Patent Application
20120128499
The present invention relates to structural adhesive compositions and more particularly to 2K structural adhesive compositions.
Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. Considerable efforts are being made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor with multiple wind turbine blades. The wind turbine blades are shaped as elongated airfoils configured to provide rotational forces in response to wind. These wind turbine blades transform the kinetic energy of wind into a rotational torque or force that drives one or more coupled generators by methods well known to those of skill in the art.
One current approach to manufacturing wind turbine blades is to produce each blade either as two half shells and a spar, or as two half shells with an integral spar. In both cases, the two half shells are bonded together along their edges with an adhesive material to form the complete blade. Typically, the adhesive material is a two-component (2K) structural adhesive material that includes two components that chemically react (i.e., crosslink) when mixed under ambient or slightly thermal conditions to bond together the half shells. Alternatively, one-component (1K) adhesives may be utilized that require an external energy source (heat, radiation or moisture) in order to facilitate the chemical reaction.
The adhesives that are utilized to couple the wind turbine blade halves must be able to withstand the centrifugal forces applied to each blade during use and maintain bond strength for the blade's lifetime under constant thermal cycling and environmental attack. In addition, these adhesive materials should be relatively easy to apply.
In addition, for 2K adhesives, pot life is an important consideration. The term “pot life”, as those of ordinary skill in the adhesives arts recognizes, may be defined as the length of time for the adhesive mixture to reach 50° C., and is generally defined as the time period in which the adhesive composition is sufficiently liquid such that it may be applied to a substrate material to be bonded. An adhesive material with a shorter pot life is wherein the two components react more quickly, and an adhesive material with longer pot life is wherein the two components react more slowly.
The present invention is directed towards adhesive compositions that provide sufficient bond strength, are easy to apply, and have sufficiently long pot lives for use in bonding together substrate materials such as wind turbine blades.
One embodiment of the present invention discloses an adhesive composition comprising (a) a first component comprising (i) an epoxy-adduct formed as a reaction product of reactants comprising a first epoxy compound, a polyol, and an anhydride and/or a diacid; and (b) a second component that chemically reacts with the first component.
In one embodiment, the second component comprises an amine compound.
Other related embodiments disclose multi-component composite coatings, coated substrates, and methods for coating a substrate.
For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims, are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances.
As noted above, in general, the present invention discloses 2K (“Two-Component”) structural adhesive compositions that are used to bond together two substrate materials. The adhesive is applied to either one or both of the materials being bonded. The pieces are aligned and pressure and spacers may be added to control bond thickness. A thermal blanket may be used to aid in the curing process.
Suitable substrate materials that may be bonded by the 2K structural adhesive components include but are not limited to materials such as, metals or metal alloys, natural materials such as wood, polymeric materials such as hard plastics, or composite materials.
The 2K structural adhesive composition includes two chemical components that, when mixed prior to application, chemically react with each other and harden (i.e., cure) in ambient or slightly thermal conditions.
The 2K (“Two-Component”) structural adhesive compositions of the present invention are suitable for use in bonding the two half shells of wind turbine blades. In this application, the mixed adhesive composition is applied along the edges of one or both of the half shells of the wind turbine blades. The half shells are then pressed together and the adhesive is allowed to cure for a number of hours. Preferably, a thermal blanket (at about 70° C.) is applied to the half shells to aid in the curing process. The half shells, or other components of wind turbine blades, may be formed from metals such as aluminum, metal alloys such as steel, woods such balsa wood, polymeric materials such as hard plastics, or composite materials such as fiber reinforced plastics. In one embodiment, the half shells are formed from fiberglass composites or carbon fiber composites.
As noted above, the 2K structural adhesives of the present invention are formed from two chemical components, namely, a first component and a second component which are mixed just prior to application. The first component (i.e., an epoxy component) preferably comprises an epoxy-adduct and another epoxy compound, or second epoxy compound. The second component preferably comprises a curing component that reacts with the first component to form a bond that provides the substrates to which it is applied with desirable bonding characteristics. Preferably, the curing component is an amine compound, although other curing components such as sulfide curing components may alternatively be utilized.
