Ultraviolet (UV) curable gasket

Abstract

Ultraviolet (UV) curable shims that can be used to fill gaps or spaces are disclosed. The UV curable gasket consists of a layer of reinforcing fibers embedded in a curable resin matrix that is solid at room temperature and forms a crosslinked material upon exposure to UV light. The UV curable gasket may utilize two types of resin chemistry: (i) a free radical curable resin composition, which is an acrylate-based composition, and (ii) a cationic curable resin composition, which is an epoxy resin-based composition.

Description

[0001] Typically, shims function to eliminate gaps or spaces between assembled structural components. In aerospace applications, such shims are commonly required to properly assemble structural components and ensure the structural integrity of the aircraft. Aerospace assembly necessitates joining structural components together at their mating surfaces without leaving any gaps between the mating surfaces exceeding a predetermined allowance. Gaps exceeding the predetermined allowance must be filled with shims to provide the desired aerodynamic performance and structural integrity.

[0002] Liquid and solid gaskets are commercially available. Liquid gaskets for aerospace applications are typically used to fill gaps of 3 mm or less. These liquid gaskets are not suitable for larger gaps or voids. For assembling composite components, solid gaskets are typically made of composite materials similar to those used in the composite components. For aerospace composite components, currently used liquid and solid gaskets are based on epoxy-amine curing chemistry or similar thermosetting chemistry, which requires heating at high temperatures and long curing cycles.

[0003] There remains a need for solid gaskets that require less processing time and less energy consumption compared to current thermosetting gaskets, allowing for higher productivity during the assembly of structural components. For aerospace applications, such solid gaskets should also possess the required physical properties, such as high dry and wet glass transition temperatures (T0) after curing. g ) and moisture resistance.

[0004] This document discloses a UV-curable gasket that can be used to fill gaps or spaces. This UV-curable gasket achieves rapid curing times (on the order of minutes) and exhibits excellent physical properties after curing. The UV-curable gasket according to this disclosure consists of a reinforcing fiber layer embedded in a curable resin matrix that is solid at room temperature (20°C–25°C) and forms a cross-linked material upon exposure to UV light. Prior to UV curing, the curable gasket is in the form of a flexible sheet of fiber-reinforced resin matrix, which can be machined to desired sizes and shapes. This UV-curable gasket is not B-stage (i.e., not partially cured) and is stable at room temperature. In this context, the term "stable" means that the curable gasket can be stored at room temperature and does not undergo a cross-linking reaction when left at room temperature. This stability at room temperature is an advantage over other curable gasket materials that require refrigeration. Furthermore, the UV-curable gasket contains no heat-sensitive raw materials and requires only UV exposure to achieve complete curing, i.e., no heating to elevated temperatures is required. Unlike solvent-based UV-curable coatings on the market today, the resin matrix of UV-curable pads is solvent-free. Solvent-free resins are preferred because the presence of solvents and volatile organic compounds (VOCs) can lead to safety and regulatory issues.

[0005] In addition, the resin matrix of the UV-curable gasket contains a unique toughening component that allows for a less brittle curable material with good processability (or lamination) and low tack (i.e., low stickiness to the touch). Tackiness is a measure of the mechanical resistance that needs to be overcome to separate a material from another substrate. Furthermore, the resin matrix of the gasket is formulated to provide a final UV-curable material with desired mechanical properties, as well as moisture resistance and fluid resistance. Desired mechanical properties include high dry and wet glass transition temperatures (T0) after curing. g High humidity T g Curing materials are permitted to be used at temperatures above normal operating temperature.

[0006] Following UV exposure, the cured gaskets disclosed herein can have a dry T-temperature greater than 200°C, more specifically 232°C–250°C. g and a humid T greater than 204°C, more specifically 215°C-232°C g The T disclosed in this article g The value was determined using a rheometer in torsional mode via a rheological method. This method starts with the storage modulus, as described in TA Instruments' article titled "Measurement of Glass Transition Temperatures by Dynamic Mechanical Analysis and Rheology," which measures the T value. g The article can be found at https: / / www.tainstruments.com / pdf / literature / RH100.pdf. As an example, T... g The initial Tg of the storage modulus can be obtained by measuring it on an AR 2000EX rheometer in torsional rectangular mode. Using this rheometer, the initial Tg of the cured resin sample can be measured at the intersection of the extrapolated tangents drawn from points on the storage modulus curve before and after the glass transition event. g .

[0007] Two types of resin chemicals are available for use in the UV-curable gaskets disclosed herein: (i) cationic curable resin compositions, which are epoxy resin-based compositions, and (ii) free radical curable resin compositions, which are acrylate-based compositions.

[0008] UV curing chemistry requires a UV energy source to generate UV light to initiate the polymerization reaction. The UV portion of the electromagnetic spectrum is divided into three distinct wavelength bands: UVA (315-400 nm), UVB (280-315 nm), and UVC (100-280 nm). UVA (315-400 nm) is the most commonly used UV light in industrial applications. For both cationic and free radical resin compositions, a photoinitiator is required. A photoinitiator absorbs UV light and, upon exposure to the correct UV wavelength, generates an excited state that can induce a chemical reaction, leading to the polymerization and curing of the resin composition.

[0009] Cationic curing resin

[0010] The cationic curing resin compositions used for the purposes disclosed herein contain a combination of alicyclic epoxy resins, oxetane resins, thioonium or iodonium photoinitiators, and toughening components.

[0011] According to one embodiment, the curable resin matrix of the gasket is formed from a cationic curable resin composition comprising the following components:

[0012] (a) A combination of two or more alicyclic epoxy resins, wherein at least one of the alicyclic epoxy resins is solid at room temperature;

[0013] (b) Oxybutane resin (as a reactive diluent or epoxy modifier);

[0014] (c) Cationic photoinitiators selected from thionium and iodonium salts; and

[0015] (d) Toughening component, which is selected from: polyacrylate liquid elastomer, epoxidized polybutadiene, polyarylsulfone polymer, polyether diamine and acrylic block copolymer.

[0016] In some embodiments, the relative weight percentages of these components are as follows, based on the total weight of the resin composition:

[0017] (a) 65% to 75%;

[0018] (b) 5% to 13%;

[0019] (c) 0.1% to 5%;

[0020] (d) 10% to 25%.

