Storage stable curable liquid silicone composition

Abstract

A method for preparing a curable liquid silicone composition includes: (a) combining the following components to form a catalyst / inhibitor masterbatch: (i) a platinum hydrosilylation catalyst; (ii) a tetrahydrocarbylthiuram disulfide having a flow point of 50 DEG C or higher; and (iii) an aromatic silicone carrier; and (b) combining the catalyst / inhibitor masterbatch with a vinyl functional silicone and a silyl hydride functional silicone to form a curable composition.

Description

Technical Field

[0001] This invention relates to a curable organosilicon composition and its preparation method. Background Technology

[0002] Curable liquid silicone compositions can be used as secondary insulators for electric motors because they provide the desired level of electrical insulation and thermal protection. Curable liquid silicone compositions for such applications typically contain a silicone with vinyl (Vi) functional groups and a silicone crosslinker containing multiple silyl hydride (SiH) functional groups. Curable liquid silicone compositions also typically contain a hydrosilylation catalyst. The Vi and SiH groups undergo hydrosilylation to cure the composition. Hydrosilylation occurs more rapidly at elevated temperatures, but it can also occur at lower temperatures, which can lead to storage instability in curable liquid silicone compositions.

[0003] One method to increase the storage stability of curable liquid silicone compositions is to add inhibitors to prevent hydrosilylation curing at lower temperatures. For example, US4260726 describes adding an organic compound containing the [=NC(-S-)2-] subunit to a curable liquid silicone composition to reduce viscosity buildup when the curable composition ages at 80°C (indicating increased storage stability), while still achieving rapid curing reactivity at 175°C. However, the method in US4260726 still results in viscosity buildup of the composition at 80°C. It is desirable to determine a way to achieve storage stability of curable liquid silicone compositions that results in less viscosity buildup during storage than that achievable by the method disclosed in US4260726, while also achieving rapid initiation of curing at temperatures above 120°C. Summary of the Invention

[0004] This invention is partly a result of discovering a specific challenge in achieving storage stability of curable liquid silicone compositions containing inhibitors to prevent hydrosilylation curing at lower temperatures when the inhibitor has a flow point of 50°C or higher. When the inhibitor has a flow point of 50°C or higher, the inhibitor requires a longer time to dissociate into the composition, and hydrosilylation may occur, leading to viscosity buildup as it dissociates.

[0005] This invention provides a method for preparing a curable liquid silicone composition using an inhibitor with a flow point of 50°C or higher, wherein the curable liquid silicone composition exhibits enhanced storage stability, as demonstrated by less viscosity buildup during storage compared to compositions obtained by simply adding an inhibitor to a catalyst and a reactive silicone composition, as described in US426076. Tests of liquid silicone compositions prepared according to the method disclosed in US426076 have shown a viscosity increase of 40% or more when stored at 80°C for 150 hours. Liquid silicone compositions prepared according to the method of the invention experience a viscosity buildup of 20% or less, or even 10% or less, even when using an inhibitor with a flow point of 50°C or higher, when stored at 80°C for 150 hours. Furthermore, liquid silicone compositions prepared according to the method of the invention exhibit rapid curing, as indicated by the degree of exothermic reaction at 25°C or lower when using a heating rate of 20°C / min from 25°C to 300°C, and an exothermic onset temperature (curing start) above 120°C. Furthermore, the method of the present invention may contain less than 5% by weight, or even less than 2% by weight, or even less than 1% by weight of organic solvent, and may be completely free of organic solvent, such that the liquid organosilicon composition prepared according to the present invention has less than 5% by weight, less than 2% by weight, less than 1% by weight of organic solvent, or even free of organic solvent.

[0006] Surprisingly, this invention results from the discovery that by first adding a hydrosilylation catalyst and an inhibitor together to form a masterbatch, and then adding the masterbatch to a curable liquid silicone, the resulting curable silicone composition exhibits significantly better storage stability than curable silicone compositions formed by adding an inhibitor to a composition already containing a curable liquid silicone and a catalyst. Unbound by theory, it is possible that when mixed together to form a masterbatch, the inhibitor can dissociate and complex with the catalyst, without the catalyst initiating the hydrosilylation reaction upon inhibitor dissociation. Complexing the catalyst with the inhibitor prevents the catalyst from catalyzing the curing of the curable liquid silicone composition, while still allowing sufficient dissociation to exhibit rapid curing at temperatures above 120°C. In contrast, when the catalyst and an inhibitor with a flow point of 50°C or higher are added separately to a composition already containing both curable liquid silicone, curing and viscosity buildup can occur before the solid inhibitor can dissociate and complex with the catalyst.

[0007] In a first aspect, the present invention is a method for preparing a curable liquid silicone composition, the method comprising: (a) combining the following components to form a catalyst / inhibitor masterbatch: (i) a platinum hydride silanization catalyst; (ii) a tetrahydrothiuram disulfide having a flow point of 50°C or higher; and (iii) an aromatic silicone carrier fluid; and (b) combining the catalyst / inhibitor masterbatch with vinyl-functionalized silicones and silylhydride-functionalized silicones to form a curable composition.

