Preparation of aroma inks and screen printing applications

As a functional ink for aroma printing, the aroma ink is mainly composed of a binder, a colorant, an auxiliary agent, and a spice microcapsule. Among them, the ink is mainly composed of esters, alcohols or ketones, aromatic hydrocarbons, and the main components of the perfume are alcohols, phenols, ethers, aldehydes, ketones or esters, etc. In general, the two can coexist. Fragrance ink In order to maintain the stability and durability of the fragrance, the fragrance is made into a microcapsule with fragrance and then penetrated into the ink for screen printing. During the use of the fragrance print, the microcapsules are broken due to friction and the like to release the fragrance.

Aroma ink preparation technology

In the production process of aroma inks, the composition of the ink is the same as that of ordinary inks. The most important technique is the preparation of microcapsules. Microcapsule production technology is a new technology developed in the 1950s. It was originally applied to the production of carbonless copy paper, and has now been widely used in food, medicine, liquid crystal, printing and dyeing and other fields. In printing, its main function is to reduce volatility, control release, isolate active ingredients, good separation state and so on.

The so-called microcapsule technology is to wrap small droplets or solid particles in a polymer film to make microcapsules with a very small diameter and mix them into a desired carrier as an additive. The method of making the capsule firstly refines the coated material and then uses this

Aroma ink technical characteristics and application in screen printing

These fine particles are the core, depositing, coating, and filming polymers on their surfaces. This process is called microencapsulation. The two phases separated by the coating and the capsule wall are called cores, cores or fillers, while the peripheral capsule walls are called skins, shells or protective membranes. The size of the microcapsules is generally 5 to 200 μm, and the thickness of the capsule wall is generally 0.2 to several micrometers. In the production, since the size of the spice microcapsules is small, the aggregates formed when the adhesions are gathered together form a large number of aggregates, so that the mechanical grinding is used to disperse them to a desired degree. When the aroma ink is prepared, it can be stirred by a dispersing device if necessary, and a high-speed impeller mixer is an ideal fragrance ink dispersion agitation device.

The composition of the essence is very complicated, and the organic components contained in the essence are mostly substances that are volatile and chemically unstable. Therefore, during use and storage, it is inevitable that they will volatilize or be degraded. In order to protect the essence from external environmental factors and prolong the period of releasing the fragrance, it is best to microencapsulate the essence, slowly oxidize after contact with the air, and continuously release the aroma, thereby greatly prolonging the period of its fragrance protection. There are also flavor microcapsules that only react to each other with the catalysis of environmental factors such as ultraviolet (sun) radiation, oxygen (air) circulation, heating, and humidity changes to produce flavoring substances, thus avoiding the aroma of printed matter under normal circumstances. Invalid fugitive.

The shape of the microcapsules is similar to our common containers, which are under a few hundred micrometers in size. The materials and processes for making them are various and their uses are very wide. There are two types of aromatized microcapsules: one is the type of “sustained release” that emphasizes, and the capsule wall has many micropores, which can slowly release the fragrance and lasting fragrance. At the same time, the capsule wall has a certain degree of toughness and resistance to mechanical impact. Strong ability, but more sensitive to the environment, such as the temperature can increase the release of flavor faster; Another kind of wall is more "strong", more slowly for environmental changes, but the wall is fragile, under the external force can be the flavor Released at one time.

With the increasing demand for prints, in addition to the pursuit of the visual beauty of the printing effect, the fragrance printing is also the direction of efforts. The earliest was the addition of perfume inks to ink or paper for printing. This method is simple, but not long-lasting. Since 1972, printing has been carried out using fragrance inks that are encapsulated in microcapsules. Because the spices are closed by the micelles, they are slowly emitted, so this print can last long. The gelatin particles with a wall thickness of 1 μm or less and a diameter of 10 μm to 30 μm can be dispersed in ink to perform screen printing, and are mainly used in magazines, advertisements, leaflets, brochures, menus, calendars, teaching calendars, and clothing. The main points of the screen printing process for fragrance ink are as follows:

1. Selection of scent ink screen printing screen

(1) The surface of the monofilament plain woven wire mesh is smooth, and therefore the ink permeability is better than that of the twisted yarn (silk yarn spun from multiple fine fibers), so the screen printing mesh should be adopted as much as possible. Monofilament flat woven wire mesh.

(2) Due to the coarse particles of the microcapsules, the nylon mesh has good permeability, and can use ink with large viscosity and large particles, and has high elasticity and flexibility, so the nylon single screen is an ideal choice.

(3) The mesh width of the screen should be at least 3 to 4 times the diameter of the pigment particles in the ink.

