JPH09224488A - Container for raising seedling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a container for raising a seedling composed of a polyester polymer whose main component is lactic acid and having specified properties suppressing the proliferation of bad pathogenic bacteria, accelerating the growth of plants, having a long life, being naturally decomposed with improved environmental contamination resistance and being useful for the agriculture and horticulture. SOLUTION: This container is composed of a polyester polymer whose main component is lactic acid and is crystallized so as to (i) turn the melting point 3 of the crystal of the polymer to be equal to or higher than 120 deg.C, preferably equal to or higher than 130 deg.C, and (ii) turn the heat of fusion of the crystal to be equal to or more than 10J/g, preferably equal to or more than 20J/g, and also, (iii) the crystal is practically unoriented. Also, it is preferable that the container for raising the seedling is molded from the polymer containing a crystalline nucleus agent (talc or the like, for instance) and/or the one for which a crystallization acceleration component (polybutylene terephthalate or the like, for instance) is copolymerized or/and mixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seedling raising container for growing seedlings of a plant in which the raised seedling can be planted together with the container.

[0002]

2. Description of the Related Art Seedling raising containers that can be planted as they are are characterized by high planting survival rate because planting is easy and labor-saving and the seedlings are not damaged.
It is widely demanded in fields such as civil engineering. However, conventional synthetic resin pots and flower pots have a problem of environmental pollution because they are not decomposed in soil after planting, and also have a problem of inhibiting root growth of plants.

In recent years, naturally decomposable resins such as aliphatic polyesters have been developed, and it is already well known to apply them to seedling raising pots (PETROTEC Vol. 18, No. 3, page 197 (1995)). Among the aliphatic polyesters, polylactic acid and modified polylactic acid containing it as the main component are excellent in properties such as strength, heat resistance, and melt-moldability, and are likely to be cheaper in mass production in the future. Is expected.

Needless to say, the seedling-growing container must maintain sufficient strength while growing the seedlings and during the period until the planting work. The period for raising seedlings varies depending on the type of plant or seedling, but is short for about 3 to 6 months, slightly long for 1 to 2 years, and particularly long for 3 to 5 years.
The natural decomposition rate of aliphatic polyester varies depending on temperature, humidity, soil properties, types of soil bacteria, etc., but the life of conventional aliphatic polyester containers is often as short as about 6 months or less, and it takes a long time before planting. For example, many of them are unsuitable for purposes that require one year or more.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel seedling raising container which is completely degradable in a natural environment and improved to withstand a longer seedling raising period.

[0006]

The object of the present invention is (1).
Consisting of a polyester polymer whose main component is lactic acid,
(2) The melting point of the crystal of the polymer is 120 ° C. or higher, (3) the crystal is crystallized so that the melting endotherm of the crystal is 10 Joule / gram or higher, and (4) the crystal is substantially Achieved by a molded new container for raising seedlings, which is characterized in that it is not orientated.

Here, the polyester polymer containing lactic acid as a main component is a polyester polymer composition containing 50% by weight or more of components derived from L-lactic acid and / or D-lactic acid.
It includes all poly L-lactic acid homopolymers, poly D-lactic acid homopolymers, poly L / D lactic acid copolymers, and copolymers containing 50% by weight or less of other components or a mixture thereof.

As the components to be copolymerized, those capable of forming an ester bond are preferable. For example, (1) an aliphatic hydroxycarboxylic acid such as glycolic acid or hydroxybutylcarboxylic acid, (2) glycolide, butyrolactone or caprolactone. Aliphatic lactone, (3) Aliphatic diol such as ethylene glycol, propylene glycol, butanediol, hexanediol, etc., (4) Diethylene glycol, triethylene glycol, polyethylene glycol (PEG), polypropylene glycol (PPG), polybutylene ether , PEG / PPG
Aliphatic ether glycols such as copolymers and oligomers thereof, (5) polybutylene carbonate glycols, polyhexane carbonate glycols, polyalkylene carbonate glycols such as polyoctane carbonate glycols and oligomers thereof, (6) succinic acid, adipic acid, azelaine Examples thereof include acids, sebacic acid, and aliphatic dicarboxylic acids such as decanedicarboxylic acid. Besides this, terephthalic acid, isophthalic acid, phthalic acid,
Aromatic components such as naphthalenedicarboxylic acid are also applicable. The polyester polymerization raw material can be randomly copolymerized and / or block copolymerized with polylactic acid. Generally, in random copolymerization, the crystallinity of the polymer tends to be impaired, and the copolymerization ratio (weight ratio) is preferably about 20% or less, particularly about 1 to 10%. On the other hand, in block copolymerization, impact resistance and the like can be improved without impairing crystallinity, and the copolymerization ratio is 5
It can be 0% or less, particularly about 1 to 40%, and 3 to
A range of 35% is widely used.