[0008] This invention can be used to form curable organosilicon compositions with enhanced storage stability. Detailed Implementation

[0009] When a date is not indicated by a test method number, the test method refers to the most recent test method as of the priority date of this document. References to test methods include references to both the testing association and the test method number. The following test method abbreviations and designations apply to this document: ASTM refers to ASTM International Society Methods; END refers to European Standards; DIN refers to the German Institute for Standardization; ISO refers to the International Organization for Standardization; and UL refers to Underwriters Laboratories.

[0010] Products identified by their trade names refer to compositions available under those trade names as of the priority date of this document.

[0011] "Multiple" means two or more. "And / or" means "and, or as an alternative." Unless otherwise specified, all ranges include the endpoints.

[0012] "Organosilicon" refers to polysiloxanes, which are molecules containing multiple siloxane units. Siloxane units are typically identified using the abbreviations M, D, T, and Q. M-type siloxane units refer to those with the chemical formula R... a 3SiO 1 / 2 The unit. D-type siloxane units refer to those with the chemical formula R. a 2SiO 2 / 2 The unit. A T-type siloxane unit refers to a unit with the chemical formula R. a SiO 3 / 2 The Q-type siloxane unit refers to a unit with the chemical formula SiO. 4 / 2 The unit. In these general formulas, each R aEach time it appears, it is independently selected from hydrogen, a hydrocarbon group (substituted or unsubstituted), a hydroxyl group, an alkoxy group, or essentially any other group bonded to a silicon atom. O refers to an oxygen atom bonded to silicon, which is also bonded to a silicon atom in another siloxane unit. The subscript is a multiple of ½ to reflect the bonding of oxygen to this silicon atom and to another silicon atom in another siloxane unit, which also has a multiple of ½ in the denominator, with both siloxane units reflecting ½ ownership of the same oxygen atom. The number in the oxygen subscript reflects how much oxygen is bonded to the specified silicon atom, which is also bonded to a silicon atom in another siloxane unit. Typically, there is a subscript associated with the siloxane unit itself to indicate the relative amount of siloxane units in the molecule. If the subscript associated with the siloxane unit is greater than one, the subscript refers to the average number of those siloxane units in the molecule. If the subscript associated with the siloxane unit is less than one, the subscript refers to the average molar ratio of the siloxane unit associated with that subscript to the total number of moles of all siloxane units in the molecule. The subscript 1 is usually not specified, so if a siloxane unit does not include a subscript, it should be understood as having a subscript 1. The chemical formula of organosilicon is usually listed in blocks for siloxane units, but this does not necessarily mean block polymerization (i.e., siloxane units exist as blocks in the molecule), but rather it is presented in blocks for convenience to indicate how much of each siloxane unit is present in the polymer in total.

[0013] "Resin-like polysiloxanes" or "resins" contain 30 mol percent (mol%) or more, and may contain 50 mol percent or more, 70 mol percent or more, 90 mol percent or more, or even 100 mol percent of Q-type, T-type, or a combination of Q-type and T-type siloxane units. In contrast, "non-resin-like" organosilicones, which are often simply referred to as "polymers," "polymeric," or "linear" organosilicones, siloxanes, or polysiloxanes, contain less than 30 mol percent of a combination of Q-type and T-type siloxane units, and typically contain only M-type and D-type siloxane units.

[0014] The "hydrosilyl" functional group refers to a group with hydrogen atoms that are directly bonded to silicon atoms to form a SiH group.

[0015] "DSC exothermic rate" refers to the temperature range defined from the onset of exothermic reaction to the peak exothermic temperature. In other words, DSC exothermic rate is the value of (peak exothermic temperature) minus (exothermic onset temperature). DSC exothermic rate is a measure of how quickly a composition cures once curing begins, with shorter values ​​corresponding to faster curing.

[0016] "Solid" refers to a state of matter that is imperceptible to the naked eye and flows.

[0017] The "flow point" refers to the melting point of crystalline materials and the glass transition temperature of amorphous materials. If a material has both a melting point and a glass transition temperature, the flow point is the lower of the two. Essentially, the flow point is the temperature at which a solid (non-flowing) material transforms into a state where it can flow. The flow point of a material is determined using ASTM Method D3418 by differential scanning calorimetry (DSC).

[0018] This invention relates to a method for preparing a curable liquid silicone composition. "Cureable" means that the composition has components that can react with each other in an additive manner to form a crosslinked material. "Liquid" means that the composition is capable of flowing at 25°C and 101 kPa. As a "silicone composition," the composition comprises at least one silicone component.

[0019] The method comprises two steps: (a) combining the following components to form a catalyst / inhibitor masterbatch: (i) a platinum hydride silanization catalyst; (ii) a tetrahydrothiuram disulfide; and (iii) an aromatic organosilicon carrier; and (b) combining the catalyst / inhibitor masterbatch with vinyl-functional organosilicon and silyl hydride-functional organosilicon to form a curable composition.

