Aqueous dispersions of alkyl ketene dimers and uses thereof

Abstract

The invention relates to an aqueous dispersion of an alkyl ketene dimer. The aqueous dispersion comprises alkyl ketene dimer particles dispersed in an aqueous continuous phase and a stabilizer that is a cationic alpha-(1, 3-glucan) polymer. The aqueous dispersion comprises more (given in% by weight) alkyl ketene dimers than cationic alpha-(1, 3-glucan) polymers.

Description

Technical Field

[0001] The present invention relates to an aqueous dispersion of alkyl ketene dimer according to the preamble of the appended independent claims and its use. Background Art

[0002] Sizing agents are used in the manufacture of paper, cardboard or the like to reduce or prevent the penetration of water, moisture and other liquids (such as printing ink) into the structure of the paper, cardboard or the like. In internal sizing, the sizing agent is added to the furnish, where it interacts with the fibers to enhance the water resistance of the paper or cardboard. In surface sizing, the sizing agent can be added to the surface of a partially or fully dried web of paper, cardboard or the like to seal the web surface and thus reduce the penetration of liquids (especially water) and moisture into the web.

[0003] Alkyl ketene dimer is a sizing agent commonly used in the manufacture of paper, cardboard or the like. Alkyl ketene dimer is typically supplied in the form of an aqueous dispersion prepared by chemical manufacturers and transported to the factory site. The dispersion should have appropriate stability to allow it to be transported from the manufacturing site to the point of use at the factory and also to allow storage at the factory for a certain period of time (if required). Alkyl ketene dispersions are usually stabilized by using starch or synthetic polymers as stabilizers. However, in view of the ongoing demand for increased sustainability, traditional stabilizers are not optimal. Synthetic polymers are typically made from non-renewable sources based on petroleum. On the other hand, starch is obtained from renewable sources, but starch is usually produced from plants that can be used for feeding humans and / or animals. Cultivating plants for starch production occupies valuable farmland that could otherwise be used for food production. Therefore, it would be beneficial to find new stabilizers that are bio-based, renewable and derived from natural sources that cannot be used as food or feed.

[0004] Using starch as a stabilizer in sizing dispersions may pose an increased risk of bacterial growth and deposition problems during the manufacture of paper or cardboard, as starch provides nutrients for the bacteria present in the process.

[0005] In view of the above, there is a need for a new and effective stabilizer that can be used to stabilize aqueous dispersions of alkyl ketene dimer. In the current effort to achieve sustainable development, the stabilizer should be derived from renewable sources and should not be based on petrochemical products. Summary of the Invention

[0006] It is an object of the present invention to minimize or even eliminate the disadvantages present in the prior art.

[0007] The present invention also provides an aqueous dispersion of alkyl ketene dimer having a sustainable stabilizer, which provides good stability to the dispersion and improved sizing performance.

[0008] These objects are achieved by the present invention, which has the features presented in the characterizing part of the independent claims below. Some preferred embodiments of the present invention are presented in the dependent claims. Unless otherwise explicitly stated, the features recited in the dependent claims can be freely combined with each other. In addition, unless otherwise explicitly stated, all features and advantages described in the specification and claims apply to all aspects of the present invention.

[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 stabilizer which is a cationic α-(1,3→glucan) polymer, wherein the aqueous dispersion comprises more (given in wt%) alkyl ketene dimer than the cationic α-(1,3→glucan) polymer.

[0010] A typical use of the aqueous dispersion according to the present invention is for manufacturing a cellulose fiber web such as paper, cardboard, tissue or the like.

[0011] A typical method for manufacturing a cellulose fiber web (such as paper, cardboard, tissue or the like) comprises:

[0012] - forming a fiber furnish comprising cellulose fibers;

[0013] - forming the fiber furnish into a cellulose fiber web; and

[0014] - drying the cellulose fiber web;

[0015] wherein the aqueous dispersion according to the present invention is added to the fiber furnish as an internal sizing agent and / or added to the cellulose fiber web as a surface sizing agent.

