Rapid low-temperature curing moldable silicone composition

Abstract

The two-part curable silicone composition contains, as separate parts, (a) a first part having an alkenyl-functional prepolymer that is a hydrosilylation reaction product of a first part premix containing a platinum hydrosilylation catalyst, an alkenyl-functional linear polyorganosiloxane, an alkenyl-functional resinous polyorganosiloxane, and a linear SiH-functional chain extender, and (b) a second part having a linear alkenyl-functional polyorganosiloxane, a resinous alkenyl-functional polyorganosiloxane, a resinous SiH-functional polyorganosiloxane crosslinker, and a hydrosilylation cure inhibitor, wherein the alkenyl-functional component and the SiH-functional component are present in the two-part curable silicone composition such that the SiH / C=C ratio is 1.4 or less, and the composition contains 6 parts per million or less by weight of platinum and 0.01 weight percent or more of a hydrosilylation cure inhibitor, in concentrations based on the combined weight of the first part and the second part.

Description

[Technical field]

[0001] The present invention relates to a two-part curable moldable silicone composition. [Background technology]

[0002] Introduction Optically moldable silicone compositions are useful, for example, in the manufacture of automobile headlamps. However, optically moldable silicone compositions typically need to be cured at temperatures ranging from 150 degrees Celsius (°C) or higher. It is desirable to identify optically moldable silicone compositions that can be cured at temperatures of 110°C or lower so that other polymers, such as polycarbonates, can be used in co-molding processes without the need to heat them above their melting points. In particular, it is desirable to achieve a "rapid" cure at temperatures of 110°C or lower, where "rapid" and related terms with respect to cure refer to a rate of 1 deciNewton in a moving die rheometer test (defined herein below) in 60 seconds or less. * Meter (deciNewton * It is defined as achieving a viscosity of at least 1.0 MPa (dNm).

[0003] The optical moldable silicone composition can be a hydrosilylation curable composition. The hydrosilylation reaction can be cured at a temperature of 110°C or less by increasing the curing time, but this does not meet the requirement of rapid curing.

[0004] Other approaches to shorten the cure time of hydrosilylation reaction are to increase the platinum catalyst concentration, decrease the inhibitor concentration, or increase the silicon hydride (SiH) crosslinker concentration. However, using platinum catalyst at a concentration of more than 6 parts per million (ppm) by weight of the composition tends to cause the resulting reaction product to undesirably yellow over time. Decreasing the inhibitor concentration to less than 0.01 weight percent (wt%) by weight of the composition reduces the pot life or working time of the composition and can undesirably cause premature curing during the injection molding process. Increasing the molar concentration of silyl hydride groups (SiH) relative to the molar concentration of alkenyl groups directly or indirectly bonded to silicone (C=C) to a molar ratio (SiH / C=C ratio) of more than about 1.6 can result in an optically moldable silicone composition that undesirably becomes brittle over time.

[0005] Therefore, it would be desirable to identify a moldable silicone composition that can be rapidly cured by hydrosilylation at temperatures up to 110° C. without the need for more than 6 ppm platinum based on the weight of the composition or less than 0.01 wt % inhibitors based on the weight of the composition, and that has a SiH / C═C ratio of less than 1.6, which would advance the art of optically moldable silicone formulations. Summary of the Invention

[0006] The present invention provides a moldable silicone composition that can be rapidly cured by hydrosilylation at temperatures up to 110° C. without the need for more than 6 ppm platinum based on the weight of the composition or less than 0.01% by weight inhibitors based on the weight of the composition, and has a SiH / C═C ratio of less than 1.6.

[0007] The present invention provides a two-part curable composition comprising a first part and a second part, (a) a first portion is an alkenyl-functional prepolymer composition prepared by the hydrosilylation reaction of an alkenyl-functional linear and an alkenyl-functional resinous polyorganosiloxane with a linear silicon hydride (SiH)-functional chain extender; (b) The second part is the result of the discovery that the desired properties can be achieved using a two-part curable composition comprising resinous and linear alkenyl-functional polyorganosiloxanes, a resinous SiH-functional polyorganosiloxane crosslinker, and a hydrosilylation cure inhibitor.

