Thermally activatable latently reactive adhesive film

Abstract

The invention relates to a thermally activatable reactive adhesive film comprising a carrier film made of thermoplastic polyurethane, which is coated on at least one side with a latently reactive, thermally activatable adhesive compound.

Claims

1. A thermoactivatable reactive adhesive film, comprising a backing foil of thermoplastic polyurethane which is coated on at least one side with a latent-reactive, thermoactivatable adhesive compound, wherein the adhesive compound comprises a polyurethane and a reactive resin comprising a thermoactivatable isocyanate, and wherein a push-out force of the thermoactivatable reactive adhesive film is from 135 to 300 N/2.5 cm.sup.2 when an adhesive bonding operation happened at a pressing temperature of 120° C.

2. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the softening temperature of the backing foil of thermoplastic polyurethane is greater than 120° C.

3. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the backing foil of thermoplastic polyurethane includes polyetherpolyurethane.

4. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the thermoactivatable isocyanate is an isocyanate based on isophorone diisocyanate or toluene diisocyanate.

5. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the polyurethane is based on polyesterpolyurethane.

6. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the total thickness of the thermoactivable reactive film is 40 to 400 μm.

7. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the ratio of a thickness of the backing foil of thermoplastic polyurethane to a thickness) of the adhesive compound is greater than 0.3.

8. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the softening temperature of the backing foil of thermoplastic polyurethane is greater than 150° C.

9. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein a tensile shear strength of the thermoactivatable reactive adhesive film is from 8.5 to 10 MPa.

10. The thermoactivatable reactive adhesive film as claimed in claim 7, wherein the ratio of the thickness of the backing foil of thermoplastic polyurethane to the thickness of the adhesive compound is approximately 1.

11. The thermoactivatable reactive adhesive film as claimed in claim 7, wherein a tensile shear strength of the thermoactivatable reactive adhesive film is from 8.5 to 10 MPa.

12. The thermoactivatable reactive adhesive film as claimed in claim 1, wherein the polyurethane comprises: a semicrystalline polyesterpolyurethane.

13. The thermoactivatable reactive adhesive film as claimed in claim 12, wherein the thermoactivatable isocyanate is an isocyanate based on isophorone diisocyanate or toluene diisocyanate.

14. A thermoactivatable reactive adhesive film, comprising a backing foil of thermoplastic polyurethane which is coated on at least one side with a latent-reactive, thermoactivatable adhesive compound, wherein the adhesive compound comprises a polyurethane and a reactive resin comprising a thermoactivatable isocyanate, and wherein a push-out force of the thermoactivatable reactive adhesive film is from 500 to 620 N/2.5 cm.sup.2 when an adhesive bonding operation happened at a pressing temperature of 200° C.

15. A thermoactivatable reactive adhesive film, comprising a backing foil of thermoplastic polyurethane which is coated on at least one side with a latent-reactive, thermoactivatable adhesive compound, wherein the adhesive compound comprises a polyurethane and a reactive resin comprising a thermoactivatable isocyanate, wherein a shear adhesive failure temperature (SAFT) of the thermoactivatable reactive adhesive film is from 160° C. to 180° C.

Description

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

(1) Thermoactivatable Reactive Adhesive Compounds

(2) Thermoactivatable reactive adhesive compounds are familiar to the skilled person. They are, essentially, thermoplastic polymers such as, for example, polyesters, copolyesters, polyolefins, polyamides or polyurethanes to which reactive resins have been added or which themselves comprise reactive components. Reactive resins come from the group, for example, of the epoxy resins, melamine resins, phenolic resins, or the polyisocyanates. Included among thermoactivatable reactive adhesive compounds are those based on epoxy resin, consisting substantially of liquid and solid epoxy resins, impact modifiers, and latent-reactive crosslinking systems such as dicyandiamide, for example. Further thermoactivatable reactive adhesive compounds are those based on cyanoacrylate, which crosslink by the influence of moisture and are described for example in WO 2013/174430.

(3) The adhesive compounds of the invention are based preferably on polyurethane, more preferably on polyesterpolyurethane. The reactive resin is preferably a polyisocyanate, more preferably a polyisocyanate based on isophorone diisocyanate (IPDI) or toluene diisocyanate (TDI).

