JP2013166851A - Polymer/silica composite and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a polymer/silica composite capable of forming a silica particle having a high filling factor inside a closed cell of the polymer/silica composite.SOLUTION: A method of producing a polymer/silica composite 40, wherein silica particles 42 are contained inside closed cells 24 of a foam 20, includes the steps of: compatibilizing a polymer having a polyester structure, silicon alkoxide and carbon dioxide together under an optional pressure condition to prepare a uniform phase 10; decompressing the uniform phase 10 to make the polymer foam for forming the foam 20 having the closed cells 24; and newly adding water to the foam 20 to hydrolyze the silicon alkoxide exuded inside the closed cells 24 to form the silica particles 42.

Description

  The present invention relates to a polymer-silica composite and a method for producing the same.

 Polymer foams (hereinafter sometimes simply referred to as foams) are used in various structural materials and functional materials for the purpose of reducing the amount of resin used, reducing weight, improving heat insulation properties, and the like. Such a foam is generally obtained by dissolving a high-pressure gas such as chlorofluorocarbon, nitrogen, carbon dioxide or the like in a polymer and then foaming it under reduced pressure or the like, or mixing and kneading a compound that generates a gas, by thermal decomposition or the like. Manufactured by a method such as foaming. Bubbles formed by foaming are generally closed cells.

Various functions can be imparted to the foam by incorporating other substances into the closed cells.
For example, in a foamed polymer-based heat insulating material such as polyurethane, the heat insulating property is improved by foaming using a fluorocarbon gas having low heat transfer properties. Since the chlorofluorocarbon gas is gradually replaced with air, the heat insulation property of the foam using the chlorofluorocarbon gas has a disadvantage that it gradually decreases.

For such a problem, a foam having inorganic ultrafine powder in closed cells has been proposed (Patent Document 1). According to the invention of Patent Document 1, the heat insulation is improved.
In addition, for example, a foam having movable particles in closed cells has been proposed (Patent Documents 2 and 3). According to the inventions of Patent Documents 2 and 3, improvement in sound insulation and vibration damping is achieved.
In Patent Document 1, a urethane foam base, a foaming agent, and inorganic powder are kneaded and foam-cured to obtain a foam structure having fine particles in closed cells. In Patent Documents 2 to 3, fine particles are included in closed cells by mixing a foaming agent, coated inorganic particles, and a polymer, followed by foaming. However, in the invention of Patent Document 1, the fine particles are not necessarily included in the closed cells but are also dispersed in the polymer matrix, and the presence state of the inorganic ultrafine powder in the closed cells is not uniform. Further, in the inventions of Patent Documents 2 to 3, it is suitable for including the inorganic particles sufficiently smaller than the bubble diameter of the closed cells in the closed cells, but the ratio of the volume of the inorganic particles to the volume of the closed cells ( It is not easy to increase the filling rate.

As a method for producing a foam containing an inorganic substance in a closed cell at a high filling rate, a step of forming a uniform phase composed of a supercritical fluid, a metal compound and a polymer, a foamed polymer in which the uniform phase is decompressed to foam the polymer Inorganic / polymer comprising the steps of: a step of phase-separating the supercritical fluid and the metal compound in the bubbles by reducing the pressure; and a step of decomposing the metal compound to fill the bubbles of the foamed polymer with the metal oxide A method for producing a composite molded body has been proposed (Patent Document 4). According to invention of patent document 4, it is a composite containing an inorganic substance, and can fill a metal oxide in the closed cell of a foam.
In addition, a step of mixing a silicon alkoxide, a polymer, and a supercritical fluid to form a uniform phase, a step of decompressing the uniform phase to foam the polymer and filling the silicon alkoxide into a foam cell, A method for producing a light-transmitting flexible heat insulating material including a step of decomposing alkoxide has been proposed (Patent Document 5). According to the invention of Patent Document 5, silica can be filled into the closed cells of the foam.

JP 63-238140 A Japanese Patent No. 2818862 JP 2006-089555 A JP 2007-332242 A JP 2008-045013 A

The foam is required to further improve various properties such as heat insulation and soundproofing. For example, in order to further enhance the heat insulation, it is preferable that silica be integrated into closed cells and included at a high filling rate in order to effectively suppress convective heat transfer. In order to improve soundproofing properties, it is preferable that the encapsulated particles are movable in closed cells.
However, in the foam manufactured by the conventional technology, silica is precipitated as fine particles in closed cells and does not become an integral particle, and the silica filling rate in closed cells is further increased. It was difficult.
Accordingly, an object of the present invention is to provide a method for producing a polymer-silica composite capable of forming silica particles having a high filling rate in closed cells.

