JPH11226986A - Manufacturing method of injection molded articles made of starch-based biodegradable plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a starch powder having a masterbatch composed of a biodegradable resin, and without deteriorating the physical properties of a molded article to be obtained, and preferably to adversely affect the water content of the starch powder. To provide a method of eliminating molded articles directly. SOLUTION: Starch powder 10 to 70% by weight and biodegradable resin 30 to 90% by weight are quantitatively introduced directly into an injection molding machine using a quantitative feeder without prior mixing and injection molding. For producing a starch-based biodegradable plastic molded article. Preferably, a low moisture starch powder having a moisture content of 5% or less is used as the starch powder, or a low moisture starch powder having a moisture content of 5% or less is obtained by drying the raw starch powder with a vent. After that, it is supplied to an injection molding machine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plastic molded article containing biodegradable starch, and more particularly to a method using injection molding.

[0002]

2. Description of the Related Art Various types of composites comprising starch and a biodegradable resin are known. For example, a complex composed of starch and polylactic acid (Japanese Unexamined Patent Publication No.
No. 39398), and a composite comprising starch and a biodegradable aliphatic polyester (Japanese Patent Publication No. 7-78167).

[0003] However, a molded body composed of the starch and the biodegradable resin is prepared as a masterbatch in which starch powder as a raw material and a biodegradable resin are pelletized. Thus, a film, a sheet, and the like are formed. This is because the starch as a raw material is a powder (usually about 300 mesh pass), whereas the biodegradable resin is in the form of pellets or granules and is difficult to mix uniformly. If the starch and the biodegradable resin remain inhomogeneous, a molded article having uniform physical properties (degradability and mechanical properties) cannot be obtained. However, an extra step is required for pelletizing a composite (master batch) composed of a starch powder and a biodegradable resin, resulting in a problem that the cost of a molded product is increased.

Accordingly, a first object of the present invention is to provide a method for directly forming a molded product without using a starch powder as a masterbatch comprising a biodegradable resin and without impairing the physical properties of the obtained molded product. Is to provide.

[0005] The starch powder usually contains 10 to 18% of water. For this reason, there is a problem that physical properties such as mechanical strength are degraded when pellets of starch powder / biodegradable resin composite are formed from easily hydrolyzed resins such as aliphatic polyesters. In addition, the starch was often gelatinized in the extruder under the influence of starch moisture, and the gelatinized starch was unevenly dispersed in the complex, and a beautiful molded product was not obtained due to foaming.

Accordingly, it is a further object of the present invention to provide a masterbatch composed of a biodegradable resin without using a starch powder, without impairing the physical properties of a molded article to be obtained, and having an adverse effect on the water content of the starch powder. It is an object of the present invention to provide a method for eliminating a direct molded article.

[0007]

SUMMARY OF THE INVENTION The present invention provides a starch powder of 10 to 10 wt.
A method for producing a starch-based biodegradable plastic molded product, wherein 70% by weight and 30 to 90% by weight of a biodegradable resin are directly introduced into an injection molding machine for injection molding without prior mixing. . Further, in the present invention, it is preferable to use low-moisture starch powder having a water content of 5% or less as the starch powder, and dry the raw starch powder with a vent to obtain a low-moisture content of 5% or less. It is preferable that the water-based starch powder is supplied to an injection molding machine after being formed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production method of the present invention, at least starch powder and a biodegradable resin are used as raw materials. Starch in the present invention, for example, potato, corn, sweet potato, tapioca, sago palm, rice, raw starch obtained from wheat and the like, etherification, esterification,
Includes processed starch that has been subjected to crosslinking, oxidation, acid treatment, etc. The starch powder refers to an ordinary starch powder that is industrially produced, and may have a particle diameter of about 300 mesh pass, for example.

The above-mentioned biodegradable resin has biodegradability,
Any resin that can be injection-molded may be used. Examples of such a resin include polyhydroxybutyrate (PHB)
And its derivatives, polycaprolactone (PCL), polyethylene adipate (PEA), polylactic acid (PLA) and its derivatives, aliphatic polyesters composed of various diols and dicarboxylic acids, polyamino acids, acetylcellulose, and the like, but are not limited thereto. Not done.

