Title of Invention

"AN ARTICLE WHICH IS RADIATION CURABLE TO AN OPTICAL RESINOUS ARTICLE"

Abstract

Blends of monofunctional and multifunctional (mcth)acrylaie monomers, optionally in addition to oligomeric multi functional (mcth)acrylaies), can be cured by ultraviolet radiation in contact with a photoinitiator to produce optical resinous articles having a glass transition temperature of at least 35 *C and having physical properties making them suitable for use as microstruc-ture-bearing articles.

Full Text

RADIATION CURABLE MICROSTRUCTURE-BEARING ARTICLES BACKGROUND OF THE INVENTION This invention relates to die replication of microstructure-bearing surfaces, and more particularly to a genus of resinous compositions capable of such replication. Microstructure replication in resinous surfaces is of importance in such diverse technical fields as the fabrication of traffic signs, in which reflectivity is provided by cube-comer embossed sheeting; the production of Fresnel ophthalmic lens elements and flexible video disks; and the fabrication of "brightness enhancement" or "light management" films (hereinafter sometimes designated "LMF" for brevity) for liquid crystal displays. For replication purposes, it is necessary that the resin have optimum physical properties, including a glass transition temperature (Tg) high enough for shape retention during storage and use and viscoelastic properties facilitating shaping, typically by molding, and long-term shape retention which includes the microstructure aspects of the shaped articles. Suitable viscoelastic properties include moduli in the glassy and rubbery states within certain ranges, as well as suitable transition temperatures between those states. Many suitable resinous compositions for the replication of microstructure are disclosed in the patent literature. A patent whose disclosure is generic to a large variety of such compositions is US Patent 4,576,850. The compositions described therein are characterized by "hard" and "soft" segments or moieties in combination with radiation-polymerizable moieties. Most often, all three of these types of segments are present in the same molecule. A key feature of the "hard" segments is the presence therein of cyclic (i.e., carbocyclic or heterocyclic) groups. Later-issued patents frequently make reference to 4,576,850 for its disclosure of suitable polymeric compositions and precursors therefor. It is of interest, however, to develop additional resinous LMF materials not disclosed in the above-identified patent or other publications. SUMMARY OF THE INVENTION The present invention is based on materials having excellent propert es having microstnicture. the discovery of a genus of acrylic-based resinous for the fabrication of LMF's and other articles The invention includes articles wh ch are radiation curable to optical resinous articles having surfaces with a replicated nicrostructure comprising a plurality of utilitarian discontinuities having an optical p irpose, said optical resinous articles having a glass transition temperature of at least'. articles so prepared. 5°C. Also included are the cured optical resinous are free from carbocyclic and heterocyclic Said radiation curable articles polymerizable moieties and comprise: (A) at least one monofunctiona] a crylic monomer selected from the group consisting of: at least one monomeric t-aikyf |(meth)acrylate, at least one monomeric N-sub^tituted or N,N-disubstituted (meth)acrylamide and (3) at least one C\* primary or secondary alkyl (meth)acrylate; at least one multifunctional (njieth)acrylate or (meth)acrylamide monomer; optionally, at least one oligon^eric multifunctional (meth)acrylate; and at least one photoinitiator. BRIEF DESCRIPTION OF THE|DRAWINGS FIGURE 1 is a schematic view o a LMF in a backlit liquid crystal display. FIGURE 2 is a plot of the articles prepared according to the pre fcrred dynamic tensile moduli of illustrative cured invention. DETAILED DESCRIPTION; PREFERRED EMBODIMENTS The optical resinous articles of the present invention are characterized by a surface with replicated microstructure comprising a plurality of utilitarian discontinuities, such as projections and depressions, which surface may be readily released from a mold after radiation curing without loss of the detail of the mold and with retention of the replication of such detail under a wide variety of conditions during use. The articles have a wide variety of desired properties, such as toughness, flexibility, optical clarity and homogeneity, and resistance to common solvents. The microstructures of such articles have high thermal dimensional stability, resistance to abrasion and impact, and integrity even when the articles are bent to an angle as great as 180°. The term "microstructure" is used herein as defined and explained in the aforementioned US Patent 4,576,850, the disclosure of which is incorporated by reference herein. Thus, it means the configuration of a surface which depicts or characterizes the predetermined desired utilitarian purpose or function of the article having the microstructure. Discontinuities such as projections and indentations in the surface of said article will deviate in profile from the average center line drawn through the microstructure such that the sum of the areas embraced by the surface profile above the