Aqueous dispersion of alkyl ketene dimer and its use

Abstract

The invention relates to an aqueous dispersion of alkyl ketene dimer. The aqueous dispersion comprises alkyl ketene dimer particles dispersed in an aqueous continuous phase and a stabilizing agent which is a cationic α-(1,3→glucan) polymer. The aqueous dispersion comprises more alkyl ketene dimer than cationic α-(1,3→glucan) polymer, given as weight-%.

Description

[0001] The present invention relates to an aqueous dispersion of alkyl ketene dimer and its use according to the preambles of enclosed independent claims.

[0002] Sizing agents are used in manufacture of paper, board or the like for decreasing or preventing of the penetration of water, moisture and other liquids, such as printing inks, into the structure of the paper, board or the like. In internal sizing, the sizing agent is added to the fibre furnish, where it interacts with the fibres in order to increase the water repellency of the paper or board. In surface sizing, the sizing agent can be added on the surface of the partially or wholly dried web of paper, board or the like, for sealing off the web surface and thus achieving a decrease in penetration of liquids, especially water, and moisture into the web.

[0003] Alkyl ketene dimer is a commonly used sizing agent in the manufacture of paper, board or the like. Alkyl ketene dimer is typically supplied in form of an aqueous dispersion, prepared by a chemical manufacturer and transported to the mill location. The dispersion should have appropriate stability to allow its transport from the manufacturing site to the location of use at the mill and also to allow a certain storage time at the mill, if needed. The alkyl ketene dispersions are usually stabilized by using starch or synthetic polymers as stabilizing agents. However, the traditional stabilizing agents are not optimal in view of the on-going need for increased sustainability. Synthetic polymers are usually manufactured from petroleum-based non-renewable sources. Starch, on the other hand, is obtained from renewable sources, but it is usually produced from plants that could be used for feeding humans and / or animals. Growing plants for starch production use valuable farming land that could be used for food production instead. Therefore, it would be beneficial to find new stabilizing agents, which would be bio-based, renewable and originate from natural sources that primarily cannot be used as food or feed.

[0004] Use of starch as a stabilizing agent in sizing dispersions may cause an increased risk for bacterial growth and deposit problems in the manufacturing process of paper or board, as the starch provides nutrition for bacteria existing in the process.

[0005] In view of the above, there is a need for new effective stabilizing agents that can be used for stabilizing aqueous dispersions of alkyl ketene dimer. Under the present strive for sustainability the stabilizing agent should originate from renewable sources and should not be based on petrochemical products.

[0006] An object of the present invention is to minimise or even eliminate the disadvantages existing in the prior art.

[0007] An object of the present invention is also to provide an aqueous dispersion of alkyl ketene dimer with a sustainable stabilizing agent, which provides the dispersion with good stability as well as improved performance in sizing.

[0008] These objects are attained with the invention having the characteristics presented below in the characterising parts of the independent claims. Some preferred embodiments of the invention are presented in the dependent claims. The features recited in the dependent claims are freely combinable with each other unless otherwise explicitly stated. Furthermore, all features and advantages described in the specification and the claims apply for all aspects of the invention, unless otherwise explicitly stated.

[0009] A typical aqueous dispersion of alkyl ketene dimer according to the present invention comprises alkyl ketene dimer particles dispersed in an aqueous continuous phase and a stabilizing agent which is a cationic α-(1,3→glucan) polymer, wherein the aqueous dispersion comprises more alkyl ketene dimer than cationic α-(1,3→glucan) polymer, given as weight-%.

[0010] A typical use according to the present invention of an aqueous dispersion according to the invention is for manufacture of a cellulosic fibrous web, such as paper, board, tissue or the like.

[0011] A typical method for manufacture of a cellulosic fibrous web, such as paper, board, tissue or the like, comprising

[0012] forming a fibre stock comprising cellulosic fibres,

[0013] forming the fibre stock into a cellulosic fibrous web, and

[0014] drying the cellulosic fibrous web,

[0015] wherein an aqueous dispersion according to the invention is added to the fibre stock as an internal sizing agent and / or on the cellulosic fibrous web as a surface sizing agent.

[0016] The present invention also encompasses the use of cationic α-(1,3→glucan) polymer, as defined and described in this text, as a stabilizing agent for an aqueous dispersion of alkyl ketene dimer.

