Crosslinked resin particles and method for producing same

Abstract

Provided are crosslinked resin particles including a polyhydroxyalkanoate-based resin, having a gel fraction of 50% or more, and having a volume average particle diameter of 0.1 μm to 10 μm. The polyhydroxyalkanoate-based resin may be a poly(3-hydroxyalkanoate)-based resin. The crosslinked resin particles can be produced by crosslinking the polyhydroxyalkanoate-based resin in the presence of a peroxide in an aqueous dispersion of the polyhydroxyalkanoate-based resin particles.

Description

Crosslinked resin particles and method for producing the same

[0001] The present invention relates to crosslinked resin particles and a method for producing the same.

[0002] It has been known that introducing a crosslinked structure into a resin can improve the resin's hardness, heat resistance, solvent resistance, etc. Small resin particles composed of resins with such crosslinked structures are used in a variety of applications, such as modifiers for thermoplastic resins, spacers, antiblocking agents, and matting agents.

[0003] Known resin materials constituting such crosslinked resin particles include acrylic resins, acrylic silicone resins, polystyrene, and the like (see, for example, Patent Documents 1 and 2).

[0004] On the other hand, plastic waste is a burden on the global environment, affecting ecosystems, emitting harmful gases when burned, and contributing to global warming due to the large amount of heat generated by combustion. Therefore, there has been active development of biodegradable plastics as a material that can solve these problems.

[0005] Patent Document 3 describes crosslinking of poly(3-hydroxyalkanoate), a type of biodegradable plastic, by melt-kneading the resin in the presence of an organic peroxide. However, it describes that the crosslinked resin produced by melt-kneading in this way is used to form films or sheets, and does not describe at all the production of small particle size crosslinked resin particles.

[0006] JP 2009-56770 A JP 2003-82191 A International Publication No. 2019 / 022008

[0007] To date, small crosslinked resin particles made of biodegradable plastics and exhibiting biodegradability have not been known.

[0008] In view of the above-mentioned current situation, an object of the present invention is to provide novel crosslinked resin particles having biodegradability.

[0009] As a result of extensive research, the present inventors have succeeded in producing novel crosslinked resin particles using a polyhydroxyalkanoate resin, which is a biodegradable resin, and have thus completed the present invention.

[0010] Specifically, the present invention relates to crosslinked resin particles containing a polyhydroxyalkanoate resin, having a gel fraction of 50% or more, and a volume average particle diameter of 0.1 μm to 10 μm. The present invention also relates to an aqueous dispersion in which the crosslinked resin particles are dispersed in an aqueous medium. Furthermore, the present invention also relates to a method for producing the crosslinked resin particles, which includes a step of crosslinking the polyhydroxyalkanoate resin in the aqueous dispersion of polyhydroxyalkanoate resin particles in the presence of a peroxide.

[0011] According to the present invention, novel crosslinked resin particles having biodegradability can be provided.

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0013] <Crosslinked Resin Particles> The crosslinked resin particles according to this embodiment are particles that are composed of a polyhydroxyalkanoate-based resin as a main resin component. Hereinafter, the polyhydroxyalkanoate-based resin may be abbreviated as "PHA."

[0014] <PHA> "PHA" is a general term for polymers having hydroxyalkanoic acid as a monomer unit, and is generally biodegradable. PHA is an aliphatic polyester, preferably a polyester not containing an aromatic ring.

[0015] The PHA is not particularly limited, but examples thereof include polyglycolic acid, poly(3-hydroxyalkanoate)-based resins, and poly(4-hydroxyalkanoate)-based resins. Only one type of PHA may be used, or two or more types may be used in combination. Of these, poly(3-hydroxyalkanoate)-based resins are preferred. Hereinafter, poly(3-hydroxyalkanoate)-based resins may be abbreviated as "P3HA."

[0016] The P3HA has the formula: [—CHR—CH ２ 3-hydroxyalkanoic acid repeating units represented by the formula: —CO—O— (wherein R is C ｎ H ２ｎ＋１ where n is an integer of 1 to 15.) as an essential repeating unit. The P3HA preferably contains 50 mol % or more, and more preferably 70 mol % or more, of the total monomer repeating units (100 mol %) of the 3-hydroxyalkanoic acid repeating units.

[0017] P3HA is not particularly limited, but examples thereof include poly(3-hydroxybutyrate) (abbreviation: P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), etc. Only one type of P3HA may be used, or two or more types may be used in combination.

[0018] P3HA can be produced by microorganisms. Such microbially produced P3HA is usually P3HA composed only of D-form (R-form) hydroxyalkanoic acid repeating units. Among microbially produced P3HAs, P3HB and P3HB3HH are preferred, with P3HB3HH being more preferred, due to ease of industrial production.

[0019] When P3HA contains 3-hydroxybutanoic acid (3HB) repeating units, from the viewpoint of the balance between flexibility and strength, the composition ratio of 3HB repeating units in all monomer repeating units (100 mol%) is preferably 60 to 99 mol%, more preferably 65 to 97 mol%, and even more preferably 67 to 95 mol%. When the composition ratio of 3HB repeating units is 60 mol% or more, the rigidity of the crosslinked resin particles can be further improved. On the other hand, when the composition ratio of 3HB repeating units is 99 mol% or less, the flexibility of the crosslinked resin particles tends to be further improved. The monomer composition ratio of P3HA can be measured by gas chromatography or the like (see, for example, WO 2014 / 020838). Two or more types of P3HA having different composition ratios of 3HB repeating units may be used in combination.

