WO1992006131A1

WO1992006131A1 - Ore-filled compositions

Info

Publication number: WO1992006131A1
Application number: PCT/CA1991/000344
Authority: WO
Inventors: Martin John Lilley; Raymond Hector Servant
Original assignee: Du Pont Canada Inc.
Priority date: 1990-10-02
Filing date: 1991-09-25
Publication date: 1992-04-16
Also published as: GB9021364D0; AU8611791A

Abstract

Highly filled materials are disclosed. The material is formed from a composition of 4-19 % by weight of a defined polar thermoplastic polymer, 0-10 % by weight of a plasticizer and 81-96 % by weight of an ore concentrate. Preferably, the material provides attenuation against energy of greater than 0.1 keV that is equivalent to at least 0.1 mm of lead. The material may be used for containers, in apparel and other end-uses for protection against e.g. x-rays and gamma rays, as sound proofing and in electrical applications, depending on the particular ore selected.

Description

ORE-FILLED COMPOSITIONS

The present invention relates to filled polymer compositions, including highly filled compositions of polymers and elastomers, that are formed using an ore concentrate as the filler, for use in a variety of end-uses, including attenuation of or protection against sound and electromagnetic radiation and as energy conducting materials. Articles formed from the composition, which contain in excess of 80% filler in a matrix of for instance polymer or elastomer, may be flexible or rigid, depending on the nature of the filler and the material used as the matrix.

Highly filled compositions are capable of being used in a wide variety of applications, especially protection against sound and against electromagnetic radiation and in electrically conductive applications e.g. shielding of apparatus. Examples include mobile flexible X-ray screens, folding X-ray doors, flexible electrical conductors, sound insulating materials, electromagnetic energy screens for apparel e.g. protection against x-rays and beta and gamma radiation, flexible magnets, electrical resistant heating mats and the like, and electrical grounding systems. In some such end-uses, it is important that the material be flexible and resistant against cracking e.g. apparel or containers, whereas in other end-uses it is preferred that the material be rigid e.g. in wall panels or ceiling tiles, or semi-rigid e.g. floor tiles. A number of filled materials have been proposed for use as protection against radiation. Examples of highly-filled polymers and elastomers are described in Canadian patent application No. 2 003 879 of M.J. Lilley, J.M. MacLeod and R.H. Servant, filed 1989 November 24. Japanese patent application No. 58-053928 of K. Yamamoto,

ⁱ published 1983 March 30, discloses an elastic (rubber) foam material containing large quantities of metal constituents e.g. lead oxide; the use of material containing barium ferrite/nickel ferrite and barium ferrite/magnesium ferrite for protection against magnetism is also disclosed.

Japanese patent application No. 57-141430 of K. Yamamoto, published 1982 September 01, discloses a leaded foam material comprising a foamed material having as its base a natural or synthetic rubber. The publication refers to organic and inorganic lead compounds, and exemplifies lead oxide in amounts of 80-87.3% by weight.

Although the prior art reports compositions of fillers and polymers on a weight basis, it is the amount of filler on a volume basis that is understood to be more important, especially with respect to processing of the compositions. Generally, polymers filled to 5-25% by volume retain a high degree of flexibility, resilience, elongation, elasticity and the like, whereas polymers filled to 20-50% by volume, if achievable with the aid of plasticizers and suitable combinations of polymers and fillers, tend to be rigid or semi-rigid and brittle. In the latter, the polymer is essentially a binder or adhesive for the filler. So-called vinyl floor tiles are an example of highly filled polymer compositions, and they are generally brittle with low flexibility.

While in some instances e.g. radiation protection apparel, it is advantageous to be able to provide a level of protection equivalent to other apparel but to do so with less weight, in some end-uses weight is a less critical factor. In those instances, it may be more advantageous to be able to provide equivalent protection but at lower cost. A highly filled polymeric material formed from a composition of a thermoplastic polymer and containing ore concentrates, that may be used as an

SUBSTITUTE SHEET energy absorptive or conductive material e.g. for x-rays, gamma rays, sound or electricity, has now been found.

Accordingly, the present invention provides a highly filled composition comprising: (a) 4-19% by weight of a thermoplastic polymer selected from copolymers of ethylene with at least one of vinyl alkanoate, alkyl acrylate, alkyl methacrylate, glycidyl methacrylate, acrylic acid, methacrylic acid and carbon monoxide, and mixtures thereof, ionomers of such copolymers, and such copolymers that have been grafted with a monomer selected from the group consisting of ethylenically unsaturated carboxylic acids and anhydrides and other derivatives thereof;

(b) 0-10% by weight of a plasticizer for such copolymers; and

(c) 81-96% by weight of a solid ore concentrate containing at least 60%, especially at least 65%, by weight of an element or compound thereof, measured on a dry basis, said element having an atomic number of at least 24.

