WO2020201935A1 - Biodegradable polyester-based resin expanded particle, method for producing biodegradable polyester-based resin expanded particle, biodegradable polyester-based resin expanded molded article, and method for producing biodegradable polyester-based resin expanded molded article - Google Patents

Abstract

The present invention provides biodegradable polyester-based resin expanded particles having excellent expandability while having crystallinity, as a result of setting a biodegradable polyester-based resin having crystallinity into a specific crystal state. The present invention also provides a biodegradable polyester-based resin expanded molded article that is lightweight and has excellent strength.

Description

Method for producing biodegradable polyester-based resin foam particles, biodegradable polyester-based resin foamed particles, biodegradable polyester-based resin foam molded product, and method for producing biodegradable polyester-based resin foamed molded product.

The present invention relates to biodegradable polyester-based resin foam particles and biodegradable polyester-based resin foam molded articles, and methods for producing these.
The present application claims priority based on Japanese Patent Application No. 2019-067189 filed on March 29, 2019, the contents of which are incorporated herein by reference.

Conventionally, biodegradable polyester resins such as polylactic acid and polybutylene succinate are widely known.
As the biodegradable polyester resin, a copolymer containing lactic acid, butylene succinate, butylene adipate or the like and ethylene terephthalate or carbonate as a constituent unit is also known.

It is being studied to use this kind of biodegradable polyester resin as a raw material for an extruded foam molded product or a bead foam molded product (see Patent Document 1 below).

Japanese Patent Application Laid-Open No. 2001-098105

When a resin foam molded product is formed using a biodegradable polyester resin, as described in Examples of Patent Document 1, there is a problem that foaming is inhibited by the resin exhibiting crystallinity. There is.
Specifically, in the examples of Patent Document 1, a foamed molded product is good for a substantially completely amorphous biodegradable polyester resin in which the calorific value of melting is not observed by the measurement with a differential scanning calorimeter (DSC). However, it is described that only a foamed molded product having an extremely small expansion ratio can be obtained with a crystalline resin (Sample P-1) having a heat of fusion of "13.9 J / g".

However, the crystallinity of the biodegradable polyester resin is an important factor for exerting excellent strength in the biodegradable polyester resin foam molded product.
Therefore, with respect to the conventional biodegradable polyester resin foam molded product, the biodegradable polyester resin contained in the foam molded product exhibits crystallinity, and at the same time, a good foaming ratio is obtained and light weight is exhibited. However, such a request has not been fully achieved.
Therefore, the present invention provides biodegradable polyester-based resin foamed particles having crystallinity and good foamability, and a method for producing the same, and further, lightweight and highly strong biodegradable polyester-based resin foamed. An object of the present invention is to provide a molded product and a method for producing the same.

The present inventor has made diligent studies in order to solve the above problems, and by putting the biodegradable polyester resin having crystallinity into a specific crystalline state, the biodegradable polyester resin foamed particles are in a good foamed state. Therefore, the present invention has been completed by finding that it can be useful as a material for forming a biodegradable polyester resin foam molded product having excellent light weight.

In order to solve the above problems, the present invention
Biodegradable polyester resin foamed particles containing biodegradable polyester resin.
Using a differential scanning calorimeter,
With the first temperature rise from 30 ° C to 200 ° C at a temperature rise rate of 10 ° C / min,
With a temperature drop rate of 10 ° C / min from 200 ° C to 30 ° C,
When the second temperature rise from 30 ° C. to 200 ° C. at a temperature rise rate of 10 ° C./min was carried out in order.
The melting peak observed on the first DSC curve (1) obtained by the first temperature rise is such that the melting peak on the second DSC curve (2) obtained by the second temperature rise is on the high temperature side. It is separated into the low temperature side, and the top of the peak on the high temperature side and the top of the peak on the low temperature side are ± 15 ° C. of the peak top of the melting peak in the second DSC curve (2). Provided are biodegradable polyester-based resin foam particles located within the range.

Further, the present invention is a method for producing biodegradable polyester-based resin foamed particles for producing such biodegradable polyester-based resin foamed particles.
The biodegradable polyester resin particles containing the biodegradable polyester resin are heat-treated at a temperature within ± 6 ° C. of the melting peak temperature (Tm) of the biodegradable polyester resin, and then heat-treated. The first DSC curve (1) is obtained by further performing a cooling treatment of cooling at a cooling rate of 0.1 ° C./min or more and 5 ° C./min or less until the temperature becomes 50 ° C. or more lower than the melting peak temperature (Tm). In 1), the heat-treated resin particles in which the peaks appear on the high-temperature side and the low-temperature side are obtained, and then a foaming agent is applied to the heat-treated resin particles at a temperature lower than the peak on the low-temperature side of the heat-treated resin particles. Provided is a method for producing biodegradable polyester resin foam particles, which is impregnated to obtain foamable resin particles and then heated to foam the foamable resin particles.

The present invention also provides a biodegradable polyester-based resin foam molded product, which is partially or wholly composed of the above-mentioned biodegradable polyester-based resin foamed particles.

