JP2008247950A - Composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily producible composite material having light weight and improved strength, elastic modulus, heat resistance, gas barrier property, etc., of a resin. <P>SOLUTION: The composite material 4 is produced by kneading a porous structure 2 and a resin 3 to crush the porous structure 2 and disperse the crushed material in the resin 3 to obtain a composite material 1 and mixing and dispersing hollow particles 5 in the composite material 1 to decrease the specific gravity of the product below the specific gravity of the resin. The porous structure 2 is crushed during the kneading of the porous structure 2 and the resin 3 by the kneading force to homogeneously disperse the crushed material in nanometer-order and improve the strength, elastic modulus, etc. An easily producible composite material having light weight and improved strength, elastic modulus, heat resistance, gas barrier property, etc., can be produced without increasing the specific gravity by dispersing the hollow particles 5 in the composite material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composite material that can be used for various products and parts that are light and require strength, such as household appliances such as vacuum cleaners, automobile interior parts, and bumpers.

  Conventionally, physical properties such as resin strength have been improved by adding spherical, plate-like, or fibrous fillers to the resin. Although this method improves the strength and the like, there is a problem that the specific gravity of the resin to which the filler is added becomes large. In order to avoid this, the so-called nanocomposite material, in which the object to be dispersed is crushed with a crusher to produce nanoparticles and then dispersed into the resin by melt kneading using a kneader or an extruder, is used to increase the specific gravity. Without improving the physical properties such as strength and elastic modulus. Further, as a method for more reliably obtaining a nanocomposite material, an organic dispersion obtained by intercalating and dispersing a layered clay mineral as an object to be dispersed is mixed with an organic solution in which a resin is dissolved, and then the solvent is removed. Thus, there has been proposed a method of obtaining a homogeneously dispersed composite material without causing secondary aggregation (secondary particles are formed by aggregation) (for example, see Patent Document 1).

On the other hand, a method has also been proposed in which a hollow glass sphere having a particle specific gravity of 0.5 g / cc or less and an average particle size of 20 μm or less is used as a filler and is added to a resin or rubber to produce a lightweight molded product. (For example, refer to Patent Document 2).
JP-A-6-41346 JP 2001-172031 A

  However, the conventional intercalation method has problems such that the dispersion target is limited to a layered substance that can be intercalated and that the resin is limited to a resin that dissolves in an organic solution. At the same time, it is usually necessary to add about 3 to 5 wt% of inorganic filler in order to make a nanocomposite material. However, the specific gravity of the resin is around 1 g / cc, which is much smaller than the specific gravity of the inorganic filler. There is a problem that the specific gravity of the resin becomes slightly heavier than that of the original resin.

  On the other hand, the method of adding a hollow glass sphere as a filler and adding it to a resin, rubber or the like has a problem that physical properties such as strength, elastic modulus and impact resistance are remarkably lowered.

  The present invention solves the above-mentioned conventional problems, and aims to provide a composite material that is light and easy to produce with improved resin strength, elastic modulus, heat resistance, gas barrier properties, and the like. is there.

  In order to solve the above-mentioned conventional problems, the composite material of the present invention is obtained by crushing a porous structure by kneading the porous structure and resin and dispersing it in the resin to obtain a composite. Hollow particles are mixed and dispersed to make the specific gravity equal to or lower than the specific gravity of the resin.

  In this way, the porous structure is crushed by the force during the kneading of the porous structure and the resin, and the strength and elastic modulus are improved by uniformly dispersing in the nano order. By dispersing, it is possible to provide a light and simple composite material with improved strength, elastic modulus, heat resistance, gas barrier property and the like without increasing specific gravity.

  The composite material of the present invention can provide a light and simple composite material with improved strength, elastic modulus, heat resistance, gas barrier property and the like without increasing specific gravity.

  In the first invention, the porous structure is crushed by kneading the porous structure and the resin and dispersed in the resin to obtain a composite, and hollow particles are mixed and dispersed in the composite to obtain the specific gravity of the resin. By using the following composite material, the porous structure is crushed by the force during the kneading of the porous structure and resin, and the strength and elastic modulus are improved by dispersing it uniformly on the nano order. Further, by dispersing the hollow particles, it is possible to provide a light and simple composite material with improved strength, elastic modulus, heat resistance, gas barrier property and the like without increasing the specific gravity.

