A surface sizing agent for papermaking, an on-line preparation method thereof, and an on-line sizing method

Abstract

The application provides a surface sizing agent for papermaking, which is prepared from the following raw materials in parts by mass: 70-85 parts of alkyl alkenone dimer emulsion, 10-20 parts of polydimethyl diallyl ammonium chloride, 5-15 parts of fixing agent, 1-5 parts of stabilizer, and 0-20 parts of water. The surface sizing agent can be prepared and added on line at the papermaking site, can improve the water resistance of paper, and can reduce or even stop the use of internal sizing agent, and solve the problems of system pollution and increased slurry caused by internal sizing agent. The surface sizing agent can also form a stereoscopic film structure with starch, filler and fine fiber network, improve the surface strength, and better meet the use requirements of paper.

Description

Technical Field

[0001] This invention belongs to the field of sizing agent technology, specifically relating to a surface sizing agent for papermaking, its online preparation method, and its online sizing method. Background Technology

[0002] Surface sizing is a process in paper and paperboard processing, typically located in the later part of the drying section of a paper machine. It involves applying a layer of sizing agent to the paper sheet while it is not completely dry but still possesses a certain strength. Subsequent drying forms a film on the surface of the paper and paperboard, thereby improving their water resistance, surface strength, and smoothness. Currently, paper mills commonly use surface sizing starch (including oxidized starch, enzyme-converted starch, and thermally converted starch) in combination with a certain proportion of surface sizing agents. The main surface sizing agents are AKD-type, styrene-acrylic, and propylene-acrylic, prepared by suppliers and sold as chemical commodities. These agents are expensive, require high levels of surfactants, and their effectiveness is affected by prolonged storage.

[0003] With the rapid development of the paper industry, the sizing process is shifting from a combination of traditional in-pulp sizing and surface sizing to mostly or entirely surface sizing. Reducing in-pulp sizing can reduce in-pulp system contamination and pulp decay, extend the washing cycle and spare parts usage cycle, and reduce wet end paper breaks.

[0004] Therefore, a simple and cost-effective online preparation method for surface sizing agents is provided. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a surface sizing agent for papermaking, an online preparation method thereon, and an online sizing method. The surface sizing agent provided by the present invention can be prepared and added online on the papermaking site, which can improve the water resistance of paper, reduce or even stop the use of internal sizing agents, and solve the problems of system pollution and increased pulp decay caused by internal sizing agents.

[0006] This invention provides a surface sizing agent for papermaking, prepared from raw materials comprising the following parts by weight:

[0007] 70-85 parts of alkyl ketene dimer emulsion, 10-20 parts of polydimethyldiallylammonium chloride, 5-15 parts of fixative, 1-5 parts of stabilizer, and 0-20 parts of water.

[0008] Preferably, the stabilizer is selected from one or more of zirconium oxychloride, acetic acid, and potassium sorbate.

[0009] Preferably, the fixing agent is selected from aluminum sulfate and / or aluminum chloride.

[0010] The present invention also provides an online preparation method for the above-mentioned surface sizing agent, comprising the following steps:

[0011] An alkyl ketene dimer emulsion, polydimethyldiallylammonium chloride, a setting agent, and a stabilizer are mixed to obtain a surface sizing agent.

[0012] Preferably, the online preparation method includes the following steps:

[0013] (1) Prepare raw materials according to the weight parts, and add the alkyl ketene dimer emulsion into the mixing tank and stir;

[0014] (2) Add the stabilizer to the alkyl ketene dimer emulsion in step (1) and stir to obtain a mixture;

[0015] (3) Add the fixative to the mixture in step (2) and stir to obtain a mixed emulsion;

[0016] (4) After the mixed emulsion is transported to the mixing storage tank, it is pumped to the gluing tank. Polydimethyldiallyl ammonium chloride is added to the pumping pipeline, and water is added for online dilution. The mixture is then mixed through the pipeline mixer to obtain the online added surface sizing agent.

[0017] Preferably, the stirring time in step (2) is 10 to 20 minutes and the stirring rate is 50 to 120 r / min.