In addition to the above polyester polymerization raw materials,
For example, an isocyanate compound, an epoxy compound, a monofunctional compound, or a trifunctional or higher-functional compound can be used as a subordinate.

The purpose of modifying polylactic acid by copolymerization or mixing is to improve melting point (polymerization temperature and molding temperature), melt fluidity, moldability, toughness, impact strength, flexibility and elastic recovery. , Adhesion, reduction of crystallization temperature, improvement of hydrophilicity and water repellency, improvement of transparency, improvement or suppression of decomposability, and the like.

Among the aliphatic polyesters, polylactic acid (homopolymer) and modified polylactic acid containing it as a main component are excellent in properties such as strength, heat resistance and ease of melt molding,
Moreover, if mass production is performed in the future, the cost is likely to be low,
The most practical application is expected. In addition, polylactic acid-based polymer has a characteristic that its decomposition rate under natural environment (in soil, fresh water, seawater, in compost, etc.) is smaller than that of other aliphatic polyesters and that it has a long life, so that it can be grown for a long time. Suitable for applications that require The present invention further reduces the degradability of the polylactic acid-based polymer and improves it so that it can withstand a long seedling raising period. The polylactic acid homopolymer has a high glass transition point of about 58 ° C., the crystallization start temperature at the time of heating is about 90 ° C., and the crystallization peak (center) temperature is 115 to 125.
℃, for example, injection molded products are cooled rapidly,
It is almost in an amorphous state. Amorphous products are transparent and soft, but have low strength, fast decomposition rate, and relatively short life. Extruded sheets and the like are also rapidly cooled, so they are amorphous, and those obtained by vacuum or pressure molding them are also amorphous. The present invention suppresses the decomposition rate and prolongs the life by crystallizing the polymer of these molded products. The effect of extending the life due to crystallization depends on the decomposition conditions,
Although it varies depending on the thickness and shape of the molded product, it is recognized that it is 10% or more, and in most cases, about 20% to 200% (3 times).

FIGS. 1 and 2 are examples of endothermic and exothermic curves (DSC curves) of crystalline polylactic acid type polymers when heated by a scanning differential calorimeter (DSC). FIG. 1 shows a measurement example of a molded product which is not so much crystallized, 1 is a change in baseline due to glass transition, 2 is an exothermic peak due to crystallization, and 3 is an endothermic peak due to melting. The amount of heat of the exothermic or endothermic peak indicates the crystallinity of the polymer. The amount of heat generation and the amount of heat absorption are proportional to the area of the shaded area in the figure. The lower the crystallinity of the molded product, the larger the amount of heat generated by crystallization (peak 2). FIG. 2 is a DSC curve of a sufficiently crystallized molded product. Baseline change 1 due to glass transition and exothermic peak 2 due to crystallization are not observed, but only endothermic peak 3 due to melting of crystals is observed.

In the DSC analysis (heating method) of the molded product,
Difference Hd between melting endotherm H3 (absolute value) and crystallization exotherm H2
= H3-H2 is proportional to the crystallinity of the molded product, and if completely amorphous, H3 = H2 and Hd is zero. In the example of FIG. 2, H2 = 0 and H3 = Hd. For the purpose of the present invention, Hd (absolute value) must be 10 Joules (J) / gram (g) or more, and 20 J /
g or more, particularly preferably 30 J / g or more, 4
Most preferably, it is 0 J / g or more. The melting endotherm of the fully crystallized polylactic acid homopolymer is about 50 J / g.

In the DSC measurement, the amount of sample is about 10 mg and the rate of temperature rise is 10 ° C./min in nitrogen gas. Further, when two or more melting point peaks are observed by mixing or copolymerization of the second component, the melting point is the center value (extreme value) of the peak of the maximum temperature, and the melting endothermic amount of all melting endothermic peaks. The total amount of heat absorption.