[0020] The catalyst / inhibitor masterbatch comprises: (i) a platinum hydrosilylation catalyst; (ii) a tetraalkylthiuram disulfide having a flow point of 50 degrees Celsius (°C) or higher; and (iii) an aromatic organosilicon carrier fluid. The catalyst / inhibitor masterbatch is prepared by combining these three components. Other components may or may not be combined with these three components when forming the catalyst / inhibitor masterbatch. Within the widest scope of the invention, the components of the masterbatch can be combined in any order and in any manner. Particularly for smaller-scale preparations, it may be useful to first disperse the individual components in the aromatic organosilicon carrier fluid before mixing them together to promote homogeneous mixing of the components to form the masterbatch. For example, the inhibitor may be mixed with the aromatic organosilicon carrier fluid, and separately, the catalyst may be mixed with the aromatic organosilicon carrier fluid, and the two mixtures may subsequently be combined to form the masterbatch. Therefore, the catalyst / inhibitor masterbatch may contain or consist of the following or a combination of the following: (i) platinum hydrosilylation catalyst; (ii) tetradisulfide thiuram having a flow point of 50°C or higher; and (iii) aromatic organosilicon carrier fluid.

[0021] Platinum hydrosilylation catalysts can be any platinum-containing catalyst or any combination of more than one platinum-containing catalyst that can be used to catalyze hydrosilylation reactions. Platinum hydrosilylation catalysts include compounds and complexes such as platinum(O)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt catalyst), H2PtCl6, di-μ.-carbonyldi-π.-cyclopentadienyldinickel, platinum-carbonyl complexes, platinum-divinyltetramethyldisiloxane complexes, platinum cyclovinylmethylsiloxane complexes, platinum acetylacetonate (acac), platinum black, platinum compounds (such as chloroplatinic acid, chloroplatinic acid hexahydrate, the reaction product of chloroplatinic acid with a monohydric alcohol, bis(ethyl acetoacetate)platinum, bis(acetylacetonate)platinum, platinum dichloride), and platinum compounds complexed with olefins or low molecular weight polyorganosiloxanes, or platinum compounds microencapsulated in a matrix or core-shell structure.

[0022] Within the broadest scope of this invention, tetraalkylthiuram disulfide is any one or any combination of more than one component selected from the group consisting of tetraalkylthiuram disulfide and tetraarylthiuram disulfide, having a flow point of 50°C or higher, preferably 60°C or higher, and possibly 65°C or higher, while typically 200°C or lower, preferably 180°C or lower, more preferably 170°C or lower, and possibly 160°C or lower. Preferably, tetraalkylthiuram disulfide is any one or any combination of more than one component selected from the group consisting of: tetrabenzylthiuram disulfide (flow point 124°C, Sigma-Aldrich), tetramethylthiuram disulfide (flow point 156°C to 158°C, Sigma-Aldrich), tetraethylthiuram disulfide (flow point 69°C to 71°C, Sigma-Aldrich), tetra(isopropyl)thiuram disulfide (flow point 115°C to 117°C, Sigma-Aldrich), and tetra(isobutyl)thiuram disulfide (flow point 73.5°C to 74.5°C, ChemBK). Conversely, tetra(n-butyl)thiuram disulfide (flow point 33°C, Fisher Scientific) is outside the scope of the inhibitors of this invention.

[0023] The desired concentration of tetradisulfide thiuram is such that the molar ratio of tetradisulfide thiuram to platinum in the hydrosilylation catalyst is in the range of 0.9 to 3.

[0024] The composition comprises an aromatic organosilicon carrier fluid. Desiredly, the aromatic organosilicon fluid is a non-resin-based organosilicon having side aryl groups. Examples of two suitable aromatic organosilicon fluids for use as carrier fluids include those having chemical compositions (I) and (II), respectively:

[0025]

[0026]

[0027] Where "Vi" refers to a vinyl group; "Ph" refers to a phenyl group; the subscript m has a value of 5 or greater, and can be 10 or greater, 20 or greater, 25 or greater, 30 or greater, 40 or greater, 50 or greater, 75 or greater, 100 or greater, 150 or greater, 200 or greater, 250 or greater, 300 or greater, 350 or greater, 400 or greater, or even 450 or greater, while usually 500 or less, and can be 475 or less, 425 or less, 375 or less, 325 or less, 275 or less, 225 or less, 175 or less, 125 or less, 75 or less, 50 or less, 40 or less, or even 30 or less. And the subscript n has a value of 2 or greater, and can be 5 or greater, 10 or greater, 20 or greater, 25 or greater, 30 or greater, 40 or greater, 50 or greater, 75 or greater, 100 or greater, 150 or greater, 200 or greater, 250 or greater, 300 or greater, 350 or greater, 400 or greater, or even 450 or greater, while usually 500 or less, and can be 475 or less, 425 or less, 375 or less, 325 or less, 275 or less, 225 or less, 175 or less, 125 or less, 75 or less, 50 or less, 40 or less, 30 or less, 20 or less, 10 or less, or even 8 or less.

