ADDITIVE STABILIZATION

Abstract

There is provided a process for stabilizing additive concentrates comprising or consisting of one or more additives in dialkylsilanol terminated polydiorganosiloxane polymers for use in condensation curable organosiloxane compositions. Processes for making condensation curable organosiloxane compositions incorporating the additive concentrates as well as the use of the stabilized additive concentrates in condensation cure organosiloxane compositions are also described. The stabilizer used is a polydialkylsiloxane having the general formula: R.sup.3.sub.3—Si—O—((R.sup.2).sub.2SiO).sub.d—Si—R.sup.3.sub.3 where R.sup.2 is an alkyl or phenyl group, each R.sup.3 group may be the same or different and are selected from R.sup.2 alkenyl or alkynyl groups and the average value of d is between 7 and 20, in an amount of from 0.5 to 5 wt. % of the composition.

Claims

1. A process for preparing a stabilized additive concentrate suitable for use in condensation curable organosiloxane compositions, said process comprising: mixing (i) a solid additive in an amount of from 25 to 80 wt. % of the composition with (ii) a liquid carrier comprising a dialkylsilanol terminated polydiorganosiloxane polymer in an amount of from 20 to 75 wt. % of the composition with (iii) a stabilizer comprising or consisting of a polydialkylsiloxane having the general formula:
R.sup.3.sub.3—Si—O—((R.sup.2).sub.2SiO).sub.d—Si—R.sup.3.sub.3 where R.sup.2 is an alkyl or phenyl group, each R.sup.3 group may be the same or different and are selected from R.sup.2 alkenyl or alkynyl groups and the average value of d is between 7 and 20, in an amount of from 0.5 to 5 wt. % of the composition.

2. The process for preparing a stabilized additive concentrate in accordance with claim 1, wherein solid additive (i) is selected from a solid additive utilised in a condensation curable organosiloxane composition selected from non-reinforcing fillers, electrically conducting fillers, heat conducting fillers, pigments, co-catalysts, heat stabilizing agents, flame retardants, UV stabilizers, fungicides and/or biocides and encapsulated fungicides and/or biocides.

3. The process for preparing a stabilized additive concentrate in accordance with claim 1, wherein solid additive (i) produces an acidic solution when dissolved in water.

4. The process for preparing a stabilized additive concentrate in accordance with claim 1, wherein the stabilized additive concentrate is one or more pigments or heat stabilizing agents or a mixture thereof.

5. The process for preparing a stabilized additive concentrate in accordance with claim 4, wherein the one or more pigments or heat stabilizing agents or a mixture thereof is selected from yellow iron oxide, red iron oxide, black iron oxide, carbon black, titanium dioxide, chromium oxide, bismuth vanadium oxide, zinc oxide, cerium oxide, cerium hydroxide and/or mixtures thereof.

6. The process for preparing a stabilized additive concentrate in accordance with claim 5, wherein the one or more pigments or heat stabilizing agents or a mixture thereof is selected from yellow iron oxide, red iron oxide and/or black iron oxide.

7. The process for preparing a stabilized additive concentrate in accordance with claim 1, wherein liquid carrier (ii) is a dialkylsilanol terminated polydimethylsiloxane having the structure
HO(R.sub.2)Si—O—(R.sup.1.sub.vSiO.sub.(4-v)/2).sub.w—Si—(R.sub.2)OH in which each R is an alkyl, alkenyl or aryl group; each R.sup.1 may be the same or different and is a hydroxyl group, hydrolysable group, alkyl group, alkenyl group or aryl group; v is 0, 1 or 2, and w is an integer such that said dialkylsilanol terminated polydiorganosiloxane has a viscosity of from 5,000 to 50,000 mPa.Math.s at 25° C.

8. The process for preparing a stabilized additive concentrate in accordance with claim 1, wherein the average value of d in stabilizer (ii) is between 7 and 15.

9. A stabilized additive concentrate obtained or obtainable by the process of claim 1.

10. A process for preparing a condensation curable organosiloxane composition, said process comprising: preparing at least one stabilized additive concentrate (e) in accordance with claim 1; and mixing stabilized additive concentrate (e) with (a) a polydiorganosiloxane having at least two hydroxy groups or hydrolysable groups per molecule, (b) one or more silane or siloxane cross-linkers reactive with the at least two hydroxy groups or hydrolysable groups of polydiorganosiloxane (a), (c) a condensation cure catalyst, and (d) one or more reinforcing fillers or semi-reinforcing fillers.

