POLYURETHANE BASED HOT MELT ADHESIVE

Abstract

Hot melt adhesive including a randomly hydroxyl functionalized branched olefin copolymer has: number average molecular weight between 10 to 50 kg/mol, crystallinity content below 30%, enthalpy between 5 to 65 J/g, polydispersity index from 2 to 6, melting temperature between 40 and 120 C., optionally, more than two hydroxyl functionalities per polymer chain and consisting of at least 80 mol % of a unit of formula (1), optionally a unit of formula (2), and between 0.1 to 1 mol %, of a unit of formula (3):

##STR00001## wherein: R.sup.1 is H or CH.sub.3; R.sup.2 is a C.sub.0-10 hydrocarbyl group; R.sup.3 is a C.sub.2-10 hydrocarbyl group, and the hydroxyl functionalized olefin copolymer has undergone an addition reaction with a di-, tri-or polyisocyanates of formula (4):

OCNR.sup.4NCO).sub.n Wherein, R.sup.4 is a C.sub.1-10 hydrocarbyl group.

Claims

1. A polyurethane based hot melt adhesive comprising a randomly hydroxyl functionalized branched olefin copolymer having: a number average molecular weight (M.sub.n) between 10 to 50 kg/mol, measured according to the ISO 16014-4 and ASTM D6474 methods at 150 C. on a Polymer Char GPC-IR built around an Agilent GC oven model 7890 an enthalpy (H) between 5 to 65 J/g, measured according to ISO 11357-1:2016 using a Differential Scanning Calorimeter Q100 from TA Instruments, a polydispersity index (PDI) from 2 to 6, measured according to the method ISO 16014-4 and ASTM D6474 methods at 150 C. on a Polymer Char GPC-IR built around an Agilent GC oven model 7890, a melting temperature (T.sub.m) between 40 and 120 C., measured according to ISO 11357-1:2016 using a Differential Scanning Calorimeter Q100 from TA Instruments, at least two or more hydroxyl functionalities per polymer chain, and wherein the randomly hydroxyl functionalized branched olefin copolymer is at least partly crystalline and has a crystallinity (X.sub.c) level below 40% and above 1%, measured according to ISO 11357-1:2016 using a Differential Scanning Calorimeter Q100 from TA Instruments, and wherein the randomly hydroxyl functionalized branched olefin copolymer consists of: at least 80 mol % of a constituent unit represented by the following formula (1), optionally a constituent unit represented by the following formula (2), and between 0.1 to 1 mol %, of a constituent unit represented by the following formula (3): ##STR00005## wherein: R.sup.1 is H or CH.sub.3, R.sup.2 is a hydrocarbyl group having 0 to 10 carbon atoms, R.sup.3 is a hydrocarbyl group having 2 to 10 carbon atoms, and wherein the hydroxyl functionalized olefin copolymer has been undergone an addition reaction with a di-, tri-or poly-isocyanates represented by the following formula (4):
OCNR.sup.4NCO).sub.n wherein: R.sup.4 is hydrocarbyl group having 1 to 10 carbon atoms, and. n is 1 to 4.

2. The polyurethane based hot melt adhesive according to claim 1 wherein the constituent unit represented by the formula (3) is selected from the group consisting of 3-buten-1-ol, 3-buten-2-ol, 5-hexen-1-ol, 5-hexene-1,2-diol, 7-octen-1-ol, 7-octen-1,2-diol, 5-norbornene-2-methanol, and 10-undecen-1-ol.

3. The polyurethane based hot melt adhesive according to claim 1, wherein the polymerization has been performed using a solution process.

4. The polyurethane based hot melt adhesive according to claim 3, wherein a purification step consisting of removing traces of inorganic impurities, which remain in the resin after polymerization, has been performed prior the addition reaction.

5. The polyurethane-based hot melt adhesive according to claim 1, comprising the following cross-linked system ##STR00006## wherein z, z is 0.1 to 1 mol %, x, x is at least 80 mol %, y is 0 or 100(x+z) mol %, and y is 0 or 100(x+z) mol %, R.sup.1 is H or CH.sub.3, R.sup.2 is a hydrocarbyl group having 0 to 10 carbon atoms, R.sup.3 is a hydrocarbyl group having 2 to 10 carbon atoms, R.sup.4 is hydrocarbyl group having 1 to 10 carbon atoms, and n is 1 to 4.

6. A method comprising: applying the polyurethane based hot melt adhesive according to claim 1 to glue together metals, glass, polar polymers or metals to glass, metal to polar polymers, glass to polar polymers, metals to polyolefins, glass to polyolefins or polar polymers to polyolefins.

