JP2015083651A - Polylactic acid-based resin composition an expanded body containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid-based resin composition capable of well and stably providing an expanded body with high expansion ratio by forming a branched structure having melting viscosity and melting tensile force suitable for expansion molding in a polylactic resin.SOLUTION: There is provided a resin composition which is manufactured by adding 0.1 to 6 pts.mass of organic peroxide containing 3,6,9-trimethyl-1,4,7-triperoxonane (B) and 0.05 to 5 pts.mass of an air bubble modifier (C) to 100 pts.mass of a polylactic resin (A) and melting and mixing, and satisfies the following (1) to (3) at the same time. (1) Melt flow rate is 0.2 to 7 g/10 mins. (2) A value of melting tensile force measured at 190°C is 30 mN to 200 mN. (3) A crystallization speed index is 0.5 to 30.

Description

  The present invention relates to a polylactic acid resin composition having a melt viscosity and melt tension particularly suitable for foam molding and a foam using the same.

  Conventionally, plastics are used in many fields as bottles, trays, various containers, and various molded products. Since most of these plastics are not biodegradable, there is a problem that waste treatment is necessary. In addition, the discarded plastics have problems such as damage to the landscape and marine living environment being destroyed.

  Under such circumstances, biodegradable plastics are actively studied. Among them, biodegradable aliphatic polyesters have been studied in order to obtain performance suitable for practical use, but generally have a low melting point and a low crystallization rate, so that they have heat resistance and mechanical properties. Low strength. In addition, the melt viscosity and the melt tension are low, so that there are problems such as a problem of drawing down at the time of molding and a sufficient expansion ratio cannot be obtained. Therefore, in order to be put into practical use, it is necessary to improve the melt viscosity and melt tension, to exhibit strain hardening at the time of measuring the extension viscosity, and to improve the crystallization speed.

  In general, in order to develop a strain-hardening property in a resin, a method of using a biodegradable resin and causing crosslinking by melt kneading with a peroxide or a reactive compound is simple and the degree of branching can be freely changed. A lot of research has been done in this respect. However, the method using an acid anhydride or polyvalent carboxylic acid as in Patent Document 1 is not practical because the reactivity is likely to be uneven, or the pressure needs to be reduced. In addition, the methods using polyvalent isocyanates as in Patent Documents 2 and 3 are established as technologies that have reached a practical level, such as molecular weight is likely to decrease during remelting, and safety during operation is problematic. Not. The method disclosed in Patent Document 4 uses an organic peroxide, or crosslinks and gelates using an organic peroxide and two or more compounds having an unsaturated bond. It tends to occur and has a high viscosity, making it difficult to dispense the polymer. Moreover, the production efficiency is not good and coloration and decomposition are likely to occur. Furthermore, there exists a problem that the quality of a molded object or a foam falls by presence of a gel.

Japanese Patent Laid-Open No. 11-60928 Japanese Patent No. 2571329 JP 2000-17037 A JP-A-10-324766

  The present invention solves the above-mentioned problems, and by forming a branched structure having a melt viscosity and a melt tension suitable for foam molding in a polylactic acid resin, the present invention achieves a good and stable high foaming ratio. An object of the present invention is to provide a polylactic acid resin composition capable of obtaining a foam.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors conducted a crosslinking reaction with an organic peroxide containing a specific peroxide, thereby achieving a melt viscosity and melt tension suitable for foam molding. It has been found that a polylactic acid-based resin that can be obtained and can obtain a foam having a high expansion ratio can be obtained.

That is, the gist of the present invention is the following (A) and (B).
(A) Polyperoxide (A) An organic peroxide containing 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonan (B) per 100 parts by mass of polylactic acid resin (A) ) 0.1 to 6 parts by mass and bubble regulator (C) 0.05 to 5 parts by mass, and melt-kneaded to satisfy the following (1) to (3) simultaneously A polylactic acid-based resin composition characterized by that.
(1) The melt flow rate is 0.2 to 7 g / 10 minutes.
(2) The melt tension value measured at 190 ° C. is 30 mN to 200 mN.
(3) The crystallization rate index is 0.5-30.
(B) A foam comprising the polylactic acid resin composition described in (a).

Since the polylactic acid resin composition of the present invention is obtained by melt-kneading an organic peroxide containing a specific peroxide, the polylactic acid-based resin composition has a melt viscosity and melt tension suitable for foaming by a crosslinking reaction. Become. Moreover, the crystallization speed can be increased by using an organic peroxide containing a specific peroxide in combination with a bubble regulator.
Thus, by using the polylactic acid resin composition of the present invention, a foam having a high foaming ratio can be obtained with high productivity.

  As the polylactic acid resin (A) used in the present invention, a polymer mainly composed of L lactic acid and D lactic acid can be used, and other resins may be used as necessary as long as the effects of the present invention are not impaired. The components may be copolymerized.

  Examples of other copolymer component units include polyvalent carboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones, and the like. Specifically, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, Azelaic acid, sebacic acid, dodecanedioic acid, fumaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium sulfoisophthalic acid, etc. Polyvalent carboxylic acids, ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 1,4-cyclohexanedimethanol, neopentylglycol, glycerin, trimethylol Lopan, pentaerythritol, bisphenol A, polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc., glycolic acid, Hydroxy carboxylic acids such as hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid, hydroxybenzoic acid, glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, Lactones such as β- or γ-butyrolactone, pivalolactone, and δ-valerolactone can be used. These polylactic acid resins may be used alone or in combination of two or more.

  As such polylactic acid resin, those synthesized by a conventionally known method, that is, a method of directly polymerizing from lactic acid, a method of ring-opening polymerization of lactide, and the like can be used.