As a result of intensive studies, the present inventors have made a polymer, silicon alkoxide, and carbon dioxide into a homogeneous phase, and when the homogeneous phase is decompressed to cause the polymer to foam, a large amount of silicon alkoxide is contained on the polymer side. After the silicon alkoxide is phase-separated from the polymer and exuded on the inner wall of the bubble, a sufficient amount of water is added to the amount of the alkoxide and hydrolyzed to form silica. It has been found that typical silica particles can be formed in closed cells. Furthermore, even if the carbon dioxide used is not necessarily in a supercritical state, it was confirmed that a three-component homogeneous mixed state may be realized.
Based on these findings, after forming a homogeneous phase of silicon alkoxide, a specific polymer and carbon dioxide under an arbitrary pressure condition, the homogeneous phase is decompressed to foam the polymer, and then the alkoxide is present in the presence of water. As a result, the production of a polymer-silica composite in which the packing rate of silica particles in closed cells was increased was completed.

That is, the method for producing a polymer-silica composite of the present invention is a method for producing a polymer-silica composite in which silica particles are included in closed cells in a foam, in which the polymer having a polyester structure, silicon alkoxide, and carbon dioxide are used. And a step of forming a homogeneous phase by decompressing the homogeneous phase to foam the polymer to form a foam having closed cells, and adding a new phase to the foam. A step of hydrolyzing the silicon alkoxide exuded into the closed cells to form the silica particles.
The polymer is preferably polylactic acid and / or polymethyl methacrylate, the silicon alkoxide preferably has a methoxysilane structure, and the silicon alkoxide is more preferably tetramethoxysilane or an oligomer thereof. .

The polymer-silica composite of the present invention is a polymer-silica composite in which silica particles are included in closed cells of a polymer foam having a polyester structure. The outer diameter of the silica particles is included in the independent bubbles included in the polymer-silica composite. It is characterized by being 50 to 100% of the bubble diameter of the bubbles.
More preferably, one silica particle is included in the closed cell.

  According to the present invention, silica particles having a high filling rate can be formed in closed cells of a polymer-silica composite.

It is process drawing explaining the manufacturing method of a polymer silica composite. 2 is a SEM photograph of the polymer-silica composite of Example 1. 2 is a SEM photograph of the polymer-silica composite of Example 1. 2 is a SEM photograph of the polymer-silica composite of Example 2. 2 is a SEM photograph of the polymer-silica composite of Example 2. 2 is a SEM photograph of the polymer-silica composite of Example 2. 4 is a SEM photograph of the polymer-silica composite of Example 3. 4 is a SEM photograph of the polymer-silica composite of Example 3. 4 is a SEM photograph of the polymer-silica composite of Reference Example 2. 4 is a SEM photograph of the polymer-silica composite of Reference Example 2.

(Polymer / silica composite)
The polymer-silica composite of the present invention has a foam having closed cells and silica particles encapsulated in the closed cells of the foam.

Although the magnitude | size of a closed cell is not specifically limited, For example, it is preferable that a closed cell with a bubble diameter of 1-100 micrometers is included. If the bubble diameter is not less than the above lower limit value, various properties of the polymer-silica composite can be enhanced, and if it is not more than the above upper limit value, the strength of the polymer-silica composite can be easily increased.
The cell diameter of the closed cell is a value measured by observing the cross section of the polymer-silica composite using a scanning electron microscope (SEM), and is the longest when the closed cell is not a true circle in the observed image. The diameter was taken as the bubble diameter.

In the foam, in addition to closed cells, open cells may be formed. However, from the viewpoint of improving various properties of the polymer-silica composite, it is preferable that many closed cells are formed.
The porosity in the foam is appropriately determined according to the use of the polymer-silica composite.

The shape of the silica particles is determined according to the shape of the closed cells containing the silica particles.
Although the magnitude | size of a silica particle is not specifically limited, For example, 0.1 micrometer or more in outer diameter is preferable, and 0.5-50 micrometers is more preferable.
The size of the silica particles relative to the size of the closed cells is appropriately determined in consideration of the use of the polymer-silica composite. For example, the outer diameter of the silica particles is 50 times the bubble size of the closed cells containing the silica particles. -100% is preferable, and 70-100% is more preferable. If it is more than the said lower limit, the filling rate of the silica particle in a closed cell will increase more, and the various characteristics of a polymer silica composite will be improved more.
The outer diameter of the silica particles is a value measured by observing the cross section of the polymer-silica composite using SEM, and when the silica particles are not true circles in the observed image, the longest diameter is taken as the outer diameter. .

