GB2359084A - Filled resin compositions - Google Patents

Abstract

A resin composition comprises a polymer base including a first polymer component and a second polymer component; and a particulate filler component including a low density filler material having a density of 1.0g/cm<SP>3</SP> or less and a high density filler material having a density of 2.0g/cm<SP>3</SP> or more. The high density filler material is present in an amount of 50% or more by weight of the resin composition. The first and second polymer components may be a polyol component and an isocyanate component, and the composition may be used to fill joints in electrical cables.

Description

RESIN COMPOSITIONS This invention relates to resin compositions, particularly, but not exclusively, for use in electrical applications, for example in the filling of joints in electrical cables. The invention also relates to joints filled by such resin compositions and methods of making such joints Thermosetting and more especially cold-setting (i.e. setting at ambient temperature) resin compositions are in common use in the field of filling joints in electric cables, especially power cables for service at low and medium voltages. Such known resins are typically compositions based on polyurethane, acrylate or methacrylate, polyester (including vinyl ester), and epoxy resin systems. These known resins typically exhibit good flow characteristics to enable efficient filling of the voids within cable joints with good wetting of the surfaces therewithin, resulting in good electrical protection and physical durability of the joint region, but such resins are relatively expensive.

In an effort to move towards lower cost resin formulations for joint application, without compromising the electrical and physical properties of the resulting cured polymer, it is known to incorporate a particulate calcium carbonate filler (e.g. calmote UF) to assist in keeping the silica sand suspended in the resin composition during curing. However, the addition of the calmote increases the viscosity of the mixed resin composition which makes it difficult to mix the components together and has a deleterious effect on the pourability of the resin composition and its adhesion for example to the electrical components in a cable joint. Known three-pack resin compositions typically have a specific gravity of 1.7 or more and/or a viscosity (according to a measurement method described hereinafter) of more than 15 Pa.s.

Accordingly, in a first aspect of the present invention, there is provided a resin composition comprising a first polymer component; a second polymer component; and a particulate filler component including a a low density filler material having a density of about 1.0 g/cm3 or less, preferably 0.8g/cm3 or less, and a high density filler material having a density of about 2.0 g/cm3 or more, wherein the high density filler material is present in an amount of 50% or more by weight of the resin composition. The high density filler material is preferably present in an amount of more than 50% by weight of the resin composition. The resin composition of the first aspect of the present invention may be a cured resin composition or an uncured resin composition. It is further known to provide two-pack compositions wherein the resin includes a two-component polymer in which the two components are stored separately until use and the filler material is included with one of the polymer components. However, there is a problem with such systems in keeping the filler material suspended in the relevant polymer component during storage. Thus, these two-pack compositions often have a fairly short shelf-life as the filler material may sink to the bottom or float to the top of the relevant polymer component which in turn has a deleterious effect on the cured resin composition. In an attempt to overcome these problems, three-pack compositions are also well known wherein the filler material is stored separately from the two resin polymer components (which are also stored separately from each other). These three-pack compositions have the advantage of an increased shelf-life but can suffer problems when the three components are mixed prior to the use of the resin composition to fill for example a cable joint.

Known three-pack resin compositions typically include silica sand as the sole filler component. However, the silica sand tends to sink through the mixed resin composition whilst the resin is curing, which results in a non-uniform cured resin product. To overcome this problem, it is known to formulate three-pack resin compositions which include a second filler material, typically a In accordance with a fourth aspect of the present invention, there is provided an electrical apparatus including one or more cable joints made according to the third aspect of the invention.

The combination of a polymer component, a low density filler and a high density filler results in a resin composition which is relatively cheap to produce and easy to use. The composition has good flow properties, so that in its application to cable joints, there results good penetration of the composition into the voids between the cables and other elements of the joint and also resulting in good wetting of the surfaces therewithin. When the resin composition is cured, this provides a filled joint of excellent physical strength and durability and good electrical stress resistance properties.

The present invention will now be described in more detail, in terms of its preferred features and preferred embodiments and further herein below in terms of the illustrated non-limiting examples.