  The polylactic acid resin (A) of the present invention is preferably a crystalline polylactic acid resin from the standpoint of crystallization rate index and heat resistance, among which the D-form content is 0 to 7.0 mol%. Is preferred. Among these, the range of D-form content of 0.1-6.0 mol% is preferable, and it is more preferable that it is 1.0-5.0 mol%. When the D-form content is more than 7.0 mol%, it is difficult to control the crystallization rate index within a predetermined range, and the crystallinity is lowered, so that the heat resistance of the obtained molded product is also improved. Since it becomes low, it is not preferable.

  In the present invention, the D-form content of the polylactic acid resin (A) is a ratio (mol%) occupied by the D lactic acid unit in the total lactic acid units constituting the polylactic acid resin (A). Therefore, for example, in the case of a polylactic acid resin (A) having a D-form content of 1.0 mol%, the polylactic acid resin (A) has a proportion of 1.0 mol% of D lactic acid units, and L lactic acid The proportion of units is 99.0 mol%.

  In the present invention, the D-form content of the polylactic acid resin (A) is, as will be described later in the Examples, methylated all of L-lactic acid and D-lactic acid obtained by decomposing the polylactic acid resin (A), It is calculated by a method of analyzing the methyl ester of L lactic acid and the methyl ester of D lactic acid with a gas chromatography analyzer.

  The content of the polylactic acid resin (A) in the polylactic acid-based resin composition of the present invention is preferably 50% by mass or more, particularly 80% by mass or more, and more preferably 90% by mass or more. preferable. When the content of the polylactic acid resin (A) is less than 50% by mass, the ratio of other resins and the like increases, so that the foaming performance as a resin composition is lowered, and will be described later (1) to (3). It is difficult to satisfy the characteristic value.

  That is, the polylactic acid resin composition of the present invention may contain a thermoplastic resin other than the polylactic acid resin (A). Examples of such a thermoplastic resin include polyethylene (PE), polystyrene ( PS), polypropylene (PP), acrylonitrile styrene (ABS), acrylonitrile styrene (AS), polylactic acid (PLA), polyamide (PA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), poly Examples include arylate (PAR), styrene-ethylene-butadiene-styrene (SEBS), ethylene-α-olefin copolymer, and ethylene-propylene-diene rubber (EPDM).

The polylactic acid-based resin composition of the present invention is obtained by adding a specific amount of a specific organic peroxide (B) and a cell regulator (C) to the polylactic acid resin (A) as described above, followed by melt-kneading. Therefore, it has a melt viscosity and melt tension suitable for foaming, and an excellent characteristic value for crystallization speed. That is, the following (1) to (3) are satisfied simultaneously.
(1) The melt flow rate is 0.2 to 7 g / 10 minutes.
(2) The melt tension value measured at 190 ° C. is 30 mN to 200 mN.
(3) The crystallization rate index is 0.5-30.

  The organic peroxide (B) in the present invention contains 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonan. 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane has a one-minute half-life temperature of 190 ° C. It is assumed that the polylactic acid resin composition can be given a melt viscosity and melt tension suitable for foaming.

  The content of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonan in the organic peroxide (B) The content is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and most preferably 90% by mass or more. As described above, the content of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonan in the organic peroxide (B) is less than 20% by mass ( It tends to be difficult to obtain a resin composition having the characteristic values of 1) to (3).

  In the present invention, organic peroxides (B) other than 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane can also be used. For example, hydroperoxides such as t-butyl hydroperoxide, p-menthane hydroperoxide, cumene hydroperoxide, dicumyl peroxide, t-butylcumyl peroxide, α, α′-bis (t-butylperoxy-m-isopropyl) Benzene, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) -3-hexyne, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, etc. Of dialkyl peroxides, diacyl peroxides such as dipropionyl peroxide, benzoyl peroxide, 2,2-di (t-butylperoxy) butane, 1,1-di (t-hexylperoxy) cyclohexane, 1,1-di (t -Butylperoxy) -2-methylcyclohexane, 1, Peroxyketals such as 1-di (t-butylperoxy) cyclohexane, peroxyesters such as t-butylperoxyacetate and t-butylperoxybenzoate, peroxy such as t-butylperoxyisopropylcarbonate and di (isopropylperoxy) dicarbonate Carbonates, alkylsilyl peroxides such as t-butyltrimethylsilyl peroxide, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, 3,6-diethyl-3,6-dimethyl-1, Examples include cyclic peroxides such as 2,4,5-tetroxane.

  Among them, di-t-butyl peroxide and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane are 3,6,9-triethyl-3,6,9-trimethyl-1,4,7. -When used in combination with tripperoxonane, the polylactic acid resin composition can be given excellent foamability (higher melt tension and lower crystallization rate index). When used in combination, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane (M) and di-t-butyl peroxide or 2,5-dimethyl-2, The mass ratio of 5-di (t-butylperoxy) hexane (N) is preferably 40/60 to 95/5, and more preferably 60/40 to 90/10.

The addition amount of the organic peroxide (B) is required to be 0.1 to 6 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A), and in particular, 0.5 to 5 parts by mass. More preferably, it is 1 to 4 parts by mass. If the amount is less than 0.1 part by mass, the melt viscosity and melt tension suitable for foaming cannot be provided, and the melt viscosity and melt tension are both low, and the resin composition satisfying the characteristic values of (1) and (2) It will not be possible. Furthermore, the improvement of the crystallization rate is insufficient, and the resin composition satisfying (3) cannot be obtained.
Even when the addition amount of the organic peroxide (B) exceeds 6 parts by mass, the melt viscosity and melt tension suitable for foaming cannot be provided, and both the melt viscosity and melt tension become high, and (1), ( The resin composition that satisfies the characteristic value of 2) cannot be obtained.

