Section V Leather Printing

First, leather printing In the tanning production, from the raw material leather to the leather to the leather to dry all need to be finishing processing, in order to improve the use of leather performance. Leather finishing is a combination of technology and art. Some processes are to improve the physical properties of the product, while others provide a comfortable feel to the leather, and some processes can increase the beauty of the leather. For example, softness, softness, and softness can improve the softness of the leather; calendering can make the leather body firm and strong, and increase the tensile strength of the leather; light and iron, in order to improve the surface gloss and flatness of the leather. Embossing, embossing, and color printing are used to give the leather a beautiful appearance. Polishing can increase the value of leather and make suede.
Here only the processing methods related to printing in leather finishing are explained.
(a) Surface Treatment of Leather (1) Degreasing and Delustering Wipe with a mixture of 250 mL of acetone, 1000 mL of water, 200 mL of ethyl acetate, 50 mL of lactic acid, and 50 mL of ammonia (0.5%).
(2) Anti-mildew treatment After 45 minutes of degreasing, use a mildew-proof liquid (take 3 parts of pentachlorophenol sodium and other anti-mould agents in 97 parts of turpentine or the like solvent) and brush it again.
(2) Embossed embossing is the application of a variety of patterns on the surface of the leather to increase the color of the leather, decorate the leather surface, and further increase the value of the leather.
Embossing equipment can be used to replace the plate on the ironing machine with a variety of patterns carved metal plate, the ironing machine into an embossing machine. Another special embossing machine is a pattern carved on the copper Roller, embossed leather between the flower roller and the pad roller, it pressed on the pattern. The embossed copper roller is heated by the heating wire so that the pressed pattern is clear and has a good setting.
When leather embossing, the embossing pattern is very important to connect, so that the joints naturally, to avoid the design dislocation and joint pressure loss at the joint.
Embossed leather should be slightly tidal, about 20% moisture content. This pattern is more clear.
(C) Direct printing Direct printing is made by thin metal plate or thicker oiled paper, and the solution of the dye is directly brushed and dyed on the leather. This printing method is the simplest, but it is easy to render stains, resulting in lines that are not Clear.
Direct printing can also apply a dye or starch paste to the leather surface through a hollow pattern, so that the resulting pattern is relatively fixed. After the color paste is dried and shaped, a steam bath is performed to increase the dyeing effect of the color paste. Finally, the starch paste on the leather was washed off with cold water.
The direct printing method can only be used for patterns with dark flowers.
(D) anti-inking printing This process is the insoluble inorganic materials and starch paste, fixed to the surface of the leather through the hollow plate as a dye-resistant layer, and then dyeing. In the anti-dyeing agent, some chemical agents may also be added to destroy the dyeing effect, so as to produce a dye-resistant color pattern.
(5) Discharging Printing Discharging and printing is the method of removing the background color from the dyed leather with a dye discharge agent to form a pattern. Leather dyeing uses direct dyes and acid dyes. The two dyes are mostly azo dyes according to their chemical structure. If treated with a reducing agent, its azo structure will be destroyed and lose its original color. This reaction can be expressed by the following formula:
RN=NR'+4(H)→RNH2+R'NH2
Dyeing of dyes is based on the above principle. The reducing agent can be discharged into pastes by printing. The most effective reducing agent is a carved white block with the formula NaHSO2·CH2O·2H2O. It produces a strong reduction at 80-100°C.
The addition of a dye that is not affected by the reducing agent in the whitening agent (flux puller) can simultaneously produce the effect of "pulling out" and "staining." Salt-based dyes are commonly used in combination with whitewashed blocks. Dispensing agents are prepared as follows:
Salt-based dye 1 part of water to adjust the paste for the degree of carving white block 3-5 parts of alcohol 1 part of acetic acid 1 part of tannin 1 part of starch 10 parts When formulated, first dissolve the dye with alcohol and aldehyde acid, and then adjust the dye Paste, cooled and then transferred to the previously dissolved carved white block.
After the discharge is completed, wash the extra discharge slurry with cold water. Since the discharge printing is mostly used for deep-ground leather, it does not stain.