Further, in the present invention, the biodegradable polyester-based resin foam particles as described above are housed in a mold cavity, and the biodegradable polyester-based resin foam particles are heat-sealed in the cavity, thereby forming the cavity. Provided is a method for producing a biodegradable polyester resin foam molded product, which produces a biodegradable polyester resin foam molded product corresponding to a shape.

INDUSTRIAL APPLICABILITY According to the present invention, a biodegradable polyester resin foamed particles that have good foamability while having crystallinity and a method for producing the same are provided, and further, a biodegradable polyester resin that is lightweight and has excellent strength. A foam molded product and a method for producing the same are provided.

It is a figure which shows the DSC curve (1) of the PBS resin particle in Example 1. FIG. It is a figure which shows the DSC curve (1) of the PBS resin particle in the comparative example 1. FIG.

Hereinafter, embodiments of the present invention will be described.
The biodegradable polyester-based resin foamed particles of the present embodiment (hereinafter, also simply referred to as “resin foamed particles”) are, for example, biodegradable polyester-based resin foamed molded products such as bead foamed molded products (hereinafter, simply “resin foamed”). It is also used as a raw material for "molded products").

First, the resin composition constituting the biodegradable polyester-based resin foamed particles will be described.
In the resin composition of the present embodiment, the resin as the main component thereof is a biodegradable polyester resin.
The resin composition may contain additives and the like described later in addition to the biodegradable polyester resin.

Examples of the biodegradable polyester resin according to the present embodiment include an aliphatic polyester resin obtained by polycondensation of glycol and an aliphatic dicarboxylic acid.
Examples of the aliphatic polyester resin include polyethylene succinate, polybutylene succinate, polyhexamethylene succinate, polyethylene adipate, polyhexamethylene adipate, polybutylene adipate, polyethylene oxalate, polybutylene succinate, and poly. Examples thereof include neopentyl oxalate, polyethylene sebacate, polybutylene sebacate, polyhexamethylene sebacate, polybutylene succinate adipate, and polybutylene succinate carbonate.

The biodegradable polyester resin according to the present embodiment is, for example, poly (α-hydroxy acid) such as polyglycolic acid or polylactic acid, or a copolymer thereof, poly (ε-caprolactone) or poly (β-propio). Poly (ω-hydroxyalkanoate) such as lactone), poly (3-hydroxybutyrate), poly (3-hydroxyvariate), poly (3-hydroxycaprolate), poly (3-hydroxyheptanoate) ), Poly (β-hydroxyalkanoate) such as poly (3-hydroxyoctanoate), and aliphatic polyester resins such as poly (4-hydroxybutyrate) may be used.

If necessary, the biodegradable polyester resin may be modified so as to form a branched structure or a crosslinked structure.
A chain extender such as carbodiimide can be used to introduce a branched structure or a crosslinked structure into a biodegradable polyester resin.
Modification with a chain extender is a functional that can be condensed with hydroxyl groups and carboxyl groups present in the molecular structure of biodegradable polyester resins such as acrylic organic compounds, epoxy organic compounds, and isocyanate organic compounds. This can be done using a compound having one or more groups.
That is, the modification can be carried out by a method of binding an acrylic organic compound, an epoxy organic compound, an isocyanate organic compound or the like to a biodegradable polyester resin by a reaction.

The modification of the biodegradable polyester resin by the crosslinked structure or the branched structure can be carried out by, for example, a method of reacting the molecules of the biodegradable polyester resin with a radical initiator.
Such a reaction can be carried out using an extruder such as a twin-screw extruder.

Among the above-mentioned modification methods, it is preferable to react the molecules of the biodegradable polyester resin with a radical initiator in that the inclusion of other components after the modification can be suppressed.
When the molecules of the biodegradable polyester resin were reacted with each other using a radical initiator having an appropriate reactivity, the decomposition starting point of the biodegradable polyester resin in the extruder was generated by the radical initiator. It is attacked by free radicals, and the site becomes a cross-linking point (branch point) and is stabilized.
The biodegradable polyester resin has increased thermal stability due to such modification, and it is difficult for the biodegradable polyester resin to have a low molecular weight when passing through an extruder.

Examples of the radical initiator include organic peroxides, azo compounds, halogen molecules and the like.
Of these, organic peroxides are preferred.
Examples of the organic peroxide used in the present embodiment include peroxyesters, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides.

Examples of the peroxy ester include t-butyl peroxy-2-ethylhexyl carbonate, t-hexyl peroxyisopropyl monocarbonate, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, and t-butyl peroxylaurate. , T-Butylperoxy-3,5,5-trimethylhexanoate, t-Butylperoxyacetate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, and t-butylperoxyisopropyl. Examples include monocarbonate.

Examples of the hydroperoxide include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide and the like.

Examples of the dialkyl peroxide include dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di (t-butylperoxy) hexin-3.

Examples of the diacyl peroxide include dibenzoyl peroxide, di (4-methylbenzoyl) peroxide, and di (3-methylbenzoyl) peroxide.

Examples of the peroxydicarbonate include di (2-ethylhexyl) peroxydicarbonate and diisopropylperoxydicarbonate.

Examples of the peroxyketal include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, and 2,2-di (t). -Butyl peroxy) butane, n-butyl 4,4-di- (t-butyl peroxy) valerate, 2,2-bis (4,5-di-t-butyl peroxycyclohexyl) propane and the like can be mentioned. ..

