1. Label ink overview
Label printing is a branch of the printing industry with considerable growth potential. The labeling industry, in particular the self-adhesive label industry, is still thriving, continuing to grow for many years, and its profit margins have always been among the highest in the printing industry, which cannot help but attract the attention of the industry. The higher profit margins of the self-adhesive label industry are related to its own high technological content, especially the technological content of the self-adhesive materials.
Among self-adhesive label materials, compared with paper self-adhesive labels, film self-adhesive label materials have the characteristics of good water resistance, good transparency, high strength, and good durability. Therefore, their use in daily chemical and electronic products is increasing. According to the different types of film, self-adhesive film materials can be divided into polyethylene (PE), polypropylene (PP), polyester (PET), polyvinyl chloride (PVC), polystyrene (PS), polyolefin (PE and PP blends), and other types. Compared with the printability of paper, the biggest difference between film is that its surface is not absorbent. UV ink printing uses ultraviolet light to instantly dry the ink and it has good adhesion to the film surface. Therefore, at present, most printing companies use UV ink to print film stickers.
1.2 Preparation of UV label ink
Performance requirements for UV label ink
(1) Adhesion
For labels, the adhesion (also known as fastness) of the ink is the most basic requirement. Stick 3M-600 tape completely to the printed matter for 20 seconds, then quickly pull it off at a 45° angle and observe whether any ink comes off the tape. If more than 20% of the ink is peeled off, it can be determined that the adhesion of the printing ink to the substrate is poor. In this case, the problem can be solved in the following ways.
① Conduct corona treatment before printing. Corona treatment uses high frequency and high voltage to generate corona discharge on the surface of the treated plastic, producing low-temperature plasma. The surface of the plastic becomes rough and increases its wettability with polar solvents, thereby increasing the adhesion to the substrate surface.
② Print a primer. A primer is applied first, which improves the adhesion of the ink after printing.
③ Add an adhesion promoter to the ink to improve its adhesion.
④ Add a wax or silicone-based additive to the ink at a concentration of 2% to 8% to improve its adhesion. This type of additive can improve the smoothness of the ink surface, but it is only a deceptive tape fastness, commonly known as false fastness.
(2) Flow
The flow of the ink is closely related to its viscosity. An excessively high or low viscosity is not conducive to printing. The viscosity of the ink also varies in different seasons or with changes in temperature and humidity. Generally speaking, the ink can be used directly in summer. However, in winter, due to the lower temperature, 2% to 5% of ink conditioner should be added to the ink before use, and then stirred well before use. If too much black ink thinner is added, the ink will become too thin, which will affect the ink transfer and color reproduction of the printed dots. You can also consider adding a de-viscosity agent (also known as a viscosity reducer), which has the effect of reducing the ink viscosity, while the ink viscosity and yield value change very little. This allows the ink to adapt to some poor substrate materials and has better conditions to display printability. Therefore, controlling the viscosity and viscosity of the ink is quite important.
(3) Drying properties
The drying properties of UV inks also have a significant impact on label printing. If drying is too fast, it can easily cause dry plate phenomenon, while if drying is too slow, it can easily cause the back of the printed roll to stick and become dirty. Generally speaking, UV inks can meet the drying conditions of label printing machines because the printing speed of label printing machines is relatively slow, generally 20-70m/min, rarely exceeding 100m/min. When the ink does not dry completely, it is necessary to consider whether the printing speed is too fast or the curing speed of the ink formulation is too slow. In order to ensure the normal printing speed, a suitable amount of photo-curing initiator can be added, generally 1%-3%.
(4) Abrasion resistance
Among the requirements for ink performance on labels, abrasion resistance is the most common. This is because the finished printed label may be subject to friction during the labeling process or during transportation, which can damage the label surface. Before mass production, an abrasion resistance test must be performed. How do you choose an ink for labels that have high abrasion resistance requirements? First, choose inks and varnishes with a hard film and a smooth surface. Second, when the ink and varnish cannot meet customer requirements, wax or silicone additives can be added to the ink and varnish to improve the smoothness of the surface and meet performance requirements.
(5) Light fastness
For labels with lightfastness requirements, inks with high lightfastness ratings must be used. Otherwise, the labels will fade after a period of time due to sunlight and artificial light exposure, resulting in defective products and customer complaints. The general test method is to place the printed product in a lightfastness tester and select the appropriate test time and lightfastness intensity for testing.
(6) Other
① When encountering products with hot stamping requirements, try to avoid using inks and auxiliaries containing wax or silicone, as these types of auxiliaries will affect the subsequent hot stamping effect.
