EP4612205A1

EP4612205A1 - Single-component structural adhesive

Info

Publication number: EP4612205A1
Application number: EP23801908.7A
Authority: EP
Inventors: Ling Jie TONG; Jiaxing SUN
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2022-11-04
Filing date: 2023-11-01
Publication date: 2025-09-10
Also published as: CN118027865A; WO2024095186A1

Abstract

The present invention provides a single-component structural adhesive, the single-component structural adhesive including: 50 weight percent to 60 weight percent of an epoxy resin having an epoxy equivalent weight of less than 190 grams per equivalent; 38 weight percent to 48 weight percent of a thiol having four or more functionalities; and 1 weight percent to 12 weight percent a latent catalyst, the total weight of the single-component structural adhesive being 100 weight percent. According to the single- component structural adhesive of a technical solution of the present invention, it is possible to achieve fast curing at a lower temperature, and a cured product thereof has a high glass-transition temperature (Tg) and a high bonding strength.

Description

SINGLE-COMPONENT STRUCTURAL ADHESIVE

Technical Field

The present invention relates to the technical field of structural adhesives; in particular, the present invention provides a single-component structural adhesive which is capable of achieving fast curing at a lower temperature and a cured product of which has a high glass-transition temperature (Tg) and a high bonding strength.

Background Art

Commonly used epoxy adhesives include single-component (IK) adhesives and two-component (2K) adhesives. Compared to two-component (2K) adhesives, single-component (IK) adhesives are more convenient to use, and so are widely used in the assembly of mobile hand-held devices, automotive industry devices, electronic device assemblies, and the like. In addition, single -component (IK) adhesives typically have advantages in industrial environments relative to two-component (2K) adhesives, because singlecomponent (IK) adhesives typically exhibit better strength properties and corrosion resistance properties, and better tolerance to surface defects and materials (e g., manufacturing oils that may be present). However, in order to achieve sufficient curing, single-component (IK) adhesives typically need to be cured at an elevated temperature (e g., over 100°C), and for a longer period of time.

Summary

Thus, it is important to develop a single-component structural adhesive that is capable of achieving fast curing at a lower temperature.

Starting from the technical problem identified above, the objective of the present invention is to provide a single -component (IK) structural adhesive, wherein the single -component structural adhesive is capable of achieving fast curing at a lower temperature, and a cured product thereof has a high glasstransition temperature (Tg) and a high bonding strength.

The inventors have conducted intensive and detailed research to accomplish the present invention. According to one aspect of the present invention, a single-component structural adhesive is provided, comprising:

50 weight percent (wt%) to 60 wt% of an epoxy resin having an epoxy equivalent weight of less than 190 grams per equivalent (g/eq);

38 wt% to 48 wt% of a thiol having four or more functionalities; and

1 wt% to 12 wt% of a latent catalyst, wherein the total weight of the single -component structural adhesive is 100 wt%.

Compared with the existing techniques in the art, the present invention has the following advantages: the single-component structural adhesive according to the technical solution of the present invention is capable of achieving complete curing at a lower temperature (about 65 °C) in a shorter period of time (about 30 minutes), and a cured product thereof has a high glass-transition temperature (Tg) and a high bonding strength.

Detailed Description

It should be appreciated that various other embodiments could be devised and modified by a person skilled in the art in light of the teachings of this description without departing from the scope or spirit of the present disclosure. Therefore, the following particular embodiments are not restrictive in meaning.

Unless otherwise indicated, all numbers used in this description and claims for the dimensions, quantities, and physicochemical properties of features should be construed to be modified by the term “approximately” in all instances. Accordingly, unless indicated to the contrary, the above numerical parameters listed in the description and attached claims are all approximations, which can be properly altered by a person skilled in the art using desired properties sought to be obtained from the teachings disclosed herein. The use of numerical ranges indicated by endpoints includes all numbers within that range and any range within that range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc.

Currently, single-component adhesives are widely used to assemble mobile hand-held devices, automotive industry devices, electronic device assemblies, and the like. In many scenarios in these industrial fields, there are high requirements for curing temperature and curing speed of adhesives For example, the curing temperature of an adhesive should be as low as possible in order to avoid causing deformation of bonded components. In addition, some specific components (e.g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.) are required to have high-temperature resistance at the site of bonding, and accordingly, the adhesives are required to have a high glass-transition temperature (Tg) at the site of curing. Having conducted in-depth and meticulous work, the inventors of the present invention have found that by specifically selecting the components of a single-component adhesive and the amounts thereof, a single-component structural adhesive can be provided which is capable of achieving fast curing at a lower temperature, a cured product thereof having a high glass-transition temperature (Tg) and a high bonding strength.