[0021] As used in this disclosure, the term "room temperature" refers to a temperature in the range of 20°C to 25°C.

[0022] The cationic curable resin composition may further comprise a photosensitizer (or sensitizer), inorganic filler, or flow control agent in particulate form (e.g., powder). In addition to the cationic photoinitiator described above, the cationic curable resin composition may further comprise a type I photoinitiator.

[0023] The cationic curing resin composition contains no epoxy curing agents (or curing agents) containing reactive amino groups or other epoxy curing agents that require thermal activation and are typically present in conventional thermosetting epoxy compositions. If chosen as a toughening component, polyether diamine will be the only amine compound in the resin composition. Preferably, the cationic curing resin composition contains no free radical polymerizable acrylates or methacrylates that are not polyacrylate liquid elastomers or PMMA-b-PBA-b-PMMA triblock copolymers. That is, if chosen as a toughening component, polyacrylate liquid elastomers or PMMA-b-PBA-b-PMMA triblock copolymers or combinations thereof will be the only acrylate / methacrylate component in the resin composition.

[0024] Alicyclic epoxy resin

[0025] Alicyclic epoxy resins are characterized by non-aromatic saturated rings in their molecular structure. As used herein, the term "epoxy resin" refers to monomers, oligomers, and precursors containing one or more epoxy groups. Alicyclic epoxy resins used in cationic curing resin compositions are compounds having at least one alicyclic backbone (or saturated carbide ring) and two or more epoxy groups per molecule. Suitable alicyclic epoxy resins include compounds represented by the following general formula (I):

[0026] .

[0027] In general formula (I), X represents a single bond or a linking group. Linking groups include, for example, divalent hydrocarbon groups, carbonyl groups (-CO-), ether bonds (-O-), ester bonds (-COO-), amide bonds (-CONH-), carbonate bonds (-OCOO-), and groups containing two or more of these groups linked to each other. Divalent hydrocarbon groups are preferably examples of straight-chain or branched alkylene groups having 1 to 18 carbon atoms (those having 1 to 6 carbon atoms are more preferred); and divalent alicyclic hydrocarbon groups (those having divalent cycloalkylene groups are more preferred). Straight-chain or branched alkylene groups are represented by methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene. Divalent alicyclic hydrocarbon groups are represented by 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylene.

[0028] Examples of suitable bifunctional alicyclic epoxides include epoxides having the following chemical structures:

[0029]

[0030] Where n represents an integer from 1 to 30.

[0031] In a preferred embodiment, the cationic curing epoxy resin composition contains a combination of alicyclic epoxy resins, at least one of which is a solid resin at room temperature.

[0032] A suitable example of a solid alicyclic epoxy resin is EHPE3150 from Daicel Corp., poly[(2-epoxyethylene)-1,2-cyclohexanediol]2-ethyl-2-(hydroxymethyl)-1,3-propylene glycol ether], represented by the following chemical structure:

[0033]

[0034] Where R represents a straight-chain or branched saturated aliphatic hydrocarbon group containing 6 or more carbon atoms; n represents an integer from 1 to 50.

[0035] In some embodiments, the combination of alicyclic epoxy resins includes at least one liquid resin that is liquid at room temperature.

[0036] Suitable liquid alicyclic epoxy resins are those with a viscosity of less than 1000 mPa·s at 25°C, as determined by a Brookfield viscometer.

[0037] Examples of commercially available liquid alicyclic epoxy resins are Celloxide™ 2021P (methyl (3',4'-epoxycyclohexane)3,4-epoxycyclohexylcarboxylate) and Celloxide™ 2081 (ε-caprolactone modified with 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate). Further examples of liquid resins include 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (Uvicure S105 from Lambson), represented by the following chemical structure:

[0038] ,as well as

[0039] Bis((3,4-epoxycyclohexyl)methyl)adipate (from Ramson's Uvicure S128) is represented by the following chemical structure:

[0040]

[0041] The combination of alicyclic epoxy resins constitutes more than 50% of the resin matrix by weight. More specifically, the total amount of all alicyclic epoxy resins in the combination can be in the range of 50% to 65% by weight based on the total weight of the resin matrix, and in some embodiments, 65% to 75% by weight.

[0042] reactive diluents

[0043] When used in combination with alicyclic epoxy resins, oxetane resins, which have low viscosity, can act as reactive diluents. Oxetane resins are resins with a four-membered ring having at least three carbon atoms and one oxygen atom (as shown below):

[0044] .

[0045] Suitable low-viscosity compounds include oxobutane resins having a viscosity of 300 mPa·s or less at 25°C, as determined by a Brookfield viscometer, preferably 15-100 mPa·s at 25°C.

[0046] Examples of oxetane resins that can be used as reactive diluents are: 3-ethyloxetane-3-methanol, commercially available as UviCure S130 from Ramson (Sartomer), a liquid alcohol-functionalized oxetane with a viscosity of 15-25 mPa·s at 25°C; 1,4-bis[(3-ethyl-3-oxetane-methoxy)methyl]benzene, commercially available as Uvicure S150 from Ramson (a liquid difunctional oxetane resin with a viscosity of 150-220 mPa·s at 25°C); and 4,4-bis(3-ethyl-3-oxetane-methoxymethyl)biphenyl, commercially available as Uvicure S160 from Ramson (a liquid difunctional oxetane resin with a viscosity of 240-300 mPa·s at 25°C).

[0047] The oxetane resin may be present in an amount of 0.1% to 20% (including 5% to 13%) by weight based on the total weight of the resin composition.

[0048] Photoinitiator

[0049] Suitable cationic photoinitiators are thioonium and iodonium salts that can produce Brønsted acid. Iodonium salts can be selected from diaryliodonium, triaryliodonium, aromatic iodonium, and any combination thereof. Thionium salts can be selected from aromatic thioonium salts.

[0050] Examples of suitable thioonium salts are: (thioalkyldiphenyl-4,1-diyl)bis(diphenylthioonium)bis(hexafluoroantimonate) (commercially available from Ramson as Speedcure 976s); (thioalkyldiphenyl-4,1-diyl)bis(diphenylthioonium)bis(hexafluoroantimonate) (commercially available from Ramson as Speedcure 976D); and (4-{[4-(diphenylthioonium)phenyl]thioonium}phenyl)diphenylthioonium bis(hexafluorophosphate) in propylene carbonate (commercially available from Ramson as Speedcure 992).