11. A condensation curable organosiloxane composition obtained or obtainable by: preparing at least one stabilized additive concentrate (e) in accordance with claim 1; and mixing stabilized additive concentrate (e) with (a) a polydiorganosiloxane having at least two hydroxy groups or hydrolysable groups per molecule, (b) one or more silane or siloxane cross-linkers reactive with the at least two hydroxy groups or hydrolysable groups of polydiorganosiloxane (a), (c) a condensation cure catalyst, and (d) one or more reinforcing fillers or semi-reinforcing fillers.

12. The condensation curable organosiloxane composition in accordance with claim 11, wherein the composition is stored in two or more parts prior to utilization.

13. A condensation curable organosiloxane composition comprising the stabilized additive concentrate prepared in accordance with claim 1.

14. The condensation curable organosiloxane composition in accordance with claim 13, suitable as a coating, a caulking, a sealing, a mold making or an encapsulating material.

15. The condensation curable organosiloxane composition in accordance with claim 13, suitable in solar, automotive, electronics, construction and/or structural glazing and/or insulating glazing applications.

Description

EXAMPLES

[0141] In the following examples, unless otherwise indicated, all viscosities mentioned were measured at 25° C. using either a Brookfield® rotational viscometer with spindle LV-4 (designed for viscosities in the range between 1,000-2,000,000 mPa.Math.s) or a Brookfield® rotational viscometer with spindle LV-1 (designed for viscosities in the range between 15 -20,000 mPa.Math.s) for viscosities less than 1000 mPa.Math.s and adapting the speed according to the polymer viscosity.

[0142] A first series of experiments were undertaken comparing three additive concentrates, in which 55 wt % of a red iron oxide having a pH of 5.3 was utilised as the additive (i) and was mixed with 45 wt. % of a dimethylsilanol terminated polydimethylsiloxane having a viscosity of 2000 mPa.Math.s at 25° C. (liquid carrier (ii)). Once thoroughly mixed, no stabilizer was added in comp. 1; magnesium oxide was added as a stabilizer in an amount equal to 1 wt. % of the total weight of the additive (i) and liquid carrier (ii) in Comp. 2 and a trimethyl terminated polydimethylsiloxane of the average structure

Me.sub.3-Si—O-((Me).sub.2SiO).sub.9—Si-Me.sub.3

i.e. an average degree of polymerisation (DP) of 11 was added as stabilizer in an amount equal to 1 wt. % of the total weight of the additive (i) and liquid carrier (ii) in Ex. 1. The viscosity of samples of each of Comp. 1, Comp. 2 and Ex. 1 were determined without aging or were aged for a variety of periods of time in an accelerated aging study thereof. All viscosity measurements for these tests were carried out using an AR 2000EX Rheometer sold commercially by TA Instruments of New Castle, DE, USA with a 20 mm Steel plate and measurements were taken at shear rate of 10 s.sup.−1, at a plate temperature of 50° C. The results are provided in Table 1 below.

TABLE-US-00001 TABLE 1 Accelerated aging study of Additive concentrates (Pa .Math. s) Storage Conditions Comp. 1 Comp. 2 Ex. 1 50° C. 0 days 47 52 36 50° C. 7 days 94 82 66 50° C. 14 days 107 83 80 50° C. 21 days 116 115 85 50° C. 28 days 133 119 97

[0143] It can be noted from the accelerated aging study above that the addition of trimethyl terminated polydimethylsiloxane (iii) to the iron oxide (i) and carrier fluid (ii) mixture in Ex. 1 resulted in a much slower increase in viscosity with aging than either Comp. 1 (no stabilizer) or Comp. 2 (known acid acceptor MgO added as stabilizer). This indicated that the carrier fluid is less prone to condensation in the presence of the acidic iron oxide when the trimethyl terminated polydimethylsiloxane is included in the formulation. Thus, the trimethyl terminated polydimethylsiloxane is shown to inhibit this condensation reaction (known to increase viscosity) and stabilize the solution to a greater degree.

This is considered to be an important effect as the condensation of the carrier fluid polymer not only increases viscosity and reduces processability but consequently will reduces the number of available crosslink sites during the cure of condensation curable organosiloxane compositions to their respective elastomers producing a softer (lower durometer) material. This has been further evaluated by the elastomer studies below.

Formulated Part A

[0144] Unaged samples of Comp. 1, Comp. 2 and Ex. 1 additive concentrates were then used in the preparation of respective two-part condensation curable organosiloxane compositions. The respective additive concentrate was mixed into a part A composition using the compositions indicated in Table 2a below.

