Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-12-13
2004-04-06
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S437000, C525S440030, C525S446000, C524S803000, C524S806000
Reexamination Certificate
active
06716911
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing an aqueous biodegradable polyester dispersion.
BACKGROUND ART
Aqueous resin dispersions have many advantages meeting current requirements such as easy handling property and safety for operators and operation environment as compared with resin solutions in solvents and are in wide use. However, most of these aqueous resin dispersions are not biodegradable, except rubber latices, and thus put a certain load on the environment when they are discarded.
Very few aqueous dispersions (hereinafter referred to as emulsions) of biodegradable resins are disclosed or reported in patent applications and scientific reports, and most of them are aliphatic polyesters or starch derivatives. These aqueous dispersions must have a high solid concentration or a high viscosity for practical use. However, these conventional aqueous dispersions of biodegradable resins give almost no consideration to these points. For example, regarding the solid concentration by weight (hereinafter referred to “solid concentration”), disclosed are a polyhydroxyalkanoate emulsion having a solid concentration of 2.5% by weight (hereinafter simply referred to as %) (PCT International Publication No. WO97/04036), a starch derivative emulsion having a solid concentration of 18% to 28.2% (Japanese Unexamined Patent Application Publication No. 9-77910), a polycaprolactone emulsion having a solid concentration of 14.5% to 22.1% (Japanese Unexamined Patent Application Publication No. 8-81634), and an aliphatic polyester emulsion having a solid concentration of 19.3% to 32.0% (Japanese Unexamined Patent Application Publication No. 11-92712). These documents fail to describe viscosities of these emulsions.
The emulsions of biodegradable resins in the documents are produced by dissolving a solid resin in a solvent to yield a solution, and mixing and stirring the solution with an aqueous emulsifier solution (solution phase-inversion emulsification).
Accordingly, it is an object of the present invention to provide a method for producing an aqueous biodegradable polyester dispersion that has a high solid concentration and a high viscosity and is very advantageous in practical use.
SUMMARY OF INVENTION
(1) The present invention provides a method for producing an aqueous biodegradable polyester dispersion, the method comprising the step of mixing and kneading a molten biodegradable polyester, an aqueous emulsifier solution having a surface tension in terms of 1.0% by weight aqueous solution at 20° C. of less than or equal to 63 mN/m, and other additives according to necessity to thereby yield an aqueous dispersion having a solid concentration of equal to or more than 40% by weight and a viscosity at 20° C. of equal to or more than 1000 mPa·s.
(2) In the method for producing an aqueous biodegradable polyester dispersion according to (1), the ratio &eegr;
O
/&eegr;
W
of the viscosity &eegr;
O
of the molten biodegradable polyester to the viscosity &eegr;
W
of the aqueous emulsifier solution may be less than or equal to 150.
(3) In the method for producing an aqueous biodegradable polyester dispersion according to (1) or (2), the biodegradable polyester may have the following constitutional repeating unit:
wherein R
1
and R
2
are each an alkylene group containing 2 to 10 carbon atoms or an alicyclic hydrocarbon group containing 5 or 6 carbon atoms.
(4) In the method for producing an aqueous biodegradable polyester dispersion according to (1) or (2); the biodegradable polyester may structurally comprise the constitutional repeating unit described in (3) being combined through at least the following unit:
wherein R
3
is a diisocyanate residue,
and/or
the following unit:
(5) In the method for producing an aqueous biodegradable polyester dispersion according to (1) or (2), the biodegradable polyester may structurally comprise the constitutional repeating unit described in (3) being combined through at least the following unit:
and/or
the following unit:
and/or
the following unit:
wherein R
4
is an alkylene group containing 2 to 6 carbon atoms.
(6) In the method for producing an aqueous biodegradable polyester dispersion according to (1) or (2), the biodegradable polyester may have the following constitutional repeating unit:
wherein R
5
is a hydrogen, an alkyl group containing 1 to 19 carbon atoms, or an alkenyl group containing 1 to 19 carbon atoms; and n is a number from 1 to about 4.
(7) In the method for producing an aqueous biodegradable polyester dispersion according to (1) or (2), the biodegradable polyester may structurally comprise the constitutional repeating unit described in (6) being combined through at least the following unit:
wherein R
3
is a diisocyanate residue,
and/or
the following unit:
(8) In the method for producing an aqueous biodegradable polyester dispersion according to (1) or (2), the biodegradable polyester may structurally comprise the constitutional repeating unit described in (6) being combined through at least the following unit:
and/or
the following unit
and/or
the following unit:
wherein R
4
is an alkylene group containing 2 to 6 carbon atoms.
(9) In the method for producing an aqueous biodegradable polyester dispersion according to any one of (1) to (8), the emulsifier may be a poly(vinyl alcohol) or a nonionic surfactant having a polyoxyethylene chain.
(10) In the method for producing an aqueous biodegradable polyester dispersion according to any one of (1) to (9), a peak particle size may be less than or equal to 3 &mgr;m where the peak particle size is the diameter at a peak in a particle size distribution curve.
(11) In the method for producing an aqueous biodegradable polyester dispersion according to (10), the step of mixing and kneading may be performed using a screw extruder.
(12) In the method for producing an aqueous biodegradable polyester dispersion according to (11), the screw extruder may be a corotating twin-screw extruder or a grinder extruder.
(13) In the method for producing an aqueous biodegradable polyester dispersion according to (11) or (12), the aqueous emulsifier solution may be supplied separately at two or more points of the screw extruder.
Japanese Unexamined Patent Application Publication No. 56-2149 discloses a process of melting a resin and mixing the molten resin with an aqueous emulsifier solution (melt emulsification), and Japanese Unexamined Patent Application Publication No. 4-20532 discloses a process of mixing a molten mixture of a resin and an emulsifier with water. These techniques are intended to yield polyolefin resin emulsions and are irrelevant to aqueous dispersions of biodegradable polyesters, the subject matter of the present invention. Specifically, such biodegradable polyesters are different from the polyolefin resins in physical properties, particularly in surface-chemical properties with respect to water, which are important for emulsification. In addition, the biodegradable polyesters are generally more susceptible to hydrolysis than the polyolefin resins. No report has been made on the application of melt emulsification to biodegradable polyesters.
DISCLOSURE OF INVENTION
The present invention will be illustrated in further detail below. The terms “biodegradability” and “being biodegradable” used herein mean a property of being decomposed by microorganisms in soil or water in a natural environment ultimately into, for example, carbon dioxide gas and water.
Such biodegradable polyesters for use in the present invention include, for example, polyesters having a constitutional repeating unit represented by Chemical Formula (1);
biodegradable polyesters having the constitutional repeating unit of Chemical Formula (1) combined through a unit represented by Chemical Formula (2) and/or a unit represented by Chemical Formula (3) and/or a unit represented by Chemical Formula (4) and/or a unit represented by Chemical Formula (5) and/or a unit represented by Chemical Formula (6); and
polyesters having a constitutional repeating unit represented by Chemical Formula (7).
Exam
Doi Yukio
Imaizumi Mitsuhiro
Ishioka Ryoji
Okino Yoshiro
Acquah Samuel A.
Showa Highpolymer Co. Ltd.
Sughrue & Mion, PLLC
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