[0020] The microorganism that produces P3HA is not particularly limited as long as it has the ability to produce P3HA. For example, the first P3HB-producing bacterium was Bacillus megaterium, discovered in 1925, and other naturally occurring microorganisms such as Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus are known. In these microorganisms, P3HB accumulates intracellularly.

[0021] Furthermore, Aeromonas caviae, a P3HB3HH-producing bacterium, is known as a producer of copolymers of 3HB and other hydroxyalkanoates. In particular, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)) into which genes encoding P3HA synthases have been introduced is preferred to increase the productivity of P3HB3HH. Microbial cells obtained by culturing such microorganisms under appropriate conditions and accumulating P3HA within the cells are used. In addition to the above, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may be used depending on the P3HA to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0022] The molecular weight of the PHA is not particularly limited, but the weight-average molecular weight is preferably 50,000 to 3,000,000, more preferably 100,000 to 2,000,000, and more preferably 150,000 to 1,500,000. By setting the weight-average molecular weight to 50,000 or more, it is possible to avoid the tendency for the crosslinked resin particles to have low strength or to be sticky due to low molecular weight components. On the other hand, PHAs with a weight-average molecular weight exceeding 3,000,000 may be difficult to produce or handle for the purposes of the present invention. The weight-average molecular weight is measured before the PHA is crosslinked.

[0023] The weight-average molecular weight can be measured using gel permeation chromatography (GPC) (Shimadzu Corporation's "High Performance Liquid Chromatograph 20A System"), using polystyrene gel (Showa Denko K.K.'s "K-G 4A" or "K-806M" or the like) as a column, and chloroform as a mobile phase, and can be determined as a molecular weight converted into polystyrene. In this case, a calibration curve can be prepared using polystyrenes with weight-average molecular weights of 31,400, 197,000, 668,000, and 1,920,000. As the column for the GPC, a column appropriate for measuring the molecular weight can be used.

[0024] <Gel Fraction> The crosslinked resin particles according to this embodiment have a crosslinked structure in which molecular chains of PHA are bonded to each other. Because the crosslinked resin particles according to this embodiment have a certain amount or more of such crosslinked structure, they exhibit a high gel fraction, specifically, a gel fraction of 50% or more. By exhibiting such a high gel fraction, the hardness, heat resistance, solvent resistance, etc. of the resin particles containing PHA can be improved.

[0025] The gel fraction value is preferably 60% or more, more preferably 70% or more, even more preferably 75% or more, and particularly preferably 80% or more. It may also be 85% or more, or even 90% or more. The upper limit of the gel fraction is not particularly limited as long as it is 100% or less. From the viewpoint of production efficiency of crosslinked resin particles, however, it is preferably 99.5% or less, more preferably 99% or less. It may also be 98% or less, 97% or less, or 96% or less.

[0026] The gel fraction is a value measured as follows. Dried crosslinked resin particles are added to chloroform to a concentration of 0.7% by weight, and dissolved at 60°C for 30 minutes to obtain a chloroform solution. After leaving the solution at room temperature for 3 hours, the chloroform solution is filtered through a membrane filter with a pore size of 0.45 μm. The gel remaining on the filter is dried, and the weight of the filter is measured, and the gel fraction is calculated using the following formula: Gel fraction = (weight of filter including dried gel - weight of filter only) / weight of crosslinked resin particles used in measurement x 100 (%)

[0027] <Average particle size> The crosslinked resin particles according to this embodiment have a volume average particle size in the range of 0.1 μm or more and 10 μm or less. Having such a particle size allows them to be used in various applications, as will be described later. From the viewpoint of practical use, the lower limit of the particle size is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. Furthermore, from the viewpoint of productivity (such as PHA production and crosslinking treatment), the upper limit of the particle size is preferably 8 μm or less, more preferably 5 μm or less.

[0028] The volume average particle size is a value measured when the crosslinked resin particles are dispersed in an aqueous solvent. A general-purpose measuring device can be used as the measuring device, and an example of such a device is Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd.

[0029] <Peroxide> The crosslinking type of the crosslinked resin particles according to this embodiment is not particularly limited, but it is preferable that the crosslinking is performed using a peroxide. When a peroxide is used, radicals generated by decomposition of the peroxide act on PHA molecules, directly bonding PHA molecular chains to each other, thereby forming the crosslinked structure.

[0030] The peroxide may be an organic peroxide or an inorganic peroxide, but is preferably an organic peroxide because it can increase the gel fraction more efficiently.

[0031] As the organic peroxide, it is preferable to use at least one selected from the group consisting of diacyl peroxides, alkyl peroxy esters, dialkyl peroxides, hydroperoxides, peroxyketals, peroxycarbonates, and peroxydicarbonates, taking into consideration the heating temperature and time during the crosslinking treatment.

