Printing machine printing technology

The printed mold plate is the surface of the printed graphic etched on a steel plate or a flushed photopolymer diaphragm. When printing, the scraper (commonly used 0.25-0.5mm thick with good elasticity, absolutely straight steel or copper pieces made of the blade mouth) will scrape the ink into the etched pictures and pictures, and the remaining ink back into the ink grains. When printing, the flexible soft printing offset head will then transfer the ink from the template to the substrate.

The rubber head made of silicone rubber shall transfer the ink from the above steel sample to the substrate. The rubber head must be soft and free of stain. So it can be printed on different shapes, different hardness and different quality of bearings, such as lighters, circular arc pens, toys, home equipment, switches, keyboards, buttons and other electronic and automatic devices.

1.The advantages of pad printing and the characteristics of covering force.

Advantages: 

- -A variety of optional substrate- -fast cylinder printing speed

-Print hard, hollow objects- -synchronize with assembly and production line

- -Fine printed lines- -closed system operation, slow solvent volatilization, without spending too much time paying attention to ink, such as ink viscosity

-Easy to operate

-Multi-color printing-fast drying, low energy cost

- -Change time is short, especially suitable for printing small objects- -the operation space does not need to be too large, save the space

- -Low printing costs

Features of covering force:

- -Print objects of different shapes

- -Can be printed on the surfaces of different classes

2. Requirements of pad printing 

-2.1 Shape and comparison of printing offset head

Printing head is an important part of the process of printing machine and printing, which directly affects the transfer rate and printing quality of ink. All standard rubber head shapes have one feature in common: the printing surface is convex, with a certain Angle from the edge to the printing area in the middle. This convex surface affects the ink transfer, but maintains the cleanliness of the ink printing. Semcle, conical head is ideal, can rotate evenly to prevent bubbles, but also easy to transfer the ink from the steel template to the substrate, but the shape of the head can sometimes be square or rectangular. If it is a square, you must ensure that the middle is conical, so that the glue head is easy to turn. The results of the rectangular head are not ideal, because the head can only move in two vertical directions.

2.2 The size of the rubber head

Should ensure the sharpness of the line and the printing of no stain, and the rubber head should be selected larger (that is, the effective projection area of the rubber head is greater than the graphic area on the steel sample). Because the smaller the deformation of the glue head, the sharper the printing line, at the same time, the glue head is slightly larger than the actual printed pictures, especially for some special printing, but the pressure required by the large glue head is also required, the more expensive the price is.

2.3 Hardness of the rubber head

The hardness of the rubber head is usually 2-18, the special hardness from 0-40 above, the higher the number, the greater the hardness. Hardness affects the printing quality and printing life, hard rubber head printing effect is good, long life. But in most cases not too hard rubber head, because it can damage the printing material; similarly, the soft rubber head can be used for uneven surface, such as the workpiece with large curvature of the bearing surface. Therefore, the choice of more hard glue head, depends on the pressure size of the printing, the greater the pressure, the harder the glue head. But the glue head pressure should not be too big, otherwise the substrate will have small cracks, easy to appear stains. In short, when the printing line is more thin, the rubber head is relatively soft, printed on the plane, the rubber head can be hard, for the printed surface garden arc or uneven surface should choose a softer rubber head.

2.4 Quality of silicone rubber used in the rubber head and the transfer of ink:

The printing rubber head is made of elastic materials such as silicone rubber and polychloride ethyl formate resin. There are two main types of silicone rubber: polymerization type and adding polymerization type.

From the physical properties such as anti-pull, anti-solvent, plus the polymerization of the glue head than the polymerization of the glue head is better, of course, the price of raw materials is also expensive. The smoothness of the surface is a decisive factor in determining the quality of printing, such as small stains or air bubbles can affect the printing. At the beginning of the printing shift, the new glue head may not be able to absorb the ink, which can be tested on the paper or cleaned with alcohol to solve. It can also be cleaned with diluent, and the adhesive head can be immediately sucked ink from the steel sample; If the ink transfer is not very well, the adhesive head can be used to remove the dust off the adhesive head. At the same time, the rise and fall degree of the ink pad head will also affect the amount of ink transfer.

2.5 Life span of the rubber head

Generally, a rubber head can be printed about 5000~10000 times, but it also depends on the type of ink used and the printing quality requirements. With a single component ink, the life of the glue head is longer, while the double component ink is shorter. The size, shape, hardness and material shape of the rubber head will affect the service life. If the printing Angle is more sharp or particularly curved object, the glue head printed 1000~5000 times will damage. Silicone oil is used for rubber head cleaning.

