WO1997046758A1

WO1997046758A1 - Cement composition as mineral charge for paper

Info

Publication number: WO1997046758A1
Application number: PCT/EP1997/002829
Authority: WO
Inventors: Luigi Cassar; Bonaventura Focher; Giorgio Capretti; Guido Coppetti
Original assignee: Italcementi S.P.A.
Priority date: 1996-06-03
Filing date: 1997-05-30
Publication date: 1997-12-11
Also published as: IT1282781B1; ITMI961125A0; ITMI961125A1; AU3170397A

Abstract

The present invention refers to a cement-based matter composition useful as a filler for the production of paper, in particular cement having suitable granulometric size, and used, if necessary, in presence of retarding additives.

Description

CEMENTCOMPOSITIONAS MINERALCHARGEFOR PAPER

Field of the invention

The present invention refers to a cement based matter composition useful as substantially inorganic filler for the production of paper. In particular the matter composition according to the invention may be used in case paper is produced by an acαd or neutral or alkaline sizing procedure. In the present text: - by the word "paper" we mean to indicate also the paperboard, the card and similar products which imply the use of inorganic charges. Prior art

Pigments and mineral charges are commonly used in the paper sector in order to increase the volume of produced paper under the same amount of cellulosic fibers employed, to improve the opacity of the obtained paper, to obtain particular surface charac eristics or to give improved mechanical properties to the obtained sheet of paper. The use of the mineral charges is widespread but it is not free of drawbacks. Titanium dioxide is for example a pigment very useful to obtain some of the above reported effects, but it is very expensive, whereas a less expensive material, such as for example clay does not always allow to obtain a material with the desired qualities. Another problem relative to the use of the minenl charges consists of the sizing of the paper. The sizing of the paper, which allows to reduce the water absorption by the fibers forming the same, is carried out by various methods, substantially differing among them depending on whether they are carried out in an acid, neutral or alkaline environment .

In an acid environment, at pH values ranging from 4.5 to 6.5, the sizing agents (normally rosin or its derivatives with various saponification degrees) are precipitated on the fibers by addition of a suitable precipitating agent (aluminum sulfate or aluminum polychloride) .

In a neutral or alkaline environment, the sizing agents are synthetic substances (for example the diketenes) which do not need to be combined with precipitating agents being already reactive to cellulose.

In the latter case, given the lower flocculating capacity of the synthetic sizing agents with respect to the system rosin or tall oil/aluminum salt, other substances having the aim to facilitate the retention of the sizing agents in the paper ribbon forming on the cloth of the continuous machine are added to the aqueous suspension of fibers.

These substances, acting as retention agents or sizing adjuvants, consist of modified starchs, polyamines, polyacrylamides , polyethylenamines and similar, which unfortunately have the drawback of a high price.

The mostly used sizing system is therefore the acid one based on rosin and aluminum sulfate. Unfortunately the reaction between the aluminum salt and the rosin, releases acidity and it becomes extremely difficult to use this kind of sizing in case calcium carbonate is used as mineral charge for the paper, because part of the aluminum sulfate, added to precipitate the rosin, reacts with calcium carbonate with a consequent high consumption and with formation of foams m the plant, due to the formation of gaseous carbon dioxide. Moreover, the papers manufactured in an acid environment undergo a fast degradation by acid hydrolysis of the cellulose, therefore they have a very reduced useful life length with respect to the neutral or alkaline papers.

It is apparent that the same problem occurs in case paper is prepared using a fraction of recycled paper containing calcium carbonate. When calcium carbonate is used as a charge is then necessary to avoid the use of acid sizing agents and this fact took it that calcium carbonate, even if it is a low cost product and even if it allows to obtain paper with high whiteness degree, is often ignored as charge in favour of other inorganic products, such as calcium sulfate or kaolin. One of the reasons of the missed use of the cement in the industrial countries to produce paper is to be found m the difference of composition and properties which the cements of the past had w th respect to those nowadays produced and normalized.

Also the manufacturing methods of paper have had an evolution which led to the use of new processes with substantial changes either of the chemical aspects (alkaline environment instead of acid) or of the technological process.

