FR2578870A1 - PROCESS FOR THE PREPARATION OF A FIBROUS FOIL BY PAPERWAY TO ENHANCE RETENTION AND IN PARTICULAR OPACITY. - Google Patents

Abstract

New method for the preparation of a fibrous sheet by using paper manufacturing techniques in order to improve the retention and particularly the opacity, said method being characterized in that 1) an aqueous suspension of fibrous is prepared; 2) an aqueous suspension of mineral filler and binder is prepared wherein the filler/binder mixture is preflocculated by means of a cationic flocculent; 3) at the head circuits of the paper machine and before the head box of the latter, the aqueous suspension of the preflocculated filler-binder mixture is introduced into the aqueous suspension of fibers so that (i) the average diameter of the flocks of the filler-binder mixture added into said fiber suspension is comprised between 0.01 and 0.3mm, and (ii) the contact duration of said filler-binder mixture with the fibers in the resultant suspension is comprised between 10 and 60 seconds; 4) before the heat box, a cationic flocculent is introduced into the aqueous suspension of the mixture of fibers-filler-binder obtained in the stage (3), so that the contact duration of said floculent with the mixture of fibers-filler-binder is shorter than 45 seconds; 5) the resulting aqueous suspension is introduced into the head box and forms a sheet on a paper machine which is pressed and dried.

Description

Process for the preparation of a fibrous sheet by papermaking to improve the retention and in particular the opacity.

 The present invention relates to a novel process for the preparation of a fibrous sheet by the papermaking method for improving, in general, the retention and, in particular, that of opacifying agents, by limiting the manufacturing costs and preserving or improving the mechanical properties compared to previously known techniques. It also concerns, as a new industrial product, the fibrous sheet obtained by this process.

 This new process is particularly useful in the manufacture of paper and paperboard, particularly in the field of printing-writing, packaging, coatings and specialty papers. It is particularly advantageous for the retention of mineral fillers such as opacifying agents in order to improve the opacity, in particular opacity-contrast and opacity with oil.

We know that the Applicant has already advocated in
FR-A-2 492 425, a process for the preparation of a fibrous sheet by the papermaking process, according to which the mixture of the inorganic filler and the organic binder is prefloculated before being incorporated in the head circuits of the machine. paper, in the aqueous suspension of the fibers previously treated with an organic anionic polymer (which enhances the anionic power of the fibrous suspension), a flocculant being then introduced before the headbox in the resulting aqueous suspension comprising the fibers, the load mineral and binder. This method makes it possible to increase the retention compared with conventional or previously known papermaking techniques.

According to the invention, a new process is proposed which leads to even higher results compared to the process described in document FR-A-2 492 425 mentioned above, in particular with regard to retention. According to the invention, the improvement of the retention results from the implementation of particular operating procedures: - optimization of the average diameter of the load-binder flocs, - limitation of contact times, before the headbox,
load-binding flocs with the fibers, on the one hand, and the flocculant
with the fiber-filler-binder mixture, on the other hand.

 According to another aspect of the invention, the new method that is recommended is particularly advantageous for improving the retention of opacifying means.

 It is known that titanium oxide, particularly of rutile or anatase variety, is an opacity and bleaching pigment commonly used in paints, inks, plastics, paper and cardboard, cosmetics and ceramics. because of its high hiding power conferred by its high refractive index and UV absorption

 The increasingly excessive cost of TiO2 (of the order of 10 to 11 FF / kg at present) has led users to consider more economical alternatives. In the paper industry, attempts to replace titanium oxide with a mixture of TiO 2 and another more economical mineral filler selected in particular from talc, kaolin, alumina hydrate and CaCO 3 have been unsatisfactory both in terms of opacity than that of retention.

 According to the French patent application No. 84 19957 of December 26, 1984 (TALCS DE LUZENAC), is recommended a new opacity pigment particularly interesting vis-à-vis opacity-contrast and especially opacity to oil. This opacity pigment consists of a mixture of 10 to 70% by weight of TiO 2 and 30 to 90% by weight of an adjuvant selected from lamellar silicates, and is obtained by co-milling TiO 2 and said lamellar adjuvant in order to to generate an adsorption of titanium oxide on the fragmented particles of the adjuvant. Among the lamellar silicates which are suitable according to this patent application, mention is made especially of talc (hydrous magnesium silicate), chlorite (hydrated magnesium aluminum silicate), kaolin, mica, phlogopite and mixtures thereof.

 By implementing the process of the invention, the retention is improved and savings in manufacturing costs are achieved while preserving or improving the mechanical properties of the fibrous sheets compared with the prior art paper techniques, when TiO 2 is used. as sole = opacifying haras, on the one hand, and the said more economic opacity pigment, object of the aforementioned French patent application No. 84 19957, on the other hand.

 In particular, it has been found (see for this purpose the results of comparative tests given below) using the opacity pigment referred to above, that (i) the method of FR-A-2 492 425 gives fibrous sheets having properties (in particular retention and opacity) much higher than those obtained according to conventional papermaking techniques, and (ii) the method according to the invention improves said properties with respect to said conventional techniques and FR-A-2 492 425.

 Moreover, when TiO2 is replaced by the opacity pigment according to the aforementioned French application, the quantity of the inorganic filler entering the paper must be increased (for example, 4 parts by weight of TiO 2 are replaced by 7 parts by weight of a cobbled mixture of 80% by weight of lamellar silicate and 20% by weight of TiO 2) to obtain an equivalent opacity.

However, it is known that when the content of the mineral filler is increased, the mechanical properties of the resulting fibrous sheet are reduced.

