What Are Barrier Properties in Resins?

In resins, **barrier properties** refer to,

A property that makes it difficult for gases, liquids, moisture, and the like to pass through the resin

That is what it means.

This is a very important property in food packaging, automotive parts, medical containers, and other applications.

The Concept of Barrier Properties

Let’s consider plastic bottles, for example.

Oxygen enters from the outside.

Carbon dioxide escapes to the outside.

Water evaporates.

When these phenomena occur, product quality deteriorates.

Therefore,

resins that are

resistant to oxygen permeation

resistant to carbon dioxide permeation

resistant to water vapor permeation

are required.

This is described as having “high barrier properties.”

Main Substances Targeted by Barriers

Subject	Examples of Uses
O₂	Preventing Food Oxidation
H₂O	Maintaining the Quality of Dried Foods
CO₂	Carbonated Beverages
Fuel steam	Automotive Fuel Tank
Aromatic Compounds	Coffee, Tea, and Perfume

Why Do Properties Vary by Resin?

There are gaps between molecular chains (free volume) within the resin.

・Resins with high barrier properties

・Molecular chains are densely packed

・High degree of crystallinity

・Strong intermolecular forces

↓

Result: Gases have difficulty passing through

Resins with low barrier properties

Large gaps between molecular chains

Soft, like rubber

↓

Result: Gases pass through easily

Barrier Properties by Resin Type

These are general guidelines for oxygen barrier properties.

Resin	Barrier properties
PE	Low
PP	Low
PS	Low
PET	Moderate
PA	High
EVOH	Very high
PVDC	Very high

In food packaging,

PE

PP

alone do not provide sufficient barrier properties, so

EVOH

PA

are often laminated together.

Barrier Properties in Automotive Parts

Due to strict fuel vapor regulations in the automotive industry,

fuel tanks frequently use

HDPE

EVOH

multilayer structures.

Cross-sectional Diagram

HDPE ↓ Adhesive Layer ↓ EVOH ↓ Adhesive Layer ↓ HDPE

The EVOH layer blocks fuel vapors.

Common Issues with Injection-Molded Parts

For example,

ECU housings,

sensor housings,

and LED lamps

may

malfunction due to moisture intrusion.

Therefore,

material selection,

wall thickness settings,

and gasket design

are used to ensure the necessary barrier performance.

To put it simply for molding engineers:

Barrier property refers to “how resistant a resin is to the passage of gases and liquids.”

In injection molding in particular,

oxygen barrier properties

water vapor barrier properties

fuel barrier properties

are important, and

common materials like PP and PE have low barrier properties, while EVOH and nylon have high barrier properties.

Furthermore, barrier properties depend not only on the material but also on

crystallinity

orientation

wall thickness

temperature

humidity

. In particular, since PA and EVOH experience a decline in barrier performance when they absorb moisture, care must be taken during material selection.