The equivalent ratio of amine to epoxy in the adhesive composition may vary from about 0.5:1 to about 1.5:1. Preferably, the equivalent ratio of amine to epoxy is from 1.0:1 to 1.25:1. Most preferably, the equivalent ratio of amine to epoxy is slightly above 1:1. As described herein, the equivalents of epoxy used in calculating the equivalent ratio of epoxy are based on the epoxy equivalent weight of the first component, and the equivalents of amine used in calculating the equivalent ratio of amine are based on the amine hydrogen equivalent weight (AHEW) of the second component.
In one embodiment, the epoxy-adduct is formed as the reaction product of reactants comprising a first epoxy compound, a polyol, and an anhydride.
In another embodiment, the epoxy-adduct is formed as the reaction product of reactants comprising a first epoxy compound, a polyol, and a diacid.
In still another embodiment, the epoxy-adduct is formed as the reaction product of reactants comprising a first epoxy compound, a polyol, an anhydride, and a diacid.
In these embodiments, the epoxy-adduct comprises from 3 to 50 weight percent, and more preferably from 3 to 25 weight percent of the first component, while the second epoxy compound comprises from 50 to 97 weight percent, and more preferably from 75 to 97 weight percent of the first component.
Useful first epoxy compounds that can be used to form the epoxy-adduct include polyepoxides. Suitable polyepoxides include polyglycidyl ethers of Bisphenol A, such as EPON® 828 and 1001 epoxy resins, and Bisphenol F diepoxides, such as EPON® 862, which are commercially available from Hexion Specialty Chemicals, Inc. Other useful polyepoxides include polyglycidyl ethers of polyhydric alcohols, polyglycidyl esters of polycarboxylic acids, polyepoxides that are derived from the epoxidation of an olefinically unsaturated alicyclic compound, polyepoxides containing oxyalkylene groups in the epoxy molecule, and epoxy novolac resins. Still other non-limiting first epoxy compounds include epoxidized Bisphenol A novolacs, epoxidized phenolic novolacs, epoxidized cresylic novolac, and triglycidyl p-aminophenol bismaleiimide.
Useful polyols that may be used to form the epoxy-adduct include diols, triols, tetraols and higher functional polyols. The polyols can be based on a polyether chain derived from ethylene glycol, propylene glycol, butylenes glycol, hexylene glycol and the like and mixtures thereof. The polyol can also be based on a polyester chain derived from ring opening polymerization of caprolactone. Suitable polyols may also include polyether polyol, polyurethane polyol, polyurea polyol, acrylic polyol, polyester polyol, polybutadiene polyol, hydrogenated polybutadiene polyol, polycarbonate polyols, polysiloxane polyol, and combinations thereof. Polyamines corresponding to polyols can also be used, and in this case, amides instead of carboxylic esters will be formed with acids and anhydrides.
Suitable diols that may be utilized to form the epoxy-adduct are diols having a hydroxyl equivalent weight of between 30 and 1000. Exemplary diols having a hydroxyl equivalent weight from 30 to 1000 include diols sold under the trade name Terathane®, including Terathane® 250, available from Invista. Other exemplary diols having a hydroxyl equivalent weight from 30 to 1000 include ethylene glycol and its polyether diols, propylene glycol and its polyether diols, butylenes glycol and its polyether diols, hexylene glycols and its polyether diols, polyester diols synthesized by ring opening polymerization of caprolactone, and urethane diols synthesized by reaction of cyclic carbonates with diamines. Combination of these diols and polyether diols derived from combination various diols described above could also be used. Dimer diols may also be used including those sold under trade names Pripol® and Solvermol™ available from Cognis Corporation.
