Printing ink deinking causes and exclusion

In the packaging printing, streaks or pale colors occasionally occur, that is, no ink and ink failure. This is due to the overall gelation of the ink due to the swelling of the ink system's pigments and fillers.

The theoretical explanation is that the ink yield value is too high to form a cheese. In fact, there are too many pigments and fillers in the ink, which cause the ink to gel or water in the storage. The author made a cursory discussion on this issue and communicated with colleagues in the packaging and printing industry about troubleshooting.

First, the ink gel and acid and alkali concept

In the early use of oxidative-drying and osmotic drying inks, the problem of gelation of the ink was often encountered, but occasionally encountered in solvent-based (volatile drying) and water-based inks. The cause of gelation is very complicated (including ink manufacturing processes such as pre- and post-drying of driers). The author believes that there are several reasons for gelation:

1. The resin molecular weight of the ink system is too large (viscosity is too high);
2. There are too many solid components (even small viscosity resin binders are no exception);
3, the acid value of the ink system is too high;
4, pigments, fillers with alkaline;
5, too much desiccant content or put the additives in the wrong order (such as ink before and after the production of two kinds of results will appear);
6. The solvent of the ink system is especially excessively fast drying solvent.

The first two of the above reasons belong to the category of physics and can be easily avoided and eliminated by experienced ink manufacturers or packaging and printing operators. The latter four are chemical reactions. In this regard, the author once talked about “the use of coupling agents in water-washable inks”, “China Packaging News” on September 20, 1997, “Packaging Digest of Foreign Countries”, and “Guangdong Packaging” in 1998. The acid-base relationship was described for proton donors and proton acceptors. In the 1998 issue of "Guangdong Packaging" and "China Packaging" magazine, the author's "Research on Green Packaging Printing Ink" published a paper on the molecular weight of 330 rosin resin in the use of high-pigment carbon black to produce solvent-based flexible fast-drying ink gelation, In the case of failure of the stack, the advantages and disadvantages of its strongly acidic pigment carbon black pigment and rosin acid value were described. When the acid-base characteristics of pigments are not compatible with the acid-base characteristics of the binders, a variety of combinations of resins, pigments, and fillers can be used, or a suitable solvent can be used to make up or improve. This is a common remedy.

In chemical reactions, macroscopic properties can mutate when the stoichiometric concentration reaches a certain value (strictly speaking, a very narrow concentration range). At this time, the active molecules of the ink system begin to associate to form aggregates of colloidal particles of unequal sizes. Such aggregates are called micelles or micelles, also known as associative colloids. The important characteristic of micelles is solubilization, which greatly increases the solubility of the originally insoluble or sparingly soluble substances (commonly known as bloating), thereby accelerating the chemical reactions. The reaction mechanism is likely to have a close relationship with the binder, especially the pigment dispersion process.

Second, eliminate swelling, to avoid the effective way of gelatinization

In addition to the above reasons, in the storage, the ink system driers can also directly affect the viscosity of the ink and the precipitation of pigments and fillers. For example, a highly viscous alkyd resin and a basic pigment zinc oxide are ground together in the presence of a driers to promote gelation and swell of the ink during storage. This is due to the reaction of free fatty acids and basic pigments during thermal processing. Therefore, when inks are manufactured from high viscosity ink materials, lead, cobalt, and manganese driers should not be added during the grinding process. However, swelling tendency can be reduced after adding 1% benzoic acid. Another drawback of driers is that they can accelerate pigment settling during storage. For example, when titanium dioxide is used to make inks, zinc naphthenate is added during grinding, and the pigments tend to precipitate and form a lump. Therefore, adding a driers before the pigments are grinded will result in poor storage of the ink, bloating, gelation, and sedimentation.

In recent years, people have proposed such remedial measures around swollen, gelatinized and precipitated agglomerates of packaging printing inks. This kind of passive operation not only increases the production cost of packaging and printing manufacturers, delays the time, but also increases the difficulty of processing. The reasons for gelation, thickening, and clumping of the ink system include salt-based pigments and saponification of linking materials with higher acid values ​​or containing free fatty acids, which causes the binder material to agglomerate and gel, the ink system absorbs water, and the pigment content is too high. , poor compatibility with the link material and grease additives. There are four remedies as follows:

1. When it is too thick or the gelation occurs due to the high degree of polymerization of the binder, it is diluted with aliphatic hydrocarbons, esters, and ketones.
2. The saponification ink and rosin are used to release the high acid value material.
3, the commonly used method in the past, add naphthalic acid metal salt in the ink.
4, ink need to add inorganic salt control.

In response to the above failures, the author analyzed and screened out the commercially available anti-expansion and plastic-breaking new material--Yizhen Tianyang Chemical Factory (National Inspection-Exempt Product) improved phosphester titanate coupling agent, in addition to having excellent dispersion of pigments. In addition to its performance, it can also make swelled, gelled packaging printing inks 'back to back'. Only by adding 3-5% anti-bloating and gel breaker to the swelled ink during the printing process can the above failure be suppressed. In the ink formulation, it is only necessary to directly add the pigment and filler 1.5-2.5% anti-expansion breaker to avoid ink swelling and gelation. It can also use toluene or xylene to dilute the product with 1:1 ratio and add ink to grind, which can greatly improve the dispersibility of the pigment, and at the same time prevent the printing ink from being swollen during production, storage and printing. Colloids, precipitates caused by streaks or color light failure. In addition, the degree of branching of the ink can be greatly increased, the adhesion of the ink film can be increased, the baking temperature and the blowing amount of the solvent ink can be reduced, and the fluidity of the printing ink can be effectively maintained.