JP6583909B2 - Polylactic acid resin foamed molded article - Google Patents

Description

  The present invention relates to a polylactic acid-based resin expanded particle molded body.

  In recent years, awareness of the global environment has increased, and polylactic acid has attracted attention as a carbon-neutral material that can replace conventional resins made from petroleum resources. Polylactic acid is made from a plant such as corn as a starting material, and is a low environmental load thermoplastic resin from the viewpoint of carbon neutral. Such polylactic acid is expected to be used as an environmentally friendly plant-derived general-purpose resin for foaming, and foams using polylactic acid as a raw material have been studied. Among them, the polylactic acid foamed particle molded body can obtain a foamed body having a desired shape by in-mold molding without being restricted in shape as in the conventional polystyrene foamed particle molded body and polyolefin foamed particle molded body. It is particularly promising as having the possibility of being able to easily design physical properties in accordance with purposes such as lightness, shock-absorbing properties, and heat insulating properties.

  However, since heat resistance is required for the polylactic acid foamed particle molded body that is put to practical use, it is necessary to use a crystalline polylactic acid resin as a base resin of the polylactic acid resin foamed particle molded body. However, the crystalline polylactic acid-based resin expanded particles are difficult to fuse at the time of in-mold molding as compared with the polystyrene-based resin expanded particles, and thus have a problem with respect to the fusibility.

  As a technique for improving the fusing property of crystalline polylactic acid-based resin expanded particles, inventions such as Patent Documents 1 to 4 have been made. Patent Document 1 discloses foamed particles made of a polylactic acid-based resin in a state where crystallization has not progressed sufficiently. Patent Document 2 discloses polylactic acid-based resin expanded particles in which secondary foamability is optimized by controlling the crystal structure. Patent Documents 3 and 4 disclose foamed particles in which the surface of the foamed particles is coated with a resin having excellent fusion properties. With these technologies, the fusibility of the polylactic acid-based resin expanded particles is improved, and the in-mold moldability is greatly improved.

JP 2004-83890 A International Publication WO2012 / 086305 International Publication WO2011 / 145391 Special table 2010-525099 gazette

  The foamed particle molded body has various shapes having a thin wall portion, a fitting portion, and the like. In order to form a thin part and a fitting part, it is necessary to use foamed particles with a small particle diameter because the narrow mold space must be filled with foamed particles. However, in the above Patent Documents 1 to 4, no consideration has been given to the in-mold moldability of the polylactic acid-based resin expanded particles having a small particle diameter.

  In view of the above-mentioned problems of the prior art, the present invention provides a molded surface of fine polylactic acid-based resin foamed particles, in which the foamed particles are sufficiently fused with each other, and there are no voids between the foamed particles. It is an object of the present invention to provide a polylactic acid-based resin expanded particle molded body having the following.

According to this invention, the polylactic acid-type resin expanded particle molded object shown below is provided.
[1] In a foamed particle molded body having an apparent density of 15 to 68 kg / m ³ formed by in-mold molding of foamed particles containing a crystalline polylactic acid resin,
The number of the expanded particles constituting the expanded particle molded body in a plan view is 15 or more per unit area [cm ² ], and the average weight per expanded particle is 0.1 to 1.5 mg. state, and it is specific (tensile strength / apparent density) is ^{10 [kPa · m 3 / kg} ] or the apparent density of PP bead molding [kg / ^{m 3]} tensile strength to [kPa], the mold molding The foamed particles used are melted from 23 ° C. at a heating rate of 10 ° C./min based on the heat flux differential scanning calorimetry described in JIS K7122-1987, using 1-2 mg of the foamed particles as a measurement sample. A first DSC curve obtained when heating and melting to a temperature 30 ° C. higher than the end of the peak, and then maintaining for 10 minutes at a temperature 30 ° C. higher than the end of the melting peak, followed by a cooling rate of 10 ° C./min At 40 In the second DSC curve obtained when cooled to 30 ° C. and heated again to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 10 ° C./min, the first DSC curve includes 2 Having a crystal structure in which a melting peak having an apex temperature does not appear on the higher temperature side (excluding the reference apex temperature) than the reference apex temperature based on the apex temperature of the melting peak of the second DSC curve, or A melting peak having an apex temperature appears on a higher temperature side (excluding the reference apex temperature) than the reference apex temperature, and the melting peak calorie has a crystal structure of less than 1 J / g; crystallinity is not less than 20%, and polylactic acid resin foamed bead molded article, wherein Rukoto which have a fusion-enhancing layers on the surface of the expanded beads.
[2] The polylactic acid-based resin expanded particle molded article according to 1 above, wherein the expanded foam molded article has a thin portion having a thickness of 10 mm or less.

The polylactic acid-based resin expanded particle molded body of the present invention is obtained by in-mold molding of expanded particles containing a crystalline polylactic acid-based resin, and the number of expanded particles constituting the expanded particle molded body in plan view is When the ratio is not less than the specific number and the ratio of the tensile strength [kPa] to the apparent density [kg / m ³ ] (tensile strength / apparent density) is not less than the specific value, the expanded particles are sufficiently fused to each other. And has a smooth surface since there are no voids between the expanded particles. As a result, it is possible to form a foamed particle molded body having a thin-walled portion exhibiting sufficient mechanical strength and a fitting portion that can be smoothly fitted using a polylactic acid resin foamed particle having a small particle diameter. Become.

FIG. 1 is an illustration of the first DSC curve (I) of expanded particles obtained by heat flux differential scanning calorimetry. FIG. 2 is an illustration of the second DSC curve (I) of the expanded particles obtained by heat flux differential scanning calorimetry. FIG. 3 is an illustration of the second DSC curve (II) showing the endothermic amount (Br: endo) of the measurement sample obtained by heat flux differential scanning calorimetry. FIG. 4 is an example of the second DSC curve (II) showing the endothermic amount (Br: endo) of the measurement sample obtained by heat flux differential scanning calorimetry. FIG. 5 is an example of the first DSC curve (II) showing the calorific value (Bf: exo) and the endothermic amount (Bf: endo) of the measurement sample obtained by heat flux differential scanning calorimetry. FIG. 6 is an example of the first DSC curve (II) showing the calorific value (Bf: exo) and the endothermic amount (Bf: endo) of the measurement sample obtained by heat flux differential scanning calorimetry. FIG. 7 is an example of the first DSC curve (II) showing the calorific value (Bf: exo) and the endothermic amount (Bf: endo) of the measurement sample obtained by heat flux differential scanning calorimetry.

Hereinafter, the polylactic acid-based resin expanded particle molded body of the present invention will be described in detail.
The polylactic acid-based resin expanded particle molded body of the present invention (hereinafter, also simply referred to as “foamed particle molded body”) is an expanded particle molded body formed by in-mold molding of expanded particles containing a crystalline polylactic acid-based resin. It is formed from expanded particles having a small particle diameter.

The polylactic acid-based resin expanded particles (hereinafter also simply referred to as expanded particles) constituting the expanded particle molded body of the present invention have a polylactic acid-based resin as a base resin.
The polylactic acid resin is preferably a polymer containing 50 mol% or more of component units derived from lactic acid. Examples of the polylactic acid-based resin include (a) a polymer of lactic acid, (b) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, and (c) lactic acid, an aliphatic polyhydric alcohol, and an aliphatic polyvalent carboxylic acid. (D) a copolymer of lactic acid and an aliphatic polyhydric carboxylic acid, (e) a copolymer of lactic acid and an aliphatic polyhydric alcohol, (f) depending on any combination of these (a) to (e) Mixtures and the like are included. The polylactic acid also includes what are called stereocomplex polylactic acid and stereoblock polylactic acid. Specific examples of lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid or their cyclic dimer L-lactide, D-lactide, DL-lactide or a mixture thereof.

  Examples of the other aliphatic hydroxycarboxylic acid in (b) include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, and hydroxyheptanoic acid. Examples of the aliphatic polyhydric alcohol in (c) and (e) include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, decamethylene. Examples include glycol, glycerin, trimethylolpropane, and pentaerythritol. Examples of the aliphatic polyvalent carboxylic acid in (c) and (d) include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, and propanetricarboxylic acid. , Pyromellitic acid, pyromellitic anhydride and the like.

