| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | April 6, 2004 |
| PATENT TITLE |
Method for producing aqueous biodegradable polyester dispersion |
| PATENT ABSTRACT |
The invention provides a method for producing an aqueous biodegradable polyester dispersion and includes 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.degree. C. of 63 mN/m or less, and other additives according to necessity to yield an aqueous dispersion having a solid concentration of 40% by weight or more and a viscosity at 20.degree. C. of 1000 mPa.multidot.s or more. The invention can 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. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | December 13, 2002 |
| PATENT CT FILE DATE | June 15, 2001 |
| PATENT CT NUMBER | This data is not available for free |
| PATENT CT PUB NUMBER | This data is not available for free |
| PATENT CT PUB DATE | December 20, 2001 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. 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.degree. C. of less than or equal to 63 mN/m, and other additives according to necessity to yield an aqueous dispersion having a solid concentration of equal to or more than 40% by weight and a viscosity at 20.degree. C. of equal to or more than 1000 mPa.multidot.s. 2. The method for producing an aqueous biodegradable polyester dispersion according to claim 1, wherein the ratio .eta..sub.O /.eta..sub.W of the viscosity .eta..sub.O of the molten biodegradable polyester to the viscosity .eta..sub.W of the aqueous emulsifier solution is less than or equal to 150. 3. The method for producing an aqueous biodegradable polyester dispersion according to claim 1 or 2, wherein the biodegradable polyester has the following constitutional repeating unit: ##STR14## wherein R.sup.1 and R.sup.2 are each an alkylene group containing 2 to 10 carbon atoms or an alicyclic hydrocarbon group containing 5 or 6 carbon atoms. 4. The method for producing an aqueous biodegradable polyester dispersion according to claim 1 or 2, wherein the biodegradable polyester structurally comprises the constitutional repeating unit according to claim 3 being combined through at least the following unit: ##STR15## wherein R.sup.3 is a diisocyanate residue, and/or the following unit: ##STR16## 5. The method for producing an aqueous biodegradable polyester dispersion according to claim 1 or 2, wherein the biodegradable polyester structurally comprises the constitutional repeating unit according to claim 3 being combined through at least the following unit: ##STR17## and/or the following unit: ##STR18## and/or the following unit: ##STR19## wherein R.sup.4 is an alkylene group containing 2 to 6 carbon atoms. 6. The method for producing an aqueous biodegradable polyester dispersion according to claim 1 or 2, wherein the biodegradable polyester has the following constitutional repeating unit: ##STR20## wherein R.sup.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. The method for producing an aqueous biodegradable polyester dispersion according to claim 1 or 2, wherein the biodegradable polyester structurally comprises the constitutional repeating unit according to claim 6 being combined through at least the following unit: ##STR21## wherein R.sup.3 is a diisocyanate residue; and/or the following unit: ##STR22## 8. The method for producing an aqueous biodegradable polyester dispersion according to claim 1 or 2, wherein the biodegradable polyester structurally comprises the constitutional repeating unit according to claim 6 being combined through at least the following unit: ##STR23## and/or the following unit ##STR24## and/or the following unit: ##STR25## wherein R.sup.4 is an alkylene group containing 2 to 6 carbon atoms. 9. The method for producing an aqueous biodegradable polyester dispersion according to claim 1, wherein the emulsifier is a poly(vinyl alcohol) or a nonionic surfactant having a polyoxyethylene chain. 10. The method for producing an aqueous biodegradable polyester dispersion according to claim 1, wherein a peak particle size is less than or equal to 3 .mu.m, where the peak particle size is the diameter at a peak in a particle size distribution curve. 11. The method for producing an aqueous biodegradable polyester dispersion according to claim 1, wherein the step of mixing and kneading is performed using a screw extruder. 12. The method for producing an aqueous biodegradable polyester dispersion according to claim 11, wherein the screw extruder is a corotating twin-screw extruder or a grinder extruder. 13. The method for producing an aqueous biodegradable polyester dispersion according to claim 11 or claim 12, wherein the aqueous emulsifier solution is supplied separately at two or more points of the screw extruder. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
