JP5280606B2 - Resin composition for closed cell molded body and closed cell molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for closed cell formed article, having excellent biodegradability and capable of producing a light-weight highly rigid closed cell formed article even at a high forming temperature, and provide a masterbatch pellet using the composition, a closed cell formed article, a closed cell composite formed article and a method for forming a closed cell formed article. <P>SOLUTION: The resin composition for closed cell formed article contains a polylactic acid resin and heat-expandable microcapsules. The heat-expandable microcapsule is composed of a shell containing a copolymer having a segment derived from nitrile monomer and a segment derived from a radically polymerizable unsaturated carboxylic acid monomer having a 3-8C carbon chain having radically polymerizable unsaturated bond and 0.1-10 wt.% metal cation and a core agent comprising a volatile expanding agent encapsulated in the shell. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

A resin composition for closed-cell molded bodies that has excellent biodegradability and can produce a lightweight and highly rigid closed-cell molded body even when the molding temperature is high, and the same The present invention relates to a method for producing a master batch pellet, a closed cell molded body, a closed cell composite molded body, and a closed cell molded body.

Since the resin foam can express various performances such as heat insulation, heat insulation, sound insulation, sound absorption, vibration proofing, weight reduction, etc. by changing the state of the material and formed bubbles, etc., It is used for various purposes. Examples of such resin foams include polyvinyl chloride and olefin-based thermoplastics on the surface of foamed resins such as foamed polyurethane, foamed polypropylene, foamed polyethylene, and foamed polyvinyl chloride obtained by foaming a chemical foaming agent. A resin sheet made of an elastomer or the like, a cushion material made of a composite molded body in which a fabric or the like is bonded to such a resin sheet as a skin material, and the like are used. In recent years, a foam with a skin obtained by injection-molding a thermoplastic elastomer containing a chemical foaming agent and a resin for the skin by the cavity move method is not proposed, which is a laminate of skin materials. ing.

However, these foams are difficult to recover and recycle after use, and since they are hardly decomposed in the natural environment, they have the property of remaining semi-permanently even when buried in the ground. Yes. Moreover, when such a foam was thrown away, not only the scenery was damaged, but also the living environment of marine organisms was destroyed.

In order to solve these problems, biodegradable thermoplastic polymers have been studied. For example, polylactic acid and lactic acid polymers such as copolymers of lactic acid and other aliphatic hydroxycarboxylic acids have been developed. Yes. Examples of such biodegradable polymers include those that are 100% biodegradable within a few months to one year in the body of an animal, or that start degrading in a few weeks in a moist environment such as soil or seawater. Some have various properties, such as those that decompose in one to several years, and the products after decomposition have the property of becoming harmless to the human body, such as carbon dioxide, water, and lactic acid. Among them, polylactic acid has the advantages that it has become possible to produce a large amount of L-lactic acid as a raw material at a low cost by using a fermentation method, and has the advantage that the decomposition rate in compost is fast. It is expected to be widely used as a degradable polymer. In addition, since polylactic acid is plant-derived biomass, it also conforms to the concept of “carbon neutral” that does not affect the increase or decrease of carbon dioxide, and CO ₂ emissions can be reduced by substituting petroleum-based materials. Can be reduced in total, making it an environmentally friendly material.

Examples of foam materials using biodegradable polymers such as polylactic acid include those disclosed in Patent Documents 1 to 6. However, these techniques relate to a foam and a method for producing a foam obtained by adding a volatile foaming agent, a decomposable foaming agent, or the like to a raw material resin composition and using an extrusion foaming method in which foaming is performed simultaneously with extrusion. Therefore, the bubbles formed in the molded body become open cells, and the molded body may have insufficient rigidity and light weight.
Patent Document 7 discloses an unfoamed polylactic acid-based foamable molded article having a crystallinity of 0 to 20%, which is injection-molded in a state where a volatile foaming agent is absorbed in a polylactic acid-based resin. Yes. In this technique, a foamed molded article having biodegradability can be obtained by heating and foaming a foamable resin composition in a mold. However, in such a polylactic acid-based foamable molded article, since a volatile foaming agent is used as a foaming agent, a molded article having excellent appearance, such as a defect such as silver occurring on the surface of the resulting molded article, is obtained. I couldn't. In addition, since the bubbles formed inside the molded body are not completely closed cells, there is a problem that sufficient strength cannot be obtained.

On the other hand, in recent years, attempts have been made to produce foamed molded articles using thermally expandable microcapsules instead of chemical foaming agents. For example, Patent Document 8 discloses radical crosslinkable elastomers and thermoplastic resins. There is described a thermoplastic elastomer foam obtained by foaming a crosslinked thermoplastic elastomer composition comprising:
However, the commercially available heat-expandable microcapsules used in such thermoplastic elastomer foams are foams at low temperatures, and are not heat-expandable microcapsules intended for use at high temperatures. Therefore, the size of the closed cells of the obtained foam is not constant, and it is difficult to obtain a closed cell molded body in which uniform closed cells are formed.

In addition, a volatile swelling agent was microencapsulated using a polymer obtained from a polymerization component containing 80% by weight or more of a nitrile monomer, 20% by weight or less of a non-nitrile monomer and 0.1 to 1% by weight of a crosslinking agent. As a thermally expandable microcapsule, Patent Document 9 discloses a thermally expandable microcapsule in which the non-nitrile monomer is a methacrylic acid ester or an acrylic acid ester. Such a heat-expandable microcapsule is superior in heat resistance compared to conventional heat-expandable microcapsules and is said not to foam at 140 ° C. or lower, but in practice, heating is continued at 130 to 140 ° C. for about 1 minute. Some of the microcapsules thermally expand, and with this method, it was difficult to obtain a maximum foaming temperature of 180 ° C. or higher.

