JPH0365878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an organic fiber composite material useful as a thermal neutron shielding material.

Some of the fibrous structures used as thermal neutron shielding materials include work clothes used in areas where thermal neutrons may leak, such as around nuclear reactors, and materials used to avoid neutron irradiation when neutrons are used for treatment. There are demands for shielding materials that cover the desired areas and protective clothing against neutron bombs, but it is currently difficult to find good materials because there are few elements with large thermal neutron absorption cross sections.

Lithium, boron, cadmium, etc. are known as elements with large thermal neutron absorption cross sections.
The problem with fibrous structures containing large amounts of these elements is that in the case of lithium, there are no substances that are stable in air and poorly soluble in water or organic solvents. In the case of boron, there are few poorly soluble substances, and boron carbide,
Only a few materials are known that have high melting points and are difficult to process, such as boron nitride and heavy metal borides. In the case of lithium and boron, the atomic weight is small, so even if they are stabilized by making them into complex compounds, the content is low and the effect is poor. In the case of cadmium, the problem is that it is highly toxic, so it is not desirable to use it in areas where it will come into contact with the human body. Other elements have the problem of being difficult to use because they are expensive and produced in small quantities.

As a conventional fibrous structure used as a thermal neutron shielding material, there is one shown in JP-A-58-31117. This is a composite fiber whose core component is polyethylene fiber mixed with lithium fluoride, boron carbide, or boron nitride. Although this method is excellent as a method for producing thermal neutron shielding fibers, it has the problem that lithium fluoride, boron carbide, or boron nitride are all materials that are difficult to pulverize. When spinning a polymer mixed with solid powder, the upper limit to which solid powder can be added increases as the particle size decreases, but since these solid powders are difficult to atomize, the moldability of those mixed with polyethylene is extremely low. Unfortunately, the sheath is made into fibers using a resin with good moldability, but because the ratio of the sheath component is large, it is not possible to reduce the space where no neutron absorbing component exists, and it is necessary to sufficiently increase the neutron shielding efficiency. has the disadvantage that it needs to be very thick. Therefore, products of satisfactory quality cannot be obtained for uses such as work clothes that require active activities.

A known method is to knead a thermal neutron-absorbing solid powder into a synthetic resin and form it into a sheet or plate (Japanese Unexamined Patent Publications Nos. 173795/1982, 172297/1983, and 151897/1982). Needless to say, it is not possible to manufacture clothes that can be worn sufficiently from sheet-like or plate-like products obtained by such methods.

One possible method is to mix a thermal neutron-absorbing solid powder with a synthetic resin and coat it on the fibrous structure, but this method also does not allow the particle size of the solid powder to be made small enough, so it is necessary to mix the solid powder in a high concentration. The processability of the mixed synthetic resin is poor, and it is difficult to form a coating layer of satisfactory quality. When the concentration of solid powder is low, a fairly thick coating is required to achieve a sufficiently high neutron shielding efficiency.
The resulting material would be of such a nature that it could hardly be used as a material for work clothes.

The present invention is an organic fiber composite material with excellent thermal neutron absorption properties that has improved the above-mentioned problems of the prior art. The present invention provides a thermal neutron absorbing organic fiber comprising a thermally sprayed product containing an element with a large thermal neutron absorption cross section and a sheet-like material whose main component is an organic fiber having a lower melting point than the thermally sprayed product. It is a composite material. The purpose of making a neutron absorbing material into a thermal spray molded product is to make it possible to omit or significantly reduce the amount of the binder layer between the neutron absorbing materials and between the fiber materials, and to reduce the molding cost per weight of the neutron absorbing material. That's true. Thermal spraying is performed by forming fibers, mainly organic fibers, into a sheet shape. If necessary, the sheet-like material is further processed to return it to its original shape or to be shaped into a shape according to the intended use.

As a highly efficient technique for coating inorganic materials, thermal spraying is known as a high-efficiency coating method in which the coated material is made of high-temperature fine particles that can be fused and is sprayed onto the workpiece together with a high-temperature fluid to create molded products. It is widely used as a surface processing technology. Recently, it has been used for surface processing of ceramics and other materials, but it is difficult for heat transfer to occur during processing for materials with low thermal conductivity and low heat resistance, such as organic fiber materials. , the temperature of the object to be sprayed increases due to the heat brought in by the spraying material,
It has been said that fibers deteriorate and do not bond properly. Also, if you try to avoid this by lowering the temperature of the spray fluid or spraying from a distance,
It has been said that the thermal spray particles no longer integrate and bond with the fiber material. Therefore, it is a well-established theory that thermal spray materials cannot be processed unless they have a melting point lower than the softening point or thermal decomposition temperature of the fiber material.

