AU745075B2 - Light diffusing adhesive - Google Patents

Description

-Our Ref:7463493 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT *n

C

t* Applicant(s): Minnesota Mining and Manufacturing Company 3M Center PO Box 33427 Saint Paul Minnesota 55133-3427 United States of America DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Address for Service: Invention Title: Light diffusing adhesive The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 -1- Light Diffusing Adhesive Technical Field The present invention relates to light diffusing material, in particular to light diffusion adhesive having excellent light diffusing properties with low back scattering.

Background of the Invention Information displays, such as liquid crystal displays and rear projection screens, often rely on light-diffusing optical constructions for efficient operation and enhanced readability. Such light-diffusing constructions assume critical roles in these displays by forward scattering the light from a source without a significant loss in the intensity of the forward scattered light. This scattered, yet high transmittance, resultant light gives such displays a desirable background brightness by reducing the amount of incident light which is scattered or reflected back toward the light source. Elimination or restriction of such "baclscattered" light is a key factor in designing these light-diffusing constructions.

One approach in designing light-diffusing constructions is the filling or embedding of rigid, transparent or translucent plastic films with particles. When properly sized, prepared and formulated with a plastic film, these particles can scatter and diffuse incident light. However, the use of some particles can lead to certain undesirable and deleterious optical effects which detract from the overall brightness or transmittance of the incident light. For example, when some inorganic particles such as titania powders or if particles which are too small on the order of the wavelength of the incident light) are used in light-diffusing constructions, a significant loss in brightness can result due to high levels of backscatter. Conversely, particles having a large diameter with respect to the Swavelength of the incident light and/or if the refractive index of the particles is identical or very similar with the continuous plastic film, then little light diffusion occurs.

Additionally, some particle-filled plastic films, although effective as lightdiffusing layers, can alter the polarity of the light as it travels through the film. In e -i -i -2some constructions, for example, liquid crystal displays, any significant depolarization of the light by the light-diffusing film or component can result in the loss of image quality.

Summary of the Invention In one aspect the invention provides a light diffusing adhesive comprising a pressure sensitive adhesive matrix having a refractive index of n filled with organic polymeric microparticles having an average diameter of about 0.5 /m to about 30 im and having a refractive index ofn 2 such that Ini-n2| is in the range of 10 0.01 to 0.2 and the combination of the pressure sensitive adhesive matrix and organic polymeric microparticles has a transmittance of greater than 80% of S: incident intensity and a backscatter of less than 20%, wherein pressure sensitive adhesive matrix is a film former or a pressure sensitive microsphere-based adhesive composition and the organic polymeric microparticles are prepared from 15 fluorinated acrylate monomers or fluorinated methacrylate monomers having refractive indices in the range of 1.34 to 1.44.

.***Advantageously, the adhesive matrix can be both water and solvent borne thus permitting greater flexibility in choice of adhesive for controlling optical performance. Further, the adhesive matrix can be a film former or microsphere based. Light diffusing microparticles used in the present invention can be prepared using a variety of polymerization methods, allowing the user more opportunity to control the size, composition, morphology and overall characteristics of the microparticles.

Furthermore, the proper balance of particle sizes, particle compositions, refractive indices, particle loadings and other properties and parameters can be tailored to adjust light diffusing properties according to an intended end-use.

Attachment or adherence of such light diffusing adhesives to other polarizing films, reflective substrates or other optical components is also provided by this invention. Due to the adhesive nature of these light diffusing materials, there is no I- 2a need for additional layers of adhesive for laminating or bonding for surface attachment to substrates that could be detrimental to the optical performance of the light management device. Additionally, this invention provides a material that is not only light diffsing but is flexible, as well.

Advantageously, the light diffu~sing adhesive of the present invention does not significantly backscatter incident light or de-polarize transmitted light.

-3- Description of the Preferred Embodiment(s) The light diffusing adhesive of the present invention comprises a mixture of a pressure-sensitive adhesive matrix having a refractive index of n, filled with organic, polymeric microparticles having a refractive index n 2 wherein the absolute differencein th ive indices of matrix and microparticles, that is, Jnl-n21 is greater than zero and is typically in the range of 0.01 to 0.2.

