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Precautions for using benzene-free ink
Time: 2013-05-08 Source: Packaging Frontier Reading: 13022 times
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Wenzhou Junchuan Machinery Equipment Co., Ltd.

In recent years, the state has attached great importance to the safety of food and its packaging materials , and has successively introduced relevant regulations and standards. The implementation of the Food Safety Law in June 2009 and GB9685-2008, and the implementation of the new GB / T10004-2008 national standard in August, put tremendous pressure on the flexible packaging industry. GB9685 and GB / T10004 stipulate that in addition to the detection of benzenes, the total residual solvent must not exceed 5mg / m2. This has a lot of impact on the color printing industry, mainly gravure printing in the flexible packaging industry , especially in the process of using benzene-containing inks to benzene-free inks, the increase in the cost of color printing packaging and many printing problems encountered during the operation. It's a headache. Aiming at the problems in the use of benzene-free inks in gravure, the author briefly explains the knowledge and experience of using benzene-free inks.
Domestic and foreign ink companies have introduced various systems of benzene-free inks, which can be basically divided into three types of systems:
I. Acrylic copolymer modified alcohol-soluble system inks, mainly for BOPP film printing. These inks use acrylic resin as the binder and alcohol (ethanol) as the real solvent; esters (butyl ester, ethyl ester) as auxiliary solvents. The volatilization rate is used as a thinner for such inks.
The common problems of alcohol-soluble inks in gravure printing are:
1. Shallow screen printing small dots are easy to lose, and difficult to print;
2. Severe blocking phenomenon and poor fatigue resistance. Taking printing speed of 140m / min as an example, the printing viscosity after dilution is 15s (No. 3 Zahn Cup). After 20min, observe the printed sample, the blue and red light net parts. There is a slight blockage, and the printing effect is significantly better year-on-year after wiping the surface with decontamination powder; the same process is unchanged, the ink viscosity is reduced to 12 seconds, the relative duration is longer, but it is emphasized here that if the printing viscosity is not strictly controlled ( Relative to benzene ink printing, the blocking is relatively slight when the viscosity is high), especially when the printing viscosity is getting higher and higher, the blocking phenomenon will be more serious, causing print quality problems.
At present, domestic alcohol-based inks are relatively mature, such as New Oriental, Sichuan Development and other ink companies. When printing BOPP, alcohol-soluble white inks are more mature and can reduce the cost of printing.
2. Chlorinated polypropylene-modified benzene-free inks. These system inks are ester-soluble inks, which mainly use n-propyl ester, ethyl ester, and butyl ester as diluent solvents. Some manufacturers need to add a small amount of methyl ethyl ketone to prevent ink precipitation and agglomeration. Increase ink solubility. This type of system ink is also mainly for BOPP film printing.
These inks are more expensive than polyurethane- modified inks, and the main purpose is to gradually replace the benzene-chlorinated polypropylene inks that have been used for more than two decades, but the overall cost is still higher and contains chlorine. At present, it is mostly used in light food packaging such as instant noodles. BOPP / VMCPP dry lamination has a peel strength of 0.8 ~ 1N, and BOPP / PE dry lamination has a peel strength of 0.4 ~ 0.7N. These inks have more problems in gravure printing than benzene-chlorinated polypropylene inks. As an aromatic solvent, toluene is the most suitable among solvents in terms of boiling point, volatility, and solubility of the resin. There is almost no comparable solvent among all solvents. Therefore, in the printing, only the solvent of toluene can also maintain the solubility and release of chlorinated polypropylene ink. However, in the use of modified chlorinated polypropylene non-benzene inks, the substituted solvents, n-propyl ester and butyl ester are inert solvents with high boiling points and difficult to volatilize. In addition, the solubility of the ink resin is relatively poor. During printing, if the printing viscosity is not controlled for a long time and the real and auxiliary solvents are not replenished in time, it will cause great print quality problems.
At present, the relatively mature chlorinated polypropylene-modified benzene-free inks in China include New Oriental Ink-2010NT series, Bauhinia GSK, etc. When replacing such benzene-free inks, please consult the technical staff of the ink company in time for relevant precautions.
