阅读说明：本技术 粘合剂组合物 (Adhesive composition ) 是由 S·格伦德 S·施马特洛赫 J·孔茨 于 2019-02-20 设计创作，主要内容包括：一种聚氨酯粘合剂组合物、更具体地一种双组分聚氨酯粘合剂,其包含(a)至少一种异氰酸酯组分,以及(b)至少一种多元醇组分,其中所述多元醇组分(b)包含(bi)至少一种第一多元醇化合物、(bii)至少一种第二多元醇化合物和(biii)至少一种扩链剂；以及一种用于制造以上粘合剂组合物的方法。(A polyurethane adhesive composition, more specifically a two-component polyurethane adhesive, comprising (a) at least one isocyanate component, and (b) at least one polyol component, wherein the polyol component (b) comprises (bi) at least one first polyol compound, (bii) at least one second polyol compound, and (biii) at least one chain extender; and a method for manufacturing the above adhesive composition.)

1. An adhesive composition comprising:

(a) at least one isocyanate component, and

(b) at least one polyol component, wherein the polyol component comprises (bi) at least one first polyol compound, (bii) at least one second polyol compound having a functionality of greater than about 2 and an equivalent weight of less than about 200; and (biii) at least one chain extender, wherein the chain extender comprises a compound having about 2 hydroxyl groups and an equivalent weight of less than about 200.

2. The composition of claim 1, wherein the at least one second polyol compound has a functionality of 3 or greater and an equivalent weight of less than about 100.

3. The composition of claim 1, further comprising at least one catalyst.

4. The composition of claim 3, wherein the at least one catalyst is at least one tin-containing organic catalyst.

5. The composition of claim 3, wherein the at least one catalyst comprises a combination of (α) at least one tin-containing organic compound and (β) at least one amine compound.

6. The composition of claim 3, wherein the at least one catalyst is added to the at least one isocyanate component (a); wherein the at least one catalyst is added to the at least one polyol component (b); or wherein the at least one catalyst is added to both the at least one isocyanate component (a) and the at least one polyol component (b).

7. The composition of claim 1, further comprising at least one filler.

8. The composition of claim 7, wherein the at least one filler is selected from the group consisting of: inorganic filler particles, metal particles, thermoset polymer particles, thermoplastic particles, carbon black, carbon particles, and mixtures thereof.

9. The composition of claim 7, wherein the at least one filler is added to the at least one isocyanate component (a); wherein the at least one filler is added to the at least one polyol component (b); or wherein the at least one filler is added to both the at least one isocyanate component (a) and the at least one polyol component (b).

10. The composition of claim 1, wherein the at least one catalyst is at least one tin-containing organic catalyst.

11. The composition of claim 1, wherein the at least one first polyol compound is at least one prepolymer.

12. The composition of claim 11, wherein the at least one prepolymer comprises an isocyanate functional reaction product of (a) at least one polyol compound and (B) at least one polyisocyanate compound.

13. The composition of claim 1, wherein the at least one second polyol compound is glycerol.

14. The composition of claim 1, wherein the at least one isocyanate component (a) is present in the composition at a concentration of from about 0.01 weight percent to about 60 weight percent; and wherein the at least one polyol component (b) is present in an amount of about

The concentration of 0.1 weight percent to about 20 weight percent is present in the composition.

15. The composition of claim 3, wherein the at least one catalyst is present in the composition at a concentration of about 0.005 weight percent to about 2.0 weight percent.

16. The composition of claim 7, wherein the at least one filler is present in the composition at a concentration of about 0.1 weight percent to about 60 weight percent.

17. The composition of claim 1, further comprising at least one gas scavenger, at least one water scavenger, or a mixture thereof.

18. The composition of claim 1, wherein the composition has an open time of greater than 8 minutes; an overlap shear strength of greater than about 1.0 megapascals after one hour at 23 ℃ and 50% relative humidity; and an elongation at break of greater than about 150%.

19. The composition of claim 1, comprising a two-component polyurethane adhesive.

20. A method for preparing a two-component polyurethane adhesive composition, the method comprising blending together:

(a) at least one isocyanate component, and

(b) at least one polyol component, wherein the polyol component comprises (bi) at least one first polyol compound, (bii) at least one second polyol compound having a functionality of greater than about 2 and an equivalent weight of less than about 200; and (biii) at least one chain extender, wherein the chain extender comprises a compound having about 2 hydroxyl groups and an equivalent weight of less than about 200.

21. The method of claim 20, wherein the composition further comprises at least one catalyst.

22. The method of claim 20, wherein the composition further comprises at least one filler.

23. A method for bonding at least a first substrate to at least a second substrate, the method comprising:

(I) contacting the at least a first substrate with the adhesive composition of claim 1;

(II) contacting the at least second substrate with the adhesive composition present on the at least first substrate; and

(III) heating the at least first and second substrates and the adhesive composition to a temperature of from about 5 ℃ to about 80 ℃.

Technical Field

The present invention relates to an adhesive composition; and more particularly, the present invention relates to a two-component polyurethane adhesive composition that is particularly useful in automotive applications.

Background

Reinforced composites are increasingly used in modern vehicle design due to performance advantages and light weight vehicle requirements. Adhesive bonding is the most preferred assembly technique for composite materials because bonding does not destroy the composite structure (unlike mechanical fastening, such as screw bonding or riveting, for example). Typically, the use of adhesive technology for part assembly is aimed at optimizing the production process in order to achieve rapid adhesive application, rapid strength build-up and rapid development of handling strength. In some cases, speeding up adhesive application, adhesive strength build up, and development of adhesive handling strength can be achieved through a heating process. For example, in contrast to thermal curing using a conventional convection oven, an infrared-based heating process may enable lap shear strengths greater than (>) 1.0 megapascals (MPa) to be achieved with very short cycle times (e.g., 1-3 minutes (min)).

Furthermore, flexibility is required in the process for providing a fast strength build-up of the adhesive. Process flexibility is defined as long open time. The "open time" is the time elapsed between the application of the adhesive to the first substrate and the joining of the second substrate to the first substrate. Furthermore, long mixer stand-alone times are required to reduce the flushing intervals and thus reduce the material waste generated by the process. The "mixer independent time" is the period of time between two successive applications of a mixed two-part or two-component (2K) adhesive, which 2K adhesive can be held in a mixer unit (static or dynamic) without gelling of the adhesive. After mixing the two components of the 2K adhesive, it is desirable that the adhesive remain workable for as long as possible so that the adhesive can bond to a substrate. In addition to long open times, it is also desirable to exhibit a fast strength build-up adhesive after the 2K adhesive reaches its open time at room temperature (RT; about 25 degrees Celsius (C.)), to provide the handling strength of the adhesive after a short time (e.g., one hour (hr) or less). The aforementioned binders are typically latent binders. By "latent adhesive" is meant a 2K adhesive having a long open time (e.g., > 8 minutes) followed by a fast cure time (e.g., faster than 60 minutes).

Polyurethane (PU) is a well-known type of adhesive, belonging to the 2K type; and may provide some of the benefits described above with respect to open time and fast set time. The 2K PU adhesive is composed of a resin component including one or more polyisocyanate compounds and a curing agent component including one or more polyol compounds. When the two components (a) and (b) are mixed, the one or more polyisocyanate compounds and the one or more polyol compounds react to form a cured polyurethane adhesive. The polyurethane adhesive may be formulated to cure at room temperature or after exposure to certain conditions (e.g., elevated temperature). As the adhesive cures, the adhesive can form a strong adhesive bond with many types of substrates.

The 2K PU adhesive can be used in various applications, and in a preferred embodiment, the 2K PU adhesive can be advantageously used in the construction of passenger vehicles, particularly when welding of two dissimilar materials is difficult or even impossible to achieve during construction of passenger vehicles. Two-component adhesive compositions are particularly useful where the application requires rapid curing, especially where the two components are not storage stable when in contact with each other. By "storage stable" is meant that the composition does not cure during storage. It is desirable that the 2K PU adhesive composition exhibit suitable "open time" and fast cure.

