A method for preparing a surface sizing agent for white paper

Abstract

The application relates to a preparation method of a white card paper surface sizing agent and relates to the technical field of white card paper surface sizing agent preparation technology. The application comprises the following steps: synthesizing and preparing a primary polymer; preparing a starch liquid; simultaneously adding the primary polymer and the surface sizing starch liquid into a comprehensive reaction kettle, keeping the reaction temperature at 50-80 DEG C, and reacting for 1-2 hours; finally, adding 0.1-0.8% of hydroquinone in total absolute dryness, and reacting for 10 minutes, so that the finished product is obtained. Through free radical reaction, a hydrophobic compound is grafted on the starch to make the starch have a sizing effect, reduce the COBB value of the base paper, reduce the surface water absorption and control the absorption of the base paper to the coating adhesive, the prepared sizing agent has good compatibility, the characteristics of hardening and brittleness can be improved, and the folding endurance of the card paper can be improved.

Description

Technical Field

[0001] This invention relates to the field of white cardboard surface sizing agent preparation technology, and specifically to a method for preparing a white cardboard surface sizing agent. Background Technology

[0002] Double-sided coated white cardboard is mainly used for tobacco and alcohol packaging, as well as book and magazine covers, business cards, hang tags, desk calendars, and shopping bags. Additionally, white cardboard can be used for food packaging, such as common milk cartons. The front side is usually printed with attractive designs, and some packaging-grade cardboard is gold-plated or laminated. The production and related technologies of white cardboard fall under the scope of the papermaking industry.

[0003] Currently, according to the requirements of cardboard printing, surface coating is generally carried out during production to increase the smoothness and gloss of the paper surface and reduce its roughness. The purpose of surface sizing of the base paper is mainly to control the absorption and penetration of moisture and adhesives in the coating during the coating process, reduce adhesive consumption during coating, and prevent linting and dusting during the printing process. The surface sizing agent needs to have good compatibility with the coating and the sizing starch, and should not have a negative impact on the strength properties of the base paper. The amount of sizing on the base paper will affect the folding endurance of the finished paper, and cardboard, as a high-grade packaging paper for household use, needs to be folded into packaging boxes of different sizes. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings and deficiencies of existing technologies by providing a method for preparing a surface sizing agent for white cardboard. This method involves grafting prepolymerized hydrophobic compounds onto starch via a free radical reaction, enabling the starch to possess sizing properties, reducing the COBB value of the base paper, decreasing surface water absorption, and controlling the absorption of coating adhesives by the base paper. The prepared sizing agent exhibits good compatibility, improves stiffness and brittleness, and helps enhance the folding endurance of the cardboard.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: its operation steps are as follows:

[0006] Step 1, Synthesis and preparation of primary polymer: First, add 20-30 parts by mass of deionized water, heat to 40-60℃, add 0.2-0.8 parts of methyl persulfate or ammonium persulfate, and then slowly add 10-18 parts of styrene, 20-28 parts of butyl acrylate and 4-8 parts of myristic acid respectively. After the temperature rises, react for 2-3 hours and set aside.

[0007] Step 2, preparation of starch solution: First, add 50 parts softened water, then add 45 parts corn starch or cassava starch to prepare starch solution. Heat the starch solution to 30-35℃, add 10% NaOH solution to adjust the pH value to 8-9; then add 2-8% of the dry starch weight of acetic anhydride, and continuously add alkali solution to maintain the pH value at 8-9. After the reaction is maintained for 10-30 minutes, add 0.1-0.5% of the dry starch weight of ammonium persulfate or methyl persulfate to obtain the surface starch solution.

[0008] Step 3: Preparation of the finished product: Add the primary polymer and the surface starch solution to the integrated reaction vessel at the same time, maintain the reaction temperature at 50-80℃, and react for 1-2 hours. Finally, add 0.1-0.8% of the total dry weight of hydroquinone and react for another 10 minutes to obtain the finished product.

[0009] Preferably, in step one, the temperature is increased to 50°C.

[0010] Preferably, the solid content of the finished product is 18-30%.

[0011] Preferably, the mass ratio of the primary polymer to the surface starch solution in step three is 1:3 to 1:6.

[0012] Preferably, both the primary polymer preparation reactor and the starch solution preparation reactor are equipped with pressure transmitters to provide pressure control signals to the CPU. The flow meter PLC is set to control the flow rate. Once the flow rate reaches the set flow rate, the centrifugal pump automatically stops, and the addition time of each synthetic component is maintained at 1-2 hours.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for preparing a sizing agent for white cardboard. By grafting prepolymerized hydrophobic compounds onto starch through free radical reaction, the starch is made to have a sizing effect, reducing the COBB value of the base paper, reducing surface water absorption, and controlling the absorption of coating adhesives by the base paper. The sizing agent prepared by this invention has good compatibility, can improve the characteristics of stiffness and brittleness, and helps to improve the folding endurance of cardboard. Attached Figure Description

[0014] Figure 1 This is a comparative image table showing the compatibility test results of this invention with starch solution.

[0015] Figure 2 This is a comparison table of COBB values ​​obtained by coating the surface sizing agent prepared in this invention and existing styrene-based surface sizing agents onto unsizing cardboard base paper.

[0016] Figure 3 This is a performance comparison table of the surface sizing agent prepared by this invention and existing styrene-based surface sizing agents in actual machine tests. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. The preferred embodiments described are only examples. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This specific implementation method adopts the following technical solution: its operation steps are as follows:

[0019] Step 1, Preparation of primary polymer: First, add 20-30 parts by mass of deionized water, heat to 40-60℃, add 0.2-0.8 parts of methyl persulfate or ammonium persulfate, and then slowly add 10-18 parts of styrene, 20-28 parts of butyl acrylate and 4-8 parts of myristic acid respectively. After the temperature rises to 50℃, react for 2-3 hours and set aside.

