The properties of ink binders significantly affect various properties of printing inks. Polyurethane ink binder has the advantages of easy use, stable performance, strong adhesion, etc., and can be dissolved in alcohol, ester, ketone and other solvents or their mixed solvents, and has developed rapidly. With the strengthening of people's awareness of environmental protection, the research and development direction of seeking low-boiling point, low-toxic or non-toxic solvents has become the ink binder. Although water-based inks have been commercialized, their performance has not yet reached the standard of solvent-based inks.
Polyurethane ink connecting materials include two types: polyester and polyether. Among them, polyester polyurethane has good adhesion and bonding strength to non-polar substrates (such as BOPP, PE, PET, etc.), and heat resistance. better. However, the disadvantage is that polyester polyurethane is more suitable for ester solvent system, and polyether polyurethane can just make up for this deficiency.
In this paper, starting from the formulation design, a self-made special polyol was selected to synthesize a polyurethane ink vehicle WANCOL913 that can be infinitely soluble in alcohol solvents. The application performance of the ink vehicle was tested, showing that the ink vehicle has strong adhesion and dispersibility. Good application properties, good pigment adaptability, shallow mesh transfer and reconstitution, and good anti-rebound properties.
I. Experimental part
1. Main raw materials and equipment
Main raw materials: isophorone diisocyanate (IPDI): industrial grade, Bayer company; homemade special polyols: homemade; ethyl acetate (EA): urethane grade, Tianjin Jincheng Chemical Plant; isopropyl alcohol (IPA) : Industrial grade, Jinan Hengrun Biochemical Co., Ltd .; Chain extender KL01: Homemade.
Main equipment: electric stirrer, oil bath, "quick hand" swing machine, proofing machine, scraper fineness meter, corona pen, etc.
In a round three-necked flask equipped with a thermometer, a stirrer, and a dry round-bottomed flask, the self-made special polyol and IPDI were sequentially added, and the temperature was raised to 100 ° C for 5 hours to make the -NCO content reach a predetermined value (di-n-butylamine titration analysis). Polymer; Dilute with temperature and dilute with solvent, add the chain extender KL01 dropwise under high-speed stirring, and stop the drop when the viscosity reaches the required value, to obtain a single-component solvent-based polyurethane linker with appropriate solid content and viscosity.
Application performance test: The prepared polyurethane ink connecting material is prepared into an ink, and the viscosity, adhesion, gloss, color concentration, alcohol solubility, and anti-rebound properties of the ink are tested.
(1) Viscosity: GB / T13217.4-1991 (coated with No. 4 cup);
(2) Adhesiveness: blow dry the printed coating film, and then apply a special 3M tape on the printed film. After uniform rubbing, peel off quickly, and check the surface state of the printed film after peeling. The visual measurement criteria are: good-more than 90% of printed film residue; pass-60 to 90% of printed film residue; poor-less than 60% of printed film residue;
(3) Gloss, color density, reconstitution: visual inspection;
(4) Anti-back tack: The printed coating film is blow-dried and placed in an oven at 60 ° C. for 10 minutes.
Results and discussion
1. Outstanding pigment dispersion
The connecting material is a colloidal fluid with a certain viscosity. Its function is to act as a carrier for pigments. It mixes and connects solid particles such as powdery pigments. The colorant is evenly dispersed in it and depends on its wetting effect. It is easier to be ground on the grinding machine. For pigment wetting and dispersion, in addition to selecting a suitable dispersant, high-quality binders also play a very important role in dispersion. Good dispersion results in excellent printing adaptability, because good dispersion can not only provide low fineness, high gloss, high color density and hiding power, but also extend the storage stability of the ink, not thicken, and always have sufficient fluidity .
Wanhua Chemical (Beijing) has been developing polyurethane ink binders since 2011. The WANCOL903 series of alcohol-soluble products has been recognized and adopted by many famous ink manufacturers for its excellent application performance and wide adaptability. The alcohol-soluble products are more environmentally friendly and cost-effective, and they have gradually been well received and favored by the majority of ink manufacturers.
WANCOL913 uses special self-made polyol as the main raw material and is produced by a unique and stable production process. Not only improves the stability of the connecting material itself, but also improves the adaptability to the pigment and the color development, and more effectively ensures the storage stability of the ink. Its stability is compared with the sample of a domestic manufacturer and the import of a similar mainstream product under the same ink formulation conditions as shown in Table 1.