One way to achieve long open times and fast cure is by formulating the adhesive to be heat activated for curing. Such adhesives cure slowly at ambient temperatures, allowing the adhesive to be applied to and the substrate to be placed while the adhesive remains usable. The resulting substrate assembly can then be fully and rapidly cured at room or elevated temperatures to form an assembly with a strong bond.

It is desirable to provide a 2K PU adhesive that provides increased latency (latency), resulting in an improved adhesive that has longer open time and rapid handling strength build while maintaining the mechanical properties of the adhesive.

Disclosure of Invention

The present invention relates to a two-component polyurethane (2K PU) adhesive composition (or formulation) comprising (a) at least one isocyanate component, and (b) at least one polyol component, wherein the polyol component comprises (bi) at least one first polyol compound, (bi) at least one second polyol compound having a functionality > 2 and an Equivalent Weight (EW) of less than (<) 200; and (biii) at least one chain extender, wherein the chain extender comprises a compound having 2 hydroxyl groups and an EW < 200. In a preferred embodiment, the adhesive composition may comprise (c) optionally, at least one catalyst; and in another preferred embodiment, the adhesive composition may comprise (d) optionally, at least one filler. Optional catalysts and/or fillers may be added to the isocyanate component (a) and/or the polyol component (b).

The present invention provides a 2K PU adhesive formulation with improved latency without compromising the mechanical properties of the inventive adhesive. The present invention also provides a 2K PU adhesive composition comprising: (1) exhibit increased open time when adhesive is used; (2) capable of being cured at ambient temperature; (3) capable of bonding to a variety of materials such as aluminum, magnesium, sheet molding compounds, carbon fiber composites, and coated metals; and (4) the ability to bond dissimilar materials.

Detailed Description

"isocyanate component (a)", or "IsoC" for short, refers herein to a composition comprising one or more isocyanate functional polyisocyanate compounds wherein at least one of the molecules of the polyisocyanate compound has at least one isocyanate (NCO) functional group. The IsoC may be a monomeric or polymeric compound or a mixture of such compounds.

"polyol component (b)", or abbreviated "PolC" herein refers to an ingredient comprising one or more polyol functional compounds wherein at least one of the molecules of the polyol functional compound has at least one polyol functional group. PolC may be a monomeric or polymeric compound or a mixture of such compounds.

In one general embodiment, the present invention includes a polyurethane adhesive composition, more specifically a 2K PU adhesive, comprising (a) at least one isocyanate component, and (b) at least one polyol component, wherein the polyol component (b) comprises: (bi) at least one first polyol compound, (bii) at least one second polyol compound, wherein the second polyol compound is different from the first polyol compound, and (biii) at least one chain extender. The novel adhesives of the present invention comprise as the second polyol component (bii) a high functional polyol (e.g., a polyol having a functionality of > 2 and an EW of < 200) suitable for providing beneficial properties to the adhesive, such as longer open time and faster strength build. The improved waiting time of the adhesives of the invention can be obtained from an increased crosslinking density, which leads to a reduction in the elongation at break of the adhesive. It has been surprisingly found that when a second polyol, such as a trifunctional, low molecular weight glycerol molecule, is used to form the adhesive composition of the present invention, the latency of the adhesive composition is improved and the mechanical properties of the adhesive composition are not compromised. It has also been unexpectedly found that when a trifunctional chain extender (like glycerol, for example) is used in the 2K PU adhesive composition of the invention, the waiting time of the 2K PU adhesive can be improved, resulting in a 2K PU adhesive with a longer open time and faster strength build up, without compromising the mechanical properties of the 2K PU adhesive, such as elongation at break.

The 2K PU adhesive formulations of the present invention comprise at least one isocyanate component as component (a) of the formulation, i.e. the isocyanate component (a) useful in the present invention may comprise one or more isocyanate-containing compounds. Thus, the isocyanate component (a)) of the adhesive formulation of the present invention may be (1) at least one isocyanate-containing monomeric compound, (2) a mixture of compounds, wherein at least one of the compounds in the mixture is an isocyanate-containing monomeric compound, (3) at least one isocyanate-containing polymer or prepolymer compound, or (4) a mixture of isocyanate-containing monomeric and isocyanate-containing polymer or prepolymer compounds.

For example, component (a) useful in the adhesive formulation of the present invention may include aromatic polyisocyanate compounds, aliphatic polyisocyanate compounds, or mixtures thereof; and such polyisocyanate compounds may be added to the adhesive formulation as monomer compounds or as prepolymer compounds. Some examples of polyisocyanate compounds useful in the present invention include, for example, aromatic MDI (methylene diphenyl diisocyanate) such as143, which is a liquefied MDI, having a functionality of 2.2 and a viscosity of 40 mPa-s; isonate 220, which is a polymeric MDI having a functionality of 2.7 and a viscosity of 220 mPa-s; 4, 4' -methylene-diphenyl diisocyanate; 2, 2' -methylene diphenyl diisocyanate; 2, 4-methylene diphenyl diisocyanate; and mixtures thereof. Isonate is a trademark of The Dow Chemical Company and products of Isonate are available from The Dow Chemical Company.

The aliphatic polyisocyanate compounds useful in the present invention may include, for example, Desmodur N3400 and Desmodur N3300, which are aliphatic polyisocyanate compounds based on hexamethylene diisocyanate. Desmodur N3400 is Hexamethylene Diisocyanate (HDI) uretdione and is also known as HDI-dimer; and Desmodur N3300 is HDI-isocyanate (HDI-isocyanerate) and is also known as HDI-trimer. Desmodur is a trademark of scientific, Inc. (Covestro) and the product Desmodur is available from scientific, Inc.

In another embodiment, the isocyanate moiety-containing polyisocyanate compound useful as isocyanate component (a) in the adhesives of the present invention may, for example, comprise an isocyanate-containing prepolymer (or isocyanate-terminated prepolymer). For example, the prepolymer may include an MDI-terminated prepolymer formed from EO (ethylene oxide) and/or PO (propylene oxide) based polyol compounds such as diols, triols, or mixtures thereof. The prepolymer may have an EW in one embodiment of up to about 2,500, and in another embodiment of about to about 5,000, in yet another embodiment of about 1,000 to about 4,000, and in yet another embodiment of about 2,000 to about 3,500.

In a preferred embodiment, the isocyanate component (a) is preferably a mixture of: (1) one or more isocyanate-terminated prepolymers having at least 2 isocyanate groups per molecule and an isocyanate EW in the range of from about 700 to about 3, 500, and (2) one or more low EW polyisocyanate compounds having an isocyanate EW up to about 350 and an isocyanate group per molecule in the range of from about 2 to about 4. In a general embodiment, when such a mixture is present, the prepolymer can comprise from about 20 weight percent (wt%) to about 80 wt% of the weight of the isocyanate component (a). In some other embodiments of the mixture, the prepolymer may comprise from about 20 wt% to about 70 wt% in one embodiment, from about 20 wt% to about 65 wt% in another embodiment, or from about 30 wt% to about 60 wt% in yet another embodiment, based on the weight of the isocyanate component (a). In one embodiment, when such a mixture is present, the low EW polyisocyanate compound can comprise from about 1% to about 50% by weight of the isocyanate component (a). The isocyanate content in isocyanate component (a) may be about 1 wt% or greater in one embodiment, about 6 wt% or greater in another embodiment, about 8 wt% or greater in yet another embodiment, and about 10 wt% or greater in yet another embodiment. The isocyanate content in the isocyanate functional prepolymer may be about 35 wt% or less in one embodiment, about 30 wt% or less in another embodiment, about 25 wt% or less in yet another embodiment, and about 15 wt% or less in yet another embodiment.

