JP2011068734A - Polylactic acid resin foam, method for producing the same, and expansion-molded product obtained by molding the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid resin foam having excellent secondary expansion property and capable of performing in-mold expansion molding easily. <P>SOLUTION: This polylactic acid resin foam is produced by extrusion-foaming a polylactic acid resin composition including a crystalline polylactic acid resin, a pyrolytic chemical foaming agent and a physical foaming agent. The polylactic acid resin foam has an area average cell diameter of 1-200 μm. The polylactic acid resin foam has a ratio of ≥0.6 of the area average cell diameter of an outside in a foam cross-section to that of an inside in the foam cross-section, and has a rate of change of ≥1.5 in an expansion ratio before and after the secondary expansion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polylactic acid-based resin foam having excellent secondary foamability and capable of being easily subjected to in-mold foam molding, a foamed molded body formed by molding the polylactic acid-based resin foam, and the poly The present invention relates to a method for producing a lactic acid resin foam.

  In recent years, aliphatic polyesters having features such as biodegradability and plant origin are attracting attention from the viewpoint of reducing environmental impact. Among the aliphatic polyesters, polylactic acid is not only excellent in mechanical properties but also uses starch and corn as raw materials and can be mass-produced. Furthermore, the polylactic acid resin foam foamed with a foaming agent is a cushioning material and packaging material similar to conventional foamed moldings derived from petroleum raw materials, taking advantage of its light weight, cushioning properties, sound deadening properties, heat insulation properties, etc. Can be used for silencer and building materials.

  Up to now, there have been many reports on prior art relating to foamed particles (particulate foams) by the bead foaming method using amorphous polylactic acid with low optical purity and foamed molded bodies formed by molding the foamed particles. (For example, refer to Patent Document 1). However, since it is amorphous, it is inferior in heat resistance, and the heat resistance of the obtained foam was about 50 ° C. For this reason, the foamed molded product obtained by molding the foam particles has a problem that it is inferior in dimensional stability when heated to 60 ° C. or more, and is limited to low temperature applications.

  In addition, as a prior art related to expanded particles and expanded molded articles, which are made of crystalline polylactic acid with high optical purity and have excellent heat resistance, primary expanded particles prepared so as to keep the degree of crystallinity low by an extrusion foaming method. Has been reported to be subjected to in-mold foaming and crystallized after secondary foaming (see, for example, Patent Document 2). However, in this case, advanced techniques are required in the method for controlling the degree of crystallinity of the foamed particles and the method of foaming in the mold, and since the secondary foamability is poor, a foamed molded article can be easily produced. It wasn't.

  In addition, in the production of a styrene resin foam or the like, a technique in which a physical foaming agent and a pyrolytic chemical foaming agent are used in combination has been reported (for example, see Patent Document 3). However, in this case, since there are both large bubbles (for example, bubbles of about 200 to 500 μm) and fine bubbles (for example, bubbles of 0.1 μm or less), the secondary foamability is inferior, and a foam molded article is obtained. There is a problem that even if it is obtained, the appearance is impaired.

JP 2005-264166 A JP 2007-100025 A JP 2005-041516 A

  The present invention solves the above-mentioned problems of the prior art, and comprises a crystalline polylactic acid resin, a pyrolytic chemical foaming agent, and a physical foaming agent, and has excellent secondary foaming properties and is easily in-mold. It is an object of the present invention to provide a polylactic acid resin foam that can be foam-molded and a method for producing the polylactic acid resin foam. It is another object of the present invention to provide a foamed molded article having a small volume change rate after heating obtained from the polylactic acid-based resin foam and having a stable dimension and excellent appearance.

  As a result of intensive studies to solve the above problems, the present inventors have used a polylactic acid resin composition comprising a crystalline polylactic acid resin, a pyrolytic chemical foaming agent, and a physical foaming agent. By adjusting the amount of addition and extrusion conditions, etc., the area average cell diameter of the polylactic acid resin foam is 1 to 200 μm, the area average cell diameter outside the foam cross section and the area average cell diameter inside It was found that the ratio was 0.6 or more, and the rate of change in the expansion ratio before and after secondary foaming could be 1.5 or more. And, such a polylactic acid-based resin foam has significantly improved secondary foamability, and can easily be subjected to in-mold foam molding. Further, when it is made into a foam molded body, there is little volume change after heating, The inventors have found that a foamed molded article having an excellent appearance can be obtained, and arrived at the present invention based on such knowledge.

That is, the gist of the present invention is as follows.
(1) A polylactic acid resin foam obtained by extrusion foaming a polylactic acid resin composition comprising a crystalline polylactic acid resin, a thermal decomposable chemical foaming agent, and a physical foaming agent, wherein the polylactic acid The area average cell diameter of the resin-based resin foam is 1 to 200 μm, and the ratio of the area average cell diameter outside the cross section of the polylactic acid-based resin foam to the area average cell diameter inside is 0.6 or more, 2 A polylactic acid resin foam characterized in that the rate of change in the expansion ratio before and after the next foaming is 1.5 or more.
(2) The polylactic acid resin foam according to (1), wherein the pyrolyzable chemical foaming agent comprises an azo compound.
(3) The polylactic acid resin foam according to (1) or (2), wherein the shape is particulate.
(4) A foam molded article obtained by in-mold foam molding of the polylactic acid resin foam of (1) to (3).
(5) A method for producing a foamed product of (1) to (3), wherein 0.01 to 3 parts by mass of a pyrolytic chemical foaming agent is supplied to an extruder with respect to 100 parts by mass of a polylactic acid resin. And a method for producing a polylactic acid-based resin foam, which comprises extrusion foaming in the presence of a physical foaming agent.

  The polylactic acid resin foam of the present invention uses a polylactic acid resin composition comprising a crystalline polylactic acid resin, a thermal decomposable chemical foaming agent and a physical foaming agent, and has an area average cell diameter of 1 to 1. 200 μm, the ratio of the area average cell diameter outside the foam cross section to the area average cell diameter inside is 0.6 or more, and the rate of change of the expansion ratio before and after the secondary foaming is 1.5 or more. It has foaming properties and can easily be subjected to in-mold foam molding. The polylactic acid-based resin foam of the present invention can be easily obtained by molding, and the obtained foamed molded article of the present invention is excellent in dimensional stability after heating. It has heat resistance that can be used satisfactorily even in a high-temperature atmosphere exceeding ℃, and has an excellent appearance.