 The form of the silica particles is appropriately determined in consideration of the use of the polymer / silica composite, and may be a solid structure or a hollow structure. Silica particles may be solid or gelled.

The number of silica particles included in one closed cell is not particularly limited, but is preferably one. If the number of silica particles is one, the filling rate can be further increased and various properties of the polymer-silica composite can be further increased.
One silica particle included in one closed cell means that two or more silica particles are present in the closed cell when the polymer-silica composite is observed by SEM (2000 times). Means not allowed.

 The content of silica particles in the polymer-silica composite is appropriately determined in consideration of the use of the polymer-silica composite. For example, the silica content in the polymer-silica composite is 10 to 50% by mass. If it is more than the said lower limit, various characteristics of a polymer silica composite can be improved more, and if it is below the said upper limit, the mechanical strength of a polymer silica composite can be improved more.

(Production method of polymer / silica composite)
First, the principle of the method for producing a polymer-silica composite of the present invention will be described below with reference to FIG.
A polymer, a metal compound, and carbon dioxide are appropriately selected to form a uniform phase 10 in which three components are uniformly mixed under high pressure. In the system that forms the homogeneous phase 10, by adjusting the temperature and pressure, the three components are in a uniform state, the two of the three components are mixed, the three components are separated, and so on. Can be controlled.

 When the uniform phase 10 in which the three components are uniformly mixed is decompressed, the foam 20 is formed along with the phase separation. Generally, since the affinity between silicon alkoxide, which is a metal compound, and carbon dioxide is higher than the affinity with each polymer, the two components of silicon alkoxide and carbon dioxide are first phase-separated from the polymer to form closed cells 24. Form. When the silicon alkoxide is hydrolyzed in this state, the silica component aggregates in the closed cells 24, and for example, the structure described in Patent Document 4 is obtained.

In the case where the affinity between each other is high, such as a polymer having a polyester structure (hereinafter sometimes simply referred to as a polymer) and a silicon alkoxide, the conditions for phase separation of the polymer and the silicon alkoxide are not balanced. However, the phase separation may take time due to the influence of viscosity and the like. That is, where the silicon alkoxide and carbon dioxide should be separated from the polymer, the separation of the silicon alkoxide from the polymer matrix 22 is slow, so that the silicon alkoxide gradually exudes from the inner wall of the closed cell 24 generated by the carbon dioxide separation. It becomes a state (state of reference numeral 30 in FIG. 1).
By controlling the process of hydrolyzing and polycondensing silicon alkoxide to form silica particles in closed cells 24, silica particles having different structures can be obtained. The process of hydrolyzing and polycondensing silicon alkoxide can be controlled by the amount of water added and the amount of catalyst such as acid or base added. By hydrolyzing the silicon alkoxide exuded on the inner wall of the closed cell 24 in the presence of a sufficient amount of water, silica particles grow along the inner wall of the closed cell 24. For example, an integral spherical silica The polymer-silica composite 40 in which the particles 42 are formed is obtained. Depending on the bubble diameter of the closed cells 24 and the amount of silicon alkoxide exuded, and the atmosphere of the drying step after hydrolysis, the silica particles 42 have a solid structure, a hollow structure such as a monolith or capsule, or a gel. Either structure can be adopted, and depending on the degree of shrinkage, the closed cell 24 has a relatively high filling rate.

Here, when the silicon alkoxide is rapidly hydrolyzed by using a base catalyst or the like after the closed cells 24 are formed, the silicon alkoxide is sufficiently separated from the polymer matrix 22 (reference numeral 30a in FIG. 1). To be disassembled and immobilized. Therefore, when the silicon alkoxide is rapidly hydrolyzed, the silica is dispersed in the polymer matrix 22, and the polymer-silica composite 40a having a structure in which the polymer matrix 22 is made porous is obtained.
Further, for example, in the methods described in Patent Documents 4 and 5, silicon alkoxide is hydrolyzed by water generated by polymerization of a polymer or the like. In the methods described in Patent Documents 4 and 5, since the water required for hydrolyzing the silicon alkoxide is insufficient, silica does not grow on the inner wall of the closed cell 24 and accumulates in the closed cell 24 as fine particles. To do.