center line is equal to the sum of the areas below the line, said line being essentially parallel to the nominal surface (bearing the microstructure) of the article. The heights of said deviations will typically be about ± 0.005 to ± 750 microns through a representative characteristic length of the surface, e.g., 1-30 cm, as measured by an optical or electron microscope. Said average center line can be piano, concave, convex, aspheric or combinations thereof. Articles where said deviations are of low order, e.g., from ± 0.005 to ± 0.1 or, preferably, to ±0.05 microns, and said deviations are of infrequent or minimal occurrence, i.e., the surface is free of any significant discontinuities, are those where the microstructure-bearing surface is an essentially "flat" or " smooth" surface, such articles being useful, for example, as precision optical elements or elements with a precision optical interface, such as ophthalmic lenses. Articles where said deviations are of low order and of frequent occurrence include those having anti-reflective microstructure. Articles where said deviations are of high order, e.g., from ±0.1 to ± 750 microns, and attributable to microstructure comprising a plurality of utilitarian discontinuities which are the same or different and spaced apart or articles such as retroreflective cub e-comer and LMF's. The microstructure-b taring of both said low and high order extraneous or non-utilitarian discontinuities not significantly interfere with of said articles. It may be neces sary composition whose shrinkage extraneous discontinuities, e.g., a contiguous in a random or ordered manner, are sheeting, linear Fresnel lenses, video discs surface can contain utilitarian discontinuities . The microstructure-bearing surface may contain so long as the amounts or types thereof do or| adversely affect the predetermined desired utilities or desirable to select a particular oligomeric i|pon curing does not result in such interfering imposition which shrinks only 2-6%. Details of LMF construction Patent 5,900,287, the disclosure Refening to FIGURE 1, a includes a LMF 11 which is typ crystal display panel 14. The bac 16 such as a fluorescent lamp, toward the liquid crystal display also toward the liquid crystal from the light guide 18 thereby panel 14, enabling a sharper ima and allowing the power of the brightness. The LMF 11 is the such as computers, personal t anl back lit configuration are provided, for example, in US of which is also incorporated by reference herein, liquid crystal display generally indicated at 10 cally positioned between a diffuser 12 and a liquid lit liquid crystal display also includes a light source light guide 18 for transporting light for reflection ianel 14, and a white reflector 20 for reflecting light d splay panel. The LMF 11 collimates light emitted i icreasing the brightness of the liquid crystal display ,e to be produced by the liquid crystal display panel ght source 16 to be reduced to produce a selected >acklit liquid crystal display is useful in equipment evisions, video recorders, mobile communication displays. and avic nic instrument The articles of the invention arc only a portion of the article, cured, the substrate and/or othei during and after the radiation the material of which they components, all polymerizable heterocyclic moieties. Component which is itself selected from four radiation curable. This includes the situation where usjually the microstructure-bearing coating, is actually portions of the article remaining unchanged before, cu ing operation. An important feature of said articles is ire fabricated. Said material has three essential :omponents therein being free from carbocyclic and A is at least one monofunctional acrylic monomer groups. The term "acrylic monomer" as used herein designates esters and amides of acrylic and methacrylic acids, the inclusion of both acids being designated by the parenthesized construction "(rneth)acrylic". Group 1 of component A includes monomeric t-alkyl (meth)acrylates; i.e., alkyl (meth)acryiates having a tertiary carbon atom attached to the alkoxy oxygen atom. For the most part these are €4* alkyl (meth)acrylates, with t-butyl (meth)acrylates being particularly preferred and t-butyl acrylate being most preferred. Group 2 includes monomeric N-substituted and N,N-disubstituted (meth)acrylamides, especially acrylamides. These include N-alkylacrylamides and N,N-dialkylacrylamides, especially those containing cm alkyl groups. Particularly preferred are N-isopropylacrylamide, N-t-butylacrylamide, N,N-dimethylacrylamide and N,N-diethylacrylamide. Group 3 includes Q.g primary and secondary alkyl (meth)acrylates which may contain substituents on the alkyl groups. Illustrative unsubstituted compounds are methyl acrylate, methyl methacrylate, ethyl acrylate and 1-propyl acrylate. Illustrative substituted compounds, which may also function as reactive diluents, are the 2-(N-butylcarbamyl)ethyl (meth)acrylates. The €1.3 (meth)acrylates are usually preferred, with methyl acrylate and ethyl acrylate being most preferred. Other suitable reactive diluents are enumerated in the aforementioned US Patent 4,576,850. . The radiation curable compositions forming the articles of the invention also include component B, which is at least one multifunctional (meth)acrylate or (meth)acrylamide monomer