The weight ratio of matrix to microparticles, based on solids, is from about 1:1 to about 50:1, preferably from about 4:1 to about 25:1. While many factors can affect the light diffusing properties of the adhesives of the present invention, the ratio of the matrix to microparticles is a significant factor. Generally, when the ratio of matrix to microparticles is too large, there is an insufficient concentration of particles to adequately diffuse incident light and a thicker film is required. On the other hand, when microparticle concentration goes beyond 50% of the matrix, brightness and transmittance deteriorates.

Other factors that can affect the light diffusing characteristics of the adhesive include for example, the microparticle size, the refractive index differential between the matrix and the microparticles, the gradient in refractive index between the matrix and the microparticles, the thickness of the dried light diffusing adhesive when coated onto a substrate, and the intrinsic properties of the microparticle components, for example, degree of crystallinity, organic or inorganic character, absorption properties and the like.

To obtain the optical properties in this light diffusing adhesive layer, the Sabsolute difference between the refractive index of the pressure-sensitive adhesive matrix (ni) and the micropaticle filler is greater than zero and is typically in 25 the range of 0.01 to 0.2. Values for refractive indices of these components can be obtained directly through the use of standard refractometric methods (for example, using an Abbe refractometer according to ASTM Test Method D542) or, more conveniently, by consulting various tabular sources of refractive index data for polymeric materials (for example, Polymer Handbook, 3rd. ed., New 30 York, John Wiley Sons, 1989. pp. VI/451-V/461) Should this absolute difference in refractive indices approach zero, then a poorly- or non-diffusing transparent or nearly transparent composite could result.

-4- This insufficient differential of the refractive indices might be overcome by adding more particles and/or increasing the thickness of the adhesive layer. However, these corrective measures could result in an adhesive layer having diminished brightness.

The adhesive layer is light-diffusing in nature: that is, the adhesive layer can bend the incident light beam, yet still retain a high level of transmittance (generally greater than about 80% of incident intensity, preferably about 85% to about 95%, most preferably about 90% to about 95%) after passing through the adhesive layer. Furthermore, backscatter of these adhesives is typically less than about 20%, preferably in the range of about 1 to about In general, light diffusing materials have the ability to uniformly scatter light forward fromthe light source. Uniformity of the scattered light is measured in terms of its bend angle, wherein "bend angle" means the viewing angle at which the gain drops to 1/3 of its on-axis value. The larger the bend angle, the more uniform the scattered light. However, higher bend angles usually come at the expense of brightness (luminous transmission). Alternatively, losses in luminous transmission could be due to excessive backscattered light. Thus, optimization of light diffusing material depends on the balance between particle concentration, index of refraction difference, thickness of the diffuser and particle size.

The pressure-sensitive adhesive matrix is defined as an adhesive material that is aggressively tacky at room temperature, for example, about 20 to 22 0 C and firmly adheres to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure, yet has a sufficiently cohesive and elastic nature so that, despite its aggressive tackiness, can be handled with the 25 fingers and removed from smooth surfaces without leaving a residue (Pressure- Sensitive Tape Council Test Methods, 1985, p. Such adhesives may be S: inherently tacky or may be elastomeric materials compounded with compatible tackifying resins. Furthermore, these adhesive matrices can be film forming compositions or tacky microspheres. The pressure-sensitive adhesive matrix can 30 be formed by a variety of polymerization methods, including solution, suspension, emulsion and bulk techniques. Examples of useful pressure-sensitive adhesive S matrix compositions include but are not limited to (meth)acrylates, tackified t 7--7 -7 silicones, and tackified styrene-isoprene or tackified styrene-butadiene block copolymers.

A preferred class of pressure-sensitive adhesive matrices are film-forming (meth)acrylates compositions due to their ready availability, ease of preparation and formulation, and superior optical properties and stability. A consideration in the selection of the matrix is the compatibility of this matrix with the microparticles. For example, matrices comprising water-borne (meth)acrylic emulsions or latices are particularly compatible with water-based microparticles prepared by suspension or emulsion techniques. Likewise, solvent-borne matrices tend to be more compatible with microparticles prepared out of non-aqueous media.

Another preferred class of pressure-sensitive adhesive matrices are pressure-sensitive adhesive microspheres having a diameter of about 0.5 rlm to about 150 mn, preferably about 1 pm to about 70 pm, most preferably about 2 pm to about 30 m. Such microsphere matrices can be prepared by suspension, dispersion, direct emulsion and modified emulsion techniques. Preferably, pressure-sensitive adhesive microsphere matrices are prepared according to suspension polymerization methods described in, for example, U.S. Patent Nos.

