Bottle Screen Printing and Selection of Screen Printing Materials

In screen printing, bottle printing has a decisive position. It can be said that except for packaging and CD screen printing, bottle printing ranks third in silk screen printing. The substrates printed by the bottle mainly include plastics and glass. The plastics mainly include PVC (polyvinyl chloride), PP (polypropylene), PE (polyethylene), and PET (polyester).

The screen printing of bottles will be introduced from the following aspects: prepress processing, selection of screen printing materials, and attention issues.

Bottle prepress processing

Glass bottle printing

    To ensure that the surface of the bottle is clean (mainly without oil, sweat, dust, etc.), it is best to wipe it with alcohol before printing. After wiping, it is forbidden to touch the surface of the bottle by hand to avoid contamination of the bottle.

Plastic bottle printing

In the past period of time, PVC materials have been playing an important role in bottle printing due to their low price, good printability, and acid and alkali resistance. In general, since PVC is a polar material, it is generally not surface treated prior to printing, but sometimes due to the aging of PVC products or the plasticizers and additives in the products transferred to the surface will reduce the adhesion of the ink, can use anhydrous alcohol in the bottle Wipe the surface to increase the adhesion of the ink.

Since PP, PE, and PET have properties such as wear resistance, good plasticity, impact resistance, chemical resistance, etc., they are mostly used for making bottles and containers, but PE, PP, or PET are non-polar or weakly polar materials. In order to obtain the ink, the substrate Good adhesion, must polarize PP, PE, PET, so that the surface tension of the bottle to 50dyn / cm or more (in general, the ink is the best adhesion of the substrate is the most basic condition is the substrate surface tension at least 50dyn/cm or more). The methods of polarization treatment for PP, PE, and PET include flame treatment, corona treatment, and the like.

All in all, before printing, we must ensure that the substrate surface is clean and effective polarization treatment, which is the most critical prerequisite for screen printing bottles.

Screen printing material selection

Wire mesh

    The screen printing of the bottle generally chooses polyester or nylon mesh of 140-165 mesh/cm to ensure the hiding power of the ink layer and the complete curing of the UV ink during printing.

It is recommended to use Swiss SEFAR (Seifa) and Sanhe SST series screens, which are highly popular with customers due to their high tension and stability, excellent screen ink performance, strong abrasion resistance, and excellent adhesion to photosensitive materials.

Photosensitive material

In screen printing, photosensitive materials generally have the characteristics of good resolution, good bridging performance, high resistance to printing force, and easy recovery of screens. Bottle printing is no exception. In order to achieve the perfect combination of finesse and high-strength printing, Kemerai and Ketutai photographic materials are the ideal choice.

Squeegee

The hardness of the squeegee is generally 75 to 85 degrees, and the specification can be 5*25 flat or sharp, and the squeegee should have characteristics such as wear resistance and solvent resistance. The United States PLEGER, French FIMOR (Pegasus) is a good polyurethane squeegee.

Ink

The quality of the ink will directly affect the printing effect. Ink quality includes ink brightness, adhesion, chemical resistance, softness, and environmental protection. After several years of testing and comparison, the author recommended several excellent quality bottle inks to silk screen counterparts.

1 Solvent type bottle ink: SW-2000, SEIKO-1000, NAZDA-CER series products

The above ink is characterized by two components, good printability, strong hiding power, bright colors, strong adhesion, and low price.

2UV type bottle ink: SW-UVPE, NORCOTE-PPC series products

PPC series and SW-UVPE series inks are specially designed for bottle printing. They can be used for processed PP and PE plastics as well as PET, PVC, PS and other materials that have not been treated or treated. Especially for printing on PET materials, due to its high temperature resistance, the flame treatment will produce a high rejection rate, while the Noguchi PPC series (one-component UV-curable ink) and Sanhe SW-UVPE series bottles of ink are Printing on untreated PET material is quite excellent.

Chemical physical properties:

Adhesion. The above two series of bottles of ink and bottle surface adhesion, excellent adhesion between layers;

â–³ chemical resistance. After thorough photocuring, it has good chemical resistance to most common chemicals;

â–³ Fine text and pattern reproducibility;

â–³ Contains no harmful substances such as heavy metals, NVP, etc., full color is in accordance with EN-71 standard;

â–³ fast curing, suitable for automatic high-speed printing.