[0032] Specific examples of such organic peroxides include butyl peroxy neododecanoate, octanoyl peroxide, dilauroyl peroxide, succinic peroxide, a mixture of toluoyl peroxide and benzoyl peroxide, benzoyl peroxide, bis(butylperoxy)trimethylcyclohexane, butyl peroxylaurate, dimethyldi(benzoylperoxy)hexane, bis(butylperoxy)methylcyclohexane, bis(butylperoxy)cyclohexane, and butylperoxybenzo ester, butyl bis(butylperoxy)valerate, dicumyl peroxide, di-t-hexyl peroxide, t-butylperoxy 2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxymethyl monocarbonate, t-pentylperoxymethyl monocarbonate, t-hexylperoxymethyl monocarbonate, t-heptylperoxymethyl monocarbonate, t-octylperoxymethyl monocarbonate, 1 , 1,3,3-tetramethylbutylperoxymethyl monocarbonate, t-butylperoxyethyl monocarbonate, t-pentylperoxyethyl monocarbonate, t-hexylperoxyethyl monocarbonate, t-heptylperoxyethyl monocarbonate, t-octylperoxyethyl monocarbonate, 1,1,3,3-tetramethylbutylperoxyethyl monocarbonate, t-butylperoxy n-propyl monocarbonate, t-pentylperoxy n-propyl monocarbonate, t-hexylperoxy peroxy isopropyl monocarbonate, t-heptylperoxy isopropyl monocarbonate, t-octylperoxy isopropyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy isopropyl monocarbonate, t-butylperoxy isopropyl monocarbonate, t-pentylperoxy isopropyl monocarbonate, t-hexylperoxy isopropyl monocarbonate, t-heptylperoxy isopropyl monocarbonate, t-octylperoxy isopropyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy isopropyl monocarbonate, t-butylperoxy n-butyl monocarbonate, t-pentylperoxy n-butyl monocarbonate, t-hexylperoxy n-butyl monocarbonate, t-heptylperoxy n-butyl monocarbonate, t-octylperoxy n-butyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy n-butyl monocarbonate, t-butylperoxy isobutyl monocarbonate, t-pentylperoxy isobutyl monocarbonate, t -Hexylperoxy isobutyl monocarbonate, t-heptylperoxy isobutyl monocarbonate, t-octylperoxy isobutyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy isobutyl monocarbonate, t-butylperoxy sec-butyl monocarbonate, t-pentylperoxy sec-butyl monocarbonate, t-hexylperoxy sec-butyl monocarbonate, t-heptylperoxy sec-butyl monocarbonate, t-octylperoxy sec-butyl monocarbonate t-butylperoxy t-butyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy sec-butyl monocarbonate, t-butylperoxy t-butyl monocarbonate, t-pentylperoxy t-butyl monocarbonate, t-hexylperoxy t-butyl monocarbonate, t-heptylperoxy t-butyl monocarbonate, t-octylperoxy t-butyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy t-butyl monocarbonate, t-butylperoxy 2-ethylhexyl monocarbonate, t-pentylperoxy 2-ethylhexyl monocarbonate ethylhexyl monocarbonate, t-hexylperoxy 2-ethylhexyl monocarbonate, t-heptylperoxy 2-ethylhexyl monocarbonate, t-octylperoxy 2-ethylhexyl monocarbonate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexyl monocarbonate, diisobutyl peroxide, cumyl peroxy neodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, bis(4-t-butylcyclohexyl) peroxydicarbonate, bis(2-ethylhexyl) peroxydicarbonate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, disuccinic acid peroxide, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy) Examples of organic peroxides include hexane, t-hexylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, t-butylperoxy-2-ethylhexyl carbonate, t-butylperoxyisopropyl carbonate, 1,6-bis(t-butylperoxycarbonyloxy)hexane, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxyacetate, t-butylperoxybenzoate, t-amylperoxy-3,5,5-trimethylhexanoate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, and 2,2-di-t-butylperoxybutane. One organic peroxide may be used alone, or two or more organic peroxides may be used in combination.

[0033] Among these, t-butylperoxyisopropyl monocarbonate, t-pentylperoxyisopropyl monocarbonate, t-hexylperoxyisopropyl monocarbonate, t-butylperoxy2-ethylhexyl monocarbonate, t-pentylperoxy2-ethylhexyl monocarbonate, t-hexylperoxy2-ethylhexyl monocarbonate, t-amylperoxyisopropyl monocarbonate, di-t-hexyl peroxide, t-butylperoxy2-ethylhexyl monocarbonate, Peroxymethylbutylperoxyisobutyrate, t-hexylperoxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, and 1,1,3,3-tetramethylbutylperoxyneodecanoate are preferred organic peroxides because they can efficiently promote crosslinking of PHA.

[0034] The peroxide is preferably a compound having a one-hour half-life temperature of 200° C. or less, more preferably 170° C. or less, and even more preferably 140° C. or less, so that the heating temperature during the crosslinking treatment can be set low. The lower limit may be 50° C. or more, 60° C. or more, or 70° C. or more.

