CA2231008A1 - Polymeric composition for radiation shielding - Google Patents
Polymeric composition for radiation shielding Download PDFInfo
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- CA2231008A1 CA2231008A1 CA 2231008 CA2231008A CA2231008A1 CA 2231008 A1 CA2231008 A1 CA 2231008A1 CA 2231008 CA2231008 CA 2231008 CA 2231008 A CA2231008 A CA 2231008A CA 2231008 A1 CA2231008 A1 CA 2231008A1
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Abstract
The polymeric composition for radiation shielding includes a resinous binder with a radiation absorbing material suspended substantially homogeneously throughout the resinous binder. A thixotropic agent is dispersed within the resinous binder to act as a suspending agent. The thixotropic agent is present in an amount sufficient to substantially suspend the absorbing material in the resinous binder. The thixotropic agent acts to maintain a homogeneous dispersion of large amounts of radiation absorbing material before and during the resinous binder curing or setting process. In some embodiments, the thixotropic agent also acts as a supporting or reinforcing agent, thereby adding to the strength and stability of the shielding material after the resinous binder cures. In certain embodiments, the radiation absorbing material can comprise up to about 95% by weight of the total composition, or up to about 66% by volume of the total composition. In some formulations, the mixed material may be applied by hand to encapsulate sources of radiation or to repair dents or holes in existing shielding material. In other formulations, the mixed material may be injected into molds or fed into extruders to obtain desired shapes.
Description
POLYMERIC COMPOSITION FOR RADIATION SHIELDING
FIELD OF THE INVENTION
The present invention relates to material for radiation shielding, and more particularly to radiation shielding material made of resinous binders with radiation absorbing material dispersed homogeneously therethrough.
BACKGROUND PRIOR ART
It is well known that radiation resulting from medical, industrial, military, and other sources can be harmful. Care must be taken to shield living organisms and certain non-living objects from exposure to such harmful radiation. It is well known to use plates of radiation absorbing metals, such as lead plates, for radiation shields. However, such plates are often heavy, difficult to work with and apply, and often susceptible to damage, such as denting, through normal usage. Therefore, some focus has been directed towards using resinous binders or plastic materials having radiation absorbing material, such as lead, dispersed therethrough for radiation shielding material. Such material is easier to work with and mold into desired shapes, and is often more durable. However, it has often been a problem maintaining a homogeneous dispersion of the radiation absorbing material throughout the resinous binder. Often the absorbing material will settle to the lower portions of the resinous binder due to gravitational forces. This settling occurs rapidly in the time period before the resinous binder cures or sets during the production of the shielding material. AS a result, the dispersion of radiation absorbing material is not homogeneous throughout the shielding material and areas of low radiation shielding result.
It has also been found that if sufficient radiation absorbing materials are incorporated to achieve the required shielding, the product is frequently not strong enough to support its own weight, and also tends to tear or split when it is flexed.
Conversely, if the amount of radiation absorbing material is adjusted so as to obtain a product which is self supporting and/or has adequate flexibility, its shielding capability is inadequate or is only adequate if the material is used in a thickness which creates problems due to its bulk and also restricts the ability of the material to flex.
It is known to disperse large quantities of lead throughout a plasticizer resinous matrix to form a moldable putty shielding material, as is shown in U.S.
Patent No. 2,162,178. However, the problem with such putty substances is that they do not cure to a hardened state, and do not exhibit the strength and structure necessary for many shielding uses.
Laminates have been developed which incorporate radiation absorbing material and laminate such material with layers of structural supporting material.
However, such laminates can be difficult and expensive to manufacture, and are restricted in shapes and usage.
SUMMARY OF THE INVENTION
The invention provides an improved radiation shielding material.
One object of this invention is to provide an improved polymeric composition for radiation shielding.
Another object of the invention is to provide a polymeric composition with a high lead equivalency for radiation shielding.
Another object of the invention is to provide a polymeric radiation shielding material that has a substantially homogeneous dispersion of radiation absorbing material therethrough with minimal areas of low shielding capability.
Another object of the invention is to provide a polymeric radiation shielding material with a high concentration of radiation absorbing material while maintaining a high level of strength and stability.
Another object of this invention is to provide a polymeric radiation shielding material that is relatively injection moldable.
Another object of the invention is to provide for a polymeric radiation shielding material that is extrudable.
Another object of the invention is to provide a radiation shielding material that can be prepared and applied to an area in a liquid or putty state which then cures or hardens to a solid state having a high level of strength and stability.
Another object of the invention is to provide a polymeric radiation shielding material that is relatively lightweight and easy to work with.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description and claims.
One embodiment of the invention provides a polymeric composition having a high radiation shielding effectiveness containing up to about 66% by volume radiation absorbing material. The composition includes a resinous binder, a radiation absorbing material suspended substantially homogeneously throughout the resinous binder, and a thixotropic agent dispersed in the resinous binder to act as a suspending agent. The thixotropic agent is present in an amount sufficient to substantially suspend the absorbing material in the resinous binder.
The thixotropic agent acts to help produce the high radiation shielding effectiveness throughout the shielding material by acting to maintain a homogeneous dispersion of large amounts of absorbing material before, during, and after the resinous binder sets or cures. In some embodiments, the thixotropic agent also acts as a supporting or reinforcing agent, thereby adding to the strength and stability of the shielding material after it cures. In certain embodiments, the absorbing material can comprise up to about 95% by weight of the total composition, and due to the thixotropic agent, this large amount of absorbing material is homogeneously dispersed throughout the binder, and the shielding material maintains strength and stability. In some formulations, the shielding material may be applied by hand to encapsulate sources of radiation or to repair dents or holes in existing shielding material. In other formulations, the shielding material may be injected into molds or fed into extruders to obtain desired shapes.
In another embodiment of the invention, the resinous binder includes a thermoset epoxy resin binder comprising an epoxy base component and a curing agent including cycloaliphatic polyamine. The radiation absorbing material includes lead powder suspended substantially homogeneously throughout the resinous binder, and the thixotropic agent includes aramid fibers dispersed in the resinous binder to act as a suspending agent for the lead powder, and to act as a reinforcing agent. The lead powder can comprise up to about 95% by weight of the total composition, or about 665 by volume of the total composition, and the shielding material maintains good strength and stability. Prior to setting, the shielding material may be applied by hand to encapsulate sources of radiation or it may be injected into molds or extruded to obtain desired shapes.
Another embodiment of the invention includes an epoxy base component. The epoxy base component is for use in forming a polymeric shielding material containing up to about 66% by volume radiation absorbing material and therefore having a high radiation shielding effectiveness. The epoxy base component is formulated such that when the epoxy base component is mixed with a curing agent component, the polymeric shielding material is formed. The epoxy base component includes an epoxy resin, a thixotropic agent, and a radiation absorbing material.
Another embodiment of the invention includes a curing agent component. The curing agent component is for use in forming a polymeric shielding material containing up to about 66% by volume radiation absorbing material and therefore having a high radiation shielding effectiveness. The curing agent component is formulated such that when said curing agent component is mixed with an epoxy base component, the polymeric shielding material is formed. The curing agent component includes a curing agent, a thixotropic agent, and a radiation absorbing material.
Another embodiment of the invention includes a polymeric composition including a resinous binder, and a high level of a radiation absorbing material suspended substantially homogeneously throughout the resinous binder. The radiation absorbing material comprises from about 55% to about 66% by volume of the total composition. In certain embodiments the radiation absorbing material comprises from about 91%
to about 95% by weight of the total composition. In some embodiments, the radiation absorbing material is lead powder.
Before embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention provides a composition designed as shielding to absorb and shield against radiation. The composition includes polymeric materials having radiation absorbing material and a thixotropic agent homogeneously dispersed therethrough. The radiation absorbing material and thixotropic agent are homogeneously dispersed throughout a resinous binder.
