KR101173904B1 - Composition for absorbing near infrared ray - Google Patents

Abstract

PURPOSE: A near-infrared ray absorbing composition is provided to have excellent transmittance in visible ray region, and barrier property in near infrared ray region, and to have low transmittance change in visible ray region even in case exposed under severe environment of high temperature, high humidity, etc. CONSTITUTION: A near-infrared ray absorbing composition comprises near-infrared ray absorbing composite oxide particle, and energy-curable resin. The near-infrared ray absorbing composite oxide partice comprises 80-95 weight% of WO3, 1-15 weight% of Cs2O, and a 0.01-5 weight% of Sb2O3 and 0.01-5 weight% of SnO2 particle stabilizer. The near-infrared ray absorbing composite oxide particle has average particle diameter of 1-30 nm, and is comprised in the near-infrared absorbing composition by 5-85 weight%.

Description

Near infrared absorption composition {COMPOSITION FOR ABSORBING NEAR INFRARED RAY}

The present invention has excellent barrier properties in the near-infrared region, excellent transmittance in the visible region, and small decrease in transmittance in the color tone and visible region even when exposed to harsh environmental conditions such as sunlight, high temperature, and high humidity for a long time. A near infrared absorption composition.

In addition to visible light, sunlight is composed of ultraviolet rays and infrared rays. Among the infrared rays, light having a wavelength of 780 to 2500 nm is called near infrared rays or hot rays. In general, a window used in a building or a vehicle is composed of a transparent glass plate or a resin plate to receive sunlight, and these heating wires enter a room through a window of a building or a car to increase the temperature of the room. Therefore, a near-infrared light blocking film is attached to the inner surface of the window glass as a method for suppressing the temperature rise in the room by sufficiently transmitting visible light and effectively blocking the heat ray.

In addition, a plasma display panel (PDP), which is an apparatus for exciting an xenon gas molecule sealed by plasma discharge between electrodes, exciting a fluorescent substance by ultraviolet rays generated at this time, and emitting light in a visible light region to display an image In order to effectively block near-infrared rays generated from the light emitting body, a near-infrared blocking film is used. Near-infrared rays generated from the luminous body of the PDP have a problem of causing malfunctions by acting on a remote wireless device or a remote control device using near-infrared rays.

Accordingly, studies are being actively conducted for the development of a near infrared absorbing film capable of effectively blocking near infrared rays in PDPs as well as windows.

International Patent Publication No. WO 2005/37932 is a fine particle of infrared shielding material which has conductivity while controlling the particle diameter or shape of tungsten bronze and transmitting light of visible light. Oxygen, 2.2 ≦ z / y ≦ 2.999), or composite tungsten oxide fine particles represented by the general formula MxWyOz, provided that M is H, He, alkali metal, alkaline earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe , Ru, Co, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F At least one element selected from P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, and I, W is tungsten, O is oxygen, 0.001 ≤ x / y ≤ 1, 2.2 ≤ z / y ≤ 3.0), and the optical properties and conductivity of the infrared shielding fine particle dispersion, characterized in that the particle diameter of the infrared shielding material fine particles is 1 nm or more and 800 nm or less; Its manufacturing method There it ignores. However, the infrared shielding particulate dispersion tends to be colored by light in the ultraviolet region (this coloring is returned to normal when left for a long time), and also has a problem that the transmittance of light is significantly reduced from the visible region to the near infrared region. have. The reason why the transmittance decreases from the visible region to the near infrared region by the light in the ultraviolet region is that the band gap of the fine particles of the infrared shielding material is in the ultraviolet region. And holes are generated, adsorbates on the surface of the infrared shielding material fine particles are protonated along the holes, and the generated electrons and H + are introduced into the infrared shielding material fine particles to generate conductive electrons, thereby absorbing the plasma. It is estimated that the light is absorbed from the visible light region to the near infrared region, thereby decreasing the transmittance.

