WO2019177689A1

WO2019177689A1 - Curable polysiloxane composition

Info

Publication number: WO2019177689A1
Application number: PCT/US2019/014109
Authority: WO
Inventors: Yanhu WEI; Steven Swier; Lizhi Liu
Original assignee: Dow Silicones Corporation
Priority date: 2018-03-16
Filing date: 2019-01-18
Publication date: 2019-09-19
Also published as: TW201940554A

Abstract

A curable polysiloxane composition comprising from 10 to 95 wt% of a silanol- functional polysiloxane comprising siloxane units (R¹R²SiO_2/2)a(R³SiO_3/2)b, from 5 to 5000 ppm of a UV latent base catalyst, and from 5 to 90 wt% of particulate phosphors, fillers or a combination thereof; wherein a is from 0.1 to 0.9, b is from 0.1 to 0.9, a+b is at least 0.95; R¹, R² and R³ independently represent hydroxyl or C₁-C₂₀ organic substituent groups; and the silanol-functional polysiloxane comprises from 5 to 50 mole% silanol groups.

Description

CURABLE POLYSILOXANE COMPOSITION

Technical Field

[0001] This invention relates to a curable polysiloxane composition comprising a UV latent base catalyst.

Background

[0002] Polysiloxane materials are useful as industrial solutions for heat- and light-stable encapsulants and protecting materials, as well as a substrate for functional components such as phosphors in the rapidly expanding electronics and optical applications. For efficient and high throughput manufacturing, there is a desire and need for these preparations to cure quickly under moderate conditions. Multitude of polysiloxane compositions have been developed for such purposes. Certain polysiloxane materials that are useful for these applications, in particular condensation cure resin-linear silicones, typically contain unreacted silanol which can be cured with base catalysts, usually amine catalysts. For example, U.S. Application Publication No. 2014/357827 discloses resin-linear silicones cured with amine catalysts, but amine catalysts often do not function effectively in the presence of certain inorganic particulate solids like phosphors or fillers. The inhibition slows down or prevents curing of the composition containing these particulate solids, which are necessary and/or highly useful in the aforementioned applications. U.S. Application Publication No.

2014/335448 describes a photosensitive siloxane resin composition which may contain photobase generators as hardening agents, but the composition does not comprise fillers or phosphors and does not address the cure inhibition issue. U.S. Patent No. 6096483 describes photobase generators to cure a composition of hydrosilyl containing polysiloxanes and silanol containing crosslinkers, but does not address inhibition of UV cure. U.S. Application Publication No. 2005/266344 describes a radiation curable composition comprising a siloxane resin, photoacid or base generator and a curing acceleration catalyst using silsesquioxane resin with low Mw and a quaternary ammonium salt, but the resin

composition is limited.

[0003] Prior publications do not teach a solution to the inhibitory effect of solid components in a composition, and do not offer a satisfactory solution to the technical problem faced by the industry. Summary of the Invention

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

(a) from 10 to 95 wt % of a silanol-functional polysiloxane comprising siloxane units

(R¹R²Si02/2)a(R³Si03/2)b, (b) from 5 to 5000 ppm of a UV latent base catalyst, and (c) from 5 to 90 wt % of particulate phosphors, fillers or a combination thereof; wherein a is from 0.1 to 0.9, b is from 0.1 to 0.9, a+b is at least 0.95 and no more than 1; R¹ _, R² and R³

independently represent hydroxyl or C1-C20 organic substituent groups; and the silanol- functional polysiloxane comprises from 5 to 50 mole% silanol groups. The weight percent is shown relative to the sum of the weight of component (a) polysiloxane and component (c) the particulates (phosphor + filler), i.e. excluding catalyst and any solvent which may be present.

Detailed Description of the Invention

[0005] Percentages are weight percentages (wt%) and temperatures are in °C unless specified otherwise. Operations were performed at room temperature (25 °C) unless specified otherwise. An“organic substituent group” comprises carbon and hydrogen atoms, and may also contain heteroatoms selected from oxygen, nitrogen, silicon, sulfur, phosphorus, bromine, chlorine and fluorine. Preferably, an organic substituent group comprises no more than three oxygen, nitrogen and silicon atoms, preferably no more than two, preferably no more than one, preferably none. A“hydrocarbyl” group is a substituent derived from an aliphatic or aromatic hydrocarbon, which may be linear, branched or cyclic and which may have one or more substituents selected from chloro, fluoro, methyl, ethyl, methoxy and ethoxy. Preferably, hydrocarbyl groups are unsubstituted. Alkyl groups are saturated hydrocarbyl groups that may be straight or branched. Preferably, alkyl groups have from one to six carbon atoms, preferably one or two. Preferably, alkyl groups are unsubstituted. Aryl groups are substituent groups derived from aromatic hydrocarbon compounds which can be mono- or poly-nuclear, and which can have up to three nitrogen atoms substituted for carbon atoms, preferably no more than two, preferably no more than one, preferably none. Aryl groups may be substituted by chloro, fluoro, methyl, ethyl, methoxy or ethoxy groups. Preferably, aryl groups are unsubstituted.

