Optically clear (meth)acrylate adhesives with improved surface cure properties

Abstract

UV-curable (meth)acrylate compositions incorporating thiol-containing components exhibit increased surface reaction conversion rates and improved dry-to-the-touch surface cure characteristics.

Description

[Technical field]

[0001] The present disclosure relates to ultraviolet light curable (meth)acrylate compositions that exhibit improved surface cure when exposed to air during photocure, thereby eliminating tacky surfaces and improving adhesion properties. [Background technology]

[0002] It is known that UV-curable (meth)acrylate compositions do not readily cure at the surface under ambient air conditions due to photoinitiator quenching and free radical scavenging by oxygen molecules. In molding applications where the surface of the mold has high oxygen permeability, such as silicone rubber molds (e.g., polydimethylsiloxane (PDMS)), oxygen reduces UV curing efficiency, especially at the adhesive interface of the mold. Furthermore, certain mold-strengthening additives, such as silica, commonly used in silicone and other molds, absorb, scatter or block UV light, preventing complete curing of the surface, further increasing this inefficiency.

[0003] Traditional strategies to reduce oxygen inhibition result in yellowing of the final product, which is unacceptable in the application design of optical adhesives. For example, attempts to increase the concentration of photoinitiators or select the type of photoinitiator were not without yellowing. Blends of surface-cure and deep-cure photoinitiators also resulted in yellowing. Other attempts to solve the surface cure problem also resulted in a lack of optical clarity. For example, using wax as a barrier material (leading to haze), using amines to accelerate the cure (yellowing and color instability), using cationic free radical cure instead of UV cure (yellowing and color instability), and using triphenylphosphine (leading to haze).

[0004] Methods for preparing and using non-yellowing high refractive index optical adhesives have been previously described in various Henkel patent applications, including International Patent Application Publication Nos. WO2018 / 170371 and WO2019 / 000375, and U.S. Patent Application Publication No. US2019 / 0218434.

[0005] It would be advantageous to provide a (meth)acrylate adhesive composition that has a high surface cure efficiency (dry feel) when light cured in ambient air, and also has a high refractive index and remains optically clear with no visually observable yellowing. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 170371 [Patent Document 2] International Publication No. 2019 / 000375 [Patent Document 3] U.S. Patent Application Publication No. 2019-0218434 Summary of the Invention [Means for solving the problem]

[0007] The present invention incorporates a multifunctional thiol into an ultraviolet-curable (meth)acrylate adhesive composition in an amount of about 5% by weight to about 40% by weight of the total composition to enhance the oxygen resistance of the adhesive surface and increase the surface cure in the presence of oxygen during ultraviolet curing.

[0008] In one aspect of the present invention, there is provided an oxygen-resistant, non-yellowing optical adhesive composition comprising a multifunctional component selected from the group consisting of multifunctional thiols, multifunctional thiol-vinyl ethers, multifunctional thiol-allyl ethers, and combinations thereof, wherein the component is present in an amount of about 5% to about 40% by weight of the total composition; a multifunctional (meth)acrylate component; and a photoinitiator, wherein upon photocuring the composition in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by at least 40% reaction conversion at the composition surface; and the composition upon curing has a refractive index (RI) of 1.6≧RI≧1.55.

[0009] In another aspect of the invention: a. discharging an oxygen resistant, non-yellowing optical adhesive composition, comprising: a multifunctional component selected from the group consisting of multifunctional thiols, multifunctional thiol-vinyl ethers, multifunctional thiol-allyl ethers, and combinations thereof, wherein said component is present in an amount of about 5% to about 40% by weight of the total composition; a multifunctional (meth)acrylate component; and a photoinitiator, into an oxygen permeable mold; b. photocuring the composition in the oxygen-permeable mold in the presence of oxygen to obtain a molded article that exhibits oxygen resistance as evidenced by at least 40% reactive conversion at the surface of the composition and has a refractive index (RI) of 1.6 > RI > 1.55; A method is provided for molding an oxygen-resistant, non-yellowing optical adhesive composition to achieve high surface conversion rates, including

[0010] If desired, in addition to UV curing, thermal curing may be employed to further ensure complete cure.

[0011] When the composition is photocured in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by at least 60% reactive conversion at the adhesive surface when the adhesive surface is exposed to oxygen, preferably at least 80% reactive conversion at the adhesive surface, and more preferably at least about 90% reactive conversion at the adhesive surface.