 According to the invention, the disadvantage of the increase in the mineral filler content is overcome by preserving or even improving the mechanical properties such as in particular the breaking and bursting strengths, in particular when a good opacity is sought. .

The process for the preparation of a fibrous sheet by papermaking techniques, which is recommended according to the invention for improving retention, in which the prefloculated mixture is introduced at the level of the overhead circuits of the paper machine. a flocculating agent for the mineral filler and the organic binder in the aqueous fiber suspension, and then introducing a flocculating agent before the headbox into the resulting aqueous suspension, said method being characterized in that
10) an aqueous suspension of fibers is prepared
20) an aqueous suspension of mined charge is prepared
and binder in which the mixture
binder is preflocculated by means of a flocculant
cationic
30) at the head circuits of the machine
paper and before the headbox of this one, one
introduce the aqueous suspension of the mixture charge
preflocculated binder in the aqueous suspension of
fibers, so that (i) the average diameter
flocs of the load-binding mixture that we introduce
in said fiber suspension is included
between 0.01 and 0.3 mm, and (ii) the contact time of the
said charge-binder mixture with the fibers in the
resulting suspension is between 10 and 60
seconds
40) before the headbox, a flocculant is introduced
cationic in the aqueous suspension of the mixture
fibers-filler-binder obtained in stage 30), such
way that the duration of contact of said flocculant with
said fiber-filler-binder mixture is lower
at 45 seconds
50) the resulting aqueous suspension is introduced into
the headbox and form a sheet on machine
paper that is pressed and dried.

 By "fibrous sheet" is meant here a composite material comprising fibers, a mineral filler, a binding agent and at least one flocculating means. This composite material, which is prepared by papermaking, can also contain one or more conventional additives in paper. With respect to this definition the term "fibrous sheet" includes paper and paperboard where the predominant fibers are cellulosic fibers, on the one hand, and nonwovens or synthetic papers where the fibers used are essentially non-cellulosic fibers , on the other hand.

 The composite material obtained according to the aforementioned method is useful as a printing-writing medium, a coating medium, a packaging medium or for obtaining special media (in particular photographic media, carbonless media and media for stratification).

 When the inorganic filler consists essentially of or contains an opacifying means, the composite material according to the invention is particularly advantageous especially in (i) the field of supports intended for impregnation with phenolic and / or melamine resins for the production of laminated or laminated panels, in order to avoid the transparency of the material, (ii) the field of packaging supports (food packaging in particular) which must remain opaque in contact with grease or after complexing with waxes, resins and / or polymers which tend to affect the opacity of the final product.

 All the fibers are suitable for the preparation of the fibrous sheet according to the invention, in particular natural organic fibers (cellulosic fibers) or synthetic fibers (polyamide, polyester, polyalkylene, polyacrylate fibers) and mineral fibers (glass fibers, ceramic, acicular gypsum, carbon and rock wool) and mixtures thereof.

Noble wood fibers are preferably used, namely unbleached, semi-bleached or bleached softwood and hardwood fibers possibly associated with recovery fibers from, for example, waste paper and textiles. It is also possible to combine cellulosic fibers with high synthetic polymer fibers such as polyamide, polyester, polyethylene, polypropylene fibers or mineral fibers such as glass, ceramic, calcium sulphate fibers. and carbon, or cellulose regeneration fibers, or mixtures thereof.

 Advantageously, it is recommended to add an anionic means in the aqueous suspension of the fibers of stage 10 in order to render said fibers substantive by reinforcing their anionic power. This means, which contributes to improving the fiber-filler bonds and consequently the internal cohesion of the fibrous sheet, is introduced into the said aqueous suspension of the fibers before the incorporation in the stage 30 of the flocculated particles of the filler-binder mixture. Preferably, this anionic means will be chosen from polymers of the poyacrylic derivative type, such as polyacrylamides (in particular modified polyacrylamides having a high average molecular weight, of the order of 5 × 10 -10 6 to 10 7), polymetacrylamides, sodium polyacrylates and polymethacrylates. , potassium and ammonium.

 The amount of anionic means is a function of the anionicity of the pulp used, which is related to the manufacturing process (kraft or bisulfite pulp) but also to the conditions for washing the pulp before use. Kraft pulp from an integrated plant has an anionic character much more pronounced than a pulp dried and stored before being sent to the paper machine.

In practice, a dose of 0.02% to 0.5% by weight of anionic means with respect to the weight of the fibrous sheet will be used, and preferably 0.05% to 0.2% of said means relative to the weight of the fibrous sheet. the fibrous leaf.

 The mineral fillers according to the invention are essentially non-binding mineral fillers. Particularly suitable are the usual inorganic fillers in the paper industry and in the paint industry, such as, for example, talc, kaolin, natural calcium carbonate, precipitated or originating from the regeneration operations of black liquors extracted from the cooking of kraft pulps and more especially after the causticization operation, magnesium carbonate, alumina hydrates, calcium sulphate, colloidal silica, barium sulphate, titanium dioxide, satin white (calcium sulphoaluminate hydrate), hydrochloride, magnesium hydroxide, or mixtures thereof. Also suitable is the opacity pigment described in the aforementioned French patent application No. 84 19957.

 This opacity pigment is obtained by co-milling TiO 2 and lamellar silicate so that the fragmented TiO 2 particles are adsorbed on the new activated surfaces resulting from the fragmentation of the lamellar silicate. The above-mentioned French patent application demonstrates how and why this pigment is distinguished, both in terms of structure and in terms of final opacity, of the physical mixtures of the two ingredients previously envisaged.