Polytetrahydrofuran-based polyols sold under the trade name Terathane®, including Terathane® 650, available from Invista, may be used. In addition, polyols based on dimer diols sold under the trade names Pripol® and Empol®, available from Cognis Corporation, or bio-based polyols, such as the tetrafunctional polyol Agrol 4.0, available from BioBased Technologies, may also be utilized.
Useful anhydride compounds to functionalize the polyol with acid groups include hexahydrophthalic anhydride and its derivatives (e.g. methyl hexahydrophthalic anhydride); phthalic anhydride and its derivatives (e.g. methyl phthalic anhydride); maleic anhydride; succinic anhydride; trimelletic anhydride; pyromelletic dianyhydrige (PMDA); 3,3′, 4,4′-oxydiphthalic dianhydride (ODPA); 3,3′, 4,4′-benzopherone tetracarboxylic dianhydride (BTDA); and 4,4′-diphthalic (hexamfluoroisopropylidene) anhydride (6FDA). Useful diacid compounds to functionalize the polyol with acid groups include phthalic acid and its derivates (e.g. methyl phthalic acid), hexahydrophthalic acid and its derivatives (e.g. methyl hexahydrophthalic acid), maleic acid, succinic acid, adipic acid, etc. Any diacid and anhydride can be used; however, anhydrides are preferred.
In one embodiment, the polyol comprises a diol, the anhydride comprises a monoanhydride, and the first epoxy compound comprises a diepoxy compound, wherein the mole ratio of diol, monoanhydride, and diepoxy compounds in the epoxy-adduct may vary from 0.5:0.8:1.0 to 0.5:1.0:6.
In another embodiment, the polyol comprises a diol, the anhydride comprises a monoanhydride, and the first epoxy compound comprises a diepoxy compound, wherein the mole ratio of diol, monoanhydride, and diepoxy compounds in the epoxy-adduct may vary from 0.5:0.8:0.6 to 0.5:1.0:6.0.
In another embodiment, the second epoxy compound of the first component is a diepoxide compound that has an epoxy equivalent weight of between about 150 and about 1000. Suitable diepoxides having an epoxy equivalent weight of between about 150 and about 1000 include polyglycidyl ethers of Bisphenol A, such as EPON® 828 and 1001 epoxy resins, and Bisphenol F diepoxides, such as EPON® 862, which are commercially available from Hexion Specialty Chemicals, Inc.
In another embodiment, the second epoxy compound of the first component is a diepoxide compound or a higher functional epoxides (collectively, a “polyepoxide”), including polyglycidyl ethers of polyhydric alcohols, polyglycidyl esters of polycarboxylic acids, polyepoxides that are derived from the epoxidation of an olefinically unsaturated alicyclic compound, polyepoxides containing oxyalkylene groups in the epoxy molecule, and epoxy novolac resins.
Still other non-limiting second epoxy compounds include epoxidized Bisphenol A novolacs, epoxidized phenolic novolacs, epoxidized cresylic novolac, and triglycidyl p-aminophenol bismaleiimide.
In another embodiment, the second epoxy compound of the first component comprises an epoxy-dimer acid adduct. The epoxy-dimer acid adduct may be formed as the reaction product of reactants comprising a diepoxide compound (such as a Bisphenol A epoxy compound) and a dimer acid (such as a C10-C12 dimer acid).
In another embodiment, the second epoxy compound of the first component comprises a carboxyl-terminated butadiene-acrylonitrile copolymer modified epoxy compound.
Useful amine compounds that may be used include primary amines, secondary amines, tertiary amines, and combinations thereof. Useful amine compounds that can be used include diamines, triamines, tetramines, and higher functional polyamines.
