CZ430599A3 - Process for producing paper by making use of gel-forming system - Google Patents

Abstract

Method for producing paper by forming and drying aqueous pulp containing cellulose pulp and mineral a filler, the principle of which is to be placed in the paper stock sheet formation incorporates a gel-forming system containing a polymer, which contains at least one hydroxyl group the amount is less than 5% by weight, based on the weight mineral fillers and cellulose pulp. This polymer is selected from the group consisting of polyvinyl alcohol, galactomannan containing at least two vicinal hydroxyl groups and hydrophobic modified cellulose as well as mixtures thereof; borate-based crosslinking agent in the form of an aqueous solution, wherein the crosslinking agent / polymer weight ratio containing at least one hydroxyl group 0.025 to 2. Also described is paper produced in this manner and the use of this paper in the manufacture of laminates.

Description

A method of making paper using a gel forming system

Technical field

The present invention relates to a novel process for the production of paper using a gelling system to improve the retention of incorporated mineral fillers. The invention also relates to a method of making paper using a gelling system which significantly improves the opacity of the obtained paper. In addition, the mechanical properties of the obtained paper, such as its stiffness and tear resistance, as well as other properties, such as the whiteness of the paper, are improved. In addition, with the gelling system of the present invention, further advantages can be achieved with regard to the quality and recyclability of the white water which is lost in the papermaking process as well as the paper torn during papermaking.

BACKGROUND OF THE INVENTION

There are many problems in paper manufacturing. One of the basic efforts is to reduce the cost of paper by reducing the amount of cellulose fibers in the pulp composition. A further effort is to reduce the concentration of waste water, which is imposed by increasingly stringent environmental pollution standards.

Various means have been proposed in the manufacture of paper to reduce the cost of paper and attempt to improve its quality. One such approach is to add relatively inexpensive mineral fillers to the paper being produced to replace these fillers in the paper.

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paper pulp fibers. Otherwise, it is known that some mineral fillers are specifically used to improve some properties of paper. For example, titanium dioxide in the form of anatase or rutile is used to improve paper opacity. This is particularly the case for laminated papers, which are commonly referred to as decorative papers.

Unfortunately, when the addition of mineral binders improves some properties of the paper, such an addition generally results in a deterioration of some paper characteristics, such as a deterioration in the mechanical properties of the paper, such as a deterioration in dry and wet tear resistance.

In addition, the addition of mineral fillers whose particles have micrometric dimensions encounters the problem of retention of these particles in the paper: during the formation of a paper sheet on a paper machine screen, the mineral binder particles tend to penetrate through the screen resulting in white water with high concentration of this filler. This in turn results in problems in the level of wastewater treatment before it is discharged into watercourses and in the quality of the paper produced. In addition, the non-retained filler will lose its effectiveness during subsequent recycling. Although the use of retention agents reduces the problem of lack of retention, this solution is not entirely satisfactory. For example, in the case of retention of opacifying fillers such as titanium dioxide, the use of retention fillers of the electrically charged polymer type causes a loss of opacification efficiency due to too intense and too dense flocculation.

The use of less expensive and inferior pulp has been tested, but this has led to a significant deterioration in the paper characteristics and often an excessive amount of fines that are not retained in the production process.

paper and passes into waste white water, which in turn causes problems in the treatment of such waste water.

SUMMARY OF THE INVENTION

The Applicant has now developed a new papermaking process using a gel forming system that greatly improves the retention of mineral fillers, fibers and other substances in the sheet of paper stock.

It is therefore an object of the present invention to provide a gel forming system and method for producing paper that produces paper having improved properties, including opaque mineral filler yield, tear resistance, whiteness, and other desirable properties, by optimizing the use of mineral fillers.

Another object of the invention is to provide a paper having an increased concentration of mineral fillers and at the same time acceptable tear resistance and other acceptable properties.

Other features of the invention and advantages attained by the invention will be apparent from the description below, and in particular from tests, tables and figures, which illustrate various features of the invention.