Specifically, the present invention provides a single -component structural adhesive, comprising: 50 wt% to 60 wt% of an epoxy resin having an epoxy equivalent weight of less than 190 g/eq;

38 wt% to 48 wt% of a thiol having four or more functionalities; and

Epoxy resms that can be used in the present invention include a wide variety of curable epoxy compounds and combinations thereof. Useful epoxy resins include liquids, solids, and mixtures thereof. In order for the cured product of the single-component structural adhesive to have high bonding performance and high Tg, it is required to control the epoxy equivalent weight of the epoxy resin to be less than 190 g/eq. Preferably, the epoxy equivalent weight of the epoxy resin is greater than or equal to 130 g/eq and less than 190 g/eq. Preferably, the epoxy equivalent weight of the epoxy resin is greater than or equal to 130 g/eq and less than or equal to 180 g/eq. According to certain preferred embodiments of the present invention, the epoxy resin is a difunctional epoxy resin, a trifunctional epoxy resin, or a mixture thereof. The term “difunctional epoxy resin” refers to an epoxy resin having two epoxy functional groups per molecule. The term “trifunctional epoxy resin” refers to an epoxy resin having three epoxy functional groups per molecule. Preferably, the epoxy resin is selected from among one or more in a group consisting of a difiinctional naphthalene-type epoxy resin, a difimctional bisphenol Z-type epoxy resin, and a trifunctional phenolic epoxy resin. Commercially available examples of epoxy resins that can be used in the present invention include: YLSE-900S (a difunctional naphthalene-type epoxy resin having an epoxy equivalent weight of about 135 g/eq), produced by GLK Global Co., Ltd., Korea; SRSZ-200 (a difunctional bisphenol Z-type epoxy resin having an epoxy equivalent weight of about 180 g/eq), produced by GLK Global Co., Ltd., Korea; and HP-7250 (a trifunctional phenolic epoxy resin having an epoxy equivalent weight of about 162 g/eq), produced by DIC Corporation, Japan. Preferably, in order to simultaneously have excellent bonding performance and Tg performance, the single-component structural adhesive comprises 28 wt% or more of a trifunctional epoxy resin. The single -component structural adhesive comprises 50 wt% to 60 wt%, preferably 51 wt% to 60 wt% of the epoxy resin.

The single-component structural adhesive according to the present invention further comprises a thiol compound as a component that reacts with the epoxy resin to achieve curing. The thiol compound is a highly functional thiol (i.e., a thiol having four or more functionalities). In the present invention, the term “thiol having four or more functionalities” refers to a thiol compound containing four or more thiol groups per molecule. Preferably, the thiol having four or more functionalities is a tetrafunctional thiol, a hexafunctional thiol, or a mixture thereof. More preferably, in order to simultaneously have excellent bonding performance and Tg performance, the thiol having four or more functionalities is a hexafunctional thiol. Preferably, the thiol having four or more functionalities is pentaerythritol tetrakis(3- mercaptopropionate), dipentaerythritol hexa(3-mercaptopropionate), or a mixture thereof. Commercially available examples of thiols having four or more functionalities that can be used in the present invention include: Thiocure 340 (pentaerythritol tetrakis(3-mercaptopropionate)), produced by Bruno Bock Chemische Fabrik GmbH & Co., Ltd., Germany; and Thiocure 360 (dipentaerythritol hexa(3- mercaptopropionate)), produced by Bruno Bock Chemische Fabrik GmbH & Co., Ltd., Germany. The single-component structural adhesive comprises 38 wt%to 48 wt%, preferably 39 wt%to 47 wt% ofathiol having four or more functionalities.

