In US 4,506,058 there are disclosed certain moisture curable RTV silicone formulations which employ as an adhesion promoter a urea compound of the formula:

where R ¹ is a C ₍₁ .τ> monovalent hydrocarbon radical,- R ² is a C ₍ ,. ₄₎ alkyl radical, C _{ .. ₄₎ acyl radical or a radical of the formula -CH ₂ CH ₂ 0) _n R ⁴ , where n is 1 or 2 and R ⁴ is a C _{( )} alkyl radical. R ³ is a C ₍₁ . _1β) divalent hydrocarbon radical free of aliphatic unsaturation attached to a nitrogen atom of the urea nucleus through a non- aromatic carbon atom, Z is hydrogen or a C _{( )} alkyl radical and y equals 0 or 1. In US 4,847,396 there is disclosed a moisture curable RTV silicone formula employing a urea compound of the formula:

where R\ R ² and R ³ are similarly defined, R* and R ⁵ are H, hydrocarbyl or halohydrocarbyl, g and h are 0 or 1, and a+b+g = f+g+h = 3.

SUBSTITUTE SHEET

In US 3,671 ,562 there is described compound:

O

H ₂ N-C-NH(CH ₂ ) Si(OCH ₃ )3 (3)

and related mono urea compounds. Such compounds are disclosed as coupling agents for improving bonding of organic polymers to glass substrates. Use of these compounds in RTV silicone formulations or for bonding to metal substrates is not suggested by this reference.

Summary of the Invention

It has now been discovered that the urea compounds disclosed in US 3,675,562 may be employed as adhesion promoters in RTV silicone substrates giving superior metal bonding performance to the bis-silyl urea compounds of US 4,506,058 and 4,847,396, in similar formulations. Therefore, in one aspect there is provided a moisture curing RTV silicone formulation employing an adhesive promoting effective amount of a compound of the formula:

where R' is a one-to-seven carbon atom monovalent hydrocarbon group, R" is a monovalent hydrocarbon radical, optionally interrupted by one or more ether oxygen atoms, R'" is a divalent hydrocarbon radical and x is 0 or 1.

In a still further aspect there is provided a process for bonding or sealing metal substrates comprising applying a composition as just described, between the substrates, and then joining the substrates in the presence of moisture until bonded.

SUBSTITUTE SHEET

Detailed Description of the Invention

In accordance with the present invention there is provided a silicone composition which is storage stable in the substantial absence of moisture and which composition vulcanizes at room temperature on exposure to moisture comprising in admixture:

A) a reactive polyorganosiloxane consisting essentially of repeating units of the formula:

where R is a hydrocarbon or halohydrocarbon group, said reactive polyorganosiloxane having moisture curable end groups thereon,

B) a cure inducing effective amount of a condensation catalyst, and

C) an adhesion promoting effective amount of a compound of the formula:

where R' is a one-to-seven-carbon atom monovalent hydrocarbon group, R" is a monovalent hydrocarbon radical, optionally interrupted by one or more ether oxygen atoms, R'" is a divalent hydrocarbon radical and x is 0 or 1.

Generally polyorganosiloxane (A) can be any polyorganosiloxane consisting essentially of repeating units of formula (1) and which is terminated with radicals which will effect crosslinking upon exposure to moisture. Such polyorganosiloxanes are well known to those skilled in the art, but of particular interest in the present invention are polyorganosiloxanes wherein the silicone at each chain end is silanol terminated. Suitably the polyorganosiloxane (D) is a

SUBSTITUTE SHEET

silanol terminated polydimethylsiloxane which has a viscosity at 25° C of 2,000 cps - 250,000 cps, preferably about 4,000 cps to about 50,000 cps.

Effective amounts of condensation catalysts which can be used in the practice of the present invention to facilitate the cure of the room temperature vulcanizable compositions are, for example, from about 0.001 % to about 1 % based on the weight of polyorganosiloxane (A). Preferably the condensation catalyst is a tin compound such as dibutyltindilaurate, dibutyltindiacetate, dibutyltindimethoxide, stannous octoate, stannous oieat, stannous naphthenate and the like. Dimethyltinbis-neodecanoate is particularly preferred. Titanium compounds which can be used are, for example,

1 ,3-propanedioxytitanium bis(ethylacetoacetate); 1 ,3-pr opanedioxytitanium bis(acetylacetonate); diisopropoxytitanium bis(acetylacetonate); titanium naphthenate, tetrabutyltitanate and the like. In addition, beta-dicarbonyltitanium compounds as shown in Weyenberg, U.S. Patent No. 3,334,067, can be used as condensation catalysts in the present invention. Additional catalysts which are well known in the art are provided in a rather exhaustive list in US 4,395,526, White et al. Of course, there may be utilized mixtures of suitable condensation catalysts.