  Furthermore, according to the method for producing a polylactic acid resin foam of the present invention, the polylactic acid resin foam of the present invention can be obtained with high productivity.

The schematic diagram of the elongation time and elongation viscosity at the time of calculating | requiring the inclination a1 (a2 / a1; strain hardening coefficient) of the elongation stage after the bending point and the inclination a2 (a2 / a1; strain hardening coefficient) after the bending point until the bending point appears is shown. The electron micrograph of the cross section (TD cross section) of the foam (strand shape) obtained in Example 1 is shown. The electron micrograph of the cross section (TD cross section) of the foam (strand shape) obtained by the comparative example 1 is shown. The electron micrograph of the cross section (TD cross section) of the foam (strand shape) obtained by the comparative example 2 is shown.

Hereinafter, the present invention will be described in detail.
The polylactic acid resin foam of the present invention (hereinafter sometimes simply referred to as “foam”) is a polylactic acid resin composition (hereinafter referred to as “polylactic acid resin composition”) comprising a polylactic acid resin, a thermal decomposable chemical foaming agent and a physical foaming agent. Or simply referred to as “resin composition”).

  The polylactic acid-based resin is a resin containing polylactic acid as a main component, and preferably contains 40% by mass or more of polylactic acid from the viewpoint of reducing environmental load. When the polylactic acid is contained in an amount of 60% by mass or more, the degree of plant origin is increased, more preferably 80% by mass or more.

Furthermore, in the foam of the present invention, the polylactic acid resin needs to be crystalline in order to have heat resistance that can be used even in a high temperature atmosphere exceeding 100 ° C.
Especially, it is preferable that the D-form content rate of polylactic acid is 8% or less, or 92% or more. Since the melting point is high and crystallization easily proceeds, the D-form content is preferably 4% or less, or preferably 96% or more, and more preferably the D-form content is 2% or less. Or 98% or more.
Polylactic acid having a D-form content of more than 8% or less than 92% has a very low crystallization rate and substantially no crystallization, resulting in insufficient heat resistance.

  In the said polylactic acid-type resin, in the range which does not impair the effect of this invention, other resin components other than the polylactic acid which is a main component can be contained. Examples of the resin component other than polylactic acid include polyester resin, polyethylene resin, polypropylene resin, polystyrene resin, and polyacrylic acid resin. Polyester resins include hydroxy acid polycondensates other than polylactic acid, ring-opening polymers of lactones such as polycaprolactone, and aliphatic polyhydric alcohols such as polybutylene succinate, polybutylene adipate, polybutylene succinate adipate, and fat. A polycondensation product with an aliphatic polycarboxylic acid, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene adipate terephthalate, and the like, an aliphatic polyhydric alcohol, an aliphatic polycarboxylic acid, and an aromatic polycarboxylic acid Examples include polycondensates. These resins may be used alone or in combination of two or more.

The polylactic acid resin in the present invention preferably has rheological properties suitable for foaming. Examples of rheological properties include indicators such as strain hardening and melt tension.
Regarding the strain hardening property, in the time-elongation viscosity curve obtained by measuring the extension viscosity at a temperature 10 ° C. higher than the melting point of the polylactic acid-based resin, the inclination a1 of the linear region in the initial elongation until the inflection point appears, and the inflection point When the ratio (a2 / a1; strain hardening coefficient) to the slope a2 of the later elongation is 1.05 or more and less than 50, it is a polylactic acid resin that exhibits strain hardening properties suitable for foaming. It can be said (see FIG. 1).

  As a method for controlling the strain hardening property, a method of modifying the polylactic acid by adding a crosslinking agent or a thickener is preferably used. For example, polylactic acid and (meth) acrylic acid ester having two or more (meth) acrylic groups in the molecule, or one or more (meth) acrylic groups and one or more glycidyl groups or vinyl groups By melt-kneading the compound and the peroxide, a polylactic acid-based resin having strain-hardening properties and suitable for foaming can be obtained. Alternatively, a polylactic acid resin suitable for foaming can also be obtained by melt-kneading polylactic acid and a compound having two or more glycidyl groups, isocyanate groups or carbodiimide groups in the molecule.

  The melt tension is preferably 40 to 1000 mN from the viewpoint of foamability. It is more preferably 50 to 800 mN, and further preferably 60 to 400 mN.

The melt tension is measured by the following method.
The pellet-shaped resin composition dried in advance is filled into a cylinder of a capillary rheometer (Toyo Seiki Seisakusho, trade name “Capillograph 1C”) set at 190 ° C., and the piston is placed on the cylinder and heated for 5 minutes. . Thereafter, the strand extruded at a piston speed of 10 mm / min is drawn from the die (1 mmφ × 10 mm length) at the bottom of the cylinder at an initial speed of 1 mm / min, and the tension is detected with a tensiometer. Thereafter, the take-up speed is gradually increased, and the tension when the strand is ruptured is defined as melt tension (mN).

In the present invention, the melting point of the polylactic acid-based resin is preferably 140 to 190 ° C, more preferably 160 to 190 ° C, from the viewpoint of improving the crystallinity.
The content ratio of the polylactic acid resin to the polylactic acid resin composition is preferably 25% by mass or more, more preferably 50% by mass or more, and even more preferably 80% by mass or more from the viewpoint of reducing environmental burden. Is preferred.

  And in the polylactic acid-type resin composition which forms the foam of this invention, the thermal decomposition type chemical foaming agent and the physical foaming agent are added with the above polylactic acid-type resin. For this reason, there is an advantage that fine and independent bubbles can be generated as compared with the case where the pyrolytic chemical foaming agent and the physical foaming agent are added to the polylactic acid resin alone.

