Milk Packaging Film Gravure Process Specification and Common Failures

In order to ensure the printing quality of milk packaging film, it is necessary to pay attention to the control of the process conditions such as tension of the material roll, printing pressure, printing speed and drying temperature in the printing process, formulate a set of stable and reliable process standards, standardize the process flow, and ensure the scale production. The smooth progress.

Process specifications

1. The tension of the roll should not be too high: In the polyethylene film printing, controlling the tension of the roll is a key link. Because the stretch rate of the polyethylene film is relatively large, it is prone to tensile deformation under the action of the drawing tension of the printing press. If the tension value is too large, the polyethylene film will have a large tensile deformation, which may result in overprinting. Affects the quality and accuracy of the printed matter. Therefore, the value of the print tension should be set to be smaller to prevent overprinting and graphic distortion due to overstretching of the polyethylene film.

2. Control the printing pressure: According to the characteristics of the printing method, the performance of the printing ink and the performance of the printing material, the printing pressure is controlled within an appropriate range. If the printing pressure is too large or too small, the quality of the printed matter may be adversely affected. . Printing pressure is too high, the ink is easy to spread, resulting in graphic thickening, widening, and even paste version, the bar code can not read; printing pressure is too small, the amount of ink is insufficient, the graphic is easy to thin, narrow, and even defective.

3. Appropriate printing speed: Although the printing speed is high, it will increase the production efficiency and output and shorten the production cycle, but the printing speed is not as fast as possible. The size of the printing speed should match the drying speed of the ink, the viscosity, the temperature of the drying oven, and the temperature and humidity conditions in the workshop. If a domestic gravure printing machine is used, the printing speed is generally controlled below 100 m/min.

4. Reasonably set the drying temperature: The temperature setting of the drying oven of the printing machine should not be too high, generally around 40°C, otherwise it will easily cause the polyethylene film shrinkage deformation to be too large, which will affect the overlay accuracy. When setting the temperature of the drying oven, it is necessary to comprehensively consider the characteristics of the printing materials, the printing speed, the tension of the material roll, and the size of the printing pattern, so as to ensure that the ink is fully dried and the fastness of the ink is enhanced.

Printing points

(1) Do a good job in the inspection of the quality of raw and auxiliary materials (films, inks, solvents, etc.), and ensure that qualified raw and auxiliary materials enter the production process. This is the prerequisite for ensuring the printing quality of the packaging film.

(2) "Customer Satisfaction" is the highest criterion and final desire of each printing company. Therefore, the inspection of the finished products must be completed to ensure that qualified products are delivered to the customers.

(3) The plastic film after corona treatment should be used as soon as possible, and it is better to use it now. After storing for a period of time, the corona treatment effect of the film will be deteriorated, and the surface tension value will be gradually attenuated with the extension of the waiting time. When the machine is printed, it may not meet the requirements. Therefore, it is stored for a period of time. The plastic film must be carefully tested for its surface tension before use. Once the surface tension value is found to be insufficient, corona treatment must be performed again, otherwise the printing quality will be affected.

(4) In the actual production, the appropriate film and ink should be selected according to the filling conditions such as filling speed, sterilization conditions, and dairy shelf life of the automatic filling machine, and the printing process parameters should be adjusted and controlled according to the actual situation to standardize the process flow. , guarantee the printing quality.

(5) In the deployment of ink, should be used with the tune, and observe the printing effect at any time, pay attention to maintaining the consistency of the ink hue, to avoid print color differences. Different batches of printing materials or inks will often cause certain differences in the same batch of printing jobs. Therefore, in the long-lived printing or large batch printing, the same batch of films produced by the same manufacturer should be used as much as possible. And ink.

(6) The changes in temperature and humidity in the printing shop have a certain impact on the properties of the printing materials and inks. Too dry environments can cause the film to become static and difficult to print; too humid environments can cause insufficient drying of the ink and affect the ink layer. firmness. Therefore, the environmental temperature and relative humidity in the printing shop should be strictly controlled, as far as possible to keep it relatively constant, and to ensure good ventilation. In general, the temperature in the workshop is controlled at 18-25°C, and the relative humidity is preferably 60%-70%.

