Syringe Needle Joint Strength After Sterilization
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Solution Overview
Problem
Syringes with injection needles experience a decrease in joint strength between the needle and the outer cylinder due to sterilization by autoclave or ethylene oxide gas, leading to potential detachment or insertion issues during use.
Innovation Solution
A syringe design featuring a metallic injection needle with an uneven surface roughness of at least 0.2 µm on the joint portion, which is fixed inside the cylinder tip through insert molding or heat welding, providing a strong anchor effect that maintains joint strength even after sterilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sterilization by autoclave or ethylene oxide gas is performed, then the syringe achieves sterile status, but the joint strength between the injection needle and outer cylinder decreases
Solution Approach 1:
The uneven portion is formed on the injection needle surface before the sterilization process. This preliminary surface treatment creates mechanical interlocking features that remain effective after sterilization, preventing the joint strength degradation that normally occurs when resin flowability increases during autoclave or ethylene oxide gas sterilization.
Solution Approach 2:
An uneven portion is created at the specific joint portion where the injection needle meets the outer cylinder. This localized surface modification concentrates the mechanical interlocking effect precisely where it is needed to maintain joint strength during sterilization, without affecting other parts of the needle.
2Ease of manufacture
If the injection needle is jointed to the outer cylinder using conventional insert molding, then manufacturing is simplified, but the joint strength is insufficient after sterilization
Solution Approach 1:
The uneven portion is formed only at the joint portion of the injection needle, creating localized mechanical interlocking features. This selective surface treatment maintains conventional insert molding simplicity while significantly improving joint strength retention after sterilization by providing anchor points for the resin.
Solution Approach 2:
The surface unevenness is prepared in advance before the insert molding process. This preliminary surface preparation ensures that when molten resin is injected during molding, it can mechanically interlock with the uneven portion, creating a strong joint that withstands sterilization-induced resin flowability changes.
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 anchor effect enhances the joint strength between the injection needle and the outer cylinder, preventing unintentional detachment or insertion issues during sterilization and use, while allowing for cost-effective manufacturing and reduced material waste.
Implementation Method 1
an uneven portion having an average surface roughness of at least 0.2 μm is formed in a region having an area of at least 1 mm2
Implementation Method 2
The injection needle is fixed inside the cylinder tip by insert molding or heat welding
Data Source
Figure 1
Figure 2
Figure 3(a)~3(f)
AI summary
The present invention provides a syringe with an injection needle in which an injection needle is firmly jointed to an outer cylinder without decreasing joint strength between the injection needle and the outer cylinder even when stress to fasten the injection needle fixed to the outer cylinder is relieved by applying sterilization by an autoclave or ethylene oxide gas. The syringe with an injection needle 1 includes: an outer cylinder 2 molded with resin and including a cylinder tip 21 at a distal end, an opening 25 at a proximal end, and a barrel section 23 provided with a cavity 22 located therebetween and configured to be filled with medicinal solution 5; a j oint portion 30 fixed to the cylinder tip 21; and an injection needle 3 projecting to a distal end side beyond the cylinder tip 21 and allowing communication between inside and outside of the outer cylinder 2. The injection needle 3 is fixed to the cylinder tip 21 by insert molding or heat welding, an uneven portion 32 having average surface roughness of 0.2 µm or more is formed on a region having an area of 1 mm2 or more on an outer peripheral surface of the joint portion 30, and sterilization by an autoclave or ethylene oxide gas is applied to the outer cylinder 2 where the injection needle 3 is firmly fixed by virtue of the resin which closely contacts and covers the uneven portion 32.