[0035] Particularly preferred organic peroxides exhibiting such a one-hour half-life temperature include t-butylperoxyisopropyl monocarbonate, t-butylperoxy 2-ethylhexyl monocarbonate, di-sec-butylperoxydicarbonate, t-butylperoxy 2-ethylhexanoate, t-butylperoxyisobutyrate, t-hexylperoxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, t-butylperoxypivalate, t-hexylperoxypivalate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, and 1,1,3,3-tetramethylbutylperoxyneodecanoate.

[0036] When the peroxide is an inorganic peroxide, examples of the inorganic peroxide include hydrogen peroxide, potassium peroxide, calcium peroxide, sodium peroxide, magnesium peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate, taking into consideration the heating temperature and time during the crosslinking treatment. Among these, hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate are preferred because they are easy to handle and have decomposition temperatures suitable for the heating temperature during the crosslinking treatment. One type of inorganic peroxide may be used alone, or two or more types may be used in combination. Furthermore, an organic peroxide and an inorganic peroxide may be used in combination.

[0037] The crosslinked structure in the crosslinked resin particles according to the present embodiment may be introduced using only a peroxide, or may be introduced using both a peroxide and a polyfunctional compound, which makes it possible to increase the gel fraction of the crosslinked resin particles with a smaller amount of peroxide.

[0038] The polyfunctional compound refers to a compound having two or more functional groups capable of crosslinking PHA in one molecule. Although not particularly limited, a compound having reactivity with radicals generated from peroxide is preferred, and a compound having two or more radical reactive groups in one molecule is particularly preferred. The radical reactive group is preferably at least one selected from the group consisting of a vinyl group, an allyl group, an acryloyl group, or a methacryloyl group.

[0039] Such polyfunctional compounds are not particularly limited, but examples thereof include allyl (meth)acrylate, allyl alkyl (meth)acrylates, allyloxyalkyl (meth)acrylates, polyfunctional (meth)acrylates having two or more (meth)acrylic groups such as ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol (meth)acrylate, divinylbenzene, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, and divinylbenzene. Preferred are allyl methacrylate, triallyl isocyanurate, butanediol di(meth)acrylate, and divinylbenzene, and particularly preferred are allyl methacrylate and triallyl isocyanurate.

[0040] When a crosslinked structure is formed in the presence of a polyfunctional compound, the resulting crosslinked resin particles may generally contain a structure derived from the polyfunctional compound, in which case molecular chains of the PHA are bonded to each other via the structure derived from the polyfunctional compound.

[0041] The crosslinked resin particles according to this embodiment may be composed solely of a PHA having a crosslinked structure, or may further contain components other than the PHA having a crosslinked structure, such as resins other than PHA, antioxidants, hydrolysis inhibitors, antiblocking agents, crystal nucleating agents, and ultraviolet absorbers.

[0042] The proportion of PHA in the crosslinked resin particles according to this embodiment is not particularly limited, but may be 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more. It may also be 99% by weight or more. There is no particular upper limit, and it is sufficient as long as it is 100% by weight or less.

[0043] Examples of resins other than PHA include aliphatic polyesters having a structure in which an aliphatic diol and an aliphatic dicarboxylic acid are polycondensed, and aliphatic-aromatic polyesters having both an aliphatic compound and an aromatic compound as monomers. Examples of the former include polyethylene succinate, polybutylene succinate (PBS), polyhexamethylene succinate, polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polybutylene succinate adipate (PBSA), polyethylene sebacate, and polybutylene sebacate. Examples of the latter include poly(butylene adipate-co-butylene terephthalate) (PBAT), poly(butylene sebacate-co-butylene terephthalate), poly(butylene azelate-co-butylene terephthalate), poly(butylene succinate-co-butylene terephthalate) (PBST), etc. The other resins may be used singly or in combination of two or more.

[0044] The crosslinked resin particles according to the present embodiment are different from the expanded resin particles disclosed in WO 2007 / 049694 and WO 2019 / 146555, and are preferably non-expanded, i.e., substantially free of air bubbles inside the particles.

[0045] When not foamed, the crosslinked resin particles according to this embodiment have a relatively high apparent density of 0.6 g / cm ３ It is preferable that the density exceeds 0.7 g / cm ３ More preferably, it is 0.9 g / cm or more. ３ The apparent density of the crosslinked resin particles can be determined by the method described in JIS K0061 (Method for measuring density and specific gravity of chemical products) or JIS Z8807 (Method for measuring density and specific gravity of solids).

[0046] The average weight per particle of the crosslinked resin particles according to this embodiment is not particularly limited, but since the crosslinked resin particles have a small particle size with a volume average particle diameter of 10 μm or less, the value is far less than 0.1 mg.

[0047] The crosslinked resin particles according to this embodiment may be dried, and the shape of the dried particles may be powder, pellets, crumbs, sheets, or the like, depending on the drying method.

[0048] <Aqueous Dispersion> One aspect of this embodiment may be an aqueous dispersion in which the crosslinked resin particles are dispersed in an aqueous medium. The aqueous medium contained in the aqueous dispersion may be water alone, or may be a mixed solvent of water and a water-compatible organic solvent. In the mixed solvent, the concentration of the water-compatible organic solvent is not particularly limited as long as it is equal to or lower than the solubility in water of the organic solvent used.

