JP2010222407A - Thermally expandable microcapsule and foam molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide thermally expandable microcapsules which have excellent thermal resistance and can achieve a high expansion ratio, and can therefore be suitably used in kneading molding added with strong shear force, calendering, extrusion molding, injection molding and the like; and to provide a foam molded product using the thermally expandable microcapsules. <P>SOLUTION: The thermally expandable microcapsules includes a shell composed of a polymer which contains a volatile inflating agent, as a core agent. The shell is composed of a polymer obtained by polymerizing a monomer composition containing: 30-40 wt.% polymerizable monomer (I) composed of acrylonitrile and methacrylonitrile; 30-50 wt.% 3-8C radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group; ≥0.1 wt.% polymerizable monomer (III) having two or more double bonds in the molecule; and a polymerizable monomer (IV) having a solubility parameter of the homopolymer of not greater than 10. The content of the acrylonitrile in the polymerizable monomer (I) is 10-60 wt.%, and the monomer composition contains 0.1-10 pts.wt., based on 100 pts.wt. of all the monomer components, metal cation salt capable of forming an ionic bond to the 3-8C radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

Since the present invention has excellent heat resistance and can realize a high expansion ratio, it can be suitably used for kneading molding, calendar molding, extrusion molding, injection molding, etc. to which a strong shearing force is applied. About. The present invention also relates to a foamed molded article using the thermally expandable microcapsule.

Thermally expandable microcapsules are used in a wide range of applications as a design-imparting agent and a lightening agent, and are also used in paints for the purpose of weight reduction such as foamed ink and wallpaper.
As such a heat-expandable microcapsule, one in which a volatile expansion agent that becomes gaseous at a temperature below the softening point of the shell polymer is included in a thermoplastic shell polymer is widely known. In Patent Document 1, an oily mixed liquid obtained by mixing a volatile expansion agent such as a low-boiling point aliphatic hydrocarbon with a monomer is added to an aqueous dispersion medium containing a dispersant together with an oil-soluble polymerization catalyst while stirring. A method for producing thermally expandable microcapsules encapsulating a volatile swelling agent by performing suspension polymerization is disclosed.

However, although the thermally expandable microcapsule obtained by this method can be thermally expanded at a relatively low temperature of about 80 to 130 ° C., the expanded microcapsule is ruptured or contracted when heated at a high temperature or for a long time. In other words, since the expansion ratio is reduced, there is a drawback that it is not possible to obtain thermally expandable microcapsules having excellent heat resistance.

On the other hand, in Patent Document 2, a polymer obtained from a polymerization component containing 80 to 97% by weight of a nitrile monomer, 20 to 3% by weight of a non-nitrile monomer and 0.1 to 1% by weight of a trifunctional crosslinking agent is shelled. And a method for producing a thermally expandable microcapsule encapsulating a volatile expansion agent is disclosed.
Patent Document 3 uses 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, and uses a volatile swelling agent. In the thermally expandable microcapsules encapsulating, a thermally expandable microcapsule in which the non-nitrile monomer is a methacrylic acid ester or an acrylic acid ester is disclosed.

Thermally expandable microcapsules obtained by these methods are superior in heat resistance compared to conventional microcapsules and are said not to foam at 140 ° C. or lower, but actually continue heating at 130 to 140 ° C. for about 1 minute. Some of the microcapsules are thermally expanded, and it has been difficult to obtain thermally expandable microcapsules having excellent heat resistance with a maximum foaming temperature of 180 ° C. or higher.

Furthermore, Patent Document 4 discloses an ethylenically unsaturated monomer having 85% by weight or more of a nitrile group for the purpose of obtaining a thermally expandable microcapsule having a maximum foaming temperature of 180 ° C. or higher, preferably 190 ° C. or higher. There is disclosed a thermally expandable microcapsule comprising a foaming agent having a shell polymer comprising a homopolymer or a copolymer and 50% by weight or more of isooctane.
In such a heat-expandable microcapsule, although the maximum foaming temperature is a very high value, the subsequent expanded state cannot be maintained, and it has been difficult to use for a long time in a high temperature region.

Furthermore, Patent Document 5 defines a monomer that constitutes the shell of the heat-expandable microcapsule, so that it has a good foaming performance in a wide range of foaming temperature, particularly high temperature (160 ° C. or higher), and has heat resistance. A heat-expandable microcapsule with improved s is disclosed. However, this thermally expandable microcapsule has a high maximum foaming temperature, but when used in molding processes such as kneading molding, calendar molding, extrusion molding, injection molding, etc., in which strong shearing force is applied, especially injection molding, In the melt-kneading process, a so-called “sag” phenomenon may occur or may be crushed due to heat resistance and strength problems of the thermally expandable microcapsules.

