Three-layer co-extruded heavy packaging film production line passed Guangdong provincial appraisal

The M3B-900QA three-layer co-extruded heavy-packaging film production line developed by a plastics equipment company in Guangdong Province, China, has been installed, commissioned, and tested by users for continuous operation. The operation is stable and the performance is good. The film products are clearly stratified without mixing. Uniform thickness, physical and mechanical properties (including tensile strength at break, tear strength, dart drop impact strength, etc.) are good, high yield, low energy consumption, and user satisfaction. The production line passed the appraisal of scientific and technological achievements organized by the Science and Technology Department of Guangdong Province recently. The appraisal committee-considers that the production line is the first in the country and the technology level is at the leading position in China.

With the continuous development of China's economy, the demand for blown film for heavy bags has been increasing in various industries, and the scope of application has been continuously expanding. Especially in the past two years, the production scale of plastic synthetic resin production equipment has been continuously expanded, and the production capacity has been greatly improved. However, the traditional composite woven bags must be blown through plastic film, drawing, plastic coating (laminating), printing, slitting, A series of complicated processes, such as sealing and bag-making, has low production capacity. At the same time, due to the low strength of traditional composite woven bags, poor barrier capability to moisture, and the possibility of damage to packaging products, it cannot meet the need for large-scale production and packaging of synthetic resins. In order to meet the needs of large-scale production of synthetic resin automatic packaging lines for high-speed filling, large-scale storage, transportation, and automatic palletizing, China has begun to introduce a multi-step process that can realize continuous automatic molding—opening filling—heat sealing and so on. The new heavy-duty packaging film product during the operation process not only greatly improves the packaging efficiency, but also the simplification of the bag making process. It only requires co-extrusion blow molding, (online or off-line) printing, and sealing and bag-making, which also greatly reduces the overall packaging cost. , And it is suitable for the packaging of synthetic resin such as PA, EVOH, PVA, PET, etc. with strict water content control. At the same time, as the raw materials for heavy packaging films are mainly low-melt-index LDPE, LLDPE, MLLDPE, and MDPE, it is easy to recycle and recycle the raw materials. The recycled waste materials can maintain good mechanical properties through secondary granulation and can be processed more importantly. The plastic products meet the requirements of environmental protection and full use of resources, and have higher comprehensive performance in packaging, storage, transportation, moisture protection and external viewing, and have become common repacking materials in developed countries such as Europe. Large petrochemical companies also all require the adoption of this new packaging method. This new type of heavy packaging material can not only meet the needs of modernized packaging of petrochemical industry products, but also has broad prospects for the promotion of packaging of rice, soybeans and other agricultural and sideline products, pesticides, fertilizers, and daily products.

The main structure of the machine

M3B-900QA three-layer co-extruded heavy-packaging film production line is mainly composed of two parts, one part is blown film line, mainly consists of automatic metering system, three single-screw extruders, hydraulic screen changing device, three-layer co-extrusion head, and cooling. System, rotary traction system, thickness inspection system, winder and electrical control system; the other part is printing line, mainly consists of unwinding machine, corona treater, four-color double-sided printing unit, embossing inserting unit and Winder and other components. After the various raw materials and additives are measured, they are automatically added to the hopper at a set ratio, and are melted in an extruder. The extruded molten resin enters a ring die to form a membrane tube and is extruded from the cooling air duct in the center of the die. In air, the membrane tube is inflated to a design-oriented tubular film (referred to as a bubble). After being cooled by the internal and external air, it enters the herringbone ply to fold the film bubble, and the folded film is led by the film rotary traction device to the winder through the idle guide roller, and the rolled film is loaded into the unwinding of the printing line. Machine unwinding, corona treatment, and then printed, embossed, folded, rolled packaging factory.

