MXPA97002230A - Silicone sealant compositions modified with oximosili - Google Patents

Abstract

A method for forming a seal between two or more non-porous substrates is described by adding an oxosilicon compound to a ready-made vulcanizable silicone sealant composition at room temperature, which comprises a polydiorganosiloxane with alkoxy ends, a crosslinking agent having methoxy or ethoxy bonded to silicon, a filler, a titanate catalyst and by-product of methanol or ethanol that are obtained during the manufacture of the silicone sealant composition, apply the sealant composition to at least two non-porous substrates to form a set of an uncured sealing composition which binds them together, subjecting the whole to conditions which would ordinarily form harmful bubbles if the oximosilicon compound were not present and completely cure the composition to form a set of at least two non-porous substrates adhered by the cured sealant composition that is essentially li of harmful bubbles. Such a method is valuable for forming joints, which are used in the intercom combustion engine industry.

Description

OXYMOSILITIZED SILICONE SEALANT COMPOSITIONS Description of the Invention This invention relates to a method for adhering a vulcanizable silicone sealant (or sealing compound) (RTV) at room temperature to substrates in a nested or confined configuration. The use of silicone sealing compounds (or sealants) to adhere substrates together in various configurations, such as in joint formation, has been widely applied in the automotive industry for internal combustion engines. Neutral silicone senator compounds (or sealants) for such purposes are highly desirable because they have little or no detrimental effects on the metal or plastic substrates against which they are cured. However, when such sealants (or sealants) are used, especially those which contain alkoxy groups bonded by silicon and titanate curing catalysts, bubbles are detrimentally formed in the sealer (or sealant) during the curing process. . In addition, this situation is exacerbated when the sealing composition (or sealing compound) is used in embedded or confined configurations and when the substrates are heated during the curing process, such as at temperatures greater than 40 ° C. The bubbles are unacceptable and increase the chances that the cured product will fail to perform its intended function, when compared to the salting compositions not cured under such conditions. The reason for the REF: 24379 formation of bubbles under such conditions has not been specifically determined, but it is believed that the by-products of alcohols formed during the preparation of the strapping composition accumulate in small cavities or receptacles within the mass and that during the curing process the alcohols are vaporized and trapped in the sealing composition that cures quickly to produce the bubbles. It is believed that there may be other explanations for the phenomenon of bubble formation and one does not wish to be limited to this specific theory. It is known from US Pat. No. 4,956,435 to prepare a composition comprising a polydiorganosiloxane blocked at the end by trialkoxysilethylene, a crosslinking agent of alkoxysilane, an oxime compound and titanium catalyst to produce a faster neutral curing composition compared to the prior art compositions without the oxime compound. However, this method does not treat or solve the problem of bubble formation. The sealing compound compositions or bubble sealing compositions therein, for example a joint formed in place (FIPG) can result in reduced physical properties that lead to failures such as leaks. This condition can lead to operational problems. The solution to this problem of bubble formation is the object of the present invention. It is an object of the invention to eliminate the problem of bubble formation in sealing compositions which are cured in confined configurations, especially where the substrates which confine a composition of the sealing compound are hot. This invention features a method for forming a seal between at least two non-porous substrates, comprising: (I) adding from 0.5 to 3 percent by weight based on the total weight of an RTV silicone sealant composition (temperature curable) environment), of an oximosilicon compound which is an oximosilane or a mixture of oxosilanes and which has a general formula RxSi (OX) and (OR1) z wherein R is methyl, ethyl, vinyl or phenyl, R1 is methyl or ethyl, OX is an alkylmethylketoxyme in which the alkyl group has 1 to 5 carbon atoms, x has an average value of 0 to 2 inclusive, and has an average value of 2 to 4 inclusive, z has an average value of 0 to 2 inclusive, the sum of x, y and z are 4 and the mixture of oximosilanes has at least 80% of the oximosilane molecules with 2 or more alkylmethylketoxim groups per molecule to a silicone salt composition Prepared RTV comprising a polydiorganosiloxane having end groups containing a silicon atom with at least two alkoxy groups bonded to silicon or alkoxyalkoxy groups, wherein the alkoxy is methoxy, ethoxy, propoxy or butoxy and the alkoxyalkoxy is ethoxymethoxy, methoxyethoxy, methoxymethoxy or ethoxyethoxy, a crosslinking agent having at least three alkoxy groups bonded to silicon per molecule, wherein the alkoxy is methoxy or ethoxy, a filler, a titanium catalyst to promote curing at room temperature of the sealant composition. silicone and by-product of methanol or ethanol formed during the preparation of the RTV silicone sealant composition (vulcanizable at room temperature); (II) applying the silicone sealant composition resulting from (I) to at least one non-porous substrate, to form a set of the uncured silicone sealant composition that adheres the non-porous substrate to at least one