JP2000230073A - Porous silica/rubber composite material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composite material excellent in heat insulation properties and mechanical properties by drying a product of gelation of a silicon alkoxide or its derivative and a rubber having reactive organic functional groups. SOLUTION: The rubber having reactive organic functional groups is desirably an epoxidized natural rubber, an epoxidized styrene/butadiene/styrene block copolymer, a carboxylated nitrile rubber, a carboxylated polybutadiene, an acrylic rubber, or a derivative thereof. The silicon alkoxide or the derivative thereof is desirably tetramethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-phenyl-γ- aminopropyltrimethoxysilane, or the like. The composite material is desirably one prepared by mixing 30-99 pts.wt. silicon alkoxide or derivative thereof with 1-70 pts.wt. rubber having reactive organic functional groups or one having a bulk density of 0.01-0.5 g/cm3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous silica / rubber composite material that can be used as a heat insulating material and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, plastic foam has been widely used as a heat insulating / cooling material, a sound absorbing material, a cushioning material, and the like, mainly in a temperature range below room temperature. The plastic foam has advantages such as high flexibility, light weight, good workability, no dust generation, and high impact resistance as compared with the inorganic porous body. However, when the plastic foam has a closed-cell structure, the overall thermal conductivity can be reduced by filling the gas with a low thermal conductivity in the bubbles.
In this case, the gas to be used is mostly specific CFCs or alternative CFCs, and the use thereof is regulated or is likely to be regulated in the future. In addition, since these gases penetrate and diffuse through the foam membrane in the long term, there is also a problem that the thermal conductivity is inevitably deteriorated with time. On the other hand, when the plastic foam has an open-cell structure, such a problem does not occur because the gas is air, but the pores formed by foaming are as large as several μm to several mm, and are accompanied by the flow of air. Heat transfer occurs and the thermal conductivity of the entire foam increases.

On the other hand, in recent years, a material called aerogel has been developed as a new type of heat insulating material. Airgel is a method of hydrolyzing, polymerizing, or the like a metal alkoxide or halide, or an organic compound to form an alcogel, and replacing the organic phase in the alcogel with a solvent such as alcohol or carbon dioxide gas. A substance obtained by extracting a solvent in a supercritical state and being a porous body having an aggregate of fine particles as a skeleton.
Airgel production methods were described in the early 1930s by S.A. S.
It was first reported in Nature by Kistler. Kistler produced aerogels by adding hydrochloric acid to an aqueous solution of sodium silicate to cause gelation, washing this with water and alcohol, and removing the alcohol in a supercritical state. This method took several weeks to manufacture, but in the early 1960s S.M. J. Teshne et al. Reported a method for producing an alcogel by hydrolyzing tetramethoxysilane, and the production time was greatly reduced. Then A. J. Hunt et al. Reported a method using tetraethoxysilane instead of toxic tetramethoxysilane, and a method using carbon dioxide gas instead of explosive alcohol during supercritical drying. This airgel is known as a new heat insulating material having characteristics such as thermal conductivity similar to that of plastic foam, light weight, nonflammability, no generation of dust, and light transmissivity.

[0004]

However, aerogels have problems such as brittleness, poor workability, and high manufacturing cost, and have not been widely used. Airgel is brittle because the porosity is as high as 90% or more and the solid content is low, the bond of -O-Si-O- that forms the skeleton of the aerogel is amorphous and relatively weak, and -O-Si Because the -O- bond has a three-dimensional structure, the lattice is strongly restrained and the flexibility is low.

The present invention has been made in view of the above circumstances, and has as its object to provide a porous silica-rubber composite material having not only a high heat insulating effect but also excellent mechanical properties. .

[0006]

In order to achieve the above-mentioned object, the present invention provides a method of drying a gel of a silicon alkoxide or a derivative thereof and a rubber having a reactive organic functional group. A porous silica-rubber composite material is provided. Further, the present invention provides a method for producing a porous silica-rubber composite material, comprising gelling a silicon alkoxide or a derivative thereof and a rubber having a reactive organic functional group dissolved in an organic solvent, and drying the gel. I will provide a.

