Classifications

• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/70—Inorganic compounds forming new compounds in situ, e.g. within the pulp or paper, by chemical reaction with other substances added separately
• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/675—Oxides, hydroxides or carbonates

Definitions

• the present invention relates to a process for manufacturing a paper sheet comprising calcium carbonate in the form of calcite.
• papers include mineral fillers on the one hand to lower their costs, the fillers being less expensive than cellulosic fibers and on the other hand to provide or improve certain physical and mechanical characteristics.
• Kaolin, talc, titanium oxide, aluminum hydroxide, satin white, calcium carbonate in ground or precipitated form are used in particular as fillers.
• these charges are prepared ex-situ for the manufacture of paper; they are incorporated into the paper fibers and retained thanks to the addition of retention agents.
• the development of papermaking in an alkaline medium to ensure the permanence of the paper to promote the use of calcium carbonate.
• Calcium carbonate has several crystallographic forms. The most stable and usual form is calcite, another slightly less common form is aragonite, the least stable form is vaterite. The calcite and aragonite crystals are rhombohedral in shape while the vaterite crystals are spherical in shape.
• Papermaking processes have been proposed which make it possible to precipitate calcium carbonate in situ on papermaking fibers and to fix them without adding a retention agent. Such methods have in particular been described in the patents mentioned below.
• the calcium carbonate crystals are fixed to the fibers and a high level of retention is obtained compared to the addition of calcium carbonate in a paper composition which requires retention. This process takes place in a diluted medium characteristic of the paper process.
• the object of the present invention is to provide a paper sheet comprising calcium carbonate in its widespread form of calcite and with an improved appearance.
• the Applicant has demonstrated that it is possible to act on the crystallographic forms of calcium carbonate by using the in situ precipitation process of calcium carbonate by varying the order and the durations of bringing the various compositions into contact. clearance to precipitate and fix in situ the calcium carbonate on the fibers during the manufacture of a sheet of paper.
• the invention provides a method for manufacturing a sheet of paper comprising paper fibers and calcium carbonate mainly in the form of calcite crystals directly linked to the paper fibers, which is characterized in that it comprises the following steps:
• an aqueous composition comprising calcium hydrogenocarbonates and / or hydrated and / or dissolved carbon dioxide, an aqueous composition comprising calcium hydroxide, so as to precipitate calcium carbonate in the form of vaterite crystals,
• vaterite crystals are left to transform into calcite crystals in contact with the fibers, - then this mixture containing the calcite crystals attached to the fibers is sent to the canvas of the paper machine for draining and formation of the paper sheet,
• the process for manufacturing the sheet is characterized in that the composition comprising calcium hydroxide is added after that comprising calcium hydrogenocarbonates and / or hydrated and / or dissolved carbon dioxide
• the process for manufacturing the sheet is characterized in that the composition comprising the calcium hydrogenocarbonates results from a mixture in aqueous medium on the one hand of recycled calcium carbonate and on the other hand of carbon dioxide.
• the recycled calcium carbonate comes from recycled paper products, in particular from recycled paper fibers and / or from recycled white water.
• the recycled white water comes from the drainage water from the fibrous suspension on the canvas of the paper machine. They include fine elements, in particular fillers such as calcium carbonate and possibly other alkaline or alkaline-earth compounds and cellulosic fibers (called "fines") not retained on the canvas, these fibers themselves comprising fillers.
• fines cellulosic fibers
• Like others possible sources of recycled paper products there are recycled paper fibers from old paper, in particular de-inked and then possibly bleached, from recycled broken paper, these products also containing fillers such as calcium carbonate and possibly other alkali or alkaline- earth. Another source could be de-inking sludge or other paper sludge.
• carbon dioxide is added at different places in the circuit of the paper machine.
• this addition is made before the point of addition of the calcium hydroxide in order to ensure the dissolution of the gas and therefore then to promote the speed of the reaction with the calcium hydroxide to form the precipitate of the vaterite crystals.
• carbon dioxide is added to the white water recycling circuit of the paper machine.
• carbon dioxide carbon dioxide
• the method is characterized in that this addition of said gaseous carbon dioxide takes place between the point of reception of white water under canvas of the paper machine and the mineralizer. This promotes the total dissolution of the gas before reaction with calcium hydroxide. Indeed, it is preferable that carbon dioxide is added to the white water recycling circuit so that it is completely dissolved, in free form, hydrated or in the form of calcium hydrogen carbonates or other alkali or alkaline- earthy depending on the presence of such ions.
• An advantage of this process is not to put the fibers in contact with alkaline product, which improves the homogeneity of the paper, called epair, because in alkaline medium the fibers tend to agglomerate. During the recrystallization of the carbonate in the presence of fibers, the medium remains neutral, hence better effectiveness of the bonding agents and of the optical agents, sensitive to the alkaline pH.
