Polythiol with amine accelerators in adhesive
1. Limitations of commonly used curing agents and advantages of mercaptans:
In the field of epoxy curing, currently commonly used curing agents such as anhydrides, dicyandiamines, imidazoles, aromatic amines, etc., they often require specific high or medium temperature environments to induce a curing reaction in epoxy resins. This means that these curing agents have obvious limitations in applications where temperature is strictly limited, such as where heat treatment is not possible.
Thiol-based curing agents stand out for their ability to cure quickly at room and low temperatures, a characteristic that greatly broadens the range of applications for which epoxy resins can be cured. For example, mercaptans can play a key role in temperature-sensitive surfaces or in low-temperature construction scenarios. And its curing products have good toughness, which has a positive significance to improve the mechanical properties of cured materials, such as impact resistance, flexibility and so on. From the type of view, the common mercaptan curing agent in the form of liquid oligomer or multi mercaptan monomer, different structure of the mercaptan curing agent due to the chemical structure of the differences in the interaction with the accelerator will have a different performance, which leads to the curing temperature and curing time varies. This requires that in practical applications, the appropriate structure of the mercaptan curing agent and the corresponding accelerator should be selected accurately according to the specific process requirements and the use of the environment, in order to achieve the desired curing effect.
2. Characteristics of mercaptan structure:
From the perspective of chemical structure, mercaptan is a class of non-aromatic compounds containing sulfhydryl functional group (-SH), and its formation principle can be understood as the product of replacement of oxygen atom by sulfur atom in ordinary alcohol. It is this structural uniqueness that gives mercaptans their special chemical properties, making them capable of reacting quickly with epoxy at room temperature, and the curing time is usually around 5 minutes, which makes them outstanding among many curing agents in terms of fast curing speed. Especially in thin-layer curing, thin-layer curing is very critical for the bonding of precision parts or surface treatment with high demands on appearance, such as in the bonding of electronic components to fill small gaps and repair of precision instrument housings, etc. This performance advantage of mercaptan ensures that the curing process is precise and efficient, and does not affect the surrounding parts too much due to the curing process.
3. Application areas of mercaptan
3.1 Epoxy curing agents:
In the case of two-component epoxy-cured quick-drying adhesives, when using DMP as an accelerator, mercaptans are able to cure in as little as 1 – 5 minutes at low temperatures below -20°C. This is a good example of how mercaptans can be used to cure a two-component epoxy adhesive in just 1 – 5 minutes at low temperatures. This data demonstrates the efficient curing ability of mercaptan curing agents at low temperatures. In contrast to conventional curing agents, which require medium to high temperatures to cure, the low temperature of -20°C restricts the use of most curing agents, whereas mercaptans are able to work quickly in this environment. This makes mercaptans the ideal choice for outdoor projects in cold regions, repair of articles in low temperature storage environments or processing of materials in low-temperature production plants, guaranteeing the fast cure time of epoxy materials even at low temperatures. In low temperatures, epoxy resin materials can still quickly reach the ideal curing state to meet the corresponding performance requirements.
3.2 UV curing adhesives:
Thiols are used in light-curing nail polish, photoresists, and photosensitive resins for 3D printing, where high film thicknesses are cured quickly and with low energy. In 3D printing, for example, high film thickness means that thicker parts can be molded in a single pass, while fast low-energy curing reduces print time, improves productivity and lowers energy consumption. Moreover, it can adapt to a variety of different light conditions such as 415nm, 365nm wavelength LED cold light source, high-pressure mercury lamps and lasers, which reflects its good light adaptability and can function properly under different light curing equipment environments. Excellent surface dryness indicates that the surface state after curing is good, there will be no sticky and other undesirable conditions, and good compatibility with the main resin to ensure that there will be no phase separation in the mixing process will not affect the quality of the curing and material properties of the problem, transparent, colorless and odorless is to meet the appearance of the application of environmental protection and other aspects of the higher requirements of the scenario, such as the use of light-curing nail polish in the nail industry, you need to ensure that the coating after the Beautiful and odorless.
3.3 UV Ink:
In UV offset printing, gravure, rolling coating and other low film thickness, low energy, fast printing process applications, mercaptan can effectively improve the curing rate, which is essential to improve printing productivity. In modern high-speed printing lines, fast curing enables the ink to dry and set quickly, which facilitates subsequent process operations and reduces scuffing, sticking and other print quality problems caused by undried ink. At the same time, the dry surface of the coating film does not stick to the characteristics of the further guarantee the quality of the printed products, so that the appearance of the neat and clean. Improve the anti-yellowing performance can extend the service life of the printed materials, so that in the process of long-term preservation or use, the appearance of the color can remain relatively stable, for some of the long-term display of printed materials such as book covers, posters, etc. is particularly important. Enhance the adhesion properties of metal, glass, polymer materials and other different types of materials, it broadens the scope of its application, whether in metal packaging printing, glass products, decorative printing or plastic products can play a role in printing and other fields, to improve the degree of ink and substrate bonding firmness, to ensure that the printed content of the durability.