Patent Document 6 discloses a thermally expandable microcapsule using as a shell a polymer obtained by polymerizing a monomer containing a carboxyl group and a monomer having a group that reacts with the carboxyl group. In such a heat-expandable microcapsule, the three-dimensional cross-linking density is increased, so that even when the shell after foaming is very thin, it exhibits a strong resistance to shrinkage, and the heat resistance is drastically improved.
However, even when such a method is used, there are still problems in heat resistance and strength, and there is a limit to the expansion ratio after molding such as injection molding.
Therefore, even when used for kneading molding, calender molding, extrusion molding, injection molding, etc., which has excellent heat resistance and expansion ratio and a strong shear force is applied, it is difficult to cause sag etc. There was a need for thermally expandable microcapsules that could be made.

Japanese Examined Patent Publication No. 42-26524 Japanese Patent Publication No. 5-15499 Japanese Patent No. 2894990 European Patent Application No. 1149628 International Publication WO2003 / 099955 International Publication No. WO 1999/43758

Since the present invention has excellent heat resistance and can realize a high expansion ratio, it can be suitably used for kneading molding, calendar molding, extrusion molding, injection molding, etc. to which a strong shearing force is applied. The purpose is to provide. Another object of the present invention is to provide a foamed molded article using the thermally expandable microcapsule.

The present invention relates to a thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a shell made of a polymer, and the shell is a polymerizable monomer (I) 30 to 40 consisting of acrylonitrile and methacrylonitrile. % By weight, 3 to 8 carbon-containing radically polymerizable unsaturated carboxylic acid monomer (II) having a carboxyl group, 30 to 50% by weight, polymerizable monomer (III) 0.1 having two or more double bonds in the molecule Containing acrylonitrile in the polymerizable monomer (I), comprising a polymer obtained by polymerizing a monomer composition containing a polymerizable monomer (IV) having a solubility parameter of 10% or less by weight and not less than 10% by weight. The amount of the monomer composition is 10 to 60% by weight, and the monomer composition further comprises a radically polymerizable radical having 3 to 8 carbon atoms having a carboxyl group. The ionic-bondable metal cation salt with respect to 100 parts by weight of the total monomer components to the saturated carboxylic acid monomer (II), a thermally expandable microcapsules containing 0.1-10 parts by weight.
The present invention is described in detail below.

The lower limit of the content of the polymerizable monomer (I) composed of acrylonitrile and methacrylonitrile in the monomer composition is 30% by weight, and the upper limit is 40% by weight. When the content of the polymerizable monomer (I) composed of acrylonitrile and methacrylonitrile in the monomer composition is less than 30% by weight, the gas barrier property of the shell is lowered, so that the expansion ratio is lowered. When the content of the polymerizable monomer (I) in the monomer composition exceeds 40% by weight, the resulting thermally expandable microcapsule is thermally expanded in the presence of an inert gas such as carbon dioxide. Property becomes too high, and the expansion ratio decreases. Considering the use in the presence of an inert gas such as carbon dioxide, the preferable lower limit of the content of the polymerizable monomer (I) is 32% by weight, and the preferable upper limit is 38% by weight.

In the polymerizable monomer (I) composed of acrylonitrile and methacrylonitrile in the monomer composition, the lower limit of the content of acrylonitrile in the polymerizable monomer (I) is 10% by weight, and the upper limit is 60% by weight. A polymerization rate falls that content of the said acrylonitrile is less than 10 weight%. When the content of acrylonitrile exceeds 60% by weight, acrylonitrile is highly polar. Therefore, the radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms having a carboxyl group and a metal cation salt are used. In the case of ionic crosslinking, it becomes difficult to desorb water from the particles in the dehydration step, which is a subsequent step, and dehydration cannot be performed. The minimum with preferable content of the said acrylonitrile is 20 weight%, and a preferable upper limit is 40 weight%.

Examples of the radical polymerizable unsaturated carboxylic acid monomer (II) having the carboxyl group and having 3 to 8 carbon atoms in the monomer composition include, for example, one free carboxyl group per molecule for ionic crosslinking. More specifically, for example, unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, cinnamic acid, maleic acid, itaconic acid, fumaric acid, citraconic acid, Unsaturated dicarboxylic acid such as chloromaleic acid or its anhydride or unsaturated dicarboxylic acid such as monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate Acid monoesters and their derivatives, these are May be used in Germany, it may be used in combination of two or more thereof. Of these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are particularly preferable.

The preferable lower limit of the content of the radical polymerizable unsaturated carboxylic acid monomer (II) having the carboxyl group and having 3 to 8 carbon atoms in the monomer composition is 15% by weight, and the preferable upper limit is 40% by weight. . When the content of the radical polymerizable unsaturated carboxylic acid monomer (II) is less than 15% by weight, the maximum foaming temperature may be 180 ° C. or less, and the radical polymerizable unsaturated carboxylic acid monomer (II) When the content exceeds 40% by weight, the maximum foaming temperature is improved, but the foaming ratio is lowered. The minimum with more preferable content of the said radical polymerizable unsaturated carboxylic acid monomer (II) is 20 weight%, and a more preferable upper limit is 35 weight%.