The co-grinding can be carried out dry by introducing
TiO 2 and lamellar silicate in a gaseous stream adapted to drive the particles of both produced at a supersonic velocity and to project them against each other to obtain the abovementioned fragmentation and adsorption, in particular by means of a mill type "JET-O-MIZER" (manufactured by the Company
Fluid-Energy) or "COX" (manufactured by Cox-Brothers and CO).

The co-milling can also be carried out wet by preparing a liquid suspension containing the starting materials in divided form and stirring this suspension in the presence of solid balls so as to break the particles of the two products between the balls in order to obtain the fragmentation and adsorption referred to above, in particular by means of a grinder of the type "BALL CRUSHER
BABCOCK ".

 Said opacity pigment is a mixture consisting of 10 to 70% by weight of TiO2 and 90 to 30% by weight of lamellar silicate (talc, chlorite, kaolin, mica, phlogopite and mixtures thereof) it advantageously has a mean particle size ( as defined in said French application) between 0.5 and 1.5 microns and is obtained by co-milling TiO 2 having an average particle size of 60 to 100 microns and lamellar silicate having an average particle size greater than 2. 5 microns and preferably between 8 and 12 microns.

 The opacity pigment preferred for the opacity of the fibrous sheets according to the invention will be a mixture as described above consisting of 10 to 50% by weight of TiO 2 and 90 to 50% by weight of lamellar silicate, especially a pigment having a mean particle size d50 = 0.5 to 1.5 yen and obtained by co-milling a mixture of 20% by weight of TiO2 (d50 = 80 μm) and 80% by weight of a talcchlorite (1 : 1) (d50 = lOum). The above-mentioned French application recommends, in particular for opacity-contrast, a pigment consisting of 30 to 50% by weight of TiO 2 and 70 to 50% by weight of layered silicate, and for opacity to oil a pigment consisting of 10 30% by weight of TiO2 and 90 to 70% by weight of lamellar silicate.

 The weight ratio mineral-fiber load is not critical, it can be in particular between 0.01 and 6, depending on the desired applications.

 For example, in printing-writing, the amount of inorganic filler in the fibrous sheet may vary from 5 to 40% by weight, and especially from 10 to 30% by weight relative to the weight ae.Bdite fibrous sheet. For various coatings for the building, the loading rate may be greater than 50% by weight relative to the weight of the fibrous sheet. For bag-type packaging applications of small, medium or large capacity or for kraft envelopes or tape media, address for example, the amount of mineral filler may vary between 2 and 15% by weight relative to the weight of the fibrous sheet .

 The organic binder that can be used in the process according to the invention is any organic binder, natural or synthetic, usually used in paper milling. It binds the constituents of the material together and improves the physical properties of the sheet material.

Among the binders which are suitable according to the invention, mention may notably be made of native or chemically, enzymatically or thermally modified starches, dextrins, polyvinyl alcohols, casein, animal glue, plant proteins, esters and the like.
cellulosics such as carboxymethylcellulose, alginates, dispersions of synthetic polymers such as carboxylated or non-carboxylated styrene butadiene latices, acrylic latices, styrene-acrylic latices, vinyl acetate latices, neoprene latices, latex latices, acrylonitrile, vinyl chloride latices and mixtures thereof.

 The amount of binder is a function of the intended end use for the sheet material; it may especially vary between 1 and 40 parts by weight, and preferably between 1 and 25 parts by weight, relative to 100 parts by weight of fibers and mineral filler.

 The preflocculation of the mineral filler-binder mixture of stage 20 is carried out by means of a flocculant which aims to ionically destabilize said filler-binder mixture before mixing with the fibers. This product, hereinafter referred to as "flocculant I", will advantageously be chosen from cationic organic flocculants rather than from inorganic cationic flocculants such as aluminum sulphate and aluminum polychlorides.

 Among the organic cationic flocculants which are suitable in the process of the invention, mention may be made in particular of polyethyleneimine, polyamide-amine, polyalkylamine in particular crosslinked, polyacrylamide in particular modified, quaternary ammonium such as in particular chloride-hydroxypropyltrimethylammonium chloride and cationic starches .

The cationic organic flocculant intervening at stage 20 is incorporated, in the form of an aqueous solution or suspension, preferably continuously, in the aqueous suspension containing the inorganic filler and the organic binder, in an amount generally of between 0.006 and 5 parts by weight. and preferably between 0.01 and 2 parts by weight per 100 parts by weight of the mixture of mineral filler and binder. The exact amount to use depends on four factors
the concentration of the aqueous suspension of charge and binder
the flocculant-charge-binder contact time, which is related to the configuration of the paper machine head circuits
- agitation, and
the cationic power of the flocculant.

 However, as a rule, this amount is set so that the preflocculation of the filler-binder mixture is essentially carried out in one minute at most.

 According to one characteristic of the invention, it is important that, during the implementation of stage 30, 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 preflocculated mixture is introduced into the aqueous suspension of fibers. If the average diameter of said flocs is less than 0.01 mm, the underfloor losses can increase, and if the average diameter of said flocs is greater than 0.3 mm, there are serious risks that the fibrous sheet formed is not uniform or that the epair is not good.

 According to another characteristic of the invention, it is important that the premixed charge-binder mixture is introduced at the stage 30 as close as possible to the headbox, so that the duration of contact of the mixture-filler-binder with the fibers is between 10 and 60 seconds, and preferably between 10 and 45 seconds. If said contact time is greater than 60 seconds, fiber-filler-binder flocs will be too large and the fibrous sheets may therefore not be uniform.

 Finally, it is important that, at stage 40, the cationic flocculant, which is incorporated in the fiber blend mixture of stage 30, be introduced into the head circuits close to the headbox so that the duration of contact of said flocculant with the fiber-filler-binder mixture is less than 45 seconds and preferably between 8 and 30 seconds.