The thixotropic agent is included in the formulation to act as a suspending agent for the radiation absorbing material. The thixotropic agent maintains the radiation absorbing material in suspension sufficiently well to allow for the maintenance of a homogeneous dispersion of the absorbing material throughout the binder.
As used herein, "resinous binder" means a synthetic organic resin or a man-made high polymer including thermoset and thermoplastic compounds that are moldable in an uncured or unset state, and that are compatible with the radiation absorbing material and thixotropic agent used. Most any resinous binder that does not interfere with the purpose of the radiation shielding material can be used. The desirable characteristics of the resinous binder include mechanical strength, chemical stability and compatibility with the absorbing material and thixotropic agent. Choice of the resinous binder will for the large part depend on the expected conditions of use and exposure of the radiation shielding material.
It is preferable to use a resin binder that has properties that are appropriate to the environment in which it will be used. For example, it is often desirable to use a resinous binder that is resistant to the effects of heat and radiation.
Suitable resinous binders include, but are not limited to: thermoset epoxies, phenolic resins, unsaturated polyesters, polyurethanes, polyureas, polyvinyl chloride homo- and co-polymers, polyolefins, vinylesters, methacrylates, polycarbonates, polyethers, polyamides, co-polyetheresters, polyphenylene ethers, co-polyestercarbonates, polyaryl ethers, polyamide imides, polystyrenes, acrylonitrile butadiene styrene copolymers, and mixtures thereof. Thermoset epoxy resin based systems are preferred, particularly those employing a liquid epoxy resin base component cured with a cycloaliphatic polyamine resin because such systems are worker friendly in that they are non-critical in handling, cure well over a wide temperature range and are quite tolerant of imperfectly prepared substrates. Furthermore the epoxy resin/cycloaliphatic polyamine mixture employed in the most preferred embodiments has been shown to be particularly resistant to the effects of intense ionizing radiation during DBA testing for nuclear applications. A particularly suitable and commercially available epoxy resin is Ciba Geigy #6005, marketed by Ciba Geigy Corporation, Three Skyline Drive, Hawthorne, New York 10532. A particularly suitable and commercially available cycloaliphatic polyamine resin curing agent is Air Products #2280, marketed by Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195-1501.
As used herein, ~radiation absorbing material"
generally means a material that efficiently absorbs incident high energy radiation such as X-ray, gamma and beta radiation so that appreciable attenuation occurs within a relatively short path. Other desirable attributes for most general applications include commercial availability in the physical form desired for reasonable cost, chemical and physical stability and manageable toxicity. Suitable radiation absorbing materials include materials which exhibit a substantial radiation absorbing property, and are compatible with the resinous binder and the thixotropic agent.
Suitable radiation absorbing materials include: lead, bismuth, tungsten, depleted uranium, tin, copper, silver, nickel stainless steel, and mixtures thereof.
More preferably, due to their high radiation shielding effectiveness, the radiation absorbing material is one of the following: lead, bismuth, tungsten, depleted uranium, and mixtures thereof. Due to its availability, high shielding effectiveness, and low cost, the most generally preferred radiation absorbing material is lead.
Although the radiation absorbing material may be in many different physical forms, such as in fibers or flakes, it is preferred that the radiation absorbing material be in a generally spherical powder form. Due to the reduction in physical interaction between powder particles as compared to the physical interaction between flakes or fibers in the mixture, more powder can be put into the composition, thereby increasing the shielding ability of the shielding material. It is preferred that the radiation absorbing material powder comprises generally spherical particles having an average diameter ranging from about 50 to about 250 microns. It is more preferable that the absorbing material powder comprises generally spherical particles having an average diameter ranging from about 100 to about 150 microns. Such particles permit a high amount of radiation material loading, storage stability and ease of manufacturing and use. A particularly suitable commercially available lead powder is Lead powder-150 micron, a product marketed by Vulcan Lead Products, Inc., 1400 West Pierce Street, Milwaukee, WI 53204.
The invention provides that the radiation absorbing material can comprises up to about 95% by weight of the total composition, or up to about 665 by volume of the total composition. The loading of the absorbing material used is largely dependent upon the most desirable viscosities and shielding ability for the applications intended. As more absorbing material is added to a formulation, the better the shielding capabilities, but the more viscous the mixture becomes.
For better shielding properties of the composition while still allowing workability of the composition before curing or setting, it is preferred that the absorbing material comprises from about 50% to about 95% by weight of the total composition, or from about 20% to about 66% by volume of the total composition.
It is more preferred that absorbing material comprises from about 75% to about 94% by weight of the total composition, or from about 40% to about 65% by volume of the total composition. It is even more preferred that the radiation absorbing material comprises from about 85% to about 94% by weight of the total composition, or from about 50% to about 60% by volume of the total composition. It is most preferred that the radiation absorbing material comprises about 93% by weight of the total composition, or about 57% by volume of the total composition. In some embodiments, the radiation absorbing material comprises about 95% by weight of the total composition. In other embodiments, the radiation absorbing material comprises about 66% by volume of the total composition.
As used herein, ~thixotropic agent~ means compounds which, when combined with resinous binders, act to form gels that liquify when agitated and return to the gel form when at rest, and act to maintain and suspend the dispersion of radiation absorbing material within the resinous binder. The thixotropic agent is dispersed in the resinous binder to act as a suspending agent for the absorbing material thereby maintaining a homogeneous dispersion of the absorbing material throughout the shielding material. The thixotropic agent acts to maintain a homogeneous dispersion of the absorbing material before and during the resinous binder curing or setting process. Therefore, during transportation, storage and handling of the uncured or unset mixture including the resinous binder, the absorbing material remains substantially homogeneously dispersed within the resinous binder. During the curing or setting of the binder, the thixotropic agent maintains the homogenous dispersion of the absorbing material.
Most thixotropic agents that are compatible with the resinous binder and the absorbing material are suitable for use in the formulation. Suitable thixotropic agents include: aramid fibers, polyolefin fibers, bentonite clay, derivatives of bentonite clay, hydrogenated castor oil, derivatives of hydrogenated castor oil, pyrogenic silica, and mixtures thereof.
Aramid fibers, polyolefin fibers, or mixtures thereof are preferred due to the high structural support provided by such fibers, with aramid fibers being most preferred due to their resistance to heat and added structural support. Of the aramid fibers, Kevlar~
fiber, marketed by Du Pont Company, is most preferred.
Kevlar~ fiber has been found to offer the best overall mix of properties and, additionally, serves to toughen and reinforce the shielding material.
The aramid fibers acting as a thixotropic agent generally average between about 0.3 millimeters and about 10 millimeters in length. For better texture and consistency of the formulation, it is preferred that the aramid fibers average between about 0.5 millimeters and about 5 millimeters in length.
Generally, the thixotropic agent comprises from about 0.05% to about 1.0% by weight of the total composition, depending upon the amount of material present, the amount of structural support desired, and the desired viscosity of the uncured mixture. For an uncured mixture having a moldable putty viscosity, the thixotropic agent more preferably comprises from about 0.10% to about 0.5% by weight of the total composition.
Even more preferably, the thixotropic agent comprises from about 0.2~ to about 0.25% by weight of the total composition, and most preferably comprises about 0.22%
by weight of the total composition. To produce an uncured mixture having more of a pourable liquid viscosity, the thixotropic agent more preferably comprises from about 0.05% to about 0.15% by weight of the total composition. Even more preferably, the thixotropic agent comprises from about 0.08% to about 0.12% by weight of the total composition, and most preferably comprises about 0.11% by weight of the total composition.
