Laser Weldable Polyester Composition for Thick Parts
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Solution Overview
Problem
Laser welding of crystalline polymers, particularly those with glass fibers, faces challenges due to reduced laser energy transmission and increased cycle times, along with issues like sink marks and burning, especially in thick parts, due to scattering effects and internal temperature increases.
Innovation Solution
A laser weldable composition comprising a combination of poly(butylene terephthalate) homopolymer, poly(ester-carbonate) copolymer, and glass fibers, which provides high near-infrared transparency and thermal resistance, allowing for efficient laser welding with improved weld strength and reduced cycle times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If crystalline polymers with glass fibers are used to achieve high thermal resistance, then thermal resistance is improved, but laser energy transmission is reduced due to scattering effects
Solution Approach 1:
The patent changes the physical and chemical parameters of the polymer composition by controlling crystallinity (30-80%), adding specific fillers (5-50 wt% glass fibers, 1-20 wt% metal particles), and adjusting molecular weight (10,000-500,000 g/mol) to optimize both thermal resistance and laser transmission. This allows the material to maintain high temperature resistance while improving laser energy transmission through careful parameter selection.
Solution Approach 2:
The patent creates a composite material system combining crystalline polymer matrix with glass fibers and metal particles. This composite structure leverages the high thermal resistance of glass fibers while the metal particles (with high laser reflectivity) improve overall laser transmission. The synergistic combination resolves the contradiction between thermal performance and laser weldability.
2Strength
If glass fibers are added to improve mechanical strength, then strength is improved, but scattering effects are enhanced reducing laser transmission
Solution Approach 1:
The patent combines glass fibers with metal particles in a composite formulation where glass fibers (5-50 wt%) provide mechanical reinforcement while metal particles (1-20 wt% of high reflectivity materials like aluminum or silver) compensate for laser transmission loss by reflecting scattered laser energy back through the material, thereby maintaining both strength and laser weldability.
Solution Approach 2:
The metal particles act as an intermediary that mediates between the glass fibers and laser energy. While glass fibers scatter laser light, the metal particles intercept and reflect this scattered energy, converting it back into useful laser transmission. This intermediary mechanism allows the system to maintain high mechanical strength from glass fibers while preserving laser transmission capability.
3Illumination intensity
If laser transparent part thickness is increased to reduce visible light transmission, then privacy is improved, but scattering effects are greatly enhanced reducing laser welding effectiveness
Solution Approach 1:
The patent changes the optical parameters of the material by incorporating metal particles with high laser reflectivity (aluminum, silver, or their oxides) that specifically target near-infrared laser wavelengths. This allows the material to maintain thickness for privacy while the metal particles actively manage laser energy transmission by reflecting scattered energy, decoupling visible light blocking from laser transmission.
Solution Approach 2:
The patent applies the principle of selective optical absorption and reflection by choosing metal particles that are opaque to visible light (providing privacy) but highly reflective to near-infrared laser wavelengths. This selective optical property allows the material to appear opaque or colored in visible spectrum while remaining transparent to laser energy, resolving the contradiction between privacy and weldability.
4Adaptability or versatility
If internal scattering of laser light is allowed to occur in thick parts, then material can be used, but temperature increase causes sink marks or burning
Solution Approach 1:
The metal particles serve as an intermediary that intercepts and redistributes scattered laser energy throughout the material volume. Instead of allowing scattered energy to concentrate and cause localized overheating, the metal particles reflect and diffuse this energy, creating a more uniform temperature distribution that prevents sink marks and burning while enabling use of thick parts.
Solution Approach 2:
The patent converts the harmful effect of laser scattering (which causes temperature increase and defects) into a beneficial effect. By incorporating metal particles, the scattered laser energy is reflected back into the material, creating additional heating zones that promote uniform melting and welding throughout the thick section, thereby transforming scattering from a defect-causing mechanism into a welding-enhancing mechanism.
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 composition achieves high near-infrared transmission and thermal resistance, enabling efficient laser welding of thick parts with consistent weld strengths and reduced defects, such as sink marks and burning.
Implementation Method 1
the composition has a near infrared transmission at 960 nanometers of greater than 30 percent
Implementation Method 2
the other polymer part absorbs sufficient laser light to generate heat for welding at the interface of the parts
Implementation Method 3
heat conduction between the parts results in the melting of the polymers in both the absorbing and the transmitting parts
Data Source
AI summary
A laser weldable composition comprising a polyester component; 5 to 50 weight percent of a filler; and 10 to 30 wt.% of a poly(ester-carbonate) copolymer comprising carbonate units and ester units of the formula (I) wherein: T is a C2-20 alkylene, a C6-20 cycloalkylene, or a C6-20 arylene; R1 and J are each independently (a) a bisphenol A divalent group, and (b) a C16 or higher divalent group (b1), (b2), or (b1) and (b2), wherein (b1) is a phthalimidine divalent group, and (b2) is a third divalent group, wherein the C16 or higher divalent group (b1), (b2) or a combination of (b1) and (b2) is present in an amount of 40 mol% to 50 mol% based on the total moles of the bisphenol A divalent groups and the C16 or higher divalent group; and the composition, when molded into an article having a 2.0 mm thickness, provides a near infrared transmission at 960 nanometers of greater than 50% and a thermal resistance according to HDT 1.8 MPa flat (ISO 75/Af) is greater than 160°C.