MOISTURE-CURABLE ELECTRICALLY-INSULATING RESIN

Abstract: The invention refers to a low-toxicity moisture-curable resin comprising at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one hydroxyl or hydrolyzable group, whereby said organic polymer is crosslinkable through formation of siloxane bonds, at least one curing catalyst (B), at least one molecular sieve (C), and water (D), wherein the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, Ri, of at least 10,000 MOhm.

Description: MOISTURE-CURABLE ELECTRICALLY-INSULATING RESIN Field of the Invention The present invention relates to moisture-curable resins comprising one or more organic polymers bearing silicon-containing end groups, one or more curing catalysts, one or more molecular sieves and water. The resins can be cured to form void-free resin masses suitable for use as potting compounds and as insulating resins for electrical cable splices, particularly low-voltage splices. Background Pourable resins which cure quickly at ambient temperatures to form hard, tough masses have been used for many years to protect and insulate electronic parts and electrical cable splices. Such resins used in large underground cable splices have great demands placed upon them because they must function under adverse conditions such as fluctuating temperatures, high humidity, standing water and high temperatures generated by the passage of current. Increasing awareness of environmental issues have encouraged development of new resin formulations with reduced levels of materials which are known to be environmental or health hazards. These resin formulations comprise moisture-curable compositions based on polymers bearing hydrolyzable silicon-containing end groups. US 3,971,751 describes a composition comprising a polyether having silicon end groups which is curable to a rubber-like substance upon exposure to atmospheric moisture at room temperature which is useable as a sealing material or adhesive. Curing catalysts and fillers such as calcium carbonate are described. Japanese patent 3-6941 (1991) describes a room temperature curable composition comprising a) 100 parts by weight of a polymer comprising a polyether segment bearing hydrolyzable silicon-containing radicals capable of causing a crosslinking reaction b) 0.01 to 30 parts by weight zeolite and c) 0.0001 to 10 parts by weight curing catalyst. Zeolite, as one of a group of silicious materials, is added to the resin to prevent deactivation of the curing agents at exposed surface of the resin which are cast on release liners to form thin films and sheets. Such polymers allow continued employment of certain useful polymeric backbone segments such as polyethers and polyurethanes, while offering new end-group chemistries for the curing of such polymers. Thus isocyanate chemistry, commonly used as a crosslinking mechanism for polymers used in insulating resins, can be replaced with reactive silicon chemistry. Use of new end group chemistries, however, requires that new resin compositions be found which meet the requirements generally imposed in electrical applications and in particular in insulation of electrical splices in for example, low (up to IK Volt) or medium (up to 36K Volt) voltage applications. Such requirements typically include: room temperature curability, appropriate viscosity, good adhesion to cable jacket, high volume resistivity, high electrical resistance, an appropriate pot life, a high hardness, non- foaming in the presence of water and low moisture pickup. Up until now, no resin compositions are known which can meet the low-toxicity (isocyanate free) requirements currently demanded while at the same time providing superior handling properties and final electrical characteristics. It is now an object of the present invention to provide a pourable, preferably solvent free, room temperature curable, low-toxicity resin composition having appropriate electrical properties when cured, in particular insulating characteristics making it suitable for use in electrical applications and in particular for insulation of low- or medium-voltage electrical splices. Further objects of the present invention will become clear from the description hereinafter. Summary of the invention The present invention provides a low-toxicity moisture-curable resin comprising (A) at least one polymer having an organic backbone and at least one silicon- containing end group having at least one hydroxyl group or hydrolyzable group, whereby said polymer is crosslinkable through formation of one or more siloxane bonds, (B) at least one curing catalyst, (C) at least one molecular sieve, and (D) water, wherein the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, R„ of at least 10,000 MOhm (10 10 Ω) measured according to the test method specified in the test method section below. The invention also provides a method for preparing a low-toxicity moisture- curable resin comprising the steps of a) preparing a mixture comprising at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one hydroxyl or hydrolyzable group, whereby said polymer is crosslinkable through formation of one or more siloxane bonds, at least one molecular sieve (C) and water (D), b) degassing said mixture, and c) adding at least one curing catalyst (B) to said mixture, wherein the amounts of molecular sieve and water are selected so that the cured resin has an insulation resistance, Rj, of at least 10,000 MOhm. The invention also provides a kit of two parts, wherein part I comprises at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one hydroxyl or hydrolyzable group, whereby said polymer is crosslinkable through formation of one or more siloxane bonds, at least one molecular sieve (C) and water (D), wherein the amounts of molecular sieve (C) and water (D) and are selected so that the insulation resistance, R„ of the cured resin is at least 10,000 MOhm, and wherein part II comprises at least one curing catalyst (B). Further, the present invention provides for a low-voltage cable joint comprising a mold body containing an electrical splice, wherein the mold body is filled with the resin composition of the present invention with subsequent curing. Finally, the present invention provides the use of such a resin composition for electrical applications. Detailed description of the invention The present invention concerns a low-toxicity moisture-curable resin comprising (A) at least one polymer having an organic backbone and at least one silicon- containing end