As an example of thermal spraying processing for organic fibers, it is known that lead is thermally sprayed onto cotton cloth to produce radiation shielding work clothes. In addition, JP-A-52-66798 discloses that epoxy resin prepolymer, polyethylene, polypropylene, nylon 11
An example is disclosed in which thermal spraying is performed using the powder as a thermal spraying powder. In all of these examples, the melting point of the organic fiber is higher than the melting point of the thermal spray material, and although the maximum temperature of the plasma is around 10,000℃,
The practical thermal spray processing temperature has been thought to be slightly lower than the melting point or pyrolysis temperature of the organic fiber.
The present inventor happened to discover that this established theory is wrong while researching thermal spraying technology, and arrived at the present invention. Furthermore, JP-A-48-52644 discloses that when copper is sprayed directly onto a hard vinyl chloride plate, a sprayed coating with weak bonding strength is obtained; It is stated that if copper is sprayed in a semi-cured state, a sprayed coating with strong bonding strength can be obtained. This method is considered to be an advantageous method for joining plastic sheets and metal, but for joining cloth foil and metal, the process is more flexible compared to laminating cloth foil and metal film. Generally speaking, lamination processing with a large value is considered to be more advantageous. However, if an intermediate layer having better heat resistance and chemical resistance than the thermosetting resin is provided, a novel product can be obtained since the presence of the intermediate layer will have a greater protective effect on the organic fibers in the fabric.
For example, if a metal (alloy) with a slightly lower melting point than the organic fiber is used as the intermediate layer, when a high melting point metal is sprayed, the latent heat of melting absorbs the heat brought in by the sprayed material and exhibits a protective effect. While considering thermal spraying using such an intermediate layer, due to an experimental error, a metal with a higher melting point than the organic fibers was sprayed onto the area where the intermediate layer was not present, and that area became higher than the area where the intermediate layer was present. It was found that the peel strength was high, and from this we learned that the conventional theory was wrong.

As a result of various studies, the inventors of the present invention have found that by shortening the contact time per contact with the high-temperature fluid used for thermal spraying and by cooling it as quickly as possible after contact, the inventors have found that the organic It has been discovered that sheet-like composite materials can be obtained by thermal spraying inorganic materials such as metals and ceramics that have a much higher melting point than the melting point of fibers. If the thickness of the molded product produced by thermal spraying is insufficient, this operation may be repeated.

Sheet materials include woven materials, knitted materials, non-woven materials, and paper. (Hereinafter, such a structure will be referred to as a sheet-like product.) The sheet-like product that has been thermally sprayed can be used as it is or after passing through a commonly used fiber processing process. You can unravel the condition and use thread ropes etc. one by one. In the case of netting, it can be processed into a flat shape by stretching it in the direction of the grain. It is also possible to thermally spray a sheet-like material, slit it into a tape shape, and twist or string it into a rope shape. The sheet-like material can be subjected to various processes that can be applied to ordinary fibrous materials before, after, or at the same time as thermal spraying.

The contact time between the high-temperature fluid used for thermal spraying and the sheet material mainly composed of organic fibers is 1 second or less per time, preferably 1/10 to 1/10000 seconds. Specifically, the thermal spray gun, the sheet material, or both are moved, and their relative speed, that is, the relative speed of the feeding speed of the sheet material and the central axis of the high temperature fluid for thermal spraying, is adjusted to 0.1 m/
The speed shall be at least 100 m/sec. Specific devices include a device that sprays cloth by slowly feeding it while a thermal spray gun is reciprocated at a fairly high speed in a direction almost perpendicular to the sheet, and a device that connects the sheets like an endless belt and runs the sheet at high speed in a ring while spraying. An apparatus that performs thermal spraying by slowly moving a gun, or an apparatus that performs thermal spraying using a thermal spraying gun that moves slowly by moving the sheet back and forth between a reversible take-up device and an unwinding device can be used.

In carrying out the present invention, the sheet material to be thermally sprayed and the high-temperature fluid used for thermal spraying are cooled rapidly in as short a time as possible after they are separated from each other. Cooling is preferably carried out by spraying a gas or a gas in which various liquids and solids are dispersed onto the thermally sprayed molding.
Preferably, air or an inert gas is blown.
The flow velocity is at least 1 m/sec, preferably at least 10 m/sec and at most the speed of sound. It is preferable that cooling is also performed from the back side of the sheet-like material. For cooling from the back side, it is preferable to use a solid cooling device provided with an internal heat removal mechanism, such as a rotating roller or a plate-like cooling device of various shapes. This is because by bringing the sheet material into close contact with a solid cooling device, it is possible to prevent the sheet material from undulating due to the fluid flow for thermal spraying and cooling, thereby making the thermal spraying non-uniform.

