WO2017031659A1

WO2017031659A1 - Nonwoven diffuser elements

Info

Publication number: WO2017031659A1
Application number: PCT/CN2015/087891
Authority: WO
Inventors: Zhigang Yu; Yihang Lv; Guanglei DU; Rui Chen; Naiyong Jing; William Blake Kolb; Jiaqi XUE
Original assignee: 3M Innovative Properties Company
Priority date: 2015-08-24
Filing date: 2015-08-24
Publication date: 2017-03-02
Also published as: TW201723537A

Abstract

Diffuser elements comprise (a) a nonwoven fabric comprising fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5, and (b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric. The resin has a T_g of about -10 to about 100℃. The resin pores have a size of about 200 nm to about 2 μm in at least one dimension.

Description

NONWOVEN DIFFUSER ELEMENTS

FIELD

This invention relates to nonwoven diffusers and to light emitting devices and displays with nonwoven diffusers.

BACKGROUND

Liquid crystal displays (LCDs) are used in devices such as smartphones, tablets laptop computers, monitors and televisions. Some LCDs are “edge-lit” and include a light source that is located on the side of the display, with a light guide positioned to guide the light from the light source to the back of the LCD panel. Other LCDs are directly illuminated using a number of light sources positioned behind the LCD panel. This “direct” arrangement is common with larger displays because the light power requirements, to achieve a certain level of display brightness, increase with the square of the display size, whereas the available real estate for locating light sources along the side of the display only increases linearly with display size.

Many LCD devices utilize a diffuser to help produce even lighting. Direct lit LCDs, for example, often use a diffuser plate or film to hide the images of the light sources, or the “hot spots” , that can be seen through the panel. Edge-lit LCD devices can also use a diffusion film on the front surface side of the light guide to ensure the uniformity of the light emitted from the device.

Diffuser plates can be made from transparent resin containing small diffusion particles. These plates can deform or warp after exposure to the elevated temperatures of the light sources. Diffusion films or sheets can be made with a bead coating layer on a clear plastic substrate. Such diffusion films often exhibit relatively weak diffusion capability, however. In addition, diffusion plates and diffusion films or sheets can be expensive to manufacture.

Nonwoven materials have also been considered for use as diffusers, particularly because of their low cost. It can be very difficult, however, to obtain nonwoven materials that are uniform enough yet still have sufficient mechanical strength for use in LCD applications.

SUMMARY

In view of the foregoing, we recognize that there is a need in the art for improved diffuser elements for use in LCD devices.

Briefly, in one aspect, the present invention provides diffuser elements comprising (a) a nonwoven fabric comprising fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5, and (b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric, the resin having a Tg of about-10 to about 100℃ and the resin pores having a size of about 200 nm to about 2 μm in at least one dimension. The diffuser element is from about 30 to about 150 μm thick and has a basis weight of about 30 to about 190 g/m². The coating weight of the resin is from about 15％to about 50％of the total weight of the diffuser element.

In another aspect, the present invention provides diffuser element comprising (a) a nonwoven fabric comprising porous fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5, the intra-fiber pores having a mean diameter of about 200 nm to about 2 μm, wherein the total volume of the intra-fiber pores is X percent of the total volume of the fibers and (b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric, the resin pores having a diameter of about 200 nm to about 2 μm, wherein the total volume of the resin pores is Y percent of the total volume of the resin coating. X is within about 1000％of Y, X is about 10％or less, and Y is about 10％of less. In yet another aspect, the present invention provides diffuser element comprising (a) a nonwoven fabric comprising porous fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5, the intra-fiber pores having a mean diameter of about 200 nm to about 2 μm, wherein the total volume of the intra-fiber pores is X percent of the total volume of the fibers and (b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric, the resin pores having a diameter within about 30％of the mean diameter of the intra-fiber pores, wherein the total volume of the resin pores is Y percent of the total volume of the resin coating. X is within about 1000％of Y, X is about 5％or less, and Y is about 5％of less.

The diffuser elements of the invention are a low cost alternative for providing similar light diffusion in LCD devices as other higher cost diffusion technologies. As compared to nonwoven diffusers without resin coatings, the diffuser elements of the invention provide improved diffusion and fiber hiding.

The diffuser elements of the invention can also be utilized for providing uniform light in other cost sensitive general illumination applications such as lightboxes and lamps (for example, light emitting diode (LED) lamps) .

In another aspect, the present invention provides light emitting devices and displays comprising the diffuser elements of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of scatter power per square meter as function of angle for pore sizes as modeled according to Example 7.