In 1975 (USP 4,081,286) the use of cement in the formulation of coats has been proposed in order to improve exclusively the properties of glazed paper, but the proposed cement material was hydrated before use and not added in bulk. In the cited Patent significant resistance data are not reported but only classical brightness data. - A -

Technical problem

Paper s so an important substance for our civilization, that any improvement one may introduce in the process of its production represents a result worthy of being pursued through a continuous and assiduous research.

Among the various research sectors in the paper field, particular emphasis have the studies for changing the charges added to paper, especially during the production stage of the same, as they allow a considerable saving of cellulose under the same conditions of volume of obtained paper, and at the same time give paper particular technical properties of high interest for the destination uses. It s highly desirable to have available charges able to increase in a substantial way a combination of physico mechanical properties which with difficulty the principal charges currently available would provide.

In particular good values of bulkiness , traction index, breaking length and energy, and internal delamination strength (Scott Bond) are highly qualifying properties and not easily achievable with traditional charges even of recent use, such as for example precipitated calcium carbonate. Summary of the invention

The Applicant, having a century-old experience in the cement sector, found that it is possible to use cement, m a not yet hydrated form, suitably selected from those fulfilling the requirements of the Italian standard UNI ENV 197. as filler or mineral charge for paper in order to improve its cited physico-mechanica] characteristics. We could observe that the compositions according to the invention bind to the cellulose fibers in a better way than the normal mineral charges thus giving a greater retention of the charge itself, under the same concentration of the charge in the suspension of fibers which is used to manufacture the paper. A further advantage obtained using the cement based chemical compositions according to the present invention is that the obtained paper under the same mineral charge content, has mechanical resistance characteristics better than those containing clay or calcium carbonate, without creating the problems of the latter product. Finally, the characteristic capability to react with water which cement has, reduces the amount of water which must be eliminated from the wet ribbon which is formed in the paper machine and then reduces the relative energetic consumption normally used in order to evaporate it. A further advantage one has when a cement is used having a Pe percentage lower than 0.5°° by weight, preferably lower than 0-3% by weight, and a brilliance greater than 8 ", preferably greater than 90% , relates to the fact that the increase of the observed mechanical characteristics are not to the detriment of other characteristics peculiar for some kinds of paper, such as brightness and opacity. One has another advantage if one uses some organic retarding additives which allow to use agents for the sizing of paper- even m an acid environment and ensure in a total manner that in a paper plant the cement particles suspended into water do not catch in any way in the pipes, in the reservoirs, n the pumps or on the net of the continuous machine, creating obstructions and inefficiencies of difficult solution. It is therefore an object of the invention the use of a not hydrated cement composition as additive or as mineral charge for the production of paper having improved mechanical characteristics characterized in that it comprises at least one cement m accordance with UNI ENV 197.1 standard, and in that the cement particles have size lower than 50 μm, preferably lower than 30 μm.

Detailed description of the invention

Preferred object of the invention is the use of a cement composition as described above, further characterized in that the cement has a ferric oxide content lower than 0.5$ by weight, preferably lower than 0. 5% by weight, and that has brilliance greater than 85/_°, preferably greater than 90%- Brilliance is the ability to reflect incident light (which s a characteristic property of white bodies opposed to that of black bodies), expressed as per cent ratio between the light reflected by a cement sample surface and the light reflected by the same area of a MgO surface (the cement sample is obtained by kneading the cement powder with water according to known methods, forming in a proper shape and leaving to set).

In another preferred aspect of the invention the cement composition having cement particles lower than 50 μm further contains at least one organic substance selected from the group consisting of ligmnsulfonate, hydroxycarboxylic acids having from 3 to 20 carbon atoms or their alkaline or alkaline-earth salts, aliphatic or aromatic amines having a number of carbon atoms from to 12, and carbohydrates, which are in turn selected among mono-, poly- saccharides and the oxidation products thereof.

The hydraulic cement which may be used in the present invention must be a silicate based cement, for example Portland cement or a limestone Portland cement or a mixture cement such as a portland-pozzolana cement.

Optionally, one may use mixtures of two or more different hydraulic cements. Characterizing aspect is that the cements satisfy the requirements reported in the Italian standard UNI ENV 197.1 (February 1993). The matter composition according to the invention is further characterized in that it contains cement whose particles have size lower than 0 μm, meant as the "99% lower than 50 μm" [μm = micrometers].

