JP7431590B2 - Fixing and joining methods for adhesive tape and display members - Google Patents

Description

The present invention relates to an adhesive tape and a method for fixing and joining display members using the adhesive tape.

Adhesive tapes are used for assembly in portable electronic devices such as mobile phones and personal digital assistants (PDAs) (for example, Patent Documents 1 and 2). Adhesive tapes are also used for fixing in-vehicle electronic equipment components such as in-vehicle panels to vehicle bodies.

Japanese Patent Application Publication No. 2009-242541 Japanese Patent Application Publication No. 2009-258274

On the other hand, in the manufacture of display devices, adhesive tapes are used to fix the housing and the display member. When fixing a member using such an adhesive tape, the degree of adhesion of the adhesive tape becomes uneven due to non-uniform thickness of the casing or display member. If uneven adhesion occurs, stress is generated, deforming the casing or display member and causing display unevenness, so adhesive tapes used in the manufacture of display devices must have stress relaxation properties. In particular, adhesive tapes used in large-sized display devices are required to have higher stress relaxation properties because stress tends to increase. Conventional adhesive tapes achieve stress relaxation by filling the difference (gap) in the thickness of the adhesive area with the thickness of the tape. However, as large displays have become thinner in recent years, adhesive tapes have also become thinner, making it difficult to alleviate stress due to the thickness of the tape.

An object of the present invention is to provide an adhesive tape that can exhibit high stress relaxation properties even when the adhesive tape is thin, and a method for fixing and joining display members using the adhesive tape.

The present invention is an adhesive tape having an adhesive layer on at least one side of a base material, and the adhesive tape has a hysteresis loss rate of 30% or more and 80% or less.
The present invention will be explained in detail below.

The adhesive tape of the present invention has a hysteresis loss rate of 30% or more and 80% or less.
Hysteresis loss refers to a phenomenon in which a portion of the force applied to deform an object is converted into thermal energy or the like and is lost. By using a material that causes hysteresis loss in the adhesive tape, part of the applied force can be released to the outside. As a result, the force that deforms the adhesive tape is reduced, and stress relaxation properties can be improved. The adhesive tape of the present invention can exhibit sufficient stress relaxation properties by having a hysteresis loss rate of 30% or more, and can have sufficient strength as an adhesive tape by having a hysteresis loss rate of 80% or less. .
From the viewpoint of further increasing stress relaxation and strength, the hysteresis loss rate is preferably 32% or more, more preferably 34% or more, even more preferably 35% or more, and even more preferably 36% or more. Even more preferred. Further, from the same viewpoint, the hysteresis loss rate is preferably 70% or less, more preferably 60% or less, even more preferably 55% or less, and even more preferably 50% or less. preferable.
The above hysteresis loss rate can be adjusted by lowering the density and increasing flexibility. The above density can be adjusted depending on the type and structure of the base material.

The above hysteresis loss rate can be measured by the following method.
First, a test piece is prepared by cutting the obtained adhesive tape into a size of 20 mm x 20 mm and laminating a plurality of these pieces until the length becomes 5 mm or more. Next, for the obtained test piece, a Kerr deflection curve was plotted in accordance with JIS K 6400-2, except that the speed was 10 mm/min and the pressure was limited to 50% of the initial thickness, and the hysteresis loss was determined. Calculate the rate.

The adhesive tape of the present invention preferably has a 25% compressive strength of 8 kPa or more and 50 kPa or less.
When the 25% compressive strength of the adhesive tape is within the above range, the flexibility of the adhesive tape is increased, so stress relaxation properties can be improved, and the hysteresis loss rate can be easily adjusted within the above range. Furthermore, when the 25% compressive strength is 8 kPa or more, the strength of the adhesive tape becomes sufficiently high, and the adhesive tape becomes difficult to peel off even when restoring force or repulsion force is applied. When the 25% compressive strength of the base material is 50 kPa or less, the pressure-sensitive adhesive tape can be sufficiently crimped and the adhesive tape becomes difficult to peel off. From the viewpoint of further increasing the stress relaxation properties of the adhesive tape, the lower limit of the above 25% compressive strength is preferably 9 kPa, still more preferably 10 kPa, even more preferably 12 kPa, still more preferably 40 kPa, still more preferably 30 kPa. , an even more preferable upper limit is 20 kPa.
Note that the above 25% compressive strength can be measured by a method based on JIS K 6254. Further, the above 25% compressive strength can be adjusted by the density, type, and foam structure of the base material.

The adhesive tape of the present invention preferably has a 50% compressive strength of 30 kPa or more and 650 kPa or less.
By having the 50% compressive strength of the adhesive tape within the above range, flexibility is maintained even when large stress is applied to the adhesive tape, making it possible to further improve stress relaxation properties and to reduce the hysteresis loss rate. The above range allows for easier adjustment. From the viewpoint of further increasing the stress relaxation properties of the adhesive tape, the lower limit of the above 50% compressive strength is preferably 40 kPa, still more preferably 50 kPa, even more preferably 60 kPa, still more preferably 250 kPa, still more preferably 150 kPa. , an even more preferable upper limit is 100 kPa.
Note that the 50% compressive strength can be measured in the same manner as the 25% compressive strength. Further, the above 50% compressive strength can be adjusted by the density, type, and foam structure of the base material.

The adhesive tape of the present invention preferably has a shear storage modulus (log G' (-20°C)) of 6.5 lgPa or more and 8.0 lgPa at -20°C.
When the shear storage modulus (log G' (-20°C)) of the adhesive tape at -20°C is within the above range, the force during pressure bonding of the tape is difficult to escape, and the pressure bonding becomes easy. A more preferable lower limit of the above logG' (-20° C.) is 6.8 logPa, an even more preferable lower limit is 7.0 logPa, a more preferable upper limit is 7.9 logPa, and an even more preferable upper limit is 7.8 logPa. The above log G' (-20°C) can be adjusted depending on the type and thickness of the base material and adhesive.
The above log G' (-20°C) was measured using a viscoelastic spectrometer (e.g., DVA-200 manufactured by IT Kansei Control Co., Ltd.) under the conditions of constant temperature increase tensile mode at 10°C/min and 10Hz. It can be obtained as the storage modulus at -20°C when measuring the physical viscoelastic spectrum.

