This article is going to introduce the details of production process of plastic weaving, especially of Polypropylene woven fabric, pp woven bags and relative packaging products producing.
Process characteristics and control mode of polypropylene fabric weaving and bags making devices.
The plastic weaving device is composed of multiple equipment and processes, with simple process flow, easy control of process parameters, easy operation, high production efficiency, stable and reliable work, convenient, simple and safe operation and maintenance. Devices are used in different steps of plastic woven products manufacturing. The production process of plastic woven products is mainly divided into plastic granulation, flat wire drawing, circular weaving, coating / lamination, printing, cutting, sewing and packaging.
1. Polypropylene granulation
Polypropylene powder, various additives and activated calcium carbonate are poured into the high-speed mixer according to a certain proportion and sequence. After mixing from low speed to high speed for a certain time, they are put into the hopper and transported through the feeding screw, so that the materials enter the barrel from the feeding port. After melting and plasticizing of the barrel and screw, the strips are continuously and stably extruded. The strips are cooled and shaped by the water tank, and then hygroscopic by the hygroscopic fan Cooling by fan. The strips are cut by the granulator, screened by the vibrating screen, transported by the conveying fan to the fluidized bed for boiling drying treatment, and then into the material pool. Then the material in the material pool is sucked into the storage tank by the feeder. After the particles pass the inspection, the whole production process is completed by quantitative packaging.
2. Polypropylene drawing process
After the raw material Polypropylene and additives enters into the extruder, it is heated at 190-250 ℃ and sheared by the screw and barrel. After plasticization, the material is extruded at constant pressure. After forming the film head, the molten film enters into the cooling water. After cooling, the film is cut into embryo wires by the blade. The embryo filament is stretched to form flat filament in the oven with high temperature. Then the flat filament is heat set on the hot roller, shrinks at low traction speed, and is treated by the cold roller at low temperature. Finally, the flat filament is wound and formed by the disk differential tension winding system. It comes the polypropylene narrow tapes, that’s the base structure of pp woven fabric and pp woven sacks.
Main technological indexes of plastic flat yarn (Tapes) production.
The technological indexes of flat yarn production are mainly divided into four categories:
1. Physical and chemical modification index. It mainly includes blending modification, blending ratio, adding ratio of functional additives and blending ratio of recycled materials.
2. Physical property and rheological index. It mainly includes draft ratio, inflation ratio and retraction ratio;
3. Mechanical performance index. It mainly includes breaking force, relative breaking force, elongation at break, linear velocity and linear density deviation;
4. Tolerance dimension index. It mainly includes the thickness and width of flat filament ( yarn).
3. Circular weaving process
First of all, the warp is drawn out from the bottom of each row of spindles on the warp frame. The porcelain hole of the warp frame is the first long vertical plate, the thread pressing rod, the diameter feeding guide rod, the wire guiding rod, the second long vertical plate, the wire guiding rod, the magnetic hole, the tension rod, the brown wire, the round steel buckle, the warp fixing ring and the reserved cloth base. The weft yarn is loaded into the shed, the machine is started, the shuttle is driven by the shuttle pushing device to make the shuttle move in a circle, and the cylinder plain fabric is woven under the close cooperation of the warp supply system and the shuttle pushing device. The woven fabric is pulled upward by the traction device on the top of the loom. After passing through the guide roller, it is wound by the winding device behind the warp frame. When the winding diameter reaches about 0.8m, it is unloaded and sent to the next process.
Main process index of plastic circular woven fabric.
1. Weaving density.
Weaving density refers to the number of warp and weft yarns in a 100 mm × 100 mm braid. The national standard specifies the weaving density as well as the density tolerance. The weaving density mainly depends on the application of the PP Woven bags and some are purely up to the customers. The density of commonly used woven fabric is 36 × 36 pieces / 10cm, 40 × 40 pieces/10 cm, 48 × 48 / 10 cm. (Some countries are using mesh density per square inch, like 7×7, 10×10, 14×14 etc.)
2. Tensile strength of woven fabric.
Tensile strength is also called tensile capacity, tensile force. For pp woven fabric, it bears tensile strength in warp and weft directions, so it is called warp tensile strength or weft tensile strength also.
3. Weight per unit area of pp woven fabric.
The weight per unit area of woven fabric is expressed by gram weight per square meter, which is an important technical index of woven fabric. Gram weight per square meter mainly depends on the density of warp and weft and the thickness of flat yarn. Gram weight per square meter affects the tensile strength and load capacity of woven fabric. PP woven bags manufacturers control their costs of material by adjusting the g/m2 of the pp woven fabric what they are using.