The present invention is based on the surprising discovery that a self- bonding room temperature vulcanizable composition is obtained when an effective amount of a mono-silyl urea compound of formula (5) is also included in the RTV composition. Generally an effective amount of adhesion promoter of formula (5) will range from about 0.05 to about 10 parts by weight per 100 parts by weight of polyorganosiloxane (A).

As indicated Jhereinabove, it is necessary that the bis-silyl urea adhesion promoter of the present invention have two or three OR" radicals bonded to each silicon atom. Also it is preferable that R" be a methyl or ethyl group; e.g. each silicon atom preferably has three methoxy or ethoxy radicals bonded thereto. However, R" can generally be any alkyl radical of 1 to 4 carbon atoms such as formyl, acetyl or propionyl; or any -alkoxyethyl radical such as β-methoxyethyl, β- ethoxyethyl or β-butoxyethyl; or any radical of the formula -CH ₂ CH ₂ 0) _n R"" where π is 1 or 2 and R"" is a C ₍₁ ^ alkyl radical such as -CH ₂ CH ₂ 0) ₂ CH ₃ or -CH ₂ CH ₂ O) ₂ C ₄ H _e .

R', if present, can be any monovalent hydrocarbon radical of up to 7 carbon atoms such as methyl, ethyl, hexyl, vinyl, allyl, hexenyl, phenyl, cyclohexyl, cyclopentyl and cyclopentenyl.

R'" can be any divalent hydrocarbon radical most suitably a C, - C _β alkylene group.

There is also incorporated into the RTV composition of the invention a crosslinking silane compound. Various crosslinkers are known, all characterized by the presence of three or four hydrolyzable groups attached to the silane silicon atom. Most common are the trialkoxy, triamino, triacetoxy or trioxime substituted silanes. In the compositions of the invention trioxime silanes such as methyltris-methylethylketoximosilane or vinyltris-methylethylketoximosilane are preferred, suitably at levels of about 3 to about 9, preferably about 4 to about 6, ketoxime groups per silanol group.

The composition may also employ a plasticizer. Typically the plasticizer is a trimethylsilyl terminated dimethylsiloxane employed at levels of up to about 40% by weight of the composition.

In order to reinforce the polymer network as well as to impart non-sag properties to the system, a thixotropic agent is added to the overall composition.

This agent which also adds physical strength to the system desirably is a treated or an untreated silica filler with a treated fumed silica filler being preferred. Treated or untreated silica fillers are well known to the art and generally any such conventional filler can be utilized. Suitable levels range from about 0.1% to about

5% by weight of the compositions. Typically, the silica filler has a very high surface area such as about 100-300M ² /gram. Optionally, from about 0.1 to about 5% by weight and preferably from about 0.2 to about 3% by weight based upon the total weight of the overall system or composition of a thermal aging additive can be utilized. This optional component functions to reduce oxidation and thermal rearrangement of polymers at elevated temperatures. These antioxidants may include materials like cerium neodecanoate, rare earth octoates and iron octoates. Representative samples can also usually include thermal aging additives such as carbon black, iron oxide powder, and titanium dioxide. Naturally, other pigments can be utilized.

Another optional ingredient is an inert non-reinforcing filler such as ground quartz, calcium carbonate, talc, clay, various silicate compounds and other materials well known in the art. The amount utilized is from about 5% to about 60% by weight bases upon the total weight of the sealant composition. Especially preferred fillers are stearic acid treated calcium carbonate fillers having particle sizes below about 0.06 microns, suitably 0.04-0.05 microns. Such fillers are commercially available and may be conveniently employed at levels of about 5% to about 70% of the total weight of the composition, preferably about 15% - 40% of the. total composition. In automotive engine sealant formulations another particularly useful filler is iron aluminum silicate which further improves the fluid immersion properties of the cured compositions particularly in engine coolant. A suitable filler is Ferrosil 14, sold by Kaopolite, Inc., Union, NJ, 98% of which has a particle size of 14 microns or less. Preserved levels of iron aluminum silicate range from 5% to 40% based on the total weight of the composition. The compositions of the invention may further comprise other additives known in the art such as pigments, odor masks or other additives known to improve the properties of RTV silicones for particular applications.

The compositions of the instant invention are formed by mixing the various ingredients together in the substantial absence of moisture. This mixing is carried out in the substantial absence of moisture because moisture will cause the ingredients to prematurely vulcanize. After mixing the composition is storage stable as long as moisture is prevented from contacting the composition. The physical properties of the composition will remain essentially unchanged for one year or more after packaging.

Compositions of this invention can also be utilized as a two component system. Such two component systems generally comprise as the basic ingredients as polyorganosiloxane base polymer and a filler in one package, and an alkyl silicate crosslinking agent mixed with a condensation catalyst as the second package. The compositions prepared in this manner are stored as such and when it is desired to cure the composition the two packages are mixed together and cured to form a silicone elastomeric composition.