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

[0017] It has now unexpectedly been found that cationic α-(1,3→glucan) polymers can be used as stabilizers for aqueous dispersions of alkyl ketene dimers, whereby stable dispersions with good stability can be obtained, while providing unexpectedly improved sizing efficiency compared to conventional alkyl ketene dispersions. When used as stabilizers, cationic α-(1,3→glucan) polymers can increase or maintain the content of dispersion components derived from renewable sources, while minimizing the amount of components that can be used for food / feed production. Dispersions stabilized with cationic α-(1,3→glucan) polymers show significantly improved sizing efficiency, which offers the possibility of reducing the amount of sizing used and thus reducing chemical consumption and costs in the production of paper, cardboard or the like.

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

[0019] The aqueous dispersion of the present invention contains more (given in weight %) alkyl ketene dimer than cationic α-(1,3→glucan) polymer as the 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 essentially acts as a stabilizer for the alkyl ketene dimer particles dispersed in the aqueous continuous phase. According to one embodiment of the present invention, the aqueous dispersion may contain α-(1,3→glucan) polymer and alkyl ketene dimer in a weight ratio of 1:2 to 1:8, preferably 1:3 to 1:7, more preferably 1:4 to 1:6 (polymer:alkyl ketene dimer). Unexpectedly, a relatively small amount of cationic α-(1,3→glucan) polymer in proportion to the alkyl ketene dimer can provide improved stability to the aqueous dispersion.

[0020] According to one embodiment, the aqueous dispersion may contain 0.1 - 20 wt%, preferably 1 - 10 wt%, more preferably 1 - 5 wt%, sometimes even 1.5 - 5 wt% of cationic α-(1,3→glucan) polymer calculated based on the total weight of the aqueous dispersion. Advantageously, good stabilization effects can be obtained even when using a relatively small amount of cationic α-(1,3→glucan) polymer. In this way, the total amount of stabilizer can be reduced, and the desired dispersion stability can still be obtained without compromising other desired properties.

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

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

[0023] The α-(1,3→glucan) polymer used in the present invention is cationic, i.e., the polymer comprises cationic substituents. This means that the α-(1,3→glucan) polymer comprises cationic substituents that replace (substitute for) the hydroxyl groups of the polysaccharide backbone of the polymer. The α-(1,3→glucan) polymer can comprise at least one cationic substituent selected from substituted ammonium groups. The cationic substituent can be a substituted ammonium group, preferably a quaternary ammonium group, more preferably a trialkylammonium group. The ammonium group can be substituted by at least one methyl, hydroxymethyl, hydroxyethyl, and / or hydroxypropyl group. For example, the alkyl group in the trialkylammonium group can be one of the following groups: methyl, hydroxymethyl, hydroxyethyl, or hydroxypropyl, or any combination thereof. The substituted ammonium group can be, for example, a trimethylammonium group. The alkyl groups in the substituted ammonium group can be the same or different from each other. The cationic substituent improves the water solubility of the α-(1,3→glucan) polymer, and in some embodiments, the α-(1,3→glucan) polymer is completely water-soluble. According to a preferred embodiment of the present invention, the α-(1,3→glucan) polymer can have a cationic charge density value in the 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 present invention, the α-(1,3→glucan) polymer used as a stabilizer can have a degree of substitution in the range of 0.05-3, preferably 0.05-2.0, more preferably 0.1-1.5, and even more preferably 0.1-1. The degree of substitution refers to the average number of substituted hydroxyl groups in each D-glucose unit in the polysaccharide backbone of the α-(1,3→glucan) polymer. Since there are 3 hydroxyl groups in each D-glucose unit, the degree of substitution can be not higher than 3.

[0025] According to one embodiment of the present invention, the α-(1,3→glucan) polymer may have a degree of polymerization in the range of 55 - 10,000, preferably 55 - 5,000, more preferably 100 - 1,000.

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

[0027] The aqueous dispersion may contain 1 - 25% by weight, preferably 5 - 20% by weight, more preferably 8 - 18% by weight of alkyl ketene dimer based on the total weight of the aqueous dispersion. The alkyl ketene dimer particles dispersed in the aqueous continuous phase of the dispersion may have a particle size D95 in the range of 1 - 100 μm, preferably 10 - 100 μm, more preferably 20 - 95 μm. The particle size D95 represents that 95% of the total particles are smaller than a given value. When used as a stabilizer, the cationic α-(1,3→glucan) polymer can provide a stable dispersion with a high alkyl ketene dimer content.