[0018] Preferably, the stirring time in step (3) is 5 to 10 minutes and the stirring rate is 50 to 120 r / min.

[0019] Preferably, the interior of the pipe mixer in step (4) has a spiral petal structure.

[0020] The present invention also provides an online sizing method for a surface sizing agent for papermaking, wherein the surface sizing agent is mixed with surface starch in a feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0021] Preferably, the mixing ratio of the surface sizing agent to the surface starch is 1:(4-8).

[0022] Compared with existing technologies, this invention provides a surface sizing agent for papermaking, prepared from raw materials comprising the following parts by weight: 70-85 parts of alkyl ketene dimer emulsion, 10-20 parts of polydimethyldiallyl ammonium chloride, 5-15 parts of a fixative, 1-5 parts of a stabilizer, and 0-20 parts of water. The surface sizing agent provided by this invention can be prepared and added online at the papermaking site, improving the water resistance of paper, reducing or even eliminating the use of internal sizing agents, and solving the problems of system contamination and increased pulp spoilage caused by internal sizing agents. It can also form a three-dimensional film structure with starch, fillers, and fine fiber networks, improving surface strength and better meeting the needs of paper use. Attached Figure Description

[0023] Figure 1 The production process flow diagram for the online preparation of surface sizing agents provided by the present invention is shown. Detailed Implementation

[0024] This invention provides a surface sizing agent for papermaking, prepared from raw materials comprising the following parts by weight:

[0025] 70-85 parts of alkyl ketene dimer emulsion, 10-20 parts of polydimethyldiallylammonium chloride, 5-15 parts of fixative, 1-5 parts of stabilizer, and 0-20 parts of water.

[0026] The papermaking surface sizing agent provided by the present invention comprises 70 to 85 parts of alkyl ketene dimer emulsion, which can be any value between 70, 75, 80, 85, or 70 to 85 parts.

[0027] The papermaking surface sizing agent provided by this invention further includes 10-20 parts of polydimethyldiallyl ammonium chloride, which can be 10, 12, 14, 15, 16, 18, 20, or any value between 10 and 20 parts. In this invention, the polydimethyldiallyl ammonium chloride is a crosslinking agent. Polydimethyldiallyl ammonium chloride contains a large number of cationic groups and has efficient electrostatic neutralization and adsorption effects. It can form a formaldehyde-free complex with alkyl ketene dimers, starch, fillers, and fine fibers to create a three-dimensional film structure, thereby improving the surface strength of the paper.

[0028] The papermaking surface sizing agent provided by the present invention further includes 5 to 15 parts of a fixing agent, which can be 5, 7, 10, 12, 15, or any value between 5 and 15 parts. In the present invention, the fixing agent is selected from aluminum sulfate and / or aluminum chloride, preferably aluminum sulfate.

[0029] The papermaking surface sizing agent provided by the present invention further includes 1 to 5 parts of a stabilizer, which can be 1, 2, 3, 4, 5, or any value between 1 and 5 parts. In the present invention, the stabilizer is selected from one or more of zirconium oxychloride, acetic acid, and potassium sorbate, preferably zirconium oxychloride.

[0030] The papermaking surface sizing agent provided by the present invention also includes 0 to 20 parts of water, which is used to adjust the concentration of the surface sizing agent. It can be added or not.

[0031] The present invention also provides an online preparation method for the above-mentioned surface sizing agent, comprising the following steps:

[0032] An alkyl ketene dimer emulsion, polydimethyldiallylammonium chloride, a setting agent, and a stabilizer are mixed to obtain a surface sizing agent.

[0033] Specifically, the online preparation method of the surface sizing agent includes the following steps:

[0034] (1) Prepare raw materials according to the weight parts, and add the alkyl ketene dimer emulsion into the mixing tank and stir;

[0035] (2) Add the stabilizer to the alkyl ketene dimer emulsion in step (1) and stir to obtain a mixture;

[0036] (3) Add the fixative to the mixture in step (2) and stir to obtain a mixed emulsion;

[0037] (4) After the mixed emulsion is transported to the mixing storage tank, it is pumped to the gluing tank. Polydimethyldiallyl ammonium chloride is added to the pumping pipeline, and water is added for online dilution. The mixture is then mixed through the pipeline mixer to obtain the online added surface sizing agent.

