Toothbrush Head Injection Molding Sink Mark Prevention
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Solution Overview
Problem
The challenge is to produce a toothbrush head with a complex internal structure that is optically flawless, particularly on the back side, while maintaining a thin profile for comfortable use, as existing methods face issues with uneven plastic flow and material shrinkage during injection molding, leading to optical defects and sink marks.
Innovation Solution
The solution involves a toothbrush head design with varying distances between blind holes and the back side, featuring beveled or rounded transitions, uniform wall thicknesses, and strategically placed blind holes of different depths to ensure even cooling and material distribution, along with an inhomogeneous internal structure that includes cavities and a free area for an electric functional element, which helps in managing material shrinkage and turbulence during injection molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the head geometry is made complex to meet functional requirements, then the functionality is improved, but optical defects and sink marks occur during injection molding
Solution Approach 1:
The patent applies local quality by creating a heterogeneous internal structure with different material thicknesses in specific regions. The back side of the head is designed with reduced material thickness (0.5-2.5mm) in areas prone to sink marks, while other regions maintain sufficient thickness for structural integrity. This localized variation in material distribution prevents optical defects without compromising overall functionality.
Solution Approach 2:
The patent changes the physical parameters of the head geometry by varying wall thicknesses and creating cavities strategically positioned to control plastic flow and cooling. By adjusting these geometric parameters, the invention optimizes both the functional complexity and manufacturing quality, eliminating sink marks while maintaining adaptive functionality.
2Ease of operation
If the head thickness is reduced for comfortable use, then ease of operation is improved, but structural integrity and manufacturing quality deteriorate
Solution Approach 1:
The patent implements local quality by creating non-uniform wall thickness distribution throughout the head. The back side features reduced thickness (0.5-2.5mm) for comfort and defect prevention, while bristle-bearing areas and structural zones maintain adequate thickness. This localized differentiation allows thin overall profile without sacrificing manufacturing quality.
Solution Approach 2:
The patent resolves the thickness contradiction by transitioning from uniform 2D wall thickness to a 3D varied thickness profile. By introducing depth variation and cavities, the design achieves comfortable thinness in critical areas while maintaining structural integrity in load-bearing regions, effectively using the third dimension to solve the apparent contradiction.
3Reliability
If blind holes are placed deeper to accommodate bristles, then bristle retention is improved, but plastic flow uniformity and cooling evenness deteriorate
Solution Approach 1:
The patent applies local quality by varying blind hole depths based on functional requirements in different regions. Bristle retention areas have deeper holes, while areas prone to flow turbulence have shallower holes or optimized positioning. This localized differentiation maintains bristle retention reliability while preserving plastic flow uniformity throughout the head.
Solution Approach 2:
The patent uses preliminary action by strategically positioning and sizing blind holes during the design phase to anticipate and prevent plastic flow issues. The blind hole configuration is optimized beforehand to guide plastic flow smoothly, preventing turbulence and ensuring uniform cooling, while still providing adequate depth for bristle retention.
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
This approach allows for the production of a toothbrush head with a thin, comfortable design that is free of optical defects, ensuring uniform material thickness and preventing sink marks, while accommodating complex internal structures and functional elements.
Implementation Method 1
The plastic flowing into the tooling used to inject the head during the injection molding process is subject to turbulence between the various stuffing blind holes and other recesses or cavities of the molded part
Implementation Method 2
This problem is exacerbated when plastics are used for the head that have a greater shrinkage behavior on cooling after the injection molding process
Data Source
Figure 1~4
AI summary
The present invention relates to a toothbrush comprising a handle, a neck section, and a head (1), wherein the head (1) is provided with bristle tufts (6) by means of anchor packing (15) arranged in a complex internal geometry. To enable an optically flawless injection-molded part, material cross-sections in the head (1), particularly in the area of the blind holes (11, 12, 13, 14) provided for packing, are taken into account.