JP5095937B2 - Reflective adhesive tape - Google Patents

Description

  The present invention relates to a reflective adhesive tape, and more particularly to a reflective adhesive tape suitably used for a backlight light source of a liquid crystal display or a display body. In particular, it can be used for a backlight unit having a thickness of 1 cm or less used for a thin panel using a light source such as an LED or a cold cathode tube such as a mobile phone or a PDA.

  In recent years, reflecting materials have been used in various fields, and in particular, many of them are used as one of main components of liquid crystal display devices such as mobile phones, personal computers, and televisions. Among them, it is important for liquid crystal display devices used in portable devices to be able to increase brightness, reduce thickness, save power, and reduce weight, and supply limited light sources to the liquid crystal part as efficiently as possible. Therefore, there is a demand for a reflective material that has high reflection efficiency and high brightness. Under such circumstances, it has been proposed to use a reflective adhesive tape that is used for fixing various components and is effective in efficiently using a light source, and has good light reflectivity on at least one surface.

  Conventionally, as a base material of a highly reflective adhesive tape, a metal plate such as a metal plate made by bonding a reflective sheet having a metal thin film layer mainly composed of silver to the surface of a metal plate or a white pigment coated A white polyethylene terephthalate sheet is used as a reflection sheet (see, for example, Patent Documents 1 and 2). In addition to a polyethylene terephthalate sheet, a polyolefin-based reflective sheet has also been reported (see Patent Document 3). As a material of the reflective adhesive tape, a reflective adhesive tape provided with an adhesive layer using a white resin film, a metal film, various films provided with a metal thin film layer, or the like as a base material has been used.

In addition, some reflective sheets comprising a sheet having fine bubbles, a porous sheet containing a specific amount of inorganic filler, and a laminated sheet thereof have been reported. (For example, refer to Patent Documents 4, 5, and 6) This realizes more excellent light reflectivity by including a large number of reflection layers not only on the surface of the reflection sheet but also inside thereof. Moreover, a reflective adhesive tape having high light reflectivity while being thin by forming an adhesive layer containing a fluorescent brightening agent on the reflective surface of a white polyethylene terephthalate sheet has also been reported (Patent Document 7). ). However, in the invention described in the above-mentioned patent document, it is necessary to increase the thickness of the sheet itself, to increase the number of bubbles, or to increase the number of inorganic fillers in order to further improve the reflection characteristics as the reflection sheet. As a result, since the mechanical strength is reduced, it is difficult to reduce the thickness of the film, and the detachment of the inorganic filler becomes obvious, which may cause a serious problem as foreign matter is generated by the end user. In addition, when metal is used, there are problems such as troubles caused by defective electrical signals in overcrowded display devices. So far, while having high reflection characteristics, thinning, retention of mechanical characteristics, inorganic A reflection sheet that satisfies all of the prevention of detachment of the filler is desired.
JP-A-2-13925 JP 59-8882 A Japanese Utility Model Publication No. 57-60119 Japanese Patent Laid-Open No. 7-230004 JP 2002-09881 A Japanese Utility Model Publication No. 2003-136619 JP 2004-231737 A

  An object of the present invention is to solve the above-mentioned problems and to obtain a reflective adhesive tape that is excellent in thinning while having high reflection characteristics.

The present invention is as follows.
[1] the inorganic particles and the porous sheet is at least 5 dl / g porosity consists the intrinsic viscosity having a Lupo Riechiren of 50 to 85% adhesive layer provided on one or both sides of the porous sheet A reflective adhesive tape having a reflectance of 80% or more at a wavelength of 550 nm, wherein the porous sheet comprises 80% of the inorganic particles in a weight percentage based on the total amount of the inorganic particles and the polyethylene. A reflective adhesive tape containing ~ 92% and having a thickness of 7 to 80 µm.
[ 2 ] The reflective adhesive tape as described above, wherein the porous sheet is stretched in at least one axial direction.
[ 3 ] The reflective adhesive tape as described above, wherein a base sheet is bonded to at least one surface of the porous sheet.
[ 4 ] The reflective adhesive tape as described above, wherein the base sheet is made of a thermoplastic resin.
[ 5 ] The reflective adhesive tape as described above, wherein the thermoplastic resin is polyester or polyolefin.