  The pyrolytic chemical foaming agent acts as a bubble regulator during extrusion foaming to form fine bubbles, and further plays a role of newly generating fine bubbles during secondary foaming. In the present invention, extrusion foaming refers to foaming the resin composition obtained in the present invention using an extrusion foaming machine. In the present invention, secondary foaming refers to obtaining a molded body by further foaming a foam obtained by extrusion foaming. Details of extrusion foaming and secondary foaming will be described later.

  Pyrolytic chemical foaming agent is a foaming agent that generates gas by heating above the decomposition temperature to foam the resin. Both organic thermal decomposition chemical foaming agent and inorganic thermal decomposition chemical foaming agent Are preferably used. Examples of the organic pyrolytic chemical foaming agent include azo compounds, nitroso compounds, hydrazine derivatives, semicarbazide compounds, azide compounds, and tetrazole compounds. Representative examples include azodicarbonamide (ADCA), N, N′-dinitrosopentamethylenetetramine (DPT), 4,4′-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA) and the like. Can be mentioned. Examples of the inorganic pyrolytic chemical foaming agent include bicarbonate, carbonate, nitrite and the like. A typical example is sodium bicarbonate. Among these, an organic chemical foaming agent in which a decomposition reaction rapidly occurs when a certain temperature is reached is more preferable. Among these, an azo compound is particularly preferable from the viewpoint of having a decomposition temperature close to the temperature of melt extrusion of a polylactic acid resin and having the most versatility.

The decomposition temperature of the thermally decomposable chemical foaming agent is preferably 180 to 230 ° C., more preferably 190 to 220 ° C., in accordance with the melt extrusion temperature of the polylactic acid resin.
Said thermal decomposition type chemical foaming agent may be used independently, and may be used in combination of 2 or more type.

  The addition amount of the pyrolytic chemical foaming agent is usually preferably 0.01 to 3 parts by weight, more preferably 0.01 to 2 parts by weight, and 0.1 to 1 part by weight with respect to 100 parts by weight of the polylactic acid resin. Part is more preferable. The larger the amount of the pyrolytic chemical foaming agent added, the smaller the area average cell diameter described later. However, if it exceeds 3 parts by mass, foaming by the physical foaming agent may be hindered and the expansion ratio may be reduced. On the other hand, if it is less than 0.01 part by weight, the effect of adding the above-described pyrolytic chemical foaming agent may not be sufficiently achieved.

  In addition, since a thermal decomposition type chemical foaming agent decomposes | disassembles at the time of a heating and generate | occur | produces gas, the thermal decomposition type chemical foaming agent may not fully be contained in the foam after melt-kneading or extrusion foaming. Therefore, in order to adjust the decomposition temperature of the pyrolytic chemical foaming agent, a foaming aid may be used as long as the effects of the present invention are not impaired. Examples of the foaming aid include urea, zinc oxide, magnesium oxide, zinc stearate, barium stearate, calcium hydroxide and the like.

  Next, the physical foaming agent will be described. The physical foaming agent used in the present invention is a foaming agent that foams a resin with a gas expanded by a temperature change or pressure change without a chemical reaction, and grows microbubbles contained by the pyrolytic chemical foaming agent. It plays a main role in extrusion foaming. As the physical foaming agent, either an organic physical foaming agent or an inorganic physical foaming agent can be suitably used.

  Examples of organic physical foaming agents include propane, normal butane, isobutane, cyclobutane, normal pentane, isopentane, normal hexane, cyclohexane, and the like; trichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, 1-chloro-1,1 -Halogenated hydrocarbons such as difluoroethane and 1,2,2,2-tetrafluoroethane; and ethers such as dimethyl ether and methyl ethyl ether.

  Examples of the inorganic foaming agent include water, nitrogen, carbon dioxide, argon, air and the like. Among these, propane, butanes, pentanes, and carbon dioxide are preferably used. These foaming agents are used alone or in combination of two or more.

  The addition amount of the physical foaming agent is 1 to 8 parts by mass with respect to 100 parts by mass of the polylactic acid resin composition when an organic physical foaming agent such as a hydrocarbon having a relatively high solubility in the polylactic acid resin is used. Is preferable, and particularly preferably 1 to 4 parts by mass.

  The addition amount when using an inorganic physical foaming agent such as carbon dioxide having relatively low solubility in the polylactic acid resin is 0.1 to 1.5 parts by mass with respect to 100 parts by mass of the polylactic acid resin composition. Is preferable, and 0.1 to 0.6 parts by mass is particularly preferable. In either case, if the amount is too smaller than the above range, foaming does not occur sufficiently and the expansion ratio may be small. In addition, sufficient secondary foamability may not be obtained, and the change rate of the expansion ratio before and after the secondary foaming of the obtained foam may be less than 1.5. On the other hand, if there are too many physical foaming agents beyond the above range, bubbles breakage occurs, or bubbles are coalesced inside the foam, and the area average bubbles outside the foam cross section shown in the formula (1) described later The ratio between the diameter and the inner area average bubble diameter (bubble diameter ratio) may be small. Furthermore, bubbles that are not closed by being connected to the foam surface (open bubbles) are generated, and sufficient secondary foamability cannot be obtained, and in-mold foam molding may not be performed.

  In general, when an inorganic physical foaming agent such as carbon dioxide having a relatively low solubility in a polylactic acid-based resin is used in extrusion foaming, the polylactic acid-based resin can be extruded and foamed. It is difficult to obtain a foam having excellent foamability. However, in the present invention, by using the above pyrolytic chemical foaming agent, it is possible to sufficiently foam by extrusion foaming and at the same time obtain a foam having excellent secondary foamability. It becomes.

  In the present invention, a cell regulator may be added to the polylactic acid resin composition for the purpose of obtaining finer bubbles. Examples of the air conditioner include titanium oxide, talc, kaolin, clay, calcium silicate, silica, sodium citrate, calcium carbonate, diatomaceous earth, calcined perlite, zeolite, bentonite, glass, limestone, calcium sulfate, aluminum oxide, titanium oxide. , Magnesium carbonate, sodium carbonate, ferric carbonate, polytetrafluoroethylene powder and the like. The cell regulator preferably has an average particle diameter of 0.1 to 100 μm, more preferably 1 to 20 μm, in view of dispersibility and the target cell diameter.