[0008] Part of the discovery of this invention was the discovery of the requirements for the first part of the two-part composition, particularly the characteristics relating to the alkenyl-functional prepolymer. For example, if the SiH-functional chain extender has a degree of polymerization (DP) of less than 100, the concentration of the chain extender when forming the prepolymer must be less than 5 weight percent based on the combined weight of the first and second parts, otherwise the viscosity of the first part will be too high (50,000 millipascals or less). * The second part cannot be mixed with the HMeSiO 2 / 2 It has been found that the second part should be free of linear polyorganosiloxanes having SiH functionality as the only siloxane unit, as such linear polyorganosiloxanes slow down the cure during the first 60 seconds.

[0009] In a first aspect, the invention provides a process for the preparation of a polymerizable composition comprising, as separate parts, (a) a first part comprising an alkenyl-functional prepolymer that is the hydrosilylation reaction product of a first part premix comprising: (i) a platinum hydrosilylation catalyst; (ii) an alkenyl-functional linear polyorganosiloxane; (iii) an alkenyl-functional resinous polyorganosiloxane; and (iv) a linear SiH-functional chain extender having an average of two SiH groups per molecule, the linear SiH-functional chain extender being present in a concentration, by weight percent based on the combined weight of the first and second parts, of greater than or equal to 0.25 weight percent and less than or equal to 5 weight percent for DPs of 100 or greater, and less than 5 weight percent for DPs of less than 100; (b) a second part comprising: (i) a linear alkenyl-functional polyorganosiloxane, (ii) a resinous alkenyl-functional polyorganosiloxane, (iii) a resinous SiH-functional polyorganosiloxane crosslinker, and (iv) a hydrosilylation cure inhibitor, wherein the alkenyl-functional component and the SiH-functional component are present in the two-part curable silicone composition such that the two-part curable silicone composition has a SiH / C=C ratio of 1.4 or less, and the composition contains 6 parts per million or less by weight of platinum and 0.01 weight percent or more of a hydrosilylation cure inhibitor, in a concentration based on the combined weight of the first part and the second part.

[0010] The compositions of the present invention are useful as moldable silicone formulations that can be used as optically moldable silicone formulations. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Test methods refer to the test method most recent to the priority date of this document unless a date is given with the test method number. Reference to a test method includes both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International Method, END refers to European Norm, DIN refers to Deutsches Institut fur Normung, ISO refers to the International Organization for Standards, and UL refers to the Underwriters Laboratory.

[0012] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0013] "Plurality" means two or more. "And / or" means "and, or in the alternative." All ranges are inclusive of the endpoints unless otherwise indicated.

[0014] It is common to define the chemical composition of a polysiloxane by identifying the siloxane units in the polysiloxane. There are four siloxane units used to form the silicone, namely, R a 3SiO 1 / 2 ("M-type" siloxane units), R a 2SiO 2 / 2 ("D-type" siloxane units), R a SiO 3 / 2 ("T-type" siloxane units), and SiO 4 / 2 ("Q" siloxane units). In these common names, R amay independently at each occurrence be hydrogen, a hydrocarbyl group (substituted or unsubstituted), hydroxyl, alkoxyl, or essentially any other group bonded to a silicon atom. O refers to an oxygen atom bonded to a silicon atom of another siloxane unit. The subscript is a multiple of 1 / 2 to reflect that the oxygen is bonded to this silicon atom and also to another silicon atom of another siloxane unit that also has a multiple of 1 / 2 in the denominator, both siloxane units reflecting 1 / 2 ownership of the same oxygen atom. The number in the oxygen subscript reflects the number of oxygens bonded to a particular silicon atom that is also bonded to a silicon atom of another siloxane unit. Typically, there is a subscript attached to the siloxane unit itself to indicate the relative amount of siloxane units in the molecule. If the subscript attached to the siloxane unit is greater than 1, the subscript refers to the average number of those siloxane units in the molecule. When the subscript associated with a siloxane unit is less than 1, the subscript refers to the average molar ratio of all siloxane units that correspond to the associated siloxane unit. The subscript 1 is typically not recited, so if a siloxane unit does not contain a subscript, it is understood to have a subscript 1. Note that although the siloxane units are present in blocks, this does not necessarily imply block polymerization, but rather is presented in blocks for convenience to indicate how many of each siloxane unit are present in the polymer in total.

