Various techniques are used in tissue creation and tissue binding in the production process. These techniques differ according to the type of fiber and the usage areas of the product.
Production in staple fibers;
It starts with the preparation of the fibers and ends with the creation of the tissue, fixing the tissue, transforming and finishing.
In continuous fibers
The process starts with the formation of the polymer melt and fiber production and then goes through the same stages as the staple fiber production.
After the fiber is ready for production, it is laid to form a cheesecloth, and the resulting cheesecloth is fixed by various methods. In the production of continuous fiber, the formation of the fibers and the laying of the cheesecloth occur simultaneously. The surfaces produced with these production steps, various finishing processes are applied according to the usage area, and then they are cut and sewn and become ready for use.
The nonwoven surface production process, which starts with the preparation of the raw material and ends with the finishing processes, is shown schematically below:
Texture Formation Techniques on Cheese Based Non-Woven Surfaces
The first step for the products to become texture; Determining the properties of the product to be made, choosing the fibers to be used, blending the properties of the fiber to be used. In the tissue forming section, fiber or filament is laid and formed into a layer. The raw material used can be in the form of staple fibers, granules or solutions. The choice of texture creation technique can be made by looking at the structure of the raw material.
As seen above;
if the fiber is cut;
One of the dry laying techniques, mechanical laying, air laying and a combination of them, mechanical and air laying is used.
In the continuous fiber laying technique;
One of the techniques of endless fiber laying, melt spraying and electrostatic laying is used.
CONTINUOUS ELAST LAYING TECHNIQUES
Staple fibers are used in the production made with the dry-laid technique. The process in this technique; The determination of the product properties to be produced, the preparation of the fibers determined according to the product properties, starts with the removal of the determined fibers from the bales, and ends with the bale opener, mixing, coarse opening, fine opening and blending. The texture creation process is; It is carried out with the help of mechanical and air paving or a combination of these. As with all techniques, the choice of fiber to be used is very important. In fiber selection, it should be used with fibers with good absorbency, abrasion resistance, bursting strength, permeability and softness properties.
Mechanical laying; It is the most widely used texture laying technique in the textile industry today. It is possible to examine mechanically obtained cheesecloth-based nonwoven surfaces in three layers. The first layer is the upper surface, the second is the middle or filling layer, and the third is the carrier (base) layer. However, in practice, it is possible to come across with two plates. In the mechanical laying technique, the fibers in bale are made parallel by combing after fine opening and rough opening operations are carried out according to the product feature. The stages in the mechanical laying process are explained below, in order.
a-Opening and Threshing
The raw material required for the cheesecloth surface is shipped to the machine in bales. The fibers taken from the properly opened bales are sent to the opening unit to realize the desired mixture. In the bale opener, with the help of electrically adjustable scales, certain weights are weighed and the desired mixtures are obtained and sent to the card.
The scanning process takes place at the tangent point of the drum and the working cylinder, and the fibers taken from the working cylinders by the plucker are combed and subjected to the scanning process again until they become parallel.
Since the fibers are made parallel in the carding machine, it causes the strength and other properties of the formed tissue to be better in the machine direction, and the opposite situation in the cross direction. In order to ensure that the fibers are oriented in different directions, the tissue laying device must be used. Moreover; In order to eliminate the regional differences in the cheesecloth formed and to adjust the weight of the nonwoven surface that is aimed to be produced, tissue laying devices are needed.
Tissue laying process;
It can be performed in three ways as parallel, diagonal and vertical paving.
In parallel laying
Cheesecloths coming from 3 different directions are laid on top of each other in parallel and then conveyed to the tissue fixation unit by means of conveyor belts.
It is the most widely used tissue laying technique. The principle of the technique is based on the process of laying a single cheesecloth layer by layer. In this technique, the comb web fed by the feeding band is laid on the conveyor band, which moves perpendicular to the conveyor bands, crosswise, with the transport rollers moving back and forth. In the tissues obtained in this way, the orientation of the fibers in one direction is prevented.
Vertical laying method
Most of the fibers in webs produced with cotton are located in the direction perpendicular to the area of the material; The resulting structure shows high resistance to compression and elastic recovery due to the location of the fibers. In this laying form; The cheesecloth fed with the comb moving up and down is pulled by the needle and the working cylinder at the end of the pressure rod moving back and forth, and a fold (lamella) is formed from the cheesecloth. The said fold is pushed between the conveyor belt and the grid by a working roller, and the laying process is completed.
