Method and apparatus for on-site production of alkyl ketene dimer emulsion, alkyl ketene dimer emulsion, and its use

Abstract

A method for on-site production of an alkenyl ketene dimer (AKD) emulsion, comprising premixing AKD wax and a heated emulsifier solution containing starch and / or a synthetic polymer in a two-stage premixing unit, and then emulsifying the pre-emulsion of AKD in an emulsification unit. The two-stage premixing unit comprises a first low-shear premixing unit for mixing the heated emulsifier solution with the AKD wax to obtain a mixture containing molten AKD wax and an emulsifier, and a second high-shear premixing unit for mixing the mixture containing the molten AKD wax and emulsifier to obtain a pre-emulsion of AKD. The alkenyl ketene dimer emulsion produced by the method comprises AKD and an emulsifier containing starch and / or a synthetic polymer starch, wherein the median particle size distribution of AKD is greater than 0.5 μm, typically in the range of 0.5 to 5 μm.

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for on-site production of an alkyl ketene dimer (AKD) emulsion according to the independent claims described below. The present invention also relates to an AKD emulsion produced by the method according to the present invention and its use.

Background Art

[0002] Emulsions or dispersions of hydrophobic sizing agents are used in the production of paper or paperboard to reduce the rate of liquid penetration into the structure of the paper or paperboard. The most commonly used hydrophobic cellulose-reactive sizing agents in paper or paperboard production are alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA). A polymer is added in the emulsification process of the hydrophobic agent so that the hydrophobic agent is retained by the anionic cellulose fiber material. In most cases, the polymer consists of starch and / or synthetic polymers, which also have a stabilizing effect on the emulsion.

[0003] ASA emulsions are manufactured by a so-called on-site process, that is, in close proximity to where the ASA emulsion is applied at the paper or cardboard manufacturing plant. This is due to the fact that ASA has a tendency to hydrolyze. Therefore, the finished ASA emulsion cannot be stored, especially under unfavorable conditions such as high temperatures. AKD emulsions are more stable than ASA emulsions and can be stored for long periods without losing their sizing effect. Therefore, AKD sizing agents are currently supplied to paper and cardboard manufacturers as ready-made sizing agent emulsions, meaning that AKD emulsions are manufactured off-site. However, these emulsions have several drawbacks. For example, in many cases, the emulsions are transported over considerable distances to the paper or cardboard manufacturing plant, which is uneconomical. Furthermore, conventional processes for manufacturing AKD emulsions off-site use expensive high-pressure homogenizers, which are necessary to produce emulsions with relatively small particle sizes (median values ​​of particle size distribution of approximately 0.4 μm). For the emulsion to maintain stability during storage, the AKD must have small particle sizes. Smaller particle sizes are also considered beneficial for good sizing efficiency.

[0004] A conventional process for producing AKD emulsion is shown in Figure 1. The conventional process for producing AKD emulsion involves first gelatinizing starch, melting AKD wax, and then mixing the gelatinized starch and the melted AKD wax. After mixing, emulsification is performed using a high-pressure homogenizer, and then the resulting AKD emulsion is cooled to obtain an AKD emulsion for transport to a paper or cardboard manufacturing plant.

[0005] To circumvent the drawbacks of AKD emulsions, it has been proposed in the past to prepare them directly at the point of use, i.e., the paper or cardboard manufacturing plant. However, the problem is that emulsifying AKD is not easy and requires considerable know-how and expensive mixing equipment, namely a high-pressure homogenizer to produce AKD emulsions with the same small particle size as off-site produced products. Installing high-pressure homogenizers in all paper or cardboard plants is not practical. Therefore, there is a need for a cost-effective method for producing AKD emulsions on-site at paper or cardboard plants. [Overview of the project] [Problems that the invention aims to solve]

[0006] One objective of the present invention is to reduce, or even eliminate, the aforementioned problems that appear in the prior art. In particular, one object of the present invention is to provide a novel method for producing alkyl ketene dimer (AKD) emulsions on-site in a paper or cardboard manufacturing plant.

[0007] Furthermore, the present invention provides a novel AKD emulsion. In particular, to achieve the above objectives, the present invention is characterized by the features set forth in the enclosed independent claims. [Means for solving the problem]

[0008] To achieve these objectives, the present invention is characterized by the features set forth in the independent claims described below. The embodiments and advantages mentioned herein, where applicable, relate to both methods, apparatus, and AKD emulsion products and their uses, although not always specifically noted.

