JP6863878B2 - Additive-curable silicone compositions, cured products, and optics - Google Patents

Description

The present invention relates to an addition-curable silicone composition, a cured product, and an optical element.

The addition-curable silicone composition contains a polyorganosiloxane containing an aliphatic unsaturated group such as an alkenyl group, and is cured by a hydrosilylation reaction to give a cured product. The cured product thus obtained is excellent in heat resistance, cold resistance, and electrical insulation, and is transparent, so that it is used in various optical applications.

Silicone rubber used for optical applications is required to have high transparency and high refractive index, and in order to achieve this, a method of using a dimethylsiloxane / diphenylsiloxane copolymer or polymethylphenylsiloxane as the main skeleton is generally performed. (Patent Documents 1 to 9).

However, when a conventional composition combining a branched organopolysiloxane and a linear organopolysiloxane was used in order to increase the strength of the cured product, a product that sufficiently satisfied the mechanical properties could not be obtained. ..

Japanese Unexamined Patent Publication No. 2005-307015 Japanese Unexamined Patent Publication No. 2004-143361 Japanese Unexamined Patent Publication No. 2004-186168 Japanese Unexamined Patent Publication No. 2004-292807 Japanese Unexamined Patent Publication No. 2004-359756 Japanese Unexamined Patent Publication No. 2005-076003 Japanese Unexamined Patent Publication No. 2005-105217 Japanese Unexamined Patent Publication No. 2010-132795 Japanese Unexamined Patent Publication No. 2014-205823

The present invention has been made in view of the above circumstances, and has high transparency and a refractive index, good strength characteristics (mechanical characteristics), and additional curing that gives a cured product that can be used as an optical element encapsulant. It is an object of the present invention to provide a mold silicone composition.

（式中、Ｒ^１及びＲ^２は同種又は異種の非置換もしくは置換の一価炭化水素基であり、Ｒ^３はフェニル基又はナフチル基であり、ａは０〜５０の整数であり、ｂは０〜１００の整数であり、かつ、ａ＋ｂは１以上の整数である。括弧が付されたシロキサン単位の配列はランダムであってもブロックであってもよい。）
（Ｂ）下記式（２）で表されるシロキサン単位を有するオルガノハイドロジェンポリシロキサン化合物、

及び、（Ｃ）白金族金属を含むヒドロシリル化触媒を含む付加硬化型シリコーン組成物を提供する。 In order to achieve the above problems, in the present invention, (A) an organopolysiloxane compound represented by the following formula (1),

(In the formula, R ¹ and R ² are homovalent or heterologous unsubstituted or substituted monovalent hydrocarbon groups, R ³ is a phenyl group or a naphthyl group, a is an integer of 0 to 50, and b is an integer of 0 to 50. It is an integer from 0 to 100, and a + b is an integer of 1 or more. The parenthesized sequence of siloxane units may be random or block.)
(B) An organohydrogenpolysiloxane compound having a siloxane unit represented by the following formula (2),

And (C) an addition-curable silicone composition containing a hydrosilylation catalyst containing a platinum group metal.

Such an addition-curable silicone composition can provide a cured product having high transparency and a refractive index and good strength characteristics.

Further, in the above formula (1), ^{it is preferable that R 1} and R ² are a methyl group or a phenyl group.

If it is such a thing, it can be suitably used as the component (A).

Further, in the above formula (1), ^{it is preferable that R 1} is a methyl group and R ² is a phenyl group.

Such a material has particularly high transparency, refractive index, and strength characteristics, and can be suitably used as the component (A).

（式（４）中、ｌは１〜５の整数であり、ｍは１〜５の整数である。ｌ及びｍが付された括弧内のシロキサン単位の配列はランダムであってもブロックであってもよい。） Further, it is preferable that the organohydrogenpolysiloxane compound of the component (B) is one or more compounds selected from the organohydrogenpolysiloxane compounds represented by the following formulas (3) to (6).

(In formula (4), l is an integer of 1 to 5, m is an integer of 1 to 5. The arrangement of siloxane units in parentheses with l and m is a block even if it is random. May be.)

If it is such a thing, it can be suitably used as the component (B).

