JP2007314670A - Foamed polylactic acid-resin particle molding and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamed polylactic acid-resin particle molding improved in heat resistance and a method for producing the same. <P>SOLUTION: This foamed polylactic acid-resin particle molding is obtained by mixing almost uniformly >50 vol.% and <99 vol.% foamed resin particles consisting of (5/95) to (95/5) molar ratio of its L-form and D-form compounds and >1 vol.% to <50 mol% foamed resin particles consisting of a resin different from the polylactic acid-resin, and fusion-bonding them with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a foamed particle molded body comprising polylactic acid-based resin expanded particles and a method for producing the same.

  In recent years, plastic foams characterized by lightness, shock-absorbing properties, heat insulation properties, moldability, etc. have good functionality and handleability, and are often used mainly for packaging containers and shock-absorbing materials. On the other hand, plastics do not decompose, or even if they are decomposed, it takes a long time. If they are left in the natural world, there is a possibility that they will lead to pollution of the natural environment, which is a social problem. For this purpose, biodegradable plastics that are decomposed by microorganisms in the natural environment have been studied, and aliphatic polyester foams such as polylactic acid and polybutylene succinate, starch foams, etc. have been commercialized so far. .

  Among them, biodegradable plastics made from plants do not use petroleum resources, and carbon dioxide absorption and fixation effects associated with plant growth are expected as one of the measures to prevent global warming. Yes.

The plant-derived biodegradable plastics include (1) microbially-produced aliphatic polyesters such as polyhydroxyalkanoates (in the present invention, particularly poly (3-hydroxyalkanoates), ie, P3HA), and (2) corn. And polylactic acid obtained by polymerization of lactic acid obtained from plants such as In particular, polylactic acid (2) has been actively researched and developed as a plant-derived biodegradable plastic that is most practically used at present. As a feature, it is a material excellent in environmental compatibility using a plant as a raw material. For example, a relatively hard property similar to polystyrene can be obtained. However, the foamed particles obtained by foaming polylactic acid and the molded body thereof have a problem that the volume of the foamed particles expands significantly under high temperature and high humidity conditions and cannot be used under severe conditions such as overseas export. As an approach for solving the problem, for example, by making a foamed particle a resin composition in which polyvinyl acetate is mixed with polylactic acid, the barrier property against foaming gas and air of polylactic acid is reduced (Patent Document 1). Examples include adjusting the L-form and D-form ratio of polylactic acid and performing heat treatment during molding (Patent Document 2). However, as in Patent Document 1, in the case of improving the resin characteristics as a resin mixture to form expanded particles, it is difficult to create a completely mixed state in the resin blend system. It can be seen that foaming properties are inhibited, such as improvement in the amount of water is not expected. Moreover, in patent document 2, since the heat processing time is required at the time of molding, the total molding time becomes long, and as a result, the problem that the manufacturing cost becomes high remains.
JP 2006-22242 A Japanese Patent Laid-Open No. 2003-301068

  In view of the above problems, an object of the present invention is to provide a polylactic acid-based resin expanded particle molded body having improved heat resistance and a method for producing the same.

  As a result of intensive studies to solve the above problems, the present inventors have mixed polylactic acid resin expanded particles and expanded particles composed of other resins substantially uniformly, filled a mold, and then heat molded. As a result, the inventors have found that the heat-resistant problem of the foamed molded article made of the polylactic acid-based resin expanded particles can be solved, thereby completing the present invention.

  That is, according to the first aspect of the present invention, the foamed resin particles composed of a polylactic acid resin having a molar ratio of L-form to D-form of 5/95 to 95/5 are more than 50 volume% and 99 volume% or less. The present invention relates to a molded article of polylactic acid resin foamed particles obtained by mixing resin foam particles made of a resin different from lactic acid resin in an amount of 1% by volume or more and less than 50% by volume, and fusing them together.

As a preferred embodiment,
(1) Resin different from polylactic acid resin is represented by the formula (1)
[—O—CHR—CH ₂ —CO—] (1)
(Here, R is an alkyl group represented by C _n H _{2n + 1} , and n is an integer of 1-15)
A copolymer comprising one or more units represented by the following (hereinafter, poly (3-hydroxyalkanoate): abbreviated as P3HA).
(2) P3HA is poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter abbreviated as PHBH).
(3) In the composition of the copolymerization component of PHBH, poly (3-hydroxyhexanoate) is 1 mol% or more and 20 mol% or less.
The present invention relates to the above-mentioned polylactic acid-based resin expanded particle molded body.