Printing suggestions:

â–³ Stir before use, add thinner or varnish to adjust the viscosity of the ink;

â–³ The colors of the same series ink can be mixed with each other without affecting the chemical and physical properties of the ink.

Curing conditions

The ink should be cured immediately after printing at a UV lamp of 280 to 320 nm. The curing speed depends on the ink ink layer thickness and the lamp power.

Problems to be noticed in bottle printing

Bottle surface treatment is not complete

    Non-polar and weak polar bottles for PP, PE and PET must be polarized. Polarization effects can be measured by “water treatment”. If handled well, a layer of plastic can be formed on the surface of the plastic bottle. The dense "water film" is often referred to as "Sheung Shui" by silk screen counterparts.

Polarization treatment timeliness

The effect of polarization treatment has a certain timeliness, the longer the time, the worse the effect and the worse the binding force with the ink. In order to ensure the adhesion of ink, it should be printed in time after processing. The survey found that due to the limitations of the customer's production process, polarisation and printing in most printing plants are not the same sector, which can cause printing lags and thus affect the adhesion of inks and bottles.

Squeegee hardness and angle selection

Squeegee hardness and angle have a greater influence on the fineness of the screen printing and the amount of ink. Fine pattern printing generally requires the use of a harder squeegee. As for the angle of the squeegee, the theoretical optimum angle is 45°. At this time, the edge of the squeegee is in direct contact with the screen. Taking into account the pressure during printing, the angle of the squeegee should be greater than 45° when in use. If the hardness of the squeegee is too small and the angle is improperly selected, the amount of ink under the ink will increase, affecting the degree of curing of the ink, and thus affecting the adhesion of the ink.

Screen selection

In bottle printing, especially when printing with UV inks, the choice of screens is more stringent. The number of screen meshes is ideally between 140 and 165 mesh/cm. This is to ensure that the UV light penetrates completely through the ink layer during UV curing and ensures that the ink is fully cured.

Be sure to stir the ink before use

Ink must be fully stirred before use is the most basic principle of ink use. This is because the specific gravity of resins, solvents, pigments, and auxiliaries in the ink is different, and the delamination phenomenon is inevitable after the ink is left for a period of time. If it is not fully stirred before use, the lighter weight components will precipitate on the upper layer and the components with higher specific gravity will precipitate. As a result, the quality of the inks often reacted by the customer will be unstable, and the hiding power and adhesion of the ink used before and after will be different.

Metal ink printing

When printing metallic inks, screens that allow metal particles to pass through should be selected. The mesh size is generally 120 mesh/cm or lower, and metal pigments will reduce the use time of mixed inks. It is advisable to mix metal inks that can be used for one day. In this way, “the phenomenon that metal inks are increasingly dumb” can be avoided.

Different inks require different energy when cured

In general, black, white, yellow, and red inks require higher energy during UV bottle ink curing. Therefore, the curing speed of the UV curing device should be appropriately reduced to increase the ink curing time. In addition, the curing time of the different color mixing varnish must be confirmed by testing.

The ratio of two-component inks

In the bottle printing, most of the solvent inks that are currently popular are two-component inks, and the proportion must be fixed when the inks are proportioned. For example, SEIKO-1000 series inks, the ratio of the main agent and hardener must be 7:3. In addition, the formulated ink must be used up on the same day.

Curing equipment

Here mainly refers to UV curing lamps. The curing lamp must ensure that the wavelength, power, and energy meet the UV ink curing requirements. The three are indispensable. Otherwise, they will cause no curing, incomplete curing, or embrittlement of the ink layer, further affecting the adhesion and softness of the ink.

Pay attention to the adhesion of multicolor overprint

Although the interlayer adhesion of SW-UVPE and NORCOTE-PPC inks is very good, care should be taken when printing six or more colors to ensure that each layer of the print before the last layer is completely cured, thus ensuring that the ink is Good interlayer adhesion.

As long as you choose the right system solution, and pay attention to the frequently occurring problems before printing, printing, and printing, and avoid problems, bottle printing is not a very difficult thing.