  The reflective adhesive tape of the present invention has an excellent characteristic of high reflection while being an unprecedented thin film. Therefore, it can be suitably used as a highly reflective adhesive tape, particularly by being attached to a component in a small and medium liquid crystal display device such as a mobile phone or a notebook personal computer.

Hereinafter, the present invention will be described in detail.
[Porous sheet]
The porous sheet in the present invention is made of a thermoplastic resin containing inorganic particles, and has a space (void) in which a large number of pores are connected. Such a porous sheet has good reflection characteristics by having such voids. The porosity is 50 to 85%, preferably 55 to 80%.

  Examples of the inorganic particles include calcium carbonate, barium sulfate, barium titanate, titanium oxide, talc, clay, silica, and aluminosilicate. It is preferable to apply inorganic particles from the viewpoint of reflection efficiency, cost, and disposal of the sheet. Among them, calcium carbonate, barium sulfate, titanium oxide, silica, and aluminosilicate are particularly preferable.

  As the shape of the particles, a spherical shape, a plate shape, a flat shape, or the like can be used. This is because, in particular, in the case of a plate shape or a flat shape, when the stretching is performed, the surface direction of the particles is arranged relatively in parallel with the layered structure in the sheet, and the effect of assisting the reflection of light is easily exhibited.

  The inorganic particles preferably have an average particle size of 0.01 to 10 μm. If the average particle size is less than 0.01 μm, the reflection performance is lacking, which is not preferable. On the other hand, if the thickness exceeds 10 μm, tearing occurs during the production of the sheet, resulting in a decrease in productivity and an increase in the diffuse reflection component, resulting in a reflection characteristic equal to or lower than that of a conventional white film.

The porous sheet contains 80 to 92% of the particles and 8 to 20% of the thermoplastic resin in a weight percentage based on the total amount of the particles and the thermoplastic resin. If such particles content is high particle content of from 9 6% may issue in mechanical strength occurs. On the other hand, when the particle content is less than 50%, the reflection / scattering interface composed of the thermoplastic resin, the air layer, and the particles decreases, so that sufficient reflection characteristics cannot be obtained.

The thermoplastic resin is polyethylene .

The thermoplastic resin having an intrinsic viscosity of substantially at least 5 dl / g (ultra) Ru high molecular weight polyethylene Tona. If it is less than 5 dl / g, the strength of the sheet may be insufficient.

  The porous sheet in the present invention preferably has a specific gravity of 2.0 or less from the viewpoint of weight reduction.

The porous sheet of the present invention is thick Ru der less 80 [mu] m. When the thickness is greater than 80 μm, it hardly contributes to the improvement of reflection characteristics. The lower limit of the thickness is 7 μm. If it is smaller than 7 μm, the reflection characteristics tend to be unstable.

  The porous sheet of the present invention is preferably oriented by stretching in at least one axial direction. By stretching, a layered porous structure is developed. Such a structure increases the reflection interface, and at the same time, its reflection component expresses not only scattering reflection but also regular reflection component, so it contributes to suppressing the glare due to reflection at the same time as reflecting like a mirror. It is thought that.

  Examples of such stretching methods include longitudinal and transverse sequential biaxial stretching, longitudinal and transverse simultaneous biaxial stretching, longitudinal and uniaxial stretching, and lateral uniaxial stretching, and good reflection characteristics are obtained by controlling the directionality and intensity distribution of reflected light. For this purpose, longitudinal and lateral simultaneous biaxial stretching or longitudinal and lateral sequential biaxial stretching is preferable, and longitudinal and lateral sequential biaxial stretching is most preferable in consideration of productivity and cost.

