CA2088217A1 - Continuous preparation of aqueous secondary polyacrylate dispersions - Google Patents
Continuous preparation of aqueous secondary polyacrylate dispersionsInfo
- Publication number
- CA2088217A1 CA2088217A1 CA 2088217 CA2088217A CA2088217A1 CA 2088217 A1 CA2088217 A1 CA 2088217A1 CA 2088217 CA2088217 CA 2088217 CA 2088217 A CA2088217 A CA 2088217A CA 2088217 A1 CA2088217 A1 CA 2088217A1
- Authority
- CA
- Canada
- Prior art keywords
- screw extruder
- copolymer
- solvent
- sec
- dispersing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000006185 dispersion Substances 0.000 title claims abstract description 35
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 229920000058 polyacrylate Polymers 0.000 title claims description 10
- 229920001577 copolymer Polymers 0.000 claims abstract description 43
- 238000006386 neutralization reaction Methods 0.000 claims abstract description 21
- 238000010008 shearing Methods 0.000 claims abstract description 7
- 238000010924 continuous production Methods 0.000 claims abstract description 5
- 239000004925 Acrylic resin Substances 0.000 claims abstract description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 17
- 238000002156 mixing Methods 0.000 claims description 11
- 239000002253 acid Substances 0.000 claims description 6
- 230000002378 acidificating effect Effects 0.000 claims description 4
- 150000007942 carboxylates Chemical group 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 239000002245 particle Substances 0.000 claims description 3
- 239000004816 latex Substances 0.000 claims description 2
- 229920000126 latex Polymers 0.000 claims description 2
- 238000010926 purge Methods 0.000 claims description 2
- 239000002270 dispersing agent Substances 0.000 claims 1
- 239000000463 material Substances 0.000 claims 1
- 229940070721 polyacrylate Drugs 0.000 abstract description 9
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 20
- 239000000243 solution Substances 0.000 description 19
- 239000002904 solvent Substances 0.000 description 19
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 10
- 235000011114 ammonium hydroxide Nutrition 0.000 description 10
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 9
- ZXEKIIBDNHEJCQ-UHFFFAOYSA-N isobutanol Chemical group CC(C)CO ZXEKIIBDNHEJCQ-UHFFFAOYSA-N 0.000 description 8
- 239000003960 organic solvent Substances 0.000 description 7
- 229920000642 polymer Polymers 0.000 description 7
- 229910021529 ammonia Inorganic materials 0.000 description 5
- 238000004821 distillation Methods 0.000 description 4
- 239000011347 resin Substances 0.000 description 4
- 229920005989 resin Polymers 0.000 description 4
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 description 3
- 239000000084 colloidal system Substances 0.000 description 3
- 238000004898 kneading Methods 0.000 description 3
- 230000001681 protective effect Effects 0.000 description 3
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 2
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 2
- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical compound C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 description 2
- 150000001252 acrylic acid derivatives Chemical class 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 239000000178 monomer Substances 0.000 description 2
- 230000003472 neutralizing effect Effects 0.000 description 2
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 2
- 239000002952 polymeric resin Substances 0.000 description 2
- 238000006116 polymerization reaction Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000004094 surface-active agent Substances 0.000 description 2
- 229920003002 synthetic resin Polymers 0.000 description 2
- 229920002818 (Hydroxyethyl)methacrylate Polymers 0.000 description 1
- 239000004821 Contact adhesive Substances 0.000 description 1
- 101100117236 Drosophila melanogaster speck gene Proteins 0.000 description 1
- 239000004908 Emulsion polymer Substances 0.000 description 1
- WOBHKFSMXKNTIM-UHFFFAOYSA-N Hydroxyethyl methacrylate Chemical compound CC(=C)C(=O)OCCO WOBHKFSMXKNTIM-UHFFFAOYSA-N 0.000 description 1
- VVQNEPGJFQJSBK-UHFFFAOYSA-N Methyl methacrylate Chemical compound COC(=O)C(C)=C VVQNEPGJFQJSBK-UHFFFAOYSA-N 0.000 description 1
- UEEJHVSXFDXPFK-UHFFFAOYSA-N N-dimethylaminoethanol Chemical compound CN(C)CCO UEEJHVSXFDXPFK-UHFFFAOYSA-N 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 150000001412 amines Chemical class 0.000 description 1
- CQEYYJKEWSMYFG-UHFFFAOYSA-N butyl acrylate Chemical compound CCCCOC(=O)C=C CQEYYJKEWSMYFG-UHFFFAOYSA-N 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000007334 copolymerization reaction Methods 0.000 description 1
- 229960002887 deanol Drugs 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000012972 dimethylethanolamine Substances 0.000 description 1
- 239000003995 emulsifying agent Substances 0.000 description 1
- 235000021183 entrée Nutrition 0.000 description 1
- 239000011552 falling film Substances 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 230000009477 glass transition Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 235000011837 pasties Nutrition 0.000 description 1
- 238000010526 radical polymerization reaction Methods 0.000 description 1
- 150000003254 radicals Chemical class 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
Landscapes
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Compositions Of Macromolecular Compounds (AREA)
Abstract
O.Z. 0050/42977 Abstract of the Disclosure: Aqueous secondary poly-acrylate dispersions having a long shelf life and based on the polyacrylate resin systems are prepared by means of intensively dispersing screw extruders by a continuous process, on which the preparation of the secondary dispersion is carried out, after neutralization of the solvent-free copolymer melt or of the dissolved copolymer, in the shearing section of the screw extruder, and the specific energy input is 0.001-0.25 kWh/kg, the residence time in the shear field is 0.1-120 sec and the shear gradient is 1,000-12,000 1/sec.
