CA1326975C

CA1326975C - Silicone primer compositions

Info

Publication number: CA1326975C
Application number: CA000530278A
Authority: CA
Inventors: Duane Franklin Merrill
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1986-02-18
Filing date: 1987-02-20
Publication date: 1994-02-15
Anticipated expiration: 2011-02-15
Also published as: JPS62218466A

Abstract

SILICONE PRIMER COMPOSITIONS

Abstract of the Disclosure There is provided a primer composition comprising:

(a) the reaction product of (i) from about 50 weight percent to about 90 weight percent of component (a) of at least one resinous organopolysiloxane, and (ii) from about 10 weight percent to about 50 weight percent of component (a) of at least one substantially linear polydiorganosiloxane;

(b) an amount of alkyl silicate, tetraalkyltitanate or mixture thereof effective to render the primer essentially tack-free upon curing; and (c) an amount of solvent effective for dispersing components (a) and (b).

Description

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Background of the Invention - The present invention--generally relates to silicone primer compositions. More particularly, the present invention relates to silicone primer compositions which are especially useful for improving adhesion of silicone pressure sensitive adhesives to low energy surfaces such as silicone rubber, Teflon ~ , Kapton ~ , ethylene propylene diene monomer membrane and the like.

Silicone transfer adhesive systems can be prepared by applying a silicone release coating on a suitable substrate, for example, supercalendered kraft paper or Mylar ~ , and then applying a high phenyl content silicone pressure sensitive adhesive to the release coating. The doubly coated substrate is then laminated to a second substrate to which the pressure sensitive adhesive will adhere when the- substrates are separated. Thus, the high phenyl content silicone adhesive is transferred from the release coated substrate to the second substrate, which can then be applied to a desired surface.

Although such high phenyl content pressure sensitive adhesives will bond to a wide variety of substrates, they do not adhere well to low energy surfaces such as silicone rubber, Teflon ~ , Kapton ~ , ethylene propylene diene monomer membrane and the like. It is therefore necessary to first apply a suitable primer to the surface to which the pressure sensitive adhesive is to be applied.

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60SI-927/0254p GLL:mz Methyl pressure sensitive adhesives adhere to silicone rubber and other low energy surfaces and act as primers for transfer of phenyl pressure sensitive adhesives, however, they retain a non-cured, high tack appearance. When modified with a silicone resin, for example, an MQ resin, so as to provide a non-tacky surface, the phenyl pressure sensitive adhesive will not adhere thereto. Moreover, when methyl pressure sensitive adhesives are crosslinked with, for example, ~-aminopropyltri-ethoxysilane, the phenyl pressure sensitive adhesive will again not adhere thereto.

.. . .
Harper, U.S. Patent No. 3,377,309, discloses a primer for bonding room temperature vulcani~able silicone rubber compositions to other surfaces which consists essentially of 1 to 75 percent by weight of a phenyl-containing siloxane resin which is a ccpolymer that consists essentially of phenyl and methylsiloxane units and has a phenyl to silicon ratio in the range of 0.1:1 to 1:1, a methyl to silicon ratio in the range of 0.6:1 to 1.1:1 and the total of the phenyl and methyl to silicon ratio being in the range of 0.8:1 to 1.8:1; 0.1 to 10 ~ percent by weight of an alkylsilicate; 0.01 to 2 percent by weight of a chlorosilane; and the balance being non-halogenated solvent.

Young, U.S. Patent No. 3,671,483, provides a primer composition consisting essentially of a mixture of 1 part by weight of an aikoxy silicon compound; 0.75 to 2.5 parts by weight of tetraalkyltitanate; 0.75 to 5 parts by weight of an organosilicon compound of the formula CF3CH2CH2 Si (OSi~CH3)2X)3 .

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60SI-927/0254p SLL:mz in which each X is hydrogen or -CH2CH2Si(OOCCH3)3; and - from 1 to ? parts _by weight_of_ an organic solvent having a boiling point no greater than 150DC and selected from the group consisting of ketonesj hydrocarbons and halogenated hydro-S carbons.