The present invention also provides a cured product obtained by curing the addition-curable silicone composition.

Such a cured product can be suitably used as an optical element encapsulant.

Furthermore, the present invention provides an optical element sealed with a cured product of the addition-curable silicone composition.

Since the cured product of the present invention has high transparency and refractive index and good strength characteristics, the optical element sealed with such a cured product has high reliability.

As described above, the addition-curable silicone composition of the present invention has high transparency, high refractive index, and good strength characteristics by being cured, and can be suitably used as an optical element encapsulant. A cured product that can be obtained can be obtained.

As described above, there has been a demand for the development of an add-curable silicone composition that has high transparency and refractive index, has good strength characteristics, and provides a cured product that can be used as an optical element encapsulant.

As a result of diligent studies on the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved with an addition-curable silicone composition containing the components (A), (B), and (C) described later. , The present invention has been completed.

（式中、Ｒ^１及びＲ^２は同種又は異種の非置換もしくは置換の一価炭化水素基であり、Ｒ^３はフェニル基又はナフチル基であり、ａは０〜５０の整数であり、ｂは０〜１００の整数であり、かつ、ａ＋ｂは１以上の整数である。括弧が付されたシロキサン単位の配列はランダムであってもブロックであってもよい。）
（Ｂ）下記式（２）で表されるシロキサン単位を有するオルガノハイドロジェンポリシロキサン化合物、

及び、（Ｃ）白金族金属を含むヒドロシリル化触媒、
を含む付加硬化型シリコーン組成物である。 That is, the present invention describes (A) an organopolysiloxane compound represented by the following formula (1).

(In the formula, R ¹ and R ² are homovalent or heterologous unsubstituted or substituted monovalent hydrocarbon groups, R ³ is a phenyl group or a naphthyl group, a is an integer of 0 to 50, and b is an integer of 0 to 50. It is an integer from 0 to 100, and a + b is an integer of 1 or more. The parenthesized sequence of siloxane units may be random or block.)
(B) An organohydrogenpolysiloxane compound having a siloxane unit represented by the following formula (2),

And (C) a hydrosilylation catalyst containing a platinum group metal,
It is an addition hardening type silicone composition containing.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[Additionally curable silicone composition]
The addition-curable silicone composition of the present invention contains the following components (A), (B), and (C). Hereinafter, each component will be described in detail.

（式中、Ｒ^１及びＲ^２は同種又は異種の非置換もしくは置換の一価炭化水素基であり、Ｒ^３はフェニル基又はナフチル基であり、ａは０〜５０の整数であり、ｂは０〜１００の整数であり、かつ、ａ＋ｂは１以上の整数である。括弧が付されたシロキサン単位の配列はランダムであってもブロックであってもよい。） <Ingredient (A)>
The component (A) consists of repeating a siloxane unit having a phenyl group in the side chain and / or a siloxane unit having a phenyl group or a naphthyl group in the side chain, and contains a vinyl group bonded to a silicon atom at both ends of the molecular chain. It is a linear diorganopolysiloxane sealed with a triorganosyloxy group and is represented by the formula (1).

(In the formula, R ¹ and R ² are homovalent or heterologous unsubstituted or substituted monovalent hydrocarbon groups, R ³ is a phenyl group or a naphthyl group, a is an integer of 0 to 50, and b is an integer of 0 to 50. It is an integer from 0 to 100, and a + b is an integer of 1 or more. The parenthesized sequence of siloxane units may be random or block.)

^{Examples of the unsubstituted or substituted monovalent hydrocarbon group represented by R 1} and R ² in the above formula (1) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and sec. -Alkyl group having 1 to 6 carbon atoms such as butyl group and tert-butyl group; haloalkyl group having 1 to 4 carbon atoms such as chloromethyl group and 3,3,3-trifluoropropyl group; phenyl group and trill Aryl groups having 6 to 10 carbon atoms such as groups; alkenyl groups having 1 to 6 carbon atoms such as vinyl groups and allyl groups can be mentioned. Among them, an alkyl group having 1 to 6 carbon atoms, a phenyl group and a vinyl group are preferable, and among them, an alkyl group having 1 to 6 carbon atoms, a phenyl group and a vinyl group are preferable, and a methyl group and a phenyl group are more preferable. Yes, particularly preferably R ¹ is a methyl group and R ² is a phenyl group.

