Performance characteristics, testing, and common problems of soft can packaging materials for food packaging bags

Compared to canned foods in rigid packaging such as tinplate and glass bottles, soft cans are retort pouches made of packaging materials composed of composite films such as polyester, aluminum foil, and polyolefin, and are made into long-term preservation bagged foods through sealing and sterilization.

 

 

 

 

Generally, food packaging bags and soft cans are two different concepts:

Food packaging bags refer to fixed-volume packaging whose container shape can change after filling or removing the contents. The materials are generally plastic films, aluminum foil, paper, fiber products, and their composite materials.

Soft cans are a type of food packaging bag, referring to bag-shaped or shaped containers made of plastic films or metal foils and their composite films. After filling and processing products, they are heat-sealed and heat (or pressure) sterilized to achieve commercially sterile packaged food.

Soft canned food has a relatively short history.

In 1958, the US Army Research Institute began researching military soft cans. In 1977, some retort pouches were approved by the US Food and Drug Administration (FDA) and the US Department of Agriculture (USDA) and officially put into production and sale.

In terms of large-scale commercial production of soft canned food in the world, Japan has the largest industrial scale and the most varieties. In 1968, Japan achieved the commercialization of retort pouch packaged curry products. In 1975, it formulated the standard (JAS) for soft canned food, and in 1977, it formulated the definition and manufacturing standard for soft cans.

Since then, the market for various retort pouch foods in Japan has developed rapidly, and the supporting facilities such as packaging materials and processing equipment are quite complete and advanced.

Originating in the United States, soft cans represent the second innovation in food packaging history and are known as the second generation of canned food. Its processing principles and methods are similar to rigid cans, but because its packaging window is soft, it is called a "soft can," and in Europe and America, it is called Retort Pouch Foods or Flexible Can.

Japan collectively refers to these soft can products as "retort food," derived from the English word "Retort" (sterilization). Currently, there are more than 10,000 varieties of soft cans in the world.

The statement in the market that retort pouch food is labeled as "vacuum packaging" is unscientific because vacuum sealing after filling retort pouches with food is to remove oxygen from the bag and reduce pressure, which is only one process. High-temperature (or pressure) sterilization is the real means by which retort pouch food achieves its shelf life.

Soft can packaging forms have various appearances such as bag-shaped, box-shaped, cup-shaped, and bowl-shaped. Among bag-shaped soft cans, there are also stand-up pouches and ordinary pouches.

I. Characteristics of Soft Cans

 

 

 

 

1. High-temperature sterilization can be used, and the time is short, and the nutrients of the contents are rarely damaged

The composite film of soft can packaging can withstand high temperatures above 120℃, and the heat transfer is fast, and the cooling time after sterilization is also short. The entire sterilization time is shortened by 1/2 compared to rigid cans, which helps maintain the original characteristics of the contents.

2. It can be stored or circulated at room temperature for a long time, and the preservation is stable

Soft cans are sealed and temperature-controlled sterilized products, so they do not require special storage conditions such as refrigeration. They can be safely stored in ordinary warehouses and shelves at room temperature. The soft can packaging material is chemically stable, and its surface has no metal ions, so it will not react chemically with the contents.

3. Convenient to carry, easy to open, safe, and time-saving

4. Energy saving and cost reduction

Soft canned food is heated for consumption. Just put it in boiling water and boil it for 3-5 minutes to save a lot of energy.

5. Soft cans are easily damaged and leak, causing the contents to spoil

Because the seal of soft can packaging is soft, it is easily damaged by external pressure, reducing the vacuum degree and causing contamination and spoilage.

II. Performance Characteristics of High-Temperature Retort Packaging Materials

 

 

 

 

 

High-temperature retort packaging materials refer to films or bags made of multi-layer films with different functions and adhesives through dry lamination, which can be heat-sealed and can withstand high-temperature retort.

The high-temperature retort mentioned here includes three situations: one is semi-high-temperature retort at 100℃-121℃, one is high-temperature retort at 121℃-135℃, and the other is ultra-high-temperature retort above 135℃.

Because high-temperature retort packaging materials must withstand high-temperature sterilization and a longer shelf life at room temperature, the following requirements are placed on the materials:

First, good barrier properties;

Second, good heat resistance and low-temperature resistance;

Third, good puncture resistance;

Fourth, good lamination strength and heat sealing strength;

Fifth, the inks and adhesives used must also have good heat resistance and low-temperature resistance.

PET-C and NY-C represent high-barrier PET and high-barrier NY, respectively;

PET, NY, and AL are all good temperature-resistant materials;

CPP.

Because there are ordinary types and high-temperature retort types, CPP must choose high-temperature retort types.

Currently, most high-temperature retort CPPs are imported from Japan and Europe. CPPs sterilized below 121℃ can currently be produced by some large CPP manufacturers in China, so domestic materials can be considered.

The specific type of CPP needs to be selected according to the subsequent sterilization conditions and applications. If it is used for easy-peel applications, easy-peel CPP needs to be selected.

Inks and adhesives should also use high-temperature retort grade. High-temperature retort adhesives are divided into aliphatic and aromatic types. From a safety perspective, it is recommended to use aliphatic high-temperature retort adhesives as much as possible, especially for products exported to countries with high safety requirements.

High-temperature retort packaging includes high-temperature retort films and pouches. High-temperature retort packaging must provide adequate protection for the contents, so high-temperature retort food products have a series of quality requirements for this type of packaging.

Sixth, the hygienic performance should comply with the provisions of GB9683-88.

Seventh, the residual solvent content shall not exceed 10mg/m2.