4. Characteristics and applications of polythiol
Characteristics:
As a special form of mercaptan, polymer mercaptan has been used as a commercialized epoxy curing agent for more than 35 years, which indicates that it has been verified by long time market test and practical application, with reliable performance and stable quality. It offers some unique and key performance advantages over the countless other types of curing agents on the market.
Its ability to cure quickly at room temperature is very convenient in practical applications, eliminating the need for additional heating equipment, reducing the complexity and cost of the curing process, and avoiding the adverse effects that heating may have on the cured material or the surrounding environment. Moreover, its curing speed is not so sensitive to the amount of adhesive dispensing, which is in sharp contrast to general amine curing agents, where the larger the amount of amine curing agent dispensing is, the faster the curing speed is, whereas the curing speed of polysulfanol is relatively stable in the case of different dispensing amounts, which makes it possible to play the curing role more steadily and ensure that the cured material or surrounding environment is not affected by heating, and the curing speed is not so sensitive to the amount of dispensing, in contrast to general amine curing agents, where the larger the dispensing amount of amine curing agent dispensing is, the faster the curing speed is. This enables the poly mercaptan to play a more stable curing role and ensure the consistency of each curing effect.
In addition, polymer mercaptan also has the characteristics of low toxicity, which in the increasingly stringent environmental requirements of the present, so that its application in food packaging, medical equipment and other high safety requirements of the field of application has become possible; light color is conducive to maintaining the appearance of the material after curing the aesthetics of the curing process will not be due to the curing agent itself lead to material discoloration; excellent adhesion to ensure that it is able to firmly bond different materials together to meet the strength requirements of a variety of structural connections; it can also be used as a curing agent to ensure the consistency of the curing effect each time. It can also be used as an accelerator to speed up the reaction of other amine curing agents, which reflects its versatility in the curing system, and can be used in conjunction with other curing agents to flexibly adjust the speed and effect of the curing reaction according to the actual needs.
5. Application Scenarios:
Polymer mercaptan is widely used in many fields, for example, in coatings, it can improve the curing speed and quality of coatings, and make the coating dry quickly to form a good protective and decorative effect, which is suitable for architectural exterior coatings, furniture paints, etc.; in the field of sealants, by using its good adhesion and curing properties, it can effectively seal all kinds of crevices to prevent the leakage of liquids and gases, which can be used in the scenes of automobile engine sealing and pipeline sealing; for industrial patching, it can be used in the field of industrial patching. Scenarios can be used; for industrial patches, can quickly repair and curing of damaged parts, restore the structural integrity and function of the components, such as metal equipment surface wear repair, conveyor belt breakage repair, etc.; in the rapid repair of flooring, can be made in a short period of time so that the repair part of the curing to achieve the use of strength, to reduce the impact on the normal use of commonly used in shopping malls, factories and other public places of the maintenance of the floor; potting adhesive In the application, the electronic components can be potting protection, so that it is free from the influence of the external environment, by virtue of its low toxicity and other advantages to protect the use of electronic equipment safety and stability. At the same time, it serves as a promoter for other curing systems, and can work synergistically with different types of curing agents to optimize the entire curing reaction process, expanding its application value in a variety of complex curing systems.
In terms of sales specifications, there are two forms of amine-containing accelerators and accelerator-free forms. Promoter-free polymer mercaptans (e.g., GPM800) allow formulators to better add suitable promoters on their own according to specific process requirements, usage environment, and desired curing speeds, thus precisely controlling the curing speeds and realizing product versatility to meet the individual needs of different customers. Standard five-minute curing mercaptans (e.g. GPM888) already have accelerators added, making them easy to use for those who have regular requirements for curing speed and who seek simplicity of operation. The fastest curing mercaptans (e.g. GPM895FC) can reach a gel time of 40 seconds / 20g, such a very fast gel speed in some of the curing efficiency requirements of the emergency repair, rapid production and other scenarios have a unique application advantages, such as in some of the need to quickly resume production of industrial production line equipment repair, after a sudden disaster of the temporary facilities set up and other situations, can quickly play a curing role, to ensure that the relevant facilities are put into use as soon as possible. It can be used to ensure that the relevant facilities are put into use as soon as possible.