The monomer composition contains a polymerizable monomer (III) having two or more double bonds in the molecule. The polymerizable monomer (III) has a role as a crosslinking agent. By containing the said polymerizable monomer (III), the intensity | strength of a shell can be strengthened and it becomes difficult to break a cell wall at the time of thermal expansion. In the present invention, although the content of the polymerizable monomer (I) is as low as 30 to 40% by weight, polymerization having two or more double bonds in the molecule is possible even in such a low concentration. Addition of the functional monomer (III) can suppress a decrease in gas barrier properties.

Examples of the polymerizable monomer (III) include monomers having two or more radically polymerizable double bonds. Specific examples include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, Ethylene 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 weight average molecular weight of 200 to 600, glycerin di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene Xide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol-tricyclode Examples include candi (meth) acrylate. Among these, a bifunctional compound such as polyethylene glycol is a phenomenon called so-called “sag” because microcapsules that are thermally expanded are difficult to contract even in a high-temperature region exceeding 200 ° C. and are easily maintained in an expanded state. Is preferably used. Among these, acrylates such as di (meth) acrylate of polyethylene glycol having a weight average molecular weight of 200 to 600 are particularly preferable.

The lower limit of the content of the polymerizable monomer (III) in the monomer composition is 0.1% by weight, and the preferable upper limit is 3% by weight. When the content of the polymerizable monomer (III) is less than 0.1% by weight, the effect as a crosslinking agent is not exhibited, and when the polymerizable monomer (III) exceeds 3% by weight, foaming is caused. The magnification is reduced. The minimum with preferable content of the said polymerizable monomer (III) is 0.1 weight%, and a more preferable upper limit is 1 weight%.

The monomer composition contains a polymerizable monomer (IV) having a homopolymer solubility parameter of 10 or less. Since the polymerizable monomer (IV) having a homopolymer solubility parameter of 10 or less has high polarity, the radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms and a metal cation salt having a carboxyl group in particular. In the dehydration step, which is a subsequent step, it is difficult to desorb water from the particles, and it is possible to prevent a problem that dehydration cannot be performed.

Examples of the polymerizable monomer (IV) include methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isobornyl methacrylate, vinyl monomers such as vinyl chloride, vinylidene chloride, vinyl acetate, and styrene. Is mentioned. Of these, methyl methacrylate, ethyl methacrylate, vinyl acetate and the like are preferably used.
The minimum with preferable content of the said polymerizable monomer (IV) is 10 weight%, and a preferable upper limit is 30 weight%. If the content of the polymerizable monomer (IV) is less than 10% by weight, it may not be dehydrated as described above. If it exceeds 30% by weight, the gas barrier property of the cell wall is lowered and the thermal expansibility is likely to deteriorate, which is not preferable.

The monomer composition further contains a metal cation salt that is ionically bonded to a radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms having a carboxyl group.
By containing the metal cation salt, ionic cross-linking occurs with the carboxyl group of the radical polymerizable unsaturated carboxylic acid monomer (II), so that cross-linking efficiency can be increased and heat resistance can be increased. Become. As a result, it is possible to obtain a thermally expandable microcapsule that does not burst 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.

The metal cation of the metal cation salt is not particularly limited as long as it is a metal cation that reacts with the radical polymerizable unsaturated carboxylic acid monomer (II) to be ionically crosslinked, and examples thereof include Na, K, Li, Zn, Examples include ions such as Mg, Ca, Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, and Pb. These are preferably added as hydroxides. Among these, ions of Ca, Zn, and Al, which are divalent to trivalent metal cations, are preferable, and Zn ions are particularly preferable. These metal cation salts may be used independently and may use 2 or more types together.

In addition, although it does not specifically limit as a combination in the case of using 2 or more types of the said metal cation salt, It uses combining the ion of alkali metal or alkaline-earth metal, and metal cations other than the said alkali metal or alkaline-earth metal. Is preferred. By having ions of the alkali metal or alkaline earth metal, a functional group such as a carboxyl group is activated, and the reaction between the metal cation other than the alkali metal or alkaline earth metal and the carboxyl group or the like is promoted. Can do. Examples of the alkali metal or alkaline earth metal include Na, K, Li, Ca, Ba, and Sr. Among them, it is preferable to use strong basic Na, K, and the like.

The preferable lower limit of the addition amount of the metal cation salt is 0.1 parts by weight and the preferable upper limit is 10 parts by weight with respect to 100 parts by weight of the total monomer components. If the content of the metal cation salt is less than 0.1 parts by weight, heat resistance may not be effective, and if the content of the metal cation salt exceeds 10 parts by weight, the expansion ratio is extremely poor. May be. The minimum with more preferable content of the said metal cation salt is 0.5 weight part, and a more preferable upper limit is 5 weight part.

