JPH0873721A - Biodegradable plastic composition and molded article obtained therefrom - Google Patents

Abstract

PURPOSE: To provide a biodegradable plastic composition which economically gives a molded article having a three-dimensional structure and excellent in both rigidity and impact resistance and molded articles made therefrom. CONSTITUTION: This composition consists of a polycaprolactone resin having a weight-average molecular weight of at least 50,000, a polyhydroxybutyric acid resin having a weight-average molecular weight of at least 400,000 and a filler, the filler, content being 25-50wt.% based on the total of the polycaprolactone resin, the polyhydroxybutyric acid resin and the filler and the polyhydroxybutyric acid resin accounting for 30-45wt.% of the total of the polycaprolactone resin and the polyhydroxybutyric acid resin.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biodegradable plastic composition and a molded article thereof.

[0002]

2. Description of the Related Art Heretofore, various plastics which are biodegradable in soil have been known. Among these plastics, aliphatic polyester is relatively excellent in microbial degradability, but among them, synthetically produced polycaprolactone resin has strong flexibility, and alone has three-dimensional structural physical properties. It is unsuitable as a material for required molded products. Further, polyhydroxybutyric acid resins, which have high structural strength and are not flexible, often have poor impact resistance. Even if the impact resistance is good, if a filler such as talc is added to further improve the structural strength, the impact resistance is extremely lowered. Therefore, as shown in US Pat. No. 3,921,333, it has been attempted to improve rigidity by adding a filler to a polyhydroxybutyric acid resin which is flexible and has good impact resistance. Impact resistance decreases as the content of filler in the material increases. In order to improve its impact resistance, addition of a rubber component such as SBR may be considered, but SBR
Etc. cannot be said to be a preferable composition because they remain without being biodegraded. On the other hand, Japanese Patent Application Laid-Open No. 6-107934 discloses the impact resistance of flexible polycaprolactone (PCL) as poly-β-.
Although it has been shown to improve by adding hydroxybutyric acid (PHB), the impact resistance under severe conditions containing a relatively large amount of filler and the like has not been examined. Further, in Japanese Patent Publication No. 5-70696, PHB
The talc and other fillers have been added to improve rigidity.
Impact resistance is higher than PHB homopolymer even if a PHB resin component is used alone.
If it exceeds, it will significantly decrease. As a countermeasure against this, PCL with good impact resistance is added to the resin component, but the elastic modulus of the resin component decreases because the elastic modulus of the PHB component is low and PCL with a lower elastic modulus is added. However, a composition having a high elastic modulus cannot be obtained unless a large amount of filler is used.
Moreover, it is unavoidable that the impact resistance is lowered when the elastic modulus is forcibly increased in this way.

As described above, a biodegradable plastic having a high impact resistance and a structural strength (rigidity) and containing a large amount of a filler which causes a low raw material price has not been realized. On the other hand, there are many molded products having a three-dimensional structure that require both high structural strength and impact resistance. For example, golf tees, pins, piles, etc., must be stiff because they must be stabbed in hard soil to some extent, and then golf tees are hit with a club. There is no problem if it breaks after being hit, but if it breaks too much, it will increase the amount of waste. In addition, pins and piles must be impact-resistant because they will be hit when driving. In addition, as for the packaging material, if the packaging material is deformed or damaged by being carried, stacked, or dropped, not only will the commercial value be lowered, but also the protection of the contents is at risk, so rigidity and impact resistance are required. Also,
In recent years, automatic packaging machines have come to be used, and when the contents are packed in the packaging materials by such machines, the above physical properties are required when the packaging materials are taken out, the contents are filled, and the film packaging is sealed. Often. That is, there is a demand for the development of an inexpensive, highly rigid and impact-resistant filled biodegradable plastic composition for a three-dimensional structure.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a biodegradable plastic composition and a molded article thereof, which affords a molded article having a three-dimensional structure excellent in both rigidity and impact resistance at low cost. It is an issue.

