Patent ID: 12256629

DETAILED DESCRIPTION

For a better understanding, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings.

References to the color of the phosphor and LED die refer generally to its emission color unless otherwise specified. Thus, a blue LED die emits a blue light, a yellow phosphor emits a yellow light and so on.

In accordance with an object of the present invention, there is provided a method for preparing a wavelength converting film, the method comprising mixing at least one phosphor, a polysiloxane and optionally an organic solvent, thereby preparing a mixture, placing the mixture on a substrate, pre-curing the mixture on the substrate, thereby preparing a wavelength converting film.

A wavelength converting film according to the present disclosure is a film that converts light of a certain first wavelength to light of a certain second wavelength.

According to the method of the present invention, at least one phosphor, a polysiloxane and optionally an organic solvent is mixed.

A phosphor is a material that converts light of a certain first wavelength to light of a certain second wavelength.

The phosphor may be selected from common phosphors. In an embodiment, the phosphor is selected from the group consisting of garnets, nitridosilicates, oxynitridosilicates, alumonitridosilicates, alumooxynitridosilicates, oxysilicates, perovskites, silicates and combinations thereof.

Exemplary phosphors may be selected from the following list of phosphors:(RE1−xEUx)3(Al1−yA′y)5O12where RE is at least one of Y, Lu, Tb, and Gd, x is in a range 0<x≤0.1, A′ is at least one of Sc and Ga, and y is in a range 0≤y≤1);(RE1−xCex)3(Al5-2yMgySiy)O12where RE is at least one of Y, Lu, Tb, and Gd, x is in a range 0<x≤0.1, and y is in a range 0≤y≤2;(RE1−xCex)3Al5-ySiyO12-yNywhere RE is at least one of Y, Lu, Tb, and Gd, x is in a range 0<x≤0.1, and y is in a range 0≤y≤0.5;(RE1−xCex)2CaMg2Si3O12:Ce3+where RE is at least one of Y, Lu, Tb, and Gd, and x is in a range 0<y≤0.1,(AE1−xEUx)2Si5N8where AE is at least one of Ca, Sr, and Ba, and x is in a range 0<x≤0.1;(AE1−xEUx)AlSiN3where AE is at least one of Ca, Sr, and Ba, an x is in a range 0<x≤0.1;(Sr1−xEUx)LiAl3N4where x is in a range 0<x≤0.1;(AE1−xEUx)3Ga3N5where AE is at least one of Ca, Sr, and Ba, and x is in a range 0<x≤0.1;(AE1−xEUx)Si2O2N2where AE is at least one of Ca, Sr, and Ba, and x is in a range 0<x≤0.1;(AExEUy)Si12−2x−3yAl2x+3yOyN16−ywhere AE is at least one of Ca, Sr, and Ba, x is in a range 0.2≤x≤2.2, and y is in a range 0<y≤0.1;(AE1−xEUx)2SiO4where AE is at least one of Ca, Sr, and Ba, and x is in a range 0<x≤0.1; and(AE1−xEUx)3SiO5where AE is at least one of Ca, Sr, and Ba, and x is in a range 0<x≤0.1.

The exemplary phosphors might also incorporate fluoride, chloride, bromide or iodide ions.

The at least one phosphor might be one type of phosphor, or might be a mixture of phosphors. The phosphor, or the mixture of phosphors might be selected to obtain a specific desired second wavelength, when used in a wavelength converter that converts light of a certain first wavelength to light of a certain second wavelength.

The phosphor might be present in an amount of between about 1 wt. % to about 80 wt. %, preferably from about 5 wt. % to about 65 wt. %, more preferably from about 25 to about 65 wt. %, based on the total weight of the mixture comprising the at least one phosphor, the polysiloxane and optionally the organic solvent.

The mixture comprises further a polysiloxane. A polysiloxane is a polymer with —Si(R)2O— units, wherein R is an organic residue, preferably an alkyl, aryl, or cycloalkyl residue. The polysiloxane might be a polysiloxane of a specific formula, e.g., of formula (I) or might be a mixture of different polysiloxanes, e.g., different polysiloxanes of formula (I).

In an embodiment, the polysiloxane is a polysiloxane of formula (I):

whereinn:m=1:1 to 10:1;A1, A2, A3are independently selected from the group consisting of C1-C6alkyl, C6-C12aryl, and C3-C12cycloalkyl.

The ratio of indices “n” and “m” might be selected from 1:1 to 10:1, preferably from 3:1 to 8:1, more preferably from 4:1 to 6:1.

