The current situation and development of multi-layer co extruded cast barrier film Ⅰ
In recent years, with the rapid development of the economy and the increasing competition in the market, consumers' functional requirements for plastic films have gradually increased. Traditional single material films can no longer meet the needs of consumers, and multi-layer co extruded films that integrate multiple functions have rapidly developed. In addition, with the increasing demand for environmental protection in society, it is necessary to minimize the generation of waste while meeting the packaging function. Multi layer co extruded film has the advantages of low cost, simple operation, almost no environmental pollution, and reusability, which is in line with the national development policy. With the rapid development of the food, electronics, medical, and chemical industries and the continuous rise in domestic labor costs, automatic packaging will increasingly replace manual packaging, providing a favorable development environment for the development of multi-layer co extrusion films.
Processing method of multi-layer co extruded film
Co extrusion technology is a one-step processing process that uses two or more single screw extruders or twin-screw extruders to simultaneously extrude two or more polymers and form multi-layer plate or sheet structures in one head. It has the characteristics of low production cost, simple process, low energy consumption, high production efficiency, and a wide variety of products. The forming methods of multi-layer co extruded films can be roughly divided into: top blowing cold method, bottom blowing water-cooled method, and casting method.
The upper air cooling method relies on air cooling for membrane cooling, which has a slow cooling rate, high crystallinity, high strength, but low flexibility and transparency. Additionally, the stability of membrane bubbles is difficult to control, resulting in significant thickness deviation of the membrane.
Downward water cooling method: The cooling of the membrane is achieved through cold water cooling, which has a fast cooling rate, low crystallinity, high flexibility and transparency of the membrane, and difficult control of the stability of the membrane bubbles, resulting in significant thickness deviation of the membrane. The casting method relies on cooling rollers to achieve fast cooling speed, high flexibility and transparency of the film, stable film shaping, and small thickness deviation of the film.
Compared with the above blown air cooling method and the bottom blown air cooling method, the structure of the film is more flexible and versatile, and the conversion between different structures is faster. In summary, each of these three methods has its own advantages and disadvantages, and different processing methods should be selected according to the needs of the product.
Introduction to the properties of commonly used resins for multi-layer co extruded cast barrier film
(1) Low density polyethylene (LDPE): 0.915-0.925g/CM ³, melting point 105-126 ℃, excellent low temperature resistance, good flexibility, transparency, heat sealing, excellent moisture resistance, high breathability, good melt flowability, and thermal stability.
(2) Linear low-density polyethylene (LLDPE): with a density range of 0.92-0.93g/CM ³, it has a melting point 10-20C higher than LDPE and excellent low temperature resistance. It has good toughness, puncture resistance, heat sealing, moisture resistance, high breathability, and high viscosity of the melt.
(3) Metallocene polyethylene (MLLDPE): with a density range of 0.915-0.92g/CM ³, a melting point similar to LDPE, and better toughness, rigidity, transparency than ordinary PE. It has excellent low-temperature heat sealing and high heat sealing strength, as well as better oil and chemical resistance than ordinary PE.
(4) Homo polypropylene (HOPP): with a density range of 089-0.91g/CM ³, melting point of 170-172 ℃, good moisture resistance, good transparency, high breathability, excellent chemical resistance, poor weather resistance, and low low-temperature impact strength.
(5) COPP: Density range of 0.89-0.90g/CM ³, melting point of 121-150 ℃, good chemical resistance, good transparency, good heat sealing performance, and stronger low-temperature resistance than HOPP
(6) Acid anhydride modified polypropylene mixture (TIE PP): density range of 0.89-0.90g/CM ³, melting point of 135-165 ℃, mainly used for bonding PP with PA or EVOH.
(7) Acid anhydride modified linear modified low-density polyethylene polymer (TIE PE): density range of 0.90-0.93g/CM ³, melting point of 110-130 ℃, mainly used for bonding PE, PA, EVOH.
(8) Polyamide 6 (PA6): Density range of 1.12-1.15 g/CM ³, melting point of 215-225 ℃, good strength and toughness, excellent puncture resistance, good heat and cold resistance, good oxygen resistance, high moisture absorption, good wear resistance, and good transparency.
(9) Ethylene vinyl alcohol copolymer (EVOH): density range of 1.13-1.21g/CM ³, melting point of 158-189 ℃, good oxygen barrier performance, fragrance retention, transparency, good oil resistance, organic solvent resistance, excellent weather resistance, easy to absorb moisture, and the barrier performance decreases after moisture absorption.
(10) Polybutylene terephthalate (PBT): with a density range of 1.3-1.35g/CM ³ and a melting point of 224-227 ℃, it has excellent rigidity, toughness, high heat resistance, weather resistance, self-lubricating properties, good oil resistance, low water absorption, and oxygen resistance similar to PA.
Typical structure and application of multi-layer co extruded barrier film
Multi layer co extruded cast barrier film is mainly used in plastic flexible packaging, and the packaging materials for plastic flexible packaging generally need to meet the following requirements：
1. Due to the ability of oxygen to cause oxidative degradation of fats and proteins, it is necessary to have excellent ability to block oxygen.
2. Due to the entry or evaporation of water vapor, it can cause changes in food taste and must have excellent water vapor barrier ability.
To prevent odors from entering or fragrance from evaporating, and to ensure the original flavor of food, it is necessary to have excellent ability to block aromas.
To meet the needs of sealed storage, it is necessary to have good heat sealing performance.
5. In order to extend the storage time of the product, it is necessary to have a certain degree of low temperature resistance.
6. Meet the requirements of sterilization, avoid microbial damage to food, and have a certain degree of heat resistance
7. Good printability is required for the aesthetic decoration and necessary information of the product.
To protect food and meet the needs of handling and transportation, it is necessary to have strong mechanical properties.
9. Other optical performance requirements.