 The cationic flocculant of stage 49, which is hereinafter referred to as "flocculant II", will be chosen from organic and inorganic ion destabilization agents. Flocculant II, like flocculant I, may be a cationic organic substance or, unlike flocculent I, a cationic mineral substance such as, for example, aluminum sulphate and aluminum polychloride. Of course, flocculant II may be identical to flocculant I.

 When the flocculant I; is a cationic mineral such as for example aluminum sulphate, there is a risk that the white water, which is collected in the wet part of the paper machine, especially under the cloth, and that the the size of the load-binder flocs is recycled, because of their A12 (SO4) content. To mitigate this risk, two solutions are preconated: do not put the recycled white water in contact with the aqueous suspension of the charge-binder mixture from stage 20 to the beginning of stage 30, or provide a shearing device for decreasing the average floc diameter of said batch-binder mixture just prior to introduction into the aqueous suspension of stage 30 fibers.

 According to another characteristic of the invention, the ionic demand of the fibers in the suspension containing said fibers, the mineral filler and the binder obtained in stage 30 is less than or equal to 20 milliequivalents per gram of dry matter. For a fibrous sheet intended for the field of packaging, in particular bags, the ionic demand will in particular be from 1 to 4 milliequivalents per gram, and for a fibrous sheet intended for the field of printing, the ionic demand will notably be the order of 10 milliequivalents per gram.

In addition to the fibers, the mineral filler, the organic binder, the anionic polymer and the cationic flocculants I and II, it is possible to use, in the process for preparing a fibrous sheet according to the invention, various conventional additives in papermaking such as
- The bonding agents usually used in paper mills to reduce the water sensitivity of the sheet, such as modified rosins, paraffin emulsions, alkyl ketene dimers,
pH-regulating agents, for example aluminum sulphate (which can act as flocculant II, as indicated above), or sulfuric acid to adjust the pH between 4.5 and 6 for a bonding in medium acid,
antifoam agents,
- optical brighteners,
- coloring or shading agents,
wet strength agents such as urea-formaldehyde, melamine-formaldehyde, glyoxal, cross-linked cationic polyalkylamine amines, melamine-formaldehyde condensation products and amino-caprolate acid,
fungicidal and / or bactericidal agents as well as conventional auxiliary additives for printing-writing coating baths such as dispersing agents (in particular haxanetaphosphate and sodium pyrophosphate), lubricating agents (especially fatty acid derivatives); for example sodium or calcium salts) and viscosity regulating agents (especially gelatin, ethylenediamine and urea).

 The method according to the invention, with regard to the above-mentioned contact times comprises a large number of continuous operations.

 The best mode of implementation of this method is given below.

Stage 10
a) cellulosic fibers in aqueous suspension from pulping in a pulper (non-integrated plant) or directly from the pulp mill (integrated plant) are stored at a concentration of 40-400 g / l with stirring in a vat
b) the cellulosic fibers are refined in a conventional Schoepper.Regler degree between 15 and 65 depending on the application, at a variable concentration of between 20 and 350 g / l, in particular between 20 and 60 g / l, at the using standard conical or double-disc reamers, or especially between 250 and 350 g / l, with special refiners for high concentration refining, especially in the case of the manufacture of packaging supports, in order to obtain a high resistance to At this level it is possible to introduce, if necessary, the organic and / or mineral fibers that are to be associated with the cellulosic fibers.
c) the anionic means required as indicated above are added with stirring to make the fibers substantive, at a dose of between 0.02 and 0.5% and preferably 0.05 to 0.2% by weight relative to weight of the fibrous sheet.

Stage 20
a) The inorganic filler is dispersed in an aqueous medium at a concentration of between 150 and 600 g / l, preferably at a concentration of 300-400 g / l. This inorganic filler may consist entirely of an opacifying agent or of a mixture of several fillers including an opacifying agent. Preferably, the opacifying agent is here a cobbled mixture (d50 = 0.5 1.5 μm) obtained from 80% by weight of talc-chlorite (1: 1) by weight (d50 = 10 m) and of 20% by weight of TiO2 (d50 = 80 m).

 b) The organic binder ready for use if it is a latex or after cooking if it is native starches, etherified, oxidized or subject to enzymatic degradation, dextrins or esters of starches, is in the form of an aqueous preparation at a concentration of between 20 and 300 g / l, preferably between 20 and 200 g / l. The preferred binder is native starch.

c) mixing is carried out with stirring, preferably
continuously, the aqueous suspension of the load
mineral and aqueous preparation of the binder.

This operation is advantageously carried out in a
conical dynamic mixer with propeller which ensures a
perfect homogeneity of the charge-binder mixture.

Flocculant I is incorporated in said charge mixture
binder after being diluted with water from 10 to
100 times (dilution greater than 10 times and lower
or equal to 100 times). The amount of flocculant I that
one introduces is between 0.006 and 5 parts in
weight, and preferably between 0.01 and 2 parts in
weight per 100 parts by dry weight of the mixture
binder.

 In practice, the charge suspension is introduced continuously, on the one hand, and the aqueous binder preparation, on the other hand, each in the vicinity of the top of a conical spiral mixer with a propeller; the flocculant I is introduced continuously in the vicinity of the middle of the height of said mixer which comprises, near its lower end, a dilution water inlet, to carry out the required dilutions. The charged mixture thus preflocculated is continuously collected at the lower end of the mixer.