[0020] Step 2, preparation of starch solution: First, add 50 parts softened water, then add 45 parts corn starch or cassava starch to prepare starch solution. Heat the starch solution to 30-35℃, add 10% NaOH solution to adjust the pH value to 8-9; then add 2-8% of the dry starch weight of acetic anhydride, and continuously add alkali solution to maintain the pH value at 8-9. After the reaction is maintained for 10-30 minutes, add 0.1-0.5% of the dry starch weight of ammonium persulfate or methyl persulfate to obtain the surface starch solution.

[0021] Step 3: Preparation of the finished product: Add the primary polymer and the surface starch solution to the integrated reaction vessel at the same time. The mass ratio of the primary polymer to the surface starch solution is 1:3 to 1:6. Maintain the reaction temperature at 50-80℃ and the reaction time at 1-2 hours. Finally, add 0.1-0.8% of the total dry weight of hydroquinone and react for another 10 minutes to obtain the finished product. The solid content of the finished product is 18-30%.

[0022] Experimental test:

[0023] 1. The surface sizing agent prepared according to this invention was subjected to compatibility testing with starch solution and coatings. See details below. Figure 1 It can be seen that the surface sizing agent prepared by the present invention does not have compatibility issues with starch liquid and coatings.

[0024] 2. The COBB value of the surface sizing agent prepared according to this invention was determined by comparing it with that of existing styrene-based surface sizing agents. The specific evaluation and comparison method is as follows: Starch slurry after on-site cooking was taken, and the surface sizing agent prepared according to this invention and the existing styrene-based surface sizing agent were added at solid contents of 4%, 8%, 12%, and 20%, respectively. After mixing for 5 minutes, the mixed surface sizing solution was applied to the unsizing base paper of the cardboard, and then the COBB values ​​of different schemes were measured. See details below. Figure 2It can be seen that, compared with existing styrene-based surface sizing agents, the surface sizing agent prepared by the present invention can effectively reduce the COBB value of paper. At a dosage of 4%, the relative COBB value of the surface sizing agent prepared by the present invention increases by 8%, and at a dosage of 20%, the relative increase in COBB value of the surface sizing agent prepared by the present invention is 35%. The surface sizing agent prepared by the preparation method of the present invention has a better sizing effect.

[0025] 3. The surface sizing agent prepared according to this invention was compared with existing styrene-based surface sizing agents in an on-machine test. See details below. Figure 3 It can be seen that the surface sizing agent prepared by the present invention has good sizing performance and can significantly improve the folding endurance of the paper. The folding endurance is increased from the original 22 times to 35 times, which meets the product requirement of ≥15 times. The IGT and IR of the paper are significantly improved. The starch-based characteristics of the surface sizing agent prepared by the present invention can not only give it good compatibility with other chemicals, but also have a reinforcing effect. The transparent toughness of esterified starch can give white cardboard good folding endurance and reduce the folding burst phenomenon that occurs in conventional applications.

[0026] The beneficial effects of this specific embodiment after adopting the above process are as follows:

[0027] 1. The surface sizing agent prepared by this invention has a relatively good sizing effect;

[0028] 2. The surface sizing agent prepared by this invention has a significant enhancing effect on the folding resistance and surface strength of white cardboard;

[0029] 3. The surface sizing agent prepared by this invention can also reduce the cracking phenomenon that occurs during the application of cardboard.

[0030] For those skilled in the art, modifications can be made to the technical solutions described in the foregoing embodiments, and equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A method for preparing a sizing agent for white cardboard, characterized in that: Its operation steps are as follows: Step (1), Synthesis and preparation of primary polymer: First, add 20-30 parts by mass of deionized water, heat to 40-60℃, add 0.2-0.8 parts of potassium persulfate or ammonium persulfate, and then slowly add 10-18 parts of styrene, 20-28 parts of butyl acrylate and 4-8 parts of myristic acid respectively. After the temperature rises to 50℃, react for 2-3 hours and set aside. Step (II) Preparation of starch solution: First, add 50 parts of softened water, then add 45 parts of corn starch or cassava starch to prepare starch solution. Heat the starch solution to 30-35℃, add 10% NaOH solution to adjust the pH value to 8-9; then add 2-8% of the dry starch weight of acetic anhydride, and continuously add alkali solution to maintain the pH value at 8-9. After the reaction is maintained for 10-30 minutes, add 0.1-0.5% of the dry starch weight of ammonium persulfate or potassium persulfate to obtain the surface starch solution. Step (3), Preparation of the finished product: Add the primary polymer and the surface starch solution to the integrated reaction vessel at the same time. The mass ratio of the primary polymer to the surface starch solution is 1:3 to 1:

6. Maintain the reaction temperature at 50-80℃ and the reaction time at 1-2 hours. Finally, add 0.1-0.8% of the total dry weight of hydroquinone and react for another 10 minutes to obtain the finished product.

2. The method for preparing a surface sizing agent for white cardboard according to claim 1, characterized in that: The solid content of the finished product is 18-30%.

3. The method for preparing a surface sizing agent for white cardboard according to claim 1, characterized in that: Both the primary polymer preparation reactor and the starch solution preparation reactor are equipped with pressure transmitters to provide pressure control signals to the CPU. The flow meter PLC is set to control the flow rate. Once the flow rate reaches the set flow rate, the centrifugal pump automatically stops. The addition time of each synthetic component is maintained at 1-2 hours.

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