Furthermore, there is a patent for a thermally expandable microcapsule comprising a shell polymer comprising a homopolymer or copolymer of an ethylenically unsaturated monomer containing 85% by weight or more of a nitrile monomer and a foaming agent containing 50% by weight or more of isooctane. It is disclosed in Document 10. According to this, it is said that a thermally expandable microcapsule having a maximum foaming temperature of preferably 190 ° C. or higher (most preferably 200 ° C. or higher) is obtained, and the maximum foaming temperature is very high.
However, such thermally expandable microcapsules having a maximum foaming temperature of 190 ° C. or higher showed high heat resistance against heating for a short time during molding. In the case of preparing a master batch by kneading at a temperature of about 0 ° C., there is a problem that some thermally expandable microcapsules expand during the kneading.
JP-A-4-304244 Japanese Patent Laid-Open No. 5-140361 JP-A-5-170965 JP-A-6-240037 JP-A-6-287347 JP-A-9-263651 JP 2000-136255 A Japanese Patent Laid-Open No. 11-343362 Japanese Patent No. 2894990 European Patent Application No. 1149628

In view of the above situation, the present invention provides a resin for closed cell molded bodies that has excellent biodegradability and can produce a lightweight and highly rigid closed cell molded body even when the molding temperature is high. It is an object of the present invention to provide a composition and a method for producing a master batch pellet, a closed cell molded body, a closed cell composite molded body, and a closed cell molded body using the composition.

The present invention is a resin composition for a closed cell molded article comprising a polylactic acid resin and a thermally expandable microcapsule, wherein the thermally expandable microcapsule has a segment derived from a nitrile monomer and a carboxyl group. And a copolymer having a segment derived from a radically polymerizable unsaturated carboxylic acid monomer having 3 to 8 carbon atoms in a carbon chain having a radically polymerizable unsaturated bond, and 0.1 to 10 metal cations. It is a resin composition for closed-cell molded bodies in which a volatile expansion agent is included as a core agent in a shell containing wt%.
The present invention is described in detail below.

As a result of intensive studies, the inventors of the present invention contain a polylactic acid resin, a copolymer derived from a nitrile monomer, and a copolymer having a segment derived from a predetermined radical polymerizable unsaturated carboxylic acid monomer and a metal cation. When a molded body is produced using a resin composition containing a thermally expandable microcapsule encapsulating a volatile swelling agent in a shell that has excellent biodegradability and a high molding temperature Even in this case, it has been found that closed cells are uniformly formed and a lightweight and highly rigid closed cell molded body can be produced, and the present invention has been completed.

The resin composition for closed-cell molded bodies of the present invention contains a polylactic acid resin.
The polylactic acid-based resin is a biodegradable thermoplastic resin. At the time of decomposition, the ester bond of polylactic acid is hydrolyzed to lactic acid, and finally, due to the action of microorganisms, carbon dioxide and water are finally used. become. Therefore, the closed-cell molded body obtained using the resin composition for closed-cell molded body of the present invention can have environmental adaptability and does not affect the increase or decrease of carbon dioxide, “carbon neutral” It will be in line with the idea. Moreover, the closed cell molded object which has high rigidity can be obtained by having the polylactic acid-type resin as a matrix for the resin composition for closed cell molded objects of this invention.

Examples of the polylactic acid-based resin include polylactic acid, a copolymer of lactic acid and hydroxycarboxylic acid, a copolymer of lactic acid, an aliphatic polyhydric alcohol, and an aliphatic polybasic acid. Examples thereof include laceia (manufactured by Mitsui Chemicals), lactone (manufactured by Kanebo Gosei Co., Ltd.), Terramac (manufactured by Unitika), ecorouge (manufactured by Mitsubishi Plastics), and the like.
The polylactic acid-based resin can be produced, for example, by polymerizing the lactic acid using lactic acid, which is biomass produced by fermentation of starch and sugar, as a raw material.

The preferable lower limit of the average molecular weight of the polylactic acid resin is 10,000, and the preferable upper limit is 500,000. If it is less than 10,000, the strength when it is formed may be lowered, and if it exceeds 500,000, the viscosity in the molten state becomes too high and the molding processability may be deteriorated.

The minimum with preferable content of the said polylactic acid-type resin in the resin composition for closed-cell molded objects of this invention is 50 weight%, and a preferable upper limit is 98 weight%. If it is less than 50% by weight, there may be a problem in terms of strength and the like of the resulting molded product. If it exceeds 98% by weight, the resulting molded product will have fewer bubbles, resulting in various performances such as weight reduction. You may not be able to demonstrate it.

The resin composition for closed-cell molded articles of the present invention contains thermally expandable microcapsules.
The heat-expandable microcapsule includes a segment derived from a nitrile monomer and a radical polymerizable unsaturated carboxylic acid monomer having a carboxyl group and a carbon chain having a radical polymerizable unsaturated bond and having 3 to 8 carbon atoms. And a shell containing a copolymer having a segment derived from.
Since a polymer obtained by polymerizing the nitrile monomer is extremely excellent in gas barrier properties, a shell made of a copolymer having a segment derived from a nitrile monomer is also excellent in gas barrier properties. Therefore, the thermally expandable microcapsule having such a shell can prevent the volatile swelling agent volatilized at the time of expansion from permeating through the shell and preventing sag at a high temperature.
Examples of the nitrile monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and any mixture thereof. Of these, acrylonitrile or methacrylonitrile is preferably used. Also preferred is a mixture of acrylonitrile and methacrylonitrile.