Second, artificial leather embossing (a) artificial leather Artificial leather is a mixture of resins, plasticizers, stabilizers and other additives, coated or affixed to the substrate, made by a certain process. Polyvinyl chloride is mostly used in resins. Through the formulation design to change various components, different types and different performances of artificial leather can be made, such as cold-resistant, flame-resistant artificial leather, non-foaming and foaming artificial leather and so on. There are two types of base materials:
1 cotton cloth, including city cloth, bleaching cloth, canvas, knitted fabric.
2 cellulose, including paper, non-woven fabrics.
The production methods of artificial leather include: calendaring, extrusion and squeegeeing. The smearing method can be divided into a direct smearing method and an indirect smearing method.
(B) Surface Treatment Due to the high content of plasticizer in the PVC artificial leather, the surface of the product is sticky, and due to the migration of the plasticizer, it will cause the hand to feel sticky and difficult to remove the dust, so it must be surface treated. There are two methods: one is to coat the surface with a thin layer of surface treatment agent, and the other is to put a layer of polyvinyl chloride film on the surface.
(3) Embossing In order to make the surface of the leather of the PVC artificial leather have the same effect, a pattern similar to the leather texture is rolled on the surface of the leather, which is called embossing. At present, mechanical embossing is generally used. There are two types of embossing machines, one is the direct connection between the back of the oven and the coating machine directly connected to the production line, and the other is a separate type of embossing. In many foreign countries, independent embossing can be used, which is not limited by coating calendering or plasticizing and foaming speed, but the embossing speed can be adjusted according to the depth of the pattern and the simple and complex design to ensure the quality of embossing. At the same time in the exchange of flower roll does not affect the production of the previous process.
The embossing machine has a variety of structures, but generally consists of an embossing roller and a rubber roller. The roller arrangement is mostly vertical, so that it is easy to observe the embossing effect and change the flower roller. Pressurization between rollers is now using air pressure.
(1) The embossing roller of ordinary leather embossing machine is made of seamless steel pipe, and the surface is made into various patterns by mechanical pressing or chemical corrosion treatment, such as: sheepskin grain, cowhide grain, orange peel and so on. In order to make the roller surface rust-proof and resistant to the main chrome plating layer, the cooling water inside the roller cools the pressed pattern to ensure the embossing effect and protects the rubber roller.
The rubber roller is made of seamless steel pipe wrapped with heat-resistant rubber. Generally used is a rubber with a Shore hardness of 85°-89°. The drum surface requires smooth, non-stick cloth or resin pellets. For a certain period of time, the rubber is prone to expansion due to heat, and the unevenness of the concave surface is caused by the mixing of impurities. Therefore, it needs to be turned or ground on a lathe. When it is used to a certain extent, it can not be used anymore, and all rubber layers will be replaced with new ones. .
A set of screw lifting and pressurizing mechanisms is arranged on the shafts at both ends of the embossing roller to regulate the line pressure between the embossing roller and the rubber roller. Line pressure is too small, the leather surface pattern is not easy to clear, but the line pressure over the assembly will be laminated to death.
(2) Foam leather embossing machine The embossing belt of foam artificial leather adopts gap embossing machine. This embossing machine needs to maintain a certain gap between two rollers. The crevice clearance is adjusted with the wedge, and the size is adjusted with the depth of the pattern. The average thickness of artificial leather is 15%-25%. Artificial leather after embossing to thinning, generally not less than 30% is appropriate. In addition, the flower roller and the rubber roller are driven at the same peripheral speed, which can protect the cell structure and elasticity of artificial leather and ensure the quality of embossing.
(3) Cooling and embossing of artificial leather after embossing are very hot and must be sufficiently cooled. Incomplete cooling of artificial leather will cause adhesion and shrinkage. The cooling of the artificial leather is carried out on a set of cooling rollers, each group generally consisting of 3 to 4 cooling rollers. The chill roll is made of steel plated chrome-plated finish. Both ends are open type, there is a certain level of cooling water inside the roller, and many outflows; also clip wall type, with cooling water in the interlayer.