other non-porous substrate; (III) subjecting the assembly to conditions which form the detrimental bubbles if the oximosilicon compound is not present before curing of the silicone sealant composition; and (IV) completely curing the silicone sealant composition, thereby generating a set of at least two non-porous substrates adhered with a cured silicone sealant, which is essentially free of detrimental bubbles. The method of this invention comprises modifying an RTV silicone sealant composition (vulcanizable at room temperature) by mixing 0.5 to 3 weight percent inclusive, based on the total weight of the silicone sealant composition, of an oximosilicon compound. The resulting uncured product is then brought into contact with at least one non-porous substrate surface and an assembly is formed by adhering at least one other non-porous substrate with the uncured RTV silicone sealant composition. This forms a confined configuration, especially under conditions where the configuration is exposed to a temperature of at least 40 ° C, during the curing process. Next, the combination of the substrate and the sealant composition is exposed to curing conditions, such as atmospheric moisture, to thereby obtain a silicone sealant adhered to at least two substrates in a confined configuration. This method, which uses an oxysilicon compound, results in a configuration wherein at least two substrates are adhered by the silicone sealant having a reduced number of bubbles compared to an equivalent silicone sealant without the oximosilicon compound. . In addition to the reduction in the number of bubbles, the bubbles are generally smaller in size. For this invention, a "confined configuration" is one in which the silicone sealant composition during curing has at least one small surface exposed to a moisture-containing atmosphere. For example, a surface of a joint has an exposed edge which is small compared to the total joint and total sealing surfaces, which is exposed to air in contact with non-porous substrates. Because the compositions of this invention cure by exposure to moisture in the atmosphere, exposure to the atmosphere is necessary. The method of the present invention employs oximosilicon compounds in amounts of 0.5 to 3 weight percent inclusive, based on the total weight of the RTV silicone sealant composition (0.5-3% by weight of the oximosilicon compound and 97-99.5% in weight of a prepared RTV composition). Preferably, the amount of the oximosilicon compound added to the prepared RTV silicone sealant composition is 0.5 to 2 weight percent. These amounts of the oximosilicon compounds provide the required reduction in bubble formation and do not significantly change the curing properties, the curing properties of the silicone sealant or affect the adhesion between the cured silicone sealant (or sealant) and the substrates The oximosilicon compound can be added as mixtures with solvents. Some of the oximosilicon compounds are more easily handled when some organic solvents are present such as toluene or hexane. Preferably no solvents are used. The oximosilicon compounds useful in the method of the present invention are oximosilanes or mixtures of oximosilanes. These are those which contain at least two alkylmethyl keto groups per molecule and are selected from those defined by the general formula R? Si (OX) and (OR1) z (A) in which R is methyl, ethyl, vinyl, or phenyl; R1 is methyl or ethyl, x has an average value of 0 to 2 inclusive; and has an average value of 2 to 4 inclusive, z has an average value of 0 to 2 and the sum of x, y and z is 4. OX represents an alkylmethylcetoxim group and are those ketoxim groups in which the alkyl has from 1 to 5 carbon atoms, in which methyl, ethyl, propyl (n-propyl and isopropyl), butyl (n-butyl and isobutyl) and amyl are included. Examples of the oximosilanes of formula (A) are methyltri (ethylmethylketoxime) silane, methyltri (dimethylketoxy) silane, ethyltri (ethylmethylketoxime) silane, tetra (ethylmethylketoxime) silane, vinyltri (ethylmethyl ketoxime) silane, phenyltri (ethylmethylketoxy) silane, metildi ( ethylmethylketoxime) metoxysilane, methoxythri (ethylmethylcemethyl) silane, dimethoxydi (ethylmethylketoxime) silane, methyldi (ethylmethylketoxime) ethoxysilane, ethoxytrim (ethylmethylketoxide) silane, diethoxyidi (ethylmethylketoxide) silane, methyltrimethylpropylmethyl silane, and Htrl (but i I mtit - ketoxim) silane, vinyltri (amylmethylketoxime) silane, metildi (isopropylmethylketoxime) -methoxysilane and various mixtures of oximosilanes in which at least 80% of the silane molecules have at least two alkylmethyl keto groups per molecule. Preferred mixtures of oximosilanes are those in which x is 1, R is methyl, R 1 is methyl, and is less than 3, g is greater than 0.1 and the sum of x, y and z is 4. A preferred alkylmethylketoxim is ethylmethylketoxim. In mixtures of the oximosilanes, other silanes may be present as long as the combined mixture is within the general formula (A). Examples of such silanes are methyl (ethylmethylketoxime) dimethoxysilane, trimethoxy (ethylmethylketoxime) -silane, ethyl (ethylmethyl-ketoxime) dimethoxysilane, methyl (ethylmethylketoxime) diethoxysilane, triethoxy (ethylmethyl ketoxime) silane and ethyl (ethylmethylketoxime) diethoxysilane. The preferred oximosilicon compound is vinyltri (ethylmethylketoxy) silane. The oximosilicon compound is mixed with a prepared RTV silicone sealant composition, which comprises a polydiorganosiloxane having end groups containing a silicon atom having at least two silicon-linked alkoxy groups selected from the methoxy, ethoxy, propoxy groups and butoxy or alkoxyalkoxy selected from methoxymethoxy, ethoxymethoxy, methoxyethoxy and ethoxy ethoxy, a crosslinking agent having at least three alkoxy