Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1042—Use of chelating agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• the invention relates to a process for bleaching a chemical pulp.
• the first step of a conventional chemical pulp bleaching sequence aims to complete the delignification of the unbleached pulp as it occurs after the cooking operation.
• This first delignifying step is traditionally carried out by treating the unbleached pulp with chlorine in an acid medium or by a chlorine-chlorine dioxide association, in mixture or in sequence, so as to react with the residual lignin of the pulp and give rise to chlorolignins which can be extracted from the pulp by dissolving these chlorolignins in an alkaline medium in a subsequent treatment step.
• the invention remedies these drawbacks of known methods by providing a new method for delignification and / or bleaching of chemical paper pulps which makes it possible to achieve high levels of whiteness without degrading the cellulose too strongly and without using chlorinated reagents.
• the invention relates to a process for bleaching a chemical paper pulp by means of a sequence of treatment steps comprising at least the following steps, carried out in order: QPA where the acronym Q represents a step of decontaminating the paste into its transition metals, the acronym A represents a step with a non-peroxygenated acid and the acronyms P represent a step with alkaline hydrogen peroxide.
• QPA represents a step of decontaminating the paste into its transition metals
• the acronym A represents a step with a non-peroxygenated acid
• the acronyms P represent a step with alkaline hydrogen peroxide.
• the invention relates to a process for bleaching a chemical pulp by means of a sequence of steps according to which the processing steps are free of chlorinated reagents and the sequence comprises the following steps, carried out in order: QPAP
• chemical paper pulp By chemical paper pulp is meant the pulp having undergone a delignifying treatment in the presence of chemical reagents such as sodium sulfide in alkaline medium (kraft or sulfate cooking), sulfur dioxide or a metal salt of sulfurous acid in an acid medium (cooking with sulfite or bisulfite).
• chemical reagents such as sodium sulfide in alkaline medium (kraft or sulfate cooking), sulfur dioxide or a metal salt of sulfurous acid in an acid medium (cooking with sulfite or bisulfite).
• the invention is particularly intended for pasta which has undergone kraft cooking or sulphite cooking.
• All types of wood used for the production of chemical pulp are suitable for implementing the process of the invention and, in particular those used for kraft and sulfite pulp, namely resinous woods, for example, various species of pines and firs and deciduous woods such as, for example, beech, oak, eucalyptus and hornbeam.
• the first step is a step of decontaminating the pulp into its transition metals (step Q).
• step Q consists in treating the pulp with at least one sequestering agent such as an inorganic phosphate or polyphosphate, such as, for example, a pyrophosphate or an alkali metal metaphosphate, a poly- carboxylate or an organic aminopolycarboxylate such as, for example, tartaric, citric, gluconic, ethylene-diaminetetraacetic, diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly- ⁇ -hydroxy-acrylic acid and its salts or an organic polyphosphonate ethylenediaminetetramethylenephosphonic acids, diethylene-triaminepenta (methylenephosphonic), cyclohexanediaminetetra-methylenephosphonic and their salts.
• the sequestrant is generally used in step Q in an amount of at most 1.5 g of sequestrant per 100 g of dry pulp. Most often, this amount is at most 1.0 g of sequestering agent for 100 g of dry dough. It is often at least 0.01 g / 100 g of dry paste.
• step Q it is also possible, according to this first variant, to add a small amount of acid in step Q.
• the amount of acid used to do this will generally be adjusted to impose on the medium a pH of approximately 5.
• Step Q can also, according to a second variant, consist of a treatment with an acid free of a sequestrant, followed by an addition of soluble magnesium salt in an amount such that the weight ratio of the amount of Mg to that of Mn present in the dough is at least 30. It is also generally not useful that the amount of Mg exceeds that for which the weight ratio Mg / Mn is equal to 10 ⁇ .
• the term “acid” is intended to denote the anhydrides or inorganic acids such as sulfur dioxide and sulfuric, sulfurous, hydrochloric, phosphoric and nitric acids or their acid salts, as well as organic acids such as carboxylic or phosphonic acids or their salts acids.
