discoloration of printed polyethylene films.
White polyethylene film.
However, there is no reference or sufficient explanation for the role of printing in this discoloration.
The research presented in this paper aims to understand the chemical interaction between the ink composition and the composition of the film, resulting in discoloration of the film.
Accurate description of the role of different ink components in film discoloration is invaluable for the industry of printing or coating olefin films.
There is no science without observation.
\"The discoloration of materials is not only undesirable, but sometimes expensive products need to be handled.
Discoloration is caused by a series of complex situations that vary from problem to problem.
Therefore, a single explanation to solve the problem of discoloration may not be possible.
Color change is best explained on the box. by-case basis.
During observation, one or more of the following phenomena can lead to these phenomena: Ink, substrate, environment and even processing conditions.
For the scope of this article, we limit the display of printed polyethylene film.
Suppliers such as Ciba-have recorded in detail the discoloration of polyethylene films in packaging materials
Geigy and DuPont.
Although, their topic has some similarities with the Pan-yellow of the film, it does not discuss the printing material, nor does it cover the role of the printing ink in discoloration.
In the flexible packaging industry, we observe the discoloration of a large number of printed polyethyleneprint areas.
This allows us to conduct a comprehensive survey of the chemical and/or physical interactions of ink, substrate, environment and processing conditions.
The project discussion systematically studied the discoloration phenomenon in a converter and gave the results.
The study was conducted in the laboratory and on-site.
We have collected some data to narrow down our research. and-
Therefore, the results and presentation of the discussion will follow the same steps --wise manner.
The first round: Preliminary Data collection focus areas discussed initially with suppliers are: * chemical of film resin from suppliers.
* Additives for film processing.
* Frequency and time of occurrence.
* Exposure conditions for printed materials.
* Type of ink being used.
Interviews and meetings with a wide range of suppliers and suppliers are important for an accurate understanding of all essential elements.
Preliminary information shows that in many cases, there are both BHT and similar phenol antioxidants in the film additive packaging, as well as anti-slip additives and anti-slip agents. static agents.
The color change of opaque polyethylene is more obvious (containing[TiO. sub. 2]pigment)
Clear than the movie.
According to the converter, the incidence of yellowing is higher in summer or warm storage conditions. The stain-
Like the color on the edge of the printing roller from the top to the core in the non-printed areas.
Also, when these issues are narrowed down
In order to avoid the pollution of particles and smoke in the air, discoloration has occurred.
However, color change does not occur when the same printed material is converted into a finished bag and stored in corrugated boxes under similar atmospheric conditions.
In addition, the film roll without printing will shrink-
Packaging no color.
It was also noted that different inks from different ink manufacturers showed varying degrees of discoloration.
All inks are surface printing inks, based on cellulose and polyamide-types.
Conclusion preliminary information allows us to investigate the following possible causes of discoloration: * film additives.
* Relationship of temperature rise.
* Storage and shrinkage of printed materials in boxes-wrapping.
The second round: the design of Experiment 1 according to the above information, we asked the converter to provide us with white polyethylene films of two antioxidants and their standard films.
The laboratory investigation was conducted using ink in the color of the car.
Because it\'s not, so bazole purple paint
Migration in nature, thus eliminating the migration of pigments as a cause of discoloration. For our cross-
By inspection, these inks are made from 0% to 100% with different proportions of nitrated cotton and polyamide.
We use similar methods to make ink from cellulose and polyurethane.
These are the resins commonly used in polyethylene film surface printing applications inks.
All of the above ink and film variables are printed in a flexo version, leaving about 2 inch of the non-
Print film on both sides.
As an experimental control, a sample of ordinary film was used.
Preliminary data from the converter indicate that discoloration occurs most frequently under high temperature and closed conditions (shrink-wrap).
So we exposed all the samples individually in the fan outlined below: * turn on room temperature.
* Room temperature in closed glass jar. * At 120[degrees]F in open. * At 120[degrees]
In a closed glass jar.
The sample was exposed for 48 hours under the above conditions and then color change was observed.
Results and observations first, there was no discoloration in the ordinary film sample.
Secondly, there are both cellulose and polyamide in the discolored ink, as well as cellulose and polyurethane resin.
There is only one sample of resin in the ink that does not change color.
Third, the samples exposed in the open container do not change color.
Fourth, print samples only on films containing BHT or other phenol antioxidants (some Irganox)
Color change is displayed.
Finally, printed samples on films with higher antioxidant content of phenol showed a stronger discoloration than those on films with lower antioxidant content of phenol.
To sum up, discoloration needs to meet the following conditions: * phenol antioxidants must exist.
* The ink must contain both nitrated cotton and polyamide or nitrated cotton and polyurethane.
* Rising temperature.
* Closed environment.
