DVD printing ink "shrinkage" climate test

At a recent technical conference held by Dolby, the company focused on topics such as DVD-disc printing. The standard explanation for "shrinkage" is not the only topic. Dolby believes that climate testing is a key factor in DVD printing.

Guy Masse (DUBUIT, France)

(a) CD

You may ask: What is the role of continuous development of new products in CD printing?

In fact, the CD copy industry did not decline. Although the CD industry has been for 20 years, it may be that 10 to 20 years later, 20% to 40% of music CDs will be sold via the Internet. However, we estimate that it will exist 10 ~15 years. By then, CD-Audio may be down to the level of vinyl today, but now we have to consider the current CD printing industry to innovate.

In fact, screen printing has proven to be the most effective way of printing on optical discs. More than 90% of CD printing today is screen-printed. Screen printing covers a wide range of fields, from monochrome text and image printing to four-color printing.

The main development of screen printing is to obtain a thinner wire diameter, thereby reducing the ink and film thickness. The automatic screen coating process can obtain thinner film thickness and finer dot resolution. These factors prompted us to adjust the ink's fluidity. In the past, some formula inks could pass through 140T screens, but now they cannot pass through 150, 165T or finer meshes. At the same time, the increase in the speed of the squeegee has also made this problem so severe that it has now reached 4,000,5,200 sheets/hour, and the next-generation machine of Dolby has a squeegee speed of 6,000 sheets/hour.

When you learn about CD printing, some new products such as fluorescent, phosphorescent, luminescent, pearlescent inks, textile varnishes, squeegee varnish, etc. can help customers to produce products that can take a place in the market.

(b) DVD

All indications are that DVDs have settled firmly in the market. Most CD copy factories can produce DVD-5 and DVD-10, which are very popular in the multimedia field, and are now promoting DVD-9 with higher requirements and longer playback time.

Ink manufacturers have little interest in double-sided DVDs (DVD-10, 14, 18) because only the inner ring on the second side can be printed. We can say that DVD technology is also an innovative technology and improved technology. We have the same feeling in DVD ink formulations. The improvement is the most critical development, which has been discussed in CD screen printing: the use of finer mesh and the increased speed of the machine require adjustment of ink flow. In the DVD market, there are similar requirements to produce highly competitive products to enhance the printing effect.

Innovation comes from the fact that DVD innovation requires new ink formulations. Because DVDs spin much faster than CDs, and use smaller components to inject on thinner discs, they require a higher response to the ink on the PC and are easily affected by the printing effect on the outer surface. The higher recording/reading speed of DVD requires a narrower tilt angle than CD. Therefore, UV inks used on DVDs must have less influence on the tilt angle, which is a major problem.

(3) Recordable CD

Burning CDs, especially the CD-R, represents a new type of market, especially in the area of ​​Asia where it is actively developing. The growing demand to promote the development of special coating varnish has produced a more excellent disc base (master).

A single CD-R can be individually designed or used:

- Pencils and felt-tips - We have developed special writable varnish that can be printed directly on the digital.

- Direct digital printing is currently only used for a small amount of CD-R printing. However, it is only a matter of time before the CD-R can be used for digital printing in high-volume production so that printing is quick and economical. We have developed ink coatings for digital printing: inkjet light absorbing layer (IJAL) and thermal transfer receiving layer (TTRL).

(D) Other disc printing methods

UV waterless offset printing and the recent emergence of UV flexo printing directly threaten the dominance of screen printing. UV waterless offset printing can make the surface of the disc more delicate, especially when printed on white net. We believe that offset printing will continue to be used in conjunction with screen printing, especially in the field of high-definition DVD-Video four-color printing.

However, offset printing is constrained by the following factors:

- There are only a few offset presses in the field of optical disc printing.

- There is an unavoidable difficulty with UV waterless offset printing: it requires strict control of the printing plate temperature and special UV inks compatible with TORAY printing plates.

UV flexible boards are printed on the CD, and the DVD industry is still a new type of printing. However, in the recent use of UV flexographic printing, all the major parameters in the printing process (such as: anilox roller, scraping blade, flexible plate, printing plate adhesion, etc.) have been greatly improved. Because of its economic advantages, it will be a compelling printing method in the future.

These new printing methods are used in the optical disc industry and their precipitation performance is weak, so we can ignore their impact on the deformation of the disc.

(5) 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. (to be continued)