[0049] The organic solvent is not particularly limited, but examples thereof include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, and heptanol; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, and piperidine. Among these, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile, and propionitrile are preferred because they are easily removable. Furthermore, methanol, ethanol, 1-propanol, 2-propanol, butanol, and acetone are more preferred because they are easily available. Furthermore, methanol, ethanol, and acetone are particularly preferred.

[0050] The content of water in the entire aqueous medium constituting the aqueous dispersion is preferably 5 to 100% by weight, more preferably 10% by weight or more, more preferably 30% by weight or more, even more preferably 50% by weight or more, particularly preferably 70% by weight or more, and may be 90% by weight or more, or even 95% by weight or more.

[0051] The concentration of the crosslinked resin particles in the aqueous dispersion is not particularly limited, but may be, for example, about 1 to 60 wt %. The aqueous dispersion may also contain a dispersant, which will be described later.

[0052] <Method for producing crosslinked resin particles> An example of a method for producing the crosslinked resin particles according to this embodiment will be specifically described. The crosslinked resin particles according to this embodiment can be produced by crosslinking PHA in the presence of a peroxide in an aqueous dispersion containing PHA particles before crosslinking treatment. In order to efficiently crosslink the PHA, it is preferable to heat the aqueous dispersion of PHA particles containing a peroxide to a temperature suitable for decomposing the peroxide.

[0053] More specifically, the method for producing crosslinked resin particles preferably includes the steps of: (1) preparing an aqueous dispersion of PHA particles in which pre-crosslinked PHA particles are dispersed in water; (2) adding a peroxide to the aqueous dispersion of PHA particles to impregnate the PHA particles with the peroxide; and (3) heating the aqueous dispersion of PHA particles impregnated with the peroxide to a heating temperature to crosslink the PHA. Furthermore, the method more preferably includes the step of (4) maintaining the heating temperature after all the peroxide has been added.

[0054] In step (1), the aqueous dispersion of PHA particles may be an aqueous dispersion obtained by culturing a PHA-producing microorganism to accumulate PHA in the cells, disrupting the cells in the culture solution, and separating and removing the cell components, or an aqueous dispersion obtained by concentrating or diluting the aqueous dispersion. According to such a method, the process from producing PHA particles by culturing a PHA-producing microorganism to crosslinking treatment can be carried out without separating the PHA particles from water.

[0055] Alternatively, an aqueous dispersion of PHA particles can be prepared by dispersing dried PHA particles in water. The aqueous dispersion may contain, in addition to water, the above-mentioned water-compatible organic solvent.

[0056] In the aqueous dispersion, the volume average particle diameter of the PHA particles is preferably within the same range as that of the crosslinked resin particles. In the case of PHA particles produced by a PHA-producing microorganism, the volume average particle diameter can usually be within the above range, so that an aqueous dispersion of PHA particles having a desired volume average particle diameter can be obtained without carrying out a special step for adjusting the particle diameter.

[0057] The concentration of the PHA particles in the aqueous dispersion is not particularly limited and can be set appropriately, but may be, for example, about 1 to 70% by weight, preferably about 5 to 50% by weight.

[0058] The aqueous dispersion of PHA particles preferably contains a dispersant in order to improve the dispersibility of PHA particles and to make the crosslinking reaction proceed uniformly.As the dispersant, for example, anionic surfactants such as dioctyl sodium sulfosuccinate, sodium dodecyl sulfate, sodium lauryl sulfate, sodium oleate, etc.; cationic surfactants such as lauryl trimethyl ammonium chloride, etc.; nonionic surfactants such as glycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, etc.; water-soluble polymers such as polyvinyl alcohol, ethylene-modified polyvinyl alcohol, polyvinylpyrrolidone, methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, polymethacrylic acid, sodium polymethacrylate, etc.These dispersants may be used alone or in combination of two or more.

[0059] When a dispersant is used, the amount thereof to be added is not particularly limited, but may be, for example, 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and particularly preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of PHA particles.

[0060] In step (2), a peroxide is added to the aqueous dispersion of PHA particles obtained in step (1) to impregnate the PHA particles with the peroxide. The peroxide may be any of those described above. The peroxide may be added in various forms, such as a solid or liquid. Alternatively, a liquid diluted with a diluent or the like may be added. The peroxide may be added all at once, continuously, or in portions.

[0061] When a peroxide and the polyfunctional compound are used in combination, it is preferable to add the polyfunctional compound to the aqueous dispersion of PHA particles in step (2). The polyfunctional compound can be any of those described above. The polyfunctional compound can be added in various forms, such as solid or liquid. A liquid diluted with a diluent or the like may also be added. The polyfunctional compound may be added all at once, continuously, or in portions.

[0062] To impregnate the PHA particles with the peroxide and any polyfunctional compound, after or while adding these compounds to an aqueous dispersion of PHA particles, the temperature of the aqueous dispersion is set to, for example, 0°C or higher but lower than a temperature suitable for decomposing the peroxide employed in the next step (3), and the temperature is maintained for, for example, about 1 minute to 5 hours while stirring the aqueous dispersion. Specifically, the temperature of the aqueous dispersion during impregnation may be about 10 to 60°C.

