JP2016069493A - Double-sided adhesive tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided adhesive tape which is thin and excellent in light-shielding properties and is used for adhering and fixing components for constituting a portable electronic apparatus to an apparatus body.SOLUTION: There is provided a double-sided adhesive tape having acrylic adhesive layers on both surfaces of a substrate. The substrate is composed of a polyolefin resin and a polyolefin foam containing 0.1 pt.wt. or more of a colorant based on 100 pts.wt. of the polyolefin resin, the substrate has a density of 0.4 to 0.8 g/cm, a thickness of 100 to 250 μm and an average cell wall thickness of 4 μm or more and the double-sided adhesive tape has a total thickness of 400 μm or less.SELECTED DRAWING: None

Description

The present invention relates to a thin double-sided pressure-sensitive adhesive tape that is used for adhesively fixing components constituting a portable electronic device to a device main body and having excellent light shielding properties.

Mobile electronic devices such as mobile phones and personal digital assistants (PDAs) are designed so that they do not come off or break even if an impact is applied in consideration of falling from the user's hand to the foot. Fixed arrangements or device body designs are being considered. Therefore, a double-sided pressure-sensitive adhesive tape that is used for fixing the component to the main body of the device is desired to prevent the component from coming off even when an impact is applied, and not to apply a strong shock to the component. ing.

For example, a double-sided pressure-sensitive adhesive tape having a base material made of a polyolefin foam has been studied as an impact absorbing tape for fixing a component constituting a portable electronic device to the device body.
In Patent Documents 1 and 2, an acrylic pressure-sensitive adhesive layer is laminated and integrated on at least one surface of a base material layer, and the base material layer has a specific cross-linking degree and a foam aspect ratio. A shock absorbing tape is described.

In recent years, there has been a demand for designs that make portable electronic devices thinner and lighter, and double-sided adhesive tapes are also becoming thinner. For this reason, the double-sided pressure-sensitive adhesive tape having a base material made of polyolefin foam has a problem that the light shielding property is lowered as it becomes thin because the base material is a foam and air bubbles are present in the base material. Yes. When the light shielding property of the double-sided pressure-sensitive adhesive tape is lowered, for example, when the double-sided pressure-sensitive adhesive tape is used for bonding and fixing the front plate to the device body, light leakage from the inside of the device may occur. In addition, when a double-sided pressure-sensitive adhesive tape is used as the light shielding tape of the backlight unit, the backlight may not be sufficiently shielded.

JP 2009-242541 A JP 2009-258274 A

An object of this invention is to provide the thin double-sided adhesive tape excellent in light-shielding property used in order to adhere | attach and fix the components which comprise a portable electronic device to an apparatus main body.

The present invention is a double-sided pressure-sensitive adhesive tape having an acrylic pressure-sensitive adhesive layer on both sides of a base material, the base material comprising a polyolefin resin and a colorant of 0.1 part by weight or more with respect to 100 parts by weight of the polyolefin resin. The substrate has a density of 0.4 to 0.8 g / cm ³ , a thickness of 100 to 250 μm, an average cell wall thickness of 4 μm or more, and a total thickness of the double-sided pressure-sensitive adhesive tape. The double-sided pressure-sensitive adhesive tape is 400 μm or less.
The present invention is described in detail below.

The present inventor uses a specific polyolefin foam for a base material in a double-sided pressure-sensitive adhesive tape having an acrylic pressure-sensitive adhesive layer on both sides of the base material, and further sets the density, thickness and average cell wall thickness of the base material to a specific range. As a result of the adjustment, it was found that even with a thin double-sided pressure-sensitive adhesive tape, excellent light shielding properties can be obtained, and the present invention has been completed.

The double-sided pressure-sensitive adhesive tape of the present invention has an acrylic pressure-sensitive adhesive layer on both sides of the substrate.
The said base material consists of a polyolefin foam containing a polyolefin resin and 0.1 weight part or more of coloring agent with respect to 100 weight part of said polyolefin resin.

The polyolefin foam is not particularly limited as long as it is a foam containing the polyolefin resin and 0.1 part by weight or more of a colorant with respect to 100 parts by weight of the polyolefin resin. For example, a polyethylene foam, Examples thereof include polypropylene-based foams and ethylene-propylene-based foams.

The polyolefin resin is not particularly limited, but is obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst in order to adjust the density, thickness and average cell wall thickness of the substrate to the intended ranges. Polyolefin resin is preferred. Among these, a polyethylene resin obtained using a metallocene compound is more preferable.
Examples of the metallocene compounds include Kaminsky catalysts.

