At present, plastic gravure inks are mainly divided into solvent-based gravure WE printing inks, chlorinated polypropylene inks, polyamide inks and polyurethane inks. At present, chlorinated polypropylene inks commonly used in the country are composed of chlorinated polypropylene resin, pigment, toluene, xylene and the like. Alcohol-soluble gravure ink is made of alcohol-soluble polyammonium, and contains trace amounts of toluene and benzene. Alcohol ester inks (benzene-free, ketone-free) are alcohol-soluble polyurethane inks, and the diluent is ethyl acetate and ethanol. They are low-odor and do not contain benzene and ketones. Water-based gravure ink is an environmentally-friendly ink composed of water-based resin, advanced pigments, additives and water.
Second, environmental protection problems of plastic film gravure printing There are many cases of pollution caused by the problem of ink: Gansu potato chips, milk powder, beef jerky, candy, dried lentils and other packaging bags , Chengdu, Chongqing Weiwei beans, spicy food, Zhejiang Aluminum snack food packaging, Hebei, Shanxi biscuit packaging, Qingdao clothing composite packaging bags, etc.
Reason: Solvent type gravure printing ink uses toluene xylene as solvent, which accounts for 30% ~ 50% of gravure printing ink. Highly volatile solvents contain aromatic hydrocarbons, which are toxic and flammable. The measured benzene content in Gansu food bags was 9.7 mg / m2. Excess benzene is extremely harmful to the human body. It is a carcinogenic chemical that can cause leukemia and cause serious pollution to the production environment. The gravure printing speed is high, and volatile inks must be used to meet the printing requirements. This makes gravure environmental protection issues particularly prominent in all printing processes, mainly organic solvents such as benzene and residues of heavy metals.
Standards and usage regulations: In North America, Europe, Japan and other countries, the use of benzene-based inks has been banned, and only environmentally friendly gravure inks can be used. China has promulgated the Food Sanitation Law and implemented the QS certification and market access system. On August 1, 2009, the new national standard GB / T2008 "Packaging plastic composite film, bag dry compounding, extrusion compounding" was stipulated: the total amount of residual solvent is less than 5mg / m2, and benzene solvents are not detected. Inks and adhesives in composite packaging materials do not currently have separate sanitary standards or nationally uniform product standards. Only corporate standards.
Third, the characteristics of plastic film water-based gravure printing ink:
Water-based inks are universal inks for surface printing and back printing with high solid content and low viscosity. Water-based inks get rid of organic solvents other than alcohols, improve the working environment, eliminate toxic and harmful substances in solvent-based inks, and eliminate the pollution of packaged goods. It is used in corona-treated BOPP, PE, PVC and other film printed food bags, pharmaceutical packaging bags, beverage bags and other packaging and printing products. Adapt to printing speed of 30 ~ 100m / min, non-combustible, non-explosive, non-toxic, non-irritating, stable ink, colorful, non-corrosive printing plate, easy operation, good adhesion after printing, strong water resistance, etc. The speed can meet the needs of the printing house, and four-color overprint and spot color printing are available.
Ink and wash applications are mainly flexographic printing and gravure printing. Flexographic ink has been widely used in the printing of packaging paper, cigarette cases, paper boxes and other paper products. Reason: Paper products evaporate and absorb and dry well. The application of water-based gravure inks to plastic film printing is still in its infancy in China. This is mainly because water-based inks cannot fully meet the performance of solvent-based inks in terms of adhesion and printing speed in gravure printing.
Water-based ink is the only non-toxic ink approved by the American Food and Drug Association.
Fourth, WE plastic film water-based gravure printing ink case analysis and performance comparison table The case analysis is as follows:
Case 1: Gravure printing machine, electric engraving plate, plate depth 45um, printing speed 40m / min, drying temperature 60 ~ 70 ℃, printing material: BOPP film, ink type: WE-0833 Tianlan ink.
Case two: gravure printing machine, electric engraving plate, 45um plate depth, printing speed 70m / min, drying temperature 60 ~ 65 ℃, printing material: BOPP film, water-based laminating film after printing. Ink Variety: WE-0863 green ink.
