Monchengladbach, Germany-March 20, 2020-Humans are the only primates without fur, can protect themselves from elements, and first use animal skin and fur to protect themselves from cold or ultraviolet radiation The impact depends on where they are in the world.
More than 5,000 years ago, people developed fabrics woven from plant fibers and wool, which brought many advantages such as warmth, softness and breathability, and UV protection. The development of dyeing gradually led to the concept of fashion.
However, there is still a problem-to provide rainwater for people in humid climate areas and later seafarers. Until recently, fur and leather were widely used for this purpose.
Until the 19th century, Scottish textile manufacturer and inventor Charles Macintosh finally developed a viable solution. Although the use of rubber waterproof clothing was not a new idea, as early as the Columbus era, the Aztec People began to use this method.
Later, French scientists made the balloon airtight and impermeable by impregnating the fabric with rubber dissolved in turpentine, but this solvent could not make garments satisfactorily.
Macintosh also first impregnated thick wool fabrics with natural rubber solutions. The result is waterproof, but it smells oily and sticky due to wool grease.
Only when a method is developed to coat one side of the fabric and sulfur is added to the dryer to heat the rubber (vulcanization process), Macintosh coated fabrics can be commercialized.
Unfortunately, the coating method of the fabric and in which drying oven is unknown, but this development laid the foundation for the fabric coating as we know it today.
There are two fundamentally different basic coating processes-air knife coating and roll knife coating.
In air knife coating, the squeegee strip is brushed on the surface of the fabric, pressing the high-viscosity paint into the space between the materials.
It is impossible to apply low-viscosity chemicals with this method, otherwise the paste will drip into the mesh/woven gap.
However, first use an air knife coating where the fabric needs to be sealed, such as an umbrella, to prevent spray from entering the interior. Other examples include shower curtains, raincoats, luggage and backpack fabrics, tents, etc.
Air knife coating is also used for mattress tick and upholstery fabrics. In this case, a dual-function back coating will be applied-making the material liquid impermeable and fixing it. For upholstery fabrics, this can fix the pile, but it can also be used to achieve technical effects, such as fire protection.
In fashion and decorative goods, air knife coatings are also used for single-sided coloring, while the textile materials of shoes are coated to make them waterproof.
Air knife coatings for technical textiles have a wide range of applications, from filter cloth to textile seals to carbon fiber impregnation.
In addition to coating with thickened pastes, there is also air knife foam coating. In this case, the physical foam is produced in a special foam machine (similar to whipped cream) and placed in front of the coating knife. Use a knife to press the foam into the fabric and destroy the foam.
This so-called unstable foam coating is used, for example, for over-dyed jeans. In the colored/uncolored version, the non-woven fabric is also fixed and covered in this way.
The term “unstable” does not mean that this is a bad bubble. The unstable foam is stable for at least five minutes at room temperature and does not decompose, but the bubbles then burst under a knife, or at the latest when the foam is subsequently heated in a dryer.
Air-knife foam coating has many advantages-by diluting the coating chemicals with air, less drying force is required and penetration depth is lower, while maintaining the breathability of the fabric.
In roll-knife coating (also called nip coating), the application using the knife is actually in flight without touching the upper side of the fabric.
This has various effects on the final product. For example, the application in the nip covers the surface of the textile with a coating compound, so that this side of the fabric has a plastic-like surface, which is determined by the chemical method used.
Well-known examples of roller knife coated fabrics are tarpaulins, life jackets, carpet backing, upholstery fabrics, trunk lids, sealing materials, etc.
Compared with air knife coating, roller knife coating has high requirements on the accuracy of the machine. However, today a combination of these two coating types is mainly offered.
For this reason, the coating bar is designed to be level adjustable, and the accuracy achieved depends on the supplier of the coating machine.
The hob can be used with an air knife or with a paste, for example in the coating of PVC tarpaulins, emergency slides, inflatable boats and gaskets.
Unstable and stable foam is used in roll knife coating. If a layer of unstable foam is applied, it will decompose in the first zone of the dryer.
For example, the hob coating of unstable foam (also called “volatile foam”) is used in the production of jeans to dye the denim material on one side. By applying colored foam on the surface, a good dyeing effect can be achieved, and it can be easily washed off in industrial washing to achieve the desired “stone washing” effect.
The stable foam still exists during the drying process in the dryer (under very mild drying conditions) and remains in the dryer as a foam layer.
A good example of applying a paint with a stable foam roller is in the production of shading fabrics for blinds or curtains. These products require special treatment to maintain the softness of the fabric and to ensure that the curtain can still be rolled up and down.
To achieve this goal, a special coating called Black-Out has been established, which includes a three-stage stable foam coating series using a hob.
The first layer of paint is usually white, then the black layer, and then the white layer. Dry these three layers and calender them with a calender after each layer is applied. Then, the fourth dryer channel cures all three layers and may add a final topcoat to improve grip.
This process is complicated and expensive, and errors may result in rejection of the entire production run, so experienced and well-trained personnel are required.
A similar process is used in the production of advertising banners, which is called “blocking.” This is a multi-layer foam paint that prevents the image/text of the banner from leaking out of the back of the material.
Let’s go back to the Macintosh and apply the rubber coating, which is an amazing application for the roller coater.
The applied rubber layer is so waterproof and impermeable that this type of material can also be used for light boats, life rafts, life jackets and emergency slides on airplanes.
However, this basic waterproof fabric has a problem with clothing, that is, it does not allow the moisture generated by the wearer to escape.
Therefore, the textile industry is facing the challenge of developing a material that can prevent rain but also allows the wearer to breathe.
Perhaps the first product that can meet this challenge is (and still is) sold in the form of Gore-Tex® for outdoor apparel. However, Gore-Tex® is not a coated fabric, but a laminated waterproof and breathable membrane.
The availability of water vapor permeable polyurethane dispersions also allows direct coating on the interior of the fabric. This is where the hob coating is applied. Depending on the required stress, stable foam coatings and paste coatings are used.
Laminating is usually understood as joining two or more layers of textiles, films, membranes or layers made of wool together, and in order to hold the two layers together, an adhesive is required. The adhesive It can be applied by coating or screen printing.
In wet lamination, the adhesive is first applied to the first layer, and then the second layer is placed in the wet application before the two materials are dried and fixed together.
In dry lamination, an adhesive is applied to a first material and dried, and then a second layer is applied to it by high pressure, usually by a calender.
During this process, apply a layer of foam with a roller doctor blade and carefully dry it. The second layer is then put into the dry foam through a calender. However, after that, the laminate must still be heat-fixed. Foam lamination has the softest touch. In the case of polyurethane foam, lamination also has heat resistance because the adhesive is not thermoplastic after fixing.
In this article, I tried to provide an overview of textile coating technology and hope to draw a conclusion by listing only some of the coating materials encountered in daily use.
We can start with mattress covers, slippers, shower curtains and bathroom mats, then put on a table with a coated tablecloth, and then go to the corridor to get a rain jacket and umbrella. In automobiles, from seat covers to trunks, countless kinds of coated fabrics are found. Commuters will encounter many coated materials when riding trains or buses.
Textile coating is still a profitable future technology. As an example, with the increase in lightweight structures, fiber-reinforced materials have become more and more important. Here, textiles or fibrous scrims are only used to reinforce the plastic matrix, but the production process is similar and therefore represents another growth area for textile coatings.