Development of weather-resistant dermatoglyphic powder coating

Abstract: This article mainly studies powder coatings with dermatoglyphic effects with different weather resistance grades for outdoor use
.
Through the discussion and analysis of raw materials, preparation technology and main influencing factors, a highly decorative powder coating suitable for outdoor applications has been developed
.

The surface of the coating film made by this powder coating has a very clear skin texture effect, obvious decorative type, good covering effect, good mechanical properties, and good protection on the surface of the object;

At the same time, the weather resistance level of this kind of powder coating can be designed according to the requirements, and the highest can meet the requirements of AAMA2604 standard.

In addition, this kind of powder coating can form a film at one time, with low cost, and easy to promote and apply online coatingol.
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1 Technical background

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At present, powder coatings have been widely used in architectural aluminum profiles, aluminum veneers, curtain walls, security doors, household appliances and other general industries
.

The appearance of the powder coating after film formation mainly includes leveling, sand grain, wrinkle, matting, etc.

These coating films mainly provide protection for the substrate, but are not decorative and artistic

2 Preparation process and formula

2.
1 Raw materials

The raw materials used to synthesize weather-resistant skin texture powder coatings include: general polyester resins, super weather-resistant polyester resins, fluorocarbon resins, curing agents, pigments, fillers and additives (including accelerators, brighteners, matting agents, UV light absorbers, stabilizers, leveling agents, defoaming agents, deaerating agents, wrinkle agents, floating toner) or the like

.

In this paper, the method of adding incompatible substances and curing agents with different curing speeds are used to obtain texture effects of different shapes
.

Utilize the incompatibility between polymer products and modified inorganic materials to produce different leveling states during film formation, and adjust the curing speed and viscosity of the system to make the powder particles solidify when they are not fully leveled.

Thereby forming a special dermatoglyph effect

The aging of the coating film refers to the phenomenon that the coating is aging or damaged under the action of comprehensive factors such as ultraviolet rays, moisture, temperature changes, air (oxygen) gas, and chemical pollutants in the atmosphere
.

Among them, the main aging phenomenon is photo-oxygen degradation caused by sunlight and air (oxygen) gas.
In particular, 295-350nm ultraviolet radiation in sunlight will most damage the coating polymer degradation
.

When the coating film contains benzene rings, carbonyl groups, ketones, unsaturated bonds, tertiary carbons and other groups that can easily absorb ultraviolet rays, the damage to the coating will be more serious, and the presence of oxygen will further accelerate the process of photooxidation degradation
.

In addition to sunlight, rainwater and acid gases in the atmosphere (N02, S02, etc.
) are also important aging factors at present
.

Polyester resins are easily hydrolyzed because they contain ester bonds, and acid gas soluble in water will catalyze the hydrolysis and cleavage of resin ester bonds more quickly
.

In addition, most of the commonly used pigments and fillers in polyester powder coatings based on carboxyl end groups are alkaline, and chemically react with the coating film
.

For heat, it can accelerate the vibration of the molecules in the polyester structure, so that it breaks and undergoes thermal degradation.
In the presence of oxygen, the destructive effect is more serious
.
These factors ultimately affect the appearance, color and durability of the coating film, and greatly reduce the service life of the coating film
.

It can be seen that the weather resistance of the coating film is closely related to the composition of the coating, and the weather resistance of the base polyester resin in the coating formulation plays a key role in the weather resistance of the coating film
.

The resin raw materials used in this paper are weather-resistant polyester, super weather-resistant polyester resin and fluorocarbon resin of European building material grade
.

2.
2.
3 Selection of curing agent

The weather resistance of the coating film depends not only on the structure of the curing agent itself, but also on its aggregate structure
.
The tightness of the structure after curing obviously also contributes to the improvement of the weather resistance of the coating film
.

At present, the most commonly used curing agents in weather-resistant polyester powder coatings are TGIC (triglycidyl isocyanurate) and HAA (hydroxyalkyl amide).
The aging resistance of the TGIC system is better than that of the hydroxyalkyl amide system in the long-term durability
.

Because the TGIC trifunctional group provides sufficient activity, the structure does not contain benzene ring and ether, and the stable triazine ring ensures good heat resistance and weather resistance
.

The coating cured by TGIC has high cross-linking density and high adhesion of the coating film.
The end group content of the coating polymer is relatively reduced and the UV resistance of the coating is improved.
However, the disadvantage is that there is physiological toxicity
.