FIG. 2 is a graph of scattering power per square meter as a function of angle for a combination of pore sizes as modeled according to Example 7.

FIG. 3 is a graph of scattering power per square meter square as a function of angle for nonwoven fibers as modeled according to Example 7.

FIG. 4 is a graph of scattering power per square meter as a function of angle for fiber surface scattering/pores inside fiber and for pores in coated resin according to Example 7.

FIG. 5 shows print images used in the Examples.

DETAILED DESCRIPTION

The diffuser elements of the invention comprise a nonwoven fabric that is coated with resin. In some embodiments, the nonwoven fabric comprises fibers having a fiber diameter of less than about 50 μm, less than 25 μm or in a range from about 1 to about 25 μm or from about 10 to about 25 μm. In some embodiments, the fibers have an aspect ratio of length/diameter of greater than 5. In some embodiments, the nonwoven fabric can have a basis weight of about 10 to about 120 g/m², about 40 to about 120 g/m², about 50 to about 110 g/m² or about 70 to about 100 g/m². In some embodiments, the nonwoven fabric has a density of about 0.1 g/cc or greater, about 0.15 g/cc or greater or about 0.2 g/cc or greater. In some embodiments, the nonwoven fabric comprises fibers having intra-fiber pores (that is, pores inside the fiber) , wherein the mean diameter of the intra-fiber pores is about 200 nm to about 2 μm. As used herein, the diameter of an intra-fiber pore is the minimum length of the intra-fiber pore in any dimension.

The nonwoven fabric can be formed of any useful polymeric material such as, for example, polyethylene, polypropylene, or polyethylene terephthalate or engineering plastics such as polybutylene terephthalate or polyphenylene sulfide. In some embodiments, the nonwoven fabric can be formed of glass fibers.

The nonwoven fabric can be formed by any useful process. It can be formed, for example, via a wet laid process, a carding process, a meltblown process, spunbond, dry laid, or spunbond-meltblown-spunbond. In some embodiments, the nonwoven fabric is generally non-orientated. In other embodiments, the nowoven fabric is orientated.

Examples of useful commercially available nonwoven fabrics include spunbond nonwoven material TP-60 from Shandong Taipeng Nonwoven Company (Tai’ an, Shandong, China) , wetlaid nonwoven material Hirosen 40 from Hirose Paper Manufacturing Co. (Kochi, Japan) , Freudenberg Nonwovens 2431 and 2483 (Weinheim, Germany) , Asahi Kasei Corporation A5130 (Tokyo, Japan) , Crane&Co. RS 8.5 (Dalton, Massachusetts, USA) , Midwest Filtration Company Uniblend 100 (Cincinnati, Ohio, USA) and Kolon Finon C303 (Gwacheon, Korea) .

The fibers of the nonwoven fabric are coated with a resin. The coating composition is a latex composition comprising water and a resin having a glass-transition temperature (T_g) of about -10 to about 100℃, or in some embodiments preferably about 0 to about 30℃.

Examples of useful resins include polyethylene-vinyl acetate, polyacrylate, poly (acrylate-styrene) , polyurethane, polystyrene butadiene, polyethylene and combinations thereof. In some embodiments, polyacrylate or poly (acrylate-styrene) is preferred.

The solids concentration of the resin (that is, the percent solids of latex resin) is typically about 5％to about 60％, or about 10％to about 50％. In some embodiments, the resin droplets dispersed in the water have a diameter of about 1 μm or less.

Any useful coating technology can be used to apply the latex coating composition to the nonwoven fabric. For example, coating techniques such as wire-wound metering rod, gravure, reverse roll coating, dip coating and the like may be utilized. In some embodiments, wire-wound metering rod coating, also called Meyer bar coating, is a preferred coating technique.

After coating, the coated nonwoven fabric is dried. It can be dried at a temperature from about 20 to about 150℃, preferably at a temperature from about 80 to about 100℃. In some embodiments, it is preferable to dry the coated nonwoven fabric at a temperature above the T_g of the resin. In some embodiments, drying at a temperature above the resin’s T_g promotes formation of nano-sized pores in the dried resin coating.

The resulting dried diffuser element has porous resin on the surfaces of the fibers within the nonwoven fabric. The porous resin coating may fill in the area between some fibers and/or span from one fiber across to another fiber. In some embodiments, there are inter-fiber pores between the coated fibers having a size of about 2000 nm or greater in at least one dimension. The density of these inter-fiber pores can be, for example, about 10, 000 per mm³ or greater. In some embodiments the basis weight of the resulting dried diffuser element is about 30 to about 190 g/m² or about 70 to about 170 g/m². The resulting dried diffuser element typically has a porosity of about 30％to about 55％.

