In our previous interview, you explained that specifications currently required for Wrinkle Removing Rolls are becoming increasingly more severe. At this time, I'd like to ask you what advantages your no-bow and linear Wrinkle Removing Rolls have.
Tsuchida: Frankly speaking, just to overcome the problems encountered with conventional bow rolls, I have developed no-bow and linear expander rolls. Accordingly, the biggest advantage of the no-bow and linear expander rolls comes down to the fact that they can achieve uniform web spreading and expansion throughout the web width. Conventional bow rolls are structurally disadvantageous in that the web is excessively stretched at its center and loosened at the edges, because the line tension at the web center is greater than it is at other portions of the web. To be more specific, a bow roll is designed to spread the web through its center projection ("curvature height"). This inevitably causes the web edge portions to become loosened and distorted, resulting in wrinkles. This causes a dilemma - when provisions are made to minimize wrinkles inevitably generated at the web edges, the spreading and expanding effect at the web's center is also reduced.
Does this mean that the user is required to exercise his ingenuity when using a bow roll?
Tsuchida: Yes. Dependent on the flexibility of the web material, there are cases where the structural problems of a bow roll may seriously affect the web, or conversely, affect it very little. The user is therefore required to designate a "curvature height" dependent on web flexibility and required quality. More specifically, a well-balanced "curvature height" should be designated for an individual web, either a soft film or a rather hard paper, dependent on its flexibility and the quality required for the final product. Even so, uniform web expansion can never be achieved throughout the web width. Accordingly, when a high-quality final product is required, web edge portions are disadvantageously inevitably rejected.
Please explain web flexibility in more detail.
Tsuchida: In order from softest to hardest, webs may be arranged in this order - textile fabrics, films, nonwovens, paper, glassfiber, and metallic foil. Of course, there are rather hard fabrics, such as carpets, and thin soft paper sheets. So, all webs may not always be classified in the above-mentioned order.
What are the implications of different problems occurring dependent on the varied flexibility of web materials?
Tsuchida: To cite some examples, soft fabrics and films have some restoration force. So, there is a chance that slight stretching at the web center and slight slack at the web edges are restored to a degree during conveyance in the production line. However, rigid metallic foil, for example, has extremely low restoration properties. Accordingly, when excessively stretched at its center and loosened at its edges, in extreme cases, the foil is disadvantageously actually formed into the shape of a bowl. As for glassfiber fabric webs, their centers can be excessively stretched and their edges reduced to floating in midair. This causes wrinkles or creases, resulting in weft distortion.
Does this mean that a bow rolls could be used with soft fabrics or films?
Tsuchida: Not necessarily. Even for a soft fabric, excessive center stretching and edge loosening cannot be restored in a perfect manner. This disadvantageously causes weft distortion. For example, when bow rolls are used before take-up rolls in washing machines, and the fabric is repeatedly passed through washing machines and bow rolls, weft distortion is increased on an ongoing basis. In extreme cases, such weft distortion becomes so great it canÍt be corrected, even with the use of a weft straightener.
How about films?
Tsuchida: It depends on which processing step is disposed as the subsequent step, as well as the degree of quality required at this subsequent step. For example, even for a winding step generally regarded as easy, a bow roll could hardly be used when the film is required to be wound on a cylindrical core, with the film's edges exactly flush to the core edges (not in the shape of bamboo shoots), if it is required that the winding diameter be uniform throughout the film width, when it is required that the film be wound with uniform tension, or the like. For an application where a coating step comes after a bow roll, it is difficult to properly coat fluttery film edges with paste, isn't it? For an application where a printing step comes after a bow roll, the printing pattern cannot be printed properly as designed. For an application where a metallizing step comes after a bow roll, the evaporated metallic layer is not uniform in thickness. In short, a bow roll cannot be used when a high-quality product is required.
What does "high-quality" mean, more specifically?
Tsuchida: Using metalized film as an example, there are a variety of possible products, from decorative ones used for Christmas trees, to those used as insulating wrapping of an artificial satellite launched by a rocket. In wrapping an artificial satellite for insulating purpose, a number of aluminum-evaporated films are used. However, such insulating films must satisfy severe requirements in regards to thickness, weight, surface conditions and the like. It would be difficult to use a bow roll on a production line for producing such high-quality aluminum evaporated films. In addition to the structural problems mentioned, a bow roll is disadvantageous in view of web side-movement (inclination or deviation).
What does this mean?
Tsuchida: If the web widthwise center is positionally shifted from the widthwise center of a bow roll, the web tends to slip and be inclined toward the roll side where the majority of the web is being applied. This may escalate into a large wrinkling or creasing problem. In extreme cases, the web might end up breaking.
It is a fairly sticky issue, isn't it?
Tsuchida: Over the years, many people at production sites using bow rolls make this request: "We DO desire something which can expandingly convey, among our processing steps, a web in an unaffected, flat and intact manner without any excessive stretching, side-movement, slack, and wrinkling. My response was the Flat Expander that I developed, with the aim of being a no-bow, linear expander roll.
That was about 30 years ago. It was when Japan's high economic growth had just begun, wasn't it?
Tsuchida: Yes, it was. In the very beginning, I focused development on a no-bow, linear expander roll, which could simply "expandingly convey a web in an unaffected, flat, and intact manner among processing steps". But, it has now evolved into a ROLL that must satisfy a number of the requirements mentioned in our previous interview.
Next time, I'll ask you about that linear Flat Expander (FE).