For assistance in assuring complete mixing of the components, it is desirable, but not strictly necessary, to add pigment to the formulation. Suitable pigments include: titanium dioxide, black iron oxide, carbon black, lampblack, metallic aluminum flake, and phthalocyanine blue or green, and mixtures thereof.
Other commonly used colored pigments could also be used.
For an embodiment of the invention being made from an epoxy base component and a separate curing agent component, it is desirable, but not strictly necessary, to add pigment to each component with different color pigments in order that a third shade results from their mixing.
According to the invention, it would be possible to homogeneously disperse an absorbing material and a thixotropic agent into a molten thermoplastic resin which would be allowed to solidify for storage and transportation and which would be remelted immediately prior to application or injection into a mold or feeding into an extruder. After the mixture is applied, molded or formed into a desired shape, it would be allowed to set or cure, resulting in a radiation shielding material. The homogeneous dispersion of the radiation absorbing material would be substantially retained throughout each of these steps, and produces a final radiation shielding material having a substantially homogeneous dispersion of radiation absorbing material.
Also according to the invention, it is possible to disperse the absorbing material and the thixotropic CA 0223l008 l998-03-04 agent into an epoxy base component and a separate curing agent component. The two components remain separate for storage and transportation. When it is desired to produce a polymeric shielding material, the two components are mixed. Prior to setting, the mixed material is applied by hand to encapsulate sources of radiation or it is injected into molds or extruded to obtain desired shapes. The homogeneous dispersion of the absorbing material is substantially retained throughout each of these steps, and produces a final radiation shielding material having a substantially homogeneous dispersion of radiation absorbing material.
The following examples are intended to exemplify embodiments of the invention and are not to be construed as limitations thereof.
EXAMPLES
EXAMPLE NO. 1: RADIATION SNIELDING MATERIAL THAT IS
MOr.n~Rr.~ PUTTY PRIOR TO SETTING/CURING
A first shielding material in accordance with the invention was prepared. This particular shielding material was a moldable putty in an uncured state, and hardened as the resinous binder cured. The shielding material was prepared by first admixing lead powder, color pigment, and a thixotropic agent, Kevlar~, into an epoxy base component, (CIBA GEIGY #6005), and into a separate curing agent component, cycloaliphatic polyamine resin (AIR PRODUCTS #2280). The ingredients were added in amounts in accordance with the weight percentages given in tables 1 and 2, respectively for each component. The two components remained separate until it was desired to produce the shielding material, at which time the two components were mixed to form a moldable putty. Prior to setting, the mixed material can be applied by hand or by other means to encapsulate sources of radiation, repair existing shields, or may be molded or formed into desired shapes. In this case, the material was applied by hand to form a sheet. Upon curing of the binder, a polymeric radiation shielding material was produced having a homogeneous dispersion of radiation absorbing material therethrough, and maintaining a high level of strength and stability.
As shown in Table 3, the final composition contains about 90.89% radiation absorbing material (lead) by weight of the total composition. The composition of the base component is listed in Table 1, the composition of the curing agent is listed in Table 2, and the mixing ratio of the two components along with the composition of the mixed components, or the final product, is listed in Table 3.
The resinous portion of this formula was derived from a formulation which performs very well in Design Basic Accident testing (hereinafter "DBA test"). The final radiation shielding composition passed the ASTM
D-3911 DBA test. Testing at 2.2 x 106 rads/hour to a total dose of 1.1 X 109 rads showed the exceptional performance of this system. The final radiation shielding material is hard, tough, and has a very uniform distribution of lead across the matrix.
EPOXY BASE COMPONENT:% W/W S. G.VOL .
CIBA GEIGY #6005 8.66 1.167.466 KEVLAR FIBER #lF5430.21 1.440.146 SYNTH. BLACK IRON OXIDE 0.22 4.50 0.049 LEAD POWDER - 150 MICRON 90.9111.30 8.045 100.00 (6.37)15.706 CURING AGENT COMPONENT: % w/w S. G . VOL .
AIR PRODUCTS #2280 7.93 1.067.481 KEVLAR FIBER #lF5430.23 1.440.160 RUTILE TITANIUM DIOXIDE 0.99 4.00 0.248 LEAD POWDER - 150 MICRON 90.8511.30 8.040 100.00 (6.28)15.929 MIXING RATIO:
EPOXY BASE COMPONENT/CURING AGENT COMPONENT:
1,155.1/756.8 = 1.53/1.00 w/w 181.3/120.5 = 1.50/1.00 v/v MIXED COMPONENTS: % w/w S.G. VOL.
CIBA GEIGY #6005 5.23 1.16 4.509 AIR PRODUCTS #2280 3.14 1.06 2.962 KEVLAR FIBER #lF5430.22 1.44 0.153 SYNTH. BLACK IRON OXIDE 0.13 4.50 0.029 RUTILE TITANIUM DIOXIDE 0.39 4.00 0.098 LEAD POWDER - 150 MICRON 90.89 11.30 8.043 100.00 (6.33) 15.794 EXANPLE NO. 2: RADIATION SHIELDING MATERIAL THAT IS
PUMPABLE/POURABLE PRIOR TO SETTING/CURING
A second shielding material in accordance with the invention was also prepared. This particular shielding material was a pourable liquid in an uncured state, and hardened as the resinous binder cured. The shielding material was prepared by first a~m;x;ng lead powder, and a thixotropic agent, Kevlar~, into an epoxy base component, (CIBA GEIGY #6005), and into a separate curing agent component, cycloaliphatic polyamine resin (AIR PRODUCTS #2280). The ingredients were added in amounts in accordance with the weight percentages given in tables 4 and 5, respectively for each component.
The two components remained separate until it was desired to produce the shielding material, at which time the two components were mixed to form a pourable liquid. Prior to setting, the mixed material may be poured or pumped into an injection mold or extruder, or may be applied by hand to form a desired shape of a shielding material. In this case the mixed material was poured into a prepared void within a cylindrical form to form a radiation shield suitable for, say, a pipe or other cylindrical shape. Upon curing of the binder, a polymeric radiation shielding material was procured having a homogeneous dispersion of radiation material therethrough, and maintaining a high level of strength and stability.
As is shown by Table 6, the final composition contains about 89.30% radiation absorbing material, (lead) by weight of the total composition. The composition of the base component is listed in Table 4, the composition of the curing agent is listed in Table 5, and the mixing ratio of the two components along with the composition of the mixed components, or the final product, is listed in Table 6.
This formula also performs very well in the ASTM
D-3911 DBA test. Testing at 2.2 x 106 rads/hour to a total dose of 1.1 X 109 rads showed the exceptional performance of this system.
EPOXY BASE COMPONENT:% w/w S.G. VOL.
CIBA GEIGY #6005 10.92 1.16 9.414 KEVLAR FIBER #lF5430.11 1.44 0.076 LEAD POWDER - 150 MICRON 88.97 11.30 7.873 100.00 (5.76)17.363 CURING AGENT COMPONENT: % W/W S.G. VOL.
AIR PRODUCTS #228010.08 1.06 9.509 KEVLAR FIBER #lF5430.11 1.44 0.076 LEAD POWDER - 150 MICRON 89.81 11.30 7.948 100.00 (5.70)17.533 MIXING RATIO
EPOXY BASE COMPONENT/CURING AGENT COMPONENT:
9,458.9/5,731.7 = 1.65/1.00 w/w 995.3/653.4 = 1.52/1.00 v/v MIXED COMPONENTS: %w/w S.G. VOL.