(4) On thermal activation, the thermoplastic polymer on the one hand is “activated”, and so it softens to the point of the melt. On the other hand, though, the reactive resin is activated at the same or a higher temperature. This means that only at or above this activation temperature do the functional groups of the reactive resin react with the base polymers, and the adhesive compound cures. At lower temperatures, the intention is that the reactive resins shall not react, so that the reactive adhesive film can be kept for months. A variety of mechanisms are possible which initiate the curing at the activation temperature: for example, the reactive resin may be present in solid form and may melt only at the activation temperature and hence be made available. Another pathway is the deactivation of the reactive resins through surface deactivation. This deactivation is negated at the activation temperature (e.g., at or above the glass transition temperature) and curing commences. A further possibility is that of chemical blocking of the reactive groups. At a defined temperature, the blocking is reversible and curing commences. Another method is that of the insolubility of the reactive resin in the (semi)crystalline polymer. At or above the decrystallization temperature, solubility comes in and the curing commences.

(5) In the context of this invention, preference is given to surface-deactivated polyisocyanate and to Isocyanates which become active at the decrystallization temperature.

(6) Backing Foils

(7) In the case of the carrier foils it is possible to employ all thermoplastic polymers that are suitable and known to the skilled person, such as, for example, polyesters, polyolefins, polyamides, polyacrylates or polyurethanes. Preference is given to using a thermoplastic polyurethane foil, more preferably a polyurethane foil composed of polyetherpolyurethane.

(8) The melting point or melting range of the carrier foil is selected such that it lies at or above the activation temperature of the reactive adhesive compound, or the bonding temperature. It is possible accordingly to select whether, during the bonding procedure, the carrier foil remains solid or softens or melts. Within these possibilities, the skilled person is able to optimize the mechanical properties before and after bonding. The softening range of the carrier foil of the invention is preferably above 120° C., more preferably above 150° C.

(9) The thickness of the foil, together with the thicknesses of the adhesive layers, is selected such that the total thickness of the adhesive film is from 40 to 400 μm. Here, the skilled person is able to select the distribution of the thicknesses, over the carrier foil and the adhesive layer or layers, in such a way as to optimize the mechanical properties before and after bonding, and the bleeding.

(10) Production Methods

(11) The adhesive film is produced by single-sided or double-sided coating of the carrier foil with the reactive adhesive compound. The reactive adhesive compound may take the form of a 100% system, i.e., solvent-free, or a solvent-containing adhesive compound or dispersion-based adhesive compound. The adhesive compound is preferably in the form of a dispersion-based adhesive compound, and is mixed from a polyurethane dispersion and a dispersion of the deactivated isocyanate. The dispersion-based adhesive compound is coated onto the liner by means of a suitable coating method, and dried. This sheetlike adhesive compound is then laminated onto one side of the carrier foil to produce a solid laminate. A second sheetlike adhesive compound is laminated onto the second side of the carrier foil, and the second liner is removed. This gives an adhesive film consisting of a central carrier foil and two layers of reactive adhesive compound that are lined at least on one side by a liner.

(12) Adhesive Bonding Operation

(13) The materials to be bonded depend on the specific use. Common materials here are plastics, metals, glass, and textiles. Examples would include the bonding of substrates of polycarbonate sheets to one another and the bonding of polycarbonate sheet to aluminum plate. Applications are located, for example, in the electronics industry, in component construction in the automobile industry, and in textile lamination in the context of industrial textiles.

(14) The adhesive bonding operation here is accomplished generally in these steps: 1. Fixing of the adhesive film on a substrate. This is done purely mechanically or else by prelamination—that is, heating of the adhesive film and/or of the substrate to a temperature at which the layer of adhesive compound facing the substrate melts but is not yet chemically activated. As a result of the melting, the adhesive film is able to wet the first substrate. After cooling, the first substrate is provisionally bonded, but the film is not yet cured. 2. Removal of the liner still present. 3. Placement of the second substrate on the open side of the adhesive film. 4. Application of pressure and temperature to the assembly for a specified time. This is accompanied by thermal activation of all the layers. 5. Optionally, cooling of the assembly.
Experimental Section:
Materials

(15) TABLE-US-00001 Material Supplier Description Dispercoll U Covestro AG Aqueous polyurethane dispersion of 56 semicrystalline polyesterpolyurethane. The polyurethane has a melting point of around 60° C. Dispercoll U Covestro AG Aqueous polyurethane dispersion of XP 2702 semicrystalline polyesterpolyurethane for crosslinking with IPDI trimer. The polyurethane has a melting point of around 60° C. Dispercoll BL Covestro AG Aqueous dispersion of a reactive XP 2514 isocyanate based on TDI dimer. Aqualink D-HT Aquaspersions Aqueous dispersion of a surface- Ltd. deactivated IPDI trimer. Activation starts from around 70° C. Borchigel A Borchers Thickener based on an anionic acrylic LA GmbH polymer Platilon U073, Covestro AG Carrier foil: polyurethane foil based Thickness on polyetherpolyurethane, softening 50 μm and point 160-200° C. 100 μm