SUMMARY OF THE INVENTION The present invention is based on the discovery of a gel-forming system and a method of making paper using this gel-forming system, which greatly improves the retention of mineral fillers and other paper characteristics and which makes it possible to optimize the effect of mineral binders present.

Increasing the retention of mineral binders and fines in the papermaking process of the present invention reduces the problem of whitewater contamination of the watercourse.

In addition, it is facilitated to recycle the paper waste formed by the scrap paper and the marginal areas of the paper due to the presence of the components of the gelling system in the paper, which allows the waste paper to be easily converted into a paper pulp.

In general, the gel forming system of the invention comprises:

a polymer comprising at least one hydroxyl group, the amount of which is less than 5% by weight, based on the weight of the mineral fillers and cellulose pulp, the polymer being selected from the group consisting of:

. polyvinyl alcohol,. galatomannan containing at least two vicinal hydroxyl groups,. cellulose modified with hydrophobic groups to achieve water solubility,. and mixtures thereof, and a crosslinking agent in an aqueous solution comprising an element selected from the group consisting of borate, zirconate, titanate, and mixtures thereof, wherein the weight ratio of the crosslinker to the polymer containing at least one hydroxyl group is 0.025 to 2.

The amount of solids (dry matter) in said gel-forming system is 0.02 to 18% by weight, preferably 0.5 to 5% by weight, based on the weight of the stock.

The mineral fillers used in the present invention are of a different nature and are particularly chosen depending on the type of paper being produced and its future use. Useful mineral fillers include all conventional mineral fillers whose surface is at least partially anionic in nature.

Examples of mineral fillers include, but are not limited to, kaolin, clay, chalk, calcium carbonate, titanium dioxide, silica, and mixtures thereof.

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The mineral fillers are normally added in the form of an aqueous dispersion having a concentration that is adequate to the paper type produced.

Many commercially available products can be used as fillers for papermaking. Examples of such products include, but are not limited to, kaolin from ECC, Omyafill calcium from OMYA and Calopake calcium from Rhone-Poulenc, titanium dioxide Finntitan from Kemira and titanium dioxide Rhoditan from Rhone-Poulenc.

Among the polymers of the gelling system, non-limiting examples of hydrophobic modified celluloses include carboxymethylcellulose (CMC), ethylhydroxyethylcellulose (EHEC), hydroxyethylcellulose (HEC) and methylethylcellulose (MEC).

Numerous commercially available modified celluloses may be used for said papermaking. For example, ethylhydroxyethylcellulose may be derived from the Blanose product line from Aqualon and the Bermocoll product line from Akzo Nobel. Other modified celluloses can be found in the Hercules product line.

When polyvinyl alcohol is used as a component of said gelling system, polyvinyl alcohol is generally used in the presence of borate. For example, the polyvinyl alcohol is selected from the Mowiol product line of Hoechst or the Rhodoviol product line of Rhone-Poulenc.

Preferably, the polymer is selected from the group consisting of galactomannans containing at least two vicinal hydroxyl groups, in particular guar gum. With respect to guar gums, it has been found that their reactive centers are particularly accessible, so that small amounts of guar gums can be used to achieve a satisfactory effect.

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When a guar gum gel-forming system is used as one of the components of the system, the mineral fillers are retained to a significant extent in the final product and the paper produced has improved resistance compared to paper obtained by a process not involving the use of a gel-forming system.

Guar gum may be of natural origin or may be chemically modified. Natural guar gum is an extract of the seed albumen of some plants, such as Cyamopsis Tetragonalobus. The macromolecule of guar gum consists of:

a backbone consisting of monomeric β-D-mannose sugar units bound to each other by bonds (1-4) and α-D-galactose side units bound to β-D-mannose units by bonds (1-6).

Commercially available products include, for example, the Meyproid, Meyprobond, Meyprofilm and Meyprogat series as well as Jeyar from Meyhall, guar gums from System Bio Industry, and guar gums from Colloid Natural International.