CIBA GEIGY #6005 6.62 1.16 5.707 AIR PRODUCTS #22803.97 1.06 3.745 KEVLAR FIBER #lF5430.11 1.44 0.076 LEAD POWDER - 150 MICRON 89.30 11.30 7.903 100.00 (5.74)17.431 Mixing and dispersion of the ingredients to form each of the separate components for examples 1 and 2 were accomplished using conventional "High Speed Dispersion~ equipment or similar mixing equipment. In this case the reference to ~high speed~ refers to the ease and quickness of production rather than the speed of any moving parts. The dispersion equipment is no more than an electric motor connected to a vertical shaft through pulleys and a variable speed drive. The shaft is fitted with a disc shaped blade at its base.
The blade has "sawteeth" up and down-turned around the edge set at not quite a tangent to the disc. One 10 source of such a disperser is Hockmeyer, IncThe equipment was run under low speed, high torque, conditions to uniformly disperse the lead material, fibers and color pigments throughout the individual components. During the course of raw material additions to the resinous ingredients the temperature of the batch becomes elevated due to the mechanical work being performed. A mixing procedure was carried out separately for each of the separate epoxy base and curing agent components in the above examples. For each separate component, the ingredients were separately loaded into a simple cylindrical mixing vessel and mixes as described below:
a) Add the resin ingredients (either #6005 liquid epoxy resin or the #2280 curing agent).
b) Move the mixing vessel under the disperser and with the disperser running at minimum speed slowly add the pre-weighed Kevlar #lF543 fiber. Mix until evenly dispersed throughout the mix - about 10 minutes.
c) Pre-weigh and add any color pigment required by the formulation and continue mixing.
d) Pre-weigh and add the lead powder under slow speed agitation. As the lead is added the mixture will gradually thicken. Add lead as quickly as the disperser can disperse the powder into the resinous mixture. It may be necessary to assist mixing towards the end of the addition by moving the mixture with paddles and/or by adjusting the height of the mixing blade and/or its speed of rotation.
The mutually reactive components for each example were stored separately and then mixed immediately before use to form the final shielding material.
Both of the final shielding material compositions of examples 1 and 2 comprise a large quantity of finely divided lead powder uniformly dispersed in an epoxy/curing agent resin mixture. The resinous ingredients in each example is highly loaded with lead powder in order to mAx;m;ze the effectiveness of the mixture as a radiation shield. The amount of lead used in each application has been largely developed to yield the most desirable viscosities and shielding capabilities for the applications intended. It is possible to obtain concentrations of approximately 50%
by volume of radiation lead powder in the total formulation while retaining a fluid, easily workable viscosity. The major difference between the two formula given in examples 1 and 2 is the amount of lead powder and Kevlar~ present in the formulations, thus effecting the viscosity of the formulations. Example 1 produces an uncured mixture that is a moldable putty, while example 2 produces a mixture that is a pourable liquid until curing results in an infusible solid.
The Kevlar0 fibers reinforce the formulation and assist in suspending the lead powder to retard settlement. The Kevlar~ fibers also enhance the mechanical properties of the composition and contribute to absorbing material suspension. The Kevlar~ also yields a stiff, thixotropic paste which assists application in thick layers. The heat resistance of Kevlar~ is extremely high with essentially no degradation in properties to almost 800~F.
The titanium dioxide and synthetic black iron oxide in example 1 are present as pigments to highlight areas of unmixed components which show up as streaks of light or dark material in the mix. In formulations of the type given as examples, the individual components are stable indefinitely and, if improperly mixed, may never cure. Once mixed with each other in the correct ratio the two components proceed with their curing reaction in a very definite and predictable way.
Various of the features are set forth in the following claims.
FIELD OF THE INVENTION
The present invention relates to material for radiation shielding, and more particularly to radiation shielding material made of resinous binders with radiation absorbing material dispersed homogeneously therethrough.
BACKGROUND PRIOR ART
It is well known that radiation resulting from medical, industrial, military, and other sources can be harmful. Care must be taken to shield living organisms and certain non-living objects from exposure to such harmful radiation. It is well known to use plates of radiation absorbing metals, such as lead plates, for radiation shields. However, such plates are often heavy, difficult to work with and apply, and often susceptible to damage, such as denting, through normal usage. Therefore, some focus has been directed towards using resinous binders or plastic materials having radiation absorbing material, such as lead, dispersed therethrough for radiation shielding material. Such material is easier to work with and mold into desired shapes, and is often more durable. However, it has often been a problem maintaining a homogeneous dispersion of the radiation absorbing material throughout the resinous binder. Often the absorbing material will settle to the lower portions of the resinous binder due to gravitational forces. This settling occurs rapidly in the time period before the resinous binder cures or sets during the production of the shielding material. AS a result, the dispersion of radiation absorbing material is not homogeneous throughout the shielding material and areas of low radiation shielding result.
It has also been found that if sufficient radiation absorbing materials are incorporated to achieve the required shielding, the product is frequently not strong enough to support its own weight, and also tends to tear or split when it is flexed.
Conversely, if the amount of radiation absorbing material is adjusted so as to obtain a product which is self supporting and/or has adequate flexibility, its shielding capability is inadequate or is only adequate if the material is used in a thickness which creates problems due to its bulk and also restricts the ability of the material to flex.
It is known to disperse large quantities of lead throughout a plasticizer resinous matrix to form a moldable putty shielding material, as is shown in U.S.
Patent No. 2,162,178. However, the problem with such putty substances is that they do not cure to a hardened state, and do not exhibit the strength and structure necessary for many shielding uses.
Laminates have been developed which incorporate radiation absorbing material and laminate such material with layers of structural supporting material.
However, such laminates can be difficult and expensive to manufacture, and are restricted in shapes and usage.
SUMMARY OF THE INVENTION
The invention provides an improved radiation shielding material.
One object of this invention is to provide an improved polymeric composition for radiation shielding.
Another object of the invention is to provide a polymeric composition with a high lead equivalency for radiation shielding.
Another object of the invention is to provide a polymeric radiation shielding material that has a substantially homogeneous dispersion of radiation absorbing material therethrough with minimal areas of low shielding capability.
Another object of the invention is to provide a polymeric radiation shielding material with a high concentration of radiation absorbing material while maintaining a high level of strength and stability.
Another object of this invention is to provide a polymeric radiation shielding material that is relatively injection moldable.
Another object of the invention is to provide for a polymeric radiation shielding material that is extrudable.
Another object of the invention is to provide a radiation shielding material that can be prepared and applied to an area in a liquid or putty state which then cures or hardens to a solid state having a high level of strength and stability.
Another object of the invention is to provide a polymeric radiation shielding material that is relatively lightweight and easy to work with.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description and claims.
One embodiment of the invention provides a polymeric composition having a high radiation shielding effectiveness containing up to about 66% by volume radiation absorbing material. The composition includes a resinous binder, a radiation absorbing material suspended substantially homogeneously throughout the resinous binder, and a thixotropic agent dispersed in the resinous binder to act as a suspending agent. The thixotropic agent is present in an amount sufficient to substantially suspend the absorbing material in the resinous binder.
The thixotropic agent acts to help produce the high radiation shielding effectiveness throughout the shielding material by acting to maintain a homogeneous dispersion of large amounts of absorbing material before, during, and after the resinous binder sets or cures. In some embodiments, the thixotropic agent also acts as a supporting or reinforcing agent, thereby adding to the strength and stability of the shielding material after it cures. In certain embodiments, the absorbing material can comprise up to about 95% by weight of the total composition, and due to the thixotropic agent, this large amount of absorbing material is homogeneously dispersed throughout the binder, and the shielding material maintains strength and stability. In some formulations, the shielding material may be applied by hand to encapsulate sources of radiation or to repair dents or holes in existing shielding material. In other formulations, the shielding material may be injected into molds or fed into extruders to obtain desired shapes.
