EP0000415B1 - Verfahren zur Herstellung von wässrigen Suspensionen, die wenigstens 65 Gew. % Calciumkarbonat enthalten - Google Patents

Verfahren zur Herstellung von wässrigen Suspensionen, die wenigstens 65 Gew. % Calciumkarbonat enthalten Download PDF

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Publication number
EP0000415B1
EP0000415B1 EP78200085A EP78200085A EP0000415B1 EP 0000415 B1 EP0000415 B1 EP 0000415B1 EP 78200085 A EP78200085 A EP 78200085A EP 78200085 A EP78200085 A EP 78200085A EP 0000415 B1 EP0000415 B1 EP 0000415B1
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EP
European Patent Office
Prior art keywords
calcium carbonate
process according
polyelectrolyte
alkali metal
concentrate
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Expired
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EP78200085A
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English (en)
French (fr)
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EP0000415A1 (de
Inventor
Jacques Brahm
Jean-Pierre De Rath
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Solvay SA
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Solvay SA
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Publication of EP0000415A1 publication Critical patent/EP0000415A1/de
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D17/00—Pigment pastes, e.g. for mixing in paints
    • C09D17/004—Pigment pastes, e.g. for mixing in paints containing an inorganic pigment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/182—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/182—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds
    • C01F11/183—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds the additive being an organic compound
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/185—After-treatment, e.g. grinding, purification, conversion of crystal morphology
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/02—Compounds of alkaline earth metals or magnesium
    • C09C1/021—Calcium carbonates
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/36—Coatings with pigments
    • D21H19/38—Coatings with pigments characterised by the pigments
    • D21H19/385—Oxides, hydroxides or carbonates
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/36—Coatings with pigments
    • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
    • D21H19/52—Cellulose; Derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer

Definitions

  • the subject of the present invention is the preparation of concentrated aqueous suspensions of calcium carbonate, by crystallization of calcium carbonate in an aqueous medium.
  • concentrated aqueous generally containing 65 to 80% by weight of crystals.
  • This known method has the disadvantage of requiring an expensive grinding operation. This is in fact imposed by the need to break up the numerous coarse agglomerates of calcium carbonate crystals present in the wet calcium carbonate concentrate. In addition to its unfavorable influence on the cost of the process, this grinding operation has the drawback of giving rise to the formation of calcium carbonate fines, which are generally not suitable as a filler.
  • the filter cakes obtained by this known process are in the form of aqueous suspensions of fine crystals, very suitable as a filler in stationery, in plastics and in paints.
  • concentration of calcium carbonate crystals in these aqueous suspensions is generally insufficient to allow them to be stored and handled economically, so that it is necessary to concentrate them by evaporating them.
  • the Applicant has now found that by carrying out the crystallization under special conditions, it is possible to obtain concentrated aqueous suspensions of fine and regular crystals of calcium carbonate, generally containing more than 65% by weight of dry matter, without requiring grinding or evaporation.
  • the invention therefore relates to a process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate, according to which crystalline calcium carbonate in dilute aqueous medium is separated from the dilute aqueous suspension of calcium carbonate resulting, a wet calcium carbonate concentrate and said calcium carbonate concentrate is fluidized and homogenized in the presence of a dispersing agent, the crystallization of the calcium carbonate being carried out in the presence of a water-soluble polyelectrolyte and the separation of the wet concentrate from the diluted aqueous suspension being carried out by mechanical means.
  • polyelectrolyte is understood to mean a polymeric substance whose monomeric units have ionizable groups, and which is composed, on the one hand, of a macroion formed from ionic groups of the same sign, linked together by chemical bonds and, on the other hand, a series of counterions of charge opposite to that of the macroion (Encyclopedia of Polymer Science and Technology - John Wiley & Sons - 1969 - Vol. 10, p. 781).
  • polyacids or their salts, which are polyelectrolytes which, by dissociating, give rise to polymeric anions (polyanions) and to elementary cations such as, for example, protons or monovalent cations derived from alkali metals (Op. cit., p. 781 to 784).
  • Polyacids with a weak acid character are preferably used, defined as being polyacids whose pK, measured on a 0.01 N solution in pure water, is greater than 4, preferably 6 (Op. Cit., p. 787 to 788).
  • Polyacids with a weak acid character which are very suitable in the context of the invention are those derived from polymers comprising at least one carboxylic group per 10 carbon atoms.
  • polyacids which can be used in the process according to the invention mention may in particular be made of polymers derived from acrylic, methacrylic and alpha-hydroxyacrylic acids, copolymers of maleic acid, carboxylated derivatives of cellulose ethers, and their alkali metal salts.
  • particularly advantageous polyelectrolytes include the alkali metal salts of polyacrylic acids and their derivatives such as poly-alpha-hydroxyacrylic acids, more particularly that known under the name of Polysel CA (BASF) which is based on sodium polyacrylate.
  • BASF Polysel CA
  • the crystalli sation of calcium carbonate in an aqueous medium can be carried out by any means known per se, for example by reacting a solution of ammonium carbonate or alkali metal.
  • the crystallization of calcium carbonate is advantageously carried out by carbonating a milk of lime, preferably by means of a gas containing CO 2 .
  • a lime milk titrating between 25 and 350, preferably between 50 and 250, kg of CaO per m 3 which is prepared in a manner well known per se , by dispersing quicklime in water from the calcination of limestone in a lime kiln.
  • a gas poor in C0 2 for example boiler fumes containing 5 to 15% by volume of C0 2 .
  • a gas rich in C0 2 containing more than 30% of CO z , such as the gas recovered from lime kilns.
  • the respective amounts of milk of lime and carbonation gas must be sufficient to ensure as complete carbonation of the lime as possible. These quantities obviously depend on the respective concentrations of the milk of lime and of the gas, as well as on the working conditions, and they can, in each particular case, be easily established by experience.
  • the crystallization is preferably carried out at a temperature of the order of 25 to 60 ° C., for example close to 30 to 50 ° C.
  • the amount of polymer incorporated into the aqueous medium depends on various factors, including the working conditions during crystallization and the nature of the polymer used; it can be easily determined by experience, in each case.
  • the calcium carbonate is crystallized by carbonating a lime milk
  • calcium carbonate concentrate is understood to mean a wet cake of calcium carbonate, which has been formed from the abovementioned dilute aqueous suspension of calcium carbonate.
  • essentially mechanical separation means are used.
  • a mechanical separation means it is possible, for example, in accordance with the invention, to use filtration, wringing or decantation of the dilute aqueous suspension, which are techniques well known per se. As a variant, it is also possible to combine two or more separate mechanical separation means.
  • filtration which is a technique well known per se, the filter cake collected on the filter then constituting the aforementioned wet concentrate.
  • filtration of the diluted suspension is advantageously carried out under pressure, for example between 0.5 and 15 kg / cm 2 , and it is optionally followed by compression of the filter cake under a pressure between 1 and 20 kg / cm 2 and a sweep by a current of air under a pressure of 0.5 to 6 kg / cm 2.