The main technical parameters:
The maximum width of the product (folding diameter): 750mm
Product thickness: 0.15～0.25mm
Maximum output: 180kg/h
Product thickness uniformity ≤±6%
Product width error ≤ ± 5mm
Product Structure: A/B/C (25%/50%/25%)
Insert depth: (45-110mm) ± 5mm
Blown film highest mechanical line speed: 45m/min
Printing, embossing and edging machine line speed: 50m/min
The largest closing and unwinding diameter: 11500mm
Printing device color group: 4 groups (can be any combination)

4, the main raw material and product structure raw materials: blown film grade LDPE, LLDPE, MLLDPE, MDPE and processing aids.
Product Structure: A/B/C(1/2/1)

Key technologies

1. Raw material extrusion system for heavy packaging film

(1) In the past, manual weighing and mixed feeding methods were poorly equipped and unevenly mixed. Now applying a multi-component automatic weighing feeding system not only solves the above problems, but also plays an important role in ensuring the longitudinal quality of the film. Its working principle is to transfer raw materials to each gravity hopper through vacuum and adopt the principle of weight reduction to determine the feeding amount of various components. The system calculates and controls the speed of the extrusion screw by comparing the measured feed quantity with the target value set by the process. When the amount of extrusion is changed due to a production target or process, the system recalculates the feed rate percentage at the same time to ensure the amount of feed.

(2) The resin used for heavy packaging film has a lower melt index and usually requires the addition of various modifiers such as slip agents, barrier agents, antistatic agents, etc. These resins are generally used in the screw processing process due to the long The time withstands higher shearing and the material temperature keeps rising, which can easily lead to overheated decomposition of the extruded material. In order to solve this difficulty, the use of a suitable barrier section and a decentralized mixing design not only ensures sufficient shearing of the two types of resin, but also allows the melt temperature to be controlled.

(3) The traditional three-layer co-extrusion contact head generally adopts the lateral feeding structure, and the processing equipment is simple, so the thickness uniformity of the product cannot be ensured, and the dead-end flow path structure is adopted; the size of the flow passage hole and the distribution of the shooting hole The clearances of the runners are all accurately calculated and simulated by computer. The die head adopts advanced processing equipment to process, and the gap between the layers is ensured from the processing technology; at the same time, the surface of the flow channel also achieves high processing quality, ensuring the smooth and smooth flow channel. In addition, the die material is made of imported alloy steel, which guarantees the processing quality and service performance. The heating element is made of ceramic, so that the die is heated fully and evenly, which is beneficial to the plasticization of the material flow.

2. cooling system

Due to the thicker film thickness of the heavy packaging, between 0.15 ~ 0.25mm, much thicker than the ordinary packaging film, how to effectively solve the film cooling is the key to the success of the project, general packaging film equipment using ordinary cooling air ring and Room temperature air cooling is difficult to meet the molding requirements. This machine has effectively solved this problem from four aspects.

(1) The double-nozzle negative pressure air ring is mainly composed of a plenum, two independent upper and lower air outlets, and a group of adjustable wind protection rings. The air outlet is pre-cooled to pre-cool the badly extruded tube, eliminate the vacuum of the die, and form an air cushion layer where the bubble is not attached to the air ring wall, so that the molten steel tube is initially blown and cooled when it is initially stretched. It has a large amount of air, rapid cooling of the bubble, and plays the role of supporting care bubble. There is no small hole in the windshield, and the negative pressure creates a third cooling, making the bubble more stable and the cooling effect better.

(2) The IBC bubble internal cooling system is an important component for the production of multi-layer coextrusion barriers and other functional films. Therefore, we directly apply the very mature IBC bubble internal cooling technology to the project to achieve continuous The hot air discharges and takes away the gaseous molecular substances generated by the heating of the plastics while blowing in the same amount of cold air, controlling the internal temperature rise of the bubble film and rapid cooling of the bubble film, increasing the film yield, transparency, physical and mechanical properties, and purifying the bubble film. Internal air, improve the surface hygienic indicators and other purposes.

(3) The three-roller traction device effectively cools the film by using cooling water to cool the roller, which greatly improves the speed of molding.

