| In face of challenges with the use of traditional laundry machines, Hong Kong knitwear industry gathered experts to design a new machine that avoid challenges in the aspects of pilling, excessive milling and shrinkage so as to meet buyers' requirements. |
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| Prototype of the new wet finishing system |
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Three types of wet finishing equipment are generally used by knitwear production facilities of Hong Kong.
1. Side loaded rotary drum washer is popular among Asian knitters. This laundry machine, however, has little function to control rotation speed and water flow. Pilling and shrinkage is often found.
2. Side paddle machinery works gently and relies on paddle for circulation, making it suitable for processing worsted and cashmere knitwear. However, it requires a high liquor ratio of 25:1, resulting in a high level of water and energy consumption. Knitwear processed is often stretched or deformed.
3. Fully automatic washer / extractor machinery is an advanced garment finishing machine, usually incorporating a built-in hydro-extractor that is programmable with automatic chemical dispensing device. Human error is thus minimized. A high capital investment is needed for such a machine, which may not be affordable for small and mid-size enterprises.
With a HK$1.45 million (US$187,000) of funding provided by the Innovation and Technology Fund under the Hong Kong S.A.R. government, The Hong Kong Research Institute of Textiles and Apparel (HKRITA) in collaboration with the Hong Kong Productivity Council (HKPC) in a research team to jointly develop an innovative wet finishing machine. HKRITA provides services in product development, technical transfer and commercialization to improve the competitiveness of the textiles and apparel industry in Hong Kong.
A number of parameters influence dyeing and finishing effects of knitwear.
Liquor ratio and liquor level
Liquor ratio and liquor level influence the mechanical severity of a washing action. Liquor acts as a "cushion" in the apparel finishing processing while the machine rotates. Therefore, the liquor level of a traditional wet finishing machine is often up to half height of the machine resulting in a high liquor ratio.
Rotation speed
Many traditional wet finishing machines do not have a control on the rotate-per-minute speed, causing a greater chance of excessive friction, stretching or pilling on knitwear.
Temperature
Traditional wet finishing machines usually do not have proper temperature control while finishing temperature should be kept stable and constant from batch to batch.
Liquor circulation
Independent bath circulation of liquor is needed to ensure a uniform level of dyeing and finishing with knitwear.
More factors will have an impact on the dyeing and finishing effects:
Processing time
Type and quantity of chemicals
Water hardness
PH value of liquor
Fiber types
Color and depth of shade of knitwear
Performance requirement
Types of finishing required
Fibre and fabric construction
Taking into account the above considerations, the research team identified some desired features of a wet finishing system that suits the needs of Hong Kong knitters.
Adequate supply and control of water and steam
Adjustable rotating speed settings
Temperature controller to provide adjustments on temperature and how fast the temperature is changed
Effective circulation to permit optimum liquor exchange between the knitwear and the bath
Automatic chemical dispensing device
A prototype of wet finishing machine was thus designed by a research team to suit the above needs from the experience of industry players in Hong Kong. About 20 local technicians attended the evaluation to rate the sample treated by the two systems. In the evaluation, five points were considered as most satisfactory.
Under the same conditions, the prototype outperforms a traditional wet-processing machine in hand feel and color difference |
First, a better overall result achieved by the new prototype was found in the evaluation.
Material: 20'S/2 all-cotton yarn with 7GG plain structure in bleach white
Trial condition: Liquor ratio: 1:28, detergent: 3%, and silicone softener: 3%
The research team also conducted the following evaluation to highlight the following wet-processing effect:
1. Evaluation of shrink-resistant treatment on wool
Wet-Finishing
Material: 9GG 2/16 Nm 100% lambswool
Liquor ratio: 1:20
Dylanize salt: 5%
Polymer TEC: 5%
Test result: oxidation time is reduced to 25 minutes
Felting shrinkage test result: Passed according to Woolmark TM31 (1 x 7A, 2 x 5A)
In the above tests, the prototype was found to have deliver good anti-bacterial treatment |
2. Evaluation of anti-bacterial treatment
Anti-microbial finish
Material: Cotton/nylon/elastic stockings
Material weight: 15.4lb
Liquor ratio: 1:20
Liquor volume: 120L
AEM (anti-microbial agent): 5%
Passerelle (moisture management): 2%
3. Evaluation of shrink-resistant treatment on cashmere knitwear
Liquor ratio: 1:20
Shorter oxidating time: 30 minutes
Shorter total processing time: 116 minutes
Test result: The prototype was able to perform an average shrinkage of -0.1% on cashmere knitwear. Based on the test standard of a major UK chain retailer, shrinkage ranges from -3 % to -13 %.
4. Knitwear dyeing test
Material: 7-needle single-side knitted knitwear of 20'S/2 all-cotton yarn
Liquor ratio: 1:15
Dyestuff: Levafix CA - 0.6% w.o.m.
Test result: Uniform dyeing effect
As shown through the above tests, this garment and accessory wet-processing system developed by Hong Kong R&D professionals can achieve desirable effect in multiple functions such as water level, chemicals, shrinkproof, antibacterial and dyeing. Also, it can meet demanding environmental requirements in the modern world. Under current production environment that imposes high requirements on creative design and quality elements, this represents an innovative R&D achievement for local garment enterprises.
Dr. K.C. Ho is Director, Research & Development, Hong Kong Research Institute of Textiles and Apparel
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