[0012] Products made from the compositions of the present invention are particularly useful in applications such as adhesive products having optical clarity and good light stability. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a reference graph of the absorbance / wavelength spectrum of (meth)acrylates, showing the wavenumbers at which C═C has the strongest absorption. [Diagram 2] FIG. 2 is a graph of the test results of % surface reaction conversion over time for comparative compositions DF-10 and DF-13A, and inventive compositions 97 (immediately after UV exposure) and 97A (after UV and thermal cure / UVT). [Diagram 3] FIG. 3 is a graphical representation of the % surface reaction conversion test results after only UV / 1635 cm- ultraviolet curing for compositions 97D, 98A, 98D, 98E, and 99B of the present invention, tested under three different test conditions: 1) in ambient air, not covered with a polymer layer; 2) in ambient air, covered with an oxygen-permeable polydimethylsiloxane polymer (PDMS) to simulate a silicone rubber mold; and 3) in ambient air, covered with a gas-permeable layer of polyethylene terephthalate (PET). [Figure 4] FIG. 4 is a graphical representation of the % surface reaction conversion test results after UV / 1635 cm- UV cure followed by a 100° C. thermal cure for 1 hour for compositions 97D, 98A, 98D, 98E and 99B of the present invention, tested under three different test conditions: 1) in ambient air, not covered with a polymer layer; 2) in ambient air, covered with an oxygen-permeable polydimethylsiloxane polymer (PDMS) to simulate a silicone rubber mold; and 3) in ambient air, covered with a gas-permeable layer of polyethylene terephthalate (PET). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The term "(meth)acrylate" refers to both "acrylate" and "methacrylate," or either one of them.

[0015] The term "(meth)acrylic" refers to both or either "acrylic" and "methacrylic".

[0016] The term "monomer" refers to a polymer building block that has a defined molecular structure and can react to form part of a polymer.

[0017] The term "oligomer" refers to a molecule that contains at least two repeating units.

[0018] The term "hydrocarbon or hydrocarbyl group" refers to an organic compound composed of carbon and hydrogen. Examples of hydrocarbon groups include, but are not limited to, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, tertiary butyl, isobutyl, etc.; alkenyl groups such as vinyl, allyl, butenyl, pentenyl, hexenyl, etc.; aralkyl groups such as benzyl, phenethyl, -(2,4,6-trimethylphenyl)propyl, etc.; aryl groups such as phenyl, tolyl, xylyl, etc.

[0019] The term "optionally substituted" in the term "optionally substituted hydrocarbon group" means that one or more hydrogens on the hydrocarbon group may be replaced with a corresponding number of substituents, preferably selected from halogen, nitro, azido, amino, carbonyl, ester, cyano, sulfide, sulfate, sulfoxide, sulfone, sulfonic acid groups, and the like.

[0020] The term "glass transition temperature" refers to the temperature at which a polymer transitions between a highly elastic state and a glassy state. Glass transition temperature may be measured, for example, by differential scanning calorimetry (DSC).

[0021] The composition of the present invention may generally have the following components and their contents:

[0022] [Table 1]

[0023] [Crosslinkable methacrylate component] The acrylates contemplated for use in the practice of the present invention are well known in the art, see, for example, U.S. Patent No. 5,717,034, the entire contents of which are incorporated herein by reference.

[0024] The multifunctional (meth)acrylate may be present in an amount of from about 10 to about 40% by weight of the total composition, desirably from about 20 to about 40% by weight, and more desirably from about 25 to about 35% by weight.

[0025] Examples of acrylates contemplated for use herein include monofunctional (meth)acrylates, difunctional (meth)acrylates, trifunctional (meth)acrylates, multifunctional (meth)acrylates, and the like.

[0026] Examples of bifunctional (meth)acrylates include hexanediol dimethacrylate, hydroxyacryloyloxypropyl methacrylate, hexanediol diacrylate, urethane acrylate, epoxy acrylate, bisphenol A type epoxy acrylate, modified epoxy acrylate, fatty acid modified epoxy acrylate, amine modified bisphenol A type epoxy acrylate, allyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethoxylated bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, glycerin dimethacrylate, polypropylene glycol diacrylate, propoxylated ethoxylated bisphenol A diacrylate, 9,9-bis(4-(2-acryloyloxyethoxy)phenyl)fluorene, tricyclodecane diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, PO modified neopentyl glycol diacrylate, tricyclodecane dimethanol diacrylate, 1,12-dodecane diol dimethacrylate, and the like.

[0027] Examples of trifunctional (meth)acrylates include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxy triacrylate, polyether triacrylate, and glycerin propoxy triacrylate.

[0028] Examples of polyfunctional (meth)acrylates include dipentaerythritol polyacrylate, dipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxy tetraacrylate, and ditrimethylolpropane tetraacrylate.

[0029] Additional examples of acrylates contemplated for use in the practice of the present invention include those described in U.S. Patent No. 5,717,034, the entire contents of which are incorporated herein by reference. Multifunctional (meth)acrylates may include epoxy acrylates.