Young, U.S. Patent No. 3,677,998, relates to primer compo-sitions consisting essentially of a mixture of from 2.5 to 8 parts by weight of a tetraorganotitanate; from 2.5 to 8 parts by weight of tetra (methoxyethoxy)~ silane; from 1.5 to 3.5 parts by weight of a toluene soluble hydroxylated methylsilox-ane resin; from 1.0 to 5 parts by weight of an acetate compound; and 38.5 to 111.5 parts by weight of a hydrocarbon solvent.

- Ceyzeriat et al., U.S. Patent Nos. 3,92?,246 and 3,965,280, describes an organopolysiloxane composition consisting essentially of (i) 100 parts of a silanol terminated polydiorganosiloxane; (ii) 1 to 15 parts of an organosilicon compound which is either (a) a monomer of the RxSi(OCH2CH2)aOR )4-x~ or (b) a polymer resulting from the partial hydrolysis of at least one monomer of the formula Si(OR')4; (iii) 0.2 to 6 parts of an organic derivative of titanium which is either (a) a mDnomer of the formula Ti( (OCH2CH2)bOR " )4, (b) a polymer resulting from the partial hydrolysis of at least one monomer of the formula Ti(OR ")4, or (c) a titanium chelate, and (iv) 0.5 to 8 parts of an organosilicon resin.

Favre et al., U.S. Patent No. 4,143,088, discloses an organosilicon composition which comprises (a) 100 parts by weight of a silanol terminated polydiorganosiloxane; ~b) 15 to .,_ ... .. , .. . ., . , . . _ .. . . : . . .. ... .. . . ...

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60SI-927/0254p GLL:mz S0 parts by weight of an organosilicon resin; (c) 2 to 25 parts by weight of an alkoxylated organosilicon compound; and (d) 0.5 to 18 parts by weight of an organic derivative of titanium.

Summary of the Invention It is an object of the present invention to provide novel primer compositions.

It is a further object of the present invention to provide primer compositions especially useful for improving the adhesion of silicone pressure sensitive adhesives to low energy lOsurfaces.

It is a further object of the present invention to provide methods for making silicone primer compositions.

In accordance with the foregoing objects, there are provided silicone primer compositions, comprising:

15(a) the reaction product of (i) from about 50 to about 90 weight percent of at least one resinous organopolysiloxane, and (ii) from about 10 to about 50 weight percent of at least one substantially linear polydiorgano-20siloxane;
(b) an amount of alkyl silicate, tetraalkyltitanate ormixture thereof effective to render the composition essentially tack-free upon curing; and . . . _ . .
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60SI-927/0254p GLL:mz (c) an amount of solvent effective for dispersing components (a) and (b).

Description of the Invention .
In accordance with one aspect of the present invention there are provided silicone primer compositions, comprising:
-(a) the reaction product of (i) from about 50 to about 90 weight percent of at least one resinous organopolysiloxane, and .
(ii) from about 10 to about 50 weight percent of at least one substantially linear polydiorgano-siloxane; ~
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(b) an amount of alkyl silicate, tetraalkyltitanate or mixture thereof effective to render the composition essFntially tack-free upon curing; and (c) an amount of solvent effective for dispersing components (a) and (b).

Resinous organopolysiloxane (a)(i) i5 preferably a copolymer of R3SiOo 5 units and SiO2 units, wherein R is a monovalent hydrocarbon radical, preferably methyl, and the ratio of R3SiOo 5 units to SiO2 units is from about O.S:l to about 1:1. Such resins are known in the art as MQ resins and are described, for example, in U.S. Patent No. 2,736,721 to Dexter; U.S. Patent No. 2,857,356 to Goodwin, Jr.; and U.S.
Patent No. 2,676,182 to Daudt et al.

1326~7rj 60SI-927/0254p GLL:mz It is also contemplated that such MQ resins may include difunctional si!oxy units of the formula R25iO in an amount such that the ratio of difunctional siloxy units to tetrafunc-tional siioxy units is up to about O.l:l, where R is as previously defined. Other suitable resins will be obvious to those of ordinary skill in the art.
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Generally, resinous organopolysiloxane (a)(i)-- can be employed in an amount ranging from about 50 to about 90 weight percent based on component (a). More preferably, the organo-silicon is present in an amount of from about 55 to about 80 weight percent and, most preferably, from about 65 to about 75 weight percent of component (a).

