1、PET plastic profile
Poly ethylene terephthalate, mainly including poly ethylene terephthalate PET and poly two terephthalate PBT. Polyethylene terephthalate, also known as polyester resin, commonly known as polyester resin. It is a condensation of ethylene glycol and ethylene glycol, and PBT together with the thermoplastic polyester, or saturated polyester. Polyester is a thermoplastic linear saturated polyester, represented by PET, including PET, PBT, PEN, PCT and its copolymers. PET is the development of the earliest, the largest production, the most widely used polyester products. PET recycled plastics can be used in food packaging, can be used to achieve unlimited recycling. This is the environmental protection technology in China reach. Because of the plastic packaging materials from the oil, in order to save resources, many developed countries have developed a plastic packaging recycling technology, in early 1991, had to be recycled PET plastic slice used as food packaging materials.
2、development status of PET plastics in China
At present, our country's pet pet plastic packaging containers are mainly confined to two-way stretch polyester blow molding bottles. So the following mainly from the development of China's PET bottle to introduce the development of China's PET plastic status, and cited two cases of PET bottle production industry leading group. China biaxially oriented polyester bottle blow molding in plastic packaging industry started late, but since the eighties of the 20th century from Japan introduced injection stretch blow moulding PET bottle production line that in cola drinks on behalf of the packaging made very good effect, subsequent to the introduction of a large foreign advanced injection stretch blow moulding PET bottle production equipment, also in digesting foreign advanced technology based, research and development with independent intellectual property rights, suitable for China's national conditions, simple structure of the two-step pet stretch blow molding machine, it and general injection machine with the use of the general injection machine manufacturing of pet preforms, bottles of biaxially oriented PET blowing. Domestic two-step biaxially oriented PET blow molding machine in, some models can not only produce ordinary pet biaxially oriented bottles, can produce thermostable biaxially oriented PET bottles, can the volume of production basically covers the import equipment can produce from dozens of ML vials to a broad range of 5 gallon VAT. These simple type blow molding machine not only has low cost and advantages of flexibility and control properly can produce excellent quality and good practicability of biaxially oriented PET bottle blowing; therefore, it has been generally accepted by the plastics processing industry at home and abroad, in addition to the use of a large number of domestic, some export.
In spite of these equipment and imported advanced equipment still exist between the production efficiency is low, the gap between poor automation, product size precision poor. For some particularly demanding applications in the field of its application still has certain difficulty. In addition, multilayer co blow moulding PET bottle production equipment in China is yet to be developed, but domestic two-step biaxially oriented PET blowing bottle machine utilization for promoting the rapid development of the production of PET bottles to can not be ignored, a huge role in promoting. At present, both of our pet bottle production enterprises with manufacturing the well-known enterprises in the world's most advanced pet bottle automatic production line of large-scale backbone enterprises. At the same time, there are a lot of using our designed for the manufacture of a variety of different degree of automation of simple and practical bidirectional PET bottle blowing machine of small and medium enterprises, showing an unprecedented flowers are blooming, the prosperous situation. With the rapid development of PET bottle, the production of bottle grade PET resin in our country has been developed rapidly.According to reports, in 1995 China's bottle grade PET resin dosage was 100 thousand T, of which domestic production is 60 thousand T, in 2000 China's bottle grade PET resin dosage is 520 thousand T, domestic production capacity has reached 500 thousand T. Nbsp;
The mainstream products in the domestic PET bottles, initially only limited packaging containers used in drinks such as Coca Cola, mineral water, distilled water, applications to its excellent performance and reasonable price to obtain the user generally welcomed, on the basis of the beverage packaging successful application, in recent years, PET bottles has in the application of heat-resistant bottled drinks black tea, green tea, juice and edible oil, cosmetics, pharmaceuticals, pesticides, and other industries are extended. According to reports, my pet bottle production in 1996 to 30 million, 1998 rose 50 billion, in 2000 reached 80 billion, 2001 90 million, in 2002 reached 100 billion, 2004 130 billion become plastic packaging materials are increasing, the maximum amplitude of varieties.
PET bottle plastic molding equipment in our country has great prospects for development, at the same time, we should see a large gap between the PET bottle plastic molding equipment and industrial developed countries. International typical pet preform injection molding machine production equipment for Canada HUSKEY pet injection molding machine, is internationally recognized as a leader, so we should seriously study the performance characteristics and institutional characteristics, performance characteristics, the development of more advantageous properties of pet preform injection molding machine. Today in the international market, domestic pet plastic bottle billet equipment, if there is no technical advantage in performance, that developed out of the equipment can only when the exhibits, not when the commodity PET bottle blow molding production process of poly (ethylene terephthalate) (PET) bottle blow molding production according to the different type billet preforming can be divided for injection stretch blow molding (injection stretch blow) and extrusion stretch blow molding (hereinafter referred to as extrusion blow). In the two method, due to the control of injection stretch blow molding process, high production efficiency, less waste and more common. PET bottle blow molding can be divided into two categories, one is a pressure bottle, such as filling carbonated beverage bottle; on the other a class without pressure bottle, such as filling water, tea, oil bottle. Tea beverage bottles is the mixing of the poly naphthalate) (pen) plastic poly aryl ester composite bottles PET bottles or pet and thermal modified, in classification is a hot bottle, heat resistant above 80 DEG C; Aquarius is a bottle of cold, the heat resistance is not required. In the forming process, the hot bottle is similar to the cold bottle. The paper mainly discusses the forming process of the pressure beverage bottle in the cold bottle.