[0051] Suitable examples of iodonium salts are: bis(4-dodecylphenyl)iodonium hexafluoroantimonate (commercially available from Ramson as Speedcure 937); bis-(4-tert-butylphenyl)iodonium hexafluorophosphate (commercially available from Ramson as Speedcure 938 and Speedcure 938D in reactive solvents); and 4-isopropyl-4'-methyldiphenyliodonium tetra(pentafluorophenyl)borate (commercially available from Ramson as Speedcure 939).

[0052] The amount of cationic photoinitiator in the resin matrix can be in the range of 0.1% to 5% by weight based on the total weight of the resin composition.

[0053] In addition to the aforementioned cationic photoinitiators, the cationic curable resin composition may further comprise a type I photoinitiator in an amount of 0.01% to 1% by weight based on the total weight of the resin composition, in order to catalyze the reaction. Type I photoinitiators will be described in more detail subsequently with reference to radical-curable resin compositions.

[0054] photosensitizer

[0055] In some embodiments, a photosensitizer (or sensitizer) is added to increase the rate of photoinitiated polymerization or to change the wavelength at which polymerization occurs. When using a photosensitizer, photoinitiators that absorb at shorter wavelengths can be used in combination.

[0056] Suitable photosensitizers include anthracene, xanthones, thioxanthone, benzophenone, acetophenone, dicaprocene, methyl ketone, xanthone, pyrene methanol, pyrene, perylene, quinone, benzoyl ester, and any combination thereof. Specific examples of anthracene are 9,10-dibutoxyanthracene and 9,10-diethoxyanthracene. Commercially available examples of anthracene photosensitizers are those from the ANTHRACURE UVS series from Kawasaki Kasei Chemicals Ltd.

[0057] The amount of photosensitizer in the resin matrix can range from 0.01% to 5% by weight based on the total weight of the resin composition.

[0058] Fillers and flow control agents

[0059] Inorganic fillers or flow control agents in particulate form (e.g., powder) can be added to resin compositions of curable resin matrices to alter rheology or impart additional properties to the resin matrix, such as heat resistance, refractoriness, or electrical conductivity. Inorganic fillers may include fumed silica, ceramic microspheres, calcium carbonate, alumina, and any combination thereof. Ceramic microspheres are small, spherical, hollow bodies. Each microsphere consists of a shell surrounding a hollow core. Examples of commercially available ceramic microspheres are sold by Zeelan Industries, Inc. under the trade name Zeeospheres®, such as G-200, G210, and W-200.

[0060] The amount of inorganic filler or flow control agent in the resin composition may be in the range of 0.1% to 5% by weight based on the total weight of the resin composition.

[0061] Free radical cured resin

[0062] The free radical curing resin compositions used for the purposes disclosed herein contain low-viscosity (meth)acrylate monomers, solid acrylate polymers or solid cellulose ester polymers, dendritic acrylate oligomers, free radical photoinitiators, and toughening components.

[0063] According to one embodiment, the free radical curable resin composition comprises the following components:

[0064] (a) Low-viscosity (meth)acrylate monomers or oligomers that are free radical polymerizable and have a viscosity of less than 24,000 cP (mPa·s) at 60°C;

[0065] (b) A homopolymer or copolymer of methyl methacrylate that is solid at room temperature, or a cellulose ester polymer that is solid at room temperature, and preferably, the cellulose ester polymer has a T0 greater than 100°C. g T g It was determined using a rheometer in torsional mode via rheological methods;

[0066] (c) Thioether dendritic acrylates;

[0067] (d) One or more free radical photoinitiators; and

[0068] (e) A toughening component selected from: polyacrylate liquid elastomers, epoxidized polybutadiene, acrylic block copolymers, and combinations thereof.

[0069] As used herein, the term "(meth)acrylate" refers to both acrylate and methacrylate, as well as acrylic acid and methacrylic acid. As used herein, the term "room temperature" refers to a temperature in the range of 20°C to 25°C.

[0070] The free radical polymerizable monomer or oligomer may be selected from urethane (meth)acrylates, epoxy (meth)acrylates without epoxy functional groups, and polyester (meth)acrylates. In some embodiments, the free radical polymerizable acrylate or methacrylate monomer or oligomer is a urethane (meth)acrylate monomer or oligomer with a functionality of 1 to 6.

[0071] The free radical curing resin composition may further comprise one or more additional components selected from the following: inorganic fillers or flow control agents in particulate form (e.g., powder), acrylate functional impact modifiers, and wetting agents.

[0072] Preferably, the free radical curable resin composition does not contain epoxy resin. Therefore, it is distinguishable from hybrid resin compositions containing polymerizable acrylates, epoxy resins, photoinitiators, and epoxy curing agents. Such hybrid resin compositions contain both UV-curable and thermocurable components.

[0073] Examples A and B below are representative of free radical curable resin compositions:

[0074] Example A

[0075]

[0076] Example B

[0077]

[0078] The quantities shown are in "wt%", which refers to the weight percentage based on the total weight of the resin composition.

[0079] (meth)acrylate monomers

[0080] The (meth)acrylate monomer may be selected from alkyl acrylates and / or alkyl methacrylates. The monomer may be aliphatic, straight-chain and / or branched acrylic and / or methacrylate monomers, and / or cyclic methacrylate monomers, and / or aromatic methacrylate monomers. Preferably, the (meth)acrylate monomer is selected from acrylic acid, methacrylic acid, alkyl acrylic monomers, alkyl methacrylate monomers, and mixtures thereof, wherein the alkyl group contains 1 to 22 straight-chain, branched, or cyclic carbons; the alkyl group preferably contains 1 to 12 straight-chain, branched, or cyclic carbons.

[0081] (Meth)acrylate monomers can have a functionality of 1 to 6, that is, monofunctional up to hexafunctional.

[0082] One or more low-viscosity or liquid (meth)acrylate monomers can be added as diluents to free radical curing resin compositions to reduce the viscosity of the resin composition. These diluent monomers are in liquid form at room temperature or have a viscosity of less than 100 cP at 25°C.

