Analysis of the Method of Reducing Solvent Residues in Printed Products (2)

Third, the complex process of solvent residue control

Composite material:
The barrier property of the material has a great influence on the residual amount of the solvent. For example, the BOPP/PE structure can easily volatilize the solvent. For a structure with good barrier properties, such as KBOPP/PE (PP), the solvent is not easily volatilized. Product solvents with a double-layer barrier structure are hardest to evaporate, and it is difficult to eliminate the over-standard after compounding, such as PET/VMPET/PE KBOPP/VMPET/PE.

2. Type and quality of compound glue Solvent-free glue and water-based glue do not contain organic solvents, which can solve the problem of solvent residue. Everyone has this experience, the same solvent-based polyurethane adhesive, different manufacturers of glue in the same material, the same process, the solvent residue after compounding is very different, this is because the soft segment contains active hydrogen hydroxyl The hard segments contain active hydrogen biuret groups, urethane groups, and these active hydrogen-containing groups can form intermolecular hydrogen bonds with the hydrogen bonds in the ethyl acetate molecules. The formation of intermolecular hydrogen bonds will restrict the release of ethyl esters. The greater the density of hydrogen bonds, the stronger the binding to ethyl ester, and the higher the residual ethyl ester under the same conditions, so the frequent replacement of glue manufacturers for cost reduction is not possible. We have done tests and used other factories to dry and re-use single-layer products under the same conditions for other conditions. After maturation for 2.5 hours in a curing chamber at 45 degrees,
The glue solvent residue in the factory A was used: toluene 3.65 mg/m2, ethyl ester 7.87 mg/m2.
The glue solvent residue of B factory was used: toluene 4.02 mg/m2, ethyl ester 21.59 mg/m2.
The amount of ethyl ester is almost 3 times that of the former

3. Influence of Moisture In the composite production, water not only affects the appearance quality and composite strength of the printed product, but also affects the release of the solvent.

The source of moisture: NY film is most likely to absorb water, PET, VMPET, AL surface is easy to absorb water, BOPP, PE film is relatively good, water content in solvent, and in the production process due to continuous evaporation of solvent away a lot of heat , will cause the moisture in the air to cool on the surface of the roller and the rubber roller.

4. The effect of the laminating machine on the solvent residue is mainly manifested in:
A. Design of drying tunnel B, intake and exhaust volume configuration C, direction of exhaust air duct D, configuration of drying tunnel temperature

5. Compound process A. Strictly enforce the process discipline. Once the qualified process is strictly followed, do not change raw materials easily. Any changes in parameters must be tracked and monitored in a timely manner.
B. Effect of coating thickness: The larger the amount of glue per unit area, the thicker the coating surface and the less volatile the solvent.
C. The influence of the temperature gradient of the drying tunnel: Generally, the three-temperature zone is set to 60 degrees, 70 degrees, and 80 degrees, respectively, but it should be properly adjusted according to the speed, the amount of glue, and the amount of toluene in the printing film machine. .
D. Impact of speed: The slower the speed, the lower the residual solvent, but it must be prevented that the speed is too low, which causes the heating temperature of the aluminized film to be too high, causing the peeling strength to decrease.
E. Impact of toluene residue in printing: According to the statistics of the test data, if the residual amount of toluene solvent is high, the residual amount of ethyl acetate after compounding is relatively high, and it is generally 1.5 to 2 times higher, so the printing process is reduced. After the amount of toluene remained, the residual amount of ethyl ester in the compounding step also decreased accordingly.
F. Management of the curing room: The curing room must be forced to ventilate. Generally, the wind is forced to discharge once every 30 minutes. The composite membrane should be erected. Do not place it directly on the ground. The temperature fluctuation of the curing chamber should be as small as possible.
H. If solvent residue is found in the curing room, the handling is very troublesome. If it is a two-layer structure with poor barrier properties, such as: BOPP/VMCPP, BOPP/PE can be saved by dry re-drying. We once used the BOPP/VMCPP structural solvent residual toluene 5.44mg/m2, ethyl ester: 15.48mg/m2 products through the oven temperature of 55 degrees, 75 degrees, 85 degrees, machine speed 20 meters per minute, bake two times After the solvent residue was reduced to toluene: 2.01 mg/m2, ethyl ester: 6.54 mg/m2. However, if the multilayered structure with good barrier properties exceeds the standard, it can only be scrapped.

IV. Representativeness and accuracy of sampling and testing

Even if it is the same sample, because of the different sampling methods, the solvent residual value is very different, which requires the sampling must be standardized, the method must be unified.
A. Don't slow down when sampling. Make sure to sample online. This can represent the entire volume.
B. Immediately after sampling, seal in an aluminum foil bag without odor or in a glass bottle with a rubber stopper.
C. The tester should perform the test immediately after opening the bag or bottle. It cannot be placed in the air for a long time. Because the monolayer membrane solvent is easily volatilized, the entire roll membrane is less volatile.
D, the same sample to do three times, take the average.
E, if the difference is too large to re-sampling detection.
F. The chromatograph should be subjected to the aging test as required.
G. To prevent inaccurate data caused by instrument deviations, it is often necessary to perform positive comparisons with authoritative testing departments or the end user's instrument.

Fifth, the impact of finished product storage, transportation process A, printing and composite semi-finished products should be placed in a ventilation and pollution-free environment, if the time is sufficient, the printing film is best placed more than 24 hours and then recombined.
B. The finished film should be packed in paper as much as possible, without the use of waste printing film or waste composite film in order to facilitate ventilation.
C. Bag products shall be left for 4 hours after leaving the machine and then be packaged after the heat is discharged.
D. Do not tie bags with rubber bands.
E. The paper core of the finished product packaging must also be controlled. Pulp and glue may produce odors.
F. Finished products are strictly prohibited from being stored in the same room as ink and thinner materials.
G. It is best to ventilate during transportation.
H. Cargo trucks should be dedicated. There have been packaging films that have been returned due to odors. However, there are no reasons to check the inside of the company. The last problem was found in the rental trucks. The goods on board were pesticides. Due to lax packaging caused by leakage of odor.

These are some of our experiences in production practice and are for your reference only.

Author: Liushao Lan Zhang Wenqin (Jinyu (Henan) Packaging Co., Ltd.)