[0015] In siloxane terminology, as used herein, the terms "resin" or "resinous" are used to describe siloxanes having a material level of siloxane unit branching characterized as having an average of greater than three siloxane units selected from T-type, Q-type, or combinations of T-type and Q-type siloxane units in a single molecule. In contrast, "linear" siloxanes contain an average of no more than three, preferably no more than two, more preferably no more than one, and may contain zero or more of T-type, Q-type, or combinations of T-type and Q-type siloxane units in a single molecule.

[0016] "Degree of polymerization" or "DP" refers to the average number of repeating siloxane units in a siloxane molecule. For example, in the following molecule, the DP would be equal to the value of the subscript d: ViMeSiO-[MeSiO] d -SiMeVi. Silicon-29 Nuclear Magnetic Resonance ( 29 DP is determined by Si NMR spectroscopy.

[0017] The weight average molecular weight of the resinous siloxanes is determined by gel permeation chromatography using light scattering, refractive index, and viscometric detectors with polystyrene standards.

[0018] "SiH / C=C ratio" or "SiH / C=C" is the molar ratio of silylhydride hydrogen atoms to alkenyl groups (preferably terminal alkenyl groups) that are directly or indirectly bonded to silicon atoms. The alkenyl groups are preferably vinyl groups, in which case this ratio is often specified as the SiH / SiVi ratio. Proton nuclear magnetic resonance ( 1 The SiH / C=C ratio is determined by H NMR spectroscopy. Analytical samples are prepared in deuterated chloroform by combining a known amount of sample with a known amount of internal standard (1,4-dioxane). Spectra are collected using an Aligent 400-MR NMR instrument equipped with a 5 millimeter ONeNMR probe. Data are analyzed using MesReNova x64 software. Weight percentages of alkenyl (C=C) and SiH groups are calculated by integrating the relevant proton resonances against those of the internal standard.

[0019] The present invention is a two-part curable silicone composition comprising separate first and second parts. The two-part curable silicone composition comprises an alkenyl-functional component in the first part and a silylhydride (SiH)-functional component in the second part. When the first and second parts are mixed together, the alkenyl and SiH functional groups in the two parts react to cure the silicone composition. The first and second parts of the two-part curable silicone composition remain separate from each other until it is desired to cure the two-part silicone composition, which is what is meant by "separating the first and second parts."

[0020] The first part comprises an alkenyl-functional prepolymer component that is the hydrosilylation reaction product of a first part premix comprising a platinum hydrosilylation catalyst, an alkenyl-functional linear polyorganosiloxane, an alkenyl-functional resinous polyorganosiloxane, and a linear SiH-functional chain extender.

[0021] The catalyst is a platinum hydrosilylation catalyst. Examples of the platinum hydrosilylation catalyst include compounds and complexes such as platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Karstedt catalyst), HPtCl, 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, reaction products of chloroplatinic acid and monohydric alcohols, platinum bis(ethylacetoacetate), platinum bis(acetylacetonate), platinum dichloride, and complexes of platinum compounds with olefins or low molecular weight polyorganosiloxanes, or platinum compounds microencapsulated in a matrix or core-shell structure. The platinum catalyst may be part of a solution containing complexes of platinum with low molecular weight polyorganosiloxanes, including platinum complexes of 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane. These complexes may be microencapsulated in a resin matrix. The platinum catalyst may be platinum complexes of 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane.

[0022] Desirably, the platinum catalyst is present in a concentration low enough to provide no more than 6 parts per million (ppm) by weight of platinum based on the combined weight of the first and second portions. Typically, the concentration of platinum from the platinum catalyst is 2 ppm or more, and may be 3 ppm or more, 4 ppm or more, or even 5 ppm or more.

[0023] The alkenyl-functional linear polyorganosiloxane desirably contains an average of two or more alkenyl groups per molecule. Desirably, the alkenyl-functional linear polyorganosiloxane contains two or more terminal alkenyl groups, which are bonded to silicon atoms at the ends of the linear siloxane molecule. Preferably, there is at least one alkenyl group at each end of the alkenyl-functional linear polyorganosiloxane. The alkenyl groups themselves are desirably terminal alkenyl groups, i.e., there is a carbon-carbon double bond (C=C) between the two carbon atoms furthest from where the alkene is bonded to the silicon atom. Each alkene may have 2 or more, 3 or more, 4 or more, 5 or more, or even 6 or more carbon atoms, while typically containing 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, or even 3 or less carbon atoms. Desirably, each alkene is a vinyl group ("Vi").

