Drawstring Bag Hem Seam Positioning for Tear Prevention
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Solution Overview
Problem
The hem seams in existing drawstring bags are prone to tearing when lifting filled bags, leading to customer complaints and reduced acceptance due to the weakening of the film material during welding and the introduction of tensile forces at the hem seam.
Innovation Solution
The drawstring bag design features a hem seam positioned no more than 40 mm from the hem fold, allowing the bag to be gripped below the seam, reducing the risk of tearing, and incorporating measures such as precise web control and adjustable welding devices to prevent drawstrings from being welded into the seam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the hem seam is positioned at a larger distance from the hem fold (more than 40 mm), then the drawstring can be wider and welding displacement can be tolerated, but the tensile force during lifting is introduced into the hem seam causing it to tear
Solution Approach 1:
The patent changes the critical parameter of hem seam position from a conventional large distance (>40mm) to a specific small distance (≤40mm) from the hem fold. This parameter change ensures that when the user grips the bag, the force is applied below the hem seam on the side wall, not on the weakened hem seam area, thereby preventing tearing while maintaining operational ease
2Strength
If the hem seam is positioned closer to the hem fold (≤40 mm), then the tensile force is transferred to the side wall below the seam reducing tearing risk, but the drawstring may be welded into the hem seam due to film web displacement during high-speed production
Solution Approach 1:
The patent positions the hem seam at a predetermined safe distance (≤40mm) from the hem fold before production issues occur. This preliminary positioning creates a safety buffer that prevents drawstring welding into the hem seam even when film web displacement occurs during high-speed production, maintaining both structural strength and manufacturing reliability
Solution Approach 2:
The reduced distance positioning acts as a cushioning measure against welding errors. By placing the hem seam closer to the hem fold, the design creates a protective buffer zone that absorbs the impact of potential welding misalignment, preventing the drawstring from being welded into the hem seam and maintaining bag integrity
3Ease of manufacture
If a large distance is maintained between hem seam and hem fold, then manufacturing with web displacement is easier, but the hem seam becomes a potential tear point when the bag is lifted
Solution Approach 1:
The patent inverts the conventional wisdom by changing the hem seam distance parameter from large (>40mm) to small (≤40mm). This counterintuitive parameter change simultaneously addresses both manufacturing ease and tear prevention: the close positioning ensures force application below the seam during use, while the predictable geometry simplifies welding alignment
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 design significantly reduces the risk of hem seam tearing, ensuring the bag can be lifted securely without compromising the seam integrity, even when used by smaller individuals, and allows for comfortable handling and secure closure.
Implementation Method 1
The side seams and the hem seams are designed as weld seams in which several layers of the film material are welded together thermo-mechanically by means of a welding bar
Implementation Method 2
The side seams and the hem seams are designed as weld seams in which several layers of the film material are welded together thermo-mechanically by means of a welding bar or by means of hot air
Implementation Method 3
The side seams and the hem seams are designed as weld seams in which several layers of the film material are welded together thermo-mechanically by means of a welding bar or by means of hot air or by means of ultrasound
Data Source
Figure 1~2
AI summary
A drawstring bag made of foil material comprising: - two side walls overlapping around a bottom fold line, - each having a folded-over hem opposite the bottom fold line, - the side walls including the hems being connected laterally by side seams extending perpendicular to the bottom fold line, - the hems enclosing a bag opening, - a drawstring being arranged in each hem, and - each hem being connected to a side wall at a distance of a hem fold over which it is connected, by the same side wall via a hem seam running parallel to the bottom fold line, wherein the distance of the hem seam from the hem fold is at most 40 mm, so that when grasped by hand the drawstring bag is held below the hem seam between the palm and fingertips and the pulling force between the palm and fingertips is introduced into the side walls below the hem seam.