Laser Marking Polymer Substrates with Thermochromic Pigments
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Solution Overview
Problem
Conventional laser marking and engraving on polymers often result in limited color options, with markings typically appearing dark or light due to carbonization or foaming, and the use of laser pigments can affect the polymer's appearance and processability.
Innovation Solution
A method involving a substrate with at least one layer of polymer and irreversible thermochromic pigment, where a pulsed laser beam is used to create carbon or vapor traces, with subsequent pulses positioned close to the previous trace to enhance color appearance by reducing the dark or light appearance and promoting further color change of the thermochromic pigments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional laser marking is used on polymers, then the marking process is simple and rapid, but the color appearance is limited to dark or light shades due to carbonization or foaming
Solution Approach 1:
The patent applies parameter changes by utilizing irreversible thermochromic pigments that undergo permanent color transformation when exposed to laser-induced heat. The pigments change from a first color state to a second color state through thermal activation, enabling diverse color markings (e.g., yellow, green, red, blue, purple, orange) beyond the conventional dark/light shades. This parameter change approach transforms the thermal response from merely structural (carbonization/foaming) to optical (color change).
Solution Approach 2:
The patent directly implements color changes by incorporating irreversible thermochromic pigments into the polymer substrate. These pigments are specifically selected to exhibit permanent color transformation at the laser processing temperature range. The color change mechanism is intrinsic to the pigment material, allowing the marking to display vibrant colors determined by the pigment type rather than being limited to carbonization black or foam white.
2Manufacturing precision
If laser marking pigments are added to enhance marking outcome, then the laser marking effectiveness is improved, but the appearance and processability of the polymer are affected
Solution Approach 1:
The patent uses parameter changes by selecting thermochromic pigments with specific activation temperatures that match the laser processing conditions. The pigments remain stable during normal polymer processing (below activation temperature) but transform at the higher laser-induced temperatures. This temperature-dependent parameter change allows the polymer to maintain its normal processability during manufacturing while achieving effective color marking during laser treatment.
Solution Approach 2:
The patent applies preliminary action by pre-incorporating the irreversible thermochromic pigments into the polymer substrate before laser processing. The pigments are distributed throughout the polymer matrix in advance, ready to undergo color transformation when the laser beam passes through. This preliminary preparation ensures that the marking effectiveness is achieved without requiring additional pigments or coatings during the actual laser marking process, thus avoiding interference with polymer processability.
3Productivity
If the distance between consecutive laser pulses is large, then the processing speed is faster, but the colorfulness and vibrancy of the marking is reduced
Solution Approach 1:
The patent applies periodic action by using pulsed laser irradiation with optimized pulse intervals. The laser delivers energy in discrete pulses rather than continuous irradiation, allowing the polymer and pigments to respond to each pulse while maintaining progress along the marking path. The pulse frequency and spacing are optimized to ensure each pulse contributes to color transformation without excessive overlap, balancing processing speed with color vibrancy.
Solution Approach 2:
The patent implements local quality by concentrating laser energy at specific focal points where consecutive pulses overlap or are closely spaced. This creates localized zones of enhanced thermal effect and color transformation, while other areas maintain faster processing rates. The varying pulse spacing creates a gradient of color intensity that enhances overall marking vibrancy without uniformly sacrificing processing speed across the entire marking area.
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
This method improves the colorfulness and appearance of laser markings by reducing the dark or light appearance of carbon or vapor traces, allowing for deeper and more vibrant color changes, and enables the creation of colored markings without the need for additional laser pigments, which can alter the polymer's properties.
Implementation Method 1
generating a carbon trace or vapor trace within or on the at least one layer by irradiating the substrate with a pulsed laser beam
Implementation Method 2
The absorbed energy is high enough to locally raise the temperature above the decomposition temperature of the polymer and cause thermal degradation of the polymer. The polymer thus carbonizes
Implementation Method 3
Some polymers however do not carbonize, but vaporize and start building a white foam, also called vapor trace
Implementation Method 4
providing a substrate with at least one layer, wherein the at least one layer comprises a polymer and an irreversible thermochromic pigment
Data Source
AI summary
The invention is directed to a method for laser engraving and/or laser marking comprising the steps of: - providing a substrate with at least one layer, wherein the at least one layer comprises a polymer and an irreversible thermochromic pigment, - generating a carbon trace or vapor trace within or on the at least one layer by irradiating the substrate with a pulsed laser beam, such that a focus spot of the laser beam is within or on the at least one layer at a first predetermined position, and - irradiating the substrate with the pulsed laser beam such that the focus spot of a consecutive laser pulse is within or on the at least one layer at a predetermined consecutive position and a distance between the first position and the consecutive position is less or equal to twofold a diameter of the carbon trace or vapor trace. Furthermore, the invention is directed to a laser marked and/or engraved article produced by said method and to an article for laser engraving and/or laser marking.