[0030] [Multifunctional thiol component] The multifunctional thiol component may be selected from the group consisting of trifunctional thiols, tetrafunctional thiols, thiol-acrylates, polymeric thiol-acrylates, and combinations thereof. The multifunctional thiol component may be present in an amount of about 5% to about 40% by weight of the total composition, desirably about 5% to about 30% by weight, and more desirably about 5% to about 25% by weight.

[0031] Other examples of multifunctional thiols include the following commercially available compounds: Showa Denko Karenz MT PEI (tetrafunctional secondary thiol); Showa Denko Karenz MT NR1 (trifunctional secondary thiol); Showa Denko Karenz MT Bl (bifunctional secondary thiol); and Ornex Ebecryl LED02. Mixtures of multifunctional thiols are also useful.

[0032] [Photoinitiator] Suitable radical photoinitiators include type I alpha-cleavage initiators such as acetophenone derivatives, such as 2-hydroxy-2-methylpropiophenone and 1-hydroxycyclohexyl phenyl ketone; acylphosphine oxide derivatives, such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; benzoin ether derivatives, such as benzoin methyl ether and benzoin ethyl ether; etc. Commercially available radical photoinitiators include Irgacure 651, Irgacure 184, Irgacure 907, and Darocur 1173 from BASF.

[0033] Type II photoinitiators are also suitable and include benzophenone, isopropylthioxanthone, and anthraquinone. Many substituted derivatives of the aforementioned compounds may also be used. The selection of photoinitiators for radiation curable adhesives is well known to those skilled in the art of radiation curing. Photoinitiator systems consist of one or more photoinitiators and, optionally, one or more photosensitizers. The selection of a suitable photoinitiator depends largely on the particular application in which the adhesive is to be used. A suitable photoinitiator is one that exhibits a light absorption spectrum that is different from the resin and other additives in the adhesive. The amount of photoinitiator typically ranges from about 0.01 to about 10 parts, preferably from about 0.1 to about 5 parts, based on 100 parts of the total weight of the adhesive.

[0034] [Additional additives] Examples of additives contemplated for use herein include diluents, fillers, antioxidants, pigments, colorants, plasticizers, rheology modifiers, accelerators, catalysts, monomers, polymers, block copolymers, and combinations thereof.

[0035] Examples of useful monofunctional (meth)acrylate monomers include phenylphenol acrylate, methoxypolyethylene acrylate, acryloyloxyethyl succinate, fatty acid acrylate, methacryloyloxyethyl phthalate, phenoxyethylene glycol methacrylate, fatty acid methacrylate, carboxyethyl acrylate, isobornyl acrylate, isobutyl acrylate, t-butyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, dihydrocyclopentadiethyl acrylate, cyclohexyl methacrylate, t-butyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, 4-hydroxybutyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, ethyl carbitol acrylate, phenoxyethyl acrylate, methoxytriethylene glycol acrylate, monopentaerythritol acrylate, dipentaerythritol acrylate, tripentaerythritol acrylate, polypentaerythritol acrylate, and the like.

[0036] If fillers are added to the composition, high refractive index fillers are desirable.

[0037] Various aspects of the present invention are illustrated by the following non-limiting examples. The examples are for illustrative purposes and are not intended to limit any practice of the present invention. It will be understood that changes and modifications can be made without departing from the spirit and scope of the invention. Those skilled in the art will readily know how to synthesize or commercially obtain the reagents and components described herein. EXAMPLES

[0038] [Estimation of reaction conversion using ATR-FTIR] ATR-FTIR was used to monitor the reaction conversion. -The THC=O peak at 1635 cm was used as an internal reference to estimate the reaction conversion after UV and UV plus thermal (UVT) curing according to the equation shown below: - The reduction in the peak area of ​​the acrylate C=C band is used.

[0039]

number

[0040] The ATR-FTIR technique is limited to a sample penetration depth of 0.5-5 microns. Therefore, conversion at the surface may be detected. The conversion rate is high, at about 800 mW / cm. 2 After UV irradiation and heat treatment after UV irradiation, - and 810cm - This is indicated by a decrease in the C=C band.

[0041] Composition 97A of the present invention exhibited a significant decrease in absorbance over time after UV and UVH irradiation, as shown in FIG. 1, indicating greater reactive conversion at the surface of the adhesive cured in ambient air using an air permeable mold, specifically a silicone rubber mold.

[0042] The conventional compositions DF-10 and DF-13A did not contain a thiol-containing component. In contrast, the inventive composition 97A contained a thiol-containing component. The respective formulations are as follows:

[0043] [Table 2]

[0044] [Table 3]

[0045] As shown in the % conversion graph in Figure 2, the compositions of the present invention have significantly increased conversion compared to the comparative example that does not contain thiol. The conversion of comparative compositions DF-10 and DF-13A is less than 20% when exposed to air during cure.

