As the core carrier of commercial visual communication, the quality of spray painting (advertising spray painting) directly affects the transmission effect of brand image. The following systematically elaborates on quality assessment methods from four dimensions: technical parameters, material characteristics, manufacturing processes, and sensory experience, combined with industry standards and practical cases.
1、 Technical parameters: Hard indicators for quantitative evaluation
1. Resolution and pixel density
Standard requirements: Outdoor advertisements must have a resolution of at least 72dpi (viewing distance of 3 meters or more), and indoor displays must have a resolution of at least 144dpi (up close viewing).
Verification method: Observe the edges of the image with a magnifying glass. If there are jagged pixel blocks or color block discontinuities, the resolution does not meet the standard.
Case: Due to insufficient resolution (actual 50dpi), the hanging flag printing of a certain shopping mall resulted in mosaic on the faces of people 3 meters away, forcing the brand to remake it.
2. Color reproduction degree
Key parameters: Color difference value Δ E ≤ 3 (difficult for human eyes to distinguish differences), color saturation ≥ 85% (based on Pantone color chart comparison).
Testing tool: Use a spectrophotometer (such as X-Rite i1Pro) to measure the Lab * value and compare it with the original design file.
Tip for avoiding pitfalls: Beware of spray painting companies using "approximate colors" instead of brand VI colors (such as replacing Pantone 185C red with low saturation orange red).
3. Ink weather resistance
Outdoor scene: UV ink needs to pass ASTM G154 standard, undergo artificial accelerated aging test for 2000 hours (equivalent to 2 years in natural environment), and have color fastness ≥ level 4 (ISO 105-B02).
Test method: Dip a cotton cloth in 95% alcohol and rub the image 50 times with 500g pressure. If there is fading or ink layer peeling, it is considered unqualified.
2、 Material properties: the physical basis for bearing mass
1. Substrate adaptability
Material type, core indicators, quality risks
PVC lightbox with a weight of ≥ 510g/㎡ and a tear strength of ≥ 300N/5cm is prone to tearing due to insufficient weight and poor wind resistance
The transmittance of PET lamp sheet is 85% -90%, and the haze is ≤ 8%. The low transmittance causes the image to appear gray
3M car film peeling strength ≥ 15N/25mm, temperature resistance -40 ℃~90 ℃, insufficient adhesion, easy to peel off, high temperature warping
2. Ink compatibility
Solvent based ink: It needs to undergo a chemical reaction with the substrate coating to cure. If the substrate is not subjected to corona treatment, poor adhesion of the ink layer may occur (100 grid test ≤ 3B).
UV ink: It needs to match the surface tension of the substrate (generally required to be ≥ 38 dynes), otherwise it is prone to orange peel after curing.
3、 Production process: the key link that determines the success or failure of details
1. Seam treatment
Outdoor large-scale display: The seam width should be ≤ 2mm, the ink volume in the overlapping area should be reduced by 30% to avoid overlapping, and the color difference Δ E after splicing should be ≤ 2.
Inspection technique: Use a flashlight to shoot diagonally at the scene at night. If there are obvious bright lines or shadows at the seams, it is a process defect.
2. Film coating process
Light film/matte film selection: Light film enhances color brightness (suitable for daily chemical products), matte film reduces reflection (suitable for luxury advertising).
Film coating temperature: It needs to be controlled between 80 ℃ -100 ℃. If the temperature is too high, the film surface will shrink and wrinkle, while if it is too low, the viscosity will be insufficient and it is easy to peel off.
3. Edge wrapping and closing
Metal edging: A 1.2mm thick aluminum alloy profile is required, with a 45 ° beveled joint at the corner and a gap of ≤ 0.5mm.
Silicone edging: used for curved images (such as cylindrical lightboxes), with a thickness of ≥ 3mm to avoid light leakage.
4、 Sensory experience: intuitive judgment from the user's perspective
1. Visual acuity
Remote testing: Standing at 3 times the height of the screen for observation, the edges of the text should have no jagged edges, and the gradient color transition should be natural.
2. Tactile feedback
UV relief process: The height of the protrusion should be controlled between 0.1-0.3mm. If it is too high, it is prone to dust accumulation, and if it is too low, it has no tactile sensation.
Matte texture: achieved through special ink, requiring fingertip friction to verify wear resistance (≥ 500 times without wear).
3. Environmental adaptability
Waterproof test: Use a spray bottle to continuously spray the screen at a 45 ° angle for 3 minutes, and the water stains should roll off in a bead shape without penetration.
UV resistance test: After being exposed to direct sunlight at noon for 1 hour in summer, the color temperature change of outdoor images should be ≤ 200K (to avoid yellowing or blurriness).