JPH0732537A - Reflective sheet - Google Patents

Abstract

PURPOSE:To provide a reflective sheet which is compact and light-weight, and has excellent impact resistance and flexibility by laminating a flexible substrate with a high reflective layer on one surface, and a flexible polymer film by an adhesive layer. CONSTITUTION:For a reflective sheet, a high reflective layer 2 is formed on a flexible substrate 1 to substantially shut out an ultraviolet ray of which the light transmittance at a wave length of 380-300nm is 10% or lower, to make a flexible substrate 5 on which a high reflective layer is formed. The reflective sheet is made by bonding the high reflective layer side of the substrate 5 and a flexible polymer film 4 by an adhesive layer 3. Also, on one surface of the flexible substrate 1, a thin film containing silver, of which the visible light reflection factor is 80% or higher, is formed as a high reflective layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflecting sheet using a light reflecting film having a flexible substrate such as a plastic film as a base material and a metal thin film having a high reflectance laminated thereon. The reflection sheet according to the present invention can be suitably used for a mirror, a reflection mirror inside an electronic device, and a lamp house for a fluorescent lamp in a backlight of a liquid crystal display device.

[0002]

2. Description of the Related Art A light reflecting film using a flexible substrate such as a plastic film is lighter in weight, excellent in impact resistance and more flexible than a glass-based mirror. This light reflection film is processed by laminating it to an aluminum plate, etc., and then used as a reflection plate for copiers, solar heat collectors, light reflection plates for plant factories, high light reflection plates for fluorescent lamps, and backlights for liquid crystal display devices. Its use is expanding as a reflector for automobiles. In recent years, a reflection sheet has been used as a lamp house for a backlight in response to a demand for thinner, smaller and lighter liquid crystal display devices.

A reflective sheet having a silver thin film layer formed on a general-purpose plastic film has a high reflectance in the initial stage of use. However, when the inventors of the present invention evaluated it by continuously using it as a lamp house of a liquid crystal backlight, a decrease in brightness was recognized after several hundred hours, and continuous use for about 2,000 hours was observed. Therefore, it was found that the brightness sharply decreased. When the present inventors were pursuing the cause, heat, environmental factors such as light, the reflectance of the reflection sheet is remarkably reduced by the ultraviolet rays from the fluorescent lamp in particular, and the function as the lamp house of the backlight is satisfied. It has been found that there is a technical problem of disappearing.

[0004]

The object of the present invention is a reflecting sheet having a small size, a light weight, impact resistance and flexibility, and the reflecting sheet has a high reflection. The reflective sheet has a high reflectance and does not decrease in reflectance due to environmental factors such as heat and light.

[0005]

DISCLOSURE OF THE INVENTION As a result of earnest studies to achieve this object, the present inventors have found that wavelengths of 380 to 300n
The present invention has been completed by discovering that the problem can be solved by forming a highly reflective layer containing silver on one surface of a flexible substrate that substantially blocks ultraviolet rays having a light transmittance of 10% or less in m. is there.

According to the present invention, silver or a highly reflective layer containing silver is formed on one surface of a flexible substrate which has a light transmittance of 10% or less at a wavelength of 380 to 300 nm and which substantially blocks ultraviolet rays. A flexible reflective sheet having a flexible polymer film provided on it through an adhesive layer, and the visible light reflectance of a flexible substrate having a highly reflective layer is 80%. A flexible reflection sheet which is the above, and which further comprises a flexible substrate which forms a high reflection layer and which substantially blocks the ultraviolet rays, and an adhesive layer which adheres the flexible polymer film. A reflective sheet having an adhesive strength of 100 g / cm or more and an adhesive layer thickness of 0.5 μm or more and 50 μm or less.

The flexible substrate used in the reflective sheet of the present invention is a substrate that substantially blocks ultraviolet rays, and is 380.
A flexible substrate having a light transmittance of 10% or less at a wavelength of 300 nm. According to the present invention, durability against light, heat, etc. is remarkably improved, and reliability as a reflection sheet is remarkably improved. Further, the reflection sheet of the present invention is lightweight, has excellent impact resistance, is flexible, and is used as a mirror, as well as a reflection sheet for power saving of a plant factory, an energy-saving type high reflection sheet. It is also effectively used for fluorescent lamps and high-brightness reflective sheets for liquid crystal display backlights.