[0009] A typical method for on-site production of an alkenyl ketene dimer (AKD) emulsion according to the present invention is: Premixing a solid alkenyl ketene dimer (AKD) wax with a heated emulsifier solution containing starch and / or a synthetic polymer in a two-stage premixing unit, wherein the two-stage premixing unit includes a first low-shear premixing unit that mixes the heated emulsifier solution with the solid AKD wax to obtain a mixture containing molten AKD wax and emulsifier, and a second high-shear premixing unit that mixes the mixture containing the molten AKD wax and emulsifier to obtain a pre-emulsion of AKD, and Emulsifying the AKD preemulsion with an emulsification unit. Includes.

[0010] A typical apparatus for on-site production of alkenyl ketene dimer (AKD) emulsion according to the present invention is: A two-stage premixing unit including a first low-shear premixing unit and a second high-shear premixing unit, and Emulsification unit, preferably an emulsification unit for ambient pressure or atmospheric pressure, Includes.

[0011] A typical alkenyl ketene dimer (AKD) emulsion according to the present invention comprises an alkenyl ketene dimer (AKD) and an emulsifier containing starch and / or a synthetic polymer, wherein the median value of the particle size distribution of AKD is greater than 0.5 μm or greater than 1 μm, typically in the range of 0.5 to 5 μm or 1 to 5 μm, and more typically in the range of 0.5 to 2 μm or 1 to 2 μm. According to a preferred embodiment of the present invention, the alkenyl ketene dimer (AKD) emulsion comprises an alkenyl ketene dimer (AKD) and starch, more preferably AKD and cationic starch, wherein the median value of the particle size distribution of AKD is greater than 0.5 μm or greater than 1 μm, typically in the range of 0.5 to 5 μm or 1 to 5 μm, and more typically in the range of 0.5 to 2 μm or 1 to 2 μm. A typical AKD emulsion according to the present invention is produced by the method according to the present invention. The AKD emulsion according to the present invention is typically used as a sizing agent in the manufacture of paper or cardboard.

[0012] Surprisingly, it has been found that AKD emulsion can be easily manufactured on-site at a paper or cardboard factory by using a specific premixing of AKD wax with a heated emulsifier solution containing starch and / or synthetic polymers. A typical method according to the present invention involves two steps in the premixing of AKD wax and a heated emulsifier solution. In the method of the present invention, the AKD wax is melted by a heated emulsifier solution containing starch and / or synthetic polymers in the premixing stage. In a preferred embodiment of the present invention, the AKD wax is melted by a cooked starch solution. More specifically, in an on-site method embodiment according to the present invention, solid AKD wax is melted using existing cooked starch, typically cooked cationic starch, at a paper or cardboard factory. Premixing is performed in a two-stage premixing unit, comprising a low-shear premixing stage of AKD wax and a heated emulsifier solution, wherein the heated emulsifier solution melts the solid AKD wax, and a high-shear premixing stage of the mixture of the molten AKD wax and the emulsifier, wherein a pre-emulsification of AKD is obtained. After the premixing stage, the pre-emulsification of AKD is supplied to an emulsification unit, typically at ambient or atmospheric pressure, to produce an AKD emulsion, which can be used as a sizing agent in the manufacture of paper or cardboard. The premixing stage of the method according to the present invention allows the use of various emulsification units selected from the group including low-shear emulsification units and high-shear emulsification units. However, since the pre-emulsification is already produced in the two-stage premixing, there is no need to use an expensive high-pressure homogenizer for emulsification. The on-site method according to the present invention typically uses an inexpensive ambient pressure or atmospheric pressure emulsifying unit, rather than an expensive high-pressure homogenizer unit.

[0013] The method according to the present invention eliminates a separate AKD wax melting stage that uses a heated emulsifier solution containing starch and / or synthetic polymers to melt the AKD wax. In a preferred embodiment of the present invention, heat-treated starch available at paper or cardboard manufacturing plants, typically heat-treated cationic starch used as a strength additive in the manufacture of paper or cardboard, can be used in the method according to the present invention. Starch available at paper or cardboard manufacturing plants typically has a higher molecular weight than starch used in off-site emulsification processes of AKD. The on-site method according to the present invention can use higher molecular weight starch because the larger particle size of the AKD emulsion is not a problem if the resulting AKD emulsion is used substantially soon after emulsification and not stored for long periods. Therefore, the increase in particle size and the potential impact of the increase in particle size on the loss of storage stability of the AKD emulsion can be ignored. The on-site AKD emulsion produced according to the present invention is acceptable even with a larger particle size, giving a degree of freedom in that there is no need to worry about storage stability.