and which serves as a crosslinking agent By "multifunctional (meth)acrylate monomer" is meant a monomeric (i.e., non-polymerized) compound containing more than one (meth)acrylic group. Compounds suitable for use as component B include polyol poly(meth)acrylates, typically prepared from aliphatic diols, triols and/or tetraols containing 2-10 carbon atoms. Examples of* suitable poly(meth)acrylates are ethylene glycol diacrylate, 1,6-hexanediol diacrylate, 2-ethyl-2-hydroxymethyl-l,3-propanediol triacrylate (trimethylolpropane triacrylate), di(trimethylolpropane) tetraacrylate, pentaerythritol tetraacrylate, the corresponding methacrylates and the (meth)acrylates of alkoxylated (usually ethoxylated) derivatives of said polyols. Also included are N,N'- alkylenebisacrylamides, particularly those containing a cm alkylene group. Particularly preferred is N,N'-metl ylenebisacrylamide. Optional component C, when prei ent, may serve the purposes of affording improved ductility and minimizing shrinkag e upon polymerization. It is at least one oligomeric multifunctional (meth)acrylate, vsually a di(meth)acrylate. Suitable materials for component C include the oligoneric polyether di(meth)acrylates having a glass transition temperature of at mo it 23°C. Examples are poly(ethylene glycol) and poly(propylene glycol) di(meth)a irylates, typically having molecular weights in the range of about 300-1,000. Compounds of this type are commercially available under several trade names. Also incluc led are di(meth)acrylates of polyester polyols and oligomers thereof, as exemplified by such commercially available compounds as "CN-292", a low viscosity polye >ter acrylate oligomer commercially available from Sartomer Co. Optional component C may alsc be an oligomeric urethane di(meth)acrylate. Such materials may be prepared, for ex imple, by the reaction of an alkylene diisocyanate of the formula OCN-R3-NCO with * diol of the formula HO-R4-OH, wherein each of R3 and R4 is independently a Ca-ioo Alkylene group, to form a urethane diol diisocyanate, followed by reaction with a hydroxyalkyl (meth)acrylate. For example, a preferred compound of this type may be prepared from 2,2,4-trimethylhexylene diisocyanate, poly(caprolactone)diol and 2-hydf-oxyethyl methacrylate. Component D of the radiation photoinitiator effective to promdte ultraviolet radiation. Suitable materials aforementioned US Patent 4,576 Polymer Technology. Examples ketones, thioalkylphenyl morj holinoalkyl Particularly useful in many instances "Darocur 4265", comprising a (2,4,6-trimethylbenzoyl)diphen curable articles of this invention is at least one polymerization of said articles upon exposure to for use as photoinitiators are identified in the 850 and in such reference works as Encyclopedia of ire benzoin ethers, hydroxy- and alkoxyalkyl phenyl ketones and acylphosphine oxides, is a commercially available material designated mixture of 2-hydroxy-2-propyl phenyl ketone and y phosphine oxide. Other important features of the articles formed by curing. These invention are the properties of the optical resinous include a glass transition temperature (Tg) of at least 35°C, preferably at least 40°C. Cured articles having glass transition temperatures lower than 35°C are not within the scope of the invention. Other preferred properties include a tensile strength in the range of about 70-700 kg/cm2, a modulus of elasticity in the range of about 140-14,000 kg/cm2, an elongation to break in the range of about 5-300%, an optical homogeneity of at least about 91% transmission, a haze value of less than about 5%, a birefringence of less than about 0.002 and a dynamic tensile modulus, E', that falls within the boundary of the area A-B-C-D in FIGURE 2. Said figure is a modified version of Figure 1 of the aforementioned US Patent 4,576,850, converting dynamic shear modulus (G1) in dynes/cm2 to dynamic tensile modulus in Pascals. The proportions of the components forming the curable articles of this invention may be widely varied, subject only to the Tg limitation and, preferably, one or more of the other preferred property profiles described hereinabove. Most often, components A and B each constitute about 1-98% by weight and component C, when present, about 5-75% of the article, based on total polymerizable components (usually the total of components A, B and C). Component D, the photoinitiator, is present in a minor amount effective to promote polymerization upon exposure to ultraviolet radiation, generally in the range of about 0.005-3.0% and preferably about 0.005-1.0% based on total polymerizable components. The radiation curable articles of mis invention may be prepared by simply blending the components thereof, with efficient mixing to produce a homogeneous mixture. It is often preferred to remove air bubbles by application of vacuum or the like, with gentle heating if the mixture is viscous, and casting or otherwise creating a film of the resulting blend on a desired surface. The film can then be charged to a mold bearing the microstructure to be replicated and polymerized by exposure to ultraviolet radiation, producing cured optical resinous articles of the invention having the aforementioned properties. If polymerized on a surface other than the one on which it is to be used, the optical resinous article can be transferred to another