[0083] Examples of suitable acrylate diluent monomers include EBECRIL® IBOA (isoborneol acrylate), supplied by Allnex, a monofunctional liquid monomer that polymerizes upon exposure to a free radical source. Another example is Sartomer SR 351LV (trimethylolpropane triacrylate or TMPTA), supplied by Sartomer, a trifunctional liquid monomer.

[0084] (Meth)acrylate oligomers

[0085] As used herein, “oligomer” is a polymer unit containing 2 to about 100 monomer units, i.e., a degree of polymerization of 2 to about 100.

[0086] Oligomers can be monofunctional or polyfunctional (meth)acrylates. Oligomers can contain aliphatic or aromatic backbone structures.

[0087] Uraffinate (meth)acrylate oligomers are particularly suitable. Uraffinates (meth)acrylates are typically the product of the reaction of at least one hydroxyl-functionalized methacrylate and isocyanate together with an optional alcohol or diol in the presence of a catalyst. Generally, urethane (meth)acrylates exhibit excellent weather resistance and good abrasion resistance. Furthermore, they show good adhesion to plastics and metals and impart chemical and solvent resistance.

[0088] Examples of commercially available urethane acrylate oligomers include:

[0089] EBECRYL® 8606, aliphatic urethane tetraacrylate; EBECRYL® 4859, bifunctional aliphatic urethane methacrylate; EBECRYL® 5781, aliphatic urethane diacrylate; EBECRYL® 5129, hexafunctional aliphatic urethane acrylate, all from Zhanxin Company; and Bomar® BR-941, a hexafunctional aliphatic polyether urethane acrylate supplied by DYMAX.

[0090] Epoxy (meth)acrylates do not have epoxy functional groups, but may have hydroxyl functional groups. They are fast-curing resins with excellent chemical resistance, adhesion, and high hardness. Commercially available examples of epoxy (meth)acrylates include Sartomer® CN120A75 and Allnex EBECRYL 3708, EBECRYL 605 (modified bisphenol A epoxy diacrylate), etc.

[0091] Polyester (meth)acrylates are synthesized from organic acids and polyols. They have low viscosity and excellent scratch and abrasion resistance. They are fast-curing and offer reasonable outdoor durability.

[0092] Examples of commercially available polyester acrylates include: Sartamomer® CN704, Sartamomer® CN2610, and Sartamomer® 203 from Arkema, and Ebecryl® 837, Ebecryl® 892, and Ebecryl® 812 from Zyxel.

[0093] Solid methacrylate and cellulose ester polymers

[0094] Examples of commercially available solid methacrylates include Elvacite 4026, which has a curing temperature of 75°C. g Solid methyl methacrylate copolymers; and NeoCryl® B-728, which is solid at room temperature and has a Tc of 111°C after curing. g methyl methacrylate homopolymer.

[0095] A suitable example of a cellulose ester polymer is Bomar JL-106E, which is solid at room temperature and has a Tc of 118°C after curing. g Acrylamidomethyl-substituted cellulose ester polymers.

[0096] Dendritic acrylates

[0097] Thioether dendritic acrylates are dendritic oligomers with hyperbranched structures and numerous reactive functional groups. Here, the term "dendritic" refers to the shape in which monomers branch radially from a core and polymerize and diffuse radially. Preferred thioether dendritic acrylates have a functionality of at least 15, more specifically 15 to 50. In a preferred embodiment, the thioether dendritic acrylate has a functionality of 30 and a curing temperature greater than 350°C (662°F). g T gThis was determined through dynamic mechanical analysis (DMA). As an example, this 30-functional sulfide dendritic acrylate is commercially available as BDT-4330 from Bomar (formerly Dymax Oligomers & Coatings). When sulfide dendritic acrylates are incorporated into curable resin matrix formulations, dry curing temperatures above 200°C can be achieved. g For example, for a cured hardened matrix, 240°C-250°C.

[0098] Free radical photoinitiators

[0099] Free radical photoinitiators can be classified into Type I and Type II. Type I photoinitiators break down upon exposure to radiation, generating free radical species capable of initiating the polymerization of unsaturated compounds. Type II photoinitiators are compounds that do not break down upon exposure to radiation and generally do not initiate free radical chain polymerization unless a co-initiator is present. Upon exposure to radiation, the interaction between Type II photoinitiators and co-initiators leads to the generation of free radical species capable of initiating the polymerization of UV-curable resins.

[0100] Suitable type I photoinitiators include: acetophenone; hydroxyacetophenone; aminoacetophenone; and phosphine oxide.

[0101] Specific examples are: 2-hydroxy-2-methyl-1-phenylpropanone (SpeedCure® 73); 1-hydroxycyclohexylphenyl ketone (SpeedCure® 84); 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (SpeedCure® 2959); 2,2-dimethoxy-2-phenylacetophenone (SpeedCure® BKL); 2-methyl-1-[4-(methylthio)phenyl]2-morpholinopropane-1-one (SpeedCure® 97); 2-benzyl-2-dimethylamino-4-morpholinobutyrophenyl (SpeedCure® BDMB); 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (SpeedCure® TPO); and phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide (SpeedCure® BPO).

[0102] Suitable type II photoinitiators include: benzophenone and substituted benzophenone; benzoyl carbamate; and thioxanone.

[0103] Specific examples are: benzophenone (SpeedCure® BP); 4-methylbenzophenone (SpeedCure® MBP); methyl-2-benzoylbenzoate (SpeedCure® MBB); 4-phenylbenzophenone (SpeedCure® PBZ); methylbenzoyl benzoate (SpeedCure® MBF); 2-isopropylthioxanthone (SpeedCure® 2-ITX); 1-chloro-4-propoxythioxanthone (SpeedCure® CPTX); and 2,4-diethylthioxanthone (SpeedCure® DETX).

[0104] One or more photoinitiators can be used in combination with amine synergists. Suitable amine synergists are aminobenzoates. Specific examples are: ethyl-4-(dimethylamino)benzoate (SpeedCure® EDB); 2-ethylhexyl-4-(dimethylamino)benzoate (SpeedCure® EHA); and 2-butoxyethyl-4-(dimethylamino)benzoate (SpeedCure® BEDB). All SpeedCure products mentioned herein are available from Ramson Laboratories.