The porous resin coating can comprise pores having at least one dimension in the range of about 200 nm to about 2 μm. As used herein, the term “pore” means a small opening in the otherwise solid resin. The pores may be open or closed (for example, an enclosed air pocket) . In some embodiments, the resin coating further comprises nanopores having all dimensions less than 200 nm. The density of the nanopores can be, for example, about 100 per μm³ or greater.

In some embodiments the resin pores have a diameter that is within (plus or minus) about 30％of the mean diameter of the intra-fiber pores and wherein the density of the resin pores is within (plus or minus) about 1000％, or about 500％, of the density of the intra-fiber pores. As used herein, the diameter of a resin pore is the minimum length of the resin pore in any dimension. In some embodiments, the total volume of the intra-fiber pores is less than about 10％, or about 5％, of the total volume of the fibers and/or the total volume of the resin pores is less than about 10％, or about 5％, of the total volume of the resin coating.

The porous coating of the invention helps to hide the nonwoven fibers and also enhances the diffusion of the nonwoven fabric versus a non-coated nonwoven fabric. A non-coated nonwoven fabric has only one optical interface, the air-to-fiber interface. The porous coating creates two new optical interfaces, the fiber-to-resin interface and the resin-to-air interface, which increase light reflection and refraction and therefore enhance light diffusion.

In an uncoated nonwoven, light is scattered primarily by the surface of the fibers, the interface between the fibers and surrounding air, and the air pores inside the fibers (that is, the intra-fiber pores) . Where the density of fibers in the nonwoven is high, the scattering is strong, and where the density is low, the scattering is weak. This non-uniformity of scattering leads to differences in visual appearance. Parts of the nonwoven with stronger scattering appear darker, and parts with weaker scattering appear lighter at a normal viewing angle. In a display, this difference can be quite apparent to a viewer.

When the nonwoven fabric is coated with a resin, the resin fills space between the fibers and the refractive index of the resin is close to matching that of the fibers. The resin coating therefore has the effect of weakening the scattering coming from the fiber by replacing the polymer-to-air interface with a polymer-to-polymer interface. Where there is no fiber, the air pores in the resin of dimensions of about 200 nm up to about 2 μm provide scattering that is not present in an uncoated nonwoven fabric.

The net effect is to match the scattering derived from the fibers and the pores within the fibers (that is, the intra-fiber pores) with the scattering from the pores in the resin-only areas outside the fibers. This matching of scattering is shown, for example, in FIG. 4.

In some embodiments, the diffuser elements of the invention have a clarity of about 50％or less, or about 20％or less. In some embodiments, the diffuser elements of the invention have a transmission of about 50％or greater or about 70％or greater.

The diffuser elements of the invention can be utilized to provide diffusion in light emitting devices such as, for example, as lightboxes, lamps (for example, light emitting diode (LED) lamps) , LCD displays and the like.

Light emitting devices include a light source such as, for example, an LED or a cold cathode fluorescent lamp (CCFL) . Display systems typically include a LCD panel and a light source. The diffuser element of the invention can be disposed between the light source and the LCD panel. The display system can be an edge-lit or a back-lit display system. The display system can also include other commonly used components such as a lightguide, a reflection plate, prims sheets, reflective polarizers and the like. In some embodiments, when a lightguide is present in the display system, the diffuser element can be disposed on the front surface side of the lightguide.

The diffuser elements of the invention can be useful in signage applications. For example, the diffuser element can be used as a printable media in a lightbox for advertising. The diffuser element of the invention can be printed with an ink such as, for example, a solvent, latex or UV ink using methods known in the art.

In some embodiments, the diffuser element of the invention is coated with an additional ink reception coating to provide a printable diffuser element with good ink reception, transmission and diffusion properties. This printable diffuser element is especially useful for low cost high resolution lightbox advertisements using LED backlight sources.

Examples of coatings that are useful for the ink reception coating include those comprising polyacrylates, polyurethane, poly (vinyl acetate) , poly (ethylene-vinyl acetate) , polyvinyl alcohol, polyvinylpyrrolidone, polyamide, polystyrene, poly (styrene-acrylate) , poly (styrene-maleic anhydride) , poly (styrene butadiene) , cellulose, epoxy, amine salt of a carboxylate acrylic resin, polydiallyldimethylammonium chloride and cationic polymers. Preferably, the additional ink reception coating composition is a latex composition comprising water and polyacrylate. The solids concentration of the polyacrylate is typically about 10％to about 60％. In some embodiments, the resin droplets dispersed in the water have a diameter of about 1 μm or less.

