Wet polyurethane synthetic leather production process-Iota

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News > Dynamic industry > Wet polyurethane synthetic leather production process

Wet polyurethane synthetic leather production process

Wet polyurethane synthetic leather production method is to join the polyurethane resin in the wet DMF solvents and other fillers and additives into the mixture, after vacuum degassing machine, impregnated or coated on the fabric, and then placed in a solvent (DMF) having affinity with the incompatibility of the polyurethane resin in water, the solvent (DMF) was replaced with water, gradually solidified urethane resin, thereby forming a porous film, i.e. microporous polyurethane grain layer, customarily referred Bass (English transliteration BASS), the implication is the substrate (semi-finished leather) means, bass through dry veneer or surface after finishing, such as surface printing, embossing, dermabrasion and other processes in order to become PU synthetic leather Finished. Wet polyurethane synthetic leather with good breathability, moisture permeability, smooth feel plump, good mechanical strength, especially from the structure similar to natural leather, wet synthetic leather production process can be divided into single bass coating, dipping Three law and impregnated coating method, the use of fabric types of textile fabrics and nonwovens.
(A), a single coating process polyurethane Bass
1, the production process
After unwinding fabric cloth storage rack soaked into the dip tank, and then extruded through a squeeze roll most of the water by removing part of the water wheel ironing while ironing fabric, then coated with a slurry coater , then enter the coagulation bath into film, and then thoroughly rinsed with water, drying stereotypes, cooling into large volume bass.
2, the main raw material
A, a polyurethane resin: general wet resin usually, dermabrasion special, dedicated and cold impregnating resin, resin modulus (100%) ranging from 2.0MPa to 30.0MPa. According to Bass softness, use low modulus resin grades, single-coated bass due to the small cell, density, often adding a large amount of wood powder and other fillers, so when the product is used in cold regions, to fully consider the product of cold resistance using cold can be good resin.
B, wood powder: used in a single-coated bass in a certain amount of wood powder, both to reduce product costs, but also play a role in the solidification process skeleton, different types of wood powder manufacturers, which different coefficients of expansion, thus Under the same circumstances the same other material having a viscosity values are not the same, but also directly affect the quality and the corresponding cost of the product, wood powder fineness requirements are generally to reach more than 400 mesh.
C, the anionic surfactant (C-70, C-90): also known as fast penetrants, hydrophilic. Primarily as DMF and water to speed up the exchange rate, increase production speed, while the fine of the cell. Anionic surfactants may generate a spherical cell structure, increased elasticity, air permeability, moisture permeability. General amount between 0.5% to 2.5%, as Cadogan, coating easy to rewind smoothness decline.
D, nonionic surfactant (S-80): hydrophobic, the surface can be delayed solidification rate and therefore the interior of DMF and water can be exchanged more quickly, the needle may be generated cell structure, an amount of 1 % -3%, affected by excessive production speeds.
E, the solvent (DMF): DMF for dissolving and diluting the urethane resin. Directly with the resin, to adjust the viscosity of the mixed solution, DMF large amount of time, in the solidification process, improve the solidification rate and increases the cell structure.
F, paste: products should be used in a single solvent system of DMF is usually added in an amount of 5% -8%.
G, fabric: Single Bass coated fabric used mainly in weaving, single from felt, based on their volume of cotton yarn little direct impact on the water-soaked time.
3, the production process operation points
A, the preparation of a polyurethane paste:
Higher slurry viscosity required for single-coated bass, the general control 7000-9000Pa.s. Order of addition are more important ingredients. Usually in the container first join DMF, followed by the addition of wood flour, and stir with a mixer for about 10min, to ensure wood powder dispersed in DMF. If the first DMF is mixed with polyurethane stirred together, followed by the addition of wood flour, wood flour will make the agglomeration, can not be sufficiently dispersed in a resin solution, even if filtered, wood agglomerate are easily blocked filter, serious can not be used to prepare the slurry viscosity to meet the requirements, the use of a vacuum bubble machine degassing 40min, if the high slurry viscosity, degassing time may be extended, and finally with 60 to 100 mesh strainer filter.
B, fabric soaking treatment:
Send fabric, cloth storage rack through the dip tank, and then pressure roll the fabric in the water squeezed by ironing the fabric round hot sticky. Soaking treatment effect, there are two, one is to improve the fabric moisture, prevent infiltration Ruji Bu pulp tissue, resulting in through the end of the phenomenon, waste of raw materials. The second is to skim the fabric poor, tank outside except water, should be 1% of an anionic surfactant to improve the hydrophilic fabric, improve the appearance of quality bass.
