JP2023110156A - Biodegradable resin composition - Google Patents

Abstract

To provide a biodegradable resin composition that has a biodegradation rate controlled for delayed biodegradation without a significant change in physical properties.SOLUTION: A biodegradable resin composition comprises 1.0-5.3 pts.mass of borate hydrate relative to 100 pts.mass of a biodegradable resin.SELECTED DRAWING: Figure 1

Description

The present invention relates to biodegradable resin compositions.

In recent years, concerns about ecological and environmental pollution due to marine disposal of plastic products have become apparent. In countries around the world, various regulations are being enacted from the viewpoint of environmental pollution prevention. For example, in Europe, regulations and laws are being enacted banning the use of single-use plastic shopping bags and single-use plastic container cups and plates in retail. Products that can be composted at home (home compostable products) are required to be exempt from the use prohibition measures of this law. ). Recently, there is a growing demand for marine biodegradable plastic products that can be decomposed even in the sea.

Conventionally, biodegradable plastics (biodegradable resins) include polybutylene terephthalate/adipate (hereinafter abbreviated as PBAT), polylactic acid (hereinafter abbreviated as PLA), and polybutylene succinate (hereinafter abbreviated as PLA). PBS), polybutylene succinate/adipate (hereinafter abbreviated as PBSA), polyhydroxyalkanoate (hereinafter abbreviated as PHA), and the like are known. Furthermore, PHA includes poly(3-hydroxybutyrate) (hereinafter abbreviated as PHB), poly(3-hydroxybutyrate/3-hydroxyvalerate) (hereinafter abbreviated as PHBV), poly(3-hydroxy butyrate/3-hydroxyhexanoate) (hereinafter abbreviated as PHBH), poly(3-hydroxybutyrate/4-hydroxybutyrate), and the like.

These resins not only have different biodegradation speeds and decomposition rates, but also have different mechanical properties such as tensile elongation at break and flexural modulus. Each resin is combined or mixed with other secondary materials and additives according to the needs.

Biodegradable resin products are completely biodegradable in the natural world and in composting equipment, but on the other hand, they need to retain functions (for example, mechanical strength) that endure use during use. Therefore, there is a demand for a technique for controlling the biodegradation rate depending on the place of use, period of use, application, and the like.
Especially in agriculture, fisheries, civil engineering materials, etc., which are used outdoors, the usage environment is diverse. could not fully fulfill its purpose. Therefore, there has been a need for a technique for delaying the biodegradation rate beyond that of conventional biodegradable resins.

Patent Document 1 discloses a biodegradable agricultural plastic sheet in which the entire sheet is made of a biodegradable plastic, in which the biodegradation rate is slower at both side edges in the width direction of the sheet than at the center of the sheet. A degradable agricultural plastic sheet is disclosed, and Patent Document 2 discloses a sheet that is partially thickened, partially coated with a non-biodegradable resin or a slow biodegradable resin, and partially non-biodegradable Parts with a slow biodegradation rate are removed by methods such as bonding, fusing, two-color molding, or co-extrusion molding of biodegradable resins or resins with a slow biodegradation rate, and partially applying or adding bactericides or antifungal agents. An agricultural film is disclosed.
In addition, Patent Document 3 discloses a biodegradable resin composition containing an aliphatic polyester, starch, and an aliphatic aromatic polyester and having a controlled decomposition rate, and Patent Document 4 discloses an inorganic antibacterial agent Disclosed is a biodegradable resin composition whose biodegradation rate is controlled by containing

JP-A-9-107808 Japanese Unexamined Patent Application Publication No. 2001-17008 Japanese Patent Application Laid-Open No. 2008-13602 JP-A-5-117507

According to the conventional techniques (Patent Documents 1 and 2) in which the molded body is partially thickened, it is possible to maintain the required strength for a certain period of time, but physical properties such as flexibility are inferior to the molded body with the original thickness. As it changes, the weight also increases, so there were concerns that the original performance could not be maintained and the cost would increase.

As in Patent Document 3, according to the technique of combining with a slow biodegradable resin, biodegradation can be delayed compared to the original biodegradable resin. There was a possibility that the physical properties would fluctuate greatly.
In addition, as in Patent Document 4, according to the technique of blending a bactericide or an antibacterial agent, it is possible to adjust the biodegradation rate without changing the physical properties so much, but these bactericides and antibacterial agents include: Compounds and heavy metals that do not originally exist in nature are released into the environment, so even after the biodegradable resin is biodegraded, only these remain in the soil and soil, and there is a risk of adversely affecting the ecosystem. there were.

The present invention has been made in view of this background, and the biodegradation rate is adjusted so that the biodegradation is delayed without significantly changing physical properties such as mechanical properties and flexibility of the biodegradable resin itself. , to provide a biodegradable resin composition that finally biodegrades completely and a molded product thereof.

The present inventors have made intensive studies to solve the above problems, and found that the biodegradation rate can be adjusted so as to delay biodegradation by adding a specific amount of borate hydrate to the biodegradable resin. The present invention has been achieved.

That is, the gist of the present invention resides in the following [1] to [5].
[1] A biodegradable resin composition containing 1.0 to 5.3 parts by mass of a borate hydrate per 100 parts by mass of a biodegradable resin.
[2] The biodegradable resin composition according to [1], wherein the borate hydrate is sodium tetraborate hydrate.
[3] The biodegradable resin composition according to [2], wherein the sodium tetraborate hydrate has a hydration number of 5 to 10. However, the hydration number is the value _of n when the composition formula of sodium tetraborate _hydrate is expressed in the _form of _Na2B4O7.nH2O .
[4] The biodegradable resin composition according to any one of [1] to [3], wherein the biodegradable resin is an aliphatic polyester resin.
[5] The biodegradable resin composition according to [4], wherein the aliphatic polyester-based resin is a polyester containing a structural unit derived from an aliphatic diol and a structural unit derived from an aliphatic dicarboxylic acid as a main component. thing.

According to the present invention, a biodegradable resin composition that can adjust the biodegradation rate so as to delay biodegradation without significantly changing the physical properties of the biodegradable resin itself, and finally biodegrades. goods are provided.

1 is a graph showing the relationship between elapsed days and weight retention in biodegradability tests of Example 1 and Comparative Examples 1 and 2 of the present invention.

Embodiments of the present invention will be described in detail below.
The present invention is not limited to the following description, and can be arbitrarily modified without departing from the gist of the present invention. In this specification, when a numerical value or a physical property value is sandwiched before and after the "~", it is used to include the values before and after it.

[Borate hydrate]
The biodegradable resin composition of the present invention is characterized by containing a certain amount of borate hydrate relative to the biodegradable resin.

Boric acid and its salts are substances that are originally widely distributed in the soil and sea in the natural world (see, for example, "Environmental Health Criteria No. 204 Boron"). Borate is also an essential trace element for plants, and is defined as a "boronous fertilizer" in the official fertilizer standards established by the Ministry of Agriculture, Forestry and Fisheries. Therefore, even if the borate component is gradually released into the environment from the biodegradable resin composition of the present invention, it is considered that the adverse effect on the environment is extremely small.

