Eurailmag - #15 - March 2007 - (Page 30)

Coatings NEW CONCEPTS FOR THE PERMANENT PROTECTION OF LACQUERED SURFACES OF VEHICLES AGAINST OPERATIONAL EFFECTS AND VANDALISM DR. JOACHIM KRÜGER • DEUTSCHE BAHN AG TEXT PRESENTED BY DR KRÜGER AT THE ECOLROMAT CONFERENCE, OCTOBER 2006, MULHOUSE (FRANCE) Coating Lacquers on Polysiloxane Basis Two packed Siloxane-epoxy hybrid systems exhibit high resistance against cleaning materials and solvents. Application as a clear varnish and as a coloured lacquer on water-borne 2K top coats. Painting over after sanding (case with repairs) is possible. Coloured 2K Polysiloxane can be coated by itself. Graffiti can be removed easily; "shadows" remain after removal of some inks. Resistance of the 2KPolysiloxane against Exterior cleaning agent Graffiti removal agent Artificial weathering (global radiation) Criteria No softening, no swelling No cracks, bubbles, debonding, matting Impact duration > 8 hrs. > 120 min 4000 hrs. EXTERNAL LACQUERING OF RAILWAY VEHICLES IS SUBJECT TO A MULTITUDE OF EFFECTS • Normal weathering through solar radiation connected with humidity • Dirtying through brake dust and wear from wheel-rail contact, wear from contact wire and current collectors, soot, grease, insects on the front of locomotives and driving trailers • Abrasion and scratching by stone particles, effects of brush washing systems and abrasive materials used for the removal of graffiti • Effects of agents used for exterior cleaning and removal of graffiti USE OF SELF-ADHESIVE FOILS In the nineties, transparent graffiti protection foil was applied of local transport vehicles. Consisted of a polyethlene terephthalate foil with a permanent acrylate adhesive. Applied to 1K-acrylate dispersion coating. Coloured "sandwich foils" were also applied. All these effects result in: • Degradation of gloss • Scratches caused of cleaning-machine brushes and contact with branches • Discolouration caused of cleaning agents • Remains of railway-specific dirt • Remains of graffiti and smears • Loss of cleanability, difficult removal of graffiti The foils remained on the vehicles for up to 7 years and exhibited the following: • Good removability of the graffiti • Development of uniform “silky gloss”, degree of gloss approx. 45/60° • Only slight yellowing • No embrittlement, retention of the elasticity to a large extent However, the following disadvantages were noted: • Partial loss of adherence in the area of the edges of the foil and partial debonding of the graffiti protection foil from base foil in the case of "sandwich foils" (delamination). • Difficult removal of foils from the surface of the vehicle; adhesive remains had to be cleaned off the vehicle surface with solvent Measures for improvement: • Improvement of the previous top coats with respect to resistance to weathering and cleaning • Application of new kinds of top coats for vehicles on a polysiloxane basis • Use of self-adhesive foils with graffiti protection and colouring • Additional protection of the top coats with thin “preservation layers“ © DB AG Requirements are placed on coloured self-adhesive foils ("sandwich foils") for the outer skin of railways vehicles: • Adhesive bondability + 5 to + 35°C, in dry or wet laying procedure • Adequate adhesive force: 10 to 25 N/25 mm wide • No debonding of the foil from the vehicle, no delamination of the protective foil from the base foil • Temperature resistance: – 35 to + 90°C • Dimensional stability: Shrinkage in the glued condition ≤ 0.2% • Resistance - Against weathering (> 7 years, no shrinkage, no cracks, no delamination) - Against exterior cleaning agents (acids and alkalis in the pH range 0.5 to 12.2) - Against graffiti removal agent • Removability - Of dirt ("brake dust", grease, oil) - Of graffiti (spray lacquers, undersealing, latex paints, ink), repeatedly and without residues • Removability of the foils from the outer skin of the vehicle up to at least 7 years after adhesion on without tearing and without adhesive remains IMPROVEMENT OF THE PREVIOUS TOP COATS Resistance of the waterborne 2K-PUR top coats to Exterior cleaning agent Graffiti removal agent Criteria Quality 2000 > 2hrs. > 15 min Quality 2006 Sheet 39, Para. 1.4 > 4 hrs. > 60 min No softening, no swelling Waterborne 2K-polyurethane lacques in compliance TL 918 300, sheet 39, para. 1.4 have been improved substantially with respect to resistance to cleaning and graffiti removal agents. Removal of graffiti from water-borne and solvent based 2K top-coats remains problematic. Special inks cannot be eliminated without "shadows". Issue 15 EURAILmag Business & Technology

Table of Contents for the Digital Edition of Eurailmag - #15 - March 2007

SOMMAIRE
NOTICE BOARD
COATINGS
NEWS
SERVICES
INFRASTRUCTURE
HIGH-SPEED LINES
TUNNELS
PEOPLE
ROLLING STOCK
WEBSITE DIRECTORY

Eurailmag - #15 - March 2007

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