  The organic oxide (B) reacts with the polylactic acid resin at the time of melt kneading, decomposes into a low molecular weight substance and volatilizes, and therefore hardly remains in the polylactic acid resin composition after the melt kneading.

  Next, the cell regulator (C) used in the present invention is titanium oxide, talc, kaolin, clay, calcium silicate, silica, sodium citrate, calcium carbonate, diatomaceous earth, calcined perlite, zeolite, bentonite, limestone, calcium sulfate. , Aluminum oxide, tin oxide, magnesium carbonate, sodium carbonate, ferric carbonate, and polytetrafluoroethylene powder. Among these, talc is preferably used because it is excellent in the effect of improving the crystallization speed.

  The addition amount of the bubble regulator (C) is 0.05 to 5 parts by mass, and preferably 0.2 to 3 parts by mass. When the addition amount of the air bubble adjusting agent (C) exceeds 5 parts by mass, the crystallization rate becomes too low, and the resin composition satisfying the characteristic value of (3) cannot be obtained. On the other hand, when the addition amount of the bubble regulator (C) is less than 0.05 parts by mass, the crystallization rate index exceeds 30, so that even in this case, the resin composition satisfying the characteristic value of (3) can be obtained. It will be impossible. Further, the obtained foam has a large cell diameter and a large average cell diameter.

In addition, in the polylactic acid resin composition of the present invention, when the organic peroxide (B) or the cell regulator (C) is added to the polylactic acid resin (A) and melt kneaded, a crosslinking agent is added. Also good.
As the cross-linking agent, since it has high reactivity with polylactic acid resin, it is difficult for the monomer to remain, and the resin is less colored, it has two or more (meth) acrylic groups in the molecule, or one or more (meth A (meth) acrylic acid ester compound having an acrylic group and one or more glycidyl groups or vinyl groups is preferred. Specific compounds include glycidyl methacrylate, glycidyl acrylate, glycerol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, allyloxy polyethylene glycol monoacrylate, allyloxy polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol. Diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polytetramethylene glycol dimethacrylate, and these alkylene glycols may be copolymers of alkylenes of various lengths, but also butanediol methacrylate, butanediol acrylate, etc. Can be mentioned. Of these, polyethylene glycol dimethacrylate is preferable. A preferable addition amount is 0.01 to 20 parts by mass per 100 parts by mass of the polylactic acid resin.

And the polylactic acid-type resin composition of this invention has melt viscosity suitable for foaming, and satisfies the characteristic value of (1). That is, the melt flow rate (hereinafter sometimes referred to as MFR) is 0.2 to 7 g / 10 minutes. The melt viscosity of the polylactic acid resin composition is an extremely important factor for obtaining a foam having a high expansion ratio. The MFR is preferably 0.5 to 5 g / 10 minutes, and most preferably 0.8 to 4 g / 10 minutes.
In order to form a foam, it is known that the higher the melt viscosity, the better the foamability. However, if the MFR is less than 0.2 g / 10 min, the resin does not stretch during foaming, so that bubbles grow. Only a molded product with a low expansion ratio can be obtained. Further, when such an MFR resin composition is to be obtained, problems arise in terms of paying out the polymer and controlling the degree of polymerization.
On the other hand, when the MFR exceeds 7 g / 10 min, it becomes difficult to form a foam, for example, the melt viscosity is too low and bubble breakage occurs. Moreover, even if a foam is obtained, since bubble breakage occurs, the expansion ratio is low and the bubble diameter is coarse.

  The MFR in the present invention is measured at a temperature of 190 ° C. and a load of 2.16 kgf according to the method described in JIS K-7210.

  In the polylactic acid resin composition of the present invention, according to the method described in JIS K-7210, MFR measured at a temperature of 190 ° C. and a load of 2.16 kgf is MFR-1, and according to the method described in JIS K-7210. When the MFR measured at a temperature of 190 ° C. and a load of 13.225 kgf is MFR-2, the ratio (MFR-2 / MFR-1) of both is preferably 15 or more, and more preferably 18 or more. preferable. The value of MFR-2 / MFR-1 is also a measure of the molecular weight distribution and linear branching of the resin composition. The higher the value of MFR-2 / MFR-1, the wider the molecular weight distribution and the higher the linear branching. A foam having a high expansion ratio can be obtained stably and stably. If the value of MFR-2 / MFR-1 is less than 15, the resulting foam tends to have a low foaming ratio.

And the polylactic acid-type resin composition of this invention has a melt tension suitable for foaming, and satisfies the characteristic value of (2). That is, the value of melt tension measured at 190 ° C. is 30 mN to 200 mN, preferably 50 mN to 180 mN, and more preferably 60 mN to 150 mN. When the melt tension is less than 30 mN, when foam molding is performed, the resin is cut or torn, so the foaming ratio is low and the bubble diameter is large.
On the other hand, when the melt tension exceeds 200 mN, when foam molding is performed, since the resin does not stretch, bubbles do not grow, and the resulting molded product has a low foaming ratio. In addition, molding fluidity may be significantly reduced.

  The melt tension in the present invention is measured as follows. The measurement is performed using a Capillograph 1C manufactured by Toyo Seiki Seisakusho (cylinder inner diameter 9.55 mm, orifice inner diameter 1.0 mm, length 10.0 mm). First, the set temperature of the cylinder and the orifice is set to 190 ° C., the polylactic acid resin composition (measurement sample) is filled in the cylinder, and left for 5 minutes, and then the molten resin at 190 ° C. with a piston speed of 10 mm / min. Is extruded into a strand from the orifice. The strand is wound while passing through a circular guide of a tension detection pulley having a lower diameter of 40 mm, and a load applied to the circular guide is detected by a tensiometer. The winding speed is gradually increased, and the tension at which the strand breaks (that is, the maximum measurable tension) is taken as the melt tension.

