DE102011005076A1 - Continuous mixing of organosilicon compounds with highly dispersed fillers and optionally other components in a mixing unit comprising housing and mixing body whose rotating mixing elements exhibit specified rotating speeds - Google Patents

Abstract

Continuous mixing of organosilicon compounds with highly dispersed fillers and optionally other components in a mixing unit comprising housing and mixing body whose rotating mixing elements exhibit rotating speeds of at least 1 m/second, is claimed, where a surface of the inner wall of the housing is covered at least to 20 area percentage with a material, which consists of at least 50 wt.% of polytetrafluoroethylene, where the layer thickness is at least 0.5 mm. An independent claim is included for a device comprising the mixing unit.

Description

The invention relates to a process for the continuous preparation of compositions based on organosilicon compounds, in particular organopolysiloxane compositions which can be crosslinked at room temperature, in mixers with high circulating speeds of the mixing elements.

One-component organopolysiloxane compositions which are storable with the exclusion of moisture and crosslink under the influence of moisture at room temperature, so-called RTV1 sealing compounds, have been known for a long time.

In their production, it is particularly important to mix very large amounts of highly dispersed silicic acid into the highly viscous organopolysiloxane in as short a time as possible. The solution of this mixing task therefore requires the use of mixing units with high speeds. Because of the high productivity, continuously operating mixing units are particularly preferred.

EP-B1-1884541 describes, for example, the use of mixing units with a rotor / stator mixing system. In this mixing system takes place first with an axial, vertical mixing shaft, are arranged on the mixing blades, a premix of highly dispersed silica and crosslinkable organopolysiloxane. Subsequently, the mixture is conveyed to complete the mixing process by a rotor / stator mixing system.

However, a major disadvantage of such mixing units with fast-rotating mixing elements is that it comes through friction of unwetted Füllstoffteilchen to the metallic components of the mixing units to a strong abrasion. This abrasion is particularly pronounced in the region of the inner wall of the mixer, since the filler particles which are thrown outwards and have not yet been dispersed are intensively rubbed against the inner wall of the mixer by the rapid rotational movement of the mixing elements.

It is therefore state of the art that both the surfaces of the mixing tools and the container inner wall of these mixing units are hardened or coated with high-quality, corrosion-resistant and hard wear protection materials. Such offered by the industry coating materials are z. As diamond, glass, ceramics, carbides, oxides or nitrides. It is the principle that a higher hardness is always associated with a better abrasion resistance. That is, very hard materials are preferred as the surface because with them, less undesirable abrasion results during mixing.

A well-known method is z. B. the application of wear protection layers on the base materials with the so-called build-up welding. In this process, a high alloy protective layer (eg, a cobalt or nickel based hard alloy) is applied to a lower alloy base material (eg, X5CrNi18-10). The thickness of the protective layer is about 2-3 mm. So describes DE-B4-197 54 291 For example, the application of armor layers on machine components.

The hardness of steels and their wear protection layers is z. B. with Vickers method (HV, ( ISO 6507-1: 2005 ; German version EN ISO 6507-1: 2005 )) certainly. Depending on the alloy, it is typically between 150 and 400 HV for steels. To reduce abrasion, the industry offers wear protection coatings with hardnesses above 1000 HV.

However, the application of wear protection layers is technically very demanding and very expensive. Nevertheless, due to the still existing strong abrasion often repairs to the mixing units must be performed, which is very time consuming and longer production downtime means.

In addition to the usual metallic wear protection coatings but other coatings were recommended. DE-GM-19 52 755 teaches z. B. the installation of polyurethane parts in concrete mixers. This is to prevent the seizing of coarse-grained sand and gravel between the slowly rotating mixing blade and the inner wall of the mixer. The plastic covering is arranged so that it protrudes beyond the metallic mixing element and sweeps over the inner wall during the rotational movement. In DE-C2-198 56 622 However, it should be noted that such plastic layers are expected to wear very quickly.

Another optimization of the metal parts of mixers is in DE-C2-39 03 897 described. Here, a composite material is produced, wherein to obtain the desired high hardness of the wear protection layer only the pores and cracks of the layer are filled with PTFE. The proportion of the plastic on the inner surface of the mixer is only a few area percent. Furthermore, this invention relates to the preparation of rubber mixtures. That is, with the raw materials used such as carbon blacks, there is little or no abrasion anyway. Furthermore, the mixture is made due to the low speed of internal mixers or because of the low Diameter of extruders at low rotational speeds of the mixing elements, which also greatly limits the abrasion.

The invention relates to a process for the continuous mixing of organosilicon compounds (A) with highly dispersed fillers (B) and optionally further constituents in a mixing unit containing housing and mixing element whose rotating mixing elements have rotational speeds of at least 1 m / s, characterized in that the surface the inner wall of the housing is at least 20 area percent covered with a material which consists of at least 50 wt .-% of PTFE, wherein the layer thickness is at least 0.5 mm.

Another object of the present invention is a device comprising a mixing unit containing the housing and mixing element whose mixing elements have rotational speeds of at least 1 m / s, characterized in that the surface of the inner wall of the housing is at least 20 area percent covered with a material, which consists of at least 50 wt .-% of PTFE, wherein the layer thickness is at least 0.5 mm.

