Error analysis and control of high precision window patching machine

Window patching machine is a kind of printing and packaging equipment, which is mainly used in the carton manufacturing field of packaging industry. The purpose of it is to paste film on the see-through window on the gift box, cosmetic box, tissue box, corrugated paper box and other packaging boxes. According to the different structure of the carton box window, the attached film is divided into two kinds of normal pasting film and special shape film, normal pasting film is suitable for the window is located on one surface of the carton, it is easy to ensure the accuracy of window pasting. But the special shape film on special shape box has crease line and gap, the carton forming film along the line with the carton folding, film gap and the corresponding carton window edge position, carton on two or more side has the see through window, so that customers could see the goods in the box in multi-angle, to get more information about internal goods, increase consumption experience; And the appearance of the packaging box design is more flexible and diverse, beautiful and unique, to give consumers a sense of beauty.

High-grade special-shaped packaging cartons requires high film sticking precision. If the film sticking precision is low, there will be box explosion (carton cracking) or distortion and other defects after the carton molding, resulting in waste products; If packing box on window edge and the gap between the bottom of the gap is greater than 0.5 mm, forming film on the carton appears very sharp gap, the gap is very easy to scratch the skin, causing personal injury, this is very strict, especially in EU countries as a safety rules, a child’s toy box, for example, if a person’s fingers or other parts of the body by the sharp film gap scratches, supply of goods are for personal injury compensation.

High-precision packaging carton window lamination needs high-precision window patching machine. In recent years, the high accuracy stick window patching machine  has improved, but the key technology such as speed, precision and qualified rate remains to be further improved, also can’t meet the demand of market, there are still a large proportion of high precision packaging carton, relying on a large number of human hand window pasting, slow, low accuracy, the worker labor intensity is big, take up the production site. The research and analysis of the error of high-grade special-shaped carton window patching can help to improve the technical level of high-precision window patching machine and meet the demand of high-grade carton producing market.

Error method and precision index of special-shaped carton lamination

High-grade packaging box generally use is greater than 0.2 mm thick film paste window, due to the thin film thickness, first of all need to die cut into single alien film, and then place them on the carton. Single heteromorphic film can be designed on multiple sides and multiple window positions of the carton. This kind of special-shaped film requires high precision and difficulty in sticking Windows, which requires special equipment to stick Windows.
The film sticking error of the special – shaped packing box can be divided into transverse error and longitudinal error is a schematic diagram of the expansion of a special-shaped carton box with a see-through window. In the figure, J represents the offset of the special-shaped film broken line and the corresponding carton broken line, which is called the film transverse error. M represents the gap size between the front edge gap of the film and the front edge of the corresponding carton window; K represents the gap size between the back edge gap of the film and the back edge of the corresponding carton window; the difference between m and K, namely (m-K), represents the longitudinal error of the film lamination. If the transverse error value J and the longitudinal error value (M-K) are larger, the film sticking accuracy will be lower.
According to the industry standard JB/T13213-2017 Printing Machinery Carton Window Lamination Machine, the lamination error requirements for shaped carton boxes are: transverse error ± 0.6 m m and longitudinal error ±0.5 mm, which are the most basic qualified requirements for the precision of window lamination equipment in China. This requirement is too low for high-grade cartons. In the box making industry, such as toy boxes, cosmetics boxes and other high-end packaging boxes exported to Europe, the M value and K value are respectively designed as 0.5 mm for die-cutting carton and sheet hetero-film. After the film is pasted, the vertical film error (M-K) requires ±0.3 mm, and the horizontal film error J value requires ±0.5 mm.

