The hottest section II optical ink

Section 2 optical ink

(IV) light cured binder

light cured binder is mainly composed of light cured resin or prepolymer, crosslinking agent (monovalent crosslinker or prepolymer crosslinker), photosensitizer and polymerization inhibitor

1. Light cured resin or prepolymer

light cured resin or prepolymer has a great influence on the curing speed, gloss, clarity, adhesion, toughness and resistance of UV ink ② according to the requirements of the verification regulation, the repeatability error of the indication of the level 1 experimental machine is 1.0%, and the friction and fastness are all greatly affected

at present, there are two kinds of photo curing resins used more in the ink industry: one is unsaturated polyester, which is usually a linear polymer compound formed by condensation of saturated or unsaturated diols and saturated or unsaturated dibasic acids (anhydrides); The other is acrylic resin. For example, saturated or unsaturated polyester containing hydroxyl is esterified with acrylic acid, or acrylic unsaturated polyester, acrylic polyether, acrylic epoxy resin and acrylic polyurethane are prepared by other methods

in practical applications, a large part of them are not resins, but esters of unsaturated compounds, such as trimethylolpropane triacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, isophthalic acid diacrylate, etc. However, they can be used together with photo curing resin, which is conducive to light polymerization and curing

the following focuses on the relationship between the molecular structure and properties of raw materials used in the preparation of unsaturated polyester

commonly used raw materials include diols and polyols, saturated dibasic acids and unsaturated dibasic acids, and their effects on the properties of polyester can be summarized as follows: after the implementation of the regulations

(1) diols and polyols have different effects on the properties of polyester. Different diols have different effects on the properties of polyester, such as ethylene glycol (hoch2-ch2oh), which has good molecular symmetry, large hardness, high crystallization tendency and poor miscibility with styrene monomer

compared with ethylene glycol, propylene glycol (hoch2-choh-ch3) has one more methyl group in the molecular structure, which improves the water resistance, reduces the crystallization tendency, and improves the miscibility with styrene

compared with ethylene glycol, neopentyl glycol has two more methyl groups in its molecular structure, which improves the water resistance and flexibility of polyester

monodiethylene glycol or polyglycol [hoch2 ≮ ch2-o-ch2 ≯ nch2oh], where n=1 is monodiethylene glycol, n=2 is triethylene glycol, etc. The longer the molecular chain of diol is, the more flexible the resin is; However, due to the increase of ether oxygen bond in the molecule, the moisture absorption of polyester is increased; Due to the existence of ether oxygen bond in the molecule, the polyester has certain air drying performance

ternary alcohols such as trimethylolpropane [ch3ch2c (CH2OH) 3] can produce high viscosity polyester, and the resulting polyester has better water resistance

a small amount of Quaternary alcohols such as pentaerythritol [c (CH2OH) 4] added to the formula will improve the gloss of UV curing ink and the hardness of ink film. In addition, polyols used include certain alcohols, sorbitol, dipentaerythritol, etc., which can increase the strength and corrosion resistance of polyester

here are examples to illustrate the effects of resins obtained from different diols and dicarboxylic acids (including 50% maleic anhydride) on the light curing speed and film hardness. The comparison results are shown in the table

table light curing speed and film hardness of unsaturated polyester with different diols

relative speed of diol light curing relative hardness of film * relative speed of diol light curing relative hardness of film * ethylene glycol

neopentyl glycol 10

3.3 48

72 propylene glycol

hydrogenated bisphenol a 10

10 54

76 * the hardness of tinplate is 100, and the film thickness is 5 μ m。

it can be seen that except neopentyl glycol, the other three diols have the same light curing rate, but the relative hardness of the film is different, among which hydrogenated bisphenol A is the hardest and monoethylene glycol is the hardest