C, coating solidification:
By fabric treated by coating station, using a knife coating method, coating the slurry mixture evenly coated on the fabric. When used as a substrate from the felt, should pay attention to the direction from the felt surface napped, smooth hair coat, bass and smooth surface. Reverse hair coat, bass rough surface. Thickness of the coating is too thin, can not cover wool cloth, Bass surface roughness, hair feel plate inelastic, thick coating could easily lead to cell uneven surface layer and the substrate separation defects. Coagulated coagulating liquid tank is composed of water and DMF, DMF's content is generally 20% --- 25%.
Production grinding 皮贝斯, content control in 10% DMF - 15%. The content of the high solidification speed will affect, and solids content of the resulting water increases, the concentration of DMF is too low not only increases the cost of recovery, also allows Bass surface shrinkage increases, resulting in migration to the water rapidly bead DMF, and penetration of water into the material layer speed is slower. Have a certain shrinkage during solidification in the slurry, coating thinning, and a certain degree of curling. To prevent curling, on the one hand to ensure the coagulation bath DMF concentration, on the other hand when the ingredients can add some S-80, delayed coagulation surface, increasing the cell. You can also use clamps selvedge and increase tension roller method to prevent curling.
Coagulating bath temperature is generally room temperature, heating in winter may be appropriate, generally controlled at 25 ℃, too high a temperature will decrease the coating breaking strength, modulus of the film decreased, the surface uniformity is deteriorated, but homogeneous porous structure. Solidified coating layer into the water from the tank to the solidification solidified completely, about 8-15min, which is formulated resin grades, water, DMF concentration and temperature are closely related. Before completely solidified material layer not in contact with the guide rollers, otherwise it will damage the surface layer.
D, washing, drying, coiling:
Polyurethane coating layer after complete solidification, within its cell layer still remains a certain amount of DMF, DMF must force emerge in these water tank when such removal is not clean, it will cause Bass surface pitting and other defects after drying. In the process control to ensure that the content of the last washing tank DMF at 1%, so as to ensure the removal and clean bass DMF, DMF in order to wash out the speed and reduce the bass in remaining in the DMF, wash tank generally require warming operation.
Practice has proved that a great influence on the temperature of water tank DMF wash-out rate and the residual amount of DMF bass. In the washing process, especially in the second half of the wash tank, because remaining in the DMF has been very little bass. Therefore, the impact of bass in the wash water residence time of DMF degree wash its impact is far less pressing times larger. After Bass washed clean, to remove the water, to be drying. Oven temperature should not be too high, generally not more than 150 ℃, at the entrance, Yinbei Si contains a lot of moisture, temperature can be higher, as the evaporation of water at the rear of the oven temperature can be lower, generally 120 ℃ can be.
(II) from the felt is impregnated polyurethane Bass
1, the production process
Unwinding from the felt, cloth storage rolls by heating to remove moisture after ironing ironing impregnated into the groove, polyurethane impregnated with the slurry. Idler roll through the gap, the excess slurry is scraped into a coagulation tank, coating is formed by a squeeze roll out most of the DMF solution, then washed with water, dried, winding the bass.
2, the main raw material
A, a polyurethane resin: explanation consistent with the single coating method.
B, wood powder: Bass impregnated with the formulation, wood powder was used to small, usually no more than 10%, the fineness of 400 mesh or more.
C, additives: Bass impregnated with the formulation, in addition to the use of C-70 and S-80 aids, there are several special additives.
① antifoaming agents: mainly composed of liquid silicone, the main role is to eliminate the air in the slurry, reduce the bass surface pinholes. Generally silicone oil and DMF poor compatibility, it should not be applied. Design formula should be used in a certain compatibility with DMF, foaming ability of special additives. The amount is generally 0.5-1 parts, the amount is too small does not work, a large amount of time due to poor compatibility with DMF, Bass will appear leathery surface sag.
② leveling agent: leveling agent is a modified silicone additives. The main role is to improve the surface smoothness of the bass, increase the affinity between the resin and the fabric. The amount of resin is generally 0.1% by weight.
③ Water: Water may also be used as an additive for impregnating bass formulations, to adjust the cell structure, to accelerate the solidification rate.
D, solvent DMF: Bass impregnated with the formulation, DMF in an amount of up to 1.5 times the mass of the resin to 2 times.