Mixtures prepared by the process according to the invention may be any mixtures containing organosilicon compounds and fillers which may be crosslinkable or uncrosslinkable, with crosslinkable compositions being preferred.

The crosslinkable compositions which can be prepared by processes according to the invention are preferably compositions crosslinkable by condensation reaction.

In the context of the present invention, the term "condensation reaction" should also encompass an optionally preceding hydrolysis step.

The organosilicon compounds (A) used according to the invention are preferably those comprising units of the formula R _a Y _b SiO _{(4-ab) / 2} (I), in which
R may be the same or different and SiC-bonded, optionally substituted hydrocarbon radicals which may be interrupted by oxygen atoms means
Y may be the same or different and means condensable radicals,
a is 0, 1, 2 or 3, preferably 1 or 2, and
b is 0, 1, 2 or 3, preferably 0, 1 or 2, particularly preferably 0,
with the proviso that the sum of a + b is less than or equal to 3 and at least two Y radicals per molecule are present.

Radicals R are preferably monovalent hydrocarbon radicals having 1 to 18 carbon atoms which are optionally substituted by halogen atoms, amino groups, ether groups, ester groups, epoxy groups, mercapto groups, cyano groups or (poly) glycol radicals, the latter being composed of oxyethylene and / or oxypropylene units are, particularly preferably alkyl radicals having 1 to 12 carbon atoms, in particular the methyl radical. It may be at residual R but also divalent radicals z. B. connect two silyl groups together.

Examples of radicals R are alkyl radicals, such as the methyl, ethyl, n-propyl, iso-propyl, 1-n-butyl, 2-n-butyl, isobutyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, tert-pentyl; 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 the cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl radicals; Alkenyl radicals such as the vinyl, 1-propenyl and 2-propenyl radicals; Aryl radicals, such as the phenyl, naphthyl, anthryl and phenanthryl radicals; Alkaryl radicals, such as o-, m-, p-tolyl radicals; Xylyl radicals and ethylphenyl radicals; and aralkyl radicals, such as the benzyl radical, the α- and the β-phenylethyl radical.

Examples of substituted radicals R are methoxyethyl, ethoxyethyl and ethoxyethoxyethyl or chloropropyl and Trifluorpropylrest and methyl groups with nitrogen, phosphorus, oxygen, sulfur or carbonyl group bound organic radicals such. N-morpholinomethyl, cyclohexylaminomethyl, dibutylaminomethyl-dimethylaminomethyl, diethylamino, dihexylaminomethyl, n-hexylaminomethyl, octylaminomethyl, methylmercapto, ethylmercapto, ethoxymethyl, N-phenylaminomethyl, methacryloxymethyl, isocyanatomethyl, N Pyrrolidinomethyl, N-piperidino and O-methylcarbamatomethyl radicals.

Examples of divalent radicals R are the ethylene radical, Polyisobutylendiylreste and propanediylterminierte polypropylene glycol.

The condensable groups Y, which have used, used in the crosslinking reaction organosilicon compounds (A), may be hydroxyl and any of oxygen atom or nitrogen atom Silicon atom bound, optionally substituted hydrocarbon radicals.

Preferably, radical Y is hydroxyl, radical -OR ¹ , such as methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, tert-butoxy and 2-methoxyethoxy radical, where R ¹ denotes optionally substituted hydrocarbon radicals which may be interrupted by oxygen atoms, acyloxy radicals, such as the acetoxy radical, amino radicals, such as methylamino, dimethylamino, ethylamino, diethylamino and cyclohexylamino radicals, amido radicals, such as N- Methylacetamido and Benzamidorest, Aminoxyreste, such as the Diethylaminoxyrest, Oximoreste, such as Methylethylketoximo-, Methylisobutylketoximo- and acetone oxime, and Enoxyreste, such as the 2-Propenoxyrest.

Examples of radicals R ¹ are the monovalent radicals given for R.

Radical R ¹ is preferably an alkyl radical having 1 to 12 carbon atoms, more preferably the methyl or ethyl radical.

Particularly preferably, radical Y is hydroxyl radical, radical -OR ¹ where R ¹ has the abovementioned meaning, and acyloxy radicals, in particular acetoxy, methoxy and ethoxy radicals.

The organosilicon compounds (A) used according to the invention are preferably those of the formulas Y _3-f R _f Si-O- (SiR ₂ -O) _e -SiR _f Y _3-f (II) and Y _3-f R _f Si-O- (R ³ -O) _h -SiR _f Y _3-f (III), in which
R and Y may each be the same or different and have one of the meanings given above,
R ^{3 may be the} same or different and is divalent, optionally substituted hydrocarbon radicals,
e is 30 to 3000,
f is 0, 1 or 2 and
h is 30 to 1000.

Preferably, f is 2 when Y is -OH and f is 1 or 0 when Y is -OH otherwise.