Box making industry also have a small amount of high-grade packaging, such as a part of the apple mobile phone packaging carton.When designing the box, m and k value is design equal to 0.3 mm respectively, after finishing the film pasting, the longitudinal sticker error (m – k) was required to + / – 0.15 mm, lateral film error of j values was required + / – 0.3 mm, such a film pasting especially need high precision requirement, want to use the equipment to fast steady window patching is very difficult, some companies to do the research and development,but stability good equipment is still few, and still is difficult problem in the development of industry.
In addition, it always will appear worse accuracy in exceptional box after window patching,so it generally measured by the qualified rate. In the industry standard JB/T13213-2017 <Printing Machinery Window Patching Machine>, the qualified rate of special-shaped film window patching is stipulated as 95%. In fact, in the box factory to high-grade packaging box window patching qualified rate of higher requirements.

Analysis on the reason of film error of window patching machine

In recent years, the development of window patching machine for high-grade special packaging carton box, compared with manual window patching has characteristics,such as, high film pasting precision, fast film pasting speed, high pass rate. But also often appear the film precision is out of line, the occurrence of waste products and other problems. There are many reasons for high precision window pasting errors, some of them are difficult to control or eliminate. Therefore, only by comprehensively analyzing the causes of errors and adopting effective control measures and elimination methods, can the performance of the window patching machine be improved and the film precision be high. The following error causes have a great impact on the film sticking accuracy:

The influence of paper box material and paper box die-cutting quality
The paper box materials that can be used for equipment film mainly include gray board, card board and corrugated board. The gray board is soft, the paper box is easy to be deformed in the process of conveying and positioning, and the film error will be larger. The paper box should be avoided in design. Card board and corrugated paper is relatively good, high precision of carton conveying, high precision of sticking window. The die-cutting process of the paper box has many factors affecting the precision of the window, mainly the die-cutting precision, the burr caused by the die-cutting and the quality of the die-cutting poly-line; General flat pressing die-cutting machine die-cutting box, each version will row more than one cardboard box, a version of the die cut down a number of cardboard boxes between each other there will be errors, which is adverse to the equipment film.

Influence of thickness of special-shaped film and die-cutting quality
The special-shaped film material is mostly PVC and PET, the thickness of 0.2 mm ~ 0.5 mm is in the majority, the thickness of the film is less than 0.2 mm soft deformation, film error is larger, less used on high-grade packaging carton; If the thickness of the film is more than 0.5 mm, the film is too hard to absorb the sucker, and it is difficult to take the film, which affects the continuous film taking and leads to film failure. Selecting appropriate film thickness is helpful to reduce the error of film sticking and improve the quality of carton. In die-cutting special-shaped film, similar to die-cutting box, but also each die-cutting version row more than a film, a die-cutting version die-cutting down more than a film will have errors, will make the film error is large.

The influence of box window size and window structure
Carton window, the greater the great error in the films, and the structure of the window on the sticker accuracy also have an impact, the impact to particular case is particular analysis, generally, the window is located in three or more cartons surface, stick window difficulty is bigger, the paster low accuracy, and the window area, the greater the number of window, the accuracy of sticker will be more lower.
Electrostatic effects produced in the carton and the film
In the process of window Posting, the paper box and the film will produce static electricity. Although the static electricity produced by the paper box is very small, it will also affect the rapid transmission accuracy and transmission continuity of the paper box. The static electricity produced in the film is a very tricky problem, not only static electricity is easy to produce, and the static electricity produced is large, which is not easy to eliminate, which seriously affects the absorption, separation and paste of the film, and even leads to scratches between the film, film quality is not guaranteed, resulting in unnecessary waste.

Carton conveying positioning error
For continuous non-stop laminating window machine (dynamic laminating), laminating speed is high, but affected by motion inertia, position detection error, correction error and other factors will lead to positioning error is large; And for the carton to stop and then paste film paste window machine (static paste film), is the use of positioning gauge will be in the static accurate positioning of the carton, the suction cup paste film on the carton, the window precision is relatively high, but the window speed is low.

 Influence of window edge gluing quality
There is a layer of adhesive between the carton and the film. It is necessary to bond and seal and bond firmly. The glue coating of the carton window is uneven, or the glue leakage will cause the film deviation, affecting the film precision and the forming quality of the carton.