Examples of the ketone peroxide include methyl ethyl ketone peroxide and acetylacetone peroxide.

The organic peroxide is preferably a peroxy ester.
Further, among the peroxyesters, the organic peroxide used for modifying the biodegradable polyester resin is preferably a peroxycarbonate-based organic peroxide.
The organic peroxide used for modifying the biodegradable polyester resin in the present embodiment is preferably a peroxymonocarbonate-based organic peroxide among the peroxycarbonate-based organic peroxides, and t-butyl. Peroxyisopropyl monocarbonate is particularly preferred.

The above-mentioned organic peroxide is usually used in a content of 0.1 part by mass or more with respect to 100 parts by mass of the biodegradable polyester resin to be modified, although it depends on its molecular weight and the like.
The content of the organic peroxide is preferably 0.2 parts by mass or more, and particularly preferably 0.3 parts by mass or more.
The content of the organic peroxide is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, and particularly preferably 1.0 part by mass or less.
By modifying the biodegradable polyester-based resin with an organic peroxide at such a content, the modified biodegradable polyester-based resin can be made suitable for foaming.

By setting the content of the organic peroxide as described above to 0.1 parts by mass or more, the effect of modification on the biodegradable polyester resin can be more reliably exhibited.
Further, by setting the content of the organic peroxide to 2.0 parts by mass or less, it is possible to prevent a large amount of gel from being mixed in the biodegradable polyester resin after modification.

The biodegradable polyester resin preferably does not have a long chain branch.
The biodegradable polyester resin of the present embodiment is preferably an aliphatic polyester resin from the viewpoint of biodegradability.
When all the biodegradable polyester resins contained in the resin composition are 100% by mass, the proportion of the aliphatic polyester resin is preferably 85% by mass or more, and preferably 90% by mass or more. More preferably, it is 95% by mass or more.
It is particularly preferable that all the biodegradable polyester resins contained in the resin composition are aliphatic polyester resins.

Of these, polybutylene succinate is particularly preferable as the biodegradable polyester resin used in the present embodiment.
When all the biodegradable polyester resins contained in the resin composition are 100% by mass, the proportion of polybutylene succinate is preferably 85% by mass or more, and more preferably 90% by mass or more. It is preferably 95% by mass or more, and more preferably 95% by mass or more.
It is particularly preferable that all the biodegradable polyester resins contained in the resin composition are polybutylene succinate.

In this embodiment, one of the above-exemplified biodegradable aliphatic polyester resins may be selected and used, and a plurality of of the above-exemplified biodegradable aliphatic polyester resins may be mixed and used. It can also be used, and a biodegradable aliphatic polyester resin other than the above examples may be used.

Examples of the additive contained in the resin composition include polymers other than biodegradable polyester resins, inorganic substances such as inorganic fillers, and various rubber / plastic agents.

Examples of the polymer other than the biodegradable polyester resin that can be contained in the resin composition include a polymer-type antistatic agent, a fluorine-based resin used as a bubble modifier, and a rubber-based modifier.

The ratio of the biodegradable polyester resin to all the polymers contained in the resin composition constituting the resin foam particles is 85% by mass in order to make the resin foam particles and the resin foam molded body exhibit excellent biodegradability. The above is preferable, 90% by mass or more is more preferable, and 95% by mass or more is further preferable.

The resin composition may optionally contain additives such as shrinkage inhibitors for the purpose of further improving its foam moldability.
The content of the additive is preferably in the range of 0.05 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the biodegradable polyester resin.

Examples of the shrinkage inhibitor include laurate monoglyceride, palmitate monoglyceride, stearic acid monoglyceride, pentaerythlit monocaplate, pentaerythlit monooleate, pentaerythlit monolaurate, dipentaerythlit distearate, and sorbitan. Monooleate, sorbitanseski sugar oil fatty acid ester, sorbitan monopalmitate, sorbitan monolaurate, sorbitan monostearate, mannitan monooleate, mannitan monolaurate and other polyhydric alcohols and ester compounds of higher fatty acids Other examples include higher alkylamines, fatty acid amides, and complete esters of higher fatty acids.

As the shrinkage inhibitor, one of the above-exemplified ones may be selected and used, or a plurality of types of the above-exemplified shrinkage inhibitor may be mixed and used, and those known as shrinkage inhibitors other than the above-mentioned examples are known. May be used. Of these, monoglyceride stearate is particularly preferable.

As the resin composition, a commonly used bubble adjusting agent can be used for the purpose of forming a good bubble structure at the time of foaming. Examples of the bubble adjusting agent include fine powder of a fluorine-based resin such as polytetrafluoroethylene, talc, aluminum hydroxide, silica and the like.
Further, the decomposition-type foaming agent described later can be used as a bubble adjusting agent because the foaming state can be adjusted by using it in combination with a volatile foaming agent.

