Gravure printing "six questions"

One Question: How to Solve Electrostatic Problems in Gravure Printing

answer:

First, the electrostatic problem caused by gravure printing appears in the printing:

1, beard - is the ink flying out of the edge of the printed pattern or text, beard-like;

2. The markings on the printed part of the field often appear at a depth of 5-20 μm, which is due to the displacement of the ink on the printing film that has been affected by static electricity;

3, edge exclusion - appear when gravure printing overprint. The boundary between the first color ink and the film of the post printing ink does not agree well with the second color ink, resulting in repulsion, so that the white border of the ink is not printed between the two colors.

Second, static electricity in gravure printing comes from the following aspects:

l. The self-contained BOPP film has a large amount of static electricity, and can be replaced with a thin film produced by a different manufacturer or subjected to an antistatic treatment and then used.

2. There are mainly the following aspects when causing electrostatic failure in the printing process:

1 During high-speed printing, the long-term friction between the BOPP film and the rubber pressure roller generates a large amount of static electricity;

2 The climate is dry and the humidity is too low;

3 The characteristics of the ink itself or its own antistatic ability is insufficient, resulting in static electricity;

4 The antistatic device of the device has no effect, and it cannot play the role of eliminating static electricity.

Third, for electrostatic fault can be considered or dealt with from the following aspects:

1. Regularly check whether the antistatic device of the device can play an antistatic role;

2. In the dry climate, the printing environment must maintain a certain humidity;

3, try to use non-static printed film, or static elimination of printed film;

4, in the diluted solvent, add polar solvents, such as butanone, isopropanol, ethanol, etc., less ethyl. In the BOPP film printing process, 5% to 20% isopropyl alcohol can be added to the BOPP film ink to eliminate static electricity during the printing process:

5, can also be added in the actual printing process AE-2 super-concentrated electrostatic or 3500A antistatic to solve the "whiskers" like static, for the "edge exclusion" problem, you can increase the ink printing viscosity or use BK-201 help Agent and BK-202 additives, etc.

6, in the design of ink formulations, but also fully consider the ability of the ink to eliminate static electricity, you can add 2% to 8% of the isopropanol in the formula, while adding 0.1% to 0.5% of the AE-2 super concentrated antistatic Agent or 0.5% to 2% of 3500A antistatic agent to solve.

Second question: How to solve the layering problem of composite white ink in CL-PP system during storage?

answer:

The composite ink with CL-PP system is generally composed of three resins: EVA, MP45 and CL-PP. Due to the combination of the three resins and the wetting of the pigment, the polyamide resin and the nitrocellulose resin in the printing ink are not as good. Therefore, incompatibility occurs easily in the system, and even pigment sedimentation occurs. For composite white inks, the specific gravity of titanium dioxide is greater than that of other pigments, which accelerates the separation of the pigment from the resin system, ie, delamination.

Layering issues can be resolved from the following aspects:

1, choose the right titanium dioxide. Due to the great difference in the properties of different brands of titanium dioxide, some titanium dioxide and EVA, MP45 and CL-PP three resin system can be a good affinity, such as JR701 is better than other brands of titanium dioxide.

2. Select the appropriate dispersant and antistatic agent. Since dispersants and antistatic agents are usually surfactants, some can help disperse pigments, but they can easily cause instability in the system. It is recommended to use 3500A antistatic agent or L-18 dispersant. In the formula that can easily cause delamination, some L-18 dispersants can be used less, and part of the 3500A electrostatic agent can be replaced.

3, pay attention to check the side effects between additives. Many companies produce CL-PP system white ink, according to different user requirements and the printing environment, using different additives, and sometimes these additives will have certain side effects, and even lead to ink stratification. For this problem, experiments can be made on the compatibility of various additives and the situation after standing can be observed.

4, choose the right CL-PP. For domestic ink companies, the range of CL-PPs currently used is relatively wide, and suitable CL-PP resins can be selected according to their own formulation system.

Three questions: How to solve the CL-PP system complex white point problem?

answer:

After CL-PP system composite white ink printing and aluminum film composite curing, the emergence of composite white point problem, a few years ago many ink companies can not be solved, but at present many ink companies have found a way to solve, according to The latest situation we understand can be resolved from the following aspects:

1, try to reduce the solvent residue of the ink due to residual in the ink film in a small amount of solvent, after compounding, was blocked between two layers of film, in the aging, this part of the residual solvent by 50 °C temperature drying, Gradually volatilize from the ink film, the two films are separated to form a white spot. Reducing the residual solvent in the ink can significantly reduce the formation of white spots.

2, adjust the ink formula to improve the surface gloss of the ink.

Increasing the surface gloss of the ink layer can greatly reduce the pits on the surface of the ink (ie, empty spots), so that the surface of the print is close to a smooth film, thereby reducing the composite white point.

