JP2006077197A - Radiation protective synthetic resin paste composition and radiation protective gloves - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radiation protective synthetic resin paste composition that contains a tungsten powder having no undesirable influence on the human body, where the tungsten powder is hard to settle out, and also that is suitable for forming a thin-wall formed article by dip forming with a simple process, and to provide radiation protective gloves which have good fit-feeling and handiness. <P>SOLUTION: The radiation protective synthetic resin paste composition contains 100 pts.wt. of a synthetic resin paste and 200-300 pts.wt. of the tungsten powder having an average particle diameter of 15-30 μm, with the thixotropic index being adjusted to 0.15-0.25. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radiation protective synthetic resin paste composition suitable for forming a thin film molded article such as a radiation protective glove.

  Workers in an environment that is exposed to radiation, such as X-ray engineers, should wear protective clothing and gloves that shield the radiation in order to minimize the exposure. As such protective gloves, those containing lead that shields radiation are known. However, lead is not preferable because it is toxic to the human body, and there is a problem that the mounting feeling and workability are poor because the thickness is necessary to sufficiently shield radiation.

  On the other hand, a glove containing tungsten powder instead of lead has been devised (for example, see Patent Document 1). The glove is molded from a composition obtained by adding tungsten powder to natural rubber or synthetic rubber latex. However, the specific gravity of tungsten powder is extremely high, so that there is a problem that the tungsten powder settles if the latex is left for a predetermined time. In order to uniformly disperse the tungsten powder in the latex during the molding process, the latex is constantly stirred by a stirring blade or a circulation mechanism. However, for example, a new equipment investment is required to provide a stirring blade and a circulation mechanism in the submerged layer, and there is a problem that the manufacturing cost increases.

  On the other hand, in order to maintain the suspension state of tungsten powder in natural rubber latex or resin emulsion without the need for equipment as described above, the viscosity of rubber latex or resin emulsion is increased using a thickener or the like. Is disclosed (for example, see Patent Document 2). Specifically, it is disclosed that 20 vol% or more of tungsten powder having an average particle size of 0.4 to 5.0 μm is contained in rubber latex or resin emulsion, and the viscosity is 80 cp or more.

U.S. Pat. No. 5,001,354 Japanese Patent Laid-Open No. 2001-124892

  Generally, a vulcanization accelerator is used for film formation of natural rubber latex, but the vulcanization accelerator may cause rough skin and allergies, and for film formation of natural rubber latex and resin emulsion, A process of forming an adhesive layer on the matrix and a process of removing the adhesive remaining after film formation are required. Compared to immersion molding using synthetic resin pastes such as vinyl chloride resin and acrylic resin Man-hours are high and manufacturing costs are high.

  Further, in Patent Document 2, tungsten powder having an average particle size of 0.4 to 5.0 μm is added in an amount of 20% by volume or more based on natural rubber latex or resin emulsion. Generally, as apparent from the stokes equation. In addition, as the average particle size of the tungsten powder is smaller, the settling rate is slower. Therefore, it is preferable that the average particle size is small in order to make the tungsten powder uniformly dispersed.

  On the other hand, as shown in Table 1, even if the tungsten powder has the same weight, the smaller the average particle diameter, the larger the apparent volume FV, and the volume TV decreases by tapping. This means that the smaller the average particle size, the larger the void volume between the particles relative to the total volume. In Patent Document 2 and the like, tungsten powder is specified and added in volume% to natural rubber latex or resin emulsion. However, the apparent volume FV differs depending on the particle size, and also before and after tapping. Even if tungsten powder is added at a constant volume%, the added weight is not always constant. Therefore, even when a certain volume% of tungsten powder is contained in natural rubber latex or resin emulsion, the weight of tungsten powder per unit area of film formation is constant depending on conditions such as the average particle diameter of tungsten powder and the presence or absence of tapping. Therefore, the radiation transmittance or shielding rate of the molded gloves or the like is not constant, and the quality of radiation protection becomes unstable.

  Also, when adding a certain weight of tungsten powder, it is easy to disperse uniformly if the average particle size is small, but the apparent volume increases and the viscosity of the radiation protective synthetic resin paste composition increases, so A molded product with a thin film cannot be molded by the molding method. For example, if the thickness of a glove increases, a feeling of wearing and workability will worsen. On the other hand, if the average particle size is large, the apparent volume is small and the viscosity does not increase so much, but there is a problem that it tends to settle as described above. Here, if the viscosity of the composition is increased by a thickener, there is a problem that the film of the molded product is also thickened.

