JP6957538B2 - A method for producing a liquid silicone elastomer composition for a radiation shielding material, a method for producing a liquid silicone elastomer composition for a radiation shielding material, and a radiation shielding silicone rubber molded product. - Google Patents

Description

The present invention relates to a liquid silicone elastomer composition for a radiation shielding material containing organopolysiloxane as a main component and filled with tungsten powder, a method for producing the same, and a radiation shielding silicone rubber molded product obtained by curing the composition.

In the work of handling radioactive substances or in the environment where radiation is present, radiation shielding materials are used for the purpose of preventing radiation exposure to the human body. As conventional radiation shielding materials, metal plates such as lead and iron, and structural materials such as mortar and concrete are used, but when a certain level of radiation shielding efficiency is required, all of them are thick, heavy, and hard. Was there.

Of these, lead is known to have the highest radiation shielding efficiency, and because it is relatively soft as a metal, it is used in protective aprons (attached with lead plates) used by engineers who handle medical radiation, and in nuclear facilities. It is used as a lead wool mat (filament-like metallic lead woven fabric) used for local shielding. However, since lead is toxic to the human body, there is a concern that it may cause health hazards to workers.

Iron is a widely used metal that is cheap and safe for the human body, but its radiation shielding efficiency is not so high, so if you try to replace lead, you will need several times the thickness, such as windows and It is not very practical except for shielding the openings of buildings such as doors and shielding vehicles.

Mortar, concrete, etc. have a great radiation shielding effect if a certain thickness is secured, but due to their nature, they cannot be used practically except for nuclear facilities such as reactor containment vessels and nuclear fuel storage.

Therefore, there has been an increasing demand for materials that are safe for the human body, inexpensive, and flexible like rubber. It is known that when a rubber material is filled with a high-density substance, it becomes a radiation-shielding rubber. Further, Patent Document 2 discloses a technique relating to a radiation shielding material in which butyl rubber and polyisobutylene rubber are filled with tungsten powder.

Further, Patent Document 3 describes a technique relating to an addition-curable liquid silicone rubber composition composed of a vinyl group-containing polyorganosiloxane, polyorganohydrogensiloxane, tungsten powder, and a platinum catalyst, and a γ-ray shielding material obtained by curing the composition. It is disclosed.

Japanese Patent No. 4686538 Japanese Unexamined Patent Publication No. 2013-242270 Special Fair 7-66073 Gazette

Patent Document 3 is a curable liquid silicone elastomer composition containing a large amount of tungsten powder (highly filled), and is a silica powder generally used in silicone rubber compositions in order to increase the filling rate of the tungsten powder. It is characterized by not using a reinforcing filler such as. However, if the reinforcing filler is not used, the mechanical strength of the cured product will decrease. Therefore, instead of the reinforcing filler, R ₃ SiO _1/2 unit and SiO ₂ unit (R is an aliphatic in the formula). A solid resin-like vinyl group-containing silicone polymer composed of a monovalent hydrocarbon group containing no unsaturated bond and a group selected from vinyl groups) was blended as an essential component. As a result, the viscosity of the composition containing the vinyl group-containing silicone polymer can be kept lower than that of the composition containing a reinforcing filler such as silica powder, and when molding the cured product, the viscosity can be suppressed. It is said that it is easy to handle.

However, when the composition has a low viscosity, when ^{a tungsten powder having a density of more than 19 g / cm 3} as a simple substance is highly filled in the addition-curable liquid silicone elastomer composition, sedimentation separation of the tungsten powder may occur during storage. I am concerned. Since it is difficult to redisperse the precipitated tungsten powder by stirring or the like, there is an increasing demand for a composition that suppresses the precipitation of the tungsten powder and improves the storage stability.

In view of these points, an object of the present invention is to provide a liquid silicone elastomer composition for a radiation shielding material in which precipitation of tungsten powder is suppressed.

