Continuous process for making storage stable organopolysiloxane compositions

The invention relates to a process for producing storage-stable organopolysiloxane compositions, in which organopolysiloxanes and pre-hydrophobic oxidizing reinforcing fillers are mixed and kneaded in a kneading machine with kneading chambers arranged next to one another in series.

Compositions of organopolysiloxane and hydrophobic oxidic reinforcing filler must be kneaded intensively in order to disperse the filler uniformly, to improve the storage stability of the compositions and to achieve good mechanical properties of the silicone rubber vulcanizates prepared from the compositions.

A method for the continuous production of silicone compositions which can be condensed at room temperature using pyrogenic silica is described in US Pat. No. 4,737,561. There, the constituents of the silicone masses are first combined in a continuously operating closed mixer and then catalyst is mixed, homogenized and degassed in an oscillating pilgrim kneader.

AU-A-91 76 256 describes a process for the continuous production of base materials for addition-crosslinkable silicone materials. In a twin-screw extruder, vinyl-terminated polydimethylsiloxane, hydrophilic pyrogenic silica, water and hexamethyldisilazane are mixed. The hydrophilic silica is made hydrophobic by water and hexamethyldisilazane. The hydrophobization therefore takes place in situ.

The screw reactors described above, namely oscillating pilgrim step kneaders and twin-screw extruders, do not allow the silicone materials to be kneaded sufficiently intensively, since the insufficient residence time of the materials in the reactor space can be varied only slightly. Even if the throughput is reduced, the dwell time hardly changes because the screws have a constant conveying effect. If the speed is reduced, the dwell time can be extended somewhat, but the kneading effect is reduced.

In addition, the in-situ method described in AU-A-91 76 256 has the disadvantage of high emissions which occur on every kneading machine and are therefore difficult to control. Furthermore, a targeted control of the hydrophobization is hardly possible and corrections of the filler contents of the compositions are no longer possible because suitable fillers are missing.

A method for pre-hydrophobicizing oxidic reinforcing filler is described in US-A-5,057,151. There, the hydrophilic filler is made hydrophobic in an excess of hydrophobicizing agent under mechanical stress. Excess hydrophobizing agent is then drawn off and returned to the process.

When pre-hydrophobizing the filler, it is possible to control the degree of hydrophobization in a targeted manner and to vary it within wide limits, high and / or uniform degrees of hydrophobization being possible, which is a requirement for many applications. The method for pre-hydrophobization allows the filler to be hydrophobicized in such a way that so-called simple mixing of the hydrophobicized filler with organopolysiloxane and subsequent kneading of the mixture. Base materials for crosslinkable organopolysiloxane compositions can be produced. The use of previously hydrophobic filler leads to a significant increase in the capacity of the mixing elements. Emissions are limited to a central system, namely the water repellent system, and are therefore easier to control. The consumption of water repellents can be significantly reduced compared to the in-situ process. The filler content of the compositions can easily be corrected subsequently by adding further filler.

In discontinuous kneaders, such as double-bowl kneaders, compositions of organopolysiloxane and hydrophobic oxidic reinforcing filler (= base materials) with high storage stability can be produced, in which the silicone rubber vulcanizates produced on the basis of the compositions have very good mechanical properties.

However, the discontinuous kneaders require very long batch times of up to 25 hours. Because of the resulting low space-time yields, the preparation of the compositions is very expensive. After the kneading process has ended, the kneaders are tilted in order to discharge the compositions from the kneaders. Since the compositions, in particular the highly viscous compositions, only flow incompletely from the kneaders, manual help is required and the kneaders have to be scraped out. The kneaders work under protective gas, since gases can collect in the gas space, which can form explosive mixtures in the presence of oxygen. The kneading process can also not be controlled, since only after kneading the composition can it be determined whether the product quality corresponds to the specification. If the target value deviates, the entire batch must be reworked.

The present invention has for its object to provide a method for producing a composition consisting of organopolysiloxane and hydrophobic oxidic reinforcing filler, in which large space-time yields can be achieved and the compositions can be kneaded intensively, the kneading process being easy to control.

