MASKING OF WINDOW FLANGES WITH AN ADHESIVE TAPE COMPRISING A SELF-ADHESIVE COMPOSITION BASED ON CROSSLINKED VINYLAROMATIC BLOCK COPOLYMERS

Abstract
Use of an adhesive tape for masking substrates, especially substrates coated with cathodic electrocoat (CED) material, more preferably window flanges, with a single-layer or multi-layer backing and applied to one side thereof a self-adhesive composition comprising metal chelate-crosslinkable vinylaromatic block copolymers, preferably styrene block copolymers, which are blended at least with one or more tackifier resins, the vinylaromatic block copolymers being at least partly acid-modified or acid anhydride-modified.
Description
EXAMPLES

Described below are the adhesive tapes with which masking was performed.


Example 1

An adhesive composed of 50 parts of Kraton FG 1901 (SEBS, no diblock, with 30 per cent by weight (referred to below only as “%”) styrene content and, in grafted form, about 2% of maleic anhydride, product of the company Kraton), 50 parts of Kraton FG 1924 (SEBS with about 40% diblock, 13% block polystyrene and about 1% maleic anhydride, from Kraton), 90 parts of Regalite R 1100 (hydrogenated hydrocarbon resin with a softening point of about 110° C., from Eastman) and 20 parts of Regalite R 1010 (hydrogenated liquid hydrocarbon resin from Eastman) and 2 parts of aluminium acetylacetonate was dissolved in a mixture of toluene and isopropanol in a ratio of 9 to 1 and the solution was coated directly onto a 100 μm PET film, using a coating bar, in such a way that drying resulted in an adhesive coatweight of 25 g/m2. Prior to its use, the specimen was lined with a siliconized release paper.


Example 2

As Example 1, but using an adhesive with a composition of 50 parts Kraton FG 1901, 50 parts Kraton FG 1924, 120 parts Pentalyn H (hydrogenated rosin ester from Eastman), 15 parts Ondina G 41 (white oil with low naphthenic fraction, from Shell) and 2 parts titanyl acetylacetonate.


Example 3

As Example 1, but using an adhesive with a composition of 50 parts Kraton FG 1901, 50 parts Kraton FG 1924, 70 parts Dercolyte A 115 (α-pinene resin with a softening point of about 115° C., from DRT), 40 parts Wingtack 10 (liquid hydrocarbon resin from Goodyear) and 2 parts acetylacetonate.


Counterexample 1

As Example 1, but using an adhesive composed of 50 parts Kraton G 1650 (SEBS, no diblock, with 30% styrene content, no maleic anhydride, product of the company Kraton), 50 parts Kraton G 1657 (SEBS with about 40% diblock, 13% block polystyrene, no maleic anhydride, from Kraton), 90 parts Regalite R 1100 and 20 parts Regalite R 1010.


Counterexample 2

As Example 1, but using an adhesive with a composition of 50 parts Kraton G 1650, 50 parts Kraton G 1657, 120 parts Pentalyn H and 15 parts Ondina G 41.


Counterexample 3

As Example 1, but carrying out priming with a solution of 2 parts of natural rubber in toluene, which had been mixed with 1 part of diphenylmethane diisocyanate, with a coatweight of 0.3 g/m2. In a downstream operation this primer was coated with a natural rubber self-adhesive composition. The self-adhesive composition consisted of 100 parts natural rubber, 10 parts zinc oxide, 20 parts Pentalyn H, 10 parts Vulkaresen PA 510 (reactive alkylphenol resin from Schenectady), 50 parts Regalite R 1100 and 5 parts Ondina G 41.


Counterexample 4

As Example 1, but carrying out priming with a solution of polyvinylidene chloride in toluene. In a downstream operation an acrylic ester copolymer as self-adhesive composition was coated onto this primer. The self-adhesive composition consisted of 40 parts butyl acrylate, 40 parts 2-ethylhexyl acrylate, 12 parts vinyl acetate, 5 parts methyl acrylate and 3 parts acrylic acid.


Test Criteria

Decisive test criteria considered important, and thus employed, for the present addressed problem were as follows:

    • adhesive residues on the cathodic electrocoat after thermal loading in bonds with a defined radius
    • adhesion defect of window adhesive on the sites formerly bonded with adhesive masking tapes described in the examples


Test Implementation

Adhesive Residues


Strips 15 mm wide were cut as test strips from the coated specimens. These test strips were adhered, as far as possible without creases, and with a radius of 200 mm, to a metal panel coated with cathodic electrocoat (Cathoguard 500 from BASF) and baked according to manufacturer instructions, this adhering was possible only with slight stretching of the backing.


Subsequently the panel thus bonded was placed in a heating cabinet which had been preheated to 170° C., and left there for an hour. After the panel had cooled, the external radius of the test strip was assessed for adhesive residues.


