JP2007186692A - Method for producing polylactic acid-based resin expandable beads - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based expanded foam through a simplified production process with improved productivity by a beads method to afford the foam with expandability, moldability and convenience. <P>SOLUTION: Expandable beads are obtained by melt-kneading and extruding, using an extruder, a mixture of a polylactic acid-based resin, a crosslinking agent and a foaming agent followed by cutting the extruded kneaded product. Thereby, the polylactic acid-based expanded foam having expandability and moldability equivalent to the case with conventional process can be obtained while simplifying both of the crosslinking step and the impregnating step into a single step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to expandable particles of a polylactic acid resin. More specifically, the present invention relates to an expandable particle of polylactic acid resin obtained by performing a crosslinking step and an impregnation step in one step when producing a polylactic acid-based foamed molded article by a bead method, and a method for producing the same.

  As an alternative to foamed polyolefin and foamed polystyrene using fossil resources as raw materials, Patent Document 1 proposes a foamed molded product using polylactic acid as a main raw material. This foamed molded product uses starch, which is a non-petroleum resource, as a starting material, and can be said to be very desirable from the viewpoint of global resource protection and environmental conservation. Further, the polylactic acid-based foamed molded article, like the polystyrene-based foamed molded article, was able to be transported to a processor in the state of unfoamed expandable particles, and was obtained by pre-foaming the expandable particles on the contractor side. It also has the advantages of conventional foamed molded products, such as pre-expanded particles can be molded in the mold.

  In general, when performing foam molding in a bead method, for example, polystyrene-based foam molded products are roughly divided into (1) a styrene monomer suspension polymerization and foaming agent impregnation step, and (2) pre-expanding of expandable particles. And (3) a step of forming pre-expanded particles in a mold.

  On the other hand, the method for producing a polylactic acid-based foam molded article by the bead method described in Patent Document 1 includes (1) a step of crosslinking a polylactic acid-based resin, (2) a step of impregnating a foaming agent, and (3) foaming. 4 steps, the step of pre-foaming the conductive particles, and the step of molding the pre-foamed particles in the mold, and the number of steps involved in crosslinking is increased compared to the production step of a general polystyrene foam molded article. Since polylactic acid-based resins are more expensive than general-purpose resin groups, it is desired to eliminate these problems to improve productivity and reduce manufacturing costs.

As another technique for obtaining a foamed molded product from a polylactic acid-based resin, for example, Patent Document 2 discloses a density of 0.15 obtained by absorbing a foaming agent in a thermoplastic polymer composition composed of a copolymer of polylactic acid or hydroxycarboxylic acid. ˜0.5 g / cm ³ degradable polymer expandable particles are disclosed.

  Patent Document 3 discloses non-crosslinked polylactic acid resin foamable particles composed of a polylactic acid resin having a specific melt viscosity, crystal melting heat quantity and crystal melting endothermic curve, and a foaming agent.

  However, in these technologies, foamed particles are prepared without performing special treatment on the polylactic acid resin. However, in the case of the polylactic acid resin, it is difficult to obtain appropriate conditions for foaming as it is, so that the low foaming ratio is low. There is a problem that only pre-expanded particles can be obtained and the moldability is deteriorated. In fact, we made a foamed molded product of polylactic acid resin according to the description in the patent document. However, the ratio of the pre-expanded particles is as low as about 20 times. I couldn't. Therefore, it is essential to perform treatments such as crosslinking or increasing the molecular weight of the polylactic acid resin itself.

  On the other hand, Patent Document 4 discloses a method in which a biodegradable polyester resin and a foaming agent are kneaded with an extruder, extruded as a foamed strand, and the foamed strand is cut to obtain pre-expanded particles.

  In this method, the impregnation step and the pre-foaming step are made into one step, and pre-foamed particles can be obtained continuously. However, when the base resin is polylactic acid, as described above, the foaming ratio is low without crosslinking, Formability also deteriorates. In addition, since this method makes it impossible to carry in an unfoamed state, it has to be carried in a state of bulky pre-expanded particles, which causes a problem that the transportation cost becomes expensive.