Depending on the nature of the polymer, the polymer may be used in the form of an aqueous solution.

Crosslinking agents are either prepared from basic raw materials or commercially available products are used.

For example, the borate ion is obtained from boric acid and sodium hydroxide or borax.

For example, the zirconate is prepared from zirconium acetate or zirconium chloride. As a commercially available ready-to-use product, Zirkomplex PN from Rhone-Poulenc can be used.

For example, the titanate can be prepared from titanium bromide.

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Within the scope of the invention, the most interesting quantitative and qualitative results are obtained when a borate ion is used as a crosslinking agent together with a galactomannan containing vicinal hydroxyl units, in particular guar gum.

in particular at least two seconds together with

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

Now, the above problems caused by the addition of these fillers can be eliminated or at least greatly reduced within the scope of the invention by using the gel-forming system of the invention, which allows the addition of more mineral fillers than was usually added to achieve the specific properties of the paper produced.

Thus, it is possible using the gel forming system of the present invention to produce paper that contains fewer fillers and yet retains its opacity. In this way, the mechanical properties of the paper (e.g., elasticity modulus, traction index, traction energy absorption) have the same or even higher values than previously achieved with papers obtained from conventional papers.

The sheet of paper after drying has a significantly better resistance when using the method according to the invention. It has also been found that when the above-mentioned mineral fillers or analogous fillers are used in the pulp, these mineral fillers are effectively retained in the sheet of paper and do not adversely affect the resistance of the sheet to non-gelatinizing paper sheets. system according to the invention, wherein said negative effect is exerted.

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Although the mechanism that occurs in the pulp during drying of the paper in the presence of the gel-forming system has not yet been fully elucidated, it is believed that the gel-forming system combines with fibers and fillers to form a complex gel structure. In fact, the sheet of paper during the production of the paper must undergo a dewatering step which can deeply modify the structure of the colloids as well as their distribution. Changes in the structure of aggregates during dewatering can affect the retention rate of mineral fillers as well as the opacity of the paper obtained. A sharp increase in the viscosity of this environment makes it possible to stiffen the structures and slow down the migration processes that cause otherwise evolving paper structure variations. This assumption forms the basis of the mechanism used by the invention: during dewatering, a gel structure is formed in the cellulosic network, which will trap the fillers in order to maintain the suspension properties of the particles during this critical stage.

In the papermaking process, the components of the gel forming system and filler are added simultaneously or in any sequential order to the fibrous dispersion prior to forming the sheet of paper in the papermaking machine. These components are added to the mixing vat or to a point of the system where appropriate mixing is already provided to cause proper dispersion of the components.

In a preferred variant, the gel forming system and the fillers are first mixed together and then added to the stock prior to forming the sheet in the paper machine.

According to another preferred variant, a part of the mineral fillers, preferably 20 to 90 wt. of the total amount of mineral fillers, after which a gel-forming system is added to the paper stock and after formation of the gel structure, the remaining amount of mineral fillers is added before forming a sheet of paper in the paper machine. V ·

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At this stage, the stock is then vigorously mixed before forming a sheet of paper.

It has been found that in the papermaking process utilizing the gel forming system of the present invention, the pH of the pulp is not an extremely critical parameter and should generally be less than 11, preferably 5 to 9.

Other additives such as defoamers and binders may also be blended into the pulp. In this regard, care should be taken that these additional ingredients do not hinder the formation of the gel structure and that the content of these ingredients in the recycled white water does not increase to the extent that it prevents the formation of the gel structure. Thus, it is preferred to add said additives at the site of the papermaking process where said gel structure has already been formed.

The improvements achieved using the gel forming system have the same order of magnitude for both chemical and mechanical and thermo-mechanical properties.

During the research work, it has been found that the principles of the invention are applicable to the production of all types and qualities of papers. For example, printing paper, wrapping paper and laminated paper may be mentioned in this regard.