[0005]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies to solve the above problems, and found that a blend of a polycaprolactone resin and a filler having low rigidity and good impact resistance was highly It has been found that a composition which gives a molded article excellent in both impact resistance and rigidity can be obtained by adding a specific amount of a polyhydroxybutyric acid resin which is rigid and inferior in impact resistance, and completed the present invention.

That is, according to the present invention, a polycaprolactone resin having a weight average molecular weight of 50,000 or more, a polyhydroxybutyric acid resin having a weight average molecular weight of 400,000 or more, and a filler are used. The content is in the range of 25 to 50% by weight with respect to the total amount of the polycaprolactone resin, the polyhydroxybutyric acid resin, and the filler, and the content of the polyhydroxybutyric acid resin with respect to the total amount of the polycaprolactone resin and the polyhydroxybutyric acid resin is There is provided a biodegradable plastic composition and a molded article thereof, characterized in that the proportion thereof is in the range of 30 to 45% by weight.

As the polycaprolactone resin in the present invention, homopolymer poly-ε-caprolactone (PCL) and its copolymer are used, and the comonomer content in the copolymer is 5 mol% or less. The weight molecular weight of PCL is 50,000 or more, preferably 100,000 to 200,000. When the molecular weight of the polycaprolactone resin is smaller than the above range, the moldability of the composition is deteriorated and the impact resistance of the resulting molded article is deteriorated. From the viewpoint of impact resistance, a polymer having a higher molecular weight is more preferable.

The polyhydroxybutyric acid resin is a homopolymer of poly-3-hydroxybutyrate (PH).
B) and its copolymer are used, and the weight average molecular weight thereof is 400,000 or more, particularly 600,000 or more, preferably 600,000 to 1
It is 500,000. When the molecular weight of the polyhydroxybutyric acid resin is smaller than the above range, the rigidity of the resulting molded article is not significantly lowered, but the impact resistance is lowered, so that the higher molecular weight is preferable. Hydroxyvalerate (HV) is known as a comonomer for PHB copolymers.
Since the rigidity of the molded article decreases as the content increases, the comonomer content in the copolymer is preferably 3 mol% or less.

As the comonomer introduced into PCL and PHB, known copolymerizable compounds can be used without any limitation. Examples of suitable comonomers are monomers of aliphatic polyesters such as valerate and lactic acid, and other aliphatic lactones.

In the present invention, it is necessary to use the polycaprolactone resin and the polyhydroxybutyric acid resin in a specific weight ratio, and the polyhydroxybutyric acid resin is 30 to 45% by weight based on the total amount of both. Preferably 33
The proportion of the polycaprolactone resin is 70 to 55% by weight, preferably 67 to 60% by weight. If the ratio of the two resins deviates from the above range, it becomes impossible to obtain a molded product excellent in both rigidity and impact resistance.

As the filler used in the present invention, inorganic powder, organic powder or the like is used. Examples of the inorganic powder include talc, calcium carbonate, clay, silica, mica, alumina, etc., but since talc, silica, etc. have a surface close to neutral, it is possible to avoid a significant decrease in the molecular weight of the resin during melt-kneading. It is suitable as a filler for the present composition. The average particle size of these fillers is 0.5 to 20 μm, preferably <1 to
It is 10 μm. On the other hand, as the organic powder, starch obtained from starch-containing materials such as potatoes, rice and wheat, corn, and tapioca, starch derivatives obtained by copolymerizing starch with vinyl monomers such as vinyl acetate and acrylate, and wood. Plant powders such as powder, pulp powder, and cellulose powder are included. The average particle size of these organic powders is 1 to 50 μm, preferably 1 to 20 μm.
μm. These fillers are used alone or in the form of a mixture of two or more kinds. Needless to say, the surface of these fillers can be treated with various coupling agents, if necessary.

