Economic progress has promoted the development of plastics processing industry. Since the 80s of last century, plastic calendaring products have been widely concerned with high efficiency, high quality and low cost. The research work of PVC has made great progress under this background. PVC, polyvinyl chloride (PVC), is a synthetic resin which has a profound influence in many fields. PVC transparent sheet is an important part of it, its production process is more complex, and is affected by mechanical equipment, construction technology, natural environment and human factors. Some links are still weak, and need improvement. The defects of the product should be dealt with in time, and the corresponding methods should be done. The products produced only have the quality assurance. This paper analyzes the problems and puts forward some suggestions.
1.There are bubbles in the sheet.
1.1 problem discovery
In mid July 2012, a garment company in Shanghai needed to produce a batch of heat shrinkable films. The most popular PVC film in the world is the shrink film, which includes lacquer, adhesive and PVC, which has good ductility and heat resistance. It is found in the product that some small bubbles exist, which make the performance of the shrinkable film have a certain hindrance.
1.2 Analysis of problems
After communicating with the company's professionals, it is preliminarily suspected that there are more volatile substances in the material, resulting in bubbles caused by volatilization. According to the company, it was found that in August, the precipitation in Shanghai area was much, the humidity of the air was large and the PVC used was easy to be dampened, which resulted in the high water content.
At the site of the inspection, on the basis of the company's production process, the material is about 100kg. As the temperature rises, the mixture is gradually changing, the temperature more than 85 DEG C, more and more substances volatilized, attached to the surface of the machine, the formation of fog water vapor. The mixture was blown by the extrusion film equipment, and many small bubbles existed in the production of the shrinkage film.
The production process should be adjusted, the mixing time should be prolonged, and the mixing method of high and low speed should be adopted. In order to reduce water content, the discharging temperature can be appropriately raised to evaporate too much moisture. After the process is adjusted, the temperature is raised to facilitate the discharge of water, and the final production of small bubbles in the shrinkage film is greatly reduced and the quality is improved. If the water content in the raw material ratio is too high, not up to the standard production, can prolong mixing time, the volatiles from, or directly replace the raw materials; some volatile additives is too high, not easy to discharge, in the selection of raw materials should be avoided when the raw materials, and the choice of high quality additives.
2. pieces of MICROTEK are overloaded
2.1 problem discovery
When a packaging company in Beijing produces packaging film, it is tested that many products have too many crystal points and do not conform to the standard.
2.2 Analysis of problems
Crystal is because plasticizing resin particles caused by the failure of, there are many factors, such as the formulation of PVC suspension polymerization of vinyl chloride monomer, including water quality and additives varieties and usage; then the construction process, including mixing method, feed step speed and temperature rise of the use of equipment and other technology etc.. In addition, it is also related to the processing methods and conditions of PVC resin, including the processing time, temperature and the amount and quality of the additives.
In the process of polymerization, once the crystal point is generated, it is almost fixed, so that no plasticizer is absorbed at any time during processing, so it is difficult to plasticate and eventually form "fish eye" crystal spot which is difficult to remove. The crystal point may also be caused by high or uneven distribution of resin particle size. The crystal spots formed in such cases are easy to be removed, and the formulation and processing technology can be adjusted properly. The experiment shows that when the resin absorbs less plasticizer, the weight and relative molecular mass will increase correspondingly, so the processing technology must be adjusted at the same time, otherwise it will increase the difficulty of production.
The removal of crystal points can be solved by adjusting the mixing process, extrusion process and processing technology. ?
(1)First, effectively prolong the mixing time and improve the temperature of the mixture, so that the auxiliaries can be distributed more evenly, and the mixing speed should be high and low. Prolong the curing time of the blend, and try to set aside 24h and then put it into operation. After this adjustment, the problems in the production of the products have been greatly improved.
(2) many products have its fixed processing formula and special auxiliary. The proportions of raw materials and the properties of auxiliaries in the formulation are all related to the plasticization of products. During processing, we must choose the corresponding raw materials, equipment and proportion according to the specific circumstances.
(3)The PVC transparent sheet is mainly based on twin screw extruder production, to improve plasticizing properties of materials, reduce the incidence of problems, can be adjusted to the production equipment, such as increasing the head pressure, increase the shear force of the screw, reset the melting area of barrel temperature.
3.The color of the sheet is yellow
3.1 problem discovery
A company in Guangdong, the production of medical packaging film, choice is PVC material, to produce the product color is yellow.
3.2 Analysis of problems
The reasons for this phenomenon can be summarized as following three points: (1) fe3+ content in PVC resin is too high, so that its quality is poor, its stability is low, whiteness and aging whiteness are low. In the formula, the stabilizer mixing ratio is too low, and the standard is slightly inconsistent, although there are a variety of additives, but in production, manufacturers in order to reduce the cost as far as possible to minimize the amount of additives, it is difficult to play a role, once the process of fluctuations, is very easy to appear quality problems. (3) the temperature control device of the processing equipment fails. The temperature of the machine is obviously lower than the actual temperature, so that during the processing, the PVC material decomposes, resulting in the product's yellowish color.
To further analyze this problem, select several different PVC resin for comparison, A and B represent problems of resin, C resin has a good performance on behalf of the normal resin D on behalf of other manufacturers, the whiteness and aging whiteness were determined in accordance with the national standards for testing, can be seen from the test results no matter, whiteness, or aging whiteness, A, B two PVC resin value than C, D two A, B low, but also to meet the specified standard, which means that the relevant product quality in whiteness and old whitened degree of large, small changes will old whitening degree due to huge differences of color sheet.
From the above analysis, the reason that the product color is yellow is various, if the resin stability is poor, we need to replace the resin as much as possible. In addition, when dispensing, it is necessary to add enough dose to all kinds of elements, which can be a little richer to prevent sudden change. However, if the dosage is not enough, it will inevitably affect the formulation, resulting in the failure of its function. The equipment used for production must be checked regularly. Once the problem is found, it should be maintained in time. The temperature control device should pay attention to its accuracy, so as not to cause unnecessary losses.
4. concluding remarks
PVC transparent sheet is widely used and significant in the production process, affected by many reasons, there will be a lot of problems. In this article, we analyzed several common problems, in addition, warping the sheet fracture problems in production,need to be solved by detailed situations.