CA1266149A

CA1266149A - Room temperature vulcanizable silicone compositions having improved adhesion

Info

Publication number: CA1266149A
Application number: CA000511048A
Authority: CA
Inventors: Gary Morgan Lucas
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1985-06-18
Filing date: 1986-06-06
Publication date: 1990-02-20
Also published as: JPS6243460A; JPH0579703B2

Abstract

ROOM TEMPERATURE VULCANIZABLE SILICONE
COMPOSITIONS HAVING IMPROVED ADHESION
ABSTRACT OF THE DISCLOSURE

There is provided a room temperature vulcanizable silicone rubber composition which upon curing to the solid, elastic state exhibits improved adhesion to various substrates, comprising:

(a) a polydiorganosiloxane wherein the silicon atom at each polymer chain end has bonded thereto at least two hydrolyzable groups, (b) an effective amount of non-chelate condensation catalyst, and (c) an effective amount of metal chelate adhesion promoter.

Description

60S~ 9~g --ROOM TEMPERATURE VULCANIZABLE SILICONE

Background of the Intention The present invention relates to room temperature vulcaniz-able silicone rubber compositions which exhibit improved adhe-sion upon curing. More particularly, the present invention relates to room temperature vulcanizable silicone rubber compo-sitions comprising a polydiorganosiloxane wherein the silicon atom at each polymer chain end is ~erminated with at least two hydrolyzable groups, a non-chelate condensation catalyst, and a metal chelate adhesion promoter.

Prior to the present invention it was well known in the art that various metal salts of carboxylic acids, metal chelates, organic acids and organic bases could be used as condensation catalysts for room temperature vulcanizable silicone rubber compositions.

Evans~ U.S. Pat. No. 3,622,529, discloses a composition stable under substantially anhydrous conditions and curable to the solid, elastic state in the presence of moisture which comprises a silanol chainstopped polydiorganosiloxane, an imid-atosilane of the formula 60SI-99g/02~0p/GLL:mz (ROC = N ~ ~

Si - (R )d (R20)b where R and R are each organic radicals of not more than 18 carbon atoms selected from hydrocarbyl, halohydrocarbyl, nitro-hydrocarbyl and alkoxyhydrocarbyl; R1 is hydrogen or a radical selected from hydrocarbyl~ halohydrocarbyl, and cyano-alkyl; R3 is hydrogen or an organic radical of not more than 18 carbon atoms selected from hydrocarbyl, halohydrocarbyl, nitrohydrocarbyl, alkoxyhydrocarbyl, dialkylamino, and wherein R4 is an organic radical selected from aliphatic hydrocarbyl, aliphatic halohydrocarbyl, aliphatic nitrohydro-carbyl and N

R6 ~

60SI-999/0200p/GLL:mz where R5 and R6 are each aliphatic hydrocarbyl, a is an integer from 2 to 4, inclusive, b is an integer from 0 to 2, inclusive, d is 0 or 1, and the sum of a, b and d is 4, and, optionally, a minor amount of carboxylic acid salt and/or chelate of a metal ranging from lead to manganese, inclusive, in the electromotive series of metals.

5mith et al., U.S. Pat. No. 3,708,467, discloses a composi-tion stable under substantially anhydrous conditions and curable to the solid, elastic state which comprises a silanol chainstopped polydiorganosiloxane, a silane represented by the formula RmSi(ORl)4 m where R and Rl are radicals having not more than about 8 carbon atoms selected from the group consisting or hydrocarbyl, halohydrocarbyl and cyano lower alkyl, and a catalyst system containing a first catalyst which is a salt, alkoxide, hydroxide or oxide of a metal ranging from lead to manganese in the electromotive series of metals and 2 second catalyst which is a titanium chelate.

The present invention is based on the surprising discovery that improved adhesion is obtained if a polydiorganosiloxane having the silicon atom at each polymer chain end terminated with at least two hydrolyzable groups is employed in combina-tion with a non-chelate condensation catalyst and a metal chelate adhesion promoter.

Summary of the_l_ver,tion ~t is an object of the present invention to provide room temperature vulcanizable silicone rubber compositions which exhibit improved adhesion to various substrates upon curing.

