DE19905767A1 - Organopolysiloxane compositions useful for the pressure-free crosslinking of silicone rubber extrudates are crosslinked by specific organic peroxide compounds - Google Patents

Abstract

Organopolysiloxane compositions (OPSC) are obtained from an organopolysiloxane and a crosslinking agent containing bis-4-methylbenzoylperoxide (PMBP) and one or more compounds selected from: benzoylperoxide, dicumylperoxide, 2,5-dimethylhexane-2.5-di-t-butyl peroxide and di-t-butyl peroxide.

Description

The invention relates to organopolysiloxane compositions and Process for making the same.

For the pressure-free crosslinking of silicone rubber extrudates currently only 2,4-dichlorobenzoyl peroxide (US 4,260,536) and Paramethylbenzyl peroxide in question. Both have peroxides Disadvantage. Thus, 2,4-dichlorobenzoyl peroxide partially forms toxic fission products and paramethylbenzyl peroxide leads to a strong smell, the Vulcanization speed is slow and transparent Vulcanizates can show a slight yellow color.

The object of the invention is to overcome the disadvantages of the prior art Overcoming technology, especially fast networking without smell and yellowing.

The object is achieved by the invention.

The invention relates to organopolysiloxane compositions can be produced on the basis of an organopolysiloxane and a crosslinker containing bis-4-methylbenzoyl peroxide - (= PMBP) and a single connection or at least two of the Compounds from the group consisting of benzoyl peroxide, Dicumyl peroxide, 2,5 dimethyl-hexane-2,5-di-tertiary butyl peroxide (= DHBP), ditertiary butyl peroxide.

All peroxidically crosslinkable organopolysiloxanes can be used as organopolysiloxanes, preferably organopolysiloxanes (A) composed of units of the general formula

wherein
R can be the same or different and means optionally substituted hydrocarbon radical.
r is 0, 1, 2 or 3 and has an average numerical value of 1.9 to 2.1.

Examples of hydrocarbon radicals R are alkyl radicals, such as the Methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, tert.- Pentyl radical, hexyl radicals, such as the n-hexyl radical, heptyl radicals, such as the n-heptyl radical, octyl radicals, such as the n-octyl radical and iso- Octyl radicals, such as the 2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonyl radical, decyl radicals, such as the n-decyl radical, dodecyl radicals, such as the n-dodecyl radical, octadecyl radicals, such as the n-octadecyl radical; Cycloalkyl radicals, such as cyclopentyl, cyclohexyl, Cycloheptyl and methylcyclohexyl; Aryl residues like that Phenyl, biphenyl, naphthyl and anthryl and phenanthryl; Alkaryl residues, such as o-, m-, p-tolyl residues, xylyl residues and Ethylphenyl residues; Aralkyl radicals, such as the benzyl radical, the α and the β-phenylethyl radical.

Examples of substituted hydrocarbon radicals R are halogenated alkyl radicals, such as 3-chloropropyl, 3,3,3- Trifluoropropyl and the Perfluorhexylethylrest, halogenated Aryl radicals, such as the p-chlorophenyl and p-chlorobenzyl radicals.

The radical R is preferably hydrogen atom and Hydrocarbon residues with 1 to 8 carbon atoms, especially preferably around the methyl radical.

Further examples of radicals R are vinyl, allyl, Methallyl, 1-propenyl, 1-butenyl, 1-pentenyl, 5-hexenyl, Butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl, Cyclohexenyl, ethynyl, propargyl and 1-propynyl.

The radical R is preferably alkenyl radicals with 2 to 8 carbon atoms, particularly preferably around the vinyl radical.  

In the case of optionally substituted hydrocarbon radicals with 1 up to 8 carbon atoms are the methyl, vinyl, phenyl and 3,3,3-trifluoropropyl radical is particularly preferred.

Preferably at least 70 mol% of that in the Organopolysiloxane (A) from units of formula (I) contained Si atoms alkyl radicals, especially methyl radicals. Do the organopolysiloxanes contain Si-bound methyl and / or 3,3,3-trifluoropropyl residues or Si-bonded vinyl and / or phenyl radicals, so it is the latter preferably by amounts of 0.001-30 mol%.