In the monomer composition, a polymerization initiator is contained in order to polymerize the monomer.
As the polymerization initiator, for example, dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, azo compound and the like 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, diacyl peroxide, 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 Steal, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-oxydicarbonate, diisopropylperoxydicarbonate, di (2-ethylethylperoxy) dicarbonate, dimethoxybutylperoxydicarbonate Peroxydicarbonates such as di (3-methyl-3-methoxybutylperoxy) dicarbonate, 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4- And azo compounds such as dimethylvaleronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), and the like.

The preferable lower limit of the weight average molecular weight of the polymer constituting the shell is 100,000, and the preferable upper limit is 2 million. When the weight average molecular weight is less than 100,000, the strength of the shell may be reduced. When the weight average molecular weight exceeds 2 million, the strength of the shell becomes too high, and the expansion ratio may be reduced.

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 of the present invention, a volatile expansion 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. Examples include hydrogen, chlorofluorocarbons such as CCl ₃ F, CCl ₂ F ₂ , CClF ₃ , and CClF ₂ -CClF ₂ , tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane. It is done. Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, and mixtures thereof are preferred. These volatile swelling agents may be used alone or in combination of two or more.

In the thermally expandable microcapsule of the present invention, it is preferable to use a low-boiling hydrocarbon having 5 or less carbon atoms among the above-described volatile expansion agents. By using such a hydrocarbon, it is possible to obtain a thermally expandable microcapsule having a high expansion ratio and promptly starting foaming.
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.

In the thermally expandable microcapsule of the present invention, the preferred lower limit of the content of the volatile swelling agent used as the core agent is 10% by weight, and the preferred upper limit is 25% by weight.
The thickness of the shell varies depending on the content of the core agent, but if the core agent content is reduced and the shell becomes too thick, the foaming performance is reduced, and if the core agent content is increased, the shell strength is reduced. To do. When the content of the core agent is 10 to 25% by weight, it becomes possible to achieve both prevention of sag of the thermally expandable microcapsule and improvement of foaming performance.

The preferable lower limit of the volume average particle diameter of the thermally expandable microcapsule of the present invention is 10 μm, and the preferable upper limit is 50 μm. If the thickness is less than 5 μm, the resulting molded body has too small bubbles, which may result in insufficient weight reduction of the molded body. If the thickness exceeds 50 μm, the resulting molded body has excessively large bubbles, resulting in strength and the like. May cause problems. A more preferred lower limit is 15 μm, and a more preferred upper limit is 40 μm.

In the thermally expandable microcapsule of the present invention, a preferable lower limit of the maximum foaming temperature (Tmax) is 200 ° C. When the temperature is lower than 200 ° C., the heat resistance becomes low, and thus the thermally expandable microcapsule may rupture and shrink in a high temperature region or during molding. Moreover, when using as a masterbatch pellet etc., it foams by shearing at the time of pellet manufacture, and an unfoamed masterbatch pellet cannot be manufactured stably. A more preferred lower limit is 210 ° C. In the present specification, the maximum foaming temperature means the temperature at which the thermally expandable microcapsule reaches the maximum displacement when the diameter is measured while heating the thermally expandable microcapsule from room temperature.

Moreover, the preferable upper limit of foaming start temperature (Ts) is 180 degreeC. Above 180 ° C, especially in the case of injection molding, in core back foam molding, where the mold is fully filled with resin material and then opened to the point where you want to foam the mold, the resin temperature cools down during the core back foaming process and the expansion ratio May not go up. A more preferred lower limit is 130 ° C and a preferred upper limit is 160 ° C.

The heat-expandable microcapsule of the present invention has a maximum particle diameter of 15 to 40 μm before foaming and a shell thickness of 1 to 8 μm when heated continuously at 200 ° C. at atmospheric pressure. It is preferable that the expansion time is 5 times or more and the holding time in a state where the expansion ratio is 5 times or more is 10 minutes or more. By satisfying such conditions, the foaming property at the time of heating is excellent, and the particle diameter is maintained even after foaming, so that a high foaming ratio can be realized.
If the maximum foaming ratio is less than 5 times, foaming performance is inferior. For example, there are cases where the foaming ratio of the obtained molded product does not reach a desired value of 2 times or more. If the holding time of the foaming ratio of 5 times or more is less than 10 minutes, it becomes easy to sag after foaming, resulting in problems such as the foaming ratio of the resulting molded product does not reach a desired value of 2 times or more. There is.
In addition, the holding time in the state where the maximum expansion ratio and the expansion ratio are 5 times or more can be measured by using, for example, the apparatuses and apparatuses shown in FIGS.