Examples of radical R ³ are alkylene radicals, such as the methylene, ethylene, n-propylene, iso-propylene, n-butylene, iso-butylene, tert-butylene, n-pentylene, iso-pentylene -, neo-pentylene, tert-pentylene radical, hexylene radicals, heptylene radicals, octylene radicals, nonylene radicals, decylene radicals, dodecylene radicals and octadecylene radicals; Cycloalkylene radicals, such as cyclopentylene radical, alkenylene radicals, such as the vinylene, n-hexenylene, cyclohexenylene, 1-propenylene, allylene, butenylene and 4-pentenylene radicals; Alkynylene radicals, such as the ethynylene and propargylene radical; Arylene radicals, such as the phenylene, naphthylene, anthrylene and phenanthrylene radical; Alkarylene radicals, such as o-, m-, p-tolylene radicals, xylylene radicals and ethylphenylene radicals; and aralkylene radicals, such as the benzylene radical, the α- and the β-phenylethylene radical, alkylene radicals being preferred and ethylene and propylene radicals being preferred.

Component (A) is particularly preferably organopolysiloxanes consisting of units of the formula (I).

Examples of organosilicon compounds (A) used according to the invention are
(AcO) ₂ MeSiO [SiMe ₂ O] _200-2000 SiMe (OAc) ₂
(AcO) ₂ ViSiO [SiMe ₂ O] _200-2000 SiVi (OAc) ₂
(AcO) ₂ MeSiO [SiMe ₂ O] _200-2000 SiVi (OAc) ₂
(MeO) ₂ MeSiO [SiMe ₂ O] _200-2000 SiMe (OMe) ₂ ,
(HO) Me ₂ SiO [SiMe ₂ O] _200-2000 SiMe ₂ (OH),
(EtO) ₂ MeSiO [SiMe ₂ O] _200-2000 SiMe (OEt) ₂ ,
(MeO) ₂ ViSiO [SiMe ₂ O] _200-2000 SiVi (OMe) ₂ ,
(EtO) ₂ ViSiO [SiMe ₂ O] _200-2000 SiVi (OEt) ₂ ,
(MeO) ₂ MeSiO [SiMe ₂ O] _200-2000 SiVi (OMe) ₂
(EtO) ₂ (C ₆ H ₁₁ NHCH ₂ ) SiO [SiMe ₂ O] _200-2000 Si (CH ₂ NHC ₆ H ₁₁ ) (OEt) ₂ ,
(MeO) ₂ MeSi (CH ₂ ) ₃ O - ([CH (CH ₃ ) CH ₂ ] -O) _50-500 (CH ₂ ) ₃ SiMe (OMe) ₂
(MeO) ₂ MeSi (CH ₂ ) ₃ NH-COO - ([CH (CH ₃ ) CH ₂ ] -O) _50-500 CO-NH- (CH ₂ ) ₃ SiMe (OMe) ₂
and
(MeO) ₂ MeSiCH ₂ -NH-COO - ([CH (CH ₃ ) CH ₂ ] -O) _50-500 OC-NH-CH ₂ SiMe (OMe) ₂ ,
where Ac is acetyl, Me is methyl, Et is ethyl and Vi is vinyl.

The organosilicon compounds (A) used according to the invention have a viscosity of preferably 100 to 10 ⁶ mPas, more preferably from 10 ³ to 350 000 mPas, in each case at 25 ° C.

The organosilicon compounds (A) are commercially available products or can be prepared by methods customary in silicon and carbon chemistry.

Examples of fillers (B) are non-reinforcing fillers having a BET surface area of up to 10 m ² / g, such as ground calcium carbonates, partially reinforcing fillers having a BET surface area greater than 10 m ² / g, such as precipitated calcium carbonates, or reinforcing fillers, ie fillers having a BET surface area of more than 50 m ² / g, such as pyrogenically prepared silica, precipitated silica and silicon-aluminum mixed oxides of large BET surface areas.

The fillers (B) used according to the invention may be rendered hydrophobic by known processes, for example by treatment with organosilanes or siloxanes or with stearic acid or by etherification of hydroxyl groups to alkoxy groups.

The filler (B) used according to the invention is preferably calcium carbonates and pyrogenically prepared silicas.

5 to 300 parts by weight, more preferably 8 to 200 parts by weight, in particular 10 to 150 parts by weight of filler (B), in each case based on 100 parts by weight of component (A), are preferably used in the process according to the invention.

In addition to the components (A) and (B) described above, the compositions of the invention may now contain all other substances which have hitherto been used in mixtures containing organosilicon compounds and fillers, in particular in compositions crosslinkable by condensation reaction, such. As crosslinker (C) and additives (D).

Crosslinkers (C) can be used in the process according to the invention. These may be any known crosslinkers having at least three condensable radicals, for example silanes or siloxanes having at least three organyloxy groups.

The optionally used crosslinkers (C) are preferably organosilicon compounds of the formula Z _c SiR ² _(4-c) (IV), in which
R ^{2 may be} identical or different and monovalent, SiC-bonded, optionally substituted hydrocarbon radicals which may be interrupted by oxygen atoms, means
Z may be the same or different and has a meaning mentioned above for Y, except hydroxyl group, and
c is 3 or 4,
and their partial hydrolysates.

The partial hydrolysates may be partial homohydrolysates, i. H. Partial hydrolysates of one type of organosilicon compound of formula (IV), as well as partial co-hydrolysates, d. H. Partial hydrolysates of at least two different types of organosilicon compounds of the formula (IV).