In air laying technique; It is based on the accumulation of the fibers carried by the air flow on the perforated suction drum with the help of air suction. In this machine, the fibers are fed with the help of delivery rollers and feeding rollers, then they are combed into single fibers by means of the wires on the scanning drum. The fibers in question are deposited on the perforated drum with air suction to form the tissue and the resulting tissue is transferred to the fixing unit. The most distinctive feature of the air-laying process is that it works with very short fibers. The fiber length used is maximum 76 mm. With this technique, less debris is formed and softer tissues can be made. In addition, there are also undesirable aspects such as high energy consumption and poor opening of the fiber tufts. Air-laid nonwoven fabrics are used in the field of cleaning and hygiene.
C-Combination of Mechanical and Air Laying
In order to eliminate the undesirable aspects of carding and airlaying techniques, systems with the characteristics of both techniques have been developed. These systems are; It is formed by adding cylinders to the carding machine, obtaining centrifugal and air flow thanks to the rotational speeds of these cylinders, or by increasing the number of drums in the carding machine and adding a vacuum cylinder to the system. By using these systems; More homogeneous, more isotropic textures can be produced than tissues obtained only by scanning or only air-laid methods.
In the wet laying technique, where texture can be created from fibers with a length of 2-30 mm; The fibers are mixed with water using various chemicals and a homogeneous suspension is obtained. The resulting suspension is poured onto the perforated and moving band to form a cheesecloth. The resulting cheesecloth is then subjected to drying. The structure produced by adding chemicals to the tissue formed before drying can also be fixed when dried. The production rate of this method is very high, but it is not economical since high energy is required for drying the tissue.
CONTINUOUS FIBER LAYING TECHNIQUES
Continuous fiber laying technique; It is based on gluing the obtained fibers together by bonding (fixing) techniques after the polymer melt is converted directly into cheesecloth. The fibers are separated by electrostatic charges or air jets during the formation of tissue layers. The collecting surface is perforated to prevent heterogeneous settlement and air damage. Binding of tissues is provided by hot needles, hot rollers or by melting certain areas of polymers. Molecular orientation increases at the attachment points, therefore, highly undrawn fibers, thermal bonding fibers, PP, PET, PA fibers with high molecular weight are used. In this technique, the bonding process can be applied during the spinning of the fibers or it can be applied as a separate process. If several bonding methods are used on the same tissue, the tissue becomes more flexible. Nonwoven surfaces produced in this way show lower weight and higher strength properties.
Texture forming techniques in continuous fibers;
It can be performed in 4 different ways: endless fiber laying, melt spraying, electrostatic laying and instant texture creation.
A-Endless Fiber Spreading (Spunbond) Technique
In this technique, which is known as one of the most common texture creation methods; fiber formation and tissue formation occur simultaneously. In this technique, thermoplastic fiber chips in polymer form are melted and sprayed from nozzles under constant pressure, similar to artificial fiber production (Figure 20). The filaments formed are cooled and subjected to tension in order to ensure proper orientation of the molecules in the fiber structure. The fibers are laid on the conveyor belt, which has a porous structure. Nonwoven surfaces are obtained by connecting the fibers to each other with thermal, mechanical or chemical techniques applied immediately after the formation of the texture. Non-woven surfaces produced with this technique are more voluminous, harder and uncast; but it is more durable.
In the melt spray technique, it is possible to obtain fibers directly from the thermoplastic polymer melt, similar to the endless fiber laying process. This technique differs from the endless fiber laying method with its features such as high speed, hot air and the ability to produce finer fibers.
In this technique, there is a special compartment where the filaments are formed, the fibers are drawn here, dispersed by the rapid air flow and solidified by the effect of the air and become discontinuous. The fibers in this state are collected on an accumulating surface and the texture is formed. A non-woven surface is obtained by fixing the created texture. Nonwoven surfaces obtained by melt spraying technique; They are used in face masks, surgical gloves, disposable gowns, sterile dressings, pads used by women and absorbent products for adults, respiratory protection products, liquid vessel bags, cigarette filters and some special HEPA filters.
C-Electrostatic Laying Technique
The basis of this technique; It is based on the principle of transforming the polymer melt into fiber and forming the tissue with the help of the forces in the electrostatic field between two opposite electrodes that are electrostatically charged by being polarized by electric current. The fibers obtained from the polymer in the electrostatic field are collected on the accumulating surface perpendicular to the plane with the electrostatic effect and turned into texture.
D-Immediate Texture Creation (Flash Spun) Method
In this technique, which is carried out similarly to the endless fiber system, high density polymer dissolved in a suitable solvent is sprayed into a container held at a set constant pressure. Inside the container, the solvent evaporates rapidly, leaving a continuous pile of fibers. The fiber stack formed is collected on a template and the texture is formed.