group having at least one hydroxyl or hydrolyzable group, whereby said polymer is crosslinkable through formation of one or more siloxane bonds, (B) at least one curing catalyst (C) at least one molecular sieve, and (D) water, wherein the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, R,, of at least 10,000 MOhm measured according to the test method specified in the test method section below. The resin composition of the present invention comprises at least one polymer having an organic backbone and at least one silicon-containing end group having at least one hydroxyl or hydrolyzable group. Polymers bearing hydrolyzable silicon-containing end groups, denoted as component (A) of the composition of the present invention, may comprise any organic backbone chain. Specific examples of organic backbones useful in the present invention comprise polyethers having repeating units of the formula -R-O- in which R is a divalent organic group, preferably a divalent alkylene group (as described, for example, in Japanese patent application No. 335798/1987); polyacrylates obtainable through radical polymerization of an acrylate, acrylate copolymers of an acrylate with, for example, vinyl acetate, acrylonitrile, methylmethacrylate or styrene (as described, for example, in Japanese Patent Kokai Publication No. 168014/1984); saturated hydrocarbon based polymers such as isoprene-based polymers and hydrogenated diene-based polymers (described, for example, in Japanese patent application Nos. 327938/1987 and 330890/1987); polyethers modified with vinyl monomers which can be prepared by polymerizing vinyl monomers (such as, for example, (meth)acrylates where the alcohol residue has 1-12 carbon atoms, vinyl acetate, styrene or acrylonitrile) in polyethers which have been prepared by polymerizing cyclic ethers (such as propylene oxide, ethylene oxide or tetrahydrofuran), and polyurethanes described, for example, in US 5,587,502. Among them, polyethers containing at least 50%> by weight, preferably at least 70%. by weight and most preferably at least 90%> by weight of the repeating units of the formula: -R-O- I in which R is a divalent organic group, preferably a divalent alkylene group and especially preferably R is propylene, are preferred. The polyether polymer segment may be of any molecular weight which results in the formation of a curable resin composition which is liquid and pourable at ambient temperatures. Molecular weight of the polyether polymer segment is preferably in the range of 500 - 20,000 as measured by number average molecular weight, M„. M n is preferably 1,000 - 10,000 and most preferably 1,000 - 5,000. The silicon-containing end groups of polymer (A) are well known groups and can be crosslinked even at ambient temperatures. A typical example of such a group may be represented by the formula (II) wherein X is a hydroxyl or a hydrolyzable group, provided that when two or more X groups are present, they may be the same or different, R 1 is a monovalent hydrocarbon group having 1 - 20 C atoms, or R 1 is a triorganosiloxy group of the formula: R3- Si-O- in which R 2 is a monovalent hydrocarbon group having 1 to 20 carbon atoms provided that the three R 2 groups may be the same or different and that when two or more R 1 groups are present, they may be the same or different, "a" is 0, 1, 2, or 3, "b v is 0, 1, or 2 provided that the sum of "a" and "b" is at least 1, preferably from 1 to 4. and "m" is 0 or an integer of 1 to 18 provided that when "m" is > 2, the bracketed groups may be the same or different. The silicon-containing end group may also be a triorganosiloxy group of the formula III: wherein X and R 1 are the same as defined for II above and "c" is 1, 2 or 3 is preferable. Specific examples of the hydrolyzable group are a hydrogen atom, a halogen atom, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amide group, an aminoxy group, a mercapto group or an alkenyloxy group. Among them, alkoxy groups having 1 to 8 carbon atoms are preferable since they are hydrolyzed under mild conditions and easily handleable. One to three hydrolyzable group can be bonded to one silicon atom. In a preferred embodiment, the reactive silicon atom bears two hydrolyzable groups. The silanol group can be formed through hydrolysis of the hydrolyzable silicon- containing group. Specific examples of the group R 1 are alkyl groups (for example, methyl or ethyl), cycloalkyl groups (for example, cyclohexyl), aryl groups (for example, phenyl), aralkyl groups (for example, benzyl), alkenyl groups (for example, vinyl) or a trimethylsiloxy group. When the silicon atoms are bonded to the organic backbone through siloxane linkages, the silicon-containing reactive group preferably contains < 20 silicon atoms. The polymer of component (A) bearing hydrolyzable silicon-containing end groups has more than one, preferably 1.2 to 6 silicon-containing reactive groups in a molecule on the average. When the number of the silicon-containing group in a molecule is less than about 1.2 on the average, the curable composition is not effectively cured and the improvement of the properties is not satisfactorily achieved. When the average number of the silicon-containing reactive groups exceeds six, the cured polymer tends to lose flexibility. The silicon-containing group may be introduced into the polymer by such methods as disclose in Japanese patent Application Nos. 335798/1987 and 330890/1987 and Japanese Patent Kokei Publication No 168014/1984. Preferred as component (A) of the present invention are polyethers having silicon-containing end groups bearing hydrolyzable groups and which are crosslinkable through formation of one or more siloxane bonds. Such materials are commercially available, for example, as SAT 010 from Kaneka (Tokyo, Japan), (polypropylene oxide having silicon-containing hydrolyzable end groups, having a molecular weight of approximately 3,000); as SAT 030 from Kaneka (Tokyo, Japan), (polypropylene oxide having silicon-containing hydrolyzable end groups having a molecular weight of approximately 5,000); or as SAT 303 from Kaneka (Tokyo, Japan), (polypropylene oxide having silicon-containing hydrolyzable end groups having a molecular weight of approximately 8,500). The resin composition of the present invention also comprises at least one curing catalyst (B) which is effective in catalyzing the hydrolysis of the hydrolyzable group and/or the subsequent silanol crosslinking reaction. Any of the conventional curing catalysts which