Suitable primary amines include alkyl diamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, neopentyldiamine, 1,8-diaminooctane, 1,10-diaminodecane, 1,-12-diaminododecane and the like; 1,5-diamino-3-oxapentane, diethylene-triamine, triethylenetetramine, tetraethylenepentamine and the like; cycloaliphatic diamines such as 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, bis(aminomethyl)norbornane and the like; aromatic alkyl diamines such as 1,3-bis(aminomethyl)benzene (m-xylene diamine) and 1,4-bis(aminomethyl)benzene (p-xylenediamine) and their reaction products with epichlorohydrin such as Gaskamine 328 and the like; amine-terminated polyethyleneglycol such as Huntsman Corporation Jeffamine ED series and amine-terminated polypropylene glycol such as Huntsman Corporation Jeffamine D series; and amine-terminated polytetrahydrofurane such as Huntsman Jeffamine EDR series. Primary amines having a functionality higher than 2 include, for example, the Jeffamine T series, available from Huntsman Corporation, which are amine-terminated propoxylated trimethylolpropane or glycerol and aminated propoxylated pentaerythritols.
Still other amines that may be utilized include isophorone diamine, methenediamine, 4,8-diamino-tricyclio[5.2.1.0]decane and N-aminoethylpiperazine.
Preferred amine compounds include triethylenetetramine (TETA), isophorone diamine, 1,3 bis(aminomethyl)cyclohexane, and polypropylene oxide-based polyetheramines.
Preferred polypropylene oxide-based polyetheramines include the Jeffamine series products available from Huntsman Chemical of Houston, Tex. Jeffamine series products are polyetheramines characterized by repeating oxypropylene units in their respective structures.
One exemplary class of Jeffamine products, the so-called “Jeffamine D” series products, are amine terminated PPGs (propylene glycols) with the following representative structure (Formula (I)):
wherein x is 2 to 70.
Jeffamine D-230 is one D series product that is preferably used. Jeffamine D-230 has an average molecular weight of about 230 (wherein x is 2.5) and an amine hydrogen equivalent weight (AHEW) of about 60. Other exemplary Jeffamine D series products that may be used according to Formula (I) include those wherein x is from 2.5 to 68.
Another series of polypropylene oxide-based polyetheramines that are preferably used are predominantly tetrafunctional, primary amines with a number average molecular weight from 200 to 2000, and more preferably from 600 to 700, and having an AHEW of greater than 60, and more preferably from 70 to 90. Jeffamine XTJ-616 is one preferred polypropylene oxide-based polyetheramines that may be utilized in the present invention. Jeffamine XTJ-616 has a number average molecular weight of about 660 and an AHEW of 83.
Higher AHEW amine compounds, such as Jeffamine XTJ-616 and Jeffamine D-230, may be particularly useful in 2K adhesive composition wherein a longer pot life is desired. Conventional tetramines, such as triethylenetetramine, with lower AHEWS have substantially shorter pot lives by comparison. This present invention thus provides a way to manipulate pot life with tetrafunctional amines such as Jeffamine XTJ-616.
In still another embodiment, reinforcement fillers may be added to the adhesive composition as a part of the first component or as a part of the second component, or both.
Useful reinforcement fillers that may be introduced to the adhesive composition to provide improved mechanical properties include fibrous materials such as fiberglass, fibrous titanium dioxide, whisker type calcium carbonate (aragonite), and carbon fiber (multi-wall carbon nanotube). In addition, fiber glass ground to 5 microns or wider and to 50 microns or longer may also provide additional tensile strength. More preferably, fiber glass ground to 5 microns or wider and to 100-300 microns in length is utilized. Preferably, such reinforcement fillers, if utilized, comprise from 2 to 20 weight percent of the adhesive composition.
In still another embodiment, fillers, thixotropes, colorants, tints and other materials may be added to the first or second component of the adhesive composition.
Useful thixotropes that may be used include untreated fumed silica and treated fumed silica, Castor wax, clay, and organo clay. In addition, fibers such as synthetic fibers like Aramid® fiber and Kevlar® fiber, acrylic fibers, and engineered cellulose fiber may also be utilized.
Useful colorants or tints may include red iron pigment, titanium dioxide, calcium carbonate, and phthalocyanine blue.
Useful fillers that may be used in conjunction with thixotropes may include inorganic fillers such as inorganic clay or silica.