Specific examples of the method for producing polylactic acid used in the present invention include, for example, a method of direct dehydration polycondensation using lactic acid or a mixture of lactic acid and aliphatic hydroxycarboxylic acid as a raw material (for example, disclosed in US Pat. No. 5,310,865). Production method), ring-opening polymerization method for polymerizing cyclic dimer (lactide) of lactic acid (for example, production method disclosed in US Pat. No. 2,758,987), cyclic dimer of lactic acid and aliphatic hydroxycarboxylic acid For example, a ring-opening polymerization method in which lactide or glycolide and ε-caprolactone are polymerized in the presence of a catalyst (for example, a production method disclosed in US Pat. No. 4,057,537), lactic acid, aliphatic dihydric alcohol, and aliphatic dihydric acid. A method of directly dehydrating polycondensation of a mixture of basic acids (for example, the production method disclosed in US Pat. No. 5,428,126), lactic acid and aliphatic divalent A method of condensing alcohol, an aliphatic dibasic acid and a polymer in the presence of an organic solvent (for example, a production method disclosed in European Patent Publication No. 071880 A2), dehydration polycondensation of a lactic acid polymer in the presence of a catalyst In producing a polyester polymer by carrying out the reaction, there can be mentioned, for example, a method of performing solid phase polymerization in at least a part of the steps, but the production method is not particularly limited. In addition, a small amount of an aliphatic polyhydric alcohol such as glycerin, an aliphatic polybasic acid such as butanetetracarboxylic acid, a polyhydric alcohol such as a polysaccharide may be coexisted and copolymerized. The molecular weight may be increased by using a binder (polymer chain extender) such as a polyisocyanate compound. Further, it may be branched by a branching agent typified by a polyhydric aliphatic alcohol such as pentaerythlit.

The polylactic acid resin constituting the expanded particles used in the present invention contains a crystalline polylactic acid resin. Specifically, (i) what consists only of crystalline polylactic acid, and (ii) what consists of a polylactic acid mixture of crystalline polylactic acid and non-crystalline polylactic acid are mentioned.
Here, the crystalline polylactic acid has a crystalline structure by containing L-lactide or D-lactide as a main component, and has an endotherm (Br: endo) measured after heat treatment by the following measurement method. Preferably it is 25 J / g or more, more preferably 30 J / g or more, and further 35 J / g or more. The upper limit of (Br: endo) is approximately 70 J / g, preferably 60 J / g.

The endothermic amount ( Br: endo) is measured in accordance with a heat flux differential scanning calorimetry method described in JIS K7122-1987. After heating and melting to a temperature higher by 30 ° C., maintaining at that temperature for 10 minutes, cooling to 110 ° C. at a cooling rate of 2 ° C./min, holding at that temperature for 120 minutes, then at a cooling rate of 2 ° C./min After the heat treatment cooled to 40 ° C., the DSC curve (hereinafter referred to as the second DSC curve (II) obtained at the time of heating and melting again to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min. It is a value obtained based on. An example of the second DSC curve (II) is shown in FIG.

  As shown in FIG. 3, the endothermic amount (Br: endo) is a point a where the melting peak departs from the low-temperature side baseline of the melting peak of the second DSC curve (II), and the melting peak is high. A point returning to the base line on the side is a point b, and a value obtained from a straight line connecting the point a and the point b and an area of the endothermic amount surrounded by the DSC curve. Also, the apparatus should be adjusted so that the baseline is as straight as possible, and if the baseline is inevitably curved as shown in FIG. 4, the curved baseline on the low temperature side of the melting peak should be The drawing is performed while maintaining the curved state and extending to the high temperature side, the point at which the melting peak moves away from the curved low temperature side baseline is point a, and the curved baseline at the high temperature side of the melting peak is the curved state of the curved line. A point where the melting peak returns to the curved high temperature side baseline is set as a point b.

  In addition, in the measurement of (Br: endo), the reason why the holding condition at 110 ° C. for 120 minutes, the cooling rate of 2 ° C./min and the heating rate of 2 ° C./min are adopted as the measurement conditions of the DSC curve of the measurement sample. This is because the purpose is to obtain the endothermic amount (Br: endo) in a state where the crystallization of the measurement sample made of polylactic acid resin is advanced as much as possible.

In the present invention, the polylactic acid can be mixed with other resins within a range that does not impair the objects and effects of the present invention. Polylactic acid is contained in a mixed resin of polylactic acid and another resin in an amount of 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more.
Examples of other resins that can be mixed with polylactic acid include polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, polyester-based resins other than polylactic acid-based resins, and the like. Among them, aliphatic ester component units are at least 35 mol%. A biodegradable aliphatic polyester-based resin is preferable. In this case, the aliphatic polyester resins include hydroxy acid polycondensates other than polylactic acid, ring-opening polymers of lactones such as polycaprolactone, polybutylene succinate, polybutylene adipate, polybutylene succinate adipate, poly Examples include polycondensates of aliphatic polyhydric alcohols such as (butylene adipate / terephthalate) and aliphatic polycarboxylic acids.

  The polylactic acid used in the present invention is preferably blocked at the molecular chain end. As a result, hydrolysis during the production process of the polylactic acid-based resin foamed particles can be more reliably suppressed, and the dispersion medium release foaming described later is facilitated. Without being trapped, it is easy to obtain the polylactic acid-based resin expanded particles that reliably suppress the occurrence of high temperature peaks and can withstand hydrolysis of the resin during molding in the mold. Furthermore, the durability of the polylactic acid-based resin expanded particle molded body obtained by in-mold molding is improved.

As said terminal blocker, a carbodiimide compound, an oxazoline compound, an isocyanate compound, an epoxy compound etc. can be used, for example. Of these, carbodiimide compounds are preferred.
Specifically, aromatic monocarbodiimides such as bis (dipropylphenyl) carbodiimide (eg, Stabaxol 1-LF manufactured by Rhein Chemie), aromatic polycarbodiimides (eg, Stabaxol P manufactured by Rhein Chemie, Stabaxol P400 manufactured by Rhein Chemie) And aliphatic polycarbodiimides such as poly (4-4′-dicyclohexylmethanecarbodiimide) (for example, Carbodilite LA-1 manufactured by Nisshinbo Chemical Co., Ltd.).
These end-capping agents may be used alone or in combination of two or more.
Moreover, 0.1-5 weight part is preferable per 100 weight part of polylactic acids, and, as for the compounding quantity of terminal blocker, 0.5-3 weight part is more preferable.

  Thus, the polylactic acid used in the present invention is preferably a modified polylactic acid resin modified with one or more modifiers selected from carbodiimide compounds, epoxy compounds, isocyanate compounds, and the like. More preferred is a modified polylactic acid modified with a carbodiimide compound.

  Further, the base resin constituting the expanded particles of the present invention can be mixed with other resins as described above within a range not impairing the objects and effects of the present invention. In this case, since the values of the heat absorption amount and the heat generation amount described later in the present invention vary when other resins are mixed, a mixed resin of polylactic acid and another resin is used as a base resin. Regarding the constitution of the endothermic amount and the calorific value in the present invention, not the base resin composed of the mixed resin but only polylactic acid among the polylactic acid and other resins constituting the base resin will be described later in the present invention. It is only necessary to satisfy the configuration of the endothermic amount and the calorific value.

  Examples of additives that can be added to the expanded particles of the present invention include colorants, flame retardants, antistatic agents, weathering agents, and conductivity-imparting agents.

In addition, when an additive is added to the base resin, the additive can be kneaded into the base resin as it is, but usually the additive is taken into consideration for the dispersibility of the additive in the base resin. It is preferable to prepare a master batch and knead it with the base resin.
Although the compounding quantity of the said additive changes with kinds of additive, it is preferable normally to be 0.001-20 weight part with respect to 100 weight part of base resin, and also 0.01-5 weight part.

In the foamed particle molded body of the present invention, the number of the foamed particles in a plan view is 10 or more per unit area [cm ² ]. That is, the foamed particle molded body of the present invention is composed of fine foamed particles. In order to obtain a foamed particle molded body having a thin part with a thickness of 10 mm or less and further 5 mm or less, 12 or more are preferable, and 15 or more are more preferable. The upper limit is about 100, preferably 50.

In this specification, the number of the expanded particles in a plan view refers to the number of expanded particles appearing on the surface per unit area [cm ² ] when the expanded molded article is observed from the outside. The measuring method is obtained by counting the number of expanded particles appearing on a 4 cm × 4 cm plane and converting the number per 1 cm ² . When a plane of 4 cm × 4 cm cannot be taken, the measurement is performed for an area of at least 1 cm ² or more. Regarding the expanded particles crossing each side of the measurement surface, the two adjacent sides are counted and the other two adjacent sides are not counted. For example, for the two pieces of the upper side and the right side, when the number of expanded particles intersecting with these pieces is measured, the two pieces of the lower side and the left side of the expanded particles intersecting with these pieces The number is not measured. When the number of expanded particles appearing on the surface cannot be counted, it is possible to measure the cut surface.