When the thermally expandable microcapsule of the present invention is heated at 6 MPa and 200 ° C. in an inert gas atmosphere, the thermally expandable microcapsule having an average particle diameter before foaming of 15 to 40 μm and a shell thickness of 1 to 8 μm, The maximum expansion ratio is 6 times or more, and when the pressure is reduced to 0.1 to 0.3 MPa / second and returned to the atmospheric pressure, the expansion ratio is 5 times or more, and the expansion ratio is 5 times or more. It is preferable that the holding time in a certain state is 10 minutes or more. By satisfying such conditions, the foaming is performed at atmospheric pressure or higher even in the presence of an inert gas such as carbon dioxide, and the particle diameter is maintained after foaming. Even when it is added at the time of molding, a high expansion ratio can be realized.
In particular, in the case of coexistence with an inert gas such as carbon dioxide, when the maximum foaming ratio is less than 6 times, the foaming performance is inferior. For example, the obtained molded article has a foaming ratio of 6 times or more. Compared to expandable microcapsules, problems such as not being significantly increased occur. In addition, the foaming ratio when the pressure is reduced to 0.1 to 0.3 MPa / second and returned to the atmospheric pressure is less than 5 times, or the holding time in a state of 5 times or more is less than 10 minutes Since it becomes easy to sag after foaming, as a result, there arises a problem that it does not rise remarkably as compared with a thermally expandable microcapsule having a foaming ratio of 6 times or more. The maximum expansion ratio, the expansion ratio when the pressure is reduced to 0.1 to 0.3 MPa / second and returned to atmospheric pressure, and the retention time at which the expansion ratio is 5 times or more are shown in FIG. It can measure by using the apparatus shown in FIG. 4 and using the apparatus shown in FIG.

The method for producing the thermally expandable microcapsule of the present invention is not particularly limited. For example, the step of preparing an aqueous medium, the polymerizable monomer (I) composed of acrylonitrile and methacrylonitrile (30) to 40% by weight, the carboxyl group 30 to 50% by weight of a radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms, 0.1% by weight or more of a polymerizable monomer (III) having two or more double bonds in the molecule, and It contains a polymerizable monomer (IV) having a homopolymer solubility parameter of 10 or less, and can be ionically bonded to a radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms having a carboxyl group. Monomer composition containing 0.1 to 10 parts by weight of metal cation salt with respect to 100 parts by weight of all monomer components, and volatile A step of an oily mixture containing a tonicity agent dispersed in an aqueous medium, and can be produced by performing the step of polymerizing the monomer.

When producing the heat-expandable microcapsules of the present invention, a step of preparing an aqueous medium is first performed. 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 microcapsules, and the like, but a preferred lower limit is preferably 0.1 parts by weight with respect to 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 preferred lower limit is 0.05 parts by weight and a preferred 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 a thermally expandable microcapsule, a polymerizable monomer (I) composed of acrylonitrile and methacrylonitrile 30 to 40% by weight, a radically polymerizable unsaturated carboxylic acid monomer having 3 to 8 carbon atoms having a carboxyl group (II) 30 to 50% by weight, a polymerizable monomer having two or more double bonds in the molecule (III) 0.1% by weight or more, and a homopolymer having a solubility parameter of 10 or less (IV And a metal cation salt capable of ionic bonding to a radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms having a carboxyl group, based on 100 parts by weight of all monomer components. A process for dispersing an oily mixture containing a monomer composition containing 1 to 10 parts by weight and a volatile swelling agent in an aqueous medium It is carried out. 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.

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 stationary dispersion apparatus may be supplied with an aqueous dispersion medium and an oil-based mixed liquid separately, or may be supplied with a premixed and stirred dispersion liquid.

The heat-expandable microcapsule of the present invention is produced by, for example, performing a step of polymerizing a monomer by heating, a step of dehydrating, and a step of drying the dispersion obtained through the above-described steps. be able to. 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.

The thermally expandable microcapsules of the present invention, a resin composition or a master batch pellet obtained by adding a matrix resin such as a thermoplastic resin, is molded using a molding method such as injection molding or extrusion molding, and by heating during molding, A foam-molded article can be produced by foaming the thermally expandable microcapsule. Such a foam-molded article is also one aspect of the present invention.
The foamed molded article of the present invention obtained by such a method has high appearance quality, has closed cells uniformly formed, has excellent lightness, heat insulation, impact resistance, rigidity, etc. It can be suitably used for applications such as building materials for automobiles, automobile members, and shoe soles.

The thermoplastic resin is particularly preferably a thermoplastic resin used as a molding material for injection molding and extrusion molding. Specifically, for example, polyolefin resins such as polyethylene, ethylene-vinyl acetate copolymer, polypropylene, Polyvinyl chloride resin, polystyrene, high impact polystyrene, acrylonitrile-styrene copolymer, polystyrene resin such as ABS resin, polyamide resin, polyacetal resin, acrylic resin, cellulose resin such as cellulose acetate, polystyrene heat Plastic elastomer, Polyolefin thermoplastic elastomer, Polystyrene thermoplastic elastomer, Polyurethane thermoplastic elastomer, Polyester thermoplastic elastomer, Polyamide thermoplastic elastomer, 1,2-polybutadiene Thermoplastic elastomers such as thermoplastic elastomers, ethylene-vinyl acetate copolymer thermoplastic elastomers, natural rubber thermoplastic elastomers, fluororubber thermoplastic elastomers, trans-polyisoprene thermoplastic elastomers, chlorinated polyethylene thermoplastic elastomers And thermoplastic elastomers are used. In addition, these may be used independently and may use 2 or more types together.