When the nitrile monomer is a mixture of acrylonitrile and methacrylonitrile, the preferred lower limit of the ratio of acrylonitrile to methacrylonitrile (acrylonitrile / methacrylonitrile) is 0.5, and the preferred upper limit is 2.0. When it is less than 0.5, the polymerization yield may be deteriorated, and when it exceeds 2.0, the maximum expansion ratio may be lowered. A more preferred lower limit is 0.65, and a more preferred upper limit is 1.0.

The upper limit with preferable content of the segment originating in the said nitrile-type monomer in the said copolymer is 70 weight%. If it exceeds 70% by weight, the degree of crosslinking becomes higher than necessary due to the interaction with the metal cation, and the heat resistance is improved, but the expansion ratio may be drastically lowered.

The copolymer is a radical polymerizable unsaturated carboxylic acid monomer having a carboxyl group and a carbon chain having a radical polymerizable unsaturated bond and having 3 to 8 carbon atoms (hereinafter simply referred to as radical polymerizable unsaturated carboxylic acid). A segment derived from (also referred to as a monomer).
In the radical polymerizable unsaturated carboxylic acid monomer, the lower limit of the carbon number of the carbon chain having a radical polymerizable unsaturated bond is 3, and the upper limit is 8. When it exceeds 8, a molecule | numerator will become bulky and gas barrier property will fall.

The radical polymerizable unsaturated carboxylic acid monomer has one or more free carboxyl groups per molecule for ionic crosslinking with a metal cation described later. For example, acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, silica Unsaturated monocarboxylic acids such as cinnamate; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, citraconic acid and chloromaleic acid and their anhydrides or monomethyl maleate, monoethyl maleate, monobutyl maleate, fumaric acid Examples thereof include monoesters of unsaturated dicarboxylic acids such as monomethyl, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, and derivatives thereof. These may be used alone or in combination of two or more. Among these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are preferable. Among them, methacrylic acid has a high glass transition temperature and a low bulk. This is more preferable because the gas barrier property is not impaired.

The preferable lower limit of the content of the segment derived from the radical polymerizable unsaturated carboxylic acid monomer in the copolymer is 10% by weight, and the preferable upper limit is 50% by weight. If it is less than 10% by weight, the maximum foaming temperature may be 180 ° C. or less, and if it exceeds 50% by weight, the maximum foaming temperature is increased, but the expansion ratio is unfavorable.

The copolymer may have a segment other than the segment derived from the nitrile monomer and the segment derived from the radical polymerizable unsaturated carboxylic acid monomer, if necessary. Examples of such segments include, but are not limited to, acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate, iso Examples include methacrylic acid esters such as bornyl methacrylate; segments derived from vinyl monomers such as vinyl acetate and styrene. These monomers can be appropriately selected and used depending on the properties required for the thermally expandable microcapsules, and among them, methyl methacrylate, ethyl methacrylate, methyl acrylate and the like are preferably used.
However, the content of such a segment is preferably less than 10% by weight. If it is 10% by weight or more, the gas barrier property of the shell may be lowered.

The minimum with a preferable weight average molecular weight of the said copolymer is 100,000, and a preferable upper limit is 2 million. If it is less than 100,000, the strength of the shell may be reduced, and if it exceeds 2 million, the strength of the shell becomes too high, and the expansion ratio may be reduced.

The thermally expandable microcapsule contains a metal cation in the shell.
When the shell contains a metal cation, the metal cation reacts with the carboxyl group of the copolymer constituting the shell, and the copolymer is considered to be ionically crosslinked. It is possible to obtain a thermally expandable microcapsule that does not rupture or shrink for a long time in a high temperature region. In addition, since the elastic modulus of the shell is difficult to decrease even in a high temperature region, even when molding processing such as kneading molding, calender molding, extrusion molding, injection molding, etc. to which a strong shear force is applied, the thermal expansion micro Capsule rupture and shrinkage do not occur.
In addition, the ionic crosslinking mentioned above means that a bridge | crosslinking is formed between the free carboxyl groups which exist as a side chain of the said copolymer. The number of arranged carboxyl groups per metal cation varies depending on the metal species.

The metal cation is not particularly limited as long as it is a metal cation that reacts with the carboxyl group of the copolymer to ionically crosslink the copolymer. For example, Li, Na, K, Zn, Mg, Ca, Examples include Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, and Pb. These may be used alone or in combination of two or more. Among these, ions of Ca, Zn, and Al are preferable, and Zn ions are particularly preferable.
In addition, although it does not specifically limit as a combination when using the said metal cation 2 or more types, It is preferable to use combining the ion of an alkali metal, and metal cations other than the said alkali metal. By having the alkali metal ion, a functional group such as a carboxyl group is activated, and the reaction between the metal cation other than the alkali metal and the carboxyl group of the copolymer can be promoted.
Examples of the alkali metal include Na, K, and Li.

The lower limit of the content of the metal cation in the shell is 0.1% by weight, and the upper limit is 10% by weight. If the amount is less than 0.1% by weight, the copolymer cannot be sufficiently ionically crosslinked, and the effect of improving the heat resistance cannot be obtained. Even if the amount exceeds 10% by weight, a further effect is obtained. Absent. A preferred lower limit is 0.5% by weight.
In addition, content of the said metal cation can be measured using an atomic absorption spectrophotometer (AA-680, Shimadzu Corp. make), for example.