(4) The system also uses cooling air instead of conventional room temperature air to cool the inside and outside of the film. The refrigeration system is mainly composed of a chiller, a cooling tower, an air heat exchanger, etc. The air of the blower receives the refrigerated air via the heat exchanger, the temperature is generally about 15° C., and is equipped with the wind pressure and temperature display.

3. Horizontal film rotary traction system

Adopt the new advanced horizontal film rotary traction technology. The system adopts fan gear drive, air cushion roller, rubber spiral tension flattening roller and other structures. The rotating herringbone device is made of anti-adhesive sprayed aluminum alloy balance rolling roller and refined red wood bar double layer adjustable structure. In different temperature conditions and friction coefficient pigment film production; the first and second traction devices use speed and tension mode for automatic control, to maintain the smooth operation of the film membrane. The horizontal film rotation traction system slowly spreads the thin and thin points of the film to the various positions on the film roll with a ±360* rotation angle. The resulting film surface is flat and the film roll circle accuracy High quality and good appearance.

4. Double ultrasonic centering correcting device

Due to the oscillating structure of the rotating traction system, the film will have a certain deviation from the center of the film path during the movement. In order to make the end surface of the film roll neat, a film correction device is used to correct the film path of the film. Due to the conventional structure of the thin film photoelectric correction device, a slight wrinkle of the thin film may occur during the correction process, which affects the quality of the thin film. In order to ensure the effective rectification of high-definition film products, today's foreign advanced double ultrasonic centering device correcting film, to achieve the end of the film neat, thin surface smooth, avoid wrinkles, to ensure product quality.

5. Winder

At present, the domestic and packaging plastic film blow molding equipment is basically a manually operated film winder, and the technology is very backward. In order to achieve a certain degree of automation and advanced level of the machine, the winder has independent research and development, and has a film tension control, double-cut double film, on-line trimming and slitting, automatic length measurement, automatic tracking, high-speed "flying knife "Automatic film breaking, automatic roll change, automatic roll unloading and other functions, to achieve the purpose of ensuring the quality of film products rolling. In addition, due to the fact that the thickness of the heavy packaging film is much thicker than other packaging films, the rewinding film of the same length will be nearly double the diameter of the other packaging film. To solve this problem, the winder is designed. At the time, we fully considered the need for large winding diameters.

6. Multi-color printing unit

Ordinary gravure printing machines can only realize single-sided printing, and gravure printing must be equipped with a variety of printing rollers in the case of a large number of printing types, that is, occupying space and increasing costs. This machine uses a satellite flexographic printing machine, which features the entire roll printing to change the printing length without changing the rollers and gears, truly realizes universal size printing and bag making, and has the characteristics of stable printing, high yield, accurate printing, and clear character diagrams. And high production efficiency, a process of double-sided printing, the production cost is low, easy to operate and so on.

7. Embossing machine

In order to meet the needs of large-scale production, the surface of the film for heavy packaging bags is required to have a rough pattern, which can not only make the stacking layer of the packaged goods more convenient and convenient for transportation, but also save the storage area. Embossing machines are designed to meet this need. The pressure roller is arranged inside and outside the bubble, and the roller surface of the internal pressure roller has a protrusion. The external pressure roller presses the film surface through the adjustment of the cylinder and the hand wheel, so that the film surface produces a rough pattern from the inside to the outside. At the same time, the position of embossing can also be adjusted by the guide roller bracket.

8, the production process of heavy packaging film

Because the heavy-duty film requires high strength, barrier properties, cold resistance, and facilitates subsequent sealing, heat sealing, cooling, and stacking, etc. of the packaging machine, it is necessary to add slip agent, opening agent, barrier agent, and antistatic agent during processing. Agents and other modifiers, in addition to special environmental factors such as severe cold, high temperature or strong ultraviolet region need to add specific additives. Therefore, in the process of blowing, according to different process recipes, various tests have been performed to solve the various requirements for heavy packaging film. At the same time, in order to facilitate the process adjustment and the monitoring of the technical state of the extrusion process, high temperature melt pressure and melt temperature sensors are required before and after the screen changing device.

9, electric control