JP2002235059A - Highly transparent double-sided pressure-sensitive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided pressure-sensitive adhesive sheet having high light transmitting properties and excellent impact resistance and further to provide a portable type electronic equipment in which parts are fixed by using the double-sided pressure-sensitive adhesive sheet. SOLUTION: The double-sided pressure-sensitive adhesive sheet has >=40% light transmittance over the wavelength region of 400-700 nm and <=-10 deg.C temperature at which the loss tangent of an adhesive mass layer exhibits the maximum value at 1 Hz frequency and >=1 maximum value of the loss tangent. The portable type electronic equipment has the parts fixed by using the double- sided pressure-sensitive adhesive sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided pressure-sensitive adhesive sheet having high light transmittance and excellent impact resistance, and a portable electronic device in which components are fixed using the double-sided pressure-sensitive adhesive sheet.

[0002]

2. Description of the Related Art Double-sided pressure-sensitive adhesive tapes are used for fixing parts in various industrial fields because of their good workability and workability. In particular, when the parts to be fixed have a complicated shape or when productivity in an automation line is required, the adhesive is more advantageous than the adhesive. I have.

[0003] Many portable electronic devices employ a system in which a display window is provided in a housing and an internal light source is turned on and off to emit visual information in order to facilitate user operation of the device. In the case of a mobile phone as an example, a display window for notifying the incoming call is provided on the housing of the mobile phone so that the incoming call state can be easily checked visually. The display window is provided with a transparent plastic protective plate for shielding the inside of the housing from the outside. Conventionally, the protective plate is fixed to the housing with a double-sided pressure-sensitive adhesive sheet, but since the conventional double-sided pressure-sensitive adhesive sheet generally has a low light transmittance, a double-sided pressure-sensitive adhesive sheet provided with a light transmission window in the center and processed into a frame shape is used. Have been used.
This requires not only a processing step for the double-sided pressure-sensitive adhesive sheet, but also a high-precision adhesion to the transparent plastic protective plate, which is a major cause of lowering the productivity and the yield. In addition, portable electronic devices are often dropped accidentally due to their usage. At that time, there has been a problem that the components fixed with the conventional double-sided adhesive sheet easily fall off due to the impact of the drop.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a double-sided pressure-sensitive adhesive sheet which has a high light-transmitting property without the need for providing the light-transmitting window and has excellent impact resistance. An object of the present invention is to provide a portable electronic device in which components are fixed using an adhesive sheet.

[0005]

Means for Solving the Problems The present inventors have proposed that
The light transmittance is 40% or more over a wavelength range of 700 nm, and at a frequency of 1 Hz, the temperature at which the loss tangent of the adhesive layer exhibits a maximum value is -10 ° C or less, and the maximum value of the loss tangent is 1 or more. Providing a double-sided pressure-sensitive adhesive sheet,
Further, the above-mentioned problem has been solved by providing a portable electronic device in which components are fixed using the double-sided pressure-sensitive adhesive sheet.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The double-sided pressure-sensitive adhesive sheet of the present invention has a light transmittance of 40% or more over a visible light region having a wavelength of 400 to 700 nm. 2. Description of the Related Art Conventionally, non-woven fabrics are often used as a support for a double-sided pressure-sensitive adhesive sheet for fixing components of a portable electronic device. This is because the impact resistance of the pressure-sensitive adhesive layer to the nonwoven fabric makes it easier to obtain the impact resistance of the double-sided pressure-sensitive adhesive sheet. However, when a nonwoven fabric is used, the visible light transmittance of the double-sided pressure-sensitive adhesive sheet is low. Therefore, when the double-sided pressure-sensitive adhesive sheet is used for fixing the transparent plastic protective plate, it is necessary to provide light transmission holes.

In order to increase the visible light transmittance of the double-sided pressure-sensitive adhesive sheet, a transparent plastic film may be used for the support. As such a plastic film, for example, polyethylene terephthalate film,
Examples include a polyethylene film, a polypropylene film, a polystyrene film, and triacetyl cellulose. For the highly transparent double-sided pressure-sensitive adhesive sheet of the present invention, a polyethylene terephthalate film is preferable because of its high adhesiveness to the pressure-sensitive adhesive layer and high tensile strength. The surface of the plastic film used as the support of the double-sided pressure-sensitive adhesive sheet of the present invention may be subjected to a corona treatment or an anchor coating treatment in order to improve the adhesiveness with the pressure-sensitive adhesive. As for the thickness of the support, those having a thickness of 4 to 200 μm, which has been generally used, can be used. 10
Those having a thickness of 100 μm are more preferable.