Although not indicated in formula (IV), the organosilicon compounds optionally used according to the invention may, due to their production, have a low proportion of hydroxyl groups, preferably up to a maximum of 5% of all Si-bonded radicals.

If the crosslinkers (C) optionally used in the process according to the invention are partial hydrolyzates of organosilicon compounds of the formula (IV), those having up to 10 silicon atoms are preferred.

Examples of radical R ² are the monovalent examples given above for radical R, preference being given to hydrocarbon radicals having 1 to 12 carbon atoms and the methyl and vinyl radicals being particularly preferred.

Examples of Z are the examples given for Y except hydroxyl group.

Z is preferably -OR ¹ where R ¹ is one of the abovementioned meanings, acyloxy radicals and oxime radicals.

The crosslinkers (C) optionally used in the process according to the invention are preferably tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3-cyanopropyltrimethoxysilane, 3-cyanopropyltriethoxysilane, 3- (glycidoxy) propyltriethoxysilane , 1,2-bis (trimethoxysilyl) ethane, cyclohexylaminomethyltriethoxysilane, morpholinomethyltrimethoxysilane, 1,2-bis (triethoxysilyl) ethane, methyltris (methylethylketoximo) silane, vinyltris (methylethylketoximo) silane, methyltris (acetonoximo) silane, ethyltris (acetonoximo) silane, vinyltris (acetonoximo) silane, phenyltris (acetonoximo) silane, tetrakis (methylethylketoximo) silane, methyltriacetoxysilane, ethyltriacetoxysilane, vinyltriacetoxysilane, dimethyldiacetoxysilane, methylvinyldiacetoxysilane and partial hydrolysates of said organosilicon compounds, such as. B. hexaethoxydisiloxane.

The crosslinkers (C) optionally used according to the invention are particularly preferably tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, 1,2-bis (trimethoxysilyl) ethane, 1,2-bis (triethoxysilyl) ethane , Methyltris (methylethylketoximo) silane, vinyltris (methylethylketoximo) silane, methyltriacetoxysilane, ethyltriacetoxysilane, vinyltriacetoxysilane and their partial hydrolysates, in particular methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltris (methylethylketoximo) silane, vinyltris (methylethylketoximo) silane, methyltriacetoxysilane, Ethyltriacetoxysilane, vinyltriacetoxysilane and their partial hydrolysates.

The crosslinkers (C) optionally used according to the invention are commercially available products or can be prepared by processes known in silicon chemistry.

If crosslinkers (C) are used, which is preferred, these are amounts of preferably 0.01 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, in particular 3 to 8 parts by weight, based in each case on 100 parts by weight of organosilicon compound (A) ,

The optionally used additives (D) are preferably non-reactive silicone oils, organic extenders, catalysts, adhesion promoters, plasticizers, such as solid or liquid silicone resins, stabilizers which influence, for example, the storage stability and reactivity of the mixture, water scavengers, Additives which optimize the properties of the uncured or cured material, rheology additives, substances which control the reactivity of the composition, color pigments, heat stabilizers and fungicides, particularly preferably plasticizers, catalysts, adhesion promoters, rheology additives, fungicides and color pigment.

Additives (D) can also - if desired - be mixed in a further, downstream process step.

All components of the mixture may also be mixed, if desired, into two or more aliquots at different times and optionally in premixes.

The components used in the process according to the invention may each be a type of such a component as well as a mixture of at least two types of a respective component.

The mixing unit according to the invention preferably consists of a solid housing, preferably of metal, and of one or more therein arranged, rotating mixing elements, which are preferably also made of metal. The mixing element is preferably formed by a mixing shaft, which preferably leads through the housing to the outside, and by mixing elements, which are located on the mixing shaft in the inner part of the housing. Further preferably, the mixing shaft is driven by the part located outside of the housing, for example by a motor. Due to the rotational movement of the mixing shaft about the mixing axis, the mixing elements within the housing sweep rotationally symmetric areas. The sum of the regions formed by the rotation of a mixing element is called a mixing zone. Within a mixing zone, the individual regions may also overlap, which is preferred. Several mixing elements form several mixing zones, which also preferably overlap. The mixing shaft can be arranged horizontally, vertically or at any angle to the earth's surface, preferably it is arranged vertically. Optionally, by additional fixed internals, for example on the inner wall of the housing, the mixing effect can be enhanced. Preferably, the interior space formed by the inner wall of the housing is not substantially larger than the areas swept by the rotating mixing elements. This means that as few or small or even no dead spaces are present, ie spaces in which there is virtually no mixing of the mix, because these spaces are not covered by rotating mixing elements. However, this also means that the distance between the rotating mixing elements and the inner wall of the housing is preferably as small as possible. Particularly preferably, the distance between the rotating mixing elements and the inner wall of the housing is in each case smaller than 0.2 times the diameter of the rotational cross section formed by the rotation of a mixing element.

In the context of the present invention, the mixing zone plus associated dead spaces is referred to as the mixing space.

