The quality of the ink directly affects the printability and the quality of the printed packaging products. The quality of the ink is firstly the hue to meet the printing needs, followed by the viscosity and viscosity of the ink to meet the printing process, and then the dryness, friction resistance, and light fastness of the ink to meet the requirements of the subsequent process and product circulation of the product. More recently there has been a demand for low migration of inks. With the evolution of the diversity and complexity of printing processes, the performance requirements for printing inks are also gradually increasing, and the fineness, gloss, and transparency of inks are all used as routine ink testing items. This article briefly introduces some of the more important test items.
The first is the standard ink proofing. Many mainstream UV lamp suppliers are involved in UV LED technology. At the same time, as the European Union revised the WEET standard (more detailed than RoHs), it is proposed to completely ban mercury lamps by 2015. At this time, the entire industry and related products will face a new opportunity.
Another reason why the market is optimistic about UV LED is that UV LED has achieved many applications that mercury lamps cannot do. Some ink suppliers have also developed corresponding inks with UV LED system suppliers, such as the EkoCure series of inks developed by Flint Group. Bottomless film products can be printed on Mark Andy's narrow-width flexo printing machine, and OMSO's full-servo multi-color screen printing machine can directly print plastic and glass bottles using UVLED technology.
Domestic UV LED technology and market situation
The domestic LED industry started a little later than foreign countries. At present, the electronics, optics, glass crafts, and spraying lamp industries have developed quite maturely, while the printing field has just started. A few years ago, in the advertising inkjet industry, due to domestic vicious competition, the UV inkjet market was flooded with low-grade chips and indigenous packaging products, which caused a bad initial impression of poor quality domestic products. On the contrary, although the prices of foreign products High, but sales have been good.
Although the domestic UV LED has just started, it has a huge prospect. The general trend of packaging printing must be environmental protection, effectiveness, and energy saving. UV LED is very consistent with the current industry development trend, and can help printers open up more fields and applications, taking advantage of the advantages of UV LED technology, coupled with the intervention of some large ink manufacturers , UV LED technology will bring a new opportunity to the printing industry.
The prerequisite for the ink testing project to be carried out is to carry out standard ink proofing. If the proofing process is not standard, the proofs are not uniform enough, or the repeatability is not good, then the subsequent test data will be meaningless. ISO 2834 specifies the standard ink proofing method. For example: use the IGT C1 printability Tester to evaluate the offset printing four-color ink. Under the specified temperature and humidity conditions, use the IGT quantitative ink injector to measure the specific gravity of the ink through a high-precision balance. After setting the printing pressure and speed, take a certain amount of ink and disperse the ink evenly in the ink distribution unit of the C1 printing suitability meter. After the rubber printing plate is inked, place the printing plate in a high-precision balance and reset it to zero; The evaluation is printed on standard test paper and the printed disc is weighed to obtain the weight of ink transferred to the substrate. According to ink specific gravity, ink transfer amount and printing area, the thickness of ink layer can be obtained. In this way, a sample that meets the requirements can be obtained for subsequent ink testing.
The hue and transparency of ink is one of the basic items of ink testing. According to the ISO 2834 proofing method guidelines, the ink to be tested is printed on standard paper that meets the requirements, and the thickness of the ink layer is controlled to be 0.7-1.1 μm. After drying, use a Spectrophotometer that meets the standards, set the measurement conditions and select the correct pad according to the standard requirements, and measure the CIE L*a*b* data of the ink proofing strip, so as to obtain the difference between the ink color and the standard value and the ink color. Transparency, to evaluate the hue and transparency of the ink.
According to ISO12634, use the IGT tackTester tack Tester to test the tack of offset printing ink. Under the specified temperature and humidity conditions, set the ink distribution speed and time. Adjust the constant temperature water area, fill the ink with the IGT quantitative ink injector, and start to distribute the ink. With the change of time and speed, the viscosity of the ink begins to fluctuate. During the test, you can connect to the software to record the measurement data or directly view the viscosity value at fixed intervals on the device to evaluate the viscosity of the ink. If the viscosity is too high and the adhesion is low, it is easy to produce paper fluff; on the contrary, if the viscosity is too small and the adhesion is too strong, it will affect the transfer of ink, so that the correct color reproduction cannot be obtained during the printing process.
For paste ink (offset printing), the viscosity of the ink can be tested according to the ISO12644 drop stick method. In the specified temperature and humidity environment, adjust the constant temperature water area, use the IGT Viscometer Laray Viscometer, take a certain amount of ink (enough to fill the gap between the drop rod and the ring hole), put the drop rod on the top of the ring hole and start pushing the ink and put the drop Push the rod down to coat the surface of the drop rod and the surface of the ring hole with an even ink layer; when testing, place the drop rod on the top of the ring hole and add weights, then push the button that fixes the drop rod to slide the drop rod down , and press the timer on the device at the same time; after the test, according to the weight value of adding different weights and the corresponding falling time of the drop bar, the viscosity curve of the ink can be calculated with the help of software, and the viscosity of the ink can be evaluated by this. If the viscosity of the ink is too high, it will easily cause the printed sheet to be dirty, ink transfer, uneven ink distribution, paper wool and paper powder will be pulled off, causing the layout to paste or bloom; if the ink viscosity is too low, it will easily cause printing bars caused by slippage Marks, as well as bad imprints caused by poor ink transfer, such as light, floating and dirty.
Ink dryness (penetrating drying) testing can be carried out by using the IGT printing suitability Tester to spread the test ink on standard paper, and then pressing it with blank standard paper after a certain period of time at a fixed pressure. According to the standard paper pattern when pressing The dryness of the ink was evaluated by the amount of ink transferred to the blank standard paper. The more ink transferred, the slower the drying speed of the ink. If the time is short, the back of the printed matter may be smudged due to the slow drying speed of the ink.
The rubbing resistance of the ink can be tested by the IGT QuartantTester after the color development and sampling of the IGT printing suitability Tester; The xenon lamp box measures the color status of the simulated printed matter after a certain period of time to evaluate the light fastness of the ink.
At present, publishing and packaging printed matter are gradually developing in the direction of personalization, diversification and high-grade. In order to meet the new changes in the printing market, printing companies continue to update and improve printing equipment, and there are various types of printing substrates. In order to meet the printing needs of high-quality products in the market, the requirements for various performance indicators of inks are getting higher and higher, and the multiple test items of inks are gradually being paid attention to. More and more large and medium-sized printing and packaging companies have purchased or are purchasing IGT series. Inkfish paper testing equipment to better control the printing quality and meet the requirements of end customers.
