First, let us introduce the concept of cast film. Cast film is a non-stretched, non-oriented flat extruded film produced by the melt casting and rapid quenching process of a cast film machine. It is available in two forms: single-layer casting and multi-layer co-extrusion casting. Compared with blown film, its characteristics include faster production speed, higher output, and excellent optical properties such as transparency, gloss, and thickness uniformity.

However, do we fully understand the importance of resin selection in the production of cast film? What kind of resin should we choose?

(1) Selection of Resin Type

The choice of resin type is the foundation for producing the desired cast film. The resin selected should be the type whose inherent properties are closest to the target modification performance, in order to minimize the amount of additives required. For example, for wear resistance modification, the preferred resin types should be selected from the three major wear-resistant resins: PA, POM, and UHMWPE. Similarly, for transparency modification, the preferred resin types should be selected from the three major transparent resins: PS, PMMA, and PC.

(2) Selection of Resin Grade

Many manufacturers do not pay sufficient attention to this aspect during cast film production. Different grades of the same resin can have significantly different properties. The grade chosen should be the one whose properties are closest to the desired modification performance. For example, for heat-resistant PP modification, one should select from PP grades with heat deflection temperatures ranging from 100°C to 140°C, aiming for a grade that inherently withstands 140°C, such as PP-4012 from SK Corporation.

(3) Selection of Resin Fluidity/Melt Flowability

This step is relatively abstract and can only be truly understood through experimentation; there is no clear-cut standard. The viscosities of the various plasticizing materials in the formulation should be close to each other to ensure good processing fluidity. For materials with significantly different viscosities, a transition material should be added to reduce the viscosity gradient. For example, in PA66 toughening and flame-retardant formulations, PA6 is often added as a transition material; in PA6 toughening and flame-retardant formulations, HDPE is often added as a transition material.

Different processing methods require different levels of fluidity.

Different types of plastics have different flowabilities. Plastics can be broadly classified into low-fluidity plastics, high-fluidity plastics, and non-flowable plastics, as detailed below:

Low-fluidity plastics — PS, HIPS, ABS, PE, PP, PA, etc.

High-fluidity plastics — PC, MPPO, PPS, etc.

Non-flowable plastics — PTFE, UHMWPE, PPO, etc.

Even within the same plastic type, fluidity can vary significantly due to differences in molecular weight and molecular weight distribution. Therefore, the same raw material is available in different grades. Different processing methods require different fluidity levels, resulting in grades classified as injection-molding grade, extrusion grade, blow-molding grade, calandering grade, etc.

Different modification objectives also require different fluidity levels. For example, highly filled systems require good fluidity, such as magnetic plastics, filled compounds, and halogen-free flame-retardant cable materials.

(4) Selectivity of Resin Toward Additives

Literally, “additives” are agents that facilitate the successful forming of cast film. It is important to note that certain resins cannot be used with specific additives. For example, PPS must not contain lead- or copper-based additives, and PC must not use antimony trioxide, as these can cause depolymerization. In addition, the acidity/alkalinity of additives should be compatible with that of the resin; otherwise, reactions between them may occur, with serious consequences.

Cast Film Machine — can be used to produce PE, CPE, EVA, and other plastic films, as well as transparent films, embossed films (patterns can be customized according to customer samples), glossy films, etc.

Properties of Cast Film: Non-brittle at low temperatures, non-tacky at high temperatures up to 45°C, good hand feel, lightweight, non-toxic, odorless, and with low environmental pollution after use.

Wide Range of Film Applications: It can be used as the bottom sheet for sanitary products, such as sanitary napkins and diapers; for daily necessities, such as disposable gloves, shoe covers, shower caps, sleeve covers, aprons, surgical gowns, cleaning garments, tablecloths, umbrellas, shower curtains, etc. It is also used as lining film, packaging film, base film for perforated films, and various types of roll film materials.