Since the sheet material to be thermally sprayed in the present invention is porous, a portion of the thermal spray material may pass through the sheet material and come out to the back side. The equipment that cools the sheet-like material to be thermally sprayed from the back side must be maintained under conditions that will not allow the thermal spraying material to adhere to it.
The surface temperature is maintained below 200°C, preferably below 100°C. The cooling device is preferably attached with an auxiliary device for bringing the sheet material to be thermally sprayed into close contact with the cooling device, and further preferably with a device for scraping off the thermally sprayed material when it adheres.

A feature of the composite material of the present invention is that a sheet-like material mainly composed of organic fibers and a thermally sprayed material containing an element with a large thermal neutron absorption cross section are integrated in a multilayered manner, and the bond between the two components is The force appears to be due to the bonding force on the organic fiber surface and the entangled structure at the interface between the two components. Such structures can be formed even in conditions where there are significant discontinuities in molded parts containing elements with large thermal neutron absorption cross sections, and the presence of such discontinuities makes them highly flexible. A highly durable composite material is formed.

Thermal spray processing of materials containing elements with large thermal neutron absorption cross sections when producing the composite materials of the present invention is carried out at a temperature that allows the raw materials to be melted or sintered in plasma generated by flames, electric discharges, etc. After the fine particles are formed, they are carried by a plasma stream or a high-temperature air stream and are made to collide with the sheet-like material. The relative velocity between the sheet material and the central axis of the high-temperature fluid used for thermal spraying is
The speed is 0.1 m/sec or more and 100 m/sec or less, and the sheet-like material is rapidly cooled immediately after it is separated from the high-temperature fluid. As a result, the sheet-like material can be taken out of the high-temperature fluid used for thermal spraying before deterioration due to heat progresses.
Cooling of the sheet-like material can also be added at a stage before it comes into contact with the hot fluid. With this cooling,
The heat capacity of the sheet-like material increases and deterioration is suppressed.
This operation is repeated until the amount of thermal spraying reaches a desired value, and the material to be thermally sprayed is formed into a film, sponge, or scale shape on the sheet-like object. Here, the fine particles carried by the plasma flow or the high-temperature air flow are melted entirely, their surface layer, or their binder component, and are accelerated to near-sonic or supersonic speeds and collide with the sheet-like object. The particles are compressed to the fiber surface by their own momentum and form a film, and some of the particles pierce and adhere to the fiber surface. In addition, a part of the particles penetrates into the sheet-like material through the gaps between the fibers and fuses with subsequent particles to form a network structure. Particles pressed onto the surface of organic fibers soften and melt near the surface of the organic fiber due to the amount of heat they possess, but by cooling this at a sufficient rate, the core of the fiber can be softened. It has been found that it is possible to form a thermally sprayed coating layer without using a thermal spray coating. Depending on the thermal spraying conditions, the particles can be formed into a continuous film, an intermittent film, or a layered film. Furthermore, by incorporating particles that do not melt during thermal spraying, a sintered body-like molded product or a sponge-like molded product can be obtained.

Thermal spraying may be carried out on one side or both sides of a sheet material mainly made of organic fibers. The thermal spray material may be a single compound of an element with a large thermal neutron absorption cross section or may contain a binder component and the like. Although it is simple and cost-effective to use only one type of thermal spray material, some boron compounds and lithium compounds have extremely poor sintering properties, so sufficient adhesion strength cannot be obtained without a binder. In some cases, it is preferable to use a binder. For thermal spraying using a binder, the binder may be simply mixed and thermally sprayed, or the surface of the neutron absorbing material particles may be coated with the binder and then thermally sprayed.

If the sheet-like material is like a rope, the sprayed particles will not wrap around sufficiently, so it is necessary to spray from many directions in order to obtain a uniform sprayed molded product.

As the thermal spraying method in the present invention, any conventionally known method can be applied, but there is a method in which the thermal spraying material is introduced in powder form into a flame or plasma jet, and a method in which the thermal spraying material is sprayed in a flame or arc discharge. A method of introducing a rod-shaped thermal spray material, crushing it, melting it, and thermal spraying is preferred for producing the composite material of the present invention.