Among the application possibilities of paper making, laminated paper commonly referred to as decorative paper is an option giving very positive results, which means increased retention of fillers as well as improved quality of laminated paper, in particular improved opacity. In this case, the bulk of the mineral fillers are titanium dioxide, which means that the titanium dioxide content can be 45% by weight, based on the weight of the paper.

The invention therefore also relates to laminated paper (i.e. laminated paper). In this case, the papermaking is carried out in the presence of a wetting agent. The agent is, for example, a quaternary ammonium salt of epichlorohydrin-based polymers, for example epichlorohydrin / dimethylamine polymers.

The invention also relates to laminates based on laminated yet at least one (for example, a resin of papers containing in addition a heat-curable urea-formaldehyde type resin, a melamine-type melamine-formaldehyde type resin, etc.) and at least one opacifying pigment such as titanium dioxide.

resin, phenolic resin or

Any known method of making laminated paper can be used to prepare the laminates of the invention. The invention is not limited to any specific method of preparing said laminate.

In the following, the invention will be explained in more detail by way of examples of specific embodiments thereof, which examples are for the purpose of illustration only and are not to be construed as limiting the scope of the invention as defined by the claims.

DETAILED DESCRIPTION OF THE INVENTION

The tests below illustrate, without limitation, the advantages and properties associated with the paper of the invention and the process for its manufacture. These tests were performed in the manufacture of laminated paper.

The first series of tests relates to the evaluation of the retention capacity of the gel-forming system of the invention during papermaking.

Another series of tests relates to the evaluation of paper properties achieved in the method of the invention.

The products used are commercially available products:

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- the titanium dioxide used in the examples is a rutile modification of titanium dioxide, which is commercially available from Rhone-Poulenc under the designation Rhoditan RL 18,

the guar gum used in the examples is guar gum commercially available from Meyhall under the designation Meyprogat 30, the zirconate comes from a solution of the zirconium lactate complex commercially available from Rhone-Poulenc under the designation Zircomplex PN, the polyaminoamidepichlorohydrin (PAE) resin is R4947 Ceca a

- the pulp consists of a refined mixture (30-35 ° according to Shopper) of 70 wt. eucalyptus and 30% conifer.

A) Retention tests

1) Material used

Retention measurements were performed by a method known as bol BRITT.

This method consists in measuring the chemical retention of fillers while eliminating the formation of the fibrous mat responsible for mechanical retention based on the filter effect. Thus, 500 ml of the dispersion of fibers, fillers and additives to be tested are kept under stirring, with only 100 first ml being drawn through a sieve. After determining the individual amounts of fibers and fillers passed into the filtrate, the total retention (fibers + fillers) and the retention of fillers are calculated.

This retention measurement method is described by K.Britt and J. E. Unbehend in Research Report 75, 1/10 1981, published by the Empire State Paper Research Institute ESPRA, Suracuse, N.Y. 13210, EUA.

A filter bowl equipped with a 610 µm sieve was used for these measurements.

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Tested system

The tests were carried out using an aqueous system containing:

0.375 wt. cellulose pulps (100 parts),

-0.3 wt. titanium dioxide Rhoditan RL18 (80 parts) was added

0.1 to 6 wt. % guar gum and 0.01 to 1.2 wt. borax (% by weight based on the weight of titanium dioxide) and added

0.8 wt. PAE resin based on cellulose fiber weight.

i) Preparation of base suspension and dilution

Cellulose (15 g) was pre-pulped in 500 ml of filtered water in a Dispermat chamber for 10 minutes at 3000 rpm. Guar gum (5% solution) is then introduced under magnetic stirring, followed by borate (2% borax base solution) into an RL18 type titanium dioxide suspension having an anionic nature at pH 7. The fillers are admixed to the pulped cellulose and mixed in a chamber. Dispermat for 5 minutes at 1000 rpm. The mixture was poured into a 10 liter mixer equipped with a stirring blade. The mixture was then diluted to 4 liters. The mixture is maintained under agitation throughout the handling to ensure a homogeneous character of the mixture when sampling.