The surface area of the inner wall of the housing, which is formed when the diameter of the cylindrical mixing zone formed by the mixing element is increased to such an extent that it meets the preferably likewise cylindrical inner wall of the housing, is preferably 20 to 90 area percent of the inner wall of the housing , more preferably 30 to 70 area percent.

Preferably, the housing encloses a rotationally symmetrical, in particular cylindrical, interior. If individual mixing elements are of different sizes or if mixing elements of different geometry are used, then the mixing space can also consist of different, preferably in each case cylindrical, subspaces.

Furthermore, at least one inlet and at least one outlet opening for the mix are located in the housing of the mixing unit according to the invention. The mixing unit can be additionally heated or cooled. Furthermore, a plurality of mixing elements may be located in the mixing unit and / or different types and sizes of mixing elements simultaneously on a mixing shaft be arranged, such. As rectangular or trapezoidal mixing blades, so-called butterfly mixing blades, helical mixing elements or rotor / stator mixing systems. If several, identical or different mixing shafts are arranged, which is not preferred, then they can also rotate at different speeds.

It is a measure of the speed of rotation and thus a measure of the speed of wetting of the filler and the strength of the shear effect on the mix during the mixing process, the so-called circulation speed.

The speed of rotation in the sense of the invention refers to the path of an outer boundary of a mixing element which, in a certain time unit, rotates it about an axis, which is indicated in meters per second (m / s). High orbital speeds are achieved especially with large mixing elements with high speeds.

According to the invention, circulation speeds of more than 1 meter per second (m / s) are used, with circulation speeds of more than 2 m / s being preferred and those in the range of 3 to 20 m / s being particularly preferred.

Preferably high circulation speeds are achieved by high speeds. In this case, rotational speeds of more than 100 revolutions per minute (rpm) are preferred, rotational speeds of more than 200 rpm are particularly preferred, and rotational speeds of 300 to 5000 rpm are very particularly preferred. High speeds ensure that the wetting of the filler (B) with organosilicon compound (A) takes place as quickly as possible.

The mixing unit according to the invention preferably contains two different subspaces, wherein a subspace contains a rotor-stator system. As an example of the basic structure and operation of such an aggregate is on this EP-B1-1884541 , Example 1, which is to be included in the disclosure of the invention.

A particularly preferred mixing unit consists of an upper, cylindrical subspace in which a premixing of the components takes place, such as the cylindrical structure (12) in FIG EP-B1-1884541 Example 1, and from a lower cylindrical subspace in which, with the aid of a rotor / stator mixing system, the mixing is completed, such as the mixing device (5) in EP-B1-1884541 , There is preferably no mechanical delimitation between the two subspaces. In this mixing unit according to the invention, a mixing element which consists of a vertically arranged mixing shaft and mixing elements arranged thereon rotates. In the upper cylindrical subspace are preferably rectangular mixing elements. In the lower subspace of the rotor is mounted on the mixing shaft. The provided with teeth and slots stator, however, is firmly connected to the housing.

In the process according to the invention, highly dispersed filler, preferably silica, (B), organosilicon compound (A) and, if appropriate, further constituents of the mixture firstly pass, preferably from above, into the first subspace. There, the mix is premixed using preferably rectangular mixer blades. That is, especially in the upper compartment still large amounts of unwetted filler (B) are present. The previously observed strong abrasion according to mixing units of the prior art takes place mainly in this upper subspace.

The lower subspace, which preferably contains the rotor / stator mixing system, has a slightly larger diameter. The mixture moved from above from the first subspace into the second subspace is thrown outward by the rotation of the rotor and pushed out of the mixer through the interspaces of the stator. If necessary, still unwetted Füllstoffteilchen are thrown with the rotor not on surfaces of machine parts, but on exactly the layer of the mixed material, which is located between the rotor and stator. The abrasion is very low. As a result of the pressure of the subsequent mixed material, the mixture which is already behind the stator is pressed out of the outlet opening of the mixer. In this case, the pressure difference between inlet and outlet opening is preferably adapted specifically to the mixing task to be solved.

Subsequently, the mixture, in particular in the case of sealants, by further process steps, such. B. degassing or mixing in other mixture components to be completed.

In the upper subspace of the mixing unit according to the invention, a plurality of preferably rectangular mixing elements pass over a cylindrical mixing zone through the rotating mixing shaft. A characteristic of this mixing zone is that the distance between this mixing zone and the inner wall of the housing of the first mixing chamber is at most 20 cm. In other words, the point of the mixing element furthest away from the mixing axis is at most 20 cm from the inner wall of the housing of the upper mixing space. Preferably, the distance is less than 10 cm, and most preferably the distance is 0.1 to 5 cm.

At a smaller distance, there is a very strong shear of the unwetted filler particles between the mixing elements and the inner wall, which would lead to extremely strong abrasion. At a greater distance, the mixing effect of such an aggregate is very ineffective.

In the lower subspace of the mixing unit according to the invention preferred is the rotor-stator system.

Preference is given to rotors with diameters of 10 to 100 cm, with rotors of 20 to 50 cm being particularly preferred. On the rotor preferably evolute mixing elements are arranged. Since these need not be very high, the lower mixing chamber has the shape of a flat cylinder.