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

[0029] The aqueous dispersion may further contain a surfactant, a biocide, and / or alum.

[0030] According to one embodiment, the aqueous dispersion may contain one or more surfactants, which may be selected from the group consisting of: condensation products of phenol sulfonic acid and formaldehyde; condensation products of naphthalene sulfonic acid and formaldehyde; and condensation products of naphthalene sulfonic acid, phenol, formaldehyde, and urea, wherein the sulfonic acid groups of the condensation products may be protonated or deprotonated. The aqueous dispersion may contain 0.01 - 1% by weight, preferably 0.05 - 0.7% by weight, more preferably 0.1 - 0.5% by weight of the surfactant based on the total weight of the dispersion. In the case where the dispersion contains two or more surfactants, the given value represents the total amount of all surfactants present.

[0031] The aqueous dispersion may further comprise one or more biocides. The biocide may be selected from 5-chloro-2-methyl-2H-isothiazol-3-one, 2-methyl-2-H-isothiazol-3-one, 2-bromo-2-nitropropane-1,3-diol, or any mixture thereof. According to one embodiment of the present invention, the aqueous dispersion may comprise 0.001 - 0.015 wt%, preferably 0.001 - 0.01 wt% of the biocide, based on the total weight of the aqueous dispersion. In the case where the aqueous dispersion comprises two or more biocides, the given value represents 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 an amount of 0.1 - 5 wt%, preferably 0.2 - 4 wt%, more preferably 0.5 - 3 wt%, based on the total weight of the aqueous dispersion. However, the presence of alum or other aluminum compounds is not mandatory, and according to one embodiment, the aqueous dispersion is free of aluminum compounds such as alum.

[0033] According to one embodiment, the aqueous dispersion of alkyl ketene dimer is free of starch and / or synthetic polymers other than alkyl ketene dimer. The aqueous continuous phase of the dispersion preferably contains no other solvents except water, i.e., the solvent forming the continuous phase of the dispersion is preferably only water. Preferably, the aqueous dispersion does not contain organic solvents, and the continuous phase of the dispersion consists of water.

[0034] The aqueous dispersion of alkyl ketene dimer may have a pH value of ≤5, preferably ≤4. The pH may, for example, be in the range of 2 to 5, preferably in the range of 3 to 4. The pH of the dispersion can be adjusted to the desired level by using conventional accepted methods, such as by adding a suitable strong acid, such as sulfuric acid and / or a buffer.

[0035] The aqueous dispersion can be obtained by homogenizing molten alkyl ketene dimer wax in an aqueous continuous phase in the presence of a stabilizer. Using a cationic α-(1,3→glucan) polymer as a stabilizer allows the use of conventional methods to manufacture the dispersion of alkyl ketene dimer, which is advantageous for large-scale production.

[0036] An aqueous dispersion of alkyl ketene dimer can have a stability of at least one week, preferably at least two weeks, more preferably at least three weeks, which is measured by the change in the viscosity of the dispersion over time. The viscosity of the aqueous dispersion preferably changes by less than 10%, more preferably less than 7.5%, within a defined time period. This means that the viscosity of the dispersion is measured directly after the preparation of the dispersion to obtain a first viscosity value. After allowing the dispersion to stand for a defined time period (e.g., 1 week, 2 weeks, or 3 weeks), the viscosity of the dispersion is measured again to obtain a second viscosity value. 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%, the dispersion is considered stable.

[0037] The aqueous dispersion of the present invention can be used to manufacture cellulose fiber webs, such as paper, cardboard, paper towels, or the like. In particular, the aqueous dispersion can be used as an internal sizing agent or for surface sizing of cellulose fiber webs (such as paper or cardboard). When used as an internal sizing agent for manufacturing paper, cardboard, or the like, the aqueous dispersion can be added to a fiber suspension containing cellulose fibers in an amount such that the addition amount of alkyl ketene dimer is in the range of 0.25 - 5 kg / metric ton or 1 - 5 kg / metric ton (in the form of active agent / the produced fiber web, given as dry weight). Description of the Drawings

[0038] Figure 1 Shows the sizing performance of dispersion A (which is an alkyl ketene dimer dispersion stabilized with an α-(1,3→glucan) polymer), dispersion B (which is an alkyl ketene dimer dispersion stabilized with starch), and dispersion C (which is an alkyl ketene dimer dispersion stabilized with polyamide - amine - epichlorohydrin (PAE)). Detailed Description

[0039] Experiments

[0040] Some embodiments of the present invention are described in the following non - limiting examples.