  • the temperature at which filtration is carried out as well as any compression and sweeping is not have not been shown to have a significant influence on the filtration result.
  • it can for example be carried out between 15 and 50 ° C, advantageously at room temperature.
  • the fluidization of the calcium carbonate concentrate consists in subjecting it to mechanical work which transforms it into a fluid, pumpable aqueous suspension. It is generally carried out, in a manner known per se, by mixing the concentrate, for example by means of a paddle, disc or rotary cone mixer.
  • the homogenization has the function of ensuring an efficient, homogeneous dispersion of the calcium carbonate crystals in the above-mentioned fluid aqueous suspension resulting from the fluidization operation. It is generally obtained by subjecting it to turbulence or intense shearing work by means of a high-speed disperser, for example of the paddle, disc or knife type.
  • the fluidization and the homogenization are preferably carried out separately.
  • the function of the dispersing agent used during fluidization and homogenization is to facilitate the dispersion of the calcium carbonate crystals, by avoiding the formation of crystal agglomerates.
  • It can for example consist of an inorganic dispersing agent, such as the commercial dispersing agent known under the name of Calgon (Calgon Corp.), which is based on polyphosphate of alkali metal.
  • the dispersing agent can also consist, at least partially, of an organic dispersing agent, for example a dispersing agent chosen from polyelectrolytes, preferably polyacids.
  • dispersing agents which have been found to be particularly effective are those known as Polysel CA (BASF) which is a dispersing agent based on sodium polyacrylate and die Dispagil (Rhône-Progil) which is a dispersing agent based on polyphosphate and alkali metal polyacrylate.
  • BASF Polysel CA
  • Rhône-Progil die Dispagil
  • the dispersing agent is preferably added to the calcium carbonate concentrate before carrying out the fluidization and homogenization. It can optionally be added to the dilute aqueous suspension of calcium carbonate, before separation of the calcium carbonate concentrate. However, it has been observed in practice that it is preferable to add the dispersing agent to the calcium carbonate concentrate, after having separated it from the aqueous suspension, since this results, all other things being equal, a decrease in the amount of dispersing agent required.
  • the amount of dispersing agent used to fluidize and homogenize the calcium carbonate concentrate depends on various factors, including the nature of the dispersing agent, the particle size of the calcium carbonate crystals and the calcium carbonate content of the concentrate. It can be easily determined by experience in each case. Generally, it is advantageously between 2 and 10 g, preferably 4 and 8 g, per kg of calcium carbonate from the concentrate.
  • the process according to the invention makes it possible to obtain easily, quickly and economically, concentrated, stable aqueous suspensions of regular crystals of calcium carbonate, generally containing at least 65%, preferably from 68 to 75%, by weight of crystals, without the need for expensive evaporation treatment or grinding.
  • These co-centered suspensions lend themselves well to long-term storage and handling:, without their stability being affected.
  • the calcium carbonate crystals they contain are well formed and regular and are well suited as a filler in stationery, paints and in the manufacture of plastics.
  • a milk of lime was carbonated with a gas containing CO 2 .
  • the dilute aqueous suspension of calcium carbonate thus obtained was then filtered under a maximum pressure of 4.5 kg / cm 2 , the filter cake obtained was compressed under a maximum pressure of 17 kg / cm 2 to wring it out, then subjected to an air sweep under pressure equal to 5.3 kg / cm 2 for 10 minutes, thus providing a wet concentrate of calcium carbonate.
  • This calcium carbonate concentrate was then fluidized and then homogenized by passing successively through a kneader and then through a disperser, thus providing an aqueous suspension of calcium carbonate.
  • Examples 1 and 2 relate to tests in accordance with the invention.
  • Polysel CA which is a commercial polyelectrolyte based on sodium polyacrylate, was introduced into the milk of lime, which titrated approximately 120 kg of CaO per m 3 .
  • the amount of Polysel CA introduced into the milk of lime was adjusted so that it corresponds approximately to 2.5 g of Polysel CA per kg of crystallized calcium carbonate.
  • the milk of lime was then carbonated with a gas containing between 23 and 27% of CO 2 , at a rate of 1350 m 3 / h, for 7 h 15 min. The temperature was maintained at 37 ° C.
  • the calcium carbonate concentrate collected on the filter was fluidized and homogenized in the presence of Calgon which is a commercial dispersing agent based on sodium polyphospliate. 7 g of Calgon were used per kg of calcium carbonate in the concentrate. There was thus obtained a concentrated aqueous suspension containing 68% of regular crystals of calcium carbonate. This aqueous suspension remained stable for more than 30 days.
  • Example 1 The test of Example 1 was repeated, using a milk of lime titrating about 120 kg of CaO per m 3 and a gas containing between 29 and 32% of CO2 The carbonation, carried out at 32 ° C, lasted 7 h 35 min., with a gas flow of between 1200 and 1350 m 3 / h. The amount of Polysel CA was adjusted to correspond to 5 g per kg of calcium carbonate.
  • the concentrated aqueous suspension of calcium carbonate obtained contained 71.7% by weight of calcium carbonate crystals; it remained stable for more than 30 days.
  • Example 3 On the other hand, immediately reveals the advantage of the process according to the invention which makes it possible to obtain easily, without evaporation, by simple filtration, stable aqueous suspensions containing at least 68% by weight of calcium carbonate crystals.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Wood Science & Technology (AREA)
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Claims (18)

