To achieve ideal curing effects, several factors need considered, including:
1. Form of curing room and ideal status: speed and amount of hot wind from heating device and tunnel; ground and two or several sides of curing room have sufficient and uniform temperature hot wind; small difference between actual and set temperature, and heat preservation and waste discharge meet the requests; film rolls are easy to move and take.
2. Products meet the technical requests.
3. The functions, corona value, heat resistance, etc. of lamination fims.
4. Adhesives: solvent adhesive, solventless adhesive, single or double component water base adhesive, hot melt adhesive, etc.
This paper mainly focuses on lamination films and adhesives.
1. Lamination Films
The physical, heat resistance and barrier performance of PE film, which is widely used, will be better, when the density of PE rises. PE films with same density but different produce processes have different performances.
CPE can be cooled fast, with low crystallinity, high transparency and low turbidity. But molecular arrangement is irregularly, making it bad barrier performance, which is high transmittance. And it’s the same with LDPE. Therefore, curing temperature shouldn’t be too high when using PE films. When the heat resistance of PE is improvement, the curing temperature can be higher.
2.1 Ethyl Based Adhesive
According to performances of lamination films and adhesives, curing conditions can be divided into different levels:
1. Temperature 35℃, time 24-48h
2. Temperature 35-40℃, time 24-48h
3. Temperature 42-45℃, time 48-72h
4. Temperature 45-55℃, time 48-96h
5. Special, temperature over 100℃, time according to technical support.
For common products, considering the density, thickness, anti-block, heat resistance performance of films as well as size of bags, curing temperature shouldn’t be too high. Usually, 42-45℃ or below is enough, time 48-72 hours.
Outer lamination films, which require high performance and fine heat resistance are suitable for high temperature curing, like over 50℃. Inner films, like PE or heat sealing CPP, are suitable for 42-45℃, curing time may be longer.
Boiling or retort products, which need high performance and high heat resistance, should accord to the curing conditions which adhesive factory provides.
Curing time should accord to the reaction completion rate, friction coefficient and heat sealing performance.
Special products may need higher curing temperature.
2.2 Solventless Adhesive
If sealing performance meets the requirement, for solventless laminating products, of which inner films have low density, the adhesives have many free monomers, making it hard to seal. Therefore, low temperature curing is recommended, for 38-40℃.
If the reaction completion rate meets the requirement, longer curing time should be considered.
If heat sealing films have high density, the curing temperature should be 40-45℃. If reaction completion rate and heat sealing performance need improving, the curing time should be longer.
Strictly test is a must before mass production, to ensure the quality.
What’s more, humidity should be considered. Especially on a dry winter, proper humidity can accelerate reaction rate.
2.3 Water Based Adhesives
When laminating VMCPP, lamination machine must be dry enough, or the aluminized layer will be oxidized. During curing, the temperature shouldn’t be too high or too low. High temperature will lead to high friction coefficient.
2.4 Hot Melt Adhesive
Usually choose natural curing, but adhesion performance after melting should be noticed.
3. Strictly Control Curing Temperature
According to researches, on the aspect of reaction rate, there is nearly no reaction under 30℃. Over 30℃, every 10℃ higher, the reaction rate improve about 4 times. But it’s not correct to improve the temperature to accelerate reaction rate blindly, several factors should be noticed：actual reaction rate, friction coefficient and heat sealing strength.
To achieve the best curing result, curing temperature should be divided into different aspects, according to lamination films and structures.
For present, common problems are as below:
One, curing temperature is too low, making low reaction rate, and the product has problems after hot sealed or boiled.
Two, curing temperature is too high and hot sealing film has low density. The product has bad hot sealing performance, high friction coefficient and bad anti-block effects.
To achieve the best curing effect, curing temperature and time should be decided by environment temperature and humidity, film performance and adhesive performance.
Post time: Apr-22-2021