FI81157B - Process for the manufacture of a fibre web using a paper manufacturing technique - Google Patents

Description

81157

The present invention relates to a new method for producing a fibrous web by a papermaking process, with the aim of obtaining an overall improvement in retention properties, in particular opacification. them in relation to the prior art. The invention also relates to a fibrous web obtained by this method in the form of a new industrial product.

This new method can be used especially in the production of paper and board, especially in the printing / writing, packaging, surface materials and specialty paper sectors. It is particularly advantageous in connection with the retention of mineral fillers, such as opacifiers, thereby improving the opacity, in particular the opacity contrast and the opacity for the oil.

It is known that the applicant has already recommended in FR Patent 2,492,425 a method of making a fibrous web by a papermaking process in which a mixture of mineral filler and organic binder is pre-flocculated before it is added to the stern of a paper machine by reinforcing fibers previously treated with an anionic polymer. ), to the aqueous suspension, after which the flocculant is added to the aqueous suspension formed upstream of the headbox, which contains the fibers, the mineral filler and the binder. This method allows retention to be increased relative to conventional or other papermaking techniques known in the art.

According to the invention, a new method is proposed which gives even better results than the method described in the above-mentioned FR-2 81157 patent publication 2 492 425, in particular as regards retention. According to the invention, the improvement in retention results from the application of special operating conditions: - optimization of the average diameter of the filler / binder flocs, and - limitation of contact times upstream of the filler between the filler / binder flocs and fibers and flocculants and fiber / filler / binder mixture.

As a further feature of the invention, the proposed new method is particularly advantageous for improving the retention of opacifiers.

Titanium oxide, especially rutile and anatase, is an opacifying and bleaching pigment known to be commonly used in paints, inks, plastics, paper and board, cosmetics and ceramics due to its good opacity due to its high refractive index and its UV radiation.

The unreasonably rising price of TiO2 (currently in the range of 10-11 FF / kg) has led users to consider other alternative solutions. In the paper industry, attempts to replace titanium oxide with a mixture of TiO 2 and some other more economical mineral filler selected from the group consisting of talc, kaolin, aluminum hydroxide, and CaCOg have proved unsatisfactory in terms of opacity and retention.

According to FR patent application 84 19957 (TALCS DE LUZENAC) filed on 26 December 1984, a new opacifying pigment is recommended, which is particularly valuable due to its opacity contrast and in particular its opacity to oil. This opacifying pigment consists of a mixture of 10-70% by weight of TiO 2 and 30-90% by weight of an excipient selected from lamellar silicates, obtained by grinding TiO 2 together with said lamellar excipient, thus that the fragmented particles of the excipient are caused to adsorb titanium oxide. Talc (magnesium silicate hydrate), chlorite (magnesium aluminum silicate hydrate), kaolin, mica, phlogopite and mixtures thereof are particularly mentioned as lamellar silicates which are suitable according to said patent application.

By carrying out the method according to the invention, retention is improved and savings in manufacturing costs are achieved, while at the same time the mechanical properties of the fibrous web are maintained or improved compared to the prior art papermaking technique, when TiO 2 is used as the sole opacifying filler and the subject of patent application 84 19957.

In particular, it has been found (cf. the results of the comparative tests below) that by using the above-mentioned opacifying pigment, (i) the method of FR-A-2 492 425 gives a fibrous web which has significantly better properties (especially retention and opacity) than conventional papermaking techniques. obtained, and (ii) that the method according to the invention improves said properties in relation to said conventional technique as well as FR-A-2 492 425.

In addition, when TiO 2 is replaced by the opacifying pigment according to the above-mentioned FR application, it is necessary to increase the amount of mineral filler added to the paper (e.g. 4 parts by weight of TiO 2 are replaced by 7 parts by weight of a powdered mixture of 80% by weight of lamellar silicate and 20 parts by weight). no-% TiO 2) to achieve the same opacity. However, it is known that the mechanical properties of the resulting fibrous web deteriorate as the proportion of mineral filler increases.

4,81157

According to the invention, the disadvantage associated with increasing the proportion of mineral filler is avoided, and at the same time mechanical properties such as tear strength and puncture resistance are maintained or even improved, especially when good opacity is sought.

