Crosslinked Polymeric Film with Segmented Thermal Resistance

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Solution Overview

Problem

Conventional thermoplastic films and articles lose heat sealing and welding properties when cross-linked, limiting their use above the polymer melting point due to the inherent melting behavior of their polymeric components, and there is a need for materials that maintain dimensional stability and heat sealing capabilities at elevated temperatures.

Innovation Solution

A film comprising layers of ethylene-based or propylene-based polymers, cross-linked using radiation and/or chemicals, which maintains heat sealing properties and dimensional stability above the polymer melting point, achieved by using specific polymer compositions such as ethylene/α-olefin/diene interpolymer and propylene/ethylene interpolymer with controlled weight percentages and densities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If thermoplastic films are cross-linked to improve thermal resistance, then dimensional stability above melting point is improved, but heat sealing and welding properties are lost

Engineering Contradiction:

Improvethermal resistanceVSAvoidheat sealing properties

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The film structure is divided into multiple layers with different cross-linking degrees. The outer layers are heavily cross-linked for thermal stability, while the inner heat sealable layer remains lightly cross-linked or uncross-linked to maintain sealing properties. This segmentation allows each layer to perform its specific function optimally.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the film have different cross-linking densities. The outer layers exhibit high cross-linking density for dimensional stability, while the inner layer has low or no cross-linking for heat sealing capability. This local differentiation resolves the contradiction between thermal resistance and sealability.

Inventive Principle:

Principle #3Local quality

2Strength

If thermoplastic films are cross-linked to improve mechanical properties, then puncture resistance is improved, but weldability is lost

Engineering Contradiction:

Improvepuncture resistanceVSAvoidweldability

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The film is segmented into outer structural layers that are cross-linked for puncture resistance and an inner welding layer that is not cross-linked to maintain weldability. This allows the film to be both puncture-resistant and weldable.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The film combines cross-linked thermoplastic material in outer layers with uncross-linked thermoplastic material in the inner layer, creating a composite structure that simultaneously provides mechanical strength and weldability.

Inventive Principle:

Principle #40Composite materials

3Ease of manufacture

If conventional thermoplastic films are used at elevated temperatures, then processing is simplified, but dimensional stability is poor due to melting behavior

Engineering Contradiction:

Improveprocessing simplicityVSAvoiddimensional stability

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The cross-linking transformation changes the fundamental parameters of the polymer structure from linear chains to a three-dimensional network. This parameter change eliminates melting behavior while maintaining processability, as the cross-linked structure provides thermal stability without requiring complex processing.

Inventive Principle:

Principle #35Parameter changes

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

The solution provides a film with improved mechanical properties, puncture resistance, and a broad heat sealing window, enabling use in high-temperature applications, including radiation sterilization and stretch or shrink film processes, while maintaining heat sealing and welding capabilities.

Implementation Method 1

The film is cross-linked using radiation and/or chemicals

Methodology Applied

Scientific EffectRadiation cross-linking: Photopolymerisation

Implementation Method 2

The film is cross-linked using radiation and/or chemicals

Methodology Applied

Scientific EffectChemical cross-linking: Chemical Bonding

Data Source

PatentUS8916647B2Crosslinked films and articles prepared from the same

Publication Date: 2014.12.23 DOW GLOBAL TECHNOLOGIES LLC

AI summary

The invention provides cross-linked polymeric films, laminates, membranes or other polymeric articles, which show rubber like heat resistance (hot set) and dimensional stability above the polymer melting point, while maintaining heat sealing properties. For example, the invention provides a film comprising at least one layer formed from a composition comprising the following components: A) at least one polymer selected from the group consisting of the following: i) an ethylene-based polymer, ii) an ethylene/α-olefin/diene interpolymer, and ii) a C4-C10 olefin-based polymer; B) at least one polymer selected from the group consisting of a propylene/ethylene interpolymer and a propylene/&alpha,- -olefin interpolymer; and wherein the film is crosslinked using radiation and/or chemicals.