Patent Application
20080093021
Fabrication of a semifinished product H or a sandwich composite S is further illustrated schematically below with the help of the drawings. The same reference numbers are attached to the same elements in the different figures. Movements and forces are indicated by arrows.
In
The first time period I indicates the situation before mixing. At least component K1 is heated, and consequently its viscosity η1 decreases. In this example, component K2 is not heated and has viscosity η2.
The second time period II indicates the situation during mixing. The mixture of components K1 and K2 has viscosity ηM immediately after mixing.
The third time period III indicates the stage of crosslinking and storage of semifinished product H. The strength or viscosity rises, due to cooling and crosslinking, from the mixture viscosity ηM to a constant viscosity or strength ηH of the semifinished product H.
The fourth time period IV indicates the forming process. The viscosity or strength remains essentially constant during the forming process.
The fifth time period V indicates the curing and construction of sandwich composite S. The viscosity or strength rises throughout the second crosslinking stage, and after cooling reaches the final strength ηE of the sandwich composite S.
a here shows a semifinished product H which is placed in a forming apparatus. The forming apparatus has a die cavity 6 as well as a punch 7. The punch 7 is moved toward the die cavity by means of a press, such as a hydraulic press, whereby semifinished product H is pressed into the recess of die cavity 6 by the punch.
b shows the final stage of the pressing process. Formed part U was made from semifinished product H, which had conformed to the contours of die cavity 6 without wavy, puckered, or wrinkled bulges being formed and without the adhesive being squeezed out from between substrates S1 and S2.
c shows formed part U as it comes out of the forming apparatus.
Finally,
A few examples are given below which illustrate the invention further but do not limit the scope of the invention in any way. The raw materials used in the examples are as follows:
General preparation for preparing epoxy adduct B and its mixture with A (=A/B premix):
A/B Premix PM1
Under vacuum and with stirring at 110° C., 123.9 g of a dimeric fatty acid, 1.1 g triphenylphosphine, and 57.3 g adipic acid were reacted for 5 hours with 658 g of liquid DGEBA epoxy resin, with epoxy content of 5.45 eq/kg, until a constant epoxy concentration of 2.85 eq/kg was achieved. After the end of the reaction, an additional 226.3 g of liquid DGEBA epoxy resin was added to the reaction mixture.
Then other mixtures PM2 to PM4 were prepared. For this purpose, the adipic acid was replaced by various aromatic alcohols in such a way that a theoretically identical epoxy content of 2.80-2.95 eq/kg was achieved in the binder:
A/B Premix PM2
Under vacuum and with stirring at 110° C., 123.9 g of a dimeric fatty acid, 1.1 g triphenylphosphine, and 95.0 g of 2,2-bis(4-hydroxyphenyl)propane (=bisphenol A) were reacted for 5 hours with 658 g of liquid DGEBA epoxy resin, with epoxy content of 5.45 eq/kg, until a constant epoxy concentration of 2.95 eq/kg was achieved. After the end of the reaction, an additional 226.3 g of liquid DGEBA epoxy resin was added to the reaction mixture.
A/B Premix PM3
Under vacuum and with stirring at 110° C., 123.9 g of a dimeric fatty acid, 28.3 g adipic acid, 1.1 g triphenylphosphine, and 47.3 g bis(4-hydroxyphenyl)sulfone were reacted for 5 hours with 658 g of liquid DGEBA epoxy resin, with epoxy content of 5.45 eq/kg, until a constant epoxy concentration of 2.85 eq/kg was achieved. After the end of the reaction, an additional 226.3 g of liquid DGEBA epoxy resin was added to the reaction mixture.
A/B Premix PM4
Under vacuum and with stirring at 110° C., 123.9 g of a dimeric fatty acid, 1.1 g triphenylphosphine, and 71.3 g bis(4-hydroxyphenyl)sulfone were reacted for 5 hours with 658 g of liquid DGEBA epoxy resin, with epoxy content of 5.45 eq/kg, until a constant epoxy concentration of 2.82 eq/kg was achieved. After the end of the reaction, an additional 226.3 g of liquid DGEBA epoxy resin was added to the reaction mixture.