In a preferred embodiment of the material of the present invention, the ore concentrate has been obtained from an ore by flotation techniques.

In another embodiment, the element of the concentrate is mercury, barium, tin, lead, antimony, bismuth, chromium, iron and/or nickel.

In a further embodiment, the composition is in the form of a layer having a thickness such that the amount of attenuation of electromagnetic radiation having energies of greater than 10 keV is the equivalent of at least 0.1 mm of lead, the element having an atomic number of at least 50.

In yet another embodiment, the polymer composition has a flexural modulus in the range of 1 to 100 MPa. The present invention provides a composition formed

T from a composition comprising 4-19% by weight of a thermoplastic polymer, 0-10% by weight of plasticizer and 81-96% by weight of a solid ore concentrate; the latter is also referred to herein as filler. The polymer used to form the layer of the material of the present invention is selected from copolymers of ethylene with at least one of vinyl alkanoate, alkyl aer late, alkyl methacrylate, glycidyl methacrylate, acrylic acid, methacrylic acid and carbon monoxide, and mixtures thereof. The polymer may also be an ionomer of such copolymers, especially an ionomer in which the metallic ion is sodium, zinc or aluminum. In addition, the polymer may be such a copolymer that has been grafted with a monomer selected from the group consisting of ethylenically unsaturated carboxylic acids and anhydrides and other derivatives thereof. Examples of such polymers include ethylene/vinyl acetate copolymers, ethylene/methyl acrylate copolymers, ethylene/methyl methacrylate copolymers, ethylene/acrylic acid copolymers, ethylene/alkyl acrylate/glycidyl methacrylate copolymers, ethylene/methacrylic acid copolymers, ethylene/n-butyl acrylate/carbon monoxide copolymers, ethylene/vinyl acetate/carbon monoxide copolymers and related polymers, and sodium and zinc ionomers of ethylene/acrylic acid and methacrylic acid. As used herein, it is understood that copolymers may have more than two monomers i.e. include polymers sometimes referred to as terpolymers. The grafted polymers include such copolymers that have been grafted with maleic acid or maleic anhydride. In addition, the polymers may be cross-linked, subsequent to polymerization, with ionizing radiation or cross-linking agents in order to modify the properties of the polymer. Many examples of such polymers are available commercially e.g. from Du Pont Canada Inc., and/or the techniques for the fabrication

'B f

SU ij ϋ i ϋ s t :T and/or modification of such polymers are known in the art. In embodiments of the invention, the thermoplastic polymer of the composition may also include polyvinyl chloride in low proportions i.e. in minor amounts. The composition also contains an ore concentrate. The ore concentrate contains at least 60% by weight of an element or compound thereof, especially at least 65% by weight of the element or compound thereof, measured on a dry basis. The element has an atomic number of at least 24, and in embodiments an atomic number of at least 50. In preferred embodiments, the element is mercury, barium, tin, lead, antimony, bismuth, chromium, iron and/or nickel. The ore may have the element in the form of compounds, and be substantially comprised of oxides, carbonates, sulphates, halides especially fluorides and iodides, hydroxides, tungstates, carbides, sulphides, uranates and tellurides or salts of organic acids e.g. acetates, stearates, naphthenates, benzoates, formates, propionates, and other organotin and organolead compounds. The ore concentrate should be compatible with the copolymer component of the composition, although there may be interactions between the components that enhance the properties of the resultant composition. The elements or compounds are used in a finely divided form and are uniformly dispersed throughout the thermoplastic polymer.

The particle size distribution and particle shape are important parameters with respect to the compositions, especially to maximize the filler loading for a predetermined flexibility and elasticity or to maximize flexibility and elasticity at a predetermined filler loading. For instance, fine particles when coated with polymer require a considerable volume in comparison to the amount of filler. Thus, in preferred embodiments of the present invention, the filler used in the

SUBSTITUTE SHEET compositions has a low level of particles smaller than 400 mesh (38 microns) . If sheet or layer are to be produced from the composition, it is preferred that the particles of largest diameter have a particle size that is not greater than 10% of the thickness of the layer or sheet e.g. a maximum particle size of 100 mesh (150 microns) is preferred. In addition, the particles are preferably spherical particles or substantially spherical particles; such particles are often produced on grinding friable particles of larger and more irregular shapes. Mathematical relationships relating to the preferred distribution of particle sizes may also be derived.