In producing the composite material of the present invention, the relative speed between the sheet material and the thermal spray gun should be adjusted in any case.
It is necessary to maintain the speed between 0.1 and 100 m/sec. If the spraying speed is less than 0.1 m/sec, cooling will be insufficient no matter how you change the thermal spraying conditions, and deterioration of the organic fibers cannot be avoided. On the other hand, at speeds close to 100 m/s, it is difficult to move the spray gun, and the only method that can be implemented is to rotate a cooling roller with a sheet-like material on it at high speed. This makes it difficult for thermal spray particles to stick. The relative speed between the sheet material and the thermal spray gun is preferably 0.5 to 20 m/sec.
When the relative speed is 0.5 m/sec or less, there are strong restrictions on the material to be sprayed and the spraying conditions, which is disadvantageous in terms of cost. If the speed is higher than 20m/sec, the length that the sheet material travels during the speed increase process at startup of the equipment will be significantly longer, and in order to maintain the uniformity of the sprayed molded product in this area, extremely complicated thermal spraying will be required. The disadvantage is that it becomes necessary to carry out quantity control, and the cost of the equipment increases significantly. The relative speed between the sheet material and the thermal spray gun is more preferably 1 to 5 m/sec. When the speed exceeds 1 m/s, many types of thermal spray materials can be sprayed under the conditions where the spray gun reaches its maximum performance, and even if the relative speed is increased further, the production rate on a weight basis of the thermal spray material will not increase. . It is possible to move the spray gun up to 5 m/sec, and below this speed many types of spray processing equipment can be used, making production extremely easy. In particular, in the case of thermal spraying on fabrics and papers, processing can be performed without stopping except when changing the supply of sheet-like materials, resulting in extremely low costs.

When thermal spraying is performed in multiple layers, thermal spraying materials with extremely high melting points can be thermally sprayed with high efficiency by sequentially spraying materials with high melting points. In particular, when metal is thermally sprayed, as the thermal spray coating becomes thicker, it becomes easier to rapidly cool the coating, and as a result, subsequent thermal spraying tends to become more efficient. In addition, when spraying in multiple layers,
By thermally spraying materials with higher hardness in sequence, it is possible to suppress the phenomenon of cracking in the thermally sprayed coating. When spraying materials with low elongation such as ceramics, first spray a soft metal such as aluminum, then spray a hard metal on top of that, and then spray ceramics on top of that to form a ceramic layer. Cracks can be significantly reduced.

A component of the organic fiber composite material of the present invention,
Sheet-like materials mainly made of organic fibers are flat-shaped materials such as woven, knitted, non-woven fabrics, braided fabrics, and paper made of natural and artificial organic fibers, and are treated with napping, flocking, block processing, resin coating, etc. Contains things that are familiar. This may contain some inorganic fibers, adhesive resins, fillers, adhesives, and various finishing agents.

A component of the organic fiber composite material of the present invention,
Thermal spray moldings containing elements with large thermal neutron absorption cross sections are thermal spray moldings of materials containing elements with large thermal neutron absorption cross sections that can be sprayed with melting points higher than the melting point or thermal decomposition temperature of organic fibers that are other components. It is a thing. Here, the elements with a large thermal neutron absorption cross section are preferably boron, lithium gadolinium, cadmium, and europium, and the nuclides with a large thermal neutron absorption cross section are ^{0 1} B, ⁶ Li,
Preferably, it is one enriched with ¹⁵⁷ Gd, ¹¹³ Cd, and ¹⁵¹ Eu. In the case of boron, preferred compounds include boron carbide, boron nitride, silicon boride, borides of various metal compounds, etc. In the case of lithium, lithium fluoride is preferred, in the case of gadolinium, gadolinium oxide, and in the case of europium, europium oxide. preferable. Binders include metals such as nickel and cobalt, alumina,
Ceramics such as titania and mullite, and plastics such as epoxy, polyester, nylon, and polyethylene can be used.

As the thermal spraying method in the present invention, any conventionally known method can be applied, but there is a method in which the thermal spraying material is introduced in powder form into a plasma jet, and a method in which the thermal spraying material is introduced in the form of a rod into a flame or arc discharge. For producing the organic fiber composite material of the present invention, a method in which a thermal spray material is introduced, crushed and melted, and a method in which the thermal spray material is introduced in powder form into a flame and thermal sprayed are preferable.

Because of the severe irregularities on the surface of the thermal spray molded product, the wear resistance and bending resistance of the composite material of the present invention cannot necessarily be said to be sufficient. To improve this, it is effective to apply a thin layer of organic polymer to the surface.
Various organic polymers can be used, but
Many are easy to use for polyurethane, acrylamide, silicone, and epoxy resins. When these resins are used in large quantities, they can improve the surface gloss, but they have the disadvantage of decreasing air permeability and fire resistance.
It is preferable that these resins contain an organic or inorganic boron compound or lithium compound.