  According to a second invention, in particular, in the first invention, the porous structure before crushing has a structure in which primary particles having a representative diameter of less than 100 nm are connected in a bead shape so that the porous structure before crushing is obtained. Since it can be crushed with weak force, it can be dispersed uniformly in the nano-order, and even hollow particles with a specific gravity smaller than that of the resin can be dispersed, improving the strength and elastic modulus without increasing the specific gravity. Composite materials can be realized.

  In the third invention, in particular, in the first invention, the hollow particles are smaller than the specific gravity of the resin and the melting point is higher than the melting point of the resin, so that the hollow of the hollow particles is not crushed when mixed into the composite. Therefore, a composite material with improved strength, elastic modulus, etc. can be realized without increasing the specific gravity.

  According to a fourth invention, in particular, in any one of the first to third inventions, the porous structure before crushing is a gel that forms a wet gel by mixing a solvent containing at least water and a gel raw material. Prepared from a hydration step, a water removal step of removing water in the wet gel, and a drying step of obtaining a porous structure by removing the solvent remaining in the wet gel removed in the water removal step It is. This makes it possible to produce a porous structure that can be easily crushed to the nano order with the force applied when kneading with the resin, so that it is possible to disperse in the nano order, and furthermore, the hollow has a smaller specific gravity than the resin. By dispersing the particles, a composite material with improved strength and elastic modulus can be realized without increasing the specific gravity.

  In the fifth invention, in particular, in the fourth invention, in the gelation step, the gel raw material is a monomer of alkoxysilane, and at least the solvent contains water, an alcohol, and an alkali catalyst for promoting gelation. This makes it possible to form a wet gel with small primary particles by using an alkoxysilane monomer, an appropriate amount of water, a solvent, and an alkaline catalyst such as aqueous ammonia or sodium hydroxide, so that the porous structure can be easily crushed and finely crushed. Can be produced on a nano-order, and even by dispersing hollow particles with a specific gravity smaller than that of the resin, a composite material with improved strength and elastic modulus can be realized without increasing the specific gravity. Can do.

  In the sixth invention, in particular, in the fourth invention, in the gelation process, a substance serving as a nucleus of primary particles is added to form a wet gel. By dispersing the particles in water, etc., a large amount of primary particles are generated, so that each growth is suppressed, and since the primary particles are made into a small wet gel, the porous structure can be easily crushed and finely crushed. A composite material with improved strength and elastic modulus can be realized without increasing specific gravity by dispersing hollow particles with a specific gravity smaller than that of resin. be able to.

  In the seventh aspect of the invention, in particular, in the fourth aspect of the invention, in the gelation process, a wet gel is formed by irradiating ultrasonic waves when forming a wet gel by irradiating ultrasonic waves to form a wet gel. Therefore, it is possible to produce a porous structure that can be easily crushed and finely crushed, and can be dispersed in the nano-order. Furthermore, by dispersing hollow particles having a specific gravity smaller than that of the resin, without increasing the specific gravity, A composite material with improved strength and elastic modulus can be realized.

  In the eighth invention, in particular, in the fourth invention, a large amount of primary particles are generated by rapid cooling by cooling the mixture and forming a wet gel after mixing the solvent and the gel raw material in the gelation step. Since each individual growth is suppressed and a wet gel with small primary particles is formed, a porous structure that can be easily crushed and finely crushed can be produced, and can be dispersed in the nano-order. By dispersing even small hollow particles, it is possible to realize a composite material with improved strength and elastic modulus without improving specific gravity.

The ninth invention has a hydrophobization step before the water removal step, particularly in the fourth invention, wherein R and R ′ represent an alkyl group, and x is 1 to 3. Any integer and hydrophobizing at least a portion of the wet gel surface using an alkylalkoxysilane represented by _Rx (R'O) _4- xSi, and a drying step It is a drying process in which drying is performed under a temperature and pressure condition below the critical point of the solvent contained in the hydrophobized wet gel. This makes it possible to easily crush to the nano-order by using the force applied when kneading with the resin without using supercritical drying by performing a hydrophobic step and selecting an appropriate solvent during the drying step. A porous structure can be produced at low cost. For this reason, it is possible to disperse in nano order, and furthermore, by dispersing hollow particles having a specific gravity smaller than that of the resin, it is possible to realize a composite material with improved strength and elastic modulus without improving the specific gravity. it can.

