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ABS plastic coating composition and coating process introduction

Welcome to follow the website name Note WeChat account

Source of information: Date of this site: 2015-05-06

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Chapter One. Coating concept, variety, composition

I. Full name of ABS

ABS finger: Acrylonitrile-butadiene-styrene terpolymer copolymer finger


2. What is paint

The coating is a complex multiphase liquid-solid dispersion system. The coating resin must be able to dissolve in the solvent to form a liquid with excellent fluidity and disperse in the liquid medium to form a stable emulsion. They are then fully mixed with pigments, fillers and additives to form Uniform and stable dispersion system.


3. What is ABS paint

ABS coating is a thermoplastic acrylic paint

The main film-forming component of 1 liquid coating is acrylic varnish

族多异氰酸酯结合而成,不同种类2液型涂料硬度可以有很大不同 The main film-forming component of 2-pack paint is acrylic polyurethane, which is a combination of hydroxyl-containing acrylic polyol and aliphatic polyisocyanate. The hardness of different 2-pack paints can be very different.

Most polymer substrates can be dissolved or swelled by the solvent in the coating to varying degrees, which is conducive to the mutual miscibility or miscibility of the coating resin and the substrate, and enhances the adhesion of the coating.


4. ABS coating composition

The composition is composed of a main film-forming substance, a secondary film-forming substance, and an auxiliary film-forming substance, and is specifically composed of a film-forming resin, a coloring pigment, a filler, a solvent, an auxiliary agent, and the like.


Film-forming resin: Source of coating characteristics and adhesion. (Main film-forming substance)

Colored pigments: The source of the color of the coating cannot be formed into a film by itself. (Second film-forming substance)

Filling: the guarantee of paint fluidity, paint film thickness and hardness, which cannot be formed into a film by itself, (secondary film-forming substance)

Solvent: the fluidity of the coating and the atomization during coating, dispersing the film-forming base material into a viscous liquid. (Auxiliary film-forming substance)

Aid: Coating workability, improving flow and leveling, dispersing the film-forming base material into a uniform liquid. (Auxiliary film-forming substance)


Chapter two. Performance, characteristics and application of each component of coating


One. Film-forming resin properties, characteristics, applications

1. Film-forming resin is also called base resin. Its function is to combine pigment, filler and resin to form a uniform and dense coating film on the substrate. After curing, it forms a coating. Adhesion to substrate, physical, chemical, and mechanical properties of the coating.

2. The film-forming resin is preferably a polymer resin whose chemical structure, surface tension, and solubility parameters (that is, the compatibility between the solvent and the resin in the coating) are similar to the substrate to achieve the best adhesion.


two. Performance, characteristics and application of colored pigments

1. Pigments are solid powders that are insoluble in water and oil, and have a specific color. They are divided into color pigments and extender pigments (ie fillers).

2. Coloring pigments: give the coating hiding power and enhance mechanical and physical properties, mainly play a role in coloring and hiding;

3. Tinting power: When a certain pigment is mixed with other pigments in the base material, it can show the ability of the color of other pigments without affecting the color of the coating.

4. Hiding power: Due to the effect of the pigment, the minimum amount of concealment that can be used to cover the coated surface depends on the difference between the refractive index of the pigment and the oil. The larger the better.

The so-called light resistance and weather resistance of pigments, pigments will change to different degrees under the action of light and atmosphere

5. Three primary colors: red, yellow, and blue. The three colors are the most basic colors, also called the first colors. The raw materials for color paints can no longer be decomposed by themselves. The red, yellow, blue, white, Five black color masterbatches.


three. Performance, characteristics and application of filler

1. Filler is filling pigment (also known as constitution pigment)

2. It is a powdery substance without hiding power and coloring power. It is mainly resistant to chemicals, weathering, good abrasion resistance, neutral, and improves the rheological properties of coatings, sealing properties, temperature resistance, mechanical properties, and construction Performance and can significantly reduce the cost of coatings.


four. Performance, characteristics and application of solvents

1. The solvent is a volatile organic liquid. As long as the two coatings have similar properties, the two solvents can be used universally.

2. The main role of the solvent is to dissolve or disperse the film-forming resin into a uniform and stable liquid dispersion system, reduce the viscosity of the coating, facilitate coating preparation, and form into a film. It must be completely evaporated without residue during the process of forming the coating. It is important The indicators are solubility and volatility.

3. The other main role of the solvent is to dissolve or swell the substrate. It is best not to dissolve the substrate and only play the role of swelling. In particular, do not dissolve and migrate additives such as plasticizers in the plastic and migrate to the surface of the substrate.

