WO2010005294A1

WO2010005294A1 - A method for manufacturing a lens to be added to a led, and a lens obtained with that method

Info

Publication number: WO2010005294A1
Application number: PCT/NL2009/050344
Authority: WO
Inventors: Marinus Johannes Van Og
Original assignee: Stichting Administratiekantoor Vomgroup
Priority date: 2008-06-15
Filing date: 2009-06-15
Publication date: 2010-01-14
Also published as: EP2310175A1; NL2003027A1; EA201100047A1; EA019225B1; NL2003027C

Abstract

A lens to be added to a LED is manufactured by introducing liquid acrylate basic material into a mould with a suitably modelled mould cavity. The mould is embodied in material transparent to UV radiation, such as silicone rubber. After injection of the acrylate basic material into the mould, irradiation of the mould takes place with UV radiation such that the acrylate basic material cures to form a lens of the desired form. After curing of the material the mould is opened and the obtained lens is removed.

Description

A METHOD FOR MANUFACTURING A LENS TO BE ADDED TO A LED, AND A LENS OBTAINED WITH THAT METHOD

The invention lies in the field of LED technology (Light Emitting Diode) . Known and usual is a technique known as "chip on board" in combination with a lens for the purpose of obtaining the desired directional characteristic, for instance a semi-spherical lens.

The use of polycarbonate for the material of the lens is known. Polycarbonate has the drawback that, in the case of high-power applications and at radiation in the wavelength range of about 400-430 nm, it displays a relatively rapid ageing, in particular a yellowish discoloration.

According to the invention use is made, as material for the lens, of a viscous liquid acrylate material curing rapidly under the action of UV radiation. This material is known per se and is marketed by the company Dijmex.

According to the invention use is further made of a mould transparent to UV radiation. A suitable material for the mould is a silicone rubber. The manufacture of a lens takes place by making a master mould on the basis of ceramic balls on a metal substrate, making a silicone rubber working mould therefrom and using this, after enclosure in an aluminium mould with recesses, for the purpose of injecting said lens material. Use is made of injection needles which can pierce through narrow openings in the mould material in order to carry the more or less oily viscous acrylate material under some pressure through the needle into the mould cavities. Irradiation with UV radiation then takes place through the walls of the mould. The initially liquid acrylate basic material is hereby cured, so that a cured lens of acrylate material with the desired shape is obtained. During the manufacture of the mould it is necessary to take into account that the silicone rubber exhibits a certain (slight) shrink. This must be taken into account when dimensioning the master mould. The relevant dimensions must therefore be increased by the same amount as the shrink of the silicone rubber.

An excellent flow over a surface can be realized by using a plasma treatment in an argon/oxygen environment. An easy release is obtained by adding a small quantity of silicone oil to the silicone rubber material. Such a material is available on the market as bleeding silicone rubber.

Prior to injection nitrogen is blown in, whereby oxygen is expelled and air bubbles are prevented. Use is made of a cleanliness level class 5 cleanroom.

The described method can be described as "liquid moulding".

All types of lens can be made according to the described method, except those with an undercut or other non-releasing form. For the manufacture hereof it is possible to work in two stages, i.e. first making a first structure which is subjected to a basic curing, subsequently making a second structure which is to be placed thereon and which is also subjected to a basic curing, and finally a final curing in a UV chamber with a high UV-intensity.

It should generally be noted that the timing of the UV radiation is critical. The material according to the invention adheres in practically ideal manner to silver, gold and ceramic. Any form of roughness {etching} is not necessary. The surfaces may be as smooth as glass.

Some applications: * For glass horticulture use can be made of an array of LEDs in a combination of deep red and blue. An array of for instance 40 LEDs may be very suitable.

* A studio lamp for television studio applications can comprise an array with LEDs of different colours. The array can be controllable, whereby within certain limits substantially all intensities and colours can be realized.

* The same principle can also be applied for household use. The method according to the invention is extremely flexible and very widely applicable. The invention also relates to a lens obtained by applying the described method.