60SI-g99/0200p/GLL:mz It is another object of the present invention to provide methods for making room temperature vulcanizable silicone rubber compositions which exhibit improved adhesion to various substrates upon curing.

In accordance with one aspect of the present invention there is provided a room temperature vulcanizable silicone rubber composition having improved adhesion upon curing, c~mprising:

(a) a polydiorganosiloxane wherein the silicon atom at each polymer chain end is terminated with at least two hydrolyzable radicals, (b) an effective amount of non-chelate condensation catalyst, and (c) an effective amount of metal chelate adhesion promoter.

Description of the Invention The present invention provides room temperature vulcaniz-able silicone rubber compositions which cure to the solid, elastic state upon exposure to moisture and exhibit improved adhesion to various substrates, comprising:

(a) a polydiorganosiloxane wherein the silicon atom at each polymer ehain end is terminated with at least two hydrolyzàble radicals, 60SI-999/0200p/GLL:mz (b) an effective amount of non-chelate condensation catalyst, and (c) an effective amount of metal chelate adhesion promoter.

Polydiorganosiloxanes wherein the silicon atom at each polymer chain end is tenminated with at least two hydrolyzable radicals are known in the art. Such polydiorganosiloxanes can be represented by the general formula ( p,2 ) a ~ R ~ ( R2 ) (R )3-~a~b) ! ~siot si (OR )3-(a~b) Xb R ~n Xb where R is a C(l 13) mpnoYalent substituted or unsubstituted hydrocarbon radical, which is preferably methyl, or a mixture of a major amount of methyl and a minor amount of phenyl, cyanoethyl, trifluoropropylO vinyl or mixture thereof; Rl is a C(l 8) aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals or a C(7 13) aralkyl radical; R2 ls a C(l 13) monovalent substituted or unsubstituted hydrocarbon radical; X is a hydrolyzable group selected from the group consisting of amido, amino, carbamato, enoxy, imidato, 60SI-999/0200p/GLL:mz isocyanato, oximato, thioisocyanato and ureido radicals, a equals 0 or 1, b equals 0 to 2, inclusive~ the sum of a ~ b equals 0 to 3, and n is an integer up to about 2500.
Preferably Rl and R2 are methyl.
Polydiorganositoxanes within the scope of the above formula I. are known in the art, for example, those described in United State~ Patent Number 4,395,526 to White~et al, which ~atent is a~signed to the sam~ assignee as the present invention.

It is especially preferable that polydiorganosiloxane (a) have at least two alkoxy groups bonded to the silicon atom at each polymer chain end. These polyalkoxy terminated polydi-organosiloxanes can be made, for example, by following the teaching of-Chung, in U~ited Stat~s Patent ~umber 4,515,~3~.- - -The condensation catalyst (b) used in the practice of the invention can be any of those known in the art except for metal chelates. The reason that metal chelates are excluded is that in the present invention metal chelates commonly employed as condensation catalysts are utilized as adhesion promoters.
Thus, those skilled in the art will appreciate that although the metal chelates will inherently function as condensation catalysts, in the present invention they are utilized primarily as a means for improving the adhesion of the cured silicone composition to various substrates.
Accordingly, for purposes of the present lnventlon, the condensation catalyst can be selected from, for example, metal salts of monocarboxylic acids and dicarboxylic acids, metal alkoxides, organic bases, organic acids, and the like. Prefer-6051-999/0~09p/GLL:mz red condensation catalysts are metal salts of carboxylic ~cids and especially pre~erred are tin compounds such ~s dibutyltin-ditaurate, dibutyltindiacetate, dibutyltindimethoxide~ carbo-methoxyphenyl tin tris-uberate, tin octoate, dimethyl tin dibutyrate, triethyl tin tartrate, tin oleate and tin naphthen-ate. Dibutyl tin diacetate is particularly preferred.

Examples of other metal condensation catalysts are ~ircon-ium octoate, lead 2-ethyloctoate, iron 2-ethylhexoate, cobalt

2-ethylhexoate, manganese 2-ethylhexoate, zinc 2-ethylhexoate, antimony octoate, bismuth naphthenate~ zinc naphthenate and zinc stearate.