7. The polyurethane based hot melt adhesive according to claim 1, having at least one of the following binding properties measured according to the ASTM D1002-10(2019) with a Zwick type Z020 tensile tester equipped with a 10 kN load cell: steel to steel with a Lap Shear Strength above 3 MPa, aluminum to aluminum with a Lap Shear Strength above 3 MPa, or polyolefin to polyolefin with a Lap Shear Strength above 3 MPa.

8. The polyurethane based hot melt adhesive according to claim 1, having a storage modulus (E) at 20 C. above 115 MPa, and at 40 C. above 2030 MPa, measured according to the method described in the section Dynamic Mechanical Thermal Analysis (DMTA) of the present application, and a Loss modulus (E) at 20 C. above 17 MPa and at 40 C. above 36 MPa measured according to Dynamic Mechanical Thermal Analysis (DMTA).

Description

BRIEF DESCRIPTION TO THE DRAWINGS

[0032] FIG. 1 is the 1H NMR spectrum of EX1,

[0033] FIG. 2 is the 1H NMR spectrum of EX2,

[0034] FIG. 3 is the 1H NMR spectrum of EX3, and

[0035] FIG. 4 is the 1H NMR spectrum of EX4.

DETAILED DESCRIPTION

[0036] The present invention preferably relates to a polyolefin-based hot melt adhesive resin comprising hydroxyl functionalities that are reacted with di-tri-or poly-isocyanates to form a cross-linked system.

[0037] Besides the known high adhesive strength of polyurethane adhesives, the polyolefin-based polyurethane hot melt adhesives of the invention are expected to provide excellent durability due to the high water barrier of the polyolefins. Using relatively high molecular weight randomly branched hydroxyl-functionalized olefin copolymer resins, the corresponding polyurethane hot melt adhesive will not only show good adhesion to polar substrates such as metals, glass and polar polymers, but also to low surface energy materials such as polyolefins.

[0038] To ensure a well-crosslinked system that will guarantee strong bonding to various substrates, it is preferably that the randomly hydroxyl functionalized branched olefin copolymer contain more than two hydroxyl functionalities per polymer chain. In a preferred embodiment, the randomly hydroxyl functionalized branched olefin copolymer contains at least two or more hydroxyl functionalities per polymer chain.

[0039] According to the invention, the polyolefin-based hot melt adhesive resin comprises a copolymer of at least one first olefin monomer and a hydroxyl functionalized C.sub.2 to C.sub.12, preferably C.sub.4 to C.sub.12, more preferably C.sub.4 to C.sub.10 olefin monomer, which has been undergone an addition reaction with a di-, tri-or poly-isocyanates resulting in to a cross-linked system according to formula (5):

##STR00003##

wherein [0040] z, z is 0.1 to 1 mol %, [0041] x, x is at least 80 mol %, [0042] y is 0 or 100(x+z) mol %, and y is 0 or 100(x+z) mol %, [0043] R1 is H or CH3, [0044] R2 is selected from the list comprising: hydrocarbyl group having 0 to 10 carbon atoms, preferentially 2 to 6 and more preferentially 6 when R.sup.1H, and preferably 0, 2 or 4 when R.sup.1CH.sub.3, [0045] R.sup.3 is a hydrocarbyl group having 2 to 10 carbon atoms, preferentially 2 to 8, preferentially 4 to 8, more preferentially 4 or 6, [0046] R.sup.4 is hydrocalbyl group having 1 to 10 carbon atoms, [0047] n is 1 to 4, preferentially 1 to 2, more preferentially 1.

[0048] In some embodiment, due to the nature of the environmental reaction, not all the hydroxyl group present in the copolymer have reacted with an isocyanate functionality, preferably at least 40% of the OH groups have been reacted, preferably more than 50%.

[0049] As not all the hydroxyl group present in the copolymer react, in some embodiment, it is preferred to have more than 2 hydroxyl functionalities per polymer chain to ensure efficient cross-linking.

[0050] In some embodiment, the first olefin monomer is ethylene or propylene, preferably propylene.

[0051] In some embodiment, the hot melt adhesive resin according to the invention is a polyolefin-based copolymer, preferably a terpolymer resulting from the polymerization of a first olefin monomer, with optionally a second olefin monomer selected from the list comprising ethylene or C.sub.3 to C.sub.12 olefin monomer and a thirdfunctionalizedolefin monomer, which is selected from the list comprising a hydroxyl functionalized C.sub.2 to C.sub.12, preferably C.sub.4 to C.sub.12 olefin monomer.