Further, in order to appropriately ion-crosslink the carboxyl group and metal cation of the copolymer, the amount of metal cation per free carboxyl group of the copolymer is adjusted according to the desired degree of crosslinking. Although it is necessary, the preferable lower limit of the amount of the metal cation is 0.01 times mol and the preferable upper limit is 0.5 times mol with respect to the amount of carboxylic acid of the copolymer. If it is less than 0.01 times mol, the degree of cross-linking does not increase and it is difficult to obtain an effect on heat resistance. Even if it is blended in excess of 0.5 times mol, no further effect can be obtained. A more preferred lower limit is 0.05 times mol.

In the thermally expandable microcapsule, a preferable lower limit of the degree of crosslinking of the shell is 75% by weight. If it is less than 75% by weight, the maximum foaming temperature may be lowered.
The degree of cross-linking includes both covalent cross-linking by a cross-linking agent and cross-linking that is ionically cross-linked by the free carboxyl group of the copolymer and the metal cation.
In the thermally expandable microcapsule, part or all of the free carboxyl group of the copolymer is ionized to form a carboxyl anion and form an ionic bond using the metal cation as a counter cation. The degree of crosslinking can be easily adjusted by the cation content.
Moreover, the said ion bridge | crosslinking can be confirmed by the absorption by the asymmetrical expansion / contraction motion of COO- around 1500-1600 cm < ^-1 >, for example, when an infrared absorption spectrum measurement is performed.

In the thermally expandable microcapsule, a preferable lower limit of the degree of neutralization of the shell is 5%. If it is less than 5%, the maximum foaming temperature may be lowered.
In addition, the said neutralization degree represents the ratio of the carboxyl group which the said metal cation couple | bonded among the free carboxyl groups which the said copolymer has.

The shell may contain a crosslinking agent. By containing the said crosslinking agent, the intensity | strength of a shell can be strengthened and it becomes difficult to foam a cell wall at the time of thermal expansion.
The crosslinking agent is not particularly limited, and generally, a monomer having two or more radical polymerizable double bonds is preferably used. Specific examples include, for example, divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,4-butanediol di (meth) ) Acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, di (meth) acrylate of polyethylene glycol having a molecular weight of 200 to 600, glycerin di (meth) acrylate, tri Methylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate Triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol - tricyclodecane (meth) acrylate. Among these, since the thermally expanded microcapsules are difficult to contract even in a high temperature region exceeding 200 ° C., and easily maintain the expanded state, bifunctional crosslinking agents such as di (meth) acrylate of polyethylene glycol are preferred. A trifunctional cross-linking agent such as tri (meth) acrylate of trimethylolpropane is more preferable.

The minimum with preferable content of the said crosslinking agent in the said shell is 0.1 weight%, and a preferable upper limit is 3 weight%. A more preferred lower limit is 0.1% by weight, and a more preferred upper limit is 1% by weight.

The shell may further contain a stabilizer, an ultraviolet absorber, an antioxidant, an antistatic agent, a flame retardant, a silane coupling agent, a colorant, and the like as necessary.

In the thermally expandable microcapsule, a volatile swelling agent is included as a core agent in the shell.
The volatile swelling agent is a substance that becomes gaseous at a temperature below the softening point of the polymer constituting the shell, and a low-boiling organic solvent is suitable.
Examples of the volatile swelling agent include low molecular weight carbonization such as ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, and petroleum ether. Hydrogen; chlorofluorocarbons such as CCl ₃ F, CCl ₂ F ₂ , CClF ₃ , CClF ₂ —CClF ₂ ; tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane It is done. These may be used alone or in combination of two or more.

In the thermally expandable microcapsule, it is preferable to use a hydrocarbon having a boiling point of 60 ° C. or higher among the above-described volatile expanders. By using such a hydrocarbon, the thermally expandable microcapsule is not easily broken even under high temperature and high shear conditions during molding, and a thermally expandable microcapsule having excellent heat resistance can be obtained.

Examples of the hydrocarbon having a boiling point of 60 ° C. or higher include n-hexane and heptane. In addition, each hydrocarbon having a boiling point of 60 ° C. or higher may be used alone or in combination with a hydrocarbon having a boiling point of less than 60 ° C.
Moreover, it is good also as using the thermal decomposition type compound which thermally decomposes by heating and becomes a gaseous state as a volatile expansion | swelling agent.

As for the said thermally expansible microcapsule, the minimum with a preferable maximum foaming temperature is 200 degreeC. If it is less than 200 ° C., the microcapsules that have expanded during high temperature or long-time heating may rupture or shrink, and the foaming ratio may decrease.
In the present specification, the maximum foaming temperature is when the diameter of the thermally expandable microcapsule becomes maximum when the diameter is measured while heating the thermally expandable microcapsule from room temperature (maximum displacement). It means temperature.

The preferable lower limit of the average particle diameter of the thermally expandable microcapsule is 1 μm, and the preferable upper limit is 500 μm. If the thickness is less than 1 μm, the resulting molded body has too small bubbles, which may result in insufficient weight reduction of the molded body. If the thickness exceeds 500 μm, the resulting molded body will have excessively large bubbles, resulting in strength and the like. May cause problems. A more preferred lower limit is 2 μm, a more preferred upper limit is 350 μm, a still more preferred lower limit is 5 μm, and a still more preferred upper limit is 50 μm.