are known to cure the polymer bearing hydrolyzable silicon-containing end groups of component (A) may be used in the present invention. Specific examples of the curing catalyst (B) are titanates (e.g. tetrabutyltitanate or tetrapropyl titanate), tin carboxylate salts (e.g. dibutyltin dilaurate, dibutyltin maleate, dibutyltin diacetate, tin octylate or tin napthenate), organic zirconium compounds (e.g. zirconium tetraisopropoxide or zirconium tetrabutoxide), reaction products of dibutyltin oxide with phthalates, chelate compounds such as organic aluminum compounds (e.g. aluminum trisacetylacetonate, aluminum trisethylacetylacetonate or diisopropoxyaluminum ethylacetoacetonate). dibutyltin diacetylacetonate, zirconium tetraacetylacetonate, titanium tetraacetylacetonate and the like; lead octanoate; amines (e.g. butylamine, monoethanolamine, tetraethylenetriamine, guanidine, 2-ethyl-4-methylimidazole or 1.8- diazabicyclo [5.4.0] undecene-7 (DBU)) or their salts with carboxylic acids; and other acid or base catalysts which are known as silanol catalysts. Among them, the organic aluminum compounds such as aluminum trisacetylacetonate, aluminum trisethylacetylacetonate and diisopropoxyaluminum ethylacetoacetonate, the organic zirconium compounds such as zirconium tetraacetylacetonate, zirconium tetraisopropoxide and zirconium tetrabutoxide, the organic titanium compounds such as tetrabutyltitanate, tetrapropyltitanate and titanium tetraacetylacetonate, the tin (II) compounds such as dibutyl tin diacetylacetonate and the adduct of dioctylphthalate with dibutyltin are preferred since they provide a curing rate which allows mixing and pouring of the resin in a reasonable time frame and provide a controlled rate of heat evolution. The curing catalyst (B) is preferably used in an amount of from 0.1 to 5 percentage by weight, more preferably from 0.1 to 0.3 percentage by weight of the resin composition. When the amount of curing catalyst (B) is less than 0.1 percentage by weight, insufficient catalytic effect is obtained, while if the amount of (B) exceeds 5 percentage by weight, the resin composition is cured too quickly so that time allowed, for example, for mixing the resin and filling the mold cavity is insufficient. The resin composition of the present invention also comprises at least one molecular sieve, denoted as component (C). A molecular sieve is defined to be any material which can exclude molecular species by size. A preferred type of molecular sieves are zeolites, crystalline silicate or aluminosilicate framework structures with channels of a diameter of less than 1.2 nm. Other molecular sieves are based on silicate frameworks where boron, gallium or iron replace aluminum. Still other classes of molecular sieves are materials where germanium replaces silicon in the aluminosilicate framework. Materials which are included in the present definition of molecular sieves are described in "Molecular Sieves" in Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., 1995, pp. 888-925. Although the inventors do not wish to be bound by such theory, it may be assumed that molecular sieves increase the electrical resistance of the cured resin composition by entrapment of small polar molecules, particularly methanol, liberated during the hydrolysis and subsequent crosslinking reactions of the organic polymer (A) bearing silicon containing reactive groups. Molecular sieves are useful in the present invention in amounts of 0.4 weight per cent to 25 weight per cent with respect to the mass of the resin. Especially preferred is an amount of 5 weight per cent to 15 weight per cent, while an amount of about 7 weight per cent is most preferred. It was found by the present inventors that an effective amount of molecular sieves (C) for a given amount of water (D) can be estimated based on the calculated amount of small polar molecules such as methanol liberated from the polymer (A) during the hydrolysis and subsequent silanol crosslinking reaction. The mass of small polar molecules liberated during the hydrolysis reaction is calculated taking into account the amount of water and assuming complete hydrolysis of the silicon-containing reactive groups of polymer (A). This mass is then multiplied by a factor of about 4-6. more preferably about 5 to give the effective amount of molecular sieves. This finding of the present inventors correlates with the usual assumption given in the literature that molecular sieves such as zeolites can absorb approximately 20%. of their own weight in methanol, irrespective of their particular type. If water is added to the resin composition in excess of the stoichiometric amount with respect to the hydrolyzable groups, then additional molecular sieves must be added to absorb this amount of water. Thus the effective amount of molecular sieve is not dependent only on the amount of small organic molecules such as methanol which are released, but also on the amount of unconsumed water in the system. It was found that the insulation resistance of the cured resin depends upon the free amount of small organic molecules and/or water, and that this amount has to be controlled carefully in order to give the desired value of the insulation resistance of at least lθ'° Ω. The person skilled in the art can easily control the free amount of small organic molecules and/or water by taking into consideration the molecular weight of the organic polymer (A), the number of silicon-containing groups, the number of hydrolyzable groups in each silicon-containing group, and then adjusting the amount of molecular sieves and water. In the resins of the present invention the amount of molecular sieves must be balanced with the amount of water added to the resin and selected in such a manner that the cured resin has an insulation resistance, R„ of at least 10,000 MOhm. If an insufficient amount of molecular sieves are added, small polar molecules generated by the crosslinking reaction (such as methanol) are not absorbed and are still free in the cured resin mass, resulting in reduced and insufficient insulation resistance for the electrical applications desired. If a large excess of molecular sieves is employed, the electrical properties of the cured resin remain good, but the mechanical properties such as Shore A hardness and tensile strength are adversely affected. Molecular sieves which have been found to be useful in the present invention include, but are not limited to, 13 Angstrom molecular sieves, available as BAYLITH W