The present invention will be explained below with reference to Examples.

Example 1 Cloth made of vinylon spun yarn (fabric weight 220 g/m ² , plain weave,
Boron carbide powder (particle size 44 to 88 μm) was thermally sprayed to a thickness of about 25 μm using a plasma spray system 7M device manufactured by Metco, Inc. (density: 42 particles/inch x 42 particles/inch). Thermal spraying conditions were: voltage 50 volts, current 160 amperes, argon flow rate 2 normal cubic meters/hour, cloth feed speed 2.2 msec (one contact time with the spray fluid flame 0.014 seconds), and the moving speed of the thermal spray gun (the cloth feed direction and (right angle) 0.05 m/sec, the distance between the spray gun and the cloth was 120 to 140 mm, and the number of sprays was 16 times. 12 toward the point where the cloth escapes from the spray fluid flame.
Cooling air was sent at a flow rate of m/sec for rapid cooling.

The surface condition of the fabric thus obtained is good;
The texture is slightly harder than the raw material vinylon cloth, but it does not show any roughness. When expressing the stiffness of a cloth by the distance that a horizontally protruding cloth hangs from the tip of the support base to a line drawn diagonally downward at 45 degrees, a value of 10 cm is obtained, compared to 7 cm for the vinylon cloth used as the raw material.
I noticed that it had become a little harder due to the thermal spraying.
However, this value is not so large that it poses a particular problem as a characteristic of the cloth.

The abrasion resistance of this fabric was examined using a Taber type abrasion tester. Assuming that the end point of wear is the point at which 1/2 of the cloth surface becomes vinylon fiber, the wear wheel CS-17 and the load are
When a wear test was conducted at 500g, the wear life was
It was 300 times.

The peeling resistance of the ceramic layer was investigated. I repeated pasting and peeling off the sellotape 20 times, but
No substantial peeling was observed.

In order to investigate the wash resistance of this cloth, we washed it for 10 minutes in a 0.5% synthetic detergent solution using a commercially available electric washing machine (Hitachi PF2500 Aozora (registered trademark)).
There were no substantial changes.

When we layered 10 sheets of this cloth and measured the transmittance of thermal neutron beams, it was 3.6×10 ^-2 , indicating that it has excellent shielding ability.

Example 2 The same vinylon cloth as in Example 1 was thermally sprayed with boron nitride and cermet (Meteco 301NS) powder using a thermospray gun 6P manufactured by Metco, USA. Thermal spraying conditions were: oxygen flow rate of 2.2 normal cubic meters/hour, acetylene flow rate of 1.0 normal cubic meters/hour, powder supply rate of 2.2 kg/hour,
Cloth feed speed 2.2m/sec, thermal spray gun movement speed 0.1
m/sec, distance between spray gun and cloth 200 mm, number of sprays 24
It was hot. Towards the point where the cloth escapes from the spray flame
Cooling air was sent at a flow rate of 10 m/sec to cool the cloth.

The average thickness of the thermally sprayed molded product on cloth thus obtained was about 105 μm, and the surface had an appearance similar to that of a metal material with a matte finish. The texture is a little harder and a little rougher than the raw vinylon cloth, but it's not uncomfortable. The cloth protruding horizontally from the tip of the support
When expressing the stiffness of the fabric by the distance it hangs down to a line drawn downward at 45 degrees, a value of 18 cm was obtained, compared to 7 cm for the vinylon fabric used as the raw material, indicating that it has become considerably harder due to thermal spraying. However, this value is not so large that it poses a problem when worn for work clothes or the like.

The abrasion resistance of this fabric was examined using a Taber type abrasion tester. 1/2 of the cloth surface as the end point of wear
As the point where becomes vinylon fiber, wear ring CS-17,
When a wear test was conducted under a load of 500g, the wear life was 600 times.

In order to examine the peeling resistance of the aluminum layer, cellophane tape was applied and peeled 20 times, but no substantial peeling was observed.

In order to examine the washing resistance of this fabric, it was washed for 10 minutes in a 0.5% synthetic detergent solution using a commercially available electric washing machine (Hitachi PF2500 Aozora (registered trademark)), but there was no substantial change.

When we stacked 10 sheets of this cloth and measured the thermal neutron beam transmittance, it was 7.5 x 10 ^-2 , indicating that it has excellent shielding ability.

Claims (1)

[Claims] 1. A thermal neutron-absorbing organic fiber composite material comprising a thermally sprayed material containing an element with a large thermal neutron absorption cross section and a sheet-like material whose main component is an organic fiber having a lower melting point than the thermally sprayed material. .