WO2000032873A1

WO2000032873A1 - Paper making method using a novel retention system comprising a precipitated silica and a cationic polymer

Info

Publication number: WO2000032873A1
Application number: PCT/FR1998/002598
Authority: WO
Inventors: Marie-Odile Lafon; Herbert Hruschka
Original assignee: Rhodia Chimie
Priority date: 1997-08-01
Filing date: 1998-12-02
Publication date: 2000-06-08
Also published as: EP1135555B1; CA2354647C; ATE352670T1; DE69836985T2; AU1439699A; FR2766849A1; NO331149B1; DE69836985D1; DK1135555T3; ES2277396T3; FR2766849B1; NO20012666D0; NO20012666L; EP1135555A1; CA2354647A1

Abstract

The invention concerns a novel method for making paper based on cellulose fibre in sheet form, wherein a novel retention system comprising a suspension of precipitated silica and a cationic polymer is used for improving in particular the retention of the incorporated mineral fillers. The invention also concerns a method for making paper using a retention system which substantially improves draining. More precisely, the invention concerns the use of a precipitated silica and a cationic polymer comprising a cationic guar gum and/or a cationic starch.

Description

PAPERMAKING PROCESS USING A NEW SYSTEM

RETENTION CONTAINING PRECIPITATED SILICA

AND A CATIONIC POLYMER

The present invention relates to a new process for manufacturing paper based on cellulose fiber in sheet form, in which a new retention system comprising a suspension of precipitated silica and a cationic polymer is used to improve in particular the retention of the incorporated mineral fillers. . The present invention also relates to a process for making paper using a retention system which appreciably improves drainage (or drainage), that is to say the speed with which water flows from the suspension of fibers. More specifically, the invention relates to the use of an aqueous suspension of precipitated silica and of a cationic polymer comprising a cationic galactomannan and / or a cationic starch.

In addition, the mechanical properties of the paper obtained according to the process of the invention are improved, for example the rigidity and the tear resistance as well as other properties such as whiteness. In addition, the retention system according to the invention can have advantages with regard to the quality and recyclability of white water from the paper manufacturing process as well as paper broken during the manufacturing process.

Paper making poses many problems. One of the permanent concerns is to decrease the cost of paper by decreasing the quantity of cellulose fibers in the composition of the pulp. Another approach consists in reducing the concentration of aqueous discharges due to the increasingly severe environmental constraints.

Papermakers have proposed various ways to reduce the cost of paper and try to improve its properties. One of the approaches used is the addition of inexpensive mineral fillers in the papermaking process to replace the fiber. On the other hand, certain mineral fillers are specifically used to improve certain properties of the paper. Thus, for example, titanium oxide is used in its anatase and / or rutile forms to improve the opacity of the papers, in particular in the case of laminated papers.

Unfortunately, the addition of mineral fillers which are micrometric particles comes up against the problem of retention: during the formation of the sheet on the canvas of the paper machine, the mineral particles tend to pass through this canvas, this which generates circuits of charged white water. This poses problems in terms of reject processing but also in terms of sheet quality. To date, the prior art proposes the use of retention agents to reduce the problem of lack of retention. However, many solutions proposed to date are not economically viable to allow their use for the preparation of any type of paper. Indeed, some retention agents or retention systems are complex and expensive products, which therefore does not allow their use for ordinary quality products.

Now, the Applicant has developed a new paper manufacturing process using a new retention system which considerably increases the retention of mineral fillers, fibers and other materials in the paper sheet. Another object of the invention is to provide a retention system and a process for manufacturing paper in which the properties of the paper obtained, including for example the opacity yield of mineral fillers, the tear strengths, the whiteness and other necessary properties are improved, by optimizing the use of mineral fillers. Of course, the optimization is done according to the type of load used.

Another object of the invention is to provide a paper having a high concentration of mineral fillers which has a tear resistance and other acceptable characteristics.

Other objects and advantages of the invention will follow on reading the description below and in particular in the tests, tables and figures illustrating various characteristics of the invention.

The present invention is based on the development of a retention system and of the process for manufacturing paper using it which markedly increases the retention of mineral fillers and other characteristics of the paper and which allows the optimization of the action. mineral fillers present within the pulp.

The increased retention of mineral filler and fines as part of our papermaking process alleviates the problems of white water contamination.