from Bayer (Leverkusen. Germany), Type 4 Angstrom molecular sieves, available from Union Carbide, 3 Angstrom molecular sieves, available as BAYLITH L from Bayer (Leverkusen, Germany) and hydrophilic deodorizing molecular sieves, available as SMELLRITE 5000 from Universal Oil Products. Particularly preferred are molecular sieves having a pore size between 10 and 15 Angstroms, such as BAYLITH W. Molecular sieves (C) used in the present invention are preferably dried before use to avoid addition of undetermined amounts of water to the resin, thus requiring the addition of undetermined and excess amounts of molecular sieves. The resin composition of the present invention also comprises water, the amount of which has to be carefully controlled. When used in cable splices, for example, resin compositions of the present invention are commonly used in amounts up to 10 kilograms. The resin composition is prepared by mixing the components (A) through (D) in a method described hereinafter and pouring the resulting fluid into a large mold body surrounding an electrical splice. Since the resin mass may have a very low surface to volume ratio, it is unlikely that sufficient moisture can be absorbed from the air or from surfaces to insure complete and uniform cure. Especially when large amounts of resin of, for example, 4 kg or more are employed, areas deep within the resin mass are exposed to limited amounts of adventitious moisture. Therefore a certain amount of water has to be intentionally included to ensure curing throughout the resin mass. Since the presence of free small polar molecules such as methanol and water can reduce the electrical resistance of resins, it is critical that sufficient water be added to achieve uniform and complete cure. On the other hand, large excesses of water should be avoided as these would be detrimental to the final electrical properties. The preferred amount of water (D) to be added corresponds to at least 25% of the stoichiometric amount of water, defined as that amount of water necessary to hydrolyze all of the hydrolyzable groups present in component (A). A preferred amount of water is 40 to 60 %> of the stoichiometric amount, with the most preferred amount of water being about 50%> of the stoichiometric amount. Less than the stoichiometric amount of water can be used to achieve full curing because water itself is a by-product of the condensation reaction. For every two water molecules consumed by the hydrolysis reaction, one is regenerated during the crosslinking reaction. These water molecules can be essentially "recycled' " into the hydrolysis reaction and are effectively available to promote further crosslinking. The addition of the appropriate amount of water is essential in producing large masses of cured resin which is uniformly hardened, free of entrapped voids and exhibits the required insulation resistance. If an insufficient amount of water is added, then curing of the resin throughout its bulk does not occur and the resin does not have the final strength required. An amount of water in excess of the stoichiometric amount with regard to the hydrolyzable groups of the silicon-containing groups can be employed, if a corresponding amount of molecular sieves is present to absorb that amount of water. If, however, a large excess of water is added, for example greater than about 300 percent of the stoichiometric amount, then excess water which cannot be captured by molecular sieves may remain in the cured resin. This excess water leads to inferior electrical properties, especially to inferior values for insulation resistance. Adding a large excess of molecular sieves to absorb large excess of water, however, results in negative impact on the physical properties of the cured resin. In a preferred embodiment of the resin according to the invention the total amount of the free small organic molecules such as methanol which is liberated during hydrolysis and the subsequent condensation reaction, and free water is less than 0.4 wt. % with respect to the mass of the resin, more preferably less than 0.3 wt. % and especially preferably not more than 0.2 wt. %. Examples of the present invention as summarized in Tables 1, 3, 4 and 5 show that if the calculated sum of small molecules such as water and methanol is above 0.4% by weight, then the insulation resistance, R„ of the cured resin is below the desired minimum of 10,000 MOhm. The resin composition of the present invention may optionally comprise other materials and additives. Among the most useful of optional additives are fillers, which are commonly employed either singly or in combination to provide an appropriate and usable viscosity as well as to improve hardness. Certain moisture-curable polymers (A) suitable for the present invention have an inherent viscosity such that additional filler may not be required. Fillers useful as optional additives to the resin compositions of the present invention include, but are not limited to, silicon dioxide, titanium dioxide, carbon black, talc, diatomaceous earth, particulate polymeric fillers, glass beads and glass microbubbles, ceramic particles and calcium carbonate. Preferred as a filler is calcium carbonate, as well as mixtures of calcium carbonate and glass microbubbles. If added, the filler component is preferably present in the resin composition in a ratio of filler to polymer (A) of 1 :2 to 2: 1. Preferably, the filler is added in approximately equal amounts by weight to organic polymer (A) (1 : 1). The filler is preferably added in an amount such that the viscosity of the uncured resin composition is less than about 20,000 cps at 23°C. If too much filler is added, the resin becomes so viscous that it cannot be poured into the mold or another shape- forming container and mechanical properties degenerate. If insufficient filler is added, the uncured resin viscosity in some cases may be too low for proper casting into the mold or forming device, or may leak through seams in molds or other containers, and the cured resin may not have sufficient hardness. A preferred range of viscosity of the uncured resin composition is 5,000-15,000 cps at 23 °C. It is highly advisable that the filler component must be dried before inclusion in the resin composition of the present invention. Most fillers contain moisture in amounts which vary depending on the type of filler, manufacturing process and product quality control. Since it is critical to the present invention that the amount of water be