[0024] The alkenyl-functional linear polyorganosiloxane may have an average chemical composition (I): [ViMe2SiO 1 / 2 ]2[Me2SiO 2 / 2 ] d (I) (where Vi refers to a vinyl group, Me refers to a methyl group, and the subscript d indicates the (CH3)2SiO 2 / 2 The average number of units may be 300 or more, 350 or more, 400 or more, or even 450 or more, while typically having values ​​of 700 or less, 650 or less, 600 or less, or even 550 or less.

[0025] The concentration of the alkenyl-functional linear polyorganosiloxane in the first part premix is ​​typically 40 weight percent (wt%) or more, 45 wt% or more, 50 wt% or more, or even 55 wt% or more, based on the combined weight of the alkenyl-functional linear polyorganosiloxane and the alkenyl-functional resinous polyorganosiloxane in the first part premix, while at the same time typically is 60 wt% or less, 55 wt% or less, 50 wt% or less, or even 45 wt% or less.

[0026] The alkenyl-functional resinous polyorganosiloxane is a polyorganosiloxane resin, i.e., RSiO 3 / 2 and SiO 4 / 2 The alkenyl-functional resinous polyorganosiloxanes are branched molecules containing an average of more than three siloxane units per molecule, selected from siloxane groups, where R is a hydrocarbyl group that typically contains 8 carbon atoms or less, and may contain 7, 6, 5, 4, 3, or even 2 carbon atoms, but may also contain 1 or more carbon atoms. Desirably, the alkenyl-functional resinous polyorganosiloxanes contain an average of 2 or more alkenyl groups per molecule, and may contain 3 or more alkenyl groups per molecule. The alkenyl group itself is desirably the terminal alkenyl group of the alkene bonded to the silicon atom, i.e., there is a carbon-carbon double bond (C=C) between the two carbon atoms furthest from where the alkene is bonded to the silicon atom. Each alkene can have 2 or more, 3 or more, 4 or more, 5 or more, or even 6 or more carbon atoms, while typically containing no more than 8, no more than 7, no more than 6, no more than 5, no more than 4, or even no more than 3 carbon atoms. Desirably, each alkene is a vinyl group.

[0027] The alkenyl-functional resinous polyorganosiloxane may have the average chemical formula (II): [ViMe2SiO 1 / 2 ] m’ [MeSiO 1 / 2 ] m [SiO 4 / 2 ] q [HO 1 / 2 ] n (II) (wherein Vi refers to a vinyl group, Me refers to a methyl group, the subscripts refer to the average molar ratio of the linking group to all listed groups, m' has a value in the range of 0.05 to 0.10, m has a value in the range of 0.40 to 0.50, q has a value in the range of 0.40 to 0.50, and n has a value in the range of 0.00 to 0.05).

[0028] The concentration of the alkenyl-functional linear polyorganosiloxane in the first part premix is ​​typically 40 weight percent (wt%) or more, 45 wt% or more, 50 wt% or more, or even 55 wt% or more, based on the combined weight of the alkenyl-functional linear polyorganosiloxane and the alkenyl-functional resinous polyorganosiloxane in the first part premix, while at the same time typically is 60 wt% or less, 55 wt% or less, 50 wt% or less, or even 45 wt% or less.

[0029] Desirably, the alkenyl-functional resinous polyorganosiloxane in the first portion has a weight average molecular weight of 3000 Daltons (Da) or more, 3100 Da or more, 3200 Da or more, 3300 Da or more, 3400 Da or more, 3500 Da or more, 3600 Da or more, 3700 Da or more, 3800 Da or more, or even 3900 Da or more, but at the same time, typically is 4000 Da or less, and can be 3900 Da or less, 3800 Da or less, 3700 Da or less, 3600 Da or less, 3500 Da or less, 3400 Da or less, 3300 Da or less, 3200 Da or less, or even 3100 Da or less.

