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Bifunctional UV monomer

Release time:

2025-01-10 17:02

A difunctional UV monomer, as its name suggests, contains two reactive functional groups per molecule that can participate in curing reactions. These reactive groups are typically acrylate or methacrylate types; however, acrylates currently dominate nearly half of the market! Compared to their monofunctional counterparts, difunctional UV monomers not only exhibit faster curing speeds and significantly higher cross-linking densities in the resulting film, but also maintain excellent dilutability. As the number of functional groups increases, so does the molecular weight, and consequently, the viscosity rises accordingly. This results in lower volatility and reduced odor.

The following introduces some common bifunctional UV monomers.

I. DPGDA/TPGDA

These two UV monomers are propylene glycol diacrylates.

DPGDA: Di(propylene glycol) diacrylate.

DPGDA is characterized by low volatility, low viscosity, excellent dilutability, and rapid curing speed.

TPGDA: Tripropylene Glycol Diacrylate.

TPGDA has one additional propoxy group compared to DPGDA, resulting in better flexibility, slightly lower viscosity, better dilutability, faster curing speed, less skin irritation, and a lower price. It is currently the most commonly used difunctional UV monomer.

II. HDDA

HDDA: 1,6-Hexanediol diacrylate.

HDDA is known for its low viscosity, strong diluting properties, and excellent resin dissolving power. It exhibits good adhesion to plastic substrates and can enhance the flexibility of cured films. Compared to TPGDA, HDDA is more irritating to the skin and slightly more expensive.

III. NPGDA/2PO-NPGDA

These two UV monomers are neopentyl glycol-based diacrylates.

NPGDA: Neopentyl glycol diacrylate.

NPGDA features low viscosity, excellent dilutability, high reactivity, a high glass transition temperature (Tg), and rapid curing; however, it exhibits significant skin irritation.

2PO-NPGDA: Propoxylated neopentyl glycol diacrylate.

After the addition of a propoxy group, the skin irritation of NPGDA was reduced. The cured film exhibits high tensile strength, good elongation, and low shrinkage.

IV. Ethoxylated BPADA

Bisphenol A diacrylate ethoxylated, with main grades including 2EO-BPADA, 4EO-BPADA, and 10EO-BPADA.

By introducing an ethoxy group between the bisphenol A unit and the acrylate moiety, the resulting structure is similar to that of bisphenol A epoxy acrylate; both contain the bisphenol A structure and thus exhibit characteristics such as high hardness, high refractive index, heat resistance, and chemical resistance.

Standard bisphenol A epoxy acrylate has two bisphenol A structures and exhibits a viscosity of tens of thousands of cps at room temperature; in contrast, ethoxylated bisphenol A acrylate contains only one bisphenol A moiety and has a room-temperature viscosity of just 1,000 cps—significantly lower than that of bisphenol A epoxy acrylate. Moreover, as the number of ethoxy groups increases, the viscosity decreases further, while the flexibility and hydrophilicity of the cured film also improve.

V. PEGDA

PEGDA: Polyethylene glycol diacrylate.

Based on molecular weight, PEGDA is categorized into PEG(200)DA, PEG(400)DA, and PEG(600)DA. Their cured films are relatively soft, exhibiting moderate tensile strength and elongation at break. As the molecular weight increases, both viscosity and flexibility rise, while the glass transition temperature (Tg) and skin irritation potential decrease. At the same time, hydrophilicity also increases—truly a case of “a girl changing with age; the longer she grows, the gentler she becomes.”

The above are common bifunctional UV monomers.

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