The amount of thermally expandable microcapsules added to 100 parts by weight of the thermoplastic resin is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight. Moreover, it can also use together with chemical foaming agents, such as sodium hydrogencarbonate (bicarbonate) and ADCA (azo type), and can obtain a foaming ratio higher than using the said chemical foaming agent independently.

The method for producing the master batch pellet is not particularly limited. For example, a matrix resin such as a thermoplastic resin and raw materials such as various additives are kneaded in advance using a same-direction twin-screw extruder or the like. Next, after heating to a predetermined temperature and adding a foaming agent such as the thermal expansion microcapsule of the present invention, the kneaded product obtained by further kneading is cut into a desired size with a pelletizer to form a pellet. And a method of preparing master batch pellets.
Alternatively, a master batch pellet in the form of a pellet may be manufactured by kneading a matrix resin such as a thermoplastic resin or a raw material such as a thermally expandable microcapsule with a batch kneader and then granulating with a granulator. .
The kneading machine 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 molding method of the foamed molded product of the present invention is not particularly limited, and examples thereof include kneading molding, calendar molding, extrusion molding, injection molding, and the like. In the case of injection molding, the construction method is not particularly limited, and a short-short method in which a part of the resin material is put into a mold and foamed, or a core back method in which the mold is fully filled with the resin material and then the mold is opened to the desired position Etc.

In addition, as a method for molding the foamed molded article, for example, a step of preparing a foamable resin composition by mixing a thermoplastic resin and a thermally expandable microcapsule under pressure in an injection molding machine or an extruder, A step of impregnating an expandable resin composition with an inert gas in a high pressure state or a supercritical state, and injection or extrusion of the expandable resin composition melted at a temperature equal to or higher than the expansion start temperature of the thermally expandable microcapsule By doing so, a method having a step of foaming the thermally expandable microcapsule can be used.

The pressure in the step of impregnating the inert gas is preferably set to a high pressure state of 1 MPa or more, and further to a supercritical state in order to increase the impregnation rate of the inert gas into the thermoplastic resin or the thermally expandable microcapsule. However, when the inert gas is carbon dioxide, if impregnation is performed at 60 MPa or more, the cell diameter and the cell density are greatly changed only by slightly changing the impregnation pressure, so that it is difficult to control the cell diameter and the cell density.
The temperature in the step of impregnating the inert gas is preferably about 10 to 350 ° C, for example.

In the step of impregnating with the inert gas, the inert gas used is not particularly limited as long as it is inert with respect to the thermoplastic resin, and examples thereof include carbon dioxide and nitrogen gas. These inert gases may be used alone or in combination.

The supply position of the inert gas in the step of impregnating the inert gas is not particularly limited, and may be, for example, a gas inlet provided in a heating barrel of the molding machine, a hopper of the molding machine, or the like.
1 and 2 are sectional views showing an example of an injection molding machine used in the method for molding a foamed molded product. 1 and 2, 4 is a cylinder, 5 is a screw, 6 is a shut-off nozzle, 9 is a mold, and the mold 7 includes a fixed mold 8 and a movable mold 9.
The supply position of the inert gas may be a gas inlet 2 provided in the heating barrel 1 of the injection molding machine shown in FIG. 1, and the hopper 3 in the heating barrel 1 of the injection molding machine shown in FIG. It may be a part.

When injection molding is performed in the step of injection molding or extrusion molding the foamable resin composition, the foamable resin composition is discharged and filled into the mold cavity at a very high speed, and then the mold cavity It is preferred to reduce the pressure rapidly. As a method for reducing the pressure, for example, a movable mold or a slide piece constituting the mold can be moved (retracted) in the cavity expansion direction.

The method of forming by performing the step of impregnating the inert gas may be a batch method or a continuous method, but a continuous method is preferable. According to the continuous method, for example, the thermoplastic resin and the heat-expandable microcapsule are melt-mixed under pressure at a predetermined temperature or higher using an extruder such as a single-screw extruder or a twin-screw extruder. After injecting a high-pressure inert gas and sufficiently impregnating the gas in the thermoplastic resin, the foamable resin composition is injected into the mold cavity at a temperature higher than the expansion start temperature of the thermally expandable microcapsule. Alternatively, after extrusion through a mold, a foamed molded article can be obtained by rapidly reducing the pressure.