Printing speed: In the first and second printing cases, the printing speeds are 40m / min and 70m / min respectively. Water-based ink gravure plastic film printing can be printed without revision. If light printing is changed, the printing plate depth is 15-25um, and the printing speed can be increased to 100m / min or higher. Drying temperature: 50 ~ 60 ℃ is suitable, and the air volume should be large, so that the ink transferred to the film can be dried quickly. In the second case, the printing speed of the gravure printing machine was 30m / min faster than that in the first case because of the good ventilation and drying conditions.
pH value: The pH value of the water-based ink is controlled at 8 ~ 9 before leaving the factory, and generally does not need to be adjusted.
Ink viscosity: The accuracy and consistency of ink viscosity during gravure printing is key. If the viscosity is too high, the transfer performance of the ink will be poor, and it will easily cause ill effects such as dirty printing and paste printing. If the viscosity is too low, it will cause light color, enlarged dots, and uneven ink transfer. The viscosity of water-based inks has been controlled before leaving the factory, and the viscosity is controlled at 15 ~ 25s / 25 ℃. The viscosity can also be adjusted with pure water during use.
Fastness to adhesion: BOPP films and other commonly used in printing are non-polar polymers, and surface treatment must be performed before printing. In the first and second cases, the film used was a BOPP film with a corona-treated surface tension of 38 dyne / cm, and it showed excellent adhesion after printing. Compared with similar products at home and abroad, the adhesion fastness of WE-type plastic film water-based gravure ink printing is quite good.
Gloss: The gloss of water-based ink gravure plastic film printing and paper printing to achieve and exceed the gloss of solvent-based printing products, in both cases received unanimous praise.
Peel strength: In case 2 of printing of water-based ink gravure plastic film, the BOPP film after lamination was tested: longitudinal peel strength 1N / 15mm, transverse peel strength 1N / 15mm. Generally, the peeling strength of chloroacrylic ink printing products is 1.5-2.5N / 15mm, and the peeling strength of benzene solvent-based ink printing products is greater than the peeling strength of chloroacrylic ink printing products and the peeling strength of water-based ink printing products. In the second case, the water-based laminating adhesive is used. It has high bonding strength with water-based inks. Therefore, the plastic film gravure water-based ink must be laminated with the matching water-based laminating adhesive in order to meet the requirements of peel strength and truly Only by meeting environmental protection requirements can it be accepted by the market.
Temperature and humidity: The temperature in the printing shop should be controlled between 18 ° C and 28 ° C, and the humidity in the printing shop should be controlled between 55 ° C and 75 ° C. Of the printed cases, only case two met the temperature requirements.
From the case of ink printing, we learned that the color printing packaging factory's selection and requirements for gravure water-based inks: water-based inks must have a good price-performance ratio, high color density, stable hue, high gloss, low viscosity, high adhesion fastness, fast drying, and Meet the needs of low, medium and high speed printing. Color printing and packaging factories agree with and accept gravure water-based ink printing.
Conclusions after testing and production of the three inks: 1 # The main deficiency of the main product is that the adhesion is slightly worse, the viscosity is large, and it can barely be used in production. The 2 # product can be used on 30 ~ 100m / min gravure printing machine, but it also has the defect of poor adhesion fastness. After production and printing, it is proved that the performance of WE-type water-based gravure ink has fully met the requirements of gravure printing machine production. It has reached the advanced level of similar products at home and abroad in the main performance indicators such as adhesion fastness, drying speed, color density and gloss. .
V. Precautions for using WE plastic film water-based gravure ink:
1. Before use, clean the printing plate, scraper, ink tank, etc. thoroughly with solvent, washing powder water, and clear water. There must be no residue. The original ink tank needs to be covered with a plastic film.
2. Before use, adjust the viscosity of the ink with demineralized water or purified water, ethanol, isopropanol, and control the viscosity: 10 ~ 20s / 25 ℃, the addition amount is 5% ~ -10% of ink. After adjusting the viscosity, do not add water to the ink during printing. If new ink is added, adjust the viscosity again to maintain the same color before and after printing.
