[Abstract] The effects of preparation of composite special materials, LDPE and composite technology on the bonding strength were discussed. The experimental results show that adding 0.4% of molecular weight modifier at 240 °C for extrusion produces special composite materials with good performance. The addition of 25% to 30% LDPE in the material has the highest peel strength. The higher peel strength can be obtained by adjusting the bonding temperature, the bonding speed, and the gap length.
The paper-plastic compound bag is compounded with a PP woven fabric and a kraft paper, and is sealed in a tubular form by extrusion of the melt material, and is then closed. The price of PP woven fabrics is good for tear resistance, but it is widely used, but its strength is not high and it is not suitable for loading powdered materials. Kraft paper is non-toxic, easy to print, and has certain rigidity, but its mechanical strength is not high. The combination of PP woven cloth and kraft paper can exert the advantages of the two, and can produce composite bags with certain rigidity and moisture resistance.
The combination of PP woven fabric and kraft paper is the key to making high-quality packaging bags. The composite used EVA hot-melt extrusion or EVA float coating, but the price is high. At this stage, people generally use high-MI PP extrusion composites.
Many industries require the use of such paper-plastic composite bags, which has led to a surge in domestic demand. At home, hundreds of composite bag production lines have taken place in China. However, when using ordinary PP extrusion, the product quality is not high and the defects are numerous. In the work, we solved the compounding process of composite bags for a number of packaging bag manufacturers. This article summarizes the work, modified the composite PP powder, and discussed the optimization of the composite process.
1 Experimental part 1.1 The main raw material PP powder, MI7g/10min, Zhongtian Group's products; LDPE, 1C7A, Beijing Yanshan Petrochemical Company Chemical Plant 1 products; molecular weight regulator, industrial grade, commercially available; other additives are the city Sales of industrial grade.
1.2 Instrument and equipment RC-90 torque rheometer, Germany HAAKE company;
XRL-400 flow rate rate measuring instrument, Science and Education Instrument Factory of Jilin University;
LWX-10 micro-controlled electronic tensile testing machine, Guangzhou Experimental Instrument Factory;
S-90-150 type paper-plastic composite production line, Prachanda Plastic Machinery Factory.
1.3 Composite Process The PP powder and the added additives are well mixed. The HAAKE rheometer conical twin-screw extruder is extruded and modified at the set temperature and speed to determine the MI of the modified material. , select the optimized formula according to the standard. According to the optimized formulation and good material, after granulation on the German F2-125/1-25 unit, the composite product is tested according to the performance of the international test special material.
The prepared composite material was added to the LDPE extrusion line on the production line to test the strength, adjust the LDPE addition amount, and after adjustment, adjust the other process conditions.
2 Results and discussion 2.1 Preparation of composite special materials 2.1.1 Development of basic coating PP requires good fluidity, ie, large MI value, good film formation, ie, narrow molecular weight distribution. In the liquid phase bulk polymerization of propylene, the MI of the product can be controlled by adjusting the concentration of hydrogen in the polymerization tank. When the concentration of hydrogen is high, the molecular weight of PP is low and the flowability is good. However, the products of different batches have large fluctuations in MI and wide molecular weight distribution. This affects film formation and is not desirable.
Adding molecular weight modifiers to thermochemical degradation of high molecular weight PP, its high molecular weight level decomposition is far greater than the low molecular weight level, so that the molecular weight of the polymer decreases, the molecular weight distribution becomes significantly narrower, and the melt fluidity improves. The film-forming property becomes better and the adhesion with the substrate is improved.
2.1.2 Determination of the dosage of molecular weight modifier After selecting the molecular weight regulator, its amount directly affects the performance of the special material.
2.1.3 Determination of preparation temperature The process conditions that affect the performance of the composite during the modification are mainly the temperature and the extrusion rate, especially the extrusion temperature and the influence of the extrusion temperature on the MI.
With the increase of temperature, the half-life of the regulator decreases, the decomposition rate increases, and the degradation of the PP molecular chain, especially the macromolecular chain, increases, and the MI value increases. When the temperature is too low, the decomposition of the regulator is incomplete, affecting the compounding of the special material, so the temperature can not be too low; but if the temperature is too high, after the temperature exceeds 240°C, the decomposition temperature is too fast, easily causing cross-linking and easily causing discoloration. Therefore, the extrusion temperature is set to 240°C.
2.2 Effect of LDPE Content on Peel Strength When using PP extrusion melt coating, the coating is firm, brittle, and reduces the peel strength. It is best to use a flexible B-C random copolymer. Copolymers are not only expensive, but the choice of models is limited, so add the appropriate amount of LDPE in PP to improve the peel strength, feel and softness of the coating. The LDPE was blended with PP to form a standard spline at 310°C with a PP braided cloth and kraft paper, and its peel strength was tested.
2.3 The effect of composite process on peel strength The composite process includes composite temperature, composite speed and air gap length, all of which have a greater impact on the composite strength.
The composite temperature mainly affects the melt viscosity and surface oxidation. The higher the temperature, the lower the melt viscosity, the greater the surface oxidation, the more carbonyl groups are formed, and the easier it is to bond with the two, especially the kraft paper, so that the peel strength becomes higher. Big. However, if the temperature is too high, the PP braid will be blown. Therefore, the temperature is generally limited to the non-blown PP braid. In most cases, the temperature is less than 350°C.
The smaller the composite velocity, the greater the thickness of the composite layer, the longer time for the melt to stop in the air, the more oxidation, and the greater the adhesive strength. However, the compounding speed is too small, the production efficiency is low, the equipment utilization is low, and the production cost increases. When the peel strength is satisfied, the compounding speed is increased as much as possible, and the compounding speed is generally between 100 and 400 m/min.
The length of the air gap is the length of the bond between the extrusion die and the press roll and the cooling roll. The length of the air gap affects the residence time of the melt in the air and affects the degree of surface oxidation. The length of the air gap also affects the temperature of the bond point. As the air gap length increases, the surface layer of the solution increases in oxidation, but the sticking point temperature decreases, so the composite strength does not necessarily increase. However, the temperature can be increased at this time and the composite strength can be increased. However, if the air gap length is too large, the surface oxidation will be severe and the heat seal will be affected.
In fact, the interaction between the three described, increase the air gap length, can increase the compound temperature, increase the compound velocity; increase the compound velocity, can increase the temperature, reduce the air gap length. The best composite process can only be debugged for each device. Even for the same equipment, different climatic conditions, there are different optimal composite process parameters. Through the orthogonal test can get the process parameters suitable for the conditions at that time. Therefore, each manufacturer should conduct an orthogonal test on the above factors to determine the best process conditions.
Our compounded coating material was compounded on the equipment of Hubei Chusheng Paper & Plastic Packing Co., Ltd. After optimized debugging of the process, the composite strength reached 3.63N/25mm, exceeding the standard of 3.0N25mm, and the production effect was good. (Xu Heng Wu Youjun Chen Xuhuang) (Department of Chemical Engineering, Hubei Institute of Technology, Wuhan 430068, China)
Optimization of Composite Process of Paper-plastic Composite Packaging
December 20 08:08:26, 2023
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