As described above, the expanded particles used in the present invention are fine particles, and the average weight per particle is preferably 0.1 mg or more and less than 2 mg, more preferably lower limit is 0.3 mg, and still more preferably 0.2 mg. The upper limit is more preferably 1.5 mg, and even more preferably 1.2 mg.
Incidentally, the foamed particles are those obtained by foaming the below polylactic acid-based resins grain child, average weight per one of the expanded beads is equal to the average weight per resin particles.

Usually, in-mold molding of thermoplastic resin foam particles is performed by filling the foam particles into a molding cavity and heating them with a heating medium such as steam to melt the surface of the foam particles and then releasing the pressure for secondary foaming. This is done by fusing the expanded particles together. When the particle size of the expanded particles is small, the specific surface area of the expanded particles increases, so the heat medium dissipation rate in the expanded particles increases at the time of pressure release, and therefore the secondary expansion rate tends to decrease. The gap tends to be large, and it becomes difficult to fuse the expanded particles uniformly.
In expanded particles containing a crystalline polylactic acid-based resin, when the particle size is reduced, it is particularly difficult to achieve a balance between the secondary expandability and the fusion property, and if the secondary expandability is suppressed too much, the expanded particles Even if they are fused, many voids remain between the expanded particles, and even if the secondary expandability is too good, the expanded particles cannot be heated uniformly, and the expanded particles are heated to a moldable temperature. In this case, it is difficult for the conventional technology to obtain a foamed molded article having good foamed particle shape by molding the foamed particle containing a crystalline polylactic acid resin having a small particle diameter. It was.

In the foamed particle molded body of the present invention, the ratio of the tensile strength [kPa] to the apparent density [kg / m ³ ] (tensile strength / apparent density) of the foamed particle molded body is 10 [kPa · m ³ / kg]. or more, it is preferably ^{12 [kPa · m 3 / kg} ] or more, and more preferably ^{14 [kPa · m 3 / kg} ] or more. The ratio in the above range (tensile strength / apparent density) is achieved by the fact that the expanded particles are sufficiently fused together and there are few voids between the expanded particles on the surface of the expanded particle molded body. On the other hand, the upper limit is about 20 [kPa · m ³ / kg].

The apparent density of the foamed particle molded body is preferably 15 to 250 kg / m ³ from the balance between lightness and mechanical strength. Its lower limit is preferably 20 kg / ^{m 3,} more preferably 30kg / ^{m 3,} the upper limit is preferably ^{150kg / m 3, 100kg / m} 3 and more preferably.

  Moreover, it is preferable that the tensile strength of a foamed particle molded object is 390-2800 kPa. The lower limit thereof is more preferably 450 kPa, further preferably 500 kPa, and the upper limit thereof is more preferably 1800 kPa, further preferably 1200 kPa.

The bulk density of the expanded particles in the present specification is calculated as follows.
The expanded particles are allowed to stand for 10 days in a temperature-controlled room under conditions of atmospheric pressure, relative humidity 50%, and 23 ° C. Next, the weight W1 (g) of the expanded particle group of about 500 ml left in the same constant temperature room for 10 days is measured, and the measured expanded particle group is water having a temperature of 23 ° C. using a tool such as a wire mesh. Sink into a measuring cylinder containing. Next, the volume V1 (L) of the expanded particle group read from the rise in the water level, after subtracting the volume of the tool such as a wire mesh, is measured, and the weight W1 of the expanded particle group placed in the measuring cylinder is divided by the volume V1 ( W1 / V1) to obtain the apparent density. The apparent density is divided by 1.6 to obtain the bulk density of the expanded particles.

  The tensile strength is obtained by dividing the maximum load up to cutting by the cross-sectional area of the test piece (the width of the test piece × the thickness of the test piece) based on the tensile test method described in JIS K6767: 1999. .

  The expanded particles used in the present invention are 23 ° C. at a heating rate of 10 ° C./min based on the heat flux differential scanning calorimetry described in JIS K7122-1987, using 1-2 mg of the expanded particles as a measurement sample. From the first DSC curve obtained when heating and melting to 30 ° C. higher than the end of the melting peak, and then maintained for 10 minutes at a temperature 30 ° C. higher than the end of the melting peak, followed by a cooling rate of 10 ° C. In the second DSC curve obtained by cooling to 40 ° C./min and again heating and melting to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 10 ° C./min, the first DSC The curve is based on the peak temperature of the melting peak of the second DSC curve, and has a melting peak having a peak temperature higher than the reference peak temperature (excluding the reference peak temperature). (Hereinafter, also referred to as "high-temperature peak".) Are those having substantially no crystal structure. Specifically, even if a high temperature peak appears, the high temperature peak heat amount is preferably less than 1 J / g, more preferably 0.5 J / g or less, and particularly preferably no high temperature peak appears.

  As will be described later, the expanded particles used in the present invention improve the heat resistance at the time of in-mold molding to prevent foam breakage and foam well, and further prevent shrinkage after thermoforming. In order to obtain a foamed particle molded body having a desired size, it is necessary to increase the crystallinity of the foamed particles. When the crystallinity is increased and a high temperature peak exists, secondary foaming at the time of in-mold molding is excessively inhibited, and the force for pressing the foam particles at the time of in-mold molding becomes weak, so that the foam particles are fused. May deteriorate. Further, if the foamed particles are further heated so as to sufficiently secondary-foam the foamed particles, bubbles of the foamed particles are destroyed, and there is a possibility that a good foamed particle molded body cannot be obtained.

  As described above, the polylactic acid-based resin expanded particles of the present invention have a crystal structure that does not substantially exhibit a high temperature peak. Next, the high temperature peak will be described in detail. 1 obtained by raising the foamed particles at a rate of 10 ° C./min from 23 ° C. to 30 ° C. higher than the end of the melting peak, based on the heat flux differential scanning calorimetry described in JIS K7122 (1987) The first DSC curve (hereinafter also referred to as the first DSC curve (I)) and then maintained at a temperature 30 ° C. higher than the end of the melting peak for 10 minutes, and then at a cooling rate of 10 ° C./min. The second DSC curve (hereinafter referred to as the second DSC curve (I)) obtained when cooled to 30 ° C. and heated to 30 ° C. higher than the end of the melting peak at a heating rate of 10 ° C./min. The peak temperature of the melting peak of the second DSC curve (however, when a plurality of melting peaks appear in the second DSC curve (I) or a shoulder portion appears on the high temperature side of the melting peak). In the case of the melting peak apex and shoulder inflection points, the melting peak apex temperature or shoulder inflection temperature on the highest temperature side is the melting peak of the second DSC curve (I). The melting peak having an apex temperature on the higher temperature side (excluding the reference apex temperature) than the reference apex temperature is a high temperature peak. A melting peak having a peak temperature on the lower temperature side (including the reference peak temperature) than the reference peak temperature is also referred to as a low temperature peak. One or more high temperature peaks and low temperature peaks each appear.

The high temperature peak appears only in the first DSC curve (I) of the expanded particles obtained by the differential scanning calorimetry, and does not appear in the second DSC curve (I). The presence or absence of the high temperature peak appears in the first DSC curve (I) of the expanded particles when a polylactic acid resin crystal is grown by performing the heat treatment described later, and the heat treatment is performed so as to suppress the crystal growth. For example, it will not appear. The low temperature peak appearing in the first DSC curve (I) of the expanded particles is a melting peak due to an inherent crystal structure that appears in ordinary molding processing of a polylactic acid resin.
The phenomenon that a high temperature peak appears or disappears in the first DSC curve (I) of such expanded particles is caused by secondary crystals formed by thermal history when the expanded particles are obtained by expanding the resin particles. It can be considered that it is caused.

