JPS6116295B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to unique siloxane compositions that cure to form dielectric silicone compounds. In particular, the compositions disclosed herein are capable of curing readily at ambient or elevated temperatures and withstanding extremely low temperatures (approximately -120°C) without deleterious effects on the physical properties of the gel and its low-temperature properties. It is specifically formulated to produce a silicone gel that can be used. The primary use of gels formulated according to the present invention is as dielectric potting gels. The use of silicone potting materials to encapsulate electrical components is well documented. U.S. Pat. No. 3,436,366, issued April 1, 1969 to Modic, uses silicone materials to provide electrical insulation and varying degrees of protection from thermal and mechanical abuse. The method has been described above. Modic
The patent also describes the possibility of formulating dielectric potting materials with polyorganosiloxanes having only methyl and vinyl substituents. However, these substituents are arranged in such a way as to promote a large amount of cross-linking to produce sufficient tear strength. In particular, Modic combines methylvinylsiloxane units and _SiO2
teaches the use of organopolysiloxanes having units. Both of these units promote crosslinking to a high degree and yield products that have little in common with the flexible gels of the present invention. Additionally, Modic materials do not exhibit the unique low temperature properties that the gels of the present invention possess. US Pat. No. 3,020,260, issued to Nelson on February 6, 1962, is possibly also relevant to the present invention. Example 10 thereof describes a silicone gel formulated from a siloxane copolymer with only methyl and vinyl substituents. More precisely, the Nelson patent states (1)Me ₂ SiO,
Copolymer consisting of MeViSiO ₂ and Me ₃ SiO ₅
86.95 parts _by weight and (2) Me ₂ SiO, MeSiO _1.5 and
A method of formulating silicone potting gels is taught by reacting a blend of 8.27 parts by weight of a copolymer consisting of Me ₃ SiO ₅ with 4.78 parts by weight of an organohydrogensiloxane crosslinking agent in the presence of a platinum catalyst. The symbol "Me" represents a " _-CH3 " group, and the symbol "Vi" represents a "-CH= _CH2 " group. The silicone potting gel obtained from the Nelson formulation gives rise to a dielectric silicone gel, but due to the proportion of units used and the presence of units with intermediate vinyl functionality (MeViSiO) it has no structural properties and therefore It does not exhibit the low temperature stability that siloxane gels produced according to the present invention have. U.S. Patent No. 22, 1968, issued on January 22, 1968
No. 3,361,714, Omietanski discloses certain "comb" and "star" polymers with low temperature properties. These polymers have the general formula (However, R and R ¹ are monovalent hydrocarbon groups, R ² is a monovalent hydrocarbon group or a substituted monovalent hydrocarbon group, n is 0 to 25, and m is 1 ~21, w is greater than 0, z' is hydrogen or _R3Si- , and z is hydrogen or _R3SiO- .
Omietanski teaches that elastomers and liquids exhibiting low temperature properties can be obtained cured with organic peroxides. Noting the properties and limitations of known and described silicone potting materials, we attempted to formulate siloxane gels from siloxane polymers with only methyl and vinyl substituents. However, these known units have been combined to provide novel polymerizable compositions that rapidly harden to gels at ambient or elevated temperatures and maintain their gel properties at cryogenic temperatures. Therefore, we (a) essentially (CH ₃ ) ₂ SiO 80-96.5 mol%;
_{CH3SiO1.5 2.0-10.0} mol _% , _{( CH3} ) _{3SiO0.5 1.25}
~6.0 mol% and ( _CH3 ) ₂ ( _CH2 =CH) _SiO0 .
