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Technical characteristics of multilayer co extrusion blown film production equipment

2021-03-27 8

In the global plastic packaging film market, the proportion of multi-layer co extrusion film with nylon is increasing. Nowadays, the consumption of nylon in Europe, America and Japan is increasing by more than 10% every year, and in China, the consumption of nylon increases by 30% every year. However, nylon accounts for only 10% - 15% of the components of multi-layer high barrier packaging film. It can be seen that the use of this kind of packaging film is increasing in daily life, and It will also be more popular, which can extend the shelf life of various foods by more than twice. The production of high-grade plastic packaging film industry is of great potential in the present and the next ten years.

The film blowing unit is mainly composed of several parts, such as extruder, head, air ring internal cooling, traction and winding. A set of high quality film blowing unit requires defects that cannot be found in the whole process from extrusion to winding. If there is any problem in the design principle and manufacturing quality of any link, the quality of products produced will be reduced a lot, which affects the use and the sales This problem should be paid attention to.

From the current situation of China's film blowing machine manufacturing, it can be seen that low technology content is a major problem. The technical level of the film blowing machine directly affects the quality of products. This is why many powerful manufacturers can not buy advanced equipment abroad, but the high equipment price increases the production cost and has affected the competitiveness in the market. According to the technical difficulty and importance, some developed countries in Europe and America put the technology of machine head and winding in the first place, and also strive to improve the blowing process to improve the quality of products. However, China and other countries have great differences in national conditions. Too many projects will increase the production cost, but the quality of products will not be improved In addition, we should make necessary improvements to China's national conditions, and at the same time ensure that the cost will be gradually reduced and the sales will be expanded.

Characteristics of the technology of 2-layer co extrusion film blowing

Many technologies in the multi-layer co extrusion membrane unit have been well applied and developed in China. For example, extruder technology has fully met the requirements according to the current situation in China. People have invested a lot in it and achieved gratifying results. In the industry, people call it the host, while the rest is called auxiliary machine. It is the improvement of these auxiliary technology, which is greatly improved The quality of the products is improved.

(1) At present, many Chinese insiders know that there are many kinds of multi-layer co extrusion heads, and there are many domestic literature. However, due to the limitations of the region, the contents written are not detailed and accurate. This paper introduces a multi channel plane superposition head.

The picture shows a five layer co extrusion double flow plane superposition head, which is made of disc shaped sheet superposition. Each layer of disc has two feeding ports, which can extrude two layers of film, so that each layer of plate is heated evenly and the plasticizing performance is effectively improved. Therefore, the film blown by the five layer co extrusion stack head can achieve ten layers of effect, and the error of product thickness is within 5%. The heat insulation layer is added between the disc and the disc, which can control the temperature of each machine head separately. The difference between adjacent layers can be as high as 80 ℃. According to different production requirements. It can be removed, increased or rearranged to reduce the cost. The whole machine head is made of 38crmoaia material, which has good thermal stability. After special heat treatment process and internal electroplating polishing, the strength of film is guaranteed, raw materials are saved, and plasticization performance is improved and product quality is improved. The results show that the strength of the multi-layer co extrusion film is 30% higher than that of the same kind of composite film. Under the same strength, the material of the film is more than 20% less than that of the same kind of composite film.

Compared with the conical stack head, under the same conditions, the plane superposition head is compact, and its actual height is only 60% of the conical stack head, which improves the effective height of the tower. In the seven and nine layer co extrusion film blowing unit, this head has an absolute advantage;

As insiders know, in the multi-layer co extrusion film blowing process, the plasticizing temperature of LDPE and PA is very different. Only the head can be produced independently. The surface of the conical stack head can be heated independently, but the detailed analysis is not proper. It can be seen from the profile that the cylinder part of LDPE and PA is relatively independent, but the conical part has been inserted into another layer In the cylinder, the heat conduction of metal will interfere with each other in the long-term production process. Only by increasing the insulation layer can the temperature difference between the two adjacent materials be ensured. This design idea is very obvious in plane superposition head.