0.01-5 mass parts is preferable with respect to 100 mass parts of polylactic acid-type resin compositions, and, as for content of a bubble regulator, 0.1-3 mass parts is especially preferable. If the amount is less than 0.01 parts by mass, the effect of adding the air conditioner does not appear and the foam bubbles become coarse, and the area-average cell diameter described later may increase, or the appearance may be impaired. On the other hand, if it exceeds 5 parts by mass, foam breakage is likely to occur during extrusion foaming, so that the closed cell ratio may be reduced or the appearance may be impaired. In addition, since many of the cell regulators also function as crystal nucleating agents, when added excessively, crystallization of polylactic acid may be promoted excessively, and secondary foamability and foam moldability may be impaired.
In the present invention, the area average cell diameter of the foam can be adjusted mainly by adjusting the addition amount of the pyrolytic chemical foaming agent in the polylactic acid resin composition.

  The area average bubble diameter of the foam represents the average value of the diameters of the bubbles. When the foam is cut, the bubbles appearing on the cut surface are those obtained by cutting any part of the spherical bubbles, but those calculated from the mean square of the bubble diameter of the bubble cut surface are as follows. It is an area average bubble diameter. The area average bubble diameter is related to the secondary foaming property and is calculated as follows.

First, the foam obtained by extrusion foaming is frozen with liquid nitrogen, and the frozen foam is cut in a TD direction with a thickness of 100 μm by a microtome. Next, using an ion sputtering (manufactured by Hitachi High-Tech, trade name “Hitachi Ion Sputter E1030”), the cut surface is subjected to a sputter coating process of 5 nm with platinum. The sputter coating treatment conditions are as follows: degree of vacuum: 8 Pa, voltage: 0.4 kV, current: 15 mA, time: 60 seconds, gas: argon. Next, the cut surface subjected to the sputter coating treatment is observed with a scanning electron microscope (trade name “S4000” manufactured by Hitachi, Ltd.), and the diameters (bubble diameters) of all the bubbles are measured. When the bubbles are not circular but elliptical, the average value of the short diameter and diameter is taken as the bubble diameter. In addition, when the number of bubble diameters per cut surface exceeds 200, the bubble diameter is measured for the semi-circular or quarter cut surface bubbles. Then, the area average bubble diameter is calculated by the following formula (a).
(A) Area average bubble diameter = [(bubble diameter of TD cross section) ² ] / [sum of bubble diameter of TD cross section]
The TD direction refers to a direction perpendicular to the extrusion direction of the foam, and the TD cross section indicates a cross section when the foam is cut in the TD direction.

  In the present invention, the area average bubble diameter is required to be 1 to 200 μm, and since gas dissipation can be further suppressed, it is preferably 1 to 150 μm, and more preferably 1 to 80 μm. When the area average bubble diameter exceeds 200 μm, there is a problem that the gas in the bubbles is easily dissipated and the secondary foaming property is impaired or the appearance of the foamed molded product is impaired. On the other hand, when the area average cell diameter is less than 1 μm, foaming is not sufficient, the foaming ratio is low, and the secondary foaming property is also poor.

  In the present invention, the foam cross section (TD cross section) is divided into an outer side and an inner side so that the area is equally divided. The cross-sectional shape is not particularly limited, and any shape can be adopted. For example, in the case of a circular shape, the center side is defined as the inner side from the segmented boundary line, and the circumferential side is defined from the segmented boundary line. It is on the outside. In the case of a circle, the TD cross section is divided by a concentric circle having a radius of 71 when the radius of the TD cross section is 100, and the center side from the boundary line is set to the inner side, and the circumferential side from the boundary line is set to the outer side. . At this time, the outer and inner areas are equally divided.

In the present invention, the bubble diameter ratio is a ratio of the area average bubble diameter outside the foam cross section to the area average bubble diameter inside and is involved in secondary foamability.
The bubble diameter ratio is calculated by the following formula (A).
(A) Bubble diameter ratio = (Area average cell diameter outside the TD cross section of the foam) / (Area average cell diameter inside the TD cross section of the foam)
In the above formula (A), the outer and inner area average bubble diameters are determined by the above formula (A).
In the present invention, the bubble diameter ratio is adjusted to 0.6 or more by adjusting the bubble diameter mainly by adjusting the addition amount of the pyrolytic chemical foaming agent and simultaneously adjusting the addition amount of the physical foaming agent. Can do. Among these, the bubble diameter ratio is preferably 0.75 or more, and more preferably 0.9 or more. When the bubble diameter ratio is less than 0.6, foam breakage and bubble coalescence frequently occur at the time of foam production, so gas is not retained inside the foam during secondary foaming, and sufficient secondary There is a problem that foamability cannot be obtained.

  In the polylactic acid resin composition of the present invention, a foaming aid may be used in addition to the above-mentioned cell regulator, within the range that does not impair the effects of the present invention for the purpose of improving the expansion ratio. The foaming aid is not particularly limited, and examples thereof include lower alcohols, ketones, benzene and toluene.

  Furthermore, an additive can be added to the polylactic acid resin composition of the present invention as long as the effects of the present invention are not impaired. Additives include heat stabilizers, antioxidants, pigments, weathering agents, flame retardants, plasticizers, dispersants, crystal nucleating agents, lubricants, mold release agents, antistatic agents, crosslinking agents, chain extenders, and end-capping agents. Agents, fillers and the like. These additives are generally added during melt-kneading, extrusion foaming, or polymerization.

  Examples of heat stabilizers and antioxidants include phosphite organic compounds, hindered phenol compounds, benzotriazole compounds, triazine compounds, hindered amine compounds, sulfur compounds, copper compounds, alkali metal halides, or Mixtures of these can be used.

  Examples of the crystal nucleating agent include titanium oxide, talc, kaolin, clay, calcium silicate, silica, sodium citrate, calcium carbonate, diatomaceous earth, calcined perlite, zeolite, bentonite, glass, limestone, calcium sulfate, aluminum oxide, titanium oxide. , Magnesium carbonate, sodium carbonate, ferric carbonate, polytetrafluoroethylene powder and the like.