[0046] In contrast, compositions of the present invention containing a thiol-containing component (thiol acrylate) showed approximately 20% conversion after 3 seconds of UV irradiation and approximately 50% conversion after heat curing at 80° C. for 1.5 hours.

[0047] [Table 4]

[0048] Tables 4 and 5 show additional inventive compositions 98A-99E, respectively, that contain a thiol-containing component.

[0049] As shown in the table and graphically in Figures 3-5, the compositions of the present invention provide a significant and surprising improvement in surface reaction conversion over comparative compositions DF-10 and DF-13A. Each composition was cured and tested in open air; cured and tested in ambient air while covered with an oxygen-permeable silicone rubber layer (polydimethylsiloxane (PDMS)) to mimic curing in a mold; and cured and tested in ambient air while covered with a gas-permeable polyethylene terephthalate (PET) layer.

[0050] As demonstrated by the test data recorded in the table, the thiol-containing compositions of the present invention exhibit higher reaction conversion rates on surfaces in ambient air as compared to comparative compositions that do not contain a thiol-containing component.

[0051] [Table 5]

[0052] [Table 6]

Claims

1. a multifunctional component selected from the group consisting of multifunctional thiols, multifunctional thiol-vinyl ethers, multifunctional thiol-allyl ethers, and combinations thereof, said component being present in an amount of about 5% to about 40% by weight of the total composition; a multifunctional (meth)acrylate component; and Photoinitiator; An oxygen resistant, non-yellowing optical adhesive composition comprising: A composition, wherein when the composition is photocured in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by a reaction conversion at the surface of the composition of at least 40%, and the refractive index (RI) of the cured composition is 1.6>RI>1.

55.

2. 10. The composition of claim 1, wherein when the composition is photocured in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by at least 60% reactive conversion at the adhesive surface when the adhesive surface is exposed to oxygen.

3. 10. The composition of claim 1, wherein when the composition is photocured in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by at least 80% reactive conversion at the adhesive surface when the adhesive surface is exposed to oxygen.

4. 10. The composition of claim 1, wherein when the composition is photocured in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by at least 90% reaction conversion at the adhesive surface when the adhesive surface is exposed to oxygen.

5. The composition of claim 1, wherein the multifunctional component is selected from the group consisting of trifunctional thiols, tetrafunctional thiols, thiol acrylates, polymeric thiol-acrylates, and combinations thereof.

6. The composition of claim 1, wherein the multifunctional thiol or multifunctional thiol-vinyl ether component is present in an amount of about 5% to about 25% by weight of the total composition.

7. The composition of claim 1, wherein the multifunctional (meth)acrylate component is present in an amount of about 10% to about 40% by weight of the total composition.

8. The composition of claim 1 further comprising a high refractive index filler.

9. The composition of claim 1 further comprising an antioxidant.

10. The composition of claim 1 , wherein the multifunctional (meth)acrylate comprises an epoxy acrylate.

11. 1. A method for forming an oxygen resistant, non-yellowing optical adhesive composition to achieve high surface conversion, comprising: a. a multifunctional component selected from the group consisting of multifunctional thiols, multifunctional thiol-vinyl ethers, multifunctional thiol-allyl ethers, and combinations thereof, said component being present in an amount of about 5% to about 40% by weight of the total composition; a multifunctional (meth)acrylate component; and Photoinitiator; discharging an oxygen resistant non-yellowing optical adhesive composition comprising: b. photocuring the composition in the presence of oxygen to obtain a molded article that exhibits oxygen resistance as evidenced by at least 40% reactive conversion at the surface of the composition and has a refractive index (RI) of 1.6>RI>1.55; The method includes:

12. The method of claim 11 further comprising a heat curing step.

13. 12. The method of claim 11, wherein when the composition is photocured in the presence of oxygen at the bonding surface, the composition exhibits oxygen resistance as evidenced by at least 80% reactive conversion at the bonding surface.

14. 12. The composition of claim 11, wherein when the composition is photocured in the presence of oxygen at the adhesive surface, the composition exhibits oxygen resistance as evidenced by at least 90% reaction conversion at the adhesive surface.

15. The composition of claim 11, wherein the multifunctional component is selected from the group consisting of trifunctional thiols, tetrafunctional thiols, thiol acrylates, polymeric thiol-acrylates, and combinations thereof.

16. The composition of claim 11, wherein the multifunctional thiol or multifunctional thiol-vinyl ether component is present in an amount of about 5% to about 25% by weight of the total composition.

17. The composition of claim 11, wherein the multifunctional (meth)acrylate component is present in an amount of about 10% to about 40% by weight of the total composition.

18. The composition of claim 11 further comprising a high refractive index filler.

19. The composition of claim 11 further comprising an antioxidant.

20. The composition of claim 1 , wherein the multifunctional (meth)acrylate is an epoxy acrylate.

21. 12. An article of manufacture made by the method of claim 11.

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