JP7683191B2 - biodegradable resin particles - Google Patents

Description

The present invention relates to biodegradable resin particles.

Patent Document 1 discloses "a cellulose material having improved biodegradability by being coated with a water-soluble polymer."
Patent Document 1 discloses polyethyleneimine as a water-soluble polymer.

Patent Document 2 discloses a "cosmetic method for changing the appearance of the skin, changing the feel of the skin, and/or protecting the skin, the cosmetic method comprising a step of applying onto the skin a self-supporting cosmetic sheet comprising at least one biocompatible and/or biodegradable hydrophobic polymer layer, the self-supporting cosmetic sheet having a thickness of 10 to 1000 nm, preferably 30 to 500 nm, more preferably 50 to 300 nm."
Patent Document 2 discloses a layer containing polyethyleneimine as a hydrophobic polymer layer.

Patent Document 3 discloses a "biodegradable resin composition comprising (A) a thermoplastic synthetic resin, (B) an inorganic filler, and (C) a biodegradable organic material, wherein the amount of component (A) is 49 mass % or less based on the total amount of the composition, and the mass ratio of component (B) to component (C) ((B)/(C)) is in the range of 3/7 to 7/3."
Patent Document 3 discloses that at least one selected from liquid paraffin, metal soap, silicone, side-chain crystalline polyolefin, stearic acid, and polyglutamic acid is blended as a binder component (D) in a biodegradable resin composition.

JP 2004-256579 A JP 2015-512863 A JP 2011-225643 A

The object of the present invention is to provide biodegradable resin particles that have a slow initial biodegradation rate while still having a high biodegradation rate over time, compared to biodegradable resin particles having only a layer containing at least one cationic resin selected from polyalkyleneimine, polyallylamine, and polyvinylamine on the surface of a base particle containing a biodegradable resin.

Specific means for solving the above problems include the following aspects:

<1> A base particle containing a biodegradable resin;
a first layer on the surface of the base particle, the first layer including at least one cationic resin selected from the group consisting of polyalkyleneimine, polyallylamine, and polyvinylamine;
a second layer on the first layer, the second layer including an anionic or nonionic hydrophobic compound;
Biodegradable resin particles having the above structure.
<2> The biodegradable resin particles according to <1>, wherein the hydrophobic compound is at least one selected from the group consisting of a silicone compound, a hydrocarbon compound, a fatty acid compound, an acrylic resin, a polyester resin, and a urethane resin.
<3> The biodegradable resin particles according to <2>, wherein the silicone compound is at least one selected from the group consisting of dimethylpolysiloxane, methylpolysiloxane, MQ resin, and silicone rubber.
<4> The biodegradable resin particles according to <2> or <3>, wherein the hydrocarbon compound is at least one selected from the group consisting of paraffin wax, microcrystalline wax, polyethylene wax, and polypropylene wax.
<5> The biodegradable resin particles according to any one of <2> to <4>, wherein the fatty acid compound is at least one selected from the group consisting of carnauba wax, rice wax, candelilla wax, palm wax, castor oil wax, soybean oil wax, and sunflower oil wax.
<6> The biodegradable resin particles according to any one of <1> to <5>, wherein the polyalkyleneimine is a polyalkyleneimine having a structural unit having an alkylene group having 1 to 4 carbon atoms.
<7> The biodegradable resin particles according to <6>, wherein the polyalkyleneimine having a structural unit having an alkylene group having 1 to 4 carbon atoms is polyethyleneimine.
<8> The biodegradable resin particles according to any one of <1> to <7>, wherein the biodegradable resin is at least one selected from the group consisting of a cellulose resin and a polyester resin.
<9> The biodegradable resin particles according to <8>, wherein the biodegradable resin is a cellulose resin.
<10> The biodegradable resin particles according to <9>, wherein the cellulose resin is a cellulose acylate having two or more types of acyl groups.
<11> The biodegradable resin particles according to <9> or <10>, which do not have a functional group that reacts with the cellulose resin and contain at least one of an aromatic compound having a long-chain aliphatic group, a phenolic hydroxyl group, and a monoglycidyl ether group directly bonded to an aromatic group, and at least one fatty acid ester.
<12> The biodegradable resin particles according to <11>, wherein the aromatic compound is a cardanol compound.
<13> The biodegradable resin particles according to <12>, wherein the cardanol compound is at least one compound selected from the group consisting of a compound represented by the following general formula (CDN1) and a compound represented by the following general formula (CDN1-e):

(In general formula (CDN1), R ¹ represents an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. R ² represents a hydroxy group, a carboxy group, an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. P 2 represents an integer of 0 to 4. When P 2 is 2 or more, a plurality of R ^2s may be the same group or different groups.)

(In general formula (CDN1-e), L _EP represents a single bond or a divalent linking group. In general formula (CDN1-e), R ¹ , R ² and P2 have the same meanings as R ¹ , R ² and P2 in general formula (CDN1), respectively.)
<14> The biodegradable resin particles according to any one of <11> to <13>, wherein the base particles contain cellulose acetate propionate as the cellulose resin and a cardanol compound as the aromatic compound.
<15> The biodegradable resin particle according to any one of <11> to <13>, wherein the base particle contains cellulose acetate butyrate as the cellulose resin and the fatty acid ester.
<16> The biodegradable resin particles according to any one of <1> to <15>, wherein a mass ratio of a coating amount of the cationic resin to a coating amount of the hydrophobic compound (coating amount of the cationic resin/coating amount of the hydrophobic compound) is 0.1 or more and 10 or less.
<17> The biodegradable resin particles according to <16>, wherein the amount of the cationic resin coated on the base particle is 0.1% by mass or more and 10% by mass or less.
<18> The biodegradable resin particles according to any one of <1> to <17>, wherein the cationic resin has a number average molecular weight of 10,000 or more and 85,000 or less.
<19> A base particle containing a biodegradable resin,
a compound layer on the surface of the base particle;
having
The biodegradable resin particles have a water contact angle of 70° or more and 120° or less when pelletized.
<20> A base particle containing a biodegradable resin,
a compound layer on the surface of the base particle;
having
Biodegradable resin particles having an aerobic biodegradation rate of 20% or less after 3 months, measured according to a method conforming to ISO-14855-2 (2018).
<21> A base particle containing a biodegradable resin,
a compound layer on the surface of the base particle;
having
A biodegradable resin particle in which, when the surface of the biodegradable resin particle is measured by X-ray photoelectron spectroscopy (XPS), the relationship between the carbon atom amount Cs, the silicon atom amount Sis, and the oxygen atom amount Os satisfies the formula A: (Cs+Sis)/Os≧3.
<22> The biodegradable resin particles according to <21>, in which, when the surface of the biodegradable resin particles after three minutes of surface etching is measured by X-ray photoelectron spectroscopy (XPS), the relationship between the carbon atom amount Ce, the silicon atom amount Sie and the oxygen atom amount Oe satisfies the formula B: (Ce+Sie)/Oe≧3.

According to the invention related to <1>, <2>, <3>, <4>, <5>, <6>, <7>, or <8>, there is provided a biodegradable resin particle having a slow initial biodegradation rate while maintaining a biodegradation rate over time, as compared with a biodegradable resin particle having only a layer containing at least one cationic resin selected from polyalkyleneimine, polyallylamine, and polyvinylamine on the surface of a base particle containing a biodegradable resin.
According to the invention related to item <9>, there are provided biodegradable resin particles which have a faster biodegradation rate over time and a slower initial biodegradation rate than when the biodegradable resin is a polyester resin.
According to the invention related to <10>, there are provided biodegradable resin particles which have a faster biodegradation rate over time and a slower initial biodegradation rate than when the cellulose resin is a cellulose acylate having one type of acyl group.
According to the invention related to <11>, there is provided a biodegradable resin particle which has excellent hydrolysis resistance while retaining biodegradability, even when it contains at least one of an aromatic compound and a fatty acid ester together with a cellulose resin as the biodegradable resin, as compared with a biodegradable resin particle having only a layer containing at least one cationic resin selected from polyalkyleneimine, polyallylamine, and polyvinylamine on the surface of a base particle containing a biodegradable resin.
According to the invention related to <12> or <13>, there is provided a biodegradable resin particle which has excellent hydrolysis resistance while having biodegradability, as compared with a case in which an alkyl-modified phenol novolac epoxy resin is used as an aromatic compound.
According to the invention related to <14> or <15>, biodegradable resin particles are provided which have excellent hydrolysis resistance while retaining biodegradability, as compared with a case in which the base particles contain cellulose acetate butyrate as the cellulose resin and a cardanol compound as the aromatic compound, or a case in which the base particles contain cellulose acetate propionate as the cellulose resin and a fatty acid ester.

According to the invention related to <16>, there is provided a biodegradable resin particle having a faster biodegradation rate over time and a slower initial biodegradation rate, compared to when the mass ratio of the cationic resin to the hydrophobic compound is less than 0.1 or more than 10.
According to the invention related to <17>, there is provided a biodegradable resin particle having a faster biodegradation rate over time and a slower initial biodegradation rate, compared to when the amount of cationic resin coated on the base particles is less than 0.1 mass % or more than 10 mass %.
According to the invention related to <18>, there are provided biodegradable resin particles which have a faster biodegradation rate over time and a slower initial biodegradation rate, compared with cases where the number average molecular weight of the cationic resin is less than 10,000 or more than 85,000.

According to the invention related to <19>, there is provided biodegradable resin particles which have a compound layer on the surface of a base particle containing a biodegradable resin, and which have a slow initial biodegradation rate while maintaining a biodegradation rate over time compared to biodegradable resin particles which have a water contact angle of less than 70° when the biodegradable resin particles are pelletized.
According to the invention related to <20>, there is provided biodegradable resin particles having a compound layer on the surface of base particles containing a biodegradable resin, and having a slow initial biodegradation rate while maintaining a biodegradation rate over time compared to biodegradable resin particles having an aerobic biodegradation rate of more than 20% after 3 months, as measured by a method conforming to ISO-14855-2 (2018).
According to the invention related to <21>, there is provided a biodegradable resin particle having a compound layer on the surface of a base particle containing a biodegradable resin, and having a slow initial biodegradation rate while maintaining a biodegradation rate over time, as compared with biodegradable resin particles that do not satisfy formula A: (Cs+Sis)/Os≧3.
According to the invention related to <22>, there is provided a biodegradable resin particle having a compound layer on the surface of a base particle containing a biodegradable resin, and having a slow initial biodegradation rate while maintaining a biodegradation rate over time, compared to biodegradable resin particles that do not satisfy formula B: (Ce+Sie)/Oe≧3.