Polydiorganosiloxane (a3(ii) can be any substantially linear polydiorganosiloxane which contains condensable groups.
Preferably, polydiorganosiloxane (a)(ii) is a silanol termin-ated polymer having the general formula !
HO ~siot H (I) ~RJ x where R is a monovalent hydrocarbon radical, preferably methyl, and x is an integer such that the viscosity is at least about lOO,OOO centipoise at 25C. More preferably, the viscosity is from about 500,000 centipoise to about 2,500,000 centipoise at 25C and, most preferably, is from about 750,00D centipoise to :: . : ~ ,, ~ ^ .: : .
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about 1,250,000 centipoise at 25C. It has been found that optimal properties are imparted to the primer composition when substantially all of the R radicals are methyl radicals. Methods for preparing polydiorganosiloxanes of formula I as well as polymers having other suitable condensable groups, for example, alkoxy groups, are well known in the art.
Although polydiorganosiloxane (a)(ii) can be present in an amount ranging from about 10 weight percent to about 50 weight percent of component (a), preferably it is employed in an amount ranging from about 20 weight percent to about 45 weight percent and, most preferably, in an amount ranging from about 25 weight percent to about 35 weight percent.
Preparation of component (a) from resinous organopolysiloxane (a)(i) and polydiorganosiloxane (a)(ii) is relatively simple in that it merely requires mixing the two components together and then heating the mixture to effect co-condensation. In 20 general, such co-condensation is effected by heating the reaction mixture to a temperature of from about 80C to about 150C. Those of ordinary skill in the art will be able to prepare component (a) without undue experimentation. Alternatively, component (a) . 25 may be obtained from a commercial source as a pressure B sensitive adhesive, for example PSA 529 available from General Electric Company. PSA 529 is a silicone pressure sensitive adhesive having a silicone content of 55%, a specific gravity of 0.984-1.008, a density of 8.2-8.4 pounds per gallon, a viscosity of 1000-5000 centipoise at 25C, an adhesion of 1440-2800 g/2.54cm, and containing flammable solvents such as toluene.
PSA 529 is the reaction product of a resinous ''`~, :

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- 7a - 60SI-927 organopolysiloxane (a)(i) and a polydiorganosiloxane (a)(ii). In order to obtain maximum cohesive strength, it is necessary to eliminate the solvents from PSA 529 and to cure the adhesive by adding benzoyl peroxide (1-2% based on silicone) and heating the solvent-free tape for 1.5-2 minutes at 9oC
followed by 2 minutes at 165C or by ad~ing an ' aminofunctional silane catalyst, e.g., ~ , also available from General Electric Company, for room temperature curing. To obtain maximum physical properties, it is necessary to add an amount of the catalyst that will eventually cause complete cure of the PSA 529 adhesive. Completely cured PSA 529 adhesive is tack-free and is not useful for pressure sensitive adhesive applications.
Component (b) is an amount of alkyl silicate, tetraalkyltitanate or mixture thereof in an amount effective to render the composition essentially tack-free upon curing. Generally, an effective amount of component (b) is from about 1 to about 15 parts by weight per 100 parts by weight of component (a). More /
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60SI-927/0254p GLL:mz preferably, component (b) is present in an amount ranging from about 4 to about_l~ parts by weiqht and, most preferably, is present in an amount ranging from about 6 to about lO parts by weight per lOO parts by weight of component (a).
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Experience thus far has shown that especially effective primer compositions are obtained when a mixture of alkyl silicate and tetraalkyltitanate is utilized.~ When such a mixture is employed, preferably the alkyl silicate i5 present in an amount ranging from about l to about lO parts by weight 0 and the tetraalkyltitanate is present in an amount ranging from about 0.5 to about 5 parts by weight per lOO parts by weight of component (a). More preferably, the alkyl silicate is present in an amount of from about 3 to about 9 parts by weight and the tetraalkyltitanate is present in an amount ranging from about l to about 3 parts by weight per lOO parts by weight of component (a). Optimal results have been obtained when the alkyl silicate is present in an amount of from about 5 to about 8 parts by weight and the tetraalkyltitanate is present in an amount of from about l to about 2 parts by weight per lOO parts by weight of component (a).