The method for producing a polymer-silica composite of the present invention has been completed based on the above-described principle, and is a step in which a polymer, silicon alkoxide, and carbon dioxide are mixed under an arbitrary pressure condition to form a homogeneous phase (phase). Melting step), depressurizing the homogeneous phase to foam the polymer to form a foam having closed cells (foaming step), and adding water to the foam to exude into the closed cells And a step of hydrolyzing the silicon alkoxide to form silica particles (hydrolysis step).
Hereinafter, an example of the method for producing the polymer-silica composite of the present invention will be described.

<Compatibilization process>
The compatibility step is a step in which a polymer, silicon alkoxide, and carbon dioxide are mixed under an arbitrary pressure condition to form a uniform phase. For example, in the compatibility step, a polymer and silicon alkoxide, which have been dried in advance, are placed in a pressure-resistant container whose temperature can be adjusted at an arbitrary ratio, carbon dioxide is introduced into the pressure-resistant container, and the polymer, carbon dioxide, and silicon alkoxide are in a homogeneous phase. The pressure condition and the temperature condition for forming are included.

The polymer of the present invention has a polyester structure, has an affinity with both carbon dioxide and silicon alkoxide, and under a given pressure condition, the three components of polymer, silicon alkoxide, and carbon dioxide are in a uniform mixed state. Any dicarboxylic acid monomer such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, adipic acid, sebacic acid, ethylene glycol, propylene glycol, 1,4-butylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polypropylene glycol, polyoxytetramethylene glycol, alkylene oxide adducts of bisphenol compounds or derivatives thereof, or trimethylolpropane Copolymers with diols such as glycerin and pentaerythritol or polyhydric alcohol monomers; (Co) polymers such as lactic acid, p-hydroxybenzoic acid, and hydroxycarboxylic acids such as 2,6-hydroxynaphthoic acid; methacrylic (Co) polymers of methacrylic acid alkyl esters such as methyl acid; and mixtures thereof. Of these polymers, polymethyl methacrylate and polylactic acid are preferably used because of their good miscibility with both carbon dioxide and silicon alkoxide. Further, those obtained by mixing an elastomer such as acrylic rubber with these polymers are excellent in porosity and bubble stability, and are more preferable.
In addition, the structure of said (co) polymer is not specifically limited, Any of random polymerization, block polymerization, etc. may be sufficient. Further, the stereoregularity of the polymer may be any of isotactic, atactic, and syndiotactic.
These polymers may be used individually by 1 type, and may be used in combination of 2 or more type.

 For polymers, commonly used additives such as plasticizers, stabilizers, impact resistance improvers, flame retardants, crystal nucleating agents, lubricants, antistatic agents, surfactants, pigments, dyes, fillers, oxidation Inhibitors, processing aids, ultraviolet absorbers, antifogging agents, antibacterial agents, antifungal agents and the like may be used alone or in combination of two or more.

The form of the polymer when placed in the pressure vessel is not particularly limited, and may be a molded body or a molten state.
Examples of the method for drying the polymer include a vacuum drying method.

The silicon alkoxide of the present invention is not particularly limited as long as it has an affinity for carbon dioxide and a polymer, but one having a methoxysilane (CH ₃ OSi—) structure is preferable. As the silicon alkoxide having a methoxysilane structure, for example, tetramethoxysilane and its oligomer are preferably used. If necessary, the silicon alkoxide may contain one or more auxiliary agents for controlling the surface tension and the decomposition behavior.

 The carbon dioxide in the present invention is not limited as long as it can form a homogeneous phase with the polymer and silicon alkoxide under any pressure condition and any temperature condition. For example, the state is not limited, and may be a supercritical fluid, subcritical fluid, or gas. There may be. For example, in Patent Documents 4 and 5, carbon dioxide is supplied to the reaction apparatus as a supercritical fluid. However, the carbon dioxide of the present invention is not limited to the form in which it is supplied to the reaction apparatus. It is sufficient to be compatible with the polymer and silicon alkoxide under the following temperature conditions. Carbon dioxide may be a mixed gas with other gases such as nitrogen gas as long as it can form a homogeneous phase.

 The amount of silicon alkoxide in the homogeneous phase is determined according to various properties required for the polymer-silica composite, and for example, a molar ratio (hereinafter referred to as “silica in silicon alkoxide” / [polymer (monomer unit unit)]). , Sometimes referred to as silica / polymer ratio), preferably 0.05 to 0.7, more preferably 0.1 to 0.5. If the silica / polymer ratio is less than the above lower limit value, it is difficult to form silica particles with a high filling rate. If the silica / polymer ratio exceeds the above upper limit value, the polymer / silica composite becomes close to the properties of inorganic silica, and the strength, flexibility and toughness are impaired. There is a fear.