Description
O.Z. 0050/42~77 Cont inUous preparation of aqueous secondar~
olYacrylate dispersions The present invention relates to a continuous process for the preparation of aqueous secondary poly-acrylate dispersions having a long shelf life and based on polyacrylate resin systems by means of intensively dispersing screw extruders.
Preferably used resins are self-emulsifying poly-acrylates. The systems are self-emulsifying owing to the content of hydrophilic groups. These hydrophilic groups are preferably acid groups which, after neutralization and salt formation, render the polymer emulsifiable in water. The polyacrylates are prepared by free radical solution copolymerization of (meth)acrylates and possibly vinylaromatics. Particularly preferred monomers are acrylic acid, n-butyl acrylate, methyl methacrylate, hydroxyethyl methacrylate and styrene. The self-emulsifying resins to be dispersed may be copolymers containing acrylic acid, which are described in, for example, German Published Application DAS 2,507,842.
Mixtures of two copolymers, only one of which contains monomers carrying acid groups as a comonomer building block, are particularly preferred. After the neutraliza-tion step, these acid groups are of decisive importance for the dispersibility of the copolymer mixture. These systems are described in European Patent 225,612.
The acid number of typical copolymer mixtures is from 12 to 35. The molecular weights (MM) are typically of the order of from 70,000 to 100,000. The copolymers are obtained in organic solvents by free radical polymer-ization. The preferred solvent is isobutanol. The solids contents of the solution polymers are typically from 70 to 85% by weight. The viscosities of the solvent-containing systems are of the order of 40 Pa.s at 90C. The melt viscosities of the sol~ent-ree : polymers are from 100 to 10,000 Pa.s at 120C. The neutralizing agent used is preferably aqueous ammonia.
, - . ., - , . .
,~ .
olYacrylate dispersions The present invention relates to a continuous process for the preparation of aqueous secondary poly-acrylate dispersions having a long shelf life and based on polyacrylate resin systems by means of intensively dispersing screw extruders.
Preferably used resins are self-emulsifying poly-acrylates. The systems are self-emulsifying owing to the content of hydrophilic groups. These hydrophilic groups are preferably acid groups which, after neutralization and salt formation, render the polymer emulsifiable in water. The polyacrylates are prepared by free radical solution copolymerization of (meth)acrylates and possibly vinylaromatics. Particularly preferred monomers are acrylic acid, n-butyl acrylate, methyl methacrylate, hydroxyethyl methacrylate and styrene. The self-emulsifying resins to be dispersed may be copolymers containing acrylic acid, which are described in, for example, German Published Application DAS 2,507,842.
Mixtures of two copolymers, only one of which contains monomers carrying acid groups as a comonomer building block, are particularly preferred. After the neutraliza-tion step, these acid groups are of decisive importance for the dispersibility of the copolymer mixture. These systems are described in European Patent 225,612.
The acid number of typical copolymer mixtures is from 12 to 35. The molecular weights (MM) are typically of the order of from 70,000 to 100,000. The copolymers are obtained in organic solvents by free radical polymer-ization. The preferred solvent is isobutanol. The solids contents of the solution polymers are typically from 70 to 85% by weight. The viscosities of the solvent-containing systems are of the order of 40 Pa.s at 90C. The melt viscosities of the sol~ent-ree : polymers are from 100 to 10,000 Pa.s at 120C. The neutralizing agent used is preferably aqueous ammonia.
, - . ., - , . .
,~ .
2 ~ 1 7 ., .
- 2 - O.~. 0050/42977 , The ammonia concentration may be preferably from 5 to 25%
by weight. In addition to ammonia, organic amines, for example triethylamine, dimethylethanolamine, etc., are also suitable.
The dispersion is stabilized by the carboxylate groups which are present at the surface o the latex particles. Such secondary dispersions are free of emulsifiers or protective colloids. Film propercies can therefore be achieved with these systems, for example high water resistance, which cannot be realized with ` emulsion polymers (primary dispersions).
i According to the prior art, aqueous secondary polyacrylate dispersions are prepared from copolymer ? solutions by the following process steps:
1) Neutralization of acidic or basic groups with bases or acids 2) Dispersion of the dissolved polymer in water ~` 3) Removal of the organic solvent by distillation.
.' Usually, these process steps are carried out in stirred kettles and are likewise described iII European Patent 225,612. The removal of the organic solvent by distillation can be effected in the stirred kettle only after the polymer has been dispersed, since the viscosity ~` of the polymers without the solvent would be too high to ?, 25 enable them to be dispersed in a stirred kettle.
disadvantage of this procedure is that water is evaporated off with the organic solvent and the energy `~ costs are thus increased. Consequently, the cycle time `~ for the preparation of the dispersion also increase.
However, the most serious disadvantage of this process is the expensive distillation step for separating off the ~; water from the organic solvent, which is necessary when working up the distillate.
According to German Laid-Open Application DOS
~ 35 3,911,945, the organic solvent can be separated from the y polymer resin before the dispersing process in the ~ ` stirred kettle in the case of certain contact adhesive ;~' ~ ' , ~ . . ..
.
2D~8~ l~
- 2 - O.~. 0050/42977 , The ammonia concentration may be preferably from 5 to 25%
by weight. In addition to ammonia, organic amines, for example triethylamine, dimethylethanolamine, etc., are also suitable.
The dispersion is stabilized by the carboxylate groups which are present at the surface o the latex particles. Such secondary dispersions are free of emulsifiers or protective colloids. Film propercies can therefore be achieved with these systems, for example high water resistance, which cannot be realized with ` emulsion polymers (primary dispersions).
i According to the prior art, aqueous secondary polyacrylate dispersions are prepared from copolymer ? solutions by the following process steps:
1) Neutralization of acidic or basic groups with bases or acids 2) Dispersion of the dissolved polymer in water ~` 3) Removal of the organic solvent by distillation.
