summaryCast CPP film is a widely used packaging material, and its oxygen and water barrier properties will be significantly improved after aluminum plating. Due to differences in aluminum plating layer thickness, process, and technology, the barrier effect after aluminum plating will also vary greatly. This article will start with the testing requirements of CPP cast film, based on the introduction of barrier testing methods, compare the barrier properties of CPP cast film before and after aluminum plating, and briefly explain other testing items of CPP cast film.

KeywordsCast film CPP, aluminum plating, packaging material, oxygen and water resistance, barrier properties

Cast CPP film is a non stretch, non oriented flat extruded film produced by melt casting quenching. It has two methods: single-layer casting and multi-layer co extrusion casting. Compared with blown film technology, its characteristics are fast production speed, high yield, and excellent transparency, gloss, and thickness uniformity of the film. Meanwhile, due to the flat extrusion process, the subsequent processes of the film, such as printing and lamination, are extremely convenient and have a wide range of applications in food and pharmaceutical packaging.

1. Barrier testing requirements for cast CPP

1.1Barrier properties of packaging materials

The so-called barrier property usually refers to the ability of packaging materials to block oxygen and water vapor. The stronger the barrier property, the less likely oxygen and water vapor in the air will enter the interior of the packaging, and naturally will not affect the contents inside the packaging. Packaging materials with strong barrier properties are usually called high barrier materials, but rather low barrier materials. The ability of packaging materials to block oxygen and water vapor is one of the key factors determining the shelf life of products. Generally speaking, the shelf life of high barrier materials is longer than that of low barrier materials.

1.2The impact of oxygen and water vapor on food safety

It is not difficult to know that the oxygen content in our living environment is 20.9%, but the humidity varies greatly depending on the region, season, and time period. Even in the same region, the humidity is constantly changing, and the difference between the north and south is even greater. The existence of humidity in the environment is beyond people's control and intervention. The presence of oxygen and moisture in the environment creates obstacles to the preservation, circulation, and preservation of food. We have all had similar experiences. In hot and humid environments, food quickly rots and deteriorates, even at an astonishing speed. The reason is that with the assistance of oxygen and moisture, bacteria that have not been killed in food multiply at a very alarming rate. Bacterial reproduction and metabolism are the most important factors leading to food spoilage. The reason is also a key factor affecting food safety. It is not difficult to see that in order to ensure food safety, product quality, and ensure that food can reach consumers in a "fresh" state, in addition to circulation control factors, the most important thing is to cut off the fundamental source of food spoilage, which is to cut off the nutrient supply for bacterial reproduction. Cutting off the nutrient supply chain of bacteria also controls the speed of bacterial reproduction, which is equivalent to extending the shelf life of food. Most bacteria rely on oxygen and moisture as breeding conditions. If packaging materials can effectively block oxygen and moisture in the air in research and design, it will inevitably increase the guarantee of food safety.

Therefore, the barrier properties of packaging materials determine how much oxygen and moisture enter the interior of product packaging, which is related to the shelf life and food safety of packaging materials. So the testing and analysis of the barrier performance of packaging materials has become particularly important, as it is related to the shelf life and food safety of food.

2. Introduction to the Barrier Testing Method for Cast CPP

2.1Introduction to Oxygen Transmittance Testing Method

There are currently two popular methods both domestically and internationally:

2.1.1Pressure difference method

Differential pressure method, also known as vacuum differential pressure method.

Testing principle: Place the test sample between two testing chambers, first evacuate the lower chamber, and then evacuate the entire system. When a specific vacuum degree is reached, close the testing lower chamber, and introduce the test gas (oxygen or other test gases can be used) into the upper chamber, creating a constant pressure difference on both sides of the test sample (usually 1 atm=101 kPa). Due to the existence of the pressure difference, oxygen will "penetrate" the thin film from the high-pressure side to the low-pressure side. The amount of oxygen permeation can be measured by the pressure sensor on the low-pressure side, thus obtaining the barrier data of the packaging material.

2.1.2Isobaric method

Isobaric method, also known as Coulomb electric quantity method.

Testing principle: The test sample is clamped between two testing chambers, with flowing oxygen on one side of the sample and flowing nitrogen on the other side. Oxygen will "penetrate" the film from the high concentration side to the nitrogen side of the sample, and the oxygen that penetrates to the nitrogen side will be carried by the flowing nitrogen to the oxygen sensor. By analyzing and calculating the signal size of the oxygen sensor, the oxygen barrier data of the packaging material can be obtained.

2.2 List of testing methods for water vapor permeability

Table 1 Test Method for Water Vapor Transmittance

3. Comparison of Barrier Properties of Cast CPP Before and After Aluminum Plating

The CPP cast film experiment was conducted using the GTR-7001 gas permeability testing system and WVTR-9001 water vapor permeability testing system produced by Jinan Sike Testing Technology Co., Ltd.

Table 2 Comparison of Barrier Properties of CPP Before and After Aluminum Plating

Note: The sample is provided by the customer. Due to unknown aluminum coating thickness and process, the data in the table is for reference only!

4. The importance of other performance indicators of cast CPP

With the continuous increase in market demand, the application field of cast CPP is still expanding and developing rapidly, and the products and materials used in cast film are also constantly updated. To ensure the position and market share of the cast film in the packaging market, it is not enough to only consider the barrier properties of the cast film. It is also necessary to control its friction coefficient, elastic modulus, heat sealing performance, yield strength, and thickness indicators in order to meet the needs of packaging material re production and market development.

5. Conclusion

CPP cast film material has excellent packaging characteristics, coupled with increasingly innovative improvement technologies, it is bound to greatly promote the innovation, promotion, and application of cast film. Overall, with the development and progress of society, market demand continues to increase, and the application of cast film will be increasingly used in various fields of packaging, while also playing a positive role in promoting the progress of the entire packaging market.