Polypropylene-Polyurethane Laminate for Complex Injection Molding
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Solution Overview
Problem
Existing methods for producing molded articles with complex shapes using printed polypropylene sheets often result in whitening, cracking, or peeling of the print layer due to chemical resistance and deformation, limiting their decorative effectiveness and applicability to exterior components.
Innovation Solution
A laminate comprising a transparent polypropylene layer and a polyurethane resin layer with specific tensile-rupture elongation and softening point ranges, rapidly cooled and laminated to absorb elongation during forming, preventing print layer cracking and maintaining transparency, even in complex shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a printed polypropylene sheet is used for injection molding to produce complex-shaped molded articles, then the manufacturing process can be simplified and productivity improved, but the polypropylene sheet whitens and the print layer cracks or peels off due to chemical resistance and large deformation
Solution Approach 1:
The patent divides the polypropylene sheet into multiple functional layers: a transparent polypropylene base layer and a separate resin layer containing the print pattern. This segmentation allows each layer to perform its specific function - the base layer provides structural integrity and transparency, while the resin layer protects the print from cracking and peeling during molding of complex shapes
Solution Approach 2:
The patent creates a composite structure by laminating a resin layer onto the transparent polypropylene sheet. This composite material combines the transparency and moldability of polypropylene with the protective and adhesive properties of the resin layer, preventing whitening and print layer failure while maintaining manufacturing efficiency
2Strength
If specific print materials are used to improve adhesion on polypropylene sheets, then the print layer adhesion improves, but the decorative effect is limited and printability is restricted
Solution Approach 1:
The patent changes the key parameter of the resin layer - its tensile-rupture elongation - to be 150% or more. This parameter change allows the resin layer to stretch and deform with the molded article without cracking, while still maintaining strong adhesion to the print layer, thus improving both adhesion strength and decorative versatility
3Reliability
If the polypropylene sheet is rapidly cooled to maintain transparency, then the appearance quality improves, but the sheet becomes more prone to whitening when formed into complex shapes
Solution Approach 1:
The patent applies a resin layer beforehand onto the transparent polypropylene sheet to cushion and absorb the stresses that occur during molding of complex shapes. This pre-applied resin layer prevents the polypropylene from whitening by compensating for deformation stresses, while the rapid cooling maintains transparency
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 laminate ensures stable adhesion and durability of the print layer on complex-shaped molded articles, preventing whitening and cracking, thus enhancing decorative effectiveness and designability.
Implementation Method 1
the elongation during the forming process is absorbed by the resin layer (B) and is not likely to be transferred to, for instance, a print layer provided on the resin layer (B)
Implementation Method 2
the transparent polypropylene layer (A) is formed by rapidly cooling a molten resin of the polypropylene resin
Data Source
AI summary
A resin sheet is manufactured by: forming a rapidly-cooled transparent polypropylene sheet by rapidly cooling a molten polypropylene resin; laminating on the rapidly-cooled transparent polypropylene sheet a resin layer of polyurethane resin, the polyurethane resin having a tensile-rupture elongation in a range from 150% to 900% and a softening point in a range from 50 degrees C. to 180 degrees C.; and laminating a print layer on the resin layer. A molded article having a non-planar molding made of the resin sheet is provided by insert molding. The molding is formed into a complicated shape where a part of the molding has: 150% or more of an elongation ratio; 0.8 or less of a film-thickness ratio (B/A) before and after the sheet is molded; and/or a surface area ratio (Y/X) before and after the sheet is molded in a range from 1.5 to 5.