POLYCHLOROPRENE-BASED CONTACT ADHESIVES CONTAINING ETHYLENE-VINYL ACETATE COPOLYMER

Abstract

Contact adhesive compositions comprising polychloroprene and, based on the polychloroprene content, 10 to 99 wt % of ethylene-vinyl acetate copolymer exhibit outstanding adhesion to substrates such as ethylene-vinyl acetate copolymers, thermoplastic elastomers or flexible PVC. The contact adhesive compositions of the invention are especially suitable for use in the bonding of articles, preferably articles in which at least part of the articles to be bonded consists of polyurethane, flexible PVC, ethylene-vinyl acetate copolymers and/or thermoplastic elastomers. This allows the adhesive composition to be employed widely in the footwear industry, for the bonding of roofing membranes containing flexible PVC, ethylene-propylene-diene rubber (EPDM) and/or ethylene-vinyl acetate copolymers, or for the bonding of synthetic leather based on flexible PVC.

Claims

1. Contact adhesive composition comprising: polychloroprene, 10 to 99 wt %, based on polychloroprene content, of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 18 to 90, and 60-95 wt % of solvent, based on a total weight of the contact adhesive composition.

2. (canceled)

3. Contact adhesive composition according to claim 1, comprising 60-95 wt % of solvent, and also a total of 5-40 wt % of polychloroprene and ethylene-vinyl acetate copolymer, based in each case on the total weight of the contact adhesive composition.

4. Contact adhesive composition according to claim 1, comprising 0.1-35 wt %, of further components, selected from resins, magnesium oxide, zinc oxide, isocyanate-based crosslinkers, and ageing inhibitors, based on the total weight of the contact adhesive composition.

5. Contact adhesive composition according to claim 1, which is free from methyl methacrylate.

6. Contact adhesive composition according to claim 1, further comprising terpene phenolic resin, alkyl-phenolic resin, coumarone-indene resin, -methylstyrene resin, chlorinated rubber, silica, and/or resin acid esters.

7. Contact adhesive composition according to claim 1, wherein the polychloroprene has a weight-average molecular weight Mw of more than 200 000 daltons.

8. Contact adhesive composition according to claim 1, comprising one or more isocyanate-based crosslinkers selected from di- and polyisocyanates.

9. A method of bonding an article in which at least part of the article to be bonded consists of polyurethane rubber, flexible PVC, ethylene-vinyl acetate copolymers and/or thermoplastic elastomers, said method comprising bonding the articles with a contact adhesive composition according to claim 1.

10. Method according to claim 9, wherein the article is a footwear item.

11. Method according to claim 9, wherein the articles is a roofing membrance comprising flexible PVC, ethylene-propylene-diene rubber and/or ethylene-vinyl acetate copolymers, or the article is synthetic leather based on flexible PVC.

12. Method according to claim 9, wherein the contact adhesive composition, in solution in a solvent, is applied to a surface of the article to be bonded to another surface, the solvent is evaporated at least partially by flashing off or under reduced pressure, and then surfaces covered with the adhesive are pressed against one another.

13. Method according to claim 11, wherein the solvent is evaporated at a temperature of between 0 C. and 80 C.

14. Method according to claim 11, wherein, after the evaporation of the solvent, the adhesive is heat-activated at a temperature of between 40 C. and 100 C.

15. A footwear item obtainable by the method according to claim 10.

Description

EXAMPLES

[0042] The invention is elucidated in more detail below with reference to examples:

[0043] Production of Specimens and Implementation of the Tensile Peel Test (Based on DIN EN 1392:2006):

[0044] The specimens used were composed of polyvinyl chloride with 30% plasticizer fraction (flexible PVC) and with dimensions of 200 mm30 mm4 mm. The specimens were abraded three times with a sanding machine (Jet 10-20 plus drum sander) using 80-grade sandpaper, on one side. The test specimens were subsequently trimmed in length to 100 mm30 mm4 mm and were degreased by being wiped down with a paper cloth soaked with ethyl methyl ketone.

[0045] For bonding by the contact bonding method, the adhesive was applied doubly to the flexible PVC test specimen, leaving 3 cm to the edge free of adhesive. The waiting time between the two applications was 10 min. Pairs of flexible PVC test specimens, 15 minutes after the second application, were placed on top of one another so as to overlap completely with the adhesive-free areas against one another. Immediately thereafter the test specimens were pressed at 0.4 Pa.

[0046] For bonding by the heat-activation method, the adhesive was applied doubly to two flexible PVC test specimens, leaving 3 cm to the edge free of adhesive. The waiting time between the two applications was 10 min. The solvent was then flashed off for 24 h. The subsequent heat activation took place in a heating cabinet at 70 C. for 10 min. Pairs of test specimens were placed on top of one another so as to overlap completely with the adhesive-free areas having been in contact, and pressing took place at 0.4 Pa.

