WO2019108318A1

WO2019108318A1 - Highly transparent curable silicone composition

Info

Publication number: WO2019108318A1
Application number: PCT/US2018/056413
Authority: WO
Inventors: Edward K. Nyutu; Joel Mcdonald
Original assignee: Dow Silicones Corporation
Priority date: 2017-12-01
Filing date: 2018-10-18
Publication date: 2019-06-06
Also published as: TW201925351A

Abstract

A curable silicone composition comprising: (A1) 40 to 70 parts by weight of a linear organopolysiloxane having DP from 150 to 10,000 and comprising from 2-25 alkenyl groups; (A2) 30 to 60 parts by weight of a resin type polysiloxane comprising units having structures (R1 2 R2SiO1/2)a, (R1 3SiO1/2)b, and (SiO4/2)c where R1 is alkyl, and R2 is alkenyl; where a+b+c is from 0.90 to 1; component (A2) further containing less than 5 ppm calcium, less than 5 ppm iron, less than 5 ppm sodium, and APHA color less than 30; and comprising particles having a diameter greater than 500 nm in an amount less than 200,000 per gram;where (A1) and (A2) add up to 100 parts by weight; (B) 1 to 25 wt% of a crosslinker relative to the total amount of the curable silicone composition; and (C) 0.1-100ppm of a hydrosilylation catalyst relative to the total amount of the curable silicone composition.

Description

HIGHLY TRANSPARENT CURABLE SILICONE COMPOSITION

FIELD OF INVENTION

[0001] This invention relates to a curable silicone composition having extremely high optical transparency in the visible range.

BACKGROUND

[0002] Hydro silylation curable silicone compositions comprising alkylsiloxane units are known, including encapsulants for light emitting diodes (LED), but the known compositions do not exhibit a combination of good mechanical properties and high transparency. Curable silicone compositions for these applications have been produced, e.g., in US8389650. However, this reference does not teach the compositions disclosed herein.

[0003] The problem solved by this invention is the need for improved curable silicone compositions.

SUMMARY OF THE INVENTION

[0004] The present invention provides a curable silicone composition comprising:

(Al) 40 to 70 parts by weight of a linear polysiloxane having DP from 150 to 10,000 and comprising from 2 to 25 R^ groups;

(A2) 30 to 60 parts by weight of a resin-type organopolysiloxane comprising units having structures (R^ R¾iO_]/2 _a, (R ' 3S i O _] /2 h _' ^and (Si04/2)_c where R ' is alkyl, and R^ is alkenyl; where a+b+c is from 0.9 to 1; the resin-type organopolysiloxane comprises less than 5 ppm calcium, less than 5 ppm iron, less than 5 ppm sodium, and APHA color less than 30; and the resin type organopolysiloxane comprises particles having a diameter greater than 500 nm in an amount less than 200,000 per gram, where (Al) and (A2) add up to 100 parts by weight;

(B) 1 to 25 wt% of a crosslinker relative to the total amount of the curable silicone composition; and

(C) O.l-lOOppm by weight of a hydrosilylation catalyst relative to the total amount of the curable silicone composition.

DETAILED DESCRIPTION OF THE INVENTION

[0005] Percentages are weight percentages (wt %) and temperatures are in Celsius (°C) unless specified otherwise. Operations were performed at room temperature (20 - 25 °C) unless specified otherwise. As used herein,“alkyl” group means aliphatically saturated group, that, unless otherwise specified, consist of carbon and hydrogen, non-limiting examples of which are methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, undecyl, dodecyl, octadecyl, and eicosyl, and their isomers when there are more than 3 carbon atoms.“Cycloalkyl” means alkyl where some or all carbon atoms participate in forming a circular structure with no aliphatic unsaturation within the circle, exemplified by cyclopentyl and cyclohexyl. As used herein,“alkenyl” group means a group having an aliphatically unsaturated bond and consisting of carbon and hydrogen, non-limiting examples of which are vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl octadecenyl, nonadecenyl, eicosenyl and their isomers where there are more than 3 carbon atoms. As used herein,“aryl” group means group derived from monocylic and polycyclic aromatic hydrocarbons, by removal of a hydrogen atom from a ring carbon atom, the non-limiting examples of which are phenyl, tolyl, xylyl, naphthyl, benzyl, and phenylethyl. The term“ppm” refers to weight parts per million. As used herein, “substantially straight-chain molecular structure,” means a molecular structure comprises for the most part divalent siloxy units (R2S1O2/2 units or“D” units), terminated by monovalent siloxy units (R 3S i O _] /2 units or“M” units), but may have some branching or small amounts, i.e., no more than 1 mole %, preferably no more than 0.5 mole %, of trivalent siloxy units (RS1O3/2 or“T” units), or tetravalent siloxy units (S1O4/2 or“Q” units).

[0006] As used herein, unless otherwise indicated, molecular weights, M_n, M_w and M_z have the conventional meanings and are determined by gel permeation chromatography using polystyrene size markers as the standards. Molecular weights are reported herein in units of g/mol. “DP” means degree of polymerization, i.e. the number of monomers found in a polymer molecule. For linear polysiloxane, DP is determined by 29Si-NMR, from the ratio of the number of terminal siloxy unit (R3S1O-) and the number of the chain-forming divalent siloxy unit (-R2S1O-). In certain resins, the DP is accurately calculated from the structure of the starting materials. In other situations, DP is calculated from the molecular size of the polymer determined by gel permeation chromatography using polystyrene as the standard samples and the known side chains; a siloxy unit with methyl groups attached is approximately 100 g/mole. Amounts of various siloxane units are number averages.