The above-mentioned transparent plastic can be used as a support, but in the present invention, it is preferable to use a nonwoven fabric in order to obtain a double-sided PSA sheet having excellent impact resistance. In this case, the basis weight 3 spun by the spun bond method
If the nonwoven fabric is 0 g / m ² or less, the wavelength is 400 to 700.
The light transmittance of the double-sided pressure-sensitive adhesive sheet can be 40% or more over a visible light region of nm. Examples of the fiber that can be spun by the spun bond method include polyester, polypropylene, polyethylene, nylon, and cellulose. In spunbonded nonwoven fabric, long fibers self-adhere, so that not only the strength required for practical use is obtained without adding a strength improver or adhesive, but also the adhesive is sufficiently impregnated between the fibers, resulting in high light rays. There is an advantage that transmittance can be obtained.

[0009] The support for the double-sided PSA sheet of the present invention is used.
The nonwoven fabric used has a basis weight of 30 g / m²The following is preferable,
More preferably, 10 to 20 g / m²It is. The basis weight is 30g
/ M ²Insufficient impregnation of non-woven fabric with adhesive
, And the joints of the fibers remain to lower the light transmittance.

For the double-sided pressure-sensitive adhesive sheet of the present invention, in order to increase the light transmittance, a transparent plastic film or a nonwoven fabric having a small basis weight, in which the impact resistance of the pressure-sensitive adhesive layer is hardly obtained, is used. Therefore, in the present invention, at 1 Hz, a pressure-sensitive adhesive layer having a temperature at which the loss tangent has a maximum value of -10 ° C. or less at 1 Hz and a maximum value of the loss tangent of 1 or more is formed. Thereby, both high transparency and impact resistance could be achieved.

In general, when a structure in which components are fixed with a double-sided pressure-sensitive adhesive sheet falls, the structure vibrates in a frequency range specific to the shape due to the impact. This is called a natural frequency region. Energy in this frequency range (vibration energy) is transmitted to the parts joined to the structure via the double-sided pressure-sensitive adhesive sheet. Therefore, as the vibration energy absorption of the double-sided pressure-sensitive adhesive sheet is higher, the vibration energy transmitted to the component is smaller, and the component is less likely to fall off. Energy absorption here is the ratio of converting mechanical energy to heat energy, and the higher the viscosity ratio of the adhesive layer, which is a viscoelastic body having both viscous and elastic properties, It will be excellent in energy absorption.
When the elasticity (storage modulus) and the viscosity (loss modulus) of the pressure-sensitive adhesive layer, that is, the viscoelastic body, are measured for each frequency, the higher the frequency, the higher the value. This means that the higher the frequency, the stronger the properties of the elastic body appear.

On the other hand, the loss tangent, which is a value obtained by dividing the viscosity by the elasticity, increases as the frequency becomes higher, reaches a maximum value at a certain point, and then decreases again. On the frequency side lower than the maximum value, it exhibits behavior as a viscoelastic body (adhesive) in which viscosity and elasticity coexist, and on the frequency range higher than the maximum value, it behaves as a glassy solid. Therefore, the vibration energy in the high frequency range cannot be absorbed by the frequency having the maximum value. On the other hand, when the maximum value exceeds 1, the viscosity exceeds the elasticity and the energy absorption becomes large. Generally, in a viscoelastic body, a viscoelastic function obtained at an arbitrary temperature T is expressed by time (or frequency).
By converting to the unit, it can be converted to the value of the reference temperature T _0. This property is called a temperature-time (or temperature-frequency) conversion rule, and when this conversion method is applied, a high frequency region is correlated with a low temperature region, and for example, 10 ³ Hz at 25 ° C. becomes -10 ° C. At 1 Hz.

As described above, when the frequency or temperature at which the loss tangent of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet has a maximum value is in the natural frequency region or temperature region generated when the electronic device falls, the maximum value is obtained. Vibration energy in a frequency range exceeding the frequency (or a temperature range equal to or lower than the temperature showing the maximum value) cannot reach the component without being absorbed by the pressure-sensitive adhesive layer, and the component tends to fall off.