The foaming agent used when forming the resin foam particles in the resin composition is not particularly limited, but is a volatile foaming agent that becomes a gas at normal temperature (23 ° C.) and normal pressure (1 atm), and a gas by thermal decomposition. A decomposing foaming agent to be generated can be adopted, and as the volatile foaming agent, for example, an inert gas, an aliphatic hydrocarbon, an alicyclic hydrocarbon, or the like can be adopted.
Examples of the inert gas include carbon dioxide, nitrogen and the like, and examples of the aliphatic hydrocarbon include propane, normal butane, isobutane, normal pentane, isopentane and the like, and the aliphatic hydrocarbon includes the alicyclic hydrocarbon. For example, cyclopentane, cyclohexane and the like can be mentioned.
Among the above, carbon dioxide is particularly preferably used in the present embodiment.

When all the biodegradable polyester resins contained in the resin composition are 100% by mass, the proportion of the foaming agent is 1% by mass to 8% by mass, preferably 1% by mass to 7% by mass, and more preferably. 2, 2% by mass to 7% by mass.

Examples of the decomposing foaming agent include organic acids such as azodicarbonamide, dinitrosopentamethylenetetramine, sodium bicarbonate or citric acid, or a mixture thereof and a bicarbonate.

Examples of the additive that can be contained in the resin composition include lubricants, antioxidants, antistatic agents, flame retardants, ultraviolet absorbers, light stabilizers, colorants, and inorganic fillers. In addition, the resin composition may appropriately contain additives other than these.

The resin foamed particles can be produced by using a general foaming machine used for producing polystyrene resin foamed particles or the like, and the resin particles made of the resin composition are foamed by steam heating, hot air heating, or the like. Can be formed by

As the resin foaming particles, resin particles (hereinafter, also referred to as “raw grains”) composed of the resin composition containing a biodegradable polyester resin are prepared, and the above-mentioned foaming is performed on the resin particles (raw grains). A predetermined degree of foaming can be prepared by impregnating the agent, spreading an antistatic agent, an antibonding agent, or the like on the surface of the particles, putting the agent into a foaming machine, and heating until a desired bulk density is reached.

The bulk density of the resin foam particles in the present embodiment is 12 kg / m ³ or more and 500 kg / m ³ or less, preferably 30 kg / cm ³ or more and 500 kg / m ³ or less.
If the bulk density of the resin foam particles is less than 12 kg / m ³ , shrinkage is likely to occur during foam molding, and the strength of the obtained resin foam molded product may not be sufficiently good.
On the other hand, if the bulk density of the resin foam particles exceeds 500 kg / m ³ , the resin foam molded product may not be sufficiently lightweight.
The bulk density of the resin foam particles can be determined, for example, as follows.

(Measuring method of bulk density)
Approximately 1,000 cm ³ of resin foam particles are prepared, and the resin foam particles are filled in a graduated cylinder up to a scale of 1,000 cm ³ .
The graduated cylinder is visually observed from the horizontal direction, and if even one of the resin foam particles reaches the scale of 1,000 cm ³ , the filling of the resin foam particles into the graduated cylinder is completed at that point.
Next, the mass of the resin foamed particles filled in the graduated cylinder is weighed with two significant figures after the decimal point, and the mass is defined as W (g). Then, the bulk density of the foamed particles can be obtained by the following formula.
Bulk density (kg / m ³ ) = W

The bulk factor of the resin foamed particles in the present embodiment is 2 times or more and 50 times or less, preferably 3 times or more and 45 times or less, and more preferably 4 times or more and 40 times or less.
Here, the bulk multiple means a value obtained by integrating the resin density with the reciprocal of the bulk density.

The average bubble diameter of the resin foam particles in the present embodiment is preferably in the range of 30 μm or more and 300 μm or less.
The average cell diameter of the resin foamed particles is more preferably 50 μm or more and 250 μm or less, and further preferably 50 μm or more and 200 μm or less.

(Measuring method of average cell diameter)
The average cell diameter of the resin foamed particles can be measured based on an image obtained by photographing a cross section of the resin foamed particles cut so as to be roughly divided into two at the center with a scanning electron microscope. ..
Specifically, a photograph of the cross section is taken using a scanning electron microscope (for example, "S-3000N" manufactured by Hitachi, Ltd., "S-3400N" manufactured by Hitachi High-Technologies Corporation).
When determining the average cell diameter in a resin foam molded product, photography was performed by photographing the central portion of each of two resin foam particles randomly selected from the resin foam particles that are considered to be cut so as to be roughly divided into two at the central portion. To do.
In the photographing, the direction in which the bubbles are relatively long is the vertical direction, and the direction orthogonal to this direction is the horizontal direction, and two photographs are taken at one place.
A total of 4 images are printed on A4 paper, 2 images in each of the vertical and horizontal directions, and the average chord length (t) of the bubbles is calculated from the number of bubbles on an arbitrary straight line (length 60 mm) parallel to the vertical and horizontal directions. Calculated by
However, any straight line should be drawn so that the bubbles do not touch only at the contact points as much as possible (if they do, they are included in the number of bubbles).
The measurement shall be performed at 6 locations each in the vertical and horizontal directions.
Average string length t (mm) = 60 / (number of bubbles x image magnification)
Then, the bubble diameter in each direction is calculated by the following formula.
D (mm) = t / 0.616
Further, the square root of the product is taken as the average cell diameter.
Average bubble diameter (mm) = (D length x D width) ^1/2

The resin foam particles are preferably made into small particles and can be in the form of a columnar shape, a substantially spherical shape, or a spherical shape, but the substantially spherical shape or a spherical shape is preferable from the viewpoint of filling property into a molding die or the like.
The raw grains for obtaining the resin foamed particles are not particularly limited, but the volume per particle is preferably 0.5 mm ³ or more and 30 mm ³ or less, and particularly preferably 1 mm ³ or more and 10 mm ³ or less. ..