[0028] The vinyl-functional organosilicon and the silylhydride-functional organosilicon can be different organosilicon molecules, or they can be the same molecule having both functional groups. Ideally, both the vinyl-functional organosilicon and the silylhydride-functional organosilicon are organosilicon resins, or the same organosilicon resin having both functional groups. Ideally, the vinyl-functional organosilicon and the silylhydride-functional organosilicon are the same organosilicon resin having both functional groups. When the vinyl-functional organosilicon and the silylhydride-functional organosilicon are the same organosilicon, the composition may still contain additional vinyl-functional organosilicon and / or silylhydride-functional organosilicon. Alternatively, when the vinyl-functional organosilicon and the silylhydride-functional organosilicon are the same organosilicon, the composition may not contain additional vinyl-functional organosilicon and / or silylhydride-functional organosilicon.

[0029] Ideally, vinyl-functionalized organosilicon and silylhydride-functionalized organosilicon are the same organosilicon resin having chemical structure (III):

[0030]

[0031] Where “Ph” refers to a phenyl group, “Vi” refers to a vinyl group, and “Me” refers to a methyl group, the subscripts a, b, c, and d refer to the molar ratio of the associated siloxane unit to the total number of siloxane units in the molecule. Subscript a has a value of 0.3 or greater, and can be 0.4 or greater, 0.43 or greater, and is usually 0.7 or less, and can be 0.5 or less, or even 0.45 or less. Subscript b has a value of 0.05 or greater, and can be 0.10 or greater, 0.12 or greater, or even 0.14 or greater, and is usually 0.2 or less, and can be 0.15 or less. Subscript c usually has a value of 0.05 or greater, and can be 0.13 or greater, 0.14 or greater, 0.15 or greater, or even 0.16 or greater, and is usually 0.2 or less, and can be 0.18 or less, or even 0.17 or less. The subscript d typically has a value of 0.15 or greater, and can be 0.20 or greater, or even 0.25 or greater, while it is typically 0.35 or less and can be 0.30 or less, or even 0.26 or less.

[0032] The molar ratio of SiH functional groups to vinyl functional groups in the curable liquid silicone composition is advantageously 0.8 or greater, and can be 1.0 or greater, 1.1 or greater, 1.2 or greater, 1.3 or greater, 1.4 or greater, or even 1.5 or greater, while it is desirable to be 2 or less.

[0033] Ideally, the concentrations of the components combined in the method of the present invention are such that the curable composition comprises a combination of the following: a platinum hydrosilylation catalyst at a concentration sufficient to provide 0.2 to 50 parts by weight of platinum per million parts by weight of the curable liquid silicone composition; a tetrahydrothiuram disulfide at a concentration sufficient to provide a molar ratio of tetrahydrothiuram disulfide to platinum from the hydrosilylation catalyst in the range of 0.9 to 3; an aromatic silicone carrier concentration in the range of 0.5% to 10% by weight based on the weight of the curable liquid silicone composition; and a molar ratio of SiH functional groups to vinyl functional groups in the range of 0.8 to 2.

[0034] The curable liquid silicone compositions of the present invention exhibit rapid curing reactivity, as indicated by the exothermic rate at 25°C or lower in DSC when heating from 25°C to 300°C at a heating rate of 20°C / min. Curing can be initiated at temperatures of 200°C or higher, 175°C or higher, 150°C or higher, or even 120°C or higher. Curing typically has a peak temperature in DSC, while the exothermic rate at DSC is measured to be less than 275°C. The curable liquid silicone compositions exhibit stability at 80°C even after aging for 150 hours or more, as demonstrated by a viscosity increase of less than 20% after aging.

[0035] Example

[0036] Examples of preparation were made using the materials listed in Table 1.

[0037] Examples (Ex) 1 to 4

[0038] Ex 1 to 4 were prepared by first preparing a masterbatch of a Pt catalyst and an inhibitor in an aromatic organosilicon carrier fluid. Organosilicon resin was added to the masterbatch and blended together to produce a curable liquid organosilicon composition.

[0039] Ex 1

[0040] Step (1). Place 0.330 g of Pt catalyst (containing 25.4 wt% Pt metal) and 9.715 g of aromatic organosilicon carrier 1 into a 20 g volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for five minutes.

[0041] Step (2). Add 0.125g of inhibitor 1 and 19.92g of aromatic silicone carrier fluid 1 to a 40g volume dental mixer cup, and mix the components together at 3000RPM for five minutes using a planetary mixer.

[0042] Step (3). In a small cup, add 10.775g of the mixture of inhibitor 1 from step (2) and aromatic silicone carrier fluid 1, and 23.12g of aromatic silicone carrier fluid 1, and then use a planetary mixer to blend together at 3000RPM for five minutes.

[0043] Step (4). Add 6.142 g of the mixture from step (1) to the mixture from step (3) and blend at 3000 RPM for two minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0044] Step (5). Add 50.001g of bifunctional silicone resin and 1.01g of catalyst / inhibitor masterbatch from step (4) to a small cup, and then blend them together at 3000RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Example 1).

