A PHOTOPOLYMER EPOXY COMPOSITION AND A PHOTOINITIATOR FOR CURING SAME

Abstract

A photopolymer composition comprising at least one cycloaliphatic epoxy compound and a photoinitiator comprising a triarylsulfonium salt.

Claims

1. A photopolymer composition comprising at least one cycloaliphatic epoxy compound and a photoinitiator comprising triarylsulfonium hexafluoro antimonate, silane, and an ester of carboxymethoxy-benzophenone with poly methyl ethylene glycol or with poly tetramethylene glycol; wherein said composition is applied in a thickness of at least 1 mm.

2. A photopolymer composition comprising at least one cycloaliphatic epoxy compound and a photoinitiator comprising a triarylsulfonium salt and comprising up to 0.5 wt% antimony hexafluoride.

3. A photopolymer composition comprising at least one cycloaliphatic epoxy compound and a photoinitiator comprising a triarylsulfonium salt and at least one bisphenol A epoxy compound constituting 20-40 wt% of the composition.

4. The photopolymer composition according to claim 3, comprising at least one acrylic compound constituting 5-10 wt% of the composition; wherein said acrylic compound is 2-(allyloxymethyl)acrylic acid methyl ester.

5. (canceled)

6. The photopolymer composition of claim 1 wherein said cycloaliphatic epoxy compound is 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (EEC).

7-8. (canceled)

9. The photopolymer composition of claim 1 further comprising at least one component selected from silica, glass fiber, and aliphatic polyester polyol.

10. (canceled)

11. The photopolymer composition of claim 1 further comprising up to 0.5 wt% of dibutoxyanthracene.

12-19. (canceled)

20. The photopolymer composition of claim 1 curable with UV irradiation of a wavelength greater than 350 nm.

21. The photopolymer composition of claim 1 exhibiting solidification of a 2 mm thick layer within 20 seconds, and hardness greater than 80 Shore D (ASTM D-2240).

22-32. (canceled)

33. The photopolymer composition of claim 2, wherein said cycloaliphatic epoxy compound is 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (EEC).

34. The photopolymer composition of claim 2, further comprising at least one component selected from silica, glass fiber, and aliphatic polyester polyol.

35. The photopolymer composition of claim 2, further comprising up to 0.5 wt% of dibutoxyanthracene.

36. The photopolymer composition of claim 2, curable with UV irradiation of a wavelength greater than 350 nm.

37. The photopolymer composition of claim 2, exhibiting solidification of a 2 mm thick layer within 20 seconds, and hardness greater than 80 Shore D (ASTM D-2240).

38. The photopolymer composition of claim 3, wherein said cycloaliphatic epoxy compound is 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (EEC).

39. The photopolymer composition of claim 3, further comprising at least one component selected from silica, glass fiber, and aliphatic polyester polyol.

40. The photopolymer composition of claim 3, further comprising up to 0.5 wt% of dibutoxyanthracene.

41. The photopolymer composition of claim 3, curable with UV irradiation of a wavelength greater than 350 nm.

42. The photopolymer composition of claim 3, exhibiting solidification of a 2 mm thick layer within 20 seconds, and hardness greater than 80 Shore D (ASTM D-2240).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying figures, wherein:

[0047] FIG. 1. shows a schematic drawing of the synthesis production process of the nanocomposite;

[0048] FIG. 2. shows the effect of non-settling of added fillers in the formulation due to the incorporation of the nano-composite in the formulation;

[0049] FIG. 3. demonstrates the dark cure effect of the epoxy formulation; by presenting the Young modulus as a function of time following initial exposure of 20 sec to 15 mW/cm2 of UV-LED @ 395 nm under air, at RT; and

[0050] FIG. 4. thermal acceleration of the dark cure effect is demonstrated through presentation of Young modulus versus time at various temperatures, following initial exposure of 20 sec to 15 mW/cm2 of UV-LED @ 395 nm under air.