Examples of the polyethylene resin obtained using the metallocene compound include, for example, a polyethylene resin obtained by copolymerizing ethylene and other α-olefin blended as necessary using the metallocene compound. Is mentioned. Examples of the other α-olefin include propene, 1-butene, 1-pentene, 1-hexene and the like.

The polyethylene resin obtained using the metallocene compound may be used in combination with other olefin resins. Examples of the other olefin resin include polyethylene, polypropylene, ethylene-propylene copolymer, and the like.
In this case, the content of the polyethylene resin obtained using the metallocene compound in the polyolefin foam is preferably 40% by weight or more. When the content of the polyethylene resin obtained using the metallocene compound is 40% by weight or more, high compressive strength can be obtained even if the polyolefin foam is thin.

The colorant is not particularly limited, and pigments, dyes and the like generally blended in a double-sided pressure-sensitive adhesive tape used for bonding and fixing a component constituting a portable electronic device to the device body can be used. Carbon black such as black, thermal black, acetylene black, channel black, lamp black, ketjen black; oxides such as iron oxide, titanium oxide, zinc oxide, magnesium oxide, cobalt oxide, copper oxide, chromium oxide, alumina; sulfuric acid Sulfates such as calcium, barium sulfate, iron sulfate and mercury sulfate; carbonates such as calcium carbonate, magnesium carbonate and dolomite; metal powders such as iron powder, copper powder, tin powder, lead powder and aluminum powder; azo pigments, Organic pigments such as phthalocyanine pigments and dioxazine pigments; graphite and the like. Of these, carbon black is preferable.

The content of the colorant in the polyolefin foam is 0.1 part by weight or more. When the content of the colorant is less than 0.1 parts by weight, the light shielding property of the double-sided pressure-sensitive adhesive tape is lowered. The minimum with preferable content of the said coloring agent is 0.5 weight part, and a more preferable minimum is 1 weight part.
The upper limit of the content of the colorant is not particularly limited. However, if too much of the colorant is added, coloring unevenness occurs due to poor dispersion, so the preferable upper limit is 10 parts by weight.

The polyolefin foam is preferably cross-linked. By crosslinking the polyolefin foam, the density, thickness and average cell wall thickness of the substrate can be easily adjusted to the intended ranges.
The method for crosslinking the polyolefin foam is not particularly limited. For example, a method of irradiating the polyolefin foam with ionizing radiation such as electron beam, α ray, β ray, γ ray, Examples include a method of decomposing the organic peroxide by heating.

The base material has a density of 0.4 to 0.8 g / cm ³ , a thickness of 100 to 250 μm, and an average cell wall thickness of 4 μm or more.
By setting the density, thickness and average cell wall thickness of the substrate within the above ranges, excellent light shielding properties can be obtained even with a thin double-sided pressure-sensitive adhesive tape.

When the density of the base material is less than 0.4 g / cm ³ , the light shielding property of the double-sided pressure-sensitive adhesive tape is lowered, or the strength of the base material is lowered and the impact resistance of the double-sided pressure-sensitive adhesive tape is lowered. A substrate having a high density such that the density exceeds 0.8 g / cm ³ is substantially not a foam. The preferable lower limit of the density of the substrate is 0.45 g / cm ³ , the preferable upper limit is 0.65 g / cm ³ , the more preferable lower limit is 0.5 g / cm ³ , and the more preferable upper limit is 0.6 g / cm ³ . is there.
The density of the base material can be measured and calculated using an electronic hydrometer (trade name “ED120T”) manufactured by Mirage in accordance with JISK-6767.

When the thickness of the base material is less than 100 μm, the light-shielding property of the double-sided pressure-sensitive adhesive tape decreases, or the strength of the base material decreases and the impact resistance of the double-sided pressure-sensitive adhesive tape decreases. When the thickness of the base material exceeds 250 μm, the flexibility of the base material is lowered, the impact resistance of the double-sided pressure-sensitive adhesive tape is lowered, and the total thickness of the double-sided pressure-sensitive adhesive tape is increased. It is no longer suitable for use in bonding and fixing to the main body. The minimum with the preferable thickness of the said base material is 120 micrometers, a preferable upper limit is 220 micrometers, a more preferable minimum is 140 micrometers, and a more preferable upper limit is 200 micrometers.