[0017] Now it has been surprisingly found out that a cationic α-(1,3→glucan) polymer can be used as a stabilizing agent for an aqueous dispersion of alkyl ketene dimer, whereby it is possible to obtain stable dispersion which has a good stability while providing an unexpectedly improved sizing efficiency in comparison to conventional alkyl ketene dispersions. The cationic α-(1,3→glucan) polymer, when used as a stabilizing agent, allows the possibility to increase or maintain the content of the dispersion components originating from renewable sources while minimising the amount of components that could be used for food / feed production. The dispersions stabilized with cationic α-(1,3→glucan) polymer show significantly improved sizing efficiency, which provides a possibility to reduce the amount of used sizing, thus reducing the chemical consumption and costs in the production of paper, board or the like.

[0018] The cationic α-(1,3→glucan) polymer is present in the aqueous continuous phase, i.e. aqueous liquid phase, of the dispersion. It is assumed, without being bound by a theory, that the cationic α-(1,3→glucan) polymer interacts with the surface of the alkyl ketene dimer particles and prevents the agglomeration of the particles.

[0019] The aqueous dispersion of the present invention comprises more alkyl ketene dimer than cationic α-(1,3→glucan) polymer, given as weight-%, as active chemical. This means that the alkyl ketene dimer is the main component of the aqueous dispersion, and the cationic α-(1,3→glucan) polymer functions essentially as a stabilizing agent for the alkyl ketene dimer particles dispersed in the aqueous continuous phase. According to one embodiment of the present invention the aqueous dispersion may comprise α-(1,3→glucan) polymer and alkyl ketene dimer in a weight ratio from 1:2 to 1:8, preferably from 1:3 to 1:7, more preferably from 1:4 to 1:6 (polymer: alkyl ketene dimer). It is unexpected that relatively small amounts of cationic α-(1,3→glucan) polymer, in proportion to the alkyl ketene dimer, can provide improved stability for the aqueous dispersion.

[0020] According to one embodiment, the aqueous dispersion may comprise 0.1-20 weight-%, preferably 1-10 weight-%, more preferably 1-5 weight-%, sometimes even 1.5-5 weight-%, of the cationic α-(1,3→glucan) polymer, calculated from total weight of the aqueous dispersion. It is advantageous that good stabilisation effect may be obtained even with relatively low amount of cationic α-(1,3→glucan) polymer. In this manner it may be possible to reduce the total amount of stabilizing agent, and still obtain desired dispersion stability without compromising other desired properties.

[0021] In the present context the “α-(1,3→glucan) polymer” denotes a polymer having a polysaccharide backbone which comprises D-glucose units linked together by glycosidic linkages. At least 70%, preferably at least 80%, more preferably at least 90% or 95%, sometimes even of 99% or 100%, of the glycosidic linkages are α-1,3-linkages. This means that in the polysaccharide backbone the α-D-glucose units are connected to each other through carbons 1 and 3 on adjacent α-D-glucose rings. The form of glycosidic linkages can be determined by a person skilled in the art by using methods known as such, for example 1HNMR.

[0022] The polysaccharide backbone of the used α-(1,3→glucan) polymer may be linear, i.e. it may be unbranched.

[0023] The α-(1,3→glucan) polymer used in the present invention is cationic, i.e. it comprises cationic substitution groups. This means that the α-(1,3→glucan) polymer comprises cationic substitution groups substituted to (replacing) the hydroxyl groups of the polysaccharide backbone of the polymer. The α-(1,3→glucan) polymer may comprise at least one cationic substitution group selected from substituted ammonium groups. The cationic substitution group may be a substituted ammonium group, preferably a quaternary ammonium group, more preferably a trialkyl ammonium group. The ammonium group may be substituted with at least one methyl group, hydroxymethyl group, hydroxyethyl group and / or hydroxypropyl group. For example, alkyl group in the trialkyl ammonium group may be one of the following: a methyl group, a hydroxymethyl group, a hydroxyethyl group or a hydroxypropyl group or any combination thereof. The substituted ammonium group may be, for example, trimethylammonium group. The alkyl groups in the substituted ammonium group may be same or different from each other. Cationic substitution groups improve the water solubility of the α-(1,3→glucan) polymer, and in some embodiments the α-(1,3→glucan) polymer is fully water-soluble. According to one preferable embodiment of the invention the α-(1,3→glucan) polymer may have a cationic charge density value in a range of 0.1-50 μeq / g, preferably 0.5-30 μeq / g, more preferably 1-10 μeq / g.

[0024] According to one embodiment of the invention the α-(1,3→glucan) polymer, which is used as the stabilizing agent, may have a substitution degree in a range of 0.05-3, preferably 0.05-2.0, more preferably 0.1-1.5, even more preferably 0.1-1. The substitution degree refers to the average number of hydroxyl groups substituted in each D-glucose unit in the polysaccharide backbone of α-(1,3→glucan) polymer. Since there are three hydroxyl groups in each D-glucose unit, the substitution degree can be no higher than 3.