The minimum with preferable content of the said heat | fever expansible microcapsule in the resin composition for closed cell molded objects of this invention is 1 weight%, and a preferable upper limit is 65 weight%. If it is less than 1% by weight, the resulting molded article has fewer bubbles and cannot exhibit various performances such as weight reduction. If it exceeds 65% by weight, the resulting molded article has strength and other aspects. May be a problem.

The method for producing the thermally expandable microcapsule is not particularly limited. For example, the step of preparing an aqueous medium, a nitrile monomer, a carbon chain having a carboxyl group and having a radically polymerizable unsaturated bond has a carbon number of carbon chain. A step of dispersing an oily mixed liquid containing a radically polymerizable unsaturated carboxylic acid monomer of 3 to 8 and a volatile swelling agent in an aqueous medium, adding a compound that generates a metal cation, the carboxyl group and the metal cation, It can be produced by carrying out the step of reacting and the step of polymerizing the monomer by heating the dispersion.

When manufacturing the said thermally expansible microcapsule, the process of preparing an aqueous medium is performed first. In a specific example, for example, an aqueous dispersion medium containing a dispersion stabilizer is prepared by adding water, a dispersion stabilizer and, if necessary, an auxiliary stabilizer to a polymerization reaction vessel. Moreover, you may add alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. as needed.

Examples of the dispersion stabilizer include silica, calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, calcium carbonate, barium carbonate, and carbonate. Examples thereof include magnesium.

The addition amount of the dispersion stabilizer is not particularly limited, and is appropriately determined depending on the type of dispersion stabilizer, the particle size of the microcapsule, and the like, but the preferred lower limit is 0.1 part by weight, preferably 100 parts by weight of the monomer. The upper limit is 20 parts by weight.

Examples of the auxiliary stabilizer include a condensation product of diethanolamine and aliphatic dicarboxylic acid, a condensation product of urea and formaldehyde, polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl Examples include alcohol, dioctyl sulfosuccinate, sorbitan ester, various emulsifiers, and the like.

Further, the combination of the dispersion stabilizer and the auxiliary stabilizer is not particularly limited. For example, a combination of colloidal silica and a condensation product, a combination of colloidal silica and a water-soluble nitrogen-containing compound, magnesium hydroxide or calcium phosphate, A combination with an emulsifier may be mentioned. In these, the combination of colloidal silica and a condensation product is preferable.
Further, the condensation product is preferably a condensation product of diethanolamine and an aliphatic dicarboxylic acid, particularly a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid.

Examples of the water-soluble nitrogen-containing compound include polyvinyl pyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl (meth) acrylate represented by polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, and polydimethylamino. Examples thereof include polydialkylaminoalkyl (meth) acrylamides represented by propylacrylamide and polydimethylaminopropylmethacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Of these, polyvinylpyrrolidone is preferably used.

The amount of colloidal silica added is appropriately determined depending on the particle size of the thermally expandable microcapsule, but the preferred lower limit is 1 part by weight and the preferred upper limit is 20 parts by weight with respect to 100 parts by weight of the vinyl monomer. A more preferred lower limit is 2 parts by weight, and a more preferred upper limit is 10 parts by weight. Further, the amount of the condensation product or the water-soluble nitrogen-containing compound is also appropriately determined depending on the particle size of the thermally expandable microcapsule, but a preferable lower limit is 0.05 parts by weight and a preferable upper limit with respect to 100 parts by weight of the monomer. Is 2 parts by weight.

In addition to the dispersion stabilizer and auxiliary stabilizer, inorganic salts such as sodium chloride and sodium sulfate may be added. By adding an inorganic salt, a thermally expandable microcapsule having a more uniform particle shape can be obtained. Usually, the amount of the inorganic salt added is preferably 0 to 100 parts by weight with respect to 100 parts by weight of the monomer.

The aqueous dispersion medium containing the above dispersion stabilizer is prepared by blending a dispersion stabilizer or auxiliary stabilizer with deionized water, and the pH of the aqueous phase at this time depends on the type of dispersion stabilizer or auxiliary stabilizer used. As appropriate. For example, when silica such as colloidal silica is used as a dispersion stabilizer, polymerization is performed in an acidic medium. To make the aqueous medium acidic, an acid such as hydrochloric acid is added as necessary to adjust the pH of the system to 3 To ˜4. On the other hand, when using magnesium hydroxide or calcium phosphate, it is polymerized in an alkaline medium.

Next, in the method for producing the thermally expandable microcapsule, a radically polymerizable unsaturated carboxylic acid having a nitrile monomer, a carboxyl group, and a carbon chain having a radically polymerizable unsaturated bond and having 3 to 8 carbon atoms. A step of dispersing an oily mixture containing a monomer and a volatile swelling agent in an aqueous medium is performed. In this step, the monomer and the volatile swelling agent may be separately added to the aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium. To the aqueous dispersion medium. At this time, the oil-based mixed liquid and the aqueous dispersion medium are prepared in separate containers in advance, and the oil-based mixed liquid is dispersed in the aqueous dispersion medium by mixing with stirring in another container, and then the polymerization reaction container. It may be added.
In order to polymerize the monomer, a polymerization initiator is used. However, the polymerization initiator may be added in advance to the oily mixed solution, and the aqueous dispersion medium and the oily mixed solution are added to the polymerization reaction vessel. It may be added after stirring and mixing.