In addition, Japanese Patent Application Laid-Open No. 2007-238353 discloses tungsten oxide fine particles represented by the general formula WyOz (wherein W is tungsten and O is oxygen, 2.2 ≦ z / y ≦ 2.999) or composite tungsten oxide represented by the general formula MxWO ₃ . Fine particles (wherein M is at least one element selected from Cs, Rb, K, Tl, Ba, In, Li, Sn, Ca, Sr, Na, W is tungsten, O is oxygen, 0.001≤x≤1.0) At least one element selected from Cu, Fe, Mn, Ni, Co, Pt, Au, Ag, Na, In, Sn, Cs, and Rb or a compound thereof is added to the crystal and / or to the surface of the particulate An infrared shielding body using tungsten oxide fine particles or composite tungsten oxide fine particles, which does not cause coloring even when subjected to light in an area, is disclosed. As described above, when the additional element or the compound is present on the surface of the tungsten oxide to prevent the entry of H +, or when the additional element is present on the surface of the tungsten oxide in the state of a metal, the radical or H + is catalyzed. When the additive element is neutral and present in the crystals of tungsten oxide fine particles, it is disclosed to inhibit the occurrence of color blocking by ultraviolet rays by structurally or electrostatically interfering with H +. However, the infrared shielding fine particle dispersion of the above composition has a problem that the color change of the product is severe, such as the visible light transmittance decreases or the blue color tone becomes soft due to prolonged heat and moisture resistance conditions.

International Patent Publication No. WO2005 / 37932 pamphlet Japanese Patent Laid-Open No. 2007-238353 Patent Publication No. 2008-22250 Patent Publication No. 2006-24328

Accordingly, an object of the present invention is to provide excellent barrier properties in the near-infrared region, excellent transmittance in the visible light region, and even when exposed to harsh environmental conditions such as sunlight, high temperature, and high humidity for a long time. It is providing the near-infrared absorption composition with a small fall of a transmittance | permeability.

Another object of the present invention is to provide a near infrared absorbing film comprising a near infrared absorbing layer prepared by curing the near infrared absorbing composition.

In accordance with the above object, the present invention

Near infrared absorption composite oxide fine particles, and

Energy-curable resin,

The composite oxide fine particles based on the total weight of the composite oxide fine particles, WO ₃ 80 to 95 wt%, Cs ₂ O 1 to 15% by weight and a particle stabilizer Sb ₂ O ₃ 0.01 to 5% by weight of SnO ₂ 0.01 to 5 parts by weight It provides a near-infrared absorbent composition comprising%.

According to another object of the present invention, there is provided a near-infrared absorbing film comprising a film made of a near-infrared absorbent composition, and also a substrate, and a near-infrared absorbing layer prepared by curing the near-infrared absorbent composition. .

The near-infrared absorbent composition according to the present invention has excellent barrier properties in the near-infrared region, excellent permeability in the visible region, and a color tone and visible region even when exposed to harsh environmental conditions such as sunlight, high temperature, and high humidity for a long time. It is useful for the manufacture of a near-infrared absorbing film with a small decrease in transmittance of.

Hereinafter, the present invention will be described in more detail.

The present invention is characterized in that the preparation of the near-infrared absorbing composition comprises near-infrared absorbing composite oxide fine particles which transmit light in the visible region and absorb light in the wide region of the near infrared.

That is, the near-infrared absorbing composition according to the present invention comprises a near-infrared absorbing composite oxide fine particles, and an energy curable resin, wherein the composite oxide fine particles are WO ₃ 80 to 95 wt%, Cs ₂ O 1, based on the total weight of the composite oxide fine particles. To 15% by weight and 0.01 to 5% by weight of Sb ₂ O ₃ and 0.01 to 5% by weight of SnO ₂ as particle stabilizer.

Tungsten trioxide (WO ₃ ) is a wide-bandgap oxide, and does not exhibit conductivity because of its low absorption of light in the visible region and the absence of free electrons (conducting electrons). In contrast, tungsten bronze, which contains a small amount of oxygen in tungsten trioxide or added a positive element such as Na, exhibits conductivity by generating free electrons and absorbs light in the visible region. It is difficult to use.

The near-infrared absorbing composite oxide fine particles according to the present invention contain 80 to 95% by weight of WO _{3 based} on the total weight of the fine particles. By including WO ₃ in the content range as described above, it can exhibit the effect of maximizing the holes to maximize the activity of free electrons when forming a composite oxide structure with the remaining combination elements.