Examples of the terminal blocking agent include carbodiimide, oxazoline, and epoxy compound.
Dispersants include industrial oils such as liquid paraffin, mineral oil, creosote oil, lubricating oil, silicone oil; vegetable oils such as corn oil, soybean oil, rapeseed oil, palm oil, linseed oil, jojoba oil; ionic or nonionic Surfactants and the like.

  Examples of the filler include inorganic fillers and organic fillers. Inorganic fillers include talc, layered silicate, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloon , Carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fiber, metal whisker, ceramic whisker, potassium titanate, boron nitride, graphite, glass fiber, carbon fiber and the like. Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood flour, okara, fir shell, bran and kenaf, and modified products thereof. These additives may be used alone or in combination of two or more.

  The foam of this invention has secondary foamability by having the above structures. Specifically, in the foam of the present invention, the rate of change in the expansion ratio before and after secondary foaming is required to be 1.5 or more, and preferably 2 times or more. When the rate of change in the expansion ratio before and after secondary foaming is less than 1.5, a foam that does not have sufficient secondary foaming properties and is sufficiently foamed by secondary foaming such as in-mold foam molding is obtained. I can't.

The rate of change in the expansion ratio before and after secondary foaming in the present invention is measured and calculated as follows.
First, the mass and the apparent volume of the polylactic acid resin composition forming the foam are measured, and the apparent density of the polylactic acid resin composition is calculated from the mass and the apparent volume.

  Next, the polylactic acid resin composition is subjected to extrusion foaming as described below to obtain a foam. Then, the mass and the apparent volume of the foam are measured, and the density of the foam is calculated from the mass and the apparent volume.

  Next, carbon dioxide was given an internal pressure of 0.5 MPa at 30 ° C. in a pressure-resistant container in a foam (in the case of a sheet shape or a strand shape, cut into foam particles having a particle diameter of 1 to 5 mm). Then, it is heated in a dry hot air at 120 ° C. without being filled in the mold, and is subjected to secondary foaming. The mass and the apparent volume of the foam after the secondary foaming are measured, and the apparent density of the foam after the secondary foaming is calculated from the mass and the apparent volume.

In the present invention, the apparent volume is measured using a wet electronic hydrometer.
Then, the expansion ratio is calculated from the following formula.
-Foaming ratio of foam before secondary foaming = (apparent density of polylactic acid resin composition) / (apparent density of foam before secondary foaming)
-Foaming ratio of foam after secondary foaming = (apparent density of polylactic acid resin composition) / (apparent density of foam after secondary foaming)
Then, the change rate of the expansion ratio before and after the secondary foaming is calculated from the expansion ratio of the foam before and after the secondary foaming by the following formula.
・ Change rate of expansion ratio before and after secondary foaming = (foaming ratio of foam after secondary foaming) / (foaming ratio of foam before secondary foaming)
Since the foam of the present invention has secondary foamability, it can be further optionally subjected to foam molding according to the application. For example, the foam is made into a strand shape, and the foam having the strand shape is cut to produce expanded particles. Next, the obtained foamed particles can be subjected to in-mold foam molding to obtain a foam molded article. That is, the foamed particles obtained from the foam of the present invention are filled in a mold for in-mold foam molding and heated to further foam the foam (secondary foaming). Obtainable.

  The foamed molded product of the present invention is obtained by secondary foaming of the foamed product of the present invention, thereby fusing the particles together, increasing the crystallinity of the polylactic acid resin, and improving heat resistance, buffering properties, and mechanical strength. It is excellent and it can be set as a foaming molding with little volume change after heating.

  When the foam of the present invention is subjected to in-mold foam molding and subjected to secondary foaming, the shape of the foam is preferably particulate. Due to the particulate form, the foam can be filled in the mold without any gap in the in-mold foam molding step. The particle diameter when the foam is made into particles is preferably 1 to 5 mm, more preferably 1 to 3 mm from the viewpoint of efficient filling.

  As a method of making the foam into particles, the foam is made into a strand shape by extrusion foaming, and thereafter. Examples of the cutting method include a pelletizer, a fan cutter, a hot cutter, and the like.

  Moreover, it is preferable that the foaming ratio (foaming ratio of the foam before secondary foaming) of the foam of the present invention is 2 to 100 times, more preferably 3 to 100 times, and further preferably 3 to 20 times. The foaming ratio of the foamed molding obtained by subjecting the foam of the present invention to secondary foaming is preferably 2 to 100 times, more preferably 4 to 100 times, and even more preferably 4 to 30 times.

Below, the manufacturing method of the polylactic acid-type resin foam of this invention is demonstrated.
The polylactic acid resin foam of the present invention is obtained by extrusion foaming a polylactic acid resin composition. In the method for producing a polylactic acid resin foam of the present invention, after adding a pyrolytic chemical foaming agent to the polylactic acid resin, the polylactic acid resin foam is supplied to an extruder and extruded and foamed in the presence of a physical foaming agent.

  As described above, the addition amount of the pyrolytic chemical foaming agent needs to be 0.01 to 3 parts by mass, more preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the polylactic acid resin. 0.1 to 1 part by mass is more preferable. When there is too much addition amount of a thermal decomposition type chemical foaming agent, it will become the hindrance at the time of foaming by a physical foaming agent. On the other hand, if it is less than 0.01 parts by mass, fine bubbles cannot be formed at the time of extrusion foaming, and secondary foamability cannot be imparted. The rate of change is less than 1.5.