[0014] The AKD emulsion produced by the method according to the present invention differs from commonly used off-site produced AKD emulsions. The AKD emulsion according to the present invention contains relatively larger AKD particles compared to off-site produced AKD emulsions without impairing sizing efficiency. The relatively larger particle size of the AKD emulsion according to the present invention, compared to conventional AKD emulsions (median value of particle size distribution of approximately 0.4 μm), unexpectedly results in improved sizing efficiency. This improvement in sizing efficiency may be due to improved retention on the fiber web. The larger particle size of the AKD emulsion, compared to conventional AKD emulsions with smaller particle sizes, may affect retention. [Brief explanation of the drawing]

[0015] Several embodiments of the present invention will be described in detail below. The accompanying drawings are part of the description. In the drawings, [Figure 1] Figure 1 shows a process diagram of a conventional off-site method for manufacturing AKD emulsion. [Figure 2] Figure 2 shows a process diagram of a method according to one embodiment of the present invention. [Figure 3] Figure 3 shows the results of the sizing test in Example 3. [Modes for carrying out the invention]

[0016] The present invention relates to a method for producing an alkenyl ketene dimer (AKD) emulsion on-site in a paper or cardboard manufacturing plant. The on-site produced AKD emulsion according to the present invention refers to an emulsion produced in a paper or cardboard manufacturing plant, which is typically used immediately without a long-term storage step. An AKD emulsion refers to an emulsion comprising, or consisting solely of, an alkenyl ketene dimer (AKD) and an emulsifier containing starch and / or a synthetic polymer. According to a preferred embodiment of the present invention, the AKD emulsion comprises, or consists solely of, an alkenyl ketene dimer (AKD) and starch, typically cationic starch. In a preferred embodiment of the present invention, the AKD emulsion is prepared using starch, typically cationic starch, as an emulsifier.

[0017] Figure 2 shows a process diagram of a method according to an embodiment of the present invention. In the method for on-site production of an AKD emulsion according to the present invention, first, in a two-stage premixing unit including a first low-shear premixing unit and a second high-shear premixing unit, an AKD wax and a heated emulsifier solution containing starch and / or a synthetic polymer are premixed. In the first low-shear premixing unit, the heated emulsifier solution containing starch and / or a synthetic polymer is mixed with the solid AKD wax to obtain a mixture containing the molten AKD wax and the emulsifier. In the second high-shear premixing unit, the mixture containing the molten AKD wax and the emulsifier is mixed to obtain a pre-emulsion of AKD. Then, the pre-emulsion of AKD is emulsified in an emulsification unit to obtain an AKD emulsion. After emulsification, the obtained AKD emulsion may be cooled before use, or the AKD emulsion may be directly transported to a paper or paperboard machine for use as an additive such as a sizing agent.

[0018] The apparatus according to the present invention for on-site production of an AKD emulsion in a paper or paperboard manufacturing plant includes at least a two-stage premixing unit including a first low-shear premixing unit and a second high-shear premixing unit, and an emulsification unit. The premixing is divided into two parts. Further, the apparatus includes means for supplying a heated emulsifier solution containing starch and / or a synthetic polymer to the first low-shear premixing unit, means for supplying the mixture containing the molten AKD wax and the emulsifier from the first low-shear premixing unit to the second high-shear premixing unit, and further means for supplying the pre-emulsion from the second high-shear premixing unit to the emulsification unit.

[0019] In the method according to the present invention, a heated emulsifier solution containing starch and / or synthetic polymer melts solid AKD wax in a first low-shear premixing unit. Simultaneously, the molten AKD wax can be uniformly dispersed in the emulsifier solution. In the method according to the present invention, the heated emulsifier solution melts the AKD wax. A separate AKD melting step in which only the AKD wax is melted in a melting chamber and the molten AKD wax is mixed with the emulsifier solution after melting is not required in the method according to the present invention. Therefore, the present invention simplifies the AKD emulsification process.

