Section 2 Optical Ink - 3

(4) Photo-curable linking materials Photo-curable linking materials are mainly composed of photo-curable resin or prepolymer, cross-linking agent (single cross-linking agent or prepolymer cross-linking agent), photosensitizer and polymerization inhibitor. .
1. Photocurable resin or prepolymer Photocurable resin or prepolymer has a great influence on the curing speed, gloss, sharpness, adhesion, toughness, abrasion resistance, and fastness of UV ink.
There are two types of photo-curable resins currently used in the ink industry: one is an unsaturated polyester, which is usually a polycondensation of a saturated or unsaturated dihydric alcohol with a saturated or unsaturated dibasic acid (anhydride). The resulting linear polymer compound; the other is an acrylic resin, such as a hydroxyl-containing saturated or unsaturated polyester esterified with acrylic acid, or other methods to obtain acrylic unsaturated polyester, acrylic polyether, Acrylic epoxy, acrylic polyurethane.
In practical applications, a large part of it is not actually a resin, but is an ester of an unsaturated compound, such as trimethylolpropane triacrylate, neopentyl glycol diacrylate, 1,6-hexanediol dimer. Acrylate, isophthalic diacrylate and the like. However, they can be used in combination with photo-curable resins to help photopolymerize and cure.
The relationship between the molecular structure and properties of the raw materials used in the preparation of unsaturated polyesters is highlighted below.
Commonly used raw materials include diols and polyols, saturated dibasic acids, and unsaturated dibasic acids. The effects on polyester properties can be briefly described as follows:
(1) Effects of diols and polyols on the properties of polyesters Different diols have different effects on the properties of polyesters, such as ethylene glycol (HOCH2-CH2OH), which has good molecular symmetry and the resulting polyester hardness. Large, high crystallization tendency, poor intermiscibility with styrene monomer.
Compared with ethylene glycol, propylene glycol (HOCH2-CHOH-CH3) has one more methyl group on its molecular structure, which improves water resistance, reduces crystallization tendency, and improves miscibility with styrene.
Compared with ethylene glycol, neopentyl glycol has two more methyl groups on the molecular structure, which improves the water resistance and flexibility of the polyester.
Diethylene Glycol or Polyethylene Glycol [HOCH2≮CH2-O-CH2≯nCH2OH] Where n=1, it is diethylene glycol, n=2 is, and is triethylene glycol. ,and many more. The longer the molecular chain of the diol, the higher the prestige of the resin; but the increase of the ether oxygen bond in the molecule increases the moisture absorption of the polyester; the presence of ether oxygen bonds in the molecule, the obtained polyester has Certain air drying performance.
Triols such as trimethylolpropane [CH3CH2C(CH2OH)3] can give high viscosity polyesters and the resulting polyesters have better water resistance.
A tetrahydric alcohol, such as pentaerythritol [C(CH2OH)4], is added to the formulation in small amounts to increase the gloss of the UV-curable ink and the hardness of the ink film. In addition, the polyhydric alcohols used include urethane, sorbitol, dipentaerythritol, etc., which can increase the strength and corrosion resistance of the polyester.
The effect of different diols and dibasic acids (of which 50% of maleic anhydride) on the speed of photocuring and the hardness of the film is illustrated. The results are shown in Table 2-23.
Table 2-23 Photocuring speed and film hardness of unsaturated polyesters of different glycols
* The hardness of tinplate is 100 and the film thickness is 5μm.
It can be seen that in addition to neopentyl glycol, the other three glycols all have the same photocuring speed, but the relative hardness of the film is different, with hydrogenated bisphenol A being the hardest and ethylene glycol the most.
(2) Effects of Dibasic Acid (Anhydride) on Properties of Polyester Two types of saturated and unsaturated dicarboxylic acids. Unsaturated dibasic acid is the most commonly used maleic anhydride and fumaric acid (abbreviated as maleic anhydride and acid), and the synthetic resin of the acid is very active. Due to the symmetrical molecular structure, various properties are better than maleic anhydride. . However, in the synthesis of unsaturated polyester resins, unsaturated acids cannot be used alone because the density of double bonds is high, and the properties are brittle, and there is no practical use.
Saturated dibasic acids, aromatic dibasic acids are commonly used phthalic anhydride, followed by isophthalic acid and terephthalic acid dicarboxylic acid. Aliphatic saturated dibasic acids commonly used are adipic acid, sebacic acid, suberic acid and sebacic acid.
The aromatic dibasic acid imparts a certain rigidity to the polyester and can increase the strength of the ultraviolet light-curable ink-ink film. Among them, phthalic anhydride is rich in sources, cheap and often used by people. Aliphatic dibasic acids have excellent flexibility and adipic acid is preferred.
The effects of maleic anhydride (maleic anhydride) and other dibasic anhydrides on the properties of the polyester are described below.
1 Effect of maleic anhydride. 60 parts of a resin made from maleic anhydride-phthalic anhydride-ethylene glycol in different ratios were photo-crosslinked under the same conditions as 40 parts of the same monomer (1,4-butanediol diacrylate). The photocuring speed and the hardness of the film having a thickness of 5 μm are shown in Table 2-24.
Table 2-24 Composition and Photo-Solid Velocity and Hardness of Maleic Anhydride and Phthalic Anhydride in Unsaturated Polyester
* The hardness of tinplate is 100 and the film thickness is 5μm.
It can be seen that the 1:1 molar ratio is best, that is, maleic anhydride preferably accounts for 50% by mole of all dibasic acids (anhydrides): the fumaric acid (distitanic acid) is essentially the same.
2 The effect of other dibasic acids. Replace the phthalic anhydride with other dibasic acids, the results obtained in a 1:1 ratio are shown in Table 2-25.
Table 2-25 Photo-Solid Velocity and Hardness of Unsaturated Polyesters with Different Diacids
* The hardness of tinplate is 100 and the film thickness is 5μm.
2. Crosslinking agent (1) The concept of cross-linking agent Unsaturated polyester is a linear polymer with unsaturated double bonds. Any monomer that can cross-link and copolymerize with this polymer will be called cross-linking monomer. Coupling agents, also known as "bridgers," crosslink linear polyesters into a network structure.
The molecular structure of the cross-linking agent has π-bonds or conjugated large π-bonds, and is a photopolymerizable reactive group, and can be found in Table 2-26.
Table 2-26 Photopolymerizable reactive groups

(2) Types of cross-linkers Cross-linkers commonly used can be divided into two categories:
Monofunctional monomer. The molecular structure of this type of compound contains an ethylenically unsaturated double bond, which is often preferred because of its reactivity and ease of handling.
2 bifunctional monomers and polyfunctional monomers. Compounds containing two or more unsaturated ethylene double bonds in the molecular structure. It can be subdivided into unsaturated esters of polyvalent alcohols with acrylates and polyvalent acids.
3 crosslinker selection principles. The ideal cross-linking agent is also an ideal reactive diluent, which can be as follows