US3438903A - Plastic radiation and acoustic barrier compositions containing a thixotropic agent - Google Patents

Description

United States Patent f US. Cl. 25247 18 Claims ABSTRACT OF THE DISCLOSURE A composition comprising a hardenable or thermoset resin, a thixotropic agent and a radiation attenuator; the hardened or cured product thereof; methods of applying this composition in a thixotropic state in the manner of plaster and hardening or curing it to yield structures shielded against noise and/or penetrating radiation, particularly in seamless applications.

This application is a contin-uation-in-part of my application S.N. 550,596, filed May 17, 1966, now abandoned, entitled Plastic Radiation and Acoustic Barriers.

This invention relates to new and improved plastic radiation and acoustic barrier compositions. More particularly, it relates to thixotropic plastic radiation and acoustic barrier compositions which may be applied by troweling or spraying to vertical surfaces without sagging or running.

These compositions comprise a hardenable or thermo set resin, a thixotropic agent and a radiation attenuator; hardened or cured products thereof; methods of applying these compositions in a thixotropic state, followed by subsequent hardening or curing; and structures shielded against noise and penetrating radiation by such applications, particularly in seamless applications.

It is well known to utilize dispersions of various heavy metals in plastics for radiation shielding purposes. Such compositions are, however, fluid and hence it has been necessary to use molds wherein they could be solidified by heat, pressure or curing reactions of various types. Their final emplacement has accordingly been in solid form and frequently makes use of nails, screws or other mechanical fastening methods.

The fluidity of these compositions has prevented their direct application to vertical surfaces which enclose sources of radiant or acoustic energy. Running and sagging of such compositions is particularly severe because of their necessarily high density which frequently reaches 6.5 g./cc. or more. Moreover, the shielding weights required for even moderately powerful sources are substantial. Typical X-ray machines operating in the usual 100-150 kvp. range require shielding of at least 4 lbs. of lead per square foot of wall area. More powerful installations, particularly those making use of radioisotopes, require several times that amount of shielding. The preparation of shielding compositions which are sufliciently plastic to permit ready application but which, once applied, are able to sustain their own Weight of 4 lbs/sq. ft. or more until hardening by some mechanism has set in, has not been possible heretofore.

Accordingly it has been standard practice to provide shielding by using lead or other radiation absorbing materials in rigid geometric shapes such as sheet or block. Such shapes are frequently incorporated into or bonded onto conventional building materials, ie plywood, concrete block, lath, etc. Use of such discontinuous shielding is subject to leakage at joints and fastenings and a variety of methods have been developed to minimize such leak- 3,438,903 Patented Apr. 15, 1969 age. Among these are overlapping lead sheets, staggering of blocks, lead-headed nails and lead-containing mortar. Nevertheless, experience shows that the installation in a typical X-ray room of many hundreds of individual shielding units, each surrounded by a seam or joint, does result in leakage at specific points. Such leakage may readily be determined by surveying the exterior walls of such rooms while penetrating radiation strikes the interior walls. Further, discontinuities in the walls such as electric switches, conduit or pipe present particularly difiicult shielding problems and are frequent sources of leakage. By contrast, the compositions of the present invention provide a completely seamless, imperforate barrier which, upon survey, is found to be free from leakage.

Accordingly it is an object of this invention to provide a radiation or acoustic barrier which may be applied to walls of ordinary construction by troweling or spraying without sagging or running. It is a further object of this invention to provide completely seamless and imperforate radiation and acoustic barriers. It is still a further object of this invention to provide radiation and acoustic barriers which offer complete design freedom with respect to size, curvature and shape. Finally it is yet another object of this invention to provide radiation and acoustic barriers which adhere strongly to a wide variety of substrates, e.g. concrete, wood, metal, ceramic, glass, plaster, etc. Other objects, features and advantages of this invention will become apparent from the following description and appended claims.

