JPH09226043A - Reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of peeling due to working of parts and integration thereafter by specifying a peel strength between a polyolefin film and a silver thin film layer and a reflectivity determined from a reflective face, in a reflector formed of a polyolefin film, a non-crystallilne ITO thin film layer, and a silver thin film layer. SOLUTION: This reflector having, as a reflective face, a polyolefin film formed of a polyolefin film 10, a non-crystalline ITO thin film layer 20, and a silver thin film layer 30 or the silver thin film layer is formed. Here, a peel strength between the polyolefin film 10 and the silver thin film layer 30 is set to 100g/cm or above. Also, a reflectivity at a wavelength 550nm determined from the reflective face side is made to be 90% or above. Also, the non- crystalline ITO thin film layer 20 is formed by sputtering under an atmosphere of high oxygen density and its respectivity value is 1×10<-2> cm or above. A content of a tin oxide of the non-crystalline ITO thin film layer 20 is 10-50wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a silver reflector having a high reflectance.

[0002]

2. Description of the Related Art Silver is a metal having a high reflectance in the visible light region. However, silver is sulfurized and blackened when it is exposed to the air for a long period of time, so it was necessary to periodically re-form a silver film on an optical mirror or the like on which silver was deposited. Therefore, it was not generally used except for some applications.

In recent years, a high-reflectance reflector using silver as a reflection film has been used mainly in a lamp reflector of a backlight portion of a liquid crystal display device as a reflector of a fluorescent lamp.
These are so-called silver reflectors composed of PET (polyethylene terephthalate) / silver thin film layer / adhesive layer / aluminum plate,
It is a so-called silver reflective sheet consisting of PET / silver thin film layer / white coating / adhesive layer / aluminum thin film layer / polymer film / white coating. By using PET, which is a transparent polymer film, as a protective layer for silver, it is possible to prevent sulfidation, chlorination, oxidation, etc. of silver due to atmospheric exposure, which has been a problem in the past, and maintain high reflectance for a long time. I succeeded in doing so. As an example of the reliability of the silver reflector and the silver reflector sheet, a high temperature test (80 ° C.) was carried out for 1000 hours. No blackening due to sulfidation was observed, and no decrease in reflectance was observed. It was High temperature and high humidity test (60 ℃, 85
% RH, 1000 hours), but similarly, no blackening and decrease in reflectance were observed. Low temperature test (-20 ℃, 1
000 hours), cold heat test (-20 ° C x 30 minutes to 60 ° C x
There was no abnormality in 30 minutes, 100 cycles).

Polyolefin films have high transparency,
In addition to moisture resistance, it has excellent electrical properties such as a low dielectric constant and a small dielectric loss tangent, making it very suitable as a strobe reflector. However, when a silver thin film layer was formed on a polypropylene film or a methylpentene copolymer film, which is a polyolefin film, sufficient adhesion could not be obtained, and the polyolefin film and the silver thin film layer were easily separated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the adhesion between the polyolefin film and the silver thin film layer, and to obtain a reflector that can be used practically. More specifically, a reflection plate comprising a polyolefin film / silver thin film layer / adhesive layer / aluminum plate, a polyolefin film /
There is no peeling due to insufficient adhesion when parts are processed (cutting, bending, etc.) in a reflective sheet made of silver thin film layer / white coating / adhesive layer / aluminum thin film layer / polymer film / white coating, and further assembling thereafter. It is intended to provide a reflector.

[0006]

[Means for Solving the Problems] That is, the inventors of the present invention have conducted extensive studies in order to solve such a problem, and as a result, have found that the polyolefin film (A) and the silver thin film layer (C) are
By using the amorphous ITO thin film layer (B) having a specific resistance of 1 × 10 ⁻² Ω · cm or more formed by sputtering in a high oxygen concentration atmosphere, the above (A) and (C) It was found that a practically sufficient adhesion between the two and a high reflectance of 90% or more can be obtained. The present invention has been made based on such findings.

