Research on Application of Powder Coatings for Building Materials to Improve Film Printing

Abstract: In the building materials industry, the surface of aluminum profiles is protected by a film, which effectively avoids dust pollution, mechanical scratches, scratches, etc.

However, in the process of use, the protective film is often degummed and residual glue, so the powder coating surface is likely to leave dark spots, mottling or even fading effects, which affects the decorative effect of the coating

Through technical analysis, the main influencing factors of the protective film adhesive falling off on the surface of the profile are the protective film, powder coating, the storage environment of the profile, and the residence time of the protective film on the surface of the profile .

This article focuses on the analysis of the film printing problems that occur after the protective film is attached to the powder coating for building materials and research solutions

1 Overview 

China's aluminum industry started in the 1950s and has experienced nearly 70 years of development.

The protective film is a layer of plastic protective film affixed to the aluminum material.

At present, there are many types of aluminum products on the market, and the surface treatment technology of aluminum materials is constantly improving

Various aluminum surface treatment technologies include: mechanical polishing, chemical polishing, anodic oxidation coloring, electrophoretic coating, chemical coloring, fluorocarbon spraying, electrostatic powder spraying, surface pattern treatment, etc.

This article focuses on the analysis of the film printing problems that occur after the protective film is attached to the powder coating for building materials and research solutions

2.
Introduction to protective film 

Protective film is an abbreviation for pressure-sensitive protective film in the building materials industry, and it is also one of the most important products in pressure-sensitive adhesives (PSA)
.

The protective film is usually made of polyolefin (PE\PVB) plastic film as the base material, acrylic polymer as the base resin of the pressure-sensitive adhesive, and several specific adhesives to be processed by coating
.

The protective film is generally polyacrylate type, divided into solvent type and water-soluble polyacrylate glue
.

2.
1 Solvent-based polyacrylate glue 

Solvent-based polyacrylate glue uses organic solvents as a medium to dissolve acrylic monomers.
The colloid is very transparent, has a relatively low initial viscosity, and is very resistant to aging, which can last up to 10 years
.

2.
2 Water-soluble polyacrylate glue 

Water-soluble polyacrylate glue uses water as a medium to dissolve acrylic monomers, and basically has the characteristics of solvent-based polyacrylate glue, but the glue should avoid and reduce contact with water vapor to avoid residual glue
.

Since water-soluble polyacrylate glue is relatively environmentally friendly and does not require a solvent recovery device, currently most of the glue is used to produce protective films
.

The basic structure of the polyacrylate protective film (Figure 1): From top to bottom: isolation layer; printing layer; film; adhesive layer
.

3.
Film printing phenomenon and analysis are prone to occur after the powder coating is pasted with a protective film

3.
1 Description of film printing phenomenon 

The protective film is only a temporary protective measure, and the protective film still needs to be torn off after transportation, cutting, installation and construction of the profile
.

However, in the process of use, the protective film is often degummed and residual glue, so the powder coating surface is likely to leave dark spots, mottling or even fading effects, which affects the decorative effect of the coating
.
 

3.
2 Analysis of the causes of film printing

Through technical analysis, the main influencing factors of the film printing phenomenon of the protective film adhesive falling off on the surface of the profile are the protective film, powder coating, the storage environment of the profile, and the residence time of the protective film on the surface of the profile
.

3.
2.
1 Protective film factors

There are five main reasons why the protective film causes the adhesive to fall off and form a film print: a) the quality of raw materials is fluctuating; b) the adhesive layer is not cured sufficiently; c) the adhesive layer is not dried; d) the protective film has relatively high adhesion; e) electricity The halo treatment is not in place
.

3.
2.
2 Powder coating factors

The powder coating melts at a certain temperature and undergoes a cross-linking reaction to form a dense coating, so it has a good protective effect on building profiles
.

However, there are some small-molecule additives in the coating, which do not participate in the formation of the network structure, but are covered by the film-forming substance, which is easy to detach or bond to other floating objects under a certain external bonding force
.

Or it can interact with the pressure-sensitive adhesive acrylate in the protective film, causing the adhesive to fall off, forming a film print from the outside
.

3.
2.
3 Factors in the residence time of the protective film on the profile

If the protective film stays on the surface of the profile for too long, it will be affected by the following factors:

a) The surface of the board is oxidizing;

b) The surface of the board is catalytic for the degradation of the glue layer;

c) The small molecular substances contained in the board penetrate into the glue layer and the cohesion of the glue is weak
.
The probability of the protective film adhesive falling off increases with the extension of the protective film's residence time on the profile surface
.

3.
2.
4 Environmental factors for storage of protective films and profiles

The storage environment causes film printing, mainly because the storage environment does not meet the requirements and causes the following problems:

a) There is moisture on the surface of the profile;

b) There is oil stain on the surface of the profile;

c) The storage temperature is too high;

d) The negative pressure is too heavy
.

The existence of these problems will greatly increase the probability of the protective film adhesive falling off
.

4.
Coating formula test and result discussion

4.
1 The influence of coating film crosslinking density

The 96/4 polyester and 93/7 polyester are selected respectively, and the reaction speed is adjusted by adding a catalyst and the full reaction is promoted
.
It can be seen from Table 1 that the higher the acid value of the resin, the greater the crosslinking density of the coating film, which is helpful to improve the film printing
.

By adding a catalyst, the reaction is more complete and the coating film has better compactness
.
The small molecules in the protective film do not easily penetrate into the coating film
.

4.
2 The influence of wax powder

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Therefore, when designing the formulation of powder coatings for building materials, we need to consider the film printing phenomenon induced by the adverse environment in the production and storage of aluminum profiles, and try to avoid and reduce the film printing problems
.