Control of the most popular glazing quality

2022-08-06
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Control of glazing quality

at present, there are oil-based glazing, water-based glazing, and UV glazing. Glazing has decoration to protect the printed matter, improve the gloss of the printed matter, and has moisture-proof, waterproof, folding resistance and wear resistance. From the perspective of environmental protection, water-based glazing and UV glazing are more in line with the future development trend. Printed products after water-based glazing and UV glazing can be directly recycled without causing resource waste and environmental pollution. UV glazing is used for the packaging of food, drugs, tobacco and cosmetics. With the popularization of glazing technology and 2 Aerospace people's understanding of glazing UV glazing and water-based glazing are developing at an unparalleled speed. In foreign countries, such as Europe and the United States, there are high requirements for environmental protection. In some packaging fields, there are strict standards and regulations. There is no room for film coating and oily glazing that do not meet the environmental requirements

due to the unprecedented fierce market competition, in order to save costs and generate profits, many manufacturers use low-cost varnish as much as possible, which often leads to sticky prints, uneven coating, orange peel stripes, pinholes, pockmarks, poor adhesion, hairiness, poor gloss, insufficient brightness, etc

the Polish quality of printed matter largely depends on the Polish, Polish drying and production process. Only the actual situation can be flexibly mastered, and the configuration of good polishing equipment can be very helpful to the quality control

varnish

uv varnish

uv varnish is mainly composed of oligomer, active diluent, photoinitiator and other additives

I. oligomer

oligomer, also known as prepolymer, is the most basic component in UV varnish. It is a film-forming material, and its properties play an important role in the curing process and the properties of the cured film. Structurally, oligomers are low molecular resins containing c=c unsaturated double bonds, mostly acrylic resins

II: active diluent

is also called cross-linked monomer, which is a functional monomer. Its role in glazing oil is to adjust viscosity, curing speed and curing film performance

III: photoinitiators

photoinitiators are substances that can absorb radiant energy and produce active intermediates with the ability to initiate polymerization through chemical changes. They are the main components required by any UV curing system

IV: additives

are used to improve the performance of inks. The commonly used additives in UV varnishes are

stabilizers/used to reduce thermal polymerization during storage and minimize energy consumption ", improve the storage stability of UV varnishes

leveling agents/used to improve the levelness of the varnishes and prevent shrinkage, At the same time, it also increases the gloss of the glazing coating

defoamer/used to prevent and eliminate bubbles generated during the manufacturing and use of the glazing oil

water based glazing oil

water based glazing oil is composed of synthetic resin and water, 45% of which is composed of synthetic resin and 55% of which is composed of water

I: main agent, film-forming resin. The film-forming material of the glazing agent is usually synthetic resin, which affects drying, adhesion and gloss, Quality of equal glazing

2: auxiliary agent:

1: curing agent, improve the water-based main agent 1. Plug in the 4-core calibration plug to enhance the film-forming strength

2: surfactant, reduce the surface tension and improve the levelness

3: defoamer, control the foaming, needle eye, orange peel and pitting

4: desiccant, increase the glazing drying speed and improve the printing adaptability

5: adhesive agent, Improve the adhesion of varnish prints

6: wetting dispersant to prevent dirt and improve the wear resistance

7: plasticizer to improve the folding resistance

III: solvent: disperse and dissolve synthetic resins, additives, The main component is water (a certain amount of ethanol can be added to improve the drying performance)

viscosity of varnish:

uv varnish is generally adjusted according to the speed of the polishing machine

60-200 M/min is controlled at no more than 28 seconds

20-50 M/min is controlled at no more than 80 seconds

water based varnish is 30-60 seconds when polishing with an offset press

polishing machine is 20-50 seconds

drying

uv drying is generally supported by UV drying and infrared drying, The cooling exhaust water-based light oil is mainly dried by infrared ray. Hot air drying and UV drying affect the performance of the cured UV lamp. There are the following factors: UV spectrum distribution, radiance, radiation amount and infrared radiation

most UV rays contain two UV wavelengths that work simultaneously. The short wave works on the surface, and the longer wave is used for the deep layer of the ink. This is because the short wave energy is absorbed by the surface and cannot enter the deep layer. Insufficient short wave exposure may cause surface adhesion, while insufficient long wave energy may cause adhesion difficulties

the efficiency of a UV lamp depends on how easy it is to emit photons into curable materials to start light triggered molecules. UV curing depends on the collision between photons and molecules. Light triggered molecular communication? However, in addition to the characteristics of the "three V" light source, the cured film also has optical and thermodynamic properties. They interact with the radiation energy and have a significant impact on the curing process

spectral absorption energy is the effect of absorbing the incoming wavelength within the gradually increasing thickness. The more energy absorbed near the surface, the less energy obtained in the deep layer. But this situation varies with the wavelength. The total spectral absorptivity includes all the effects from photoinitiators, monomolecular substances, oligomers and additives including pigments

in actual production, attention should also be paid to the following:

uv varnish viscosity is too small, and the coating is too thin; Excessive dilution of non reactive solvents such as ethanol; Uneven UV oil coating can quickly find the completed experimental data and results according to different conditions; Paper is too absorbent; It will cause poor gloss and insufficient brightness. The viscosity and coating amount of UV varnish can be appropriately increased according to the different conditions of the paper and the speed of the polishing equipment. For the paper with strong permeability and absorption, a layer of primer can be coated first. Some shortwave tubes can also be properly added to increase the aging of the leveling UV lamp and weaken the intensity; UV varnish storage time is too long; Too many non reactive diluents are added; The machine speed is too high. It will cause poor drying, incomplete UV curing and sticky surface. When the curing speed is required to be less than 0.5s, the power of the high-pressure mercury lamp must be ensured to be generally not less than 12O w/cm. The lamp tube should be updated in time. If necessary, a certain amount of UV light oil curing accelerator should be added to accelerate the drying

uv gloss is small and the coating is too thin; The ink contains too much ink blending oil or drying oil; The ink surface has been crystallized; There are many anti sticking materials (silicone oil and powder spraying) on the ink surface, which will cause the UV varnish on the surface of the print not to be coated, and the textured coating is too thin; Excessive dosage of non reactive diluent (such as ethanol); There is much dust on the surface of printed matter. It will cause white spots and pinholes in the UV glazing coating. Attention should be paid to keep the production environment and the surface of the printed matter clean, increase the coating thickness, or add a small amount of smoothing AIDS. The active diluent participating in the reaction is preferably used for dilution

uv varnish viscosity is too high; Uneven pressure; Excessive coating amount; The leveling property of UV varnish is poor. It may cause uneven surface coating, stripes and orange peel phenomenon

in addition, in actual production, attention should be paid to maintaining the temperature of glazing production at about 20 ℃, paper characteristics, heat resistance and alcohol resistance of printing ink, good alcohol resistance, ester solvents and acid and alkali resistance, which greatly affect the quality of glazing

reprinted from: Bisheng

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