Examples of nonmetal condensation catalysts are hexylam-monium acetate and benzyltrimethylammonium acetate.

Other suitable condensation catalysts will be obvious to those skilled in the art or can be easily ascertained without undue experimentation.

Generally, an effec$ive amount of condensation catalyst is from about 0,001 to about 2 parts by weight per 100 parts by weight of polydiorganosiloxane (a). More preferably, the condensation catalyst is used in an amount ranging from about 0.1 to about 1 part by weight per 100 parts by weight of polydi-organosiloxane (a).

The metal chelates employed as adhesion promoters in the practice of the present invention can be based on lead, tin, zirconium, antimony, zinc, chromium, cobalt, nickel, aluminum, gallium, germanium or titanium. Most preferably, however~ the metal chelate is a titanium chelate.

Illustrative titanium chelate compounds useful for practiciny the present invention are described in U.S. Pat. Mo. 3,334,067 to Weyenberg, U.S. Pat. No.

3,689,454 to Smith et al., and U.S. Pat. No. 4,438,039 to Beers et al.
Among the more preferred titanium chelates are, for example:

/CH3 (C2H20)9CH3 CH ~ 0 = C / H2 \ 0 - C

C ~ Ti CH C~ Ti D -C-CH3 CH3 2 CH3 ~ 2 C2H5 / (C2H5)2 /CH2 0 \ 0 = C \ CH 0 0 = C

C ~ Ti/ f H C~ Ti/ CH

~69L~

/ 9 19 (CH2) 2N

\ / C CH

CH3 2 2 ~ 2 C~ Z

:

C~3 ~ C \ 0=C
fH --o \ fHo ~

T CH T D H

CH2 0 \ ~ H2 \
O C O C

. CH3 CH3 CH ~O C CH --O ~O C

HO--C~ T CH C~ T J ~

2 --C CH2 O \O C// 2 6051 -~99/()200p/GLL :mz ~LI tlO lDcludeJ ~r~:
d~lJo~t~Aroyl~thyl~De t~t~D~tæ
~isaD~u~ dl~Pth~cryl,-te o~ysc~tatP
l~taniu~ d~Dcryl~te t~y~c~-tP
~It~DiUll' dl(cu~ylph~Dol~te)~y~cetate T3tJoiu~ dl~diDctylpho6ph~te)c~y4c~t~t~
d~(dlo~tylphc)~p~l~t2)ethy~D2 t~t~te ~t~DiU~ di (d~octy~p~rophDBph~te)o~y~c~tate dl(dioctylpyropbo6phat~)etby~eDc t~t-l~ate The following titanates are particularly preferred.

~ CH3(or ~C2H5 \ /~ \
CH2 Ti ~ ~ CH C H ~ ~ ~ ~ o CH2 0 O C 2 ~ CH
l CH3 2 60SI-999/0200p/GlL:mz It has been found that an effective ~mount of metal chelate adhesion promoter generally ranges from about 0.05 to about 2 percent by weight of polydiorganosiloxane (a). Of course, more can be used~but no particular advantage is obtained thereby.
If less than about 0.05 percent by weight of metal chelate is utilized, the adhesive bond between the silicone elastomer and the substrate is not sufficiently strong for most purposes. In more preferred embodiments the metal chelate is present in an amount of from about 0.1 to about 1.5 percent by weight of I0 polydiorganosiloxane (a). Of course, mixtures of metal che-lates are also contemplated by the present invention.
, Conventional additives such as fillers, plasticizers, crosslinking agents, scavengers for hydroxy functional groups, and the like may also be included in the compositions of the I5 present invention.

In the practice of the present invention, the room tempera-ture vulcanizable compositions can be made by agitating, for example stirring, the respective ingredients of the curable composition in the substantial absence of moisture. The temperature can vary from about 0C to about 180C depending upon the degree of blending, the type and amount of filler, etc.