The single-component structural adhesive according to the present invention further comprises a latent catalyst to catalyze a curing reaction between the epoxy resin and the thiol having four or more functionalities. Preferably, the latent catalyst is an amine-based latent catalyst. There are no special restrictions on the specific type of latent catalyst that can be used in the present invention, so long as it can effectively catalyze the curing reaction between the epoxy resm and the thiol having four or more functionalities. Preferably, the amine-based latent catalyst is selected from among one or more in a group consisting of a modified cyclic aliphatic polyamine, a modified aliphatic polyamine, and a modified amine adduct. Commercially available examples of amine-based latent catalysts that can be used in the present invention include: FXR-1020, produced by T&K TOKA Co., LTD., Japan; FXR-1081, produced by T&K TOKA Co., LTD., Japan; and MY-25, produced by Ajinomoto Fine-Techno Co., Inc., Japan. The singlecomponent structural adhesive comprises 1 wt%to 12 wt%, preferably 2 wt% to 10 wt% of a latent catalyst.

Optionally, the single-component structural adhesive according to the present invention may further comprise a silane coupling agent, the silane coupling agent being used to improve the bonding performance of the cured product of the structural adhesive. There are no special restrictions on the specific type of silane coupling agent that can be used in the present invention, and it can be appropriately selected from various silane coupling agents that are typically used in structural adhesive applications in the art. Preferably, the silane coupling agent is selected from among one or more in a group consisting of y- glycidoxypropyltrimethoxysilane, 3 -(2,3 -epoxypropoxy jpropyltriethoxysilane, 3-(2,3- epoxypropoxy)propylmethyldimethoxy silane, 3 -(2, 3 -epoxypropoxy )p ropyl mcthyldi ethoxys i lane , 3 - mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfide, and bis(3-triethoxysilylpropyl)disulfide. Commercially available examples of silane coupling agents that can be used in the present invention include: KH560 (i.e., y-glycidoxypropyltrimethoxysilane), produced by Sinopharm Chemical Reagent Co., Ltd., China.

In addition to the components mentioned above, the single-component structural adhesive according to the present invention may further comprise one or more other additives to impart one or more other properties to the structural adhesive or improve one or more other properties of the structural adhesive . Specifically, these additives include calcium carbonate, kaolin, silicon dioxide, aluminum hydroxide, aluminum oxide, aluminum nitride, diatomaceous earth, talcum powder, a toughening agent, and the like.

There are no special restrictions on the specific preparation method used for preparing the singlecomponent structural adhesive described above. For example, the components included in the singlecomponent structural adhesive can be mixed at corresponding amounts thereof and stirred well.

Various exemplary embodiments of the present invention are further described by a list of embodiments below, which should not be construed as unduly limiting the present invention:

Specific embodiment 1 is a single -component structural adhesive, comprising:

50 wt% to 60 wt% of an epoxy resin having an epoxy equivalent weight of less than 190 g/eq;

38 wt% to 48 wt% of a thiol having four or more functionalities; and

Specific embodiment 2 is the single -component structural adhesive according to specific embodiment 1, wherein the epoxy equivalent weight of the epoxy resin is greater than or equal to 130 g/eq and less than 190 g/eq.

Specific embodiment 3 is the single -component structural adhesive according to specific embodiment 1, wherein the epoxy equivalent weight of the epoxy resin is greater than or equal to 130 g/eq and less than or equal to 180 g/eq. Specific embodiment 4 is the single -component structural adhesive according to specific embodiment 1, wherein the epoxy resin is a difunctional epoxy resin, a trifunctional epoxy resin, or a mixture thereof.

Specific embodiment 5 is the single -component structural adhesive according to specific embodiment 1, wherein the epoxy resin is selected from among one or more in a group consisting of a difunctional naphthalene-type epoxy resin, a difunctional bisphenol Z-type epoxy resin, and a trifunctional phenolic epoxy resin.

Specific embodiment 6 is the single -component structural adhesive according to specific embodiment 1, wherein the single-component structural adhesive comprises 28 wt% or more of a trifunctional epoxy resin.

Specific embodiment 7 is the single -component structural adhesive according to specific embodiment 1, wherein the thiol having four or more functionalities is a tetrafunctional thiol, a hexafunctional thiol, or a mixture thereof.

Specific embodiment 8 is the single -component structural adhesive according to specific embodiment 1, wherein the thiol having four or more functionalities is a hexafunctional thiol.

Specific embodiment 9 is the single -component structural adhesive according to specific embodiment 1, wherein the thiol having four or more functionalities is pentaerythritol tetrakis(3- mercaptopropionate), dipentaerythritol hexa(3-mercaptopropionate), or a mixture thereof.

Specific embodiment 10 is the single-component structural adhesive according to specific embodiment 1, wherein the latent catalyst is an amine-based latent catalyst.