  The present invention has been made in view of such a problem, and contains tungsten powder that does not adversely affect the human body, the tungsten powder is difficult to settle, the processing process is simple, and a thin film molded product is formed by a dip molding method. An object is to provide a suitable radiation protective synthetic resin paste composition, and a radiation protective glove having good wearing feeling and workability.

  The radiation-protective synthetic resin paste composition according to the present invention contains 200 to 300 parts by weight of tungsten powder having an average particle size of 15 to 30 μm with respect to 100 parts by weight of the synthetic resin paste, and has a thixotropic index of 0.15 to 0. .25 was prepared.

  In the radiation protective synthetic resin paste composition, the present invention is characterized in that the synthetic resin paste is a vinyl chloride resin paste or an acrylic resin paste.

  Further, the present invention is characterized in that the radiation protective synthetic resin paste composition is formed by a dip molding method.

  The present invention also provides that the radiation-protective synthetic resin paste composition includes a long-chain active hydrogen compound having acrylic acid groups at both ends, and a synthetic resin obtained by polymerizing the long-chain active hydrogen compound and the synthetic resin paste. Are polymer blended.

  The thin film molded article according to the present invention is characterized in that it is formed into a film of 0.4 to 0.6 mm by a dip molding method using the radiation protective synthetic resin paste composition.

  The radiation protective glove according to the present invention is formed by a dip molding method using the radiation protective synthetic resin paste composition.

  According to the radiation-protective synthetic resin paste composition of the present invention, the average particle size of 200 to 300 parts by weight of tungsten powder with respect to 100 parts by weight of the synthetic resin paste is included, and the thixotropic index is 0.15. Since it adjusted to -0.25, it can be set as the viscosity suitable for shape | molding the thin film molded article of desired thickness while suppressing sedimentation of tungsten powder. In addition, by using tungsten powder having a large average particle size, the apparent volume can be reduced to suppress increase in the viscosity of the radiation protective synthetic resin paste composition, and the addition amount of tungsten powder can be set to a weight part within a predetermined range. By doing so, the radiation shielding performance of the thin film molded article is stabilized. In particular, it is suitable when a thin film molded article such as a radiation protective glove having a film thickness of 0.4 to 0.6 mm is formed from the present radiation protective synthetic resin paste composition by a dip molding method. Also, a thin film molded article having excellent flexibility and tensile strength is obtained by polymer blending an acrylic resin with a long-chain active hydrogen compound having an acrylic acid group at both ends into a radiation protective synthetic resin paste composition. Particularly useful in radiation protective gloves.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Synthetic resin paste]
The synthetic resin paste according to the present invention is a vinyl chloride resin or an acrylic resin paste such as acrylic acid, acrylic acid ester, methacrylic acid, and methacrylic acid ester. Particularly, the vinyl chloride resin paste has strength and workability, This is preferable from the viewpoint of cost. The synthetic resin paste is appropriately added with a plasticizer, a stabilizer, a thickener, etc., but thin film molding such as gloves formed from a radiation protective synthetic resin paste composition containing tungsten powder by a dip molding method. In order to improve the flexibility of the product, increasing the amount of plasticizer is a common technique. However, if the amount of the plasticizer is increased, the tensile strength of the film is lowered. Therefore, it is a contradictory issue to improve both the flexibility and the tensile strength only by adjusting the plasticizer.

Therefore, various plasticizers are added to make the vinyl chloride resin paste suitable for forming thin film molded products by the dip molding method, and long-chain activity having acrylic acid groups at both ends is added to the paste. Add the hydrogen compound. Thereby, a polymer blend of a vinyl chloride resin and an acrylic resin is performed, and the strength and elasticity of the thin film molded product are improved. As the long-chain active hydrogen compound, polyoxypropylene glycol, polyoxyethylene glycol, and polyoxytetramethylene glycol are suitable, and these can be polymerized by heat or an AZO-based or organic oxide-based polymerization initiator. The long chain active hydrogen compound is preferably contained in an amount of 15 to 20 parts by weight based on 100 parts by weight of the vinyl chloride resin paste resin, and the polymerization initiator is 0.5 to 5 parts by weight based on the long chain active hydrogen compound. 1.0 part by weight is contained.