The organopolysiloxanes (A) are preferably predominant from diorganosiloxane units. The end groups of the Organopolysiloxanes can include trialkylsiloxy groups, in particular the trimethylsiloxy radical or the dimethylvinylsiloxy radical; however, one or more of these alkyl groups can also pass through Hydroxy groups or alkoxy groups, such as methoxy or Ethoxy residues to be replaced.

The organopolysiloxanes (A) can be liquids or highly viscous substances. The organopolysiloxanes (A) preferably have a viscosity between 10 ³ and 10 ⁸ mm ² / s at 25 ° C.

A mixture of bis-4- is preferably used as the crosslinking agent. Methylbenzoyl peroxide - (= PMBP) and a single compound or at least two of the compounds from the group consisting of Benzoyl peroxide, dicumyl peroxide, 2,5 dimethyl-hexane-2,5-di- tertiary butyl peroxide (= DHBP), ditertiary butyl peroxide exists, in a weight ratio of 1: 0.3 to 1: 1, preferably in Ratio 1: 0.8 used. If at least two connections from the group consisting of benzoyl peroxide, dicumyl peroxide, 2.5 Dimethyl-hexane-2,5-di-tert-butyl peroxide (= DHBP), Ditertiary butyl peroxide can be used, these in any mixing ratio within the first mentioned weight ratio can be used. Are preferred in this case, however, mixtures of the same weight  Compounds from the group consisting of benzoyl peroxide, Dicumyl peroxide, 2,5 dimethyl-hexane-2,5-di-tertiary butyl peroxide (= DHBP), ditertiary butyl peroxide, where Mixtures of benzoyl peroxide and 2,5 dimethyl-hexane-2,5- di-tertiary-butyl peroxide (= DHBP) in a weight ratio of 1: 1 are particularly preferred.

The organopolysiloxanes according to the invention also contain (A) preferably reinforcing and / or non-reinforcing Fillers.

Examples of reinforcing fillers are pyrogenic or precipitated silicas with BET surface areas of at least 50 m ² / g.

The silica fillers mentioned can be hydrophilic Have character or hydrophobized by known methods his. For example, see DE 38 39 900 A (Wacker Chemie GmbH; registered on November 25, 1988) or the corresponding one US-A 5,057,151. In general, the Hydrophobization with 1 to 20 wt .-% hexamethyldisilazane and / or divinyltetramethyldisilazane and 0.5 to 5% by weight Water, each based on the total weight of the Organopolysiloxane mass, these reagents advantageously in a suitable mixing device, such as e.g. B. kneader or internal mixer to the already submitted Organopolysiloxane (A) are given before the hydrophilic Silicic acid is gradually incorporated into the mass.

Examples of non-reinforcing fillers are quartz powder, diatomaceous earth, calcium silicate, zirconium silicate, zeolites, metal oxide powders such as aluminum, titanium, iron or zinc oxide, barium silicate, barium sulfate, calcium carbonate, gypsum and plastic powders such as polyacrylonitrile powder or polytetrafluoroethylene powder. Fibrous components such as glass fibers and plastic fibers can also be used as fillers. The BET surface area of these fillers is preferably below 50 m ² / g.

The inventive, crosslinkable to form elastomers Organopolysiloxane compositions contain filler (B) in amounts of preferably 1 to 200 parts by weight, particularly preferably 30 up to 100 parts by weight, each based on 100 parts by weight Organopolysiloxane (A).

Depending on the application, the Vulcanizable to elastomers according to the invention Organopolysiloxane compositions additives (C), such as Processing aids such as plasticizers, pigments and Stabilizers such as heat stabilizers can be added.

Examples of plasticizers that can be used as additives (C) are polydimethylsiloxanes terminated with trimethylsilyl groups or hydroxyl groups with a viscosity of at most 1000 mm ² / s at 25 ° C. or also diphenylsilanediol.