[0006] As used herein,“ppm” means parts per million by weight. 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. Molecular weights are reported herein in units of g/mol. Component (a) - silanol-functional polysiloxane

[0007] The polysiloxane composition of the present invention comprises (a) silanol- functional polysiloxane, comprising siloxane units (R¹R²Si02/2)a(R³Si03/2)b. R¹, R² and R³ independently represent hydroxyl or C₁-C₂₀ organic substituent groups such that R¹ _, R² or R³ may represent hydroxyl on one siloxane unit and an organic substituent group on another siloxane unit. When R¹ _, R² or R³ group represents hydroxyl on a particular silicon atom, that siloxane unit is a silanol unit. The component (a) polysiloxane comprises from 5 to 50 mole% silanol units relative to moles of Si atoms, and all of the non-hydroxyl substituents are C₁-C₂₀ organic substituent groups. Preferably, the polysiloxane comprises at least 8 mole% silanol units, preferably at least 10 mole%; and at the same time preferably no more than 40 mole%, preferably no more than 35 mole%, preferably no more than 30 mole%, preferably no more than 25 mole%, preferably no more than 20 mole% silanol units. Preferably, R¹, R² and R³ independently are hydroxyl or C₁-C₂₀ substituted or unsubstituted hydrocarbyl groups.

Preferably, when R¹, R² or R³ is a C₁-C₂₀ substituted or unsubstituted hydrocarbyl group, it is an alkyl, alkenyl or aryl group; preferably alkyl or aryl group; preferably C₁-C₁₀ aryl or C₁-C₄ alkyl group; preferably methyl, ethyl, or phenyl group; most preferably a combination of methyl and phenyl groups. Preferably, R¹, R² and R³ independently are hydroxyl or substituted or unsubstituted hydrocarbyl groups, such hydrocarbyl groups having 1 - 20 carbon atoms, preferably 1 - 10 carbon atoms, preferably 1 - 8 carbon atoms, preferably 1 - 4 carbon atoms. In preferred embodiment, R¹ is hydroxyl or methyl and R² and R³ are hydroxyl, phenyl or C 1 -Ce alkyl; preferably R² and R³ are hydroxyl, phenyl or C₁-C₄ alkyl, preferably hydroxyl, methyl or phenyl, preferably hydroxyl or phenyl.

[0008] Subscripts“a” and“b” show the molar fraction of (R¹R²Si0_2/2) and (R³Si0_3/2), respectively, relative to the average molecular formula of the polysiloxane of component (a).

Subscript a is from 0.1 to 0.9, subscript b is from 0.1 to 0.9. The sum of a and b (“a+b”) is at least 0.95 and no more than 1. Preferably, a is at least 0.2, preferably at least 0.3, preferably at least 0.4, preferably at least 0.45; and at the same time preferably no more than 0.8, preferably no more than 0.7, preferably no more than 0.6. Preferably, b is at least 0.2, preferably at least 0.3, preferably at least 0.4; and at the same time preferably no more than

0.8, preferably no more than 0.7, preferably no more than 0.6, preferably no more than 0.55.

Preferably, a+b is at least 0.97, preferably at least 0.98, preferably at least 0.99. When a+b is less than 1, the polysiloxane comprises units other than (R¹R²Si0_2/2) and (R³Si0_3/2). Such other units may be (R^SiO 1_/2)0 or (Si0_4/2)_d, where a+b+c+d=l. c and d may each be independently zero. The polysiloxane of component (a) may have short alkylene chains (- CH₂-CH₂-) interrupting the siloxane backbone in small amounts, in particular where

(R¹R²Si02/2) and (R³Si03/2) connect.