In another embodiment of the invention, the resinous binder includes a thermoset epoxy resin binder comprising an epoxy base component and a curing agent including cycloaliphatic polyamine. The radiation absorbing material includes lead powder suspended substantially homogeneously throughout the resinous binder, and the thixotropic agent includes aramid fibers dispersed in the resinous binder to act as a suspending agent for the lead powder, and to act as a reinforcing agent. The lead powder can comprise up to about 95% by weight of the total composition, or about 665 by volume of the total composition, and the shielding material maintains good strength and stability. Prior to setting, the shielding material may be applied by hand to encapsulate sources of radiation or it may be injected into molds or extruded to obtain desired shapes.
Another embodiment of the invention includes an epoxy base component. The epoxy base component is for use in forming a polymeric shielding material containing up to about 66% by volume radiation absorbing material and therefore having a high radiation shielding effectiveness. The epoxy base component is formulated such that when the epoxy base component is mixed with a curing agent component, the polymeric shielding material is formed. The epoxy base component includes an epoxy resin, a thixotropic agent, and a radiation absorbing material.
Another embodiment of the invention includes a curing agent component. The curing agent component is for use in forming a polymeric shielding material containing up to about 66% by volume radiation absorbing material and therefore having a high radiation shielding effectiveness. The curing agent component is formulated such that when said curing agent component is mixed with an epoxy base component, the polymeric shielding material is formed. The curing agent component includes a curing agent, a thixotropic agent, and a radiation absorbing material.
Another embodiment of the invention includes a polymeric composition including a resinous binder, and a high level of a radiation absorbing material suspended substantially homogeneously throughout the resinous binder. The radiation absorbing material comprises from about 55% to about 66% by volume of the total composition. In certain embodiments the radiation absorbing material comprises from about 91%
to about 95% by weight of the total composition. In some embodiments, the radiation absorbing material is lead powder.
Before embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention provides a composition designed as shielding to absorb and shield against radiation. The composition includes polymeric materials having radiation absorbing material and a thixotropic agent homogeneously dispersed therethrough. The radiation absorbing material and thixotropic agent are homogeneously dispersed throughout a resinous binder.
The thixotropic agent is included in the formulation to act as a suspending agent for the radiation absorbing material. The thixotropic agent maintains the radiation absorbing material in suspension sufficiently well to allow for the maintenance of a homogeneous dispersion of the absorbing material throughout the binder.
As used herein, "resinous binder" means a synthetic organic resin or a man-made high polymer including thermoset and thermoplastic compounds that are moldable in an uncured or unset state, and that are compatible with the radiation absorbing material and thixotropic agent used. Most any resinous binder that does not interfere with the purpose of the radiation shielding material can be used. The desirable characteristics of the resinous binder include mechanical strength, chemical stability and compatibility with the absorbing material and thixotropic agent. Choice of the resinous binder will for the large part depend on the expected conditions of use and exposure of the radiation shielding material.
It is preferable to use a resin binder that has properties that are appropriate to the environment in which it will be used. For example, it is often desirable to use a resinous binder that is resistant to the effects of heat and radiation.
Suitable resinous binders include, but are not limited to: thermoset epoxies, phenolic resins, unsaturated polyesters, polyurethanes, polyureas, polyvinyl chloride homo- and co-polymers, polyolefins, vinylesters, methacrylates, polycarbonates, polyethers, polyamides, co-polyetheresters, polyphenylene ethers, co-polyestercarbonates, polyaryl ethers, polyamide imides, polystyrenes, acrylonitrile butadiene styrene copolymers, and mixtures thereof. Thermoset epoxy resin based systems are preferred, particularly those employing a liquid epoxy resin base component cured with a cycloaliphatic polyamine resin because such systems are worker friendly in that they are non-critical in handling, cure well over a wide temperature range and are quite tolerant of imperfectly prepared substrates. Furthermore the epoxy resin/cycloaliphatic polyamine mixture employed in the most preferred embodiments has been shown to be particularly resistant to the effects of intense ionizing radiation during DBA testing for nuclear applications. A particularly suitable and commercially available epoxy resin is Ciba Geigy #6005, marketed by Ciba Geigy Corporation, Three Skyline Drive, Hawthorne, New York 10532. A particularly suitable and commercially available cycloaliphatic polyamine resin curing agent is Air Products #2280, marketed by Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195-1501.
As used herein, ~radiation absorbing material"
generally means a material that efficiently absorbs incident high energy radiation such as X-ray, gamma and beta radiation so that appreciable attenuation occurs within a relatively short path. Other desirable attributes for most general applications include commercial availability in the physical form desired for reasonable cost, chemical and physical stability and manageable toxicity. Suitable radiation absorbing materials include materials which exhibit a substantial radiation absorbing property, and are compatible with the resinous binder and the thixotropic agent.
Suitable radiation absorbing materials include: lead, bismuth, tungsten, depleted uranium, tin, copper, silver, nickel stainless steel, and mixtures thereof.
More preferably, due to their high radiation shielding effectiveness, the radiation absorbing material is one of the following: lead, bismuth, tungsten, depleted uranium, and mixtures thereof. Due to its availability, high shielding effectiveness, and low cost, the most generally preferred radiation absorbing material is lead.
Although the radiation absorbing material may be in many different physical forms, such as in fibers or flakes, it is preferred that the radiation absorbing material be in a generally spherical powder form. Due to the reduction in physical interaction between powder particles as compared to the physical interaction between flakes or fibers in the mixture, more powder can be put into the composition, thereby increasing the shielding ability of the shielding material. It is preferred that the radiation absorbing material powder comprises generally spherical particles having an average diameter ranging from about 50 to about 250 microns. It is more preferable that the absorbing material powder comprises generally spherical particles having an average diameter ranging from about 100 to about 150 microns. Such particles permit a high amount of radiation material loading, storage stability and ease of manufacturing and use. A particularly suitable commercially available lead powder is Lead powder-150 micron, a product marketed by Vulcan Lead Products, Inc., 1400 West Pierce Street, Milwaukee, WI 53204.
The invention provides that the radiation absorbing material can comprises up to about 95% by weight of the total composition, or up to about 665 by volume of the total composition. The loading of the absorbing material used is largely dependent upon the most desirable viscosities and shielding ability for the applications intended. As more absorbing material is added to a formulation, the better the shielding capabilities, but the more viscous the mixture becomes.
For better shielding properties of the composition while still allowing workability of the composition before curing or setting, it is preferred that the absorbing material comprises from about 50% to about 95% by weight of the total composition, or from about 20% to about 66% by volume of the total composition.
It is more preferred that absorbing material comprises from about 75% to about 94% by weight of the total composition, or from about 40% to about 65% by volume of the total composition. It is even more preferred that the radiation absorbing material comprises from about 85% to about 94% by weight of the total composition, or from about 50% to about 60% by volume of the total composition. It is most preferred that the radiation absorbing material comprises about 93% by weight of the total composition, or about 57% by volume of the total composition. In some embodiments, the radiation absorbing material comprises about 95% by weight of the total composition. In other embodiments, the radiation absorbing material comprises about 66% by volume of the total composition.
As used herein, ~thixotropic agent~ means compounds which, when combined with resinous binders, act to form gels that liquify when agitated and return to the gel form when at rest, and act to maintain and suspend the dispersion of radiation absorbing material within the resinous binder. The thixotropic agent is dispersed in the resinous binder to act as a suspending agent for the absorbing material thereby maintaining a homogeneous dispersion of the absorbing material throughout the shielding material. The thixotropic agent acts to maintain a homogeneous dispersion of the absorbing material before and during the resinous binder curing or setting process. Therefore, during transportation, storage and handling of the uncured or unset mixture including the resinous binder, the absorbing material remains substantially homogeneously dispersed within the resinous binder. During the curing or setting of the binder, the thixotropic agent maintains the homogenous dispersion of the absorbing material.