[0063] The amount of peroxide used can be appropriately set in consideration of the gel fraction of the crosslinked resin particles, but for example, it is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, even more preferably 0.3 to 5 parts by weight, and particularly preferably 0.5 to 3 parts by weight, relative to 100 parts by weight of the PHA particles.

[0064] According to the manufacturing method of crosslinking PHA particles in aqueous dispersion using peroxide, crosslinking can be easily carried out while maintaining the particle size (volume) before crosslinking, and crosslinked resin particles can be easily obtained.On the other hand, it may be difficult to achieve this in the method of crosslinking resin by melt kneading in the presence of peroxide.In addition, according to the manufacturing method of crosslinking PHA particles in aqueous dispersion using peroxide, it is easy to control the temperature rise caused by the heat generated during the crosslinking reaction, and it is advantageous in efficiently obtaining crosslinked resin particles with a safe and stable crosslinked structure (quality).

[0065] The amount of the polyfunctional compound used may also be appropriately set in consideration of the gel fraction of the crosslinked resin particles, and is, for example, preferably 0.01 to 20 parts by weight, more preferably 0.05 to 15 parts by weight, even more preferably 0.1 to 10 parts by weight, even more preferably 0.2 to 5 parts by weight, and particularly preferably 0.3 to 3 parts by weight, relative to 100 parts by weight of the PHA particles.

[0066] In step (3), the aqueous dispersion of PHA particles impregnated with peroxide is heated to a temperature suitable for decomposing the peroxide. The heating temperature is preferably within a range of about 25°C above or below the one-hour half-life temperature of the peroxide. Specifically, the heating temperature is preferably 30 to 140°C, more preferably 50 to 135°C, and even more preferably 60 to 130°C. This method makes it possible to crosslink the PHA at a temperature lower than the melting temperature of the PHA, thereby avoiding deterioration of the PHA due to heating during the crosslinking treatment.

[0067] In the subsequent step (4), it is preferable to maintain the heating temperature. This allows the crosslinking reaction using the peroxide to proceed sufficiently. The time for maintaining the heating temperature is not particularly limited, but is preferably 1 minute to 15 hours, and more preferably 1 hour to 10 hours.

[0068] After the crosslinking reaction is complete, the crosslinked resin particles are separated from the aqueous dispersion and the water is removed to obtain dried crosslinked resin particles. The method for separating the crosslinked resin particles is not particularly limited, and examples thereof include filtration, centrifugation, heat drying, freeze drying, and spray drying. For example, spray drying can be used to obtain dried crosslinked resin particles directly from the aqueous dispersion. Furthermore, by extruding the crosslinked resin particles alone after separation from the aqueous dispersion, residual water can be completely removed and the crosslinked resin particles can be obtained in pellet form. Furthermore, an aggregation process using a coagulant or pH adjustment may be performed.

[0069] However, the aqueous dispersion itself after the crosslinking reaction has been completed, or an aqueous dispersion obtained by concentrating the aqueous dispersion after the crosslinking reaction to increase the concentration of crosslinked resin particles, or an aqueous dispersion obtained by diluting the aqueous dispersion after the crosslinking reaction by adding an aqueous medium also constitute one aspect of the present invention.

[0070] <Uses of Crosslinked Resin Particles> The uses of the crosslinked resin particles according to this embodiment are not particularly limited, and they can be used in the applications in which conventionally known crosslinked resin particles are used. Specific examples include, but are not limited to, resin modifiers, rheology adjusters for paints or adhesives, paint pigments, paper coating agents, matting agents, antiblocking agents, cosmetic additives, toner additives, liquid crystal spacers, coating agents, fillers for adhesive tapes, fiber processing agents, test particles for medical diagnosis, and fillers.

[0071] The crosslinked resin particles according to this embodiment are made of biodegradable PHA, and are therefore expected to be useful as environmentally friendly crosslinked resin particles that address the problem of plastic waste.

[0072] The following items list preferred embodiments of the present disclosure, but the present invention is not limited to them. [Item 1] Crosslinked resin particles comprising a polyhydroxyalkanoate resin, having a gel fraction of 50% or more, and a volume average particle diameter of 0.1 μm or more and 10 μm or less. [Item 2] Crosslinked resin particles according to item 1, wherein the polyhydroxyalkanoate resin is a poly(3-hydroxyalkanoate) resin. [Item 3] Crosslinked resin particles according to item 1 or 2, wherein the crosslinked resin particles are crosslinked using a peroxide. [Item 4] Crosslinked resin particles according to any one of items 1 to 3, wherein the crosslinked resin particles are further crosslinked in the presence of a polyfunctional compound. [Item 5] Crosslinked resin particles according to any one of items 1 to 4, wherein the crosslinked resin particles are not foamed. [Item 6] Crosslinked resin particles according to any one of items 1 to 5, wherein the proportion of the polyhydroxyalkanoate resin in the crosslinked resin particles is 80% by weight or more. [Item 7] The crosslinked resin particles according to any one of items 1 to 6, wherein the gel fraction is 70 to 100%. [Item 8] An aqueous dispersion in which the crosslinked resin particles according to any one of items 1 to 7 are dispersed in an aqueous medium. [Item 9] A method for producing the crosslinked resin particles according to any one of items 1 to 7, comprising a step of crosslinking the polyhydroxyalkanoate resin in the presence of a peroxide in an aqueous dispersion of polyhydroxyalkanoate resin particles.