An example of the first DSC curve (I) is shown in FIG. 1, and an example of the second DSC curve (I) is shown in FIG. From the comparison between FIG. 1 and FIG. 2, the melting peak having the apex temperature on the higher temperature side than the reference apex temperature in FIG. 1 on the basis of the apex temperature of the melting peak on the highest temperature side of the two melting peaks in FIG. 2. Is a high temperature peak, and a melting peak having a peak temperature on the lower temperature side than the reference peak temperature is a low temperature peak. Therefore, in FIG. 1, the melting peak a is a low temperature peak and the melting peak b is a high temperature peak.
In the present specification, the peak temperature of the melting peak having the largest area in the second DSC curve (I), that is, the peak temperature of the melting peak c is defined as the melting point (Tm) of the polylactic acid resin, The temperature at which the skirt returns to the baseline is defined as the melting end temperature (Te).

  In FIG. 1, the two melting peaks a and b are drawn with smooth curves. However, the DSC curve is not necessarily a smooth curve as described above, and the overlapping of a plurality of melting peaks becomes a DSC curve. As a whole, a plurality of low temperature peaks and a plurality of high temperature peaks may appear on the DSC curve.

As shown in FIG. 1, the high temperature peak calorific value (J / g) is defined as a point α where the melting peak departs from the low temperature side baseline of the melting peak of the first DSC curve (I), and the melting peak is on the high temperature side. The point that returns to the baseline of the graph is point β, and the point γ on the DSC curve corresponding to the valley between the low temperature peak a and the high temperature peak b is parallel to the vertical axis of the graph from the point γ to the straight line connecting the point α and the point β. When a line is drawn and the intersection is point δ, a straight line connecting point γ and point δ, a straight line connecting point δ and point β, and a portion surrounded by DSC curve (I) (shaded portion in FIG. 1) The endothermic amount corresponding to the area. Although not shown in FIG. 1, an exothermic peak may appear continuously with the melting peak a on the low temperature side of the melting peak a. In such a case, as described above, the melting peak has a low temperature. Since it is difficult to determine the point α as the point where the melting peak is separated from the base line on the side, in that case, the point where the exothermic peak is separated from the base line on the low temperature side is defined as the point α.

The expanded particles used in the present invention preferably have a crystallinity of 20% or more, more preferably 25% or more. The upper limit is approximately 35%, preferably 30%.
If the degree of crystallinity is too small, foaming tends to break due to steam heating during in-mold molding, and even if a foamed particle molded body is obtained, shrinkage after in-mold molding becomes large, and the desired dimensional accuracy is obtained. There is a risk of not being able to.

The degree of crystallinity is determined by the following equation (1).
Crystallinity = [(Bf: endo) − (Bf: exo)] / 93 × 100 (1)
Here, (Bf: endo) is the total heat absorption amount in the first DSC curve for the expanded particles, and (Bf: exo) is the total heat generation amount in the first DSC curve for the expanded particles.

  Note that [(Bf: endo)-(Bf: exo)] is the crystal part that the foamed particles already had when performing the heat flux differential scanning calorimetry, and the foamed particles in the temperature rising process during the measurement. Endotherm (Bf: endo), which is energy absorbed when the crystallized part melts, and energy released by the crystallization of the foamed particles in the temperature rising process of the heat flux differential scanning calorimetry This represents the difference from the calorific value (Bf: exo), and the larger the difference is, the closer to the value of the endothermic amount (Bf: endo), the more the crystallization of the expanded particles progressed before the measurement (the degree of crystallinity is large). ) Means.

  The endothermic amount (Bf: endo) is preferably 20 to 50 J / g. The larger the endothermic amount (Bf: endo), the higher the degree of crystallinity of the polylactic acid resin constituting the expanded particles by heat treatment, and finally the expanded particle molded body is adjusted to have a high mechanical strength. I can do it. On the other hand, when the endothermic amount (Bf: endo) is too small, there is a possibility that the mechanical strength of the foamed particle molded body, particularly the mechanical strength under high temperature conditions, may be insufficient. In this respect, (Bf: endo) is more preferably 25 J / g or more, and particularly preferably 30 J / g or more. The upper limit of (Bf: endo) is approximately 45 J / g, preferably 40 J / g.

In the present specification, the exothermic amount (Bf: exo) and endothermic amount (Bf: endo) of the expanded particles are values determined by the above conditions, and the exothermic amount (Bf: exo) and endothermic amount (Bf: endo). The measurement of is performed according to the following criteria.
The exothermic amount (Bf: exo) of the expanded particles is a point c where the exothermic peak departs from the low temperature side baseline of the exothermic peak (synonymous with the crystallization peak) of the first DSC curve (II), and the exothermic peak is high. The point returning to the base line on the side is a point d, and is a value obtained from the straight line connecting the point c and the point d and the area of the portion showing the heat generation amount surrounded by the DSC curve. In addition, the endothermic amount (Bf: endo) of the expanded particles is a melting peak at a point where the melting peak departs from the low temperature side baseline of the melting peak (synonymous with the endothermic peak) of the first DSC curve (II). The point at which the point returns to the base line on the high temperature side is a point f, and is a value obtained from the straight line connecting the point e and the point f and the area of the portion showing the endothermic amount surrounded by the DSC curve. However, the apparatus is adjusted so that the baseline in the first DSC curve (II) is as straight as possible. If the baseline is inevitably curved, the curved baseline on the low temperature side of the exothermic peak is extended to the high temperature side while maintaining the curved state of the curve. The point at which the exothermic peak deviates from the point c, and the curved base line on the high temperature side of the exothermic peak is extended to the low temperature side while maintaining the curved state of the curve, and the exothermic peak appears on the curved high temperature side baseline Let the point to return be a point d. Further, the curved base line on the low temperature side of the melting peak is drawn to extend to the high temperature side while maintaining the curved state of the curved line, and the point where the melting peak moves away from the curved low temperature side baseline is point e. Drawing is performed to extend the curved base line on the high temperature side of the peak to the low temperature side while maintaining the curved state of the curve, and the point at which the melting peak returns to the curved high temperature side baseline is defined as a point f.

  For example, in the case shown in FIG. 5, the calorific value (Bf: exo) of the expanded particles is obtained from the area of the portion showing the calorific value surrounded by the straight line connecting the points c and d defined as described above and the DSC curve. The endothermic amount (B: endo) of the expanded particles is obtained from the area of the portion indicating the endothermic amount surrounded by the straight line connecting the points e and f and the DSC curve defined as described above. In the case shown in FIG. 6, since it is difficult to determine the point d and the point e as described above, the intersection of the straight line connecting the point c and the point f determined as described above and the DSC curve. Is determined as point d (point e) to determine the heat generation amount (Bf: exo) and the heat absorption amount (Bf: endo) of the expanded particles. In addition, as shown in FIG. 7, when a small exothermic peak occurs on the low temperature side of the melting peak, the exothermic amount (Bf: exo) of the expanded particles is the first exothermic peak in FIG. It is obtained from the sum of the area A and the area B of the second exothermic peak. That is, the area A is defined as a point c where the exothermic peak moves away from the low temperature side baseline of the first exothermic peak, and a point d where the first exothermic peak returns to the high temperature side baseline. It is assumed that the area A of the portion showing the heat generation amount surrounded by the straight line connecting the point d and the DSC curve. The area B is defined as a point g where the second exothermic peak moves away from the low temperature side baseline of the second exothermic peak, a point f where the melting peak returns to the high temperature side baseline, and point g The intersection of the straight line connecting the point f and the DSC curve is defined as a point e, and is defined as the area B of the portion showing the heat generation amount surrounded by the straight line connecting the point g and the point e and the DSC curve. On the other hand, in FIG. 7, the endothermic amount (Bf: endo) of the expanded particles is a value obtained from the area of the portion indicating the endothermic amount surrounded by the straight line connecting the points e and f and the DSC curve.

The bulk density of the expanded particles used in the present invention is preferably 15 to 250 kg / m ³ .

  In addition, the average cell diameter of the polylactic acid-based resin expanded particles of the present invention is preferably 30 to 500 μm, more preferably 50 to 250 μm, from the viewpoint of further improving the in-mold moldability and the appearance of the obtained expanded foam molded body. It is more preferable that

The average cell diameter of the expanded particles is measured as follows.
Based on an enlarged photograph obtained by photographing a cut surface obtained by dividing the expanded particle into approximately equal parts by a microscope, it can be obtained as follows. In the enlarged photograph of the cut surface of the expanded particle, four line segments passing through the approximate center of the bubble cut surface are drawn from one surface of the expanded particle to the other surface. However, the line segments are drawn so as to form radial straight lines extending in eight directions at equal intervals from the approximate center of the bubble cut surface to the cut particle surface. Next, the total number N of bubbles that intersect the four line segments is determined. A total sum L (μm) of the lengths of the four line segments is obtained, and a value (L / N) obtained by dividing the total L by the total N is defined as an average cell diameter of one expanded particle. This operation is carried out for 10 expanded particles, and the value obtained by arithmetically averaging the average cell diameter of each expanded particle is taken as the average cell diameter of the expanded particles.