Most thixotropic agents that are compatible with the resinous binder and the absorbing material are suitable for use in the formulation. Suitable thixotropic agents include: aramid fibers, polyolefin fibers, bentonite clay, derivatives of bentonite clay, hydrogenated castor oil, derivatives of hydrogenated castor oil, pyrogenic silica, and mixtures thereof.
Aramid fibers, polyolefin fibers, or mixtures thereof are preferred due to the high structural support provided by such fibers, with aramid fibers being most preferred due to their resistance to heat and added structural support. Of the aramid fibers, Kevlar~
fiber, marketed by Du Pont Company, is most preferred.
Kevlar~ fiber has been found to offer the best overall mix of properties and, additionally, serves to toughen and reinforce the shielding material.
The aramid fibers acting as a thixotropic agent generally average between about 0.3 millimeters and about 10 millimeters in length. For better texture and consistency of the formulation, it is preferred that the aramid fibers average between about 0.5 millimeters and about 5 millimeters in length.
Generally, the thixotropic agent comprises from about 0.05% to about 1.0% by weight of the total composition, depending upon the amount of material present, the amount of structural support desired, and the desired viscosity of the uncured mixture. For an uncured mixture having a moldable putty viscosity, the thixotropic agent more preferably comprises from about 0.10% to about 0.5% by weight of the total composition.
Even more preferably, the thixotropic agent comprises from about 0.2~ to about 0.25% by weight of the total composition, and most preferably comprises about 0.22%
by weight of the total composition. To produce an uncured mixture having more of a pourable liquid viscosity, the thixotropic agent more preferably comprises from about 0.05% to about 0.15% by weight of the total composition. Even more preferably, the thixotropic agent comprises from about 0.08% to about 0.12% by weight of the total composition, and most preferably comprises about 0.11% by weight of the total composition.
For assistance in assuring complete mixing of the components, it is desirable, but not strictly necessary, to add pigment to the formulation. Suitable pigments include: titanium dioxide, black iron oxide, carbon black, lampblack, metallic aluminum flake, and phthalocyanine blue or green, and mixtures thereof.
Other commonly used colored pigments could also be used.
For an embodiment of the invention being made from an epoxy base component and a separate curing agent component, it is desirable, but not strictly necessary, to add pigment to each component with different color pigments in order that a third shade results from their mixing.
According to the invention, it would be possible to homogeneously disperse an absorbing material and a thixotropic agent into a molten thermoplastic resin which would be allowed to solidify for storage and transportation and which would be remelted immediately prior to application or injection into a mold or feeding into an extruder. After the mixture is applied, molded or formed into a desired shape, it would be allowed to set or cure, resulting in a radiation shielding material. The homogeneous dispersion of the radiation absorbing material would be substantially retained throughout each of these steps, and produces a final radiation shielding material having a substantially homogeneous dispersion of radiation absorbing material.
Also according to the invention, it is possible to disperse the absorbing material and the thixotropic CA 0223l008 l998-03-04 agent into an epoxy base component and a separate curing agent component. The two components remain separate for storage and transportation. When it is desired to produce a polymeric shielding material, the two components are mixed. Prior to setting, the mixed material is applied by hand to encapsulate sources of radiation or it is injected into molds or extruded to obtain desired shapes. The homogeneous dispersion of the absorbing material is substantially retained throughout each of these steps, and produces a final radiation shielding material having a substantially homogeneous dispersion of radiation absorbing material.
The following examples are intended to exemplify embodiments of the invention and are not to be construed as limitations thereof.
EXAMPLES
EXAMPLE NO. 1: RADIATION SNIELDING MATERIAL THAT IS
MOr.n~Rr.~ PUTTY PRIOR TO SETTING/CURING
A first shielding material in accordance with the invention was prepared. This particular shielding material was a moldable putty in an uncured state, and hardened as the resinous binder cured. The shielding material was prepared by first admixing lead powder, color pigment, and a thixotropic agent, Kevlar~, into an epoxy base component, (CIBA GEIGY #6005), and into a separate curing agent component, cycloaliphatic polyamine resin (AIR PRODUCTS #2280). The ingredients were added in amounts in accordance with the weight percentages given in tables 1 and 2, respectively for each component. The two components remained separate until it was desired to produce the shielding material, at which time the two components were mixed to form a moldable putty. Prior to setting, the mixed material can be applied by hand or by other means to encapsulate sources of radiation, repair existing shields, or may be molded or formed into desired shapes. In this case, the material was applied by hand to form a sheet. Upon curing of the binder, a polymeric radiation shielding material was produced having a homogeneous dispersion of radiation absorbing material therethrough, and maintaining a high level of strength and stability.
As shown in Table 3, the final composition contains about 90.89% radiation absorbing material (lead) by weight of the total composition. The composition of the base component is listed in Table 1, the composition of the curing agent is listed in Table 2, and the mixing ratio of the two components along with the composition of the mixed components, or the final product, is listed in Table 3.
The resinous portion of this formula was derived from a formulation which performs very well in Design Basic Accident testing (hereinafter "DBA test"). The final radiation shielding composition passed the ASTM
D-3911 DBA test. Testing at 2.2 x 106 rads/hour to a total dose of 1.1 X 109 rads showed the exceptional performance of this system. The final radiation shielding material is hard, tough, and has a very uniform distribution of lead across the matrix.
EPOXY BASE COMPONENT:% W/W S. G.VOL .
CIBA GEIGY #6005 8.66 1.167.466 KEVLAR FIBER #lF5430.21 1.440.146 SYNTH. BLACK IRON OXIDE 0.22 4.50 0.049 LEAD POWDER - 150 MICRON 90.9111.30 8.045 100.00 (6.37)15.706 CURING AGENT COMPONENT: % w/w S. G . VOL .
AIR PRODUCTS #2280 7.93 1.067.481 KEVLAR FIBER #lF5430.23 1.440.160 RUTILE TITANIUM DIOXIDE 0.99 4.00 0.248 LEAD POWDER - 150 MICRON 90.8511.30 8.040 100.00 (6.28)15.929 MIXING RATIO:
EPOXY BASE COMPONENT/CURING AGENT COMPONENT:
1,155.1/756.8 = 1.53/1.00 w/w 181.3/120.5 = 1.50/1.00 v/v MIXED COMPONENTS: % w/w S.G. VOL.
CIBA GEIGY #6005 5.23 1.16 4.509 AIR PRODUCTS #2280 3.14 1.06 2.962 KEVLAR FIBER #lF5430.22 1.44 0.153 SYNTH. BLACK IRON OXIDE 0.13 4.50 0.029 RUTILE TITANIUM DIOXIDE 0.39 4.00 0.098 LEAD POWDER - 150 MICRON 90.89 11.30 8.043 100.00 (6.33) 15.794 EXANPLE NO. 2: RADIATION SHIELDING MATERIAL THAT IS
PUMPABLE/POURABLE PRIOR TO SETTING/CURING
A second shielding material in accordance with the invention was also prepared. This particular shielding material was a pourable liquid in an uncured state, and hardened as the resinous binder cured. The shielding material was prepared by first a~m;x;ng lead powder, and a thixotropic agent, Kevlar~, into an epoxy base component, (CIBA GEIGY #6005), and into a separate curing agent component, cycloaliphatic polyamine resin (AIR PRODUCTS #2280). The ingredients were added in amounts in accordance with the weight percentages given in tables 4 and 5, respectively for each component.