  As described above, the addition amount of the physical foaming agent is 1 to 100 parts by mass with respect to 100 parts by mass of the polylactic acid resin when an organic physical foaming agent such as hydrocarbon having relatively high solubility in the polylactic acid resin is used. 8 parts by mass is preferable, and 1 to 4 parts by mass is particularly preferable. When an inorganic physical foaming agent such as carbon dioxide having a relatively low solubility in the polylactic acid resin is used, the physical foaming agent is added in an amount of 0.1 to 1.5 with respect to 100 parts by mass of the polylactic acid resin. A mass part is preferable, Most preferably, it is 0.1-0.6 mass part. In either case, if the amount of the physical foaming agent added is too small from the above range, the foam does not sufficiently foam and a foam having a small foaming ratio is obtained. In addition, sufficient secondary foamability may not be obtained, and the change rate of the expansion ratio before and after the secondary foaming of the obtained foam may be less than 1.5. On the other hand, if the amount of the physical foaming agent added is too much beyond the above range, foam breakage occurs, or bubbles are coalesced inside the foam, and the area outside the foam cross section shown in the above formula (A) The ratio of the average bubble diameter to the inner area average bubble diameter (bubble diameter ratio) may be small. Furthermore, bubbles (open bubbles) that are connected to the surface of the foam and are not closed are generated, and sufficient secondary foamability cannot be obtained, and the change rate of the expansion ratio before and after the secondary foaming of the obtained foam is 1. May be less than .5.

  As the extruder used for the production of the foam, a known and usual foaming extruder can be suitably used. Examples thereof include a single-screw extruder, a twin-screw extruder, and a tandem type extruder in which a plurality of extruders are connected. The barrel (cylindrical part, cylinder) of the extruder preferably has a part (melting zone) for melting the resin composition and a part (cooling zone) for cooling the obtained foam. In the present invention, the downstream side from the position where the physical foaming agent is injected and impregnated is a cooling zone, and the total of the melting zone and the cooling zone is preferably 20 or more, more preferably 30 or more. is there. Here, L indicates the length of the extruded portion (melting zone and cooling zone), and D indicates the diameter of the extruded portion.

  The melting temperature during extrusion foaming is preferably 180 to 230 ° C. Further, from the viewpoint of preventing bubble breakage, it is preferable that the temperature of the melting zone is 180 to 230 ° C, the temperature of the cooling zone is 130 to 180 ° C, and the die outlet temperature is 140 to 170 ° C.

  And by extrusion foaming, this polylactic acid-type resin composition can be extruded from a slit-shaped nozzle to make a foamed sheet shape, or it can be extruded from a round nozzle to make a foamed strand shape, thereby obtaining a foam. Furthermore, the shape of the polylactic acid-based resin foam of the present invention can be made into particles by cutting the foamed sheet or the foamed strand. Among these, from the viewpoint of handleability, it is preferable to cut the foamed strands obtained by extrusion from a round nozzle into particles.

  Moreover, in order to produce a foam molded body by secondary foaming of the foam, it is preferable to quickly cool the foam immediately after extrusion foaming to suppress the progress of crystallization. The method of cooling the foam immediately after extrusion foaming is not particularly limited, and a method of cooling by immersing in water, a method of cooling by blowing cold air, a method of cooling by contacting with a cooling plate, and the like are preferably used.

  The foam molded article of the present invention is preferably a foam molded article obtained by subjecting the foam of the present invention to in-mold foam molding. Examples of the heating medium at the time of in-mold foam molding (secondary foaming) include dry hot air, water vapor, and radiant heat, but steam is used from the viewpoint of high heating efficiency and good crystallization promotion. It is preferable to do.

  The apparatus used for in-mold foam molding is not particularly limited, and a known apparatus can be used. Examples thereof include a foaming polystyrene molding machine and a foaming polyolefin molding machine.

  As the temperature of the heating medium at the time of in-mold foam molding, although depending on the type of the heating medium and the size of the mold, while preventing crystallization before the secondary foaming, and from the viewpoint of secondary foaming without shrinking, 100-170 degreeC is preferable and 110-140 degreeC is more preferable.

  Furthermore, it is preferable to apply an internal pressure to the foam of the present invention in advance in a pressure vessel before being subjected to in-mold foam molding (secondary foaming). By applying the internal pressure, the foam exhibits a higher secondary foaming property, the fusibility between the foamed particles during molding is improved, and a foamed molded product having excellent mechanical strength can be obtained. Examples of the gas used for applying the internal pressure include air, carbon dioxide, and nitrogen. The pressure for applying the internal pressure is preferably 0.1 to 3 MPa, more preferably 0.2 to 1 MPa, from the viewpoints of gas penetration efficiency into the bubbles and shape retention. Moreover, as a temperature at the time of giving an internal pressure, below the glass transition temperature of a polylactic acid-type resin from a viewpoint of deformation | transformation prevention and crystallization suppression, 40 degrees C or less is more preferable. The time for applying the internal pressure is preferably 10 minutes or more, and more preferably 30 minutes or more, from the viewpoint of gas penetration efficiency into the bubbles.

  In addition, the foam with the internal pressure applied is heated at 50 to 90 ° C. and secondarily foamed without filling the mold, and then the internal pressure is again applied to fill the mold and heated. It may be molded (tertiary foaming). In this case, as a heating medium used for secondary foaming, it is preferable to use dry hot air that hardly promotes crystallization.