  In the tenth invention, in particular, in the ninth invention, R and R ′ are both methyl groups and x = 2, so that this raw material is called dimethyldimethoxysilane, which is inexpensive and has a hydrophobization rate. It can be hydrophobized quickly and reliably. This is because the monofunctionality of x = 1 reduces the reactivity due to the steric hindrance of three alkyl groups, and the trifunctionality of x = 3 causes all three silanol groups resulting from hydrolysis to react with silanol groups on the gel surface. This is because silanol groups remain on the gel surface and the reactivity is lowered, and dimethyldimethoxysilane does not have this. Therefore, without using supercritical drying, a porous structure that can be easily crushed to the nano-order with the force applied when kneading with the resin can be produced at a low cost, enabling dispersion at the nano-order. Further, by dispersing hollow particles having a specific gravity smaller than that of the resin, a composite material having improved strength, elastic modulus, etc. can be realized without improving the specific gravity.

  In the eleventh aspect of the invention, in particular, in any one of the first to third aspects of the invention, since the resin is a polyolefin-based resin, the surface of the porous structure has an alkyl group. It is easy to become familiar with highly polyolefin resin. For this reason, the crushed porous structure is easily dispersed homogeneously in the resin, can be dispersed in the nano order, and further by dispersing hollow particles having a specific gravity smaller than that of the resin, without increasing the specific gravity. In addition, a composite material with improved strength, elastic modulus, and the like can be realized.

  In the twelfth aspect of the invention, in particular, in any one of the first to third aspects of the invention, since the resin is a polypropylene resin, the resin is crushed by having many alkyl groups, high versatility, and low specific gravity. The porous structure easily disperses uniformly in the resin, enables nano-order dispersion, and also disperses hollow particles having a specific gravity smaller than that of the resin, thereby improving the strength and elastic modulus without increasing the specific gravity. It is possible to realize a composite material with improved characteristics.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
1 and 2 show a composite material according to Embodiment 1 of the present invention.

  As shown in FIG. 1A, during the kneading of the porous structure 2 and the resin 3, many of the particles of the porous structure 2 are crushed to a representative diameter of less than 100 nm by the force, and are uniformly mixed in the resin 3. The composite 1 is obtained by dispersing. The porous structure 2 is bonded to the resin 3 by an action such as an anchor effect or a physical bond or a chemical bond to form a complex 1. It is known that as the particle size of the dispersion becomes smaller, the shape effect decreases and the surface effect increases. By dispersing particles smaller than 100 nm in particle size, the same level of reinforcing effect (improvement in strength, elastic modulus, heat resistance, etc.) can be obtained in much smaller amounts than those obtained by dispersing micron-sized particles. Since an addition amount of about ˜5 wt% is necessary, the specific gravity of the original resin 3 is slightly heavier.

  Therefore, as shown in FIG. 1 (b), the hollow fiber 5 having a specific gravity smaller than that of the resin 3 and a melting point higher than that of the resin 3 is mixed and dispersed in the composite 1 so that the obtained reinforcing effect is not much. A composite material 4 having a specific gravity equal to or lower than the specific gravity of the resin 3 without being lowered is produced. The material, size, shape, specific gravity and the like of the hollow particles 5 used at this time are not particularly limited, but if an inorganic material is used, a reinforcing effect is easily obtained, and a smaller size is less likely to break during mixing. Also, the reinforcing effect after mixing and dispersion is enhanced. Further, when the material is silica, the shape is spherical, and the hollow particle 5 has a representative diameter of about 30 to 70 μm, the specific gravity is preferably about 0.6 g / cc. If it becomes smaller than this, the hollow particles 5 are broken at the time of mixing and dispersing or at the time of molding, and the light weight effect cannot be obtained. The size is preferably about 100 μm or less of the representative diameter, and the shape is preferably nearly spherical. Further, the addition amount is up to about 10 wt%, and if it is added more than this, the strength and elastic modulus improved as a nanocomposite material are greatly reduced.

  Therefore, for example, 5 wt% of the polypropylene resin 3 having a specific gravity of 0.9 g / cc, the porous structure 2 made of silica having a specific gravity of 2.0 g / cc, and the hollow particles 5 having an apparent specific gravity of 0.6 g / cc. When the composite material 4 is prepared by kneading and dispersing the material at 6 wt%, the specific gravity of the composite material 4 becomes 0.898 g / cc, which is smaller than the original polypropylene resin 3.