[0047] For bonding with isocyanate crosslinker, the adhesive composition was admixed with 7.5 parts by weight of Desmodur RFE (based on 100 parts of adhesive), which were stirred in thoroughly. The two-component adhesive was processed within an hour. The adhesive was applied doubly to the flexible PVC test specimen, leaving 3 cm to the edge free of adhesive. The waiting time between the two applications was 10 min. Pairs of flexible PVC test specimens, 15 minutes after the second application, were placed on top of one another so as to overlap completely with the adhesive-free areas having been in contact, and pressing took place at 0.4 Pa.

[0048] The T-peel test took place after seven days of storage of the test specimens at 23 C.

[0049] For the T-peel test based on DIN EN 1392:2006, the specimens were clamped by the adhesive-free ends into a tensile testing machine from Zwick, ZN005. Testing took place at 23 C. with a velocity of 100 mm/min. The result reported was the average peel force in newtons per millimetre width of specimen. For the calculation of the average peel force, the first 25 mm and the last 25 mm of the travel of the tensile testing machine were not evaluated. In each test series, five specimens were tested, and the average of the five tests was reported as the result.

[0050] Weight-average molar masses were determined by gel permeation chromatography. The eluent used was tetrahydrofuran (flow rate: 1.0 mL/min), the column material consisted of styrene-divinylbenzene copolymer, the column temperature was 35 C., and the eluted polymer was detected using a refractive index (RI) detector.

[0051] Production of the Adhesive Compositions:

[0052] The adhesive compositions were produced in a direct dissolution process. For this process, all of the solid constituents, apart from polychloroprene and the ethylene-vinyl acetate copolymers, were charged to a closable container, the solvents were weighed in, and then the polychloroprene and the ethylene-vinyl acetate copolymer were added. Dissolution took place on a laboratory shaker at 23 C. within 24 h.

[0053] Ingredients for the Adhesive Composition:

[0054] Baypren ALX 233-1: polychloroprene (medium-rapid crystallization) from ARLANXEO

[0055] Baypren ALX 320-2 polychloroprene (rapid crystallization) from ARLANXEO

[0056] Escorene Ultra UL 00328: ethylene-vinyl acetate copolymer with 27 wt % vinyl acetate content from Exxon Mobil Chemical

[0057] Levamelt 400: ethylene-vinyl acetate copolymer with 40 wt % vinyl acetate content from ARLANXEO

[0058] Levamelt 450: ethylene-vinyl acetate copolymer with 45 wt % vinyl acetate content from ARLANXEO

[0059] Levamelt 500: ethylene-vinyl acetate copolymer with 50 wt % vinyl acetate content from ARLANXEO

[0060] Levamelt 600: ethylene-vinyl acetate copolymer with 60 wt % vinyl acetate content from ARLANXEO

[0061] Levamelt 700: ethylene-vinyl acetate copolymer with 70 wt % vinyl acetate content from ARLANXEO

[0062] Levamelt 800: ethylene-vinyl acetate copolymer with 80 wt % vinyl acetate content from ARLANXEO

[0063] SP-560: terpene-phenolic resin from SI Group

[0064] SFP-121H: alkyl-phenolic resin from SI Group

[0065] Vulkasil C: precipitated silica from RheinChemie

[0066] Rhenofit D/A: magnesium oxide (MgO) from RheinChemie

[0067] Zinc oxide, active: zinc oxide (ZnO) from LANXESS

[0068] Vulkanox BHT: ageing inhibitor (2,6-di-tert-buty-4-methylphenol) from LANXESS

[0069] Test Specimens:

[0070] Polyvinyl chloride with 30% plasticizer fraction (flexible PVC) from Rocholl GmbH

[0071] The tables below set out the formulations and also the peel strengths achieved on flexible PVC. The comparative examples are marked in the tables with a C in front of the experiment number. The inventive examples carry the label I.

TABLE-US-00001 TABLE 1.1 Bonding by the method of heat activation without isocyanate crosslinker. (Quantities in parts by weight per 100 parts of Baypren ALX 320-2) C1 I1 I2 I3 I4 I5 I6 Baypren ALX 320-2 100 100 100 100 100 100 100 SP-560 30 Levamelt 400 30 Levamelt 450 30 Levamelt 500 30 Levamelt 600 30 Levamelt 700 30 Levamelt 800 30 MgO 4 4 4 4 4 4 4 ZnO 4 4 4 4 4 4 4 Vulkanox BHT 2 2 2 2 2 2 2 Vulkasil C 20 20 20 20 20 20 20 Toluene 463 463 463 463 463 463 463 Ethyl methyl ketone 100 100 100 100 100 100 100 Peel strength on 0.21 1.98 1.96 1.96 1.41 0.80 0.46 flexible PVC (N/mm)

