Low blue sheet papermaking process based on inhibition of asa sizing agent hydrolysis

Abstract

This application provides a low-blue-point papermaking process based on inhibiting the hydrolysis of ASA sizing agent, relating to the field of papermaking technology. The process includes six steps: emulsification of ASA sizing agent, pH adjustment, pulp preparation, ASA sizing, retention and filtration aids, and papermaking. This invention effectively inhibits the hydrolysis reaction of ASA by using a compound emulsifier of cationic starch and surfactant, a compound stabilizer of citric acid and borax, and adjusting the pH of the ASA emulsion to 3.5-4.5. Simultaneously, a retention aid system of CPAM and bentonite is used to improve the retention rate of ASA. Paper produced using this process exhibits an extended ASA emulsion stabilization time of 8-12 hours, a reduction of over 80% in the number of blue points on the paper surface, a Cobb value of 20-25 g / m², and an ASA retention rate of over 85%, significantly improving paper quality and production efficiency.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and more specifically, to a low blue spot papermaking process based on inhibiting the hydrolysis of ASA sizing agents. Background Technology

[0002] ASA (Alkenyl Succinic Anhydride) is a reactive sizing agent widely used in the paper industry. Compared with traditional AKD (alkyl ketene dimer) sizing agents, ASA has advantages such as fast sizing speed, high sizing efficiency, and minimal impact on paper machine operation, and has been widely used in high-speed paper machines.

[0003] However, ASA sizing agents have a significant technical drawback: the anhydride groups in their molecular structure readily hydrolyze with water, generating the corresponding alkenyl succinic acid. After hydrolysis, ASA not only loses its sizing activity, but the hydrolysis products also form blue spots on the paper surface, the so-called "blue spot" defect. This defect severely affects the appearance quality of the paper, especially in the production of high-grade cultural and packaging paper, where the blue spot problem becomes a key factor restricting product quality.

[0004] In the prior art, the main methods to inhibit ASA hydrolysis include: (1) lowering the pH value of the ASA emulsion to inhibit the hydrolysis reaction through an acidic environment; (2) adding emulsion stabilizers to improve the stability of the emulsion; (3) shortening the storage time of ASA so that it can be used immediately after production; and (4) optimizing the sizing process parameters to reduce the contact time between ASA and water. However, these methods have problems such as limited effectiveness, complex processes, and increased costs, and are difficult to fundamentally solve the problem of blue spots on paper caused by ASA hydrolysis.

[0005] Therefore, we have made improvements to this and proposed a low blue spot papermaking process based on inhibiting the hydrolysis of ASA sizing agents. Summary of the Invention

[0006] The purpose of this invention is to solve the problems raised in the background art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following low blue spot papermaking process based on inhibiting the hydrolysis of ASA sizing agent, in order to improve the above-mentioned problems.

[0008] The application is as follows:

[0009] Step 1: Emulsification of ASA sizing agent:

[0010] Mix ASA sizing agent with emulsifier and stabilizer at a mass ratio of 100:(2~5):(1~3), emulsify at 50~70℃ for 10~20min to obtain ASA emulsion; add pH adjuster to ASA emulsion to adjust the pH value of emulsion to 3.5~4.5.

[0011] Step 2: Slurry preparation:

[0012] Beat the pulp to a freeness of 30-50°SR and adjust the pulp concentration to 3.0-5.0%. Add ASA emulsion to the pulp at a rate of 0.3-1.0% of the oven-dry pulp mass, and mix thoroughly for 2-5 minutes. Add a retention aid at a rate of 0.05-0.2% of the oven-dry pulp mass to improve the retention rate of ASA in the paper.

[0013] Step 3: Papermaking:

[0014] The sizing pulp is then used for papermaking, with the pH value controlled at 6.5~7.5 and the drying temperature at 90~110℃, to obtain sized paper.

[0015] In a preferred embodiment of the present invention, the emulsifier is a compound of cationic starch and surfactant, wherein the mass ratio of cationic starch to surfactant is (3~5):1. The surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyoxyethylene sorbitan monostearate.

[0016] In a preferred embodiment of the present invention, the stabilizer is a compound of citric acid and borax, wherein the mass ratio of citric acid to borax is (2~4):1. This compound stabilizer can effectively complex the metal ions generated by the hydrolysis of ASA and inhibit the catalytic hydrolysis reaction.

[0017] As a preferred embodiment of the present invention, the pH adjuster is one or more of citric acid, tartaric acid, and phosphoric acid, with citric acid being preferred. Citric acid not only adjusts the pH value but also has a certain chelating effect, which helps to inhibit the hydrolysis of ASA.