Suitable alkyl silicates and tetraalkyltitanates will be apparent to those of ordinary skill in the art. Generally, alkyl silicates useful in the practice of the present invention are (i) monomers of the formula (R )4-x - Si ~ Rx (II) where R and Rl are independently selected monovalent organic radicals, preferably Cl 4 hydrocarbon radicals and, most preferably, methyl radicals, and x equals O or l; of (ii) the partial hydrolyzate of monomers of formula II.

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60SI-927/~254p GLL:mz g Particularly good results have been obtained when a mixture of monomeric silicate and a partial hydrolyzate of monomeric silicatë is employed. Excellent results have been obtained when the ratio of monomeric silicate to polymeric silicate is S from about 8:1 to about 12:1, on a weight basis. Most preferably, there is utilized i mixture of about 10 parts by weight ethyl orthosilicate and about 1 part by weight of a partial hydrolyzate thereof, for example, Ethyl Silicate 40.
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- ~ Tetraalkyltitanates useful in the practice of the present invention are (i) monomers of the formula Ti (oR2)4 (111) where R2 is a monovalent organic radical, preferably a Cl_10 hydrocarbon radical and, most preferably, a butyl radical; or (ii) the partial hydrolysis product of monomers of formula 111. Preferably, monomeric titanates are utilized in the practice of the present invention.

Component (c) can be any solvent effective for dispersing components (a) and (b). Illustrative of suitable solvents are aliphatic hydrocarbons, benzene, toluene, xylene, chloro-benzene, trichloroethylene, butyl acetate and the like. Hexane has been found to be especially satisfactory for use in the présent invention. Of course, the artisan will be able to select other suitable solvents without undue experimentation.

The amount of solvent employed in the present invention is not particularly limited. Generally, the solvent is present in an amount which makes the composition easy to apply yet , .. . - - , - , ., .. . . . .

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60SI-927/0254p ~LL:mz prDvides an adequate coating of primer upon evaporation of the solvent. Effective_results can thus be obtained when there is sufficient solvent present so as to make the primer contain from about 5 to about 50 weight percent solids. Particularly good results are obtained when the solids content of the primer is from about lO to about 30 weight percent.

The compositions of the present invention should be prepared in an apparatus which permits the ingredients to be intimately admixed in the absence of moisture. The ingredients can be incorporated in any order, preferably at atmospheric pressure or below and at ambient temperature. It has, however, been found to be advantageous to first charge the solvent to the mixing apparatus and then charge the alkyl silicate ~ monomer, the partially condensed a!kyl silicate and the tetraalkyltitanate in that order. When the foregoing are uniformly blended, the reaction product of the resinous organopolysiloxane and the linear polydiorganosiloxane is added to the mixture. Stirring is then continued until the entire mixture is uniformly blended. If necessary, the viscosity of - the primer composition can be adjusted by adding additional solvent. Compositions prepared in the foregoing manner are stable under anhydrous conditions for at least six months and usually are stable for more than one year.

In addition to being useful as a primer for silicone transfer adhesive systems, the compositions may also be used as a primer for silicone room temperature vulcanizable composi-tions and heat cured silicone rubber as well as for general purposes. In addition, the compositions of the present invention can be used as a coupler for glass reinforced . . .. .... ..... .... ... .. . . .. . . . .. . .

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6051-927iO254p GLL:mz plastics, as a thread lubricant, as a self-bonding agent for glass and Kevlar ~ mo-no fllaments ln tire cord and fabric~
weaving, and as a fabric treatment.

The compositions of the present invention can be applied by conventional methods such as roll coating, mayer rod, spraying, brushing and the like. Curing begins as soon as the solvent is evaporated. Accordingly, more rapid curing can-be obtained by exposing the coated substrate to elevated temperatures.
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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 and percentages are by weight unless otherwise noted.

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EXAMPLES

Exam?le 1 A primer comprising 26.2 weight percent ethylorthosilicate and 2.6 weight percent Ethyl Silicate 40 in mineral spirits was applied with a brush to a silicone rubber sponge. After fully drying and hydrolyzing in the presence of atmospheric moisture, a silicone transfer adhesive tape (AR-559, available from Adhesives Research, Inc.) was pressed to the primed surface.
The adhesive failed to bond to the primed surface.

Example 2 A primer composition was prepared by admixing PSA6573, available from General Electric Company, with 6 percent amino-,;. . . . ~ , .,., ... ... . . :, , - ...... . . . . .

