Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – To form particulate product
Reexamination Certificate
2000-02-15
2001-02-06
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
To form particulate product
C264S235000, C264S328160
Reexamination Certificate
active
06183679
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an injection-molded product formed from a thermoplastic resin material comprising polyglycolic acid, and more particularly to an injection-molded product of polyglycolic acid, which has excellent degradability in soil, impact resistance, toughness and heat resistance, and to a production process thereof. The injection-molded product of polyglycolic acid according to the present invention can be used in a wide variety of fields as, for example, daily sundries, stationery products, electric appliances, containers for electronic ranges, containers for boiling water pouring type instant food and various kinds of disposable ware.
BACKGROUND OF THE INVENTION
In recent years, increase in plastic waste has become a great social problem. Since many of polymeric materials have hitherto been developed and produced in search of high performance and long-term stability, they are not easily decomposed in a natural environment. Therefore, how to dispose and manage a large quantity of plastic waste which has become useless becomes a social problem on a world-wide scale. The plastic waste includes injection-molded products formed from a variety of synthetic resins, such as polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate, polyamide resins such as nylon, chlorine-containing resins such as polyvinylidene chloride, polystyrene, ABS resins, polyacetal, and polycarbonate.
Under the circumstances, biodegradable polymers, which are degraded by natural microorganisms, attract attention as polymeric materials which impose no burden on the environment. The biodegradability can be evaluated by, for example, a degradability test in soil (soil degradability test). Since injection-molded plastic products are required to have good impact resistance, toughness, heat resistance, melt processability, profitability and the like, however, any injection-molded plastic product, which fully satisfies these requirements and exhibits biodegradability, has not been yet obtained.
Among the conventional biodegradable injection-molded plastic products, for example, injection-molded products based on starch are unsatisfactory in toughness and heat resistance and involve a problem that such a plastic material is difficult to injection-mold because it is non-crystallizable. Injection-molded product based on cellulose are unsatisfactory in impact resistance, toughness and heat resistance and involve a problem that such a plastic material is difficult to injection-mold because it is low in crystallizability. Injection-molded products based on a microorganism-produced polyester involve a great problem that their production cost is very high. Injection-molded products based on a synthetic type polyester such as a polysuccinate are unsatisfactory in impact resistance, toughness and heat resistance and involve a problem that succinic acid and butanediol, which are raw materials for the polyester, are considerably expensive in addition to the fact that such a plastic material is unsatisfactory in injection moldability.
Injection-molded products based on polylactic acid, which is a semi-synthetic type polyester, must be produced through fermentation of a biological process because L-lactic acid, which is an optically active substance used as a raw material, is required to have a high purity. There is hence a limit to their production at low cost. Further, since polylactic acid has a high glass transition temperature, Tg, it also involves a problem that it is difficult to compost under ordinary composting conditions.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to cheaply provide an injection-molded plastic product, which has excellent impact resistance, toughness and heat resistance and exhibits high degradability in soil.
The present inventors have carried out an extensive investigation with a view toward overcoming the above problems involved in the prior art. As a result, it has been found that an injection-molded product formed from a thermoplastic resin material comprising polyglycolic acid having specific physical properties exhibits good degradability in soil, has excellent impact resistance, toughness and heat resistance and sufficient physical properties to replace injection-molded plastic products which have heretofore become a problem among plastic waste, and can be produced at a relatively low price.
The polyglycolic acid can be obtained, for example, by heating glycolide (i.e., a dimeric cyclic ester of glycolic acid) in the presence of a catalyst (for example, a cationic catalyst such as a tin organic carboxylate, tin halide or antimony halide), thereby subjecting it to bulk ring-opening polymerization or solution ring-opening polymerization. In order to obtain polyglycolic acid having excellent physical properties, it is preferable to use high-purity glycolide as a monomer. The high-purity glycolide can be obtained with good productivity by a process in which an oligomer of glycolic acid is mixed with a high-boiling polar organic solvent, the mixture is heated under ordinary pressure or reduced pressure to a temperature at which depolymerization of the oligomer occurs, thereby depolymerizing the oligomer in a state that the oligomer forms a solution phase, glycolide formed is distilled out together with the high-boiling polar organic solvent, and the glycolide is recovered from the distillate.
An example of a process for producing an injection-molded product from the polyglycolic acid includes a process in which the polyglycolic acid alone or a composition containing the polyglycolic acid is pelletized, the pellets thus obtained is charged into an injection molding machine to injection-mold them.
The polyglycolic acid can be industrially mass-produced by using extremely cheep raw materials of CO, H
2
O and CH
2
O or ethylene glycol. Since the injection molded product of the polyglycolic acid has degradability in soil, it scarcely imposes burden on the environment.
The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided an injection-molded product of polyglycolic acid obtainable by molding a thermoplastic resin material at an injection temperature ranging from the melting point, Tm of the polymer to 255° C., wherein the thermoplastic resin material comprises polyglycolic acid having a repeating unit represented by the following formula (1):
and the following physical properties:
(a) the melt viscosity, &eegr;* [as measured at a temperature of (the melting point, Tm of the polymer+20° C.) and a shear rate of 1,000/sec] being 30-10,000 Pa·s;
(b) the melting point, Tm being at least 150° C.;
(c) the melt enthalpy, &Dgr;Hm being at least 20 J/g; and
(d) the density being at least 1.50 g/cm
3
as measured in an unoriented, crystallized form.
According to the present invention, there is also provided a process for producing an injection-molded product of polyglycolic acid, comprising the steps of charging an injection molding machine equipped with an injection mold with pellets formed of a thermoplastic resin material which comprises polyglycolic acid having a repeating unit represented by the following formula (1):
and the following physical properties:
(a) the melt viscosity, &eegr;* [as measured at a temperature of (the melting point, Tm of the polymer+20° C.) and a shear rate of 1,000/sec] being 30-10,000 Pa·s;
(b) the melting point, Tm being at least 150° C.;
(c) the melt enthalpy, &Dgr;Hm being at least 20 J/g; and
(d) the density being at least 1.50 g/cm
3
as measured in an unoriented, crystallized form; injection-molding the pellets at a cylinder temperature of Tm to 255° C., a mold temperature of 0° C.-Tm and an injection pressure of 1-10
4
MPa; and optionally annealing the molded product for 1 second to 10 hours at a temperature ranging from the crystallization temperature, Tc
1
of the polymer to Tm.
Among the injection-molded products according to t
Hoshino Mitsuru
Kawakami Yukichika
Kouyama Toshitaka
Sato Nobuo
Shiiki Zenya
Dinsmore & Shohl LLP
Jones Kenneth M.
Kureha Kagaku Kogyo K.K.
Silbaugh Jan H.
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