Stadium 30
The preflocculated feed-binder mixer in aqueous suspension at 100-200 g / l is fed continuously to the top circuits in the aqueous suspension of the fibers prepared in stage 1, the average diameter of the flocs of said batch-binder mixture being between 0.01 and 0.3 mm, and preferably between 0.03 and 0.15 mm, the introduction of said premixed mixture being made as close as possible to the headbox so that the contact time of said charge-binder mixture with the fibers is less than 60 seconds and advantageously between 10 and 45 seconds.

Stadium 40
Upstream of the headbox is incorporated in the mixture resulting from stage 30 a small amount of flocculant II to strengthen the bond flocs eL improves: the final retention on the web of the paper machine, the contact time flocculant II with the flocculated fiber-filler-binder mixture being less than 45 seconds and preferably between 8 and 30 seconds.

Remarks
The other above-mentioned additives such as bonding agents, optical brighteners, etc. can be incorporated either after the refining of the cellulosic fibers in stage 10 or after the introduction of the preflocculated charge-binder mixture of stage 30.

 Other advantages and characteristics of the invention will be better understood on reading the following description of examples of preparation and comparative tests. All of these elements is not limiting but is given by way of illustration for a particular purpose: improvement of retention and opacity.

 For convenience, the fibrous sheets obtained according to the process of the invention are referred to as "Ex" products, the fibrous sheets according to the prior art are referenced as "A" products (conventional technique) and "B" (technical of FR-A-2 492 425).

EXAMPLE 1
Preparation of a print-writing medium
A fibrous sheet is prepared according to the best mode given above from cellulosic fibers consisting of a mixture of
bleached bisulfite fibers 40% by weight
bleached kraft hardwood fibers 60% by weight
refining .............................................. 35 SR and opacity pigment according to Example 1 of the French application
N 84 19957 obtained by co-milling a mixture of
TiO2 (anatase), d50 = 80 microns 20% by weight
Talc-chlorite (1 :: 1) by weight, d50 = 10 microns u 80% by weight
Average particle size of cobroyate ...................... d50 = 0.8 micron the other operating conditions being as follows
Average diameter (dm) of the flocs
of the mixture charge-binding introduces
at stage 3 ............................................ 0.03 = 0.15 mm
Duration of contact (tl) of the mixture
load-binder preflocculated with the
................................................. fibers 40 seconds
Contact time (t2) of the flocculant
II with fiber-filler mixture
binding 25 seconds
A useful fibrous sheet is formed as a printing medium having a basis weight of 64 g / m 2.
COMPARATIVE TEST I
The sheet obtained according to Example 1 was compared with control sheets obtained according to a conventional technique (A1) and according to the teaching of FR-A-2 492 425 (B1) having the same gramming (64 g / m), from the same cellulosic fibers (35
SR) of the same variety of TiO2 (d50 = 0.8 micron after grinding of titanium dioxide of d50 = 80 micron) for Al, and of the same opacity pigment for B1, obtaining the fibrous sheet B1 comprising in addition to the following
Average floc diameter of the charge-binder mixture introduced in Step 3 0.35-0.50 mm
Contact time t1 ............................... 80 seconds
Contact time t2 ............................... 60 seconds
The amounts of the constituents, the mechanical properties and the material costs of said sheets have been recorded in Table I below.

TABLE I
SUPPORTS FOR PRINTING-WRITING
(orammage = 64 g / m2)

<tb><SEP> Ex <SEP> 1 <SEP> B <SEP> 1 <SEP> A <SEP> 1
<tb><SEP> Composition <SEP> in <SEP> parts <SEP> in <SEP> weight
<tb> Cellulose <SEP> Fiber <SEP> (35 SR) <SEP> 100 <SEP> 100 <SEP> 100
<tb> Polymer <SEP> anionic <SEP> (a) <SEP> 0.05 <SEP> 0.05 <SEP> 0
<tb><SEP> Talc <SEP> 30 <SEP> 30 <SEP> 30
<tb> TiO2 <SEP> 0 <SEP> 0 <SEP> 3
<tb><SEP> Opacity Pigment <SEP><SEP> (b) <SEP> 5 <SEP> 5 <SEP> 0
<tb> Binders <SEP> (native <SEP> starch) <SEP> 1 <SEP> 1 <SEP> 0
<tb> Flocculant <SEP> I <SEP> (c) <SEP> 0.1 <SEP> 0.1 <SEP> 0.1
<tb> Rosin <SEP> 2 <SEP> 2 <SEP> 2
<tb> Flocculant <SEP> II <SEP> (d) <SEP> (e) <SEP> (e) <SEP> (e)
<tb> Cost <SEP> composition <SEP> FF / kg <SEP> 3.35 <SEP> 3.45 <SEP> 3.70
<tb> Properties
<tb> Retention <SEP> (%) <SEP> 82 <SEP>% <SEP> 75 <SEP>% <SEP> 70 <SEP>%
<tb> Contrast Opacity <SEP> (Photovolt) <SEP> 81 <SEP> 80 <SEP> 39
<tb> Opacity <SEP> to <SEP> Oil <SEP> 39 <SEP> 39 <SEP> 39
<tb> Length <SEP> of <SEP> break <SEP> 3555 <SEP> 3350 <SEP> 3155
<tb> average <SEP> (m)
<tb> burst index <SEP><SEP> medium <SEP> 2 <SEP> 1.8 <SEP> 1.6
<Tb>
Notes
(a) modified polyacrylamide
(b) as defined in Example 1 above
(c) polyethyleneimine
(d) aluminum sulphate
(e) in sufficient quantity to adjust the pH to 4.5-5
The results in Table I show that Ex 1 obtained by the method of the invention has mechanical properties (average breaking length, average burst index and especially retention) significantly improved compared to Al and B1, for identical opacity.