• Sulfur dioxide or alkali or alkaline earth metal bisulfites are well suited.
• bisulfite is intended to denote the acid salts of sulfurous acid corresponding to the formula Me (HS03) n, in which Me symbolizes a metal atom of valence n, n being an integer having the value 1 or 2.
• the amount of acid to be used will depend on the type of wood and the amount of metallic impurities it contains. In general, an amount of acid will be used such that the pH of the dough is at least about 5 and, preferably, about 5.5. Likewise, the amount of acid will often be adjusted so that the pH does not exceed 7 and preferably not 6.5.
• the pH will be adjusted so as to make the medium appreciably more acidic, that is to say, of pH at most equal to 5 and, preferably, at most equal to 4, 5.
• Stage Q is generally carried out at a pressure close to atmospheric pressure and at a temperature sufficient to ensure efficient consumption of the acid and / or sequestering agent and, at the same time, not too high so as not to degrade the cellulose and not to burden the energy cost of the heating means used work in said step.
• a temperature of at least 40 ° C and preferably at least 50 ° C is suitable.
• it is advantageous that the temperature does not exceed 100 ° C and preferably not 95 ° C. The best results have been obtained at 50-55 ° C.
• step Q The duration of step Q must be sufficient to ensure a complete reaction. Although longer durations have no influence on the delignification rate of the dough as well as on its intrinsic strength qualities, it is not advisable to extend the reaction time beyond that necessary for the completion of the reaction so as to limit the investment costs and the energy costs of heating the dough.
• the duration of the pretreatment can vary within wide limits depending on the type of equipment used, the choice of acid, the temperature and the pressure, for example from approximately 15 minutes to several hours. Times of at least 10 minutes and preferably at least 15 minutes are generally sufficient. Likewise, the pretreatment times generally do not exceed 90 minutes and preferably not 60 minutes. A duration of about 30 minutes has given excellent results.
• Step Q is generally carried out at a paste consistency of at least 2% dry matter and, preferably, at least 2.5% dry matter. Most often, this consistency does not exceed 15 X and preferably not 10%. The consistency of about 3% dry matter has given excellent results.
• the preferred sequence is a sequence
• step P denote steps using alkaline hydrogen peroxide.
• the nature of the alkali must be such that it has good extraction efficiency for the oxidized lignin at the same time as good solubility.
• An example of such an alkali is sodium hydroxide in an aqueous solution.
• the quantity of alkali to be used must be sufficient to maintain the pH at a value of at least 10 and preferably at least 11.
• the amount of alkali must also be adjusted to ensure sufficient consumption of the peroxide at the end of the reaction.
• step P is carried out in the absence of stabilizer, or when sodium silicate is present as stabilizer, amounts of alkali of at least 1 and at most 3 g of alkali per 100 g of dry dough is fine.
• the quantities of alkali will be increased to maintain a pH of at least 10. In this case, quantities of alkali which can go up to the maximum 8 g / 100 g dry paste can be used.
• an amount of hydrogen peroxide of at least 0.3 g H2O2 / 100 g of dry paste and preferably at least 0.5 g / 100 g of dry dough is also generally suitable that the amounts of hydrogen peroxide do not exceed 5.0 g H2O2 / 100 g of dry paste and, preferably, do not exceed 4.0 g / 100 g of dry paste.
• steps P must be adjusted so as to remain at least equal to 50 ° C. and preferably to 70 ° C. It must also not exceed 150 ° C and, preferably, not exceed 135 ° C. A temperature of 90 ° C has given excellent results.
• An advantageous variant of the process according to the invention consists in carrying out at least one of the steps P of the sequence at a high temperature of at least 100 ° C.
• the temperature of this step P is preferably at least 110 ° C. It generally does not exceed 140 ° C and preferably not 135 ° C.