In the present invention, 10 to 70% by weight of the starch powder and 30 to 90% by weight of the biodegradable resin are directly introduced into an injection molding machine for injection molding without prior mixing. Starch powder 10-70% by weight and biodegradable resin 30-
By setting the blending ratio to 90% by weight, a molded product having good moldability, mechanical strength properties, and water resistance can be obtained.
If the starch content exceeds 70% by weight, molding processing and mechanical properties are extremely reduced, which is not preferable. On the other hand, if the starch content is less than 10%, the cost merit of adding starch and the improvement of the biodegradability rate cannot be improved so much.

In the present invention, it is preferable that the starch powder and the biodegradable resin be independently and quantitatively supplied to a supply port of an injection molding machine. By supplying the starch powder and the biodegradable resin quantitatively to the supply port of the injection molding machine independently without previously mixing, it is possible to obtain a molded product in which the starch and the biodegradable resin are uniformly distributed. it can. Further, it is preferable that the quantitative supply of the starch powder and the biodegradable resin is performed using a quantitative feeder. The use of the quantitative feeder has the advantage that the quantitative supply can be performed more reliably, and a molded product in which the starch and the biodegradable resin are more uniformly distributed can be obtained. As the quantitative feeder, for example, a constant weight feeder or a constant volume feeder can be used. In particular, it is preferable to use a constant weight feeder from the viewpoint that quantitative supply can be performed more reliably.

Further, in the present invention, the use of a low-moisture starch powder having a water content of 5% or less as the starch powder prevents deterioration of the properties of the resin which is easily hydrolyzed, and also reduces the starch during molding. This is preferable from the viewpoint that gelatinization and foaming can be prevented. The moisture content of the starch powder is preferably 2% or less. The method for drying the starch powder is not specified, and any method may be used as long as it is a method for drying starch. However, in the present invention, it is preferable that the raw starch powder is dried with a vent to obtain a low moisture starch powder having a water content of 5% or less, and then supplied to an injection molding machine. In particular, it is preferable that the injection molding machine is a vented injection molding machine. In this case, the starch powder as a raw material does not need to be low moisture starch, and ordinary starch can be used. The degree of vacuum and the heating temperature at the vent are suitably adjusted so that the starch moisture content after passing through the injection molding machine is 5% or less, preferably 2% or less.

According to the production method of the present invention, for example, when using a low-moisture starch or when using a normal starch, it is dried using a vented injection molding machine, and then the starch and the biodegradable resin are respectively separated. For example, a biodegradable injection-molded product that is inexpensive and maintains mechanical strength and water resistance can be provided by supplying it directly to an injection molding machine quantitatively using a quantitative feeder.

According to the production method of the present invention, a starch-based biodegradable plastic molded article can be provided. The starch-based biodegradable plastic is composed of a composition containing at least starch and a biodegradable resin. In addition to the above components, various additives can be appropriately added as necessary. Examples of additives include vegetable proteins, pulp, lubricants, ultraviolet stabilizers, bactericides, herbicides, fertilizers, antioxidants, surfactants, pigments, and the like. The shape of the molded article of the present invention is not particularly limited as long as it can be injection-molded, and examples thereof include sheets, films, pots for raising seedlings, and the like.

[0015]

The present invention will be described below in detail with reference to examples and comparative examples. Example 1 PA # 100 (Nippon Shokuhin Kako low moisture starch, moisture 1%)
And Bionole # 3040 (showa high molecular weight aliphatic polyester) were supplied to an injection molding machine using separate constant volume feeders at a weight ratio of 50:50 to form a No. 2.5 pot. The moldability and the mold releasability were good, and the resulting pot was colored white and was uniformly molded.

