DE4210349A1 - RTV silicone rubber, crosslinked by condensation - prepd. by mixing hydroxy-terminated polysiloxane with silane and organo-metallic catalyst in form of aged or heat-treated soln. in polysiloxane - Google Patents

Abstract

Silicone rubbers which can be crosslinked by condensation reactions at room temp. (I) are mfd. by mixing, in the absence of moisture, OH-terminated polydiorgano-siloxane(s) of formula HO-(SiR20)n-H (II) with silane(s) of formula (R')4-aSiXa (III) or their partly hydrolysed prods. to give a mixt. with viscosity 500-1 million mPa.s at 25 deg.C and with a condensation catalyst of formula (R"O)bML4-b (IV) or a partial hydrolysate thereof, and opt. other additives such as cocatalystis, accelerators, stabilisers, active and inactive fillers and plasticiser oils. Catalyst (IV) is added as a mixt. wtih polydiorganosiloxane(s) of formula (R"')3Si-(OSi(R"')3 (V) with viscosity 15-50,000 mPa.s and OHs1 content 0.005-8 wt. % and this mixt. is stored at room temp. before use and/or heated at up to 200 deg.C. R, R', R"' = opt. substd. 1-8C hydrocarbyl; n, m = whole no; X = aximato, acetoxy, alkoxy, amido, aminoxy, or amino gp. M = Ti or Zr; R2 = opt. substd. 1-18C alkyl; L = dibentate chelating ligand; a = 2.1-4; b = 2-4. USE/ADVANTAGE - Used pref. as moisture-cured, 1-component (RTV-1) siloxane rubbers. The process enables the prodn. of (I) in a single mixing step, using a catalyst prepn. which is stable for long periods at room temp. coneniently handled and metered, and does not cause a sharp increase in viscosity when added to (II)

Description

The invention relates to a method for producing Room temperature through condensation cross-linking silicone rubbers, based on hydroxyl-terminated poly diorganosiloxanes.

As a base polymer for silicone chews that crosslink at room temperature schuke mostly serves a polydiorgano that can be produced inexpensively siloxane with terminal hydroxyl groups. Become a crosslinker Silanes with an average of more than two hydrolyzable groups pen used per molecule, being used as hydrolyzable groups e.g. B. alkoxy groups, acetoxy groups and oximato groups turn come. The networking is generally through a Condensation catalyst accelerated. Tin is often used for this connections such as B. dialkyltin dicarboxylates used have the disadvantage that they are so because of their toxicity are physiologically and ecologically questionable. In com Combination with alkoxy crosslinkers is also a premature Ver networking cannot be prevented by a surplus of crosslinkers (van der Weÿ, F. W .: Makromol. Chem. 181 2541 (1980)). These Disadvantages are due to the use of titanium or zirconium catalysts avoidable.

In previous processes for the production of titanium or zirconium-catalyzed silicone that crosslinks at room temperature rubber was when the base polymer was mixed with the kata a sharp increase in viscosity (e.g. DE-AS 11 77 339), which interferes with further processing flowed. This negative effect was exacerbated by the use of Titanium or zirconium chelates softened (US 3,708,467, US 3,779,986), but was still a nuisance. The person skilled in the art knows that this disturbing effect does not occur if other than hydroxyl-terminated polydiorganosiloxanes, e.g. B. Verbin  with polyalkoxysiloxy, polyoximatosiloxy or poly acetoxysiloxy end groups can be used. These are polymers but much more expensive to manufacture.

Another variant for avoiding the increase in viscosity is e.g. B. the formation of polyalkoxy end groups in a two-stage Mixing process of the hydroxyl-terminated polymer and one Crosslinker (DE-OS 37 27 565), which is an additional procedure step means and on the production of RTV-1 rubbers is limited.

It was therefore the object of the present invention to provide a con cross-linking silicone rubber based on hydroxyl group-terminated polydiorganosiloxanes with titanium and / or Manufacture zirconium catalysts in a mixing stage, where both the production of one-component rubbers (RTV-1) and also the manufacture of components for two-component chewing schuke (RTV-2) is included.