From the viewpoint of impregnating the polymer with a sufficient amount of silicon alkoxide, the amount of carbon dioxide in the homogeneous phase is preferably a sufficient amount with respect to the polymer as long as the foam can be maintained. The mass ratio represented by [carbon dioxide] / [polymer] (hereinafter sometimes referred to as CO ₂ / polymer ratio) is appropriately determined according to the type of polymer, and is preferably 0.01 to 2, for example, 0 0.05 to 1 is more preferable. If the CO ₂ / polymer ratio is less than the above lower limit value, the amount of carbon dioxide and silicon alkoxide impregnated into the polymer may be insufficient, and foam may not be formed. If the above upper limit value is exceeded, bubbles may break during foaming. Or the foam may be difficult to mold.

The pressure conditions in the compatibility step are conditions under which a polymer, silicon alkoxide, and carbon dioxide form a homogeneous phase. In many cases, the pressure condition for forming the homogeneous phase is the same as the condition for forming the two kinds of homogeneous phases of carbon dioxide and silicon alkoxide. Carbon dioxide and silicon alkoxide are known to form two homogeneous phases regardless of their composition at a predetermined pressure or higher. For example, tetramethoxysilane is 9 MPa at 40 ° C. or 120 ° C. Under the condition of 16 MPa, carbon dioxide and two homogeneous phases are formed.
The temperature condition in the compatibility step is preferably above the glass transition temperature of the polymer and below the decomposition temperature of the silicon alkoxide.

 The time of the compatibilizing step, that is, the time for holding at an arbitrary pressure condition is appropriately determined in consideration of the type and form of the polymer, and is preferably 1 to 48 hours, for example.

<Foaming process>
The foaming step is a step of decompressing the homogeneous phase obtained in the compatibility step to foam the polymer. Through this step, a foam having closed cells is formed. Note that immediately after the polymer is foamed, part or all of the silicon alkoxide is dispersed in the polymer matrix constituting the foam.

As the foaming step, for example, while maintaining the temperature in the pressure vessel at a temperature at which the uniform phase is maintained, the uniform phase is taken out from the pressure vessel and released into a space of any pressure condition to reduce the pressure, One that releases the pressure inside is mentioned. At this time, the mixture of the polymer and the silicon alkoxide becomes a foam having a porosity corresponding to these ratios.
The speed of depressurization can select optimum conditions for controlling the foam structure of the foam, such as the size of the closed cells and the porosity.
The foam structure depends on how much carbon dioxide and silicon alkoxide is contained within the polymer and how the contained carbon dioxide and silicon alkoxide phase separates.
For example, if the pressure is reduced (slow pressure reduction) at a slow rate of about 0.1 MPa / min, there is time for carbon dioxide and silicon alkoxide dissolved in the polymer to diffuse out of the polymer from the surface. For this reason, the amount of carbon dioxide and silicon alkoxide contained in the polymer is reduced, and the growth of the foam structure is suppressed.
On the other hand, for example, when the pressure is reduced (rapid pressure reduction) at a rapid rate of 1 MPa / min or more (that is, conditions under which diffusion of carbon dioxide and silicon alkoxide to the outside of the polymer is sufficiently suppressed), the solubility in both polymers By changing the abruptly to increase the degree of supersaturation, many fine bubbles can be formed.
For example, a foamed structure can be formed in both conditions under a reduced pressure rate of 2 MPa / min and under a reduced pressure rate of 20 MPa / min, but when the reduced pressure rate is 20 MPa / min, the solubility of carbon dioxide and silicon alkoxide rapidly increases. Decrease and increase supersaturation. For this reason, when the depressurization rate is 20 MPa / min, a structure is formed in which fine closed cells are included at a higher density than when the depressurization rate is 2 MPa / min.
By combining these rapid decompression and low-speed decompression as appropriate, for example, rapid decompression once to a pressure higher than normal pressure (atmospheric pressure), hold for a certain period of time, and then slow decompression to suppress the size of closed cells. The content of silicon alkoxide and the foam structure of the foam may be adjusted. Further, the silicon alkoxide may be hydrolyzed in parallel in the process of maintaining the pressure for a certain time.

