Heat and moisture resistant acrylic adhesive composition

Abstract

A two part heat and moisture resistant acrylic adhesive composition is provided and includes an initiator part comprising at least one polymer dissolved in a (meth)acrylate monomer and a free radical initiator and an activator part comprising at least one polymer dissolved in a (meth)acrylate monomer, a pyridinic reducing agent, an organometallic curing promoter and a thiourea accelerator.

Claims

1. A two part heat and moisture resistant acrylic adhesive composition comprising: a) an initiator part comprising at least one homopolymer dissolved in a (meth)acrylate monomer and a free radical initiator, wherein the at least one homopolymer is selected from the group consisting of poly(methyl methacrylate) (PMMA), polystyrene (PS), polydicyclopentadiene (PDCPD), and mixtures and blends thereof; and b) an activator part comprising at least one homopolymer dissolved in a (meth)acrylate monomer, a pyridinic reducing agent, an organometallic curing promoter and a thiourea accelerator, wherein the at least one homopolymer is selected from the group consisting of poly(methyl methacrylate) (PMMA), polystyrene (PS), polydicyclopentadiene (PDCPD), and mixtures and blends thereof.

2. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the initiator part further comprises a toluenesulfonyl chloride co-initiator.

3. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the activator part further comprises a crosslinker.

4. The two part heat and moisture resistant acrylic adhesive composition of claim 3, wherein the crosslinker is ethyleneglycol dimethacrylate.

5. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the (meth)acrylate monomer is a C.sub.1 to C.sub.20 alkyl ester of (meth)acrylic acid.

6. The two part heat and moisture resistant acrylic adhesive composition of claim 5, wherein the C.sub.1 to C.sub.20 alkyl ester of (meth)acrylic acid is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-ethyl hexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, isobornyl (meth)acrylate, and mixtures and blends thereof.

7. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the free radical initiator is cumene hydroperoxide.

8. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the organometallic curing promoter is an organometallic compound selected from the group consisting of cobalt, nickel, manganese or iron naphthenate, cobalt neodecanoate, copper octoate, copper acetylacetonate, iron hexoate, and iron propionate.

9. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the thiourea accelerator is selected from the group consisting of ethylene thiourea, 1-acetyl-2-thiourea, and 1-(2-pyridyl)-2-thiourea.

10. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the pyridinic reducing agent is 3,5-diethyl-1-phenyl-2-propyl-1,2-dihydropyridine (PDHP).

11. A method of bonding two objects together, the method comprising: a) mixing an initiator part and an activator part together to form an adhesive, wherein the initiator part comprises at least one homopolymer dissolved in a (meth)acrylate monomer and a free radical initiator, wherein the at least one homopolymer is selected from the group consisting of poly(methyl methacrylate) (PMMA), polystyrene (PS), polydicyclopentadiene (PDCPD), and mixtures and blends thereof, and wherein the activator part comprises at least one homopolymer dissolved in a (meth)acrylate monomer, a pyridinic reducing agent, an organometallic curing promoter and a thiourea accelerator, wherein the at least one homopolymer is selected from the group consisting of poly(methyl methacrylate) (PMMA), polystyrene (PS), polydicyclopentadiene (PDCPD), and mixtures and blends thereof; b) applying the adhesive to at least one surface of one of the two objects to be joined together; and c) curing the adhesive to bond the two objects together.

12. The method according to claim 11, wherein the initiator part further comprises a toluenesulfonyl chloride co-initiator.

13. The method according to claim 11, wherein the activator part further comprises a crosslinker.

14. The method according to claim 13, wherein the crosslinker is ethyleneglycol dimethacrylate.

15. The method according to claim 11, wherein the (meth)acrylate monomer is a C.sub.1 to C.sub.20 alkyl ester of (meth)acrylic acid.

16. The method according to claim 15, wherein the C.sub.1 to C.sub.20 alkyl ester of (meth)acrylic acid is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-ethyl hexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, isobornyl (meth)acrylate, and mixtures and blends thereof.