Specific embodiment 11 is the single-component structural adhesive according to specific embodiment 1, wherein the amine-based latent catalyst is selected from among one or more in a group consisting of a modified cyclic aliphatic polyamine, a modified aliphatic polyamine, and a modified amine adduct.

Specific embodiment 12 is the single-component structural adhesive according to specific embodiment 1, wherein the single-component structural adhesive further comprises less than or equal to 2 wt% a silane coupling agent.

Specific embodiment 13 is the single-component structural adhesive according to specific embodiment 12, wherein the silane coupling agent is selected from among one or more in a group consisting of y-glycidoxypropyltrimethoxysilane, 3-(2,3-epoxypropoxy)propyltriethoxysilane, 3-(2,3- epoxypropoxy)propylmethyldimethoxy silane, 3 -(2, 3 -epoxypropoxy )propylmethyldiethoxysilane , 3 - mercaptopropyltrimethoxysilane, 3-mercaptopropyltnethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfide, and bis(3-triethoxysilylpropyl)disulfide.

The present invention will be described in more detail below with reference to examples. It should be pointed out that these descriptions and examples are for the purpose of facilitating the understanding of the present invention, rather than limiting the present invention. The scope of protection of the present invention is subject to the appended claims. Examples

In the present invention, unless otherwise indicated, reagents used are all commercially available products, which are used directly without further purification. Table 1. List of raw materials

Test methods

Test of the bonding performance (overlap shear strength) and glass-transition temperature (Tg) performance of a cured product of the single-component structural adhesive Glass-transition temperature (Tg)

Specifically, 20 milligrams (mg) of a liquid single-component glue prepared and obtained in the following examples and comparative examples is loaded in a special-purpose aluminum pan for DSC, and the pan is covered. The sample is cured and tested for glass-transition temperature (Tg) using a DSC Q2000 device from TA Instruments, Inc., USA according to the following procedure: first, equilibrating at 23°C room temperature for 2 minutes, then heating to 65°C, and maintaining at a constant temperature of 65°C for 30 minutes (min); afterwards, returning to 23°C room temperature, and heating to 200°C at a rate of 20°C per min, and measuring the glass-transition temperature Tg. The results of glass-transition temperature (Tg) (unit: °C) obtained are shown in Table 2 below.

If the glass-transition temperature (Tg) of a cured product is greater than or equal to 70°C, then the single-component structural adhesive is considered to meet the basic requirements for use in particular high-temperature-resistant components (e g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.); and if the glass-transition temperature (Tg) of a cured product is greater than or equal to 80°C, then the single-component structural adhesive is considered to have excellent performance in terms of use in particular high-temperature-resistant components (e.g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.).

Bonding Performance

Specifically, two aluminum plates (etched 2024T3 aluminum) measuring 101.6 millimeters (mm) (length) x 25.4 mm (width) x 2 mm (thickness) produced by Kunshan Great Wall Printing Factory, Jiangsu, China are used. The surfaces thereof are wiped clean using isopropanol and air-dried at room temperature. The two etched 2024T3 aluminum plates are overlapped by superimposing respective ends of the two plates measuring 25.4 mm (width) x 12.7 mm (length), zero point two (0.2) gram (g) of a uniformly dispersed liquid single-component structural adhesive prepared and obtained in the following examples and comparative examples being sandwiched between the overlap regions of the two etched 2024T3 aluminum plates. Afterwards, the etched 2024T3 aluminum plates overlapped with the adhesive are baked in an oven at 65°C for 30 minutes and then placed at room temperature for 2 hours. Bonding performance (overlap shear strength) (unit: megaPascals (MPa)) is measured at room temperature (22°C to 24°C) at a drawing speed of 2.54 mm/min according to the dynamic shear test standard ASTM D1002-72 by using an Instron 5969 apparatus produced by Instron Inc., USA. The overlap shear strength (unit: MPa) results obtained are shown in Table 2 below.

If the overlap shear strength of a cured product for the aluminum plates is greater than or equal to 8 MPa, then the single-component structural adhesive is considered to meet basic requirements in terms of bonding performance; and if the lap shear strength of a cured product for the aluminum plates is greater than or equal to 10 MPa, then the single-component structural adhesive is considered to have excellent bonding performance.