controlled and known, fillers are preferably dried before use so that they do not contribute unmeasured quantities of water to the resin composition. As described above, it is essential to the invention that the amount of free water in the cured resin is minimized. The resin compositions of the present invention may also comprise one or more adhesion promoting agents commonly employed to insure good adhesion of the resin matrix to materials it is intended to protect and/or insulate, such as the jacket of an embedded electrical splice, other cable insulation materials or metal wires. Though a wide variety of adhesion-promoting agents can be used for this purpose, organosilanes such as vinyltrimethoxysilane, vinyltriethoxysilane and aminopropyltriethoxysilane have been found to be preferred. Particularly preferred is aminopropyltriethoxysilane such as Silane Al 100 (available from Union Carbide, Danbury CT, USA). One or more adhesion promoting agents can be added to the resin composition in amounts of 0.3 to 4.0 percentage by weight, preferred is about 0.5 to about 2 percent , about 1 per cent being most preferred. Optionally, the resin composition of the present invention may contain one or more plasticizers. Plasticizers preferred for use in the present invention include, but are not limited to, dioctyl phthalate, polypropylene glycol, chlorinated paraffin, liquid polybutadiene and the like. Preferred plasticizers are those which do not suppress the crosslinking reaction and those which are not hydrophilic. Inclusion of small hydrophilic polymer segments as plasticizers tends to increase the susceptibility of the cured resin to penetration by water upon long-term aging. Addition of plasticizers in an amount of up to 30 per cent by weight of the composition may be used to reduce the overall cost of the final resin and modify the physical properties of the cured resin. The invention also comprises a method for preparing a low-toxicity moisture- curable resin comprising the steps of a) preparing a mixture comprising at least one polymer (A) having an organic backbone and at least one silicon atom containing reactive group having at least one hydroxyl or hydrolyzable group, whereby said polymer is crosslinkable through formation of one or more siloxane bonds, at least one molecular sieve (C) and water (D), b) degassing said mixture, and c) adding at least one curing catalyst (B) to said mixture, wherein the amounts of molecular sieve (C) and water (D) are such that the cured resin has an insulation resistance, R,, of at least 10,000 MOhm. It has been surprisingly found that this method is essential to the invention. Other seemingly logical methods of combining the elements of the invention logically selected by an expert in this field were found not to be useful. In particular, other methods were found to have the distinct disadvantage in that the resulting cured resin was filled with voids and resembled a foam. The generation of foam during the resin- curing step is unacceptable as resin masses having voids are inherently incapable of providing the electrical and/or mechanical properties required. In particular, the following method comprising the steps of a) preparing a mixture of component (A) and water (D), b) degassing said mixture, c) adding the curing catalyst (B) and d) adding the molecular sieves (C) was found to generate large amounts of foam. Likewise, a method comprising the steps of a) preparing a mixture of polymer (A), catalyst (B) and molecular sieves (C), b) degassing the mixture and c) adding water (D) also generated large amounts of foam. These methods are not subject matter of the present invention. The present inventors found surprisingly that it is essential that polymer (A), molecular sieves (C) and water (D) are first combined and this mixture degassed before the curing catalyst (B ) is added in a final step. The present invention also comprises a kit of two parts, wherein part I comprises at least one polymer (A) having an organic backbone and at least one silicon atom containing reactive having at least one hydroxy or hydrolyzable group, whereby said polymer is crosslinkable through formation of one or more siloxane bonds, at least one molecular sieve (C) and water (D), and part II comprises at least one curing catalyst (B), wherein the amounts of molecular sieve (C) and water (D) are selected so that the cured resin has an insulation resistance, R,, of at least 10,000 MOhm. Kits of parts comprising two-part resin compositions are disclosed, for example, in U.S. Patent 2,932,385 or U.S. Patent 3,074,544. Thus U.S. Patent 3,074,544 discloses a multiple compartment, flexible, unitary package for compartmentalized accommodation and selective admixture of at least two fluent materials, comprising a normally flat envelope being joined by heat sealing to form a transversely extending rupturable seam separating the interior of said envelope into individual compartments. The seam includes masking means in the form of a substantially uniformly open web interposed between the sidewalls and through the openings of which the sidewalls are heat sealed. Another suitable kit of parts comprising a two part pouch package described in DE 42 39 288. It comprises a surrounding bag with two portion bags therein. The contents of these portion bags is kept separate by a clamp. By removing the clamp, the contents can be mixed together in the surrounding bag. A good mixing can be obtained by kneading the surrounding bag and contact with the chemicals is thus avoided. After mixing, the surrounding bag can be opened and the ready composition can then be used. The kit of part constructions described in US '385, US '544 or DE '288 can be advantageously employed in the present invention. They allow, for example, for thorough mixing of the contents of the compartments together and subsequently using the resulting homogenous composition for preparing a splice. The present invention also comprises a low-voltage (up to IK Volt) or medium- voltage (up to 36K Volt) cable joint comprising a mold body containing an electrical splice, wherein the mold body is filled with the resin composition of the present invention with subsequent moisture curing, thus forming an insulated electrical splice. Furthermore, the invention comprises the use of the resin composition of the present invention for electrical applications. The invention will now be illustrated by way of the following non-limiting examples. EXAMPLES The following test