17. The method according to claim 11, wherein the free radical initiator is selected from the group consisting of benzoyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide, dicumyl peroxide, tertiary butyl peroxyacetate, tertiary butyl perbenzoate, and mixtures thereof.

18. The method according to claim 11, wherein the organometallic curing promoter is an organometallic compound selected from the group consisting of cobalt, nickel, manganese or iron naphthenate, cobalt neodecanoate, copper octoate, copper acetylacetonate, iron hexoate, and iron propionate.

19. The method according to claim 11, wherein the thiourea accelerator is selected from the group consisting of ethylene thiourea, 1-acetyl-2-thiourea, 1-(2-pyridyl)-2-thiourea.

20. The method according to claim 11, wherein the pyridinic reducing agent is 3,5-diethyl-1-phenyl-2-propyl-1,2-dihydropyridine (PDHP).

21. The two part heat and moisture resistant acrylic adhesive composition of claim 1, further comprising a copolymer selected from the group consisting of poly(methacrylate-acrylonitrile-butadiene-styrene) (MABS), poly(methacrylate-butadiene-styrene) (MBS), poly(acrylate-styrene-acrylonitrile) (ASA), poly(acrylonitrile-butadiene-styrene) (ABS), block copolymers of butadiene or isoprene with styrene, and mixtures and blends thereof.

22. The two part heat and moisture resistant acrylic adhesive composition of claim 21, wherein the copolymer is present in an amount of less than 10% by weight of the two part heat and moisture resistant acrylic adhesive composition.

23. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the initiator part and the activator part are combined in a 1:1 ratio to form an adhesive.

24. The two part heat and moisture resistant acrylic adhesive composition of claim 1, wherein the initiator part and the activator part are combined to form an adhesive and less than 300 g/L of the (meth)acrylate monomer is present in water when the adhesive is used in a migration test performed according to European Standard EN 12873-2:2004.

25. The two part heat and moisture resistant acrylic adhesive composition of claim 1, further comprising an organic acid accelerator.

26. The two part heat and moisture resistant acrylic adhesive composition of claim 25, wherein the organic acid accelerator is methacrylic acid.

Description

EXAMPLES

(1) Ingredients

(2) The following ingredients were used in the examples provided hereinafter: Acrylic polymer (Plexiglas VS-100)Altuglas International Acrylic polymer (Optix CA-86)Plaskolite, Inc Methylmethacrylate acrylonitrile 1,3-butadiene styrene copolymer (MABS) (TR 558A)LG Chem, Ltd. Methyl methacrylate (MMA)Lucite International Inc. Methacrylic acid (MA)Lucite International Inc. Hydroxyethyl methacrylate (HEMA)Sigma-Aldrich Corporation Ethyleneglycol dimethacrylate (EGDMA)Sartomer Inc Cumene hydroperoxide (CHP)Sigma-Aldrich Corporation 4-Toluenesulfonyl chlorideSigma-Aldrich Corporation 3,5-Diethyl-1-phenyl-2-propyl-1,2-dihydropyridine (PDHP) (Reillycat ASY-2)Vertellus Specialties Inc. Cobalt neodecanoateSigma-Aldrich Corporation Copper(II) acetylacetonate (CuAcAc)Sigma-Aldrich Corporation Ethylene thiourea (ETU)Sigma-Aldrich Corporation Butylated hydroxytoluene (BHT)Sigma-Aldrich Corporation 2,6-Di-tert-butyl-4-(dimethylaminomethyl)phenol (Ethanox 4703)Albemarle Corporation Fumed silica (Aerosil 200)Evonik Industries AG Titanium dioxide (Ti-Pure R-900)DuPont
Preparation of Monomer-Polymer Solution

(3) Stock monomer-polymer solutions were prepared by dissolving the polymers in methyl (meth)acrylate monomer. A polymer in pellet or powder form and monomer were charged to a one gallon tin plated metal can and rolled on a roller mill for 24 to 72 hours to fully dissolve the polymer in the monomer and form a homogeneous syrup-like solution with concentrations ranging from about 20-50%. The viscosity of the final formula can be adjusted by adjusting the amount of monomer.

