(Cationic inks—Bright Future)
In the past 30 years, we have seen the important role played by UV technology in the printing of paper and film materials. UV technology has been developed from the narrow web flexography to the flexographic printing market. In offset printing, people also saw the advantages of the UV ink quick drying system: shorten the printing cycle and reduce the workload.
The most important feature of UV curing system is that it can improve the printing stability (drying) and shorten the waiting time of oxidative drying in the printing process.
In the past about 10 years, UV printing has had a great impact on traditional printing, mainly for flexographic printing on plastic substrates. Cationic inks have the advantages of low volatility and low odor compared to free radical systems. The odor of free radical inks is very stubborn, and today's low-volatile inks can even be used in certain food packaging industries. Another advantage of cationic inks is that they can be attached to plastic substrates. The market has been tilting towards low-volatile inks since the 1990s.
Cationic inks and coating glosses exhibit particularly good adhesion to corona-treated substrates, which is the most critical of all advantages.
In order to obtain a correct assessment of the two chemicals, we compare the performance of the two products in the following table, from which we can clearly see the advantages and disadvantages of the two.
Cationic ink properties Radical type ink medium (curing speed) Rapidly extended to 24 hours (secondary cure) Actual zero none (prevent oxidation) Slight (humidity effect) No zero (shrinkage) Excellent (plastic adhesion) Very limited
In terms of curing speed, radical inks can be dried at high-speed printing, and the curing speed of cationic inks is slightly behind. Recent developments show that improved cationic inks can accommodate 150-200m/min printing.
The benefit of the secondary cure is that the ink film appears to have cured after the print has been output from the printer, but some of the ink film has not reacted (not dried). Cationic curing techniques can continue to react until most of these materials react. In contrast, free-volatile inks can only be exposed to UV light for thorough drying. This process will result in higher volatility, especially if the unreacted low molecular weight components are more volatile. Cured polymers are usually of high molecular weight and generally do not volatilize. The volatilization of volatiles is also reflected in the extractable components. The content of extractables is an increasingly important feature of testing food packaging systems. In particular, as an analytical technique, it is possible to extract one part per billion parts of the content of ingredients, and even now is discussing the content of one trillion parts as an indicator of the content of the package. The cationic ink has a small amount of shrinkage so that it has good adhesion characteristics.
Packaging requirements and related issues:
All aspects of printing have different regulatory rules, and cationic inks did not meet the standards of standards in 2000. The by-product of exposure to light from initiators is an undesired aromatic compound, which is a prohibited ingredient listed in the food packaging ink profile. Food packaging should comply with the CEPE standard in industry standards.
According to reports in the literature, benzene is also a by-product of the cationic ink's initial stage (mid-1980s). Its content is so low that it cannot be detected at all using common analytical techniques. Many test results on printed products and printing environments show that no benzene was found, which reflects the fact that this content of benzene cannot be covered by the test methods used. The content of these substances is generally in the range of a few parts per billion (usually a single digit), which requires the use of photoinitiator packages no longer produce benzene.
From the point of view of development, most printers still choose a cationic system with excellent characteristics. The January issue of RedTeeh Europe reported: "There is no clear evidence to prevent the continued use of cationic UV curing systems designed for food packaging."
The printing shop's profile allows the environment to contain:
3ppm (TWA) EH 40/2000 (9.6 mg/m3)
EC Directive 98/83 EC - One part per billion in drinking water
The Atmospheric EU is limited to 5 μg/m3 (recommended), usually the city currently has EU levels of up to 40 and rural areas below 1.
In 1994, MAFF reported that the content of benzene in foods from petrol stations was 10 ppb. In 1998, the UK Department of Health reported that the 10 ppb content was insignificant for health.
From the above statistics, some conclusions about printing and packaging can be obtained:
The ink industry has an excellent record of ink and coating regulations and social pressure:
1974: Removed Lead in Ink Pigments Late in the 1970s: Removed Cellosolve (Ethylene Glycol)
Early 1980s: Removed toluene from food packaging instructions Late 1980s: Related benzidine yellow pigments Early 90s: Reduced use of phthalic acid plasticizers
These improvements to the inks in the chemical industry have led to predictions that alternative materials will emerge in the first half of 2001. The reason for choosing this time was to find out, identify possible alternatives, and register tests. This is an inevitable slow process, and some candidate initiators are eliminated due to high raw material prices. In the long run, this may be advantageous for materials that do not produce benzene at low surcharges. They can be used to increase the cure rate. (These new initiators must be based on the absence of benzene.)
