JP4954461B2 - POLYLACTIC ACID RESIN COMPOSITION, FOAM PARTICLE, AND FOAM MOLDED BODY - Google Patents

Description

  The present invention relates to a resin composition for a foamed molded article having polylactic acid resin as a main raw material and having hydrolysis resistance, foamability and moldability, and its foamed particles and foamed molded article thereof.

  Today, there are many plastics that are generally used from petroleum. However, petroleum is a finite natural resource, and there is a problem that it will be exhausted if it is used as it is. For this reason, the movement to make widely used plastics non-petroleum resources is accelerating every year.

  For example, polystyrene foam, one of the typical oil-derived plastics, produces nearly 200,000 tons per year in Japan alone. Many of these are for packaging materials such as fish boxes and household appliance cushioning materials, and often become garbage after use. Among them, some of the home appliance cushioning materials are recycled and used for video tape cassette housings, etc., but it is only a part, and most of the polystyrene foam products such as fish boxes are recovered and reduced and then used as fuel. ing.

  For this reason, these researchers have advanced the development which substitutes a polystyrene foam using polylactic acid which is a non-petroleum resource (patent document 1). Polylactic acid, when disposed after use, has a lower calorie burn than styrene foam and is biodegradable, so it can be decomposed by microorganisms and the like, and is decomposed into water and carbon dioxide even when landfilled. Furthermore, composting (composting) is possible, and it is a substance that does not give a burden to the global environment.

  However, polylactic acid has a property of being gradually hydrolyzed even by water in water or air, and has a problem that it is inferior in long-term quality stability. In Patent Document 1, a resin obtained by crosslinking polylactic acid with an isocyanate compound is used, but this reaction is a reaction that occurs mainly with a hydroxyl group at the end of the molecular chain, and the carboxyl group at the end of the molecular chain is blocked. Is not sufficient, and long-term quality stability in an environment with moisture is not guaranteed.

  On the other hand, hydrolysis of polylactic acid is a reaction that occurs due to the autocatalytic action of the carboxyl group at the end of the molecular chain, so that the hydrolysis of polylactic acid is highly enhanced by blocking the carboxyl group at the end of the molecular chain with a carbodiimide compound. It is known to be suppressed (Patent Document 2 and Patent Document 3).

  In Patent Document 2 and Patent Document 3, a carbodiimide compound is used for the purpose of improving the hydrolysis resistance of polylactic acid. In these examples, the carbodiimide compound is a monocarbodiimide compound in a biodegradable plastic mainly composed of polylactic acid. Alternatively, only one of the polycarbodiimide compounds is used, and a specific example in combination is not disclosed.

  Moreover, neither Patent Document 2 nor Patent Document 3 mentions a foamed molded article obtained by in-mold molding of foamed particles.

WO99 / 21915 Japanese Patent Laid-Open No. 11-80522 JP 2001-261797 A Japanese Patent Publication No. 47-33279 Japanese Patent Publication No. 52-16759 JP-A-11-322888

  An object of the present invention is to solve the above-mentioned problems of the prior art, use polylactic acid as a main raw material, have excellent hydrolysis resistance, and have a foaming property and moldability, and a polylactic acid resin composition comprising the same The goal is to develop expanded particles, as well as expanded molded articles thereof.

  The above object is achieved by blocking a part or all of the carboxyl group terminals of polylactic acid with a polycarbodiimide compound and a monocarbodiimide compound.

  The polylactic acid resin composition of the present invention is excellent in hydrolysis resistance, and in the foamed molded article, it is excellent in moldability compared with that of a polylactic acid resin composition to which only a polycarbodiimide compound or a monocarbodiimide compound is added. It can be used in a wider range of fields than before.

  As the polylactic acid resin used in the present invention, it is preferable to use a low crystalline or non-crystalline one because it does not crystallize when impregnated with a foaming agent. Specifically, the moles of L isomer and D isomer of optical isomers are used. It is preferable to use one having a ratio of 95/5 to 60/40. Resins that deviate from this molar ratio have high crystallinity and cannot be used because the expansion ratio does not increase or the foaming becomes uneven. More preferably, it is 90/10 to 85/15.

