-insoluble carboxymethyl cellulose, the hydrogen of the carboxyl group in at least 95% of the carboxymethyl groups is substituted with a metal.
Though having high strength at break both in dry and in wet enough for use, the water-decomposable fibrous sheet of the invention well decomposes in water. Accordingly, the fibrous sheet does not require a large amount of an organic solvent that will irritate the skin, and therefore has many applications, for example, for wiping the private parts of human bodies and for cleaning resin objects.
In the fibrous sheet of the invention, the metal is preferably at least one selected from the group consisting of calcium, sodium, magnesium, zinc, manganese, lithium, barium and aluminium.
Also preferably, the fibrous sheet has a basis weight falling between 30 and 80 g/m
2
. In this case, still preferably, the water-insoluble carboxymethyl cellulose content of the fibrous sheet falls between 0.5 and 10% by weight. Still preferably, the fibrous sheet has a thickness of at least 0.1 mm.
Also preferably, the fibrous sheet is a water-decomposable non-woven fabric having been subjected to water-jetting treatment, or water-decomposable paper having been prepared in a paper-making process.
Also preferably, the water-dispersible fibers constituting the fibrous sheet are fibers of at least one type selected from the group consisting of pulp, regenerated cellulose, Manila hemp, and linter pulp.
Also preferably, the fibrous sheet has a degree of decomposition in water of at most 100 seconds measured in wet according to JIS P4501, a strength at break in dry of at least 1000 g/25 mm, and a strength at break in wet of at least 100 g/25 mm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The water-decomposable fibrous sheet of the invention is described in detail hereinbelow.
For the water-decomposable fibrous sheet of the invention, used are water-dispersible fibers, i.e., fibers well dispersible in water. The dispersibility in water referred to herein has the same meaning as the decomposability in water, and is meant to indicate that the fibers constituting the sheet are decomposed and dispersed well in water when kept in contact with a large amount of water.
The water-dispersible fibers constituting the sheet of the invention may be any of natural fibers and/or chemical fibers. The natural fibers include those from wood pulp such as soft wood pulp, hard wood pulp, etc.; and also those from Manila hemp, linter pulp, etc. The chemical fibers include regenerated fibers of rayon and fibrillated rayon; synthetic fibers of polypropylene, polyvinyl alcohol, polyester, polyacrylonitrile, etc. Of those, preferred are pulp and rayon, as being well dispersible in water.
The fiber length of the water-dispersible fibers is preferably at most 20 mm for the decomposability in water of the fibrous sheet comprising the fibers. More preferably, it falls between 2 mm and 10 mm. In case where rayon is used for the water-dispersible fibers, its fineness preferably falls between 1.0 and 3.0 deniers.
The fibrous sheet of the invention contains water-insoluble carboxymethyl cellulose (CMC) serving as a binder. In this, the water-insoluble carboxymethyl cellulose has a degree of substitution for etherification falling between 0.3 and 0.6. Preferably, the water-insoluble carboxymethyl cellulose has pH of at least 5.0.
The water-insoluble carboxymethyl cellulose to be in the fibrous sheet is of a type of complete substitution in which the hydrogen of the carboxyl group in at least 95%, preferably at least 99.0%, more preferably at least 99.9% of the carboxymethyl groups is substituted with
Konishi Takayoshi
Shimizu Jyoji
Takeuchi Naohito
Darby & Darby
Griffin Steven P.
Halpern M.
Uni-Charm Corporation
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