Compound C1
A polyurethane prepolymer was prepared from MDI flakes (4,4-diphenylmethylene diisocyanate) and a polypropylene glycol with molecular weight of 2000 g/mol. The prepolymer had an NCO content of 3.7%.
Preparation of Adhesive K
Adhesive Formulations
Various adhesive compositions were prepared as specified in Table 2. In component K1, the A/B premix was uniformly mixed with prepolymer C1, dibutyltin dilaurate, Dicy, and Cabosil in a planetary mixer at a temperature of 95° C. under vacuum. Then ceramic hollow spheres were added and stirred at a stirring speed that was not too fast, in order to avoid breaking the hollow spheres. Then a cartridge was filled with K1 at a temperature between 85° C. and 95° C.
Components K1 and K2 were mixed well, in the ratio specified in Table 2, at a temperature between 85° C. and 95° C. in a Schramoid and added to a cartridge, and applied within 10 minutes after the end of mixing. For Ref. 2, no component K2 was added.
Application
Fabrication of a Semifinished Product
The adhesive, as specified in Table 2, was applied to 0.25 mm thick oiled steel sheet, covered with a second identical oiled steel sheet, and pressed to an adhesive thickness of 1 mm with a press equilibrated at about 100° C. After cooling, for adhesives K-1 to K-5 the adhesion of the sheet metal is good, so the composites can be easily handled.
In addition, when pressure is applied again by means of a press, the adhesive is not squeezed out. For the comparison adhesives Ref. 1 and Ref. 2, however, the adhesive was squeezed out when pressure was applied.
Example K-5Al corresponds to K-5, except that aluminum sheet of thickness 0.25 mm was used as the substrate instead of steel sheet.
As reference example Al/PP, 1 mm polypropylene was prepared as an interlayer between two aluminum sheets of thickness 0.25 mm.
Preparation of a Formed Part
To test the formability of the fabricated semifinished products, the deep-drawing properties were determined with the Erichsen cupping tester. A disk of diameter 64 mm was punched out from the semifinished product. A small cup-shaped indentation, a dome shape with diameter 40 mm and depth 20 mm, was deep-drawn. A ring-shaped lower holder prevented the adhesive compounds from peeling off the edge of the sheet metal.
All adhesives K-1 to K-5 could be easily formed, and there was no or only slight squeezing out of the adhesive. The reference adhesives Ref. 1 and Ref. 2 showed considerable squeezing out of the adhesive, so that at some spots essentially no more adhesive could be found between the pieces of sheet metal.
Comparing adhesives K-4 and K-5, it could be determined that K-5 exhibited better properties in deep drawing.
All adhesives K-1 to K-5 also showed identical behavior after 6 months, according to some stored semifinished stock material.
Preparation of a Sandwich Composite
All formed parts with adhesives K-1 to K-5 were cured in an oven for 25 minutes at 180° C. They all show very good curing, excellent adhesion, and good impact strength.
Since the mechanical properties have to be measured on flat substrates, we could not use the formed parts as the starting point but rather used the respective semifinished products H as follows:
The fabricated semifinished products were cured in an oven for 25 minutes at 180° C. After cooling, the mechanical properties of the sandwich composites were determined for K-5 and K-5Al.
As the reference to be compared with the sandwich composites S, we used 1.5 mm thick aluminum sheet Al-1.5 as well as polypropylene-reinforced composite Al/PP.
Test Methods
T-peel strength (DIN 53282, ISO 11339)
This test method measures the force vertical to the adhesive surface. The dimensions of T-peel strength are N/mm (=average force [N] divided by the width of the test piece [mm]).
3-point bending strength (ISO 178)
The bending strength is the strength under a 3-point bending load with 20 cm span, where a 25 [missing units] wide test piece is used. The strength [N] is measured for bending of 2 mm, 5 mm, and 10 mm.
Results
From the results in Table 3, obviously the sandwich composites according to the invention are considerably stronger than massive aluminum sheet (Al-1.5) or Al-polypropylene composite (Al/PP), despite their much reduced weight.
It has been additionally shown that the sandwich composites have exceptionally good aging resistance and adhesion, as proven by the cataplasma test (70° C./100% relative air humidity).
| Number | Date | Country | Kind |
|---|---|---|---|
| 04004189.9 | Feb 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/50801 | 2/25/2005 | WO | 00 | 10/5/2007 |