R ³ is a phenyl group or a naphthyl group, preferably a phenyl group.

In the component (A), the degree of polymerization a of the diphenylsiloxane unit is an integer of 0 to 50, preferably 1 to 10, more preferably 1 to 7, and particularly preferably 2 to 4. .. The degree of polymerization b of the methylarylsiloxane unit is an integer of 0 to 100, preferably 0 to 50, more preferably 1 to 10, and particularly preferably 2 to 4.
a + b is an integer of 1 or more, and always contains at least one of a diphenylsiloxane unit and a methylarylsiloxane unit. The arrangement of these diphenylsiloxane units and methylarylsiloxane units may be random or block.

The organopolysiloxane of the component (A) may be used alone or in combination of two or more having different molecular weights, types of organic groups bonded to silicon atoms, and the like.

The component (A) is an aliphatic unsaturated group-containing terminal encapsulant after hydrolyzing / condensing a bifunctional silane such as dichlorodiphenylsilane or dialkoxydiphenylsilane, or at the same time as hydrolysis / condensation. It can be obtained by sealing the ends.

<Ingredient (B)>
The component (B) of the present invention is an organohydrogenpolysiloxane compound having a siloxane unit represented by the following formula (2).

（式中、ｌは１〜５の整数であり、ｍは１〜５の整数である。ｌ及びｍが付された括弧内のシロキサン単位の配列はランダムであってもブロックであってもよい。）

Specific examples of the component (B) include compounds represented by the following formulas (3) to (6).

(In the formula, l is an integer of 1 to 5, m is an integer of 1 to 5. The arrangement of siloxane units in parentheses with l and m may be random or block. .)

Further, the component (B) may be used alone or in combination of two or more kinds of the component (B).

The blending amount of the component (B) is preferably such that the molar ratio of the SiH group in the component (B) to the vinyl group in the component (A) is 0.2 to 5, more preferably 0.5 to 2. Is the amount.

<Ingredient (C)>
If the hydrosilylation catalyst containing the platinum group metal of the component (C) promotes the hydrosilylation addition reaction between the vinyl group bonded to the silicon atom in the component (A) and the SiH group in the component (B). Any catalyst may be used. The component (C) may be used alone or in combination of two or more. Examples of the component (C) include platinum group metals such as platinum, palladium and rhodium, platinum chloride acid, alcohol-modified platinum chloride acid, a coordination compound between platinum chloride acid and olefins, vinylsiloxane or an acetylene compound, and tetrakis. Examples thereof include platinum group metal compounds such as (triphenylphosphine) palladium and chlorotris (triphenylphosphine) rhodium, and platinum compounds are particularly preferable.

The blending amount of the component (C) may be an effective amount as a hydrosilylation catalyst, preferably 0.1 to 1000 ppm in terms of mass of the platinum group metal element with respect to the total mass of the components (A) and (B). It is in the range, more preferably in the range of 1 to 500 ppm.

<Other ingredients>
In addition to the above-mentioned components (A) to (C), any other component may be added to the composition of the present invention. Specific examples thereof include the following. Each of these other components may be used alone or in combination of two or more.

(Alphatic unsaturated group-containing compound other than component (A))
In addition to the component (A), the composition of the present invention may contain an aliphatic unsaturated group-containing compound that undergoes an addition reaction with the component (B). As such an aliphatic unsaturated group-containing compound other than the component (A), those involved in the formation of a cured product are preferable, and compounds other than the component (A) having at least two aliphatic unsaturated groups per molecule are used. Examples include polyorganosiloxane. The molecular structure may be, for example, linear, cyclic, branched chain, three-dimensional network, or the like.

(Organohydrogensiloxane other than component (B))
Further, the composition of the present invention has a hydrogen atom (that is, a SiH group) bonded to at least two silicon atoms per molecule other than the component (B), and has an aliphatic unsaturated group. Organic silicon compounds that do not exist may be used in combination.