[0041] Example 1: Preparation of a Stable Alkyl Ketene Dispersion

[0042] A cationic α-(1,3→glucan) polymer was used as the stabilizer for dispersion A (see Table 1). The 2 wt% α-(1,3→glucan) polymer solution had a pH of 6.3, a viscosity of 23 mPas, and a charge density of +14.2 μeq / g.

[0043] Dispersion A was prepared as follows. A surfactant was added to 40 g of water and the pH was adjusted to 12.5 with NaOH. The desired amount of α-(1,3→glucan) polymer was added to the water and mixed with a magnetic stirrer for 15 minutes. Additional NaOH was added dropwise until the solution became clear and the α-(1,3→glucan) polymer was properly dissolved. The resulting solution was mixed for 3.5 hours. Then the pH of the solution was adjusted to 4.5 with sulfuric acid at room temperature (about 23 °C). The solution was heated to a temperature of 90 °C and molten alkyl ketene dimer wax was added, followed by using a T50 homogenizer for the pre-dispersion step and homogenization in a laboratory homogenizer. The resulting dispersion was cooled to a temperature of about 25 °C - 27 °C and a bactericide and alum were added to the dispersion. The pH of the dispersion was adjusted to 3.3 - 3.8.

[0044] The composition of the alkyl ketene dimer dispersion is given in Table 1. Dispersion B is a commercially available alkyl ketene dimer dispersion stabilized with starch, and Dispersion C is a commercially available alkyl ketene dimer dispersion stabilized with polyamide-amine-epichlorohydrin (PAE). Dispersion B and C were used as references.

[0045] Table 1 Composition of the alkyl ketene dimer dispersion

[0046]

[0047] Example 2 Evaluation of the sizing effect of the stabilized alkyl ketene dimer dispersion

[0048] The alkyl ketene dispersion of Example 1 was used to manufacture handsheets in the laboratory.

[0049] Handsheets of about 98 g / m 2 were manufactured on the forming section of a KCL type paper machine. The furnish used was a 50:50 blend of pine pulp and birch pulp. The furnish pH was 7.2. Cationic cooked starch (5 kg / ton dry weight) and cationic polyacrylamide (0.1 kg / ton dry weight) were added as retention aids. The alkyl ketene dispersion was dosed in amounts of 0.25 kg / ton dry weight, 0.75 kg / ton dry weight, and 1.2 kg / ton dry weight.

[0050] The handsheets were dried in an oven and cured after drying at 105 °C. The Cobb60 value was determined according to Standard ISO535, T441.

[0051] The results are shown in Figure 1 it. Figure 1The sizing performance of the following dispersions is shown: Dispersion A (solid circles, broken line) as an alkyl ketene dimer dispersion stabilized with an α-(1,3→glucan) polymer, Dispersion B (solid diamonds, dot line) as a commercially available alkyl ketene dimer dispersion stabilized with starch, and Dispersion C (hollow circles, solid line) as a commercially available alkyl ketene dimer dispersion stabilized with polyamide-amine-epichlorohydrin.

[0052] It can be seen that, compared with the commercially available dispersions B and C in which starch or a synthetic polymer is used as a stabilizer, the alkyl ketene dimer dispersion A stabilized with an α-(1,3→glucan) polymer provides better sizing performance. This improvement is significant: at the lowest dose of Dispersion A stabilized with α-(1,3→glucan), the Cobb60 value is increased by 68% compared with Dispersion B stabilized with starch, and is increased by 74% compared with Dispersion C stabilized with a synthetic polymer. This enables the same sizing effect to be obtained with less sizing amount, or alternatively, a better sizing effect to be obtained with the same sizing amount.

[0053] Even though the present invention is described with reference to the presently most practical and preferred embodiments, it should be understood that the present invention is not limited to the above embodiments, but the present invention also aims to cover different modifications and equivalent technical solutions within the scope of the appended claims.