In another embodiment, the prepolymer can be the reaction product of one or more diisocyanates having an isocyanate EW up to about 350 with: (1) at least one homopolymer of poly (propylene oxide) or any other polyol (e.g., polyester polyol, polybutylene oxide, etc.) having an EW of from about 700 to about 3,000 and having a nominal hydroxyl functionality of from about 2 to about 4 in one embodiment and from about 2 to about 3 in another embodiment; or (2) a mixture of the above component (1) with a polyether polyol having a MW of about 2,000 to about 8,000. In preferred embodiments, up to about 3 parts by weight of the above polyether polyol component (2) per part by weight of component (1) may be used. The polyether polyol may include a copolymer of about 70 wt% to about 99 wt% propylene oxide and about 1 wt% to about 30 wt% ethylene oxide; and the copolymer may have a nominal hydroxyl functionality of from about 2 to about 4 in one embodiment and from about 2 to about 3 in another embodiment. In yet another embodiment, the copolymer can also have a MW of about 3,000 to about 5,500 and a nominal functionality of about 2 to about 3.

The reaction of the polyisocyanate compound and the one or more polyol compounds produces prepolymer molecules having polyether segments that are capped with a polyisocyanate, so that the molecules have terminal isocyanate groups. Each prepolymer molecule contains a polyether segment corresponding to the hydroxyl-free structure of the polyol compound used in the reaction to form the prepolymer. If a mixture of polyol compounds is used to prepare the prepolymer, a mixture of prepolymer molecules may be formed. For example, in addition to prepolymers that may be capped with the polyols described above, in other embodiments, a variety of other prepolymers useful in the present invention may be prepared by molecular weight increase. For example, a prepolymer may have one diisocyanate in the middle of the chemical structure of the prepolymer, with two polyol groups attached to the ends of the structure, which may be capped with an isocyanate.

The isocyanate-terminated prepolymers useful as component (a) of the adhesive formulation of the present invention have an isocyanate EW in one embodiment of from about 700 to about 3, 500, in another embodiment of from about 700 to about 3, 000, and in yet another embodiment of from about 1,000 to about 3, 000. The EW for the purposes of the present invention is calculated by adding the weight of the polyol or polyols used to prepare the prepolymer and the weight of the polyisocyanate or polyisocyanates consumed in the reaction with the polyol or polyols and dividing by the moles of isocyanate groups in the resulting prepolymer. The polyisocyanate compound used to prepare the prepolymer can be any of the low EW polyisocyanate compounds mentioned below, or a mixture of two or more of these. The prepolymer has in one embodiment about 2 or more isocyanate groups per molecule, in another embodiment about 2 to about 4 isocyanate groups per molecule, or in yet another embodiment about 2 to about 3 isocyanate groups per molecule. The isocyanate groups of the prepolymer may be aromatic, aliphatic (including cycloaliphatic), or a mixture of aromatic and aliphatic isocyanate groups. The isocyanate groups on the prepolymer molecules may be aromatic. The one or more low EW polyisocyanate compounds can have an isocyanate EW, for example, in one embodiment of from about 80 to about 250, in another embodiment of from about 80 to about 200, and in yet another embodiment of from about 80 to about 180. If present in the adhesive formulation, the mixture of polyisocyanate compounds may have an average number of, for example, from about 2 to about 4 isocyanate groups/molecule in one embodiment and from about 2.3 to about 3.5 isocyanate groups/molecule in another embodiment.

All or a portion of the low EW polyisocyanate compounds can have aromatic isocyanate groups. Among the useful aromatic polyisocyanate compounds are m-phenylene diisocyanate, toluene-2, 4-diisocyanate, toluene-2, 6-diisocyanate, naphthylene-1, 5-diisocyanate, methoxyphenyl-2, 4-diisocyanate, diphenyl-methane-4, 4 ' -diisocyanate, diphenylmethane-2, 4 ' -diisocyanate, 4 ' -biphenylene diisocyanate, 3 ' -dimethoxy-4, 4 ' -biphenyl diisocyanate, 3 ' -dimethyl-4-4 ' -biphenyl diisocyanate, 3 ' -dimethyl-diphenylmethane-4, 4 ' -diisocyanate, mixtures thereof, and the like, 4, 4 ', 4 "-triphenylmethane triisocyanate, polymethylene Polyphenylisocyanate (PMDI), toluene-2, 4, 6-triisocyanate, 4' -dimethyl-di-phenylmethane-2, 2 ', 5, 5' -tetraisocyanate, and mixtures thereof. Modified aromatic polyisocyanates containing urethane, urea, biuret, carbodiimide, uretonimine (uretoneimine), allophanate (allophonate) or other groups formed by reaction of isocyanate groups may also be used in the present invention. The aromatic polyisocyanate may be MDI or PMDI (or mixtures thereof, commonly referred to as "polymeric MDI"), as well as the so-called "liquid MDI" products (which are mixtures of MDI and MDI derivatives having biuret, carbodiimide, uretonimine and/or allophanate linkages). All or a portion of the low EW polyisocyanate compounds can be one or more aliphatic polyisocyanate compounds. Examples of the aliphatic polyisocyanate compound that can be used in the present invention may include cyclohexane diisocyanate, 1, 3-and/or 1, 4-bis (isocyanatomethyl) cyclohexane, 1-methyl-cyclohexane-2, 4-diisocyanate, 1-methyl-cyclohexane-2, 6-diisocyanate, methylenedicyclohexyl diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and mixtures thereof.

At least some of the polyisocyanate groups present in the polyisocyanate component may be aromatic isocyanate groups. If a mixture of aromatic and aliphatic isocyanate groups are present in isocyanate component (a), in one embodiment about 50% by number or more are aromatic isocyanate groups, and in another embodiment about 75% by number or more are aromatic isocyanate groups. In yet another embodiment, from about 80% to about 98% by number of the isocyanate groups may be aromatic and from about 2% to about 20% by number may be aliphatic isocyanate groups. In yet another embodiment, all of the isocyanate groups of the prepolymer may be aromatic; and the isocyanate groups of the one or more polyisocyanate compounds having an isocyanate EW of up to about 350 can be a mixture of about 80% to about 95% aromatic isocyanate groups and about 5% to about 20% aliphatic isocyanate groups.

It is often convenient to prepare the isocyanate-containing prepolymer by combining a polyol compound or mixture of polyol compounds with one or more low EW polyisocyanate compounds in an amount significantly greater than that required to simply cap the one or more polyols. After reaction, the above combinations yield a mixture of prepolymer and unreacted low EW polyisocyanate compound. If desired, additional amounts of one or more polyisocyanate compounds can then be blended into this mixture. One or more polyol compounds may be combined and reacted with an excess of one or more aromatic polyisocyanate compounds to produce a mixture of prepolymer and unreacted starting polyisocyanate compounds, and this mixture may then be combined with one or more aliphatic polyisocyanate compounds. For example, the isocyanate-containing prepolymer may be prepared by: one or more polyol compounds are reacted with MDI, PMDI, polymeric MDI, derivatives of any one or more of these (containing biurets, carbodiimides, uretonimines, and/or allophanates), or mixtures of any two or more of these to produce a mixture of prepolymer and unreacted starting polyisocyanate compounds, and the mixture can then be combined with one or more aliphatic polyisocyanate compounds, especially hexamethylene diisocyanate-based aliphatic polyisocyanate compounds.

Generally, the amount of isocyanate-containing prepolymer that may be used in the adhesive formulation may be in one embodiment from about 0.01 wt% to about 80 wt%, based on the total weight of the components in the formulation; from about 1 wt% to about 70 wt% in another embodiment; from about 1 wt% to about 60 wt% in yet another embodiment; and in yet another embodiment from about 1 wt% to about 55 wt%. If the amount of the prepolymer exceeds 80 wt%, the viscosity of the formulation may be too low for the components in the formulation to be mixed with each other. If the amount of prepolymer is less than 0.01 wt%, the adhesive formulation may not function to provide a workable adhesive.