In a preferred process of the invention for producing a fibrous web by a papermaking process for improving retention, comprising the steps of 1 °) preparing an aqueous suspension of fibers, 2 °) preparing an aqueous suspension of a mineral filler and an organic binder, the filler / binder mixture being pre-flocculated from the cation; 3 °) an aqueous suspension of the pre-flocculated filler / binder mixture is added in the stern piping of the paper machine, 4 °) a cationic flocculant is added to the aqueous suspension of the fiber / filler / binder mixture obtained in step 3 °) upstream of the headbox, and 5 °) the resulting aqueous suspension is , which is compressed and dried, the method being characterized in that the aqueous suspension of step 3e) is added upstream of the headbox to the aqueous suspension of fibers so that (i) the flocculant of the filler / binder mixture added to said fiber suspension is 0.01-0.3 mm in diameter, and (ii) the contact time of said filler / binder mixture and fibers in the resulting suspension is 10-60 seconds; and in step 4e) the contact time between said flocculant and said fiber / filler / binder mixture is less than 45 seconds.

The term "fibrous web" as used herein means a composite material consisting of fibers, a mineral filler, a binder, and at least one flocculant. This composite material 5,81157 made by the papermaking process may also contain one or more excipients conventionally used in papermaking. For the purposes of this definition, the term "fibrous web" includes paper and paperboard when the fibers are predominantly cellulosic fibers, and synthetic paper and nonwovens when the fibers used are substantially non-cellulosic fibers.

The composite material obtained by the method described above can be used for printing / writing purposes, as a surface material or a packaging medium, or for the manufacture of special products (especially for the production of photographic products, carbonless carbonless papers and for lamination purposes).

When the mineral filler consists essentially of opacifying means or contains opacifying means, the composite material of the invention is particularly suitable in (i) the field of application for impregnation with phenolic and / or melamine resin laminated sheets to prevent the material from becoming translucent, and (ii) food packaging) which must remain as opacities when in contact with fats or after being formed into composites with waxes, resins and / or polymers which tend to affect the opacity of the final product.

All fibers are suitable for the production of the fibrous web according to the invention, in particular organic natural fibers (cellulose fibers) or synthetic organic fibers (polyamide, polyester, polyalkylene and polyacrylate fibers) and mineral fibers (glass, ceramic, screened gypsum and carbon fibers) and and mixtures thereof. It is recommended to use mainly wood fibers, i.e. unbleached, semi-bleached or bleached softwood and hardwood fibers, possibly together with recycled fibers obtained from, for example, waste paper and textiles. It is also possible to combine 6,81157 cellulose fibers with synthetic high polymer fibers such as polyamide, polyester, polyethylene and polypropylene fibers, or with mineral fibers such as glass, ceramic, calcium sulfate and carbon fibers, or alternatively regenerated cellulose fibers, or alternatively.

Preferably, it is recommended to add an anionic agent to the aqueous suspension of the fibers of step 1 °) to make said fibers substantive by increasing their anionic strength. This substance, which has a curative effect on the fiber-filler bonds and the internal cohesion of the fibrous web, respectively, is added to said aqueous suspension of fibers before adding the flocculated particles of the filler / binder mixture in step 3 °). This anionic agent is preferably selected from polymers of the type consisting of polyacrylic derivatives, such as polyacrylamides (especially modified polyacrylamides having a high average molecular weight of the order of 5 x 10 6-107), polymethacrylamides and sodium, potassium and ammonium polyacrylate acrylacrylates.

The amount of anionic substance depends on the anionic strength of the pulp used, which depends on the manufacturing method (kraft or bisulphite pulp) and also on the conditions under which the pulp is washed before use. Kraft pulp from an integrated mill has a much more significant anionic character than pulp that is dried and stored before being used in a paper machine. The practical dosage is 0.02 to 0.5% by weight of an anionic substance relative to the weight of the fibrous web, and preferably 0.02 to 0.2% of said substance relative to the weight of the fibrous web.

