JPS6145199B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing radiation shielding materials with improved optical transparency and mechanical strength. It is known that lead acrylates or methacrylates can be polymerized at temperatures above their melting point to yield materials with transparent radiation-shielding properties, but these materials are extremely brittle and impractical in their formation, processing, and use. I can't stand it. Although it is possible to obtain materials with improved strength by mixing and polymerizing lead acrylates or methacrylates with copolymerizable monomers such as methyl methacrylate, the polymers thus obtained are At a mixing ratio where the lead content is such that it has both a somewhat satisfactory radiation shielding ability and mechanical strength, the polymer generally loses its transparency and becomes white, translucent or opaque. For example, lead methacrylate can be mixed with methyl methacrylate in any proportion at a temperature above its melting point to give a homogeneous transparent mixture, but the content of lead methacrylate at which a transparent polymer can be obtained by polymerizing this mixture is approximately 6% by weight or less and about 95% by weight or more, the former case does not have a practical radiation shielding ability, while the latter case does not have a practical mechanical strength. In order to improve the various drawbacks of the conventional materials as described above, the present inventors first proposed that at least A polymer consisting of a base monomer containing one type as an essential component and lead acrylate or lead methacrylate and the general formula (RCOO) aPb [where a is an integer equal to the valence of lead, and R is a carbon number of 5
~20 saturated or unsaturated hydrocarbon residues. ], and the proportion of lead acrylate or methacrylate in the total monomers in the polymer and the amount of the organic acid lead in the total monomers. It has been discovered that excellent results can be obtained by specifying (Japanese Patent Application No. 84617/1984). However, in this composition, a certain degree of decrease in mechanical strength is inevitable as the lead content increases. The present invention has been made to improve the above drawbacks, and by replacing a part of the base monomer with the polyfunctional monomer and/or described below, mechanical strength and optical transparency are significantly improved. This made it possible to obtain a material with excellent radiation shielding ability. That is, the radiation shielding material according to the present invention has (A)
(a) at least one essential monomer selected from the group consisting of alkyl methacrylates having 1 to 4 alkyl carbon atoms, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, and styrene; and (b) 8 to 75% by weight based on the base monomer. general formula for (However, in the formula, R ₁ is H or CH ₃ , A is alkylene having 2 to 4 carbon atoms, and n is an integer of 2 to 60.) (However, in the formula, R ₂ is H or CH ₃ , B is a saturated or unsaturated hydrocarbon residue having 4 to 25 carbon atoms, and m is an integer of 2 to 4.) The proportion x weight % of the base monomer consisting of a base monomer and (B) a monomer mixture consisting of lead acrylate or lead methacrylate in the monomer mixture of lead acrylate or lead methacrylate and the general formula (RCOO) aPb (However, in the formula, a is an integer equal to the valence of lead, and R is a saturated or unsaturated hydrocarbon residue having 5 to 20 carbon atoms.) It can be obtained by carrying out polymerization in the presence of a radical polymerization initiator and in the coexistence of the organic acid lead such that the ratio y parts by weight to 100 parts by weight of the polymer mixture satisfies the following general formula: 200≧y≧2 (however, 9≦x≦30) () 200≧y≧2/5(x-30)+2 (however, 30≦x≦75) () In the present invention, the organic acid lead is It was unexpected that the transparency of the material would be maintained to a high degree when the material coexists within such a limited range as described above. Although its mechanism of action is not necessarily clear, it is extremely meaningful industrially and medically to produce a material that has practical radiation shielding ability, is mechanically strong, and has excellent transparency. . Further, the organic acid lead is
The essential monomer of (A)(a), the base monomer of (A)(b), and
Rather than blending the monomer mixture consisting of lead acrylate or methacrylate in (B) into a polymer obtained by polymerizing, the organic acid lead is mixed into the monomer mixture, and in the coexistence, the monomer Particularly excellent effects can be obtained by polymerizing a mixture of substances. The alkyl methacrylate used in the present invention has an alkyl group having 1 to 4 carbon atoms, such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, tert- Examples include butyl methacrylate, but methyl methacrylate is particularly preferred. Hydroxyalkyl acrylates and methacrylates have or do not have substituents, and preferred examples include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate,
3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 2-hydroxy-3-chloropropyl acrylate, 2-hydroxy-3
-Chloropropyl methacrylate, etc. Note that it is also included in the embodiment of the present invention to replace a part of the essential monomers with other copolymerizable monomers within a range that does not adversely affect the effects achieved by the present invention. Examples of such comonomers include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, vinyl acetate, vinyl chloride, acrylonitrile, methacrylonitrile, and the like. The polyfunctional monomer having the general formula and/or is preferably 8 to 75% by weight based on the total amount of the base monomer consisting of the monomer and the essential monomer (including the substituent). is 12-60% by weight.
In other words, if it is less than 8% by weight, there is no significant effect on improving mechanical strength, while if it exceeds 75% by weight, there is no longer an effect of improving strength according to the content, and in some cases, the transparency may be reduced. This results in an adverse effect on physical properties such as a decrease in carbon and a decrease in machinability. n in the monomer having the general formula is an integer of 2 to 60, preferably an integer of 3 to 30.
When n exceeds 60, there is little or no strength improvement effect. Examples include polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, and polybutylene glycol dimethacrylate. B in the monomer having the general formula has 4 carbon atoms
~25, preferably 4 to 15 saturated or unsaturated hydrocarbon residues, and m is an integer of 2 to 4, preferably 2. That is, if the number of carbon atoms in B is 3 or less, the effect of increasing mechanical strength is low, while even if the number of carbon atoms exceeds 25, the effect of increasing strength is low and the transparency is adversely affected. Representative examples include 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,3-butanediol diacrylate,
1,3-butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tetramethylolmethanetetraacrylate, tetramethylolmethanetetramethacrylate, 1,12-dodecanediol diacrylate, 1,12-dodecanediol dimethacrylate , neopentyl glycol dimethacrylate, etc. In organic acid lead with the general formula (RCOO) aPb, a is an integer equal to the valence of lead, usually 2
is an integer of ˜4, and R is a saturated or unsaturated hydrocarbon residue having 5 to 20 carbon atoms, preferably an aliphatic hydrocarbon group. That is, when the number of carbon atoms in R is 4 or less or 21 or more, the transparency and/or mechanical strength of the resulting composition will be unsatisfactory, and the object of the present invention cannot be fully achieved. Typical examples of organic lead acids include lead decanoate, lead octoate, lead 9-hexadecenoate, lead hexoate, lead linoleate, lead naphthenate, lead octylbenzoate, and the like. In the polymer composed of the base monomer and lead acrylate or methacrylate, if the content of lead acrylate or methacrylate is less than 9% by weight, it does not have a practical radiation shielding effect. If the amount exceeds 75% by weight, the effect of the present invention described above, that is, the effect of improving mechanical strength by using the polyfunctional monomer and/or as a constituent component of the base monomer will be little or no. unacceptable. According to the present invention, the proportion of lead acrylate or methacrylate in the total monomer consisting of the base monomer containing the polyfunctional monomer in the proportion described above and lead acrylate or methacrylate is x
By allowing the organic acid lead to coexist so that y parts by weight, which is the amount by weight of the organic acid lead based on 100 parts by weight of the total monomer, satisfies either the above formula or It is possible to obtain a transparent and strong radiation shielding material whose constituent component is the above polymer containing 9 to 75% by weight of lead acrylate or methacrylate, which has been impossible to produce. When the content of lead acrylate or methacrylate in the material according to the present invention is relatively small,
Although the coexistence of the organic acid lead reduces the content of lead in the material derived from lead acrylate or methacrylate, it is compensated for by the lead derived from the organic acid lead, resulting in a practical radiation shielding ability. You won't lose it. If the amount of the organic acid lead is less than the lower limit of the formula, the resulting material is generally not transparent but white, translucent or opaque, or non-uniform. Furthermore, even if a large amount of organic acid lead is used, the transparency of the material will not be improved beyond a certain limit, the mechanical strength of the material will be reduced, and the bleed phenomenon will be exceeded. The amount is preferably 100 parts by weight or less, preferably 100 parts by weight or less. The radiation shielding material according to the present invention can be produced by any method as long as the polymer composition consisting of the polymer containing lead acrylate or methacrylate and the base monomer and the organic acid lead is obtained as a result. However, for example, as described above, the monomer components and organic acid lead are mixed in a predetermined ratio, heated if necessary to make a uniform liquid, and then mixed in a mold or extruded in the presence of a physical polymerization initiator. It is convenient to carry out the polymerization in-machine. The reaction is usually -10 to +
It is carried out at a temperature of 150°C, preferably 40-130°C. The radical polymerization initiator is usually 0.001 to 5% by weight, preferably 0.02 to 1.0% by weight based on the total monomers used.
used. Representative examples include lauroyl peroxide, t-butyl peroxyisopropyl carbonate, benzoyl peroxide, dicumyl peroxide, t-butyl peroxy acetate, t-butyl peroxybenzoade, and di-t-butyl peroxide. , azobisisobutyronitrile, etc. Next, the present invention will be explained in more detail by giving Examples and Comparative Examples. Examples 1 to 7 and Comparative Examples 1 to 7 The components shown in Table 1 were mixed and dissolved by heating, and then the entire mixture was mixed as a radical weight initiator.
0.1 part by weight of t-butylperoxyisopropyl carbonate per 100 parts by weight was added and dissolved. The liquid thus obtained was injected into a cell assembled using two glass plates and a vinyl chloride resin gasket, heated to 70°C for 5 hours in a nitrogen atmosphere, and then heated to 120°C for 5 hours. Polymerization was carried out for 1 hour at temperature. After the polymerization was completed, the cell was disassembled and the transparent plate was taken out.

