WO2007073827A1

WO2007073827A1 - Structural adhesive with increased elasticity

Info

Publication number: WO2007073827A1
Application number: PCT/EP2006/011609
Authority: WO
Inventors: Hansjörg Ander; Günter Holl
Original assignee: Lohmann Gmbh & Co. Kg
Priority date: 2005-12-27
Filing date: 2006-12-04
Publication date: 2007-07-05
Also published as: DE102005062441A1; DE102005062441B4

Abstract

The invention relates to a structural adhesive with increased elasticity, consisting of at least 30 wt. % of glycidyl(meth)acrylate and monomers comprising H acid groups, the ratio of glycidyl(meth)acrylate to H acid groups being between 5:1 and 10:1. The invention also relates to a method for producing strip-type structural adhesives and to the use thereof.

Description

Structural adhesive with increased elasticity

As structural adhesives adhesives are referred to, which are used in a joint, which thereby obtains a significant share in ensuring the stability and / or function of the component. In this context, constructive bonding as well as construction or assembly adhesives or structural adhesives are also referred to.

Common structural adhesives are based on epoxy resins and often contain aromatic epoxies. In these adhesives, which are generally present in the form of a one- or two-component system, a hardener is added to the starting material which is liquid after addition of the epoxide component, which hardening agent solidifies the adhesive.

Although the joining compounds produced using conventional epoxy-based structural adhesives have high strength, they have only low stretchability and elasticity.

It was therefore an object of the present invention to provide a structural adhesive which has high strength with high ductility and elasticity.

This object can be achieved by the preparation of a glycidyl (meth) acrylate-containing adhesive, as described in the published patent application EP 1 316 597 A2. These adhesives are going through free radical polymerization to give polymers having a glass transition temperature of -60 to +50 ⁰ C and to 5 to 60 wt .-% of glycidyl (meth) acrylate, all conventional and commercially available monomers with CC double bonds suitable for the preparation of these adhesives should be. However, monomers with acid groups should at most be present in the polymer in small amounts, preferably in an amount of less than 1% by weight.

According to EP 1 316 597 A2, free-radical polymerization can be either a solvent or an emulsion polymerization or radiation-induced polymerization. Curing of the polymers can be carried out by crosslinking with customary hardeners (acids and amines). However, the described hardeners in combination with the described epoxy acrylates also give room-temperature-crosslinking systems which can not be storage-stable.

The object of the present invention was therefore not only to provide a structural adhesive which has high strength with high ductility and elasticity. The structural adhesive should simultaneously have excellent storage stability.

This object is achieved by providing an acrylate adhesive having epoxy and H-acid groups in the polymer backbone which can be prepared by UV polymerization. The structural adhesives of the invention are based on a combination of glycidyl (meth) acrylate monomers and H-acidic monomers. In this case, the degree of crosslinking of the glycidyl (meth) acrylate-containing polymers can be adjusted by varying the ratio of the monomers having H-acidic groups to glycidyl (meth) acrylate such that the resulting polymer has a desired strength. Thus, the strength of the polymer (cohesion) can be determined to be typically pressure-sensitive (tensile shear strength of 200 N / square inch (= 31 N / cm ² )) over semi-structural (tensile shear strength of about 2,000 N / square inch (= 310 N / cm) ² )) to structural joints (tensile strengths of up to 5,000 N / square inch (= 775 N / cm ² )).

In the structural adhesives of the present invention, the ratio of glycidyl (meth) acrylate to H-acidic groups is preferably 5: 1 to 10: 1, with a ratio of 10: 1 being particularly preferred.

The elasticity of the adhesive can be adjusted by the appropriate choice of monomer composition in the mixture which serves as the starting preparation for the polymerization to the adhesive. In this context, there is also talk of internal flexibilisation. Preferred monomers which may be present in the adhesives according to the invention in addition to the glycidyl (meth) acrylate and the monomers having H-acidic groups are, for example, isodecyl methacrylate and n-hexyl methacrylate. The final strength or crosslinking density of the structural adhesive according to the invention is adjusted by the ratio of epoxide groups to H-acidic groups. H-acidic groups are OH, NH and SH groups.