• the duration of steps P must be sufficient for the bleaching reaction to be as complete as possible. However, it cannot exceed this reaction time too strongly, otherwise the demotion of the whiteness of the dough will be reduced. In practice, it will be set at a value of at least 60 minutes and, preferably, at least 90 minutes. It should also most often not exceed 600 and, preferably, 500 minutes.
• steps P is generally chosen to be less than or equal to 50% by weight of dry matter and, preferably, 40% of dry matter. It will often not be less than 5% and preferably not less than 8 SI. A consistency of 10% has given good results.
• the consistency of the last step P can, as a variant, be advantageously chosen from high values of at least 25% by weight of dry matter and, preferably, 30% or more.
• the consistency of the other steps P will generally be at most 20 X. It will also be most often necessary for the consistency of the other steps P to be at least 8 X.
• step A is a step of treatment with a non-peroxygenated acid.
• non-peroxygenated acid is intended to denote any inorganic or organic acid whose molecule does not contain the peroxy group -0-0-. All the usual inorganic or organic acids used in aqueous solution, alone or as a mixture are suitable. Strong inorganic acids such as, for example, sulfuric, phosphoric, nitric or hydrochloric acid are well suited. Sulfuric acid in aqueous solution has given excellent results.
• step A The operating conditions of step A must be determined in each particular case depending on the type of pulp and the type of wood used.
• Especially advantageous pHs are those of at least about 2.5 and at most about 5.5.
• Temperature and pressure are not critical, atmospheric pressure and temperatures of at least 10 ° C to at most 100 ° C generally suitable.
• the duration of the pretreatment can vary within wide limits depending on the type of equipment used, the choice of acid, the temperature and the pressure, for example from approximately 30 minutes to several hours.
• the amount of magnesium that can be added does not exceed 0.4 g of magnesium per 100 g of dry paste and, preferably, 0.1 g / 100 g of dry paste.
• an Mg salt When an Mg salt is introduced, its amount is at least 0.005 g / 100 g of dry paste.
• step A can consist of a simple washing of the dough using an acidic aqueous solution.
• this acidic washing can be inserted between the two steps P.
• Another variant of the process according to the invention consists in repeating steps P and A a second time so as to achieve the complete sequence Q P A P A P.
• the sequence can be preceded by an oxygen step (step 0).
• This oxygen step is carried out by bringing the paste into contact with gaseous oxygen under a pressure of at least 20 kPa and at most 1000 kPa in the presence of an alkaline compound in an amount such as weight of alkaline compound relative to the weight of dry pulp, ie at least 0.5 and at most 5 X.
• a particular embodiment of the method consists in recycling all or part of the effluents from the second and / or third step P to a step P located earlier in the sequence.
• a similar recycling of the effluents from the second acid step, when it is present, to the first acid step of the sequence can also be carried out. It is also possible to combine, in the same sequence, the recycling of the effluents from steps P to a preceding step P and that of the effluents from an acid step to an preceding acid step. This recycling has the advantage of saving the chemicals used by recovering the unused reagent.
• the temperature of the oxygen step should generally be 70 ° C or more and preferably at least 80 ° C. This temperature should also not exceed 130 ° C and preferably should not exceed 120 ° C.
• the duration of the oxygen treatment must be sufficient for the reaction of the oxygen with the lignin contained in the paste to be complete. However, it cannot exceed this reaction time too strongly, otherwise it will cause deterioration in the structure of the cellulose chains of the pulp. In practice, it will be 30 minutes or more and, preferably, at least 40 minutes. Usually it will not exceed 120 minutes and preferably will not exceed 80 minutes.
• the treatment of the pulp with oxygen can also be done in the presence of a cellulose protective agent such as the soluble magnesium salts, organic sequestering agents such as polycarboxylic or phosphonic acids.
• a cellulose protective agent such as the soluble magnesium salts, organic sequestering agents such as polycarboxylic or phosphonic acids.