(Addition reaction control agent)
An addition reaction control agent can be added to the composition of the present invention in order to secure the pot life. The addition reaction control agent is not particularly limited as long as it is a compound having a curing inhibitory effect on the hydrosilylation catalyst of the component (C), and conventionally known ones can also be used. Specific examples thereof include 1,3,5,7 methylvinyl cyclotetrasiloxane, units represented by the following structural formula _{^{(R 4 2 SiO 2/2) c}} (R 4 (CH 2 = CH) SiO 2/2) d (R ⁴ ₃ SiO _1/2 ) ₂
{In the formula, R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group which may be the same or different (however, 10 mol% or more of ^{R 4 is an aryl group).} c is 0 or a positive number, and d is a positive number. } And other siloxane compounds; phosphorus-containing compounds such as triphenylphosphine; nitrogen-containing compounds such as tributylamine, tetramethylethylenediamine and benzotriazole; sulfur-containing compounds; acetylene alcohols (eg, 1-ethynylcyclohexanol, 3,5- Examples thereof include acetylene compounds such as dimethyl-1-hexin-3-ol); compounds containing two or more alkenyl groups; hydroperoxy compounds; and maleic acid derivatives. The content of this addition reaction inhibitor is not limited, but is preferably in the range of 0.0001 to 5 parts by mass with respect to 100 parts by mass of the component (A). The degree of curing inhibitory effect of the addition reaction control agent depends on the chemical structure of the addition reaction control agent. Therefore, it is preferable to adjust the addition amount of each of the addition reaction control agents to be used to an optimum amount. By adding the optimum amount of the addition reaction control agent, the composition becomes excellent in long-term storage stability and heat curability at room temperature.

(Adhesive imparting agent)
Further, the present composition may contain an adhesive imparting agent for improving the adhesiveness thereof. The adhesion-imparting agent is preferably an organosilicon compound having at least one, preferably two or more alkoxy groups bonded to a silicon atom in one molecule. Examples of this alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and a methoxyethoxy group, and a methoxy group is particularly preferable. As the groups other than alkoxy groups bonded to the silicon atom of the organosilicon compound, exemplified as R ¹ and the like, the alkyl group, the alkenyl group, the aryl group, the aralkyl group, such as the halogenated alkyl group Substituent or unsubstituted monovalent hydrocarbon group; glycidoxyalkyl group such as 3-glycidoxypropyl group, 4-glycidoxybutyl group; 2- (3,4-epoxycyclohexyl) ethyl group, 3- ( Epoxycyclohexylalkyl group such as 3,4-epoxycyclohexyl) propyl group; epoxy group-containing monovalent organic group such as oxylanylalkyl group such as 4-oxylanylbutyl group and 8-oxylanyloctyl group; 3- An acrylic group-containing monovalent organic group such as a methacryloxypropyl group; a hydrogen atom is exemplified. Specific examples thereof include a silane coupling agent such as an epoxy group-containing silane coupling agent and a (meth) acrylic group-containing silane coupling agent, and a partially hydrolyzed condensate thereof (oligomer of the silane coupling agent).

More specifically, silane compounds such as 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxidecyclohexyl) ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane; silicon atoms in one molecule. Silicon atom-bonded hydroxy in one molecule with a siloxane compound having at least one bonded alkenyl group or silicon atom-bonded hydrogen atom and at least one silicon atom-bonded alkoxy group, and a silane compound or siloxane compound having at least one silicon atom-bonded alkoxy group. Examples thereof include a mixture of a siloxane compound having at least one group and at least one silicon atom-bonded alkenyl group, methyl polysilicate, ethyl polysilicate, and epoxy group-containing ethyl polysilicate.

The adhesive is preferably a low-viscosity liquid, and its viscosity is not limited, but is preferably in the range of 1 to 500 mPa · s at 25 ° C.

Further, in the above composition, the content of this adhesive-imparting agent is not limited, but is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the component (A).

(Other optional ingredients)
The addition-curable silicone composition of the present invention may be blended with an inorganic filler such as fumed silica, silica, glass, alumina, and zinc oxide in order to further improve the strength. Further, if necessary, an organic resin fine powder such as a polymethacrylate resin; a heat resistant agent; a dye; a pigment; a flame retardant imparting agent; a solvent or the like may be blended.