Conclusion The above results draw the following conclusions: 1.
The composition of the ink either reacts to form a deep-sea product that can react with the membrane antioxidant to cause discoloration, or the ink reacts directly with the membrane antioxidant to cause discoloration. 2.
In the high temperature and sealing system, the reaction with the membrane antioxidant is accelerated. 3.
Yellowing is directly related to the concentration of antioxidants in the film.
Unresolved issues that need further study: * direct or indirect reactions to antioxidants.
* The role of ink pigments in the reaction. * The role of [TiO. sub. 2]
Because in the discolored film
* Whether the by-products are migrated or gas.
The third round: the design of the experiment II ink is carried out in the laboratory, and the resin ratio is the same as above, but there is no pigment.
These clear varnish are printed on opaque polyethylene together with transparent polyethylene film.
Both films are made with the same phenol antioxidant packaging, which results in the maximum discoloration of the second round above.
Exposure conditions are limited to 120 [degrees]
In a sealed glass jar.
The following experiments were conducted to determine whether the reaction species were migrating through polyethylene films or in nature.
A plain film sample of opaque polyethylene was placed at the bottom of the sealed jar, where a printed sample of samefilm was hung from the lid of the jar.
The jar was heated on degrees]F.
Results and observations * the transparent printed film shows discoloration but is less discolored than the printed sample on the opaque film.
* Ink resin mixture (varnish)
The result is the same color change as all samples.
* Even if there is no direct contact with the printing area, ordinary opaque film samples placed in the same jarwith as the printed samples show discoloration.
Conclusion it is well known that the visual effect of color and pigment on transparent films is smaller than that of opaque films.
Therefore, even to a lesser extent, the presence of discoloration in the transparent film will result in [TiO. sub. 2]
There is no effect on the color change of the film.
In addition, due
Coloring varnish discoloration film is the same as the coloring film previously studied, and the results show that the pigment (
In addition to migrating dyesbased)
The ink contained in the ink does not have any activity in discoloration.
Interestingly, ordinary film samples placed in the same jar but not physically in contact with printed samples also turn yellow, indicating that there is a gas by-product.
It is clear that the concentration of the gas material in the sealing system will increase, but in the open system, the gas material will spread and will not concentrate.
This conclusion is consistent with the field observation of the contraction of the printed sample
When those packages stored in corrugated boxes do not change color.
Round 4: identification of by-products and reactions to the film in order to complete our understanding of the discoloration process, we study the following: * reaction of the resin to form a reaction by-product.
* Reactions of by-products to membranes.
* Chemical properties of stains.
In sealed jars, a large number of resin mixtures are exposed at elevated temperatures.
The top space above the mixture is analyzed.
The analysis concluded that the current level of nox compounds has increased.
It is widely believed that nitrocellulose is decomposed to form NOx compounds (Figure 1).
In addition, many antioxidants are known in chemistry (such as NOx)
React with phenol antioxidants to form a quinone structure, which is a colored reagent.
This reaction is reversible under ultraviolet light;
Therefore, the yellow color fades when exposed to light (Figure 2).
Conclusion the above study provides a complete explanation for the role of ink, substrate, environment and processing conditions for printing film discoloration.
This explanation also provides temporary corrective action for the converter where the contraction-
When placed on the printing roller, the package is punched in several positions to allow the NOx gas to escape. Long-
Long-term corrective actions have since been taken.
Through the ink formula, the selection of antioxidants suitable for film production, as well as the appropriate level of antioxidants in film production, eliminates the problem of discoloration of the converter.
This issue has been monitored for more than three years and has not been discolored once.
Although experiments conducted in this study show that discoloration occurs at high temperatures, it is important to note that the same phenomenon occurs at room temperature, but for a long timescale.
Ciba Geigy, Technical Bulletin, textile chemicals, dye and chemical departments. April 1979. DuPont Co.
Textile Chemist and colorist in April 1983. 15, No. 4. C1. H (Kent)
Shah received a degree in chemistry from the University of Mumbai, India in 1965.
After working as a research and development chemist in the Indian pharmaceutical industry, he
Shah joined yingmeng in 1970 as a laboratory chemist and then as a research and development chemist and research and development laboratory manager. Mr.
Shah joined the color conversion industry as technical director in 1978 and focuses on high
Terminal packaging ink and paint. Mr.
Shah spends a lot of time on customer understanding and meeting their technical needs.
He conducted a variety of basic studies related to inks and substrates.
He is currently vice president of technology in the color change industry. Mr.
Shah also served as deputy director of the national printing ink Research Institute (NPIRI)
Is a lecturer in the NPIRI summer course, the Flexo graphic Technology Association (FTA)and TAPPI.
Won the National Association of ink manufacturers (NAPIM)
Pioneer Award for printing ink in 1994.