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.degree. 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.degree. C. of equal to or more than 1000 mPa.multidot.s. (2) In the method for producing an aqueous biodegradable polyester dispersion according to (1), the ratio .eta..sub.O /.eta..sub.W of the viscosity .eta..sub.O of the molten biodegradable polyester to the viscosity .eta..sub.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: ##STR1## wherein R.sup.1 and R.sup.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: ##STR2## wherein R.sup.3 is a diisocyanate residue, and/or the following unit: ##STR3## (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: ##STR4## and/or the following unit: ##STR5## and/or the following unit: ##STR6## wherein R.sup.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: ##STR7## wherein R.sup.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: ##STR8## wherein R.sup.3 is a diisocyanate residue, and/or the following unit: ##STR9## (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: ##STR10## and/or the following unit ##STR11## and/or the following unit: ##STR12## wherein R.sup.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 .mu.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). Examples of such biodegradable polyesters further include polyesters each having both the constitutional repeating units of Chemical Formulae (1) and (7), and the polyesters just mentioned above further having at least one of the units of Chemical Formulae (2) through (6). In addition, random and/or block copolymers and blends of these polyesters are also useful. More specifically, examples of the biodegradable polyesters having any one of the units of Chemical Formulae (1) through (6) are poly(butylene succinate), poly(butylene succinate adipate), poly(ethylene succinate), poly(ethylene succinate adipate), and reaction products prepared by combining these polyesters with hexamethylene diisocyanate or .gamma.-aminopropyltrimethoxysilane. Examples of the biodegradable polyesters having the constitutional repeating unit of Chemical Formula (7) include polycaprolactone, poly(lactic acid), poly(glycolic acid), as well as polyhydroxybutyrate-polyhydroxyvalerate copolymers, and other polyhydroxyalkanoates produced by microorganisms. The biodegradable polyesters may further includes another structure than the aforementioned structures within ranges not deteriorating their biodegradability. Examples of such biodegradable polyesters are poly(butylene succinate) prepared by introducing 25% or less of a reaction product of dehydration condensation of ethylene glycol and terephthalic acid into the constitutional repeating unit, and poly(butylene succinate terephthalate) and poly(ethylene succinate terephthalate) each containing less than or equal to 40% by mole of a terephthalate constitutional repeating unit. Emulsifiers for use in present invention should have a surface tension in terms of 1% aqueous solution at 20.degree. C. of less than or equal to 63 mN/m, preferably less than or equal to 60 mN/m, and more preferably less than or equal to 55 mN/m. If the surface tension exceeds 63 mN/m, constitutive particles of the resulting emulsion may not be sufficiently divided and thus invite coarse particles on the order of several millimeters, or a solid phase and an aqueous phase are separated to thereby fail to yield a stable emulsion. The emulsifiers include, for example, surfactants such as sodium lauryl sulfate, sodium oleate, and other anionic surfactants comprising an aliphatic acid salt containing 4 to 18 carbon atoms; lauryl trimethylammonium chloride and other cationic surfactants; N-lauryl glycine and other ampholytic surfactants; and polyoxyethylene nonylphenyl ether and other nonionic surfactants. Such nonionic surfactants also include those used as food additives such as glycerin fatty acid esters, sucrose fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, lecithin, and their ethylene oxide adducts. The emulsifiers also include water-soluble macromolecular substances such as starch, casein, and gelatin, as well as those used as food additives for thickening such as alginic acid, alginates, Locust bean gum, guar gum, gum arabic, xanthan gum, agar, carrageenan, crystalline cellulose, pectin, and other naturally-occurring macromolecular substances; hydroxyethylcellulose, methylcellulose, carboxymethyl cellulose, propylene glycol arginate, cationic modified starch, and other semisynthetic macromolecular substances; poly(vinyl alcohol), polyacrylamides, poly(vinyl pyrrolidone), poly(acrylic acid), polyvinylpyridine, poly(ethylene imine), as well as copolymers or modified products of these polymers to have an anionic, cationic, or hydrophobic constitutional unit; copolymers of vinyl monomers such as acrylic esters, methacrylic ester and styrene with acidic monomers such as acrylic acid, methacrylic acid and malic anhydride, with basic monomers such as vinylpyridine and dimethylaminoethyl methacrylate, or with hydroxyl-group-containing monomers such as hydroxyethyl acrylate, and hydroxyethyl methacrylate; and biodegradable polyesters modified with succinic anhydride, maleic anhydride, or polyethylene oxide, and other synthetic macromolecular substances. Surface acting substances other