[Tungsten powder]
The present inventor added a tungsten powder having an average particle diameter considered useful from known literature to a vinyl chloride resin paste at a predetermined volume%, and formed a thin film molded product by a known immersion molding method to increase the radiation transmittance. Tested. The results are shown in Table 2. In addition, the measurement of the transmittance | permeability of a radiation uses the industrial portable X-ray generator (Toshiba: EX-260GH-3) as an X-ray generator, tube voltage is set to 80 kV, and the X-ray which permeate | transmitted the thin film molded article is used. Measurement was performed with an X-ray dosimeter (VICTOREN: Model 500, ProbeModel 550-3-T: S / N: 105). As a result, it was found that even when tungsten powder was added at 20% by volume or more with respect to the vinyl chloride resin paste, the radiation transmittance was high and a sufficient shielding effect could not be obtained. On the other hand, the inventor pays attention to the average particle diameter and weight ratio of tungsten powder, and even if the volume% is the same, the weight ratio increases and the transmittance decreases as the average particle diameter increases. Newly found.

  From the above-mentioned knowledge, the present inventor uses a tungsten powder having an average particle size far exceeding the average particle size that has been conventionally useful, and adds the amount specified by the weight ratio to the synthetic resin paste. It was found that a radiation-protective synthetic resin paste composition that stably exhibits the radiation shielding rate and suitable for molding a thin-film molded product can be obtained. That is, the tungsten powder used in the present invention has an average particle size of 15 to 30 μm. If the average particle size is less than 15 μm, the apparent volume with respect to the weight is large, and if the necessary weight is added to the synthetic resin paste, the viscosity increases, and a thin film molded product is formed by a dip molding method, or a fiber is formed by spread molding. It becomes difficult to apply a thin coating. On the other hand, if the average particle size is larger than 30 μm, the radiation-protective synthetic resin paste composition has to have a high viscosity in order to prevent sedimentation, and is unsuitable for molding a thin film molded product by a dip molding method. . In addition, if the surface of the molded product has irregularities and is a glove, there is a problem that the feeling of wearing becomes worse. In addition, the measuring method of an average particle diameter is based on FSSS. In the present invention, the tungsten powder is contained in an amount of 200 to 300 parts by weight, particularly preferably 240 to 260 parts by weight, based on 100 parts by weight of the synthetic resin paste. If the content is less than 200 parts by weight, the weight of tungsten per unit area of the formed film is reduced. For example, the radiation transmittance is 0.3 or less (the shielding rate is 70% or more), and particularly preferably 0.8. It is difficult to make it 2 or less (80% or more), and if it exceeds 300 parts by weight, the viscosity of the radiation protective synthetic resin paste composition increases. It becomes difficult to apply a thin coating to a fiber or the like.

[Thixotropic properties]
Increasing the average particle size of the tungsten powder makes it easier for the tungsten powder to settle, but if the viscosity of the radiation protective synthetic resin paste composition is increased, the film of the thin film molded product formed by the dip molding method becomes thicker. Realizing both of these is a contradictory issue. Here, the radiation protective synthetic resin paste composition is a mixture of various substances, and its flow characteristics are extremely complicated as compared with a Newtonian fluid such as water. In general, a polymer fluid or the like is considered to be a non-Newtonian fluid, and is considered to approximate a Bingham fluid that generates a flow only when a shear stress exceeds a certain yield value. FIG. 1 shows a Newtonian fluid model, a Bingham fluid model, and a flow model of a radiation protective synthetic resin paste composition. The radiation protective synthetic resin paste composition has a predetermined yield value, which is defined as a true yield value Yt. On the other hand, the yield value of the Bingham fluid model is defined as the Bingham yield value Yb. Generally, the minimum stress that causes permanent deformation (flow) is the yield value of the fluid, but if it is a Bingham fluid, it will deform elastically without flowing at a stress below the Bingham yield value Yb, resulting in a Bingham yield value Yb. The above shows Newtonian plastic flow. In order to prevent sedimentation of tungsten powder in the radiation protective synthetic resin paste composition, it is sufficient that the yield stress is larger than its own weight w. Therefore, if the yield stress acts on the cross section πd of the tungsten powder, the Bingham yield value Yb required for the radiation protective synthetic resin paste composition is as follows.

  However, since each particle of tungsten powder is not a sphere and can only be measured as an average of diameters d distributed within a certain range, the theoretical value of the Bingham yield value Yb required for the radiation protective synthetic resin paste composition is calculated. Difficult to do. Also, the Bingham fluid is one ideal fluid, the true yield value Yt of the actual fluid is smaller than the Bingham yield value Yb, and the flow characteristics are also complicated.

  On the other hand, fluids may be softened by stress and fluidity may increase, and among these fluids, recovery is called thixotropy. For example, when particles in a fluid have a three-dimensional network structure due to cohesive force, etc., applying a constant shear stress destroys the three-dimensional network structure and gradually increases the fluidity, but maintains a constant speed. Then, structural breakdown and recovery are balanced and settled to a certain viscosity. Increasing the speed further decreases the viscosity. A thixotropic index (TI) is an example of the degree of thixotropy, and is calculated by the following equation when a B-type viscometer is used.