groups attached to silicon per molecule, wherein the alkoxy is methoxy or ethoxy; a filling; a titanium catalyst to promote the curing at room temperature of the silicon sealant composition; and by-product of methanol or ethanol formed during the preparation of the RTV silicone sealant composition. With the exception of the recognition that the methanol or ethanol byproduct is present, these RTV silicone sealant compositions are well known in the art and are commonly illustrated by US Pat. Nos. 3,151,099; 3,161,614; 3,175,993; 3,334,067; 4,871,827; 4,898,910 and 4,956,435. The amount of the methanol or ethanol by-product is expected to be less than 0.5 percent by weight of the total weight of the prepared RTV silicone sealant composition, preferably less than 0.2 percent by weight. If the amount of methanol or ethanol is greater than 0.5 weight percent, the amount of the oximosilicon compound required to have a substantial effect on the reduction of bubble formation would cause the properties, either of the sealing composition or the properties of the Sealant or cured sealant, are adversely affected. Accordingly, it is undesirable to use the method of the present invention for RTV silicone sealant compositions which contain more than 0.5 weight percent methanol and ethanol byproducts. The polydiorganosiloxanes of the RTV silicone sealant compositions prepared are those which have end groups containing silicon atoms with at least two alkoxy groups or groups alkoxyalkoxy by final group. These polydiorganosiloxanes include those in which the bonds between the silicon atoms of the polymer chain are oxygen atoms and those polymers in which the bonds of the silicon atoms are oxygen atoms and the end segments contain at least one bond of a divalent hydrocarbon radical between the silicon atoms of the polymer chain. These polydiorganosiloxanes are known in the art as described above. The polydiorganosiloxanes are also mixtures of polymers wherein some of the polydiorganosiloxanes have a final group as a "triorganosiloxy" unit, such as trimethylsiloxy or vinyldimethylsiloxy and the other final group is an alkoxy or alkoxyalkoxy unit bonded to silicon. In these blends, less than 50 percent of the total final groups are triorganosiloxy for polydiorganosiloxanes with divalent oxygen atoms that bond to the silicon atoms of the polymer chain. Preferably, less than 20 percent of the final groups are triorganosiloxy. In those polydiorganosiloxane mixtures, which have end segments, wherein the divalent hydrocarbon radicals are bonded to some of the silicon atoms of the polymer chain, there are from 3 to 40 percent of the final groups as triorganosiloxy units which are preferably vinyl dimethylsiloxy. Preferably, the triorganosiloxy end groups or ends are present in less than 20 percent of the total end groups. Each end or end group, which bears alkoxy groups or alkoxyalkoxy groups linked to the silicon have, on average, at least two alkoxy groups or two alkoxyalkoxy groups per end group silicon atom. The alkoxy groups are methoxy, ethoxy, propoxy or butoxy and the alkoxyalkoxy groups are methoxymethoxy, ethoxymethoxy, ethoxyethoxy and methoxyethoxy. Polydiorganosiloxanes having end groups containing silicon atoms with at least two alkoxy groups bonded to silicon or alkoxyalkoxy groups per end group of silicon and wherein the silicon atoms of the polymer chain are linked by oxygen atoms, are exemplified by the descriptions of the US patents 3,151, 099, 3, 161, 614 and 3,175,993 and are illustrated by the formula R < 3-n) R (3-n) (R1O) "SiO (R22S¡O) pSi.OR1)" (B) and by mixtures of polydiorganosiloxanes of formula (B) or polydiorganosiloxanes of the formula R (3 *) (R10) nSIO (R22SiO) pSiR 3 (C) In the above formulas R1 is alkyl of 1 to 5 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl and amyl or a alkoxyalkoxy of 2 to 4 carbon atoms such as methoxymethoxy, ethoxymethoxy, methoxyethoxy and? toxi ethoxy, R2 is methyl, ethyl, vinyl or phenyl; n is 2 or 3, β has an average value of at least 200. As illustrated, the alkoxy-containing end groups are those which are preferably methoxy, ethoxy or combinations thereof. The preferred polydiorganosiloxanes are polydimethylsiloxanes and especially those with viscosities at 25 ° C from 5 to 150 Pa.s. Polydiorganosiloxanes with end segments containing divalent hydrocarbon radical bonds between some of the silicon atoms of the polymer chain are also described in US Patents 3,175,993, 4,871, 827 and 4,898,910. The polydiorganosiloxanes are illustrated by the formula (R1O) nSi-Z ~ (SIO) pSI-Z-Si (OR1) "R2 R2 wherein R1, R2, n and ß are as described above, R3 is methyl, ethyl or phenyl and Z is a divalent hydrocarbon radical or a combination of divalent hydrocarbon radicals and oxygen siloxane radicals. Divalent hydrocarbon radicals are those having 2 to 18 inclusive carbon atoms and are illustrated by ethylene, propylene, butylene, pentylene and hexylene, preferably ethylene. Where Z is a combination of divalent hydrocarbon radicals and oxygen siloxane radicals, the polydiorganosiloxanes with end segments containing divalent hydrocarbon bonds and divalent oxygen atom bonds between the silicon atoms of the polymer chain have end segments containing like Z, the formula R3 R3 I I wherein c is from 1 to 6, R3 is as defined above and G is a divalent hydrocarbon radical free of aliphatic unsaturation of 2 to 18 carbon atoms. These polydiorganosiloxanes are prepared by reacting a polydiorganosiloxane blocked at the end by hydrogen with a silane having an alkenyl radical in the presence of a hydroxylation catalyst such as a platinum compound or complex. If a silane of the following formula is used, a polydiorganosiloxane will be prepared as described in US Pat. No. 3,175,993.