Example 2 PA # 100 and Cell Green PCA02 (acetylcellulose manufactured by Daicel Chemical Industries, Ltd.) were supplied to an injection molding machine using separate constant volume feeders at a weight ratio of 30:70, and seedling pots ( E type). Liquidity,
The releasability from the mold was good, and the obtained pot was colored white and was uniformly molded.

Example 3 Vent injection molding of constarch (manufactured by Nippon Shokuhin Kako Co., Ltd., moisture 13%) and Lacty # 9010 (polylactic acid manufactured by Shimadzu Corporation) using separate quantitative feeders so as to have a weight ratio of 40:60. (FS80V, manufactured by Nissei Plastic Industrial Co., Ltd.) to form a No. 2.5 pot. The temperature of the injection molding machine was 145 ° C. on the primary side, 150 ° C. on the vent, and 170 ° C. on the secondary side, and the degree of vacuum of the vent was 750 mmHg. In addition, a constant weight feeder (manufactured by Kubota) was used as a quantitative feeder for constarch. The moisture of the constarch after passing through the vent was 2%. Good moldability and mold releasability,
The resulting pot was uniformly formed without foaming.

Example 4 Constarch (manufactured by Nippon Shokuhin Kako Co., Ltd., water content: 13%) and Vionore # 3040 (aliphatic polyester manufactured by Showa Polymer) were vented using separate quantitative feeders so as to have a weight ratio of 50:50. Injection molding machine (FS8 manufactured by Nissei Plastic Industry
0V) to form a tray (S type). The temperature of the injection molding machine is 125 ° C. on the primary side, 140 ° C. on the vent, and 155 ° C. on the secondary side, and the degree of vacuum of the vent is 750 mmHg.
Met. In addition, a constant weight feeder (manufactured by Kubota) was used as a quantitative feeder for constarch. The moisture of the constarch after passing through the vent was 2%. The moldability and the mold release property were good, and the resulting pot had no foaming and the starch was dispersed neatly.

Comparative Example 1 PA # 100 was converted to constarch (manufactured by Nippon Shokuhin Kako, moisture 1).
A No. 2.5 pot was formed in the same manner as in Example 1 except that the amount was changed to 3%). Steam generation was observed during molding, and the resulting molded article had dispersed therein a transparent mass which was considered as a gelatinized product of starch. It was very brittle in strength and tended to crack immediately.

Comparative Example 2 A tray (S type) was formed in the same manner as in Example 4 except that the vent portion was not evacuated to vacuum. The moisture of the constarch after passing through the vent was 9%. In some cases, steam was generated during molding, and the raw material supply was not stable, and injection was sometimes performed while steam was still present. A large amount of starch gelatinization and air bubbles were found in the resulting molded article.

[0021]

According to the production method of the present invention, a molded product is directly formed without using a starch powder as a master batch composed of a biodegradable resin and without impairing the physical properties of the obtained molded product. A method can be provided. In addition, the use of low-moisture starch or vacuum suction of constarch with a vent at the time of injection molding and drying of the starch results in deterioration of physical properties such as mechanical strength, foaming, and starch paste, which have been problems with starch until now. Thus, an injection-molded product made of a starch-based biodegradable plastic can be favorably produced.

Claims (6)

[Claims] 1. A starch system characterized in that 10 to 70% by weight of starch powder and 30 to 90% by weight of a biodegradable resin are directly introduced into an injection molding machine without prior mixing and injection-molded. A method for producing a biodegradable plastic molded product. 2. The method according to claim 1, wherein the starch powder and the biodegradable resin are independently and quantitatively supplied to a supply port of an injection molding machine. 3. The method according to claim 1, wherein the quantitative supply of the starch powder and the biodegradable resin is performed using a quantitative feeder. 4. The method according to claim 1, wherein the fixed-quantity feeder is a constant-weight feeder or a constant-volume feeder. 5. The starch powder according to claim 1, wherein a low moisture starch powder having a water content of 5% or less is used.
The production method according to the paragraph. 6. The method according to claim 1, wherein the raw starch powder is dried with a vent to obtain a low moisture starch powder having a water content of 5% or less, and then supplied to an injection molding machine. Manufacturing method.