[0007] The porous silica-rubber composite material is obtained by combining a flexible modified rubber in a silica skeleton, has the same heat insulation performance as aerogel, and is much more effective than aerogel due to the action of rubber. It has excellent mechanical properties, especially flexibility, and excellent workability.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The porous silica-rubber composite material of the present invention uses a silicon alkoxide or a derivative thereof and a rubber having a reactive organic functional group (hereinafter simply referred to as “rubber”) as starting materials. As the silicon alkoxide, the general formula Si (OR ¹ )
₄ (R ¹ is an alkyl group), and its derivatives are represented by the general formula R
² Si (OR ¹ ) ₃ or R ² R ³ Si (OR ¹ ) ₂ or R ² R ³ R ⁴ SiOR
¹ (R ² , R ³ , and R ⁴ each independently represent an alkyl group, vinyl group, epoxy group, amino group, acrylic group, methacryloxy group, chloropropyl group, mercapto group, isocyanate group, halogen atom, etc.) Can be suitably used. Specific examples of the compound represented by the above general formula include, for example, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-n-butylsilane, and polymers thereof, and derivatives thereof include vinyltrimethoxysilane, Vinyltriethoxysilane, vinyltris (β-methoxyethoxy)
Silane, β- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxy Propyltriethoxysilane,
γ-methacryloxypropylmethyldimethoxysilane,
γ-methacryloxypropylmethyldiethoxysilane, N
-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxy Examples include silane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-isocyanatopropyltriethoxysilane, and the like. Also,
These silicon alkoxides and derivatives thereof are used after being diluted with a hydrophilic organic solvent. As the hydrophilic organic solvent used at that time, alcohols such as methanol, ethanol, propanol and butanol, tetrahydrofuran, dioxane and the like are preferable.

On the other hand, the rubber used in the present invention has a reactivity with the above-mentioned alkoxide of silicon. For example, natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber , Acrylic rubber, ethylene propylene rubber, urethane rubber, fluoro rubber, chlorosulfonated polyethylene, epichlorohydrin rubber,
And polysulfide rubbers and their derivatives. In particular, epoxidized natural rubber, epoxidized styrene-butadiene-
Styrene block copolymers, carboxylated nitrile rubber, carboxylated polybutadiene, acrylic rubber and derivatives thereof are preferred.

In producing the porous silica / rubber composite material of the present invention, first, a rubber dissolved in an organic solvent is added to a diluted solution of an alkoxide of silicon or a derivative thereof, and water is added to hydrolyze. At this time, a catalyst is added as necessary to promote the chemical reaction of hydrolysis. Both basic and acidic catalysts can be used as the catalyst. Examples of the basic catalyst include ammonia, sodium hydroxide, potassium hydroxide, and salts thereof with a weak acid, and examples of the acidic catalyst include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and salts of these with a weak alkali.

The amount of each component is arbitrary and not particularly limited, but silicon alkoxide or a derivative thereof is 30 to 99 wt%,
Rubber is preferably about 1 to 70% by weight. The amount of the organic solvent is preferably diluted so that the total amount of the silicon alkoxide or its derivative and the rubber is about 1 to 40% by weight of the total mixture. The amount of water is preferably not less than the theoretical amount required for hydrolysis. When a catalyst is used, the amount is preferably 1/10000 to 1/10 of the amount of silicon alkoxide or its derivative.

The above hydrolysis reaction produces a wet gel. The gel thus formed is dipped in an organic solvent, aged, dried, and dried to obtain the porous silica of the present invention.
A rubber composite is obtained. As a drying method, methods such as supercritical drying, vacuum freeze drying, vacuum drying, hot air drying, high frequency drying, and natural drying are possible. However, in the present invention,
The wet gel is composed of a flexible rubber in the skeleton of silica, and the rubber absorbs strain such as shrinkage during drying, and has a characteristic that cracks are unlikely to occur. It is not necessary to perform drying, and a favorable porous body can be obtained by freeze vacuum drying or natural drying. These drying methods are very simple and inexpensive methods that do not use a pressure vessel for high pressure unlike supercritical drying, and can greatly reduce the manufacturing cost.

In the above series of production methods, the skeleton formed by the silica and rubber formed differs depending on the combination of the alkoxy group or organic functional group of the alkoxide of silicon or its derivative and the organic functional group of the rubber. The following is a typical example. For example, when the organic functional group of the silicon alkoxide derivative is an isocyanate group and the rubber is an epoxy-modified natural rubber, it is considered that a skeleton is formed by the following reaction.

