JP5278640B2 - Polylactic acid resin foam molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based resin foam molding composition which can mold a foam molded product having a high cost advantage with the use of a polylactic acid-based resin having a small environmental load and a polylactic acid-based resin foam molded product using the same. <P>SOLUTION: The polylactic acid-based resin foam molding composition is obtained by melt kneading at least a polylactic acid-based resin and an epoxy group-containing acrylic polymer, and the value of the elongational viscosity &eta;<SB>e</SB>at a melting temperature +10&deg;C at a shear strain rate of 10-1,000 (1/sec) with respect to the zero shear viscosity &eta;<SB>0</SB>of the polylactic acid-based resin foam molding composition is &eta;<SB>e</SB>&ge;3&times;&eta;<SB>0</SB>. The polylactic acid-based resin foam molding composition is obtained by melt kneading 100 pts.wt. the above polylactic acid-based resin and 0.5-10 pts.wt. the above epoxy group-containing acrylic polymer. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention comprises a polylactic acid resin foam molding composition comprising a polylactic acid resin and an epoxy group-containing acrylic polymer, excellent in hydrolysis resistance and having rheological properties advantageous for foam molding, and obtained therefrom. The present invention relates to a polylactic acid-based foamed molded article.

  Conventionally, various plastic products using petroleum resources as raw materials have been used, but it is regarded as a problem in terms of environmental pollution and global warming accompanying the increase in the amount of waste. Against this background, biodegradable plastics, which are plastics that can be decomposed in the natural environment, are attracting attention.

  Among them, polylactic acid resin is biodegradable, and the raw material lactic acid can be mass-produced from plant-derived raw materials such as corn and sweet potato, and carbon dioxide, which causes global warming, circulates and is used As a so-called “carbon neutral” material, it is attracting attention as an alternative to general-purpose plastics.

With regard to polylactic acid-based resins, the price difference from general-purpose plastics has narrowed compared to the past due to the expansion of demand due to the growing interest in environmental issues and the establishment of industrial mass production technology.

As with general-purpose plastics, when considering the production of a molded body using a polylactic acid-based resin, reduction of the amount of material used by foam molding is a very effective method from the viewpoint of cost (see Patent Document 1). However, polylactic acid-based resins have a problem that the melt viscosity is low, foamed cells break during foam molding, and a molded article with a high expansion ratio cannot be obtained.
JP 2005-60689 A

  The object of the present invention was made to solve the above-mentioned problems from the prior art, and using a polylactic acid-based resin with a small environmental load, it is possible to mold a foam molded body with a large cost merit. The present invention provides a polylactic acid resin foam molding composition and a polylactic acid resin foam molding using the same.

The invention according to claim 1 is a polylactic acid resin foam molding composition in which a polymer terminal carboxyl group of a polylactic acid resin is blocked with an epoxy group-containing acrylic polymer , the polylactic acid resin foam molding The elongation viscosity η _e at a melting temperature of + 10 ° C. and a shear strain rate of 10 to 1000 (1 / second) is η relative to the zero shear viscosity η _{0 of the} polylactic acid resin foam molding composition. _e ≧ 3 × η _{0 characterized in} that a baking soda-citric acid-based foaming agent is added to a polylactic acid-based resin foam-molding composition, and the polylactic acid-based resin foam-molding composition is foam-molded. This is a polylactic acid-based resin foam molded article.

In the invention according to claim 2, the epoxy group-containing acrylic polymer is melt-kneaded at a ratio of 0.5 to 10 parts by weight with respect to 100 parts by weight of the polylactic acid resin, a polylactic acid resin foamed molded article according to claim 1 you wherein the sequestering polymer terminal carboxyl group with an epoxy group-containing acrylic polymer.

The invention according to claim 3 is characterized in that the epoxy group-containing acrylic polymer has an epoxy equivalent of 100 to 2000 g / eq, and the polylactic acid resin foam molding according to any one of claims 1 and 2 Is the body .