R P-n) H2C-CH- (C.H2.) FSi (OR1) n where e is 1 to 16, f is 0 or 1 and R1, R2, R3 and n are as defined above. If an end crown element, such as one of the following formula, is used, those polydiorganisiloxanes described by U.S. Patents 4,871,827 and 4,898,910 are produced.

R3 R3 R3 (3_n, I I I HSiOSiCH2CH2Si (OR1) p R3 R3 wherein R1, R2 and n are as defined above. Preferred polydiorganosiloxanes of this class are those described hereinabove, wherein the divalent hydrocarbon radical is ethylene and has a viscosity at 25 ° C of 5 to 150 Pa.s. The crosslinking agents of the RTV silicone sealant compositions are alkoxysilanes which have at least three alkoxy groups per molecule, wherein the alkoxy groups are either methoxy or ethoxy. These alkoxysilanes preferably contain three or four alkoxy groups per molecule and are illustrated by methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, tetraethoxysilane, mixtures of these alkoxysilanes and their partial hydrolysates. Preferably, the alkoxysilanes are methyltrimethoxysilane or mixtures, wherein the methyltrimethoxysilane comprises most of the alkoxysilanes in the mixture. The amount of the alkoxysilane crosslinking agent is preferably 1 to 10 percent by weight based on the total weight of the RTV silicone sealant composition, more preferably from 3 to 8 weight percent. As the amount of the crosslinking alkoxysilane increases, the potential for increasing the amount of methanol or ethanol byproduct is also increased and therefore the amount of bubble formation can be considered as directly proportional to the concentration of the crosslinking agent. The storage stability of the oximosilicon compound of the present invention, which contains a prepared RTV silicone sealant composition is also directly proportional to the concentration of the crosslinking agent.

The RTV silicone sealant compositions, to which the oximosilicon compound of the present invention is added, also comprise a filler that is selected from those known to be useful in RTV silicone sealants. Those fillers include ground, precipitated and colloidal calcium carbonate; calcium carbonates which are treated with stearate; crushed or ground quartz; alumina; aluminum hydroxide; titanium dioxide; diatomaceous earth; reinforcing silicas such as sulfurized silica, precipitated silica and hydrophobic reinforcing silica; iron oxide; carbon black and graphite. The amount of filler is preferably 5 to 50 percent by weight based on the total weight of the RTV silicone sealant composition. The titanium catalysts for promoting the curing of the RTV silicone sealant compositions prepared of this invention are those illustrated in US Patents 3,151,099, 3,161,614 and 3,175,993. This catalyst commonly consists of chelated tetraalkoxytite-inorganic or titanium compounds. Examples of the preferred titanium catalysts include tetraethyl titanate, tetraisopropyl titanate, tetra-n-propyl titanate, tetrabutyl titanate, bis-acetylacetyldiisopropyl titanate, titanium 2,5-diisopropyl-bis-ethylacetoacetate and 1,3-dioxypropane-titanium bis. (et? lacetoacetato). U.S. Patent 4,722,967 teaches chelated titanates in more detail. The amount of the titanium catalyst is a catalytic amount for curing the prepared silicone sealant composition of RTV and is preferably from 0.1 to 5 weight percent, based on the total weight of the prepared RTV silicone sealant composition.