[0052] In a preferred embodiment, the second olefin monomer is non-functionalized, non-activated olefin monomer, meaning an olefin monomer only consisting of carbon and hydrogen atoms.

[0053] In some embodiment, when the first olefin monomer is ethylene, preferably the second olefin monomer is 1-butene, 1-hexene or 1-octene.

[0054] In some embodiment, when the first olefin monomer is propylene, preferably the second olefin monomer is ethylene, 1-butene, 1-hexene or 1-octene.

[0055] In some embodiment, the third monomer is a hydroxyl functionalized olefin monomer, preferably 3-buten-1-ol, 3-buten-2-ol, 5-hexen-1-ol, 5-hexene-1,2-diol, 7-octen-1-ol, 7-octen-1,2-diol, 5-norbornene-2-methanol, 10-undecen-1-ol, preferably 5-hexen-1-ol.

[0056] In some embodiment, the hot melt adhesive resin is made in a solution process using a protected hydroxyl-functionalized C.sub.4 to C.sub.12, preferably C.sub.6 to C.sub.12, preferably C.sub.6 to C.sub.10, preferably C.sub.6 to C.sub.8 olefin monomer. Generally, the protection group is silyl halides, trialkyl aluminum complexes, dialkyl aluminum alkoxide complexes, dialkyl magnesium complexes, dialkyl zinc complexes or trialkyl boron complexes.

[0057] Although this is not essential, a purification step consisting in removing the traces of inorganic impurities such as aluminum hydroxide oxide species, which remained in the polymer the resin after the polymerization process, is preferred.

[0058] By doing so, the best adhesion strengths are obtained. Inventors believe that by removing the inorganic impurities from the resin, it allows to have more hydroxyl functionalities available to enhance the binding property of the resin to polar materials.

[0059] According to the invention, the addition reaction of the hydroxyl-functionalized polyolefin is performed with a di-, tri-or poly-isocyanates with an isocyanates according to formula (4)

OCNR.sup.4NCO).sub.n(4)

wherein: [0060] R.sup.4 is hydrocarbyl group having 1 to 10 carbon atoms [0061] n is 1 to 4, preferentially 1 to 2, more preferentially 1.

[0062] In some embodiment, the isocyanate is selected from the list comprising 1,6-Diisocyanatohexane (HDI), 4,4-methylene diphenyl diisocyanate (MDI), Methylene-bis (4-cyclohexylisocyanate) (HMDI).

EXAMPLES

[0063] The following formula (6) represent an non limitative example of the invention in which the used isocyanate is a di-isocyanate

##STR00004##

[0064] The tunable functionality of these functionalized olefin terpolymer HMA's makes them very suitable for gluing the same or different polar substrates such as metals, glass, wood and polar polymers.

[0065] The general apolar nature of the functionalized olefin terpolymer HMA's furthermore provides excellent adhesion to low surface energy substrates such as polyolefins (i.e. HDPE, LDPE, LLDPE, PP), making these HMA's very suitable for gluing polyolefins to polyolefins, or for gluing polyolefins to polar substrates such as metals, glass, wood and polar polymers.

[0066] The following examples are not limiting examples and have been realized with the following monomers: propylene (C.sub.3), 1-hexene (C.sub.6), and 5-hexen-1-ol (C.sub.6OH). However, other monomer could be use in order to achieve the present invention.

Synthesis of Poly (C.SUB.3.co-C.SUB.5.-co-C.SUB.6.OH)

[0067] The polymerization experiment was carried out using a stainless steel BCHI reactor (2 L) filled with pentamethylheptane (PMH) solvent (1 L) using a stirring speed of 600 rpm. Catalyst and comonomer solutions were prepared in a glove box under an inert dry nitrogen atmosphere.