In the mixing unit according to the invention, the distance between rotor and stator is only a few millimeters, preferably 0.1 to 50 mm, with 0.5 to 20 mm being particularly preferred.

In the method according to the invention, after passing through the stator, the mixed material is forced out of the mixing unit through an outlet opening in the housing. In this case, an aggregate is preferably additionally mounted in the outlet line just behind the outlet opening, with which the pressure at the outlet opening can be set specifically for the purpose of solving variable mixing tasks.

The degree of coverage in the context of the present invention refers to the ratio of covered inner surface to the total inner surface of the housing of the mixing unit, wherein the total inner surface is the sum of the covered and the uncovered surface of the inner wall of the housing, and is given in percent.

In the mixing unit according to the invention, the covering of the inner wall of the housing with the PTFE-containing material is preferably in the region which is formed when the diameter of the cylindrical mixing zone formed by the mixing element is increased to such an extent that it also preferably prefers cylindrical inner wall of the housing meets.

The person skilled in the art recognizes that it is preferred if the surface projected onto the inner wall is enlarged in such a way that further cylindrical surfaces are covered opposite to and with the conveying direction of the mixed material, since the centrifuging of the mixed material to the covering is usually not completely perpendicular with respect to the Rotary axis takes place.

According to the invention, in the upper subspace, a plurality of mixing elements are preferably present, which produce a plurality of regions projected in the manner described on the inner wall of the mixer, which are covered with the material according to the invention, more preferably 3 to 100 such mixing elements being present.

In the covering of the inner surface of the housing, it is preferable to proceed in such a way that not individual, strip-shaped rings are obtained, but rather a closed covering is achieved. Particularly preferably, this continuous, cylindrical cover is arranged there, where the rotating mixing element hurls the mixture, in particular the non-wetted or not completely wetted filler particles, against the inner wall.

This means that when using the particularly preferred mixing unit consisting of an upper, cylindrical subspace and a lower cylindrical subspace, in which by means of a rotor / stator mixing system, the mixing is completed, such as in EP-B1-1884541 described cover extends over the entire region of the inner shell of the inner surface of the upper subspace.

Possible, but not preferred, are further coverings of the interior of the preferred mixing unit. So it is z. B. not preferred to cover the teeth of the rotor or the circular bottom of the most preferred mixing member. In addition, parts of the mixing element or the entire mixing element can be covered.

The material used according to the invention for covering may be any desired and hitherto known polymeric materials which preferably contain at least 80% by weight, particularly preferably at least 90% by weight, in particular from 99 to 100% by weight, of polytetrafluoroethylene.

Examples of materials which can be used according to the invention are those which are commercially available, for example, under the trade names Algoflon, Ekafluvin, Fluone, Ftoroplast, Hostaflon (Dyneon), Heydeflon, Polyflon, Tarflen, Teflon, Soreflon, Armalon, Atlantic, Avalon, Bioflex, Bioflon, Bytac, Ceno, Coltex, Coroflon, Dayplas, Dyneon, Ebolone, Elast-o-Fluor, Fluobond, Fluone, Fluoroloy, Fluoromelt, Fluorosint, Gaflon, Haiba, Heroflon, Heroflon, Herolub, LATTYflon, Lenzing PTFE, Lubriflon, Lubriglas, microflon , Murflor, New Polyflon, Omnia, Osixo, Pamflon, PAS-PTFE, POLiTEF, Polyfluron, Polymist, Polypenco, Polytetraflon, reproflon, Repro-PTFE, Riaflon, Rulon, Semitron, Silverstone, Tecaflon, Tecaflon, Tekaflon, Tetralon, Valflon, Visiflon, Xylan and Zitex from DuPont, AGC Chemicals Americas, Dyneon (3M Company), Daikin Industries Ltd. and Solvay Solexis.

In particular, the material is 100% polytetrafluoroethylene (PTFE), which is known to the person skilled in the art and represents an unbranched, linearly structured, partially crystalline polymer of fluorine and carbon.

According to the invention, the surface of the inner wall of the housing can now be covered in any manner known and hitherto, such. B. by partial to complete lining or by coatings in which the material is chemically bonded or by physical adhesion to the surface of the inner wall, which is not preferred.

The lining of the invention nestles as closely as possible and without an open column from the inside to the inner wall of the housing.

The wall thickness of the lining according to the invention is preferably 0.2 to 10 cm, particularly preferably 0.5 cm to 5.0 cm. For wall thicknesses below 0.2 cm, the durability is very limited and the attachment difficult, thicker wall thicknesses do not improve the effectiveness further and reduce the mixing space too much.

It has proved to be advantageous if the lining according to the invention has bulges which fit in a form-fitting manner into identical recesses in the inner wall of the housing. A simple pushing in or pushing in, as for example from above, the lining in the recess already allows a sufficiently secure mechanical attachment.

Such positive connections are known in the art, for. B. as a "tongue and groove" principle.

Preferably, the positive connections are characterized in that virtually no free space between the two components to be joined remains.