According to the present invention, since it has excellent heat resistance and can realize a high expansion ratio, it can be suitably used for kneading molding, calender molding, extrusion molding, injection molding, etc. to which a strong shear force is applied. A microcapsule and a foam-molded article using the thermally expandable microcapsule can be provided.

It is sectional drawing which shows an example of the molding machine used in the shaping | molding method of the foaming molding of this invention. It is sectional drawing which shows an example of the molding machine used in the shaping | molding method of the foaming molding of this invention. It is a schematic diagram explaining the outline of the apparatus used by performance evaluation (1-3). It is a schematic diagram explaining the outline of the apparatus used by performance evaluation (1-3).

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Examples 1-10, Comparative Examples 1-8)
(Production of thermally expandable microcapsules)
In a polymerization reaction vessel, 300 parts by weight of water, 89 parts by weight of sodium chloride as a regulator, 0.07 parts by weight of sodium nitrite as a water-soluble polymerization inhibitor, and 8 parts by weight of colloidal silica (manufactured by Asahi Denka) as a dispersion stabilizer And 0.3 parts by weight of polyvinyl pyrrolidone (BASF) were added to prepare an aqueous dispersion medium. Subsequently, the dispersion liquid was prepared by adding the oil-based liquid mixture which consists of a monomer of the compounding quantity shown in Table 1 to the said aqueous dispersion medium. The resulting dispersion is stirred and mixed with a homogenizer, charged into a nitrogen-substituted pressure polymerization vessel (20 L), pressurized (0.2 MPa), and reacted at 60 ° C. for 20 hours to prepare a reaction product. did. The obtained reaction product was repeatedly dehydrated and washed with a centrifuge, then dried and thermally expanded microcapsules No. (1) to (12) were obtained. The thermally expandable microcapsule No. (13) and (14) could not be dehydrated.

(Preparation of master batch pellet)
100 parts by weight of low density polyethylene in the form of powder and pellets and 0.2 part by weight of ethylenebisstearic acid amide as a lubricant are kneaded with a Banbury mixer, and when the temperature reaches about 140 ° C., each thermal expansion shown in Table 1 50 parts by weight of the functional microcapsules were added, and the mixture was further kneaded and extruded for 30 seconds to be pelletized at the same time to obtain a master batch pellet.

(Production of molded body)
A screw-type injection molding machine equipped with an accumulator as shown in FIG. 1 is prepared by mixing master batch pellets or chemical foaming agents having an addition amount shown in Table 2 with 100 parts by weight of polypropylene resin. Was supplied to the hopper, melted and kneaded, and injection molded to obtain a plate-shaped molded body.
The molding conditions were as follows: cylinder temperature: 250 ° C., injection speed: 60 mm / sec, mold opening delay time: 0 seconds, mold temperature: 60 ° C.

In Example 10 and Comparative Example 7, CO ₂ gas was directly injected into the injection molding machine as an inert gas. As the CO ₂ gas, carbon dioxide in a supercritical state (0.3 parts by weight of carbon dioxide per 100 parts by weight of polypropylene) is used, and the heating barrel from the gas inlet 2 provided in the middle of the heating barrel 1 shown in FIG. The resin composition was poured into 1 and impregnated into the resin composition, and the composition was melted under pressure at a temperature equal to or higher than the expansion start temperature of the thermally expandable microcapsules. After injecting the obtained foamable resin composition into the cavity of the mold 7, the pressure is reduced by moving (retracting) the movable mold 9 of the mold 7 in the cavity expansion direction by 1.5 mm. A foam was obtained. The initial thickness of the cavity of the mold 7 was 1.5 mm, and the amount by which the movable mold 9 of the mold 7 was moved (retracted) in the cavity expansion direction was 1.5 mm.

(Evaluation)
The following performance was evaluated about the thermally expansible microcapsule obtained in Examples 1-10 and Comparative Examples 1-8, and a molded object. The results are shown in Tables 1 and 2.

(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) Foaming start temperature, maximum foaming temperature, maximum displacement amount Thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), foaming start temperature (Ts), maximum displacement amount (Dmax), and maximum foaming The 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) Particle diameter after foaming at 6 MPa (CO ₂ atmosphere) under atmospheric pressure, foaming ratio After the sample was placed in the pressure vessel shown in FIG. 3, the temperature in the pressure vessel was set to 200 ° C. and atmospheric pressure As shown in FIG. 4, the behavior of the foamed particles was observed from the window made of sapphire glass using a camera with a microscope in the case of the lower case and the pressure of 6 MPa (CO ₂ atmosphere). The observation is performed for 30 minutes after reaching 200 ° C., and when the pressure is 6 MPa (CO ₂ atmosphere), pressurization is performed at 200 ° C. for 10 minutes, and after observing the particle diameter, the pressure in the sealed container is reduced to 0.3 MPa / second. Then, it was confirmed that the atmospheric pressure was reached, and the particle size was further observed for 20 minutes. Table 1 shows measurement items and measurement results.