As H-acidic monomers, i. H. as monomers having H-acidic groups, aminoacrylates, aminomethacrylates, hydroxyacrylates, hydroxymethacrylates or carboxyl group-containing monomers, for example acrylic acid or methacrylic acid, can be used. Particular preference is given to hydroxyacrylates and hydroxymethacrylates, since particularly storable adhesives are obtained when they are used. As a result, in particular the storage stability of the adhesives can be improved, in particular if they are in film form or strip form.

The structural adhesives according to the invention make it possible to dispense with the use of known flexibilizers (rubbers), since the later structural composite is internally flexibilized by the use of low Tg monomers.

The structural adhesives according to the invention can also be free of aromatics by the use of glycidyl (meth) acrylate.

The particularly preferred adhesives of the present invention include

From 30 to 50% by weight of isodecyl methacrylate

25 to 40% by weight of n-hexyl methacrylate

10 to 30 wt. -5s 2, 3-epoxypropyl methacrylate

1 to 3% by weight of 2-hydroxyethyl acrylate In addition, the adhesives of the invention may comprise up to 1% by weight of one or more photoinitiators.

Particularly preferred is the combination of a photoinitiator which is selected from the group of α-hydroxy ketones, in particular 1-hydroxy-cyclohexyl-phenyl ketone (Irgacure® 184), with a photoinitiator from the group of bis-acylphosphines, preferably phenyl-bis - (2,4,6) -trimethylbenzoyl) phosphine oxide (Irgacure® 819). In the preferred combination of photoinitiators, the α-hydroxy ketone is present in an amount of 0.01 to 0.1 wt% -5s and the bis-acylphosphine in an amount of 0.5 to 0.99 wt% in the adhesive ,

In addition, catalysts for epoxide crosslinking can be added to the starting mixture. These catalysts or catalyst systems, which are also referred to as hardeners, are substances which catalytically trigger the curing of epoxy resins or epoxide-containing polymers or polymer mixtures. Basically, all common catalysts for epoxy crosslinking are suitable. For reasons of stability, however, the systems crosslinked at room temperature (eg amines) are negligible. Preference is given to catalyst systems comprising the reaction at temperatures of 80 ⁰ C or higher, particularly preferably at temperatures of 100 ⁰ C or more start (eg. B: anhydrides, ammonium salts of organic / inorganic acids, dicyandiamide cocatalyzed with urea derivatives or neutralized acids). By admixing suitable catalysts or catalyst systems for the polymerizable polymer syrup, the activation temperature and activation time for the conversion to the structural adhesive bond can be determined.

The adhesives according to the invention give a migration-stable one-component system with which, for example, carrier films can be coated.

The adhesives of the invention are suitable for the production of so-called thick film systems. That is, with these structural adhesives, adhesive tapes whose adhesive layer may have a thickness of 20 μm or more, preferably 50 μm or more and even a thickness of more than 500 μm, can be produced with these structural adhesives. Thus, the thickness of the adhesive layer may be up to 4,000 μm, with thicknesses of up to 1,500 μm being preferred and thicknesses of up to 1,000 μm being particularly preferred.

Such thick adhesive films have advantages in almost all areas of bonding compared to the known thin adhesive films, especially in the areas where a groove contributes to a significant increase in the strength of the adhesive bond. This is usually the case with Stoßverklebungen in the 90 ° angle. In the structural adhesive according to the invention, the flutes form through the melt, which is formed when the adhesive film is heated to about 160 ^° C. to 180 ^° C., and which begins to "creep" on the substrates due to the changed surface tension in both the XY direction and in the Z direction and forms it a corresponding groove in the Verklbung.