Borate-constituting anions undergo dehydration condensation to form various polyborate ions such as triborate, tetraborate, and pentaborate. These salts of polyboric acid and boric acid are collectively referred to as borates. Salts of boric acid and polyboric acid are hydrolyzed in water to enter an equilibrium state with tetrahydroxyborate ions [B(OH) ₄ ⁻ ] and boric acid [B(OH) ₃ ]. Therefore, the borate hydrate contained in the biodegradable resin composition of the present invention is not particularly limited as long as it is essentially a salt composed of borate ions or polyborate ions.

Examples of cations that constitute borates include sodium ions, potassium ions, lithium ions, magnesium ions, calcium ions, and ammonium ions. Among them, sodium salts are preferable because they are inexpensive, have low environmental toxicity, and borate salts are easily soluble in water.

Sodium tetraborate hydrate is preferred as the sodium borate. Among them, sodium _tetraborate decahydrate [ _{Na2B4O7.10H2O} ] ( _{borax )} is most preferred.

The borate contained in the biodegradable resin composition of the present invention is characterized by having water of hydration. A borate containing water of hydration releases water of crystallization when melt-kneaded with a biodegradable resin, causing crystal grains to collapse. can be uniformly finely dispersed. Therefore, even when molded into a film or fiber, a molded article having good mechanical properties, appearance and feel can be obtained.
For example, when the composition formula of sodium tetraborate is Na ₂ B ₄ O ₇ ·nH ₂ O and the hydration number n is 10 (decahydrate), water of crystallization is released at 62° C. or higher. It melts and releases water of crystallization below 200° C. for n in the range of 5-10. On the other hand, when n=0 (anhydride), the melting point is 742° C., and the crystal grains remain in their original shape even after melt-kneading, so that a good compact cannot be obtained. Therefore, the value of n is preferably 5-10.

The amount of borate hydrate contained in the biodegradable resin composition of the present invention is 1.0 to 5.3 parts by mass with respect to 100 parts by mass of the biodegradable resin. When the borate hydrate content is 1.0 parts by mass or more, the biodegradation retarding effect can be obtained. On the other hand, when the amount exceeds 5.3 parts by mass, foaming due to released moisture and reduction in molecular weight due to hydrolysis during kneading and molding may occur, and a molded product with good physical properties and appearance may not be obtained. By adjusting the blending amount within this range, the biodegradation rate can be adjusted according to the purpose and place of use of the molded article.

[Biodegradable resin]
The biodegradable resin contained in the biodegradable resin composition is a biodegradable plastic, and conventionally known biodegradable plastics can be used.
The biodegradable resin may be a polyester containing structural units derived from a diol and a structural unit derived from a dicarboxylic acid as main structural components, or may be an aliphatic oxycarboxylic acid resin (C). The "main structural unit" is usually a structural unit whose structural unit is contained in the polyester resin in an amount of 80% by mass or more, and may be 90% by mass or more, and a structural unit other than the main structural unit is It may be not contained at all, ie 100% by weight.

The polyester containing structural units derived from diols and structural units derived from dicarboxylic acid as main constituents is not particularly limited, but aliphatic polyester resin (A), aliphatic - aromatic polyester resin (B) is mentioned.
Two or more of the aliphatic polyester resin (A) and the aliphatic-aromatic polyester resin (B) may be mixed and used.

Each biodegradable resin is described below.
Incidentally, the aliphatic polyester resin (A) and the aliphatic - aromatic polyester resin (B) are polymers each having repeating units, but each repeating unit is a compound derived from each repeating unit. Also called a compound unit for For example, a repeating unit derived from an aliphatic diol is an "aliphatic diol unit", a repeating unit derived from an aliphatic dicarboxylic acid is an "aliphatic dicarboxylic acid unit", and a repeating unit derived from an aromatic dicarboxylic acid is an "aromatic dicarboxylic acid unit". Also called "acid unit".

<Aliphatic polyester resin (A)>
As the aliphatic polyester-based resin (A), an aliphatic polyester-based resin containing an aliphatic diol unit and an aliphatic dicarboxylic acid unit as main structural units is preferable.

The aliphatic polyester-based resin (A) preferably has succinic acid units, and more preferably the proportion of succinic acid units in all dicarboxylic acid units is 5 mol % or more and 100 mol % or less. The aliphatic polyester-based resin (A) may be a mixture of aliphatic polyester-based resins having different amounts of succinic acid units. containing only succinic acid units as) and an aliphatic polyester resin containing an aliphatic dicarboxylic acid unit other than succinic acid are blended, and the amount of succinic acid units in the aliphatic polyester resin (A) can be adjusted within the above preferred range.

More specifically, the aliphatic polyester resin (A) is a polyester resin containing an aliphatic diol unit represented by the following formula (1) and an aliphatic dicarboxylic acid unit represented by the following formula (2) is.
-OR ¹ -O- (1)
-OC-R ² -CO- (2)

In formula (1), R ¹ represents a divalent aliphatic hydrocarbon group. In formula (2) above, R ² represents a divalent aliphatic hydrocarbon group. The aliphatic diol units and aliphatic dicarboxylic acid units represented by the above formulas (1) and (2) may be derived from compounds derived from petroleum or from compounds derived from plant materials. No, but preferably derived from compounds derived from plant sources.

When the aliphatic polyester resin (A) is a copolymer, even if two or more aliphatic diol units represented by formula (1) are contained in the aliphatic polyester resin (A) Well, the aliphatic polyester resin (A) may contain two or more kinds of aliphatic dicarboxylic acid units represented by the formula (2).

As described above, the aliphatic dicarboxylic acid units represented by formula (2) preferably contain 5 mol % or more and 100 mol % or less of succinic acid units with respect to all dicarboxylic acid units. By setting the amount of succinic acid constitutional units in the aliphatic polyester resin (A) within the predetermined range, it is possible to obtain a biodegradable resin composition with improved moldability and excellent heat resistance and degradability. becomes. For the same reason, the amount of succinic acid units in the aliphatic polyester resin (A) is preferably 10 mol% or more, more preferably 50 mol% or more, and still more preferably 64 mol% or more with respect to all dicarboxylic acid units. , particularly preferably 68 mol % or more.
Hereinafter, the ratio of succinic acid units to all dicarboxylic acid units in the aliphatic polyester resin (A) may be referred to as "amount of succinic acid units".

In addition, the aliphatic dicarboxylic acid unit represented by the formula (2) contains 5 mol% or more and 50 mol% or less of the total dicarboxylic acid units of one or more kinds of aliphatic dicarboxylic acid units in addition to succinic acid. more preferably. By copolymerizing an aliphatic dicarboxylic acid unit other than succinic acid within the predetermined range, the crystallinity of the aliphatic polyester resin (A) can be lowered, and the biodegradation rate can be increased. . For the same reason, the amount of aliphatic dicarboxylic acid units other than succinic acid in the aliphatic polyester resin (A) is preferably 10 mol% or more and 45 mol% or less with respect to all dicarboxylic acid units, more preferably It is 15 mol % or more and 40 mol % or less.