In order to sufficiently crystallize the molded product of the polylactic acid type polymer, (1) heat the molded product at a crystallization temperature or higher, and (2) crystallize it by mixing a crystal nucleating agent with the polymer composition. And (3) mixing or / and copolymerizing a component that promotes crystallization into the polymer composition.
The heat treatment temperature of (1) is 90 for polylactic acid homopolymer.
C. or higher, particularly 100 to 140.degree. C. is preferable (the molded product is softened if the temperature is too high). Although the heat treatment time is effective even for 1 minute, it is usually 3 minutes or more, especially about 5 minutes to 2 hours. (2) The crystal nucleating agent is one that makes crystallization fast and sufficient, and includes, for example, talc, calcium silicate, calcium titanate, boron nitride, titanium oxide, zinc oxide, silica, calcium carbonate and other inorganic particles,
For example, the diameter is 10 μm or less, particularly 5 μm or less, and often 5
Examples thereof include those having a particle size of about nm to 2 μm, similarly sodium salts of saccharin, sodium benzoate, polybutylene terephthalate having a melting point higher than that of polylactic acid-based polymers, fine particles of polymers such as polypropylene and other organic compounds. These nucleating agents effectively promote crystallization and shorten the time required for crystallization, but the crystallization temperature at the time of heating cannot be changed significantly. (3) The crystallization-accelerating component lowers the crystallization temperature or increases the crystallization rate by copolymerization or mixing, and for example, a polymer or / and a plasticizer having a glass transition temperature of room temperature or lower, particularly 0 ° C. or lower is used. Can be mentioned.
In particular, an aliphatic polyester having a glass transition point of 0 ° C. or lower is most preferable for the purpose of the present invention because it can effectively lower the crystallization temperature by mixing or block copolymerization and further improve the impact resistance of the molded product.

Polylactic acid type polymer block copolymer or /
And, suitable as a mixture, aliphatic polyester having a low glass transition point, polycaprolactone, polyethylene adipate, polyethylene suberate, polyethylene azelate, polyethylene sebacate, polyethylene decamethylate, polybutylene succinate, polybutylene adipate, Dicarboxylic acid having about 2 to 20 carbon atoms, such as polybutylene sebacate, polybutylene decametylate, polyhexane adipate, polyhexane sebacate,
Examples include polymers such as diols and lactones. Also,
Their random or block copolymers are likewise applicable. The copolymerization or mixing ratio is 1 to 50%, especially 3 to 4
0% is preferred and 5-30% is most widely used.

Block copolymerization with polylactic acid may be carried out by mixing and reacting the above-mentioned polymers during melt polymerization of L-lactide, D-lactide, L / D lactide mixture and the like. For the reaction, it is effective to use a polymer having a hydroxyl group at the terminal or side chain. If the reaction temperature is too high or the reaction time is too long, transesterification proceeds and random copolymerization proceeds, so caution is required. As another method of block copolymerization, polylactic acid having a hydroxyl group at the terminal or the like and an aliphatic polymer (copolymerization component) having a hydroxyl group at the terminal or the like are mixed in a molten state or in a solvent to prepare diisocyanate or dicarboxylic acid. A polyfunctional compound such as acid dichloride or dicarboxylic acid anhydride may be reacted.

Similarly, polyethylene glycol, polypropylene glycol, polybutylene glycol having a hydroxyl group at the terminal or the like, a copolymer thereof, and an aliphatic polycarbonate having a hydroxyl group at the terminal or the like are reacted and copolymerized with polylactic acid or lactide. Thus, a crystallization promoting effect can be obtained. Similar crystallization promoting effect can be obtained by mixing these components.

The modified polylactic acid obtained by these methods is
The glass transition point is lowered to 20 to 50 ° C or below room temperature,
Similarly, the crystallization temperature (center value) when raising the temperature is 50 to 100 ° C.
It is reduced to a certain degree, and it becomes possible to crystallize even during storage at molding temperature or normal temperature. Further, even if the heat treatment is necessary, the heat treatment temperature can be lowered to, for example, about 50 to 120 ° C., and a crystallized product can be easily obtained.