  The second aspect of the present invention is that the resin foam particles made of a polylactic acid resin and the resin foam particles made of a resin different from polylactic acid are mixed almost uniformly, filled in a mold, and then heat-molded. The present invention relates to a method for producing the polylactic acid-based resin expanded particle molded body described above.

  According to the present invention, a polylactic acid-based resin foamed particle molded body having improved heat resistance and capable of obtaining a desired foaming ratio according to the mixing ratio of the foamed particles without inhibiting foamability is obtained. I can do it.

  Hereinafter, the present invention will be described in more detail.

  The polylactic acid-based resin in the present invention is, for example, glucose obtained by enzymatic decomposition of starch obtained from plant resources such as corn and sweet potato, fermented with lactic acid bacteria to give lactic acid, and 70 wt. It is said to contain more than%. As long as it contains 70% by weight or more of lactic acid as a monomer unit, it may be a copolymer with other hydroxycarboxylic acid units, as well as a homopolymer of lactic acid, or a blend with other resins.

  The polylactic acid resin used for foaming preferably has as little crystallinity as possible. The reason is that the crystalline resin is crystallized in the step of impregnating the foaming agent and inhibits foaming. In order to reduce the crystallinity, it is necessary that the molar ratio of the L-form and D-form of the polylactic acid resin having optical isomers is 5/95 to 95/5, and preferably the L-form and D-form. It is a substantially non-crystalline polylactic acid resin having a body molar ratio in the range of 60/40 to 95/5, or 5/95 to 40/60. When the molar ratio of L-form to D-form exceeds 95/5 or less than 5/95, the crystallinity is high, the foaming ratio does not increase, and foaming becomes uneven and cannot be used. More preferably, the molar ratio of L-form to D-form is in the range of 90/10 to 70/30, or 30/70 to 10/90.

  In the present invention, the resin different from the polylactic acid resin is not particularly limited, and a known resin can be used. Examples thereof include foamed particles made of a resin such as an aliphatic polyester resin such as poly (3-hydroxyalkanoate), a polyolefin resin, a polystyrene resin, a polyethylene terephthalate resin, and a urethane resin. Among these, it is preferable to use an aliphatic polyester-based resin because it is easily heat-sealed with a polylactic acid-based resin. Furthermore, it is preferable to use poly (3-hydroxyalkanoate) from the viewpoint of improving environmental compatibility and heat resistance.

  In the present invention, poly (3-hydroxyalkanoate) is a poly (3-hydroxyalkanoate) having a repeating structure composed of 3-hydroxyalkanoate represented by the formula (1) and is an aliphatic polyester produced from microorganisms. Hydroxyalkanoate) (hereinafter sometimes referred to as P3HA).

[—CHR—CH ₂ —CO—O—] Formula (1)
Here, R is an alkyl group represented by C _n H _{2n + 1} and is an integer of n = 1-15.

  As P3HA in the present invention, a homopolymer of the above-mentioned 3-hydroxyalkanoate or a copolymer comprising a combination of two or more different 3-hydroxyalkanoates, that is, a di-copolymer, a tri-copolymer, a tetra-copolymer, etc. Or a blend of two or more selected from these homopolymers and copolymers, among which n = 1 3-hydroxybutyrate, n = 2 3-hydroxyvalerate, n = 3 3-hydroxy It consists of a homopolymer such as hexanoate, 3-hydroxyoctanoate with n = 5, 3-hydroxyoctadecanoate with n = 15, or a combination of two or more 3-hydroxyalkanoate units having different n. A copolymer or a blend thereof can be preferably used. P3HA is more preferably poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), which is a copolymer of n = 1 3-hydroxybutyrate and n = 3 3-hydroxyhexanoate. The composition ratio is more preferably 3-hydroxybutyrate / 3-hydroxyhexanoate = 99/1 to 80/20 (mol / mol). When the composition ratio of 3-hydroxybutyrate / 3-hydroxyhexanoate is within the above range, processing can be performed without heating to a high temperature, so that a decrease in molecular weight due to thermal decomposition during heat processing can be suppressed. There is a tendency that much time is not required for recrystallization during processing.