The residues A1, A2and A3in formula (I) might be the same, or might be different. The residues A1, A2and A3might independently be selected from C1-C6alkyl, C6-C12aryl, and C3-C12cycloalkyl. Exemplary C1-C6alkyls are methyl, ethyl, propyl, butyl, pentyl and hexyl, wherein methyl and ethyl are preferred. Exemplary C6-C12aryl are phenyl, benzyl and naphthyl, wherein phenyl is preferred. Exemplary C3-C12cycloalkyl are cyclopropyl, cyclobutyl, cyclopentyl and cycylohexyl, wherein cyclohexyl is preferred.

In an embodiment, A1, A2, A3are methyl. In a further embodiment, A1, A2, A3are phenyl. In a further embodiment, A1and A2are methyl and A3is phenyl.

The total fraction of phenyl groups among the side groups A1, A2and A3in the formula (I) is from about 10% to 100%, preferably from about 25% to 80%, more preferably from 25% to 50% with respect to the total number of the side groups of A1, A2and A3in the formula (I).

The polysiloxane might be present in an amount of between about 1 wt. % to about 80 wt. %, preferably from about 5 wt. % to about 65 wt. %, more preferably from about 25 to about 65 wt. %, based on the total weight of the mixture comprising the at least one phosphor, the polysiloxane and optionally the organic solvent.

The mixture might further comprise an organic solvent. The organic solvent may be added to the mixture to modify viscosity. The organic solvent is selected to dissolve the polysiloxane, without destroying the polysiloxane. Exemplary organic solvents are aliphatic hydrocarbons (e.g., hexane, heptane, octane), aromatic hydrocarbons (e.g., toluene, xylene), chlorinated hydrocarbons (e.g., methylene chloride, chloroform, chlorobenzene, chlorocyclohexane), esters (e.g., ethyl acetate, butyl acetate, propyl propionate, butoxyethyl acetate, propylene glycol methyl ether acetate), ketones (e.g., acetone, methylethyl ketone, methyl ethyl ketone, methyl isobutyl ketone), and ethers (e.g., dibutyl ether, tetrahydrofurane, diphenyl ether, anisole). Preferred organic solvents are toluene, xylene, acetone, heptane, and butyl acetate, more preferred are toluene and butyl acetate.

The solvent may be added in an amount of between about 1 wt. % to about 30 wt. %, preferably in an amount of between about 1 wt. % to about 10 wt. %, with respect to the total amount of the mixture.

The mixture may be homogenized with a mixing equipment. The mixing is preferably carried out with a high speed stirrer, high shear mixer, planetary centrifugal mixer, 3-roll mill, ball mill grinder, or a combination thereof.

The mixture is placed on a substrate. The substrate is intended to hold the wavelength converting film before application e.g., to the surface of a LED die. The wavelength converting film might remain on the substrate until it is transferred, e.g. to a LED die. Alternatively, the wavelength converting film is released from the substrate when it is sufficiently dried to handle.

In an embodiment, the substrate is selected from a plastic film, or a glass.

A plastic film is a layer of an organic polymer with a thickness of between about 0.01 mm to about 5 mm, preferably of between about 0.01 mm to about 1 mm, more preferably of between about 0.05 mm to about 0.2 mm. The organic polymer might be polypropylene, polyethylene, polyvinylchloride, polyester (e.g., polyethylene terephthalate), or fluoropoplymer (e.g., polyfluoroalkoxy alkane, polyvinylidene fluoride). The plastic film might optionally be coated, e.g., the plastic film might be coated with an organosilane, silicone, or a fluorocarbon type coating layer.

The substrate might also be glass, such as borosilicate glass. The glass might have a thickness of between about 0.01 mm to about 5 mm, preferably of between about 0.01 mm to about 1 mm, more preferably of between about 0.01 mm to about 0.2 mm.

The mixture might be placed on the substrate with extrusion, tape casting, spray coating, doctor blade coating, roller coating, and screen printing.

The mixture may be solidified over time either due to evaporation of the solvent, or by condensation of a portion of the silanol groups, or by the combination of both. This might be interpreted as pre-curing.

The solidifying mechanism provided by cross-linking of the individual polymer chains of the polysiloxane via condensation of silanol groups might eliminate the need of common catalysts, e.g., platinum catalyst as in hydrosilylation and the need for moisture as in other condensation chemistries typically employed in curing of silicones. Platinum catalysts are often linked to yellowing of silicones at higher temperatures, which is undesirable in optical grade materials. Moreover, the CH2—CH2cross-linking sites produced by hydrosilylation are the weak points in the thermal decomposition of cured silicones. A further condensation method is the moisture-induced condensation, wherein during curing the access of moisture to the material is important. However, the diffusion of moisture to the LED die wavelength converting film interface is in the preset case hindered by the thickness of the film, thus making this type of cure ineffective for ensuring good adhesion between the said film and the LED die. The silanol condensation cure, by not requiring moisture or Pt catalyst as well as by creating a thermally stable Si-O-Si bond, is free of the above-mentioned deficiencies.

