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
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
• • 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
• • 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
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/02—Agents for preventing deposition on the paper mill equipment, e.g. pitch or slime control

Definitions

• the present invention relates to talc- and/or chlorite-based compositions and their use in papermaking industry processes.
• Paper is made from aqueous suspensions containing cellulose fibers which, floating on the free surface of the suspension, form a felt; this is then transformed into the final sheet by means of calendering and drying processes.
• the initial suspensions normally contain intentionally added additives, or impurities known in the field as "stickies".
• the latter may be, for example, resin particles extracted from wood fiber, if new raw material is used; or particles of glue, ink, latex or the like if (as increasingly more common) recycled paper is used.
• Larger size stickies (generally known in the field as “macro- stickies”) may be removed by means of mechanical procedures.
• small-sized stickies (“micro-stickies) may not be removed from the aqueous suspension by means of mechanical procedures.
• micro-stickies in the suspension may aggregate forming larger size particles, which may cause serious problems during the subsequent steps of manufacturing paper sheets, soiling the wires and the felts used in these productions, creating deposits and therefore stains on the sheet, or in the case of adhesion to the calendering rollers, even causing the breakage of the sheet.
• Micro-stickies may be removed, or at least made inert, by adding chemical additives or appropriate enzymes to the aqueous suspension.
• the first may however give rise to environmental impact issues, and may interfere with the chemism of the downstream processes.
• the enzymes instead, have the drawbacks of having selective efficiency on the various types of stickies (thus not ensuring good removal results with all types of micro-stickies), of being slow-acting and having sensitive efficiency with respect to variations of parameters, such as pH and temperature.
• An alternative method of removing micro-stickies is by using mineral powders.
• Suitable minerals for the purpose are micronized talc and chlorites.
• Talc and chlorites are minerals with similar chemical-physical features, and are often associated in ore deposits; both minerals, and mixtures thereof in any proportion, are suitable for the purposes of the present invention.
• talc talc only
• Talc powders of size smaller than 40 micrometers ( ⁇ m) are generally used as starting material for producing micronized talc.
• powders are introduced into high pressure and high speed air flows, and by making the flows from opposite directions collide with one another, a breakage due to particle impacts is obtained to form powders of smaller size. It is further possible to use other techniques, such as ball-tube mills, hammer mills, etc. This process is named “dry micronization” in the field; powders of a few micrometers in size are obtained in this way.
• micronized talc is widely used for the removal of micro- stickies, its efficacy is not optimal; tests carried out by the inventors demonstrated that in order to halve the amount of micro-stickies in a suspension in this way, it is needed an amount of talc of approximately 2% by weight (b.w.) with respect to the weight of cellulose.
• average diameter means a value indicated as D 50 , corresponding to the value according to which 50% b.w. of the particles have a diameter smaller than the indicated value; another value commonly indicated for briefly representing the size distribution of powder particles is value D 98 , i.e. the diameter value such that the size of 98% b.w. of the particles is smaller than such a diameter. Since talc particles are not spherical, diameter in this case means the equivalent diameter, i.e. the diameter of a sphere of equal weight
• - figure 1 diagrammatically shows a talc wet grinding system
• - figure 2 shows a graph illustrating stickies removal test results of three samples of compositions prepared according to the invention
• - figure 3 shows a graph illustrating stickies removal test results of a composition according to the invention and of two additives of the known art.
• talc be wet ground.
• Other minerals may be further associated, mainly carbonates and/or quartz.
• a raw material with various degrees of purity may be used as starting material, from rocks having a talc and chlorite content higher than 90%, to "soap-rock" containing from about 55 to 90% b.w.
• Said raw material may be as extracted from the mine or may be "pre-processed", i.e. obtained from mined material, e. g. following concentration by means of flotation.
• the raw material is first mechanically ground, to obtain powders of maximum size preferably smaller than 50 ⁇ m. These powders are then dispersed in water; the dispersion may contain up to about 45% b.w. of powders, and typically their weight content is equal to at least 25%, because at lower contents the product yield per grinding cycle is low, and therefore the process becomes economically not convenient; preferably, the dispersion contains at least 35% b.w. of said powders.
• talc powders in the dispersion it is also possible to further increase the charge of talc powders in the dispersion, thus reaching percentages of about 55% b.w., raising pH by adding NaOH or KOH, or by adding additives known in the field, such as, for example, the commercial products Lumiten ® PT or Polisalz ® S from BASF, wetting additives (e.g. surfactants), in percentages by weight lower than 1% of the total dispersion.
• wetting additives e.g. surfactants
• the dispersion thus obtained is then ground by an appropriate apparatus, e.g. a ceramic ball mill.
