Technical application of printing on plastic caps

There are two types of bottle caps: one is insert type and the other is round rotary type. Plug-in bottle caps generally do not need to be repeatedly installed, the shape is more complex, it mainly completes some functional actions, such as spraying. At present, it is mainly used in the packaging of some plastic bottles such as shower gel, hair care products and insecticides. Circular rotary bottle caps are more common and have a wider range of use. In addition to protecting the products inside the bottle, this type of bottle cap protects it from environmental influences, and also functions to deliver important information (such as sophisticated products), such as the unified group of tea beverages and portlet packaging products. Plastic bottle caps.

Therefore, the decoration of the bottle cap should not be overlooked. This article discusses the printing of text or trademarks on the surface of rotary caps.

Pad printing is the preferred printing method for plastic caps When customers receive orders for cap printing, the first thing that comes to mind is the pad printing process. The pad printing process is a unique printing method developed with the screen printing process, similar to the rubber stamp in our daily life. Pad printing adopts a relatively independent position relationship between the plate and the substrate, and no matter how strange the shape of the substrate, it can perform its task with outstanding performance. This led to the selection of the pad printing process for many tasks that were so difficult to accomplish as “universal printing”.

Using the printing process to print plastic caps has several advantages over other printing processes.
(1) It is convenient to change the varieties and the plate making is simple.
(2) Low investment. Compared with other printing equipment, pad printing equipment has the least investment.
(3) Strong adaptability. The shape of the printing head can be changed at will, which makes the adaptability of the printing technology to the shape of the printing material greatly enhanced. It is suitable for the printing of caps with different appearances and sizes. According to our investigation, about 80% of caps will not have a diameter greater than 40mm. This means that a pad printing machine with a plate area of ​​100 mm x 100 mm can print about 80% of the caps.

Plastic bottle cap printing elements

1. Ink In the printing of plastic caps, the choice of ink is crucial. Bottle caps are basically made of PP and PE materials, and the selected ink must match the type of printing material. When choosing an ink, you should pay attention to the following two points.
(1) Hardeners have been added to some inks to improve their adhesion, but they have increased the difficulty of operation. Therefore, unless the customer has special requirements, it is recommended not to use this method.
(2) It is best to use pad printing ink instead of screen printing ink. Screen printing inks have good leveling properties, while pad printing inks have better gel properties; screen printing inks have a relatively slow drying speed, and pad printing inks have a faster drying speed.
Although solvent-based screen printing inks can be used for pad printing, they are not as effective as special pad printing inks. If you need to use UV ink, you should not use screen printing UV ink, because screen printing UV ink transfer is poor. If you must use screen printing UV ink, you should add a certain amount of gelling agent.

2. The plastic head At present, generally do not pay attention to the choice of plastic head, but when printing, the choice of plastic head should be very strict. In the cap printing, circular plastic head application is more common. When choosing a plastic head, the following two points need to be noted.
(1) In the printing process of half tone images, the hardness and shape of the rubber heads used in the yellow, magenta, and cyan colors must be exactly the same, and the hardness of the rubber heads used in black may be slightly larger.
(2) Choose a good plastic head with good film release. This type of rubber head draws on the essence of the offset rubber blanket formulation to improve the printing quality of PP and PE surfaces.

3. Plates Resin caps are a sensible choice for bottle cap manufacturers who value printing quality. This printing plate is made of a nylon polymer without the need for corrosion processes, which is conducive to quality management. At present, resin gravure is more commonly used in pad printing machines produced in Europe and the United States.

4. Cost The bottle cover printing area is very small, so some people think that there is no need to worry about its cost. However, as market competition intensifies, it should still pay attention to reducing costs. This is the reason why many manufacturers use pad printing instead of flexo printing when printing caps.

At present, the cheapest single-color pad printing machine is priced at 10,000 yuan, including steel plates, clamps and plastic heads. With such a configuration, the monochrome printing cost of the bottle cap is generally not higher than 1 cent. If a fully automatic pad printing machine is used, the print volume will be less than 500,000 and the cost will be roughly the same. With over 500,000 prints, the cost will be reduced.

Plastic bottle cap printing trends

1. On-line production

Currently, in the domestic market, the most commonly used model is a stand-alone pad printer. Operators must place the products one by one, remove them after printing, and have extremely low production efficiency.

The automatic bottle cap printing machine integrates flame processing, pad printing and drying. It also has the functions of automatic loading and unloading. It is mainly used for bottle cap production of large enterprises and can greatly increase production efficiency. If you go online with the cap production line, the production efficiency will be higher.

The specific process for the on-line production of the automatic bottle cap printing machine and the cap production line is: After the bottle cap delivered from the cap production line arrives at the pad printer, the sensor issues an instruction after detecting the cap presence, and the flame processing device automatically ignites. The bottle caps are surface-treated, after which the caps enter the printing station for printing, and the printing is followed by drying. The dried caps are automatically fed into the conveyor belt.

2. Multi-color printing

With the increasing demand for value-added products, bottle caps are increasingly used for multi-color printing.

One method is to use multiple single-color pad printers to produce lines. One machine prints one color, which is achieved by color superposition. Although this process takes up a lot of manpower, it has a higher overlay precision than domestically-made rotary multi-color pad printers.

Another method is to use a multi-color pad printer. This method will undoubtedly increase production efficiency, because a single machine can operate with only one person and can place many caps at a time. However, as far as the samples printed by most manufacturers are concerned, the overprint accuracy of the multi-color pad printing machine is still not very satisfactory, which is related to the manufacturing precision of the multi-color pad printing machine itself.

3.UV printing

In Europe and the United States, the UV printing process has entered a mature period, but it is still largely blank in China. Cap UV printing process has many advantages: First of all, UV ink has a strong resistance, repeated use, printed graphics on the bottle cap will not be the finger of sweat and grease erosion. Second, UV inks basically do not have an adverse effect on the environment and the operator.

The current use of UV printing ink printing bottle caps face two major problems, one is the ink adhesion is poor, less than solvent-based ink. In Europe, MARABU TPC UV printing inks are the first choice, but this type of ink is rare in the domestic market. The second is that the cost of UV ink is high, which will increase the cost of bottle cap decoration printing, which is not conducive to its promotion.

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