Hot-melt adhesive for flocking process, new development and new challenges, the way towards sustainability
Published Date
Alberto Sadun was born on 1966 has studied Economics at Florence University, worked for a short while in England. Since 1995 he’ve joined Aigle. Now is share-holder and Managing Director.Main actual tasks are sales & marketing and development of innovative projects. Aigle is one of the leading companies manufacturing flocking and coating plants. Flocking belongs to Aigle history since the beginning of the company.
HOT MELT ADHESIVE FOR THE FLOCKING PROCESS
The below will present the outcome of recent tests conducted with the collaboration of an adhesive producer Novotex. Using the Neoflex advanced adhesives (which belongs to Novotex Group), Aigle did new tests of flocking processes with very interesting results.
• Brief introduction on PUR hot melt adhesives
PUR Hotmelt reactive adhesives are Polyurethane adhesives formulated with internal crosslinker blocked in the absence of humidity, vacuum and the presence of nitrogen. In the industrial applications the adhesive is freed from the wrapping and pressed with a hot platform completely adherent to the drum‘s internal wall, it is then fed into heated tubes up to the nozzles and containment tanks and then applied with dots applications by engraved cylinders (Rotogravure) (see pict #1), or full coating by Slot Dye application (see pict #2).
Pic #1
Pic #2
Reticulation action is developed by temperature, air and humidity. Once applied these adhesives reticulated them selves with air humidity and after about 48 hours (based on the environmental conditions and air humidity) they form a permanent and irreversible bond to the substrate and to the fibres. This guarantees the non-reactivation of the ad hesive ensuring resistance to high temperatures, hydrolysis action and washings, without delamination on the coated substrate.
• History of hotmelt adhesive test and application for flocking processes
In 2007 during the 19th Int. Flock Symposium Mr. Arne Voigt, associate researcher at Institute of Textile and Clothing Technology of TU Dresden presented an interesting study on “The use of hot melt for flocking automotive parts with the target to have all components of the same polymer”.
The study arrived to the result that “flocking is technically feasible with hot melt adhesives. The surface quality achieved is very good and is characterized by a high flock density and good abrasion resistance. So, basically, the theoretical part of the research was mostly done. However, after considering the possibility to use this kind of adhesive into the flock process we can underline two new interesting aspects:
· After 2007 we’ve never met an industrial flocking application with hot melt adhesives this, of course, it doesn’t mean that no flocker is using hotmelt adhesive but, as flocking line manufacturers, we have not seen this kind of application in operation.
· The second part of the conclusions of the 2007 study states: “Based on further modifications of the process and subsequent developments, the quantity of hot melt adhesive, energy requirement and requisite processing time must be reduced”. This is an important aspect of the hot melt application system which will be part of the following analysis.
• The new recent test in cooperation with Novotex.
Since years Aigle is producing hot melt applicators for coating and lamination lines and we’ve been in contact to Novotex and we offered them to cooperate on new tests of hotmelt application using their adhesives.
At Novotex laboratory premises we conducted several tests. Novotex suggested us to use NEOTHERM PU-3550.1 adhesive and we’ve tested it with different supports keeping as low as possible the application temperature (we’ve never overcome 120°).
We tested this adhesive with different kind of supports:
· PU Foam (see pic #3)
· Transfer paper (see pic #4)
· Pvc (see pic #5)
Pic #3
Pic #4
Pic #5
We’ve obtained by the application a dry weight between 40 and 60 gr/sqm. On Transfer paper and pvc we’ve directly coated the support; coating the PU foam we’ve applied the adhesive film by transfer technology, first we’ve applied the adhesive film onto the release paper then we’ve transferred it onto the foam.
At Novotex for coating the adhesive we’ve used a Film Applicator that foresees a hot plate where the substrate is placed; the principle of adhesive application is based on a heated substrate and a Melting gun that extrudes a string, both at a pre-set temperature (see pict #6). Interesting point for future possible industrial processes is the application technology. We think that the use of a high precision calibrated slot could be the optimal solution for reaching the uniform and constant film necessary for the good result of the flocking process (see pic #7).
Pic #6
Pic #7
• Results of the tests
We obtained very good results with all the supports tested. At the moment when this paper is written, the flocked supports are in test phases. During the Symposium we’ll present the results of obtained performance tests. We’ve been impressed by the soft touch of the flocked film split by the release paper, and in general by the good density and solidity of the flocked surface.
• Strengths of the hotmelt adhesive within flocking process:
Shorter flocking line & Sustainability(no oven needed) Effectively aflocking line with hotmelt
application is much shorter and less energy consuming than a conven-tional one. (seepict.#8). The absence of the oven, can have a high impact on the energy consumption reduction trend that actually is a goal of many industry sectors. Another important issue for a better sustainability of the flock process will be reached when we will prove that Flock fibres embedded in hotmelt adhesive can create stronger bonds between materials: this might result in having products with longer lifespans. Longer-lasting products reduce the frequency of disposal and the demand for raw materials, thereby promoting a more sustainable lifecycle.
Pic #8
Good performances
Same as the conclusion of the lecture of Mr. Voight in 2007 the surface quality achieved is very good and is it characterised by a high flock density and good abrasion resistance (to be still proven for the tests performed in Novotex).
Better recyclability
This is very interesting nowadays especially within the automotive sector. Hotmelt adhesives often leave minimal residue compared to other types of adhesives. This reduces the likelihood of contamination during recycling and can lead to higher quality recycled materials.
• Weaknesses of the hotmelt adhesive within the flocking process
Range of Applicability in flocking processes
At the moment we know that hotmelt adhesives are applicable only on flat surface or slightly curvy surfaces but not on 3D objects.
Hot application temperatures
120° C might not be suitable for all substrates
Cost of the hotmelt adhesives
PUR prices are still higher compared to common industrial adhesives currently applied.
Research
We still need more extensive research in order to achieve the point in which hotmelt adhesive will be considered a valid and reliable alternative to water and solvent based adhesives.
• Conclusions:
The studies have demonstrated that hotmelt adhesive could become in a near future at least a possible alternative as an adhesive with correct characteristics for good performances in the use of flocking process. Aigle-with the suitable equipment- and Novotex - with PUR adhesives - are ready to take on the future challenge.
This article is reprinted with permission from the European Flocking Association. Unauthorized secondary distribution is prohibited