With the continuous progress of science and technology and the scale of production, PET bottle blowing machine automation is becoming more and more high, the production efficiency is also getting higher and higher. Equipment production capacity continues to increase, from the previous production of thousands of bottles per hour to the current production of tens of thousands of bottles per hour. The operation of the past by the manual button type development for the present full computer control, greatly reducing the difficulty of the process, increased the stability of the process. Although the manufacturer is different, but the principle of equipment similar, generally including for billet system, heating system, blowing bottle system, control system and auxiliary equipment in five parts.
2, blow molding process
PET bottle blow molding process. The important factors that affect the PET bottle blow molding process are bottle blank, heating, pre blowing, mould and environment.
2.1 bottle blanks
Preparation of blow molded bottle. First of all, the pet injection molding for the preform, it requires secondary recovery material ratio can not be too high (below 5%), recovery the number of not more than two times, and the molecular weight and viscosity can not be too low (molecular weight 31000-50000, characteristic viscosity 0.78-0.85cm3 / g). Injection molded bottles need to be stored at the top of the 48h to be used. After heating, not run out of the bottle blank, must be stored at the top of the 48h can be used to re heating. Preform storage time can not be more than six months. The advantages and disadvantages of the preform are largely determined by the merits of the PET material, which should be ed to be easy to blow up and easy to form the material, and to make reasonable bottle blank forming process. Experiments show that the same viscosity of the PET material molding preform, imported raw materials than domestic materials easily blow molding; and the same batch of bottles, production date is different, blow molding process may also have a greater difference. Preform determines the blow molding process of the difficulty, the bottle blank is pure, transparent, free of impurities, no heterochromatic and note length and a halo around the spot right.
The heating oven is heated by the heating oven, and the temperature is set by the manual. Oven by far infrared lamp tube a far infrared bottle billet heating, thermal cycling by the oven and the bottom of the fan, uniform temperature in the oven. The bottle body rotates at the same time during the forward movement of the baking oven, so that the wall of the bottle body is heated evenly. The lamp arranged in the oven from top to bottom are generally "zone" shaped, two more, less intermediate. The oven heat from the tube opening number, the overall temperature setting, oven power and different heating than common control. The opening of the lamp tube must be adjusted with the pre blowing bottle. To make the oven to better play the role, adjustment of the height, the cooling plate is very important, if improper adjustment, blow molding, prone to expansion of bottle of bottle mouth bigger), stiff neck (neck material pull not open) and other defects.
2.3 pre blow
Pre blowing is a step two step blowing method is very important, it is that the blow molding process in stretching rod down and began pre blow, makes the bottle blank begun to take shape. This process in the pre blow position pre blow pressure and gas flow are three important process factors. The advantages and disadvantages of the shape of the pre blow bottle decide the difficulty of the blow molding process and the performance of the bottle. The normal pre bottle shape for the spindle, abnormal, dumbbell, handle shape, as shown in figure 2. Resulting in the abnormal shape of the reasons local heating improper, pre blowing pressure or lack of blowing flow etc., and the pre blowing bottle size depends on pre blowing pressure and pre blowing position. In order to maintain the size and shape of all pre blown bottles of the whole equipment in production, if there are differences, it is to look for the specific reasons. The size of pre blow pressure varies with the bottle size and equipment capacity, the general capacity is big, the pre blow pressure is small, the equipment production capacity is high, and the pre blow pressure is also high. Even if the same equipment used to produce the same specifications of the bottle, due to the differences in the performance of PET materials, the required pre blow pressure is not the same. Glass Fiber Reinforced PET material, smaller pre blowing pressure can make the bottle at the bottom of the correct molecular orientation; other materials or improper molding process is not appropriate preform, near the injection point has a lot of stress concentration is not easy to fade, if you blow, often at the injection point blowing broken or in capacity test of burst from the injection point, leakage. According to the orientation condition, the lamp can be removed from the 2-3 branch to the top of the injection point to be opened at the top of the injection point, and the full heating at the point of the injection point is provided. For heated secondary use of the bottle blank or storage time exceeded the preform, due to temperature arithmetic effect, the two molding process similar, compared with the normal preform, the requirements of heat less, pre blowing pressure also can be appropriately reduced.
2.4 auxiliary equipment and mould
Auxiliary equipment mainly refers to maintain the mold temperature. Mold temperature has an important role in maintaining the stability of the product. General bottle body temperature is high, the bottle bottom temperature is low. For cold bottle, because of its cooling effect on the bottom of the molecular orientation of the degree, the temperature control in 5-8 degrees Celsius is better; and the temperature of the bottom of the bottle is much higher. Mold is an important factor of effect on PET bottle blow molding process, the pros and cons of the shape of the mold will reduce or increase the difficulty of adjusting the process, such as strengthening the tendons, transition zone and the bottom of the arc thermal conditions of etc. have influences on the adjustment process.
The quality of the production environment has a greater impact on the process adjustment, a constant condition can maintain the stability of the process and product stability. PET bottle blow molding in room temperature and humidity conditions. 3 other requirements should be met at the same time to meet the stress test and pressure test requirements. Stress testing is to prevent the PET bottle beverage bottle bottom and lubricant (alkaline) contact generated in the process of molecular chain degradation and the occurrence of crack and leakage of internal quality control; voltage withstand test is to prevent gas bottle filled with certain pressure crack and quality control. In order to meet these two kinds of needs, the central point thickness to be controlled within a certain range, the general situation is the center point thin, stress test is better, the pressure is poor; the center point thick, the pressure test is good, stress test is poor. Of course, the results of stress tests also have a great relationship with the accumulation of the transition zone around the center point, which should be adjusted according to the actual experience.
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