According to the invention the resin composition includes a two-component polymer which can be any of a wide variety of curable, usually liquid, thermosetting or cold-curing or even thermoplastic, polymer compounds. The polymer includes a first polymer component, which may be The terms "first polymer component" and "second polymer component" are used herein to indicate the two components of a two-component polymer composition. The two components each may or may not be polymeric themselves, but when they are combined, they react to form the desired polymer.

The three components of the resin composition are preferably stored separately from each other prior to the use of the composition. Thus, a second aspect of the present invention provides an uncured resin precursor composition comprising the first polymer component, the second polymer component and the filler component, each described above with respect to the first aspect of the invention, wherein the components are maintained separate from each other. Accordingly, a three (or more) pack resin composition is provided by the second aspect of the present invention.

In accordance with a third aspect of .the present invention, there is provided a method of filling a cable joint comprising applying thereto a resin composition according to the first aspect of the invention, optionally in combination with a catalyst if that is necessary or desired, and allowing or causing the resin polymer to cure. Within this further aspect of the invention is a cable joint filled by the method just mentioned. include polyurethanes, (meth)acrylates, polyesters (including unsaturated polyesters), and epoxy resins. The invention is especially applicable to the use of polyurethane resins, which are already well known for use in filling cable joints. Use of the invention also extends to any other two-component polymer systems constituted by or including two polymer or copolymer precursor components which may be mixed together and allowed or caused to cure to form a cured polymer, in particular curable polymers or precursors thereto that are substantially liquid at ambient (i.e. room) temperature.

The low density filler material of the invention has a density of 1.0 g/cm3 or less, preferably 0.8g/cm3 or less, and in a preferred embodiment consists of at least one species of rounded hollow glassy particles (or, as referred to hereinafter, microspheres) of mineral material. The use of such hollow microspheres reduces the effective density of the resin composition and in consequence makes it feasible to increase the maximum volume of the resin composition that can be supplied and mixed in a single three-component pack in which the resin composition of the invention is provided for use.

Microspheres of soda borosilicate glass and soda-lime borosilicate glass are commercially readily available and suitable for use as the low density filler material in the the primary polymer precursor, and a second polymer component which may comprise an activator, such as a hardener, a cross-linker and/or a polymerisation catalyst, or a copolymer component. An example of such a two-part polymer system which is especially applicable to the invention is a polyurethane, the first polymer component being constituted by a polyol component and optionally a catalyst, and the second polymer component comprising an isocyanate component for combining with the polyol component at the desired time, in accordance with known practice. As another example of such a two-part polymer system, an epoxy polymer system may be mentioned, wherein the first polymer component comprises a primary base epoxy resin and the second polymer component comprises the hardener. As a further example, an acrylic polymer system may be used, such as where the first polymer component is an acrylic monomer (optionally in combination with an amine) and an initiator or accelerator, e.g. a peroxy component initiator such as benzoyl peroxide, or a cobalt- based accelerator as the second polymer component. Unsaturated polyester polymer systems are yet further examples of polymers which may be used in the polymer composition, these being analogous to the employment and constitution of the components to the acrylics.

Suitable polymer systems which may be employed for the resin composition in the invention as just mentioned, Weight-median particle size distributions may be measured using a CILAS 920 Grandometer according to the laboratory test method described in the Omya UK Ltd. Test Method Sheet No. CGT105 (Issue 2, 6/98), or using a Sedigraph 5100 optionally in combination with a Mastertech 51 Autosampler, according to the laboratory test method described in the Omya UK Ltd. Test Method Sheet No. CGT42 (Issue 4. 6/98), or using the technique of determining sieve residues by weight sieving as described in the Omya UK Ltd Test Method Sheet No. CTG40 (Issue 5, S/98).

Other, synthetic forms of hollow glassy microspheres may also be suitable for use in the invention, but tend to be more expensive, for example those particulate microsphere materials sold by Omya UK under the trade marks SPHERIGLASS and by 3M under the trade mark SCOTCHLITE.