In a preferred method for making the compositions of the present invention the polydiorganosiloxane having at least two hydrolyzable groups at each polymer chain end is admixed with reinforcing filler and plasticizing fluid to form an RTV base.
Thereafter, a s;lane crosslink;ng agent, a scavenger for hydroxy functional groups, condensation catalyst, and metal chelate adhesion promoter are mixed with the RTV base, 605I-999/0200p/GLL:mz In order to better enable the artisan to practice the present invention, the following examples are provided by way of illustration and not by way of limitation. All parts are by weight unless otherwise noted.

EXAMPLES

Exam A vinyldimethoxy endstopped polydimethylsiloxane W3S
prepared by charging a one gallon Ross ~ mixer equipped with a vacuum line and nitrogen purge with 100 parts by weight I0 silanol endstopped polydimethylsiloxane having a viscosity of 22,000 centipoise at 25C, 1.5 parts by weight vinyltrimethoxy-silane, 0.2 parts by weight dibutylamine and 0.05 parts by weight acetic acid. This mixture was agitated for 15 minutes at 100C under a nitrogen atmosphere. An additional 45 minutes I5 mix at 100C under a 5 mm Hg vacuum yielded a shelf stable vinyldimethoxy endstopped polydimethylsiloxane having a viscosity of 26,900 centipoise at 25~C.

Example 2 A one gallon Baker-Perkins mixer equipped with a vacuum line and nitrogen purge was charged with 100 parts by weight of the vinylmethoxy endstopped polydimethylsiloxane prepared in Example 1, 40 parts by weight of fumed silica filler treated with octamethy kyclotetrasilo%ane and hexamethyldisilazane, 40 parts by weight of a 3000 centipoise t-buytl-silanol endstopped polydimethylsiloxane, and 15 parts by weight of a 50 centipoise silanol endstopped polydimethylsiloxane. This mixture was agitated under 20 mm Hg vacuum for 60 minutes to provide an RTV
base.

, 60S~-999/0200p/GLL:mz ~o 100 parts by weight of the RTV base was added 7 parts by weight vinyltrimethoxysilane crosslinking agent, 2 parts by weight hexamethyldisilazane scav2nger for hydroxy functional groups, 1.0 part by weight dipropoxytitanium-bis-(ethylaceto-acetate) and 0.1 part by weight dibutyltindiacetate, using a Semco ~ catalyzer/mixer. Foll~wing mixing, a profile o~ the physical properties of the composition was obtained. The results are set forth in Table 1.

- T~ble l. E_a~ple 2 E~p~r~eDtal ~u~t~
Prope rty Exp~ 2 Results Sp. CrAv1ty ~.08S
AppllcatloD R~t~, g/~1D. 240 l~ck Free Tl~ in. 30 ~ov, lDch 0 05 .
Duro~reter, Shore A ~ 33 T~DSI1~, p61 ~ 5~9 E~C~D8atloD, ~ * 49~
Peel Adheslo~ ppi *R
Al ulD. 2024 80 Cold rolled atee~ 55 G~a66 83 48 hr/lOO~C Accel. Age *~
Duro~eter, Shore A 35 ~en~lle, p~l 409 ElODgatl~lD, % 461 7 d~y cure flt 5~ R .H . aDd 25 ~C
14 day cure ~t 502 R.H. ~nd 25-C

60SI-999/0200p/GLL:mz Example 3 Exa~ple 1 was repeated, using 1.5 parts by weight methyltri~
methoxysilane to provide a methyldimethoxy endstopped polydi-methylsiloxane having a viscosity of 26,500 centipoise at 25JC.

Example 4 -An RTY base was prepared as in Example 2 using the methyl-dimethoxy endstopped polymer of Example 3 and vinyltrimethoxy-silane crosslinking agent was replaced with 1 part by weight methyltrimethoxysilane crosslinking ayent. The physical properties of this composition were also obtained and are set forth in ~able 2.
~ble 2: E~p~e 4 E~perlDental R~ultc Property E3p. 4 Re6l~1t6 .
Sp . Gr~vl t y ~ . 086 App~ic~tiDD R~te~ ~lD. 224 ck Free ~ ;e, mlD, 30 ~1 ~v, ~ nch 0, 05 I>uro~eter, Shore A *~ 35 leD~lle, pol ~ 49B
E~OD,~,~t~ , 2 ~ .~50 P~el AdhPSioD ppl ~
Al u~ . 2024 74 Col d rol~ ~d steel 68 Gl ~ sc 82 48 hr/~00c Accel. ~,ge nll ~uro~ter, 5~,or~ A 3]
TeD6l1~, p61 3B2 El onga t I DD, 2 4 91 7 day c~re ~t 502 R.H. Dnd 25-C

4 d~y cure at 502 R.H. Dd 25-C

,~.