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propyltriethoxysilane. The primer was applied by brush to a silicone rubber sponge and allowed to air dry for thirty minutes. A silicone transfer adhesive tape (AR-559, available from Adhesives Research, Inc.) was pressed to the primed substrate. Essentiaily no~bonding between the adhesive and the primed substrate took place. ' Example 3 .
A mixture consisting essentially of lO parts of the primer - - -of Example l, lO parts of PSA529 (available from GeneralElectric Company) and lO parts hexane was applied with a brush to a silicone rubber sponge and allowed to air dry for 30 minutes. Silicone transfer tape (AR-559, available from Adhesives Research, Inc.) was pressed to the surface. The adhesive adhered to the primed surface, allowing for easy , . .. .. . .
removal of the carrier film. This primer, however, became too dry for transfer of adhesive in six hours and the previously applied adhesive could be removed from the primed surface.

Example 4 A mixture consisting essentially of lO parts of the primer of Example l, 20 parts of PSAS29 and lO parts of hexane was brush applied to a silicone rubber sponge and air dried for thirty minutes. Silicone transfer tape (AR-559, available from Adhesives Research, Inc.) was pressed to the primed surface.
The adhesive adhered to the primed surface, allowing for easy removal of the carrier film. The applied adhesive was tested for transfer of the adhesive over an eight hour period. The adhesive was easily transferred. The primer composition was .

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` - 6051-927/0254p GLL:mz further diluted to lOX solids in hexane. A brush applied film on silicone rubber sponge was found to be an effective primer for easy transfer of phenyl pressure sensitive adhesive.
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Example 5 The primer of Example;4 diluted to 10% solids was wiped onto one half of an aluminum test panel. The primer of Exampie 1 was wiped onto the other half of the aluminum test panel.
The primers were allowed to air dry for thirty minutes at which time strips of RTV 108 silicone rubber (available from General Electric Co~pany) were applied to the primers. The rubber strips were allowed to cure for 24 hours and then were tested for adhesion. The silicone rubber was easily separated from the half of the test panel coated with the primer of Example 1 - whereas the silicone rubber could not be pulled away from the half of the test panel coated with the primer composition of the present invention.

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Claims

1. A method for improving the adhesion of a silicone pressure sensitive adhesive to a low energy surface, comprising the steps of:
(A) applying into the low energy surface a primer layer comprising:
(1) the co-condensation product of (a) from about 50 weight percent to about 90 weight percent of component (1) of at least one resinous organopolysiloxane comprising a copolymer of R3SiO0.5 units and SiO2 units, wherein R is a monovalent hydrocarbon radical and the ratio of R3SiO0.5 units to SiO2 units is from about 0.5:1 to about 1:1, and (b) from about 10 weight percent to about 50 weight percent of component (1) of at least one substantially linear polydiorganosiloxane;
(2) an amount of alkyl silicate of the formula (R'O)4-x - Si - Rx where R and R' are independently selected C1-4 hydrocarbon radicals and x equals 0 or 1 or a partial hydrolyzate of said monomer, tetraalkyl-titanate or mixture thereof effective to render the composition essentially tack-free upon curing; and (3) an amount of solvent effective for dispersing components (1) and (2);
(B) applying a pressure sensitive adhesive onto the surface of the primer layer of step (A).

2. A method according to claim 1 wherein the low energy surface is silicone rubber, Teflon?, Kapton?, or ethylene propylene diene monomer membrane.

3. A method according to claim 2 wherein the low energy surface is silicone rubber.

4. A method according to claim 1, wherein resinous organopolysiloxane (1)(a) further comprises R2SiO units in an amount such that the ratio of R2SiO
units to SiO2 units is up to about 0.1:1, wherein R is a monovalent hydrocarbon radical.

5. A method according to claim 1, wherein resinous organopolysiloxane (1)(a) is present in an amount of from about 55 weight percent to about 80 weight percent of component (1).

6. A method according to claim 3, wherein resinous organopolysiloxane (1)(a) is present in an amount of from about 65 weight percent to about 75 weight percent of component (1).

7. A method according to claim 1, wherein polydiorganosiloxane (1)(b) has the general formula (I) where R is a monovalent hydrocarbon radical and x is an integer such that the viscosity is at least about 100,000 centipoise at 25°C.