3,691,140 (Silver); 4,166,152 (Baker et 4,495,318 (Howard); 4,786,696 (Bohnel); 4,988,467 (Delgado); and 5,045,569 (Delgado) and PCT Appl. No. WO 94/13751 (Delgado et al.).

In the preferred suspension polymerization method, the organic, polymeric nmicrospheres can be prepared by first forming an oil-in-water emulsion of an oil phase comprising any hydrophobic monomers, for example methacrylate 25 monomers and an oil soluble initiator in a water phase which comprises an aqueous medium having at least one suspension stabilizer or surfactant, such as those surfactants known to those skilled in the art. These suspension polymerization processes can optionally include other free radically reactive starting materials and are typically performed in the presence of a variety of i 30 emulsifiers, stabilizers, surfactants and/or under particular process conditions that induce the formation and prevent the agglomeration of the microspheres.

-6- Advantageously, JnicrosphericaJ matrices can be combined with Microparticles to form repositionable light diffusing adhesives.

The Preferred Pressure-sensitive adhesive matrix formulations are typically Provided from alkyl (meth)acrylate monomers. Particularly Preferred monomers are monofunctiow unsaturated (meth)acrylate esters-of non-tertiary all alcohols. The alkyl groups of these alcohols typically contain from 4 to 14, preferably 4 to 10 carbon atoms. As ho0mopolymers, these (meth)acrylate esters generally have glass transition temperatures of below about 10 0

C.

Examples Of Useful monomers include but are not limited to sec-butyl acrylate, n-butyl acrylate, isoamyl acrylate, 2-methylbutyl acrylate, 4-methyl-2pentyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, isodecyl methacrylate, dodecyl acrylate, tetradecyl acrylate and mixtures thereof Of these, isooctyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate are preferred.

(Meth)acrylate or other vinyl monomers which, as homopolymers, have glass transition temperatures of greater than about -20 to 01 0 C, for example, ethyl acrylate, tert-butyl acrylate, isobornyl acrylate, butyl methacrylate, vinyl acetate, acrylonirije, and the like, may be used in conjunction with one or more of the (meth)aczrylate monomers provided that the glass transition temperature of the resulting polymer is below about -10 0 C and has the proper pressure sensitive adhesive and optical properties.

Free radically polynierizaible polar monomers are also useful in the matrices of the present invention. These polar monomers are both somewhat oilsoluble and water-soluble. Representative examples of suitable polar monomers .include but are not limited to those selected from the group consisting of acrylic acid, methacrylic acid, itacomic acid, crotonic acid, maleic acid, fliraricacd sulfoethyl methacrylate, N-vinyl pyrrolidone, N-vinyl caprolactanm, 2 -vinyl..4,4..

diehl2oxzhioe t-butyl acrylamide, dimethyl amino ethyl acrylamide,

N-

octyl acrylamide, and ionic monomers such as sodium methacrylate, ammxonium acrylate, sodium acrylate, trimethylamine p-vinyl benzimide, 4 4 9 -trirnethyl-4 30 azonia.7oxo..8oxadec-9ene I -sulphonate, NN-dimethyl..N.{letamethacryloxy-.e1iy1) ammionium propionate betaine, trimethylamine methacryljwide, 1, 1 -dimethyl- Il-( 2 3 -dihydroxypropyl)amine methacrylimide, -7mixtures thereof and the like. Preferred polar monomers include those selected from the group consisting of monoolefinic monocarboxylic acids, monoolefnic dicarboxylic acids, acrylamides, N-substituted acrylamides, salts thereof, and mixtures thereof. Examples of such preferred polar monomers include but are not limited to those selected from the group consisting of acrylic acid, sodium acrylate, N-vinyl pyrrolidone, and mixtures thereof These adhesive matrices may or may not be crosslinked. Preferred (meth)acrylate matrices can be crosslinked using multifunctioral crosslinking agents. Useful multifunctional crosslinking agents include but are not limited to those selected from the group consisting of acrylic or methacy ilic esters ofdiols such as butanediol diacrylate, triols such as glycerol, and tetroJs such as pentaerythritol. Other useful crosslinking agents include but ae not limited to those selected from the group consisting of polyvinylic crosslinking agents, such as substituted and unsubstituted divinylbenzene; and difunction* urethane acrylates, such as Ebecrylm 270 and Ebecrylm 230 (1500 weight average molecular weight and 5000 weight average molecular weight acrylated urethanes, respectively both available from Radcure Specialties), and mixtures thereof When used, crosslinker(s) is (are) added at a level consistent with their known use and the retention of pressure sensitive adhesive properties. Such factors that are considered include but are not limited to molecular weight of the crosslinker, degree ofmultifunctionality, the crosslinker concentration, and the like. Crosslinking can alternatively occur via exposure to an appropriate energy source, such as gamma or electron beam radiation.

