Application of powder coating on reflective projection screens

Abstract: The first attempt
of powder coating applied to the screen of film reflection projection screen.
The reflective projection screen uses a special coating film formed by powder coating of aluminum alloy plate to meet the requirements of
film projection.

According to the technical requirements of powder coating for aluminum curtain, we launched OL3293# powder coating online coatingol.
com
.
This article discusses in detail the selection of raw materials, formula design and milling process, coating process, etc
.

1.
Preface
    

Powder coating not only has great advantages in environmental protection, but also has excellent performance, so the development speed is rapid
.

With the continuous development of powder coating varieties and the continuous innovation of coating technology, its application has penetrated into various fields
of the national economy.

Powder coating is used on the three-dimensional film screen screen, with good color light reflection reduction and de-imaging power, which is the first in China, and its main technical indicators are completely referred to foreign standards
.

After months of testing and demonstration, the OL3293 powder coating produced by us fully meets the standards of foreign models and relevant domestic technical standards
.

It has been solemnly confirmed by Shenzhen Huaqiang Intelligent Technology Co.
, Ltd.
, the 701st Research Institute of China Shipbuilding Industry Corporation and Wuhan Chuxiong Jianqiao Engineering Co.
, Ltd.
, and is in a leading position
among domestic counterparts.

Reflective screens include film, slide, projection, video and special-purpose reflective and transmission screens, including plastic, glass and metal
.

Among them, the metal screen curtain surface is made of hard anti-rust aluminum alloy plate (referred to as aluminum curtain panel), and the surface is sprayed by powder coating
.
The thickness of the aluminum curtain panel is 1.
0mm, there are round holes on it, the holes are distributed in a regular hexagon, the center distance between the adjacent holes is 4mm, the aperture is 1.
8mm, and the shape is a vertical faceted hemisphere with holes reflecting the screen aluminum curtain panel
.

The surface of the aluminum curtain panel is spherical, its diameter is 22m, the vertical section forms a 1600 ball crown, and the round diameter of the ball crown cutaway surface is 21.
666m
.

It is used to fix the aluminum curtain plate keel, and the distribution of longitude and latitude lines formed by it adopts the standard globe method, the arc between the adjacent two meridians is 5 degrees, the left and right symmetrical are evenly distributed, the arc between the adjacent two parallels is 10 degrees, and the upper and lower symmetrical are evenly distributed, and the specific distribution is referred to Figure 1
.

2.
Basic requirements related to powder coating

Curtain color: off-white;

Appearance of the curtain: matte fine lines and wrinkles (60° gloss 3%);

Uniformity of the spray layer of the curtain: The spray layer of the full width should be uniform, including the surface, edge and cylinder formed by each small hole of the aluminum curtain plate to ensure that the reflection brightness of different parts of the entire curtain surface is basically the same under the same lighting conditions;

Firmness of the curtain spray layer: the spray layer should be firm, and there should be no material falling off; And it can be scrubbed to clean stains, and guarantee that it will not produce any discoloration and fading for 10 years;

The color of the reflected light: the surface of the aluminum curtain plate requires good color reproduction performance, that is, the color chromaticity of the reflected light and the incident light should be consistent;

Screen resolution (sharpness): meet the projection resolution requirements of more than 80 line pairs/mm;

Color difference requirements: Although the index gives the range, the performance indicators and colors of each aluminum curtain panel must be exactly the same after determining the index to ensure the consistency
of the entire dome.

3.
Milling process
   

The production process of powder coating is divided into four processes: matching and mixing process; Hot mixing, extrusion process; Cooling and crushing process; Milling and screening process
.

3.
1 Selection of raw materials

3.
1.
1 Resin selection
Powder coating raw materials resin is the most important type of raw materials, in order to achieve the purpose of low light, we choose low acid value polyester resin, epoxy resin and cycloamidine polycarboxylic acid matting curing agent composed of polyester/epoxy hybrid powder coating system,

This system adjusts the gloss of the coating film through the ratio of polyester resin and epoxy resin with different acid values, and adjusts the coating performance
with the amount of matting curing agent.

3.
1.
2 The pigments and fillers used in the selection
formula of pigment fillers are important components
that must be added to the formula in order to meet the various performance requirements of powder coatings.

When designing powder coating formulations, the selection of pigments and filler varieties should consider many issues, such as mechanical properties, hiding power, film appearance, color and so on
.
Mainly rutile titanium dioxide, matting barium sulfate, organic bentonite, ultramarine and carbon black
.

3.
1.
3 The appropriate amount of additives added to the formula
of additives can make the powder coating achieve the required special effect
.
OL3293 powder coating is used in reflective projection screen, the curtain surface has no light effect and fine wrinkle effect, so we chose to use matting curing agent and sand texture agent to achieve the ideal effect
.

In order to ensure the fine texture of the coating film and avoid the effect of rough sand, we also added an appropriate amount of leveling additives to the formula so that the formed sand lines can be moderately flattened
.

3.
2 Formulation design
   

The mechanism of film texture formation to form a fine matte wrinkle effect is to add an appropriate amount of sand texture agent
to the matte powder coating formula.

The principle of adding sand texture agent to form a sand grain powder coating film is: when the powder coating is melt leveled, because the surface tension of the sand texture agent is less than the normal surface tension of the powder coating film, the sand texture agent dispersed at each point of the coating film changes the local tension of the coating film, and the base material with high surface tension wraps the sand texture agent with low surface tension, and finally the surface of the coating film presents a uniformly distributed sand grain.

When using this method to produce sand grain powder coating, the production extrusion and coating construction are relatively easy, decorative and protective are very good, not only the coating film mechanical properties are excellent, but also the texture reproduction is stable, the hand feel is smooth, uniform and delicate
.
The reference formula of OL3293 powder is shown in Table 1
.

3.
3 Production process
   

The prepared component materials are added to the high-speed mixer, premixed for about 5~8min, the materials are released and sent to the twin screw extruder for heating and melting, usually the temperature of the feeding section is 90~100 °C, and the temperature of the extrusion section is 110~120 °C
.

The melt extrusion material is pressed into 1mm flakes, cooled and fed into a pulverizer (ACM mill), crushed and classified
.
Powder coating is two key points in terms of production and product control: how to make the various raw materials of powder coating mix and disperse evenly so that it has the performance of coating;

How to process the mixed and dispersed materials into a powder of suitable particle size to facilitate the use
of coating.
The purpose of the first two processes is to mix the film-forming resin evenly with each other and make the pigment filler sufficiently dispersed in the resin
.

The last two processes are how to grind the powder
.
In order to achieve a fine and uniform coating film texture, the powder coating must be screened by 180~200 mesh
.

4.
Powder coating characteristics
   

OL3293# powder coating has basically the same performance as conventional powder coating, and its product performance indicators are shown in Table 2 and Table 3
.