WO2012144511A1 - Biodegradable aliphatic polyester particles, and process for producing same - Google Patents

Abstract

Biodegradable aliphatic polyester particles, preferably polyglycolic acid or polylactic acid particles, which have (A) a weight average molecular weight of 50,000 or more, (B) an average particle diameter of 5-500 μm, and (C) a water content of 900 ppm or more, and which preferably also have (D) compressive breaking strength of 1,500 gf/cm² or less when molded into a cylindrical tablet by applying a load of 100 gf/cm² at 40ºC for 24 hours in a cylindrical mold and/or (E) a weight average molecular weight retention rate of 65% or more after elapsing 50 days at 40ºC; and a process for producing the biodegradable aliphatic polyester particles, which is characterized by comprising grinding a particulate biodegradable aliphatic polyester at a temperature equal to or lower than the glass transition temperature (Tg) of the biodegradable aliphatic polyester.

Description

Biodegradable aliphatic polyester particles and method for producing the same

The present invention relates to biodegradable aliphatic polyester particles having an excellent anti-blocking effect and a method for producing the same.

Since aliphatic polyesters such as polyglycolic acid and polylactic acid are decomposed by microorganisms or enzymes existing in nature such as soil and sea, they are attracting attention as biodegradable polymer materials with a low environmental impact. Since these biodegradable aliphatic polyesters have biodegradable absorbability, they are also used as medical polymer materials such as surgical sutures and artificial skin.

As the biodegradable aliphatic polyester, polylactic acid (hereinafter sometimes referred to as “PLA”) composed of lactic acid repeating units, and polyglycolic acid composed of glycolic acid repeating units (hereinafter sometimes referred to as “PGA”). Also known are lactone polyesters such as poly-ε-caprolactone, polyhydroxybutyrate polyesters, and copolymers thereof, such as copolymers comprising glycolic acid repeating units and lactic acid repeating units.

Among biodegradable aliphatic polyesters, PLA can be obtained by using L-lactic acid as a raw material at low cost by fermentation from corn, straw, etc. The resulting poly L-lactic acid (hereinafter sometimes referred to as “PLLA”) has characteristics such as high rigidity and good transparency. However, PLAs such as PLLA have been pointed out as problems such as a slow crystallization rate and the need for post-treatment steps such as stretching.

In addition, among biodegradable aliphatic polyesters, PGA has excellent degradability, mechanical strength such as heat resistance and tensile strength, and gas barrier properties particularly when used as a film or sheet. Therefore, PGA is expected to be used as agricultural materials, various packaging (container) materials and medical polymer materials, and is being developed for use alone or in combination with other resin materials.

The methods of manufacturing products from biodegradable aliphatic polyester include extrusion molding, injection molding, compression molding, injection compression molding, transfer molding, cast molding, stampable molding, blow molding, stretched film molding, inflation film molding, and lamination. Melt molding and other molding methods such as molding, calendar molding, foam molding, RIM molding, FRP molding, powder molding or paste molding are employed. Pellets of biodegradable aliphatic polyester such as PGA used as a molding raw material for melt molding are, for example, melt-extruded biodegradable aliphatic polyester such as PGA in a strand form using a twin-screw extruder to a predetermined size. The average particle diameter obtained by cutting is of the order of several mm. As the powder of the biodegradable aliphatic polyester resin used as a molding raw material for powder molding or paste molding, biodegradable aliphatic polyester resin particles prepared in a predetermined size and shape according to the application are used.

On the other hand, focusing on the degradability, strength, etc. of biodegradable aliphatic polyesters such as PLA and PGA, raw materials in fields such as paints, coating agents, inks, toners, agricultural chemicals, pharmaceuticals, cosmetics, mining, well drilling, etc. Biodegradable aliphatic polyester particles useful as additives and the like are desired. The biodegradable aliphatic polyester particles applied to these fields are smaller than the biodegradable aliphatic polyester pellets described above, and are relatively small having a particle size and particle size distribution suitable for the purpose. Particles are required. In addition, the biodegradable aliphatic polyester particles are required to be excellent in handleability and storage stability.

In addition, the biodegradable aliphatic polyester used as a raw material resin for producing the biodegradable aliphatic polyester pellets by melt extrusion is a biodegradable aliphatic polyester recovered after the polymerization reaction, such as flakes. Used in the form of particles of desired shape and size.

Particles with a small particle size have poor handleability, increase hygroscopicity, increase surface area, increase the influence of decomposition rate, and have excellent characteristics of biodegradable aliphatic polyester. There was a risk of lowering. Furthermore, there was no risk of unexpected troubles occurring in the drying process or molding process.

Various methods for producing resin particles of biodegradable aliphatic polyester such as PLA and PGA have been proposed.

As a method for producing biodegradable aliphatic polyester particles, there are generally known a method for producing particles by cutting or pulverizing a melt-solidified product, and a method for producing particles by precipitation from a solution or dispersion. Japanese Patent Laid-Open No. 2001-288273 (Patent Document 1) discloses a polylactic acid resin powder in which a chip or block made of a PLA resin is cooled to a low temperature of −50 to −180 ° C., impact pulverized and classified. A manufacturing method is disclosed. In Japanese Patent Laid-Open No. 11-35693 (Patent Document 2), an organic solvent solution of a biodegradable aliphatic polyester and aromatic hydrocarbons are mixed at a temperature of less than 60 ° C., and the precipitated solid matter is solidified. A method for producing a liquid-degradable, powdered polyester having liquid degradability is disclosed. In Examples, PLA having a weight average molecular weight (hereinafter sometimes referred to as “Mw”) of 145,000, Mw of 10,000,000. Polybutylene succinate, and a copolymer of PLA and polybutylene succinate having an Mw of 172,000 are used as raw materials. In JP 2006-45542 A (Patent Document 3), as Production Example 3, PLA and a solvent (a mixture of dimethyl adipate, dimethyl glutarate, and dimethyl succinate (DBE (registered trademark), manufactured by DuPont) ), A PLA particle having an average primary particle size of 250 nm or less obtained at a dissolution temperature of 140 ° C. and a cooling temperature of −35 ° C., or, as Production Example 4, PGA and a solvent (bis (2-methoxyethyl) PGA particles having an average primary particle size of 150 nm or less obtained by using a) ether) at a dissolution temperature of 150 ° C. and a cooling temperature of −35 ° C. are disclosed.

However, biodegradable aliphatic polyester particles such as PLA and PGA can be used in products for the above-mentioned applications after obtaining particles having an average particle size, particle size distribution and shape suitable for the application. Until then, the biodegradable aliphatic polyester particles sometimes aggregated (blocked) while being stored or transported in the state of particles. In particular, when a load is applied to the biodegradable aliphatic polyester particles in a temperature environment near the glass transition temperature of the resin, blocking is likely to occur. For example, in the storage and transportation of particles in summer or in containers, the particles may be exposed to temperatures of 40 ° C. or higher for a long period of time. It was sought after. When blocking occurs, the handleability of the particles deteriorates, and the average particle diameter, particle size distribution and shape of the controlled particles are lost, and the desired characteristics may not be exhibited.

