introduction
In everyday life, when you open a scented greeting card sent by a friend, a scent from your nose makes you feel warm, happy, and gracious; when you pick up a perfume ad, you don’t need to spray the perfume. Emitting aromas; When you face a variety of nice dishes and realistic images that are dazzling on a fine recipe, you can smell the dish with a touch of your hand??
With the development of the market economy and the improvement of people’s living standards, fragrance printing has been widely used in prints that integrate visual and olfactory effects, such as magazines, advertisements, postcards, greeting cards, calendars, cosmetics, and food packaging. In fact, if children's books are printed with scented inks, the visual and olfactory feelings can be organically combined to improve children's reading interest. The liquid crystal ink is added to the fragrance printing, and the printed flower pattern will show different colors with the changes of the season. Touching by hand will release the fragrance of various flowers, which is the charm of the fragrance printing.
The aroma printing ink contains a relatively large number of aroma capsules, and cannot withstand excessive printing pressure. Therefore, the aroma print is mainly based on a screen printing process, and occasionally gravure printing and flexographic printing are used.
The composition and principle of fragrance ink
The ink used for fragrance printing is composed of fragrance capsules, adhesives, pigments, and other additives. The fragrance capsule is based on the principle of emulsification, and the fragrance core material as the oil phase is dispersed in the aqueous phase of a hydrophilic natural or synthetic polymer resin, such as an aqueous solution of gelatin, gum arabic, polyvinyl alcohol, and the like. After stirring, the entire system is dispersed, and the temperature is changed, and the pH is changed or a second polymer such as formaldehyde and alum is added to the salt to cause polymerization at the interface between the aqueous phase and the oil phase to precipitate the shell material. It adsorbs around the droplets of perfume droplets to form a shell, that is, a polymer film that surrounds the surface of the oil droplets. Usually, this membrane is called a wall material of a fragrance capsule. The perfume is coated in a film and gel-cured to form a capsule, finally obtaining a microcapsule containing a perfume. Flavor capsules have a diameter of 10-30 μm and a wall thickness of about 1 μm.
When the surface of the scented print is gently rubbed, the capsule in the ink is broken, and the perfume enclosed in the capsule is scattered and temporarily floats in the air to generate a fragrance. Due to the protection of the capsule, this fragrance can be stored for a long time. As long as the capsule is not broken, the fragrance can remain for years. In addition, it is worth noting that since the scented microcapsules are very tiny, a diameter of 10 to 30 μm ensures that the amount of contact and inhalation during hand rubbing is minimal and does not cause irritation to the skin and respiratory tract.
Selection of aroma printing inks
The premise of printing with a fragrance printing ink is that the printed image must be heavier in color and the printed image area should be as large as possible so that the surface of the paper can be printed with microcapsules sufficient to exert a fragrance effect. Because the aroma concentration of the scented print depends on how many scented microcapsules are printed on the print.
One of the prerequisites for aroma printing is that ink suppliers must provide a range of additional services. First, the ink supplier must have extensive practical experience in the printing process and be able to designate a supplier of flavor olein that is responsible for the microencapsulation of the flavor olein and mix the microcapsules into the printing ink, polish, or dispersion coating; Second, it also requires the ink supplier to understand and be responsible for adjusting the ink viscosity to suit the printing system used. In addition, after completing the above work, proofing must also be performed on the printing press.
In fact, not every flavor and every fragrance is suitable for making microcapsules. For example, the scent of leather, chocolate or coffee is a difficult-to-replicate fragrance. Suppliers of scented inks must perform flavor microencapsulation tests during the design phase of scent printing. In addition to performing preliminary tests on the printing presses used exclusively for testing, the aroma printing must also be carried out on the spot in the printing machine that will be subjected to the aroma printing. Otherwise, once the actual printing production is started, if the printing effect does not meet the expected requirements, it will Cause major losses.