.' Usually, these process steps are carried out in stirred kettles and are likewise described iII European Patent 225,612. The removal of the organic solvent by distillation can be effected in the stirred kettle only after the polymer has been dispersed, since the viscosity ~` of the polymers without the solvent would be too high to ?, 25 enable them to be dispersed in a stirred kettle.
disadvantage of this procedure is that water is evaporated off with the organic solvent and the energy `~ costs are thus increased. Consequently, the cycle time `~ for the preparation of the dispersion also increase.
However, the most serious disadvantage of this process is the expensive distillation step for separating off the ~; water from the organic solvent, which is necessary when working up the distillate.
According to German Laid-Open Application DOS
~ 35 3,911,945, the organic solvent can be separated from the y polymer resin before the dispersing process in the ~ ` stirred kettle in the case of certain contact adhesive ;~' ~ ' , ~ . . ..
.
2D~8~ l~
- 3 - O.Z. 0050/42977 secondary dispersions. These polymer resins ha~e a low molecular weight and a low glass transition temperature.
Owiny to the high ~iscosity of the novel polyacrylate resins, this procedure is not possible.
SEuropean Patent 384,165 describes a continuous process for the preparation of aqueous, non-self-emulsifying polymer dispersions from highly viscous reaction resins. However, surfactants or protective colloids must be added in the preparation of this disper-10sion since these systems are not self-emulsifying.
Neutralization of functional groups is therefore dis-pensed with.
In contrast to the process described in European Patent 384,165, self-emulsifying systems are used in the 15novel process.
The neutralization of the acidic or basic groups before the dispersing step with water is of decisive importance for the preparation of a novel secondary poly-acrylate dispersion.
20The neutralized carboxylate groups lead to a stable, on-spec dispersion in the dispersing step. The ~ -preparation of an on-spec dispersion by means of a high and intensive energy output is not possible without prior neutralization.
25In contrast to European Patent 384,165, the addition of surfactants or protective colloids is not necessary for the novel secondary polyacrylate disper-sions.
DE 38 30 535 describes the continuous preparation 30o~ aqueous synthetic wax dispersions. In the novel `` process, the neutralization of the solvent-free copolymer melt can also be carried out in a twin-screw extruder.
Surprisingly, however, all extruder types mentioned there are unsuitable for dispersing the neutralized, solvent-35free copolymer melt, since dispersing is not sufficiently intensive. Instead, dispersing must be carried out in the intensively mixing shearing section (rotortstator) of : ' .:
~ . , . . -. .
'~
. .
: : :.
~' ':
-. .
2 ~ 1 7 - 4 - O.Z. 0050/42977 a screw extruder.
I~ is an object of the present invention to `~ provide a continuous process for the pr~paration of aqueous secondary polyacrylate dispersions having a long shelf life.
We have found that this object is achieved, according to the invention, if the preparation of the secondary dispersions is carried out, after the neutral-~ ization of the solvent-free copolymer meltor of the : 10 dissolved copolymer, in the shearing section of a screw extruder, and the specific ~ner~y input is 0.001-0.25 kWh/kg, the residence time in the shear field is 0.1-120 sec and the shear gradient is 1,000-12,000 1/sec.
The residence time in the shear field is prefer-ably from 0.5 to 2 sec; the specific energy input is ; preferably from 0.001-0.2 kWh/kg. A specific energy input above 0.25 kWh/kg causes damage to the product, ~i while an enersy input of less than 0.001 kWh/kg leads to insufficient dispersing.
Before dispersing with wa~er, neutralization of ` acidic or basic groups of the copol~mer melt should be carried out.
This neutralization is carried out, according to the invention, by metering aqueous ammonia solution into the copolymer melt in a self-purging twin-screw extruder, for example a ZSK (Werner & Pfleiderer), and mixing it ~ with the copolymer melt in a mixing zone.
; The mixing zone used may ad~antageously comprise kneading elements, the specific energy input being 0.005 to 0.05 kWh/kg and ~` the residence time in the mixing zone being 0.1-60 sec.
Alternatively, the neutralization can also be ~ carried out in the shearing section of a screw extruder.
'~ 35 This neutralization step is of decisive impor-~` tance for the preparation of stable, on-spec di~persions in the subsequent dispersing step.
. .
.
~ -2~3~2~ ~
Owiny to the high ~iscosity of the novel polyacrylate resins, this procedure is not possible.
SEuropean Patent 384,165 describes a continuous process for the preparation of aqueous, non-self-emulsifying polymer dispersions from highly viscous reaction resins. However, surfactants or protective colloids must be added in the preparation of this disper-10sion since these systems are not self-emulsifying.
Neutralization of functional groups is therefore dis-pensed with.
In contrast to the process described in European Patent 384,165, self-emulsifying systems are used in the 15novel process.
The neutralization of the acidic or basic groups before the dispersing step with water is of decisive importance for the preparation of a novel secondary poly-acrylate dispersion.
20The neutralized carboxylate groups lead to a stable, on-spec dispersion in the dispersing step. The ~ -preparation of an on-spec dispersion by means of a high and intensive energy output is not possible without prior neutralization.
25In contrast to European Patent 384,165, the addition of surfactants or protective colloids is not necessary for the novel secondary polyacrylate disper-sions.
DE 38 30 535 describes the continuous preparation 30o~ aqueous synthetic wax dispersions. In the novel `` process, the neutralization of the solvent-free copolymer melt can also be carried out in a twin-screw extruder.
