Application in wet end of papermaking

Surfactants for sizing are important wet end chemicals that provide water resistance to paper and cardboard. They are mostly used for writing, printing, packaging, and construction paper and cardboard.

The main types of sizing agents are rosin based sizing agents and synthetic based sizing agents. The preparation of dispersed rosin size is a physical and chemical process, in which solid rosin absorbs heat and becomes liquid rosin. There is a great interfacial tension between rosin liquid and water, and reducing this interfacial tension can only be achieved by adding surfactants. Emulsifiers and dispersants for dispersing rosin gum are both surfactants. Choosing the right surfactant is the key to preparing dispersed rosin gum, and commonly used ones include anionic, cationic, and zwitterionic agents. The most commonly used emulsifier in China is anionic dispersed rosin gum, and the commonly used emulsifiers are polyoxyethylene type, such as fatty alcohol polyoxyethylene ether phosphate, sodium 2-hydroxy-3- (styrene glycol) acrylic sulfonate, sodium 2-hydroxy-3- (nonylphenoxy polyoxyethylene) acrylic sulfonate, etc. Some cationic emulsifiers such as cationic polyacrylamide, polyamide polyamide epichlorohydrin, and cationic starch are used to prepare cationic dispersed rosin size.

Synthetic sizing agents mainly include alkyl ketene dimer (AKD) and alkyl succinic anhydride (ASA). These two types of sizing agents are also known as reactive sizing agents because they contain active functional groups that can react with the hydroxyl groups of fibers and remain on the fibers. Due to their ability to accommodate high pH conditions (pH=7.5-8.5), this type of sizing agent is popular in the paper industry as it can use inexpensive calcium carbonate as a filler to improve the strength, whiteness, and papermaking performance of paper. Currently, over 50% of high-end paper in developed countries has achieved medium to alkaline papermaking. AKD and ASA are insoluble in water, and a stable AKD lotion can be prepared by using polyoxyethylene type non-ionic surfactant as emulsifier.

During the bleaching process of pulp treated with surfactants for resin control, residual resin will precipitate. If not separated in time, it will form viscous deposits that adhere to equipment, paper machine copper mesh, wool cloth, and drying cylinders, causing papermaking obstacles, affecting normal papermaking, and also causing paper diseases. In addition, with the widespread use of waste paper today, resin based substances such as adhesives, ink binders, and coating adhesives in waste paper can also create resin barriers that affect papermaking. Therefore, the research and development of resin barrier control agents have become increasingly important.

The commonly used resin barrier control agents include inorganic fillers (such as talc powder), fungicides, surfactants, chelating agents, cationic polymers, lipases, and membrane separation agents. The most commonly used surfactants are anionic surfactants, which are currently the most widely used surfactants, including higher alcohol sulfates, alkylbenzene sulfonic acids, and higher alcohols, phosphates, etc. Cationic surfactants are mainly alkyl amine salts or quaternary ammonium salts. Non ionic surfactants mainly include polyethylene glycol and polyols. In addition, there are also amphoteric surfactants and various multicomponent complexes. Stripping agent is also a resin control agent used to control the adhesion between the dryer and the paper sheet, lubricate the scraper and dryer, and control the distribution of adhesive. It mainly includes polyamide polymer lotion, such as polyvinyl alcohol lotion, mineral oil and surfactant matching platform spraying organic silicon lotion and polyamine polyamide cationic polymer.

Surfactant for defoaming

In the paper making process, the pulp contains a small amount of natural and artificially added foaming surfactants such as technical elements and fatty acids, as well as foam stabilizers such as synthetic polymers and starch. Therefore, foam will appear, causing problems such as paper breaking or holes on the paper. The main active components of defoamers used in paper making are high carbon alcohols, polyethers, fatty acid esters, organic silicon polymers, etc. They are generally prepared into water in oil lotion.

Softener for papermaking

Softness refers to the ability of surfactants to form hydrophobic groups on the surface of fibers and adsorb them in a reverse direction, reducing the dynamic and static friction coefficients of the fiber material, thereby achieving a smooth and soft feel. Sulfuric acid vinegar, sulfonated castor oil, and other anionic surfactants exhibit a softening effect when adsorbed on the surface of fibers.