This object is achieved by one or several hydroxyl-terminated polydiorganosiloxanes from general formula

HO (-SiR₂O) _n -H (1)

with one or more silanes of the general formula

R ′ _4-a SiX _a , (2)

or their partial hydrolysates, in which R and R 'are identical or different, substituted or unsubstituted C _1-8 hydrocarbon radicals, X = oximato, acetoxy, alkoxy, amido, aminoxy or amino groups, a on average 2 , 1 to 4, preferably 3 to 4, and n is an integer and the viscosity is 500 to 1,000,000 mPa · s at 25 ° C, and with an effective amount of condensation catalyst of the general formula

(R′′O) _b ML _4-b , (3)

or its partial hydrolyzates, in which M is titanium or zirconium, R ′ ′ identical or different, unsubstituted or substituted C _1-18 alkyl groups, L identical or different divalent Che latliganden and b is a number between 2 and 4, are mixed, the Catalyst as a mixture with one or more polydiorganosiloxanes of the general formula

R ′ ′ ′ ₃Si (-OSiR ′ ′ ′ ₂) _m -OSiR ′ ′ ′ ₃, (4)

is used, in which R ′ ′ ′ is the same or different substituted or unsubstituted C _1-8 hydrocarbon radicals, m is an integer, the viscosity is 15 to 50 000 mPa · s at 25 ° C and the OH _Si content 0.005 is up to 8 wt .-%, and this mixture is stored before use at room temperature and / or is thermally treated at temperatures up to 200 ° C. If necessary, other additives such as cocatalysts, accelerators, substances for storage stabilization, active and inactive fillers and plasticizer oils can be mixed in.

Examples of the radicals R and R '''are C _1-3 alkyl, trifluoropropyl, vinyl or phenyl groups. Methyl groups are particularly preferred.

The radical R 'is preferably a methyl, ethyl, vinyl or a substituted propyl radical.

The radical R '' is preferably C _3-4 alkyl or isoalkyl, such as. B. n-butyl, n-propyl, isopropyl and isobutyl.

As chelate ligands L, two-fold chelate ligands are preferred as acetoacetic ester enolates or acetylacetonates used. It can also be mixtures of several titanium and / or zirconium connections are used.

Examples of condensation accelerating catalysts which are used in the method according to the invention, are tetrabutyl titanate, tetraisopropyl titanate, tetrapropyl titanate, tetraisobutyl titanate, isopropyl-n-butylylbisacetyl acetone titanate, diisobutyl bis ethyl acetoacetate titanate, Di-n-butylbismethylacetoacetate titanate, diisopropylbismethylace toacetate titanate, tetrabutyl zirconate, tetraisopropyl zirconate, Dibutyl bismethyl acetoacetate zirconate and others to those skilled in the art known connections.  

An effective amount of catalyst is, depending on that condensation-curing silicone rubber, about 0.02 to 5 wt .-% catalyst of formula (3) based on the polydi organosiloxane of formula (1).

The titanium and or zirconium catalyst is preferably 0.1 up to 60 wt .-% in the mixture with the polydiorganosiloxane Contain formula (4), 2 to 20% by weight being particularly preferred are.

The polydiorganosiloxane of the general formula (4) preferably has a viscosity between 100 and 10,000 mPa · s at 25 ° C. and an OH _Si content of 0.01 to 0.08% by weight. Although linear triorganosiloxy-terminated polydiorganosiloxanes are preferred, reference is expressly made to the possible use of ver branched polymers, as well as to the use of polydiorganosiloxanes with OH, OR or vinyl end and / or side groups.

The use of low viscosity polydiorganosiloxanes, e.g. B. a viscosity of 20 to 200 mPa · s at 25 ° C, with terminal OH groups and an OH _Si content of 0.5 to 8 wt .-% is also possible.

The amount of the catalyst which can be used in the mixture with the polydiorganosiloxane of the formula (4) depends on a number of factors, including the OH _Si content of the polydiorganosiloxane of the formula (4). When using OH-terminated polydiorganosiloxanes, the titanium catalyst is advantageously used in a stoichiometric excess over the OH groups.

Before use, the mixture of the catalyst with the Polydiorganosiloxane stored at room temperature and / or at Temperatures up to 200 ° C thermally treated.

If you add a condensation-curing silicone rubber the catalyst / polydiorgano treated according to the invention siloxane mixture, which contains an effective amount of catalyst  contains general formula (3), so is an abrupt Vis observed increase in the viscosity when the catalyst / poly diorganosiloxane mixture immediately after production, without Storage is used. This increase in viscosity complicates the further processing a homogeneous distribution of the Kataly sator / polydiorganosiloxane mixture or makes it impossible, so that the rubber is unusable. In any case, the Further processing of the rubber is made much more difficult. The same effect is also observed when the catalyst is the Formula (3) as a substance or as a solution in a conventional organic solvents (e.g. toluene) or as a solution in one Silane of formula (2) is used, the age of this Solutions doesn't matter.