According to the present invention, I achieve these objects by indurating plastic radiation and acoustic barrier compositions comprising a hardenable or thermoset resin, its hardener or curing agent and a radiation attenuator, by the incorporation therein of a thixotropic agent. Surprisingly, such thixotropic compositions, when formulated in accordance with the present invention, are sufliciently plastic to permit application by troweling or spraying and yet will not sag or run from vertical surfaces. Even more surprisingly, the compositions of the present invention are able to sustain themselves on vertical surfaces at Weights of even 16 lbs. or more per square foot of wall area.

Thus, the compositions I have devised comprise a hardenable or thermoset resin, a thixotropic agent and a radiation attenuator which can be formulated into thixotropic compositions having, for example, the consistency of plaster or cement, and are capable of being applied to structures including vertical surfaces without sagging to the desired thickness in seamless, imperforate layers by employing the conventional techniques which are presently employed in the building trades such as by troweling or spraying, etc. and allowing the applied formulation to harden or cure, for example at ambient temperatures.

The use of such formulations allows complete architectural freedom. For example, a building or other structure can be designed without regard for radiation or accoustical requirements, in any size, curvature or shape, or of substantially any material, and all or any portion thereof can be rendered radiation or acoustic proof by applying the compositions of this invention. Thus, a hospital or clinic can be designed and built without regard to radiation problems. Thereafter any portion thereof can be converted, for example, to an X-ray laboratory by merely applying these compositions to selected areas thereof to the desired thickness in the manner of plaster to yield a seamless and imperforate radiation barrier.

Thixotropic agents have the property, when dispersed in suitable media, of exhibiting a variable viscosity which depends on the shear stress applied to the dispersion. At low shear stresses such thixotropic dispersions have high viscosities while at high shear stresses they have low viscosities. This phenomenon is believed to be due to the formation of a gel structure at low shear stresses and its progressive disruption as shear stresses increase. While this behavior is known and utilized, for example in paints and resin gel coats, the demands placed upon the thixotropic agent in the barrier compositions of the present invention far exceed those of all previous applications. On the one hand, the present barrier compositions contain high loadings of radiation attenuator which, with the additional viscosity developed by the thixotropic agent, would have been thought to preclude application by troweling or spraying. On the other hand, the extremely high density of these new compositions, coupled with the required thickness of up to /2 inch or more, would have been thought to preclude the development by the thixotropic agent of sufficient gel structure to prevent running or sagging from vertical surfaces.

Thixotropic agents vary widely in effectiveness as do the requirements of the various polymeric systems contemplated in this invention. Systems with viscous resins and high attenuator loadings will require less thixotropic agent than systems with more fluid resins and low attenuator loadings. Generally the objects of this invention are met by thixotrope concentrations from about 0.2% to about 7.5%, and in preferred compositions by about 0.2% to 2.5% by weight. Typical thixotropic agents and their approximate preferred concentrations by weight in the barrier compositions of the present invention are as follows: Colloidal silica, 0.21.0%; hydrogenated castor oil, OJ-1.5%; bentonite or kaolinite clays, 2.5-7.5% or more; carboxyl vinyl polymers such as those marketed by the B. F. Goodrich Chemical Company of Cleveland, Ohio, under the tradenames Carbopol and Carboset, 0.5-5.0%; organo-metallic complexes such as those marketed by the Lubrizol Corporation of Cleveland, Ohio, under the tra'dename Ircogel, 1.5-7.5 Colloidal cellulose such as those marketed under the trademark Avicel; colloidal asbestos such as those marketed under the trademark Avibest, by American Viscose Company. The action of colloidal silica may be further reinforced by the addition of about ODS-0.5% of a polyol such as ethylene glycol, glycerol, or a higher analogue.

