DuPont first introduced the synthetic leather Corfam made of synthetic fiber-based nonwoven in the 1960s. In the following decades, the fast-growing global economy and improving living standard boosted the growth of nonwoven-based synthetic leather similar to natural leather in structure and performance. Today, needle punched synthetic leather substrate has become the main material for synthetic leather products, with its compact three-dimensional structure, interlaced structure similar to the collagen protein of natural leather, fine simulation, excellent physical performance, and low production costs.
Synthetic leather has gone through three important technological innovations since the first-generation technology, which produced polyvinyl chloride (PVC) manmade leather by brushed-finishing weaving fabric dipped and coated with PVC resins. The second generation started with polyurethane (PU) manmade leather produced by PU resins and traditional weaving fabric and PU synthetic leather made by PU resins and nonwoven fabric. The third generation was highlighted with high-quality simulated, high-density, and high-performance superfine fiber synthetic leather, which is made by this process:
Superfine staple fibers are carded and folded according to different fiber orientation to form a fiber web; the fiber web is needle punched to form a nonwoven fabric with a structure of three-dimensional web. The nonwoven fabric is then finished through special methods such as reduction peeling, dyeing, sanding and PU attaching.
Superfine fiber synthetic leather has reached or overtaken the quality of natural leather in many aspects, including hand feel, strength, elastic resilience, air permeability, water vapor permeability, abrasion resistance, durability, and easy processability. Therefore, superfine fiber synthetic leather has become one of the best choices for making many kinds of high-quality, high-performance, and high value-added products. High-end superfine fiber synthetic leather substrate has been widely used in industries such as shoe making, bags and suitcases, apparel, automotive interiors, furniture, and home decoration. But in China, the production and application of synthetic leather has grown slowly due to the barriers of raw materials, equipment and technologies. According to the China Plastics Processing Industry Association (CPPIA) in 2013, the Chinese manmade and synthetic leather market reached 3.015 billion meters, and the share for PU synthetic leather was 2.146 billion meters. In the same year, superfine fiber synthetic leather had a market of 39.27 million meters, accounting for only 1.26% of the whole manmade and synthetic leather market. Therefore, superfine fiber synthetic leather will have a very big potential in replacing traditional PU manmade and synthetic leather.
Superfine fiber synthetic leather substrate is usually made by islands-in-sea fiber, which has tow main manufacturing methods: figured and un-figured methods. In China, most manufacturers use un-figured methods. On the other hand, figured method is seldom used in China due to difficulty of needle punching and post-processing technology and quality control.
Water-soluble superfine fiber synthetic leather uses figured technology and alkali reduction technology, which are advanced and environmentally friendly methods that accords with the national requirements for clean production of superfine fiber synthetic leather. This is because the technologies do not use methylbenzene, which ultimately resolve the problem of methylbenzene pollution to the environment. In the post-processing step, the superfine fiber synthetic leather uses water-soluble materials, which do not contain organic solvent so as to avoid the environmental pollution of solvent-type materials. Highlighted with its environmentally friendly manufacturing method, superfine fiber synthetic leather can pass through the barrier of environmental protection into the markets in Europe and North America and win the global market. Therefore, figured islands-in-sea superfine fiber synthetic leather technology has become the main direction of the Chinese industry, and the country’s demand for superfine fiber synthetic leather is growing rapidly as well.
Innovations of new-type needle punched equipment
China’s manufacturing technology for superfine fiber synthetic leather has matured after more than a decade of development and innovation of needle punching technologies. But the Chinese made equipment still have some disadvantages, as the requirements to the equipment is high and the manufacturing technology is complicated. Today, some of the complete sets of needle punching machines in China have many disadvantages, including low technology, poor structure, high material consumption, labor intensive, high noise, and low quality. As the manufacturing technologies are difficult to improve, China has for years needed to import most of its high-end islands-in-sea equipment and complete set of superfine fiber synthetic leather equipment. To boost the growth of this industry, Zhengzhou Textile Machinery Engineering & Technology Co., Ltd. (Zhengzhou Textile Machinery), a wholly owned subsidiary of Hi-Tech Heavy Industry Co., Ltd, has successfully developed new production lines for high-end figured islands-in-sea superfine fiber synthetic leather substrate, with its technological advantages in opening and cleaning, carding, lapping and winding.
The production flow includes: manual operated cotton feeding and weighing machine, blending cotton curtain opener, large chamber cotton mixer, fine cotton opener, carding fan, pneumatic hopper feeder, carding machine, leveling device, cross lapping machine, feeding machine, pre needle punching machine, main punching machine, main punching machine II, main punching machine III, face finishing needle punching machine (four boards with up and down punching), fabric storage rack, and winding machine.
There are several important characteristics worth noticing in the production line of Zhengzhou Textile Machinery.
The first one is sufficient fiber opening and mixing operation, and the guarantee of uniform and stable cotton feeding grammage.
A 3.5dtex X 51mm figured islands-in-sea fiber is used in production. This fiber easily produces static and has poor thermal stability in the opening and cleaning step. Therefore, it’s better to shorten this step as much as possible and provide appropriate opening to avoid too much impact and damage of the fiber.
The uniformity of substrate grammage is vital to the production of superfine fiber synthetic leather. To ensure the stability of the grammage of feeding cotton, the pneumatic hopper feeder feeds from the bottom from both sides. The entrance has a pneumatic balance device, which lower the speed of air and fiber, reduce air quantity in the hopper, increase the uniformity of fiber density in the machine, and fully guarantee the stability and uniformity of outputted sheet cotton.
The second is the continuity and uniformity of carding to web.