In order to achieve the above problems, the present invention
(A) 100 parts by mass of an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule,
(B) Organohydrogenpolysiloxane containing three or more hydrogen atoms bonded to silicon atoms on average in one molecule (per alkenyl group bonded to silicon atoms in the composition, bonded to the silicon atoms in the composition The number of hydrogen atoms is 0.5 to 5.0),
(C) Surface-treated reinforcing silica fine powder 10 to 100 parts by mass,
Provided are a liquid silicone elastomer composition for a radiation shielding material, which contains (D) 1,000 to 3,000 parts by mass of tungsten powder and (E) a catalytic amount of a hydrosilylation reaction catalyst.

If it is such a material, a liquid silicone elastomer composition for a radiation shielding material in which the precipitation of the tungsten powder is suppressed can be obtained.

At this time, _{a solid consisting of (F) R 3} SiO _1/2 unit and SiO ₂ unit (in the formula, R indicates a group selected from a monovalent hydrocarbon group and a vinyl group that do not contain an aliphatic unsaturated bond). It is preferably one that does not contain a resinous vinyl group-containing silicone polymer.

The elastomer composition of the present invention can impart sufficient mechanical strength without containing such a solid resin-like vinyl group-containing silicone polymer.

Further, it is preferable that the component (C) is surface-treated with hexamethyldisilazane.

With such a material, it is possible to impart an appropriate viscosity to the composition while preventing the tungsten powder from settling.

Further, it is preferable that the viscosity at 23 ° C. is 100 Pa · s or more and less than 1,000 Pa · s.

With such a viscosity, there is no concern that the tungsten powder will settle, and there is no possibility that the fluidity will deteriorate.

Further, it is preferable that the cured product obtained by curing the liquid silicone elastomer composition for a radiation shielding material has a density of 6.0 g / cm ^{3 or more at 23 ° C.}

If it is such a thing, a more sufficient radiation shielding effect can be obtained.

Further, in the present invention, in the above method for producing a liquid silicone elastomer composition for a radiation shielding material, the component (C) is used as the component (A), the untreated reinforcing silica fine powder, and the component (G). (H) Provided is a method for producing a liquid silicone elastomer composition for a radiation shielding material obtained by heat-treating a surface treatment agent while kneading it.

The component (C) used in the liquid silicone elastomer composition for a radiation shielding material of the present invention can also be obtained by such a method.

At this time, it is preferable that the component (H) is hexamethyldisilazane.

With such a material, it is possible to impart an appropriate viscosity to the composition while preventing the tungsten powder from settling.

Furthermore, the present invention provides a radiation-shielding silicone rubber molded product comprising a cured product of the above-mentioned liquid silicone elastomer composition for a radiation-shielding material.

At this time, it can be in the form of a sheet.

Such a material is a radiation shielding material that is safe for the human body, inexpensive, and flexible like rubber.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to obtain a radiation-shielding silicone rubber sheet capable of achieving the same radiation-shielding ability with a relatively thin thickness without using a metal lead plate having high radiation-shielding ability but fearing toxicity. Since it is made of rubber, it is softer than a metal lead plate, has flexibility and elongation, and is suitable for application to, for example, radiation protective equipment for the human body. Further, the liquid silicone elastomer composition for a radiation shielding material before curing is excellent in moldability because it has good flowability while preventing the highly filled tungsten powder from settling due to its appropriate viscosity. Therefore, a molded product having an arbitrary shape having radiation shielding performance can be easily obtained.

As described above, there has been a demand for the development of a liquid silicone elastomer composition for a radiation shielding material that suppresses the precipitation of tungsten powder.

As a result of diligent studies to achieve the above object, the present inventors have imparted appropriate viscosity to the composition by blending a sufficiently surface-treated reinforcing silica fine powder, and suppresses sedimentation of the tungsten powder. In addition, it is easy to handle as a liquid elastomer, and the mechanical strength is improved without necessarily blending a solid resin-like vinyl group-containing silicone polymer consisting of _{1/2 unit of R 3} SiO and 2 units of SiO as reinforcing components. A liquid silicone elastomer composition for a radiation shielding material can be obtained, and a cured product of a liquid silicone elastomer composition containing a specified amount of sufficiently surface-treated reinforcing silica fine powder and tungsten powder has a constant radiation shielding ability. We have found that we can exert the above, and have reached the present invention.