The polymerization initiator is not particularly limited, and for example, dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, azo compound and the like that are soluble in the monomer are preferably used. Specific examples include, for example, dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide; isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3, 5 , 5-trimethylhexanoyl peroxide and other diacyl peroxides; t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumylperoxyneodecanoate, (α, α-bis-neodecane Noyl peroxy) peroxye such as diisopropylbenzene Ter; bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-oxydicarbonate, diisopropyl peroxydicarbonate, di (2-ethylethylperoxy) dicarbonate, dimethoxybutyl peroxydicarbonate Peroxydicarbonates such as di (3-methyl-3-methoxybutylperoxy) dicarbonate; 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4- Examples include azo compounds such as dimethylvaleronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), and the like.

As a method of emulsifying and dispersing the oily mixed liquid in an aqueous dispersion medium with a predetermined particle size, a method of stirring with a homomixer (for example, manufactured by Tokushu Kika Kogyo Co., Ltd.) or the like, a line mixer or an element type static disperser For example, a method of passing through a static dispersion device such as the above.
The above-mentioned static dispersion device may be supplied with the aqueous dispersion medium and the polymerizable mixture separately, or may be supplied with a dispersion that has been mixed and stirred in advance.

Next, in the method for producing the thermally expandable microcapsule, a step of adding a compound that generates the metal cation (hereinafter also referred to as a metal cation supplier) and reacting the carboxyl group with the metal cation is performed. By carrying out this step, the metal cation reacts with the carboxyl group and ion-crosslinks, so that heat resistance is improved and a thermally expandable microcapsule that does not rupture or shrink for a long time in a high temperature region is produced. Is possible. In addition, since the elastic modulus of the shell is improved, even when molding such as kneading molding, calender molding, extrusion molding, injection molding or the like in which a strong shear force is applied, rupture of the thermally expandable microcapsule, There is no contraction.

The metal cation supplier may be added to the dispersion before the monomer is polymerized, or may be added after the monomer is polymerized. Further, the metal cation supplier may be added directly or in the form of a solution such as an aqueous solution.

The metal cation supplier is not particularly limited. For example, the metal cation oxide, hydroxide, phosphate, carbonate, nitrate, sulfate, chloride, nitrite, sulfite, and octylic acid described above. And salts of organic acids such as stearic acid. Of these, hydroxides, chlorides and carboxylates are preferred. Specifically, Zn (OH) ₂ , ZnO, Mg (OH) _{2 and the} like are preferable, and Zn (OH) ₂ is more preferable because there is little decrease in elastic modulus in a high temperature region.

When the metal cation supplier is added, it is preferable to add an alkali metal hydroxide in advance and then add a metal cation supplier other than the alkali metal hydroxide. By adding the alkali metal hydroxide in advance, a functional group such as a carboxyl group is activated, and the reaction with the metal cation can be promoted.
In addition, Zn (OH) ₂ has low water solubility, and it may not be possible to obtain a desired ionic crosslink by addition. However, by using such a method, for example, after adding NaOH, ZnCl in the aqueous solution is high. By adding ₂ , the same effect as the case of adding Zn (OH) ₂ can be obtained.

The alkali metal hydroxide is not particularly limited, but is preferably a hydroxide of Na, K, or Li, and more preferably a strongly basic Na or K hydroxide.

The said thermally expansible microcapsule can be manufactured by performing the process which superposes | polymerizes a monomer by heating the dispersion liquid obtained through the process mentioned above. The thermally expandable microcapsules produced by such a method have a high maximum foaming temperature, excellent heat resistance, and do not rupture or shrink even in a high temperature region or during molding.

In addition to the polylactic acid resin and the thermally expandable microcapsule, the resin composition for closed-cell molded bodies of the present invention contains various additives for the purpose of improving lightness, heat insulation, impact resistance, rigidity, and the like. It may be added. Examples of the additive include a nucleating agent, a plasticizer, an antioxidant, an ultraviolet absorber, a heat stabilizer, a flame retardant, an internal mold release agent, an inorganic additive, an antistatic agent, a surface wetting improver, a pigment, and a dispersion. Agents, lubricants and the like.

The method for producing the resin composition for closed-cell molded bodies of the present invention is not particularly limited. For example, the resin composition for closed-cell molded bodies is obtained by melt-kneading a thermally expandable microcapsule and a polylactic acid resin in a molding machine. After kneading raw materials such as polylactic acid resin excluding foaming agents such as thermally expandable microcapsules in advance, thermally expandable microcapsules, and optionally adding chemical foaming agents, etc. You may manufacture the resin composition for molded objects.
The kneading temperature is preferably a temperature lower than the foaming temperature of the thermally expandable microcapsule and higher than the melting point of the polylactic acid resin.

The resin composition for closed-cell molded bodies of the present invention can be used as a master batch pellet for manufacturing closed-cell molded bodies. Such a master batch pellet is also one aspect of the present invention.
Although it does not specifically limit as a method to manufacture the masterbatch pellet of this invention, For example, raw materials, such as a polylactic acid-type resin and various additives, are knead | mixed previously using a same-direction twin screw extruder etc. Next, after heating to a predetermined temperature and adding a foaming agent such as a thermal expansion microcapsule, the kneaded product obtained by further kneading is cut into a desired size with a pelletizer to form a master batch. The method etc. which are made into a pellet are mentioned. Alternatively, pellet-shaped master batch pellets may be produced by kneading raw materials such as polylactic acid-based resins and thermally expandable microcapsules with a batch kneader and then granulating with a granulator.
The kneader is not particularly limited as long as it can knead without destroying the thermally expandable microcapsules, and examples thereof include a pressure kneader and a Banbury mixer.