3. The printing plate adopts electric engraving plate or laser engraving plate, and the plate depth is preferably between 15 and 25um. Shallow plates can increase printing speed and save ink. It can also be printed without changing the original depth.
4. The drying temperature is preferably 50-70 ℃, and the air volume should be large so that the ink can dry quickly.
5. After the ink enters the tank, let the printing plate idle for 5min to wet the printing plate and stir. If the printed products are stopped, do not stop the printing plate from rotating, so as not to cause jams, such as plugs can be cleaned with a special plate washing solution.
6. If the pH value of ink is changed during printing, a special pH adjuster can be added to keep the pH unchanged.
7. Do not mix this product with other types of ink to prevent scrapping due to incompatible products.
Technical index of WE type plastic film water-based gravure ink product:
Color (scrape method): approximate standard sample tinting strength (scrape method): 95% ~ 105% of standard sample
Chroma (scraper fineness method): <15um
pH value: 8.0 ~ 9.0
Viscosity (check 3 cups, 25 ℃): 10 ~ 25s
Initial Dryness (Scraper Fineness Method, 25 ℃): 10 ~ 30mm
Adhesion fastness (after 24h of scratching): rubbing fastness 100% without peeling peeling fastness: 100% without peeling Inspection report of National Printing and Decoration Product Quality Supervision and Inspection Center:
TQTOO-0713-2009: VOC% standard requirements ≤ 30 measured 0.1
TQTOO-0723-2009: Lead (Pb) content mg / kg ≤ 90 measured 0.18.
Mercury (Hg), chromium (Cr), and cadmium (Cd) were not detected.
Seven, cost calculation:
Chlorinated polypropylene ink is priced at about 20 yuan / kg, and about 25 yuan / kg after adding the solvent. The price of alcohol ester ink is 20 ~ 30 yuan. The price of water-based ink is 30 ~ 35 yuan / kg. Because the ink printing plate is shallow and the plate depth is 15-25um, the ink consumption per square meter is about 75% of the solvent ink, and the actual cost is 22.5-28.3 yuan / kg. The cost of printing with water-based gravure inks is slightly higher than that of solvent-based inks and alcohol-based inks. Its excellent cost performance should be the best choice for color printing packaging factories.
Eight, the problems in the promotion of plastic film water-based gravure printing ink:
1. Due to the high technical difficulty of the production of this product, domestic ink manufacturers have not yet produced inks with better cost-effectiveness for color printing and packaging factories to choose from. The printing speed of our products is below 100m / min. Other properties such as adhesion fastness, water resistance, gloss, fluidity and printability have reached or exceeded solvent-based inks.
2. Equipment: The length of the drying tunnel of the original gravure printing machine is 1 ~ 1.5m. The original printing plates are all deep. The original ink tank cannot be cleaned. The original temperature control facilities may not be matched. Improve. It is reported that a company in Guangzhou has produced a gravure printing machine dedicated to water-based inks, which is good news.
3. Policies and regulations: At present, there are no related regulations on the production and use of plastic gravure inks in China, and there is no effective binding force. Color printing factories generally do not have the urgency to change the original production conditions, or they have weak enforcement requirements.
4. Ink production exceeds supply, resulting in disorderly price competition, cost and quality, sacrificing environmental protection requirements, as long as the price is slightly higher, it is unwilling to use it.
5. Gravure printing machine captains and operators in color printing plants are unfamiliar and unwilling to adopt them, especially those factories that use piece-rate compensation.
Plastic film water-based gravure ink is an inevitable trend for the development of gravure printing as an alternative to solvent-based inks and reducing alcohol-soluble inks. The main varieties are: magenta, medium yellow, sky blue, black, white, red, green and so on. Beijing Yingkefan Chemical Product Co., Ltd. has launched a national invention patent for the "plastic film water-based gravure printing ink" with completely independent intellectual property rights, and has now entered the actual trial.
In production practice, the author deeply felt the pollution and poisoning of the traditional gravure printing to the production environment and the helplessness of the printing workers. I would like to work with friends in the packaging and printing industry to work together for mutual benefit and win-win, and serve our country's green packaging printing. Is willing to work with colleagues in the packaging and printing industry to embrace the spring of environmental protection printing!