• An advantage of this process by introducing carbon dioxide at the start of the circuit (optimal point of dilution to hydrate the gas) and in a tool suitable for mineralization of water, is that one can more easily use a gas poor in C0 2 , recovered from boiler or lime kiln, in order to transform it into calcium hydrogen carbonate.
• the method is characterized in that the carbon dioxide is introduced in the form of dilute carbon dioxide, in particular boiler or lime kiln fumes containing 8 to 25% of C0 2 .
• the molar ratio of carbon dioxide to calcium hydroxide is equal to approximately 1, therefore stoichiometric.
• the method according to the invention is characterized in that the dilution rate of the paper fibers in the final reaction mixture is between 0.1 and 5% by weight, preferably between 0.2 and 1.5% .
• the method according to the invention is characterized in that the composition comprising calcium hydroxide is an aqueous suspension of solid particles of said calcium hydroxide, called lime milk.
• the process according to the invention is characterized in that the calcium hydroxide is in the form of an aqueous suspension of solid particles having a particle size of less than 10 ⁇ m, preferably between 0.5 and 2 ⁇ m, in particular on the order of 1 ⁇ m.
• the process according to the invention is characterized in that the paper sheet obtained comprises at least 10%, preferably at least 20%, of calcium carbonate of the calcite type thus precipitated.
• FIGS 1 to 3 schematically describe particular cases of this process, the relative proportions not being respected with respect to the real scale.
• FIG. 1 a process according to which a composition of calcium hydrogen carbonate (5) is introduced into an aqueous medium to which a suspension of calcium hydroxide (4) is added in order to precipitate the vaterite crystals and then immediately added virgin paper fibers (2) and / or recycled paper fibers (2 ') and the vaterite crystals are left to transform into calcite crystals on contact with the fibers, then the sheet (6) is formed and drained on the paper machine (M).
• M paper machine
• FIG. 2 is shown a process according to which carbon dioxide (3) is introduced into the white water recycling circuit (1) and then a suspension of calcium hydroxide (4) is added in order to precipitate the vaterite crystals and then we immediately add virgin paper fibers (2) and / or recycled paper fibers (2 ') and the vaterite crystals are left to transform into calcite crystals on contact with the fibers, then the sheet (6) is formed and drained on the machine paper (M).
• M machine paper
• FIG. 3 shows the simplified diagram of a detailed, nonlimiting example, describing the manufacture of a paper (6) loaded with 26% calcium carbonate mainly in calcite form, according to the following mode:
• the average composition of the suspension of virgin fibers (2) and recycled paper (2 ') includes 28 g / 1 of virgin fibers and 16 g / 1 of recycled paper from the same production which itself comprises 12 g / 1 of fibers and 4 g / 1 of calcium carbonate (recycled).
• the average composition of recycled white water (1) includes 1 g / 1 of fibers and 1 g / 1 of calcium carbonate (recycled).
• a quantity of carbon dioxide (3) equal to 440 kg is introduced into the short closed circuit. / h of C0 2 .
• a lime milk (4) is added at a flow rate of 7.4 m 3 / h, containing 100 g / 1 of calcium hydroxide of very fine particle size, approximately 1 ⁇ m, and lastly the suspension containing the virgin fibers (2) and the recycled paper (2 ') is introduced.
• the gas reacts almost instantly with the milk of lime to form in suspension in water unstable vaterite crystals between point a and b, then after mixing with the fibrous suspension (2,2 ') and before reaching the body At the top, the vaterite crystals turn into stable calcite.
• the suspension of fibers and fillers is then sent to the fabric of the paper machine (M) for draining and forming the sheet.
• M paper machine
• the pH of the suspension is stabilized at its final value, adjustable between 7 and 8 depending on the desired value, which corresponds to a carbon-carbon balance of the waters.
• the high opacity of the sheet (6) is obtained thanks to the very regular distribution of the crystals attached to the fibers without the aid of a retention agent and without variation in pH. Compared to a conventional charge retention process with the formation of aggregates using a retention agent, the gain in opacity is 3 to 4 points.
• Example according to the prior art A sheet according to the prior art of a calcium carbonate precipitated in situ is produced, by mixing the compounds at the same time without precisely adding the paper fibers last and without adding them immediately after having carried out the precipitate of calcium carbonate.
• the sheet obtained according to the invention comprises crystals of calcite better distributed than those in the sheet prepared according to the prior art, and therefore that the appearance of said sheet according to the invention is improved.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Paper (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8860147

Family Applications (1)

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Cited By (2)

Families Citing this family (3)

Family Cites Families (20)

• 2001
  • 2001-02-16 FR FR0102186A patent/FR2821095B1/fr not_active Expired - Fee Related
• 2002
  • 2002-02-14 EP EP02706858A patent/EP1373637A1/de not_active Withdrawn
  • 2002-02-14 US US10/467,461 patent/US7504000B2/en not_active Expired - Fee Related
  • 2002-02-14 WO PCT/FR2002/000574 patent/WO2002066735A1/fr not_active Application Discontinuation
  • 2002-02-15 AR ARP020100519A patent/AR032698A1/es unknown

Non-Patent Citations (1)

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