Complete Guide for Retort Pouch Materials and Structure

Retort pouch is a functional flexible packaging material that can maintain sealing, structural stability and content safety under high temperature conditions. It is widely used in food packaging fields that require high temperature sterilization, such as cooked food, seasonings, fast food, and meat products. In order to ensure that the product does not deform, leak or contaminate during high temperature treatment, retort pouch has strict requirements on material selection and structural design.

Retort Pouch: Ideal Packaging for Extending the Shelf Life of Foods

In the production and processing of foods, there are always two cooking processes, namely high temperature and high pressure sterilization and low temperature and normal pressure sterilization. Meat products sterilized at low temperature have a fresh taste and various nutrients are well preserved because the heating temperature is low and the meat fibers are not destroyed.

However, since it only kills pathogenic bacteria, there are still a large number of spoilage bacteria, which not only has a short shelf life, but also easily causes losses in the circulation field. The high-temperature sterilized meat products have excessive contraction of meat fibers due to the high heating temperature, and the taste is not as good as the low-temperature sterilized products, but because it kills all bacteria and eliminates the internal causes of corruption, the shelf life can be greatly extended.

If the high-temperature sterilized meat products are packed with high-barrier materials, they will not only have a long shelf life at room temperature, but also be convenient for transportation, storage and sales, which is very suitable for the consumption needs of modern society.

Therefore, vigorously developing the production of meat products that can be stored at room temperature is an important product development direction for the meat food industry. The packaging industry conforms to this development trend, makes some achievements and innovations, which can not only meet the needs of the food industry, but also win a broad market for itself.

After years of use, the high-temperature retort pouch has been proved to be an ideal sales packaging container. It has the advantages of both canned containers and boiling water-resistant plastic bags. The food can be kept intact in the bag and can be taken out and eaten after being sterilized and heated at high temperature (generally 120~135℃). It is suitable for the packaging of meat and soy products. It is convenient, hygienic and practical, and can well maintain the original flavor of the food, which is more popular with consumers.

Purpose and Classification of Sterilization of Retort Pouch

Purpose of Sterilization

To completely eliminate harmful bacteria and meet the requirements of sterility, such as sterilization of medical supplies.

After thorough sterilization, it can inhibit the growth of bacteria with little or no preservatives, extend the shelf life of the contents, and keep the original flavor of the contents for a long time at room temperature, such as various high-temperature steamed food products.

Classification of Sterilization Methods

The classification of high-temperature sterilization packaging bags is as follows according to the current internationally recognized classification:

• Retort pouch that can withstand 121℃, with a high temperature resistance time of 30-60min.
• Retort pouch that can withstand 135℃, with a temperature resistance time of 15-30min.
• Ultra-high temperature retort pouch that can withstand 145℃, currently the highest level of retort pouch, with a temperature resistance time of less than 5min.

The retort pouch that can withstand 121℃ is commonly used in the market. Generally, solid materials such as meat high-temperature cooking packaging must also meet the requirements of vacuuming.

Performance Requirements of Retort Pouch Film Substrates

The film substrate used to produce high-temperature retort pouches is the basis for meeting the cooking conditions. Usually, the substrates, specifications, combination order, and types of inks and glue to be used are determined according to the cooking conditions and characteristics of the contents of the high-temperature retort pouch.

Commonly used film substrates include: BOPET, BOPA, HDPE, RCPP, AL, co-extruded EVOH, co-extruded PVDC, co-extruded PE, etc. At present, there are also new co-extruded films with more than five layers, such as: PP/AC/EVOH/AC/PP, PP/AC/PA/EVOH/PA/AC/PP, etc. In addition, there are copolymer nylon MXD6 and ceramic vapor-deposited films such as Si0xPET12um. Due to the limitations of technical processes and price factors, multi-layer co-extruded films and ceramic vapor-deposited films are not often used in high-temperature retort pouches.