Composition [0007] A curable silicone composition is provided comprising a mixture of (Al) linear and (A2) resinous organopolysiloxane, (B) a crosslinker that is capable of reacting with (Al) and (A2), and (C) a hydrosilylation catalyst to promote crosslinking. Each of components (Al), (A2) and (B) may be a mixture of two or more components.

[0008] The “linear organopolysiloxane” (Al) has a substantially straight-chain molecular structure. Preferably, the linear organopolysiloxane (Al) has DP at least 200, preferably at least 300, preferably at least 400, preferably at least 500; and at the same time, preferably no more than 7000, preferably no more than 4000, preferably no more than 3000, preferably no more than 2000, preferably no more than 1500. Preferably, the linear organopolysiloxane has at least two groups, either located at the terminal end of the linear organopolysiloxane or pendent to the linear organopolysiloxane. Preferably, the other substituents on the linear organopolysiloxane are R ' groups. These R ' groups may be the same or different on different siloxane units; preferably they are the same. Preferably R ' is C _] -C _] Q alkyl, preferably C _] -Cg alkyl, preferably methyl, ethyl or propyl; preferably methyl. Preferably, R^ is C2-C ] Q alkenyl, preferably C2-C5 alkenyl, preferably C2-C4 alkenyl, preferably vinyl. In one preferred embodiment, (Al) has an average of at least two alkenyl groups in each molecule. Preferred alkenyl groups in (Al) include vinyl, allyl, isopropenyl, butenyl, pentenyl, hexenyl, and cyclohexenyl or a combination of any two or more thereof. The alkyl in (Al) includes methyl, ethyl, propyl, cyclopentyl, and cyclohexyl, or a combination of any two or more thereof. Preferably, the viscosity of (Al) at 25°C is from 200 to 300,000 mPa · s; preferably at least 2,000, preferably at least 6,000, preferably at least 9,000, preferably at least 12,000, preferably at least 15,000, preferably at least 18,000; and at the same time, preferably no more than 250,000 preferably no more than 200,000, preferably no more than 100,000. The approximate mass average molecular weight (M_w) of (Al) is from 5,000 to 150,000; preferably at least 8,000, preferably at least 15,000, preferably at least 50,000, preferably at least 60,000, preferably at least 70,000; and at the same time, preferably no more than 120,000. Preferably, (Al) is present in the curable silicone composition in an amount of at least 45 wt%, preferably at least 50 wt%; and at the same time, preferably no more than 65 wt%, preferably no more than 62 wt%.

[0009] In a preferred embodiment, (Al) is a diorganopolysiloxane and may include, e.g., dimethylpolysiloxanes end blocked at both molecular chain terminals by dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers endblocked at both molecular chain terminals by dimethylvinylsiloxy groups, methylvinylpolysiloxanes endblocked at both molecular chain terminals by trimethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers endblocked at both molecular chain terminals by trimethylsiloxy groups, or a combination of any two or more thereof.

[0010] In a preferred embodiment, (Al) is a mixture of two or more alkenyl-functional organopolysiloxanes which may include low- and high-viscosity alkenyl-functional organopolysiloxanes, designated (Al-l) and (Al-2), respectively. The viscosity of (Al-l) is lower than the viscosity of (Al-2). The viscosity and DP of (Al) is a weight average of the properties of (Al-l) and (Al-2). Preferably, (Al-l) has DP from 100 to 1500; preferably at least 150, preferably at least 300, preferably at least 400; and at the same time, preferably no more than 1400, preferably no more than 1200, preferably no more than 1000, preferably no more than 800, preferably no more than 700. Preferably, (Al-l) has a viscosity at 25°C from 200 to 150,000 mPa- s; preferably at least 2,000, preferably at least 3,000, preferably at least 4,000, preferably at least 5,000, preferably at least 6,000, preferably at least 7,000; and at the same time, preferably no more than 20,000, preferably no more than 17,000, preferably no more than 14,000. Preferably, (Al-2) has DP from 500 to 10,000; preferably at least 600, preferably at least 700, preferably at least 800, preferably at least 900; and at the same time preferably no more than 8,000, preferably no more than 6,000, preferably no more than 4,000, preferably no more than 2,000. Preferably, (Al-2) has a viscosity at 25°C from 20,000 to 1,000,000 mPa- s; preferably at least 30,000; preferably at least 40,000; preferably at least 50,000; and at the same time, preferably no more than 700,000, preferably no more than 400,000, preferably no more than 250,000, preferably no more than 100,000. Preferably, relative amounts of (Al-l) and (Al-2) are adjusted to achieve a target viscosity for (Al). In a preferred embodiment of the invention, the weight ratio of (Al-l):(Al-2) is from 10: 1 to 1 :10, preferably from 6: 1 to 1:2, preferably from 4: 1 to 1: 1.