Since it is possible to expect a reduction in raw material cost and an improvement in rigidity to the extent that the filler can be added in a large amount, it is desirable to add 25% by weight or more, and more preferably 30% by weight or more to the total composition. If it is less than 25% by weight, it is difficult to say that the rigidity is sufficiently improved. On the other hand, even if the addition amount exceeds 50% by weight, the composition can be kneaded and molded up to 60% by weight, but the impact resistance is extremely lowered. Therefore, the amount of the filler used in the present invention is 25 to 50% by weight, preferably 30 to 40% by weight based on the polycaprolactone resin, the polyhydroxybutyric acid resin and the filler.

The composition of the present invention can be obtained as pellets by melt-kneading the respective components and molding them into pellets. In the case of melt kneading, a kneader, a Banbury, a mixing roll or the like is used as a kneader, but when the mixture is kept at the melting temperature or higher in the presence of air oxygen for a long time, the resin is decomposed or the filler is starch. In some cases, the starch may be decomposed or charred to deteriorate and deteriorate. When the mixing method described in JP-B-1-29126 is used, the high temperature holding time can be made as short as 10 to 30 seconds, so that the deterioration of the compound can be significantly reduced. Moreover, a pellet composition can be obtained by a twin-screw extruder.

The composition of the present invention can be composed of powder or pellets of a polycaprolactone resin containing a filler and powder or pellets of a polyhydroxybutyric acid resin. Such a composition is easy to manufacture,
Moreover, it is suitable as a molding material because it can easily give a mixture having a uniform composition by melt-kneading. When melt-kneading the polycaptolactone resin, the polyhydroxybutyric acid resin, and the filler with an ordinary kneader such as a kneader,
Since the melt viscosity of the polycaprolactone resin is significantly higher than that of the polyhydroxybutyric acid resin, its uniform kneading is very difficult and takes a long time. Since it is contained in the polycaprolactone resin, no special kneading machine is required, and uniform melt kneading can be easily carried out in an extrusion molding machine or an injection molding machine. A polycaprolactone resin containing a filler is produced by a method using an ordinary kneading machine or a mixing method performed in a short time using a high-speed mixer such as a Henschel mixer or a super mixer described in JP-B-1-29126. Can be performed by using.

In order to mold the composition of the present invention into a desired shape, a conventionally known molding method can be adopted. Examples of the molding method in this case include extrusion molding, injection molding, calender molding, and various molding methods such as foam molding. Further, when the obtained molded product is in the form of a sheet, vacuum forming, pressure forming, etc. may be applied to this to perform secondary processing into a desired shape.

Further, various additives such as an antioxidant, a surfactant and a colorant may be added during the melt-kneading of the above-mentioned respective components and the melt-kneading during the molding process.

[0017]

Industrial Applicability The composition according to the present invention and a molded article obtained by using the composition are extremely unique biodegradable plastics having a high tensile elastic modulus (rigidity) and a high impact strength. High rigidity means that a molded product with a three-dimensional structure can withstand external forces sufficiently even if it is thinly designed and manufactured as a whole. For example, packaging containers are not easily stacked or crushed by lateral force. Means Also,
The compositions and moldings according to the invention have the following properties except for the inorganic filler:
It is 00% biodegradable, and most of its inorganic fillers originally existed in nature as described above.
Therefore, even when the molded article of the present invention becomes a waste after being used and becomes biodegradable in a landfill, for example, the presence of these inorganic fillers does not inhibit the biodegradation of the resin, and Since the residual inorganic filler only "returns to nature", it can be said that the composition according to the present invention and its molded article are, so to speak, earth-friendly plastics.

The composition of the present invention has microbial degradability and contains a large amount of filler, and is suitable as a molding material for inexpensively producing a molded article having excellent mechanical strength. That is, although a large amount of the filler is blended to improve the rigidity of the molded product and to reduce the raw material cost, it is possible to prevent the impact resistance from being normally lowered. The molded product of the present invention is preferably used in the form of a sheet or a container, which requires rigidity in the final product, and can be used as a laminate having the layer of the composition of the present invention as a main layer. Molded articles in which the characteristics of the composition of the present invention are effectively exhibited include food trays, food packaging containers such as bento containers, cups used outdoors, plates, spoons, forks, partitioning of packaging boxes, guessing materials, etc. Various one-way products, as well as planting pots, piles and pins for agriculture and forestry, golf tees, baskets for seed dispersal, cards and the like.