The invention relates to a method for producing organopolysiloxane compositions, in which<ul id="ul0001" list-style="none" compact="compact"><li>(1) Organopolysiloxanes that have an average of at least 2 silicon-bonded residues per molecule selected from<ul id="ul0002" list-style="none" compact="compact"><li>(a) Hydrocarbon residues with aliphatic carbon-carbon multiple bonds</li><li>(b) hydrogen atoms and</li><li>(c) hydroxyl groups and</li></ul></li><li>(2) pre-hydrophobic oxidic reinforcing fillers with a carbon content of at least 0.5% by weight obtained by the hydrophobization in a kneading machine with at least two kneading chambers arranged in series next to each other, each containing two axially parallel kneading tools which can be driven in the same or opposite directions and which openings which are passable transversely to the axes of the kneading tools are connected to one another, wherein the first kneading chamber has a loading opening and the last kneading chamber has a discharge opening, are mixed and kneaded.</li></ul>

Linear or branched organopolysiloxanes composed of units of the general formula I are preferably used as organopolysiloxanes (1) <maths id="math0001" num="(I),"><math display="block"><mrow><msubsup><mrow><mtext>R</mtext></mrow><mrow><mtext>a</mtext></mrow><mrow><mtext>1</mtext></mrow></msubsup><msubsup><mrow><mtext>R</mtext></mrow><mrow><mtext>b</mtext></mrow><mrow><mtext>2</mtext></mrow></msubsup><mtext>SiO</mtext><msub><mrow><mtext>​</mtext></mrow><mrow><mfrac><mrow><mtext>4-ab</mtext></mrow><mrow><mtext>2</mtext></mrow></mfrac></mrow></msub></mrow></math><img file="EP0807509A1_D0001.tif" /></maths>used, where<dl id="dl0001" compact="compact"><dt><b>R</b>^<b>1</b></dt><dd>monovalent C, optionally substituted with halogen atoms₁- to C₁₀-Hydrocarbon residues that are free from aliphatic carbon-carbon multiple bonds,</dd><dt><b>R</b>^<b>2</b></dt><dd>Hydrogen atoms, hydroxyl groups or monovalent hydrocarbon radicals with aliphatic carbon-carbon multiple bond with 2 to 8 carbon atoms per radical,</dd><dt><b>a</b></dt><dd>the values ​​0, 1, 2 or 3 and</dd><dt><b>b</b></dt><dd>the values ​​0, 1 or 2 mean, with the proviso that an average of at least 2 residues <b>R</b>^<b>2</b> are present per molecule.</dd></dl>

The organopolysiloxanes (1) preferably have an average viscosity of at least 10, in particular at least 1000 mPa · s, and preferably at most 10⁸, in particular at most 10⁵ mPa · s at 25 ° C.

Examples of unsubstituted hydrocarbon residues <b>R</b>^<b>1</b> are C₁- to C₁₀-Alkyl-, C₁- to C₁₀-Alkaryl or C₁- to C₁₀Aralkyl radicals whose alkyl part is saturated, or C₁- to C₁₀Aryl residues. Examples of alkyl radicals<b>R</b>^<b>1</b> are 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 and cyclohexyl radical; Heptyl residues, such as the n-heptyl residue; 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; Cycloalkyl radicals, such as the cyclohexyl radical; Examples of alkaryl residues<b>R</b>^<b>1</b> are the α- and β-phenylethyl radical; Examples of aralkyl radicals<b>R</b>^<b>1</b> are the benzyl radical and the 2,4-diethylbenzyl radical; Examples of aryl residues<b>R</b>^<b>1</b> are the phenyl radical and the naphthyl radical. Preferably means <b>R</b>^<b>1</b> C.₁- to C₆-Alkyl radicals and phenyl radicals, especially methyl and ethyl radicals.

Examples of hydrocarbon radicals substituted by halogen atoms <b>R</b>^<b>1</b> are the 3,3,3-trifluoro-n-propyl group, the 2,2,2,2 ', 2', 2'-hexafluoroisopropyl group, the heptafluoroisopropyl group, the 3-chloro-n-propyl group, the 2-ethyl bromide group and the 3-propyl bromide residue. Preferably the residues are<b>R</b>^<b>1</b> not substituted.

Examples of monovalent hydrocarbon radicals with aliphatic carbon-carbon multiple bond with 2 to 8 carbon atoms per radical <b>R</b>^<b>2</b> are alkenyl radicals, such as the vinyl, 5-hexenyl, 1-propenyl, allyl, 1-butenyl and 1-pentenyl radical; and alkynyl radicals such as the ethynyl, propargyl and 1-propynyl radical.

