POLYPROPYLENE BONDING ADHESIVE AND PROCESS

Abstract

A two-part polyurethane adhesive exhibits excellent adhesion to low surface energy substrates such as polypropylene. The adhesive consists of a polyol component and a polyisocyanate component that are combined and cured to form the adhesive bond. The polyol component is characterized in containing a monoalcohol that has a molecular weight of 100 to 2000. The presence of the monoalcohol promotes strong bonding and a cohesive failure mode that is preferred in vehicular applications.

Claims

1. A two-component polyurethane adhesive composition having a polyol component and an isocyanate component, wherein: the polyol component comprises: a) at least 15 weight percent, based on the weight of the polyol component, of one or more polyether polyols each having a nominal hydroxyl functionality of at least 2 and a hydroxyl equivalent weight of 400 to 2000, and each being selected from homopolymers of propylene oxide and copolymers of 70 to 99% by weight propylene oxide and 1 to 30% by weight ethylene oxide, the one or more polyether polyols a) having an average nominal hydroxyl functionality of 2 to 4; b) 0 to 10 weight percent, based on the weight of the polyol component, of one or more polyether polyols each having a hydroxyl equivalent weight of 100 to 399, the one or more polyether polyols b) having an average nominal functionality of at least 4; c) 0 to 10 weight percent, based on the weight of the polyol component, of a polyol having a hydroxyl functionality of at least 2 and a hydroxyl equivalent weight of less than 100; d) 2 to 40 weight percent, based on the weight of the polyol component, of a monol having a molecular weight of 100 to 2000; e) 0 to 3 parts by weight per 100 parts by weight of a) of at least one compound having at least two primary and/or secondary aliphatic amine groups; f) a catalytically effective amount of at least one urethane catalyst; and g) 5 to 60 weight percent, based on the weight of the polyol component, of at least one particulate filler; and the polyisocyanate component comprises at least one organic polyisocyanate and 0 to 50% by weight, based on the total weight of the polyisocyanate component, of at least one particulate filler.

2. The two-component polyurethane adhesive of claim 1 wherein component d) is prepared by alkoxylating an aliphatic alcohol having the structure A-OH, wherein A represents a hydrocarbyl group.

3. The two-component polyurethane adhesive of claim 1 wherein component d) is represented by the structure A-B—OH, wherein A represents a C4-20 straight-chain aliphatic hydrocarbyl group and B represents a polyether chain.

4. The two-component polyurethane adhesive of claim 1 wherein component d) has a molecular weight of 700 to 1500.

5. The two-component polyurethane adhesive of claim 1 wherein the polyol component contains 4 to 20 weight percent of component d), based on the weight of the polyol component.

6. The two-component polyurethane adhesive of claim 1 wherein the polyol component contains 2 to 10 weight percent of component b), based on the weight of the polyol component.

7. The two-component polyurethane adhesive of any claim 1 wherein the polyol component contains 0.25 to 3 weight percent of component c), based on the weight of the polyol component.

8. A method of bonding two substrates, comprising combining the polyol and polyisocyanate components of the two-component polyurethane adhesive of claim 1 to form an uncured adhesive, forming a layer of the uncured adhesive at a bondline between two substrates, and curing the uncured adhesive layer at the bondline to form a cured adhesive bonded to each of the substrates.

9. The method of claim 8 wherein the isocyanate index is 1.1 to 1.8.

10. A method of bonding a polypropylene substrate to a second substrate, comprising: I) combining the polyol and polyisocyanate components of the two-component polyurethane adhesive of claim 1 to form an uncured adhesive without previously applying a primer to the polypropylene substrate, forming a layer of the uncured adhesive at a bondline between polypropylene substrate and the second substrates, and II) curing the uncured adhesive layer at the bondline to form a cured adhesive bonded to the polypropylene substrate and the second substrate.