ii) Britt retention

A 500 ml sample is taken from the slurry mixture and introduced into a Britt container with a propeller blade at 800 rpm with stirring. After 30 seconds, PAE is added and the mixture is stirred for 30 seconds. Then, at 800 rpm, 100 ml of the mixture is withdrawn under the force of gravity, ensuring good control of the withdrawal flow rate (full opening

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99 999 9999 99 99. The 100 ml of the collected mixture is then dried for one hour at 105 ° C, then the residue is cooled in a desiccator and weighed (to an accuracy of ± 0.0001 g).

(iii) Calculations and results

The total retention rate is calculated using the following formula:

Rglobal = ((p, 5p _z ) / p,). 1 0 0, in which p ₁ represents the weight of the filler + fiber mixture in the original 500 ml sample and p ₂ represents the weight of the filtered and dried residue of 500 ml of the sample. This gives a percentage of the mass retained by chemical retention. The filter-dried residue is then calcined at 800 ° C for one hour to give a filler fraction retained by retention:

Rpxniva = ((P ₃ -5 p ₄ ) / p ₃ ) .100 in which p ₃ represents the weight of the filler fraction in the original 500 ml sample and p ₄ represents the weight of the filtered, dried and calcined residue of 100 ml of the sample. Thereby a percentage of filler retained by chemical retention is obtained. The results are summarized in Table I and shown graphically in Figure 1.

Fillers are immobilized in the pulp mass by inducing the structuring of the pulp by the synergistic effect of the guar gum / borax gelling system.

The drainage time is not negatively affected by the presence of the formed structure. Optimum retention is achieved at 1.5% guar gum and 0.75% borax based on the weight of titanium dioxide.

B) Opacity Recovery Test

Tests to determine the opaque yield were carried out on samples prepared with and without the gel forming system of the invention to determine the spatial distribution of titanium dioxide in the dried sheet. The samples were obtained as described in paragraph 2 below.

Measure the amount of titanium dioxide present in the leaf or the ash content as determined by the method described in detail in paragraph 3 below.

The optical properties of the impregnated and pressed samples were also measured. The method of this measurement is described in paragraph 4 below.

1) Tested gelling systems

(i) Guar gum / borate gel

Guar gum (in varying percentages relative to mineral fillers) was directly introduced into the aqueous mineral filler dispersion. Borate (2% borax base solution) was added to the mixture in amounts defined by the weight ratio r = borax (%) guar gum (%).

The fillers consist of titanium dioxide Rhoditan RL18 (anionic character at pH 7). The dispersion thus obtained is added to the stock.

ii) Guar gum / zirconate gel

Guar gum (in varying percentages relative to mineral fillers) was directly introduced into the aqueous mineral filler dispersion. The fillers consist of titanium dioxide Rhoditan RL18 (anionic character at pH 7). The dispersion thus obtained is added to the stock. To the diluted mixture of cellulosic fibers and fillers is added zirconate (a basic about 30% solution of Zirkomplex PN in amounts defined by weight ratio r = Zircomplex (%) guar gum (%).

2) Making samples

i) Formulation of paper

Cellulose: 15 g (representing 100 parts)

TiO ₂ 100 parts (i.e. 15 g) per 40% dispersion

PAE: 0.8 dry weight based on cellulose weight.

(ii) Pulp preparation: pulping

After moistening the cellulose with water, the cellulose tears into small squares. The cellulose squares thus obtained are gradually added to 500 ml of water mixed in the Dispermat chamber at 1000 rpm. After adding all the cellulose, the rotation speed is increased to 3000 rpm and stirring is continued for 10 minutes.

iii) Preparation of the Titanium Dioxide Dispersion g of titanium dioxide is dispersed in 60 g of water in a Pendraulik for 10 minutes at a rotation speed of 2800 rpm.

iv) Blending TiO ₂ with fibers.