As previously described, the polyol component (b) comprises (bi) at least one first polyol compound; (bii) at least one second polyol compound, wherein the second polyol compound is different from the first polyol compound; and (biii) at least one chain extender. The first polyol compound useful in the present invention may be selected from any of the various polyol compounds known in the art, such as the polyol compounds described in WO 2016205252(a1) incorporated by reference. Ingredient (bi) of component (b), i.e., the first polyol compound of polyol component (b), may be a polyether polyol or a mixture of polyether polyols. In one general embodiment, each polyether polyol has a hydroxyl EW in the range of from about 400 to about 3,000. In some embodiments, the hydroxyl EW of each polyol compound can be, for example, at least about 500 in one embodiment, at least about 800 in another embodiment, and at least about 1,000 in yet another embodiment. In other embodiments, for example, the hydroxy EW can be up to about 3,000 in one embodiment; up to about 2, 500 in another embodiment; and in yet another embodiment up to about 2,000. Each such polyether polyol has a nominal hydroxyl functionality of from about 2 to about 3. By "nominal functionality" of the polyether polyol is meant the average number of oxyalkylatable hydrogen atoms on the initiator compound which is oxyalkylated to form the polyether polyol. The actual functionality of the one or more polyether polyols may be slightly lower than the nominal functionality due to side reactions that occur during the alkoxylation process. In the case of a mixture of polyether polyols, the number average nominal functionality may be from about 2 to about 3 in one embodiment, and from about 2.5 to about 3 in another embodiment.

The one or more polyether polyols useful as the first polyol compound (component (bi)) in the present invention may be selected from homopolymers of propylene oxide and copolymers of from about 70 to about 99 weight percent propylene oxide and from about 1 to about 30 weight percent ethylene oxide. Such copolymers of propylene oxide and ethylene oxide are generally preferred if a single polyether polyol is present. If two or more polyether polyols are present, it is preferred that at least one is such a copolymer of propylene oxide and ethylene oxide. In the case of copolymers, the propylene oxide and ethylene oxide may be randomly copolymerized, block copolymerized, or both. In some embodiments, about 50% or more of the hydroxyl groups of the polyether polyol or mixture of polyether polyols are primary hydroxyl groups, with the remainder being secondary hydroxyl groups. About 70% or more of the hydroxyl groups in the polyether polyol or mixture thereof may be primary hydroxyl groups. The one or more polyether polyols, component (bi) of polyol component (b), may constitute about 35 wt% or greater of polyol component (b) in one embodiment, about 40 wt% or greater in another embodiment, and about 50 wt% or greater in yet another embodiment. In other embodiments, the one or more polyether polyol components (bi) of polyol component (b) may be about 80 wt% or less in one embodiment, about 65 wt% or less in another embodiment, and about 55 wt% or less in yet another embodiment.

In preferred embodiments, the first polyol compound can be, for example, a polyether polyol or polyester polyol having an EW of > about 200 and a functionality of > about 1. Other suitable polyol compounds for the polyol component (b) useful in the present invention may include, for example, polypropylene-based diols, such as Voranol having an equivalent molecular weight of about 500g/mol^TMVoranol of 1010L, equivalent molecular weight about 1,000 g/mol^TM2000L of a glycerine initiated propoxylated triol based on ethylene oxide having an average equivalent molecular weight of about 1, 600g/mol Voranol^TMCP 4610; and mixtures thereof.

"high functional polyol compounds," i.e., polyol compounds having a functionality of > about 2.3 (e.g., > about 3), can also be used in the present invention. For example, the high functional polyol compound useful in the present invention may include Voranol 280. Voranol280 is a sucrose initiated oxypropylene-oxyethylene polyol having a hydroxyl number of 280. Voranol is a trademark of the dow chemical company and the Voranol products are available from the dow chemical company.

Generally, the amount of the first polyol compound in the adhesive formulation may be in one embodiment from about 1 wt% to about 90 wt%, based on the total weight of the components in the formulation; from about 5 wt% to about 80 wt% in another embodiment; from about 10 wt% to about 70 wt% in yet another embodiment; and in yet another embodiment from about 20 wt% to about 60 wt%. If the amount of the first polyol compound exceeds 90 wt%, the viscosity of the resulting formulation will be too low; and if the amount of the first polyol compound is less than 1 wt%, the OH number of the polyol component (a) will be insufficient and/or the mechanical properties of the adhesive formulation will be impaired.

The ingredient (bii) of component (b), i.e., the second polyol compound of polyol component (b), may be a polyol compound or a mixture of polyol compounds. The second polyol compounds useful in the present invention can be selected from a variety of polyol compounds having a functionality of > about 2 and an EW of < about 200. The second polyol compound may be, for example, any one or more of the above-described first polyol compounds, as long as the second polyol compound is different from the first polyol compound; and the second polyol compound has a functionality of > about 2 and an EW of < about 200. The second polyol compound may include, for example, 1, 2, 3-glycerol (also known as glycerol) or other isomers of glycerol; 1, 2, 4-butanetriol (or other isomers of 1, 2, 4-butanetriol); any other polyol compound having about 3 or more hydroxyl groups and a molecular weight < about 600 g/mol; and mixtures thereof.

Generally, the amount of the second polyol compound in the adhesive formulation may be in one embodiment from about 0.1 wt% to about 10 wt%, based on the total weight of the components in the formulation; from about 0.1 wt% to about 7.5 wt% in another embodiment; from about 0.1 wt% to about 5 wt% in yet another embodiment; and in yet another embodiment from about 0.2 wt% to about 3 wt%. If the amount of the second polyol compound exceeds 10 wt%, the mechanical properties of the adhesive formulation may be impaired; and if the amount of the second polyol compound is less than 0.1 wt%, the waiting time of the adhesive formulation may be impaired.

The chain extender (ingredient (biii)) of the polyol component (b) may be one or more aliphatic diol chain extenders. The one or more aliphatic glycol chain extenders each have a hydroxyl EW in one embodiment of about 200 or less, in another embodiment of about 100 or less, in yet another embodiment of about 75 or less, and in yet another embodiment of about 60 or less. The aliphatic diol chain extender may have about 2 aliphatic hydroxyl groups per molecule. Also, the chain extender useful in the present invention may include short chain extender diols having an EW of from about 10 to about 59. In one embodiment, examples of the aliphatic diol chain extender may include monoethylene glycol (MEG), diethylene glycol, triethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 2, 3-dimethyl-1, 3-propanediol, dipropylene glycol, tripropylene glycol, 1, 4-butanediol, 1, 6-hexanediol, other linear or branched alkylene glycols having up to about 20 carbon atoms, and mixtures thereof. In a preferred embodiment, the aliphatic diol chain extender may include monoethylene glycol, 1, 4-butanediol, and mixtures thereof.

The aliphatic diol chain extender or mixture thereof may be present in an amount of from about 2.5 to about 6 equivalents per equivalent of ingredients (bi) and (bii) of polyol component (b). The chain extender may be present in an amount of about 0.1 wt% or greater in one embodiment, about 1.0 wt% or greater in another embodiment, about 2.0 wt% or greater in yet another embodiment, and about 3.0 wt% or greater in yet another embodiment of the polyol component (b). The chain extender may be present in an amount of about 10 wt% or less in one embodiment, about 9 wt% or less in another embodiment, about 8 wt% or less in yet another embodiment, about 7 wt% or less in yet another embodiment, and about 6 wt% or less in even yet another embodiment of the polyol component (b).

