What is rosin sizing agent?
Rosin sizing agent is a kind of papermaking auxiliary agent. Sizing agent is an additive for papermaking. It can give paper and paperboard anti-ink, water resistance, emulsion resistance, corrosion resistance and other properties to improve its smoothness, strength and service life. It can be divided into internal sizing agent and surface sizing agent. Internal sizing agent is added to the pulp, which can delay the penetration of liquid in the paper and paperboard. Surface sizing agent generally uses anionic polymer substances and is applied to the surface of paper or paperboard after the paper sheet is formed.
Internal sizing agent is divided into acidic sizing agent and neutral sizing agent. Acidic sizing agents mainly include white rosin sizing agent, high free rosin sizing agent, reinforced rosin sizing agent and brown rosin sizing agent. Neutral sizing agents include rosin sizing agent, synthetic sizing agent and polymer sizing agent.
Rosin is a natural resin collected or extracted from pine trees. The main components are rosin acid, dehydrorosin acid, neorosin acid, isopimaric acid, isorosin acid, etc., which are divided into glue rosin, wood rosin and tall oil rosin due to different collection methods. Sizing agent rosin is a solid obtained by distilling rosin and removing turpentine. It generally contains 80-90% rosin acid and its molecular formula is C19H29COOH. It has a saponification value of 160-180 mg KOH. The unsaponifiable matter content is ≤9%, the volatile matter is ≤0.5%, and the softening point is 73~78℃. 4-5 grade rosin is orange-yellow and transparent, and is most suitable for papermaking industry as a sizing agent. Rosin sizing agent is a pulp sizing agent that can be made into acid sizing agent and neutral sizing agent.
Paper sizing method and the role of sizing agent
Paper fiber has a strong hydrophilic tendency because it contains a large number of hydroxyl groups and can form hydrogen bonds with water. When a paper sheet is saturated with water, it will lose most of its strength. This is suitable for toilet paper and corrugated paper, but it is not necessary for most papers, such as office paper, food boxes, cosmetic boxes, grocery bags, etc. Sizing in the papermaking process is a method to improve the paper sheet’s resistance to water and liquid penetration and prevent the diffusion and penetration of water-based liquids.
There are two methods for sizing paper. One is to add the sizing agent to the pulp before the paper sheet is formed (during pulping or mixing), which is called internal sizing. The other is to apply the sizing agent to the surface of paper or paperboard after the paper sheet is formed, which is called surface sizing. Except for blotting paper, filter paper, wax paper, cigarette paper, and household paper, almost all papers need sizing. Sizing paper can improve the paper’s water resistance, oil resistance, and printing ink resistance, and at the same time improve the paper’s smoothness, hydrophobicity, and printing adaptability.
Internal sizing agent
It is a sizing agent used for internal sizing. It can be used to treat pulp, paper, and paperboard. It is a chemical added to achieve the combination with the paper web during the paper sheet forming process to obtain the performance of fluid resistance. This type of chemical is required to have hydrophilic groups and hydrophobic groups in the molecular structure, and have low surface tension, so that the droplet has a larger contact angle with the fiber surface, thereby increasing the ability of the paper to resist liquid wetting and penetration. The formed precipitate should be fully dispersed, evenly distributed, and have a large coverage area. The particles of the sizing material should be firmly attached to the surface of the fiber to obtain a stable specific surface free energy, giving the paper hydrophobicity and resistance to fluid penetration. Internal sizing agents mainly include rosin sizing agents, paraffin sizing agents, synthetic sizing agents, and polymer sizing agents.
Rosin sizing agent
It is a type of internal sizing agent, which is divided into acidic and neutral sizing agents.
(1) Acidic rosin sizing agent; Commonly used acidic rosin sizing agents include white rosin glue, high free rosin glue and reinforced rosin glue. They need alum as a precipitant. The pH value of the first two sizing agents is 4.0~5.5, and the pH value of reinforced rosin glue is 4.0~4.5. These sizing agents are not good for paper whiteness, whiteness stability, strength and durability. Calcium carbonate filler cannot be used and they are corrosive to equipment. The main varieties are:
White rosin glue: a white sizing material containing 20~30% free rosin. It is made of rosin after incomplete saponification and then emulsification. The general dosage is 1.5~2.0%. Carboxymethyl cellulose is used as a stabilizer, synergist and retention agent. All of them can improve the sizing effect;
High free rosin glue: a dispersed rosin glue containing 70~90% free rosin. Casein or soy protein is used as a stabilizer. The sizing effect is not affected by temperature and water quality. The dosage is 0.2~0.4%, which is suitable for occasions with high drying temperature;
Reinforced rosin glue: contains 20~25% free rosin, made by alkali saponification of maleic rosin or fumaric rosin (made by Diels-Alder reaction of rosin and maleic acid and fumaric acid respectively) and natural rosin, and a small amount of paraffin is added. They are collectively called maleic reinforced rosin glue and fumaric reinforced rosin glue. Because its particles are smaller than white rosin glue, it can also be used with white rosin glue to improve the sizing effect. It has high softening point, high acid value, high saponification value, and strong antioxidant stability. As a papermaking sizing agent, it has low dosage and good sizing effect;
Brown rosin glue: It is a completely saponified rosin glue with poor sizing effect and is close to being eliminated.
(2) Types of neutral rosin sizing agents include:
Anionic dispersed rosin glue (DR) is a negatively charged, milky white and fluorescent emulsion. Using polymerized alumina (PAC) as a precipitant can improve the sizing effect.
Cationic dispersed rosin glue is a self-retaining sizing agent, containing nearly 100% free rosin. The suitable sizing pH range is 6-8. The glue dosage is lower than DR. It has all the advantages of neutral sizing agents and is the most promising rosin sizing agent.
Aluminum-tall oil rosin glue: It is a dispersion of reinforced tall oil rosin and aluminum compounds in water, containing about 22% rosin. Alumina can be used without sizing. The applicable pH range is 4-8.5. It cannot be used with DR and is sensitive to shear force.