Furthermore, the polylactic acid-based resin composition of the present invention has a crystallization rate index suitable for foaming and satisfies the characteristic value of (3). That is, the crystallization rate index is 0.5 to 30, and preferably 0.5 to 25.
The crystallization rate index means that the smaller the index, the faster the crystallization during the temperature drop. If the crystallization speed index is higher than 30 minutes, it takes too much time to crystallize, the desired shape of the molded product cannot be obtained, and the cycle time in injection molding or the like becomes long, resulting in increased productivity. Deteriorate. In addition, the obtained foam is inferior in heat resistance and strength because crystallization does not proceed sufficiently.
On the other hand, if it is less than 0.5 minutes, the crystallization rate is too fast, and thus crystallization proceeds before the resin foams, and a sufficiently foamed molded article cannot be obtained.

  The crystallization rate index in the present invention is measured as follows. Using a differential scanning calorimeter DSC-7 manufactured by PerkinElmer Co., Ltd., using 7 mg of a polylactic acid resin composition as a sample, the temperature was raised from 20 ° C. to 200 ° C. at a heating rate of 500 ° C./min. After maintaining for 5 minutes, the temperature is decreased from 200 ° C. to 130 ° C. at a temperature decrease rate of 500 ° C./min, and maintained at 130 ° C. As shown in FIG. 1, the time from the isothermal start of the crystallization peak (exotherm) to the peak top when held at 130 ° C. is defined as the (crystallization temperature isotherm) crystallization rate index.

  And in the polylactic acid-based resin composition of the present invention, as long as the effects of the present invention are not impaired, a thermal stabilizer, an antioxidant, a flame retardant, a crystal nucleating agent, a terminal blocker, a dispersant, a filler, You may mix | blend additives, such as a pigment, a weathering agent, a plasticizer, a lubricant, a mold release agent, an antistatic agent, and an impact resistance improving agent. These additives may be used alone or in combination of two or more. In addition, the method of mix | blending these additives with the polylactic acid-type resin of this invention is not specifically limited.

  Examples of heat stabilizers and antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, and mixtures thereof.

  Examples of the flame retardant include a halogen flame retardant, a phosphorus flame retardant, a nitrogen flame retardant, a sulfur flame retardant, and an acid flame retardant.

  Examples of crystal nucleating agents include sorbitol compounds, benzoic acid and metal salts of those compounds, phosphate metal salts, rosin compounds, amide compounds such as ethylene bisoleic acid amide, methylene bisacrylic acid amide, and ethylene bisacrylic acid amide. Hexamethylene bis-9,10-dihydroxystearic acid bisamide, p-xylylene bis-9,10 dihydroxystearic acid amide, decanedicarboxylic acid dibenzoyl hydrazide, hexanedicarboxylic acid dibenzoyl hydrazide, 1,4-cyclohexanedicarboxylic acid dicyclohexylamide, 2,6-naphthalenedicarboxylic acid dianilide, N, N ′, N ″ -tricyclohexyltrimesic acid amide, trimesic acid tris (t-butylamide), 1,4-cyclohexanedicarboxylic acid Dianilide, 2,6-naphthalenedicarboxylic acid dicyclohexylamide, N, N′-dibenzoyl-1,4-diaminocyclohexane, N, N′-dicyclohexanecarbonyl-1,5-diaminonaphthalene, ethylenebisstearic acid amide, N, Examples thereof include organic crystal nucleating agents such as N′-ethylenebis (12-hydroxystearic acid) amide and octanedicarboxylic acid dibenzoylhydrazide.

  Examples of the terminal blocking agent include carbodiimide, oxazoline, and epoxy resin.

  Examples of the dispersant include industrial oils such as liquid paraffin, mineral oil, creosote oil, lubricating oil and silicone oil, vegetable oils such as corn oil, soybean oil, rapeseed oil, palm oil, linseed oil and jojoba oil, ionic And nonionic surfactants.

  Examples of the filler include inorganic fillers such as glass fiber and carbon fiber, organic fillers such as aramid fiber, vinylon fiber, polyimide fiber, starch, cellulose fine particles, wood powder, okara, fir shell, and bran.

Next, the manufacturing method of the polylactic acid-type resin composition of this invention is demonstrated.
A method of supplying the organic peroxide (B) using a dry blend or a powder feeder is desirable if it is solid, and a method of injecting it from the middle of the extruder using a pressure pump if it is liquid. Is desirable. An organic peroxide (B) containing 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane and a cell regulator (C) in the polylactic acid resin (A) Is preferably 190 to 240 ° C. at the time of melt kneading.

  Moreover, when melt-kneading, the peroxide master pellet which added the organic peroxide (B) to polylactic acid resin in high concentration may be produced previously, and you may add using this. By using the master pellet, the dispersibility of the organic peroxide (B) in the resin composition is improved, it becomes possible to react evenly in the polylactic acid resin composition, and the foamability is improved.

  Specific examples of master pellets include those obtained by melting and kneading organic peroxide (B) in polylactic acid resin to form pellets, mixing pellets of polylactic acid resin and peroxide powder, and pellets. And those obtained by compressing and granulating into a shape, and those obtained by mixing and attaching peroxides to the surface of polylactic acid resin pellets.