₍ b) an average of more than one silicon-bonded hydrogen atom per molecule and not more than one silicon-bonded hydrogen atom per silicon atom; Alkyl groups of 1 to 6 carbon atoms per phenyl and 3,3,3-
an organohydrogensiloxane having an organic group selected from the group consisting of trifluoropropyl and an average of 0.2 per mole of silicon-bonded vinyl;
We have developed a curable siloxane composition consisting of a homogeneous mixture consisting essentially of: an organohydrogensiloxane providing ~5.0 moles of silicon-bonded hydrogen: and (c) a platinum catalyst. The siloxane gel of the present invention is essentially a defined polyorganosiloxane cured with an organohydrogensiloxane crosslinking agent in the presence of a platinum catalyst. Polyorganosiloxanes are primarily composed of dimethylsiloxane units (Me ₂ SiO).
The presence of this particular unit can vary from 80 to 96.5 mole percent of the total siloxane units in the polymer, but optimal results are achieved when dimethylsiloxane units constitute 90 mole percent or more of the polymer. The second unit _of the polyorganosiloxane is monomethylsiloxane (MeSiO _1.5 ). This unit accounts for 2 to 10.0 mol% of the total siloxane units in the polymer.
However, good results were achieved using an amount _{of MeSiO 1.5 equal} to 3-6 mol% of the polymer. MeSiO _1.5 units are essential to introduce unique _low temperature properties into the siloxane polymer. If the polymer chain is composed only of dimethylsiloxane units without monomethylsiloxane units -
It crystallizes at 40℃ and forms a hard crystalline phase at temperatures below -40℃. The monomethylsiloxane units randomly arranged along the siloxane polymer chain allow the crystalline phase to be removed from the polymer. Therefore,
This new siloxane polymer remains in an amorphous phase upon cooling until it reaches a glass transition temperature (Tg) of -123°C. At this temperature the siloxane polymer transforms into a hard glass phase. _The third unit is a trimethylsiloxane unit (Me ₃ SiO _0.5 ). This component simply acts as an end cap for the polymer chain. This unit can be used in a range of 1.25 to 6.0 mole percent of the total organosiloxane, but is preferably used in a range of 2.5 to 5 mole percent of the polymer. The final units of the siloxane polymer are vinyl-containing siloxane units. Trowels in which this unit is dimethylvinylsiloxane (Me ₂ ViSiO ₅ ), which is characterized by a vinyl functionality in the terminal position, are essential. The primary reason for using terminal vinyl groups instead of intermediate vinyl groups (ie, MeViSiO) is to increase cure speed. The rate constant of hydrosilylation is doubled by replacing the intermediate vinyl with a terminal vinyl group. The terminal vinyl units also act as end cappers with the trimethylsiloxane units described above.
The terminal vinyl siloxane units can represent 0.25 to 4 mole percent of the total organosiloxane units in the polymer. Since the terminal vinyl unit and trimethylsiloxane unit are the terminal end of the organosiloxane polymer, it is essential that the total triorganosiloxane unit is 10 mol % or less of the entire polyorganosiloxane. Preferred curable siloxane compositions include polyorganosiloxanes consisting essentially of _87-94 mol% ( _CH3 )2SiO, _3-6 mol% _CH3SiO1.5 , _{2.5 %} ( _CH3 ) _{3SiO0.5 .}
~2.0 mol% and ( _CH3 ) ₂ ( _CH2 =CH) _SiO0 .
₅ 0.5 to 2.0 mol%, especially polyorganosiloxane (CH ₃ ) ₂ SiO 92 to 94 mol %, CH ₃ SiO _{1.5 3} to 4 mol %, (CH ₃ ) ₃ SiO _{0.5 2.5} ~
3 mol% and _{( CH3} ) ₂ ( _CH2 =CH) _SiO0.50.5
~1 mol%. The vinyl functionality of the polyorganosiloxane reacts with a suitable crosslinking agent in the presence of a catalyst and cures to form a gel-like material. A suitable crosslinking agent for the polyorganosiloxane used in this invention is the reactive component≡
It is an organohydrogen siloxane characterized by SiH. The required crosslinking agent has an average of more than one silicon-bonded hydrogen atom per molecule and no more than one silicon-bonded hydrogen atom per silicon atom. Other substituents on silicon atoms contain 1 carbon atom per group.
