JP5871828B2 - Manufacturing method of radiation shielding bag - Google Patents

Description

  The present invention relates to a radiation shielding bag used when recovering, transporting, storing, etc., radioactive materials, particularly radioactive waste.

  In an accident at a radiation facility or nuclear facility, leakage of radiation or radioactive materials may be released in large quantities inside or outside the facility. In such a case, it is necessary to take measures to quickly reduce the environmental pollution due to the diffusion of radioactive substances, human health, and the impact on the living environment.

  However, if radioactive waste is temporarily collected using a plastic bag or sandbag bag that does not have a shielding ability against radiation, there is a risk of external exposure to workers. In addition, in a radioactive waste storage place, the general public is exposed to the risk of external exposure due to the radiation emitted from the radioactive waste accumulated and concentrated when the general person approaches. Furthermore, if radioactive waste is transported or transported using a plastic bag or sandbag without a shielding ability, the radioactive material may be scattered in the atmosphere.

  Conventionally, barium sulfate is widely known as a material for radiation shielding materials, and Document 1 discloses radiation shielding including barium sulfate and a thermoplastic resin and / or thermoplastic elastomer which is a binder of the barium sulfate. The sheet used is disclosed.

JP 2007-212304 A

  By the way, when recovering, transporting, storing, etc., radioactive waste, a bag-like shape is desirable. However, the shape disclosed in Patent Document 1 is a sheet, and this sheet is a hospital, various research institutions, and inspection institutions. It is intended to be incorporated into the walls, floors and doors of radiation handling facilities such as.

  The present invention has been made to solve the above problems, and provides a radiation shielding bag that is excellent in radiation shielding ability and mechanical strength in collecting, transporting, and storing radioactive waste. With the goal.

  As a result of intensive studies to solve the above problems, the present inventor has obtained mixed pellets composed of barium sulfate and low-density polyethylene and a reproduction obtained from a film tube for an infusion bag comprising a specific linear low-density polyethylene as a constituent resin. The inventors have found that the above problems can be solved by using resin pellets, and have completed the present invention.

That is, the gist of the present invention is as follows.
[1] Mixed pellet containing barium sulfate and low-density polyethylene, and an infusion bag comprising, as waste plastic, linear low-density polyethylene made of a copolymer of ethylene and C6-C8 α-olefin as a constituent resin Recycled resin pellets that were crushed and thermoformed into pellets,
A radiation shielding bag obtained by inflation molding a mixture with
[2] When the total weight of the mixture before inflation molding is 100 parts by weight, 59.5 to 30 parts by weight of barium sulfate, 25.5 to 30 parts by weight of low density polyethylene, and 15 to 40 of recycled resin pellets The radiation shielding bag according to [1], which is contained in a range of parts by weight,
[3] Within a thickness range of 0.10 to 0.20 mm, the tensile strength (longitudinal and lateral) is both 22 to 26 MPa, the elongation (vertical and lateral) is both 600 to 800%, and the tear strength (longitudinal, The radiation shielding bag according to the above [2], wherein both (lateral) are 100 to 120 N / mm,
About.

  ADVANTAGE OF THE INVENTION According to this invention, the radiation shielding bag which is manufactured by inflation molding, is excellent in radiation shielding ability, and is excellent also in mechanical strength is provided.

  The radiation shielding bag of the present invention is obtained by inflation molding a mixture of a specific mixed pellet and a specific recycled resin pellet. The obtained radiation shielding bag has excellent radiation shielding ability and excellent mechanical strength.

The mixed pellet used as a raw material in the present invention is a pellet containing barium sulfate (BaSO ₄ ) and low density polyethylene (LDPE). In the present invention, the density of the mixed pellet is usually in the range of 1.64 to 1.80 g / cm ³ . In the present invention, the density is measured according to JIS K 7112.

BaSO ₄ may be synthesized by a conventional method, or a commercially available product may be used. As LDPE, those having an MFR (melt flow rate) of 3.0 to 4.0 g / 10 min and a density of 0.918 to 0.924 g / cm ³ are usually used. In the present invention, MFR refers to a melt flow rate (unit: g / 10 minutes) at 190 ° C. and a load of 2160 g, measured according to JIS K7210.