[0009] Preferably, the R¹R²Si0_2/2 units are present in the form of a linear polymer having from 30 to 200 units; preferably at least 50, preferably at least 70, preferably at least 80; preferably no more than 170, preferably no more than 150, preferably no more than 140, preferably no more than 130. Preferably, the polysiloxane is a block copolymer, produced by coupling a linear polysiloxane comprising R¹R²Si0_2/2 units with one or more R³Si0_3/2 units. Examples of such block copolymer can be found in U.S. Pat. No. 8,957,147. Briefly, these block copolymers are organopolysiloxanes containing "linear" R¹R²Si0_2/2 siloxy units in combination with "resin" R³Si0_3/2 siloxy units. These organosiloxane copolymers are "block" copolymers, as opposed to "random" copolymers. These organopolysiloxanes contain R¹R²Si0_2/2 and R³Si0_3/2 siloxy units, where the R¹R²Si0_2/2 units are primarily bonded together to form polymeric chains, which are referred herein as "linear blocks". The R³Si0_3/2 units are primarily bonded to each other to form branched polymeric chains, which are referred to as "non-linear blocks". A significant number of these non-linear blocks may further aggregate to form "nano-domains" when solid forms of the block copolymer are provided. More specifically, the R¹R²Si0_2/2 units are arranged in linear blocks having an average of from 10 to 400 R¹R²Si0_2/2 units per linear block, and the trisiloxy units R³Si0_3/2 are arranged in non-linear blocks having a molecular weight of at least 500 g/mol and at least 30% of the non-linear blocks are crosslinked with each other.

[0010] Component (a) is present in the amount of from 10 to 95 wt% of the polysiloxane composition of the present invention, based on the sum of the weight of component (a) polysiloxane and component (c) the particulates (phosphor + filler), i.e. excluding catalyst and any solvent which may be present. Preferably, component (a) is present, relative to the sum of the weight of component (a) polysiloxane and component (c) the particulates (phosphor + filler), in the amount of at least 15 wt% , preferably at least 20 wt%, preferably at least 25 wt%; and at the same time preferably no more than 85 wt%, preferably no more than 75 wt%, preferably no more than 70 wt%, preferably no more than 65 wt%, preferably no more than 60 wt%, preferably no more than 55 wt%, preferably no more than 50 wt%. Component (b) - UV-latent base catalyst

[0011] The polysiloxane composition of the present invention also comprises (b) UV-latent base catalyst. Preferred general structures for a latent base catalyst are shown below:

wherein NB1 designates a cyclic or acyclic tertiary amine, NB2 designates a primary or secondary amine and Ar designates a substituted or unsubstituted aryl group. Preferably, Ar comprises from 5 to 20 carbon atoms, preferably 6 to 15; preferred Ar groups include phenyl, 2-nitrophenyl, 4-nitrophenyl, 2-methoxyphenyl, 4-methoxyphenyl, 2- hydroxyphenyl, 4-hydroxyphenyl, naphthalenyl, anthracenyl and thioxanthone radical.

[0012] Preferably, each of NB1 and NB2 comprises from 5 to 30 carbon atoms, preferably from 6 to 25. The counterion is any anion which forms a salt which is stable in the polysiloxane composition. Preferred counterions include (Ph)₄B (Ph=phenyl), BF₄ , B(C6Fs)₄ , PF₆ , SbF₆ , Cl0₄ , carboxylate and phenylglyoxylate. Preferred nitrogen bases (NB1, NB2) include the following:

2B-TMG

PD Amine 6-DBA-DBU

DBU: l,8-diazabicyclo[5.4.0]undec-7-ene; DBN: l,5-diazabicyclo[4.3.0]non-5-ene; TBD: l,5,7-triazabicyclo[4.4.0]dec-5-ene; PS: proton sponge; PD: pyridine derivatives, where G stands for any substitution groups in any positions of pyridine ring; Amine: alkyl amines, where R, R’ and R” are independently hydrogen or C1-C30 hydrocarbyls; 2B-TMG: 2-tert- butyl-l,l,3,3-tetramethylguanidine; 6-DBA-DBU: 6-dibutylamino-DBU.

[0013] Examples of typical UV latent base catalysts are NB-DBU: 2-nitrobenzyl-DBU; IRGACURE 369 (now commercially available as OMNIRAD 369 from IGM Resins B.V., Waalwijk, The Netherlands): 2-benzyl-2-dimethylamino-l-(4-morpholinophenyl)-butanone- 1; NB-DOA: 2-nitrobenzyl- 1’ , 1’ -dioctyl-carbamate; AP-DBU: acetophenone-DBU.

[0014] Preferably, the amount of UV latent base catalyst, in ppm by weight based on the sum of the weight of component (a) polysiloxane, component (b) catalyst and component (c) particulates, is at least 100 ppm, preferably at least 200 ppm, preferably at least 300 ppm, preferably at least 400 ppm; and at the same time preferably no more than 4000 ppm, preferably no more than 3000, preferably no more than 2000, preferably no more than 1500 ppm. Component (c) particulate phosphors, fillers or a combination thereof

[0015] The polysiloxane composition of the present invention comprises (c) particulate phosphors, fillers or a combination thereof.

[0016] A“phosphor” is a type of wavelength converter that absorbs light at a first wavelength, and responsively emits light at a second wavelength that is different than the first wavelength. For example, a neodymium-doped yttrium- aluminum-garnet (Nd:YAG) phosphor (YAG is yttrium aluminum garnet (Y3AI5O12)), when exposed to white light, or a portion thereof other than yellow light, will responsively emit a yellow light. Phosphors include a variety of metal containing materials such as the oxides, nitrides, oxynitrides, sulfides, selenides, halides, silicates of various metals and rare-earth metals.