  The closed cell ratio of the expanded particles is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. If the closed cell ratio is too small, the secondary foamability of the foamed particles tends to be inferior, and the mechanical properties of the resulting foamed particle molded body tend to be inferior.

The closed cell ratio of the expanded particles is measured as follows.
The expanded particles are allowed to stand for 10 days in a temperature-controlled room at atmospheric pressure, relative humidity of 50% and 23 ° C. Next, in the same constant temperature room, the apparent volume Va is accurately measured by the submersion method as follows using the foamed particles after curing having a bulk volume of about 20 cm ³ as a measurement sample. After the sample for measurement in which the apparent volume Va is measured is sufficiently dried, the measurement is performed by an air comparison type hydrometer 930 manufactured by Toshiba Beckman Co., Ltd. according to the procedure C described in ASTM-D2856-70. The true volume Vx of the working sample is measured. And based on these volumes Va and Vx, the closed cell ratio is calculated by the following formula (2), and the average value of N = 5 is set as the closed cell ratio of the expanded particles.

Closed cell ratio (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (2)
However,
Vx: the sum of the true volume of the expanded particles measured by the above method, that is, the volume of the resin constituting the expanded particles and the total volume of bubbles in the closed cell portion in the expanded particles (cm ³ )
Va: The apparent volume of the expanded particles (cm ³ ) measured from the rise in the water level after the expanded particles are submerged in a graduated cylinder containing water.
W: Weight of the foam particle measurement sample (g)
ρ: Density of resin constituting expanded particles (g / cm ³ )

The expanded particles used in the present invention preferably have a fusibility improving layer on the surface. In the expanded particles of the present invention, if the fusing property is improved as compared with the expanded particles not having the fusing property improving layer, the fusing property improving layer does not need to cover the whole expanded particle.
The fusing property improving layer is made of, for example, a polymer having a melting point or a softening temperature lower than that of the crystalline polylactic acid resin constituting the expanded particles, such as polyvinyl acetate, polyvinyl alcohol, polyester, and polyesteramide. It is preferable to be configured. The method for forming the fusibility improving layer on the foam particles is not particularly limited, and the surface of the foam particles may be coated with the fusibility improving layer, and the surface of the resin particles before foaming may be improved. A fusible layer may be formed on the surface of the foamed particles by covering with a layer and foaming the resin particles.

  Next, foamed particles having a fusibility-improving layer on the surface (hereinafter referred to as “foamed particles”) obtained by foaming resin particles containing crystalline polylactic acid whose surface is covered with a fusibility-improving layer composed of a polylactic acid-based resin. , Also referred to as multilayer expanded particles).

In the multilayer foamed particles, the softening point (B) [° C.] of the polylactic acid resin constituting the fusibility improving layer constitutes a foamed layer portion (hereinafter also referred to as a foam core layer) of the multilayer foamed particles. Lower than the softening point (A) [° C.] of the polylactic acid based resin, and the difference [(A) − (B)] between the softening point (A) and the softening point (B) exceeds 0 ° C. The difference is preferably not higher than ° C., more preferably the difference is 15 to 105 ° C., and further preferably 20 to 105 ° C. Expanded particles having this difference within this range are described later, such as a co-extrusion method of a polylactic acid-based resin showing a softening point (B) and a softening point (A) constituting the fusibility improving layer and the foam core layer. By this method, it is possible to efficiently obtain multi-layer foamed particles, and the foamed particles obtained in this way are more stable and exhibit excellent heat-fusibility during in-mold molding. It becomes foamed particles.
The softening point (B) of the polylactic acid-based resin constituting the fusibility improving layer constitutes the core layer from the viewpoint of the handleability of the foamed particles and the mechanical strength at high temperatures of the obtained foamed particle molded body. The relationship with the softening point (A) of the polylactic acid resin is in the above range, and is preferably 50 ° C. or higher, more preferably 55 ° C. or higher, and particularly preferably 65 ° C. or higher.

  The softening point in this specification means the Vicat softening temperature measured by the A50 method based on JIS K7206 (1999). As a measurement test piece, after the polylactic acid resin is sufficiently dried using a vacuum oven, it is pressurized under the conditions of 200 ° C. and 20 MPa, and an air venting operation is performed as necessary so that bubbles are not mixed. A test piece having a length of 20 mm × width of 20 mm × thickness of 4 mm is prepared, and the test piece is annealed in an oven at 80 ° C. for 24 hours and used for measurement. As a measuring apparatus, “HDT / VSPT test apparatus MODEL TM-4123” manufactured by Ueshima Seisakusho Co., Ltd. can be used.

In the foamed particles comprising the foam core layer and the fusing property improving layer of the present invention, the weight ratio of the resin forming the foam core layer and the resin forming the fusing property improving layer is 99.9: 0. 0.1 to 80:20, preferably 99.7: 0.3 to 90:10, and more preferably 99.5: 0.5 to 92: 8.
Since the weight ratio between the resin forming the core layer of the foamed particles and the resin forming the fusibility improving layer is within the above range, the fusion strength between the foamed particles is increased. The foamed particle molded article obtained is particularly excellent in mechanical properties, and the mechanical properties are further improved by increasing the ratio of the foam core layer that contributes to improving the physical properties of the expanded particles.
In addition, the adjustment of the weight ratio of the resin forming the foam core layer and the resin forming the fusibility improving layer in the foam particles is the core of polylactic acid resin particles (hereinafter also referred to as resin particles). This is done by adjusting the weight ratio of the resin forming the layer and the resin forming the fusing property improving layer.

  In this invention, it is preferable that the said end blocker to the polylactic acid-type resin which comprises a foamed particle is added to the foam core layer at least, and it is added to both a foam core layer and a fusibility improvement layer. It is more preferable. Since the polylactic acid-based resin constituting at least the foam core layer, preferably both the foam core layer and the fusion-improving layer, is end-capped, hydrolysis during the production of the foamed particles of the resin can be suppressed and stable. As a result, expanded particles can be produced. Furthermore, hydrolysis during foamed particle molded body production can be suppressed, leading to stable production of the foamed particle molded body, and being able to withstand use under high temperature and humidity even when used as a product, etc. Durability improvement can be expected.

  Regarding the thickness of the fusibility improving layer of the expanded particles, it is preferable that the thickness is thinner because bubbles are less likely to be generated in the fusible improving layer and the mechanical properties of the expanded foam molded body are improved. The average thickness of the fusibility improving layer of the expanded particles is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and particularly preferably 0.3 to 5 μm. In order to adjust the average thickness of the fusibility improvement layer of the expanded particles to be within the above range, the weight ratio of the fusibility improvement layer and the core layer at the resin particle stage is adjusted to adjust the fusibility of the resin particles. What is necessary is just to adjust the average thickness of an improvement layer. The average thickness of the resin particle fusibility improving layer varies depending on the weight of the resin particles, the expansion ratio, etc., but is preferably 2 to 100 μm, more preferably 3 to 70 μm, and particularly preferably 5 to 50 μm. In the present invention, it is not necessarily excluded that the resin forming the fusibility improving layer is foamed.

  The average thickness of the fusibility improving layer of the foamed particles is measured as follows. Divide the expanded particles roughly in half, and from the enlarged cross-sectional photograph, obtain the thickness of the four layers of the fusion-improving layer at the top, bottom, left, and right of the cross-section. Say it. This operation is performed for 10 expanded particles, and the value obtained by arithmetically averaging the thicknesses of the fusibility improving layers of the respective expanded particles is defined as the average thickness of the fusibility improving layers in the expanded particles. The average thickness of the resin particle fusibility improving layer is also measured by the same method. In addition, when the fusibility improving layer is partially formed around the foam core layer, the thickness of the four fusibility improving layers may not be measured by any means. The thicknesses of the four fusibility improving layers that can be measured are obtained, and the average is defined as the thickness of the one fusible particle or resin particle fusibility improving layer. Moreover, when it is difficult to understand the thickness of the fusibility improving layer of the expanded particles, it is preferable to add resin to the resin constituting the fusibility improving layer in advance to produce the resin particles.

