BRPI0720496A2 - CELLULOSTIC PRODUCT PRODUCTION PROCESS - Google Patents

Abstract

The present invention relates to a process for the production of a cellulosic product which comprises providing an aqueous thick suspension containing cellulosic fibers having a fiber concentration of at least about 2% by weight; adding to the thick suspension an aluminum compound, alkaline earth metal salt and acid; diluting the obtained thick suspension to form a thin suspension; adding to the thin suspension one or more drainage and retention aids; and dewatering the obtained thin suspension. The invention further relates to a process for the production of a cellulosic product which comprises providing an aqueous thick suspension containing cellulosic fibers having a fiber concentration of at least about 2% by weight and an alkaline earth metal ion concentration of at least about 100 mg/l; adding to the thick suspension an aluminum compound and optionally an acid to obtain a pH of from about 4 to about 5.5; diluting the obtained thick suspension to form a thin suspension; adding to the thin suspension one or more drainage and retention aids; and dewatering the obtained thin suspension. The invention also relates to an aqueous composition comprising a mixture of an aluminum compound, alkaline earth metal salt and acid and the use of the composition.

Description

Report of the Invention Patent for "CELLULOSTIC PRODUCT PRODUCTION PROCESS".

Field of the Invention

The present invention relates to a process for producing a cellulosic product. More specifically, the invention relates to a process for the production of a cellulosic product comprising the addition of certain additives to an aqueous suspension containing cellulosic fibers before it is dehydrated to form the cellulosic product. Background of the Invention

In the papermaking technique, an aqueous suspension containing cellulosic fibers, and optional fillers and additives, is fed into an upper case that ejects the suspension into a forming wire. Water is drained from the suspension through the forming wire so that a damp paper web is formed on the wire, and the paper web is then dehydrated and dried in the drying section of the paper machine. Drainage and retention aids are conveniently introduced into the suspension to facilitate drainage and increase the adsorption of fine particles on the cellulosic fibers so that they are retained with the fibers on the wire.

Aqueous suspensions containing cellulosic fibers may contain, in addition to cellulosic fibers, compounds that have a negative impact on the production process. Such compounds can be observed in both suspensions originating from virgin pulp and recycled pulp. Compounds that are released during pulping and bleaching operations are commonly referred to as pitch. Examples of pitch include wood resins such as lipophilic extractants (fatty and resinous acids, sterols, stearyl esters, triglycerides) as well as fats, terpenes, terpenoids, waxes, etc. These compounds contribute to a high anionic load of the suspensions.

In addition, especially in closed mills where white water is widely recirculated, suspensions may also comprise filler contaminants such as salts and various wood polymers in which the filler, low filler and no filler compounds compete with adsorption and interaction with added performance chemicals such as drainage and retention aids, bonding agents, etc. Generally such disturbing compounds are referred to as anionic waste.

All of the above compounds interfere with pulp and paper production processes in various ways. To compensate for the high anionic charge caused by disturbing substances, increased amounts of cationic additives that contribute to improved dehydration and retention have been used in papermaking processes.

U.S. Patent No. 4,388,150 discloses the use of a cationic starch together with colloidal silicic acid to improve retention and drainage and to improve the characteristics of paper resulting in a papermaking process in which mineral fillers are used.

EP-A 0 700 473 describes a papermaking process wherein retention and / or dehydration is improved by adding a cationic long chain polyacrylamide to an aqueous suspension containing cellulosic fibers and then a polymeric aluminum salt. and a base or an acid.

Despite the fact that considerable improvements have been made in the drainage and retention of aqueous suspensions containing cellulosic fibers, there is still a need for improvements, especially when producing aqueous pulp products derived from mechanical pulps. . Therefore, it is an object of this invention to provide a process for the production of a cellulosic product with further improvements in drainage and retention of the production process. Other goals will follow.

Summary of the Invention The present invention is directed to a process for the production of

a cellulosic product comprising:

(i) providing an aqueous slurry containing cellulosic fibers having a fiber concentration of at least about 2% by weight; (ii) add to the thick suspension;

(I) an aluminum compound;

(II) an alkaline earth metal salt;

(III) an acid;

(iii) diluting the thick suspension obtained to form a thin suspension;

(iv) adding to the thin suspension one or more drainage and retention aids; and

(v) dehydrate the thin suspension obtained.

The present invention is also directed to a process for producing a cellulosic product comprising:

(i) provide a thick aqueous suspension containing cellulosic fibers having:

(a) a fiber concentration of at least 2% by weight;

(b) an alkaline earth metal ion concentration of at least about 100 mg / l;

(ii) adding to the slurry an aluminum compound and optionally an acid to obtain a pH of from about 4 to about 5.5;

(iii) diluting the thick suspension obtained to form a thin suspension;

(iv) adding to the thin suspension one or more drainage and retention aids; and

(v) dehydrate the thin suspension obtained.

The present invention is further directed to an aqueous composition comprising a mixture of:

(I) an aluminum compound;

(II) an alkaline earth metal salt; and

(III) an acid;

wherein the weight ratio of the aluminum compound, alkaline earth metal salt and acid ranges from about 60: 1: 0.1 to about 5: 1: 1.

