Detection and Control of Alkaline Permeability of Vacuum Aluminized Paper

Vacuum aluminum-plated paper is currently a widely used trademark printing material. Many beer labels on the market today are printed with aluminum-plated paper, which significantly improves the quality of beer labels. Because the material characteristics of aluminum-coated paper are different from ordinary coated paper, its base paper is a waterproof coated paper, and its material has relatively poor absorption and has a certain resistance to penetration. Therefore, considering the process of recycling bottles from breweries, manufacturers and printers of aluminized paper must control the alkali permeability index of aluminum-plated paper in order to ensure proper label removal during bottling.

First, testing requirements, methods and standards for alkali permeability of aluminized paper

I. Check the required materials and utensils.

To test the alkali permeability of aluminized paper, one bottle of phenolphthalein indicator must be prepared; 1 bottle of solid sodium hydroxide; 1 thermostatic furnace or electric furnace for heating; 1 thermometer at 100°C and one for hydrometer; 250ml glass cylinder, 800ml One beaker and one stopwatch.

2. Sampling requirements, testing methods and standards.

(1) sampling requirements. A sample of aluminum-plated paper with no creases or breakages on the surface was randomly selected from each shipment as test samples. At the same time, three specimens with a size of approximately 60 mm×60 mm were cut at different positions in this paper. Then, the four sides of the back of each specimen (the length of the hem is approximately 8 mm) are each folded into a 90' concave shape, and then the four corners are fixed with a staple. After the concave specimen is finished, you can evenly apply some phenolphthalein indicator on each concave surface for color development.

(2) Test methods and standards.

The concentration of NaOH solution for testing is generally required to be adjusted to between 2% and 3%, and the temperature of the solution is controlled between 80±2°C. When dispensing, firstly put proper amount of NaOH into the measuring cylinder, and then gradually pour warm water of about 60°C into the measuring cylinder. After heating the water, the temperature of NaOH solution will naturally rise, and the temperature required by the test can be almost reached. . At this time, the pycnometer can be placed in the measuring cylinder to measure the concentration of the solution. If the concentration is unfavorable, water or NaOH can be added until the desired lye concentration is determined. After the lye concentration is adjusted, it can be poured into a beaker and placed in a constant temperature oven or an electric furnace for thermal insulation and constant temperature.

During the test, place the sample face down on the person's solution and simultaneously press the stopwatch to measure the time. When the phenolphthalein on the back of the sample shows a noticeable reddish phenomenon, the stopwatch is stopped by pressing the stopwatch. This time is the alkali of the sample. Penetration test results. The raw paper base penetration time is in seconds. Its standard should be determined according to the speed of the brewery filling line and the characteristics of the bottle washing structure. For a printing factory, when formulating the methods and standards for alkali penetration testing of aluminum-coated paper, it is necessary to first understand the characteristics of the bottling line of the brewery, such as the production speed, the temperature and concentration of the bottle lye, etc., in order to work out the beer The quality control standard of the base paper required by the factory. Secondly, the quality control standards of the base paper must be communicated with suppliers in order to effectively control the quality of the base paper. It is worth noting that after the aluminized paper is printed with an ink layer, it will also affect its penetration time. Therefore, when formulating the alkali permeability standard for raw paper, this factor must be fully taken into account in order to ensure proper de-lamination of the breweries when washing bottles. In general, the speed of filling the production line is short, and the time for washing the bottle is short, and the time required for the alkali penetration of the base paper is correspondingly shorter. In fact, the alkali penetration time of the base paper is controlled to be ≤50S. Using this kind of paper to print the logos of various layout structures and ink colors, it can basically meet the bottle washing and label removal requirements of 36,000 bottles/hour production line.