<Hydrolysis step>
The hydrolysis step is a step in which water is newly added to the foam to hydrolyze the silicon alkoxide exuded into the closed cells. The polymer matrix of the foam contains silicon alkoxide as it is or in a partially decomposed state. In this step, silicon alkoxide is leached from the polymer matrix into closed cells, and a sufficient amount of water is exposed to this to hydrolyze the silicon alkoxide and polycondensate to form silica particles. By passing through this step, silica particles grow in the closed cells, and silica particles with a high filling rate are formed in the closed cells.

The method for hydrolyzing is not particularly limited, but in order to uniformly and uniformly hydrolyze the silicon alkoxide by adding water sufficiently and evenly to the inside of the foam, a method of exposing to a water vapor atmosphere under any temperature condition is preferable.
The temperature condition in the hydrolysis step is preferably a temperature that does not promote hydrolysis of the polymer. The temperature condition in the hydrolysis step is appropriately determined according to the type of polymer, and is preferably 20 to 50 ° C., for example.

Water newly added in the hydrolysis step (hereinafter sometimes referred to as “added water”) can contain optional components such as a catalyst for hydrolysis or condensation polymerization such as acid and base, if necessary.
However, as explained in the principle of the polymer / silica composite production method described above, the hydrolysis rate needs to be appropriate for the formation of silica particles. It may not be suitable to rapidly hydrolyze or polycondense silicon alkoxide using a catalyst or the like. For this reason, the content of the optional component in the added water is appropriately determined in consideration of the content of silicon alkoxide in the homogeneous phase, the type of polymer, the desired size of silica particles, and the like.

  The amount of added water is sufficient to hydrolyze the silicon alkoxide. For example, the molar ratio of added water to silicon alkoxide in the foam represented by [added water] / [silicon alkoxide (monomer unit unit in the case of oligomer)] (hereinafter referred to as added water / silica ratio). 4) is preferable, and 5-10 is more preferable. If the ratio of added water / silica is less than the above lower limit value, the packing rate of silica particles in closed cells may be too small, and even if the upper limit value is exceeded, the packing rate of silica particles cannot be further improved, and the polymer There is a risk of promoting the hydrolysis of.

  Although the time of a hydrolysis process is not specifically limited, For example, it is 6 to 48 hours. If the amount is less than the lower limit, the amount of silicon alkoxide that oozes out from the polymer matrix into the closed cells may be insufficient, and the filling rate of the silica particles may not be sufficiently increased. Further improvement of the filling rate of the polymer may not be achieved, and unnecessary hydrolysis of the polymer may be caused.

<Drying process>
In the method for producing a polymer-silica composite, a drying step may be provided after the hydrolysis step. By providing the drying step, it is possible to remove an excess amount that has not been used to hydrolyze the silicon alkoxide in the added water added in the hydrolysis step.
It does not specifically limit as a drying method, For example, a vacuum drying method etc. are mentioned.

According to this embodiment, a foam having closed cells can be formed by forming a homogeneous phase of polymer, silicon alkoxide, and carbon dioxide and reducing the pressure of the homogeneous phase.
In addition, according to this embodiment, silica particles having a high filling rate can be formed in the closed cells by newly adding water to the foam to hydrolyze the silicon alkoxide.

(Other embodiments)
In the above-described embodiment, the manufacturing method using the pressure vessel in the compatibility step has been described, but the present invention is not limited to this. For example, the polymer and silicon alkoxide are melt-kneaded using a kneading extrusion apparatus, carbon dioxide at an arbitrary pressure such as a supercritical fluid or a subcritical fluid is introduced into the kneading extrusion apparatus, and then once exceeds the normal pressure. After the pressure is reduced and maintained, the compatibilizing step and the foaming step may be performed by a series of operations by extruding from the kneading extruder to normal pressure.

  EXAMPLES Hereinafter, although an Example is shown and demonstrated about this invention, this invention is not limited to an Example.

(Evaluation method)
<Structural observation>
In the following examples, the structure of the polymer-silica composite was observed as follows.
The polymer-silica composite of each example was vacuum-dried, cleaved, and platinum-palladium was deposited on the cut surface by sputtering to prepare a sample. This sample was observed with SEM (S-800, manufactured by Hitachi, Ltd.). Observe at least 50 locations of the sample about the cell diameter of closed cells and the outer diameter of the silica particles, create a histogram by dividing the measured values into 0.5μm squares, and obtain the distribution and mode. It was. For the mode, the median value of the category was used as the representative value.

