Sheath-Core Sewing Thread Loop Control for High-Speed Sewability

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Solution Overview

Problem

Conventional sewing threads, whether made from multifilament or spun yarns, face issues with high-speed sewability, yarn strength, and seam quality due to problems like uneven loops, high frictional resistance, and susceptibility to needle heat, which limits their application in automatic sewing machines and high-speed industrial sewing.

Innovation Solution

A sewing thread with a sheath-core structure composed of under-twisted and upper-twisted multifilament yarns, featuring a controlled number and length of loops to reduce friction and enhance airflow and annealing effects, allowing for high-speed sewability and improved yarn strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If conventional multifilament yarn is processed with fluid turbulent processor to form loops, then loops are formed in the yarn, but processing cost increases and process-passage efficiency decreases

Engineering Contradiction:

Improveloop formationVSAvoidprocess-passage efficiency

Core Design Contradiction:

ShapeVSProductivity

Solution Approach 1:

The yarn is divided into core yarn and sheath yarn components with different twist directions. The core yarn receives S-twist while the sheath yarn receives Z-twist, creating segmented twist structures that enable loop formation without requiring complex fluid turbulent processors. This segmentation allows simple mechanical twisting operations to achieve the desired loop shape.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the twist parameter by applying opposite twist directions (S-twist for core, Z-twist for sheath) and different twist amounts to the core and sheath yarns. This parameter change causes the yarn to form loops naturally during the twisting process, eliminating the need for expensive fluid turbulent processing while maintaining high productivity.

Inventive Principle:

Principle #35Parameter changes

2Shape

If loops are formed in multifilament yarn, then yarn length variation is created, but unreeling failure occurs in twisting and sewing processes

Engineering Contradiction:

Improveloop structureVSAvoidunreeling stability

Core Design Contradiction:

ShapeVSReliability

Solution Approach 1:

The invention creates a composite structure with core yarn and sheath yarn having different twist characteristics. The core yarn with S-twist and sheath yarn with Z-twist work together to form controlled loops that prevent unreeling failure. The composite structure allows the loops to be formed while maintaining sufficient yarn strength and unreeling stability for high-speed sewing applications.

Inventive Principle:

Principle #40Composite materials

3Shape

If loops with large fastener effect are formed, then yarn strength is reduced, but strong fastener effect causes unreeling problems

Engineering Contradiction:

Improveloop fastener effectVSAvoidyarn strength

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

The invention applies different local qualities to the core and sheath yarns through opposite twist directions. The core yarn with S-twist provides structural support while the sheath yarn with Z-twist forms loops with controlled fastener effect. This local quality differentiation allows loops to form without excessively reducing yarn strength, as the core yarn maintains the overall structural integrity.

Inventive Principle:

Principle #3Local quality

4Strength

If conventional filament yarn is used for sewing, then mightiness is excellent, but frictional resistance on side face is large causing broken yarns in high-speed sewing

Engineering Contradiction:

ImprovemightinessVSAvoidfrictional resistance

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The invention introduces curvature by forming loops in the yarn structure. These loops create a more rounded, less flat surface profile on the yarn, reducing the frictional resistance between the yarn side face and the needle during high-speed sewing. The curved loop structures allow the yarn to better accommodate needle penetration while maintaining its strength and mightiness.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 sewing thread achieves high-speed sewability, increased yarn strength, and enhanced automatic sewing capabilities with reduced seam breakage and improved appearance quality, while maintaining stability and durability.

Implementation Method 1

accompanying airflow effect and annealing effect of needle heat are small

Methodology Applied

Scientific EffectAirflow effect: Convection

Implementation Method 2

accompanying airflow effect and annealing effect of needle heat

Methodology Applied

Scientific EffectAnnealing: Annealing

Implementation Method 3

penetration resistance against cloth. This corresponds to no suppressing effect on needle heat temperature mentioned above

Methodology Applied

Scientific EffectNeedle heat: Heating

Data Source

PatentUS7678450B2Sewing thread and process for producing the same

Publication Date: 2010.03.16 TORAY INDUSTRIES INC

AI summary

To provide a sewing thread that is excellent in high-speed sewability and automatic sewing characteristics. A sewing thread includes a plurality of under-twisted yarns provided with upper-twist, the yarns each being composed of a sheath-core structure yarn composed of two or more multifilament yarns, wherein part of the sheath-core structure yarn protrudes as loops on a yarn surface, the loops being composed of 50 to 300 loops/m with 0.7 to less than 1.2 mm length and 10 or less loops/m with 1.2 mm or more length, and wherein the yarns have a strength of 4 to 6 CN/dtex.