(2) effect of dibasic acid (anhydride) on polyester properties dibasic acid can be divided into saturated and unsaturated. The most commonly used unsaturated dibasic acids are maleic anhydride and fumaric acid (maleic anhydride and reverse acid for short). The resin synthesized by reverse acid has high activity. Due to the symmetrical molecular structure, various properties are better than maleic anhydride. However, unsaturated acid cannot be used alone in the synthesis of unsaturated polyester resin, because the double bond density is large, the property is brittle, and there is no practical use

the satisfaction of new and old customers is better improved. Saturated dibasic acids, aromatic dibasic acids commonly used are phthalic anhydride, followed by isophthalic acid and terephthalic acid. Aliphatic saturated dibasic acids commonly used are adipic acid, sebacic acid, caprylic acid and azelaic acid

aromatic dicarboxylic acids give polyester a certain rigidity, which can improve the strength of UV light curing ink film. Phthalic anhydride, which is rich in sources and cheap, is often used by people. Aliphatic dibasic acid, excellent flexibility, adipic acid is better

next, the effects of maleic anhydride (maleic anhydride) and other binary anhydrides on the properties of polyester are introduced

① effect of maleic anhydride. 60 parts of resin made of maleic anhydride phthalic anhydride ethylene glycol in different proportions, China is a large agricultural country, and 40 parts of the same monomer (1,4-butanediol diacrylate) were photocrosslinked under the same conditions. Their photocuring speed and thickness were compared to be 5 μ M, the results are shown in the table

table the composition of maleic anhydride and phthalic anhydride in unsaturated polyester, light solid speed and durality

relative hardness of maleic anhydride (molar ratio) light curing relative speed film * relative hardness of maleic anhydride (molar ratio) light curing relative speed film *3:1

2:1

1:15

4

10 52

48

44 1:3

1:37.5

5 40

30 * the hardness of the sheet is 100, and the film thickness is 5 μ m。

it can be seen that the molar ratio of 1:1 is the best, that is, maleic anhydride accounts for 50% (mol) of all dibasic acids (anhydrides), and fumaric acid (trans maleic acid) is basically the same

② effects of other dibasic acids. The results obtained by replacing phthalic anhydride with other dibasic acids in the ratio of 1:1 are shown in the table

table light solid speed and durality of unsaturated polyester with different dicarboxylic acids

relative hardness of film with relative speed of light curing of other dicarboxylic acids * relative hardness of film with relative speed of light curing of other dicarboxylic acids * phthalic anhydride

isophthalic acid 10

7.544

52 tetrahydrophthalic anhydride

tetrachlorophthalic anhydride 7.5

7.5 56

48 * with sheet hardness of 100 and film thickness of 5 μ m。

2. Crosslinking agent

(1) the concept of crosslinking agent unsaturated polyester is a linear polymer with unsaturated double bonds. Any monomer that can be crosslinked with this polymer is called crosslinking agent, also known as "bridging agent", which makes the linear polyester crosslink into a like structure

in the molecular structure of crosslinkers, they all have π bonds or conjugated large π bonds, which are active groups that can be photopolymerized, and common ones can be listed in the table

surface photopolymerizable active group

name of active group representative compound name of active group representative compound acrylic acid methacrylate methacrylate acrylamide acrylamide vinyl styrene Stilbene epoxypropyl epichlorohydrin vinyl ether oxyacetic acid vinyl ester butene dicarboxylic acid propylene ether oxypropylene alcohol alkynyl vinyl acetylene (2) types of cross-linking agents commonly used cross-linking agents can be divided into two categories:

① monofunctional monomer. The molecular structure of this kind of compounds contains an ethylene unsaturated double bond, which is often preferred due to the consideration of reaction performance and simple operation

② bifunctional monomers and multifunctional monomers. A compound containing two or more unsaturated ethylene double bonds in its molecular structure. It can be further divided into acrylic esters of polyvalent alcohols and unsaturated esters of polyvalent acids

③ selection principle of crosslinking agent. The ideal crosslinking agent is also an ideal active diluent, which can be used as follows: