JP7343220B2 - resist ink - Google Patents

Description

The present invention relates to a resist ink used as a protective film (highly reflective insulating film) for a deep ultraviolet LED substrate, and more particularly to a resist ink that efficiently diffuses and reflects deep ultraviolet rays.

Compared to the so-called UVA light with a wavelength of 320 nm to 400 nm and the so-called UVB light with a wavelength of 280 nm to 320 nm, deep ultraviolet light with a wavelength of 250 nm to 280 nm or less has much higher energy and is harmful to bacteria such as Escherichia coli, phages, and Pseudomonas aeruginosa. There are great expectations as a light that can purify water and air by sterilizing bacteria and viruses (Non-Patent Document 1). In particular, previous research has revealed that deep ultraviolet light of 265 nm has a high sterilization stress (Non-Patent Document 2).

Mercury lamps, halogen lamps, and the like are used as deep ultraviolet light sources, but these are large and consume high power, which is the reason why their application to consumer products has not expanded. Therefore, there is a need to switch to LED light sources that are smaller and consume less power.

Deep UV LEDs used for water and air purification need to irradiate a large area at once, so a so-called COB (Chip on Board) package, in which many deep UV LED chips are arranged on a substrate, is used. used. Here, deep ultraviolet LED chips have lower luminous efficiency and higher heat generation than visible light LEDs. Therefore, a material with high heat dissipation properties is required for the substrate for the COB package.

Examples of materials with high heat dissipation include metal substrates such as aluminum and copper, and ceramic substrates such as aluminum nitride. However, since the metal substrate is conductive, it is necessary to coat the surface with an insulating film in order to mount the deep ultraviolet LED chip. On the other hand, aluminum nitride substrates have excellent insulating properties and can mount deep ultraviolet LED chips without applying an insulating film, but are susceptible to deterioration due to deep ultraviolet rays. Therefore, whether it is a metal or ceramic substrate, it is necessary to form a protective film on the surface of the substrate for a COB package that does not deteriorate due to deep ultraviolet rays. This protective film is required to be a highly reflective insulating film that has both insulating properties and high reflectivity for deep ultraviolet rays.

As such a material for a protective film, a resist ink is known that is based on silicone, which does not easily deteriorate when irradiated with deep ultraviolet rays, and contains an inorganic filler (Patent Document 1, Patent Document 2). However, the resist ink disclosed herein has very low diffuse reflectance in the deep ultraviolet wavelength range, and does not contribute to improving the luminous efficiency of deep ultraviolet LEDs. Further, Patent Document 3 discloses a deep ultraviolet ray substrate using glass ceramic. This substrate also has heat dissipation properties due to heat dissipation vias, but the reflectance at 280 nm is about 75%, which is sufficient compared to substrates used for visible light LEDs (Patent Document 4, Patent Document 5). It cannot be said that it has reflectance.

Patent Document 6 discloses an LED module, in which a structure including a binder matrix and inorganic particles dispersed in the binder matrix is disclosed as a reflective layer covering at least a part of a substrate. An example is disclosed in which the particles include at least one selected from the group consisting of aluminum oxide, zirconia oxide, titanium oxide, and barium oxide, and further the average particle size of the inorganic particles is 0.1 μm or more and 50 μm or less. is disclosed. However, Patent Document 6 only describes the reflectance at wavelengths of 360 nm or more, and there is no description or suggestion about the reflectance in the wavelength range of 250 nm to 280 nm or whether there is deep ultraviolet ray resistance. .

A more detailed evaluation of Patent Document 6 reveals that although the applicant describes a very wide range of 0.01 μm or more and 50 μm or less as the average particle size of inorganic particles in the specification, the particles are not considered inorganic particles in the specification. It only shows the reflectance from 360 nm to 740 nm when the average particle size of ZrO ₂ is 2.0 μm and the content of ZrO ₂ particles is 64% by volume, and the others are used for adjusting the surface roughness Ra. It is thought that this was done.

JP2012-227292A WO2011/118108 publication JP2017-117982A Japanese Patent Application Publication No. 2011-246329 Japanese Patent Application Publication No. 2014-187158 JP 2019-125683 Publication

https://www.ultraviolet-led.com/media/japanese/a21 Water Research 130 (2018) 31-37

In the future, as the demand for improved safety through purification of water and air increases, there will be a strong demand for improved efficiency of deep ultraviolet LEDs with wavelengths of 265 nm, 254 nm, 270 nm, and 280 nm, which have excellent sterilizing effects. Therefore, there is a need for a resist ink that is less susceptible to deterioration due to deep ultraviolet rays and is highly reflective for each of these wavelengths and can be used as a protective film for a COB package substrate.

The present invention provides a resist ink that is less degraded by deep ultraviolet rays and has a high reflectance in the wavelength range of 250 nm to 280 nm, which has a high bactericidal effect, and is particularly suitable for a protective film of a COB package substrate.

In order to solve the above problems, the resist ink according to the present invention contains silicone and zirconium oxide powder as essential components.

The silicone is not particularly limited, but it is desirable that the viscosity at the working temperature (room temperature) for dispersing the zirconium oxide powder is 10 Pa·s or less. If it exceeds 10 Pa·s, the viscosity may increase during mixing with the zirconium oxide powder. If the viscosity increases during mixing, the zirconium oxide powder may not be dispersed well, and the deep ultraviolet reflectance may decrease.

Further, it is preferable to use purified silicone in order to reduce siloxane gas generated during the coating and curing process on a COB package substrate, etc. When unrefined silicone is used, siloxane gas is generated, and when it adheres to the contacts of the LED element, silicon dioxide (SiO2), a decomposed component of the gas, acts as an electrical insulator and causes contact failure.

In the present invention, the zirconium oxide powder must have an average particle diameter (D50) of 1 μm or less, and its content must be 32 wt% or more and 50 wt% or less. It has also been revealed that when the film thickness of the resist ink after curing is 30 μm or more, a high reflectance of 85% or more can be achieved in the wavelength range of 250 to 280 nm, which is deep ultraviolet rays with a high bactericidal effect.

In the present invention, it has been revealed that when the average particle diameter (D50) of the zirconium oxide powder exceeds 1 μm, a long wavelength shift of the reflection band occurs and the reflectance at 250 nm decreases. It is necessary to select a particle size that has an average particle size (D50) of 1 μm or less and is within a range where it can be uniformly dispersed (does not aggregate) in the silicone. From experience, agglomeration tends to occur when the average particle diameter is 0.2 μm or less.

The content of zirconium oxide powder needs to be 32 wt% or more. If it is less than 32 wt%, the reflectance of deep ultraviolet rays will decrease. On the other hand, if it exceeds 50 wt%, agglomeration of the zirconium oxide powder begins to occur, and the reflectance of deep ultraviolet light of 250 nm in particular decreases.

Although the shape of the particles in the zirconium oxide powder is not limited, in general, particles with a shape close to spherical are preferable compared to amorphous particles because they can reduce the specific surface area and increase the amount added.

The inorganic powder to be added includes zirconium oxide as an essential component, but other inorganic powders can be added as appropriate. At this time, inorganic powders that absorb ultraviolet rays, such as titanium oxide, cause a decrease in the reflectance of deep ultraviolet rays. Therefore, it is necessary to use an inorganic powder that does not have an ultraviolet absorption region. Examples of such inorganic powders include aluminum oxide (alumina). Further, the particle size of the inorganic powder to be added is preferably such that the average particle size (D50) is 1 μm or less, similar to the zirconium oxide powder. This is to avoid reducing the reflectance in the wavelength range of 250 nm to 280 nm.

As a method for applying the resist ink of the present invention to a COB package substrate, generally known screen printing, dispensing methods, spray printing, etc. can be used. The printed film thickness needs to be 30 μm or more in order to achieve high reflectance in the wavelength range of 250 nm to 280 nm as described above.

According to the present invention, the diffuse reflectance is as high as 85% or more in the deep ultraviolet wavelength range of 250 to 280 nm, and even when deep ultraviolet rays are irradiated for a long period of time, there is no obvious deterioration such as a decrease in deep ultraviolet reflectance or a change in color tone. It becomes possible to provide a resist ink that does not cause UV rays and has excellent resistance to deep ultraviolet rays.

FIG. 2 is a diagram showing a COB package in which a deep ultraviolet LED chip is mounted. FIG. 2 is a schematic diagram of a deep ultraviolet protective film (deep ultraviolet high reflective insulating film) formed using the resist ink of the present invention. This is an example of the reflection spectra in the ultraviolet to visible light range of a deep ultraviolet protective film on a glass substrate (sample No. 2) and an aluminum substrate formed using the resist ink of the present invention. This is an example of a reflection spectrum in the ultraviolet region of a deep ultraviolet protective film formed on a glass substrate using the resist ink of the present invention (sample No. 2). This is another example of the reflection spectrum in the ultraviolet region of a deep ultraviolet protective film on a glass substrate formed using the resist ink of the present invention (Samples No. 16 and No. 17).

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

Condensed PDMS (polydimethylsilicate) was used as the silicone. Dioctyltin (Nitto Kasei Co., Ltd.) was used as a curing agent for curing silicone.

As the zirconium oxide, powders commercially available from Daiichi Kigenso Kagaku Kogyo Co., Ltd. or Nippon Denko Co., Ltd. were used depending on the average particle diameter. Products with average particle diameters (D50) of 0.5 μm, 1 μm, 2 μm, 3 μm, and 14 μm were used to compare deep ultraviolet reflectance.

Resist ink using 0.5 μm or 1 μm as the average particle diameter (D50) of zirconium oxide powder is prepared by mixing 60 wt% PDMS, 35 wt% zirconium oxide powder, and 5 wt% solvent in a centrifugal stirrer (ARE- manufactured by THINKY). 310), and then precisely dispersed using a three-roll mill (three-roll mill manufactured by Inoue Seisakusho). The gap of the three-roll mill was set to 15 μm to perform precise dispersion. Note that Texanol was used as the solvent.

Resist ink using zirconium oxide powder with an average particle diameter (D50) of 2 μm, 3 μm, or 14 μm is made by mixing 62 wt% PDMS, 36 wt% zirconium oxide powder, and 2 wt% solvent (Texanol) using a centrifugal stirrer. Then, it was produced by precise dispersion using a three-roll mill. The gap of the three-roll mill was set to 15 μm.

Resist inks having different contents of zirconium oxide powder were prepared under the following conditions. Using zirconium oxide powder with an average particle diameter (D50) of 0.5 μm, (60 + The mixture was mixed in a vessel and then precisely dispersed in a three-roll mill. The gap of the three-roll mill was set to 15 μm. At this time, X was set to 0, 3, and 5.

Sample No. with a zirconium oxide powder content of 37%. No. 16 uses zirconium oxide powder with an average particle diameter (D50) of 0.5 μm, and mixes 58 wt% PDMS, 37 wt% zirconium oxide powder, and 5 wt% solvent (Texanol) using a centrifugal stirrer. After that, it was produced by precise dispersion using a three-roll mill. Here, the gap of the three-roll mill was set to 15 μm. In addition, sample No. 3 has a zirconium oxide powder content of 50 wt%. No. 17 uses zirconium oxide powder with an average particle diameter (D50) of 0.5 μm, and mixes 43 wt% PDMS, 50 wt% zirconium oxide powder, and 7 wt% solvent (Texanol) using a centrifugal stirrer. After that, it was produced by precise dispersion using a three-roll mill. Here, the gap of the three-roll mill was set to 15 μm.