  The porous sheet of the present invention is characterized in that a layered porous structure is formed by one sheet. The number of layers when observed from the cross-sectional direction is preferably at least 5 layers, more preferably 10 layers or more in the thickness direction of the sheet. If the number of layers is less than 5, the intensity of interface reflection is small, and high reflectance cannot be achieved.

  Although there is no restriction | limiting in particular as a manufacturing method of the said porous sheet, It can manufacture by extending | stretching a gelatinization film forming and the obtained gelatinization sheet substantially. For example, an inorganic dielectric powder is dispersed in an appropriate gelling solvent using a milling device or the like, and then a thermoplastic resin as a binder and the remainder of the appropriate gelling solvent are added to the thermoplastic resin. The resin and the solvent are dissolved by heating to form a sol.

  The solubilized composition thus obtained is shaped into a sheet at a temperature equal to or higher than the gelation temperature, and the sheet is rapidly cooled below the gel point to prepare a gelled sheet. This gelled sheet can be produced by stretching uniaxially or biaxially at a temperature equal to or higher than the glass transition point of the resin and then heat-setting. Examples of such a solvent include usually decalin, hexane, paraffin, xylene and the like when polyethylene is used as the thermoplastic resin. Two or more of these may be used in combination. In addition, the drying can be controlled, and the stretching can be performed in a state where the solvent remains to some extent.

If the porous sheet is within the scope of the object of the present invention, a lubricant, a pigment, a dye, an antioxidant, a fluorescent brightener, an antistatic agent, an antibacterial agent, an ultraviolet absorber, and a light stabilizer, if necessary. Additives that impart functionality such as an agent, a heat stabilizer, a light-shielding agent, and a matting agent can be blended.
[Adhesive layer]
The adhesive layer in the present invention is provided on one side or both sides of the porous sheet. The adhesive layer here may be semi-permanently attached to the adherend, but also includes a layer having a function as a so-called adhesive layer that can be peeled off by applying a certain level of force.

  Examples of the adhesive used to form the adhesive layer in the present invention include known acrylic adhesives or pressure-sensitive adhesives, natural rubber-based adhesives or pressure-sensitive adhesives, synthetic rubber-based adhesives or pressure-sensitive adhesives such as styrene- Isoprene block copolymers, styrene-butadiene rubbers, isoprene rubbers, polyisobutylene rubbers, butyl rubbers, vinyl ether adhesives or adhesives, silicone adhesives or adhesives, and the like can be used. Among them, an adhesive or pressure-sensitive adhesive mainly composed of a homopolymer of alkyl (meth) acrylate or a copolymer with other monomer components can be suitably used from the viewpoint of light resistance and heat resistance. Examples thereof include acrylic copolymers such as n-butyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and ethyl acrylate. Furthermore, in order to increase the cohesive strength of the adhesive, it is possible to add a crosslinking agent or to add a tackifying resin in order to improve the adhesive strength of the adhesive. In addition to the above, it is also possible to add known and conventional additives. For example, anti-aging agents, light stabilizers, plasticizers, softeners, fillers, pigments, flame retardants and the like can be added. When the adhesive tape of the present invention is a double-sided adhesive tape, the adhesive agent on the light reflective surface and the other surface may be different.

  As thickness of this contact bonding layer, 1-30 micrometers is preferable, More preferably, it is 2-20 micrometers. If it is less than 1 μm, sufficient adhesion cannot be obtained. On the other hand, when the thickness exceeds 30 μm, the thickness of the reflective adhesive tape is increased, so that it is not suitable for an adhesive tape for fixing a liquid crystal display element which is required to be thin.

The adhesive strength of the adhesive layer is preferably 1 to 15 N / 10 mm, more preferably 2 to 10 N / 10 mm. The measurement method shall conform to JIS Z 0237.
[Reflective adhesive tape]
The reflective adhesive tape of the present invention has a reflectance of 80% or more at a wavelength of 550 nm. When the reflectance is less than 80%, for example, when this reflective adhesive tape is finally used as a substrate for a backlight reflector of a liquid crystal display, sufficient brightness cannot be obtained. Further, if the reflectance is 120%, it has sufficient reflection characteristics, and in order to further increase the reflectance, the weight and bulk of the reflection sheet may be affected, so that the wavelength at 550 nm The reflectance is preferably 82.0% or more, more preferably 85.0% or more, further preferably 90.0% or more, and the upper limit is preferably 120%.