Although the second part of the 2k PU adhesive has been described with respect to the "polyol" component (b), it is well known that other isocyanate-reactive compounds may also be used in the present invention. The term "isocyanate-reactive" as used hereinCompound "includes any organic compound having nominally at least two isocyanate reactive moieties. "isocyanate-reactive moiety" refers herein to a moiety that may be an active hydrogen-containing moiety; and "active hydrogen-containing moiety" refers herein to a moiety containing a hydrogen atom due to its position in the molecule according to the Journal of the American Chemical Society by Wohler]The Zerewitinoff test, described in volume 49, page 3181 (1927), showed significant activity. Examples of such isocyanate-reactive moieties, such as active hydrogen-containing moieties, are-COOH, -OH, -NH₂、-NH-、-CONH₂, -SH, and-CONH-. Exemplary active hydrogen-containing compounds useful in the present invention, i.e., compounds containing isocyanate-reactive moieties, can include polyols, polyamines, polythiols, and polyacids. In a preferred embodiment, the isocyanate-reactive compounds useful in the present invention are polyol compounds; and in another preferred embodiment, the polyol compound may be a polyether polyol compound.

The adhesive formulation of the present invention may optionally contain at least one catalyst. Optional catalysts may be present in the isocyanate component (a) and/or the polyol component (b). Although catalysts are optional in the present invention, it is generally preferred that catalysts be present in the composition to promote the reaction of the polyol and isocyanate components. The catalyst may include, for example, one or more latent room temperature (about 25 ℃) organometallic catalysts. The latent room temperature organometallic catalyst may contain tin, zinc or bismuth. For example, the latent room temperature organometallic catalyst may include one or more catalysts from the group of: zinc alkanoates, bismuth alkanoates, tin dialkylalkanoates, tin dialkylmercaptides, tin dialkylbis (alkyl-mercaptoacetates), tin dialkylthioglycolates, or mixtures thereof.

In one embodiment, the catalyst useful in the present invention may be a tin-containing (or tin-based) latent room temperature organometallic catalyst, such as one or more of the foregoing catalysts selected from the group of: a tin dialkyl mercaptide, a tin dialkyl bis (alkylmercaptoacetate), a tin dialkyl thioglycolate, or a mixture thereof. For example, the latent tin-containing organometallic catalysts useful in the adhesive compositions of the present invention can include one or more tin-based catalysts selected from the group consisting of: tin dioctylsulfonate; dibutyl mercaptide (dibutyl mercaptide); dibutyl mercaptide; dibutyl mercaptide; bis (dodecylthio) dimethylstannane; dimethyl tin bis (2-ethylhexyl thioglycolate); a dioctyl carboxylate; tin dioctyl neodecanoate; and mixtures thereof.

Another catalyst that may be used in the adhesive formulation of the present invention includes, for example, any catalyst that may be further thermally activated (referred to as a "heat sensitive catalyst"). In one embodiment, such heat sensitive catalysts may include, for example, solid amine catalysts based on amines, such as one or more cyclic amidine catalyst compounds selected from the group of: 1, 8-diazabicyclo [5.4.0] undec-7-ene (DBU); 1, 5-diazabicyclo [4.3.0] non-5-ene; and mixtures thereof.

In another embodiment, the adhesive formulation of the present invention may include a combination of at least one of the above latent tin-containing catalysts and at least one of the above heat sensitive amine-based catalysts. Both tin-containing organic catalysts and amine-based catalysts can be readily formulated into isocyanate component (a), polyol component (b), or both isocyanate component (a) and polyol component (b) to form the 2K PU adhesives of the present invention.

In yet another embodiment, any non-tin-based metal-organic catalyst that exhibits similar curing kinetics/characteristics as the tin-based catalysts described above may be used as the catalyst component in the adhesive formulation of the present invention. For example, useful bismuth-based catalysts can include bismuth (III) neodecanoate; and useful zinc-based catalysts can include zinc neodecanoate; and mixtures of these catalysts.

In yet another embodiment, the non-tin-based catalyst or non-amine-based catalyst useful in the present invention may comprise a carboxylic acid blocked catalyst, such as a DBU carboxylic acid blocked catalyst. For example, DBU carboxylic acid blocked catalysts useful in the present invention can include TOYOCAT DB41 (DBU salts of carboxylic acids available from Tosoh corporation (TOSOH)), POLYCAT SA-102/10 (DBU salts of carboxylic acids available from Air Products), and mixtures thereof. Other catalysts useful in the present invention may include acid blocked amines, including, for example, catalysts based on tertiary amines and organic acids, such as TOYOCAT DB40, TOYOCAT DB60, and TOYOCAT DB70 available from tokoa; 1H-1, 2, 4-triazole based amine catalysts such as TOYOCAT DB30 available from Tosoh corporation; and mixtures thereof. Any other known heat sensitive amine catalyst may also be used in the present invention, such as TOYOCAT F22 available from Tosoco; triethylenediamine (TEDA); etc.; and mixtures thereof. In a preferred embodiment, the catalyst useful in the present invention may be selected from, for example, tin catalysts, such as tin di-n-octylbis [ isooctylmercaptoacetate ]; amine catalysts, such as POLYCAT SA1/10, and TOYOCAT DB 60; and mixtures thereof.

Generally, the amount of catalyst in the adhesive formulation may be in one embodiment from about 0.005 wt% to about 2.0 wt%, based on the total weight of the components in the formulation; from about 0.01 wt% to about 1.0 wt% in another embodiment; and in yet another embodiment from about 0.015 wt.% to about 0.065 wt.%. In one illustrative embodiment, for example when a tin catalyst such as di-n-octylbis [ isooctylmercaptoacetate ] tin is used in the adhesive formulation, the concentration of such catalyst in the formulation may be in one embodiment from about 0.005 wt% to about 1.0 wt% based on the molecular weight of the tin catalyst di-n-octylbis [ isooctylmercaptoacetate ] tin; from about 0.02 wt% to about 0.08 wt% in another embodiment; and in yet another embodiment from about 0.03 wt.% to about 0.05 wt.%.

In another illustrative embodiment, for example, when a heat-sensitive amine catalyst such as POLYCAT SA1/10 is used in the adhesive formulation, the concentration of such catalyst in the formulation may be from about 0.01 wt% to about 2.0 wt% in one embodiment, based on the molecular weight of POLYCAT SA 1/10; from about 0.01 wt% to about 1.0 wt% in another embodiment; and in yet another embodiment from about 0.015 wt.% to about 0.025 wt.%.

In yet another illustrative embodiment, for example, when a catalyst such as TOYOCAT DB60 is used in the adhesive formulation, the concentration of such catalyst in the formulation may be from about 0.01 wt% to about 2.0 wt% in one embodiment, based on the molecular weight of TOYOCAT DB 60; from about 0.01 wt% to about 1.0 wt% in another embodiment: and in yet another embodiment from about 0.045 wt.% to about 0.065 wt.%.

If the concentration of catalyst is below about 0.005 wt%, the catalyst used may not have effective activity in the formulation and the storage stability of the resulting formulation may be "poor", i.e., any residual water present in the formulation, for example, may deactivate small amounts of catalyst. If the concentration of the catalyst exceeds about 2.0 wt%, the reaction of the components present in the formulation may be too fast, resulting in short open times, i.e., open times of less than about 3 minutes, for example, may occur. In addition, high catalyst levels in the formulation (e.g., > about 2.0 wt%) can result in increased handling and formulation costs of the resulting formulation.

The adhesive formulation of the invention may optionally contain at least one filler. The optional filler may be at least one particulate filler. The particulate filler is a solid material at room temperature and is insoluble in the other ingredients of the polyol component (b) or the isocyanate component (a) or any of them. Fillers are materials that do not melt, volatilize, or degrade under the conditions of the curing reaction between the polyol and isocyanate components. The filler may be, for example, an inorganic filler such as glass, silica, boron oxide, boron nitride, titanium oxide, titanium nitride, fly ash, calcium carbonate, and various aluminum silicates (including clays such as wollastonite and kaolin), and the like; metal particles such as iron, titanium, aluminum, copper, brass, bronze, etc.; thermosetting polymer particles such as polyurethane, cured particles of epoxy resin, phenol-formaldehyde or cresol-formaldehyde resin, crosslinked polystyrene, or the like; thermoplastics such as polystyrene, styrene acrylonitrile copolymers, polyimides, polyamide-imides, polyetherketones, polyetheretherketones, polyethyleneimines, poly (p-phenylene sulfide), polyoxymethylene, polycarbonates, and the like; and various types of carbon such as activated carbon, graphite, carbon black, etc.; and mixtures thereof.