Other ingredients which are conventionally used in RTV silicone sealant compositions, such as adhesion promoters, fungicides, colorants, pigments, plasticizers and silane chain extending agents, such as dialkyldialkoxysianes, are added as long as they do not interfere to enhance the properties of bubble production, to deteriorate the curing properties, to erode the cured physical properties or to reduce the bond between the cured sealant and the substrates. The oximosilicon compound is added to a previously prepared RTV silicone sealant composition, to a freshly prepared one, one which has been prepared and stored and one which is obtained commercially. The oximosilicon compound of the present invention is preferably mixed with the prepared RTV silicone sealant composition, after it has been deaerated or devolatilized, because this allows smaller amounts of the oximosilicon compound to be used, due to the reduction of some of the methanol or ethanol byproduct. The amount of the oximosilicon compound required to effectively reduce or eliminate the formation of bubbles in the cured RTV silicone sealant composition is directly related to the amount of methanol and ethanol by-product in the prepared RTV silicone sealant composition. Amounts of the oximosilicon compound greater than 3 weight percent based on the total weight of the RTV silicone sealant composition tend to create undesirable physical properties in the cured sealant composition, such as increased modulus, higher percent shrinkage after curing and decreased elongation. If the amount of methanol and ethanol by-product in the prepared RTV silicone sealant composition is greater than 0.5 weight percent, based on the total weight of the composition, a de-alkanoylation step is preferably employed. This may be present in that mixing is carried out by reduced pressure (partial vacuum) and may also include heating to effectively remove the volatile components. This mixing procedure is done under conditions which exclude the exposure of the materials to atmospheric moisture, especially if the resulting modified RTV silicone sealant composition is to be packaged and stored either for packaging or subsequent use. When the preparation of the prepared RTV silicone sealant composition involves the separation of volatile components, such as a de-alkalization step, the cross-linking agents with low boiling points, can also be lost without proper precaution. Accordingly, stability during storage should be inspected to ensure that the resulting compositions, when modified with the oximosilicon compound of the present invention, are stable during storage and do not cure in storage containers. The RTV silicon sealant composition modified by the oximosilicon compound of the present invention is prepared for the purpose of adhering at least two surfaces of non-porous substrates in a confined configuration, wherein the substrates include metals, such as aluminum, steel , iron and metal alloys or materials based on organic polymer. Such metals, alloys and polymeric materials are frequently found in internal combustion engines, associated engine components and / or engine compartments. The configurations can be together, which seal various gases or liquids that are used in and around the motors to isolate them from each other, to keep them inside their respective chambers or to eliminate them from the outside environment. In a typical application, the RTV silicone sealant composition modified by the oximosilicon compound is contacted with at least one surface of a non-porous substrate by conventional means, such as extrusion, coating, injection, cutting or rolling. The surfaces of at least two of the substrates are then combined to form a confined configuration where the substrates will adhere to each other via a bond formed by means of the silicone sealant composition. If the confined configuration is in or around an internal combustion engine and consists of a joint that adheres two parts where the hot gases such as those formed by the ignition fuel, the RTV silicone sealant composition modified by the compound of The silicon of the present invention is applied to the substrates, the configuration is formed and as long as the composition is cured, the engine can be turned on surprisingly for leak testing. In such situations, the temperature increases as the engine is put into operation and the cured RTV silicone sealant composition is exposed to temperatures of at least 40 ° C. At temperatures greater than 40 ° C, the methanol or ethanol by-product will vaporize rapidly and will bubble up unless the oximosilicon compound of the present invention is present in the sealing composition as a modifier. It is believed that the methanol and ethanol byproduct tends to collect in micelles and therefore can easily form bubbles when the methanol or ethanol vaporizes. The methanol or ethanol generated during the curing process is dispersed throughout the volume of the curing composition and therefore less likely to form bubbles. The higher the temperature at which the curing sealant composition is exposed, the greater the amount of bubbles formed during the curing process, unless the oxysilicon compound is first added to the sealant composition. Also, the greater the amount of methanol and ethanol by-product present in the sealant composition, the greater the amount of bubble formation that will be observed, unless the oxysilicon compound of the present invention is added to the composition. Bubble formation can occur and occurs even under environmental conditions when positioned in a confined configuration. Of course, this is more likely to happen when the curing silicone sealing composition RTV is exposed to higher temperatures. Even under environmental curing conditions, the oximosilicon compound of the present invention reduces bubble formation when added to the silicone sealant composition. After the RTV silicone sealant composition modified by the oximosilicon compound is applied to the substrates, it is necessary to expose it to atmospheric humidity to cause it to cure and adhere the substrates together. In the confined configuration, the exposed edge of the RTV silicone sealant composition is small compared to the total volume of the curing composition. Accordingly, vaporizing methanol or ethanol have difficult escape into the atmosphere. During this curing process, the number and size of bubbles in the cured silicone sealant is minimized or eliminated in comparison with an equivalent RTV silicone sealant without the oximosilicon compound of the present invention. It is observed that undesirable bubbles form within the sealant layer, as well as at the interface between the substrates bordering the cured silicone sealant. The modified RTV silicone sealant compositions of the present invention have an increased work time compared to those sealant compositions which do not contain the oximosilicon compound. Another advantage of these compositions is that the modulus of the cured product is not increased by the use of the oximosilicon compound. The resulting silicone sealant, when used in equipment with internal combustion engine, exhibits preferably flow resistance and burst resistance, which involves fluids, lubricants and cooling fluids. The definition of "burst strength" is the resistance of a leak-curing sealant composition when gas or liquid pressure is applied to one side of a gasket, in particular resistance to hot gas pressure. When a pressure leak test is conducted on a joint to determine if the joint will be effective, such a test is preferably delayed by 20 minutes to 24 hours to ensure sufficient time for the sealing composition to cure and take an amount enough of structure or strength before cooking to pass the leak test. A pressure leak test is preferably brief in duration, usually less than 15 minutes and more preferably less than 5 minutes. The pressure leak test is carried out at 82 ° C. The pressure leak test determines whether bubble formation is a problem. Other temperatures could be used, but it is found that a temperature of 82 ° C represents an excellent condition for distinguishing between acceptably prepared RTV silicone sealant conditions, such as those which are modified with the oximosilicon compounds of the present invention and those which are not acceptable. Under such conditions of time and temperature, the formation of harmful bubbles would be negligible, if the prepared silicone salt composition RTV was not modified with the oximosilicon compound of the present invention. The thickness of the cord of an RTV silicone sealing composition is preferably between 1 and 20 mm. Such thicknesses are useful in FIPG applications Cuntas formed in place) for confined configurations, especially in the motor vehicle or in the automotive industry. This invention is further illustrated? by the following example, which is presented for the purpose of demonstrating the present invention which is suitably summarized in the claims. In the example "part" or "parts" refer to part or parts by weight and all viscosities were measured at 25 ° C.