EXAMPLE. 2
Preparation of a fibrous sheet for printing
writing 2
A fibrous sheet is prepared in 64 g / m from the cellulosic fibers and the opacity pigment according to Example 1 above with the same values for dm, t1 and respectively t2.

COMPARATIVE TRIAL II
The fibrous sheet of Example 2 was compared with a fibrous sheet (A2) obtained under substantially similar conditions with respect to the choice of cellulosic fibers, binder and flocculant I, the opacity pigment being replaced by TiO2. as in Comparative Test I above
The amounts of the constituents, the mechanical properties and the material costs of said sheets have been recorded in Table II below.

the results given in Table II confirm those given in Table I. In particular, it can be seen that
Ex 1 and Ex 2 allow savings of 7 to 10% and are very favorable, for an identical opacity, to the improvement of the retention and the mechanical properties. The economic balance can be increased by preparing sheets Ex 1 and Ex 2 in 60 g / m instead of 64 g / m in view of the very good mechanical properties of the products according to the invention.

TABLE II
SUPPORTS FOR PRINTING-WRITING
(Weight = 64 g / m)

<tb><SEP> I <SEP> I
<tb><SEP> Ex <SEP> 2 <SEP> A2
<tb> J <SEP> Compositions <SEP> in <SEP> parts <SEP> in <SEP> weight <SEP>#<SEP><SEP> I
<tb>#
<tb> j <SEP> Cellulose <SEP><SEP> (350SR) <SEP> j <SEP><SEP> 100 <SEP> j <SEP> 100
<tb><SEP>#
<tb> J <SEP> Polymers <SEP> anionic <SEP> (a) <SEP> 1 <SEP> 0.05 <SEP> 1 <SEP> 0 <SEP>#<SEP>
<tb> Talc <SEP> 0 <SEP> 0
<tb>#<SEP> TiO2 <SEP><SEP> i <SEP> O <SEP> j <SEP> 4 <SEP> l <SEP>
<tb> Opacity <SEP> Pigment <SEP> (b) <SEP> 7 <SEP> 0
<tb> Binders <SEP> native starch <SEP><SEP> 1 <SEP> 0
<tb> Flocantant <SEP> I <SEP> (c) <SEP> 0.1 <SEP> 0.1
<tb> Rosin <SEP> 2 <SEP> 2
<tb> Flocculant <SEP> II <SEP> (d) <SEP> (e) <SEP> (e)
<tb> Cost <SEP> composition <SEP> FF / kg <SEP> 3.90 <SEP> 4.30
<tb> Properties
<tb> Retention <SEP> (%) <SEP> 88 <SEP>% <SEP> 75 <SEP>%
<tb> Contrast Opacity <SEP> (Photovolt) <SEP> 79 <SEP> 78
<tb> Opacity <SEP> to <SEP> oil <SEP> j <SEP> 40.5 <SEP> 1 <SEP> 41 <SEP> j <SEP>
<tb> Length <SEP> of <SEP> breaking <SEP> average <SEP> (m) <SEP> 6150 <SEP> 5620
<tb>#<SEP><SEP><SEP> Burst Index <SEP> Medium <SEP> 1 <SEP> 4.1 <SEP> 1 <SEP> 3.6 <SEP> 1 <SEP>
<Tb>
Notes
(a) - (e): see table I
EXAMPLE 3
Preparation of a fibrous sheet for packaging
A fibrous sheet for packaging in 70 g / m 2 was prepared from a blend of cellulosic fibers comprising bleached kraft softwood fibers 50% by weight
bleached kraft fiber fibers 50% by weight refining of the opacity pigment according to Example 1 above with values dm, t1 and t2 identical to those of example 1.

COMPARATIVE TRIAL III
The product obtained according to Example 3 was compared with a conventional fibrous sheet (A3) in 70 g / m in which the opacity pigment was replaced by TiO 2, the cellulosic fibers and the average particle size of the paper TiO 2 being respectively identical to the fibers of Example 3 and the average particle size of the opacity pigment. The compositions of Ex 3 and A3, as well as the results that have been obtained, are shown in Table III.
TABLE III
PAPERS FOR PACKAGING
(orammage = 70 g / m2)

<tb><SEP> Ex <SEP> 3 <SEP> A3
<tb><SEP> Compositions <SEP> in <SEP> parts <SEP> in <SEP> weight
<tb><SEP> Cellulose Fiber <SEP><SEP> (35 SR) <SEP> 100 <SEP> 100
<tb><SEP> I <SEP> Anionic <SEP> Polymer <SEP> (a) <SEP><SEP><SEP> 0.05 <SEP> 1 <SEP> 0 <SEP>#<SEP>
<tb><SEP> TiO2 <SEP> 0 <SEP> 5
<tb><SEP> I <SEP> I
<tb><SEP> Opacity Pigment <SEP><SEP> (b) <SEP> 15 <SEP> 0
<tb><SEP> Binders <SEP> native starch <SEP><SEP> 1 <SEP> 1
<tb><SEP> I <SEP> I
<tb><SEP> Flocculant <SEP> I <SEP> (c) <SEP> 0.15 <SEP> 0.15
<tb><SEP> Rosin <SEP> 2 <SEP> 2
<tb> Flocculant <SEP> II <SEP> (d) <SEP> (e) <SEP> (e)
<tb><SEP> J <SEP> Cost <SEP> composition <SEP> FF / kg <SEP> 3.95 <SEP> 1 <SEP> 4.36 <SEP> 1 <SEP>
<tb><SEP>##
<tb><SEP> I <SEP> Properties <SEP>#<SEP> I
<tb><SEP>#
<tb><SEP> I <SEP> Contrast Opacity <SEP> (Photovolt) <SEP>#<SEP><SEP> 86 <SEP> J <SEP> 81 <SEP>#<SEP>
<tb><SEP> Opacity <SEP> to <SEP> Oil <SEP> 53 <SEP> 53
<tb><SEP> Burst <SEP> Burst <SEP> Average <SEP> 3.95 <SEP> 4
<Tb>
Notes
(a) - (e): see table I above
EXAMPLE 4 AND COMPARATIVE TRIAL IV
Preparation of a basic support for carbonless
According to the invention (Ex 4), a base support for carbonless material is prepared from a mixture of cellulosic fibers comprising
bleached kraft softwood fiber 60% by weight
bleached kraft leaf fibers 40% by weight
SO0SR refining
the opacity pigment is identical to that of Example -1 above and the dm, t and t values. The support thus has a basis weight of 40 g / m 2.