The present invention therefore relates to a process for manufacturing paper by forming and drying an aqueous paper pulp containing cellulose pulp and mineral fillers in which a system is incorporated into the mother pulp before the formation of the sheet. retention including:

(i) a suspension of precipitated silica,

(ii) and a cationic polymer chosen from a cationic starch, a cationic galactomannan and / or a mixture thereof.

The amount of solids in the gelling system is from 0.02 to 50% by weight, preferably from 1 to 30% by weight, relative to the weight of the paper pulp or mother pulp. The ratio of cationic polymer / precipitated silica must be between 1 and 10 by weight, and preferably, this ratio is between 2 and 6, the latter depending in particular on the degree of substitution of the precipitated silica and of the cationic polymer. As regards the precipitated silica suspension, this is understood to mean a silica suspension consisting of the filter cake resulting from the precipitation reaction. In other words, the silica is precipitated, the reaction medium is filtered and a filtration cake is obtained which is washed if necessary. This cake is then disintegrated and it thus forms a suspension of precipitated silica.

In general and advantageously, in the context of the present invention, an aqueous suspension of precipitated silica is used having a dry matter content of between 10 and 40% by weight, a viscosity of less than 4.10 ⁻² Pa.s for shear of 50 s. " ¹ and the quantity of silica contained in the supernatant obtained after centrifugation of the said suspension at 7,500 rpm for 30 minutes represents more than 50% of the weight of the silica contained in the suspension. More particularly, this aqueous suspension of precipitated silica has a dry matter content of between 15 and 35% by weight and, moreover, a viscosity which is less than 2.10 ⁻² Pa.s for a shear of 50 s ⁻¹ . A On this subject, reference will be made to patent application WO 96/01787 of the Applicant concerning this type of silica and the content of which must be considered to be part of the present application. The precipitated silicas are generally precipitated at a pH around the neutral pH or at basic pH, the gels being obtained at a usually acidic or very acidic pH.

In the case where the cationic polymer is a cationic galactomannan, the latter is preferably selected from galactomannans comprising at least two vicinal hydroxyl groups, in particular, cationic guars. With regard to the guars, it has been observed that their reactive centers are particularly accessible, which makes it possible to use small quantities of them to achieve a satisfactory effect.

When the retention system is used with cationic guar as one of the components, the mineral fillers are retained to a significant degree in the final product and the paper produced has improved resistance compared to a paper obtained from 'a process without a retention system.

The basic guar in cationic guar is of the natural type. Natural guar is extracted from the albumen of certain plant seeds, for example Cyamopsis Tetragonalobυs. The guar macromolecule consists of a main linear chain constructed from β-D-mannose monomeric sugars linked together by bonds (1-4), and α-D-galactose side units linked to β-D-mannoses by bonds (1-6). The preparation of cationic guars is known per se. By way of example, cationic guars are formed by reaction between hydroxyl groups of the polygalactomannan and reactive quaternary ammonium compounds.

The degree of substitution of the cationic groups of guar is generally at least 0.01 and preferably at least 0.05 and can range up to 1.0. in the context of the invention, an appropriate range extends from 0.08 to 0.5. It is assumed that the molecular weight of guar gum varies from 100,000 to 1,000,000 and, generally, it is around 220,000.

As commercial products, non-limiting examples are the products of the MEYPRO-FLOC 130, MEYO-BOND 9806, MEYO-BOND 109 series,

JAGUAR C-13-S, JAGUAR C-14-S, JAGUAR C-15, JAGUAR C-17, JAGUAR C-162 from MEYHALL and RHÔNE-POULENC Inc, GUAR CAT 10 products from CESALPINIA .

In the case where the cationic polymer is a cationic starch, this is generally chosen from those having a degree of substitution of between approximately

0.1 and 0.05 and preferably between about 0.02 and 0.04 and, more particularly, more than about 0.025 and less than about 0.04. As is well known, a starch is made cationic by substitution with an ammonium group by techniques known per se and can have varying degrees of substitution up to 0.1. For this purpose, a wide variety of ammonium compounds can be used. By way of nonlimiting example, the cationic starch can be prepared by treatment of the base starch with 3-chloro-2-hydroxypropyl-trimethylammonium chloride or 2,3-ethoxypropyl-trimethylammonium chloride, which makes it possible to obtain a cationic starch having a degree of substitution of 0.02 to 0.04. The base starch used to prepare the cationic starch can be chosen from the group consisting of potato starch, wheat starch, corn starch, barley starch, oat starch, rice starch, starch tapioca, and their mixture.

