WO2001042564A1

WO2001042564A1 - Compositions having influence on the strength of paper

Info

Publication number: WO2001042564A1
Application number: PCT/FI2000/001041
Authority: WO
Inventors: Susanna Koskinen; Taru SYRJÄNEN; Salme Koskimies
Original assignee: Neste Chemicals Oy
Priority date: 1999-12-08
Filing date: 2000-11-29
Publication date: 2001-06-14
Also published as: FI107951B; AU2174601A; FI19992633A

Abstract

The present invention relates to compositions for the treatment of fibrous material such as paper web during paper manufacturing, particularly to foamable compositions containing additives influencing the paper strength. The invention is also directed to the use of foamable compounds to improve the strength of fibrous material. The foamable composition influencing the strength of the fibrous material comprises a resin, or a mixture of resins that may be cured thermally or with an acid, a surface active agent, water, and optionally a cationic acryl amide copolymer.

Description

Compositions having influence on the strength of paper

The present invention relates to compositions for the treatment of fibrous material such as paper web during paper manufacturing, particularly to foamable compositions containing additives influencing the paper strength. The invention is also directed to the use of foamable compounds to improve the strenght of fibrous material.

It is known to form paper and nonwoven fabric by disposing a slurry of fibers suspended in a liquid, generally in water, in layers on a porous support called the wire. The wire allows the liquid to flow therethrough while most of the fibers are retained on the wire to form a web or a felt wherein all the fibers are tangled together substantially in the plane of the web.

In this method, problems are caused by the natural flocculation of the fibers, that is, the tendency to form flakes or aggregates that are difficult to break. They may thus be incorporated into the web being formed, influencing the smoothness of the web and its final properties. This problem is particularly severe when handling of slurries containing long or synthetic fibers, or having a high fiber content. This is the case when a heavy web is produced or when fibers causing a slow dewatering by nature are used or the speed of the paper machine is high, or when it is important to lower the treatment costs of the drained liquid.

The problem due to the flocculation of the fibers may be reduced by dispersing the fibers to very high volumes of water. In this case, the fiber concentration is from 10 to 100 mg/1 rather than from 1 to 10 g/1, which is the concentration generally used. It is, however, commercially uneconomic to handle such high water volumes. As a solution to this flocculation problem, a method has been suggested wherein the fibers are dispersed in a liquid polymeric medium having a high viscosity, such as aqueous sugar or natural gum mixtures. Because of the high viscosity of the medium, the drainage thereof through the web being formed and the wire supporting it is slow and troublesome, and accordingly, this method is not particularly suitable for continuous large scale production of fiber products.

To solve this problem, the patent publication US 3937273 suggests a method wherein the headbox slice of the paper machine is modified to be very low and adjusted with sharp bends in series. As the fiber suspension passes through the slice, the bends cause in the suspension very intense small scale turbulences that break the flakes or aggregates formed. Then the suspension flows to a second low slice and passes on the wire forming the paper web in a normal manner for a paper machine.

Patent GB 1209409 discloses a method wherein a uniform fiber suspension is produced in a foam provided by dispersing air in water in the presence of a foaming additive. Such foams may be drained off relatively easily, and thus, they do not restrict the performance of the paper machine inacceptably. The favourable rheology of the foams is believed to result from the pseudoplastic behaviour of the densely packed resistant bubbles, limiting the migration of the fibers, and thus preventing the formation of flakes and aggregates. However, owing to this behaviour, the high quality of the suspension is preserved, and the drainage is quick.

Patent GB 1129757 presents a method and an apparatus for forming a fiber web from a foaming medium. The chemical nature of the surface active agent is not critical provided that the foaming capacity thereof is sufficient to provide a thick viscose foam of small air bubbles. The surface active agent may be an anionic, cationic or non-ionic agent. In this method, the fiber product may be produced by dispersing the fibers in a foamed liquid medium. This medium is produced by dispersing air as ex- tremely fine bubbles in an aqueous solution containing a surface active agent. The dispersion is carried out using high shear force to attain the desired properties. The publication underlines that the air content of the foamed liquid medium must be at least 65 % by volume.