11. The method of claim 10 wherein the polypropylene substrate has a surface energy of no more than 75 mN/m.

12. The method of claim 11 wherein the polypropylene substrate has a surface energy of 30 to 65 mN/m.

13. The method of claim 10 wherein the polypropylene substrate is, prior to step I), flame- or plasma-treated.

14. The method of claim 10 wherein no primer is applied to the polypropylene substrate prior to step I.

Description

EXAMPLES 1-5 AND COMPARATIVE SAMPLES A-B

[0095] Comparative Sample A is made from the following formulation:

TABLE-US-00001 TABLE 1 Ingredient Parts By Weight Polyol Component Polyol A 32.1 Polyol B 3.5 Polyamine 0.5 Catalyst A 0.15 Catalyst C 0.25 Filler Mixture 58 Dessicant 5.5 Polyol Component Total Weight 100 Polyisocyanate Component Polyisocyanate 98

[0096] The polyol component is made by combining the listed ingredients at room temperature and thoroughly mixing.

[0097] Comparative Sample B has the same composition as Comparative Sample A, except 2 parts of the Epoxy Silane are added to the Polyisocyanate Component.

[0098] Example 1 has the same composition as Comparative Sample A, except 7 parts of Polyol A are replaced with an equal weight of Monol 1, as indicated in Table 2.

[0099] Examples 2-5 have the same composition as Comparative Sample B, except varying amounts of Polyol A are replaced with an equal weight of Monol 1, as indicated in Table 2.

[0100] Each of Comparative Samples A and B and Examples 1-5 are evaluated as adhesives for flame-treated talc-filled polypropylene and for flame-treated glass fiber-filled polypropylene. The talc-filled polypropylene is an injection molding grade polypropylene containing 30-40% talc, based on total product weight. The glass-filled polypropylene is a long-glass filled injection molding grade polypropylene containing 30% glass fibers, based on total product weight. In each case, the polypropylene is formed into a 2 mm thick foil and flame treated by passing the foil through an Arcotec Arcogas FTS101D flame treatment unit under conditions of air:propane ratio-25:1; conveyor belt speed-600 mm/s; distance of flame to substrate-60 mm; propane flow rate-2 L/min. This treatment raises the surface energy of the polypropylene samples from 28-30 mN/m to 40-60 mN/m, as determined by applying an alcoholic ISO 8296 testing ink provided by the equipment supplier.

[0101] Lap shear specimens are prepared by filling the polyol and polyisocyanate components into separate cartridges that are mounted onto a dual cartridge dispensing gun equipped with a 8-10 mm static mixer unit. The adhesive is dispensed onto one of a pair of flame treated talc-filled polypropylene or flame treated glass fiber-fillled polypropylene test specimens and formed into a 15×25×1.5 mm layer. No primer is applied to the substrates before forming the adhesive layer. The adhesive is cured for 3 days at room temperature (22-24° C.) and ambient humidity. Lap shear strength is then measured according to DIN EN 1465 (2009) using a Zwick 1435 tensile tester equipped with a FHM 860.00.00 or 8606.04.00 mounting device. In each case the adhesive is applied 15-240 minutes after the flame treatment. The samples are evaluated visually for failure mode, with debonding of the adhesive from one or both substrates indicating adhesive failure and tearing of the adhesive layer without separation of the adhesive from the substrate layers indicating cohesive failure.

[0102] Results are as indicated in Table 2.

TABLE-US-00002 TABLE 2 Comp. Comp. Property A* B* Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Wt. % Polyol A.sup.1 32.1 32.1 25.1 28.6 25.1 21.6 18.1 Wt. % Monol 1.sup.2 0 0 7 3.5 7 10.5 15 Wt. % Epoxy Silane.sup.3 0 2 0 2 2 2 2 Talc-Filled PP.sup.4 Lap Shear Str., MPa 3.71 3.26 3.23 3.10 2.57 2.24 1.96 Failure Mode.sup.6 65CF/ 95CF/ 97CF/ 100CF 100CF 100CF 100CF 35AF 5AF 3AF Glass-Filled PP.sup.5 Lap Shear Str., MPa 3.53 3.63 3.49 3.20 2.84 2.33 2.02 Failure Mode.sup.6 100AF 45CF/ 97CF/ 100CF 100CF 100CF 100CF 55AF 3AF *Not an example of the invention. .sup.1Wt.-% Polyol A based on total weight of polyol component. .sup.2Wt.-% Monol 1 based on total weight of polyol component. .sup.3Wt.-% epoxy silane based on total weight of polyisocyanate component. .sup.4Results on talc-filled polypropylene substrates. .sup.5Results on glass-filled polypropylene substrates. .sup.6CF is cohesive failure, AF is adhesive failure. The values indicate the percentage of bond surface area characterized by the respective mode of failure.