The method for obtaining small particles as the raw particles is not particularly limited, and examples thereof include a generally usable method of cutting after melt extrusion to make small particles, and a pulverization method.
In the present embodiment, a method of cutting into small particles after melt extrusion is more preferable.

Next, a method for producing the resin foam particles and the resin foam molded product (bead foam molded product) will be described.
The manufacturing method of the present embodiment includes a step of preparing raw grains (raw grain preparation step), a step of primary foaming the raw grains to prepare preliminary foamed particles (primary foaming step), and a predetermined molding space inside. A molding die in which a (cavity) is formed is prepared, the pre-foamed particles are filled in the molding die, and the pre-foamed particles are heated in the molding die to cause secondary foaming of the pre-foamed particles and the pre-foamed particles. The present invention includes a step (molding step) of heat-sealing each other to produce a bead-foamed molded product in which a plurality of resin foam particles are integrated and has a shape corresponding to the cavity.

In the present embodiment, the crystal structure of the biodegradable polyester resin contained in the raw grains is optimized in order to exhibit good foamability in the primary foaming and the secondary foaming.
Specifically, in the present embodiment, the preliminary foamed particles are prepared by carrying out the following steps.
(A) After heat treatment containing a biodegradable polyester resin at a temperature within ± 6 ° C. of the melting peak temperature (Tm) of the biodegradable polyester resin, 0.1 ° C./min or more The first step of preparing the heat-treated resin particles by further performing a cooling treatment of cooling at a cooling rate of 5 ° C./min or less until the temperature becomes 50 ° C. or more lower than the melting peak temperature (Tm).
(B) The second step of impregnating the heat-treated resin particles obtained in the first step with a foaming agent at a temperature lower than the peak temperature on the low temperature side appearing in the first DSC curve (1) to obtain foamable resin particles. Process.
(C) A third step of obtaining resin foamed particles to be used as preliminary foamed particles by heating and foaming the foamable resin particles obtained in the second step.

The first step is carried out by, for example, a method of directly obtaining resin particles from a molten resin composition such as a hot-cut granulation method, and performing the heat treatment and the cooling treatment on the resin particles. Can be done. Further, in the first step, for example, the molten resin composition is once made into a resin sheet or a resin strand, and the resin sheet or the resin strand is subjected to the heat treatment and the cooling treatment, and then the resin sheet. It can also be carried out by a method of cutting the resin strand using a pelletizer or the like.

By performing the heat treatment and the cooling treatment as described above, the heat-treated resin particles and the pre-foamed particles obtained by foaming the heat-treated resin particles are in a characteristic crystalline state.
These crystalline states can be confirmed by a differential scanning calorimetry (DSC).

That is, by performing the heat treatment and the cooling treatment as described above, the heat-treated resin particles and the prefoamed particles are processed from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter. First temperature increase (first scan), temperature decrease from 200 ° C to 30 ° C at a temperature decrease rate of 10 ° C / min, and second temperature decrease from 30 ° C to 200 ° C at a temperature decrease rate of 10 ° C / min. When the temperature rise (second scan) of No. 1 was carried out in order, the melting peak on the second DSC curve (2) obtained by the second temperature rise was the melting peak temperature (Tm) of the biodegradable polyester resin. ), A single peak with a peak top is observed, but in the first DSC curve (1) obtained by the first temperature rise, this peak is observed in a state where it is divided into a high temperature side and a low temperature side. Moreover, the top of the peak on the high temperature side and the top of the peak on the low temperature side are within ± 15 ° C. of the peak top of the melting peak in the second DSC curve (2) (“Tm-15 ° C.” ~. It can be in a state of being located at "Tm + 15 ° C.").

The heat-treated resin particles and the prefoamed particles in the present embodiment have a single melting peak at the time of melting as in the second temperature rise (second scan) in the state before the heat treatment or the cooling treatment is performed. By the heat treatment and cooling treatment as described above, the melting peak can be in a bifurcated state as seen in the first temperature rise (first scan).

At this time, the heat-treated resin particles and the prefoamed particles are preferably prepared so that the amount of heat of fusion at the peak on the high temperature side is 20 J / g or more.
As a result, the heat-treated resin particles and the pre-foamed particles exhibit good foamability during primary foaming and secondary foaming, respectively.
Moreover, as is clear from showing such a melting peak, the heat-treated resin particles and the pre-foamed particles have crystallinity and can exhibit excellent strength with respect to the resin foamed molded product. it can.

When the heat-treated resin particles and the prefoamed particles have a plurality of melting peaks at the time of melting, it is only necessary to divide the peaks as described above only in the main peak in the melting temperature range, and all the melting peaks are described above. It doesn't need to be.