The invention according to claim 1 is a polylactic acid resin foam molding composition in which a polymer terminal carboxyl group of a polylactic acid resin is blocked with an epoxy group-containing acrylic polymer , the polylactic acid resin foam molding The elongation viscosity η _e at a melting temperature of + 10 ° C. and a shear strain rate of 10 to 1000 (1 / second) is η relative to the zero shear viscosity η _{0 of the} polylactic acid resin foam molding composition. _e ≧ 3 × η _{0 characterized in} that a baking soda-citric acid-based foaming agent is added to a polylactic acid-based resin foam-molding composition, and the polylactic acid-based resin foam-molding composition is foam-molded. This is a polylactic acid-based resin foam molded article. Good foamability in foaming of polylactic acid resin because the composition for foam molding of polylactic acid resin obtained by reacting polylactic acid resin and epoxy-containing acrylic polymer by melt-kneading has specific viscoelastic properties. Can be obtained.

In the invention according to claim 2, the epoxy group-containing acrylic polymer is melt-kneaded at a ratio of 0.5 to 10 parts by weight with respect to 100 parts by weight of the polylactic acid resin, a polylactic acid resin foamed molded article according to claim 1 you wherein the sequestering polymer terminal carboxyl group with an epoxy group-containing acrylic polymer. By reacting the epoxy group-containing acrylic polymer at a ratio of 0.5 to 10 parts by weight with 100 parts by weight of the polylactic acid resin by melt-kneading, it is possible to impart good foamability.

The invention according to claim 3 is characterized in that the epoxy group-containing acrylic polymer has an epoxy equivalent of 100 to 2000 g / eq, and the polylactic acid resin foam molding according to any one of claims 1 and 2 Is the body . When the epoxy group-containing acrylic polymer has an epoxy equivalent of 100 to 2000 g / eq, the terminal carboxyl group of polylactic acid can be blocked more effectively, and the molecular chain length of polylactic acid can be extended or branched molecular chains can be imparted. It is possible to improve foaming moldability and hydrolysis resistance by improving the extensional viscosity.

The polylactic acid resin foam molded article according to any one of claims 1 to 3 can be replaced with a polylactic acid resin foam molded article having a small environmental load in a conventionally used foam molded article.

  Hereinafter, the polylactic acid resin, the epoxy group-containing acrylic polymer, the foaming agent, the polylactic acid resin foam molding composition and the method for producing the foam molding used in the present invention will be described in detail.

The polylactic acid resin foam molding composition in the present invention is a polylactic acid resin foam molding composition obtained by reacting a polylactic acid resin and an epoxy group-containing acrylic polymer by melt-kneading. The value of the elongational viscosity η _e measured with a twin capillary rheometer at the melting temperature of the resin foam molding composition + 10 ° C. and the shear strain rate of 10 to 1000 (1 / second) is the zero shear viscosity η ₀ of the resin composition. In contrast, η _e ≧ 3 × η ₀ .

  A general polylactic acid-based resin has a low melt viscosity, and when used for foam molding, it is difficult to maintain foam cells, and it is difficult to obtain a good foam-molded product. In the present invention, it is necessary to react a polylactic acid resin and an epoxy group-containing acrylic polymer by melt kneading. Furthermore, in order to obtain good foaming suitability in foam molding, certain viscoelastic properties are required. As a result, the present invention has been found.

In the present invention, the extensional viscosity η _e is preferably measured by the following method.
Measuring device: Twin capillary rheometer “RH-7D” manufactured by Rosand
Long die: φ1mm, capillary length 16mm
Orifice die: φ1mm, capillary length 0.25mm
The twin capillary rheometer has a pair of barrels and a piston. A general capillary die (long die) is attached to one barrel, and an orifice die having a capillary length of almost zero is attached to the other barrel. Resin for measurement is put into each barrel and capillary, and the resin melted at a predetermined temperature is extruded from the capillary die at a controlled piston speed, and the pressure at that time is measured.
Since the shear strain rate is calculated from the piston speed and the shear stress can be calculated from the measurement pressure, the shear stress and the shear viscosity for each shear strain rate can be obtained by measurement with the piston speed changed.
Further, by assuming that the capillary length of the orifice die is zero and measuring the pressure loss P0 at the orifice die, the elongation viscosity and the elongation strain rate can be calculated by the following equations.