Table 2a Part A composition of Comps. 3 and 4 and Ex. 2

TABLE-US-00002 Comp. 3 Comp. 4 Ex. 2 (Part A) (Part A) (Part A) Comp. 1 53.7 Comp. 2 53.7 Ex. 1 53.7 Tetrapropyloxysilane 2.7 2.7 2.7 Celite ® Super Floss ® E 22.5 22.5 22.5 Diatomaceous Earth having a median particle size of 12.2 μm (supplier information) dimethylsilanol terminated 20.6 20.6 20.6 polydimethylsiloxane having a viscosity of 2000 mPa .Math. s at 25° C. Liquid carrier (ii) described above 0.37 0.37 0.37

[0145] Celite® Super Floss® E Diatomaceous Earth is commercially available from World Materials Inc.

[0146] The same part B composition was used in each example and this is depicted in Table 2b below.

TABLE-US-00003 TABLE 2b Part B composition Composition Wt. % trimethyl terminated polydimethylsiloxane having a 76.2 viscosity of 30,000 mPa .Math. s at 25° C. dimethyltin dineodecanoate (DMTDN) 5.4 Precipitated treated Calcium Carbonate having a median 15.8 particle size of 1.9 μm benzotriazole in a 1:2 weight ratio mixture with trimethyl 1.1 terminated polydimethylsiloxane water 1.5

[0147] The part A compositions of comp. 3, comp. 4 and Ex. 2 respectively were mixed with the part B composition in a 10:1 parts by weight ratio in a speed mixer at 2400 rpm for 30 seconds. The resulting blend was then poured into a mold and allowed to cure for 48 hours at room temperature before test specimens were cut and measured.

[0148] Further part A samples were prepared and placed in an oven at 50° C. for 7 and 14 days respectively to simulate an accelerated aging protocol before being allowed to cool to room temperature. Once at room temperature they were mixed with the part B composition in the manner described above and cured in the same way. The resulting elastomers were tested for Hardness, tensile strength, Elongation and MDR (S′Max) for comp. 3, comp. 4 and Ex. 2 in Tables 2c, 2d and 2e respectively.

TABLE-US-00004 TABLE 2c Comp. 3 Elastomer Physical Property Results Tensile Durometer Strength (MPa) Elongation MDR (S′Max) 0 day 50° C. 41 2 140 4 7 day 50° C. 39 2 163 3 14 days 50° C. 34 2 157 3

TABLE-US-00005 TABLE 2d Comp. 4 Elastomer Physical Property Results Tensile Durometer Strength (MPa) Elongation MDR (S′Max) 0 day 50° C. 5 1 241 0 7 day 50 C N/A N/A N/A 0 N/A = Not measured due to end of experimentation

TABLE-US-00006 TABLE 2e Ex. 2 Elastomer Physical Property Results Tensile Durometer Strength (MPa) Elongation MDR (S′Max) 0 day 50° C. 46 2 121 4 7 day 50° C. 43 2 144 4 14 days 50° C. 43 2 136 4

[0149] The Durometer results were with respect to Shore A and were measured in accordance with ASTM C661-15. The tensile strength results were measured in accordance with ASTM D412-98a(2002)e1 using Die C. Moving die rheometer (MDR) (S′Max) results were measured using a Monsanto MDR 2000 moving die rheometer from Monsanto, first mixing the part A and part B compositions, adding the resulting mixture to the bottom plate at 248° C. for 14 minutes with the S′Max (maximum torque) value recorded when material cured.

[0150] The comparative additive concentrates of comp. 2 and comp. 4 using magnesium oxide (MgO) as stabilizer showed moderate retardation of viscosity growth, but when introduced into the condensation curable organosiloxane compositions caused incomplete cure leading to extremely soft elastomeric materials with durometer values as low as 5 and incomplete cured tacky sample plates.

[0151] Inventive Example 2 where the Part A contains an additive concentrate with 1% additional trimethyl terminated polydimethylsiloxane as stabilizer, exhibits sustained performance shown by maintained values for durometer, tensile strength, elongation and maximum torque as measured with a moving die rheometer.

[0152] Comparative example 3 which uses an additive concentrate with no stabilizer, shows a decrease in the critical values for durometer and maximum torque whilst showing an increase in elongation.

These results for elastomers made using the composition of Comparative Example 3, indicates that the cured elastomeric material did not cure properly due to, in our view, a reduced number of final crosslinks due to the pre-condensation of the dimethylsilanol terminated polydimethylsiloxane having a viscosity of 2000 mPa.Math.s at 25° C. contained in the formulation and the lack of a suitable stabilizer as described herein.