[0025] According to one embodiment of the invention the α-(1,3→glucan) polymer may have a degree of polymerization in a range of 55-10 000, preferably 55-5000, more preferably 100-1000.

[0026] Preferably the α-(1,3→glucan) polymer is non-modified except for the cationization. For example, the α-(1,3→glucan) polymer is preferably non-oxidized, i.e. the α-(1,3→glucan) polymer has not been subjected to a contact with an oxidizing agent. In this manner the size, e.g. molecular weight, of the α-(1,3→glucan) polymer is maintained.

[0027] The aqueous dispersion may comprise 1-25 weight-%, preferably 5-20 weight-%, more preferably 8-18 weight-%, of alkyl ketene dimer, calculated from total weight of the aqueous dispersion. The alkyl ketene dimer particles, which are dispersed in the aqueous continuous phase of the dispersion, may have a particle size D95 in a range of 1-100 μm, preferably 10-100 μm, more preferably 20-95 μm. Particle size D95 indicates that 95% of the total particles are smaller than the given value. The cationic α-(1,3→glucan) polymer, when used as stabilizing agent, is able to provide stable dispersions with high alkyl ketene dimer content.

[0028] The alkyl ketene dimer may be C14-C22 alkyl ketene dimer, preferably C16-C18 alkyl ketene dimer, or their mixture.

[0029] The aqueous dispersion may further comprise surfactant(s), biocide(s) and / or alum.

[0030] According to one embodiment, the aqueous dispersion may comprise one or more surfactants, which may be selected from a group comprising condensation products of phenol sulphonic acid and formaldehyde; condensation products of naphthalene sulphonic acid and formaldehyde; and condensation products of naphthalene sulphonic acid, phenol, formaldehyde and urea, wherein sulphonic acid groups of the condensation products may be protonated or deprotonated. The aqueous dispersion may comprise 0.01-1 weight-%, preferably 0.05-0.7 weight-%, more preferably 0.1-0.5 weight-%, of surfactant(s), calculated from the total weight of the dispersion. In case the dispersion comprises two or more surfactants, the given values indicate the total amount of all surfactants present.

[0031] The aqueous dispersion may further comprise one or more biocides. The biocides may be selected from 5-chloro-2-methyl-2H-isothiazolin-3-one, 2-methyl-2-H-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, or any of their mixtures. According to one embodiment of the invention, the aqueous dispersion may comprise 0.001-0.015 weight-%, preferably 0.001-0.01 weight-%, of biocide(s) calculated from the total weight of the aqueous dispersion. In case the aqueous dispersion comprises two or more biocides, the given values indicate the total amount of all biocides present.

[0032] The aqueous dispersion may comprise alum. According to one embodiment the aqueous dispersion may comprise alum in amount of 0.1-5 weight-%, preferably 0.2-4 weight-%, more preferably 0.5-3 weight-%, of alum, calculated from the total weight of the aqueous dispersion. However, the presence of alum or other aluminium compounds is not mandatory, and according to one embodiment, the aqueous dispersion is free of aluminium compounds, such as alum.

[0033] According to one embodiment the aqueous dispersion of alkyl ketene dimer is free of starch and / or of synthetic polymers other than the alkyl ketene dimer. The aqueous continuous phase of the dispersion preferably does not contain other solvents than water, i.e. the solvent forming the continuous phase of the dispersion is preferably solely water. Preferably, the aqueous dispersion is free of organic solvents, and the continuous phase of the dispersion consist of water.

[0034] The aqueous dispersion of alkyl ketene dimer may have a pH value <5, preferably <4. The pH may be, for example, in a range from 2 to 5, preferably from 3 to 4. The pH of the dispersion may be adjusted to desired level by using conventionally accepted methods, e.g. by addition of a suitable strong acid, such as sulphuric acid, and / or buffering agents.

[0035] The aqueous dispersion may be obtained by homogenizing the molten alkyl ketene dimer wax in the aqueous continuous phase in a presence of the stabilizing agent. The use of the cationic α-(1,3→glucan) polymer as stabilizing agent allows the use of conventional methods for manufacturing dispersions of alkyl ketene dimer, which is advantageous in view of large-scale production.

[0036] The aqueous dispersion of alkyl ketene dimer may have a stability of at least one week, preferably at least two weeks, more preferably at least three weeks, measured as a change of dispersion viscosity, as a function of time. The viscosity of the aqueous dispersion preferably changes less than 10%, more preferably less than 7.5%, within the defined time period. This means that the viscosity of the dispersion is measured directly after the preparation of the dispersion and a first viscosity value is obtained. After the dispersion is allowed to stand a defined time period, e.g. 1 week, 2 weeks or 3 weeks, the viscosity of the dispersion is measured anew, and a second viscosity value is obtained. The dispersion is considered stable, when the difference between the first viscosity value and the second viscosity value is less than 10%, preferably less than 7.5%, more preferably less than 5%.