The pressure-sensitive adhesive layer used in the present invention has a frequency of 1H.
In z, the temperature at which the loss tangent has a maximum value is −10 ° C. or less, preferably −20 ° C. or less, and the maximum value of the loss tangent is 1 or more, preferably 1.4 or more. If there is a maximum value of the loss tangent in a temperature range exceeding -10 ° C, the vibration energy cannot be absorbed as described above, so that the component is likely to fall off when dropped. The same applies to the case where the maximum value of the loss tangent is less than 1.

Generally, in order to lower the temperature at which the loss tangent has a maximum value and to increase the maximum value of the loss tangent, it is sufficient to lower the glass transition temperature of the resin used for the adhesive.
Specifically, in the case of an acrylic resin, it can be adjusted by a method such as using a resin having a large number of carbon atoms in the alkyl side chain or reducing the amount of the tackifier resin. The loss tangent of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet in the present invention can be measured by a temperature dispersion method using a viscoelasticity tester at a frequency of 1 Hz. As the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, a known acrylic or rubber-based pressure-sensitive adhesive can be used.

When the pressure-sensitive adhesive is acrylic, it is preferable that the pressure-sensitive adhesive is an acrylic copolymer containing an acrylate having an alkyl side chain having 2 to 14 carbon atoms as a monomer component. An acrylic acid ester having an alkyl side chain having 2 to 6 carbon atoms as a monomer component;
More preferred is an acrylic copolymer containing an acrylate having an alkyl side chain of 4. further,
As a monomer component, it is preferable to add an acrylate or vinyl monomer having a polar group such as a hydroxyl group, a carboxyl group, or an amino group in a side chain in a range of 0.01 to 3% by mass.

In order to increase the cohesive strength of the pressure-sensitive adhesive, a crosslinking agent may be added to the pressure-sensitive adhesive layer. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, a chelating-based crosslinking agent, an epoxy-based crosslinking agent, and an aziridine-based crosslinking agent. The gel fraction, which is an indicator of the degree of crosslinking, is preferably in the range of 25 to 60%. The gel fraction means that the pressure-sensitive adhesive layer is
This is a value expressed as a percentage by dividing the mass of the residual gel after immersion for 4 hours by the mass before immersion.

Examples of the rubber-based pressure-sensitive adhesive include block copolymers such as styrene-isoprene-styrene, synthetic rubber-based pressure-sensitive adhesives such as polybutadiene and polybutylene, and natural rubber. If a silicone-based pressure-sensitive adhesive is used, high adhesive strength can be obtained even when the pressure-sensitive adhesive sheet is adhered to an ultraviolet-cured coating film containing silicone oil. As the silicone-based pressure-sensitive adhesive, a peroxide crosslinking type or an addition condensation type may be used alone or as a mixture. Further, an acrylic adhesive and a rubber adhesive can be used as a mixture, or an adhesive obtained by chemically bonding a silicone component to a main chain or a side chain of an acrylic polymer used for the acrylic adhesive can be used. May be used.

If necessary, various additives such as tackifiers, antioxidants, ultraviolet absorbers, fillers, pigments, dyes, and thickeners are added to the pressure-sensitive adhesive layer as long as the performance is not impaired. You may. The coating solution for the pressure-sensitive adhesive layer of the present invention is prepared by dissolving or dispersing the above-mentioned pressure-sensitive adhesive and other additives as necessary in an organic solvent. As the organic solvent, known or common organic solvents such as ethyl acetate, toluene, xylene, methanol, and isopropyl alcohol can be used alone or as a mixture.

In order to form a pressure-sensitive adhesive layer on a substrate film, a coating solution for the pressure-sensitive adhesive layer is directly applied to the substrate film with a roll coater or a die coater and dried, or the pressure-sensitive adhesive layer is once adhered to a separator. After forming the agent layer, a method of transferring to a base film is used. The preferred thickness of the pressure-sensitive adhesive layer after drying is 30 to 300 μm, more preferably 50 to 300 μm.
200 μm.