3. Polyurethane-based benzene-free inks are currently divided into benzene-free ketones and benzene-free ketones. They are mainly for PET, NY (BOPP general purpose) printing and cooking needs, but strong ink companies have relatively introduced BOPP and PET. Integrated ink, alleviating problems such as ink replacement and increasing inventory. National standards do not prohibit the use of methyl ethyl ketone solvents. The advantage of benzene-free low-ketone polyurethane ink is to improve the printability by using the strong solubility of methyl ethyl ketone in the polyurethane binder (including issues such as light screen printing, knife wire, knife line, etc.).
These inks generally use four solvents: methyl ethyl ketone, n-propyl ester, isopropyl alcohol, and butyl ester. Methyl ketone is mainly used as the dissolving resin, and n-propyl ester, ethyl ester, and butyl ester are mainly used to adjust the solvent evaporation of the ink (n-propyl ester). (The volatilization rate is between butyl ester and ethyl ester). If n-propyl ester solvent is not used, the ethyl ester volatilizes quickly, which causes dry plates, block plates, and shallow screens to be difficult to print. , Anti-stick, odor and other phenomena.
When I do printing experiments in many small color printing factories, the common problem is that n-propyl ester is difficult to buy and the price is high. Many manufacturers are unwilling to use n-propyl ester solvents, coupled with slow machine speed (large ink loading), The drying system (air volume) is poor, and serious odor or anti-sticking occurs after compound curing. Large and medium-sized color printing companies have excellent machinery and equipment, and the machine speed is basically about 200m / min. The drying system is better. In addition, the cooling effect on the printing machine is good. The overall printing effect is comparable to or even brighter than that of benzene ink. Benzene-free and ketone-free polyurethane inks use n-propyl ester, butyl ester, ethyl ester, isopropyl alcohol, and n-butanol. Generally, only two solvents, n-propyl ester and isopropyl alcohol, are used as diluents.
No matter which type of system is benzene-free ink, there are common points in gravure printing: easy blocking, shallow screen printing is less effective than benzene ink, long-term printing fatigue resistance is not as good as benzene ink, and it is sensitive to the scope of the environment, especially Under high temperature and high humidity environment, it is prone to scratching, cleaning, fogging, anti-sticking, and heavy odor (resin, ester taste). The most obvious difference is that benzene ink has been used in the flexible packaging industry. The benzene ink has not high viscosity requirements, so even if the viscosity control is not very strict, the impact on printed products is slight or no difference. This is mainly benzene. The release properties, anti-fatigue properties of ink binders and several applicable solvents have great tolerance for the printing environment and printing requirements; while the release properties and other properties of benzene-free inks are not as good as those of benzene inks, but butyl esters, Solvents such as n-propyl ester and n-butanol are commonly referred to as high boiling point inert solvents. Such solvents have good binding with the ink, and are less volatile after mixing, resulting in more ester residues; but do not use slow-drying solvents. Shallow screen transfer and printing suitability have a greater impact. Therefore, when using a variety of benzene-free inks, operations should be strictly performed in accordance with the process standards provided by the ink company, and the previous random operation should not be used; the higher the requirements for mechanical equipment, such as the faster the machine speed, the printing effect and printing cost are both It will be guaranteed and improved, especially the better drying system (machines designed to install and install air in proportion to the air intake and exhaust air) have more advantages in volatile emissions of benzene-free inks. This also requires special attention to the oven temperature when using benzene-free. If it is too high, it will have a more serious impact on the release of benzene-free ink, because the high temperature will cause the benzene-free ink binder and the solvent to quickly volatilize and cause surface drying. At the same time, the use of benzene-free inks should also pay attention to changes in the workshop environment, especially the impact of high-temperature and high-humidity seasons on the printing of benzene-free inks. When the temperature is 30 ° C and the humidity is more than 70%, blockages, knife lines, A series of printing problems such as scratching.
At present, various domestic manufacturers of benzene-free inks continue to update and improve their product performance to meet market packaging needs through research and development. When color printing manufacturers use benzene and benzene-free inks alternately, it is recommended to communicate more with the technical service personnel of the ink company. Reserve the process standards and experience of using benzene-free inks, so as to avoid economic losses and customer losses caused by replacement of new products.

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