  The polylactic acid-based resin expanded particle molded body of the present invention is obtained by substantially uniformly mixing and fusing together resin expanded particles composed of the polylactic acid-based resin and resin expanded particles composed of a resin different from the polylactic acid-based resin. The mixing ratio of the two resin foam particles can be appropriately adjusted according to the purpose, but the resin foam particles made of polylactic acid resin are used in an amount of more than 50% by volume and 99% by volume or less. 1% by volume or more and less than 50% by volume of resin foam particles made of a different resin. By mixing in this way to form a foamed molded article, it is possible to obtain a desired expansion ratio and improve heat resistance by inhibiting the foamability without depending on the mixing ratio of the expanded particles. It becomes.

  The foamed resin particles obtained by foaming the polylactic acid resin of the present invention can be produced, for example, as follows.

  First, a polylactic acid resin is impregnated with a foaming agent. The method is not particularly limited as long as sufficient pressure is applied in the presence of a foaming agent that provides desired foamability. In addition, impregnation is possible with either aqueous or non-aqueous systems.

  As the foaming agent used for imparting foaming properties, in addition to hydrocarbon-based foaming agents such as propane, n-butane, isobutane, pentane, isopentane, hexane and the like, chlorofluorocarbon can also be suitably used. Similarly, foaming agents other than halogenated hydrocarbons are preferable in view of environmental compatibility.

  A known method can be used as a method for producing the resin expanded particles made of a resin different from the polylactic acid resin used in the present invention. For example, resin foam particles obtained by foaming poly (3-hydroxyalkanoate) can be produced as follows.

  First, P3HA, which is a base resin, is heat-melted and kneaded using an extruder, kneader, Banbury mixer, roll, etc., and then used for foaming of the present invention such as cylindrical, elliptical, spherical, cubic, rectangular parallelepiped. P3HA resin particles obtained by molding into an easy particle shape are used. The weight per particle is 0.1 mg or more, preferably 0.5 mg or more. If it is less than 0.1 mg, it may be difficult to produce the P3HA resin particles themselves.

  Moreover, in order to improve foamability, it is also possible to perform resin modification using a modifier or the like. The modifier is not particularly limited as long as it improves foaming properties. For example, an isocyanate compound can be preferably used from the viewpoint of reactivity. The isocyanate compound has two or more isocyanate groups in one molecule, and types include aromatic, alicyclic, and aliphatic isocyanates. For example, aromatic isocyanates include tolylene, diphenylmethane, naphthylene, tolidine, xylene, isocyanate compounds having triphenylmethane as a skeleton, alicyclic isocyanates as isophorone, isocyanate compounds having hydrogenated diphenylmethane as a skeleton, and aliphatic isocyanates. Examples include isocyanate compounds having hexamethylene and lysine as a skeleton. Furthermore, a combination of two or more of these isocyanate compounds can also be used, but tolylene, diphenylmethane, especially polyisocyanate of diphenylmethane is preferably used in view of versatility, handleability, weather resistance and the like.

  After the P3HA resin particles thus obtained are dispersed in an aqueous dispersion medium in a closed container together with a dispersant, a foaming agent is introduced into the closed container and heated to a temperature equal to or higher than the softening temperature of the P3HA resin particles. After holding for a certain period of time near the foaming temperature, one end of the sealed container is released, and the P3HA resin particles and the aqueous dispersion medium are released into an atmosphere at a pressure lower than the pressure of the sealed container. Manufactured.

  Examples of the dispersant include inorganic substances such as tricalcium phosphate, calcium pyrophosphate, kaolin, basic magnesium carbonate, aluminum oxide, basic zinc carbonate, and anionic surfactants such as sodium dodecylbenzene sulfonate and sodium α-olefin sulfonate. In addition, normal paraffin sulfonic acid soda is used in combination. The amount of the inorganic substance is usually 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the P3HA resin, and the amount of the anionic surfactant is usually 0.001 to 0.2 parts by weight with respect to 100 parts by weight of the P3HA resin. The dispersion medium is usually water from the viewpoints of economy and handleability, but is not limited thereto.

  Examples of the blowing agent include saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane, ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, monochloromethane, dichloromethane, Halogenated hydrocarbons such as dichlorodifluoroethane, inorganic gases such as carbon dioxide, nitrogen and air, water and the like can be mentioned, but at least one of these may be used. In view of environmental compatibility, foaming agents other than halogenated hydrocarbons are preferred. The amount of foaming agent added depends on the expansion ratio of the desired pre-expanded particles, the type of foaming agent, the type of polyester resin, the ratio of resin particles to the dispersion medium, the space volume of the container, the impregnation or foaming temperature, etc., but the P3HA resin particles Usually, it is in the range of 2 to 10,000 parts by weight with respect to 100 parts by weight.