 The comparison product (A4) is obtained from the same fibers, replacing the opacity pigment with TiO2 (d50 = 0.8 micron). The corresponding results are shown in Table IV below.

TABLE IV
BASIC SUPPORTS FOR AUTOCOPIERS
(Weight: 40 g / m2)

<tb><SEP> I <SEP> I
<tb><SEP>#<SEP>#
<tb><SEP><SEP> Ex <SEP> 4 <SEP> 1 <SEP> A4 <SEP>#<SEP>
<tb> Composition <SEP> in <SEP> parts <SEP> in <SEP> weight
<tb><SEP> cellulosic <SEP> fibers <SEP> (50 SR) <SEP> 100 <SEP> j <SEP> 100 <SEP> I
<tb> Anionic <SEP> Polymer <SEP> (a) <SEP> 0.05 <SEP> 0
<tb>#<SEP> Talc <SEP><SEP> 15 <SEP> g <SEP> 15 <SEP> 1 <SEP>
<tb> TiO2 <SEP> 0 <SEP> 5
<tb> Opacity <SEP> Pigment <SEP> (b) <SEP> 15 <SEP> 0
<tb> Binders <SEP> (native <SEP> starch) <SEP> 1 <SEP> 0
<tb> Flocculant <SEP> I <SEP> (c) <SEP> 0.1 <SEP> 0.1
<tb> J <SEP> Rosin <SEP> g <SEP> 2 <SEP> @ <SEP> 2 <SEP><SEP> 21 <SEP>
<tb> Flocculant <SEP> II <SEP> (d) <SEP> (e) <SEP> (e)
<tb><SEP> I <SEP> J
<tb><SEP> I <SEP> I <SEP> J
<tb> J <SEP> Cost <SEP> composition <SEP> @ <SEP> 3.65 <SEP> 1 <SEP> 4 <SEP> l <SEP>
<tb><SEP> Properties
<tb> J <SEP> Properties <SEP> J <SEP>
<tb> Retention <SEP>% <SEP>#<SEP><SEP> 88 <SEP>% <SEP> 1 <SEP> 75 <SEP>%
<tb><SEP> I <SEP> I
<tb>#<SEP> Contrast opacity <SEP><SEP> (Photovolt) <SEP> j <SEP><SEP> 71 <SEP> 1 <SEP> 70 <SEP> j <SEP>
<tb><SEP>#<SEP>#
<tb> Opacity <SEP> to <SEP> Oil <SEP>#<SEP><SEP> 39.5 <SEP> 1 <SEP> 40 <SEP> 1 <SEP>
<tb><SEP>#<SEP>#
<tb> Length <SEP> of <SEP> Rupture <SEP> average <SEP> (m) <SEP>#<SEP><SEP> 4650 <SEP> 1 <SEP> 4255 <SEP><SEP> i <SEP >
<tb> Explosion <SEP><SEP> 2.6 <SEP> 2,3
<Tb>
Notes
(a) - (e): see table I above
EXAMPLE 5 and COMPARATIVE TEST V
Preparation of a support for stratification
A support for lamination (Ex 5) according to the invention is prepared from a mixture of cellulosic fibers comprising
bleached bisulfite softwood fibers 40% by weight bleached kraft leaf fibers 60 X by weight
refining 28 SR
the opacity pigment is identical to that of Example 1 above, as well as the values dm, t1 and t2. We obtain a support for stratification of 90 g / m.

 The comparison product (A5) is obtained from the same fibers, replacing the opacity pigment with TiO2 (d50 = 0.8 micron). The corresponding results are shown in Table V below. It is found that the economy on the cost of the composition exceeds 25%.

TABLE V
SUPPORTS FOR LAMINATE
- (Weight = 90 g / m2)

