Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1998-07-21
2001-02-20
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S158000, C162S168100, C424S402000, C428S074000, C428S208000, C428S490000
Reexamination Certificate
active
06190502
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a water-disintegratable fibrous sheet that is easily dispersed by flushing water, and more particularly, relates to a water-disintegratable fibrous sheet that is excellent in water-disintegratability, strength, heat-resistance and water-disintegratability in cold water.
BACKGROUND OF THE INVENTION
Fibrous sheets are used to cleanse human skin, e.g., skin around anus, and to clean a toilet room. The fibrous sheet is preferably water-disintegratable to be thrown away and drained in a toilet as it is. If it is not excellent in water-disintegratability, it requires a long time to be dispersed in a septic tank, and brings danger of clogging drainpipes of a toilet, when being thrown away and drained in a toilet. However, in general, a packed fibrous sheet impregnated with a cleansing liquid or the like has to be strong enough to endure conducting wiping operations while being impregnated with a cleansing liquid, and at the same time, has to keep its water-disintegratability in the event of being thrown away and drained in a toilet. Therefore, a water-disintegratable fibrous sheet that has good water-disintegratability and strength sufficient to use is demanded.
Japanese Patent Publication H7-24636, for example, discloses a water-disintegratable cleaning product composed of water-soluble binders containing a carboxyl group, metallic ions, and an organic solvent. However, the metallic ions are irritative to skin.
Japanese Laid-Open Patent H3-292924 discloses a water-disintegratable cleaning product composed of fibers containing polyvinyl alcohol impregnated with an aqueous solution of boric acid. Japanese Laid-Open Patent H6-198778 discloses a water-disintegratable sanitary napkin composed of non-woven fabric containing polyvinyl alcohol added with boric ion and bicarbonic ion. In these inventions, fibrous sheets are produced by binding each fiber using properties such that boric acid cross-links polyvinyl alcohol. However, a large amount of binder, i.e., polyvinyl alcohol, is required to produce fibrous sheets having strength sufficient to use.
Furthermore, miscellaneous products, including such water-disintegratable products, are often left in a vehicle or a warehouse during their transportation and storage, and the temperatures in such a closed space rise above the outer atmospheric temperature. In the case where they are stored in a house, they may be possibly left under a temperature of 40° C. or higher in the middle of summer. When water-disintegratable fibrous sheets which are previously impregnated are packed as finished products and then shipped to market, water-disintegratability and strength of the fibrous sheets are remarkably deteriorated if they are left under high temperature circumstances. Therefore, a water-disintegratable fibrous sheet has to retain its water-disintegratability and strength even under high temperature circumstances, that is ,its heat-resistance is important. However, there is no report relating to the heat-resistance in the water-disintegratable cleaning products and the water-disintegratable non-woven fabric disclosed in the preceding publications.
Water temperatures are generally lower than the atmospheric temperature though they vary depending on seasons. When a fibrous sheet is thrown away and drained in a toilet after used, it has to be disintegrated in water at a temperature lower than the atmospheric temperature, i.e., in cold water. However, as to the fibrous sheet using polyvinyl alcohol as a binder, its water-disintegratability is generally enhanced in response to a rise in temperatures of water, but deteriorated in response to a fall in temperatures of water.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a water-disintegratable fibrous sheet that has excellent water-disintegratability, while being strong enough to withstand wiping operations
Another object of the present invention is to provide a water-disintegratable fibrous sheet that is excellent in heat-resistance.
Still another object of the present invention is to provide a water-disintegratable fibrous sheet that is excellent in water-disintegratability even in cold water.
Still another object of the present invention is to provide a water-disintegratable fibrous sheet that does not exert harmful influence on human bodies.
The present inventors have made attention to that electrolytes have a function of salting out of polyvinyl alcohol, and have found that a water-disintegratable fibrous sheet, which is excellent in water-disintegratability, strength and heat-resistance, can be obtained by particularly using carboxylate among the electrolytes.
The present invention provides a water-disintegratable fibrous sheet comprising fibers which are bound with a water-soluble binder and formed into a sheet form, wherein the binder comprises polyvinyl alcohol and water-soluble carboxylate is added to the sheet.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the salting out of the polyvinyl alcohol with an electrolyte, such as a water-soluble carboxylate, maintains strength of the fibrous sheet, even in such a state that the fibrous sheet bound with the polyvinyl alcohol is impregnated with a cleansing liquid and the like, i.e., in a wet state. That is, a deterioration of binding strength among the fibers is prevented by the salting out of the polyvinyl alcohol with the water-soluble carboxylate. Then, when it encounters a large amount of water, the electrolyte is dissolved in water, thus the polyvinyl alcohol in a salting out state is also dissolved, and as a result, water-disintegratability is exhibited.
The water-soluble carboxylate is preferably at least one selected from the group consisting of sodium tartrate, potassium tartrate, sodium citrate, potassium citrate, sodium malate, and potassium malate. By using these salts, the water-disintegratable fibrous sheet can be produced with excellent water-disintegratability and strength. When using these salts, the carboxylate is preferably present in an amount of 1.25 g or more per 100 g of the fibers, so as to enhance strength of the water-disintegratable fibrous sheet. The water-disintegratable fibrous sheet of the present invention is preferably in a wet state, where the fibrous sheet is impregnated with an aqueous solution in which the carboxylate is dissolved, so that the carboxylate is efficiently contained in the fibrous sheet.
The polyvinyl alcohol is preferably present in an amount of 3 to 30 g per 100 g of the fibers. If the amount of the polyvinyl alcohol is more than 30 g, the resulting fibrous sheet becomes too stiff, whereas it is less than 3 g, the intended strength of the fibrous sheet cannot be obtained. From the viewpoint of water-disintegratability of the fibrous sheet, furthermore, the polyvinyl alcohol preferably has a saponification degree of 80 to 92%. It is preferred that the polyvinyl alcohol is coated as a binder on a surface of a web of fibers because of easiness of production.
The contents of the carboxylate and the polyvinyl alcohol is preferably 1.25 g or more of the carboxylate per 3 to 30 g of the polyvinyl alcohol. Water-disintegratability and strength of the water-disintegratable fibrous sheet are well-balanced in this range.
In the case where the water-disintegratable fibrous sheet of the present invention is used as wet-type tissue paper, a basis weight of the fibers is preferably 20 to 100 g/m
2
. The fibrous sheet of the present invention can be used satisfactorily as wet-type tissue paper in this range.
The water-disintegratable fibrous sheet of the present invention, which is characterized by comprising the fibers bound with the water-soluble binder and formed into the sheet form, in which the binder comprises the polyvinyl alcohol and the water-soluble carboxylate is added to the sheet, will be described in more detail below.
In the fibrous sheet of the present invention, fibers having good dispersibility in water are used. The term “dispersibility in water” used herein has the same meaning as water-disint
Konishi Takayoshi
Takeuchi Naohito
Chin Peter
Halpern Mark
Koda & Androlia
Uni-Charm Corporation
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