methods are used in the examples: Insulation Resistance, R, The insulation resistance of cured resins was measured using the following configuration. Two sector-formed aluminum wires of a length of 200 mm were stripped of insulation for about two thirds of their length. The aluminum wires had a cross- section of 50 sq. mm. The exposed wire tips were suspended in a parallel fashion with the tips inside of a stainless steel can having a height of 120 mm and a diameter of 100 mm. The tips of the wires were 20 mm from the bottom of the can and 17 mm apart. Resin samples (approximately 800 g) were prepared and poured into the can, partially embedding the exposed ends of the two wires in resin. The resin is allowed to cure at room temperature (23°C) for 24 hours. To perform the test, a DC voltage of 5000 volts was applied. The insulation resistance was recorded in units of MOhm and is calculated using the following equation: R, = p(L/A), where R, is the insulation resistance, p is the specific resistance, L is the distance between the measuring electrodes and A is the cross-sectional area of the measuring electrode. Longitudinal Water Tightness Test (VDE 0278. Part 3) This is a functional test for the determination of the long term ability of a resin to maintain its insulating function in the presence of water and under the influence of fluctuating temperature. The test method is described in detail in VDE 0278, Part 3 (Verband Deutscher Elektrotechniker). First, a low-voltage in-line splice was prepared. Four separate wires having a cross-section of 150 sq. mm were spliced using standard methods. The splice was then covered with a large two-part polymeric mold body having a length of approximately 500 mm and a circumference at its largest part of about 350 mm. Approximately four kilograms of resin was prepared by the method described in the specification and poured into the mold body, thus encapsulating the splice in resin. After the splice was prepared and the resin cured, a cut was made in the cable jacket so that water could penetrate to the resin-cable insulation interface as described the VDE Longitudinal Water Tightness Test. The completed low- voltage in-line splice, denoted hereinafter as a loop, was subjected to a variety of conditions designed to simulate long term environmental exposure. Electrical resistance was measured after the tests. A large amount of data is generated from these tests, including several different phase-to-phase measurements and phase-to-air measurements. An average value describing the overall electrical resistance is given. This should be considered as a relative measurement used for comparative purposes only. The tests were: A) immersion in water at 23 °C for 24 hours B) 63 thermocycles in air. where one thermocycle comprises 5 hours at elevated temperature followed by 3 hours of cooling. C) 63 thermocycles in water, where one thermocycle comprises 5 hours at elevated temperature followed by 3 hours of cooling. Temperatures during the thermocycle tests were 95 °C directly at the conductor, 70°C at the conductor outside the mold and 50-60°C at the outer shell of the mold. The heat necessary for the thermocycles was generated by passing a high current of low voltage through four loops connected in series as described in the standard method. Viscosity of the uncured resin Viscosity of the uncured resin was measured by cone and plate geometry viscometry using a Model CV 20 N Viscometer manufactured by Haake (Karlsruhe, Germany) with a Pk 45-4 deg cone. Results were recorded in units of milliPaschal seconds (mPs). Shore A Hardness of the cured resin After the resin composition was cured at room temperature, the Shore A Hardness was measured using a German industry standard test method (DIN 53505). Materials A Polypropyleneoxide having hydrolyzable silicon-containing end groups, molecular weight 3,000, available as SAT 010, from Kaneka (Tokyo). B Polypropyleneoxide having hydrolyzable silicon-containing end groups, molecular weight 5,000, lightly branched, available as SAT 030, from Kaneka (Tokyo). C Polypropyleneoxide having hydrolyzable silicon-containing end groups, molecular weight 8,500 (high viscosity, branched), available as S 303, from Kaneka (Tokyo). Catalysts G Dibutyltin diacetylacetonate, NEOSTAN U220, from Nitto Kasei. H Adduct of dibutyl tin and dioctylphthalate, available as # 918 from Sankyo, Japan, Molecular sieves K Molecular sieves, 13 Angstrom, available as BAYLITH W from Bayer (Leverkusen, Germany) L Molecular sieves, Type 4 Angstrom, available from Union Carbide. M Molecular sieves, 3 Angstrom, available as BAYLITH L from Bayer (Leverkusen, Germany) N Hydrophilic deodorizing molecular sieves, , available as SMELLRITE 5000 from Universal Oil Products Fillers R Calcium carbonate, available as MICRODOL 1 from Norwegian Talc. S Glass bubbles filled with inert gas, available as AMOSPHERES CN from AML International. Adhesion promoter Y Amino silane, SILANE Al 100, from Union Carbide, Danbury, CT, USA Example 1 A mixture of 36.64 parts polypropylene oxide having silicon-containing end groups having hydrolyzable groups, having a molecular weight of approximately 5000, lightly branched (available as SAT 030 from Kaneka, Tokyo), 0.60 parts deionized water, 36.64 parts CaCO 3 (available as MICRODOL 1 from Norwegian Talc) and 0.77 parts aminosilane A 1 100 (available from Union Carbide) and 24.57 parts molecular sieves (13 Angstrom, available as BAYLITH W from Bayer (Leverkusen Germany) was stirred for 10 min using a Cowles dissolver operated at approx. 