The following describes an embodiment of the present invention. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the embodiment.

In the numerical ranges described in this specification in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in this specification, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.
Each component may contain multiple types of the corresponding substance.
When referring to the amount of each component, in cases where there are multiple substances corresponding to each component, the amount refers to the total amount of the multiple substances, unless otherwise specified.
"(Meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate.

<Biodegradable resin particles>
--First embodiment--
The biodegradable resin particles according to the first embodiment have a base particle containing a biodegradable resin, a first layer on the surface of the base particle containing at least one cationic resin selected from the group consisting of polyalkyleneimine, polyallylamine, and polyvinylamine, and a second layer on the first layer containing an anionic or nonionic hydrophobic compound.

The biodegradable resin particles according to the first embodiment, due to the above-mentioned configuration, are biodegradable resin particles that have a high biodegradation rate over time (e.g., 12 months under aerobic conditions) but a low initial biodegradation rate (e.g., 3 months under aerobic conditions). The reason for this is presumed to be as follows.

Biodegradable resin particles are required to have a fast biodegradation rate. However, if the biodegradation rate is too fast, the durability of the resin particles themselves will decrease quickly. In other words, it is required that the resin particles maintain their functionality for a certain period of time (for example, a period of several years during the period of use).

Therefore, a second layer containing an anionic or nonionic hydrophobic compound is provided on the surface of a base particle containing a biodegradable resin, via a first layer containing at least one cationic resin selected from the group consisting of polyalkyleneimine, polyallylamine, and polyvinylamine.
Due to the presence of the first layer containing a cationic resin, anionic or nonionic hydrophobic compounds are adsorbed on the surface of the base particles to form a hydrophobic second layer, increasing the hydrophobicity of the surface of the biodegradable resin particles. This slows down the initial biodegradation rate, and the function of the resin particles is maintained for a certain period of time. As time passes, the biodegradation of the hydrophobic biocompounds in the second layer progresses, and the biodegradability of the base particles containing the biodegradable resin themselves is exerted over time.

Therefore, it is presumed that the biodegradable resin particles according to the first embodiment have a biodegradation rate over time, but have a slow initial biodegradation rate.

--Second embodiment--
The biodegradable resin particles according to the second embodiment have a base particle containing a biodegradable resin and a compound layer on the surface of the base particle, and have a water contact angle of 70° or more and 120° or less when the biodegradable resin particles are pelletized.

Due to the above-mentioned configuration, the biodegradable resin particles of the second embodiment are biodegradable resin particles that have a high biodegradation rate over time (e.g., 12 months under aerobic conditions), but have a low initial biodegradation rate (e.g., 3 months under aerobic conditions).
The reason is that the surface of the compound layer in the biodegradable resin particles exhibits hydrophobicity within the above-mentioned contact angle range, and the initial biodegradation rate is slowed down by suppressing the hydrolysis of the biodegradable resin of the base particle, and the function as a resin particle is maintained for a certain period of time. Then, after a certain period of time, the decomposition of the components of the compound layer of the biodegradable resin particles progresses, and over time, the biodegradability of the base particle itself containing the biodegradable resin is exerted.

--Third embodiment--
The biodegradable resin particles according to the third embodiment have a base particle containing a biodegradable resin and a compound layer on the surface of the base particle, and have an aerobic biodegradability of 20% or less after 3 months, as measured according to a method in accordance with ISO-14855-2 (2018).
Due to the above-mentioned configuration, the biodegradable resin particles of the third embodiment are biodegradable resin particles that have a biodegradation rate over time (e.g., 12 months under aerobic conditions) but a slow initial biodegradation rate (e.g., 3 months under aerobic conditions).
The reason is that the compound layer in the biodegradable resin particles lowers the aerobic biodegradation rate after 3 months, and the initial biodegradation rate is slowed down by suppressing the hydrolysis of the biodegradable resin of the base particle, so that the function of the resin particles is maintained for a certain period of time. Then, after a certain period of time, the components of the compound layer of the biodegradable resin particles are decomposed, and the base particle itself containing the biodegradable resin exhibits its biodegradability over time.

--Fourth embodiment--
The biodegradable resin particles according to the fourth embodiment have a base particle containing a biodegradable resin and a compound layer on the surface of the base particle, and when the surface of the biodegradable resin particle is measured by X-ray photoelectron spectroscopy (XPS), the relationship between the carbon atom weight Cs, the silicon atomic weight Sis, and the oxygen atomic weight Os satisfies the formula A: (Cs+Sis)/Os≧3.
Due to the above-mentioned configuration, the biodegradable resin particles of the fourth embodiment are biodegradable resin particles that have a biodegradation rate over time (e.g., 12 months under aerobic conditions) but a slow initial biodegradation rate (e.g., 3 months under aerobic conditions).
The reason is that the compound layer in the biodegradable resin particle increases the amount of carbon atoms and silicon atoms present on the surface of the biodegradable resin particle so as to satisfy formula A, thereby increasing the hydrophobicity of the surface of the biodegradable resin particle, and suppressing the hydrolysis of the biodegradable resin of the base particle, slowing down the initial biodegradation rate, and maintaining the function as a resin particle for a certain period of time.After a certain period of time, the decomposition of the components of the compound layer of the biodegradable resin particle progresses, and over time, the biodegradability of the base particle itself containing the biodegradable resin is exerted.

Furthermore, by increasing the amount of carbon atoms and silicon atoms present on the particle surface, the lipophilicity of the surface of the biodegradable resin particles is improved, and the oil absorption rate of the resin particles is increased.
Conventional biodegradable resin particles have excellent decomposability in the natural environment, but have a relatively hydrophilic structure, and therefore have low compatibility with oil or low oil absorption. For example, when conventional biodegradable resin particles are added to cosmetics, etc., if the oil absorption is low, the makeup is likely to be ruined by sebum, etc. Also, when conventional biodegradable resin particles are added to paint, if the oil absorption is low and the compatibility with oil is poor, the particles will aggregate and harden. Therefore, biodegradable resin particles with high oil absorption rate are useful in the fields of cosmetics, paints, etc., because, for example, makeup is unlikely to be ruined when added to cosmetics, and they are unlikely to aggregate when added to paint.

Here, in the biodegradable resin particles according to the second to fourth embodiments, for example, the compound layer may be a two-layer compound layer consisting of a first layer containing at least one cationic resin selected from the group consisting of polyalkyleneimine, polyallylamine, and polyvinylamine, and a second layer on the first layer containing an anionic or nonionic hydrophobic compound.
However, for example, the compound layer in the biodegradable resin particles according to the second and third embodiments is not particularly limited as long as it is a compound layer that imparts the above-mentioned properties of the biodegradable resin particles according to the second and third embodiments.

Hereinafter, biodegradable resin particles that correspond to any of the biodegradable resin particles according to the first to fourth embodiments (hereinafter also referred to as "biodegradable resin particles according to this embodiment") will be described in detail. However, an example of the biodegradable resin particles of the present invention may be any of the biodegradable resin particles according to the first to fourth embodiments.

The biodegradable resin particles according to this embodiment are described in detail below.

[Mother particle]
The base particle is a particle on which the first layer and the second layer are formed, and contains a biodegradable resin.
Examples of the base particles include particles containing a biodegradable resin as a main component, and specifically, examples of the base particles include particles containing 90 mass %, 95 mass %, 98 mass %, or 100 mass % of biodegradable resin based on the entire base particle.

-Biodegradable resin-
A biodegradable resin is a resin that is decomposed into water and carbon dioxide by microorganisms. Specifically, a biodegradable resin means a resin whose aerobic biodegradation rate measured according to ISO-14855-2 (2018) is 50% or more in one month.

Biodegradable resins include polyester resins, natural polymers, polyvinyl alcohol, etc.

Examples of the polyester resin include an aliphatic polyester resin and an aliphatic aromatic polyester resin.
Examples of aliphatic polyester resins include polylactic acid (PLA), polyglycolic acid (PGA), polyhydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polycaprolactone, polybutylene succinate (PBS), polybutylene succinate/adipate (PBSA), polyethylene succinate (PBA), and other polyhydroxyalkanoates.
Examples of the aliphatic aromatic polyester resin include polybutylene adipate/terephthalate copolymer resin (PBAH) and polytetramethylene adipate/terephthalate copolymer resin.

Natural polymers include starch, cellulose, chitin, chitosan, gluten, gelatin, zein, soy protein, collagen, keratin, etc.

Among these, from the viewpoint of improving the rate of biodegradation over time, the biodegradable resin is preferably at least one selected from the group consisting of cellulose resin and polyester resin, and more preferably cellulose resin.

The cellulose resin is preferably cellulose acylate, which is a cellulose derivative in which at least a portion of the hydroxyl groups in cellulose are substituted with acyl groups (acylation). The acyl group is a group having the structure -CO-R ^AC (R ^AC represents a hydrogen atom or a hydrocarbon group).

Cellulose acylate is, for example, a cellulose derivative represented by the following general formula (CA):

In the general formula (CA), A ¹ , A ² and A ³ each independently represent a hydrogen atom or an acyl group, and n represents an integer of 2 or more. However, at least a part of n A ^{1 s} , n A ² s and n A ³ s represent an acyl group. The n A ¹ s in a molecule may all be the same, some may be the same or different from each other. Similarly, the n A ² s and n A ³ s in a molecule may all be the same, some may be the same or different from each other.

The acyl group represented by A ¹ , A ² and A ³ may have a hydrocarbon group that is linear, branched or cyclic, but is preferably linear or branched, and more preferably linear.

The hydrocarbon group in the acyl group represented by A ¹ , A ² and A ³ may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but is more preferably a saturated hydrocarbon group.

The acyl group represented by A ¹ , A ² and A ³ is preferably an acyl group having from 1 to 6 carbon atoms. That is, the cellulose acylate is preferably an acyl group having from 1 to 6 carbon atoms.