Any useful coating technology can be used to apply the coating composition to the diffuser element. For example, coating techniques such as wire-wound metering rod, gravure, reverse roll coating, dip coating and the like may be utilized. In some embodiments, wire-wound metering rod coating, also called Meyer bar coating, is a preferred coating technique. After coating, the diffuser element is dried.

EXAMPLES

Objects and 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 unduly limit this invention.

Coating solutions

Example 1. Films were made according to the following procedure starting with a spunbond nonwoven material (TP-60 from Shandong Taipeng Nonwoven Company, Tai’ an, Shandong, China) . Samples of the nonwoven of dimensions approximately 8.3 by 11.7 inches were coated at constant speed using each of the coating solutions identified in Table 1 using a 10 micron Meyer bar. The samples were left at room temperature for 10 to 15 seconds, and then were placed into an oven for 60 seconds at 80 degrees C to dry.

One sample was left uncoated as a control.

Fiber hiding for each sample was assessed by a human observer and scored on a 1 to 5 scale, with 5 representing the best fiber hiding and 1 the worst. To determine the score, samples were placed on a light box to examine contrast (observing dense or sparse areas) , visibility of fibers, and uniformity of appearance. Fiber diameter was a critical factor for fiber visibility； typically, samples with small fiber diameters had better fiber visibility performance. A score of 1 meant that the sample had a very non-uniform appearance, with some portions appearing very dense and others very sparse. Thicknesses of dense and sparse areas appeared to be very different. Samples scoring 1 had large diameter fibers and were easily seen by the naked eye. Samples scoring 2 were more uniform, but had visible contrast between light and dark areas although less that samples scoring 1. Samples scoring 2 had visible fiber as well but less that samples scoring a 1. Samples scoring 3 were more uniform. Fibers were still weakly visible, but the variation between light and dark areas was lower than samples scoring 2. Samples scoring 4 were very uniform with little variation in contrast. Fibers were barely visible on the light box. Samples scoring 5 were very uniform, showed very little contrast and were comparable in uniformity to a good bead-coated diffuser film. Fiber diameters in samples scoring 4 or 5 were typically less than 10 microns.

Coating weight (as a percentage) was computed assuming that all pores in the nonwoven were filled by the latex solution. So, for each sample coating weight was calculated as the weight of the coated resin divided by the sum of the weight of the coated resin and the weight of the fiber.

Transmission, haze and clarity were also measured for each coated sample using a HazeGard Plus haze meter (available from BYK Gardiner, Silver Springs MD) . Transmission was also measured for each sample before coating.

Effective transmission (ET) was measured for each coated sample using a SpectraScan PR-650 SpectraColorimeter^TM (from PhotoResearch Inc., Chatsworth CA) using the procedure described, for example, in US 8, 657, 472 (Aronson et al. ) .

Table 1 records the following information on the samples: resin type and identifier, glass transition temperature (T_g in degrees C, measured by DSC (TA Discovery) or reported by manufacturer) and index of refraction for the resin, fiber hiding, transmission (before coating, then after coating) , haze, clarity and effective transmission (ET) .

Table 1

Example 2. Films were made according to the following procedure starting with a wetlaid nonwoven material (Hirosen 40 from Hirose Paper Manufacturing Co, Kochi Japan) . Samples of the nonwoven of dimensions approximately 8.3 by 11.7 inches were coated at constant speed with each of the coating solutions of Table 2 using a 10 micron Meyer bar. The samples were left at room temperature for 10 to 15 seconds, and then placed into an oven for 60 seconds at 80 degrees C to dry.

One sample was left uncoated as a control.

Fiber hiding and coating weight were determined as described in Example 1.

Transmission, haze, clarity, and effective transmission (ET) for each coated sample were also measured as described in Example 1. Transmission was also measured before coating.

Haze was also measured using an Eldim EZ Contrast 160D instrument (available from Eldim, Hérouville Saint Clair, France) because this instrument was believed to be more accurate for measurements of very high haze materials. The Eldim measurements were carried out as follows: Light from a standard D65 light source was sent through a relay lens to collimate the light, and then through a 6 mm test spot on the nonwoven sample adjacent to the Eldim instrument. Haze was then computed as the sum of the luminance (in candela per square meter) at the Eldim sensor outside a 3 degree cone in azimuth and polar angles divided by the sum of the luminance from all polar and azimuthal angles from 0 to 90 degrees. The test standard is ASTM D1003-13.

