Wet polyurethane synthetic leather production process
Wet polyurethane synthetic leather production process
The production method of wet polyurethane synthetic leather is to add DMF solvent and other fillers and additives to polyurethane wet resin to make a mixed liquid. After degassing in a vacuum machine, it is impregnated or coated on the base fabric, and then put in with the solvent (DMF) has affinity, and in water that is incompatible with polyurethane resin, the solvent (DMF) is replaced by water, and the polyurethane resin gradually solidifies, thus forming a porous film, that is, a microporous polyurethane particle surface layer, which is customarily called bass. (Transliteration of English BASS), which means base material (semi-finished leather). Bass can become polyurethane synthetic leather after dry veneer or surface modification, such as surface printing, embossing, leather grinding and other processes. Finished product. Wet-processed polyurethane synthetic leather has good air permeability, moisture permeability, smooth and plump feel, and excellent mechanical strength. In particular, it is similar to natural leather in structure. The production process of wet-processed synthetic leather can be divided into single coating method, dipping method There are three methods: method and impregnation coating method. The base fabrics used include woven fabrics and non-woven fabrics.
(1) Single coating polyurethane bass
1. Production process
The base fabric is unrolled and enters the soaking tank through the fabric storage frame to be soaked, and then most of the water is squeezed out through the squeeze roller, and part of it is removed through the ironing wheel
Moisture, iron the base fabric flat at the same time, then apply the matching slurry on the coating machine, then enter the coagulation tank to form a film, then fully wash, dry and shape, and cool into a large roll bass.
2. Main raw materials
A. Polyurethane resin: usually ordinary wet resin, special for microdermabrasion, special impregnation and cold-resistant resin, etc. The modulus of the resin (100%) ranges from 2.0MPa to 30.0MPa. According to the softness and hardness of the bass, high and low modulus grades of resin are selected. Due to the small cells and high density of the single-coated bass, a large amount of wood powder and other fillers are often added. Therefore, when the product is used in cold areas, the cold resistance of the product must be fully considered. , using resin with good cold resistance.
B. Wood powder: Using a certain amount of wood powder in single-coated bass can not only reduce the product cost, but also play a role as a skeleton in the solidification process. The expansion coefficients of wood powder from different manufacturers are different, so it is convenient When other materials are the same, their viscosity values are different, which directly affects the quality of the product and the corresponding cost. The fineness requirement of wood powder is generally more than 400 mesh.
C. Anionic surfactant (C-70, C-90): also known as rapid penetrating agent, it is hydrophilic. It mainly functions to speed up the exchange speed of DMF and water, improve the production speed, and at the same time make the cells more compact. Anionic surfactants can generate spherical cell structures and increase resilience, air permeability, and moisture permeability. Generally, the added amount is between 0.5% and 2.5%. If too much is added, the coating will easily roll back and the smoothness will decrease.
D. Nonionic surfactant (S-80): It is hydrophobic and can delay the coagulation speed of the surface, thus allowing the internal DMF to exchange with water faster, and can generate a needle-like cell structure. The added amount is 1 %-3%, excessive production speed will be affected.
E. Solvent (DMF): DMF is used to dissolve and dilute polyurethane resin. Directly mix the resin and adjust the viscosity of the mixing liquid. When the amount of DMF is large, the solidification speed and cell structure will be increased during the solidification process.
F. Color paste: A product of single solvent DMF system should be used, usually the dosage is 5%-8%.
G. Base fabric: The base fabric used for single-coated bass is mainly based on plain woven fabric and single-sided fleece fabric. The cotton content of its yarn count directly affects the time it takes for it to soak with water.
3. Key points of production process operations
A. Preparation of polyurethane slurry:
The slurry viscosity required for single-coated bass is relatively high, generally controlled at 7000-9000 Pa.s. The order in which ingredients are added is more important. Generally, DMF is added to the container first, and then the wood powder is added, and the mixer is used to stir thoroughly for about 10 minutes to ensure that the wood powder is dispersed in the DMF. If DMF and polyurethane are mixed and stirred first, and then wood powder is added, the wood powder will agglomerate and cannot be fully dispersed in the resin solution. Even if it is filtered, the agglomerated wood powder will easily block the filter, causing serious problems. It cannot be used. After the viscosity of the prepared slurry meets the requirements, a vacuum degassing machine will be used to degas it for 40 minutes. If the viscosity of the slurry is high, the degassing time can be appropriately extended, and then filtered with a 60-100 mesh filter.