The acyl group represented by A ¹ , A ² and A ³ may be a group in which a hydrogen atom in the acyl group is substituted with a halogen atom (e.g., a fluorine atom, a bromine atom, an iodine atom), an oxygen atom, a nitrogen atom or the like, but is preferably unsubstituted.

Examples of the acyl group represented by A ¹ , A ² and A ³ include a formyl group, an acetyl group, a propionyl group, a butyryl group (butanoyl group), a propenoyl group, a hexanoyl group, etc. Among these, from the viewpoint of improving the biodegradation rate of the resin particles, the acyl group is preferably an acyl group having 2 to 4 carbon atoms, and more preferably an acyl group having 2 or 3 carbon atoms.

Examples of cellulose acylates include cellulose acetate (cellulose monoacetate, cellulose diacetate (DAC), cellulose triacetate), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB).

From the viewpoint of improving the biodegradation rate of the resin particles, the cellulose acylate is preferably a cellulose acylate having two or more types of acyl groups. Specifically, from the viewpoint of improving the biodegradation rate of the resin particles, the cellulose acylate is preferably cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB), and more preferably cellulose acetate propionate (CAP).

Cellulose acylate may be used alone or in combination of two or more types.

The weight average degree of polymerization of cellulose acylate is preferably 200 to 1000, more preferably 500 to 1000, and even more preferably 600 to 1000.

The weight-average degree of polymerization of cellulose acylate is determined from the weight-average molecular weight (Mw) by the following procedure.
First, the weight average molecular weight (Mw) of the cellulose acylate is measured in terms of polystyrene using tetrahydrofuran with a gel permeation chromatography apparatus (GPC apparatus: Tosoh Corporation, HLC-8320GPC, column: TSKgel α-M).
Then, the degree of polymerization of the cellulose acylate is calculated by dividing the molecular weight of the constituent unit of the cellulose acylate. For example, when the substituent of the cellulose acylate is an acetyl group, the molecular weight of the constituent unit is 263 when the degree of substitution is 2.4, and 284 when the degree of substitution is 2.9.

From the viewpoint of improving the biodegradation rate of the resin particles, the substitution degree of the cellulose acylate is preferably 2.1 or more and 2.9 or less, more preferably 2.2 or more and 2.9 or less, even more preferably 2.3 or more and 2.9 or less, and particularly preferably 2.6 or more and 2.9 or less.

In cellulose acetate propionate (CAP), the ratio of the substitution degree of acetyl groups to propionyl groups (acetyl groups/propionyl groups) is preferably 0.01 or more and 1 or less, more preferably 0.05 or more and 0.1 or less, from the viewpoint of improving the biodegradation rate of the resin particles.

In cellulose acetate butyrate (CAB), the ratio of the degree of substitution of acetyl groups to butyryl groups (acetyl groups/butyryl groups) is preferably 0.05 or more and 3.5 or less, more preferably 0.5 or more and 3.0 or less, from the viewpoint of improving the biodegradation rate of the resin particles.

The degree of substitution of cellulose acylate is an index showing the degree to which hydroxyl groups of cellulose are substituted with acyl groups. In other words, the degree of substitution is an index showing the degree of acylation of cellulose acylate. Specifically, the degree of substitution means the intramolecular average number of substitutions in which three hydroxyl groups in a D-glucopyranose unit of cellulose acylate are substituted with acyl groups. The degree of substitution is determined from the integral ratio of the peaks of cellulose-derived hydrogen and acyl group-derived hydrogen in ^1H -NMR (JMN-ECA/manufactured by JEOL RESONANCE).

These biodegradable resins may be used alone or in combination.

-Other ingredients-
The base particles may contain other components.
Examples of other components include plasticizers, flame retardants, compatibilizers, release agents, light resistance agents, weather resistance agents, colorants, pigments, modifiers, anti-drip agents, antistatic agents, hydrolysis inhibitors, fillers, reinforcing agents (glass fibers, carbon fibers, talc, clay, mica, glass flakes, milled glass, glass beads, crystalline silica, alumina, silicon nitride, aluminum nitride, boron nitride, etc.), acid acceptors for preventing release of acetic acid (oxides such as magnesium oxide and aluminum oxide; metal hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide, and hydrotalcite; calcium carbonate; talc; etc.), and reactive trapping agents (for example, epoxy compounds, acid anhydride compounds, carbodiimides, etc.).
The content of each of the other components is preferably 0% by mass or more and 5% by mass or less based on the total amount of the base particles, where "0% by mass" means that no other components are included.

Examples of plasticizers include ester compounds, camphor, metal soaps, polyols, polyalkylene oxides, etc. As plasticizers, ester compounds are preferred from the viewpoint of improving the mechanical properties of the resin particles. One type of plasticizer may be used alone, or two or more types may be used in combination.

Examples of ester compounds include fatty acid esters (adipic acid esters, citrate esters, sebacic acid esters, azelaic acid esters, phthalic acid esters, and acetate esters), phosphate esters, condensed phosphate esters, glycol esters (e.g., benzoic acid glycol esters), and modified fatty acid esters (e.g., epoxidized fatty acid esters). Examples of the esters include monoesters, diesters, triesters, and polyesters. Among these, dicarboxylate diesters (adipic acid diesters, sebacic acid diesters, azelaic acid diesters, phthalic acid diesters, etc.) are preferred.

As a plasticizer, adipic acid ester is preferred. Adipic acid ester has high affinity with cellulose acylate and disperses almost uniformly in cellulose acylate, improving thermal fluidity more than other plasticizers.

As the adipic acid ester, a mixture of an adipic acid ester and other components may be used. Commercially available products of such mixtures include Daifatty 101 manufactured by Daihachi Chemical Industry Co., Ltd.

Fatty acid esters such as citrate esters, sebacic acid esters, azelaic acid esters, phthalic acid esters, and acetate esters include esters of fatty acids and alcohols. Examples of the alcohols include monohydric alcohols such as methanol, ethanol, propanol, butanol, and 2-ethylhexanol; and polyhydric alcohols such as glycerin, polyglycerin (diglycerin, etc.), pentaerythritol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, trimethylolpropane, trimethylolethane, and sugar alcohols.

Examples of glycols in benzoic acid glycol esters include ethylene glycol, diethylene glycol, and propylene glycol.

Epoxidized fatty acid esters are ester compounds having a structure in which the carbon-carbon unsaturated bonds of unsaturated fatty acid esters have been epoxidized (i.e., oxacyclopropane). Examples of epoxidized fatty acid esters include esters of alcohols and fatty acids in which some or all of the carbon-carbon unsaturated bonds in unsaturated fatty acids (e.g., oleic acid, palmitoleic acid, vaccenic acid, linoleic acid, linolenic acid, nervonic acid, etc.) have been epoxidized. Examples of the alcohols include monohydric alcohols such as methanol, ethanol, propanol, butanol, and 2-ethylhexanol; polyhydric alcohols such as glycerin, polyglycerin (diglycerin, etc.), pentaerythritol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, trimethylolpropane, trimethylolethane, and sugar alcohols; and the like.

The molecular weight (or weight average molecular weight) of the ester compound as a plasticizer is preferably 200 to 2000, more preferably 250 to 1500, and even more preferably 280 to 1000. Unless otherwise specified, the weight average molecular weight of the ester compound is a value measured in accordance with the method for measuring the weight average molecular weight of cellulose acylate.

Here, when a cellulose resin is used as the biodegradable resin, it is particularly preferable that the base particles contain, together with the cellulose resin, as a plasticizer, at least one of an aromatic compound (hereinafter also referred to as "aromatic compound (B1)") that does not have a functional group that reacts with the cellulose resin and has, together with a long-chain aliphatic group, at least one of a phenolic hydroxyl group and a monoglycidyl ether group directly bonded to the aromatic group, and a fatty acid ester (hereinafter also referred to as "fatty acid ester (B2)").
Although cellulose resin is not easily hydrolyzed by itself, it is difficult to mold it due to its poor flexibility, so it is preferable to add a plasticizer to the cellulose resin to impart flexibility. However, cellulose resin to which a plasticizer has been added is easily hydrolyzed. Therefore, coating the base particles containing cellulose resin and a plasticizer with a second layer containing a hydrophobic compound is effective in terms of imparting hydrolysis resistance while ensuring biodegradability.
On the other hand, in order to slow down the initial biodegradation rate, it is preferable that the second layer containing a hydrophobic compound is tightly coated with the base particle.

In this regard, when at least one of aromatic compounds (B1) and fatty acid esters (B2) is used as the plasticizer to be contained in the base particles, the first layer containing a cationic resin, which functions as an adhesive layer between the base particle surface and the second layer containing a hydrophobic compound, is more firmly coated on the base particle surface. As a result, the second layer containing a hydrophobic compound is more firmly coated on the base particle, and high hydrolysis resistance can be imparted to the biodegradable resin particles while ensuring biodegradability. The reason for this is presumed to be as follows.

The aromatic compound (B1) has a benzene ring, and the benzene ring attracts electrons, making the OH group more acidic. Therefore, it has high reactivity with cationic compounds. In addition, the fatty acid ester (B2) is a compound more acidic, and therefore has high reactivity with cationic compounds. As a result, the first layer containing the cationic resin is more firmly coated on the surface of the base particle.
Therefore, it is presumed that the second layer containing the hydrophobic compound coats the base particles more firmly, and the biodegradable resin particles can be provided with high hydrolysis resistance while maintaining biodegradability, resulting in biodegradable resin particles with excellent hydrolysis resistance while maintaining biodegradability.

In particular, from the viewpoint of improving hydrolysis resistance while ensuring biodegradability, when cellulose acetate propionate is used as the cellulose resin, it is preferable to use a cardanol compound as the aromatic compound for the plasticizer.
From the same viewpoint, when cellulose acetate propionate is used as the cellulose resin, it is preferable to use an aliphatic ester as the plasticizer.

The aromatic compound (B1) will be described below.
The aromatic compound (B1) is an aromatic compound which does not have a functional group reactive with a cellulose resin and has, in addition to a long-chain aliphatic group, at least one of a phenolic hydroxyl group and a monoglycidyl ether group directly bonded to an aromatic group.
That is, the aromatic compound (B1) is a compound which does not have a functional group reactive with the cellulose acylate (A), has a long-chain aliphatic group, and has at least one of a phenolic hydroxyl group and a monoglycidyl ether group.
Here, examples of the long-chain aliphatic group include saturated aliphatic groups (alkyl groups) and unsaturated aliphatic groups (alkenyl groups, alkynyl groups) having carbon atoms of 6 to 30 (preferably 10 to 20). The aliphatic group may be linear, branched, or cyclic, with linear or branched groups being preferred, and linear groups being more preferred.

