A method to judge the crystal point of the hottest

2022-08-16
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The biggest obstacle in plastic processing is crystal point, and the most difficult problem to solve is the elimination of crystal point. Especially in the process of multi-layer coextrusion film processing, the problem of crystal point becomes particularly prominent

the origin of crystal point is complex, and it is more difficult to eliminate crystal point. In the process of coextrusion film processing, resins with different materials and processing characteristics must be formed in the same head and under the same processing conditions. In principle, it is necessary to follow the processing conditions that low temperature obeys high temperature, which is contrary to the characteristics and principles of plastic molding processing. Therefore, the generation of crystal dots is the most common and difficult problem for multilayer coextrusion films. The following is the judgment method of various crystal points

1. Nylon crystal point in nylon layer

generally, the nylon crystal point in nylon layer can be distinguished by dyeing, which can be dyed as yellow, brown or red. The non nylon crystal points usually remain white or translucent and will not be dyed

the majority of nylon crystal points are caused by the former phenomenon in the processing process of nylon raw materials: most of them are caused by the crosslinking caused by the drying of the gauze on the wet ball sensor, and some of them are caused by factors such as the equipment forming and processing area (touching the head, 90 degree angle, insufficient cleaning)

The formation and phenomenon of EVOH crystal point is very similar to that of nylon crystal point

2. The non nylon crystal point of nylon layer

mainly comes from the fact that the adhesive resin or other melts enter the nylon layer due to the mismatch of melt viscosity between layers. This mismatch between the flow velocity between layers and the melt viscosity makes it easy for one layer in a certain section of the film to be squeezed out by another layer, resulting in crystal points

3. Nylon crystal point in non nylon layer

the reasons for nylon crystal point between layers are: 1], nylon material is mixed into other extruders; 2] There is leakage between the flow channels of the traditional rotary probe; 3] The resin tree of nylon layer and adjacent layer has been used more than 100 million tons of plastic packaging products in 2014, and the viscosity of fat does not match

4. Other crystal points in the non nylon layer

these crystal points are crosslinked raw materials or unmelted resin particles. In order to determine which resin composition is except nylon or EVOH, FTIR test is usually needed to know the crystal point

but 90% of the crystal point comes from the thicker layer near the adhesive resin (PA tie crystal point layer). Of course, there are exceptions

4. Other (continuous) small crystal dots in the non nylon layer

such as continuous small crystal dots in the adhesive resin layer. This is usually caused by the problems of the adhesive resin being contaminated, insufficient mold cleaning, and the adhesive resin itself. Such continuous small crystal dots may occur in each layer, and their causes and phenomena are very similar

5. Take targeted measures after knowing the above judgment methods. 2. Sensor: the sensor is an important part of the accuracy and force measurement stability of the experimental machine. The solution method can effectively solve the crystal point problem

reprinted from: China Business Forum

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