Depending on the case and / or the nature (s) of the polymers, these will be formulated in the form of aqueous solutions. The mineral fillers used in the process are varied in nature and are chosen in particular according to the type of paper manufactured and its future use. The mineral filler material that can be used includes any common mineral filler whose surface is at least partially anionic in character.

Among the mineral fillers, non-limiting mention will be made of kaolin, clay, chalk, calcium carbonate, titanium dioxide, silica, and their mixture.

The mineral fillers are normally added in the form of an aqueous dispersion at the appropriate concentrations specific to the type of paper manufactured. Many commercial products can be used as mineral fillers for papermaking. By way of nonlimiting examples, mention will be made of kaolin from the company ECC, calcium carbonate Omyafill from the company OMYA and

Calopake from RHÔNE-POULENC, Finntitan titanium dioxide from KEMIRA and Rhoditan from RHÔNE-POULENC.

The possibility of adding mineral fillers to the paper pulp is limited by factors such as the retention of the fillers on the canvas, the dehydration of the paper pulp on the canvas, the wet and dry resistance of the paper obtained.

Now, in accordance with our invention, the problems mentioned above due to the addition of these fillers can be overcome or eliminated in a consistent manner by using our retention system which also makes it possible to add proportions of these fillers more higher than normal to obtain special properties in the paper produced.

Thus, by using the retention system of the invention, it has become possible to produce a paper which contains more fillers while retaining its mechanical properties. In this way, therefore, the mechanical properties of the paper (including the modulus of elasticity, the tensile index, the absorption of tensile energy, etc.) have values equal to or even greater than those achieved previously with papers. obtained from conventional paper pulps in which a retention agent of the prior art is optionally used.

The sheet, after drying, has greatly improved resistance characteristics when the method according to the invention is used. It has also been found that when mineral fillers such as those mentioned above and the like are used in the dough, these mineral fillers are effectively retained in the sheet and moreover have no negative effect on the strength of the sheet, this in opposition to the sheets obtained by a manufacturing process without gelling system according to the invention.

Although the mechanism that occurs within the mother pulp during the formation and drying of paper in the presence of the retention system is not fully understood, it is believed that the retention system forms an association with the fibers and with the charges to form a complex flocculating matrix.

Indeed, the manufacture of the paper sheet necessarily passes through a draining step which can profoundly modify the structure of the colloids as well as their distribution. Changes in the structure of aggregates of draining charges affect the retention rate of these as well as the opacity of the paper obtained. Thus, in the presence of the retention system of the invention, during draining, a flocculate is formed within the cellulosic network which traps the charges to preserve during this critical stage the properties that the particles have in suspension. The components of the retention system are added within the papermaking device as a mixture or separately. However, according to a preferred embodiment of the invention, the optimal results are obtained when the retention system based on precipitated silica and cationic polymer is formed in situ in the paper pulp.

Advantageously, this can be carried out by first adding the cationic polymer (guar and / or starch) in the form of an aqueous solution and separately adding to the paste the aqueous solution of silica precipitated in a mixing tank or in a point in the device where there is suitable agitation, so that the two components are dispersed with the paper-forming components and thus act simultaneously with each other and with the paper-forming components.

It has been found that, in a papermaking process using the gelling system described in the invention, the pH of the mother pulp is not excessively critical and is generally less than 11, and preferably between 5 to 9 .

Other chemical additives for the paper can be mixed within the mother pulp, such as defoamers, bonding agents, etc. In this regard, it is important to ensure that the content of these other agents does not does not interfere with the formation of the gel matrix and that the content of agent (s) in the recycled white water does not increase too much until it hinders the formation of the gel matrix. Therefore, it is preferable to add the agent (s) at a point in the system after the gel matrix has been formed.

The improvements due to the retention system are observed with an effect of the same order as well with chemical pastes as with mechanical and thermomechanical pastes. From the research and work carried out, it appears that the principles of the present invention are applicable to the manufacture of any type and quality of paper. Examples include writing printing papers, packaging papers, laminated papers.

Among one of the possibilities for preparing a type of paper, printing writing paper is one of the routes giving very positive results, that is to say, increased charge retention phenomenon and improved mechanical qualities of the paper. In this case, the majority of the fillers used is calcium carbonate.