6. Chemical reaction mechanism and related characteristics of mercaptan
6.1 Reaction mechanism:
The chemical reaction mechanism of mercaptan is relatively simple and direct, the reaction between tertiary amine accelerator and mercaptan will form mercaptan salt anion, which is a very strong nucleophilic reagent. In the chemical reaction, the nucleophilic reagent has the ability to actively attack other atoms or groups with a partial positive charge, and it is by virtue of this characteristic that the thiolate anion can quickly open the epoxy group to react, thus initiating the curing process. When the thiol salt reacts with another thiol group, a new thiol salt anion can be generated, and this regeneration process ensures that the reaction can continue, allowing the entire curing reaction to be completed successfully.
Due to the low activation energy of the reaction, which means that the energy barrier to be overcome is low, the reaction can be carried out at or below ambient temperature. The advantages of this feature are very significant, on the one hand, the reaction can occur at room temperature greatly simplifies the curing process, without additional heating equipment and energy inputs, reducing costs; on the other hand, for some materials that can not tolerate high temperatures or in the application of low-temperature environments, still be able to successfully realize the curing of the scenarios, such as in the packaging of some heat-sensitive electronic components, low-temperature outdoor construction structure For example, in the encapsulation of heat-sensitive electronic components and the repair of outdoor building structures in low-temperature environments, this low-temperature reactivity has greatly expanded the range of applications. Moreover, because it does not need to be heated to react, it can even be used for thin-layer curing on metal substrates, which often have good thermal conductivity, and are susceptible to problems such as rapid heat transfer and uneven curing effects when heated, while the ambient curing characteristics of mercaptans can well circumvent these problems and guarantee the quality and stability of thin-layer curing on metal surfaces.
6.2 Proportioning flexibility:
In terms of the ratio of mercaptan to epoxy, a 1:1 ratio of epoxy to thiol results in an excess of epoxy groups, but the presence of tertiary amine accelerators allows the excess epoxy groups to self-cure. The flexibility of this ratio has important practical significance, in the actual operation process, it is difficult to accurately follow the theoretical optimal ratio each time to glue, there will always be a certain ratio of minor changes, and the mercaptan curing agent system through the internal self-curing reaction mechanism, can make up for the slight deviation of the ratio, so that the curing reaction can still be carried out normally, to ensure that the curing effect of the relative stability of the reduction of errors in glue mixing lead to curing failure or reduce due to the curing effect. This ensures relatively stable curing results and reduces curing failures or poor material performance after curing due to compounding errors, which improves the fault tolerance of the entire curing process and the convenience of practical applications.
7. Examples of specific mercaptan curing agents and the advantages and application areas of mercaptan curing agent systems
예시:
For liquid curing agents (e.g. PE series) with mercapto functional group (-SH) at the end, it is necessary to use it together with accelerators (e.g. K-54, DMP-30) in order to effectively promote the curing reaction with epoxy resins. This indicates that in practice, these mercaptan curing agents have a specific dependence on the accelerator, and that the selection of a suitable accelerator is critical to achieving good curing results. Different accelerators may affect the curing speed, curing temperature and other key parameters, so it is necessary to reasonably select the matching accelerators according to the specific requirements and process conditions, in order to give full play to the performance advantages of this type of mercaptan curing agent.
8. Advantages and application areas:
The biggest advantage of the mercaptan curing agent system is that it can also cure quickly in low temperature and thin coating. The application in low temperature environment has been mentioned many times before, while the thin coating curing ability has an irreplaceable role in many precision processing, high-end decoration and other fields. For example, in jewelry processing, some small inlaid parts or surface decoration parts of the adhesive curing, thin coating and fast curing can ensure the accuracy of the operation, will not affect the appearance of the jewelry and the overall structure; in the transparent adhesive curing, to meet the high transparency requirements of occasions, such as optical lens bonding, high-grade glass crafts, etc., to ensure that the curing will not affect the light transmission and aesthetics; in the field of composite materials, the ability to cure in thin coating has an irreplaceable role in many areas of precision processing, such as high-end decoration. In the field of composite materials, its low-temperature fast curing characteristics can avoid the impact of high temperature on the performance of different components in the composite materials, improve the quality and efficiency of the preparation of composite materials; for the new energy field of photovoltaic, which may be involved in low-temperature environment of the component installation, maintenance and bonding of thin photovoltaic materials and other scenarios, the advantages of the mercaptan curing agent system can also ensure the smooth progress of the relevant processes, and promote the stable development of the photovoltaic industry. The advantages of mercaptan curing agent system can also guarantee the smooth progress of related processes and promote the stable development of PV industry. At the same time, in the low temperature curing of epoxy resin, industrial adhesives, road marking temperature-resistant adhesives and other fields are also by virtue of its unique advantages, play an important role in curing, to meet the diversified needs of different industries on the curing performance of adhesives.
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