That is, the present invention is (1) at least
A polyolefin-based film, which is a reflector having the structure of ABC consisting of the polyolefin-based film (A), the amorphous ITO thin film layer (B), and the silver thin-film layer (C) as the polyolefin-based film side or the silver thin-film layer side as a reflecting surface. A reflector having a peel strength of 100 g / cm or more between (A) and the silver thin film layer (C), and a reflectance of 90% or more at a wavelength of 550 nm measured from the reflecting surface side, (2) non- Crystalline I
The specific resistance of the TO thin film layer (B) formed by sputtering in a high oxygen concentration atmosphere is 1 × 10 ^-2 Ω · cm
The reflector of (1) which is the ITO thin film, and (3) the reflector of (1) or (2), wherein the content of tin oxide in the amorphous ITO thin film layer (B) is 10 to 50% by weight. It is a thing.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring to the attached drawings, FIG. 1 is a structural sectional view of the simplest reflector of the present invention, and FIG. 2 shows the reflector shown in FIG. FIG. 3 is a structural cross-sectional view of a reflector formed by laminating a polymer sheet and an adhesive layer.

The term "reflector" as used herein refers to an object that returns the light incident on the reflector to the original medium. Here, mainly 80% or more of the light in the visible region is returned to the original medium. It is an object, more preferably an object that returns 90% or more of light in the visible region to the original medium. The outline of the reflection by the reflector of the present invention will be described with reference to FIG. 1. Most of the light incident from the polyolefin film 10 side passes through the polyolefin film 10 and the amorphous ITO thin film layer 20, and the silver thin film. Reaching the layer 30, the silver thin film layer 30
The light is reflected by, passes through the amorphous ITO thin film layer 20 and the polyolefin film 10, and returns to the original medium again.

The manufacturing method of the reflector shown in FIG.
The amorphous ITO thin film layer 20 and the silver thin film layer 30 are formed on the polyolefin film 10, and the adhesive 4 is applied to the silver thin film layer surface.
0 is applied, and the adhesive surface and the metal plate or polymer sheet 50
There is a method of laminating. Lamination is generally performed after the adhesive is applied, but in addition to this, the applying step and the laminating step can be performed separately. For example, when a thermoplastic polyester adhesive is used, the applied adhesive can be melted with a hot roll or the like to perform lamination at any time.

Examples of the material of the polyolefin film 10 in the present invention include polyethylene (PE), polypropylene (PP), polymethylpentene copolymer and the like, but the material is not necessarily limited to these and is transparent to some extent. Any material having a high glass transition temperature can be used.

There is no limit to the thickness of the polyolefin film, but a thickness of about 25 to 100 μm is preferably used. Regarding the optical characteristics of the polyolefin film used, the light transmittance at a wavelength of 550 nm is preferably 80% or more. More preferably, wavelength 500-700n
m has a light transmittance of 80% or more for light in the range of m
More preferably, the light transmittance is 80% or more for light in the wavelength range of 350 to 750 nm. Light transmittance is 80
If it is less than%, the reflectance when used as a reflector is less than 90%, which is not preferable in terms of performance as a reflector.

Those skilled in the art will understand that it is preferable that the polyolefin film has the property of absorbing ultraviolet rays in order to improve the light resistance of silver. The method of forming the silver thin film layer includes a wet method and a dry method. The wet method is a general term for the plating method, and is a method of depositing silver from a solution to form a film. Specific examples include silver mirror reaction and the like. On the other hand, the dry method is a general term for vacuum film forming methods, and specific examples thereof include a resistance heating vacuum evaporation method, an electron beam heating vacuum evaporation method, an ion plating method, and an ion beam assisted vacuum evaporation method. , The sputtering method, etc. In particular, a vacuum film forming method capable of a roll-to-roll method for continuously forming a film is preferably used in the present invention.

In the vacuum deposition method, a silver raw material is an electron beam,
Melt by resistance heating, induction heating, etc., raise the vapor pressure,
Preferably, it is deposited on the surface of the substrate at 0.1 mTorr (about 0.01 Pa) or less. At this time, a gas such as argon may be introduced at a pressure of 0.1 mTorr (about 0.01 Pa) or more to cause high frequency or direct current glow discharge.