The mineral fillers of the invention are substantially non-binding mineral fillers. Particularly suitable mineral fillers are those conventionally used in the papermaking and paint industries, for example talc, kaolin, natural or doped calcium carbonate, or calcium carbonate from the regeneration treatment of black liquor which has been extracted by refining and further refining the kraft pulp. then, magnesium carbonate, aluminum hydrates, calcium sulfate, colloidal silica, barium sulfate, titanium dioxide, off-white (calcium sulfoaluminate hydrate), magnesium hydroxide, and mixtures thereof. The opacifying pigment described in the above-mentioned FR patent application 84 19957 is also suitable.

This opacifying pigment is obtained by co-milling TiO 2 and lamellar silicate so that the fragmented particles of TiO 2 are adsorbed on the new active surfaces resulting from the fragmentation of the lamellar silicate. The aforementioned FR patent application describes how and why this pigment differs both structurally and in terms of final opacity from the prior art physical mixtures of the two ingredients.

Co-milling can be performed dry by adding TiO 2 and lamellar silicate to a suitable gas stream to mix the particles of both products at supersonic speed and spray them against each other to achieve the above-mentioned fragmentation and adsorption, especially using a "JET-O-MIZER" type grinder (manufactured by Fluid Energy). COX "type grinder (manufactured by Cox Brothers and Co.). Co-milling can also be performed wet by preparing a liquid suspension containing the starting materials in divided form and mixing this suspension using solid spheres to crush particles of both products to achieve the above-mentioned fragmentation and adsorption, especially using a "BABCOCK BALL MILL" type mill.

Said opacifying pigment is a mixture containing 10-70% by weight of TiO 2 and 90-30% by weight of lamellar silicate β 81157 (talc, chlorite, kaolin, mica, phlogopite and mixtures thereof); it preferably has a mean particle size (as defined in said FR application) of 0.5 to 1.5 microns and is obtained by grinding TiO 2 with a mean particle size of 60 to 100 microns, a lamellar silicate having a mean particle size of more than 2.5 microns and preferably Θ -12 microns, together with.

The preferred opacifying pigment for the opacity of the fibrous web according to the invention is the mixture described above containing 10 to 50% by weight of TiO 2 and 90 to 50% by weight of lamellar silicate, in particular a pigment with an average particle size d 50 = 0.5 to 1.5 μm. , and obtained by co-grinding a mixture of 20% by weight of TiO 2 (d50 = 80 μm) and 80% by weight of a talc / chlorite mixture (based on 1: 1 by weight) (d50 = 10 μm). In the above-mentioned FR application, a pigment containing 30 to 50% by weight of TiO 2 and 70 to 50% by weight of lamellar silicate is especially recommended for opacity contrast, and a pigment containing 10 to 30% by weight of TiO 2 due to the opacity of the oil, and 90-70% by weight of lamellar silicate.

The weight ratio of mineral filler to fiber is not critical, and may be, in particular, 0.01-6 depending on the intended use.

For example, for weight / writing purposes, the amount of mineral filler in the fibrous web may vary between 5 and 40% by weight and in particular between 10 and 30% by weight relative to the weight of said fibrous web. In various building surface materials, the proportion of filler may be greater than 50% by weight relative to the weight of the fibrous web. When applied to packaging, such as small, medium and large bags and sacks, or kraft shells or address labels, the amount of mineral filler may vary between 2 and 15% by weight relative to the weight of the fibrous web.

Il 9 81157

The organic binder that can be used in the process of the invention is any natural or synthetic organic binder normally used in papermaking. It binds the components of the material together and makes it possible to improve the physical properties of the web material. Suitable binders according to the invention are, in particular, the following: natural starches or starches modified by chemical, enzymatic or thermal processes, dextrins, polyvinyl alcohols, casein, animal glue, vegetable proteins, non-cellulose esters such as carboxymethylcellulose, such as carboxymethylcellulose, -carboxylated styrene / butadiene latexes, acrylic latexes, styrene / acrylic latexes, vinyl acetate latexes, neoprene latexes, acrylonitrile latexes, vinyl chloride latexes and mixtures thereof.

The amount of binder depends on the end use for the web material; in particular, it may range from 1 to 40 parts by weight and preferably from 1 to 25 parts by weight / 100 parts by weight of fibers and mineral filler.