  The polycarbodiimide compound used in the present invention is not particularly limited as long as it has a plurality of carbodiimide groups in the polymer chain. The polycarbodiimide compound can be obtained by condensing an arbitrary organic diisocyanate, and a known technique can be used for the method. For example, as shown in Patent Document 2 and Patent Documents 4 to 6, those obtained by decarboxylation condensation reaction of organic diisocyanate can be used. Specific examples include poly [1,1-dicyclohexylmethane (4,4-diisocyanate)] and a urea adduct of cyclohexylamine. Nisshinbo Co., Ltd. is a fine granular polycarbodiimide compound at room temperature. “Carbodilite HMV-8CA”, “Carbodilite LA-1” and the like are more preferable in terms of availability and operability.

The monocarbodiimide compound used in the present invention is not particularly limited as long as it has one carbodiimide group. Specifically, dimethylcarbodiimide, diethylcarbodiimide, diisopropylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, di-t-butylcarbodiimide, dicyclohexylcarbodiimide, diphenylcarbodiimide, 2,2,6,6-tetramethyldiphenyl Carbodiimide, 2,2,6,6-tetraethyldiphenylcarbodiimide, 2,2,6,6-tetraisopropyldiphenylcarbodiimide, di-β-
Naphthylcarbodiimide and the like can be mentioned, but “NCN” manufactured by Matsumoto Yushi Seiyaku Co., Ltd., which is a fine granular monocarbodiimide compound at room temperature, is more preferable in terms of availability and operability.

  The total addition amount of the polycarbodiimide compound and monocarbodiimide compound used in the present invention to polylactic acid is preferably 0.5 parts by weight or more and 2.5 parts by weight or less with respect to 100 parts by weight of the polylactic acid resin. When the addition amount is within this range, the expansion ratio becomes high and the moldability becomes good. More preferably, it is 1.0 to 2.0 parts by weight.

  In addition, the weight ratio of the polycarbodiimide compound and the monocarbodiimide compound used in the present invention to the polylactic acid is preferably 3/1 to 1/3. When the weight ratio is within this range, the expansion ratio becomes high and the moldability becomes good. More preferably, it should be 5/2 to 2/5.

  Next, the manufacturing method of the polylactic acid-type resin composition of this invention is demonstrated. As a means for obtaining a polylactic acid-based resin composition by blocking a part of the carboxyl group terminal of polylactic acid with a polycarbodiimide compound and a monocarbodiimide compound, a known technique can be used, but a polycarbodiimide compound is added to pelletized polylactic acid. Is generally used, and melt kneading with a twin-screw kneader.

  The melt viscosity obtained from the extrusion amount per unit time of the polylactic acid-based resin composition thus obtained at 190 ° C., a load of 20 kg, and an orifice diameter of 2 mm is 2,000 Pa · s to 5,000 Pa · s. Preferably there is. If the melt viscosity is less than 2,000 Pa · s, the heat resistance during molding is poor, and a good foamed molded article cannot be obtained. On the other hand, if it exceeds 5,000 Pa · s, it becomes difficult to foam, and adhesion between the foamed particles becomes worse at the time of molding, so it is not suitable for the purpose of molding. If a molded article having a higher expansion ratio and higher quality is expected, it is preferable that the pressure is 2,500 Pa · s to 3,000 Pa · s.

  Furthermore, an inorganic or organic nucleating agent may be added for the purpose of making the foamed particles uniform and pores. For example, talc, mica, silica, clay mineral, calcium carbonate, organic carboxylic acid metal salt and the like can be used, but are not particularly limited thereto.

  Next, the method for producing the polylactic acid-based expandable particles of the present invention will be described. In this production method, a polylactic acid resin composition formed into pellets or beads is used as a raw material, and impregnated with a foaming agent in the presence of water.

  The amount of water added at the time of impregnation is not particularly limited as long as the dispersibility of the pellets or beads is not impaired. Also, a dispersant can be used in order to prevent the pellets or bead-like particles from sticking or fusing together.

  As the dispersant added at the time of impregnation, any of a cationic surfactant, an anionic surfactant, and a nonionic surfactant can be used, but is not particularly limited thereto.

  As the foaming agent to be impregnated into the polylactic acid resin composition, nitrogen, carbon dioxide inorganic gas, propane, butane, isobutane, pentane, isopentane and other hydrocarbons and mixtures thereof are used. Although chlorofluorocarbons are also suitable as blowing agents, it is preferable to avoid them when environmental considerations are necessary.

The impregnation conditions are adjusted according to the physical properties of the polylactic acid-based resin composition. Taking the case of an impregnation temperature of 82 ° C. as an example, the impregnation time is suitably from 60 minutes to 150 minutes.

