Melt Phase Thermoforming

The major opportunities for this new barrier resin composite are in shallow solid phase pressure thermoformed containers and in melt phase thermoformed containers. These rigid containers are typically pigmented, thus eliminating the problem of the yellow tint (Table VIII). 

The types of thermoforming processes are vacuum forming, pressure forming, melt phase thermoforming, and matched mold forming. Examples of applications of thermoformed parts are ... 

Thermoforming requires better forming temperature range and melt strength to overcome the sag problem in melt phase thermoforming. Amorphous polymers such as ABS and PS can be thermoformed over a much wider temperature than semicrystalline polymer such as PP. 

In response to the problems encoimtered in the melt-phase thermoforming of PP, the Shell Chemical Co. developed a process known as... 

In the thermoforming process, the sheet is extruded either in-line or off-line and formed, either in melt phase or solid phase, into a part of desired shape. Sheet uniformity is important. Historically, iPP has not been used in conventional melt-phase thermoforming equipment because of its narrow forming temperature range and the tendency of the melt to sag. Controlling the sag is particularly important... 

PP can be thermoformed in two distinct phases in the solid phase below its crystalline melting point and in the melt phase above its crystalline melting point. Both techniques have advantages and disadvantages. 

During the thermoforming process (see Fig. 12), the sheet is heated above the glass transition temperature and below the melting point of the crystalline phase [35]. Afterwards, the hot sheet is formed into a chilled mold using vacuum, pressure and/or mechanical force. After a cooling step, the thermoformed containers are punched out and ejected. The skeleton (30-70% of the total volume) is recycled in the same application (Fig. 12). 

However, the forming temperature is below the melting temperature of the plastic. See thermoforming, solid-phase pressure. 

Other Fabrication Methods. Another thermoplastics processing technique that is suited to some TPEs, but not to thermoset rubbers, is thermoforming. A sheet of TPE is heated to 10 to 40°C above the melting temperature of the hard crystalline phase (or glass... 

Blends of PEI with polycarbonate (PC) form phase-separated morphologies (Chun et al. 1996). Nevertheless, some PEI/PC blends (Ultem LTX) exhibiting improved melt flow and toughness were commercialized in the 1990s, but now seemed to be discontinued. PEI blended with some PC is used as thermoformable sheets (Ultem 1668, Sabic) for aircraft interior applications, to meet the process-ability and the low flammability and low smoke generation requirements. 

Formability. Materials with a broad softening range, such as PS and PC, can be thermoformed into deep-draw package shapes. Crystalline polymers, eg, HDPE and PP, are more difficult to thermoform, but solid-phase forming processes below the melting point are possible. Multilayer semirigid barrier containers are made by Shell s Solid Phase Pressure Forming Process and the patented Dow... 

---