What are the differences in glossiness among matte, high-gloss and brushed metal color coated aluminum strips？

Abstract

Color coated aluminum strips are core lightweight decorative materials widely used in architectural curtain walls, indoor ceiling systems, automotive interior trim and household appliance casings. Glossiness, defined as the capacity of a surface to reflect incident specular light, is the most intuitive distinguishing indicator of three mainstream surface treatments: matte, high-gloss and brushed metal finishing. This article compares their quantified gloss parameters, light reflection mechanisms, coating forming processes and derived functional differences based on the 60° gloss measurement standard adopted by the aluminum processing industry, and analyzes targeted application scenarios for each finish.

1. Industry Gloss Measurement Standard for Color Coated Aluminum Strips

All gloss data in this paper follow the ISO 2813 standard, which uses a 60° incident light angle for routine detection of metal coated substrates, the universal testing angle for aluminum strip manufacturers. Gloss units are expressed as gloss units (GU), where 100 GU represents a standard mirror surface with complete specular reflection. Unlike plastic coated materials, color coated aluminum strips retain partial substrate metallic reflectivity even after organic coating covering, leading to unique gloss fluctuation rules different from non-metal materials. Three finishes have fixed quantified gloss ranges verified by mainstream aluminum processing enterprises:

• Matte color coated aluminum strips: 5–40 GU

• High-gloss color coated aluminum strips: 80–95 GU

• Brushed metal color coated aluminum strips: 35–60 GU

2. Glossiness Characteristics and Optical Reflection Mechanisms

2.1 Matte Color Coated Aluminum Strips: Diffuse Reflection and Low Specular Gloss

Matte aluminum strips adopt matte polyester (PE) or polyvinylidene fluoride (PVDF) coating with evenly dispersed microscopic silica matting particles inside the paint film. The microscopic surface presents irregular concave-convex fluctuations below 10 microns. When visible light irradiates the surface, over 90% of incident light undergoes diffuse reflection instead of concentrated specular reflection. Visually, the surface shows a soft, foggy non-shiny effect with zero glare. Within the 5–40 GU range, low-matte strips (5–20 GU) eliminate almost all metallic reflection traces, while medium-matte strips (20–40 GU) retain faint underlying aluminum metallic texture. This finish cannot generate clear mirror reflections of surrounding objects under any lighting conditions.

2.2 High-Gloss Color Coated Aluminum Strips: Specular Reflection and Ultra-High Surface Reflectivity

High-gloss aluminum strips use solvent-free high-clarity topcoat without matting additives, paired with three-times roller coating and high-temperature leveling curing. The paint film surface roughness is controlled below 0.8 microns, achieving near-mirror flatness. More than 85% of incident light produces specular reflection along a fixed reflection angle. With gloss above 80 GU, the surface can form blurred mirror imaging of surrounding buildings, lights and personnel. Under direct sunlight, concentrated specular reflection generates obvious glare, which easily causes visual fatigue. Meanwhile, the high-flat surface amplifies tiny surface defects such as scratches and dust particles, making imperfections far more visible than matte finishes.

2.3 Brushed Metal Color Coated Aluminum Strips: Directional Mixed Reflection

Brushed metal aluminum strips differ fundamentally from the other two types due to pre-coating mechanical texturing. Manufacturers use stainless steel wire brushes to polish the aluminum substrate to form continuous parallel linear micro-grooves with a spacing of 0.1–0.3 mm before coating. Its gloss belongs to directional mixed reflection: light parallel to brushed lines generates weak specular reflection, while light perpendicular to brushed lines produces diffuse reflection. The overall comprehensive gloss falls between matte and high-gloss at 35–60 GU. Visually, it has uneven dynamic gloss: the surface presents bright metallic luster when viewed along the brushing direction, and foggy matte tone when viewed crosswise. Unlike pure matte finishes, it retains distinct layered metallic texture instead of flat foggy vision.

3. Process Causes of Glossiness Differences

3.1 Matte Finishing: Matting Particle Blending and Low-Leveling Curing

Matte gloss is adjusted by the proportion of inorganic matting powder in the topcoat. Higher matting powder dosage reduces surface leveling performance during curing, forming microscopic rough structures. PVDF matte coatings have more stable gloss retention than PE coatings; their gloss attenuation is less than 3 GU after 20 years of outdoor exposure, suitable for long-term outdoor use.

3.2 High-Gloss Finishing: Precision Roller Coating and Dust-Free Curing

High gloss relies on dust-free coating workshops with cleanliness above class 10,000. Tiny dust will cause localized gloss reduction. After primary prime coating and color coating, a transparent leveling topcoat is applied twice to fill substrate micro-pits. Curing temperature is increased by 15℃ compared with matte products to accelerate paint film flow and eliminate surface ripples.

3.3 Brushed Metal Finishing: Substrate Texturing Followed by Transparent Thin Coating

Brushed gloss is dominated by substrate texture rather than paint film. The topcoat used is ultra-thin transparent metal paint with a thickness of only 5–8μm, which will not cover brushed lines. Thick coating will fill micro-grooves and eliminate directional gloss differences. Post-brushing passivation treatment is required to avoid local oxidation leading to inconsistent gloss.

4. Functional and Application Differences Derived from Glossiness

5. Conclusion

The core glossiness differences of the three color coated aluminum strips originate from surface microscopic morphology and light reflection modes. High-gloss products feature high specular reflectivity and mirror-like vision with 80–95 GU; matte products feature full diffuse reflection and foggy low-gloss vision with 5–40 GU; brushed metal products feature directional mixed reflection with medium variable gloss at 35–60 GU. In practical selection, glare control requirements determine matte usage, high-end bright decorative demands determine high-gloss usage, and metallic textured aesthetic demands determine brushed metal usage. Manufacturers should match coating formulas and pretreatment processes according to on-site lighting and maintenance requirements to stabilize surface gloss consistency.