METHOD FOR PLASMA-INITIATED ADHESIVE BONDING

Abstract

The invention relates to a method for producing an adhesive bond by means of an adhesive, wherein a composition containing at least a substance reactive in a radical polyreaction and a catalytically active substance is used as the adhesive, wherein at least one metal complex from the group of the metal phthalocyanines and/or from the group of the metal porphyrins is selected as the catalytically active substance, wherein a polyreaction of the reactive substance occurs, which polyreaction is initiated by the application of a plasma.

Claims

1. A method for producing an adhesive bond by means of an adhesive, the adhesive used comprising a composition comprising at least one substance which is reactive in a radical polymerization reaction and one catalytically active substance, wherein said catalytically active substance selected is at least one metal complex from the group of the metal phthalocyanines and/or from the group of the metal porphyrins, the reactive substance undergoing a polymerization reaction which is initiated by exposure to a plasma.

2. The method as claimed in claim 1, wherein for the adhesive bond an adhesive agent is used wherein the adhesive is present in a polymeric film-former matrix.

3. The method as claimed in claim 2, wherein the polymeric film-former matrix is a thermoplastic polymer.

4. The method as claimed in claim 1, wherein thickeners have been added to the adhesive.

5. The method as claimed in claim 1, wherein one or more getter materials, more particularly zeolites, have been added to the adhesive and/or to the adhesive agent.

6. The method as claimed in claim 1, wherein the adhesive and/or the adhesive agent are/is used in film form.

7. The method as claimed in claim 1, wherein the adhesive and/or the adhesive agent possess/possesses pressure-sensitive adhesive properties.

8. The method as claimed in claim 1, wherein neither the adhesive nor the adhesive agent possess pressure-sensitive adhesive properties.

9. The method as claimed in claim 1, wherein the metals of the metal complex or of the metal complexes are selected from the group consisting of iron, cobalt, copper, nickel, aluminum, magnesium, manganese, tin and zinc.

10. The method as claimed in claim 9, wherein said metal selected is iron.

11. The method as claimed in claim 1, wherein said catalytically active substance selected is iron(II) phthalocyanine.

12. The method as claimed in claim 1, wherein said catalytically active substance selected comprises one or more cobalt porphyrins.

13. The method as claimed in claim 1, the method comprising application of a stationary or flowing process gas atmosphere.

14. The method as claimed in claim 1, wherein the plasma is generated under atmospheric pressure.

15. The method as claimed in claim 1, wherein air or water vapor is used as process gas.

16. The method as claimed in claim 15, wherein the air comprises moisture.

17. The method as claimed in claim 1, wherein the plasma comprises or is admixed with reactive gaseous substances, coating or polymerizable constituents.

18. The method as claimed in claim 1, wherein the adhesive or the adhesive agent is foamed after the plasma activation.

19. An adhesive film comprising an adhesive comprising at least one substance which is reactive in a radical polymerization reaction and one catalytically active substance, wherein said catalytically active substance selected is at least one metal complex from the group of the metal phthalocyanines and/or from the group of metal porphyrins.

20. The method as claimed in claim 2, wherein the thermoplastic polymer is a thermoplastic polyurethane, or an elastomer or a thermoplastic elastomer.

Description

Experimental Section

EXAMPLES

[0150] In a first production mode, a 20% strength acetonic solution of the film-former matrix (PU solution) is prepared first of all. This is done by weighing out 120 g of Desmomelt 530 (cf. details above) and 480 g of acetone into a screw-closure glass, and then closing the screw-closure glass. The screw-closure glass is rolled for a number of days on a roller bed, which brings about complete dissolution of the Desmomelt 530. Depending on the rolling rate, the operation lasts for about one to seven days. Alternatively, the acetonic solution can also be produced by stirring the Desmomelt 530 pellets in acetone using a commercial laboratory stirrer.

[0151] Subsequently, in proportions according to the listing below (table 1), the thus-prepared 20% strength acetonic solution of Desmomelt 530, 2-phenoxyethyl methacrylate, ethylene glycol dimethacrylate, iron(II) phthalocyanine, and optionally Purmol 3STH getter (zeolite (molecular sieve); pore size 0.3 nm (3 ), particle size <30 m, water absorption capacity 23%; from Zeochem) are mixed for 10 minutes using a commercial laboratory stirrer.

[0152] In another production mode, a 30% strength solution of Saran F-310 [noncrystalline, thermoplastic vinylidene chloride-acrylonitrile copolymer, poly(vinylidene chloride-co-acrylonitrile); CAS No. 9010-76-8] in acetone is mixed with 2-phenoxyethyl methacrylate, ethylene glycol dimethacrylate, iron(II) phthalocyanine, and Purmol 3STH getter for 10 minutes using a commercial laboratory stirrer (for proportions see example 5 in table 1).