That is, the present invention
(A) 100 parts by mass of an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule,
(B) Organohydrogenpolysiloxane containing three or more hydrogen atoms bonded to silicon atoms on average in one molecule (per alkenyl group bonded to silicon atoms in the composition, bonded to the silicon atoms in the composition The number of hydrogen atoms is 0.5 to 5.0),
(C) Surface-treated reinforcing silica fine powder 10 to 100 parts by mass,
(D) Tungsten powder A liquid silicone elastomer composition for a radiation shielding material containing 1,000 to 3,000 parts by mass and (E) a catalytic amount of a hydrosilylation reaction catalyst.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

The organopolysiloxane of the component (A) of the liquid silicone elastomer composition for a radiation shielding material of the present invention contains an alkenyl group bonded to at least two silicon atoms in one molecule, and is usually a hydrosilylation-curable type. It is a known one used as a base polymer of liquid silicone rubber. Generally, for example, it is represented by the following average composition formula (Chemical formula I).

（式中、Ｒ１は炭素数１〜６の置換又は非置換の一価炭化水素基で、具体例としてはメチル基、エチル基、プロピル基、ブチル基、ペンチル基、ヘキシル基等のアルキル基、ビニル基、アリル基、ブテニル基、ペンテニル基、ヘキセニル基等のアルケニル基、シクロヘキシル基、シクロヘキセニル基、フェニル基などの非置換一価炭化水素基、３，３，３−トリフルオロプロピル基、シアノメチル基等の上記一価炭化水素基の水素原子の少なくとも一部がハロゲン原子やシアノ基で置換された置換アルキル基（置換一価炭化水素基）である。複数の置換基は異なっていても同一であってもよいが、分子中にアルケニル基を二個以上含んでいることが必要である。また、ａは１．９５〜２．０５の範囲の数である。）

(In the formula, R1 is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, and specific examples thereof include an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group and a hexyl group. Alkenyl group such as vinyl group, allyl group, butenyl group, pentenyl group, hexenyl group, unsubstituted monovalent hydrocarbon group such as cyclohexyl group, cyclohexenyl group, phenyl group, 3,3,3-trifluoropropyl group, cyanomethyl A substituted alkyl group (substituted monovalent hydrocarbon group) in which at least a part of the hydrogen atom of the above monovalent hydrocarbon group such as a group is substituted with a halogen atom or a cyano group. A plurality of substituents are the same even if they are different. However, it is necessary that the molecule contains two or more alkenyl groups, and a is a number in the range of 1.95 to 2.05.)

The organopolysiloxane of the component (A) may be linear or branched. Preferably, the main chain consists _{of repeating R1 2} SiO units, and a linear organopolysiloxane having both ends of the molecular chain _{sealed in R1 3} SiO units is exemplified, and the substituent bonded to the silicon atom is a methyl group. , The phenyl group is preferable, the average degree of polymerization is 100 to 1,000, and the viscosity at 23 ° C. is preferably 200 to 100,000 mPa · s. Further, the alkenyl group bonded to the silicon atom, which must be contained in two or more in one molecule, is preferably a vinyl group, which may be at the end of the molecular chain or the side chain, but at both ends. Those containing two are preferable.

The organohydrogenpolysiloxane as a component (B) of the liquid silicone elastomer composition for a radiation shielding material of the present invention contains hydrogen atoms bonded to at least three or more silicon atoms on average in one molecule, and is described below. Conventionally known organohydrogenpolysiloxane represented by the average composition formula (Chemical Formula II) can be applied.

（式中、Ｒ２は炭素数１〜６の置換又は非置換の一価炭化水素基で、具体例としてはメチル基、エチル基、プロピル基、ブチル基、ペンチル基、ヘキシル基等のアルキル基、シクロヘキシル基、シクロヘキセニル基、フェニル基などの非置換一価炭化水素基、３，３，３−トリフルオロプロピル基、シアノメチル基等の上記一価炭化水素基の水素原子の少なくとも一部がハロゲン原子やシアノ基で置換された置換アルキル基（置換一価炭化水素基）である。ｂは０．７〜２．１、ｃは０．１８〜１．０、かつｂ＋ｃは０．８〜３．０、好ましくはｂは０．８〜２．０、ｃは０．２〜１．０、かつｂ＋ｃは１．０〜２．５を満足する正数で示される。）