The matter composition according to the invention may be added, typically in amounts from 0.1 to 40% by weight (the cement composition amount being expressed as substantially dry material, as marketed) with respect to the cellulose fibers (expressed as stove dry fibers), in a mixture for paper containing sizing agents either of acid or neutral or alkaline kind.

It is necessary to point out that, with respect to the use of conventional charges such as kaolin and calcium carbonate, the cements object of the invention surprisingly allow benefits in terms of the physico-mechanical characteristics of paper to be obtained either with low addition percentages, that is considering the cement as a filler (amount lower than >% by weight with respect to the fibers), or with high addition percentages, that is considering the cement as a charge (amount greater than 5% by weight with respect to fiber). According to some particular embodiments of the present invention, the present cement compositions are added in amounts of from 0.1 to 5% by weight with respect to the cellulose fibers. 97/46758 PCΪ7EP97/02829

- 8 -

Tests have been carried out about the characteristics of the paper obtained using the cement compositions according to the invention as a filler or as a charge.

A further object of the present invention is represented by the paper containing the present cement composition, preferably in the above specified amounts with respect to the cellulose fibers content.

In Table 1 the properties of the paper charged with a white

Italcementi cement (Italbianco having the characteristics reported in

Table 2) are reported. As one notices with two kinds of paper pulps and a proportion of ingredients of 0.25% of cement with respect to the fiber one notices an improvement of nearly every most relevant physico-mechanical characteristics.

In particular one notices beside an increase of the ashes an improvement of tensile strength, of the extension, of the breaking energy and of the internal bond (Scott Bond) in confirmation of the increased retentive capacity of the fiber panel

In Figure 1 one notices in particular as in presence of an ashes percentage ranging from 0.5 and 1 the traction index increases in a significant manner. This effect does not turn out to be present with the use of traditional fillers.

Tests have also been carried out with sheets having cement contents greater than 5% ■

In order to point out the good performing characteristics of the additions of the invention the results have been compared w th the properties that the sheet of paper reaches with the use of a traditional charge such as calcium carbonate. The data are gathered in Table 3- The tests have been carried out on pine bleached kraft pulp in presence of 1% by weight of cationic starch.

The starch added in such percentages has a retentive effect helping the charge to remain on the sheet without affecting its characteristics.

In general one may notice, as it is known, that the mechanical properties of paper decrease as the addition of mineral charges increases. If we however compare the properties of the sheet of paper charged with cement with respect to tho properties obtained by carbonate additions it is possible to notice an improvement of some important mechanical properties. In order to do a correct comparison it is necessary to compare the additions under the same content of ashes, because the ashes content affects the physico-mechanical characteristics of paper. It is therefore correct to evaluate sample 1 with respect to the comparison sample 3 an sample 2 with respect to the comparison sample 4. The parameter increasing in the most relevant way is that one concerning bulkiness, which n the paper prepared with cement additions is higher not only with respect to the comparison samples but also to the chargeless reference.

This parameter is important because greater bulkiness values corresponds to a more refined and then of greater quality paper. Another relevant parameter is the tearing index. As this parameter is not directly influenced by the kind of charge, it gives in fact a precise idea of the stronger bond existing among the fibers in relation to the kind of addition. As one notices, the values of the tearing index are greater for the sheets of paper treated with cement with respect to the carbonate.

In Table 4 the reference standards are reported for the determination of the physical, mechanical and optical properties of the paper and the cement according to which the tests have been carried out, whose results are reported in Tables 1 and 3-

It is clear that n case one wants to produce a white colour paper, such as that one achievable with calcium carbonate, white cements and suitable additives which do not alter the colour will be used. For example the ligmnsulfonates ought not to be used. If the colour of the produced paper has not particular importance for the use to which it s destined, the cement used to prepare the composition to add to the paper pulp may be also the normal grey cement.

The organic substances which are used in order to prepare the matter compositions according to the present invention are already used in the cement sector because some of them have retarding effects on the cement setting in the normal use conditions of the same, other are water-proofing, still other are fluidifying. The amounts range in general from 0.1 to 5% by weight with respect to whole dry composition of at least an organic substance selected from the group consisting of ligmnsulfonates, hydroxycarboxylic acids having from 3 to 20 carbon atoms and their alkaline or alkaline-earth salts, aliphatic and aromatic amines having a number of carbon atoms from 3 to 12, carbohydrates either mono- or poly-saccharides and the relative oxidation products. The cement composition and the paper according to the present invention are typically prepared at the usual temperatures for paper manufacture, such as room temperature (e.g. at +15°C/+30°C) . According to a preferred aspect of the present invention the cement defined according to UNI ENV 137-1 standard is grinded in order to obtain the desired particles size then optionally added with the above defined organic substances, and then the cement composition is added to the cellulose pulp in powder as such or in aqueous suspension before the hydration process starts.