Second, the number of factors affecting the alkali permeability of aluminized paper

1. The effect of raw paper properties on the lye permeability:

The test results show that the nature of the base paper largely determines the time of its alkali penetration. If the base paper has a high tightness value, the alkali penetration time is correspondingly slow; the fibrous tissue of the base paper is hard, good in stiffness, good in toughness, and its alkali penetration time is also slow; the base paper has a large thickness, and its alkali penetration time is also correspondingly Slow; conversely, if the texture of the original paper is loose, soft, and the paper is thin, the alkali penetration time is correspondingly faster. The depth of the embossing also affects the lye penetration of the aluminized paper to a large extent. This can be inferred from the fact that the penetration phenomenon is most likely to occur at the creases and deep lines of the sample during inspection observation. It can be seen that the deep embossing of the aluminized paper makes it easy for the lye to penetrate after the fibrous tissue and coating on the paper surface are damaged. However, the embossing depth of the aluminized paper is correspondingly poor, and the stretching coefficient is also large, which inevitably leads to the occurrence of misprinting. Aluminized paper embossed deep in the amount of ink absorption, coloring effect is also poor, and the printed product is also easy to stick dirty. Aluminized paper has deep embossing, and the printing pressure is correspondingly larger, and the rough paper surface also tends to make the printing plate wear faster. The embossing is lighter. On the one hand, it helps to increase the stiffness of the base paper. On the other hand, it can effectively prevent the deformation of the trademark. In addition, the thickness of the base paper coating and the resistance to erosion have a great influence on the alkali permeability of the aluminized paper. The author in the detection of a variety of aluminum coated paper found that some embossed paper is very shallow embossing, paper fiber is also relatively hard, but the lye penetration can still meet the testing standards; this illustrates this point. Therefore, from the perspective of facilitating bottle removal from the brewery, the coating of the base paper must be resistant to alkali. Therefore, the author believes that the control of alkali permeability of aluminized paper is a passive process approach by using the method of increasing the depth of embossing to meet the requirements of bottling and removing the bottle from the brewery. By improving the coating characteristics of the base paper, the alkali penetration time of the aluminized paper is in line with the requirements of the subsequent process, and it is an ideal technical measure.

The effect of temperature and concentration of 2-NaOH solution on the permeability of the Al-plating paper lye.

The test results show that the temperature and concentration of the NaOH solution have a certain influence on the alkali penetration time of the aluminized paper. : When the NaOH solution temperature is low (less than 50~C), the alkali penetration time of the aluminized paper is significantly faster. In addition, the concentration of NaOH solution is large, and the alkali penetration time is also fast. On the contrary, the alkali penetration time is slow. However, the temperature and concentration of the lye in the aluminized paper must be compatible with the temperature and concentration of the lye in the brewer's washing bottle. In this way, the printing factory can test the qualified aluminized paper and make the finished trademark to meet the brewery. Wash bottle off the standard process requirements.

Third, the impact of printing ink on the permeability of aluminized paper brand lye

In the test, we found that the printing ink has a certain influence on the lye permeability of the aluminum-plated paper, especially the inks such as green, gold, black, etc., which have the most obvious influence on the lye permeability of the aluminum-plated paper. The color of these brands is markedly slow when the lye is tested. In addition, the thickness of the printing ink layer will also affect the lye permeability of the aluminized paper brand, and the thicker the brand is, the slower the penetration of the lye will be. Therefore, when printing, the “deep ink thin printing” process should be used as soon as possible, that is, the hue of the ink should be appropriately deepened to make the printing ink layer thinner. This can not only meet the printing hue requirements, but also help prevent the printing products from being dirty. It can better meet the needs of bottling bottle off the standard.

In summary, the factors influencing the permeation performance of aluminum-coated paper lye are many, and the characteristics of raw paper are the main factors that affect the permeability of aluminum-coated paper lye. The base paper is also the source link of product quality. Once the nature of the paper is After shaping, it is difficult to remedy. If the quality control of the aluminized paper manufacturer is not in place, the printing factory does not carry out inspection checks, and blindly puts it into print use. This may be caused by non-permeability of the lye, so that some blisters will not appear when the bottle is washed, resulting in poor as a result of. Therefore, aluminum-plated paper manufacturers and printing companies must jointly conduct gate control in order to effectively control the quality of aluminum-plated paper. To do this, the printing factory will timely feedback the problems found in the inspection of the base paper to the aluminized paper manufacturers so that the quality of the base paper can be continuously improved and the source quality of the trademark can be better controlled.

(Author/ Kang Qilai)
Source: China Packaging News