The present invention is further directed to the use of the aqueous composition as an additive in a process for the production of a cellulosic product. Detailed Description of the Invention

In accordance with the present invention it has been observed that drainage and retention can be improved without any significant loss of formation, or even with improvements in paper formation, by a process comprising the addition of an aluminum compound. acid alkaline earth metal salt in an aqueous suspension containing cellulosic fibers having a fiber concentration of at least about 2% by weight, also referred to herein as a thick suspension, diluting the thick suspension to form a thin suspension, also referred to herein as a dilute suspension, and adding to the fine suspension one or more drainage and retention aids and dehydration of the thin suspension obtained to form the cellulosic product.

The present invention provides improvements in drainage, retention and yield in the production of cellulosic products of all types of cellulosic suspensions, and in particular suspensions containing mechanical or recycled pulp, and suspensions having high salt (high conductivity) and colloidal substance contents. , and in papermaking processes with a high degree of whitewater occlusion, that is, extensive whitewater recycling and limited freshwater supply. By the present invention it is possible to increase the speed of the paper machine and to use lower dosages of additives to provide corresponding drainage and / or retention effects, thereby washing out an improved papermaking process and economic benefits. .

Aluminum compounds which may be used according to the invention include alum, aluminate, for example sodium or potassium aluminate, aluminum chloride, aluminum nitrate, and polyaluminium compounds containing both chloride and sulfate ions. , polyaluminium silicate sulfate, and mixtures thereof. Polyaluminium compounds may also contain other anions, for example phosphoric acid anions, organic acids such as citric acid and oxalic acid. Alum, as used herein, includes not only a double salt of potassium aluminum sulfate K2SO4xAl2 (SO4) 3x24H20, but also aluminum sulfate AI2 (SO4) 3x14H20, AI2 (SO4) 3x18H20 and mixtures thereof. Examples of suitable aluminum compounds include those described in U.S. Patent No. 5,127.94, which is hereby incorporated by reference. Conveniently, the aluminum compound is selected from alum, aluminum chloride, polyaluminium compounds such as polyaluminium chloride and polyaluminium sulfate silicate, and aluminate, preferably alum.

Alkaline earth metal salts which may be used in accordance with the invention include magnesium, calcium and barium salts. The salts may have an anion selected from halides, sulfates, carbonates, nitrates or organic acids. Conveniently, the alkaline earth metal salt is selected from magnesium and calcium salts, for example magnesium chloride, magnesium sulfate, calcium chloride and barium sulfate. Preferably, the alkaline earth metal salt is a magnesium salt. In a preferred embodiment of the invention, the alkaline earth metal salt is added to the thick suspension to obtain an alkaline earth metal ion concentration of at least about 100 mg / l, suitably at least about 150 mg / l and preferably at least 200 mg / l. The thick suspension may have a high concentration of alkaline earth metal salts based on Ca2 + and Mg2 + ions whose salts may be derived from the cellulosic fibers and fillers used to form the suspension, particularly in integrated mills where an aqueous fiber suspension The pulp mill concentrate is mixed with water to form a dilute suspension suitable for papermaking in the paper mill. Salts may also be derived from various additives introduced into the slurry and from fresh water supplied to the process. Salt concentration is generally higher in processes where white water is widely recirculated, which can lead to considerable salt accumulation in the water circulation in the process. Therefore, a thick suspension having an alkaline earth metal ion concentration of at least about 100 mg / l may be provided without any further addition of an alkaline earth metal salt.

Acids which may be used according to the invention include inorganic acids, for example sulfuric acid, hydrochloric acid, phosphoric acid, hydrochloric acid and nitric acid, and organic acids such as carboxylic acids, for example acid oxalic and citric acid. Preferably the acid is an inorganic acid, preferably hydrochloric acid or sulfuric acid. The acid is added to the slurry to obtain a pH within the range of about 2 to about 6, for example within the range of about 4 to about 5.5. The defined pH range can also be obtained only by adding the aluminum compound to the thick suspension. In another preferred embodiment of the invention, an acid is optionally added to the thick suspension to obtain a pH of from about 4 to about 10.5. Preferably, the addition of optional aluminum compound and acid according to the invention results in a reduction in the pH of the thick suspension to the indicated range. For example, the thick suspension to which the aluminum compound and optional acid are added may have a pH of at least about 6, for example at least about 6.5.