  Next, the foam of the present invention will be described. The foam of the present invention comprises the polylactic acid resin composition of the present invention. The method for producing the foam from the polylactic acid-based resin composition of the present invention is not limited, and the foam is obtained by an extrusion foaming method, a bead foaming method, or an injection foaming method using an injection molding machine or the like. Things. The foam of the present invention includes foams obtained by these methods, which are further molded in a mold or foam-molded by in-mold foam molding.

The manufacturing method of the foam of this invention is demonstrated.
First, (i) the extrusion foaming method is a method in which a resin is previously blended with a decomposable foaming agent that decomposes at the melting temperature of the resin, or a volatile foaming agent is injected directly into the extruder, It is a method of extruding from a slit nozzle or a round nozzle to obtain a sheet or a strand (foam). And a foaming molding can be obtained by shape | molding these sheets and strands in metal mold | dies, such as a vacuum forming machine. When obtaining a foamed molded product with a vacuum molding machine or the like, immediately after the preheating sheet temperature is set to (Tg + 40 ° C.) to (Tm-5 ° C.), it is molded with a mold having a temperature of 20 ° C. to (Tm-20 ° C.). It is preferable to do. If the temperature of the preheated sheet is too high, the sheet will be drawn down and cannot be molded, and if the temperature is too low, the molded sheet will not be stretched enough to cause cracking or deep drawing. There is. On the other hand, if the mold temperature is too low, the heat resistance of the resulting container may be insufficient, and if the mold temperature is too high, the sheet will adhere to the mold and the release of the molded product will deteriorate. In addition, uneven thickness may occur in the molded product, or the impact resistance may be reduced.

(Ii) With the bead foaming method, polylactic acid resin fine particles are prepared in advance, impregnated with a volatile foaming agent under pressure, and then foamed with changes in temperature and pressure to form expanded fine particles (foam). How to get. And the foaming molding can be obtained by carrying out in-mold foam molding of the obtained foaming fine particles.
Moreover, when obtaining a foaming molding, the combined method of (i) and (ii) may be sufficient. That is, this is a method in which the foamed strand produced by the extrusion foaming method of (i) is cut into foamed particles and used for in-mold foam molding described in (ii).

  The cylinder temperature of the extruder used by the extrusion foaming method of (i) is preferably equal to or higher than the melting point (Tm) or flow start temperature (Tf) of the polylactic acid resin, and more preferably 180 to 230 ° C. It is more preferable to set it as 190-220 degreeC. The temperature of the nozzle is preferably 130 to 190 ° C, and more preferably 140 to 180 ° C.

  Furthermore, (iii) the injection foaming method is a method in which a volatile foaming agent is injected into an injection molding machine, or a resin composition blended with a decomposable foaming agent is introduced into an injection molding machine, and the melt is put into a mold cavity. Injection core back type injection molding method in which when the molten resin reaches the vicinity of the flow end, the mold core (die plate) adjacent to the mold cavity is retracted in the direction in which the thickness of the middle cavity expands. This is a method of obtaining a foam by, for example. The cylinder temperature of the injection molding machine is preferably 180 to 230 ° C., more preferably 190 to 220 ° C. from the viewpoint of obtaining a good melt-kneaded product. The injected volatile foaming agent or decomposable foaming agent is preferably mechanically kneaded with the molten polylactic acid resin, so that a high-concentration foaming agent is uniformly dissolved in the molten polylactic acid resin. .

  The mold temperature when filling the melt obtained here into the mold or when cooling it later is 50 to 120 ° C. from the viewpoint of improving the molding speed of the polylactic acid resin and suppressing deformation of the molded product. Of these, 60 to 110 ° C is preferable, and 70 to 100 ° C is more preferable. In the present invention, the mold temperature is determined by measuring the temperature of the cooling water for cooling the mold or the temperature near the cavity of the mold. When the melt is filled in the mold, a pressure drop occurs due to cooling and shrinkage in the mold, and the inactive substance becomes less soluble in the polylactic acid resin and cannot be dissolved. A foam having a wide foam cell is obtained.

  Examples of the volatile foaming agent used in the above-mentioned methods (i) to (iii) and in-mold foaming include various inorganic compounds such as nitrogen, carbon dioxide and water, and various types such as methane, ethane, propane, butane and pentane. Examples include hydrocarbons, chlorofluorocarbon compounds, ethers such as dimethyl ether and methyl ethyl ether, and organic solvents represented by various alcohols such as ethanol and methanol. Of these, carbon dioxide and / or butane are preferably used.

  Examples of the decomposable foaming agent used in the above method (i) or (iii) include thermally decomposable groups such as azo, N-nitroso, heterocyclic nitrogen-containing and sulfonyl hydrazide groups. And inorganic compounds such as ammonium carbonate and sodium hydrogen carbonate. Specific examples thereof include azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, diazoaminobenzene, dinitrosopentamethylenetetramine, N, N′-dimethyl-N, N′-dinitrosotephthalamide, benzenesulfonyl Hydrazide, 4,4′-oxy-bis (benzenesulfonyl) hydrazide, diphenylsulfone-3,3′-disulfonylhydrazide, 4-toluenesulfonyl hydrazide, 4,4′-oxy-bis (benzenesulfonyl) semicarbazide, 4- Toluenesulfonyl semicarbazide, barium azodicarboxylate, 5-phenyltetrazole, trihydrazinotriazine, 4-toluenesulfonyl azide, 4,4′-diphenyldisulfonyl azide and the like.

  The injection amount of the volatile foaming agent in (i) extrusion foaming method, (ii) bead foaming method or in-mold foaming is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the polylactic acid resin composition. More preferably, it is 5-5 mass parts, More preferably, it is 1-3 mass parts. If the injection amount is less than 0.1 parts by mass, the amount of gas to be foamed is small, the foaming ratio when foaming the polylactic acid-based resin composition for foam molding may not increase, and the mass reduction effect may not be obtained, When the amount exceeds 10 parts by mass, foam breakage during foaming and strength reduction of the obtained foam occur, which is not preferable.