<Silica content>
In the following examples, the silica content was measured as follows.
The polymer-silica composite was vacuum dried to prepare a sample. This sample was heated to 500 ° C. under a nitrogen atmosphere with a thermal analyzer (TG / DTA6200, manufactured by SII Nanotechnology Co., Ltd.), and the mass of the residual component at 500 ° C. was measured. Asked.

  [Silica content (mass%)] = {[mass of residual component at 500 ° C.] / [Mass of sample before heating]} × 100 (1)

Example 1
Tetramethoxysilane 5 cm ³ (5 g) was placed in a pressure vessel (capacity 50 cm ³ ). Amorphous polylactic acid (Biopolymer 4060D, molecular weight 158,000, manufactured by Nature Works) was formed into a plate shape having a diameter of 5 mm and a thickness of 1 mm by hot pressing, and sufficiently dried in vacuum to obtain a plate polymer. Eight plate polymers (mass meter 0.18 g) were put in a pressure vessel so as not to contact with tetramethoxysilane. The mass ratio of polylactic acid: tetramethoxysilane was 1:25. After introducing high-pressure (6 MPa) carbon dioxide into the pressure vessel, it was heated to 80 ° C. and 20 MPa, and this state was maintained for 24 hours. Under these conditions, the three components were completely compatible, and a homogeneous phase was formed (compatibility process). Thereafter, the pressure was reduced to normal pressure by rapid pressure reduction (1.0 MPa / min) to foam the polymer (foaming step). Immediately after the pressure vessel reached normal pressure, the foam was taken out of the pressure vessel. Distilled water (100 cm ³ ) was placed in a sealed container (inner diameter: 80 mm), the foam was placed on a pedestal provided in the sealed container so that the foam did not directly touch the distilled water, and the sealed container was covered. Then, it left still at room temperature (25 degreeC) for 1 day, and hydrolyzed tetramethoxysilane (hydrolysis process). After tetramethoxysilane was hydrolyzed, it was vacuum dried to obtain the polymer-silica composite of this example.

SEM observation photographs of the polymer-silica composite of this example are shown in FIGS. Although the polymer-silica composite of this example partially contained large bubbles, the polymer-silica composite had closed cells having a bubble diameter of 4.0 to 13.5 μm (mode value: 9.75 μm). Further, the majority of closed cells contained spherical silica particles having an outer diameter of 3.0 to 12.0 μm (mode value: 7.75 μm). Many of these silica particles were movable in closed cells.
The silica content of the polymer-silica composite of this example was 20.4% by mass.

(Example 2)
A polymer / silica composite was obtained in the same manner as in Example 1, except that polymethyl methacrylate (PMMA, average weight molecular weight 120,000, manufactured by Sigma-Aldrich) was used instead of amorphous polylactic acid.

SEM observation photographs of the polymer-silica composite of this example are shown in FIGS. The polymer-silica composite of this example has a homogeneous foam structure in which most of the closed cells have a bubble diameter of 2.0 to 6.5 μm (mode 3.75 μm). Spherical silica particles having an outer diameter of 1.5 to 5.0 μm (mode 3.75 μm) were included. Many of these silica particles were movable in closed cells.
Some silica particles were in a crushed state (reference numeral 142 in FIG. 6). This observation suggests that the silica particles have a hollow structure. The silica content of the polymer-silica composite of this example was 15.1% by mass.

(Example 3)
A polymer-silica composite was obtained in the same manner as in Example 1 except that an acrylic resin (Acrypet IRK304, manufactured by Mitsubishi Rayon Co., Ltd.) was used instead of the amorphous polylactic acid.

 SEM observation photographs of the polymer-silica composite of this example are shown in FIGS. In the polymer-silica composite of this example, most of the closed cells are distributed in a bubble diameter of 1.0 to 9.5 μm, and bimodal having two peaks at 1.75 μm (mode) and 5.25 μm. It showed a foamed structure. The majority of closed cells contain spherical silica particles, and the outer diameters of these silica particles are distributed in the range of 0.5 to 9.5 μm. Depending on the bimodal structure of closed cells, 1.75 μm ( Mode) and 4.25 μm. Many of these silica particles were movable in closed cells. The silica content of the polymer / silica composite of this example was 22.6% by mass.