Therefore, measures to change the storage method (low temperature storage, flat stacking, etc.) have been taken, but there remains a problem that changing the storage method leads to an increase in manufacturing cost, and further improvement has been demanded. In addition, biodegradable aliphatic polyester particles may be hydrolyzed during storage in the presence of moisture, and may be thermally decomposed during melt molding, resulting in a decrease in molecular weight, and a decrease in strength and other mechanical properties. Therefore, further improvement has been demanded.

JP 2001-288273 A JP 11-35693 A JP 2006-45542 A

The problem of the present invention is that the anti-blocking effect is high, and the anti-blocking effect persists even after long-term storage, and further the molecular weight reduction due to hydrolysis does not occur if desired, and biodegradable aliphatic polyester particles, and It is in providing the manufacturing method.

In order to solve the above-mentioned problems, the present inventors have continued to analyze the phenomenon that blocking of biodegradable aliphatic polyester particles occurs, and in particular, biodegradable fat obtained by the so-called impact pulverization method. The group polyester particles were found to have a softened surface and a large proportion of non-crystalline parts due to the shearing force during pulverization. As a result of further investigations on the relationship between particle characteristics and blocking, it has been surprisingly required to reduce the molecular weight as much as possible due to concerns that the molecular weight may decrease due to hydrolysis or thermal decomposition. The inventors have found that the above problems can be solved by controlling the water content of the biodegradable aliphatic polyester particles so as to be at least a predetermined amount, thereby completing the present invention.

That is, according to the present invention, (A) the weight average molecular weight is 50,000 or more; (B) the average particle diameter is 5 to 500 μm; and (C) the water content is 900 ppm or more. Biodegradable aliphatic polyester particles are provided.

In addition, according to the present invention, the following biodegradable aliphatic polyester particles (1) to (3) are provided as embodiments.
(1) Further, (D) the compression fracture strength of the cylindrical tablet formed by applying a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in a cylindrical mold is 1,500 gf / cm ² or less. Said biodegradable aliphatic polyester particles.
(2) Further, (E) The biodegradable aliphatic polyester particles as described above, wherein the weight average molecular weight retention after 50 days at a temperature of 40 ° C. is 65% or more.
(3) The biodegradable aliphatic polyester particles described above, wherein the biodegradable aliphatic polyester contained in the biodegradable aliphatic polyester particles is PGA, PLA, or a mixture thereof.

Furthermore, according to the present invention, the biodegradable aliphatic polyester particle production method described above, wherein the particulate biodegradable aliphatic polyester is pulverized at a temperature lower than the glass transition temperature (Tg) of the biodegradable aliphatic polyester. Is provided. The particulate form is a general term for various shapes usually possessed by the biodegradable aliphatic polyester such as powder, flakes, particles or pellets.

According to the present invention, the biodegradable aliphatic polyester particles have (A) a weight average molecular weight of 50,000 or more; (B) an average particle diameter of 5 to 500 μm; and (C) a water content of 900 ppm or more; Preferably, (D) the compression fracture strength of the cylindrical tablet formed by applying a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in a cylindrical mold is 1,500 gf / cm ^2. And / or (E) The retention of the weight average molecular weight after 50 days at a temperature of 40 ° C. is 65% or more, so that the anti-blocking effect is high, and the anti-blocking effect is maintained even after long-term storage. There is an effect of providing biodegradable aliphatic polyester particles such as PGA particles and PLA particles that are sustained and do not cause a decrease in molecular weight due to hydrolysis if desired.

According to the present invention, the biodegradable aliphatic polyester particles are obtained by pulverizing the particulate biodegradable aliphatic polyester at a temperature not higher than the glass transition temperature (Tg) of the biodegradable aliphatic polyester. The effect that it can obtain easily is show | played.

1. Biodegradable aliphatic polyester The biodegradable aliphatic polyester contained in the biodegradable aliphatic polyester particles of the present invention includes glycolic acid and glycolic acid containing glycolide (GL), which is a bimolecular cyclic ester of glycolic acid. Lactic acid and lactate containing lactide which is a bimolecular cyclic ester of lactic acid, ethylene oxalate (ie, 1,4-dioxane-2,3-dione), lactones (eg, β-propiolactone, β- Butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone, β-methyl-δ-valerolactone, ε-caprolactone, etc.), carbonates (eg, trimethylene carbonate), ethers (eg, 1,3-dioxane), Cyclic monomers such as ether esters (eg, dioxanone); 3- Hydroxycarboxylic acids such as droxypropanoic acid, 4-hydroxybutanoic acid and 6-hydroxycaproic acid or alkyl esters thereof; aliphatic diols such as ethylene glycol and 1,4-butanediol; and succinic acid and adipic acid Examples include substantially equimolar mixtures with aliphatic carboxylic acids or alkyl esters thereof; homopolymers or copolymers of aliphatic ester monomers such as: Among them, the formula: (—O—CH (R) —C (O) —) [R is a hydrogen atom or a methyl group. ] The biodegradable aliphatic polyester which has 70 mass% or more of the glycolic acid or lactic acid repeating unit represented by these is preferable. Specifically, PGA, that is, a homopolymer of glycolic acid, or a copolymer having a glycolic acid repeating unit of 70% by mass or more; repeating poly L-lactic acid, poly D-lactic acid, L-lactic acid, or D-lactic acid PLA, such as a copolymer having 70% by mass or more of a unit, or a mixture thereof; more preferably, a mixture of PGA and PLA. Particularly preferred is PGA or PLA from the viewpoints of decomposability, heat resistance and mechanical strength.

These biodegradable aliphatic polyesters can be synthesized, for example, by dehydration polycondensation of α-hydroxycarboxylic acids such as glycolic acid and lactic acid known per se. In order to efficiently synthesize a high molecular weight biodegradable aliphatic polyester, generally, a method of synthesizing a bimolecular cyclic ester of α-hydroxycarboxylic acid and subjecting the cyclic ester to ring-opening polymerization is employed. . For example, PLA is obtained by ring-opening polymerization of lactide, which is a bimolecular cyclic ester of lactic acid. PGA is obtained by ring-opening polymerization of glycolide, which is a bimolecular cyclic ester of glycolic acid.

PLA can be synthesized by the above-described method, and commercially available products include, for example, “Lacia” (registered trademark) series (such as Lacia H-100, H-280, H-400, H-440) ( "Ingeo" (registered trademark) (manufactured by Natureworks), such as 3001D, 3051D, 4032D, 4042D, 6201D, 6251D, 7000D, and 7032D, Ecoplastic U'z S-09, S-12 "Ecoplastic U'z series" (manufactured by Toyota Motor Corporation), "Viro Ecole (registered trademark)" (manufactured by Toyobo Co., Ltd.), etc. From the viewpoint of sex, it is preferably selected.

Hereinafter, the biodegradable aliphatic polyester will be further described mainly using PGA as an example, but PLA and other biodegradable aliphatic polyesters can also take a form for carrying out the invention according to PGA. .