[0020] According to one embodiment of the present invention, the first low-shear premixing unit includes a reservoir and a stirrer located within the reservoir. In one exemplary embodiment of the present invention, the first low-shear premixing unit includes an impeller stirrer, but other types of stirrers may be used to provide sufficient shear to obtain a homogeneous mixture containing molten AKD wax and emulsifier. The mixing speed and mixing time can be adjusted as desired. In one embodiment of the present invention, the low-shear premixing may be achieved by a stirrer using, for example, a rotational speed of less than 500 rpm. According to one embodiment of the present invention, the low-shear premixing may be achieved by a stirrer using, for example, a rotational speed of 100 to 500 rpm or 100 to 400 rpm. According to one embodiment of the present invention, the temperature of the mixture containing molten AKD wax and emulsifier is typically above 70°C or above 80°C during the first low-shear premixing.

[0021] In the second high-shear premixing unit, a mixture containing molten AKD wax and an emulsifier from the first low-shear premixing unit is mixed using high-shear mixing, where the molten AKD wax is uniformly dispersed in the emulsifier solution, and further a pre-emulsion of AKD is produced. According to an embodiment of the present invention, the second high-shear premixing unit includes a reservoir and a stirrer disposed within the reservoir. In an embodiment of the present invention, the second high-shear premixing unit includes an impeller stirrer or an impeller stirrer including a plurality of impellers, although other types of stirrers can also be used. The second high-shear premixing unit is used to continue the mixing of the molten AKD wax and the emulsifier to obtain a homogeneous pre-emulsion of AKD. In an embodiment according to the present invention, the high-shear premixing may be achieved by a stirrer using a rotational speed of, for example, 500 to 1000 rpm. According to the present invention, the rotational speed in the second high-shear premixing unit is higher than the rotational speed in the first low-shear premixing unit. Thus, according to an embodiment of the present invention, the high-shear premixing may be achieved by a stirrer using a rotational speed of, for example, 500 to 1000 rpm, where the rotational speed is selected to be faster than the rotational speed in the first low-shear premixing unit. Mixing is continued in the second high-shear premixing unit until a pre-emulsion is obtained. Due to the prior mixing in the first low-shear premixing unit, a long mixing time is not required. In an embodiment of the present invention, the mixing time in the second high-shear mixing unit may preferably be 5 minutes or less, typically 1 to 5 minutes.

[0022] A pre-emulsification of AKD is supplied from a second high-shear pre-mixing unit to an emulsification unit to produce an emulsion of AKD. The pre-emulsification of AKD may be emulsified in any suitable emulsification unit, emulsifier, or device capable of generating appropriate shear force in an aqueous system. For example, the pre-emulsification of AKD may be sheared in a homogenizer, high-speed mixer, disperser, rotor-stator mixer, mixer with two counter-rotating rotors, centrifugal pump device providing a straight or back-rotation flow, high-pressure device, shear pump, etc. In a preferred embodiment of the present invention, an emulsification unit operating at ambient pressure or atmospheric pressure, such as an atmospheric pressure mixing unit, can be used as the emulsification unit. Suitable devices and homogenizers are well known to those skilled in the art and are commercially available, for example, under the trade names Cavitron® and Burks Pump®. The emulsification according to the present invention does not require the use of a high-pressure homogenizer, and emulsification can be performed at ambient pressure or atmospheric pressure. Therefore, since the preliminary emulsification of AKD is already performed in the two-stage preliminary mixing stage, a less expensive emulsification unit can be used.

[0023] According to one embodiment of the present invention, the preemulsion is emulsified, and a rotational speed of 500 to 1000 rpm is applied to the preemulsion which comprises or consists solely of AKD and an emulsifier comprising starch and / or a synthetic polymer, preferably a preemulsion which comprises or consists solely of AKD and cationic starch. The AKD emulsion according to the present invention can be prepared in a continuous or batch manner. In the method according to the present invention, solid AKD wax is melted by an emulsifier solution heated in a first low-shear premixing unit. Typically, the solid AKD wax is in the form of fine particles, such as flakes, prills, or powder. The properties of AKD wax may vary. Different types of AKD wax have different melting temperatures. The melting temperature of AKD wax may be in the range of, for example, 40-50°C, 40-65°C, or 80-95°C. A suitable AKD wax can be selected based on the application. According to one embodiment of the present invention, the temperature of the emulsifier is typically above 70°C or above 80°C in the first low-shear premixing unit, and the temperature of the emulsifier depends on the AKD wax.