[0045] Ex 2

[0046] Step (1). Place 0.923g of Pt catalyst (containing 25.4% by weight of Pt metal) and 19.09g of aromatic organosilicon carrier 1 into a 40g volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for five minutes.

[0047] Step (2). Add 0.377g inhibitor 2 and 19.628g aromatic silicone carrier fluid 1 to a 40g volume dental mixer cup, and mix the components together at 3000RPM for five minutes using a planetary mixer.

[0048] Step (3). In a small cup, add 4.046g of the mixture of inhibitor 2 from step (2) and aromatic silicone carrier fluid 1, along with 31.986g of aromatic silicone carrier fluid 1, and then use a planetary mixer to blend together at 3000 RPM for five minutes.

[0049] Step (4). Add 4.028 g of the mixture from step (1) to the mixture from step (3) and blend at 3000 RPM for two minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0050] Step (5). Add 50.157g of bifunctional silicone resin and 1.012g of catalyst / inhibitor masterbatch from step (4) to a small cup, and then blend them together at 3000RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Example 2).

[0051] Ex 3

[0052] Step (1). Place 0.304 g of Pt catalyst (containing 25.4 wt% Pt metal) and 9.70 g of aromatic organosilicon carrier 2 into a 20 g volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for five minutes.

[0053] Step (2). Add 0.111g inhibitor 1 and 19.90g aromatic silicone carrier fluid 2 to a 40g volume dental mixer cup, and mix the components together at 3000RPM for five minutes using a planetary mixer.

[0054] Step (3). In a small cup, add 10.97g of the mixture of inhibitor 1 from step (2) and aromatic silicone carrier fluid 2, along with 23.31g of aromatic silicone carrier fluid 2, and then use a planetary mixer to blend together at 3000 RPM for five minutes.

[0055] Step (4). Add 6.137 g of the mixture from step (1) to the mixture from step (3) and blend at 3000 RPM for two minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0056] Step (5). Add 5.029 g of bifunctional silicone resin and 1.109 g of catalyst / inhibitor masterbatch from step (4) to a small cup, and then blend them together at 3000 RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Example 3).

[0057] Ex 4

[0058] Step (1). Place 0.214g of Pt catalyst (containing 25.4% by weight of Pt metal) and 10.948g of aromatic organosilicon carrier 1 into a 20g volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for five minutes.

[0059] Step (2). Add 0.110g of inhibitor 6 and 21.418g of aromatic silicone carrier fluid 1 to a 40g volume dental mixer cup, and mix the components together at 3000RPM for five minutes using a planetary mixer.

[0060] Step (3). In a small cup, add 17.798g of the mixture of inhibitor 6 from step (2) and aromatic silicone carrier fluid 1, along with 213.486g of aromatic silicone carrier fluid 1, and then use a planetary mixer to blend together at 3000 RPM for five minutes.

[0061] Step (4). Add 9.069 g of the mixture from step (1) to the mixture from step (3) and blend at 3000 RPM for two minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0062] Step (5). Add 60.001g of bifunctional silicone resin and 1.202g of catalyst / inhibitor masterbatch from step (4) to a 100g volume dental mixer cup, and then blend them together at 3000RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Example 4).

[0063] Comparative Examples (Comp Ex) A and B

[0064] Comp Ex A and B are prepared by combining a mixture of Pt catalyst and bifunctional silicone resin with a mixture of inhibitors (two different inhibitors, one for each Comp Ex) and bifunctional silicone resin to produce a curable liquid silicone composition. This procedure contrasts with Ex 1 through 4 by the absence of an aromatic silicone carrier and the use of blending the silicone resin with the catalyst other than the inhibitor, instead of forming a masterbatch of catalyst and inhibitor before exposing the catalyst or inhibitor to the silicone resin.

[0065] Comp Ex A

[0066] Step (1). Add 0.024g of Pt catalyst and 49.337g of bifunctional silicone resin to a small cup, and then use a planetary mixer to mix them at 3000RPM for five minutes.

[0067] Step (2). Add 0.0021g of inhibitor 1 and 46.606g of bifunctional silicone resin to the small cup and blend at 300RPM for five minutes using a planetary mixer.

[0068] Step (3). Add 10.883 g of bifunctional silicone resin to a small cup, and add 38.495 g of the mixture from step (2), followed by 10.66 g of the mixture from step (1). Use a planetary mixer to blend the components together at 3000 RPM for 5 minutes to form a curable liquid silicone composition (Comp Ex A).

[0069] Comp Ex B

[0070] Step (1). Add 0.024g of Pt catalyst and 49.337g of bifunctional silicone resin to a small cup, and then use a planetary mixer to mix them at 3000RPM for five minutes.

[0071] Step (2). Add 0.0093g of inhibitor 2 and 50.155g of bifunctional silicone resin to the small cup and blend at 300RPM for five minutes using a planetary mixer.

