JP2022071863A - Adhesive tape - Google Patents

Abstract

To provide an adhesive tape having excellent impact absorption.SOLUTION: An adhesive tape has an impact absorbing sheet, and an adhesive layer laminated on at least one side of the impact absorbing sheet. The impact absorbing sheet has a loss tangent tanδ of 0.8 or more at 23°C in a frequency range of 1.0×103.5-1.0×104 Hz. In tensile measurement, if an elongation at break is defined as X(%) and a strength at break is defined as Y(MPa), X≥400 and (Y/X)×100≥0.1 hold true.SELECTED DRAWING: None

Description

The present invention relates to an adhesive tape.

Adhesive tapes are used for assembly in mobile 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 device parts such as in-vehicle panels to the vehicle body.

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

Adhesive tapes used for fixing portable electronic device parts, in-vehicle electronic device parts, and the like are required to have high adhesive strength and impact resistance that does not peel off even when impacted. On the other hand, in recent years, portable electronic devices, in-vehicle electronic devices, etc. tend to have more complicated shapes due to higher functionality. be. In such a case, the adhesive tape is required to have excellent flexibility to follow the shape of the adherend.

As an adhesive tape having excellent flexibility and impact resistance, for example, an adhesive tape using a foam base material obtained by foaming a polyolefin resin or the like is known. However, in recent years, in electronic devices, the width of the outer frame (frame) of a display display has been narrowed, that is, the so-called narrow frame has been narrowed, and the adhesive tape used in such a narrow area has a narrower width than before. It has become. As an adhesive tape used for assembling or fixing electronic device parts, even if the adhesive tape is narrowed or the shape of the adherend is complicated in this way, it is peeled off and adhered when it receives an impact. There is a demand for an adhesive tape with even better shock absorption that can prevent damage to the body.

An object of the present invention is to provide an adhesive tape having excellent shock absorption.

The present invention is an adhesive tape having a shock absorbing sheet and an adhesive layer laminated on at least one surface of the shock absorbing sheet, and the shock absorbing sheet has a frequency of 1.0 × 10 at 23 ° C. When the loss tangent tan δ at ^3.5 to 1.0 × 10 ⁴ Hz is 0.8 or more, the breaking elongation in tensile measurement is X (%), and the breaking strength is Y (MPa), X ≧ 400 and An adhesive tape satisfying (Y / X) × 100 ≧ 0.1.
The present invention will be described in detail below.

The present inventors analyzed factors affecting shock absorption in an adhesive tape having a shock absorbing sheet and a pressure-sensitive adhesive layer laminated on at least one surface of the shock absorbing sheet. As a result, the present inventors adjusted the loss tangent tan δ of the shock absorbing sheet in a specific frequency range at 23 ° C. to a specific range, and set the breaking elongation in tensile measurement to X (%) and the breaking strength to Y (MPa). We have found that the shock absorption of the adhesive tape can be improved by adjusting X and Y so as to satisfy a specific formula, and have completed the present invention.

The pressure-sensitive adhesive tape of the present invention has a shock-absorbing sheet and a pressure-sensitive adhesive layer laminated on at least one surface of the shock-absorbing sheet.
The shock absorbing sheet has a lower limit of 0.8 for the loss tangent tan δ at a frequency of 1.0 × 10 ^3.5 to 1.0 × 10 ⁴ Hz at 23 ° C. Since the loss tangent tan δ in the frequency range at 23 ° C. is 0.8 or more, the amount of deformation of the shock absorbing sheet immediately after being impacted increases, so that the adhesive tape of the present invention has excellent shock absorption. Can have sex. The preferable lower limit of the loss tangent tan δ in the frequency range at 23 ° C. is 0.9, the more preferable lower limit is 1.0, and the further preferable lower limit is 1.1. The upper limit of the loss tangent tan δ in the frequency range at 23 ° C. is not particularly limited, but the preferable upper limit is 3.0 because the deformation of the shock absorbing sheet is suppressed and the handling during processing is easy. The upper limit is 2.7, and a more preferable upper limit is 2.5.
The loss tangent tan δ of the shock absorbing sheet at a frequency of 1.0 × 10 ^3.5 to 1.0 × 10 ⁴ Hz at 23 ° C. is a viscoelastic spectrometer (for example, DVA-200 manufactured by IT Measurement Control Co., Ltd.). Etc.) can be used for measurement. More specifically, the target sample is cut to 5 mm × 30 mm, fixed at a chuck interval of 15 mm, and the tensile viscoelastic modulus is measured under the conditions of a heating rate of 5 ° C./min and −40 to 140 ° C. Then, the loss tangent tan δ is calculated by synthesizing the master curve at the reference temperature of 23 ° C.

The method of adjusting the loss tangent tan δ in the frequency range at 23 ° C. to the above range is not particularly limited. For example, a block copolymer having a hard block and a soft block as described later is applied to the shock absorbing sheet. Examples include the method to be used. Above all, it is preferable to adjust the content of the hard block and the content of the structure derived from the (meth) acrylic monomer having a glass transition temperature of the homopolymer in the soft block of −50 ° C. or lower. .. Further, a method of adjusting the apparent density of the shock absorbing sheet, a method of adjusting the content of foamed particles (particularly hollow organic particles) in the shock absorbing sheet, and the like can also be mentioned.