As described above, when producing a polylactic acid-based foamed molded article by the bead method, the manufacturing process is simplified, and the foamability, moldability, and convenience of conveyance, etc. of conventional polylactic acid-based foamed molded articles are further improved. There is no example in which is expressed.
International Publication No. 99/021915 Pamphlet Japanese Patent Laid-Open No. 5-170966 JP 2002-20525 A JP 2002-302567 A

  The problem to be solved by the present invention is that, when producing a polylactic acid-based foamed molded article by the bead method, the production process is simplified, the productivity is improved, and at the same time, the polylactic acid having foamability, moldability and convenience. It is providing a type | system | group foaming molding.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have extruded a polylactic acid resin, a crosslinking agent, and a foaming agent after melt-kneading with an extruder, and cutting the extruded kneaded product, It has been found that the cross-linking step and the impregnation step can be made into one step, and the present invention has been completed.

  That is, the first of the present invention is characterized in that a polylactic acid resin, a crosslinking agent, and a foaming agent are melt-kneaded with an extruder and then extruded, and the extruded kneaded product is cut into foamable particles. The present invention relates to a method for producing polylactic acid resin expandable particles. In a preferred embodiment, the polylactic acid-based resin is characterized in that the molar ratio of L-form and D-form of lactic acid monomer is 95/5 to 60/40, or 40/60 to 5/95. The present invention relates to a method for producing lactic acid resin expandable particles. More preferably, the crosslinking agent is a polyisocyanate compound having an isocyanate group ≧ 2.0 equivalents / mol, and 0.5 to 5.0 parts by weight of the polyisocyanate compound is blended with respect to 100 parts by weight of the polylactic acid resin. The method for producing expandable particles of polylactic acid resin described above, more preferably, impregnating 1.0 part by weight or more and 10.0 parts by weight or less of foaming agent with respect to 100 parts by weight of polylactic acid resin. The present invention relates to the above-described method for producing polylactic acid-based resin expandable particles. The second of the present invention relates to polylactic acid-based resin expandable particles having an apparent specific gravity of 0.25 to 1.25 g / cm 3 obtained by the production method described above.

  According to the method for producing expandable particles of the polylactic acid-based resin of the present invention, since the crosslinking step and the impregnation step can be made into one step, it is not necessary to add an excessive blowing agent in the impregnation step, and energy efficiency is also improved. Good, expandable particles can be produced continuously. Moreover, the polylactic acid-type foam which has the foamability and moldability equivalent to the polylactic acid-type foam molding manufactured by the conventional manufacturing method is obtained.

  Hereinafter, the present invention will be described in detail. The polylactic acid-based resin expandable particles of the present invention are obtained by melt-kneading a polylactic acid-based resin, a cross-linking agent, and a foaming agent with an extruder and then extruding and cutting the extruded kneaded product.

  The polylactic acid resin used in the present invention has a molar ratio of L-form and D-form of lactic acid monomer in the range of 95/5 to 60/40, or 40/60 to 5/95, preferably 90/10 to 70. / 30 or 30/70 to 10/90. When the molar ratio of the L-form and the D-form is in the range of 95/5 to 60/40, or 40/60 to 5/95, a foamed molded article with a high magnification can be easily obtained because of low crystallinity. In addition, the polylactic acid-based resin may be partially replaced with hydroxycarboxylic acid, dicarboxylic acid, diol, etc., which can be exchanged for lactic acid, or partially branched and cross-linked with epoxidized soybean oil, epoxidized linseed oil, etc. good.

  As a crosslinking agent used for this invention, at least 1 sort (s) of general crosslinking agents, such as a polyisocyanate compound, a peroxide, an acid anhydride, an epoxy compound, can be used.

