Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1996-08-21
1998-02-03
Mosley, Terressa
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
2641761, 264219, 528176, 528271, C08G 6302
Patent
active
057145695
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an aliphatic polyester resin and a method for producing same having sufficient molecular weight for practical use and specific melt properties (excellent in melt tension and remarkable non-linear elongational viscosity characteristics). Particularly, the present invention relates to the aliphatic polyester resin and the method for producing it, with the resin having improved melt properties relative to prior resins as well as excellent forming stability, thickness uniformity and the like in any forming procedure.
BACKGROUND ART
Conventionally, although plastics are used in various industries, large amounts of plastic waste have the possibility of polluting rivers, oceans, and soil to become a great social problem. To prevent such pollution the development of biodegradable plastics has been desired; for example, poly(3-hydroxybutylate) produced by fermentation methods using microorganisms, blends of general-purpose plastics and starch, a naturally occurring polymer, and the like are already known. The former polymer has a drawback in that it is poor in molding properties because the polymer has a heat decomposition temperature close to its melting point and raw material efficiency is very bad because it is produced by microorganisms. On the other hand, since the naturally occurring polymer of the latter does not by itself have thermoplasticity, the polymer has defects in molding properties, and is greatly limited in its range of application.
On the other hand, although it is known that aliphatic polyesters are biodegradable, they have hardly been used because molecular weight high enough to achieve a practical molded product cannot be obtained. Recently, it has been found that a ring-opening polymerization of .epsilon.-caprolactone produces a higher molecular weight polymer, and it has been proposed to use the polymer as a biodegradable resin. However, the resulting polymer is limited to only special applications because of a low melting point of 62.degree. C. and the high cost thereof.
Therefore, some of the inventors of the present invention proposed high-molecular weight aliphatic polyesters having sufficient physical properties for practical use, for instance, in Japanese Patent Laid-Open Nos. 4-189823, 5-70579, 5-179016, and Japanese Patent Application No. 6-246445.
These aliphatic polyester resins exhibit excellent biodegradability and physical properties having a high utility value.
However, it has become apparent that, in comparison with popularly used resins such as polyethylene resins and polypropylene resins, the above-mentioned polyester resins still have the following problems that need to be improved: (i) moldability of the resins is sometimes impaired by drawdown in blow molding and in sheet thermoforming; (ii) the product loss sometimes increases in laminate molding and film casting because of an increase in neck-in; (iii) the stability of cells is occasionally impaired (due to open cells or open bubbles) to some extent in extrusion foam molding and bead foam molding using a chemical foaming agent and/or a volatile foaming agent; (iv) the stability of film-forming is sometimes impaired to some extent in inflation film forming, resulting in poor appearance of the rolled film; and (v) in stretch blow molding, molding becomes sometimes impossible because the thickness of products becomes uneven so that some holes occur during the stretching process.
Further, the thickness uniformity and form stability of the aliphatic polyester resins should be improved.
The following means may be used to overcome the foregoing problems: controlling the molecular weight of aliphatic polyester resins to an optimum value; elevating the temperature controlling level of molding machines; and improvement of devices for molding machines, such as improvement of air rings or stabilizing plates used for inflation film forming. However, by using these means it is difficult to obtain a large increase, e.g., 20 to 30%, in the molding rate.
Conventional low density polyet
Fujihira Ryutaro
Fujimaki Takashi
Ichikawa Yasushi
Imaizumi Mitsuhiro
Kimura Hideharu
Mosley Terressa
Showa Denko K.K.
Showa Highpolymer Co. Ltd.
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