According to the method of the present invention, the mixture on the substrate is pre-cured. Pre-cured according to the present invention might be understand, that the mixture is converted from a liquid state into a thermoplastic state. Pre-curing is preferably carried out at temperatures of between about 30° C. to about 150° C., preferably from about 50° C. to about 130° C., more preferably from about 70° C. to about 120° C. Pre-curing is carried out for about 3 hours to about 72 hours, preferably for about 5 hours to about 20 hours, more preferably for about 10 hours to about 15 hours.

In an embodiment, the pre-curing is carried out at 50° C. to about 130° C. for about 5 hours to about 20 hours. In an alternative embodiment, the pre-curing is carried out at 70° C. to about 120° C. for about 10 hours to about 15 hours.

The pre-curing might be carried out under an inert atmosphere, e.g., under a nitrogen atmosphere, or an argon atmosphere. Alternatively, the pre-curing might be carried out under vacuum.

In an embodiment of the present invention, the method further comprises the step of removing the substrate. The substrate is preferably removed when the substrate is plastic film. The substrate might be removed mechanically by peeling.

In an embodiment of the present invention, the method further comprises the step of adding a catalyst and/or a filler material. A catalyst might be added to accelerate the pre-curing and thus the reaction of the condensation of the silanol groups of the polysiloxane to obtain a thermoplastic state. As a catalyst any catalyst that accelerates the reaction of silanol groups. Typical catalysts may be inorganic metal catalysts, or organic catalysts. The inorganic metal catalyst may be selected from tin compounds, aluminum compounds, and titanium compounds. Exemplary catalysts may be titanium alkoxides (such as titanium butoxide, titanium isopropoxide), aluminum alkoxides (such as aluminum s-butoxide bis(ethylacetoacetate)), and organic salts of tin (such as bis(2-ethylhexanoate)tin, dibutyltin dilaurate). The catalyst may also be an organic catalyst. Organic catalysts may be organic bases (such as amines, pyridines, guanidines), or combination thereof. The catalyst may also be a combination of said inorganic metal catalysts and said organic catalysts. The catalyst may be added in an amount of between about 0.1 wt. % to about 3 wt. %, preferably from about 0.2 wt. % to about 1 wt. %, more preferably from about 0.5 wt. % to about 1 wt. %, with respect to the amount of the polysiloxane.

A filler material might also be added in the method of the present invention. The filler material might be added in addition to the catalyst, or alternatively to the catalyst. A filler material might be a material that modifies light scattering, modifies rheological properties, increases the refractive index or thermal conductivity, etc. The filler may be selected from inorganic compounds, such as oxides, or dioxides. Typical fillers are titanium dioxide, silicon dioxide, zirconium dioxide, aluminum oxide, cerium oxide, zinc oxide, etc., or combinations thereof. The filler may be added in an amount of between about 1 wt. % to about 65 wt. %, preferably from about 5 wt. % to about 65 wt. %, more preferably from about 25 wt. % to about 65 wt. %, with respect to the mixture.

The present invention is further directed to a wavelength converting film prepared by a method according to the present invention.

The present invention is also directed to a method for preparing a light-emitting device, the method comprising the steps of providing a LED die, placing a wavelength converter film according to the present invention on the LED die, optionally removing the substrate, curing the wavelength converter film, thereby preparing a light-emitting device, wherein the wavelength converter film is placed with the side opposite the substrate on the LED die.

A LED die is an object that emits light of a certain first wavelength, e.g., blue light.

According to the method for preparing a light-emitting device of the present invention a wavelength converter film according to the present invention is placed on the LED die. As disclosed herein the wavelength converter film is prepared by a method comprising mixing at least one phosphor, a polysiloxane and optionally an organic solvent, thereby preparing a mixture, placing the mixture on a substrate, pre-curing the mixture on the substrate, thereby preparing a wavelength converting film.

The at least one phosphor, the polysiloxane, the organic solvent, the substrate and the pre-curing correspond to the respective features as described herein.

The wavelength converting film by itself has pressure sensitive adhesive properties, thus eliminating the need for an additional adhesive layer between the wavelength converting film and the LED die. In some embodiments, the wavelength converting film shows adhesive properties at room temperature. In alternative embodiments, the wavelength converting film shows adhesive properties at temperatures higher than room temperature, preferably at temperatures higher than 30° C.