[0072] Step (3). Add 37.35 g of bifunctional silicone resin to the fraction and add 12.003 g of the mixture from step (2), followed by 10.73 g of the mixture from step (1). Use a planetary mixer to blend the components together at 3000 RPM for 5 minutes to form a curable liquid silicone composition (Comp Ex B).

[0073] Comp Ex C and D

[0074] Comp Ex C and D are prepared by combining a bifunctional silicone resin with a Pt catalyst in an aromatic silicone carrier fluid. Inhibitors (two different inhibitors, one for each Comp Ex) are then added and mixed to form a curable liquid silicone composition. This procedure contrasts with Ex 1 through 4 by: blending the silicone resin with the catalyst other than the inhibitor, and blending the silicone resin with the inhibitor, rather than forming a masterbatch of catalyst and inhibitor before exposing the catalyst or inhibitor to the silicone resin.

[0075] Comp Ex C

[0076] Step (1). Add 3.14g of Pt catalyst and 76.84g of aromatic organosilicon carrier 1 to a small cup, and then use a planetary mixer to blend at 3000RPM for five minutes to prepare a 1% solution of catalyst in aromatic organosilicon carrier.

[0077] Step (2). Add 49.885g of bifunctional silicone resin and 0.114g of the mixture from step (1) to a small cup, and then blend at 3000RPM for five minutes using a planetary mixer.

[0078] Step (3). Add 0.00171 g of inhibitor 1 to the mixture from step (2) and blend at 3000 RPM for 5 minutes using a planetary mixer to prepare a curable liquid silicone composition (Comp Ex C).

[0079] Comp Ex D

[0080] Step (1). Add 3.14g of Pt catalyst and 76.84g of aromatic organosilicon carrier 1 to a small cup, and then use a planetary mixer to blend at 3000RPM for five minutes to prepare a 1% solution of catalyst in aromatic organosilicon carrier.

[0081] Step (2). Add 49.852g of bifunctional silicone resin and 0.120g of the mixture from step (1) to a small cup, and then blend at 3000RPM for five minutes using a planetary mixer.

[0082] Step (3). Add 0.002 g of inhibitor 2 to the mixture from step (2) and blend at 3000 RPM for 5 minutes using a planetary mixer to prepare a curable liquid silicone composition (Comp Ex D).

[0083] Comp Ex E and F

[0084] CompEx E and F are prepared by combining a bifunctional silicone resin with a Pt catalyst in an organic carrier fluid. Inhibitors (two different inhibitors, one for each CompEx) are then added and mixed to form a curable liquid silicone composition. This procedure contrasts with Ex 1 through 4 by: blending the silicone resin with the catalyst other than the inhibitor, and blending the silicone resin with the inhibitor, rather than forming a masterbatch of catalyst and inhibitor before exposing the catalyst or inhibitor to the silicone resin.

[0085] Comp Ex E

[0086] Step (1). Add 1.57 g of Pt catalyst and 38.44 g of carrier fluid 3 to a small cup to prepare a 1% solution of the catalyst in toluene. Mix at 3000 RPM for five minutes using a planetary mixer.

[0087] Step (2). Add 49.748g of bifunctional silicone resin and 0.111g of the mixture from step (1) to the small cup. Mix at 3000RPM for five minutes using a planetary mixer.

[0088] Step (3). Add 0.175g of inhibitor 1 and 17.36g of carrier fluid 3 to a small cup and blend at 3000RPM for 2 minutes using a planetary mixer to form a mixture. Add 0.149g of this mixture to the mixture from step (2) and blend at 3000RPM for 5 minutes using a planetary mixer to prepare a curable liquid silicone composition (Comp Ex E).

[0089] Comp Ex F

[0090] Step (1). Add 1.57 g of Pt catalyst and 38.44 g of carrier fluid 3 to a small cup to prepare a 1% solution of the catalyst in toluene. Mix at 3000 RPM for five minutes using a planetary mixer.

[0091] Step (2). Add 49.748g of bifunctional silicone resin and 0.108g of the mixture from step (1) to the small cup. Mix at 3000RPM for five minutes using a planetary mixer.

[0092] Step (3). Add 0.216 g of inhibitor 2 and 17.44 g of carrier fluid 3 to a small cup and blend at 3000 RPM for 2 minutes using a planetary mixer to form a mixture. Add 0.151 g of this mixture to the mixture from step (2) and blend at 3000 RPM for 5 minutes using a planetary mixer to prepare a curable liquid silicone composition (Comp Ex F).

[0093] Comp Ex G and H

[0094] Comp Ex G and H are prepared using a mixing procedure similar to that of Ex 1 to 3 (the difference being the use of different inhibitors than those used in Ex 1 to 4). Comp Ex G and H illustrate the need for the use of a tetradisulfide thiuram inhibitor in the method of the present invention to achieve the desired rapid curing of the resulting curable liquid silicone composition.

[0095] Comp Ex G

[0096] Step (1). Place 0.959 g of Pt catalyst (containing 25.4 wt% Pt metal) and 19.193 g of aromatic organosilicon carrier 1 into a 40 g (g) volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for three minutes.