The hollow microspheres which preferably, constitute the low density filler material are of a generally round shape and ideally (though not necessarily, despite the name given to them in this specification) approximate to spherical. This shape offers the lowest possible surface area to volume ratio, which minimises the area of resin absorption and thus maximises the volume of the polymer components that can be displaced by a given weight of the low density filler material. This is important because invention. Additionally, hollow microspheres derived from fly-ash (e.g. from power stations and which may be regarded as alumina silicate glasses) are also readily available, satisfactory for use in the invention and less expensive, and they may therefore be preferred. Generally, the hollow particles of the low density filler material will contain a substantially inert gas atmosphere, derived from the environment in which they were formed. Typically, a gaseous filling of 70% CO2 and 30% N2 may be employed, such as is the case of fly-ash.

The aforementioned microsphere species, and those which generally are most suitable for use in the invention, tend to have a broad range of weight-median particle size (i.e. diameter) distribution. Such particle sizes predominantly in the approximate range from about 50 to about 500#.m are broadly suitable. The grade of fly-ash microspheres sold by Trelleborg Fillite Limited, Runcorn, UK, under the trade mark FILLITE (otherwise known by the name "Cenospheres") as FILLITE PG has been found to be particularly satisfactory and has a particle size distribution such that at least 97% of the particles passes through a 300#m mesh, 40% to 60% through a 150#.m mesh, 15% to 30% through a 1001m mesh and 2% to 10% through a 501m mesh. FILLITE grades SG (500), SG(300) and 52/7S may also be suitable. less preferred than the inorganic hollow microspheres exemplified above because the organic hollow microspheres tend to be sensitive to temperature and/or certain optional additives, such as plasticizers, which may be used in the resin composition.

A wide variety of inorganic mineral substances may be used, either singly or in combination, as the high density filler material. An especially preferred example of the high density filler material is silica sand, because of its easy availability in different grades and because it is a very cheap material. Other mineral substances which may be used for the high density filler material in the invention include various ground or precipitated grades of calcium carbonate, such as sources of limestone, marble, calcite, chalk, aragonite, dolomite and calcium-magnesium carbonate, as well as china clay (Kaolin), magnesium sulphate, wollastonite and alumina trihydrate.

The high density fillers suitable for use in the present invention are preferably used as powders with an average particle size greater than that of the low density fillers. Especially preferred high density fillers comprise silica sand, more preferably Sand C30 (also known as Chelford 30 grade) available from Hepworth Minerals and Chemicals, Sandbach, Cheshire, UK. generally the preferred hollow microspheres have a density of about 0.7 g/cm3, so this shape of particle leads to a good volume displacement per unit weight.

The rounded or preferably spherical shape of the particles furthermore contributes little to the viscosity properties of the polymer, unlike the contribution made by high density filler materials, such as chalk or silica sand. The spheres act like ball-bearings within the resin material and offer little resistance to flow, leading to little or no adverse effect on viscosity, yet allowing easy dispersion within the resin material during the mixing stage. This is also assisted by the low degree of polymer absorption at the surface of the microsphere filler particles resulting from the glassy nature of the surface.

Other examples of low density fillers which may be used in the present invention include for example hollow organic microspheres, such as polyvinylidene chloride (PVDC)/acrylonitrile (AN) microspheres which are available under the trade mark EXPANCEL from KemaNord, Sweden, and also under the trade mark MIRALITE from Pierce and Stevens Chemical Corporation, New York, USA, and phenolic hollow microspheres which are available under the trade mark UCAR (referred to as phenolic microballoons) from Union Carbide Corp, CT, USA. These organic hollow microspheres are often microspheres. Additional high density filler materials may be added at a level of 0 to 15% in either the first polymer or as a further separate high density filler component. However, the low density filler will always be packaged separately from the first polymer component owing to the phase separation, and the short shelf-life problems, associated with combining the low density filler material and the first polymer component, e.g. the polyol component.