(4) Initiator Part

(5) Polymer solutions, monomers, stabilizers and the Initiators Part except for the free radical initiators were added to a Max 100 plastic cup (160 ml) from FlackTek Inc. The mixing cup was placed into a dual asymmetric centrifugal FlackTek SpeedMixer (DAC 150.1 FV) by Hauschild Engineering, Germany. The contents were mixed twice consecutively for one minute each at a speed of 3,000 rpm to insure that high viscosity polymer solutions and solid ingredients were fully mixed and homogeneous. Fillers were then added to the mixing cup which was mixed for one minute at a speed of 3,000 rpm forming a homogeneous paste. After the mixture was cooled down to about room temperature, the free radical initiator was added into the mixing cup and mixed for one minute at a speed of 3,000 rpm.

(6) Activator Part

(7) Polymer solutions, monomers, crosslinkers, stabilizers and the Activator Part components except for the pyridinic reducing agent (dihydropyridine (PDHP)) were added to a Max 100 plastic cup (160 ml). The mixing cup was placed into a dual asymmetric centrifugal FlackTek SpeedMixer (DAC 150.1 FV). The contents were mixed twice consecutively for one minute each at a speed of 3,000 rpm to insure that high viscosity polymer solutions and solid ingredients were fully mixed and homogeneous. Fillers were then added to the mixing cup which was mixed for one minute at a speed of 3,000 rpm forming a homogeneous paste. After the mixture was cooled down to about room temperature, the pyridinic reducing agent (dihydropyridine (PDHP)) was added into the mixing cup and mixed for one minute at a speed of 3,000 rpm.

(8) Mixing and Application of Adhesives

(9) The Initiator Part and Activator Part were stored in the separate chambers of a 50 ml dual cartridge from Sulzer Mixpac Ltd, Switzerland in a 1:1 volume ratio respectively. The cartridge was then placed in a hand-held dispenser. A static mixer was attached to the cartridge. To apply the adhesive, the Initiator Part and Activator Part pastes were combined and mixed by the simultaneous extrusion through the static mixer, and were directly applied onto the test substrates. When Initiator Part and Activator Part pastes were mixed, free radical initiators in the Initiator Part were activated by the activators in the Activator Part to generate free radicals to initiate the polymerization of monomers. The mixed paste gradually increases viscosity and eventually is harden to form a strong bond to the substrate. Various two part acrylic adhesive compositions were then evaluated.

(10) Lap Shear Bond Strength

(11) Samples of the adhesive composition were evaluated to measure the lap shear bond strength and failure mode. The adhesive compositions were dispensed onto a substrate with dimensions 2 inch1 inch inch thick (50.8 mm25.4 mm6.4 mm). The surface of the substrates was cleaned with methyl ethyl ketone (MEK) and dried prior to bonding. Two pieces of PETG plastic sheet (1 inch long, 0.5 inch wide, 20 mil thick) (25.4 mm12.7 mm0.5 mm) were used as spacer and placed to each end of the first substrate. The mixed adhesive compositions were applied and spread near the center of the substrate to cover a 1 inch1 inch (25.4 mm25.4 mm) area. A second substrate was brought against the adhesive compositions to form an overlap adhesive joint with 1 inch (25.4 mm) overlap. The adhesive joint was fixtured with a clamp and allowed to cure at room temperature (i.e., about 23 C.) for 24 hours. Four adhesive joints were made with each adhesive formulation. The adhesive joint was tested until failure by compression loading on a material testing machine (United Testing System, Model STM-20) equipped with a 20,000 lb. (9072 kg) load cell at a rate of 0.05 inch (1.27 mm) per minute. The lap shear strengths are an average of four measurements and are reported in psi (pound per square inch) to the nearest whole number. The debonded adhesive joints were visually inspected to determine the failure mode.