The two components remained separate until it was desired to produce the shielding material, at which time the two components were mixed to form a pourable liquid. Prior to setting, the mixed material may be poured or pumped into an injection mold or extruder, or may be applied by hand to form a desired shape of a shielding material. In this case the mixed material was poured into a prepared void within a cylindrical form to form a radiation shield suitable for, say, a pipe or other cylindrical shape. Upon curing of the binder, a polymeric radiation shielding material was procured having a homogeneous dispersion of radiation material therethrough, and maintaining a high level of strength and stability.
As is shown by Table 6, the final composition contains about 89.30% radiation absorbing material, (lead) by weight of the total composition. The composition of the base component is listed in Table 4, the composition of the curing agent is listed in Table 5, and the mixing ratio of the two components along with the composition of the mixed components, or the final product, is listed in Table 6.
This formula also performs very well in the ASTM
D-3911 DBA test. Testing at 2.2 x 106 rads/hour to a total dose of 1.1 X 109 rads showed the exceptional performance of this system.
EPOXY BASE COMPONENT:% w/w S.G. VOL.
CIBA GEIGY #6005 10.92 1.16 9.414 KEVLAR FIBER #lF5430.11 1.44 0.076 LEAD POWDER - 150 MICRON 88.97 11.30 7.873 100.00 (5.76)17.363 CURING AGENT COMPONENT: % W/W S.G. VOL.
AIR PRODUCTS #228010.08 1.06 9.509 KEVLAR FIBER #lF5430.11 1.44 0.076 LEAD POWDER - 150 MICRON 89.81 11.30 7.948 100.00 (5.70)17.533 MIXING RATIO
EPOXY BASE COMPONENT/CURING AGENT COMPONENT:
9,458.9/5,731.7 = 1.65/1.00 w/w 995.3/653.4 = 1.52/1.00 v/v MIXED COMPONENTS: %w/w S.G. VOL.
CIBA GEIGY #6005 6.62 1.16 5.707 AIR PRODUCTS #22803.97 1.06 3.745 KEVLAR FIBER #lF5430.11 1.44 0.076 LEAD POWDER - 150 MICRON 89.30 11.30 7.903 100.00 (5.74)17.431 Mixing and dispersion of the ingredients to form each of the separate components for examples 1 and 2 were accomplished using conventional "High Speed Dispersion~ equipment or similar mixing equipment. In this case the reference to ~high speed~ refers to the ease and quickness of production rather than the speed of any moving parts. The dispersion equipment is no more than an electric motor connected to a vertical shaft through pulleys and a variable speed drive. The shaft is fitted with a disc shaped blade at its base.
The blade has "sawteeth" up and down-turned around the edge set at not quite a tangent to the disc. One 10 source of such a disperser is Hockmeyer, IncThe equipment was run under low speed, high torque, conditions to uniformly disperse the lead material, fibers and color pigments throughout the individual components. During the course of raw material additions to the resinous ingredients the temperature of the batch becomes elevated due to the mechanical work being performed. A mixing procedure was carried out separately for each of the separate epoxy base and curing agent components in the above examples. For each separate component, the ingredients were separately loaded into a simple cylindrical mixing vessel and mixes as described below:
a) Add the resin ingredients (either #6005 liquid epoxy resin or the #2280 curing agent).
b) Move the mixing vessel under the disperser and with the disperser running at minimum speed slowly add the pre-weighed Kevlar #lF543 fiber. Mix until evenly dispersed throughout the mix - about 10 minutes.
c) Pre-weigh and add any color pigment required by the formulation and continue mixing.
d) Pre-weigh and add the lead powder under slow speed agitation. As the lead is added the mixture will gradually thicken. Add lead as quickly as the disperser can disperse the powder into the resinous mixture. It may be necessary to assist mixing towards the end of the addition by moving the mixture with paddles and/or by adjusting the height of the mixing blade and/or its speed of rotation.
The mutually reactive components for each example were stored separately and then mixed immediately before use to form the final shielding material.
Both of the final shielding material compositions of examples 1 and 2 comprise a large quantity of finely divided lead powder uniformly dispersed in an epoxy/curing agent resin mixture. The resinous ingredients in each example is highly loaded with lead powder in order to mAx;m;ze the effectiveness of the mixture as a radiation shield. The amount of lead used in each application has been largely developed to yield the most desirable viscosities and shielding capabilities for the applications intended. It is possible to obtain concentrations of approximately 50%
by volume of radiation lead powder in the total formulation while retaining a fluid, easily workable viscosity. The major difference between the two formula given in examples 1 and 2 is the amount of lead powder and Kevlar~ present in the formulations, thus effecting the viscosity of the formulations. Example 1 produces an uncured mixture that is a moldable putty, while example 2 produces a mixture that is a pourable liquid until curing results in an infusible solid.
The Kevlar0 fibers reinforce the formulation and assist in suspending the lead powder to retard settlement. The Kevlar~ fibers also enhance the mechanical properties of the composition and contribute to absorbing material suspension. The Kevlar~ also yields a stiff, thixotropic paste which assists application in thick layers. The heat resistance of Kevlar~ is extremely high with essentially no degradation in properties to almost 800~F.
The titanium dioxide and synthetic black iron oxide in example 1 are present as pigments to highlight areas of unmixed components which show up as streaks of light or dark material in the mix. In formulations of the type given as examples, the individual components are stable indefinitely and, if improperly mixed, may never cure. Once mixed with each other in the correct ratio the two components proceed with their curing reaction in a very definite and predictable way.
Various of the features are set forth in the following claims.
Claims (31)
1. A polymeric composition having a high radiation shielding effectiveness containing up to about 66% by volume radiation absorbing material, comprising:
a resinous binder;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder;
a thixotropic agent dispersed in said resinous binder to act as a suspending agent in an amount sufficient to substantially suspend said absorbing material in said resinous binder.
a resinous binder;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder;
a thixotropic agent dispersed in said resinous binder to act as a suspending agent in an amount sufficient to substantially suspend said absorbing material in said resinous binder.
2. A composition as in claim 1 wherein said resinous binder includes a resin selected from the group consisting of thermoset epoxies, phenolic resins, unsaturated polyesters, polyurethanes, polyureas, polyvinyl chloride homo- and co-polymers, polyolefins, vinylesters, methacrylates, polycarbonates, polyethers, polyamides, co-polyetheresters, polyphenylene ethers, co-polyestercarbonates, polyaryl ethers, polyamide imides, polystyrenes, acrylonitrile butadiene styrene copolymers, and mixtures thereof.
3. A composition as in claim 1 wherein said absorbing material is selected from the group consisting of lead, bismuth, tungsten, depleted uranium, and mixtures thereof.
4. A composition as in claim 1, wherein said absorbing material comprises up to about 95% by weight of the total composition.
5. A composition as in claim 1 wherein said thixotropic agent is selected from the group consisting of polyolefin fibers, aramid fibers, and mixtures thereof, and wherein said thixotropic agent also acts as a reinforcing agent.
6. A composition as in claim 5, wherein said thixotropic agent is aramid fibers.
7. A composition as in claim 1, wherein said thixotropic agent comprises from about 0.05% to about 1.0% by weight of the total composition.
