# Patent

## Title
Cloud point-resistant adhesives and laminates

## Abstract

Optically clear adhesives and laminates that include the adhesives are provided. The adhesives and laminates remain haze-free and are cloud point-resistant when placed in environments of high humidity and elevated temperature. The adhesives and laminates are useful in optical electronic display applications.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser. No. 12/245,341, filed Oct. 3, 2008, now pending, the disclosure of which is incorporated by reference in its entirety.


FIELD
The present disclosure relates to optically clear adhesives and laminates that include the adhesives.
BACKGROUND
Optically clear pressure sensitive adhesives (OCAs) are finding wide applications in optical displays. Such applications include bonding polarizers to modules of a liquid crystal display (LCD) and attaching various optical films to a glass lens in, for example, mobile hand held (MHH) devices. During use, the display can be subjected to various environmental conditions, such as high temperature and/or high humidity.
It has been observed that OCAs can exhibit a cloud point, (turn hazy/“white”) after subjecting optical laminates of optical films and OCAs to high temperature/humidity accelerated aging tests and subsequently cooling the laminates down to ambient conditions. While still hot, the laminates may be perfectly clear, even when saturated with moisture. But upon cooling they can exhibit a cloud point and turn hazy or “white”. Frequently, the haze will disappear over time upon storage of the laminate under ambient conditions. The haze disappearance can often be accelerated by gently heating the optical laminates.
SUMMARY
There is a need for OCAs that remain clear and defect free when incorporated into optical displays, such as LCDs. There is a need for cloud point-resistant adhesives and laminates that do not become hazy when subjected to various environmental conditions such as temperature and humidity changes.
In one aspect, an optically clear laminate is provided that includes a first substrate having at least one major surface, a second substrate having at least one major surface, and a cloud point-resistant, optically clear adhesive composition situated between and in contact with at least one major surface of the first substrate and at least one major surface of the second substrate, wherein the adhesive composition is derived from precursors that include from about 75 to about 95 parts by weight of an alkyl acrylate having 1 to 14 carbon in the alkyl group, from 0 to about 5 parts of a copolymerizable polar monomer; and from about 1 to about 25 parts of a hydrophilic polymeric compound based upon 100 parts of the alkyl acrylate and the copolymerizable polar monomer.
In another aspect, an optically clear laminate is provided that includes a first substrate having at least one major surface, a second substrate having at least one major surface; and a cloud point-resistant, optically clear adhesive composition situated between and in contact with at least one major surface of the first substrate and at least one major surface of the second substrate, wherein the adhesive composition is derived from precursors that include from about 60 to about 95 parts by weight of an alkyl acrylate having 1 to 14 carbon atoms in the alkyl group, from 0 to about 5 parts of a copolymerizable polar monomer, and from about 5 to about 50 parts of a hydroxyl-containing monomer that has an OH equivalent weight of less than 400.
In yet another aspect, an optically clear adhesive composition is provided that is derived from precursors that comprise from about 75 to about 95 parts by weight of an alkyl acrylate having 1 to 14 carbon in the alkyl group, from 0 to about 5 parts of a copolymerizable polar monomer, and from about 1 to about 25 parts of a hydrophilic polymeric compound based upon 100 parts of the alkyl acrylate and the copolymerizable polar monomer.
In a further aspect, an optically clear laminate is provided that includes a first substrate having at least one major surface, a second substrate having at least one major surface, and a cloud point-resistant, optically clear adhesive composition situated between and in contact with at least one major surface of the first substrate and at least one major surface of the second substrate, wherein the adhesive has a moisture-vapor transmission rate of at least 400 g/m2/day.
By incorporating hydrophilic moieties in the OCA matrix, haze-free, cloud point-resistant OCAs can be obtained which remain clear even after high temperature/humidity accelerated aging tests. The provided OCA's are suitable for use in, for example, laminating polarizers to optical LCDs, attaching various optical films to glass lenses in mobile handheld devices, and other adhesive application that require optical clarity in various temperature and humidity environments.
Although not wishing to be bound by theory, it is thought that the haze appears when the OCA becomes saturated with water at elevated temperatures, and the concentration of water exceeds the cloud point when quickly cooled due to poor compatibility of the moisture with the OCA matrix. This can result in localized phase separation of small water droplets, which due to a mismatch in refractive index with the OCA matrix causes haze or a “white” appearance. If the droplets remain very small (e.g., a few hundred nanometers or less) or the water remains fully solubilized in the adhesive under ambient conditions, the OCA and its bond line with the substrate will stay clear while it re-equilibrates its moisture content with the environment. To facilitate re-equilibration of the moisture with its environment, it is also anticipated that the moisture-vapor transmission rate of the OCA needs to be high enough to transport the water at a sufficiently high rate to prevent localized water accumulation which may lead to light scattering and haze.
As used herein:
“cloud point” refers to the temperature at which a mixture of adhesive and water separate into a continuous adhesive phase and a dispersed water phase, where the dispersed phase is larger than the wavelength of light and thus make the adhesive appear “white” or cloudy;
“(meth)acrylate” or “(meth)acrylic” refers to either the acid or the ester or amide derivative of acrylic acid or methacrylic acid;
“white” or “cloudy” refers to an adhesive or laminate that is highly translucent so that it is difficult or impossible to visually observe an image though the adhesive or laminate;



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of a laminate of an optical film, a substrate and an embodied adhesive.