The organopolysiloxanes (1) preferably have at least 90, in particular at least 95 mol% of units of the general formula I in which the sum <maths id="math0002" num=""><math display="inline"><mrow><mtext>a + b = 2</mtext></mrow></math><img file="EP0807509A1_D0002.tif" /></maths> is.

The organopolysiloxanes (1) preferably have at least 60, in particular at least 80, especially at least 95 mol% of units of the general formula I in which b has the value 0.

Per 100 parts by weight of the organopolysiloxanes (1), at least 5, preferably at least 10, in particular at least 20 parts by weight and at most 200, preferably at most 150, in particular at most 100 parts by weight of pre-hydrophobic oxidizing reinforcing fillers (2) are used.

The fillers (2) are preferably pre-hydrophobicized powdery fillers, such as pyrogenic silica, precipitated silica and silicon-aluminum mixed oxides, or fibrous fillers, such as asbestos. It can be a type of filler, a mixture of at least two fillers can also be used. The carbon content of the fillers (2) obtained by the hydrophobization is preferably at least 1% by weight and preferably at most 6% by weight. When determining the carbon content of the fillers (2), drying for at least 2 hours at at least 200 ° C. ensures that the measured carbon content relates to the hydrophobic layer of the fillers (2).

Pyrogenically prepared silica and precipitated silica are particularly preferred as reinforcing fillers (2). The BET surface area of ​​the fillers (2) is preferably at least 50 m²/ g, in particular at least 100 m²/ g, especially at least 150 m²/G.

The fillers (2) have been rendered hydrophobic by treatment with, for example, organosilanes, -silazanes or -siloxanes or by etherification of hydroxyl groups to give alkoxy groups. A preferred method for water repellency is described in US-A-5,057,151.

The organopolysiloxanes (1a) which have hydrocarbon radicals with aliphatic carbon-carbon multiple bonds preferably have an average of 2 to 10, in particular 2 to 4, aliphatic carbon-carbon multiple bonds per molecule. The terminal units of the general formula I preferably have aliphatic carbon-carbon multiple bonds. The aliphatic carbon-carbon multiple bonds are preferably double bonds. The organopolysiloxanes (1a) preferably have an average viscosity of at least 100, in particular at least 1000 mPa · s, and preferably at most 10⁵, in particular at most 5 x 10⁴ mPa · s at 25 ° C.

The organopolysiloxanes (1b) with Si-bonded hydrogen atoms preferably have an average of 2 to 50, in particular 5 to 20 Si-bonded hydrogen atoms per molecule. The organopolysiloxanes (1b) preferably have an average viscosity of at least 10, in particular at least 30 mPa · s, and preferably at most 10⁶, in particular at most 10000 mPa · s at 25 ° C.

The organopolysiloxanes (1c) which have Si-bonded hydroxyl groups preferably have 2 to 4 hydroxyl groups per molecule. They preferably have terminal hydroxyl groups. The organopolysiloxanes (1c) preferably have an average viscosity of at least 10, in particular at least 1000 mPa · s, and preferably at most 10⁸, in particular at most 5 x 10⁶ mPa · s at 25 ° C.

The average residence time of the composition in the kneading machine is preferably at most one hour, in particular at most 30 minutes.

If a kneading machine with a net volume of 100 l is used according to the invention, 200 kg / h of organopolysiloxane composition can be produced without problems with an average residence time of 15 to 20 min, ie approx. 4000 kg / d. Comparable 3000 kg of organopolysiloxane compositions which are stable in storage are obtained when working in a discontinuous tilting kneader with a net volume of 4000 l and an average residence time of 20 h. With the tilt kneader, additional time for emptying and, if necessary, cleaning must be added.

The organopolysiloxane compositions which contain pre-hydrophobic oxidic reinforcing fillers (2) have a particularly good storage stability if only part of the organopolysiloxanes (1) are mixed with the fillers (2) in a first step, the mixture in a second step Temperature of preferably at most 130 ° C is kneaded, until the viscosity of the mixture has reached a constant value and in a third step the mixture is mixed with the rest of the organopolysiloxanes (1). 30 to 80% by weight of the organopolysiloxanes (1) are preferably used in the first step.