Examples of aromatic compounds (B1) include compounds in which a phenolic hydroxyl group is substituted on a monocyclic ring, a condensed ring (a polycyclic ring having two or more aromatic rings), a polynuclear ring (a polycyclic ring in which aromatic rings are bonded to each other by carbon-carbon bonds), or a heterocyclic ring (a monocyclic heterocyclic ring, a condensed ring containing a heterocyclic ring, a polynuclear ring containing a heterocyclic ring, etc.) together with a long-chain aliphatic group.

Specific examples of the aromatic compound (B1) include cardanol compounds, phenalkamine compounds, phenol resins, phenol novolac type epoxy resins, phenol resol type epoxy resins, phenol modified palm oil, phenol modified soybean oil, and phenol modified linseed oil.
Among these, from the viewpoint of improving biodegradability, cardanol compounds are preferred as the aromatic compound (B1).

Cardanol compounds refer to components contained in naturally derived compounds made from cashews (e.g., compounds represented by the following structural formulas (b-1) to (b-4)) or derivatives of the above components.

The cardanol compound may be a mixture of naturally occurring compounds derived from cashews (hereinafter also referred to as a "cashew-derived mixture").

The cardanol compound may be a derivative from a cashew-derived mixture. Examples of derivatives from cashew-derived mixtures include the following mixtures and simple substances:

- A mixture in which the composition ratio of each component in the cashew-derived mixture has been adjusted - A single entity in which only a specific component is isolated from the cashew-derived mixture - A mixture containing a modified product obtained by modifying a component in the cashew-derived mixture - A mixture containing a polymer obtained by polymerizing a component in the cashew-derived mixture - A mixture containing a modified polymer obtained by modifying and polymerizing a component in the cashew-derived mixture - A mixture containing a modified product obtained by further modifying a component in the mixture in which the composition ratio has been adjusted - A mixture containing a polymer obtained by further polymerizing a component in the mixture in which the composition ratio has been adjusted - A mixture containing a modified polymer obtained by further modifying and polymerizing a component in the mixture in which the composition ratio has been adjusted - A modified product obtained by further modifying the isolated single entity - A polymer obtained by further polymerizing the isolated single entity - A modified polymer obtained by further modifying and polymerizing the isolated single entity Here, the single entity also includes polymers such as dimers and trimers.

From the viewpoint of improving the biodegradation rate of the resin particles, the cardanol compound is preferably at least one compound selected from the group consisting of compounds represented by general formula (CDN1) and polymers obtained by polymerizing compounds represented by general formula (CDN1).

In the general formula (CDN1), R ¹ represents an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. R ² represents a hydroxyl group, a carboxyl group, an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. P2 represents an integer of 0 to 4. When P2 is 2 or more, the multiple R ^2s may be the same group or different groups.

In general formula (CDN1), the alkyl group which may have a substituent represented by R ¹ is preferably an alkyl group having 3 to 30 carbon atoms, more preferably an alkyl group having 5 to 25 carbon atoms, and further preferably an alkyl group having 8 to 20 carbon atoms.
Examples of the substituent include a hydroxy group; a substituent containing an ether bond, such as an epoxy group or a methoxy group; and a substituent containing an ester bond, such as an acetyl group or a propionyl group.
Examples of the alkyl group which may have a substituent include a pentadecane-1-yl group, a heptan-1-yl group, an octan-1-yl group, a nonan-1-yl group, a decan-1-yl group, an undecane-1-yl group, a dodecane-1-yl group, and a tetradecane-1-yl group.

In general formula (CDN1), the unsaturated aliphatic group represented by R ¹ which has a double bond and which may have a substituent is preferably an unsaturated aliphatic group having 3 to 30 carbon atoms, more preferably an unsaturated aliphatic group having 5 to 25 carbon atoms, and even more preferably an unsaturated aliphatic group having 8 to 20 carbon atoms.
The unsaturated aliphatic group preferably has 1 or more and 3 or less double bonds.
Examples of the substituent include those exemplified as the substituent for the alkyl group.
Examples of the unsaturated aliphatic group having a double bond and optionally having a substituent include a pentadec-8-en-1-yl group, a pentadeca-8,11-dien-1-yl group, a pentadeca-8,11,14-trien-1-yl group, a pentadec-7-en-1-yl group, a pentadeca-7,10-dien-1-yl group, and a pentadeca-7,10,14-trien-1-yl group.

In the general formula (CDN1), R ¹ is preferably a pentadec-8-en-1-yl group, a pentadeca-8,11-dien-1-yl group, a pentadeca-8,11,14-trien-1-yl group, a pentadec-7-en-1-yl group, a pentadeca-7,10-dien-1-yl group, or a pentadeca-7,10,14-trien-1-yl group.

In general formula (CDN1), preferred examples of the alkyl group which may have a substituent and the unsaturated aliphatic group which has a double bond and may have a substituent, represented by ^R2 , include the same as those exemplified above as the alkyl group ^which may have a substituent and the unsaturated aliphatic group which has a double bond and may have a substituent, represented by R1.

The compound represented by the general formula (CDN1) may be further modified. For example, it may be epoxidized. From the viewpoint of improving the biodegradation rate of the resin particles, it is preferable that the compound represented by the general formula (CDN1) has a structure in which the hydroxy group is replaced with the following group (EP), that is, the compound represented by the general formula (CDN1-e) below.

In the group (EP) and general formula (CDN1-e), L _EP represents a single bond or a divalent linking group. In general formula (CDN1-e), R ¹ , R ² and P2 have the same meanings as R ¹ , R ² and P2 in general formula (CDN1), respectively.

In the group (EP) and the general formula (CDN1-e), examples of the divalent linking group represented by L _EP include an alkylene group which may have a substituent (preferably an alkylene group having 1 to 4 carbon atoms, more preferably an alkylene group having 1 carbon atom), a -CH ₂ CH ₂ OCH ₂ CH ₂ - group, and the like.
Examples of the substituent include the same as those exemplified as the substituent for R ¹ in formula (CDN1).

_LEP is preferably a methylene group.

A polymer formed by polymerizing a compound represented by general formula (CDN1) refers to a polymer formed by polymerizing at least two or more compounds represented by general formula (CDN1) with or without a linking group.

An example of a polymer formed by polymerizing a compound represented by general formula (CDN1) is a compound represented by the following general formula (CDN2).

In the general formula (CDN2), R ¹¹ , R ¹² and R ¹³ each independently represent an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. R ²¹ , R ²² and R ²³ each independently represent a hydroxyl group, a carboxyl group, an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. P21 and P23 each independently represent an integer of 0 to 3, and P22 represents an integer of 0 to 2. ^{L 1} and L ² each independently represent a divalent linking group. n represents an integer of 0 to 10. When P21 is 2 or more, a plurality of R ²¹ , when P22 is 2 or more, a plurality of R ²² , and when P23 is 2 or more, a plurality of R ²³ may each be the same group or different groups. When n is 2 or more, the multiple R ¹² , R ²² and L ¹ may be the same or different groups, and when n is 2 or more, the multiple P22 may be the same or different numbers.

In general formula (CDN2), preferred examples of the alkyl group which may have a substituent and the unsaturated aliphatic group which has a double bond and may have a substituent represented by R ¹¹ , R ¹² , R ¹³ , R ^{21 ,} R ²² and R 23 include those listed as R ¹ in general formula (CDN1).

In general formula (CDN2), examples of the divalent linking group represented by ^L1 and ^L2 include an alkylene group which may have a substituent (preferably an alkylene group having 2 to 30 carbon atoms, more preferably an alkylene group having 5 to 20 carbon atoms).
Examples of the substituent include the same as those exemplified as the substituent for R ¹ in formula (CDN1).

In general formula (CDN2), n is preferably 1 or more and 10 or less, and more preferably 1 or more and 5 or less.

The compound represented by the general formula (CDN2) may be further modified. For example, it may be epoxidized, specifically, a compound in which the hydroxy group of the compound represented by the general formula (CDN2) is replaced with a group (EP), that is, a compound represented by the following general formula (CDN2-e).

In general formula (CDN2-e), R ¹¹ , R ¹² , R ¹³ , R ²¹ , R ²² , R ²³ , P21, P22, P23, L ¹ , L ² and n are each synonymous with R ¹¹ , R 12, R ¹³ , R ²¹ , R ²² , R ²³ , ^P21 , P22, P23, L ¹ , L ² and n in general formula (CDN2), respectively.
In formula (CDN2-e), L _EP1 , L _EP2 and L _EP3 each independently represent a single bond or a divalent linking group. When n is 2 or more, a plurality of L _EP2 's may be the same or different groups.

In general formula (CDN2-e), preferred examples of the divalent linking group represented by L _EP1 , L _EP2 and L _EP3 include those recited as the divalent linking group represented by L _EP in general formula (CDN1-e).

The polymer formed by polymerization of the compound represented by the general formula (CDN1) may be, for example, a polymer formed by three-dimensional cross-linking polymerization of at least three or more compounds represented by the general formula (CDN1) with or without a linking group. The polymer formed by three-dimensional cross-linking polymerization of the compound represented by the general formula (CDN1) may be, for example, a compound represented by the following structural formula.

In the above structural formula, R ¹⁰ , R ²⁰ and P20 are the same as R ¹ , R ² and P2 in general formula (CDN1). ^{L 10} represents a single bond or a divalent linking group. A plurality of R ¹⁰ , R ²⁰ and L ¹⁰ may be the same group or different groups. A plurality of P ²⁰ may be the same number or different numbers.

In the above structural formula, examples of the divalent linking group represented by ^L10 include an alkylene group which may have a substituent (preferably an alkylene group having 2 to 30 carbon atoms, more preferably an alkylene group having 5 to 20 carbon atoms).
Examples of the substituent include the same as those exemplified as the substituent for R ¹ in formula (CDN1).