Patent GB 1329409 discloses improvements to increase the smoothness of the web. The method shows the influence of the air content of the foam on the behaviour of the fibers in a foamed medium. Fiber material may be produced by using foamed liquid medium having an air content higher than 65 %. There is an air level at which the fi- bers tend to aggregate in the foamed medium although they are very evenly dispersed in it. Moreover, the size distribution of the bubbles in the foamed liquid medium is very critical. According to this publication, not all foamed liquid media produced by dispersing gas as bubbles in a liquid containing a surface active agent are suitable for the dispersion of fibers, but instead, some of them may be used to aggregate fibers (and particles) rather than to disperse them. This phenomenon may be used to improve the retention of certain materials on the web. Further, according to this publication, the fibers are dispersed very evenly and uniformly throughout the foamed liquid medium containing gas from 55 to 75 % by volume. If the gas content is below 55 % by volume, the number of the gas bubbles incorporated into the foam is relatively small, and the size distribution thereof is relatively wide. They then divide the medium into liquid pockets, in which the fibers accumulate. Since the viscosity of the liquid is relatively low, the fibers may migrate freely and thus aggregate in the liquid pockets. On the other hand, if the gas content is above 75 % by volume and the size distribution of the bubbles is very uniform, then the packing density of the bubbles is so high that the spherical bubbles will deform and adopt a polyhedric form. In the medium containing such bubbles, there are surface tension forces in the planes of the lamellas between the bubbles attracting the fibers to junction lines of the lamellas being formed between the bubbles. This causes aggregation of the fibers to bundles that follow these lines. Although such aggregation is found to a certain extent in cases where the gas content is above 75 % by volume, the dispersion of fibers in such a foam is on an average better than in a medium comprising only water. The number of the gas bubbles, and the shape and size thereof in the medium are factors that determine the tendency of a particular foamed liquid medium to favour the dispersion, or the aggregation of fibers.

To attain an adequate stability of the foam, the concentration of the foaming additive should be relatively high in the fiber suspension to enable the foam to carry the dispersed fibers from the dispersing apparatus to the wire. It is believed that surface ac- tive agents interfere with forces forming bonds between the fibers, and thus the presence thereof decreases the density and the strenght of a paper product obtained with a web forming method using foam. It has been possible to reduce this problem to some extent by using fiber with a higher degree of milling, or by adding reinforcing agents thereto. However, the reduction of the amount of the surface active agent needed would be a better solution.

An object of the present invention is to provide a foamable composition improving the strength of fibrous material, particularly wood fiber material. This composition may be used in the production of paper wherein the fibers are dispersed in a foaming liquid medium resulting in a uniform fiber web with a good specific volume. Another object of the invention is the use of a compound that may be foamed easily and sufficiently in said composition, the foam forming ability thereof, the stability of the foam obtained therewith, the influence thereof on the strength of the fiber bonds, and other properties being in particular suitable for the production of paper.

The characteristic features of the foamable composition according to the invention, and of its use in the production of paper are presented in the appended claims. It has now been found that the objects of the invention may be attained and the drawbacks of the methods of prior art may be avoided or substantially reduced with the solution of the invention. The composition of the invention comprises a surface active agent, a resin that may be cured thermally or with an acid, such as a urea- formaldehyde or a melamin-formaldehyde resin, or a mixture thereof, and water. In addition, the composition may also contain a cationic acryl amide copolymer. The constituents are mixed together in the form of sufficiently dilute aqueous solutions in the following order: resin, copolymer, surface active agent, water, and acid.

The resin, preferably an aqueous solution of urea- formaldehyde, is added in an amount varying from 0.5 to 5 %, by weight, preferably from 0.5 to 3 %, by weight relative to the dry weight of the fibers, calculated as dry resin. The dry matter content of the urea-formaldehyde resin is from 30 to 60 %, by weight, preferably from 35 to 50 %, by weight, the molar ratio of formaldehyde to urea being from 1.8 to 3.8 : 1. The resin is preferably diluted to form an aqueous solution having a concentration from 1 to 5 %, by weight.