Example 1 (El)

Fifty g of the difunctional naphthalene -type epoxy resm YLSE-900S, 48 g of the hexafiinctional thiol Thiocure 360, and 2 g of the amine-based latent catalyst FXR-1081 were added to a container. Afterwards, the mixture was stirred manually for 2 minutes then stirred using a THINKY mixer for 5 minutes at a rotational speed of 500 rotations per minute (rpm), and afterwards, the mixture was stirred manually for 2 minutes then stirred using a THINKY mixer for 5 minutes at a rotational speed of 500 rpm, so as to obtain single-component structural adhesive 1.

The single-component structure adhesive 1 obtained was tested for bonding performance (overlap shear strength) and glass-transition temperature (Tg) performance according to the adhesive performance (overlap shear strength) and glass-transition temperature (Tg) performance test methods described in detail above, and the results are shown in Table 2 below.

Examples 2-13 (E2-E13) and Comparative examples 1-4 (CE1-CE4)

In Examples 2-13 (E2-E13) and Comparative Examples 1-4 (CE1-CE4), operations were carried out in a manner similar to those in Example 1, with only the types of the components and the amounts thereof being changed as shown in Table 2 below, so as to obtain single-component structural adhesives 2- 13 and comparative single-component structural adhesives 1-4.

The single -component structural adhesives 2-13 and comparative single -component structural adhesives 1-4 obtained were tested for bonding performance (overlap shear strength) and glass-transition temperature (Tg) performance according to the adhesive performance (overlap shear strength) and glasstransition temperature (Tg) performance test methods described in detail above, and the results are shown in Table 2 below.

Table 2. Composition and performance test results of the single-component structural adhesives prepared in Examples 1-13 (E1-E13) and Comparative Examples 1-4 (CE1-CE4)

As can be seen from the results shown in Table 2 above, when the components of a structural adhesive and the amounts thereof were specifically selected from within the scope of the present invention, a single-component structural adhesive could be provided which was capable of achieving fast curing (curing time of about 30 minutes) at a lower temperature (as low as 65°C), and a cured product thereof had a high glass-transition temperature (Tg) (i.e., a Tg of higher than or equal to 70°C) and a high bonding strength (an overlap shear strength of greater than or equal to 8 MPa).

It can be seen from the results of Examples 7-13 in Table 2 that when the amount of the trifunctional epoxy resin (i.e., trifunctional phenolic epoxy resin) in the structural adhesive was greater than or equal to 28 wt%, the single-component structural adhesive obtained simultaneously could achieve an excellent high glass-transition temperature (Tg) (i.e., a Tg of higher than or equal to 80°C) and an excellent bonding strength (i.e., an overlap shear strength of greater than or equal to 10 MPa). A comparison of the results of Example 6 with those of Example 7 can prove that an amount of trifunctional epoxy resin (i.e., trifunctional phenolic epoxy resin) of greater than or equal to 28 wt% is useful for achieving a balance between the aforementioned excellent performances.

It can be seen by comparing the results of Comparative Example 1 with those of Example 1 that when the amount of epoxy resin was decreased to be outside of the scope of the present invention (i.e., 47 wt%) and the amount of thiol was increased to be outside of the scope of the present invention (i.e., 51 wt%), both the bonding performance and the glass-transition temperature performance of the singlecomponent structural adhesive obtained deteriorated. In particular, the glass-transition temperature decreased to 66°C, failing to meet the basic requirements for use in bonding particular high-temperature- resistant components (e.g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.).

It can be seen by comparing the results of Comparative Example 2 with those of Example 2 that when the amount of tetrafunctional thiol was decreased to be outside of the scope of the present invention (i.e., 35 wt%), both the bonding performance and the glass-transition temperature performance of the single-component structural adhesive obtained deteriorated substantially, wherein the glass-transition temperature decreased to 65 °C, failing to meet the basic requirements for use in bonding particular high- temperature-resistant components (e.g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.), and the overlap shear strength for the aluminum plates decreased to 7.0 MPa, failing to meet basic requirements in terms of bonding performance.

It can be seen by comparing the results of Comparative Example 3 with those of Example 12 that when the same amount of trifunctional thiol (i.e., trimethylolpropane tri(3 -mercaptopropionate)) was used in place of hexafunctional thiol (i.e., dipentaerythritol hexa(3 -mercaptopropionate)), both the bonding performance and the glass-transition temperature performance of the single -component structural adhesive obtained deteriorated substantially, wherein the glass-transition temperature decreased to 64°C, failing to meet the basic requirements for use in bonding particular high-temperature-resistant components (e.g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.), and the overlap shear strength for the aluminum plates decreased to 7.7 MPa, failing to meet basic requirements in terms of bonding performance.