When the average cell wall thickness of the base material is less than 4 μm, the light shielding property of the double-sided pressure-sensitive adhesive tape is lowered, or the strength of the base material is lowered and the impact resistance of the double-sided pressure-sensitive adhesive tape is lowered. A preferable lower limit of the average cell wall thickness of the substrate is 5 μm, and a more preferable lower limit is 6 μm.
Although the upper limit of the average cell wall thickness of the base material is not particularly limited, the preferable upper limit is 15 μm and the more preferable upper limit is 10 μm from the viewpoint of ensuring the flexibility of the double-sided pressure-sensitive adhesive tape.
The cell wall thickness means the minimum value of the wall thickness between adjacent cells (bubbles) present in the polyolefin foam, and the average cell wall thickness of the base material is obtained by cutting the base material in the thickness direction. The cross section is observed 450 times with an optical microscope (for example, VHX-500 manufactured by Keyence Corporation), and the cell wall thicknesses of 30 randomly selected cells are measured, and these can be averaged and calculated.

The method for producing the substrate is not particularly limited. For example, a foamable resin composition containing the polyolefin resin, a foaming agent, and the colorant is prepared, and the foamable resin composition is added to an extruder. A method of foaming a foaming agent when extruding into a sheet and using the resulting polyolefin foam as necessary is preferred.
At this time, as a method of adjusting the density of the base material and the average cell wall thickness to a target range, for example, a method of adjusting the degree of crosslinking of the polyolefin foam, a method of adjusting the content of the foaming agent, etc. Is mentioned.

The foaming agent is not particularly limited, and foaming agents generally used for the polyolefin foam can be used. For example, azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide, etc. Is mentioned.

The content of the foaming agent may be adjusted so that the density of the base material and the average cell wall thickness can be adjusted, but a preferable lower limit with respect to 100 parts by weight of the polyolefin resin is 0.1 part by weight, and a preferable upper limit is 20 parts by weight. Part. When the content of the foaming agent is less than 0.1 parts by weight, the foaming ratio of the base material may decrease, the density of the base material may be too high, or the average cell wall thickness may be too thick. When the content of the foaming agent exceeds 20 parts by weight, the foaming ratio of the base material may be too high, the density of the base material may be too low, or the average cell wall thickness may be too thin. The more preferable lower limit of the content of the foaming agent with respect to 100 parts by weight of the polyolefin resin is 1 part by weight, and the more preferable upper limit is 10 parts by weight.

In the double-sided pressure-sensitive adhesive tape of the present invention, the acrylic adhesive layers on both sides may have the same composition or different compositions.

The acrylic copolymer constituting the acrylic pressure-sensitive adhesive layer is preferably obtained by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate.
The preferable content of butyl acrylate in the total monomer mixture is 40 to 80% by weight. When the content of butyl acrylate is less than 40% by weight, the acrylic pressure-sensitive adhesive layer becomes too soft and the cohesive force is lowered, and may be peeled off when a strong impact is applied. When the content of butyl acrylate exceeds 80% by weight, the acrylic pressure-sensitive adhesive layer becomes hard and has a reduced adhesive force or tack, and may be peeled off when a strong impact is applied.
The preferable content of 2-ethylhexyl acrylate in the total monomer mixture is 10 to 40% by weight. When the content of 2-ethylhexyl acrylate is less than 10% by weight, the acrylic pressure-sensitive adhesive layer may be peeled off when the adhesive force is reduced and a strong impact is applied. When the content of 2-ethylhexyl acrylate exceeds 40% by weight, the acrylic pressure-sensitive adhesive layer becomes too soft and the cohesive force is lowered, and may be peeled off when a strong impact is applied.

The monomer mixture may contain other polymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate as necessary.
Examples of other polymerizable monomers that can be copolymerized include, for example, carbon number of alkyl groups such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and isopropyl (meth) acrylate. 1 to 3 (meth) acrylic acid alkyl ester, tridecyl methacrylate, and (meth) acrylic acid alkyl ester having 13 to 18 carbon atoms such as stearyl (meth) acrylate, hydroxyalkyl (meth) acrylate , Glycerin dimethacrylate, glycidyl (meth) acrylate, 2-methacryloyloxyethyl isocyanate, (meth) acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid and the like.

In order to copolymerize the monomer mixture to obtain the acrylic copolymer, the monomer mixture may be radically reacted in the presence of a polymerization initiator. As a method of radical reaction of the monomer mixture, that is, a polymerization method, a conventionally known method is used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.
The said polymerization initiator is not specifically limited, For example, an organic peroxide, an azo compound, etc. are mentioned. Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5 -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Examples include isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination of two or more.

