KR20010033007A - Addition Cross-linking Silicone Rubber Mixtures, a Method for Their Production and Their Use - Google Patents

Abstract

The invention relates to addition cross-linking silicone rubbers, a method for their production and their use.

Description

Addition Cross-linking Silicone Rubber Mixtures, a Method for Their Production and Their Use}

The present invention relates to addition crosslinked silicone rubbers, methods for their preparation and their use.

Addition crosslinking silicone rubbers are distinguished by a wide range of applications. This use also includes use as, for example, high voltage insulators, prevention devices and the like.

For applications in this field, organopolysiloxane elastomers need to have high arc resistance and high creep resistance with good mechanical properties.

It is known that arc resistance and creep resistance are improved by the addition of aluminum dioxide and / or aluminum hydroxide, but the mechanical properties are relatively degraded. In addition, these materials cannot be processed in an injection molding machine because of their high viscosity.

German Patent Publication No. 3 831 478 discloses the use of addition crosslinking silicone elastomers which may contain titanium dioxide and zinc oxide in addition to the bulking filler described above. These materials can be crosslinked under platinum catalysts but have the disadvantage of not having a long shelf life in the uncrosslinked state. German Patent Publication No. 3 048 207 also discloses a flame retardant material containing magnesium oxide and optionally further additives, for example TiO ₂ , in addition to hydrous alumina.

However, these materials have the disadvantage of short shelf life and too little creep resistance.

It is therefore an object of the present invention to provide an addition crosslinked polysiloxane material which has creep resistance and arc resistance, does not have the disadvantages of the prior art, and which can be processed by injection molding techniques.

The inventors have finally discovered that addition crosslinked organopolysiloxane materials which contain zinc oxide and optionally titanium dioxide, in addition to aluminum oxide compounds, have the desired property profiles.

Therefore, the present invention

(a) 20 to 40% by weight of one or more straight or branched organopolysiloxanes containing from 0.0002 to 5% by weight of alkenyl groups having a viscosity of 1 to 10000 g / cm · s (0.1 to 1000 Pas),

(b) at least one hydrogensiloxane having at least three SiH functional groups per molecule in an amount such that the molar ratio of SiH groups to total Si-bonded alkenyl groups is at least 2.0: 1,

(c) 0.01 to 250 ppm of at least one Pt catalyst and optionally an inhibitor,

(d) 35 to 55% by weight of aluminum hydroxide, alumina and / or mixed oxides / hydroxides thereof,

(e) 5 to 25% by weight of one or more, optionally surface modified fillers having a specific surface area of 150 to 500 m ² / g,

(f) 1 to 5% by weight of metal oxides of at least one zinc having a BET surface area of 30 to 70 m ² / g (optionally 0 to 5% by weight of metal oxides of at least one titanium having a BET surface area of 35 to 65 m ² / g And optionally)

(g) other adjuvants, where the total amount of all components is 100% by weight

It relates to an additional crosslinked silicone rubber blend comprising essentially.

(a) The term organopolysiloxane includes all polysiloxanes currently used in organopolysiloxane materials. Preferred are siloxanes comprising units of formula (I) which contain at least 0.0002 to 5% by weight of alkenyl groups.

(R) _y SiO _{(4-y) / 2}

In the formula,

R represents a monovalent aliphatic radical having 1 to 8 carbon atoms and an alkenyl radical having 2 to 8 carbon atoms,

y is 1.95 to 2.01.

Preferably, (a) has a dimethylvinylsilyloxy terminus.

In a preferred embodiment of the invention, the (a) organopolysiloxane according to the invention has a viscosity of 0.01 to 1000 Pas, particularly preferably 10 to 80 Pas.

Viscosity is measured according to DIN 53 019 at 20 ° C.

In the present invention, (b) the hydrogensiloxane is preferably a straight-chain, cyclic or cyclic moiety comprising a unit of formula (II) having an average of at least 3, preferably 10 to 20, Si-bonded hydrogen atoms per molecule. Branched organopolysiloxane.

(R ¹ ) _w (H) _z SiO _{(4-wz) / 2}

In the formula,

R ¹ is a monovalent aliphatic radical having 1 to 8 carbon atoms,

w is 0, 1, 2 or 3,

z is 0, 1 or 2,

w + z is 0, 1, 2 or 3.

(b) The hydrogensiloxane preferably has a viscosity of 0.03 to 1 Pas.

(b) The hydrogensiloxane may further contain an organopolysiloxane having a number of SiH groups of less than three.

The catalyst (c) for the crosslinking reaction is preferably a Pt (0) complex with alkenyl siloxane as ligand at a catalytic amount of Pt 0.01 to 250 ppm.