The pre-flocculation of the mineral filler / binder mixture of step 2 °) is carried out using a flocculant intended to ionically destabilize said filler / binder mixture before mixing it with the fibers. This preparation, hereinafter referred to as "flocculant I", is preferably selected from organic cationic flocculants rather than mineral cationic flocculants such as aluminum sulphate and aluminum polychlorides.

Among the organic cationic flocculants suitable for the process according to the invention, mention may be made in particular of the following: polyethyleneimines, polyamideamines, polyalkylamines, in particular crosslinked polyalkylamines, polyacrylamides, in particular modified polyacrylamides, quaternary ammonium compounds, quaternary ammonium compounds, such as

10 81157

The organic cationic flocculant to be added in step 2 °) is added as an aqueous solution or suspension, preferably as a continuous process, to an aqueous suspension containing a mineral filler and an organic binder in an amount generally of 0.006 to 5 parts by weight and preferably 0.01 to 2 parts by weight. / 100 parts by weight of a mixture of mineral filler and binder. The exact amount to be used depends on four factors: - the concentration of the aqueous suspension of filler and binder; - the flocculant / filler / binder contact time, which depends on the structure of the piping at the stern of the paper machine; - mixing, and - the cationic strength of the flocculant.

As a general rule, however, this amount is adjusted so that the pre-flocculation of the filler / binder mixture takes place in substantially one minute at most.

According to one feature of the invention, when performing step 3e), it is important that the average diameter of the flocs of the filler / binder mixture is between 0.01 and 0.3 mm and preferably between 0.03 and 0.15 mm when said pre-flocculated mixture is introduced into an aqueous suspension of fibers. If the average diameter of said flocs is less than 0.01 mm, the losses on the wire may increase, and if the average diameter of said flocs is more than 0.3 mm, there is a high risk that the web to be formed will not become smooth or its formation is not good.

According to a further feature of the invention, it is important that the pre-flocculated filler / binder mixture in step 3 °) is added as close as possible to the headbox, so that the contact time between the filler / binder mixture and the fibers is 10-60 seconds and preferably 10-45 seconds. If said contact time is longer than 60 seconds, the fiber / filler / binder flocs become too large, so that the fibrous web may not be smooth.

il 81157

Finally, in step 4e) it is important that the cationic flocculant added to the fiber / filler / binder mixture formed in step 3 °) should be added to the stern piping very close to the headbox so that the contact time between said flocculant and the fiber / filler / binder mixture is less than 45 seconds and preferably between 8-30 seconds.

the cationic flocculant of step 4 °, hereinafter referred to as "flocculant II", is selected from the group consisting of organic and mineral ionic destabilizers. Like flocculant I, fluculant II may be an organic cationic substance or, in contrast to flocculant I, a mineral cationic substance, for example aluminum sulphate or aluminum polychloride. Flocculant II can, of course, be the same as flocculant I.

When flocculant II is a mineral cationic substance, for example aluminum sulphate, there is a risk that circulating water taken from the wet end of the paper machine, especially under the wire, and recycled may increase the size of the filler / binder flocs due to its Al2 (SO4) 3 content. To avoid this risk, two solutions are recommended: no recycled circulating water is introduced into the aqueous filler / binder mixture in step 2 °) before the start of step 3 °) or a friction device is used to reduce the average diameter of said filler / binder flocs just before adding it to the fiber aqueous suspension in step 3 °).

According to another feature of the invention, the ionic requirement of said fibers in the suspension obtained in step 3 °) containing fibers, a mineral filler and a binder is less than or equal to 20 milliequivalents / gram of solids. The ionic requirement of a fibrous web intended for packaging use, in particular bags and sacks, is in particular 1-4 milliequivalents / gram, and of an fibrous web intended for printing / writing use, in particular of the order of 10 milliequivalents / gram.