Some customers gave up using cationic inks, but cationic inks showed great advantages in the printing process, so many customers continued to use them. They see that the ink industry will raise problems and find solutions, as well as the excellent records mentioned above. All of these must have a positive attitude and technical direction, better adapt to new standards, and continue to use this current "unpopular" material.
With the continuous development of printing technology, such "problem challenges" will continue to occur. When the issue is raised, especially after the analysis technology has been improved, it is very necessary for us to carefully consider our way out and better adapt our rules.
Case studies from the field of application where real benefits are derived from this technology are developing in the following two areas:
1. The cation-coated adhesive binder gravure printing has a very fast printing speed. After that, there are two cases when the adhesive coating is used: either it is not dry (there is a solvent) or it waits for 24 hours to make it. Cured to a certain strength. One of the benefits of flexographic printing is the use of adhesives on the press unit, lamination and curing at normal printing speeds, and in a few minutes the laminate of the print can be cured and can be cut on the press, followed by Can be directly to the customer. With the UV adhesive, there is no problem of volatilization of the solvent to create an odor. By using a newly developed white pigment binder, printing houses can remove the traditional solvent problems caused by back-whitening, followed by white ink lamination. The effect of solvent retention has attracted widespread attention, and it is now easy to reduce the residual solvent content per square meter to a single digit. OPP film, that is, polyethylene, polyether, metal film base can use an adhesive film.
2, cationic ink - shrink film (flexible version again with the gravure competition) The vast majority of the shrink film market is occupied by solvent gravure, very few are obtained by solvent-based flexo, in fact use is Water ink. Flexographic printers have found that the ink system that can achieve the desired quality in flexo printing is a UV curable ink that has no solvent volatilization and excellent print consistency. When the shrinkage amount reaches 70%, the free volatile type ink and the mixed dry type ink have to exhibit poor adhesion. Cationic inks have passed this required test and become unique ink systems for OPS, PVC and OPP materials. The advantages of cationic inks in management and storage are obvious.
In short, cationic ink technology has a market, and there are more and more new regions and new industries interested in it, such as glass, metal and ceramic pasteability and so on. It can not only be used for flexo printing, but has also been expanded into the field of inkjet technology, and has demonstrated excellent performance and benefits in the inkjet field.
In the past 30 years, we have seen the important role played by UV technology in the printing of paper and film materials. UV technology has been developed from the narrow web flexography to the flexographic printing market. In offset printing, people also saw the advantages of the UV ink quick drying system: shorten the printing cycle and reduce the workload.
The most important feature of UV curing system is that it can improve the printing stability (drying) and shorten the waiting time of oxidative drying in the printing process.
In the past about 10 years, UV printing has had a great impact on traditional printing, mainly for flexographic printing on plastic substrates. Cationic inks have the advantages of low volatility and low odor compared to free radical systems. The odor of free radical inks is very stubborn, and today's low-volatile inks can even be used in certain food packaging industries. Another advantage of cationic inks is that they can be attached to plastic substrates. The market has been tilting towards low-volatile inks since the 1990s.
Cationic inks and coating glosses exhibit particularly good adhesion to corona-treated substrates, which is the most critical of all advantages.
In order to obtain a correct assessment of the two chemicals, we compare the performance of the two products in the following table, from which we can clearly see the advantages and disadvantages of the two.
Cationic ink properties Radical type ink medium (curing speed) Rapidly extended to 24 hours (secondary cure) Actual zero none (prevent oxidation) Slight (humidity effect) No zero (shrinkage) Excellent (plastic adhesion) Very limited
In terms of curing speed, radical inks can be dried at high-speed printing, and the curing speed of cationic inks is slightly behind. Recent developments show that improved cationic inks can accommodate 150-200m/min printing.
The benefit of the secondary cure is that the ink film appears to have cured after the print has been output from the printer, but some of the ink film has not reacted (not dried). Cationic curing techniques can continue to react until most of these materials react. In contrast, free-volatile inks can only be exposed to UV light for thorough drying. This process will result in higher volatility, especially if the unreacted low molecular weight components are more volatile. Cured polymers are usually of high molecular weight and generally do not volatilize. The volatilization of volatiles is also reflected in the extractable components. The content of extractables is an increasingly important feature of testing food packaging systems. In particular, as an analytical technique, it is possible to extract one part per billion parts of the content of ingredients, and even now is discussing the content of one trillion parts as an indicator of the content of the package. The cationic ink has a small amount of shrinkage so that it has good adhesion characteristics.