[0011] For the resin-type organopolysiloxane (A2), preferably, a ratio of the total number of moles R¾iO]y2 and R SiO 2 units to 1 mole of the S1O4/2 unit is from 0.8 to 1.02, preferably at least 0.83. When a ratio of the total number of moles of

R¾iO _]/2 and R^SiC)^ units to 1 mole of the S1O4/2 unit is less than one, preferably the remainder comprises at least 90% silanol units by moles. R ' groups on the siloxane units may in some cases be different on different siloxane units,

groups also may be different on different siloxane units. For the resin-type organopolysiloxane (A2), preferably,“a,” the molar fraction of (R R¾iO_]/2) units (“alkenyl units”), is from 0.02 to 0.11, preferably at least 0.025, preferably at least 0.03; and at the same time, preferably no more than 0.08, preferably no more than 0.07, preferably no more than 0.06. Preferably,“b,” the molar fraction of (R ^ 3S i O _] /2 units, is from

0.30 to 0.60, preferably at least 0.35, preferably at least 0.40; and at the same time, preferably no more than 0.55, preferably no more than 0.5. Preferably,“c,” the molar fraction of (S1O4/2) units (“Q units”), is from 0.40 to 0.63, preferably at least 0.42, preferably at least 0.45, preferably at least 0.48; and at the same time, preferably no more than 0.60, preferably no more than 0.58. Preferably, a+b+c is at least 0.91, preferably at least 0.93, preferably at least 0.95, preferably at least 0.97; and 0.8 < (a+b)/c < 1.02. When a+b+c is less than one, the remaining units are mostly silanol units. “R!” groups on the siloxane units may in some cases be different on different siloxane units, and“R^” groups also may be different on different siloxane units. In a preferred embodiment, R ' represents the same alkyl group wherever it appears. Preferably R ' is C _] -C _] Q alkyl, preferably C -Cg alkyl, preferably methyl, ethyl or propyl; preferably methyl.

Preferably, R^ is C2-C1_Q alkenyl, preferably C2-C5 alkenyl, preferably C2-C4 alkenyl, preferably vinyl. Preferably, the molar ratio of alkenyl substituents to Q units is from 0.5:1 to 1.8:1, preferably from 0.7:1 to 1:1. Preferably, the resin-type organopolysiloxane (A2) has M_w from 20,000 to 50,000; preferably at least 22,000, preferably at least 23,000; preferably no more than 40,000, preferably no more than 35,000, preferably no more than 30,000. Preferably, (A2) is present in the curable silicone composition in an amount of at least 33 wt%, preferably at least 36 wt%; and at the same time, preferably no more than 55 wt%, preferably no more than 50 wt%, preferably no more than 45 wt%.

[0012] Preferably, prior to the addition to the curable silicone composition, (A2) is purified by filtration. Preferably, the concentration of (A2) in the solution is from 10 to 50 wt%. Preferably, (A2) is in an organic solvent, where the organic solvent may be a hydrocarbon or ether solvent, preferably having from four to twenty carbon atoms. Filtration is believed to remove the ionic impurities, metallic impurities, and resin agglomerates. Preferred filtration media include surface and depth filters with and without filter aids (adsorbents such as diatomaceous earth, perlite, etc.). Surface filters are essentially discrete membranes which functions by retaining impurities on the surface via mechanical straining, while depth filters use a porous filtration medium to retain impurities throughout the medium, rather than just on the surface. Unlike surface media which have a tendency to clog rapidly, depth filters typically have a higher capacity to retain contaminants, hence have reduced tendency to clog filter media. Depth filters are preferred due to their efficient removal of color, metallic contaminants, and large resinous agglomerates while resisting rapid filter clogging. (A2) in a solvent may be pressure filtered through a depth filtering medium having pore size ranging from 5pm to 50 pm. Preferably, resin-type organopolysiloxane (A2) comprises less than 2 ppm calcium (preferably less than 1 ppm), less than 2 ppm iron (preferably less than 1 ppm), less than 2 ppm sodium (preferably less than 1 ppm), and APHA color (as defined by American Society for Testing and Materials (ASTM) D1209) less than 20 (preferably less than 15). Preferably, as used as a component of the curable composition, the resin-type organopolysiloxane (A2) comprises particles having a diameter greater than 500 nm in an amount less than 50,000 per gram, preferably less than 30,000 per gram.

[0013] In the above description, total weight of (Al) + (A2) is 70 to 99 wt% of the curable silicone composition; preferably at least 80 wt%, preferably at least 85 wt%, preferably at least 90 wt%; preferably no more than 97 wt%. The relative amounts of (Al) and (A2) are such that, relative to the sum of (Al) and (A2) being 100 parts by weight, (Al) is 40 to 70 parts by weight and (A2) is 30 to 60 parts by weight.

[0014J The crosslinker (B) is preferably an organopolysiloxane having an average of at least three silicon-bonded hydrogen atoms in each molecule, wherein the silicon-bonded groups other than the silicon-bonded hydrogen are alkyl groups. Such alkyl groups are preferably C _] -C ] Q alkyl or cycloalkyl; preferably methyl, ethyl, propyl, cyclopentyl, cyclohexyl; more preferably methyl. Component (B) is present in the curable composition in an amount that provides about 0.4 to about 4.0 moles silicon-bonded hydrogen in (B) per 1 mole of the total alkenyl in component (A).