[Polyglycolic acid (PGA)]
PGA particularly preferably used as a raw material for the biodegradable aliphatic polyester particles of the present invention is a glycolic acid composed only of a glycolic acid repeating unit represented by the formula: (—O—CH ₂ —C (O) —). In addition to a homopolymer (including a ring-opened polymer of glycolide (GL), which is a bimolecular cyclic ester of glycolic acid), a PGA copolymer containing 50% by mass or more of the glycolic acid repeating unit is included.

Examples of comonomers that give a PGA copolymer together with glycolic acid monomers such as glycolide include ethylene oxalate (ie, 1,4-dioxane-2,3-dione), lactides, lactones, carbonates, ethers. Monomers, ether esters, amides, etc .; carboxylic acids such as lactic acid, 3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 6-hydroxycaproic acid or alkyl esters thereof; ethylene glycol , Substantially equimolar mixtures of aliphatic diols such as 1,4-butanediol and aliphatic dicarboxylic acids such as succinic acid and adipic acid or alkyl esters thereof; or two or more of these Can do. These comonomers can be used as a starting material for giving a PGA copolymer together with the glycolic acid monomer such as glycolide.

The glycolic acid repeating unit in the PGA used as the raw material of the PGA particles of the present invention is 50% by mass or more, preferably 70% by mass or more, more preferably 85% by mass or more, still more preferably 95% by mass or more, particularly preferably. Is a PGA homopolymer of 98% by weight or more, most preferably 99% by weight or more. If the proportion of glycolic acid repeating units is too small, the strength and degradability expected for PGA will be poor. The repeating unit other than the glycolic acid repeating unit is 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less, still more preferably 5% by mass or less, and particularly preferably 2% by mass or less. Most preferably, it is used in a proportion of 1% by mass or less, and may not contain any repeating unit other than the glycolic acid repeating unit.

The PGA used as a raw material for the PGA particles of the present invention is obtained by polymerizing 50 to 100% by mass of glycolide and 50 to 0% by mass of the above-mentioned other comonomer in order to efficiently produce a desired high molecular weight polymer. PGA is preferred. The other comonomer may be a cyclic monomer between two molecules, or may be a mixture of both instead of a cyclic monomer. In order to obtain PGA particles intended by the present invention, a cyclic monomer is used. preferable. Hereinafter, PGA obtained by ring-opening polymerization of 50 to 100% by mass of glycolide and 50 to 0% by mass of other cyclic monomers will be described in detail.

[Glycolide]
Glycolide that forms PGA by ring-opening polymerization is a bimolecular cyclic ester of glycolic acid, which is a kind of hydroxycarboxylic acid. Although the manufacturing method of glycolide is not specifically limited, Generally, it can obtain by thermally depolymerizing a glycolic acid oligomer. As a depolymerization method for glycolic acid oligomers, for example, a melt depolymerization method, a solid phase depolymerization method, a solution depolymerization method, etc. can be adopted, and glycolide obtained as a cyclic condensate of chloroacetate should also be used. Can do. If desired, glycolide containing glycolic acid can be used up to 20% by mass of the glycolide amount.

The PGA used as a raw material for the PGA particles of the present invention may be formed by ring-opening polymerization of only glycolide, but may also be formed by simultaneously ring-opening polymerization using another cyclic monomer as a copolymerization component. Good. In the case of forming a copolymer, the proportion of glycolide is 50% by mass or more, preferably 70% by mass or more, more preferably 85% by mass or more, still more preferably 95% by mass or more, and particularly preferably 98% by mass. % Or more, and most preferably 99% by mass or more of a substantially PGA homopolymer.

[Other cyclic monomers]
Other cyclic monomers that can be used as a copolymerization component with glycolide include lactones (for example, β-propiolactone, β-butyrolactone, in addition to bicyclic esters of other hydroxycarboxylic acids such as lactide). Cyclic monomers such as pivalolactone, γ-butyrolactone, δ-valerolactone, β-methyl-δ-valerolactone, ε-caprolactone, trimethylene carbonate, 1,3-dioxane and the like can be used. Other preferable cyclic monomers are bimolecular cyclic esters of other hydroxycarboxylic acids. Examples of hydroxycarboxylic acids include L-lactic acid, D-lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α- Hydroxyvaleric acid, α-hydroxycaproic acid, α-hydroxyisocaproic acid, α-hydroxyheptanoic acid, α-hydroxyoctanoic acid, α-hydroxydecanoic acid, α-hydroxymyristic acid, α-hydroxystearic acid, and these Examples include alkyl-substituted products. Another particularly preferable cyclic monomer is lactide, which is a bimolecular cyclic ester of lactic acid, and may be any of L-form, D-form, racemate, and a mixture thereof.

The other cyclic monomer is 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less, still more preferably 5% by mass or less, particularly preferably 2% by mass or less, and most preferably 1% by mass. Used in the following proportions. By ring-opening copolymerization of glycolide and other cyclic monomers, the melting point of PGA (copolymer) is lowered to lower the processing temperature, and the crystallization speed is controlled to improve extrusion processability and stretch processability. You can do it. However, when the use ratio of these cyclic monomers is too large, the crystallinity of the formed PGA (copolymer) is impaired, and heat resistance, gas barrier properties, mechanical strength, and the like are lowered. In addition, when PGA is formed from glycolide 100 mass%, another cyclic monomer is 0 mass%, and this PGA is also included in the scope of the present invention.

(Ring-opening polymerization reaction)
The ring-opening polymerization or ring-opening copolymerization of glycolide (hereinafter sometimes collectively referred to as “ring-opening (co) polymerization”) is preferably carried out in the presence of a small amount of a catalyst. The catalyst is not particularly limited. For example, a tin-based compound such as tin halide (for example, tin dichloride, tin tetrachloride) and organic carboxylate (for example, tin octoate such as tin 2-ethylhexanoate). Titanium compounds such as alkoxy titanates; aluminum compounds such as alkoxy aluminum; zirconium compounds such as zirconium acetylacetone; antimony compounds such as antimony halide and antimony oxide; The amount of the catalyst used is preferably about 1 to 1,000 ppm, more preferably about 3 to 300 ppm in terms of mass ratio with respect to the cyclic ester.

Glycolide ring-opening (co) polymerization uses higher alcohols such as lauryl alcohol, other alcohols, and water and other protic compounds as molecular weight regulators in order to control the physical properties such as molecular weight and melt viscosity of PGA. can do. Glycolide usually contains trace amounts of water and hydroxycarboxylic acid compounds composed of glycolic acid and linear glycolic acid oligomers as impurities, and these compounds also act on the polymerization reaction. Therefore, the concentration of these impurities is quantified as a molar concentration by, for example, neutralizing titration of the amount of carboxylic acid in these compounds, and alcohols and water are added as protic compounds according to the target molecular weight, etc. The molecular weight and the like of the produced PGA can be adjusted by controlling the molar concentration of the protic compound with respect to glycolide. Moreover, you may add polyhydric alcohols, such as glycerol, for a physical property improvement.