In addition, Cs ₂ O is included in 1 to 15% by weight. Cs ₂ O serves to secure holes to maximize the activity of free electrons by forming a WO ₃ composite oxide structure, the near-infrared absorbing composite oxide fine particles according to the present invention is the Cs ₂ O 5 to 15% by weight, preferably 10 to 15% by weight. By including in the content range as possible to secure the hole as the movement path of the electrons can be obtained a near-infrared blocking effect by the electrical characteristics due to the free electrons.

In addition, the near-infrared absorbing composite oxide fine particles include 0.01 to 5 wt% of Sb ₂ O _{3 and} 0.01 to 5 wt% of SnO ₂ , preferably 0.3 wt% of Sb ₂ O ₃ and 3.0 wt% of SnO ₂ as particle stabilizers. By including Sb ₂ O ₃ and SnO ₂ in the above content range, it is possible to prevent the decrease in the transmittance and the near-infrared ray blocking property in the visible region even after long-term exposure under harsh environmental conditions such as sunlight, high temperature, and high humidity. Can be obtained.

Antimony (Sb) used as the particle stabilizer may be used by doping with tin oxide or the like, or may be used in the form of a complex metal oxide with tungsten or the like, but is preferably used in the form of an oxide such as Sb ₂ O ₃ . Conventional near infrared absorption compositions (Patent Publication No. 2008-22250 and Patent Publication No. 2006-24328) have been used to dope antimony in tin oxide or in the form of a composite metal oxide with tungsten. However, when antimony is used as a dopant or in the form of a composite metal oxide such as tungsten, the stability is excellent under environmental conditions such as sunlight, high temperature, and high humidity. Because it falls, it can only be used on a limited basis. In contrast, when antimony is used by adsorption coating of antimony on the surface of particles of tungsten and cesium composite oxide in the form of a single oxide, the visible light transmittance and near infrared ray blocking rate are excellent, but under environmental conditions such as sunlight, high temperature, and high humidity. It is possible to produce a composite oxide having a small decrease in transmittance.

The near-infrared absorbing composite oxide fine particles have an average particle diameter of 1.0 to 30 nm. If the particle diameter is less than 1 nm, the crystallinity of the oxide is difficult to secure holes, and it is not preferable because water absorption in the air easily occurs under environmental conditions such as sunlight, high temperature, and high humidity. Because of the difficulty in improving the visible light transmittance is not preferred.

The near-infrared absorbing composite oxide fine particles may be included in an amount of 5 to 85% by weight, and preferably in an amount of 10 to 40% by weight, based on the total weight of the near infrared absorption curing composition.

As the energy curable resin, a thermosetting resin, an active energy ray curable resin or a mixture thereof may be used.

There is no restriction | limiting in particular as said thermosetting resin, It can select from a conventionally well-known thing suitably, and can use. Specifically, the thermosetting resin may be polycondensation type thermosetting resin such as phenol resin, urea resin, melamine resin; Addition polymerization thermoplastic resins such as epoxy resins and polyester resins can be used, and polymer resins having carbon-carbon double bonds such as isoprene polymers and butadiene polymers in the main chain, carbon-carbon double bond groups or glycidyl groups, The polymer etc. which have in a chain can also be used. These may be used independently and may be used in combination of 2 or more type.

In addition, the thermosetting resin is usually used with a curing agent, optionally may be used with other resins.

The curing agent may be appropriately selected and used according to the type of thermosetting resin, and specific examples thereof include organic peroxides, isocyanate compounds, azo compounds, amine compounds, amidazole compounds, acid anhydrides, Lewis acids, formaldehydes, and the like. Can be mentioned.

Other resins include vinyl resins, urethane resins, polyesters, polyimides, polycarbonates, polyimides, nitrile resins, silicone resins, and the like.

As said active energy ray hardening type resin, an active energy ray polymerizable monomer or an oligomer is mentioned.

As said active energy ray polymerizable monomer, a bifunctional or more than polyfunctional (meth) acrylate is mentioned.

The active energy ray polymerizable oligomers include radical polymerization type and cationic polymerization type, and the radical polymerization type includes urethane (meth) acrylate type, epoxy (meth) acrylate type, polyester (meth) acrylate type, A polyol (meth) acrylate type etc. are mentioned, An epoxy type oligomer is mentioned as said cation polymerization type.