surface. Such a polymerization process lends itself to rapid, mass production of articles with no adverse environmental impact because no or only a minor amount of solvent or other volatiles are evolved and he polymerization can be carried out at ambient temperatures and pressures. The p rocess also lends itself to replication of articles with microstructure comprising utili arian discontinuities, such as projections and depressions, which are readily rel thermal dimensional stability, rei istance to abrasion and impact, and integrity even when the articles are bent. mold and with retention of the conditions during use. The artic properties, such as toughness, resistance to common solvents, replication of such detail under a wide variety of es can be formed with a wide variety of desired flexibility, optical clarity and homogeneity, and the microstructure of such articles having high The invention is illustrated by th by weight unless otherwise indicated photoinitiator are based on total all examples fell within the regioi : following examples. All parts and percentages are . Percentages of monomeric constituents and of •nonomeric constituents. Dynamic tensile moduli in A-B-C-D of FIGURE 2. EXAMPLES 1-5 To a 3-necked flask equipped mechanical stirrer was charged 3 50 mg of dibutyltin dilaurate. Th polycaprolactone dioj (Mn. 530) 60°C. The mixture was then stirred 55°C and a mixture of 18.7 hydroquinone monomethyi ether range of 54-58°C. The mixture i of the reaction was verified by oligomeric urethane dirnethacri'late, dimethacrylate". with an.addition funnel, temperature probe and .2 ml of 2,2,4-trimethylhexane 1,6-diisocyanate and 5 addition funnel was charged with 39.75 g of warm which was added to the contents of the flask at 55-at 65°C for 14 hours. The flask was then cooled to ml of 2-hydroxyethyl methacrylate and 100 mg was added while maintaining the temperature in the vas stirred at 55°C for 10-12 hours until completion nfrared spectroscopy. The product was the desired , hereinafter sometimes designated "oligomer In each example, a mixture of some examples, pentaerythritol into a scintillation vial and 3°A components were mixed with placed in a vacuum oven and o igomer dimethacrylate, methyl methacrylate and, in riacrylate in a total dmount of 5-10 g were weighed of "Darocur 4265" photoinitiator was added. The vortex mixer. The uncapped scintillation vial was oven evacuated to remove air bubbles from the ine solution. If the coating mixture was highly viscous, the temperature of the vacuum oven was increased to 50°C to facilitate the removal of air bubbles. Approximately one gram of the mixture was then poured into an aluminum pan 5 cm in diameter. The pan was tilted to spread the mixture across the entire bottom of the pan. If the mixture was viscous, the pan was placed in a circulating air oven set at 80°C to heat the mixture, which allowed for easier spreading of the mixture across the bottom of the pan. The spread and leveled solution was then polymerized by ultraviolet radiation in an ultraviolet processor. Two 600-watt bulbs were used with a belt speed of 12 ft./min, lamp to belt distance of 4 inches, and the coating was passed 10 times through the processor. A culture dish was placed upside down over the aluminum pan containing the coating in order to prevent the pan from being blown around on the belt. The product films were analyzed for glassy plateau modulus (G), rubbery plateau modulus (R) and glass transition temperature (Tg) using a Rhcometrics Solids Analyzer. The results are given in Table 1. (Table Remove) EXAMPLES 6-14 The polymerization procedure of of t-butyl acrylate with, in tetraethyJene g]ycol diacrylate, trimethylolpropane triacrylate am given in Table II. (Table Remove) Examples 1-5 was performed on a series of mixtures various examples, "CN-292" polyester acrylate, trimethylolpropane triacrylate and ethoxylated employing 0.01% of photoinitiator. The results are EXAMPLES 15-24 The polymerization procedure oF Examples 6-14 was perfonned on a series of mixtures of N,N-dimethylacryte nide or N,N-diethylacrylamide with, in various examples, N.N-methylenebisacryl imide and 1,6-hexanediol diacrylate. The results are given in Table III. (TableRemove) 'Second Tg at 232°C. EXAMPLES 25-31 The polymerization procedure mixtures of t-butyl acrylate and poly(propyJene glycol Mn 540] Example 1. The results are given i qf Examples 6-14 was performed on a series of ,6-hexanediol diacrylate and, in various examples, diacrylate and the oligomer dimethacrylate of ft> Table IV. (Table Remove)EXAMPLES 32-38 The polymerization procedure or Examples 6-14 was performed on a series of mixtures of N,N-dimethylacrylamJde, 1,6-hexanediol diacrylate and, in various examples, polypropylene glycol Mn 540) diacrylate and the oligomer dimethacrylate of Example 1. The results are given in Table V. (Table Remove) EXAMPLES 39-42 The polymerization procedure c mixtures of N,N-dimethylacryJarr polypropylene glycol Mn 540) diacryl TABLE VI f Examples 6-14 was performed on a series of ide, t-butyl acrylate, 1,6-hexanediol diacrylate and ate. The results are given in Table VI (Table Remove) What is claimed is: 1. An article which is radiation curable to an optical resinous article having a surface with a replicated microstructure comprising a plurality of utilitarian