1st product with pre-applied adhesive (PAA) Not acceptable by the market without PAA. Invention in 1840 revolutionised any kind of mail and logistics

Transcription

1 1st product with pre-applied adhesive (PAA) Not acceptable by the market without PAA Invention in 1840 revolutionised any kind of mail and logistics

2 Vorapplizierbare Strukturklebstoffe - ein neues klebtechnisches Konzept für die industrielle Fertigung Pre-applicable structural adhesives - a new bonding concept for industrial production Andreas Hartwig, Andreas Lühring, Matthias Popp, Manfred Peschka Fraunhofer-IFAM, Bremen andreas.hartwig@ifam.fraunhofer.de Suppliers Convention & Hannover Messe, Hannover 2014

3 Pre-applied adhesives (PAA) are widely used for non-structural applications E.g. stamps, PAA with activation by moisture or PSA and removal of release paper

4 Pre-applied adhesives (PAA) are widely used for non-structural applications Or envelopes PSA, removal of release paper Contact adhesives Moisture activation

5 Pre-applied adhesives (PAA) are widely used for non-structural applications Sticker and labels, removal of release paper Foto: Klicker/

6 Application of PAA in structural bonding? Pre-Applied Structural Adhesives = PASA Use of the Fraunhofer IFAM PASA technology will improve product design, productivity and quality! PASA are usually solid and tack free at ambient conditions

7 Motivation Application of PASA has numerous advantage compared to liquid or paste adhesives: Handling of parts with adhesive becomes simpler as both are already connected. No harm of contamination by the adhesive during assembling. Adhesive application can be carried out at different places than assembling. Sealing of a prepared surface by the PASA. No use of liquid chemicals during assembling required.

8 Requirements on PASA Quick curing but long shelf live PASA Good adhesion on part in uncured state Tack free but good wetting

9 Chemistry of PASA Most commercial adhesives are not sufficient for (real) quick curing. Bubble formation and britteling occur. Controll of shelf live difficult, increase of viscosity not obvious. Application and processing outside typical conditions, but in other branches adoptable solutions available. Right chemistry combined with processing teaches how to prepare parts with tack free, highly reactive adhesives.

10 I. Dual-cure with different curing reactions Property profile: Liquid or paste like adhesive. After UV-irradiation formation of a tackfree, thermoplastic adhesive layer. Thermal activation, adhesive melts and wets second part followed by chemical curing. Chemistry: Acrylate or methacrylate combined with epoxy resin. Curing step 1: Radical polymerisation of the acrylate or methacrylate by UV light. Curing step 2: Thermal cross-linking of the epoxy groups, e.g. by dicyandiamide.

11 II. Thermally curable dispersion of solid resin Property profile: Dispersion of a solid adhesive in water. After evaporation of the water a homogeneous, tackfree, thermoplastic and reactive adhesive layer is formed. Thermal activation: melting and cross-linking. Chemistry: Dispersion of solid epoxy resins combined with latent hardener (e.g. dicy, microencapsulation, urones or imidazoles.

12 III. Thermally curable hot melt Property profile: Tackfree up to 50 C Melting C Curing > 100 C Adhesive preparation: Mixing of the single components in the melt below curing temperature. Very proper control of preparation conditions! Application: Application as melt, alternatively powder application with sinter process. Chemistry: Reactive, solid epoxy resins on the base of bisphenole-a, novolak and the like.

13 Example 1: Bonded fastener

14 Bonded studs as fastener for transportation industry Application of small amounts of liquid adhesives in automotive assembling not acceptable. Pre-applied thermally reactive hot melt based on epoxy resin, Quick curing in some seconds. Tackfree up to 50 C. Combined development of heating process, adhesive formulation and design / stud geometry. Development of a process for adhesive manufacturing and application required.

15 Adhesive production and application hrung Flexibilisator + Härter + (Füllstoffe) Harz + Füllstoffe ierung M M chung likation Mixing of components in molten state: low temperature and short time, otherwise reaction starts Studs with PASA (real studs applied in automotive look much different)

16 Temperatur [ C] Curing process: Inductive heating Zeit [s] Very high heating rates. Proper controll of heating process. Automatisation possible. Temperature during inductive heating

17 Zugscherfestigkeit [MPa] Adhesives properties Quick curing and bond formation. Tackfree at 50 C. High strength on different substrates. Tolerant against contaminations Erwärmungszeit [s] Lap-shear strength of an epoxide based hot melt PASA on AlMg3 without pre-treatment

18 Example 2: Bonded blanks

19 Local reinforcement of sheet metal Production of parts with lower metal thickness lightweight constructions. Local reinforcement difficult, use of past like adhesives does not fit in the production conditions of sheet metal parts. New way of adhesive bonding required for production of such parts. Reinforcement of engine hood at the lock as example.

