Screen printing solvent characteristics and safe use

Solvents play an important role in screen printing. The development of a safe and practical universal solvent is just as important as the development of a cure for all diseases. Regardless of what material the printer prints on and the shape of the object, it must learn how to use the solvent.

Screen printing uses many chemical solutions. Some of these solutions are used to dilute the ink, delay and speed up the drying of the ink, and some to improve the hiding power of the ink or to clean the screen plate after printing, to remove the screen plate or emulsion layer, and to clean the screen before the film is installed, and Other uses. A simple definition of a solution is a mixture of solute and solvent. Solutes are dissolved substances that can be solids, liquids, or gases. The solvent is the liquid used to dissolve the solute. The solvent is often an organic solvent that dissolves the solid material, such as a resin. For the printer, the solvent is a compound that dissolves other substances to form a solution. It is used to change the state of solid materials during printing, coating, and screen reprocessing. Solvents are treatments developed in specific environments.

Because screen printers not only use different types of ink, but also use different solvents, they must be familiar with common solvents, be familiar with the type of solvent and the properties of the solvent. Solvents and inks are equally important. It can be used to change the viscosity of inks, dissolve solids, use as a propellant and plasticizer. If used improperly, it can cause danger, increase costs, waste time, print failures, reduce efficiency, and lose customers. Ink manufacturers often specify the appropriate solvents, emphasizing that users use the products specified by the manufacturer. The printer also needs to be aware that the solvent that easily dissolves some ink may not have solubility to another ink. Today's inks are the result of experiments and chemical formulas that may change the formula after adding the solvent. For example, if a printer prints with acrylic ink, any of the following solvents such as esters, ketones, ethers, toluene, vinyl chloride, etc. will affect it. However, the ink manufacturer knows the ink formulation and can recommend the most effective solvents for diluting and preventing drying. The same goes for other screen printing inks. In addition, the ink and polishing agent are artificially synthesized and can be printed on the surface of different materials. The solvent used may be slightly different for specific situations, but it must be the same. As an example of a sticky liquid for partially dissolving or softening a knife-cut paint film, a commonly used adhesive liquid is a ketone or an ester. They are all improved products of solvents and thinners, will not completely dissolve the film layer, will not be oxidized, can be used safely, and will not cause damage to the skin. Therefore, it is obvious that the solvent used for a particular purpose must be used according to the specific instructions.

In general, the paint, varnish, paint, and ink industries use the following solvents: turpentine, alcohols, esters, ketones, common alcohols, coal tars, petroleum hydrocarbons, and plasticizers. The most important solvent for printers is petroleum hydrocarbons. Hydrocarbons are chemical compounds composed of hydrogen and oxygen. They can be divided into two groups, one is aliphatic hydrocarbons and the other is aromatic hydrocarbons. The chemical difference between the two is that the hydrogen and oxygen arrangements in the two groups of hydrocarbon molecules are different. However, from the actual use point of view, the difference between the two is that the dissolving power is different.

Examples of aliphatic hydrocarbon solvents include mineral spirits, kerosene, naphtha, and benzene. Aliphatic hydrocarbon solvents have a low solubility and a KB of 27 to 50. The KB value indicates the solubility standard of the solvent obtained by the Kauri-Butanol experiment. The KB value is a measure of hydroxide solubility. Solubility is the ability of a liquid to dissolve a substance. It can reduce the viscosity of the material and increase the rheology of the material. The solvency is to prevent precipitation or decomposition in solid form. For example, the solubility of toluene was tested to be 105 KB, which indicates that it has a strong solvency, and the solubility of kerosene is 29 KB, indicating that it has a lower solvency.

Aromatic hydrocarbon solvents have medium and high solubility, and the KB value is about 60-90. Toluene and xylene have higher solubility and the KB value is about 80~115.

In addition to aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents, printers use alcohol, ketone, ester, and chloride solvents. Alcohol solvents such as methanol and butanol; ester solvents such as ethyl acetate, pentaacetate and isobutyl acetate; ketone solvents such as acetone, methyl ethyl ketone (MEK); chloride solvents such as carbon tetrachloride, dichlorinated Ethylene and trichloroethylene.

The quality requirements of the solvent for the printer are no different from those for other industries, but it emphasizes the consistency of the solvent. Solvents should have the same operating characteristics when used under the same conditions. If possible, the solvent should be odorless or have the same odor and not be oxidized. Solvents should have as high a combustion point and flammability rating as possible; should have a suitable evaporation rate; help dissolve the resin in the solution, the binder or compound; should help prevent the ink from drying during printing and have Helps the penetration of ink. To do all of this is undoubtedly a very difficult matter, so the printer must know how to safely use different solvents.