  Next, the manufacturing method of the polylactic acid-type expanded particle of this invention is demonstrated. A known technique can be used for foaming the polylactic acid-based expandable particles obtained by impregnation with a foaming agent, but a method of foaming by contacting with a mixed gas of high-temperature steam and air is common.

  In order to prevent a phenomenon (blocking) in which foamed particles are fused with each other at the time of foaming, it is possible to use an anti-blocking agent as long as foamability and moldability are not significantly impaired.

  As the anti-blocking agent, those used as an anti-blocking agent for polystyrene foam can be generally used, and examples thereof include metal salts of higher fatty acids, but are not particularly limited thereto. Specifically, magnesium stearate, calcium stearate, zinc stearate, or the like can be used, and these can be used alone or in combination of two or more.

  Next, the manufacturing method of the polylactic acid-type foaming molding of this invention is demonstrated. A known technique can be used to mold the polylactic acid-based foamed particles obtained by foaming, but a general method is to introduce the foamed particles into a mold and perform in-mold molding. Although high-temperature steam is used for heating during molding in the mold, it is preferable to use low-heat capacity steam using a gas in which high-temperature steam and air are mixed.

  The present invention will be described in more detail below by way of examples, but these examples do not limit the present invention. First, the physical property evaluation method is introduced.

<Melt viscosity>
Measurement was performed using a CFT-500D manufactured by Shimadzu Corporation at a temperature of 190 ° C., a load of 20 kg, and an orifice diameter of 2 mm.

<Hydrolysis resistance test>
The change with time of the melt viscosity of the resin under constant temperature and humidity conditions of 60 ° C. and 80% RH was examined. As an index representing the hydrolysis resistance, a two-stage evaluation was performed (◯: viscosity retention after 5 days exceeded 50%, x: viscosity retention after 5 days less than 50%).

<Foaming ratio>
The weight and volume of the polylactic acid-based expanded particles were measured, and the expansion ratio was calculated by the following formula (1).
(Expansion ratio (times)) = (Volume of expanded particles) / (Weight of expanded particles) (1)

(Examples 1-4)
A polylactic acid having an optical isomer L-form and D-form molar ratio of 88/12 and a melt viscosity of 2,070 Pa · s was used. After adding a polycarbodiimide compound (“Carbodilite LA-1” manufactured by Nisshinbo Industries Inc.) and a monocarbodiimide compound (“NCN” manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) to this, the cylinder temperature was measured by a twin-screw kneader (TEM35B manufactured by Toshiba Machine Co., Ltd.). A polylactic acid resin composition was obtained by melt-kneading at 185 ° C., and a melt viscosity measurement and a hydrolysis resistance test were performed (Table 1).

(Comparative Examples 1-3)
A polylactic acid having an optical isomer L-form and D-form molar ratio of 88/12 and a melt viscosity of 2,070 Pa · s was used. Polycarbodiimide compound (Nisshinbo Co., Ltd. “
Carbodilite LA-1 ") was added and then melt kneaded at a cylinder temperature of 185 ° C with a twin-screw kneader (TEM35B manufactured by Toshiba Machine Co., Ltd.) to obtain a polylactic acid resin composition, and measurement of melt viscosity and hydrolysis resistance A sex test was performed (Table 1).

(Comparative Example 4)
A polylactic acid having an optical isomer L-form and D-form molar ratio of 88/12 and a melt viscosity of 2,070 Pa · s was used. After adding a monocarbodiimide compound (“NCN” manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) to this, it was melt-kneaded at a cylinder temperature of 185 ° C. by a twin-screw kneader (TEM35B manufactured by Toshiba Machine Co., Ltd.) to obtain a polylactic acid resin composition. The melt viscosity measurement and the hydrolysis resistance test were performed (Table 1).

  As a representative example of the hydrolysis resistance test, the change over time in the melt viscosity of the polylactic acid resin and the polylactic acid resin composition of Example 2 is shown in FIG.

