In daily life, when you open a scented greeting card sent by a friend, a tangy scent will make you feel warm, pleasant, and cordial; when you pick up a perfume ad, you do n’t need to spray perfume, it can be on the picture It emits a scent; when you are dazzled by the various beautiful dishes and realistic pictures on the exquisite recipe, you can smell the scent of this dish with a touch of your hand.
With the development of the market economy and the improvement of people's living standards, scent printing has been widely used in printed matter such as magazines, advertisements, postcards, greeting cards, calendars, cosmetics and food packaging that integrate visual and olfactory effects. In fact, if children's books are printed with scented inks, the combination of sight and smell can also increase children's interest in reading. Liquid crystal ink is added to the scent printing, and the printed flower patterns will show different colors with the seasons. Touching with your hands will release the scent of various flowers. This is the charm of scent printing.
The scent capsules contained in the scent printing ink are relatively coarse and cannot withstand excessive printing pressure. Therefore, the scent prints are mainly screen printing, and occasionally gravure printing and flexographic printing are also used.
Composition and principle of fragrance ink
The ink used for fragrance printing is composed of fragrance capsules, adhesives, pigments and other additives. According to the principle of emulsification, the fragrance capsules disperse the perfume core material as the oil phase in the aqueous phase of hydrophilic natural or synthetic polymer resins, such as gelatin, gum arabic, polyvinyl alcohol and other aqueous solutions. After stirring to disperse the entire system, through temperature changes, and changing the pH value or adding salts and secondary polymers such as formaldehyde, alum, etc., a polymerization reaction occurs at the interface of the water phase and the oil phase, the shell material is precipitated, and it is dispersed And adsorbed around the perfume droplet particles to form a shell, that is, a polymer film surrounding the surface of the oil droplets, which is usually called the wall material of the fragrance capsule. The fragrance is coated in the film, and the gel is cured to form a capsule, and finally a microcapsule containing fragrance is obtained. The diameter of the fragrance microcapsules is 10 to 30 μm, and the wall thickness is about 1 μm.
When you gently rub the surface of the scented print, the capsule in the ink will break, and the fragrance enclosed in the capsule will fly out and temporarily float in the air to produce a fragrance. Due to the protection of the capsule, this fragrance can be kept for a long time. As long as the capsules are not broken, the fragrance can be kept for several years. It is also worth noting that, because the scented microcapsules are very small, the diameter of 10-30 μm can ensure that the amount of contact and inhalation is very small when wiped by hand, and will not cause irritation to the skin and respiratory tract.
Selection of fragrance printing ink
The premise of printing with scent printing ink is that the printed image must have a heavier tone, and the printed image area should be as large as possible, so that the microcapsules on the surface of the paper can be used to play the role of fragrance. Because the scent concentration of the scent print depends on how many scent microcapsules are printed on the print.
A better and more effective method is to apply a layer of oily polish with scented microcapsules on the surface of the printed product. The commonly used method is to coat the printed image with a printing unit. In the coating process, one must ensure a sufficient coating amount, and at the same time, there must be good powder spraying measures, otherwise, there will be problems such as smearing and adhesion of the printed matter caused by wet pressure drying in general oily glazing. . The amount of fragrance coating applied to paper prints can be easily checked visually. As long as you carefully check the smoothness and gloss of the varnish coating, you can make a judgment.
One of the prerequisites for fragrance printing is that ink suppliers must provide a range of additional services. First of all, the ink supplier must have a wealth of practical experience in the printing process, and can designate a fragrance oil essence supplier, responsible for the microencapsulation of fragrance oil essence, and mix the microcapsules into printing ink, polish or dispersing paint; Secondly, the ink supplier is required to understand and be responsible for adjusting the viscosity of the ink to adapt it to the printing system used. In addition, after completing the above work, you must also carry out proofing verification on the printing press.
In fact, not every flavor and every fragrance is suitable for making microcapsules, such as leather, chocolate or coffee is difficult to replicate. Suppliers of fragrance inks must conduct fragrance microencapsulation tests at the design stage of fragrance printing. In addition to the preliminary test on the printing machine dedicated for testing, the spot proofing must be carried out on the printing machine that will be used for fragrance printing. Otherwise, once the actual printing production is put into practice, if the printing effect does not meet the expected requirements, it will be Cause significant losses.