Here, the main peak is biodecomposed in accordance with DSC measurement (JIS K7121: 1987, 2012 "Plastic transition temperature measuring method" and JIS K7122: 1987, 2012 "Plastic transition heat measuring method"). Using a differential scanning calorimeter (“DSC7000X, AS-3” manufactured by Hitachi High-Tech Science Co., Ltd.) with 5 to 7 mg of particles made of a sex polyester resin, the temperature rises from 30 ° C to 200 ° C at a heating rate of 10 ° C / min. DSC curve obtained when heating is performed, the temperature is lowered from 200 ° C. to 30 ° C. at a temperature lowering rate of 10 ° C./min, and then the temperature is further heated again from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min (2). When there is only one melting peak in the DSC curve (2), it means that peak, and when there are multiple melting peaks, it means the peak with the highest peak height.

In the following, among the melting peaks in the DSC curve (1), the main melting in the DSC curve (2) is among the two changing melting peaks based on the peak temperature of the melting peak in the DSC curve (2). The melting peak on the low temperature side of the peak is referred to as the low temperature side peak, and the temperature at that time is referred to as the low temperature side peak temperature.
Further, the melting peak on the high temperature side of the main melting peak is referred to as the high temperature side peak, and the temperature at that time is referred to as the high temperature side peak temperature.

The amount of heat of fusion of the high temperature side peak is the peak bottom between the low temperature side peak and the high temperature side peak (the apex of the DSC curve) and the point where the DSC curve passes the high temperature side peak and returns to the high temperature side baseline again. It is calculated from the straight line connecting the above and the part surrounded by the DSC curve.

The method of heat treatment is not particularly limited except for conditions that cause deterioration of the resin, but a warm air heating method is preferable.
It is important to control the heating conditions within the temperature range of ± 6 ° C (“Tm-6 ° C” to “Tm + 6 ° C”) of the main peak temperature of the biodegradable polyester resin, and the heating time is once. Although it depends on the amount to be treated, the temperature may be maintained at the set temperature for 30 minutes to 1 hour after confirming that the entire resin particles have reached the set temperature.
If it is shorter than 30 minutes, unevenness of the heat treatment may occur between the central portion and the surface portion of the resin particles.
The foamed particles obtained by pre-foaming such resin particles may be inferior in foamability.

In the cooling treatment, as described above, 0.1 ° C./min or more from the heat treatment temperature to at least a temperature 50 ° C. lower than the melting peak temperature (Tm) of the biodegradable polyester resin (Tm-50 ° C.). The resin particles are cooled at a cooling rate of 5 ° C./min or less.
The cooling treatment at the cooling rate (0.1 ° C./min or more and 5 ° C./min or less) is preferably performed until the resin particles after the heat treatment are 50 ° C. or lower, and the resin particles are 30 ° C. or lower. It is more preferable to carry out until it becomes.
As a result, a crystal structure characteristic of the heat-treated resin particles and the pre-foamed particles can be obtained.
Good productivity is exhibited by setting the cooling rate to 0.1 ° C./min or more.
Further, by setting the cooling rate to 5 ° C./min or less, it is possible to suppress the occurrence of variation in the crystal structure between the particles.
Further, this heat treatment and cooling treatment are also effective when performed on the pre-foamed particles.

The second step of impregnating the heat-treated resin particles prepared as described above with a foaming agent can be performed by using a pressure vessel such as an autoclave.
Specifically, a method of bringing the heat-treated resin particles into contact with a volatile foaming agent in a pressure vessel such as an autoclave under a pressurized atmosphere can be mentioned.
When carbon dioxide or the like is used as the volatile foaming agent, the impregnation of the foaming agent may be carried out under supercritical conditions exceeding the critical point.

The primary foaming step and the molding step are preferably performed under a temperature condition between the low temperature side peak temperature and the high temperature side peak temperature.
By performing the molding process at a temperature higher than the peak temperature on the low temperature side, it is easy to obtain a resin foam molded product having a beautiful appearance, and it is easy to obtain a resin foam molded product having excellent strength.
Further, when the molding process is performed at a temperature lower than the peak temperature on the high temperature side, the obtained resin foam molded product is less likely to shrink, and it is easy to obtain a resin foam molded product having a good appearance in which the shape of the cavity is accurately reflected. Become.

As described above, in the present embodiment, biodegradable polyester-based resin foamed particles that have crystallinity but exhibit good foamability are provided, and further, a biodegradable polyester-based resin that is lightweight and has excellent strength. Foam moldings are provided.
Although the above examples are given in the present embodiment, the present invention is not limited to the above examples.

Hereinafter, examples of producing the resin foam particles and the resin foam molded product will be specifically described with reference to Examples, but the present invention is not limited to the following examples.

(Example 1)
Polybutylene succinate (hereinafter referred to as "PBS") (manufactured by PTT MCC Biochem, trade name "BioPBS, FZ91", density = 1,260 kg / m ³ ) is extruded at a resin temperature of 208 ° C. The particles were granulated to obtain substantially spherical PBS resin particles having L / D = 0.9 and an average particle size of 0.8 mm.