• FIG. 1 diagrammatically shows a possible talc wet grinding system.
• System 10 consists of a tank 11 , in which talc and water are introduced in the desired proportions; a pump 12, which allows to recirculate the dispersion in the system; a heat exchanger 13, which avoids the dispersion from overheating upon grinding; and the actual grinding apparatus 14, which may be a ball mill (generally ceramic balls).
• the four components are connected to one another in a closed circuit in which the dispersion moves in the direction of the arrows; the tank 11 is preferably provided with a mixer (e.g. a helical mixer, not shown in the figure) run for the entire duration of the process in order to ensure the homogeneity of the dispersion.
• the heat exchanger 13 is optional and may not be present or excluded from the processing fluid recirculation by means of a by-pass line (not shown), e.g. if the grinding is short and thus the generated amounts of heat are not excessive.
• the wet ground talc may be used in the aqueous dispersion form, as obtained with the above-described process; such dispersions are commonly known as "slurries" in the field.
• water may be removed from the dispersion. It is however preferable not to proceed with a complete drying of the talc; the term "complete drying" in the field does not mean reaching a zero water content; talc is considered completely dried when its humidity content is lower than 0.5% b.w.
• a certain residual degree of humidity in the product is desirable because it ensures an easier re- dispersion thereof in water, feature which is useful for preparing papermaking suspensions.
• the humidity further confers a lower dust content to the product, which improves the features of hygiene both in the departments where the powder is made and where it is used; a complete drying would thus represent a waste of energy which is not justified by the required result.
• the ground talc is dried to a residual degree of humidity comprised between 2 and 8% b.w. of the final product; the residual humidity is monitored during the drying process by taking small amounts of the product and subjecting them to a weight loss test in thermobaiance at 105 0 C which, leading to the complete drying, determines the amount of water present in the sample.
• Various known methods may be used to dry the talc, such as, for example, drying in ventilated ovens, under fixed or fluidized bed conditions, or by atomizing, also called “spray drying", i.e. by atomizing the dispersion in a (generally cylindrical) drying chamber, in which a counterflow of hot air is made on dispersion micro-drops.
• the wet ground talc is used to produce a composition
• a smectite preferably a bentonite.
• an amount of smectite is added to the talc so that its percentage by weight is in the range of 0.1%-5%, and preferably of 1 %-3%, of the talc/smectite mixture.
• the smectite when used in the form of slurry, the smectite has the effect of stabilizing the dispersion of the powders, thus preventing the sedimentation thereof; this effect is particularly advantageous because it avoids the formation of muds on the bottom of the storage or transportation containers, which would then be difficult to be re-distributed to obtain a homogenous dispersion.
• the solid talc/smectite mixtures are preferably used in the form of micro- granules; the presence of smectite has the effect of considerably reducing the tendency of micro-granules to form powders as compared to talc alone, thus protecting the users from inhalation; furthermore, it makes the granules more tough, preserving the shape and therefore the fluidity thereof.
• the talc/smectite mixtures may be obtained using the same previously described talc wet grinding process, adding the desired amount of smectite to the solid load initially fed in the grinding apparatus.
• the sum of the weights of talc and smectite may be in the range of 25%-65%, and preferably of 38%-45%, of the total weight of the dispersion.
• the slurry is dried to maintain a degree of humidity of the final powder in the range of about 2-8% b.w. of the product. Even in this case, the presence of residual humidity ensures the advantage of re-dispersion speed in water already mentioned for talc alone.
• Chemical components known in the formulation of additives for papermaking industry such as cationizing components (e.g. quaternary amines), anionizing components (such as the Lumiten ® PT or Polisalz ® S products from BASF) or strong bases (e.g. NaOH) may be added to either talc used alone or the mixtures with smectite.
• cationizing components e.g. quaternary amines
• anionizing components such as the Lumiten ® PT or Polisalz ® S products from BASF
• strong bases e.g. NaOH
• This example refers to the production of a dispersion comprising talc according to the invention.
• a grinding system of the type diagrammatically illustrated in figure 1 is used; the tank 11 is provided with a helical mixer for continuously homogenizing the dispersion.
• the grinding apparatus 14 is an AHM 200 model agitated bead mill from Hosokawa Alpine AG (Augsburg, Germany), loaded with zirconium oxide beads having a diameter in the range of 0.8-1 mm; the beads occupy about 80% of the internal volume of the grinding chamber, and are actuated by a rotor shaft.
• the dispersion is circulated in the system at a flow speed of 6 l/min by means of pump 12, and the grinding proceeds for 20 minutes; the energy consumed in the process is also monitored, this being an important monitoring parameter.
• the grinding is then interrupted, a fraction of the dispersion is collected and its pH and viscosity features at 22 °C are measured, using a Brookfield DV-I+ Viscometer with impeller number 2, both at a rotation speed of 10 rpm and of 100 rpm.
• Another dispersion fraction is collected and dried, and the powder thus obtained is characterized to measure its average diameter (D 50 ), by means of the aforementioned SediGraph 5120 instrument, and the specific surface thereof, by means of a BET gauge.