The organic group is typically selected from the group consisting of alkyl groups having 2 to 6 alkyl groups, phenyl, and 3,3,3-trifluoropropyl. The amount of crosslinking agent used must be sufficient to provide 0.2-5.0 moles of ≡SiH to 1 mole of SiVi. 0.5/1～
A molar ratio in the range of 0.95/1 has been found to be very satisfactory as a result of the preferred crosslinking agent functionality containing at least two ≡SiH moieties per molecule. An example of an organohydrogensiloxane compound that can be used in the practice of this invention is 1,3,5,7-tetramethylcyclotetrasiloxane containing one silicon-bonded methyl group and one silicon-bonded hydrogen atom per silicon atom. It is. This cyclic polymer
Produced by hydrolysis of _MeHSiC2 . Other crosslinking agents are dimethylhydrogensiloxane-terminated polydimethylsiloxane HMe ₂ Si (OMeSi)
xH (where x is 1 to 30). This polymer is produced by cohydrolysis of HMe ₂ SiC and Me ₂ SiC ₂ or equilibration of HMe ₂ SiOSiMe ₂ H and (Me ₂ SiO) ₄ . Another type of crosslinking compositions are those consisting of polymers of dimethylsiloxane, methylhydrogen and trimethylsiloxane units and containing from at least 4 to 20 or more silicon atoms per molecule.
This composition is produced by equilibration of Me ₃ SiO (MeHSiO) x SiMe ₃ and (Me ₂ SiO) ₄ . Preferred organohydrogensiloxanes are those having the formula H( _CH3 )Si[OSi( _CH3 ) ₂ ] _xOSi ( _CH3 ) _2H , where x is from 5 to 20. This organohydrogensiloxane is used to crosslink the previous polyorganosiloxane under a platinum catalyst to obtain a gel and constitutes a preferred embodiment of the invention. The most preferred ratio of silicon-bonded hydrogen to silicon-bonded vinyl is from 0.5/1 to 0.95/1. The platinum catalysts used in this invention include all known platinum catalysts effective for catalyzing the reaction between silicon-bonded hydrogen and vinyl groups. These substances are 1958
The chloroplatinic acid catalyst disclosed in U.S. Patent No. 2,823,218 issued to Speier et al.
Includes reaction products of organosilicon compounds and chloroplatinic acid as described by Willing in No. 3,419,593. Also, U.S. Patent No. 3,159,601 issued December 1, 1964 to Ashby;
platinum hydrocarbon complexes shown in No. 3159662;
Platinum acetylacetonate as shown in U.S. Pat. No. 3,723,497 issued March 27, 1973 to Baney and U.S. Pat.
The platinum alcoholate catalysts described by Lamoreaux in No. 3,220,972 can be used. For any particular platinum catalyst selected, the practitioner can determine the optimum effective amount of catalyst to promote cure. Platinum catalysts could be effectively used in amounts sufficient to provide approximately 0.1 to 40 ppm by weight of platinum to the total formulation. the above
The particular platinum catalyst disclosed in Example 1 of the Willing patent has been found to be particularly effective when used to provide 5 to 10 ppm of platinum atoms by weight to the total formulation. To increase processing time, the practitioner may use certain compounds known in the art to vary the hardening acceleration. For example, US Patent No. 8, issued June 8, 1965.
Aromatic heterocyclic nitrogen compounds disclosed in No. 3188299, pyridazine, pyrazine, quinoline, 2-
2'-biquinoline, bipyridine, naphthyridine, quinaldine, dialkylformamide, thioamide, alkylthiourea and ethylenethiourea,
Organophosphorus compounds as disclosed in U.S. Pat. No. 3,188,300, issued June 8, 1965, June 1965
Benzotriazole as disclosed in U.S. Pat. No. 3,192,181, issued September 29, 1967.
nitrile compounds, such as those disclosed in U.S. Pat. No. 3,344,111, issued May 14, 1968; Patent No.