The zero shear viscosity η ₀ is the viscosity in the region where the viscosity is almost constant regardless of the shear strain rate, and the shear viscosity at a sufficiently low shear strain rate compared to the reciprocal of the longest relaxation time (relaxation rate) of the measured material. Represents.

  In order to improve foaming suitability in foam molding, it is known to impart strain hardening property in extensional deformation. Strain hardenability refers to the property that the extensional viscosity increases as the amount of strain due to extensional deformation increases. When the resin is extended and deformed by foaming, the expansion and deformation are not concentrated, and the foamed cells grow uniformly. Can do. In the case of a strain-softening resin, the stretched and deformed region due to foaming is concentrated and deformed, which easily causes foaming of foamed cells.

In the present invention, the value of the extensional viscosity η _e measured with a twin capillary rheometer at the melting temperature of the polylactic acid-based resin foam molding composition + 10 ° C. and the shear strain rate of 10 to 1000 (1 / second) is the resin composition. It is necessary to satisfy the relationship of η _e ≧ 3 × η ₀ with respect to the zero shear viscosity η _{0 of the} object. When η _e is less than 3 × η ₀ , good foaming characteristics in foam molding cannot be obtained. This is considered to be due to the fact that sufficient strain hardening is not obtained when η _e is less than 3 × η ₀ .

  Regarding the evaluation of strain hardening, Meissner type extensional viscosity measurement is common and widely used, but the strain rate to be measured is limited to the low strain rate region because of the measurement principle. In contrast, elongational viscosity measurement with a twin capillary rheometer gives information on behavior in the high strain rate region and is closer to the resin behavior in actual extrusion foaming.

  In the present invention, a polylactic acid-based resin and an epoxy group-containing acrylic polymer are melt-kneaded and reacted to give a branch point to the polylactic acid-based resin, thereby improving the elongational viscosity, and thus improving the foaming characteristics. . Further, improvement of hydrolyzability by blocking the carboxyl polymer terminal of the polylactic acid resin by melt kneading is one of the effects.

  The polylactic acid resin is a highly hydrolyzable material, and the presence of a carboxyl group at the polymer terminal of the polylactic acid resin promotes hydrolysis of the polylactic acid resin. Hydrolysis of the polylactic acid resin can be prevented by blocking the polymer terminal carboxyl group of the polylactic acid resin with an epoxy group-containing acrylic polymer that is highly reactive with the carboxyl group.

  In addition, when using a baking soda-based foaming agent, which is a general chemical foaming agent, there is a problem in that hydrolysis of the polylactic acid-based resin proceeds due to the influence of moisture generated by the foaming process, causing defective molding. This is improved by using the polylactic acid resin foam molding composition according to the invention.

  The polylactic acid resin foam molding composition of the present invention is prepared by reacting an epoxy group-containing acrylic polymer at a ratio of 0.5 to 10 parts by weight with 100 parts by weight of a polylactic acid resin by melt kneading. Good foaming suitability can be imparted.

  When the ratio of the epoxy group-containing acrylic polymer is less than 0.5 parts by weight, the reaction amount with the polylactic acid resin is small, and the improvement in elongational viscosity which is the effect of the present invention cannot be obtained. Moreover, even when added in excess of 10 parts by weight, no further improvement in elongational viscosity can be obtained due to the relationship with the amount of the polymer terminal carboxyl group of the polylactic acid resin, and further, the polylactic acid resin foam molding composition This causes problems such as a decrease in mechanical properties and a decrease in biodegradability of the foam-molded product using the above.

