GB2249552A - Curable siloxane sealant - Google Patents

Abstract

Compositions which cure at or about normal ambient temperatures comprising by weight (A) 100 parts of a polydiorganosiloxane. (B) a curing agent for the polydiorganosiloxane, (c) from 5 to 45 parts of particulate mica in which at least 75 percent by weight of the particles have an aspect ratio in the range from 15/1 to 100/1 and an average diameter of from 30 to 100 microns, and (D) at least 5 parts of a reinforcing or extending filler. The invention also includes a sealed multi-pane insulating glass unit in which at least a part of the sealing means comprises the cured product of the composition. The use of a specific amount of mica is stated to decrease gas- permeability.

Description

CURABLE SILOXANE COMPOSITIONS This invention relates to siloxane compositions which are curable to elastomers having reduced permeability to gases, and to the use of such compositions in multiple-pane insulating glass units.

Curable siloxane compositions have for many years been employed in a variety of applications. One type of curable siloxane composition has the ability to cure to an elastomer at normal ambient or slightly elevated temperatures, either spontaneously on mixing the components or as a result of exposure to moisture. Such compositions are generally termed room temperature vulcanisable (or RTVs) and they have been formulated into sealant materials having excellent physical properties, adhesion to substrates and weatherability. Such properties, as well as the ability to cure at normal ambient temperatures, have rendered the materials particularly suitable for use in the construction industry, for example in the sealing of glazed units to masonry structures.Another application of the sealant materials has involved their use as secondary, edge sealants in the fabrication of multiple-pane insulating glass units. According to earlier designs the units contained dry air in the interior space and were sealed at the periphery to prevent, as far as possible, the ingress of atmospheric moisture and the resulting misting of the glass panes. However, their use in the latter application has been restricted by the high vapour permeability of the conventional siloxane sealant materials. It has been proposed in U.S. Patent 4,131,588 to reduce the rate of water vapour transmission through certain siloxane sealant compositions by the incorporation therein of at least 75 parts by weight of mica per 100 parts by weight of siloxane base polymer.It has been found that the inclusion of such large proportions of mica result in a composition which is difficult to handle and which when cured has poor physical properties. In addition more recent developments in the insulated glazing art have been directed to improving the thermal and sound insulating properties of the units and now include filling the interior space with gases such as argon and sulphur hexafluoride. As a result of such innovation the problem of achieving a satisfactory seal becomes more the prevention of the egress of such gases rather than the ingress of water vapour.

We have now discovered that a significant reduction in the permeability of curable siloxane compositions to gases such as argon and sulphur hexafluoride can be attained by the incorporation of mica at much lower levels than those proposed in U.S. Patent 4,131,588. The use of such lower levels of mica represents a significant benefit inasmuch as it reduces handling difficulties and results in a sealant having satisfactory physical properties.

Accordingly, this invention provides a room temperature vulcanisable composition comprising by weight (A) 100 parts of a curable polydiorganosiloxane having a viscosity in the range from 150 to 100,000 mPa.s at 250C and wherein the organic substituents attached to silicon are selected from alkyl groups having from 1 to 10 carbon atoms, aryl, alkaryl and aralkyl groups having from 6 to 8 carbon atoms and alkenyl groups having from 2 to 8 carbon atoms, at least 30% of the said substituents being methyl groups, (B) a curing agent for polydiorganosiloxane (A), (C) from 5 to 45 parts of particulate mica wherein at least 75 percent by weight of the particles have an average diameter of from 30 to 100 microns and an aspect ratio in the range from 25/1 to 100/1, and (D) at least 5 parts of a reinforcing or extending filler.

The invention also includes a sealed multi-pane insulating glass unit comprising at least two spaced glass panes in which at least a part of the sealing means is the product of curing the composition comprising (A) to (D) as above defined.

