How to make release paper​?

Release paper, an essential material in numerous industries, plays a pivotal role in facilitating the separation of adhered substances. Whether it's in the manufacturing of adhesives, labels, or composites, the proper production of release paper is crucial. The production of release paper is mainly divided into 5 steps: Base Paper Selection, Coating Preparation, Coating Application, Drying and Curing, and Inspection and Winding. Here's an in - depth look at the step - by - step process of creating this versatile product.

Step 1: Base Paper Selection​

The journey of making release paper begins with choosing the right base paper. High - quality kraft paper is a popular choice due to its strength and durability. Kraft paper is produced from wood pulp through a chemical pulping process called the kraft process. This process involves cooking the wood chips in a mixture of sodium hydroxide and sodium sulfide, which breaks down the lignin in the wood, leaving behind strong cellulose fibers.​

However, depending on the end - use requirements, other types of paper such as wood - free paper can also be utilized. Wood - free paper is made from chemical pulp that has been bleached to remove impurities, resulting in a smoother and more uniform surface. The base paper should have appropriate absorbency. If it's too absorbent, it may soak up too much of the coating material, affecting the release properties. On the other hand, if it has low absorbency, the coating may not adhere properly.​

Step 2: Coating Preparation​

The coating is the heart of release paper, and it is typically a silicone - based compound. Silicone polymers are the main ingredients, which provide the release functionality. These polymers are long - chain molecules with a backbone of silicon and oxygen atoms, giving them unique properties such as low surface energy, flexibility, and heat resistance.​

Solvents are added to the silicone polymers to adjust the viscosity of the coating mixture. This allows for easy application onto the base paper. Common solvents used include toluene, xylene, and various types of alcohols. Additives are also incorporated into the coating formulation. These additives can enhance different aspects of the coating. For example, adhesion promoters are used to improve the bond between the silicone coating and the base paper. Fillers may be added to increase the thickness and durability of the coating, while antioxidants can protect the silicone from degradation over time.​

Step 3: Coating Application​

There are several methods for applying the silicone coating onto the base paper. Roll coating is a widely used technique. In this process, the base paper is passed through a series of rollers. One of the rollers is coated with the silicone mixture, and as the paper moves, the coating is transferred onto the paper's surface. The pressure and speed of the rollers can be adjusted to control the thickness of the coating.​

Knife coating is another option. Here, a knife - like blade is used to spread the coating evenly across the surface of the moving base paper. The distance between the knife and the paper determines the thickness of the applied coating. Spraying is also employed in some cases, especially when a very thin and even coating is required. However, spraying can be more challenging to control in terms of coating thickness compared to roll or knife coating.​

Step 4: Drying and Curing​

After the coating has been applied, the paper needs to be dried to remove the solvents from the coating. This is usually done in a drying oven. The temperature and residence time in the oven are carefully controlled. If the temperature is too low, the solvents may not evaporate completely, affecting the curing process. On the other hand, if the temperature is too high, it may cause the coating to over - cure or even damage the base paper.​

Once dried, the coating needs to be cured. Curing is the process of cross - linking the silicone polymers to form a strong and stable release layer. There are different curing methods. Heat curing is a common approach, where the paper is exposed to a specific temperature for a set period. Ultraviolet (UV) curing is also increasingly popular. In UV curing, the coated paper is exposed to UV light, which activates photo - initiators in the coating, causing the silicone polymers to cross - link rapidly.​

Step 5: Inspection and Winding​

The final step in the production of release paper is inspection. Quality control inspectors check the paper for any defects. They look for uneven coating, bubbles, scratches, or any other imperfections that could affect the release properties. Automated inspection systems may also be used, which can detect even the smallest defects using cameras and image - processing software.​

Once the release paper passes the inspection, it is wound onto large rolls. The winding process needs to be done carefully to ensure that the paper is wound evenly and without any creases or wrinkles. The rolls are then packaged and prepared for distribution to various industries that rely on release paper for their manufacturing processes.

In conclusion, the production of release paper is a complex and precise process that requires careful selection of materials, accurate application of coatings, and strict quality control. By following these steps, manufacturers can produce high - quality release paper that meets the diverse needs of different industries.