(12) Reactivity Time and Maximum Exotherm Temperature

(13) Reactivity time is defined as the time to reach the maximum temperature of an exothermic reaction from start of mixing a certain amount of adhesive. A time was started immediately when three grams of adhesive compositions were mixed and dispensed into a small disposable cup. A type K thermocouple connected to an Extech 421502 Digital Thermometer was then inserted into the mixed adhesive. The time elapsed in total minutes:seconds from start of mixing to the maximum-recorded temperature was recorded as reactivity time. The maximum exotherm temperature reached was recorded.

(14) Hydrostatic Sustained Pressure Strength

(15) Time-to-failure of plastic pipe joint prepared with the adhesive compositions under constant hydraulic pressure was determined according to the procedures described in ASTM D1598: Standard Test Method for Time-to-Failure of Plastic Pipe under Constant Internal Pressure. Some test conditions were modified and specified as herein. Used 40MM PN25 CPVC pipe and fitting to prepare a test assembly containing 2 6-inch pipes and 1 coupling. The surface of the bonded area was cleaned with methyl ethyl ketone (MEK) and dried prior to bonding. The adhesive compositions were applied and the pipe joint was cured at room temperature for 24 hours. The pipe joint was then conditioned at 180 F. (82 C.) for 96 hours and tested by applying a constant hydrostatic pressure of 288 psi until failure. Leakage or separation at the joint tested causing loss of pressure shall constitute failure.

(16) The following examples further illustrate the embodiments of the present invention. Neither these examples nor any of the foregoing disclosure should be construed as limiting in any way the scope of the present invention. Unless otherwise indicated, all parts and percentages are by weight.

Examples 1-5

(17) The Initiator Part and the Activator Part with various compositions of 2 different acrylic polymers of Plexiglas VS-100 and Optix CA-86, different monomers (MMA, MA, HEMA and EGDMA), CHP initiator, different accelerators (PDHP, ETU and cobalt neodecanoate), and BHT stabilizer were prepared using the procedures described above. The formulations and properties are summarized in Table 1.

(18) TABLE-US-00001 TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Initiator Part (WT. %) Plexiglas VS-100 33.29 33.29 Optix CA-86 29 29 29 Methyl methacrylate (MMA) 47.09 47.09 51.5 51.5 51.5 Methacrylic acid (MA) 7 7 7 7 7 Cumene hydroperoxide (CHP) 2 2 1 1 1 Butylated hydroxytoluene (BHT) 0.12 0.12 1 1 1 Aerosil 200 0.5 0.5 0.5 0.5 0.5 Ti-Pure R-900 10 10 10 10 10 Activator Part (WT. %) Plexiglas VS-100 33.17 33.26 Optix CA-86 30.52 30.44 30.34 Methyl methacrylate (MMA) 44.424 44.284 53.824 53.704 53.554 Hydroxyethyl methacrylate (HEMA) 8 8 Ethyleneglycol dimethacrylate (EGDMA) 3 3 3 3 3 Butylated hydroxytoluene (BHT) 0.1 0.1 0.1 0.1 0.1 PDHP (Reillycat ASY-2) 0.8 0.8 2 2 2 Cobalt neodecanoate 0.006 0.006 0.006 0.006 0.006 Ethylene thiourea (ETU) 0.05 0.05 0.25 0.5 Aerosil 200 0.5 0.5 0.5 0.5 0.5 Ti-Pure R-900 10 10 10 10 10 Reactivity Time slow setting 1100 2344 1436 1116 Max. Exotherm Temperature ( C.)/3 g 88 27.9 46.2 55.0 Lap Shear Strength on CPVC (psi) 2265 1992 973 913 Lap Shear Failure Mode Substrate Substrate Adhesive Adhesive Heat resistance in 80 C. water Soft Soft Soft Soft

Examples 6-10

(19) The Initiator Part and the Activator Part with various compositions of Optix CA-86 acrylic polymer, MABS TR558A impact modifier, monomers (MMA, MA and EGDMA), 2 initiators (CHP and 4-Toluenesulfonyl chloride), accelerators (PDHP, ETU CuAcAc and cobalt neodecanoate) and stabilizers (BHT and Ethanox 4703) were prepared using the procedures described above. The formulations and properties are summarized in Table 2.