DETAILED DESCRIPTION
In the following description, reference is made to the accompanying set of drawings that form a part of the description hereof and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.
Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.
An optically clear laminate is provided. The laminate includes a first substrate having at least one major surface, a second substrate having at least one major surface and a cloud point-resistant, optically clear adhesive composition. By cloud point-resistant it is meant that the adhesive composition, which is initially optically clear, remains optically clear after exposure to high temperature and humidity environments and subsequent cooling to ambient conditions. Optically clear adhesives are commonly used to mount optical films, such as polarizers or retardation plates, to substrate displays, such as liquid crystal cells in LCD applications. As such, the OCA is used to laminate the film to the substrate display to form an optically clear laminate. When used in a laminate, a cloud point-resistant, optically clear adhesive allows the laminate to remain virtually haze free or clear after exposure to nonambient temperature and humidity conditions.
The provided adhesive compositions incorporate hydrophilic moieties into the OCA to obtain haze-free optical laminates that remain haze-free even after high temperature/humidity accelerated aging tests. In one aspect, the provided adhesive compositions are derived from precursors that include from about 75 to about 95 parts by weight of an alkyl acrylate having 1 to 14 carbon in the alkyl group. The alkyl acrylate can include aliphatic, cycloaliphatic, or aromatic alkyl groups. Useful alkyl acrylates (i.e., acrylic acid alkyl ester monomers) include linear or branched monofunctional acrylates or methacrylates of non-tertiary alkyl alcohols, the alkyl groups of which have from 1 up to 14 and, in particular, from 1 up to 12 carbon atoms. Useful monomers include, for example, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, n-nonyl (meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isobutyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl meth(acrylate), benzyl meth(acrylate), and 2-methylbutyl (meth)acrylate, and combinations thereof.
The provided adhesive composition precursors also include from about 0 to about 5 parts of a copolymerizable polar monomer such as acrylic monomer containing carboxylic acid, amide, urethane, or urea functional groups. Weak polar monomers like N-vinyllactams may also be included. A useful N-vinyl lactam is N-vinylcaprolactam. In general, the polar monomer content in the adhesive can include less than about 5 parts by weight or even less than about 3 parts by weight of one or more polar monomers. Polar monomers that are only weakly polar may be incorporated at higher levels, for example 10 parts by weight or less. Useful carboxylic acids include acrylic acid and methacrylic acid. Useful amides include N-vinyl caprolactam, N-vinyl pyrrolidone, (meth)acrylamide, N-methyl (meth)acrylamide, N,N-dimethyl acrylamide, N,N-dimethyl meth(acrylamide), and N-octyl (meth)acrylamide.
The provided adhesive compositions also include from about 1 to about 25 parts of a hydrophilic polymeric compound based upon 100 parts of the alkyl acrylate and the copolymerizable polar monomer. The hydrophilic polymeric compound typically has a average molecular weight (Mn) of greater than about 500, or greater than about 1000, or even higher. Suitable hydrophilic polymeric compounds include poly(ethylene oxide) segments, hydroxyl functionality, or a combination thereof. The combination of poly(ethylene oxide) and hydroxyl functionality in the polymer needs to be high enough to make the resulting polymer hydrophilic. By “hydrophilic” it is meant that the polymeric compound can incorporate at least 25 weight percent of water without phase separation. Typically, suitable hydrophilic polymeric compounds may contain poly(ethylene oxide) segments that include at least 10, at least 20, or even at least 30 ethylene oxide units. Alternatively, suitable hydrophilic polymeric compounds include at least 25 weight percent of oxygen in the form of ethylene glycol groups from poly(ethylene oxide) or hydroxyl functionality based upon the hydrocarbon content of the polymer. Useful hydrophilic polymer compounds may be copolymerizable or non-copolymerizable with the adhesive composition, as long as they remain miscible with the adhesive and yield an optically clear adhesive composition. Copolymerizable, hydrophilic polymer compounds include, for example, CD552, available from Sartomer Company, Exton, Pa., which is a monofunctional methoxylated polyethylene glycol (550) methacrylate, or SR9036, also available from Sartomer, that is an ethoxylated bisphenol A dimethacrylate that has 30 polymerized ethylene oxide groups between the bisphenol A moiety and each methacrylate group. Other examples include phenoxypolyethylene glycol acrylate available from Jarchem Industries Inc., Newark, N.J. Other examples of polymeric hydrophilic compounds include poly acrylamide, poly-N,N-dimethylacrylamide, and poly-N-vinylpyrrolidone.