The pulped cellulose is diluted to a volume of 1 liter. It is then fed into a mixer equipped with a blade with stirring. A TiO ₂ slurry (37.5 g) was added and the resulting mixture was stirred for 5 minutes. Finally, the mixture is diluted to a volume of 4 liters to obtain samples of paper having a basis weight of 80 g / m ² .

v) Making samples of paper

500 ml of the well homogenized suspension are introduced into a mixing cylinder. PAE (commercial solution, which is diluted 10-fold to obtain an acceptable handling volume) in an amount of 1 ml is added. The cylinder is then inverted several times to obtain a good mixing of the cylinder contents. The contents of the cylinder are then introduced into a drain pan filled with 6 liters of distilled water. The mixture is mixed by bubbling through it.

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washer and placed in the oven for 7 minutes. The sample is weighed accurately and the volume is adjusted to achieve the desired grammage (basis weight).

When the sheet has the required weight and has no manufacturing defects, it is intended for subsequent operations to determine its chemical and optical properties.

3) Measurement of ash content

Measure the amount of titanium dioxide present in the 80 g / m ² sheet by calculating a third of the paper sample at 800 ° C for one hour. Calculate the percentage of titanium dioxide in the sheet as follows:

Vacuum calcination

Ash content (%) = _

Before calcination under vacuum

From this one can derive one of the physical characteristics of sheet production (for a mixture of 100 parts fiber and 100 parts TiO ₂ ):

retention (%) = final amount = ash content initial amount 100

200

The amount of ash determines the amount of mineral fillers present in the leaf. Retention is expressed by the amount of mineral fillers retained in the sheet during manufacture. This determination was carried out using NF 03-047 method (Papier, Carton et Pate: Metodes d'essais, Method A, 4eme Edition, 1985).

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4) Determination of opacity of impregnated and pressed sheets

i) Preparation of melamine-formaldehyde resin (Inilam 3240 resin from CECA)

Heat 400 g of water to 60 ° C. When this temperature is reached, 245 g of pre-weighed resin are poured dropwise into the heated water. When all of the resin had dissolved, the solution was stirred at 60 ° C for 30 minutes. After cooling, the solution is filtered through a 50 µm cloth.

ii) impregnation-compression

The 7 cm x 10 cm strips of paper are cut out. These strips are then impregnated by capillary forces by being laid on the resin for 1 minute. The sheets of impregnated paper are then pressed between two glass rods and allowed to dry for 2 minutes in an oven at 120 ° C. The strips are then impregnated a second time by immersion in resin for 1 minute. They are then squeezed between a glass rod and a steel rod and subsequently dried for 3 minutes in an oven at 120 ° C. The strips thus obtained are then fixed to the substrate formed from the bottom up by two white backing layers and three kraft backing layers (a kind of solid wrapping paper), the paper web being in direct contact with the kraft backing layers. The resulting laminates are pressed for 8 minutes at 150 ° C and 10 MPa.

iii) Measurement of optical properties

The opacity measurement of the laminates is performed by evaluating the contrast ratio for each test paper between the kraft background zone and the white layer background using the Elrepho 2000 spectro-colorimeter opacity function of Datacolor.

5) Test results

(i) Guar gum / borate gel

obtained by compilation and 100 parts of fillers.

The results are summarized in Table II and Figure 2 and compared with a control curve of the experimental results for 50 The gel-forming system increases the retention of fillers, in particular by forming large structures that retain more efficiently. The gel-forming system also increases opacity. The large filler structures formed are better spatially distributed in the sheet of paper. These results show that it is possible to structure the aqueous environment already during dewatering of the pulp and emphasize the practical importance of this mechanism. Most efficient is a gel forming system comprising 1.5% guar gum based on the weight of titanium dioxide at a borax / guar gum ratio of 0.5. It should be noted that in the presence of this guar gum / borax structure, it is possible to achieve the same opacity as the classical formulation, using 10% less TiO ₂ .

ii) Guar gum / zirconate gel

The results obtained are shown in Table III and Figure 3 and compared with the control curve obtained in the 50 and 100 parts filler tests performed in various studies. The gel forming system enhances the retention of fillers and opacity, in particular by forming large, low mobile structures that retain better in the sheet of paper and which better distribute the fillers in the space of the paper sheet.

