Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1996-12-20
2001-07-31
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S210000, C526S211000, C526S206000, C526S224000, C526S301000, C526S307200, C524S555000
Reexamination Certificate
active
06268449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing temperature-responsive polymers that may be formed into a thermally-processable material which exhibits flushability properties when immersed in water such that the temperature-responsive polymer may be used in a disposable absorbent product to impart flushability properties to the product. The process prepares the temperature-responsive polymer in an aqueous solution using a chain transfer agent.
2. Description of the Related Art
Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. As such, the outer cover backsheet materials of the disposable absorbent products are typically made of liquid-insoluble and liquid impermeable materials, such as polypropylene films, that exhibit a sufficient strength and handling capability so that the disposable absorbent product retains its integrity during use by a wearer and does not allow leakage of the liquid insulting the product.
Although current disposable baby diapers and other disposable absorbent products have been generally accepted by the public, these products still have need of improvement in specific areas. For example, many disposable absorbent products can be difficult to dispose of into an aqueous environment. For example, attempts to flush many disposable absorbent products down a toilet into a sewage system typically lead to blockage of the toilet or pipes connecting the toilet to the sewage system. In particular, the outer cover materials typically used in the disposable absorbent products generally do not disintegrate or disperse when flushed down a toilet so that the disposable absorbent product cannot be disposed of in this way. If the outer cover materials are made very thin in order to reduce the overall bulk of the disposable absorbent product so as to reduce the likelihood of blockage of a toilet or a sewage pipe, then the outer cover material typically will not exhibit sufficient strength to prevent tearing or ripping as the outer cover material is subjected to the stresses of normal use by a wearer.
As such, there is a need for new materials that are relatively easy to process and may be used in disposable absorbent products that generally retain their integrity and strength during use, but after such use, the products may be disposed of into an aqueous environment. For example, the disposable absorbent product may be easily and efficiently disposed of by flushing the disposable absorbent product down a toilet. Such a disposable absorbent product would then be capable of being degraded by a liquid sewage system as compared to having to be disposed of into a landfill or other solid waste disposal system.
Processes known to be useful in preparing temperature-responsive polymers include free-radical solution polymerization, inverse suspension polymerization, or polymerization in organic solvents. However, such processes have generally been found to result in the temperature-responsive polymer being substantially crosslinked and/or exhibiting an intrinsic viscosity that is too high so as to prevent the temperature-responsive polymer from being capable of being thermally processable.
As such, there is a need for a process that is relatively easy to use and which process results in a temperature-responsive polymer that may then be thermally processed to prepare a material form that may be used in a disposable absorbent product to impart flushability properties to the product.
SUMMARY OF THE INVENTION
In one aspect, the present invention concerns a process for preparing a temperature-responsive polymer that exhibits an effectively low intrinsic viscosity such that the temperature-responsive polymer may then be thermally processed to prepare a flushable material.
In one embodiment of the present invention, the process comprises forming a mixture comprising water, an effective amount of a chain transfer agent, a monomer capable of being polymerized to prepare a temperature-responsive polymer, and a reaction catalyst, wherein the mixture is prepared under conditions effective to polymerize the monomer to form a temperature-responsive polymer that exhibits an intrinsic viscosity that is at least about 50 percent less than the intrinsic viscosity exhibited by an otherwise substantially identical temperature-responsive polymer that is prepared without using the chain transfer agent.
In another aspect, it is desirable to provide a temperature-responsive polymer that exhibits an effectively low intrinsic viscosity such that the temperature-responsive polymer may then be thermally or solution processed to prepare a flushable material.
In one embodiment, these goals are achieved in a temperature-responsive polymer that exhibits an intrinsic viscosity that is less than about 200 cubic centimeters per gram.
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a process for preparing a temperature-responsive polymer that exhibits an effectively low intrinsic viscosity such that the temperature-responsive polymer may then be thermally processed to prepare a flushable material.
As used herein, the term “temperature-responsive polymer” is meant to represent a polymer whose water-solubility is dependent on temperature such that the polymer will be generally water soluble below a specific temperature but will be generally water insoluble above the specific temperature. As will be appreciated by those skilled in the art, the specific temperature upon which the water-solubility of a polymer is dependent will generally vary from polymer to polymer. For purposes of the present invention, it is generally desired that the temperature upon which the water-solubility of a polymer is dependent will desirably be between about 20° C. to about 65° C., suitably between about 20° C. to about 35° C., more suitably between about 23° C. to about 28° C., and most suitably about 24° C.
Examples of polymers that are temperature-responsive and may be prepared according to the process of the present invention are polymers whose respective monomers can undergo free radical polymerization including, but are not limited to, poly(N-substituted acrylamides) such as poly(N-isopropylacrylamide), poly(N-propylacrylamide), poly(N-ethoxypropylacrylamide), and poly(N,N-diethylacrylamide), and poly(N-substituted methacrylamides) such as poly(N-isopropyl methacrylamide) and poly(N-ethoxypropyl methacrylamide). In addition, copolymers of these materials may also be prepared that is temperature-responsive. Copolymerization may permit the selection and commingling of advantageous properties of various polymers.
The process of the present invention generally comprises forming a mixture comprising water, an effective amount of a chain transfer agent, a monomer capable of being polymerized to prepare a temperature-responsive polymer, and a reaction catalyst, wherein the mixture is prepared under conditions effective to polymerize the monomer to form a temperature-responsive polymer that exhibits an intrinsic viscosity that is at least about 50 percent less than the intrinsic viscosity exhibited by an otherwise substantially identical temperature-responsive polymer that is prepared without using a chain transfer agent such as isopropanol.
The reaction mixture is typically pre
Chang Yihua
Mumick Pavneet Singh
Kilpatrick & Stockton LLP
Kimberly--Clark Worldwide, Inc.
Wilson Donald R.
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