• the test results are shown in Table 1.
• EXAMPLE 2 This example relates to the production of a dispersion comprising talc and smectite according to the invention.
• Example 2 The test in example 2 is repeated, in this case continuing the grinding for 60 minutes.
• a dispersion fraction and a powder fraction are characterized as described in example 1 (in this case, viscosity at 100 rpm could not be measured, being too high for the reading scale of the instrument); the results are shown in Table 1.
• Table 1 Table 1
• the stickies removal features from papermaking aqueous suspensions using the dispersions of the invention are evaluated.
• a series of aqueous suspensions of de-inked cellulose (from recycled paper) taken from a paper mill is prepared; each suspension contains 5% b.w. of cellulose.
• compositions of the invention are produced in the form of aqueous dispersions, by diluting the fractions of liquid dispersions prepared in examples 1 , 2, 3 and 4 with water to obtain a concentration of 10% b.w. of solids.
• Different volumes of the dispersions according to the invention are added to each cellulose aqueous suspension, to obtain suspensions which respectively contain 0.5%, 1.0%, 1.5% and 2.0% b.w. of solids of the composition of the invention with respect to the weight of cellulose (a series is produced for each of the dispersions in examples 1-4).
• the cellulose suspensions thus produced are stirred by means of a helical stirrer for 1 minute and then left to rest for 5 minutes; at the end of the procedure, the number of particles of stickies present in each suspension is evaluated; Allen's hemocytometer method is used, which includes counting the number of particles in a known volume of liquid deposited in a specific cell under optical microscope; the number of particles is then normalized to 1 cubic centimeter. The same method is used to evaluate the number of particles present in a comparative sample, consisting in the cellulose suspension alone. The results of the measurements carried out on samples with the dispersion of the invention and on the comparative sample (0%) are shown in Table 2. The test results are also provided in the form of a graph in figure 2.
• a new series of aqueous suspensions of de-inked cellulose taken from a paper mill is prepared, as described in example 5.
• Cellulose suspensions are filled with variable amounts (equal to those in example 5) of the dispersions T and Tc, and with variable amounts of the dispersion prepared in example 3.
• the procedure of stirring, resting and measuring the number of stickies described in example 5 is repeated on the suspensions thus obtained, as well as on a suspension of cellulose only.
• the results are shown in Table 3 and in the form of a graph in figure 3.
• This example refers to a drying test of a composition sample of the invention.
• a fraction of the aqueous dispersion prepared as shown in example 3 is subjected to drying, by means of the spray-drying technique.
• the dispersion having an initial density of 1.312 g/l and a water content of 62.5% b.w., is fed at 25 0 C into an ATM-6 laboratory atomizer from Sacmi lmola S. C. (Imola (BO), Italy) which atomizes it into a treatment tower, in which air at about 350 0 C is introduced; a slight vacuum of 10 hectopascals (hPa) is maintained in the tower to segregate the powders inside.
• the residual humidity of the product obtained from the process, which at the tower outlet has a temperature of 60 0 C and appears in micro-granular form, is measured by means of thermo-gravimetric analysis and results equal to 6% b.w. of the sample.
• micro-granular product is subjected to a vibrating sieve test to define the grain size distribution; the results are shown in Table 4.
• This micro-granular product has a low dust content and a high fluidity, despite the residual humidity; furthermore, it is easily dispersible in water under stirring.
• a sample of talc produced as described in example 1 is dried with the procedure described in example 7, until a degree of residual humidity of 3% is obtained.
• the talc thus produced is tested as shown in the procedure of example 5, i.e. by adding it to a series of aqueous suspensions, each containing 5% b.w. of de-inked cellulose from recycled paper; the granular talc is added until suspensions are obtained, which contain respectively 0.5%, 1.0%, 1.5% and 2.0% b.w. of solid with respect to the weight of cellulose.
• the stickies removal test results are shown in Table 5.
• test in example 8 is repeated, using this time a sample of the talc/bentonite composition produced as described in example 4.
• the test results are shown in Table 5.
• a talc dispersion made according to the invention has considerably higher stickies removal features than the two dispersions (T and Tc) normally used in the field, produced according to known methods.
• the data in table 5, relating to the use of compositions dried before use, show stickies removal values comparable to those of the dispersion of example 3.
• the comparison of data in tables 2 and 3 further shows that even the least effective sample made according to the invention (sample of example 2) has stickies removal features either similar to (with low charge by weight of the inventive composition as compared to the cellulose to be treated) or higher than (with charge equal to or higher than 1 % b.w. as compared to the cellulose to be treated) the two comparative samples T and Tc.

Landscapes

• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=41059951

Family Applications (1)

Country Status (2)

Cited By (1)

Family Cites Families (10)

• 2008
  • 2008-12-15 WO PCT/IT2008/000763 patent/WO2010070682A1/en active Application Filing
  • 2008-12-15 EP EP08876126A patent/EP2376707A1/de not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events