In the adhesive tape of the present invention, the value of (hysteresis loss rate/tape thickness) x 100 is preferably 4.5% or more.
When the value of (hysteresis loss rate/tape thickness) x 100 of the adhesive tape is within the above range, the adhesive tape can have high stress relaxation properties even though it is thin. From the viewpoint of producing an adhesive tape that is thinner and has high stress relaxation properties, the lower limit of the above (hysteresis loss rate/base material thickness) x 100 is more preferably 5.0%, still more preferably 5.2%, and even more preferably The lower limit is 5.5%, a particularly preferred lower limit is 5.7%, an especially preferred lower limit is 6%, a very preferred lower limit is 6.2%, an even more preferred lower limit is 6.4%, and a most preferred lower limit is 6.5%. It is. The upper limit of the above (hysteresis loss rate/substrate thickness) x 100 is preferably 10%, more preferably 9%, and even more preferably 8%, from the viewpoint of producing an adhesive tape that is thinner and has higher strength.
In addition, in the above (hysteresis loss rate/tape thickness)×100, the tape thickness refers to the total thickness of the adhesive tape when converted in units of μm.

The adhesive tape of the present invention preferably has a thickness of 0.1 mm or more and 2.5 mm or less.
When the thickness of the adhesive tape is within the above range, it can be used for fixing parts of thin electronic devices. From the viewpoint of further increasing the thickness and strength of the adhesive tape, the lower limit of the thickness of the adhesive tape is more preferably 0.2 mm, still more preferably 0.3 mm, and still more preferably 0.4 mm. Further, the upper limit of the thickness of the adhesive tape is more preferably 2 mm, still more preferably 1.5 mm, even more preferably 1.2 mm, particularly preferably 0.9 mm, particularly preferably 0.8 mm, and very preferably The upper limit is 0.7 mm.
Note that the thickness of the adhesive tape can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo).

The adhesive tape of the present invention preferably has a base material composition ratio of 70% or more and 95% or less.
When the proportion of the base material of the adhesive tape is within the above range, the hysteresis loss rate can be easily adjusted within the above range. A more preferable lower limit of the base material composition ratio is 75%, an even more preferable lower limit is 80%, a more preferable upper limit is 90%, and an even more preferable upper limit is 85%. In addition, the said base material composition ratio refers to the ratio which the thickness of a base material occupies in the thickness of the whole adhesive tape.

The base material is preferably made of foam.
When the base material is made of a foam, the density of the base material can be lowered, flexibility can be increased, and the hysteresis loss rate can be easily adjusted within the above range.
The foam is not particularly limited, and examples thereof include foams such as polyurethane foam, polyolefin foam, and acrylic foam, and rubber-based resins. Among these, the base material is preferably a polyolefin foam or a polyurethane foam, and more preferably a polyurethane foam, since the hysteresis loss rate can be easily adjusted to the range described above. Furthermore, among polyurethane foams, polyester-based polyurethane foams are particularly preferred.

Examples of the polyurethane foam include polyurethane foams produced by heating and curing a urethane resin composition containing a polyisocyanate and a polyol.
The polyisocyanate is not particularly limited, and examples include aromatic polyisocyanates and aliphatic polyisocyanates used in general polyurethane foams. Specifically, for example, 4,4'-diphenylmethane diisocyanate (MDI), tolylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, paraphenylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate. , 2,4,4-trimethylhexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylylene diisocyanate, hexamethylene diisocyanate, hydrogenated MDI, isophorone diisocyanate, and the like. Further, examples of the polyisocyanate include urethane prepolymers having isocyanate groups. These polyisocyanates may be used alone or in combination of two or more.

The above polyol is not particularly limited, and includes polyols used in general polyurethane foams. Specific examples include polyether polyols, polyester polyols, polyether ester polyols, and the like. Examples of the polyol include short chain diols such as trifunctional polyether polyol ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, glycerin, and trimethylolpropane. These polyols may be used alone or in combination of two or more.

The weight average molecular weight of the polyol is not particularly limited, but a preferable lower limit is 1,000 and a preferable upper limit is 12,000. When the weight average molecular weight of the polyol is within the above range, it is possible to prevent the base material from becoming too flexible and decreasing in strength.

The isocyanate index of the polyisocyanate in the urethane resin composition is not particularly limited, but a preferable lower limit is 70 and a preferable upper limit is 120.
The isocyanate index is an index related to the isocyanate equivalent in the reaction between an isocyanate and an active hydrogen-containing compound. When the isocyanate index is less than 100, it means that the reactive groups such as hydroxyl groups are in excess of the isocyanate groups, and when the isocyanate index exceeds 100, it means that the isocyanate groups are in excess of the reactive groups such as hydroxyl groups.
When the isocyanate index is 70 or more, crosslinking by the polyisocyanate is sufficient, and the base material can have appropriate flexibility. When the isocyanate index is 120 or less, it is possible to prevent the base material from being cured due to excessive crosslinking by the polyisocyanate. Moreover, if the isocyanate index is within the above range, the flexibility of the base material will increase, so that the stress relaxation properties of the base material can be improved.

The urethane resin composition may contain a catalyst, if necessary.
Examples of the above catalysts include organic tin compounds such as stannath octoate, dibutyltin diacetate, and dibutyltin dilaurate, organic zinc compounds such as zinc octylate, organic nickel compounds such as nickel acetylacetoate and nickel diacetylacetoate, and iron acetyl Examples include organic iron compounds such as acetoate. The above-mentioned catalysts include alkali metal or alkaline earth metal alkoxides such as sodium acetate, metal catalysts such as phenoxide, triethylamine, triethylenediamine, N-methylmorpholine dimethylaminomethylphenol, imidazole, 1,8-diazabicyclo[5 .4.0] Tertiary amine catalysts such as undecene, organic acid salts, etc. may also be mentioned. Among these, organic tin compounds are preferred. These catalysts may be used alone or in combination of two or more.
The amount of the catalyst added is not particularly limited, but a preferable lower limit is 0.05 parts by weight, a preferable upper limit is 5.0 parts by weight, and a more preferable upper limit is 4.0 parts by weight, based on 100 parts by weight of the polyol.

The urethane resin composition may contain a blowing agent, if necessary.
Examples of the above-mentioned blowing agent include blowing agents used in general polyurethane foams. Specific examples include water, pentane, cyclopentane, hexane, cyclohexane, dichloromethane, carbon dioxide, and the like.
The amount of the blowing agent added is not particularly limited and may be an appropriate amount, but when the blowing agent is water, it is usually about 0.1 to 3 parts by weight per 100 parts by weight of the polyol. be.