As for the weight average molecular weight (Mw) of the said acrylic copolymer, a preferable minimum is 400,000 and a preferable upper limit is 1.5 million. When the weight average molecular weight is less than 400,000, the acrylic pressure-sensitive adhesive layer may have a reduced cohesive force and an adhesive force at the adherend interface. When the weight average molecular weight exceeds 1,500,000, the acrylic pressure-sensitive adhesive layer may be peeled off when the adhesive force is reduced and a strong impact is applied. A more preferable lower limit of the weight average molecular weight is 500,000, and a more preferable upper limit is 1,200,000.
In order to adjust the weight average molecular weight within the above range, polymerization conditions such as a polymerization initiator and a polymerization temperature may be adjusted.
In addition, a weight average molecular weight (Mw) is a weight average molecular weight of standard polystyrene conversion by GPC (Gel Permeation Chromatography: gel permeation chromatography).

The acrylic pressure-sensitive adhesive layer may contain a tackifier resin.
Examples of the tackifier resins include rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, coumarone indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, and C9 resins. Examples thereof include petroleum resins and C5-C9 copolymer petroleum resins. These tackifying resins may be used alone or in combination of two or more.

Although content of the said tackifying resin is not specifically limited, The preferable minimum with respect to 100 weight part of said acrylic copolymers is 10 weight part, and a preferable upper limit is 50 weight part. When the content of the tackifying resin is less than 10 parts by weight, the acrylic pressure-sensitive adhesive layer may be peeled off from the adherend due to peeling stress caused by deformation of the adherend when a strong impact is applied. is there. When the content of the tackifying resin exceeds 50 parts by weight, the acrylic pressure-sensitive adhesive layer becomes hard and the adhesive force or tack is lowered, and may be peeled off when a strong impact is applied.

In the acrylic pressure-sensitive adhesive layer, a crosslinking structure is formed between the main chains of the resin (the acrylic copolymer and / or the tackifying resin) constituting the acrylic pressure-sensitive adhesive layer by adding a crosslinking agent. It is preferable.
The said crosslinking agent is not specifically limited, For example, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy-type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned. Of these, isocyanate-based crosslinking agents are preferred. By adding an isocyanate-based crosslinking agent to the acrylic pressure-sensitive adhesive layer, the isocyanate group of the isocyanate-based cross-linking agent reacts with the alcoholic hydroxyl group in the resin constituting the acrylic pressure-sensitive adhesive layer, and the acrylic pressure-sensitive adhesive layer. The cross-linking becomes loose. Therefore, the acrylic pressure-sensitive adhesive layer can disperse the peeling stress applied intermittently, and is resistant to peeling from the adherend against the peeling stress caused by the deformation of the adherend when a strong impact is applied. Will be improved.
The addition amount of the crosslinking agent is preferably 0.01 to 10 parts by weight and more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the acrylic copolymer.

Even if the crosslinking degree of the acrylic pressure-sensitive adhesive layer is too high or too low, the acrylic pressure-sensitive adhesive layer may be easily peeled off from the adherend due to peeling stress caused by the deformation of the adherend. 5-40 weight% is preferable, 10-40 weight% is more preferable, 15-35 weight% is especially preferable.
The degree of cross-linking of the acrylic pressure-sensitive adhesive layer was determined by taking W1 (g) of the acrylic pressure-sensitive adhesive layer and immersing this acrylic pressure-sensitive adhesive layer in ethyl acetate at 23 ° C. for 24 hours to make the insoluble matter 200 mesh wire mesh. The residue on the wire mesh is vacuum-dried, and the weight W2 (g) of the dried residue is measured, and calculated by the following formula (1).
Crosslinking degree (% by weight) = 100 × W2 / W1 (1)

Although the thickness of the said acrylic adhesive layer is not specifically limited, It is preferable that the thickness (thickness of the acrylic adhesive layer of one side) of the said acrylic adhesive layer is 10-150 micrometers. If the thickness of the acrylic pressure-sensitive adhesive layer is less than 10 μm, the impact resistance of the double-sided pressure-sensitive adhesive tape may be lowered. When the thickness of the acrylic pressure-sensitive adhesive layer exceeds 150 μm, the reworkability or removability of the double-sided pressure-sensitive adhesive tape may be impaired.