[0017] Examples of suitable particulate phosphors comprise at least one of YAG (Y3AI5O12); Ce:YAG; Zn₂Si0₄:Mn (Willemite); ZnS:Ag+(Zn,Cd)S:Ag; ZnS:Ag+ZnS:Cu+Y₂0₂S:Eu; ZnO:Zn; KC1; ZnS:Ag,Cl or ZnS:Zn; (KF,MgF₂):Mn; (Zn,Cd)S:Ag or (Zn,Cd)S:Cu;

Y₂0₂S:Eu+Fe₂0₃, ZnS:Cu,Al; ZnS:Ag+Co-on-Al₂0₃;(KF,MgF₂):Mn; (Zn,Cd)S:Cu,Cl; ZnS:Cu or ZnS:Cu,Ag; MgF₂:Mn; (Zn,Mg)F₂:Mn; Zn₂Si0₄:Mn,As; ZnS:Ag+(Zn,Cd)S:Cu; Gd₂0₂S:Tb; Y₂0₂S:Tb; Y₃Al₅0i₂:Ce; Y₂Si0₅:Ce; Y₃Al₅0i₂:Tb; ZnS:Ag,Al; ZnS:Ag;

ZnS:Cu,Al or ZnS:Cu,Au,Al; (Zn,Cd)S:Cu,Cl+(Zn,Cd)S:Ag,Cl; Y₂Si0₅:Tb; Y₂OS:Tb;

Y₃(Al,Ga)₅0i₂:Ce; Y₃(Al,Ga)₅0i₂:Tb; InB0₃:Tb; InB0₃:Eu; InB0₃:Tb+InB0₃:Eu;

InB0₃:Tb+InB0₃:Eu+ZnS:Ag; (Ba,Eu)Mg₂Ali60₂₇; (Ce,Tb)MgAlnOi9;

BaMgAl ioOi7:Eu,Mn; BaMg₂Ali₆0₂₇:Eu(II); BaMgAlioOi7:Eu,Mn;

BaMg₂Ali₆0₂₇:Eu(II),Mn(II); Ceo_.67Tbo_.33MgAlnOi9:Ce,Tb; Zn₂Si0₄:Mn,Sb₂0₃;

CaSi0₃:Pb,Mn; CaW0₄ (Scheelite); CaW0₄:Pb; MgW0₄; (Sr,Eu,Ba,Ca)₅(P0₄)₃Cl;

Sr₅Cl(P0₄)₃:Eu(II); (Ca,Sr,Ba)₃(P0₄)₂Cl₂:Eu; (Sr,Ca,Ba)io(P0₄)₆Cl₂:Eu; Sr₂P₂0₇:Sn(II); Sr₆P5BO₂₀:Eu; Ca₅F(P0₄)₃:Sb; (Ba,Ti)₂P₂0₇:Ti; 3Sr₃(P0₄)₂.SrF₂:Sb,Mn; Sr₅F(P0₄)₃:Sb,Mn; Sr₅F(P0 )₃:Sb,Mn; LaP0 :Ce,Tb; (La,Ce,Tb)P0 ;(La,Ce,Tb)P0 :Ce,Tb;

Ca₃(P0 )₂.CaF₂:Ce,Mn; (Ca,Zn,Mg)₃ (P0 )₂:Sn; (Zn,Sr)₃(P0 )₂:Mn; (Sr,Mg)₃(P0 )₂:Sn; (Sr,Mg)₃(P0₄)₂: Sn(II) ; Ca₅F(P0₄)₃:Sb,Mn; Ca₅(F,Cl)(P0₄)₃:Sb,Mn; (Y,Eu)₂0₃; Y₂0₃:Eu(III); Mg₄(F)Ge0₆:Mn; Mg₄(F)(Ge,Sn)0₆:Mn; Y(P,V)0₄:Eu; YV0₄:Eu; Y₂0₂S:Eu; 3.5 MgO · 0.5 MgF₂ · Ge0₂ :Mn; Mg₅As₂0n:Mn; SrAl₂0₇:Pb; LaMgAlnOi9:Ce; LaP0₄:Ce; SrAli₂0i₉:Ce; BaSi₂0₅:Pb; SrFB₂0₃:Eu(II); SrB₄0₇:Eu; Sr₂MgSi₂0₇:Pb; MgGa₂0₄:Mn(II); Gd₂0₂S:Tb; Gd₂0₂S:Eu; Gd₂0₂S:Pr; Gd₂0₂S:Pr,Ce,F; Y₂0₂S:Tb; Y₂0₂S:Eu; Y₂0₂S:Pr;