discontinuities having an optical purpose, said optical resinous article having a glass transition temperature of at least 35°C; said radiation curable article being free from carbocyclic and heterocyclic polymerizable moieties and comprise: (A) at least one monofunctional acrylic monomer selected from the group consisting of: at least one monomeric t-alkyl (meth)acrylate, at least one monomeric N-substituted or N,N-disubstituted (meth)acrylamide and at least one d^ primary or secondary alky! (meth)acrylate; at least one multifunctional (meth)acrylate or (meth)acrylamide monomer; optionally, at least one oligomeric multifunctional (meth)acrylate; and at least one photoinitiator. An article according to claim 1 which is radiation curable to an optical resinous article having a glass transition temperature of at least 40°C. An article according to claim 1 having a dynamic tensile modulus that falls within the boundary of the area A-B-C-D in FIGURE 2. An article according to claim 1 comprising component A-l. An article according to claim 4 wherein component A-l is a t-butyl (meth)acrylate. An article according to claim 1 comprising component A-2. An article according to claim 6 wherein component A-2 is N-isopropylacrylamide, N-t-butylacrylamide, N,N-dimethylacrylamide or N,N-diethylacrylamide. An article according to claim 1 An article according to claim ! mcthacrylatc, ethyl acrylate, (meth)acrylate. comprising component A-3. wherein component A-3 is methyl acrylate, methyl -propyl acrylate or a 2-(N-butylcarbamyl)ethyl An article according to claim 1 wherein component B is at least one polyol poly(meth)acrylate. An article according to claim 10 wherein component B is ethylene glycol di(meth)acrylate, 1,6-hexanedicl di(meth)acrylate, 2-ethyl-2-hydroxymethyl-l,3- propanediol tri(meth)acrylate, pentaerythritol tetra(meth)acrylat di(trimethylolpropane) tetra(meth)acrylate or 12. An article according to cla|m 1 wherein component B is at least one N,N'- alkylenebisacrylamide. 13. An article according | to claim 12 wherein component B is N.N'-methylenebisacrylamide. An article according to claim 11 comprising component C. An article according to claim] 14 wherein component C is an oligomeric polyether di(meth)acrylate having a glass transition temperature of at most 23°C. An article according to claim! 14 wherein component C is a di(meth)acrylate of a polyester polyol or an oligomer thereof. An article according to clahfo 16 wherein component C is polyethylene glycol) di(meth)acrylate or poly(propylehe glycol) di(meth)acrylate. An article according to clainf 14 wherein component C is an oligomeric urethane di(meth)acrylate. An article according to claim IS wherein component C is a reaction product of 2,2,4-trimethylhexane 1 ,6-diisocyanate, polycaprolactone diol and 2-hydroxyethyl methacrylate. An article according to claim 1 wherein component A constitutes about 10-98% by weight based on total polymerizable components. An article which is radiation curable to an optical resinous article having a surface with a replicated microstructure comprising a plurality of utilitarian discontinuities having an optical purpose, said optical resinous article having a glass transition temperature of at least 40°C; said. radiation curable article being free from carbocyclic and heterocyclic polymerizable moieties and comprising: (A) at least one monofunctional acrylic monomer selected from the group consisting of: t-butyl (meth)acrylate, N-isopropylacrylamide, N-t-butylacrylamide, N,N-dimethylacrylamide or N,N- diethylacrylamide, and methyl acrylate, methyl methacrylate, ethyl acrylate, 1-propyl acrylate or a 2-(N- burylcarbamyl)ethyl (meth)acrylate, at least one multifunctional (meth)acrylate or (meth)acrylamide monomer selected from the group consisting of ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-ethyl-2-hydroxymethyl-l,3-propanediol tri(meth)acrylate, di(trimethylolpropane) tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate and N.N'-methylenebisacrylamide, and optionally, at least one oligomeric multifunctional (meth)acrylate selected from the group consisting of oligomeric polyether di(meth)acry)ates having a glass transition temperature of at most 23°C, di(meth)acrylates of polyester polyols and oligomers thereof, and oligomeric urethane di(meth)acrylates; and at least one photoinitiator. An article according to claim 21 wh -in compone'V C is a reaction product of 2,2,4-trimethylhexane 1 ,6-diisodyanate, polycaprolactoi.3 diol and 2-hydroxyethyl methacrylate. An optical resinous article formed by ultraviolet radiation curing of an article according to claim I. An optical resinous article formed by ultraviolet radiation curing of an article according to claim 4. An optical resinous article formed by ultraviolet radiation curing of an article according to claim 6. An optical resinous article formed by ultraviolet radiation curing of an article according to claim 8. . An optical resinous article formed by ultraviolet radiation curing of an article according to claim 10. An optical resinous article formed by ultraviolet radiation curing of an article according to claim 12. An optical resinous article formed by ultraviolet radiation curing of an article according to claim 14. An optical resinous article formed by ultraviolet radiation curing of an article according to claim 21.

