JP2003092926A - Lightweight biodegradable soil and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide soil comprising a lightweight biodegradable polyester resin excellent in mechanical strength, and having no anxiety of causing bad influence upon growth of plants. SOLUTION: The lightweight biodegradable soil comprises a biodegradable polyester containing >=50 mol% of an α- and/or β-hydroxycarboxylic acid unit, and has apparent specific gravity of <=0.9 g/cm<3> . The method for producing the soil comprises the process of foaming 100 pts.mass of the biodegradable polyester resin containing >=50 mol% of the α- and/or β-hydroxycarboxylic acid unit using 0.01-30 pts.mass of a pyrolytic foaming agent or volatile foaming agent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a soil composed of a biodegradable polyester resin which has biodegradability, is lightweight and has excellent mechanical strength, and does not adversely affect the growth of plants.

[0002]

[Prior Art] Plant growth, gardening, gardening,
With regard to soil such as sand, soil, stones and rocks used for agricultural work, there is a strong demand for weight reduction in various situations such as transportation, replanting and installation on the rooftop. In the past, natural materials such as diatomaceous earth and Kanuma soil, which have a relatively low specific gravity, as well as processed obsidian and pearlite perlite, artificial materials such as porous glass beads and styrofoam have been used.

Of these, natural ones such as diatomaceous earth and Kanuma soil, obsidian, pearlite and porous glass beads have a problem that their specific gravities are not sufficiently low. In addition, artificial materials such as Styrofoam foamed with resin have a low specific gravity and can be lightened, but they remain in the soil for a long time and are left in the soil as garbage when they are no longer needed. There was a problem in terms of environment.

Therefore, in recent years, lightweight soil using a biodegradable resin has been produced. However, for example, Japanese Patent Application Laid-Open No. 7-26262 discloses that the weight reduction is achieved when the granular material synthesized from glycol and an aliphatic dibasic acid is a foam. The biodegradable resin synthesized from dibasic acid does not have sufficiently high strength, which is a problem particularly when the expansion ratio is high.

In addition to this, a lightweight soil using cellulose is disclosed in JP-A-2000-86793 and 2000-344.
Although disclosed in Japanese Patent Nos. 926 and 2001-211741, these have drawbacks such as needing to be carbonized, and a basic skeleton being cellulose, which makes them susceptible to insects and the like.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems and is biodegradable, lightweight, and excellent in mechanical strength, which adversely affects the growth of plants. It is to provide a soil composed of a biodegradable polyester resin that does not extend.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the inventors of the present invention have found that α- and / or β-hydroxycarboxylic acid units are contained in an amount of 50 mol% or more. The inventors have found that a lightweight biodegradable soil having an apparent specific gravity of 0.9 g / cm ³ or less, which is produced by melt-kneading a degradable polyester resin, solves the problem and has reached the present invention.

That is, the gist of the present invention is as follows. (1) Biodegradable lightweight, which is made of a biodegradable polyester resin containing 50 mol% or more of α- and / or β-hydroxycarboxylic acid units and has an apparent specific gravity of 0.9 g / cm ³ or less. soil. (2) The biodegradable lightweight soil according to (1) above, wherein the α-hydroxycarboxylic acid unit is D-lactic acid and / or L-lactic acid. (3) Biodegradable polyester resin 10 containing 50 mol% or more of α- and / or β-hydroxycarboxylic acid units
0 parts by mass of a pyrolytic foaming agent or a volatile foaming agent 0.01
The method for producing a biodegradable lightweight soil according to the above (1) or (2), which comprises foaming with 30 to 30 parts by mass. (4) The method for producing a biodegradable lightweight soil according to the above (3), wherein 100 parts by mass of the biodegradable polyester resin is crosslinked with 0.01 to 10 parts by mass of a crosslinking agent and then foamed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The biodegradable polyester resin used in the present invention must contain 50 mol% or more of α- and / or β-hydroxycarboxylic acid units. When the α- and / or β-hydroxycarboxylic acid unit is less than 50 mol%, the resulting biodegradable lightweight soil has low mechanical strength. Examples of α- and / or β-hydroxycarboxylic acid units include D
-Lactic acid, L-lactic acid, or a mixture thereof, glycolic acid, 3-hydroxybutyric acid, 3-hydroxyvaleric acid, 3-
Examples thereof include hydroxycaproic acid.