EXAMPLE 1 RTV silicone sealant compositions prepared by mixing in a Ross ™ mixer (a double planetary can mixer) were obtained, 100 parts of a polydiorganosiloxane mixture having a viscosity of 65 Pa.s, made by the process described in U.S. Patent 4,898,910 and having polydiorganosiloxanes of the formulas Me Me I I I I Saw (Me) 2SiO (Me2SiO) qSiC2H4S¡OSiC2H4Si (OMß) 3 Me Me Me Me Me Me Me Me (MeO) 3SiC2H4SiOSiC2H4SiO (Me2SiO) qSiC2H4SiOSiC2H4Si (OMe) 3 Me Me Me Me Me Me where Me is methyl, Vi is vinyl and g has an average value such that the viscosity is 65 Pa.s and 20 percent of the end groups are vinyl dimethylsiloxy units, with 11.1 parts of a crosslinking agent mixture of 70. percent by weight of methyltrimethoxysilane, 16 percent by weight of bis- (ethylacetoacetate) of diisopropoxytitanium, 5 percent by weight of tetrabutylitanate, 3.3 percent by weight of 3-mercaptopropyltrimethoxysilane, 2 percent by weight of beta-aminoethyl-gamma -aminopropyltrimethoxysilane, 1.4 weight percent methanol and 2.3 weight percent impurities. The resulting mixture is stirred for 5 minutes while a vacuum is removed, then 9.4 parts of sulfurized silica filler is added and mixed for two minutes without applying vacuum before adding 60.3 parts of precipitated calcium carbonate which had a surface treated with stearate, 4 parts of a ground calcium carbonate and 0.09 parts of a black pigment. After these fillers are added, the resulting mixture is mixed for 15 minutes while a vacuum is drawn to obtain the prepared RTV silicone sealant composition. Then, three different oximosilicon compounds are mixed with this silicone sealant composition by using a Semkit (R) mixer. The oximosilicon compounds were vinyltrim (ethylmethylketoxime) silane (VTO), methyltrim (ethylmethylketoxime) silane (MTO) and a mixture of oximosilane (OX-MIX) of 47 weight percent of ethoxytri (ethylmethylketoxime) silane, 36 weight percent of diethoxydi (ethylmethylketoxy) silane, 7 weight percent of triethoxy- (ethylmethylketoxy) silane, 8 weight percent of tetra (ethylmethylketoxy) silane and 2 weight percent of impurities. Each oximosilicon compound was added in concentrations to provide 0.5% by weight, 1.0% by weight, and 1.5% by weight to make compositions for evaluation of bubble formation, wherein the combination of the sealant composition and the oximosilicon compound was of 100% by weight. Immediately prior to the addition of the oximosilicon compound, the prepared RTV silicone sealant composition contained 0.239 weight percent methanol, based on the total weight of the sealant composition. This preparation was designated Process A in Table 1. Additional RTV silicone sealant compositions were prepared as described above, except that mixing times and vacuum times were different. After the silica filler was added to the mixture of polydiorganosiloxane and the crosslinking agent, the resulting mixture was mixed for 3 minutes, then the mixture was mixed for an additional 20 minutes while vacuum was applied. This preparation set was designated Process B. Prior to the addition of the oximosilicon compound, the prepared RTV silicone sealant composition contained 0.125 weight percent methanol based on the total weight of the composition. A control or reference RTV silicone sealant composition, without the addition of the oximosilicon compound of the present invention and each of those process A and B sealant compositions with the added oximosilicon compound, were tested for Bubble formation A bead of the RTV silicone sealant composition was placed on the surface of an acrylic panel with the use of wedges to obtain a thickness of 5 mm, when another acrylic panel was placed on the acrylic panel that carried the cord of the silicone sealant composition. Each acrylic panel was 7.62 cm by 7.62 cm. A heavy block of granite was placed on top of the acrylic panel of this assembly to distribute the force evenly. Each test panel, thus prepared, was exposed to elevated temperatures for one hour after curing began. This temperature was 82 ° C and was obtained by placing the test panels in a forced air oven. The test conditions were 5 minutes long. The acrylic panels were transparent, in such a way that the formation of bubbles could be observed visually through the panels without altering the RTV silicone sealing gasket. A 90 Watt incandescent lamp was used to observe the formation of bubbles through the acrylic panels. There were two types of observed bubble formation, a "surface bubble formation" which was the formation of pin-size holes in the surface between the curing silicone sealing composition RTV and the acrylic panel. The other type consisted of "internal voids" which was the formation of bubbles within the curing mass of the RTV silicone sealant composition. It was determined that the formation of bubbles which produced the internal voids was the most detrimental to the