Injection Molding Pretreatment for Moisture-Sensitive Plastics

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Solution Overview

Problem

Existing injection molding technologies are inadequate for processing sensitive plastics, such as those with high moisture content or polyesters, as they react to natural atmospheric moisture, leading to material property changes like reduced strength or altered color, and are not suitable for recycling plastics like polylactic acid (PLA), which requires careful drying and crystallization to maintain quality.

Innovation Solution

A two-stage process involving a pretreatment step in a special preparation container where the plastic material is heated, mixed, and crystallized, followed by injection molding, using a device with a worm gear system that ensures homogenization and drying under controlled conditions, including vacuum or protective gas treatment to prevent degradation, allowing for the production of high-quality preforms with maintained mechanical properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional injection molding is used for sensitive plastics, then processing speed and productivity are maintained, but material properties deteriorate due to moisture reaction leading to reduced strength and altered color

Engineering Contradiction:

Improveprocessing speedVSAvoidmaterial property stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary action by implementing a pretreatment step before injection molding where plastic material is dried and crystallized in a preparation container. This preliminary processing removes moisture and establishes proper crystalline structure, preventing material degradation during subsequent injection molding and ensuring consistent mechanical properties and color stability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs an inert atmosphere principle by conducting the pretreatment process in a preparation container that can be sealed and filled with inert gas or maintained under vacuum. This protects moisture-sensitive plastics from atmospheric moisture during heating and drying, preventing hydrolysis and material property deterioration while maintaining processing efficiency.

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

2Adaptability or versatility

If conventional injection molding is used for plastics like PLA, then general processing capability is maintained, but recycling quality deteriorates without proper drying and crystallization

Engineering Contradiction:

Improverecycling capabilityVSAvoidrecycled product quality

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs parameter changes by controlling temperature, time, and atmospheric conditions in the preparation container during pretreatment. By optimizing these parameters, the process achieves proper drying and crystallization of recycled plastics like PLA, transforming them into a state suitable for high-quality injection molding and ensuring food-grade quality in the final product.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a two-stage process with pretreatment is implemented, then material quality and mechanical properties are improved, but device complexity increases

Engineering Contradiction:

Improvemechanical property maintenanceVSAvoidprocess structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies merging by integrating the preparation container directly with the injection molding device, combining the pretreatment and injection molding functions into a unified system. The preparation container is positioned to feed directly into the injection molding unit, eliminating the need for separate handling and transfer operations, thus reducing overall process complexity despite adding a pretreatment stage.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent employs universality by designing the preparation container to perform multiple functions: drying, crystallization, and material homogenization. This multi-functional approach consolidates several pretreatment operations into a single device, reducing the number of separate components needed and simplifying the overall system architecture while maintaining improved material quality.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Stability of the object's composition

If a preparation container with mixing and comminution tools is used, then material homogeneity and viscosity are improved, but device complexity and energy consumption increase

Engineering Contradiction:

Improvematerial homogeneityVSAvoidenergy consumption

Core Design Contradiction:

Stability of the object's compositionVSUse of energy by moving object

Solution Approach 1:

The patent applies local quality by positioning mixing and comminution tools strategically within the preparation container to create localized high-shear zones where material homogenization is most needed. This targeted approach concentrates energy input in specific regions rather than uniformly throughout the container, achieving effective mixing and viscosity control with reduced overall energy consumption.

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables efficient and cost-effective processing of sensitive plastics, ensuring high viscosity and food-grade quality of recycled products, with no negative effects on mechanical properties, and allows for the production of high-value preforms suitable for foodstuff packaging.

Implementation Method 1

Using this mixing and/or comminution tool, the polymeric material is impinged on by mechanical energy, with the result that the polymeric material is heated, but not melted

Methodology Applied

Scientific EffectMechanical impingement heating: Friction

Implementation Method 2

The polymeric material is kept at high vacuum for a specific average dwell time. During the main treatment, volatile substances are removed by evaporation from the polymeric material

Methodology Applied

Scientific EffectVacuum drying: Evaporation

Implementation Method 3

During the main treatment, volatile substances are removed by evaporation from the polymeric material

Methodology Applied

Scientific EffectDesorption: Desorption

Implementation Method 4

the polymeric material being evenly and constantly moved and mixed

Methodology Applied

Scientific EffectMechanical mixing: Stirring

Implementation Method 5

the polymeric material is crystallized, dried and cleaned in one step

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Data Source

PatentUS8419997B2Method and device for injection molding plastic material

Publication Date: 2013.04.16 EREMA ENGINEERING RECYCLING MASCHINEN & ANLAGEN GMBH

AI summary

The present invention relates to a method and to a device for injection molding plastic material, wherein the starting plastic material to be treated is first subjected to a pretreatment, wherein the plastic material is heated in a receiving container at a temperature below the melting temperature while constantly being mixed, and thereby at the same time is crystallized, dried and/or cleaned and/or the intrinsic viscosity thereof is increased. According to the invention, the plastic material pretreated in this way is transferred into a screw injection molding machine (10) having a screw (16) rotating in a housing (17) and being axially displaceable therein and/or acting as a piston, is plasticized in said screw, and molded into a molded part, for example a preform.