Examples of heat stabilizers used as additives (C) can be used are transition metal fatty acid salts, such as iron octoate, transition metal silanolates such as iron silanolate, and cerium (IV) compounds.

In addition, the compositions according to the invention contain, except Color pigments, preferably no other substances.

In the respective for the production of the compositions according to the invention components used can be a single one Kind of such a component, as well as a mixture of at least two different types of such a component act.

Another object of the invention is a method for Manufacture of organopolysiloxane compositions, thereby characterized in that an organopolysiloxane and a crosslinker  containing bis-4-methylbenzoyl peroxide - (= PMBP) and one single connection or at least two of the connections the group consisting of benzoyl peroxide, dicumyl peroxide, 2.5 Dimethyl-hexane-2,5-di-tertiary-butyl peroxide (= DHBP), Ditertiary butyl peroxide, preferably in a ratio 1: 0.3 to 1: 1 can be mixed.

The organopolysiloxane is preferably organopolysiloxane (A), which has the same meaning as above.

The preparation of the peroxidically crosslinkable according to the invention Organopolysiloxane compositions can be made by known methods, such as simply mixing the individual Components. Incorporation of those used according to the invention low molecular weight organosilicon compounds can different ways of mixing, z. B. in one any step of mixing the individual components of the Silicone rubber compound. Advantageously, for preparation the peroxidically crosslinkable compositions according to the invention low molecular weight organosilicon compounds during the Incorporation of the filler mixed into the mass. A another possibility is the application of the invention used low molecular weight organosilicon compound on the Filler by mixing in a powder mixer or by Mix in a suspension of filler, inert organic Solvent and low molecular weight organosilicon compound and then stripping off the organic solvent until to dryness in order to then with this, equally with the Filler as a carrier to be introduced. Another One possibility is that the one used according to the invention low molecular weight organosilicon compound by chemical Reaction, for example analogous to that described above Process variant 2, produced on and on the filler is left.

The peroxidically crosslinkable compositions according to the invention can be networked under the same conditions as that previously known peroxidically crosslinkable compositions.  

The peroxidically crosslinkable compositions according to the invention have the Advantage that the elastomers made from it are very good mechanical properties, especially with regard to the Show tear resistance. Furthermore, they show none Yellowing and do not lead to odor nuisance.

The organopolysiloxane compositions according to the invention and the Elastomers produced therefrom according to the invention can be used by everyone Purposes are used for which also to date elastomers crosslinkable organopolysiloxane compositions or elastomers are used were. The inventive ones are particularly suitable Organopolysiloxane compositions and those according to the invention manufactured elastomers for applications that have a require improved tear resistance, such as. B. Hoses, cable jackets, automotive parts and Seals.

example 1

100 parts of a diorganopolysiloxane endblocked by trimethylsiloxy groups from 99.93 mol percent of dimethylsiloxane units and 0.07 mol percent of vinylmethylsiloxane units with a viscosity of 8.10 ⁶ mPa.s at 25 ° C. are first produced in a kneader operated at 150 ° C. with 50 parts of pyrogen in the gas phase Silicon dioxide with a surface area of 200 m ² / g, then with 1 part of dimethylpolysiloxane end-blocked by trimethylsiloxy groups with a viscosity of 96 mPa.s at 25 ° C., then with 7 parts of a dimethylpolysiloxane each having an Si-bonded hydroxyl group in the terminal units a viscosity of 40 mPa.s at 25 ° C for crosslinking, a mixture of 1 wt .-% bis-4-methylbenzoyl peroxide - (= PMBP) and 0.8 wt .-% benzoyl peroxide is mixed.