The evaluation criteria were as follows:

    • + for no or minimal adhesive residues
    • − for distinctly visible adhesive residues


Adhesion Defects

Strips 15 mm wide were cut as test strips from the coated specimens. These test strips were adhered in a straight line without creases to a metal panel coated with cathodic electrocoat (Cathoguard 500) and baked according to manufacturer instructions.


The panel thus bonded was subsequently placed in a heating cabinet, which had been preheated to 170° C., and left there for an hour and forty minutes. After the panel had cooled, the test strip was removed, and a reactive one-component PU window adhesive (Sikaflex DM2 from Sika), which for the purpose of improved processing had been preheated to 50° C., was applied, in the form of a triangular bead with a width of about 1 cm and a height of 1 cm, to the site of former bonding. The triangular profile, whose base lay on the cathodic electrocoat, was pressed flat, using a polyethylene plate, so that the bead subsequently had a height of about 0.5 cm and a width of about 1.2 cm.


The metal panel was stored for ten days at 23° C.±1° C. and at a relative humidity of 50%±1% for the adhesive to cure.


After curing had taken place, the bead of adhesive was raised at one prepared end and peeled from the metal panel at an angle of approximately 90°.


If bonding has been effective, exclusively cohesion failure occurs within the adhesive bead—that is, no adhesion failure to the cathodic electrocoat. Continued peeling of the bead is then achieved by making incisions with a knife into the cohesively fracturing bead residue down to the electrocoat.


In the case of adhesion failure, the bead of adhesive can be peeled from the electrocoat without substantial residues. If the proportion of adhesion fraction is more than 10%, the test is classed as failed.


The evaluation criteria used were as follows:

    • + for less than 10% adhesion fracture
    • − for more than 10% adhesion fracture


Results

The results of the masking solutions are summarized in the following table.
















Adhesive residues
Adhesion defects




















Example 1
+
+



Example 2
+
+



Example 3
+
+



Counterexample 1

+



Counterexample 2

+



Counterexample 3
+




Counterexample 4
+











It is apparent that the masking solutions of the invention meet both important criteria simultaneously, whereas the prior-art counterexamples each meet only one, and are therefore unsuitable.

Claims
  • 1. A method of masking a substrate, said method comprising applying an adhesive tape to said substrate, said adhesive tape comprising a single-layer or multi-layer backing and a self-adhesive composition applied to one side thereof, said self-adhesive composition comprising metal chelate-crosslinkable vinylaromatic block copolymers, which are blended at least with one or more tackifier resins, the vinylaromatic block copolymers being at least partly acid-modified or acid anhydride-modified.
  • 2. The method according to claim 1, wherein the the vinylaromatic block copolymers are partly acid-modified or acid anhydride-modified to an extent between 0.5 and 4 per cent by weight, based on each block copolymer as a whole.
  • 3. The method according to claim 1, wherein the self-adhesive composition comprise a fraction of 20 to 70 per cent by weigh of vinylaromatic block copolymer.
  • 4. The method according to the vinylaromatic block copolymers are formed of vinylaromatics (A blocks), and blocks formed by polymerization of 1,3-dienes (B blocks).
  • 5. The method according to at claim 1, wherein the self-adhesive composition is composed of at least one acid-modified or acid anhydride-modified vinylaromatic block copolymer, at least one metal chelate of the following formula: (R1O)nM(XR2Y)m
  • 6. The method according to claim 1, wherein the self-adhesive composition is crosslinked with the aid of chelate ligands, and the chelate ligands used are those formed from the reaction of the following compounds: triethanolamine, 2,4-pentanedione, 2-ethyl-1,3-hexanediol or lactic acid.
  • 7. The method according to claim 1, wherein the self-adhesive composition is crosslinked with the aid of crosslinkers, and the crosslinkers used are aluminium acetylacetonates c titanium acetylacetonates.
  • 8. The method according to claim 1, wherein self-adhesive composition further comprises one or more of blend components, plasticizers, ageing inhibitors, processing aids, fillers, dyes and; stabilizers.
  • 9. The method according to claim 1, wherein self-adhesive composition is applied to the backing in a coatweight between 5 and 80 g/m2.
  • 10. The method according to claim 1, wherein adhesive tape exhibits a bond strength on the CED substrates of between 1 and 8 N/cm, and/or a peel strength from a cathodic electrocoat after thermal exposure of up to 100 minutes at 170° C. in the range between 2 and 10 N/cm.
  • 11. Window flange masked with an adhesive tape according to the method of claim 1.
  • 12. Car with a window flange according claim 11.
Priority Claims (1)
Number Date Country Kind
10 2006 023 936.9 May 2006 DE national