As the sputtering method, a DC magnetron sputtering method, an rf magnetron sputtering method, an ion beam sputtering method, an ECR sputtering method, a conventional rf sputtering method, a conventional DC sputtering method, or the like can be used. In the sputtering method, a silver plate-shaped target may be used as a raw material, and helium, neon, argon, krypton, xenon, or the like may be used as a sputtering gas, but argon is preferably used. The purity of the gas is
It is preferably at least 99%, more preferably at least 99.5%.

The thickness of the silver thin film layer is 70 nm to 300 nm.
Is more preferable, and more preferably 100 nm to 200 nm. If the thickness is much smaller than 70 nm, the thickness of silver is not sufficient, so that there is transmitted light and the reflectance is lowered. On the other hand, if the film thickness exceeds 300 nm and is too thick, the reflectance does not increase, a saturation tendency is exhibited, and the adhesion of the silver layer to the polyolefin-based film decreases, which is not preferable. For the silver thin film layer, gold, which does not affect the performance,
Metal impurities such as copper, nickel, iron, cobalt, tungsten, molybdenum, tantalum, chromium, indium, manganese, titanium and aluminum may be contained.

In the present invention, a polyolefin film and
An amorphous ITO thin film layer is formed between the silver thin film layers. IT
O is an oxide of indium and tin (Indium Tin Oxide)
And is a kind of transparent conductive film. Other transparent conductive films
As a thin metal film such as gold, silver, platinum, palladium,
Half oxide such as indium oxide, stannic oxide, zinc oxide
Conductor thin film, multilayer thin film made of metal oxide and metal (Example
For example, there are indium oxide / silver / indium oxide).
Among these, ITO is particularly excellent in conductivity and transparency,
Furthermore, the pattern of electrodes can be formed by etching.
Widely used because of its features such as easy
You. The resistivity of the ITO film is usually 5 × 10 ^-Five~ 1 × 10
^-3Ω · cm, transmittance is 80 to 90%.

The amorphous ITO thin film means that it is crystalline in the X-ray diffraction pattern by the θ-2θ method.
It does not show the In ₂ O ₃ (222) peak at θ = 30 ° to 31 ° and the In ₂ O ₃ (400) peak at 2θ = 35 ° to 36 °. FIG. 3 shows an example of amorphous ITO and crystalline ITO patterns. In the amorphous ITO, peaks (222) and (400) observed in crystalline ITO are not seen.

The content of tin oxide in the amorphous ITO thin film layer is preferably 10 to 50% by weight. If the amount is less than 10% by weight, the crystal structure of indium oxide tends to be obtained and the indium oxide does not become amorphous. If it is much more than 50% by weight,
This time, it becomes easy to take the crystal structure of tin oxide and it does not become amorphous.

As a method for forming the amorphous ITO thin film layer, a dry method can be mentioned. As a raw material, there are a method of using a metal of indium and tin and oxidizing it during film formation, and a method of using an oxide of indium and tin from the beginning. The former is generally called a reactive film forming method. For example, in the reactive sputtering method, a target made of indium and tin is used as a raw material, argon is used as a sputtering gas, and oxygen is used as a reactive gas. When a sintered body target of indium oxide and tin oxide is used as a raw material, argon is used as a sputtering gas and a small amount of oxygen gas is used as a reactive gas to supplement oxygen lost during sputtering. The purity of the gas used is preferably 99% or more, more preferably 99.5% or more.

The specific resistance value of the ITO thin film changes depending on the oxygen concentration. By a DC magnetron sputtering method, a sintered body of indium oxide and tin oxide (composition ratio In ₂
O ₃ : SnO ₂ = 80: 20 wt%) is used, and the relationship between the specific resistance value of the ITO thin film and the oxygen concentration is shown in FIG. 4 when the total pressure of argon and oxygen is 266 mPas. The graph is convex downward, and it can be seen that there is an optimum value at which the specific resistance becomes the lowest.