The urethane resin composition may contain a foam stabilizer, if necessary.
As the foam stabilizer, any foam stabilizer for polyurethane foam can be used without particular limitation, such as a foam stabilizer with foam-breaking properties (hereinafter referred to as a foam-breaker) or a foam stabilizer with good foam regulating properties. foam stabilizers (hereinafter simply referred to as foam stabilizers), and the like. The above-mentioned foam-breaking agent and foam stabilizer may be used alone or in combination. When a foam-breaking agent and a foam stabilizer are used together, in combination with the structure of the polyol compound and water foaming, an excellent cell morphology as an open-cell polyurethane foam can be obtained, and the above-mentioned hysteresis loss rate can be achieved. This can make it easier to satisfy the range.

Examples of the foam stabilizer include silicone foam stabilizers such as dimethylsiloxane, polyether dimethylsiloxane, and phenylmethylsiloxane. Among these, polyether dimethylsiloxane is preferred, and among polyether dimethylsiloxanes, block copolymers of dimethylpolysiloxane and polyether are more preferred. Other foam stabilizers include graft copolymers of polyoxyalkylene glycol, which is a polymer of ethylene oxide or propylene oxide, and polydimethylsiloxane, in which the oxyethylene group content in the polyoxyalkylene is 70 to 100. Mol% silicone foam stabilizers are preferably used. Specific commercially available products include SH-193, SF-2937 (manufactured by Dow Corning Toray Silicone Co., Ltd.), and B-8465 (manufactured by Evonik Degussa Japan).
The blending amount of the foam stabilizer is preferably 0.1 parts by weight or more, more preferably 0.4 parts by weight or more, and 7 parts by weight or less based on 100 parts by weight of the polyol compound. The amount is preferably 5 parts by weight or less, and more preferably 5 parts by weight or less.

The above-mentioned foam-breaking agent is a foam stabilizer that has a strong effect of destroying (opening) cells (bubbles) formed in the foaming reaction of polyurethane foam. As the foam-breaking agent, commercially available products such as SILBK9210 (manufactured by Bikkemie) and BF2470 (manufactured by Evonik Degussa Japan) are preferably used.
The amount of the foam-breaking agent blended is preferably 0.01 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the polyol compound.

The urethane resin composition may contain additives commonly used in the production of polyurethane foams, such as ultraviolet absorbers, antioxidants, organic fillers, inorganic fillers, and colorants, as necessary. good.

As a method for producing the polyurethane foam, for example, a urethane resin composition (liquid) prepared by mechanically mixing air, nitrogen, etc. and foaming is applied to the surface of a release liner or a resin film. Examples include a method of producing a foam by heating and curing (mechanical floss method). Other methods include a method (chemical foaming method) in which the polyisocyanate is reacted with the raw material for forming the polyurethane foam to generate gas. Among these, the mechanical floss method is preferred. A polyurethane foam obtained by the mechanical flossing method tends to have a higher density and a finer and more uniform cell structure than a polyurethane foam obtained by the chemical foaming method.

Examples of the resin constituting the polyolefin foam include polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer, and the like. Among these, polyethylene resin is preferred. Examples of the polyethylene resin include polyethylene resins polymerized with polymerization catalysts such as Ziegler-Natta compounds, metallocene compounds, and chromium oxide compounds.

Further, as the polyethylene resin, linear low density polyethylene is preferable. By using linear low-density polyethylene, high flexibility is imparted to the foam, and the foam layer and skin layer can be made thinner.
The linear low density polyethylene is preferably a linear low density polyethylene obtained by copolymerizing ethylene and, if necessary, a small amount of α-olefin. In this case, the content of ethylene is not particularly limited, but is preferably 75% by weight or more, more preferably 90% by weight or more based on the total monomer amount.
Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Among these, α-olefins having 4 to 10 carbon atoms are preferred.

The foam may have an open cell structure or a closed cell structure, but preferably has an open cell structure. Since the foam has an open cell structure, when the base material is deformed by an external force, the air inside the foam cells can escape to the outside, increasing flexibility and adjusting the hysteresis loss rate within the above range. It can be made easier.

FIG. 1 shows a schematic diagram of a cross section of a base material having an open cell structure and a cross section of a base material having a closed cell structure.
As shown in Figure 1, the open cell structure (left in the figure) is a cell structure in which adjacent foam cells 7 are bonded together to form an open cell, and the closed cell structure (right in the figure) This is a cell structure in which adjacent foam cells 7 are not connected to each other and exist independently. Note that independent foam cells may be present in the open cell structure as long as the open cell structure is not impaired.

Examples of methods for determining whether the foam has an open cell structure include the following method.
The foam was cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, and then cut along a plane parallel to the thickness direction with a razor blade. Using a digital microscope (for example, "VHX-500" manufactured by Keyence Corporation), take an enlarged photograph of the obtained cut surface at a magnification of 100 to 500 times, and take a picture of the area where adjacent foam cells are joined. If a plurality of are confirmed, it can be determined that the base material has an open cell structure.

It is preferable that the foam has an open cell ratio of 95% or less.
When the proportion of open cells in the cells of the foam is within the above range, the flexibility is further increased and the hysteresis loss rate can be easily adjusted within the above range. A more preferable upper limit of the open cell ratio is 93%, and an even more preferable upper limit is 91%. The lower limit of the open cell ratio is not particularly limited and is usually 0% or more, and when the foam is a polyurethane foam, the lower limit of the open cell ratio is generally about 90% by volume. In a preferred embodiment of the present invention, the foam may have a closed cell structure or an open cell structure, but the flexibility can be easily controlled and the hysteresis loss can be adjusted within the above range. It is preferable to have an open cell structure from the viewpoint of making it easier to clean.
Note that the open cell ratio is calculated by the following formula (1) using an X-ray CT device and image analysis software.
Open cell rate (volume %) = open cell volume / cell volume x 100 (1)
In formula (1), the open cell volume is the sum of the volumes of all the open cells contained in the foam of the sample to be measured, and the cell volume is the sum of the volumes of all the open cells contained in the foam of the sample to be measured. is the total volume of

The average and standard deviation of the long diameter distribution of the cells in the foam are not particularly limited, but a preferable upper limit of the average long diameter distribution of the cells is 80 μm, and a preferable upper limit of the standard deviation of the long diameter distribution of the cells is 45 μm.
By adjusting the average and standard deviation of the long diameter distribution to the above range and suppressing the bubble size and the variation in bubble size to below a certain level, flexibility is further increased and the hysteresis loss rate is adjusted to the above range. It can be made easier. In addition, if the bubbles are too large or the size of the bubbles varies, especially when using a thin and narrow double-sided adhesive tape, localized areas of low strength are likely to occur in the foam. Interlayer failure of the foam or peeling of the adhesive tape tends to occur starting from the above locations. By adjusting the average and standard deviation of the above-mentioned length distribution to the above range and suppressing the bubble size and the variation in bubble size to below a certain level, the strength of the adhesive tape can be made more uniform, and the strength of the adhesive tape can be further improved. can be improved.