Thixotropes are generally most effective when their distribution in the resin phase is such that their ultimate particle size is attained. This ultimate distribution is achieved by mixing under high shear conditions such as provided, for example, by the Cowles Dissolver or Dispersonic. Various other means of reducing the thixotropic agent to its ultimate particle size, including particularly grinding and ultrasonic action, may also be utilized. Although lead is the preferred powdered radiation attenuator, other metals of high atomic number and high density, as well as their compounds, salts and mixtures or alloys, may be used in the present invention. Among the powdered radiation attenuators which can be used are, beside lead, the metals wolfram, bismuth, tantalum, thallium, uranium, gold, silver, iron and the compounds ferrophosphorus, lead sulfate, lead chromate, lead oxide, lead hydroxide, lead sulfide and the corresponding compounds of the other above-named metals. Other useable radiation attenuators will be readily apparent to those skilled in the art.

It will be understood that according to the method of application and intended use of the present radiation and acoustic barriers the size of the attenuator particles may vary considerably. For barriers where rough surfaces are acceptable or desirable particle sizes of about 80 mesh or coarser may be used. For smoother coatings smaller attenuator particles, to about 400 mesh or less, are preferred. A controlled range of particle sizes will permit a closer packing within the resin matrix since the finer particles will fit into the interstices left by the larger particles. Barrier compositions comprised of such multiple particle sizesare therefore especially effective.

A major factor in the effectiveness and applicability of the new plastic shielding compositions is the proportion of attenuator contained therein. A high proportion of attenuator results in a very effective barrier which will, however, respond poorly to troweling or spraying. Conversely, a low proportion of attenuator provides a less effective barrier but enhanced applicability. While the new radiation and acoustic barriers can be formulated with any attenuator concentration up to and even above about 9 8% by weight, high barrier values combined with excellent application characteristics are obtained with attenuator concentrations from about 75% to about by weight.

The attenuator particles are bound into a cohesive whole by the resin. It is apparent that the adhesive characteristics of the resin, with respect to both the attenuator particles and the substrate to which the composition is to be applied, are an important consideration. The same is true of the mechanical properties of the resin. The new radiation and acoustic barriers can be formulated with hardenable or thermoset resins such as epoxy, unsaturated polyester or polyurethane resin, each in combination with a suitable hardener or curing agent. Other suitable hardenable or thermoset resins may also be employed. The resin generally comprises less than about 25% by weight of the new barrier compositions and in preferred formulations comprises from about 1.5% to about 20% by weight.

The function of the hardener or curing agent is to cure the hardenable or thermoset resin and any of the hardeners known to the art may be used. Epoxy resins, for example, are commonly cured by primary-secondary aliphatic amines such as diethylenetriamine, triethylenetetramine or tetraethylenepentamine; by ethylene oxide or propylene oxide adducts of the above such as N-(hydroxyethyl) diethylenetriamine or N,N'-bis (hydroxyethyl) -diethylenetriamine; by cyanoethylated primary-secondary aliphatic amines; by primary-tertiary aliphatic amines such as diethylaminopropylamine or dimethylaminopropylamine; by aromatic amines such as m-xylylenediamine; by liquid epoxy/amine adducts; by secondary amines such as piperidine; by polyamides of long chain fatty acids such as those marketed by General Mills under the tradename Versamid; by long chain polyamines such as the C -C alkyl diamines marketed by Armour & Co. under the trade name Duomeen and by Ciba Products Company under the trade name Lancast A; by various liquid thiokol polymers such as those marketed by Thiokol Chemical Company under the designations LP-Z, LP3 and LP8; by phenolic tertiary amines such as dimethylaminomethylphenol and tri-(dimethylaminomethyl)-phenol; by mixtures of the above and by many other hardeners or curing agents, catalysts or initiators which are known to those skilled in the art.

Unsaturated polyesters are generally catalyzed by peroxy, azo or other compounds capable of generating free radicals. Typical hardeners or curing agents include benzoyl peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide and cumene hydroperoxide. Systems intended for room temperature cure generally make use of a promoter or accelerator such as cobalt naphthenate, triethanolamine, triisopropanolamine, dimethyl phenylphosphine, stannous chloride or other multivalent metal salts in the lower oxidation state, alkali metal sulfonates and others well known to the art. All of these are useful in the present invention and may be used therein.