4. Solvents for acrylic paints are prepared by mixing ketone, ester, alcohol, and ether solvents.

Ketones: true solvent, acetone, low boiling point, fast volatility, easy to absorb water, easy to whiten, but strong dissolving power,

Cyclohexanone, high boiling point, non-volatile, anti-whitening

Ester action: True solvent, strong solubility to resin, strong erosion to substrate.

Alcohol effect: co-solvent, to ease the erosion of the substrate

Ether function: help solvent, promote leveling, reduce the erosion of substrate

5. The solvent combination includes the proper combination of the resin's true solvent, co-solvent, and diluent (poor solvent used to adjust the leveling, drying speed, and cost of the coating) to achieve the best solubility, volatility, and price. balance


Fives. Performance, characteristics and application of additives

Adjust and improve the comprehensive performance of coatings and coatings. Wetting and dispersing agents are mainly used in coating formulations and production processes, as well as other anti-floating agents and anti-sagging agents.

third chapter. Coating film formation mechanism


One. Paint adhesion

1. The first step in the adhesion of plastics and coatings is the wetting of the coating on the surface of the product. The coating wets the surface of the product, replacing the air and water adsorbed on the surface. At the same time, the solvent volatilizes or dissolves the surface of the product. The solubility parameter is selected properly, so that an intermixed layer is formed on the surface of the paint film


two. Coating dry

1. Physical drying:

That is, all the solvents in the coating are volatilized, and its drying speed depends entirely on the volatilization speed of the solvents in the film-forming material;

2. Chemical drying:

For example, the two-component coating film is formed by two-component chemical reaction (ie, cross-linking and curing reaction), and the film-forming speed is mainly determined by the speed of chemical reaction. However, the solidification of chemical reactions also begins with the evaporation of solvents.

3. Drying process: (four stages)

(1) Congealed or tight:

The solvent is almost completely volatilized, the viscosity of the paint is significantly increased, and the paint film continues to be sticky and dusty;

(2) The surface is not stained with soil: no trace is left on the hand, and the resistance to slight force is weak;

(3) Actual drying: no marks are left on the hand-pressed film layer, the coating film is hard, and it can resist mechanical action;

(4) Completely dry: The dry hardness of the entire coating film will no longer increase;

(5) Every time the temperature is increased or decreased by 14 ° C, the baking time is shortened or extended by 30 minutes.

(6) Thermal deformation temperature: ABS 70 ~ 107 ℃ PC 120 ~ 150 ℃

(7) The common ABS coatings are mostly dry at room temperature (or forced drying), of which the 1-pack type is solvent-volatile and the 2-pack type is self-reactive crosslinkable.


Chapter Four. Surface treatment before painting


I. Purpose and role

Plastic products must be subjected to a certain surface treatment before painting. The basic purpose is to improve the surface physical, chemical properties, improve adhesion, commonly used solvent cleaning, surface grinding, exposing a new and more active surface, while increasing the surface of the substrate. Roughness is good for adhesion.

1. Eliminate surface static, remove adsorbed dust, and clean with solvent or surfactant

2. Remove the release agent, use solvent scrubbing or alkaline washing or ultrasonic cleaning

3. Surface modification to enhance coating adhesion


two. Common surface treatment methods

1. Solvent treatment method: remove plasticizer, mold release agent, antistatic agent, lubricant, antioxidant, etc. on the surface of substrate

Removes low-molecular oligomers and monomers from polymer substrates

Decomposition or separation products after oxidative decomposition or powdering on the substrate surface

Solvent dissolves part of the amorphous surface, resulting in increased surface roughness

After the solvent treatment, the surface of the substrate swells moderately, which is beneficial to the mutual dissolution and combination of the substrate and the coating. Before painting, spray a solvent with strong solubility to soften the surface and paint before the solvent is completely evaporated. Enhance adhesion.

2. Surfactant: Auxiliaries and surface processing agents to remove surface dust and migrate to the surface. It is more convenient and easier to remove inorganic impurities, and solvent treatment is more effective to remove grease.

3. Chemical reagent method: The introduction of polar or reactive functional groups on the surface of plastic or rubber substrates through oxidation and other reactions, and the formation of a porous structure on the surface at the same time improves the wettability and adhesion of the coating to the substrate. Improve the printability of substrates.

4. Annealing: the most common and effective method to eliminate surface stress and change crystallinity

During the molding process, uneven cooling may cause residual stress or local crystallization on the surface or the surface. They are not conducive to the wetting of the coating and the adhesion of the coating. Before the solvent treatment, an annealing treatment is performed to remove the residual stress. Better reduce the occurrence of cracks.