It was not expected that an aged catalyst / polydi organosiloxane mixture has a different behavior than that freshly made mixture or the catalyst as a substance alone or in a conventional organic solvent or Silane of formula (2) dissolved. So it was surprising that in in some cases, storage over several days in the room temperature was enough to make the extreme increase in viscosity so strong to reduce the production of the silicone rubber no more problems and still a good Kataly network activity was observed.

The time of storage and / or thermal treatment depends on many factors. This includes the type of catalyst, its concentration in the mixture to be aged, the OH _Si content of the polydiorganosiloxane, the temperature and the content of small amounts of water traces that can hardly be avoided technically. The degree of aging has to be greater, the higher the catalyst concentration required for perfect curing of the silicone rubber produced according to the invention. The more the processing in the manufacture of the silicone rubber is impaired by an increase in viscosity, the more complete the aging process must be. The aging of the catalyst can also take place in the production of the titanium or zirconium chelate if this takes place in the presence of the polydiorganosiloxane of the general formula (4) and is optionally continued by storage at room temperature and / or thermal treatment.

An advantage of the method according to the invention is that the catalyst / polydiorganosiloxane mixtures at moist exclusion are stable for a long time and a light and allow convenient dosing of titanium chelates, which at Tending to crystallize at room temperature.

The silicone rubber produced according to the invention cures under the influence of humidity to form an elastomer. It is preferably used as a one-component rubber (RTV-1) manufactured in essentially anhydrous conditions and is at Exclusion of humidity can be stored for a long time. The Erfin But manure can also be beneficial in making two Component rubber (RTV-2), that is a rubber that processed immediately after all components have been mixed, be applied. It is both possible that a compo nente the polydiorganosiloxane of formula (1) and the invented contains, according to the invention, aged catalyst mixture and the other component is the silane of the general formula (2); as well as that the inventive mixing of the aged Catalyst mixture with a rubber that the poly contains diorganosiloxane of the formula (1) and the crosslinker the user.

A particularly preferred application of the present Er invention is the manufacture of silicone rubber Use of alkoxysilanes. Such silanes are e.g. B. Tetraethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, Methyltrimethoxysilane, vinyltrimethoxysilane and their partial hydrolyzates and others known to those skilled in the art Links.

Embodiments

In the following, the invention will be described in more detail using a few examples are explained.

All concentrations are given in parts by mass. The Vis cosities were measured at 25 ° C. It was dried with Starting materials worked.

example 1

5 parts of tetrabutyl titanate were mixed with 95 parts of trimethylsiloxy-terminated polydimethylsiloxane (viscosity 500 mPa · s, OH _Si content 350 ppm). The catalyst / polydiorganosiloxane mixture was stored for one week with exclusion of moisture at room temperature. 25 parts of hydroxyl-terminated polydimethyldisiloxane (viscosity 5400 mPas, OH _Si content 0.1% by weight) were then stirred with 3 parts of this mixture. There was only a very slow and slight increase in viscosity that did not interfere with further processing. After adding 1.5 parts of methyltrimethoxysilane, the mixture crosslinked within 4 hours to form a tack-free elastomer.

The same effect was achieved by heating the freshly prepared catalyst / polydiorganosiloxane mixture reached to 100 ° C.

Example 2 (comparative example)

25 parts of hydroxyl-terminated polydimethyldisiloxane (as in Example 1) with 0.15 parts of tetrabutyl titanate mixed. There was a sharp increase in viscosity, which caused none due to lack of homogeneity immediate further processing was possible.  

Example 3

5 parts of tetrabutyl titanate were mixed with 95 parts of hydroxyl-terminated polydimethylsiloxane (viscosity 5400 mPas, OH _Si content 0.1% by weight) with exclusion of moisture (stoichiometric excess of the titanium catalyst compared to the OH groups). There was no thickening. After adding silane, there was no crosslinking when air humidity entered. After two weeks of storage, 20 parts of this mixture were mixed with 231 parts of the same polydiorganosiloxane. There was no annoying thickening; after adding silane, the system crosslinked to form an elastomer.

Example 4 (comparative example)

There were 250 parts of the hydroxyl-terminated polydimethyl siloxane mixed with 1 part of tetrabutyl titanate. It occurred immediately a strong thickening on the further processing made impossible.

Example 5

25 parts of hydroxyl-terminated polydimethylsiloxane (as in Example 1) became 0.5 parts of a 4 weeks at room temperature aged mixture of 5 wt .-% tetrabutyl titanate and Trimethylsiloxy-terminated polydimethylsiloxane analogous to Bei given game 1. There was no increase in viscosity. To Addition of 2 parts of vinyl trimethoxysilane crosslinked the mixture to an elastomer.  