60Sl-999/0200p/GLL:~z Example 5 In this example, Example 4 was repeated without the addition of titanium chelate. The results are set forth in ~able 3.

Table 3: Ex~p~e 5 E~pPri eDtal Recult6 E~p. 5 RP~U1t6 Property 1 .083 Sp. Gravi ty 201 Appllcatl OD Rate, g/~lD.
Tack Free Ti~e, ~io. O.OS
Fl ow, i Dch 31 Duros;eter, Shore A t Te n~ i 1 e , p~ i 50 2 EIC~DgatiOD~ 2 Pee~ Adhe~loD pp~
Al u~ . 2024 Cold roll ed ~teel GIA~ .
48 hr/lOO~C Acc~ e Duro~eter, SP~ore A
TeD6il e, pti El onga t i o~, 2 7 ~day cure at 5G~ R.H. and 25DC
14 day cure at 50~ R~H. and 25 C

60SI-99g/0200p/GLL:mz Example 6 Example 4 was again r~peated, h~wever, this time 1.0 part by weight aminoethylaminopropyltrimethoxysilane was used as an adhesion promoter in place of the titanium chelate. The results are reported in Table 4.

~bl ~ 4: ~a~pl e 6 E ~P~r1~DeDta1 Rr~ul P ro pe r t y Esp . S Re 6u 1 t Sp GrB~lty 1.080 ,~ppllcatioD Rate, ~/~Dln. 281 ~ck Free Tl~e, ~1D. 20 ~10W, 1DC~
Duro~eter, Shore A ~ 4~
Sen~11e, p61 ~' 472 EloDgatioD~ Z h 41D
Pee~ Adhe~loD ppi **
1~ u~. 2024 12 Cold rolled 6teel 4 Gla6~ 14 48 hr/~00C Accel. A~e l~
D-lro~eter, Shore A 38 Ie r~ p6 i L02 E~O~atlOD, a 45~

7 day cure ~t 507. R.H. and 25C
~* 14 day cure at 50~ R.H. and 25C

60SI-999/0200p/GLL:mz Example 7 ~ xample 4 was repeated, however, this time 1.0 parts by weight of 1,3-dioxypropanetitanium-bis(acetylacetonate) was used as the adhesion promoter. The test results are pr~Yided in ~able 5.

Table ~: E~J~ple 7 E~p~rl~ta~ R~ulta Property E3p. 7 Re~ul t6 -Sp Gra~ity gl 1 089 TPck Free ll~e, 010.
~ow, inch Duro~eter, Shore ~ * 42 TeD61le, p61 64l E~oD~stl~n, S
Peel Adhesio~ ppl ~
A]u~. 2024 71 Cold rol~ed 6teel 5~
Glass 86 48 hrll~ooc Accel~ A~e e*
Duro~Pter, Shore A 34 TeDl;ile, p6i 441 El OD&a t i OD, ~ 519 7 d~y cure at 50~ R.H. aDd 25CC
~* 14 day cure at 50~ R.H. aDd 25C

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A curable composition, comprising:
(a) a polydiorganosiloxane wherein the silicon atom at each polymer chain end is terminated with at least two hydrolyzable groups, (b) an effective amount of non-chelate condensation catalyst, and (c) an effective amount of metal chelate adhesion promoter.

2. A composition as in claim 1, wherein the polydiorganosiloxane has the general formula where R is a C(1-13) monovalent substituted or unsubstituted hydrocarbon radical; R1 is a C(1-8) aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals or a C(7-13) aralkyl radical; R2 is a C(1-13) monovalent substituted or unsubstituted hydrocarbon radical; X is a hydrolyzable group selected from the group consisting of amido, amino, carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato and ureido radicals; a equals 0 or 1, b equals 0 to 2, inclusive;
the sum of a + b equals 0 to 3, inclusive; and n is an integer up to about 2500.