The curable polydiorganosiloxanes (A) employed in the compositions of this invention are those having a viscosity in the range from 150 to 100,000 mPa.s at 250C. The organic substituents attached to the silicon atoms are selected from alkyl groups having from 1 to 10 carbon atoms, for example methyl, propyl, hexyl and decyl, alkenyl groups having from 2 to 8 carbon atoms, for example vinyl, allyl and hexenyl, and aryl, alkaryl and aralkyl groups having from 6 to 8 carbon atoms, for example phenyl, tolyl and phenylethyl. At least 30 percent of the total substituents should be methyl. Preferred from an economic stand point are polydiorganosiloxanes in which substantially all of the silicon-bonded substituents are methyl. However, it has been found that the presence of larger substituents such as phenyl can contribute to the reduction in gas permeability.Therefore, where maximum reduction in permeability is required the preferred polydiorganosiloxanes are those having a proportion, preferably up to 75 percent of the total, of larger substituents, the most preferred being the polymethylphenylsiloxanes. As hereinafter described polydiorganosiloxanes (A) will contain, in addition to the substituents hereinabove mentioned, silicon-bonded reactive groups by means of which the desired room temperature curing can be effected. Such groups may be, for example, hydroxyl, alkoxy, oximo or acyloxy and are normally attached to the terminal silicon atoms of the polydiorganosiloxane.

Component (B) of the compositions of this invention is a curing agent which is effective in converting polydiorganosiloxane (A) to the solid elastic state at normal ambient or slightly elevated temperatures, usually about 15 to 300C. Polydiorganosiloxane (A) and curing agent (B) thus comprise a room temperature vulcanising system. A variety of compositions based on such systems are wellknown in the art and any of these can be employed as the basis of the compositions of the present invention.

Examples of such compositions are: (i) vulcanisable organosiloxane compositions based on an organosiloxane polymer having in the molecule silicon-bonded oxime radicals, and/or a mixture of an organosiloxane polymer having silanol groups and a silane having at least 3 silicon-bonded oxime groups. Such compo sitions are described for example in U.K.

Patents 975 603 and 990 107; (ii) vulcanisable organosiloxane compositions based on an organosiloxane polymer having terminal silicon-bonded acyloxy groups, and/or a mixture of a silanol-terminated organosiloxane polymer and a silane having at least 3 silicon-bonded acyloxy groups per molecule.

Such compositions are described for example in U.K. Patents 862 576, 894 758 and 920 036; (iii) vulcanisable compositions based on an organo siloxane polymer having terminal silicon bonded amide or amino groups, and/or a mixture of silanol-terminated organosiloxane polymer and a silylamine or silylamide. Such vulcanisable compositions are described for example in U.K. Patents 1 078 214 and 1 175 794, and (iv) vulcanisable organosiloxane compositions based on an organosiloxane polymer having in the molecule silicon-bonded alkoxy groups, and/or a mixture of an organosiloxane polymer having silanol groups with a silane having alkoxy groups or a partial hydrolysis product of said silane, for example ethyl polysilicate.

Compositions of this type are described in U.K. Patents 957 255, 962 061 and 841 825.

It will thus be understood by those skilled in the art that the curing agent (B) may be a silane or siloxane crosslinking agent, a catalyst such as an organo metal compound, for example stannous octoate, dibutyltin dilaurate or a titanium chelate, or the curing agent may comprise both of these. The proportion of curing agent (B) employed in the compositions will depend on the type of curing reaction desired. For example when the curing agent is a metal compound catalyst it will generally be employed in catalytic quantities, that is from about 0.05 to 5 parts by weight based on 100 parts of (A). When a silane or siloxane crosslinking agent is employed it is normally incorporated into the composition in an amount of from about 0.2 to about 20 parts per 100 parts of (A).