In the present invention, the high-concentration oxygen atmosphere means
It is an atmosphere containing more oxygen than the argon / oxygen partial pressure ratio at which the specific resistance of the ITO thin film becomes the minimum. In FIG. 4, it means that the oxygen concentration is in the range of about 1.5% or more. The relationship between the specific resistance of the ITO thin film and the oxygen partial pressure ratio during film formation differs depending on the density of the target used, the composition ratio of indium oxide and tin oxide, the film formation rate, and the like. Specific resistance is 1 × 10 ^-2 Ω
-The oxygen partial pressure of cm or more can be easily obtained experimentally. When a sintered body of indium oxide and tin oxide is used for the target, it is about 3 to 40%, and when an indium tin alloy is used for the target, it is 40 to 8%.
It is about 0%. In the example shown in FIG. 4, it is about 4% or more. If the specific resistance is much lower than 1 × 10 ⁻² Ω · cm, sufficient adhesion, which is the object of the present invention, cannot be obtained between the polyolefin film and the silver thin film layer. In addition, even if the oxygen concentration is other than in a high oxygen atmosphere, sufficient adhesion cannot be obtained.

The thickness of the amorphous ITO thin film layer is 1 nm to 2 nm.
00 nm is preferable, and more preferably 10 nm to 100
nm. If the thickness is less than 1 nm, the adhesion between the polyolefin film and the silver thin film layer cannot be sufficiently improved. On the other hand, if the film thickness is excessively thicker than 200 nm, the reflectance as a reflector is lowered due to absorption by the amorphous ITO thin film layer, and the adhesiveness to the polyolefin film is lowered, which is not preferable. Note that optimizing the film thickness by optical calculation is a routine procedure for those skilled in the art.

In the present invention, the film thickness can be measured by a stylus roughness meter, a repetitive reflection interferometer, a microbalance, a crystal oscillator method, etc., but the crystal oscillator method can measure the film thickness during film formation. It is suitable for obtaining a desired film thickness. There is also a method in which the conditions for film formation are determined in advance, a film is formed on a sample substrate, the relationship between the film formation time and the film thickness is examined, and the film is controlled by the film formation time. Further, between the amorphous ITO thin film layer and the silver thin film layer, Ti having a film thickness of about 0.1 to 5 nm,
The use of a trace amount metal layer of W, Cu, V, Zn or the like is preferable for suppressing the photodegradation of the silver thin film layer.

Further, after forming the silver thin film layer, for the purpose of further protecting the silver thin film layer and improving the slipperiness of the film,
It is understood by those skilled in the art that it is effective to stack a metal layer of a single metal or alloy such as Inconel, chromium, nickel, titanium, aluminum, molybdenum, and tungsten in a thickness of 10 nm to 30 nm. In addition,
When the amorphous ITO thin film layer is provided on the film, the film surface may be subjected to corona discharge treatment, glow discharge treatment, surface chemical treatment, surface roughening treatment, etc. It will be a conventional means used by those skilled in the art as a means for improving the adhesion of the.

The reflectance of the thus-produced reflector is preferably 90% or more, more preferably 92% or more, and further preferably 94% or more. In the present invention, the reflectance is a value for light having a wavelength of 550 nm.

In the present invention, the peel strength is an index showing the adhesive force between the polyolefin film and the amorphous ITO thin film layer or the silver thin film layer, and is necessary for peeling the formed thin film from the polyolefin film. Power. The measuring method is as follows. First, a thin film side of a polyolefin-based film having a width of X cm is adhered to a flat hard substrate (metal plate or the like) with an adhesive. Next, after the adhesive has dried sufficiently, the polyolefin film is vertically (9
0 °). The force required at this time is divided by the film width X cm to obtain the adhesive force per unit width (g / cm), which is the peel strength. At this time, note that the adhesive strength of the adhesive used is greater than the adhesive strength between the polyolefin film and the thin film layer. Further, the peeling surface at this time is between the olefin film and the amorphous ITO thin film layer,
It is possible that the space between the amorphous ITO thin film layer and the silver thin film layer is
Here, it is more important that the peel strength obtained by the above method has a practically sufficient value, rather than where the peeling surface is. Practically necessary adhesion is 1 at 90 ° peel strength
It is 00 g / cm, preferably 300 g / cm, and more preferably 600 g / cm. 100 g /
If it does not reach cm, the silver thin film layer is easily peeled off.