(In the formula, R2 is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, and specific examples thereof include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group and hexyl group. At least a part of hydrogen atoms of the above monovalent hydrocarbon groups such as unsubstituted monovalent hydrocarbon groups such as cyclohexyl group, cyclohexenyl group and phenyl group, 3,3,3-trifluoropropyl group and cyanomethyl group are halogen atoms. Or a substituted alkyl group substituted with a cyano group (substituted monovalent hydrocarbon group). B is 0.7 to 2.1, c is 0.18 to 1.0, and b + c is 0.8 to 3. 0, preferably b is indicated by a positive number satisfying 0.8 to 2.0, c is indicated by 0.2 to 1.0, and b + c is indicated by a positive number satisfying 1.0 to 2.5.)

The molecular structure of the organohydrogenpolysiloxane may be linear, cyclic, branched, or three-dimensional network. In this case, the number of silicon atoms (or the degree of polymerization) in one molecule is 2 to 300, and particularly 4 to 200, which are liquid at room temperature, are preferably used. The hydrogen atom bonded to the silicon atom may be at the end of the molecular chain, at the side chain, or at both of them.

Specifically, as the component (B), both-terminal trimethylsiloxy group-blocking methylhydrogenpolysiloxane, both-terminal trimethylsiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer, and both-terminal dimethylhydrogensiloxy group-blocking dimethyl Polysiloxane, dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer at both ends, trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane copolymer at both ends, trimethylsiloxy group-blocked methylhydrogensiloxane at both ends Diphenylsiloxane / dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane / dimethylsiloxane copolymer, cyclic methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, (CH ₃ ) ₂ HSiO _{1 A} copolymer consisting of _{2 units and 4/2} units of SiO, a _{copolymer consisting of 1/2} unit of _{(CH 3} ) ₂ HSiO, _4/2 units of SiO and _3/2 units of _{(C 6} H _{5) SiO} And so on.

The blending amount of the component (B) is an alkenyl group bonded to a silicon atom in the composition in order to impart appropriate rubber properties, that is, strength, elongation and hardness to the cured product of the liquid silicone elastomer composition for radiation shielding material. The number of hydrogen atoms bonded to silicon atoms in the composition is 0.5 to 5.0 per piece. Below this range, the strength is weak, the hardness is soft, and the cured product has surface adhesiveness, and above this range, the cured product becomes hard and brittle.

As the surface-treated reinforcing silica fine powder of the component (C) of the liquid silicone elastomer composition for a radiation shielding material of the present invention, a powder having a treatment agent applied to the surface may be used in advance. Even if it is obtained by heat treatment while kneading the reinforcing silica fine powder whose surface as the component (G) is untreated, the organopolysiloxane of the component (A), and the surface treatment agent of the component (H). good. The type of these reinforcing silica fine powders is not particularly limited as long as they are used as a reinforcing agent for ordinary silicone rubber, and fumed silica or precipitated silica ^{having a specific surface area of 50 to 400 m 2 / g.} Is preferably used. These may be used alone or in combination of two or more.

The blending amount of the component (C) is 10 to 100 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A), but if it is less than 10 parts by mass, the liquid silicone elastomer composition for a radiation shielding material is obtained. The viscosity to be imparted is insufficient, the tungsten powder will settle, and the mechanical strength of the cured product when this is cured will be insufficient. On the other hand, if it exceeds 100 parts by mass, the amount of tungsten powder that can be filled decreases, so that a certain radiation shielding ability cannot be exhibited. It is preferably in the range of 30 to 60 parts by mass, and both imparting appropriate viscosity and reinforcing for mechanical strength are compatible.

As a method of heat-treating the untreated reinforcing silica fine powder of the component (G), the organopolysiloxane of the component (A), and the surface treatment agent of the component (H) while kneading, for example, in a kneading apparatus (A). A predetermined amount of water for hydrolyzing the component, the (H) component, and the (H) component was charged, and the mixture was kneaded while gradually adding the (G) component, and the predetermined amount of the (G) component was added. By the way, this is achieved by continuing kneading for 2 to 6 hours while heating to 120 to 180 ° C.