Although the compositions of this invention may utilise any room temperature curing reaction the preferred compositions are those of the so-called 2 part type, for example those described under (iv) above which comprise a mixture of a polydiorganosiloxane having terminal silanol (-SioH) groups, an alkoxy silane or siloxane, for example methyltrimethoxysilane, ethylpolysilicate or n-propylpolysilicate and a metal salt of a carboxylic acid, for example stannous octoate, dibutyltin dilaurate or dioctyltin dilaurate. As is well known such compositions are normally prepared and stored as two packages, the packages being mixed at the point of use.

Component (C) is a particulate mica wherein at least 75 percent by weight of the particles have an average diameter of from 30 to 100 microns and an aspect ratio in the range from 25/1 to 100/1. For the purpose of this invention the aspect ratio of the particles is defined as the ratio of the average diameter to the average thickness of the particles. Mica of the type required for use according to this invention may be obtained by wet or dry processes. Not more than 45 parts of mica should be present. It has been found that increasing the amount of mica above this level provides no further advantage and can result in a loss of the benefits obtained at lower loadings.

The compositions of this invention contain at least 5 parts of a reinforcing and/or an extending filler in addition to (C). Examples of such fillers include fume silica, precipitated silica, crushed quartz, aluminium oxide, calcium carbonates, which may be of the ground or precipitated types, microballoons and clays. The fillers, particularly those such as the reinforcing silicas and calcium carbonate may be treated, for example by coating with organosilicon compounds or calcium stearate. It is preferred that at least a part of the filler (D) is calcium carbonate. At least 5 parts and up to about 100 parts of filler (D) may be present depending on the physical or other properties desired in the cured elastomer.

In addition to ingredients (A) to (D) the curable compositions may optionally contain additives for modifying the elastomer properties. For example there may be incorporated into the compositions plasticisers such as triorganosilyl endstopped polydimethylsiloxanes, pigments such as titanium dioxide, carbon black and iron oxide, additives, for example aminoalkyl- and epoxyalkyl- silanes for improving the adhesion of the cured elastomer to glass, metal or other substrates and low molecular weight polydiorganosiloxanes as in situ filler treatments or for modifying the elastomeric modulus. Preparation of the compositions can be effected by known mixing techniques. As hereinbefore stated they may be formulated into the single package or multiple package configurations depending on type.

The compositions of this invention cure at ambient, or slightly elevated, temperatures to elastomers having permeability to argon and other gases which is significantly reduced in comparison with elastomers not containing the specific mica filler (D). In addition, the ability to achieve such a reduction at low loadings of mica enables the retention of acceptable physical properties in the elastomer. Such benefits render the compositions particularly adapted for use as primary or secondary sealants in multi-pane insulating glass units.

The following Examples, in which the parts and percentages are expressed by weight, illustrate the invention. In the Examples the membrane permeability is expressed in cm cm cm 2 sec. (cm Hg) -1 x 10 units Example 1 Four base compositions were prepared by mixing together * Polydimethylsiloxane having a viscosity of 12,000 mPa.s at 250C 100 parts Treated CaCO3 filler x ** Mica y Hydroxyl-terminated polydimethyls iloxane having a M.Wt of approximately 900 3 parts * A mixture of polydimethylsiloxanes having on average more than one but less than two terminal silicon-bonded hydroxyl groups per molecule.

** Wet ground, 32 micron particle size, 30/1 aspect ratio.

The filler contents x and y were varied as follows: x (parts) V (parts) Base 1 80 20 Base 2 70 30 Base 3 55 45 Control 100 0 Each of the bases (100 parts) was mixed with a catalyst composition (6.5 parts) consisting of n-propylorthosilicate (2.4 parts) and dibutyltin dilaurate (0.12 part) dispersed in a liquid polydimethylsiloxane (4.0 parts). The catalysed compositions were poured into a mould formed by two polyethylene sheets separated by a spacer having a thickness of 0.5mm. The compositions were allowed to cure for 7 days at laboratory ambient temperature (about 200C) and the resulting siloxane elastomer membranes removed from the moulds.