Acetylenic compounds disclosed in U.S. Pat. No. 3,445,420, vinylsilazane disclosed in U.S. Pat. stannous, mercuric, bismuth(+3), cuprous and cupric salts disclosed in U.S. Pat. No. 3,532,649, issued October 6, 1970. , polymethylvinylsiloxane cyclics mentioned in U.S. Pat. No. 3,923,705, issued Dec. 2, 1975, and others known in the art may be used. The above cited patents are listed to provide additional details of methods of using platinum catalyst poisons, specific platinum catalyst poisons, and platinum catalysts. The polyorganosiloxanes unique to this invention can be prepared by cohydrolysis of the corresponding chlorosiloxanes or equilibration of the combined siloxane composition to provide the required molar ratios of the components. The latter method using potassium silanolate as the equilibrium catalyst is preferred. Representative polyorganosiloxanes of the invention can be prepared by equilibration according to the following examples; Example 1 Copolymer A Me ₂ ViSi (OSiMe ₂ ) ₆ OSiViMe ₂ 61.2 g, Me ₃ Si
A mixture containing 236.2 g of (OSiMe ₂ ) ₂ OSiMe ₃ and 937.4 g of (Me ₂ SiO) x cyclics, where x is 4 to 6, was heated at 160 °C for 1 h under N ₂ purge with potassium as the equilibrium catalyst. Cyranolate (KOSi≡) 1K/
A ratio of 2500si was used and equilibrated. While maintaining temperature and stirring constantly, add _{MeSiO 1.5 (} 21.3 wt%), Me ₂ SiO ₍ 74.1 wt%), and Me ₃ SiO _0.5
765 g of hydrolyzate containing (4.6% by weight) were slowly added and the resulting mixture was equilibrated for 3 hours.
The reaction mixture was neutralized with _CO2 and then filtered. The polymer exhibited a viscosity of approximately 0.0002 ^{m 2} /S. Copolymer B Me ₂ ViSi (OSiMe ₂ ) ₆ OSiViMe ₂ 61.2g, Me ₃ Si
Equilibration procedure using 24.7 g of (OSiMe ₂ ) ₂ OSiMe ₃ and 1853.3 g of (Me ₂ SiO) x cyclics, where x is 4 to 6, and 170.8 g of the hydrolyzate used to prepare copolymer A. repeated. The reaction mixture was neutralized and filtered. The resulting polymer has a viscosity of approx.
It showed 0.002cm/S. _{Composition of copolymer A MeSiO 1.5 9.0 mol} % _{Me 2 ViSiO .} Mo% Me ₃ SiO _{0.5 0.95} mol % Me ₂ SiO 96.30 mol % Then, it has various viscosities. Copolymers A and B were physically blended to produce a polyorganosiloxane of siloxane unit composition. Representative polymers of the type obtained from such blends include polymer blends and.