The ore concentrate is preferably formed from an ore by flotation techniques. Such techniques are well known in the art, and include treatment of powdered rock or other ore source with water and/or foam. The resultant ore concentrates are thus usually in a so-called wet form, typically containing about 4-7% by weight of water. While the ore concentrates may be dried separately prior to use, this imposes an economic penalty. The present invention will permit use of ore concentrates containing water, although it will normally be technically advantageous to use ore concentrates with low levels of water e.g. 0-4% water or to remove part of the water during processing. Ores that have components with an affinity for forming hydrates are less preferred in the present invention. Mesh sizes that are preferred for the filled compositions also tend to be similar to the mesh sizes typically used in milling, grinding and flotation processes for preparation of ore concentrates. In the use of "wet" ores, the selection of the polymer or elastomer and the method of processing may be important. Since 5% by weight of water in a wet ore may approach 5% by weight and 15% by volume of the composition, the presence of water has a significant

SHEET effect on the filler/polymer ratio and properties, and processing characteristics.

If the composition is formed by processing at temperatures above 100^βC, evaporation of water may result in undesirable porosity in the resultant product. Thus, in a preferred embodiment, the compositions are prepared by processing at temperatures below 100^βC, and preferably below 90^βC, without hydrolysis of the polymer or plasticizer by water. Alternatively, the compositions may be prepared at temperatures above 100°C, providing that hydrolysis of polymer or plasticizer is not of concern. Suitable venting may be used to remove water from the composition during preparation of the compositions. Such processing may be carried out by calendaring or using an extruder with a sheeting die. For some application e.g. electrical end-uses, the ore concentrate should be used in a dry state.

Examples of ore that may be used in the composition of the invention are as follows: Cinnabar (contains HgS) ; Barytes (contains BaSO^) ;

Witherite (contains BaC0₃) ; Cassiterite (contains Snθ₂) ; Galena (contains PbS) ; Cerrusite (contains PbC0₃) ; Anglesite (contains PbS0₄) ; Stibnite (contains SbS₂) ; Bis uthite (contains Bi₂(S0₄)₃) ; Bismuth Glance (contains Bi₂S₃) ; Chromite (contains FeO.Cr₂0₃); Magnetite (contains Fe₃0₄) ; Ferric Oxide (contains Fe₂0₃) ; Pentlandite (contains (Fe.Ni)S). These ores may be used in compositions intended for use in one or more of the following end-uses, depending on the particular ore concentrate: attenuation of electromagnetic radiation, x-rays and gamma rays; sound proofing; magnetic material; and static dispersion and electrical conductivity applications.

The composition of the invention comprises 81-96% by weight of the inorganic compounds and especially 85-95%

SUBSTITUTE SHEET by weight of ore concentrate.

The composition may also contain a plasticizer for the copolymer of the composition. Any such plasticizer must be compatible with the copolymer, and be of a type and used in an amount that does not result in bleeding or blooming of the plasticizer from the resultant composition. Moreover, the plasticizer must be compatible with the inorganic component added as part of the composition. Examples of such plasticizers include aromatic processing oils e.g. Sunthene™ 4240 plasticizer, trioctyl trimellitate, diisononyl phthalate and dioctyl phthalate. Other examples include other phthalate esters, phosphate esters, fatty acid esters, adipates, azelates, oleates, sebacates and sulfonamides. The polymer composition may contain antioxidants, UV and other stabilizers, fire retardants and pigments, as will be appreciated by those skilled in the art.

The composition contains 4-19% by weight of the copolymer and 0-10% by weight of plasticizer. In preferred embodiments, the composition contains 7-10% by weight of copolymer and 5-8% by weight of plasticizer. If the composition is in the form of a layer, the layer is preferably of a thickness suitable for the absorption of energy or for electrical conductivity. In particular, the thickness is such that the amount of attenuation of electromagnetic radiation having energies of greater than 0.1 keV e.g. x-rays, is the equivalent of at least 0.1 mm of lead. In preferred embodiments, the thickness is such that the amount of attenuation is the equivalent of at least 0.1 mm, especially 0.25 mm of lead and in particular at least 0.5 mm of lead. Such equivalency is measured in the manner for determination of lead equivalency known in the art, using x-rays having an energy of 100 kV (also referred to as kVp) , as described in the aforementioned patent application of

SUBSTITUTE SHEE M.J. Lilley, J.M. MacLeod and R.H. Servant. In more general terms, equivalence is determined by measuring the broad area transmission of radiation of a sample of material for a radiation beam of known energy. The transmission is then measured in the same manner for a set of samples of commercially-pure lead of different known thicknesses, and the equivalence for the test sample is obtained by interpolation. Such equivalence only applies to the energy spectrum used in the test measurements. For diagnostic x-ray protection, a typical energy spectrum is obtained when a potential of lOOkVp is applied to an x-ray tube. Transmission is defined as the ratio of the exposure (coulombs/kg-air) measured in an ionization chamber with material in the beam to the corresponding exposure obtained without material in the beam.