According to the order of surface layer (or printing layer), barrier layer and heat sealing layer, the structure of composite packaging materials can be combined. There are also single-layer materials that can be used as both printing layer and barrier layer, so the packaging bag can be designed as two, three, four or more layers according to needs, such as: BOPET/RCPP, BOPA/RCPP, BOPET/BOPA/RCPP, BOPET/AL/RCPP, BOPE-T/AL/BOPA/RCPP, etc.

For the thickness of the substrate, it is usually selected as: BOPET12um, BOPA15um, AL7um or AL9um, RCPP50um, RCPP70um, RCPP80um, RCPP100um, etc. For the barrier layer, BOPA and AL are usually selected. According to actual needs, BOPA25um and AL12um are also selected. The thickness of RCPP selected for high-temperature retort pouch with large capacity and special requirements is also more than 100um. In order to overcome the defect of RCPP not being resistant to falling, liquid packaging bags generally add additives to the film to enhance its anti-fall performance.

Glue and Ink Requirements

The chemical materials selected for high-temperature cooking packaging materials mainly refer to inks, glues and solvents.

Ink

Ordinary inks are not resistant to high temperatures. They will delaminate after cooking and some colors will change. High-temperature cooking inks should be inks with two-component reactive polyurethane as the linker. They have good printing adhesion and can withstand high-temperature cooking after cross-linking and curing reaction. They can form a very strong bond with glue.

At the same time, for large-area spot colors and white patterns, matching ink curing agents must also be selected. When selecting inks, special attention should be paid to distinguishing between ordinary inks, inks that can withstand boiling below 100°C and inks that can withstand high-temperature cooking above 121°C to avoid misuse.

Glue

The glue should be of high temperature cooking resistance grade, which is generally considered to meet the requirements of steaming above 121℃. After compounding, it must have good bonding strength, high temperature resistance and heat resistance. Currently, the most commonly used is two-component polyurethane glue.

Solvent

The solvent should be well matched with ink and glue, and can meet the process requirements, but it should not affect the high temperature cooking resistance of ink and glue.

Structural Analysis of Retort Pouch

Based on the economic performance and physical and chemical properties of the material, the commonly used retort pouch mainly adopts the following structure:

Two-Layer Structure

• PET/CPP
• BOPA/CPP
• GL-PET/CPP

Three-Layer Structure

• PET/AL/CPP
• BOPA/AL/CPP
• PET/BOPA/CPP
• GL-PET/BOPA/CPP
• PET/PVDC/CPP
• PET/EVOH/CPP
• BOPA/EVOH/CPP

Four-Layer Structure

• PET/PA/AL/CPP
• PET/AL/PA/CPP

Multi-Layer Structure

• PET/EVOH co-extruded film/CPP
• PET/PVDC co-extruded film/CPP
• PA/PVDC co-extruded film/CPP
• PET/EVOH co-extruded film
• PA/PVDC co-extruded film

Structural Characteristics of Retort Pouch

The basic structure of retort pouch consists of surface layer/middle layer/heat-sealing layer. The surface layer materials are generally PET and BOPA, which play the role of strength support, heat resistance and good printability. The middle layer uses AL, PVDC, EVOH, and BOPA, which mainly play the role of barrier, light-shielding, and double-sided composite. The heat-sealing layer uses various types of CPP, co-extruded PP and PVDC, EVOH co-extruded films. LLDPE film is also used for cooking below 110℃, which mainly plays the role of heat sealing, puncture resistance, and chemical resistance. The material must also have low adsorption and good hygiene.

Summary

As a special food packaging pouch, Retort Pouch must not only require good high temperature resistance and barrier properties, but also meet safety and environmental protection. Through the correct material selection and structural design, it can ensure that the food is kept in the best condition during cooking, storage and transportation.

باقة ستانلي provides a variety of types of retort pouch, including customized services, and can select the appropriate film substrate and structural design according to customer needs. Whether you need high temperature sterilization packaging or low temperature fresh-keeping packaging, we can provide you with the best solution.

If you have any questions or needs about retort pouch, please contact our professional team, we will wholeheartedly provide you with consultation and service.