[0068] The reactor was first heated to 40 C. followed by the addition of TiBA (1.0 M solution in toluene, 2 mL), 1-hexene (neat 10 mL), and triethylaluminum (TEA)-pacified 5-hexen-1-ol (1.0 M solution in toluene, TEA:5-hexen-1-ol (mol ratio)=1, 10 mL). The reactor was charged at 40 C. with gaseous propylene (100 g) and the reactor was heated up to the desired polymerization temperature of 130 C. resulting in a partial propylene pressure of about 15 bar. Once the set temperature was reached, the polymerization reaction was initiated by the injection of the pre-activated catalyst precursor bis((2-oxoyl-3-(dibenzo-1H-pyrrole-1-yl)-5-(methyl) phenyl)-2-phenoxy)-2,4-pentanediylhafnium (IV) dimethyl [CAS 958665-18-4]; other name hafnium [[2,2-[(1,3-dimethyl-1,3-propanediyl)bis(oxy-O)]bis[3-(9H-carbazol-9-yl)-5-methyl[1,1-biphenyl]-2-olato-O]](2-)]dimethyl] (Hf-O4, 2 mol) in MAO (30 wt % solution in toluene, 11.2 mmol). The reaction was stopped by pouring the polymer solution into a container flask containing demineralized water/iPrOH (50 wt %, 1 L) and Irganox 1010 (1.0 M, 2 mmol). The resulting suspension was filtered and dried at 80 C. in a vacuum oven, prior the addition of Irganox 1010 as an antioxidant. The poly (propylene-co-1-hexene-co-5-hexen-1-ol) (25.6 g) was obtained as a white powder.

Deashing Protocol

[0069] The terpolymer obtain from the solution process may be purify in order to remove trace of inorganic impurities, such as aluminum hydroxide oxides. To do so, the poly (C.sub.3-co-C.sub.6-CO-C.sub.6OH) (10 g) (Table 1, entry 1) was dispersed in mixture of dry toluene (400 ml) and concentrated (37%) HCl (10 ml, 0.13 mol, 4.74 g) and heated under reflux until the terpolymer dissolved. Once the polymer was properly dissolved, methanol (250 ml) was added to the hot mixture and the mixture was heated under stirring at 90-100 C. for 1 additional hour. Then the polymer was precipitated in cold methanol, filtered and washed 2 with methanol. The yield of purification process was 85%.

Polyurethane Synthesize Protocol

EX2: poly (C.sub.3-co-C.sub.6-co-C.sub.6O-(MDI).

[0070] Deashed and degassed poly (C.sub.3-co-C.sub.6-co-C.sub.6OH) (0.4 mol % OH; Mn=26.6 kg-mol1; PDI=4.6; 5.6.Math.104 mol, 15 g; Table 1, entry 1) was dissolved in 400 ml of dry toluene at 110 C. The process was carried out under reflux and nitrogen atmosphere. When homogenous mixture was obtained, freshly distilled 4,4-methylene diphenyl diisocyanate (1.5.Math.103 mol, 0.375 g) (MDI) was introduced to the thus obtained polymer solution. After 10 min, dibutyltin dilaurate as a catalyst was added (7.9.Math.104 mol; 0.498 g). The reaction was carried out for 22 h under nitrogen atmosphere at 110 C. The product was recovered by precipitation in cold methanol and dried under reduced pressure at 60 C. The yield of the reaction was 87%. The final product obtained after drying was partially cross-linked and therefore difficult to dissolve in common organic solvents e.g. 1,2-dichlorobenzene

EX3: poly (C.sub.3-co-C.sub.6-co-C.sub.6-O-(HDI) and EX4 poly(C.sub.3-co-C.sub.6-co-C.sub.6O-(HMDI)

[0071] EX3 and EX4 were synthesized under analogue conditions and protocol that the ones used for EX2 at the exception that 4,4-methylene diphenyl diisocyanate (MDI) has been replace respectively by 1,6-Diisocyanatohexane (HDI) and Methylene-bis (4-cyclohexylisocyanate) (HMDI).

TABLE-US-00001 TABLE 1 Characteristics of copolymer and terpolymers with different composition produced according to the abovementioned protocols. OH C.sub.3:C.sub.2-6-8: Xc group M.sub.n PDI T.sub.m H.sub.m EX Composition C.sub.6OH* [%] mol % [kg/mol] (M.sub.w/M.sub.n) [ C.] [J/g] EX1 poly(C.sub.3-co-C.sub.6-co-C.sub.6OH) 96.3:3.4:0.3 13.5 0.4 26.6 4.6 88.2 27.9 EX 2 poly(C.sub.3-co-C.sub.6-co-C.sub.6O-(MDI) 96.3:3.4:0.3 12.5 * * 87.5 25.8 EX 3 poly(C.sub.3-co-C.sub.6-co-C.sub.6O-HDI) 96.3:3.4:0.3 10.9 * * 87.4 22.5 EX 4 poly(C.sub.3-co-C.sub.6-co-C.sub.6O-(HMDI) 96.3:3.4:0.3 13.9 * * 86.0 22.5 *not soluble in 1,2-dichlorobenzine