The blending ratio of BaSO ₄ and LDPE in the mixed pellet is when the total weight of each component is 100 parts by weight from the viewpoint of the molding process characteristics in the manufacturing process of the radiation shielding bag and the shielding ability of the obtained radiation shielding bag. BaSO ₄ is preferably 70 to 50 parts by weight and LDPE is preferably 30 to 50 parts by weight.

In the production of mixed pellets, a predetermined amount of BaSO ₄ and LDPE are uniformly mixed with a mixer such as a tumbler, and the obtained dry blend product is put into a pellet manufacturing apparatus, and LDPE which is a resin component at 180 to 220 ° C. And a method of extruding and cutting in accordance with a conventional method.

  The recycled resin pellet used as a raw material in the present invention is an infusion bag having a linear low density polyethylene (LLDPE) made of a copolymer of ethylene and a C6-C8 α-olefin as a waste plastic. The film tube was pulverized and heat-molded into pellets. The film tube before being pelletized is discarded in the infusion bag manufacturing process.

  The LLDPE constituting the recycled resin pellet is a copolymer (preferably a random copolymer) of ethylene and an α-olefin having 6 to 8 carbon atoms. Examples of the α-olefin include 1-hexene, 1-heptene, 1-octene and the like. When an α-olefin having a carbon number of less than 6 is used, it is difficult to produce a bag body having a large drawdown property and a good thickness distribution at the time of molding the radiation shielding bag, and the mechanical properties of the produced radiation shielding bag. The strength is also inferior to practicality.

  The LLDPE is produced by polymerizing ethylene and α-olefin using a known Ziegler catalyst or metallocene catalyst using a solution method, a slurry method, or a gas phase method. In the present invention, among the above production methods, LLDPE produced by a solution method using a metallocene catalyst is preferable. In the present invention, one type of LLDPE may be used alone, or a plurality of LLDPEs having different α-olefins may be used in combination.

In addition, the recycled resin pellets have a density of 0.918 to 0.935 g / cm ³ and an MFR of 0.01 considering the molding process characteristics in the manufacturing process of the radiation shielding bag and the film strength of the obtained radiation shielding bag. It is preferable that it exists in the range of -10g / 10min.

  In the production of the recycled resin pellets, the film tube discarded in the infusion bag manufacturing process is pulverized into several cm square using a pulverizer, and the obtained pulverized product is put into a pellet manufacturing apparatus. Examples include a method in which the pulverized product is melted at 0 ° C., and extruded and cut according to a conventional method.

The mixing ratio of the mixed pellet and the recycled resin pellet is mixed when the total weight of each component is 100 parts by weight from the viewpoint of the processing characteristics in the manufacturing process of the radiation shielding bag and the shielding ability of the obtained radiation shielding bag. It is preferable that the pellet is 85 to 60 parts by weight and the recycled resin pellet is 15 to 40 parts by weight. That is, in consideration of BaSO ₄ and LDPE, which are constituent materials of the mixed pellet, when the total weight of the three components is 100 parts by weight, BaSO ₄ is 59.5 to 30 parts by weight and LDPE is 25.5 to 30 parts. The parts by weight and the recycled resin pellets are preferably in the range of 15 to 40 parts by weight.

The radiation shielding bag of the present invention contains other components as needed in addition to BaSO ₄ and LDPE and the recycled resin pellets, which are constituent materials of the mixed pellets, as long as the effects of the present invention are not affected. You may let them. Examples of other components include a plasticizer, an antioxidant, an ultraviolet absorber, an anti-aging agent, a flame retardant, and a slip agent. Other components may be included in advance when the mixed pellets or the recycled resin pellets are produced, or when the mixed pellets and the recycled resin pellets are mixed in the inflation molding described later. You may make it mix | blend with.

  Examples of the plasticizer include phthalic acid ester, trimellitic acid ester, pyromellitic acid ester, aliphatic monobasic acid ester, aliphatic dibasic acid ester, phosphoric acid ester, polyhydric alcohol ester, epoxy plasticizer, Polymer type plasticizers, chlorinated paraffins and the like can be mentioned. These can be used alone or in combination of two or more.

  Examples of the antioxidant include hindered amine compounds, hydroquinone compounds, hindered phenol compounds, sulfur-containing compounds, and phosphorus-containing compounds. These can be used alone or in combination of two or more.

  Examples of the ultraviolet absorber include benzophenone compounds, benzotriazole compounds, and triazine compounds. These can be used alone or in combination of two or more.