than the above substances can be additionally used within ranges not deteriorating the biodegradability of the resulting aqueous biodegradable polyester dispersion. For satisfactory biodegradability, preferred emulsifiers include partially saponified poly(vinyl alcohol)s inclusive of acetic acid group built-up type; partially saponified poly(vinyl alcohol)s having a sulfonic group, carboxyl group or amino group; and water-soluble biodegradable polyesters having a carboxyl group or polyoxyethylene residue. Among them, poly(vinyl alcohol)s and nonionic surfactants having a polyoxyethylene chain are typically preferred. The ratio .eta..sub.O /.eta..sub.W of the viscosity of the molten biodegradable polyester .eta..sub.O to the viscosity .eta..sub.W of the aqueous emulsifier solution is preferably less than or equal to 150, more preferably less than or equal to 100, and typically preferably less than or equal to 60, wherein the viscosity .eta..sub.O means the viscosity of the biodegradable polyester at a temperature 30.degree. C. higher than the melt temperature (Tm) of the biodegradable polyester; and the viscosity .eta..sub.W means the viscosity of the aqueous emulsifier solution at a temperature of 80.degree. C. A ratio .eta..sub.O /.eta..sub.W out of this range may invite coarse particles in large amounts, separation of the solid phase and the aqueous phase, or W/O emulsions or solids at ambient temperature, and thereby target products are not obtained in many cases. To control the viscosities to satisfy the above specified condition, the biodegradable polyester can further comprise a plasticizer or the aqueous emulsifier solution can further comprise a thickener. The amount of the emulsifier is preferably more than 5% by weight, for example from 6 to 25% by weight, relative to the biodegradable polyester. The biodegradable polyester must be melted and the aqueous emulsifier solution must be prepared before performing the method of the present invention. The aqueous emulsifier solution can be prepared according to a regular dissolution procedure, and the melting of the biodegradable polyester will be illustrated below. The biodegradable polyester is melted by heating to a temperature higher than its melting point. The melting is generally performed at a temperature higher than the melting point by 10.degree. C. or more using a drum, an emulsification equipment or an extruder. The volatile content of the melt is preferably less than or equal to 0.3%. If the volatile content exceeds 0.3%, the molten biodegradable polyester yields foams upon mixing with the aqueous emulsifier solution, and the resulting mixture is not sufficiently sheared and milled to cause coarse particles. Next, mixing of the molten biodegradable polyester (the biodegradable polyester melt) and the aqueous emulsifier solution, more specifically, dispersion of the former into the latter will be illustrated. The dispersion is believed to occur in the following manner. Initially, a W/O disperse system comprising the molten biodegradable polyester as a continuous phase and the aqueous emulsifier solution as a disperse phase is formed at early stages of dispersion. Next, phase inversion occurs after continuous kneading to yield an O/W dispersion system comprising the aqueous emulsifier solution as a continuous phase and the biodegradable polyester as a disperse phase. It has been observed that finer particles can be obtained with a steep viscosity-increase immediately before phase inversion. To increase the viscosity more steeply and to further extent, it is effective to finely disperse the aqueous phase component in the W/O dispersion system before phase inversion, which requires a large shearing force. Dispersion means to yield such a large shearing force as to finely divide the particles include, for example, homomixers, homogenizers, colloid mills, extruders, kneader-ruders, and agitators (dispersers) having modified helical blades for use in highly viscous liquids. Among them preferred are high-performance disperse that disperse an material by local mixing by means of a high-speed disperser and by rotation and revolution of a blade capable of equally agitating the whole material (hereinafter referred to as "high-performance dispersers"), corotating twin-screw extruders, grinder extruders, and other screw extruders. In any dispersing apparatus, (i) the aqueous emulsifier solution is added to the molten biodegradable polyester with stirring, or (ii) the aqueous emulsifier solution and the molten biodegradable polyester are charged into the dispersing apparatus concurrently and are then agitated to start the mixing and dispersing process. The extruders can perform the procedure (i), and the high-performance dispersers can perform any of the procedures (i) and (ii). For example, when a corotating twin screw extruder or grinder extruder is used, the biodegradable polyester is continuously fed to the extruder through its hopper, and separately the aqueous emulsifier solution is injected into the extruder through a supply port