According to the method for preparing a light-emitting device of the present invention, the substrate is optionally removed. Removing the substrate is preferably carried out when the substrate is glass.

In a further step of the method for preparing a light-emitting device of the present invention, is curing the wavelength converter film. In an embodiment of the present invention, the curing is carried out at a temperature of between about 100° C. to about 200° C. The curing may be carried out at a temperature of between about 120° C. to about 180° C., preferably at a temperature of between about 140° C. to about 160° C. The curing might be for about 2 hours to about 20 hours, preferably for about 8 hours to about 16 hours, more preferably for about 10 hours to about 12 hours.

In an embodiment, the curing is at a temperature of between about 100° C. to about 200° C. for about 5 hours to about 20 hours. In an alternative embodiment, the curing is at a temperature of between about 120° C. to about 180° C. for about 8 hours to about 12 hours.

The curing might be carried out under an inert atmosphere, e.g., under a nitrogen atmosphere, or an argon atmosphere.

In an embodiment of the present invention, the method for preparing a light-emitting device of the present invention further comprises the step of dicing the light-emitting device. Suitable dicing methods are those applied for semiconductor dicing. The dicing might be carried out by saw dicing, or laser dicing. The dicing might also be understood as a singulation of individual light emitting devices.

In one embodiment of the invention the wavelength converting film comprising the substrate is positioned over the array of LED dies mounted on a solid support plate, or over the wafer of LED dies, followed by pressing the wavelength converting film to the surface of the dies thus providing the direct contact between the surface of the said dies and the said wavelength converting film. The pressing may be performed by passing the assembly through a pair of rolls or by lowering a flat plate on the top of the assembly, or by vacuum lamination, or by any other suitable method. The support sheet may then be released followed by curing the wavelength converting film on the top of the LED dies by explosion to elevated temperature. The cured assembly is separated into individual LED elements each containing the layer of the wavelength converting film on the top of the individual LED die.

In another embodiment of the invention the wavelength converting film is removed from the substrate and positioned on the top of the array of LED dies or on the entire wafer of LED dies. The resulting assembly may be exposed to an elevated temperature to cure the wavelength converting film. The cured assembly may be separated into individual elements each containing the layer of the wavelength converting film on the top of the individual LED die.

The present invention is further directed to a light-emitting device prepared by a method of the present invention.

A light-emitting device of the present invention might be used in general lighting, stage lighting, infrared lighting, automotive lighting, sensing, displays, etc.

FIG.1shows a method of preparing a wavelength converting film. In a first step A at least one phosphor, a polysiloxane and optionally an organic solvent are mixed, thereby preparing a mixture. In a further step B, the mixture is applied on a substrate. In a further step C, the mixture on the substrate is pre-cured, thereby preparing a wavelength converter film.

FIG.2shows a wavelength converting film100. The mixture103is on a substrate101. The mixture103was prepared by mixing 4.150 g of polysiloxane+3% silica (24.47 wt. %), 12.460 g phosphor (73.47 wt. %) and 0.350 g propyl propionate (2.06 wt. %).

FIG.3shows a method for preparing a light-emitting device. In a first step A, a LED die is provided. In a subsequent step B, a wavelength converter film according to the present invention is placed on a LED die. In a further step C, the substrate is optionally removed. In a further step D, the wavelength converter film is cured.

FIG.4shows a light-emitting device200comprising a LED die201, a wavelength converting film without a substrate100′ comprising filler material102. The LED die201might emit blue light and the wavelength converting film without substrate100′ is placed in direct contact with the LED die201. The wavelength converting film without substrate100′ comprises filler material102. The filler material might be titanium dioxide, silicon dioxide, zirconium dioxide, aluminum oxide, cerium oxide, zinc oxide, etc., or combinations thereof., that enhances the light scattering of the blue light emitted from the LED die201.

FIG.5shows a method for preparing a light-emitting device200. In a first step, a mixture103comprising at least one phosphor, a polysiloxane and optionally an organic solvent is applied with doctor blade104on a substrate101. The substrate101might be a polyester film. After keeping the mixture103on the substrate101at room temperature, the temperature is elevated for 12 to 24 hours at 60 to 100° C. for pre-curing the mixture103on the substrate101. After the pre-curing, the mixture is in a thermoplastic state and thus, the wavelength converting film100is prepared. Subsequently, the wavelength converting film100is placed on the LED die201with a roller105. At the same time the, substrate101(e.g., the polyester film) is peeled off. In a final step, curing at a temperature of 150° C. for 4 hours leads to a light-emitting device200comprising a wavelength converting film without a substrate100′ and a LED die201.