The cationic acryl amide copolymer is added in an amount of 0 - 3 %, preferably 0.5 - 1 %, calculated as dry copolymer, relative to the dry weight of the fibers. The cati- onic acryl amide copolymer is typically used as an aqueous 10 - 50 % solution having a cationicity of 20 - 100 %, preferably 25 - 80 %, the molecular weight of the copolymer being between 10,000 and 300,000, preferably between 50,000 and 300,000. The cationic acryl amide copolymer may be produced from monomers comprising acryl amide, or from monomers in copolymeric cationic form, such as quater- nary acryl amide alkyl-N-alkylamine, secondary or tertiary acryl amine alkyl-N- alkylamine, or primary acryl amine, esters of acrylic acid, the alcohol moiety thereof being a quaternary n-alkylamine alkoxide, or from a secondary or tertiary n- alkylamine alkoxide, or a primary amine alkoxide. To this mixture, an anionic or neutral surface active agent is added, such as an eth- oxylated alkyl sulphate (AES) having from 12 to 14 carbon atoms in its alkyl chain, or a salt thereof, an alkyl glycoside or a salt thereof, or a synthesis product of alkenyl succinic anhydride and alkyl glycoside, or a salt thereof.

The synthesis product between alkenyl succinic anhydride (ASA) and alkyl glycoside (AG) may be produced according to Scheme 1 from alkenyl succinic anhydride having from 10 to 24 carbon atoms, preferably from 10 to 20 carbon atoms in its alkenyl chain, and from alkyl glycoside having from 1 to 20 carbon atoms, preferably from 8 to 10 carbon atoms in its alkyl chain. In the synthesis, the molar ratio of ASA to AG is 0.1 - 10 : 1, preferably 0.75 — 1.25 : 1. It is carried out at a temperature of 60 - 100 °C, in an inert atmosphere, preferably in a nitrogen atmosphere. The synthesis product obtained may be converted to a corresponding salt by adding a base such as sodium hydoxide to adjust the pH of the mixture to a value from 5 to 10, preferably 7.

Scheme 1

iNfeCH

AG ASA

Rι = Cι-Cιo -alkyl R₂ = Cι₄-C₂o -alkenyl The surface active agent is preferably an ethoxylated alkyl sulphate, or a sodium salt thereof, or alkyl glycoside or a sodium salt thereof being added in an amount of 0.1 - 7 %, by weight, preferably 2 - 3 %, by weight, relative to the dry weight of the fibers, or a sodium salt of the synthesis product of alkenyl succinic anhydride and alkyl glycoside, being added in an amount of 1 - 30 %, by weight, preferably 15 - 25 %, by weight, relative to the dry weight of the fibers, or a mixture of the above substances.

Moreover, an acid such as hydrochloric acid or acetic acid may be added to the mix- ture to adjust the pH thereof below 6. Water may be added to disperse the fibers at a consistency suitable for the production of paper.

Alternatively, the constituents of the composition according to the invention may be added individually to the fiber suspension without mixing them first together.

In the production process of paper or nonwoven fabric, the composition of the invention or the constituents thereof are added to the fiber suspension at one or several suitable points of the process. The foaming of the mixture is preferably carried out by means of high shear in a suitable manner by using known foaming apparatuses wherein gas inert to the compounds present, such as nitrogen or air is fed into the mixture. In this way, the strength of paper or nonwoven fabric may be improved in production methods based on web formation using foam.

The advantages of the composition of the invention include superior foam forming ability and stability of the foam. It clearly improves the paper strength even at low levels of the surface active agent, making the method economical also for so-called ordinary paper grades. That is, the use of the composition is not limited only to soft tissues. The invention is now illustrated in more detail by means of some preferable embodiments described in the following examples, without intending to limit the invention thereto.

Example 1

The semiester (SI) between an alkyl glycoside and an alkenyl succinic acid is produced from alkenyl succinic acid and alkyl glycoside, the molar ratio of the starting compounds being 1:1 in the synthesis. To the alkyl glycoside (aqueous solution 60 %, by weight 66.66 g, or 0.13 moles), alkenyl succinic acid (30.10 g, or 0.13 moles) is quickly added at the temperature of 80 °C while mixing at 200 rpm. The reaction mixture is allowed to react under nitrogen atmosphere, at the temperature of 80 - 85 °C for four hours, while mixing at the speed of 200 rpm. The mixture is allowed to cool to room temperature. The synthesis product SI weighs 92.44 g, the water content thereof is 24.4 %, by weight, Ri being a C₈-Cιo -mixture, R being a C₁₆-C₁₈ -mixture.