[0019]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, the physical properties of raw materials and molded products (sheets and molded products) used in Examples and Comparative Examples are evaluated and measured as follows.

Raw materials: (A) Polycaprolactone TONEP787 (manufactured by Union Carbide Co.) Tensile modulus: 3377 kgf / cm ² Weight average molecular weight: 172,000 (B) Poly-3 -hydroxybutyric acid (PHB) PHB is disclosed in JP-A-62. It was produced by the method using a microorganism described in Japanese Patent No. 1055094. Tensile elastic modulus: 25900 kgf / cm ² Weight average molecular weight: 1050,000 (C) Filler Inorganic filler Talc FVS (manufactured by Wandou Kogyo Co., Ltd.) Average particle size: 8 μm Organic filler Cornstarch W (manufactured by Nippon Shokubai Co., Ltd.) Average particle size : 16 μm

Evaluation of Physical Properties and Measuring Method: (1) Tensile Elastic Modulus Tensile elastic modulus is used to evaluate the rigidity of the sheet (AST
M D882). Shimadzu Corporation: Autograph AGS-500S is used. (2) Impact test 50% breaking energy is determined using a DuPont impact tester as an evaluation of the impact resistance of the sheet (JIS K72l).
l Calculated according to the falling weight impact test law for hard plastics). Room temperature 20 ° C, radius of impact 4.7 mm, horn 50, 1
Select 00, 200g as appropriate. The sheet was fixed on all sides. (3) Waist / Bending Strength As an evaluation of the rigidity of a molded product, a food container is molded, and its waist strength is determined by the method shown in FIG. 1 and its bending strength is determined by the method shown in FIG. When the waist strength is low, there is a problem that the container is deformed when the wrap is hung on the container, which is serious especially when hung on the automatic wrapper. In addition, if the bending strength is weak, the contents will be crushed when trying to stack and stack them, or the contents will be deformed when you hold the container, or when you wrap the container. It will be transformed. Both of these strengths are important strengths for a container-shaped molded product and are preferably high. As a measuring device, Shimadzu Corporation: Autograph AGS-5
00S is used. However, the head speed is 50 mm
/ Min. And

Examples 1 to 4 High speed mixing mixer (Super mixer SM manufactured by Kawata Co., Ltd.)
Cl00) was partially modified so that the temperature of the mixing tank could be raised to 250 ° C. Pellets of PCL and talc are thrown here and mixed and heated. After about 20 minutes, when the load on the rotary motor suddenly increased, the contents were discharged to a low rotation cooling tank, and the rotation was continued to blow air to cool and solidify to obtain a coarse-grained blended body (talc-containing PCL). Obtained. P in the above blend
HB pellets were added and premixed with a mixer, and the mixture was kneaded with an extruder SE-65 (65φ vent type) manufactured by Toshiba Machine Co., Ltd. and extruded through a T die to obtain a 0.43 mm thick sheet. In this case, the talc content is 30% by weight.
Or 40% by weight, PCL in mixed polyester resin
The weight ratio of PHB to PHB was 2: 1 or 3: 2. In addition, this sheet is 18 cm in length and 12 in width by a single-shot vacuum forming machine.
cm and a depth of 2.5 cm were molded into a food container and subjected to a strength test and a DuPont impact test. Table 1 below shows the measurement results of the mixing ratio of the raw materials and the physical properties of the sheet and the container. As is clear from Table 1, the talc content is set to 30% by weight or 40% by weight, and PCL in the mixed polyester is
If the weight ratio of PHB and PHB is 2: 1 or 3: 2,
The sheet exhibited a sufficiently high impact strength despite its high tensile modulus. Further, the container is the PH of Comparative Example 4.
Compared to the one without B, it showed higher rigidity and exhibited higher resistance to impact force. Furthermore, the container was applicable to automatic packaging machines.