[0097] Step (2). Add 0.44g of inhibitor 3 and 9.829g of aromatic silicone carrier fluid 1 to a 40g volume dental mixer cup, and mix the components together at 3000RPM for five minutes using a planetary mixer.

[0098] Step (3). In a small cup, add 5.94g of the mixture of inhibitor 3 from step (2) and aromatic silicone carrier fluid 1, along with 3.137g of aromatic silicone carrier fluid 1, and then use a planetary mixer to blend together at 3000 RPM for five minutes.

[0099] Step (4). Add 0.979 g of the mixture from step (1) to the mixture from step (3) and blend at 3000 RPM for two minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0100] Step (5). Add 5.003 g of bifunctional silicone resin and 0.114 g of catalyst / inhibitor masterbatch from step (4) to a small cup, and then blend them together at 3000 RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Comparison G).

[0101] Comp Ex H

[0102] Step (1). Place 0.959 g of Pt catalyst (containing 25.4 wt% Pt metal) and 19.193 g of aromatic organosilicon carrier 1 into a 40 g volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for five minutes.

[0103] Step (2). Add 0.94g of the mixture from step (1), 0.516g of inhibitor 4, 0.522g of inhibitor 5, and 8.034g of aromatic organosilicon carrier fluid 1 to a 20g volume dental mixer cup, and mix the components together at 3000RPM for three minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0104] Step (3). Add 5.016 g of bifunctional silicone resin and 0.098 g of catalyst / inhibitor masterbatch from step (2) to a small cup, and then blend them together at 3000 RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Comparative H).

[0105] Comp Ex I and J

[0106] Comp Ex I was prepared using a mixing procedure similar to that of Ex 1 through 4 (the difference being the use of tetra(n-butyl)thiuram disulfide as the inhibitor). Comp Ex J was prepared using a mixing procedure similar to that of Comp Ex C and D. Comp Ex I and J demonstrate that when the inhibitor is liquid at temperatures below 50°C, storage stability is sufficient regardless of whether the curable composition is prepared using a masterbatch procedure. This illustrates that storage stability is a unique challenge when using inhibitors with a flow point of 50°C or higher in reactive silicone compositions.

[0107] Comp Ex I

[0108] Step (1). Place 0.923g of Pt catalyst (containing 25.4% by weight of Pt metal) and 19.09g of aromatic organosilicon carrier 1 into a 40g volume dental mixer cup, and then use a planetary mixer to mix the components together at 3000 rpm for five minutes.

[0109] Step (2). Add 0.261g of inhibitor 7 and 9.762g of aromatic silicone carrier fluid 1 to a 20g volume dental mixer cup, and mix the components together at 3000RPM for five minutes using a planetary mixer.

[0110] Step (3). In a small cup, add 4.00g of the mixture of inhibitor 7 from step (2) and aromatic silicone carrier fluid 1, along with 32.006g of aromatic silicone carrier fluid 1, and then use a planetary mixer to blend together at 3000RPM for five minutes.

[0111] Step (4). Add 4.054 g of the mixture from step (1) to the mixture from step (3) and blend at 3000 RPM for two minutes using a planetary mixer to form a catalyst / inhibitor masterbatch.

[0112] Step (5). Add 50.095g of bifunctional silicone resin and 1.011g of catalyst / inhibitor masterbatch from step (4) to a small cup, and then blend them together at 3000RPM for two minutes using a planetary mixer to produce a curable liquid silicone composition (Comparative Example I).

[0113] Comp Ex J

[0114] Step (1). Add 3.14g of Pt catalyst and 76.848g of aromatic organosilicon carrier 1 to a small cup, and then use a planetary mixer to blend at 3000RPM for five minutes to prepare a 1% solution of catalyst in aromatic organosilicon carrier.

[0115] Step (2). Add 49.887g of bifunctional silicone resin and 0.110g of the mixture from step (1) to a small cup, and then blend at 3000RPM for five minutes using a planetary mixer.

[0116] Step (3). Add 0.002 g of inhibitor 7 to the mixture from step (2) and blend at 3000 RPM for 5 minutes using a planetary mixer to prepare a curable liquid silicone composition (Comp Ex J).

[0117] Sample characterization

[0118] The storage stability and rapid curing of each sample in the curable liquid silicone composition were characterized. The test methods are as follows, and the results are shown in Table 2.

[0119] Storage stability

[0120] Storage stability was characterized by measuring the increase in viscosity during sample aging. The goal was to achieve a viscosity increase of less than 20% after aging at 80°C for 150 hours. The viscosity of the samples was measured using a Brookfield DV3T cone / plate (CP40) viscometer, with a Haake K20 / DC3 water circulating bath maintaining the sample temperature at 25°C. The initial viscosity was measured immediately after sample preparation. The samples were then aged, and the viscosity of the aged samples was measured. Unless otherwise specified, the samples were aged in an oven at 80°C for 150 hours.

