Photocatalytic Coating for Algae Prevention on Plastic Substrates
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Solution Overview
Problem
Coated flat plastic materials used in wet environments, such as greenhouses and swimming pools, tend to develop algae due to high humidity, and existing photocatalytic coatings that inhibit algae growth often damage the plastic substrate and require complex, costly additions like silver or copper, which are environmentally harmful.
Innovation Solution
A coated flat plastic material with a thermoplastic substrate and a three-layer coating system comprising a sol adhesion promoter layer, a water-spreading layer consisting of silicon dioxide, and a photocatalytically active layer with titanium dioxide particles, applied in an in-line process that is cost-effective, quick-drying, and free from biocidal components like silver and copper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photocatalytically active layers with silver or copper are applied to suppress algae growth, then the effectiveness against algae and bacteria is improved, but the complexity and cost of the coating increases and environmental harm is caused
Solution Approach 1:
The patent removes silver and copper components from the photocatalytic coating formulation, extracting the harmful biocidal elements while retaining the core photocatalytic functionality through titanium dioxide alone. This simplifies the coating composition and eliminates environmental concerns associated with heavy metal biocides.
Solution Approach 2:
The invention replaces expensive, environmentally harmful biocidal additives (silver, copper) with a simpler, more sustainable photocatalytic system based on titanium dioxide. The coating achieves its antifouling effect through photocatalysis alone, without requiring costly biocidal components that need to be replenished or that cause environmental contamination.
2Reliability
If photocatalytically active layers with high aggressiveness are applied to combat bacterial growth, then the initial bacterial growth is suppressed, but the underlying layers and base plastic are damaged through degradation
Solution Approach 1:
The patent modifies the photocatalytic system parameters by using titanium dioxide particles with specific size ranges (0.5-10 μm) and controlling the titania content (0.1-10% by weight). These parameter adjustments optimize the photocatalytic activity to be sufficient for antifouling while reducing the aggressiveness that would cause substrate degradation. The controlled particle size and concentration balance effectiveness with substrate protection.
3Productivity
If quick-drying coating systems are used for in-line production, then the productivity is improved, but the adhesion and stability of the coating may be compromised
Solution Approach 1:
The patent introduces a sol adhesion promoter layer as an intermediary between the substrate and the photocatalytic topcoat. This intermediate layer ensures strong adhesion of the quick-drying photocatalytic coating to the substrate, preventing coating failure that would otherwise result from rapid drying. The adhesion promoter mediates the bonding, allowing fast processing without sacrificing coating stability.
4Reliability
If dispersions with high titanium dioxide content are used to enhance photocatalytic activity, then the algae prevention is improved, but the transparency and aesthetic appearance of the coating deteriorates
Solution Approach 1:
The patent optimizes the titanium dioxide particle size parameters (0.5-10 μm) and controls the titania content within specific ranges (0.1-10% by weight). These parameter adjustments ensure sufficient photocatalytic activity for algae prevention while maintaining the coating's transparency and aesthetic appearance. The controlled particle size prevents excessive light scattering that would reduce clarity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The coating effectively prevents algae growth without damaging the plastic substrate, is environmentally friendly, and provides long-term stability and transparency, while being suitable for use in wet environments with reduced environmental impact.
Implementation Method 1
a sol adhesion promoter layer (b1+2) with a layer thickness of 1 µm to 50 µm, comprising an adhesion promoter and a colloid sol
Implementation Method 2
water-spreading layer (b2) with a layer thickness of 0.05 µm to 2 µm... water that comes onto their surface does not contract into separate drops, but that the drops spread out and flow together to form a closed layer
Implementation Method 3
photocatalytically active layer (b3)... which can be said to have a self-cleaning and/or antimicrobial or antifouling (algicidal, fungicidal) effect... the growth of fungi or algae is suppressed
Data Source
AI summary
Coated sheet-like plastic material comprising a) as base body a thermoplastic substrate; and b) on the base body a photocatalytically active coating comprising - a water-spreading layer, which is either a sol adhesion-promoter layer b1+2), comprising an adhesion promoter and a colloidal sol, or a colloidal sol layer b2), which is arranged on an adhesion-promoter layer b1) applied to the substrate a), and - a photocatalytically active layer b3), which is arranged on the water-spreading layer b1+2) or b2) and can be obtained by applying and drying a mixture comprising in % by weight, based on the solids content of the mixture, b31) 1 to 25% titanium dioxide and b32) 75 to 99% silicon dioxide and/or a water-insoluble metal oxide or an anionically modified silicon dioxide or metal oxide; wherein the titanium dioxide is particulate, with a mean particle size of the primary particles of less than 10 nm. In-line process for the production thereof and use as roofing and glazing material, preferably in wet areas. The coated sheet-like plastic material of the invention combines the water spreading with the photocatalytic action without the thermoplastic substrates being damaged. The coated sheet-like plastic substrate according to the invention is produced in a less complex, cost-effective and rapid in-line process and, when it is used, is satisfactory owing to the stability of the substrate and the action of the coating against initial algae formation.