Measurement of the absorbence of x-rays is made by the method described hereinafter in the examples.

In a further preferred embodiment, the composition has a flexural modulus in the range of 1 to 100 MPa, and especially in the range of 1.5 to 12 MPa. Flexural modulus is measured by the procedure of ASTM D-790. The flexural modulus of the composition is important in applications such as apparel e.g. to provide apparel that is practical for wearing or which is capable of being used as a material for containers.

If the material is to be used as electromagnetic energy absorption material in the form of apparel, it requires an acceptable flexibility and drape. Such a term is understood in the art of fabrics and related industries, and relates to the ability of the material to conform to the contours of a human body or other shapes.

The compositions of the present invention may be obtained by feeding the ingredients to melt compounding or similar equipment, the actual equipment depending in part on the actual composition to be prepared and the melt processing characteristics of that composition. Examples of compounding equipment include two-roll mills, Banbury mixers, Farr ll™ continuous mixers, Buss™ co-kneaders, Gelimat™ high intensity mixers and the like. Compositions of high content of inorganic component and/or containing grafted polymers may be more difficult to process so as to obtain uniform compositions, and may require the use of high intensity mixers or the like. For instance, compositions of the invention may be compounded using a Banbury twin rotor internal mixer by addition of all of the ingredients into the mixer. It may, however, be preferable to prepare concentrates of plasticizer and/or the elements or compounds in polymer, and then compound the combinations of the concentrates in a high shear mixer; such use of concentrates may be less hazardous to operators of the equipment. The composition may be formed into sheet by extrusion, calendering, compression moulding or the like, a preferred method being by calendering. The present invention may be used in the form of apparel to protect the wearer from radiation, especially x-ray radiation, or shields for apparatus that produces radiation. The apparel may be in the form of full garments or in the form of vests or the like to protect portions of the human body. Alternately, compositions of the present invention may be used to form containers for radiation emitting products.

The present invention is illustrated by the following examples; unless noted to the contrary, all particles were 100-200 mesh:

Example I A series of compositions were prepared with the same polymer and plasticizer compositions but with differing filler amounts and type. The fillers used were galena ore or galena ore containing 5.0% by weight of water.

The polymers were Elvax* 170 ethylene/vinyl acetate copolymer and an ethylene/vinyl acetate copolymer that had been grafted with maleic anhydride. The plasticizer was Sunthene 4240 aromatic processing oil.

The compositions were prepared by compounding on a Brabender™ mixing apparatus and formed into sheet by compression moulding.

Physical property measurements were made on the compositions, using the following procedures:

Melt Index - procedure of ASTM D-1238 (condition E) Tensile Strength - procedure of ASTM D-412 Elongation - procedure of ASTM D-412 Flexural Modulus - procedure of ASTM D-790 Further details and the results obtained were as follows:

SUBSTITUTE SHEET TABLE I

Run No. Composition

Elvax 170 Grafted EVA Plasticizer Galena

Moisture content after processing (%)

1.7 2.0 3.5 3.3

Note: * = contained 5% by weight of water NM = not measured Density is reported in g/cm³;

Melt index is reported in dg/min; Tensile strength is reported in MPa; Elongation is reported as a percentage; Flexural modulus is reported in MPa and was measured on samples having a thickness of 120 mil (3.18mm)

The compositions were all easily processed and formed flexible, strong sheets. Run 4 shows that the ore may be processed without drying. Runs 1 and 2 show that the higher plasticizer ratio in Run 1 resulted in increased elongation and lower ultimate tensile strength. The higher ultimate tensile strength, lower melt index and lower elongation of Run 3 compared with Run 2 are believed to be due to the higher moisture content of the compositions.

Example II The procedure of Example I was repeated using Elvax™ 265 ethylene/vinyl acetate copolymer and Nordel 2744 ethylene/propylene elastomer. In addition, some

SUBSTITUTE SHEET compositions contained Kemamide™ U slip agent.

Further details and the results obtained are given in Table II.