The preferred thickness of the reflective adhesive tape of the present invention is 10 to 100 μm, more preferably 15 to 50 μm. When the thickness is less than 10 μm, it is not preferable because troubles such as deterioration in handling properties when the sheets are bonded to each other occur. On the other hand, when the thickness exceeds 100 μm, it is difficult to meet the recent demand for thinning the reflection film.
[Method for producing reflective adhesive tape]
In the reflective adhesive tape of the present invention, an adhesive layer is formed on at least one surface of the porous sheet.

As a method for forming such an adhesive layer, it can be formed on a porous sheet by a generally used method. For example, the adhesive composition is directly applied to the porous film and dried, or the adhesive composition is once applied on the separator, dried, and then bonded to at least one surface of the porous sheet, and then the separator. The method of peeling off and transferring an adhesive layer on a porous sheet can be mentioned. The latter method is more preferable from the viewpoint of reflectance. As a method for forming the adhesive layer on the separator, a common coating method such as a comma coater method, a gravure method, or the like can be used. This can be selected according to the fluidity of the adhesive. The conditions at the time of application or bonding, such as temperature, pressure, and time, can be adjusted while looking at the type of adhesive and the characteristics of the resulting reflective adhesive sheet.
[Base material sheet]
In the present invention, a substrate sheet is bonded to at least one surface of the porous sheet as necessary for reasons such as improved handling properties. By laminating the base material sheet, mechanical properties that are often insufficient with a porous sheet alone, particularly handling performance during assembly such as insertion or installation in a liquid crystal backlight panel by a user can be improved.

  The base material sheet used for the reflective surface needs to be transparent because it affects the reflection characteristics, but the base material sheet installed on the surface side where the light is incident (sometimes referred to as the reflective surface side) is highly transparent. It is preferable to have a property of 2% or less as haze.

  A thermoplastic resin is preferable as the material of the base sheet. Examples of the thermoplastic resin include polyester and polyolefin.

  As the thickness of the base material sheet, a thinner one is preferable because the entire reflection sheet can be thinned, but a preferable specific range is 4 to 25 μm. If the thickness is less than 4 μm, problems such as handling of the base sheet may occur. In the case of 25 μm or more, depending on the case, it may not be possible to meet the demand for thinning the reflection sheet.

  Also, the base material sheet on the side where the incident light passes through the porous sheet (non-reflective surface side) is excellent in handling property of the base material sheet itself and the reflective sheet. It is desirable to use a superior one. The base material sheet on the non-reflective surface side can be the same as the base material sheet on the reflective surface side. For example, a metal foil made of aluminum or steel can also be used. In addition, the same kind and the same thickness of the base material sheet to bond together are more preferable at the point of dimensional stability. Moreover, it is also possible to adjust thickness with the base material sheet of a non-reflective surface side according to a use.

  As a bonding method when the base sheet is bonded to at least one side of the porous sheet, the adhesive composition is directly applied to the porous sheet and dried, or an adhesive layer is formed on the surface of the base sheet And a method of laminating the porous sheet. As a method for forming the adhesive layer on the substrate sheet, a common coating method such as a comma coater method, a gravure method, or the like can be used. This can be selected according to the fluidity of the adhesive. The nip conditions at the time of bonding, such as temperature, pressure, and time, can be adjusted while looking at the type of adhesive and the characteristics of the reflective sheet. The thickness of the adhesive layer is preferably thinner from the viewpoint of reflection characteristics. The thickness is preferably 10 μm or less, more preferably 5 μm or less. If it exceeds 10 μm, the reflection characteristics, thermal dimensional stability, handling properties, etc. are affected, which is not preferable.

