Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
2000-09-29
2004-10-26
Juska, Cheryl A. (Department: 1771)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C442S408000, C442S409000, C442S414000, C162S157600, C162S157700, C162S158000, C162S181600, C162S181700, C428S311310
Reexamination Certificate
active
06808598
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 such 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.
2. Description of the Related Art
To wipe the skin of human bodies including the private parts thereof, or to clean toilets and thereabouts, the fibrous sheet are used as wiper sheets. The strength of the wiper sheets must be enough for wiper applications. For easy and effective use, many such wiper sheets are wetted with a detergent chemical or the like previous to being used. Therefore, the wiper sheets must have high strength in wet to such a degree that they are well fit for wiping with them wetted with such a detergent chemical or the like.
On the other hand, this type of the sheets are preferably decomposable in water in order that they could be directly disposed of in toilets after their use. This is because, if poorly water-decomposable 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, etc.
Accordingly, the 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 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 disposed of in toilets. However, it is extremely difficult to produce sheets having well-balanced decomposability in water and strength.
For increasing the wet strength of fibrous sheets without lowering the decomposability in water thereof, a binder for binding the constituent fibers to each other and also various compounds for enhancing the effect of the binder are added to the sheets. For example, Japanese Unexamined Patent Publication (Kokai) No. Heisei 2-149237 discloses a water-decomposable cleaning article made of water-decomposable paper that contains a carboxyl group-having water-soluble binder, in which an alkaline earth metal such as manganese and zinc is infiltrated into the water-decomposable paper along with an organic solvent. Japanese Unexamined Patent Publication (Kokai) Nos. Heisei 9-132896 and 9-132897 disclose water-decomposable sheets which contain water-insoluble or water-swellable carboxymethyl cellulose serving as a binder, along with sodium carbonate added thereto. Japanese Unexamined Patent Publication (Kokai) No. Heisei 11-187983 discloses a water-decomposable fibrous sheet which contains an alkyl cellulose serving as a binder, along with a copolymer, an amino acid derivative and an electrolyte. However, the fibrous sheets disclosed therein have some problems. They are often sticky if containing a large amount of such a binder. They shall contain a large amount of a metallic compound serving as an electrolyte in order that the binder therein is salted out to increase the wet strength of the sheets. Using the sheets having such a large metal content for wiping the skin is unfavorable.
Japanese Unexamined Patent Publication (Kokai) No. Heisei 1-168999 discloses a water-dispersible cleaning article made of easily water-dispersible paper prepared from a mixture of from 60 to 99% by mass of water-dispersible fibers for paper and from 1 to 40% by mass of water-insoluble carboxymethylated pulp, wherein the paper carries an active material-containing organic compound applied thereto. However, a large amount of the active material-containing organic compound (e.g., mono- or polyalcohols, oils and fats, etc.) is infiltrated into the cleaning article in order to increase the wet strength of the article. If containing a large amount of a skin-irritating compound such as alcohol or the like, sheets could not be used for wiping the private parts of babies and infants. Furthermore, if containing a large amount of an organic solvent, the sheets will damage resin objects.
SUMMARY OF THE INVENTION
One 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.
Another object of the invention is to provide such a water-decomposable fibrous sheet for various wiper applications, for example, for wiping the private parts of human bodies and for cleaning resin objects.
Still another object is to provide such a water-decomposable fibrous sheet comfortably usable with no sticky feel.
According to an aspect of the invention, a water-decomposable fibrous sheet may comprise water-dispersible fibers having a fiber length of at most 20 mm and a gel compound. Though having high strength at break both in dry and in wet, the water-decomposable fibrous sheet of the invention well decomposes in water when in wet.
Preferably, the gel compound is formed from colloidal particulates and an electrolyte. More preferably, the colloidal particulates are colloidal silica. Still preferably, the colloidal silica content of the sheet falls between 0.25 g and 25 g in terms of silicic acid anhydride, relative to 100 g of the fibers constituting the sheet. Still preferably, the sheet contains an aqueous solution infiltrated thereinto and the aqueous solution contains at least 0.2% by mass of the electrolyte.
Also preferably, the sheet further contains a binder for binding the fibers to each other. More preferably, the binder is at least one compound selected from a group consisting of alkyl celluloses, carboxymethyl cellulose, polyvinyl alcohol, modified polyvinyl alcohols, sodium polyacrylate, sodium alginate, polyethylene oxide, starch, and modified starches.
Preferably, the sheet is so constructed that a layer containing the binder and the colloidal silica is formed on the surface of a fibrous layer of the water-dispersible fibers. Also preferably, it is so constructed that a layer of the binder is formed on the surface of the fibrous layer of the water-dispersible fibers containing the colloidal silica. Also preferably, the sheet contains the colloidal silica and the binder in the fibrous layer of the water-dispersible fibers.
Preferably, the fibrous layer is of a water-decomposable non-woven fabric having been subjected to water-jetting treatment. Also preferably, the fibrous layer is of a water-decomposable paper having been prepared in a paper-making process.
Preferably, a weight of the fibers constituting the sheet falls from 30 to 80 g/m
2
.
Also preferably, the sheet has a degree of decomposition in water of at most 200 seconds measured in wet according to JIS P-4501, a strength at break in dry of at least 1400 g/25 mm, and a strength at break in wet of at least 150 g/25 mm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The water-decomposable fibrous sheet of the invention will be described in detail hereinunder.
The water-dispersible fibers constituting the sheet of the invention are meant to indicate 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 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. Among those, preferred are pulp and rayon, as being well dispersible in water. Further usable herein are biodegradable fibers of polylactic acid, polycaprolactone, aliphatic polyesters such as polybutylene
Konishi Takayoshi
Takeuchi Naohito
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