• Magnesium salts are preferred, in particular, magnesium sulfate heptahydrate used in an amount of 0.02 to 1% by weight relative to the dry paste.
• the consistency of the paste in step 0 is generally not less than 8% by weight of dry matter and, preferably, not less than 10 X. This consistency usually does not exceed 30 X by weight of dry matter and preferably 25 X.
• step 0 can also be carried out in the presence of hydrogen peroxide (step Op).
• the amount of hydrogen peroxide which can be incorporated in step 0 is generally not less than 0.2 g H2O2 per 100 g of dry paste and, most often, not less than 0.5 g. Likewise, we will usually not exceed 2.5 g H2O2 per 100 g of dry paste and, most often, not 2 g.
• the first step P can also be reinforced by the presence of gaseous oxygen (step Eop).
• the oxygen pressure used will most often be at least 20 kPa and at most 1000 kPa.
• an additional enzymatic step consisting in treating the dough with at least one enzyme can be incorporated at any point in the sequence of treatment steps.
• This enzymatic treatment can also be carried out before or after the stage of oxygen pretreatment.
• enzyme is intended to denote any enzyme capable of facilitating the delignification, by the treatment steps subsequent to the treatment step with the enzyme, of an unbleached chemical paper pulp originating from the cooking operation or from a chemical paper pulp that has already been subjected to an oxygen treatment step.
• an alkalophilic enzyme will be used, that is to say an enzyme whose maximum efficiency is located in a zone of alkaline pH, and very particularly at a pH of 7.5 and above.
• a category of enzymes well suited to the process according to the invention are hemicellulases. These enzymes are capable of reacting with hemicelluloses on which the lignin present in the dough is fixed.
• the hemicellulases used in the process according to the invention are xylanases, that is to say heicellololytic enzymes capable of cutting the xylan bonds which constitute a major part of the interface between lignin and rest of the carbohydrates.
• xylanase in accordance with the process according to the invention is 1, - ⁇ -D-xylane xylanohydrolase, EC 3.2.1.8.
• the xylanases preferred in the methods according to the invention can be of various origins. In particular, they may have been secreted by a wide range of bacteria and fungi.
• Xylanases of bacterial origin are particularly interesting.
• the xylanases secreted by bacteria of the genus Bacillus have given good results.
• Xylanases derived from bacteria of the genus Bacillus and of the species pumilus have given excellent results. Of these, xylanases from Bacillus pumilus PRL B12 are particularly interesting.
• the xylanases of Bacillus pumilus PRL B12 according to the invention can come directly from a strain of Bacillus pumilus PRL B12 or a host strain of a different microorganism which has previously been genetically engineered to express the genes coding for the degradation of xylans from Bacillus pumilus PRL B12.
• a purified xylanase will be used which does not contain other enzymes.
• the xylanase according to the process according to the invention does not contain cellulase so as not to destroy the polymeric cellulose chains of the pulp.
• An interesting variant of the process according to the invention consists in carrying out the enzymatic step X in the presence of at least one sequestering agent of metal ions.
• the metal ion sequestrants can advantageously be chosen from the sequestrants suitable for step Q which are described above.
• the process according to the invention applies to the bleaching of all kinds of chemical pulp. It is well suited for deli ⁇ gnifying kraft and sulfite pastes. It is particularly well suited for processing kraft pasta.
• step Q step with DTPA (step Q): DTPA content, g / lOOg paste dry: 0.2 temperature, degrees C: 90 duration, min: 60 consistency, X by weight of dry matter: 4
• 2nd stage hydrogen peroxide stage (stage P): H2O2 content, g / 100g dry paste: 5 NaOH content, g / 100g dry paste: 4 DTMPANay content, g / lOOg of dry paste 0 to 1 MgS ⁇ -7H2 ⁇ content, g / lOOg dry paste at 0.5 temperature, degrees C: 90 and 120 duration, min: 120 consistency, X by weight of dry matter 10 where DTMPANay represents the heptasodium salt of diethylene triaminepenta acid (methylene phosphonic).