Then, the synthesis product SI is converted to its sodium salt. To the synthesis prod- uct SI (aqueous 75.8 %, by weight, solution, 5.0 g, or 9.92 mmoles), an equimolar amount of sodium hydroxide (1.0 M solution, 9.29 ml, or 9.28 mmoles) is added while agitating the mixture gently with a glass rod. The weight of the resulting sodium salt of the synthesis product SI is 14.3 g, the water content thereof being 63.4 %, by weight. Examples 2 - 8

Aqueous solutions having a different composition were prepared from urea- formaldehyde resin, sodium salt of an ethoxylated alkyl sulphate (AES), or the syn- thesis product SI, and polyacryl amide copolymer (PAM). The foaming and strengthening performances of these compositions were determined. Table 1 shows the results obtained. Foaming was carried out with a rod mixer in a 3000 ml beaker filled with a measured amount (250 ml) of the aqueous solution. Foaming performance means the volume of the foam immediately after foaming, the mixing time being 1 minute. Air content means the relative volume of air in the foam compared to the volume of the foamed solution. Strengthening performance and adhesion were tested with the glass plate method. In this method, a glass plate is wetted with the particular solution, a moist cellulose sheet is placed thereon and pressed into intimate contact with the glass plate. The plate is freely dried in an oven for about 20 hours at 80 °C. Hydrogen bonds forming between the moist sheet and the glass plate are influenced by chemicals either strenghtening or weakening them. The influence was tested with fingers by pulling the sheet carefully off the glass plate after drying. The concentrations are percentages by weight relative to the total weight of the solution. No fibers are included, but the concentration thereof is supposed to be 1 % by weight. Based on this, the metering of the chemicals was calculated relative to 1 kg of water.

Table 1

Foaming and strengthening performances of the compound in different compositions

In Examples 2 to 5, the surface active agent is the sodium salt of an ethoxylated alkyl sulphate.

In Examples 6 to 8, the surface active agent is the sodium salt of the synthesis product S 1.

Examples 9 - 18

Aqueous solutions having a different composition were prepared from urea- formaldehyde resin, sodium salt of an ethoxylated alkyl sulphate, or the synthesis product SI, and polyacryl amide copolymer (PAM). The strengthening performance of these compositions were determined. Table 2 shows the results obtained. The strengthening performance was tested with a method wherein sheets having the grammage of 60 g/m² were made by adapting the standard SCAN-C 26:2. On these sheets, about 5 g of the solution to be tested was sprayed, and then, two sheets were placed against each other, pressed, dried and aerated according to the standard. Thereafter, the bonding of the sheet pair was measured by adapting the standard TAPPI T 833 pm-94, and using the Scott Bond Tester -apparatus. In this apparatus, a clip fixed to the sheet with a double-sided adhesive tape is knocked off with a pendulum, thus cracking the sheet. The energy needed to split the paper in the plane direction may be read from the apparatus. In this way, the influence of the chemicals on the bonding between the fibers may to some extent be determined quantitatively.

Table 2

Strengthening performance of different compositions as measured with Scott Bond Tester -apparatus

In Example 9, no chemicals are added between the sheets

In Examples 10 - 16, the surface active agent was a sodium salt of an ethoxylated alkyl sulphate

In Examples 17 - 18, the surface active agent was the sodium salt of the synthesis product S 1. * Concentrations are in % by weight relative to the dry weight of the fibers. Examples 19 - 23

Adapting the standard SCAN-C 26:2, sheets having the grammage of 60 g/m² were made from 1 %, by weight, fiber suspension. To this suspension, urea- formaldehyde resin, sodium salt of an ethoxylated alkyl sulphate, or the synthesis product SI, and polyacryl amide copolymer were added to obtain different compositions. The strengthening influence of these compositions on the tensile strength of the sheet made from a solution was measured with the Scott Bond Tester -apparatus. Tensile strength was measured by adapting the standard SCAN-P 38:80. The results are shown in Table 3.

