Biaxially Oriented LLDPE Film Blend Processability
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Solution Overview
Problem
The processing of biaxially oriented films made from metallocene-catalyzed linear low density polyethylenes (mLLDPEs) is challenging due to their relatively low viscosity and narrow molecular weight distribution, which hinders the formation of high-quality films with desirable properties such as toughness and optics.
Innovation Solution
A film comprising a blend of at least 20 wt% of a first linear LLDPE and 20 wt% of a second LLDPE, with specific density and melt index ranges, and optionally a short chain branched LLDPE, which are metallocene-catalyzed and exhibit broader molecular weight distributions, improving processability and maintaining toughness, along with a method involving extrusion and biaxial orientation to achieve high TD and MD orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallocene-catalyzed LLDPE is used to make films, then toughness and optics are improved, but processability deteriorates due to low viscosity and narrow molecular weight distribution
Solution Approach 1:
The patent combines multiple LLDPE resins with different molecular weight distributions into a blend composition. The first LLDPE resin has a narrow MWD (1.0 < Mw/Mn ≤ 3.0) providing toughness, while the second LLDPE resin has a broader MWD (3.0 < Mw/Mn ≤ 6.0) improving processability. This merging of materials resolves the contradiction by achieving both toughness and processability in the final film.
Solution Approach 2:
The patent creates a composite polymer composition blending LLDPE resins with different catalytic origins (metallocene and non-metallocene) to achieve complementary properties. The composite structure allows the narrow MWD component to provide toughness while the broader MWD component facilitates processing, resolving the technical contradiction through material composition design.
2Manufacturing precision
If metallocene-catalyzed LLDPE is used, then film quality and optics are enhanced, but extrusion requires higher back pressure and amperage
Solution Approach 1:
The patent merges LLDPE resins with different flow characteristics into a blend. The broader MWD component (3.0 < Mw/Mn ≤ 6.0) acts as a processability enhancer that reduces the energy required for extrusion while the narrow MWD component (1.0 < Mw/Mn ≤ 3.0) maintains film quality. This combination resolves the contradiction between film quality and extrusion energy consumption.
Solution Approach 2:
The patent changes the molecular weight distribution parameter of the polymer composition by blending resins with different MWD characteristics. This parameter change reduces the viscosity and improves flow characteristics during extrusion, thereby reducing back pressure and amperage requirements while maintaining the film quality provided by the metallocene-catalyzed component.
3Strength
If narrow molecular weight distribution LLDPE is used, then toughness is superior, but film formation becomes challenging
Solution Approach 1:
The patent combines LLDPE resins with contrasting molecular weight distributions in a controlled blend ratio (40-80 wt% narrow MWD, 20-60 wt% broader MWD). The narrow MWD resin (1.0 < Mw/Mn ≤ 3.0) provides superior toughness, while the broader MWD resin (3.0 < Mw/Mn ≤ 6.0) facilitates film formation. This merging resolves the contradiction by allowing both toughness and ease of film formation to coexist in the final product.
Solution Approach 2:
The patent creates a composite LLDPE system blending metallocene-catalyzed resin (narrow MWD) with non-metallocene catalyzed resin (broader MWD). The composite structure enables the narrow MWD component to contribute toughness while the broader MWD component enables proper film formation, resolving the technical contradiction through compositional design.
Data Source
AI summary
Disclosed in one aspect is a film comprising at least one core layer comprising a blend of at least 20 wt%, by weight of the core layer, of a first linear LLDPE having a molecular weight distribution (Mw/Mn) within the range of from 1.0 to 4.0; and at least 20 wt%, by weight of the core layer, of a second LLDPE - in a certain embodiment a short- chain branched LLDPE - having a molecular weight distribution (Mw/Mn) within the range of from 1.0 to 7.0; characterized in that the density of the second LLDPE is greater than the density of the first LLDPE by at least 0.002 g/cm3; and/or the I2 of the second LLDPE is greater than the I2 of the first LLDPE by at least 0.5 dg/min. In certain embodiments, the first and second LLDPEs are produced by a metallocene-catalyzed reaction. In yet another embodiment, the combined molecular weight distribution (Mw/Mn) of the first and second LLDPEs is greater than 4.0.