B. Water immersion treatment of base fabric:
The base fabric is sent and put into the soaking tank through the fabric storage rack, and then the moisture in the base fabric is squeezed out with a squeeze roller, and the base fabric is ironed semi-dry through the ironing wheel. The water immersion treatment has two functions. One is to increase the humidity of the fabric and prevent the slurry from penetrating into the base fabric structure, resulting in bottom penetration and waste of raw materials. Second, for base fabrics with poor degreasing properties, in addition to clean water, 1% anionic surfactant should be added to the water tank to improve the hydrophilicity of the base fabric and improve the appearance quality of the base fabric.
C. Coating and solidification:
The treated base fabric passes through the coating table and the slurry mixture is evenly coated on the base fabric using the knife coating method. When using fleece cloth as the base, pay attention to the direction of the fluff on the surface of the fleece cloth, and apply it along the fluff to ensure a smooth surface. Coated with reverse hair, the surface of the bass is rough. The thickness of the coating is too thin and cannot cover the hair of the cloth. The surface of the bass is rough and the hair board feels inelastic. The coating is too thick and can easily cause defects such as uneven cells and separation of the surface layer from the base material. The coagulation liquid in the coagulation tank is composed of water and DMF. The content of DMF is generally 20%—25%.
When producing ground bass, the content of DMFFinally, use a scraper to scrape off the excess slurry. The scraper gap is also an important factor affecting the surface quality of the bass. If the scraper gap is too small, it is easy to leak cloth lint, resulting in an uneven surface; if the gap is too large, it is easy to have two layers of skin on the surface. The size of the gap must be adjusted appropriately according to the length of the fluffing cloth, and then it is put into water to solidify. The angle at which the bass enters the water should be vertical solidification. After entering the water, the horizontal distance should not be too long, preferably 6-8M. The quality of the fleece cloth is a key factor in the quality of the bass. Fleece cloth with poor degreasing and poor hydrophilicity will cause a large number of pinholes on the surface of the bass, and may even cause surface delamination. Therefore, base fabrics for wet processes have strict requirements on degreasing properties and hydrophilicity. A simple method to test the hydrophilicity of fleece fabric is the height-climbing test, that is, immerse the lower end of a cloth strip about 30MM wide and 200MM long in water, and after a certain period of time (for example, 30 minutes), measure the height of the water climbing up the cloth. high. The higher you climb, the better the water-soakability of the cloth. The above method is actually a method to check the capillary effect of cloth base. When there is a problem with the inherent quality of the base fabric, no matter how you correct the formula, it will be of no use.
(3) Washing, drying, and coiling: The thickness of impregnated bass is generally thicker, so the washing and drying times are correspondingly longer.
(3) Fleece cloth impregnated with polyurethane base
1. Production process
Note: 1. Fleece cloth unwinding 2. Impregnation tank 3, squeeze roller 4, pre-coagulation tank 5, squeeze roller 6, ironing roller 7, coating table 8, solidification 9. Squeeze roller
The method of impregnating fleece cloth with polyurethane base is to first impregnate the fleece cloth with polyurethane slurry, then put it in water to solidify. After extrusion, ironing and basically drying, apply a layer of polyurethane compound liquid on the front, and then put it in water to solidify. The surface of the impregnated coated bass is smooth, with fine wrinkles and a strong leather feel.
2. Main raw materials
The raw materials used for impregnated and coated bass leather are basically the same as those used for single-impregnated and single-coated bass leather. In the formula of impregnated and coated bass, the formula of the coating liquid is basically the same as that of single-coated bass, and the viscosity of the impregnation liquid formula is Lower than the single dipped bass recipe. Since the liquid retention rate of the fluffed cloth after impregnation is very low in the impregnated bass, there is no need to add defoamer and leveling agent, and there is no need to use S-80. Only C-70 can be used to increase the exchange speed between water and DMF.
3. Key points and precautions for production process operations
The viscosity of the impregnating liquid for impregnation coating should be as low as possible, and the liquid retention rate of the fluffed cloth should be as small as possible. After pre-coagulation, the base fabric must be fully ironed and dried. Otherwise, bubbles or chicken claw marks may easily occur during the solidification process after applying liquid paint. Impregnated coated Bess leather has very strict requirements on fleece fabric. The fleece on the back should be longer and the fleece on the front should be shorter. The structure of the cloth is denser than that of single impregnated cloth. The raised cloth must have good hydrophilicity. If the quality of the raised cloth is not good, bubbles and chicken claw marks will also occur.
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