Therefore, the biodegradable polyester resin used in the present invention is preferably polylactic acid, polyglycolic acid, poly (3-hydroxybutyric acid), poly (3-hydroxyvaleric acid), poly (3-hydroxycaproic acid). , And copolymers thereof, and mixtures thereof. Among these, polylactic acid is more preferable because it has excellent moldability, is low in cost, and is easily available.

The biodegradable polyester resin used here is usually produced by a known melt polymerization method, or in combination with a solid phase polymerization method. In addition, poly (3-hydroxybutyric acid) and poly (3-hydroxyvaleric acid) can be produced by microorganisms.

The biodegradable polyester resin used in the present invention contains, if necessary, other biodegradable resin components within a range that does not significantly impair the heat resistance of poly (α- and / or β-hydroxycarboxylic acid). Can be copolymerized or mixed. Other biodegradable resins include aliphatic polyesters composed of dicarboxylic acids and diols represented by poly (ethylene succinate) and poly (butylene succinate), and poly (ω-caprolactone) represented by poly (ε-caprolactone). -Hydroxyalkanoate), poly (butylene succinate-co-butylene terephthalate) and (butylene adipate-co-butylene terephthalate), which are biodegradable even if they contain an aromatic component, as well as polyesteramide, polyester carbonate, starch And the like.

The molecular weight of the biodegradable polyester resin used in the present invention is not particularly limited, but the weight average molecular weight is preferably 30,000 or more and 1,000,000 or less, and more preferably 50,000 or more and 1,000,000 or less. It is preferable. When the weight average molecular weight is less than 30,000, the melt viscosity of the resin is too low, which is not preferable. On the contrary, if it exceeds 1,000,000, the moldability of the resin is rapidly lowered, which is not preferable.

In the present invention, as a method for producing lightweight soil, a method of foaming a biodegradable polyester resin to form a porous body is desirable. The holes can be adjusted to be independent bubbles or communicating holes depending on the usage conditions. Specifically, as a method for obtaining lightweight soil, (1) a method of producing fine particles from a biodegradable polyester resin, impregnating them with water, an organic solvent or the like, and foaming them by changing pressure or temperature,
(2) There is a method in which a biodegradable polyester resin is melt-kneaded using a kneading machine, a decomposable foaming agent or a volatile foaming agent is added to the mixture to foam, and then the soil is adjusted to a size required. In particular, the latter method is a desirable method because a lightweight soil can be continuously produced by preparing a foamed strand having a required diameter by using an extruder type device and then cutting the foamed strand into a required length.

Examples of the decomposition type foaming agent include azo compounds represented by azodicarbonamide and barium azodicarboxylate, nitroso compounds represented by N, N'-dinitrosopentamethylenetetramine, and 4,4 '. −
Examples thereof include hydrazine compounds represented by oxybis (benzenesulfonylhydrazide) and hydradicarbonamide, and inorganic compounds such as sodium hydrogen carbonate.

When a volatile foaming agent is used, it is effective to inject it from the middle of the extruder to foam it. Examples of the foaming agent in this case include inorganic compounds such as nitrogen, carbon dioxide and water, hydrocarbon compounds such as methane, ethane and butane, freon compounds and organic solvents represented by alcohols such as ethanol and methanol. You can The amount of foaming agent used is 10 biodegradable polyester resin.
It is preferably 0.01 to 30 parts by mass with respect to 0 parts by mass. If the amount of the foaming agent added is more than 30 parts by mass, the foaming may be liable to occur and the cost becomes high, which is not preferable.

In the foaming of the biodegradable polyester resin, the biodegradable polyester resin may be used as it is, but when the cells are made finer or the foaming rate is made higher, it may be cross-linked or other ultra high. A molecular weight polymer may be added. The cross-linking agent is not particularly limited, but examples thereof include polyvalent isocyanate compounds, (meth) acrylate compounds, polyvalent carboxylic acid compounds, and polyvalent epoxy compounds. Upon crosslinking, a peroxide may be used together.
Further, it is preferable to reduce the amount of the cross-linking agent and the peroxide as much as possible in order to make the communicating holes in order to have water permeability and water retention.

When a cross-linking agent is added, the amount thereof is 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass, based on 100 parts by mass of the biodegradable polyester. If the amount exceeds 10 parts by mass, the degree of crosslinking is too strong and the operability is impaired, which is not preferable.