SThe microparticles of the light diffusing adhesive of the present invention are polymeric and can be prepared by a number of well-known techniques, such as, suspension, dispersion, direct emulsion and modified emulsion polymerizations.

The microparticles typically have a diameter of about 0.

5 g m to about 30 inm, preferably about 1 pm to about 15 pm, most preferably about 2 prn to about 30 30 To meet the refractive index differential with preferred acrylate pressure prredacylatepressure sensitive adhesive matrices, which typically have refractive indices of about 1.46 Sto about 1.48, organic, polymeric microparticles having somewhat lower or higher -~sa ~sa refra~ctive indices are essential. Mcroparticles having a sufficiently lower index of refraction than these preferred acrylate pressure sensitive adhesive matrices can be prepared from fluorinated acrylate or methacrylate monomers. Such fluorinated (meth)acrylate monomers form polymers having refractive indices in the range of about 1.34 to about 1.44 depending on the chain length and/or degree of branching of the fluoroalkyl substituents of these monomers. Examples of usefl fluorinated acrylate or methacrylate monomers include pentadecafluorootl acrylate, unadecafluorohexyl acrylate, nonafluoropentyl aciylate, heptafluorobutyl acrylate, octafluoropentyl acrylate, pentafluoropropyl acrylate, trifluoroacrylate, triisofluoroisopropyl methacrylate, and trifluoroethyl methaciylate.

Conversely, nhicroparticles having a sufficiently higher imdex of refraction than these preferred acrylate pressure sensitive adhesive matrices can be preferably prepared from free radically polymerizable monomers having cycloaliphatic, substituted cycloaliphatic, aromatic or substituted aromatic substituents. The homopolymers of such free radically polymerizable monomers generally have refractive indices in the range of about 1.49 to about 1.63. Useful examples of such free radically polymerizable monomers include 3 -methylcyclohexcyl methacrylate, 4 -methylcyclohexyl methacrylate, 2 -inethylcyclohexyl methacrylate, bornyl methacrylate, cyclohexyl methacrylate, I -methylcyclohexyl methacrylate, 2chlorocyclohexyl methacrylate, benzyl methacrylate, phenoxy methacrylate, Polyphenyl methacrylate, a-methyl styrene, styrene, vinyl neononate, halogenated Ve~g.methacrylates, 2 -chlorocyclohexyl methacrylate, 2-bromoethyl methacrylate and the like.

These microparticles may or may not be crossliniced. Preferred 25 (meth)acrylate microparticles can be crosslinked using multifujnctional crosslining agents. Useful nmultiflunctional crosslinking agents include but are not limited to those selected from the group consisting of acrylic or methacrylic esters of dials such as butanediol diacrylate, triols such as glycerol, and tetrols such as pentaerytlujtol. Other usefli crosslinking agents include but are not limited to 30 those selected from the group consisting of poyiyi cosik agents, such *Ct...as substituted and unsubstituted divinylbenzene; and diliinctional urethane aczylates, such as Ebeczylm 270 and Ebecrylm 230 (1500 weight average -9molecular weight and 5000 weight average molecular weight acrylated urethanes, respectively both available from Radcure Specialties), and mixtures thereof.

When used, crosslinker(s) is (are) added at a level consistent with their known use and the desired physical and optical properties. Such factors that are considered include but are not limited to molecular weight of the crosslinker, degree of multifiinctionality, the crosslinker concentration, and the like.

Crosshnking can alternatively occur via exposure to an appropriate energy source, such as gamma, or electron beam radiation.

T ;he pressure sensitive adhesive matrix can be coated on suitable flexib~le or inflexible'backing materials by conventional coating techniques such as knife coating or Meyer bar coating or use of an extrusion die.

Suitable backing materials for the aqueous or solvent based coatings include but are not limited to those selected from the group consisting of paper, plastic fil ms, cellulose acetate, ethyl cellulose, woven or nonwoven fabric formed of synthetic or natural materials, metal, metallized polymeric filn, ceramic sheet material, and the like. Primers or binders may be used thereon.