Table 2 records the following information on the samples: resin type and identifier, glass transition temperature (T_g in degrees C, measured by DSC (TA Discovery) or reported by manufacturer) and index of refraction for the resin, fiber hiding, transmission (before coating, then after coating) , haze, clarity and effective transmission.

Table 2

Example 3. Films were made according to the following procedure starting with a second wetlaid nonwoven material of higher coating weight (Asahi WS7A05-6 from Asahi Kasei Fibers, Tokyo, Japan) . Samples of the nonwoven of dimensions approximately 8.3 by 11.7 inches were coated at constant speed with NeoCryl A-1092 polyacrylate-styrene latex using a 10 micron Meyer bar. The samples were left at room temperature for 10 to 15 seconds, and then placed into an oven for 60 seconds at 80 degrees C to dry.

One sample was left uncoated as a control.

Fiber hiding and coating weight were determined as described in Example 1.

Transmission, haze, clarity, and effective transmission (ET) for each coated sample were also measured as described in Example 1. Transmission was also measured before coating. Haze was also measured using an Eldim EZ Contrast 160D instrument as in Example 2.

Table 3 records the following information on the samples: resin type and identifier, glass transition temperature (T_g in degrees C, measured by DSC (TA Discovery) ) and index of refraction for the resin, fiber hiding, transmission (before coating, then after coating) , haze, clarity and effective transmission (ET) .

Table 3

Example 4. Films were made according to the following procedure starting with a wetlaid nonwoven material (Hirosen 40 from Hirose Paper Manufacturing Co, Kochi Japan) to study the relationship between coating weight and fiber hiding/diffusion. Samples of the nonwoven of dimensions approximately 8.3 by 11.7 inches were coated with Acronyl 7015G at constant speed with a 10 micron Meyer bar. Eight different solid concentrations for the resins were used to achieve a range of coating weights. The samples were left at room temperature for 10 to 15 seconds, and then placed into an oven for 60 seconds at 80 degrees C to dry. One sample was left uncoated as a control.

Resin filling rate was computed as the ratio of the volume of the resin to the volume of the original free space (the pores) in the nonwoven. Using the assumption that the coating solution can occupy all the free space in the nonwoven without any residue on the web surface, then after drying, the filling rate should be equal to the volume concentration of the coating solution. So the filling rate (as a percentage) was computed as the weight concentration of the solution times the density of the solution divided by the density of the resin.

Fiber hiding and coating weight were determined as described in Example 1.

Transmission, haze, clarity, and effective transmission (ET) for each coated sample were also measured as described in Example 1. Haze was also measured using an Eldim EZ Contrast 160D instrument as in Example 2.

Table 4 records information on the samples. : Filling rate (as a percentage) was computed as described above. Haze (via Eldim measurement) , coating weight (as a percentage) , transmission, haze, clarity, effective transmission (ET) and fiber hiding were all determined as in Example 1.

Table 4

Example 5. Films were made as in Example 1 except that the nonwovens used were selected from Table 5 below. (The Asahi WS7A05-6 nonwoven is available from Asahi Kasei Fibers, Tokyo Japan； Hirose nonwovens are available from Hirose Paper Manufacturing Co, Kochi Japan； the MPM nonwoven is available from Monadnock Non-Wovens. Mount Pocono PA； TP nonwovens are available from Shandong Taipeng Nonwoven Company, Tai’ an, Shandong, China； and the Freudenberg nonwoven is available from Freudenberg Spunweb Co, Los Angeles CA. )

Besides the resin and coating weight used for each sample, Table 5 also shows basis weight before and after coating (in grams per square meter) , porosity of the nonwoven before and after coating, and the thickness of the nonwoven.

Percent porosity was determined using 10 cm by 10 cm samples. First, percent solidity for the uncoated nonwoven sample was computed as the weight of the sample divided by the product of the volume of the sample and the density of the nonwoven fiber. (Volume of the sample was computed as 100 cm² times the thickness of the sample. ) Percent porosity of the uncoated nonwoven was then computed as

1-percent solidity for uncoated nonwoven.

Percent solidity of the resin was determined by the following procedure. A 10 cm by 10 cm coated nonwoven sample was weighed and its thickness was measured. It was then placed into a dichloromethane solvent, soaked for 3 days to dissolve the resin, dried for 60 seconds in an oven at 80 degrees C, and dried for two more days at 25 degrees C. Its weight was measured again. Weight of the resin in the original sample was computed as the difference between the weight of the coated sample and the weight of the dried sample. Percent solidity of the resin was computed as the weight of the resin divided by the product of the volume of the coated nonwoven sample and the density of the resin.

