Selection of Pad printing machine

printellautomation.comPad Printing

Are you looking for pad printing machine or thinking how to purchase pad printing machines?

Following are the guidelines which will help you in selecting the right type of machine for your requirements.

1) Type of machine, open inkwell or closed cup.

2) The number of colours you require to print

3) Size of the print area.

4) Overall product size and its weight.

5) Quantity required per day for printing.

6) Quality of print you expect from the machine.

7) Hours of production machine will be running in a day.

8) Features available for setting the machine parameters to achieve the highest quality prints.

9) Surrounding area of the machine for installation, e.g. Medical, Height temperature etc.

10) Any special requirements.

11) Maintenance cost of the machine.

12) Manufacturers reputation and after-sales service.

There are other factors which are also important such as,

1) Cost of Machine and peripheral equipments.

2) Cost of printing per colour.

3) Cost of pad printing consumables.

4) Space required of operation.

5) Electricity cost.

6) Requirement of the machine for pre-treatment or post-treatment.

7) Any permission required from government officials.

8) Skill or semi-skilled labour requirement.

9) Easy diagnostic of the machine issues.

10) List of spare parts and life of were and tare parts.

11) Compatibility of inks to machine and product.

Pad printing machines come in various types of shapes and sizes. India major two types are more common.

1) Open inkwell 

In this process, inkwell contains the ink. Spreading of the ink is done by roller attached to the machine.

Ink which spread on the plate goes into the cavity created by the etching process and get filled.

Machine has a thin edge blade whose work it to scrape while going back to the inkwell. The etched areas get filled with ink. Blade removes the excess ink for the plate.

Scraping of the ink depends on the thickness of the blade. For sharp image use thin blase and patchwork use thick blade. Blades edge plat important roll in quality print.

After the blade scraps the ink, silicon pad comes down and give the required pressure to pick up the ink from etching areas. The ink should be semi-dry before the pickup so the entire film will form and avoid the spread of the image.

The ink also dries on the pad securing firmness of image. Pad move towards the product and gives pressure on the product. Ink gets transfer on the product. To decide the pad pressure, the shape of the product is one of the parameters.

 Advantages of this process.

1) Printing can be possible on large areas.

2) Plate cost is cheaper.

3) One plate can accommodate many designs.

4) As the ink is open one can see ink level ink the ink tray.

Disadvantages of this process.

1) The major disadvantage of open-inkwell is, it attracts dust.

2) Evaporation on thinner is more, hence thinner required is in more quantity.

3) Print shade changes, addition of thinner at frequent interval.

4) Production loss is considerably more in this process.

5) Cleaning of the inkwell is an essential part. It takes a lot of time.

6) It is essential to clean all the parts like ink roller, ink tray, and blade. Ink residue may damage the print quality.

7) Additional cost of cleaning solvent, cotton wast, compared to other processes.

2) Closed cup pad printing machines.

In this process, instead of ink tray, ink cup is used. Ink cup store the ink, which moves front and back or sideways. Inks get filled in the depression created by the etching process. Cup with along with cup ring scrap the ink form plate. It does the same work as doctor blade in open inkwell.

Cup ring is available in different sizes and materials. Most common are-

a) Metal.

b) Ceramics.

c) Tungsten.

Pad picks up the image from etching areas and transfers the image on to product with required pressure.

Advantages of closed-cup system.

The main advantage of this process is the handling of ink.

1) Inks is in the cup so no dust issue.

2) evaporation for the thinner is minimal, as the cup edge seals the ink from all the sides.

3) No or less ink falling of the cup. So no ink mess.

4) No need to remove ink every day after production. In the case of two-pack ink require cleaning due to the short shelf life of the ink.

5) Print shade remains the same due to less thinner intervals.

6) More production due to less stoppages in the production.

7) Horizontal travel of cup can print a larger image.

Disadvantages of this process.

1) Cup ring is the core part of the machine and also the most fragile part. If the edge of the ring damages, it is not repairable. It leaves unnecessary ink stains or line behind. Pad pick this ink while printing. Print quality suffers due to unwanted ink.

2) Ring cost is high.

3) Etching plate is expensive.

4) Etching plate require high accuracy

5) Number of designs a plate accumulate is less due to cup diameter.

 6) Suitable for small print areas.

Other pad printing process.

Rotary pad printing process.

In this process, the machine uses a cylindrical pad and a drum. Drum has etched portion on its surface. The ink flows on the round cliche, a doctor blade scraps the excess ink from the cliche. Pad which is rotating same time pick up the ink and transfers on the product. 

Advantages of this process.

1) The main advantage of this process is high speed. One can print 1,20,000 impression per hr.

2) This process prints fine details.

3) These machines can print a 360-degree parts.

4)They are suitable for continuous printing, For example, Interval marking.

Disadvantages.

1) manufacture make these machine as per the requirements of the customer. They require huge investment.

2) They and made for specific products, so can’t use for other products.

3) Due to high speed, automation for feeding and unloading is a must.

4) Ink layer is minimal due to high speed.

5) Monitoring of ink viscosity is more important.

Accessories for pad printing machine.

1) Shuttle :

Shuttle is a system by which more than two colours get printed. Shuttle is made with pneumatic cylinders or by servo motor.

Shuttle is available in 1 colour to 7 colours depending upon the requirement.

Product moves with the shuttle under each pad carrying the colour image. So if it is three colour print. Shuttle will take first impression for the first pad. Then the jig will be moved by shuttle to the second position. When pad prints second position it will move to third position for printing. After the third print is over, it will go back to the original place.

Product requires one jig in suttle system, On the other hand, as the total impression are grater than one the speed of production reduces. For example, If machine prints a single colour product @ 1200 /hour, with three colour shuttle, it will be printing 400 products per hour.

Index table.

To overcome the lower production issue with shuttle indexing system was introduced.

Three indexing systems are more popular.

1) Round Indexing

2) Linear Indexing

3) Oval indexing.

In this process, the number of jigs are more. Etch jig goes under each pad once and moves ahead for another print.

The first jig comes under the first pad gets the impression and moves under the second pad for printing. The first jig forwards and second jig come under first pad. All the pads come down for the second impression. The product gets the second impression with the first jig.

Product on the second jig gets its first impression.

This process goes on as per the number of colours available on the machine. By this indexing process, machine production speed remains the same, and with each pad stroke, one complete product comes out.

Custome purpose pad printing machines.

90-degree pad printing machines.

These machines are similar to the regular pad printing machine. They have additional feature is, after picking up the ink from the plate the pad moves 90 degrees and makes the horizontal stroke of printing. Some products are overweight and can not be handle easily under machine. This machine is suitable for such products.

CNC pad printing machines.

New technology innovation in the pad printing process is taking place. With servo motors and programmable logic controllers (PLC) and Human Machine Interface (HMI), Managing complex printing logic with this equipments is easy. This machines can print many colours, can repeat the number of impressions on a single product with different pressure. When low production and complex printing is essential, these machines perform efficiently with any number of colours.

Flame treatment unit.

Materials like PP and HDPE has low surface tension and needs flame treatment before printing. Product require oxidation treatment to increase the surface tension on the product. Mixture of LPG gas and compressed air forms blue flame. Product travels through this and achieves the treatment.

 Post curing by hot air:

Some inks require hot air to dry completely. Product surface may require softening of the material for penetration of the ink. Two-pack ink requires heat for cross-linking of the polymers to have proper adhesion on the surface. Glass, metal, and polyamide surfaces require this treatment.

Solvent cleaning machines:

Pad, plates cup and other material which comes in contact with printing ink requires this machine.

Solvent machine and ultrasonic machine are suitable for this application.