Liquid silicone rubber with improved compression set

• US 5,977,249 A
• Filed: 07/14/1997
• Issued: 11/02/1999
• Est. Priority Date: 08/29/1996
• Status: Expired due to Term

• Current Assignee: Wacker-Chemie GmbH (Dr. Alexander Wacker Familiengesellschaft Mit Beschrã¤Nkter Haftung)
• Original Assignee: Wacker-Chemie GmbH (Dr. Alexander Wacker Familiengesellschaft Mit Beschrã¤Nkter Haftung)
• Inventors: Kovar, Ingomar, Kammerer, Johann, Strassberger, Walter, Bosch, Erhard, Matejcek, Klaus-Michael
• Primary Examiner(s): Marquis, Melvyn I.
• Assistant Examiner(s): Milstead, Mark W.
• Application Number:
  US08/891,922
• Time in Patent Office: 841 Days
• Field of Search: 524/82, 524/723, 524/742, 524/750, 528/23, 528/15
• US Class Current: 524/723
• CPC Class Codes: C08G 77/12 containing silicon bound to hydrogen C08G77/045 takes precedence
• CPC Class Codes: C08G 77/20 containing silicon bound to unsaturated aliphatic groups C08G77/045 takes precedence
• CPC Class Codes: C08G 77/392 containing sulfur
• CPC Class Codes: C08K 5/36 Sulfur-, selenium-, or tellurium-containing compounds C08K5/0091 takes precedence
• CPC Class Codes: C08K 5/5406 containing elements other than oxygen or nitrogen
• CPC Class Codes: C08L 2666/28 Non-macromolecular organic substances
• CPC Class Codes: C08L 83/00 Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 83/04 Polysiloxanes
• CPC Class Codes: F02F 7/006 Camshaft or pushrod housings

Abstract

The present invention relates to compositions which crosslink to give elastomers, comprising;

(A) a polyorganosiloxane (I) with at least two alkenyl groups per molecule and a metallic catalyst (IV) and

(B) a polyorganosiloxane (II) with at least two silicon-bonded hydrogen atoms and an organic sulfur compound (III).

Claims

1. A two component, addition-crosslinkable organopolysiloxane composition which crosslinks to give an elastomer, comprising;

(A) a first component comprising a polyorganosiloxane (I) with at least two alkenyl groups per molecule and a metallic catalyst (IV) which promotes addition crosslinking, and

(B) a second component comprising a polyorganosiloxane (II) with at least two silicon-bonded hydrogen atoms, and an organic sulfur compound (III).

2. A two component composition which crosslinks to give an elastomer, as claimed in claim 1, wherein component (B) further comprises a polyorganosiloxane (I).

3. A two component composition which crosslinks to give an elastomer, as claimed in claim 1, wherein the organic sulfur compound is supplied as a surface modified inorganic filler containing said sulfur compound.

4. A two component composition which crosslinks to give an elastomer, as claimed in claim 1, wherein the organic sulfur compound is 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, a polydimethylsiloxane-co-mercaptoalkyl compound, octadecane-1-thiol or mixture thereof.

5. A two component composition which crosslinks to give an elastomer, as claimed in claim 1, wherein the organic sulfur compound is present in amounts of from 0.0001% to 2% by weight, based on the weight of the entire composition.

6. A process for preparing an addition-crosslinked elastomer with low compression set which comprises mixing component (A) and component (B) of claim 1 together and curing the mixture obtained.

7. An addition-crosslinked organopolysiloxane elastomer with low compression set prepared by the process of claim 6, wherein the elastomer has not been post-cured.

8. A composition which crosslinks to give an elastomer, as claimed in claim 1, wherein the composition, when vulcanized but not post-cured, has low compression set of less than 50%.

17. The two-component addition-crosslinkable composition of claim 1 which when cured is transparent.

9. A two component, addition-crosslinkable organopolysiloxane composition, comprising:

(A) a first component comprising a polyorganosiloxane (I) with at least two alkenyl groups per molecule, and a metallic catalyst which promotes addition-crosslinking; and

(B) a second component comprising a polyorganosiloxane (II) with at least two silicon-bonded hydrogen atoms per molecule, and an effective, compression set-reducing amount of a silane bearing at least one sulfur-containing group, a thio-functional siloxane, or a mixture thereof.