The ring-opening (co) polymerization of glycolide may be bulk polymerization or solution polymerization, but in many cases, bulk polymerization is employed. There are various types of polymerization equipment for bulk polymerization, such as an extruder type, a vertical type with paddle blades, a vertical type with helical ribbon blades, a horizontal type such as an extruder type and a kneader type, an ampoule type, a plate type and a tubular type. The device can be selected as appropriate. Moreover, various reaction tanks can be used for solution polymerization.

The polymerization temperature can be appropriately set according to the purpose within a range from 120 ° C. to 300 ° C. which is a substantial polymerization start temperature. The polymerization temperature is preferably 130 to 270 ° C., more preferably 140 to 260 ° C., and particularly preferably 150 to 250 ° C. If the polymerization temperature is too low, the molecular weight distribution of the produced PGA tends to be wide. If the polymerization temperature is too high, the produced PGA is susceptible to thermal decomposition. The polymerization time is in the range of 3 minutes to 50 hours, preferably 5 minutes to 30 hours. If the polymerization time is too short, the polymerization does not proceed sufficiently and a predetermined molecular weight cannot be realized. If the polymerization time is too long, the produced PGA tends to be colored.

After making the produced PGA into a solid state, solid phase polymerization may be further performed if desired. The solid phase polymerization means an operation of performing heat treatment while maintaining a solid state by heating at a temperature lower than the melting point (Tm) of PGA described later. By this solid phase polymerization, low molecular weight components such as unreacted monomers and oligomers are volatilized and removed. The solid phase polymerization is preferably performed for 1 to 100 hours, more preferably 2 to 50 hours, particularly preferably 3 to 30 hours.

Further, PGA in a solid state is melt-kneaded within the temperature range of the melting point (Tm) or higher, preferably the melting point (Tm) + 38 ° C. or more, more preferably the melting point (Tm) + 38 ° C. to the melting point (Tm) + 100 ° C. The crystallinity may be controlled by giving a thermal history by the process.

As raw materials for producing the PGA particles of the present invention, in addition to PGA, other aliphatic polyesters, polyglycols such as polyethylene glycol and polypropylene glycol, modified polyvinyl alcohol, polyurethane, Other resins such as polyamides such as poly-L-lysine, plasticizers, antioxidants, heat stabilizers, end-capping agents, UV absorbers, lubricants, mold release agents, waxes, colorants, crystallization promotion Additives that are usually blended such as an agent, a hydrogen ion concentration regulator, and fillers such as reinforcing fibers can be blended as necessary. The compounding amount of these additives and the like is usually 30 parts by mass or less, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and 5 parts by mass or less or 1 part by mass or less with respect to 100 parts by mass of PGA. The amount may be fine.

In particular, it is preferable to add a carboxyl group end-capping agent to PGA because the long-term storage stability of PGA particles is improved. That is, by adding a carboxyl group terminal blocking agent, the hydrolysis resistance of the PGA particles is improved, and the molecular weight reduction during storage can be further suppressed. As a carboxyl group terminal blocker, a compound having a carboxyl group terminal blocker and known as a water resistance improver for aliphatic polyesters can be used. Examples of carboxyl group end-capping agents include carbodiimide compounds such as N, N-2,6-diisopropylphenylcarbodiimide; 2,2′-m-phenylenebis (2-oxazoline), 2,2′-p-phenylene Oxazoline compounds such as bis (2-oxazoline), 2-phenyl-2-oxazoline and styrene / isopropenyl-2-oxazoline; oxazine compounds such as 2-methoxy-5,6-dihydro-4H-1,3-oxazine; And epoxy compounds such as N-glycidylphthalimide, cyclohexene oxide, and tris (2,3-epoxypropyl) isocyanurate. Among these carboxyl group end-capping agents, carbodiimide compounds are preferred, and any of aromatic, alicyclic, and aliphatic carbodiimide compounds are used, but aromatic carbodiimide compounds are particularly preferred, and particularly high purity. Gives water resistance improvement effect. The carboxyl group end-capping agent is usually used in a proportion of 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass, more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of PGA.

Further, it is more preferable to add a heat stabilizer to PGA, since the long-term storage stability of PGA particles is further improved. Thermal stabilizers include cyclic neopentanetetrayl bis (2,6-di-tert-butyl-4-methylphenyl) phosphite, cyclic neopentanetetrayl bis (2,4-di-tert-butylphenyl) ) Phosphite having a pentaerythritol skeleton structure such as phosphite, cyclic neopentanetetraylbis (octadecyl) phosphite; mono- or di-stearyl acid phosphate or a mixture thereof, preferably having 8 to 8 carbon atoms Phosphoric acid alkyl ester or phosphorous acid alkyl ester having 24 alkyl groups; carbonate carbonate such as calcium carbonate and strontium carbonate; bis [2- (2-hydroxybenzoyl) hydrazine] generally known as a polymerization catalyst deactivator Dodecanoic acid, N, N ' Hydrazine compounds having a -CONHNHCO- unit such as bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine; 3- (N-salicyloyl) amino-1,2,4- And triazole compounds such as triazole; triazine compounds; and the like. The heat stabilizer is usually 3 parts by mass or less, preferably 0.001 to 1 part by mass, more preferably 0.005 to 0.5 part by mass, and particularly preferably 0.01 to 0. It is used at a ratio of 1 part by mass (100 to 1,000 ppm).

2. Biodegradable Aliphatic Polyester Particles The biodegradable aliphatic polyester particles of the present invention are particles mainly composed of biodegradable aliphatic polyester, preferably PGA particles, PLA particles, or mixed particles of PGA and PLA. is there. Hereinafter, PGA particles will be described as examples of biodegradable aliphatic polyester particles. However, PLA particles, mixed particles of PGA and PLA, or other biodegradable aliphatic polyester particles are also referred to as PGA particles. The form for carrying out the invention can be taken accordingly.

The PGA particles which are the biodegradable aliphatic polyester particles of the present invention have (A) a weight average molecular weight of 50,000 or more; (B) an average particle diameter of 5 to 500 μm; and (C) a water content of 900 ppm or more. A particle characterized by the following:

[Weight average molecular weight (Mw)]
The weight average molecular weight (Mw) of the PGA contained in the PGA particles of the present invention is 50,000 or more, usually within the range of 5 to 1.5 million, more preferably 6 to 1.3 million, and still more preferably 7 A value in the range of ˜1.1 million, particularly preferably in the range of 100,000 to 1,000,000 is selected. The weight average molecular weight (Mw) of PGA is determined by a gel permeation chromatography (GPC) apparatus. Specifically, a PGA sample is dissolved in hexafluoroisopropanol (HFIP) in which sodium trifluoroacetate is dissolved at a predetermined concentration, and then filtered through a membrane filter to obtain a sample solution. The weight average molecular weight (Mw) is calculated from the result of measuring the molecular weight after injection into the apparatus.

In addition, the weight average molecular weight (Mw) of the PLA contained in the PLA particles of the present invention is preferably in the range of 5 to 1,200,000, more preferably 6 to 1,000,000, and even more preferably in the range of 7 to 800,000.