[0038] In step (2), the stirring time is 10 to 20 minutes and the stirring rate is 50 to 120 r / min.

[0039] The stirring time in step (3) is 5 to 10 minutes, and the stirring speed is 50 to 120 r / min.

[0040] In this invention, the type of stirrer used for stirring is a paddle stirrer.

[0041] The internal structure of the pipeline mixer in step (4) is a spiral petal structure, which does not require additional hybrid power. All of the above equipment is commercially available.

[0042] The present invention also provides an online sizing method for a surface sizing agent for papermaking, wherein the surface sizing agent is mixed with surface starch in a feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0043] The mixing ratio of the surface sizing agent to the surface starch is 1:(4-8), which can be any value between 1:4, 1:5, 1:6, 1:7, 1:8, or 1:(4-8).

[0044] See Figure 1 , Figure 1 The production process flow diagram for the online preparation of surface sizing agents provided by the present invention is shown.

[0045] The advantages and effects of this invention are as follows:

[0046] The papermaking surface sizing agent provided by this invention can be prepared and added online, exhibiting strong reactivity and avoiding the negative effects of long-term storage of commercial surface sizing agents. Based on the water absorption and surface strength of the finished paper, the proportions of raw materials such as alkyl ketene dimer emulsion and polydimethyl diallyl ammonium chloride can be quickly adjusted online, resulting in high process control efficiency. The on-site preparation and addition of the papermaking surface sizing agent provided by this invention is less costly than purchasing commercial surface sizing agents.

[0047] The surface sizing agent of the present invention contains alkyl ketene dimer emulsion, polydimethyldiallylammonium chloride, stabilizer and setting agent. The various components work together to give the surface sizing agent better properties. During online preparation, a paddle agitator and a pipeline static mixer are used to make the auxiliary components more uniformly mixed. Uniform mixing is more conducive to improving the use effect of the auxiliary agent, improving the performance of paper, and better meeting the needs of papermaking.

[0048] To further understand the present invention, the following description, in conjunction with embodiments, illustrates the surface sizing agent for papermaking provided by the present invention, its online preparation method, and its online sizing method. The scope of protection of the present invention is not limited by the following embodiments.

[0049] Example 1:

[0050] Prepare 75 parts of alkyl ketene dimer emulsion, 15 parts of polydimethyldiallyl ammonium chloride, 8 parts of aluminum sulfate, and 2 parts of zirconium oxychloride.

[0051] Add 75 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at a speed of 80 r / min;

[0052] Add 2 parts of zirconium oxychloride to the mixing tank and stir for 20 minutes.

[0053] Add 8 parts of aluminum sulfate to the mixing tank and stir for 10 minutes.

[0054] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0055] The raw materials are pumped from the mixing and storage tank to the gluing tank. 15 parts of polydimethyldiallyl ammonium chloride are added to the pumping pipeline, and 15 parts of water are added for online dilution. The mixture is then mixed by the pipeline mixer to become the surface sizing agent that can be added online.

[0056] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0057] Example 2:

[0058] Prepare 70 parts of alkyl ketene dimer emulsion, 20 parts of polydimethyldiallyl ammonium chloride, 6 parts of aluminum sulfate, and 4 parts of zirconium oxychloride.

[0059] Add 70 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at a speed of 100 r / min.

[0060] Add 4 parts of zirconium oxychloride to the mixing tank and stir for 20 minutes.

[0061] Add 6 parts of aluminum sulfate to the mixing tank and stir for 10 minutes.

[0062] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0063] The raw materials are pumped from the mixing and storage tank to the gluing tank. 20 parts of polydimethyldiallyl ammonium chloride are added to the pumping pipeline, and 10 parts of water are added for online dilution. The mixture is then mixed by the pipeline mixer to become an online surface sizing agent.