  (Iii) The addition amount of the volatile foaming agent and the decomposable foaming agent in the injection foaming method is preferably 0.05 to 2 parts by mass, and 0.1 to 1 part by mass with respect to 100 parts by mass of the polylactic acid resin composition. Is more preferable. If the addition amount is less than 0.05 parts by mass, the amount of gas to be foamed is small, the foaming ratio when foaming the foamed polylactic acid resin composition may not increase, and the mass reduction effect may not be obtained, When the amount exceeds 2 parts by mass, the strength of the obtained foam is decreased, and in the injection foaming, appearance defects such as silver streak may occur, which is not preferable.

  And in the case of the foamed body (including foamed molded body) of the present invention obtained by the above methods (i) to (ii), the foaming ratio is preferably 7 to 25 times, and more preferably 8 to 22 times. Preferably, it is 10 to 20 times. If the expansion ratio is less than 7 times, the mass reduction effect may not be obtained, and if it is 25 times or more, it is difficult to maintain the strength.

  The average cell diameter of these foams is preferably 500 μm or less, more preferably 450 μm or less, and further preferably 400 μm or less. When the average cell diameter exceeds 500 μm, the surface smoothness of the foam may decrease, and the strength of the foam may decrease.

  As for the crystallinity of these foams, the crystallinity of the polylactic acid resin composition constituting them is preferably 10% or more, and more preferably 12% or more. When the crystallinity is low, the heat resistance is poor. The upper limit of the degree of crystallinity varies depending on the state or form of the polylactic acid resin assembly to be applied, and the higher the better.

  The heating dimensional change rate of these foams is preferably within 3%, and more preferably within 2%. If the dimensional change rate is 3% or more, it cannot be used for applications requiring precise dimensional stability, and the crystallinity is not sufficient.

The heating dimensional change rate of the foam is calculated by the following formula by heating the foam at 120 ° C. for 24 hours with a hot air dryer, measuring the volume before and after the heat treatment. V1: Volume of the foam before heating, V2: Volume of the foam after heating.
Volume change rate (%) = (V2−V1) / V1 × 100

  Moreover, (iii) In the case of the injection foam obtained by the injection foaming method, the expansion ratio is preferably 1.15 to 3.0, and more preferably 1.25 to 2.8. If the expansion ratio is less than 1.15, the effect of reducing the weight of the foam is insufficient. On the other hand, when the expansion ratio exceeds 3.0, the foam cell in the core part may be coarsened in the foam or the skin part may become thin, and the strength of the foam decreases.

  The average cell diameter of the injection foam is preferably 300 μm or less, more preferably 250 μm or less, and further preferably 200 μm or less. When the average cell diameter exceeds 300 μm, the surface smoothness of the foam may be lowered, and the strength of the foam may be lowered.

  The crystallinity of the injection foam is preferably 10% or more, more preferably 15% or more, and more preferably 20% or more of the polylactic acid resin composition constituting them. It is preferable that When the degree of crystallinity is low, the heat resistance and dimensional stability are poor. The upper limit of the crystallinity varies depending on the state or form of the polylactic acid resin composition to be applied, and the higher the better.

In addition, the bending strength of the injection foam is preferably 80 MPa or more, more preferably 90 MPa or more, and even more preferably 100 MPa or more.
The bending strength of the injection foam is measured by applying a load at a deformation rate of 1 mm / min according to JISK-7171, and the yield point or the breaking point is defined as the bending strength.

The expansion ratio of the foam is calculated as follows. First, the masses of the polylactic acid resin composition and the foam are measured, and then the apparent volume of these is measured using a wet electronic hydrometer (“EW-300SG” manufactured by Alpha Mirage). And each apparent density is computed from the mass and apparent volume of a polylactic acid-type resin composition and a foam, and it computes from the following formula | equation.
Foaming ratio = (apparent density of polylactic acid resin composition) / (apparent density of foam)

  Moreover, the average bubble diameter of a foam measures the diameter of 50 bubbles (cell) with an optical microscope (magnification: 20-50 times), and makes it the average value. In addition, the diameter of a bubble means a major axis diameter.

  Furthermore, the crystallinity of the foam is measured by the WAXD reflection method using an X-ray diffractometer (manufactured by Rigaku Denki Kogyo Co., Ltd., RAD-rB, Cu-Kα ray), and crystallized from the integrated intensity ratio by the multiple peak separation method. Find the degree.

  The foam of the present invention is used for packaging materials, packing materials, cushioning materials, heat insulating materials, heat insulating materials, cold insulating materials, sound deadening materials, sound absorbing materials, sound insulating materials, vibration damping materials, building materials, cushion materials, materials, containers, etc. Can do. Specific applications include, for example, sofas, bed mats, chairs, bedding, mattresses, light covers, plush toys, slippers, cushions, helmets, carpets, pillows, shoes, pouches, mats, crash pads, sponges, stationery, toys, DIY products, panels, tatami core materials, mannequins, automotive interior parts / cushions, car seats, deadning, door trims, sun visors, automotive vibration damping / sound absorbing materials, sports mats, fitness equipment, sports protectors, beat boards, Ground fence, leisure sheet, medical mattress, medical supplies, care supplies, rehabilitation supplies, heat insulating materials for construction, building joint materials, face door materials, building curing materials, reflectors, industrial trays, tubes, pipe covers, air conditioner insulation Piping, gasket core material, concrete formwork, civil engineering joint, joint Prevention panels, protective materials, lightweight soil, embankment, artificial soil, packaging materials and packaging materials, packaging materials, wrapping, packaging materials and packaging materials for fresh products, vegetables and fruits, packaging materials and buffer packaging materials for electronic devices, etc. Insulating food / vegetables such as fresh foods / vegetables / fruits, food containers such as cup ramen / lunch boxes, food trays, beverage containers, agricultural materials, foamed models, and diaphragms for speakers.