[0030] The linear SiH functional chain extender is a polyorganosiloxane having an average of two SiH groups per molecule. The SiH functional chain extender may have the average chemical formula (III): [Me3SiO 1 / 2 ] m’ [HMe2SiO 1 / 2 ] m’’ [MeSiO 2 / 2 ] d’ [MeHSiO 2 / 2 ] d’’ (III) in which Me refers to a methyl group, the subscript indicates the average number of bound siloxane units in each molecule, subscript d' has an average value ranging from 5 to 200 and can be 5 or more, 10 or more, 20 or more, 25 or more, 50 or more, 75 or more, 100 or more, or even 150 or more, but also having a value of 200 or less, 175 or less, 150 or less, 125 or less, 100 or less, 75 or less, 50 or less, or even 25 or less, and subscript d'' is 0 or 1, with the proviso that the sum of m' and m'' is 2 and the sum of m' and d'' is 2 such that the molecules have an average of 2 silyl hydride groups.

[0031] The concentration of the SiH-functional chain extender in the premix of the first part is 0.25% by weight or more, and can be 0.5% by weight or more, 1.0% by weight or more, 1.5% by weight or more, 2.0% by weight or more, 2.5% by weight or more, 3.0% by weight or more, 3.5% by weight or more, 4.0% by weight or more, or even 4.5% by weight or more, based on the total weight of the first and second parts, but at the same time has an upper concentration limit depending on the degree of polymerization (DP) of the SiH-functional chain extender. When the DP is 100 or more, the upper concentration limit is 5.0% by weight or less, and can be 4.5% by weight or less, 4.0% by weight or less, 3.5% by weight or less, 3.0% by weight or less, or even 2.5% by weight or less. When the DP is less than 100, the upper limit is less than 5.0% by weight, preferably 4.5% by weight or less, 4.0% by weight or less, 3.5% by weight or less, 3.0% by weight or less, or even 2.5% by weight or less. Lower concentrations of chain extenders with lower DP are required because if the chain extender is short, the resulting prepolymer will have less mobility or flexibility, and if the chain extender concentration is too high, the viscosity may become too high in the first part.

[0032] The first part is prepared by combining the components of the first part prepolymer, mixing them together, and then reacting them to form a prepolymer by a hydrosilylation reaction between the SiH groups of the SiH functional chain extender and the alkenyl groups of the alkenyl functional linear polyorganosiloxane and / or alkenyl functional resinous polyorganosiloxane. The hydrosilylation reaction can occur at 25 degrees Celsius (°C) by allowing the premix to solidify for at least 24 hours. Alternatively, the hydrosilylation reaction can occur at a temperature above 25°C, which can require less than 24 hours. Desirably, essentially all of the SiH groups of the chain extender are reacted, but the alkenyl groups are present in excess relative to the SiH groups such that a prepolymer with residual alkenyl groups is produced. It is also expected that unreacted alkenyl-functional linear polyorganosiloxanes and / or unreacted alkenyl-functional resinous polyorganosiloxanes will be present in the first portion as well as the alkenyl-functional prepolymer.

[0033] The second part of the two-part curable silicone composition comprises a linear alkenyl-functional polyorganosiloxane, a resinous alkenyl-functional polyorganosiloxane, a resinous SiH-functional polyorganosiloxane crosslinker, and a hydrosilylation cure inhibitor. The second part desirably comprises HMeSiO 2 / 2 It does not include linear polyorganosiloxanes that have SiH functionality only on the siloxane units.

[0034] The linear alkenyl-functional polyorganosiloxane in the second part is selected from those described for the first part and may be the same or different from the linear alkenyl-functional polyorganosiloxane in the first part. The concentration of the alkenyl-functional linear polyorganosiloxane in the second part is typically 40% by weight or more, 45% by weight or more, 50% by weight or more, or even 55% by weight or more, relative to the weight of the second part, but at the same time is typically 60% by weight or less, 55% by weight or less, 50% by weight or less, or even 45% by weight or less.