Example 6 (comparative example)

Analogous to Example 3, except that the addition of the catalyst / Polydiorganosiloxane mixture after 18 hours of storage took place. An extreme increase in viscosity occurred immediately, so that this mixture could not be processed further.

Example 7

60 parts of a mixture of 100 parts of hydroxyl-terminated polydimethylsiloxane and 5 parts of methyltrimethoxysilane were mixed with 2 parts of a 5% strength mixture of dibutyl-bis (methylacetoacetato) titanate and a trimethylsiloxy-terminated polydimethylsiloxane (viscosity 500 mPa · s, viscosity 350 OHP), stored for 4 weeks at room temperature _Si ) mixed. There was no very strong increase in viscosity (only a doubling within 2 hours), so that the mixture was still easy to handle. The mixture was stable with the exclusion of moisture and cured to form an elastomer in the presence of atmospheric moisture.

Example 8

57 parts of hydroxyl-terminated polydimethylsiloxane were with 3.2 parts of a 4 weeks stored at room temperature 5% mixture of dibutyl bis (methylacetoacetato) titanate and Methyltrimethoxysilan mixed. The increased Viscosity within 10 minutes ten times what the further processing steps significantly more difficult.  

Examples 9 to 20 (Table 1)

These examples are intended to use the variety of the invention baren polydiorganosiloxanes of the general formula (4) in the for use the production of the silicone rubber according to the invention hint the catalyst / polydimethylsiloxane mixtures. Various polydimethylsiloxanes were made with tetrabutyl titanate mixed in a ratio of 95: 5. 1 part of this mixture was A) with 10 parts of a polydimethylsiloxane with terminal OH Groups and a viscosity of 5000 mPa · s and B) with 10 parts a mixture of 900 parts of the polydimethylsiloxane from A) and 40 parts of methyltrimethoxysilane mixed. The Viscosity increase assessed, and for B) the skin formation time (SOT) determined. That was after different storage times Catalyst / polydimethylsiloxane mixture repeated.

The results are summarized in Table 1, which means
G: gel formation, which makes further processing impossible,
S: rapid, strong thickening, which makes processing much more difficult,
L: slow to imperceptible thickening that causes no problems.

Table 1

Was the catalyst / polydimethylsiloxane mixture immediately after used in their manufacture, gel formation occurred in any case on.

Examples 21 to 31 (Table 2)

These examples are intended to illustrate the breadth of the catalysts that can be used of the general formula (3) in the Her for the invention position of the silicone rubber used catalyst / poly suggest dimethylsiloxane mixtures. The catalysts were in Ratio 5:95 with the polydimethylsiloxane of Example 13 mixed and the procedure was analogous to Examples 9 to 20. The results are summarized in Table 2, which like Table 1 can be read.  

Table 2

Examples 32 to 38 (Table 3)

These examples are intended to show the possible range of variation in the Mixing ratios for the production according to the invention of the silicone rubber used catalyst / polydimethylsi Indicate loxane mixtures. It was as in Examples 9 to 20 procedure, with the exception that the mixing ratios in the tetrabutyl titanate / polydimethylsiloxane mixture is variable were, and the mixture of the polymer A and the polymer / silane mixture B according to the actual catalyst concentrations Tration was added so that they are in the mixtures in examples Correspond to 9 to 20.

Examples 32 to 34 were with the polydimethylsiloxane from Example 9, and Examples 35 to 38 with the polydimethylsiloxane of Example 17. The results are in Table 3 compiled, which can be read as Table 1.

Table 3

Examples 39 to 61 (Table 4)

These examples are intended to show the effect of a thermal treatment at different catalysts and temperatures illustrate. It became the polydimethylsiloxane of Example 17 used. The time t is the time it takes to complete thermal aging at the specified temperature Obtain catalyst mixture in one procedure according to Examples 9 to 38 only slow to imperceptible thickening leads.

Table 4

Example 62

100 parts of hydroxyl-terminated polydimethylsiloxane one Viscosity of 50,000 mPa · s became pyrogenic with 10 parts Silica, 50 parts of chalk precipitated, 30 parts of trimetyl siloxy-terminated polydimethylsiloxane with a viscosity of 500 mPa · s and 3 parts of vinyl trisbutanone oximatosilane in a kneader Kneaded for 15 minutes. Then 2 parts were a 4 weeks stored 5% mixture of diisopropyl bis (methylaceto acetato) titanate and a trimethylsiloxy-terminated polydi Added methylsiloxane and kneaded for a further 15 minutes. It no increase in viscosity was observed. In the absence of air the mixture was storable.