The above (1) heat treatment, (2) nucleating agent, (3)
In addition to the crystallization accelerator, the molded product can be crystallized by stretching and orientation, but this is disadvantageous because a special process is used or the number of processes is increased. The present invention is, for example, injection-molded and then heat-treated to crystallize without substantially stretching orientation. The product according to the present invention has a crystal orientation degree of 40% or less, often 30% or less. . (The crystal orientation of a fully stretched product is 50% or more, often 60% or more). The crystal orientation degree OR (%) is X
When the half-value width (angle) of the main diffraction peak in the line diffraction method is θ °, OR (%) = (180 ° −θ °) × 1
It is calculated by an approximate expression of 00/180 °.

The seedling raising container is manufactured (molded), transported, raised,
It is necessary to maintain sufficient strength and prevent damage during transportation, storage and planting (planting) of seedlings. Therefore, it is preferable that the tensile strength, bending strength, impact strength and the like are sufficiently high. In particular, since polylactic acid homopolymer has a low impact strength of about 2 kg · cm / cm, the components having a low glass transition point as described above are mixed or / and block copolymerized to give an impact strength of 3 kg · cm / cm or more. Those having an impact strength of 4 kg · cm / cm or more are most preferable. Here, the impact strength (impact value) is ASTM
According to the method of D256, width 0.635mm, thickness 1
Using a notched test piece of 2.7 mm and a depth of 2.54 mm, impact is applied from the notch direction to obtain impact energy (unit: kg · cm), which is converted per 1 cm width.

The polymer must have a sufficient molecular weight in order to impart the desired strength to the container for raising seedlings of the present invention.
The weight average molecular weight of the polymer used in the present invention must be 50,000 or more, preferably 70,000 or more, and the range of 80 to 300,000 is most widely used.

The molding method of the container is not particularly limited, but melt injection molding, extrusion molding, and a method of deforming the molded product under heating with a mold or gas pressure are preferably used.

The shape of the container for raising seedlings of the present invention is not particularly limited, but a shape that effectively wraps and protects the roots of plants and the soil and compost surrounding them is preferable. An ordinary flower pot shape, a flower pot shape, a sack shape, a bag shape, a cage shape, a combination of these divided into two or more (used in combination), and any other. However, considering that the container for raising seedlings of the present invention has a long life, after planting, a plurality of holes or the like through which the roots extend to the outside, especially 3
It is preferable to provide about 30 pieces.

If desired, the polymer forming the container of the present invention may include coloring agents such as pigments and dyes, metal particles, inorganic or organic particles and other fillers, crystal nucleating agents, antioxidants, and the like.
Stabilizers such as ultraviolet absorbers, antistatic agents, lubricants, release agents, water repellents, plasticizers and other additives can be added.

In the following examples,% and parts are weight ratios unless otherwise specified. The molecular weight of the aliphatic polyester is the weight average value of the dispersion of the polymer component excluding the component having a molecular weight of 1000 or less in GPC analysis of a 0.1% chloroform solution of the sample.

[0027]

【Example】

[Example 1] L-lactide having an optical purity of 99.5% or more was mixed with 50 ppm of tin octylate as a catalyst, and 2
After continuously supplying to a shaft kneading extruder and reacting at 188 ° C. for 12 minutes, it was extruded from a die and cooled with water, and then cut to obtain a chip C1 of poly L-lactic acid homopolymer. After drying, the chip C1 is heat-treated in a nitrogen stream at 140 ° C. for 4 hours (solid-state polymerization).
After that, it was washed with acetone containing 0.1% of hydrochloric acid, and further washed 5 times with acetone containing no hydrochloric acid to completely remove the catalyst and the residual monomer to obtain a chip C2. Chip C
The molecular weight of 2 is 176,000, and the impact strength of the injection-molded test piece is 2.2 kg · cm / cm. Chip C
2 was extruded from a T-shaped die at 210 ° C. and cooled by a cooling roll at 20 ° C. to produce an unstretched sheet S1 having a thickness of 0.4 mm. Heat the sheet S1 gradually over 60 minutes to 120 ° C.
Sheet S2 was obtained by heat treatment for 2 hours. Width from sheet 1
cm, 10 cm in length to make a test piece, soil depth 10
The sample was embedded in a cm and the strength taken out was measured every month, and the period (half-life) at which the strength was half that of the unembedded product was determined. Experimental data are shown in Table 1. As can be seen from Table 1, the half-life is extended by about 2 times due to crystallization by heat treatment.

