PET molecular structure with rigid benzene ring and polar ester base, PET is characterized by large rigidity, poor toughness, its vitrification temperature and melting point is high, is a typical crystalline polymer. Easily hydrolyzed under high temperature and humidity conditions, density: 1.38-1.41.

* Performance

1. Mechanical properties

Has a certain brittleness, low impact strength, mechanical properties and crystallization degree and orientation, and is anisotropic, after adding glass fiber, its mechanical properties have been improved.

2. Thermal properties

PET has a more obvious melting point, 256–265℃, vitrification temperature of 81 ℃, low viscosity after melting, good fluidity, decomposition temperature of 300℃.

3. Water absorption

PET has a certain degree of water absorption, before processing must be dry, PET gas tightness is better.

4. Optical properties

PET has good light transmittance, high transparency, is related to crystallinity, high crystallinity transparency decreased.

5. Chemical resistance

The chemical resistance at room temperature is better, and with the increase of temperature, the chemical resistance decreases, and it is easy to hydrolyze under high temperature and humidity.

6. weatherability

Long-term exposure to the outdoors, its mechanical properties decreased, after adding glass fiber, weatherability enhanced

* Processing

1.PET with water absorption, moisture containing raw materials in high temperature and humidity will appear hydrolysis, resulting in discoloration of products, brittle, so before processing must be fully dry. Drying temperature 140–170℃, time 4-6H, for the transparency requirements of the product must be dry full, otherwise, the rate of defective products increased, mainly bubbles, It is best to use a wet drying method.

2. Heating shrinkage Pipe temperature

Because PET has obvious melting point and easy decomposition, so its processing temperature is narrower, the general barrel temperature is 240–290℃, when the temperature is higher than 295 ℃ will appear decomposition, blackening, PET processing molding, the temperature of the barrel should be strictly controlled.

3. Mold temperature

PET is a crystalline polymer, crystallization speed is slow, to obtain high crystallization products, the mold temperature selection is higher, generally 100–130℃, and longer cooling time, in order to obtain a higher transparency of the product, the mold temperature is lower, generally 20–30℃, so that it quickly cooled to below the vitrification temperature, Without a stereotyped structure, crystallization can reduce transparency.

4. Injection speed, pressure, back pressure

As a result of PET melting state, low viscosity, good fluidity, easy to fill the mold, can be used faster injection speed and lower injection pressure, back pressure is not too high, high back pressure, large shear, melting temperature rise, easy to decompose, at the same time will appear salivation, drawing and other phenomena, but the back pressure is too low due

5. Hot Runner

PET injection Molding processing, can use hot runner, especially bottle embryo, can improve work efficiency, the use of hot runner, its temperature control is very important, temperature is too high, will be salivation, drawing, temperature is too low, products will appear fusion pattern, low transparency and other defects.

6. Post-processing

PET crystallization, orientation temperature is high, and the orientation will not be relaxed, the product has dimensional accuracy requirements, generally after treatment.

*PET Special Screw

The PET special screw double-walled heat shrinkable tube designed for PET characteristics has good effect in the actual production of PET bottle embryo, and has the advantages of stable quality, high finished product rate and high production efficiency.

The characteristics of the screw;

1. The same type of machine using large diameter screw, long diameter ratio is large

2. Compression is relatively small, homogenization section with secondary thread

3. The feeding section is longer and the snail groove is darker

Advantages:

1. The use of large diameter screw, the feeding section is longer, the screw groove is deep, improve the conveying capacity, the amount of melt glue, melt glue speed, the same specifications of the model, injection volume, high production efficiency.

2. The use of double thread, long diameter is relatively large, screw parameter optimization design, strengthen the ability of plasticizing, homogenization, exhaust, reduce the appearance of white dots, bubbles, silver grain and other defects, to ensure the quality of products, improve the yield and production efficiency.

PET热缩管性能工艺解剖

PET分子结构中带有刚性的苯环和极性的酯基,PET表现为刚性大、韧性差,其玻璃化温度和熔点高,是典型的结晶型聚合物。在高温高湿条件下易水解，密度：1.38—1.41.

*性能

1.力学性能

呈一定的脆性,冲击强度较低,力学性能与结晶程度和取向有关,且呈各向异性,加入玻璃纤维后,其力学性能有改善.

2.热性能

PET具有较明显的熔点,256–265℃,玻璃化温度81℃,熔融后的粘度较低,流动性好,分解温度为300℃.

3.吸水性

PET具有一定的吸水性,加工前须干燥,PET的气密性较好.

4.光学性能

PET具有良好的透光性,透明度高,与结晶度有关,结晶度高透明度下降.

5.耐化学性能

室温下耐化学性能较好,随着温度升高,耐化学性能下降,高温高湿下易水解.

6.耐候性

长期暴露于室外,其力学性能下降,加入玻璃纤维后,耐候性增强

*加工

1.PET具有吸水性,含有水分的原料在高温高湿下会出现水解,导致制品变色,变脆,所以加工前必须充分干燥.干燥温度140–170℃,时间4—6H,对于透明度要求高的制品一定要干燥充分,否则,次品率增加,主要是气泡,最好采用抽湿干燥方式.

2.加热缩管工温度

由于PET有明显的熔点和易分解,所以其加工温度较窄,一般机筒温度为240–290℃,当温度高于295℃时会出现分解,变黑,PET的加工成型，机筒的温度要严格控制。

3．模具温度

PET是结晶型聚合物，结晶速度慢，若要得到高结晶的制品，则模具温度选取较高，一般为100–130℃，和较长的冷却时间，若要得到透明度较高的制品，则模具温度较低，一般为20–30℃，让其快速冷却至玻璃化温度以下，呈无定型结构，结晶会使透明度下降。

4.注射速度、压力、背压

由于PET熔融状态下,粘度较低,流动性好,容易充模,可以采用较快的注射速度和较低的注射压力,背压也不能太高,背压过高,剪切大,熔体温升大,易分解,同时会出现流涎、拉丝等现象,但背压太低会因排气不良,制品有气泡.

5.热流道

PET注塑加工,可以采用热流道,特别是瓶胚,可以提高工作效率,采用热流道,其温度控制很重要,温度太高,会流涎、拉丝,温度太低,制品会出现熔合纹、透明度低等缺陷.

6.后处理

PET结晶、取向温度较高,且取向后不会松弛,制品有尺寸精度要求的,一般要后处理.

*PET专用螺杆

针对PET的特性而设计的PET专用螺杆双壁热缩管,在PET瓶胚的实际生产中效果不错,具有质量稳定、成品率高、生产效率高的优点.

螺杆的特点;

1.同一型号机器中采用大直径的螺杆,长径比较大

2.压缩比较小,均化段设有副螺纹

3.加料段较长,螺槽较深

优点:

1.采用大直径螺杆,加料段较长,螺槽较深,提高输送能力,熔胶量大、熔胶速度快,对同规格的机型,注射量大、生产效率高.

2.采用双螺纹,长径比较大,螺杆参数优化设计,加强塑化、均化、排气的能力,减少制品出现白点、气泡、银纹等缺陷,保证制品的质量,提高成品率和生产效率.