TABLE-US-00002 TABLE 1.2 Bonding by the method of heat activation without isocyanate crosslinker. (Quantities in parts by weight per 100 parts of Baypren ALX 320-2) C2 I7 I8 I9 I10 I11 I12 Baypren ALX 320-2 100 100 100 100 100 100 100 SP-560 15 30 Levamelt 600 15 30 60 90 15 30 MgO 4 4 4 4 4 4 4 ZnO 4 4 4 4 4 4 4 Vulkanox BHT 2 2 2 2 2 2 2 Toluene 463 463 463 463 463 463 463 Ethyl methyl ketone 100 100 100 100 100 100 100 Peel strength on 0.28 0.48 1.11 2.04 2.19 0.85 1.02 flexible PVC (N/mm)

TABLE-US-00003 TABLE 2 Bonding by the method of contact bonding without heat activation and without isocyanate crosslinker. (Quantities in parts by weight per 100 parts of Baypren ALX 320-2) C3 I13 I14 I15 Baypren ALX 320-2 100 100 100 100 SFP-121 30 Levamelt 600 30 30 Levamelt 700 30 MgO 4 4 4 4 ZnO 4 4 4 4 Vulkanox BHT 2 2 2 2 Vulkasil C 20 20 Toluene 463 463 463 463 Ethyl methyl ketone 100 100 100 100 Peel strength on flexible 0.19 0.80 0.65 0.63 PVC (N/mm)

TABLE-US-00004 TABLE 3 Bonding by the method of contact bonding without heat activation and with isocyanate crosslinker. (Quantities in parts by weight per 100 parts of polychloroprene (Baypren ALX 320-2 or Baypren ALX 233-1)) C4 I17 I18 I19 I20 I21 I22 I23 I24 I25 Baypren ALX 320-2 100 100 100 100 100 100 100 100 100 Baypren ALX 233-1 100 SP-560 30 15 Escorene 0328 30 Levamelt 400 30 Levamelt 450 30 Levamelt 500 30 Levamelt 600 30 15 30 Levamelt 700 30 Levamelt 800 30 MgO 4 4 4 4 4 4 4 4 4 4 ZnO 4 4 4 4 4 4 4 4 4 4 Vulkanox BHT 2 2 2 2 2 2 2 2 2 2 Vulkasil C 20 20 20 20 20 20 20 20 20 20 Toluene 463 463 463 463 463 463 463 463 463 463 Ethyl methyl ketone 100 100 100 100 100 100 100 100 100 100 Peel strength on 0.28 0.45 0.97 1.60 1.42 1.94 1.50 1.31 0.81 1.72 flexible PVC (N/mm)

[0072] Comparative examples C1-C4 shown in Tables 1.1, 1.2, 2 and 3 represent typical polychloroprene-based formulations according to the prior art. These formulations can be used without problems for the bonding of a multiplicity of materials. As the tables set out above show, however, the formulations are not suitable for the bonding of flexible PVC. The inadequate peel forces arise independently of the mode of processing (heat activation (Tab. 1.1, 1.2), contact method (Tab. 2), isocyanate crosslinking (Tab. 3)). Even a variation in the resin used does not produce any improvement in the peel strength on flexible PVC (Tables 1.1, 1.2, 2 and 3).

[0073] Tables 1.1, 1.2, 2 and 3 show that the use of an ethylene-vinyl acetate copolymer in the adhesive composition brings about a significant improvement in the bond strength on flexible PVC. Where ethylene-vinyl acetate copolymers are used, an improvement is achieved in the adhesive properties on flexible PVC (Tab. 1.1). As can be seen from Table 1.2, the amount of ethylene-vinyl acetate copolymer used can be varied over a wide range. The inventive adhesive composition may be admixed, furthermore, with conventional resins, such as, for example, terpene-phenolic resin (Tab. 1.2, 3) or other auxiliaries such as silica (Tab. 1.1, 2 and 3). The improvement in the bonding outcome is achieved not only in the method with heat activation (Tab. 1.1, 1.2) but also in the contact bonding method (Tab. 2). Likewise possible is the use of the inventive adhesive compositions in combination with isocyanate crosslinkers in a two-component process (Tab. 3). Tab. 3 shows, moreover, that the desirably high peel forces on flexible PVC are independent of the molecular structure of the polychloroprene used. Flexible PVC can be bonded not only with rapidly crystallizing varieties but also with those that crystallize with medium rapidity (Table 3, Example 25). The likewise very good adhesive properties of the formulations of the invention on other substrates such as styrene-butadiene rubber, for example, allow this adhesive to be deployed very universally.