[0018] As a preferred embodiment of the present invention, the retention aid is a compound system of cationic polyacrylamide and bentonite, wherein the amount of CPAM added is 0.03~0.1% of the oven-dried slurry mass, and the amount of bentonite added is 0.2~0.5% of the oven-dried slurry mass.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Significantly inhibits ASA hydrolysis: This invention extends the stabilization time of ASA emulsion from the traditional 2-4 hours to 8-12 hours through comprehensive measures such as optimizing the emulsification process, adding compound stabilizers, and adjusting pH value, effectively inhibiting the hydrolysis reaction of ASA.

[0021] (2) Significantly reduce blue spots on paper: The number of blue spots on paper produced by the process of this invention is reduced by more than 80% compared with the traditional process, and the appearance quality of paper is significantly improved, meeting the quality requirements of high-grade cultural paper and packaging paper.

[0022] (3) Improve sizing efficiency: By optimizing the retention and filtration system, the retention rate of ASA is increased to over 85%, and the sizing degree (Cobb value) can reach 20-25 g / m², resulting in excellent sizing effect.

[0023] (4) Reduced production costs: The process of this invention is simple, the raw materials are readily available, and there is no need to increase expensive equipment investment. The overall production cost is reduced by 10%-15% compared with the traditional process, which has good economic benefits.

[0024] (5) Environmentally friendly: The raw materials used in this invention are all environmentally friendly materials, which do not contain toxic or harmful substances, and the production process is pollution-free, which is in line with the development trend of green papermaking. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] It should be noted that, unless otherwise specified, the embodiments and features and technical solutions in the present invention can be combined with each other.

[0027] Example 1:

[0028] 100 parts of ASA sizing agent, 3 parts of cationic starch and sodium dodecyl sulfate compound emulsifier (mass ratio 4:1), and 2 parts of citric acid and borax compound stabilizer (mass ratio 3:1) were mixed and emulsified at 60℃ for 15 minutes to obtain an ASA emulsion. Citric acid was added to the ASA emulsion to adjust the pH to 4.0. Bleached chemical softwood pulp was beaten to a freeness of 40°SR and the pulp concentration was adjusted to 4.0%. The ASA emulsion was added to the pulp at an ASA addition amount of 0.6% of the oven-dry pulp mass, and the mixture was stirred for 3 minutes. Then, 0.05 parts of CPAM and 0.3 parts of bentonite were added as retention aids, stirred for 1 minute, and then papermaking was carried out. The papermaking pH was controlled at 7.0, and the drying temperature was 100℃ to obtain sized paper.

[0029] Test results: ASA emulsion stability time was 10 hours; paper Cobb value was 22 g / m²; number of blue spots on the paper surface was 3 / m² (compared to 25 / m² for traditional processes); ASA retention rate was 88%.

[0030] Example 2:

[0031] 100 parts of ASA sizing agent, 2 parts of cationic starch and hexadecyltrimethylammonium bromide compound emulsifier (mass ratio 3:1), and 1 part of citric acid and borax compound stabilizer (mass ratio 2:1) were mixed and emulsified at 55°C for 12 minutes to obtain an ASA emulsion. Tartaric acid was added to the ASA emulsion to adjust the pH to 3.8. Bleached chemical hardwood pulp was beaten to a freeness of 35°SR and the pulp concentration was adjusted to 3.5%. The ASA emulsion was added to the pulp at an ASA addition amount of 0.5% of the oven-dry pulp mass, and the mixture was stirred for 2.5 minutes. Then, 0.04 parts of CPAM and 0.25 parts of bentonite were added as retention aids, stirred for 1 minute, and then papermaking was carried out. The papermaking pH was controlled at 6.8, and the drying temperature was 95°C to obtain sized paper.

[0032] Test results: ASA emulsion stability time was 9 hours; paper Cobb value was 24 g / m²; number of blue spots on the paper surface was 4 / m²; ASA retention rate was 86%.

[0033] Example 3:

[0034] 100 parts of ASA sizing agent, 4 parts of cationic starch and polyoxyethylene sorbitan monostearate emulsifier (mass ratio 5:1), and 3 parts of citric acid and borax stabilizer (mass ratio 4:1) were mixed and emulsified at 65°C for 18 minutes to obtain an ASA emulsion. Phosphoric acid was added to the ASA emulsion to adjust the pH to 4.2. A mixture of chemimechanical pulp and chemical pulp (mass ratio 3:7) was beaten to a freeness of 45°SR, and the pulp concentration was adjusted to 4.5%. The ASA emulsion was added to the pulp, with the ASA addition amount being 0.8% of the oven-dry pulp mass, and the mixture was stirred for 4 minutes. Then, 0.08 parts of CPAM and 0.4 parts of bentonite were added as retention aids, and the mixture was stirred for 1 minute before papermaking. The papermaking pH was controlled at 7.2, and the drying temperature was 105°C to obtain sized paper.