According to a preferred embodiment of the invention, one or more

More of the aluminum compounds, alkaline earth metal salts and acids are added to a thick suspension of a papermaking process. The thick suspension may be derived from various pulp species, such as a chemical pulp, such as sulfate and sulfite pulp, mechanical pulp, such as thermo-mechanical pulp, chemo-thermomechanical pulp, orgasolv pulp, refiner pulp. or sawdust from either softwood or hardwood, or fibers derived from an annual plant such as elephant grass, bagasse, flax, straw, etc., and suspensions based on recycled fibers. In a preferred embodiment of the invention, the thick suspension contains mechanical pulp derived cellulosic fibers, and preferably the mechanical pulp content is at least 50% by weight based on the total weight of the pulp. One or more of the aluminum compound, alkaline earth metal salt and / or acid may be added subsequent to chemical digestion, such as after the brown load washer, or after pulp refining (chemo- ) mechanical. Generally, the pulp is targeted in a multistage bleaching process comprising different bleaching stages. Examples of suitable bleaching stages include chlorine bleaching stages, for example, chlorine and elemental chlorine dioxide bleaching stages, chlorine-free bleaching stages, for example peroxide stages such as ozone, hydrogen peroxide and peracetic acid. , and combinations of chlorine and non-chlorine bleaching and oxidation stages, optionally in combination with reduction stages such as dithionite treatment. The pulp may be subjected to hydrogen peroxide bleaching and one or more of the aluminum compounds, alkaline earth metal salts and acids are added after the bleaching stages. In a preferred embodiment of the invention, one or more of the aluminum compounds, alkaline earth metal salts and acids are added to the thick suspension at the dilution point after the bleaching stage. In another preferred embodiment of the invention, one or more of the aluminum compounds, alkaline earth metal salts and acids are added to the slurry in a mixer 15 before the slurry reaches the pulp storage tank. In another preferred embodiment of the invention, one or more of the aluminum compounds, alkaline earth metal salts and acids are added to the thick suspension after the storage tank on the way to the paper mill mixing bowl. At the point of addition to the aluminum compound, alkaline earth metal salt and acid, the thick suspension has a fiber concentration of at least about 2%, suitably at least about 3% and preferably at least about 3.5% by weight. The concentration may be up to about 10% by weight. Preferably, when the acid aluminum, salt and alkaline earth metal compound is added to the slurry of a pulp making process, the slurry obtained is subsequently used in a paper mill process. integrated.

The aluminum compound, alkaline earth metal salt and acid, also referred to herein as the components, may be separately or simultaneously added to the thick suspension. When components are separately added, they can be added in any order. Conveniently, the aluminum compound is added prior to the addition of the alkaline earth metal salt and / or acid, and the alkaline earth metal salt may be added before, simultaneously or after the acid. When components are simultaneously added, they may be added separately and / or in the form of a mixture. Examples of suitable simultaneous addition methods include the addition of the three components separately, in a composition comprising the components, and by the addition of one of the components separately and two of the components as a mixture. The mixture may comprise the aluminum compound and one or both of the alkaline earth metal salt and acid. In a preferred embodiment of the invention, the aluminum compound and the alkaline earth metal salt are simultaneously added as a mixture, and the acid is optionally added to the thick suspension.

The present invention further relates to an aqueous composition comprising a mixture of the above components as well as their use. The aqueous composition is suitably used as an additive in a process for the production of a cellulosic product, preferably as a drainage and retention aid in such a process. Preferably, the composition is used in combination with one or more drainage and / or retention aids, which preferably comprises at least one cationic polymeric retention agent and which is preferably added to the thin suspension. Preferably, the composition is aqueous. The aluminum compound, alkaline earth metal salt and acid may be present in a dry matter content ranging within a wide range of 5 to 99 wt%, suitably 20 to 90 wt%. The components may be present in the composition in a weight ratio of aluminum compound, alkaline earth metal salt and acid from about 60: 1: 0.01 to about 5: 1: 0.1. The composition according to the invention can be readily prepared by mixing the aluminum compound, alkaline earth metal salt and acid, preferably under stirring.

The components according to the invention may be added

to the thick suspension in amounts that may vary within wide limits. Generally, components are added in amounts that provide better drainage, retention and / or yield in the papermaking process than those obtained when components are not added. The aluminum compound is generally added in an amount of at least about 10 kg / tonne, referring to a metric tonne and based on the dry weight of the thick suspension, often at least about 30 kg / tonne. , and the upper limit is usually around 90 kg / ton and suitably around 40 kg / ton. Similarly, if used, alkaline earth metal salt is generally added in an amount of at least about 0.5 kg / ton, often at least 10 1.0 kg / ton, and the upper limit is usually around 40 kg / ton and suitably around 35 kg / ton. Similarly, the acid is generally added in an amount of at least about 0.01 kg / ton, often at least about 0.05 kg / ton and the upper limit is usually around 2.0 kg. / ton and adequately around 1.5 kg / ton. When using the aqueous composition according to the invention, it is generally added in an amount of at least about 10 kg / ton, often at least about 30 kg / ton, and the upper limit is conveniently around 120 kg. / ton and appropriately around 50 kg / ton.

Subsequent to the addition to the thick suspension of the aluminum compound, alkaline earth metal salt and acid according to the invention, the thick suspension is diluted to form a thin aqueous suspension containing cellulosic fibers having a fiber concentration of less than 2% by weight, herein also referred to as a thin suspension. The thin suspension generally has a fiber concentration of from about 0.2 to about 25, from 1.5 wt%, for example from about 0.5 to about 1.0 wt%. Dilution may be effected by any aqueous phase such as, for example, water, aqueous solution and aqueous suspension, for example white water or clarified white water.

Following the addition of the aluminum compound, alkaline earth metal salt and acid according to the invention, if desired, the pH of the thick or thin aqueous suspension may be increased to be in the range of from about 5.5 to about 10%. suitably from about 6 to about 9, and preferably from about 6 to about 8, by the addition of a base. Examples of suitable bases include alkali metal bicarbonates and carbonates and alkali metal hydroxides, conveniently sodium bicarbonate, sodium carbonate and sodium hydroxide, preferably sodium hydroxide.

The base may be added before, simultaneously or after the addition of drainage and retention aids. The base is preferably added before adding drainage and retention aids.