The invention will now be elucidated in more detail on the basis of the following non-limitative figures, in which: figure 1 shows a top view of a LED lighting element with LEDs provided with lenses according to the present invention; figure 2 shows a side view of the LED lighting element of figure 1; figure 3 shows the side view of the LED lighting element of figure 2 during a step in the manufacture thereof; figure 4 shows the side view of the LED lighting element of figure 2 during a further step in the manufacture thereof; figure 5 shows a cross-section of a mould of aluminium and silicone material for the manufacture of the lens according to the present invention; figure 6 is a perspective view of the mould of figure 5; figure 7 shows a lens manufactured with the method according to the present invention; figure 8 shows a lens manufactured with the method according to the present invention; figure 9 shows a lens manufactured with the method according to the present invention; figure 10 shows a lens manufactured with the method according to the present invention; figure 11 shows a cross-section of a mould of crystal glass for manufacturing the lens according to the present invention; figure 12 shows a perspective view of a mould of crystal glass for manufacturing the lens according to the present invention; figure 13 shows a flow diagram of the method for manufacturing a lens according to the present invention.

Figure 1 shows a top view of a LED lighting element 1 with LEDs provided with lenses 4 according to the present invention. LED lighting element 1 comprises a printed circuit board 2 provided with a printed circuit 5 to which the LEDs are connected. Arranged on the LEDs are lenses manufactured making use of the method according to the invention.

Figure 2 shows a side view of the LED lighting element 1 of figure 1.

Figure 3 shows a side view of the LED lighting element of figure 2 during a step in the manufacture thereof, wherein a LED 7 is provided on printed circuit board 6. LED 7 is not yet provided with a lens. A phosphor-comprising layer 8 has however been applied, this contributing on the one hand to the adhesion of the lens to be arranged in a following step (see figure 4} and helping on the other to increase the light output of the LED lighting element to be thus obtained. In the shown example the phosphor-comprising layer 8 is applied over the whole width of printed circuit board 6. In a practical situation it is however possible to opt for application of this layer 8 around LEDs 7 with only a small overlap. Figure 4 shows the LED lighting element of figure 3 during a step in the manufacture thereof, wherein an acrylate material 9 is arranged on the phosphor- comprising layer 8 for the purpose of forming the lens. Just as the phosphor-comprising layer 8, the acrylate material is applied in this example over the whole width of the printed circuit board. Such a method of application can be reliably performed using the moulds to be described with reference to the following figures. In an alternative embodiment the formed lenses are however concentrated around the LEDs 7 themselves, and only connected to each other by means of a network of channels suitable for the injection.

Figure 5 shows a first embodiment of a mould for applying the acrylate material for the purpose of forming the lenses. The mould consists of a lower mould part 10 and an upper mould part 13, both preferably, though not exclusively, embodied in aluminium. For the purpose of placing onto each other in the correct manner the mould parts are provided with holes 11 for dowels. Provided in lower mould part 10 is a recess 12 for arranging therein of a printed circuit board. Above this printed circuit board can then be arranged a transparent mould part 14 which is provided with at least one filling opening 15 for the acrylate material, and a venter or riser pipe 16 for the acrylate material. The transparent mould part comprises the recesses 17 for the lenses to be formed on the LEDs provided on the printed circuit board. After arranging of the acrylate material, which preferably takes place in a light-proof cabinet, it is then irradiated with UV radiation via transparent mould part 14 until the resulting lenses remain form- retaining after removal of the mould. The printed circuit board thus provided with acrylate can then be subjected to a further processing step, or be further cured by means of UV radiation outside the mould. Figure 6 shows a perspective view of a mould which is similar to the mould of figure 5 and which is adapted to manufacture a plurality of LED lighting elements simultaneously, and is provided for this purpose with compartments 12a-12g. Figures 7-10 show diverse embodiments of lenses, wherein a first part 20b of the lens is formed according to the above described method, wherein lens 20b is arranged on a LED 19 provided on a printed circuit board 18, and a second part 20a is manufactured in a separate mould or a separate mould part. The first and the second mould part are urged against each other in not yet fully cured state, whereby they adhere to each other. A final curing is subsequently obtained by means of further exposure to UV radiation. The embodiments shown in figures 7-10 can also be manufactured according to an alternative method, wherein the flexible mould part 14 can be taken apart and consists of a plurality of parts. Figure 11 shows a completely hard mould, preferably formed from quartz glass, consisting of a first mould part 21 and a second mould part 22, both of which mould part are provided with holes 23 for centering pins for mutual alignment of the mould parts. Quartz glass is preferred because of the excellent UV-transmitting properties thereof. First mould part 21 is provided with a recess 21a for a printed circuit board, and second mould part 22 comprises recesses 26 for the purpose of forming the lenses. Recesses 26 can be filled using the respective filling opening 24 and riser pipe 25 for the acrylate material. The mould is provided with compartments 21a - 21g for containing a plurality of printed circuit boards with LEDs.