1. Verfahren zur Herstellung wäßriger Suspensionen enthaltend mindestens 65 Gew.-% Calciumcarbonat, wobei man Calciumcarbonat in wäßrigem verdünnten Milieu kristallisiert, von der sich ergebenden verdünnten wäßrigen Suspension des Calciumcarbonates ein feuchtes Calciumcarbonat-Konzentrat abtrennt und dieses in Anwesenheit eines Dispersionsmittels fluidisiert und homogenisiert, dadurch gekennzeichnet, daß man das Calciumcarbonat in Anwesenheit eines wasserlöslichen Polyelektrolyten kristallisiert und daß man das Calciumcarbonat-Konzentrat von der verdünnten Calciumcarbonat-Suspension auf mechanische Weise abtrennt.
2. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß man den Polyelektrolyten auswählt unter den Polysäuren und ihren Alkälimetallsalzen. -
3. Verfahren gemäß Anspruch 2, dadurch gekennzeichnet, daß man den Polyelektrolyten auswählt unter den schwach sauren Polysäuren und inren Alkalimetallsalzen.
4. Verfahren gemäß Anspruch 3, dadurch gekennzeichnet, daß man den Polyelektrolyten auswählt unter den Polysäuren, die von Polymeren abgeleitet sind und mindestens eine Carboxylgruppe je 10 Kohlenstoffatomen enthalten und ihren Alkalimetallsalzen.
5. Verfahren gemäß Anspruch 4, dadurch gekennzeichnet, daß man den Polyelektrolyten auswählt unter den Polymeren abgeleitet von Acrylsäure, Methacrylsäure und alpha-Hydroxyacrylsäure, den Copolymeren von Maleinsäure, den carboxylierten Derivaten der Celluloseäther und ihren Alkalimetallsalzen.
6. Verfahren gemäß Anspruch 5, dadurch gekennzeichnet, daß der Polyelektrolyt ein Natriumpolyacrylat ist.
7. Verfahren gemäß Anspruch 5, dadurch gekennzeichnet, daß der Polyelektrolyt ein Natrium-poly-alpha-hydroxyacrylat ist.
8. Verfahren gemäß einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, daß man zur Kristallisation des Calciumcarbonats Kalkmilch cärbonatisiert.
9. Verfahren gemäß Anspruch 8, dadurch gekennzeichnet, daß man Kalkmilch mit einem C02-haltigen Gas carbonatisiert.
10. Verfahren gemäß einem der Ansprüche 8 oder 9, dadurch gekennzeichnet, daß man Kalkmilch bei einer Temperatur zwischen 25 und 60° C carbonatisiert.
11. Verfahren gemäß einem der Ansprüche 8 bis 10, dadurch gekennzeichnet, daß man als Polyelektrolyten ein Alkalimetallpolyacrylat einsetzt in einer in dem verdünnten wäßrigen Kristallisaationsmilieu geregelten Menge derart, daß die verdünnte Suspension 1-10 g des Alkalimetallpolyacrylats je kg Trockenmasse enthält.
12. Verfahren gemäß Anspruch 11, dadurch gekennzeichnet, daß die verdünnte Suspension 2-6 g Alkalimetallpolyacrylat je kg Trockenmasse enthält.
13. Verfahren gemäß einem der Ansprüche 1 bis 12, dadurch gekennzeichnet, daß die mechanische Abtrennung erfolgt durch Filtration der verdünnten Calciumcarbonat-Suspension.
14. Verfahren gemäß einem der Ansprüche 1 bis 13, dadurch gekennzeichnet, daß die mechanische Abtrennung durch Absaugung erfolgt.
15. Verfahren gemäß Anspruch 14, dadurch gekennzeichnet, daß man die verdünnte wäßrige Calciumcarbonat-Suspension filtriert und den sich ergebenden Filterkuchen durch Zusammendrücken absaugt und einem Luftstrom unterwirft.
16. Verfahren gemäß einem der Ansprüche 1 bis 15, dadurch gekennzeichnet, daß man zur Fluidisierung und Homogenisierung des Caiciu,ncarbonat-Konzentrats 2-10 g Dispersionsmittel je kg Calciumcarbonat einsetzt.
17. Verfahren gemäß Anspruch 16, dadurch gekennzeichnet, daß man 4-8 g Dispersionsmittel einsetzt:
18. Verfahren gemäß einem der Ansprüche 1 bis 17, dadurch gekennzeichnet, daß man das Dispersionsmittel direkt in das Calciumcarbonat-Konzentrat einführt.
EP78200085A 1977-07-11 1978-07-07 Verfahren zur Herstellung von wässrigen Suspensionen, die wenigstens 65 Gew. % Calciumkarbonat enthalten Expired EP0000415B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
LU77723A LU77723A1 (fr) 1977-07-11 1977-07-11 Procede pour la preparation de suspensions aqueuses concentrees de carbonate de calcium
LU77723 1977-07-11