[Melting point (Tm)]
The melting point (Tm, hereinafter sometimes referred to as “crystalline melting point”) of PGA contained in the PGA particles of the present invention is usually 197 to 245 ° C., and the weight average molecular weight (Mw), molecular weight distribution, and types of copolymer components And it can adjust with a content rate etc. The melting point (Tm) of PGA is preferably 200 to 240 ° C., more preferably 205 to 235 ° C., and particularly preferably 210 to 230 ° C. The melting point (Tm) of the homopolymer of PGA is usually about 220 ° C. If the melting point (Tm) is too low, the heat resistance and strength may be insufficient. If the melting point (Tm) is too high, processability may be insufficient, particle formation may not be sufficiently controlled, and the resulting PGA particle size may not be in a desired range. The melting point (Tm) of PGA is determined in a nitrogen atmosphere using a differential scanning calorimeter (DSC). Specifically, the sample PGA corresponds to a temperature from room temperature to 280 ° C. [crystal melting point (Tm) +55 to 60 ° C.] at a rate of temperature increase of 20 ° C./min in a nitrogen atmosphere using DSC. ] Is the temperature of the endothermic peak accompanying crystal melting, which is detected during the temperature rising process. When a plurality of absorption peaks are observed, the peak having the largest endothermic peak area is defined as the melting point (Tm).

Also, the melting point (Tm) of PLA contained in the PLA particles of the present invention is preferably in the range of 145 to 185 ° C., more preferably 150 to 182 ° C., and further preferably 155 to 180 ° C.

[Glass transition temperature (Tg)]
The glass transition temperature (Tg) of PGA contained in the PGA particles of the present invention is usually 25 to 60 ° C., preferably 30 to 50 ° C., more preferably 35 to 45 ° C. The glass transition temperature (Tg) of PGA can be adjusted by the weight average molecular weight (Mw), the molecular weight distribution, the type and content ratio of the copolymerization component, and the like. The glass transition temperature (Tg) of PGA is determined in a nitrogen atmosphere using a differential scanning calorimeter (DSC), similarly to the measurement of the melting point (Tm). Specifically, the sample PGA is heated to about 280 ° C. (crystalline melting point (Tm) + around 50 ° C.), held at this temperature for 2 minutes, and then rapidly cooled with liquid nitrogen (about 100 ° C./min). When the obtained amorphous sample is reheated from near room temperature to 100 ° C. at a temperature increase rate of 20 ° C./min in a nitrogen atmosphere using DSC, the transition temperature from the glass state to the rubber state is An intermediate point of the end temperature is defined as a glass transition temperature (Tg) (hereinafter sometimes referred to as “intermediate point glass transition temperature”). If the glass transition temperature (Tg) is too low, the surface of the PGA particles may be excessively softened and particle blocking may easily occur. If the glass transition temperature (Tg) is too high, workability may deteriorate in powder molding or the like.

The glass transition temperature (Tg) of PLA contained in the PLA particles of the present invention is preferably in the range of 45 to 75 ° C., more preferably 50 to 70 ° C., and still more preferably 55 to 65 ° C.

[Average particle size (50% D)]
The average particle size of the biodegradable aliphatic polyester particles such as PGA particles or PLA particles of the present invention is 5 to 500 μm as the average particle size (50% D). The average particle size (50% D) of the biodegradable aliphatic polyester particles is the cumulative weight from the small particle size side using the particle size distribution of the particles measured and determined using a laser diffraction particle size distribution analyzer. Means a value represented by a particle size of 50%.

The average particle size (50% D) of the biodegradable aliphatic polyester particles of the present invention is preferably in the range of 7 to 450 μm, more preferably 10 to 400 μm, still more preferably 20 to 300 μm, and particularly preferably 30 to 200 μm. is there. If the average particle size (50% D) is too small, the handling property, storage property or storage property of the particles may not be good. If the average particle size (50% D) is too large, it may be difficult to use in the intended application. For example, if the average particle size is too large, the dispersibility in water will deteriorate, making it difficult to use in the paint, coating and toner fields. When the average particle size (50% D) is in the range of 5 to 500 μm, the flowability of the biodegradable aliphatic polyester particles is good, the particles are easy to handle, preserve and store, and the product In the molding and use of biodegradable aliphatic polyester particles, particles having a desired particle size can be obtained very easily.

〔amount of water〕
The biodegradable aliphatic polyester particles such as PGA particles or PLA particles of the present invention have a water content of 900 ppm or more. The water content of the biodegradable aliphatic polyester particles of the present invention is measured using a Karl Fischer moisture meter with a vaporizer (CA-100 (vaporizer: VA-100) manufactured by Mitsubishi Chemical Corporation). Specifically, when the biodegradable aliphatic polyester particles are PGA particles, the sample particles of 2 g of PGA particles are placed in a vaporizer heated to 220 ° C. (melting point of PGA particles) in advance and vaporized. After flowing dry nitrogen gas from the apparatus to the Karl Fischer moisture meter at 250 ml / min and introducing the sample into the vaporizer, the vaporized water is introduced into the Karl Fischer liquid, so that the electric conductivity is +0. The end point was the time when the voltage dropped to 1 mV.

The water content of the biodegradable aliphatic polyester particles such as PGA particles is preferably 900 ppm or more, more preferably 1,500 ppm or more, still more preferably 2,000 ppm or more, and particularly preferably 3,000 ppm or more. When the water content of the biodegradable aliphatic polyester particles such as PGA particles is less than 900 ppm, blocking tends to occur and the handleability may be inferior. There is no particular upper limit on the water content of the biodegradable aliphatic polyester particles such as PGA particles, but usually 10,000 ppm or less from the viewpoint of maintaining the shape of the biodegradable aliphatic polyester particles and preventing the occurrence of unexpected hydrolysis. In many cases, it is 9,000 ppm or less, and more preferably 7,000 ppm or less.

[Compressive fracture strength of cylindrical tablets]
Furthermore, the biodegradable aliphatic polyester particles such as PGA particles or PLA particles of the present invention are compressed in a cylindrical tablet formed by applying a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in a cylindrical mold. When the breaking strength is 1,500 gf / cm ² or less, the biodegradable aliphatic polyester particles are less likely to be blocked even during storage or transportation in the summer or containers that may be exposed to high temperatures, Moreover, even if particle blocking occurs once, the blocking state can be eliminated very easily. On the other hand, in the biodegradable aliphatic polyester particles having a compression fracture strength of the cylindrical tablet exceeding 1,500 gf / cm ² , it is difficult to eliminate the blocked state of the blocked biodegradable aliphatic polyester particles. In addition, biodegradable aliphatic polyester particles having a particle size required for the intended use cannot be easily obtained. Compression breaking strength of cylindrical tablets is preferably 1,000 gf / cm ² or less, more preferably 600 gf / cm ² or less, more preferably 400 gf / cm ² or less, particularly preferably 200 gf / cm ² or less in the range, Most preferably, it is 100 gf / cm ² or less. The lower limit of the compressive fracture strength of the cylindrical tablet is not particularly limited, but is usually 10 gf / cm ² , often 20 gf / cm ² , and in some cases, about 30 gf / cm ² may be used.