In another aspect, the provided laminates include adhesive compositions derived from precursors that include from about 60 parts by weight to about 95 parts by weight of an alkyl acrylate having 1 to 14 carbons in the alkyl group and from about 0 parts by weight to about 5 parts by weight of a copolymerizable polar monomer. The alkyl acrylate and the copolymerizable polar monomer are described above. The precursors also include from about 5 parts by weight to about 50 parts by weight of a hydrophilic, hydroxyl functional monomeric compound based upon 100 parts of the alkyl acrylate and the copolymerizable polar monomer or monomers. The hydrophilic, hydroxyl functional monomeric compound typically has a hydroxyl equivalent weight of less than 400. The hydroxyl equivalent molecular weight is defined as the molecular weight of the monomeric compound divided by the number of hydroxyl groups in the monomeric compound. Useful monomers of this type include 2-hydroxyethyl acrylate and methacrylate, 3-hydroxypropyl acrylate and methacrylate, 4-hydroxybutyl acrylate and methacrylate, 2-hydroxyethylacrylamide, and N-hydroxypropylacrylamide. Additionally, hydroxy functional monomers based on glycols derived from ethyleneoxide or propyleneoxide can also be used. An example of this type of monomer includes an hydroxyl terminated polypropylene glycol acrylate, available as BISOMER PPA 6 from Cognis, Germany. Diols and triols that have hydroxyl equivalent weights of less than 400 are also contemplated for the hydrophilic monomeric compound.
The pressure sensitive adhesive can be inherently tacky. If desired, tackifiers can be added to the precursor mixture before formation of the pressure sensitive adhesive. Useful tackifiers include, for example, rosin ester resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, and terpene resins. In general, light-colored tackifiers selected from hydrogenated rosin esters, terpenes, or aromatic hydrocarbon resins can be used.
Other materials can be added for special purposes, including, for example, oils, plasticizers, antioxidants, UV stabilizers, pigments, curing agents, polymer additives, and other additives provided that they do not significantly reduce the optical clarity of the pressure sensitive adhesive.
The provided adhesive compositions may have additional components added to the precursor mixture. For example, the mixture may include a multifunctional crosslinker. Such crosslinkers include thermal crosslinkers which are activated during the drying step of preparing solvent coated adhesives and crosslinkers that copolymerize during the polymerization step. Such thermal crosslinkers may include multifunctional isocyanates, aziridines, multifunctional (meth)acrylates, and epoxy compounds. Exemplary crosslinkers include difunctional acrylates such as 1,6-hexanediol diacrylate or multifunctional acrylates such as are known to those of skill in the art. Useful isocyanate crosslinkers include, for example, an aromatic diisocyanate available as DESMODUR L-75 from Bayer, Cologne, Germany. Ultraviolet, or “UV”, activated crosslinkers can also be used to crosslink the pressure sensitive adhesive. Such UV crosslinkers may include benzophenones and 4-acryloxybenzophenones.
In addition, the precursor mixtures for the provided adhesive compositions can include a thermal or a photoinitiator. Examples of thermal initiators include peroxides such as benzoyl peroxide and its derivatives or azo compounds such as VAZO 67, available from E. I. du Pont de Nemours and Co. Wilmington, Del., which is 2,2′-azobis-(2-methylbutyronitrile), or V-601, available from Wako Specialty Chemicals, Richmond, Va., which is dimethyl-2,2′-azobisisobutyrate. A variety of peroxide or azo compounds are available that can be used to initiate thermal polymerization at a wide variety of temperatures. The precursor mixtures can include a photoinitiator. Particularly useful are initiators such as IRGACURE 651, available from Ciba Chemicals, Tarrytown, N.Y., which is 2,2-dimethoxy-2-phenylacetophenone. Typically, the crosslinker, if present, is added to the precursor mixtures in an amount of from about 0.05 parts by weight to about 5.00 parts by weight based upon the other constituents in the mixture. The initiators are typically added to the precursor mixtures in the amount of from 0.05 parts by weight to about 2 parts by weight. The precursor mixtures can be polymerized and/or cross-linked using actinic radiation or heat to form the adhesive composition as described above and in the Examples below.