A more preferable upper limit of the average length distribution is 70 μm, an even more preferable upper limit is 65 μm, and an even more preferable upper limit is 60 μm. The average lower limit of the length distribution is not particularly limited, and is determined depending on the relationship between the cell volume fraction and the thickness of the foam, but the practical lower limit is about 10 μm.
A more preferable upper limit of the standard deviation of the length distribution is 40 μm, an even more preferable upper limit is 35 μm, and an even more preferable upper limit is 30 μm. The lower limit of the standard deviation of the long diameter distribution is not particularly limited, and is preferable as it is smaller because there is less variation in the size of the bubbles, but the limit in terms of manufacturing technology is about 10 μm.
Note that the average and standard deviation of the bubble length distribution are calculated by determining the bubble length distribution using an X-ray CT device and image analysis software, and calculating the average and standard deviation from the obtained length diameter distribution.

The preferable lower limit of the density of the base material is 100 kg/m ³ and the preferable upper limit is 500 kg/m ³ .
When the density of the base material is 100 kg/m ³ or more, the strength of the base material and the adhesive tape can be sufficiently increased. If the density of the base material is 500 kg/m ³ or less, sufficient flexibility can be ensured, so that the hysteresis loss rate of the adhesive tape can be easily adjusted within the above range. A more preferable lower limit of the base material is 120 kg/m ³ , a more preferable upper limit is 450 kg/m ³ , an even more preferable lower limit is 160 kg/m ³ , and an even more preferable upper limit is 400 kg/m ³ .
Note that the density can be measured using an electronic hydrometer (for example, "ED120T" manufactured by Mirage) in accordance with JIS K 6401 (when polyurethane is used) and JIS K 6767 (when polyethylene is used).

The 25% compressive strength of the base material is not particularly limited, but a preferable lower limit is 8 kPa, and a preferable upper limit is 50 kPa. When the 25% compressive strength of the base material is within the above range, the density of the base material is lowered and the flexibility of the resulting adhesive tape is increased, making it easier to adjust the hysteresis loss rate within the above range. . A more preferable lower limit of the 25% compressive strength of the base material is 9 kPa, a more preferable upper limit is 45 kPa, an even more preferable lower limit is 10 kPa, and an even more preferable upper limit is 40 kPa.
Note that the 25% compressive strength can be determined by measuring according to JIS K 6254.

The glass transition point (Tg) of the above substrate is not particularly limited, but is preferably -30°C or higher and 20°C or lower. When the glass transition point is within the above range, the base material tends to have appropriate flexibility, and the hysteresis loss rate of the resulting adhesive tape can be easily adjusted within the above range. A more preferable upper limit of the glass transition point is -25°C, an even more preferable lower limit is -20°C, an even more preferable lower limit is -15°C, an especially preferable lower limit is -10°C, a more preferable upper limit is 15°C, and an even more preferable upper limit is 10°C. ℃, and the even more preferable upper limit is 7℃.
The glass transition point can be measured, for example, using a differential scanning calorimeter (for example, DSC-6200R, manufactured by Seiko Electronics Co., Ltd.) at a heating rate of 10° C./min in accordance with JIS K7121. can.

The thickness of the base material is not particularly limited, but is preferably 0.05 mm or more and 2.0 mm or less.
When the thickness of the base material is within the above range, the resulting adhesive tape can be made thin, and the adhesive tape can be used for fixing components in the manufacture of thin electronic devices.
From the viewpoint of further increasing the thinness and strength of the base material, the lower limit of the thickness of the base material is more preferably 0.1 mm, still more preferably 0.2 mm, even more preferably 0.25 mm, and particularly preferably 0.3 mm. It is. Further, the upper limit of the thickness of the base material is more preferably 1.7 mm, still more preferably 1.5 mm, even more preferably 1.3 mm, particularly preferably 1 mm, particularly preferably 0.9 mm, and very preferably The upper limit is 0.8 mm.
Note that the thickness of the base material can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo).

The adhesive tape of the present invention preferably has a resin sheet integrated with the base material.
By using the resin sheet, it is possible to prevent the base material from stretching and breaking during handling, and it is possible to impart reworkability to the adhesive tape. The base material may have the resin sheet on one side or both sides of the base material.
The resin constituting the resin sheet is not particularly limited, and examples include polyester resins such as polyethylene terephthalate, acrylic resins, polyethylene resins, polypropylene resins, polyvinyl chloride, epoxy resins, silicone resins, phenol resins, polyimides, Examples include polyester and polycarbonate. Among these, thermoplastic resins are preferred. In addition, when the said base material has the said resin sheet on both surfaces of the said base material, it is preferable that at least one resin sheet consists of thermoplastic resin. That is, in the adhesive tape of the present invention, it is preferable that at least one of the resin sheets is made of a thermoplastic resin.

The above-mentioned thermoplastic resin is not particularly limited, and examples thereof include styrene-based (co)polymers, olefin-based (co)polymers, vinyl chloride-based (co)polymers, polyether ester-based triblock-based (co)polymers, Examples include polyester (co)polymers, urethane (co)polymers, amide (co)polymers, acrylic (co)polymers, and the like. Among these, the above-mentioned thermoplastic resin is acrylic because it has excellent strength, elongation, flexibility, and self-adhesiveness as an elastic body, can exhibit high reworkability, and can further improve the adhesion between the resin sheet and the base material. It is preferable that they are a type (co)polymer, a styrene type (co)polymer or an olefin type (co)polymer. Furthermore, an acrylic (co)polymer or a styrene (co)polymer is more preferable, and a styrene (co)polymer is even more preferable.

When the resin constituting the resin sheet is a thermoplastic resin, the resin sheet preferably has a tensile modulus of 200 MPa or less. By using a flexible resin with a tensile modulus of 200 MPa or less, the flexibility of the entire adhesive tape is ensured, making it easy to wind up the double-sided adhesive tape into a roll, and handling properties are significantly improved. In particular, when the base material has the resin sheet on both sides of the base material, if at least one of the resin sheets has the tensile modulus described above, it is possible to suppress breakage of the base material, impart reworkability, and improve handleability. This is preferable because it allows The lower limit of the tensile modulus of the resin sheet is not particularly limited, but is preferably, for example, 1 MPa.
The above tensile modulus can be measured by a method according to JIS K 7161. Specifically, a test piece is prepared by punching out a resin sheet into a dumbbell shape using, for example, a punching blade "Tensile Type 1 Dumbbell Shape" manufactured by Kobunshi Keiki Co., Ltd. or the like. The tensile modulus of the obtained test piece is measured at a tensile speed of 100 mm/min using, for example, "Autograph AGS-X" manufactured by Shimadzu Corporation. The tensile modulus is calculated from the slope of the tensile strength between 1 and 3% strain.