i2 81157

In addition to fibers, mineral filler, organic binder, anionic polymer and cationic flocculants I and II, various excipients conventionally used in papermaking can be used in the process of the invention for producing fibrous web, for example: , paraffin emulsions and alkyl ketene dimers, - pH adjusters, for example aluminum sulphate (which may be added as flocculant II, as above) or sulfuric acid, to adjust the pH to between 4,5 and 6 in an acidic medium for gluing, - defoamers, - fluorescent reducing agents, dyes or tinting agents, - wet strength agents such as urea / formaldehyde, melamine formaldehyde, glyoxal, crosslinked cationic polyalkylene amines and preparations obtained from melamine / formaldehyde by condensation of echide and aminocaproic acid, and - fungicides and / or bactericides and other additives conventionally used in coating baths for printing / writing products, such as dispersants (in particular sodium hexa-metaphosphate and pyrophosphate), lubricants (especially fatty acid derivatives), ) and viscosity regulators (especially gelatin, ethylenediamine and urea).

In view of the above-mentioned contact times, the method according to the invention involves a large number of continuous operations.

Hereinafter, a preferred embodiment of this method will be described.

i3 81157 lie 1 ° (a) Cellulose fibers in aqueous suspension, obtained by grinding in a fiberizer (non-integrated mill) or directly from the pulp department (integrated mill), are stored under mixing in a container at a concentration of 40 to 400 g / l.

(b) The cellulose fibers are ground in the usual way to 15 to 65 Schoepper-Riegler degrees, depending on the application, in various concentrations between 20 and 350 g / l, in particular between 20 and 60 g / l, using standard conical or double disc grinders, or especially between 250-350 g / l with special grinders for high concentrations, especially when grinding the packaging material to obtain high tear strength. Organic and / or mineral fibers that are desired to be incorporated into the cellulosic fibers may be added at this point as needed.

c) The anionic agent required to make the fibers substantial is added in a dose of between 0.02-0.5% and preferably 0.05-0.2% by weight based on the weight of the fibrous web.

Step 2 ° a) The mineral filler is dispersed in an aqueous medium at a concentration of 150-600 g / l and preferably at a concentration of 300-400 g / l. The mineral filler of this can consist exclusively of an opacifier or a mixture of several fillers, which contains in particular an opacifier. Preferably, the opacifier here is a co-ground mixture (d50 = 0.5-1.5 μm) obtained from 80% by weight of talc / chlorite (1: 1 by weight) (d50 = 10 μm) and 20% by weight. % TiO 2 (d50 = 80 μm).

(b) An organic binder, ready for use if it is latex, or boiled if it is natural, etherified i4 81157 or oxidised starch or starch which has undergone enzymatic digestion, dextrin or starch ester, is prepared as an aqueous mixture with a concentration of 20- 300 g / l and preferably 20-200 g / l. The recommended binder is natural starch.

c) The aqueous suspension of mineral filler is mixed with the aqueous binder mixture while stirring and preferably in a continuous process. This operation is preferably performed in a dynamic conical mixer with a propeller, which ensures complete homogeneity of the binder / filler mixture. Flocculant I is added to said filler / binder mixture after diluting 10-100 times with water (more than 10-fold dilution and equal to or less than 100-fold). The amount of added flocculant I is 0.006 to 5 parts by weight and preferably 0.01 to 2 parts by weight / 100 parts by dry weight of the filler / binder mixture.

In practice, on the one hand, the filler suspension and, on the other hand, the aqueous binder mixture are each continuously added to the region of the top of the propeller-driven dynamic cone mixer; flocculant I is continuously added about halfway to said mixer, where in the region of the lower end there is a feed point for the dilution water to enable the necessary dilution operations to be carried out. In this way, the pre-flocculated filler / sieve mixture is continuously collected at the lower end of the mixer.

step 3 ° A pre-flocculated filler / binder mixture in the form of an aqueous suspension containing 100-200 g / l is continuously added in the stern piping to the aqueous suspension of fibers prepared in step 1 °, said filler / binder mixture having a mean flock diameter of 0.01-0.3 mm and preferably 0.03-0 , 15 mm, and wherein said pre-flocculated mixture is added as close as possible to the headbox so that the contact time between said filler / binder mixture is less than 60 seconds, and preferably 10-45 seconds.