Table 3

Strengthening performance of the compositions in solution sheets

In Example 19, no chemicals are used for producing the sheets In Examples 20 - 22, the surface active agent was a sodium salt of an ethoxylated alkyl sulphate

In Example 23, the surface active agent was the sodium salt of the synthesis product SI.

* Concentrations are calculated relative to the total weight of the pulp; if it is desired to express these values relative to the dry weight of the fibers, the numerical data should be multiplied by 100. Examples 4

Sheets were made from 1 %, by weight, suspension. The suspension was first foamed in a foaming apparatus, at 3000 rpm for four minutes. Thereafter, sheets with the grammage of 60 g/m were made from the foam with a hand mould according to the standard SCAN-C 26:2. Scott Bond and tensile strengths were determined with the sheets. The results are shown in Table 4.

Table 4

Strengthening performances of the composition in foam sheets

In Examples 24 - 26, the surface active agent was the sodium salt of an ethoxylated alkyl sulphate.

In Example 27, the surface active agent was the sodium salt of the synthesis product

SI.

* Concentrations are calculated relative to the total weight of the pulp; if it is desired to express these values relative to the dry weight of the fibers, the numerical data should be multiplied by 100.

Claims

1. Foamable composition influencing the strength of a fibrous material, characterized in that the composition comprises a resin, or a mixture of resins that may be cured thermally or with an acid, a surface active agent, water, and optionally a cationic acryl amide copolymer, the surface active agent being an ethoxylated alkyl sulphate, or a salt thereof, alkyl glycoside or a salt thereof, a synthesis product of alkenyl succinic anhydride and alkyl glycoside, or a salt thereof, or a mixture of the said substances.

2. Composition according to Claim 1, characterized in that the resins that may be cured thermally or with an acid is a urea-formaldehyde or a melamin- formaldehyde resin, or a mixture thereof.

3. Composition according to Claim 1 or 2, characterized in that the resin is urea- formaldehyde resin, having a dry matter content from 30 to 60 %, by weight, preferably from 35 to 50 %, by weight, wherein the molar ratio of formaldehyde to urea is from 1.8 to 3.8 : 1.

4. Composition according to any of Claims 1 - 3, characterized in that the composition comprises 0.1 - 7 %, by weight, of the surface active agent relative to the dry weight of the fibers in the case the surface active agent is an ethoxylated alkyl sulphate having 12 - 14 carbon atoms in its alkyl chain, the sodium salt thereof, an alkyl glycoside,. or the sodium salt thereof, or the composition comprises 1 - 30 %, by weight, of the surface active agent relative to the dry weight of the fibers in the case the surface active agent is a synthesis product of alkenyl succinic anhydride and alkyl glycoside.

5. Composition according to any of Claims 1 - 4, characterized in that the composition comprises the resin that may be cured thermally or with an acid in an amount of 0.5 - 5 % by weight, and the cationic acryl amide copolymer in an amount of 0 - 3 %, by weight, relative to the dry weight of the fibers.

6. Composition according to any of Claims 1 - 5, characterized in that the cationic acryl amide copolymer may be produced from monomers comprising acryl amide, or from monomers in copolymeric cationic form, such as quaternary acryl amide alkyl-N-alkylamine, secondary or tertiary acryl amine alkyl-N-alkylamine, or primary acryl amine, esters of acrylic acid, the alcohol moiety thereof being a quaternary n-alkylamine alkoxide, or from a secondary or tertiary n-alkylamine alkoxide, or a primary amine alkoxide.

7. Composition according to any of Claims 1 - 6, characterized in that the ca- tionicity of the cationic acryl amide copolymer is from 20 to 100 %, preferably from 25 to 80 %, the molecular weight thereof being between 10,000 and 300,000, preferably between 50,000 and 300,000.

8. Use of the composition according to any of Claims 1 - 7 in the production proc- ess of paper or nonwoven fabric based on web formation using foam.

9. Method for improving the strength of a fibrous material, characterized in that in the production process of paper or nonwoven fabric based on web formation using foam, the composition according to any of Claims 1 - 7, or the constituents thereof are added to the fiber suspension.