Zn(0.5)Cd(0.4)S:Ag; Zn(0.4)Cd(0.6)S:Ag; CdW0₄; CaW0₄; MgW0₄;

Y₂Si0₅:Ce;YAl0₃:Ce; Y₃Al₅0i₂:Ce; Y₃(Al,Ga)₅0i₂:Ce; CdS:In; ZnO:Ga; ZnO:Zn;

(Zn,Cd)S:Cu,Al; ZnS:Cu,Al,Au; ZnCdS:Ag,Cu; ZnS:Ag; anthracene, EJ-212, Zn₂Si0₄:Mn; ZnS:Cu; NaPTl; CshTl; LiF/ZnS:Ag; LiF/ZnSCu,Al,Au; and nitrides such as ,

LaAl(Si₆Al₃)N₇0₃:Ce³⁺; Cao_.898Ceo_.o₆₈Si₉Al₃ONi₅; La_4.9Ceo_.iSi₃Oi₂N; Lao_.96Ceo_.o₄Si0₂N; La_2.82Ce_0.i8Si₈O₄Nii; (Ca,Sr,Ba)Si₂0₂N₂:Eu²⁺; (Sr,Ba)YSi₄N₇:Eu²⁺; (Ca,Sr,Ba)₂Si₅N₈:Eu²⁺; and (Sr,Ca)AlSiN₃:Eu²⁺.

[0018] A particulate filler, as used herein, means any finely divided organic or inorganic solid other than a particulate phosphor. The size of the particles need not be of any particular size, but preferably are fine particulates.“Fine particulates” are particulates having a mean particle size of 0.01 pm (micrometer) to 50 pm, as measured by laser diffraction particle size analyzers (for example CILAS920 Particle Size Analyzer or Beckman Coulter LS 13 320 SW) according to the operation software and shown as number average particle size. For particles smaller than those having 1 pm, scanning electron microscopy is used to visualize and measure particle size. For convenience, the average particle size may be estimated based on measuring the surface area according to 8-11 ASTM D4315 or by using sieves of various mesh sizes and calculating the average from the cumulative weight of each size fractions.

[0019] Particulate fillers useful in the composition may be reinforcing fillers, conductive fillers (thermally and/or electrically conductive), pigments (not phosphors), and extending fillers. Particulate fillers may be thixotropic. Any particulate filler may be added to the polysiloxane composition, but the advantage of the polysiloxane composition of the present invention is more apparent when the filler particulates have surface characteristics that would cause inhibition of non-latent UV base catalysts such as DBU. Such fillers would have active groups on the surface, most typically oxides, that would cause inhibition of base catalysts. The surface of the fillers may also be seen has having acidic properties. Without wishing to be bound by the theory, the inhibition of organic base catalysts by phosphor/fillers is likely caused mainly due to two reasons: (1) the fillers that cause catalyst inhibition comprise many Lewis acid sites (e.g., the metal cation centers) on the surface, which may cause organic bases to tightly bind to them, and (2) the large and porous surfaces of fillers can confine the tightly binding organic bases and prevent them from presenting the active catalytic site even upon heating. Examples of suitable particulate fillers that show inhibition of base catalysts include but are not limited to at least one of SiCk, TiCk, AI2O3, ZrCk, BaTiCk, Ta₂05, Fe^Ck, ZnO, and SrTiCk, A1N, S13N4, and BN. Preferably, the particulate filler may be fumed silica or titanium oxide that have been shown to cause inhibition of conventional base catalysts.

[0020] Preferably, the polysiloxane composition comprises at least 15 wt% of the particulates, preferably at least 25 wt%, preferably at least 30 wt%, preferably at least 35 wt%, preferably at least 40 wt%, preferably at least 45 wt%, preferably at least 50 wt%; and at the same time preferably no more than 85 wt%, preferably no more than 80 wt%, preferably no more than 75 wt%, preferably no more than 70 wt%. Preferably, the polysiloxane comprises at least 8 mole% silanol groups, preferably at least 10 mole%; and at the same time, preferably no more than 40 mole%, preferably no more than 35 mole%, preferably no more than 30 mole%, preferably no more than 25 mole%, preferably no more than 20 mole%. Other components.

[0021] Preferably, the curable polysiloxane composition further comprises one or more solvents used to adjust the viscosity of the composition. The amount of solvent to achieve a desired viscosity is easily determined for a particular composition, but preferably solvent(s) is present in an amount from >0 to 50 wt%, based on the sum of the weight of components (a), (b) and (c), preferably from 5 to 30 wt%. Any solvent chemically compatible with the other components and capable of reducing viscosity may be used, but preferred solvents include hydrocarbons, esters, ketones; preferably Ce-C i x hydrocarbons, C3-C18 esters, C4-C18 ketones; preferably toluene, heptane, propyl propionate, butyl acetate, methyl isobutyl ketone.