Examples of the surface treatment agent for the component (H) include silazanes such as hexamethyldisilazane and 1,3-divinyl-1,1,3,3-tetramethyldisilazane, and silanols such as trimethylsilanol and vinyldimethylsilanol. , Trimethylmethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, vinyltrimethoxysilane and other alkoxysilanes are exemplified. Even if the silica fine powder having the treatment agent applied to the surface in the powder state in advance is heat-treated while kneading the organopolysiloxane of the component (A) and the surface treatment agent of the component (H). There is no problem.

The tungsten powder of the component (D) of the liquid silicone elastomer composition for radiation shielding material of the present invention may have any shape such as spherical, crushed, and scaly, but for high filling in the liquid silicone elastomer composition, Spherical is preferable, and the surface of the particles may or may not be surface-treated. The average particle size is preferably 1 to 100 μm, and more preferably 2 to 10 μm. It is also possible to mix and use two or more types of tungsten powder having different average particle sizes for the purpose of fine packing.

The blending amount of the component (D) is 1,000 to 3,000 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A), but if it is less than 1,000 parts by mass, a constant radiation shielding ability is obtained. Not reachable. On the other hand, if it exceeds 3,000 parts by mass, the composition loses fluidity and it becomes difficult to mold the cured product. It is preferably in the range of 1,500 to 2,000 parts by mass, and has both radiation shielding property and good moldability.

The method for filling the liquid silicone elastomer composition of the tungsten powder of the component (D) is as follows, for example, a predetermined amount of the liquid silicone elastomer composition is charged into a planetary mixer or the like in which the stirring blade revolves while rotating, and the component (D) is added thereto. It may be mixed by stirring while gradually adding. After the predetermined amount of the component (D) has been added, a heat treatment or a vacuum defoaming step can be added if necessary.

As the hydrosilylation reaction catalyst of the component (E) of the liquid silicone elastomer composition for radiation shielding material of the present invention, known ones can be applied, for example, platinum black, second platinum chloride, platinum chloride acid, and platinum chloride acid. Examples thereof include a reaction product with a valent alcohol, a complex of platinum chloride acid and olefins, a platinum-based catalyst such as platinum bisacetoacetate, a palladium-based catalyst, and a rhodium-based catalyst. The blending amount of this hydrosilylation reaction catalyst can be a catalytic amount, and is usually 0.5 to 1,000 ppm, preferably 1 with respect to the total amount of the liquid silicone elastomer composition for a radiation shielding material as a platinum group metal. It is about 200 ppm.

A hydrosilylation reaction retarder may be added to the liquid silicone elastomer composition for a radiation shielding material of the present invention in order to secure the pot life. These include 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3,5-triallyl-1,3,5-triazine-2,4,6. Examples include polyfunctional alkenyl compounds such as-(1H, 3H, 5H) -trione (triallyl isocyanurate), acetylene alcohol derivatives such as 1-ethynylcyclohexanol and 3,5-dimethyl-1-hexin-3-ol. Will be done.

Further, in the liquid silicone elastomer composition for a radiation shielding material of the present invention, one molecule of organopolysiloxane containing an alkenyl group bonded to less than two silicon atoms in one molecule and one molecule of hydrogen atom bonded to a silicon atom. Organohydrogenpolysiloxane containing less than 3 on average, organopolysiloxane containing no alkenyl group bonded to silicon atom and hydrogen atom bonded to silicon atom, various silane coupling agents, titanium-based, zirconium-based, etc. A condensation catalyst or the like may be blended. Further, dyes, pigments, mold release agents, antistatic agents, diluents, thixophilic imparting agents and the like can be blended. Each of these optional components may be used alone or in combination of two or more.

The liquid silicone elastomer composition for a radiation shielding material of the present invention has a viscosity at 23 ° C. of 100 Pa · s or more and 1,000 Pa · s in order to achieve both suppression of sedimentation of highly filled tungsten powder and fluidity during molding. It is preferably less than s. If the viscosity is 100 Pa · s or more, there is no concern that the tungsten powder will settle, and if the viscosity is 1,000 Pa · s or less, the fluidity will deteriorate and molding will not be difficult. A more preferable viscosity is 200 to 500 pa · s.