TABLE-US-00001 TABLE 1 All amounts in wt %; for PU and F310, the solids content is stated (without acetone) PU F310 PEM EGDM EPC 3STH Example 1 68.1 30 1.4 0.5 Example 2 68.1 25.5 1.4 0.5 4.5 Example 3 68.5 25.6 1.4 3 Example 4 65.5 24.5 1.35 0.65 8.6 Example 5 71.2 22.2 1.2 0.2 5.2 Example 6 68.1 30 1.4 0.33 PU: Desmomelt 530, used as 20% solution in acetone F310: Saran F310, used as 30% solution in acetone PEM: 2-phenoxyethyl methacrylate EGDM: Ethylene glycol dimethacrylate EPC: Iron(II) phthalocyanine 3STH: Purmol 3STH getter

[0153] The homogeneous mixture obtained in each case is coated out using a commercial laboratory coating unit (for example, from SMO (Sondermachinen Oschersleben GmbH)) with a coating knife on a siliconized polyester terephthalate sheet. The acetone is subsequently evaporated off in a drying cabinet at 60 C. to 80 C. for 10 minutes. The slot width on coating out is set such that evaporation of the solvent leaves a film having a thickness of 150 m. The pressure-sensitively adhesive film obtained is lined with a siliconized polyester sheet prior to bonding.

[0154] Before the plasma treatment, the adhesive films located between the siliconized polyester sheets were each cut into rectangular specimens measuring 13 mm*20 mm.

[0155] Plasma treatment took place with a dielectrically hindered surface discharge geometrically comparable with Oehmigen et al., Plasma Processes and Polymers 7, 2010. The dielectric was fabricated from Al.sub.2O.sub.3. The electrode structure was lined with a protective layer of glass on the side facing the substrate. The plasma was excited with a sinusoidal high voltage of 9.2 kV at a frequency of 15.9 KHz. The treatment times varied between 1 s and 10 s.

[0156] In a first series of tests, adhesive film specimens of examples 1 to 5 were treated on one side with plasma. For a single-side initiation, the liner was first removed from one side of the specimens, and the adhesive was adhered over the full area onto a shear test plate made of steel (stainless steel 302 according to ASTM A 666; 50 mm125 mm1.1 mm, glossy annealed surface, surface roughness 5025 nm arithmetic mean deviation from the baseline). The adhesive face now exposed was treated in the plasma at a distance of about 0.3 mm from the electrode. Subsequently, within 2 minutes, a second steel shear test plate (specification as for first steel plate) was joined onto the second adhesive film face and pressed on briefly by hand.

Results

[0157]

TABLE-US-00002 TABLE 2 Treatment method Result Example 1 Plasma Adhesive film becomes solid Example 1 UV No polymerization/crosslinking, adhesive film retains original condition Example 2 Plasma Adhesive film becomes solid, faster than for example 1 with plasma treatment Example 3 Plasma No polymerization/crosslinking, adhesive film retains original condition Example 4 Plasma Adhesive film becomes solid Example 5 Plasma Adhesive film becomes solid

[0158] The curing time is generally less than 16 hours, but partial strength is achieved after just a few hours.

[0159] The specimens produced with the adhesive according to example 6 in table 1 and with the protocols above were plasma-treated on both sides, and their shear strength was measured after curing.

[0160] For this purpose, first of all, the liner was removed from one side of the specimens, and the top face of the adhesive film, which was now exposed, was treated in the plasma, in accordance with the plasma treatment conditions stated above, at a distance of about 0.3 mm from the electrode.

[0161] Subsequently, within 2 minutes, a first shear test plate made of steel (stainless steel 302 according to ASTM A 666; 50 mm125 mm1.1 mm, glossy annealed surface, surface roughness 5025 nm arithmetic mean deviation from the baseline) was joined onto the treated side of the adhesive film, so that the adhesive film surface was fully covered, and was pressed on briefly by hand, after which the second liner was removed. The as yet untreated side of the adhesive film, which was now exposed, was subsequently treated in a plasma under the same conditions, and a second steel shear test plate (specification as for the first steel plate) was joined onto the treated second side of the adhesive film, so that this side as well was fully covered, and was likewise pressed on briefly by hand. Produced accordingly was an assembly composed of the two steel plates bonded in parallel by the adhesive film. The bond area between the steel plates was therefore 260 mm.sup.2 (adhesive film specimen dimensions 13 mm20 mm; see above). The positioning of the bond of the steel plates took place with a slight offset, so that one steel plate in each case jutted out somewhat from two opposing sides of the assembly. The adhesively bonded assembly was then cured for a time of 16 hours.

[0162] For the measurement of the shear strength, the assembly was clamped into a tensile testing machine, by clamping the protruding edge of one of the steel plates into a mount of the tensile testing machine, and the opposite protruding edge of the second steel plate into a second mount of the tensile testing machine. Using the tensile testing machine, the two steel plates could be pulled apart parallel to one another, with the bond exposed to shearing. The maximum force immediately before failure of the bonded assembly (parting of the steel plates from one another) was ascertained, and is reported in table 2, based in each case on the bond area.

TABLE-US-00003 TABLE 3 Measurement values for different plasma conditions with reference to example 6 Treatment side Treatment time per side [s] Shear strength [MPa] One-sided 1 0.38 0.14 Double-sided 1 1.92 0.45 Double-sided 2 2.96 0.30 Double-sided 5 3.68 0.03 Double-sided 10 3.71 0.04