The aliphatic diol that gives the diol unit represented by formula (1) is not particularly limited, but from the viewpoint of moldability and mechanical strength, aliphatic diols having 2 to 10 carbon atoms are preferable, and 4 or more carbon atoms. Aliphatic diols of 6 or less are particularly preferred. Examples include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, etc. Among them, 1,4-butanediol is particularly preferred. Two or more kinds of the aliphatic diols may be used.

The aliphatic dicarboxylic acid component that provides the aliphatic dicarboxylic acid unit represented by formula (2) is not particularly limited, but aliphatic dicarboxylic acids having 2 to 40 carbon atoms and derivatives thereof such as alkyl esters are preferable. Aliphatic dicarboxylic acids having 4 to 10 carbon atoms and their derivatives such as alkyl esters are particularly preferred. Examples of aliphatic dicarboxylic acids having 2 to 40 carbon atoms other than succinic acid and derivatives such as alkyl esters thereof include adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, and alkyl esters thereof. Among them, adipic acid and sebacic acid are preferred, and adipic acid is particularly preferred. Two or more types of the aliphatic dicarboxylic acid components may be used, and in this case, a combination of succinic acid and adipic acid is preferred.

Aliphatic polyester resin (A) is a repeating unit derived from an aliphatic oxycarboxylic acid (
aliphatic oxycarboxylic acid unit). Specific examples of aliphatic oxycarboxylic acid components that provide aliphatic oxycarboxylic acid units include lactic acid, glycolic acid, 2-hydroxy-n-butyric acid, 2-hydroxycaproic acid, 6-hydroxycaproic acid, 2-hydroxy -3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-hydroxyisocaproic acid, 6-hydroxycaproic acid, etc., or derivatives such as lower alkyl esters or intramolecular esters thereof. When optical isomers exist in these compounds, they may be D-, L-, or racemic, and may be solid, liquid, or aqueous solution. Among these, lactic acid or glycolic acid or derivatives thereof are particularly preferred. These aliphatic oxycarboxylic acids may be used alone or as a mixture of two or more.

When the aliphatic polyester-based resin (A) contains these aliphatic oxycarboxylic acid units, the content thereof is, from the viewpoint of moldability, 100 mol% of all structural units constituting the aliphatic polyester-based resin (A). is preferably 20 mol % or less, more preferably 10 mol % or less, still more preferably 5 mol % or less, and most preferably 0 mol % (not included).

In addition, the aliphatic polyester resin (A) is a trifunctional or higher aliphatic polyhydric alcohol, a trifunctional or higher aliphatic polycarboxylic acid or an acid anhydride thereof, or a trifunctional or higher aliphatic polyoxycarboxylic acid component. The melt viscosity may be increased by copolymerizing the.

Specific examples of trifunctional aliphatic polyhydric alcohols include trimethylolpropane and glycerin, and specific examples of tetrafunctional aliphatic polyhydric alcohols include pentaerythritol. These may be used alone or in combination of two or more.
Specific examples of trifunctional aliphatic polycarboxylic acids or acid anhydrides thereof include propanetricarboxylic acid or acid anhydrides thereof, and specific examples of tetrafunctional polycarboxylic acids or acid anhydrides thereof include: cyclopentanetetracarboxylic acid or its acid anhydride, and the like. These may be used alone or in combination of two or more.

In addition, the trifunctional aliphatic oxycarboxylic acid includes (i) a type having two carboxyl groups and one hydroxyl group in the same molecule, and (ii) a type having one carboxyl group and two hydroxyl groups. Any type can be used, but from the viewpoint of moldability, mechanical strength and molded product appearance, (i) two carboxyl groups and one hydroxyl group such as malic acid are combined in the same molecule. A type having such an acid is preferable, and more specifically, malic acid is preferably used. In addition, the tetrafunctional aliphatic oxycarboxylic acid component has (i) a type in which three carboxyl groups and one hydroxyl group are shared in the same molecule, (ii) two carboxyl groups and two hydroxyl groups. and (iii) a type in which three hydroxyl groups and one carboxyl group are shared in the same molecule. Those having more than one are preferable, and more specific examples include citric acid, tartaric acid, and the like. These may be used alone or in combination of two or more.

When the aliphatic polyester resin (A) contains such structural units derived from trifunctional or higher functional components, the content thereof is 100 mol% of the total structural units constituting the aliphatic polyester resin (A), The lower limit is usually 0 mol % or more, preferably 0.01 mol % or more, and the upper limit is usually 5 mol % or less, preferably 2.5 mol % or less.

As the method for producing the aliphatic polyester-based resin (A), a known method for producing polyester can be employed. Moreover, the polycondensation reaction at this time is not particularly limited, as it is possible to set appropriate conditions that have been conventionally employed. Usually, a method is adopted in which the degree of polymerization is further increased by carrying out an operation under reduced pressure after allowing the esterification reaction to proceed.

When the diol component forming the diol unit and the dicarboxylic acid component forming the dicarboxylic acid unit are reacted during the production of the aliphatic polyester resin (A), the produced aliphatic polyester resin (A) is the target The usage amounts of the diol component and the dicarboxylic acid component are set so as to have a composition of Usually, the diol component and the dicarboxylic acid component are reacted in substantially equimolar amounts, but since the diol component distills out during the esterification reaction, it is usually 1 to 20 mol % in excess of the dicarboxylic acid component. Used.

When the aliphatic polyester resin (A) contains components (optional components) other than essential components such as aliphatic oxycarboxylic acid units and polyfunctional component units, the aliphatic oxycarboxylic acid units and polyfunctional component units are also included. The corresponding compounds (monomers and oligomers) are subjected to the reaction so as to obtain the desired composition. At this time, there are no restrictions on the timing and method of introducing the above optional components into the reaction system, and they are optional as long as the aliphatic polyester resin (A) can be produced.

For example, the timing and method of introducing the aliphatic oxycarboxylic acid into the reaction system is not particularly limited as long as it is before the polycondensation reaction between the diol component and the dicarboxylic acid component. (2) a method in which the catalyst is introduced into the reaction system at the time of charging the raw materials and mixed at the same time;

As for the timing of introduction of the compound forming the polyfunctional component unit, it may be charged at the same time as other monomers or oligomers in the initial stage of polymerization, or may be charged before starting pressure reduction after the transesterification reaction, but other monomers may be introduced. In terms of simplification of the process, it is preferable to charge simultaneously with or oligomer.

Aliphatic polyester resin (A) is usually produced in the presence of a catalyst. As the catalyst, any catalyst that can be used in the production of known polyester-based resins can be arbitrarily selected as long as the effects of the present invention are not significantly impaired. Metal compounds such as germanium, titanium, zirconium, hafnium, antimony, tin, magnesium, calcium, and zinc are suitable. Among them, germanium compounds and titanium compounds are preferable.