The permeabilities of the membranes to argon were measured employing a Brugger GDP permeability tester. The physical properties of the cured catalysed bases were measured on samples separately prepared for that purpose.

The results obtained were as follows: Tensile Elongation Permeability Strength(MPa) at break(%0 Base 1 99 1.4 75 Base 2 75 1.5 67 Base 3 60 1.3 57 Control 320 1.8 170 Example 2 The procedure of Example 1 was repeated except that the mica component was replaced with the same quantities of a wet ground mica having a particle size of 100 micron and an aspect ratio of 55/1.The bases were designated Bases 4, 5 and 6 respectively with increasing mica content, and the results obtained were as follows: Tensile Elongation Permeability Strength(MPa) at break(%) Base 4 108 1.5 95 Base 5 79 1.3 70 Base 6 64 1.5 75 Example 3 When the procedure of Example 1 was repeated employing a wet ground mica having a particle size of 70 micron and an aspect ratio of 100/1 the bases were designated respectively Bases 7, 8 and 9 and the following test results were obtained:: Tensile Elongation Permeability Strenath(MPa) at break(%) Base 7 90 1.3 64 Base 8 72 1.9 77 Base 9 59 2.1 66 Example 4 The procedure of Example 3 was twice repeated except that the polydimethylsiloxane component of the base was replaced by a polyphenylmethylsiloxane having terminal silanol groups and a viscosity of 12,000 mPa.s at 250C. In one experiment the polyphenylmethylsiloxane was prepared by the copolymerisation of low molecular weight polydimethylsiloxanes and polyphenylmethylsiloxanes in a ratio such that the ratio of total methyl groups to phenyl groups was 3/1. In the second experiment the polyphenylmethylsiloxane had a ratio of methyl groups to phenyl groups of 3/7.

Values for x and y were 34.5 and 14.75 respectively.

The cured membranes were tested for permeability to argon. A value of 23 was obtained in the case of the 3/1 copolymer and 12 for the 3/7 copolymer.

Example 5 Compositions according to the invention prepared as described in Examples 1 to 4 herein were employed to manufacture multi-pane insulating glass units. When tested, each of the units was found to comply with DIN 1286, part 2, which sets a maximum of 1% gas leakage rate per annum.

Claims (6)

1. A room temperature vulcanisable composition comprising by weight (A) 100 parts of a curable polydiorganosiloxane having a viscosity in the range from 150 to 100,000 mPa.s at 250C and wherein the organic substituents attached to silicon are selected from alkyl groups having from 1 to 10 carbon atoms, aryl, alkaryl and aralkyl groups having from 6 to 8 carbon atoms and alkenyl groups having from 2 to 8 carbon atoms, at least 30% of the said substituents being methyl groups, (B) a curing agent for polydiorganosiloxane (A), (C) from 5 to 45 parts of particulate mica wherein at least 75 percent by weight of the particles have an average diameter of from 30 to 100 microns and an aspect ratio in the range from 25/1 to 100/1, and (D) at least 5 parts of a reinforcing or extending filler.

2. A composition as claimed in Claim 1 wherein the curing agent (B) comprises a silane and/or siloxane having siliconbonded alkoxy groups and a metal salt of a carboxylic acid.

3. A composition as claimed in Claim 1 or Claim 2 wherein up to 75 percent of the organic substituents in polydiorganosiloxane (A) are silicon-bonded phenyl groups.

4. A composition as claimed in any one of the preceding claims wherein the mica (C) is present in a proportion of from 10 to 30 parts by weight.

5. A composition as claimed in any one of the preceding claims wherein at least a part of filler (D) is calcium carbonate.

6. A sealed multi-pane insulating glass unit comprising at least two spaced glass panes and sealing means intended to prevent or reduce the passage of gases into or from the space defined between said glass panes, at least a part of said sealing means comprising the product obtained by curing the composition claimed in any one of the preceding claims.