Next, a resist ink containing zirconium oxide powder and other inorganic powders was prepared under the following conditions. Using zirconium oxide powder with an average particle diameter (D50) of 0.5 μm, 35 wt% zirconium oxide powder, (60-Y) wt% PDMS, Ywt% inorganic powder, and 5 wt% solvent (Texanol) were centrifuged. The mixture was mixed using a separate stirrer and then precisely dispersed using a three-roll mill. The gap of the three-roll mill was set to 10 μm. At this time, Y was set to 30 and 20. Titanium oxide (Ti-Pure R-101 manufactured by Chemours) and aluminum oxide (AL-S43B manufactured by Sumitomo Chemical or AL-45-A manufactured by Showa Denko) were used as inorganic powders.

(Application to the board)
A curing agent (dioctyltin (Nitto Kasei Co., Ltd.)) was added to the resist ink in an amount of 1 wt %, and the resist ink was printed on a glass substrate by screen printing using a #325 mesh. The film thickness was adjusted by changing the number of printed layers. After printing, the resist ink was cured at 180° C. for 2 hours to prepare a glass substrate with a deep ultraviolet high reflection protective film.

(Deep UV resistance)
The produced glass substrate with a deep ultraviolet high reflection protective film was irradiated with ultraviolet rays having a wavelength of 265 nm and adjusted to 37 mW/cm 2 for 1000 hours. Changes in reflectance at a wavelength of 265 nm before and after irradiation were measured.

(reflectance measurement)
The deep ultraviolet reflectance of the produced deep ultraviolet reflective substrate and the substrate after ultraviolet irradiation was measured using a spectrophotometer. Spectralon (manufactured by Labsphere) was used as a base, and the diffuse reflectance was measured using an integrating sphere.

Table 1 shows the reflectance of high reflective substrates obtained by applying resist inks prepared using zirconium oxide powders (content is 32 wt% in each case) with different particle diameters (D50) and crosslinking and curing. . Also shown is the deep ultraviolet reflectance when the coating film thickness is changed in the case of a particle size of 0.5 μm. From Table 1, it can be seen that the reflective substrates obtained by applying and cross-linking a resist ink prepared using zirconium oxide with a particle size of 1 μm or less have a film thickness of 250 μm or less, except for the case where the film thickness is less than 30 μm (sample No. 1). It can be seen that a high reflectance of 85% or more is obtained in the wavelength region of 280 nm. Furthermore, although a reflectance of 85% or more was obtained with a film thickness of 30 μm, it was found that the reflectance increased when the film thickness was further increased. When coated with a thickness of 100 μm (sample No. 4), it exhibits a reflectance of 90% or more in the wavelength range of 250 nm to 280 nm. On the other hand, it was found that when the average particle diameter of the zirconium oxide powder exceeded 1 μm, the reflectance, especially on the short wavelength side (250 nm), decreased rapidly (Sample No. 6 to Sample No. 12).

Table 2 shows the reflectance of deep ultraviolet reflective substrates obtained by applying resist inks with different contents of zirconium oxide powder and crosslinking and curing. It can be seen that when the content of zirconium oxide powder is 32 wt% or more, a high reflectance of 85% or more is obtained in the wavelength region of 250 to 280 nm.

Table 3 shows the reflectance of a highly reflective substrate obtained by coating and crosslinking a resist ink prepared by mixing zirconium oxide powder and other inorganic powders. The deep ultraviolet reflectance of the sample containing titanium oxide powder was greatly reduced. This is due to the fact that titanium oxide absorbs ultraviolet light. It can be seen that in the substrate containing aluminum oxide powder, a high reflectance of 85% or more in the wavelength range of 250 to 280 nm is obtained only when powder with an average particle diameter (D50) of 0.8 μm is used. .

