Configuration of narrow-web printing machines
 
Configuration  
Application hints  

Configuration of narrow-web printing machines

Here's how to ensure problem-free foil transfer:

 

Coordinated processes

 

  • The nip roller unit should immediately follow the printing of the UV adhesive; the nip roller should be manually or pneumatically adjustable.

 

  • The web material should be guided in such a way that the printed side cannot come into contact with the face rollers as these could injure the not yet cured adhesive.

 

  • The UV lamp should immediately follow the nip roller unit. Locating a counter-pressure roller under the UV lamp improves the contact between the foil and the material thereby facilitating curing.

 

  • Foil release should occur immediately after the UV lamp and at the flattest angle possible so that the carrier foil layer of the cold foil releases well from the transferred design.

     

Clean transfer

 

  • The cold foil web must be absolutely wrinkle-free when fed to the nip roller otherwise perfect transfer will not be possible. The same applies to the subsequent transport of the substrate web, with the applied cold foil, to the UV lamp. The transfer results can also be negatively impacted by any contamination or entrapped air between the cold foil and the material web, or even dust on the material web.

 

Suitable lamp systems

 

  • All commonly available UV lamp systems with an output greater than 180 W/cm (the required lamp output depends on the actual printing speed) are suitable for curing the adhesive. Conventional high-pressure mercury UV lamps provide very good results.

  

Required quantity of adhesive

 

  • The criteria for determining the required quantity of UV adhesive are the material properties (smooth, absorbent) and the design of the cold foiling. Less adhesive is required for fine lettering or lines than for large areas; porous or matt materials also require larger quantities of adhesive than smooth, non-absorbent plastics. Based on experience, the required quantity of applied adhesive can vary between 3 and 10 g/m2 depending on the material properties.

 

  • The processing instructions provided by adhesive manufacturers should always be followed. The same applies to their recommendations regarding the use of additives like antifoaming agents, adhesion promoters or photoinitiators.

 

Cold foils that can be used

 

  • Only cold foils specifically developed for this process will deliver a perfect transfer result. Some cold foils with particular color tones and effects cannot be used with this process due to their insufficient transparency to UV light. The service team of the cold foil manufacturer can provide advice regarding this.

 

Application hints

 

Printing of the UV adhesive:

 

  • Use the correct flexographic printing plate; the hardness value should range between 65 and 70° Shore A

  • Use a suitable adhesive tape to fasten the flexographic printing plate to the printing cylinder

  • Use the correct UV adhesive - see the sections previous

  • Use a suitable anilox roller with an appropriate volume; the correct coating weight depends on both the substrate and the design.
    High coating weight: 120 lines /cm ( approx. 300 lines / inch, 8 cm³/m² = 5.2 BCM)
    Medium coating weight: 180 lines / cm ( approx. 440 lines / inch, 6 cm³/m² = 3.9 BCM)
    Low coating weight: 220 lines / cm ( approx. 550 lines / inch, 4.5 cm³/m² = 2.6 BCM)

 

Laminating the cold foil onto the UV adhesive:

 

  • The hardness of the nip rollers is very important and should be around 90° Shore A.

     

UV curing

 

  • The distance between the laminating station and the UV curing unit should be no greater than 1 m. If the distance is greater, premature release, wrinkle or bubble formation can occur, which will negatively impact on the transfer.

     

Separation of the cold foil carrier

 

  • The release angle should be adjustable. Depending on the material, this release angle can be anywhere between very shallow and very high.

 

Things to be considered when using cold foils:

 

  • The foil tension must be controlled - a too high tension can lead to wrinkles in the lengthwise direction, a too low tension can result in poor guiding of the foil.

 

  • The speed of cold foil transfer is important. A too low speed can sometimes result in poorer transfer; a too high speed can result in inadequate curing of the UV adhesive.

 

  • Selecting the design: It is necessary to ensure that the cold foil is in register with the substrate web. There is no means of saving foil. Labels with a border achieve the best utilization of the foil.

 

  • Selecting the correct substrate: Not all available materials are suitable for use with cold foils. To date it has not been possible to use structured, rough, or highly absorbent materials. Smooth, less absorbent, or plastic materials should therefore generally be selected.

 

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