Surprisingly, however, all extruder types mentioned there are unsuitable for dispersing the neutralized, solvent-35free copolymer melt, since dispersing is not sufficiently intensive. Instead, dispersing must be carried out in the intensively mixing shearing section (rotortstator) of : ' .:
~ . , . . -. .
'~
. .
: : :.
~' ':
-. .
2 ~ 1 7 - 4 - O.Z. 0050/42977 a screw extruder.
I~ is an object of the present invention to `~ provide a continuous process for the pr~paration of aqueous secondary polyacrylate dispersions having a long shelf life.
We have found that this object is achieved, according to the invention, if the preparation of the secondary dispersions is carried out, after the neutral-~ ization of the solvent-free copolymer meltor of the : 10 dissolved copolymer, in the shearing section of a screw extruder, and the specific ~ner~y input is 0.001-0.25 kWh/kg, the residence time in the shear field is 0.1-120 sec and the shear gradient is 1,000-12,000 1/sec.
The residence time in the shear field is prefer-ably from 0.5 to 2 sec; the specific energy input is ; preferably from 0.001-0.2 kWh/kg. A specific energy input above 0.25 kWh/kg causes damage to the product, ~i while an enersy input of less than 0.001 kWh/kg leads to insufficient dispersing.
Before dispersing with wa~er, neutralization of ` acidic or basic groups of the copol~mer melt should be carried out.
This neutralization is carried out, according to the invention, by metering aqueous ammonia solution into the copolymer melt in a self-purging twin-screw extruder, for example a ZSK (Werner & Pfleiderer), and mixing it ~ with the copolymer melt in a mixing zone.
; The mixing zone used may ad~antageously comprise kneading elements, the specific energy input being 0.005 to 0.05 kWh/kg and ~` the residence time in the mixing zone being 0.1-60 sec.
Alternatively, the neutralization can also be ~ carried out in the shearing section of a screw extruder.
'~ 35 This neutralization step is of decisive impor-~` tance for the preparation of stable, on-spec di~persions in the subsequent dispersing step.
. .
.
~ -2~3~2~ ~
- 5 - O.Z. 0050/42977 The secondary dispersions prepared by this n~wly developed process are speck-free and have a long shelf life and an on-spec particle size distribution.
This leads to high-quality secondary polyacrylate dispersions.
An object of the present invention was to dis-perse the solvent-free copolymer melt in order to dispense with the expensive distillation process for separating water from the organic solvent.
This object is achieved by first dis~illing off the solvent from the solvent-containing copolymer solu-tion. Some of the solvent may be removed in the stirred kettle itself after the polymerization. The further removal of the solvent is part of the prior art and can be carried out, for example, in a stopper tube degasser or in a twin-screw extruder.
It is advantageous to remove from the dispersion some of the ammonia, preferably used for n~utralization, in a devolatili~ation step after the dispersing. This leads to dispersions having a substantially lower vis-cosity. The devolatilization step is part of the prior art and can be carried out, for example, in a Fryma vacuum deaerator, a falling film evaporator or a twin-screw extruder or in a stirred kettle having a stripping 2S apparatus.
An apparatus which can advantageously be used for the process according to the present invention is shown in the process flow diagram.
The highly viscous copolymer solution is stored in kettle 1, and the solvent content may correspond to the solvent content required for the polymerization or may have already been reduced in a preceding stripping operation, which is sufficiently known from the prior ~ art.
i 35 To ensure that the copolymer solutian exhibits flow, the kettle 1 can be heated. 'rhe shut-off valve 2 is installed between kettle 1 and the gear pump 3. The .~ , - - : , '~- ,, ; :
.~ .
This leads to high-quality secondary polyacrylate dispersions.
An object of the present invention was to dis-perse the solvent-free copolymer melt in order to dispense with the expensive distillation process for separating water from the organic solvent.
This object is achieved by first dis~illing off the solvent from the solvent-containing copolymer solu-tion. Some of the solvent may be removed in the stirred kettle itself after the polymerization. The further removal of the solvent is part of the prior art and can be carried out, for example, in a stopper tube degasser or in a twin-screw extruder.
It is advantageous to remove from the dispersion some of the ammonia, preferably used for n~utralization, in a devolatili~ation step after the dispersing. This leads to dispersions having a substantially lower vis-cosity. The devolatilization step is part of the prior art and can be carried out, for example, in a Fryma vacuum deaerator, a falling film evaporator or a twin-screw extruder or in a stirred kettle having a stripping 2S apparatus.
An apparatus which can advantageously be used for the process according to the present invention is shown in the process flow diagram.
The highly viscous copolymer solution is stored in kettle 1, and the solvent content may correspond to the solvent content required for the polymerization or may have already been reduced in a preceding stripping operation, which is sufficiently known from the prior ~ art.
i 35 To ensure that the copolymer solutian exhibits flow, the kettle 1 can be heated. 'rhe shut-off valve 2 is installed between kettle 1 and the gear pump 3. The .~ , - - : , '~- ,, ; :
.~ .
- 6 - O.Z. 0050/42977 copolymer solution i5 metered in by means of the gear pump of the heatable twin-screw extruder 14, which is driven by an electric motor 10. The first section of the screw extruder ll serves as a pressure build-up zone, while the remaining solvent is evaporated from the copolymer solution by means of reduced pressure 4 in the second screw section 12. The solvent can be collected in the cold trap S. The valve 6 serves as an outflow valve for the cold trap 5.
The aqueous ammonia solution for neutralization the carboxylate groups is stored in the kettle 7. The ammonia solution having an ammonia concentration of, preferably, 5-25% by weight of ammonia can be metered into the twin-screw extruder via the reciprocating pump.