DETAILED DESCRIPTION OF THE INVENTION

[0051] It has now been found that a photopolymer composition containing epoxy compounds, triarylsulfonium hexafluoro antimonite, and tris(trimethylsilyl)silane, solidifies quickly when cured with a gentle UV light of UV LED, while forming a polymer with good mechanical and electric properties. The quickly acting photoinitiator in accordance with the invention, abbreviated QPI throughout the description (QPI standing for Quick Photo Initiator), enabled solidification of 2-3 mm thick layers by UV of 395 nm within 20 seconds or less. The solidification times are lower for a PI according to an exemplary embodiment of the invention than for standard PI employed in the field. In some exemplary embodiments of the invention, cure parameters, including time and thickness, are advantageous for 3D printing formulations.

[0052] A photopolymer composition according to some embodiments includes at least one cycloaliphatic epoxy compound and a photoinitiator comprising a triarylsulfonium salt is suitable for providing a toughened cured resin, particularly by adding a nano composite toughening agent. In one preferred embodiment of the invention, a photopolymer composition according to the invention, comprising photoinitiator QPI described above, is combined with a SiO.sub.2-Polyester Nano composite Toughening & Anti settling agent based on fumed silica particles whose hydroxyl groups are esterified with fatty acids, preferably via a reaction of silica with a diester of an aliphatic diol polyster. In a preferred embodiment of the invention, said reaction includes adding silane at a higher temperature, while obtaining transparent organic-inorganic nanocomposite (FIG. 1) to be employed as a toughening additive to the photopolymer composition of the invention. The toughener nano composite is added to the composition before curing, resulting in two improved properties: firstly the cured polymer is tougher, and secondly the nanocomposite stabilizes an eventual suspension of glass fiber or other fillers in the composition before curing and prevents settling glass fibers (FIG. 2). The Quick-curing Photopolymer Nanocomposite (QPN) additive, comprising derivatized silica, is used with glass fibers and provides very strong nanocomposite comprising product.

[0053] In some exemplary embodiments of the invention, the compositon includes cycloaliphatic epoxy compounds, and a photoinitiator comprising at least triarylsulfonium hexafluoro antimonate, and, in various embodiments of the invention, components selected at least from esters of carboxymethoxy-benzophenone, aliphatic polyester polyols, dibutoxyanthracene, tris(trimethylsilyl)silane, a bisphenol A epoxy compound and acrylic compound, exhibits advantageous features when the composition is UV-cured, particularly when the composition further comprises silica and glass fibers. The advantageous features include fast curing/solidifying, no oxygen inhibition, reduced shrinkage, dark post-cure (which is continuing the cure process after UV initiation even when the light source is removed, “in dark”), whereas the product has high T.sub.g, high tensile and flexure strength, good electrical properties (excellent arc and tracking resistance, low dielectric constant and dissipation), UV stability and weatherability due to the aliphatic backbone of the polymer and, moreover, the system exhibits a low skin sensitization due to the high light wavelength. Using LED sources of gentle UV radiation, such as comprising 395 nm, is not only significantly less dangerous from the viewpoint of eventual inadvertent skin irradiation, but it also obviates the elimination of ozone, which is produced by mercury light sources.

[0054] Said cycloaliphatic epoxy compounds may include one or more materials selected from EEC, hydrogenated bisphenol A diglycidyl ether (HBD), epoxy acrylates, and others. Said bisphenol A epoxy compound may include one or more materials selected from bisphenol A diglycidyl ether (BADGE), bisphenol F diglycidyl ether (BFDGE), and others. Said acrylic compound may include one or more materials selected from 2-(allyloxymethyl)acrylic acid methyl ester, 2-(allyloxyethyl)acrylic acid methyl ester, and others.

[0055] The system of the invention is easy to use, fast cure, and safe, and provides a tough product; the composition before curing has good flowability at room temperature, and it can be stably stored for future use, at least for 2 months, such as at least 3 months or at least 4 months or at least 5 months or at least 6 months. Cationic curing mechanism exhibits curing within seconds under UV LED, or more when employing nano-composite toughening system. The nano-composite toughening system renders the product high impact strength and long term weather resistance. The product and the method for preparing it are non-hazardous and safe for the environment. Photopolymerization system of the invention belongs to green technologies, as it is characterized by low electrical power input and energy requirements, low temperature operation and no volatile organic compound release.