EXAMPLES

(16) Reactive Adhesive Compound 1:

(17) 100 parts of Dispercoll U XP 2702, 20 parts of Aqualink D-HT, and 1.3 parts of Borchigel A LA are mixed by stirring.

(18) Reactive Adhesive Compound 2:

(19) 100 parts of Dispercoll U 56, 13 parts of Dispercoll BL XP 2514, and 0.5 part of Borchigel A LA are mixed by stirring.

Inventive Example 1

(20) A liner (siliconized glassine paper) is knife-coated with reactive adhesive compound 1. It is subsequently dried at 50° C. for 10 minutes. The drying temperature must not exceed 50° C., so as not to cause premature thermal activation. The application rate is set so that the layer thickness after drying is 50 μm. This film of adhesive compound is applied by lamination at 60° C. to the polyurethane foil which is 100 μm thick. The reverse face of the polyurethane foil is likewise laminated with a second 50 μm film of adhesive compound 1, and a liner is removed. This gives a thermoactivatable reactive adhesive film with a thickness of 200 μm.

Inventive Example 2

(21) A liner (siliconized glassine paper) is knife-coated with reactive adhesive compound 1. It is subsequently dried at 50° C. for 10 minutes. The drying temperature must not exceed 50° C., so as not to cause premature thermal activation. The application rate is set so that the layer thickness after drying is 25 μm. This film of adhesive compound is applied by lamination at 60° C. to the polyurethane foil which is 50 μm thick. The reverse face of the polyurethane foil is likewise laminated with a second 25 μm film of adhesive compound 1, and one of the two liners then present is removed. This gives a thermoactivatable reactive adhesive film with a thickness of 100 μm.

Inventive Example 3

(22) A liner (siliconized glassine paper) is knife-coated with reactive adhesive compound 2. It is subsequently dried at 50° C. for 10 minutes. The drying temperature must not exceed 50° C., so as not to cause premature thermal activation. The application rate is set so that the layer thickness after drying is 25 μm. This film of adhesive compound is applied by lamination at 60° C. to the polyurethane foil which is 50 μm thick. The reverse face of the polyurethane foil is likewise laminated with a second 25 μm film of adhesive compound 2, and one of the two liners then present is removed. This gives a thermoactivatable reactive adhesive film with a thickness of 100 μm.

Comparative Example 1

(23) A liner (siliconized glassine paper) is knife-coated with reactive adhesive compound 1. It is subsequently dried at 50° C. for 10 minutes. The drying temperature must not exceed 50° C., so as not to cause premature thermal activation. The application rate is set so that the layer thickness after drying is 50 μm. Four of these layers are applied to one another by lamination at 60° C. This produces a thickness of 200 μm of a thermoactivatable reactive adhesive film without carrier foil.

Comparative Example 2

(24) A liner (siliconized glassine paper) is knife-coated with reactive adhesive compound 2. It is subsequently dried at 50° C. for 10 minutes. The drying temperature must not exceed 50° C., so as not to cause premature thermal activation. The application rate is set so that the layer thickness after drying is 50 μm. Two of these layers are applied to one another by lamination at 60° C. This produces a thickness of 100 μm of a thermoactivatable reactive adhesive film without carrier foil.

(25) Measurement Methods:

(26) Tensile Shear Strength

(27) Sample Preparation

(28) The adhesive film (with the liner removed) is fixed between two polycarbonate sheets (PC, width 2.5 cm, length 7 cm, thickness 0.3 cm) overlappingly and flush to the edges, with an area of 312.5 mm.sup.2. The adhesive bonding operation takes place in a hot press at 120° C. and a pressure of 2.5 bar for 5 minutes. The test specimens are subsequently cooled to room temperature under pressure and are stored for 24 hours in a conditioned atmosphere.

(29) Testing

(30) The tensile shear test takes place on a Zwick testing machine between two clamping jaws, with a tensioning velocity of 2 mm/min. The maximum point on the force-displacement curve is the tensile shear strength, and is reported in MPa (=N/mm.sup.2). The average from 5 test specimens is taken.