5,000 rpm. The mixture was then degassed using a conventional vacuum line until no more bubbles were observed in the mixture, thus forming Part I. To insure good dispersion of molecular sieves in the final resin composition, a predispersion of sieves in organic polymer (A) was prepared. Catalyst H (adduct of dibutyl tin and dioctylphthalate, available as #918 from Sankyo, Japan), comprising Part II, was added in the amount of 0.77 parts directly to Part I after degassing. Stirring was continued for about 3 minutes by hand using a spatula to insure homogeneous dispersion. Amounts of the components were calculated so that no free water or methanol would remain in the cured resin. The resin was then poured immediately into a cup-shaped mold in which two electrodes were suspended as described under the test method "Insulation Resistance, R," and cured at 23° C for 24 hours. The insulation resistance of the cured resin composition was measured as described under the test method "Insulation Resistance" and recorded in Table 1 as Rj. The measured insulation resistance was >10,000 MOhm. Example 2 Example 1 was repeated with identical components with the exception that the levels were varied slightly. Again, amounts were selected so as to have no free water or methanol in the cured resin. The resin composition were prepared and cured as in Example 1 and insulation resistance, R j , measured as above. The insulation resistance of Example 2 was > 10,000 MOhm. Comparative Example 1 A resin composition was prepared by the procedure given in Example 1 using 49.00 parts SAT 010, 0.60 parts water, 49.00 parts filler R and 1.00 parts adhesion promoter Y. The curing agent employed was 0.40 parts catalyst G (dibutyltin diacetylacetonate, available as NEOSTANN U220 from Nitto Kasei). The calculated amount of free MeOH/H 2 O was 2.10 weight percent and no molecular sieves were present. The measured insulation resistance, Rj, of the cured resin was 500 MOhm. Comparative Example 2 A resin composition was prepared by the method of Example 1 using materials identical to those in Example 1. Fewer molecular sieves were added as well as a larger excess of water as summarized in Table 1. The calculated amount of free MeOH/H 2 O was 0.84 wt. percent. The insulation resistance, R j5 was measured as 2,500 MOhm. Example 3-4 and Comparative Example 3 Three resin compositions were prepared by the method described in Example 1. Each resin comprised the same components at the same levels with the exception that the type of molecular sieve was varied, in particular the pore size. Example 3 contained molecular sieve K (13 Angstrom), Example 4 contained molecular sieve M (3 Angstrom) and Comparative Example 3 contained molecular sieve L (4 Angstrom). Insulation resistance of the three materials was measured as 20,000 MOhm, 10,000 MOhm and 8,000 MOhm, respectively. This series of example demonstrates that molecular sieves having a large pore size are most effective in providing high values of insulation resistance, Rj. The resin compositions and the measured insulation resistance, R,, are summarized in Table 2. Table 1 * % of the stoichiometric amount of water required to hydrolyze all hydrolyzable groups ** calculation based on the assumption of complete hydrolysis of the silicon-containing reactive groups of polymers (7) and of an absorption capacity of the molecular sieves of 20% of their own mass Table 2 * % of the stoichiometric amount of water required to hydrolyze all hyrolyzable groups Examples 5-6 The resin compositions of Examples 5-6 were compounded on a large scale to provide about 4 kg of finished resin composition. The resin compositions are summarized in Table 3. The resin was poured directly after mixing into a large two-part mold body encasing a low voltage splice and allowed to cure at 23 °C for approximately 24 hours. The resin encapsulated splice, referred to hereinafter as a loop, was then subjected to rigorous practical tests prescribed by the VDE as in the method described under Test Methods. Test results are summarized in Table 4. Smaller portions of the same resin were cast into small molds and/or formed into sheets commonly used for the measurement of physical properties such as Shore A hardness and cured at a temperature of 23° C for 24 hours. Test results are summarized in Table 4. Example 7 Example 7 was prepared using a mixture of two different polymers A and B. A hydrophilic deodorizing molecular sieve, available as SMELLRITE 5000 from Universal Oil Products, denoted as N, was also employed. Example 8 Example 8 was prepared as Example 5, with the exception that both a mixture of two polymers A and B as well as a mixture of two molecular sieves K and N were employed. Example 9 Example 9 was prepared in a manner similar to Example 8, with the exception that a mixtures of fillers was used as well. In addition to CaCO 3 of previous examples, hollow glass microspheres filled with inert gas (available as AMOSPHERES CN from AML International) were used to aid in reducing resin density. Comparative Example 4 A resin composition was prepared which contained no molecular sieves. The insulation resistance of the cured resin composition was found to be 250 MOhm. A large splice was prepared using the resin composition of Comparative Example 5 and the loop thus formed was subjected to the VDE test and showed a value of 30 Mohm. Comparative Example 5 The resin of comparative Example 5 was prepared by the method of Example 1. Molecular sieves and water were present at such levels that the free MeOH/H 2 O in the cured resin was 0.72 wt. percent. An insulation resistance of 3,500 MOhm was measured. Table 3 * % of the stoichiometric amount of water required to hydrolyze all hyrolyzable groups ** calculation based on the assumption of complete hydrolysis of the silicon-containing reactive groups of polymers (7) and of an absorption capacity of the molecular sieves of 20% of their own mass Table 4 Examples 10-13 Examples 10-13 were prepared as in Example 1. Each of the resin compositions was prepared using polymer B SAT 030 (polypropyleneoxide having hydrolyzable silicon end groups, molecular weight 5,000, lightly branched, available as SAT 030, from Kaneka (Tokyo)), molecular sieves K (Baylith W), water, catalyst H (adduct of dibutyl tin and dioctylphthalate), CaCO 3 filler R (MICRODOL 1 from Norwegian Talc) as well as adhesion promoter Y (Silane Al 100) in weight percentages indicated respectively in Table 5. The calculated amount of free MeOH/H 2 0 was zero and was reflected in the high values of insulation resistance, R,. Resin compositions as well as test results are summarized in Table 5. Comparative Examples 6-13 Resin compositions were prepared as in Example 1. Water and molecular sieves were added in amounts, the combination of which resulted in sufficient water/methanol (greater than 0.4 weight percent) residue that the insulation resistance of the cured resin was less than 10,000 MOhm. Table 5 * % of the stoichiometric amount of water required to hydrolyze all hydrolyzable groups ** calculation based on the assumption of complete hydrolysis of the silicon-containing reactive groups of polymers (7) and of an absorption capacity of the molecular sieves of 20% of their own mass