The carding machine increases opening and carding effects by using double cylinders, double doffers, and double coagulation structure. Skin-core tearing in fiber carding is reduced by feeding with a down roller, and choosing appropriate configuration of needle and fabric. The uniformity of fiber web is ensured by efficiently controlling air flow by providing high-precision grid and guard plate and using high-strength aluminum alloy in making of the working roll and stripping roll to reduce deformation. The machine also uses a combination of multiple motors driving independently and frequency conversion technology to increase the manufacturing process’ automation and precision. The speed of each motor can be set independently and increase or decrease synchronously in proportion according to the output speed of fiber web, which can keep the fiber web quantity unchanged when the machine speed changes. The coefficient of variation (CV) of fiber web weigh is smaller or equal to 3.0%. The results of using these technologies include good web laying effect, and no cloud and vertical and horizontal stripes.
The third is the influence of lapping quality.
High-end superfine fiber synthetic leather has strict requirements to the thickness deviation, apparent density and uniformity, which influence the needle depth in the needle-punching step. If the requirements are not met, leather quality problems such as bad hand feel and big color and luster difference will occur after post-treatment steps such as impregnating, alkali reduction and grinding.
The cross lapping machine is equipped with a fegulating device, which combines the profiling function. The system has multiple speed controlling points along the fabric width. They are used to control the thickness of cotton web from the carding machine by the speed difference of fluted roll, which the web passes through. The fiber web formed by the lapping machine has an ideal shape of thick middle and thin both sides. As a result, the uniformity of output web is increased.
For products with a grammage of more than 300 grams, as there are too many lapping layers of fiber web, the quality of single-layer cotton web will have a big influence on the subsequent process. There are several ways to effectively reduce the air’s impact on fiber web in high-speed motion so as to increase fiber web quality. They include: use lapping carriages with less high-module carbon fiber rollers; increase the stability of carriages; add an edge guide device in the outlet of the lapping machine.
The fourth is the innovation of needle punching technologies and equipment configuration.
The fluffy fiber web from lapping enters the pre-punching step, which brings most impact on substrate stretching. If the stretching is too big, the vertical and horizontal strength cannot be satisfied, and there will be unrecoverable needle marks in the fabric surface. Optimizing the design of the feeding machine, feeding rollers and web guide boards and increasing the number of web guide boards, the fiber feeding point will become very close to the needle punching area, which will facilitate the fluffy fiber web to enter the needle punching area so as to reduce unexpected stretching.
The main punching step uses up-and-down punching machines covering different positions, which reduce the number of devices and stretching. The proportion of vertical strength and horizontal strength is close to 1:1. This improves fabric surface quality and increases the producing speed under the same equipment.
This system uses four-board up-and-down punching, with a structure that integrates two boards for down punching and two boards for up punching. As a result, the front side and back side of the fabric has a uniform appearance and high strength. Fine and neat fabric surface is thus produced, without defects such as needle marks and stripes.
The fifth is the use of automation integration in the complete equipment set.
A high-end superfine fiber substrate production line consists of a series of equipment of opening and cleaning, carding, lapping, needle punching and winding. The whole line is flexible, with a high level of electromechanical integration, digitization and networking. Different manufacturing conditions should be adjusted according to different raw materials to ensure the quality of the needle punching nonwoven.
The production line integrates the technologies of automotive control, variable frequency driving and servo driving by using a Programmable Logic Control (PLC) system. The operation table has functions of setting up technological parameters, real time monitoring, information processing, automatic fault alarm, automatically adjusting the output width, and synchronous control of input and output speed. Therefore, the line ensures the stability and reliability of production by its excellent performance in technological adjustment, fault alarm, online testing, data storage, and remote control. The needle frequency, speed and depth can be adjusted at any time without stopping production. The perfect functions of electric control and automation can reduce the labor intensity for nonwoven production.
Applications and prospects
The new-type, high-speed and high-efficient nonwoven fabric equipment made by Zhengzhou Textile Machinery has been successfully used in the production of high-end islands-in-sea superfine fiber leather substrate. The benefits noted by clients in real time production include: reduce the damage on fiber; increase the three-dimensional entanglement of fibers; reduce unexpected stretching of fabric surface; reduce needle marks in fabric surface so as to get good appearance and performance; meet the requirements of customers of superfine fiber synthetic leather in various technical indicators; good processability; and after post-processing, sofa leather made by superfine fiber synthetic leather has excellent hand feel, reaching or overtaking similar products from other global players in performances such as abrasion resistance, comfort ability, and color and luster.
The superfine fiber industry is growing fast due to the continuously exploring of different applications. To meet the demands from high-end customers, Hi-Tech Heavy Industry Co., Ltd. works with clients to focus more on the development of high-end shoe leather, mid- to high-end and high value-added automotive interior leather, and breathable clothing leather.
The economic growth increases the labor cost, and the outflow of technology workers today is larger than before, which force traditional textile companies to adapt to the new situation. In this circumstance, the future trends for textile producers include choosing products that can be switched quickly and at low cost, energy savings, high speed, high efficiency, good quality, low maintenance or non-maintenance, smart machines, and creating better value added products. Zhengzhou Textile Machinery has a history of more than six decades of textile machinery development, covering opening and cleaning, manmade fiber, dyeing and printing, warp sizing, and nonwoven, with a wide range of manufacturing methods and equipment, matured technologies, appropriate structure and good spinnable property. It is the first manufacturer with complete equipment set for spunlacing and needle punching nonwoven, with strong capacity for technologies, manufacturing, installation, complement, quality and precision control for nonwoven equipment. It is increasing the manufacturing levels for China’s equipment, and leading the market by creating more high-quality, high-performance, and high-value added products.