TABLE-US-00002 TABLE 2 Lap shear test results. Lap Shear Strength [MPa] EX ALUMINUM/ALUMINUM STEEL/STEEL PP/PP EX1 7.66 0.13 13.5 1.12 6.5 0.3 EX2 5.95 0.65 9.47 0.86 5.5 0.3 EX3 5.90 0.59 4.88 1.64 5.3 0.3 EX4 4.70 0.33 5.51 0.54 4.5 0.3

TABLE-US-00003 TABLE 3 Dynamic Mechanical Thermal Analysis Storage modulus (E) [MPa] Loss modulus (E)[MPa] Entry Tg C. 40 C. 0 C. 20 C. 70 C. 40 C. 0 C. 20 C. 70 C. EX1 1.33 2015 381 112 5.6 35.8 115.7 14.5 0.5 EX2 1.66 2221 534 120 13 40.5 171.3 17.2 1.0 EX3 0.01 2814 569 148 11.7 46 188.7 18.5 0.9 EX4 3.29 2045 643 132 7.2 36.2 187.5 21.5 0.6

[0072] FIGS. 1, 2, 3 and 4 are the 1H NMR spectra of respectively EX1, EX2, EX3 and EX4 in which it can be observe the functionality level and the comonomer composition.

Measurements

Size Exclusion Chromatography (SEC)

[0073] SEC measurements were performed according to ISO 16014-4 and ASTM D6474 methods at 150 C. on a Polymer Char GPC-IR built around an Agilent GC oven model 7890, equipped with an autosampler and the Integrated Detector IR4. 1,2-Dichlorobenzene (o-DCB) was used as an eluent at a flow rate of 1 mL/min. The data were processed using Calculations Software GPC One. The molecular weights (Mn) (Mw) and PDI were calculated with respect to polyethylene or polystyrene standards.

Liquid-State 1H NMR

[0074] .sup.1H NMR and 13C NMR spectra were recorded at room temperature or at 80 C. using a Varian Mercury Vx spectrometer operating at Larmor frequencies of 400 MHz and 100.62 MHZ for .sup.1H and .sup.13C, respectively. For .sup.1H NMR experiments, the spectral width was 6402.0 Hz, acquisition time 1.998 s and the number of recorded scans equal to 64. .sup.13C NMR spectra were recorded with a spectral width of 24154.6 Hz, an acquisition time of 1.3 s, and 256 scans.

Differential Scanning Calorimetry (DSC)

[0075] Melting (T.sub.m) temperatures as well as enthalpies of the melting point (H [J/g]) of the transitions were measured according to the ISO 11357-1:2016 using a Differential Scanning Calorimeter Q100 from TA Instruments. The measurements were carried out at a heating and cooling rate of 10 C./min from-50 C. to 240 C. The transitions were deducted from the second heating and cooling curves.

[0076] The DSC has been used for the determination of the Crystallinity (X.sub.c) content by comparing the enthalpies of melting transition of the sample with melting transition of the 100% crystalline polypropylene.

Dynamic Mechanical Thermal Analysis (DMTA)

[0077] Storage modulus (E) and Loss modulus (E)[MPa] were measured using a TA Instruments Q800 DMA. Samples were tested by strain-controlled temperature ramp with the frequency of 1 Hz. The temperature profile was from 150 C. to the melting of the polymers with the ramp 3 C./min. The glass transition temperature was calculated as the peak of the tangent delta signal.

Compression-Molding Experiments

[0078] The film samples, used for the lap shear test, were prepared via compression-molding using PP ISO settings on LabEcon 600 high-temperature press (Fontijne Presses, the Netherlands). Namely, the films (25 mm12.5 mm0.5 mm) of functionalized polyolefins were loaded between the substrates: PP-PP, Steel-Steel, Aluminum-Aluminum or their combination with overlap surface 12.5 mm. Then, the compression-molding cycle was applied: heating to 130 C., stabilizing for 3 min with no force applied, 5 min with 100 kN (0.63 MPa) normal force and cooling down to 40 C. with 10 C./min and 100 kN (0.63 MPa) normal force.

Lap Shear Strength

[0079] The measurements were performed according to the ASTM D1002-10 (2019) with a Zwick type Z020 tensile tester equipped with a 10 kN load cell. Before measurements, samples were conditioned for 7 days at room temperature. The tests were performed on specimens (10 cm2.5 cm) with surface overlapping 12.5 mm. A grip-to-grip separation of 140 mm was used. The samples were pre-stressed to 3 N, then loaded with a constant cross-head speed 100 mm/min. To calculate the lap shear strength the reported force value divided by the bonding surface (25 mm12.5 mm) of the specimens. The reported values are an average of at least 5 measurements of each composition.