This means that in order to add the composition according to the invention to the paper, an aqueous suspension of the cement or cement composition s prepared by dispersion of the same in water in such an amount as to have from 0.1 to 30% by weight of solid in suspension, under vigorous stirring, which is continued for a time from 30 minutes to 2 hours, in order to homogenize the composition in an optimal way. After said time, the suspension may be immediately added to the cellulosic fibers, or further kept under stirring, so that the suspended solid is not left to decant, till the moment of its introduction into the supension of cellulosic fibers, provided that no substantial hydration occurs.

According to another typical aspect of the present invention, the matter composition useful as mineral charge for paper is prepared by dry grinding the normal production cement to the selected particles size and subsequent mixing with the selected organic substance.

The matter composition according to the invention to be added to the cellulosic fibers suspension to manufacture paper may be prepared directly in the form of an aqueous suspension near the paper production plant. In this form of embodiment of the invention the cement and optionally the selected organic substance are directly mixed in the aqueous medium and the suspension is run into a colloid mill in order to reduce the cement particles size to values lower than 50 μm. The suspension leaving the colloid mill is then directly sent to the machine to produce paper.

Hereinafter we report some Examples of practical realization of compositions according to the invention and their use in the preparation of paper. EXAMPLE 1

A cellulose pulp has been prepared mixing 300 g of pine bleached kraft pulp with 700 g of fir wood. The chemical pine and fir wood pulps have been refined m hollander according to UNI 8l62 standard to about 22 and 0 SR respectively with a 5-5 kg load. They have been, then, thickened, granulated and stored in refrigerator till the moment of use. The mechanical pulp showed, after pulping according to UNI 8l66 standard, a freeness equal to about 75 SR.

1000 g of type I Portland cement according to the European standard ENV 197-1 (Italbianco Italce enti) having the chemical-physico- mechanical characteristics reported in Table 2, have been introduced into an Alpine type MikroplexR laboratory separator until completely going through a 0 μm sieve. MANUFACTURING Of THE SHEETS

The pulp has been pulped for 10 minutes in a laboratory standard pulper according to UNI 8l66 standard. The slips of paper have been prepared from a 5 g/1 suspension of the fiber in net water added under mild stirring with 2.5 g of cement prepared as described above. The cationic starch having a substitution degree of 0.045 moles/mol (AMIL0FAX 3300) has been added in the measure of 1% on the stove dry fiber. The manufacturing of the slips of paper from about 60 or 80

2 g/m has been carried out on the standard sheet maker equipped with a

400 NIT cloth according to the Aticelca MC 217 method.

The slips of paper have been dried and conditioned at 23 °C and 50% R.H. (relative humidity) before of the physico-mechanical analyses.

The results are reported in Table 1.

EXAMPLE 2

The tes t has been carried out subs tan i al ly as des c ribed in the

Example 1 with the only variati on that a m ix ture 200 g o f pine bleached kraft pulp with 800 g of fir wood pulp refined n the same way was used .

The results relating to the obtained sheets are described in Table 1.

EXAMPLE 3

The cellulose pulp has been prepared substantially as described in the Example 1 but using only pine kraft pulp refined in Valley at 28 SR.

With respect to the Example 1 the cement has been used as charge in amounts of 16.6 and 2Q . G% respectively with respect to the cellulose pulp.

By compari son shee ts o f paper have been p rep ared us ing c al c ium carbonate as additive .

The results relating to the sheets obtained ar e described n Table 3 -

EXAMPLE 4

Sizing tests have been carried out using a mixture consisting of pine bleached kraft pulp (30%) refined in hollander at 28 °SR and mechanical fir wood pulp (70%). The above cited mixture diluted by net water at 0.6% was added with a modified synthetic adhesive and subsequently with the charge in the measure of 15% on the stove dry mixture .