Germanium compounds that can be used as catalysts include, for example, organic germanium compounds such as tetraalkoxygermanium, and inorganic germanium compounds such as germanium oxide and germanium chloride. Among them, germanium oxide, tetraethoxygermanium, tetrabutoxygermanium, and the like are preferable in terms of price and availability, and germanium oxide is particularly preferable.

Examples of titanium compounds that can be used as catalysts include organic titanium compounds such as tetraalkoxy titanium such as tetrapropyl titanate, tetrabutyl titanate, tetraphenyl titanate and the like. Among them, tetrapropyl titanate, tetrabutyl titanate, and the like are preferable in terms of price and availability.

In addition, other catalysts may be used in combination as long as the object of the present invention is not impaired. In addition, a catalyst may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

The amount of the catalyst used is arbitrary as long as it does not significantly impair the effects of the present invention. % by mass or less, preferably 1.5% by mass or less. Below the lower limit of this range, the effect of the catalyst may not appear, and above the upper limit, the production cost may increase, the resulting polymer may be markedly colored, and the hydrolysis resistance may decrease.

The introduction timing of the catalyst is not particularly limited as long as it is before the polycondensation reaction, and it may be introduced at the time of charging the raw materials or at the start of depressurization. When introducing an aliphatic oxycarboxylic acid unit, either introduce it at the same time as a monomer or oligomer that forms an aliphatic oxycarboxylic acid unit such as lactic acid or glycolic acid at the time of raw material charging, or dissolve the catalyst in an aqueous aliphatic oxycarboxylic acid solution. A method of dissolving the catalyst in an aqueous aliphatic oxycarboxylic acid solution and introducing the catalyst is particularly preferable because the rate of polymerization increases.

Reaction conditions such as temperature, polymerization time, and pressure when producing the aliphatic polyester-based resin (A) are arbitrary as long as they do not significantly impair the effects of the present invention. And/or the reaction temperature of the transesterification reaction has a lower limit of usually 150° C. or higher, preferably 180° C. or higher, and an upper limit of usually 260° C. or lower, preferably 250° C. or lower. Moreover, the reaction atmosphere is usually an inert atmosphere such as nitrogen or argon. Furthermore, the reaction pressure is usually from normal pressure to 10 kPa, with normal pressure being preferred. The reaction time has a lower limit of generally 1 hour or longer and an upper limit of generally 10 hours or shorter, preferably 6 hours or shorter, and more preferably 4 hours or shorter. If the reaction temperature is too high, excessive formation of unsaturated bonds may occur, and gelation may occur due to the unsaturated bonds, making it difficult to control the polymerization.

Further, in the polycondensation reaction after the ester reaction and/or transesterification reaction between the dicarboxylic acid component and the diol component, the lower limit of the pressure is usually 0.01×10 ³ Pa or more, preferably 0.03×10 ³ Pa or more. , the upper limit of which is usually 1.4×10 ³ Pa or less, preferably 0.4×10 ³ Pa or less. As for the reaction temperature at this time, the lower limit is usually 150° C. or higher, preferably 180° C. or higher, and the upper limit is usually 260° C. or lower, preferably 250° C. or lower. Furthermore, the lower limit of the reaction time is usually 2 hours or more, and the upper limit is usually 15 hours or less, preferably 10 hours or less. If the reaction temperature is too high, excessive formation of unsaturated bonds may cause gelation caused by the unsaturated bonds, making it difficult to control the polymerization.

A chain extender such as a carbonate compound or a diisocyanate compound may be used during the production of the aliphatic polyester resin (A). In this case, the amount of the chain extender is usually 10 as a ratio of carbonate bonds and urethane bonds in the aliphatic polyester resin (A) when the total structural units constituting the aliphatic polyester resin are 100 mol%. mol % or less, preferably 5 mol % or less, more preferably 3 mol % or less. However, if a urethane bond or a carbonate bond is present in the aliphatic polyester resin (A), biodegradability may be inhibited. The carbonate bond is less than 1 mol%, preferably 0.5 mol% or less, more preferably 0.1 mol% or less, and the urethane bond is 0.55 mol% or less, preferably 0.3 mol% or less, more preferably is 0.12 mol % or less, more preferably 0.05 mol % or less. This amount is 0.9 parts by mass or less, preferably 0.5 parts by mass or less, more preferably 0.2 parts by mass or less, still more preferably 0 parts by mass when converted to 100 parts by mass of the aliphatic polyester resin (A). .1 part by mass or less. In particular, if the amount of urethane bonds exceeds the above upper limit, the decomposition of the urethane bonds in the film forming process, etc., may cause problems such as smoke and odor from the molten film from the die outlet. In some cases, film breakage due to foaming may occur and stable molding may not be possible.
The amount of carbonate bonds and the amount of urethane bonds in the aliphatic polyester-based resin (A) can be obtained by calculation from NMR measurement results such as ¹ H-NMR and ¹³ C-NMR.

Specific examples of the carbonate compound as the chain extender include diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, and ethylene carbonate. , diamyl carbonate, dicyclohexyl carbonate and the like. In addition, carbonate compounds composed of the same or different hydroxy compounds derived from hydroxy compounds such as phenols and alcohols can also be used.

Specific examples of diisocyanate compounds include 2,4-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, tetramethylxylylene diisocyanate, 2,4,6-triisopropylphenyl diisocyanate, 4,4'-diphenylmethane diisocyanate, tolidine diisocyanate, etc. are exemplified by the known diisocyanates of

Other chain extenders such as dioxazolines and silicate esters may also be used.
Specific examples of silicate esters include tetramethoxysilane, dimethoxydiphenylsilane, dimethoxydimethylsilane, and diphenyldihydroxysilane.

High-molecular-weight polyester resins using these chain extenders (coupling agents) can also be produced using conventional techniques. After completion of the polycondensation, the chain extender is added to the reaction system in a uniform molten state without a solvent, and reacted with the polyester obtained by the polycondensation.

More specifically, a terminal group obtained by catalytically reacting a diol component and a dicarboxylic acid component has substantially a hydroxyl group, and has a weight average molecular weight (Mw) of 20,000 or more, preferably 40,000. By reacting the above polyester with the chain extender, a polyester resin having a higher molecular weight can be obtained. Prepolymers with a weight-average molecular weight of 20,000 or more can be used with a small amount of a chain extender even under severe conditions such as a molten state. Molecular weight polyester resins can be produced. Here, the weight-average molecular weight (Mw) of the polyester-based resin is obtained as a value converted to monodisperse polystyrene from a value measured by gel permeation chromatography (GPC) at a measurement temperature of 40° C. using chloroform as a solvent.

Therefore, for example, when the diisocyanate compound described above is used as a chain extender to further increase the molecular weight of the polyester resin, a prepolymer having a weight average molecular weight of 20,000 or more, preferably 40,000 or more can be used. preferable. If the weight-average molecular weight is less than 20,000, the amount of the diisocyanate compound used to increase the molecular weight is increased, which may result in a decrease in heat resistance. Using such a prepolymer, a polyester resin having a urethane bond having a linear structure linked via a urethane bond derived from a diisocyanate compound is produced.