[0056] The photoinitiator according to the invention, QPI, may be employed as a hybrid photo/thermal cationic cure initiator providing ultra-fast and also deep curing of cycloaliphatic epoxy resin systems, enabling photo-cure by using UV-LED lamps eventually combined with thermal cure.

[0057] The photoinitiator according to the invention, QPI, is a hybrid cationic/free radical photoinitiator for UV LED curable epoxies. In one aspect of the invention, QPI comprises photo energy shifting ingredients, and/or free-radical photoinitiators. The photoinitiator of the invention may comprise a mixture of sulfonium based photo and thermal cure initiators. The photoinitiator of the invention may comprise a color purifying additive, such as ultramarine blue.

[0058] In another aspect of the invention, nano based toughener (QPN) for cationic cure cycloaliphatic epoxy systems is employed, comprising an organic-inorganic nanocomposite and exhibiting transparency which makes it advantageously usable for epoxy based UV curing.

[0059] The additional objects, advantages, and novel features of various embodiments of the invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.

EXAMPLES

[0060] Reference is now made to the following examples, which together with the above descriptions, illustrate the invention in a non limiting fashion.

Materials and Methods

[0061] The following materials and methods are used in performance of experiments described in examples hereinbelow: [0062] Triarylsulfonium hexafluoro antimonate (TSHA, such as 50% in 50% material in propylene carbonate of Sigma Aldrich or of Insight High Technology IHT-PI 436); [0063] Ester of carboxymethoxy-benzophenone with poly tetramethylene glycol or with poly methylethylene glycol (ECBP), such as Omnipol BP of IGM Resins; [0064] Tris(trimethylsilyl)silane (TTS); [0065] Antimony hexafluoride based catalyst (AHC) for thermal initiated cationic polymerization, such as K-PURE® CXC-1612 of King Industries; [0066] 3,4-Epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (EEC), such as Celloxide 2021P of Daicel; [0067] Methylene Blue (MB); [0068] Ester of a polyol such as a dendritic polyester polyol, for example a branched ester of a polyol like PEG with low fatty acids (EP), such as Boltorn® H2004 of Perstorp; [0069] Ultramarine Blue 08 (UMB); [0070] 9,10-Dibutoxyanthracene (DBA), for example of Kawasaki Kasei Chemicals Ltd.; [0071] Polyether crosslinkable additive (PEC), such as of BYK Additives & Instruments; [0072] Fumed silica (FS), Aerosil R 805 of Evonic Industries; [0073] Hydrophilic fumed silica, Aerosil 380; [0074] Polyester polyol (PEP), such as of King Industries; [0075] Glycidyloxypropyl)trimethoxysilane (GTS), of Sigma-Aldrich; [0076] Glass fibers (GF); [0077] Hydrogenated bisphenol A diglycidyl ether (HBD), such as of Nagase; [0078] Bisphenol A diglycidyl ether (BADGE), also known as diglycidyl ether of bisphenol A (DGEBA), CAS number 25068-38-6, such as of Sigma; and [0079] 2-(allyloxymethyl)acrylic acid methyl ester, also known as methyl 2-((allyloxy)methyl)acrylate, CAS number 219828-90-9.

Example 1

Preparation Procedure

[0080] In one experiment, a photopolymer composition in accordance with the invention was prepared by performing the following steps.

[0081] A) The photoinitiator mixture (mixture 1, abbreviated QPI) was prepared by mixing 2.63 g of TSHA in propylene carbonate 1:1, 0.14 g of silane, 0.81 g of ECBP, and 0.14 g of AH. B) The curing indicator mixture (mixture2) was prepared by dissolving MB in EEC to 0.25 wt% solution.

[0082] C) The color purifying solution (mixture 3) was prepared by dissolving UMB to 1% solution in DP.

[0083] D) The EEC mixture (mixture 4) was prepared by mixing 29.5 g of EEC, 0.3 g parts of said mixture 2, 0.58 g of PE, and 0.19 g of DBA, while intensively stirring with 1.54 g of.

