Traditional large infusion glass bottles have been replaced by new PP plastic infusion bottles for decades. PP plastic large infusion bottle has the unparalleled advantages of glass bottles: first, it is resistant to impact and not easy to break; second, it is lighter in weight, which can greatly reduce transportation costs; third is one molding, no secondary pollution; Toxic, no side effects on the human body; - Fifth, the manufacturing cost is low, calculated in a single bottle, which is only about 40% of the cost of the glass bottle. In addition, the high-quality and low-cost disposable plastic bottle omits the cleaning and disinfection process, and also saves related energy, which can simplify a considerable part of the production process.
PP plastic large infusion bottle consists of bottle body (preform), inner cover, outer cover, lifting ring and inner plug. The composition is as follows (Fig. 1). The production is mainly injection, and the material is mainly BOPP. The above products are in the production process. The defects produced are mainly bubbles, vacuum bubbles and black spots in the product. The causes and solutions for these defects are analyzed as follows.
Bottle body (preform), the production of large infusion bottles is first injection molding of preforms with injection molding machine, which is what we often call PP preforms, the material used is BOPP. If the PP preform has a process defect during the injection process, it will be directly reflected on the blown bottle, so sometimes the bottle is defective, we have to find a problem on the preform. The defects of the PP preform and the bottle caused by the preform are mainly bubble problems, and the bubble has already produced as shown in Fig. 2 when the preform is 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 where the bubbles appear. The bubble at this position in Figure 2 is due to poor plasticization. In the process, we can solve the problem by increasing the back pressure, reducing the screw speed and increasing the temperature of the cylinder. However, the production efficiency will be reduced, which is unbearable, so professional injection molding machine manufacturers will process by changing the structure of the screw. This will solve the bubble problem without reducing production efficiency and even increase production efficiency.
This is the case where gas is generated in the middle of the product; if bubbles are generated at the mouth of the bottle, as shown in Figure 4, there will generally be white spots, white lines or burnt focus, which is a standard phenomenon of poor exhaust. It is caused by poor exhaust gas, multi-stage injection can be used, and the last section is injected slowly, which reduces the clamping force and improves the exhaust effect of the mold. As shown in Figure 5, there is also a "bubble" at this position. In fact, there is no "steam" in the "bubble" of this place, but a standard vacuum bubble. Because of the insufficient holding time during injection, there is a backflow phenomenon. Caused by shrinkage, so it is necessary to increase the holding time and holding pressure.
In addition, after the blowing is completed, the defects of Fig. 6 and Fig. 7 occasionally appear. The horizontal pleats of Fig. 6 appear after blowing, the preform number is indefinite, the pleats are on the inner wall of the bottle, and the temperature is warmed when blowing. Not enough, that is to say, the external temperature of the preform reaches the high elastic state of the plastic during blowing. However, the internal temperature of the preform was not reached, so that the inner wall of the preform was hardly pulled when the bottle was blown, thereby causing lateral wrinkles, and the bottle which was blown out had a rough surface and defects such as pits. Therefore, the defect of Fig. 6 has nothing to do with the preform itself, and there is a problem in the blowing process.
The defect of Fig. 7 is related to the injection molding process and the mold of the preform. The longitudinal stripe of Fig. 7 appears on the fixed preform, and the longitudinal stripe is studied to be related to the peeling of the preform during demolding, and the preform is molded during demolding. The cavity scrapes out the same stripe as the stripping direction, and these strips are enlarged at the time of blowing to cause the above defects. So the clever craftsman found that if you throw the problematic preform core light, the problem can be solved, but it will appear again after a while, which shows that this is not the key to the problem. In fact, the scratch of the preform by the mold core is related to the overmolding force of the product. The excessive mold force is related to the injection pressure and the excessive pressure. If the injection pressure and pressure are too large, then why? Does the other cavity not have this problem? Later studies found that the mold embedding force of this cavity preform is related to its gate. After measurement, the preform cavity of the problem is larger than the other cavity. This is where the problem lies. The gate is large, the pressure is transmitted well, and the mold blanking force is large, so the mold release scratch will occur. Generally, the gate of the PP preform is 2 mm (also 3 mm). If the gate of one of its preforms exceeds 2.1mm. The above problem will occur.
The eccentricity of the preform is the main reason for the uneven thickness of the bottle wall. The main reason for the eccentricity of the preform is that the injection pressure and the holding pressure are too large, causing the mold core to be eccentric; the core itself is inclined or the core strength is not good, which will cause The above question.
Cover, PP + elastomer. Due to the presence of elastomers. Therefore, the main defects of the cover are black spots and vacuum bubbles, as shown in Figure 8. This is a typical rubber decomposition black spot, because PP has better temperature resistance than elastomer. Therefore, the elastomer is easily decomposed to produce black spots. The process can be solved by lowering the barrel temperature, back pressure and rate of fire, but it is difficult to adjust and there are some side effects. It is better to solve the screw structure of the injection molding machine. The special screw of PP of Datong Machinery can effectively solve this problem. Vacuum bubbles are likely to occur at the edges of the outer cover. As shown in Fig. 8, the water is mainly formed by shrinkage, and the problem can be solved by a method such as holding pressure.
Inner cover, material PP + elastomer. In addition to black spots like the outer cover, the inner cover is most prone to air bubbles, as shown in Fig. 9, especially in the edge of the inner cover. Since the edge of the inner cover is not very thick, the probability of occurrence of vacuum bubbles is not very large, and is generally a bubble. The reason is poor exhaust. Since it is the last part of the rubber flow, and the injection molding machine used is relatively large, the exhaust gas is normal, and can generally be solved by reducing the rate of fire and the clamping force.
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