The taste of the paper printing ink itself affects the scent printing effect. Therefore, in the case of aroma printing, inks with a small taste should be selected and tested on paper and ink. In addition, additives in printing inks may change the expected scent of the prints due to volatilization, so care must be taken when performing scent printing.
At present, the types of fragrances used in the aroma printing market are mainly the following types.
Fruity: green apple, cherry, blueberry, strawberry, watermelon, guarana, orange, pineapple, grapefruit, grape, banana, apple, grape, peach, lemon.
Flowers and herbs: artichokes, cosmos, camellia, amaranth, cherry blossom, orange blossom, amaryllis, camellia, rose, calamus, purple, wild rose, plum, primrose, hyacinth, orchid, jasmine, rattan, yuca, Reeds, daffodils, mother chrysanthemums, daffodils, primroses, carnations, lily of the valley, lilacs, chrysanthemums, violets, lavender, osmanthus, dahlias, gentian, gardenia, tulips, lilies.
Beverages and foods: whiskey, cocoa tea, mustard, curry, coconut, pine mill, garlic, pepper, tea, toffee, cola, mayonnaise, lemon tea, coffee, vanilla, milk tea, chocolate, peanuts. Others: Fog, mosquito-repellent incense, forest, cedarwood, coriander, cinnamon, mint, sage, white sandalwood, soap, pine.
Scented ink printing market
The screen mesh should be larger than the particles of the fragrance ink. Since the microcapsule particles in the fragrance ink are relatively thick, it is desirable to select a nylon mesh having good permeability when selecting the mesh, and the degree of opening is larger and the mesh number is about 150 mesh.
The squeegee is generally made of urethane rubber. The squeegee has no porosity, corrosion resistance, and is stable in volume. It can be used in Shore hardness 60-90. Screen printing has higher requirements for ink viscosity, and the ideal viscosity value is about 2 Pa·s or so. Viscosity inks are viscosity-adjusted prior to screen printing, preferably with a viscometer, then weighed and added with a certain amount of diluent to give it a suitable viscosity. When printing aroma inks, the speed (the printing speed here refers to the speed at which the squeegee runs) must not be so fast that the squeegee friction produces too much heat and the temperature is too high to cause the microcapsule particles to break. In order to ensure quality, the knife speed 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, the ink filling may be insufficient, the imprinting may be incomplete, or the ink release speed may not keep up. As a result, the adhesive section after the ink scraping may be too long, which affects the printing quality.
The ink filling and ink release speeds are related to the size of the external force, the mesh size, and the rheological properties of the ink. The speed of the squeegee at the speed V through the aperture M should be equal to the time the ink passes through the screen thickness F from top to bottom, ie:
M / V = ​​F / V1 where V1
For the ink flow speed in the mesh. If the aperture M of the mesh is known, the shear rate of the ink can be found:
S= V1/(M/2)=2FV/M 2
In the formula, S represents the inherent rheological properties of the ink, which determines the flow of the ink. Regardless of the combination of the screen and the tool speed, the same ink flow rate can be ensured as long as the shear rate remains constant.
It can be seen that using this formula, the tool speed can be changed. For scent screen printing, in order to match the speed of the knife with the speed of ink filling and ink release to obtain a good print quality, under the conditions that satisfy the above relationship, an appropriate S value should be selected to ensure that the microcapsules are not heated. rupture.
Aroma printing pressure can not be too large, you can try to find the right pressure. In the test printing process, in addition to paying attention to whether the ink on the plate after the scraping plate is even or not, it is also necessary to observe whether the microcapsules are broken and whether there is any fragrance floating out.
The drying temperature of the fragrant screen printing ink should not be too high, otherwise the microcapsules will be broken and cannot be dried with ultraviolet rays. We believe that the ideal drying method is evaporation drying. Properly increasing the drying temperature and increasing the air flow rate can increase the drying speed of the ink layer. Since the gas density of the screen printing ink solvent is greater than the air density, the air blowing effect from the lower part is good when the air is sent to the drying table.