3. Requirements for steel plates

Steel templates can be used to transfer printed graphics, and which steel templates are used depends on the printing quality and quantity. To ensure the fluency of printing, the graphic distance on the steel template is at least 25mm and fixed in the middle. If it is a long line or fine line, the Angle of the scraper blade and the steel template into 5-15, to ensure that the scraper will not scrape too much ink. Multiple experiments show that the etching depth of 25um is most suitable for printing, because the amount of ink in each transfer is less. If the etching depth is 25um, the ink film thickness is 12um, and the remaining ink remains in the steel plate. Because the ink contains 40-60% diluent, the dried ink film is 5-8um thick, sometimes only 2um. The etching depth of fine fonts is 15um, while up to 30um in large areas. The materials commonly used to make steel template are T8, T10 tool steel and CrwMn, 9 Mn 2 V alloy steel. According to the determination of HRC => 45-60, no matter which kind of steel is used, the Rz value of the grinding and polishing surface before the etching pattern should be <0.8-0.2um, so it is important to grind the steel plate.

4. Printing ink

To achieve the desired printing effect, a removable printing ink must be used. Because the amount of ink transferred each time is less, the color content of the transfer ink is higher. Characteristics of the ink include:

- -Easy to operate- -large color concentration

- -Long storage period- -good covering and fine ink

- -No harm to health

--Protect the environment-quick drying (about 3 seconds)

--Easy cleaning-below the substrate surface tension and ideal viscosity

--Good adhesion, the material does not need pretreatment and postprocessing

- -A wide range of applications for various seals

Note: Due to the different scope of use, the requirements for ink are also different.

4.1 Composition and function

The ink contains adhesives, pigments, solvents and additives. The adhesive material contains one or more resins. Resins in the most cases are generally powdered and must be dissolved in an appropriate solvent or mixed solvent. The selection and synthesis of the resin determines the printing characteristics of the ink, such as the transfer and adhesion to the substrate, gloss, and chemical resistance. Solvent is the decisive factor of the drying speed of printing ink, and the printing speed and adhesion. The effect of slow drying agent on printing is not too great, because the speed of printing is generally very fast, only needed when using fast drying ink, such as using Baolong KSU series ink. The slow drying agent is evaporated slowly, so it does not have much impact on printing. The diluent is included in the solvent, and the diluent is mixed with the ink to obtain the ideal viscosity, which facilitates the ink transfer and transfer effect. The pigment reflects the hue of the ink and determines its base color. Can be divided into organic and inorganic pigments, the pigment does not contain heavy metals, large color concentration. The additives are generally used in small quantities, and their role is to adjust the characteristics of the ink, such as fluidity, viscous operability or surface characteristics. Auxiliaries have leveling agent, thickening agent, etc. No matter what kind of ink, it should be used each time, and fully mixed, in order to ensure the printing viscosity, the ink should be appropriately adjusted in the printing, to ensure the continuous printing.

4.2 feature

The printing requirements vary as follows:

--The printing surface shall be dumb, half light, smooth or highlight.

— Chemical resistance, UV resistance.

-Light resistance, scratch rub resistance or saline resistance.

- -The printing surface should be transparent or well covered up.

4.3 Ink type

--Physical dry ink (single component)  

--Chemical curing ink (double component)

- -UV curing type ink

--Water-based ink

Single component ink added diluent can obtain the ideal printing viscosity, the drying mode is physical evaporation type, some thermoplastic substrate such as PS, PC, PVC will be slightly dissolved, this dissolution makes the ink and the substrate directly bonded, so scratch resistance, good adhesion.

The chemical resistance of two-component ink is higher. Generally, the hardening agent needs to be added to the ink, but it must be noted to add before printing production. If the addition time is too long, the effect is not good. Complete drying depends on the ambient temperature; it takes several days to dry at room temperature 20. Therefore, do not conduct scratch resistance and adhesion test too early.

Thermosetting ink is generally two-component ink, the resin connection of this ink will not occur at room temperature, only under high temperature conditions.

The oxidized ink reacts through air oxidation, and the reaction speed is generally slow, for 1~2 days at room temperature.

The transfer of the printing ink mainly depends on the evaporation of the solvent, which binds the ink film and adjusts the adhesion of the ink. Good covering force is achieved by the transfer of the ink film layer. Due to the lack of solvent in UV ink, the ink film layer cannot be changed. This transfer is "water transfer", and the transfer is difficult.

The application field of UV curing ink is generally high-quality transfer printing.

The advantages of UV ink are: -steel template ink is not dry-quality is guaranteed-less wear of the steel sample-fast drying speed-no solvent 

UV ink disadvantages: -high energy requirements, the requirements of UV curing equipment.- -The requirement of cleaning the rubber head is higher, and the viscosity requirement is not as good as solvent ink- -fine printing is inferior to solvent ink

Water-based ink has not been used for printing, because the yield is low, drying speed, viscosity, adhesion, evaporation speed are not as solvent as ink.

4.4 Preparation work before printing

The amount of diluent and hardening agent should be carefully weighed; the treatment; some bearings have oil or silicon, the surface can be printed, the simplest method is to clean with alcohol. PP or PE can be treated with a corona or a flame. The corona treatment is 20,000 volts, and the flame can be adjusted during the flame treatment. Another method is to treat the surface with PP water. Some plastic has strong static electricity on its surface, which can be treated with an ionizer. When multi-color printing, the drying can be accelerated through a ventilation system. But it must be noted that the seal can not be straight to the ink blow