The taste of paper printing ink itself will affect the fragrance printing effect. Therefore, when performing fragrance printing, the ink with less taste should be selected, and the paper and ink should be tested. In addition, the additives in the printing ink will change the expected fragrance of the printed product due to volatilization, so be careful when printing fragrance.
At present, there are mainly the following types of fragrance types used in fragrance printing on the market.
Fruity: green apple, cherry, blue berry, strawberry, watermelon, white melon, orange, pineapple, grapefruit, grape, banana, apple, grape, peach, lemon.
Flowers and plants: Acacia, cosmos, camellia, thistle, cherry blossom, orange blossom, amaryllis, camellia, rose, calamus, purple flower, wild rose, plum, primrose, hyacinth, orchid, jasmine, vine, sage grass, Sagebrush, Daffodil, Matricaria, Narcissus, Primrose, Carnation, Lily of the Valley, Lilac Flower, Chrysanthemum, Violet, Lavender, Dandelion, Dahlia, Gentian, Gardenia, Tulip, Lily
Drinks and food: whiskey, cocoa tea, mustard, curry, coconut, pine umbrella mill, garlic, pepper, powdered tea, toffee, cola, mayonnaise, lemon tea, coffee, vanilla, milk tea, chocolate, peanuts. Others: mist, mosquito coil, forest, cedar musk, cypress, cinnamon, mint, sage, white sandalwood, soap, pine.
Scented ink
The screen mesh should be larger than the particles of fragrance ink. Because the microcapsule particles in the scented ink are relatively coarse, it is advisable to choose a nylon monofilament with good permeability when selecting the silk screen, and the opening degree is larger, and the mesh number is about 150 mesh.
The squeegee is generally made of polyurethane rubber. This squeegee has no porosity, corrosion resistance, and stable volume. It can be selected within 60 to 90 Shore hardness. Screen printing has high requirements for ink viscosity, and the ideal viscosity value is about 2Pa ​​· s. The fragrance ink should be adjusted for viscosity before screen printing. It is best to measure with a viscometer, then weigh and add a certain amount of thinner to make it have a suitable viscosity. The speed of printing fragrance ink (the printing speed here refers to the speed of the doctor blade running) can not be too fast, so as to avoid too much heat generated by the doctor blade friction and the temperature is too high to cause the microcapsule particles to rupture. In order to ensure the quality, the speed of the knife should be compatible with the speed of filling and releasing ink. The knife speed is too slow, which affects the production speed; the knife speed is too fast, which will cause insufficient ink filling, incomplete imprinting, or the ink release speed cannot keep up, so that the adhesion section is too long after scraping the ink, which affects the printing quality.
Both ink filling and ink releasing speed are related to the external force, mesh size and ink rheological properties. The doctor blade passes through the aperture M at a speed V, and the time required should be equal to the time that the ink passes through the screen thickness F from top to bottom, ie:
M / V = ​​F / V1 where V1
It is the flow speed of ink in the mesh. If the diameter M of the mesh is known, the shear rate of the ink can be obtained:
S = V1 / (M / 2) = 2FV / M2
In the formula, S represents the inherent rheological characteristics of the ink, which determines the flow rate of the ink. No matter how the screen and knife speed are combined, as long as the shear rate remains unchanged, the same ink flow rate can be guaranteed.
This shows that with this formula, the knife speed can be changed. For the scented screen printing, in order to adapt the knife speed to the speed of filling and releasing ink to obtain good printing quality, under the conditions of satisfying the above relationship, an appropriate S value should also be selected to ensure that the microcapsules are not heated by heat rupture.
The pressure of the scented screen printing cannot be too great, and the suitable pressure can be found by trial printing. In the trial printing process, in addition to paying attention to whether the ink on the plate surface is even after the scraper scrapes, it is also necessary to observe whether the microcapsules are broken and whether there is fragrance floating out.
The drying temperature of the scented screen printing ink should not be too high, otherwise the microcapsules will break and cannot be dried with ultraviolet light. We believe that the ideal drying method is volatile 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, when blowing air to the drying table, the effect of blowing air from the lower part is better.
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