[0105] Acrylic functional impact modifier

[0106] Acrylate-functionalized impact modifiers can be added to free-radical curing resin compositions to provide additional toughening without hindering curing properties due to the acrylate functional groups. If present, the amount of impact modifier is up to 10 wt% based on the total weight of the resin composition.

[0107] An example is Paraaloid 2691A, available from Dow Plastics, a methyl methacrylate-butadiene-styrene (MBS) polymer in granular form. Methyl methacrylate-styrene (MBS), also known as impact-modified styrene-methyl methacrylate (SMMA), consists of rubber particles dispersed within its methyl methacrylate-styrene polymer matrix. It is a transparent engineering and commercial thermoplastic with excellent transparency, high impact strength, good stiffness, and good resistance to many chemicals.

[0108] wetting agent

[0109] Wetting agents can be added to cationic or free radical curing resin compositions to improve surface adhesion to composite or metallic substrates, resulting in better adhesion properties. The amount of wetting agent can be up to 5 wt% based on the total weight of the resin composition.

[0110] Suitable wetting agents typically consist of hydrophilic and hydrophobic segments. Wetting agents used in this application can be of the following types: siloxanes, polyether-modified siloxanes, sulfosuccinates, gemini surfactants (dimeric structures consisting of two hydrophobic chains and two hydrophilic heads, connected by spacer groups at or near the head groups), and alcohol alkoxylates.

[0111] One commercially available example is SURFYNOL® AS 5080 from Evonik, an organic wetting agent composed of a blend of gemini surfactants. This wetting agent has the ability to reduce both equilibrium and dynamic surface tension. Another example of a suitable wetting agent is BYK-3763 from BYK, a silicone-containing surface additive that improves substrate wetting and prevents surface defects. This wetting agent is a solution of polyether-modified polydimethylsiloxane. An example of an alcohol alkoxylate is SURFYNOL® AS 5180 from Evonik.

[0112] Fillers and flow control agents

[0113] The inorganic fillers and flow control agents that can be added to the free radical curing resin composition are the same as those described above for the cationic curing resin composition. If present, the amount of filler or flow control agent can be up to 10 wt% based on the total weight of the resin composition.

[0114] toughening components

[0115] The toughening components used in cationic curable resin compositions and free radical curable resin compositions may be selected from: polyacrylate liquid elastomers, epoxidized polybutadiene, polyarylsulfone polymers, polyether diamines, and acrylic block copolymers.

[0116] Polyacrylate liquid elastomers are solvent-free liquids at room temperature. Particularly suitable are (meth)acrylate-functionalized poly(acrylates).

[0117] The (meth)acrylate-functionalized poly(acrylate) preferably has at least two (meth)acrylate functional groups, is a combination of two or more monofunctionalized (meth)acrylate-functionalized poly(acrylate), or is a combination of monofunctionalized (meth)acrylate-functionalized poly(acrylate) and a (meth)acrylate-functionalized poly(acrylate) having at least two (meth)acrylate functional groups.

[0118] (Meth)acrylate-functionalized poly(acrylate) can be derived from a blend of at least 80% by weight of certain monofunctional (meth)acrylate monomers selected from alkyl (meth)acrylates, aralkyl esters, hydroxyalkyl esters and phenyl esters and 0-20% by weight of monofunctional non-(meth)acrylate vinyl monomers selected from maleic anhydride, maleate ester, fumarate and vinyl ester, acrylonitrile, styrene, butadiene, vinyl acrylonitrile, N,N-dimethylacrylamide, N-vinylpyrrolidone, acrylmorpholine, N-vinylcaprolactam and N-vinylformate.

[0119] In other words, (meth)acrylate-functionalized poly(acrylate) can be defined with respect to the following main chain:

[0120] -(A)x-(B)y-

[0121] Wherein A represents one or more comonomer units selected from nonfunctional alkyl or aralkyl mono(meth)acrylates, and B represents one or more comonomer units selected from alkyl or aralkyl monofunctionalized (meth)acrylates (selected from alkoxyalkyl or aroxyalkyl groups substituted with or not substituted with heteroatoms, O, S, N, P, or halogens) or non(meth)acrylate vinyl monomers such as maleic anhydride, wherein x and y represent the fractions of A and B, respectively, and x is at least 0.30 and at most 0.95, and y is at least 0.05 and at most 0.70. Although the above structure indicates a block copolymer, random incorporation of A and B units distributed within the polymer backbone can occur and may be preferred.

[0122] (Meth)acrylate-functionalized poly(acrylate) can have a number average molecular weight (Mn) in the range of 1,000-100,000, such as in the range of 5,000-80,000 or 5,000-50,000, as determined by gel permeation chromatography (GPC).

[0123] GPC measurements can be performed using a polystyrene gel column with chloroform as the mobile phase, and the number-average molecular weight (Mn) can be determined relative to a polystyrene standard.

[0124] Examples of suitable (meth)acrylate-functionalized poly(acrylate) liquid elastomers are those supplied by Kaneka Corporation under the trade name XMAP (such as XMAP RC100C and XMAP SA100S).

[0125] Epoxidized polybutadiene is formed by introducing epoxy groups via the oxidation of the vinyl groups of 1,2-polybutadiene. Preferred epoxidized polybutadiene has the following chemical formula:

[0126]

[0127] Where m = 4-11; n = 12-35.

[0128] Examples of commercially available products are JP-100 (220 poise at 45°C) and JP-200 (1000 poise at 45°C) from Nippon Soda Co., Ltd.

[0129] Polyarylsulfone polymers include polyethersulfone (PES), polyether ethersulfone (PEES), and copolymers of PES and PEES.

[0130] Preferred polyether diamines have a weight-average molecular weight (MW) of 10,000 g / mol or higher, as determined by gel permeation chromatography (GPC). Particularly suitable are amine-functionalized butyl ether elastomers having the following chemical structure:

[0131]

[0132] Where n is the degree of aggregation and is an integer from 50 to 150.

[0133] A suitable example of a polyether diamine is poly(oxy-1,4-butanediyl), α-(4-amino-butyl)-ω-(4-aminobutoxy), which is commercially available as Dynamar™ HC 1101 from Dyneon (a division of 3M), with a molecular weight of about 10,000 g / mol.