  The adhesive layer can be formed using a general adhesive or double-sided tape. As the adhesive, for example, a modified olefin, polyester, epoxy, urethane, nylon, or acrylic adhesive can be used. Use of an adhesive having excellent transparency is preferable because the reduction in reflection characteristics is small. In addition, the adhesion | attachment described here is an idea of permanent adhesion | attachment, and means that it cannot attach or detach easily.

Hereinafter, although the specific example of this invention is given and demonstrated, this invention is not limited to this.
In addition, the value in an Example was measured with the following method.
(1) Reflectance:
An integrating sphere is attached to a spectrophotometer (trade name “UV-3101PC” manufactured by Shimadzu Corporation), and the reflectance is 400 to 800 nm at a measurement light incident (reflection) angle of 5 ° when the BaSO ₄ white plate is 100%. Measured over time. The reflectance (%) at a wavelength of 550 nm is shown in the following table.
(2) Porosity:
It calculated | required by the following formula | equation from the apparent density (rho) and true density (rho) 0 of the porous sheet measured by the well-known method.

Porosity = (ρ0−ρ) / ρ0 × 100 (%)
(3) Sheet thickness:
After the cross section was taken out by the freezing cleaving method, it was measured in a non-contact manner with a scanning electron microscope or a laser microscope.

[Example 1]
To 20 parts by weight of decalin is added 13 parts by weight of paraffin and 5 parts by weight of ultrahigh molecular weight polyethylene (made by Ticona Co.) having an intrinsic viscosity of 15 dl / g (measured in decalin at 135 ° C.) and 2 parts by weight of a dispersant. 62 parts by weight of titanium (manufactured by Sakai Chemical Co., Ltd.) was dispersed. The dispersion was dissolved at 160 ° C. using a biaxial kneading extruder and extruded at 160 ° C. through a flat film extrusion die. Next, the extruded product was cooled and solidified, and heat-treated at 80 ° C. for 30 minutes. This sheet was stretched 4.5 times in the MD direction at 120 ° C., then 11 times in the TD direction, and heat-set at 130 ° C. Thereafter, it was washed with methylochrome, dried, and heat-set at 120 ° C. to prepare a porous sheet having a thickness of 75 μm, a porosity of 68%, and an inorganic particle content of 90% by weight.

  Next, 8 parts by weight of a rosin resin and 4 parts by weight of an isocyanate crosslinking agent are blended with 100 parts by weight of an acrylic ester copolymer having an average molecular weight of 400,000, and an adhesive having a solid content of 50% is dissolved in toluene. It was adjusted.

  The reflective adhesive tape was prepared by coating the pressure-sensitive adhesive on a separator (polyester film ("Purex") with a thickness of 75 μm so that the thickness after drying would be 9 μm, and drying at 100 ° C. for 1 minute. The adhesive layer was obtained by transferring the adhesive layer onto both sides of the porous sheet and laminating it with a hot roll at 80 ° C. under a pressure of 1 kgf / cm (9.8 N). Was used as a bonding tape between the backlight constituent members in the liquid crystal display device and a bonding tape between the liquid crystal peripheral members, and the visibility of the end portion in the liquid crystal display was good. This reflective adhesive tape has high reflectivity and good handling properties without problems.

[Example 2]
A thinner sheet prepared in Example 1 was prepared with the same composition as in Example 1, and stretched 4.5 times in the MD direction at 120 ° C., then 11 times in the TD direction, and heat-set at 130 ° C. Went. Thereafter, it was washed with methyloic acid, dried, and heat-set at 120 ° C. to prepare a porous sheet having a thickness of 45 μm, a porosity of 67%, and an inorganic particle content of 91% by weight.

  Thereafter, a reflective adhesive tape was prepared in the same manner as in Example 1. The properties of the resulting reflective adhesive tape are shown in Table 1.

[Example 3]
A thinner sheet prepared in Example 1 was prepared with the same composition as in Example 1, stretched 5 times in the MD direction at 120 ° C., then 11 times in the TD direction, and heat-set at 130 ° C. It was. Thereafter, it was washed with methyloic acid, dried, and heat-set at 120 ° C. to prepare a porous sheet having a thickness of 23 μm, a porosity of 69%, and an inorganic particle content of 90% by weight.