  The foamed body and foamed molded body of the present invention make use of its light weight, heat resistance, heat insulation, impact resistance, cushioning, and sound insulation properties to provide packaging materials, packing materials, cushioning materials, heat insulating materials, heat insulating materials, cold insulating materials. It can be used as a material, a sound deadening material, a sound absorbing material, a soundproof material, a vibration damping material, a building material, a cushion material, a material, a container, and the like. Specific examples include sofas, bed mats, chairs, bedding, mattresses, light covers, plush toys, slippers, cushions, helmets, carpets, pillows, shoes, pouches, mats, crash pads, sponges, stationery, toys, DIY supplies, Panels, tatami core materials, mannequins, automotive interior components, cushions, car seats, deadening, door trims, sun visors, automotive damping materials, sound absorbing materials, sports mats, fitness equipment, sports protectors, beat boards, ground fences, Leisure sheets, medical mattresses, medical supplies, care supplies, rehabilitation supplies, heat insulating materials for construction, building joint materials, face door materials, building curing materials, reflective materials, industrial trays, tubes, pipe covers, air conditioner heat insulating piping, gaskets Core material, concrete formwork, civil joints, icicle prevention pad , Protective materials, lightweight soil, embankment, artificial soil, packaging materials / packaging materials, packaging materials, wrapping, packaging materials / packaging materials for fresh products / vegetables / fruits, packaging materials / buffer packaging materials for electronic devices, fresh food Examples include food containers such as food / vegetables / fruits, food containers such as cup ramen / lunch boxes, edible trays, beverage containers, agricultural materials, foam models, and speaker diaphragms.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited only to an Example. In addition, the measurement and evaluation of the characteristic value in an Example were performed as follows.
(I) Melting point Using a differential scanning calorimeter (trade name “DSC-7” manufactured by Perkin Elmer Co., Ltd.), the melting point was measured under the condition of a heating rate of 10 ° C./min.
(Ii) Strain hardening coefficient (a2 / a1) (see FIG. 1)
A polylactic acid resin was press-molded at 210 ° C. to prepare a sheet having a thickness of 1 mm, and cut into a size of 60 mm × 7 mm × 1 mm to obtain a test piece. Using an extensional viscosity measuring device (trade name “RME” manufactured by Rheometric Co., Ltd.), both ends of the obtained test piece were supported by metal belt clamps. Next, stretch deformation is applied to the measurement sample at a strain rate of 0.1 sec ⁻¹ at a temperature 10 ° C. higher than the melting point of the polylactic acid resin, and stress (unit: Pa) applied to the pinch roller during the deformation is detected and stretched. The viscosity (unit: Pa · s) was determined. Further, in the logarithmic plot of elongation time and elongation viscosity, the ratio (a2 / a1) between the slope a1 of the linear region at the initial stage of elongation until the inflection point appears and the slope a2 of the later stage of elongation after the inflection point was calculated.
(Iii) Melt tension Measured by the method described above.
(Iv) Foaming ratio The apparent volume of the polylactic acid-based resin composition used, the obtained foam, and the obtained foamed molded article was measured using a wet electronic hydrometer (trade name “EW-300SG” manufactured by Alpha Mirage). The masses of these polylactic acid resin compositions, foams, and foamed molded products were measured, the apparent density was calculated from the apparent volume and mass, and the expansion ratio was determined from the following equation.
-Foam expansion ratio of foam = (apparent density of polylactic acid resin composition) / (apparent density of foam)
-Foaming ratio of foam molded article = (apparent density of polylactic acid resin composition) / (apparent density of foam molded article)
(V) Area-average cell diameter of foam The measurement was carried out by the method described above and calculated.
(Vi) Bubble diameter ratio Calculated by the above method.
(Vii) Rate of change in expansion ratio before and after secondary foaming Measurement and calculation were performed by the method described above.
(Viii) Evaluation of in-mold foam moldability The fusing properties of the foam-molded particles at the time of in-mold foam molding were visually confirmed and evaluated according to the following criteria.
○: Fusing well.
Δ: Partially fused, but the shape cannot be maintained.
X: not fused and not shaped.
In addition, what was (circle) in the said evaluation shall be able to endure practical use.
(Ix) Heated dimensional stability The obtained foamed molded product was heat-treated at 100 ° C. for 24 hours with a hot air dryer. The volume change rate before and after the heat treatment was evaluated according to the following criteria.
◯: Volume change rate is less than 5% ×: Volume change rate is 5% or more Note that the volume change rate was obtained from the following equation.
Volume change rate (%) = (Y−X) / X × 100
X: Volume of foam molded body before heating Y: Volume of foam molded body after heating

[material]
Various raw materials used in Examples and Comparative Examples are shown.
Polylactic acid-based resin A: crystalline polylactic acid for foaming (product name “HV-6250H” manufactured by Unitika)
Melting point: 165 ° C., D-form: 1.4%, strain hardening coefficient: 2.5, melt tension 110 mN
B: Crystalline polylactic acid for injection molding (product name “TE-6000”, manufactured by Unitika Ltd.)
Melting point: 165 ° C., D-form: 1.4%, strain hardening coefficient: 1.8, melt tension: 50 mN
・ Pyrolytic chemical foaming agent C: Azodicarbonamide (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name “Vinhoyl AC # 1C”)
Decomposition temperature: 199 ° C, median diameter: 7 µm
D: Azodicarbonamide (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name “Binihol AC # 3”)
Decomposition temperature: 208 ° C., median diameter: 17 μm
E: N, N′-dinitrosopentamethylenetetramine (manufactured by Eiwa Chemical Industry Co., Ltd., trade name “Cellular L-70” decomposition temperature 205 ° C.
-Physical foaming agent F: Carbon dioxide G: Normal butane-Bubble regulator H: Fine powder talc (trade name “MW-HST”, average particle diameter: 2.5 μm, manufactured by Hayashi Kasei Co., Ltd.)

Example 1
Biaxial extrusion foaming machine (manufactured by Ikegai Co., Ltd., trade name “PCM-30”, screw diameter: 29 mm, L / D: 30, nozzle diameter: 0.8 mm, number of holes: 30 holes, melting zone temperature (melting temperature): 210 ° C., cooling zone temperature: 135 to 160 ° C., die outlet temperature: 155 ° C.), and supplying polylactic acid resin A and pyrolytic chemical foaming agent C so as to achieve the addition amount shown in Table 1, From the middle of the extruder, the physical foaming agent F was injected using a liquefied carbon dioxide injection device (manufactured by Showa Carbon Dioxide Co., Ltd.) so as to have the addition amount shown in Table 1. The obtained polylactic acid-based resin composition was extruded at a discharge rate of 12 kg / h and extruded and foamed from a nozzle to produce a strand-shaped foam. The strand-shaped foam was immersed in water and cooled, and then processed into particles by a pelletizer to obtain expanded particles having a diameter of 2 mm. The expansion ratio of the expanded particles obtained at this time was 4 times.

  The obtained foamed particles were put in a pressure vessel, filled with carbon dioxide to 0.5 MPa, and an internal pressure was applied at 30 ° C. for 1 hour. The foamed particles taken out from the pressure vessel were immediately filled into a mold and heated with 120 ° C. water vapor to perform in-mold foam molding to obtain a foam molded article. The foaming ratio of the foamed molded product obtained at this time was 7 times.