[0103] Comparative Sample A shows how the control adhesive fails in the undesired adhesive failure mode, particularly on the glass-filled polypropylene substrate. Comparative Sample B demonstrates that adding a coupling agent (epoxy silane) leads to a decrease in the adhesive failure mode in favor of the desired cohesive failure mode. However, the undesired failure mode with the glass-filled polypropylene substrates is close to 50%.

[0104] Example 1 demonstrates the effect of replacing a part of Polyol A with a monol. Essentially 100% cohesive failure mode is obtained on even the glass-filled polypropylene substrate, even in the absence of the epoxy silane coupling agent.

[0105] Examples 2-5 show 100% cohesive failure on both substrates when the epoxy silane coupling agent is included in the polyisocyanate component. These results are seen across a range of amounts of Monol 1, from 3.5 to 15% by weight of the polyol component. Some loss of lap shear strength is seen, as is to be expected due to the lower average hydroxyl functionality of the isocyanate-reactive materials in the polyol component; this leads to a reduced crosslink density in the cured adhesive.

EXAMPLES 6 AND 7

[0106] Examples 6 and 7 are made and tested in the same manner as previous examples. The adhesive formulations and test results are as indicated in Table 3.

TABLE-US-00003 TABLE 3 Ex. 6 Ex. 7 Ingredient Parts By Weight Parts by Weight Polyol Component Polyol A 25.1 25.1 Polyol B 3.5 3.5 Monol 2 7 0 Monol 3 0 7 Polyamine 0.5 0.5 Catalyst A 0.15 0.15 Catalyst C 0.25 0.25 Filler Mixture 58 58 Dessicant 5.5 5.5 Polyol Component Total Weight 100 100 Polyisocyanate Component Polyisocyanate 98 98 Epoxy Silane 2 2 Talc-Filled PP.sup.1 Lap Shear Str., MPa 2.51 2.64 Failure Mode.sup.3 100CF 100CF Glass-Filled PP.sup.2 Lap Shear Str., MPa 2.69 2.59 Failure Mode.sup.3 100CF 100CF .sup.1Results on talc-filled polypropylene substrates. .sup.2Results on glass-filled polypropylene substrates. .sup.3CF is cohesive failure, AF is adhesive failure. The values indicate the percentage of bond surface area characterized by the respective mode of failure.

[0107] As the data in Table 3 shows, the desired cohesive failure mode is seen with both of Examples 6 and 7, even on the glass-filled polypropylene adhesives.

EXAMPLES 8 AND 9

[0108] Examples 8 and 9 are made and tested in the same manner as previous examples. The adhesive formulations and test results are as indicated in Table 4.

TABLE-US-00004 TABLE 4 Ex. 8 Ex. 9 Ingredient Parts By Weight Parts by Weight Polyol Component Polyol A 28 24.07 Polyol B 2.5 4 Monol 1 0 7 Monol 4 5 0 1,4-butanediol 0.5 0 Catalyst A 0 0.18 Catalyst B 0.25 0 Catalyst C 0.25 0.25 Filler Mixture 58 59 Dessicant 5.5 5.5 Polyol Component Total Weight 100 100 Polyisocyanate Component Polyisocyanate 98 98 Epoxy Silane 2 2 Talc-Filled PP.sup.1 Lap Shear Str., MPa 2.82 Not done Failure Mode.sup.3 100CF Glass-Filled PP.sup.2 Lap Shear Str., MPa 3.05 2.48 Failure Mode.sup.3 100CF 100CF .sup.1Results on talc-filled polypropylene substrates. .sup.2Results on glass-filled polypropylene substrates. .sup.3CF is cohesive failure, AF is adhesive failure. The values indicate the percentage of bond surface area characterized by the respective mode of failure.

[0109] As the data in Table 4 shows, the desired cohesive failure mode is seen with both of Examples 8 and 9, even on the glass-filled polypropylene adhesives.