Hereinafter, the present invention will be described more specifically with reference to examples. The measurement methods and evaluation methods of characteristic values in Examples and Comparative Examples are as follows.
(1) MFR value of polylactic acid-based resin composition Measured by the above method. The MFR measured at a temperature of 190 ° C. and a load of 2.16 kgf was MFR-1, and the MFR measured at a temperature of 190 ° C. and a load of 13.225 kgf was MFR-2.
(2) D-form content of polylactic acid resin After adding 0.3 g of polylactic acid resin (or polylactic acid resin composition) to 6 mL of 1N potassium hydroxide / methanol solution and thoroughly stirring at 65 ° C., 450 μL of sulfuric acid And stirred at 65 ° C. for decomposition. 5 mL of this decomposed product, 3 mL of pure water, and 13 mL of methylene chloride were mixed and shaken. After standing and separated, about 1.5 mL of the lower organic layer was collected and filtered with a HPLC disk filter having a pore size of 0.45 μm. Gas chromatography measurement was performed using HP-6890 Series GC system manufactured by Hewlett Packard. The ratio of the peak area of D-lactic acid methyl ester to the total peak area of lactate methyl ester was calculated, and this was defined as the D-form content (mol%).
(3) Melt tension and crystallization rate index of polylactic acid resin composition Measured by the above method.
(4) Apparent density and foam expansion ratio of polylactic acid resin composition and foam (sheet, food tray, injection foam) were measured by the above method.
(5) Average cell diameter of foam, crystallinity, heating dimensional change rate (only for food tray), bending strength (only injection foam)
It was measured by the method described above.

The raw materials used in the examples and comparative examples are as follows.
[Polylactic acid resin]
A-1: Eco Plastic U'z S-12 manufactured by Toyota Motor Corporation; weight average molecular weight 130,000, MFR value 8 g / 10 min, D-form content 0.1 mol%, melting point 178 ° C
A-2: Terramac TE-4000 manufactured by Unitika Ltd .; weight average molecular weight 130,000, MFR value 10 g / 10 min, D-form content 1.4 mol%, melting point 165 ° C.
A-3: Nature Works 8052D; weight average molecular weight 140,000, MFR value 5 g / 10 min, D-form content 4.5 mol%, melting point 152 ° C.
A-4: Nature Works 6302D; weight average molecular weight 130,000, MFR value 12 g / 10 min, D-form content 10 mol%, melting point 113 ° C.
[Organic peroxide]
B-1: “Trigonox 301 (Liquid)” manufactured by Kayaku Akzo Co., Ltd. (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-tripperoxonane with a purity of 43.9% Including)
B-2: “Perhexa 25B (liquid)” manufactured by NOF Corporation [containing 2,5-dimethyl-2,5-di (t-butylperoxy) hexane at a purity of 95.4%]
B-3: "Perbutyl D (liquid)" manufactured by NOF Corporation (containing di-t-dibutyl peroxide at a purity of 98%)
(Bubble conditioner)
C-1: Talc (“MW-HST” manufactured by Hayashi Kasei Co., Ltd., average particle size: 2.5 μm)

Example 1
Using a biaxial extruder (“PCM-30” manufactured by Ikegai Co., Ltd., die diameter: 4 mm × 3 holes), the extrusion head temperature was set to 230 ° C., the die outlet temperature was set to 210 ° C., and polylactic acid resin (A- 1) was supplied. 1 part by mass of talc (C-1) was added as a foam regulator to 100 parts by mass of the polylactic acid resin (A-1). Trigonox 301 was injected from the middle of the kneader so that the content of (B-1) was 0.2 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A-1). And after melt-kneading, it extruded and processed into the pellet form, and obtained the polylactic acid-type resin composition.
Next, the obtained polylactic acid-based resin composition was subjected to an extrusion foaming tester equipped with a circle die (diameter 65 mm, lip width 0.7 mm) at the tip of a biaxial extruder ("PCM-45" manufactured by Ikegai Co., Ltd.) A foam sheet was prepared by adding 2% by mass of carbon dioxide gas at a cylinder temperature of 200 ° C. and a discharge rate of 50 kg / h, and the obtained foam sheet had an apparent density of 0.16 g / cm consisting of closed cells. ^3. It was a uniform sheet with an expansion ratio of 8. Using this sheet, a mold for integrally molding the lid and the container using a vacuum / pressure forming machine (manufactured by Asano Laboratories) (Container squeezing ratio (L / D) = 0.5) At this time, molding was performed at a sheet temperature of 110 ° C., a mold temperature of 110 ° C., and a press time of 5 seconds.

Examples 2-12, Comparative Examples 1-11
A polylactic acid-based resin composition was obtained in the same manner as in Example 1 except that the types and amounts of the polylactic acid resin, organic peroxide, and bubble regulator were changed to those shown in Table 1.
And the foam sheet was obtained like Example 1 using the obtained polylactic acid-type resin composition, and the food tray was obtained like Example 1 using the obtained sheet | seat further.