In still another embodiment, if needed, a catalyst may be introduced to the adhesive composition, preferably as a part of the second component, to promote the reaction of the epoxide groups of first component and amine groups of the second component.
Useful catalysts that may be introduced to the adhesive composition include Ancamide® products available from Air Products and products marketed as “Accelerators” available from the Huntsman Corporation. One exemplary catalyst is piperazine-base Accelerator 399 (AHEW: 145) available from the Huntsman Corporation. When utilized, such catalysts comprise between 0 and about 10 percent by weight of the total adhesive composition.
In addition, a catalytic effect may be expected from the reaction product of epichlorohydrin from the first component and the amine compound from the second component in an equivalent ratio of 1:1. An example of such a product is Tetrad® and Tetrad®C available from Mitsubishi Gas Chemical Corporation.
Illustrating the invention are the following examples that are not to be considered as limiting the invention to their details. All parts and percentages in the examples, as well as throughout the specification, are by weight unless otherwise indicated.
To a four-neck flask fitted with condenser, thermometer, stirrer, and nitrogen inlet, add 304.6 grams of hexahydrophthalic anhydride and 248.1 grams of Terathane® 250. Heat the mixture to 100° C. with stirring under nitrogen atmosphere and hold the reaction mixture at 100° C. for 155 minutes. Cool the reaction mixture to 60° C. and then add 1431.6 grams of EPON 828 and 15.0 grams of triphenyl phosphine. Heat the reaction mixture to 110° C. and hold at this temperature for 150 minutes. Then, cool the mixture to room temperature. The resultant compound has 99.89% solids, an acid value of 0.2, and an epoxy equivalent weight of 380.7. The resultant compound is the epoxy adduct of the first component of the 2K adhesive material listed in Part 1 of Table 1 below.
Evaluation of Adhesives with and without Epoxy-Adduct; Evaluation of Adhesive Systems with Varying Amine Hydroxyl Equivalent Weights
The following examples compare 2K adhesive compositions without an epoxy-adduct (Example 1) to those with an epoxy-adduct (Examples 2-4). The formulations for the first component (Part 1) and second component (Part 2) of the 2K adhesive compositions are shown in Table 1.
1BISPHENOL A-EPICHLOROHYDRIN RESIN available from HUNTSMAN ADVANCED MATERIALS
2Synthesis example
3Silane treated chopped fiberglass from FIBERTEC
4PRECIPITATED CALCIUM CARBONATE available from SHIRAISHI KOGYO KAISHA
5HYDROPHOBIC FUMED SILICA available from WACKER CHEMIE AG
6ORG YELLOW TINT BASE available from ELEMENTIS SPECIALTIES
7POLYOXYALKYLENEAMINE available from HUNTSMAN
8POLYOXYALKYLENEAMINE available from HUNTSMAN
9TRIETHYLENETETRAMINE available from DOW CHEMICAL CO
10ISOPHORONE DIAMINE available from EVONIK AG
11MIX OF ALKANOLAMINE/PIPERAZINE DERVATIVE available from HUNTSMAN
12PHTHALO BLUE PIGMENT DISPERSION available from ELEMENTIS SPECIALTIES
In each of the Examples, the raw materials listed in Table 1 were mixed using a Speedmixer DAC 600 FVZ (commercially available from FlackTek, Inc.). Ingredients 1 and 2 were mixed for 2 minutes at 2350 revolutions per minute (“RPM”) in Part 1. Then, items 3 to 6 were added and mixed for one minute at 2350 RPM. Items 7 to 11 were mixed for 1 minute in Part 2 and then the rest of the ingredients were added and mixed for one minute in Part 2. During the mixing process, the mixture was examined with a spatula and given additional mix time, if necessary, to ensure uniformity. The final step of the mixing process involved mixing the mixture with an air motor prop in a vacuum sealed apparatus for 5 minutes at 28 to 30 inches of vacuum pressure. After the final mixing step with the air motor prop, the adhesive compositions were ready for testing.