  FIG. 2 shows the porous structure 11 before crushing the porous structure 2 dispersed in the resin 3. The primary particles 13 having a representative diameter of about 1 to 100 nm (less than 100 nm) are chemically formed. Alternatively, a skeleton physically connected in a bead shape forms a solid portion 12, and has a porous structure because of a space portion 15 having a diameter of an interparticle distance 14 and a large number of pores. Since the portion connecting the primary particles 13 is almost point contact, the bulk body of the porous structure 11 before crushing is very fragile, and the portion connecting the primary particles 13 is cut and easily broken up to about 50 μm. be able to. However, since the porous structure 11 before crushing has a large porosity and is very light (its own weight is small), it is difficult to crush to 1 μm or less by a crushing method using a mixer or the like, and peaks at about 20 to 40 μm. And has a particle size distribution of about 1 to 50 μm.

  In addition, the shape of the porous structure 11 before crushing is not limited to a spherical shape. Further, considering that the portion connecting the primary particles 13 is weak and this portion is broken, it is better that the primary particle diameter is as small as possible. In particular, when it is attempted to disperse at 100 nm or less, the primary particle size needs to be 100 nm or less. The size of the primary particle diameter is determined by the reaction in the gelation step, and this part will be described in Embodiment 2.

  Next, a method for kneading the porous structure 11 and the resin 3 before crushing will be described.

  The porous structure 11 before crushing is desirably crushed to 50 μm or less before kneading with the resin 3. When the porous structure 11 of several mm to several cm is kneaded with the resin 3, the porous structure 11 is crushed to 1 μm or less. It takes too much time to cause deterioration of the resin 3. The kneading is performed using a normal kneader and no special kneader is required. However, in consideration of uniform dispersion in the nano order, a biaxial extruder or the like having a strong kneading force is desirable.

  A method for mixing and dispersing the hollow particles 5 in the composite 1 produced by the above method will be described.

  Also in this case, a normal kneader is used, and a special kneader is not required. However, if kneading is performed with a strong force, the hollow particles 5 may be broken. It is desirable.

  The resin 3 is not particularly limited. However, since the surface of the porous structure is hydrophobized, it is compatible with the polyolefin resin and can be kneaded into polyethylene, polypropylene, and the like without any problem. In addition, it can be kneaded with various resins such as vinyl chloride resin, polystyrene, ABS (acrylonitrile-butadiene-styrene) resin, polyester (PET, PBT, etc.), nylon resin, polyacetal, polycarbonate, phenol resin, and epoxy resin.

  Such a composite material 1 has the same specific gravity as the original resin 3 and has high heat resistance and strength. Therefore, it is light and strong, such as household appliances such as vacuum cleaners, automobile interior parts, and bumpers. It can be used for various products and parts.

(Embodiment 2)
Next, the composite material in Embodiment 2 of this invention is demonstrated. The structure of the composite material is the same as that of the first embodiment.

  Here, the manufacturing method of the porous structure 11 before crushing using supercritical drying for the drying process used for the composite material 4 in the present embodiment will be described. The manufacturing process mainly consists of the following three processes.

(1) Gelation step (formation of wet gel)
(2) Water removal step (removal of water in wet gel)
(3) Drying step (solvent removal in wet gel)
Hereinafter, each step will be described.

(1) Gelation step (formation of wet gel)
In this embodiment mode, a wet gel is prepared by a sol-gel method. Specifically, hydrolysis and polycondensation of the gel raw material are promoted in the solvent by using metal alkoxide as the gel raw material, and mixing a solvent such as water and alcohol with a catalyst for accelerating gelation as necessary. To form a wet gel. Moreover, a wet gel can also be produced by using water glass as a gel raw material and mixing with a catalyst for promoting gelation as required. Examples of the gel raw material used in the manufacture of the present embodiment include alkoxides such as silicon, aluminum, zirconium, and titanium that are generally used in the sol-gel method. Among these, a compound containing silicon as a metal, that is, alkoxysilane is preferable from the viewpoint of easy availability and low cost.

  Wet gel is formed by adding alkoxysilane, alcohol as solvent, acid or base as water for promoting gelation, and water to hydrolyze and polycondensate alkoxysilane. To do. The wet gel produces silica particles having a three-dimensional network structure in which silicon atoms and oxygen atoms are alternately bonded, and the silica particles are polymerized to form primary particles 13 which are beaded to form a solid portion 12. In addition, the interparticle distance 14 of the primary particles 13 becomes a gap, that is, a space portion 15, so that a solvent such as water enters.