5. Surface grinding method: For the substrate base material or the primer (including the previous paint) is too smooth and hard, it can be roughened by artificial sandpaper, and then rough-coated.

The substrate substrate or the surface of the primer loses its activity, which is not conducive to the adhesion of the topcoat. It can be sanded by artificial sandpaper to expose the active layer before topcoating.

6. Primer treatment: the primer and the topcoat are complementary: the primer lacks aesthetics, poor weather resistance, the topcoat is easily absorbed by the substrate, the filling is not good, and the adhesion is poor.

Good adhesion, good adhesion to the substrate, easy to fall off without special damage;

It has good filling and sanding properties. After grinding, it can fill fine defects on the surface of the substrate to a certain extent;

Has good solvent resistance. Most of the primers must be top-coated after the primer is applied. This requires the primer to be able to resist the strong solvents in the top-coat after they are dry.

The primer and the topcoat have a good binding force. With the help of the solvent in the topcoat, the surface of the primer can be slightly redissolved, so that there is a slightly soluble bonding layer between the primer and the topcoat to improve the bonding force.


chapter Five. Painting Process Introduction

1. What is paint viscosity

That is, the friction generated when the liquid flows, that is, the internal friction.

Low viscosity: caused fluidity, uneven film thickness

High viscosity: clogging the nozzle, poor paint atomization, poor leveling, and uneven surface.

Coating viscosity can change with temperature change;

Around 30 ° C: the viscosity is lower than normal temperature,

35 ℃: Viscosity will rise than normal temperature, because the solvent evaporates faster

Below 5 ℃: false thick


2. What is paint fineness

Refers to the thickness of the pigment particles in the paint or the degree of uniform dispersion


Three. Coating fineness effect

1. The fineness of the coating will affect the gloss of the coating film: the gloss of the coating film is related to the smoothness of the surface.

2. When various pigments are added to the paint, the unevenness of the pigment particles directly affects the smoothness of the coating film and the gloss of the coating film;

3. When the pigment particles are small and the amount is small, the effect on the surface smoothness is small, and the gloss of the coating film is high;

4. When the pigment particles are coarse and the amount is large, the effect on the surface smoothness is large, and the gloss of the coating film is low;

Therefore, in the production of paint, it is common to adjust the amount of pigment to make the coating mold have different brightness.


III. Environmental impact

The main environmental impact factors are: ambient temperature, relative humidity

The best ambient humidity temperature is 15 ~ 25 ℃, and the best relative humidity is 60% ~ 75%


Use of solvents

1. The solvent is a mixture of ketone, ester, alcohol and ether solvents. Its important indicators are solubility and volatility (ie, volatility rate).

2. During the film formation of the coating, due to solvent evaporation, cooling or chemical cross-linking reactions, and the dissolved or swollen polymer substrate during the film formation process, the internal stress caused by the volume shrinkage caused by the solvent volatilization, the internal stress and the solvent volatilization Speed dependent, stress can be reduced by controlling solvent evaporation rate and temperature change rate

3. Internal stress can be divided into shrinkage stress, thermal stress, and deformation stress, which are directly related to coating adhesion.

4. The volatilization rate of the solvent has a great relationship with the degree of erosion and leveling of the substrate. If the volatilization rate is fast, the substrate is weak in etching, the leveling is poor, and the volatilization rate is slow. Good leveling,

5. Requirements for solvents in different seasons:

Summer: easy to evaporate the solvent quickly, poor leveling, use a solvent with low volatility

Winter: Prone to slow solvent volatilization, easy to sag, use fast-drying solvents

High-temperature and high-humidity season: easy to produce whitening phenomenon, use slow-drying solvent

Relative humidity RH <60%, the solvent volatilization speed will increase. Slow-drying solvents should be added appropriately. RH> 75%, easy to absorb water and turn white, need to add propylene glycol ether mixture of moisture-proof agent.


4. Wet-on-wet process:

After spraying a single coat of paint, dry it for a while at room temperature, so that the solvent in the coating film has a certain degree of volatilization. The surface is close to the touch and does not stick to the hands. Then, the second coat is applied and then dried at one time.


Chapter Six. Relationship between painting quality and painting process


What is a toughener:

Substances (lipids) that can enhance the film's elasticity and adhesion in film-forming materials, such as acrylic paints, the coating film is too hard, easily brittle, and the adhesion is not good, so the use of toughening agents is to improve the performance of coatings One of the most commonly used methods

Thermoplastic acrylic resin paint has a low solid content. To achieve a certain brightness, it needs to be sprayed multiple times. The viscosity is slightly thick. When painting, silk flowers are easy to appear, the coating is rough, and the solvent resistance is poor.