Next, the obtained PBS resin particles were heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter, and the melting peak of the PBS resin particles was obtained from the DSC curve (1). The temperature of the peak top at the melting peak is determined, then the temperature is lowered from 200 ° C. to 30 ° C. at a temperature lowering rate of 10 ° C./min, and then further heated from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. The temperature of the melting peak and the peak top of the melting peak was determined from the DSC curve (2) obtained.
As a result, both the DSC curve (1) and the DSC curve (2) showed only a single melting peak, and the temperature at the peak top was 112.8 ° C.
From this measurement, it was confirmed that the melting peak temperature (Tm) of PBS used for forming the resin particles was approximately 113 ° C.

These PBS resin particles are heat-treated in an oven at 113 ° C. for 2 hours, and then cooled to 30 ° C. at a cooling rate of 1 ° C./min to be heat-treated, and are also referred to as “heat-treated resin particles”. ) Was obtained.

The obtained heat-treated PBS resin particles are heated again from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter, and the melting peak is determined by the DSC curve (1) obtained. Upon confirmation, two peaks were observed, and the top temperatures of the peaks were 108.6 ° C and 120.5 ° C, respectively. The heat of fusion of the peak on the high temperature side was 61.5 J / g. Next, foam molding is performed from the DSC curve (2) obtained by lowering the temperature from 200 ° C. to 30 ° C. at a temperature lowering rate of 10 ° C./min and then heating from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. When the melting peak and melting peak temperature of the body were determined, there was only one peak, and the temperature at the top of the peak was 113.0 ° C.

Next, 100 parts by mass (1,000 g) of the heat-treated resin particles were put into a sealable 10 L pressure vessel, and the inside of the pressure vessel was pressurized to a gauge pressure of 3 MPa using carbon dioxide, and then at room temperature (about 20 ° C.). The heat-treated resin particles were impregnated with carbon dioxide as a foaming agent for 24 hours in the above environment to prepare foamable resin particles.

After the impregnation was completed, the carbon dioxide gas in the pressure vessel was slowly decompressed, and the foamable resin particles inside were taken out. Immediately after taking out the foamable resin particles, 100 parts by mass (1,000 g) of the foamable resin particles and 0.3 parts by mass (3 g) of calcium carbonate as a binding inhibitor were mixed.
After that, the foamable resin particles are put into a foaming machine equipped with a stirrer, and foamed using 0.03 MPa of steam while stirring to foam the prefoamed particles (bulk density 130 kg / m ³ ) having a bulk factor of 10 times (bulk density 130 kg / m ³ ). Primary foam particles) were obtained.

The obtained prefoamed particles were put into a 10 L pressure vessel and sealed.
The inside of the closed pressure vessel was increased to a gauge pressure of 1 MPa using nitrogen gas, and then left for 24 hours to apply an internal pressure.
The nitrogen gas in the pressure vessel to which the internal pressure was applied was slowly decompressed, the preliminary foamed particles were taken out, and immediately foam molding was performed using a molding machine.
Pre-foamed particles are filled in a molding mold having a cavity of length 200 mm × width 200 mm × thickness 10 mm, and water vapor of 0.04 MPa to 0.05 MPa is introduced for 20 seconds to heat and cool, so that the foaming ratio is 9 times. A resin foam molded product having a good appearance was obtained.

As a result of obtaining the DSC curve (1) obtained by heating the obtained resin foam molded product from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter, 2 One melting peak was observed, and the peak temperatures were 109.6 ° C and 121.0 ° C, respectively.
Next, foam molding is performed from the DSC curve (2) obtained by lowering the temperature from 200 ° C. to 30 ° C. at a temperature lowering rate of 10 ° C./min and then heating from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. When the melting peak and melting peak temperature of the body were determined, there was only one peak, and the temperature at the top of the peak was 113.0 ° C.
By such measurement, it was confirmed that the crystalline state by the heat treatment performed in the state of the first raw grain persisted until the final resin foam molded product.

(Example 2)
The method was the same as in Example 1 except that the heat treatment conditions for the PBS resin particles were 114 ° C. and 2 hours. As a result of obtaining the DSC curve (1), two melting peaks were observed, and the peak temperatures were 110.1 ° C. and 120.3 ° C., respectively. The heat of fusion of the peak on the high temperature side was 52.6 J / g. The resin foam molded product obtained here showed a good appearance as in Example 1.

(Example 3)
The method was the same as in Example 1 except that the heat treatment conditions for the PBS resin particles were 116 ° C. and 2 hours. As a result of obtaining the DSC curve (1), two melting peaks were observed, and the peak temperatures were 113.7 ° C and 122.6 ° C, respectively. The heat of fusion of the peak on the high temperature side was 29.9 J / g. The resin foam molded product obtained here showed a good appearance as in Example 1.

(Example 4)
The method was the same as in Example 1 except that the heat treatment conditions for the PBS resin particles were 118 ° C. and 2 hours. As a result of determining the DSC curve (1), two melting peaks were observed, and the peak temperatures were 112.6 ° C and 121.2 ° C, respectively. The heat of fusion of the peak on the high temperature side was 25.5 J / g. The resin foam molded product obtained here showed a good appearance as in Example 1.

