PDF《Hytrel》

Product Information ? polyester elastomer Hytrel ? Rheology and Handling Hytrel polyester elastomers are true thermoplastic polymers that are processed using conventional thermoplastic techniques.

They are semicrystalline materials characterized by relatively sharp melting points, temperature-sensitive viscosities, and, except for some low hardness grades, rapid crystallization. This bulletin reviews the melt characteristics of the various types of Hytrel and the effects of melt temperature and shear rate on the shear viscosity, and compares the melt rheology of Hytrel with that of various other thermoplastic polymers. In addi- tion, the effects of moisture are reviewed, and suggested drying procedures are given along with recommendations on the use of regrind. Melting Characteristics Melting characteristics of Hytrel thermoplastic elastomer as determined by differential scanning calorimetry using ASTM Method D1238 are shown in Table 1. The melt temperature at the die should always be equal to or greater than the temperature at which the polymer is completely melted. Table

1 Thermal Properties of Hytrel Melting Temperature Melt Complete Crystallization Temperature (Peak of Endotherm), (Extrapolated End Point), (Peak of Exotherm), Type of Hytrel °C (°F) °C (°F) °C (°F) High Productivity G3548W

156 (313)

180 (356)

107 (225) G4074

170 (338)

190 (374)

120 (248) G4078W

170 (338)

190 (374)

120 (248) G4774, G4778

208 (406)

225 (437)

170 (338) G5544

215 (419)

230 (446)

173 (343) High Performance

4056 150 (302)

170 (338)

70 (158)

4069 193 (379)

210 (410)

112 (234)

4556 193 (379)

220 (428)

115 (239)

5526 203 (397)

220 (428)

147 (297)

5556 203 (397)

220 (428)

145 (293)

6356 211 (412)

230 (446)

155 (311)

7246 218 (424)

232 (450)

162 (324)

8238 223 (433)

235 (455)

170 (338) Specialty

3078 170 (338)

200 (392)

78 (172) 5555HS

203 (397)

216 (421)

166 (330) HTR4275BK

196 (385)

213 (415)

173 (343) HTR5612BK

196 (385)

213 (415)

173 (343) HTR6108

168 (334)

193 (379)

66 (151) HTR8068

169 (336)

185 (365)

140 (284) HTR8139LV

192 (378)

202 (396) ― HTR8171

150 (302)

188 (370) ― HTR8206

200 (392)

223 (433) ― HTY-401 (R2)

2 Melt Rheology The effect of shear rate on viscosity at typical processing temperatures for the basic types of Hytrel is shown in Figure 1. The viscosity versus shear rate curves for polymers of Hytrel are rela- tively flat, especially at low shear rates. Viscosity does not decrease with increasing shear rate as much as for some other polymers. This means that the resistance to flow of polymers of Hytrel with increases in screw or ram speed may be somewhat greater than experienced with some other poly- mers. This can result in higher torque or injection- pressure requirements. The effect of temperature change on polymer melt viscosity for shear rates of

100 and

1000 secC1 are shown in Figures

2 and 3, respectively. A signifi- cant change in melt viscosity can be effected by a nominal change in melt temperature. Therefore, injection molding processing temperatures are often increased to reduce viscosity and facilitate mold filling. Conversely, in extrusion the melt temperature can be decreased to provide greater melt strength for dimensional stability of the extrudate. The effect of injection pressure on melt flow of Hytrel through long narrow channels is shown in Figures

4 and 5. Increases in flow can also be attained by increasing melt or mold temperatures. Because of the rapid crystallization rate and viscos- ity/shear rate characteristics of Hytrel, relatively high pressures or high melt temperatures are re- quired to fill long shallow cavities, especially below 1.6 mm (1/16 in) cavity depth. The melt viscosity characteristics of Hytrel enable these polymers to be used in a wide range of pro- cessing techniques, from low shear operations (such as rotational molding) to medium and high shear operations (such as extrusion and injection mold- ing). Very high viscosity grades, HTR5612BK and HTR4275BK are designed primarily for blow molding and extrusion. Figure