3, through a different composite method to solve

1 Adopt “repeated” approach For the printed film with composite white spots that has already appeared, when it is compounded, it can be coated with glue on one side of the aluminized film and then compounded with the printing film after being glued. This method is suitable for many occasions. effective.

(2) Increasing the amount of glue as much as possible Increasing the amount of glue can obviously make the surface of the ink layer on the print more smooth, which is favorable for combining with the aluminized film and reducing the white point problem caused by the pits on the surface of the ink layer.

3 Slow down the speed of dry compounding and appropriately increase the temperature during dry compounding

Slowing down the speed of dry compounding and appropriately increasing the temperature during dry compounding can effectively reduce the solvent residue in the ink and glue and reduce the composite white point.

Four questions: How to improve the gravure printing ink adhesion?

answer:

1, first of all to determine the ink is printed on what substrate, due to the great difference in adhesion of ink on different substrates, generally based on the printed substrate choose the right polyamide resin, can be selected by experiment, can also be used YMT polyamide resin.

2. The adhesion of the ink produced with polyamide resin on the BOPP film is normal. This problem can be solved by adding BK-515 aldehydes and ketones resin (BK-515 itself has many polar genes and can perform well with BOPP film. The attachment is generally 2% to 8% of the formulation.

Five questions: How to reduce the amount of solvent residue in food packaging printing?

answer:

Solvent residue problem has always been a difficult problem for ink companies. The state has already required the residual amount of benzene solvents to meet the hygiene requirements for BOPP/PE composite packaging. The residual amount of benzene solvents must reach 3mg/m2 or less, with the continuous improvement of people's food hygiene requirements. How to reduce the residual amount of solvent in food packaging E-brush has become a key issue for ink companies.

According to our understanding of the situation can be reduced from the following aspects of food packaging printing solvent residue:

1. In EVA-40W, MP-45, and CL-PP three kinds of books, CL-PP always has the highest residual solvent and EV-40W has the least residual solvent, so it can guarantee the composite strength. Under the conditions, the content of CL-PP can be appropriately reduced to increase the content of EVA-4OW;

2, choose the right CL-PP. The solvent residue caused by different manufacturers of CL-PP in the compound ink is very different. If the formula cost can be accepted, the PP803MWS produced by Japanese papermaking can be reduced to 50% under the same amount of conditions.

3. Add a part of ethyl ester and residual solvent reducer when dissolving EVA-40w, MP-45 and CL-PP, which can effectively reduce the residual amount of toluene solvent in the ink film;

4. Check whether the solvent used for the ink and the solvent used for printing are pure. If there is a small amount of high-boiling solvent, it may cause the solvent residue to be too high, and even cause severe odor in the printed matter;

5. Adjustments in the printing and compounding process:

1 Minimize the use of toluene solvents when preparing dilution solvents. You can use toluene:acetic acid:butanone=2:5:3 mixed solvent;

2 in the printing process to improve the printing machine drying tunnel exhaust, appropriate to increase the temperature of the drying tunnel, if the conditions allow after the white ink can be printed, open the drying tunnel for multiple drying:

3 The viscosity of the ink can be properly reduced during the printing process.

Question 6: How to solve the problem of reverse printing in the printing process?

answer:

Anti-envelope printing is particularly noticeable at low to medium speeds. The phenomenon of reverse printing at high speeds is greatly reduced. The key to solving the problem of reverse printing is to analyze the reasons for clear printing. In reverse printing, the ink is generally printed before the ink is reversed. On the printing plate of the ink, it enters the ink tank of the posterior color, changes the color of the ink of the latter color, finally causes the printing to be unable to continue, if the yellow ink gradually turns into the light green color, the red ink turns into the purple color gradually.

Generally can be solved from the following aspects:

1. Adjust the ratio of the ink dilution solvent to reduce the dissolving ability of the ink after the color ink is in contact with the ink of the preceding color. That is, when diluting the color ink, add a part of isopropyl alcohol and try to use less toluene. ;

2. Improve the speed of printing. Increasing the printing speed can significantly reduce the contact time between the ink of the back color and the ink of the front color. This is especially obvious for reverse printing at low speed printing, and there is basically no reason for the reverse printing in high-speed printing. This may be limited by the printing equipment and the printing environment during actual printing;

3, adjust the composition of printing ink formulations

First of all, you can use the method of improving the adhesion of the ink on the BOPP film, so that when the two inks are in contact, the ink of the front color is still attached to the BOPP film. In the ink of the CL-PP system, the CL-PP can generally be increased. Content is solved.

Secondly, the drying speed of the ink of the preceding color can be increased, the temperature of the drying path of the ink of the preceding color can be increased, and the presence of a small amount of non-volatile solvent in the ink ink film can be prevented.