Polyurethane resin systems may be hardened or cured by Water; by various polyols such as butynediol, triethylene glycol, dimethyl propylene glycol, glycerol monophenyl ether and their mixtures; by amines such as dimethylethanolamine, methyl morpholine and methylenebis-(o-chloroaniline); b titanate esters; and by various other cross-linking agents which will be apparent to those skilled in the art.

It is well known that the addition of various other components to these several resin systems will advantageously modify their properties in specific directions, and such modifications may readily be incorporated into the prescut invention. For example, the addition of small quantities of bisphenol-A will substantially shorten the cure time of epoxy resins. Up to about -20% of nonreacting flexibilizers such as pine oil will increase the flexibility of cured epoxy systems. Various organic and inorganic compounds of chlorine, bromine or phosphorus impart fire resistance. Many other additives, extenders, colorants, stabilizers, etc. are well known to the art.

The addition of surfactants to the present radiation and acoustic barriers is of particular advantage. Surfactants facilitate the dispersion of the thixotrope, prevent agglomeration of the thixotrope or the powdered radiation attenuator during storage and permit adjustment of the surface tension of the final composition to a value which is optimum for either troweling or spraying. When a surfactant is used it may be of virtually any kind, ionic or nonionic. Suitable surfactants include the alkyl ethers of polyethylene glycol, ethoxylated octyl or nonyl phenol, polyoxyethylene sorbitan monolaurate, polyoxyethylene stearate, polyoxyethylene lauryl alcohol, sodium heptadecyl sulfate, sodium di-(2-ethylhexyl) phosphate, sodium tetradecyl sulfate; sodium 2-ethylhexyl sulfate, various polydimethylsiloxanes, etc.

According to the present invention, the hardenable or thermoset resin, thixotropic agent and, if used, surfactant are mixed in varying proportions depending on their nature and the intended use in a high shear mixer. The mixture so produced is then further combined with the powdered radiation attenuator and the hardener or curing agent in a sigma 01' blade-type mixer whereupon it may be directly applied to walls and other vertical substratem without danger of sagging or running.

Further details of the invention are given in the following examples, which illustrate specific compositions and methods of making same but are not to be considered as limiting. On the contrary, persons skilled in the resin compounding art should be able to develop other variations and modifications of this invention without departing from its spirit or from the scope of the appended claims.

Example 1 Parts Epon 815 (Shell Chemical Co. epoxy resin) 100 Cab-O-Sil M5 (Cabot Corporation colloidal silica) 6.5 Glycerol 1.6 Triethylenetetramine 12.5 Lead powder, 200 mesh 1230 The epoxy resin and Cab-O-Sil were mixed with a mechanical stirrer until a homogeneous mixture was obtained. This was then further subjected to high shear mixing in a Cowles Dissolver for ten minutes. The glycerol was then added and high shear mixing was continued for another few minutes to achieve a uniform mass. The resultant composition was transferred to a sigma-blade mixer where it was combined with the lead powder and triethylenetetramine. The plastic barrier composition so produced is suitable for troweling onto vertical substrates without sagging or running. I

The radiation attenuating properties of the above composition were compared with those of lead sheet by using the 662 kev. gamma rays from Cs and a Victoreen r meter. 0.264 inch of the above composition were found to be equivalent to 0.159 inch of lead. Accordingly, on a thickness basis, the above composition is 60% as effective as lead.

Example 2 Parts Araldite 507 (Ciba epoxy resin) 100 Cab-O-Sil EH5 (Cabot Corp. colloidal silica) 7.7 Glycerol 2.0 Diethylenetriamine 11.0 Lead powder, 325 mesh 985 The composition was mixed in the same manner as that of Example 1 and provides a plastic shielding composition suitable for spray application onto vertical surfaces of various types without sagging or running.