The cationic groups in cationic surfactants can directly bond with negatively charged fibers, while hydrophobic groups form low-energy surfaces on the outside of the fibers, resulting in particularly good flexibility. Fatty acid bisamide epichlorohydrin is mainly used for paper with high flexibility requirements, such as toilet paper, wrinkle paper, sanitary napkins, handkerchiefs, napkins, etc.

Bipolar ionic surfactants have a wide range of applications. Their cationic groups can form a bond with fibers, while their anionic groups can bind with fibers through polyelectrolytes or aluminum ions in pulp. They can also cause hydrophobic groups to align outward, greatly reducing surface energy. Examples of such surfactants include 1 (. 9 'aminoethyl). 2. Seventeen alkyl imidazoline carboxylic acid derivatives. In addition, both cationic and amphoteric surfactants have antibacterial and bactericidal properties, which can effectively prevent paper from moldy.

Organosilicon surfactants belong to special surfactants, and cationic organosilicon quaternary ammonium salts are mainly used as softeners. There are also many other types of softeners, such as stearic acid polyoxyethylene ester, polyoxyethylene lanolin, emulsified wax, etc.

Softener for papermaking

Softness refers to the ability of surfactants to form hydrophobic groups on the surface of fibers and adsorb them in a reverse direction, reducing the dynamic and static friction coefficients of the fiber material, thereby achieving a smooth and soft feel. Sulfuric acid vinegar, sulfonated castor oil, and other anionic surfactants exhibit a softening effect when adsorbed on the surface of fibers.

The cationic groups in cationic surfactants can directly bond with negatively charged fibers, while hydrophobic groups form low-energy surfaces on the outside of the fibers, resulting in particularly good flexibility. Fatty acid bisamide epichlorohydrin is mainly used for paper with high flexibility requirements, such as toilet paper, wrinkle paper, sanitary napkins, handkerchiefs, napkins, etc.

Bipolar ionic surfactants have a wide range of applications. Their cationic groups can form a bond with fibers, while their anionic groups can bind with fibers through polyelectrolytes or aluminum ions in pulp. They can also cause hydrophobic groups to align outward, greatly reducing surface energy. Examples of such surfactants include 1 (. 9 'aminoethyl). 2. Seventeen alkyl imidazoline carboxylic acid derivatives. In addition, both cationic and amphoteric surfactants have antibacterial and bactericidal properties, which can effectively prevent paper from moldy.

Organosilicon surfactants belong to special surfactants, and cationic organosilicon quaternary ammonium salts are mainly used as softeners.

There are also many other types of softeners, such as stearic acid polyoxyethylene ester, polyoxyethylene lanolin, emulsified wax, etc.

Antistatic agent

In the production of special processed paper, sometimes anti-static problems may be encountered. Using surfactants to treat the liquid can produce a hydrophilic outer surface. That is, as an anti-static agent, the surfactant forms a positive adsorption on the surface of the material, forming a hydrophobic group on the material surface. Hydrophilic groups extend into space, increasing the ion conductivity and moisture absorption conductivity of fibers, resulting in discharge phenomena and a decrease in surface resistance, thereby preventing static electricity accumulation. Surfactants used as anti-static agents have large hydrophobic groups and strong hydrophilic groups. The cationic surfactants have the highest usage and best performance, followed by amphoteric surfactants.

Fiber dispersant

The main function of fiber dispersants is to reduce fiber flocculation and improve paper forming. Fiber dispersants can form a bilayer structure on the surface of fibers. The polar end of the outer dispersant has strong affinity with water, increasing the degree of wetting by water and repelling static electricity to achieve dispersion. Commonly used fiber dispersants include partially hydrolyzed polyacrylamide (PAM), polyethylene oxide (PlEO), etc. PEO has high viscosity, good water solubility, and good lubricity. Adding less than 0.05% to high-end toilet paper can achieve good dispersion effect.

