Propylene Block Copolymer Moldability Modifier for Auto Exterior Parts
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Solution Overview
Problem
Current polypropylene resin compositions for automobile parts face issues with flow marks and voids during injection molding, leading to impaired appearance and increased production costs, particularly in the manufacture of lightweight, thin-walled components like bumpers, where existing solutions either compromise on physical properties or require excessive amounts of expensive ethylene elastomers.
Innovation Solution
A polypropylene resin composition incorporating a moldability modifier comprising a propylene block copolymer with a broad molecular weight distribution, combining a high fluidity crystalline propylene polymer portion and a high molecular weight propylene/ethylene random copolymer portion, which is added in small amounts to improve molding process characteristics and reduce the use of expensive ethylene elastomers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polypropylene resin compositions are molded into thinner moldings in shorter molding time, then productivity is improved, but flow marks and voids occur leading to appearance failures
Solution Approach 1:
The invention changes the molecular weight distribution parameters of the propylene block copolymer, specifically setting the weight average molecular weight to 100,000-1,000,000 and the number average molecular weight to 50,000-200,000, creating a broad distribution that optimizes both flow characteristics and structural integrity during rapid molding processes
Solution Approach 2:
The invention creates a composite resin composition blending propylene block copolymer with ethylene/propylene copolymer in a specific ratio (70-99.9 wt% and 0.1-30 wt% respectively), combining the high fluidity of the block copolymer with the elastomeric properties of the copolymer to achieve both rapid molding and defect-free appearance
2Strength
If ethylene thermoplastic elastomer component is increased to improve impact resistance, then physical properties are improved, but manufacturing cost increases
Solution Approach 1:
The invention optimizes the molecular weight parameters of the propylene block copolymer, setting weight average molecular weight to 100,000-1,000,000 and number average molecular weight to 50,000-200,000, which enhances the base resin's toughness and impact resistance, reducing reliance on expensive elastomer additives
Solution Approach 2:
The invention uses a cost-effective propylene block copolymer with controlled molecular weight distribution as the primary resin base, replacing the need for large amounts of expensive ethylene thermoplastic elastomers while maintaining adequate impact resistance for the application
3Productivity
If pressing time is shortened to improve production cycle, then productivity is improved, but rimple-like molding failure due to voids occurs
Solution Approach 1:
The invention adjusts the molecular weight distribution parameters of the propylene block copolymer, specifically setting the weight average molecular weight to 100,000-1,000,000 and the number average molecular weight to 50,000-200,000, which optimizes the resin's flow and packing characteristics to prevent void formation during rapid pressing cycles
Solution Approach 2:
The invention blends propylene block copolymer with ethylene/propylene copolymer in a specific ratio (70-99.9 wt% and 0.1-30 wt% respectively), where the copolymer component acts as an elastomeric modifier that suppresses void formation and rimple defects during short pressing times, maintaining molding quality despite reduced cycle time
Data Source
AI summary
A moldability modifier capable of improving molding processability, and a polypropylene resin composition using the same suitable for automobile exterior parts are provided. The invention relates to a moldability modifier comprising propylene block copolymer (A) containing from 80 to 98 wt % of a propylene homopolymer portion (A1) and from 2 to 20 wt % of a propylene/ethylene random copolymer portion (A2), wherein the MFR of (A1) is 300 g/10 min or more, the ethylene content of (A2) is from 10 to 70 wt %, the [η] of (A2) is 6.5 dl/g or more, and the MFR as a whole is 40 g/10 min or more; and propylene block copolymer (B) containing from 20 to 79 wt % of a propylene polymer portion (B1) and from 21 to 80 wt % of a propylene/ethylene random copolymer portion (B2), wherein the MFR of (B1) is 20 g/10 min or more, the ethylene content of (B2) is from 20 to 70 wt %, the [η] of (B2) is from 2.5 to 9.0 dl/g, and the MFR as a whole is from 0.1 to 50 g/10 min; and a polypropylene resin composition using the same.