• the contents of DTMPANa and the temperatures used in each of the examples IR to 8R were as follows:
• the paste was washed with demineralized water at room temperature.
• Example 9 (in accordance with the invention) The same dough sample as in Examples IR to 8R was bleached according to the QPA P sequence. The operating conditions carried out were as follows: step: step with DTPA (step Q) :
• H2SO4 (for pH 5): 0.54 DTPA content, g / lOOg dry paste: 0.2 temperature, degrees C: 90 duration, min: 60 consistency, X by weight of dry matter: 4
• 2nd stage hydrogen peroxide stage (stage P): H2O2 content, g / lOOg dry paste: 3 NaOH content, g / lOOg dry paste: 4 DTMPANay content, g / lOOg dry paste: 0.25 temperature, degrees C: 120 duration, min: 120 consistency, X by weight of dry matter: 10 3rd step: sulfuric acid step (step A):
• step P step with hydrogen peroxide (step P): H2O2 content, g / lOOg dry paste: 2 NaOH content, g / lOOg dry paste: 1.7 Na silicate content 38 ° Bé, g / lOOg dry paste: 3 MgS ⁇ 4.7H2 ⁇ content, g / lOOg dry paste: 1 temperature, degrees C: 120 duration, min: 180 consistency, X by weight of dry matter: 30
• the paste was washed with demineralized water at room temperature.
• the kappa index and the whiteness of the dough were determined.
• step 0 step with oxygen
• step 0 pressure, bar: 6 content in NaOH
• g / lOOg dry paste 4 MgS ⁇ 4.7H2 ⁇ content
• g / lOOg dry paste 0.5 temperature, degrees C: 120 duration, min: 60 consistency
• step DTPA step Q: DTPA content, g / lOOg dry paste: 0.12 temperature, degrees C: 55 duration, min: 30 consistency, X by weight of dry matter: 3
• step P step with hydrogen peroxide (step P) H2O2 content, g / lOOg dry paste: 3 NaOH content, g / lOOg dry paste: 4 DTMPANay content, g / lOOg dry paste: 0.25 content in MgSO4.7H2 ⁇ , g / 100g dry paste: 1 temperature, degrees C: 120 duration, min: 120 consistency, X by weight of dry matter: 10 where DTMPANay represents the heptasodium salt of diethylene triaminepenta acid (methylenephosphonic acid).
• stage P hydrogen peroxide stage
• stage P hydrogen peroxide stage
• g / lOOg dry paste 1 NaOH content
• g / lOOg dry paste 1.5 M
• S en -7H2 ⁇ content g / lOOg dry paste
• Temperature 1 temperature
• degrees C 120 duration
• min 180 consistency
• X by weight of dry matter 30
• the paste was washed with demineralized water at room temperature.
• step 0 oxygen step (step 0): pressure, bar: 6 NaOH content, g / 100g dry paste: 4 MgS ⁇ 4-7H2 ⁇ content, g / lOOg dry paste: 0.5 temperature, degrees C: 120 duration, min: 60 consistency, X by weight of dry matter: 12
• DTPA stage (stage Q): DTPA content, g / lOOg dry paste: 0.12 temperature, degrees C: 55 duration, min: 30 consistency, X by weight of dry matter: 3
• 3rd stage hydrogen peroxide stage (stage P): H2O2 content ,. g / lOOg dry paste: 3 NaOH content, g / lOOg dry paste: 4 DTMPANay content, g / lOOg dry paste: 0.25 MgS ⁇ 4-7H2 ⁇ content, g / lOOg dry paste: 1 temperature, degrees C: 120 duration, min: 120 consistency, X by weight of dry matter: 10 where DTMPANay represents the heptasodium salt of diethylene triaminepenta acid (methylene phosphonic).