  As the polyisocyanate compound, aromatic, alicyclic, and aliphatic polyisocyanate compounds can be used. As the aromatic polyisocyanate, polyisocyanate compounds having a skeleton of tolylene, diphenylmethane, naphthylene, and triphenylmethane are available. Can be mentioned. Examples of the alicyclic polyisocyanate include a polyisocyanate compound having a skeleton of isophorone and diphenylmethane hydroxide, and examples of the aliphatic polyisocyanate include a polyisocyanate compound having a skeleton of hexamethylene and lysine.

  Peroxides include benzoyl peroxide, bis (butylperoxy) trimethylcyclohexane, bis (butylperoxy) cyclododecane, butylbis (butylperoxy) valerate, dicumyl peroxide, butylperoxybenzoate, dibutyl peroxide, Examples thereof include organic oxides such as bis (butylperoxy) diisopropylbenzene, dimethyldi (butylperoxy) hexane, dimethyldi (butylperoxy) hexyne, and butylperoxycumene.

  Examples of the acid anhydride include trimellitic anhydride, pyromellitic anhydride, ethylene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, styrene-maleic anhydride copolymer, and the like.

  Epoxy compounds include glycidyl methacrylate-methyl methacrylate copolymer, glycidyl methacrylate-styrene copolymer, glycidyl methacrylate-styrene-butyl acrylate copolymer, polyethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, coconut fatty acid glycidyl ester. And various glycidyl ethers and various glycidyl esters such as epoxidized soybean oil and epoxidized linseed oil.

  Among these cross-linking agents, there is little torque increase due to cross-linking thickening at the time of kneading, and polyisocyanate compounds that can be post-thickened by urea bond, urethane bond, allophanate bond, etc. by heating in the presence of moisture after kneading. Preferably used. Among the polyisocyanate compounds, polyisocyanate compounds having tolylene and diphenylmethane skeletons, particularly polyisocyanates of diphenylmethane are preferably used in view of versatility, handleability, weather resistance, and the like.

  The addition amount of the crosslinking agent is preferably 0.1 parts by weight or more and 5.0 parts by weight or less with respect to 100 parts by weight of the polylactic acid resin, for example, polyisocyanate having isocyanate groups ≧ 2.0 equivalents / mol. When a compound is used, the amount of the compound added is preferably 0.5 parts by weight or more and 5.0 parts by weight or less, more preferably 1.0 part by weight or more with respect to 100 parts by weight of the polylactic acid resin. 3.0 parts by weight or less. If the addition amount is 0.5 parts by weight or more, there is a tendency to increase the melt viscosity of the polylactic acid resin composition to a region suitable for foaming, and if it is 5.0 parts by weight or less, the melt viscosity that does not inhibit foaming. This is preferable because it tends to be a region.

  Examples of the foaming agent used in the present invention include inorganic gas, volatile foaming agent, and water. Examples of the inorganic gas include carbon dioxide and nitrogen. Examples of the volatile foaming agent include propane, n-butane, i. -Aliphatic hydrocarbons such as butane, pentane, cyclopentane, heptane, halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoroethane, dichlorotetrafluoroethane, tetrafluoroethane, methyl chloride, etc. . In addition, the above-mentioned foaming agents can be used alone or in combination.

  The addition amount of the foaming agent is preferably 1.0 part by weight or more and 10.0 parts by weight or less, and more preferably 3.0 parts by weight or more and 8.0 parts by weight with respect to 100 parts by weight of the polylactic acid resin. Or less. If the addition amount is 1.0 part by weight or more, a desired foaming ratio tends to be obtained, and if it is 10.0 parts by weight or less, foaming tends not to be inhibited, which is preferable. In the case of obtaining conventional expandable resin particles, an excessive foaming agent had to be used in order to allow the expandable particles to contain a predetermined foaming agent in the impregnation step. The foaming agent can be impregnated without using it.