[0084] E) The glycidyl silane mixture (mixture 5) was prepared by mixing 0.53 g of GTS, 22.03 g of PEP, while intensively stirring with 3.98 g of FS at 150° C. for about 30 minutes; and

[0085] F) Mixtures 4 and 5 were combined while well stirring for about 15 minutes, followed by admixing 18.0 g of GF, 2.0 g of FS, and 0.6 g of mixture 3, followed by admixing 15.04 g of HBD while mixing at 50° C. for about 10 minutes; followed by adding 3.70 g of QPI (mixture 1) while stirring about 10 more minutes, and adjusting the final viscosity by admixing about 2.00 g of FS.

[0086] About 100 g photopolymer composition was obtained and examined during curing with 395 nm UV LED. The composition did not show sensitivity to oxygen, and it quickly solidified, providing a polymer of which mechanical and electric properties were characterized.

[0087] Viscosity before curing and thixotropic character of the mixture were found to be between 15,000 cP and 1,000,000 cP, I.T being > 4. The cured material exhibited tensile strength of 74 MPa, elongation 2.5, and hardness D85.

Example 2

[0088] The photoinitiator according to the invention (QPI-2000) and a standard photoinitiator (PI-436) used in the field were employed for curing three resins: A) resin based on EEC prepared as described in Example 1, B) resin based on epoxy-methacrylate, and C) resin based on epoxy-bisphenol A. Three different initiator concentrations in the range of 2-5% were employed, and two different irradiation intensities in the range of about 0.2-0.4 W/cm.sup.2 were employed. The solidification times were measured, according to visual test and hardness test. The results are presented in following Table 1.

TABLE-US-00001 Cure and solidification times (in seconds) at different initiator concentrations (wt%) and different irradiations (in W/cm.sup.2) at wavelength of 395 nm, for different resins and for the initiator of invention (QPI) and for a standard initiator (PI-436) Resin Resin A Resin B Resin C UV intensity 0.427 0.197 0.427 0.197 0.427 0.197 initiator concentration Cure and solidification times 2% QPI 28 87 36 68 22 52 3% QPI 20 60 20 61 16 42 5% QPI 15 42 14 50 12 33 Resin Resin A Resin B Resin C UV intensity 0.427 0.197 0.427 0.197 0.427 0.197 initiator concentration Cure and solidification times 2% PI-436 36 108 55 240< 32 69 3% PI-436 27 90 36 100 28 57 5% PI-436 21 72 21 79 22 48

[0089] The results clearly show that the photoinitiator according to the invention provides shorter curing/solidification times than the standard intitiator for all resins and all concentrations and all irradiations.

Example 3

[0090] The effect also known as “dark cure”, relating to a phenomena when the photopolymer continues to cure after initial illumination even when the UV LED light source is removed, was verified by evaluating Young modulus vs. time and is presented in FIG. 3. Twenty samples of 1 mm thick layer of a composition as described in Example 1 were exposed for 20 sec to 15 mW/cm.sup.2 of UV-LED, 395 nm, under air. The samples were then placed in a “black box” in order to prevent additional exposure to illumination. Every 10 min, Young modulus was measured in a sample using DMA (Dynamic Mechanical Analysis) with maximum force of 18 N, at RT. The data, fitted to an exponential, demonstrate that full cure was achieved after approximately 150 min. After about 200 minutes samples do not break under the DMA’s maximal force of 18 N.

[0091] FIG. 4 demonstrates the effect of temperature on the rate of “dark cure”. The experiment described in FIG. 3 was repeated, with DMA measurements at various elevated temperatures. The results presented in FIG. 4 show that exposure to 90° C. will shorten the cure time at “dark cure” from appx 150 min to 30 sec.

Example 4

[0092] Toughened cured polymer was prepared by incorporating the nano-material of the derivatized silica (FIG. 1) into the material as described in Example 1, employing high shear mixing and elevated temperature, while obtaining quickly-cured photopolymer.

[0093] Nano based toughener in accordance with one aspect of the invention, was tested and compared with agents generally used for epoxies, including core-shell rubber particles (butadiene/styrene, polybutadiene or acrylate), core shell toughened resins ALBIDUR® (Siloxane), rubber modified epoxies (butadiene-acrylonitrile rubbers / CTBN), thermoplastic granulated or dissolved polymers. (PES, PEEK or PEI), nanosilica containing epoxy resins NANOPOX® (surface modified silica), mineral / inorganic fillers.

[0094] The material according to the invention provided better results when measuring material fractures.