[0035] The resinous alkenyl-functional polyorganosiloxane in the second portion is selected from those described for the first portion and may be the same or different from the resinous alkenyl-functional polyorganosiloxane in the first portion. The concentration of the alkenyl-functional resinous polyorganosiloxane in the second portion is typically 40 weight percent (wt%) or more, 45 wt% or more, 50 wt% or more, or even 55 wt% or more, based on the total weight of the alkenyl-functional linear polyorganosiloxane and the alkenyl-functional resinous polyorganosiloxane in the second portion, but at the same time is typically 60 wt% or less, 55 wt% or less, 50 wt% or less, or even 45 wt% or less.

[0036] The resinous SiH functional polyorganosiloxane crosslinker in the second portion is desirably selected from one or more having the average chemical formula (IV): (HMeSiO 1 / 2 ) a (MeSiO 2 / 2 ) b (SiO 4 / 2 ) c (HO 1 / 2 ) d (IV) (In the formula, Me refers to a methyl group; the subscripts indicate the average molar ratio of bonded siloxane units in the molecule, and the sum of the subscripts a, b, c, and d preferably total 1.00; The subscript a typically has an average value of 0.01 or more, 0.02 or more, 0.03 or more, or even 0.04 or more, but at the same time is typically 0.05 or less, and can be 0.04 or less, 0.03 or less, or even 0.02 or less; The subscript b typically has an average value of greater than or equal to 0.50, or even greater than or equal to 0.60, and typically has an average value of less than or equal to 0.70, or even less than or equal to 0.60; The subscript c typically has an average value of 0.20 or more, and even 0.30 or more, while typically being 0.40 or less, and can be 0.30 or less; The subscript d has an average value of 0.00 or greater, and can be 0.01 or greater, 0.02 or greater, 0.03 or greater, or even 0.04 or greater, but at the same time is typically 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or even 0.01 or less.

[0037] The concentration of the resinous SiH functional crosslinker in the second part is sufficient such that the molar ratio of SiH functional groups to alkenyl groups (C=C groups) (SiH / C=C ratio), in a combination of equal parts by weight of the first and second parts, is 1.4 or less, and can be 1.3 or less, 1.26 or less, or even 1.2 or less, while at the same time desirably being 1.0 or more, 1.1 or more, preferably 1.2 or more, and can be 1.3 or more.

[0038] The concentration of the resinous SiH-functional crosslinker in the second portion can be, for example, 8 wt.% or more, 9 wt.% or more, 10 wt.% or more, 11 wt.% or more, 12 wt.% or more, 13 wt.% or more, 14 wt.% or more, or even 15 wt.% or more, while at the same time being 18 wt.% or less, 17 wt.% or less, 16 wt.% or less, 15 wt.% or less, 14 wt.% or less, 13 wt.% or less, 12 wt.% or less, 11 wt.% or less, or even 10 wt.% or less, based on the weight of the second portion.

[0039] The weight average molecular weight of the resinous SiH functional polyorganosiloxane crosslinker in the second portion is typically 75 Daltons (Da) or more, 100 Da or more, 150 Da or more, 200 Da or more, 250 Da or more, 300 Da or more, 400 Da or more, 450 Da or more, 500 Da or more, 550 Da or more, 600 Da or more, 650 Da or more, 700 Da or more, 750 Da or more, or even 800 Da or more, while at the same time typically 850 Da or less, 840 Da or less, 830 Da or less, 820 Da or less, 815 Da or less, 810 Da or less, or even 800 Da or less.

[0040] The second part contains a hydrosilylation cure inhibitor. The hydrosilylation cure inhibitor can serve to provide storage stability by stabilizing the hydrosilylation reactants from premature curing. Examples of suitable cure inhibitors include acetylenic compounds such as 2-methyl-3-butyn-2-ol, 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, 3-phenyl-1-butyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,1-dimethyl-2-propynyl)oxy)trimethylsilane; and methyl(tris(1,1-dimethyl-2-propynyloxy))silane; 3-methyl-3-penten-1-yne, and 3,5- ene-yne ​​compounds such as dimethyl-3-hexen-1-yne; triazoles such as benzotriazole; hydrazine-based compounds; phosphine-based compounds; mercaptan-based compounds; and cycloalkenyl siloxanes including methylvinyl cyclosiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenyl cyclotetrasiloxane, or any combination of two or more thereof.