In the present invention, inhibitors are all conventional compounds which have been used to date for the purposes of the present invention. Examples of these preferred inhibitors are 1,3-divinyl-tetramethyldisiloxane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane in amounts of 50 to 10,000 ppm. , 2-methylbutyn-2-ol or 1-ethynylcyclohexanol.

Aluminum hydroxide, alumina and / or their mixed oxides / hydroxides such as AlO (OH) are preferably compounds having a BET surface area of 3 to 6 m ² / g as measured by N ₂ absorption means.

In the present invention, the filler (s) preferably have a BET surface area of 50 to 400 m ² / g, for example measured by N ₂ absorbing means, and also reinforcing fillers which can be surface treated, for example exothermic Silica, and / or extendable fillers such as quartz powder.

Surface treatment also provides in that state silazanes such as hexamethylsilazane and / or divinyltetramethyldisilazane, and vinylalkoxysilanes such as, for example, vinyltrimethoxysilane, and water or other conventional fillers. This can be done by adding a composition.

(f) a metal oxide of zinc is preferably a titanium oxide with a compound having a BET specific surface area of 45 to 55 m ² / g and BET surface area 45 to 55 m ² / g as measured by N ₂ absorption means.

In another preferred embodiment of the invention, the blend also contains (g) other adjuvants, for example inorganic colored pigments such as iron oxide or cobalt spinel.

The invention also comprises: (a) at least one organopolysiloxane, (c) catalyst, (d) aluminum hydroxide and (f) metal oxide, optionally (e) filler and / or (g) adjuvant, and (a) at least one organopolysiloxane, (b) at least one hydrogensiloxane and optionally (e) filler and (d) aluminum hydroxide, (g) adjuvants and / or (c) inhibitors and (f) metal oxides. To a process for producing an addition crosslinked silicone rubber blend according to the invention, characterized in that it is mixed in separate mixtures and these two mixtures are only combined in an injection molding machine or in an upstream mixing head and subsequently in a static mixer. It is about.

Preferably the high viscosity material is mixed by means of a suitable mixer, for example a kneader, dissolver or planetary flow mixer.

In one embodiment of the process according to the invention, the filler becomes hydrophobic, preferably in that state hexamethyldisilazane and / or divinyltetramethyldisilazane and water are added to impart hydrophobicity.

In imparting hydrophobicity in this state, preferably (a) organopolysiloxane, (e) filler and (d) aluminum hydroxide and waterproofing agent, preferably hexamethyldisilazane and / or divinyltetramethyldisila The cup is preferably stirred at a temperature of 90 to 100 ° C. for at least 20 minutes in a mixing device suitable for high viscosity materials such as kneaders, dissolvers or planetary flow mixers, and then initially at a temperature of 150 to 160 ° C. Excess composition and water are removed under vacuum at vacuum followed by a pressure of 100 to 20 millibars. Then, the other components ((b) and (f)) or (c), (f) and optionally (g) are mixed over 10 to 30 minutes.

The invention also relates to the use of the addition crosslinked silicone rubber blend according to the invention for producing silicone elastomers having creep resistance and arc resistance.

The following examples illustrate the invention without any limitation, and all parts shown herein represent parts by weight.

<Example 1>

(A) 75 parts by weight of a vinyl-terminated polydimethylsiloxane mixture having an average viscosity of 40 Pas was mixed with 10 parts by weight of hexamethyldisilazane and 5 parts by weight of water at 25 ° C. in a dissolver having a planetary flow gear, and then (e) ) 31 parts by weight of pyrogenically prepared silica having a specific surface area of 300 m ² / g according to BET, (d) 110 parts by weight of low sodium aluminum trihydroxy and (f) 2 parts by weight of pyrogenically produced titanium dioxide. It was stirred with to obtain a homogeneous material. The mixture was first heated to 100 ° C., stirred for 2 hours in a sealed dissolver, and then water and excess silazane were removed at 160 ° C. under vacuum.

After cooling the material to 90 ° C., (a) 33 parts by weight of a vinyl-terminated polydimethylsiloxane mixture having an average viscosity of 5 Pas at 25 ° C., and (c) a symmetrical divinyl tetramethyldisiloxane of chloroplatinic acid, 0.05 part by weight of a platinum catalyst containing 0.15% of platinum in the form of a complex was added. The substance thus obtained is represented by component A below.

In the dissolver with planetary flow gear, (a) a vinyl-terminated polydimethylsiloxane mixture having an average viscosity of 40 Pas at 25 ° C. is mixed with 10 parts by weight of hexamethyldisilazane and 5 parts by weight of water, and then (e) ) 32 parts by weight of pyrogenically prepared silica having a specific surface area of 300 m ² / g according to BET, (d) 110 parts by weight of low sodium aluminum trihydroxy and (f) 2 parts by weight of pyrogenically produced titanium dioxide. And stirred to obtain a homogeneous material. The mixture was first heated to 100 ° C., stirred for 2 hours in a closed dissolver, and then water and excess silazane were removed at 160 ° C. under vacuum.