Example 3 Parts Araldite 507 (Ciba epoxy resin) Cab-O-Sil M-5 (Cabot Corp. colloidal silica) 8.0 Glycerol 2.0 Versamid (General Mills polyamide) 35 Lead powder, 200 mesh 1450 Six parts of colloidal silica were mixed with 100 parts of epoxy resin and dispersed under high shear conditions for ten minutes. 1.5 parts of glycerol were added to this mixture and high shear mixing was continued for another minute. The remaining colloidal silica, i.e. 2.0 parts, was similarly dispersed under high shear conditions in 35 parts of Versamid 125, which mixture was then reinforced with the remaining 05 part of glycerol. The two viscous resin mixtures were then combined with the powdered lead in a blade-type mixer and troweled onto the intended substrate. The product cures to a semi-flexible radiation and acoustic barrier which is particularly useful under conditions where the substrata may not be entirely stable dimensionally or where such barriers must maintain long term flexibility.

Example 4 The formulation of Example 3 was repeated except that 50 parts of Lancast A (Ciba Products Company) were used instead of 35 parts of Versamid 125. The colloidal silica and glycerol were again divided between the resin and the hardener, two thirds of each being mixed under high shear into the former, and one third into the latter. The product again is a flexible radiation and acoustic barrier which is able to continuously adapt itself to dimensionally unstable substratas such as wood.

Example 5a Parts Araldite 506 (Ciba epoxy resin) 100 Thixcin R (Baker Castor Oil Co. hydrogenated castor oil) 12.5 Dow Corning 201 (Polydimethylsiloxane) 0.5 Triethylenetetramine 12.5 Lead powder, 325 mesh 1250 A mixture of the epoxy resin and the silicone surfactant was heated to 120130 F. at which point the Thixcin R was stirred in. The resultant mixture was subjected to high shear mixing action at 120-130" F. for 15 minutes after which it was further mixed with the lead powder and curing agent in a blade-type mixer. The resultant formulation is very satisfactory for trowel application to vertical surfaces.

Example 5b The formulation of Example 5a was repeated except that the thixotrope was omitted. The resultant composition was troweled to a thickness of inch onto a wall seven feet high. By the time cure was achieved 82% of the applied composition has drained to the floor.

Example 6 The formulation of Example 5a was repeated except that 15.0 parts of Thixatrol ST (Baker Castor Oil Co. hydrogenated castor oil) were substituted for Thixcin R and 2050 parts of 300 mesh Wolfram powder were substituted for lead powder. Dispersion of Thixatrol ST was accomplished under high shear conditions at F. The resultant barrier composition can be applied directly to walls and on a thickness basis is approximately as efl'ective as lead sheet.

7 Example 7 Parts Laminac 4110 (Cyanamid Chem. Co. polyester resin) 100 Cab-O-Sil M (Cabot Corp. colloidal silica) 7.5 Ucon LB1717 (Union Carbide surfactant) 1.0 Methyl ethyl ketone peroxide 0.5 Cobalt naphthenate 0.1

Lead powder, 200 mesh 1100 The colloidal silica was dispersed in a mixture of the polyester resin and the surfactant with high shear equipment for minutes. The mixture so produced was introduced to a blade-type mixer and further mixed with methyl ethyl ketone peroxide and cobalt naphenate. When a smooth mixture was obtained the lead powder was added and mixing was continued until complete dispersion had been attained. The resultant plastic radiation and acoustic barrier composition is suitable for both trowel or spray application to vertical surfaces without sagging or running.

It is understood that the above examples are for illustrative purposes only and that modifications may be made without departing from the inventive concept of the present invention and that I intend the scope of the present invention to be set forth by the hereunto appended claims.

