Curable Adhesive Compound and Reactive Adhesive Tapes Based Thereon

Abstract

The invention relates to a thermally curable adhesive compound consisting of the following components: (A) 4.9 to 34.9 wt % (relative to the total amount of the curable adhesive compound) of an epoxide-functionalized (co)polymer having a weight-average molar mass in the range of 5,000 g/mol to 200,000 g/mol, based on more than 30 to 100 wt %, preferably 50 to 100 wt %, (relative to the total amount of the monomers on which the epoxide-functionalized (co)polymer is based) of at least one type of (meth)acrylic (co)monomer (a) functionalized with an epoxy group, (B) 0.1 to 5 wt % (relative to the total amount of the curable adhesive compound) of at least one thermally activatable curing agent for a cationic curing of epoxides, (C) 65 to 95 wt % (relative to the total amount of the curable adhesive compound) of at least one type of matrix polymer as a film-forming agent, (D) optionally 0 to 30 wt % of additional components.

Claims

1. A thermally curable adhesive composition comprising the following components: (A) 4.9% to 34.9% by weight (based on the entirety of the curable adhesive composition) of an epoxy-functionalized (co)polymer having a weight-average molar mass in the range from 5 000 g/mol to 200 000 g/mol, based on more than 30% to 100% by weight, (based on the entirety of the parent monomers of the epoxy-functionalized (co)polymer) of at least one type of (meth)acrylic (co)monomer (a) functionalized with an epoxy group, (B) 0.1% to 5% by weight (based on the entirety of the curable adhesive composition) of at least one thermally activatable curing agent for cationic curing of epoxides, (C) 65% to 95% by weight (based on the entirety of the curable adhesive composition) of at least one type of matrix polymer as film former, (D) optionally 0% to 30% by weight of further constituents.

2. The thermally curable adhesive composition as claimed in claim 1, wherein the weight-average molar mass of the epoxy-functionalized (co)polymer is at least 10 000 g/mol.

3. The thermally curable adhesive composition as claimed in claim 1, wherein the weight-average molar mass of the epoxy-functionalized (co)polymer is at most 150 000 g/mol.

4. The thermally curable adhesive composition as claimed in claim 1, having pressure-sensitive adhesive properties.

5. The thermally curable adhesive composition as claimed in claim 1, wherein cycloaliphatic epoxides are used for one, more than one or all the (meth)acrylic (co)monomers (a) functionalized with an epoxy group.

6. The thermally curable adhesive composition as claimed in claim 5, wherein the cycloaliphatic epoxides are 3,4-epoxycyclohexyl-substituted monomers.

7. The thermally curable adhesive composition as claimed in claim 1, wherein the at least one thermally activatable curing agent for cationic curing of epoxides is a thermally activatable acid former.

8. The thermally curable adhesive composition as claimed in claim 1, wherein the thermally activatable curing agent used for cationic curing of epoxides is one or more agents selected from the following list: pyridinium salts, ammonium salts, sulfonium salts, and lanthanoid triflates.

9. A method of bonding two substrates by means of a thermally curable adhesive composition as claimed in claim 1, comprising the following process steps: a) fixing the first substrate on a holder; b) positioning the second substrate to be bonded by a reactive adhesive tape having at least one layer of curable adhesive composition of claim 1 on the second substrate; c) applying pressure and temperature; d) removing the bonded composite from the holder.

10. A composite obtainable by bonding two substrates by means of a thermally curable adhesive composition as claimed in claim 1 with curing of the adhesive composition.

11. The thermally curable adhesive composition of claim 1, wherein the epoxy-functionalized (co)polymer has a weight-average molar mass in the range from 5 000 g/mol to 200 000 g/mol, based on 50% to 100% by weight, (based on the entirety of the parent monomers of the epoxy-functionalized (co)polymer) of at least one type of (meth)acrylic (co)monomer (a) functionalized with an epoxy group.

12. The thermally curable adhesive composition of claim 2, wherein the weight-average molar mass of the epoxy-functionalized (co)polymer is at least 20 000 g/mol.

13. The thermally curable adhesive composition of claim 3, wherein the weight-average molar mass of the epoxy-functionalized (co)polymer is at most 100 000 g/mol.

14. The thermally curable adhesive composition of claim 6, wherein the cycloaliphatic epoxides are selected from the group consisting of 3,4-epoxycyclohexylmethyl methacrylate, 3,4-epoxycyclohexyl methylacrylate, 3,4-epoxycyclohexyl methacrylate, and 3,4-epoxycyclohexyl acrylate.