After cooling the mixture to 90 ° C., (a) 22 parts by weight of a vinyl-terminated polydimethylsiloxane mixture having an average viscosity of 10 Pas at 25 ° C., (f) 4 parts by weight of activated zinc oxide, (b) an average per molecule 22 parts by weight of a mixture of trimethylsilyl-terminated polyorganosiloxane crosslinker having 8 methylhydrogensiloxane units and 100 dimethylsiloxane units, and (c) 0.2 parts by weight of ethynylcyclohexanol as inhibitor. The substance thus obtained is shown as component B below.

50 parts by weight of each of the components A and B described above were stirred together and cured at 175 ° C. for 10 minutes to produce sheets 2 or 6 mm thick. The sheet was then heated in a forced circulation oven at 200 ° C. for 4 hours. For all cured products produced in this way, the reactivity, mechanical properties and arc resistance according to DIN 57 441 and IEC Publ. Creep resistance according to 587 was tested.

Reactive t60 1 day later 3.7 sec Reactive t60 21 days later 3.9 sec Reactive t60 183 days later 4.2 sec The tensile strength DIN 53 504 S2 4.0 N / mm ² Shinto DIN 53 504 S2 600% Shore A Hardness DIN 53 505 40 Arc-resistant DIN 57 441 HL 2 Creep Resistant IEC Publ. 587 1 A 3.5

Claims (6)

(a) 20 to 40% by weight of one or more linear or branched organopolysiloxanes containing 0.0002 to 5% by weight of alkenyl groups having a viscosity of 0.1 to 1000 Pas, (b) at least one hydrogensiloxane having at least three SiH functional groups per molecule in an amount such that the molar ratio of SiH groups to total Si-bonded alkenyl groups is at least 2.0: 1, (c) 0.01 to 250 ppm of one or more Pt catalysts and optionally inhibitors, (d) 35 to 55% by weight of aluminum hydroxide, alumina and / or mixed oxides / hydroxides thereof, (e) 5 to 25% by weight of one or more, optionally surface modified fillers having a specific surface area of 150 to 500 m ² / g, (f) 1 to 5% by weight of metal oxides of at least one zinc having a BET surface area of 30 to 70 m ² / g (optionally 0 to 5% by weight of metal oxides of at least one titanium having a BET surface area of 35 to 65 m ² / g And optionally) (g) other adjuvants, where the total amount of all components is 100% by weight Addition crosslinked silicone rubber blend, characterized in that it comprises essentially. The addition crosslinking silicone rubber blend according to claim 1, wherein (a) the organopolysiloxane is a siloxane comprising units of formula (I) containing at least 0.0002 to 5% by weight of alkenyl groups. <Formula I> (R) _y SiO _{(4-y) / 2} In the formula, R represents a monovalent aliphatic radical having 1 to 8 carbon atoms and an alkenyl radical having 2 to 8 carbon atoms, y is 1.95 to 2.01. The addition crosslinking according to claim 1 or 2, wherein (b) the hydrogensiloxane is a siloxane comprising a unit of formula (II) in which at least three Si-bonded hydrogen atoms are present per molecule. Silicone rubber blend. <Formula II> (R ¹ ) _w (H) _z SiO _{(4-wz) / 2} In the formula, R ¹ is a monovalent aliphatic radical having 1 to 8 carbon atoms, w is 0, 1, 2 or 3, z is 0, 1 or 2, w + z is 0, 1, 2 or 3. 1. (a) at least one organopolysiloxane, (c) catalyst, (d) aluminum hydroxide and (f) metal oxide, optionally (e) filler and / or (g) adjuvant, and 2. (a) (B) at least one organopolysiloxane, (b) at least one hydrogensiloxane and optionally (e) filler and (d) aluminum hydroxide, (g) adjuvants and / or (c) inhibitors and (f) metal oxides in separate mixtures. The addition crosslinking silicone rubber blend according to any one of claims 1 to 3, characterized in that it mixes and combines these two mixtures only in an injection molding machine or in an upstream mixing head and subsequently in a static mixer. Method of preparation. 5. A process according to claim 4, wherein hexamethyldisilazane and / or divinyltetramethyldisilazane and water are added to make the (e) filler and (d) aluminum hydroxide hydrophobic in that state. . Use of an addition crosslinked silicone rubber blend according to any one of claims 1 to 3 for preparing silicone elastomers having creep resistance and arc resistance.