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Common Problems And Solutions For Finishing Of Shoe Upper Leather

2014/3/13 13:08:00 18

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common shoe finishing leather finishing problems generally have the following categories.

1. solvent problem

the main solvent used in shoemaking is toluene and acetone.

The coating layer partially dilated and softened with solvent, and then dissolved and dropped. It usually occurs in the front and back parts.

Solution:

(1) choose crosslinking or epoxy resin modified polyurethane or acrylic resin as film-forming agent. These resins have good solvent resistance.

(2) dry filling treatment can enhance the solvent resistance of the coating layer.

(3) appropriately increasing the amount of protein binder in the coating liquid can enhance the deep solvent resistance.

(4) spray crosslinking agent, curing crosslinking.

2. the problem of moisture resistance and water resistance is less than /strong > /p >

moisture resistance and water resistance is a very important index of shoe upper leather. In the process of wearing leather shoes, there is often a water environment. Therefore, it is also often encountered the problem of moisture resistance and water resistance.

The main reasons of moisture resistance and water resistance are:

(1) the top coat is sensitive to water.

The solution is to apply top coat or spray water brightener.

When topping, if cheese is used, it can be fixed with formaldehyde. Adding a small amount of silicon containing compounds in the top finishing liquid can also enhance its water resistance.

(2) excessive water sensitive substances, such as surfactants and water-resistant resins, were used in the finishing fluid.

The solution is to avoid using excessive surfactants and choose water-resistant resins.

(3) the temperature and pressure of the pressboard are too high, and the middle finishing agent is not complete.

The solution is to avoid excessive use of wax and silicon compounds when coating, reducing the temperature and pressure of the pressboard.

(4) uses organic pigments and dyes.

The selected pigments should have good permeability and avoid excessive dyes in the upper finishing formula.

3. dry friction and abrasion problems

when dry cloth is used to rub the leather surface, it will erase the skin color. This shows that the leather has poor dry friction resistance.

During walking, the trousers often rub with the heel of the shoe, so that the finishing film on the surface of the shoe is erased and the color is inconsistent.

There are several reasons for this phenomenon:

(1) the coating layer is too soft.

The solution is that the finishing agents used are better and harder when finishing the upper layer.

(2) the pigment is not completely stickup or too poor, because the proportion of pigment in paint is too large.

The solution is to increase the resin ratio and use penetrant.

(3) the skin pores are too open and lack of wear resistance.

The solution is to apply dry filling to increase the wear resistance of the leather and to strengthen the fixing of the finishing fluid.

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4. the problem of leather cracking is /p >

in areas with dry and cold climate, the problem of skin chap is often encountered. It can be greatly improved through the technology of wetting back (wet leather) before it is stretched.

the main causes of skin cracking are:

(1) the surface of shoe upper leather is too crisp.

The reason is that neutralization is improper, resulting in no uniform penetration of retanning agent and excessive combination of grain surface.

The solution is to redesign the formulation of the water field.

(2) shoe upper leather loose and low grade.

The solution is to dry up the loose leather and add some oil into the resin so that the treated leather is not too hard to prevent the vamp from cracking during the wearing process.

After repeated filling, the skin can not be placed too long and should not be worn too much.

(3) the undercoat is too hard.

Improper choice of base coat resin or insufficient dosage.

The solution is to increase the proportion of soft resin in the primer formula.

5. the problem of split pulp

when the skin is bent or stretched, sometimes it appears the phenomenon of color becoming shallow. It is usually referred to as astigmatism, and the phenomenon of coating layer cracking will often occur in severe cases, which is often referred to as cracking. This is a common problem.

the main reasons are: .

(1) the elasticity of leather is too large (the elongation of shoe upper leather is not greater than 30%), and the elongation of coating is too small.

The solution is to adjust the formula so that the elongation of the coating is close to that of the skin.

(2) the base coating agent is too hard, and the top finishing agent is too hard.

The solution is to increase the dosage of soft resin, increase the amount of film forming agent, and reduce the amount of hard resin and pigment paste.