In one general embodiment, the particulate filler may be in the form of particles having a size of about 50 nanometers (nm) to about 100 micrometers (μm). In other embodiments, the filler may have a particle size (d50) of about 250nm or greater in one embodiment, about 500nm or greater in another embodiment, and about 1 μm or greater in yet another embodiment. In other embodiments, the filler may have a particle size (d50) of about 50 μm or less in one embodiment, about 25 μm or less in another embodiment, and about 10 μm or less in yet another embodiment. The particle size of particles having a size below about 100nm is conveniently measured using dynamic light scattering or laser diffraction methods.

In some embodiments, the particulate filler particles may have an aspect ratio of up to about 5 in one embodiment, up to about 2 in another embodiment, and up to about 1.5 in yet another embodiment. In other embodiments, some or all of the filler particles may be grafted to one or more polyether polyols of the polyol component (b).

Generally, in one embodiment, when a filler is present in the adhesive formulation, the filler comprises no more than about 80 wt% of the total weight of the adhesive formulation. In other embodiments, the amount of filler present in the adhesive formulation may generally be from about 0.1 wt% to about 80 wt% in one embodiment, based on the total weight of the components in the formulation; from about 0.1 wt% to about 70 wt% in another embodiment; from about 0.1 wt% to about 60 wt% in yet another embodiment; from about 0.1 wt% to about 50 wt% in yet another embodiment; from about 0.1 wt% to about 40 wt% in even yet another embodiment; from about 0.1 wt% to about 30 wt% in even yet another embodiment; from about 0.1 wt% to about 25 wt% in even yet another embodiment; and in even yet another embodiment from about 0.1 wt% to about 20 wt%.

Optional fillers may be present in the isocyanate component (a) and/or the polyol component (b). For example, in one illustrative embodiment of the present invention, the filler may be carbon black, and a predetermined concentration of carbon black may be present in isocyanate component (a). When carbon black is present in isocyanate component (a) and no other fillers are present, the carbon black filler may comprise, for example, in one embodiment, from about 1 wt% to about 50 wt% of isocyanate component (a), based on the weight of isocyanate component (a); from about 2 wt% to about 40 wt% in another embodiment; from about 5 wt% to about 30 wt% in yet another embodiment; and in yet another embodiment from about 10 wt% to about 25 wt%.

In another illustrative embodiment of the present invention, a predetermined concentration of filler may be present in the polyol component (b). When present in the polyol component (b), the filler may comprise, for example, in one embodiment, from about 1 wt% to about 80 wt% of the polyol component (b), based on the weight of the polyol component (a); from about 5 wt% to about 70 wt% in another embodiment; from about 10 wt% to about in yet another embodiment

60 wt%; and in yet another embodiment from about 20 wt% to about 60 wt%.

The filler present in the polyol component (b) may be the same as the filler in the isocyanate component (a); or the filler present in the polyol component (b) may be different from the filler in the isocyanate component (a). For example, in one preferred embodiment, the carbon black filler may be used in isocyanate component (a) at a concentration of, for example, about 15 wt% to about 20 wt%; and calcined clay, calcium carbonate or talc may be used in the polyol component (b) in an amount of, for example, about 30 wt% to about 60 wt%. The filler can be readily formulated into the isocyanate component (a), the polyol component (b), or both the isocyanate component (a) and the polyol component (b) to form the 2K PU adhesives of the present invention.

The adhesive formulation of the present invention may further comprise one or more other optional components that may be present in the polyol component (b) and/or the isocyanate component (a). For example, another optional ingredient useful in the present invention may include one or more dispersing aids that wet the surface of the filler particles and aid in their dispersion into the one or more polyether polyols. These may also have a viscosity-reducing effect. Among these dispersing aids are, for example, various dispersants sold under the trade names BYK, DISPERBYK and ANTI-TERRA-U by BYK Chemie, such as the alkylammonium salts of low molecular weight polycarboxylic acid polymers and salts of unsaturated polyamine amides and low molecular weight acidic polyesters, and fluorinated surfactants, such as FC-4430, FC-4432 and FC-4434 from 3M (3M Corporation). When present in the polyol component (b), the above dispersing aids may, for example, constitute up to about 2 wt% of the polyol component in one embodiment and up to about 1 wt% of the polyol component in another embodiment.

Another useful optional ingredient useful in the present invention, particularly when used in the polyol component (b), may include desiccants such as fumed silica, hydrophobically modified fumed silica, silica gels, aerogels, various zeolites, molecular sieves, and the like; and mixtures thereof. For example, when present in component (b), the one or more drying agents may be present in about 1 wt% or more in one embodiment, about 5 wt% or less in another embodiment, and about 4 wt% or less in yet another embodiment, based on the weight of the polyol component. In another embodiment, a drying agent may not be present in the polyol component or the adhesive composition.

Optionally, the adhesive formulations of the present invention may be formulated with a variety of other optional additives to achieve specific functional properties while maintaining the superior benefits/characteristics of the present adhesive products. For example, in one embodiment, optional additives that may be used in the formulation may include gas scavengers and water scavengers to avoid additional water absorption by the adhesive and to avoid NCO-water reactions. CO due to the reaction of NCO with Water₂The release, such unwanted reaction may lead to bubble formation in the adhesive.

In another embodiment, compatibilizers may be used in the formulation to further improve wetting properties and to improve mixing between the polyol component (b) and the isocyanate component (a).

In yet another embodiment, chemical rheology modifiers may be used in the formulation. In general, for example, different grades of polyamines having different molecular weights and functionalities can be used in the present inventionA compound (I) is provided. In one embodiment, the polyamine compound includes, for example, any one or more of the following compounds: jeffamine T403 trimer with molecular weight of 403g/mol, Jeffamine D400 dimer with molecular weight of 400g/mol, Jeffamine D200 dimer with molecular weight of 200g/mol, and mixtures thereof. Chemical rheology modifiers may be used in the present invention to provide rapid initial gelation of the formulation, which in turn provides the benefit of good sag resistance. Furthermore, the rapid increase in viscosity after curing the formulation reduces the formation of CO during thermally accelerated curing₂The risk of (c). Additional optional compounds or mixtures of additives may be added to the adhesive formulations of the present invention as desired.

When used in adhesive formulations, the optional components may be present in an amount generally in one embodiment from 0 wt% to about 15 wt%; from about 0.1 wt% to about 10 wt% in another embodiment; and in yet another embodiment from about 1 wt% to about 5 wt%. In a preferred embodiment, when molecular sieves are used, the amount of molecular sieve can be, for example, from about 1 wt% to about 5 wt%. In another preferred embodiment, when an amine product such as Jeffamine product is used, the amount of Jeffamine can be, for example, from about 0.1 wt% to about 2 wt%.

In one broad embodiment, the method for preparing the 2K PU adhesive formulation of the present invention includes providing at least one isocyanate component (a) and providing at least one polyol component (b) as described above. In preferred embodiments, the polyol component (b) comprises (bi) at least one first polyol compound; (bii) at least one second polyol compound having a functionality > about 2 and an EW < about 200; and (biii) at least one chain extender having about 2 hydroxyl groups (OH) and an EW < about 200. When the adhesive of the present invention is ready for use in bonding substrates together, the above components (a) and (b) may be mixed, blended or blended together, producing a reaction product when the combination of components (a) and (b) cures. One or more additional optional components may be added to the formulation as desired. For example, at least one catalyst and/or at least one filler may be added to the adhesive formulation in component (a), component (b), or both, before components (a) and (b) are mixed together or after components (a) and (b) are mixed together.