Use for the curable polysiloxane composition

[0022] The curable polysiloxane composition described herein may be used for any application where curing a silicone composition by UV is desirable, but particularly useful in optical applications where polysiloxane -based encapsulants and remote phosphor is needed. The curable polysiloxane is substantially transparent to visible light and is well suited for optical use. The curable polysiloxane composition may be formed into film and applied in position, after which it is fully cured. Thus, one aspect of the invention is phosphor containing film formed by curing the curable polysiloxane composition. Such film may have any thickness such as 10, 20, 30, 50, 100, 125, or 150 micrometers, and may be as thick as 200, 300, or 500 micrometers. Film may be manufactured by coating the curable polysiloxane composition onto a substrate or a release liner. Such film may be used as light emitting diode (LED) encapsulant or, positioned away from the direct contact with the LED, as remote phosphor. The LED may be incorporated into various optical devices.

Methods and definitions

[0023] The following terms are used herein with the intention to give them the meanings as described below. The articles“a”,“an”, and“the” each refer to one or more.“Combination” means two or more items put together by any method.“May” indicates a choice. Weight percent is shown as wt%. Molar percent is shown as mole%.

[0024] Molar fraction of siloxane units and side chains were determined by ^^Si-NMR and H-NMR. NMR samples of test materials were prepared by weighing about 4 grams of solvent free polysiloxane material (prepared by drying sample overnight at room temperature), and 4 grams of 0.04M Cr(acac)₃ solution in CDCL into a vial and mixing thoroughly. Samples were then transferred into a silicon- free NMR tube. Spectra were acquired using a Varian Mercury 400 MHz NMR.

[0025] Silanol content of a sample was calculated from the integration values of the

T(Ph,OZ) and T(Ph,OZ2) regions in the 29Si NMR spectrum. T(Alkyl) groups were considered fully condensed (assumption) and subtracted from the T(Ph,OZ) region. The T(Alkyl) content was calculated by multiplying the integration value of D(Me ) from ²⁹Si NMR by the fraction (mols Si of coupling agent/mols Si of PDMS used in the synthesis formulation).

[0026] Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain both a reference to the testing society and the test method number. ASTM refers to ASTM International.

Examples

[0027] These examples are intended to illustrate the invention to one skilled in the art and should not be interpreted as limiting are not necessarily meant to limit the scope of the invention set forth in the claims.

Methods

[0028] UV irradiation: The coated films were irradiated by using a Fusion UV System Inc. Coater (now Heraeus Noblelight, Hanau, Germany) with a UV power of 1-5 J/cm² before folding for rheology test. The UV coater provides a broad UV band from 200 nm to 450 nm.

[0029] Rheology test: Rheology test was done by using the ARES-G2 Rheometer (TA Instruments, New Castle, Delaware, USA) following a program of ramping from 70°C to 125 (or 150) °C with l0°C/min and isothermal at 125 (or 150) °C for 60 min.

Preparation of Polysiloxane-1:

[0030] Step I: capping silanol-terminated polyphenylmethylsiloxane with

methyltriacetoxysilane/ethyltriacetoxysilane (MTA/ETA): 18.49 g (0.0813 mole Si) mixed MTA and ETA (1:1 ratio) were added to a solution of 880 g polyphenylmethylsiloxane (6.456 mole Si) in a glove box under nitrogen, followed by stirring at room temperature for 1 hour to obtain the capped siloxane solution.

[0031] Step II: preparing the Polysiloxane-1 copolymer: a mixture of 720 g (5.271 mole Si) phenyl-T resin (comprising C H S O units, Mw: about 2000, silanol content: about 65 mole%) and 601 g propyl propionate was added into a 5L 4-neck round bottom flask equipped with a thermometer, mechanic stir, a water-cooled condenser attached with a Dean- Stark apparatus under a nitrogen blanket. The Dean-Stark apparatus was prefilled with propyl propionate and a heating mantle was used for heating. The reaction was heated at reflux for 30 min and 3.82 g water was removed. Then the capped siloxane solution from Step I was added to the phenyl-T resin solution quickly, followed by refluxing for 2 hours with 5.58 g water removed. At H5°C, about 134.1 g MT A/ETA (1:1 ratio, 0.589 mole) was added to the reaction mixture, and then heated at reflux for 2 hours with about 2.72 g water removed. Finally three times of water treatment were done to the reaction. For each water treatment, the reaction was cooled to l00°C, 174 g deionized water was added, and then heated at reflux for a while and water was removed by azeotropic distillation. At last, partial solvents were removed by distillation to increase the final non-volatile content (NVC) to 73.4% as the Poly siloxane- 1 product solution for future use. The prepared Polysiloxane-l contains about 15 mole% silanol.