(Comparative Example 1)
A polymer-silica composite of this example was obtained in the same manner as in Example 2 except that distilled water was not newly added in the hydrolysis step. When the obtained polymer-silica composite was observed by SEM, the closed cells had a homogeneous foam structure with a cell diameter of 2.5 to 9.5 μm (mode value 6.25 μm). However, silica particles having an outer diameter that would be 50% or more of the bubble diameter were not formed in the closed cells. On the other hand, silica fine particles were deposited on the inner wall of the closed cell. The silica content of the polymer-silica composite of this example was 10.5% by mass.

(Comparative Example 2)
A polymer-silica composite of this example was obtained in the same manner as in Example 1 except that polystyrene resin (average weight molecular weight 192,000, manufactured by Aldrich) was used instead of amorphous polylactic acid. SEM observation of the polymer / silica composite of this example revealed that a heterogeneous foam structure was formed, the polymer matrix and the silica component were mixed, and a structure in which silica particles were included in closed cells was not observed. It was. The silica content of the polymer-silica composite of this example was 21% by mass.

(Comparative Example 3)
A polymer-silica composite of this example was obtained in the same manner as in Example 1 except that a low density polyethylene resin (manufactured by Aldrich) was used instead of amorphous polylactic acid. When the polymer-silica composite of this example was observed with an SEM, the number of closed cells was extremely small, and silica particles in the closed cells were not observed.

(Reference Example 1)
A polymer-silica composite of this example was obtained in the same manner as in Example 1 except that 0.1 mol / L aqueous ammonia was used instead of distilled water. When the polymer-silica composite of this example was observed by SEM, it was a structure in which silica particles having an outer diameter of 10 to 20 μm were aggregated in the polymer matrix. Further, the silica particles were composed of fine particles having an outer diameter of 10 to 30 nm. However, silica particles were not observed in the closed cells. The silica content in the polymer-silica composite of this example was 47.8% by mass.

(Reference Example 2)
A polymer / silica composite of this example was obtained in the same manner as in Example 2 except that 0.1 mol / L aqueous ammonia was used instead of distilled water.
SEM observation photographs of the polymer-silica composite of this example are shown in FIGS. The polymer-silica composite of this example had a homogeneous foam structure with a closed cell bubble diameter of 2.0 to 5.5 μm (mode: 3.75 μm), but the bubble diameter was several tens of nanometers in the polymer matrix. It was a porous structure having closed cells. In addition, in this example, no silica particles were observed in the closed cells, and silica precipitates 142a (FIG. 10) were observed in the closed cells. The silica content of the polymer-silica composite of this example was 13.6% by mass.

(Reference Example 3)
A polymer-silica composite of this example was obtained in the same manner as in Example 3 except that 0.1 mol / L aqueous ammonia was used instead of distilled water.
SEM observation of the polymer-silica composite of this example shows a porous structure that is entirely porous and includes particulate matter having an outer diameter of 0.3 nm or less. The closed cells and the silica particles inside the closed cells are clearly Not observed. The silica content of the polymer-silica composite of this example was 34.2% by mass.

From the above results, it was found that silica particles having a high filling rate can be formed in closed cells by applying the present invention.
In addition, from the results of Reference Examples 1 to 3, ammonia water is used as the additive water in the combination of polylactic acid and tetramethoxysilane, the combination of PMMA and tetramethoxysilane, and the combination of acrylic resin and tetramethoxysilane. It was found that the formation of silica particles was inhibited.

10 homogeneous phase 20 foam 24 closed cell 40 polymer-silica composite 42 silica particles

Claims (6)

In a method for producing a polymer-silica composite in which silica particles are included in closed cells in a foam,
A step in which a polymer having a polyester structure, silicon alkoxide, and carbon dioxide are mixed under an arbitrary pressure condition to form a homogeneous phase;
Decompressing the homogeneous phase to foam the polymer to form a foam having closed cells;
Adding water to the foam to hydrolyze the silicon alkoxide leached into the closed cells to form the silica particles;
A method for producing a polymer-silica composite comprising:  The method for producing a polymer-silica composite according to claim 1, wherein the polymer is polylactic acid and / or polymethyl methacrylate.  The method for producing a polymer-silica composite according to claim 1, wherein the silicon alkoxide has a methoxysilane structure.  The method for producing a polymer-silica composite according to any one of claims 1 to 3, wherein the silicon alkoxide is tetramethoxysilane or an oligomer thereof. In a polymer-silica composite in which silica particles are included in closed cells of a polymer foam having a polyester structure,
The outer diameter of the silica particles is a polymer-silica composite having 50 to 100% of the bubble diameter of the enclosed closed cells.  The polymer-silica composite according to claim 5, wherein one silica particle is included in the closed cell.