The blending amount of the peroxide is 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the biodegradable polyester resin. If it exceeds 10 parts by mass, the unreacted portion increases, which is not preferable in terms of cost. If the biodegradability of the polylactic acid modified with the crosslinking agent / peroxide falls within this range, the decomposition rate will slightly decrease, but the biodegradability will not be impaired.

The apparent specific gravity of the biodegradable lightweight soil of the present invention varies depending on its use, but it must be 0.9 g / cm ³ or less in order to have the effect of weight reduction. The range is preferably 0.01 to 0.8 g / cm ³ , and more preferably 0.02 to 0.7 g / cm ³ . An apparent specific gravity of less than 0.01 g / cm ³ is not preferable because it is blown by the wind. The apparent specific gravity can be controlled by the concentration of the foaming agent and the foaming conditions.

The compressive strength of the biodegradable lightweight soil of the present invention is
It is preferably 0.3 to 20 MPa at the time of 10% deformation. If the compressive strength at 10% deformation is lower than 0.3 MPa, it may be broken when used as soil or stone, and it may be difficult to support the plant body. Two
It is difficult to make the value larger than 0 MPa. Further, the compressive elastic modulus is preferably 50 MPa to 2 GPa. When it is less than 50 MPa, there is a problem in strength in use, and when it is more than 2 GPa, it becomes brittle, which is not preferable.

In the present invention, the biodegradable polyester resin is a pigment, a heat stabilizer, an antioxidant, a weatherproofing agent, a flame retardant, a plasticizer, as long as its characteristics are not significantly impaired.
It is also possible to add a lubricant, a release agent, an antistatic agent, a filler and the like. As the heat stabilizer and antioxidant, for example, hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, halides of alkali metals, or a mixture thereof can be used.
As the inorganic filler, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon, carbon black, Examples thereof include zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fibers, metal whiskers, ceramic whiskers, potassium titanate, boron nitride, graphite, glass fibers and carbon fibers. Organic fillers include starch, cellulose fine particles, wood flour, okara, fir shell,
Examples include naturally occurring polymers such as bran and modified products thereof.

The method of mixing the other biodegradable polyester resin of the present invention with other thermoplastic resins, the above-mentioned fillers, etc. is not particularly limited, and is usually known after heating and melting, for example. The kneading may be performed by a kneading method using a single-screw extruder, a twin-screw extruder, a roll kneader, a Brabender or the like. It is also effective to use a static mixer or a dynamic mixer together.

[0024]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples.

The measuring methods used in the evaluation of Examples and Comparative Examples are as follows. (1) Molecular weight: using a gel permeation chromatography (GPC) device (manufactured by Shimadzu Corporation) equipped with a differential refractive index detector,
Tetrahydrofuran was used as an eluent and determined at 40 ° C. in terms of standard polystyrene. (2) Compressive strength and elastic modulus: Measured with a compressive strength measuring device (manufactured by Intesco) according to JIS K7220. (3) Apparent specific gravity: Calculated by dividing the mass of the foam by the volume that increases when the obtained foam is immersed in water. (4) Foaming ratio: Calculated from the ratio of the volume increased when the obtained foam was immersed in water and the volume of the foam and the volume obtained from the true density of the resin.

Example 1 Talc as a foaming nucleating agent (Hayashi Kasei Co., Ltd., average particle diameter 2.5 μm)
m) Polylactic acid added with 0.5 part by mass (NaturWorks 4030D manufactured by Cargill Dow, weight average molecular weight 2)
100,000 parts by weight of 100,000, L-body 99%, D-body 1%: Resin A, a molding machine (a twin-screw extruder PCM-30 manufactured by Ikegai, die diameter 4 mm x 3 holes, extrusion head temperature; 200 ° C, die) Outlet temperature; 180 ° C.). Using a pump in the middle of the molding machine, 0.5 parts by mass of polyethylene glycol dimethacrylate (made by NOF Corporation: PEGM) as a crosslinking agent and 0.5 parts by mass of di-t-butyl peroxide (made by NOF Corporation) as a peroxide were respectively injected. , Extruded and processed into pellets. After drying this crosslinked resin pellet once,
Liquefied carbon dioxide was used as a foaming agent, and a continuous foamed strand was produced using a molding machine (Ikegai biaxial extrusion molding machine PCM-30, discharge hole diameter 1 mmΦ, extrusion melting temperature; 200 ° C., die outlet temperature: 160 ° C.). . The discharged foamed strand was cut into a length of 3 mm with a cutter. Table 1 shows the apparent specific gravity and the expansion ratio of the obtained expanded pellets.