In the reflector of the present invention, a transparent protective layer may be provided on the polyolefin film opposite to the silver thin film layer. With such a protective layer, the influence of external environmental factors such as surface hardness, light resistance, gas resistance and water resistance of the reflection sheet can be further suppressed. Examples of substances that can be used to form such a protective layer include, for example, acrylic resins such as polymethylmethacrylate, polyacrylonitrile resins, polymethacrylonitrile resins, silicon resins such as polymers obtained from ethyl silicate, and polyesters. In addition to organic substances such as resins and fluororesins, inorganic substances such as silicon oxide, zinc oxide, and titanium oxide are useful, and especially 4
It is preferable to stack a layer capable of cutting light having a wavelength of 00 nm or less, preferably 380 nm or less, to 10% or less in order to prevent photodegradation (ultraviolet ray deterioration) of the silver layer.

Examples of the method for forming the transparent protective layer include existing methods such as coating and laminating films. In addition, the thickness of the transparent protective layer is required to exhibit a protective effect within a range that does not reduce the light reflectivity and does not impair the flexibility. Can be

[0030]

The present invention will be described below with reference to examples. The reflectance, peel strength, specific resistance, and crystallinity in the examples and comparative examples were evaluated by the following methods. 1) Reflectance The reflectance was measured by installing a 150φ integrating sphere on a Hitachi automatic recording spectrophotometer (U-3400). 2) Peel strength Peel strength is Toyo Seiki Seisakusho Strograph M50
It measured using. The pulling angle was 90 °, the pulling speed was 50 mm / min, and the sample width was 1 cm. 3) Specific resistance The specific resistance r [Ω · cm] was obtained by the product of the sheet resistance R [Ω / □] and the film thickness t [cm], r = R × t. The sheet resistance value was determined by the 4-terminal method, and the film thickness was determined by a stylus roughness meter. 4) Crystallinity Crystallinity is determined by taking an X-ray pattern according to the θ-2θ method and taking 2θ
= 30 ° to 31 ° In ₂ O ₃ (222) peak and 2θ = 35 ° to 36 ° In ₂ O ₃ (400) peak.

Example 1 Indium oxide and tin oxide (composition) were formed on a polypropylene film (manufactured by Toray Industries, Inc., polypropylene film, 2570 type, thickness 25 μm, total light transmittance = 92%) by DC magnetron sputtering. The target is a sintered body having a ratio of In ₂ O ₃ : SnO ₂ = 80: 20 WT%, argon of 99.5% purity is used as a sputtering gas, oxygen of 99.5% purity is used as a reactive gas, and ITO is formed into a film thickness. It was formed to have a thickness of 70 nm. At this time, the oxygen partial pressure is 13.3 m with respect to the total pressure of 266 mPa.
Pa (oxygen concentration 5%) was used to create a high oxygen concentration atmosphere. The film was taken out from the sputtering apparatus, and the specific resistance of the ITO thin film was measured and found to be 4.5 × 10 ^-2 Ω · cm. The crystallinity was examined by X-ray diffractometry and it was found to be amorphous. The above operation was repeated to form ITO on the polypropylene film, and this time, without taking it out from the vacuum apparatus, targeting 99.9% pure silver,
Using 9.5% argon as a sputtering gas, silver was further laminated to a thickness of 150 nm. When the reflectance of the obtained reflector was measured from the polypropylene film side, the reflectance was 9
It was 5.3%. When the peel strength was measured, it was 50
It was 0 g / cm.

[Example 2] A methylpentene copolymer film (manufactured by Mitsui Petrochemical Industry Co., Ltd., TPX) was used as the film.
Film, X-22 type, thickness = 30 μm, total light transmittance = 94%), and oxygen partial pressure is 21.3 mPa
A reflector was produced in the same manner as in Example 1 except that the oxygen concentration was 8%. The resistivity of ITO thin film is 8.9 × 10 ^-2
Ω · cm, and was amorphous. When the obtained reflector was measured from the methylpentene copolymer film side, the reflectance was 95.6%. The peel strength was measured and found to be 550 g / cm.