COMPARATIVE EXAMPLE A

[0032] 5g of silanol containing Polysiloxane-l (containing 15 mole% silanol) were mixed with DBU (200ppm) in a SpeedMixer™ (Flack Tek Inc., Landrum, South Carolina, USA) to achieve a homogeneous paste. The paste was coated on a siliconized polyethylene terephthalate (PET) film at 125 pm thickness using a drawdown bar. The coated film was pre-baked at 70°C for 30 minute to remove all solvent. The coated film was folded and hot pressed into 1 millimeter thick puck and then punched to 1 inch (2.54 cm) diameter for rheology test. The temperature profile of the rheometer was from 70°C to l25°C at l0°C/minute and then dwell for 60 minutes. The film cured within 0.1 min at the test conditions.

COMPARATIVE EXAMPLE B

[0033] 5g of Polysiloxane-l were mixed with DBU (200ppm) and lOg phosphors

(commercial YAG type phosphors from MATERION, Mayfield Heights, Ohio, USA) in a SpeedMixer to achieve a homogeneous paste. The paste was coated on a siliconized PET film at 125 pm thickness using a drawdown bar. The coated film was pre-baked at 70°C for 30 minute to remove all solvent. The coated film was folded and hot pressed into 1 millimeter thick puck and then punched to 1 inch (2.54 cm) diameter for rheology test. The temperature profile of the rheology was from 70°C to 125 °C at lO°C/minute and then dwell for 60 minutes. The film did not cure at the test conditions

EXAMPLE 1

[0034] 5g of Polysiloxane-1 were mixed with NB-DBU (2-nitrobenzyl-DBU, synthesized by the inventors) (800ppm) and lOg phosphors (YAG) in a SpeedMixer to achieve a

homogeneous paste. The paste was coated on a siliconized PET film at 125 pm thickness using a drawdown bar. The coated film was pre-baked at 70°C for 30 minute to remove all solvent. Without ultraviolet (UV) irradiation, the coated film was folded and hot pressed into 1 millimeter thick puck and then punched to 1 inch diameter for rheology test. The temperature profile of the rheometer was from 70°C to l25°C at l0°C/minute and then dwell for 60 minutes. The film did not cure at the test conditions.

EXAMPLE 2

[0035] 5g of Polysiloxane-1 were mixed with NB-DBU (800ppm) and lOg phosphors (YAG) in a SpeedMixer to achieve a homogeneous paste. The paste was coated on a siliconized PET film at 125 pm thickness using a drawdown bar. The coated film was pre-baked at 70°C for 30 minute to remove all solvent. The coated film was first irradiated with 365 nm UV light (3J/cm²) and then folded and hot pressed into 1 millimeter thick puck and then punched to 1 inch (2.54 cm) diameter for rheology test. The temperature profile of the rheometer was from 70°C to l25°C at l0°C/minute and then dwell for 60 minutes. The film cured within 3 minutes.

EXAMPLE 3

[0036] 5g of Polysiloxane-1 were mixed with NB-DBU (800ppm) in a SpeedMixer to achieve a homogeneous paste. The paste was coated on a siliconized PET film at 125 pm thickness using a drawdown bar. The coated film was pre-baked at 70°C for 30 minute to remove all solvent. The coated film was irradiated with 365 nm UV light (3J/cm²) and then folded and hot pressed into 1 millimeter thick puck and then punched to 1 inch (2.54 cm) diameter for rheology test. The temperature profile of the rheometer was from 70°C to 125 °C at l0°C/minute and then dwell for 60 minutes. The film cured within half a minute.

[0037] Table 1 shows the key data from rheology tests for EXAMPLES 1-3 and

COMPARATIVE EXAMPLES A-B. 800 ppm NB-DBU can theoretically release 200 ppm DBU upon UV irradiation. The time for Tan5=l indicates the cure speed. The shorter the time, the faster the cure speed is.

Table 1

[0038] The data from COMPARATIVE EXAMPLES A and B show that the addition of phosphor YAG-D (about 67 wt%) almost completely inhibited the catalytic activity of DBU catalysts. However, replacing DBU by UV latent DBU catalysts, for example NB-DBU, overcomes the phosphor inhibition issue of DBU. The rheology results from EXAMPLE 1-3 clearly indicate that the addition of 67 wt% YAG phosphors to the formulation containing NB-DBU catalysts (EXAMPLE 2) does not slow the cure speed down much compared with that of the formulation without phosphors (EXAMPLE 3) with UV irradiation to release DBU catalysts. The formulation of EXAMPLE 1 containing NB-DBU and phosphor YAG shows no cure without UV irradiation to release DBU catalysts.