It can be seen by comparing the results of Comparative Example 4 with those of Example 3 that when the same amount of difunctional bisphenol A-type epoxy resin having an epoxy equivalent of 190 was used in place of difunctional bisphenol Z-type epoxy resin having an epoxy equivalent of 180, both the bonding performance and the glass-transition temperature performance of the single-component structural adhesive obtained deteriorated substantially, wherein the glass-transition temperature decreased to 56°C, failing to meet the basic requirements for use in bonding particular high-temperature-resistant components (e.g., sports equipment, bicycles, laminated magnet parts, electronic devices, etc.), and the overlap shear strength for the aluminum plates decreased to 7.3 MPa, failing to meet basic requirements in terms of bonding performance.

Although the above particular embodiments comprise many specific details for the purpose of illustration, those skilled in the art should understand that many variations, modifications, replacements and changes to these details all fall within the scope ofthe present invention as claimed in the claims. Therefore, the disclosure as described in the specific embodiments does not pose any limitation to the present invention as claimed in the claims. The proper scope of the present invention should be defined by the claims and proper legal equivalents thereof. All references referred to are incorporated herein by reference in their entireties.

Claims

What is claimed is:

1. A single-component structural adhesive, the single-component structural adhesive comprising:

50 weight percent to 60 weight percent of an epoxy resin having an epoxy equivalent weight of less than 190 grams per equivalent;

38 weight percent to 48 weight percent of a thiol having four or more functionalities; and

1 weight percent to 12 weight percent of a latent catalyst, wherein the total weight of the single-component structural adhesive is 100 weight percent.

2. The single-component structural adhesive according to claim 1, wherein the epoxy equivalent weight of the epoxy resin is greater than or equal to 130 grams per equivalent and less than 190 grams per equivalent.

3. The single -component structural adhesive according to claim 1 or 2, wherein the epoxy equivalent weight of the epoxy resin is greater than or equal to 130 grams per equivalent and less than or equal to 180 grams per equivalent.

4. The single-component structural adhesive according to any one of claims 1 to 3, wherein the epoxy resin is a difunctional epoxy resin, a trifunctional epoxy resin, or a mixture thereof.

5. The single-component structural adhesive according to any one of claims 1 to 4, wherein the epoxy resin is selected from among one or more in a group consisting of a difunctional naphthalene -type epoxy resin, a difunctional bisphenol Z-type epoxy resin, and a trifunctional phenolic epoxy resin.

6. The single -component structural adhesive according to any one of claims 1 to 5, wherein the singlecomponent structural adhesive comprises 28 weight percent or more of a trifunctional epoxy resin.

7. The single -component structural adhesive according to any one of claims 1 to 6, wherein the thiol having four or more functionalities is a tetrafunctional thiol, a hexafunctional thiol, or a mixture thereof.

8. The single -component structural adhesive according to any one of claims 1 to 7, wherein the thiol having four or more functionalities is a hexafimctional thiol.

9. The single -component structural adhesive according to any one of claims 1 to 8, wherein the thiol having four or more functionalities is pentaerythritol tetrakis(3 -mercaptopropionate), dipentaerythritol hexa(3-mercaptopropionate), or a mixture thereof.

10. The single-component structural adhesive according to any one of claims 1 to 9, wherein the latent catalyst is an amine-based latent catalyst.

11. The single-component structural adhesive according to claim 10, wherein the amme-based latent catalyst is selected from among one or more in a group consisting of a modified cyclic aliphatic polyamine, a modified aliphatic polyamine, and a modified amine adduct.

12. The single-component structural adhesive according to any one of claims 1 to 11, wherein the single-component structural adhesive further comprises less than or equal to 2 weight percent of a silane coupling agent.

13. The single -component structural adhesive according to claim 12, wherein the silane coupling agent is selected from among one or more in a group consisting of y-glycidoxypropyltrimethoxysilane, 3- (2,3-epoxypropoxy)propyltriethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane, 3-(2,3- epoxypropoxy)propylmethyldiethoxysilane, 3-mercaptopropyltrimethoxysilane, 3- mercaptopropyltriethoxysilane, bis(3-triethoxysilylpropyl) tetrasulfide, and bis(3- triethoxysilylpropyl)disulfide