At present, China's flexible packaging technology has developed rapidly, and the level has continued to increase. The flexible packaging materials produced are of various styles. Among them, composite flexible packaging materials have now become one of the more mature major packaging materials in China. For example, the film substrates used are PET, BOPP, PE, CPP, and AL, etc. In the future, the trend of flexible packaging will develop in the direction of high barrier properties and high temperature cooking resistance. In particular, external flexible packaging materials such as food and pharmaceuticals require high-temperature anti-virus, environmental protection and sanitation and other high-performance. This requires a composite printing ink that is suitable for such high-performance conditions and suitable for high-temperature cooking resistance. As a result, high-temperature retort-resistant gravure plastic composite inks came into being.
Generally speaking, high-temperature retort-resistant gravure plastic composite ink is generally composed of a coloring material, a grinding resin, a polyurethane binder, a solvent, and a part of an auxiliary agent. High-temperature resistant cooking pigments for gravure plastic composite inks must first be resistant to solvents, secondly they must be resistant to high-temperature cooking, and resistant to migration, and can withstand temperatures above 150 ° C without decomposition and discoloration. According to the standard, all black pigments used in inks are carbon black; most of the white pigments are rutile titanium dioxide; among the gravure cooking inks, they are the most stable and resistant pigments. The two types of inorganic pigments have heat resistance and migration resistance. Unbeatable, especially its heat resistance far exceeds 300 ℃. Color inks should be tested and selected conditionally, for example, pigmented condensation azos, benzimidazolone azos, phthalocyanine blue, and phthalocyanine green. They can all undergo discoloration at a high temperature of 200 ° C.
The binder used in gravure cooking inks is mainly polyurethane. The resin is the backbone of the ink. The resin molecules generally contain -NCO groups, the degree of polymerization of the molecules is less, but the molecular structure is complex and there are many types. Among them are toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polyphenyl polymethyl polyisocyanate (PAPI), and trihydroxy polyether (glycerin polyether). The commercially available polyurethane binder for gravure cooking inks is a modified polyurethane monomer resin solution that introduces some important molecular functional groups, mainly divided into two types, polyether or polyester. Gravure made from this type of polyurethane The cooking ink has high tensile strength, good oil and solvent resistance, excellent heat insulation and barrier properties after film formation; especially high temperature cooking resistance. Generally, the cooking temperature design conditions are above 150 ° C. The use of HDI or MDI monomers in cooking ink formulations can reduce the yellowing of TDI-type polyurethanes at ultra-high temperatures. In addition, when selecting the polyurethane resin liquid for ink, the ink must be made to have excellent adhesion to plastic films, the ink film has good heat resistance and boiling resistance, good solvent release, and low residue. Good wettability and high gloss.
Solvents and auxiliaries are an important part of the gravure composite cooking ink. It is a vital part of the ink manufacturing process and ink printing adaptability and film formation. The main solvents of the ink are esters, ketone alcohols, aromatic hydrocarbon solvents; the auxiliary agents are mainly dispersant, antistatic agent, anti-sticking agent, etc.
In summary, traditional gravure white ink primers are prone to yellowing at lower temperatures (such as about 150 ° C). Some users need to withstand high temperatures above 200 ° C (such as printing) in post-processing after printing is completed. The printing film with white ink and the steel plate are compounded at a high temperature of 220 ° C, and are used instead of the iron barrel manufacturing process with an inner coating to form various barrel-shaped containers with a multilayer composite structure. Can not meet the requirements. Therefore, such inks need to be improved to meet the requirements of some special post-processing processes.
Technical Application Through the analysis of the background of the above research, the factor that causes the yellowing of white ink for gravure plastic cooking is that the aromatic polyurethane is easy to yellow at higher temperatures. For yellowing due to polyurethane, we can use aliphatic polyurethane instead of aromatic polyurethane to reduce yellowing, and we can eliminate it by stabilizing the aromatic polyurethane. The conventional method of use is to stabilize it by adding stabilizers. There are two ways of action: one is the addition of energy transfer aids. At higher temperatures, the energy transfer aids first absorb heat and decompose to achieve the purpose of protecting each other. The second is the addition of stable macromolecular substances that chemically react with each other at higher temperatures to produce stable macromolecular substances. The new products do not affect the final performance of the product. It is clear then that a measure has a significant effect. This article introduces the method of manufacturing gravure plastic composite ultra-high temperature cooking white ink based on ordinary plastic gravure cooking white ink by adding a macromolecular stabilizer.