Packaging requirements and related issues:
All aspects of printing have different regulatory rules, and cationic inks did not meet the standards of standards in 2000. The by-product of exposure to light from initiators is an undesired aromatic compound, which is a prohibited ingredient listed in the food packaging ink profile. Food packaging should comply with the CEPE standard in industry standards.
According to reports in the literature, benzene is also a by-product of the cationic ink's initial stage (mid-1980s). Its content is so low that it cannot be detected at all using common analytical techniques. Many test results on printed products and printing environments show that no benzene was found, which reflects the fact that this content of benzene cannot be covered by the test methods used. The content of these substances is generally in the range of a few parts per billion (usually a single digit), which requires the use of photoinitiator packages no longer produce benzene.
From the point of view of development, most printers still choose a cationic system with excellent characteristics. The January issue of RedTeeh Europe reported: "There is no clear evidence to prevent the continued use of cationic UV curing systems designed for food packaging."
The printing shop's profile allows the environment to contain:
3ppm (TWA) EH 40/2000 (9.6 mg/m3)
EC Directive 98/83 EC - One part per billion in drinking water
The Atmospheric EU is limited to 5 μg/m3 (recommended), usually the city currently has EU levels of up to 40 and rural areas below 1.
In 1994, MAFF reported that the content of benzene in foods from petrol stations was 10 ppb. In 1998, the UK Department of Health reported that the 10 ppb content was insignificant for health.
From the above statistics, some conclusions about printing and packaging can be obtained:
The ink industry has an excellent record of ink and coating regulations and social pressure:
1974: Removed Lead in Ink Pigments Late in the 1970s: Removed Cellosolve (Ethylene Glycol)
Early 1980s: Removed toluene from food packaging instructions Late 1980s: Related benzidine yellow pigments Early 90s: Reduced use of phthalic acid plasticizers
These improvements to the inks in the chemical industry have led to predictions that alternative materials will emerge in the first half of 2001. The reason for choosing this time was to find out, identify possible alternatives, and register tests. This is an inevitable slow process, and some candidate initiators are eliminated due to high raw material prices. In the long run, this may be advantageous for materials that do not produce benzene at low surcharges. They can be used to increase the cure rate. (These new initiators must be based on the absence of benzene.)
Some customers gave up using cationic inks, but cationic inks showed great advantages in the printing process, so many customers continued to use them. They see that the ink industry will raise problems and find solutions, as well as the excellent records mentioned above. All of these must have a positive attitude and technical direction, better adapt to new standards, and continue to use this current "unpopular" material.
With the continuous development of printing technology, such "problem challenges" will continue to occur. When the issue is raised, especially after the analysis technology has been improved, it is very necessary for us to carefully consider our way out and better adapt our rules.
Case studies from the field of application where real benefits are derived from this technology are developing in the following two areas:
1. The cation-coated adhesive binder gravure printing has a very fast printing speed. After that, there are two cases when the adhesive coating is used: either it is not dry (there is a solvent) or it waits for 24 hours to make it. Cured to a certain strength. One of the benefits of flexographic printing is the use of adhesives on the press unit, lamination and curing at normal printing speeds, and in a few minutes the laminate of the print can be cured and can be cut on the press, followed by Can be directly to the customer. With the UV adhesive, there is no problem of volatilization of the solvent to create an odor. By using a newly developed white pigment binder, printing houses can remove the traditional solvent problems caused by back-whitening, followed by white ink lamination. The effect of solvent retention has attracted widespread attention, and it is now easy to reduce the residual solvent content per square meter to a single digit. OPP film, that is, polyethylene, polyether, metal film base can use an adhesive film.
2, cationic ink - shrink film (flexible version again with the gravure competition) The vast majority of the shrink film market is occupied by solvent gravure, very few are obtained by solvent-based flexo, in fact use is Water ink. Flexographic printers have found that the ink system that can achieve the desired quality in flexo printing is a UV curable ink that has no solvent volatilization and excellent print consistency. When the shrinkage amount reaches 70%, the free volatile type ink and the mixed dry type ink have to exhibit poor adhesion. Cationic inks have passed this required test and become unique ink systems for OPS, PVC and OPP materials. The advantages of cationic inks in management and storage are obvious.
In short, cationic ink technology has a market, and there are more and more new regions and new industries interested in it, such as glass, metal and ceramic pasteability and so on. It can not only be used for flexo printing, but has also been expanded into the field of inkjet technology, and has demonstrated excellent performance and benefits in the inkjet field.
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