Cross-linked shrink film Manufacturer

The POF crosslinking film also meets the crystal point problems

As we all know, crystal dots are a common problem in thin film manufacturers. For transparent plastic bags, crystal dots obviously affect the appearance of transparent plastic bags. For the rubber bag which requires high quality printing quality, especially the large area of the rubber bag printing, the "white spot" waste produced by the crystal point is a large proportion of the waste in the industrial production process of the rubber bag. Therefore, controlling the generation of crystal dots and eliminating the cause of crystal spots are important technological steps to improve the technical level of plastic bags industry.

1. What is the crystal point

The crystal point is actually "over polymer", that is, the molecular weight of the polymer is higher than that of the surrounding polymer. Because of the high molecular weight, polymers with higher melting point at the point of crystallization have higher viscosity when melted. At the crystal point, the polymer can not be dispersed evenly and mixed with the surrounding polymer when the film is blown, and after the melt is blown into the film, it solidifies before the surrounding polymer. Therefore, the formation of "arrowhead" or "spherical" over polymer coagulant is customarily known as "Crystal Point".

The cause of the 2. crystal point

Material cause

(1) there are residual catalysts in the polymer.

(2) polymer melt is stuck to the metal surface of production equipment, including polymerization equipment and blown film equipment, and remains at high temperature.

(3) catalysts continue to catalyze polymerization of polymers, thus forming excessive polymers.

The oxygen contained in polymer will also produce crystal dots in polymer melts (adding a certain amount of antioxidants to prevent oxygen from producing crystalline dots).

Technological reasons

(1) the crystal point caused by the polymerization process. Different polymerization devices and processes have different effects on the generation of crystal dots. For example, some factory raw materials, because of high production technology, the residue of the catalyst content in the polymer is low, the structure of the equipment is good, so the crystal point of the raw material itself is less. However, due to the problems of production technology and equipment, some raw materials contain more crystalline dots.

(2) the crystal point caused by the process. For example, thin films prepared by good molding equipment have fewer crystal dots. The thin film made by the poor equipment has more crystal points.

3. methods to reduce or basically eliminate crystal points

To sum up, there are two ways to eliminate crystal spots in film blowing process.

(1) increase the fineness of the filter for processing equipment (for example, changing the filter to 120 mesh, or even 150 mesh for ultra-thin film).

(2) add surface lubricants in the production process so that the processed polymer melts can not adhere to the surface of the blown film equipment.

In the process of production, although a fine filter can be used to filter the primary crystal points in most of the polymers and also to filter the crystal points caused by the viscosity of the polymer on the surface of the screw, the problem is that the back pressure of the equipment is improved, which is difficult for some old type of equipment. Therefore, relying on diligent filters can also help to control crystal spots.

So far, a more efficient method of crystal point control is to use high-performance fluorine process auxiliaries. High performance fluorine process aids, because its polymer molecules have the characteristics of high polarity, make it rapidly overflow from olefin polymers (such as PE, PP) melts and adhere to the metal surface of the equipment, thereby eliminating the viscous layer of polymer melt on the surface of the equipment metal.

Therefore, the polymer melt can be pushed forward at a constant speed, eliminating the prolonged heat of the polymer melt on the surface of the metal, preventing the continuous polymerization of the residual catalyst to the polymer, and finally preventing the crystal point produced in the film forming process.

On the other hand, because the fluorine process aids can also adhere to the surface of the filter screen, the resistance of polymer melt flowing through the screen decreases. Therefore, the use of fluorine process auxiliaries provides technological conditions for the use of finer filters. The adoption of finer screen is an important technological measure to filter out the primary crystal point produced by polymer production.