The reflection sheet of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the reflective sheet of the present invention has a highly reflective layer 2 formed on a flexible substrate 1 that substantially blocks ultraviolet rays having a light transmittance of 10% or less at a wavelength of 380 to 300 nm. A reflective sheet manufactured by using a flexible substrate 5 having a highly reflective layer formed thereon, and bonding the highly reflective layer side of the substrate 5 and the flexible polymer film 4 via an adhesive layer 3.

The flexible substrate having the highly reflective layer used in the present invention is a substrate that substantially blocks ultraviolet rays, and preferably has a transmittance of light having a wavelength of 380 to 300 nm of 10% or less. And a thin film containing silver having a visible light reflectance of 80% or more is formed as a highly reflective layer on one surface of the flexible substrate. This flexible substrate has a light transmittance of 70% at a wavelength of 550 nm.
Or more, preferably 80% or more, and desirably 3
It is desirable that the light transmittance of 80 to 300 nm is 10% or less, preferably 1% or less. As such a flexible substrate, a film or sheet made of a homopolymer or a copolymer, a plastic film or sheet mixed with an ultraviolet absorber, an ultraviolet absorber or an ultraviolet ray such as zinc oxide is cut. It is a plastic film or sheet on which a layer for forming is formed.

Examples of preferred flexible substrates include biaxially oriented polypropylene containing an ultraviolet absorber, polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polybutylene terephthalate. To (P
BT), an acrylic resin containing an ultraviolet absorber, the same methacrylic resin, and polyether ether ketone (PEE)
K), polyarylates, polyetherimides, homopolymers or copolymers such as polyimide.
Particularly preferably, PET containing an ultraviolet absorber is preferably used. The thickness of these flexible substrates is preferably thin from the viewpoint of cost reduction of the reflective sheet or productivity in forming the reflective layer, and from the winding property (handling property) in forming the reflective layer, A thicker layer is easier to handle. The thickness of the film is preferably 5 μm or more, more preferably 20 μm or more, and preferably 250 μm or less.

In the present invention, the silver or highly reflective layer containing silver is formed on one surface of the flexible substrate as described above. The method for forming such a silver or thin film layer containing silver is as follows. A plating method, a vacuum deposition method, a sputtering method, an ion plating method, an ionization deposition method, an ion cluster-beam deposition method or the like can be used.

The thickness of the thin film layer containing silver is 20 to 500 n.
m is preferable, and is 5 for cost reduction and high reflectance.
0 to 200 nm is more preferable. More preferably 80
~ 150 nm is desirable. It is an object of the present invention that the thin film layer containing silver contains a trace amount of another metal and a metal compound, and that the thin film layer containing silver and two or more thin film layers of other metal are laminated to form a reflective layer. It is possible within the range where it is not damaged. It is also possible to form an anticorrosive metal layer of Ti, Cr, Ni or the like on the outermost layer of the high reflection layer.

In the present invention, a flexible polymer film is further provided thereon via an adhesive layer. Examples of the flexible polymer film include biaxially oriented polypropylene and polyethylene terephthalate (PET). , Polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), acrylic resins, methacrylic resins, polyether ether ketones (PEEK), polyarylates, polyetherimides, homopolymers such as polyimide, or Copolymers can be mentioned. A polyethylene terephthalate film is particularly preferable, and a film having a white appearance is preferable. Further, the thickness of these flexible polymer films is preferably thin from the viewpoint of cost reduction and easiness of bending, and from the viewpoint of handling (handling property) and shape retention when laminating with a reflective layer, thicker one is preferable. good. A preferable film thickness is 5 μm to 500 μm.
m, more preferably 10 μm to 200 μm, 15
μm to 100 μm is preferable.