The pressure-sensitive adhesive precursors can be blended to form an optically clear mixture. The mixture can be polymerized by exposure to heat or actinic radiation (to decompose initiators in the mixture). This can be done prior to the addition of a crosslinker to form a coatable syrup to which, subsequently, one or more crosslinkers, and additional initiators can be added, the syrup can be coated on a liner, and cured (i.e., cross-linked) by an addition exposure to initiating conditions for the added initiators. Alternatively, the crosslinker and initiators can be added to the monomer mixture and the monomer mixture can be both polymerized and cured in one step. The desired coating viscosity can determine which procedure used. The disclosed adhesive compositions or precursors may be coated by any variety of known coating techniques such as roll coating, spray coating, knife coating, die coating, and the like. Alternatively, the adhesive precursor composition may also be delivered as a liquid to fill the gap between the two substrates and subsequently be exposed to heat or UV to polymerize and cure the composition. The thickness of the adhesive layer in the articles of disclosure tends to be at greater than about 5 micrometers, greater than about 10 micrometers, greater than about 15 micrometers, or even greater than about 20 micrometers. The thickness is often less than about 1000 micrometers, less than about 250 micrometers, less than about 200 micrometers, or even less than about 175 micrometers. For example, the thickness can be from about 5 to about 1000 micrometers, from about 10 to about 500 micrometers, from about 25 to about 250 micrometers, or from about 50 to about 175 micrometers. The greater the thickness of the adhesive the more cloud point resistant the adhesive has to be in order to be useful in a display application.
The pressure sensitive adhesive layer may be optically clear. As used herein, the term “optically clear” refers to a material that has a luminous transmission of greater than about 90 percent, a haze of less than about 2 percent, and opacity of less than about 1 percent in the 400 to 700 nm wavelength range. Both the luminous transmission and the haze can be determined using, for example, ASTM-D 1003-95. Typically, the optically clear adhesive may be visually free of bubbles.
The pressure sensitive adhesive layer desirably maintains optical clarity, bond strength, and resistance to delamination over the lifetime of the article in which it is used. Whether an adhesive will likely have these desirable characteristics can be determined using an accelerated aging test. The pressure sensitive adhesive layer can be positioned between two substrates for this test. The resulting laminate is then exposed to elevated temperatures, optionally, combined with elevated humidity conditions, for a period of time. For example, the cloud point-resistant pressure sensitive adhesive layer can often retain its optical clarity after aging at 90° C. for approximately 500 hours without humidity control (i.e., the relative humidity in the oven is usually below about 10 percent or below about 20 percent). Alternatively, the cloud point resistant pressure sensitive adhesive can often retain its optical clarity after aging at 70° C. for approximately 72 hours with a relative humidity of about 90 percent. Most importantly, the cloud point resistant pressure sensitive adhesive can often retain its optical clarity after aging at 70° C. for approximately 72 hours with a relative humidity of about 90 percent and rapid (i.e. within minutes) cooling to ambient conditions. After aging, the average transmission of the adhesive between 450 nanometers (nm) and 650 nm can be greater than about 85 percent and the haze can be less than about 2 percent.
Laminates are provided that include an optical film or optically clear substrate and a cloud point resistant optically clear pressure sensitive adhesive layer adjacent to at least one major surface of the optical film or substrate. The articles can further include another substrate (e.g., permanently or temporarily attached to the pressure sensitive adhesive layer), another adhesive layer, or a combination thereof. As used herein, the term “adjacent” can be used to refer to two layers that are in direct contact or that are separated by one or more thin layers, such as primer or hard coating. Often, adjacent layers are in direct contact. Additionally, laminates are provided that include a cloud point resistant pressure sensitive adhesive layer positioned between two substrates, wherein at least one of the substrates is an optical film. Optical films intentionally enhance, manipulate, control, maintain, transmit, reflect, refract, absorb, retard, or otherwise alter light that impinges upon a surface of the film. Films included in the laminates include classes of material that have optical functions, such as polarizers, interference polarizers, reflective polarizers, diffusers, colored optical films, mirrors, louvered optical film, light control films, transparent sheets, brightness enhancement film, anti-glare, and anti-reflective films, and the like. Films for the provided laminates can also include retarder plates such as quarter-wave and half-wave phase retardation optical elements. Other optically clear films include anti-splinter films and electromagnetic interference filters.
