Introduction to Non-Woven Bag Manufacturing
Finishing Treatments: There are two possible treatments to be applied to the composite web; these are wet treatment and dry treatment. Wet treatment includes the method of producing slurry where the polymer is in the state of a sol. To simplify, a slurry is made and then this is manufactured into a composite web by removing the excess solvent and then drying it. The dry treatment method is simply taking the composite web and simply fusing the fibers by heating them to a temperature akin to the melting point to produce a web.
Composite web formation: Composite web formation is essentially producing PP fibers from the PP polymer solution or chips. Here, three methods can be applied. PP non-woven spunbond: The chips are melted at 230-240°C and extruded through the die by air at a set temperature. High tensile molecular orientation causes the polymer to crystallize and form a filament. These filaments are drawn (stretched in the machine direction) and immediately cooled by air. Finally, they are rolled onto their intended product. PP non-woven melt blown: This is a high-tech method which involves the use of an extruder that will melt the polymer which is then extruded through a set of spinneret nozzles, the temperature and pressure from this process results in a stream of ‘melt’ which is then blown by hot air onto a cooler belt. The random cross laid and overlapping of the filament is then bonded (with heat, chemical or mechanical treatment) to produce a web.
Making slurry: In the procedure of making slurry, the polymer material is dissolved in an excess volume of solvent and stirred with a magnetic stirrer for a suitable time. The polymer here forms a sol. Then it is precipitated in a precipitating bath to form a gel. This gel is rinsed several times and filtered to remove the solvent, then the gel is broken into chips. These chips are then drained and dried to make slurry.
The term “non-woven” first came into use in the 1940s, describing a complex and relatively new manufacturing process in the industry. When produced, these bags can a lower environmental impact than those made from other materials. Non-woven polypropylene is a fabric-like material created from spunbond polypropylene, a byproduct of crude oil refining. The production process involves melting the polypropylene and extruding it to produce long continuous fibers. These fibers are then air-cooled and bonded together through chemical, heat, or mechanical means to form a web. The key steps in the manufacturing process include creating a slurry, forming a composite web, and applying finishing treatments. This detailed process results in a versatile material ideally suited for various applications, including environmentally friendly non-woven bags.
Technological Advancements in Non-Woven Bag Production
In the past two decades, technology in non-woven plants has changed dramatically. The industry has changed from one of producing mainly needlepunched fabrics for relatively low-value added products to one where staple and filament spinning techniques are now being used. The need for sophisticated webs has led to developments in alternative reinforcement techniques (adding strength to the web using fewer raw materials) and more uniform methods of laying down the fibers. This, in turn, demands higher precision in web formation. Many non-woven bag companies are new to the non-woven industry, typically being plastic film or textile manufacturers. As such, many overseas machinery suppliers see the non-woven company as an opportunity for them to gain a footing in the market. The result has been the introduction of a wealth of new processing to an industry that has, for too long, been stagnant. In most cases where technology has been introduced, it has been to add value to the end product in some way. Some large retailers have color requirements for their bags, which has led to the purchase of printing machines and inks to add logos to the bags.
Innovation is most evident in Asia, where there is a demand for higher quality products and tighter environmental and toxicology controls. One Chinese company has designed an entire production line with the end product being a bag made from a single fabric, as opposed to the industry standard method of heat sealing cut-offs from other products or using the bag as a dustbin for offcuts. This has been achieved by producing machinery for PP and PET staple fiber needlepunching to make the fabrics. Digital printing machines show great promise for adding intricate multicolored designs to bags with the added bonus of no ink wastage and lower use of toxicology as opposed to traditionally printed laminated PP bags. Many companies seeking differentiation of their products are now able to source these bags at a cost not significantly higher than normal laminated bags, giving the industry scope in the future to upgrade the majority of bags from single-layer spunbond.
Improved Efficiency through Advanced Manufacturing Techniques
Improved efficiency and productivity are the essence of success in the organization. Efficiency in the conventional bag manufacturing process is hampered mostly due to thread cutting and stitching process. Material losses during the process of thread cutting and final product cutting are substantial. Typically, material loss is about 8-10%. Losses are during the cutting process and 2-3% loss is during the stitching process. Stitching process typically has a productivity rate of 800 stitches/min using 8 operators stitching for 8 hours results in 25,000 stitches on bags sewn per day, convert into 900 bags of 28 kg each. To increase the stitching productivity and reduce the material losses, Ultrasonic sewing and cutting technology is introduced. Ultrasonic sewing efficiently fuses the fabric together without the need for thread and creates a clean sealed edge that resists fraying. Ultrasonic sewing has a productivity rate of 200-1200 stitches/min using 2-4 operators stitching for 8 hours results in 25,000 stitches/bags sewn per day. Material losses during the ultrasonic cutting process are marginal about 1-2%. Analysis shows that ultrasonic stitching and cutting process has a 5-10 times faster productivity rate than conventional sewing process.