  Antiaging agents include, for example, naphthylamine compounds, diphenylamine compounds, p-phenylenediamine compounds, quinoline compounds, hydroquinone derivative compounds, monophenol compounds, bisphenol compounds, trisphenol compounds, polyphenol compounds, Examples thereof include a thiobisphenol compound, a hindered phenol compound, a phosphite compound, an imidazole compound, a nickel dithiocarbamate salt compound, and a phosphate compound. These can be used alone or in combination of two or more.

  Examples of the flame retardant include organic flame retardants, inorganic flame retardants, and reactive flame retardants. These can be used alone or in combination of two or more.

  Examples of organic flame retardants include brominated epoxy compounds, brominated alkyltriazine compounds, brominated bisphenol epoxy resins, brominated bisphenol phenoxy resins, brominated bisphenol polycarbonate resins, brominated polystyrene resins, brominated crosslinks. Halogen flame retardants such as polystyrene resin, brominated bisphenol cyanurate resin, brominated polyphenylene ether, decabromodiphenyl oxide, tetrabromobisphenol A and oligomers thereof; trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate , Trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixy Phosphate esters such as nyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, dimethyl ethyl phosphate, methyl dibutyl phosphate, ethyl dipropyl phosphate, hydroxyphenyl diphenyl phosphate, modified compounds thereof, condensed phosphate ester compounds, Phosphorus flame retardants such as phosphazene derivatives containing phosphorus element and nitrogen element; polytetrafluoroethylene, guanidine salt, silicone compound, phosphazene compound and the like.

  Examples of the inorganic flame retardant include aluminum hydroxide, antimony oxide, magnesium hydroxide, zinc borate, zirconium compound, molybdenum compound, and zinc stannate. Examples of the reactive flame retardant include tetrabromobisphenol A, dibromophenol glycidyl ether, brominated aromatic triazine, tribromophenol, tetrabromophthalate, tetrachlorophthalic anhydride, dibromoneopentyl glycol, poly (pentabromo). Benzyl polyacrylate), chlorendic acid (hett acid), chlorendic anhydride (hett acid anhydride), brominated phenol glycidyl ether, dibromocresyl glycidyl ether, and the like.

Examples of the slip agent include fatty acid ester, hydrocarbon resin, paraffin, higher fatty acid, oxy fatty acid, fatty acid amide (for example, C _2-34 saturated or unsaturated acid amide such as erucic acid amide, preferably C _4-30 saturated. or non飽酸amides, preferably C _8-24 saturated or unsaturated飽酸amide), alkylene bis fatty acid amides, aliphatic ketones, fatty acid lower alcohol esters, fatty acid polyhydric alcohol esters, fatty acid polyglycol esters, fatty alcohols, polyhydric Examples include alcohol, polyglycol, polyglycerol, metal soap, and modified silicone.

  The radioactive shielding bag of the present invention has a mechanical strength in the range of 0.10 to 0.20 mm, and the tensile strength (longitudinal and lateral) is both 22 to 26 MPa and the elongation (vertical and lateral) is both 600. It is preferable that both ~ 800% and tear strength (longitudinal and lateral) are in the range of 100 to 120 N / mm. In the present invention, the tensile strength and elongation are measured in accordance with JIS Z 1702. In the present invention, the tear strength is measured according to JIS K 7128-3.

  The radiation shielding bag of the present invention is manufactured by performing inflation molding. In performing inflation molding, first, a predetermined amount of mixed pellets and recycled resin pellets are uniformly mixed with a mixer such as a tumbler. Next, the obtained dry blend product is put into an extruder, and the melted and kneaded resin is extruded into a tube shape through a slit of a cylindrical die, and the pressure of gas (usually air) blown into the tube is set. A wide range of films can be produced by adjusting. The thickness of the film can be adjusted by selecting the extrusion rate of the molten resin and the blow-up ratio (BUR). In the present invention, the thickness in the range of 0.10 to 0.30 mm is usually used. The temperature of the molten resin at the time of extrusion is usually selected within a range of about 180 to 220 ° C.