Chapter VII. Analysis and prevention of coating film pathological

1. Powder coating

1. Phenomenon: The structure of the paint film collapses, the pigment particles are exposed and fall off in powder form.

2. Reason: The polymer resin macromolecule on the surface of the paint film undergoes chemical degradation process under the action of heat, ultraviolet rays, wind and rain, and oxygen, resulting in the formation of small molecular compounds and loss of adhesion, so that the pigment particles come off.

3. Countermeasures: Pigment performance has a decisive influence on powdering, and the ratio of pigment to base material is improper. The amount of varnish is small, and the proportion of pigment and filler is too large. When the coating is added with an excessive amount of thinner, the coating is too thin. Pigments such as calcium carbonate, zinc barium white, and titanium dioxide are added to the pigment.


two. Coating whitening

1. Phenomenon: The coating produces a cloud-like white paint film during drying or after film formation, which is usually generated by solvent evaporation dry coating

2. Reason: a> The solvent volatilizes too quickly, which causes the coating surface temperature to drop sharply, and the moisture in the air is caused by fogging on the coating surface.

b> The ratio of the true solvent to the diluent in the solvent is imbalanced, or the true solvent volatilizes too quickly, leaving the proportion of the poor solvent to increase, which reduces the solubility of the resin and precipitates the resin.

c> When painting in high humidity season, alcohol solvents or alcohol-based mixed solvents are used to absorb water easily. The moisture in the compressed air is not separated, but mixed into the paint or the paint itself has water, and the surface of the substrate is not dry.

3. Countermeasures: Choose appropriate solvents and diluents, control their evaporation rate, prevent the coating surface temperature from being too low, and prevent polymer precipitation

When the humidity is high, it should be heated by hot air or heating to reduce the relative humidity of the air. The substrate should be heated and the surface should be dried.

Ensure that the temperature is higher than the ambient temperature, add a moisture-proof agent to the coating, and spray the white coating to prevent white water.


Three. The coating is rough:

Phenomenon: The surface of the coating film is rough, particles, protrusions, etc., and feels rough

Reasons: 1. The fineness of the coating itself is too coarse, that is, the pigment is coarse and the amount is too much.

2. Coating viscosity is too high

3. The spray gun is too far from the workpiece surface, and the spray gun pressure is too high

4. Uneven coating agitation


four. Sagging, leveling

Phenomenon: Sagging: Coating on a vertical surface. During the film formation process, the paint film flows downward due to gravity. After film formation, the surface is uneven, the thickness is uneven and the bottom edge is thick

Leveling: When coating on a horizontal surface, the coating spreads around due to gravity. After film formation, the surface is flat and the thickness is uniform.

Relationship: leveling and sagging are contradictory relationships

Reason: In essence, the leveling and sagging are related to the fluidity or rheological characteristics of the coating during the coating process and the drying process.

Generally speaking, low viscosity is good for leveling when coating; high viscosity is good for preventing sagging when film is dried.

The viscosity of the coating has a great relationship with the volatilization rate of the solvent. The volatilization is fast and the viscosity is increased, which is good for anti-sagging, but not easy to level.

Temperature has a great influence on viscosity

Countermeasures: Correct selection of solvents and diluents, control of paint viscosity and viscosity changes during drying

Strict film thickness management, clearly control spraying parameters: coating amount, air pressure, gun speed, angle, direction, distance, etc.

Strict painting management environment: temperature, humidity, ventilation and ventilation, heating rate


Fives. Shiny surface

phenomenon:

Cause: Coating viscosity is too high

The gun speed is too slow, the spray gun is too close to the workpiece surface, and the output is large

Coating film thickness is too large, pigment particles sink

The pigment particles are small and the amount is small.


6. Pigment shedding

Phenomenon: When the surface of the coating is tested with adhesive tape, the pigment particles in the coating come out, and the resin in the coating does not fall off to expose the substrate.

Reason: The pigment particles are not completely covered by the resin macromolecules or the coating force is not strong. Under external effects, the particles are exposed outside the resin macromolecules or fall off.

Countermeasures: 1. Reduce pigment particles and dosage

2. Increase the solid content in the resin.

3. Increase the amount of dark particles and reduce the amount of floating particles.

4. Properly increase film thickness to facilitate pigment particle sedimentation

5. Properly increase viscosity, or use slow-drying day water to minimize flying oil

6. Increase the spray gun pressure, reduce the distance between the spray gun and the workpiece surface


Seven. Poor adhesion

Phenomenon: When the surface of the coating is tested with adhesive tape, both the pigment particles and the resin in the coating fall off and the substrate is exposed.


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