  Various additives may be added to the resin expanded particles used in the present invention as long as the required performance is not impaired. Here, additives can be used according to purposes such as antioxidants, UV absorbers, dyes, pigments and other colorants, plasticizers, lubricants, crystallization nucleating agents, inorganic fillers, etc. The compounding agent which has property is preferable. Additives include inorganic compounds such as silica, talc, calcium silicate, wollastonite, kaolin, clay, mica, zinc oxide, titanium oxide, silicon oxide, sodium stearate, magnesium stearate, calcium stearate and stearic acid Fatty acid metal salts such as barium, liquid paraffin, olefin wax, stearyl amide compound, and the like are exemplified, but the invention is not limited to these. In addition, when it is necessary to adjust the bubble diameter of the expanded particles, a bubble adjusting agent is added. Inorganic nucleating agents include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, baking soda, alumina, barium sulfate, aluminum oxide, bentonite, etc. The amount is usually 0.005 to 2 parts by weight.

  The resin foam particles made of the polylactic acid resin and the resin foam particles made of a resin different from the polylactic acid resin obtained as described above are subjected to pressure aging with pressurized air, if necessary. The foamed resin particles are heated and fused to each other by introducing water vapor into the mold, and the foamed polylactic acid resin particles. A shaped body is produced. The molding heating conditions and the like can be appropriately selected depending on the type of resin foam particles used, the mixing ratio, and the like.

  The polylactic acid-based resin expanded particle molded body thus obtained has improved heat resistance, and can have a desired expansion ratio without impairing expandability due to the mixing ratio of the expanded particles.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” are based on weight. Substances used in the present invention were abbreviated as follows.
PLA: Polylactic acid resin P3HA: Poly (3-hydroxyalkanoate)
PHBH: poly (3-hydroxybutyrate-co-3-hydroxyhexanoate)
HH ratio: mole fraction of hydroxyhexanoate in PHBH (mol%)

<Method for measuring expansion ratio of PLA expanded particles and molded body>
A graduated cylinder containing ethanol at 23 ° C. was prepared, and 500 or more PLA expanded particles, PHBH expanded particles (foamed particle group) left in the graduated cylinder for 7 days under the conditions of 50% relative humidity, 23 ° C. and 1 atm. ) And a foamed resin group that has been cut out to an appropriate size using a wire mesh and the like, and a volume V (cm ³ ), it is given by the following equation from the resin density ρ (g / cm ³ ).
Foaming ratio = V / (W / ρ)

<Method for measuring the closed cell ratio of PLA expanded particles and molded products>
It measured according to ASTM D-2856 using a multi-pynometer (manufactured by Beckman Japan Co., Ltd.).

<Heat resistance of PLA expanded particle molding>
A test piece of 100 × 100 × 30 mm was cut out from the PLA expanded particle molded body, treated in a constant temperature and humidity chamber (60 ° C., relative humidity 80%) for 24 hours, and measured from longitudinal, lateral and thickness measurements before and after treatment. The volume change rate of was calculated.

<Manufacture of PLA foam particles>
100 parts by weight of PLA (specific gravity 1.2 g / ml) having a D-form ratio of 10%, a number average molecular weight of 100,000 and a weight average molecular weight of 210,000 and 2 parts by weight of the same polyisocyanate compound are melt-kneaded, and an underwater cutter is used. A bead-shaped resin composition having a diameter of about 1 mm was used. Next, each bead-shaped resin composition was aged and secondary crosslinked in warm water at 42 ° C. for 15 hours, then dehydrated and dried, and impregnated with a blowing agent. For the impregnation of the foaming agent, 4.3 kg of each aged bead is charged into a 10 L rotating drum type sealed container, 215 g of methanol and 1720 g of isobutane are added, impregnation is performed at 85 ° C. for 3 hours, and air-drying is performed at room temperature, and foaming is performed. A bead-shaped resin composition impregnated with an agent was obtained. It was foamed with a pre-foaming machine for expanded polystyrene (Dysen Kogyo Co., Ltd. DYHL-300) to obtain PLA expanded particles having an expansion ratio of 35 times and an closed cell ratio of 98%.