The pressure during chain extension is usually 0.01 MPa or more and 1 MPa or less, preferably 0.05 MPa or more and 0.5 MPa or less, more preferably 0.07 MPa or more and 0.3 MPa or less, but normal pressure is most preferable.

Regarding the reaction temperature during chain extension, the lower limit is usually 100°C or higher, preferably 150°C or higher, more preferably 190°C or higher, most preferably 200°C or higher, and the upper limit is usually 250°C or lower, preferably 240°C or lower. More preferably, it is 230° C. or less. If the reaction temperature is too low, the viscosity will be high, making uniform reaction difficult and high stirring power will be required.

The chain extension time has a lower limit of usually 0.1 minute or more, preferably 1 minute or more, more preferably 5 minutes or more, and an upper limit of usually 5 hours or less, preferably 1 hour or less, more preferably 30 minutes or less. , most preferably 15 minutes or less. If the chain extension time is too short, the effect of adding the chain extender tends not to be exhibited, and if it is too long, the polyester resin tends to gel or decompose.

The molecular weight of the aliphatic polyester resin (A) can be measured by gel permeation chromatography (GPC). It is preferably 20,000 or more and 500,000 or less, more preferably 50,000 or more and 400,000 or less, because it is advantageous in moldability and mechanical strength.

The melt flow rate (MFR) of the aliphatic polyester-based resin (A) is a value measured at 190° C. and a load of 2.16 kg based on JIS K7210 (1999), and is usually 0.1 g/10 min or more and 100 g/10 minutes or less, preferably 50 g/10 minutes or less, particularly preferably 40 g/10 minutes or less, from the viewpoint of moldability and mechanical strength. The MFR of the aliphatic polyester-based resin (A) can be adjusted by the molecular weight.

The melting point of the aliphatic polyester resin (A) is preferably 70°C or higher, more preferably 75°C or higher, and preferably 170°C or lower, more preferably 150°C or lower, and particularly preferably lower than 130°C. . When there are multiple melting points, at least one melting point is preferably within the above range.
Further, the elastic modulus of the aliphatic polyester resin (A) is preferably 180-1000 MPa.
If the melting point is outside the above range, moldability is poor, and if the elastic modulus is less than 180 MPa, problems with moldability tend to occur.

The method of adjusting the melting point and elastic modulus of the aliphatic polyester resin (A) is not particularly limited. Adjustments can be made by adjusting or combining them.

The aliphatic polyester resin (A) is not limited to one type, and two or more types of aliphatic polyester resins (A) having different constitutional unit types, constitutional unit ratios, production methods, physical properties, etc. can be blended and used.

<Aliphatic-aromatic polyester resin (B)>
As the aliphatic-aromatic polyester resin (B), at least part of the repeating units of the above-mentioned aliphatic polyester resin (A) is replaced with an aromatic compound unit, preferably the above-mentioned aliphatic A polyester containing an aliphatic diol unit, an aliphatic dicarboxylic acid unit and an aromatic dicarboxylic acid unit as main structural units, in which a part of the aliphatic dicarboxylic acid units of the polyester resin (A) is replaced with an aromatic dicarboxylic acid unit system resin is exemplified.

Examples of the aromatic compound unit include an aromatic diol unit having an optionally substituted aromatic hydrocarbon group, and an aromatic dicarboxylic acid having an optionally substituted aromatic hydrocarbon group. unit, an aromatic dicarboxylic acid unit having an optionally substituted aromatic heterocyclic group, an aromatic oxycarboxylic acid unit having an optionally substituted aromatic hydrocarbon group, and the like. . The aromatic hydrocarbon group and aromatic heterocyclic group may be monocyclic, or may be a combination of multiple rings bonded or condensed. Specific examples of the aromatic hydrocarbon group include 1,2-phenylene group, 1,3-phenylene group, 1,4-phenylene group, dinaphthylene group, diphenylene group and the like. A specific example of the aromatic heterocyclic group includes a 2,5-furandyl group.

Specific examples of aromatic dicarboxylic acid components that provide aromatic dicarboxylic acid units include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, and 2,5-furandicarboxylic acid. Among them, terephthalic acid is preferred.

The aromatic dicarboxylic acid component may be a derivative of an aromatic dicarboxylic acid compound. For example, derivatives of the aromatic dicarboxylic acid components exemplified above are preferable, and among them, lower alkyl esters having 1 to 4 carbon atoms, acid anhydrides, and the like can be mentioned. Specific examples of derivatives of aromatic dicarboxylic acid compounds include lower alkyl esters such as methyl esters, ethyl esters, propyl esters and butyl esters of the aromatic dicarboxylic acid components exemplified above; aromatic dicarboxylic acids exemplified above such as succinic anhydride. Cyclic acid anhydrides of acid components; and the like. Among them, dimethyl terephthalate is preferred.

Specific examples of aromatic diol components that provide aromatic diol units include xylylene glycol, 4,4′-dihydroxybiphenyl, 2,2-bis(4′-hydroxyphenyl)propane, 2,2-bis( 4'-β-hydroxyethoxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, bis(4-β-hydroxyethoxyphenyl)sulfonic acid and the like. The aromatic diol component may be a derivative of an aromatic diol compound. A compound having a structure in which a plurality of aliphatic diol compounds and/or aromatic diol compounds are dehydrated and condensed with each other may also be used.

Specific examples of aromatic oxycarboxylic acid components that give aromatic oxycarboxylic acid units include p-hydroxybenzoic acid and p-β-hydroxyethoxybenzoic acid. The aromatic oxycarboxylic acid component may be a derivative of an aromatic oxycarboxylic acid compound. It may also be a compound (oligomer) having a structure in which a plurality of aliphatic oxycarboxylic acid compounds and/or aromatic oxycarboxylic acid compounds are dehydrated and condensed with each other. That is, an oligomer may be used as the raw material.

When optical isomers exist in the aromatic compound components that provide these aromatic compound units, any of the D-, L-, and racemic isomers may be used. Further, the aromatic compound component is not limited to the above examples as long as it can provide aromatic compound units. Furthermore, one aromatic compound component may be used alone, or two or more thereof may be used in any combination and ratio.

As the aliphatic-aromatic polyester resin (B), it is preferable to use an aromatic dicarboxylic acid component as a component that provides aromatic compound units. It is preferably 10 mol % or more and 80 mol % or less based on the total amount of units and aromatic dicarboxylic acid units (100 mol %). Further, it is preferable to use terephthalic acid or 2,5-furandicarboxylic acid as the aromatic dicarboxylic acid component. In that case, the aliphatic-aromatic polyester resin (B) is polybutylene terephthalate adipate and/or polybutylene. A terephthalate succinate resin is preferred. Polybutylene-2,5-furandicarboxylate-based resins are also preferred as the aliphatic-aromatic polyester-based resin (B).