(2) Evaluation of molded body (2-1) Foaming ratio A value obtained by dividing the plate thickness of the molded body after foaming by the plate thickness of the molded body before foaming was calculated as the foaming ratio. And the average value and standard deviation of the expansion ratio of 10 molded articles were obtained.

(2-2) Appearance (molded product surface, cross section)
The presence or absence of silver streaks on the surface of the molded product was visually observed. Moreover, the bubble state of the cross section was observed using the SEM apparatus.

(2-3) Measurement of density The density of the obtained molded body was measured by a method based on JIS K-7112 A method (submersion method in water).

As shown in Tables 1 and 2, the thermally expandable microcapsule No. (1)-(7) show the high heat resistance whose maximum foaming temperature is 200 degreeC or more. Thermally expandable microcapsules No. In (1) to (7), the particle diameter after foaming when heated under atmospheric pressure exceeds 100 μm, the particle diameter after maximum foaming at 6 MPa (CO ₂ atmosphere) exceeds 130 μm, and the final particle diameter is also 100 μm. Therefore, such a thermally expandable microcapsule No. 1 has good foaming performance. As for the molded bodies (Examples 1 to 7) using (1) to (7), molded articles having low density and excellent lightness were obtained. Moreover, if even in molding at a combination system and CO ₂ gasification of the chemical blowing agent CO ₂ is generated, without the addition of heat-expandable microcapsules as can be seen from Examples 8-10 (Comparative Examples 6 and 8) The foaming ratio was higher than that.

According to the present invention, since it has excellent heat resistance and can realize a high expansion ratio, it can be suitably used for kneading molding, calender molding, extrusion molding, injection molding, etc. to which a strong shear force is applied. Microcapsules can be provided. Moreover, according to this invention, the foaming molding using this thermally expansible microcapsule can be provided.

1 Heating barrel 2 Gas inlet 3 Hopper 4 Cylinder 5 Screw 6 Shut-off nozzle 7 Mold 8 Fixed mold 9 Movable mold 11 Sample 12 Heater 13 Thermocouple 14 Spacer 15 Sapphire glass 16 O-ring 17 Camera with microscope

Claims (8)

A thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a polymer shell,
The shell is a polymerizable monomer (I) 30 to 40% by weight consisting of acrylonitrile and methacrylonitrile, a radically polymerizable unsaturated carboxylic acid monomer (II) 3 to 8% by weight having a carboxyl group, a molecule A monomer composition containing a polymerizable monomer (III) having at least 0.1% by weight of a polymerizable monomer (III) having two or more double bonds therein and a polymerizable monomer (IV) having a homopolymer solubility parameter of 10 or less is polymerized. A polymer consisting of
The content of acrylonitrile in the polymerizable monomer (I) is 10 to 60% by weight, and
The monomer composition further comprises a metal cation salt capable of ion binding to a radically polymerizable unsaturated carboxylic acid monomer (II) having 3 to 8 carbon atoms having a carboxyl group, based on 100 parts by weight of all monomer components. A thermally expandable microcapsule containing 0.1 to 10 parts by weight. When a thermally expandable microcapsule having an average particle diameter before foaming of 15 to 40 μm and a shell thickness of 1 to 8 μm is continuously heated at 200 ° C. at atmospheric pressure, the maximum foaming ratio is 5 times or more, and The heat-expandable microcapsule according to claim 1, wherein a holding time in a state where the expansion ratio is 5 times or more is 10 minutes or more. When a heat-expandable microcapsule having an average particle diameter before foaming of 15 to 40 μm and a shell thickness of 1 to 8 μm is heated at 6 MPa and 200 ° C. in an inert gas atmosphere, the maximum foaming ratio is 6 times or more, And,
When the pressure is reduced to 0.1 to 0.3 MPa / second and returned to atmospheric pressure, the expansion ratio is 5 times or more, and the holding time in a state where the expansion ratio is 5 times or more is 10 minutes or more. The thermally expandable microcapsule according to claim 1. The thermally expandable microcapsule according to claim 1, 2 or 3, wherein the maximum foaming temperature is 200 ° C or higher. A foamed molded article comprising the thermally expandable microcapsule according to claim 1, 2, 3 or 4. A method for producing a foamed molded article, comprising using the thermally expandable microcapsule according to claim 1, 2, 3, or 4 and a chemical foaming agent in combination. A step of preparing a foamable resin composition by mixing a thermoplastic resin and the thermally expandable microcapsule according to claim 1, 2, 3, or 4 under pressure in an injection molding machine or an extruder, the foamable resin A step of impregnating the composition with an inert gas, and injection molding or extrusion molding of the expandable resin composition melted at a temperature equal to or higher than the expansion start temperature of the thermally expandable microcapsule, thereby A method for producing a foamed molded article, comprising a step of foaming a capsule. A foam molded article obtained by the method for producing a foam molded article according to claim 6 or 7.

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