(31) SAFT Test

(32) Sample Preparation

(33) The adhesive film (with the liner removed) is fixed between two polyester foils (PET, width 2.5 cm, length 7 cm, thickness 0.1 mm) overlappingly and flush to the edges, with an area of 312.5 mm.sup.2. The adhesive bonding operation takes place in a hot press at 120° C. and a pressure of 2.5 bar for 5 minutes. The test specimens are subsequently cooled to room temperature under pressure and are stored for 24 hours in a conditioned atmosphere.

(34) Testing

(35) The test specimens are suspended vertically in a forced-air drying cabinet and loaded with a weight of 10N in each case. The starting temperature is 50° C. Every 30 minutes, a check is made of whether the samples are holding, and the temperature is raised by 10 kelvins. The test is ended at a maximum of 200° C. The SAFT is then the temperature at which all three test specimens have still held.

(36) Push-Out Test

(37) Sample Preparation

(38) The adhesive film is punched out with a circular punch to a diameter of 18 mm.

(39) The first substrate consists of a sheet of polycarbonate or aluminum (width 2.5 cm, length 7 cm, thickness 0.3 cm) which has been provided centrally with a hole of diameter 9 mm. The circular adhesive film is placed on this substrate centrally with respect to the hole. The second substrate consists of a circular sheet of polycarbonate or aluminum in the same size as the adhesive film (diameter 18 mm). The operation of bonding the test specimen takes place in a hot press at a pressure of 2.5 bar for 5 minutes. The test specimens are subsequently cooled to room temperature under pressure and are stored for 24 hours in a conditioned atmosphere.

(40) Two different pushing temperatures were selected:

(41) 120° C. pushing temperature: Polycarbonate is bonded to polycarbonate.

(42) 200° C. pushing temperature: Anodized aluminum is bonded to anodized aluminum.

(43) Testing

(44) The test specimens are placed on a mandrel of diameter 8 mm, so that the mandrel is able to push the second, circular substrate away from the first substrate. The machine approaches with a fitting counter-pushing tool at a testing velocity of 100 mm/min and pushes the mandrel through the sample against the circular substrate. The test ends at the maximum force of the force-displacement curve. The push-out value is this maximum force and is indicated in N/2.5 cm.sup.2. The average from 3 measurements is reported.

(45) Table 1: Test Values for the Inventive and Comparative Examples

(46) Layer Thickness Ratio

(47) Layer thickness ratio is intended here to mean the ratio of the thickness of the carrier foil to the sum of the thicknesses of the reactive adhesive layers, i.e.:

(48) Layer thickness ratio=thickness of carrier foil/sum of the thicknesses of reactive adhesive layers and ought to be greater than 0.3.

(49) TABLE-US-00002 Tensile Push-out Push-out shear force after force after Bleed Layer Thickness strength SAFT 120° C. 200° C. test thickness [μm] [MPa] ° C. [N/2.5 cm.sup.2] [N/2.5 cm.sup.2] [%] ratio Inventive Reactive 200 10 180 300 620 50 1.0 example 1 adhesive compound 1 with backing foil Inventive Reactive 100 9.6 170 250 600 50 1.0 example 2 adhesive compund 1 with backing foil Inventive Reactive 100 8.5 160 135 500 50 1.0 example 3 adhesive compound 2 with backing foil Comparative Reactive 200 10 >200 180 400 124 0 example 1 adhesive compound 1 without backing foil Comparative Reactive 100 8.7 >200 135 350 110 0 example 2 adhesive compound 2 without backing foil

(50) The test values in table 1 show that the adhesive films of the invention (inventive examples 1 to 3) for the same thickness achieve the same tensile shear strengths as the adhesive films without carriers (comparative examples 1 and 2). This is the case both for adhesive compound 1 and for adhesive compound 2.

(51) Conversely, the adhesive films according to the invention (examples 1 to 3) exhibit a lower bleeding behavior than the adhesive films without backing (comparative examples 1 and 2).

(52) The SAFT value of the adhesive films according to the invention is somewhat lower than for the comparative examples. This is presumably because of the softening of the backing foil. The service temperatures of such bonds, however, are generally below 150° C. even at the peak. Within this range, there would be no difference in the examples in terms of the temperature stability of the bonds.

(53) At pushing temperatures both of 120° C. and of 200° C., the push-out forces are at a level the same as or higher than in the case of the comparative examples.