15. The thermally curable adhesive composition of claim 8, wherein the thermally activatable curing agent comprises anilinium salts and/or thiolanium salts.

16. The method of claim 9, wherein step c) is by means of a hot press ram.

17. The composite of claim 10, obtained by the method of claim 9.

Description

EXAMPLES

[0163]

TABLE-US-00003 Raw materials used Vazo 52 2,2-azobis(2,4-dimethylvaleronitrile) from DuPont TTA15 3,4-epoxycyclohexylmethyl methacrylate from Tetrachem K-Pure CXC 1614 thermal activator based on a quaternary from King ammonium salt of trifluoromethanesulfonic acid Industries K-Pure CXC 1615 thermal activator based on an amine salt of from King trifluoromethanesulfonic acid industries K-Pure CXC 1612 thermal activator based on a quaternary from King ammonium antimony hexafluoride industries Desmomelt 530 polyurethane from Covestro Uvacure 1500 (3,4-epoxycyclohexane)methyl (3,4-epoxy- from Allnex cyclohexyl)carboxylate Syna Epoxy S28 bis(3,4-epoxycyclohexylmethyl) adipate from Synasia Dynasylan GLYEO 3-glycidyloxypropyltriethoxysilane from Evonik

Production of the Adhesive Compositions and Reactive Adhesive Tape Specimens

Example A

[0164] A pressure-resistant 2 L polymerization reactor of a conventional type for free-radical polymerizations was charged with 100 g of 3,4-epoxycyclohexylmethyl methacrylate and 396 g of methyl ethyl ketone. After passing nitrogen gas through while stirring for 45 minutes, the reactor was heated up to product temperature 70 C. and evacuated to boiling. Subsequently, 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. The reaction is conducted at a constant product temperature of 70 C. under evaporative cooling. After a reaction time of 1 h, 100 g of 3,4-epoxycyclohexylmethyl methacrylate that had been preheated to 70 C. and through which nitrogen had been passed for 45 minutes were added, and 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. After a reaction time of 2 h, 100 g of 3,4-epoxycyclohexylmethyl methacrylate that had been preheated to 70 C. and through which nitrogen had been passed for 45 minutes were added, and 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. After a reaction time of 3 h, 100 g of 3,4-epoxycyclohexylmethyl methacrylate that had been preheated to 70 C. and through which nitrogen had been passed for 45 minutes were added, and 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. The reaction was terminated after 24 h reaction time and cooled to room temperature.

[0165] The molar mass of the resulting polymer was 15 900 g/mol.

[0166] The glass transition temperature of the uncured polymer was 32 C. (first heating ramp) and 72 C. (second heating ramp).

Example B

[0167] A pressure-resistant 2 L polymerization reactor of a conventional type for free-radical polymerizations was charged with 400 g of 3,4-epoxycyclohexylmethyl methacrylate, 420 g of isopropanol and 726 g of methyl ethyl ketone. After passing nitrogen gas through while stirring for 45 minutes, the reactor was heated up to product temperature 65 C. and evacuated to boiling. Subsequently, 4.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 8.0 g of methyl ethyl ketone were added. The reaction is conducted at a constant product temperature of 65 C. under evaporative cooling. After a reaction time of 7 h, 4.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 8.0 g of methyl ethyl ketone were added. The reaction was terminated after 24 h reaction time and cooled to room temperature.

[0168] The molar mass of the resulting polymer was 25 900 g/mol.

[0169] The glass transition temperature of the uncured polymer was 34 C. (first heating ramp) and 68 C. (second heating ramp).

Example C

[0170] A pressure-resistant 2 L polymerization reactor of a conventional type for free-radical polymerizations was charged with 400 g of 3,4-epoxycyclohexylmethyl methacrylate, 420 g of isopropanol and 150 g of methyl ethyl ketone. After passing nitrogen gas through while stirring for 45 minutes, the reactor was heated up to product temperature 65 C. and evacuated to boiling. Subsequently, 1.6 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 30.4 g of isopropanol were added. The reaction is conducted at a constant product temperature of 65 C. under evaporative cooling. After a reaction time of 7 h, 1.6 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 30.4 g of isopropanol were added. After a reaction time of 14 hours, the mixture was diluted with 100 g of methyl ethyl ketone. The reaction was terminated after 24 h reaction time and cooled to room temperature.