Error between film taking and film sticking
When the sucker absorbs the film, each film should be in the same position, and there should be measures to eliminate static electricity, otherwise the film accuracy can not be guaranteed. When pasting film, if the carton is dynamic pasting on the carton in the process of motion, the error is larger, if the carton stops static pasting error is smaller.

Bonding, pressing and stacking
The paper box and the film also need to be pressed together, otherwise the adhesive layer is slightly convex, and the adhesive layer needs a certain time to cure, the paper box in the process of stacking friction will cause the film out of position, bring unnecessary errors.

Methods and measures for improving the precision of film sticking

Although the material of the carton and the film has an impact on the film precision, it has no relationship with the window sticking equipment. The box factory should consider these problems when designing the carton and the film, which will not be discussed here. As mentioned above, the reason for the film error is directly related to the film sticking window machine equipment. The corresponding elimination methods and control measures should be taken to reduce the error in order to improve the precision and quality of the carton.
Quality control of die-cutting of carton and film
Cartons to focus on the quality of the die cutting dimension precision, the window of the carton and film is corresponding to the line and the gap of accuracy requirement, and the equipment the paster, sensor (or visual system) to detect the location of the carton, general with carton window edge as a detection line, so the window die cutting high dimension accuracy requirement, at the same time, the die cutting out one carton size consistency is very important. Cartons generally in flat die cutting machine processing, a die cutting plate to row a plurality of carton sample, a plurality of carton sample due to die cutting error between each other, directly affect the precision of the film on the carton. In order to eliminate the error, ideally after die cutting of the different position on the carton sample according to the die cutting version numbered sequentially, stick a window when the same number of cartons for completion window, again, in a number of cartons, if the window appear error, to counterpoint to adjust window machine equipment, can eliminate the error of the die-cutting carton impact on the accuracy of sticker. Of course, if a die-cutting version only row a carton sample die-cutting, so although the production efficiency will be lower, but die-cutting down the carton size consistency is good, stick to the window when the equipment is well adjusted, can work continuously without adjustment. In addition, the die-cutting burr problem is related to the paper box material, die-cutting knife and so on, but also affects the window precision of the paper box, need to pay attention to eliminate, which is to solve in the die-cutting process.
The film die-cutting quality should also focus on solving the die-cutting dimensional accuracy, that is, the precision of each die-cutting poly-line at both ends of the gap is very important, die-cutting typesetting and sequential numbering method and paper box die-cutting method is the same, and to maintain the consistency of the size of each film die-cutting. The edge of the film is also the sensor (or visual system) detection of the baseline, if there is a burr, not only the detection error is large, but also may have an impact on continuous film absorption and film, to use good performance of die-cutting equipment and die-cutting knife processing, to eliminate burr.

Electrostatic elimination measures in the film
Carton and film processing process will have static electricity, the static electricity generated in the carton is relatively small, the separation and transportation of the carton is not affected, the control of the working environment of the window can prevent static electricity. The static charge generated in the film is large and it is difficult to reduce or eliminate it. According to the actual experience of sticking Windows, the following methods are concluded to eliminate static electricity: one is to maintain appropriate environmental conditions sticking Windows; Two is the production of film in the film raw materials to add anti-static agent, film is not easy to generate static electricity; Three is the film die-cutting process after the addition of electrostatic bar to eliminate static electricity; Four is to try to use film with film, part of the film in order to prevent scratches and have a layer of film, film after film is not easy to generate static electricity, the film is not bonded to each other; Five is the film placed on the rack with a static rod and blowing mouth, a certain amount of blowing air can not only eliminate static electricity, but also can make the sucker absorb film easy to separate. In order to achieve the desired effect of electrostatic removal, many methods should be used at the same time when necessary.