The width of various woven fabrics directly affects the bag making process. For tubular fabrics, the width is expressed by warping, which is equal to half of the circumference. Width also involves the shrinkage rate. After cutting, printing and sewing, the width of the bag is slightly smaller than that of the cloth width which just been woven, which we call it width retraction.
5. Touching of PP woven fabric.
Pure PP woven fabric is thicker, crisp and coarser. HDPE flat yarn knitted fabric is softer, lubricated and not dense. Adding calcium masterbatch to Polypropylene material will make the fabric crisper, and by adding a certain percentage of HDPE to PP will make it the woven fabric softer. The fabric which was woven by narrow tapes would be softer, and the ones which was woven by wider tapes, would be coarser. To overlap the tapes in rules when weaving will comes out anti-slip surface pp woven fabric.
4. Post processing of Woven fabric / Woven bags
There are many kinds of techniques to make the original woven fabric into various woven products. It can be said that each kind of woven product has its own production process. The types are roughly the same, and the processes may be roughly the same or completely different.
(1) PP Woven bags ( Uncoated)
Its production process is: the original tubular PP woven fabric is processed into woven bag through printing, cutting, sewing and other steps. According to the different equipment applied, it can be cut before printing, or printed before cutting. The most advanced automatic cutting and sewing machine what Mornpackaging have now can continuously finish job of printing, cutting, sewing, gusseting, liner inserting processes all in one device only. For some particular applications, the pp woven bags can be made with valve or with block bottom as well. For single layer flat woven fabric, it can be made into bags also by bonding the middle seam.
The technological indexes of PP woven bag making mainly include the appearance tolerance, the breaking force in the direction of seam bottom and seam edge, the clarity of printing ink, the cleanliness of other parts after printing, the accuracy of layout position, the stitch, the stitch distance, and the defects of stitching off and thread breaking standard.
(2) Coated / Laminated PP woven bags.
Production method of 2-in-1 or 3-in-1 laminated woven bags are to compound the film or paper onto PP woven fabric. The obtained tubular cloth or sheet cloth can be cut, printed, sewn and made into ordinary sewing bag, and can also be punched, folded, cut, printed and sewed into cement bag. The obtained sheet cloth can be sewed, printed, cut, pasted and made into block bottom bag. It can also be welded, rolled and made into tarpaulin and geotextile.
The key process of coated or laminated material is lamination. Instead of using glue, this coating or lamination process take melt Polypropylene and Polyethylene resin as adhesive material. 2-in-1 are just to coat the pp woven fabric with melt lamination resin, 3-in-1 are using another layer of film or paper onto the pp woven material during the process of coating. For those bag requires multi colors designs printed which flexo printing could not meet the requirements, Bopp laminated bags will be an excellent choice, to print the designs onto the Bopp film by gravure printing machines, then laminate the printed Bopp film onto the base pp woven fabric.
(3) Various types of pp woven fabrics.
Mornpackaging are exporting original pp woven tubular fabric without any after-treatments in rolls to worldwide customers, buyers import the rolls as raw material for bags making and do post processes in their own country. Also, for single layer pp woven fabric sheet, it can be used as Tarpaulins, geotextile, mattress covers and so on.
Processing flow chart for Polypropylene Woven sacks manufacturing:
5. Manufacturing process of PE Liners
The extruder heats the polyethylene material (HDPE / LDPE) and extrudes it stably after melting and plasticizing. The cylindrical film is extruded by the die and inflated by compressed air to form a tube bubble. The cooling air ring is cooled and fixed, then pulled into the herringbone plywood to fold, and then it is transferred to the winding roller through the traction roller and transmission roller. Finally, the cutting and heat closing process is carried out to complete the production of the inner liner, and finally liner being inserted or sewn in the PP woven bag or FIBC.
6. About Recycled Polypropylene Material
It may take decades for polypropylene to degrade, and countless polypropylene woven bags are consumed in industry and agriculture every year, in order to protect the human environment and reduce the production cost to a certain extent, the recycling of polypropylene woven bags is full of value. After the used polypropylene woven bag is recycled and cleaned, it can be made into usable plastic particles again by recycling granulation process, and then mixed with new polypropylene particles according to a certain proportion to produce a more low-cost woven bag product, which is suitable for the product packaging with not particularly high hygiene requirements. So it goes back and forth.