(3) the coating layer is too thin, and the upper oil greasy spray is too heavy, which destroys the finishing layer.

In order to solve the problem of wet resistance of coating, some factories have sprayed excessive oil and polish oil. After solving the problem of wet wiping, the problem of splitting is also introduced. So we must pay attention to the balance of technology.

6. problem of pulp dropping

shoe upper leather has to undergo very complicated environmental changes during its use. If the coating is not firmly adhered to, it will often encounter the phenomenon of coating off the pulp. Serious delamination will occur, so we must attach great importance to it.

The main reasons are:

(1) the resin adhered to the bottom is not strong.

The solution is to increase the proportion of adhesive resin in the bottom finishing formula.

The adhesion of the resin depends on its chemical properties and the size of the emulsion dispersed particles. When the chemical structure of the resin is determined, the adhesive force is stronger when the emulsion particles are thinner.

(2) the amount of painting is insufficient.

When painting operation, the amount of painting is not enough, the resin can not infiltrate the leather surface in a short time, and can not fully contact with the leather, and the fastness of the coating will be greatly reduced. At this time, the operation should be properly adjusted to make the coating amount adequate.

The use of brush instead of spray can increase the penetration time and the adhesive area of the finishing agent to leather.

(3) the effect of the status of the leathers on the adhesive fastness of the coating.

When the water absorbency of the leather is very poor, or the oil and dirt on the leather surface, the resin cannot permeate the surface of the leather, so the adhesive force is not enough.

At this time, the skin surface should be properly treated to increase its water absorbency, such as clean surface operation, or adding leveling agent or penetrant in the formula.

(4) the proportion of resins, auxiliaries and pigments is not good in the finishing formula.

The solution is to adjust the type and dosage of resins and auxiliaries to reduce the amount of wax and filler.

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7. the problem of heat resistance and pressure resistance

shoe upper leather for molding and molding shoes must be heat resistant and pressure resistant.

In general, shoe factories often use high temperature pressing methods to press the wrinkles on the leather surface, causing some dyestuffs or organic coatings in the coating to become black or even sticky.

the main reasons are: .

(1) the thermal plasticity of the finishing fluid is too high.

The solution is to adjust the formula and increase the amount of casein.

(2) lack of lubricity.

The solution is to increase the lubricity of leather by adding a little stronger wax and a smooth feel.

(3) dyes and organic coatings are sensitive to heat.

The solution is to select materials that are less sensitive to heat and do not fade.

8. the problem of light fastness

After exposure for a period of time, the color of the leather surface becomes darker and yellowed, resulting in P being unable to continue to be used.

The reasons are:

(1) leather discoloration is caused by oil, vegetable tannin or synthetic tannin discoloration.

Light fastness of light coloured leather is a very important index. Light and grease resistant tannins should be selected.

(2) coating discoloration.

The solution is to use butadiene resin, aromatic polyurethane resin and nitrocellulose varnish instead of butadiene resin, and choose light resistant resin, pigment, dyestuff and varnish.

9., the problem of cold resistance (weather resistance)

cold tolerance is mainly due to the coating cracking when leather is exposed to low temperature. The main reasons are:

(1) at low temperature, the coating lacks softness.

Polyurethane, butadiene and other cold resistant resins should be selected to reduce the consumption of acrylic resin, casein and other cold resistant film forming materials.

(2) the proportion of resin in paint formulation is too low.

The solution is to increase the amount of resin.

(3) the cold resistance of the upper gloss oil is poor.

Special light oil or varnish can be used to improve the cold resistance of leather, while nitrocellulose varnish has poor cold resistance.

making physical properties of shoe upper leather is very difficult. At the same time, it is also unrealistic to require shoe factories to purchase completely according to the physical and chemical indexes formulated by the state or enterprises.

Shoe factories usually inspect leather according to non-standard methods, so the production of upper leather can not be isolated. We must have a better understanding of the basic requirements of shoemaking and wearing process so as to control scientifically during the process.