Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-03-07
2002-01-01
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S054310, C525S288000, C525S296000, C525S329500, C525S329800, C525S329900, C525S340000, C525S360000, C525S364000, C525S374000, C525S377000, C525S378000, C525S379000, C525S380000, C525S386000, C525S418000
Reexamination Certificate
active
06335398
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a super absorbent polymer composition in which a super absorbent polymer has improved stability. More particularly, it relates to a super absorbent polymer composition in which a super absorbent polymer is protected against decomposition and/or deterioration even in a water-containing state, i.e., containing an aqueous liquid or a body fluid such as urine, blood and sweat.
BACKGROUND ART
Super absorbent polymers have been used widely as an absorbent material in disposable diapers for babies, adults and persons suffering from incontinence or sanitary napkins in the field of sanitation; water-retaining materials in the field of agriculture and horticulture; and coagulants for sludge, materials for preventing dew drop condensation or water stopping materials in the field of construction. It is known that water-soluble high-molecular weight compounds constituting such super absorbent polymers undergo reduction in molecular weight and deterioration with time in the presence of radical generating species, such as hydrogen peroxide or L-ascorbic acid or salts thereof.
Body fluids such as urine, blood and sweat contain L-ascorbic acid or salts thereof. Therefore, it has been a great problem that a super absorbent polymer used in a disposable diaper or a sanitary napkin having absorbed therein such a body fluid undergoes decomposition and deterioration with time by the action of the radical species generated from L-ascorbic acid or salts thereof and therefore reduces its capacity of retaining the body fluid.
The decomposition of a super absorbent polymer due to radical generating species is pronounced in its water-containing state in an air atmosphere, especially in the presence of an aqueous solution containing transition metal ions, such as iron and copper, capable of having an oxidation number of 2 or more.
This is because a trace amount of a transition metal ion, such as iron and copper, acts as a catalyst to markedly accelerate the decomposition reaction (radical generating reaction) of hydrogen peroxide, or L-ascorbic acid or salts thereof, as described in J. Am. Chem. Soc., 89, No. 16, 4176 (1967) and Free Radical Research Communications, 1, No. 6, 349 (1986).
These transition metal ions are known, like radical generating species such as hydrogen peroxide or L-ascorbic acid or salts thereof, to cause depolymerization of water-soluble polymers with time (see, e.g., Carbohydrate Research, 4, 63 (1967)).
Means that have been widely employed for suppressing decomposition and deterioration of super absorbent polymers include (1) sealing of a super absorbent polymer under reduced pressure or in a nitrogen atmosphere to avoid contact with air (especially with oxygen), (2) use of highly purified water and reagents to inhibit incorporation of metal ions into a super absorbent polymer, (3) addition of an antioxidant or a reducing agent to a super absorbent polymer, (4) addition of a protein or an enzyme to a super absorbent polymer, and (5) addition of a metal chelating agent, such as citric acid, (poly)phosphoric acid or salts thereof, or ethylenediaminetetraacetic acid (EDTA) or salts thereof, to a super absorbent polymer (JP-A-63-146964 corresponding to EP-A-257951).
In many cases, however, means (1) and (2) are impossible to carry out for some end uses of a super absorbent polymer. Means (3), (4) and (5) including addition of a known additive suppress decomposition and deterioration of a super absorbent polymer, but the effect exerted is not always sufficient. Cases are often met with in which the additive must be added in a large quantity or an additive having a very strong action must be used. Under such a situation, it is likely that the inherent physical properties or performances of super absorbent polymers should be impaired seriously. Additionally, where the system containing a super absorbent polymer is used in direct contact with a human body or a plant or an animal, adverse influences on the living system give rise to a problem.
In fact, various methods for suppressing decomposition and deterioration of super absorbent polymers have been proposed to date. For example, Japanese Patent Application Laid-Open 63-272349 (corresponding to EP-A-268459, U.S. Pat. No. 4,959,060), Japanese Patent Publication 5-34383 (corresponding to EP-A-249391, U.S. Pat. No. 4,972,019), and Japanese Patent Application Laid-Open 2-255804 (corresponding to EP-A-372981) and 3-179008 disclose a method of using additives such as a sulfur-containing reducing agent, an oxygen-containing reducing inorganic salt, a water-soluble chain transfer agent. Nevertheless, these additives have a disadvantage of giving off an offensive odor or being an irritant and/or an allergen and need sufficient care for safety when actually used under such conditions that the additive may contact with a human body. Thus, an additive having higher safety has been keenly demanded.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to provide a super absorbent polymer composition in which the super absorbent polymer can exist stably without undergoing decomposition and deterioration even in the presence of an aqueous solution or water containing radical generating species, such as hydrogen peroxide or L-ascorbic acid or salts thereof, and which has high safety for a living system.
The present inventors have conducted extensive investigations to solve the above-mentioned problem. As a result, they have found that a super absorbent polymer in a water-absorbing state can be stabilized by inhibiting a decomposition reaction (radical generating reaction) of radical generating species, such as hydrogen peroxide or L-ascorbic acid or salts thereof and that this can be achieved by completely sequestering a transition metal ion acting as a catalyst for the radical generating reaction by converting the transition metal ion into a water-insoluble chelate.
The present invention has been reached based on the above finding. That is, the above object of the present invention is accomplished by a super absorbent polymer composition comprising a chelating compound (A) which has a site capable of forming a chelate with a copper ion and whose copper salt has a solubility in physiological saline at 25° C. of 0.01% by weight or less (excluding &bgr;-diketone derivatives) and a super absorbent polymer (B), wherein said chelating compound (A) is present in an amount of from 0.0001 to 30 parts by weight per 100 parts by weight of said super absorbent polymer (B).
The super absorbent polymer composition of the present invention is effectively used, though dependent on the kind of the super absorbent polymer used, in combination with cosmetics or food additives containing radical generating species, such as ascorbic acid. The super absorbent polymer composition of the present invention is particularly suitable as an absorbent material of sanitary articles.
DETAILED DESCRIPTION OF THE INVENTION
The super absorbent polymer composition of the present invention will be described below in detail.
The super absorbent polymer (B) which can be used in the present invention is not particularly limited. Examples of usable super absorbent polymer (B) include partially crosslinked polymers having a carboxyl group or salts thereof, such as a crosslinked polyacrylic acid salt, a crosslinked poly(vinyl alcohol/acrylic acid salt) copolymer, a (crosslinked) starch-acrylic acid salt graft copolymer, and a crosslinked polyvinyl alcohol-poly(maleic anhydride salt) graft copolymer; and partially crosslinked polysaccharides, such as a crosslinked carboxymethyl cellulose salt. From the viewpoint of water absorption capacity, it is preferable to use a crosslinked polyacrylic acid salt or a (crosslinked) starch-acrylic acid salt graft copolymer, with a crosslinked polyacrylic acid salt being especially preferred.
These super absorbent polymers (B) may be used either individually or in combination of two or more thereof.
The salt in the super absorbent polymers includes, for example, an alkali metal salt, a
Amiya Takayuki
Hanada Yoko
Miyanaga Seiichi
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Reddick Judy M.
LandOfFree
Super absorbent polymer composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Super absorbent polymer composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Super absorbent polymer composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2820552