[0134] Suitable acrylic block copolymers are those supplied by Arkema and sold under the trade name Nanostrength®. A preferred block copolymer is Nanostrength® M52N, a poly(methyl methacrylate-butyl acrylate-methyl methacrylate) (PMMA-b-PBA-b-PMMA) block copolymer, which is a triblock copolymer consisting of a poly(butyl acrylate) central block and poly(methyl methacrylate) flanking blocks.

[0135] Reinforcing fibers

[0136] The reinforcing fibers used in gaskets can be in the form of woven or nonwoven fabrics. Woven fabrics consist of continuous fibers arranged in a woven pattern. The woven pattern is unrestricted and can be plain weave, twill weave, square plain weave, satin weave, etc. Nonwoven fabrics consist of randomly oriented fibers. The fibers can be selected from glass fibers, carbon fibers, aramid fibers, quartz fibers, polyester fibers, and combinations thereof.

[0137] The areal weight of reinforcing fabrics can range from 500 to 1500 g / m².2 (or gsm) range. In some embodiments, the fiber reinforcement is a heavy woven glass fabric, such as a twill woven E-glass fabric with an area weight of 876 gsm.

[0138] The resin content relative to the fiber reinforcement can be between 30% and 70% by weight, preferably in the range of 50%. The thickness of the UV-cured coating material can be between 0.01 inches and 0.06 inches.

[0139] Manufacturing method

[0140] The components of a cationic or free radical curable resin composition can be mixed, for example, by adding them to a high-speed mixing vessel with shear blades. Liquid resins can be added and stirred at room temperature. For the addition of solid acrylate resins, cellulose ester polymers, or toughening agents, the temperature of the mixture will need to be raised to the melting temperature of the components, for example, 150°F–250°F (or 65°C–121°C). Once a homogeneous mixture is obtained, the resin composition can be coated onto reinforcing fabrics using conventional film coating techniques to produce a supported, UV-curable resin film. The coating temperature can be in the range of 150°F–250°F (or 65°C–121°C).

[0141] Fabrics can be impregnated with resin films to form UV-curable pads, also known as "prepregs." Impregnation can be accomplished by continuously moving the fabric web and pressing a continuous resin film against the side of the web or by pressing two resin films against opposite sides of the web. Impregnation can be promoted by applying heat and pressure (e.g., 150°F–180°F (or 65.5°C–82.2°C) and 40–60 psi). The conditions during impregnation do not cause the resin to cure.

[0142] After impregnating the fabric with a resin film, the UV-curable prepreg can be cut, shaped, and prepared for UV curing or alternatively stored at room temperature until ready for use. The UV-curable prepreg is tacky to the touch and can be easily applied to substrates such as composite or metal substrates. The tacky prepreg can still be removed and modified if needed before curing.

[0143] Any conventional UV light source can be used for UV curing, such as a mercury vapor lamp or a UV LED lamp. The type, intensity, and wavelength of the UV lamp can vary. The wavelength of the UV lamp can be between 100 and 400 nm. Preferably, the UV light will be a light source in the UVA range (315-400 nm). The lamp power can be from 50 watts to 500 watts. The distance between the UV lamp and the substrate can vary depending on the intensity of the light source.

[0144] For gaskets containing cationic curing resin compositions, the curing time can be from 1 minute to 1 hour, plus possible additional post-curing or dark curing time. For gaskets containing free radical curing resins, the curing time can be from 30 seconds to 10 minutes. Gaskets in sheet form (also referred to herein as “sheets”) can be stacked and cured, allowing multiple sheets to cure simultaneously. The number of sheets depends on the light intensity of the UV lamp. For example, the number of sheets can be from 2 to 5.

[0145] Example

[0146] Example 1

[0147] Free radical cured formulations

[0148] Table 1 shows the resin compositions formulated for free radical curing. Amounts are reported as a weight percentage (wt%) based on the total weight of the resin composition.

[0149] Table 1

[0150]

[0151] Mix the components of each resin composition using a high-speed mixer with high-shear blades. To dissolve the solid acrylate resin, heat the mixture to 230°F (110°C). Blend the components except the photoinitiator until homogeneous or for about 30 minutes. Then add the photoinitiator as a final step and blend for about 5 minutes.

[0152] To form gaskets from the resin compositions disclosed in Table 1, each resin composition was degassed after mixing and then coated at 200°F (93.3°C) to form two UV-curable resin films. After coating, a fabric carrier was placed between the two UV-curable films. The resin films were pressed into the fabric carrier by holding at 180°F (82.2°C) and 60 psi for 30 minutes.

[0153] Each resin composition disclosed in Table 1 was cured and evaluated to determine the glass transition temperature (T). g T was measured using an AR2000EX rheometer in torsional rectangular mode. g And T g The results are reported in Table 2. For this test, each resin composition was placed in a 50 mm × 12 mm × 3 mm mold and cured by placing the mold under UV light for 2 minutes to ensure complete curing. The cured samples were measured in torsion mode at 0.05% strain from 23°C to 275°C. To determine the wet T... g The cured sample was conditioned for 30 days at 160°F (70°C) and 95% relative humidity.

[0154] Table 2

[0155]

[0156] The results in Table 2 show that resins A, B, C, D, and E can be completely cured within 30 seconds to 5 minutes, and exhibit very high glass transition temperatures (T0) for UV-curable materials. g Values ​​reach up to 450°F (232°C). These values ​​are higher than typical values ​​for acrylate-based materials, which typically have T values ​​up to 350°F (176°C). g value.

[0157] Further testing of cured resin B was conducted to determine its resistance to fluid exposure, and the results are reported in Table 3. The solvents used for fluid exposure in Table 3 were selected based on common fluids that may be encountered in aerospace and industrial applications. JP-4 is a jet fuel / jet propellant containing a mixture of aliphatic and aromatic hydrocarbons, corrosion inhibitors, and anti-icing additives. Skydrol from Eastman is a fire-retardant hydraulic fluid made from a fire-retardant phosphate base with various oil additives to inhibit corrosion.

[0158] Table 3

[0159]

[0160] Example 2

[0161] Cationic cured formulations

[0162] Five resin compositions (resins FJ) suitable for cationic curing were prepared according to the formulations shown in Table 4. Amounts are reported as a weight percentage (wt%) based on the total weight of the resin compositions.