[0014]

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When the organic functional group of the silicon alkoxide derivative is an epoxy group and the rubber is a carboxyl-modified NBR group,

[0016]

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A skeleton is formed by the above reaction. The porous silica / rubber composite thus obtained is considered to have a skeleton formed by chemically bonding silica and rubber, and the rubber component in the skeleton imparts flexibility to the porous body. Can be In addition, since the diameter of the pores is very small, from several nm to several hundreds of nm, the circulation of air hardly occurs, and the accompanying heat transfer is suppressed. Further, since the bulk density is as small as 0.01 to 0.5 g / cm ³ , the solid portion is small, and the heat conduction through this portion is also suppressed. As described above, the porous silica / rubber composite material according to the present invention is a new material having high flexibility and good workability that has solved the problems of plastic foam and airgel.

[0018]

The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereto. (Example 1) Epoxy-modified natural rubber (Maraysian Rubber)
To 2.0 g of “Epoxyprene 50” manufactured by Producer's Research Association U.K.), 38.0 g of 1,4-dioxane was added, and the mixture was stirred well and dissolved. To this solution was added γ-isocyanatopropyltriethoxysilane (“A-13
10 ”) 4.0 g and 50.6 g of 1,4-dioxane were added and stirred well. To this, 2.7 g each of aqueous ammonia (2.0 mol / l) and aqueous ammonium fluoride (0.2 mol / l) were added dropwise, and after further stirring, the mixture was allowed to stand in a 50 ° C. atmosphere to gel. The completed wet gel was removed from the container, immersed in 1,4-dioxane, and cured at 50 ° C. After dehydration so that the moisture in the wet gel was 2 wt% or less, the sample was frozen in a freezer at -30 ° C. Place the frozen sample in a vacuum dryer,
While heating to 5 ° C, 1,4-dioxane was sublimated to obtain a porous silica / rubber composite. The porous silica-rubber composite material thus manufactured is a flexible material having fine pores, a bulk density of 0.07 g / cm ³ , and a thermal conductivity (measured by a flat plate comparison method) of 0.028 W / mK. Met.

(Examples 2 to 4, Comparative Example 1) Tables 1 to 4 show examples 2 to 4 in which the types and amounts of the silicon alkoxide derivative and the rubber were changed in the same manner as in Example 1. Also,
The same table as Comparative Example 1 shows a case where the device was manufactured without containing an alkoxide derivative of silicon.

[0020]

[Table 1]

Example 5 38.0 g of tetrahydrofuran was added to 2.0 g of carboxyl-modified NBR (“Nipol 1072” manufactured by Zeon Corporation) and dissolved by stirring well. In addition, γ-
5.0 g of glycidoxypropyltrimethoxysilane (“KBM 403” manufactured by Shin-Etsu Silicone) and 46.6 g of tetrahydrofuran
g was added and stirred well. Add ammonia water (2.0
mol / l) and aqueous ammonium fluoride (0.2 mol / l) for 10.
After 2 g of the mixture was added dropwise and further stirred, the mixture was left standing in a 50 ° C. atmosphere to gel. The completed wet gel was removed from the container, immersed in tetrahydrofuran and cured at 50 ° C. After dehydrating the moisture in the wet gel to 2 wt% or less,
The sample was placed in a critical point dryer and the device was sealed. Then, by introducing the CO ₂ therein is pressurized liquefied tetrahydrofuran was discharged by diffusing into CO ₂ with CO ₂ to a critical point drier outside. After the discharge was completed, the critical point dryer was sealed, heated and pressurized, so that the temperature and pressure became equal to or higher than the CO ₂ critical point. Thereafter, the pressure was lowered and the temperature was lowered, and after returning to normal pressure and normal temperature, the dried gel was taken out to obtain a porous silica / rubber composite material. The porous silica / rubber composite material thus produced is a flexible material having fine pores and a bulk density of 0.08.
g / cm ³ and thermal conductivity (measured by a flat plate comparison method) were 0.028 W / mK.

(Examples 6 to 8, Comparative Example 2) Tables 2 and 3 show examples 6 to 8 in which the types and amounts of the silicon alkoxide derivative and the rubber were changed in the same manner as in Example 5. Also,
The case where no silicon alkoxide derivative is contained is shown in the same table as Comparative Example 2.