Specific examples of electronic equipment suitable for fixing parts using the double-sided pressure-sensitive adhesive sheet of the present invention include a mobile phone, a portable personal computer, and a portable information terminal. Due to its high light transmittance, it is attached to the entire surface of a transparent plastic protective plate without providing a light transmission hole, especially in the display window of a mobile phone that notifies the incoming call by blinking a light emitting diode, among portable electronic devices. This can be fixed. In addition, even when the portable electronic device in which the component is fixed by the double-sided pressure-sensitive adhesive sheet of the present invention is accidentally dropped, the impact is absorbed by the pressure-sensitive adhesive layer, so that the component fixed by the double-sided pressure-sensitive adhesive sheet is not easily dropped. This has the effect.

[0022]

The present invention will be specifically described below with reference to examples. Unless otherwise specified, “parts” means “parts by mass” and “%” means “% by mass”.

[Preparation of pressure-sensitive adhesive layer composition (1)] In a reaction vessel equipped with a stirrer, a cold flow cooler, a thermometer, a dropping funnel and a nitrogen gas inlet, 54.4 parts by weight of butyl acrylate (hereinafter referred to as "part"), 40 parts of 2-ethylhexyl acrylate, 3.5 parts of vinyl acetate, 2.0 parts of acrylic acid, 100 parts by weight of monomer of 0.1 part of β-hydroxyethyl acrylate, 0.2 part of 2,2′-azobisisobutyronitrile Is dissolved in 100 parts of ethyl acetate, and the mixture is dissolved at 80 ° C. in a stream of nitrogen.
After stirring for an hour, the concentration was adjusted by adding ethyl acetate to obtain an acrylic copolymer solution having a mass average molecular weight of 700,000 and a nonvolatile content of 40%. To 100 parts of the acrylic copolymer solution, 1 part of an isocyanate-based crosslinking agent (“Coronate L-45” manufactured by Nippon Polyurethane Co., solid content: 45%) was added, and the mixture was stirred for 15 minutes. ) Got.

[Preparation of composition (2) for pressure-sensitive adhesive layer] 92.9 parts by weight (hereinafter referred to as "parts") of butyl acrylate in a reaction vessel equipped with a stirrer, a cold flow cooler, a thermometer, a dropping funnel and a nitrogen gas inlet. , Vinyl acetate 4 parts, acrylic acid 3 parts, β-hydroxyethyl acrylate 0.1 part monomer 10
0 parts by weight, 2,2'-azobisisobutyronitrile
2 parts in 100 parts of ethyl acetate and dissolved in a stream of nitrogen.
The mixture was stirred at 8 ° C for 8 hours to obtain an acrylic copolymer solution having a mass average molecular weight of 800,000. To the acrylic copolymer solution, polymerized rosin pentaerythritol ester ("D135" manufactured by Arakawa Chemical Co., Ltd.) was added in an amount of 30% to the acrylic copolymer, and ethyl acetate was further added to adjust the concentration to 40%. An agent solution was obtained. To 100 parts of the above adhesive solution, 1.5 parts of an isocyanate-based crosslinking agent (“Coronate L-45” manufactured by Nippon Polyurethane Co., solid content: 45%) was added, and 15 parts of
The mixture was stirred for 2 minutes to obtain a pressure-sensitive adhesive layer composition (2).

(EXAMPLE) Thickness of 75 whose surface is treated with release agent
The pressure-sensitive adhesive layer composition (1) was applied on a μm polyester film so that the thickness after drying was 70 μm, and dried at 80 ° C. for 3 minutes. The obtained pressure-sensitive adhesive layer was transferred onto both surfaces of a nonwoven fabric (“Benlyse PS140” manufactured by Asahi Kasei Kogyo Co., Ltd.) with a basis weight of 14 g / m ² using cellulose fibers spun by a wet spunbond method, and heated at 40 ° C. with a hot roll at 60 ° C. A pressure of ² cm ² was applied to the inside of the nonwoven fabric layer to impregnate the adhesive. Thereafter, the mixture was aged at 40 ° C. for 2 days to obtain a double-sided PSA sheet.