Publications (2)

Publication Number Publication Date
EP0000415A1 EP0000415A1 (de) 1979-01-24
EP0000415B1 true EP0000415B1 (de) 1981-04-29

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EP78200085A Expired EP0000415B1 (de) 1977-07-11 1978-07-07 Verfahren zur Herstellung von wässrigen Suspensionen, die wenigstens 65 Gew. % Calciumkarbonat enthalten

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Country Link
US (1) US4242318A (de)
EP (1) EP0000415B1 (de)
JP (1) JPS5418498A (de)
AT (1) AT372695B (de)
BG (1) BG49609A3 (de)
DE (1) DE2860643D1 (de)
DK (1) DK308478A (de)
ES (1) ES471586A1 (de)
FI (1) FI62272C (de)
IN (1) IN147648B (de)
IT (1) IT1099568B (de)
LU (1) LU77723A1 (de)

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GB1204511A (en) * 1967-03-14 1970-09-09 English Clays Lovering Pochin Improvements in or relating to pigments
GB1285891A (en) * 1968-10-15 1972-08-16 English Clays Lovering Pochin Improvements in or relating to the treatment of minerals
BE755970A (fr) * 1969-09-10 1971-02-15 English Clays Lovering Pochin Pigment mixte se composant d'un pigment a l'argile et d'un pigment au cabonate de calcium
JPS5112319B2 (de) * 1972-08-01 1976-04-17
GB1447566A (en) * 1974-02-14 1976-08-25 Ici Ltd Production of calcium carbonate
US3945843A (en) * 1974-07-22 1976-03-23 Nalco Chemical Company Acrylic acid copolymer as pigment dispersant
GB1472701A (en) * 1975-01-03 1977-05-04 English Clays Lovering Pochin Production of aqueous calcium carbonate suspensions
LU71867A1 (de) * 1975-02-17 1977-01-05

Also Published As

Publication number Publication date
ES471586A1 (es) 1979-01-16
EP0000415A1 (de) 1979-01-24
ATA496878A (de) 1983-03-15
LU77723A1 (fr) 1979-03-26
DK308478A (da) 1979-01-12
JPS5418498A (en) 1979-02-10
DE2860643D1 (en) 1981-08-06
IT1099568B (it) 1985-09-18
FI62272C (fi) 1982-12-10
IN147648B (de) 1980-05-17
JPS6317771B2 (de) 1988-04-15
IT7825558A0 (it) 1978-07-11
FI62272B (fi) 1982-08-31
US4242318A (en) 1980-12-30
FI781991A (fi) 1979-01-12
AT372695B (de) 1983-11-10
BG49609A3 (en) 1991-12-16

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