Further, in order to suppress the occurrence of coloring, cloudiness, oxidative deterioration, etc. of the cured product, a conventionally known antioxidant such as 2,6-di-t-butyl-4-methylphenol is added to the composition of the present invention. be able to.

Further, in order to adjust the hardness after curing, an organopolysiloxane represented by the following unit structural formula,
(R ⁵ SiO _3/2 ) _e (R ⁵ ₂ SiO _2/2 ) _f (R ⁵ ₃ SiO _1/2 ) _g (XO _1/2 ) _h
{In the formula, R ⁵ may be the same or different, substituted or unsubstituted monovalent hydrocarbon group (where 0.1 to 50 mol% of ^{R 5} is an alkenyl group and 10 mol% of ^{R 5.} The above is an aryl group), and X is a hydrogen atom or an alkyl group. e is a positive number, f is 0 or a positive number, g is 0 or a positive number, h is 0 or a positive number, and (f + g + h) / e is 0 to 3. } May be added.

Further, in order to impart resistance to photodegradation, a light stabilizer such as a hindered amine-based stabilizer can be added to the composition of the present invention.

[Cured product]
The silicone composition of the present invention can be cured by a known curing method under known curing conditions. Specifically, the composition can be cured by heating at preferably 80 to 200 ° C., more preferably 100 to 160 ° C. The heating time may be about 0.5 minutes to 5 hours, particularly about 1 minute to 3 hours, but when accuracy such as LED sealing is required, it is preferable to lengthen the curing time. The form of the obtained cured product is not particularly limited, and may be, for example, any of a gel cured product, an elastomer cured product, and a resin cured product. The cured product is preferably colorless and transparent and has a high refractive index (refractive index of 1.52 or more, particularly 1.53 to 1.65). Further, the cured product preferably forms a cured product having a hardness specified in JIS of 30 or more with a durometer A, and the cured product has a tensile strength of 1.0 MPa or more and a cutting elongation of 70%. The above is preferable.

The cured product obtained by curing the addition-curable silicone composition of the present invention has high transparency, high refractive index, and good strength characteristics. In addition, the cured product is excellent in heat resistance, cold resistance, and electrical insulation like the cured product of a normal add-curable silicone composition. Therefore, the cured product obtained by curing the addition-curable silicone composition of the present invention can be suitably used as an optical element encapsulant.

[Optical element]
Examples of the optical element sealed by the encapsulant made of the composition of the present invention include LEDs, semiconductor lasers, photodiodes, phototransistors, solar cells, CCDs and the like. In such an optical element, a sealing material made of the composition of the present invention is applied to the optical element, and the applied sealing agent is applied under known curing conditions by a known curing method, specifically described above. It can be sealed by curing as per. In this way, it is possible to obtain a highly reliable optical element sealed with a cured product of the addition-curable silicone composition of the present invention.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples and the like.

The viscosity in the examples is a value measured using a rotational viscometer at 25 ° C. The refractive index was measured using a digital refractometer RX-5000 manufactured by ATAGO to measure the refractive index at a wavelength of 589 nm at 25 ° C., the vinyl value was measured according to the titration method using a Hanus solution, and the amount of hydrogen gas generated was measured according to the cracking method using an alkaline aqueous solution. ..

[Examples 1 and 2, Comparative Examples 1 and 3]
The following components were mixed in the blending amounts shown in Table 1 to prepare an addition-curable silicone composition. The numerical values of each component in Table 1 represent parts by mass.