The screw section 13, equipped with kneading elements, serves as a mixing zone for mixing the solvent~free copolymer melt with the aqueous ammonia solution and hence for neutralizing said melt. In addition, the screw zone 13 functions as a pressure build-up zone in order to meter the neutralized, solvent-free copolymer melt into the screw extruder 26.
A high-speed single-screw extruder which is driven by an electric motor 21 can be used as screw extruder 26 having a shearing section.
The screw extruder can be heated via a double jacket with cooling/heating media 27.
The solvent-free, neutralized copolymer melt is metered into the first section of the screw extruder 22.
This screw section is equipped with conveying screws which transport the copolymer melt into the dispersing zones 23 and 24. Dispersing is effected in the dispers-ing zones 23 and 24 by adding water. Adding water at two points is advantageous; the addition of water at only one point may lead to speck formation.
The demineralised water is stored in the ke~tles 15 and 18~ the kettles are heatable in order to heat the demineralised water. The valves 16 and 19 serve as ..
.
;' .. . .
. . :
~ ~8 ~ ~
The aqueous ammonia solution for neutralization the carboxylate groups is stored in the kettle 7. The ammonia solution having an ammonia concentration of, preferably, 5-25% by weight of ammonia can be metered into the twin-screw extruder via the reciprocating pump.
The screw section 13, equipped with kneading elements, serves as a mixing zone for mixing the solvent~free copolymer melt with the aqueous ammonia solution and hence for neutralizing said melt. In addition, the screw zone 13 functions as a pressure build-up zone in order to meter the neutralized, solvent-free copolymer melt into the screw extruder 26.
A high-speed single-screw extruder which is driven by an electric motor 21 can be used as screw extruder 26 having a shearing section.
The screw extruder can be heated via a double jacket with cooling/heating media 27.
The solvent-free, neutralized copolymer melt is metered into the first section of the screw extruder 22.
This screw section is equipped with conveying screws which transport the copolymer melt into the dispersing zones 23 and 24. Dispersing is effected in the dispers-ing zones 23 and 24 by adding water. Adding water at two points is advantageous; the addition of water at only one point may lead to speck formation.
The demineralised water is stored in the ke~tles 15 and 18~ the kettles are heatable in order to heat the demineralised water. The valves 16 and 19 serve as ..
.
;' .. . .
. . :
~ ~8 ~ ~
- 7 - O.Z. 0050/4Z977 :.
shut-off members. The demineralised water is metered by means of reciprocating pumps 17 and 20.
The dispersing zones 23 and 24 must be in the form of dispersing mixing zones having a narrow shear 5rate distribution, in order to minimize the required dispersing time.
The dispersing zones 23 and 24 are designed so that a specific energy input of from 0.001 to 0.25 kWh/k~, a shear gradient of from 1,000 to 12,000 sec~1 and a 10residence time of from 0.1 to 120 sec can be set.
Specific energies greater than 0.25 kWh/kg cause damage to the product, while an energy input of less than 0.001 kWh/kg leads to insufficient dispersing.
Rotor~stator systems having narrow gap widths can 15advantageously be used.
: ~ The aqueous secondary polyacrylate dispersion 28 is discharged continuously from the screw extruder by means of the conveying screws in the screw section 25.
20A copolymer solution according to Example 2 of European Patent 225,612, having a solvent content of 23%, is metered into the twin-screw extruder (ZSK) by means of a gear pump.
A mass flow of copolymer solution of 20.9 kg/h 25is established.
The solvent (isobutanol) is completely evaporated off in the devolatilization barrel of the ZSK at 120C
and is collected in a cold trap.
Further along the ZS~, 2.1% strength aqueous 30ammonia solution is added by means of a reciprocating ~ump, in order completely to neutralize the solvent-free ` ` copolymer.
~` The established mass flow of the a~mnonia solution is 4 kg/h.
35In the mixing zone of the ZSK, which is equipped with kneading elements, the residence time in the shear ` ~ field is 21 sec and the speci~ic energy input is , , :
, ~, "`` 2~3i~ ~Pjl _ ~ _ o.z. 0050/4~977 0.01 k~h/kg.
The solvent-free, neutralized copol~mer is metered from the ZSX, at 80~C, into the high-speed single-screw extruder.
The speed is 1,000 rpm.
In the single-screw extruder, twu dispersing stages with rotor/stators are used in order gradually to add demineralised water heated to 80C.
The established mass flow is 8 kgJh at the first water addition pump and 8.4 kg/h at the second water addition ~ump.
The shear gradient in the rotor/stator having a gap width of 0.5 mm is 5,500 s~~, the residence tLme in the shear field of the rotor/stator is 11 sec and the specific energy input is 0.03 kWh/kg.
Characteristics of the dispersion are shown in Table 1, column l. The viscosity of the dispersion can be reduced by downstream removal of gaseous NH3.
A copolymer solution according to Example 2 of European Pa-tent 225,612, having a solvent content of 23%, is metered into a twin-screw extruder (ZSK) hy means of a gear pump.
A mass flow of copolymer solution of 20.2 kg/h is established.
The solvent (isobutanol) is completely evaporated off in the devolatilization barrel of the ZSK at 120C
and is collected in a cold trap.
The solvent-free copolymer is metered, at 80~C, from the ZSK into the high-speed single-screw extruder.
The speed of the single-screw extruder is 800 rpm.
In the single-screw extruder, ~hree dispersing stages with rotor/stators are used in order first to carry out the neutralization step and then gradually to add demineralised water heated to 60C.
In the first dispersing stage of the single-screw . ~ . .
~-.~ . .
.
shut-off members. The demineralised water is metered by means of reciprocating pumps 17 and 20.
