DVD Disk Printing Ink "Shrink" Outer Perspective (2)

DVD printing: printing effect

Now let's talk about an important topic: DVD printing and DVD printing have additional requirements for technology and printing.

According to its philosophy and work links, we can see that DVD requires a narrower tilt angle tolerance than CD. The flatness of the disc is a very important parameter in DVD printing. The DVD manual states that the deflection beam (offset angle α) of the reading laser must not exceed ±0.8° in the direction of the radiation (half of the standard CD value) or ±0.3° in the tangential direction.

As a result, two key issues arise:

- Does the printing affect the flatness of the disc and affect the disc playback function?

- If so, how can this effect be avoided in the printing process?

This is a hot topic. We were very surprised by the opinions expressed in an article a few months ago. The article said that the impact of CD printing on the tilt angle is not important or not important at all. At this time, we learned that some customers began to encounter problems in the printing of different specifications of optical discs. But in general, many DVDs still use standard screen printing inks and meet specifications.

Recently there has been a general concern about the problems caused by shrinkage. "Low shinkage" means that the ink does not shrink or shrink to a small extent during UV curing. Over-contraction may warp the disc so that the reading beam cannot focus when reading.

For us, the key issue is the lack of accuracy of the two important features listed on the DVD manual:

- Adhesion of ink. This factor is not mentioned in the standard ink. The adhesion of the ink to the surface of the DVD PC must be much stronger than the UV coating varnish adhering to the surface of the CD. The good adhesion performance helps to maintain good scratch resistance or nailing resistance. It also allows white inks to be printed during offset printing to prevent white oil spills from contaminating offset printing equipment.

- Testing between printing and tilt angle measurements. This is the so-called climate test used to simulate the climatic conditions mentioned in the DVD manual.

If you do not study these two parameters in detail, you will declare that printing will not affect the tilt angle. If printing is done after printing (no climate test), many standard screen printing inks can use a good tilt angle when used.

Test after climate test

And we at Dolby not only considered these two parameters - ink adhesion and tilt angle caused by coating after climatic tests - but also considered issues that may arise in the later stages of higher-level DVD reproduction.

The best way to control and understand the effects of coating is to measure the radiation and tangent deviations of different formulations after measuring the climate test in the laboratory.

In order to conduct this study, we need a system that can measure the most accurate value. We use the Dr. Schenk deviation analyzer and climate test (80°C, 85% relative humidity, 72 hours).

First we must say that printing is not the only factor that affects the tilt angle. Of course, we have to consider the shape of the master disk before printing. We know that each DVD disc's thickness tolerance (only 100 microns) is much smaller than the CD (200 microns on the red manual). Adhesives are also very important. Do not forget that the final measurement of the tilt angle after the climate test depends not only on printing but also on the evolution of the DVD disc itself. In some cases, the different effects of various aspects of optical disc duplication can make their measurements inaccurate. In the study, we chose a DVD with a very good flatness, but it was impossible to take into account changes in the structure of the DVD after the climate test.

Tilting factors are obviously sensitive to heat, and problems can easily arise if the dwell time under DVD UV curing light is too long. According to our experiments, the deviation of the radiation was changed after the DVD had passed 10 times under a UV lamp (300 W/cm, 10 m/min). Although we can say that testing with another disc will result in different results, we can be sure that heat does have an effect on the tilt angle. Even if the impact is small, it will affect the printing effect together with other factors.