Three, Performance Test of High-Temperature Retort Packaging Materials

 

 

 

 

1. Packaging Sealability Test

The sealing performance of the material is tested by methods such as inflation with compressed air and underwater extrusion. The test can effectively compare and evaluate the sealing performance of the packaging and provide a basis for determining relevant production technical indicators.

2. Packaging Pressure Resistance and Drop Resistance Test

By testing the pressure resistance and drop resistance of high-temperature retort packaging, the rupture resistance and proportion during the turnover process can be controlled.

Because the conditions during the turnover process vary greatly, pressure resistance tests are performed on individual packages and drop resistance tests are performed on the entire box of products, and multiple tests are performed in different directions to comprehensively analyze the pressure resistance and drop resistance performance of the packaging products, and solve problems caused by packaging damage during transportation or transfer.

3. Mechanical Strength Test of High-Temperature Retort Packaging

The mechanical strength of packaging materials includes the composite peel strength, heat sealing strength, tensile strength, etc. If the test indicators do not meet the standards, they are easily broken or fractured during packaging and transportation. A universal tensile testing machine can be used to test and determine whether they meet the relevant national and industry standards and standard methods.

4. Barrier Performance Test

High-temperature retort products generally contain highly nutritious contents such as meat products, which are easily oxidized and deteriorated. Even within the shelf life, their taste varies with the date.

Therefore, in order to ensure their nutrition, flavor and quality, barrier materials must be used, and therefore, the packaging materials must undergo strict oxygen and moisture permeability tests.

5. Residual Solvent Detection

Since printing and lamination are two very important processes in the high-temperature retort production process, and the use of solvents is necessary in the printing and lamination processes, solvents are high-molecular chemical materials with a certain irritating odor and harm to the human body. Foreign laws and regulations have very strict control indicators for some solvents such as toluene butanone. Therefore, solvent residues must be tested during the production of printing semi-finished products, composite semi-finished products, and finished products to ensure that the products are healthy and safe.

Four, Common Problems of High-Temperature Retort Flexible Packaging Products

 

 

 

 

Although high-temperature retort flexible packaging has been developed for many years, there are still many common quality problems in actual use, some of which occur during the packaging material production process, and some occur during use due to insufficient understanding of flexible packaging or the use of sterilization equipment suitable for rigid canned sterilization without necessary process adjustments.

The common problems are as follows.

1. Pouch Swelling:

The main reasons include contamination of the seal causing false sealing, leading to oxygen entering the bag, thus causing bacterial growth and pouch swelling; or incomplete sealing due to the sealing tunnel at the seal, causing the contents to deteriorate and ferment and causing pouch swelling; or the selection of raw materials with poor barrier properties, allowing oxygen to enter, causing the contents to deteriorate and swell; or punctures or friction on the bag surface during production or transportation due to bone spurs or sharp foreign objects, which will also cause contamination of the contents and deterioration and swelling.

2. Pouch Bursting:

Due to improper back pressure control during retorting, the internal pressure of the bag is much greater than the environmental pressure inside the retort, which can cause pouch swelling or even bursting.

If the contents are liquid, severe bumps during production and transportation can cause excessive impact of the liquid inside the bag on the bag edges, which may lead to bag breakage.

Or due to severe pouch swelling, the edges cannot withstand the pressure and burst.

3. Wrinkles on the Pouch Surface After High-Temperature Retorting:

Due to improper selection of raw materials, the sensitivity of different components of the composite material to the temperature during retorting is significantly different, resulting in different deformation amounts and wrinkles on the pouch surface.

In addition, due to poor back pressure control, excessive back pressure causes permanent deformation of the material; it is also possible that the vacuum degree is too high during vacuum sealing, causing material deformation.

4. Heat Seal Edge Cracking:

The possible reasons for this phenomenon are that the sealing temperature and pressure are too high in the bag making process, which damages the material and reduces the strength of the seal; or heat sealing bubbles appear at the seal, creating local weak points in the heat seal that crack under external force.

Improper selection of adhesives or inks, under high temperature and high pressure during heat sealing or high temperature and high pressure during high-temperature retorting, reduces the composite strength, resulting in composite delamination, and ultimately the sealing strength is only the strength of the heat sealing layer material. When it cannot withstand internal and external forces, seal edge cracking will occur.

With the continuous improvement of people's living standards and the continuous acceleration of the pace of life, the demand for fast, safe, and convenient packaging is becoming increasingly urgent. Therefore, the demand for high-temperature retort packaging is showing a continuous upward trend, and higher requirements are also put forward for the performance and functions of high-temperature retort packaging.

For example, it is required that the packaging material provides more effective protection for the contents, including better barrier properties, better strength and weather resistance; more reasonable design; more environmentally friendly, recyclable; personalized; therefore, transparent and visible high-barrier high-temperature retort packaging is gradually becoming a popular trend in high-temperature retort flexible packaging.

Compared with traditional aluminum foil retort packaging, due to the use of transparent and visible high-temperature retort packaging, consumers can directly see the quality and color of the contents, the packaging bag can pass through a metal detector, can be used directly in a microwave oven, and the barrier performance can also reach below 1.0.

Now, this flexible packaging material has been successfully applied to canned food packaging. This packaging uses transparent, high-temperature retort, high-barrier materials compounded with NY, PET, and CPP.

Its unique high barrier performance, UV barrier performance, and barrier maintenance after bagging are especially suitable for packaging with high barrier and UV barrier performance requirements, such as salted mushrooms, bamboo shoots, water chestnuts, rice, corn, vegetables, fruits, etc. At the same time, this packaging can prevent the contents from deteriorating or discoloring during the shelf life, and it can completely replace tinplate can packaging.