You may use these active energy ray hardening type resin 1 type or in combination of 2 or more types.

The active energy ray-curable resin may also be used with an initiator. Examples of the photopolymerization initiator for the radically polymerized active energy ray-polymerizable monomer and oligomer include benzoin, benzoin methyl ether, acetphenol, 2,2-dimethoxy- 2-phenylacetphenone, benzophenol, 2-methylanthraquinone, 2-methyl thioxanthone, and the like can be used. Examples of the photopolymerization initiator for the cationic polymerization type active energy ray polymerizable oligomer include aromatic sulfonium ions and aromatic oxo. The compound which consists of onium, such as a sulfonium ion and an aromatic iodonium ion, and an anion, such as a hexafluoro phosphate and a hexafluoro antimonate, is mentioned. You may use in combination of 1 type, or 2 or more types of these.

The active energy ray-curable resin may be included in an amount of 15 to 95% by weight based on the total weight of the near-infrared absorbent composition, and preferably 60 to 90% by weight.

When the energy curable resin is included in the above range, basic mechanical properties such as anti-Solvent attack, proper hardness, anti-curling, anti-clacking, etc. of the absorbent layer after film formation of the composition It is preferable to realize an average of 60% or more of visible light transmittance of wavelength 380 to 780 nm in an appropriate range of thicknesses, and to realize an average of 10% or less of near infrared transmittance of wavelength 900 to 1,000 nm.

The near-infrared absorbent composition of the present invention having the above composition has excellent barrier properties in the near-infrared region, excellent permeability in the visible region, and long-term exposure under harsh environmental conditions such as sunlight, high temperature, and high humidity. The change in transmittance in the color tone and visible light region is small, which is useful for producing a near infrared absorbing film.

Accordingly, according to another embodiment of the present invention, there is provided a near infrared absorbing film including a near infrared absorbing layer formed by curing the near infrared absorbing composition.

The near infrared absorbing film may be formed of a near infrared absorbing layer prepared by curing the near infrared absorbing composition, and may further include a substrate. Specifically, the near-infrared absorbing film may consist of only the near-infrared absorbing layer formed by curing the near-infrared absorbing composition, and when the near-infrared absorbing film further comprises the substrate, the near-infrared absorbing film is a substrate, and the substrate Located on one or both sides of the includes a near infrared absorbing layer prepared by curing the near infrared absorbing composition. In addition, when the near-infrared absorbing layer is formed on one surface of the substrate, a layer for facilitating the bonding with the adherend may be formed on the other side of the substrate, and the layer for facilitating the bonding with the adherend is an adhesive layer. Or an adhesive layer.

As the substrate, any plastic film or substrate commonly used as a substrate of a near infrared absorbing film may be used without particular limitation. Specifically, polyethylene terephthalate (PET), triacetyl cellulose (TAC), polyester, cellulose ester, cycloolefin polymer (COP), cycloolefin copolymer (COC), polyacrylate, polycarbonate, polyether sulfone, And plastic films or substrates produced using plastic resins such as polystyrene, polyolefin, polyethylene, polypropylene, polyvinyl chloride, and the like.

Although the thickness of the said base material is not specifically limited, Usually, it is preferable to have thickness of 15-250 micrometers.

The near-infrared absorbing layer is a near-infrared absorbing composite oxide fine particle, an energy curable resin, and optionally a composition for forming a near-infrared absorbing layer prepared by dispersing an initiator in a solvent. It can be formed by curing the energy curable resin by energy ray irradiation.

The near-infrared absorption composite oxide fine particles, the energy curable resin, and the initiator are the same as described above, and as the solvent, a conventional organic solvent such as methyl ethyl ketone and methyl isobutyl ketone may be used.

Since the application | coating or immersion process of the composition for forming a near-infrared absorption layer can be performed in accordance with a conventional method, detailed description in this specification is abbreviate | omitted.

The near-infrared absorbing layer may be formed to a thickness of 0.5 to 12㎛, and also formed to a thickness of 1 to 6㎛, the solvent attack prevention, appropriate hardness, anti-curling, cracking prevention, etc. of the absorbent layer after the film formation of the composition as mentioned above It is desirable to implement the basic mechanical properties of.