In some embodiments, the resulting laminates can be optical elements or can be used to prepare optical elements. As used herein, the term “optical element” refers to an article that has an optical effect or optical application. The optical elements can be used, for example, in electronic displays, architectural applications, transportation applications, projection applications, photonics applications, and graphics applications. Suitable optical elements include, but are not limited to, glazing (e.g., windows and windshields), screens or displays, cathode ray tubes, and reflectors.
Exemplary optically clear substrates include, but are not limited to a display panel, such as liquid crystal display, an OLED display, a touch panel, electrowetting display or a cathode ray tube, a window or glazing, an optical component such as a reflector, polarizer, diffraction grating, mirror, or cover lens, another film such as a decorative film or another optical film.
Representative examples of optically clear substrates include glass and polymeric substrates including those that contain polycarbonates, polyesters (e.g., polyethylene terephthalates and polyethylene naphthalates), polyurethanes, poly(meth)acrylates (e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins such as polyethylenes, polypropylenes, and cellulose triacetates. Typically, cover lenses can be made of glass, polymethyl methacrylates, or polycarbonate.
In other embodiments, the substrate can be a release liner. Any suitable release liner can be used. Exemplary release liners include those prepared from paper (e.g., Kraft paper) or polymeric material (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethanes, polyesters such as polyethylene terephthalate, and the like). At least some release liners are coated with a layer of a release agent such as a silicone-containing material or a fluorocarbon-containing material. Exemplary release liners include, but are not limited to, liners commercially available from CP Film (Martinsville, Va.) under the trade designation “T-30” and “T-10” that have a silicone release coating on polyethylene terephthalate film.
The release liner can be removed to adhere the optical film to another substrate (i.e., removal of the release liner exposes a surface of an adhesive layer that subsequently can be bonded to another substrate surface). Often, the adhesive layer is permanently bonded to this other substrate, although in some cases the adhesion may be limited to allow for reworking of the display.
The laminates have at least one of the following properties: the pressure sensitive adhesive layer has optical transmissivity over a useful lifetime of the article, the pressure sensitive adhesive can maintain a sufficient bond strength between layers of the article, the pressure sensitive adhesive can resist or avoid delamination, and the pressure sensitive adhesive can resist bubbling of the adhesive layer over a useful lifetime. The resistance to bubble formation and retention of optical transmissivity can be evaluated using accelerated aging tests. Laminates can often withstand exposure to elevated temperatures (e.g., 60 to 90° C.), optionally, under elevated humidity conditions (e.g., 80 to 90 percent relative humidity), for a period of time (e.g., 1 day to 1 month). In particular the laminates of this disclosure maintain their low haze and high transmission, even after prolonged exposure to elevated temperatures and elevated humidity (e.g., 60 to 90° C. and 80 to 90 percent relative humidity) followed by a rapid cool down to ambient condition (e.g. cooling to room temperature within minutes after exposure to the elevated heat and elevated humidity).
The adhesive compositions of the present disclosure may be applied directly to one or both sides of an optical element such as a polarizer. The polarizer may include additional layers such as an anti-glare layer, a protective layer, a reflective layer, a phase retardation layer, a wide-angle compensation layer, and a brightness enhancing layer. In some embodiments, the pressure sensitive adhesives of the present disclosure may be applied to one or both sides of a liquid crystal cell. It may also be used to adhere a polarizer to a liquid crystal cell. Yet another exemplary set of optical laminates include the application of a cover lens to a LCD panel, the application of a touch panel to an LCD panel, the application of a cover lens to a touch panel, or combinations thereof.
FIG. 1 is a cross sectional illustration of an embodiment of a provided optically clear laminate. The laminate 100 has cloud point-resistant adhesive composition 104 coated onto substrate 102. Optical film 106 is in contact with adhesive composition 104. The laminate provides an optically clear, haze resistant optical element.
Objects and advantages of this disclosure are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.
EXAMPLES