The thickness of the resin sheet is not particularly limited, but a preferable lower limit is 10 μm and a preferable upper limit is 100 μm. If the thickness of the resin sheet is 10 μm or more, the resin sheet will be difficult to break even when the resin sheet is pulled. If the thickness of the resin sheet is 100 μm or less, deterioration in followability to an adherend may be suppressed.

The resin sheet may be colored. By coloring the resin sheet, light-shielding properties can be imparted to the adhesive tape.
The method of coloring the resin sheet is not particularly limited, and examples include a method of kneading particles of carbon black, titanium oxide, etc. or fine air bubbles into the resin constituting the resin sheet, and a method of applying ink to the surface of the resin sheet. Examples include methods.

The method of forming the resin sheet on the base material is not particularly limited, but for example, it may be formed by placing a resin sheet on the base material and heat-sealing it, or by forming the base material on the resin sheet. be able to.

The adhesive tape of the present invention has an adhesive layer on at least one side.
When adhesive layers are formed on both sides of the base material, the adhesive layers may have the same composition or may have different compositions.
The adhesive layer is not particularly limited, and examples thereof include an acrylic adhesive layer, a rubber adhesive layer, a urethane adhesive layer, a silicone adhesive layer, and the like. Among these, an acrylic adhesive layer is preferred because it is relatively stable against light, heat, moisture, etc., and has low selectivity to adherends.

The acrylic copolymer constituting the acrylic adhesive layer is obtained by copolymerizing a monomer mixture. Among these, it is preferable to copolymerize a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate.
The preferred content of 2-ethylhexyl acrylate in the total monomer mixture is 20 to 100% by weight. When the content of 2-ethylhexyl acrylate is 20% by weight or more, the acrylic adhesive layer has appropriate hardness and sufficient cohesive force, and the adhesive strength of the adhesive tape increases.
The preferred content of butyl acrylate in the total monomer mixture is 0 to 60% by weight. When the content of butyl acrylate is 60% by weight or less, it is possible to prevent the acrylic pressure-sensitive adhesive layer from becoming hard and reducing its tackiness and wettability (adhesive strength at the interface with the adherend).

The monomer mixture may contain other copolymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate, if necessary.
Other polymerizable monomers that can be copolymerized include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, etc. having a carbon number of an alkyl group. (meth)acrylic acid alkyl esters having 1 to 3 carbon atoms, tridecyl methacrylate, (meth)acrylic acid alkyl esters having 13 to 18 carbon atoms in the alkyl group such as stearyl (meth)acrylate, and hydroxyalkyl (meth)acrylates. , glycerin dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, and other functional monomers.

In order to copolymerize the monomer mixture to obtain the acrylic copolymer, the monomer mixture may be subjected to a radical reaction in the presence of a polymerization initiator. As a method for radically reacting the monomer mixture, that is, as a polymerization method, conventionally known methods are used, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.
The polymerization initiator is not particularly limited, and examples thereof include organic peroxides, azo compounds, and the like. Examples of the organic peroxides 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, azobiscyclohexanecarbonitrile, and the like. These polymerization initiators may be used alone or in combination of two or more.

The preferable lower limit of the weight average molecular weight (Mw) of the acrylic copolymer is 400,000, and the preferable upper limit is 1,700,000. If the weight average molecular weight is 400,000 or more, the acrylic adhesive layer will have appropriate hardness and sufficient cohesive force, and the adhesive strength of the adhesive tape will increase. If the weight average molecular weight is 1.7 million or less, the adhesive force of the acrylic adhesive layer will be sufficient. A more preferable lower limit of the weight average molecular weight is 500,000, and a more preferable upper limit is 1.4 million. In order to adjust the weight average molecular weight within the above range, the polymerization conditions such as the polymerization initiator and polymerization temperature may be adjusted.

The preferable upper limit of the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic copolymer is 10.0. If Mw/Mn is 10.0 or less, the content of low molecular weight components etc. will be reduced, so the cohesive force and wettability (adhesive strength at the interface with the adherend) of the acrylic adhesive layer will be high, Adhesive strength increases. A more preferable upper limit of Mw/Mn is 5.0, and an even more preferable upper limit is 3.0. In order to adjust Mw/Mn within the above range, the polymerization conditions such as the polymerization initiator and polymerization temperature may be adjusted.
Note that the number average molecular weight (Mn) and the weight average molecular weight (Mw) are weight average molecular weights in terms of standard polystyrene determined by GPC (Gel Permeation Chromatography). For GPC, for example, 2690 Separations Module (manufactured by Waters) can be used.

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

The content of the tackifier resin is not particularly limited, but the preferable lower limit is 10 parts by weight and the preferable upper limit is 60 parts by weight based on 100 parts by weight of the resin (for example, acrylic copolymer) that is the main component of the adhesive layer. . If the content of the tackifier resin is 10 parts by weight or more, the adhesive force of the adhesive layer will be high. When the content of the tackifying resin is 60 parts by weight or less, the adhesive layer is prevented from becoming too hard and the adhesive strength, tackiness, or wettability (adhesive strength at the interface with the adherend) is reduced. can do.

The adhesive layer has a crosslinked structure formed between the main chains of the resin (for example, the acrylic copolymer, the tackifier resin, etc.) that constitutes the adhesive layer by adding a crosslinking agent. is preferred.
The crosslinking agent is not particularly limited, and examples thereof include isocyanate crosslinking agents, aziridine crosslinking agents, epoxy crosslinking agents, metal chelate crosslinking agents, and the like. Among these, isocyanate-based crosslinking agents are preferred. By adding an isocyanate-based crosslinking agent to the adhesive layer, the isocyanate group of the isocyanate-based crosslinking agent and the alcohol in the resin (e.g., the acrylic copolymer, the tackifier resin, etc.) constituting the adhesive layer are combined. The crosslinking of the pressure-sensitive adhesive layer becomes loose due to the reaction with the hydroxyl groups. Therefore, the adhesive layer can disperse the peeling stress that is applied intermittently, and the adhesive strength of the adhesive tape is further improved.
The amount of the crosslinking agent added is preferably 0.01 to 10 parts by weight, and preferably 0.1 to 7 parts by weight, based on 100 parts by weight of the resin (for example, the acrylic copolymer) that is the main component of the adhesive layer. is more preferable.