Part 1 and Part 2 are targeted for 2:1 volume mix ratio. In some instances, appropriate weight ratios were determined to test properties. Amine to epoxy ratio is kept slightly over one for all the examples to insure complete reaction of epoxy as shown in the result section of Table 1. Appropriate weight ratio of Part 1 and Part 2 were weighed and mixed in the DAC mixer for one minute at 2350 RPM and immediately mixed under vacuum as described in previous paragraph. The mixed sample was then subjected to the following tests:
Lap-Shear Testing: 25 mm×100 mm Coupons were cut from 6-ply unidirectional glass/epoxy laminates supplied by MFG, Inc. with peel ply removed. Coupons were scribed at one end at 12.5 mm. Adhesive was applied evenly on one of the coupons within the scribed area for each bond assembly. Uniformity of bond thickness is insured by adding 1.0±0.5 mm glass spacer beads. Spacer beads should be sprinkled evenly over the material, covering no more than 5% of the total bond area. The other test coupon is placed on the bond area and spring loaded clips, such as Binder Clips from Office Max or Mini Spring Clamp from Home Depot, are attached, one to each side of the bond, to hold the assembly together during bake. Care is given to align parallel edges. Excess adhesive that is squeezed out is removed with a spatula before baking. Bond assemblies were given an open time of 15 to 30 minutes and baked at 70 degrees Celsius for six hours, and after cooling, remaining excess was sanded. Bonds were conditioned at room temperature for at least 24 hours. Bonds were inserted in wedge action grips and pulled apart at a rate of 10 mm per minute using an Instron model 5567 in tensile mode. Lap Shear strength was calculated by Instron's Blue Hill software package.
Free film mechanical properties: The same adhesive mix was used to prepare void free dog-bone shaped free film by skiving material with care to avoid any air pockets.
Load controlled lap-shear fatigue test was done using the same laminate and coupon construction as described in the previous paragraph. An automated system utilizing Instron, servo-controlled, hydraulically actuated, closed loop test equipment, and a personal computer with software designed by Westmoreland Mechanical Testing and Research, Inc. provided the means for machine control. Each specimen was inserted in wedge action grips along with frictionally retained shims with thickness equal to that of the fiberglass substrates and bond-line to ensure axial loading. The test was run at room temperature with an R-ratio of 0.1 at 5 Hz sinusoidal waveform and load application of 8 MPa. Testing was continued until 432,000 cycles or failure.
Evaluation of Pot Life with Adhesives Having Varying Amine Hydroxy Equivalent Weights:
Table 2 shows pot life comparison between propylene oxide-based polyether tetramine, Jeffamine XTJ-616, and ethylene oxide-based triethylenetetramine in similar formulas, wherein the amine/epoxy ratio was maintained between 1.03 and 1.05. The formulations and results are shown in Table 2:
In this experiment, both formulas (Examples 5 and 6) utilized the same amount of Accelerator 399 which also has significant influence on pot-life. If Accelerator 399 was absent, the pot life was found to be significantly higher.
Pot-life is defined as the interval from time when Part 1 (the epoxy component) and Part 2 (the amine component) were mixed and to time when internal temperature of adhesive reaches 50° C. in 415 ml. of mass. Part 1 and Part 2 were mixed in a 2 to 1 volume ratio using a static mixer; P C COX pneumatic dual applicator dispensed mixed adhesive into a paper cup marked with 415 ml. level line and initial time was noted. The cup was immediately placed in 25° C. water bath with a thereto-couple inserted to the center location of the mixed adhesive mass. PC based data logger was employed to record temperature every minute to determine Pot-life, time taken to reach 50° C., the peak temperature, and the time to reach the peak temperature.
In this experiment, the effect of the addition of fiberglass as a reinforcement filler was compared in a sample formulation as described in Table 3:
Examples 7 and 8 in Table 3 are a comparative study without and with microglass 9132 (fiberglass strands with an average of 220 micron length). Results indicate significant increase in modulus when microglass 9132 is present.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