20 Process Adhesive application on the coil or metal sheets. PASA forms tackfree layer and coil can be wound up. Final curing in KTL or other oven. Coil Cutting Fixation, spot welding Deep drawing KTL reinforce coil with PASA VB PASA GB base coil

21 Adhesives development After test of different concepts use of an epoxy resin dispersion as base adhesive. Requirements, beside the typical things: Cutable wihout contamination of tools. Deformable together with sheet metal during deep drawing. Tackfree at room temperature. Good adhesion in uncured state. Long shelf life. etc.

22 Formulation of the adhesives Start formulation: Amount [%] Resins Pudis12 33,33% Epis316 33,33% Fillers and Additives Water 32,50% Hardener Hady12 0,90% Formulation after first improvement: Amount [%] Resins Pudis12 29,50% Epis316 49,16% Fillers and Additives Inikor3c 9,83% Addis14 0,39% Water 9,83% Hardener Hady12 1,28% Strength: 16,5 MPa (oily steel) 18,3 MPa (degreased) (Curing: 180 C, 30 min.) - Corrosion of the steel observed Strength: 14,6 MPa (oily steel) 20,6 MPa (degreased) (Curing: 180 C, 30 min.) - No corrosion

23 Bending test with the not cured adhesive Adhesive with PU: no change during bending test Adhesive without PU: no adhesion, breaks during bending PU as additive improves adhesion and most other properties

24 Test of deep drawing properties by Erichsen deepening Not cured adhesive with PU. Adhesive layer fails at high deformation degrees. Cured adhesive with PU. Very good adhesion and failure of the steel.

25 For fixation of the two sheet metals spot welding is required Sheet metal Welding electrode Electrical connection required. Adhesive layer between sheet metal pieces to be bonded which leads to electrical insulation. Adhesive must be removed / pressed away which is no problem for liquid adhesives. Welding electrode Adhesive Sheet metal 2 Spot welding works well with the new adhesive! Process of spot welding Quelle: TU Chemnitz

26 Examination of the welding spots yields proper connection through the adhesive H 340 DP 800 5mm 5mm 600μm

27 Demonstration: patch work in automotive part Local reinforcement of the sheet metal possible. Reduction of total thickness of the sheet metal leading to lighter construction and lower cost. Thickness decreases / harm of breaks or failure Sheet metal thickness increases during deep drawing

28 Demonstrator: patch work in automotive part pocket to hold the inlay die part of the blank holder bottom die geometry of engine hood die and blank holder geometry of engine hood Work performed by IFUM (Hannover University)

29 Demonstrator: proper local reinforcement

30 Demonstrator PASA was applied on coil. Reinforcement of engine hood was successful. No problems during KTL. Springback of reinforcing sheet metal sometimes critical. Adhesive layer partially too thin work on application of thicker layers.

31 Expire of adhesives shelf-live? Mechanical fastener, the staples are obviously not the perfect solution. In case of non-structural adhesives fixation with other methods possible. Tape

32 Control of shelf-life Adhesive and substrate form a uniform part. Expire of adhesive shelf-life means that the complete part can not be used any longer. Application of additional adhesives or mechanical fastener not possible like in non-structural bonding. Parts logistics and control of the adhesives state must even be more perfect than in conventional production.

33 Control of shelf-life and cure state simple by colour reaction PASA changes colour if the shelf-life is expired and by having a different colour completeness of cure can be checked visually. Can also be transferred to other adhesives. fresh expired cured

34 Conclusions Proper combination of chemistry and processing enables the development of adhesive sufficient as PASA. really quick curing with good bond properties. long and controlled shelf-life. tackfree at ambient conditions. Visual inspection of shelf-life and cure state is possible and can be transferred to other adhesives. PASA has the potential to improve assembling in industrial production significantly and might become the second revolution in which pre-applied adhesives are involved after invention of the stamp.

35 Thank you for your most valuable your time and attention. Mehr Informationen zur Klebtechnik und der klebtechnischen Infrastruktur in Deutschland in Halle 6, Stand B45