Cylindrical inserts made of PTFE are preferred according to the invention. These lie flat against the inner wall of the housing. The insert according to the invention is preferably mechanically held, for example, by the fact that the inner diameter in the lower edge of the upper mixing space is somewhat smaller. In addition to this fully extending rectangular edge is fully arranged a groove. Behind this groove, the appropriate spring of the PTFE cylinder is inserted when the cylindrical insert is inserted from above into the mixing chamber. In addition, the PTFE cylinder is held by a further tongue and groove arrangement in the upper region of the upper mixing space. In this case, a metal cylinder is inserted from above so that the likewise fully extending groove of the metal cylinder pushes the spring of the PTFE cylinder to the inner wall. Subsequently, the attached metal cylinder can be additionally screwed to the inner wall.

According to the invention, the projecting holder, the PTFE cylinder and the upper, metallic fastening cylinder each have the same inner diameter, thus forming a uniformly smooth inner wall of the upper mixing chamber.

Surprisingly, it has been found that by using polytetrafluoroethylene-containing material as a protective layer on the inner walls of mixing units, which is a very soft material compared to wear-resistant coated steel, only very slight abrasion phenomena occur in the production of filler-containing silicone compositions. This was not to be expected by the skilled person precisely because of the high rotational speeds of the mixing elements and the resulting particularly high stress on the inner wall with non-wetted or only partially wetted filler particles.

The inventive method has the advantage that it is easy to carry out and the surface of the inner wall of the mixing unit is very well protected against abrasion.

The method according to the invention and the device according to the invention have the advantage that very long operating times of the production plant can be realized.

The inventive method and the device according to the invention have the advantage that the mixing unit can be cleaned quickly, z. B. by simply wiping off adhesions.

The form-fitting linings of the method according to the invention and of the device according to the invention have the advantage that they can be exchanged quickly and with little effort.

The linings of the method according to the invention or of the device according to the invention have the advantage that they have very good corrosion protection properties.

In the examples below, all parts by percentages are by weight unless otherwise specified. Furthermore, all viscosity data refer to a temperature of 25 ° C. Unless otherwise stated, the following are Examples at a pressure of the surrounding atmosphere, ie at about 1000 hPa, and room temperature, ie at about 20 ° C, or at a temperature that occurs when adding the reactants at room temperature without additional heating or cooling performed.

example 1

In a rotor-stator mixing unit, according to the basic structure of the examples in EP-B1-1884541 , Over 4 side openings in the upper mixing space per hour 1000 kg of a mixture of 70% of a polydimethylsiloxane having randomly distributed diacetoxymethylsilyl end groups and diacetoxyethylsilyl end groups in the stoichiometric ratio of about 1: 2, with a viscosity of 80000 mPas, 25.5% α, ω-bis-trimethylsiloxypolydimethylsiloxane having a viscosity of 1000 mPas and 4.5 of an oligomer mixture of acetoxysilanes (commercially available under the name "crosslinker ES 24" at Wacker Chemie AG, D-Munich) and 82 kg / h of a fumed silica with a BET surface area of 150 m ² / g (commercially available under the name HDK ^® V 15 from Wacker Chemie AG, D-Munich) in free fall. The mixer was operated at 1200 rpm. In the upper cylindrical subspace of the mixing shaft in each case 3 rectangular mixing elements, which formed 4 ring-shaped and staggered arranged rings on the mixing shaft attached. These 12 mixing elements caused a partial wetting of the fumed silica and a promotion of the mix in the lower subspace. In the lower subspace the rotor-stator / system was arranged. The rotor with an inner diameter of 430 mm had 6 evolute conveying members. The stator is provided with comb-like recesses, that is to say with 42 teeth of a width of 13 mm, which are at a distance of 9 mm. He has an inner diameter of 432 mm. On the way to the outlet opening, no further mixing energy was supplied to the product. At the inlet opening and in the discharge pipe approx. 20 cm behind the outlet pressure gauges are attached. At the inlet opening, the pressure of the surrounding atmosphere was approximately 1000 hPa. A ball valve installed in the discharge line after the pressure gauge was closed by hand so far that a pressure of approximately 1500 hPa was established at the outlet opening.

The mixing unit was lined on the cylindrical inner wall in the region of the upper compartment with a 7.5 mm thick PTFE layer. For this purpose, a cylinder made of PTFE with an inner diameter of 260 mm was introduced from above into the mixing chamber. This cylinder was mechanically fixed at the bottom and top, each with a full tongue and groove arrangement. The height of the upper mixing chamber in the area of the mixing blades was 279 mm. The length of the PTFE cylinder was 210 mm.

All dimensions in millimeters have a tolerance of +/- 0.2 millimeters.

The inlet openings for the polymer are passed through the PTFE cylinder.

The upper compartment had an inner diameter of 26.0 cm and a height of 28.0 cm. The circular surfaces of the imaginary lid and the floor are not taken into account in the calculation of the inner surface of the upper mixing space, because they are objectively absent. The lower compartment had an inner diameter of 48.0 cm and an inner height of 7.5 cm.

This results in an area of the PTFE covering as a cylinder shell of the upper subspace of 2886 cm ² , an uncovered inner surface of the lower subspace including the bottom and the circular segment-shaped cover of 4 280 cm ² . Taking into account the inlet openings for the polymer or the tongue / groove holder and the outlet opening for the mix results in a covered area of the inner surface of the mixing unit of 2 282 cm ² and an uncovered area of 4 236 cm ² . Thus, the degree of coverage of the mixing unit according to the invention is 35.0 percent.