The dispersing zones 23 and 24 must be in the form of dispersing mixing zones having a narrow shear 5rate distribution, in order to minimize the required dispersing time.
The dispersing zones 23 and 24 are designed so that a specific energy input of from 0.001 to 0.25 kWh/k~, a shear gradient of from 1,000 to 12,000 sec~1 and a 10residence time of from 0.1 to 120 sec can be set.
Specific energies greater than 0.25 kWh/kg cause damage to the product, while an energy input of less than 0.001 kWh/kg leads to insufficient dispersing.
Rotor~stator systems having narrow gap widths can 15advantageously be used.
: ~ The aqueous secondary polyacrylate dispersion 28 is discharged continuously from the screw extruder by means of the conveying screws in the screw section 25.
20A copolymer solution according to Example 2 of European Patent 225,612, having a solvent content of 23%, is metered into the twin-screw extruder (ZSK) by means of a gear pump.
A mass flow of copolymer solution of 20.9 kg/h 25is established.
The solvent (isobutanol) is completely evaporated off in the devolatilization barrel of the ZSK at 120C
and is collected in a cold trap.
Further along the ZS~, 2.1% strength aqueous 30ammonia solution is added by means of a reciprocating ~ump, in order completely to neutralize the solvent-free ` ` copolymer.
~` The established mass flow of the a~mnonia solution is 4 kg/h.
35In the mixing zone of the ZSK, which is equipped with kneading elements, the residence time in the shear ` ~ field is 21 sec and the speci~ic energy input is , , :
, ~, "`` 2~3i~ ~Pjl _ ~ _ o.z. 0050/4~977 0.01 k~h/kg.
The solvent-free, neutralized copol~mer is metered from the ZSX, at 80~C, into the high-speed single-screw extruder.
The speed is 1,000 rpm.
In the single-screw extruder, twu dispersing stages with rotor/stators are used in order gradually to add demineralised water heated to 80C.
The established mass flow is 8 kgJh at the first water addition pump and 8.4 kg/h at the second water addition ~ump.
The shear gradient in the rotor/stator having a gap width of 0.5 mm is 5,500 s~~, the residence tLme in the shear field of the rotor/stator is 11 sec and the specific energy input is 0.03 kWh/kg.
Characteristics of the dispersion are shown in Table 1, column l. The viscosity of the dispersion can be reduced by downstream removal of gaseous NH3.
A copolymer solution according to Example 2 of European Pa-tent 225,612, having a solvent content of 23%, is metered into a twin-screw extruder (ZSK) hy means of a gear pump.
A mass flow of copolymer solution of 20.2 kg/h is established.
The solvent (isobutanol) is completely evaporated off in the devolatilization barrel of the ZSK at 120C
and is collected in a cold trap.
The solvent-free copolymer is metered, at 80~C, from the ZSK into the high-speed single-screw extruder.
The speed of the single-screw extruder is 800 rpm.
In the single-screw extruder, ~hree dispersing stages with rotor/stators are used in order first to carry out the neutralization step and then gradually to add demineralised water heated to 60C.
In the first dispersing stage of the single-screw . ~ . .
~-.~ . .
.
8 ~ ~ ~
_ g - o.Z. ~050/42977 , .
extruder, 4.3~ strength aqueous ammonia solution is added by means of a reciprocating pump in order completely to neutralize the solvent-free copolymex.
The established mass flow of the ammonia solution 5is 2.1 kg/h.
The residence time in the neutralization zone of the singlP-screw extruder is 24 sec.
In the subsequent two dispersing stages, demineralised water is gradually added. The mass flow 10is set at 8 kg/h at the first water addition point and 10 kg/h at the second water addi~ion point.
The shear gradient in the rotor/stator having a gap width of 0.5 mm is 4,400 5-1, the residence time in the shear field of the rotor/stator is 15 sec and the 15specific energy input is 0.1 kWh~kg.
The characteristics of the dispersion are shown in Table 1, column 2.
The viscosity of the dispersion can be reduced by downstream removal of gaseous NH3 .
A copolymer solution according to Example 2 of EP-A 225,612, having a solvent content of 23~, is metered into a twin-screw extruder (ZSK) by means of a gear pump~
A mass flow of copolymer solution of 20.2 kg/h 25is established.
In the devolatilization barrel of the ZSK, the copolymer solution is concentrated to a solvent content of 12% by weight at 120C.
The concentrated copolymer solution is metered, 30at 120C, rom the ZSK into the high-speed single-screw extruder.
The speed of the single-screw extruder is 1,000 rpm.
In the single-screw extruder, three dispersing 35stages with rotor/stators are used in order ~irst to carry out the neutralization step and then gradually to add demineralised water heated to 60C.
-:
,:
. ........................ .. .
"' , .
2 ~
. .
- 10 ~ O.Z. 0050/~2977 In the first dispersing stage of the single-screw extruder, 4.3~ strength aqueous a~onia solukion is ~dded by means of a reciprocating pump in order completely to neutralize the solvent-free copolymer.
The established mass flow of the ammonia solution ` is 2.1 kg/h.
The residence time in the neutralization zone of the single-screw extruder is 20 sec.
In the subsequent two dispersing stages, demineralised water is gradually added. The mass flow is set at 8 kg/h at the first water addition point and 10 kg/h at the second water addition point.
The shear gradient in the rotor/stator having a gap width of 0.5 mm is 5,500 s-1, the residence time in the shear field of the rotor/stator is 14 sec and the specific energy input is 0.06 kWh/kg.
- The characteristics of the dispersion are shown in Table 1, column 3.
A copolymer solution according to Example 2 of EP-A 225,612, heated to 80C and having a solvent content of 23~, is metered into the single-screw extruder (ZSK) by means of a gear pump.