Although the amount of isocyanate component (a) and the amount of polyol component (b) that may be used to make the reaction product that makes up the adhesive formulation may vary, once the isocyanate component (a) and the polyol component (b) are formulated (separately and individually) and the two components are ready to be combined to form the reaction product adhesive, the isocyanate component (a) and the polyol component (b) are generally mixed in a 1: 1 volume ratio. For example, the ratio of isocyanate component (a) to polyol component (b) may be from about 198: 2 to about 2: 198 in one embodiment, from about 195: 5 to about 5: 195 in another embodiment, from about 10: 190 to about 190: 10 in yet another embodiment, from about 20: 180 to about 180: 20 in yet another embodiment, and from about 70: 130 to about 130: 70 in even yet another embodiment; from about 80: 120 to about 120: 80 in even yet another embodiment; from about 90: 110 to about 110: 90 in yet another embodiment; from about 95: 105 to about 105: 95 in yet another embodiment; and in even yet another embodiment from about 98: 102 to about 102: 98. If the concentration ratio of isocyanate component (a) to polyol component (b) is outside the range of about 198: 2 to about 2: 198, the adhesive formulation may not exhibit effective adhesion or the adhesion may be poor or no adhesion. If the concentration ratio of isocyanate component (a) to polyol component (b) is outside the range of about 198: 2 to about 2: 198, the formulation may not exhibit good mechanical or good rheological properties; and/or large amounts of NCO may form in the formulation, which may disadvantageously result in the product becoming brittle, i.e. the product has a low elongation at break.

When component (a) and component (b) are made separately and individually, the desired ingredients and optional ingredients can be mixed together at the desired concentrations discussed above and in one embodiment at a temperature of from about 5 ℃ to about 80 ℃, in another embodiment from about 10 ℃ to about 60 ℃, and in yet another embodiment from about 15 ℃ to about 50 ℃. In a preferred embodiment, mixing the above ingredients to form components (a) and (b) may be performed under vacuum. The order of mixing of the ingredients is not critical, and two or more compounds may be mixed together, with the remaining ingredients subsequently added. The binder formulation ingredients that make up components (a) and (b) may be mixed together by any known mixing method and apparatus.

In another broad embodiment, the invention includes a method of bonding two substrates, the method comprising forming a 2K PU adhesive layer at a bonding interface (bondline) between the two substrates, and curing the layer at the bonding interface to form a cured adhesive bonded to each substrate. For example, the method may include combining the isocyanate component (a) and the polyol component (b) of a two-component polyurethane adhesive, forming an adhesive layer at a bonding interface between two substrates to form an assembly, partially curing the adhesive layer at the bonding interface by applying heat or infrared radiation to a portion of the assembly, and completing the curing of the adhesive layer in a subsequent and separate curing step.

The application of the 2K PU adhesive to the substrates to be bonded together can be carried out by any known apparatus, such as a metering/mixing/dispensing apparatus, which can apply predetermined amounts of the isocyanate component (a) and the polyol component (b) in combination (as an adhesive) to selected portions of the substrates. For example, in an automotive manufacturing process, components (a) and (b) are provided in two separate tank vessels of several gallon size. Component (a) is then withdrawn from one tank and component (b) is simultaneously withdrawn from the other tank and the two streams are combined together as a combined adhesive component using known static or dynamic mixers and applied to a substrate. The partial curing step may be performed by curing only the one or more predetermined localized portions of the adhesive layer at the bonding interface by applying heat to only the one or more predetermined localized portions of the assembly to produce an adhesive layer having at least a partially cured portion and an uncured portion, and the uncured portion of the adhesive layer may then be cured in a subsequent and separate curing step.

In a preferred general embodiment, a method of bonding at least a first substrate to at least a second substrate may comprise the steps of: (1) contacting a polyol component (b) and an isocyanate component (a) as disclosed herein and mixing the components to form a homogeneous adhesive mixture; (2) applying the adhesive mixture to at least a portion of a first substrate; (3) contacting a second substrate with the first substrate such that the mixture is disposed between the first and second substrates forming a bonding interface; and (4) exposing at least a portion of the mixture to heat under conditions such that the mixture is partially fully cured such that the first and second substrates are sufficiently bonded (i.e., have sufficient strength) such that the substrates can move. The method may further optionally comprise step (5): the two partially cured substrates are heated at a temperature and for a time to fully cure the mixture to bond the two substrates together. The heat may be applied in step (4) by any known heating means, such as by infrared heating. The time between steps (4) and (5) may be about 1 hour or more in one embodiment, and about 24 hours or more in another embodiment; and in still other embodiments any time between the above two time periods or longer.

By curing the 2k PU adhesive composition of the present invention, a structure is formed comprising two or more substrates bonded together with a cured adhesive based on the curable adhesive composition disclosed herein, wherein the cured adhesive is disposed between portions of each substrate. In one embodiment, the substrate may comprise a dissimilar substrate, i.e., a substrate of a different material selected from materials such as metal, glass, plastic, thermoset resin, fiber reinforced plastic, or mixtures thereof. In a preferred embodiment, one or both of the substrates may be fiber reinforced plastic.

One of the advantages of the formulations of the invention is that good waiting times can be achieved while maintaining the mechanical properties of the formulations. While other methods of increasing the waiting time have been previously attempted, such as by using other ingredients (e.g., Voranol 280), such previous attempts have resulted in sacrificing the mechanical properties of the adhesive, e.g., achieving an elongation at break of < about 150%. On the other hand, in one embodiment, the formulation of the present invention can achieve long open time > about 8min, high lap shear strength after 1h RT > about 2MPa, with elongation at break > about 150%.

The adhesive formulations of the present invention produced by the methods of the present invention have several advantageous properties and benefits compared to conventional adhesive formulations. For example, some properties exhibited by adhesive formulations may include increased waiting times, longer open times, and faster build up of handling strength.

For example, the adhesive exhibits a longer open time, and the open time may typically be > about 8min in one embodiment, > about 9min in another embodiment, and > about 10min in yet another embodiment. In other embodiments, the formulations of the present invention may exhibit an open time of > about 8min to about 20min in one embodiment; from about 9min to about 20min in another embodiment; and in yet another embodiment from about 10min to about 20 min.

In yet another embodiment, the handling strength build of the adhesive formulation of the present invention, as measured by lap shear strength after 1h RT, can be generally > about 1MPa, in another embodiment > about 1.5MPa, and in yet another embodiment > about 2 MPa. In still other embodiments, the lap shear strength of the adhesive formulation after 1h RT may be from about 1MPa to about 4MPa in one embodiment, from about 1.5MPa to about 4MPa in another embodiment, and from about 2MPa to about 3MPa in another embodiment.

The adhesive formulations of the present invention may also exhibit an elongation at break of > about 150% in one embodiment, in another embodiment > about 170%, and in yet another embodiment > about 200%. In other embodiments, the elongation at break of the adhesive formulation may be, for example, > about 150% to < about 600%, in another embodiment > about 150% to about 300%, and in yet another embodiment about 170% to about 200%.

The 2K polyurethane adhesives of the invention are useful, for example, for bonding together: a composite material; coated metals such as electron coated steel, electron coated aluminum, and the like; and Sheet Molding Compounds (SMC); and mixtures of such materials.

Examples of the invention

The following examples are given to illustrate the invention in further detail but are not to be construed as limiting the scope of the claims. All parts and percentages are by weight unless otherwise indicated.

The various raw materials used in the examples are explained below:

desmodur N3400, available from Corsai, is an aliphatic polyisocyanate compound based on hexamethylene diisocyanate.

Isonate M143 is a liquefied MDI having a functionality of 2.2 and a viscosity of 40 mPa-s. Isonate M143 is available from the Dow chemical company (Dow).

Metatin T713 is a tin-based dibutyl tin mercaptide catalyst; and is available from ACIMA corporation.

Di-n-octylbis [ isooctylmercaptoacetic acid ] tin, tin-based dioctyltin mercaptide catalyst.