C) Test to determine mechanical wet strength

Tests performed to determine the mechanical resistance of the paper were carried out on paper samples obtained with and without the gel forming system of the invention. The procedure described in paragraph B2) was used. Guar gum and borax are added to the filler dispersion as in Bii). Paper samples having a width of 1.5 cm are cut out of the paper. These samples are exposed to 105 ° C for 10 minutes and then immersed in distilled water for 10 minutes before measuring the burst strength. Measurement of the specified tear force • · · ····························· Performed by Adamel Lhomargy DY 30 MTS dynamometer (see Fig. 4).

The results show that the presence of the gel structure of the invention improves the mechanical properties of the obtained sheet of paper. In the following tables guar gum is abbreviated as guar.

In the attached drawings:

Fig. 1 shows the dependence of filler retention (according to Britt) on the borax / guar gum ratio, with solid circles and solid squares representing systems containing 1.5% and 1.5%, respectively. 6% guar gum based on the weight of titanium dioxide; on the x-axis of the graph, the ratio r = borax / guar gum is plotted, and on the y-axis, the percent filler retention is plotted, the horizontal line with the x-axis representing the control assay;

Fig. 2 shows the opacity of the impregnated and pressed sheets on the amount of titanium dioxide for different amounts of the guar gum / borax gel-forming structure; on the x-axis of the graph, the ash content is plotted as a percentage, while the y-axis plots opacity as a percentage; the rising line in the graph represents the dependence of the control assay;

Fig. 3 shows the opacity of the impregnated and pressed sheets on the amount of titanium dioxide for different amounts of the guar gum / zirconate gel-forming structure; the x-axis of the graph shows the ash content as a percentage, while the y-axis of the graph shows the opacity as a percentage; the rising line in the graph represents the control assay dependency;

Figure 4 shows the rupture force versus r = borax / guar gum ratio, with solid rings and solid squares representing systems containing 0.5% and 0.5%, respectively. 1.5% guar gum based on the weight of titanium dioxide; on the x-axis of the graph, the ratio r is plotted, while «· 0

000 000 • · • 0 on the y-axis of this graph shows the breaking force F in Newtons and the line parallel to the x-axis represents the dependence of the control determination.

Table I

System (100 parts fiber) Oooele content (%). TiO ₂ 80 parts 30.5 TiO ₂ + 1.5% guar 31.6 TiO ₂ + 1.5% guar + 0.375% borax 38.3 TiO ₂ + 1.5% guar + 0.75% borax 43.0 TiO ₂ + 1.5% guar + 1.5% borax 34.0 TiO ₂ ♦ 6% guar 35.1 TiO ₂ + 6% guar + 1.5% borax 37.3 TiO ₂ + 6% guar + 3% borax 30.0 TiO ₂ + 6% guar + 6% borax 28.2

Table II

System (100 parts fiber) Ash content (%). Opacity (%) ₂₁₀₀ parts of TiO 36.0 89.9 TiO ₂ + 0.5% guar 35.3 90.5 TiO ₂ + 0.5% guar + 0.25% borax 38.0 92.3 TiO ₂ + 1.5% guar 35.9 90.7 TiO ₂ + 1.5% guar + 0.375% borax 37.6 91.6 TiO ₂ + 1.5% guar + 0.75% borax 39.7 92.5 TiO ₂ + 1.5% guar + 1.5% borax 37.4 91.7 TiO ₂ + 2.5% guar 35.8 91.4 TiO ₂ + 2.5% guar + 1.25% borax 33.8 91.1 TiO ₂ + 6% guar 35.9 91.7 TiO ₂ + 8% guar + 3% borax 34.7 90.1