  Thereafter, a reflective adhesive tape was prepared in the same manner as in Example 1. The properties of the resulting reflective adhesive tape are shown in Table 1.

[Example 4]
A thinner sheet produced in Example 1 was prepared with the same composition as in Example 1, and stretched by 5.5 times in the MD direction at 120 ° C. and then 12 times in the TD direction, and heat-fixed at 130 ° C. Went. Thereafter, it was washed with methyloic acid, dried, and heat-set at 120 ° C. to prepare a porous sheet having a thickness of 9 μm, a porosity of 70%, and an inorganic particle content of 90% by weight.

  Thereafter, a reflective adhesive tape was prepared in the same manner as in Example 1. The properties of the resulting reflective adhesive tape are shown in Table 1.

[Example 5]
A thinner sheet produced in Example 1 was prepared with the same composition as in Example 1, and stretched by 5.5 times in the MD direction at 120 ° C. and then 12 times in the TD direction, and heat-fixed at 130 ° C. Went. Thereafter, it was washed with methyloic acid, dried, and heat-set at 120 ° C. to prepare a porous sheet having a thickness of 9 μm, a porosity of 70%, and an inorganic particle content of 90% by weight. A porous sheet with a base material sheet is created by laminating a PET film (“Tetron” HB3 film (25 μm thick) made by Teijin DuPont Film) with an acrylic resin coated on one side and an adhesive layer (2 μm thick). did.

  Thereafter, a reflective adhesive tape was prepared in the same manner as in Example 1. In this case, an adhesive layer was formed on the base sheet side. The properties of the resulting reflective adhesive tape are shown in Table 1.

[Comparative Example 1]
A thinner sheet prepared in Example 1 was prepared with the same composition as in Example 1, stretched 6 times in the MD direction at 120 ° C., then 13 times in the TD direction, and heat-set at 130 ° C. It was. Thereafter, it was washed with methyloic acid, dried, and heat-set at 120 ° C. to prepare a porous sheet having a thickness of 4.5 μm, a porosity of 71%, and an inorganic particle content of 89% by weight.

  Thereafter, an adhesive tape was prepared in the same manner as in Example 1. The properties of the obtained adhesive tape are shown in Table 1. This adhesive tape has insufficient reflectivity and handling properties.

[Comparative Example 2]
Instead of the porous sheet used in Example 1, “Teflex” (13 μm) manufactured by Teijin DuPont Films Ltd. was used. Thereafter, an adhesive tape was prepared in the same manner as in Example 1. The properties of the obtained adhesive tape are shown in Table 1.

  The reflective adhesive sheet of the present invention is excellent in reflection characteristics and handling properties, and can be thinned as a whole, so that it can meet the demand for thinning, for example, LEDs such as mobile phones and PDAs, and cold cathode tubes. It is useful for a backlight unit having a thickness of 1 cm or less used for a thin panel having a light source.

Claims (5)

Organic and inorganic particles and the porous sheet is at least 5 dl / g porosity consists the intrinsic viscosity having a Lupo Riechiren of 50 to 85% and an adhesive layer provided on one or both sides of the porous sheet A reflective adhesive tape having a reflectance of 80% or more at a wavelength of 550 nm, wherein the porous sheet contains 80 to 92% of the inorganic particles in a weight percentage based on the total amount of the inorganic particles and the polyethylene. A reflective adhesive tape containing and having a thickness of 7 to 80 μm. The reflective adhesive tape according to claim 1, wherein the porous sheet is stretched in at least one axial direction. The reflective adhesive tape according to claim 1 or 2, wherein a base sheet is bonded to at least one side of the porous sheet. The reflective adhesive tape according to claim 3, wherein the base sheet is made of a thermoplastic resin. The reflective adhesive tape according to claim 4, wherein the thermoplastic resin is polyester or polyolefin.