<Impregnation of foaming agent>
The polylactic acid resin compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were pelletized or bead-like particles, and then impregnated with a foaming agent. That is, the same amount of polylactic acid resin composition and water are mixed in a rotary pressure-resistant container, and isobutane as a foaming agent is 25% with respect to the polylactic acid resin composition, and a surfactant (Sanyo Kasei Co., Ltd.). "Ionette DO-1000") 1.5% of the polylactic acid resin composition was injected into the sealed state, and the pressure vessel was rotated at 15 revolutions / minute, and the temperature inside the pressure vessel was 1 hour. The temperature was raised from 30 ° C. to 82 ° C., then held at 82 ° C. for 2 hours, and then further lowered from 82 ° C. to 50 ° C. in 40 minutes. Polylactic acid-based expandable particles were obtained by air drying.

<Prefoaming; Preparation of foamed particles>
Next, the polylactic acid-based foamed particles are heated from 50 ° C. to 76 ° C. in about 1 minute with a mixed gas of high-temperature water vapor and air, and held at 76 ° C. for about 1 minute and 30 seconds, thereby polylactic acid-based foamed particles. Particles were obtained.

<Molding>
The polylactic acid-based expanded particles were stored at room temperature under atmospheric pressure for 3 days, and then filled with polylactic acid-based expanded particles in a mold having a length of 307 mm, a width of 307 mm, and a thickness of 30 mm, followed by in-mold molding. About the obtained polylactic acid-based foamed molded article, three stages (◎: shape and good adhesion of foam particles, ○: good shape but poor adhesion of foam particles, ×: poor adhesion of shape and foam particles) Visual evaluation was performed.

  From Table 1, when a polycarbodiimide compound and a monocarbodiimide compound are used in combination as in the examples, the hydrolysis resistance is good, high foaming is possible, and the moldability and shape of the foamed particles A foamed molded article having good adhesion can be obtained. However, in Example 3, the expansion ratio is slightly low, and in order to obtain a higher expansion ratio and good moldability, the addition weight ratio of the polycarbodiimide compound and the monocarbodiimide compound is 5/2 to 2/5. It turns out that it is preferable.

  On the other hand, when only a polycarbodiimide compound is used like Comparative Examples 1-3, it turns out that there is no resin composition from which hydrolysis resistance and a moldability become favorable. When only the monocarbodiimide compound was used as in Comparative Example 4, the hydrolysis resistance was good, but regarding the moldability, the foamed molded product contracted and the moldability was poor.

  In Comparative Example 1, the bead-like particles were stuck together during the impregnation, and it was not possible to proceed to the foaming process and the molding process.

  From the above results, it is clear that a foamed molded article having excellent hydrolysis resistance and excellent foamability and moldability is limited to the case where the present invention is used.

  The polylactic acid-based foam molded article of the present invention is excellent in hydrolysis resistance, foamability and moldability, and can be used even in an environment where it is always in contact with moisture or used for a long period of time. It can be used for materials for agriculture, horticulture, and civil engineering. Specifically, in addition to floats, cushioning materials, heat insulating materials, fish boxes, and the like, they can be widely used as substitutes in fields where polystyrene foam is conventionally used.

Changes in melt viscosity over time of the polylactic acid resin and the polylactic acid resin composition of Example 2.

Claims (8)

A polylactic acid-based foamable resin composition obtained by impregnating a polylactic acid-based resin composition obtained by blocking a part or all of the carboxyl group terminals of polylactic acid with a polycarbodiimide compound and a monocarbodiimide compound . The total addition amount of the polycarbodiimide compound and the monocarbodiimide compound in the polylactic acid resin composition is 0.5 to 2.5 parts by weight with respect to 100 parts by weight of the polylactic acid resin, and the polycarbodiimide The polylactic acid-based foamable resin composition according to claim 1, wherein an addition weight ratio of the compound and the monocarbodiimide compound is 3/1 to 1/3 . 190 ° C. of the polylactic acid-based resin composition, load 20 kg, polylactic acid according to claim 1 or 2 melting viscosity that put the orifice diameter 2mm is not more than 2,000 Pa · s or more 5,000 Pa · s -Based foamable resin composition .   The polylactic acid-based foamable resin composition according to any one of claims 1 to 3, wherein the foaming agent is a hydrocarbon. The polylactic acid-type expandable particle which consists of a polylactic acid-type expandable resin composition of any one of Claims 1-4.   Polylactic acid-based expanded particles obtained by foaming the polylactic acid-based expandable particles according to claim 5.   The polylactic acid-based expanded particles according to claim 6, wherein the expansion ratio is 30 times or more.   A polylactic acid-based foam molded article obtained by molding the polylactic acid-based foamed particle according to claim 6.