3. A composition as in claim 2, wherein R
is methyl or a mixture of a major amount of methyl and a minor amount of phenyl, cyanoethyl, trifluoropropyl, vinyl or mixture thereof; R1 is methyl; and R2 is methyl.

4. A composition as in claim 3, wherein the polydiorganosiloxane has at least two methoxy groups bonded to the silicon atom at each polymer chain end.

5. A composition as in claim 2, wherein the condensation catalyst is a metal salt of a monocarboxylic acid, a metal salt of a dicarboxylic acid, a metal alkoxide, an organic base, an organic acid or mixture thereof.

6. A composition as in claim 5, wherein the condensation catalyst is a metal salt of a monocarboxylic acid, a metal salt of a dicarboxylic acid, a metal alkoxide or mixture thereof.

7. A composition as in claim 6, wherein the metal is tin.

8. A composition as in claim 5, wherein the condensation catalyst is present in an amount of from about 0.001 to about 2 parts by weight per 100 parts by weight of polydiorganosiloxane.

9. A composition as in claim 2, wherein the metal chelate is based on a metal selected from the group consisting of lead, tin, zirconium, antimony, zinc, chromium, cobalt, nickel, aluminum, gallium, germanium and titanium.

10. A composition as in claim 9, wherein the metal chelate is a titanium chelate.

11. A composition as in claim 5, wherein the metal chelate is a titanium chelate.

12. A composition as in claim 10, wherein the titanium chelate is present in an amount of from about 0.05 to about 2 parts by weight per 100 parts by weight of the polydiorganosiloxane.

13. A composition as in claim 11, wherein the titanium chelate is present in an amount of from about 0.05 to about 2 parts by weight per 100 parts by weight of the polydiorganosiloxane.

14. The cured composition of claim 1.

15. The cured composition of claim 2.

16. A method for making a curable composition, comprising:
(I) mixing under substantially anhydrous conditions:
(a) a polydiorganosiloxane wherein the silicon atom at each polymer chain end is terminated with at least two hydrolyzable groups, (b) an effective amount of non-chelate condensation catalyst, and (c) an effective amount of metal chelate adhesion promoter.

17. A method as in claim 16, wherein the polydiorganosiloxane has the general formula where R is a C(1-13) monovalent substituted or unsubstituted hydrocarbon radical; R1 is a C(1-8) aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone and alkylcyano radicals or a C(7-13) aralkyl radical; R2 is a C(1-13) monovalent substituted or unsubstituted hydrocarbon radical; X is a hydrolyzable group selected from the group consisting of amido, amino, carbamato, enoxy, imidato, isocyanato, oximato, thioisocyanato and ureido radicals; a equals 0 or 1, b equals 0 to 2, inclusive;
the sum of a + b equals 0 to 3, inclusive; and n is an integer up to about 2500.

18. a method as in claim 17, wherein the polydiorganosiloxane has at least two alkoxy groups bonded to the silicon atom at each polymer chain end.

19. A method as in claim 17, wherein the condensation catalyst is a metal salt of a monocarboxylic acid, a metal salt of a dicarboxylic acid, a metal alkoxide, an organic base, an organic acid, or mixture thereof.

20. A method as in claim 17, wherein the condensation catalyst is a metal salt of a monocarboxylic acid, a metal salt of a dicarboxylic acid, a metal alkoxide, or mixture thereof.

21. A method as in claim 20, wherein the metal is tin.

22. A method as in claim 21, wherein the condensation catalyst is present in an amount of from about 0.001 to about 2 parts by weight per 100 parts by weight of polydiorganosiloxane.

23. A metho s in claim 16, wherein the metal chelate is based on a metal selected from the group consisting of lead, tin, zirconium, antimony, zinc, chromium, cobalt, nickel, aluminum, gallium, germanium and titanium.

24. A method as in claim 16, 17 or 18, wherein the metal chelate is a titanium chelate.

25. A method as in claim 22, wherein the titanium chelate is present in an amount of from about 0.05 to about 2 parts by weight per 100 parts by weight of polydiorganosiloxane.