  The polylactic acid-based resin in the present invention is a polymer containing L-lactic acid and / or D-lactic acid as a main constituent component, but may contain a copolymer component other than lactic acid. Other copolymer components include glycol compounds such as ethylene glycol and propylene glycol, dicarboxylic acids such as oxalic acid and terephthalic acid, hydroxycarboxylic acids such as glycolic acid and hydroxybenzoic acid, and lactones such as caprolactone and propiolactone. Can be mentioned. As a method for producing a polylactic acid-based resin, a known polymerization method can be used, and examples thereof include a direct polymerization method from lactic acid and a ring-opening polymerization method via lactide.

  The epoxy group-containing acrylic polymer in the present invention is a copolymer of glycidyl acrylate and / or glycidyl methacrylate and an acrylic monomer, or glycidyl acrylate and / or methacrylic acid. The copolymer of acid glycidyl, an acrylic acid-type monomer, and the monomer containing another polymerizable double bond is shown.

Examples of the acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, ( (Meth) acrylic acid esters such as (meth) acrylic acid dodecyl, (meth) acrylic acid octadecyl, (meth) acrylic acid esters, (meth) acrylic acid polypropylene glycol, (meth) acrylic acid polyethylene glycol (meth) acrylic groups Acid esters, unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid and their salts, unsaturated dicarboxylic acids such as fumaric acid and itaconic acid, their acid anhydrides and their salts, fumaric acid Dimethyl, diethyl fumarate, di-n-butyl fumarate, diisobutyl fumarate, di-tuma fumarate Butyl, dimethyl itaconate, di-n- butyl, methyl ethyl fumarate, methyl -n- butyl fumarate, methyl ethyl itaconate, etc. dicarboxylic acid esters such as itaconic acid ethyl -t- butyl.

  Examples of the other monomer containing a polymerizable double bond include styrene derivatives such as styrene, α-methylstyrene, and chlorostyrene, unsaturated ketones such as methyl vinyl ketone and n-butyl vinyl ketone, vinyl acetate, and butyric acid. Vinyl esters such as vinyl, vinyl ethers such as methyl vinyl ether and n-butyl vinyl ether, vinyl cyanides such as acrylonitrile, methacrylonitrile, vinylidene cyanide, acrylamide and its alkyl-substituted amides, vinyl sulfonic acid, allyl sulfonic acid And vinyl compounds such as unsaturated sulfonic acids such as methallylsulfonic acid and p-styrenesulfonic acid and salts thereof, and N-maleimide such as N-phenylmaleimide and N-cyclohexylmaleimide.

  The epoxy group-containing acrylic polymer used in the present invention is required to have an epoxy equivalent of 100 to 1000 g / eq. When the epoxy equivalent is less than 100 g / eq, it becomes difficult to control the reaction that occurs during extrusion molding or melt kneading with other components. Further, when the epoxy equivalent exceeds 2000 g / eq, the characteristics of the present invention, such as the extension of the molecular chain length of the polylactic acid-based resin and the extension of the branched molecular chain, the improvement of the hydrolysis resistance, and the like are obtained. I can't.

In the present invention, it is preferable to further add a reaction catalyst of a polylactic acid resin and an epoxy group-containing acrylic polymer. The reaction catalyst referred to here is a compound that promotes the reaction between the carboxyl group-reactive end-blocking agent and the terminal carboxyl group of polylactic acid or the carboxyl group of an acidic low molecular weight compound, such as an alkali metal compound or alkaline earth. Examples thereof include metal compounds, tertiary amine compounds, imidazole compound quaternary ammonium salts, phosphate esters, phosphine compounds, and phosphonium salts.

The method of melt kneading the polylactic acid resin and the epoxy group-containing acrylic polymer is not particularly limited. For example, a method of kneading with a Banbury mixer and pelletizing with a pelletizer, or a twin-screw extrusion kneader The composition for polylactic acid-based resin foam molding of the present invention can be obtained by a method of mixing and pelletizing by, for example.