Paper samples of about 80 g/m have been manufactured. The paper has been conditioned at 23 °C and 50 % of relative humidity and then analyzed. The results relative to the obtained sheets are described in Table 5-

TABLE 1: Properties of the papers charged with cement. Effect of the use of cement at low dosages (filler)

PINE KRAFT PULP % 30 30 20 20

FIR MECHANICAL PULP % 70 70 80 80

CEMENT % 0 0.25 0 0.25

CATIONIC STARCH g/100g 1 1 1 1

FREENESS SR 52 55 66 60

SHEET PROPERTIES

BRIGHTNESS % 64.3 65-5 64.4 64.2

OPACITY % 89-2 90.5 90.8 91-8

SUBSTANCE g/m² 59-6 64.2 60.2 63-5

BULK DENSITY Kg/m³ 540 555 510 530

BULKINESS cπH/g 1.85 1.80 1.96 1.89

TRACTION INDEX N m/g 38.7 42.8 30.0 35-8

BREAKING LENGTH m 3945 4365 3060 3650

EXTENSION % 2.48 2.54 I.83 2.17

BREAKING ENERGY J/Kg 620 720 340 500

SCOTT BOND J/m² 275 355 190 350

TEARING INDEX mNm /g 7.12 7-00 6.60 6.00

ASHES % 0.48 0.72 0-55 0.74

TABLE 2- Chemical and physico-mechanical characteristics of the used cement

CHEMICAL ANALYSIS

Loss on ignition 2.68 %

Brilliance 90.0

Predominant wavelength 69 nm

Purity 2.3 %

F O.38O %

X-RAY SPECTROMETRIC ANALYSIS

SiO- 21.80 %

Al₂0o 3.60 %

Fe₂0 0.25 %

CaO 65.86 %

MgO 0.98 %

SO, 3-15 %

Na₂0 O.83 % κ₂o 0.10 %

SrO 0.08 % Mn₂0 <0.04 % p₂o₅ 0.09 %

Tι0₂ 0.03 %

MECHANICAL AND PHYSICAL REQUIREMENTS

Average weight prisms 577.00 g ., Compressive strength after 2 days 39.9 N/mnr Compressive strength after 7 days 59.7 N/mm² Compressive strength after 28 days 72.1 N/mπT Flexure strength after 2 days 6 1 N/mm² Flexure strength after 7 days 7-4 N/mm² Flexure strength after 28 days 8.5 N/mm² Cement mortar consistency 95 Water cement mortar consistency 30.; ? "1

- o Setting start time 1.55 h.min Setting end time 2.32 h.min Volume stability (Le Chatelier) 0 mm TABLE 5 ' Physico-mechanical properties of the papers charged with cement. Comparison with similar papers charged with calcium carbonate

1 2 3 4

SAMPLE Re^'f. Cement Cement Carbon, Carbon. paper charged charged charged charged paper paper paper paper

PULP % 100 83-4 71.4 55-5 44.6

CEMENT % 0 16.6 28.6 0 0

CARBONATE % 0 0 0 44.5 55-4

CATIONIC STARCH g/lOOg 1 1 1 1 1

FREENESS °SR 28 25 24 23 22

SHEET PROPERTIES

BRIGHTNESS % 81.4 81 .6 82.2 85 86

OPACITY % 74.2 79.8 81.5 80.7 81.7

BASIS WEIGHT g/m² 63-0 63.4 63-4 63.3 65.5

BULKINESS cn /g 1.34 1.50 1.52 ι.4ι 1.33

TRACTION INDEX N m/g 54 46.7 39-4 43-6 31.8

BREAKING LENGTH m 5500 4760 4020 4440 3240

EXTENSION % 2.88 3.40 2.94 2.72 2.46

BREAKING ENERGY J/Kg 1020 1070 740 800 520

SCOTT BOND J/m² 360 330 210 230 110

TEARING INDEX mNm /g 8.12 7-03 5-70 7-01 5.52

ASHES % 0.43 10.52 19.0 9.1 22.2

Ref. Reference TABLE 4: Reference standards for the determination of the physical, mechanical and optical properties of the paper