[0015] The molecular structure of (B) is not particularly limited and can be, for example, straight chain, partially branched straight chain, branched chain, cyclic, or dendritic, wherein straight chain, partially branched straight chain, and dendritic are preferred. There are no limitations on the bonding position of the silicon-bonded hydrogen in component (B), and the silicon-bonded hydrogen may be bonded in, for example, terminal position on the molecular chain and/or side chain position on the molecular chain. Component (B) may preferably comprise an organopolysiloxane that contains at least about 0.7 wt % silicon-bonded hydrogen atom and that comprises HR^SiO^ units, wherein

is C ] -C ] Q alkyl or cycloalkyl; (preferably methyl, ethyl, propyl, cyclopentyl, cyclohexyl; preferably methyl), and S1O4/2 units, in a ratio ranging from about 1.5 to about 3.8 moles of HR^SiO^ units per 1 mole of S1O4/2 units. Component

(B) may further optionally comprise (B-2), an organopolysiloxane having a substantially straight chain molecular structure, with at least about 0.1 wt %, and more preferably at least 0.3 wt %, silicon-bonded hydrogen, wherein the silicon-bonded groups other than the silicon-bonded hydrogen are Ci_io alkyl, at 0 wt % to 50 wt % of component (B) . Preferably, component (B) further comprises R^SiO^ units. The ratio of the total number of moles of HR^SiO_]^ ^and

R^ 3 S i O _] /2 units to 1 mole of the S1O4/2 unit in component (B) is preferably in the range from

1.50 to 2.50 and more preferably is in the range from 1.80 to 2.20. Preferably, component (B) has a viscosity at 25°C from 1 to 10,000 mPa-s; preferably at least 5, preferably at least 10, preferably at least 20 mPa-s; preferably no more than 5,000, preferably no more than 2,000, preferably no more than 1,000 mPa· s. The silicon-bonded groups in component (B) other than the silicon-bonded hydrogen are alkyl such as methyl, ethyl, propyl, cyclopentyl, cyclohexyl, and so forth, wherein methyl is preferred. Preferably, (B) is present in the curable silicone composition in an amount of at least 3 wt%, preferably at least 3.5 wt%, preferably at least 4 wt%; and at the same time, preferably no more than 20 wt%, preferably no more than 15 wt%, preferably no more than 12 wt%, preferably no more than 10 wt%.

[0016] A specific example of a preferred component (B) is the organopolysiloxane given by (Si04/2)4(H(CH3)2Si01/2)8’ ^a straight-chain organopolysiloxane which contains at least 0.3 wt% and preferably at least 0.7 wt% silicon-bonded hydrogen. Preferred specific examples of component (B-2) are dimethylsiloxane-methylhydrogensiloxane copolymers endblocked at both molecular chain terminals by dimethylhydrogensiloxy groups, methylhydrogenpolysiloxanes endblocked at both molecular chain terminals by trimethylsiloxy groups, dimethylsiloxane- methylhydrogensiloxane copolymers endblocked at both molecular chain terminals by trimethylsiloxy groups, and mixtures of two or more of the preceding. [0017] A hydro silylation catalyst (C) is present in the curable silicone composition. Preferably, the hydro silylation catalyst is present in the curable silicone composition in a catalytic quantity, preferably in an amount sufficient to promote curing of the composition. Suitable hydrosilylation catalysts include, without limitation, a platinum group metal which includes platinum, rhodium, ruthenium, palladium, osmium, or iridium metal or an organometallic compound thereof and a combination of any two or more thereof. In a preferred embodiment, the hydrosilylation catalyst is platinum black; platinum compounds such as chloroplatinic acid and chloroplatinic acid hexahydrate; a reaction product of chloroplatinic acid and a monohydric alcohol; platinum bis(ethylacetoacetate), platinum bis(acetylacetonate), platinum dichloride, and complexes of the platinum compounds with olefins or low molecular weight organopolysiloxanes or platinum compounds microencapsulated in a matrix or core-shell type structure. Preferably, (C) is present in an amount of at least 0.5 ppm, preferably at least 1 ppm; preferably no more than 50 ppm, preferably no more than 20 ppm, preferably no more than 10 ppm, all amounts expressed in ppm of Pt metal in the curable silicone composition.

[0018] Preferably, the curable silicone composition further comprises an inhibitor for hydrosilylation (D). Preferred inhibitors include, e.g., alkyne alcohols (e.g., 2-methyl-3-butyn- 2-ol, 3,5-dimethyl-l-hexyn-3-ol, l-ethynyl-l-cyclohexanol and phenylbutynol); ene-yne compounds (e.g., 3-methyl-3-penten-l-yne and 3,5-dimethyl-3-hexen-l-yne); as well as 1,3, 5, 7- tetramethyl-l,3,5,7-tetravinylcyclotetrasiloxane, l,3,5,7-tetramethyl-l,3,5,7- tetrahexenylcyclotetrasiloxane and benzotriazole. Preferably, the inhibitor(s) is present in the composition in an amount from 10 to 5,000 ppm on a weight basis relative to the total weight of the composition.

[0019] Optionally, the curable silicone composition may further include one or more additional ingredients. The additional ingredient or combination of ingredients may include, for example, a mold release agent, a filler, an adhesion promoter, a heat stabilizer, a flame retardant, a reactive diluent, an oxidation inhibitor, or a combination of any two or more thereof.

[0020] Optical device components may be produced using the composition as described herein by a method including shaping the composition and curing the composition to form a cured product, for example, for use in an optical device. Shaping the composition may be performed by injection molding, transfer molding, casting, extrusion, overmolding, compression molding, or cavity molding to produce a molded, cast, potted, dispensed, or extruded article. The method of shaping the composition will depend on various factors including a size and/or a shape of the optical device to be produced and the composition selected.