  The extruded tube is cooled from the outside by gas (usually air) and / or liquid (usually water). The method of cooling with water is called water-cooled inflation molding, and a film having excellent transparency can be obtained. However, since the sizing ring is changed when changing the width of the film, the workability is poor. A method of cooling with air is called air-cooled inflation molding, and various cooling devices and methods have been proposed. Broadly speaking, there are a method of performing air cooling in one stage and a method of performing in multiple stages. Multi-stage air-cooled inflation molding has good film forming stability, less trouble during film formation, and high cooling efficiency, so that a relatively highly transparent film can be obtained. In the present invention, any of the above cooling methods can be selected, but air-cooled inflation molding is preferred in that the thickness and width can be easily changed according to the application.

  The radiation shielding bag of the present invention can be suitably used, for example, when collecting, transporting or storing radioactive waste. Specifically, radioactive waste is put in a radiation shielding bag, and the opening of the bag is preferably bound using, for example, a binding band. A single radiation shielding bag may be used as described above, but it is more preferable to use two or three overlapping layers because it can effectively prevent secondary damage caused by scattering or leakage of radioactive waste. . The size of the radiation shielding bag is arbitrary, but is usually selected in the range of 200 to 900 mm in length and 300 to 900 mm in width.

  In the present invention, the film tube obtained by the inflation molding can also be used as an inner bag of a bag-like packaging material (for example, a flexible container bag (hereinafter abbreviated as a flexible container), for example, as an asbestos collection bag. For example, the film tube may be applied as an inner bag of a flexible container, such as a film tube having a length of 2400 to 2900 mm, a width of 1800 to 1900 mm, and a thickness of 0.15 to 0.20 mm. The flexible container manufactured in this way is excellent in radiation shielding ability even if it is mixed in radioactive waste, and asbestos. It is also expected to have an effect of preventing scattering and exposure.

  Hereinafter, the present invention will be described in more detail with reference to test examples and the like, but the present invention is not limited thereto. In the following, “%” means “% by weight” unless otherwise specified.

A. Production example 1 of radiation shielding bag
1. Raw material (mixed pellets of barium sulfate and low density polyethylene)
Barium sulfate (trade name: B-54, manufactured by Sakai Chemical Industry Co., Ltd.) 60% and low density polyethylene (trade name: UH411, MFR: 3.5 g / 10 min, density: 0.921 g / cm ³ , Nippon Polyethylene (Made by Co., Ltd.) 40% was dry blended with a tumbler, the obtained blended product was put into a pellet manufacturing apparatus, the resin content was melted at 180-220 ° C., and the resulting melt was made into a large number of 3 mm diameters. The mixed pellet was obtained by extruding from the hole and cutting to a thickness of about 2 to 3 mm with a cutter.
(Recycled resin pellets of linear low density polyethylene made of ethylene / 1-hexene copolymer)
As a waste plastic, a tubular film tube for an infusion bag comprising C6-LLDPE (trade name: Ultozex, manufactured by Prime Polymer Co., Ltd.) made of an ethylene / 1-hexene copolymer in a 2-3 cm square. The obtained pulverized material is put into a pellet manufacturing apparatus and melted at 180 to 220 ° C., and the obtained molten material is extruded from a large number of holes having a diameter of 3 mm, and is cut into a thickness of about 2 to 3 mm by a cutter. As a result, recycled resin pellets of C6-LLDPE were obtained.

2. Film tube manufacturing and bag making process 75% mixed pellets and 25% recycled resin pellets were dry blended with a tumbler, then air-cooled inflation molding was performed under the following conditions using the following extruder, the thickness was 0.15 mm, A film tube having a width of 450 mm was continuously produced and wound up by a winding device. Next, the film tube wound up in the previous step is put on a bag making machine, sealed at about 200 to 220 ° C. with a gap of 585 mm, and cut to form a vertical length of 585 mm, a horizontal length of 450 mm, and an opening at the top. The radiation shielding bag which has was manufactured.