[0037] The aqueous dispersion of the present invention may be used in manufacture of cellulosic fibrous webs, such as paper, board, tissue or the like. Especially, the aqueous dispersion may be used as an internal sizing agent or for surface sizing for a cellulosic fibrous web, such as paper or board. When used as an internal sizing agent for manufacture of paper, board or the like, the aqueous dispersion may be added to a fibre suspension comprising cellulosic fibres in an amount that results alkyl ketene dimer addition in a range of 0.25-5 kg / metric ton or 1-5 kg / metric ton, given as active agent per produced fibrous web, as dry.DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 shows the sizing performance of Dispersion A which is an alkyl ketene dimer dispersion stabilized with α-(1,3→glucan) polymer; Dispersion B, which is a dispersion of alkyl ketene dimer, stabilized with starch; and Dispersion C, which is a dispersion of alkyl ketene dimer, stabilized with polyamidoamine epichlorohydrin (PAE).EXPERIMENTAL

[0039] Some embodiments of the present invention are described in the following non-limiting examples.Example 1: Preparation of Stabilized Alkyl Ketene Dispersion

[0040] Cationic α-(1,3→glucan) polymer was used as stabilizing agent for Dispersion A (see Table 1). 2 weight-% solution of the α-(1,3→glucan) polymer had pH 6.3, viscosity 23 mPas and charge density+14.2 μeq / g.

[0041] Dispersion A was prepared as follows. A surfactant was added to 40 g water and the pH was adjusted to 12.5 with NaOH. A desired amount of α-(1,3→glucan) polymer was added to the water and mixed for 15 minutes with magnetic stirrer. Additional NaOH was added dropwise until the solution was clear and α-(1,3→glucan) polymer properly dissolved. The obtained solution was mixed for 3.5 hours. After that the pH of the solution was adjusted to 4.5 with sulphuric acid at the room temperature (about 23° C.). Solution was heated to a temperature of 90° C. and melted alkyl ketene dimer wax added, followed by pre-dispersing step with Ultra-Turrax® T50 homogenizer and homogenization in a laboratory homogenizer. The obtained dispersion was cooled to a temperature ca 25-27° C., and biocide and alum was added to the dispersion. pH of the dispersion was adjusted to 3.3-3.8.

[0042] The compositions of alkyl ketene dimer dispersion are given in Table 1. Dispersion B was a commercial alkyl ketene dimer dispersion stabilized with starch, and Dispersion C was a commercial alkyl ketene dimer dispersion stabilized with polyamidoamine epichlorohydrin (PAE). Dispersions B and C were used as a reference.TABLE 1Compositions of alkyl ketene dimer dispersionsDispersion BDispersion CDispersion A(reference)(reference)Alkyl ketene dimer1019.215.2[weight-%]Stabilizing agent2.03.849.97[weight-%]Surfactant0.140.440.06[weight-%]Biocide0.020.100.09[weight-%]Alum0.561.742.0[weight-%]Example 2 Evaluation of the Sizing Effect of Stabilized Alkyl Ketene Dimer Dispersions

[0043] Alkyl ketene dispersions of Example 1 were used in manufacture of handsheets in laboratory.

[0044] Handsheets, about 98 g / m2, were made on a KCL type paper machine former. The used furnish was a 50:50 blend of pinewood pulp and birch pulp. Furnish pH was 7.2. Cationic cooked starch, 5 kg / ton dry, and cationic polyacrylamide 0.1 kg / ton dry, were added as retention agents. Alkyl ketene dispersion was dosed in amount of 0.25 kg / ton dry, 0.75 kg / ton dry and 1.2 kg / ton dry.

[0045] Handsheets were dried in a drying cabinet and cured after drying at 105° C. Cobb60 values were determined according to standard ISO 535, T441.

[0046] The results are shown in FIG. 1. FIG. 1 shows the sizing performance of Dispersion A which was an alkyl ketene dimer dispersion stabilized with a-(1,3→glucan) polymer (filled circles, broken line), Dispersion B which was a commercial alkyl ketene dimer dispersion stabilized with starch (filled diamonds, dot line), and Dispersion C which was a commercial alkyl ketene dimer dispersion stabilized with polyamidoamine epichlorohydrin (unfilled circles, solid line).