The pressure-sensitive adhesive properties of the light diffusing adhesives may be altered by addition of tackifyring resin and/or plasticizer. It is also within the scope of this invention to include various other components, such as colorants, neutralizin g agents such as sodium hyplroxide, etc., fillers, stabilizers, or various polymeric additives. The amounts of these additional components are added to the pressure sensitive adhesive matrix in an amount consistent with the known too* uses of these components.

.Wh en the light diffiising adhesive of the present invention is used in combination with suitable backings and substrates, a variety of optical devices can be obtained. Such devices include but are not limited to, sign boards, illumination covers, partitions, decorative films, films for rear projection screens, conformable films, skylights, and the like. The foregoing list of articles is by no means S. q exhaustive and should not be construed to limit the scope of this invention.

Ojcsand advantages of this invention 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 S unduly limit this invention. All materials are commercially available or known to those skilled in the art unless otherwise stated or apparent.

Test Methods BendAngle The attenuation of on-axis gain and angular spread caused by the light diffusing adhesive was measured using a HeNe laser used in a transmission geometry. A Beamscan scanning system with a 25 p m aperture was used as the detector that scanned the scattered beam in the vertical plane. The bend angle is defined as the viewing angle at which the gain dropped to 1/3 of its on-axis value.

Luminous Transmission The luminous transmission of the light diffusing adhesive layer was measured using a Perkin-Elmer Lambda-19 Spectrophotometer in transmission mode.

Depolaricadon The ability of the diffusing adhesives to depolarize light was measured using a Perkin-Elmer Lambda-19 Spectrophotometer with one dichroic polarizer placed at the beam entrance slit and other sheet placed immediately before the integrating sphere in which light is collected. The diffusing adhesive was placed between the polarizers, which were crossed. If the diffusing adhesive affects the state ofpolorization of the light, then, an increase in the transmission would be observed. The averaged deviation from total extinction over the visible range (400-700 nm) is reported.

Backscatter The backscatter in the light diffusing adhesive was characterized with a Perkin-Elmer Lambda-19 Spectrophotometer. The sample was placed in reflective mode with a black backing behind it to absorb transmitted light. An integrating sphere was used to measure both specutarly and diffusely reflected light. First surface reflection are subtracted from the reported values. The backscattered light was measured as a function of wavelength over the visible range (400-700 nm) and the average deviation is reported.

11- Index ofRefraction A Metricon prism coupler was used to determine the indices of refraction of these adhesives at a wavelength of 632.8 nm. Indices were measured in the x, y and z direction, but were found to be the same in all directions.

Preparation of the Organic, Polymeric Microparticles Example I Preparation of Waterborne Poly(styrene) Particles by Suspension Polymerization Method 6 grams of Standapol T A (ammonium lauryl sulfate commercially available from Hercules, Inc.) and 3 grams ofpoly(vinyl alcohol) were dissolved in 240 grams of deionized water. 2 grams of Lucido "75 (75% benzoyl peroxide from ElfAtochem) was dissolved in 150 grams of styrene and then charged to the above aqueous mixture. The above mixture was emulsified in a Gaulin homogenizer such that the styrene monomer droplet size was 1 micron or less.

This emulsion was then charged to 1 liter reactor, stirred at 300 RPM and heated to 70*C for 16 hours. The resulting particle sibe was approximately 2 microns as viewed with an optical microscope and had an index of refraction of 1.59.

xanle A: Preparation of Waterborne Poly(NEO-9) Particles by Suspension Polymerizatrion Method 7 grams of Standapol" A (ammonium lauryl sulfate commercially available 20 from Hercules, Inc.) and 1 gram ofpoly(vinyl alcohol) were dissolved in 390 grams of deionized water. 1 gram of lauryl peroxide, 2.1 grams of acrylic acid and 2.1 grams of 1,6 hexanediol diacrylate were dissolved in 205.8 grams of vinyl neononate (commercially available from Union Carbide under the tradename "NEO-9") and then charged to the above aqueous mixture. The above mixture 25 was emulsified in a Gaulin homogenizer such that the styrene monomer droplet size was 1 micron or less. This emulsion was then charged to 0.5 liter reactor, stirred at 300 RPM and heated to 60°C for 8 hours. The resulting particle size was approximately 2 microns as viewed with an optical microscope and had an index of refraction of 1.49.