The process variant broken down into three steps can be carried out in a kneading machine which has at least three kneading chambers, the kneading chambers used for the third step having at least one additional loading opening.

The rest of the organopolysiloxanes (1) are preferably added in at least two, in particular at least three, kneading chambers in the third step, with less organopolysiloxanes (1) being added in the first kneading chamber of the third step than in the further kneading chambers. When the organopolysiloxanes (1) are added in several kneading chambers in the third step, a particularly homogeneous organopolysiloxane composition is obtained.

The kneading machine used according to the invention allows the intensity of the kneading process and the dwell time to be controlled because the speed and direction of rotation of the kneading tools in the individual kneading chambers can be set independently of one another. For example, the speeds in the pilot plant can be 1 to 400 rpm. With a suitable choice of mixing and kneading tools, even higher speeds are possible.

With the process variant broken down into three steps, the kneading tools of the kneading chambers can be operated at lower speeds in the first and in the second step than in the third step. For example, the speeds in the third step are two to five times as high as in the first and second steps. If the first step is carried out in several kneading chambers, the kneading tools can preferably be operated in the opposite direction in one of the kneading chambers. This improves the filling level of the kneading machine and thus the residence time.

Since there is no free gas space in the kneading machine, shielding gas can be dispensed with.

The product discharge from the kneading machine is not a problem because the finished compositions can be easily transported to the discharge opening by the kneading tools. The last kneading chamber preferably has pump blades for the product discharge.

The kneading machine preferably has at least three, in particular at least five kneading chambers.

Sieves, baffle plates or sliders for stowing the organopolysiloxane compositions can be attached between individual or all of the kneading chambers. These elements can be adjustable in terms of their position and the passage opening you can release. This allows the residence time in the individual chambers to be influenced.

The kneading tools are preferably kneading blades, rollers or polygonal disks.

In addition to the loading opening of the first kneading chamber, there are preferably further loading openings in the kneading machine which lead into the individual kneading chambers or are arranged between two kneading chambers. Each kneading chamber preferably has a loading opening. In particular, the loading opening of the first kneading chamber is suitable for loading with solid material and the other loading openings are provided for the addition of liquids. Each kneading chamber preferably has a separately controllable drive, each of which preferably has a torque measurement. The torque is a measure of the viscosity of the mixture in the chamber.

The kneading chambers can preferably be heated or cooled, in particular can be operated individually at different temperatures. Kneading generates frictional heat, which is preferably partially removed by cooling in order to avoid overheating of the composition. The temperature during kneading, in particular in the case of the process variant broken down into three steps, is at most 150 ° C. in the second step.

The kneading tools are preferably overhung. The bearing-side housing end wall is then provided with openings for the drive shafts of the kneading tools. The housing of the kneading chambers preferably has a separation point running transversely to the tool axes, so that the housing part facing away from the bearing can be moved away from the separation point and the kneading tools in the axial direction of the drive shafts. A kneading machine designed in this way is particularly easy to clean.

Such a kneading machine is described in DE-C-40 05 823.

A kneading machine is in <b>Fig.1,</b> outlined as a cut in the area of ​​the kneading chambers: The kneading machine <b>1</b> has six kneading chambers arranged side by side <b>2</b> on, each with two axially parallel kneading tools <b>3</b> included and through across the axes <b>4</b> of the kneading tools passable openings <b>5</b> are interconnected. The first kneading chamber<b>2</b> has a loading opening <b>6</b> for solids and the last kneading chamber <b>2</b> a discharge opening <b>7</b> on. The last kneading chamber<b>2</b> has pump wings <b>8</b> for the product discharge. Between the second and third kneading chambers<b>2</b>, and between the fourth and fifth kneading chambers <b>2</b> are sieves <b>9</b> appropriate. Next to the loading opening<b>6</b> the first kneading chamber <b>2</b> are further loading openings <b>6</b> present in a single kneading chamber <b>2</b> lead or between two kneading chambers <b>2</b> are arranged.

The organopolysiloxane compositions are stable on storage and are particularly suitable as base materials for the production of high-quality condensation-crosslinking, peroxidically crosslinking and addition-crosslinking organopolysiloxane rubber compositions, in particular two-component compositions.