The results of evaluating deep ultraviolet resistance are shown in Table 1. The deep ultraviolet ray resistance was determined by irradiating ultraviolet rays with a wavelength of 265 nm at 37 mW/cm2 for 1000 hours, and measuring the change in reflectance at a wavelength of 265 nm before and after irradiation. In the sample (No. 12) using large particles with an average particle diameter of 14 μm as zirconium oxide powder, the reflectance increased, but the reason is unknown. Other than that, sample No. The amount of change in all samples 2, 5, 6, and 10 was around 4%. Sample No. In samples 2 and 5, the reflectance at 265 nm after irradiation was 85% or more.

As described above, by applying a resist ink that has a high diffuse reflectance in the deep ultraviolet wavelength region of 250 to 280 nm and excellent resistance to deep ultraviolet rays, a glass substrate with a protective film that is highly reflective in the deep ultraviolet region was fabricated.

FIG. 1 shows a COB substrate on which a deep ultraviolet LED chip 3 is mounted. Four deep ultraviolet LED chips 3 are arranged in series by gold wires 4, and can irradiate deep ultraviolet rays over a wide range. The deep ultraviolet rays irradiated backward are reflected forward without being transmitted or absorbed by the protective film (highly reflective insulating film) 5 formed using the resist ink of the present invention, increasing the amount of deep ultraviolet rays. .

FIG. 2 is an enlarged view of a protective film (highly reflective insulating film) 5 formed using the resist ink of the present invention, in which zirconium oxide powder 8 with a predetermined particle size is contained in a silicone matrix 7. It is dispersed in The thickness of the highly reflective insulating film 5 is 30 μm or more. When this protective film was formed on a glass substrate, it was semitransparent (in appearance) in the visible light range.

FIG. 3 shows sample No. 2 shows the reflectance over a wide range from the deep ultraviolet region to the visible light region (solid line). While the reflectance in the visible light range is around 70% to 30%, it selectively shows a high reflectance of 85% or more in the deep ultraviolet wavelength range of 250 nm to 280 nm, which is the most important wavelength range for sterilization. It can be seen that An example in which the same protective film was formed on an aluminum substrate with a film thickness of 47 μm is shown by a broken line in FIG. On an aluminum substrate, the reflectance from the substrate itself contributes to the reflectance, but while the reflectance is 60 to 80% in the visible light range, it is selective in the wavelength range of 250 nm to 280 nm. It can be seen that the reflectance is as high as 90% or more. FIG. 4 shows sample No. This is an enlarged view of the reflection spectrum in the deep ultraviolet region of No. 2, and it is clear that the reflectance is as high as 85% or more in the wavelength region of 250 nm to 280 nm.

FIG. 5 shows sample No. The reflection spectra in the deep ultraviolet region of Nos. 16 and 17 show a high reflectance of 85% or more in the wavelength region of 250 nm to 280 nm, but as the content of zirconium oxide powder increases, the effect of aggregation appears. Therefore, although the reflectance on the long wavelength side increases, the reflectance on the short wavelength side decreases. When the content of zirconium oxide powder becomes 50 wt%, the reflectance at 250 nm becomes 85%.

1... Electrode 2... Sealing resin 3... Deep UV LED chip 4... Gold wire 5... Protective film (high reflective insulation film)
6...Metal substrate 7...Silicone 8...Zirconium oxide powder

Claims (2)

A resist ink, which contains silicone as an essential component and zirconium oxide powder with an average particle size (D50) of 0.5 μm or more and 1 μm or less in an amount of 32 wt% or more and 37 wt% or less, and a film of 30 μm or more and 100 μm or less on a base material. A resist ink characterized by having a diffuse reflectance of 85% or more in a wavelength range of 250 to 280 nm when applied thickly and crosslinked and cured.
2. The resist ink according to claim 1, wherein the decrease in reflectance at a wavelength of 265 nm is 5% or less after irradiation with deep ultraviolet rays at a wavelength of 265 nm for 1000 hours.

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