One or more drainage and retention aids are used according to the invention, preferably in a papermaking process. The process comprises diluting the thick suspension, which may be obtained from the pulping process, to form a final suspension, adding to the thin suspension one or more drainage and retention aids and dehydrating the suspension obtained. The term "drainage and retention aids" as used herein refers to one or more additives which, when added to a suspension containing cellulosic fibers, provides better drainage and retention than is obtained when no additives are added. said one or more additives.

Examples of suitable drainage and retention aids include cationic and anionic organic polymers, silicon materials, and mixtures thereof. The use of organic polymers and silicon materials as drainage and retention aids or as flocculating agents is well known in the art. Preferably at least one cationic polymer is used is used as a drainage and retention agent. The term "cationic polymer" as used herein refers to an organic polymer having one or more cationic groups. The cationic polymer may also contain anionic groups as long as the polymer has a full cationic charge. The term "anionic polymer" as used herein refers to an organic polymer having one or more anionic groups. The anionic polymer may also contain cationic groups as long as the polymer has a full anionic charge.

Suitable polymers for use in the process may be derived from natural or synthetic sources, and they may be linear, branched or cross-linked. Examples of suitable polymers include cationic polysaccharides, preferably starches; cationic and anionic chain growth polymers, preferably cationic and anionic acrylamide-based polymers; as well as cationic poly (diallyl dimethyl ammonium chloride); cationic polyethylene imines; cationic polyamines; cationic polyamide amines and vinylamide-based polymers. Cationic starch and cationic acrylamide based polymers are particularly preferred polymers and they may be used alone, together or with other polymers, for example other cationic and / or anionic polymers. The weighted average molecular weight of the polymer is suitably above 1,000,000 and preferably above

2,000,000. The upper bound is not critical; it can be around 50,000,000, usually 30,000,000 and suitably around 25,000,000. However, the molecular weight of polymers derived from natural sources may be higher.

Examples of suitable silicon materials include anionic silica-based particles and smectite-type anionic clays. Preferably, the silicon material has particles in the colloidal particle size range. Anionic silica based particles, i.e. SiO2 or silicic acid based particles 20 are preferably used and such particles are generally provided as aqueous colloidal dispersions, so-called sols. Examples of suitable silica-based particles include colloidal silica and different types of homopolymerized or copolymerized polysilicic acid, for example polymeric silicic acid, polysilicic acid microgel, polysilicate and polysilicate microgel. Silica-based sols may be modified and contain other elements, for example aluminum, boron, nitrogen, zirconium, gallium, titanium and more, which may be present in the aqueous phase and / or silica-based particles. . Examples of suitable silica-based particles of this type include colloidal aluminum modified silica, aluminum silicates, polyaluminyl silicate and polyaluminosilicate microgel. Mixtures of such suitable silica-based particles may also be used. Examples of drainage and retention aids comprising anonic silica-based particles include those described in U.S. Patent No. 4,388,250; 4,927,498; 4,954,220; 4,961,825; 4,980,025; 5,127,994; 5,176,891; 5,368,833; 5,447,604; 5,470,435; 5,543,014; 5,571,494;

5,573,674; 5,584,966; 5,603,805; 5,688,482 and 5,707,493; which are hereby incorporated herein by reference.

Examples of suitable anionic silica-based particles include those having an average particle size below about 100 nm, preferably below about 20 nm and more preferably in the range from about 1 to about 10 nm. While conventional in silica chemistry, particle size refers to the average size of primary particles, which may be aggregated or non-aggregated. The specific surface area of the silica-based particles is suitably above 50 m 2 / g and preferably above 100 m 2 / g. Generally, the specific surface area may be up to about 1700 m2 / g and preferably up to 1000 m2 / g. Specific surface area is measured by titration with NaOH in a well known manner, for example as described by G.W. Sears in Analytical Chemistry 28 (1956): 12, 1981-1983 and U.S. Patent No. 5,176,891. The given area thus represents the specific average surface area of the particles.

In a preferred embodiment of the invention, use is made of silica-based particles which are present in a sol having an S value in the range of 8 to 50%, preferably 10 to 40%. The S value can be measured and calculated as described by Iler & Dalton in J. Phys. Chem. 60 (1956), 25 955-957. The S value indicates the degree of aggregation or microgel formation and a lower S value is indicative of a higher degree of aggregation.

Examples of suitable smectite-type anionic clays include those that carry a negative charge on the surface, including montmorillonite / bentonite, hectorite, beidelite, nontronite, saponite, laponite, preferably bentonite. Examples of suitable anionic bentonite clays include those described in U.S. Patent 4,753,710; 5,071,512 and 5,607,552, which are hereby incorporated by reference.

Cationic coagulants, also referred to as anionic waste pickers and clamps, can of course likewise be used in the process according to the invention. Examples of suitable cationic coagulants include water soluble organic polymeric coagulants. Cationic coagulants may be used alone or together, ie a polymeric coagulant may be used in combination with an inorganic coagulant. Examples of suitable water soluble organic polymer cationic coagulants include cationic polyamines, polyamide amines, polyethylene imines, dicyandiamide condensation polymers and ethylenically unsaturated water soluble monomer polymers or monomer mixture which is formed from 50 to 100% molar cationic monomer and 0 to 50 mol% of another monomer. The amount of cationic monomer is generally at least 80 mol%, suitably 100%. Examples of suitable ethylenically unsaturated cationic monomers include dialkylaminoalkyl (meth) acrylates and -acrylamides, preferably in quaternized form, and diallyl dialkyl chlorides. ammonium, for example diallyl dimethyl ammonium chloride (DADMAC), preferably DADMAC homopolymers and copolymers. Organic polymeric cationic coagulants generally have a weighted average molecular weight in the range of 1,000 to

3,000,000, suitably from 5,000 to 700,000, and preferably from 10,000 to 500,000.