Even with classic overlap bonding, in which a technical zero gap can not be realized, the thick-film system is advantageous because thicker adhesive layers are able to ensure a significantly better gap bridging. With the thick-film system according to the invention, it is therefore also possible to bond materials whose composite has a large adhesive gap due to high manufacturing tolerances.

Further advantages result from the changed mechanical characteristics when using thicker adhesive gaps, which come into play particularly in vibration damping.

The tape form structural adhesives of the present invention can be prepared by mixing the starting compounds into a polymerizable syrup which, when applied to a substrate, is cured by exposure to ultraviolet light (UV light).

For the preparation of the preferred structural adhesives

30 to 50% by weight of zsodecyl methacrylate, 25 to 40% by weight of n-hexyl methacrylate, 10 to 30% by weight of 2, 3-epoxypropyl methacrylate, and 1 to 3% by weight of 2-hydroxyethyl acrylate

into a polymerizable syrup to which the photoinitiator is added. In the production of the structural adhesives according to the invention, it is particularly preferable to use a combination of two photoinitiators. Initially, only the photoinitiator which is to be used in lesser amounts is added to the polymerizable syrup. This syrup is exposed to a first exposure to UV light. This "pre-crosslinking" leads to a few, but very high-molecular-weight polymer chains, then the further photoinitiator is added to the precrosslinked syrup, the syrup is applied to a sheet-like substrate and subjected to curing by irradiation with UV light, preferably in a nitrogen atmosphere.

Particularly preferred is the combination of a photoinitiator which is selected from the group of α-hydroxy ketones, in particular 1-hydroxy-cycloh.exyl-phenyl ketone (Irgacure® 184), with a photoinitiator from the group of bis-acylphosphines, preferably phenyl bis (2, 4, 6) -trimethylbenzoyl) -phosphine oxide (Irgacure® 819). In the preferred combination of photoinitiators, the α-hydroxy ketone is present in an amount of from 0.01 to 0.1 weight percent and the bis-acylphosphine in an amount of from 0.5 to 0.99 weight percent in the adhesive ,

Pre-crosslinking takes place in the wavelength range of UV-A to UV-B radiation, the dose used being highly dependent on the reactivity of the monomer composition. Preferably, the pre-crosslinking process is controlled by viscosity-torque correlation, with viscosity values typically being 5 to 10 Pas. In addition, catalysts for epoxide crosslinking can be added to the starting mixture. For this reason, all common catalysts for epoxy crosslinking are suitable. For reasons of stability, however, the systems crosslinked at room temperature (eg amines) are negligible. Preference is given to catalyst systems comprising the reaction at temperatures of 80 ⁰ C or higher, particularly preferably at temperatures of 100 ⁰ C or more start (eg. B: anhydrides, ammonium salts of organic / inorganic acids, dicyandiamide cocatalyzed with urea derivatives or neutralized acids).

The significant increase in the viscosity of the syrup due to the pre-crosslinking makes it possible to apply the precrosslinked polymer syrup with a thickness of up to 4,000 μm to a substrate. The addition of the further photoinitiator is necessary so that the mass can be reacted quickly and with low residual monomer content.

Since all the functional groups necessary for the crosslinking are incorporated into the polymer backbone, a very homogeneous product is obtained, which is not subject to any change due to a migration of its or at least one of its constituents.

The present invention thus also encompasses ribbon-shaped structural adhesives which comprise the polymers according to the invention or the polymers prepared by the process according to the invention, in particular ribbon-shaped structural adhesives the coating of which has a thickness of 20 μm or more, preferably 50 μm or more, and more preferably 500 μm or more. Particularly preferred tape-shaped structural adhesives have a coating with a thickness of up to 4,000 μm, preferably with a thickness of up to 1,500 μm.

The present invention also provides peelable carrier films which are coated with a polymer according to the invention.