Having thus described my invention what I claim as new and desire to obtain by Letters Patent is:

1. A wall to be used for Shielding against penetrating radiation and noise comprising a thermoset resin, a powdered radiation attenuator selected from the group consisting of metals of high atomic number and high density and compounds, salts, mixtures, and alloys of said metals, and a thixotropic agent.

2. The wall of claim 1 wherein the thermoset resin is present in said composition in an amount of about 1.5% to 25% by weight, the powdered radiation attenuator is present in said composition in an amount of about 75 to 98% by weight, and the thixotropic agent is present in said composition in an amount of about 0.2% to 7.5% by weight.

3. The wall of claim 1 wherein the thixotropic agent is a member selected from the group consisting of colloidal silica, hydrogenated castor oil, carboxy vinyl polymer, bentonite, kaolinite clay, colloidal cellulose and colloidal asbestos.

4. The wall of claim 1 wherein the thixotropic agent is present in said composition in an amount of about 0.2 to 7.5% by weight of the composition.

5. The wall of claim 1 wherein the thermoset resin is a resin selected from the group consisting of an epoxy resin, an unsaturated polyester resin and a polyurethane resin.

6. The wall of claim 1 wherein said composition has incorporated therein a minor amount of surfactant.

7. A plastic radiation and acoustic barrier composition of matter having a viscosity enabling it to 'be applied without sagging on vertical surfaces comprising a thermoset resin, a powdered radiation attenuator selected from the group consisting of metals of high atomic number and high density and compounds, salts, mixtures, and alloys of said metals, and a thixotropic agent.

8. The composition of claim 7 wherein the thermoset resin is present in an amount of about 1.5% to 25% by weight, the powdered radiation attenuator is present in an amount of about to 98% by weight, and the thixotropic agent is present in an amount of about 0.2% to 7.5% by weight.

9. The composition of matter of claim 7 wherein the thermoset resin is a resin selected from the group consisting of an epoxy resin, an unsaturated polyester resin, and a polyurethane resin.

10. The composition of matter of claim 7 wherein the radiation attenuator is a member selected from the group consisting of lead, Wolfram, bismuth, tantalum and ferrophosphorus.

11. The composition of matter of claim 7 wherein the thixotropic agent is selected from the group consisting of colloidal silica, hydrogenated castor oil, carboxy vinyl polymer, bentonite, kaolinite clay, colloidal cellulose and colloidal asbestos.

12. The composition of matter of claim 7 further containing a minor amount of surfactant.

13. A block to be used for shielding against penetrating radiation and noise comprising a thermoset resin, a powdered radiation attenuator selected from the group consisting of metals of high atomic number and high density and compounds, salts, mixtures, and alloys of said metals, and a thixotropic agent.

14. The block of claim 13 wherein the thermoset resin is present in said composition in an amount of about 1.5 to 25 by weight, the powdered radiation attenuator is present in said composition in an amount of about 75% to 98% by weight, and the thixotropic agent is present in said composition in an amount of about 0.2% to 7.5% by weight.

15. The block of claim 13 wherein the thixotropic agent is a member selected from the group consisting of colloidal silica, hydrogenated castor oil, carboxy vinyl polymer, bentonite, kaolinite clay, colloidal cellulose and colloidal asbestos.

16. The block of claim 13 wherein the thermoset resin is a resin selected from the group consisting of an epoxy resin, an unsaturated polyester resin and a polyurethane resin.

17. The block of claim 13 wherein the radiation attenuator is a member selected from the group consisting of lead, Wolfram, bismuth, tantalum, and ferrophosphorus.

18. The block of claim 13 wherein said composition has incorporated therein a minor amount of surfactant.

References Cited UNITED STATES PATENTS 3,200,085 8/1965 Guglielmo 252-473 3,230,375 1/1966 Van Wagoner et al. 252-478 X 3,247,130 4/1966 Isbell 252478 CARL D. QUARFORTH, Primary Examiner.

S. J. LECHERT, Assistant Examiner.