12- Exaple IB. Preparation of Waterorne Poly (Benl Methacrylate) Particles by Suspension Polymerization Method grams of StandapolTM A (ammonium lauryl sulfate commercially available from Hercules, Inc.) and 1.5 grams ofPVP-K90 (poly(vinyl pyrrolidone) commercially available from GAF) were dissolved in 480 grams of deionized water. 0.47 grams oflauryl peroxide was dissolved in 128 grams benzyl methacrylate and then charged to the above aqueous mixture. The above mixture was emulsified in a Gaulin homogenizer such that the styrene monomer droplet size was 1 micron or less. This emulsion was then charged to 1 liter reactor, stirred at 300 RPM and heated to 65*C for 5 hours. The resulting particle size was approximately 2 microns as viewed with an optical microscope and had an index of refraction of 1.57.

Eample 2: Preparation of Solventborne Poly(styrene) Particles by Dispersion Polymerization Method 9 grams ofPVP-K15 (a poly(vinyl pyrrolidone) stabilizer commercially available from GAF, Inc.) and 1.5 grams of Aersol TM OT100 (sodium dioctyl sulfosuccinate commercially available from American Cyanamid) were dissolved in 195 grams of ethanol. 2.1 grams ofVazo T M 64 (2,2'-azobis(isobutyronitrile) from Dupont) and 1.05 grams of 1,6-hexanediol diacrylate were dissolved in 105 grams 20 of styrene. The two mixtures were combined and than charged to 0.5 liter reactor stirred at 250 RPM and heated to 70*C for 16 hours. The resulting particle size was approximately 9 microns as viewed with an optical microscope and had an index of refraction of 1.59.

Table I below lists the index of refraction of the diffusing particles: 25 TABLE 1 Polymer n a poly(styrene) 1.59 poly(benzyl methacrylate) 1.568 poly(NEO-9)* 1.49 Neo-9 is a C-9 branched vinyl ester from Union Carbide 13 Preparation of Pressure-.Sensitive Adhesive Matrix Microparticies Exaffple 3 FPreparution of Preswue.Sengive Adhesive Matrix Micros; ee bY Suspension Polymerizaion Methodhre I gram of sodium dodecyl benzene sulfonate, and 2.4 gramns of sodium styrene sulfonate (NaSS) wee-disolved in 360 grams of deionized water. 7.2 grams of polY(ethylene oxide) 16 acrylate (PEO) and 1.05 grams of benzoyl peroxide from Elf Atochen) were dissolved in 23 0.4 grams. of isooctyl acrylate (10A). The above mixture was emulsified in a Gaulin homogenizer such that the droplet size was I micron or less. This emulsion was then charged to 1 liter reactor, stirred at 400 RPM and heated to 65 0 C for 4 hours. The 96/3/1 IOA/PEQINaSS resulting particles had a size of approximately 2 Microns as viewed with an optical nucroscope and had an index of refraction of 1.47.

Example 4: Preparation of Pressure.Sensinve Adhesive Matrix Microsp heres by Suspension Polymriaon Method Mcrospheres containing acrylic acid (AA) in a 97/2/1 IOA1PEO/AA weight ratio were prepared in accordance with Example 3. The resulting microspheres had a size of approximately 2 microns as viewed with an optical microscope and had an index of refraction of 1.47.

EXaMle 5: Preparation of Pressure.SengsifiveAdhesive Matrix Microsp here by :20 Suspension PolymeiiZation Method .o.Mcrospheres containing hydroxybutyl acrylate (ElA) in a 96/2/2 o.IQAIPEO/JHBA weight ratio were prepared in accordance with Example 3. The resulting particles had a size of approximately 2 micrometers as viewed with an optical microscope and had an index of refraction of 1.469.

Commercially Available Pressure-Sensitive Adhesive Matrices o Table 2 lists the tradenanie, supplier, and index of refraction of the acrylic emulsion pressure-sensitive adhesive matrices used in the following examples.

Matrix

A

B

C

D

-14- Table 2 Tradenamne Supplier RhodotakM 300 Rhone-Poulenc MorFstik Thm 2 14 Morton Adhesives UCARThI 965 Union Carbide Flexcryl "4625 Air Products 1.468 1.47 1.494 1.471 Examles Light-Diffstsing Adhesive Compositions Using Acrylic Emulsion Pressure..Sensitive Adhesiv Matrices combined with Poly(stypene) Microparrcles A series of light-diffuising adhesive compositions were prepared by blending 10% by weight of the organic, polymeric microparticles of Example 1 with several acrylic emulsion Pressure-senitive adhesive matrices. Once blended, the light difflusing adhesive compositions were coated onto PET at 4 mils wet and dried at 60 0 C for 10 minutes. Following drying, the lumkinous transmission, bend angle, backscatter and depolarization for the Iight-diffirsing adhesive compositions were measured as described above and the results of these measuremnents are reported in. Tables 3 a and 3b.

a. a Example Matrix (wtO%) 6 A(00).