POLYCAT SA-1/10 is a solid amine catalyst based on solid DBU (1, 8-diazabicyclo [5.4.0] undec-7-ene) with a phenolic counterion; and is available from ACIMA corporation.

Voranol 2000L is a polypropylene homopolymer having an average molecular weight of 1,000 g/mol and an OH number of about 55 mgKOH/g; and is available from the dow company.

Voranol CP4610 is a glycerol-initiated propoxylated triol based on ethylene oxide having an average molecular weight of 1, 800g/mol and an OH number of about 35mg KOH/g; and is available from the dow company.

1, 4-butanediol is available from Arco Chemical and distributed by Schweizer hallChemie.

Polestar 200R is a mean particle size of about 2 microns (. mu.m) (90% > 10 μm) and a BET surface area of 8.5m²Calcined china clay (55% SiO) in a pH range of 6.0 to 6.5/g₂，45％Al₂O₃). Polestar 200R is available from England porcelain Inc. (IMERYS).

Aerosil R202 is a hydrophobically modified polydimethylsiloxane coated fumed silica; and are available from winning Industries, inc (Evonik Industries).

Printex 30 is a carbon black filler commercially available from Alzchem chemical company.

Toyocat DB60 is a catalyst based on the salts of tertiary amines with organic acids; and is commercially available from Tosoh corporation.

Vestinol 9 is 100% diisononyl phthalate and is used as plasticizer in the T-715 prepolymer technique; and is available from winning companies (Evonik).

Voranol280 is a sucrose-initiated oxypropylene-oxyethylene polyol compound with a hydroxyl number of 280, a functionality of 7, a molecular weight of 400g/mol, and an EW of 200. Voranol280 is available from the Dow company.

VORAFORCE^TM5300 is a dow resin grade for producing carbon fiber reinforced Composite (CFRP) parts in an RTM process.

BETAWIPE^TM4800 is a solvent-based adhesion promoter available from the Dow Automotive Systems service.

Test method

The following tests were performed according to procedures known to those skilled in the art.

Time of airing

Adhesive beads of 30cm to 50cm in length were manually extruded onto polyethylene foil. Manual application of the 2K polyurethane adhesive is effected by means of a double-barrel application gun, such as, for example, a stationary static mixer unit having a diameter of 8 millimeters (mm) or 10mm and 24 mixing elements and applying a pressure of at least 6 barAnd TS 400. The applied adhesive bead was continuously compressed with a spatula until the adhesive no longer adhered to the wooden surface of the spatula. Defining the time of measurement as adhesive"open time".

Reactivity

The reactivity of the 2K PU adhesives was measured by rheology in oscillation mode with parallel plates 20mm in diameter and 1mm apart. The reactivity measurement was carried out at 10Hz with a constant deformation of 0.062%. Plotting complex viscosity versus time; and the time at which the viscosity slope changes by more than 30 ° is considered "reactive".

Shear strength

The shear strength measurements are carried out according to DIN EN 1465 (7 months 2009) on a suitable shear strength measuring device, such as, for example, a shear strength device Zwick 1435 with a FHM 8606.00.00 or 8606.04.00 mounting device. The e-coated substrate was a Cathoguard 500 e-coated steel sheet with the following dimensions: 100 mm. times.25 mm. times.0.8 mm. By using BETACCLEAN^TM3350 (heptane) cleaning solvent solution cleans the electronically coated substrate. The flash time of the solvent after cleaning before adhesive application was 5 min. The CFRP substrate is from DOW CFRP VORAFORCE^TM5300 VORAFORCE having the following dimensions^TMGrading plate: 100 mm. times.45 mm. times.2.2 mm. CFRP substrates can be ground or used without cleaning or mechanical pretreatment. When polishing was performed, the polishing was performed manually on a wet CFRP plate using a 320-polishing pad until a uniform optical appearance was obtained. The plates were dried continuously at 80 ℃ for 8 hours. Adhesive bond sizes of 10mm by 25mm by 1.5mm were used for lap shear samples. Lap shear samples were tested after a curing time of 1 hour at 23 ℃/50% relative humidity (r.h.) or after the thermally accelerated curing process described below, respectively.

Tensile test

Tensile testing was performed on 7 day RT-cured 2mm thick plates (called Dogbones 5A) according to the test described in DIN 527-2 (6 months 2012).

Examples 1 and 2 and comparative examples A-C

The open time of the adhesive compositions of comparative examples a to C and examples 1 and 2 was measured by the rheological reactivity test described above. With electron-coated steel substrates

Lap shear strength was measured at 1 hour and 7 days RT. The bonding dimension is 15mm multiplied by 25mm

1.5 mm. Tensile testing was performed on the Dogbones 5A test specimens as described above. The results of the tests performed on the Dogbones 5A samples using various adhesives are described in table I.

Comparative example A contained 49 wt% trifunctional Voranol CP4610 and 5 wt% 1, 4-butanediol as chain extender. Comparative example a contained no Voranol280 or glycerol component. In contrast, Voranol CP4610 in comparative example a will form a soft segment when the polyol component (PolC) is reacted with the isocyanate component (IsoC). Also, when PolC reacts with IsoC, 1, 4-butanediol will form hard segments. Although the results in the table describe that comparative example a exhibited good elongation at break (244%), the 1h RT lap shear strength was only 1.23MPa and the open time (or tack free time) was only 8 min.

The presence of high functional polyol compounds (e.g., Voranol 280) in the adhesive formulation may result in improved waiting times as indicated by longer open time and higher 1h RT lap shear strength, but the use of high functional polyol compounds (e.g., Voranol 280) may compromise the mechanical properties of the adhesive formulation with such polyol compounds. For example, comparative example B contains 5 wt% Voranol280 and comparative example C contains 10 wt% Voranol 280. Also, the 1, 4-butanediol content in the formulations of comparative example B and comparative example C was 4 wt% (comparative example B) and 3 wt% (comparative example C). Incorporation of Voranol280 in the adhesive formulations of comparative examples B and C resulted in adhesives exhibiting longer open times and higher 1h RT lap shear strength. However, when Voranol280, in particular more than 5 wt% of Voranol280, is added to the composition of the comparative example, the mechanical properties are significantly reduced, as indicated by a reduced elongation at break of 144% (see comparative example B) and 102% (see comparative example C). It has been surprisingly found that when the chain extender 1, 4-butanediol is replaced with a small molecular weight 3-functional polyol compound such as glycerol, the latency of the formulation is improved while the elongation at break of the adhesive is maintained at a high level (e.g., > 150%), as exhibited by the formulations of the present invention (see examples 1 and 2). This can be attributed to the fact that: glycerol has a similar molecular weight to 1, 4-butanediol but a higher functionality; and, therefore, higher functionality is incorporated into the hard segments.

Example 1 contains 4 wt% 1, 4-butanediol and 0.7 wt% glycerol. The open time of the adhesive of example 1 was 9.5min, which was longer than the open time of comparative examples a and B. Additionally, the 1-hr RT lap shear strength of example 1 was 2.1MPa, which was higher than the 1-hr RT lap shear strength of comparative examples A and B. The elongation at break of the adhesive of example 1 was 171%, which is significantly higher than the elongation at break of comparative examples B and C.

Example 2 contains 3 wt% 1, 4-butanediol and 1.4 wt% glycerol. The open time of the adhesive composition of example 2 was 13min, much longer than the open time of comparative examples A, B and C. Additionally, the 1-hr RT lap shear strength of the adhesive formulation of example 2 was 2.98MPa, which was higher than the 1-hr RT lap shear strength of comparative examples A, B and C. The elongation at break of the adhesive of example 2 was 158%, which was higher than the elongation at break of comparative examples B and C. The results described in table I show that the use of a trifunctional chain extender such as glycerol unexpectedly improves the latency of the adhesive composition while maintaining the good elongation at break characteristics of the adhesive composition.

Table I-adhesive composition and performance data