Example 2
The expanded particles obtained in Example 1 were put in a pressure vessel, filled with carbon dioxide to 0.5 MPa, and an internal pressure was applied at 30 ° C. for 1 hour. Thereafter, the foamed particles were heated with hot air at 70 ° C. for 2 minutes to cause secondary foaming, and then an internal pressure was again applied at 30 ° C. for 1 hour. Next, the foamed particles taken out from the pressure vessel were immediately filled into the mold and heated with 120 ° C. water vapor to perform in-mold foam molding (tertiary foaming) to obtain a foam molded article.

Examples 3-20, Comparative Examples 1-9
Except for changing the type of polylactic acid resin, the type of thermal decomposable chemical foaming agent, the type of physical foaming agent, the amount of these additives, and the presence or absence of a cell regulator as shown in Table 1, it was the same as in Example 1. A foam and a foam molded product were obtained.

  Tables 1 and 2 show the evaluations of the foams and foamed molded products obtained in Examples and Comparative Examples.

表１から明らかなように、実施例１〜２０のポリ乳酸系樹脂組成物から得られる発泡体は、面積平均気泡径が小さく、気泡径比も大きく、２次発泡前後の発泡倍率の変化率が１．５以上であったので、２次発泡性に優れ、型内発泡成形性に優れた発泡成形体を得ることができた。そして、得られた発泡成形体は加熱後の体積変化が少なく寸法の安定したものであり、外観も良好であった。

As is clear from Table 1, the foams obtained from the polylactic acid-based resin compositions of Examples 1 to 20 have a small area average cell diameter and a large cell diameter ratio, and the rate of change in the expansion ratio before and after secondary foaming. Was 1.5 or more, it was possible to obtain a foam molded article having excellent secondary foamability and excellent in-mold foam moldability. The obtained foamed molded article had little volume change after heating, had a stable dimension, and had a good appearance.

  Since the pyrolytic chemical foaming agent was not added to the polylactic acid resin composition of Comparative Example 1, the obtained foam had a large area average cell diameter as shown in FIG. The change rate of the expansion ratio before and after became small. For this reason, the secondary foamability was poor and a foamed molded article could not be produced.

  In Comparative Example 2, since the amount of the physical foaming agent added in the polylactic acid resin composition was too large, the obtained foam had many bubbles as shown in FIG. The change rate of the expansion ratio before and after became small. For this reason, the secondary foamability was poor and a foamed molded article could not be produced.

  In Comparative Example 3, since the amount of the physical foaming agent added in the polylactic acid resin composition was too small, the obtained foam had a small area average cell diameter and a cell diameter ratio of 0.6 or more. The change rate of the expansion ratio before and after secondary foaming was small. For this reason, the secondary foamability was poor and the in-mold foamability was poor.

  In Comparative Example 4, since the pyrolytic chemical foaming agent was not added to the polylactic acid-based resin composition, the rate of change in the expansion ratio before and after the secondary foaming was small even when the bubble regulator was added. . For this reason, the secondary foamability was poor, and a foamed molded product could not be produced.

  In Comparative Example 5, since there was too much addition amount of the thermal decomposition type chemical foaming agent in the polylactic acid-based resin composition, the foaming was inhibited, and the obtained foam was not sufficiently foamed (foaming ratio was small), The rate of change of the expansion ratio before and after secondary foaming was small. For this reason, the secondary foamability was poor and a foamed molded article could not be produced.

  In Comparative Example 6, since the addition amount of the pyrolytic chemical foaming agent in the polylactic acid resin composition was too small, the obtained foam had a large area average cell diameter and a change in the expansion ratio before and after the secondary foaming. The rate was small. For this reason, the secondary foamability was poor and a foamed molded article could not be produced.

  In Comparative Example 7, the amount of the pyrolytic chemical foaming agent and physical foaming agent added in the polylactic acid-based resin composition was too small, so the obtained foam did not foam sufficiently (low expansion ratio), 2 The rate of change in the expansion ratio before and after the next expansion was small. For this reason, the secondary foamability was poor and a foamed molded article could not be produced.

  In Comparative Example 8, since both the pyrolytic chemical foaming agent and the physical foaming agent in the polylactic acid-based resin composition are too much added, there are many foam breaks, the bubble diameter ratio is small, and the foaming ratio before and after the secondary foaming. The change rate of became small. For this reason, the secondary foamability was poor, and a foamed molded article could not be molded.

  In Comparative Example 9, since the physical foaming agent was not added to the polylactic acid resin composition, the obtained foam did not foam sufficiently (the foaming ratio was small), and the rate of change in the foaming ratio before and after secondary foaming. Became small. For this reason, the secondary foamability was poor and a foamed molded article could not be produced.

Claims (5)

  A polylactic acid resin foam obtained by extrusion foaming a polylactic acid resin composition comprising a crystalline polylactic acid resin, a pyrolytic chemical foaming agent, and a physical foaming agent, the polylactic acid resin foaming The area average cell diameter of the body is 1 to 200 μm, and the ratio of the area average cell diameter outside the cross section of the polylactic acid-based resin foam to the area average cell diameter inside is 0.6 or more. The polylactic acid-based resin foam is characterized in that the rate of change in the foaming ratio is 1.5 or more.   2. The polylactic acid resin foam according to claim 1, wherein the thermally decomposable chemical foaming agent comprises an azo compound.   The polylactic acid resin foam according to claim 1 or 2, wherein the shape is particulate.   The foaming molding formed by carrying out the in-mold foam molding of the polylactic acid-type resin foam in any one of Claims 1-3.   It is a method of manufacturing the foam of Claims 1-3, Comprising: With respect to 100 mass parts of polylactic acid-type resin, 0.01-3 mass parts of thermal decomposition type chemical foaming agents are supplied to an extruder, and physical A method for producing a polylactic acid-based resin foam, which comprises extrusion foaming in the presence of a foaming agent.

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