The invention further comprises methods for producing a structural joining connection between molded parts, comprising coating a molded article with a polymer or structural adhesive according to the invention, then adhering the joining parts, and subsequently curing the polymer or structural adhesive by heat treatment, which can be carried out under normal atmosphere (atmospheric oxygen) without difficulty. or in a nitrogen atmosphere.

Thus, molded parts joined by the structural adhesive according to the invention are also included in the invention, which have been obtained by the method according to the invention for producing a structural joining connection between molded parts.

In the following, the invention will be illustrated by way of example by means of preferred compositions and the illustration of the preferred preparation process, which embodiments are not to be construed as limiting the spirit and essence of the invention in any way. Example 1: Composition IA

Ingredient% by weight

2-hydroxyethyl acrylate 2.83

2, 3-epoxypropylmethacrylate 28.29 ϊsodecylmethacrylate 34.88 n-hexylmethacrylate 28.29

Irgacure® 184 0.05

Dicyandiamide 2.83

N, N "-4- (methyl-m-phenylene-2,83 bis- (N'-dimethyl-urea)

Example 2: Composition IB

Ingredient% by weight

Composition IA 99.3 Irgacure® 819 0.7

Example 3: Composition 2A

Ingredient% by weight

2-hydroxyethyl acrylate 3.00

2, 3-epoxypropyl methacrylate 30.00

Isodecyl methacrylate 36.95 n-hexyl methacrylate 30.00

Irgacure® 184 0.05 Example 4: Composition 2B

Ingredient% by weight

Composition 2A 96.3

Trifluoromethanesulfonic acid-3,0 diethylamine salt

Irgacure® 819 0.7

Example 5: Composition 3A

Ingredient% by weight -%

2-hydroxyethyl acrylate 1.50

2, 3-epoxypropyl methacrylate 15.00

Isodecyl methacrylate 45.00 n-hexyl methacrylate 38.40

Irgacure® 184 0.10

Example 6: Composition 3B

Ingredient% by weight -%

Composition 3A 97.3

Trifluoromethanesulfonate / n- 2.0

Butanol (3: 1)

Irgacure® 819 0.7 Example 7: Production of the Thick Film System:

For the preparation of structural adhesives, first, polymerizable syrups according to the above compositions (IA, 2A and 3A) were prepared. After precrosslinking by irradiation with UV light, a further photoinitiator (Irgacure® 819) and optionally the catalyst for the epoxide crosslinking were added to the precrosslinked syrups, so that the compositions IB, 2B or 3B were obtained.

After a 0.6 mm thick layer of the respective precrosslinked and with the further photoinitiator and optionally catalyst for the epoxy crosslinking polymer syrup on a PET carrier film, these layers were cured by irradiation with ultraviolet light in a nitrogen atmosphere. Slightly adhesive films were obtained.

Example 8: Tensile shear strengths

In order to determine the tensile shear strengths of joint joints made with an acrylate thick film system according to any of Examples 1-6, two sheets of a sanded substrate were bonded together on a 321.5 mm ² area. The bond was for 30 min. at 160 ⁰ C and a load of 1,500 g (Ex 1 and 2) or with 300 g (Ex 3 to 6) cured. The tensile shear strengths were about 4,800 N / square inch for joint compounds with composition IA (Example 1) or composition IB (Example 2), approximately 5,000 N / Square inch for joint compounds with composition 2A (Example 3) or composition 2B (Example 4); and about 4,200 N / Square inch for joint joints with composition 3A (Ex 5) or Compound 3B (Ex 6).

Claims

claims

A polymer obtainable by radical polymerization which consists of at least 30% by weight of glycidyl (meth) acrylate and comprises monomers having H-acidic groups, the ratio of

Glycidyl (meth) acrylate to H-acid groups at 5: 1 to 10: 1.

2. Polymer according to claim 1, characterized in that the monomers are selected with H-acidic groups from the group, the amino acrylates, aminomethacrylates,

Hydroxy (meth) acrylates and carboxyl-containing monomers such as acrylic acid and methacrylic acid.