[0024] In the method according to the present invention, an emulsifier containing starch and / or a synthetic polymer is used as the emulsifier. In one preferred embodiment of the present invention, the emulsifier solution contains starch, preferably cationic starch. The starch solution, preferably cationic starch solution, is prepared by cooking a starch mixture containing starch and water. Thus, the cationic starch solution is an aqueous solution of starch that has been cooked according to a method well known to those skilled in the art. The cooking can be done in a jet cooker or batch, or by any other suitable method for cooking starch. The temperature during the starch cooking is typically 95 to 150°C. Any type of starch is acceptable for the preparation of the AKD emulsion in the present invention, but cationic starch is preferred. In one exemplary embodiment, the starch includes tapioca starch, corn starch, maize starch, and / or potato starch. In one typical embodiment of the present invention, the starch is in the form of a starch solution containing 2 to 6% by weight of starch calculated from the total weight of the solution. In one embodiment of the present invention, AKD wax is melted using a heat-treated starch solution, preferably a heat-treated cationic starch solution.

[0025] In a preferred embodiment of the present invention, the starch comprises cationic starch. Cationic starch is the most commonly found starch in sizing agent compositions used in the manufacture of paper or cardboard. However, anionic starch and amphoteric starch can also be used. Thus, the starch is substituted by chemical modification with cationic groups and / or anionic groups, preferably cationic groups. Accordingly, in a typical embodiment of the present invention, the AKD wax and the heat-treated cationic starch solution are first pre-mixed in a two-stage pre-mixing unit. In a first low-shear pre-mixing unit, the cationic starch solution is mixed with solid AKD wax to obtain a mixture containing molten AKD wax and cationic starch, and in a second high-shear pre-mixing unit, the mixture containing molten AKD wax and starch is mixed to obtain an AKD pre-emulsification. The AKD pre-emulsification is then emulsified in an emulsification unit, preferably a low-shear emulsification unit, to obtain an AKD emulsion.

[0026] According to one embodiment of the present invention, starches having a higher molecular weight than those used in off-site AKD emulsification processes can be used. Starches already available at paper or cardboard manufacturing plants are typically used in the method according to the present invention. Cationic starches are commonly used in papermaking, for example, as strengthening agents. According to one exemplary embodiment of the present invention, the starch in the starch solution may have a weight-average molecular weight (MW) greater than 5,000,000 g / mol, preferably greater than 7,500,000 g / mol, and more preferably greater than 10,000,000 g / mol. When using higher molecular weight starches, typically cationic starches available at paper or cardboard manufacturing plants (so-called factory starches), it has been observed that the on-site AKD emulsion according to the present invention is used directly without storage, or the AKD emulsion is stored for only a short time, so there is no need to produce AKD emulsions with small particle sizes, and therefore less shear force or energy is required to produce the AKD emulsion.

[0027] The molecular weight of a polymer may be measured by various methods known to those skilled in the art. For example, the molecular weight may be measured using gel permeation chromatography (GPC). Alternatively, or in addition to the above, the molecular weight of a polymer may be measured by GPC / light scattering / viscosity measurement, also known as triple-detection GPC, which uses refractive index detectors (with or without UV detectors), dilution solution viscosity measurement, and light scattering in sequence to determine the molecular weight, distribution, and associated solution parameters.

[0028] According to one embodiment of the present invention, the starch is cationic starch containing cationic groups. In one embodiment of the present invention, the cationic starch has a degree of substitution (DS) of 0.02 or more, which indicates the average number of cationic groups in the starch per glucose unit. Typically, the DS is in the range of 0.02 to 0.06. According to one embodiment of the present invention, the cationic starch has a charge density of 0.4 to 1.5 meq / g.

[0029] According to one embodiment of the method of the present invention, the temperature of the heat-treated starch is typically above 80°C, allowing the AKD wax to melt in a first low-shear premixing unit. The required temperature depends on the melting temperature of the AKD wax.

[0030] According to one embodiment of the present invention, the emulsifier solution may contain a synthetic polymer. In one embodiment of the present invention, the synthetic polymer may include a cationic synthetic polymer or an amphoteric polymer. The synthetic polymer may include, for example, a polyamine or an amphoteric polyacrylamide.

[0031] In the method according to the present invention, the synthetic polymer is heated before mixing with the AKD wax so that the heated synthetic polymer solution melts the AKD wax in a first low-shear premixing unit.