The PTFE used had the following characteristics: pure virgin PTFE, composition 100% polyterafluoroethylene, color white, waxy, density 2.16 g / cm ³ to DIN EN ISO 1183 , Tensile strength 25 N / mm ² , elongation at break 300%, modulus of elasticity 700 MPa, ball-indentation hardness 28 N / mm ² DIN ISO 2039-1 , Coefficient of sliding friction 0.08-0.10 and sliding friction wear approx. 210 μm / km, max. Operating temperature continuously approx. 260 ° C, briefly approx. 300 ° C. It was purchased from PTFE NÜNCHRITZ GMBH & CO. KG, Glaubitz, Germany.

The mixture emerging from the discharge line was passed without further delivery device into a twin-screw kneader where it was vented and degassed. At the same time, in the twin-screw kneader, 1082 kg of the product per hour were continuously mixed with 0.5 kg of a mixture of 20% dibutyltin diacetate and 80% organic plasticizer. Finally, the finished mass was packed in moisture-proof barrels, at the same time from a side nozzle moisture-proof PE cartridges were filled for testing purposes.

A homogeneous mixture was obtained, which remains homogeneous even when stored for several months in a 300 ml PE cartridge. It is formed no inhomogeneities due to local cross-linking of the mixture.

To assess the appearance, the masses were each applied to a glass plate in a layer about 0.1 mm thick. The look of the mixture was good, a few small specks were found.

The expression rate of 390 g / min was determined from 310 ml PE cartridges under a pressure of 6.2 bar and a nozzle diameter of 3.0 mm.

The mass formed a skin after 20 minutes at 23 ° C and a relative humidity of 50 and cured within 7 days to a rubber elastic material with a Shore A hardness of 18.

Continuous operation of the plant was possible over a period of 3 months, with one-hour cleaning after 1 and 2 months respectively.

Comparative Example 1

The procedure described in Example 1 is repeated with the modification that the mixing unit used had no PTFE lining, but a wear protection layer of Deloro Stellite company; Germany, with a Vickers hardness of 800 (RCoCrA2690 Cobalt Based Alloys).

Several hours of cleaning was necessary every 2 weeks because of product inhomogeneities. After 3 months, very strong abrasion was noted in the area of the inner wall of the upper mixing chamber. The inner surface of the housing had many, several millimeters deep scratches in the area of rotating mixing blades. It had to be applied a new anti-wear layer.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1884541 B1 [0004, 0064, 0065, 0065, 0080, 0100]
• DE 19754291 B4 [0007]
• DE 1952755 [0010]
• DE 19856622 C2 [0010]
• DE 3903897 C2 [0011]

Cited non-patent literature

• ISO 6507-1: 2005 [0008]
• ISO 6507-1: 2005 [0008]
• DIN EN ISO 1183 [0106]
• DIN ISO 2039-1 [0106]

Claims (10)

A process for the continuous mixing of organosilicon compounds (A) with highly dispersed fillers (B) and optionally further constituents in a mixing unit comprising housing and mixing element whose rotating mixing elements have rotational speeds of at least 1 m / s, characterized in that the surface of the inner wall of the housing at least to 20 area percent is covered with a material which consists of at least 50 wt .-% of PTFE, wherein the layer thickness is at least 0.5 mm. Process according to Claim 1, characterized in that the organosilicon compounds (A) are those containing units of the formula R _a Y _b SiO _{(4-ab) / 2} (I) where R may be the same or different and is SiC-bonded, optionally substituted hydrocarbon radicals which may be interrupted by oxygen atoms, Y may be the same or different and is a condensable radical, a is 0, 1, 2 or 3 and b is 0 , 1, 2 or 3, with the proviso that the sum of a + b is less than or equal to 3 and at least two Y radicals per molecule are present. Process according to Claim 1 or 2, characterized in that filler (B) is calcium carbonates and pyrogenically prepared silicic acids. Method according to one or more of claims 1 to 3, characterized in that the distance between the rotating mixing elements and the inner wall of the housing is in each case less than 0.2 times the diameter of the rotational cross section formed by the rotation of a mixing element. Method according to one or more of claims 1 to 4, characterized in that rotational speeds in the range of 3 to 20 m / s. Method according to one or more of claims 1 to 5, characterized in that the mixing unit contains two different subspaces, wherein a subspace contains a rotor-stator system. Method according to one or more of claims 1 to 6, characterized in that it is the material used for covering those materials containing at least 80 wt .-% polytertrafluoroethylene. Method according to one or more of claims 1 to 7, characterized in that the wall thickness of the lining is 0.2 to 10 cm. Device comprising a mixing unit containing housing and mixing element whose mixing elements have rotational speeds of at least 1 m / s during rotation, characterized in that the surface of the inner wall of the housing is covered at least to 20 area percent with a material which is at least 50 wt .-% made of PTFE, wherein the layer thickness is at least 0.5 mm. Apparatus according to claim 9, characterized in that the mixing unit has a mixing shaft.