Step 4 °

On the upstream side of the headbox, a small amount of flocculant II is added to the mixture from step 3 ° to strengthen flocculation and improve final retention on the paper machine wire, with a contact time between flocculant II and the flocculated fiber / filler / binder mixture of less than 45 seconds, and preferably 8-30. seconds.

remarks

The other additives mentioned above, such as adhesives, fluorescent whiteners, etc., can be added either after grinding the cellulosic fibers in step le or after adding the pre-flocculated filler / binder mixture in step 3e.

Other advantages and features of the invention will be better understood from the following description of preparation examples and comparative tests. This portion is not intended to limit the invention, but is presented for illustrative purposes only, bearing in mind one primary purpose: improving retention and opacity.

For convenience, the fibrous webs obtained by the process of the invention are referred to as "Es" products and the prior art fiber webs are referred to as "A" products (conventional technique) and "B" products (FR-A-2 492 425 technique).

ie 81157

Example 1:

Manufacture of printed matter

Made as a fibrous web according to the best embodiment described above, starting from cellulosic fibers comprising the following blend: bleached bisulfite softwood fibers 40% by weight bleached kraft hardwood fibers 60% by weight

grinding 35® SR

and the opacification pigment according to Example 1 of FR Application 84 19957 obtained by co-grinding a mixture of:

TiO 2 (anatase), d50 = 80 microns 20 wt% talc / chlorite (1: 1 wt%), d50 = 10 microns 80 wt% average particle size of the co-milled product d50 = 0.8 microns, with other operating conditions as follows: in step 3 ° average flocculant diameter (dm) of added filler / binder mixture 0.03-0.15 mm contact time (tj) between pre-flocculated filler / binder mixture and fibers 40 seconds contact time between flocculant II and fiber / filler / binder mixture 25 seconds

A fibrous web is obtained which can be used as a printing / writing material at a weight of 64 g / m 2.

Comparison test I

The web obtained according to Example 1 was compared with reference webs obtained by conventional techniques (A 1 and FR-A-2 492 425 () having the same weight (64 g / m 2) and starting from the same cellulose fibers (35® SR), the same TiO 2 grade (d50 = 0.8 microns after grinding titanium dioxide with d50 = 80 microns) Time, and the same opacification pigment for B ^, whereby the fibrous web B ^ n was prepared under the following conditions: i7 81157 in step 3 ° the average diameter of the flocs of the added filler / binder mixture 0.35-0.50 mm contact time 80 seconds contact time t2 60 seconds The quantities, mechanical properties and material costs of said web components are shown in Table I below.

Table I

Weight / writing material (weight «64 g / m2)

Composition by weight Es 1 cellulose fibers (35e SR) 100 100 100 anionic polymer (a) 0.05 0.05 0 talc 30 30 30

TiO 2 0 03 opacifying pigment (b) 5 50 binders (natural starch) 1 10 flocculants 1 (c) 0,1 0,1 0,1 rosin 2 22 flocculants II (d) _ (jy_ (jy_ (e))

Composition price, FF / kg_3.35_3.45 3.70

Properties retention (%) 82% 75% 70% opacity contrast (Photovolt) 81 80 80 opacity for oil 39 39 39 avg. breaking length (m) 3555 3350 3155 avg. puhkaisulujuusluku_2_1,8_1,6

Notes (a) modified polyacrylamide (b) as ed. (c) polyethyleneimine (d) aluminum sulphate as defined in Example 1 (e) in an amount sufficient to adjust the pH to 4.5-5_

The results in Table I show that the mechanical properties of Es 1 obtained by the process of the invention (average breaking strength ιβ 81157, average puncture strength and especially retention) are considerably better than those of A 1 and B 2 with the same opacity.

Example 2:

Preparation of a fibrous web for weight / writing purposes A fibrous web weighing 64 g / m 2 is prepared from the cellulosic fibers and opacifying pigment according to Example 1 above, with the same values of dm, t1 and t2.

Comparative test II

The fibrous web of Example 2 was compared to a fibrous web (A2) obtained under substantially analogous conditions for the selection of cellulose fibers, binder and flocculant I, with the opacifying pigment replaced by TiO 2 as in the previous comparative test I.

The quantities, mechanical properties and material costs of the components of said webs are shown in Table II below.