Example 2

100 parts of a diorganopolysiloxane endblocked by trimethylsiloxy groups from 99.93 mol percent of dimethylsiloxane units and 0.07 mol percent of vinylmethylsiloxane units with a viscosity of 8.10 ⁶ mPa.s at 25 ° C. are first produced in a kneader operated at 150 ° C. with 50 parts pyrogenically in the gas phase Silicon dioxide with a surface area of 200 m ² / g, then with 1 part of dimethylpolysiloxane end-blocked by trimethylsiloxy groups with a viscosity of 96 mPa.s at 25 ° C., then with 7 parts of a dimethylpolysiloxane each having an Si-bonded hydroxyl group in the terminal units a viscosity of 40 mPa.s at 25 ° C for crosslinking is a mixture of 1 wt .-% bis-4-methylbenzoyl peroxide - (= PMBP) and 0.8 wt .-% of an equal mixture of benzoyl peroxide and 2.5 dimethyl -hexane-2,5-di-tertiary butyl peroxide (= DHBP) mixed.

Comparative Example 1

The procedure described in Examples 1 and 2 will be repeated with the modification that only 1.5% by weight as crosslinker PMBP is mixed in.

Comparative Example 2

The procedure described in Example 1 is repeated with the change that only 1.5% by weight Benzoyl peroxide is mixed in.

Comparative Example 3

The procedure described in Example 2 is repeated with the modification that as a crosslinker only a mixture of 1.5% by weight of benzoyl peroxide and 2.5 dimethyl-hexane-2,5-di-tertiary butyl peroxide (= DHBP) is mixed.  

With the mass according to Examples 1 and 2, and the comparative mixtures 1, 2 and 3, an electrical conductor (strand 1.5 mm ² ) is isolated using an extrusion. The wall thickness of the insulation is 0.6 mm. An extruder with a 45/10 d screw with crosshead is used for this. The temperature of the heating duct at the entrance is 470 ° C in the middle 350 ° C and at the end 250 ° C. The take-off speed is 20 m / min. The dwell time in the heating duct is 20 sec.

Result Cable according to example 1 and 2

Bubble-free, fully networked insulation, only minimal Odor nuisance, negligible yellowing of the Isolation.

Cable according to comparative example 1

Slightly under-networked insulation, sometimes light Blistering, strong smell, yellowing of the Isolation. For sufficient networking is one Extension of the dwell time to 25 seconds required.

Cable according to comparative examples 2 and 3

Bubble insulation, sticky surface, none Odor nuisance, no yellowing.

Claims (4)

1. Organopolysiloxane masses can be produced on the basis of an organopolysiloxane and a crosslinker containing bis- 4-methylbenzoyl peroxide - (= PMBP) and one Compound or at least two of the compounds from the Group consisting of benzoyl peroxide, dicumyl peroxide, 2.5 Dimethyl-hexane-2,5-di-tertiary-butyl peroxide (= DHBP), Ditertiary butyl peroxide exists. 2. Organopolysiloxane compositions according to claim 1, characterized characterized in that the crosslinker containing bis-4- Methylbenzoyl peroxide - (= PMBP) and a single compound or at least two of the compounds from the group that from benzoyl peroxide, dicumyl peroxide, 2.5 dimethyl-hexane-2.5- di-tertiary-butyl peroxide (= DHBP), di-tertiary-butyl peroxide exists in a weight ratio of 1: 0.3 to 1: 1 is. 3. Process for the preparation of organopolysiloxane compositions, characterized in that an organopolysiloxane and a Crosslinker containing bis-4-methylbenzoyl peroxide - (= PMBP) and a single connection or at least two of the Compounds from the group consisting of benzoyl peroxide, Dicumyl peroxide, 2,5 dimethyl-hexane-2,5-di-tertiary butyl peroxide (= DHBP), ditertiary butyl peroxide exists, be mixed. 4. Process for the preparation of organopolysiloxane compositions Claim 3, characterized in that a crosslinker containing bis-4-methylbenzoyl peroxide - (= PMBP) and a single connection or at least two of the Compounds from the group consisting of benzoyl peroxide, Dicumyl peroxide, 2,5 dimethyl-hexane-2,5-di-tertiary butyl peroxide (= DHBP), ditertiary butyl peroxide exists in Weight ratio 1: 0.3 to 1: 1 can be mixed.