8. A method according to claim 7, wherein the viscosity is from about 500,000 centipoise to about 2,500,000 centipoise at 25°C.

9. A method according to claim 8, wherein the viscosity is from about 750,000 centipoise to about 1,250,000 centipoise at 25°C.

10. A method according to claim 7, wherein polydiorganosiloxane (1)(b) has the general formula (I) where substantially all of the R radicals are methyl radicals and x is an integer such that the viscosity of polydiorganosiloxane (1)(b) is from about 750,000 centipoise to about 1,250,000 centipoise at 25°C.

11. A method according to claim 1, wherein polydiorganosiloxane (1)(b) is present in an amount of from about 20 weight percent to about 45 weight percent of component (1).

12. A method according to claim 11, wherein polydiorganosiloxane (1)(b) is present in an amount of from about 25 weight percent to about 35 weight percent of component (1).

13. A method according to claim 1, wherein component (2) is present in an amount of from about 1 part by weight to about 15 parts by weight per 100 parts by weight of component (1).

14. A method according to claim 13, wherein component (2) is present in an amount of from about 4 parts by weight to about 12 parts by weight per 100 parts by weight of component (1).

15. A method according to claim 1, wherein component (2) is present in an amount of from about 6 parts by weight to about 10 parts by weight per 100 parts by weight of component (1).

16. A method according to claim 1, wherein the alkyl silicate is a monomer of the formula (R1O)4-x - Si - Rx where R and R1 are independently selected monovalent organic radicals and x equals 0 or 1; or (ii) a partial hydrolyzate of said monomer.

17. A method according to claim 16, wherein the alkyl silicate comprises a mixture of monomeric silicate and the partial hydrolyzate of said monomeric silicate.

18. A method according to claim 17 wherein the ratio of monomeric silicate to the partial hydrolyzate of said monomeric silicate is from about 8:1 to about 12:1, on a weight basis.

19. A method according to claim 18, wherein the alkyl silicate comprises a mixture of about 10 parts by weight of ethyl orthosilicate and about 1 part by weight of the partial hydrolyzate of ethyl orthosilicate.

20. A method according to claim 1, wherein the tetraalkyltitanate is (i) a monomer of the formula Ti(OR2)4 where R2 is a monovalent organic radical or (ii) a partial hydrolyzate of said monomer.

21. A method according to claim 1, wherein component (2) comprises from about 1 part by weight to about 10 parts by weight alkyl silicate and from about 0.5 parts by weight to about 5 parts by weight tetraalkyltitanate.

22. A method according to claim 21, wherein component (2) comprises from about 3 parts by weight to about 9 parts by weight alkyl silicate and from about 1 part by weight to about 3 parts by weight tetraalkyltitanate.

23. A method according to claim 1, wherein the solvent is selected from the group consisting of aliphatic hydrocarbons, benzene, toluene, xylene, chlorobenzene, trichloroethylene and butyl acetate.

24. A method according to claim 1, wherein the solvent is present in an amount sufficient to provide a solids content of from about 5 weight percent to about 50 weight percent.

25. A method according to claim 24, wherein the solvent is present in an amount sufficient to provide a solids content of from about 10 weight percent to about 30 weight percent.

26. A composite comprising:
(A) a low energy surface;
(B) a primer layer situated on the low energy surface, the primer layer comprising:
(1) the co-condensation product of (a) from about 50 weight percent to about 90 weight percent of component (1) of at least one resinous organopolysiloxane comprising a copolymer of R3SiO0.5 units and SiO2 units, wherein R is a monovalent hydrocarbon radical and the ratio of R3SiO0.5 units to SiO2 units is from about 0.5:1 to about 1:1, and (b) from about 10 weight percent to about 50 weight percent of component (1) of at least one substantially linear polydiorganosiloxane;
(2) an amount of alkyl silicate of the formula (R'0)4-x - Si - Rx where R and R' are independently selected C1-4 hydrocarbon radicals and x equals 0 or 1 or a partial hydrolyzate of said monomer, tetraalkyl-titanate or mixture thereof effective to render the composition essentially tack-free upon curing; and Claim 26 continued:
(3) an amount of solvent effective for dispersing components (1) and (2);
(C) a pressure sensitive adhesive situated on the surface of the primer layer.