  By performing in-mold molding using the foamed particles of the present invention, a polylactic acid resin foamed particle molded body is obtained. The shape is not particularly limited, and plate-like, columnar, container-like, and block-like shapes are naturally stable in three-dimensional complicated shapes, particularly those having thin thin portions or fitting portions. Can be obtained.

  The foamed particle molded body becomes a foamed particle molded body having excellent heat resistance such as rigidity, compressive strength at high temperature, and dimensional stability by further heat treatment and further crystallization of the polylactic acid resin.

  As described above, the foamed particle molded body obtained as described above is lightweight and excellent in mechanical properties, and since fine foam particles are used, a thin portion and a fitting portion can be provided. The thickness of the thin portion is preferably 10 mm or less, more preferably 5 mm or less.

  From the viewpoint of mechanical strength such as compression properties, the closed cell ratio of the foamed particle molded body is preferably 60% or more, more preferably 70% or more, and further preferably 80% or more.

The measurement of the closed cell ratio of the foamed particle molded body was performed by cutting a sample of 25 × 25 × 30 mm from the center of the foamed particle molded body (cutting off all skin) and using it as a measurement sample. It can be obtained in the same manner as the measurement. If a sample of the above size cannot be cut out, a plurality of samples may be cut out and used for measurement so that the total volume of the samples approaches 18750 mm ³ .

The foamed particle molded body of the present invention is excellent in the fusion property between the foamed particles, and the fusion rate is preferably 50% or more, more preferably 60% or more, and particularly preferably 80% or more. A foamed particle molded body having a high fusion rate is excellent in mechanical properties, particularly bending strength.
The fusing rate means a material destruction rate based on the number of fractured surface foamed particles when the foamed particle molded body is ruptured. The unfused part does not break the material and peels at the interface of the foamed particles. To do. A method for measuring the fusion rate will be described later.

Next, the manufacturing method of the polylactic acid-type resin expanded particle molded object of this invention is demonstrated.
First, examples of the method for producing foamed particles in the present invention include an extrusion foaming method, a gas impregnation prefoaming method, a dispersion medium discharge foaming method, and other foaming methods based on these methods and principles.

  The extrusion foaming method includes, for example, melt-kneading a polylactic acid resin in an extruder, press-fitting a physical foaming agent into the extruder, and kneading to obtain a foamable molten resin. This is a method for producing expanded particles by cutting a strand-like foam obtained by extrusion. In this method, the resin particle production process, the foaming agent impregnation process, and the foaming process are performed as one process using one extruder. Regarding this method, refer to JP2007-100025A and International Publication WO2008 / 123367. In addition, when obtaining the foamed particles in the present invention by an extrusion foaming method, a fusibility improving layer can be formed on the surface of the foamed particles by a coextrusion foaming method.

  The gas impregnation pre-foaming method, for example, melts and kneads a polylactic acid-based resin with an extruder, then extrudes it into strands and cuts it, and then fills the resin particles in a pressure-tight sealed container. The resin foam is impregnated with the foaming agent by press-fitting a physical foaming agent into the pressure vessel, and the foamable resin particles are put into a pre-foaming machine, and steam, hot air, or the like The foamed resin particles are foamed by heating with a heating medium such as a mixture of the above to obtain foamed particles. In the step of impregnating the resin particles with the foaming agent by press-fitting a physical foaming agent into the pressure vessel, a liquid phase impregnation method or a gas phase impregnation method can be appropriately selected. In the gas impregnation pre-foaming method, the resin particle production process, the foaming agent impregnation process, and the foaming process are performed as separate processes. For this method, refer to JP 2000-136261 A, JP 2006-282750 A, and the like. In the case where the expanded particles in the present invention are obtained by the gas impregnation pre-expanding method, resin particles having a fusibility improving layer formed on the surface of the core layer are prepared by a coextrusion molding method described later, and the resin particles are By causing foaming, a fusibility improving layer can be formed on the surface of the foamed particles.

  In the dispersion medium release foaming method, for example, resin particles are produced in the same manner as described above, and the resin particles are dispersed in an aqueous medium in a sealed container and heated to be impregnated with a physical foaming agent to obtain foamable resin particles. The foamable resin particles are produced by discharging the foamable resin particles together with an aqueous medium from a closed container at a foaming suitable temperature. In this method, the resin particle production step, the foaming agent impregnation step, and the foaming step can be performed as separate steps, but the foaming agent impregnation step and the foaming step are usually performed as one step. Hereinafter, the production method of the polylactic acid-based resin expanded particles will be described in detail with a focus on the dispersion medium release foaming method.

In the resin particle production process, the resin particles can be produced by a strand cut method, an underwater cut method, or the like in which additives necessary for the base resin are blended, extruded, and pelletized.
Resin particles comprising the core layer and the fusion-improving layer include, for example, Japanese Patent Publication No. 41-16125, Japanese Patent Publication No. 43-23858, Japanese Patent Publication No. 44-29522, Japanese Patent Publication No. 60-185816. Can be produced using the coextrusion molding technique described in the above.

The average weight per resin particle is preferably 0.1 mg or more and less than 2 mg because the foamed particles can be obtained.
If the average weight is too light, the production of resin particles becomes special. On the other hand, when the average weight is too heavy, there is a possibility that a desired thin part or fitting part cannot be obtained.
As the shape of the resin particles, a columnar shape, a spherical shape, a prismatic shape, an elliptical spherical shape, a cylindrical shape, or the like can be adopted. Foamed particles obtained by foaming such resin particles have a shape substantially corresponding to the shape of the resin particles before foaming.

  In the step of obtaining the resin particles by melting and kneading the base resin with an extruder as described above to obtain resin particles, it is preferable to dry the polylactic acid resin, which is a constituent component of the base resin, in advance. In this case, deterioration due to hydrolysis of the polylactic acid resin can be suppressed. Moreover, in order to suppress degradation due to hydrolysis of the polylactic acid-based resin, a method of removing moisture from the polylactic acid-based resin by performing vacuum suction using an extruder with a vent port can be employed. By removing water from the polylactic acid-based resin, it is possible to suppress the generation of bubbles in the resin particles and improve the stability during extrusion production.

Next, the foaming agent impregnation step and the foaming step in the dispersion medium releasing foaming method will be described.
In the dispersion medium discharge foaming method, for example, the resin particles are dispersed and heated together with the dispersion medium and the physical foaming agent in the pressure resistant container, or the resin particles are dispersed and heated together with the dispersion medium in the pressure resistant container, and then physically foamed. The resin particles are impregnated with a physical foaming agent by press-fitting an agent into the pressure vessel to obtain expandable resin particles. Next, the expandable resin particles are expanded by releasing the expandable resin particles together with the dispersion medium under a pressure lower than that in the pressure vessel, thereby obtaining expanded particles.

A foaming aid can be added in advance to the resin particles. Examples of the foaming aid include inorganic substances such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, silica, polytetrafluoroethylene, polyethylene wax, polycarbonate, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, High molecular weight materials such as polycyclohexanedimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, silicone, methyl methacrylate copolymer, and crosslinked polystyrene can be employed.
Of the above foaming aids, polytetrafluoroethylene, polyethylene wax, cross-linked polystyrene and the like are preferable in the present invention, and hydrophobic polytetrafluoroethylene powder is more preferable.

  When adding a foaming aid to the base resin, the foaming aid can be kneaded into the base resin as it is, but in consideration of dispersibility, etc. It is preferable to knead the base resin.

  Since the apparent density and the bubble diameter of the expanded particles of the present invention vary depending on the amount of the foaming aid added, the effect of adjusting them can be expected. Usually, it is preferable to add 0.001 to 5 parts by weight of a foaming assistant to 100 parts by weight of the base resin, more preferably 0.005 to 3 parts by weight, and still more preferably 0.01 to 2 parts by weight. It is.

Since polylactic acid-based resins are easily hydrolyzed, it is preferable to avoid the hydrophilic substances as much as possible and to select and add hydrophobic substances as additives to the base resin. By adopting a hydrophobic foaming aid as the foaming aid, the effect as a foaming aid can be obtained while suppressing deterioration due to hydrolysis of the polylactic acid-based resin.
In this case, it is possible to reduce the apparent density (improve the expansion ratio) and make the bubble diameter uniform while sufficiently suppressing the hydrolysis of the polylactic acid resin.