(Example 5)
The method was the same as in Example 1 except that the heat treatment conditions for the PBS resin particles were 110 ° C. and 2 hours. As a result of obtaining the DSC curve (1), two melting peaks were observed, and the peak temperatures were 101.0 ° C. and 118.4 ° C., respectively. The heat of fusion of the peak on the high temperature side was 77.9 J / g. The resin foam molded product obtained here showed a good appearance as in Example 1.

(Example 6)
The heat treatment of the PBS resin particles was carried out in the same manner as in Example 1 except that the heat treatment conditions were set to 108 ° C. and 2 hours. As a result of determining the DSC curve (1), two melting peaks were observed, and the peak temperatures were 100.1 ° C and 117.4 ° C, respectively. The heat of fusion of the peak on the high temperature side was 71.8 J / g. The resin foam molded product obtained here showed a good appearance as in Example 1.

(Comparative Example 1)
The procedure was the same as in Example 1 except that the PBS resin particles were not heat-treated. As a result of determining the DSC curve (1), no two melting peaks were observed. The bulk factor of the obtained resin foamed particles was as low as 1.2 times, and a resin foamed molded product could not be obtained.

(Comparative Example 2)
The method was the same as in Example 1 except that the heat treatment conditions for the PBS resin particles were 120 ° C. and 2 hours. As a result of determining the DSC curve (1), no two melting peaks were observed. The bulk factor of the obtained resin foamed particles was as low as 1.2 times, and a resin foamed molded product could not be obtained. In addition, the particles were large and flat, and could not be used in practice.

(Comparative Example 3)
The method was the same as in Example 1 except that the heat treatment temperature of the PBS resin particles was set to 106 ° C. for 2 hours. As a result of determining the DSC curve (1), no two melting peaks were observed. The bulk factor of the obtained resin foamed particles was as low as 1.3 times, and a resin foamed molded product could not be obtained.

As is clear from the above, according to the present invention, biodegradable polyester-based resin foamed particles that have crystallinity but exhibit good foamability are provided, and further, they are lightweight and excellent in strength. A biodegradable polyester-based resin foam molded product is provided.

Claims (9)

1. Biodegradable polyester resin foamed particles containing biodegradable polyester resin.
   Using a differential scanning calorimeter,
   With the first temperature rise from 30 ° C to 200 ° C at a temperature rise rate of 10 ° C / min,
   With a temperature drop rate of 10 ° C / min from 200 ° C to 30 ° C,
   A second temperature rise from 30 ° C to 200 ° C at a temperature rise rate of 10 ° C / min,
   When you carry out in order
   The melting peak observed on the first DSC curve (1) obtained by the first temperature rise is such that the melting peak on the second DSC curve (2) obtained by the second temperature rise is on the high temperature side. It is separated into the low temperature side, and the top of the peak on the high temperature side and the top of the peak on the low temperature side are ± 15 ° C. of the peak top of the melting peak in the second DSC curve (2). Biodegradable polyester resin foam particles located within the range.
2. The biodegradable polyester-based resin foamed particles according to claim 1, wherein the heat of fusion of the peak on the high temperature side in the first DSC curve (1) is 20 J / g or more.
3. The biodegradable polyester resin foamed particles according to claim 1, wherein part or all of the biodegradable polyester resin is an aliphatic polyester resin.
4. The biodegradable polyester resin foamed particles according to claim 1, wherein the bulk multiple is 2 times or more and 50 times or less, and the average cell diameter is 30 μm or more and 300 μm or less.
5. The biodegradable polyester resin foamed particles according to claim 1, wherein part or all of the biodegradable polyester resin is polybutylene succinate.
6. A method for producing biodegradable polyester-based resin foamed particles according to claim 1, wherein the biodegradable polyester-based resin foamed particles are produced.
   The biodegradable polyester resin particles containing the biodegradable polyester resin are heat-treated at a temperature within ± 6 ° C. of the melting peak temperature (Tm) of the biodegradable polyester resin, and then heat-treated. The first DSC curve (1) is obtained by further performing a cooling treatment of cooling at a cooling rate of 0.1 ° C./min or more and 5 ° C./min or less until the temperature becomes 50 ° C. or more lower than the melting peak temperature (Tm). In 1), the heat-treated resin particles in which the peaks appear on the high-temperature side and the low-temperature side are obtained, and then a foaming agent is applied to the heat-treated resin particles at a temperature lower than the peak on the low-temperature side of the heat-treated resin particles. A method for producing biodegradable polyester-based resin foam particles, which is impregnated to obtain foamable resin particles and then heated to foam the foamable resin particles.
7. The method for producing biodegradable polyester-based resin foamed particles according to claim 6, wherein the foaming agent is carbon dioxide.
8. A biodegradable polyester resin foam molded product partially or wholly composed of the biodegradable polyester resin foam particles according to claim 1.
9. The biodegradable polyester-based resin foam particles according to claim 1 are housed in a molding cavity, and the biodegradable polyester-based resin foam particles are heat-sealed in the cavity to correspond to the shape of the cavity. A method for producing a biodegradable polyester resin foam molded product, which comprises producing a biodegradable polyester resin foam molded product.

Images