Table: To incorporate samples of polymer blends and polyorganosiloxanes represented by blends into gels in accordance with the present invention, the appropriate amount of polymer was first weighed and the platinum catalyst was added thereto. This composition was stirred and the crosslinking compound was added to it. The mixture was then transferred to a small container and cured in a heated oil bath. The reference polymer blends and polymer blends were combined with a crosslinking agent of the formula HMe ₂ Si (OSiMe ₂ ) to ₁₄ OSiMe ₂ H and chlorosilane with sym-divinyltetramethyldisiloxane as disclosed in Example 1 of the Willing patent, supra. Certain siloxane compositions were produced by mixing and curing platinum catalysts obtained by reacting platinic acid. The specific platinum catalyst complex used contained 0.85% platinum by weight. Penetration was measured to the nearest 0.1 mm using a precision penetrometer with a 4.5 g probe attached to a 15 g plunger. The penetration of the probe into 50 g of gel sample cured at 150° C. for 1/2 hour was measured. Penetration readings were taken after 5 seconds. High penetrations (greater than 10.0 mm) indicate "soft" gels, while low penetrations (less than 3 mm) indicate "hard" gels. Gel curing time has a 7/8″ spindle
Measurements were made using a Tecam gelation timer. The spindle was inserted into a 100 g sample immersed in a 135°C oil bath. The time required for gel formation (curing) to increase resistance to the spindle and trip a timer on the spindle was recorded. The low temperature properties of the gel were measured by Dupont 900 Differential Thermal Analysis Calorimeter DTA. About 20 mg of the gel sample, which had been cooled to -140°C with liquid nitrogen, was heated with DTA at a rate of 10°C per minute. Tables 1 and 2 show the composition and characteristics of a number of gels produced in accordance with the present invention. From the above, the gel produced according to the present invention is approximately -
It was found that the glass phase transitions to a liquid phase at 120°C (Tg). No intermediate crystalline phase was observed. Example 2 To illustrate the essential characteristics of polyorganosiloxanes for use in formulating siloxane gels according to the invention, the following gels were prepared and evaluated: Comparative formulation ViMe ₂ SiO-terminated polydimethylsiloxane, Polymer A _{consisting of} ViMe ₂ Si ( ^OMe ₂ Si ₎
Consisting of ViMe ₂ SiO _{0.5 0.75} mol%, Me ₃ SiO _{0.5 6.57} mol% and Me ₂ SiO 83.68 mol%, vinyl content 0.27
It was mixed with Polymer B having a weight percent and a viscosity of 0.00019 m ² /S. Polymer A Polymer B is 1:1
Blended by weight. 50g of this polymer blend and the average formula Me ₃ Si
(OMe ₂ Si) ₃ (OMeHSi) ₅ Mix 0.37 g of ≡SiH crosslinking agent with OSiMe ₃ and the platinum catalyst disclosed in Example 1 of the above Willing patent (12 wt ppm platinum relative to the final mixture). did. This procedure was performed in the same manner as disclosed in Example 10 of US Pat. No. 3,020,260, supra. The resulting mixture was divided into a first part and a second part.
The first part was left at room temperature. It hardened into a gel in 45 minutes. The first part was cured at 150°C in 30 minutes. The resulting gel had a penetrometer reading of 4.1 mm. Phase transition temperature analysis using differential scanning calorimetry represents the melting temperature and glass transition temperature, respectively -50℃
It showed a phase transition at -120℃. These two transition temperatures indicate that the gel can maintain low-temperature structural integrity up to -50°C. At temperatures below this point, a crystalline phase forms and the gel becomes hard. The formation of the crystalline phase is thought to be due to _the lack of MeSiO _1.5 in Polymer A. Also, polymer B
Even with 9 mole percent MeSiO _1.5 units, the resulting polyorganosiloxane was a physical blend of methyl and vinylsiloxy units and not a siloxane polymer _consisting of essential units of each. Although the compositions of the present invention can be prepared by simply mixing together the various ingredients in any desired manner as described above, sometimes these compositions are prepared as two separate packages. It is most convenient to combine the two components when converting the preset composition to a hardened gel state. For this two-component formulation, it is convenient to include the organopolysiloxane component and the platinum catalyst in the first package. The second package can contain an organohydrogensiloxane and, conveniently, a portion of an organopolysiloxane. When selecting the contents of the two packages, both the platinum catalyst component and the organohydrogensiloxane component should not be included in the same package. The following examples demonstrate preferred embodiments of the invention. Example 3 Curable gel composition Polymer blend 100 parts by weight Crosslinking agent [HMe ₂ Si (OSiMe ₂ ) to ₁₄ OSiMe ₂ H] 5.14 Platinum catalyst. 0946 〃 (MeViSiO) ₄ . [0294] For convenience, it is desirable to package the curable gel composition in two-component form. The contents of each component are shown below. Component A Polymer Blend 50g Platinum Catalyst 0.09 Component B Polymer Blend 45.11g Crosslinking Agent 4.89g (MeViSiO) ₄ 0.028g Components A and B were mixed in a 1:1 weight ratio for curing and the following properties were evaluated. : Curing time (100g at 135℃) 6.1 minutes Penetration of 4.5mm sample cured for 30 minutes (at 150℃) Curing time (at 25℃) 5 hours Within the scope of the present invention manufactured according to the above examples The cured gels can be advantageously used as conformal coatings to protect electronic circuits where low temperature stability is important, for example in space electronics. The use of protective coatings that are low temperature stable is important because it has been observed that physical changes in the protective coating, such as from a gel phase to a crystalline phase, can destroy and damage the coated circuitry. be.