disposed at any position other than the point where the resin is melted. Then the biodegradable polyester is melted, is mixed and kneaded with the aqueous emulsifier solution, or is further mixed and kneaded with water at a temperature lower than or equal to 100.degree. C. and thereby continuously yields an aqueous dispersion of the biodegradable polyester. In this procedure, two or more supply ports can be arranged according to necessity. When a high-performance disperser is used, the biodegradable polyester is charged into the disperser, is heated and melted; the aqueous emulsifier solution is added to the molten biodegradable polyester with stirring in one installment or dropwise and thereby yield a target aqueous dispersion of the biodegradable polyester. When the biodegradable polyester has a melting point of equal to or higher than 100.degree. C., the biodegradable polyester may further comprise a plasticizer to lower the melting point, or a pressure-tight apparatus is used. As a result, the mixing and dispersing procedure can be performed in the same manner as above. The aqueous dispersion of biodegradable polyester prepared by the melt emulsification may have a solid concentration of from 40% to 65% by weight, preferably from 50% to 65% by weight, and more preferably from 55% to 65% by weight, and a viscosity at 20.degree. C. of from 10.sup.3 mPa.multidot.s to 10.sup.4 mPa.multidot.s, preferably from 1500 mPa.multidot.s to 10.sup.4 mPa.multidot.s, and more preferably from 2000 mPa.multidot.s to 10.sup.4 mPa.multidot.s. The solid concentration and viscosity can be appropriately determined according to the purpose of the aqueous dispersion, and the aqueous dispersion may be diluted where necessary. In the aqueous dispersion, the biodegradable polyester constitutes micron-to submicron-fine particles. The peak particle size is generally less than or equal to 10 .mu.m, and preferably less than or equal to 5 .mu.m and more preferably less than or equal to 3 .mu.m, while depending on its intended purpose. Troubles induced by standing still, such as sedimentation of emulsion particles or separation of water, can be prevented by controlling the viscosity in consideration of the particle size. The aqueous dispersion has pH in the range of from 3 to 7 in many cases. When the aqueous dispersion is acidic with pH lower than 3 or is basic with pH higher than 7, standing conditions (temperature and time) must be carefully set to avoid hydrolysis. The aqueous biodegradable polyester dispersions prepared according to the present invention can be formulated into compositions further comprising any of additives such as plasticizers, tackifiers, fillers, pigments, dispersion stabilizers, and chemical agents such as insecticides, pharmaceutical drugs and agricultural chemicals according to necessity. Such additives are incorporated into the aqueous dispersions by means of processes according to their forms, properties, and formulation amounts, as well as intended purposes of the resulting compositions. For example, pellets comprising the biodegradable polyester and the additives previously are previously prepared and are used; the additives are added to the melt phase and/or aqueous phase in any process step of the melt emulsification; or the additives are added to extruded products. Promising fields by function in which the aqueous dispersions can be used in practice include, for example, adhesion, coating, sustained release, and forming or molding as excipients. When the biodegradable polyester as emulsion particles must be coalesced in practical use, means for coalescence, such as heating, pressurization, addition of solvents or plasticizers, are required. However, these means are not required when the aqueous dispersions are used in applications in which the particles coalesce with each other as a result of evaporation of water, such as in pressure sensitive adhesion. The adhesion function (adhesion capability) means not only narrow definition of adhesion to bond wood, boards, cloths, and glass, but also includes capability of serving as adhesives in the broad sense of term. Such adhesives are used to bond organic materials such as wood pulp, staple fibers, wood pieces, leather chips, synthetic fibers, and synthetic webs; or inorganic materials such as rock wool, cement, white marble, asbestos, clay, porcelain clay, powders of metals, and metal oxides to form reinforced paper, pulp molds, nonwoven fabrics, artificial leather, inorganic fiber boards, and inorganic building boards. They are also used to impregnate paper, cloths and other materials to reinforce and toughen the materials to thereby yield book jackets, starched bed sheets, and starched shirts. When the aqueous dispersions are used in these applications, the resulting products are biodegradable, can be easily decomposed in a natural environment after discarded and thus do not invite environmental pollution caused by discarded articles. Moreover, when the aqueous dispersion is used as a heat sealing agent for paper, it can exhibit