Are Woven Polypropylene Bags Waterproof?
Are pp woven bags waterproof? As far as the woven bag itself is concerned, because the woven bag is made of warp and weft tapes, there is only overlap between the tapes, which does not have sealing property. Therefore, the liquid will be left through the gap between the tapes, so the woven bag itself is not waterproof.
However, due to the special requirements of chemical industry, cement, chemical fertilizer, sugar and other industries for packaging, a considerable number of plastic woven bags must have the function of waterproof and sealing. At present, there are mainly two types of waterproof and sealed woven bags produced and applied in the market: one is the ordinary separate combined packaging bag with outer woven bag and inside liner inserted or stitched bag. The other is the composite woven bag coated with a layer of plastic film on the PP woven cloth, which will include two types also, either polypropylene coated woven bag or pp woven laminated bag.
The production equipment and process of the first kind of separated inner lining membrane woven bag are relatively simple, the equipment investment is low, and the application is very wide. The inner and outer bags are separated. The inner bag is blown film bag, which can be divided into LDPE and HDPE. The outer bag is ordinary PP woven bag, and the length and width of the inner bag are slightly larger than the outer bag. When loading materials, the inner and outer bags are uneven and easy to be damaged. In the early years, the inner and outer bags of the inner lining membrane bag and the outer bag need to be set together manually, and the inner and outer bags at the mouth of the bag need to be aligned and sewed, so the production efficiency is low, the waste of manpower is large, and the continuous and efficient production cannot be carried out. A skilled operator can only complete about 1000 bags by hand every day, and only about 300 bags can be sewn by hinge sewing machine every day. Nowadays, with the improvement of all-in-one machine, there are many machinery manufacturers in China that can produce all-in-one machines for bag cutting, sewing and lining. The technology has been widely used and tends to be mature, greatly improving the production efficiency.
Another kind of Coated plastic woven bag production must go through the coating process, using the extrusion coating machine to coat a layer of plastic film with a thickness of about 0.02 ~ 0.04mm on the outside of the woven pp cloth. Or at the same time, to use the coating material as the bonding medium, and then composite a layer of BOPP film on the surface, can achieve better waterproof effect, it was named BOPP pp woven laminated bag. When doing coating, the temperature of the extruded film is about 300 ℃, and the newly extruded film is combined with the braid by a pair of cooling rollers. However, such high temperature reduces the strength of the cloth surface, reduces the elasticity, increases the brittleness of the bag surface, and makes the bag easier to be damaged in the falling tests.
WHAT IS ARE VALVE BAGS?
Valve bags are packaging bags filled by machines. They come in plastic or paper. Here at Western Packaging, we are a wholesale manufacturer who offers the paper version, with many options. The three main things to consider are size, closure type, and coatings.
CHOOSE THE RIGHT SIZE
Paper valve bags come in a large range of sizes. We offer small to very large paper valve bags and multiple sizes in between. It is important to verify which sizes your valve bag machine handles.
DETERMINE WHICH TYPE OF CLOSURE YOU NEED
Once the size is determined, the type of closure is determined. All valve bags are automatically closed. The specific method of how this closing happens falls into three categories.
1. SELF- SEALING
The first and most common is self-sealing. These valve bags use the pressure of the contents to close and seal the bag.
2. HEAT SEALED
Alternatively, some bags can be sealed by heat. This may be a better option for the product and requires a machine and set up capable of this method.
3. ULTRASONIC SEALS
The third type of closure is much less common. Bags can be sealed ultrasonically. These valve bags are only used in very specific and limited industries. They require clean and sterile environments and very special machinery.
WHICH COATING IS BEST
Once the size and type of closure are decided, coatings in and on the bags is decided. The options are extensive. Western Packaging offers all the most common, and some uncommon, coatings available. The specific coating(s) depends on the product and the package’s method of storage, shipment, and display.
There is a large variety of coatings available. The coating options vary based on if the coating is going to be placed on the inside or outside of the bag. Some products may benefit from a coating on both.
THE DIFFERENCE BETWEEN INSIDE COATS
The inside coating is most important when the product contained in the bag is food or non-food products. In these situations, a food-safe coating must be applied to the inside of the bag. This coating helps ensure the contents remain safe for consumption, and also maintains the freshness. Interior coatings also help minimize moisture entering the product and/or keep the product from seeping out. These are very important features for many products.
Some outside coatings provide the same or similar benefits. Coatings can be applied to block moisture, block contamination of the interior from the outside, or make the bag easier to handle. While protection of the contents of the packaging is most important, ease of storage is also important. Outside coatings can be used to minimize friction when bags rub together and therefore help to minimize bag damage and loss of product. A simple coating can also help the filled bag maintain its shape.