Figure 13 shows a flow diagram of the method for manufacturing a lens according to the present invention. Step 27 here shows the feed of printed circuit boards, which are subjected in step 28 to a plasma cleaning. In step 29 a printed circuit board is placed in a mould, such as a mould as shown in figures 5, 6, 11 or 12, after which in step 30 a first layer of material, for instance a phosphor-comprising layer, is applied as shown in figure 3. Subsequently in step 31 the first layer of material is caused to cure and in step 32 a scond layer of material is then applied, in particular an acrylate material, as shown in figure 4. The method according to the present invention can have the particular feature that the acrylate material is provided with a sinter material, formed particularly by globules, for instance formed from titanium, neodymium or lanthanum. These globules preferably have a diameter of about 20 micrometres, and have facets. The arranging of these globules, for instance between 0.1 and 0.2 g per 50 cc acrylate material, results in an improved light output, and particularly in an improved refractive index of the lens. Where between 1.5 and 1.6 is normally achieved, it has been found possible to achieve a refractive index between 1.95 and 2.00 by means of adding the globules according to the invention.

In a following step 33 a first curing of the acrylate material is obtained by exposing the mould with the acrylate layer received therein to LJV radiation until the thus formed lens is form-retaining, and in step 34 can be taken out of the mould. After release of the lens the mould is used once again and in step 29 again placed in a mould in which a printed circuit board is arranged. In a step 35 the lens is meanwhile in a step 35 further cured under the further influence of UV radiation, or in accordance with another suitable curing method. After a further processing in step 36 the thus obtained end product is further transported for incorporation in step 37 into for instance light fittings or other light units-

Claims

1. Method for manufacturing a lens to be added to a LED, which method comprises the following steps, to be performed in suitable sequence, of: providing a liquid acrylate basic material which cures under the action of ultraviolet (UV) radiation and which is transparent after curing; providing a mould, the form of which corresponds to the form of the lens to be manufactured; pre-manufacturing the mould from material which is substantially transparent to UV radiation; injecting the acrylate basic material into the mould; irradiating the mould with UV radiation such that the acrylate basic material cures; opening the mould; and taking the thus obtained lens out of the mould.

2. Method as claimed in claim 1, comprising of applying a phosphor-comprising layer to the printed circuit board prior to injection of the acrylate basic material into the mould.

3. Method as claimed in claim 1 or 2, comprising of adding to the acrylate basic material a sinter material, such as globules provided with facets, for instance titanium, neodymium or lanthanum globules, this prior to curing.

4. Method as claimed in any of the foregoing claims, comprising of: arranging on the not yet fully cured lens, formed on a LED and taken out of the mould, a second not yet fully cured lens formed from acrylate basic material; and curing the thus assembled lens under the further action of UV radiation.

5. Method as claimed in any of the foregoing claims, wherein the pre-manufacture of the mould of material substantially transparent to UV radiation comprises of manufacturing at least one mould part from silicone rubber or crystal glass.

6. Method as claimed in any of the foregoing claims, comprising of manufacturing simultaneously in one mould a number of lenses for a number of end products, such as LED lighting elements.

7. Method as claimed in any of the foregoing claims, comprising of adding the lens to a LED arranged on a printed circuit board.

8. Method as claimed in claim 7, comprising of applying a phosphor-comprising layer to the LED prior to arranging of the acrylate material, and subsequently adding the lens to the LED.

9. Lens obtained by applying a method as claimed in any of the foregoing claims.

10. LED lighting element, comprising the lens as claimed in claim 9.

11. Mould for use in the method as claimed in any of the claims 1-8.