[0047] It is seen that alkyl ketene dimer dispersion A, stabilized with α-(1,3→glucan) polymer provided better sizing performance compared to commercial dispersions B and C, where starch or synthetic polymer is used as stabilizing agent. The improvement is significant: at the lowest dose of Dispersion A, stabilized with α-(1,3→glucan), the improvement in Cobb60 value was 68% compared to Dispersion B, stabilized with starch, and 74% compared to Dispersion C, stabilized with synthetic polymer. This enables use of less sizing amount for the same sizing effect or alternatively an improved sizing effect with the same sizing amount.

[0048] Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.

Claims

1. An aqueous dispersion of alkyl ketene dimer, the aqueous dispersion comprising alkyl ketene dimer particles dispersed in an aqueous continuous phase and a stabilizing agent which is a cationic α-(1,3→glucan) polymer, wherein the aqueous dispersion comprises more alkyl ketene dimer than cationic α-(1,3→glucan) polymer, given as weight-%.

2. The aqueous dispersion according to claim 1, wherein the aqueous dispersion comprises 0.1-20 weight-%, preferably 1-10 weight-%, more preferably 1-5 weight-%, of the cationic α-(1,3→glucan) polymer, calculated from total weight of the aqueous dispersion.

3. The aqueous dispersion according to claim 1, wherein the aqueous dispersion comprises 1-25 weight-%, preferably 5-20 weight-%, more preferably 8-18 weight-%, of alkyl ketene dimer, calculated from total weight of the aqueous dispersion.

4. The aqueous dispersion according to claim 1, wherein the aqueous dispersion comprises α-(1,3→glucan) polymer and alkyl ketene dimer in a weight ratio from 1:2 to 1:8, preferably from 1:3 to 1:7, more preferably from 1:4 to 1:6 (polymer: alkyl ketene dimer).

5. The aqueous dispersion according to claim 1, wherein α-(1,3→glucan) polymer has a substitution degree in a range of 0.05-3, preferably 0.05-2.0, more preferably 0.1-1.5, even more preferably 0.1-1.

6. The aqueous dispersion according to claim 1, wherein the α-(1,3→glucan) polymer comprises cationic substitution groups selected from substituted ammonium groups.

7. The aqueous dispersion according to claim 6, wherein the ammonium group is substituted with at least one methyl group, hydroxymethyl group, hydroxyethyl group and / or hydroxypropyl group.

8. The aqueous dispersion according to claim 1, wherein α-(1,3→glucan) polymer has a charge density value in a range of 0.1-50 μeq / g, preferably 0.5-30 μeq / g, more preferably 1-10 μeq / g.

9. The aqueous dispersion according to claim 1, wherein α-(1,3→glucan) polymer has a degree of polymerization in a range of 55-10 000, preferably 55-5000, more preferably 100-1000.

10. The aqueous dispersion according to claim 1, wherein the alkyl ketene dimer is C14-C22 alkyl ketene dimer, preferably C16-C18 alkyl ketene dimer.

11. The aqueous dispersion according to claim 1, wherein the aqueous dispersion further comprises surfactant(s), biocide(s) and / or alum.

12. The aqueous dispersion according to claim 11, wherein the aqueous dispersion comprises0.01-1 weight-%, preferably 0.05-0.7 weight-%, more preferably 0.1-0.5 weight-%, of surfactant(s),0.001-0.015 weight-%, preferably 0.001-0.01 weight-%, of biocide(s), and / or0.1-5 weight-%, preferably 0.2-4 weight-%, more preferably 0.5-3 weight-%, of alum,calculated from the total weight of the aqueous dispersion.

13. The aqueous dispersion according to claim 1, wherein alkyl ketene dimer particles have a particle size D95 in a range of 10-100 μm, preferably 20-95 μm.

14. The aqueous dispersion according to claim 1, wherein the aqueous dispersion has a pH value in a range of 3-4.

15. The aqueous dispersion according to claim 1, wherein the aqueous dispersion is obtained by homogenizing the alkyl ketene dimer in the aqueous phase in a presence of the stabilizing agent.

16. The aqueous dispersion according to claim 1, wherein the aqueous dispersion has a stability of at least one week, measured as a change of dispersion viscosity.

17. (canceled)18. (canceled)19. (canceled)20. A method for manufacture of a cellulosic fibrous web, such as paper, board, tissue or the like, comprisingforming a fibre stock comprising cellulosic fibres,forming the fibre stock into a cellulosic fibrous web, anddrying the cellulosic fibrous web,wherein an aqueous dispersion according to claim 1 is added to the fibre stock as an internal sizing agent and / or on the cellulosic fibrous web as a surface sizing agent.

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