Finally, percent porosity of the coated nonwoven was computed as

1– (percent solidity for uncoated nonwoven) – (percent solidity of resin) .

Table 5

Example 6. Using selected areas from three samples of the film made in Example 2-B, pores inside the nonwoven fiber were examined and counted. The nonwoven fibers made of PET were about 7 microns in diameter and had a refractive index of 1.58. Using an index matching fluid to wet out the outer fiber surfaces and an optical microscope at 100X magnification, counts were made of the number of pores in a length of the fiber. Fiber porosity was also determined. The results are reported in Table 6. The average number of pores per 40 micron fiber length was 112.3, the average fiber porosity was 0.48％, and the overall number of pores in 1500 cubic micrometers was 0.073 per cubic micron.

Pores in the coated resin were also counted using several SEM images taken at 15, 000 to 50,000X magnification. The average number of pores with a size greater than 2 microns in at least one dimension was about 30. The average number of pores with all dimensions less than 200 nanometers was about 100 per cubic micron.

Table 6

Example7. Using additional SEM images from the samples made in Example 2-B, counts were made of pores with diameters in the size ranges 200-400 nanometers, 400-800 nanometers, 800 nanometers to 1.4 microns, and 1.4 microns to 2 microns. The area within the SEMs where the counts were taken was measured as well as the portion of that area that included only resin. Then the number density (number of pores per cubic micron) was computed based on the thickness times the area, wherein the thickness was the average of the pore size for each category –for example, 300 nm thickness for pores in the 200-400 nm range, 600 nm thickness for the 400-800 nm range. Values for each of these are reported in Table 7A. Also reported are sums of the number density across pore sizes, and averages over the five SEM images.

For the same five SEM images, Table 7B shows the volume percentage of resin occupied by all pores and the volume percentage of resin occupied by pores of size 400 to 800 nanometers.

Table 7A

Table 7B

Example 8. Scattering of visible light by pores smaller than 2 microns was modeled via software (using Mieplot from www. philliplaven. com/mieplot. htm) . The software computed the scattered power (in Watts per square meter) from an ensemble of pores such as were characterized in Example 7 and quantified in Tables 7A and 7B. FIG. 1 shows scattering power per square meter as a function of angle for four categories of pore sizes: 200-400 nm, 400-800 nm, 800-1400 nm, and 1400-2000 nm.

FIG. 2 shows scattering power per square meter as a function of angle computed by the model for two classes of pores. The first class consisted of pores from the combination of 200-400 nm 400-800 nm pores in the fiber-free resin area. The second class consisted of pores inside the fibers.

FIG. 3 shows modeling results of scattering power per square meter using a geometric optics model of scattering from nonwoven fibers. The fibers were modeled as cylinders (with diameter 7 microns) immersed in a medium whose refractive index differs from that of the fiber by 0.1

FIG. 4 shows combined results for scattering power per square meter as a function of angle for two components. One component included fiber surface scattering and pores inside the fiber. The second included pores of sizes in the range from 200 nm to 2000 nm in the coated resin.

Example 9. In this and the following examples the resins of Table 8 were used. (Estane is available from Lubrizol Advanced Materials, Cleveland OH. All the other material sources were previously identified. ) One layer of Acronyl 504ap was coated on an 11 inch by 14 inch sheet of 85 gpm wetlaid PET nonwoven (PMY-85 from Mitsubishi Paper Mills, Tokyo Japan) . The sample was coated as before using a 10 micron Meyer bar operating at a constant speed. After sitting at room temperature for 10–15 seconds, the sample was placed into an oven at 80 degrees C for 1–2 minutes to dry. Transmission, clarity and fiber hiding were determined as before, and haze was measured using the Eldim technique previously described. Efficiency was determined as follows: Luminous flux was measured both with and without the coated nonwoven on a panel light source. Efficiency was computed as the ratio of the first to the second. (The light output of the panel was measured using an integrated sphere (Illumia Pro 500-050 from Pro-Lite Technology, North Sutton NH) . The sample test size was about 8 inches square； the panel light source was placed at the center of the integrating sphere. )

An image was printed on the sample using the following technique: A wide format inkjet printer with 8 pass/1200dpi without any ICC profile was used to print images selected from those in FIG. 5. Temperature was adjusted to match the printer setting. Print quality was evaluated with the following criteria:

·In the needlework photo, whether three different color can be obviously distinguished.