[0035] Test results: ASA emulsion stability time was 11 hours; paper Cobb value was 20 g / m²; number of blue spots on the paper surface was 2 / m²; ASA retention rate was 90%.

[0036] Comparative example (traditional process)

[0037] 100 parts of ASA sizing agent and 3 parts of cationic starch emulsifier were mixed and emulsified at 60°C for 15 minutes to obtain an ASA emulsion. The pulp was bleached chemical softwood pulp with a freeness of 40°SR and a pulp concentration of 4.0%. The ASA emulsion was added to the pulp at an ASA addition rate of 0.6% of the oven-dry pulp mass, and the mixture was stirred for 3 minutes before direct papermaking. The papermaking pH was 7.0, and the drying temperature was 100°C.

[0038] Test results: ASA emulsion stability time was 3 hours; paper Cobb value was 28 g / m²; number of blue spots on the paper surface was 25 / m²; ASA retention rate was 72%.

[0039] The test results of the above embodiments were compared with those of the comparative examples, and the results are shown in Table 1 below.

[0040] Emulsion stability time (h) 10 9 11 3 Cobb value (g / m²) 22 24 20 28 Number of blue dots (dots / m²) 3 4 2 25

[0041] As shown in Table 1, compared with the traditional process (comparative example), the process of the present invention (Examples 1-3) extends the ASA emulsion stabilization time by about 3-4 times, reduces the number of blue spots on the paper by more than 80%, increases the sizing degree (Cobb value) by 12-29%, and increases the ASA retention rate by 19-25%. These data fully demonstrate the significant effect of the present invention in inhibiting ASA hydrolysis and reducing blue spots on the paper.

[0042] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] Obviously, the embodiments described above are merely some embodiments of the present invention, and not all embodiments. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features.

Claims

1. A papermaking process with low blue spot on the paper surface based on inhibiting the hydrolysis of ASA sizing agent, characterized in that, Includes the following steps: Step 1: Emulsification of ASA sizing agent: Mix the ASA sizing agent with the emulsifier and stabilizer, and emulsify at 50~70℃ for 10~20 min to obtain the ASA emulsion; add a pH adjuster to the ASA emulsion to adjust the pH value to 3.5~4.

5. Step 2: Slurry preparation: Beat the pulp to a freeness of 30-50°SR and adjust the pulp concentration to 3.0-5.0%. Add ASA emulsion to the pulp at a rate of 0.3-1.0% of the oven-dry pulp mass, and mix thoroughly for 2-5 minutes. Add a retention aid at a rate of 0.05-0.2% of the oven-dry pulp mass. Step 3: Papermaking: The sizing pulp is then used for papermaking, with the pH value controlled at 6.5~7.5 and the drying temperature at 90~110℃, to obtain sized paper.

2. The papermaking process according to claim 1, characterized in that, The emulsifier is a compound of cationic starch and surfactant, with a mass ratio of cationic starch to surfactant of (3-5):

1.

3. The papermaking process according to claim 2, characterized in that, The surfactant is selected from one or more of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyoxyethylene sorbitan monostearate.

4. The papermaking process according to claim 1, characterized in that, The stabilizer is a compound of citric acid and borax, with a mass ratio of citric acid to borax of (2-4):

1.

5. The papermaking process according to claim 1, characterized in that, The pH adjuster is one or more of citric acid, tartaric acid, and phosphoric acid.

6. The papermaking process according to claim 5, characterized in that, The pH adjuster is citric acid.

7. The papermaking process according to claim 1, characterized in that, The retention aid is a compound system of cationic polyacrylamide and bentonite.

8. The papermaking process according to claim 7, characterized in that, The amount of CPAM added is 0.03~0.1% of the oven-dried slurry mass, and the amount of bentonite added is 0.2~0.5% of the oven-dried slurry mass.

9. The papermaking process according to claim 1, characterized in that, The pulp is bleached chemical wood pulp, chemimechanical pulp, or a mixture thereof.

10. The papermaking process according to any one of claims 1 to 9, characterized in that, The stability time of the ASA emulsion is 8-12 hours, the Cobb value of the paper is 20-25 g / m², and the number of blue spots on the paper surface is less than 5 per m².