Claims

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

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

3. The aqueous dispersion according to claim 1 or 2, characterized in that, Said aqueous dispersion comprises 1 - 25% by weight, preferably 5 - 20% by weight, more preferably 8 - 18% by weight of alkyl ketene dimer, calculated on the total weight of the aqueous dispersion.

4. The aqueous dispersion according to claim 1, 2 or 3, characterized in that, Said aqueous dispersion comprises an α-(1,3→glucan) polymer and alkyl ketene dimer in a weight ratio of 1:2 to 1:8, preferably 1:3 to 1:7, more preferably 1:4 to 1:6 (polymer:alkyl ketene dimer).

5. The aqueous dispersion according to any one of the preceding claims 1-4, characterized in that, The α-(1,3→glucan) polymer has a degree of substitution in the 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 any one of the preceding claims 1-5, characterized in that, Said α-(1,3→glucan) polymer comprises a cationic substituent selected from substituted ammonium groups.

7. The aqueous dispersion according to claim 6, characterized in that, Said ammonium group is substituted by at least one methyl, hydroxymethyl, hydroxyethyl and / or hydroxypropyl group.

8. The aqueous dispersion according to any one of the preceding claims 1-7, characterized in that, The α-(1,3→glucan) polymer has a charge density value in the 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 any one of the preceding claims 1-8, characterized in that, The α-(1,3→glucan) polymer has a degree of polymerization in the range of 55 - 10000, preferably 55 - 5000, more preferably 100 - 1000.

10. The aqueous dispersion according to any one of the preceding claims 1-9, characterized in that, Said alkyl ketene dimer is a C14 - C22 alkyl ketene dimer, preferably a C16 - C18 alkyl ketene dimer.

11. The aqueous dispersion according to any one of the preceding claims 1-10, characterized in that, Said aqueous dispersion further comprises a surfactant, a biocide and / or alum.

12. The aqueous dispersion according to claim 11, wherein Said aqueous dispersion comprises, calculated on the total weight of the aqueous dispersion: - 0.01 - 1% by weight, preferably 0.05 - 0.7% by weight, more preferably 0.1 - 0.5% by weight of surfactant, - 0.001 - 0.015% by weight, preferably 0.001 - 0.01% by weight of biocide, and / or - 0.1 - 5% by weight, preferably 0.2 - 4% by weight, more preferably 0.5 - 3% by weight of alum.

13. The aqueous dispersion according to any one of the preceding claims 1-12, characterized in that, The alkyl ketene dimer particles have a particle size D95 in the range of 10 - 100 μm, preferably 20 - 95 μm.

14. The aqueous dispersion according to any one of the preceding claims 1 to 13, characterized in that, Said aqueous dispersion has a pH value in the range of 3 - 4.

15. The aqueous dispersion according to any one of the preceding claims 1-14, characterized in that, Said aqueous dispersion is obtained by homogenizing said alkyl ketene dimer in an aqueous phase in the presence of said stabilizer.

16. The aqueous dispersion according to any one of the preceding claims 1-15, characterized in that, Said aqueous dispersion has a stability of at least one week as measured by the change in the dispersion viscosity.

17. Use of a cationic α-(1,3→glucan) polymer as a stabilizer for an aqueous dispersion of an alkyl ketene dimer.

18. The use according to claim 17, wherein, The cationic α-(1,3→glucan) polymer has a degree of substitution in the range of 0.05 - 3, preferably 0.05 - 2.0, more preferably 0.1 - 1.5, even more preferably 0.1 - 1, and / or a cationic charge density in the range of 0.1 - 50 μeq / g, preferably 0.5 - 30 μeq / g, more preferably 1 - 10 μeq / g.

19. Use of the aqueous dispersion according to any one of claims 1 - 16 for the manufacture of a cellulose fiber web such as paper, cardboard, tissue paper or the like, said aqueous dispersion being preferably used as an internal sizing agent or for surface sizing.

20. A method for manufacturing a cellulose fiber web such as paper, cardboard, tissue paper or the like, comprising: - forming a fiber furnish comprising cellulose fibers; - shaping the fiber furnish into a cellulose fiber web; and - drying the cellulose fiber web; wherein the aqueous dispersion according to any one of claims 1 - 16 is added to the fiber furnish as an internal sizing agent and / or to the cellulose fiber web as a surface sizing agent.

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