  As a result of intensive studies, the inventors have made it possible to suppress the settling of tungsten powder by setting the true yield value Yt of the radiation protective synthetic resin paste composition to have a certain thixotropy in the radiation protective synthetic resin paste composition. It was found that the viscosity can be adjusted to a value suitable for a thin film molded article having a desired thickness, and the effect can be stably exhibited by setting the thixotropic index within a certain range. As shown in Table 3, the vinyl chloride resin paste was prepared to have a predetermined viscosity and a thixotropic index, and each sample added with a predetermined part by weight of tungsten powder having an average particle size of 28 μm was placed in a cylindrical container having an outer diameter of 55 mm × height of 305 mm. Filled with 500 ml, 15 ml each of the radiation protective synthetic resin paste composition of the uppermost layer portion, the central layer portion and the lowermost layer portion was sampled with a whole pipette over time, and the density (g / cc) was measured. The results are shown in Table 4. Moreover, it replaced with the vinyl chloride resin paste and the same test was done with the acrylic resin paste. The results are shown in Tables 5 and 6.

  From these results, it can be seen that the radiation protective synthetic resin paste composition can suppress changes in density even after 24 hours by adjusting the thixotropic index to 0.15 to 0.25. That is, when the synthetic resin paste is left in a tank or the like, the shearing force due to the settling of the tungsten powder is below the yield value, so the radiation protective synthetic resin paste composition does not flow, and the settling of the tungsten powder is suppressed. A uniform dispersion state can be maintained. On the other hand, for example, a plurality of mother molds are continuously moved by a dip molding method, and the shear stress greater than the yield value is applied to the radiation protective synthetic resin paste composition by being immersed and pulled up in the radiation protective synthetic resin paste composition. Is added, the thickness of the radiation protective synthetic resin paste composition adhering to the matrix or the like can be reduced to a desired thickness by appropriately adjusting the viscosity. If the thixotropic index is lower than 0.15, the settling of the tungsten powder is fast, and if it is higher than 0.25, it becomes difficult to fluidize by a dip molding method or the like.

  The thixotropic agent added to the radiation protective synthetic resin paste composition is a bentonite that improves the yield value and develops thixotropy by generating an internal structure with a weak binding force in the plasticizer of the radiation protective synthetic resin paste composition. There are silica-based thixotropic agents and silica-based thixotropic agents that improve the yield value by immobilizing the plasticizer due to its high oil absorption and immobilize it. Bentonite-type thixotropic agents are preferred because of their low viscosity.

Further, when the radiation protective synthetic resin paste composition becomes higher than the desired viscosity by adding tungsten powder and a thixotropic agent, a viscosity reducing agent may be added. However, for example, if a low-boiling-point paraffinic hydrocarbon solvent is used, the physical properties of the molded film may be lowered. Therefore, like 2-hydroxybutyl acrylate and 2-hydroxypropyl acrylate, the viscosity is low and the viscosity reducing action is large. An acrylic acid ester having an acrylic acid group that is compatible with a vinyl chloride resin or an acrylic resin and is polymerized or cross-linked by heating or a polymerization initiator is suitable as a viscosity reducing agent.

[Thin film molded products]
The radiation protective synthetic resin paste composition is suitable for molding a thin film molded product. Specifically, it is suitable for molding clothes such as gloves and an apron for protecting a person working in an environment exposed to radiation. The film thickness of these thin film molded products is preferably 0.4 to 0.6 mm. If the thickness is less than 0.4 mm, for example, it is difficult to achieve a radiation shielding rate of 70% or more, particularly preferably 80% or more. If the thickness is more than 0.6 mm, for example, a glove can provide a feeling of wearing and workability. Becomes worse.