In the dispersion medium releasing foaming method, as described above, for example, resin particles are dispersed in a dispersion medium such as water in a pressurizable closed container (for example, an autoclave), a dispersant is added, and a required amount of foaming agent is added. After impregnating and pressurizing and stirring under heating for a required time to impregnate the polylactic acid resin particles with the foaming agent, the container contents are released below the pressure inside the container to lower the pressure range, thereby foaming the resin particles, Expanded particles are obtained. At the time of this discharge, it is preferable to discharge the container with back pressure. Moreover, when obtaining expanded particles having a particularly low apparent density (high expansion ratio), the expanded particles obtained by the above-described method are subjected to a normal curing step under atmospheric pressure, and can be pressurized again. And the pressure is increased by, for example, 0.01 to 0.10 MPa (G) with a pressurized gas such as air to increase the pressure in the foamed particles. Then, by using a heating medium such as hot air, steam or a mixture of air and steam, expanded particles having a lower apparent density can be obtained (this process is hereinafter referred to as two-stage foaming).
In addition, from the viewpoint of obtaining foamed particles having a low apparent density as compared with the extrusion foaming method, and obtaining foamed particles having excellent in-moldability and good physical properties, the production method of the foamed particles is as described above. A gas impregnation prefoaming method and a dispersion medium releasing foaming method are preferred, and a dispersion medium releasing foaming method is particularly preferred.

  As the dispersion medium in which the resin particles are dispersed, other than the above-described water, any material that does not dissolve the polylactic acid-based resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like. Water is preferable.

Further, when dispersing the resin particles in the dispersion medium, a dispersant can be added to the dispersion medium as necessary.
Examples of the dispersant include inorganic substances such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, titanium oxide, zinc oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, kaolin, mica, and clay, and polyvinylpyrrolidone. , Water-soluble polymer protective colloid agents such as polyvinyl alcohol and methylcellulose. In addition, as a dispersion aid, an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium alkanesulfonate can be added to the dispersion medium.
These dispersing agents can be used in an amount of 0.05 to 3 parts by weight per 100 parts by weight of the resin particles, and these dispersing aids can be used in an amount of 0.001 to 0.3 parts by weight per 100 parts by weight of the resin particles. .

Examples of the blowing agent include hydrocarbons such as butane, pentane and hexane, organic physical blowing agents such as halogenated hydrocarbons such as trichlorofluoromethane, dichlorofluoromethane, tetrachlorodifluoroethane, and dichloromethane, carbon dioxide, nitrogen, An inorganic physical foaming agent such as an inorganic gas such as air or water can be used alone or in combination of two or more. Among these physical foaming agents, it is preferable to use a physical foaming agent mainly composed of an inorganic physical foaming agent such as carbon dioxide, nitrogen or air. More preferred is carbon dioxide.
The term “inorganic physical foaming agent as a main component” means that the inorganic physical foaming agent in 100 mol% of the total physical foaming agent is 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more. Means that.

  The addition amount of the physical foaming agent can be appropriately adjusted according to the type of foaming agent, the blending amount of the additive, the apparent density of the desired foamed particles, and the like. For example, the inorganic physical foaming agent is used in an amount of generally 0.1 to 30 parts by weight, preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight per 100 parts by weight of the base resin.

  In the present invention, as described above, it is necessary to obtain expanded particles in which a high temperature peak does not appear in the DSC curve. As a method for that purpose, it is preferable to foam the resin particles under conditions such that secondary crystallization of polylactic acid does not occur. When producing expanded particles by the above-mentioned dispersion medium releasing foaming method, the expansion temperature is in the range of the melting point of crystalline polylactic acid constituting the expanded particles from −22 ° C. to + 10 ° C., and the retention time at the expansion temperature is within 60 minutes. It is preferable that

Next, the manufacturing method of the expanded particle molding of this invention is demonstrated. In manufacturing the foamed particle molded body, a known in-mold molding method can be employed.
For example, a compression molding method, a cracking molding method, a pressure molding method, a compression filling molding method, a normal pressure filling molding method (for example, Japanese Patent Publication No. 46-38359, Japanese Patent Publication No. 51) using a conventionally known foamed particle molding die. No. 22951, Japanese Patent Publication No. 4-46217, Japanese Patent Publication No. 6-22919, Japanese Patent Publication No. 6-49795, etc.).

  In-mold molding method that is usually preferably performed, the foam particles are filled into a cavity of a conventionally known thermoplastic resin foam particle molding mold that can be heated and cooled and that can be opened and closed and sealed, The foamed particles are expanded by supplying water vapor with a saturated vapor pressure of 0.01 to 0.25 MPa (G), preferably 0.01 to 0.20 MPa (G), and heating the foamed particles in a mold. Examples thereof include a batch type in-mold molding method in which the foamed particle molded body obtained by fusing and then cooling is taken out from the cavity, and a continuous in-mold molding method described later.

  As the method for supplying the water vapor, a conventionally known method in which heating methods such as one heating, reverse one heating, and main heating are appropriately combined can be adopted. In particular, a method of heating the expanded particles in the order of preliminary heating, one-side heating, reverse one-side heating, and main heating is preferable.

  The foamed particle molded body continuously supplies the foamed particles into a mold formed by a belt that moves continuously along the upper and lower sides of the passage, and the saturated vapor pressure is reduced when passing through the steam heating region. 0.01 to 0.25 MPa (G) of water vapor is supplied to expand and fuse the expanded particles, and then cooled by passing through a cooling region, and then the obtained expanded expanded particles are taken out from the passage, It can also be produced by a continuous in-mold molding method (for example, see JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.) which is sequentially cut into lengths.

Prior to in-mold molding, foamed particles obtained by the above method are filled into a pressurizable sealed container, and foaming is performed by increasing the pressure in the foamed particles by pressurizing with a pressurized gas such as air. After the pressure inside the particles is adjusted to 0.01 to 0.15 MPa (G), the foamed particles are taken out from the container and molded in the mold, thereby further improving the in-mold moldability of the foamed particles. I can do it.

  Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples.

  Table 1 shows the raw materials used for producing the expanded particles.

Examples 1 to 7, Comparative Examples 1 and 2
As an apparatus for producing multilayer resin particles, an extruder having a core layer forming extruder with an inner diameter of 65 mm and an extruder provided with a co-extrusion die for forming a multilayer strand on the outlet side of an extruder with an inner diameter of 30 mm for improving the fusing property is used. It was.
In the extruder for forming the core layer and the extruder for forming the fusibility improving layer, the base resin and the carbodiimide (Bioamide 100, end-capping agent) for forming the core layer and the fusibility improving layer shown in Table 1, respectively. (Rhein Chemie) was supplied to each extruder at the ratio shown in Table 2, and melt-kneaded at 200 to 220 ° C. The melt-kneaded material is introduced into the co-extrusion die, merged in the die, and from the fine pores of the die attached to the tip of the extruder, the multi-strand is formed as a multilayer strand in which a fusibility improving layer is formed on the side surface of the core layer. The extruded and co-extruded strand was cooled with water, cut with a pelletizer so that the weight was as shown in Table 2, and dried to obtain multilayer resin particles.
In addition, polytetrafluoroethylene powder (trade name: TFW-1000, manufactured by Seishin Enterprise Co., Ltd.) is supplied in a master batch so that the content of the polylactic acid resin in the core layer is 1000 ppm by weight as a foam regulator. did. A phthalocyanine green pigment was added to the polylactic acid resin of the fusibility improving layer in a master batch so that the content was 100 ppm by weight. In Example 7, 30% by weight of polybutylene succinate (product name: Bionore # 1001, manufactured by Showa Denko KK, melting point 114 ° C.) was blended in the fusibility improving layer.
The crystallinity of the raw material was calculated by the formula (1) by the above method.

Next, polylactic acid resin foamed particles were produced using the multilayer resin particles.
First, 1 kg of the resin particles obtained as described above were charged into a 5 L autoclave equipped with a stirrer together with 3 L of water as a dispersion medium, and 0.45 parts by weight of aluminum oxide as a dispersant in the dispersion medium. A surfactant (trade name: Neogen S-20F, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., sodium alkylbenzene sulfonate) was added as an active ingredient in an amount of 0.01 part by weight. Next, carbon dioxide was injected into the autoclave until the pressure in the autoclave reached 1.0 MPa (G). And it heated up to the foaming temperature shown in Table 1 under stirring, and carbon dioxide was further injected until it became the pressure shown in Table 2, and it hold | maintained at the foaming temperature shown in Table 2 for 15 minutes. Thereafter, the contents in the autoclave were released under atmospheric pressure while applying a back pressure with nitrogen to obtain expanded polylactic acid resin particles having an apparent density shown in Table 2. In addition, the addition amount (parts by weight) of the dispersant and the surfactant is an amount with respect to 100 parts by weight of the polylactic acid resin particles.