[0121] Rapid curing test

[0122] The curing rate of the samples was assessed using differential scanning calorimetry (DSC). A TA Q2000 DSC instrument with a liquid nitrogen cooling system was used. A 10 mg sample was used in a perforated DSC disk. DSC scans were collected at sampling intervals of one second per point. The sample was first equilibrated at -100 °C and then heated to 300 °C at a rate of 20 °C / min. The initial exothermic temperature (exothermic onset temperature) and the achieved peak temperature (peak exothermic temperature) were noted. If the difference between the onset temperature and the peak exothermic temperature (i.e., the DSC exothermic rate) was less than 25 °C, the sample was considered to have undergone “rapid curing.” If the temperature difference (DSC exothermic rate) was greater than 25 °C, the sample was not considered to have undergone “rapid curing.” In other words, if curing lasted 25 minutes or longer (with a temperature ramp of one degree per minute), curing was not considered “rapid curing.”

[0123] result

[0124] Comparison of results from Ex 1 to 4 with those from Comp Ex A to F reveals that premixing the inhibitor and catalyst to form a masterbatch before exposing the reactive silicone to the catalyst produces a significantly more stable reactive composition compared to procedures where the catalyst is combined with the reactive resin without premixing with the inhibitor. This is evidenced by a viscosity increase of less than 20% after aging at 80°C for 150 hours. Unbound by theory, it is believed that the catalyst and inhibitor form a stable complex when premixed together, and that this complex inhibits the catalyst-driven reaction of the reactive silicone. However, when heated above 200°C, the complex appears to release the catalyst to trigger rapid curing.

[0125] The benefits of the method steps of this invention are not apparent for any inhibitor, but only for the tetradisulfide thiuram inhibitor. A comparison of the DSC results of Ex 1 to 4 with the DSC results of Comp Ex G and H reveals that using different types of inhibitors does not result in rapid curing of the obtained curable liquid silicone composition.

[0126]

Claims

1. A method for making a curable liquid silicone composition, the method comprising: (a) combining to form a catalyst / inhibitor masterbatch: (i) a platinum hydrosilylation catalyst; (ii) a tetrahydrocarbyl thiuram disulfide having a flow point of 50 degrees Celsius and higher; and (iii) an aromatic silicone fluid; and (b) combining the catalyst / inhibitor masterbatch with a vinyl-functional silicone and a silyl hydride-functional silicone to form a curable composition.

2. The method of claim 1, wherein the tetrahydrocarbyl thiuram disulfide is selected from the group consisting of tetrabenzyl thiuram disulfide, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetraisopropyl thiuram disulfide, and tetraisobutyl thiuram disulfide.

3. The method of any preceding claim, wherein the platinum hydrosilylation catalyst is Karstedt’s catalyst.

4. The method of any preceding claim, wherein the molar ratio of tetrahydrocarbyl thiuram disulfide to platinum in the hydrosilylation catalyst is in the range of 0.9 to 3.

5. The method of any preceding claim, wherein the aromatic silicone fluid is any one material or a combination of more than one material having chemical composition (I) or (II): wherein “Vi” refers to a vinyl group; “Ph” refers to a phenyl group; subscript m has a value of 5 or greater while being 500 or less; and subscript n has a value of 2 or greater while being 500 or less. [(CH3)2ViSiO 1 / 2 ]2[(CH3)PhSiO 2 / 2 ] m (I) [(CH3)2(OH)SiO 1 / 2 ]2[(CH3)PhSiO 2 / 2 ] n (II) 6. The method of any preceding claim, wherein the vinyl-functional silicone and the silyl hydride-functional silicone are silicone resins.

7. The method of any preceding claim, wherein the vinyl-functional silicone and the silyl hydride-functional silicone are the same silicone containing both vinyl-functional groups and silyl hydride-functional groups.

9. The method of any preceding claim, wherein the concentration of the platinum hydrosilylation catalyst is in the range of 0.2 parts by weight to 50 parts by weight per million parts by weight of the curable liquid silicone composition, the concentration of the tetrahydrocarbyl thiuram disulfide is sufficient to achieve a molar ratio of tetrahydrocarbyl thiuram disulfide to platinum from the hydrosilylation catalyst in the range of 0.9 to 3, the concentration of the aromatic silicone fluid is up to 10% by weight of the curable liquid silicone composition, and the molar ratio of SiH-functional groups to vinyl-functional groups is in the range of 0.8 to 2.

8. The method of any preceding claim, wherein the vinyl-functional silicone has the chemical formula: (PhSiO 3 / 2 ) a (ViMeSiO 2 / 2 ) b (HMeSiO 2 / 2 ) c [(Me)3SiO 1 / 2 ] d ; wherein Ph refers to a phenyl group, Vi refers to a vinyl group, Me refers to a methyl group, the subscripts a, b, c, and d refer to the molar ratio of the associated siloxane unit relative to the moles of all siloxane units in the molecule, and the subscript a is in the range of 0.3 to 0.7, the subscript b is in the range of 0.05 to 0.2, the subscript c is in the range of 0.05 to 0.2, and the subscript d is in the range of 0.15 to 0.

35. ​

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