The degree of crosslinking of the adhesive layer is preferably 5 to 70% by weight, and preferably 10 to 55% by weight, because if it is too high or too low, it may easily peel off from the adherend when large stress is applied. More preferably, 15 to 50% by weight is particularly preferred.
The degree of crosslinking of the adhesive layer was determined by taking W ₁ (g) of the adhesive layer, immersing the adhesive layer in ethyl acetate at 23°C for 24 hours, and filtering the insoluble matter through a 200 mesh wire mesh. Then, the residue on the wire mesh is vacuum-dried, and the weight W ₂ (g) of the dried residue is measured and calculated using the following formula (1).
Degree of crosslinking (weight %) = 100 x W ₂ /W ₁ (1)

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferable lower limit of the thickness of the pressure-sensitive adhesive layer on one side is 0.01 mm, and the preferable upper limit is 0.1 mm. When the thickness of the adhesive layer is 0.01 mm or more, the tackiness of the adhesive layer can be prevented from decreasing, and the adhesive tape can be successfully attached to an adherend. When the thickness of the adhesive layer is 0.1 mm or less, it is possible to suppress the adhesive from seeping out when processing the adhesive layer or the adhesive tape, and to prevent processing defects. A more preferable lower limit of the thickness of the adhesive layer is 0.015 mm, and a more preferable upper limit is 0.09 mm.
Note that the thickness of the adhesive layer can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo).

The adhesive layer may contain a silane coupling agent for the purpose of improving adhesive strength. The silane coupling agent is not particularly limited, and examples thereof include epoxysilanes, acrylic silanes, methacrylsilanes, aminosilanes, isocyanate silanes, and the like.

The adhesive layer may contain a coloring material for the purpose of imparting light-shielding properties. The above-mentioned coloring material is not particularly limited, and examples thereof include carbon black, aniline black, titanium oxide, and the like. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable.

Examples of the method for manufacturing the adhesive tape of the present invention include the following methods.
First, a solution of adhesive A is prepared by adding a solvent to the acrylic copolymer, tackifier resin, crosslinking agent, etc. if necessary, and this solution of adhesive A is applied to the surface of the base material. The adhesive layer A is formed by completely drying and removing the solvent. Next, a release film is placed on the formed adhesive layer A with its release-treated surface facing the adhesive layer A.
Next, a release film different from the above-mentioned release film is prepared, and a solution of adhesive B is applied to the release-treated surface of the release film, and the solvent in the solution is completely dried and removed. A laminated film in which an adhesive layer B is formed on the surface of a mold film is produced. The obtained laminated film is laminated on the back surface of the base material on which the adhesive layer A is formed, with the adhesive layer B facing the back surface of the base material to produce a laminate. Then, by pressurizing the laminate with a rubber roller or the like, it is possible to obtain an adhesive tape that has adhesive layers on both sides of the base material and the surface of the adhesive layer is covered with a release film.

In addition, two sets of laminated films were produced in the same manner, and these laminated films were stacked on both sides of the base material with the adhesive layer of the laminated film facing the base material to produce a laminate. By pressing this laminate with a rubber roller or the like, an adhesive tape having adhesive layers on both sides of the base material and the surface of the adhesive layer covered with a release film may be obtained.
Furthermore, if the adhesive layer is formed on only one side of the base material using the above two methods, the adhesive layer will have an adhesive layer on one side of the base material and the surface of the adhesive layer will be covered with a release film. You can get the tape.

The use of the adhesive tape of the present invention is not particularly limited, and is used, for example, for fixing parts of portable electronic equipment, parts of automotive electronic equipment, and the like. The shape of the adhesive tape of the present invention for these uses is not particularly limited, but examples include rectangular, frame-shaped, circular, oval, donut-shaped, and the like.

Articles to which the adhesive tape of the present invention can be used include, for example, flat panel displays used in TVs, monitors, portable electronic devices, etc., camera modules for portable electronic devices, internal parts of portable electronic devices, vehicle interiors, home appliances (e.g. , TVs, air conditioners, refrigerators, etc.). Examples of adherends of the adhesive tape of the present invention include side panels, back panels of portable electronic devices, various nameplates, decorative films, decorative films, and the like.
In particular, since the adhesive tape of the present invention is thin and has excellent stress relaxation properties, it is preferably used for fixing components in the manufacture of electronic devices, etc., and particularly for use in display members in the manufacture of display devices. It is preferable to use it for fixing and joining to a housing or the like.
A method for fixing and joining display members using such an adhesive tape of the present invention is also one of the present inventions.

According to the present invention, it is possible to provide an adhesive tape that can exhibit high stress relaxation properties even when the adhesive tape is thin, and a method for fixing and joining a display member using the adhesive tape.

FIG. 2 is a schematic diagram of a cross section of a base material having an open cell structure and a cross section of a base material having a closed cell structure. FIG. 3 is a schematic diagram illustrating a sample for evaluating display unevenness. It is a schematic diagram explaining evaluation of interlayer strength.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

(Manufacture of base material)
(Production of polyurethane 1 (PU1) foam)
0.7 parts by weight of an amine catalyst, 1 part by weight of a foam stabilizer, and 0.05 parts by weight of a foam-breaker were added to 89 parts by weight of polypropylene glycol and 11 parts by weight of ε-caprolactam, and the mixture was stirred. Dinuclear monomeric MDI was adjusted to have an isocyanate index of 100 and added thereto. Thereafter, the solution was mixed with nitrogen gas and stirred to a concentration of 240 kg/m ³ to obtain a solution containing fine bubbles. The solution was applied to a predetermined thickness on a 50 μm thick PET separator using an applicator, and the foam raw materials were reacted to obtain a polyurethane (PU) foam with a thickness of 550 μm. The details of the composition are as follows.
Amine catalyst: DABCO LV33, Sankyo Air Products Foam stabilizer: SZ5740M, Dow Corning Toray Foam Breaking Agent: SILBK9210, BYK Chemie PET separator: V-2, Nipper Co., Ltd.

The obtained polyurethane 1 (PU1) foam was cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, and then cut along a plane parallel to the thickness direction with a razor blade. As a result of taking an enlarged photograph of the obtained cut surface at 100x magnification using a digital microscope (manufactured by Keyence Corporation, "VHX-500"), it was confirmed that adjacent foam cells were connected to each other. This confirmed that the polyurethane 1 (PU1) foam had an open cell structure. In addition, the density of the obtained polyurethane 1 (PU1) foam was measured using an electronic hydrometer (manufactured by Mirage, "ED120T") in accordance with JIS K 6401, and was found to be 240 kg/ ^m3 . . The 25% compressive strength of the obtained polyurethane (PU) foam was determined to be 11.4 kPa in accordance with JIS K 6254. Furthermore, the glass transition point of the obtained polyurethane (PU) foam was measured using a differential scanning calorimeter (DSC-6200R, manufactured by Seiko Electronic Industries, Inc.) at a heating rate of 10°C/min in accordance with JIS K 7121. As a result of the measurement, the temperature was 5°C.