[0021] In one preferred embodiment, the cured composition can be used in an electronic or optical device application. The electronic or optical device can be a charged coupled device, a light emitting diode, a lighting device using a light emitting diode as the light source, a lightguide, an optical camera, a photo-coupler, or a waveguide, for example. In an optical device the cured composition preferably is used to facilitate evenly illuminating a surface of the optical device from which light is extracted.

[0022] The composition also may be used to form cured silicone product with more than 92% light transmittance at 400nm and an optical path length of lcm, i.e., highly transparent. The highly transparent, cured silicone product is a molded, cast or extruded article and may include a substrate that forms a single article with a cured silicone layer. The composition may be applied to optical parts, including, without limitation, lens, reflectors, sheets, films, bars and tubing by any fabrication method. The composition may be used for electronics, displays, soft lithography, and medical and healthcare devices.

[0023] The present invention is further directed to a method for producing the curable silicone composition. The method comprises filtering a solution of the resin type organopolysiloxane (A2), preferably in an organic solvent. Preferably, the concentration of (A2) in the solution is from 10 to 50 wt%. Preferably, the organic solvent is a hydrocarbon or ether solvent, preferably having from four to twenty carbon atoms. The produced material is then pressure filtered through a depth filtering medium having pore size ranging from 5pm to 50 pm.

[0024] Preferably, (A2) is a high molecular weight vinyl-terminated organopolysiloxane produced via vinylation of silanol-terminated organopolysiloxane from the sodium silicate route with vinyldimethylchlorosilane (Me2ViSiCl). Filtering this material through a cartridge filter with absolute pore rating of < 20pm rapidly clogs the filter. Media with larger pore sizes (> 50 pm) produces a filtered product which gives undesirable optical characteristics in the final cured silicone composition. The method reduces the color, haze, metallic/ionic impurities and resinous agglomerates in high molecular weight alkenyl functionalized organopolysiloxane resin solution without adversely affecting the resin solution solid content (nonvolatile content, NVC), viscosity, vinyl content, molecular weight, etc., while maintaining high filtration flux rates. The method comprises the step of passing resin solution through a structured or unstructured depth filter with average retention rating of < 50mih and filtration being done under conditions resulting in a reduction of iron, calcium, sodium impurities to < lppm, color to < 10 APHA, oversized particle concentrations (>500nm diameter) < 100,000 particles/gram in the filtered resin solution, while retaining the resin solid contents, vinyl content, and associated final cured composition characteristics (hardness, elongation, tensile strength, etc.)

[0025] The vinyl-functional organopolysiloxane resin solution (A2) with mass average molecular weight >22,000 g/mol produced via sodium silicate process and vinyl-functionalized using vinylchlorosilane (e.g. Me2ViSiCl) were specially treated after processing with structured depth media with average nominal pore diameter in the range of about lpm to 100 pm to reduce the outlier oversized resin agglomerates (>500nm in diameter) concentration to <100,000 particles/gram as determined by single particles optical sizer (SPOS) and color as determined by color photometry to <10 APHA units. A preferred media is made from diatomaceous earth and/or perlite and self-binding matrix of cellulose fiber with positive zeta potential.

[0026] Preferably, the non- structured depth media comprises a filter membrane with average pore diameter within the range of about 5pm-30pm with filter aids such as diatomaceous earth or structured depth filter where the filter element comprises of a filter aid (diatomaceous earth or perlite, etc.) impregnated in a self-binding matrix of cellulose fiber. For non-structured depth elements utilizing filter aids, diatomaceous earth (Celite, Imerys Filtration, USA) the preferred medium value of the particle size distribution (d5_Q) is in the range of ~20-50pm.

EXAMPLES

[0027] The curable silicone composition of the present invention will be described in detail through examples and comparative examples. In the examples, the viscosity is the value at 25° C and parts indicates mass percent. The composition of the materials used in the examples for components A, B, C and the reaction inhibitor are described below. Here, Me and Vi designate methyl and the vinyl groups, respectively.

Component al exemplifying Component (Al):

[0028] (al-l)- a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups at both molecular chain terminals, that has a viscosity of 10,000 mPa- s, mass average M_w of approximately 40,000, DP of 550 and a vinyl group content of 0.10 wt %. [0029] (al-2)- a dimethylpolysiloxane endblocked by dimethylvinylsiloxy groups at both molecular chain terminals, that has a viscosity of 60,000 mPa- s, mass average M_w of approximately 75,000, DP of 1,000 and a vinyl group content of 0.09 wt %.

Component a2 exemplifying Component (A2):

[0030] (a2-l): an organopolysiloxane resin given by the average unit formula

(ViMe2SiO 2)0.04(^^e3SiO 1/2)q.4q(^ΐq4/2)q.56’ that has a mass-average molecular weight of approximately 24,600, a vinyl group content of 1.9 wt %, and a ratio of the total number of moles of R^2 R¾iO]V2’ R SiO]72 units to 1 mole of the S1O4/2 unit of 0.84. Silanol amount of 2.1 wt.%, calcium amount of 1.3 ppm, iron amount of about 1.5 ppm, sodium amount of 0.8ppm, color APHA of 33.6, and oversized particles (>500nm) concentration of about 438,000 particles/gram.