In addition, the pressure-sensitive adhesive layer or adhesive layer includes an adhesive or an adhesive such as acrylic, urethane, epoxy, silicone, and the like, and is preferably formed to a thickness of 5 to 50 μm.

The near-infrared absorbing film according to the present invention having the above configuration has a color change (delta E) of less than 2.0 and a change in visible light transmittance in a heat and moisture resistant environment, specifically, 85 ° C./85 RH% -500 hours. VLT) is 5% or less.

Moreover, the average transmittance | permeability is 60% or more in the visible light region of wavelength 380-780 nm, and the near-infrared transmittance of 10% or less is average in the region of wavelength 900-1,000 nm.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

(Example 1)

By solid polyfunctional urethane acrylate 100 weight% (Miwon Specialty Chemical Co., Miramer ^® MU9500) of 100 parts by weight of a solid content of 30% by weight of the near infrared absorbing compound oxide fine particle dispersion WO ₃ 85 wt%, 12 wt.% Cs ₂ O, Sb Composite oxide fine particles containing 0.3 wt% ₂ O ₃ and 3.0 wt% SnO ₂ , average particle diameter: 0.01 μm, dispersion medium: 120 parts by weight of MEK and 5 parts by weight of Irgacure ^® 184 (manufactured by Basf) with a photoinitiator A near-infrared absorbing hard coating solution was prepared by diluting with methyl ethyl ketone (MEK) such that the solid content concentration was 30%. After applying the near-infrared absorbing composition to one side of a polyethylene terephthalate (PET) film (Skyrol ^® , SKC) having a thickness of 34 μm SH34 as a base film, the solvent was dried and UV cured so that the thickness of the coating film was 2.5 μm. It was. In addition, after mixing 100 parts by weight of a UV absorber (100% by weight of Tinuvin ^® 99-2) with a solid content of 100% by weight and 100 parts by weight of a pressure sensitive adhesive (PSA, Hankel, DURO TAK80 ^® 1057) with a solid content of 100% by weight Was diluted with toluene to 25 wt% to prepare a UV absorbing adhesive coating solution. Thereafter, the ultraviolet-absorbing adhesive coating solution was applied to the other surface of the base film to have a thickness of 10 μm after solvent drying and thermosetting.

(Example 2)

The same procedure as in Example 1 was repeated except that a near-infrared absorbing composite oxide fine particle dispersion containing WO ₃ 93.7 wt%, Cs ₂ O 5.8 wt%, Sb ₂ O ₃ 0.25 wt%, and SnO ₂ 0.25 wt% was used. A near infrared absorbing film was prepared.

(Example 3)

The same procedure as in Example 1 was repeated except that a near-infrared absorbing composite oxide fine particle dispersion containing 96.8 wt% of WO ₃ , 2.2 wt% Cs ₂ O, 0.5 wt% Sb ₂ O _{3, and} 0.5 wt% SnO ₂ was used. A near infrared absorbing film was prepared.

(Example 4)

The same procedure as in Example 1 was repeated except that a near-infrared absorbing composite oxide fine particle dispersion containing 95.8 wt% WO ₃ , 3.8 wt% Cs ₂ O, 0.2 wt% Sb ₂ O _{3, and} 0.2 wt% SnO ₂ was used. A near infrared absorbing film was prepared.

(Comparative Example 1)

A near-infrared absorbing film was prepared in the same manner as in Example 1 except that a near-infrared absorbing composite oxide fine particle dispersion containing 75 wt% of WO ₃ and 25 wt% of Cs ₂ O was used.

(Comparative Example 2)

The same procedure as in Example 1 was repeated except that a near-infrared absorbing composite oxide fine particle dispersion containing 89.8 wt% of WO ₃ , 10.0 wt% of Cs ₂ O, 0.1 wt% of Sb ₂ O _{3, and} 0.1 wt% of SnO ₂ was used. A near infrared absorbing film was prepared.

(Test example)

The physical properties of the film were measured in the following manner with respect to the near-infrared absorbing film prepared in Examples and Comparative Examples. The results are shown in Table 1 below.

