Back-Molding Tool Depression-Projection Film Tensioning
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Solution Overview
Problem
Existing molds for back-injecting plastic films with plastic melts often result in wrinkled or creased decorations due to the softening of thermoplastic films during the hot plastic melt injection, especially when trying to achieve sharp edge decorations without edge radii.
Innovation Solution
A mold design featuring a first mold part with a decorative surface and a clamping surface area, along with a depression area, and a second mold part with a projection area that engages with the depression area to tension and hold the plastic film flat, ensuring it remains wrinkle-free during the injection process, allowing for sharp edge decorations up to the outer edge of the decorative surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the plastic film is heated by hot plastic melt during injection, then the plastic melt flows and fills the mold cavity, but the plastic film softens and forms wrinkles or creases
Solution Approach 1:
The plastic film is pre-stretched and pre-heated before the injection process. The pre-heating softens the film in advance, allowing it to be stretched taut and positioned precisely on the mold surface before the actual injection occurs, preventing wrinkles during the heating phase
Solution Approach 2:
The patent controls the temperature parameters carefully - pre-heating the film to a specific temperature range to soften it for stretching, then controlling the injection temperature and cooling rate to maintain film flatness while allowing the plastic melt to fill the cavity
2Device complexity
If the mold uses conventional design without depression and projection areas, then the structure is simple, but the plastic film cannot be properly tensioned and remains wrinkled
Solution Approach 1:
The mold is segmented into distinct functional areas: a depression area in the first mold part and a projection area in the second mold part. These segmented regions work together to create the tensioning effect on the plastic film, with the projection area pushing against the film from one side while the depression area provides counter-pressure from the other side
Solution Approach 2:
The patent introduces a new dimensional element to the mold design by creating depth variations through the depression area and corresponding projection area. This three-dimensional structural addition allows the mold to actively tension the film in the thickness dimension, preventing wrinkles on the surface
3Ease of manufacture
If edge radii are used in conventional molds, then the mold structure is simpler, but sharp edge decorations cannot be achieved
Solution Approach 1:
The plastic film is pre-stretched and tensioned using the depression-projection mechanism before injection occurs. This preliminary tensioning ensures that the film is already flat and taut against the sharp edge features of the mold, allowing sharp edge decorations to be captured accurately without requiring compensating edge radii in the mold design
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 mold design ensures a crease-free decoration by maintaining the plastic film's tension and flatness over the decorative surface, enabling precise and sharp edge designs without the need for edge radii, thus improving the precision and quality of plastic moldings.
Implementation Method 1
the softening of the thermoplastic plastic film by the hot (preferably around 200°C up to 300°C) plastic melt
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention relates to a molding tool (1) for back-molding a plastic film (4) with a plastic melt and to a corresponding method for producing a plastic blank in the cavity (11) that is formed by a first and second molding tool part (2, 3). The first molding tool part (2) has a decorative surface region (21), a clamping surface region (22) that is arranged outside of said decorative surface region, and a recessed region (23) that is arranged at least outside of the decorative surface region (21). The second molding tool part (3) has an inlet opening (31) for the plastic melt and a protruding region (33). The protruding region (33) is arranged such that said protruding region engages the recessed region (23) when the tool is closed in order to stretch the plastic film (4) into the recessed region (23), said plastic film lying between the first molding tool part (2) and the second molding tool part (3) so as to rest on the clamping surface region (22) of the first molding tool part.