The closed cell molding is performed by molding the resin composition or master batch pellet for the closed cell molded body of the present invention using a molding method such as injection molding and foaming the thermally expandable microcapsule by heating during molding. The body can be manufactured. Such a closed-cell molded body is also one of the present invention, and a method for producing such a closed-cell molded body is also one of the present invention.
In the method for producing a closed-cell molded body of the present invention, the closed-cell crushing is achieved by using the resin composition or master batch pellet of the present invention that has high heat resistance and reaches the maximum expansion ratio at a high temperature. It is possible to obtain a molded body without any. Moreover, the closed cell molded body of the present invention obtained by such a method has closed cells uniformly formed, and has excellent lightness, heat insulation, impact resistance, rigidity, etc. It can use suitably for uses, such as a member for a use and a shoe sole.

Examples of the molding method used for producing the closed cell molded body of the present invention include blow molding, calender molding, extrusion molding and the like in addition to the above injection molding. Among these molding methods, injection molding is preferred because the effect of the present invention that uniform closed cells can be formed without collapsing bubbles even when the molding temperature is high. In addition, extrusion molding is preferable because molding at high temperatures is possible while preventing breakage of particles due to shear, regardless of whether it is uniaxial or biaxial.

In the method for producing a closed-cell molded body of the present invention, the preferable lower limit of the temperature during molding is 150 ° C., and the preferable upper limit is 240 ° C. If it is less than 150 ° C., foaming may be insufficient. If it exceeds 240 ° C., the molding temperature may be too high, and closed cells may not be formed uniformly. A more preferred lower limit is 190 ° C., and a more preferred upper limit is 220 ° C.

The closed cell molded body of the present invention can be formed into a composite molded body by laminating a skin material on the surface, and can be processed into a secondary product and a tertiary product. Such a closed cell composite molded body using the closed cell molded body of the present invention is also one aspect of the present invention.
Examples of the skin material include leather, resin film, woven fabric, and non-woven fabric. In addition, as the above-mentioned skin material, it may be a composite molded body having a design such as a grain or a grain pattern on the surface, using genuine leather, a silicone stamper with irregularities transferred from stone, wood, etc. Further, a hard foam layer serving as an aggregate may be formed on the surface to form a composite structure having a three-layer structure.
Further, by using a metal as the skin material and injection molding the resin composition for closed cell molded body of the present invention on the metal, a metal integral mold metal / resin hybrid molded body can be obtained.

The present invention has an excellent biodegradability, and even when the molding temperature is high, a resin composition for closed cell molded bodies that can produce a lightweight and highly rigid closed cell molded body, and This is a method for producing a master batch pellet, closed cell molded body, closed cell composite molded body, and closed cell molded body using the same.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Examples 1 and 2)
(Production of thermally expandable microcapsules)
8 L of water, 10 parts by weight of colloidal silica (manufactured by Asahi Denka Co., Ltd.) and 0.3 part by weight of polyvinylpyrrolidone (manufactured by BASF) were charged as a dispersion stabilizer in a polymerization reaction vessel to prepare an aqueous dispersion medium. Next, an oily mixed liquid composed of a monomer, a cross-linking agent, a volatile swelling agent and a polymerization initiator shown in Table 1 was added to the water-soluble dispersion medium, and a metal cation supplier having a compounding quantity shown in Table 1 was added. Was added to prepare a dispersion. The resulting dispersion is stirred and mixed with a homogenizer, charged into a pressure polymerizer (20 L) purged with nitrogen, pressurized (0.2 MPa), and reacted at 60 ° C. for 20 hours to prepare a reaction product. did. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules.

(Preparation of master batch pellet)
Thermally expandable microcapsules obtained by kneading 100 parts by weight of low-density polyethylene in powder form and pellets and 0.2 part by weight of ethylenebisstearic acid amide as a lubricant with a Banbury mixer and reaching about 140 ° C. 50 parts by weight was added, and the mixture was further kneaded for 30 seconds and extruded to be pelletized at the same time to obtain master batch pellets.

(Production of molded body)
Obtained from a hopper of a screw-type injection molding machine equipped with an accumulator by mixing 5 parts by weight of the obtained master batch pellets and 100 parts by weight of a polylactic acid resin (LACEA M-151S Q04 manufactured by Mitsui Chemicals). The obtained mixed pellets were supplied, melted and kneaded, and injection molded to obtain a plate-shaped molded body. The molding conditions were a cylinder temperature: 200 ° C. and an injection speed: 60 mm / sec.

(Comparative Example 1)
A molded body was produced in the same manner as in Example 1 except that no thermally expandable microcapsule was added.

(Comparative Examples 2 and 3)
A molded body was produced in the same manner as in Example 1 except that the thermally expandable microcapsules obtained by adding the monomers and metal cations having the blending amounts shown in Table 1 were used.

(Comparative Examples 4 and 5)
A molded body was produced in the same manner as in Example 1 except that an inorganic chemical foaming agent (Polyslen, manufactured by Eiwa Kasei Kogyo Co., Ltd.) having the blending amount shown in Table 2 was added instead of the master batch pellet.

(Evaluation)
About the heat-expandable microcapsules, master batch pellets and molded bodies obtained in Examples 1 and 2 and Comparative Examples 1 to 5, performance (volume average particle diameter, degree of crosslinking, metal cation concentration, foaming start temperature, maximum foaming temperature) , Maximum displacement amount). The results are shown in Table 1.