• step A step with an acid
• step A H2SO4 content, g / 100g dry paste:
• step A H2SO4 content, g / 100g dry paste:
• step A H2SO4 content, g / 100g dry paste:
• step A H2SO4 content, g / 100g dry paste:
• step A H2SO4 content, g / 100g dry paste:
• step A H2SO4 content, g / 100g dry paste:
• step B H2SO4 content, g / 100g dry paste:
• Example 11 1.08 (pH 3)
• Example 12 0.52 (pH 5)
• step P step with hydrogen peroxide (step P): H2O2 content, g / lOOg dry paste: 1 NaOH content, g / lOOg dry paste: 1.5 Na silicate content 38 ° Bé, g / lOOg of dry paste: 3 MgS ⁇ 4-7H2 ⁇ content, g / lOOg dry paste: 1 temperature, degrees C: 120 duration, min: 180 consistency, X by weight of dry matter: 30
• the paste was washed with demineralized water at room temperature.
• the kappa index and the whiteness of the dough were determined.
• the same pulp sample as in Examples IR to 14 was bleached using the sequence 0 XQPAP by using in step X an amount of xylanase derived from Bacillus pumilus PRL B12 corresponding to 10 XU / g of dry pulp .
• the XU Xylanase Unit
• the XU is defined as being the quantity of xylanase which, under the conditions of the test, catalyzes the release of reducing sugars equivalent, in reducing power, to 1 micromole of glucose per minute.
• step 0 oxygen step
• step 0 pressure
• bar 6 NaOH content
• g / 100g dry paste 4 MgS ⁇ .7H2 ⁇ content
• g / lOOg dry paste 0
• 5 temperature, degrees C 120 duration
• min 60 consistency
• X by weight of dry matter 12
• step X enzyme step
• step P step with hydrogen peroxide (step P): H2O2 content, g / lOOg dry paste: 4 NaOH content, g / lOOg dry paste: 4 DTMPANay content, g / 100g dry paste: 0.25 MgS ⁇ 4.7H2 ⁇ content, g / 100g dry paste : 1 temperature, degrees C: 120 duration, min: 120 consistency, X by weight of dry matter: 10 where DTMPANay represents the heptasodium salt of diethylene triaminepenta (methylene phosphonic) acid.
• stage A sulfuric acid stage
• stage B hydrogen peroxide stage
• step P hydrogen peroxide stage
• step P H2O2 content
• g / lOOg dry paste 1 (Ex. 15) and 2 (Ex.
• the kappa index and the whiteness of the dough were determined.

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Citations (3)

• 1993
  • 1993-11-04 BE BE9301215A patent/BE1007700A3/fr not_active IP Right Cessation
• 1994
  • 1994-10-28 AT AT94931026T patent/ATE166118T1/de not_active IP Right Cessation
  • 1994-10-28 WO PCT/EP1994/003591 patent/WO1995012709A1/fr not_active Application Discontinuation
  • 1994-10-28 NZ NZ274852A patent/NZ274852A/en unknown
  • 1994-10-28 AU AU79940/94A patent/AU7994094A/en not_active Abandoned
  • 1994-10-28 CA CA002175817A patent/CA2175817A1/fr not_active Abandoned
  • 1994-10-28 DE DE69410286T patent/DE69410286T2/de not_active Revoked
  • 1994-10-28 EP EP94931026A patent/EP0726979B1/de not_active Revoked
  • 1994-10-28 BR BR9407976A patent/BR9407976A/pt not_active Application Discontinuation
  • 1994-10-28 JP JP7513015A patent/JPH09507096A/ja active Pending
  • 1994-10-28 ES ES94931026T patent/ES2119234T3/es not_active Expired - Lifetime
  • 1994-10-31 ZA ZA948562A patent/ZA948562B/xx unknown
  • 1994-11-04 MA MA23689A patent/MA23365A1/fr unknown
• 1996
  • 1996-05-03 FI FI961895A patent/FI961895A0/fi unknown
  • 1996-05-03 NO NO961817A patent/NO961817L/no unknown

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