[0031] (a2-2): an organopolysiloxane resin given by the average unit formula

(ViMe2SiO 1/2)0.04 (hl^e3SiO 2)0.40(SiO4/2)0.56’ that has a mass-average molecular weight of approximately 24,600, a vinyl group content of 1.9 wt %, and a ratio of the total number of moles of R^2 R^SiOi/2 and R^SiOi^ units to 1 mole of the S1O4/2 unit of 0.84. Silanol amount of 2.1 wt.%, calcium amount of 0.3 ppm, iron amount of 0.2 ppm, sodium amount of 0.4 ppm, color APHA of 5, and oversized particles (>500nm) concentration of about 23,000 particles/gram. Component b exemplifying Component (B ):

[0032] An organopolysiloxane given by the average unit formula (S i O4/2 )4(H(C H 3 ) 2S i 01/2 8- that has a viscosity of approximately 20 mPa· s and a silicon-bonded hydrogen atom content of approximately 0.97 wt %.

Component c exemplifying Component (C):

[0033] Hydro silylation catalyst: l,3-divinyltetramethyldisiloxane complex of platinum. The platinum metal content is approximately 5200 ppm.

Component d exemplifying Component (D):

[0034] Hydro silylation inhibitor: 3,5-dimethyl-l-hexyn-3-ol.

Comparative Examples 1-5 (C. Ex. 1-5) and Inventive Example 1 (Ex. 1)

[0035] The materials shown in Table 1 (for comparative Examples 1-5 and Example 1) were mixed in a common vessel to form homogenous blends by utilizing asymmetrical centrifugal mixer (Hauschild SpeedMixer DAZ 150FVZ) at 3,400 rpm for 60s to produce curable silicone compositions. The resulting compositions were molded under heat to produce the 3mm thick cured sheet for mechanical testing (hardness, tensile strength and elongation), various molded articles with lengths (l.Ocm- lOcm) for optical measurements and 3.2cm thick blocks for hydrothermal optical measurements. The results are given in Table 2 and 3.

Table 1.

* 0.06wt% of formulation=(0.06g Pt catalyst solution /lOOg curable silicone composition) x 0.0052g Pt/lg (5200ppm) Pt catalyst solution=3.lppm Pt

Test, Measurements and Evaluation Methods: Cured silicone compositions

[0036] Optical (light transmittance and attenuation) characterization: 1.0 cm, 2.5 cm, 5.0 cm, and 10.0 cm cured blocks were prepared by curing the composition in the mold of each size at 60 °C for 14 hours. The samples are removed from the mold cavities and subjected to an additional curing step of l50°C for 1 hour. The optical properties of the molded slab samples were then collected with a Perkin Elmer Lambda950 UV-Vis-NIR spectrophotometer. The spectrophotometer was operated at a slow scanning speed, 1 nm slit width, over a wavelength range from 200-800 nm. The reported light transmittance values are not corrected for surface reflections (so called Fresnel reflections) due to refractive index differences between the air and the silicone article. Optical attenuation coefficient (a, cm 1) which includes combined light transmittance losses due to scattering, haze, and absorption as a function of wavelength were then determined. The practical Alpha (a) minimum for silicone materials is -0.004 cm 1 (at 400nm) as determined using this method. Lower a, (<0.010 cm l at 400nm) is desired. [0037] The optical characteristics (%transmittance and yellow index) of cured silicone compositions (3.2 cm thick blocks) were determined before and after hydrothermal aging (85 °C/85% RH) for several hours (up to 1000 h) with a Perkin Elmer Lambda950 UV-Vis-NIR spectrophotometer with integrating sphere.

[0038] Mechanical characterization: vinyl-terminated dimethylpolysiloxane (al), vinyl functional silicone resin (a2), Pt catalyst (c), hydrogen functional cross-linker (b), and hydrosilylation inhibitor are added to a common vessel and mixed by asymmetric centrifugal mixing on a planetary mixer (Hauschild SpeedMixer DAZ 150FVZ) at 3,540 rpm for 20 seconds. The material is then subjected to injection molding, in which a load of material is injected under pressure of 5.2 N/mm^ into a metal mold cavity heated at 150 °C for 15 sec. of holding time and 30 sec. of cure time to produce an ASTM Die C specimen. Once removed from the mold cavity, the samples are subjected to an additional curing step of 150 °C for 1 hour. The measurement of mechanical properties was performed on an Instron Mechanical Tester in accordance to ASTM D412-06A at a speed of 20 in/min. Hardness was measured on a Shore A Durometer in accordance with ASTM D2240.

Table 2. Cured articles optical characteristics at 400nm and 650nm

Table 3. Vinylpolysiloxane resin composition and cured silicone elastomer physical, optical and mechanical characteristics

(0039] The composition in comparative non-inventive Example #1 used (100%) untreated vinylpolysiloxane resin with M_w>22,000 g/mol and the cured product obtained from this composition had poor light transmittance properties at 400nm and 650nm at various optical path lengths (1 - lOcm) which corresponds to higher light attenuation coefficients at 400 and 650nm. Furthermore, in the cured product prepared in Example #1 had lower light transmittance before and after hydrothermal aging due to yellowing. The polysiloxane resin solution had higher metallic impurities (Fe>lppm, Ca>lppm, Na>lppm), color > 30 APHA units and oversized particles concentration > 200,000 particles/gram (0.5-330um).

[0040] In contrast, with respect to comparative non-inventive Examples #2-#5. The cured product obtained with various mixtures of untreated and specially treated vinylpolysiloxane resin resulted in cured articles with significantly improved light transmittances at 400nm and low attenuation coefficients (400/650nm) with increasing use of treated resin contents. Moreover, hydrothermally aged articles showed significantly suppressed yellowing with long-term aging. Table 3.