The mixture crosslinked in the presence of atmospheric moisture. To The following characteristic values were determined over 7 days:  

Example 63

140 parts of hydroxyl-terminated polydimethylsiloxane with a viscosity of 50 mPa · s and with an OH _Si content of 0.05% by weight, 60 parts of trimethylsiloxy-terminated polydimethylsiloxane with a viscosity of 500 mPa · s, 100 parts of precipitated chalk and 6 parts of vinyltrimethoxysilane were mixed in a kneader mixed.

• A) For this, 8 parts of a mixture stored for 10 days were made Diisobutyl bis (ethylacetoacetato) titanate and polydimethyl given siloxane of Example 26 from Table 2. There was none Thickening one. The skin formation time is 10 minutes. After 10 Days, the following characteristic values were determined: tensile strength 0.6 MPa, Elongation at break 260%, Shore A hardness 18.
• B) 0.4 parts of diisobutyl-bis (ethylacetoacetato) given titanate. There was an immediate thickening, which the further processing much more difficult. The skin formation time was 10 minutes. After 10 days, the following parameters were found determined: tensile strength 0.6 MPa, elongation at break 220%, Shore-A- Hardness 20. Due to the poor mixing, a very hard large scatter of the measured values between the individual test specimens observed.

Claims (9)

1. Process for the preparation of a silicone rubber which crosslinks at room temperature by condensation reactions, obtained by mixing under essentially anhydrous conditions of
one or more hydroxyl-terminated polydiorganosiloxanes of the general formula HO (-SiR₂O) _n -H (1) with one or more silanes of the general formula R ' _4-a SiX _a , (2) or. whose partial hydrolyzates, wherein R and R 'independently of one another the same or different, substituted or unsubstituted C _1-8 hydrocarbon radicals, X = oximato, acetoxy, alkoxy, amido, aminoxy or amino groups, a on average 2.1 to 4 and n is an integer and the viscosity is 500 to 1,000,000 mPa · s at 25 ° C, and with
an effective amount of the condensation-accelerating catalyst of the general formula (R′′O) _b ML _4-b , (3) or its partial hydrolyzates, in which M is titanium or zirconium, R ′ ′ identical or different unsubstituted or substituted C _1-18 - Alkyl groups, L mean identical or different divalent Che latliganden and b is a number between 2 and 4, and
optionally further additives such as cocatalysts, accelerators, substances for storage stabilization, active and inactive fillers and plasticizer oils, characterized in that
that the catalyst is used as a mixture with one or more poly diorganosiloxanes of the general formula: R '''₃Si(-OSiR''' ₂) _m -OSiR '''₃, (4), wherein R''' the same or different Substituted or unsubstituted C _1-8 hydrocarbon radicals means, in is an integer, the viscosity 15 to 50,000 mPa · s at 25 ° C and the OH _Si content 0.005 to 8 wt .-%, and this mixture before Use stored at room temperature and / or thermally treated at temperatures up to 200 ° C. 2. The method according to claim 1, characterized in that the polydiorganosiloxane of the general formula (4) has a viscosity between 100 and 10,000 mPa · s at 25 ° C and an OH _Si content of 0.01 to 0.08 wt. % having. 3. The method according to claim 1, characterized in that the Catalyst with 0.1 to 60 wt .-% is contained in the mixture. 4. The method according to claim 1 and 2, characterized in that the polydiorganosiloxane of the general formula (4) is a trimethylsiloxy-terminated polydimethylsiloxane with an OH _Si content of 0.01 to 0.08 wt .-%. 5. The method according to claim 1 to 4, characterized in that the catalyst with 0.1 to 20 wt .-% in the mixture is. 6. The method according to claim 1 and 2, characterized in that the polydiorganosiloxane of the general formula (4) is a hydroxyl-terminated polydimethylsiloxane with a viscosity of 20 to 200 mPa · s at 25 ° C and an OH _Si content of 0.5 to 8 % By weight. 7. The method according to claim 1 and 6, characterized in that the catalyst contained 0.5 to 60 wt .-% in the mixture is. 8. The method according to claim 1, characterized in that the Polydiorganosiloxane of the general formula (4) the same Structure like the polydiorganosiloxane of the general formula (1) having. 9. The method according to claim 1, characterized in that the Mixture is stored at room temperature for at least 3 days.