Is the packaging, PP woven bag waterproof? This is a question that many users and manufacturers are interested in.
If it's just woven PP, then no. The Woven PP mantle is made up of plastic that is spun and knitted. Since it's just knitting without bonding, the yarns in the middle will have gaps. Liquids can pass through these spaces, so PP woven fabrics are not water-resistant.
However, due to the special packaging requirements of the chemical, cement, fertilizer, and sugar industries... a large amount of PP woven bags need to be water-resistant. Currently, there are 2 types of PP woven packaging with water resistance on the market. One adds a waterproof lining on the inside, like a layer of HDPE bags. Another type is coated with a thin layer of plastic on the outside of the woven PP fabric.
How to prevent water from PP woven bags
With the first type, the requirements for equipment and methods are very simple. The investment capital is also not high and its application is also very wide. Inner and outer packaging are separate. The inside is usually a heat-cut plastic bag, like HDPE, or LDPE. Outer is a normal PP woven bag. The lining pocket is usually longer than the outer sheath. Therefore, when packing goods, the difference between the 2 layers easily causes the inner layer to be damaged.
PE lined PP bag
Previously, 2 layers of bags needed to be interlocked, and the loading mouth needed to be folded to sew. Therefore, productivity is very low, and human resources are wasted. A skilled worker can only finish about 1000 bags/day and can only sew about 300 bags/day. Currently, with automated lines, the cutting and stitching of bags are fully automatic. With increasingly perfect technology and techniques, production capacity is greatly enhanced.
BOPP laminated PP bags
With coated PP woven bags, a coating is required. This layer is from 0.02 to 0.04mm thick and covers the outer surface of the woven PP layer. Or, an extra layer of BOPP can be applied over the coating, increasing the water resistance even further. During coating, the temperature is up to 300°C. This temperature reduces the elasticity, and increases the brittleness of the PP layer, making the bag easily damaged when dropped from a height.