(Production of polyurethane 2-12 (PU2-12) foam)
A polyurethane 2-12 (PU2-12) foam was obtained in the same manner as PU1, except that the composition of polyol and polyisocyanate and the isocyanate index were as shown in Tables 1 and 2, and the mixing conditions with nitrogen gas and foaming conditions were adjusted. Each measurement was carried out.

(Production of polyethylene 1 (PE1) foam)
100 parts by mass of a polyolefin resin, 5 parts by mass of a thermally decomposable blowing agent, 1 part by mass of a decomposition temperature regulator, and 0.4 parts by mass of an antioxidant were fed into an extruder and melted and kneaded at 130° C. to a thickness of about 0. A foam composition in the form of a long sheet of .2 mm was extruded.
Next, both sides of the elongated sheet-like foam composition were crosslinked by irradiating 4.5 Mrad of electron beams with an accelerating voltage of 500 kV. After that, it is continuously fed into a foaming furnace maintained at 250°C using hot air and an infrared heater to heat and foam, and while foaming, the MD stretching ratio is 2.5 times, and the TD stretching ratio is 2.5 times. By stretching it twice, a foamed sheet with a thickness of 0.5 mm was obtained. Each measurement was performed on the obtained polyethylene foam. The details of the composition are as follows.
Polyolefin resin: Linear low-density polyethylene, "Exact3027" manufactured by Exxon Chemical Co., density: 0.900 g/cm ³
Pyrolytic blowing agent: Azodicarbonamide Decomposition temperature regulator: Zinc oxide Antioxidant: 2,6-di-t-butyl-p-cresol

(Production of polyethylene 2 (PE2) foam)
When producing a long sheet-shaped foam composition, the amount of polyolefin resin blended was 70 parts by weight, 30 parts by weight of ethylene-1-octene copolymer was added, and the amount of blowing agent was 7 parts by weight. The MD draw ratio was changed to 2.0 times, and the TD draw ratio was changed to 2.0 times. Except for these points, a polyethylene 2 (PE2) foam was obtained in the same manner as the production of the PE1 foam, and each measurement was performed.
Ethylene-1-octene copolymer: Linear low-density polyethylene that is an ethylene-1-octene copolymer obtained using a metallocene compound polymerization catalyst, "Affinity KC8852" manufactured by Dow Chemical Company, density 0.875 g /cm ³ , melting point (DSC method) Tm: 66°C

(Preparation of adhesive)
52 parts by weight of ethyl acetate was placed in a reactor equipped with a thermometer, a stirrer, and a cooling tube, and the atmosphere was purged with nitrogen, and then the reactor was heated to start reflux. Thirty minutes after the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 7 parts by weight of butyl acrylate, 90 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 0.2 parts by weight of 2-hydroxyethyl acrylate was evenly and gradually dropped therein over 1 hour and 30 minutes. Made it react. 30 minutes after the completion of the dropwise addition, 0.1 part by weight of azobisisobutyronitrile was added, and the polymerization reaction was further carried out for 5 hours. Ethyl acetate was added to the reactor and cooled while diluting to obtain a solid content of 35% by weight. A solution of acrylic copolymer (a) was obtained. The weight average molecular weight of the obtained acrylic copolymer (a) was measured by GPC using "2690 Separations Module" manufactured by Water as a column and found to be 710,000. The ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw/Mn) was 2.0.
Based on 100 parts by weight of the solid content of the obtained acrylic copolymer (a), 15 parts by weight of polymerized rosin ester with a softening point of 150°C, 10 parts by weight of terpene phenol with a softening point of 145°C, and rosin ester with a softening point of 70°C. 10 parts by weight were added. Furthermore, 30 parts by weight of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.) and 3.0 parts by weight of an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., trade name "Coronate L45") were added and stirred to obtain an adhesive solution. Ta.

(Example 1)
(1) Production of adhesive tape Prepare a release paper with a thickness of 150 μm, apply an adhesive solution to the release-treated surface of the release paper, and dry it at 100°C for 5 minutes to form an acrylic adhesive layer with a thickness of 70 μm. Formed. This acrylic adhesive layer was bonded to the surface of a polyurethane 1 (PU1) foam having a thickness of 550 mm. Then, in the same manner, the same acrylic adhesive layer as above was laminated to the opposite surface of this polyurethane 1 (PU1) foam. Thereafter, curing was performed by heating at 40° C. for 48 hours. As a result, an adhesive tape with a thickness of 690 μm whose both sides were covered with release paper and a thickness of 150 μm was obtained.

(2) Measurement of hysteresis loss rate The obtained adhesive tape was cut into 20 mm x 20 mm, and a plurality of these were laminated to a thickness of 5 mm or more to prepare a test piece. For the obtained test piece, a Kerr deflection curve was drawn in accordance with JIS K6400-2, except that the speed was 10 mm/min and the pressure was up to 50% of the initial thickness, and the hysteresis loss rate was calculated. The results are shown in Table 3.

(3) Measurement of 25% compressive strength and 50% compressive strength The 25% compressive strength and 50% compressive strength of the obtained adhesive tape were determined by measuring according to JIS K 6254. The results are shown in Table 3.

(4) Measurement of shear storage modulus (log G' (-20 °C)) at -20°C DVA-200) under the conditions of constant rate temperature rise tensile mode at 10° C./min and 10 Hz. The results are shown in Table 3.

(Examples 2 to 9, Comparative Examples 1 to 5)
An adhesive tape was obtained in the same manner as in Example 1 except that the composition of the adhesive tape was as shown in Tables 3 and 4, and each measurement was performed.

(Example 10)
A release paper with a thickness of 150 μm was prepared, and an adhesive solution was applied to the release-treated surface of the release paper and dried at 100° C. for 5 minutes to form an acrylic adhesive layer with a thickness of 40 μm. On the other hand, a polyurethane 2 (PU2) foam having a thickness of 550 mm was foamed on polyethylene terephthalate (X30, manufactured by Toray Industries, Inc., thickness 50 μm) to integrate the foam and the resin sheet. Thereafter, the surface of the foam on which the resin sheet was not laminated was bonded to the obtained acrylic adhesive layer. Next, in the same manner, the same acrylic adhesive layer as above was attached to the surface of the foam on which the resin sheet was laminated. Thereafter, curing was performed by heating at 40° C. for 48 hours. Thereby, an adhesive tape with a thickness of 680 μm whose both sides were covered with release paper and a thickness of 150 μm was obtained. The same measurements as in Example 1 were performed on the obtained adhesive tape.