The macromolecule polymer is from a resin XXX223 produced by a major company in the United States. Its active ingredient is 100%. Its molecular structure characteristics are specifically expressed as follows: 1. It can dissolve almost all single solvents in solvent-based gravure inks. Medium (because of its rich polar and non-polar groups). 2. It can strengthen the binding fastness of the ink layer to the substrate. (The molecular structure not only has strong adsorption groups for plastics and inorganic materials, but also the entire molecular structure also has a good internal plasticizing effect, and the internal stress shrinks when the film is cross-linked at high temperature); 3. It can be used rarely Achieve the effect of eliminating yellowing (the structure has repeating active group units). 4. Excellent storage stability.
XXX223 has a bisphenol A type symmetrical structure and is rich in numerous reactive functional groups (such as epoxy groups at both ends of the molecule and hydroxyl groups on adjacent carbon atoms near the bisphenol A type structure), and added functional functional groups ( Such as epoxy group) has flexible reaction characteristics, that is, at a relatively low temperature (80 ~ 150 ° C), the epoxy group can crosslink with the (hydroxyl) group in polyurethane, and the degree of effective binding is higher; It is much more difficult for the hydroxyl group on the adjacent carbon atom of the bisphenol A structure to participate in the cross-linking reaction than the epoxy group. It often requires a higher temperature (about 200 ° C) to participate in the reaction with the hydroxyl group to form a more stable compound of. In addition, the hydroxyl group of the functional epoxy polymer also plays a role in inhibiting the formation of biphenyl compounds at high temperatures and the risk of yellowing of some high molecular weight aromatic polyurethane resins.
We examine the effects of the addition of XXX223 on the ink from the following properties: ink storage stability, printing stability, adhesion of various plastic films, composite strength of various composite structures, and high-temperature cooking resistance.
Technical implementation test comparison Formula of ordinary cooking white plastic gravure ink (see Table-1): (in percentage)
Add 0.5% and 1.0% of XXX223 (by weight) to the white ink formula above
1. Test the thermal stability of the ink.
Test method: The undiluted raw ink is passed through a 6 # steel wire scraper, coated on a PET film with a thickness of 20um at high temperature, and placed in an oven and a closed cooking kettle at different temperatures and at different times. Observe the yellowing of the ink layer.
Obviously, the heat resistance yellowing performance of ordinary cooking compound white ink in the range of 0.5% to 1.0% by weight of XXX223 was improved.
2. Investigation of ink storage stability and other basic properties. (See Table-3)
From Table-3, it is clear that the fastness performance and printing performance and stability performance of the ink after adding XXX223 are comparable to those of ordinary steamed white ink. However, the ink of XXX223 has the risk of sticking back when printing, and with the addition of XXX223 With the increase, the anti-stick back performance of the ink is getting worse. Therefore, it is necessary to add an anti-stick backing agent at the same time as adding XXX223 epoxy resin. Silicone is used as the anti-adhesive backing additive, and the added amount is 0.6% part by weight of the original ink, and the added amount of XXX223 is 0.7% part.
Repeat the thermal stability, ink storage stability and other basic performance tests of the above inks (see Table-4)
It can be seen from Table-4 that the added amount of silica is 0.6% part by weight of the original ink, and the added amount of XXX223 is 0.7% part, which is suitable for the heat yellowing resistance of ordinary gravure composite white ink.
3. Investigation of composite strength of various structures of ink.
Using Gaomeng two-component cooking glue for dry compounding, the compound strength was tested at 45 ℃ after compounding for 48 hours. The larger the value, the better. (Strength unit: g / 15mm) see table-5
From Table-5, it can be seen that the composite strength of various structures is significantly improved after the addition of XXX223. This is because the cross-linking of XXX223 containing hydroxyl and epoxy groups with the two-component composite glue has a far greater degree of cross-linking. Higher than normal cooking gravure white ink without addition.
Summary The manufacturing method of ultra-high temperature anti-yellowing solvent-resistant cooking-resistant gravure white ink belongs to the field of ink technology. The gravure anti-high temperature yellowing and retort-resistant white ink is composed of a special polymer, 0.75% by weight of water, plus 0.6% of inert silica, and 98.7% by weight of a commercially available retort-resistant white ink. The manufacturing method includes directly mixing special high polymer in a commercially-available cooking-resistant white ink and directly stirring at high speed for 5 to 10 minutes, wherein the rotation speed of the mixer is 2000 rpm to obtain ultra-high-temperature-resistant cooking composite white ink. The advantages of this technology are: resistance to high temperature yellowing above 200 ℃, simple production process, high gloss, excellent fastness to substrate, high composite strength, excellent hiding power, and good storage stability.