Agentes de colación del papel: procesos de fabricación, campos de aplicación, seguridad y almacenamiento

1. Introduction: The Complete Lifecycle of Sizing Agents

Paper sizing agents are essential chemical additives that transform porous cellulose fiber networks into functional materials with controlled liquid resistance, strength, and printability. Understanding the complete lifecycle of these chemicals—from their synthesis and manufacturing to their application, safe handling, and storage—is essential for papermakers seeking to optimize performance, reduce costs, and ensure operational reliability.

This article provides a comprehensive technical overview of the manufacturing processes for major sizing agent types, their application fields, safety considerations, and storage and transportation requirements. From cationic and anionic rosin sizes to AKD and styrene-maleic anhydride surface sizing agents, each product category presents unique manufacturing challenges and handling requirements.

LY Chem Technology Co., Ltd. , with over two decades of experience in paper chemicals manufacturing, offers a comprehensive range of sizing solutions—including LY-CRS and LY-ARS rosin-based sizes, LY-AKD301 and LY-AKD302 AKD sizing agents, and LY-BB201 styrene-acrylate surface sizing agent. Our products are manufactured under ISO 9001 quality management and are subject to rigorous quality control at every stage of production.

2. Manufacturing Processes for Major Sizing Agent Types

2.1 Cationic Sizing Agents

Cationic sizing agents are manufactured through a multi-step synthetic process that yields products with positive surface charge—enhancing their affinity for negatively charged cellulose fibers.

The synthesis begins with the copolymerization of α-olefins with maleic anhydride. The resulting copolymer is then subjected to imidization—reacting it with a polyamine that contains at least one tertiary amino group and one primary amino group. Finally, the imide-amine intermediate undergoes quaternization with epichlorohydrin in the presence of water.

The cationic charge imparted through this process is critical for sizing performance. When added to the papermaking system, the positively charged sizing agent particles are attracted to the negatively charged cellulose fibers, ensuring efficient retention and uniform distribution throughout the sheet.

2.2 Lignin-Rosin Sizing Agents

Lignin-rosin sizing agents represent a sustainable approach to sizing agent manufacturing, utilizing lignin—a natural polymer abundant in plant biomass—as a modifying agent.

The preparation method involves dissolving lignin and rosin in anhydrous ethanol at a mass ratio of 1:0.25–4, followed by stirring and drying to obtain a powder product. This approach not only simplifies the preparation process but also improves paper strength properties. Studies have demonstrated that lignin-modified rosin sizing agents display outstanding sizing performance and desirable stability, with great potential for applications in liquid packaging board.

This manufacturing method addresses the lignin heterogeneity issue through a green integrated ethanol fractionation strategy, representing a sustainable and valorized approach to applying lignin biomass.

2.3 Anionic Rosin Sizing Agents

Anionic rosin sizing agents are produced using self-made anionic acrylic copolymers to emulsify rosin. The optimal rosin-to-emulsifier mass ratio is 1:1.

This high-dispersion rosin sizing agent can be used as a neutral sizing agent in pulp. The anionic acrylic copolymer emulsification process yields a rosin latex emulsion with smaller particle size, contributing to enhanced stability and performance.

Conventional anionic rosin emulsions are typically dispersed and stabilized with anionic surfactants. Anionic rosin emulsions can be added to anionic size-press starch solutions, while cationic rosin emulsions are compatible with cationic starch solutions.

2.4 AKD (Alkyl Ketene Dimer)

AKD is a reactive sizing agent that forms covalent bonds with cellulose fibers. The conventional manufacturing method for AKD uses triethylamine as an acid-binding agent to facilitate the self-polymerization of fatty acid chlorides, forming ring-structured alkyl ketene dimers.

Solvent-free AKD synthesis has emerged as the mainstream direction. In this process, tertiary amine and fatty acid chloride are used as raw materials. The tertiary amine is heated to 30–90°C, and the fatty acid chloride is slowly added under stirring.

A specific example is derived from the dimerization of the ketene of stearic acid, which is generated by pyrolysis of stearoyl chloride. This solvent-free approach eliminates organic solvents from production, addressing concerns about solvent residues and environmental impact. It also avoids the high energy consumption associated with the distillation method for recovering excess tertiary amine.

2.5 Styrene-Maleic Anhydride (SMA) Surface Sizing Agents

SMA surface sizing agents are synthetic polymers commonly used in surface sizing applications. These resins are anionic and are compatible with most anionic and nonionic size press additives. They should be used in starch at pH values of 7.0–9.5.