【table】

[Table] Table 2 shows the properties of the casting plate material thus obtained. In addition, in the same table, the total light transmittance is
Measurements were made in accordance with ASTMD1003, and in-situ shock strength was measured in accordance with DIN53453 (without notches).

【table】

【table】

Claims (1)

[Scope of Claims] 1 (A) (a) at least one essential monomer selected from the group consisting of alkyl methacrylates having 1 to 4 alkyl carbon atoms, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, and styrene; and (b) ) General formula of 8 to 75% by weight per base monomer (However, in the formula, R ₁ is H or CH ₃ , A is alkylene having 2 to 4 carbon atoms, and n is an integer of 2 to 60.) (However, in the formula, R ₂ is H or CH ₃ , B is a saturated or unsaturated hydrocarbon residue having 4 to 25 carbon atoms, and m is an integer of 2 to 4.) and (B) a monomer mixture consisting of lead acrylate or lead methacrylate, the ratio of the lead acrylate or lead methacrylate in the monomer mixture x weight %, and (C)
General formula (RCOO) aPb (wherein, a is an integer equal to the valence of lead, and R is a carbon number of 5 to
20 saturated or unsaturated hydrocarbon residues. ) The monomer mixture of organic acid lead represented by 100
The organic acid lead is present in the presence of a radical polymerization initiator in an amount of 0.001 to 5% by weight based on the monomer mixture so that the ratio y parts by weight to parts by weight satisfies either the following general formula or Let me -10~+
A method for producing a radiation shielding material characterized by polymerizing at a temperature of 150°C. 200≧y≧2 (however, 9≦X≦30) () 200≧y≧2/5 (X-30)+2 (however, 30≦X≦75) ()