Solvents are chemical substances and their proper use involves many aspects such as solubility, solvent type, boiling point, evaporation rate, burning point, flammability rating, toxicity, and so on. Classified by the evaporation rate, the solvent can be divided into: rapid evaporation, medium-speed evaporation, slow evaporation and ultra-slow evaporation. Acetone, ethyl acetate and benzene are of the fast evaporation type; ethanol and toluene are of the medium speed evaporation type; pentanol and butanol are of the slow evaporation type; and ethyl lactate and butyl cellosolve are very slow evaporation solvents. In general, the fastest evaporation and lowest boiling solvents are the most flammable. The fast-drying inks used in screen printing require fast evaporation and a boiling point that is as high as possible. Such inks are often printed in a dry environment and in an environment with a ventilation system. The evaporation rate of the solvent has been confirmed by the experts and is very important. It has also been taken seriously by the manufacturer. Solvent and ink vapors are expelled from the work environment as quickly as possible to increase production safety.

There is a potential danger in the use of solvents, so it is essential to understand as much solvent knowledge as possible. Some solvents such as pentane, mineral spirits, ethanol, ethyl acetate, petroleum benzene, and heptane are harmless, while some solvents such as toluene, xylene, amyl acetate, butanol, amyl alcohol and the like are more dangerous. Benzene, methanol, formaldehyde and carbon tetrachloride are undoubtedly more dangerous solvents. Industrial solvents have a physiological effect on the human body and can be poisoned by long-term operations, especially at high concentrations. Their toxicity differs depending on the type of the solvent, the ink, or the type of the solvent in contact.

The safe use of industrial solvents includes eliminating the effects of inhaling vaporized gases, eliminating the effects on the skin, eliminating the effects of soaking the solution in the body and eliminating fire. In response to these potential hazards, each country, place, unit, and solvent manufacturer has a clear description of working conditions and industrial safety standards. The printer must strictly comply with these safety standards for production.

To prevent the inhalation of boil-off gas, especially toxic gases, the workshop must have proper ventilation. Always wear gloves to prevent solvents from corroding the skin when it comes into contact with solvents for long periods of time. When using a very dangerous solvent, wear a mask. For industrial solvents, there is a maximum safety permissible concentration (MAC) in units of parts per million (PPM). Solvents added to the solution can make the solution toxic or destroy the working properties of the original product.

The degree of flammability is based on a reference data, that is, diethyl ether is 100 points, and carbon tetrachloride is the lowest point. The higher the flammability, the greater the possibility of solvent burning. For example, the flammability of kerosene is 40, the flammability of toluene is 75-80, the acetone is 90, and the benzene is 95-100.

Most solvents have a description of the burning point when they are sold. The point of combustion of a solvent is the lowest temperature at which it burns. Fast drying and low boiling solvents are the most flammable. This means that in a closed workshop, a low-burning point solvent is used. If the solvent vapor does not drain out, the shop is filled with steam, and the heat emitted by the larger lamp will ignite the vapor.

The combustion point varies with the solvent. Some solvents will burn at 0 degrees Fahrenheit, and some may not burn at 260 degrees Fahrenheit.

The flammable solvent itself will not burn, but its vapor will burn. The density of the solvent vapor is greater than that of air and is located in the lower space of the plant. Therefore, in order to discharge the vapor faster and better, the vent hole is preferably installed as close to the floor as possible. When screen printing workshops use flammable solvents, it is important to control the concentration of solvent vapors to avoid potential hazards.

Safe use of solvents

Although the solvents are different and the types are complex, the instructions for use of the solvents and the precautions must be concise and standardized. Even a harmless solvent should be taken seriously. Each solvent, like each ink, is stored in a safe container. Each container should be clearly labeled, including the name of the solvent, instructions for use, and precautions for use. Store the container in a dark place with the bottle up. When you open the bottle cap, keep it away from your face. Solvents such as acetone with high volatility and low combustion point must be stored to prevent the accumulation of vapors. If the solvent is stored using a storage tank, the storage tank must be grounded to eliminate static electricity.

The most effective way to store solvents is to store them in areas that are far from the work shop. The large screen-printing shop uses a variety of inks and solvents and usually places solvents, inks, and paints in specific areas. These areas must be strictly fire-resistant. The fire protection equipment must be complete and well ventilated. The exhaust device is to prevent the solvent vapor concentration from being too large, so as to avoid a fire.

Source: Bison