[Production method]
For forming a thin film molded article, a dip molding method or a spread molding method is suitable, and particularly a glove is preferably a dip molding method. On the other hand, the spread molding method is suitable for applying a radiation-protective synthetic resin paste composition to fibers and the like to produce a garment having a laminated structure of fibers and a sheet-like thin film molded article. A known process can be used for the dip molding method and the spread molding method. For example, in the case of the dip molding method, a matrix such as a glove heated to a predetermined temperature in a layer filled with the radiation protective synthetic resin paste composition. The radiation-protective synthetic resin paste composition is attached to the matrix with a predetermined thickness by immersing the matrix, the matrix is pulled up from the radiation-protective synthetic resin paste composition, heated to form a film, and after cooling, The formed thin film molded product is demolded. When forming thin film molded products such as gloves by such a dip molding method, the process of forming an adhesive layer on the matrix such as natural rubber, synthetic rubber latex and synthetic resin emulsion, and residual adhesion The step of removing the agent is unnecessary, and it is only necessary to immerse the mother mold in one immersion tank filled with the radiation protective synthetic resin paste composition. Therefore, there are advantages that the number of steps is small and the manufacturing cost is low. In addition, the immersion molding method using the present radiation protective synthetic resin paste composition is not limited to the production method using only one tank, and another film such as a slipping layer is formed on the film formed using the radiation protective synthetic resin paste composition. Of course, it may be laminated. On the other hand, in the case of spread molding, after applying a radiation protective synthetic resin paste composition to a fiber or the like, the radiation protective synthetic resin paste composition is averaged to a predetermined thickness with a blade while moving the fiber. Film.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the examples, and various modifications can be made without departing from the gist of the present invention.
[Radioprotective synthetic resin paste composition]
50 parts by weight of a benzoate plasticizer (Versicol Chemical: Benzoflex 9-88, 2088) and 100 parts by weight of an acrylic plasticizer (Toagosei Co., Ltd.) with respect to 100 parts by weight of a vinyl chloride resin paste resin (Tosoh: Luuron # 815) : ARON XP-1025) 20 parts by weight, 12 parts by weight of adipic ester plasticizer (Dai Nippon Ink: DINA) were added, and a stabilizer and a filler were further added to obtain a synthetic resin paste having a basic composition.

  30 parts by weight of bentonite thixotropic agent (Shiraishi Kogyo: Orben Z) and 10 parts by weight of 2-hydroxypropyl acrylate (Kyoeisha Chemical Co., Ltd .: HOP-A) as a thickener for 100 parts by weight of the synthetic resin paste having the above basic composition 20 parts by weight of acrylic acid ester (Kyoeisha Chemical Co., Ltd .: PTMG-A-250) is added to further ensure the flexibility and tensile strength of the glove film, and further a polymerization initiator (Wako Pure Chemicals: V -601) was added to 0.5 parts by weight with respect to the acrylate ester to obtain a synthetic resin paste.

To 100 parts by weight of the synthetic resin paste, 240 parts by weight of tungsten powder (Allide material) having an average particle size of 28 μm is added, and the radiation protective synthetic resin paste composition is stirred to uniformly disperse the tungsten powder. It was.

[Production of radiation protective gloves]
The synthetic resin paste is maintained at 30 to 40 ° C., and a base of a glove heated to 47 to 53 ° C. is immersed and adhered, and the temperature is adjusted to 180 to 190 ° C. in a heating furnace for 20 to 25 minutes. A film was formed by heating, and after air cooling, the mold was inverted from the mother mold to obtain a glove.

[Evaluation]
The obtained radiation protective gloves had a film thickness of 0.55 mm and could be molded with a desired thickness. Further, the transmittance when irradiated with X-rays generated at a tube voltage of 80 kV was 0.18, and good radiation shielding performance with a shielding rate of 80% or more was exhibited. Furthermore, the film properties such as flexibility and tensile strength, wearing feeling and workability of radiation protective gloves were also good.

It is a figure which shows the flow characteristic of a Newtonian fluid model, a Bingham fluid model, and a radiation protection synthetic resin paste composition.

Claims (6)

  Radiation characterized by containing 200 to 300 parts by weight of tungsten powder having an average particle size of 15 to 30 μm and a thixotropic index of 0.15 to 0.25 with respect to 100 parts by weight of synthetic resin paste. Protective synthetic resin paste composition.   The radiation protective synthetic resin paste composition according to claim 1, wherein the synthetic resin paste is a vinyl chloride resin paste or an acrylic resin paste.   The radiation protective synthetic resin paste composition according to claim 1 or 2, wherein the radiation protective synthetic resin paste composition is formed by a dip molding method.   The radiation-protective synthetic resin paste composition includes a long-chain active hydrogen compound having acrylic acid groups at both ends, and a polymer blend of the long-chain active hydrogen compound and a synthetic resin by the synthetic resin paste are polymer-blended. The radiation protective synthetic resin paste composition according to any one of claims 1 to 3, wherein the composition is a radiation protective synthetic resin paste composition.   A thin film molded article, which is molded into a film of 0.4 to 0.6 mm by a dip molding method using the radiation protective synthetic resin paste composition according to any one of claims 1 to 4.   A radiation protective glove formed by a dip molding method using the radiation protective synthetic resin paste composition according to any one of claims 1 to 4.

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