7 B(90) 8 C(90) 9 D(90) Table 3a Microparticle (wto) EX- 1(10) EX. 1(10) Ex. 1(10) EX. 1 Luminous Tranmssion 87.2 86.6 91.5 Example 6 7 8 9 Bend Angle 4.68 5.75 5.05 5.0 Table 3b Backscamter Depolarization Extinction) 4.65 7.36 5.27 0.57 1.75 1.62 4.82 0.67 EVamples 10-13 ad Comparatve Exvan~le Light-Difjrusjng Adhesive Compositions Using Mi crosp here Pressure..Sensfive A dhesive Matrice combined with Poly(styrene) MicropaWgcles Examples 10-13 illustrate the use of the organic, Polymeric mnicroparticles of Example 1 mixed in a matrix comprising the Pressure-sensitive adhesive microspheres of Example 3 at varying weight ratios. The microparticle/matrix mixtures were blended, coated and dried as described in Examples 6-9 and the luminous transmission, bend angle, backscatter and depolarization for the lightdiffusing adhesive compositions were measured as described above. The results of these measurements and the results of similar measurements on a coating solely comprising the microsphere matrix of Example 3 (Comparative Example C 1) are reported in Tables 4a and 4b.

Table 4a Example Matrix Microparticle Luminous Transmission Ex. 3(95) Ex. 1(5) 90.4%~ 11 Ex. 3(93) Ex. 1(7) 90.3 Vo 12 Ex. 3(90) Ex. 1(10) 88.7 Vo 13 Ex. 3(80) Ex. 1 (20) 84.2 V Cl Ex. 3 (100) 92.6 Example Bend Backscattter Depolarizaton Angle (0o Extinction) 3.7 2.76 1.4 11 4.55 2.12 0.53 12 5.73 4.76 1.52 13 6.95 6.55 0.24 Cl 2.4 0.76 1.27 15 Examples 14-16 ad Comparative Examples C-2 C-4. Light-Diffusing Adhesive Compositions Using Microsphere Pressure-.Sensridve Adhesive Matrces combined with Various Organic, Polymeric Microparticles Examples 14-16 illustrate the use of the organic, polymeric microparticles of Example 1, 1lA and l B -mixed in a matrix comprising the pressure-sensitive adhesive microspheres of Example 3-5 at varying weight ratios. The micropartcle/marx mixtures were blended, coated and dried as described in Examples 6-9 and the luminous transmission, bend angle, backscatter and -16depolarization for the light-diffUsing adhesive compositions were measured as described above. The results of these measurements, and the results of similar measurements on a coating solely comprising the mnicrosphere matrices of Example 3-5 (Comparative Example C2-C4), are reported in Tables 5a and Example Matrix (Wto/) 14 Ex. 3(91, C2 Ex. 3(10( Ex. 4(K6 C3 Ex. 4(10C 16 Ex. 5(70] C4 Ex. 5(100 Example Bend Angle 14 2.52 C2 2.40 15 3.90 C3 60 16 6.40 C4 2.3 Table Mcroparticle (wt0/) Ex. IA(9) I1A(O) Ex. 1(4) Ex. 1 (0) Ex. IB (30) Ex. 1B Table Sb Backscattter.

0.91 0.76 1.13 1.11 5.95 1.15 Luminous Transmission 93.1% 92.6% 94.4% 93.4% 83.5% 92.7% Depolarization.

Extinction) 4.4 1.27 2.4 7.63 Examples 17-19 and Comparative Examples CS-C7:- Light-D6ffusing Adhesive Compositios Using Solvent-borne Acrylic Pressure.Sensilive.Adhesive Matrices. combined with Organic Polymeric Mficropwilicles and Inorganic Polymeric Microparticles This set of examples show that the use of an inorganic particle (titanium dioxide)-resujted in higher deviations from total extinction (depolarization) and backscatter than analogous light-diffusing adhesive compositions which employed organic, Polymeric microparticles. Light-diffusing adhesives were prepared from both the dispersion Polymerized poly(styrene) particles Of Examiple 2 and titanium dioxide particles at three Particle concentrations in Arosetm 1085 (pressure sensitive adhesive matrix), a solvent based acrylic pressure sensitive adhesive having a refractive index of 1.468 commercially available from Ashland Chemicals.

