UV-curable ResinOxetane

Characteristics of ARON OXETANE

1 High-speed curing of epoxy resin

Generally, epoxy resin has a quick initiation reaction but slow propagation reaction, and because it will only yield an oligomer with a molecular weight in the thousands of mass units, its physical properties can only be set to be hard and brittle. However, the polymerization of oxetane resins is slow to start: it will not happen immediately even when exposed to light, but only when the concentration of the initiator type exceeds a certain level and it produces a polymer with a molecular weight in the tens of thousands of mass units. When epoxy resin is combined with oxetane resin in such a way that makes the most of their respective characteristics, it is possible to cover their individual shortcomings. In other words, when epoxy resin with quick initiation is added to oxetane resin, the curing speed may be equivalent or superior to that of the cycloaliphatic epoxy used for light cationic polymerization. As the added epoxy increases, the molecular weight of the resulting polymer is slightly less than in the case of using oxetane resin alone, but it is sufficient as a high polymer and it is possible to design cured substances with extensibility and toughness. Because the reactivity of epoxy resin is not improved by mixing oxetane resin, it is necessary to mix in a large amount of oxetane resin when rapid curing is needed.

2．Dark reaction (post polymerization)

Cationic curable resin is characterized by the fact that polymerization progresses even after exposure to ultraviolet light. Normally, it takes four hours until cycloaliphatic epoxy resin is cured to exhibit solvent resistance. Oxetane resin is so reactive that post-curing is rapid. An appropriate type of resin produces adequate performance after nearly ten minutes of ultraviolet irradiation.

3. Impact of the addition of small quantities on physical properties

The physical properties of cured products change after a small amount of oxetane resin is added. If the content of highly reactive oxetane resin is only 10–20%, Tg of the resin after ultraviolet curing rises by some 10°C. This is thought to reflect a rise in the system temperature caused by the reaction heat from the small volume of oxetane resin. Adding a small amount oxetane resin also increases breaking strength.

4. Adhesiveness

In the majority of cases, adhesive strength declines after the addition of oxetane resin. It is so reactive that it produces a small hydroxyl group derived from the initiator and that reaction occurs in a short time. For these reasons, the stress caused by curing shrinkage is concentrated on the boundary surface. Especially if the adherend is made of plastic, it is necessary, for example, to reduce the curing speed or to blend a material with high wettability into the adherend. Effective methods of increasing adhesiveness include adding a high molecular weight resin or glycidyl ether epoxy resin to control the reaction speed and heated aging to eliminate internal stress.

5. Mixing with glycidyl ether epoxy resin

Monofunctional and bifunctional oxetane resins have very low viscosity and make it possible to blend a larger amount of high viscosity resin to extend the range of mixing formulas. In addition, with the high reactivity of oxetane resin, it is possible to blend glycidyl ether epoxy resin, such as bisphenol-A type and novolac type resin, or epoxy modified butadiene and other resins marketed as epoxy modified polymer. Normally such resins cannot be used for cationic polymerization because of their poor reactivity. This is one of the most effective blending solutions for producing adhesives and sealing agents.

6. Storage stability

For most materials composed solely of epoxy resin, the molecular weight and perceived viscosity do not rise after a small amount of acid is generated from initiators with degradation over time. If oxetane resin is blended, high molecular weight polymer is generated to increase viscosity. In such cases, it is necessary to use a different initiator with higher stability or to add some stabilizer.

7. Impact of moisture

Ultraviolet cationic curing is considered to be affected by moisture. In most cases, no marked reaction inhibition occurs when water is added to the mixture. However, atmospheric moisture has a significant impact. Generally, oxetane resin is more sensitive to water than epoxy resin, but it can be used in a stable state in any place where the atmospheric humidity can be controlled.

Applications of UV-curable Resins

1. Light-curable materials (ARONIX and ARON OXETANE)

Polymerization of UV-curable Resins is promoted by radicals and cations generated from initiators with exposure to light. Given the advantage of this reaction, UV-curable Resins are widely used in a number of fields. Generally, using UV-curable Resin can minimize the amount of solvent, so it is possible to design environment-friendly products. Light curing has the following advantages:

The speed of light curing of ARON OXETANE in an unblended state is not especially high. Blending with epoxy resin prior to light curing drastically improves the speed of light curing and the properties of the cured products.

1-1. Light-curable inks and paints

Light-curable inks and UV-curable inks, characterized by their high curing speed, have been in practical use since around 1970 for sheet-fed printing and web offset printing. Lately, their applications have expanded to gravure inks and inkjet inks. They are indispensable as materials for a range of resist inks that take advantage of image forming properties. Light-curable or UV-curable coating agents are widely used for protective coatings and hard coatings for paper, wood, plastics, and metals, and are also used for other products used in daily life, including beverage cans, fiber optic materials, and mobile phones.

1-2. Electron beam curable coating agents

Radical polymerization is a method of hardening (curing) the coating surface using an electron beam. Because it does not involve the use of light initiators, it can be used for materials impenetrable to light including metallic films and high-concentration pigments. It also increases adhesiveness. Despite these features, it is subject to severe limitations relating to facilities and has yet to find widespread application.

1-3. Light-curable adhesives

As with other types of adhesives, light-curable adhesives produce a polymer in the polymerization reaction and harden to produce an adhesive capability. They are unique in that a chain of polymerization reactions is triggered by light irradiation. Apart from that, they do not require mixing of two different fluids, they offer freedom in the set time and they exhibit good storage stability. In recent years, they have enjoyed enormous demand for use in DVDs and other data storage applications.

1-4. Resist materials

These are used in both etching and solder resists. Materials that include carboxylic acid to contribute to their alkaline developing ability are used. In recent years, use in LCD color filters has progressed. They are also used in press plates for flexography printing used in newspaper printing and the like.

2．Reforming of epoxy resin (ARONIX and ARON OXETANE)

2-1. Improvement in curing performance of light-curable epoxy (ARON OXETANE)

This is the most significant feature of ARON OXETANE. Light-curable epoxy resin shows quick initiation and slow propagation. Because it is difficult to obtain any substance with high molecular weight, the resulting material is always hard and fragile. ARON OXETANE is characterized by slow initiation. Polymerization does not immediately start with exposure to light. However, when the initiator generated from initiators reaches a certain concentration, high-speed polymerization occurs to form a high molecular weight material with extensibility and toughness. Based on this difference in polymerization characteristics, light-curable epoxy resin may be combined with ARON OXETANE to enhance the curing speed and to increase the molecular weight of polymerized material for improved heat and alkali resistance.