The BOPP film touch membrane production methods mainly include tube membrane membrane method of peace.
Tube membrane is a two-way stretching method in one step.
Flat film method is divided into two-way step stretched and two-step stretch two methods.
Tube membrane method has some advantages such as simple equipment, less investment, covers an area of small, material loss, simple operation, etc.
but due to the low production efficiency, the product thickness tolerance big disadvantages, such as almost no development since the 1980 s, is now only used in the production of BOPP special varieties, such as heat shrinkable film.
Two-way step stretching the product of the legal system to balance performance, little in the process of tensile rupture, but because of its complicated equipment, manufacturing difficulty, the price is expensive, edge material loss, more difficult to restricted problems such as high speed, the product thickness, at present has not been large-scale use.
Step and two-way stretching method mature equipment, high efficiency, suitable for mass production, is used by most enterprises.
industrialized production of BOPP film touch membrane with the main components of the main ingredient is PP.
PP is a kind of typical stereoregular polymers, according to the hydrocarbon molecules on either side of the plane distribution, can be divided into isotactic PP, syndiotactic PP and PP random.
Isotactic PP and syndiotactic PP with different crystalline structure of isotactic PP with all other nuclear crystallization in the form of three-dimensional growth and syndiotactic PP mainly by all other nuclear way of two-dimensional crystal, formed the appearance size irregular small chip, and due to the molecular structure of syndiotactic PP neat degree is low, making syndiotactic PP has lower crystallization rate and crystallinity.
study indicates that the larger the isotactic degree, the faster the crystallization rate, film product yield strength and surface hardness will increase obviously, and the random internal lubricant and PP in polymer and polymer orientation and contribute to the improvement of the optical properties of thin films.
At present, there is a great variety of BOPP film, the performance difference is very big also, the main cause of this situation is to use different raw materials and production process.
Practice has proved that only the isotactic PP mass fraction of 95%
The mass fraction of 97%, random PP for 3%
5% of the PP is only suitable for production of BOPP pre-coating film, and melt flow rate of 2 - is generally selected
4 g / 10 min of PP.
in addition, through the PP film touch film on the surface of a total of extrusion, low melting point of layer or one multilayer copolymer can expand the scope of application of BOPP film in the packaging industry.
Longitudinal and transverse stretching than stretching ratio is an important process parameters, both the longitudinal tensile ratio, or transverse stretching ratio, the physical and mechanical properties of BOPP film has a significant impact.
In a certain temperature, the greater the draw ratio, the greater the orientation degree of PP molecular chain.
Mechanical strength of the film increased, modulus, elongation at break decreases, and increase the impact strength and folding resistance, air permeability, good gloss.
the orientation in the process of producing BOPP film mainly occurs in the process of longitudinal extension and transverse tensile, after longitudinal tensile, polymer chain in uniaxial longitudinal orientation, greatly improving the casting pieces of longitudinal mechanical properties, and the lateral performance degradation.
After further transverse tensile, polymer chain in biaxially oriented state.
with the improvement of molecule chain orientation degree, number of straight chain segment membrane increased, folding chain segment number corresponding to reduce, the connection between the chip segments gradually increased, the density and strength increase, and the elongation at break down.
So the two-way stretch can be integrated to improve the performance of PP film.
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