Example 5

Preparation Procedure

[0095] In order to improve impact resistance and increase heat deflection temperature of a resin as describe in Example 1, a photopolymer composition in accordance with the invention was prepared by performing the following steps.

[0096] A) The photoinitiator mixture (mixture 1, abbreviated QPI) was prepared by mixing 2.63 g of TSHA in propylene carbonate 1:1, 0.14 g of silane, 0.81 g of ECBP, and 0.14 g of AH.

[0097] B) The EEC mixture was prepared by mixing 7 gr of 2-(allyloxymethyl)acrylic acid methyl ester, 0.06 gr of 9,10-Dibutoxyanthracene, 42.5 g of (3′,4′-Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate( EEC), 5.4 gr of epoxy compound blend (ODP-OH-B0177-02), 5.4 gr of Aliphatic polyester diol with primary hydroxyl groups, 0.75 gr [3-(2,3-epoxypropoxy)propyl]trimethoxysilane, 0.35 gr Polyether.

[0098] Mix the above components for approx. 10 min so as to obtain a homogeneous liquid.

[0099] C) Add 2 gr of Silane, trimethoxyoctyl-, hydrolysis products with silica make sure proper wetting, slowly add 18 gr of Fibrous glass (composition consisting principally of oxides of silicon, calcium, aluminum, magnesium and boron fused in an amorphous vitreous state), and additional 4 gr of Silane, trimethoxyoctyl-, hydrolysis products with silica. Make sure temp does not exceed 70°C.

[0100] D) Add 10 gr of Hydrogenated bisphenol A diglycidyl ether diacrylate and mix well for 10 min. temp of mixture should not exceed 50°C. Finally add 4.0 gr of QPI (mixture 1) while stirring about 10 more minutes.

[0101] About 100 g photopolymer composition was obtained and examined during curing with 395 nm UV LED. The composition did not show sensitivity to oxygen, and it quickly solidified, providing a polymer of which mechanical and electric properties were characterized.

[0102] Table 2 compares the mechanical properties of two different exemplary embodiments of the invention.

TABLE-US-00002 Comparison of properties of two different exemplary embodiments of the invention Example 1 Example 5 Hardness, ASTM D-2240, Shore D 85 88 Flexural Strength, ASTM D-790, MPa 27 77 Flexural Modulus, ASTM D-790, MPa 400 5501 Izod Impact, ASTM 256, kJ/m.sup.2 2.0 3.5 Heat Distortion Point, ISO-75, °C 77 95

[0103] While the invention has been described using some specific examples, many modifications and variations are possible. It is therefore understood that the invention is not limited in any way, other than by the scope of the appended claims.

[0104] It is expected that during the life of this patent many variations thereon will be developed and the scope of the invention includes all such new technologies a priori.

[0105] As used herein the term “about” refers to ±10% of the recited value.

[0106] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0107] Specifically, a variety of numerical indicators have been utilized. It should be understood that these numerical indicators could vary even further based upon a variety of engineering principles, materials, intended use and designs incorporated into the various embodiments of the invention. Additionally, components and/or actions ascribed to exemplary embodiments of the invention and depicted as a single unit may be divided into subunits. Conversely, components and/or actions ascribed to exemplary embodiments of the invention and depicted as sub-units/individual actions may be combined into a single unit/action with the described/depicted function.

[0108] Alternatively, or additionally, features used to describe a method or a process can be used to characterize an apparatus and features used to describe an apparatus can be used to characterize a method or a process.

[0109] It should be further understood that the individual features described hereinabove can be combined in all possible combinations and sub-combinations to produce additional embodiments of the invention. The examples given above are exemplary in nature and are not intended to limit the scope of the invention which is defined solely by the following claims.

[0110] Each recitation of an embodiment of the invention that includes a specific feature, part, component, module or process is an explicit statement that additional embodiments of the invention not including the recited feature, part, component, module or process exist.

[0111] Alternatively or additionally, various exemplary embodiments of the invention exclude any specific feature, part, component, module, process or element which is not specifically disclosed herein.

[0112] All publications, references, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.

[0113] The terms “include”, and “have” and their conjugates as used herein mean “including but not necessarily limited to”.