Claims: Claims 1. A low-toxicity moisture-curable resin comprising: a) at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one group selected from hydroxyl and hydrolyzable groups, whereby said organic polymer is crosslinkable through formation of siloxane bonds, b) at least one curing catalyst (B), c) at least one molecular sieve (C), and d) water (D), wherein the amounts of (C) and (D) are selected such that a cured resin having an insulation resistance, R,, of at least 10,000 MOhm is formed. 2. A resin according to Claim 1 where water (D) is present in an amount of from about 25 to about 60 % of the stoichiometric amount of said hydrolyzable groups. 3. A resin according to claim 1 , wherein free small organic molecules are liberated during the hydrolysis of the hydrolyzable groups of the silicon-containing end groups or from subsequent crosslinkers thereof, and wherein less than 0.4 wt. % water is present in said cured resin. 4. A resin composition according to claim 1 wherein said polymer (A) comprises a polyether backbone having repeating units of formula I -R-O- I wherein R is a divalent organic alkylene group which can be linear or branched, and comprises 1-10 C atoms. 5. A resin composition according to claim 4 wherein R is an alkylene group having 3 carbon atoms. 6. A resin composition according to claim 1 where said polymer (A) has a number average molecular weight (M n ) of from 500 to 20,000. 7. A resin composition according to claim 1 wherein said silicon-containing end group has at least one hydrolyzable group of formula II wherein X is a hydroxyl or a hydrolyzable group, provided that when two or more X groups are present, they may be the same or different, R 1 is a monovalent hydrocarbon group having 1-20 C atoms, or R' is a triorganosiloxy group of the formula: R 3 - Si-O- in which R 2 is a monovalent hydrocarbon group having 1 to 20 carbon atoms provided that the three R 2 groups may be the same or different and that when two or more R 1 groups are present, they may be the same or different, "a" is 0, 1, 2, or 3, "b" is 0, 1, or 2 provided that the sum of "a" and "b" is at least 1 , preferably from 1 to 4, and "m" is 0 or an integer of 1 to 18 provided that when "m" is > 2, the bracketed groups may be the same or different. 8. A resin composition according to claim 1 wherein the curing catalyst (B) comprises at least one organotin compound. 9. A resin composition according to claim 1 wherein at least one molecular sieve (C) has a pore size of from 10 to 15 Angstroms. 10. A method for preparing a low-toxicity moisture-curable resin having an insulation resistance of at least 10,000 MOhm comprising the steps of a) preparing a mixture comprising at least one polymer (A ) having an organic backbone and at least one silicon-containing end group having at least group selected from hydroxyl and hydrolyzable groups, whereby said polymer (A) is crosslinkable through formation of siloxane bonds, at least one molecular sieve (C) and water (D), b) degassing said mixture, and c) adding at least one curing catalyst (B) to said mixture, whereby the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, R,, of at least 10,000 MOhm. 1 1. A kit of two parts, wherein part I comprises a mixture comprising at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one hydroxyl or hydrolyzable group, whereby said polymer is crosslinkable through formation of a siloxane bond, at least one molecular sieve (C) and water (D), and part II comprises at least one curing catalyst (B), whereby the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, R,, of at least 10,000 MOhm. 12. A low-voltage cable joint comprising a mold body containing an electrical splice, wherein the mold body is filled with the resin composition according to claim 1 with subsequent curing. AMENDED CLAIMS [received by the International Bureau on 29 July 1998 (29.07.98); original claims 4 and 11 amended; remaining claims unchanged (2 pages)] 1. A low-toxicity moisture-curable resin comprising: a) at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one group selected from hydroxyl and hydrolyzable groups, whereby said organic polymer is crosslinkable through formation of siloxane bonds. b) at least one curing catalyst (B). c) at least one molecular sieve (C). and d) water (D), wherein the amounts of (C) and (D) are selected such that a cured resin having an insulation resistance. Rj, of at least 10.000 MOhm is formed. 2. A resin according to Claim 1 where water (D) is present in an amount of from about 25 to about 60 % of the stoichiometric amount of said hydrolyzable groups. 3. A resin according to claim 1 , wherein free small organic molecules are liberated during the hydrolysis of the hydrolyzable groups of the silicon-containing end groups or from subsequent crosslinkers thereof, and wherein less than 0.4 wt. % water is present in said cured resin. 4. A resin composition according to claim 1 wherein said polymer (A) comprises a polyether backbone having repeating units of formula I -R-O- I wherein R is a divalent organic alkylene group which can be linear or branched, and comprises 1-10 carbon atoms. 5. Λ resin composition according to claim 4 wherein R is an alkylene group having 3 carbon atoms. 6. A resin composition according to claim 1 where said polymer (A) has a number average molecular weight (M n ) of from 500 to 20.000. b) degassing said mixture, and c) adding at least one curing catalyst (B) to said mixture, whereby the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, Ri, of at least 10,000 MOhm. 11. A kit of two parts to form the moisture curable resin of claim 1 , wherein part I comprises a mixture comprising at least one polymer (A) having an organic backbone and at least one silicon-containing end group having at least one hydroxyl or hydrolyzable group, whereby said polymer is crosslinkable through formation of a siloxane bond, at least one molecular sieve (C) and water (D), and part II comprises at least one curing catalyst (B), whereby the amounts of (C) and (D) are selected so that the cured resin has an insulation resistance, Ri, of at least 10,000 MOhm. 12. A low-voltage cable joint comprising a mold body containing an electrical splice, wherein the mold body is filled with the resin composition according to claim 1 with subsequent curing.

Inventors: BARUCHA DIETER, STEPPUTTIS MANFRED, XU FRANK Y, BARUCHA, DIETER, STEPPUTTIS, MANFRED, XU, FRANK, Y.
Applicants: BARUCHA DIETER, MINNESOTA MINING & MFG, STEPPUTTIS MANFRED, XU FRANK Y, BARUCHA, DIETER, MINNESOTA MINING AND MANUFACTURING COMPANY, STEPPUTTIS, MANFRED, XU, FRANK, Y.
Application year: 1997
Main classification: H01B3
IPC codes: H01B3