[0023]

[Table 2]

Example 9 19.0 g of 1,4-dioxane was added to 1.0 g of ethylene acrylic rubber ("Esprene 2752" manufactured by Sumitomo Chemical Co., Ltd.), and the mixture was stirred well and dissolved. to this,
Γ-isocyanatopropyltriethoxysilane (“A-1310” manufactured by Nippon Unicar) 4.0 as an alkoxide derivative
g, and 2.0 g of tetraethoxysilane (“Ethylsilicate 28” manufactured by Colcoat) as an alkoxide, 69.8 g of 1,4-dioxane were added and stirred well. Aqueous ammonia (2.0 mol / l) and ammonium fluoride (0.2 mol / l)
After 2.1 g of each of (1) and (2) was added dropwise and further stirred, the mixture was allowed to stand in a 50 ° C. atmosphere to gel. The completed wet gel was removed from the container, immersed in 1,4-dioxane, and cured at 50 ° C. After dehydrating the wet gel to a water content of 2 wt% or less, the sample was taken out of the solution and allowed to stand at atmospheric pressure for 1,
4-Dioxane was vaporized to obtain a porous silica-rubber composite. The porous silica / rubber composite material thus produced is a flexible material having fine pores and a bulk density of 0.12.
g / cm ³ , and thermal conductivity (measured by a flat plate comparison method) was 0.032 W / mK.

(Examples 10 to 12, Comparative Example 3) Example 9
Table 3 shows Examples 10 to 12 in which the types and amounts of the alkoxide derivative of silicon and the rubber were changed in the same manner as described above. In addition, a case where no silicon alkoxide derivative is used is shown in the same table as Comparative Example 3.

[0026]

[Table 3]

The porous silica / rubber composite material of each embodiment is as follows:
Both have flexibility and low thermal conductivity.

[0028]

As described above, the porous silica / rubber composite material of the present invention is a composite of a flexible rubber in a silica skeleton and has the same heat insulation performance as airgel. , It has much better mechanical properties than airgel, especially flexibility, and has excellent workability,
For example, good workability can be obtained when a heat insulating material is used.

Continuation of the front page F term (reference) 4F074 AA06 AA08 AA09 AA12 AA13 AA14 AA25 AA26 AA30 AA38 AA48 AA76 AA78 AA87 AD17 CB34 CC06X CC29Y CC46 DA02 DA32 4J002 AC011 AC031 AC061 AC071 AC081 AC091 EB BB EB 001 EX076 GL00

Claims (7)

[Claims] An alkoxide of silicon or a derivative thereof,
A porous silica-rubber composite material obtained by drying a gelled product with a rubber having a reactive organic functional group. 2. A rubber having a reactive organic functional group is a natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber, acrylic rubber, ethylene propylene rubber, urethane rubber, fluorine rubber, The porous silica / rubber composite according to claim 1, wherein the porous silica / rubber composite is selected from chlorosulfonated polyethylene, epichlorohydrin rubber, polysulfide rubber, and derivatives thereof. 3. The rubber having a reactive organic functional group is an epoxidized natural rubber, an epoxidized styrene-butadiene-styrene block copolymer, a carboxylated nitrile rubber,
The porous silica / rubber composite according to claim 1, wherein the composite is selected from carboxylated polybutadiene, acrylic rubber and derivatives thereof. 4. An alkoxide of silicon or a derivative thereof,
Tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-n-butylsilane and their polymers, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β (amino Ethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-
Aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane and γ-
The porous silica / rubber composite according to any one of claims 1 to 3, wherein the porous silica / rubber composite is selected from isocyanatepropyltriethoxysilane. 5. An alkoxide of silicon or a derivative thereof.
The porous silica / rubber composite material according to any one of claims 1 to 4, wherein 1 to 70 parts by weight of a rubber having a reactive organic functional group is added to 99 parts by weight. 6. The porous silica / rubber composite according to claim 1, wherein the bulk density is 0.01 to 0.5 g / cm ³ . 7. An alkoxide of silicon or a derivative thereof,
Porous silica characterized by gelling a rubber with reactive organic functional groups dissolved in an organic solvent and drying.
Manufacturing method of rubber composite.