[0163] Mix the components of each resin composition using a high-speed mixer with high-shear blades. To dissolve the solid components, heat the mixture to 230°F (110°C). Blend the components except the photoinitiator until homogeneous or for about 30 minutes. Add the photoinitiator as a final step and blend with the other components for about 5 minutes.

[0164] Each resin composition disclosed in Table 4 was cured by placing each resin composition in a 50 mm × 12 mm × 3 mm mold and placing the mold under UV light for 2 minutes to ensure complete curing (i.e., 100% curing degree), and the curing time is also reported in Table 4.

[0165] Table 4

[0166]

[0167] The cationic curable compositions in Table 4 differ from commercially available, thermosetting epoxy resins because of their reduced curing time. All resins FJ cure in less than 60 minutes upon exposure to UV light. Commercially available epoxy composites typically require curing times greater than 60 minutes, more typically 90 to 360 minutes, such as Solvay MTM® 46 prepreg, Toray 2511 prepreg, and Hexcel HexPly® M21 prepreg. Therefore, the faster curing times offered by the UV-curable resins in Table 4 result in increased production and processing rates. Higher throughput and continuous processing, in turn, lead to lower costs and lower energy consumption, enabling more sustainable processes.

[0168] To form gaskets from the resin compositions disclosed in Table 4, each resin composition was degassed after mixing and then coated at 200°F (93.3°C) to form two UV-curable resin films. After coating, a fabric carrier was placed between the two UV-curable films. The resin films were pressed into the fabric carrier by holding at 180°F (82.2°C) at 60 psi for 30 min.

[0169] Example 3

[0170] Comparison of free radical cured formulations

[0171] For comparison, resin compositions (mixtures 1-4) suitable for free radical curing were prepared according to the formulations disclosed in Tables 5 and 6. Amounts are reported as a weight percentage (wt%) based on the total weight of the resin compositions.

[0172] The resulting resin was cured by UV radiation, and the Tc of the cured material was measured. g The results are reported in Tables 5 and 6. T was measured using an AR 2000EX rheometer in torsional rectangular mode. g To determine the wet T g The cured sample was conditioned for 30 days at 160°F (70°C) and 95% relative humidity.

[0173] Table 5

[0174]

[0175] Table 6

[0176]

[0177] Compared to the cured resins based on the resin compositions shown in Table 1, the cured resins based on the resin compositions (mixtures 1-4) disclosed in Tables 5 and 6 exhibit significantly lower dry and wet T values. g Lower T gThe low T value limits the application of such resins in many aerospace and industrial applications that require robust and high-strength materials. Furthermore, the lower T value... g The value (which is typical for most free radical curing acrylate formulations) has broadly limited the use of UV curing for certain applications, such as aerospace applications.

Claims

1. A UV-curable pad comprising a reinforcing fiber layer embedded in or impregnated with a curable resin matrix, wherein the curable resin matrix is ​​solid at room temperature (20°C-25°C) and comprises: (a) At least one free radical polymerizable acrylate or methacrylate monomer or oligomer having a viscosity of less than 24,000 cP at 60°C. (b) methyl methacrylate homopolymers or copolymers that are solid at room temperature or cellulose ester polymers that are solid at room temperature; (c) Thioether dendritic acrylates; (d) One or more free radical photoinitiators; and (e) A toughening component selected from: polyacrylate liquid elastomers, epoxidized polybutadiene and acrylic block copolymers, and combinations thereof.

2. The UV-curable gasket according to claim 2, wherein, The at least one free radical polymerizable acrylate or methacrylate monomer or oligomer (a) is a urethane (meth)acrylate with a functionality of 1 to 6.

3. The UV-curable gasket according to claim 1 or 2, wherein, Cellulose ester polymers have a T value greater than 100°C. g T g It was determined using a rheometer in torsion mode via rheological methods.

4. The UV-curable gasket according to any one of the preceding claims, wherein, The at least one free radical polymerizable acrylate or methacrylate monomer is in liquid form at room temperature or has a viscosity of less than 100 cP at 25°C.

5. The UV-curable gasket according to any one of the preceding claims, wherein, The sulfide dendritic acrylate has a functionality of at least 15, preferably 30.

6. The UV-curable gasket according to any one of the preceding claims, wherein, The toughening component is (meth)acrylate-functionalized poly(acrylate).

7. The UV-curable gasket according to any one of claims 1 to 5, wherein, The toughening component is epoxidized polybutadiene with the following chemical formula: Where m = 4-11; n = 12-35.

8. The UV-curable gasket according to any one of claims 1 to 5, wherein, The toughening component is a poly(methyl methacrylate-butyl acrylate-methyl methacrylate) (or PMMA-b-PBA-b-PMMA) triblock copolymer.

9. The UV-curable gasket according to any one of the preceding claims, wherein, The one or more free radical photoinitiators are selected from type I and type II photoinitiators. Preferably, the type I photoinitiator is selected from acetophenone, hydroxyacetophenone, aminoacetophenone and phosphine oxide, and the type II photoinitiator is selected from benzophenone and substituted benzophenone, benzoyl ester and thioxanone.

10. The UV-curable gasket according to any one of the preceding claims, wherein, The relative amounts of components (a) to (e), expressed as a weight percentage (wt%) based on the total weight of the resin matrix, are as follows: (a) 1-10 wt% of free radical polymerizable acrylates or methacrylates having a viscosity of less than 24,000 cP at 60°C; (b) 15-30 wt% of methyl methacrylate homopolymers or copolymers that are solid at room temperature or cellulose ester polymers that are solid at room temperature; (c) 15-50 wt% of sulfide dendritic acrylate; (d) 0.1-10 wt% of one or more free radical photoinitiators; and (e) 2-10 wt% toughening components.

11. The UV-curable gasket according to any one of the preceding claims, wherein, The curable resin matrix further comprises at least one polymerizable oligomer containing 2 to 100 monomer units and selected from urethane (meth) acrylates, epoxy (meth) acrylates without epoxy functional groups and polyester (meth) acrylates, preferably in an amount of 25-50 wt% based on the total weight of the resin matrix.

12. The UV-curable gasket according to any one of the preceding claims, wherein, The curable resin matrix further comprises a methacrylate-butadiene-styrene (MBS) polymer, preferably in an amount of 0.1-10 wt% based on the total weight of the resin matrix.