10. The two component composition of claim 9, wherein said silane bearing at least one sulfur-containing group comprises:

a) a mercaptoalkyl alkylalkoxysilane of the formula

space="preserve" listing-type="equation">(R.sup.5 O).sub.3-n R.sup.6.sub.n Si--R.sup.7 --SH;

b) a bis(trialkoxysilylalkyl)mono-, di-, or polysulfane of the formula

space="preserve" listing-type="equation">{(R.sup.8 O).sub.3 Si--R.sup.9 .brket open-st..sub.2 S.sub.n ;

c) a thiocyanatoalkyltrialkoxysilane of the formula

space="preserve" listing-type="equation">(R.sup.10 O).sub.3 Si--R.sup.11 --SCN;

d) a filler which has been contacted with one or more of a), b) or c);

or

e) mixtures of any of a)-d),

wherein R⁵ is a substituted or unsubstituted, aliphatically saturated monovalent hydrocarbon radical having from 1 to 10 carbon atoms, R⁶ is a substituted or unsubstituted, aliphatically saturated monovalent hydrocarbon radical having from 1 to 10 carbon atoms, R⁷ is a substituted or unsubstituted, aliphatically saturated bivalent hydrocarbon radical having from 1 to 10 carbon atoms,

R⁸ and R¹⁰ are as defined for R⁵,

R⁹ and R¹¹ are as defined for R⁷, and

n is 1-10.

11. The two component composition of claim 10 wherein said filler comprises silica.

12. The two component composition of claim 10 wherein said silane bearing at least one sulfur-containing group and said thio-functional siloxane comprises one or more compounds selected from the group consisting of

3-mercaptopropyltrimethoxysilane,

polydimethylsiloxane-co-mercaptoethylsiloxane, and

polydimethylsiloxane-co-mercaptopropylsiloxane.

18. The two-component addition-crosslinkable composition of claim 9 which when cured is transparent.

13. A two component, addition-crosslinkable organopolysiloxane composition which crosslinks to give an elastomer, comprising;

(A) a first component comprising a polyorganosiloxane (I) with at least two alkenyl groups per molecule and a metallic catalyst (IV) which promotes addition crosslinking, and

(B) a second component comprising a polyorganosiloxane (II) with at least two silicon-bonded hydrogen atoms, and an organic sulfur compound (III);

wherein said organic sulfur compound (III) is selected from a group consisting of thiols;

mercaptoimidazoles;

mercaptobenzimidazoles;

ketene X,S-acetals;

where X is N or S;

thioacetals;

sulfanes;

disulfanes;

polysulfanes;

thioamides;

thioureas;

thiuram;

bisthiocarbamoyl di- or polysulfanes;

thiuronium salts;

thiocarbamates;

dithiocarbamates; and

their Zn, Fe, Ni, Co, and Cu salts;

thiocyanates;

isothiocyanates;

thioaldehydes;

thioketones;

thiolactones;

thiocarboxylic acids;

thiophene;

1,2- and 1,3-dithiols;

1,2- and 1,3-dithiolehtiones;

mercaptothiazoles;

mercaptodithiazoles;

benzodithioles;

benzodithiolethiones;

benzthiazole;

phenothiazines;

thianthrenes; and

mixtures thereof.

14. A two component composition which crosslinks to give an elastomer, as claimed in claim 13, wherein the organic sulfur compound is supplied as a surface modified inorganic filler containing said sulfur compound.

15. A two component composition which crosslinks to give an elastomer, as claimed in claim 13, wherein the organic sulfur compound is present in amounts of from 0.0001% to 2% by weight, based on the weight of the entire composition.

19. The two-component addition-crosslinkable composition of claim 13 which when cured is transparent.

16. A method of decreasing the variation of compression set in two component addition-crosslinked organopolysiloxane elastomers which are stored prior to use, said method comprising adding to at least one component of said two component elastomer, from about 0.0001 weight percent to about 2 weight percent of an organic sulfur compound.