What is PVC knife coated tarpaulin?

PVC knife coated tarpaulin is also known as raincloth or thatch, which is a kind of waterproof material with high-strength polyester mesh as the base cloth. It is made by coating polyester canvas with polyvinyl chloride (PVC) paste resin and adding various chemical additives such as speed booster, mildew inhibitor, antioxidant and antistatic agent, etc., and then plasticized at high temperature.

The base fabric is the "skeleton" of the tarpaulin, which directly determines the tensile strength and tear resistance of the product. Generally, base cloth of PVC tarpaulin are high-strength polyester cloth with different mesh counts. There are woven fabric and knitted fabric for base cloth. Knitted base fabric are usually used for inflated tarpaulin, while woven fabric are suitable for other usage tarpaulin. The weaving method is mostly plain or twill to ensure that the strength of the base cloth is balanced in the warp and weft directions. The density should be controlled to avoid too sparse, resulting in excessive coating penetration, or too dense, affecting the adhesion of the coating. And the base fabric will be pretreated including cleaning and heat setting to ensure the PVC painting can firmly adhered on it.

PVC coating is the core of tarpaulin waterproofing, weathering and corrosion resistance, the slurry needs to be accurately proportioned according to the performance requirements, the main ingredients include: PVC resin powder and other auxiliaries paintings, such as plasticiser, colorant and calcium carbonate powder. Put PVC resin powder, plasticizer, stabilizer, etc. into the high-speed mixer according to the proportion (rotational speed of 800-1200r/min), heating to 80-100 ℃ and stirring for 30 minutes, so that the resin is fully dissolved. The final slurry needs to control the viscosity. Too thin is easy to penetrate the base cloth, while too thick is easy to appear bubbles in the coating. Jinze only use brand-new raw materials. Compared with products from other factories, they are more durable.

"Knife coating" is the key to the making process of PVC knife coated tarpaulin. The thickness of the coating is precisely controlled by the scraper, which is different from the dipping and spraying process, and realizes a more homogeneous coating and a tighter bonding with the base fabric. 

1. The base cloth enters the coating machine through the guide roller, and first passes through the tension roller to keep flat. The tension was controlled between 50 to 80N to avoid stretching deformation.

2. The surface of the base cloth evenly spread PVC painting, the upper scraper which is made of wear-resistant alloy steel and the base cloth to maintain a fixed gap. The gap is set by the thickness of the product demand. In this step, excess PVC painting is scraped to form a uniform coating.

3. If thick coating is required, it should be divided into 2-3 coats. The first thin coating (0.3-0.5mm), and then the second layer after plasticizing, to avoid internal air bubbles caused by a single over-thick coating.

4. Plasticizing and baking: In order to make the coating "one" with the base fabric, the coated base fabric needs to be plasticized at high temperatures to melt and cross-link the PVC slurry, forming a continuous film and firmly bonding it to the base fabric. Incomplete plasticization will lead to brittle coating, poor water resistance; excessive plasticization, PVC decomposition, odor and easy to aging.

5. Cooling and Shaping: To fix tarpaulin’s dimensions and properties, the plasticized tarpaulin needs to be cooled down immediately to set the shape. The PVC knife coated tarpaulin is cooled by 3-5 sets of cooling rollers, which rapidly cools it down to below 50°C by heat exchange; This step can avoid wrinkles on the surface of the coating and at the same time to enhance the bonding between the base fabric and the coating.

After all these making steps, we still need do the post-processing step to optimize the PVC tarpaulin’s  details and appearance. Trim the PVC tarpaulin hairy edges on both sides with a round knife to ensure a neat width. Jinze can custom various width according to customer requirements. Popular width are 2-5m.