Film sticking method and film absorption
Window sticking machine film, film is generally absorbed with suckers, because the film is soft, if the number of suckers is small film is not easy to be controlled and deformation, film is not allowed, so the number of suckers more film positioning is more accurate, and multiple suction plate surface to adjust to maintain in the same plane. Dynamic and pasted membrane (carton no pause) generally adopts synchronous type films take put institutions, its window speed is high, generally in 2 ~ 4 suction cups are in the front of the thin film direction absorption edge, thin film, following the running track of suction cup run below set a Joe film board to gradually contact with carton laminating film, stick film front first contact box, back-end finally with carton stick together, so that the drawbacks of the film the back-end is have trace migration to form a larger lateral error, the solution is in accordance with the film path in set a side gauge, respectively, on both sides will run film direction until the film in the fall on the carton.
Static film sticking method (carton stop) film, film by the suction cup grab perpendicular to the carton plane stick down, so the film needs 4 or more evenly arranged in the film plane sucker suction and then put down, so the accuracy is relatively high, but the speed is low.
When the film is absorbed, the influence of vacuum suction on the error can not be ignored. Large suction is easy to make the film deformation. When the suction is released, the film should also release the deformation and run erroneous. Sucker suction size can be achieved by adjusting the size of the vacuum pressure, it’s important to note that in a film, vacuum suction release has a process in the suction cups, suction release slowly will produce the paster error, should choose to blow function, can vacuum generator or design can increase blow function, which release the suction moment increasing strength will be quick release film, will improve the paster precision.

Position detection of film and carton

In order to accurately affix the film on the carton, it is necessary to detect the position of the carton and the film before the paste is put. The closer the detection sensor is to the film and the carton, the better. The more advanced detection method used by the high-precision window sticking machine is the vision system, which is characterized by accurate detection position. It can realize dynamic adjustment to eliminate errors with the coordination of the servo drive mechanism, which is an ideal way to paste the film. But the cost is high, the detection of the box is not a problem, and the detection of soft, transparent film technology is not mature, suitable for static laminating way laminating window machine.
In addition to the visual system, another detection method is that the color code sensor detects the position of the carton, and the photoelectric sensor detects the edge position of the film. Both of these detection methods detect one or two edges of the carton or film. In order to obtain high precision film, synchronous film sticking device needs to have high mechanical accuracy and mechanical rigidity, so that the positioning of the paper box and film is accurate, this method is more suitable for dynamic film running at high speed.

 Influence of environmental conditions
The quality of cartons is greatly affected when the environmental conditions of cartons are not suitable. When the carton is pasting the film, the general ambient temperature is kept at 18℃ ~ 25℃, the relative humidity is kept at 50% ~ 60% more appropriate, and the environment is kept clean and dust-free. Under such environmental conditions, the deformation of the carton and the film is small, and the electrostatic generation is small, which helps to improve the film precision of the carton.

Other measures to improve the film accuracy
The film and the carton between the coating layer on the precision of the film also has an impact, the thickness of the coating layer, the uniformity of the coating layer has a certain impact, to ensure the bonding strength of the coating layer as thin as possible, the more uniform the better. In addition, the cold glue solidification time is long, pressing, stacking process will also cause the relative dislocation of the film and the carton, you can use the characteristics of hot melt glue rapid solidification, glue gun ejected small glue points will film and carton first positioning, cold glue and then solidify completely bonded firmly sealed.

Summary

There are many reasons for error of special-shaped cartons, which involve raw materials of cartons and films, die-cutting forming, packaging, transportation and storage, working environment of window factories, performance of window equipment and other factors. In order to obtain high film accuracy and pass rate, it is necessary to control the error reasons one by one, and ignoring one factor will not achieve the ideal effect. It is more important to correctly deal with the relationship between the film speed and the film precision of the window sticking equipment, which are a pair of contradictions. In the research and development of the window sticking equipment, we should distinguish the primary and secondary, while taking into account the specific analysis of the specific problems, continue to explore the new window sticking process method, and constantly improve the performance of the equipment.