The adhesive used in the present invention is an adhesive which is adhered with the aid of heat or a catalyst, and specific examples include a silicone adhesive, a polyester thermosetting adhesive, an epoxy adhesive, A general adhesive such as a polyurethane adhesive, a cyanoacrylate adhesive, or a hot melt adhesive can be used. The thickness of the adhesive is not particularly limited, but is usually 0.5 μm to 50 μm, preferably 1 μm to 20 μm. The adhesion strength between the flexible substrate on which the highly reflective layer formed of this adhesive is formed and the flexible polymer film is 1 measured by 180 degree peel strength.
It is desirable that the amount is 00 g / cm or more. If the adhesion strength is not reached, the lamp house has a radius of curvature of 1 to 5
When bent to about mm, the flexible substrate may be lifted from the flexible polymer film, causing deformation.

In the reflection sheet of the present invention, a transparent protective layer may be provided on the flexible substrate opposite to the high reflection layer. By such a protective layer, the surface hardness of the reflection sheet, light resistance,
The influence of external environmental factors such as gas resistance and water resistance 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, In addition to organic substances such as polyester resin and fluororesin, inorganic substances such as silicon oxide, zinc oxide, and titanium oxide are useful, and particularly have the ability to cut light with a wavelength of 400 nm or less, preferably 380 nm or less to 10% or less. It is preferable to stack the layers having the same in order to prevent photodegradation (ultraviolet ray deterioration) of the silver layer, which is one of the objects of the present invention. Examples of the method for forming the transparent protective layer include existing methods such as coating and film laminating. Further, the thickness of the transparent protective layer depends on the material and the application thereof so that the transparent protective layer exerts a protective effect within a range that does not lower the light reflectivity which is the object of the present invention and does not impair flexibility. It is used after being changed appropriately. Hereinafter, an example of an embodiment of the present invention will be described with reference to examples.

[0016]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Moreover, the measurement of each physical property was performed by the following method. Light transmittance (%) In order to evaluate the light transmittance, the spectral transmittance was measured with a spectrophotometer (U-3400, manufactured by Hitachi, Ltd.). Light reflectance (%) In order to evaluate the light reflectance, 150
A φ integrating sphere accessory was attached and the spectral reflectance was measured. Adhesion strength In order to evaluate the adhesion strength between the flexible substrate and the flexible polymer film after the completion of adhesion, a flexible substrate with a width of 1 cm was measured by a universal testing machine (Strograph) manufactured by Toyo Seiki Seisakusho. The peel strength with the flexible polymer film was measured. UV degradation accelerated test Qpanel is used to evaluate the UV degradation accelerated test.
UV-A light was irradiated at a substrate temperature of 50 ° C. by QUV manufactured by the same company, and the change in reflectance was measured, and the time required for the reflectance at 600 nm to become 80% or less was measured.

Example 1 A biaxially stretched polyethylene terephthalate film having a thickness of 25 μm provided with an acrylic hard coat layer (5 μm) which substantially blocks ultraviolet rays containing a benzotriazole type ultraviolet absorber was subjected to direct current magnetron sputtering. A silver thin film layer having a film thickness of 100 nm was formed. Table 1 shows the light transmittances at wavelengths of 380, 350, and 300 nm before forming the silver thin film layer. Biaxially stretched P on which the silver thin film is formed
ET film and white polyethylene terephthalate film with a thickness of 50 μm (PET film (trade name) manufactured by Toray)
E-20) is a melamine cross-linked polyester resin (Mitsui Toatsu Chemicals, Inc., Almatex (trade name) P647B).
It laminated | stacked using C) and produced the light reflection sheet.

The adhesive strength at this time was 500 g / cm. The thickness of the adhesive was about 10 μm. An ultraviolet ray deterioration-promoting test of this light reflection sheet (specifically, the reflection sheet is irradiated with light having a wavelength of 400 to 315 nm of ultraviolet light), and the reflectance of incident light having a wavelength of 600 nm becomes 80% of the initial value. The time until it became was measured as the deterioration time.
Table 2 shows the results and the reflectance before the ultraviolet deterioration accelerating test. The reflection sheet showed almost no change in reflectance even after 5000 hours had passed, and the deterioration time was 5,000 hours or more, which was excellent durability.