Drainage and retention aid (s) may be added to the thin suspension in the conventional manner and in any order. When using a silicon material, it is preferable to add a cationic polymer to the thin suspension before adding the silicon material, even if the opposite order of addition can also be used. It is further preferable to add a cationic polymer before a shear stage, which can be selected from pumping, mixing, cleaning, etc., and to add the silicon material after this shear stage. When a cationic coagulant is used, it is preferably introduced into the suspension prior to the introduction of cationic polymer and silicon material, if used. Alternatively, the cationic coagulant and the cationic polymer may be introduced into the suspension essentially simultaneously, separately or in admixture, for example, as described in U.S. Patent No. 5,858,174, which is by herein incorporated by reference.

5 The drainage and retention aid (s) may be added

the slurry to be dehydrated in amounts which may vary within broad limits depending, inter alia, on the type and number of additives, type of cellulosic suspension, salt content, salt type, filler content, type loading, moment of addition, degree of occlusion of white water, 10 etc. Generally, the drainage and retention aid (s) are / are added in amounts that provide better drainage and retention than those obtained when not using additives. The cationic polymer is generally added in an amount of at least about 0.001 wt%, often at least about 0.005 wt%, based on the dry cellulosic suspension, and the upper limit is usually around 3%. and suitably about 1.5% by weight. Commonly applied addition amounts of cationic polymer are from about 0.01% to about 0.5% by weight. Anionic materials, for example silicon materials, i.e. anionic silica-based particles and smectite-like anionic clays, and anionic organic polymers, are generally added in an amount of at least about 0.001. % by weight, often at least about 0.005% by weight, based on the dry cellulosic suspension, and the upper limit is generally around 1.0% and suitably around 0.6% by weight.

When a cationic coagulant is used in the process, it can

be added in an amount of at least about 0.001% by weight, calculated as dry coagulant in dry cellulosic suspension. Conveniently, the amounts range from about 0.05 to about 3.0%, preferably from about 0.1 to about 2.0%.

In the process, other components may naturally be in-

in the cellulosic suspension. Examples of such components include conventional fillers, optical brightening agents, sizing agents, dry strengths, wet strengths, etc. Examples of suitable conventional fillers include kaolin, aluminum silicate, titanium dioxide, plaster, talc, natural and synthetic calcium carbonates, for example chalk, crushed marble and precipitated calcium carbonate, hydrogenated aluminum oxides (carbon dioxide trihydroxides). aluminum), calcium sulphate, barium sulphate, calcium oxalate, etc. Examples of suitable sizing agents include cellulose-free reactive sizing agents, for example, resin-based sizing agents such as resin-based soaps, resin-based emulsions / dispersions, and reactive sizing agents. to 10 cellulose, for example, acid anhydride emulsions / dispersions such as alkenyl succinic anhydrides (ASA), alkenyl and alkyl ketene dimers (AKD) and multimers. Examples of suitable wet strength agents include polyamines and polyaminoamides.

The present invention further encompasses papermaking processes where white water is widely recycled, or recirculated, that is, with a high degree of white water occlusion, for example, where from 0 to 30 tons of water. candy are used per ton of dry paper produced, generally less than 20, preferably less than 15, more preferably less than 10, and notably less than 5 tones of water. 20 fresh per ton of paper. Fresh water can be introduced into the process at any stage. For example, fresh water may be mixed with cellulosic fibers to form a cellulosic suspension, and fresh water may be mixed with a thick cellulosic suspension for dilution to form a thin cellulosic suspension.

The process according to the invention is used for the production

of a cellulosic product and preferably paper. The term "paper" as used herein includes not only paper and its production, but also other web-like products, such as, for example, boards and cardboard, and their production. The process may be used in the production of paper of different types of suspensions and cellulosic fibers as defined above, and the suspensions should preferably contain at least 25% and more preferably at least 50% by weight of such. fiber based on dry substance.

Preferably, the invention is applied to paper machines producing wood-containing paper and recycled fiber-based paper such as SC, LWC and different types of book and press papers, and to machines producing paper and wood-free writing, the term wood-free which means less than about 15% of wood-containing fibers. Examples of preferred applications of the invention include the production of multilayer paper and paper layers from cellulosic suspensions containing at least 50% by weight of 10 mechanical and / or recycled fibers. Preferably the invention is applied to paper machines operating at a speed of from 300 to 3000 m / min and more preferably from 500 to 2500 m / min.

The invention is further illustrated by the following Examples which, however, are not intended to limit it. Parts and% refer to parts by weight and% by weight, respectively, unless otherwise stated.

Example 1

The drainage performance achieved by the present process was assessed using a Dynamic Drainage Analyzer (DDA), available from Akribi Kemikonsulter AB1 Sweden, which measures the drainage time of a determined volume of an aqueous suspension containing cellulosic fibers through a wire when a plug is removed and a vacuum 35 KPa (0.35 bar) is applied where the wire side is opposite to the side where cellulosic suspension is present. The first passage retention was assessed by a nephelometer for measuring the filtrate turbidity, the white water obtained by draining the suspension. Turbidity was measured in NTU (Nephelometric Turbidity Units). The higher the NTU, the less material is retained.