The speed of the single-screw extruder is l,000 rpm.
In the single-screw extruder, three disparsing ` stages having rotor/stators are used in order first to carry out the neutralization step and then gradually to add demineralised water heated to 60C.
In the first dispersing stage of the single-screw extruder, 4.3% strength aqueous ammonia solution is added by means of a reciprocating pump in order completely to neutralize the copolymer solution.
The established mass flow of the ammonia solution is 2.1 kg/h.
The residence time in the neutralization zone oi the single-screw extruder is 19 sec.
, , .- ~ :
.
- 2~3~
~ O.Z. 0050/42977 In the subsequent kwo dispersing stages, demineralised water is gradually added. The mass flow is set at 8 kg/h at the first water addition point and 10 kg/h at the second water addition point.
The shear gradient in the rotor/stator ha~ing a gap width of 0.5 mm is 5,500 s-l, the residence tlme in the shear field of the rotor/stator is 13 sec and the specific energy input is 0.01 kWh/kg.
The characteristics o~ the dispersion are shown in Table 1, column 4.
Characteristics of the dispersions from Examples 1 to 4:
Example No. ~ 2 ¦ 3 4 Solids content (X by weight) 43.2 41.9 40.3 38.4 pH 9.4 9.5 9.5 9 3 LT value 56 49 61 76 _ Isobutanol conten~ (X by weight) 0.4 0.4 4.9 12.6 Viscosity (mPa.s) 42,000 pasty . 900 4,000
_ g - o.Z. ~050/42977 , .
extruder, 4.3~ strength aqueous ammonia solution is added by means of a reciprocating pump in order completely to neutralize the solvent-free copolymex.
The established mass flow of the ammonia solution 5is 2.1 kg/h.
The residence time in the neutralization zone of the singlP-screw extruder is 24 sec.
In the subsequent two dispersing stages, demineralised water is gradually added. The mass flow 10is set at 8 kg/h at the first water addition point and 10 kg/h at the second water addi~ion point.
The shear gradient in the rotor/stator having a gap width of 0.5 mm is 4,400 5-1, the residence time in the shear field of the rotor/stator is 15 sec and the 15specific energy input is 0.1 kWh~kg.
The characteristics of the dispersion are shown in Table 1, column 2.
The viscosity of the dispersion can be reduced by downstream removal of gaseous NH3 .
A copolymer solution according to Example 2 of EP-A 225,612, having a solvent content of 23~, is metered into a twin-screw extruder (ZSK) by means of a gear pump~
A mass flow of copolymer solution of 20.2 kg/h 25is established.
In the devolatilization barrel of the ZSK, the copolymer solution is concentrated to a solvent content of 12% by weight at 120C.
The concentrated copolymer solution is metered, 30at 120C, rom the ZSK into the high-speed single-screw extruder.
The speed of the single-screw extruder is 1,000 rpm.
In the single-screw extruder, three dispersing 35stages with rotor/stators are used in order ~irst to carry out the neutralization step and then gradually to add demineralised water heated to 60C.
-:
,:
. ........................ .. .
"' , .
2 ~
. .
- 10 ~ O.Z. 0050/~2977 In the first dispersing stage of the single-screw extruder, 4.3~ strength aqueous a~onia solukion is ~dded by means of a reciprocating pump in order completely to neutralize the solvent-free copolymer.
The established mass flow of the ammonia solution ` is 2.1 kg/h.
The residence time in the neutralization zone of the single-screw extruder is 20 sec.
In the subsequent two dispersing stages, demineralised water is gradually added. The mass flow is set at 8 kg/h at the first water addition point and 10 kg/h at the second water addition point.
The shear gradient in the rotor/stator having a gap width of 0.5 mm is 5,500 s-1, the residence time in the shear field of the rotor/stator is 14 sec and the specific energy input is 0.06 kWh/kg.
- The characteristics of the dispersion are shown in Table 1, column 3.
A copolymer solution according to Example 2 of EP-A 225,612, heated to 80C and having a solvent content of 23~, is metered into the single-screw extruder (ZSK) by means of a gear pump.
The speed of the single-screw extruder is l,000 rpm.
In the single-screw extruder, three disparsing ` stages having rotor/stators are used in order first to carry out the neutralization step and then gradually to add demineralised water heated to 60C.
In the first dispersing stage of the single-screw extruder, 4.3% strength aqueous ammonia solution is added by means of a reciprocating pump in order completely to neutralize the copolymer solution.
The established mass flow of the ammonia solution is 2.1 kg/h.
The residence time in the neutralization zone oi the single-screw extruder is 19 sec.
, , .- ~ :
.
- 2~3~
~ O.Z. 0050/42977 In the subsequent kwo dispersing stages, demineralised water is gradually added. The mass flow is set at 8 kg/h at the first water addition point and 10 kg/h at the second water addition point.
The shear gradient in the rotor/stator ha~ing a gap width of 0.5 mm is 5,500 s-l, the residence tlme in the shear field of the rotor/stator is 13 sec and the specific energy input is 0.01 kWh/kg.
The characteristics o~ the dispersion are shown in Table 1, column 4.