[0064] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0065] Example 3:

[0066] Prepare 80 parts of alkyl ketene dimer emulsion, 12 parts of polydimethyldiallyl ammonium chloride, 7 parts of aluminum sulfate, and 1 part of zirconium oxychloride.

[0067] Add 80 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at a speed of 50 r / min;

[0068] Add 1 part of zirconium oxychloride to the mixing tank and stir for 15 minutes;

[0069] Add 7 parts of aluminum sulfate to the mixing tank and stir for 8 minutes.

[0070] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0071] The raw materials are pumped from the mixing and storage tank to the gluing tank. 12 parts of polydimethyldiallyl ammonium chloride are added to the pumping pipeline, and 8 parts of water are added for online dilution. The mixture is then mixed through the pipeline mixer to become an online surface sizing agent.

[0072] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0073] Example 4:

[0074] Prepare 78 parts of alkyl ketene dimer emulsion, 11 parts of polydimethyldiallylammonium chloride, 8 parts of aluminum sulfate, and 3 parts of zirconium oxychloride.

[0075] Add 78 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at 800 r / min.

[0076] Add 3 parts of zirconium oxychloride to the mixing tank and stir for 15 minutes.

[0077] Add 8 parts of aluminum sulfate to the mixing tank and stir for 10 minutes.

[0078] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0079] The raw materials are pumped from the mixing and storage tank to the gluing tank. 11 parts of polydimethyldiallyl ammonium chloride are added to the pumping pipeline, and 5 parts of water are added for online dilution. The mixture is then mixed by the pipeline mixer to become the surface sizing agent that can be added online.

[0080] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0081] Example 5:

[0082] Prepare 83 parts of alkyl ketene dimer emulsion, 10 parts of polydimethyldiallyl ammonium chloride, 5 parts of aluminum sulfate, and 2 parts of zirconium oxychloride.

[0083] Add 83 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at a speed of 100 r / min.

[0084] Add 2 parts of zirconium oxychloride to the mixing tank and stir for 20 minutes.

[0085] Add 5 parts of aluminum sulfate to the mixing tank and stir for 10 minutes.

[0086] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0087] The raw materials are pumped from the mixing and storage tank to the gluing tank. 10 parts of polydimethyldiallyl ammonium chloride are added to the pumping pipeline, and 0 parts of water are added for online dilution. The mixture is then mixed through the pipeline mixer to become an online surface sizing agent.

[0088] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0089] Experimental Example 1:

[0090] Add approximately 3000 kg of water and 750 kg of oxidized starch to a gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in a starch storage tank and pump it to a feeding tank. Add the surface sizing agent prepared in Example 1 at 10% of the starch amount, mix thoroughly and load onto the machine, and test the Cobb value and IGT surface printing strength of the paper.

[0091] The amount of AKD added to the pulp during papermaking is 2kg.

[0092] Experimental Example 2:

[0093] Add approximately 3000 kg of water and 750 kg of oxidized starch to a gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in a starch storage tank and pump it to a feeding tank. Add the surface sizing agent prepared in Example 2 at 10% of the starch amount, mix thoroughly and load onto the machine, and test the Cobb value and IGT surface printing strength of the paper.

[0094] The amount of AKD added to the pulp during papermaking is 2kg.

[0095] Experimental Example 3:

[0096] Add approximately 3000 kg of water and 750 kg of oxidized starch to a gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in a starch storage tank and pump it to a feeding tank. Add the surface sizing agent prepared in Example 3 at 10% of the starch amount, mix thoroughly and load onto the machine, and test the Cobb value and IGT surface printing strength of the paper.

[0097] The amount of AKD added to the pulp during papermaking is 3 kg.

[0098] Experimental Example 4:

[0099] Add approximately 3000 kg of water and 750 kg of oxidized starch to a gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in a starch storage tank and pump it to a feeding tank. Add the surface sizing agent prepared in Example 4 at 10% of the starch amount, mix thoroughly and load onto the machine, and test the Cobb value and IGT surface printing strength of the paper.