  Next, the raw material alkoxysilane will be described. Examples of the alkoxysilane include tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane, trialkoxysilanes, alkoxysilanes such as dialkoxysilane, oligomers thereof, and the like, and mixtures thereof. In particular, tetramethoxysilane is suitable for use in this embodiment because it has a high silica content and is easily available at low cost. Tetramethoxysilane is suitable for the present embodiment because it has a high reaction rate, that is, a hydrolysis rate and a condensation polymerization rate, and can suppress the growth of the primary particles 13. Furthermore, a tetramer or a 10-mer oligomer in which alkoxysilane has been reacted in advance can be used. However, if an oligomer is used, primary particles 13 are likely to grow and primary particles 13 become large. It is desirable to use the monomer.

  As the gelation catalyst, a general organic acid, inorganic acid, organic base, or inorganic base is used. Examples of organic acids include acetic acid, citric acid, inorganic acids, sulfuric acid, hydrochloric acid, nitric acid, organic bases such as piperidine, and inorganic bases such as ammonia, formamide, and dimethylformamide.

  When an alkali catalyst is used, hydrolysis is fast and all alkoxyl groups are replaced with hydroxyl groups, so that polycondensation reactions occur in many places, and the growth of primary particles 13 does not progress much. Therefore, this embodiment is very advantageous. On the other hand, when an acid catalyst is used, hydrolysis is slow and at the same time a polymerization reaction occurs, so that primary particles grow greatly. Therefore, an alkaline catalyst is desirable in this embodiment.

  When ultrasonic irradiation is performed at the time of preparing the wet gel, generation of primary particles starts at many places, so that the growth of each primary particle can be suppressed. In addition, by adding a solution in which fine particles such as colloidal silica are dispersed in the water used when preparing the wet gel, the generation of primary particles starts from that as the core, so the number of primary particle generation points can be increased. , The growth of each primary particle can be suppressed. In addition, immediately after mixing alkoxysilane and water and a solvent and an alkali catalyst, the core of primary particle generation can be created by quenching with liquid nitrogen or the like, so the same effect as adding colloidal silica is obtained. be able to.

  After gelation, the formed wet gel is placed in a heated atmosphere as necessary, and the gel is aged by condensing unreacted silanol groups in the gel to increase the strength and suppress shrinkage during drying Although it is effective to do so, if the strength is increased too much, it becomes difficult to be crushed during kneading.

(2) Water removal step (removal of water in wet gel)
The water removal step is a step of removing water in the wet gel and replacing it with a solvent having a lower critical temperature and lower critical pressure. When the wet gel is normally dried with hot air, it shrinks and crushes the pores due to the surface tension when the solvent dries, the primary particles 13 are close to each other, and the strength increases, making it difficult to be crushed during kneading. The force ΔP applied to the hole is generally expressed by (Equation 1).

  Here, ΔP represents the capillary force, γ represents the surface tension of the solvent, θ represents the contact angle between the solvent and the skeleton, and d represents the pore diameter.

  Therefore, in order to reduce the capillary force, it is necessary to increase the contact angle θ or reduce the surface tension γ. When the solvent in the wet gel is in a supercritical state, the surface tension γ is zero and no capillary force is generated. For this reason, since the hole, that is, the space portion 15 does not shrink, the porous structure 11 can be obtained. However, since the critical temperature and pressure are usually large, there is a problem in safety and it is very expensive. Therefore, it is desired to use a solvent having a critical temperature and a critical pressure as low as possible during drying, particularly a solvent having a small critical pressure.

  As the water removal method, either solvent replacement or heating distillation is desirable. First, solvent replacement will be described.

  The general solvent replacement is performed by immersing the formed wet gel in a water-soluble solvent and replacing the solvent with the solvent in the gel. The solvent used at this time is not particularly limited as long as it is a water-soluble solvent and has a critical temperature and a critical pressure smaller than water (critical temperature: 374.2 ° C., critical pressure: 218.3 atm).

  For example, methanol (critical temperature: 240 ° C., critical pressure: 78.5 atm), ethanol (critical temperature: 243.1 ° C., critical pressure: 63 atm), propanol and tertiary-butanol, ethylene glycol, glycerol as water-soluble alcohols In addition to ketones and ethers such as acetone (critical temperature: 235.5 ° C., critical pressure: 46.6 atm), 1,4-dioxane, tetrahydrofuran, 1,3-dioxolane (critical temperature: 193.8 ° C., critical pressure: 36.2 atm), formamides such as dimethylformamide, lower carboxylic acids such as formic acid, acetic acid (critical temperature: 321.6 ° C., critical pressure: 57.1 atm) and propionic acid, Mixtures of these can be used. Among these, it is desirable to use alcohols such as methanol and ethanol which are inexpensive and easily available.