② During the printing process, when mixing spot colors or disposing of waste or leftover ink, avoid mixing inks from different manufacturers or series together. Otherwise, the phenomenon of non-miscibility of inks may occur, affecting the printed label products.
③ When printing electronic product labels, inks from the low-halogen series should be used. And the printing unit must be cleaned before printing to avoid contamination of the oil black, which will affect the printing quality.
④ Printed products produced by printing companies that undertake overseas printing business, such as the low-migration food labels required in Europe, should comply with local laws and regulations.
Although UV inks have the advantages of fast drying, good printing results, good scratch resistance and good solvent resistance, they often encounter problems during the printing and processing of self-adhesive labels. The most common problem is poor adhesion of UV inks to the surface of film materials.
Because UV label inks are mainly used for self-adhesive labels, and the substrates of self-adhesive labels are all kinds of plastic films, UV label inks are actually UV plastic inks. Printing on plastics is a very active area of the packaging printing market, and printing on plastic substrates is a growing and challenging market. UV inks are just right for this market because UV drying is a low-temperature instantaneous drying method with fast curing speed, which means faster production speed without affecting the plastic substrate; and because there is no need to use a heating drying device, it also reduces energy consumption and harm to the environment.
Unlike wood and paper, plastic is a non-absorbent substrate. It cannot rely on the penetration of the ink into the substrate to produce various mechanical anchors to achieve adhesion. Compared with metal, which is also a non-absorbent substrate, plastic is an “inert” material. There are almost no active sites on the surface that can react with the components in the ink, and no chemical bonds can be formed to achieve effective adhesion. Therefore, adhesion between plastic and UV ink is quite difficult, and usually only relies on the weak intermolecular forces between the ink and the plastic surface to generate mutual adsorption. This requires UV plastic inks to have a low surface tension and good wetting ability to the substrate. If the ink components contain a certain amount of polar groups (such as hydroxyl groups, carboxyl groups, etc.), they can form a certain amount of hydrogen bonds with some polar plastic surfaces or pre-treated plastic surfaces, which will greatly promote the adhesion between UV plastic inks and plastic surfaces. If the reactive diluent used in the UV plastic ink can slightly swell the plastic surface, thereby forming a thin interpenetrating network structure between the ink layer and the plastic surface, the adhesion between the UV plastic ink and the plastic surface can be significantly improved. Sometimes, in order to ensure that the UV plastic ink has high surface hardness and excellent resistance, the ink layer is required to have a high cross-linking density. However, the high cross-linking density produces excessive volume shrinkage, which is very detrimental to the adhesion of the ink layer.
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| Polythiol/Polymercaptan | ||
| DMES Monomer | Bis(2-mercaptoethyl) sulfide | 3570-55-6 |
| DMPT Monomer | THIOCURE DMPT | 131538-00-6 |
| PETMP Monomer | 7575-23-7 | |
| PM839 Monomer | Polyoxy(methyl-1,2-ethanediyl) | 72244-98-5 |
| Monofunctional Monomer | ||
| HEMA Monomer | 2-hydroxyethyl methacrylate | 868-77-9 |
| HPMA Monomer | 2-Hydroxypropyl methacrylate | 27813-02-1 |
| THFA Monomer | Tetrahydrofurfuryl acrylate | 2399-48-6 |