As for the double-sided adhesive tape of this invention, the total thickness of a double-sided adhesive tape is 400 micrometers or less. The double-sided pressure-sensitive adhesive tape of the present invention has excellent light shielding properties even when the total thickness is thin.
When the total thickness of the double-sided pressure-sensitive adhesive tape exceeds 400 μm, it becomes unsuitable for applications in which components constituting the portable electronic device are adhesively fixed to the device body. The upper limit with preferable total thickness of a double-sided adhesive tape is 350 micrometers, and a more preferable upper limit is 300 micrometers.
Although the minimum of the total thickness of the double-sided adhesive tape of this invention is not specifically limited, From a viewpoint of ensuring sufficient adhesive force and impact resistance of a double-sided adhesive tape, a preferable minimum is 80 micrometers.

As a manufacturing method of the double-sided adhesive tape of this invention, the following methods are mentioned, for example.
First, a solution of an adhesive A is prepared by adding a solvent to an acrylic copolymer, a tackifier resin, and a cross-linking agent as necessary, and the solution of the adhesive A is applied to the surface of the substrate. The acrylic adhesive layer A is formed by completely removing and removing the solvent. Next, a release film is overlaid on the formed acrylic pressure-sensitive adhesive layer A so that the release treatment surface faces the acrylic pressure-sensitive adhesive layer A.
Next, a release film different from the above release film is prepared, the adhesive B solution is applied to the release treatment surface of the release film, and the solvent in the solution is completely removed by drying, thereby releasing the release film. A laminated film in which the acrylic pressure-sensitive adhesive layer B is formed on the surface of the mold film is produced. The obtained laminated film is superposed on the back surface of the base material on which the acrylic pressure-sensitive adhesive layer A is formed, with the acrylic pressure-sensitive adhesive layer B facing the back surface of the base material to produce a laminate. Then, by pressing the laminate with a rubber roller or the like, a double-sided pressure-sensitive adhesive tape having an acrylic pressure-sensitive adhesive layer on both surfaces of the base material and having the surface of the acrylic pressure-sensitive adhesive layer covered with a release film can be obtained. it can.

In addition, two sets of laminated films are produced in the same manner, and a laminated body is produced by superposing these laminated films on both sides of the base material with the acrylic adhesive layer of the laminated film facing the base material. Then, by pressing this laminate with a rubber roller or the like, a double-sided pressure-sensitive adhesive tape having an acrylic pressure-sensitive adhesive layer on both surfaces of the base material and the surface of the acrylic pressure-sensitive adhesive layer covered with a release film can be obtained. Good.

The use of the double-sided pressure-sensitive adhesive tape of the present invention is not particularly limited, but the use of bonding and fixing components constituting a portable electronic device to the device main body is preferable. Specifically, the double-sided pressure-sensitive adhesive tape of the present invention can be used for adhering and fixing the front plate to the apparatus main body and as a light shielding tape for the backlight unit.
The shape of the double-sided pressure-sensitive adhesive tape of the present invention in these applications is not particularly limited, and examples thereof include a rectangle, a frame shape, a circle, an ellipse, and a donut shape.

The double-sided pressure-sensitive adhesive tape of the present invention preferably has a total light transmittance of 0.5% or less. Since the total light transmittance is 0.5% or less, the double-sided pressure-sensitive adhesive tape of the present invention is thin and excellent in light-shielding properties, suitable for use in adhering and fixing components constituting portable electronic devices to the device body. It becomes. When the total light transmittance exceeds 0.5%, for example, when a double-sided pressure-sensitive adhesive tape is used to adhere and fix the front plate to the device body, light leakage from the inside of the device may occur. In addition, when a double-sided pressure-sensitive adhesive tape is used as the light shielding tape of the backlight unit, the backlight may not be sufficiently shielded. A more preferable upper limit of the total light transmittance is 0.05%.
The total light transmittance can be measured using a haze meter (for example, Haze Meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd.) at 23 ° C. and a humidity of 50%.

ADVANTAGE OF THE INVENTION According to this invention, the thin double-sided adhesive tape excellent in light-shielding property used in order to adhere | attach and fix the components which comprise a portable electronic device to an apparatus main body can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Preparation of adhesive (1))
In a reactor equipped with a thermometer, a stirrer, and a condenser, butyl acrylate 70 parts by weight, 2-ethylhexyl acrylate 27 parts by weight, acrylic acid 3 parts by weight, 2-hydroxyethyl acrylate 0.2 parts by weight, and ethyl acetate 80 parts by weight After adding nitrogen and replacing with nitrogen, the reactor was heated to start refluxing. Subsequently, 0.1 part by weight of azobisisobutyronitrile was added as a polymerization initiator in the reactor. The solution was refluxed at 70 ° C. for 5 hours to obtain a solution of the acrylic copolymer (a). When the weight average molecular weight of the obtained acrylic copolymer (a) was measured by a GPC method using “2690 Separations Model” manufactured by Water as a column, it was 710,000.
10 parts by weight of rosin ester, 10 parts by weight of terpene phenol, ethyl acetate (Fuji Chemical) with respect to 100 parts by weight of the solid content of the acrylic copolymer (a) contained in the solution of the obtained acrylic copolymer (a) 125 parts by weight of an isocyanate-based crosslinking agent (trade name “Coronate L45” manufactured by Nippon Polyurethane Co., Ltd.) was added and stirred to obtain an adhesive (1).