Table 2 shows the production conditions of the polylactic acid-based resin expanded particles (the pressure in the sealed container and the expansion temperature).
Moreover, various physical properties of the obtained expanded particles were measured. The results are shown in Table 2.

Next, a foamed particle molded body was produced using the foamed particles.
The obtained foamed particles are filled into a mold for molding a flat molded article of 250 mm × 200 mm × 20 mm (cracking 4 mm) and molded in-mold by pressure molding by steam heating to form a flat foam particle molded article. Got. In Example 5, expanded particles to which an internal pressure of 0.05 MPa (G) was applied were used.
The heating method is described in Table 3 after supplying steam for 8 seconds with the double-sided drain valve open and preheating (exhaust process), and then closing the double-sided drain valve for 8 seconds from both sides. Heated with steam at a pressure of.

After completion of heating, the pressure was released, and after cooling with water until the surface pressure due to the foaming force of the molded body decreased to 0.02 MPa (G), the mold was opened and the molded body was taken out of the mold. The obtained molded body was cured in an oven at 40 ° C. for 15 hours, then cured in an oven at 70 ° C. for 15 hours, and then gradually cooled to room temperature. In this way, a foamed particle molded body was obtained.
Similarly, a foamed particle molded body was obtained using a mold for molding a casing molded body (outer dimensions 40 mm × 60 mm × 85 mm) having a thin portion of 5 mm.
Various properties were measured and evaluated for the foamed particle molded body thus obtained. The results are shown in Table 3.

Each item was measured and evaluated as follows.

[Bulk density of expanded particles]
The expanded particles are allowed to stand for 10 days in a temperature-controlled room at atmospheric pressure, relative humidity of 50% and 23 ° C. Next, the weight W1 (g) of the foam particle group after curing of about 500 ml is measured in the same temperature chamber, and the weight of the measured foam particle group is measured with water at a temperature of 23 ° C. using a tool such as a wire mesh. Sink into the graduated cylinder. Next, the volume V1 (L) of the expanded particle group, which is read from the rise in the water level, by subtracting the volume below the surface of the tool such as a wire mesh, is measured, and the weight W1 of the expanded particle group placed in the measuring cylinder is determined as the volume V1. The apparent density (kg / cm ³ ) was determined by dividing by (W1 / V1). The value obtained by dividing this apparent density by 1.6 was taken as the bulk density (kg / cm ³ ) of the expanded particles.

[Endotherm (Bf: endo) and calorific value (Bf: exo), crystallinity]
It was measured by the method described above.

[Closed cell ratio]
It was measured by the method described above.

[Average bubble diameter]
It was measured by the method described above.

“Number of expanded particles per 1 cm ² ”
The surface of the foamed particle molded body was observed, the number of foamed particles present in a 4 cm × 4 cm square was determined, and the unit was converted.
This was repeated 5 times, and the arithmetic average value of the expanded particles existing within 1 cm ² was determined.

"Surface smoothness of molded products"
The surface of the foamed particle molded body was observed with the naked eye and evaluated according to the following criteria.
A: The surface of the foamed particle molded body has a good surface state with few particle gaps and no unevenness.
◯: Particle gaps and / or irregularities are slightly observed on the surface of the foamed particle molded body.
Δ: Particle gaps and / or irregularities are clearly observed on the surface of the foamed particle molded body.
X: The particle | grain space | interval and / or unevenness | corrugation are remarkable on the surface of a foaming particle molded object.

[Fusion rate]
The fusion rate was measured and evaluated by the following method. The foamed particle molded body is bent and broken, and the number of foamed particles (C1) and the number of broken foamed particles (C2) present on the fractured surface are determined, and the ratio of the foamed particles broken to the foamed particles (C2 / C1) × 100) was calculated as the material fracture rate. The above measurement was performed 5 times using different test pieces, the respective material destruction rates were obtained, and the arithmetic average value thereof was defined as the fusion rate.

"Shrinkage factor"
The lateral dimensional change of the foamed particle molded body after curing with respect to the dimension of the flat plate mold was determined by the following equation.
Shrinkage rate (%) = (1− (minimum dimension (mm) / 250 mm in transverse direction of foamed particle molded body after curing)) × 100

"Appearance density of molded body"
It calculated | required by dividing the weight of a foamed particle molded object by the volume of a foamed particle molded object. In addition, the volume of the foamed particle molded body was determined by a submerging method.

[Recovery]
The surface of the obtained foamed particle molded body had wrinkles and shrinkage, and those that did not retain the mold shape were determined to be rejected and indicated as x. A foamed particle molded body that did not have wrinkles or shrinkage and retained the shape of the mold was determined to be acceptable and indicated as ◯.

[Tensile strength]
A measurement sample (dumbbell-shaped No. 1 as defined in JIS K6251; thickness 10 mm (with a molding skin on one side)) cut out from a flat foam particle molded body was left for 24 hours at 23 ° C. and 50% humidity. In accordance with K6767 (1999), the tensile test was carried out five times at a test speed of 500 mm / min, the tensile strength in each test piece was determined from the maximum load up to cutting, and was described as the arithmetic mean value thereof. .

[Tensile strength / apparent density]
The tensile strength / apparent density was obtained by dividing the tensile strength [kPa] by the apparent density [kg / m ³ ].

  From Table 2, the foamed particle molded products of Examples 1 to 7 satisfy the range specified by the present invention in terms of the ratio of tensile strength / apparent density, and have surface smoothness, recoverability, fusion property, and mechanical strength. It was confirmed that the foamed particle molded body was excellent in dimensional stability.

  On the other hand, Comparative Example 1 is an example in which the amount of heat at the high temperature peak of the foamed particles used for the production of the foamed particle compact is too high. The specified range was not satisfied, the fusing property was inferior, the gap between the expanded particles was large, and the surface smoothness was inferior. In addition, in order to improve the secondary foamability at the time of molding in the mold, the molding steam pressure was increased and molding was performed in the mold, but the foamed particle molded body contracted greatly, and also a good foamed particle molded body was obtained. I couldn't.

Comparative Example 2 is an example where the degree of crystallinity of the foamed particles used in the production of the foamed particle molded body is low, and the obtained foamed particle molded body has a range in which the ratio of tensile strength / apparent density is specified in the present invention. Unsatisfactory, poor fusion and surface smoothness, large dimensional shrinkage, and could not obtain a good foamed particle molded body.

Claims (2)

In a foamed particle molded body having an apparent density of 15 to 68 kg / m ³ formed by in-mold molding of foamed particles containing a crystalline polylactic acid-based resin,
The number of the expanded particles constituting the expanded particle molded body in a plan view is 15 or more per unit area [cm ² ], and the average weight per expanded particle is 0.1 to 1.5 mg. state, and it is specific (tensile strength / apparent density) is ^{10 [kPa · m 3 / kg} ] or the apparent density of PP bead molding [kg / ^{m 3]} tensile strength to [kPa], the mold molding The foamed particles used are melted from 23 ° C. at a heating rate of 10 ° C./min based on the heat flux differential scanning calorimetry described in JIS K7122-1987, using 1-2 mg of the foamed particles as a measurement sample. A first DSC curve obtained when heating and melting to a temperature 30 ° C. higher than the end of the peak, and then maintaining for 10 minutes at a temperature 30 ° C. higher than the end of the melting peak, followed by a cooling rate of 10 ° C./min At 40 In the second DSC curve obtained when cooled to 30 ° C. and heated again to a temperature 30 ° C. higher than the end of the melting peak at a heating rate of 10 ° C./min, the first DSC curve includes 2 Having a crystal structure in which a melting peak having an apex temperature does not appear on the higher temperature side (excluding the reference apex temperature) than the reference apex temperature based on the apex temperature of the melting peak of the second DSC curve, or A melting peak having an apex temperature appears on a higher temperature side (excluding the reference apex temperature) than the reference apex temperature, and the melting peak calorie has a crystal structure of less than 1 J / g; crystallinity is not less than 20%, and polylactic acid resin foamed bead molded article, wherein Rukoto which have a fusion-enhancing layers on the surface of the expanded beads.
The said foaming particle molded object has a thin part 10 mm or less in thickness, The polylactic acid-type resin expanded particle molded object of Claim 1 characterized by the above-mentioned.