In the present invention, the polylactic acid-based resin foam molding composition includes a heat stabilizer, an acid neutralizer, a UV absorber, a light stabilizer, a colorant such as a pigment and a dye, a filler, a lubricant, as necessary. Crystal nucleating agents, flame retardants, and the like can also be added.

Among these additives, hindered phenols, sulfurs, phosphoruss, etc. as heat stabilizers, stearic acid metal salts, hydrotalcite, etc. as acid neutralizers, benzotriazoles, benzoates as ultraviolet absorbers, etc. Benzophenone, triazine, etc., and light stabilizers include hindered amines.

Examples of flame retardants include halogen flame retardants, phosphorus flame retardants, and chlorine flame retardants. Fillers include calcium carbonate, silica, titanium oxide, barium sulfate, zinc oxide, alumina, talc, mica, magnesium silicate, and titanium. Examples include potassium acid, magnesium sulfate, aluminum hydroxide, magnesium hydroxide, iron oxide, carbon black, metal powder, paper powder, and wood powder.

As lubricants, hydrocarbon lubricants, fatty acids, higher alcohols, fatty acid amides, metal soaps, esters, fluorines, etc., pigments are condensed azo, insoluble azo, quinacridone, isoindoline, anthraquinone, imidazolone, cobalt, There are pearl pigments such as phthalocyanine, carbon, titanium oxide, iron oxide, and mica, and these additives are generally used in any combination.

As the crystal nucleating agent, inorganic crystal nucleating agents such as talc, clay and zeolite, and organic carboxylic acid metal salts such as calcium stearate, magnesium stearate and calcium benzoate are generally used as polymer crystal nucleating agents. Can be used.

In the present invention, the foaming technique is not particularly limited, and any known technique can be used. Generally, it can be classified into chemical foaming that generates gas by thermal decomposition or chemical reaction, and physical foaming that heats and vaporizes a low-boiling point liquid, and an inorganic system that uses sodium bicarbonate as the chemical foaming agent. As the foaming agent, and organic foaming agents, azo series typified by azodicarbonamide and barium azodicarboxylate, nitroso series typified by N, N′-dinitrosopentamethylenetetramine, 4,4′-oxybis ( Benzylsulfonylhydrazide) and hydrazide typified by hydradicarbonamide can be used in any combination.

Among these, baking soda-citric acid foaming agent, which is a combination of sodium bicarbonate and citric acid or its salt, requires no additional equipment such as a gas supply device compared to physical foaming. -Use of a citric acid-based foaming agent is preferred because it has advantages such as easy adjustment of the amount added (foaming ratio). Examples of citric acid or salts thereof include citric acid or salts of citric acid with various metals, specifically sodium citrate, potassium citrate, calcium citrate and the like.

However, in the foam molding of a polylactic acid resin using a baking soda-citric acid foaming agent, hydrolysis of the polylactic acid resin becomes a problem. Although the sodium foam (sodium hydrogen carbonate) uses a chemical reaction between the primary foaming that becomes sodium carbonate by the reaction using water as a catalyst and the secondary foaming that is caused by the reaction of sodium hydrogen carbonate and citric acid. Hydrolysis of the polylactic acid-based resin due to water generated during this reaction becomes a problem. By reducing the molecular weight due to hydrolysis of the polylactic acid-based resin, the mechanical properties of the molded product are lowered, and by reducing the melt viscosity of the polylactic acid-based resin and consuming water necessary for primary foaming by hydrolysis, It becomes difficult to form good foam cells.
However, in the present invention, since the hydrolysis resistance is improved by blocking the carboxyl group of the polylactic acid-based resin, it is possible to use a baking soda-citric acid-based foaming agent.

In this invention, in order to shape | mold a polylactic acid-type resin foam molding, the said polylactic acid-type resin foam molding composition and a foaming agent are added, and it foams in a shaping | molding process. Although it does not specifically limit as a foaming method, A foaming molding can be obtained by normal profile extrusion molding and sheet | seat extrusion molding.
Conventionally, foamed molded products made of polyolefin, polyurethane, polystyrene, polyvinyl chloride resin, etc. have been widely used for weight reduction of heat insulating materials, buffering agents, soundproofing materials, building materials, various structural members, In these fields, substitution with a polylactic acid-based resin foam molded body having a small environmental load becomes possible.