3. Polymer according to claim 1 or 2, comprising 30 to 50% by weight of isodecyl methacrylate,

25 to 40% by weight of n-hexyl methacrylate, 10 to 30% by weight of Ss 2, 3-epoxypropyl methacrylate and 1 to 3% by weight of 2-hydroxyethyl acrylate.

4. A process for producing a structural adhesive in tape form, characterized by

Preparing a polymerizable syrup comprising at least 30% by weight of glycidyl (meth) acrylate, monomers having H-acidic groups, wherein the ratio of

Glycidyl (meth) acrylate to H-acidic groups is 5: 1 to 10: 1, and 0.01 to 0.1 wt. -5s of a first photoinitiator;

- Pre-crosslinking of the polymerizable syrup by irradiation with UV light; Adding a second photoinitiator to the pre-crosslinked syrup in an amount of 0.5 to 0.99 wt. -9 s;

- coating a carrier foil with the syrup; and

- Crosslinking of the polymer layer by irradiation with UV light.

5. The method according to claim 4, characterized in that the monomers are selected with H-acidic groups from the group, the Αminoacrylate, aminomethacrylates,

6. The method according to claim 4 or 5, characterized in that the polymerizable syrup comprises a monomer mixture

30 to 50% by weight of isodecyl methacrylate

From 25 to 40% by weight of n-hexyl methacrylate

10 to 30% GΘW.-9 & 2, 3-epoxypropyl methacrylate

1 to 3 parts by weight 9 & 2-hydroxyethyl acrylate.

7. The method according to any one of claims 4 to 6, characterized in that the first photoinitiator is selected from the group of α-hydroxy ketones, with 1-hydroxycyclohexyl-phenyl ketone is preferred.

8. The method according to any one of claims 4 to 7, characterized in that the second photoinitiator is selected from the group of bis-acylphosphines, with phenyl bis (2,4,6) -trimethylbenzoyl) phosphine oxide is preferred.

9. The method according to any one of claims 4 to 8, characterized in that the polymerizable syrup comprises a catalyst-hardener system or the polymerizable syrup after pre-crosslinking a catalyst-hardener system is added.

10. The method according to claim 9, characterized in that the catalyst-hardener system is selected from the group consisting of dicyandiamide, aromatic urea derivatives, preferably N, N ¹ '-4- (methyl-m-phenylene) -bis (N ¹ , N ¹ - dimethyl) urea, and neutralized acids, preferably the diethylamine salt of trifluoromethanesulfonic acid or a mixture of trifluoromethanesulfonate and n-butanol (3: 1)

11. The method according to any one of claims 4 to 10, characterized in that the carrier film is coated with the syrup in a thickness of 20 to 4000 .mu.m, preferably from 50 to 1500 .mu.m and more preferably from 500 mm to 1000 .mu.m.

12. The method according to any one of claims 4 to 11, characterized in that the carrier film is removable from the polymer.

13. A tape-shaped structural adhesive comprising a polymer according to any one of claims 1 to 3 or prepared by a method according to any one of claims 4 to 12.

A belt-shaped structural adhesive according to claim 13, characterized in that the coating has a thickness of 20 μm or more, preferably 50 μm or more and more preferably 500 μm or more.

15. A tape-shaped structural adhesive according to claim 13 or 14, characterized in that the coating has a thickness of up to 4,000 μm, preferably a thickness of up to 1,500 μm.

16. Peelable carrier film coated with a polymer according to one of claims 1 to 3.

17. A method for producing a structural joining connection between moldings, comprising the

Coating of a molding with a polymer according to any one of claims 1 to 3 or a structural adhesive according to any one of claims 13 to 15,

- Bonding of the parts to be joined, and

- Hardening of the polymer by heat treatment.

18. The method according to claim 17, characterized in that the curing takes place in a nitrogen atmosphere.

19. Structural adhesive bonded moldings obtainable by a process according to any one of claims 17 or 18.