<Molding conditions>
(1) Extruder: 90mm manufactured by Sumitomo Heavy Industries Modern Co., Ltd.
(2) Set temperature:
-Cylinder-inlet: 180 ° C, cylinder-intermediate: 183 ° C, cylinder-outlet: 185 ° C
・ Adapter for connecting cylinder and die: 185 ℃
-Die inlet: 188 ° C, Dice outlet: 186 ° C
(3) Screw rotation: 55 rotations / min
(4) Discharge rate: 290 kg / H
(5) Take-up speed: 6.3 m / min (6) Motor current: 300A

3. Evaluation <Appearance>
Fish eyes were not observed with the naked eye, and it was confirmed that no non-melted product was produced when a dry blend product of mixed pellets and recycled resin pellets was melted.
<Mechanical strength>
The test film was cut out from the radiation shielding bag obtained above, and the tensile strength and elongation were measured according to JIS Z 1702, and the tear strength was measured according to JIS K 7128-3. In addition, as a comparative example, a C4-LLDPE plastic bag used for collecting asbestos (trade name: asbestos collection bag, ethylene 1-butene copolymer, manufactured by Uo Kasei Kogyo Co., Ltd., thickness 0.15 mm ), The tensile strength, elongation and tear strength were measured in the same manner as described above. Table 1 shows the results.

  From the results in Table 1, it was found that the radiation shielding bag of Production Example 1 had the same mechanical strength as the asbestos collection bag.

<Shielding ability against radiation>
Standard radiation source (radioactivity standard gamma volume radiation source (Japan) Isotope Association, line type code: MX033MR, nuclide: mixed nuclide, radiation source) in the radiation shielding bag (one or two layers) of Production Example 1 No. 355) was added, the opening of the bag was bound and sealed, and then the radiation dose 1 cm outside from the surface of the bag was measured using a survey meter (Rad Eye B20-ER, manufactured by Thermo) Table 2 The results are shown in.

From the results of Table 2, the radiation shielding bag of Production Example 1 shows a certain radiation shielding ability even when one sheet is used in a sealed state (shielding rate 23%), and one sheet is used when two sheets are stacked. It was found that the radiation shielding ability was further improved compared to the time (shielding rate 38%).

B. Production example 2 of radiation shielding bag
As a waste plastic, instead of a tubular film tube for an infusion bag comprising C6-LLDPE (trade name: Ultozex, manufactured by Prime Polymer Co., Ltd.) made of an ethylene / 1-hexene copolymer, Except for using a tubular film tube for an infusion bag comprising C8-LLDPE (trade name: Novatec, manufactured by Nippon Polyethylene Co., Ltd.) made of 1-octene copolymer as the constituent resin, the above-mentioned “A. Radiation shielding”. A radiation shielding bag was produced in the same manner as in Bag Production Example 1 and the mechanical strength was measured.

(result)
The molding processability was good, and the mechanical strength and radiation shielding ability of the obtained radiation shielding bag were the same as those obtained in “A. Production Example 1 of radiation shielding bag”.

C. Production example 3 of radiation shielding bag
As a waste plastic, instead of a tubular film tube for an infusion bag comprising C6-LLDPE (trade name: Ultozex, manufactured by Prime Polymer Co., Ltd.) made of an ethylene / 1-hexene copolymer, “A. Production example 1 of radiation shielding bag” except that a bag body comprising C4-LLDPE made of 1-butene copolymer (trade name: Moretech, manufactured by Prime Polymer Co., Ltd.) as a constituent resin was used. A radiation shielding bag was produced in the same manner as described above, and the mechanical strength was measured.

(result)
It was difficult to produce a bag body having a large melt-down property during molding and a good thickness distribution. When the test film was cut out from the obtained bag body and the mechanical strength was measured, the film was found to have a tensile strength (longitudinal, lateral) as compared to that obtained in “A. Production example 1 of radiation shielding bag”. ), Elongation and tear strength (longitudinal and lateral) were remarkably inferior, and it was confirmed that they have no practicality.

Since the radiation shielding bag of the present invention is excellent in radiation shielding ability and mechanical strength, it can be widely applied to collection, transportation, storage and the like of radioactive waste.

Claims (2)

Recycled pellets containing mixed pellets containing barium sulfate and low-density polyethylene, and linear low-density polyethylene made of a copolymer of ethylene and C6-C8 α-olefin, and then heat-molded into pellets Mix the resin pellets ,
To inflation molding a mixture obtained by the mixing
A method for producing a radiation shielding bag. The total weight of the mixture before inflation molding is 100 parts by weight, the mixture is 59.5 to 30 parts by weight of barium sulfate, 25.5 to 30 parts by weight of low density polyethylene, recycled resin pellets 15 Formulated in the range of ~ 40 parts by weight
The manufacturing method of the radiation shielding bag of Claim 1 characterized by the above-mentioned.