The cellulosic suspension used was derived from a mixture of thermo mechanical pulp (TMP) (70%) and sawdust pulp (SGW) (30%) that was bleached by hydrogen peroxide / sodium silicate. The suspension was diluted with water at 4% fiber concentration and treated with a mixture comprising alum and magnesium sulfate salt in a weight ratio of 35: 1.87. After or treatment, the pH was reduced to about 5 by the addition of sulfuric acid (H2SO4) and maintained at 40 ° C for 30 min. The suspension was then diluted with water to 1 wt% fiber concentration and the pH was maintained at 5 by additional sulfuric acid prior to the DDA test.

Samples were placed into the muffled DDA glass vial. Retention and dehydration aids were added as follows:

(i) 15 seconds before the suspension drains, varying quantities

of cationic polyacrylamide (Eka PL 1510).

(ii) 5 seconds before the suspension drains, 0,5 kg / tonne of particles

anionic silica-based cells (Eka NP 320).

Quantities are based on the dry weight of the cellulosic suspension and ton refers to one metric ton in all examples. Test numbers 1 to 3, 5 to 7, 9, 10, and 12 to 18 were used for comparison and test numbers 4, 8, and 11 show the results obtained by treatment according to the invention.

Table 1

Tes¬ Addition of Addition of Blend Time Addition Alum Mixture (Alu- Polymer Drainage No. [kg / ton] m and: MgSO4) Cationic [s] [NTU] [kg / ton] [kg / ton] 1 0 0 0.5 19.3 214 2 15 0 0.5 17.9 214 3 35 0 0.5 15 196 4 0 35: 1.87 0.5 12.0 176 5 0 0 1.0 15 , 3 205 6 15 0 ^ 1.0 15.3 197 7 35 0 1.0 11.9 172 8 0 35: 1.87 1.0 9.3 124 9 15 0 1.25 14.7 190 10 35 0 1,25 10,5 148 Tes¬ Addition of Addition of Addition of Blend Time Alum Mixture (Alu¬ Polymer Drainage No. [kg / ton] me: MgSO4) Cationic [s] [NTU] [kg / ton] [kg / ton] 11 0 35: 1.87 1.25 7.1 101 12 0 0 1.5 14.4 165 13 15 0 1.5 14.0 190 14 35 0 1.5 9.2 126 15 0 0 2.0 12.2 146 16 15 0 2.0 10.5 164 17 0 0 3.0 9.6 121 18 15 0 3.0 8.2 137 As can be seen from the results presented in the Table 1, the suspension treated with alum and magnesium sulfate according to the present invention resulted in improved drainage and retention performance.

than the alum-treated suspension and the suspension that was not treated at all.

Example 2

In this example, drainage and retention performance was evaluated according to the general procedure of Example 1, except that a cationic coagulant was also used. Cationic coagulant and retention and dehydration aids were added as follows:

(i) 30 seconds before drainage of the suspension, varying amounts of cationic polyacrylamide coagulant (Eka ATC 5439).

(ii) 15 seconds before suspension draining, 0.5 kg / ton cationic polyacrylamide retention aids (Eka PL

1510)

(iii) 5 seconds before draining the suspension, 0.5 kg / ton of anionic silica-based dry particulate pulp (Eka NP 320).

Test nos. 19 to 21, 24 to 26, 28 to 30 and 32 to 34 were used for comparison and test noses 23, 27 and 31 show the treatment according to the invention. Table 2

Tes¬ Addition of Addition of Turbidity Addition te Alume [kg / t] Mixture (Alu- Coagulan¬ Drainage [NTU] No. (TieiMgSO4) te Cationi¬ [s] [kg / ton] co [kg / ton] 19 0 0 0 19.3 214 20 15 0 0 15 214 21 35 0 0 17.9 196 22 0 35: 1.87 0 12 176 23 0 35: 1.87 0.25 11 130 24 0 0 0.5 16.1 200 25 15 0 0.5 11.3 202 26 35 0 0.5 15.3 160 27 0 35: 1.87 0.5 8.8 99 28 0 0 0.75 15.7 178 29 15 0 0.75 9.9 200 30 35 0 0.75 14.9 129 31 0 35: 1.87 0.75 7.3 85 32 0 0 1.0 14.2 171 33 15 0 1.0 8.5 178 34 35 0 1.0 13.8 103 How can be seen from the results presented in Table 2,

the alum and magnesium sulphate treated suspension according to the present invention resulted in better drainage and retention performance than the alum only suspension and the suspension which was not treated at all.

Example 3

In this example, the yield of the process was evaluated using the composition according to the invention comprising alum and magnesium sulfate.