[0032] In embodiments of the present invention, AKD wax and an emulsifier containing starch and / or a synthetic polymer are mixed in a weight ratio of 10:1 to 6:1 in a first low-shear premixing unit. In exemplary embodiments, AKD wax and emulsifier are mixed in a weight ratio of about 5:1 in a first low-shear premixing unit.

[0033] The alkenyl ketene dimer (AKD) emulsion according to the present invention comprises an alkenyl ketene dimer (AKD) and an emulsifier containing starch and / or a synthetic polymer, wherein the AKD has a median particle size distribution greater than 0.5 μm or greater than 1 μm, typically in the range of 0.5 to 5 μm or 1 to 5 μm. In one embodiment of the present invention, 90% of the AKD particles in the AKD emulsion have a diameter in the range of 0.5 to 5 μm or 1 to 5 μm, more typically in the range of 0.5 to 2 μm or 1 to 2 μm, and the AKD emulsion is produced by the method of the present invention.

[0034] The AKD emulsion according to the present invention is typically used as a sizing agent, preferably an internal sizing agent, in the manufacture of paper or cardboard. A typical method for manufacturing sized paper or sized cardboard from cellulose stock involves adding the AKD emulsion according to the present invention as a sizing agent during the manufacture of the paper or cardboard. Preferably, the sizing agent composition can be added at any suitable point of addition. The amount added may vary depending on different process parameters such as the type of pulp and filler used, the temperature in the system, and the presence of interfering substances. [Examples]

[0035] experiment Example 1: On-site AKD emulsion production test A pre-emulsification of AKD is prepared using a two-stage pre-mixing unit according to the present invention instead of an AKD wax melting chamber. In a first pre-mixing unit equipped with an impeller stirrer, AKD wax (AKD-1840) is uniformly mixed into a heat-treated cationic starch solution (corn starch, DS=0.02, temperature above 80°C) at a relatively low shear force (approximately 100 rpm). A second pre-mixing unit equipped with an impeller stirrer and a relatively high shear force (500-1000 rpm) is used to further mix the molten AKD wax and cationic starch to prepare a pre-emulsification of AKD before entering a Cavitron® emulsification unit (an emulsification unit used to produce ASA emulsion). Two different Cavitron® operating conditions, high shear (40A) and low shear (30A), were used to emulsify the pre-emulsification of AKD.

[0036] In the experiment, the ratio of AKD to cationic starch was approximately 5:1. The final solid content of the AKD emulsion was 12.62% by weight. The particle size of AKD(D90) after emulsification under high shear treatment (40A) was 3 μm, while the particle size after emulsification under low shear treatment (30A) was 2.15 μm. Despite providing more circulation during emulsification under the 40A condition, the particle size was slightly larger under the 40A condition than under the 30A condition.

[0037] The on-site sizing of AKD emulsion will be tested in the laboratory compared to a commercially available AKD emulsion (12.5%) as a reference. Mill-refined bleached hardwood pulp (LBKP) will be used at 100 g / m². 2 It is used in the manufacture of hand seats. The degree of sizing is shown in Table 1.

[0038] Table 1. [Table 1]

[0039] Compared to commercially available AKD emulsions, the two on-site AKD emulsions showed better sizing efficiency, and AKD emulsion 40A, which has a slightly larger particle size, showed better sizing efficiency than AKD emulsion 30A.

[0040] Example 2: On-site AKD emulsion production test A batch production test was conducted to manufacture AKD emulsion on-site. In this test, a pre-emulsion of AKD was prepared using a two-stage pre-mixing unit according to the present invention. The emulsification unit was a Burks Pump™ type small ASA unit. The sizing efficiency of the on-site AKD emulsion was compared with that of a commercially available AKD emulsion (12.5%). The effect on sizing efficiency when 50% of the commercially available AKD emulsion was replaced with the on-site AKD emulsion was also tested. The degree of sizing is shown in Table 2.

[0041] In the experiment, the ratio of AKD (AKD-1840) to cationic starch (corn starch, DS=0.02) was approximately 5:1. The final solid content of the AKD emulsion was 13.15% by weight.

[0042] Table 2. [Table 2]

[0043] The sizing efficiency of the on-site-produced AKD was substantially the same as that of the commercially available off-site-produced AKD emulsion used as a reference.