The compound represented by the above structural formula may be further modified, for example, epoxidized. Specifically, the compound may have a structure in which the hydroxyl group of the compound represented by the above structural formula is replaced with a group (EP), and examples thereof include the compound represented by the following structural formula, that is, a polymer in which the compound represented by the general formula (CDN1-e) is three-dimensionally cross-linked and polymerized.

In the above structural formula, R ¹⁰ , R ²⁰ and P20 are respectively defined as R ¹ , R ² and P2 in general formula (CDN1-e). L ¹⁰ represents a single bond or a divalent linking group. A plurality of R ¹⁰ , R ²⁰ and L ¹⁰ may be the same group or different groups. A plurality of P ²⁰ may be the same number or different numbers.

In the above structural formula, examples of the divalent linking group represented by ^L10 include an alkylene group which may have a substituent (preferably an alkylene group having 2 to 30 carbon atoms, more preferably an alkylene group having 5 to 20 carbon atoms).
Examples of the substituent include the same as those exemplified as the substituent for R ¹ in formula (CDN1).

From the viewpoint of improving the transparency of the resin molded body, the cardanol compound preferably contains a cardanol compound having an epoxy group, and is more preferably a cardanol compound having an epoxy group.

Commercially available cardanol compounds may be used. Examples of commercially available products include NX-2024, Ultra LITE 2023, NX-2026, GX-2503, NC-510, LITE 2020, NX-9001, NX-9004, NX-9007, NX-9008, NX-9201, and NX-9203 manufactured by Cardolite Corporation, and LB-7000, LB-7250, and CD-5L manufactured by Tohoku Kako Co., Ltd. Commercially available cardanol compounds having an epoxy group include NC-513, NC-514S, NC-547, LITE513E, and Ultra LTE 513 manufactured by Cardolite Corporation.

From the viewpoint of improving the biodegradation rate of the resin molded body, the hydroxyl value of the cardanol compound is preferably 100 mgKOH/g or more, more preferably 120 mgKOH/g or more, and even more preferably 150 mgKOH/g or more. The hydroxyl value of the cardanol compound is measured according to ISO 14900 Method A.

When a cardanol compound having an epoxy group is used as the cardanol compound, the epoxy equivalent is preferably from 300 to 500, more preferably from 350 to 480, and even more preferably from 400 to 470, from the viewpoint of improving the transparency of the resin molded product. The epoxy equivalent of the cardanol compound having an epoxy group is measured in accordance with ISO 3001.

From the viewpoint of improving the biodegradation rate of the resin molded body, the molecular weight of the cardanol compound is preferably 250 or more and 1,000 or less, more preferably 280 or more and 800 or less, and even more preferably 300 or more and 500 or less.

The cardanol compounds may be used alone or in combination of two or more.

The fatty acid ester (B2) will be described below.
The fatty acid ester (B2) may be any one of a monoester, a diester, a triester, and a polyester.

Examples of the fatty acid ester (B2) include aliphatic monocarboxylates (acetate esters, etc.), aliphatic dicarboxylates (succinate esters, adipic acid esters, azelaic acid esters, sebacic acid esters, stearic acid esters, etc.), aliphatic tricarboxylates (citric acid esters, isocitrate esters, etc.), epoxidized fatty acid esters (epoxidized soybean oil, epoxidized linseed oil, epoxidized rapeseed fatty acid isobutyl, epoxidized fatty acid 2-ethylhexyl), fatty acid methyl esters, and sucrose esters.
The fatty acid ester may be acylated with an alkyl carboxylic acid anhydride (e.g., a linear or branched alkyl carboxylic acid anhydride having 2 to 6 (preferably 2 to 3) carbon atoms, such as acetic anhydride, propionic anhydride, butyric anhydride, or valeric anhydride).

Fatty acid esters (B2) include aliphatic dicarboxylic acid esters (particularly adipic acid esters and sebacic acid) and aliphatic tricarboxylic acid esters (particularly citrate esters).

Specific examples of adipic acid esters include adipic acid diesters represented by the following general formula (AE) and adipic acid polyesters represented by the following general formula (APE).

In general formula (AE), R ^AE1 and R ^AE2 each independently represent an alkyl group or a polyoxyalkyl group [—(C _x H _2x —O) _y —R ^A1 ] (wherein R ^A1 represents an alkyl group, x represents an integer of 1 or more and 10 or less, and y represents an integer of 1 or more and 10 or less).

In general formula (APE), R ^AE1 and R ^AE2 each independently represent an alkyl group or a polyoxyalkyl group [-(C _x H _2x -O) _y -R ^A1 ] (wherein R ^A1 represents an alkyl group, x represents an integer of 1 or more and 10 or less, and y represents an integer of 1 or more and 10 or less), R ^AE3 represents an alkylene group, m1 represents an integer of 1 or more and 10 or less, and m2 represents an integer of 1 or more and 20 or less.

In general formulae (AE) and (APE), the alkyl group represented by R ^AE1 and R ^AE2 is preferably an alkyl group having from 1 to 12 carbon atoms, more preferably an alkyl group having from 4 to 10 carbon atoms, and still more preferably an alkyl group having 8 carbon atoms. The alkyl group represented by R ^AE1 and R ^AE2 may be linear, branched, or cyclic, and is preferably linear or branched.

In general formulas (AE) and (APE), in the polyoxyalkyl group [-( _CxH2x -O) _y - ^R ] represented by ^RAE1 _and ^RAE2 , the alkyl group represented by ^R is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. The alkyl group represented by ^R may be linear, branched, or cyclic, and is preferably linear or branched.

In general formula (APE), the alkylene group represented by R ^AE3 is preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 4 carbon atoms. The alkylene group may be linear, branched, or cyclic, and is preferably linear or branched.

In general formula (APE), m1 is preferably an integer of 1 or more and 5 or less, and m2 is preferably an integer of 1 or more and 10 or less.

In general formulas (AE) and (APE), the groups represented by the symbols may be substituted with a substituent. Examples of the substituent include an alkyl group, an aryl group, and a hydroxyl group.

As the adipic acid ester, a mixture of an adipic acid ester and other components may be used. Commercially available products of such mixtures include Daifatty 101 manufactured by Daihachi Chemical Industry Co., Ltd.

Sebacic acid esters and citrate esters include alkyl esters of citric acid having 1 to 12 carbon atoms (preferably 1 to 8 carbon atoms).

Examples of the citrate ester include alkyl esters of citric acid having 1 to 12 carbon atoms (preferably 1 to 8). The citrate ester may be a citrate ester acylated with an alkyl carboxylic acid anhydride (e.g., a linear or branched alkyl carboxylic acid anhydride having 2 to 6 carbon atoms (preferably 2 to 3 carbon atoms), such as acetic anhydride, propionic anhydride, butyric anhydride, or valeric anhydride).

The molecular weight (or weight average molecular weight) of the fatty acid ester (B2) is preferably 200 to 2000, more preferably 250 to 1500, and even more preferably 280 to 1000. Unless otherwise specified, the weight average molecular weight of the ester compound is a value measured in accordance with the method for measuring the weight average molecular weight of cellulose acylate.

The content of aromatic compounds, fatty acid esters, or the total content of aromatic compounds and fatty acid esters is preferably 1% by mass or more and 50% by mass or less, and more preferably 1% by mass or more and 30% by mass or less, based on the cellulose resin.

The base particles may contain other resins other than the biodegradable resin. However, when other resins are contained, the content of the other resins relative to the total amount of the resin composition is preferably 5% by mass or less, and preferably less than 1% by mass. It is more preferable that the other resins are not contained (i.e., 0% by mass).
Examples of other resins include conventionally known thermoplastic resins, specifically, polycarbonate resins; polypropylene resins; polyester resins; polyolefin resins; polyester carbonate resins; polyphenylene ether resins; polyphenylene sulfide resins; polysulfone resins; polyethersulfone resins; polyarylene resins; polyetherimide resins; polyacetal resins; polyvinyl acetal resins; polyketone resins; polyether ketone resins; polyether ether ketone resins; polyaryl ketone resins; polyether nitrile resins; liquid crystal resins; polybenzimidazole resins; polypa Examples of the resin include lavane acid resins, vinyl polymers or copolymers obtained by polymerizing or copolymerizing one or more vinyl monomers selected from the group consisting of aromatic alkenyl compounds, methacrylic acid esters, acrylic acid esters, and vinyl cyanide compounds, diene-aromatic alkenyl compound copolymers, vinyl cyanide-diene-aromatic alkenyl compound copolymers, aromatic alkenyl compound-diene-vinyl cyanide-N-phenylmaleimide copolymers, vinyl cyanide-(ethylene-diene-propylene (EPDM))-aromatic alkenyl compound copolymers, vinyl chloride resins, and chlorinated vinyl chloride resins. These resins may be used alone or in combination of two or more.

[First layer]
The first layer is a resin layer present on the surface of the base particle, and contains at least one cationic resin selected from the group consisting of polyalkyleneimine, polyallylamine, and polyvinylamine.

The cationic resin may be any of polyalkyleneimine, polyallylamine, and polyvinylamine, but polyalkyleneimine is preferred from the viewpoints of increasing the rate of biodegradation over time and decreasing the initial rate of biodegradation.

From the viewpoint of increasing the biodegradation rate over time and decreasing the initial biodegradation rate, the polyalkyleneimine is preferably a polyalkyleneimine having a structural unit with an alkylene group having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms), and more preferably polyethyleneimine.

In particular, polyethyleneimine is a compound with high adhesion and high water absorption. This is because the amino group of polyethyleneimine forms a hydrogen bond with a hydroxyl group, an ionic bond with a carboxyl group, and a covalent bond with a carbonyl group. Since polyethyleneimine has a polar group (amino group) and a hydrophobic group (ethylene group) in its structure, it has the property of easily bonding different substances.
Moreover, polyethyleneimine is a compound having high cationicity, and therefore, polyethyleneimine exists as a polycation in water and neutralizes and adsorbs anionic substances.
In addition, polyethyleneimine is a highly reactive compound because it has a highly reactive primary amino group or secondary amino group, and therefore it reacts easily with various compounds.
Therefore, when polyethyleneimine is used as the polyalkyleneimine, the base particles are more firmly coated with the second layer containing the hydrophobic compound, and while the base particles have a biodegradation rate over time, the initial biodegradation rate tends to be slower.