HAA has higher activity and can be cured at a lower temperature.
It releases low molecular compounds during curing.
If the coating is too thick, pinholes are easy to appear.
The storage stability of powder coatings is better than TGIC, and the weather resistance is equivalent to that of TGIC, but the heat resistance is better than TGIC.
Poor, the coating film is prone to yellowing
.
This article chooses TGIC as the curing agent
.

2.
2.
4 Pigments and fillers

Weather-resistant polyester powder coatings also have higher requirements for pigments and fillers.
For pigments, in addition to the hiding power, tinting power, dispersibility, and thermal stability of the pigment, the light stability and resistance of the pigment must also be considered.
Oxidation and moisture resistance make the color retention, chalking resistance and physical properties of the powder coatings produced lasting
.

For example, titanium yellow and ultramarine blue have good light resistance, heat resistance, and weather resistance.
The weather resistance and heat resistance of silicon-coated pigments have also been significantly improved.
The important role is to absorb ultraviolet rays, which can greatly improve the weather resistance
.

For fillers, in order to reduce the cost of powder coatings, a certain amount of fillers are added to the formulation of powder coatings.
Its tinting power and hiding power are poor, and it mainly plays a role of filling and reinforcement
.

Commonly used fillers are barium sulfate, quartz powder, sericite powder, etc.
, among which quartz powder provides long-term durability and the weather resistance of sericite powder is also very good
.
If you choose easy-dispersible pigments and fillers, it is also helpful for the weather resistance of the coating film
.

2.
2.
5 Additives

Additives also have a great influence on weather resistance
.
Commonly used auxiliaries include ultraviolet absorbers, free radical scavengers, light shielding agents, etc.
They can protect the coating film, reduce the penetration of ultraviolet rays, and capture free radicals
.

At the same time, there is a synergistic effect among some additives, so the weather resistance of non-single additives will be more improved
.
If used together with antioxidants, it will greatly slow down the atmospheric aging of the coating film and increase its weather resistance
.

2.
2.
6 Product formula

The formula structure of the base powder used in this article is very similar to the formula of ordinary wrinkle powder coatings.
The typical formula is shown in Table 1
.
 

Table 1

2.
3 Preparation process

In this experiment, two powders, base powder and flour, were melted and extruded separately, and then processed by a bonding machine, and then sieved to form a finished product, sprayed and baked to form a skin-like apparent coating film
.

3 Results and discussion

3.
1 Characterization of surface texture effect
According to the formula in Table 1, we produced sample 1, sample 2, and sample 3 respectively, and their appearance effects are shown in the following figure:
Sample 1
Sample 2
Sample 3
We can see that sample 1, sample 2 and sample 3 have very clear skin-like effects, soft luster, and very good visual and tactile performance
.

3.
2 The other performance tests of sample 1, sample 2 and sample 3 are shown in the following table:
table 3
From Table 3, we can see that the performance of sample 1 fully meets the standard requirements of the aluminum profile industry (GB5237.
4-2008 Part 1), and is completely suitable for outdoor profile use.
In theory, it can be used outdoors for 3-5 years;
The weather resistance, salt spray resistance, acid and alkali resistance of sample 2 are significantly improved compared with sample 1, and it is before American standards AAMA2603 and AAMA2604.
It is recommended to use it outdoors for 5-10 years; sample 3 has weather resistance and salt resistance Fogging and acid and alkali resistance are better than sample 2, which meets the requirements of American standard AAMA2604
.

3.
3 The influence of wrinkle agent on coating film
The amount of wrinkle agent has a great influence on the effect of the coating film texture.
When the powder coating is baked and cured, the surface tension of the melt leveling film is large, while the surface tension of the wrinkle agent is small;
Because the compatibility between two substances with different surface tensions is not good, the one with the smaller surface tension cannot completely reduce the surface tension of the one with the larger surface tension.
The coexistence of the two substances with different surface tension makes the coating film Produce uniform skin texture effect
.

The dosage of wrinkle agent used in this article is 0.
05% of the total formula, and the dosage of general wrinkle powder coating is 0.
08～0.
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Through the research in this article, we have mastered a new method for preparing weather-resistant dermatoglyphic powder coatings
.
With the rapid economic development, countries are paying more and more attention to the living environment, the application fields of powder coatings are gradually expanding, and the pace of market development is accelerating.
With good weather resistance, the market demand is getting bigger and bigger
.