(20) TABLE-US-00002 TABLE 2 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Initiator Part (WT. %) Optix CA-86 16.4 16 16 16 16 MABS TR558A 9.6 9.6 9.6 9.6 9.6 Methyl methacrylate (MMA) 53 52.4 52.4 52.4 52.4 Methacrylic acid (MA) 7 7 7 7 7 Cumene hydroperoxide (CHP) 2 2 2 2 2 4-Toluenesulfonyl chloride 1 1 1 1 Butylated hydroxytoluene (BHT) 1.5 1.5 1.5 1.5 1.5 Aerosil 200 0.5 0.5 0.5 0.5 0.5 Ti-Pure R-900 10 10 10 10 10 Activator Part (WT. %) Optix CA-86 18.12 18.12 17.97 16.74 16.14 MABS TR558A 9.6 9.6 9.6 9.6 9.6 Methyl methacrylate (MMA) 52.58 52.58 52.78 54.01 50.21 Ethyleneglycol dimethacrylate (EGDMA) 8 8 8 8 8 Butylated hydroxytoluene (BHT) 0.1 0.1 0.1 Ethanox 4703 0.1 0.1 PDHP (Reillycat ASY-2) 1 1 1 1 2 Cobalt neodecanoate 0.006 0.006 Copper(II) acetylacetonate (CuAcAc) 0.00025 0.00025 0.0005 Ethylene thiourea (ETU) 0.05 0.05 0.05 0.05 0.05 Aerosil 200 0.5 0.5 0.5 0.5 0.5 Ti-Pure R-900 10 10 10 10 10 Reactivity Time 37 1527 1421 1122 1436 Max. Exotherm Temperature ( C.)/3 g 26.3 89.2 81.6 98.8 91.7 Lap Shear Strength on CPVC (psi) 2296 2356 2284 2369 2481 Lap Shear Failure Mode Substrate Substrate Substrate Substrate Substrate Heat resistance in 80 C. water Soft Hard Hard Hard Hard

(21) Several adhesive formulas were selected to perform a hydrostatic sustained pressure strength test. The test results were summarized in Table 3.

(22) TABLE-US-00003 TABLE 3 Ex. 3 Ex. 7 Ex. 8 Time to Failure (hr) 1541 4836 5220 Failure Mode Leak at bondline Pipe failure Pipe failure * Test conditions: 180 F. & 288 psi on a 40 MM PN25 CPVC Pipe joint

(23) The examples clearly illustrate that the adhesive compositions containing a combination of free radical initiators such as cumene hydroperoxide (CHP) and 4-toluenesulfonyl chloride, and a combination of activators such as PDHP (Reillycat ASY-2), copper (II) acetylacetonate (CuAcAc), ethylene thiourea (ETU) have superior heat and moisture resistance in 80 C. water under pressure of inventive adhesive compositions on CPVC pipe joints.

(24) Migration Test

(25) The migration test was performed according to the European Standard EN 12873-2:2004. The migration water collected from the CPVC pipe joints assembled with the adhesive was analyzed by GC-MS (gas chromatography-mass spectrometry). The adhesive of Example 8 was used for the migration test. The concentration of MMA monomer in the migration water was less than 300 ug/L, meeting the requirements as described in the Positive List of Monomers for Production of Organic Materials and Cementitious Products Intended for Use in Contact with Drinking WaterJune 2005, Other ingredients were found to be trace amounts or undetectable within the detection limits of the analysis.

(26) The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. The invention is defined by the following claims, with equivalents of the claims to be included therein.