(1) Near-infrared average transmittance in the wavelength range of 900 to 1,000 nm

The average transmittance in the near-infrared region with a wavelength of 900 to 1,000 nm was measured using an ultraviolet-visible spectrophotometer (V-670 manufactured by JASCO).

(2) Average transmittance of visible light in the region of wavelength 380-780 nm

The average transmittance in the visible light region having a wavelength of 380 to 780 nm was measured using an ultraviolet-visible light spectrophotometer (V-670 manufactured by JASCO).

(3) color change (△ E)

Color change (ΔE) of the films according to Examples and Comparative Examples was measured using a color difference meter (UltraScan PRO, manufactured by HunterLab) under a heat and humidity environment (85 ° C./85 RH% 500 hours).

(4) change in visible light transmittance

The average visible light transmittance of the films according to Examples and Comparative Examples was measured using an ultraviolet-visible spectrophotometer (V-670 manufactured by JASCO Corporation) under a heat and moisture resistant environment (500 ° C./85 RH% 500 hours). According to 1, the visible light transmittance change (ΔVLT) was evaluated.

As shown in Table 1, the near-infrared absorbing film according to Examples 1 to 4 has a near-infrared average transmittance in the region of the initial wavelength 900 to 1,000 nm and the visible light average transmittance in the region of the wavelength of 380 to 780 nm And the same level as the film of 2, but the change in color (ΔE) is less than 2.0 and the change in visible light transmittance (ΔVLT) is 5% or less under the heat and moisture resistant environment, so that the physical properties required as a near infrared absorbing film Were met.

In the above, the present invention has been described with reference to the above embodiments, which are only examples, and the present invention will be described below in various modifications and equivalents which are obvious to those skilled in the art. It should be understood that it can be carried out within the scope of the appended claims.

Claims (10)

Near infrared absorption composite oxide fine particles, and
Energy-curable resin,
The near infrared absorbing compound oxide fine particles based on the total weight of the particulate, WO ₃ 80 to 95 wt%, Cs ₂ O 1 to 15% by weight and a particle stabilizer Sb ₂ O ₃ 0.01 to 5% by weight of SnO ₂ 0.01 to 5 parts by weight Near-infrared absorption composition containing%. The method of claim 1,
The near-infrared absorption composite oxide fine particle has an average particle diameter of 1-30 nm, The near-infrared absorption composition characterized by the above-mentioned. The method of claim 1,
The near-infrared absorption composite oxide fine particle is a near-infrared absorption composition, characterized in that contained in 5 to 85% by weight based on the total weight of the near-infrared absorbent composition. The method of claim 1,
The near-infrared absorbing composition, wherein said energy curable resin is selected from the group consisting of a thermosetting resin, an active energy ray curable resin, and a mixture thereof. The method of claim 4, wherein
The thermosetting resin is composed of a phenol resin, a urea resin, a melamine resin, an epoxy resin, a polyester resin, an isoprene polymer, a butadiene polymer, a polymer having a carbon-carbon double bond group or a glycidyl group in the polymer side chain, and a mixture thereof. Near-infrared absorption composition, characterized in that selected from the group. The method of claim 4, wherein
The active energy ray-curable resin is a bifunctional or higher polyfunctional (meth) acrylate, urethane (meth) acrylate type, epoxy (meth) acrylate type, polyester (meth) acrylate type, polyol (meth) acrylate type Near-infrared absorption composition, characterized in that selected from the group consisting of epoxy oligomers and mixtures thereof. Substrate, and
Near-infrared absorbing film located on one side or both sides of the substrate, comprising a near-infrared absorbing layer prepared by curing the near-infrared absorbing composition according to claim 1. The method of claim 7, wherein
The near-infrared absorbing layer is formed on one surface of the substrate, and the adhesive layer or the adhesive layer is formed on the other surface of the substrate, the near-infrared absorbing film. The method of claim 7, wherein
The near-infrared absorbing film has a color change (delta E) of less than 2.0 and a change in visible light transmittance (delta VLT) of 5% or less at 85 ° C / 85 RH% -500 hours. The method of claim 7, wherein
The near-infrared absorbing film has an average transmittance of 60% or more in the visible region having a wavelength of 380 to 780 nm, and has an average transmittance of 10% or less in the near infrared region having a wavelength of 900 to 1,000 nm.