[0041] With respect to the inventive Example #1. The cured product obtained from composition utilizing 100% specially treated vinylpolysiloxane resin resulted in cured articles with extremely high light transmittance at 400nm at various optical path-lengths and ultra-low light attenuation for silicone compositions of 0.006cm 1 and 0.002cm ' at 400nm and 650nm, respectively. (Table 2 and 3). The polysiloxane resin solution had low metallic impurities, Fedpprn (preferably <0.5ppm), Cadppm, Nadppm), color < 30 APHA but preferably <10 APHA units and oversized particles concentration <200,000 particles/gram (0.5-330pm), preferably <100,000.

[0042] With respect to inventive Examples #1, the enhancement of light transparency of cured materials did not result in deleterious effects on other properties (e.g. hardness, elongation and tensile strength).

Alkenyl- siloxane resin solutions characterization:

[0043] Samples preparation for structural (M_w) characterization: alkenyl-functional resins (A2) were analyzed by triple detection gel permeation chromatography for molecular weight determination. The chromatographic equipment consisted of a Waters 515 pump, a Waters 717 auto sampler and a Waters 2410 differential refractometer. The separation was made with two (300 mm x 7.5 mm) Polymer Laboratories PLgel 5 pm Mixed-C columns (molecular weight separation range of 200 to 2,000,000), preceded by a PLgel 5 pm guard column (50 mm x 7.5 mm). The analyses were performed using HPLC grade toluene flowing at 1 .0 mL/min as the eluent, and the columns and detector were both controlled at 45 °C. The samples were prepared in toluene at 5 pg/mL, solvated at room temperature for about three hours with occasional shaking, and filtered through 0.45 pm PTFE syringe filters prior to analysis. An injection volume of 75 pm was used and data was collected for 25 minutes. Data collection and analyses were performed using ThermoLabsystems Atlas chromatography software and Polymer Laboratories Cirrus GPC software. Molecular weight averages were determined relative to a calibration curve (3rd order) created using polystyrene standards covering the molecular weight range of 580 - 2,300,000. [0044] Samples preparation for outlier resin oversized particle evaluations: An AccuSizer, model 780, from Particle Sizing Systems was used to measure the particle concentration in the samples. The AccuSizer uses the technique of Single Particle Optical Sensing (SPOS) also known as light obscuration to size particles in the range of 0.5 to 400 microns (LE400-0.5 sensor). The particle size data was collected with a flow rate of 60 mL/min for 2 minutes. The alkenyl organopolysiloxane resin samples in 30 wt. % xylene were quantitatively dispersed in toluene at resin: solvent ratio of 1:99 by weight, to allow for the calculation of the particle concentration. An equivalent spherical diameter was used to characterize the size of the particles and no correction for particle shape has been made. Particle size measurements were performed over the size range from approximately 0.5 to 330 microns. Particles outside this size range may be present. Those particles outside the measurement range were not included in the reported statistics.

[0045] Samples preparation for resin solution color photometry (APHA): As per ASTM D1209 and ASTM D5386. The method uses certified calibration standards and 5.0 cm path- length Quartz cell with the Lovibond PFX 195/1 Tintometer.

[0046] Samples preparation for resin solution elemental composition analysis by ICP-MS:

The alkenyl organopolysiloxane resin samples in 30 wt. % xylene were digested in HF: HNO3

(1: 1) using a Milestone UltraWave. Analysis was completed on a Thermo iCAP Q ICP-MS with internal standards added online as part of the analysis procedure.

Examples of different filter types and effect on resin haze and color characteristics and ease of filtration:

[0047] Surface filter: The unfiltered vinyl terminated organopolysiloxane resin dispersed in -30 wt. % xylene was filtered through a nylon or PTFE membrane filter with pore size of 5-l00pm using stainless steel filter housing under a pressure of 20psig. The influent and effluent samples were collected for particle sizing (SPOS), color and turbidity analysis, molecular weight determination (GPC) and elemental impurity composition analysis (GC-MS). At finer pore sizes (<20pm) the color, haze, level of contaminants and resin agglomerates was reduced significantly, however the filtration rates were too low for manufacturing level viability (due to rapid filter clogging). With larger pore sizes (>50pm) the filtration rates moderately improved, however the level of contaminants did not reduce to desired levels. Treatment of resin with media not manufacturing viable. [0048] Surface filter with filter aid (unstructured depth filter): The unfiltered vinyl terminated organopolysiloxane resin dispersed in -30 wt. % xylene with up to 10 wt. % filter aid (diatomaceous earth, based on unfiltered resin) was filtered through a nylon or PTFE or cotton membrane filters with pore size of 5-l00pm using stainless steel filter housing under pressure. Alternatively, the filter aid was pre-coated on the filter membrane prior to passing the resin solution. The influent and effluent samples were collected for particle sizing (SPOS), color and turbidity analysis, molecular weight determination (GPC) and elemental impurity composition analysis (GC-MS). At finer media pore sizes (<20pm) the color, haze, level of contaminants and resin agglomerates was reduced significantly, with improved filtration rates depending on the type of filter aid and conditions used. With larger pore sizes (>50um) the filtration rates improved, however the level of contaminants did not reduce to desired levels and the filter aid particles retention on the membrane surface was not effective leading to hazy samples. With optimal filter aid loadings, filter aid type selection and filter aid pre-coat or body-feed characteristics, this media type could achieve desired filtration rates/flux and contaminants removal.

