How to improve the performance of LDPE blown film?

Increase intensity

The tensile strength is related to the average molecular weight of the resin, the density and processing conditions. For LDPE, with the increase of melt flow rate (MFR), the molecular weight decreases and the tensile strength decreases; With the increase of LDPE density, the crystallinity increases and the tensile strength increases. With the increase of LDPE expansion ratio, traction ratio and processing temperature, the tensile strength increases slightly.

 

In LDPE particles, adding a certain amount of MDPE and HDPE particles can improve the tensile strength of LDPE blown film.

 

There is good compatibility between various PEs, and its performance can be improved by blending, and the strength of the blown film after blending is the product of the performance of each blended component alone and the weight percentage of the component in the blend.

 

The strength of polypropylene is high, but the compatibility of polypropylene and LDPE is general and cannot be completely compatible. When PP is blended with LDPE, ethylene-containing monomer should be used for copolymer propylene blending or EVA as a compatibilizer.

 

Improves slippage

 

The film has good slippage, and can fully fill the specified weight in a short filling time, in order to improve the slippery performance of the film, lubricant can be added to LDPE particles.

 

Can be used as LDPE lubricants: liquid or solid paraffin; Stearic acid and stearate; amides, such as stearate amide and oleic amide; Low molecular weight PE wax, etc.

 

Due to the decrease in the heat sealability of the film with the addition of lubricant, the heat sealing fastness is reduced, the surface printability of the film deteriorates, and it is not easy to bond the ink to the surface. The addition amount can generally be between 0.2% ~ 0.4%, and the dynamic friction coefficient of the inner layer of the liquid packaging film and the composite film of powder solid packaging is generally required to be between 0.2 ~ 0.4.

 

Improved heat sealing performance: inclusion

 

The so-called heat sealability of inclusions means that the hot cover can be well sealed if it is contaminated with dust, grease and packaging.

 

The best heat sealability of inclusions is ionic resin, which can even be heat sealed under the liquid level to make bags, followed by MPE and LLDPE, metallocene polyethylene (mPE) has similar inclusion heat sealability as LLDPE.

 

After the use of LLDPE mixed with LDPE, although it can improve the heat sealing of inclusions of LDPE blowing film, improve the strength and toughness of LDPE blowing film, but also increase the heat sealing temperature of LDPE blowing film, generally speaking, the same MFR LDPE and LLDPE particles, LLDPE melting point is higher than LDPE10 °C.

Improved low temperature heat sealability

 

Low-temperature heat sealability is a necessary feature of soft plastic packaging materials used in high-speed automatic packaging machines, which can speed up the heat sealing speed at lower temperatures.

 

Commonly used to improve LDPE blown film blended resin is EVA, metallocene polyethylene (mPE) and other low melting point ethylene copolymers, EVA melting point with the increase of VA content and decrease, for example: VA content 14% EVA melting point of 85 ~ 93 °C, when the VA content is 28%, EVA melting point is 62 ~ 75 °C, so the use of LDPE and EVA blending can obtain low temperature heat sealing good LDPE blowing film, but the disadvantage is that EVA is softer than LDPE, low strength.

 

When using LDPE+EVA blends, it is best to use a thicker blown film to improve the strength of the heat seal.

 

It is best to use mPE to improve the low-temperature heat sealability of LDPE blown film, and at the same time can obtain better processing performance and good strength.

 

The melting point of mPE, most of the grades are between 85~108 °C, lower than the melting point of LDPE, and the melt strength of mPE is higher than that of LLDPE, therefore, when mPE blows the film, the foam has good stability, good blowing processability, good melt adhesion, high heat sealing strength and high reliability.

 

Generally, the amount of mPE is between 10~20%, because the price of mPE is more expensive, therefore, too high mixing ratio, will make the cost rise, not conducive to competition.

 

Nanjing Haisi Extrusion supply plastic extruder for LDPE/LLDPE/MDPE/HDPE compounding and modification and recycling.

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