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Claims (1)

[Claims] 1 (a) essentially (CH ₃ ) ₂ SiO 80 to 96.5 mol%,
_{CH3SiO1.5 2.0-10.0} mol _% , _{( CH3} ) _{3SiO0.5 1.25}
~6.0 mol% and ( _CH3 ) ₂ ( _CH2 =CH) _SiO0 .
₍ b) an average of more than one silicon-bonded hydrogen atom per molecule and no more than one silicon-bonded hydrogen atom per silicon atom; Alkyl groups with 1 to 6 carbon atoms per group, phenyl and 3,3,3-
an organohydrogensiloxane having an organic group selected from the group consisting of trifluoropropyl and an average of 0.2 per mole of silicon-bonded vinyl;
A curable siloxane composition consisting of a homogeneous mixture consisting essentially of an organohydrogensiloxane providing ~5.0 moles of silicon-bonded hydrogen; and (c) a platinum catalyst. 2 The polyorganosixane essentially contains (CH ₃ ) ₂ SiO 87-94 mol %, CH ₃ SiO _{1 .5} 3-6 mol %, (CH ₃ ) ₃ SiO _{0 .5} 0.5-2.0 mol % and (CH ₃ ) ₂
The curable siloxane composition of claim 1, comprising _{0.5 to} 2.0 mol% of ( _CH2 =CH)SiO0.5. 3. The polyorganosixane essentially contains ₉₂ to 94 mol% of ( _CH3 )2SiO, _{3 to} 4 mol% of CH3SiO1.5, _2.5 to ₃ mol% of ( _CH3 ) _3SiO0.5 and ( _{CH3) .} ) ₂
A curable siloxane composition according to claim 2, comprising _0.5 to ₁ mol% of ( _CH2 =CH)SiO0.5. 4 Polyorganosiloxane essentially contains (CH ₃ ) ₃ SiO 90.5 mol%, CH ₃ SiO _{1.5 5.0} mol%,
(CH ₃ ) ₃ SiO _{0 .5} 3.8 mol% and (CH ₃ ) ₂ (CH ₂ =
A curable siloxane composition according to claim 2, comprising 0.7 mole % of CH) Si _{0 .5} . 5 Organohydrogensiloxane is H(CH ₃ ) ₂ Si
[OSi(CH ₃ ) ₂ ]xOSi(CH ₃ ) ₂ H (however, x is 5~
20), the first claim
The curable siloxane composition according to any one of Items 1 to 4. 6 Organohydrogensiloxane is H(CH ₃ ) ₂ Si
[OSi(CH ₃ ) ₂ ] xOSi(CH ₃ ) ₂ H (however, x is 5 to 20
), and the organohydrogen siloxane contains an average of 0.5 per mole of silicon-bonded vinyl.
5. The curable siloxane composition of any of claims 1-4, which provides 0.95 moles of silicon-bonded hydrogen. 7. The curable siloxane composition of claim 1, wherein the platinum catalyst provides 5 to 10 ppm platinum atoms based on the total formulation. 8 Platinum catalyst 5-10 ppm by weight of total formulation
7. The curable siloxane composition of claim 6, which provides platinum atoms of .