Materials
















EHA
2-ethylhexyl acrylate


IOA
isooctylacrylate


AA
acrylic acid


DMAPMA
N,N-dimethylaminopropylmethacrylamide, available



from Evonik Cyro LLC., Parsippany, NJ


NVC
N-vinyl caprolactam


iBOA
isobornyl acrylate


IRGACURE
2,2-dimethoxy-2-phenylacetophone, a photoinitiator


651
available from Ciba Specialty Chemicals, Tarrytown,



NY.


DESMODUR
a multifunctional isocyanate crosslinker, available


L-75
from Sartomer Company, Exton, PA.


HDDA
1,6-hexanediol diacrylate


CD552
monofunctional methoxylated polyethylene



glycol (550) methacrylate, available from Sartomer.


SR9036
ethoxylated (30) bisphenol A dimethacrylate,



available from Sartomer.


HEA
2-hydroxyethyl acrylate


4HBA
4-hydroxybutyl acrylate


PPA6
poly(propylene glycol) acrylate, available as



BISOMER PPA6 from Cognis, Germany.


VAZO 67
2,2′-azobis(2-methylbuyronitrile), a thermal



initiator available from DuPont.


BA
butyl acrylate


MA
methyl acrylate


EtOAc
ethyl acetate


IOTG
isooctyl thioglycolate


SPU
Silicone polyurea adhesive


MR200
polymethylmethacrylate panel available from



Mitsubishi Rayon, Japan


MR58
polycarbonate/polymethylmethacrylate composite



panel available from Mitsubishi Gas Chemical,



Japan









Accelerated Aging Test Method

Laminates were prepared by bonding a 125 μm thick polyester film (MELINEX 716, available from DuPont Company, Wilmington, Del.) to a float glass plate using the OCA (175 μm thickness). The laminates were placed in an oven set at 70° C./90% relative humidity (RH). After 72 hours, the laminates were taken out of the oven, cooled down to room temperature, and visually observed. In addition to the visual observation the percent transmission and % haze measurement can also be made using for example the Byk-Gardner TCS Plus spectrophotometer. In this test the same optical laminate described above is used. During the test, the background is determined using the PET and glass only. Thus the reported values are for the adhesive only. The adhesive of this disclosure typically show less than 5% haze and preferably less than 2% haze after exposure to the accelerated aging test.
In the haze test, “cloudy” means a haze of 10% or more, “slight haze” means a haze value below 5%, and “clear” means a haze value below 2%.
Moisture-Vapor Transmission Rate (MTVR)
2 mil (50 μm) thick samples of the OCA were laminated to a cheesecloth backing to support the adhesive. This sample, adhesive down, was placed over the top of a glass jar with 2.54 cm diameter opening containing 50 mL of distilled water. The adhesive was held in place with an open ring cover, insuring a tight seal between adhesive and glass jar. This sample was placed in an oven set at 20% relative humidity and a temperature of 40 degrees C. for about 24 hours with the jar upright (i.e., water does not touch the sample). By measuring the weight loss of the sample over the test period, the moisture vapor transmission rate in g/square meter/24 hours was calculated.
Example 1
A monomer premix was prepared using IRGACURE 651 (0.1 parts), EHA (55 parts), iBOA (40 parts), and NVC (5 parts). This mixture was partially polymerized under a nitrogen-rich atmosphere by exposure to ultraviolet radiation to provide a coatable syrup having a viscosity of about 3000 cps (3 Pa-S). Then HDDA (0.1 part), CD552 (5 parts), and additional IRGACURE 651 (0.16 parts) were added to the syrup and the syrup was knife-coated between two silicon-treated release lines at a thickness of 175 μm. The resulting coated material was then exposed to low intensity ultraviolet radiation (a total energy of 1 J/cm2) having a spectral output from 300-400 nm with a maximum at 351 nm. The resulting OCA was laminated according to the procedure in the Accelerated Aging Test Method section.
Example 2
The same procedure was used as in Example 1, except after the syruping process, HDDA (0.1 part), CD552 (10 parts), and additional IRGACURE 651 (0.16 parts) were used.
Example 3
A 1-L bottle was charged with VAZO67 (0.35 g), BA (58.0 g), MA (40.0 g), HEA (2.0 g), CD552 (20 parts), IOTG (0.2 parts) and toluene (280 g). The solution was deaerated with nitrogen bubbling for 10 minutes and was then heated at 58° C. in a water bath for 24 hours with agitation. Then additional EtOAc (210 g) and toluene (40 g) were added to give a viscous solution at 20% solids. The solution was mixed with Desmodur L-75 (0.10 parts) and placed on a mechanical roller for 30 minutes. The solution was then coated on a release liner and dried at 70° C. to a final OCA thickness of 25 μm. A thick OCA sample for testing was made by laminating seven 25 μm samples together.
Example 4
The same procedure was used as in Example 1, except that HDDA (0.1 part), SR9036 (2 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Example 5
The same procedure was used as in Example 1, except that HDDA (0.1 part), SR9036 (5 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Example 6
The same procedure was used as in Example 1, except that HDDA (0.1 part), HEA (10 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Example 7
The same procedure was used as in Example 1, except that HDDA (0.1 part), HEA (20 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Example 8
The same procedure was used as in Example 1, except that HDDA (0.1 part), 4HBA (10 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Example 9
The same procedure was used as in Example 1, except that HDDA (0.1 part), 4HBA (20 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Example 10
The same procedure was used as in Example 1, except that HDDA (0.1 part), BISOMER PPA6 (50 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Comparative Example 1
The same procedure was used as in Example 1, except that HDDA (0.1 part) and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.
Comparative Example 2
The same procedure was used as in Example 3, except that the monomers charge were BA (58 parts), MA (40 parts), and HEA (2 parts).
Comparative Example 3
The same procedure was used as in Example 1, except that HDDA (0.1 part), BISOMER PPA6 (20 parts), and additional IRGACURE 651 (0.16 parts) were added to the coatable syrup.







TABLE 1







Visual Observations of Laminates after


72 hours 70° C./90% RH, cooled to RT)