TABLE II

8 9

8.00 7.90

Filler Galena 90.00 88.00* 88.00*

Ore Moisture Content (%) Before

After 3.5 Properties

Density 3.82 Melt Index 10.5 Tensile str. 1.89 Elongation 20 Flex. mod. 51.0

Note: * = ore was wet NF = no flow;

Density is reported in g/cm³; Melt index is reported in dg/min; Tensile strength is reported in MPa; Elongation is reported as a percentage; Flexural modulus is reported in MPa and was measured on samples having a thickness of 120 mil (3.18mm)

All compositions were readily processible, except in Run 6. The sheet obtained was strong and flexible, with a high density. Runs 7 and 9 show the effect of addition of slip agent e.g. on the elongation obtained. Runs 6 and 8 show that addition of ethylene/propylene elastomer

SUBSTITUTE SHEET resulted in substantially the same tensile properties but significantly lower melt index.

Example III A composition of lead sulphide (90% by weight) in a blend of ethylene/vinyl acetate copolymers (6% by weight) containing Sunthene 4240 aromatic processing oil (4% by weight) was prepared; the lead sulphide was a dry blend of lead sulphide (86%) and fine silicaceous sand (14%) . The composition had a density of 4.44 g/cm³ and a filler content of 90% by weight and 55% by volume. Sheet formed from the composition was flexible, tough and resilient.

As a comparison, a composition was formed from lead sulphide (85.5% by weight) in polyvinyl chloride (8.5% by weight) and dioctyl phthalate plasticizer (6% by weight) . The composition had a density of 4.27 g/cm³ and a filler content of 85.5% by weight and 50% by volume. Sheet formed from this composition was brittle with no significant tensile strength or flexibility.

This example shows that polyvinyl chloride would have to be used at filler loadings that are lower than those used with the ethylene/vinyl acetate copolymer, and with a corresponding increase in overall weight, volume and thickness in order to achieve the same amount of x-ray attenuation. Example IV

A composition of lead sulphide (86.70% by weight) in a blend of grafted and un-grafted ethylene/vinyl acetate copolymers (8% by weight) containing Sunthene 4240 aromatic processing oil (5.32% by weight) was prepared; the lead sulphide was a dry blend of lead sulphide (86%) and fine silicaceous sand (14%) . The composition had a density of 3.63 g/cm³ and a filler content of 86.70% by weight and 50% by volume. Sheet formed from the composition was flexible, tough and resilient. Measurement of the x-ray absorption properties using

SUBSTITUTE SHEET a sheet having a thickness of 1.73 mm and weighing 6.28 kg/m² had lead equivalencies of 0.30 or 0.31 mm of lead at 60, 80, 100 amd 120 kVp.

TUTE SHEET

Claims

CLAIMS :

1. A highly filled composition comprising:

(a) 4-19% by weight of a thermoplastic polymer selected from copolymers of ethylene with at least one of vinyl alkanoate, alkyl acrylate, alkyl methacrylate, glycidyl methacrylate, acrylic acid, methacrylic acid and carbon monoxide, and mixtures thereof, ionomers of such copolymers, and such copolymers that have been grafted with a monomer selected from the group consisting of ethylenically unsaturated carboxylic acids and anhydrides and other derivatives thereof;

(b) 0-10% by weight of a plasticizer for such copolymers; and (c) 81-96% by weight of a solid ore concentrate containing at least 60%, by weight of an element or compound thereof, measured on a dry basis, said element having an atomic number of at least 24.

2. The composition of Claim 1 in which the ore concentrate has been obtained from an ore by grinding and cleaning by flotation techniques.

3. The composition of Claim 1 or Claim 2 in which the element is mercury, barium, tin, lead, antimony, bismuth, chromium, iron and/or nickel.

4. The composition of any one of Claims 1-3 in which the composition is in the form of a layer having a thickness such that the amount of attenuation of electromagnetic radiation having energies of greater than 10 keV is the equivalent of at least 0.1 mm of lead.

5. The composition of any one of Claims 1-4 in which the polymer composition has a flexural modulus in the range of 1 to 100 MPa.

6. The composition of Claim 5 in which the flexural modulus is in the range of 1.5 to 12 MPa.

7. The composition of any one of Claims 1-6 in

SUBSTITUTE SHEET which the polymer composition contains a plasticizer.

8. The composition of Claim 7 in which the polymer composition contains 7-10% by weight of copolymer and 5-8% by weight of plasticizer.

9. The composition of any one of Claims 1-8 in which the solid ore concentrate contains at least 65% by weight of the element or compound thereof.

SUBSTΪTUTE SHEET