The quantity of retention system to be used varies according to the desired effect and the characteristics of the particular components which are chosen in the preparation of said system. For example, for a given precipitation silica in a retention system, if this contains cationic guar gum with a DS of 0.3 instead of a DS of 0.7, more retention system will be needed . The examples below illustrate, without limitation, the advantages and properties associated with the paper according to the invention and its manufacturing process.

TEST?

Retention performance is mainly measured by two parameters:

- retention: quantity of charges retained on the sheet of paper, or for total retention, total quantity of fine particles retained on the sheet.

- drainage: which characterizes the speed with which water flows from the fibrous suspension. These two characteristics can be measured using different methods:

- 'BRITT Jar ^{* method} : it measures chemical retention (total and charges)

- "Shopper-Riegler" method: it allows to measure chemical retention and drainage

- Method via "Form puller": it measures the retention of fillers.

"BRITT bowl" method

This method consists in measuring the chemical retention of the charges, avoiding the formation of the fibrous mat responsible for mechanical retention by filtration effect. In fact, from a 500 ml sample of the fiber + fillers dispersion + retention system + optionally additives to be tested, maintained under stirring, only the first 100 ml are drawn off through a sieve. By determining the respective amounts of fibers and fillers passed through the filtrate, the overall retention values (fibers + fillers) and load retention are reached by calculation.

This method of measuring retention is described by K. Britt and J.E. Unbehend in Research Report 75, 1/10 1981, published by Empire State Paper Research Institute ESPRA, Syracuse, N.Y. 13210, USA.

For the measurements, a filtration bowl was used fitted with a 600 μm opening grid.

"Shopper-Riegler" method

This Shopper-Riegler method is used according to standard NFQ 50-003. The precipitated silica solution used in the examples, below silica A, has the following characteristics: - dry extract: 27.08%,

- surface = 221 m ² / g, - particle size = 40-70 nm.

The colloidal silica solution used in the examples, below silica B, has the following characteristics:

- dry extract: 9.2%; - surface = 494 m ² / g,

- particle size = 10 nm.

Example 1

This example shows the chemical retention obtained with the BRITT Jar test. i) Preparation of the mother suspension and dilution The suspensions are prepared by defibering the cellulose in

500 ml of demineralized water in a Dispermat type bowl for 10 min at 2,000 rpm.

The fillers are added to the Dispermat and agitation is maintained at 1,000 rpm for 5 minutes. The mixture obtained is then transferred to a

10 liters with a stirring blade, then diluted to a concentration of 0.5% in fibers, and finally kept stirring all the time during handling in order to ensure, during sampling, perfect homogeneity.

Then, 500 ml of the suspension mixture is taken. These 500 ml are introduced into the BRITT bowl with stirring with a propeller type blade and fitted with a 600 μm grid.

The stirring speed is fixed as a function of the desired shearing and the stirring is carried out for 30 seconds.

The starch is added followed by stirring for 30 seconds. Silica is then introduced (in the tests comprising this product). Then stir for 30 seconds.

Finally, 100 ml of the mixture are drawn off by gravity.

Prepared formulations

ii) Filtration

The 100 ml sampled are then filtered on BÙCHNER with WHATMANN filters No. 42 (ashless filters, previously dried for 1 hour at 105 ° C and then weighed to ± 0.0001 g).

The filtration residue is then carefully removed, dried for 1 hour at 105 ° C then cooled in a desiccator and weighed (± 0.0001). This allows the calculation of the overall retention rate.

The residue thus dried on a filter is then calcined (according to the Ash Rate Standard No. NFQ 03-047) to give the charge retention rate of the mixture. iiii) Calculations and Results

Overall retention and expense retention are calculated using the following formulas:

Overall retention = (P1- (5 * P2)) * 100

P1

P1 = Weight of the mixture (fillers + fibers) in the initial sample.

P2 = Weight of the residue from the 100 ml sample filtered and dried.

Load retention = (P3- (5 * P4) * 100

P3

P3 = Weight of fillers in the initial 500 ml sample.

P4 = Weight of the residue from the 100 ml sample filtered, dried, calcined.

Results

Example 2

This example shows the chemical retention and the drainage calculated according to the "Shopper-Riegler" method with the following modifications:

- Drainage measurement = time required to drain 600 ml of solution Overall retention measurement = filtration of the 600 ml and weighing of the residue, according to the same procedure as for the measurement with BRITT Jar.