Table III

System (100 parts fiber) Ash content (%) Opacity (%) ₂₁₀₀ parts Ti0 40.0 91.2 TiO ₂ + 0.5% guar + 0.1% Zircomplex 40.0 92.3 TiO ₂ + 0.5% guar + 0.2% Zircomplex 40.1 91.6 TiO ₂ + 1% guar + 0.2% Zircomplex 40.7 92.0 TiO ₂ + 1% guar + 0.4% Zircomplex 41.1 92.3 TiO ₂ + 1% guar + 0.6% Zircomplex 40.3 92.0 TiO ₂ + 2% guar + 0.4% Zircomplex 40.2 92.4 TiO ₂ + 2% guar + 0.8% Zircomplex 41.8 92.6

Claims (17)

PATENTOVÉ Claims A method of making paper by forming and drying an aqueous pulp comprising cellulose pulp and mineral fillers, characterized in that a gel forming system is incorporated into the pulp prior to sheet formation comprising: a polymer comprising at least one hydroxyl group, the amount of which is less than 5% by weight, based on the weight of the mineral fillers and cellulose pulp, the polymer being selected from the group consisting of: . polyvinyl alcohol,. galatomannan containing at least two vicinal hydroxyl groups, hydrophobic modified cellulose and mixtures thereof, and a crosslinking agent in an aqueous borate-based solution, wherein the weight ratio of the crosslinking agent to the polymer containing at least one hydroxyl group is 0.025 to 2. 2. The process of claim 1 wherein the polymer is a galactomannan containing at least two vicinal hydroxyl groups. 3. The method of claim 2 wherein the galactomannan is guar gum. ·· 0 0 · 00 00 44 • 44 4 040 4 44 44 0 44045 4 44 44 4 4 0 444445 0 0 · 44 44 4 0 44 44 444 4444 Method according to any one of the preceding claims, characterized in that the mineral fillers are selected from the group consisting of kaolin, clay, chalk, calcium carbonate, titanium dioxide, silica and mixtures thereof. The process according to claim 4, wherein the mineral filler is titanium dioxide in an amount equal to up to 45%. Method according to one of the preceding claims, characterized in that the pulp web is maintained at a value between 5 and 9. A method according to any one of the preceding claims, wherein: znače n ý that amount solid share in gel-forming system equals 0.02 to 18% weight, relative to mass paper pulp. The method of claim 7, e znače n ý that the amount of solids in the gel forming system is preferably 0.5 to 5% by weight, based on the weight of the stock. Method according to one of the preceding claims, characterized in that the components of the gel-forming system are incorporated separately into the stock prior to forming the sheet. Method according to any one of the preceding claims, characterized in that the gel-forming system is added to the mineral fillers and mixed with these fillers prior to incorporation of these fillers into the paper stock. 9 9 99 99 99 99 99,999 9,999 9 9,999 9,999 99 99 · · 9 ······ 9 9 9 9 9 9 99 99 99 99 99 99 Method according to one of Claims 1 to 8, characterized in that a part of the mineral fillers is added to the pulp, after which a gel-forming system is introduced into the pulp and after the gel structure has been formed the rest of the mineral fillers is mixed with the pulp. before creating the worksheet. A method according to claim 11, characterized in that 20 to 90% of the total fillers are added to the stock prior to forming the gel structure and that the remaining mineral fillers are added after the gel structure has been formed. Method according to one of the preceding claims, characterized in that the paper produced is laminated paper. Paper characterized in that it can be produced by a process according to any one of the preceding claims. Paper according to claim 14, characterized in that it has a titanium dioxide content of up to 45% by weight, based on the weight of said paper. Use of the paper according to claim 14 as laminated paper, writing paper or wrapping paper. Use of the paper according to claim 15 as laminated paper. The laminated paper-based laminates of claim 17 comprising at least one thermosetting resin.