Factors Affecting Transparency Of Polypropylene Thermoforming Products


The competition of polypropylene thermoforming products industry is more and more fierce, and the transparency of products also plays a role. During the production of PP extruded sheets, thermoforming and Blister products, customers often find that the transparency of the products produced is not good, and they are not as transparent as others. Thermoforming is a very complex plastic product forming process. And it can also be machined, that is the CNC machining polypropylene. There are many factors that affect the transparency of products. This guide briefly lists some factors affecting the transparency of PP thermoforming products, hoping to provide more help to product manufacturers in quality improvement and quality management, and also provide some guidance to product manufacturers in product design and equipment selection.


Influence of Raw Materials and Formula

1. Influence of homopolymer polypropylene raw materials

The raw materials used for Polypropylene Sheets and thermoforming products are usually homopolymer PP raw materials of low melting finger drawing grade, including commonly used T30S (t03h), l5e89, S1003, etc. However, the isotacticity control of drawing PP raw materials from different manufacturers is different, so the transparency and rigidity of raw materials are different, thus affecting the transparency of products. PP raw materials with low isotacticity are usually more transparent, but also softer.


2. Random copolymerization high transparent PP raw material

Random copolymerized high transparent PP raw materials contain certain ethylene copolymerization, so they have very high transparency and gloss. Some customers will mix homopolymer PP raw materials and high transparent PP raw materials in the formula to improve the transparency and gloss of the product and prepare high transparent cups. The ethylene content and the type and content of transparent agent of random copolymerized high transparent PP raw materials from different manufacturers are different, so the transparency and gloss of products mixed with different high transparent PP raw materials and homopolymer PP materials will also be affected.


3. Effect of toughening agent

In PP thermoforming and Blister products, more customers will add toughening agents to reduce the cup breaking rate or improve the low-temperature storage performance. At present, there are many kinds of toughening agents suitable for PP low-temperature toughening, but a considerable number of toughening agents will affect the transparency. Especially when the requirements for low temperature resistance are high and the amount of toughening agent added is relatively high, it is necessary to select a suitable toughening agent product to avoid negative impact on the transparency of the product.


4. Selection of transparent agent and transparent Masterbatch

There are a lot of polypropylene transparent agents in the market. There are differences in the effect and price of each kind of transparent agent, including the difficulty of dispersion and the appropriate amount of addition, as well as the difference in the antireflection effect. At the same time, since the sheet extruder is usually a single screw extruder, the shearing and dispersion ability is not strong, and the powder transparent agent may not be dispersed when used. Affecting the final transparency of the product. When preparing high transparent and high gloss thermoforming products, it is necessary to select appropriate transparent agent and transparent masterbatch.


5. Influence of leftover materials

Thermoforming and blister manufacturers usually mix a certain proportion of leftover materials. When customers produce highly transparent products, if there are some components in the leftover materials that affect the transparency, it will affect the quality and transparency of the sheet, and ultimately affect the transparency of the products. Therefore, customers need to control the production process and try to distinguish ordinary leftover materials from high-quality leftover materials.


Influence of Production Process

1. Influence of extrusion temperature

The temperature setting of sheet extrusion will have an impact on the crystallization behavior of PP products and sheet surface defects, and also on the dispersion of toughening agent, transparent agent and other components in the sheet, thus affecting the transparency of the sheet and the transparency of the final product.


2. Influence of extrusion speed

The influence of extrusion speed on sheets and products is similar to that of extrusion temperature. It also affects the dispersion of other components, the crystallization behavior and surface defects of PP sheets, thus affecting the transparency of final products. If the extrusion rate is too high, the three roll cooling cannot keep up with it, resulting in an increase in the crystallinity of the PP sheet and a decrease in the transparency of the sheet. At the same time, if the extrusion rate is too fast, it is easy to have pockmarks on the surface of PP sheet, and these pockmarks will continue to remain on the surface of the product, thus affecting the transparency of the product.


3. Influence of three roller cooling

The temperature setting of the three rollers mainly affects the crystallization behavior of the PP sheet, thus affecting the transparency of the product. The high temperature of the three rollers makes the PP sheet have high crystallinity, and it is easy to form large crystals, thus reducing the transparency.


4. Influence of hot pressing temperature

The thermoforming temperature will also have a certain impact on the transparency of the final PP thermoforming product. It needs to be within a reasonable range. Too high thermoforming temperature will lead to product fogging and decrease in product transparency and gloss. Too low temperature leads to dissatisfaction of product molding. The molding temperature range of PP products is very narrow, only a few degrees.


Influence of Mold and Drawing Head

1. Effect of stretching head

The material of the stretching head plays a very important role in thermoforming products. The selection of the material of the stretching head, the design of the shape and the surface finish will have an impact on the wall thickness distribution of the product, the height and depth of the stretching lines, and thus the transparency of the product.


2. Influence of mold

Mold design, polishing and cooling will affect the surface finish of PP products and the crystallization of PP materials, thus affecting the transparency and brightness of end products.