Similarly, when an unheated product and a heat-treated product in a flower pot (diameter 10 cm, side thickness about 0.5 mm) injection molded using the chip C2 were subjected to an embedding test in soil, a strength half-life was found. The unheated product was about 7 months and the heat-treated product was about 1.2 years, which was in good agreement with the experimental results of the sheet. This flower pot withstands a seedling raising period of one year or more.

[0029]

[Table 1] [Example 2] L-lactide 8 having an optical purity of 99.5% or more
1 part, polybutylene succinate / polybutylene adipate random = 4/1 (molar ratio) copolymer with a molecular weight of 1
20 parts of 25,000, tin octylate 50 ppm, and 1.5% of talc having a diameter of 0.7 μm as a crystal nucleating agent,
Thereafter, a chip C3 was obtained in the same manner as the chip C2 of Example 1. This polymer 3 is a modified polylactic acid obtained by block copolymerizing about 20% of polybutylene adipate / succinate copolymer, and has a molecular weight of 151,000 and an impact strength of 4.7.
It has a high melting point of 169 ° C and 80 ° C, with 169 ° C being a typical value. The glass transition temperature is 43 ° C., and the crystallization temperature (center value) is 103 ° C. An unheated sheet obtained from this polymer in the same manner as in Example 1 was subjected to S3 and heat treatment at 100 ° C. to obtain S3.
4 is assumed. The melting endotherm of the crystals of each sheet was 1.
9 J / g. S4 was 48 J / g.

Chip C4 was prepared in substantially the same manner as chip C3 except that a polybutylene adipate / succinate copolymer was block-copolymerized at about 30%. Chip C4 has a molecular weight of 143,000, a melting point of 166 ° C. and 83 ° C., a glass transition point is unclear, a temperature of about 20 ° C., a crystallization temperature of 90 ° C., and an impact strength of 4.9 kg · cm / cm. An unheated sheet obtained from this polymer in the same manner as in Example 1 was treated with S5,
What was heat-treated at 100 ° C. is designated as S6. The melting endothermic amount of the crystal of each sheet was 3.8 J / g. S6 is 46J
/ G.

Using the sheets S3 to S6, the half-life of strength in soil was measured in the same manner as in Example 1. S3 was 5.5 months, S4 was 10.4 months, and S5 was 3.7 months. S6 was 10.1 months, and it was shown that the lifespan was extended by heat treatment (crystallization).

[0032]

INDUSTRIAL APPLICABILITY According to the present invention, a container for raising seedlings having a slower decomposition rate and a longer life can be obtained, and a long period (eg 1
It is extremely useful for raising seedlings of plants that require more than one year), such as trees. Furthermore, by using other decomposition suppressing means such as a method of mixing or applying a water repellent (silicon compound, fluorine compound, oils and fats) in the container of the present invention, the life can be further extended. It can also be applied to those requiring a seedling raising period of one year or more. INDUSTRIAL APPLICABILITY According to the present invention, management of raising seedlings, storage, transportation, and planting of seedlings can be applied very easily and in a wide range, and brings the gospel to fields such as agriculture, forestry, horticulture, and civil engineering. In addition, degradation products of polymers containing lactic acid as the main component (lactic acid etc.) have the effect of suppressing the growth of bad pathogenic bacteria and further promoting the growth of plants,
Most suitable for the above applications.

[Brief description of drawings]

FIG. 1 is an example of a DSC curve in which the endothermic and exothermic amount of a polymer sample having low crystallinity at the time of temperature increase was measured by a scanning differential calorimeter.

FIG. 2 D of a fully crystallized polymer sample at elevated temperature
It is an example of an SC curve.

[Explanation of symbols]

 1 Change of baseline due to glass transition 2 Exothermic peak due to crystallization accompanying temperature rise of sample 3 Endothermic peak due to melting of crystal of sample

Claims (3)

[Claims] (1) A polyester polymer containing lactic acid as a main component, (2) the melting point of crystals of the polymer is 120 ° C. or higher, and (3) the melting endotherm of the crystals is 10 joules /
It is crystallized so that it is more than gram, and (4)
A container for raising seedlings, characterized in that the crystals are not substantially oriented. 2. The seedling-growing container according to claim 1, wherein the polymer has a melting point of 130 ° C. or higher and a melting endotherm of 20 joules / gram or higher. 3. The seedling-growing container according to claim 1, which is made of a polymer containing a crystal nucleating agent and / or a crystallization promoting component copolymerized and / or mixed.