[0041] The concentration of the hydrosilylation cure inhibitor, in weight percent relative to the weight of the second part, can be 0.01 wt.% or more, 0.02 wt.% or more, 0.03 wt.% or more, 0.04 wt.% or more, 0.05 wt.% or more, 0.10 wt.% or more, or even 0.15 wt.% or more, while at the same time typically being 0.50 wt.% or less, or even 0.30 wt.% or less, 0.20 wt.% or less, 0.1 wt.% or less, 0.05 wt.% or less, 0.01 wt.% or less.

[0042] The concentration of the hydrosilylation cure inhibitor is at least 0.01% by weight, based on the weight of the two-part curable silicone composition.

[0043] The use of two-part curable silicone composition typically involves mixing equal parts by weight of the first part and the second part together, and then curing them.Mixing equal parts by weight is not a requirement, but is ideal based on the composition teachings herein.For example, mixing can be performed in a weight ratio of 60:40, 55:45, 50:50, 45:55, 40:60, where the ratio is weight parts of the first part: weight parts of the second part.

[0044] The present invention provides a moldable silicone composition that can be rapidly cured by hydrosilylation at temperatures up to 110° C. without the need for more than 6 parts per million by weight of platinum from a hydrosilylation catalyst based on the weight of the composition or less than 0.1 weight percent by weight of a hydrosilylation inhibitor based on the weight of the composition, and that has a SiH / C═C ratio of less than 1.6. EXAMPLES

[0045] Table 1 provides information regarding the materials used in the samples described herein below.

[0046] [Table 1] SILASTIC is a trademark of Dow Corning Corporation.

[0047] Sample preparation The two-part curable samples described in the table below are prepared by forming separate first and second parts. The first part is prepared by combining the alkenyl-functional linear polyorganosiloxane A-1 component, the alkenyl-functional resinous polyorganosiloxane A-2 component, and the linear SiH-functional chain extender B-1 component in a specific weight ratio, and then blending in the hydrosilylation catalyst component. The mixture is cured at 25°C for at least 24 hours to form a prepolymer. The second part is prepared separately from the first part by blending the specific components together in a specific weight ratio.

[0048] Sample characterization The following moving die rheometer (MDR) test method is used to characterize the set time of the samples.

[0049] MDR Test Methods An AlphaTechnologies Premier MDR-2000 instrument is used for testing. A 50 micrometer thick MYLAR™ film (MYLAR is a trademark of DUPONT Teijin Films US) is placed on the weighing tray of a digital scale. Two equal parts by weight of the two-part curable silicone composition are mixed at 3500 revolutions per minute for 30 seconds and approximately 4 grams of the mixed composition is immediately weighed onto the MYLAR film. A second 50 micrometer thick MYLAR film is then covered with the blend and the sample between the MYLAR films is immediately transferred to the MDR platen at a steady state temperature of 110°C. The platen is closed against the MYLAR film to a thickness of approximately 0.5 millimeters and the bottom platen is oscillated in an arc of 1° throughout the test. Torque coefficient values ​​are collected every second for 10 minutes at 110°C to obtain a plot of the torque coefficient as a function of time as the composition cures. If the composition is less than 1 deciNewton, the torque coefficient is increased by 100%. * Determine the time it takes to reach a torque coefficient in decibels (dNm). If the sample reaches a 1 dNm torque coefficient in 60 seconds or less, it is considered "fast setting" and passes the characterization. Any longer time is not considered fast setting and fails the characterization.

[0050] The sample formulations and results are shown in the table below. The component values ​​for each sample are reported in grams.

[0051] [Table 2] * The first part gelled or was too viscous to mix with the second part. ** Did not cure within 10 minutes.

[0052]

Table 3

Claims

1. A two-part curable silicone composition comprising, as separate parts: (a) i. a platinum hydrosilylation catalyst; ii. alkenyl-functional linear polyorganosiloxane; iii. an alkenyl-functional resinous polyorganosiloxane, and iv. a first part comprising an alkenyl-functional prepolymer that is the hydrosilylation reaction product of a first part premix comprising a linear SiH-functional chain extender having an average of two SiH groups per molecule, and present at a concentration of at least 0.25 weight percent and at most 5 weight percent for DPs of 100 or greater, and at most 5 weight percent for DPs less than 100 (weight percent is based on the combined weight of the first part and the second part); (b) i. a linear alkenyl-functional polyorganosiloxane; ii. resinous alkenyl-functional polyorganosiloxanes; iii. a resinous SiH-functional polyorganosiloxane crosslinker, and a second portion comprising a hydrosilylation reaction inhibitor; Including, the alkenyl-functional component and the SiH-functional component are present in the two-part curable silicone composition such that the two-part curable silicone composition has a SiH / C=C ratio of 1.4 or less; 1. A two-part curable silicone composition, wherein the composition contains up to 6 parts per million by weight of platinum and 0.01 weight percent or more of a hydrosilylation cure inhibitor, the concentrations being based on the combined weight of the first part and the second part.