[0100] The amount of AKD added to the pulp during papermaking is 3 kg.

[0101] Experimental Example 5:

[0102] Add approximately 3000 kg of water and 750 kg of oxidized starch to a gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in a starch storage tank and pump it to a feeding tank. Add the surface sizing agent prepared in Example 5 at 10% of the starch amount, mix thoroughly and load onto the machine, and test the Cobb value and IGT surface printing strength of the paper.

[0103] The amount of AKD added to the pulp during papermaking is 0 kg.

[0104] Comparative Example 1:

[0105] Add approximately 3000 kg of water and 750 kg of oxidized starch to the gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to 15% concentration via a starch storage tank and pump to the feeding tank. Add 10% of the purchased AKD surface sizing agent according to the starch content, mix thoroughly and load onto the machine, and test the cobb value and IGT surface printing strength of the paper.

[0106] The amount of AKD added to the pulp during papermaking is 10 kg.

[0107] Comparative Example 2:

[0108] Add approximately 3000 kg of water and 750 kg of oxidized starch to the gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in the starch storage tank and pump it to the feeding tank. Add 10% of the starch weight of the purchased styrene-acrylate surface sizing agent B, mix thoroughly and load onto the machine, and test the COBB value and IGT surface printing strength of the paper.

[0109] The amount of AKD added to the pulp during papermaking is 8 kg.

[0110] Comparative Example 3:

[0111] Add approximately 3000 kg of water and 750 kg of oxidized starch to the gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in the starch storage tank and pump it to the feeding tank. Add 10% of the starch weight of the purchased acrylonitrile-acrylate surface sizing agent, mix thoroughly and load onto the machine, and test the COBB value and IGT surface printing strength of the paper.

[0112] The amount of AKD added to the pulp during papermaking is 9 kg.

[0113] Comparative Example 4:

[0114] Add approximately 3000 kg of water and 750 kg of oxidized starch to the gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in the starch storage tank, pump it to the feeding tank, add it to the surface sizing agent prepared online below at 10% of the starch amount, mix thoroughly and load it onto the machine, and test the cobb value and IGT surface printing strength of the paper.

[0115] The amount of AKD added to the pulp during papermaking is 5 kg.

[0116] The online surface sizing agent preparation method in this example is as follows:

[0117] Prepare 75 parts of alkyl ketene dimer emulsion, 8 parts of aluminum sulfate, and 2 parts of zirconium oxychloride.

[0118] Add 75 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at a speed of 80 r / min;

[0119] Add 2 parts of zirconium oxychloride to the mixing tank and stir for 20 minutes.

[0120] Add 8 parts of aluminum sulfate to the mixing tank and stir for 10 minutes.

[0121] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0122] The raw materials are pumped from the mixing and storage tank to the gluing tank. Ten parts of clean water are added to the pumping pipeline for online dilution. The mixture is then mixed by the pipeline mixer to become the surface sizing agent that can be added online.

[0123] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0124] Comparative Example 5:

[0125] Add approximately 3000 kg of water and 750 kg of oxidized starch to the gelatinization tank, stir thoroughly and heat to 96°C, gelatinize for 25 minutes, then dilute online to a concentration of 15% in the starch storage tank, pump it to the feeding tank, add it to the surface sizing agent prepared online below at 10% of the starch amount, mix thoroughly and load it onto the machine, and test the cobb value and IGT surface printing strength of the paper.

[0126] The amount of AKD added to the pulp during papermaking is 6 kg.

[0127] The online surface sizing agent preparation method in this example is as follows:

[0128] Prepare 75 parts of alkyl ketene dimer emulsion, 15 parts of polyethyleneimine (as a crosslinking agent), 8 parts of aluminum sulfate, and 2 parts of zirconium oxychloride.

[0129] Add 75 parts of alkyl ketene dimer emulsion to the mixing tank and turn on the paddle stirrer at a speed of 80 r / min;

[0130] Add 2 parts of zirconium oxychloride to the mixing tank and stir for 20 minutes.