| HDCPA Monomer | Hydrogenated dicyclopentenyl acrylate | 79637-74-4 |
| DCPMA Monomer | Dihydrodicyclopentadienyl methacrylate | 30798-39-1 |
| DCPA Monomer | Dihydrodicyclopentadienyl Acrylate | 12542-30-2 |
| DCPEMA Monomer | Dicyclopentenyloxyethyl Methacrylate | 68586-19-6 |
| DCPEOA Monomer | Dicyclopentenyloxyethyl Acrylate | 65983-31-5 |
| NP-4EA Monomer | (4) ethoxylated nonylphenol | 50974-47-5 |
| LA Monomer | Lauryl acrylate / Dodecyl acrylate | 2156-97-0 |
| THFMA Monomer | Tetrahydrofurfuryl methacrylate | 2455-24-5 |
| PHEA Monomer | 2-PHENOXYETHYL ACRYLATE | 48145-04-6 |
| LMA Monomer | Lauryl methacrylate | 142-90-5 |
| IDA Monomer | Isodecyl acrylate | 1330-61-6 |
| IBOMA Monomer | Isobornyl methacrylate | 7534-94-3 |
| IBOA Monomer | Isobornyl acrylate | 5888-33-5 |
| EOEOEA Monomer | 2-(2-Ethoxyethoxy)ethyl acrylate | 7328-17-8 |
| Multifunctional monomer | ||
| DPHA Monomer | 29570-58-9 | |
| DI-TMPTA Monomer | DI(TRIMETHYLOLPROPANE) TETRAACRYLATE | 94108-97-1 |
| Acrylamide monomer | ||
| ACMO Monomer | 4-acryloylmorpholine | 5117-12-4 |
| Di-functional Monomer | ||
| PEGDMA Monomer | Poly(ethylene glycol) dimethacrylate | 25852-47-5 |
| TPGDA Monomer | Tripropylene glycol diacrylate | 42978-66-5 |
| TEGDMA Monomer | Triethylene glycol dimethacrylate | 109-16-0 |
| PO2-NPGDA Monomer | Propoxylate neopentylene glycol diacrylate | 84170-74-1 |
| PEGDA Monomer | Polyethylene Glycol Diacrylate | 26570-48-9 |
| PDDA Monomer | Phthalate diethylene glycol diacrylate | |
| NPGDA Monomer | Neopentyl glycol diacrylate | 2223-82-7 |
| HDDA Monomer | Hexamethylene Diacrylate | 13048-33-4 |
| EO4-BPADA Monomer | ETHOXYLATED (4) BISPHENOL A DIACRYLATE | 64401-02-1 |
| EO10-BPADA Monomer | ETHOXYLATED (10) BISPHENOL A DIACRYLATE | 64401-02-1 |
| EGDMA Monomer | Ethylene glycol dimethacrylate | 97-90-5 |
| DPGDA Monomer | Dipropylene Glycol Dienoate | 57472-68-1 |
| Bis-GMA Monomer | Bisphenol A Glycidyl Methacrylate | 1565-94-2 |
| Trifunctional Monomer | ||
| TMPTMA Monomer | Trimethylolpropane trimethacrylate | 3290-92-4 |
| TMPTA Monomer | Trimethylolpropane triacrylate | 15625-89-5 |
| PETA Monomer | 3524-68-3 | |
| GPTA ( G3POTA ) Monomer | GLYCERYL PROPOXY TRIACRYLATE | 52408-84-1 |
| EO3-TMPTA Monomer | Ethoxylated trimethylolpropane triacrylate | 28961-43-5 |
| Photoresist Monomer | ||
| IPAMA Monomer | 2-isopropyl-2-adamantyl methacrylate | 297156-50-4 |
| ECPMA Monomer | 1-Ethylcyclopentyl Methacrylate | 266308-58-1 |
| ADAMA Monomer | 1-Adamantyl Methacrylate | 16887-36-8 |
| Methacrylates monomer | ||
| TBAEMA Monomer | 2-(Tert-butylamino)ethyl methacrylate | 3775-90-4 |
| NBMA Monomer | n-Butyl methacrylate | 97-88-1 |
| MEMA Monomer | 2-Methoxyethyl Methacrylate | 6976-93-8 |
| i-BMA Monomer | Isobutyl methacrylate | 97-86-9 |
| EHMA Monomer | 2-Ethylhexyl methacrylate | 688-84-6 |
| EGDMP Monomer | Ethylene glycol Bis(3-mercaptopropionate) | 22504-50-3 |
| EEMA Monomer | 2-ethoxyethyl 2-methylprop-2-enoate | 2370-63-0 |
| DMAEMA Monomer | N,M-Dimethylaminoethyl methacrylate | 2867-47-2 |
| DEAM Monomer | Diethylaminoethyl methacrylate | 105-16-8 |
| CHMA Monomer | Cyclohexyl methacrylate | 101-43-9 |
| BZMA Monomer | Benzyl methacrylate | 2495-37-6 |
| BDDMP Monomer | 1,4-Butanediol Di(3-mercaptopropionate) | 92140-97-1 |
| BDDMA Monomer | 1,4-Butanedioldimethacrylate | 2082-81-7 |
| AMA Monomer | Allyl methacrylate | 96-05-9 |
| AAEM Monomer | Acetylacetoxyethyl methacrylate | 21282-97-3 |
| Acrylates Monomer | ||
| IBA Monomer | Isobutyl acrylate | 106-63-8 |
| EMA Monomer | Ethyl methacrylate | 97-63-2 |
| DMAEA Monomer | Dimethylaminoethyl acrylate | 2439-35-2 |
| DEAEA Monomer | 2-(diethylamino)ethyl prop-2-enoate | 2426-54-2 |
| CHA Monomer | cyclohexyl prop-2-enoate | 3066-71-5 |
| BZA Monomer | benzyl prop-2-enoate | 2495-35-4 |