Influence Factors of the Curing Speed of LED UV Glue and Optimization Strategies for Equipment Parameters

LED UV glue has been widely applied in fields such as electronic manufacturing, optical assembly, and medical device manufacturing, owing to its advantages of fast curing speed and good environmental protection performance. However, the curing speed is affected by various parameters such as wavelength, light intensity, and irradiation time. If the parameter settings are inappropriate, problems such as incomplete curing and excessive internal stress may occur. Therefore, it is of great significance to conduct in-depth research on the influence laws of each parameter on the curing speed and optimize the equipment parameters.

Overview of the Curing Principle of LED UV Glue

LED UV glue is mainly composed of prepolymers, monomers, photoinitiators, and additives. When ultraviolet light of a specific wavelength irradiates the glue, the photoinitiator absorbs photon energy and generates free radicals or cations. These active particles initiate the polymerization reaction of prepolymers and monomers, forming a cross-linked network, thus realizing the curing of the glue.

Influence Laws of Wavelength on the Curing Speed

1. Absorption Characteristics of Photoinitiators

Different types of photoinitiators have different absorption peaks for ultraviolet light. For example, benzophenone-based photoinitiators have a strong absorption near 365nm, while thioxanthone-based photoinitiators have an absorption peak around 385nm. The emission wavelength of the LED UV light source needs to match the absorption peak of the photoinitiator so that the photoinitiator can efficiently generate active particles. If the wavelength does not match, most of the photon energy cannot be absorbed by the photoinitiator, and the curing speed will be significantly reduced.

2. Penetration Depth and Curing Efficiency

Generally speaking, ultraviolet light with a longer wavelength has a greater penetration depth in the glue. The penetration depth of 365nm ultraviolet light in the glue is about 0.5 – 1mm, while that of 405nm ultraviolet light can reach 1 – 2mm. For thicker glue layers, choosing an LED light source with a longer wavelength helps to achieve uniform curing from the surface to the inner layer. However, the longer the wavelength, the lower the photon energy, and the excitation efficiency of the photoinitiator may decrease. Therefore, in practical applications, an appropriate wavelength needs to be selected according to the thickness of the glue layer and the type of photoinitiator.

Influence Laws of Light Intensity on the Curing Speed

1. Relationship between Light Intensity and Reaction Rate

Within a certain range, the stronger the light intensity, the more photons are absorbed by the photoinitiator per unit time, the higher the concentration of generated active particles, the faster the polymerization reaction rate, and the faster the curing speed. According to the theory of photochemical reaction kinetics, the curing speed is proportional to the square root of the light intensity. However, when the light intensity exceeds a certain threshold, the “photo-bleaching” phenomenon will occur, that is, the photoinitiator decomposes and fails due to excessive excitation, resulting in that the curing speed no longer increases or even decreases.

2. Influence of Light Intensity Distribution

The uniformity of the light intensity distribution of the LED UV curing equipment is crucial to the curing effect. Uneven light intensity distribution will lead to the glue curing too fast or too slow locally, generating internal stress, and even causing incomplete curing. By optimizing the arrangement of LED light sources and using optical lenses for light homogenization treatment, the uniformity of the light intensity distribution can be effectively improved.

Influence Laws of Irradiation Time on the Curing Speed

1. Time Dependence of the Curing Process

The irradiation time directly affects the total photon energy absorbed by the photoinitiator. As the irradiation time increases, the polymerization reaction proceeds continuously, and the curing degree of the glue gradually improves. However, when the reaction reaches a certain degree, the concentration of active particles in the system decreases, and the polymerization reaction rate slows down. Continuing to extend the irradiation time has limited effect on improving the curing degree.

2. Negative Effects of Excessive Irradiation

Excessive extension of the irradiation time may lead to surface oxidation, yellowing, and even embrittlement of the glue. In addition, too long an irradiation time will reduce production efficiency and increase energy consumption. Therefore, it is necessary to determine the optimal irradiation time through experiments to shorten the curing cycle as much as possible on the premise of ensuring complete curing.

Optimization Strategies for Equipment Parameters

1. Wavelength Selection

Applications with thin glue layers: For glue layers with a thickness of less than 0.5mm, LED light sources with wavelengths of 365nm or 385nm can be selected to obtain a higher excitation efficiency.
Applications with thick glue layers: When the thickness of the glue layer exceeds 1mm, it is recommended to use a light source with a wavelength of 405nm to ensure deep-layer curing.
Mixed photoinitiator systems: If multiple photoinitiators are used, an LED light source with a combination of multiple wavelengths can be adopted to take into account the absorption characteristics of different photoinitiators.

2. Light Intensity Adjustment

Initial testing: Before production, determine the optimal light intensity range for the curing of the glue through a stepped light intensity test. Start with a lower light intensity and gradually increase it, and observe the performance indicators such as the hardness and adhesive strength of the glue after curing.
Dynamic adjustment: Some high-end curing equipment supports the function of dynamic light intensity adjustment. In the initial stage of curing, a higher light intensity can be used to initiate the reaction quickly. In the later stage of curing, appropriately reduce the light intensity to avoid photo-bleaching and excessive curing.

3. Setting of Irradiation Time

Experimental optimization: Through single-factor experiments, fix the wavelength and light intensity, test the curing degree of the glue under different irradiation times, draw a curing degree – time curve, and determine the optimal irradiation time.
On-line monitoring: Introduce on-line curing monitoring equipment to detect the curing state of the glue in real time, and automatically adjust the irradiation time according to the actual situation to ensure the consistency of the curing effect.

4. Collaborative Optimization of Other Equipment Parameters

Distance between the light source and the workpiece: Appropriately adjusting the distance between the light source and the workpiece can control the light intensity attenuation. Generally speaking, the closer the distance, the stronger the light intensity, but it is necessary to pay attention to avoiding damage to the workpiece caused by excessive temperature.
Conveyor speed: In pipeline production, the conveyor speed is closely related to the irradiation time. According to the curing requirements, reasonably adjust the conveyor speed to ensure that the glue can be fully cured when passing through the curing area.

Analysis of Typical Application Cases

1. Optical Lens Assembly

In the bonding of optical lenses and lens barrels, the glue is required to have high light transmittance and low internal stress after curing. Selecting an LED light source with a wavelength of 365nm, setting the light intensity to 800mW/cm², and irradiating for 10 seconds can achieve rapid curing while ensuring the optical performance.

2. Bonding of Components on Circuit Boards

For the bonding of small components on circuit boards, since the glue layer is thin, using an LED light source with a wavelength of 385nm and a light intensity of 1200mW/cm², combined with an irradiation time of 5 seconds, can avoid thermal damage to the circuit board while ensuring production efficiency.

Conclusion

The curing speed of LED UV glue is comprehensively affected by various parameters such as wavelength, light intensity, and irradiation time. By conducting in-depth research on the influence laws of each parameter and optimizing the parameter settings of the LED UV curing equipment in combination with specific application scenarios, efficient and stable curing of the glue can be achieved, and the product quality and production efficiency can be improved. In the future, with the continuous development of LED light source technology and glue formulations, the LED UV curing process will be more widely applied in more fields.

For more about influence factors of the curing speed of LED UV glue and optimization strategies for equipment parameters, you can pay a visit to DeepMaterial at https://www.uvcureadhesive.com/ for more info.