It is possible for the resin composition of the invention to include one or more minor adjunct ingredients as may be conventionally included in resin moulding compositions for electrical applications. Amounts of adjuncts up to about 5% by weight, more preferably up to about 3% by weight of the total resin composition may be tolerated. Examples of such adjunct substances include catalysts (e.g. amines in acrylic or polyester resin systems or dibutyltin dilaurate in polyurethane resin systems), desiccants (e.g. molecular sieves based on crystalline alumino silicates), wetting agents (e.g. to improve dispersion of the filler materials), air release additives (an example of which is a silicon-free polymer composition sold by BYK Chemie under the trade mark BYK A555), coupling agents (e.g. silane coupling agents, such as methacryloxy silanes for polyester, acrylate and The resin composition preferably comprises 15 to 40% of the first polymer component, 1 to 15% of the second polymer component, 50 - 80% of the high density filler material (preferably 60 - 80% and more preferably 60 70%), 0.1 to 15% of the low density filler material and 0 to 5% of a desiccant. The percentages quoted above are percentages by weight of the total resin composition. The first polymer component may include a catalyst to accelerate the curing process once the second polymer component has been added.

The resin composition preferably has a specific gravity of 1.55 or less. Additionally or alternatively, the resin composition preferably has a viscosity of 15 Pa.s or less. The viscosity may be measured using the method described hereinbelow with respect to the specific examples of the present invention.

Where the polymer is a polyurethane, the polyurethane composition preferably comprises 15 to 30% polyol (polyhydroxyl compound) or blend of polyols (e.g. castor oil and/or other polyol compounds), 6 to 12% of a hardener (an isocyanate compound), 50 to 80% high density filler (preferably 60 to 70%), 0.1 to 15% low density filler and 0 to 5% desiccant (e.g. Sylosiv). In a preferred embodiment the high density filler consists of sand and the low density filler consists of hollow glassy allowed to cure, a cured resin composition according to the first aspect of the invention is provided. One preferred example of the three-pack kit is to provide three containers, each including a relevant component of the resin composition.

When mixing the uncured resin precursor components, it is preferred to mix the first polymer component with the second polymer component and then add the filler component. However, it is also possible alternatively to mix the first polymer component with the filler component and then add the activator component, or to mix all three components together at the same time. Once the components have been mixed the uncured resin precursor may then be poured into a suitable mould and allowed or caused to cure.

The present invention will now be further illustrated by way of the following non-limiting Examples which demonstrate formulations of resin compositions in accordance with the invention.

<U>Examples</U> The polyurethane resin systems having the total formulation of components as set out in Table 1 below are suitable for use in cable joint applications in accordance methacrylate resins for example, for improving the bonding strength between the polymer and the low density filler material; typically silane coupling agents may be employed at a level of about 1% by weight of the low density filler material), cross-linking agents, dyes, colouring and anti oxidants. The adjuncts may typically be added to the first polymer component.

Ideally, the system should have a gel time of 10 to 60 minutes at 20 C, preferably 15 to 25 minutes at 20 C. This. is to allow adequate pot life for mixing and pouring the resin composition. Gel time may be measured in accordance with the manufacturer's instructions using a Techne GT3 (as supplied by Techne (Cambridge) Limited) with a standard 22mm plunger (F0985) from the onset of mixing. When measuring the gel time, the resin is pre conditioned to a temperature of 20 C.

As already mentioned, the second aspect of the present invention provides a three-pack kit including the components of the resin composition according to the first aspect of the invention. Thus, the first pack includes the first polymer component, the second pack includes the second polymer component and the third pack includes the filler component so that when the components of a11 three packs are mixed at the time of or immediately prior to application to a mould, for example a cable joint, and UK Ltd (4) Silica sand supplied by Hepworth minerals and Chemicals Limited.

Formulation 1 resulted in a resin composition which had a specific gravity of 1.52, a viscosity of 14-15 Pa.s and a gel time of 15-18 minutes; Formulation 2 resulted in a resin composition which had a specific gravity of 1.44, a viscosity of 10-12 Pa.s and a gel time of 15-18 minutes; and Formulation 3 resulted in a resin composition which had a specific gravity of 1.46, a viscosity of 10-12 Pa.s and a gel time of 15-18 minutes.