To produce condensation-crosslinking organopolysiloxane rubber compositions, additives such as pigment pastes, plasticizers, etc. are added to the organopolysiloxane compositions produced according to the invention. Vulcanizates can be produced from it with special hardeners. The organopolysiloxane compositions produced according to the invention are used as components for the production of addition-crosslinking organopolysiloxane rubber compositions<b>A</b> mixed with noble metal catalysts and optionally inhibitors for the component <b>B</b> with methyl hydrogen siloxane crosslinking agents and optionally other additives such as pigment pastes, stabilizers etc.

In the following examples, unless otherwise stated,<ul id="ul0003" list-style="none"><li>a) all quantities based on weight;</li><li>b) all pressures 0.10 MPa (abs.);</li><li>c) all temperatures 20 ° C.</li></ul>

<b>Examples</b>

example 1

: Continuous production of a base material for addition-curing liquid rubber products

On a Conterna® kneading machine from IKA-Maschinenbau Janke &amp; Kunkel GmbH &amp; Co.KG, Staufen, consisting of 12 chambers with a volume of 10 liters each, 80kg / h of polydimethylsiloxane with vinyl end groups with a viscosity of 20,000 are placed in the first chamber mPa · s and 60kg / h of a pre-hydrophobic filler with a BET surface area of ​​300 m²/ g (Wacker® HDK SKS 300) dosed. The compacted mass from chamber 2 is kneaded at speeds of 50 to 70 rpm in chambers 2 to 8 with cooling. The temperature rises to about 100 anyway^OC. Polydimethylsiloxane with vinyl end groups with a viscosity of 20,000 mPas is metered into chambers 9, 10 and 11. The throughputs are<dl id="dl0002" compact="compact"><dt>Chamber 9</dt><dd>5 kg / h</dd><dt>Chamber 10</dt><dd>15kg / h</dd><dt>Chamber 11</dt><dd>40kg / h.</dd></dl>

The speeds of the kneading tools in the chambers 9-11 are approximately 200 rpm. The chamber 12 is equipped with pump blades that convey the product into a degassing vessel. The residence time of the base mass in the kneading machine is about 15 minutes. The degassing vessel is about 5m³/ h N₂ flushed at a negative pressure of approx. 200 mbar in order to drag small amounts of volatile siloxanes into an exhaust gas cleaning system. The basic mass is discharged from the degassing container by means of a pump into a storage container via a strainer unit. The examination of the basic mass resulted in the following values:<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">measured</entry><entry namest="col3" nameend="col3" align="center">specification</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">viscosity</entry><entry namest="col2" nameend="col2" align="left">1300 Pas</entry><entry namest="col3" nameend="col3" align="left">1100-1500 Pas</entry></row><row><entry namest="col1" nameend="col1" align="left">transparency</entry><entry namest="col2" nameend="col2" align="left">Well</entry><entry namest="col3" nameend="col3" align="left">Well</entry></row><row><entry namest="col1" nameend="col1" align="left">Appearance</entry><entry namest="col2" nameend="col2" align="left">no crumple</entry><entry namest="col3" nameend="col3" align="left">no crumple</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Storage stability *</entry><entry namest="col2" nameend="col2" align="left">20%</entry><entry namest="col3" nameend="col3" align="left">&lt; 50%</entry></row></tbody></tgroup><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col3" align="justify">* When testing the storage stability, 200g of the basic mass are in a glass bottle 16h at 150^OC stored and the viscosity measured before and after storage. The increase in viscosity must not be greater than 50%.</entry></row></tbody></tgroup></table></tables>

Example 2

: Comparative test Continuous production of a base material for addition-curing liquid rubber products on a twin-screw extruder:

20kg / h of polydimethylsiloxane with a viscosity of 20,000 mPas and 15kg / h of Wacker® HDK SKS 300 were metered into a twin-screw extruder with a length of 36 D and a screw diameter of 40 mm. With a length of 25 D, a further 15 kg / h of polymer with vinyl end groups and a viscosity of 20,000 mPa.s were fed. After a short evacuation zone at approx. 32 D, the product was discharged via a strainer. The residence time was about 2 minutes, the temperature rose to 150^OC an.

Result:

<dl id="dl0003" compact="compact"><dt>viscosity</dt><dd>1800Pas</dd><dt>transparency</dt><dd>Well</dd><dt>Appearance</dt><dd>contained few knobs</dd><dt>Storage stability</dt><dd>&gt;&gt; 100% (viscosity was no longer measurable)</dd></dl>