Further, the liquid silicone elastomer composition for a radiation shielding material of the present invention preferably has a density of 6.0 g / cm ³ or more of a cured product obtained by curing the cured product at 23 ° C. In a cured product having a density of 6.0 g / cm ³ or more, the radiation transmittance when four cured product sheets having a thickness of 5 mm are stacked (20 mm) is less than 20%, that is, the radiation shielding performance is 80% or more. Sufficient effect can be obtained. A more preferable density is 7.0 g / cm ³ or more.

Further, in the present invention, in the above-mentioned method for producing a liquid silicone elastomer composition for a radiation shielding material, the component (C) is the component (A), the component (G) untreated reinforcing silica fine powder, and (H). ) Provided is a method for producing a liquid silicone elastomer composition for a radiation shielding material obtained by heat-treating a surface treatment agent while kneading it. At this time, the component (H) can be hexamethyldisilazane.

Specifically, as a method for obtaining such a component (C), a method similar to the method exemplified in the description of the component (C) can be used.

Furthermore, the present invention provides a radiation-shielding silicone rubber molded product comprising a cured product of the above-mentioned liquid silicone elastomer composition for a radiation-shielding material. At this time, the rubber molded product can be in the form of a sheet.

The liquid silicone elastomer composition for a radiation shielding material of the present invention can be used as a radiation shielding material by molding and curing the liquid silicone elastomer composition. As a molding method, a normal liquid elastomer molding method such as compression molding, extrusion molding, injection molding, transfer molding, calendar molding, etc., a casting method, a coating method, etc. are also possible, and it is sufficient to select from these. , Compression molding and calendar molding are preferable. The curing conditions may be the same as those of a normal addition-curable liquid silicone elastomer, but the curing time tends to be longer in room temperature curing and low temperature curing below 80 ° C. Since the pot life for this is shortened, it is preferable to heat-cure at 80 ° C. or higher.

A molded product obtained by curing the liquid silicone elastomer composition for a radiation shielding material of the present invention can also be obtained in the same manner as ordinary silicone rubber. For example, if a mold is created from a prototype and compression molding is performed, a molded product having the same shape as the prototype can be obtained, and if calendar molding is performed so as to have a constant thickness, a sheet-shaped molded product can be obtained.

If you want to shield the part from radiation, you can fix the part in a container, cast the liquid silicone elastomer composition for radiation shielding material of the present invention into the container, and cure the part while it is buried. A method of coating the liquid silicone elastomer composition for a radiation shielding material of the present invention so as to provide a radiation shielding layer on the surface of the component and curing the liquid silicone elastomer composition is conceivable.

The molded product obtained by curing the liquid silicone elastomer composition for radiation shielding material of the present invention can be used in medical settings as a protective device from X-rays for X-ray photography and therapeutic radiation, and can be used in nuclear power plants and nuclear energy. It can be expected to be applied as various radiation shielding materials in related research facilities and space development facilities such as artificial satellites and spacecraft. In these applications, a plate-shaped or sheet-shaped radiation shielding material having a certain thickness is cut and bonded to be processed, but it is difficult to cut and bond with a metal lead plate. On the other hand, the radiation-shielding silicone rubber sheet according to the present invention is easy to cut with a cutting tool, and if a silicone-based adhesive is used, the sheets can be bonded to each other, which is also useful for processing a radiation-shielding material.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Manufacturing Example 1]
80 parts by mass of dimethylvinylsiloxy group-blocked dimethylpolysiloxane (A-1) having a viscosity of 1,000 mPa · s at 23 ° C. was charged into a kneader mixer and stirred, and surface-treated ^{with a specific surface area of 200 m 2 / g.} 40 parts by mass of fumed silica (C-1, trade name: NSX-200, manufactured by Nippon Aerosil Co., Ltd.) was gradually added and uniformly mixed, the temperature was raised to 160 ° C., and the mixture was heated and mixed for 4 hours. Then, after cooling to 40 ° C., 20 parts by mass of (A-1) was added and further uniformly mixed to produce a base compound-1.