Application of surface sizing and coating in papermaking

Surface sizing and coating both involve applying chemicals to the surface of paper, primarily to improve its surface properties, enhance its printing performance, and overall integrity. But there are many differences between the two, the main difference being that surface gluing often only uses adhesives, while coating uses both adhesives and pigments; The adhesive used for surface coating is pressed into the paper, while the pigment applied is applied to the surface of the paper.

Surfactants for surface sizing

According to the material, it can be divided into natural and modified products and synthetic products; According to the ionic property, it can be divided into anionic, cationic and non-ionic types; according to the product form, it can be divided into aqueous solution type and lotion type. The commonly used surface adhesives have hydrophobic and hydrophilic groups, so broadly speaking, they are all surfactants. The main surface sizing agents include modified starch, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and polyacrylamide (PAM). Different surface sizing agents can be selected according to different needs. For example: ① To improve water resistance, AKD, dispersed rosin, paraffin, chromium chloride stearate, styrene maleic anhydride copolymer, and other synthetic resin latex can be used; ② To improve oil resistance, organic fluorinated compounds such as perfluoroalkyl acrylate copolymers, perfluorooctanoic acid chromium complexes, perfluoroalkyl phosphates, etc. can be added Increase anti adhesion by adding silicone resin; ④ Improve printing performance, mainly using modified starch, CMC, PVA, etc Improve dry and wet strength by adding PAM modified starch, etc To improve printing glossiness, CMC, sodium alginate, and other materials are mainly used. In order to improve the surface sizing effect, it is common to use two or more sizing agents together, and the effect is very significant.

Coating surfactants

The composition of coatings for coating processing mainly includes adhesives, pigments, and other additives. The coating itself is a complex compound, and it varies depending on the specific paper requirements and formula composition. Surfactants play an important role in the formulation of paper coatings, mainly including coating dispersants, defoamers, lubricants, preservatives, anti-static agents, and synthetic latex.

Coating dispersant: It is the most important additive in coatings, most of which are surfactants. Its performance is to ① endow pigment particles with charges, causing them to generate repulsive forces with each other; ② Covering the surface of pigment particles, it acts as a protective colloid; ③ Form a high viscosity state around the particles to prevent multiple particles from aggregating. The earliest dispersants used were phosphates, polysilicates, diammonium hydrogen phosphate, the condensation product of benzenesulfonic acid and formaldehyde, casein, Arabic resin, etc. Sodium hexametaphosphate, sodium pyrophosphate, and sodium tetraphosphate are commonly used dispersants in low solid content coatings. In high solid content coatings, high molecular weight organic dispersants such as sodium polyacrylate solution, sodium polymethacrylate and its derivatives, disodium salt solution of diisobutylene maleic anhydride copolymer, as well as alkylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether are commonly used.

Defoamer: foam is often produced in the process of coating preparation and coating, and defoamer needs to be added. There are mainly higher alcohols, fatty acid esters, tributyl phosphate, tripropyl phosphate, etc.

Lubricant: In order to improve the fluidity and lubricity of paper coatings, enhance adhesion, give paper coatings smoothness and luster, increase plasticity, prevent cracking, and improve the printability of coated paper, lubricants can be added. The most widely used lubricants currently are water-soluble metal soap surfactants represented by calcium stearate, and sodium stearate water-soluble lubricants also have a significant effect. Paraffin hydrocarbons and fatty acid amines can also be used as lubricants.

Preservatives: Some natural adhesives are prone to degradation and mold growth, so anti-corrosion spines should be added to paper coatings. Quaternary ammonium cationic surfactants, fluorinated cyclic compounds, organic bromine and sulfur compounds, N - (2-benzimidazolyl) carbamate (carbendazim), etc. have been widely used in paper coatings.

Antistatic agent: By adding octadecyltrimethylammonium fluoride, polyoxyethylene sorbitan ester, alkylphenol polyoxyethylene ether phosphate, polystyrene sulfonate, etc. to the coating formula, paper can be endowed with anti-static properties.

Synthetic latex: Synthetic latex is an important coating adhesive. In the preparation process of synthetic latex, surfactants play an important role as emulsifiers, dispersants, stabilizers, etc.
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