blocking resistance at high temperature and high humidity due to the crystallinity of the biodegradable polyester, can adhere in a short time, can be hydrolyzed and thus does not invite environmental pollution. The aqueous dispersion can thereby be used as a recyclable heat sealing agent. The aqueous biodegradable polyester dispersions prepared according to the present invention can also be used in applications requiring coating function. Coating is performed for protection or for yielding good appearance by imparting resistance such as toughness, water resistance, light resistance, chemical resistance, and aging resistance. Coating is also performed to impart sustained release properties to fertilizers and chemical agents. A variety of resins have been used in these applications, but most of such resins remain without decomposition and thus cause environmental pollution. From this viewpoint, coating of the following materials is one of the optimum applications of the aqueous biodegradable polyester dispersions. Such coating procedures include, for example, coating of materials that can be decomposed in a natural environment, such as paper, wood and leather; coating of fertilizers, agricultural chemicals, pharmaceutical preparations, and other medicated materials that exhibit effects by being delivered in a minimum dose to a target site at a predetermined rate; and coating of submersible metals, concrete, and other materials for use in shipping and constructions in oceans and rivers so as to avoid adhesion of underwater creatures such as mussels and acorn shells. Final products of the aqueous dispersions are paints, inks, and other coatings. Articles to be coated with the coatings can be selected within broad ranges including paper, cloths, wood, plastics, cement products, concrete, metals, agricultural chemicals, insecticides, pharmaceutical preparations, and fertilizers. In addition, the aqueous dispersions can also be applied to the following use owing to the crystallinity of the constitutive biodegradable polyesters. Specifically, articles obtained by coating, adhesion or impregnation of the aqueous biodegradable polyester dispersions, such as felt, are placed in a mold, are molded by the application of heat and pressure and thereby yield, for example, caps and hats, nurse's caps, and lining boxes of containers. The articles are also dried and heated and thereby yield disposable resin gloves. The aqueous biodegradable polyester dispersions prepared according to the present invention are applied to target points by using brushes, sprays, coaters, and other already available devices according to the purposes thereof. Where necessary, the coated articles are heated to a temperature equal to or higher than the melting point of the biodegradable polyester after application to complete coating. More specifically, such coating applications include, for example, wood coating, construction coating (building coating), antifouling coating, shipping coating, road marking coating, magnetic recording medium coating, and other painting applications in general senses; undercoating of recording paper, coated printing paper, printing art paper, moisture-proof paper, waterproof paper, water-repellent paper, release paper, and label paper; coating of paper, nonwoven fabrics, woven fabrics, and other materials for covering books; coating of shopping bags, paper bags, paper towels, and tissue paper; and coating of fertilizers, agricultural chemicals, and insecticides to yield sustained-release products. The adhesion and coating procedures can be performed concurrently in practical use. For example, an absorber comprising wood pulp and an absorbing agent is sandwiched between the reinforced paper as a top sheet and a sheet coated with the aqueous biodegradable polyester dispersion as a back sheet. The resulting three layers are bonded using the aqueous biodegradable polyester dispersion and thereby yield diapers (nappies), sanitary napkins, and other products that can be converted into compost. To utilize the sustained release property, a chemical agent is incorporated into the aqueous biodegradable polyester dispersion. In this case, the chemical agent is added to the biodegradable polyester in advance, is added to the melt or the aqueous emulsifier solution, or is added to the aqueous dispersion after its preparation. The resulting aqueous biodegradable polyester dispersion containing the chemical agent can be used as intact or by applying to paper, cloths, wood, leather, biodegradable plastics, and other biodegradable substrates. For example, products such as sustained-release agricultural chemicals, sustained-release fertilizers, and sustained-release and long-life anti-termite agents are spread as intact over soil. Aqueous dispersions containing pheromones and other insect pest control agents or anti-inflammatory analgesic agents for neuralgia are applied to substrates such as paper, cloths, and biodegradable plastic films before practical use. |
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