[Manufacturing Example 2]
Hydrolyze 80 parts by mass of both-terminal dimethylvinylsiloxy group-blocking dimethylpolysiloxane (A-2) having a viscosity at 23 ° C. of 10,000 mPa · s, 10 parts by mass of hexamethyldisilazane (H), and (H). 3 parts by mass of water (I) for use was charged into a kneader mixer, stirred and mixed, and 30 mass of untreated fumed silica (G, trade name: A-200, manufactured by Nippon Aerosil) ^{with a specific surface area of 200 m 2 / g.} The portions were gradually added and uniformly mixed, the temperature was raised to 160 ° C., and the mixture was heated and mixed for 4 hr. Then, when cooled to 40 ° C., 20 parts by mass of both-terminal dimethylvinylsiloxy group-blocking dimethylpolysiloxane (A-3) having a viscosity of 400 mPa · s was added and further uniformly mixed to produce a base compound-2.

[Manufacturing Example 3]
80 parts by mass of both-terminal dimethylvinylsiloxy group-blocked dimethylpolysiloxane (A-1) having a viscosity of 1,000 mPa · s at 23 ° C. and 2 parts by mass of hexamethyldisilazane (H) were charged into a kneader mixer and mixed by stirring. Then, 15 parts by mass of surface-treated fumed silica (C-1) having a specific surface area of 200 m ² / g and 30 parts by mass of amorphous sedimentation silica (C-2, trade name: Toxil USF, manufactured by Oriental Silicas). Was gradually added and uniformly mixed, the temperature was raised to 160 ° C., and the mixture was heated and mixed for 4 hr. Then, after cooling to 40 ° C., 20 parts by mass of (A-1) was added and further uniformly mixed to produce Base Compound-3.

[Examples 1 to 4, Comparative Examples 1 to 3]
Table 1 shows the formulations of the compositions used in Examples 1 to 4 and Comparative Examples 1 to 3. These compositions were uniformly stirred and mixed with a planetary mixer, mixed, defoamed under reduced pressure, and the viscosity was measured.

The raw materials listed in Table 1 are shown below. In Table 1, A1 to A3, C-1, C-2, G, H, and I were designated as base compound-1 in Example 1 and Comparative Examples 1 and 2, and base compound-in Examples 2 and 3. As No. 2, in Example 4, it was blended as base compound-3.

(Base Compound-1 to 3) The base compound (A-1) produced in Production Examples 1 to 3 at 23 ° C. with a viscosity of 1,000 mPa · s at both ends dimethylvinylsiloxy group-blocking dimethylpolysiloxane (B-1). Dimethylhydrogensiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer having a viscosity at 23 ° C. of 40 mPa · s and a SiH group content of 0.0015 mol / g (number of SiH groups per molecule: 3)
(B-2) Bi-terminal trimethylsiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer having a viscosity at 23 ° C. of 100 mPa · s and a SiH group content of 0.0055 mol / g (SiH group number per molecule: 16) Pieces)
(B-3) Didimethylhydrogensiloxy group-blocking polydimethylsiloxane at both ends with a viscosity of 20 mPa · s at 23 ° C. and a SiH group content of 0.0013 mol / g (number of SiH groups per molecule: 2)
(D) Tungsten powder: Average particle size 6.0 μm (trade name: WD1-60, manufactured by Toshiba Materials Co., Ltd.)
(E) Hydrosilylation reaction catalyst: (A-1) solution of Pt-1,1-divinyl-1,1,3,3-tetramethyldisiloxane complex (Pt concentration 1 wt%)
(F) R _{3 A solid resin-like solid resin consisting of 1/2} unit of SiO and ₂ units of SiO (in the formula, R indicates a group selected from a monovalent hydrocarbon group and a vinyl group containing no aliphatic unsaturated bond). Vinyl group-containing silicone polymer: VMQ
(J) Reaction retarder: Ethynylcyclohexanol (K) Diluent (viscosity adjuster): Both-terminal trimethylsiloxy group-blocking dimethylpolysiloxane having a viscosity of 30 mPa · s at 23 ° C.