The compressive fracture strength of the cylindrical tablet was determined by compressing the cylindrical tablet in a vertical direction at a speed of 1 mm / min using a tensile compression tester (STA-1150) manufactured by ORIENTEC, and breaking the tablet. The required maximum point load (average value of N = 3) is obtained and used as the compressive fracture strength.

A cylindrical tablet for measuring the compressive fracture strength of a cylindrical tablet of biodegradable aliphatic polyester particles is loaded with a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in the cylindrical mold. It is a columnar tablet molded. Specifically, 1 g of biodegradable aliphatic polyester particles is placed in a stainless steel cylindrical mold (inner diameter 11.3 mm (inner cross-sectional area 1 cm ² )), and a cylindrical weight (outer diameter) is formed from the top of the particles. 11.3 mm, weight 100 g) and a constant load (100 gf / cm ² ) is applied to the particles in a constant temperature bath (relative humidity 10-30%) set at a temperature of 40 ° C. is prepared by molding by settling while continuing over time load, the upper area of 1 cm ^2, the lower area of 1 cm ^2, a cylindrical tablet height 1.5 cm.

[Retention ratio of weight average molecular weight after 50 days at a temperature of 40 ° C.]
The biodegradable aliphatic polyester particles of the present invention are excellent in anti-blocking effect and excellent in long-term storage stability. Specifically, the weight average molecular weight retention after 50 days at a temperature of 40 ° C. (hereinafter sometimes simply referred to as “molecular weight retention after 50 days”), that is, the biodegradable aliphatic polyester The biodegradable aliphatic polyester particles, wherein the particles are sealed in an aluminum bag and stored in an environment at a temperature of 40 ° C. for 50 days, and the retention of the weight average molecular weight after 50 days is 65% or more. It is preferable. The molecular weight retention after the elapse of 50 days is more preferably 70% or more, further preferably 75% or more, particularly preferably 80% or more, and most preferably 90% or more. In particular, when the molecular weight retention after 50 days is 80% or more, even when the biodegradable aliphatic polyester particles are stored for 1 year or more, blocking does not occur and hydrolysis does not occur.

The molecular weight retention after the lapse of 50 days is a particle sample measured after sealing a predetermined amount of the particle sample in an aluminum bag and storing it in an environment set at 40 ° C., for example, in an oven for 50 days, that is, after 50 days. The weight average molecular weight (molecular weight after the lapse of 50 days) and the initial molecular weight, that is, the weight average molecular weight of the particle sample before storage are calculated using the following formula 1.
Formula 1: Molecular weight retention after 50 days (%) = (Molecular weight after 50 days) / (Initial molecular weight) × 100

3. Method for Producing Biodegradable Aliphatic Polyester Particles Biodegradable aliphatic polyester particles such as PGA particles or PLA particles of the present invention have (A) a weight average molecular weight of 50,000 or more; (B) an average particle diameter of 5 And (C) a moisture content of 900 ppm or more, preferably (D) a circle formed by applying a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in a cylindrical mold. The columnar tablet has a compressive fracture strength of 1,500 gf / cm ² or less; and / or (E) a weight average molecular weight retention after 50 days at a temperature of 40 ° C. of 65% or more can be obtained. As long as the manufacturing method is not particularly limited.

The biodegradable aliphatic polyester particles of the present invention are usually washed from a biodegradable aliphatic polyester such as PGA having a shape such as powder or flakes collected after the polymerization reaction, and if necessary, The obtained particulate biodegradable aliphatic polyester may be used as a starting material. In addition, a pellet-shaped biodegradable aliphatic polyester obtained by blending various additives as necessary with the particulate biodegradable aliphatic polyester and melt extrusion molding may be used as a starting material. .

[Crushing treatment]
The biodegradable aliphatic polyester particles such as the PGA particles of the present invention are various shapes such as powders, flakes, particles or pellets (as described above, these shapes are collectively referred to simply as It can be obtained by pulverizing (impact pulverizing) the biodegradable aliphatic polyester of “particulate”) with mechanical impact, and in particular, freeze-pulverizing, and classifying as necessary. Can be obtained. The biodegradable aliphatic polyester particles of the present invention can be obtained by making a biodegradable aliphatic polyester such as PGA into a solution or dispersion of an organic solvent, and then coagulating or precipitating. According to classification, it can be obtained.

From the viewpoint of high antiblocking effect, production efficiency and production cost, the biodegradable aliphatic polyester particles of the present invention are preferably produced by pulverization, more preferably produced by impact pulverization. More preferably, the biodegradable aliphatic polyester particles of the present invention can be produced by grinding at a temperature not higher than the glass transition temperature (Tg) of the biodegradable aliphatic polyester. The pulverization temperature is more preferably −60 ° C. or more and glass transition temperature (Tg) −5 ° C. or less, more preferably −55 ° C. or more and glass transition temperature (Tg) −10 ° C. or less, particularly preferably −40 ° C. or more. Temperature (Tg) −20 ° C. or less, most preferably −30 ° C. or more and glass transition temperature (Tg) −30 ° C. or less. Specifically, for example, −55 ° C. to 35 ° C., preferably −45 ° C. A temperature range such as -20 ° C, more preferably -30 ° C-15 ° C can be selected. By pulverizing the raw material particles of biodegradable aliphatic polyester such as PGA in this temperature range, particularly by impact pulverization, heat generation during pulverization is suppressed, and thermal denaturation of the particle surface or inside the particle is not caused and desired Biodegradable aliphatic polyester particles having a particle diameter, that is, (B) average particle diameter (50% D) of 5 to 500 μm can be obtained. The pulverized particles are preferably classified into particles having a predetermined size as described above.

As an apparatus for performing impact pulverization, particularly freeze pulverization, an apparatus having both a cooling unit and a pulverizing unit, more preferably a particle size adjusting unit, using a cryogenic refrigerant such as liquid nitrogen is preferable, and a jet mill, a blade mill, a pin mill, or the like is used. However, it is preferable to use a pin mill that can obtain particles having a desired particle size and shape by adjusting the clearance and rotation speed of two disk pins that rotate at high speed. The time for pulverization by the impact pulverization method varies depending on the treatment temperature at which impact pulverization is performed, but is usually 10 seconds to 20 minutes, preferably 30 seconds to 15 minutes, more preferably 1 to 10 minutes, and particularly preferably 1 minute 30. The range may be from 5 seconds to 5 minutes.

[Humidity control]
The biodegradable aliphatic polyester particles such as the PGA particles of the present invention have (C) a water content of 900 ppm or more. When the water content of the biodegradable aliphatic polyester particles obtained by performing or not performing the pulverization treatment such as impact pulverization is less than 900 ppm, the biodegradable aliphatic polyester particles are used in a constant humidity environment. Below, for example, in a constant temperature and humidity chamber for a predetermined time, or by allowing it to flow, humidity control treatment to humidify so that the amount of water becomes 900 ppm or more, or direct injection of water and mixing the particles Humidity control can be performed. Further, in order to adjust the biodegradable aliphatic polyester particles such as PGA particles having a water content of 900 ppm or more to a more preferable water content, the moisture content may be further increased by performing the above-described humidity conditioning treatment.