<tb><SEP>#<SEP>#
<tb><SEP> Ex <SEP> 5 <SEP> 5 <SEP> AS <SEP> AS
<tb>#<SEP>#
<tb> | <SEP> Composition <SEP> in <SEP> parts <SEP> in <SEP> weight
<tb> Cellulose <SEP> Fiber <SEP> (28 SR) <SEP> 100 <SEP> 100
<tb> J <SEP> Polymer <SEP> anionic <SEP> (a) <SEP> 1 <SEP> 0.05 <SEP>#<SEP>#<SEP> 0 <SEP> O
<tb> TiO2 <SEP> 10 <SEP> 30
<tb> Opacity <SEP> Pigment <SEP> (b) <SEP> 50 <SEP> 0
<tb><SEP> I <SEP> I
<tb> Binders <SEP> (native <SEP> starch) <SEP> 1 <SEP> 0
<tb> R
<tb> J <SEP> Flocculant <SEP> I <SEP> (Krmene <SEP> 557 <SEP> H) <SEP> j <SEP> 2 <SEP>#<SEP> 22
<tb><SEP> I <SEP> I
<tb> Flocculant <SEP> II <SEP> polyethyleneimine <SEP> 0.1 <SEP> 0.1
<tb> J <SEP> Cost <SEP> composition <SEP> FF / kg <SEP> 1 <SEP> 4.60 <SEP> 1 <SEP> 5.90 # <SEP>
<tb>#
<tb> Properties <SEP>
<tb> Opacity <SEP> - <SEP> contrast <SEP> (Photovolt) <SEP> 95 <SEP> 95
<tb> Opacity <SEP> to <SEP> oil <SEP> 83.5 <SEP> 84
<Tb>
Notes
(a) - (b) = see Table I above
The study of Tables I to V concludes that
(i) the opacity pigment according to the patent application
aforementioned French NO. 84 19957 (TALCS DE LUZENAC)
obtained by co-grinding is particularly interesting
on the industrial level, the results obtained here
confirming those given in said application, (ii) the method according to FR-A-2 492 425 improves the retention
and hence the opacity of the fibrous leaves when
said opacity pigment is used, and (iii) the method according to the present invention is very
favorable for opacity, since for one
same opacity, it improves the retention and
mechanical properties and leads to savings of
important raw materials compared to art
prior.

Claims (10)

A process for preparing a fibrous sheet by papermaking for improving the retention, said method, in which the mixture of the inorganic filler and the preflocculated organic binder is introduced into the top circuits of the paper machine. the aqueous suspension of fibers, then introduced before the headbox a flocculating agent in the resulting aqueous suspension, being characterized in that  10) an aqueous suspension of fibers is prepared  20) an aqueous suspension of mineral filler is prepared  and binder in which the charge-binder mixture  is preflocculated with a cationic flocculant  30) at the head circuits of the paper machine  and before the headbox of this one, one introduces  the aqueous suspension of the prefloc charge-binder mixture  in the aqueous suspension of the fibers, such  way that (i) the average diameter of the flocs of the mixture  load-binder that is introduced into said suspension  fibers are between 0.01 and 0.3 mm, and (ii)  the duration of contact of said charge-binder mixture with  the fibers in the resulting suspension are included  between 10 and 60 seconds  40) before the headbox, a flocculant is introduced  cationic in the aqueous suspension of the mixture  fibers-filler-binder obtained in stage 30), such  way that the duration of contact of said flocculant with  said fiber-filler-binder mixture is lower  at 45 seconds  50) the resulting aqueous suspension is introduced into  the headbox and form a sheet on machine  to paper that is pressed and dried. 2. Method according to claim 1, characterized in that the mineral filler contains an opacifying agent. 3. A process for preparing a fibrous sheet by paper means for improving retention and opacity, said method, wherein (i) introducing at the head circuits of the paper machine, the mixture of the mineral filler and organic binder preflocculated in the aqueous suspension of fibers, the inorganic filler containing an opacifying agent chosen from pigments consisting of a mixture of 10 to 70% by weight of TiO 2 and 90 to 30% by weight of layered silicate and obtained by co-milling of P.sub.2O.sub.2 and lamellar silicate to generate adsorption of fragmented TiO.sub.2 particles on the activated surfaces of the fragmented lamellar silicate particles, and then (ii) introducing a flocculating agent into the slurry prior to the headbox. aqueous solution, being characterized in that  10) an aqueous suspension of fibers is prepared  20) an aqueous suspension of mineral filler is prepared  and binder in which the charge-binder mixture  S ~ is preflocculated by means of a cationic flocculant  30) at the level of the head circuits of this one, one intro  the aqueous suspension of the charge-binder mixture  pre-flocculated in the aqueous suspension of the fibers,  such that (i) the average diameter of the flocs of the  charge-binding mixture which is introduced into said  suspension of the fibers is between 0.01 and  0.3 mm, and (ii) the contact time of said mixture  load-binder with the fibers in the suspension  result is between 10 and 60 seconds  40) before the headbox, a flocculant is introduced  cationic in the aqueous suspension of the mixture  fibers-filler-binder obtained in stage 30), such  way that the duration of contact of said flocculant with  said fiber-filler-binder mixture is lower  at 45 seconds  50) the resulting aqueous suspension is introduced into  the headbox and forms a sheet on machine to  paper that is pressed and dried. 4. Method according to any one of claims 1 and 3, characterized in that the fibers of stage 10 are made substantive by addition of an anionic means. 5. Method according to claim 4, characterized in that the anionic means is an anionic organic polymer used at a content of 0.02 to 0.5% by weight, and preferably 0.05 to 0.2% by weight, relative to the weight of the fibrous sheet. 6. Method according to any one of claims 1 and 3, characterized in that the average diameter of the floc load-binder mixture that is introduced in stage 30 in the aqueous suspension of the fibers is between 0.03 and 0 , 15 mm. 7. Method according to any one of claims 1 and 3, characterized in that the contact time of the charge-binder mixture preflocculated and introduced in stage 30, with the fibers is between 10 and 45 seconds. 8. Process according to any one of claims 1 and 3, characterized in that the contact time of the cationic flocculant introduced at stage 40 with the mixture fibres-charge-Xiantiscomprise between 8 and 30 seconds. 9. Process according to any one of claims 1 and 3, characterized in that the ionic demand of the fibers is less than or equal to 20 milliequivalents per gram of dry matter. 10. fibrous sheet, characterized in that it is obtained according to the method of any one of claims 1 to 9.