operation of a joint formed by an RTV silicone sealant composition. The formation of internal voids was classified from 0 to 10, where 0 was a cured sealing composition without bubble formation and 10 was a cured sealant composition with excess bubble formation. A rating of 0 was given to a test sample which had no obvious internal voids and for a given composition that had the highest specific gravity. A rating of 10 was given to a test sample which had sufficient internal void formation to reduce the specific gravity by more than 10% compared to an equivalent composition without any internal void formation. Since this formation of internal gaps with a rating of 0 to 10 was a relative evaluation, the values were subjective with respect to each other. The formation of surface bubbles was also evaluated by using a rating of 0 to 10, where 0 was essentially no bubble formation on the surface between the cured seal and the panel and exhibited many bubbles at the interface. Because the formation of internal voids was considered more critical, the formation of bubbles on the surface was not defined further, but the subjective definition was continued. In addition to the bubble formation tests, the physical properties of each RTV sealing composition were evaluated after test pieces were prepared and allowed to cure for 8 days at ambient conditions. The properties measured were durometer on the Shore A scale, tensile strength at break, elongation at break and modulus at 100% elongation. Extrusion rate was determined on the uncured RTV silicone sealant composition by extruding it through a 0.3175 cm orifice with a 620.5 KPa pressure and measuring the extruded amount in grams per minute (g / minute) . The measurements used to evaluate the curing characteristics were surface time (SOT), adhesion free time (TFT) and deep section curing (DSC). The hardness was determined according to the ASTM D 2240 standard, Scale A. The tensile strength at break, the elongation at break and the module at 100% were determined by the ASTM D 412 standard. The SOT was the time in minutes measured between the time when a bead of the sealing composition was extruded to an atmosphere containing moisture and time to which the light touch of a finger on the surface of the cord did not cause the sealing composition to adhere to the finger when it was removed. The TFT was the time in minutes between the time when a bead of the sealing composition was extruded and the time when a square of polyethylene film was placed on the bead of the sealing composition and then separated without deteriorating the surface of the bead. The DSC was determined by placing the RTV sealant composition in a small container (container of the same size used for each determination); and the surface was cut to separate the excess composition. After 24 hours, the cured part of the sealant composition was removed, rinsed and its thickness was measured and reported in Table 2, in millimeters. The DSC was an indication of the strength before cooking of each composition, where the thicker the DSC, the greater the resistance to cooking. The results of these bubble formation and physical properties tests are found in Tables 1 and 2, respectively.

Table 1 Bubble formation test Test carried out after preparation Compound value of burbí value of voids oximosilicio process on the internal surface NONE TO 1 4 NONE B 2 5 0. 5% MTO TO 0 0 0. 5% MTO B 1 0 1.0% MTO A 3 0 1.0% MTO B 3 0 1.5% MTO A 1 0 1.5% MTO B 0 0 0.5% VTO A 1 0 0.5% VTO B 10 1 1.0% VTO A 1 1 1.0% VTO B 0 0 1.5% VTO A 1 2 1.5% VTO B 1 1 0.5% OX-MIX A 0 1 1.0% OX-MIX A 0 4 1.0% OX-MIX B 1 0 1.5% OX-MIX A 1 1 Table 1 (continued) Compound bubble value void value oximosilicon internal surface process 1.5% OX-MIX B 2 0 TABLE 2 RESISTANCE TO THE TRAC-% OF ALARM COMPROMISE TO THE GATE MODULE AT SPEED 5 OF TRO ROMPIMIEN- TO THE ROMPÍ- MODULO TO THE SOT TFT OF EXTRU- 'DSC OXIMISILICIO PROCESS SHORE TO TO KPa MIENT 100% Kpa minutes minutes SION g / min mm ro NONE A 45 2275 214 1420 11 28 41.9 4.27 vo NONE B 48 2179 200 1296 17 20 36.1 5.84 10 0.5% MTO A 50 2392 216 1400 6 30 61.9 3.68 0. 5% MTO B 45 2530 228 1386 8 17 52.6 4.85 1. 0% MTO A 47 2379 206 1448 8 19 53 3.84 1. 0% MTO B 43 2737 246 1400 7 15 72.5 4.32 1.5% MTO A 44 2013 151 1600 9 22 61.2 3.76 15 1.5% MTO B 50 2441 229 1351 10 28 65.3 3.76 0.5% VTO A 47 1979 216 1089 13 40 72 3.35 RESISTANCE TO THE TRAC-% OF ALAR- COMPOSITE DURATION TO THE GATE MODULE TO THE SPEED OF TRO ROMPIMIEN- TO THE ROMPÍ- MODULO TO THE SOT TFT OF EXTRU- DSC 5 OXIMISILICIO PROCESS SHORE TO TO KPa MIENT 100% Kpa minutes minutes SION a / min . mm 1. 