The viscosity was measured using a Rheometric Scientific SRS with 40mm parallel plates set with a gap of 3mm. A 500m1 sample of the resin composition was mixed for 3 minutes following which a sample was taken for measurement. The value for the viscosity was measured at 5 minutes post mixing using a sample at 20 C.

These preferred embodiments have been described by way of an example and it will be apparent to those skilled in the art that many alternatives can be made that are still within the scope of the invention. with the preferred techniques described hereinabove. In Table 1 a11 amounts are quoted as % by weight of the total ingredients.

Table 1 Ingredient EXAMPLE 1 2 3 1. First Polymer component Di-butyl tin dilaurate 0.004 0.004 0.004 catalyst Castor Oil 18.805 20.140 19.449 Linseed oil 0.912 0.976 0.943 Desiccant (1) 0.548 0.587 0.567 2. Filler Fillite PG (2) 4.067 4.356 4.207 Calmote OF (3) 6.629 - sand C30 (4) 60.910 65.25 66.427 3. Second Polymer component 4,4 Diphenyl methane di- 8.125 8.702 8.404 isocyanate Total 100.000 100.00 100.00 Notes: (1) Sylosiv A4 (a crystalline alumina silicate), supplied by W. R Grace (2) Alumino silicate microspheres, as exemplified hereinabove (3) Ultra finely ground limestone powder supplied by Omya 5. A resin composition according to any preceding claim wherein the low density filler material has a density of 0. 8g/cm3 or less.

6. A resin composition according to any preceding claim wherein the low density filler material includes at least one species of rounded hollow glassy microspheres.

7. A resin composition according to any preceding claim wherein the high density filler material is selected from the group consisting of silica sand, limestone, marble, chalk, aragonite, dolomite, calcium-magnesium carbonate, china clay, magnesium sulphate, wollastonite and alumina trihydrate.

8. A resin composition according to any preceding claim wherein the composition comprises 15 - 40% of the first polymer component, 1 - 15% of the second polymer component, 50 - 80% of the high density filler material, 0.1 - 15% of the low density filler material and 0 - 5% of a desiccant wherein the percentages stated are percentages by weight of the total resin composition.

9. A resin composition according to claim 8, wherein the composition comprises 15 - 30% of one or more polyols, 6 120 of an isocyanate compound, 50 - 800 of the high density filler material, 0.1 - 150 of the low density

Claims (1)

1. <U>Claims</U> 1. A resin composition comprising a polymer base including a first polymer component and a second polymer component; and a particulate filler component including a low density filler material having a density of 1.0g/cm3 or less, and a high density filler material having a density of 2.0g/cm3 or more, wherein the high density filler material is present in an amount of 50% or more by weight of the resin composition. 2. A resin composition according to claim 1 wherein the polymer base comprises a polyurethane polymer, and the first polymer component comprises a polyol component and the second polymer component comprises an isocyanate component. 3. A resin composition according to claim 1 wherein the polymer base comprises an epoxy polymer, and the first polymer component comprises an epoxy resin precursor component and the second polymer component comprises a suitable hardener. 4. A resin composition according to claim 1 wherein the polymer base comprises an acrylic polymer, and the first polymer component comprises an acrylic monomer and the second polymer component comprises a suitable initiator. 14. A resin composition substantially as described in any one embodiment herein. filler material and 0 - 5% of desiccant. 10. A resin composition according to any preceding claim wherein the resin composition has a gel time of 10 to 60 minutes. 11. An uncured resin composition kit comprising a first pack which includes a first polymer component of a polymer base, a second pack which includes a second polymer component of the polymer base and a third pack which includes a particulate filler comprising a low density filler material having a density of 1.Og/cm3 or less, and a high density filler material having a density of 2.0g/cm3 or more, wherein the high density filler material is present in an amount of 50% or more by weight of the resin composition, and wherein each pack is arranged to keep its contents separate from the contents of the other packs. 12. A method of forming a cured resin composition, the method including mixing the contents of the first pack, the second pack and the third pack according to claim 11, pouring the mixed uncured resin precursor into a mould and allowing or causing the resin to cure. 13. An electrical cable joint including a resin composition according to any one of claims 1 to 10.