SUBSTITUT

The inventive formulations are especially useful in hot oily environments such as in automotive gasketing applications, where they give comparable or even improved properties compared to prior art formulations employing bis-urea compounds and existing commercial automotive gasketing silicones.

The invention may be illustrated by the following non-limiting examples.

EXAMPLE 1

A composition of the invention was prepared as follows:

Weight

Component Percent 6000 cps. silanol terminated polydimethylsiloxane 38.62 15 cs. M.D.T.OH Silicone Fluid ¹ 5.80 1000 cps. trimethylsilylterminated polydimethylsiloxane 3.86 Hydrophobic stearic acid treated precipitated CaCo ₃ ² 23.17 Iron Aluminum Silicate ³ 15.44 Hexamethyldisilazane treated fumed silica * 3.86 Aluminum pigment 0.70 Vinyl tris-methylethylketoximosilane 6.49 γ-ureidopropyltrimethoxysilane 2.00 Dimethyltinbis-neodecanoate 0.06

100.00

A plasticizer containing approximately 5 mole % trimethylsiloxy, 75 mole % dimethylsiloxy, 20 mole % methylsiloxy and 0.3 weight % OH

SoCal 322 from Kali-Chemie, Brussels, Belgium (0.04 μ average particle size)

Ferrosil 14, Kaopolite, Inc., Union, NJ

Zeothix 265, J.M. Huber Corporation, Havre de Grace, MD, treated with hexamethyldisilazane

The resulting RTV silicones were cured at 25° C, 50% relative humidity for 7 days. Lap shear adhesion was then measured (initial adhesion) and compared to results obtained on lap shears which had been immersed for 150 hours at 120°C in 5W-30 motor oil. Table 1 compares the results of these tests with lap shear results obtained when the monourea adhesion promoter was replaced with an equal weight

of Bis-γ-trimethoxysilylpropyl urea (average of 3) and when competitive automotive RTV silicones were used. The data clearly shows that the adhesion of the invention composition actually increased during extended exposure to hot oil and giving final adhesion values even better than the bis-silyl urea containing formulation.

SUBSTITUTE S

SU

EXAMPLE 2 A master batch silicone formulation J was prepared as follows:

Weight Component Percentage

20,000 cps silanol terminated polydimethylsiloxane 40.2 trimethylsilated silica 5.2 viπyl-tris-methylethylketoximosilane 4.8 stearic acid treated calcium carbonate 34.2

1000 cps trimethylsilyl terminated polydimethylsiloxane 15.5 dimethyltinbis-neodecanoate 0.1

To the master batch formulation J was added 1.46% by weight of the adhesion promoters listed in Table 2. Peel adhesions and cohesive failure % on aluminum lap shears, cured for 2 weeks at 25° C, 50% relative humidity, were determined and are recorded in Table 2 (each entry is an average of 2 tests).

Table 2

EXAMPLE 3

A master batch as in Example 2 was prepared to which was added the adhesion promoters and amounts listed in Table 3. Peel adhesion and % cohesive failure on aluminum lap shears were determined as for the examples in Table 2 except that both one week and two week values were obtained. Results are shown in Table 3.

SUBSTITUTE SHEET

Table 3

EXAMPLE 4 Specimens were prepared from the formulations prepared in Example 3 according to ASTM D-412, Die C, after 1 week curing at 25° C, 50% relative humidity. Physical property testing results on these samples (initial values) and on cured specimens which were subsequently immersed in 50° C motor oil for 1 week (final values) are reported in Table 4. The results show good property retention under the test condition.

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Table 4

Hot Oil Stability Tests with N(TrimethoxysilylpropyI) Urea

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EXAMPLE 5

A RTV silicone master batch formulation was prepared as follows:

Weight .. Component Percentage 5000 cps silanol terminated polydimethylsiloxane 39.4

15 cs. M.D.T.OH Silicone Fluid 5.9

1000 cps trimethylsilylterminated polydimethylsiloxane 3.9

Hydrophobic calcium carbonate 23.7

Iron aluminum silicate 15.8 Aluminum pigment 0.7

Treated silica 3.9

Vinyl tris-methylethylketoximosilane 6.6

Dimethyltinbis-neodecanoate 0.06

The polymer, plasticizers, fillers and pigments were mixed together under high shear mixing conditions in a vertical change can mixer at 120°C under vacuum for three hours. The batch was then cooled and the vinyltris-methylethylketoximosilane and tin catalyst added in sequence. To two portions of this master batch were added 2.0 wt % γ-ureidopropyltrimethoxysilane and 2.0 wt % bis-trimethoxysilylpropyl urea,

, respectively. Table 4 gives the results of testing the respective cured formulations after initial curing, immersion in hot 5W-30 motor oil (150 hrs at 120°C) or immersion in hot engine coolant (150 hrs., 100°C). The shear adhesion values are determined on Honda cold-tolled steel lap shears.

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Table 5

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