[0039] The cure tests from EXAMPLES 4-7 further demonstrate that the UV- latent base catalysts can greatly reduce the phosphor inhibition issue of DBU which had been seen in previous compositions.

EXAMPLE 4: Cure of film by this invented formulation without UV activation:

[0040] Polysiloxane-1 is used as the base siloxane. IRGACURE 369 was dissolved in toluene to prepare the 10 wt% stock catalyst solution. 0.5 wt% IRGACURE 369 was added into Polysiloxane-1 to have the curable organosiloxane formulation. The formulation was coated into film and tested for rheology the same way as in Comparative Example A except ramping from 70°C to l50°C and isothermal at l50°C for 60 min. The film did not cure during the test time frame, but extrapolating the data indicated that the formulation was expected to cure in 130 minutes.

EXAMPLE 5: Cure of film hv this invented formulation with UV activation:

[0041] The film in Example 4 was exposed to UV irradiation at 248nm for l000mJ/cm².

Then the exposed film was tested for rheology the same way as in Comparative Example A except ramping from 70°C to l50°C and isothermal at l50°C for 60 min. The film cured within 1 minutes.

EXAMPLE 6: Cure of phosnhor film of this invented formulation without UV activation:

[0042] 5g of this invented formulation in Example 5 were mixed with llg of phosphors (NYAG4355+NYAG4136+RR6536 at 5:5: 1 weight ratio, all phosphors from Intematix, Inc., Freemont, California, USA) on a SpeedMixer to achieve a homogeneous paste. The paste was then coated into film and tested for rheology the same way as in Comparative Example A except ramping from 70°C to l50°C and isothermal at l50°C for 60 min. The phosphor film did not cure at test condition.

EXAMPLE 7 : Cure of phosphor film of this invented formulation with UV activation:

[0043] The film in Example 6 was exposed to UV irradiation at 248nm for 2000mJ/cm².

Then the exposed phosphor film was tested for rheology the same way as in Comparative Example A except ramping from 70°C to l50°C and isothermal at l50°C for 60 min. The exposed phosphor film cured within 5 minutes.

Industrial Applicability

[0044] The curable polysiloxane composition described herein may be used for any application where curing a silicone composition by UV is desirable. The curable polysiloxane composition is particularly useful in optical applications and in photovoltaic applications including solar photovoltaic apparatuses where rapidly curing polysiloxane-based encapsulants and remote phosphor is needed.

Claims

Claim 1.

A curable polysiloxane composition comprising:

(a) from 10 to 95 wt% of a silanol-functional polysiloxane comprising siloxane units

(R¹R²Si0_2/2)a(R³Si0_3/2)b,

(b) from 5 to 5000 ppm of a UV latent base catalyst, and

(c) from 5 to 90 wt% of particulate phosphors, fillers or a combination thereof;

wherein the wt% is determined relative to the sum of the weight of component (a) polysiloxane and component (c) the particulates being 100 wt%, subscript a is from 0.1 to 0.9, b is from 0.1 to 0.9, a+b is at least 0.95 and no more than 1; R¹ _, R² and R³ independently represent hydroxyl or C1-C20 organic substituent groups; and the silanol-functional polysiloxane comprises from 5 to 50 mole% silanol groups.

Claim 2.

The composition of claim 1 in which R¹ _, R² and R³ independently represent hydroxyl, alkyl, alkenyl or aryl groups.

Claim 3.

The composition of claim 2 in which R¹ _, R² and R³ independently represent hydroxyl, C1-C10 aryl or C1-C4 alkyl.

Claim 4.

The composition of any one of claims 1 to 3 wherein the polysiloxane is a block copolymer comprising a linear portion comprising (R¹R²Si0_2/2) units and a resinous portion comprising (R³Si03/2) units.

Claim 5.

The composition of any one of claims 1 to 4 further comprising one or more solvents in a total amount up to 50 wt%, based on total weight of components (a), (b) and (c).

Claim 6.

The composition of any one of claims 1 to 5 in which the UV latent base catalyst is one of formulae (I) to (IV) (I)

wherein NB1 designates a cyclic or acyclic tertiary amine, NB2 designates a primary or secondary amine, the counterion is any anion which forms a salt which is stable in the polysiloxane composition and Ar designates a substituted or unsubstituted aryl group.

Claim 7.

The composition of claim 6 wherein the UV latent base catalyst is NB-DBU.

Claim 8.

The composition of any one of claims 1 to 7 wherein component (c) comprises a YAG phosphor.

Claim 9.

A film comprising the cured product of the composition of any of claims 1 to 8.

Claim 10.

A method of forming a film product comprising the step of coating a substrate or a liner with the composition of any of claims 1 to 8, irradiating with UV light, and heating the film to at least 70 degrees Celsius.