In a subsequent annealing step at 200° C. for 4 hours and at 250° C. for 4 hours it was shown that there are neither cracks, nor delamination.

FIG.6shows a further method for preparing a light-emitting device200. In a first step, a mixture103comprising at least one phosphor, a polysiloxane, optionally an organic solvent and optionally a filler material (e.g., Aerosil) is placed with a doctor blade104on a substrate101. The substrate101might be a polyester film. After keeping the mixture103on the substrate101at room temperature, the temperature is elevated for 12 to 24 hours at 50° C. for pre-curing the mixture103on the substrate101. After the pre-curing, the mixture is in a thermoplastic state and thus, the wavelength converting film100is prepared. The substrate101peels off the wavelength converting film100to obtain a wavelength converting film without substrate100′. The wavelength converting film without substrate100′ is optionally cut into pieces. Subsequently, the wavelength converting film without substrate100′ is placed on several LED dies201in a vacuum oven and vacuum is pulled. The temperature is elevated to 50 to 70° C.

The vacuum oven is opened to air and a curing step is carried out at a temperature of 150 for 4 hours to obtain a light-emitting device200with several LED dies201and a wavelength converting film without substrate100′.

EXAMPLES

Example 1

Material Preparation.

The mixture with the following composition was prepared:22.8 wt % of Polymer A with the following general formula:

9.5 wt % of Polymer B of the following general formula:

1.3 wt % of hydrophobically-treated fumed silica,5.7 wt % of xylene,60.7 wt % of YAG:Ce (Y3Al5O12:Ce) phosphor powder.

Polymer A, Polymer B, xylene, and hydrophobically-treated fumed silica were mixed together and homogenized using a 3-roll mill. YAG phosphor was added and distributed using a planetary mixer.

Preparation of the Self-Adhesive Layer.

A catalyst, titanium butoxide in the amount of 0.3 wt % of the mixture, was added and mixed in with a planetary mixer. The mixture with catalyst was poured into the tape casting box having a gap with the width of 100 cm and the height of 0.1 mm. The material was dispensed on a non-sticky plastic film in a form of a coating by moving the tape casting box along the film. The material was allowed to dry at room temperature for 72 hours followed by pre-curing in the oven at 60° C. for another 72 hours. The resulting coating was a sticky solid,

Application of the Material.

The plastic film with the coating was cut into 100×100 mm segments. Each segment was placed on a glass sheet as imitation of a LED die with the coating side contacting the glass. Here, glass sheet was used as an imitation of the LED die. The coating was allowed to adhere to the glass by rolling with the rubber-coated roller, the plastic film was removed, leaving the phosphor-filled polysiloxane layer directly on glass. The resulting coated glass was cured in the oven at 150° C. for 24 hours, resulting in a solid, non-sticky rubbery coating on the surface of the glass.

Example 2

Material Preparation.

The mixture of the wavelength converting film was prepared identically to the Example 1.

Preparation of the Hot-Melt Wavelength Converting Film

A catalyst, titanium butoxide, in the amount of 0.4 wt. % of the mixture was added and mixed in in a planetary mixer. The mixture with catalyst was poured into the tape casting box having a gap with the width of 100 cm and the height of 0.1 mm. The material was dispensed on a non-sticky plastic film in a form of a coating by moving the tape casting box along the film. The material was allowed to dry at room temperature for 16 hours followed by pre-curing in the oven at 120° C. for 20 hours. The resulting wavelength converting film was solid that was becoming soft and sticky upon heating above 50° C.

Application of the Material.

The wavelength converting film was removed from the plastic sheet and placed on a glass sheet Here, glass sheet was used as an imitation of the LED wafer. The assembly was placed in the vacuum lamination device, comprising of a hot plate inside the vacuum chamber. The vacuum was applied, the hot plate was heated to 60° C. in 30 s, the vacuum chamber was purged with air, and the hot plate was turned off. At the end of the process the wavelength converting film was adhered to the glass sheet. The resulting assembly was cured in the oven at 150° C. for 4 hours to produce non-sticky rubbery coating on glass.

While there have been shown and described what are at present considered to be preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims. The disclosure rather comprises any new feature as well as any combination of features, which in particular includes any combination of features in the appended claims, even if the feature or combination is not per se explicitly indicated in the claims or the examples.

REFERENCE SIGNS

100wavelength converting film100′ wavelength converting film without a substrate101substrate102filler material103mixture104casting blade105roller200light-emitting device201LED die