[0131] Add 8 parts of aluminum sulfate to the mixing tank and stir for 10 minutes.

[0132] The mixed raw materials are sent to the mixing storage tank after being mixed in the mixing tank. The mixing storage tank serves as a buffer tank for continuous online preparation.

[0133] The raw materials are pumped from the mixing and storage tank to the gluing tank. 15 parts of polyethyleneimine (as a crosslinking agent) are added to the pumping pipeline, and 18 parts of water are added for online dilution. The mixture is then mixed through the pipeline mixer to become an online surface sizing agent.

[0134] The surface sizing agent prepared online is mixed with surface starch in the feeding trough and pumped to the surface of the paper machine sizing machine for sizing.

[0135] Performance testing:

[0136] Cobb value (tested using the standard method of GB / T 1540-2002), IGT surface printing strength (tested using the standard method of GB / T22365-2008), and the performance of the surface sizing agent are judged based on the test results.

[0137] Table 1. Test results of Examples 1-5 and Comparative Examples 1-5

[0138]

[0139] The results in the table show that the test results of Examples 1-5 are significantly better than those of Comparative Examples 1-5, exhibiting better water resistance and higher surface strength. This indicates that the surface sizing agents prepared online in Examples 1-5 have better effects than commercially available surface sizing agents. Polydimethyl diallyl ammonium chloride contains a large number of cationic groups, possessing efficient electrostatic neutralization and adsorption properties. It can form formaldehyde-free complexes with alkyl ketene dimers, starch, fillers, and fine fibers, creating a three-dimensional film structure, thereby improving the surface strength of the paper. Furthermore, the surface sizing agent provided by this invention can be prepared and added online at the papermaking site, improving the water resistance of paper, reducing or even eliminating the use of internal sizing agents, and solving the problems of system contamination and increased pulp spoilage caused by internal sizing agents.

[0140] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An online sizing method for a surface sizing agent used in papermaking, characterized in that, The surface sizing agent is mixed with the surface sizing starch in the feeding trough and then pumped to the surface of the paper machine sizing machine for sizing. The surface sizing agent is prepared from the following raw materials in parts by weight: 70-85 parts of alkyl ketene dimer emulsion, 10-20 parts of polydimethyldiallylammonium chloride, 5-15 parts of fixative, 1-5 parts of stabilizer, and 0-20 parts of water; The online preparation method of the surface sizing agent includes the following steps: (1) Prepare raw materials according to the weight parts, and add the alkyl ketene dimer emulsion into the mixing tank and stir; (2) Add the stabilizer to the alkyl ketene dimer emulsion in step (1) and stir to obtain a mixture; (3) Add the fixative to the mixture in step (2) and stir to obtain a mixed emulsion; The type of agitator used for mixing is a paddle agitator. (4) After the mixed emulsion is transported to the mixing storage tank, it is pumped to the gluing tank. Polydimethyldiallylammonium chloride is added to the pumping pipeline, and water is added for online dilution. The mixture is then mixed by the pipeline mixer to obtain the online added surface sizing agent. The pipeline mixer has a spiral petal structure inside.

2. The online sizing method for the surface sizing agent for papermaking according to claim 1, characterized in that, The stabilizer is selected from one or more of zirconium oxychloride, acetic acid, and potassium sorbate.

3. The online sizing method for the surface sizing agent for papermaking according to claim 1, characterized in that, The fixing agent is selected from aluminum sulfate and / or aluminum chloride.

4. The online sizing method for the surface sizing agent for papermaking according to claim 1, characterized in that, The stirring time in step (2) is 10~20 min, and the stirring speed is 50~120 r / min.

5. The online sizing method for the surface sizing agent for papermaking according to claim 1, characterized in that, The stirring time in step (3) is 5~10 min, and the stirring speed is 50~120 r / min.

6. The online sizing method for the surface sizing agent for papermaking according to claim 1, characterized in that, The mixing ratio of the surface sizing agent to the surface starch is 1:(4-8).

Images