(Preparation of adhesive (2))
An acrylic copolymer having a weight average molecular weight of 530,000 is the same as the acrylic copolymer (a) except that the addition amount of butyl acrylate is changed to 60 parts by weight and the addition amount of 2-ethylhexyl acrylate is changed to 37 parts by weight. A solution of (b) was obtained.
A pressure-sensitive adhesive (2) was obtained in the same manner as the pressure-sensitive adhesive (1) except that the solution of the obtained acrylic copolymer (b) was used.

(Preparation of adhesive (3))
The addition amount of butyl acrylate was changed to 50 parts by weight, the addition amount of 2-ethylhexyl acrylate was changed to 40 parts by weight, and further, 7 parts by weight of ethyl acrylate was added, and the same manner as in the acrylic copolymer (a). A solution of an acrylic copolymer (c) having a weight average molecular weight of 650,000 was obtained.
A pressure-sensitive adhesive (3) was obtained in the same manner as the pressure-sensitive adhesive (1) except that the solution of the obtained acrylic copolymer (c) was used.

Example 1
A release paper having a thickness of 150 μm was prepared, the pressure-sensitive adhesive (1) was applied to the release-treated surface of the release paper, and dried at 100 ° C. for 5 minutes to form an acrylic pressure-sensitive adhesive layer having a thickness of 50 μm. This acrylic pressure-sensitive adhesive layer was bonded to the surface of a polyolefin foam having the density, thickness and average cell wall thickness shown in Table 1. Next, in the same manner, the same acrylic pressure-sensitive adhesive layer as above was bonded to the opposite surface of the polyolefin foam. This obtained the double-sided adhesive tape of the tape total thickness shown in Table 1 covered with the 150-micrometer-thick release paper.
The density of the polyolefin foam was measured and calculated using an electronic hydrometer (trade name “ED120T”) manufactured by Mirage in accordance with JISK-6767. The average cell wall thickness of the polyolefin foam was obtained by cutting the polyolefin foam in the thickness direction, observing the cross section at 450 times with an optical microscope (VHX-500, manufactured by Keyence Corporation), and randomly selecting 30 cells. The wall thickness was measured and averaged.

(Examples 2-8, Comparative Examples 1-4)
By changing the polyolefin foam to one having the density, thickness and average cell wall thickness shown in Table 1, changing the type of adhesive to that shown in Table 1, and further changing the thickness of the acrylic adhesive layer A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except that the total tape thickness was changed as shown in Table 1.

<Evaluation>
The following evaluation was performed about the double-sided adhesive tape obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Evaluation of light shielding properties (measurement of total light transmittance)
The total light transmittance of the double-sided pressure-sensitive adhesive tape was measured using a haze meter NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) at 23 ° C. and a humidity of 50%. The case where the total light transmittance was 0.5% or less was judged as ◯, and the case where it exceeded 0.5% was judged as ×.

ADVANTAGE OF THE INVENTION According to this invention, the thin double-sided adhesive tape excellent in light-shielding property used in order to adhere | attach and fix the components which comprise a portable electronic device to an apparatus main body can be provided.

Claims (3)

A double-sided adhesive tape having an acrylic adhesive layer on both sides of a substrate,
The substrate comprises a polyolefin foam containing a polyolefin resin and 0.1 parts by weight or more of a colorant with respect to 100 parts by weight of the polyolefin resin,
The substrate has a density of 0.4 to 0.8 g / cm ³ , a thickness of 100 to 250 μm, an average cell wall thickness of 4 μm or more,
A double-sided pressure-sensitive adhesive tape, wherein the total thickness of the double-sided pressure-sensitive adhesive tape is 400 µm or less. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the colorant is carbon black. 3. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the double-sided pressure-sensitive adhesive tape is used for bonding and fixing a component constituting the portable electronic device to the device main body.