Example 2 Tetoron HB (trademark) film made by Teijin Ltd., which is a polyethylene terephthalate film which substantially blocks ultraviolet rays containing an ultraviolet absorber containing an ultraviolet absorber, was prepared in the same manner as in Example 1 by the same method. A 100 nm thick silver thin film is formed, and a biaxially oriented polypropylene film having a thickness of 35 μm (foamed white OPP film (trade name) YP-2 manufactured by Toray Industries, Inc.
2) was laminated with an epoxy adhesive to prepare a light reflecting sheet. 38 before forming the silver thin film layer
The light transmittances at wavelengths of 0, 350 and 300 nm are shown in Table 1.
Shown in.

The adhesion strength between the film and the support at this time was 400 g / cm. The thickness of the adhesive is about 15
was μm. By the same method as in Example 1, an ultraviolet ray deterioration-promoting test was performed, and the deterioration time until the reflectance of incident light with a wavelength of 600 nm reached 80% of the initial value was measured. Table 2 shows the results and the reflectance before the test. Similar to Example 1, this light reflecting sheet had excellent reflectance and durability.

Comparative Example 1 A 25 μm-thick biaxially stretched PET film having no ordinary ultraviolet ray absorbing ability was mixed with a 25 μm-thick expanded white polyethylene terephthalate film (TOYOBO (trademark) Crisper) and a polyurethane adhesive. A light reflection sheet was produced by using the laminate. 38 of PET film
The light transmittances at wavelengths of 0, 350 and 300 nm are shown in Table 1.
Shown in. The adhesive strength at this time was 600 g / cm. The thickness of the adhesive was about 10 μm.

An ultraviolet ray deterioration-promoting test was conducted in the same manner as in Example 1, and the time until the reflectance of incident light having a wavelength of 600 nm reached 80% of the initial value was measured as the deterioration time.
Table 2 shows the results and the reflectance before the test. This reflective sheet changes color to reddish purple when irradiated with ultraviolet rays for 100 hours, and the reflectance is 8% of the initial value when irradiated with ultraviolet rays for 400 hours.
It decreased to 0%, and it was found that the durability against ultraviolet rays was extremely poor.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

EFFECTS OF THE INVENTION By laminating a flexible substrate having a highly reflective layer on one side and a flexible polymer film via an adhesive layer, it is lightweight and compact, and has impact resistance and flexibility. An excellent reflection sheet can be created. In addition, since the durability against light, heat, etc. is improved, the reliability as a reflection sheet is significantly improved. INDUSTRIAL APPLICABILITY The reflection sheet of the present invention is lightweight, has excellent impact resistance, is flexible, and is used as a mirror as well as a reflection sheet for power saving of a plant factory, and an energy-saving type high reflection fluorescent lamp Also, it is effectively used as a high-brightness reflective sheet of a backlight for liquid crystal display panels.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a reflection sheet of the present invention.

[Explanation of symbols]

1 The light transmittance at a wavelength of 380 to 300 nm is 10
% Or less flexible substrate 2 highly reflective layer containing silver or silver 3 adhesive layer 4 flexible polymer film 5 flexible substrate having a highly reflective layer formed thereon

Claims (3)

[Claims] 1. A highly reflective layer containing silver or silver is formed on one surface of a flexible substrate which has a light transmittance of 10% or less at a wavelength of 380 to 300 nm and which substantially blocks ultraviolet rays. A flexible reflective sheet having a flexible polymer film provided on the upper surface thereof with an adhesive layer interposed therebetween. 2. The flexible reflective sheet according to claim 1, wherein the flexible substrate having the highly reflective layer has a visible light reflectance of 80% or more. 3. A flexible substrate having a high reflection layer formed thereon, which substantially blocks ultraviolet rays, and an adhesive layer for bonding the flexible polymer film have an adhesive strength of 100 g / cm or more. The flexible reflecting sheet according to claim 1, wherein the layer thickness is 0.5 μm or more and 50 μm or less.