2. Scented ink screen printing points

(1) ink viscosity requirements

Screen printing ink viscosity should be about 2Pa ​​· s, so the fragrance ink viscosity adjustment before printing, it is best measured using a viscometer, and then weighed to add a certain amount of diluent to make it to the desired viscosity.

(2) Printing speed requirements

The printing speed should not be too fast so that the squeegee friction generates heat and the temperature is so high that the microcapsule particles break (the printing speed here is the speed of the squeegee). In order to ensure the quality, the speed of the knife should be compatible with the speed of ink filling and ink release. The speed of the knife is too slow, which affects the production speed. If the knife speed is too fast, it will result in insufficient ink filling, incomplete printing or slow ink release speed. After the ink knife sticky section is too long, affecting the printing quality.

(3) Printing pressure requirements

In order to ensure that the ink can smoothly leave the screen and normally fall onto the substrate, the printing pressure cannot be too high. The printing pressure in the screen printing process is the squeegee pressure on the screen by the squeegee. It depends on the level of the squeegee. The lower the pressure, the higher the pressure. In the trial printing process, in addition to paying attention to whether or not the ink on the plate is even after the ink is scraped, it is also necessary to observe whether the microcapsules are broken to see if there is any fragrance floating out. In this way, try to adjust the pressure while testing. The squeegee is generally made of urethane rubber material. It is non-porous, corrosion-resistant, stable in volume, and has a hardness of 60 to 90 degrees.

(4) Ink color mixing and color sequence

To obtain the correct color, the ink transfer should be performed under stable natural light, dark ink should be gradually added, and the hue of the mixture should be minimized. The more hue, the greater the gray scale. In addition, color changes before and after drying and before and after the fragrance emission should also be taken into account. For example, on a light-colored substrate with a large amount of ink absorption, the ink color after drying is often pale; the wet state, dry state, and three-phase color difference after the microcapsule ink are broken. Happening. When a large amount of ink is used and the ink adjuster is used, care should be taken to protect the microcapsules. When performing color tone printing, the problem of color sequence should also be considered. The color ink of the microcapsules should be best placed on the final printing to avoid damage to the microcapsules during subsequent printing.

(5) Drying method

The drying characteristic of the aroma screen printing ink is that the drying temperature cannot be too high, otherwise the microcapsules will be broken and the fragrance will be distributed. Therefore, infrared drying cannot be used. The ideal drying method is evaporation drying. Increasing the flow rate of air, reducing the concentration of the solvent in the ambient air, and destroying the volatile gas layer of the saturated solvent can also promote the drying of the ink layer. Since the density of the volatile gas in the ink solvent is greater than the air density, the air blowing effect from the lower part is better when blowing air to the drying table.

Two flavor ink products example

1.UV series fragrance ink

UV-97 series fragrance ink was successfully developed in Hangzhou recently. It combines microcapsule technology with UV low-temperature fast curing process to make the ink dry instantly after screen printing. The difference from the general flavor ink is that the flavor is encapsulated in the slow-release capsule of the ink, which avoids the volatilization of the flavor during storage and processing. Therefore, the flavor of the printed material is particularly long-lasting, usually more than one year. After the ink is cured, rub it gently with your finger to smell the rich flavor. The series of inks are lemon, orange, rose, wine and other fragrances, can be used for paper, gold and silver cardboard, plastic film, metal, leather and other substrates, suitable for the production of various packaging boxes, greeting cards, signs, books As well as magazine covers, it is also possible to add fragrance inks to general UV inks for printing.

Long-term flavor ink

Although scented inks have been used for printing, although they are relatively common, there are often problems such as the product scent duration is too short, the scent is easily dissipated, and the shelf life of the scented print is too short.

There is now a kind of ink that can keep aromatic for a long time. The use of high-tech micro-encapsulation technology can keep the fragrance for more than half a year. This technology encapsulates ordinary flavoring materials into microcapsules to maintain the flavor for a long period of time, and the added NCC microcapsule aroma materials can keep products in the open environment for more than half a year. NCC brand microcapsules have a particle size of 4 to 6 μm, making them ideal for screen printing and spraying. The scented greeting cards, frictional fragrance stickers, and collector's edition PVC cards printed with this ink are very popular.

in conclusion

Aroma inks have many applications in screen printing, and have gradually gained people's recognition, but the exploration of this technology continues in both technical and more extensive applications, with the aim of being based on aroma While maintaining the printability of ordinary inks, normal printing jobs can be performed as ordinary inks. We believe that with the continuous improvement of technology, fragrance inks will show more powerful functions in the field of screen printing.

Reprinted from: Screen Printing Industry

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