Propylene Block Copolymer Melt Viscoelasticity and Rigidity Balance
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Solution Overview
Problem
Propylene-based polymers face challenges in achieving a balance between rigidity and impact resistance, while also addressing molded product appearance defects such as flow marks and surface graininess, with existing methods either improving one aspect at the expense of the other or requiring additional processing steps like deashing or stereoregularity issues.
Innovation Solution
A propylene-based block copolymer with a wide molecular weight distribution, comprising a room temperature n-decane-insoluble and n-decane-soluble portion, is developed using a specific olefin polymerization catalyst system, which includes a solid titanium catalyst component and cyclic ester compounds, to enhance melt viscoelasticity, stereoregularity, and crystallization, resulting in improved rigidity, impact resistance, and appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rubber component or EPR is added to improve impact resistance, then impact resistance is improved, but rigidity is lowered
Solution Approach 1:
The patent changes the molecular weight distribution parameters of the propylene-based polymer by using a multi-stage polymerization process with different catalysts and conditions. This creates a broad molecular weight distribution with both high-molecular-weight components (providing impact resistance) and low-molecular-weight components (providing rigidity), thereby improving the balance between these properties without adding rubber components that would compromise rigidity.
2Stress or pressure
If an inorganic filler is added to make up for rigidity, then rigidity is improved, but the complexity of the composition increases
Solution Approach 1:
The patent extracts the need for inorganic fillers by achieving the desired rigidity through the optimized molecular weight distribution and crystallinity of the propylene-based polymer itself. The multi-stage polymerization process produces a polymer with inherent high rigidity due to its structural characteristics, eliminating the requirement for additional inorganic filler materials and simplifying the composition.
3Strength
If the molecular weight distribution is widened to improve impact resistance, then impact resistance is improved, but molded product appearance deteriorates due to flow marks
Solution Approach 1:
The patent applies local quality by creating distinct molecular weight regions within the polymer structure. The high-molecular-weight fraction (prepared in one stage) provides impact resistance, while the low-molecular-weight fraction (prepared in another stage) ensures good flow characteristics and smooth molded product appearance. Each molecular weight region performs its specific function locally within the overall polymer matrix.
4Stability of the object's composition
If a titanium trichloride catalyst is used to widen molecular weight distribution, then molecular weight distribution is widened, but residual metal increases requiring deashing steps
Solution Approach 1:
The patent employs a disposable catalyst system where the catalyst is completely consumed during the polymerization reaction. The multi-stage polymerization uses catalysts that are fully reacted and transformed into the polymer product, leaving no residual metal requiring deashing steps. This approach trades the reusability of the catalyst for the elimination of post-processing deashing operations.
5Manufacturing precision
If the molecular weight of the copolymer rubber is increased to improve appearance, then appearance is improved, but the polymer becomes too viscous for good processability
Solution Approach 1:
The patent segments the copolymer rubber into different molecular weight fractions through multi-stage polymerization. The first stage produces a high-molecular-weight fraction that improves appearance properties by reducing flow marks, while the second stage produces a low-molecular-weight fraction that maintains good flow characteristics and molding processability. This segmentation allows each fraction to optimize its specific function without compromising the other.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The propylene-based block copolymer achieves high melt viscoelasticity, low linear expansion coefficient, and high dimensional accuracy, reducing flow marks and surface defects, and enabling the production of molded products with excellent balance of rigidity and impact resistance.
Implementation Method 1
an olefin polymerization catalyst comprising a solid titanium catalyst component (I), an organometallic compound (II) containing a metal atom selected from Group 1, Group 2 and Group 13 of the periodic table, and if necessary, an electron donor (III)
Implementation Method 2
a cyclic ester compound (a) represented by the following formula (1) and a cyclic ester compound (b) represented by the following formula (2)
Implementation Method 3
The propylene-based block copolymer of the present invention has high melt viscoelasticity
Implementation Method 4
the room temperature n-decane-insoluble portion (Dinsol), which has specific properties and comprises a crystalline propylene-based (co)polymer
Data Source
AI summary
The present invention provides a propylene-based block copolymer having high melt viscoelasticity, excellent balance between rigidity and impact resistance, good molding processability, and excellent molded product appearance, a composition containing the copolymer, and molded products obtained therefrom. The propylene-based block copolymer comprises 5 to 80% by weight of a room temperature n-decane-soluble portion (Dsol) and 20 to 95% by weight of a room temperature n-decane-insoluble portion (Dinsol) (the total amount of the Dsol and the Dinsol is 100% by weight), and satisfies the requirements [1] to [3]: [1] the molecular weight distribution (Mw/Mn) of the Dsol is 7.0 to 30, [2] the molecular weight distribution (Mw/Mn) of the Dinsol is 7.0 to 30, and Mz/Mw thereof is 6.0 to 20, and [3] the pentad fraction (mmmm) of the Dinsol is not less than 93%.