粘度：２，０００（ｍＰａ・ｓ），ビニル価：０．２２（ｍｏｌ／１００ｇ），屈折率：１．５８６
（Ａ−２）

（式中、括弧が付されたシロキサン単位の配列はランダム又はブロックである。）
粘度：２０，０００（ｍＰａ・ｓ），ビニル価：０．０９（ｍｏｌ／１００ｇ），屈折率：１．５８１
（Ａ−３）

（式中、括弧が付されたシロキサン単位の配列はランダム又はブロックである。）
粘度：７００（ｍＰａ・ｓ），ビニル価：０．０５５（ｍｏｌ／１００ｇ），屈折率：１．５１２ (A) Ingredient:
(A-1)

Viscosity: 2,000 (mPa · s), vinyl value: 0.22 (mol / 100 g), refractive index: 1.586
(A-2)

(In the formula, the sequence of siloxane units in parentheses is random or block.)
Viscosity: 20,000 (mPa · s), vinyl value: 0.09 (mol / 100 g), refractive index: 1.581
(A-3)

(In the formula, the sequence of siloxane units in parentheses is random or block.)
Viscosity: 700 (mPa · s), vinyl value: 0.055 (mol / 100 g), refractive index: 1.512

粘度：１０（ｍＰａ・ｓ），水素ガス発生量：１３９（ｍｌ／ｇ）：，屈折率：１．５４１
（Ｂ−２）

粘度：２（ｍＰａ・ｓ），水素ガス発生量：２１０（ｍｌ／ｇ），屈折率：１．４４１ (B) Ingredient:
(B-1)

Viscosity: 10 (mPa · s), hydrogen gas generation amount: 139 (ml / g) :, refractive index: 1.541
(B-2)

Viscosity: 2 (mPa · s), hydrogen gas generation amount: 210 (ml / g), refractive index: 1.441

Component (C): Toluene solution of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex of platinum (platinum concentration 0.5% by mass)

Other ingredients:
(D) Addition reaction control agent: ethynylcyclohexanol

The characteristics of the addition-curable silicone composition obtained in Examples 1 and 2 and Comparative Examples 1 to 3 and the cured product thereof were measured as follows, and the results are shown in Table 1.

[Light transmittance of cured product]
The light transmittance at a wavelength of 400 nm at 25 ° C. of a cured product (optical path length 2.0 mm) prepared by curing the addition-curable silicone composition by heating it in a hot air circulation oven at 150 ° C. for 3 hours was measured.

[Strength characteristics of cured product]
A cured product was prepared by heating the addition-curable silicone composition in a hot air circulation oven at 150 ° C. for 4 hours. The hardness, elongation at cutting, and tensile strength of this cured product were measured according to JIS-K-6249.

The addition-curable silicone composition of the present invention provided a cured product having a high refractive index and excellent strength characteristics after curing. From this, it was found that this composition has excellent properties as an optical element encapsulating material.

_{When a crosslinked component having (CH 3} ) ₂ SiH− units is used instead of the component (B) of the present invention (Comparative Examples 1 and 2), the transparency and tensile strength of the cured product are inferior, and the present invention When a component having a dimethylsiloxane unit as a main skeleton was used instead of the component (A) in (Comparative Example 3), the results were inferior in the refractive index, tensile strength, and elongation at the time of cutting of the cured product.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

Claims (5)

(A) Organopolysiloxane compound represented by the following formula (1),

(In the formula, R ¹ and R ² are homovalent or heterologous unsubstituted or substituted monovalent hydrocarbon groups, R ³ is a phenyl group or a naphthyl group, a is an integer of 0 to 50, and b is an integer of 0 to 50. It is an integer from 0 to 100, and a + b is an integer of 1 or more. The parenthesized sequence of siloxane units may be random or block.)
(B) An organohydrogenpolysiloxane compound, which is one or more compounds selected from the organohydrogenpolysiloxane compounds represented by the following formulas (3) to (5) .

(In formula (4), l is an integer of 1 to 5, m is an integer of 1 to 5. The arrangement of siloxane units in parentheses with l and m is a block even if it is random. May be.)
as well as,
(C) An addition-curable silicone composition comprising a hydrosilylation catalyst containing a platinum group metal. The addition-curable silicone composition according to claim 1, ^{wherein R 1} and R ² are methyl groups or phenyl groups in the formula (1). The addition-curable silicone composition according to claim 1 or 2, wherein in the formula (1), R ¹ is a methyl group and R ^{2 is a phenyl group.} A cured product obtained by curing the addition-curable silicone composition according to any one of claims 1 to 3. An optical element that is sealed with the cured product according to claim 4.