2. The second portion is HMeSiO ２／２ 2. The two-part curable silicone composition of claim 1, which does not contain a linear polyorganosiloxane having SiH functionality only on the siloxane unit.

3. 10. The two-part curable silicone composition of claim 1, wherein the concentration of alkenyl-functional linear polyorganosiloxane in the first part pre-mix ranges from 40 to 60 weight percent, based on the total weight of alkenyl-functional linear and resinous polyorganosiloxanes in the first part pre-mix.

4. 10. The two-part curable silicone composition of claim 1, wherein the concentration of the alkenyl-functional linear polyorganosiloxane in the second part ranges from 40 to 60 weight percent, based on the weight of the second part.

5. 10. The two-part curable silicone composition of claim 1, wherein the concentration of resinous SiH-functional polyorganosiloxane in the second part ranges from 10 to 15 weight percent, based on the weight of the second part.

6. 2. The two-part curable silicone composition of claim 1, wherein the alkenyl-functional polyorganosiloxane is a vinyl-functional polyorganosiloxane.

7. (a) the alkenyl-functional linear polyorganosiloxane in the first portion premix and the second portion each have an average chemical composition (I): [[M] ２ SiO １／２ ] ２ [M] ２ SiO ２／２ ] ｄ (I) (where Vi refers to a vinyl group, Me refers to a methyl group, and the subscript d indicates the Me ２ SiO ２／２ The average number of units has a value ranging from 450 to 550. and (b) the alkenyl-functional resinous polyorganosiloxane in the first portion and the second portion each have an average chemical formula (II): [ViMe ２ SiO １／２ ] ｍ’ [Me ２ SiO １／２ ] ｍ [SiO ４／２ ] ｑ [HO １／２ ] ｎ (II) wherein Vi refers to a vinyl group, Me refers to a methyl group, the subscripts refer to the average molar ratio of the linking group to all listed groups, m' has a value ranging from 0.05 to 0.10, m has a value ranging from 0.40 to 0.50, q has a value ranging from 0.40 to 0.50, and n has a value ranging from 0.00 to 0.

05.

2. The two-part curable silicone composition of claim 1, having

8. The chain extender has the average chemical formula (III): [M] ３ Yes １／２ ] ｍ’ [HM% ２ Yes １／２ ] ｍ” [M] ２ Yes ２／２ ] ｄ’ [M%HSiO ２／２ ] ｄ’’ (III) where Me refers to a methyl group, the subscript indicates the average number of linked siloxane units in each molecule, subscript d' has an average value ranging from 5 to 200, and subscript d" is 0 or 1, provided that the sum of m' and m" is 2 and the sum of m' and d" is 2 so that the molecule has an average of two silylhydride groups.

2. The two-part curable silicone composition of claim 1, having

9. The resinous silylhydride functional polyorganosiloxane crosslinker has the average chemical formula (IV): (HMe ２ SiO １／２ ) ａ (Me ２ SiO ２／２ ) ｂ (SiO ４／２ ) ｃ (HO １／２ ) ｄ (IV) where Me refers to a methyl group, the subscripts indicate the average molar ratio of bonded siloxane units in the molecule, subscript a having an average value ranging from 0.01 to 0.05, subscript b having an average value ranging from 0.50 to 0.70, subscript c having an average value ranging from 0.20 to 0.40, and subscript d having an average value ranging from 0.00 to 0.

05.

2. The two-part curable silicone composition of claim 1, having

10. 10. The two-part curable silicone composition of claim 1, wherein the two-part curable silicone composition has an average SiH / C=C ratio greater than or equal to 1.0 and less than or equal to 1.26.