As described above, there is no particular upper limit on the amount of water in the biodegradable aliphatic polyester particles such as PGA particles, but from the viewpoint of maintaining the shape of the biodegradable aliphatic polyester particles and preventing the occurrence of unexpected hydrolysis. Therefore, when it is desired to reduce the moisture content, the moisture content is adjusted to a desired value by allowing the biodegradable aliphatic polyester particles to stand in a low temperature drying atmosphere for a predetermined time or to flow. Can do. As the low temperature drying atmosphere, an atmosphere having a dew point of −50 ° C. (saturated water vapor pressure 0.0381 g / m ³ ) to a dew point of −70 ° C. (saturated water vapor pressure 0.00277 g / m ³ ) can be adopted. It is preferable to perform humidity conditioning in an atmosphere with a dew point of −60 ° C. (saturated water vapor pressure of 0.0109 g / m ³ ).

In addition, when the water content of the biodegradable aliphatic polyester particles obtained without performing the pulverization treatment such as impact pulverization described above is 900 ppm or more, the humidity control treatment is not performed and the present invention is performed. Biodegradable aliphatic polyester particles are obtained.

Hereinafter, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited to these examples. The measuring method of the physical property or characteristic of the biodegradable aliphatic polyester particle in an Example and a comparative example is as follows.

[Weight average molecular weight (Mw)]
The weight average molecular weight (Mw) of the biodegradable aliphatic polyester particles was adjusted to 10 ml by dissolving 10 mg of the particle sample in hexafluoroisopropanol (HFIP) in which sodium trifluoroacetate was dissolved at a concentration of 5 mM. A sample solution was obtained by filtration through a membrane filter, 10 μl of this sample solution was injected into a GPC apparatus, and the molecular weight was measured under the following measurement conditions.

<GPC measurement conditions>
Apparatus: Showa Denko GPC104
Column: Showa Denko HFIP-806M 2 (in series connection) + Precolumn: HFIP-LG 1 Column temperature: 40 ° C.
Eluent: HFIP solution in which sodium trifluoroacetate is dissolved at a concentration of 5 mM Detector: Differential refractometer Molecular weight calibration: Prepared using 5 types of polymethyl methacrylate (manufactured by Polymer laboratories Ltd.) with different molecular weights Using the calibration curve data of the measured molecular weight

[Melting point (Tm)]
Using a differential scanning calorimeter (DSC; TC-15 manufactured by METTLER TOLEDO), 10 mg of a sample was heated from a room temperature atmosphere to a crystalline melting point (around Tm + 50 ° C.) in a nitrogen atmosphere at a heating rate of 20 ° C./min. The crystal melting point (Tm) was measured from the endothermic peak that appears when heating to temperature. When a plurality of crystal melting points were observed, the peak with the largest endothermic peak area was defined as the crystal melting point (Tm).

[Glass transition temperature (Tg)]
A 10 mg sample was heated to about 280 ° C. using a differential scanning calorimeter (DSC; TC-15 manufactured by METTLER TOLEDO), held at this temperature for 2 minutes, and then rapidly (about 100 ° C./min with liquid nitrogen). The transition region from the glassy state to the rubbery state when the amorphous sample obtained by cooling to) is reheated from a room temperature atmosphere to a temperature close to 100 ° C. at a heating rate of 20 ° C./min in a nitrogen atmosphere. The glass transition temperature (Tg) was defined as the midpoint glass transition temperature corresponding to.

[Average particle size (50% D)]
The average particle size of the biodegradable aliphatic polyester particles is obtained by dispersing the particle sample in water containing a surfactant (“SN Dispersant 7347-c diluted solution” manufactured by San Nopco Co., Ltd.). From the particle size distribution determined using a laser diffraction particle size distribution analyzer (Salada-3000S manufactured by Shimadzu Corporation), the particle size at which the cumulative weight from the small particle size side becomes 50% is calculated as the average particle size (50% D).

〔amount of water〕
The water content of the biodegradable aliphatic polyester particles was measured using a Karl Fischer moisture meter with a vaporizer (CA-100 (vaporizer: VA-100) manufactured by Mitsubishi Chemical Corporation). Specifically, 2 g of sample particles of biodegradable aliphatic polyester particles are placed in a vaporizer heated in advance by setting the melting point of the biodegradable polyester particles, and 250 ml / min from the vaporizer to the Karl Fischer moisture meter. After flowing dry nitrogen gas and introducing the sample into the vaporizer, the time when the electrical conductivity decreased to +0.1 mV from the background by introducing the vaporized water into the Karl Fischer liquid was used as the end point.

[Compressive fracture strength of cylindrical tablets]
The compressive fracture strength of the cylindrical tablet of biodegradable aliphatic polyester particles was determined by using a tensile compression tester (STA-1150) manufactured by Orientec Co., Ltd., and the cylindrical tablet prepared from the particle sample at a speed of 1 mm / min. The maximum point load (average value of N = 3) required for compressing in the vertical direction and breaking the tablet was determined.

In the cylindrical tablet, 1 g of the particle sample is placed in a stainless steel cylindrical mold (inner diameter 11.3 mm (inner cross-sectional area 1 cm ² )), and a cylindrical weight (outer diameter 11.3 mm, weight 100 g), and a constant load (100 gf / cm ² ) is applied to the particles, in a constant temperature bath (relative humidity 20%) set at a temperature of 40 ° C. It was prepared by forming into a cylindrical tablet having an upper area of 1 cm ² , a lower area of 1 cm ² and a height of 1.5 cm.

[Storability (weight average molecular weight retention after 50 days at 40 ° C. (%))]
The storage stability of the biodegradable aliphatic polyester particles is as follows: 1 kg of the particle sample is sealed in an aluminum bag and stored in an oven set at 40 ° C. for 50 days, and after 50 days, the weight average molecular weight of the particle sample (50 days). (Molecular weight after lapse of time) was measured, and evaluated from the molecular weight retention rate (%) after the lapse of 50 days calculated using the above formula 1 from the weight average molecular weight (initial molecular weight) of the particle sample before storage. . If the molecular weight retention rate (%) after 50 days is 65% or more, it can be evaluated that the storability is high.
Formula 1: Molecular weight retention after 50 days (%) = (Molecular weight after 50 days) / (Initial molecular weight) × 100

[Persistence of blocking resistance]
Persistence of blocking resistance of the particle sample was determined by weighing and enclosing 15 g of the particle sample taken out after storage for 50 days in a polyethylene bag with a chuck of 70 mm under the chuck, 50 mm bag width and 0.04 mm thickness. In a constant temperature bath at 4 ° C., a weight of 4 kg was put and a load was applied for 1 day. Then, a particle sample was taken out from the polyethylene bag with a chuck and poured onto the upper surface of a sieve having an opening of 850 μm. The state when shaken was evaluated as “blocking property after 50 days” according to the following criteria.
A: The sample remaining on the sieve mesh is less than 20% by mass.
B: 20 to 70% by mass of the sample remaining on the sieve mesh.
C: The sample remaining on the mesh of the sieve exceeds 70% by mass.

