Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-02-06
2002-10-08
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S447000, C524S451000, C524S493000, C264S210700, C264S211180
Reexamination Certificate
active
06462105
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aliphatic polyester composition for a masterbatch, and a method for producing an aliphatic polyester film using said composition. More specifically, it relates to an aliphatic polyester composition for a masterbatch which is excellent in dispersibility of an anti-blocking agent and molding stability and which is suited for producing a film having a high transparency, and a method for producing an aliphatic polyester film using said composition.
BACKGROUND OF THE INVENTION
When a film is produced using a resin, anti-blocking agents such as an inorganic filler, a wax and the like are usually added in consideration of molding stability in formation of a film, handling in fabrication of a film and the like. Further, for producing a resin having flexibility, a method in which a plasticizer, an elastomer and the like are added to a resin has been widely used. However, when these softening agents are added, molded products tend to be adhered to each other. Accordingly, an anti-blocking agent has to be added in many cases.
Meanwhile, as a biodegradable thermoplastic resin that is degraded in a natural environment, a lactic acid homopolymer, a copolymer of L-lactic acid and D,L-lactic acid or a copolymer of lactic acid and hydroxycarboxylic acid (these are hereinafter abbreviated generally as lactic acid-based polymers) have been proposed. These polymers are biodegraded by 100% by weight in animal bodies within several months to one year. When they are placed in soil or sea water, the degradation starts under wet atmosphere in several weeks, and the polymers are destroyed in approximately one to several years. Further, a degradation product has a characteristic feature that it is changed into nontoxic lactic acid, carbon dioxide and water.
Lactic acid as a raw material of polylactic acid is produced by a fermentation method or chemical synthesis. Recently, especially L-lactic acid according to a fermentation method has been mass-produced, and it becomes less costly. Further, the resulting polylactic acid has a characteristic feature that rigidity is high. In view of these facts, development of various uses has been currently carried out. Molded products, such as films and the like, obtained by injection molding, extrusion molding, blow molding and the like of these lactic acid-based polymers are excellent in rigidity, but are liable to cause blocking of molded products, and poor handing in use and mechanical adaptability in fabrication. Moreover, when a plasticizer is added to improve flexibility, molded products are more liable to cause blocking, and therefore are poor in handling and fabrication property.
It is known that silica is added to a biodegradable polymer as an inorganic filler. For example, Japanese Patent Laid-Open No. 70,696/1993 and International Patent Publication Nos. 504,731/1992 and 508,669/1993 are mentioned. Japanese Patent Laid-Open No. 70,696/1993 discloses that with respect to a material of a plastic container, a biodegradable plastic such as a poly-3-hydroxybutyrate/poly-3-hydroxyvalerate copolymer, polycaprolactone or polylactic acid is blended with 10 to 40% by weight of calcium carbonate having an average particle diameter of 20 &mgr;m or less and hydrous magnesium silicate (talc). Inorganic fillers in large amounts are added to expedite degradation of biodegradable plastics after being discarded.
International Patent Publication No. 504,731/1992 (WO-90/01521) describes that properties such, as hardness, strengths and temperature resistance are changed by adding inorganic fillers such as silica and kaolinite to lactide thermoplastics. Further, in International Patent Publication No. 508,669/1993 (WO-92/01737), calcium silicate and talc are used as a processing aid in polylactic acid as a degradable foaming material, and used as a nucleating agent in expansion-extrusion molding. However, these are not for improving the anti-blocking property of films.
Further, in the production of a resin composition for a masterbatch, the addition of a dispersing agent is generally conducted to improve dispersibility of a filler. Regarding a lactic acid-based polymer, various additives are used for modification, for example, softening, of aresin. For example, Japanese Patent Laid-Open No. 34,913/1996 discloses the addition of hydroxy-polyvalent carboxylic acid esters such as tributyl acetylcitrate and the like and polyhydric alcohol esters such as glycerol triacetate and the like. However, these additives are for imparting flexibility to a resin and not for improving dispersibility of a filler.
DISCLOSURE OF THE INVENTION
In case of molding a polymer, a so-called full compound method in which a total amount of various additives is added to a polymer, they are blended and pelletized, and the resulting pellets are fed to a molding machine for molding, or a so-called masterbatch method in which predetermined amounts of various additives are added in advance to a polymer so as to produce a masterbatch, the resulting masterbatch is diluted with a pelletized polymer, and this is fed to a molding machine for molding.
The former method is advantageous in that uniform dispersibility of various additives is good, but the total amount of the polymer is pelletized, which is not economical. Further, the latter method is advantageous in that only the polymer in an amount corresponding to the masterbatch can be pelletized. However, the dispersibility of various additives tends to be decreased.
In view of these problems, the invention aims to provide an aliphatic polyester composition for a masterbatch which is improved in dispersibility of a filler, anti-blocking property, transparency, molding stability and slipperiness and which is suited for production of an aliphatic polyester film, and a method for producing an aliphatic polyester film improved in anti-blocking property, transparency, molding stability and slipperiness using said composition.
In order to attain the aim, the present inventors have assiduously conducted investigations, and have consequently found that a resin composition obtained by adding an anti-blocking agent and, as required, a dispersing agent to an aliphatic polyester provides an aliphatic polyester film excellent in anti-blocking property, transparency, molding stability and slipperiness. This finding has led to the completion of the invention.
That is, the invention is an aliphatic polyester composition for a masterbatch comprising 100 parts by weight of an aliphatic polyester, and 0.1 to 40 parts by weight of an anti-blocking agent.
In the invention, it is preferable that the aliphatic polyester is a lactic acid-based polymer. Further, it is preferable that the anti-blocking agent is inorganic particles of at least one selected from titanium dioxide, magnesium carbonate, barium sulfate, magnesium silicate, silica, talc and kaolin. More preferable is silica. It is preferable that these anti-blocking agents have an average particle diameter of 0.007 to 0.05 &mgr;m.
As a preferable embodiment of the aliphatic polyester composition for the masterbatch in the invention, the composition containing 0.1 to 10 parts by weight, per 100 parts by weight of an aliphatic polyester, of a dispersing agent as a third component. As a preferable example of the dispersing agent, at least one compound selected from an polyhydric alcohol ester, a polybasic carboxylic acid ester and a hydroxy-polyvalent carboxylic acid ester is mentioned.
The aliphatic polyester composition for the masterbatch in the invention is preferably a composition obtained by conducting kneading, melt-extrusion and pelletization at 150 to 230° C. and then heat treatment at 40 to 100° C. for 2 to 10 hours. The production under such conditions can control crystallinity in the range of 10 to 60%.
Another aspect of the invention is a method for producing an aliphatic polyester film, which comprises adding 19 to 49 parts by weight of an aliphatic polyester to 1 part by weight of the aliphatic polyester composition for the masterbatch to form a molding material, a
Ikado Shuhei
Kuroki Takayuki
Burns Doane , Swecker, Mathis LLP
Mitsui Chemicals Inc.
Yoon Tae H.
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