  Moreover, solvent substitution is possible not only with the said water-soluble solvent but with the mixed solvent of the said water-soluble solvent and another water-insoluble solvent. Specifically, it is a mixed solvent of n-hexane, decane, nonane, octane, heptane, toluene, xylene and the like and a water-soluble solvent. Particularly preferred for industrial use such as safety and availability are octane, toluene, xylene and the like.

  Next, heating distillation will be described. When water is removed by distillation by heating, it is possible to distill water preferentially by adding a water-insoluble solvent having a boiling point higher than that of water and heating. By using a water-insoluble solvent, the organic solvent and water are naturally separated after distillation by heating, so that the solvent can be easily reused. Moreover, even if the boiling point of the water-insoluble solvent is lower than the boiling point of water, if it is added excessively, it is possible to remove water, but by further increasing the boiling point of the solvent, the selectivity of water distillation Can be increased. For this reason, compared with the case where water is removed by solvent substitution, the effect that the amount of solvent to be used can be reduced significantly is acquired. However, care should be taken because the energy used increases if the boiling point is too high.

  In addition, when water and the added solvent form an azeotrope, water and the solvent are distilled off at a constant rate, so that there is an effect that it is easy to control the removal of water. Furthermore, efficient water removal becomes possible by performing the heating and distillation under reduced pressure conditions as is done by drying an ordinary organic solvent. In particular, in the case where a gelling catalyst or the like is present, if the temperature is increased and dried by heating in a state containing water, bonds in the gel skeleton may be broken. In such a case, it is effective to prevent the temperature from rising by distilling water off under reduced pressure.

(3) Drying step (solvent removal in wet gel)
The drying method will be described. Drying is a step of removing the solvent that enters the wet gel instead of the water removed in the water removal step. A case where the solvent is ethanol will be described as an example. The internal water is removed, and the wet gel substituted with ethanol is placed in a pressure vessel, the pressure is raised above the critical pressure, and then the temperature is raised above the critical temperature to bring the ethanol into a supercritical state. Thereafter, for example, by passing a substance compatible with ethanol in a supercritical state such as carbon dioxide, ethanol is extracted and substituted with carbon dioxide, and the pressure is reduced to atmospheric pressure, and then the temperature is lowered. Thereby, the porous structure 11 can be obtained.

  In addition, after replacing a part of ethanol in the wet gel with carbon dioxide, the pressure is raised to a critical pressure of carbon dioxide or higher, and then the temperature is raised to a critical temperature or higher, and carbon dioxide is circulated in a supercritical state. Thereafter, the flow is stopped, the pressure is lowered to atmospheric pressure, and then the temperature is lowered. Thereby, the porous structure 11 that can be crushed with a relatively weak force at a lower cost and safer than the supercritical drying of ethanol can be obtained.

  The composite material 1 in which the porous structure 11 thus produced is uniformly dispersed in the nano-order in the resin 3 has the same specific gravity as the original resin 3 and has high heat resistance and strength. It can be used for various products and parts that are light and require strength, such as home appliances, automobile interior parts, and bumpers.

(Embodiment 3)
Next, the composite material in Embodiment 3 of this invention is demonstrated. The structure of the composite material is the same as that of the first embodiment.

  Here, the manufacturing method of the porous structure 11 before crushing which does not use supercritical drying for the drying process used for the composite material 4 in the present embodiment will be described. The manufacturing process mainly includes the following four processes.

(1) Gelation step (formation of wet gel)
(2) Hydrophobization step (hydrophobization of wet gel surface)
(3) Water removal step (removal of water in wet gel)
(4) Drying step (solvent removal in wet gel)
Hereinafter, each step will be described.

(1) Gelation step (formation of wet gel)
A wet gel is prepared by the same method as in the second embodiment.

(2) Hydrophobization step (hydrophobization of wet gel surface)
This step is a step of replacing the silanol group on the wet gel surface with a hydrophobic methyl group with, for example, trimethylchlorosilane, hexamethyldisilazane, dimethyldimethoxysilane or the like. This has implications for a preliminary process before the drying process. As described above, the force ΔP applied to the pores at the time of drying is expressed by (Equation 1). In this step, the contact angle θ is increased by introducing a hydrophobic group, and the capillary force ΔP generated at the time of drying is decreased. Objective. Note that the reduction of the surface tension γ will be described in the next water removal step. Hydrophobization is not limited to a methyl group, and an ethyl group, a propyl group, a fluorine functional group, a phenyl group, or the like can obtain almost the same effect, but a methyl group is desirable in consideration of reactivity and cost. .