8. A polymeric composition having a high radiation shielding effectiveness containing up to about 66% by volume radiation absorbing material, comprising:
a resinous binder including a resin selected from the group consisting of thermoset epoxies, phenolic resins, unsaturated polyesters, polyurethanes, polyureas, polyvinyl chloride homo- and co-polymers, polyolefins, vinylesters, methacrylates, polycarbonates, polyethers, polyamides, co-polyetheresters, polyphenylene ethers, co-polyestercarbonates, polyaryl ethers, polyamide imides, polystyrenes, acrylonitrile butadiene styrene copolymers, and mixtures thereof;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder, said radiation absorbing material including radiation shielding material selected from the group consisting of lead, bismuth, tungsten, depleted uranium, tin, copper, silver, nickel, stainless steel, and mixtures thereof;
a thixotropic agent dispersed in said resinous binder to act as a suspending agent in an amount sufficient to substantially suspend said absorbing material in said resinous binder, said thixotropic agent selected from the group consisting of aramid fibers, polyolefin fibers, bentonite clay, derivatives of bentonite clay, hydrogenated castor oil, derivatives of hydrogenated castor oil, pyrogenic silica, and mixtures thereof.
a resinous binder including a resin selected from the group consisting of thermoset epoxies, phenolic resins, unsaturated polyesters, polyurethanes, polyureas, polyvinyl chloride homo- and co-polymers, polyolefins, vinylesters, methacrylates, polycarbonates, polyethers, polyamides, co-polyetheresters, polyphenylene ethers, co-polyestercarbonates, polyaryl ethers, polyamide imides, polystyrenes, acrylonitrile butadiene styrene copolymers, and mixtures thereof;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder, said radiation absorbing material including radiation shielding material selected from the group consisting of lead, bismuth, tungsten, depleted uranium, tin, copper, silver, nickel, stainless steel, and mixtures thereof;
a thixotropic agent dispersed in said resinous binder to act as a suspending agent in an amount sufficient to substantially suspend said absorbing material in said resinous binder, said thixotropic agent selected from the group consisting of aramid fibers, polyolefin fibers, bentonite clay, derivatives of bentonite clay, hydrogenated castor oil, derivatives of hydrogenated castor oil, pyrogenic silica, and mixtures thereof.
9. A composition as in claim 8, wherein said absorbing material comprises up to about 95% by weight of the total composition.
10. A composition as in claim 8 wherein said thixotropic agent is selected from the group consisting of polyolefin fibers, aramid fibers, and mixtures thereof, and wherein said thixotropic agent also acts as a reinforcing agent.
11. A composition as in claim 8, wherein said thixotropic agent comprises from about 0.05% to about 1.0% by weight of the total composition.
12. A polymeric composition having a high radiation shielding effectiveness containing up to about 66% by volume radiation absorbing material, comprising:
a thermoset epoxy resin binder;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder, said radiation absorbing material including radiation shielding material selected from the group consisting of lead, bismuth, tungsten, depleted uranium, and mixtures thereof.
a thixotropic agent dispersed in said resinous binder to act as a suspending agent in an amount sufficient to substantially suspend said absorbing material in said resinous binder, said thixotropic agent selected from the group consisting of aramid fibers, polyolefin fibers, and mixtures thereof.
a thermoset epoxy resin binder;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder, said radiation absorbing material including radiation shielding material selected from the group consisting of lead, bismuth, tungsten, depleted uranium, and mixtures thereof.
a thixotropic agent dispersed in said resinous binder to act as a suspending agent in an amount sufficient to substantially suspend said absorbing material in said resinous binder, said thixotropic agent selected from the group consisting of aramid fibers, polyolefin fibers, and mixtures thereof.
13. A composition as in claim 12 wherein said resinous binder includes an epoxy base component and a curing agent component including a cycloaliphatic polyamine resin.
14. A composition as in claim 13 wherein said absorbing material is lead.
15.. A composition as in claim 12, wherein said absorbing material comprises up to about 95% by weight of the total composition.
16. A composition as in claim 12 wherein said thixotropic agent includes aramid fibers, and wherein said aramid fibers also act as reinforcing agents.
17. A composition as in claim 12, wherein said thixotropic agent comprises from about 0.05% to about 1.0% by weight of the total composition.
18. A polymeric composition having a high radiation shielding effectiveness containing up to about 66% by volume radiation absorbing material, comprising:
a thermoset epoxy resin binder comprising an epoxy base component and a curing agent including a cycloaliphatic polyamine resin;
a radiation absorbing material including lead powder suspended substantially homogeneously throughout said resinous binder to act as a radiation absorbing material;
a thixotropic agent including aramid fibers dispersed in said resinous binder to act as a suspending agent for said lead powder, and to act as a reinforcing agent.
a thermoset epoxy resin binder comprising an epoxy base component and a curing agent including a cycloaliphatic polyamine resin;
a radiation absorbing material including lead powder suspended substantially homogeneously throughout said resinous binder to act as a radiation absorbing material;
a thixotropic agent including aramid fibers dispersed in said resinous binder to act as a suspending agent for said lead powder, and to act as a reinforcing agent.
19. A composition as in claim 18, wherein said lead powder comprises up to about 95% by weight of the total composition.
20. A composition as in claim 18, wherein said aramid fibers average from about 0.3 millimeters to about 10 millimeters in length.
21. A composition as in claim 18, wherein said aramid fibers comprise from about 0.05% to about 1.0%
by weight of the total composition.
by weight of the total composition.
22. A composition as in claim 18 further including a coloring pigment.
23. An epoxy base component for use in forming a polymeric composition having a high radiation shielding effectiveness and containing up to about 66% by volume radiation absorbing material, such that when said epoxy base component is mixed with a curing agent component, the polymeric composition is formed, said epoxy base component comprising:
an epoxy resin;
a thixotropic agent; and a radiation absorbing material.
an epoxy resin;
a thixotropic agent; and a radiation absorbing material.
24. An epoxy base component as in claim 23, wherein said thixotropic agent is aramid fibers, and said radiation absorbing material is lead powder.
25. An epoxy base component as in claim 24, wherein said lead powder comprises up to about 95% by weight of the epoxy base component.
26. A curing agent component for use in forming a polymeric shielding material having a high radiation shielding effectiveness and containing up to about 66%
by volume radiation absorbing material, such that when said curing agent component is mixed with an epoxy base component, the polymeric composition is formed, said curing agent component comprising:
a curing agent;
a thixotropic agent; and a radiation absorbing material.
by volume radiation absorbing material, such that when said curing agent component is mixed with an epoxy base component, the polymeric composition is formed, said curing agent component comprising:
a curing agent;
a thixotropic agent; and a radiation absorbing material.
27. A curing agent component as in claim 26, wherein said curing agent is a cycloaliphatic polyamine resin, said thixotropic agent is aramid fibers, and said radiation absorbing material is lead powder.
28. A curing agent component as in claim 27, wherein said lead powder comprises up to about 95% by weight of the total composition of the epoxy base component.
29. A polymeric composition having a high radiation shielding effectiveness comprising:
a resinous binder;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder wherein said radiation absorbing material comprises from about 55% to about 66% by volume of the total composition.
a resinous binder;
a radiation absorbing material suspended substantially homogeneously throughout said resinous binder wherein said radiation absorbing material comprises from about 55% to about 66% by volume of the total composition.
30. A composition as in claim 29, wherein said radiation absorbing material comprises from about 91%
to about 95% by weight of the total composition.
to about 95% by weight of the total composition.
31. A composition as in claim 30, wherein said radiation absorbing material includes lead powder.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US3720097P | 1997-03-05 | 1997-03-05 | |
| US60/037,200 | 1997-03-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2231008A1 true CA2231008A1 (en) | 1998-09-05 |
Family
ID=29418167
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2231008 Abandoned CA2231008A1 (en) | 1997-03-05 | 1998-03-04 | Polymeric composition for radiation shielding |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2231008A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115058097A (en) * | 2017-10-10 | 2022-09-16 | 合肥显宏安瑞电子科技有限公司 | Ray shielding and high-voltage insulating resin composition and preparation method and application thereof |
-
1998
- 1998-03-04 CA CA 2231008 patent/CA2231008A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115058097A (en) * | 2017-10-10 | 2022-09-16 | 合肥显宏安瑞电子科技有限公司 | Ray shielding and high-voltage insulating resin composition and preparation method and application thereof |
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