Example 2 The same experiment as in Example 1 was conducted except that the cross-linking agent and the peroxide were injected in amounts of 0.1 parts by mass and 0.2 parts by mass with respect to 100 parts by mass of the resin, respectively. .

Example 3 The same experiment as in Example 2 was carried out except that hexamethylene diisocyanate (HMDI manufactured by Wako Pure Chemical Industries, Ltd.) was used as a crosslinking agent.

Example 4 The same experiment as in Example 1 was carried out except that no crosslinking agent or peroxide was used.

Examples 5 to 8 Instead of resin A, polylactic acid (Naturu manufactured by Cargill Dow) was used.
reWorks4060D, weight average molecular weight 180,000, L
The same experiment as in Examples 1 to 4 was performed except that 90% of body and 10% of body D: resin B) were used.

Examples 9 to 12 Instead of the resin A, polylactic acid (Naturu manufactured by Cargill Dow) was used.
reWorks5039B, weight average molecular weight 180,000, L
The same experiment as in Examples 1 to 4 was carried out except that 80% body and 20% D body: resin C) were used.

Examples 13 to 16 As a biodegradable polyester resin, 80 parts by mass of resin A and polybutylene succinate (Bionore 1 manufactured by Showa High Polymer Co., Ltd.) were used.
The same experiment as in Examples 1 to 4 was performed except that 20 parts by mass of 010 and a weight average molecular weight of 160,000: PBS) were used.

Example 17 Using 100 parts by mass of the crosslinked resin pellet obtained in Example 1, 3 parts by mass of a chemically pyrolyzable azodicarbonamide type foaming agent (SW7 manufactured by Eiwa Kasei) was added as a foaming agent and molded. Machine (Ikegai twin-screw extruder PCM-30, discharge hole diameter 3m
mΦ, extrusion melting temperature; 210 ° C., die exit temperature; 150
(° C) was used to prepare a continuous foamed strand, and foamed pellets were obtained in the same manner as in Example 1.

Comparative Examples 1 to 4 20 parts by mass of resin A and P as biodegradable polyester resin
The same experiment as in Examples 1 to 4 was carried out except that 80 parts by mass of BS was used.

[0035]

[Table 1]

The expanded pellets obtained in the examples were excellent in compressive strength and elastic modulus, and were intended to be lightweight. On the other hand, the foamed pellets obtained in Comparative Example, because the hydroxycarboxylic acid unit contained in the biodegradable polyester resin is small,
It was inferior in compressive strength and elastic modulus.

[0037]

According to the present invention, it has biodegradability, is lightweight, has excellent mechanical strength, does not adversely affect the growth of plants, and has various types of sand depending on its size. It becomes possible to provide soil that can be used as stones, rocks, and the like.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeru Hayase             23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd.             Shikisha Central Research Institute (72) Inventor Takuma Yano             23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd.             Shikisha Central Research Institute (72) Inventor Kazuko Yoshimura             23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd.             Shikisha Central Research Institute F term (reference) 2B022 AA05 BA01 BA21 BB01                 4F074 AA67 AA68 BA01 BA13 BA31                       BA32 BB02 BB03 BB12 BB28                       CA22 CB52 CC04Y CC06X                       CC22X DA24 DA59

Claims (4)

[Claims] 1. α- and / or β-hydroxycarboxylic acid
Biodegradable polyester containing 50 mol% or more of acid units
Made of resin with an apparent specific gravity of 0.9 g / cm ³Below
Biodegradable lightweight soil characterized by the following. 2. An α-hydroxycarboxylic acid unit is D-
The biodegradable lightweight soil according to claim 1, which is lactic acid and / or L-lactic acid. 3. A thermal decomposition type foaming agent or a volatile type foaming agent 0.01 to 30 parts by mass, 100 parts by mass of a biodegradable polyester resin containing 50 mol% or more of α- and / or β-hydroxycarboxylic acid units. The method for producing a biodegradable lightweight soil according to claim 1 or 2, wherein the method is used for foaming. 4. After crosslinking 100 parts by mass of the biodegradable polyester resin with 0.01 to 10 parts by mass of a crosslinking agent,
The method for producing a biodegradable lightweight soil according to claim 3, wherein foaming is performed.