In application, SMA is typically compounded with starch. A commercially available sodium salt of styrene maleic acid copolymer (SMA) is added to aqueous starch solutions. The sizing effect is obtained immediately upon application and drying, and drying temperature is not critical for sizing development.

Research has shown that SMA imide methyl chloride quaternary salt significantly improves the sizing efficiency of starch-based surface size compared to starch alone.

3. Application Fields

3.1 The Fundamental Purpose of Sizing

The basic purpose of paper sizing agents is to impart water resistance to paper, enabling it to resist penetration by ink, oil, water, and other liquids. This fundamental property is essential for nearly all paper grades—from writing and printing papers to packaging materials.

3.2 Rosin-Based Sizing Agents

Traditional rosin-based sizing agents—including tall oil rosin, extracted rosin, and gum rosin—remain commonly used sizing materials, with an application history spanning nearly 170 years.

Rosin sizing is typically applied under acidic conditions maintained with alum (aluminum sulfate). While cost-effective, rosin systems impose limitations including paper yellowing, equipment corrosion, and inability to use calcium carbonate fillers. Despite these drawbacks, rosin remains a viable option for many paper grades due to its low cost and proven performance.

3.3 AKD Sizing Agents

AKD, first developed by Hercules Inc. in 1956 and introduced to China in the late 1980s, has been widely applied in the sizing processes of high-grade cultural paper, specialty food packaging paper, and building materials coatings.

AKD can be used with various pulp types, including wood pulp and reed pulp, to produce various kinds of cultural paper, paper board, newsprint, food wrappers, fruit bag paper, and other wrappers requiring sizing.

Key application areas include:

• Cultural paper: Copy paper, writing paper, and high-quality printing paper where crisp text and vibrant images are essential
• Packaging paper: Enhancing durability and resistance to moisture and other liquids
• Food packaging: Providing water resistance for food-grade packaging applications
• Paperboard: Improving strength and barrier properties

The sizing mechanism of AKD involves the esterification reaction between the reactive groups in AKD molecules and the hydroxyl groups of cellulose fibers, forming a stable hydrophobic film on the fiber surface.

3.4 Surface Sizing Agents

Surface sizing agents are applied to the surface of already-formed paper to enhance water resistance, surface strength, printability, and appearance. Common synthetic surface sizing agents include copolymers of styrene and maleic anhydride (SMA), copolymers of styrene and acrylic acid (SAA), copolymers of styrene and acrylate (SAE), water-soluble polyurethane (PUD), AKD, and polyvinyl alcohol (PVA).

4. Safety Information

4.1 AKD Safety Profile

AKD is available in various forms including white flakes, blocks, or colorless transparent liquid. For qualified products, the iodine value is not less than 45 ± 1 g(I₂)/100g, the acid value is ≤ 5.5–10 mg KOH/g, and the melting point typically ranges from 51–55°C.

As a commercial emulsion, AKD typically has a solids content of 7.5%–12%, a pH value between 3.4 and 4.5, and good water solubility.

4.2 Handling Precautions

While AKD has a favorable toxicological profile with very low acute toxicity (oral LD₅₀ > 40,000 mg/kg in rats), standard industrial hygiene practices should be observed when handling all sizing agents:

• Avoid prolonged skin contact
• Use appropriate personal protective equipment (gloves, safety glasses)
• Ensure adequate ventilation in handling areas
• In case of spills, contain and clean up promptly
• Dispose of waste in accordance with local environmental regulations

4.3 Solvent Residue Considerations

Traditional solvent-based AKD synthesis uses toluene as a solvent—a substance identified by the World Health Organization as a suspected carcinogen. When toluene is used in production, there is a risk of solvent residue remaining in the final product.

Solvent-free AKD synthesis eliminates this risk, yielding products free from toluene and other harmful solvent residues. This is particularly important for papermakers serving the food packaging sector, where regulatory compliance is paramount.

LY Chem’s commitment: Our AKD products are manufactured using advanced solvent-free processes, ensuring that they are free from toluene and other harmful residues. This makes them suitable for the most demanding applications, including food-contact papers.

5. Storage and Transportation

5.1 AKD Powder Storage

AKD powder (AKD wax) is typically packaged in plastic woven bags lined with plastic, with a net weight of 25 kg per bag.