  In addition, additives such as foaming aids and nucleating agents may be used depending on the purpose. Examples of foaming aids include plasticizers, toluene, ethylbenzene, xylene, and cyclohexane. Examples of nucleating agents include inorganic powders such as talc, silicon dioxide, titanium dioxide, calcium carbonate, and sodium bicarbonate, citric acid, a mixture of sodium bicarbonate and citric acid, and the like. You can also. The addition amount of these additives is generally about 0.01 to 3 parts by weight with respect to 100 parts by weight of the polylactic acid resin, although it depends on the kind of the additive.

  In the present invention, a polylactic acid resin, a crosslinking agent, and a foam nucleating agent are supplied to an extruder. Such an extruder is not particularly limited as long as it is a conventionally used extruder, and examples thereof include a single-screw extruder, a twin-screw extruder, and a tandem type extruder in which a plurality of extruders are connected. Although mentioned, it is preferable to use a twin screw extruder or a tandem type extruder from the viewpoint of good dispersion of the crosslinking agent and the foaming agent.

  Then, the polylactic acid resin, the crosslinking agent, and the foaming nucleating agent are supplied to the extruder. The polylactic acid resin and the crosslinking agent are supplied to the extruder and melt-kneaded, and are in a molten state in the extruder. It is preferable to press-fit a foaming agent into the kneaded product using an injection pump.

  The foaming agent-containing kneaded material melt-kneaded in this way is extruded from the extrusion hole of the die head at the tip of the extruder and cut to obtain expandable particles.

  The kneading temperature by the extruder is preferably 150 ° C. or higher and 250 ° C. or lower, more preferably 180 ° C. or higher and 230 ° C. or lower. Further, the temperature and pressure at the tip of the extruder are not particularly limited as long as the kneaded product does not foam. Usually, it is 100 degreeC or more and 170 degrees C or less, and is 1 MPa or more and 30 MPa or less.

  There are various methods for cutting the kneaded product extruded from the extruder, and it is not particularly limited. However, a strand cutting method or an underwater cutting method in which the extruded strand is cut while being cooled with water or the like is preferable. .

In this way, expandable particles are obtained. The apparent specific gravity of the expandable particles is preferably 0.25 to 1.25 g / cm ^3, more preferably 0.50 to 1.20 g / cm ³ . If it is lower than 0.25 g / cm ³ , the particles become bulky and the transportation cost may increase.

  Thereafter, the polylactic acid-based foamed product of the polylactic acid-based resin of the present invention can be produced through a preliminary foaming process and an in-mold molding process similar to those of conventional foamable particles.

  As described above, according to the method for producing polylactic acid-based resin expandable particles of the present invention, the polylactic acid-based resin and the cross-linking agent are put into an extruder, and after adding the foaming agent and melt-kneading, the kneaded product is extruded. Since the extrudate kneaded product can be cut to obtain expandable particles, among the steps for producing the conventional polylactic acid-based foamed molded article already described, (1) a step of crosslinking a polylactic acid-based resin ( 2) Since the step of impregnating the foaming agent is a single step, the steps required to obtain a polylactic acid-based foamed molded product can be greatly shortened.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples at all. The evaluation was performed by the following method.

(Evaluation methods)
(1) Measuring method of apparent specific gravity of expandable particles:
The foamable particles were taken in a 2000 cm ³ container, and the mass was measured. The fourth decimal place was rounded off to the third decimal place, and the following formula was obtained.
Apparent specific gravity of expandable particles (g / cm ³ ) = mass of expandable particles (g) / apparent volume (2000 cm ³ )
The apparent specific gravity of the expanded particles was determined by the same measurement method.
(2) Formability evaluation method:
From the appearance (surface elongation, shrinkage) and the degree of internal fusion, visual evaluation was made according to the following criteria. ○: Good, ×: Poor
Example 1
Polyisocyanate compound ("Millionate MR-200", isocyanate group 2.7 to 2.8 equivalent / mol, manufactured by Nippon Polyurethane Industry Co., Ltd.) 2.0 parts by weight is supplied to a tandem extruder composed of a first stage extruder and a second stage extruder and extruded, and then 6 parts by weight of butane is supplied from an inlet in the latter half of the first stage extruder. Polylactic acid, polyisocyanate compound, and butane were melt-kneaded in a first-stage extruder and a second-stage extruder. Thereafter, the kneaded product was extruded from the extrusion hole (hole diameter 1 mmΦ, hole number: 24) of the die head at the tip of the second stage extruder, and the strand was cut while being cooled with water and dried to obtain expandable particles. . The temperature of the tandem extruder was 1 zone to 4 zones of the first stage extruder: 185 ° C, and 1 zone to 4 zones of the second stage extruder was 150 ° C.