A large batch of TMP / SGW targeted with Hydrogen Peroxide / Sodium Silicate was diluted with water at a 4% fiber concentration. This batch was well mixed and divided into four equal quantities. The suspensions obtained were treated in different ways. However, all suspensions were diluted in a constant manner and the basis weight change of the paper was evaluated. Suspension treatments are shown in Table 3. Table 3

Test No. Treatment 1 No treatment. The pH was reduced to 5 by the addition of sulfuric acid and kept at 40 ° C for 30 min. Then the suspension concentration was reduced to 1% with a determined volume. The volume determined to reach 1% was used in all tests. 2 Alum treatment at 4% pulp concentration. 35 kg / ton of alum was dosed and the pH was adjusted to 5 by the addition of sulfuric acid. This was then kept at 40 ° C for 30 min and then diluted according to Test No. 1.3. Treatment with a mixture comprising alum and magnesium sulfate at 4% pulp concentration. The mixture was mixed in such a ratio that the effective dose was 35 kg / ton alum and 1.87 kg / ton magnesium sulfate, and the pH was adjusted to 5 by the addition of sulfuric acid. This was then kept at 40 ° C for 30 min and then diluted according to Test No. 1. 4 Treatment with the mixture comprising alum and magnesium sulfate in 1% pulp concentration. The mixture was mixed in such a ratio that the effective dose is 35 kg / ton alum and 1.87 kg / ton magnesium sulfate, and the pH was adjusted to 5 by the addition of sulfuric acid. This was then kept at 40 ° C for 30 min.

All four samples had the same dilution determined by

nothing and were not compensated for solids change, handsheets were prepared according to the method described in SCAN-CN 64:00 and 5 kg / ton of cationic starch were used as a drainage and retention aid. 25 leaves were produced with white water recirculation. The last 10 leaves were used for the evaluation of a yield obtained. The increase in inorganic yield was assessed as an increase in ash content which was assessed by the method according to ISO 2144-1977. Results are presented in Table 4. Table 4

Test No. Base Weight [g / m2] Yield Increase [%] Total Organic Inorganic 1 69.37 - - - 2 70.47 0.30 1.29 1.59 3 72.07 0.50 3 40 3.90 4 71.01 0.62 1.75 2.36

As can be seen from the results presented in Table 4, the papermaking process in which alum and magnesium sulfate were used according to the present invention (Test No. 3) resulted in an increased process yield. Example 4

In this example, the paper quality was evaluated in terms of basis weight, ash content, thickness, density, mass, tensile index, tear index, air permeability, gloss, opacity, light scattering and light absorption. Comparisons between sheets of paper prepared from aqueous pulp suspensions derived from both unbleached and bleached pulp were made. Pulp suspensions were treated in different ways. The suspensions were derived from TMP / SGW (70/30) and alternatively TMP / SGW (70/30) targeted with hydrogen peroxide / sodium silicate. Test suspensions were not treated at all, treated with calcined clay or alum, magnesium sulfate and acid. Other comparisons were made in a similar manner when cationic starch was added as a drainage and retention aid in suspensions. The leaves were prepared using the standard method SCAN-CM 64:00. Suspension treatments are presented in Table 5.

Table 5

Test No. Treatment 1 TMP / SGW unbleached 2 TPM / SGW targeted with hydrogen peroxide / sodium silicate Test No. Treatment 3 TPM / SGW targeted with hydrogen peroxide / sodium silicate, addition of calcined clay in an amount of 2.5% by weight, based on the dry weight of the suspension, in a diluted cellulosic suspension having a fiber concentration of 1% by weight. 4 TPM / SGW bleached with hydrogen peroxide / sodium silicate, addition of calcined clay in an amount of 5.0 wt.% Based on the dry weight of the suspension, in a diluted cellulosic suspension having a fiber concentration of 1 wt.%. Weight. TPM / SGW targeted with hydrogen peroxide / sodium silicate, treatment with a mixture comprising alum and magnesium sulfate at 4% pulp concentration. The mixture was used in such a ratio that the effective dose was 35 kg / ton alum and 1.87 kg / ton magnesium sulfate, and pH was adjusted to 5 by the addition of sulfuric acid. This was then kept at 40 ° C for 30 min and then diluted to a fiber concentration of 1% by weight. 6 TPM / SGW targeted with hydrogen peroxide / sodium silicate, 5 kg / t cationic starch added 20 seconds before drainage. 7 TPM / SGW bleached with hydrogen peroxide / sodium silicate, addition of calcined clay in an amount of 2.5 wt%, based on the dry weight of the suspension, in a diluted cellulosic suspension having 1 wt% fiber concentration , 5 kg / ton cationic starch added 20 seconds before drainage. 8 TPM / SGW bleached with hydrogen peroxide / sodium silicate, addition of calcined clay in an amount of 5.0% by weight, based on the dry weight of the suspension, in a dilute cellulosic suspension having a fiber concentration of about 1 % by weight, 5 kg / ton of cationic starch added 20 seconds before drainage. 9 TPM / SGW targeted with hydrogen peroxide / sodium silicate, treatment with a mixture comprising alum and magnesium sulfate at 4% pulp concentration. The mixture was mixed in such a ratio that the effective dose was 35 kg / ton alum and 1.87 kg / ton magnesium sulfate, and pH was adjusted to 5 by the addition of sulfuric acid. This was then maintained at 40 ° C for 30 min, diluted to a fiber concentration of 1% by weight and then 5 kg / ton of cationic starch added 20 seconds before drainage.

