Organosiloxane compositions

Abstract

A one or more component moisture cure Organosiloxane composition that has strength in an uncured state (commonly referred to in the industry as “green strength”) and its uses. The composition comprises an organopolysiloxane polymer having a viscosity of at least 1000 mPa.Math.s at 25° C. and not less than two silicon-bonded hydroxyl groups and/or silicon bonded hydrolysable groups; a suitable catalyst; a cross-linker adapted to react with organopolysiloxane polymer when catalysed with the catalyst; and optionally one or more rheology modifiers and 0 to 10% by weight of the composition of one or more extenders or plasticisers but in particular the composition contains a precipitated calcium carbonate filler in an amount of from 50 to 70 weight % of the total composition.

Claims

1. A room temperature curable organopolysiloxane composition which has strength in an uncured state of at least 600 Pa measured after one minute, the composition consisting essentially of: a) from 20 to 45% by weight of an organopolysiloxane polymer having a viscosity of at least 1000 mPa.Math.s at 25° C. and not less than two silicon-bonded hydroxyl groups and/or silicon bonded hydrolysable groups; b) a precipitated calcium carbonate filler; c) from 0.1 to 3% by weight of a metal containing condensation catalyst; d) from 0.1 to 10% by weight of a cross-linker adapted to react with component (a), catalysed with component (c); e) one or more rheology modifiers; f) 0 to 10% by weight of the composition of one or more extenders or plasticisers; and wherein component e) is chosen from carboxylated liquid polyolefins or carboxylated liquid polybutadienes, and wherein component b) is present in an amount of from 50 and up to 75% by weight of the total composition.

2. An organopolysiloxane composition in accordance with claim 1 wherein component a has the general formula:
X-A-X.sup.1 where X and X.sup.1 are independently selected from siloxane groups which terminate in hydroxyl or hydrolysable groups and A is a siloxane containing polymeric chain, the hydroxyl-terminating or hydrolysable groups X or X.sup.1 being selected from —Si(OH).sub.3, —(R.sup.a)Si(OH).sub.2, —(R.sup.a).sub.2SiOH, —R.sup.aSi(OR.sup.b).sub.2, —Si(OR.sup.b).sub.3, —(R.sup.a).sub.2SiOR.sup.b or —(R.sup.a).sub.2 Si —R.sup.c—Si (R.sup.d).sub.p(OR.sup.b).sub.3-p, where each R.sup.a independently represents a monovalent hydrocarbyl group; each R.sup.b and R.sup.d group is independently an alkyl or alkoxy group in which the alkyl groups suitably have up to 6 carbon atoms; R.sup.c is a divalent hydrocarbon group which may be interrupted by one or more siloxane spacers having up to six silicon atoms; and p has the value 0, 1 or 2.

3. An organopolysiloxane composition in accordance with claim 2 wherein component (c) is a titanium, tin or zirconium based condensation catalyst.

4. An organopolysiloxane composition in accordance with claim 1 wherein component (b) is a treated precipitated calcium carbonate which has been treated with a treating agent selected from an organochlorosilane, an organopolysiloxane, a hexaalkyldisilazane, a fatty acid or a fatty acid derivative.

5. An organopolysiloxane composition in accordance with claim 4 wherein component (c) is a titanium, tin or zirconium based condensation catalyst.

6. An organopolysiloxane composition in accordance with claim 1 which is room temperature applicable.

7. A method of forming an elastomeric mass between surfaces which is adherent to at least two such surfaces wherein the method comprises introducing between the surfaces, a mass of a curable composition in accordance with claim 1, capable of cure to an elastomeric body and curing the composition in the presence of moisture.

8. A method in accordance with claim 7 in which the mass of curable composition is introduced between the surfaces at room temperature.

9. A cured elastomeric product obtained from the composition in accordance with claim 1.

10. A cured elastomeric product in accordance with claim 9 wherein the elastomeric product is a joint sealant, an adhesive, a moulded body, a coating, or a formed-in-place gasket.

11. A sealant or adhesive comprising the composition in accordance with claim 1.

12. A glazing structure or building unit which includes a sealant derived from a composition according to claim 1.

13. A solar panel which includes a sealant derived from a composition according to claim 1.

14. A photovoltaic panel, windscreen, headlamp or printed circuit board which includes a sealant derived from a composition according to claim 1.

15. An organopolysiloxane composition in accordance with claim 1 wherein said metal containing condensation catalyst comprises a metal chosen from tin, lead, antimony, iron, cadmium, barium, manganese, zinc, chromium, cobalt, nickel, aluminium, gallium, germanium and zirconium.

16. An organopolysiloxane composition in accordance with claim 1 wherein said metal containing condensation catalyst is a titanium, tin or zirconium based condensation catalyst.

17. An organopolysiloxane composition in accordance with claim 1 wherein said metal containing condensation catalyst has the general formula:
Ti[OR].sub.4 wherein each R is independently a monovalent, primary, secondary or tertiary aliphatic hydrocarbon group which is linear or branched and has from 1 to 10 carbon atoms.

18. An organopolysiloxane composition in accordance with claim 1 having strength in an uncured state of at least 1250 Pa measured after one minute.

19. An organopolysiloxane composition in accordance with claim 1 having strength in an uncured state of at least 1500 Pa measured after one minute.

20. An organopolysiloxane composition in accordance with claim 1 wherein component e) is a carboxylated liquid polyolefin.

21. An organopolysiloxane composition in accordance with claim 1 wherein component e) is a carboxylated liquid polybutadiene.