The aliphatic-aromatic polyester resin (B) can be produced in the same manner as the above-described aliphatic polyester resin (A) using at least an aromatic compound component as a starting material.

The molecular weight of the aliphatic-aromatic polyester resin (B) can be measured by gel permeation chromatography (GPC), and the weight average molecular weight (Mw) using monodisperse polystyrene as a standard is usually 10,000 or more and 1,000,000 or less, but since it is advantageous in terms of moldability and mechanical strength, it is preferably 30,000 or more and 800,000 or less, more preferably 50,000 or more and 600,000 or less. .

The melt flow rate (MFR) of the aliphatic-aromatic polyester resin (B) is JIS
Based on K7210 (1999), the value measured at 190 ° C. and a load of 2.16 kg is usually 0.1 g / 10 minutes or more and 100 g / 10 minutes or less, but from the viewpoint of moldability and mechanical strength, preferably 50 g /10 minutes or less, particularly preferably 30 g/10 minutes or less. The MFR of the aliphatic-aromatic polyester resin (B) can be adjusted by the molecular weight.

The melting point of the aliphatic-aromatic polyester resin (B) is usually 60°C or higher, preferably 70°C or higher, more preferably 80°C or higher, and preferably 150°C or lower, more preferably 140°C. Below, it is 120 degrees C or less especially preferably. When there are multiple melting points, at least one melting point is preferably within the above range.
The elastic modulus of the aliphatic-aromatic polyester resin (B) is preferably 180-1000 MPa.
If the melting point is outside the above range, moldability is poor, and if the elastic modulus is less than 180 MPa, problems with moldability tend to occur.

The method of adjusting the melting point and elastic modulus of the aliphatic-aromatic polyester resin (B) is not particularly limited, but for example, the type of copolymerization component of an aliphatic dicarboxylic acid component other than the aromatic dicarboxylic acid component is selected, It can be adjusted by adjusting each copolymerization ratio or by combining them.

The aliphatic-aromatic polyester resin (B) is not limited to one type, and two or more types of aliphatic-aromatic polyester resins (B) having different types of structural units, structural unit ratios, manufacturing methods, physical properties, etc. It can be used by blending.

<Aliphatic oxycarboxylic acid-based resin (C)>
The aliphatic oxycarboxylic acid-based resin (C) has aliphatic oxycarboxylic acid units as main structural units, and the aliphatic oxycarboxylic acid units are preferably represented by the following formula (3).
-OR ³ -CO- (3)
(In formula (3) above, R ³ represents a divalent aliphatic hydrocarbon group or a divalent alicyclic hydrocarbon group.)

Specific examples of the aliphatic oxycarboxylic acid component that gives the aliphatic oxycarboxylic acid unit of formula (3) include lactic acid, glycolic acid, 2-hydroxy-n-butyric acid, 2-hydroxycaproic acid, 2-hydroxy-3, 3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-hydroxyisocaproic acid, 6-hydroxycaproic acid, mixtures thereof, and the like. When optical isomers exist in these compounds, they may be D-isomers or L-isomers. Preferred among these are lactic acid and 6-hydroxycaproic acid. These aliphatic oxycarboxylic acid components can also be used in combination of two or more.

In addition, urethane bonds, amide bonds, carbonate bonds, ether bonds and the like can be introduced into the aliphatic oxycarboxylic acid resin (C) within a range that does not affect biodegradability.

The method for producing the aliphatic oxycarboxylic acid-based resin (C) is not particularly limited, and it can be produced by a known method such as a direct polymerization method of oxycarboxylic acid or a ring-opening polymerization method of a cyclic body.

The molecular weight of the aliphatic oxycarboxylic acid-based resin (C) can be measured by gel permeation chromatography (GPC), and the weight average molecular weight (Mw) using monodisperse polystyrene as a standard substance is usually 10. ,000 or more and 1,000,000 or less, preferably 20,000 or more and 500,000 or less, more preferably 50,000 or more and 400,000 or less, because they are advantageous in terms of moldability and mechanical strength.

The melt flow rate (MFR) of the aliphatic oxycarboxylic acid-based resin (C) is a value measured at 190° C. and a load of 2.16 kg based on JIS K7210 (1999), and is usually 0.1 g/10 min or more and 100 g /10 minutes or less, preferably 50 g/10 minutes or less, particularly preferably 40 g/10 minutes or less from the viewpoint of moldability and mechanical strength. The MFR of the aliphatic oxycarboxylic acid resin (C) can be adjusted by the molecular weight.

The melting point of the aliphatic oxycarboxylic acid resin (C) is preferably 50°C or higher, more preferably 55°C or higher, and preferably 200°C or lower, more preferably 190°C or lower, and particularly preferably less than 180°C. is. When there are multiple melting points, at least one melting point is preferably within the above range.
The elastic modulus of the aliphatic oxycarboxylic acid resin (C) is preferably 180-4000 MPa.
If the melting point is outside the above range, moldability is poor, and if the modulus of elasticity is less than 180 MPa, problems with moldability tend to occur.

The method of adjusting the melting point and elastic modulus of the aliphatic oxycarboxylic acid resin (C) is not particularly limited, but for example, selecting the type of copolymerization component other than the aliphatic oxycarboxylic acid, or adjusting the copolymerization ratio of each or by combining them.

As the aliphatic oxycarboxylic acid-based resin (C), polyhydroxyalkanoate (D) described below can also be preferably used.
Polyhydroxyalkanoate (hereinafter sometimes referred to as PHA) (D) has the general formula: [-CHR-CH ₂ -CO-O-] (wherein R is an alkyl group having 1 to 15 carbon atoms ) and is a copolymer containing a 3-hydroxybutyrate unit as a main structural unit.

Polyhydroxyalkanoate (D) preferably contains 80 mol % or more, more preferably 85 mol % or more, of 3-hydroxybutyrate units as a constituent component from the viewpoint of moldability and thermal stability. Also, those produced by microorganisms are preferred. Specific examples of polyhydroxyalkanoate (D) include poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyvalerate- co-3-hydroxyhexanoate) copolymer resin and the like.
In particular, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin, ie, PHBH, is preferred from the viewpoint of molding processability and physical properties of the resulting molded product.

In the polyhydroxyalkanoate (D), 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) and 3-hydroxyhexanoate (hereinafter, 3
HH), etc.), that is, the monomer ratio in the copolymer resin, from the viewpoint of molding processability and molded product quality, 3-hydroxybutyrate / comonomer = 97/3 ~ It is preferably 80/20 (mol %/mol %), more preferably 95/5 to 85/15 (mol %/mol %). If the comonomer ratio is less than 3 mol %, molding may be difficult because the molding temperature and the thermal decomposition temperature are close to each other. When the comonomer ratio exceeds 20 mol %, the crystallization of the polyhydroxyalkanoate (D) slows down, which may deteriorate the productivity.