Table 1 Comparison of stability and dispersion
Ink stability level (change in viscosity of four cups after 1 week storage at 50 ° C): A. ≤ 5S, B. 5-10mPa.S, C. ≥ 10mPa.S.
It can be seen from Table 1 that the inks prepared by WANCOL913 have good stability and good pigment dispersibility. Resin exceeds a certain imported product.
2.Excellent adhesion performance
Different resin system inks are suitable for different printing substrates. The integrated ink requires strong adhesion to substrates of different polarities (BOPP and PET film ). According to the "similar compatibility" principle, only when the matrix resin is similar or similar, the printing substrate and ink will have good Adhesiveness. In the ink system, the binder resin plays a key role in adhesion. Polyurethane resin with its excellent abrasion resistance, scratch resistance, solvent resistance, adhesion properties and good low temperature properties, high gloss, gloss retention, and application performance has a wide range of adjustability, can meet various With different requirements, it has become more and more widely used in inks, and has become one of the most important resin materials. It plays an important role in screen printing, plastic packaging and composite film printing.
WANCOL913 uses a unique self-made polyol, which significantly improves the strength of polyurethane and its adhesion to BOPP and PET films, and its performance even exceeds similar imported products abroad. Its adhesion performance is shown in Table 2 under the same ink formulation conditions as a domestic manufacturer's sample and an imported similar mainstream product.
Table 2 Comparison of adhesion performance between OPP film and PET film
The excellent adhesion performance makes WANCOL913 inks with or without accelerators.
The resolubility of the ink is a crucial factor that determines the printing quality and efficiency. In particular, the printing of human faces and fruit patterns requires higher resolubility. In color ink printing, the good resolubility can not only make the color fully display, but also can solve the problem of light screen blocking of printing plate.
When the ink with insufficient resolubility is used for shallow screen printing, due to the high-speed rotation of the cylinder in the ink tank in the light screen part of the printing plate, the remaining ink is not easy to be re-dissolved by the ink in the ink tank, resulting in the screen holes being printed lighter and lighter. , Which ultimately results in "lost points". Table 3 shows the resolubility test results of different color inks.
Table 3 Re-solubilization performance of color ink
Resolubility grade: A means clean, B means cleaner, C means partial dissolution, and D means insoluble. The solvent was ethanol: ethyl acetate = 1: 1.
Tests show that: WANCOL913 has good resolubility on red, yellow, blue, black and white inks. With suitable dispersant, it can better meet the needs of most applications.
Good resolubility can meet modern high-speed printing presses, improve production efficiency, and reduce the rejection rate, which in turn reduces production costs. WANCOL913 is used for alcohol-soluble ink, which is both environmentally friendly and low cost.
Anti-adhesion is an important physical property index of printing ink. Gravure printing is a printing method with high ink supply, good tone reproduction, and fast printing speed. After the ink is transferred to the printing substrate through the printing plate, it passes through the drying tunnel and is wound up after the organic solvent is quickly evaporated and dried. When rewinding after passing through a high-temperature drying tunnel, the surface temperature of the printed film is generally between 40 ° C and 60 ° C. At the same time, due to the rewinding pressure, if the anti-adhesion of the ink itself is not good, it will cause serious rewinding blocking. .
WANCOL913 uses self-made special polyols, which not only ensures alcohol solubility, but also improves the anti-stickiness of the ink. At the same time, the secondary chain extension process significantly improves the strength and anti-stickiness of the dry film of the binder, which can meet the requirements of high-speed printing.
Table 4 Comparison of anti-sticking properties of red ink
Pros and cons of anti-stickiness: A, B, C, D in this order means non-sticky, slightly sticky, sticky, and very sticky.
5.WANCOL913 Quality Index
See Table 5 for the quality index of alcohol-soluble polyurethane ink binder WANCOL913.
Table 5 WANCOL913 quality indicators
Third, the conclusion
WANCOL913 has outstanding pigment dispersibility and adaptability, high gloss and color density of ink, and good storage stability. Good adhesion to OPP film, can use less or no accelerator, reduce ink cost. Excellent resolubility can meet high-speed printing, improve production efficiency, reduce scrap rate and production cost. With good anti-back tack, it can be printed and rolled quickly. Completely alcohol-soluble, environmental protection and safety.