COMPARATIVE EXAMPLE 1 A polypropylene film (manufactured by Toray Industries, Inc., polypropylene film, 2570 type, thickness of 25 μm, total light transmittance = 92%) was coated on a polypropylene film by DC magnetron sputtering to obtain silver having a purity of 99.9%. Was used as a target, and argon having a purity of 99.5% was used as a sputtering gas to deposit silver to a thickness of 150 nm. When the reflectance of the obtained reflector was measured from the polypropylene film side,
The reflectance was 95.8%. The peel strength was measured and found to be 75 g / cm.

[Comparative Example 2] A methylpentene copolymer film (TPX manufactured by Mitsui Petrochemical Co., Ltd.) was used as a film.
A reflector was prepared in the same manner as in Comparative Example 1 except that a film, X-22 type, thickness = 30 μm, total light transmittance = 94%) was used. When the obtained reflector was measured from the methylpentene copolymer film side, the reflectance was 9
It was 5.5%. When the peel strength was measured, it was 65
It was g / cm.

Comparative Example 3 A reflector was prepared in the same manner as in Example 1 except that the oxygen partial pressure was 4.0 mPa (oxygen concentration 1.5%). When the specific resistance of the ITO thin film was determined, it was 1.0 × 10 ⁻³ Ω · cm. The crystallinity was examined by X-ray diffractometry and it was found to be amorphous. When the reflectance of the obtained reflector was measured from the polypropylene film side, the reflectance was 95.2%. The peel strength was measured and found to be 80 g / cm.

Comparative Example 4 IT was carried out in the same manner as in Example 1 except that the oxygen partial pressure was set to 104 mPa (oxygen concentration 39%).
An O thin film was prepared. This ITO thin film was subsequently heat-treated in vacuum at 120 ° C. for 10 hours. The specific resistance of the ITO thin film was determined to be 5.6 × 10 ⁻³ Ω · cm. Further, when the crystallinity was examined by an X-ray diffraction method, it was crystalline. The above operation is repeated to form ITO on the polypropylene film and heat-treat it. This time, without taking it out from the vacuum apparatus, the target is silver with a purity of 99.9%, the argon with a purity of 99.5% is used as the sputtering gas, and Silver was laminated to a thickness of 150 nm. When the reflectance of the obtained reflector was measured from the polypropylene film side, the reflectance =
It was 95.0%. When peel strength was measured, it was 4
It was 6 g / cm. Table 1 summarizes the above results.

[0037]

[Table 1]

[0038]

EFFECT OF THE INVENTION Amorphous ITO having a resistivity of 1 × 10 ⁻² Ω · cm or more formed by sputtering in a high oxygen concentration atmosphere between the polyolefin film (A) and the silver thin film layer (C). By using the thin film layer (B), practically sufficient adhesive force was obtained between the (A) and (B).
This makes it possible to provide a reflector having excellent electrical characteristics and a reflectance of 90% or more.

[Brief description of drawings]

FIG. 1 is a structural sectional view of a reflector of the present invention.

FIG. 2 is a structural sectional view of a reflector of the present invention.

FIG. 3 X-ray analysis pattern of amorphous and crystalline ITO

FIG. 4 is a graph showing the relationship between the specific resistance value of the ITO thin film and the oxygen concentration.

[Explanation of symbols]

 10 Polyolefin film 20 Amorphous ITO thin film layer 30 Silver thin film layer 40 Adhesive layer 50 Metal plate or polymer sheet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C23C 14/08 C23C 14/08 ND G02F 1/1335 530 G02F 1/1335 530 (72) Inventor Nobuhiro Fukuda 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. Reflection having a reflection surface on the polyolefin film side or the silver thin film layer side of ABC having at least a polyolefin film (A), an amorphous ITO thin film layer (B) and a silver thin film layer (C). As a body, the peel strength between the polyolefin film (A) and the silver thin film layer (C) is 100 g / cm or more, and the reflectance at a wavelength of 550 nm measured from the reflecting surface side is 90% or more. Reflector. 2. The reflection according to claim 1, wherein the amorphous ITO thin film layer (B) is an ITO thin film having a specific resistance of 1 × 10 ⁻² Ω · cm or more formed by sputtering in a high oxygen concentration atmosphere. body. 3. The reflector according to claim 1, wherein the content of tin oxide in the amorphous ITO thin film layer (B) is 10 to 50% by weight.