E, from the felt: Bass impregnated leather from the felt used more as a double from felt, thickness ranging from 0.4-1.2MM, according to the product thickness to choose. Impregnating process requirements from felt degreasing and hydrophilic have to be good, raising short and uniform organizational structure closely.
3, the production process operation points
Preparation of Polyurethane slurry (1): added with stirring cylinder quantitative DMF, followed by addition of wood flour, wood powder and stirred to disperse in DMF, stirring was stopped, followed by adding C-70, S-80, water, defoaming agents, leveling agents, continue stirring 5MIN, added polyurethane resin and a colorant, high speed stirring for about 20min, while the vacuum degassing, sample test with fluid viscosity, if not meet the technical requirements, you need to adjust.
(2) impregnating solidifying step: with a good paste impregnated with pump into the tank, fabric unwinding in front of the impregnating bath immersion, the ironing roller heated to remove the moisture in the fabric, or easy to produce bass leather surface two-skin phenomenon. Impregnated fabric into the slot in the polyurethane slurry infiltration Ruji Bu. Due to the continuous movement of the fabric, put air into the impregnated slurry tank, thereby generating bubbles of air in the slurry will generate pinholes in the surface of bass. For the timely addition to the elimination of these bubbles in the slurry was added defoamer formulations, recycled materials impregnated tank is very effective method that continue to bubble-free material is impregnated into the groove, while the overflow from the tank top is impregnated The material contains more bubbles overflow slurry storage dedicated barrel, let stand for defoaming after a period of time, to re-enter the impregnating tank use. Impregnated fabric from the trough out the excess paste with a spatula scrape. Blade gap is also an important factor in surface quality bass effect. When the doctor gap is too small, prone to leakage cloth hair, causing an uneven surface; the gap is too large, and easy two-skin surface phenomenon, but also according to the size of the gap length from the felt fuzz make the appropriate adjustments, then solidified into the water. Bass should be perpendicular angle into the water solidification mode is appropriate. Into the water, not too long from the horizontal direction to 6-8M appropriate, quality is a key factor from the felt bass quality. Skim poor, Hydrophilic from the felt surface can cause a lot of bass pinholes even cause surface delamination. Thus, the wet fabric of skim, hydrophilic, there are stringent requirements. A simple way to test from the felt is hydrophilic climb test, that is a width 30MM, 200MM length of cloth, its lower end immersed in water, after a certain period of time (for example, 30min), measured along the cloth climb high water height. Climb higher, the better to say Mingbu flooding. The above method is actually a method to check Burkina capillary effect. When the intrinsic quality of the fabric of the occurrence of the problem, no matter how corrected recipe, are of no avail.
(3) washing, drying, coiling: Bass impregnated thickness generally thicker, so washing, drying time accordingly longer.
(C) from the felt impregnated with polyurethane-coated Bass
1, the production process
Note: 1, 2 unwinding from the felt, impregnated tank 3, the squeeze roller 4, proclotting groove 5, squeeze rollers 6, 7 ironing roller, paint sets 8, 9. solidification squeeze rollers
After starting the felt is first impregnated with polyurethane slurry from the felt impregnated polyurethane-coated bass, into the water solidification, by extrusion, after ironing substantially dry, apply a layer of polyurethane on the front with the solution, then solidified into the water. Bass impregnated coated surface roughness, folds fine, strong sense of leather.
2, the main raw material
Impregnated leather-coated Bass basic raw materials used in the single-impregnated and coated Bass single leather raw materials used in essentially the same coating impregnated with bass formulations, coating liquid formulations and single-coated bass is basically the same, and the viscosity of formulations containing infusion is lower than the single impregnated bass recipe. Because impregnated cover bass, the impregnated felt newcomer holdup is low, it is not necessary to add defoamer and leveling agent, S-80 do not have to use only C-70 to increase the water and DMF exchange rate can be.
3, the production process operating points for attention
The viscosity of the coating is impregnated Bass infusion should be as low as possible, from the holdup felt as little as possible. After the pre-solidified, hot dry fabric to fully, otherwise, after the coating liquid paint, in the solidification process is easy to produce bubbles or chicken lines. Bass impregnated leather coat from the felt on very strict requirements, from the back of the hair was longer, the front will have shorter hair, organizational structure than the single cloth impregnated with a cloth to close. From the felt to have a good hydrophilic, when poor quality from the felt, it will also produce bubbles and chicken lines.
Problems and solutions impregnated coated bass prone in production may refer a single coating methods Bass Bass leather and leather impregnated with solutions.

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