(Comparative Example 1)
The same procedure as in Example 1 was carried out except that no polyisocyanate compound was added.

(Comparative Example 2)
L-form / D-form = 90/10 polylactic acid 100 parts by weight and polyisocyanate compound 2.0 parts by weight are kneaded with a twin screw extruder (TEM35B, Toshiba Machine Co., Ltd.) at a cylinder temperature of 185 ° C. Kneaded particles were obtained. 100 parts by weight of the obtained kneaded particles, 100 parts by weight of water, 20 parts by weight of isobutane as a blowing agent, and 10 parts by weight of acetone were charged in a pressure vessel and held at 82 ° C. for 90 minutes. After sufficiently cooling, the product was taken out and dried to obtain expandable particles.
Next, the expandable particles obtained in the above-mentioned Examples and Comparative Examples were foamed by exposing them to steam at 85 ° C. for 1 minute to obtain pre-expanded particles. After the pre-expanded particles were aged at room temperature for 2 days, they were filled in a molding die and heated with steam at 103 ° C. for 20 seconds to obtain an in-mold foam molded product. Table 1 shows evaluations regarding the apparent specific gravity and moldability of the obtained expandable particles and pre-expanded particles.

  As is clear from Table 1, the foamable particles of the polylactic acid-based resin of the examples have good prefoaming ratio and moldability, and are equivalent to the foamable particles obtained in the conventional process in Comparative Example 2. can get. However, Comparative Example 2 consists of four steps: a step of crosslinking a polylactic acid resin, a step of impregnating a foaming agent, a step of pre-foaming expandable particles, and a step of molding pre-foamed particles in a mold, On the other hand, Example 1 is advantageous in industrial production because the crosslinking step and the impregnation step are one step.

  In the same manner, in Comparative Example 1 in which the polyisocyanate compound was not added even if the process was simplified, expandable particles having a low preliminary expansion ratio and poor moldability were obtained.

  According to the foamable particles of the polylactic acid resin of the present invention and the method for producing the same, a polylactic acid foamed molded article having foamability and moldability equivalent to those of the conventional process was obtained, and the production process was simplified. This leads to an improvement in productivity and a reduction in production cost, and is very useful for the popularization of polylactic acid-based foamed molded products.

Claims (5)

  A polylactic acid-based resin expandable particle, characterized in that a polylactic acid-based resin, a crosslinking agent, and a foaming agent are melt-kneaded with an extruder and then extruded, and the extruded kneaded product is cut into expandable particles. Production method.   The polylactic acid-based resin according to claim 1, wherein the polylactic acid-based resin has a molar ratio of L-form to D-form of lactic acid monomer of 95/5 to 60/40, or 40/60 to 5/95. A method for producing expandable particles.   The crosslinking agent is a polyisocyanate compound having an isocyanate group ≧ 2.0 equivalents / mol, and the polyisocyanate compound is blended in an amount of 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the polylactic acid resin. The manufacturing method of the polylactic acid-type resin expandable particle of Claim 1 or 2.   The polylactic acid-based resin expandable particle according to any one of claims 1 to 3, wherein 100 parts by weight of the polylactic acid-based resin is impregnated with 1.0 to 10.0 parts by weight of a foaming agent. Production method. Polylactic acid-based resin expandable particles having an apparent specific gravity of 0.25 to 1.25 g / cm ³ obtained by the production method according to any one of claims 1 to 4.