Because the plane superposition machine head adopts side feeding, the turning point of the runner in the head is small, there is no dead point, and there will never be paste phenomenon when the machine is shut down and started frequently. Especially when blowing nylon, its superiority is incomparable. The design theory of this head has exceeded the traditional idea and is a leap in theory.

(2) Automatic coiler

There are two kinds of coiler in nominal classification, one is surface friction type winding machine and the other is rotary central winding machine. For different varieties, there are also surface friction coiler with central auxiliary curling, clearance surface friction coiler, central coiler with surface friction assistant, clearance type center position coiler, etc.

This kind of winder is widely used in the market, its technical points are tension control and film flattening. Flattening technology is very important in the winding. A reasonable flattening mechanism can even make up for some defects in the unit. It is necessary to point out that the function range of the flattening mechanism is limited, and the film will return to the state before flattening. Therefore, the idea of setting up leveling device between upper and lower traction is wrong, which not only increases the cost, but also can make up for some defects in the unit The film is damaged and has not worked at last, and this mechanism can only be used before the curling roll. At present, it is unreasonable to set up the flattening mechanism on the domestic winding machine without exception. The technical point of the flattening mechanism is the angle of the film, the position of the mechanism and the curvature of the bending. However, the bending diameter of the film has a great influence on the flattening effect. The smaller the bending diameter, the better the flattening effect will be. When the thickness and the number of layers of the film increase and pass through When rubbing or folding, the flattening mechanism can be removed.

The tension control requirements are related to the thickness, number of layers and the diameter of the film. Due to the improvement of mechanization level, the diameter of full roll in Europe and America is generally 1200mm. With the improvement of tension control theory, several companies have also rolled to 1500 mm in diameter. When the diameter of single film is less than 1000mm, constant tension control is generally adopted. For single or multi-layer curling with too large diameter, curve tension control should be adopted. The tension size varies with the diameter. The sensitivity of tension control mechanism should be higher, and vice versa. When the thickness and number of layers of film increase and pass the edge or fold, the surface friction winding machine must be equipped with central auxiliary crimping mechanism.

This is a surface friction winding machine with central auxiliary crimping used for the curling of the canopy film and geomembrane. First of all, it is clear that the requirements of the retractor on the accuracy and sensitivity of tension control are not high. However, the tension of this film is still very large when curling, sometimes it is large enough to slip. Here, the friction coil is the main one, and the center roll plays an auxiliary role. It is only in the middle The torque of the core coil is not enough to roll up such a large film coil, only to tighten the core function to ensure the perfect film roll. In the same way, the central winding machine with surface friction assistance is mainly centered winding, and the surface friction winding is assisted by increasing power.

This kind of winder is mainly used in the situation of small film thickness and small winding diameter. It is the largest full roll diameter not more than 400mm. Besides flattening and tension control, a rubber roller is also required to lean on the film roll. Therefore, in most cases, its winding effect is better than friction type winding machine. It is important to note that in the thin film such as cigarette film, each roll must have power to prevent the film from being scratched. (Figure 5) the picture on the right is such a winder. The domestic eight roll friction coiling used for crimping the film can not be used for winding and packing film.

(3) Improvement of blowing film technology

Blowing process mainly refers to some main steps in film blowing production, such as extrusion, molding, cooling, traction and winding. Their main purpose is to ensure the quality and output of products. When it comes to production, it is an important factor to reduce production cost. There are many factors affecting the production. However, it is easy to increase extrusion and improve the traction speed. The main purpose is to ensure the quality and output of products The factors to be considered are the design and processing level of the machine head. The multi-layer plane superposition machine head mentioned in this paper can increase the quality naturally because of the double extrusion layer, the heat absorption area is large and the plasticizing effect is good, and the quality will be improved naturally. With the increase of cooling technology, the output can be increased by 50%.

