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Lowering Ejection Force During Injection Molding of Syndiotactic Polystyrene (SPS) Compounds

IP.com Disclosure Number: IPCOM000019870D
Publication Date: 2003-Oct-03

Publishing Venue

The IP.com Prior Art Database

Related People

J. M. Warakomski: INVENTOR [+6]

Abstract

QUESTRA* syndiotactic polystyrene (SPS) is a semi-crystalline polymer that is useful as an engineering plastic, especially when compounded with glass fiber reinforcement, and other additives, such as impact modifiers and flame retardants. With a melting point of 270ºC, SPS compounds have excellent properties such as heat resistance, solvent resistance, low dielectric constant, insensitivity to moisture, low specific gravity compared to other semi-crystalline polymers, and dimensional stability. During injecting molding operations, syndiotactic polystyrene compounds generally are ejected from the mold easily. In some cases, depending on the design and condition of the tool, improved demolding is desired. Ejection force can be deceased by up to 85% by adjusting molding conditions and adding mold release agents. We will describe a full factorial designed experiment from which we developed a predictive model for ejection force based on are mold temperature, hold pressure, and melt temperature. We will also describe the effect of internal and external mold release agents. *Trademark of The Dow Chemical Company

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NOI PS&EP 2003-023

Publication for IP.com

September 9, 2003

Lowering Ejection Force During Injection Molding of Syndiotactic Polystyrene (SPS) Compounds

J.M. Warakomski, A.P. Banks, K.L. Nichols, and H. Fowler

The Dow Chemical Company

Introduction........................................................................................................................................ 1

Part 1. Effect of molding conditions on ejection force for EA533.......................................................... 2

Conclusions for Part 1, effect of molding conditions on EA533........................................................... 4

Part 2. Ejection Force as a Function of Mold Temperature................................................................... 4

Conclusions for Part 2, mold temperature study................................................................................. 6

Part 3. Description of Mold Release Agents...................................................................................... 6

Part 4. Effect of External Mold Release Agents.................................................................................. 7

Conclusions for Part 4, external mold release agent evaluation........................................................... 8

Part 5. Effect of Internal Mold Release Agents................................................................................... 8

Conclusions for Part 5, internal mold release agent evaluation........................................................... 10

Part 6. Summary.............................................................................................................................. 10

Introduction

Syndiotactic polystyrene (SPS) is a semi-crystalline polymer that is useful as an engineering plastic, especially when compounded with glass fiber reinforcement, and other additives, such as impact modifers and flame retardants. With a melting point of 270ºC, SPS compounds have excellent properties such as heat resistance, solvent resistance, low dielectric constant, insensitivity to moisture, low specific gravity compared to other semi-crystalline polymers, and dimensional stability.

During injecting molding operations, syndiotactic polystyrene compounds generally are ejected from the mold easily. In some cases, depending on the design and condition of the tool, improved demolding is desired. We have discovered that ejection force from a mold can be decreased by adjusting process conditions, by adding an internal or external mold release agent, or by combining both approaches. To measure mold releasability, we used a cylindrical ejection force tool on a Mannesmann Demag D100-275 injection molding machine. This tool produces a cylinder with one closed end having dimensions of about 4 inch high x 1.75 inch diameter, with about 1/16 inch wall thickness. An annulus pushes the part from the tool and a pressure transducer measures the required force.

This invention embodies the use of inj...