Example 13
Using a biaxial extruder (“PCM-30” manufactured by Ikegai Co., Ltd., die diameter: 4 mm × 3 holes), the extrusion head temperature was set to 230 ° C., the die outlet temperature was set to 210 ° C., and polylactic acid resin (A- 1) was supplied. 1 part by mass of talc (C-1) was added as a foam regulator to 100 parts by mass of the polylactic acid resin (A-2). Using a pump from the middle of the kneader, the content of (B-1) is 0.4 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A-1), and the content of (B-2) Was injected to 0.3 parts by mass. And after melt-kneading, it extruded and processed into the pellet form, and obtained the polylactic acid-type resin composition.
Next, the obtained polylactic acid-based resin composition was subjected to an extrusion foaming tester equipped with a circle die (diameter 65 mm, lip width 0.7 mm) at the tip of a biaxial extruder ("PCM-45" manufactured by Ikegai Co., Ltd.) The foam sheet was prepared by adding 2% by mass of butane gas at a cylinder temperature of 200 ° C. and a discharge rate of 50 kg / h, and the obtained foam sheet had an apparent density of 0.10 g / cm ³ consisting of closed cells. A uniform sheet with a foaming ratio of 13. Using this sheet, a mold for integrally molding a lid and a container part using a vacuum / pressure forming machine (manufactured by Asano Laboratories) The container was drawn at a sheet temperature of 110 ° C., a mold temperature of 110 ° C., and a pressing time of 5 seconds.

  Table 1 shows the characteristic values and evaluation results of the polylactic acid resin compositions and foams (sheets and food trays) obtained in Examples 1 to 13 and Comparative Examples 1 to 11.

  As is clear from Table 1, the polylactic acid resin compositions obtained in Examples 1 to 13 satisfied the melt flow rate, melt tension, and crystallization rate index. For this reason, the obtained foam (food tray) had a high foaming ratio, a small average cell diameter, a high crystallinity, and a low rate of change in heating dimensions.

On the other hand, the polylactic acid resin compositions obtained in Comparative Examples 1 and 8 had low melt viscosity and melt tension because the amount of organic peroxide was small. For this reason, the obtained foam had a low expansion ratio and a large average cell diameter. In the polylactic acid resin compositions obtained in Comparative Examples 2 and 9, both the melt viscosity and the melt tension were too high because the amount of organic oxide added was too large. For this reason, the obtained foam became a thing with low expansion ratio. The polylactic acid-based resin composition obtained in Comparative Example 3 had a high crystallization rate index because no bubble regulator was added. For this reason, the obtained foam had a low degree of crystallinity, a high rate of change in heating dimensionality, and a coarse bubble, resulting in a large average bubble diameter.
In the polylactic acid-based resin composition obtained in Comparative Example 4, the crystallization rate index was too small because the amount of the bubble regulator added was too large. For this reason, crystallization advanced before foaming when obtaining a foam, and the obtained foam became a thing with a low expansion ratio.
The polylactic acid-based resin composition obtained in Comparative Examples 5, 6, 10, and 11 is 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-tri as an organic peroxide. Since a material containing no peroxonan was used, both melt viscosity and melt tension were low. For this reason, the obtained foam became a thing with a low expansion ratio. Since the polylactic acid resin composition obtained in Comparative Example 7 used a polylactic acid resin having a large D-form content, the crystallization rate index was high. For this reason, the obtained foam had a low crystallinity and a high heating dimensional change rate.

Example 14
To 100 parts by mass of the polylactic acid resin composition obtained in Example 5, 0.5 part by mass of azodicarbonamide (Vinole AC # 3; manufactured by Eiwa Kasei Kogyo Co., Ltd.) as a foaming agent was added, and an injection molding machine ( FANUC S-2000i type) was used for injection molding at a cylinder temperature of 210 ° C. and a mold temperature of 110 ° C. to obtain an injection foam. At this time, a mold having a cavity having a length of 127 mm, a width of 12.7 mm, and a depth of 1.6 mm was used. The initial thickness of the foam was 1.6 mm, and the retreat distance of the die plate was set to 1.92 mm (set foaming ratio: 2.2 times) to obtain an injection foam.

Examples 15-16, Comparative Examples 12-14
An injection foam was obtained in the same manner as in Example 14 except that the type of polylactic acid resin composition used was changed to that shown in Table 2.

  Table 2 shows the characteristic values of the injection foams obtained in Examples 14 to 16 and Comparative Examples 12 to 14.

As is clear from Table 2, since the injection foams obtained in Examples 14 to 16 used the polylactic acid resin compositions obtained in Examples 5, 7, and 8, the average cell diameter was high at a high expansion ratio. Was small, crystallinity was high, and bending strength was high.
On the other hand, since the injection foam obtained in Comparative Example 12 used the polylactic acid resin composition obtained in Comparative Example 2, the foaming ratio was low. Since the injection foam obtained in Comparative Example 13 used the polylactic acid resin composition obtained in Comparative Example 3, the injection foam had low crystallinity and low bending strength. For Comparative Example 14, since a polylactic acid resin having a large D-form content was used and a resin composition (Comparative Example 7) having a high crystallization rate index was used, the crystallization rate was low, and crystallization was sufficiently performed in injection foaming. Did not proceed and a foam could not be obtained.

Claims (2)

The organic peroxide (B) containing 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane is reduced to 0 with respect to 100 parts by mass of the polylactic acid resin (A). 0.1-6 parts by mass and 0.05-5 parts by mass of the air bubble modifier (C) are added and melt-kneaded to satisfy the following (1) to (3) simultaneously: A polylactic acid resin composition.
(1) The melt flow rate is 0.2 to 7 g / 10 minutes.
(2) The melt tension value measured at 190 ° C. is 30 mN to 200 mN.
(3) The crystallization rate index is 0.5-30. A foam comprising the polylactic acid resin composition according to claim 1.