In a product, the first prototype step involved electro-punching needle technology for embossing, hole punching, and cutting the fabric (right to left) into bag pattern. This process has a 30% faster productivity than normal needle punching and hole punching scanner methods. Electro punching has no needle and only utilizes electricity and nylon rivet to melt and form the hole or cut the fabric. No fraying will occur around the hole pattern, and the edge of the pattern will be clean. This increase in the quality of the hole and pattern of the material and a reduction of the electricity to produce the same pattern led us to choose this method. During the assembly process, a sewing robot was introduced to increase the productivity of sewing bag patterns. A typical sewing machine has a sewing speed of 2500 stitches/min, comparing to the sewing robot productivity rate of 1800 stitches/min. 5-10 times trials of bag patterns showed a 20-30% faster productivity to sew the same bag pattern. Only 2 prototypes were made for the sewing robot and the plan was to increase robot productivity to match the sewing robot before full-scale production of the bag pattern.
Enhancing Quality in Non-Woven Bag Manufacturing
One of the most important aspects of a product is its visual appeal to the consumer. An excellent way to improve the look of a non-woven bag is to eliminate the needle holes that are produced during lamination. According to the traditional Newlong method, bags pass through about 2.5 sets of needle boards, each of which contains about 500 needles per square meter. With the trend in modern machinery to continuously increase production rates, there needs to be a way for these needle boards to be completely eliminated. One method to do this is to use a hot air gun to puncture holes in a pattern and fuse the layers together simultaneously. This is an overall cost-effective method, but the best results will be achieved with laser hole punching. Laser punching is a very impressive technology that will produce holes without producing any dust, and an automatic system will align the fabric before punching. Unfortunately, the machinery used for laser punching is very expensive, so this technology remains only as a brilliant idea at this stage.
A two-step welding process can be used to increase the strength of the bags. The bags are folded and the edges are welded with an ultrasonic welder to form handles. The handles are then cut and hole punched. This creates weak spots along the edge of the handle. However, if the bags are passed through a second time and the handle region is folded again and welded with an ultrasonic welder, this will bind the layers together and get rid of the weak spot. This technique can also be used to convert die cut loop handle bags to heat seal handle bags. A similar process can be used to bind the edges of D-Cut and T-shirt bags and prevent elongation of the cut portion. This technique can also be used on rice bags to prevent elongation of the handle and seam at the bottom of the bag.
Future Prospects and Innovations in the Industry
In the post-MFA era, there is a significant change to the non-woven industry in China. While some manufacturers have gone out of business, others have found that the removal of MFA has allowed them to make more profit by remaining in the industry and filling the supply chain gaps. Not surprisingly, many have turned to exports in order to mitigate costs and remain competitive. It is likely that China’s exports will continue to increase despite the actions of other countries. Conversely, the developing economies of other ASCM nations now possess a comparative advantage in the production of non-woven products due to the more cost-effective methods of production. This can be expected to result in growth of the non-woven industries in countries where one never previously existed.
Product innovation and evolution play crucial roles in shaping the future prospects of the non-woven industry. Recent paradigm shifts in development have enabled the production of more intricate staple fibers, significantly enhancing the capabilities of non-woven materials. As discussed in section 2, this advancement allows various non-wovens to exhibit characteristics similar to those of their woven counterparts, a very cost-effective method. For example, spun lace fabrics designed for the medical industry by non-woven bags manufacturers feature intricate patterns that traditional SMS fabrics could not achieve. Additionally, heightened environmental awareness has prompted many companies, including non-woven bags manufacturers, to develop greener non-woven products. This trend is expected to grow as energy costs rise and governments worldwide continue to implement environmental regulations. However, these regulations can also pose potential setbacks, often acting as technical barriers to trade and thus hindering the increased competitiveness of ASCM nations. This dual impact highlights the complex challenges and opportunities facing non-woven bags manufacturers in today’s market.