[0073] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0074] [1] Measurement conditions 1-1. Weight average molecular weight The resin to be measured was dissolved in chloroform and heated in a hot water bath at 60°C for 30 minutes. The soluble matter was filtered through a disposable PTFE filter with a 0.45 μm pore size. The filtrate was then subjected to GPC measurement under the following conditions to determine the weight average molecular weight. GPC measurement device: High performance liquid chromatograph 20A system manufactured by Shimadzu Corporation Column: K-G 4A (1 column), K-806M (2 columns) manufactured by Showa Denko K.K. Sample concentration: 1 mg / ml Free liquid: chloroform solution Free liquid flow rate: 1.0 ml / min Sample injection amount: 100 μL Analysis time: 30 minutes Standard sample: standard polystyrene

[0075] 1-2. Volume average particle diameter The volume average particle diameter of the crosslinked resin particles or base resin particles was measured in the state of resin particle latex. The measuring device used was a Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd.

[0076] 1-3. Gel Fraction A dried product of crosslinked resin particles or base resin particles was added to chloroform to a concentration of 0.7% by weight, and dissolved at 60°C for 30 minutes to obtain a chloroform solution. After allowing to stand at room temperature for 3 hours, the chloroform solution was filtered through a membrane filter with a pore size of 0.45 μm. Losses were prevented by pouring chloroform over the inside of the container and the filter multiple times to thoroughly wash the solution while filtering. The gel remaining on the filter was dried, and its weight was measured together with the filter, and the gel fraction was calculated using the following formula: Formula: Gel fraction = (weight of filter including dried gel - weight of filter only) / weight of crosslinked resin particles or base resin particles used in measurement × 100 (%)

[0077] 1-4. (Biochemical oxygen demand (BOD) test) 25 mg of frozen and crushed sample was placed in 250 ml of seawater containing 0.05 g / L of ammonium chloride and 0.1 g / L of potassium dihydrogen phosphate, and the BOD value was measured after maintaining the conditions of 30°C and constant stirring for 91 days. The BOD value was measured using an Oxitop (manufactured by Xylem) which uses a pressure sensor to measure the pressure drop of the gas phase in a sealed container under constant temperature conditions, and the CO generated by microbial respiration was measured. ２The biodegradability (%) in seawater was calculated by dividing the obtained BOD value by the theoretical oxygen consumption (the amount of oxygen required for complete decomposition into water and carbon dioxide).

[0078] [2] Raw materials for crosslinked resin particles 2-1. Base resin particles PHA-1: poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 72 / 28 (mol / mol), weight average molecular weight Mw: 700,000 to 1,500,000 PHA-2: poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 89 / 11 (mol / mol), weight average molecular weight Mw: 500,000 PHA-3: poly(3-hydroxybutyrate-co-3-hydroxyhexanoate): (3-hydroxybutyrate) / (3-hydroxyhexanoate) = 68 / 32 (mol / mol), weight average molecular weight Mw: 700,000 to 1,500,000 PHA-4: Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate): (3-hydroxybutyrate) / (3-hydroxyhexanoate)=75 / 25 (mol / mol), weight average molecular weight Mw: 600,000 to 1,500,000

[0079] 2-2. Peroxides PO-1: t-butyl peroxypivalate ("Luperox 11" manufactured by Arkema Yoshitomi Co., Ltd., 1-hour half-life temperature: 76°C) PO-2: t-butylperoxy-2-ethylhexanoate ("Luperox 26" manufactured by Arkema Yoshitomi Co., Ltd., 1-hour half-life temperature: 95°C) PO-3: t-butylperoxy-2-ethylhexyl monocarbonate ("Perbutyl E" manufactured by NOF Corporation, 1-hour half-life temperature: 119°C) PO-4: di-sec-butyl peroxydicarbonate ("Luperox 225" manufactured by Arkema Yoshitomi Co., Ltd., 1-hour half-life temperature: 69°C)

[0080] 2-3. Polyfunctional compounds CA-1: Allyl methacrylate CA-2: Triallyl isocyanurate

[0081] [3] Method for Producing Crosslinked Resin Particles The crosslinked resin particles of Examples 1 to 29 were produced using the raw materials of the types listed in the table in the amounts listed in the table, according to the procedure described below. An autoclave equipped with a stirrer, baffles, a nitrogen inlet / outlet, and a thermometer was charged with an aqueous dispersion (100 parts by weight of solids) of base resin particles dispersed in water, 200 parts by weight of deionized water, a predetermined amount of peroxide, 2 parts by weight of sodium dioctyl sulfosuccinate, and a predetermined amount of polyfunctional compound. Stirring was initiated at room temperature, and the autoclave was simultaneously purged with nitrogen. The contents of the autoclave were then stirred at the temperature and for the time specified in the impregnation conditions to impregnate the base resin particles with the peroxide and polyfunctional compound. The temperature was then raised to the reaction temperature specified in the crosslinking conditions. After reaching the reaction temperature, the reaction was continued at the reaction temperature for the reaction time specified in the crosslinking conditions, yielding an aqueous dispersion of crosslinked resin particles dispersed in water. The pH of the aqueous dispersion was adjusted, and the dispersion was then dried in an oven to obtain solidified crosslinked resin particles. The volume average particle size and gel fraction of the crosslinked resin particles obtained in each example were measured by the methods described above, and the results are shown in the table.