Description

EXAMPLE 1

(1) Table 1 Formulations of 6 compositions in accordance with the present invention and a reference material with the initial green strength for each composition.

(2) TABLE-US-00001 TABLE 1 Components (%) Ref A B C D E F G Polymer 1 39 31.5 Polymer 2 31.5 30.3 34 28.3 28.5 30.5 PCC 48 56.8 56.8 59 54 62 60 59 Catalyst 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Cross-linker 2.7 3.2 3.2 3.2 3.0 3.2 3.35 3.2 Rheology modifier 0 0 0 0.4 1.0 0 0.55 0 Plasticiser 9.3 7.5 7.5 6.1 7 5.5 6.6 0 Extender 6.3 Properties Green strength <250 750 750 1250 600 1500 1500 400 (1 min.) (Pa)

(3) Polymer 1 is a dimethylhydroxy silyl terminated polydimethylsiloxane having a viscosity of 50000 mPa.Math.s at 25° C. Polymer 2 is a dimethylhydroxy silyl terminated polydimethylsiloxane having a viscosity of 13500 mPa.Math.s at 25° C. PCC is a precipitated calcium carbonate which has been treated with a stearic acid and which is commercially available from Solvay SA under the product name Socal 312N. The catalyst used was diisopropoxytitanium Bis(Ethylacetoacetate) and the cross-linker used was methyltrimethoxysilane. The catalyst and cross-linker were added into the composition having been pre-mixed together. The optional plasticiser used was a trimethyl silyl terminated polydimethylsiloxane having a viscosity of 100 mPa.Math.s at 25° C. The optional Extender was a hydrotreated middle petroleum distillate marketed under the Trade name Pilot 900 and sold by e.g. Petrochem Carless BVBA. The optional rheology modifier used in composition C was a polyethyleneoxidepropylene oxide and in formulation D was a fumed silica sold by Cabot Corporation under the Trade Name LM150 and in composition F was a carboxylated liquid polybutadiene.

(4) The value for Green strength (1 min.) (i.e. initial green strength) given in Table 1 is defined as the maximum resistance to constant stress 1 minute after sealant/adhesive application (2 mm thick lap shear) Green strength is measured by making a polycarbonate “lap shear” by bonding two polycarbonate pieces together and identifying what weight said bonded surface area can retain. The bonded area used in the present examples was 25 mm×30 mm=750 mm.sup.2 and the green strength is given in Pa which is the weight in Newtons divided by the surface area in m.sup.2. So, if the bonded polycarbonate assembly with a 750 mm.sup.2 (0.00075 m.sup.2) bonded surface area can hold a constant weight of 100 g (1 Newton) for 10 minutes or more, it has a green strength of (1/0.00075) i.e. 1330 Pa.

(5) It will be appreciated from the green strength results depicted in Table 1 that the composition as described herein provide from 3 to greater than 5 times the initial green strength of the reference sealant formulation.

(6) All the compositions depicted in Table 1 gave acceptable cured sealants when cured but for the sake of example composition F is compared to the results of the Reference sample for cure, mechanical and adhesion properties.

(7) TABLE-US-00002 TABLE 2 Cure properties F Ref Tack Free Time (min) (ASTM D2377-94) 15 30 Green strength (Pa) (2 hrs) >15000 Pa >15000 Pa Cure in depth (24 hrs) 2 mm 2.5 mm

(8) Green strength (2 hrs) is defined as maximum resistance to constant stress 2 hours after sealant/adhesive application and is measured in the same manner as initial tack free time. It will be noted that after the two hour period the strength values of the example and the reference are about the same. The cure in depth tests were undertaken to determine how far below the surface the sealant had hardened in 24 hours by filling a suitable container (avoiding the introduction of air pockets) with sealant, curing the sealant contained in the container for the appropriate period of time at room temperature (i.e. 23-25° C.) and approximately 50% relative humidity. After the appropriate curing time the sample is removed from the container and the height of the cured sample is measured. The values are similar.

(9) Mechanical properties of the composition F and Reference sample were undertaken using the test methods indicated and the results are depicted in Table 3 (with all Tensile strength and Elongation at break measurements made using the test method first indicated). The samples were cured for a period of 3 weeks at room temperature and their properties were thereafter analysed.

(10) TABLE-US-00003 TABLE 3 Mechanical Properties Properties F REF Sheet Tensile Strength (MPa) (ASTM D412-98a) 1.5-1.8 2.2 Elongation at Break (%) (ASTM D412-98a) 150-200 400 Modulus 100% (MPa) (ASTM D638-97) 1.2-1.5 0.8 H-bar shaped samples(GI/GI) & AA/AA (ISO 8339) Tensile Strength (MPa) 0.9-1.0 1.2 Elongation (%) 40-80% 200% % Cohesive Failure 100% 100% Lap shear (PC/PC) (ASTM 3163) Tensile Strength (MPa) 1.0-1.5 MPa 2.0 MPa Elongation (%) +/−300%    >450%   Peel Test (ASTM D903) % Cohesive Failure 100% 100% Duro (Sh A) (ASTM D2240-97) 57 37

(11) It will be noted that whilst composition F had a slightly inferior tensile strength compared to the values seen for the reference composition but much higher modulus and lower movement capability (12.5% vs. 50% for Ref).

Adhesion Properties

(12) The peel test referred to above (ASTM D903) required a tape to be applied to several different surfaces for 7 days at room temperature before being removed. The surfaces used in this instance were wood glass polyvinyl chloride (PVC) and polymethylmethacrylate (PMMA) and in each case the result of the test gave 100% cohesive failure for both composition F and the Ref.