(1) Evaluation of thermally expandable microcapsules (1-1) Volume average particle size The volume average particle size was measured using a particle size distribution size meter (LA-910, manufactured by HORIBA).

(1-2) Foam start temperature, maximum foam temperature, maximum displacement thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), foam start temperature (Ts), maximum displacement (Dmax) and maximum foam temperature (Tmax) was measured. Specifically, 25 μg of a sample is put into an aluminum container having a diameter of 7 mm and a depth of 1 mm, and heated from 80 ° C. to 220 ° C. at a temperature rising rate of 5 ° C./min with a force of 0.1 N applied from above. Then, the displacement in the vertical direction of the measurement terminal was measured, and the temperature at which the displacement began to rise was defined as the foaming start temperature, the maximum value of the displacement as the maximum displacement, and the temperature at the maximum displacement as the maximum foaming temperature.

(1-3) Metal analysis 10 g of the thermally expandable microcapsule obtained was added to 20 ml of 1N hydrochloric acid, and the mixture was stirred for 2 hours, followed by filtration with filter paper. The filtrate was diluted to enter the detection range and analyzed with an atomic absorption spectrophotometer (AA-680, manufactured by Shimadzu Corporation). The amount of metal component contained in the thermally expandable microcapsule (concentration of metal cation in the particle) was calculated from the analysis result.

(2) Evaluation of Master Batch Pellet and Molded Body (2-1) Foaming State at Master Batch The foaming state at the time when the master batch pellet was produced was visually evaluated.

(2-2) Measurement of specific gravity The specific gravity of the obtained molded product was measured by a method based on JIS K-7112 A method (submersion method in water).

(2-3) Izod impact value The Izod impact value of the obtained molded product was measured by a method based on JIS K-7110.

(2-4) Cross-sectional bubble state of molded body The state of bubbles in the cross-section of the molded body was observed with a SEM apparatus at a magnification of 50 times to evaluate the state of bubbles.

As shown in Table 2, the molded bodies obtained in Examples 1 and 2 had a low specific gravity but high strength. In addition, closed cells were uniformly formed.
On the other hand, since the molded product obtained in Comparative Example 1 did not contain a foaming agent, the strength was high but the specific gravity was extremely large. In addition, the molded body obtained in Comparative Example 2 has a large specific gravity, and the molded body obtained in Comparative Example 3 is slightly foamed when formed into a masterbatch, and has a large specific gravity even when used as a molded body. It was a thing.
Furthermore, the molded body obtained in Comparative Example 4 had a large specific gravity, and open cells were observed in a part of the molded product, and the Izod impact value was also low. In the molded product obtained in Comparative Example 5, the specific gravity decreased by increasing the addition amount of the inorganic chemical foaming agent, but the Izod impact value became extremely low. Therefore, it was found that when the inorganic chemical foaming agent was used, the closed cell was not formed, so that the strength of the molded product was greatly reduced.

According to the present invention, a resin composition for closed-cell molded bodies that has excellent biodegradability and can produce a lightweight and highly rigid closed-cell molded body even when the molding temperature is high, And the manufacturing method of a masterbatch pellet using this, a closed-cell molded object, a closed-cell composite molded object, and a closed-cell molded object can be provided.

Claims (10)

A resin composition for a closed-cell molded article containing a polylactic acid-based resin and a thermally expandable microcapsule,
The thermally expandable microcapsule is a radical polymerizable unsaturated carboxylic acid monomer having a segment derived from a nitrile monomer, a carboxyl group, and a carbon chain having a radical polymerizable unsaturated bond and having 3 to 8 carbon atoms. A volatile swelling agent is included as a core agent in a copolymer containing 0.1 to 10% by weight of a copolymer having a segment derived from the above and a metal cation, and the nitrile monomer includes acrylonitrile and methacrylate. a mixture of Ronitoriru and methacrylonitrile ratio of acrylonitrile relative to the nitrile (acrylonitrile / methacrylonitrile) is Ri der 0.5-1.0,
A resin composition for closed-cell molded articles, comprising 1 to 65% by weight of the thermally expandable microcapsules . The resin composition for closed-cell molded bodies according to claim 1, wherein the volatile swelling agent is a hydrocarbon having a boiling point of 60 ° C or higher. The thermally expandable microcapsule has a maximum foaming temperature of 200 ° C or higher, and the resin composition for closed-cell molded bodies according to claim 1 or 2. The resin composition for a closed-cell molded body according to claim 1, 2, or 3, wherein the metal cation is a zinc cation. The copolymer constituting the shell of the thermally expandable microcapsule further has a segment other than a segment derived from a nitrile monomer and a segment derived from a radical polymerizable unsaturated carboxylic acid monomer. The resin composition for closed-cell molded articles according to 2, 3, or 4 . A masterbatch pellet comprising the resin composition for closed-cell molded bodies according to claim 1, 2, 3, 4 or 5 . A method for producing a closed-cell molded body, comprising using the resin composition for closed-cell molded bodies according to claim 1, 2, 3, 4, or 5 , or the master batch pellet according to claim 6 . A closed cell molded body produced by the closed cell molded body manufacturing method according to claim 7 . A closed-cell composite molded body comprising the closed-cell molded body according to claim 8 and a skin material laminated on a surface of the closed-cell molded body. The closed cell composite molded article according to claim 9 , wherein the skin material is a metal.