(Comparative Example) Thickness of 75 whose surface is treated with a release agent
Composition for adhesive layer on polyester film of μm
(2) is applied so that the thickness after drying becomes 70 μm.
And dried at 80 ° C. for 3 minutes. The obtained pressure-sensitive adhesive layer is
Wet pulp, rayon and polyvinyl alcohol fibers
Spun by the spinning method and bonded with an acrylic resin adhesive.
15g / m with ²Transfer to both sides of non-woven fabric
40N / cm²Load to the inside of the nonwoven fabric layer
The adhesive was impregnated. After aging at 40 ℃ for 2 days
An adhesive sheet was obtained. Both sides produced in Examples and Comparative Examples
The pressure-sensitive adhesive sheet was tested by the following method.
Table 1 shows the test results.

(1) Measurement of dynamic viscoelasticity of pressure-sensitive adhesive A double-sided pressure-sensitive adhesive sheet aged at 40 ° C. for 2 days was superimposed and a test piece having a thickness of 5 mm was mounted on a rheometrics viscoelasticity tester “Ares 2kSTD”. Diameter 7.9mm
And a loss tangent over a temperature range of -50 ° C to 150 ° C was measured at a frequency of 1 Hz.

(2) DuPont type impact test A 10 mm × 10 mm double-sided pressure-sensitive adhesive sheet was adhered to four corners of an acrylic plate having a thickness of 2 mm and a length and width of 50 mm.
Left at 24 ° C. for 24 hours. Next, one side was coated with an ultraviolet-curable paint ("M-55" manufactured by Origin Electric Co., Ltd.), 2 m thick.
m, an acrylic plate having the double-sided pressure-sensitive adhesive sheet adhered to the center of the painted surface of an ABS plate having a length and width of 100 mm via the double-sided pressure-sensitive adhesive sheet.
For 10 seconds. The sample left for 1 hour at 23 ° C. after pressurization was subjected to an impact from the back side of the ABS plate with a DuPont impact tester, and the number of times until the sample was dropped was measured. Those that did not fall more than 20 times were marked as 20 <. The conditions of the DuPont type impact tester were as follows: an impact load of 300 g, and a shooting core diameter of 25.
mm, and the impact height was 300 mm.

(3) Light transmittance Using a spectrophotometer (“V-520SR” manufactured by JASCO Corporation), a wavelength range of 400 to 1 in the volume direction of the double-sided pressure-sensitive adhesive sheet is used.
The light transmittance over 000 nm was measured. The measurement results showed light transmittances at wavelengths of 400, 700 and 1000 nm as representative values.

[0030]

[Table 1]

[0031]

A portable electronic device having a display window for transmitting information to a user by blinking a light emitting diode or the like,
In particular, when a transparent plastic protective plate is fixed using a double-sided adhesive sheet to a display window provided in a mobile phone or the like of a type that notifies an incoming call by blinking of a light emitting diode, the conventional double-sided adhesive sheet cannot transmit light. Because of the low rate, it was necessary to provide light transmitting holes in the double-sided pressure-sensitive adhesive sheet.
Since the double-sided pressure-sensitive adhesive sheet of the present invention has a high light transmittance, when fixing the plastic protective plate, a step of providing a light transmission hole is not required, and the plastic protective plate is stuck on the entire surface of the plastic protective plate and fixed. Can be.

In the present invention, in order to increase the light transmittance of the double-sided pressure-sensitive adhesive sheet, a transparent plastic film or a nonwoven fabric having a small basis weight is used as a support. In general, when such a support is used, it is difficult to obtain an effect of anchoring the pressure-sensitive adhesive layer to the support, so that the impact resistance of the double-sided pressure-sensitive adhesive sheet is reduced. The double-sided pressure-sensitive adhesive sheet of the present invention can be formed by the conventional technique by providing a high-impact pressure-sensitive adhesive layer on both sides of the support having a high light transmittance, as is clear from the results shown in Table 1. It has both transparency and impact resistance.

Claims (4)

[Claims] 1. A light transmittance of 40% or more over a wavelength range of 400 to 700 nm, and at a frequency of 1 Hz, a temperature at which the loss tangent of the pressure-sensitive adhesive layer shows a maximum value is -10.
C. or less, and the maximum value of the loss tangent is 1 or more. 2. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the support is a nonwoven fabric having a basis weight of 30 g / m ² or less spun by a spun bond method. 3. A portable electronic device in which components are fixed using the double-sided pressure-sensitive adhesive sheet according to claim 1. 4. The portable electronic device according to claim 3, wherein the portable electronic device is a mobile phone.