[0049] Conventional cartridge filter: The unfiltered vinyl terminated organopolysiloxane resin dispersed in -30 wt. % xylene was filtered through cartridge filters (Compax, Pentair) with pore size of 20-250pm using stainless steel filter housing under pressure. The influent and effluent samples were collected for particle sizing (SPOS), color and turbidity analysis, molecular weight determination (GPC) and elemental impurity composition analysis (GC-MS). At finer pore sizes (<20pm) the color, haze, level of contaminants and resin agglomerates was reduced significantly, however the filtration rates were too low for manufacturing level viability (rapid filter clogging). With larger pore sizes (>50pm) the filtration rates moderately improved, however the level of contaminants did not reduce to desired levels.

[0050] Structured depth filter: The unfiltered vinyl terminated organopolysiloxane resin dispersed in -30 wt. % xylene was filtered through structured depth filters (Pall or Ertel Alsop lenticular media) with retention rates range of l0-70pm using stainless steel filter housing under pressure. The influent and effluent samples were collected for particle sizing (SPOS), color and turbidity analysis, molecular weight determination (GPC) and elemental impurity composition analysis (GC-MS). At retention rates (~20pm) the color, haze, level of contaminants and resin agglomerates was reduced significantly, filtration rates were also improved. With retention rating (>20mih) the color, haze, level of contaminants and resin agglomerates were substantially reduced with desired high filtration rates (reduced tendency to clog). This is the preferred media for the treatment of composition A2 of current invention. The media is made from diatomaceous earth and/or perlite and self-binding matrix of cellulose fiber with positive zeta potential. Depth media of various type are also preferred (cartridge depth filter, pads and panels, etc.)

[0051] Table 4 shows the summary of vinyl organopolysiloxane resin solution characteristics before and after treatment with various media and elements. As illustrated depth filters (non- structured (A2-3) and structured (A2-4)) achieved reduction of resin ionic and metallic impurities, color, large resinous agglomerates, while maintaining resin solid contents (%NVC), vinyl levels with high filtration flux rates (excellent ease of filtration).

Table 4.

Average media diameter- 20pm

Claims

1. A curable silicone composition comprising:

(Al) 40 to 70 parts by weight of at least one linear organopolysiloxane having a degree of polymerization from 150 to 10,000 and comprising from 2-25 alkenyl groups;

(A2) 30 to 60 parts by weight of at least one resin-type polysiloxane comprising units having structures (R^ R^SiO ]/2)_a, (R SiO 2)b’ ^and (Si04/2 _c where R ' is alkyl, and R^ is alkenyl; where a+b+c is from 0.90 to 1; wherein (A2) further contains less than 5 ppm calcium, less than 5 ppm iron, less than 5 ppm sodium, and APHA color less than 30; and comprises particles having a diameter greater than 500 nm in an amount less than 200,000 per gram;

where (Al) and (A2) add up to 100 parts by weight;

(B) 2 to 25 wt% of a crosslinker, relative to the total amount of the curable silicone composition; and

(C) 0.1-100 ppm by weight of a hydrosilylation catalyst relative to the total amount of the curable silicone composition.

2. The composition of claim 1, wherein the crosslinker comprises an organopolysiloxane having an average of at least three silicon-bonded hydrogen atoms in each molecule, wherein the silicon-bonded groups other than the silicon-bonded hydrogen atoms are Ci_io alkyl.

3. The composition of claim 2 wherein the (Al) linear organopolysiloxane comprises silicon-bonded groups which are C^-Cg alkyl groups.

4. The composition of claim 3 in which degree of polymerization of the (Al) linear organopolysiloxane is from 200 to 3,000.

5. The composition of claim 4 in which component (Al) comprises two linear organopolysiloxanes comprising alkenyl groups, designated (Al-l) and (Al-2).

6. The composition of claim 5 in which (Al-l) has a degree of polymerization on the molar average in the range from 150 to 2,000 and (Al-2) has a degree of polymerization on the molar average in the range from 600 to 6,000, where the degree of polymeration of (Al-l) is smaller than the degree of polymerization of (A 1-2).

7. The composition of claim 1 in which a is from 0.02 to 0.08, b is from 0.3 to 0.55 and c is from 0.42 to 0.63.

8. The composition of claim 1 in which R ' is methyl and

is vinyl in (A2).

9. A method for producing a curable silicone composition comprising:

(A2) 30 to 60 parts by weight of at least one resin-type organopolysiloxane comprising units having structures (R R¾iO]/2 a- ( ' 3S i 01 /2 ) h - ^an4 (Si04/2)c where R ' is alkyl, and R^ is alkenyl; where a+b+c is from 0.90 to 1; wherein (A2) further contains less than 5 ppm calcium, less than 5 ppm iron, less than 5 ppm sodium, and APHA color less than 30; and comprising particles having a diameter greater than 500 nm in an amount less than 200,000 per gram;

where (Al) and (A2) add up to 100 parts by weight;

(B) 2 to 25 wt% of a crosslinker relative to the total curable silicone composition; and

(C) 0.1-100 ppm of a hydrosilylation catalyst;

said method comprising the step of filtering a solution of the resin-type polysiloxane (A2) prior to combining components (Al) and (A2).