Example
OCA Composition
Observation





1
EHA/iBOA/NVC/CD552
Slight Haze



55//40/5/5



2
EHA/iBOA/NVC/CD552
Clear



55//40/5/10



3
BA/MA/HEA/CD552
Clear



58/40/2/20



4
EHA/iBOA/NVC/SR9036
Slight Haze



55/40/5/2



5
EHA/iBOA/NVC/SR9036
Clear



55/40/5/5



6
EHA/iBOA/NVC/HEA
Slight Haze



55/40/5/10



7
EHA/iBOA/NVC/HEA
Clear



55/40/5/20



8
EHA/iBOA/NVC/4HBA
Slight Haze



55/40/5/10



9
EHA/iBOA/NVC/4HBA
Clear



55/40/5/20



10 
EHA/iBOA/NVC/PPA6
Clear



55/40/5/50



CE1
EHA/iBOA/NVC
Cloudy



55/40/5



CE2
BA/MA/HEA
Cloudy



58/40/2



CE3
EHA/iBOA/NVC/PPA6
Cloudy



55/40/5/20





CE = Comparative Example






The results show that cloudiness (haze) can be reduced by incorporating hydrophilic moieties in the OCA. This can be achieved through the incorporation of increasing amounts of polymeric hydrophilic compounds such as those containing polyethylene oxide (such as, for example, CD552 or SR9036) or by using monomers with high hydroxyl equivalent content (such as, for example, 4HBA or HEA). The reduction of cloudiness is enhanced when the adhesive composition from about 60 to about 95 parts by weight of an alkyl acrylate having 1 to 14 carbon atoms in the alkyl group from about 15 to about 50 parts of a hydroxyl-containing monomer that has an OH equivalent weight of less than 400.
Comparative Example 4
A monomer premix was prepared using IRGACURE 651 (0.1 parts), EHA (55 parts), iBOA (40 parts), and NVC (5 parts). This mixture was partially polymerized under a nitrogen-rich atmosphere by exposure to ultraviolet radiation to provide a coatable syrup having a viscosity of about 3000 cps (3 PaS). Then HDDA (0.15 part) and additional IRGACURE 651 (0.16 parts) were added to the syrup, which was knife-coated between two silicon-treated release lines at a thickness of 50 μm. The resulting coated material was then exposed to low intensity ultraviolet radiation (a total energy of 1 J/cm2) having a spectral output from 300-400 nm. The resulting OCA was used to prepare a test sample according to the procedure in the moisture-vapor transmission rate test description.
Comparative Example 5
The same procedure described in Comparative Example 4 was used, except that a monomer ratio of IOA (84 parts), iBOA (15 parts), and AA (1 part) and 0.1 part of HDDA was used.
Example 11
The same procedure described in Comparative Example 4 was used, except that a monomer ratio of IOA (90 parts) and AA (10 parts) and 0.1 part of HDDA was used.
Example 12
The same procedure described in Comparative Example 4 was used, except that a monomer ratio of IOA (87.5 parts) and AA (12.5 parts) and 0.065 part of HDDA was used.
Example 13
The same procedure described in Comparative Example 4 was used, except that a monomer ratio of EHA (55 parts), iBOA (15 parts) and HEA (30 part) and 0.05 part of HDDA was used.
Example 14
A pressure-sensitive adhesive composition was prepared according to the method of Example 27 of U.S. Pat. No. 6,569,521 (Sheridan), the entire contents of which are incorporated herein by reference, with the exception that the amount of each component was altered to achieve a pressure-sensitive adhesive composition with MW PDMS diamine (/1000)/moles Dytek A polyamine/% by weight MQ resin of 33/0.5/50.







TABLE 2







Moisture-vapor transmission rates of adhesives










Example
OCA composition
Hazy
MVTR (g/m2/day)













CE4
55/45/5 EHA/iBOA/NVC
Yes
282


CE5
84/15/1 IOA/iBOA/AA
Yes
315


11
90/10 IOA/AA
No
524


12
87.5/12.5 IOA/AA
No
598


13
55/15/30 EHA/iBOA/HEA
No
711


14
SPU adhesive
No
1534









The data above demonstrate that optically clear adhesives with moisture-vapor transmission rates around 300 g/m2/day or below show haziness in the accelerated aging test. Likewise, samples with a moisture-vapor transmission rate of around 400 g/m2/day or 500 g/m2/day or above show no haze development in the same test.
Example 15
A monomer premix was prepared using IRGACURE 651 (0.04 parts), DMAPMA (0.5 parts), EHA (65 parts), iBOA (20 parts), and HEA (15 parts). This mixture was partially polymerized under a nitrogen-rich atmosphere by exposure to ultraviolet radiation to provide a coatable syrup having a viscosity of about 1500 cps (1.5 PaS). Then HDDA (0.1 part) and additional IRGACURE 651 (0.11 parts) were added to the syrup and the syrup was knife-coated between two silicon-treated release lines at a thickness of 175 μm. The resulting coated material was then exposed to low intensity ultraviolet radiation (a total energy of 1 J/cm2) having a spectral output from 300-400 nm with a maximum at 351 nm. The resulting OCA was laminated between a 125 micron thick polyester film (MELINEX 617 available from DuPont) and a 1 mm thick plastic panel selected from either MR200 or MR58 (polycarbonate side). The laminated samples were exposed to a dry oven at a temperature of 85 degrees Celsius and the samples were monitored for the development of haze, delamination, and the presence of bubbles. The test was discontinued after 1 week. The observed failure mode was noted in table 3 below.
Example 16
The same procedure was used as in Example 15, except that the main monomer ratios were adjusted to EHA (60 parts), iBOA (25 parts), and HEA (15 parts).
Example 17
The same procedure was used as in Example 15, except that the main monomer ratios were adjusted to EHA (65 parts), iBOA (15 parts), and HEA (20 parts).
Example 18
The same procedure was used as in Example 15, except that the main monomer ratios were adjusted to EHA (60 parts), iBOA (20 parts), and HEA (20 parts).
Example 19
The same procedure was used as in Example 15, except that the main monomer ratios were adjusted to EHA (55 parts), iBOA (25 parts), and HEA (20 parts).
Example 20
The same procedure was used as in Example 15, except that the main monomer ratios were adjusted to EHA (60 parts), iBOA (10 parts), and HEA (30 parts). The HDDA content was also slightly lower at 0.05 parts.
Example 21
The same procedure was used as in Example 15, except that the main monomer ratios were adjusted to EHA (55 parts), iBOA (15 parts), and HEA (30 parts). The HDDA content was also slightly lower at 0.05 parts.