BRIGHTNESS % UNI 7623

OPACITY % UNI 7624

BASIS WEIGHT g/πT UNI 6440

THICKNESS mm UNI 6442

BULK DENSITY Kg/m³ UNI 6442

TRACTION INDEX N m/g UNI 6438/1

EXTENSION % UNI 6438/1

BREAKING ENERGY J/Kg UNI 6438/1

ELASTICITY MODULUS MPa UNI 6438/1

SCOTT BOND J/m² UNI 9 39

KODAK PATHE' RIGIDITY mNm UNI 8984 p

TEARING INDEX mNm /g UNI 6444

ASHES /" UNI 6445

Reference standards for the determination of the physical and mechanical properties of the cement

Average weight prisms g UNI EN 196/1-1991 Compressive strength after 2 days N/miri UNI EN 196/1-1991 Compressive strength after 28 days N/mm² UNI EN 196/1-1991 Flexure strength after 2 days N/mm² UNI EN 196/1-1991 Flexure strength after 28 days N/mm² UNI EN 196/1-1991 Cement mortar consistency UNI 7044 - 1972 Water cement mortar consistency % UNI EN 196/3-1991 Setting start time h.min UNI EN 196/3-1991 Setting end time h.min UNI EN 196/3-1991 Volume stability (Le Chatelier) mm UNI EN 196/3-1991 TABLE : Properties of the papers charged with cement or calcium carbonate and adhesive

Claims

CLAIMS 1. Use of a cement composition as filler or mineral charge for the production of paper, characterized in that it comprises at least one cement defined according to UNI ENV 197-1 standard, in not hydrated form, which has particles with a size lower than 50 μm. 2. Use of a cement composition according to claim 1, wherein particles have a size lower than 30 μm. 3- Use according to claim 1, characterized in that the cement has a ferric oxide content lower than 5% by weight, and a brilliance greater than 85%. 4. Use according to claim 3. wherein the cement ferric oxide content is lower than 3% by weight, and the brilliance is greater than 90%. 5- Use according to claim 1, characterized in that the cement composition further contains at least one organic substance selected from the group consisting of lignmesulfonates, hydroxycarboxylic acids having from 3 to 20 carbon atoms or the alkali or alkaline-earth salts thereof, aliphatic or aromatic amines having from 3 to 12 carbon atoms, carbohydrates either mono- or poly-saccharides and the oxidation products thereof. 6. Use according to claim 1, wherein the cement composition is used m amounts of 0.1% to 40% by weight of dry materials with respect to the cellulose fibers, expressed as stove dry fibers. 7. Use according to claim 6, wherein the cement composition is used in amounts of 0,1% to 5% by weight. 8. Cement composition characterized in that it comprises at least one cement defined according to UNI ENV 197-1 standard, in not hydrated form, which has particles with a size lower than 0 μm, and comprises at least one organic substance selected from the group consisting of ligninesulfonates, hydroxycarboxylic acids having from to 20 carbon atoms or the alkali or alkaline-earth salts thereof, aliphatic or aromatic amines having from 3 to 12 carbon atoms, carbohydrates either mono- or poly-sacchaπdes and the oxidation products thereof. 9. Cement composition according to claim 8, wherein the cement composition comprises from 0.1% to 5% of said organic substance. 10. A process for preparing a cement composition according to claim 8 or 9, comprising grinding normal production cement to the selected particles size, and subsequently mixing with the selected organic substance. 11. Paper containing a cement composition as defined in anyone of claims from 1 to 9- 12. A process for the preparation of paper comprising a cement composition as defined in anyone of claims from 1 to 9. in the amounts therein defined, comprising grinding a cement defined according to UNI ENV 197-1 standard to the selected particles size, optionally adding it with an organic substance as defined in claim 5. then adding the cement composition to the cellulose pulp an powder as such or in aqueous suspension before the hydration process starts. 13- The process as claimed in claim 12, wherein aqueous suspension of the cement composition is prepared by dispersing the cement in water, in an amount corresponding to from 0.1» to 0 by weight of solid in suspension, under vigorous stirring, which is continued from 30 minutes to 2 hours, to homogenize the composition. 14. The process as claimed in claim 12, wherein the cement and optionally the selected organic substance are directly mixed in an aqueous medium, and the suspension is run in a colloid mill to reduce particles size to values lower than 5 μm, then the suspension leaving the colloid mill is directly sent to the machine to produce paper. 15. Paper obtainable according to the process defined in claims from 12 to 14.