Which method is the best for hologram applications

I would like to know which method is the best for hologram applications :

 

- Direct Metallizing

OR

- Transfer Metalization

Regarding

- Brightness

- Cost

- Durability

Could you please comment ?

 

 

Answer.

 

The starting point must be the paper substrate.  Paper can be metallized but there are a number of considerations that have to be made.  Paper relies on the moisture content for some of its mechanical performance. The moisture content can vary considerably and so the vacuum pumping system has to be designed to cope with the highest possible water content which can be in excess of 20%.  The winding system will also have to cope with the paper as it becomes more fragile as the moisture content is reduced by the vacuum system. This is particularly true if the moisture content of the paper is low before the paper enters the vacuum system. If the paper dries out too much it becomes very fragile and is then much more prone to web breaks.  The reflective quality of the metallized paper depends largely on the surface roughness of the paper. Thus the grade of paper becomes important as the metallized surface has to be treated essentially to smooth the surface as much as possible if you want to produce a highly reflective metallized end product.   The metallized layer is likely to contain slightly more oxygen than if the metallization was done onto a polymer film. This is simply because of the higher background levels of water that will be present in the vacuum system.  Paper that has passed through a vacuum system is often re-hydrated, to restore the mechanical properties, before post processing.

 

It is possible to either use one of the surface smoothing layers to emboss into. Alternatively an additional coating can be used at the time of embossing.

 

 

Transfer metallization requires a polymer substrate with a release layer coated prior to metallization. The transfer process can be done hot or cold depending on the adhesive used. What is also required is some pressure to make sure there is sufficient contact to the adhesive and substrate. This pressure can be high and can cause some degradation of the holographic embossing which can result in some loss of brightness.  The aluminium brightness is usually higher than that of directly metallized paper but the difference is small and although measurable is usually not noticeable to most observers. 

 

If you are buying a metallizer from new then the cost of a metallizer for paper is likely to be slightly more expensive than one for polymer because of the heavier rolls and higher pumping requirements. 

 

Durability is more dependent on the total structure. The transfer metallized material will have some protection of the hologram because some of the release layer will remain with the metallized layer when it is transferred.  The directly metallized aluminium onto the paper may be left with the aluminium exposed or may have a protective polymer layer over coated.  Transfer metallizing usually means that the whole surface does not require metallizing or require a holographic design applied across the whole surface.  This would imply that the metallized paper would require printing after metallization to blank out areas of metal. This allows a protective layer to also be applied to the metal coating at the same time.  Transfer metallizing is designed to only place metallized, holographic devices onto areas where they are required. As such the efficient use of material can be improved.  This can allow the use of 150mm wide webs for embossing and metallizing. For example Bobst GVE produce a Holosec metallizer that is specifically designed for metallizing standard 150mm wide (6 inch wide) embossed holographic reels which are regarded as an industry standard width. This type of metallizer is a much lower cost machine than a full width paper metallizer.

 

If however the end product requires metallizing to provide some oxygen or water vapour barrier performance then the full width metallizing has the advantage over the transfer metallizing process.

 

The problem of cost is impossible for me to answer without having all the information on the final product, volumes, size, performance, etc as well as then costing all the systems required.  The first step is to decide on what you want the final product to be and to then plot out the equipment required for each process to achieve the required end product. It will then be possible to evaluate what equipment you already have and what additional equipment you need.  Once this is done it will then be possible to build up a cost model for each process and compare the cost per unit item.

 

I hope that the above information helps.