The so-called cooling technology will remind people of the wind ring, internal cooling and chiller. This is already a common technology. People think that these technologies can improve the production. However, there are not many people who use it to improve the quality. In North America, the cooling technology is mainly used to improve the quality. They use glycol refrigeration units to replace the chillers, and propose the export of air ring and internal cooling The temperature should reach 50 ℃, the purpose is to improve the cooling and crystallization speed, so as to improve the transparency, strength and toughness of the products, that is to say, to improve the economic benefits. In the cooling mode, the effect of water cooling is the best. However, from the perspective of hygiene, medical film and food packaging film are not allowed to use water cooling. Even the cold water roller in the flow is not available. Because of the difference between indoor air and cooling water temperature, the surface condensation water vapor of cooling roller will not meet the hygiene requirements. Therefore, it can be seen that the production workshop of products must also Meet these health requirements.

Because the plane superposition head feeds from the side, the head cannot rotate. Therefore, the upper traction rotation is adopted. The upper traction rotation is also divided into several types in the world. Although the shape is different, it is reliable to work. Due to the influence of the rotation principle, the film will produce periodic offset. If the cutting is not carried out during winding, the electronic deviation correction device shall be added.

North America also has an infrared thickness measurement technology, which can improve the uniformity of film by local heating of machine head. It is called that the thickness error of products can be controlled within 3.5%. For this technology, we should dialectically see whether, first, under the comprehensive influence of equipment and environment, can we produce products with an error of less than 3.5%? In addition, in order to ensure 5% error On the poor basis, how necessary is it in the consumer market to increase the equipment by 100000 dollars to achieve such a result? This is all the problems users should consider. Obviously, in the packaging film market, high-grade and high-quality products must be produced with high-tech and high-quality equipment. The development of products should be market-oriented, and the performance price ratio of equipment should be improved.

Application and development trend of film blowing technology

By improving the technology level of extrusion, molding, cooling, traction and winding of film blowing machine, we have produced high-quality multilayer co extrusion film, which is applied in all walks of life, such as infusion bags for hospitals and packaging bags for various food. In short, the production of high-strength, high barrier and high transparency packaging film has become an obvious trend. Under this premise, the quality and quality can be improved and the quality is reduced Low cost is the main task. With the market requirements and the continuous improvement of blowing technology, the number of CO extrusion layers will be more. However, in China, the specification of packaging film blowing equipment will be developing towards miniaturization.

From the influence of blowing technology on the quality of products, small size multi-layer co extrusion film blowing equipment has many advantages. First, the film quality is good; the film here refers to the high-grade film such as infusion film and high resistance diaphragm. The product produced by small size co extrusion equipment has moderate bubble diameter. The cooling effect of the cold air from the refrigeration unit is the best in this specification. Moreover, the film with smaller bending diameter is the best in both traction, rotation and winding, and the surface quality of the finished product is the best, and wrinkles are not easy to appear. Second, the performance price ratio is high; small-scale equipment is not small. The production of this five-layer plane superposition head is very large. Through the transformation of the mouth mold, small-scale film can be produced. While improving the quality, the output is also 1.5 times of other similar equipment. It has the advantages of low price, low energy consumption, high production efficiency, small rack height, low workshop height, and sanitation The living environment is well controlled and can be accepted by more users. It can be calculated by cost analysis that if the output of products produced by two small equipment is the same as that of one large equipment, the total cost of such two small equipment is less than one large equipment, and the quality of products produced by small equipment is higher than that of large equipment. Third, it is suitable for the process of cutting, and it has many parts, which will have an impact on the winding effect. At the same time, the equipment can not produce small-size barrel packaging film, such as heavy packaging bag. The small machine can blow any specification, cylinder type and split cutting packaging film within the range of 0-800mm. Without modifying any equipment configuration, it can produce the most products and meet the diversified requirements of the market. Most importantly, under this specification and cost, the products have the advantages of quality and price, and are invincible in the market competition.