100 parts by weight of polylactic acid (Mitsui Chemicals: Lacia H-400), 3 parts by weight of an epoxy group-containing acrylic polymer (Nippon Yushi: Blemmer CP-15 (epoxy equivalent 1000 g / eq)), 0.1 parts by weight of sodium stearate The parts were melt-kneaded by a twin screw extruder kneader manufactured by JSW and pelletized to prepare a polylactic acid resin foam molding composition. FIG. 1 shows the relationship between the elongation strain rate and the elongation viscosity of the polylactic acid resin foam molding composition of Example 1 measured with the above-mentioned Rosen twin capillary rheometer. (When the zero shear viscosity of the polylactic acid resin foam molding composition of Example 1 was measured using a rotary rheometer (TA2000, AR2000), η ₀ = 2500 Pa · s. It was confirmed that the relationship of η _e ≧ 3 × η ₀ , which is a necessary condition in the invention, was satisfied.

2 parts by weight of baking soda-citric acid foaming agent masterbatch (foaming agent content 80 wt%) is added to 100 parts by weight of this polylactic acid resin foam molding composition, and foam extrusion molding is carried out with a single screw extruder. did. As a final shape, it was molded into a rectangular shape having a width of 200 mm and a thickness of 6 mm, and a polylactic acid resin foamed molded article having a foaming ratio of 2.4 times could be obtained.

<Comparative Example 1>
To 100 parts by weight of polylactic acid (Mitsui Chemicals: Lacia H-400), 2 parts by weight of a baking soda-citric acid-based foaming agent masterbatch (foaming agent content 80 wt%) is added, and foam extrusion is performed by a single screw extruder. Carried out. FIG. 1 shows the relationship between the elongation strain rate and the elongation viscosity of polylactic acid measured with a twin capillary rheometer in the same manner as in Example 1. When measured using a rotary rheometer in the same manner as in Example 1, η ₀ = 4200 Pa · s and η _e <3 × η ₀ . Moreover, in the foam molding with the polylactic acid simple substance in the comparative example 1, the molded object was not able to be obtained by the fall of the melt viscosity accompanying hydrolysis of polylactic acid.

<Comparative example 2>
Foam extrusion molding was carried out in the same manner as in Comparative Example 1 except that azodicarbonamide (ADCA) was used as the foaming agent. Although hydrolysis of polylactic acid was not observed, a good foamed molded article could not be obtained due to foam breakage of the foamed cells.

It is a graph regarding the elongation strain rate and elongation viscosity of the polylactic acid-type resin foam molding composition in the Example and comparative example of this invention.

Claims (3)

A polylactic acid resin foam molding composition in which a polymer terminal carboxyl group of a polylactic acid resin is blocked with an epoxy group-containing acrylic polymer , the melting temperature of the polylactic acid resin foam molding composition + 10 ° C., Poly is such that the value of elongational viscosity η _{e at} a shear strain rate of 10 to 1000 (1 / second) is η _e ≧ 3 × η ₀ with respect to the zero shear viscosity η _{0 of the} polylactic acid resin foam molding composition. A polylactic acid resin foam molded article obtained by adding a baking soda-citric acid foaming agent to a lactic acid resin foam molding composition and foam-molding the polylactic acid resin foam molding composition. The epoxy group-containing acrylic polymer is melt-kneaded at a ratio of 0.5 to 10 parts by weight with respect to 100 parts by weight of the polylactic acid resin, and the polymer terminal carboxyl group of the polylactic acid resin contains an epoxy group. polylactic acid resin foamed molded article according to claim 1 you, characterized in that to seal the acrylic polymer. 3. The polylactic acid resin foam molded article according to claim 1, wherein the epoxy group-containing acrylic polymer has an epoxy equivalent of 100 to 2000 g / eq.