The icroparticle/matrix mixtures were blended, coated and dried as described in Examples 6-9, except the mixtures were coated onto a release liner. Once dried, -17the backscatter and depolarization for the light-diffusing adhesive compositions were measured as described above. The results of these measurements are reported in Table 6.

Table 6 Example Matrix Microparticle Backscattter Depolarization (wt% s Extinction) (wt%) 17 95 Ex. 1(5) 11.18 6.32 CS 95 TiO 2 18.44 9.18 18 90 Ex. 1(10) 13.82 5.38 C6 90 TiO 2 (10) 29.09 10.19 19 80 Ex. 1(20) 18.44 9.18 C7 80 Ti0 2 (20) 35.57 14.89 Various modifications and alterations of this invention will become *apparent to those skilled in the art without departing from the scope and principles of this invention, and it should be understood that this invention is not to be 10 unduly limited to the illustrative embodiments set forth hereinabove. All publications and patents are incorporated herein by reference to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in Australia.

Claims (1)

18- The claims defining the invention are as follows: 1. A light diffusing adhesive comprising a pressure sensitive adhesive matrix having a refractive index of nl filled with organic polymeric microparticles having an average diameter of about 0.5 /im to about 30 pm and having a refractive index of n 2 such that Ini-n 2 is in the range of 0.01 to 0.2 and the combination of the pressure sensitive adhesive matrix and organic polymeric microparticles has a transmittance of greater than 80% of incident intensity and a backscatter of less than 20%, wherein pressure sensitive adhesive matrix is a film former or a 10 pressure sensitive microsphere-based adhesive composition and the organic polymeric microparticles are prepared from fluorinated acrylate monomers or fluorinated methacrylate monomers having refractive indices in the range of 1.34 S: to 1.44. 15 2. The light diffusing adhesive according to claim 1, wherein the adhesive is 0 comprised of a mixture having a weight ratio of pressure sensitive adhesive matrix to organic polymeric microparticles, based on solids, is about 1:1 to about 50:1. o 3. The light diffusing adhesive according to claim 1, wherein the pressure- 20 sensitive adhesive matrix are pressure-sensitive adhesive microspheres having a diameter of about 0.5 jim to about 150 jm. 4. The light diffusing adhesive according to claim 1, wherein the fluorinated acrylate or methacrylate monomers are pentadecafluorooctyl acrylate, unadecafluorohexyl acrylate, nonafluoropentyl acrylate, heptafluorobutyl acrylate, octafluoropentyl acrylate, pentafluoropropyl acrylate, trifluoroacrylate, triisofluoroisopropyl methacrylate, or trifluoroethyl methacrylate. The light diffusing adhesive according to claim 1, wherein the film 30Uforming pressure sensitive adhesive matrix is (meth)acrylate compositions, tackified silicones, tackified styrene-isoprene or tackified styrene-butadiene block -19- copolymers. 6. The light diffusing adhesive according to claim 5, wherein the pressure sensitive adhesive matrix are polymers provided from alkyl (meth)acrylate esters of non-tertiary alkyl alcohols, wherein the alkyl groups of the alcohols contain from 4 to 14 carbon atoms. 7. The light diffusing adhesive according to claim 6, wherein the alkyl (meth)acrylate esters of non-tertiary alkyl alcohols are isooctyl acrylate, n-butyl 10 acrylate, 2-ethylhexyl acrylate or mixtures thereof. :.j 8. An optical device comprising a backing material wherein the backing .o material is coated on at least one major surface with a layer, either continuous or discontinuous of the light diffusing adhesive according to claim 1. 9. The optical device according to claim 8, wherein the backing material is a conformable or flexible film. 10. An optical device wherein the light diffusing adhesive is applied to either 20 one or both surfaces of a film for a rear projection screen. 11. Light diffusing adhesives according to anyone of claims 1-7 or optical devices comprising same, substantially as hereinbefore with reference to the accompanying drawings. DATED THIS 31st day of December, 2001. MINNESOTA MINING AND MANUFACTURING COMPANY u *S Its Patent Attorneys m 30 VIES COLLISON CAVE