For decades, traditional large infusion glass bottles will be replaced by new PP plastic infusion bottles. PP plastic infusion bottles have the unparalleled advantages of glass bottles: First, impact resistance, not easy to damage; Second, lighter weight, can significantly reduce transport costs; Third, a molding, will not produce secondary pollution; Fourth, no Poison does not cause side effects to the human body; - The fifth is the low manufacturing cost, which is calculated as a single bottle, which is only about 40% of the cost of the glass bottle. In addition, the disposable plastic bottles of high quality and low price omits the cleaning and disinfection process, and at the same time, the related energy is saved, and a considerable part of the production process can be simplified.
The PP plastic infusion bottle consists of a bottle (preform), an inner lid, an outer lid, a lifting ring, and an inner plug. (Figure 1). The production is mainly injection, and the material is mainly BOPP. The above products are in the production process. The main defects are the appearance of air bubbles, vacuum bubbles, black spots and black lines in the products. The reasons for these defects and their solutions are analyzed as follows.
Bottles (preforms), the production of large infusion bottles is to use injection molding machines to inject the preforms, which is what we often say PP preforms, the material is BOPP. If there is a process defect in the PP preform during the injection process, it will be directly reflected on the blown bottle, so sometimes the bottle defect, we have to find a problem on the preform. PP bottle blanks and bottle defects caused by the bottle blanks are mainly bubble problems. Bubbles have already been generated when the bottle blanks are injected. This preform is blown into a bottle as shown in Figure 3. There are several kinds of bubbles in the preform, and the reason is not the same. Generally, we judge according to the position of the bubble. Bubbles in this position as shown in Figure 2 are due to poor plasticization. In the process, we can solve this problem by increasing the back pressure, lowering the screw speed, and increasing the cylinder temperature. However, the production efficiency will be reduced, which is unbearable, so professional injection molding machine manufacturers will deal with it by changing the structure of the screw. This will not only solve the bubble problem, but will not reduce the production efficiency, and it can even increase the production efficiency.
This is the situation where gas is produced in the middle of the product; if bubbles are created at the bottle mouth, as in Figure 4, there will generally be white spots, white lines or burning spots due to the standard phenomenon of poor exhaust. It is caused by poor exhaust gas. It can use multiple injections. The last one is injected at a slow speed to reduce the clamping force and improve the mold's exhaust effect. As shown in Figure 5, “bubbles†will also appear at this position. In fact, there is no “steam†in the “bubbles†of this place, but a standard vacuum bubble. This is due to the insufficiency of the pressure holding time during injection and the phenomenon of backflow. Due to the shrinkage, it is necessary to increase the pressure holding time and holding pressure.
In addition, after the completion of the blow-molding, defects such as those shown in Figs. 6 and 7 occasionally appear. The lateral folds in Fig. 6 are after the blow-molding, the blank number is indeterminate, and the folds are formed on the inner wall of the bottle, and are heated when the bottle is blown. Not enough, that is to say, when the bottle is blown, the outside temperature of the preform reaches the high elastic state of the plastic. However, the internal temperature of the preform is not reached, so that the inner wall of the preform is rigidly dragged during the blowing of the bottle, resulting in lateral wrinkles, and the blown bottle has a rough surface and pit defects. Therefore, the defect of Fig. 6 is not related to the preform itself, which is a problem in the blowing process.
The defects of Fig. 7 are related to the injection molding process and mold of the preform. Fig. 7 shows the longitudinal stripes appearing on the fixed preforms. The study of the longitudinal stripe relates to the removal of the preform during demoulding. The preforms are molded during demoulding. The cavities scrape the same stripes as the stripping direction, and these strips are amplified during the blowing and the above defects occur. So smarter craftspeople found that if you cast off the problematic preform core, the problem can be solved, but it will appear again after some time. This shows that this is not the key to the problem. In fact, the preform is scratched by the mold core (debonded), which is related to the overmolding force of the product. The overmolding force is related to the injection pressure and the overpressure. If the injection pressure and the holding pressure are too large, why? Other cavity does not have this problem? After the study found that the cavity of the preform has a large mold force and its gate. After measurement, the cavity of the preform cavity in question is larger than the other cavity. This is where the problem lies. Large gates, good pressure transfer, and large preform molding force, will cause mold release scratches. General PP preform gate is 2mm (also 3mm). If the gate of one of its preforms exceeds 2.1mm. The above problem will occur.
The eccentricity of the preform is the main cause of the uneven thickness of the bottle wall. The eccentricity of the preform is caused by excessive injection pressure and holding pressure, which results in the eccentricity of the mold core; the core itself is inclined or the strength of the core is not good, can cause The above problem.
Cover, PP+ elastomer. Due to the presence of elastomers. Therefore, the main defects of the outer cover are black spots and vacuum bubbles, as shown in Figure 8. This is a typical compound decomposition black spot, due to the better temperature resistance of PP than elastomer. Therefore, the elastomer easily decomposes to generate black spots. The process can be solved by reducing the barrel temperature, back pressure, and rate of fire, but the adjustment is more difficult and there will be some side effects. It is better to solve the screw structure of the injection molding machine, and the PP special screw of Cosmos Machinery can effectively solve this problem. Vacuum bubbles are likely to appear at the thick edges of the outer cover, as shown in Fig. 8. The main reason is that the vacuum bubbles are formed and the problem can be solved by the method of holding pressure or the like.
Inner cover, material PP+ elastomer. In addition to the appearance of black spots like the outer cover, the inner cover is most likely to have air bubbles, as shown in FIG. 9 , in particular, air bubbles tend to appear at the edges of the inner cover. Due to the fact that the walls of the inner lid are not very thick, the chance of vacuum bubbles is not very large, usually bubbles. The reason is poor exhaust. Because it is the last part of the rubber flow, and the injection molding machine used is relatively large, the exhaust gas is very normal. Generally, it can be solved by reducing the rate of fire and the clamping force.
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