·In the photo of the woman, if human skin color and details were well represented.

·In the photo showing money, the coins showed details especially on light and dark sides.

·In the watch photo, small numerals could be seen clearly.

·In the gray area, there were no visible wave-like variations.

·In the color bar, different colors did not show any ink mixing.

·With CMYK and RGBK (Cyan-Magenta-Yellow-Black and Red-Yellow-Green-Black) , single channel color printing quality was confirmed without any issue.

According to these standards, the printing quality was rated on a 1-5 scale. A value of 5 meant the sample met all the standards. A value of 1 was the worst and indicated with unclear images.

All measured values are shown in Table 9.

Example 10. A sample was made as in Example 9, except that the resin used was Acronyl 7015G polyacrylate latex. Transmission, clarity, efficiency, haze, printing quality and fiber hiding were determined as in Example 9 and are shown in Table 9.

Example 11. A sample was made as in Example 9, except that the resin used was Estane 5715 in MEK solvent. Transmission, clarity, efficiency, haze, printing quality and fiber hiding were determined as in Example 9 and are shown in Table 9.

Example 12. A sample of the nonwoven of Example 9 was first coated with Acronyl 7015G polyacrylate latex as in that prior example. Then a second layer was coated on top of the first layer using the Acronyl 504 a poly (styrene-acrylate) latex and Meyer bar coating as before. The coated sample was dried as in Example 9. Transmission, clarity, efficiency, haze, printing quality and fiber hiding were determined as in Example 9 and are shown in Table 9.

Example 13. A sample was prepared as in Example 12 with Estane 5715 as the first layer and Acronyl 504 ap as the second layer. Transmission, clarity, efficiency, haze, printing quality and fiber hiding were determined as in Example 9 and are shown in Table 9.

Comparative 1. Performance parameters were measured for an uncoated 3M diffuser film 3735-50 (available from 3M Company, St. Paul MN) and are shown in Table 9.

Comparative 2. Performance parameters were measured for the uncoated nonwoven sample. These are shown in Table 9.

Example 14. An 11 inch by 14 inch sample of a 60 gsm spunbond nonwoven from Shandong Taipeng was coated with Acronyl 7015G resin as in Example 9, then dried as before. Haze was measured before and after coating. Printing quality and fiber hiding were assessed as before. Results are shown in Table 10.

Example 15. A sample of same nonwoven as in Example 14 was first coated with Acronyl 7015G, and then a layer of Acronyl 504 ap was coated on top of the first layer. The sample was dried and characterized as in Example 14. Results are shown in Table 10.

Example 16. A sample of the nonwoven of Example 14 was coated with Neocryl A-1092 as before, then dried and characterized as in Example 14. Results are shown in Table 10.

Example 17. A sample of the nonwoven of Example 14 was coated first with Neocryl A-1092 and then a layer of Acronyl 504 ap was coated on top of it. The sample was dried and characterized as in Example 14. Results are shown in Table 10.

Example 18. A sample of the nonwoven of Example 14 was coated first with Acronyl 7015G and then a layer of Acronyl 728 was coated on top of it. The sample was dried as in Example 14. Printing quality and fiber hiding were assessed and is shown in Table 10.

Example 19. A sample of the nonwoven of Example 14 was coated first with Acronyl 7015G and then a layer consisting of 1.3 to 1 blend (by weight) of Acronyl 728 and Styronal 7423 ap was coated on top of it. The sample was dried as in Example 14. Printing quality and fiber hiding were assessed and is shown in Table 10.

Example 20. A sample of the nonwoven of Example 14 was coated first with Acronyl 7015G and then a layer consisting of 1.4 to 1 blend (by weight) of Acronyl 728 and Joncryl 8383 was coated on top of it. The sample was dried as in Example 14. Printing quality and fiber hiding were assessed and is shown in Table 10.

Comparative 3. An uncoated ample of the nonwoven of Example 14 was characterized for printing quality and fiber hiding. The results are shown in Table 10.

Table 8

Table 9

Table 10

The complete disclosures of the publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention 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 the invention intended to be limited only by the claims set forth herein as follows.