[0171] The molar mass of the resulting polymer was 30 600 g/mol.

[0172] The glass transition temperature of the uncured polymer was 38 C. (first heating ramp) and 70 C. (second heating ramp).

[0173] It is apparent from the glass transition temperatures ascertained in the two heating ramps in the three above examples that, even in the absence of the curing agent of the invention, self-crosslinking takes place at very high temperatures and the uncured polymer in each case has a lower glass transition temperature than the (partly) cured polymer.

[0174] For the production of reactive adhesive tape specimens (examples I1-I8 and comparative examples C1-05), all the formulation constituents required (see tables 3 and 4) were dissolved in solvent and any insoluble constituents such as inorganic fillers were suspended with a dispersion disk and coated as a solution or suspension. The solvent content in the solutions was 80% by weight. The solvent used was methyl ethyl ketone. The coating was effected on a siliconized release paper. Coated and dried specimens were dried at 50 C. for 30 min. After drying, the adhesive layer thickness of the coats was 100 m (within the customary error tolerances). After 24 h, the reactive adhesive tape specimens were processed to give test specimens and these were then analyzed after a further 48 h. Details of the test specimens can be found in the respective test methods. The test results are summarized in tables 3 and 4.

[0175] Comparative example C1 shows the achievable bond strength of a nonreactive adhesive tape that forms bond strength merely via softening and solidification. Even though the bond strengths are at a high level, an adhesive tape of this kind does not meet the demands with regard to low squeeze-out propensity.

[0176] Examples I1 to I4 and C2, C3 show that an inventive proportion of curable (co)polymer (A) leads to high bond strengths, but also simultaneously the demands on low squeeze-out propensity are met well (examples I2 and I4) or very well (examples I1 and I3). If too much of the (co)polymer (A) is used, the demand for low squeeze-out propensity is no longer met (comparative examples C2 and C3).

[0177] Comparative examples C4 and C5 illustrate that, when low molecular weight reactive resins according to the prior art are used rather than the curable (co)polymers (A) of the invention, the result is excessively soft adhesive compositions. The demands with regard to low squeeze-out propensity are not met in this way.

[0178] Examples I5 to I8 confirm the advantages of the inventive procedure and additionally show, moreover, that very good resistance to moisture and heat is achieved.

TABLE-US-00004 TABLE 3 Example Example Example Example Example Example Example C1 I1 I2 C2 I3 I4 C3 (Co)polymer Example A 9.70% 29.70% 49.70% 9.70% 29.70% 49.70% (A) Example B Example C Curing agent/ CXC 1614 0.30% 0.30% 0.30% initiator (B) CXC 1615 0.30% 0.30% 0.30% Matrix polymer Desmomelt 530 100.00% 90.00% 70.00% 50.00% 90.00% 70.00% 50.00% (C) Sum total 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% Test B1 2.5 3.6 2.8 2.2 4.1 2.9 2.6 Test B2 2.6 4 2.7 2.0 3.2 3.2 2.5 Test A >1 mm 0 mm 0.9 mm >1 mm 0 mm 0.9 mm >1 mm Test E1 n.d. n.d. n.d. n.d. n.d. n.d. n.d. Test E2 n.d. n.d. n.d. n.d. n.d. n.d. n.d. (n.d.: not determined)

TABLE-US-00005 TABLE 4 Example Example Example Example Example Example C4 C5 I5 I6 I7 I8 (Co)polymer (A) Example A 9.70% Example B 9.90% 9.70% Example C 9.90% Curing agent/ CXC 1614 0.30% 0.30% 0.10% 0.30% 0.10% Initiator (B) CXC 1615 CXC 1612 0.30% Matrix polymer (C) Desmomelt 530 90.00% 80.00% 90.00% 90.00% 87.00% 87.00% Reactive resin (D2) Uvacure 1500 9.70% Synasia S28 19.70% Further Dynasylan GLYEO 3.00% 3.00% constituents (D) Sum total 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% Test B1 2.5 2.6 5.5 4.3 4.4 5.1 Test B2 3.3 3.2 4.4 4.1 4.2 4.4 Test A >1 mm >1 mm 0 mm 0 mm 0 mm 0 mm Test E1 n.d. n.d. 1.8 3.6 3.6 4.1 Test E2 n.d. n.d. 1.8 4.0 2.8 4.4