The results in Table II confirm those shown in Table I. In particular, it is found that Es 1 and Es 2 allow savings of 7-10% and are very advantageous, with the same opacity, taking into account the improved retention and mechanical properties. The economy can be further improved by making the webs Es 1 and Es 2 to weigh 60 g / m 2 instead of 64 g / m 2, taking into account the very good mechanical properties of the products according to the invention.

is 81157

Table II

Weight / writing material (weight = 64 g / m2)

Composition by weight Es 2 cellulose fibers (35e SR) 100 100 anionic polymers (a) 0.05 0 talc 0 0

TiO 2 0 4 opacifying pigment (b) 7 0 binder (natural starch) 1 0 flocculant I (c) 0.1 0.1 rosin 2 2 flocculant II (d) _ £ ej_ (e)

Price of the composition, FF / kg_3.90_4.30

Properties retention (%) 88% 75% opacity contrast (Photovolt) 79 78 opacity for oil 40.5 41 avg. breaking length (m) 6150 5620 avg. puhkaisulujuusluku_4,1_3,6

Notes (a) to (e): see Table 1_

Example 3:

Manufacture of fibrous webs for packaging purposes

For packaging purposes, a fiber web weighing 79 g / m2 is made from a mixture of cellulosic fibers containing: bleached kraft wood fibers 50% by weight bleached kraft hardwood fibers 50% by weight

grinding 35 ° SR

and the opacification pigment of Example 1 above, wherein the values of dm, t1 and t2 are the same as in Example 1.

20 81 1 57

Comparison test III

The product obtained according to Example 3 was compared with a conventional fibrous web (A3) weighing 79 g / m 2 in which the opacifying pigment had been replaced by TiO 2, the average particle size of cellulose fibers and TiO 2 in paper A3 being the same as in Example 3 and the average opacifying pigment size. The compositions of Es 3 and Aj and the results obtained are shown in Table III.

Table III

Wrapping paper (weight = 70 g / m2)

Composition by weight Es 3 A3 cellulose fibers (35 ° SR) 100 100 anionic polymers (a) 0.05 0

TiO 2 0 5 opacifying pigment (b) 15 0 binder (natural starch) 1 0 flocculant I (c) 0.15 0.15 rosin 2 2 flocculant II (d) _ [jsJ_ (e)

Price of the composition, FF / kq_3.95_4.36

Properties Opacity Contrast (Photovolt) Θ6 81 Opacity for oil 53 53 Avg. puncture strength figure_3.95_4

Notes (a) to (e): see Table 1 ed._

Example 4 and Comparative Test IV

Manufacture of carbonless base paper base material

The base material of carbonless copy paper is made according to the invention (Es 4) from a mixture of cellulosic fibers containing: 2i 81157 bleached kraft wood fibers 60% by weight bleached kraft hardwood fibers 40% by weight

grinding 50 * SR

The opacifying pigment and the values of dm, t1 and t2 are the same as in Example 1 above. The weight of the material obtained is 40 g / m 2.

The reference product (A4) is obtained from the same fibers, the opacification pigment being replaced by TiO2 (d50 = 0.8 microns). The corresponding results are shown in Table IV.

Table IV

Carbonless copy paper base material (weight = 40 g / m2)

Composition by weight Es 2 Aj ^ cellulose fibers (50e SR) 100 100 anionic polymer (a) 0.05 0 talc 15 15

TiO 2 0 5 opacifying pigment (b) 15 0 binder (natural starch) 1 0 flocculant I (c) 0.1 0.1 rosin 2 2 flocculant II (d) _ (ej_ (e)

Composition price, FF / kq_3.65_4

Properties retention (%) 88% 75% opacity contrast (Photovolt) 71 70 opacity for oil 39.5 40 avg. breaking length (m) 4650 4255 avg. puncture strength number_2.6_2.3

Notes (a) to (e): see Table 1 ed._ 22 81 1 57

Example 5 and comparative test V Preparation of laminating material

The laminating material is prepared according to the invention (Es 5) from a mixture of cellulosic fibers containing: bleached bisulphite softwood fibers 40% by weight bleached kraft hardwood fibers 60% by weight

grinding 28 ° SR

The opacification pigment is the same as in Example 1, as are the values of dm, tj_ and t2. A laminating material weighing 90 g / m 2 is obtained.