TABLE 3







Outgassing tolerance on plastic substrates










1 mm MR200
1 mm MR58












Example
OCA composition
60° C./90% RH
85° C. dry
60° C./90% RH
85° C. dry





15
65/20/15/0.10
edge bubble
edge
edge bubble
edge bubble



EHA/iBOA/HEA/HDDA

bubble


16
60/25/15/0.10
pass
pass
pass
few edge



EHA/iBOA/HEA/HDDA



bubbles


17
65/15/20/0.10
edge bubble
edge
edge bubble
edge bubble



EHA/iBOA/HEA/HDDA

bubble


18
60/20/20/0.10
pass
pass
pass
pass



EHA/iBOA/HEA/HDDA


19
55/25/20/0.10
pass
pass
pass
pass



EHA/iBOA/HEA/HDDA


20
60/10/30/0.05
pass
pass
pass
pass



EHA/iBOA/HEA/HDDA


21
55/15/30/0.05
pass
pass
pass
pass



EHA/iBOA/HEA/HDDA









The samples in Table 3 show that the formulation latitude increases as the amount of HEA in the formulation increases from 15 to 20 to 30 parts. Samples at lower levels than 15 parts of HEA could not be formulated without showing bubbles in the test. None of the samples showed any haziness or delamination from the substrate. Referring to Table 3, a “pass” designation means that the sample did not display any bubbles, undergo any delamination, or turn hazy or white upon exposure to the environmental conditions in which it was tested (60° C./85% RH or 85° C. dry) for one week as described above.
Various modifications and alterations to this disclosure will become apparent to those skilled in the art without departing from the scope and spirit of this disclosure. It should be understood that this disclosure is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of this disclosure intended to be limited only by the claims set forth herein as follows.

## Claims

1. An optically clear laminate comprising:
a first substrate having at least one major surface;
a second substrate having at least one major surface; and
a cloud point-resistant, optically clear adhesive composition situated between and in contact with at least one major surface of the first substrate and at least one major surface of the second substrate, wherein the adhesive composition is prepared by polymerizing a precursor mixture, the precursor mixture comprising:
from about 60 to about 95 parts by weight of an alkyl acrylate or a combination of alkyl acrylates having 1 to 14 carbon atoms in the alkyl group;
from greater than 0 to about 5 parts of a copolymerizable polar monomer; and
from about 5 to about 50 parts of a hydroxyl-containing monomer that has an OH equivalent weight of less than 400,


wherein the laminate has a haze value of less than 5% and an average transmission between 450 nanometers and 650 nanometers of greater than about 85% after it is placed in an environment of at least 70° C. and 90% relative humidity for 72 hours, cooled to room temperature, and measured.

2. An optically clear laminate according to claim 1, wherein the first substrate, the second substrate, or both the first substrate and the second substrate are selected from a display panel, a touch panel, an optical film, a cover lens, or window.

3. An optically clear laminate according to claim 2, wherein the cover lens comprises at least one of glass, polymethylmethacrylate, or polycarbonate.

4. An optically clear laminate according to claim 2, wherein the display panel is selected from a liquid crystal display, a plasma display, an OLED display, an electrowetting display, and a cathode ray tube display.

5. An optically clear laminate according to claim 2, wherein the optical film is selected from a reflector, a polarizer, a mirror, an anti-glare or anti-reflective film, an anti-splinter film, a diffuser, or electromagnetic interference filter.

6. A laminate according to claim 3, wherein the adhesive composition has a thickness of greater than about 100 μm.

7. A laminate according to claim 1, comprising from about 15 to about 50 parts of hydroxyl-functional monomer,
wherein the laminate does not display bubble, delaminate or turn hazy after the laminate is exposed to environmental conditions of either 1 week at 60° C. and 90% relative humidity or 1 week at 85° C. in a dry environment.

8. A laminate according to claim 7, wherein at least one of the substrates is polycarbonate or poly(methyl)methacrylate.

9. An optically clear laminate comprising:
a first substrate having at least one major surface;
a second substrate having at least one major surface; and
a cloud point-resistant, optically clear adhesive composition situated between and in contact with at least one major surface of the first substrate and at least one major surface of the second substrate, wherein the adhesive composition is prepared by polymerizing a precursor mixture, the precursor mixture comprising:
from about 60 to about 95 parts by weight of an alkyl acrylate or a combination of alkyl acrylates having 1 to 14 carbon atoms in the alkyl group, wherein the alkyl acrylate or a combination of alkyl acrylates include isobornyl (meth)acrylate; and
from about 15 to about 50 parts of a hydroxyl-containing monomer that has an OH equivalent weight of less than 400,

wherein the laminate has a haze value of less than 5% and an average transmission between 450 nanometers and 650 nanometers of greater than about 85% after it is placed in an environment of at least 70° C. and 90% relative humidity for 72 hours, cooled to room temperature, and measured.

10. An optically clear laminate according to claim 9 wherein the precursor mixture comprises:
about 80 parts by weight of an alkyl acrylate or a combination of alkyl acrylates having 1 to 14 carbon atoms in the alkyl group, wherein the alkyl acrylate or a combination of alkyl acrylates include isobornyl (meth)acrylate; and
about 15 parts of a hydroxyl-containing monomer that has an OH equivalent weight of less than 400.

11. An optically clear laminate according to claim 9, wherein the precursor mixture comprises:
from about 25 to about 86 weight percent of an alkyl acrylate or a combination of alkyl acrylates having 1 to 14 carbon atoms in the alkyl group;
from greater than 0 to about 6 weight percent of a copolymerizable polar monomer; and
from about 13 to about 33 weight percent of a hydroxyl-containing monomer that has an OH equivalent weight of less than 400 based upon 100 weight percent adhesive composition.

12. An optically clear laminate according to claim 1, wherein the haze value is less than 2%.