Comparative Examples 1 and 2 PCL and PHB were each formed into a sheet by an extruder.
Physical properties were evaluated in the same manner as in Examples 1 to 4. Table 1 shows the evaluation results
Shown in As can be seen from Table 1, PCL alone has good impact resistance but poor rigidity, and PHB alone has good rigidity but poor impact resistance. Also, neither was applicable to automatic packaging machines.

Comparative Examples 3 to 5 The same evaluations as in Examples 1 to 4 were conducted on compositions containing only PCL and talc without using PHB. Table 1 shows the evaluation results
Shown in As can be seen from Comparative Example 3 in Table 1, in order to obtain the same impact resistance as in Example 2, only 20% by weight of talc could be added, so that a high elastic modulus could not be obtained and the rigidity of the container was low. It was In addition, as can be seen from Comparative Example 5, Example 2
It is necessary to add talc in an amount of 50% by weight in order to obtain the same elastic modulus and rigidity of the container, but the impact resistance is poor. When applied to an automatic wrapping machine, the containers of Comparative Examples 3 and 4 were too flexible to be applied, and in Comparative Example 5, breakage of the container was observed.

Comparative columns 6 to 10 When the addition amount of talc is 20% by weight, the addition weight ratio of PCL and PHB is 4: 1, 2: 1, 3: 2, and the addition amount of talc is 30% by weight. Or 40% by weight, PCL
Examples 1 to 4 except that the addition ratio of PHB and PHB was 4: 1.
The same evaluation was performed. The evaluation results are shown in Table 1. In these formulations, either the tensile modulus or the impact resistance was low, and neither of them showed a satisfactory value. Further, in the test results of these containers in the automatic packaging machine, damage or deformation of the containers was noticeable in both cases.

Comparative Example 11 An experiment was conducted in the same manner as in Example 3 except that the molecular weight of PHB was 220,000. Table 3 shows the results. This composition is inferior in impact resistance to Example 3.

[0027]

[Table 1]

Example 5 The same evaluations as in Examples 1 to 4 were carried out except that cornstarch (CS) was used instead of talc. Table 2 shows the evaluation results. PH as well as the system using talc
It was confirmed that the use of B improved the rigidity and impact resistance of the container.

Comparative Example 12 The same evaluation as in Example 5 was carried out on a composition containing only PCL and CS without using PHB. Table 2 shows the evaluation results. The composition of Comparative Example 11 is inferior to Example 5 in both impact resistance and container rigidity.

[0030]

[Table 2]

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a waist strength test method for evaluating the rigidity of a container.

FIG. 2 is a schematic diagram showing a method of measuring bending strength for evaluating the rigidity of a container.

Claims (5)

[Claims] 1. A polycaprolactone resin having a weight average molecular weight of 50,000 or more, a polyhydroxybutyric acid resin having a weight average molecular weight of 400,000 or more, and a filler, wherein the content of the filler in the entire composition is a polycaprolactone resin. 25 to 50% by weight based on the total amount of polyhydroxybutyric acid resin and filler
And a ratio of the polyhydroxybutyric acid resin to the total amount of the polycaprolactone resin and the polyhydroxybutyric acid resin is in the range of 30 to 45% by weight, a biodegradable plastic composition. 2. The composition according to claim 1, wherein the filler is at least one selected from talc, silica, calcium carbonate and starch. 3. The composition according to claim 1, which comprises a mixture of a powder or pellets of a polycaprolactone resin containing a filler and a powder or pellets of a polyhydroxybutyric acid resin. 4. A biodegradable plastic molded product obtained by melt-molding the composition according to claim 1. 5. A laminated molded article comprising a biodegradable plastic layer comprising the composition according to claim 1.