The reference product (A5) is obtained from the same fibers, the opacifying pigment being replaced by TiO2 (^ 50 = 0.8 microns).

The corresponding results are shown in Table V. The cost savings of the composition are found to be more than 25%.

Table V

Laminating material (weight = 70 g / m2)

Composition by weight Es 5 A5 cellulose fibers (28 ° SR) 100 100 anionic polymers (a) 0.05 0

TiO 2 10 30 opacifying pigment (b) 50 0 binder (natural starch) l 0 flocculant I (Kumene® 557 H) 2 2 flocculant II (polyethyleneimine) 0.1_0.1

Price of the composition, FF / kg_4.60_5.90

Properties opacity contrast (Photovolt) 95 95 opacity for oil_ 83,5_84

Notes (a) - (b): see Table 1 ed._ 23 81 1 57

Examination of Tables IV makes it possible to conclude that: (i) the opacifying pigment obtained by co-milling in accordance with the aforementioned FR patent application 84 19958 (TALCS DE LUZENAC) is of particular industrial value, confirming the results obtained in this application, (ii) The method according to FR-A-2 492 425 improves the retention and the opacity of the fibrous web, respectively, when said opacifying pigment is used, and (iii) the method according to the present invention is very advantageous in terms of opacity because it improves retention and mechanical properties and provides high savings in raw materials compared to the state of the art.

Claims (10)

A process for preparing a fibrous web in a papermaking process, the purpose of which is to improve the retention, which comprises the steps in which 1 °) an aqueous suspension of fibers is prepared, 2 °) an aqueous suspension of mineral filler is prepared and organic binder, in which the filler / binder mixture is preflocculated by means of a cationic flocculant, 3 °) the preflocculated aqueous suspension of the filler / binder mixture is introduced into the inlet tubes of the papermaking machine, 4 °) a cationic flocculant is introduced into it in step 3 °) the obtained aqueous suspension of the fiber / filler / binder mixture upstream from the inlet sled, and 5 °) the received aqueous suspension is introduced into the inlet tray and on the paper machine a web is formed which is pressed and dried, characterized in that the water suspension 3 °) is added to the water suspension upstream from the inlet carriage such that ( i) the mean diameter of the flocks of the filler / binder mixture introduced into said fiber suspension is between 0.01-0.3 mm and (ii) the contact time between said filler / binder mixture and the fibers of the suspension obtained is between and 60 seconds; and in step 4 °) the contact time between said flocculant and said fiber / filler / binder mixture is less than 45 seconds. Driver according to claim 1, characterized in that the mineral filler contains an opacifier. 3. A driver according to claim 2, characterized in that the mineral filler contains an opacifier selected from pigments formed by a mixture such as 2? 81157 contains 10-70 wt% TiO2 and 90-30 wt% of lamellar silicate, which is obtained by grinding TiO2 together with lamellar silicate to obtain fragmented particles of TiO2 adsorbed on the active surfaces of the fragmented particles of the lamellar silicate. 4. A driver according to claim 1 or 3, characterized in that the fibers in the step (1 °) are subtracted by adding an anionic agent. 5. A process according to claim 4, characterized in that the anionic agent is an anionic organic polymer and is used in a proportion of 0.02 to 0.5% by weight and preferably in 0.05 to 0.2% by weight. in relation to the weight of the fiber web. 6. A driver according to claim 1 or 3, characterized in that the average diameter of the flocs in the filler / binder mixture added in step 3 ° is 0.03 - 0.15 mm. 7. A driver according to claim 1 or 3, characterized in that the contact time between the pre-flocculated filler / binder mixture supplied in step 3 °) and the fibers is 10 - 45 seconds. 8. A driver according to claim 1 or 3, characterized in that the contact time between the cationic flocculant supplied in step 4 °) and the fiber / binder / filler mixture is 8 to 30 seconds. 9. A conductor according to claim 1 or 3, characterized in that the ion requirements of the fibers are less than or equal to 20 milliequivalents per gram of solids. Fiber web prepared by a method according to any of claims 1-9.