Common faults and solutions

Fault 1: Poor adhesion of ink

Cause Analysis:
(1) The film material has a low surface tension, poor printability, and poor wettability with the ink.
(2) An excessive amount of slip agent is added to the film during the blowing process to reduce its surface tension, which affects the printability of the film, resulting in a decrease in printing fastness of the ink.
(3) Additives in the film (plasticizers, slip agents, etc.) migrate from the surface to form a weak interface layer, which affects the adhesion of the ink layer.
(4) The surface of the film is not clean and adheres to impurities such as grease, dust, and foreign matter, which affects the adhesion of the ink.
(5) The quality of the ink itself is poor, the affinity to the plastic film is not enough, or the ink performance has changed.
(6) Insufficient ink drying, more residual solvents.
Solution:
(1) Replace the film material or perform corona treatment on the film again to ensure that the surface tension value meets the requirements.
(2) Adjust the film raw material formula and control the amount of the slip agent during the film blowing process.
(3) Clean the surface of the film to remove oil and dust on the surface of the film.
(4) Replace the ink.
(5) Reduce the printing speed appropriately, or increase the drying temperature to ensure that the ink is fully dried.

Fault 2: Printing film adhesion

Cause Analysis:
(1) The film material has a low level of slip agent and is inherently sticky.
(2) The ink is sticky, as the softening point of the binder resin is too low.
(3) The ink is not completely dried, and some solvents are still not completely evaporated. After the printing film is left for a certain period of time, residual solvent continues to infiltrate, and ink sticking may occur.
(4) The printed film is wound without sufficient cooling.
(5) The winding tension is too large.
(6) The temperature and relative humidity in the workshop or warehouse are too high.
Solution:
(1) Replace the film material.
(2) Replace the ink.
(3) Properly reduce the printing speed, or increase the temperature of the drying oven, and increase the air volume so that the ink can be completely dried.
(4) After printing, the film must be sufficiently cooled by a cooling roll and then wound up.
(5) Under the premise of ensuring that the winding is neat, the winding tension should be reduced as much as possible, and the winding diameter should not be too large.
(6) Pay attention to control the temperature and relative humidity in the workshop.

Fault 3: The printed film has an odor

Cause Analysis:
(1) Some odorous auxiliaries are added during film production to produce odors.
(2) The printing speed is too fast, and the power of the drying system is not enough. As a result, the ink is not fully dried, and more solvent remains in the film. After the printing, these solvents gradually escape and the printed film has an odor.
(3) A large amount of high-boiling solvent or odorous solvent is added to the ink, and if it is not completely dried, more solvent still remains in the film.
Solution:
(1) If the odor produced by the film, replace the plastic film.
(2) Properly reduce the printing speed, increase ventilation and drying time, and ensure the ink is fully dried.
(3) Try not to use or use odor- and smelly high-boiling solvents, and use low-boiling, odor-free solvents.

Fault 4: "Frosting" of the printed film

Cause Analysis:
(1) The storage time of the film is too long or the content of the slip agent in the film is high. After a certain period of time, the slip agent in the film migrates to the surface of the film, thereby causing a "blooming" phenomenon.
(2) Excessive temperatures in the warehouse or printing room exacerbate the migration of the slip agent.
Solution:
(1) Replace the film material.
(2) Pay attention to control the temperature and relative humidity of warehouses and printing shops, and ensure good ventilation.

Question 5: Overprinting is not allowed

Cause Analysis:
(1) Since the polyethylene film itself is prone to telescopic deformation, if the tension is not properly controlled and the elongation is large, overprinting may occur.
(2) The thickness of plastic film is not uniform, and there are drawbacks such as lotus leaf and thick thin road.
(3) The drying temperature of the printing press is too high or the power of the hot air drying system is too high.
(4) The tension of each part of the press is not properly set.
Solution:
(1) Use a polyethylene film with a smaller expansion ratio.
(2) Replace the film with uniform thickness and flat surface.
(3) Properly increase the printing speed, reduce the temperature of the drying oven, and minimize unnecessary hot air drying.
(4) Adjust the tension setting of the printing press so that the tension of each part of the printing press is balanced.

Fault 6: Biting

Cause Analysis:
(1) The drying speed of the previous color ink is too slow, and it is easily stuck by the ink of the latter color during the overprinting process.
The previous color ink layer failed to completely adhere to the film, and the adhesiveness of the latter color ink was too large, the printing pressure was too high or the resin content in the ink was small, and it was possible to bite the previous color ink.