[0082] In Comparative Example 1, the volume average particle size and gel fraction of the base resin particles before the crosslinking reaction were measured by the above-mentioned methods.

[0083] The biodegradability in seawater of the crosslinked resin particles obtained in Examples 20 and 22 and commonly available cellulose (microcrystalline cellulose, manufactured by Merck) (Reference Example) was measured by the above-mentioned method. The results are shown in Table 3.

[0084]

[0085]

[0086]

[0087] Tables 1 to 3 show that in Examples 1 to 29, crosslinked resin particles containing a polyhydroxyalkanoate resin were obtained, with a gel fraction of 50% or more and a volume average particle size of 0.1 to 10 μm. On the other hand, in Comparative Example 1, in which no crosslinking reaction was performed, the gel fraction of the resin particles was extremely low at 0%. Furthermore, Table 3 shows that the crosslinked resin particles obtained in Examples 20 and 22 exhibited a higher degree of biodegradation in seawater over approximately three months than the biodegradable material cellulose (Reference Example), demonstrating good biodegradability.

Claims

1. Contains polyhydroxyalkanoate resin, Crosslinked resin particles having a gel fraction of 50% or more and a volume average particle diameter of 0.1 μm or more and 10 μm or less.

2. 2. The crosslinked resin particles according to claim 1, wherein the polyhydroxyalkanoate-based resin is a poly(3-hydroxyalkanoate)-based resin.

3. 3. The crosslinked resin particles according to claim 1, wherein the crosslinked resin particles are crosslinked using a peroxide.

4. 4. The crosslinked resin particles according to claim 3, wherein the crosslinked resin particles are further crosslinked in the presence of a polyfunctional compound.

5. 3. The crosslinked resin particles according to claim 1, wherein the crosslinked resin particles are not foamed.

6. 3. The crosslinked resin particles according to claim 1, wherein the proportion of said polyhydroxyalkanoate-based resin in said crosslinked resin particles is 80% by weight or more.

7. 3. The crosslinked resin particles according to claim 1, wherein the gel fraction is from 70 to 100%.

8. 3. An aqueous dispersion comprising the crosslinked resin particles according to claim 1 or 2 dispersed in an aqueous medium.

9. A method for producing the crosslinked resin particles according to claim 1 or 2, comprising the steps of: A method for producing a polyhydroxyalkanoate-based resin, the method comprising the step of crosslinking the polyhydroxyalkanoate-based resin in the presence of a peroxide in an aqueous dispersion of the polyhydroxyalkanoate-based resin particles.

10. The crosslinked resin particles are crosslinked using only peroxide or in the presence of peroxide and a polyfunctional compound, 3. The crosslinked resin particle according to claim 1, wherein the polyfunctional compound has at least one group selected from the group consisting of a vinyl group, an allyl group, an acryloyl group, and a methacryloyl group.

11. The crosslinked resin particles according to claim 1 or 2, wherein the volume average particle diameter is measured while the crosslinked resin particles are dispersed in an aqueous solvent.

12. The poly(3-hydroxyalkanoate) resin contains a 3-hydroxybutanoic acid repeat unit, 3. The crosslinked resin particles according to claim 2, wherein the composition ratio of the 3-hydroxybutanoic acid repeating units is 60 to 99 mol % in 100 mol % of all monomer repeating units of the poly(3-hydroxyalkanoate) resin.

13. Crosslinked resin particles as described in claim 1 or 2, wherein the crosslinked resin particles are solidified.

14. The crosslinked resin particles according to claim 7, wherein the gel fraction is 85% or more.

15. Crosslinked resin particles as described in claim 1 or 2, wherein the volume average particle diameter is 5 μm or less.

16. A step of preparing an aqueous dispersion of polyhydroxyalkanoate resin particles in which polyhydroxyalkanoate resin particles are dispersed in water; adding a peroxide to the aqueous dispersion of the polyhydroxyalkanoate-based resin particles to impregnate the polyhydroxyalkanoate-based resin particles with the peroxide; and The method according to claim 9, further comprising the step of heating the aqueous dispersion of the polyhydroxyalkanoate resin particles impregnated with the peroxide to crosslink the polyhydroxyalkanoate resin.

17. The manufacturing method described in claim 16, wherein in the preparation step, a polyhydroxyalkanoate resin-producing microorganism is cultured to accumulate the polyhydroxyalkanoate resin within the bacterial cells, the bacterial cells in the culture solution are destroyed to separate and remove the bacterial components, and then the resulting solution is optionally concentrated or diluted to obtain an aqueous dispersion of the polyhydroxyalkanoate resin particles.