[Example 1]
PGA flakes (Mw: 210,000, Tg: 45 ° C., Tm: 221 ° C.) with 100 parts by mass of N, N-2,6-diisopropylphenylcarbodiimide (DIPC manufactured by Kawaguchi Chemical Co., Ltd.) as a carboxyl group terminal blocker Melting and kneading while adding 0.3 part by mass and 0.02 part by mass of a substantially equimolar mixture of mono and distearyl acid phosphates (ADEKA ADEKA STAB AX-71 manufactured by ADEKA Corporation) as a heat stabilizer to a twin screw extruder Thus, a PGA pellet was produced. About 20 kg of the produced PGA pellets are immersed in liquid nitrogen, cooled, and then cooled with liquid nitrogen using a pin mill that can be cooled with liquid nitrogen at the time of pulverization (“Ultra Fine Pin Mill: Contraplex Series” manufactured by Hadano Sangyo Co., Ltd.) While cooling, the mixture was pulverized (impact pulverization) for 2 minutes under the conditions of a pulverization temperature of −50 ° C. and a peripheral speed of 187 m / sec to obtain PGA particles. The initial molecular weight, average particle diameter (50% D, hereinafter simply referred to as “particle diameter”), moisture content, and compression fracture strength of the cylindrical tablet (hereinafter simply referred to as “compression fracture strength”) of the obtained PGA particles. Table 1 shows the test results of blocking property after 50 days and storage properties (molecular weight retention (%) after 50 days).

[Example 2]
PGA particles were obtained in the same manner as in Example 1 except that the pulverization temperature in impact pulverization was changed to -25 ° C. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the obtained PGA particles.

Example 3
PGA particles were obtained in the same manner as in Example 1 except that the pulverization temperature in impact pulverization was changed to 5 ° C. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the obtained PGA particles.

Example 4
After about 3 mL of water was jetted onto the PGA particles obtained in Example 3, the mixture was thoroughly stirred and mixed to obtain PGA particles that were conditioned so as to increase the amount of water in the particles. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the conditioned PGA particles.

Example 5
After about 8 mL of water was jetted onto the PGA particles obtained in Example 3, the mixture was thoroughly stirred and mixed to obtain PGA particles that were conditioned so as to increase the amount of water in the particles. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the conditioned PGA particles.

Example 6
PGA particles were obtained in the same manner as in Example 3 except that PGA flakes (Mw: 210,000, Tg: 45 ° C., Tm: 221 ° C.) were used instead of the PGA pellets. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the obtained PGA particles.

Example 7
In place of the PGA pellets, PLA pellets (Nature Works 7000D, Mw: 215,000, Tg: 60 ° C., Tm: 165 ° C.) were used in the same manner as in Example 2 except that PLA pellets were used. Particles were obtained. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the obtained PLA particles.

[Comparative Example 1]
The PGA particles obtained in Example 3 were allowed to stand in an atmosphere having a dew point of −60 ° C. for 6 hours to obtain PGA particles that were conditioned so as to reduce the water content in the particles. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the conditioned PGA particles.

[Comparative Example 2]
The PGA particles obtained in Example 3 were allowed to stand in an atmosphere having a dew point of −60 ° C. for 3 hours to obtain PGA particles that were conditioned so as to reduce the water content in the particles. Table 1 shows the test results of the initial molecular weight, particle diameter, water content, compressive fracture strength, blocking property after 50 days, and storage property of the conditioned PGA particles.

From Table 1, the initial molecular weight (weight average molecular weight (Mw)) obtained by impact pulverization at a temperature in the range of −50 to 5 ° C. is 19.4 to 214,000, and the average particle diameter (D ₅₀ ) is The PGA particles or PLA particles of Examples 1 to 7 having 75 to 152 μm and a water content of 949 to 6,458 ppm have an A rating of blocking properties after 50 days, and have a high blocking resistance. Further, the retention of the weight average molecular weight after 50 days at a temperature of 40 ° C. was 73.3 to 99.9%, and it was found that the particles had excellent long-term storage properties. Furthermore, the compression fracture strength of the cylindrical tablet is 41 to 1,419 gf / cm ² , and PGA particles or PLA particles are difficult to block, and even if particle blocking once occurs, the blocking state is extremely easy. It was found that can be solved.

In contrast, the PGA particles of Comparative Examples 1 and 2 having a moisture content of 40 ppm or 268 ppm have a blocking property after 50 days of C or B evaluation, and it is found that the durability of the blocking resistance is low, It was found that the compression fracture strength of the cylindrical tablet was 1,900 gf / cm ² or 1,745 gf / cm ² , and the blocking state of the PGA particles was not easily eliminated.

According to the present invention, (A) the weight average molecular weight is 50,000 or more; (B) the average particle size is 5 to 500 μm; and (C) the water content is 900 ppm or more; The compression fracture strength of a cylindrical tablet molded by applying a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in a mold is 1,500 gf / cm ² or less; and / or (E) at a temperature of 40 ° C. By the biodegradable aliphatic polyester particles having a weight average molecular weight retention rate of 65% or more after the lapse of 50 days, the antiblocking effect is high, and the antiblocking effect continues even after long-term storage, Furthermore, since biodegradable aliphatic polyester particles that do not cause a decrease in molecular weight due to hydrolysis are provided as desired, the applicability of the biodegradable aliphatic polyester particles is increased. High availability.

According to the present invention, the biodegradable aliphatic polyester particles are obtained by pulverizing the particulate biodegradable aliphatic polyester at a temperature not higher than the glass transition temperature (Tg) of the biodegradable aliphatic polyester. Since it can be manufactured easily, the industrial applicability is high.

Claims (5)

1. (A) The weight average molecular weight is 50,000 or more;
   (B) the average particle size is 5 to 500 μm; and (C) the water content is 900 ppm or more;
   Biodegradable aliphatic polyester particles, characterized in that
2. Furthermore, (D) the compression fracture strength of a cylindrical tablet formed by applying a load of 100 gf / cm ² at a temperature of 40 ° C. for 24 hours in a cylindrical mold is 1,500 gf / cm ² or less. The biodegradable aliphatic polyester particles described in 1.
3. Furthermore, (E) The biodegradable aliphatic polyester particles according to claim 1, wherein the weight average molecular weight retention after 50 days at a temperature of 40 ° C is 65% or more.
4. The biodegradable aliphatic polyester particles according to claim 1, wherein the biodegradable aliphatic polyester contained in the biodegradable aliphatic polyester particles is polyglycolic acid, polylactic acid, or a mixture thereof.
5. The biodegradation according to any one of claims 1 to 4, wherein the particulate biodegradable aliphatic polyester is pulverized at a temperature equal to or lower than the glass transition temperature (Tg) of the biodegradable aliphatic polyester. Of producing aliphatic polyester particles.