The number average molecular weight of the cationic resin is preferably 300 to 100,000, more preferably 10,000 to 85,000, and even more preferably 50,000 to 80,000, from the viewpoints of improving the biodegradation rate over time and preventing a decrease in the initial biodegradation rate.
The number average molecular weight of the cationic resin is measured in polystyrene equivalent terms using tetrahydrofuran with a gel permeation chromatography apparatus (GPC apparatus: Tosoh Corporation, HLC-8320GPC, column: TSKgel α-M).

[Second layer]
The second layer is a compound layer disposed on the first layer, and includes an anionic or nonionic compound or a hydrophobic compound.

Examples of anionic or nonionic compounds or hydrophobic compounds include hydrophobic compounds having an anionic group (such as --COOH (carboxyl group), --SO ₃ H (sulfonic group)) and hydrophobic compounds having no cationic or anionic groups.
The hydrophobic compound refers to a compound that imparts hydrophobicity (specifically, water contact angle) to the biodegradable resin particles described below.

Examples of the hydrophobic compound include a silicone compound, a hydrocarbon compound, a fatty acid compound, an acrylic resin, a polyester resin, and a urethane resin.
Among these, from the viewpoints of improving the biodegradation rate over time and decreasing the initial biodegradation rate, at least one selected from the group consisting of at least one selected from the group consisting of silicone compounds, hydrocarbon compounds, fatty acid compounds, acrylic resins, polyester resins, and urethane resins is preferred.

Examples of silicone compounds include dimethylpolysiloxane, methylpolysiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentanesiloxane, methylcyclopolysiloxane, various modified silicone oils (alkyl-modified silicone oil, polyether-modified silicone oil, alcohol-modified silicone oil, fluorine-modified silicone oil, amino-modified silicone oil, etc.), MQ resin, silicone rubber, etc.
Among these, from the viewpoints of improving the biodegradation rate over time and decreasing the initial biodegradation rate, the silicone compound is preferably at least one selected from the group consisting of dimethylpolysiloxane, methylpolysiloxane, MQ resin, and silicone rubber.
Here, MQ resin refers to a silicone resin having M units which are monofunctional siloxane units [(CH ₃ ) ₃ SiO _1/2 ] and Q units which are tetrafunctional siloxane units [SiO _4/2 ].

Commercially available silicone compounds include silicone compounds manufactured by Shin-Etsu Chemical Co., Ltd. (KM-902, KM-903, KM-910, KM-9729, POLON-MN-ST, KM-9737A, KM-9782, KM-9738A, KM-752T, POLON-MF-33, KM-9717, X-51-1302M (MQ resin), POLON-MF-56, KM-2002-L-1, KM-2002-T, KM-9772, KM-9749, POLON-MF-40, KM-9729, X-52-1133, etc.), and silicone compounds manufactured by Wacker Asahi Kasei Silicone Co., Ltd. (BELSIL DM3112VP).

Examples of the hydrocarbon compounds include petroleum waxes (paraffin wax, microcrystalline wax, petrolatum wax, etc.) and synthetic hydrocarbon waxes (polyethylene wax, polypropylene wax, polybutene wax, Fischer-Tropsch wax, etc.).
Among these, from the viewpoint of improving the biodegradation rate over time and decreasing the initial biodegradation rate, the hydrocarbon compound is preferably at least one selected from the group consisting of paraffin wax, microcrystalline wax, polyethylene wax, and polypropylene wax.

Commercially available hydrocarbon compounds include microcrystalline wax (EMUSTAR-0001, etc.) manufactured by Nippon Seiro Co., Ltd., paraffin wax (EMUSTAR-0135, etc.) manufactured by Nippon Seiro Co., Ltd., paraffin wax (AQUACER 497, etc.) manufactured by BYK Corp., polyethylene wax (AQUACER 507, AQUACER 840, AQUACER 1547, AQUACER 272, etc.) manufactured by BYK Corp., polyethylene wax (Hitec E-2213, Hitec E-6324, etc.) manufactured by Toho Chemical Co., Ltd., polypropylene wax (AQUACER 593, etc.) manufactured by BYK Corp., and polypropylene (Hitec P-9018, Hitec P-5060P, etc.) manufactured by Toho Chemical Co., Ltd., etc.

Examples of fatty acid compounds include vegetable oils containing fatty acids (castor oil, tung oil, linseed oil, shortening, corn oil, soybean oil, sesame oil, rapeseed oil, sunflower oil, rice oil, camellia oil, coconut oil, palm oil, walnut oil, olive oil, peanut oil, almond oil, jojoba oil, cacao butter, shea butter, neem oil, safflower oil, Japan wax, candelilla wax, rice wax, carnauba wax, etc.).
Among these, from the viewpoints of improving the biodegradation rate over time and decreasing the initial biodegradation rate, at least one wax selected from the group consisting of carnauba wax, rice wax, candelilla wax, palm wax, castor oil wax, soybean oil wax, and sunflower oil wax is preferred.

Commercially available fatty acid compounds include carnauba wax (EMUSTAR-0413 (carnauba wax)) manufactured by Nippon Seiro Co., Ltd., rice wax (AQUASPROUT-7300, etc.) manufactured by Nippon Seiro Co., Ltd., palm wax (AQUASPROUT-7100, etc.) manufactured by Nippon Seiro Co., Ltd., castor oil wax (AQUASPROUT-7500, etc.) manufactured by Nippon Seiro Co., Ltd., soybean oil wax (AQUASPROUT-7200, etc.) manufactured by Nippon Seiro Co., Ltd., sunflower oil wax (AQUASPROUT-7400, etc.) manufactured by Nippon Seiro Co., Ltd., palm oil wax (Cuckoo Ace TKE, etc.) manufactured by Nippon Seiro Co., Ltd., etc.

Examples of the acrylic resin include well-known acrylic resins such as polymers of acrylic acid and polymers of alkyl acrylates.
Commercially available acrylic resins include, for example, acrylic resins manufactured by Taisei Fine Co., Ltd. (3WX-2015, 3MF-320, 3MF-333, 3MF-407, etc.), and acrylic resins manufactured by DIC Corporation (COAT SFC-6440, BONCOAT CE-6270, BONCOAT CE-6400, BONCOAT CF-2800, etc.).

Examples of the polyester resin include well-known polyester resins such as polycondensates of polyhydric alcohols and ring-opening polycondensates of cyclic lactams.
Commercially available polyester resins include, for example, polyester resins manufactured by Takamatsu Oil Co., Ltd. (A-110F, A-160P, A-520, A-613D, A-615GE, A-640, A-645GH, A-647GEX, etc.).

Examples of the urethane resin include well-known urethane resins such as polyester-based polyurethane, polyether-based polyurethane, polycarbonate-based polyurethane, etc. Furthermore, as the urethane resin, a material having a urethane polymer shell layer around an acrylic polymer core may be used.
Commercially available urethane resins include, for example, urethane resins manufactured by Taisei Fine Co., Ltd. (WEM-031U, WEM-200U, WEM-321U, WEM-3000, WBR-016U, WBR-2101, etc.).

[Content of each layer]
In the biodegradable resin particles according to this embodiment, from the viewpoint of improving the biodegradation rate over time and decreasing the initial biodegradation rate, the mass ratio of the coating amount of the cationic resin in the first layer to the coating amount of the hydrophobic compound in the second layer (coating amount of cationic resin/coating amount of hydrophobic compound) is preferably 0.05 or more and 20 or less, more preferably 0.1 or more and 10 or less, and even more preferably 0.1 or more and 3 or less.

In addition, from the viewpoint of improving the biodegradation rate over time and decreasing the initial biodegradation rate, the content of the cationic resin relative to the base particles is preferably 0.05% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less.
In addition, from the viewpoint of improving the biodegradation rate over time and decreasing the initial biodegradation rate, the content of the hydrophobic compound relative to the base particles is preferably 0.05% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less.

Here, the coating amounts of the cationic resin and the hydrophobic compound (i.e., the coating amounts of the first layer and the second layer) are measured as follows. The coating amount of the cationic resin is determined by the difference between the amount of cationic resin treated and the amount of cationic resin obtained by drying the supernatant after treatment. Similarly, the coating amount of the hydrophobic compound is determined by the difference between the amount of hydrophobic compound treated and the amount of hydrophobic compound obtained by drying the supernatant after treatment.

[Characteristics of biodegradable resin particles]
In the biodegradable resin particles according to this embodiment, the water contact angle when the biodegradable resin particles are pelletized is 70° or more and 120° or less.
If the contact angle is within the above range, the initial biodegradation rate is decreased.
The water contact angle is preferably 72° or more and 110° or less, and more preferably 75° or more and 105° or less.

After pelletizing the biodegradable particles, the water contact angle is measured in an environment of 23°C using a contact angle meter (Model CA-X, manufactured by Kyowa Interface Science Co., Ltd.) by dropping a 1 μl drop of water onto the surface of the pellet with a syringe and then measuring the water contact angle after 1 minute.

The biodegradable resin particles according to this embodiment have an aerobic biodegradation rate of 20% or less after 3 months, as measured according to a method conforming to ISO-14855-2 (2018).
When the aerobic biodegradation rate after three months is within the above range, the initial biodegradation rate is low.
The aerobic biodegradability after 3 months is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less. The lower limit is ideally 0%, but may be, for example, 1% or more.

The biodegradable resin particles according to this embodiment have a ratio of the aerobic biodegradability after 6 months to the aerobic biodegradability after 3 months (aerobic biodegradability after 6 months/aerobic biodegradability after 3 months), measured according to a method conforming to ISO-14855-2 (2018), of preferably 1.20 or more, more preferably 1.50 or more, and more preferably 2.00 or more.
In addition, the ratio of the aerobic biodegradability after 12 months to the aerobic biodegradability after 3 months (aerobic biodegradability after 12 months / aerobic biodegradability after 3 months), measured according to a method conforming to ISO-14855-2 (2018), is preferably 3.50 or more, more preferably 5.00 or more, more preferably 10.00 or more, even more preferably 15.00 or more, and more preferably 20.00 or more.