Each monomer ratio in the polyhydroxyalkanoate (D) can be measured by gas chromatography as follows.
To about 20 mg of dry PHA, 2 ml of a mixture of sulfuric acid/methanol (15/85 (mass ratio)) and 2 ml of chloroform are added, and the mixture is sealed and heated at 100° C. for 140 minutes to obtain methyl ester of PHA decomposition product. After cooling, 1.5 g of sodium bicarbonate is added little by little to neutralize and allowed to stand until the evolution of carbon dioxide ceases. After adding 4 ml of diisopropyl ether and mixing well, the monomer unit composition of the PHA decomposition product in the supernatant is analyzed by capillary gas chromatography to determine the ratio of each monomer in the copolymer resin.

The weight average molecular weight (hereinafter sometimes referred to as Mw) of the polyhydroxyalkanoate (D) can be measured by the gel permeation chromatography (GPC) described above, using monodisperse polystyrene as a standard substance. The weight average molecular weight (Mw) is usually 200,000 or more and 2,500,000 or less, but is advantageous in terms of moldability and mechanical strength, so it is preferably 250,000 or more and 2,000,000 or less, more It is preferably 300,000 or more and 1,000,000 or less. If the weight-average molecular weight is less than 200,000, the mechanical properties may be poor, and if it exceeds 2,500,000, molding may become difficult.

The melt flow rate (MFR) of the polyhydroxyalkanoate (D) is a value measured at 190°C under a load of 2.16 kg based on JIS K7210 (1999), and is preferably 1 g/10 min or more and 100 g/10 min or less. However, from the viewpoint of moldability and mechanical strength, it is more preferably 80 g/10 minutes or less, particularly preferably 50 g/10 minutes or less. The MFR of polyhydroxyalkanoate (D) can be adjusted by the molecular weight.

The melting point of the polyhydroxyalkanoate (D) is preferably 100°C or higher, more preferably 120°C or higher, and preferably 180°C or lower, more preferably 170°C or lower, particularly preferably lower than 160°C. When there are multiple melting points, at least one melting point is preferably within the above range.

Polyhydroxyalkanoate (D) is, for example, Alcaligenes eutrophus AC32 strain (international deposit based on the Budapest Treaty, international depository authority: National Institute of Advanced Industrial Science and Technology Patent Biological Depositary Center (1-1-1-Central 6, Higashi, Tsukuba City, Ibaraki Prefecture, Japan) Transferred from deposit FERM P-15786)) (J. Bacteriol., 179, 4821 (1997)).

A commercially available product can also be used as the polyhydroxyalkanoate (D). , Kaneka "PHBH X331
N", "PHBH X131A", "PHBH X151A", etc. can be used.

In the present embodiment, the aliphatic oxycarboxylic acid-based resin (C) including the polyhydroxyalkanoate (D) is not limited to one type, and two different types of structural units, structural unit ratios, production methods, physical properties, etc. More than one kind of aliphatic oxycarboxylic acid resin (C) can be blended and used.

<Other ingredients>
In addition to the borate hydrate described above, the biodegradable resin composition contains fillers (fillers), plasticizers, antistatic agents, antioxidants, light stabilizers, ultraviolet absorbers, dyes, pigments, hydrolysis Inhibitors, crystal nucleating agents, anti-blocking agents, weathering agents, heat stabilizers, flame retardants, mold release agents, anti-fogging agents, surface wettability improvers, combustion aids, dispersing aids, various surfactants, slip agents, etc. 1 or 2 or more of various additives may be contained as "other components".
The biodegradable resin composition may also contain a freshness-keeping agent, an antibacterial agent, and the like as functional additives.

These other components can be arbitrarily blended within a range that does not impair the effects of the present invention, and may be used singly or in combination of two or more.

The content of these other components in the biodegradable resin composition usually does not impair the physical properties of the biodegradable resin composition, so the total amount of the other components is It is preferably 0.01% by mass or more and 40% by mass or less with respect to the total amount.

<Method for producing biodegradable resin composition>
The biodegradable resin composition is produced by kneading the biodegradable resin and the borate hydrate in a kneader and dispersing the borate hydrate in the biodegradable resin. Further, other resins and other components used as necessary may be mixed in a kneader together with the borate hydrate and the biodegradable resin.

In this mixing step, the borate hydrate and the biodegradable resin, and other resins and other components that are used as necessary, are mixed in a predetermined ratio at the same time or in any order using a tumbler, V-type blender, Mixing is performed by a mixer such as Nauta mixer, Banbury mixer, kneading roll, extruder, etc., and preferably further melt-kneading.

The kneader used in the mixing step may be a melt kneader. The extruder may be either a twin-screw extruder or a single-screw extruder, but a twin-screw extruder is more preferred.

The temperature during melt-kneading is preferably 140 to 220°C. Within this temperature range, the time required for the melting reaction can be shortened, the deterioration of the resin can be prevented, and practical physical properties such as impact resistance and moist heat resistance can be further improved. can be done. From the same point of view, the melt-kneading temperature is more preferably 150 to 210°C.

In addition, the melt-kneading time should be avoided from the viewpoint of avoiding deterioration of the resin more reliably as described above, and is preferably 20 seconds or more and 20 minutes or less, more preferably 30 seconds. 15 minutes or less. Therefore, it is preferable to set the melt-kneading temperature and time so as to satisfy the melt-kneading conditions.

The borate hydrate is desirably powdered in advance before being mixed with the biodegradable resin. By doing so, the borate hydrate is uniformly dispersed in the biodegradable resin composition, and a molded article having excellent biodegradability and excellent mechanical properties and appearance can be obtained.

Examples of methods for obtaining a powdery borate hydrate include a method of pulverizing with a pulverizer such as a stone mill, cutter mill, jet mill, or crush mill. The particle size of the powdery borate hydrate is usually 2 mm or less, preferably 1.7 mm or less, more preferably 1.5 mm or less, from the viewpoint of being easily mixed uniformly with the biodegradable resin in a short time. is. Various known methods such as sieving can be used to measure the particle size of the borate hydrate.

Since the borate hydrate may change its hydration number due to efflorescence or moisture absorption, it is preferably stored in a sealed state until just before melt-kneading. The hydration number can be appropriately adjusted by a method such as recrystallization from an aqueous solution, exposure to moist or dry air, or drying at a predetermined temperature.
The hydration number can be measured as follows. For example, in the case of sodium tetraborate hydrate, it becomes an anhydride when heated to 350°C or higher, so the amount of weight loss when dried at this temperature to a constant weight is the amount of hydrated water contained. Conceivable. The original hydration number can be obtained by converting the amount of water of hydration into a molar ratio.