Further, a cured product sheet having a thickness of 2 mm was prepared in the following manner, and the rubber properties were measured. A polyethylene terephthalate (PET) liner and a frame having a thickness of 2 mm are laminated on a press plate, each composition is filled in the frame, and a PET liner and a press plate are further laminated on the frame, and the temperature is 120 ° C. for 10 minutes. Press molded. The cured product together with the PET liner was taken out from between the two press plates, and the PET liner was peeled off to obtain a silicone elastomer sheet having a thickness of 2 mm. For these, the rubber hardness, tensile strength, elongation at the time of cutting were measured by JIS-K6249, and the densities were further measured by the water substitution method at 23 ° C. The results are shown in Table 1.

The radiation shielding rate was evaluated for a cesium-137 (Cs137) radiation source (3 to 28 μSv). Using a radiation measuring device NaI scintillation type survey meter (TSC-172B), 10 cured product sheets having a thickness of 2 mm were stacked, and the radiation shielding rate at a thickness of 20 mm was measured. The results are shown in Table 1.

Further, in order to evaluate the storage stability (precipitation of the tungsten powder) of each composition, a non-curable composition excluding the hydrosilylation reaction catalyst of the component (E) was prepared separately from the above, and each of these was prepared in an amount of 50 ml. It was filled in a transparent glass vial, sealed, and left at room temperature for 3 months. After that, the transparent glass vial was observed, and when tungsten was settled and a liquid phase of a colorless and transparent siloxane component was confirmed in the upper layer, it was judged that the storage stability was unacceptable. The results are shown in Table 1.

In Examples 1 to 4 using the liquid silicone elastomer composition for a radiation shielding material of the present invention, good storage stability was obtained and a high radiation shielding rate was exhibited.

On the other hand, in Comparative Example 1, since the content of the tungsten powder was small, a sufficient radiation shielding rate could not be obtained. In Comparative Example 2, the content of the tungsten powder was too high, so that the fluidity was lost. Further, in Comparative Example 3, since a solid resin-like vinyl group-containing silicone polymer was used instead of the surface-treated reinforcing silica fine powder, tungsten settled and good storage stability could not be obtained. ..

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

Claims (9)

(A) 100 parts by mass of an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule,
(B) Organohydrogenpolysiloxane containing three or more hydrogen atoms bonded to silicon atoms on average in one molecule (per alkenyl group bonded to silicon atoms in the composition, bonded to the silicon atoms in the composition The number of hydrogen atoms is 0.5 to 5.0),
(C) Surface-treated reinforcing silica fine powder 10 to 100 parts by mass,
A liquid silicone elastomer composition for a radiation shielding material, which contains (D) 1,000 to 3,000 parts by mass of tungsten powder and (E) a catalytic amount of a hydrosilylation reaction catalyst. (F) R _{3 A solid resin-like solid resin consisting of 1/2} unit of SiO and ₂ units of SiO (in the formula, R indicates a group selected from a monovalent hydrocarbon group and a vinyl group containing no aliphatic unsaturated bond). The liquid silicone elastomer composition for a radiation shielding material according to claim 1, which does not contain a vinyl group-containing silicone polymer. The liquid silicone elastomer composition for a radiation shielding material according to claim 1 or 2, wherein the component (C) is surface-treated with hexamethyldisilazane. The liquid silicone elastomer composition for a radiation shielding material according to any one of claims 1 to 3, wherein the viscosity at 23 ° C. is 100 Pa · s or more and less than 1,000 Pa · s. thing. Any one of claims 1 to 4, wherein the cured product obtained by curing the liquid silicone elastomer composition for a radiation shielding material has a density of 6.0 g / cm ^{3 or more at 23 ° C.} The liquid silicone elastomer composition for a radiation shielding material according to the section. The method for producing a liquid silicone elastomer composition for a radiation shielding material according to any one of claims 1 to 5.
The radiation shielding component (C) is obtained by heat-treating the component (A), the untreated reinforcing silica fine powder, and the surface treatment agent (H) while kneading them. A method for producing a liquid silicone elastomer composition for materials. The method for producing a liquid silicone elastomer composition for a radiation shielding material according to claim 6, wherein the component (H) is hexamethyldisilazane. A radiation-shielding silicone rubber molded product comprising a cured product of the liquid silicone elastomer composition for a radiation-shielding material according to any one of claims 1 to 5. The radiation-shielding silicone rubber molded product according to claim 8, wherein the product is in the form of a sheet.