In the biodegradable resin particles according to this embodiment, when the surface of the biodegradable resin particles is measured by X-ray photoelectron spectroscopy (XPS), the relationship between the carbon atom weight Cs, the silicon atom weight Sis, and the oxygen atom weight Os satisfies the formula A: (Cs+Sis)/Os≧3.
When formula A is satisfied, the initial biodegradation rate decreases, and the lipophilicity of the surface of the biodegradable resin particles increases, increasing the oil absorption rate of the resin particles.
From the viewpoint of decreasing the initial biodegradation rate and improving the oil absorption rate, the value of "Cs + Sis)/Os" is preferably 4 or more, and more preferably 7 or more. However, the upper limit of the value of "Cs + Sis)/Os" is, for example, 95 or less, from the viewpoint of the biodegradation rate over time.
In order to set the value of (Cs+Sis)/Os) within the above range, it is preferable to coat the base particles with a second layer containing a hydrophobic compound.

In the biodegradable resin particles according to this embodiment, when the surface of the biodegradable resin particles after three minutes of surface etching is measured by X-ray photoelectron spectroscopy (XPS), it is preferable that the relationship between the carbon atom amount Ce, the silicon atom amount Sie, and the oxygen atom amount Oe satisfies the formula B: (Ce+Sie)/Oe≧3.
When formula B is satisfied, the period during which the biodegradation rate decreases becomes longer. In addition, a high oil absorption rate is easily maintained. Furthermore, even if a mechanical load is applied to the biodegradable resin particles (for example, even if the biodegradable resin particles are stirred by ultrasonic homogenization, etc.), the oil absorption rate is less likely to decrease.
From the viewpoints of maintaining the initial biodegradation rate and maintaining the oil absorption rate, the value of "(Ce+Sie)/Oe" is more preferably 4 or more, and even more preferably 7 or more. However, from the viewpoint of the biodegradation rate over time, the upper limit of the value of "(Ce+Sie)/Oe" is, for example, 95 or less.
In order to set the value of "(Ce+Sie)/Oe" within the above range, it is preferable to coat the base particles successively with a first layer containing a cationic resin and a second layer containing a hydrophobic compound.

Here, the method for measuring each atomic weight (atom %) by X-ray photoelectron spectroscopy (XPS) is as follows. The measurement is performed on the produced biodegradable particles.
The measurement is performed using an "ULVAC-PHI PHI5000 Versa Probe II" as the XPS measurement device, using monochromatic AlKα rays as the X-ray source, and setting the acceleration voltage to 15 kV. Specifically, the analysis area is set to 100 μmφ, and the number of each atom (carbon atom, silicon atom, and oxygen atom) is calculated based on the spectrum of each measured atom (carbon atom, silicon atom, and oxygen atom), and the weight of each atom (carbon atom weight, silicon atom weight, and oxygen atom weight) relative to the total atomic weight in the measurement area is calculated.

The carbon atom amount, silicon atom amount and oxygen atom amount when the surface of the biodegradable resin particle before etching is measured are calculated as the carbon atom amount Cs, the silicon atom amount Sis and the oxygen atom amount Os.
In addition, the carbon atom amount, silicon atom amount and oxygen atom amount when the surface of the biodegradable resin particle is measured after three minutes of surface etching are calculated as the carbon atom amount Ce, the silicon atom amount Sie and the oxygen atom amount Oe.
However, when the compound contained in the second layer does not contain silicon atoms, the amount of silicon atoms is 0 atom %.

The surface etching of the prepared biodegradable particles is carried out as follows.
An "ULVAC-PHI PHI5000 Versa Probe II" was used as the etching device, and etching was performed for 3 minutes using an argon gas cluster etching method using argon as the etching gas under conditions of an acceleration voltage of 5 kV and a sweep area of 2 mm x 2 mm.

The volume average particle size of the biodegradable resin particles is preferably 3 μm or more and 100 μm or less, more preferably 5 μm or more and 70 μm or less, and even more preferably 8 μm or more and 60 μm or less.
When the particle size of the granules is 3 μm or more, the number of particles per unit weight is not too large, so that the decrease in the biodegradation rate is suppressed. On the other hand, when the particle size of the biodegradable resin particles is 100 μm or less, the specific surface area is increased, and the biodegradation rate is further improved.
Therefore, the volume average particle size of the granules is preferably within the above range.

The large particle size distribution index GSDv of the biodegradable resin particles is preferably 1.5 or less, more preferably 1.3 or less, and even more preferably 1.2 or less.
When the particle size distribution of the biodegradable resin particles is made closer to uniform, regular hydrolysis proceeds by providing a constant opportunity for contact with water, and the biodegradation rate is further improved.

The volume average particle size and the large particle size distribution index GSDp of the biodegradable resin particles are measured as follows.
The particle size is measured using an LS particle size distribution measuring device "Beckman Coulter LS13 320 (manufactured by Beckman Coulter)" and the cumulative particle size distribution is plotted from the smallest diameter side on a volume basis. The particle size at 50% of the cumulative distribution is determined as the volume average particle size.
On the other hand, the cumulative particle size distribution is plotted from the small diameter side on a volume basis, and the particle size at 50% of the cumulative distribution is defined as the number average particle size D50v, and the particle size at 84% of the cumulative distribution is defined as the number particle size D84v. The large diameter side number particle size distribution index GSDv is calculated by the formula GSDv = (D84v / D50v) ^1/2 .

[Method for producing biodegradable resin particles]
As a method for producing biodegradable resin particles according to the present embodiment, for example,
a first step of mixing an aqueous dispersion in which base particles are dispersed with an aqueous solution containing a cationic resin;
a second step of extracting the base particles from the mixed solution to obtain an aqueous dispersion in which the base particles are dispersed, mixing the aqueous dispersion with an emulsion solution of an anionic or nonionic hydrophobic compound, and then drying the mixture;
The method includes the following steps:

The details are explained below.

-First step-
In the first step, base particles are prepared.
The base particles can be produced, for example, by the following method.
1) A kneading and crushing method in which the components are kneaded, and the resulting kneaded product is crushed and classified to obtain granules;
2) A dry manufacturing method in which granules obtained by the kneading and grinding method are changed in shape by mechanical impact force or thermal energy to obtain granules. 3) An aggregation and coalescence method in which particle dispersions of each component are mixed, and the particles in the dispersion are aggregated and heat-fused to obtain granules. 4) A dissolution and suspension method in which an organic solvent in which each component is dissolved is suspended in an aqueous solvent to granulate granules containing each component.

Among these, wet methods such as the aggregation-coalescence method and the dissolution-suspension method are preferable from the viewpoint of obtaining biodegradable resin particles having a volume average particle size and a large particle size distribution index GSDv described below.

Next, prepare an aqueous dispersion in which the obtained base particles are dispersed. It is advisable to wash the base particles with an acid before preparing the aqueous dispersion.

Next, the aqueous dispersion, the aqueous dispersion in which the base particles are dispersed, and an aqueous solution containing a cationic resin are mixed. As a result, for example, the hydroxyl groups of the resin contained in the base particles react with the amine sites of the cationic resin to form a first layer.

-Second process-
In the second step, the base particles on which the first layer is formed are taken out from the mixed liquid. The base particles are taken out, for example, by filtering the mixed liquid. The taken out base particles are preferably washed with water. This makes it possible to remove unreacted cationic resin.

Next, after preparing an aqueous dispersion in which the base particles are dispersed, the aqueous dispersion is mixed with an emulsion solution of an anionic or nonionic hydrophobic compound, so that the emulsion of the hydrophobic compound is adsorbed onto the first layer of the base particles.
The mixture is then dried, breaking up the emulsion of the hydrophobic compound and coating the hydrophobic compound on the first layer, thereby forming a second layer.

Through the above steps, the biodegradable resin particles according to this embodiment are obtained.

Applications of the biodegradable resin particles according to this embodiment include cosmetic base materials, rolling agents, abrasives, scrubbing agents, display spacers, materials for forming beads, light diffusing particles, resin reinforcing agents, refractive index control agents, biodegradation accelerators, fertilizers, water-absorbing particles, and granular toner particles.

The resin composition and resin molded body according to this embodiment will be described in more detail below with reference to examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the resin composition and resin molded body according to this embodiment should not be interpreted as being limited by the specific examples shown below.

<Preparing each ingredient>
The following materials were prepared:

[Biodegradable resin for base particles]
DAC: "L-50" manufactured by Daicel Corporation, cellulose diacetate, weight average degree of polymerization 570
CAB: Eastman Chemical "CAP504-0.2", cellulose acetate propionate, weight average polymerization degree 133, acetyl group substitution degree 0.04, propionyl group substitution degree 2.09
CAP: cellulose acetate propionate, weight average degree of polymerization 716, acetyl group substitution degree 0.18, propionyl group substitution degree 2.49
PLA: Polylactic acid, weight average molecular weight 180,000
PHA: Polyhydroxyalkanoic acid PBS: Polybutylene succinate, weight average molecular weight 200,000
PBSA: Polybutylene succinate adipate, weight average molecular weight 110,000
PBAT: Polybutylene adipate terephthalate, weight average molecular weight 100,000
PETS: polyethylene terephthalate/succinate copolymer, weight average molecular weight 150,000

[Plasticizer for mother particles]
CDN1: Cardolite "NX-2503", hydroxyethylated cardanol, molecular weight 296-320
CDN2: Cardolite "Ultra LITE 513", glycidyl ether of cardanol, molecular weight 354-361.
CDN3: DIC's "EPICLON 865 - alkyl modified" phenol novolac type epoxy resin alkyl modified DBA: diisobutyl adipate ATBC: triethyl O-acetyl citrate DPS: diisopropyl sebacate

[Cationic resin of the first layer]
PEI: polyethyleneimine. The number average molecular weight Mn of the materials used is shown in Table 1.
PAA: polyallylamine. The number average molecular weight Mn of the materials used is shown in Table 1.
PVAM: polyvinylamine. The number average molecular weight Mn of the materials used is shown in Table 1.

[Anionic or cationic hydrophobic compound of the second layer]
EMUSTAR-0135: Paraffin wax manufactured by Nippon Seiro Co., Ltd. POLON-MN-ST: Dimethyl silicone manufactured by Shin-Etsu Chemical Co., Ltd. KM-9717: MQ resin manufactured by Shin-Etsu Chemical Co., Ltd. BELSIL DM3112VP: Dimethicone (dimethyl silicone) manufactured by Asahi Kasei Wacker Silicone Co., Ltd.
・Hitec E-2213: Polyethylene wax manufactured by Toho Chemical Industry Co., Ltd. ・Hitec P-9018: Polypropylene wax manufactured by Toho Chemical Industry Co., Ltd. ・EMUSTA-0413: Carbana wax manufactured by Nippon Seiro Co., Ltd. ・3MF-320: Acrylic resin manufactured by Taisei Fine Co., Ltd. ・A-647GEX: Polyester resin manufactured by Takamatsu Oil Co., Ltd. ・WBR-016U: Urethane resin manufactured by Taisei Fine Co., Ltd.