Characteristics of the dispersions from Examples 1 to 4:
Example No. ~ 2 ¦ 3 4 Solids content (X by weight) 43.2 41.9 40.3 38.4 pH 9.4 9.5 9.5 9 3 LT value 56 49 61 76 _ Isobutanol conten~ (X by weight) 0.4 0.4 4.9 12.6 Viscosity (mPa.s) 42,000 pasty . 900 4,000
Claims (6)
- The embodiments of the invention in which an exclusive property or prlvileye is claimed are defined as follows:
l. A continuous process for the preparation of an aqueous secondary polyacrylate dispersion having a long shelf life and based on a polyacrylate resin system by means of intensively dispersant screw extruders, wherein the preparation of the secondary dispersion is carried out, after the neutralization of the solvent-free copolymer melt or of the dissolved copolymer, in the shearing section of a screw extruder, and the specific energy input is 0.001-0.25 kWh/kg, the residence time in the shear field is 0.1-120 sec, and the shear gradient is 1,000-12,000 l/sec. - 2. A process as claimed in claim 1, wherein, before the dispersing step with water, acidic or basic groups of the copolymer melt are neutralized.
- 3. A process as claimed in claims l and 2, wherein the neutralization of the solvent-free copolymer melt is advantageously carried out in the mixing zone of the self-purging twin-screw extruder or in the shearing section of an intensively dispersing screw extruder, and the specific energy input is 0.005-0.05 kWh/kg and the residence time in the mixing zone is 0.1-60 sec.
- 4. A process as claimed in any of claims 1 to 3, wherein the material system is self-emulsifying.
- 5. A process as claimed in any of claims 1 to 4, wherein the secondary dispersion is stabilized by the carboxylate groups present at the surface of the latex particles.
- 6. A process as claimed in any of claims 1 to 5, wherein the polyacrylate to be dispersed is a solution copolymer or preferably a mixture of two solution copoly-mers, only one of the two copolymers containing acid groups or base groups.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4202212.6 | 1992-01-28 | ||
| DE19924202212 DE4202212A1 (en) | 1992-01-28 | 1992-01-28 | CONTINUOUS METHOD FOR PRODUCING AQUEOUS POLYACRYLATE SECONDARY DISPERSIONS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2088217A1 true CA2088217A1 (en) | 1993-07-29 |
Family
ID=6450366
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2088217 Abandoned CA2088217A1 (en) | 1992-01-28 | 1993-01-27 | Continuous preparation of aqueous secondary polyacrylate dispersions |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0553620A1 (en) |
| JP (1) | JPH05247223A (en) |
| CA (1) | CA2088217A1 (en) |
| DE (1) | DE4202212A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5750613A (en) * | 1995-08-07 | 1998-05-12 | Bayer Aktiengesellschaft | Aqueous, crosslinkable binder dispersions having a low solvent content |
| US6962953B2 (en) | 2001-06-21 | 2005-11-08 | Bayer Aktiengesellschaft | Aqueous secondary dispersions |
| US7775704B2 (en) | 2003-03-21 | 2010-08-17 | Kemira Oyj | Device and method for continuously producing emulsions or dispersions |
| US10610835B2 (en) | 2010-05-07 | 2020-04-07 | Clariant International Ag | Emulsification device for continuously producing emulsions and/or dispersions |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1707256B1 (en) | 2003-03-21 | 2016-10-19 | Kemira Oyj | Device and method for continuously producing emulsions or dispersions |
| EP2636714A1 (en) | 2012-03-09 | 2013-09-11 | Basf Se | Multistage preparation of aqueous adhesive dispersions for producing self-adhesive items |
| JP6277810B2 (en) * | 2014-03-24 | 2018-02-14 | 富士ゼロックス株式会社 | Method for producing resin particle dispersion |
| DE102015114397A1 (en) * | 2015-08-28 | 2017-03-02 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Mixing and molding process for filled thermosets of organically crosslinkable composite materials, in particular for dental purposes |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4123403A (en) * | 1977-06-27 | 1978-10-31 | The Dow Chemical Company | Continuous process for preparing aqueous polymer microsuspensions |
| DE3543361A1 (en) * | 1985-12-07 | 1987-06-11 | Basf Ag | METHOD FOR PRODUCING AQUEOUS POLYMER DISPERSIONS AND USE THEREOF |
| CA1303272C (en) * | 1986-04-24 | 1992-06-09 | Mitsui Chemicals, Incorporated | Aqueous dispersion and process for preparation thereof |
| DE3830535A1 (en) * | 1988-09-08 | 1990-03-22 | Basf Ag | METHOD FOR PRODUCING AQUEOUS SYNTHESIS WAX DISPERSIONS |
| DE3905007A1 (en) * | 1989-02-18 | 1990-08-23 | Basf Ag | CONTINUOUS METHOD FOR PRODUCING AQUEOUS NON-SELF-MULULATING POLYMER DISPERSIONS |
-
1992
- 1992-01-28 DE DE19924202212 patent/DE4202212A1/en not_active Withdrawn
-
1993
- 1993-01-08 EP EP93100194A patent/EP0553620A1/en not_active Withdrawn
- 1993-01-27 CA CA 2088217 patent/CA2088217A1/en not_active Abandoned
- 1993-01-27 JP JP1149793A patent/JPH05247223A/en not_active Withdrawn
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5750613A (en) * | 1995-08-07 | 1998-05-12 | Bayer Aktiengesellschaft | Aqueous, crosslinkable binder dispersions having a low solvent content |
| US6962953B2 (en) | 2001-06-21 | 2005-11-08 | Bayer Aktiengesellschaft | Aqueous secondary dispersions |
| US7775704B2 (en) | 2003-03-21 | 2010-08-17 | Kemira Oyj | Device and method for continuously producing emulsions or dispersions |
| US10610835B2 (en) | 2010-05-07 | 2020-04-07 | Clariant International Ag | Emulsification device for continuously producing emulsions and/or dispersions |
Also Published As
| Publication number | Publication date |
|---|---|
| DE4202212A1 (en) | 1993-07-29 |
| JPH05247223A (en) | 1993-09-24 |
| EP0553620A1 (en) | 1993-08-04 |
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