  Furthermore, when trimethylchlorosilane, hexamethyldisilazane, or the like is used, gas such as hydrogen chloride or ammonia is generated, which may be used as a catalyst to break bonds in the wet gel skeleton. Moreover, when using these hydrophobizing agents, it is necessary to remove water beforehand, and one process will increase.

Therefore, in the present embodiment, R and R ′ represent an alkyl group, x represents an integer of 1 to 3, and an alkylalkoxysilane represented by R _x (R′O) _4−x Si To hydrophobize. Alkoxyalkoxysilanes used include monofunctional alkylalkoxysilanes such as methoxytrimethylsilane and ethoxytrimethylsilane, dimethoxydimethylsilane, dimethoxydiethylsilane, diethoxydimethylsilane, diethoxydiethylsilane and other bifunctional alkylalkoxysilanes, methyltrimethoxysilane And trifunctional alkylalkoxysilane compounds such as ethyltriethoxysilane. One of these or a mixture is dissolved in a solvent to be a hydrophobization treatment solution, and the wet gel is reacted with the solvent to cause the reaction.

  Since the reaction between the hydrophobizing agent and the silanol group involves hydrolysis, water is always required. Therefore, the solvent used as the hydrophobization treatment liquid is preferably a water-soluble solvent, and as the water-soluble solvent, water-soluble alcohols such as methanol, ethanol, propanol and tertiary-butanol, lower alcohols such as ethylene glycol and glycerol, and the like, Ketones and ethers such as acetone, 1,4-dioxane, tetrahydrofuran, 1,3-dioxolane, and mixtures thereof can also be used.

  In order to use alkylalkoxysilane as a hydrophobizing agent, water is required for hydrolysis, but the wet gel prepared in the gelation step contains water, so there is no need to add new water. It is also very desirable because it does not need to be dehydrated. Further, by using ammonia water as a catalyst for gelation and water and methanol as solvents, alkylalkoxysilane can be directly added to the wet gel to make it hydrophobic.

  Furthermore, it discovered that bifunctional alkyl alkoxysilane was excellent in the hydrophobization efficiency among alkyl alkoxysilane. This is because the monofunctionality reduces the reactivity due to the steric hindrance of the three alkyl groups, and the trifunctionality makes it difficult for all three silanol groups resulting from hydrolysis to react with the silanol groups on the gel surface. This may be because it remains on the gel surface. Therefore, a bifunctional alkylalkoxysilane excellent in hydrophobizing efficiency, particularly dimethyldimethoxysilane, is highly desirable because of its high reactivity. That is, preferably, R and R 'of the alkylalkoxysilane are both methyl groups and x = 2.

  Moreover, although the hydrophobization process is described after the gelation process, it can also be performed simultaneously with the gelation. However, at the same time as gelation, the hydrophobizing agent reacts with the gel raw material before polymerization to suppress the polymerization, or the amount of the required hydrophobizing agent increases due to the reaction with the gel raw material before polymerization. There is a case. Therefore, it is preferable that the hydrophobizing agent is allowed to act after the gelation is completed.

(3) Water removal step (removal of water in wet gel)
In this step, water and unreacted hydrophobizing agent in the wet gel are removed, and the amount is replaced with a solvent having a small surface tension γ. This process also has implications for the preliminary process of the drying process. According to (Equation 1), reducing the surface tension γ is also effective in reducing the capillary force.

  The surface tension of water is 0.072 N / m (25 ° C.), and other liquids such as toluene 0.027 N / m (30 ° C.) which is a general-purpose organic solvent, ethanol 0.021 N / m (25 C) and so on. Therefore, it is very important to reduce the proportion of water in the wet gel before drying and replace it with a solvent with a low surface tension instead.

  The water removal method is solvent substitution or heating distillation as in the second embodiment, but the solvent to be substituted is preferably a solvent having a small surface tension regardless of the critical temperature and critical pressure.

  For the solvent replacement, the same solvent can be used in the same manner as in Embodiment 2. However, it is desirable to use alcohols such as methanol and ethanol which are inexpensive and easily available. Further, not only a water-soluble solvent but also a mixed solvent of a water-soluble solvent and another water-insoluble solvent is possible. The method for heating distillation is the same as in the second embodiment.