[Examples A1 to A30, B1 to B29, Comparative Examples A1 to A2, B1 to B2]
(Preparation of resin pellets)
The cylinder temperature was adjusted based on the composition ratios shown in Tables 1 and 2, and kneading was carried out using a twin-screw kneader (TEX41SS, manufactured by Toshiba Machine Co., Ltd.) to obtain a resin composition in the form of pellets (hereinafter referred to as resin pellets).

(Preparation of mother particles)
When DAC, CAB, and CAP were used as the resin, base particles were obtained as follows.
300 g of resin pellets were completely dissolved in 700 g of methyl ethyl ketone. This was added to an aqueous liquid in which 100 g of calcium carbonate, 4 g of carboxymethyl cellulose, and 200 g of methyl ethyl ketone were dispersed in 1100 g of pure water, and the mixture was stirred for 3 hours. 10 g of sodium hydroxide was added to the mixture, which was then heated to 80° C. and stirred for 3 hours to remove the methyl ethyl ketone. The residue was filtered and then dispersed again in pure water to obtain a slurry of base particles.

On the other hand, when a resin other than DAC, CAB, and CAP was used as the resin, base particles were obtained as follows.
2000 g of resin pellets were melt-kneaded (kneader), the kneaded product was rolled with two rolls to form a plate, and the formed product was cooled and coarsely pulverized with a pulverizer. The coarsely pulverized product was finely pulverized with a jet mill to obtain base particles. The base particles were dispersed in pure water to obtain a base particle slurry.

(Preparation of biodegradable resin particles)
Biodegradable resin particles were obtained as follows using the materials for the first and second layers shown in Tables 1 and 2 so that the coating amounts of each layer were the amounts shown in Tables 1 and 2.
After adjusting the slurry of the base particles to have a solid content of 20%, a predetermined amount of a cationic resin solution, calculated as a pure content, was added to the solid content of the slurry, and the mixture was stirred for 1 hour at 25° C. After stirring, the residue was filtered and dispersed in pure water again to adjust the solid content to 20%, and a predetermined amount of a hydrophobic compound, calculated as a pure content, was added to the solid content of the slurry, and the mixture was stirred for 1 hour at 25° C. After stirring, the residue was filtered and the solid content was freeze-dried to obtain biodegradable resin particles.
Through the above steps, biodegradable resin particles were obtained.
In Comparative Examples A2 and B2, the first layer was not formed, and a treatment (hydrophobic compound addition treatment) was carried out to form a second layer so as to have the same coating amount as in Examples A1 and B1. However, the hydrophobic compound was difficult to adsorb, and the coating amount of the second layer was 0.0001%.

<Characteristics of biodegradable resin particles>
The properties of the biodegradable resin particles were measured according to the methods described below, and the results are shown in Tables 1 and 2.
- Water contact angle (referred to as "contact angle" in the table)
・Volume average particle size D50v
(Cs+Sis)/Os value (in the table, this is indicated as "(C+Si)/O ratio T=0")
(Ce+Sie)/Oe value (in the table, this is indicated as "(C+Si)/O ratio T=3")

<Hydrolysis resistance>
The hydrolysis resistance of the biodegradable resin particles was evaluated as follows, except that the evaluation of hydrolysis resistance was carried out only for the biodegradable resin particles of Examples B1 to B29 and Comparative Examples B1 and B2.
50 g of biodegradable resin particles were sealed in a bag made of #508/585-1μ nylon mesh (mesh size 1 μm) and immersed in distilled water adjusted to 50°C and pH 7.8 for 90 days. Thereafter, the nylon mesh containing the resin particles was removed, and the resin particles in the nylon mesh were vacuum-dried. The mass of the biodegradable resin particles after vacuum drying was measured, and the mass reduction rate of the biodegradable resin particles was measured. Evaluation was then performed according to the following criteria.
A: Mass reduction rate of 0% or more and less than 10% B: Mass reduction rate of 10% or more and less than 20% C: Mass reduction rate of 20% or more and less than 30% D: Mass reduction rate of 30% or more

<Oil absorption>
-Initial oil absorption rate-
After dispersing 1 g of the biodegradable resin particles in 10 g of linseed oil, the mixture was centrifuged at 10,000 rpm for 20 minutes, and the supernatant was gently removed. The mass of the biodegradable resin particles was then measured. The oil absorption rate was calculated using the following formula.
Formula: Oil absorption rate = (mass increase after centrifugation / mass before dispersion in linseed oil) x 100

-Oil absorption rate after stirring-
An ultrasonic homogenizer was placed in a solution in which 1 g of biodegradable resin particles was dispersed in 10 g of linseed oil, and the solution was stirred for 10 minutes by irradiating it with ultrasonic waves of 20 kHz. The stirred solution was centrifuged at 10,000 rpm for 20 minutes, and the supernatant was gently removed, after which the mass of the biodegradable resin particles was measured. The oil absorption rate was then calculated according to the above formula.

The oil absorption rate was evaluated according to the following criteria.
(A): 110% or more (B): 90% or more and 109% or less (C): 70% or more and 89% or less (D): 69% or less

<Measurement of biodegradability>
Using the obtained biodegradable resin particles, the aerobic biodegradability was measured after 3 months, 6 months, and 12 months according to a method conforming to ISO-14855-2 (2018). The results are shown in Tables 1 and 2.

From the above results, it is understood that the biodegradable resin particles of this Example have a slow initial biodegradation rate while having a high biodegradation rate over time, as compared with the biodegradable resin particles of the Comparative Example.
It is also apparent that the biodegradable resin particles of this example have a higher oil absorption rate than the biodegradable resin particles of the comparative example.
Furthermore, in the biodegradable resin particles of this embodiment, the base particles are made of cellulose resin with a specific plasticizer added as the biodegradable resin, and are successively coated with a first layer containing a cationic resin and a second layer containing a hydrophobic compound, and it can be seen that the biodegradable resin particles have excellent hydrolysis resistance while being biodegradable.

Claims (18)

A base particle including a biodegradable resin;
a first layer on the surface of the base particle, the first layer including at least one cationic resin selected from the group consisting of polyalkyleneimine, polyallylamine, and polyvinylamine;
a second layer on the first layer, the second layer including an anionic or nonionic hydrophobic compound;
Biodegradable resin particles having the above structure. The biodegradable resin particles according to claim 1, wherein the hydrophobic compound is at least one selected from the group consisting of silicone compounds, hydrocarbon compounds, fatty acid compounds, acrylic resins, polyester resins, and urethane resins. The biodegradable resin particles according to claim 2, wherein the silicone compound is at least one selected from the group consisting of dimethylpolysiloxane, methylpolysiloxane, MQ resin, and silicone rubber. The biodegradable resin particles according to claim 2 or 3, wherein the hydrocarbon compound is at least one selected from the group consisting of paraffin wax, microcrystalline wax, polyethylene wax, and polypropylene wax. The biodegradable resin particles according to any one of claims 2 to 4, wherein the fatty acid compound is at least one selected from the group consisting of carnauba wax, rice wax, candelilla wax, palm wax, castor oil wax, soybean oil wax, and sunflower oil wax. The biodegradable resin particles according to any one of claims 1 to 5, wherein the polyalkyleneimine is a polyalkyleneimine having a structural unit having an alkylene group having 1 to 4 carbon atoms. The biodegradable resin particles according to claim 6, wherein the polyalkyleneimine having a structural unit with an alkylene group having 1 to 4 carbon atoms is polyethyleneimine. The biodegradable resin particles according to any one of claims 1 to 7, wherein the biodegradable resin is at least one selected from the group consisting of cellulose resin and polyester resin. The biodegradable resin particles according to claim 8, wherein the biodegradable resin is a cellulose resin. The biodegradable resin particles according to claim 9, wherein the cellulose resin is a cellulose acylate having two or more types of acyl groups. The biodegradable resin particles according to claim 9 or 10, which do not have a functional group that reacts with the cellulose resin and contain an aromatic compound having at least one of a phenolic hydroxyl group and a monoglycidyl ether group directly bonded to an aromatic group together with a long-chain aliphatic group, and at least one fatty acid ester. The biodegradable resin particles according to claim 11, wherein the aromatic compound is a cardanol compound. The biodegradable resin particles according to claim 12, wherein the cardanol compound is at least one compound selected from the group consisting of a compound represented by the following general formula (CDN1) and a compound represented by the following general formula (CDN1-e):


(In general formula (CDN1), R ¹ represents an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. R ² represents a hydroxy group, a carboxy group, an alkyl group which may have a substituent, or an unsaturated aliphatic group which has a double bond and may have a substituent. P 2 represents an integer of 0 to 4. When P 2 is 2 or more, a plurality of R ^2s may be the same group or different groups.)


(In general formula (CDN1-e), L _EP represents a single bond or a divalent linking group. In general formula (CDN1-e), R ¹ , R ² and P2 have the same meanings as R ¹ , R ² and P2 in general formula (CDN1), respectively.) The biodegradable resin particles according to any one of claims 11 to 13, wherein the base particles contain cellulose acetate propionate as the cellulose resin and a cardanol compound as the aromatic compound. The biodegradable resin particles according to any one of claims 11 to 13, wherein the base particles contain cellulose acetate butyrate as the cellulose resin and the fatty acid ester. The biodegradable resin particles according to any one of claims 1 to 15, wherein the mass ratio of the coating amount of the cationic resin to the coating amount of the hydrophobic compound (coating amount of the cationic resin/coating amount of the hydrophobic compound) is 0.1 or more and 10 or less. The biodegradable resin particles according to claim 16, wherein the amount of the cationic resin coated on the base particles is 0.1% by mass or more and 10% by mass or less. The biodegradable resin particles according to any one of claims 1 to 17, wherein the number average molecular weight of the cationic resin is 10,000 or more and 85,000 or less.