0% VTO A 45 2096 228 1117 15 27 82.7 3.71 1.0% VTO B 49 2241 196 1386 9 26 61.7 422 G_ > O 1.5% VTO A 46 2455 240 1317 15 34 95.7 3.48 10 1.5% VTO B 51 2310 202 1413 9 25 64.8 4.06 0.5% Ox-MIX A 41 1979 214 1379 17 44 82.7 3.84 0.5% Ox-MIX B 49 2793 229 1496 11 38 48.6 4.83 1.0% Ox-MIX A 43 1848 176 1200 16 44 83.8 3.73 1.0% Ox-MIX B 48 2799 229 1503 11 42 36.9 4.52 15 1.5% Ox-MIX A 44 2144 201 1255 19 40 80.8 3.66 1.5% Ox -MIX B 48 2992 259 1510 11 41 35.6 4.42 Table 1 shows, when comparing those without oximosilicon compound to those containing oximosilicon compound, that surface gas formation and internal voids were reduced by the addition of the oximosilicon compound of the present invention. An exception to this was for the composition containing 0.5% VTO, where the gas formation on the surface actually increased, but the formation of internal voids decreased. The sealing composition with the best results was that in which 1.0% VTO was added to the silicone sealant composition to Process B. The physical properties in Table 2 did not vary severely with respect to those of the controls, which proved It is a surprising manner that the addition of the oximosilicon compound of the present invention to reduce the formation of bubbles in the cured product is an acceptable process. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following

Claims (6)

1. Claims 1. A method for forming a seal between at least two non-porous substrates, characterized in that it comprises: (i) adding from 0.5 to 3, inclusive, percent by weight based on the total weight of a vulcanizable silicone sealant composition. ambient temperature of an oximosilicon compound, which is an oximosilane or a mixture of oxosilanes and which has a general formula RxSi (OX) and (OR1) z in which R is methyl, ethyl, vinyl or phenyl, R1 is methyl or ethyl, OX is an alkylmethylketoxim, in which the alkyl group, has 1 to 5 carbon atoms inclusive, x has an average value of 0 to 2 inclusive, and has an average value of 2 to 4 inclusive, z has a average value from 0 to 2 inclusive, the sum of x, y and z is 4 and the mixture of oximosilanes has at least 80% of the oximosilane molecules with 2 or more alkylmethylketoxim groups per molecule, to the sealant composition comprising a polydiorganosiloxane which has extreme groups that co they contain a silicon atom with at least two alkoxy groups bonded to silicon or alkoxyalkoxy groups in which the alkoxy is methoxy, ethoxy, propoxy or butoxy and the alkoxyalkoxy is methoxymethoxy, methoxyethoxy, ethoxymethoxy or ethoxyethoxy; a crosslinking agent having at least three alkoxy groups attached to the silicon per molecule, wherein the alkoxy is methoxy or ethoxy, a filler; a titanium catalyst for promoting the curing at room temperature of the silicone sealant composition and byproduct of methanol or ethanol formed during the preparation of the sealant composition. (ii) applying the silicone sealant composition resulting from (i) to at least one non-porous substrate, forming a set of the uncured silicone sealant composition that adheres non-porous substrates to at least one other non-porous substrate; (iii) subjecting the assembly to conditions which form the detrimental bubbles if the oximosilicon compound is not present prior to curing the silicone sealant composition; and (iv) completely curing the silicone sealant composition, thereby generating a set of at least two non-porous substrates adhered with a cured silicone sealant which is essentially free of detrimental bubbles.
2. 2. The method according to claim 1, characterized in that the sealing composition has, as the polydiorganosiloxane, a polydiorganosiloxane of the formula R (3 \) R R R (3-n) l i l i (R1O) nSi-Z- (SiO) pSi-Z-Si (OR1) " R2 R2 wherein R 1 is methyl or ethyl, R is methyl, ethyl, vinyl, or phenyl; R is methyl, ethyl or phenyl, n is 2 or 3, p. is at least 200, and Z is a free radical of divalent hydrocarbon of aliphatic unsaturation of 2 to 18 carbon atoms or a divalent group of the formula R3 R3 -G-. { SiO) c-Si-G- R3 R3 wherein R3 is as described above, G is a free radical of divalent hydrocarbon of aliphatic unsaturation of 2 to 18 carbon atoms and c is 1 to 6 inclusive.
3. 3. The method according to claim 1, characterized in that the oxymosilicon compound is vinyltri (ethylmethylketoxy) silane or methyltri (ethylmethyl-ketoximo) silane.
4. 4. The method according to claim 1, characterized in that the oximosilicon compound consists of a mixture of oximosilanes wherein x is 1, R is methyl, R1 is methyl and y is less than 3 and z is greater than 0.1.
5. 5. The method according to claim 1, characterized in that the sealing composition is prepared by carrying out the mixing operations under reduced pressure, while the volatile components are separated before the addition of the oximosilicon compound.
6. 6. The method according to claim 1, characterized in that the non-porous substrates are parts of an internal combustion engine; The silicone sealant composition forms a joint assembly and the engine is turned on before the complete cure of the sealant composition and is put into operation for at least two minutes.