13. The UV-curable gasket according to any one of the preceding claims, wherein, The curable resin matrix further comprises a wetting agent, preferably in an amount of 0.1-5 wt% based on the total weight of the resin matrix.

14. The UV-curable gasket according to claim 13, wherein, The wetting agent is selected from: siloxanes, polyether-modified siloxanes, sulfosuccinates, gemini surfactants (dimeric structures consisting of two hydrophobic chains and two hydrophilic heads, connected by spacer groups at or near the head groups) and alcohol alkoxylates.

15. The UV-curable gasket according to any one of the preceding claims, wherein, The curable resin matrix further comprises aminobenzoate, preferably in an amount of 0.1-5 wt% based on the total weight of the resin matrix.

16. The UV-curable gasket according to any one of the preceding claims, wherein, The curable resin matrix further comprises inorganic fillers in the form of particulate matter, preferably in an amount of 0.1-10 wt% based on the total weight of the resin matrix.

17. The UV-curable gasket according to any one of the preceding claims, wherein, The inorganic filler is selected from: fumed silica, ceramic microspheres, calcium carbonate, alumina, and any combination thereof.

18. The UV-curable gasket according to any one of the preceding claims, wherein, This curable resin matrix does not contain epoxy resin.

19. A UV-curable gasket comprising a reinforcing fiber layer embedded in or impregnated with a curable resin matrix, wherein the curable resin matrix is ​​solid at room temperature (20°C-25°C) and comprises: (a) A combination of two or more alicyclic epoxy resins, at least one of which is a solid at room temperature (20°C-25°C); (b) Oxycyclic butane resin; (c) Cationic photoinitiators selected from thionium and iodonium salts; and (d) A toughening component selected from: polyacrylate liquid elastomers, epoxidized polybutadiene, polysulfone polymers, acrylic block copolymers, and combinations thereof; and The curable resin matrix does not contain any epoxy curing agent (or curing agent) containing one or more reactive amino groups that can crosslink with these alicyclic epoxy resins.

20. The UV-curable gasket according to claim 19, wherein, The relative amounts of these components, expressed as a weight percentage based on the total weight of the resin matrix, are as follows: (a) 65% to 75% alicyclic epoxy resin composition; (b) 5% to 13% of oxobutane resin; (c) 0.1% to 5% cationic photoinitiator; (d) 10% to 25% toughening components.

21. The UV-curable gasket according to claim 19 or 20, wherein, The toughening component contains a polyacrylate liquid elastomer, and the resin matrix does not contain any other polymerizable acrylates or methacrylates.

22. The UV-curable gasket according to any one of claims 19 to 21, wherein, The toughening component comprises epoxidized polybutadiene having the following chemical formula: Where m = 4-11; n = 12-35.

23. The UV-curable gasket according to any one of claims 19 to 21, wherein, The toughening component comprises polyethersulfone and a copolymer of polyether ethersulfone (PES-PEES).

24. The UV-curable gasket according to any one of claims 19 to 21, wherein, The toughening component contains a poly(methyl methacrylate-butyl acrylate-methyl methacrylate) (PMMA-b-PBA-b-PMMA) triblock copolymer and does not contain any other polymerizable acrylates or methacrylates.

25. A UV-curable gasket comprising a reinforcing fiber layer embedded in or impregnated with a curable resin matrix, wherein the curable resin matrix is ​​solid at room temperature (20°C-25°C) and comprises: (a) A combination of two or more alicyclic epoxy resins, at least one of which is a solid at room temperature (20°C-25°C); (b) Oxycyclic butane resin; (c) Cationic photoinitiators selected from thionium and iodonium salts; and (d) Polyether diamines having the following chemical structure: Where n is an integer between 50 and 150, and The polyether diamine is the only amine compound in the curable resin matrix that has a reactive amine group.

26. The UV-curable gasket according to claim 25, wherein, Based on the total weight of the resin matrix, the relative weight percentages of these components are as follows: (a) 65% to 75% alicyclic epoxy resin composition; (b) 5% to 13% of oxobutane resin; (c) 0.1% to 5% cationic photoinitiator; (d) 10% to 25% toughening components.

27. The UV-curable gasket according to claim 25 or 26, wherein, The curable resin matrix contains no polymerizable acrylates or methacrylates.

28. The UV-curable gasket according to any one of claims 19 to 27, wherein, The solid alicyclic epoxy resin is poly[(2-epoxyethylene)-1,2-cyclohexanediol]2-ethyl-2-(hydroxymethyl)-1,3-propanediol ether.

29. The UV-curable gasket according to any one of claims 19 to 28, wherein, The combination of alicyclic epoxy resins includes alicyclic epoxy resins that are liquid at room temperature (20°C-25°C).

30. The UV-curable gasket according to claim 29, wherein, This liquid alicyclic epoxy resin is 3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate or bis(3,4-epoxycyclohexylmethyl) adipate, Or a combination thereof.

31. The UV-curable gasket according to any one of claims 19 to 30, wherein, The curable resin matrix further comprises a photosensitizer, preferably in an amount of 0.01% to 5% by weight based on the total weight of the resin matrix.

32. The UV-curable gasket according to claim 31, wherein, The photosensitizer is selected from: anthracene, xanthones, thioxanthone, benzophenone, acetophenone, dicerotitanium, methyl ketone, xanthones, pyrene methanol, pyrene, perylene, quinone, benzoyl ester, and any combination thereof.

33. The UV-curable gasket according to any one of claims 19 to 32, wherein, The curable resin matrix further comprises inorganic fillers in the form of microparticles, preferably in an amount of 0.1% to 5% by weight based on the total weight of the resin matrix.

34. The UV-curable gasket according to claim 33, wherein, The inorganic filler is selected from: fumed silica, ceramic microspheres, calcium carbonate, alumina, and any combination thereof.

35. The UV-curable gasket according to any one of the preceding claims, wherein, The reinforcing fiber layer is in the form of a woven or non-woven fabric, preferably a woven fabric.

36. The UV-curable gasket according to any one of the preceding claims, wherein, These reinforcing fibers are selected from glass fibers, carbon fibers, aramid fibers, quartz fibers, polyester fibers, and combinations thereof.

Images