Documents:

2936-delnp-2005-abstract.pdf

2936-DELNP-2005-Claims-31-03-2008.pdf

2936-delnp-2005-claims.pdf

2936-DELNP-2005-Correspondence-Others-31-03-2008.pdf

2936-delnp-2005-correspondence-others.pdf

2936-DELNP-2005-Description (Complete)-31-03-2008.pdf

2936-delnp-2005-description (complete).pdf

2936-DELNP-2005-Drawings-31-03-2008.pdf

2936-delnp-2005-drawings.pdf

2936-DELNP-2005-Form-1-31-03-2008.pdf

2936-delnp-2005-form-1.pdf

2936-delnp-2005-form-18.pdf

2936-DELNP-2005-Form-2-31-03-2008.pdf

2936-delnp-2005-form-2.pdf

2936-DELNP-2005-Form-3-31-03-2008.pdf

2936-delnp-2005-form-3.pdf

2936-delnp-2005-form-5.pdf

2936-delnp-2005-form-6-(04-08-2008).pdf

2936-DELNP-2005-GPA-31-03-2008.pdf

2936-DELNP-2005-PA-31-03-2008.pdf

2936-delnp-2005-pct-220.pdf

2936-delnp-2005-pct-304.pdf

2936-delnp-2005-pct-request form.pdf

2936-delnp-2005-pct-search report.pdf