<Manufacture of PHBH expanded particles>
PHBH produced using Alcaligenes eutrophus AC32 (J. Bacteriol., 179,4821 (1997)) in which a PHA synthase gene derived from Aeromonas caviae was introduced into Alcaligenes eutrophus as a microorganism, with appropriate adjustment of raw materials and culture conditions, 100 parts by weight of PHBH (specific gravity 1.2 g / ml) having an HH ratio of 12 mol% and 2 parts by weight of a polyisocyanate compound (manufactured by Nippon Polyurethane, Millionate MR-200 (2.7 to 2.8 equivalents / mol of isocyanate groups)) After hand blending, strands extruded through a 3mmφ small hole die attached to the tip of the extruder, melt kneaded at a cylinder temperature of 145 ° C using a φ35mm single screw extruder with a kneader (Kasamatsu Lab's laboratory universal extruder) Was cut with a pelletizer to prepare a PHBH resin composition having a particle weight of 5 mg and a melting point of 135 ° C.

  After charging 100 parts by weight of the resin composition into a 4.5 L pressure vessel, adding 25 parts by weight of isobutane as a foaming agent, stirring, and raising the temperature until the temperature in the container reaches 119 ° C. (foaming temperature) After holding for 1 hour in a state where the internal pressure of the container is 1.8 MPa, the foam is discharged and foamed under atmospheric pressure through a small nozzle provided at the bottom of the pressure-resistant container, and PHBH expanded particles having an expansion ratio of 18 times and a closed cell ratio of 98% are obtained. Obtained.

Example 1
60% by volume of the PLA foamed particles and 40% by volume of the PHBH foamed particles were mixed in advance, and the mixed resin foamed particles were filled in a 300 × 400 × 30 mm mold, and 0.10 to 0.32 MPa (gauge). Water vapor was introduced into the mold, and both of the resin foam particles were heated and fused to obtain a PLA foam particle molded body having an expansion ratio of 30 times and a single air rate of 93%. The coefficient of thermal expansion of the resin foam particle molded body was 10%. Compared with Comparative Example 1, it was possible to obtain a resin expanded particle molded body in which the coefficient of thermal expansion was suppressed and the heat resistance was improved. The results are shown in Table 1.

(Example 2)
The same procedure as in Example 1 was performed except that 75% by volume of the PLA expanded particles and 25% by volume of the PHBH expanded particles were different in mixing ratio. After the introduction of water vapor, a PLA expanded particle molded body having an expansion ratio of 33 times and an air-blowing ratio of 93% was obtained. Moreover, the thermal expansion coefficient of the resin foam particle molded body was 15%. Compared with Comparative Example 1, it was possible to obtain a resin expanded particle molded body in which the coefficient of thermal expansion was suppressed and the heat resistance was improved. The results are shown in Table 1.

(Comparative Example 1)
The same operation as in Example 1 was performed except that only the PLA expanded particles were used. After the introduction of water vapor, a PLA expanded particle molded body having an expansion ratio of 35 times and a self-efficiency rate of 98% was obtained. Moreover, the thermal expansion coefficient of the resin foam particle molded body was 40%. The results are shown in Table 1.

Claims (5)

  Resin made of a resin different from the polylactic acid resin, with a foamed resin particle made of a polylactic acid resin having a molar ratio of L-form to D-form of 5/95 to 95/5 exceeding 99 vol% A molded product of polylactic acid resin foamed particles obtained by mixing 1% by volume to less than 50% by volume of foamed particles substantially uniformly and fusing them together. Resin different from polylactic acid resin is represented by the formula (1)
[—O—CHR—CH ₂ —CO—] (1)
(Here, R is an alkyl group represented by C _n H _{2n + 1} , and n is an integer of 1-15)
2. The polylactic acid-based resin expanded particle molded body according to claim 1, which is a copolymer composed of one or more units represented by the following (hereinafter referred to as poly (3-hydroxyalkanoate): abbreviated as P3HA).   The polylactic acid-based resin expanded particle molded article according to claim 1 or 2, wherein P3HA is poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter abbreviated as PHBH).   The polylactic acid-based resin expanded particle molded article according to claim 3, wherein the poly (3-hydroxyhexanoate) content is 1 mol% or more and 20 mol% or less in the composition of the copolymerization component of PHBH.   The resin foam particles made of a polylactic acid resin and the resin foam particles made of a resin different from polylactic acid are mixed almost uniformly, filled in a mold, and then heat-molded. The manufacturing method of the polylactic acid-type resin expanded particle molded object of 1 item | term.