Base weight has been rated according to ISO standard

536: 1995, ash content according to ISO 2144-1977, thickness, mass and density according to ISO 534: 1988, tensile index according to SCAN-P 67:93 kN / kg, laceration index according to ISO 1974: 1990 and air permeability according to ISO 5636-5: 2003. Table 6

Test No. Base Weight [g / m2] Ash Content [%] Thickness [pm] Density [kg / dm3] Mass [dm3 / kg] Traction Index [kN / kg] Deamination index [mNm2 / g] Air permeability [s] 1 59.38 0.43 169 351 2.85 18.4 2.97 9.0 2 62.35 1, 01 175 356 2.81 21.0 3.74 31.4 3 59.14 1.51 174 349 2.87 21.0 3.48 22.0 4 60.67 2.12 172 344 2.91 19, 2.69 22.3 58.64 2.85 175 335 2.98 17.2 3.35 13.6 6 64.83 1.24 178 364 2.75 20.9 3.48 23.0 7 63 .93 3.01 174 371 2.70 20.1 3.35 26.9 8 64.49 4.78 173 370 2.71 20.4 3.53 22.5 9 62.84 3.41 177 355 2 , 82 20.9 3.43 12.1

Paper quality was also evaluated in terms of brightness,

opacity, light scattering and light absorption. Measurements were made using Technidyne1 Color Touch equipment and according to ISO 2470 standards for brightness, ISO 2471 for opacity and ISO 9416 for light scattering and light absorption.

Table 7

Test No. Brightness [%] Opacity [%] Light scattering [m2 / kg] Light absorption [m2 / kg] 1 58.97 93.40 55.15 2.64 2 75.31 86.23 54.21 0.49 3 75.37 86.94 57.16 0.58 4 75.71 86.80 58.48 0.61 76.12 86.04 56.96 0.52 6 75.00 88.24 57, 22 0.62 7 75.90 89.24 61.86 0.62 8 77.26 90.09 67.86 0.63 9 75.84 88.07 58.70 0.64 As can be seen from the results presented in Tables 6 and 7, Test no. 9, where sheets were prepared with a process according to the present invention, showed almost the same or even better paper characteristics than sheets prepared with a papermaking process using calcined clay as an additive.

Claims (22)

A process for the production of a cellulosic product comprising: (i) providing an aqueous slurry containing cellulosic fibers having a fiber concentration of at least about 2% by weight; (ii) add to the thick suspension; (!) an aluminum compound; (II) an alkaline earth metal salt; (III) an acid; (iii) diluting the thick suspension obtained to form a thin suspension; (iv) adding to the thin suspension one or more drainage and retention aids; and (v) dehydrating the thin suspension obtained. 2. A process for producing a cellulosic product comprising: (i) providing a thick aqueous suspension containing cellulosic fibers having: (a) a fiber concentration of at least 2% by weight; (b) an alkaline earth metal ion concentration of at least about 100 mg / l; (ii) adding to the slurry an aluminum compound and optionally an acid to obtain a pH of from about 4 to about 5.5; (iii) diluting the thick suspension obtained to form a thin suspension; (iv) adding to the thin suspension one or more drainage and retention aids; and (v) dehydrating the thin suspension obtained. A process according to any one of claims 1 or 2, wherein the aluminum compound is alum, polyaluminium chloride, polyaluminium silicate sulfate, aluminate, aluminum nitrate or a mixture thereof. A process according to any one of claims 1 to 3, wherein the alkaline earth metal salt is added to the thick suspension to obtain an alkaline earth metal ion concentration of at least 100 mg / l. A process according to any one of claims 1 to 4, wherein the alkaline earth metal salt is a magnesium, calcium or barium salt. A process according to any one of claims 1 to 5, wherein the alkaline earth metal salt has an anion which is selected from halides, sulfates, carbonates, nitrates or organic acids. A process according to any preceding claim, wherein the alkaline earth metal salt is magnesium chloride, magnesium sulfate, calcium chloride or barium sulfate. A process according to any preceding claim, wherein the acid is an inorganic acid. A process according to any preceding claim, wherein the acid is hydrochloric acid or sulfuric acid. A process according to any preceding claim wherein the acid is added to the thick suspension to obtain a pH of from about 4 to about 5.5. A process according to any preceding claim, wherein upon addition of the aluminum compound, alkaline earth metal salt and acid, the pH of the thick suspension is increased to about 6 to about 8 by adding a base. A process according to any preceding claim, wherein the thick suspension has a fiber concentration of at least about 3.5 wt%. A process according to any one of the preceding claims, wherein the aqueous suspension contains mechanical pulp-derived cellulosic fibers. A process according to claim 13, wherein the pulp is a targeted hydrogen peroxide. A process according to any preceding claim, wherein: (I) the aluminum compound; (II) the alkaline earth metal salt; and (III) acid; are separately added to the suspension. A process according to any preceding claim, wherein: (I) the aluminum compound; (II) the alkaline earth metal salt; and / or (III) acid; They are added as a mixture. A process according to any preceding claim, wherein the drainage and retention aids comprise one or more cationic organic polymers. A process according to any preceding claim, wherein the drainage and retention aids comprise a silicon material. A process according to any preceding claim, wherein the drainage and retention aids comprise a cationic organic polymer which is added before a shear stage and a silicon material which is added after this shear stage. A process according to any preceding claim, wherein the drainage and retention aids comprise anionic silica-based particles. A process according to any preceding claim, wherein the cellulosic product is paper. A process according to any preceding claim, wherein the process for producing a cellulosic product takes place in an integrated paper mill.