[Molded body]
The biodegradable resin composition can be molded by various molding methods applied to general-purpose plastics. Examples of the molding method include compression molding (compression molding, laminate molding, stampable molding), injection molding, extrusion molding and co-extrusion molding (film molding by inflation method or T-die method, laminate molding, pipe molding, wire / cable molding , profiled material molding), hot press molding, blow molding (various blow molding), calendar molding, solid molding (uniaxial stretching molding, biaxial stretching molding, roll rolling molding, stretch orientation nonwoven fabric molding, thermoforming (vacuum molding, air pressure molding) molding), plastic processing, powder molding (rotating molding), various non-woven fabric molding (dry method, adhesion method, entanglement method, spunbond method, etc.), etc. Among them, injection molding, extrusion molding, compression molding, or hot press Molding, especially extrusion molding or injection molding, is preferably applied, and as specific shapes, application to sheets, films and fibers is preferred.

In addition, the biodegradable resin molding obtained by molding the biodegradable resin composition has chemical functions, electrical functions, magnetic functions, mechanical functions, friction/wear/lubricating functions, optical functions, heat It is also possible to perform various secondary processing for the purpose of imparting surface functions such as biocompatibility and biocompatibility. Examples of secondary processing include embossing, painting, adhesion, printing, metallizing (plating, etc.), machining, surface treatment (antistatic treatment, corona discharge treatment, plasma treatment, photochromism treatment, physical vapor deposition, chemical vapor deposition, coating, etc.).

[Use]
Biodegradable resin moldings are particularly suitable for agricultural and forestry materials, fishery materials, civil engineering materials, and the like, which are used outdoors, in soil, in water, or in wet environments. Specifically, extruded products (for example, film products such as agricultural mulch films, films for mushroom cultivation, tree protection films, sheet products such as water retention sheets, fishing lines, fishing nets, aquaculture nets, vegetation nets, ropes, etc. textile products), injection molded products (stakes, seedling pots, mushroom bed cultivation containers), and the like. In addition, it is also suitable for compost bags and garbage bags that are expected to be stored for a certain period of time in homes, offices, and the like.

EXAMPLES The content of the present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited by the following examples as long as the gist thereof is not exceeded. Various production conditions and values of evaluation results in the following examples have meanings as preferable values of the upper limit or the lower limit in the embodiment of the present invention. It may be a range defined by the value of the example or a combination of the values of the examples.

[Biodegradable resin]
As a biodegradable resin, the following aliphatic polyester resin (A) was used.
Aliphatic polyester resin (A): polybutylene succinate adipate (PBSA)
"BioPBS FD92PM" manufactured by PTTMCC Biochem

[Borate hydrates and anhydrides]
The following materials were used as borates.
Sodium tetraborate decahydrate: U.S. S. "Borax" manufactured _{by Borax Composition} formula: _{Na2B4O7.10H2O}
Sodium tetraborate pentahydrate: U.S. S. "Neobor" manufactured _by Borax _{Composition formula} : _Na2B4O7.5H2O
Sodium tetraborate anhydrous: U.S. S. "Dehybor" manufactured by Borax Composition formula: Na ₂ B ₄ O ₇

[Examples 1 to 3, Comparative Examples 1 to 6]
A biodegradable resin and a borate (hydrate or anhydride) are blended at the ratio shown in Table 1, and a small twin-screw kneader (manufactured by DSM "Xplore Micro 15cc Twin Screw
Compounder") was used to perform melt-kneading at 170° C. for 4 minutes in a nitrogen atmosphere. After that, the resulting resin composition was taken out as a molten strand and allowed to cool. The kneading state at this time was evaluated as follows, and the results are shown in Table 1.

<Kneadability evaluation>
The appearance at the time of taking out the strand was evaluated according to the following criteria.
Good: Kneading was completed without any problem.
Poor: Remarkably foamed.
If the evaluation is good, a bubble-free resin composition suitable for molding can be stably produced.

The strand-shaped resin composition obtained above was shredded into pellets and subjected to the following evaluations. The results are shown in Table 1.
<Intrinsic viscosity evaluation>
The intrinsic viscosity (IV) (dl/g) of the resin composition was determined using an Ubbelohde viscometer in the following manner. Using a mixed solvent of phenol/1,1,2,2-tetrachloroethane (mass ratio 1/1), a resin composition sample was dissolved at 110° C. to prepare a solution having a concentration of 0.5 g/dL. Next, the number of seconds for the sample solution and the solvent only to fall at 30° C. was measured and obtained from the following formula.
IV=((1+4K _H η _sp ) ^0.5 −1)/(2K _H C)
Here, η _sp = η/η ₀ −1, η is the number of seconds the sample solution falls, η ₀ is the number of seconds the solvent alone falls, C is the concentration of the sample solution (g/dL), and K _H is Huggins' is a constant. _KH adopted 0.33.
In the aliphatic polyester-based resin (A) used in this example, when the IV is 1.5 or more, a molded article having a small decrease in molecular weight and excellent mechanical strength can be obtained.

The pellets obtained above were molded into a sheet having a thickness of about 120 μm with a hot press molding machine set at 170°C. The state of dispersion of borate in the obtained sheet was evaluated as follows, and the results are shown in Table 1.
<Dispersibility evaluation>
The sheet was observed with transmitted light and evaluated according to the following criteria.
Good: Translucent, and almost no borate particles are visible.
Poor: Granular borate is clearly visible.
If the evaluation is good, a molded article with good appearance and feel and good mechanical strength can be obtained.

The biodegradability of the sheet obtained above was evaluated as follows, and the results are shown in FIG. <Biodegradability test>
A sheet-shaped resin composition was cut into a rectangle of 50 mm x 30 mm, and was placed in a polyethylene Tupperware container. Yawata Bussan Co., Ltd., inoculum for biodegradation test) was buried in a mixture with a mass ratio of 1:1, closed with a lid, and allowed to stand in a constant temperature bath at 28°C. Each test piece was taken out periodically to measure the change in weight, and the weight retention rate (the ratio of the weight after a predetermined number of days to the weight before starting the test) was determined.

From Table 1, if the hydration number of the borate hydrate is in the range of 5 to 10 and the content of the borate hydrate is 5.3 parts by mass or less relative to 100 parts by mass of the biodegradable resin, kneadability It can be seen that a composition having good dispersibility and good dispersibility can be obtained with little decrease in strength.

From FIG. 1, it can be seen that when the borate hydrate content is 1.0 parts by mass or more relative to 100 parts by mass of the biodegradable resin, the effect of delaying biodegradation can be obtained.

Claims (5)

A biodegradable resin composition containing 1.0 to 5.3 parts by mass of a borate hydrate per 100 parts by mass of a biodegradable resin. 2. The biodegradable resin composition according to claim 1, wherein the borate hydrate is sodium tetraborate hydrate. 3. The biodegradable resin composition according to claim 2, wherein the sodium tetraborate hydrate has a hydration number of 5-10. However, the hydration number is the value _of n when the composition formula of sodium tetraborate _hydrate is expressed in the _form of _Na2B4O7.nH2O . The biodegradable resin composition according to any one of claims 1 to 3, wherein the biodegradable resin is an aliphatic polyester resin. 5. The biodegradable resin composition according to claim 4, wherein the aliphatic polyester-based resin is a polyester containing structural units derived from an aliphatic diol and structural units derived from an aliphatic dicarboxylic acid as main constituent components.

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