Claims

A diffuser element comprising:

(a) a nonwoven fabric comprising fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5； and

(b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric, the resin having a T_g of about-10 to about 100℃ and the resin pores having a size of about 200 nm to about 2 μm in at least one dimension；

wherein the diffuser element is from about 30 to about 150 μm thick and has a basis weight of about 30 to about 190 g/m²； and

the coating weight of the resin is from about 15％ to about 50％ of the total weight of the diffuser element.
The diffuser element of claim 1 wherein the nonwoven fabric comprises polymeric fibers.
The diffuser element of claim 1 or 2 wherein the resin coating comprises polyethylene-vinyl acetate, polyacrylate, poly (acrylate-styrene) , polyurethane, polystyrene butadiene, polyethylene or combinations thereof.
The diffuser element of claim 3 wherein the resin coating comprises polyacrylate or poly (acrylate-styrene) .
The diffuser element of any of the above claims wherein the diffuser element has a porosity of about 30％ to about 55％.
The diffuser element of any of the above claims wherein the basis weight of the nonwoven fabric is about 10 to about 120 g/m².
The diffuser element of claim 6 wherein the basis weight of the nonwoven fabric is about 70 to about 100 g/m².
The diffuser element of any of the above claim wherein the resin has a T_g of about 0 to about 30℃
The diffuser element of any of the above claims wherein the diffuser element has a clarity of about 50％ or less.
The diffuser element of claim 9 wherein the diffuser element has a clarity of about 20％ or less.
The diffuser element of any of the above claims wherein the diffuser element has a transmission of about 50％ or greater.
The diffuser element of any of the above claims comprising inter-fiber pores having a size of about 2000 nm or greater in at least one dimension.
The diffuser element of claim 12 wherein the density of the inter-fiber pores is about 10,000 per mm³ or greater.
The diffuser element of any of the above claims wherein the resin coating further comprises nanopores having a size of less than 200 nm in all dimensions.
The diffuser element of claim 14 wherein the density of the nanopores is about 100 per μm³ or greater.
The diffuser element of any of the above claims wherein the nonwoven fabric comprises fibers having intra-fiber pores, wherein the mean diameter of the intra-fiber pores is about 200 nm to about 2 μm.
The diffuser element of claim 16 wherein the resin pores have a diameter within about 30％ of the mean diameter of the intra-fiber pores and wherein the density of the resin pores is within about 1000％ of the density of the intra-fiber pores.
The diffuser element of claim 17 wherein the density of the resin pores is within about 500％ of the density of the intra-fiber pores.
A diffuser element comprising:

(a) a nonwoven fabric comprising porous fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5, the intra-fiber pores having a mean diameter of about 200 nm to about 2 μm, wherein the total volume of the intra-fiber pores is X percent of the total volume of the fibers； and

(b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric, the resin pores having a diameter of about 200 nm to about 2 μm, wherein the total volume of the resin pores is Y percent of the total volume of the resin coating； wherein

X is within about 1000％ of Y,

X is about 10％ or less, and

Y is about 10％ of less.
The diffuser element of claim 19 wherein the coating weight of the resin is from about 15％ to about 50％ of the total weight of the diffuser element.
The diffuser element of claim 19 or 20 wherein the diffuser element is from about 30 to about 150 μm thick.
The diffuser element of any of claims 19–21 wherein the resin has a T_g of about 0 to about 30℃
A diffuser element comprising:

(a) a nonwoven fabric comprising porous fibers having a diameter of less than about 50 μm and a fiber aspect ratio of length/diameter of greater than about 5, the intra-fiber pores having a mean diameter of about 200 nm to about 2 μm, wherein the total volume of the intra-fiber pores is X percent of the total volume of the fibers； and

(b) a porous resin coating on the surfaces of the fibers of the nonwoven fabric, the resin pores having a diameter within about 30％ of the mean diameter of the intra-fiber pores, wherein the total volume of the resin pores is Y percent of the total volume of the resin coating； wherein

X is within about 1000％ of Y,

X is about 5％ or less, and

Y is about 5％ of less.
The diffuser element of claim 23 wherein the coating weight of the resin is from about 15％ to about 50％ of the total weight of the diffuser element.
The diffuser element of claim 23 or 24 wherein the diffuser element is from about 30 to about 150 μm thick.
The diffuser element of any of claims 23–25 wherein the resin has a T_g of about 0 to about 30℃.
The diffuser element of any of the above claims further comprising an ink receptive layer.
The diffuser element of claim 27 wherein the ink receptive layer comprises polyacrylate.
The diffuser element of any of the above claims further comprising ink printed on the diffuser element.
A display comprising:

(a) a liquid crystal display panel；

(b) a light source that emits light； and

(c) the diffuser of any of the above claims optically between the light source and the liquid crystal display panel.
The display of claim 30 further comprising a light guide that guides light from the light source and emits the light toward the diffuser element.
A light emitting device comprising:

(a) a light source that emits light； and

(b) the diffuser element of any of claims 1–29.