[0044] Example 3: AKD emulsion containing synthetic polymer Synthetic polymers containing cationic polyamines and amphoteric polyacrylamides were tested as emulsifiers in an on-site AKD manufacturing process, and AKD emulsions were prepared on a laboratory scale.

[0045] The polyamine emulsion contains 39.9 g (dry) of AKD wax, 8 g (dry) of polyamine, and 260 g of water. The amphoteric polyacrylamide emulsion contains 39.9 g (dry) of AKD wax, 8 g (dry) of polyamine, and 236 g of water. Furthermore, the amphoteric polyacrylamide + alum emulsion contains 6.11 g (dry) of alum.

[0046] The polymer was diluted with hot water (75°C) to obtain a polymer solution. Then, AKD wax was added to the polymer solution and slowly mixed. Next, the solution containing the molten AKD wax and polymer was stirred in a high-shear blender (36,000 rpm, 3 minutes). Solid content, particle size, and charge were measured. The results are shown in Table 3 below.

[0047] Table 3. [Table 3]

[0048] Sizing tests were also performed using commercially available AKD emulsion (15% product) as a reference. Mill-refined bleached hardwood pulp (LBKP) was used at 100 g / m². 2 It is used in the manufacture of hand seats. The amount of AKD input was varied. The degree of sizing is shown in Figure 3.

[0049] Compared to commercially available AKD emulsion products, the synthetic polymer-based on-site concept AKD emulsion demonstrated superior performance in laboratory tests.

Claims

1. Premixing a solid alkenyl ketene dimer (AKD) wax with a heated emulsifier solution containing starch and / or a synthetic polymer in a two-stage premixing unit, wherein the two-stage premixing unit includes a first low-shear premixing unit that mixes the heated emulsifier solution with the solid AKD wax to obtain a mixture containing molten AKD wax and emulsifier, and a second high-shear premixing unit that mixes the mixture containing the molten AKD wax and emulsifier to obtain a pre-emulsion of AKD, and Emulsifying the AKD preemulsion in the emulsification unit. A method for on-site production of an alkenyl ketene dimer (AKD) emulsion, characterized by containing the following:

2. The method according to claim 1, characterized in that the heated emulsifier solution contains starch, preferably cationic starch.

3. The method according to claim 2, characterized in that the heated emulsifier solution contains heat-treated (cooked) cationic starch.

4. The method according to any one of claims 1 to 3, characterized in that the starch in the starch solution has a weight-average molecular weight (MW) of more than 5,000,000 g / mol, preferably more than 7,500,000 g / mol, and more preferably more than 10,000,000 g / mol.

5. The method according to any one of claims 1 to 4, characterized in that the AKD wax and the emulsifier are mixed in a weight ratio of 10:1 to 6:

1.

6. The method according to any one of claims 1 to 5, characterized in that the first low-shear premixing unit and / or the second high-shear premixing unit includes a stirrer, preferably an impeller stirrer.

7. The method according to claim 6, characterized in that the rotational speed of the agitator in the first low-shear premixing unit is 100 to 500 rpm.

8. The method according to claim 6, characterized in that the rotational speed of the agitator in the second high-shear pre-mixing unit is 500 to 1000 rpm.

9. The method according to any one of claims 1 to 8, characterized in that the emulsifying unit includes an emulsifying unit for ambient pressure or atmospheric pressure.

10. A two-stage premixing unit including a first low-shear premixing unit and a second high-shear premixing unit, and Emulsification unit, preferably an emulsification unit operating at ambient pressure or atmospheric pressure, Apparatus for on-site production of alkenyl ketene dimer (AKD) emulsions, characterized by containing [a specific compound / component].

11. An alkenyl ketene dimer (AKD) emulsion, wherein the emulsion is produced by the method of any one of claims 1 to 9, and the emulsion comprises an emulsifier containing an alkenyl ketene dimer (AKD) and starch and / or a synthetic polymer, and the median value of the particle size distribution of the AKD is greater than 0.5 μm, typically in the range of 0.5 to 5 μm.

12. The AKD emulsion according to claim 11, characterized in that the emulsion contains starch, preferably cationic starch, as the emulsifier.

13. The AKD emulsion according to claim 11 or claim 12, characterized in that the AKD emulsion contains AKD and the emulsifier in a weight ratio of 10:1 to 6:

1.

14. Use of the alkenyl ketene dimer (AKD) emulsion according to any one of claims 11 to 13 as a sizing agent in the manufacture of paper or cardboard.

Images