(4) Drying step (solvent removal in wet gel)
The drying method will be described. Drying is a step of removing the solvent introduced into the wet gel in place of the water removed in the water removal step. Capillary force is remarkably reduced by the hydrophobization process and the water removal process, so that a certain degree of shrinkage can be suppressed even if hot air drying is performed in this state, and a porous structure that can be crushed with a relatively weak force is obtained. However, it is easy to obtain a porous structure that can be crushed with a weaker force by performing the drying at a pressure of at least 2 atm.

  This is because if the drying is performed under pressure, the boiling point of the solvent retained in the pores increases. At this time, since the surface tension γ is lowered by the temperature rise, the capillary force is reduced and shrinkage is effectively suppressed, which is desirable. For example, when acetone is dried under pressure, if the boiling point is raised to about 45 ° C. and raised to about 100 ° C., the surface tension decreases to about 0.005 N / m and decreases to about 0.015 N / m. It can be said that drying under pressure is sufficiently effective in suppressing shrinkage. Note that although the supercritical drying described in Embodiment 2 may be performed, the above-described method can produce a porous structure at an overwhelmingly low cost.

  The composite material 1 in which the porous structure 11 thus produced is uniformly dispersed in the nano-order in the resin 3 has the same specific gravity as the original resin 3 and has high heat resistance and strength. It can be used for various products and parts that are light and require strength, such as home appliances, automobile interior parts, and bumpers.

  As described above, the composite material according to the present invention can be easily produced lightly and with improved strength, elastic modulus, heat resistance, gas barrier properties, etc. without increasing the specific gravity. It can be used for various products and parts that are light and require strength, such as products, automobile interior parts, and bumpers. Moreover, it can utilize also as a composite material which provided electroconductivity by using the porous structure body of organic substances, such as carbon, for a dispersion | distribution target object.

(A) Schematic diagram of the composite constituting the composite material in Embodiments 1 to 3 of the present invention (b) Schematic diagram of the composite material (A) Schematic diagram of porous structure before crushing in the composite material (b) Enlarged schematic diagram of porous structure before crushing

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Composite 2 Porous structure 3 Resin 4 Composite material 5 Hollow particle 11 Porous structure before crushing 12 Solid part 13 Primary particle 14 Interparticle distance 15 Space part

Claims (12)

A composite material in which a porous structure is crushed by kneading the porous structure and a resin and dispersed in the resin to obtain a composite, and hollow particles are mixed and dispersed in the composite so that the specific gravity is less than the specific gravity of the resin. 2. The composite material according to claim 1, wherein the porous structure before crushing has a structure in which primary particles having a representative diameter of less than 100 nm are connected in a bead shape. The composite material according to claim 1, wherein the hollow particles are smaller than the specific gravity of the resin and have a melting point higher than that of the resin. The porous structure before crushing is a gelation step of forming a wet gel by mixing a solvent containing at least water and a gel raw material, a water removal step of removing water in the wet gel, and the water removal step The composite material according to any one of claims 1 to 3, wherein the composite material is produced from a drying step of obtaining a porous structure by removing the solvent remaining in the wet gel dehydrated in step (1). The composite material according to claim 4, wherein in the gelation step, the gel raw material is a monomer of alkoxysilane, and at least the solvent contains water, alcohol, and an alkali catalyst that promotes gelation. The composite material according to claim 4, wherein a substance that becomes a nucleus of primary particles is added to form a wet gel in the gelation step. The composite material according to claim 4, wherein in the gelation step, ultrasonic waves are irradiated to form a wet gel. The composite material according to claim 4, wherein in the gelation step, the solvent is mixed with the gel raw material, and then the mixture is cooled to form a wet gel. A hydrophobization step before the water removal step, wherein R and R ′ represent an alkyl group, x represents an integer of 1 to 3, and R _x (R′O) The critical point of the solvent contained in the wet gel in which at least part of the wet gel surface is hydrophobized using an alkylalkoxysilane represented by _4-x Si, and the drying step is hydrophobized on at least part of the surface The composite material according to claim 4, wherein the composite material is a drying step in which drying is performed under a temperature and pressure condition of less than 5. The composite material according to claim 9, wherein R and R ′ are both methyl groups and x = 2. The composite material according to claim 1, wherein the resin is a polyolefin-based resin. The composite material according to claim 1, wherein the resin is a polypropylene resin.