(Example 11)
A polyurethane 2 (PU2) foam with a thickness of 550 mm was foamed on polyethylene terephthalate (X30, manufactured by Toray Industries, Inc., thickness 50 μm) to integrate the foam and the resin sheet 1. Next, a resin sheet 2 (LA2250, acrylic block copolymer, manufactured by Kuraray Co., Ltd., thickness 30 μm) is heat-sealed on the surface of the PU2 foam opposite to the surface on which the resin sheet 1 is laminated. A base material was prepared in which 1/PU2 foam/resin sheet 2 were laminated and integrated in this order.
Next, a release paper with a thickness of 150 μm was prepared, and an adhesive solution was applied to the release-treated surface of the release paper and dried at 100° C. for 5 minutes to form an acrylic adhesive layer with a thickness of 40 μm. This adhesive layer was bonded to the surface of the resin sheet 1 as a base material. Next, in the same manner, the same acrylic adhesive layer as above was attached to the surface of the base material on which the resin sheet 2 was laminated. Thereafter, curing was performed by heating at 40° C. for 48 hours. Thereby, an adhesive tape whose both sides were covered with release paper was obtained. The same measurements as in Example 1 were performed on the obtained adhesive tape. Note that the tensile modulus of the resin sheet 2 was 10 MPa.

<Evaluation>
The adhesive tapes obtained in Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 3 and 4.

(1) Evaluation of display unevenness FIG. 2 shows a sample for evaluating display unevenness. As shown in FIGS. 2(a) and 2(b), a glass plate 21 measuring 256 mm wide x 182 mm high and 4 mm thick is placed 50 mm inward from one short side of the glass plate 21 with a size of 15 mm wide x 182 mm long and 0.1 mm thick. Two plates 3 were installed at 15 mm intervals, and a plate 4 measuring 15 mm wide x 182 mm long and 0.2 mm thick was placed 40 mm inward from the other short side. Next, one side of the adhesive tape 1 having a width of 10 mm was attached to the outer periphery of the glass plate so that the tapes did not overlap each other, and the tape was crimped with a squeegee. Thereafter, a glass plate 22 measuring 256 mm in width x 182 mm in length and 1 mm in thickness was attached to the other side of the adhesive tape 1 and pressed again with a squeegee to prepare a sample for evaluation. A roughness curve was created for the obtained evaluation sample using a 3D laser microscope (VR-3200, manufactured by Keyence Corporation). As shown by the broken line in Figure 2(a), the measuring range is 105 mm in the vertical direction starting from a point 5 mm inward from one long side of the sample in the vertical direction, and 105 mm in the horizontal direction from the point 5 mm inward from one long side of the sample. The area was 210 mm (210 mm x 105 mm), excluding 20 mm from both end sides.
Next, a roughness curve was created using the sample created in the same manner as above except that plates 3 and 4 were not placed as a reference, and the roughness curve of the reference was compared with the roughness curve of each sample. Display unevenness was evaluated using the following criteria.
◎: No distortion was observed even in the 0.2 mm plate portion. ○: Distortion was observed in the 0.2 mm plate portion, but no distortion was observed in the 0.1 mm plate portion. ×: 0. Distortion was observed even in the 1 mm plate portion.

(2) Evaluation of interlayer strength FIG. 3 is a schematic diagram showing a tensile test of the double-sided pressure-sensitive adhesive tape of the present invention.
As shown in Fig. 3, using an adhesive tape 1 cut to 25 mm x 25 mm, a 2 mm thick polycarbonate plate (length 50 mm x width 50 mm) 5 and a 2 mm thick stainless steel jig (30 mm x 30 mm) ( (not shown, but provided with a handle) 6 were laminated. After 5 kg of this laminate was pressed using a roller for 10 seconds, it was left to stand still for 24 hours to produce a sample in which the polycarbonate plate 5 and the jig 6 were bonded together via the adhesive tape 1. After fixing the polycarbonate plate 5 of this sample, the jig 6 was pulled at 10 mm/min in the plane direction (arrow direction in the figure) at 23°C to measure the interlaminar breaking strength (interlaminar strength) of the adhesive tape. It was measured. The obtained interlaminar strength was evaluated according to the following criteria.
◎: Interlayer strength is 140N or more ○: Interlayer strength is 100N or more and less than 140N ×: Interlayer strength is less than 100N

According to the present invention, it is possible to provide an adhesive tape that can exhibit high stress relaxation properties even when the adhesive tape is thin, and a method for fixing and joining a display member using the adhesive tape.

1 Adhesive tape 21 Glass plate (256mm x 182mm x 4mm)
22 Glass plate (256mm x 182mm x 1mm)
3 Plate (15mm x 182mm x 0.1mm)
4 board (15mm x 182mm x 0.2mm)
5 Polycarbonate plate 6 Jig 7 Foaming cell

Claims (10)

An adhesive tape having an adhesive layer on at least one side of a base material,
The base material is made of polyurethane foam,
The base material has a density of 500 kg/m ³ or less,
The adhesive tape has a hysteresis loss rate of 30% or more and 80% or less,
The value of (hysteresis loss rate/tape thickness) x 100 is 4.5% or more,
An adhesive tape having a 50% compressive strength of 30 kPa or more and 650 kPa or less . The adhesive tape according to claim 1, wherein the adhesive tape has a 25% compressive strength of 8 kPa or more and 50 kPa or less. The adhesive tape according to claim 1 or 2 , wherein the adhesive tape has a thickness of 0.1 mm or more and 2.5 mm or less. The adhesive tape according to claim 1, 2 or 3 , wherein the thickness of the base material is 0.05 mm or more and 2.0 mm or less. The adhesive tape according to claim 1, 2, 3, or 4 , wherein the base material has a resin sheet integrated with the base material. The adhesive tape according to claim 5 , wherein the base material has the resin sheet on both sides of the base material. The adhesive tape according to claim 5 or 6 , wherein the resin sheet is made of thermoplastic resin. The adhesive tape according to claim 6 , wherein at least one of the resin sheets is made of a thermoplastic resin. The adhesive tape according to claim 5, 6, 7, or 8 , wherein the resin sheet has a thickness of 10 μm or more and 100 μm or less. A method for fixing and joining display members using the adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9 .

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