Storage requirements:

• Store in a dry and cool place
• Temperature should not exceed 35°C
• Bags should be placed with the bottom raised 10 cm or more above the floor to avoid moisture
• Protect from moisture and fire
• Shelf life: 8 months from the date of production

5.2 AKD Emulsion Storage

Liquid AKD emulsions require more careful storage conditions. Commercial AKD dispersions are sufficiently stable to permit transportation, storage, and usage. In order to maximize shelf life and sizing efficiency, the dispersions should be kept at low temperatures, without being allowed to freeze.

Storage requirements for AKD emulsions:

• Store in the shade at 4–30°C
• Avoid freezing and exposure to direct sunlight
• Storage period: typically 3 months
• Products usually have a shelf life of at least one month at room temperature

As emulsions age, some loss in efficiency can occur at high temperatures or during prolonged storage. Storing the product as cool as possible without freezing ensures the highest efficiency.

5.3 Transportation Guidelines

For AKD powder:

• Transport in plastic woven bags lined with plastic
• Avoid exposure to sunlight and rain during transportation
• Handle with care to prevent damage to packaging
• Avoid stress and impact during loading and unloading

For AKD emulsions:

• Use 200 kg or 1000 kg plastic barrels
• Take care to prevent packaging and containers from being damaged, avoiding leakage
• Protect from freezing and excessive heat during transit

5.4 Surface Sizing Agent Storage

Some surface sizing agent products are also designed with good storage stability. For optimal performance, follow manufacturer-specific storage recommendations and use product within the specified shelf life.

5.5 Best Practices for Inventory Management

1. Implement FIFO (first-in, first-out) rotation to ensure older product is used before newer production
2. Monitor storage temperatures daily—especially during summer months
3. Never store near heat sources or in direct sunlight
4. Inspect incoming shipments for signs of damage, leakage, or temperature excursions
5. Document receipt dates and calculate remaining shelf life upon arrival

6. Conclusion: Managing the Complete Product Lifecycle

The performance of paper sizing agents depends not only on their chemical composition but also on the quality of manufacturing, the appropriateness of the application, and the care taken in storage and transportation. From the synthesis of cationic and anionic rosin sizes to the solvent-free production of AKD and the compounding of SMA surface sizing agents, each manufacturing process presents unique challenges and quality control requirements.

Key takeaways for papermakers and chemical buyers:

• Manufacturing quality matters: Understanding the synthesis process helps in evaluating product quality and consistency
• Application determines selection: Different paper grades and performance requirements call for different sizing agent types
• Safety is paramount: Solvent-free manufacturing eliminates residue risks for food-contact applications
• Storage conditions affect performance: Temperature control is critical for preserving AKD emulsion stability
• Proper handling extends shelf life: Following storage and transportation guidelines maximizes product value

LY Chem Technology Co., Ltd. , with over two decades of experience in paper chemicals manufacturing, offers a comprehensive range of sizing solutions manufactured to the highest quality standards:

• LY-CRS (Cationic Highly Dispersed Rosin Size): Lower aluminum sulfate consumption, near-neutral sizing for food-grade applications
• LY-ARS (Anionic Highly Dispersed Rosin Size): Tolerant of high-hardness white water, complete replacement for traditional saponified rosin size
• LY-AKD301 (Internal AKD Sizing Agent): Superior water resistance and aging resistance for cultural paper, coated paper, and packaging base paper
• LY-AKD302 (Surface AKD Sizing Agent): Enhanced ring crush strength and burst strength for corrugating medium and linerboard
• LY-BB201 (Styrene-Acrylate Surface Sizing Agent): Cationic emulsion that partially replaces internal sizing while improving ring crush strength and water resistance

Our solvent-free manufacturing processes ensure product purity, while our rigorous quality control and packaging standards guarantee that products arrive at your facility in optimal condition.

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For more information about LY Chem’s sizing solutions and our complete range of papermaking chemicals, please contact our technical sales team.

References

1. U.S. Patent 4,839,415 – Paper sizing agents, the manufacture and use of same
2. Lignin fractionation towards improved rosin emulsification behavior and advanced liquid packaging board sizing performance – ScienceDirect, 2023
3. 阴离子松香施胶剂的制备及性能 – Chinese Journal, 2019
4. Solvent-free method for preparing alkyl ketene dimer – Chinese Patent, 2017
5. Styrene maleic anhydride resins for paper sizing – TAPPI, 1994
6. AKD wax storage and handling specifications – Industry sources
7. AKD emulsion storage and transportation guidelines – TradeKorea