I Formulations used

The suspension is prepared as in Example 1, with stirring for 15 min after adding the starch, and then adding cationic guar. A stirring time of 15 seconds is observed before the optional addition of silica A or B. ii) Results

Example 3

This example shows chemical retention and drainage according to the "Shopper-Riegler" method with the following modifications:

- Drainage measurement = time required to drain 400 ml of solution.

- Overall retention measurement = turbidity measurement of the filtrate diluted 3 times. The higher the turbidity, the lower the overall retention. Formulation used

The suspension is prepared in an identical manner to that of Example 1. Firstly, add the product Aqualenc 18. Then, optionally add type A silica and, finally, add the guar under stirring at 1000 rpm . ii) Results

Example 4

This example gives the retention of fillers obtained on a form filler. i) Preparation of paper pulp

The preparation of the dough is carried out as for Example 1.

ii) Manufacture of the formettes

The pulp thus defibrated is introduced into a stirred tank of 10 liters. Then dilute with filtered water until a total volume of 4 liters is obtained. Then the diluted paste is placed under stirring for 1 min and about 500 ml of suspension are taken and placed in a test tube. Starch is added to this suspension. After stirring for 30 seconds, silica A or silica B is added, as the case may be, and the mixture is again stirred for 30 seconds.

The contents of the test tube are poured into the bowl of the form filler. It is mixed by bubbling and then the form is produced by drawing under vacuum.

The form is then collected on a cardboard support and then placed in a vacuum dryer. We then weigh the form and if necessary readjust the volume withdrawn to obtain a grammage of 60 g / m ² . iϋ) Results

Load retention (% compared to the initial load rate)

Claims

1. A method of manufacturing paper by forming and drying an aqueous paper pulp containing cellulosic pulp and mineral fillers, characterized in that a system of incorporated into the mother pulp before the formation of the sheet retention including:

(i) a cationic polymer chosen from a cationic starch, a cationic galactomannan and / or a mixture thereof, (ii) and a suspension of precipitated silica, consisting of the filter cake resulting from the precipitation reaction.

2. Method according to claim 1, characterized in that the aqueous suspension of precipitated silica has a dry matter content of between 10 and 40% by weight, a viscosity less than 4.10 ^"2 Pa.s for shear of 50 s ^-1 and an amount of silica contained in the supernatant obtained after centrifugation of said suspension at 7,500 revolutions per minute for 30 minutes represents more than 50% of the weight of the silica contained in the suspension.

3. A method of manufacturing paper according to any one of the preceding claims, characterized in that the cationic polymer is a galactomannan containing at least two vicinal groups.

4. A method of manufacturing paper according to the preceding claim, characterized in that the galactomannan has a degree of substitution of at least 0.01 and preferably of at least 0.05 and which can range up to 1.0. .

5. A method of manufacturing paper according to the preceding claim, characterized in that the cationic polymer is a cationic starch having a degree of substitution of between approximately 0.1 and 0.05 and preferably between approximately 0.02 and 0, 04.

6. A method of manufacturing paper according to any one of the preceding claims, characterized in that the mineral fillers are chosen from the group consisting of kaolin, clay, chalk, calcium carbonate, titanium oxide, silica and their mixture.

7. Method according to any one of the preceding claims, characterized in that the pH of the mother paste is maintained between 5 and 9.

8. Method according to any one of the preceding claims, characterized in that the quantity of solids in the retention system is from 0.02 to 50% by weight, relative to the weight of the mother paste.

9. Method according to any one of the preceding claims, characterized in that the ratio of cationic polymer / precipitated silica must be between 1 and 10 by weight, and preferably, this ratio is between 2 and 6, the latter depending on the degree of substitution of the precipitated silica and the cationic polymer.

10. Method according to any one of the preceding claims, characterized in that the retention system, based on precipitated silica and cationic polymer, is formed in situ in the paper pulp.

11. A method of manufacturing paper according to the preceding claim, characterized in that the in situ formation of the retention system is carried out by first adding the cationic polymer in the form of an aqueous solution and subsequently adding the pulp of the aqueous silica solution precipitated in a mixing tank or at a point on the device where there is appropriate agitation.

12. Paper capable of being obtained from the process according to any one of the preceding claims.

13. Use of the paper according to claim 12 as laminated paper, writing printing paper or packaging paper.

14. Use of the paper according to claim 13 as printing writing paper.