Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric
Reexamination Certificate
2002-03-12
2004-06-29
Juska, Cheryl A. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
C525S450000, C525S424000, C525S434000, C525S437000, C442S414000, C428S364000, C428S397000
Reexamination Certificate
active
06756331
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a lactic acid-based resin composition and a molded article thereof. More specifically, it relates to a lactic acid-based resin composition that is excellent in moldability, flexibility and safety and is easily decomposed in the natural environment after use, and a molded article thereof.
BACKGROUND ART
In general, as resins that are excellent in flexibility, heat resistance and water resistance, such resins are exemplified, as polyethylene, polypropylene, plasticized polyvinyl chloride, polyethylene terephthalate and the like, and are used as a disposal bag, a packaging bag and the like. However, these resins increase the amount of waste upon discarding after use, and because they are substantially not decomposed under the natural environment, they semipermanently remain underground even when they are discarded underground. There also arise problems in that discarded plastics impair scenery and destroy the life environments of marine organisms.
In order to cope therewith, as a polymer having biodegradability, which is a thermoplastic resin, an aliphatic polyester derived from a polyhydroxycarboxylic acid, such as polylactic acid and the like, with an aliphatic polyhydric alcohol and an aliphatic polyhydric carboxylic acid, and the like are being developed.
These polymers are completely decomposed in the body of animals within several months to one year, or when they are placed in earth or ocean water, they begin to be decomposed within several weeks under a wet environment and disappear within about one year to several years. Furthermore, they have such characteristics that the decomposed products are lactic acid, carbon dioxide and water, which are harmless to human bodies.
In particular, polylactic acid is expected to have an expanded utility field owing to the facts that L-lactic acid as the raw material can be mass-produced at low cost by the fermentation process, and it exhibits a large decomposition rate in barnyard manure, and has excellent characteristics, such as the resistance to fungus, resistance to odorization and coloring of foods, and the like.
However, polylactic acid has high rigidity and thus cannot be said that it is a resin suitable for such purposes that require flexibility, such as a film, a packaging material and the like.
In general, it has been known as a method for softening a resin that a soft polymer is blended, but when a soft general-purpose resin, such as resins including polyethylene, polypropylene, polyvinyl chloride or the like, is mixed with polylactic acid, it is impossible to develop a lactic acid-based resin composition having biodegradability and flexibility, which is the object of the invention described later. Therefore, what can impart flexibility to polylactic acid through polymer blend is limited to soft biodegradable resins. As these resins, polybutylene succinate, polyethylene succinate, polyhydroxybutyric acid, polyhydroxyvaleric acid, polycaprolactone, a copolymer and a mixture thereof, and the like are exemplified, and they have been disclosed in Japanese Patent Laid-Open No. 245866/1996 and Japanese Patent Laid-Open No. 111107/1997.
However, these soft resins have poor compatibility with polylactic acid, and there are several problems upon practical use for producing a film, a filament and the like when it is simply melted and mixed. For example, upon molding a film and a filament, because they do not sufficiently attain uniform mixing even when they are subjected to heat melting and kneading in an extruder viscosity unevenness, unevenness in thickness of a film and unevenness in diameter of a thread occur, and furthermore, breakage of a film and breakage of a thread occur, whereby stable molding is difficult.
Moreover, even though a film or a thread can be obtained, upon subsequently subjecting orientation by stretching for increasing properties, such as heat resistance, strength and the like, it is liable to be broken upon stretching, whereby stable stretching cannot be carried out, or stretching cannot be carried out with sufficient magnification. As a result, the heat resistance and the strength cannot be sufficiently improved, and such a problem is caused in that a film and a thread that can be practically used cannot be obtained.
Japanese Patent Laid-Open No. 262474/1998 discloses an agricultural sheet formed with a mixture of (A) crystalline polylactic acid having a melting point of 150° C. or more, (B) an aliphatic polyester having a melting point of 140° C. or less formed with a linear diol and an aliphatic dicarboxylic acid as main components, and (C) a block copolymer of the polylactic acid (A) and the aliphatic polyester (B), and fibers. It is also disclosed that the mixture is improved in flowability and moldability in comparison to a simple mixture of the polylactic acid and the aliphatic polyester of a linear diol and an aliphatic dicarboxylic acid. However, there is no specific disclosure of examples, and in particular, it is expected from the description of other examples that the block copolymer (C) has a molecular weight of several hundreds of thousands. However, in the case where a block polymer having such a large molecular weight is used, the effects of improvement in flowability and moldability are not sufficiently exerted as is clear from the comparative examples described later.
As has been described, it is the current situation that it is substantially difficult that a molded article, such as a film, a filament and the like, imparted with flexibility is stably obtained with good productivity only by blending a soft biodegradable resin with polylactic acid, and furthermore, it is substantially impossible with the conventional techniques to improve properties, such as heat resistance, strength and the like, by orientation and crystallization by stretching.
In the invention, 1) a technique for effectively dispersing a soft biodegradable resin with polylactic acid, 2) development of a flexible lactic acid-based resin composition, and 3) a molded article, such as a film, a filament and the like, obtained from a flexible lactic acid-based resin composition, as well as 4) development of a production process of a molded article that is highly and effectively imparted with practical properties, such as strength, heat resistance, flexibility and the like, from polylactic acid are designated as objects.
DISCLOSURE OF THE INVENTION
In order to attain the objects, the inventors have designed and explored a compound for improving the compatibility between polylactic acid and a soft biodegradable resin, and as a result, such a compound has been found that has a sufficient compatibility effect with a small amount to satisfy the objects, whereby the invention has been completed.
That is, the invention is identified by the following items [1] to [12].
[1] A lactic acid-based resin composition comprising a mixture of a mixture (A) of polylactic acid (a1) and an aliphatic polyester (a2), and an aliphatic block co-polyester (B) having a polylactic acid segment and an aliphatic polyester segment, wherein the aliphatic block co-polyester (B) satisfies all the following conditions (1) to (3):
(1) it contains a lactic acid component in an amount of from 20 to 80 wt % in terms of monomer,
(2) it has a weight average molecular weight of 1,000 or more and less than 60,000, and
(3) it has a weight average molecular weight of the polylactic acid segment of from 500 to 55, 000 and a weight average molecular weight of the aliphatic polyester segment of from 500 to 55,000.
[2] A lactic acid-based resin composition described in item [1], wherein a compositional ratio of the mixture (A) and the aliphatic block co-polyester (B) is from 0.05 to 10 parts by weight of the aliphatic block co-polyester (B) per 100 parts by weight of the mixture (A).
[3] A lactic acid-based resin composition described in item [1] or [2], wherein the aliphatic polyester (a2) has an elastic modulus measured by the test method of JIS K
Kasemura Tomoyuki
Kitahara Yasuhiro
Kuriyama Naoto
Obuchi Shoji
Takahashi Shinya
Juska Cheryl A.
Mitsui Chemicals Inc.
Salvatore Lynda
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