The impact absorbing sheet satisfies X ≧ 400 and (Y / X) × 100 ≧ 0.1 when the breaking elongation in tensile measurement is X (%) and the breaking strength is Y (MPa).
When the breaking elongation X is 400% or more, the impact absorbing sheet is easily deformed and stress can be dispersed when an impact is applied. Therefore, the adhesive tape of the present invention has excellent impact absorption. Can have sex. The preferable lower limit of the elongation at break X is 500%, the more preferable lower limit is 550%, and the further preferable lower limit is 600%. The upper limit of the elongation at break X is not particularly limited, but from the viewpoint of ensuring the strength of the impact absorbing sheet, the preferable upper limit is 2000%, the more preferable upper limit is 1700%, and the further preferable upper limit is 1500%.

When the value of (Y / X) (breaking strength / breaking elongation) × 100 is 0.1 or more, the strength of the shock absorbing sheet becomes high, and the stress is stably dispersed when impacted. Therefore, the adhesive tape of the present invention can have excellent shock absorption. The preferable lower limit of the value of (Y / X) (breaking strength / breaking elongation) × 100 is 0.2, the more preferable lower limit is 0.3, and the more preferable lower limit is 0.4. The upper limit of the value of (Y / X) (breaking strength / breaking elongation) × 100 is not particularly limited, but the preferable upper limit is 1.4 from the viewpoint of facilitating the adjustment of the breaking elongation X to the above range. The preferred upper limit is 1.3, and the more preferred upper limit is 1.2.
The breaking elongation in the tensile measurement of the impact absorbing sheet is X (%) and the breaking strength is Y (MPa) in accordance with JIS K 7161, which is a desktop precision universal testing machine (for example, manufactured by Shimadzu Corporation, Auto). It can be measured using the graph AGS-X series, etc.). More specifically, it can be measured by pulling a test piece having a length of 20 mm, a width of 10 mm and a thickness of 1 mm at a speed of 500 mm / min in an environment of −20 ° C.

The method for adjusting the values of the breaking elongation X and the above (Y / X) (breaking strength / breaking elongation) × 100 is not particularly limited, and for example, the impact absorbing sheet may be provided with a hardware as described later. Examples thereof include a method using a block copolymer having a block and a soft block. Above all, it is preferable to adjust the content of the hard block and the content of the structure derived from the (meth) acrylic monomer having a glass transition temperature of the homopolymer in the soft block of −50 ° C. or lower. .. Further, a method of adjusting the apparent density of the shock absorbing sheet, a method of adjusting the content of foamed particles (particularly hollow organic particles) in the shock absorbing sheet, and the like can also be mentioned.

In the shock absorbing sheet, the values of the loss tangent tan δ in the frequency range at 23 ° C., the breaking elongation X and the above (Y / X) (breaking strength / breaking elongation) × 100 satisfy the above ranges. Although not particularly limited, it is preferable to contain a block copolymer having a hard block and a soft block.
Since the impact absorbing sheet contains the block copolymer, the loss tangent tan δ in the frequency range at 23 ° C., the breaking elongation X and the above (Y / X) (breaking strength / breaking elongation) × It becomes easy to adjust the value of 100 to the above range, and the shock absorption of the adhesive tape is further improved.

The block copolymer is a copolymer having the hard block having a rigid structure and the soft block having a flexible structure.
The block copolymer may have a non-uniform phase-separated structure in which two blocks are difficult to be compatible with each other and islands formed by agglomeration of the hard blocks are scattered in the sea of the soft blocks. Since the islands serve as pseudo-crosslinking points, rubber elasticity can be imparted to the block copolymer, so that the impact absorption of the adhesive tape is further improved. By introducing a crosslinkable functional group as described later into the hard block, the impact absorption of the adhesive tape is further improved.
Even when the shock absorbing sheet contains a random copolymer, the adhesive tape has a structure derived from a vinyl aromatic monomer and a structure derived from a (meth) acrylic monomer, which will be described later, so that the adhesive tape can be used. It can have excellent shock absorption. It is considered that this is because the same interaction as the above-mentioned phase-separated structure works at a very small scale such as the nano level and the molecular level.

The block copolymer preferably has a structure derived from a vinyl aromatic monomer and a structure derived from a (meth) acrylic monomer. In this case, it is more preferable that the hard block contains a structure derived from the vinyl aromatic monomer, and the soft block contains a structure derived from the (meth) acrylic monomer.
Examples of the vinyl aromatic monomer include styrene, alpha-methylstyrene, paramethylstyrene, chlorostyrene and the like. These vinyl aromatic monomers may be used alone or in combination of two or more. Of these, styrene is preferable because the impact absorption of the adhesive tape is further improved. In the present specification, the structure derived from the vinyl aromatic monomer refers to the structure represented by the following general formulas (1) and (2).

In the general formulas (1) and (2), R ¹ represents a substituent having an aromatic ring. Examples of the substituent ^R1 having an aromatic ring include a phenyl group, a methylphenyl group, a chlorophenyl group and the like.

The content of the structure derived from the vinyl aromatic monomer in the block copolymer is not particularly limited, but is preferably 1% by weight or more and 30% by weight or less. When the content of the structure derived from the vinyl aromatic monomer is in the above range, the impact absorption of the adhesive tape is further improved. A more preferable lower limit of the content of the structure derived from the vinyl aromatic monomer is 1.5% by weight, a further preferable lower limit is 2% by weight, a further preferable lower limit is 2.5% by weight, and a particularly preferable lower limit is 5% by weight. A more preferable upper limit is 15% by weight, and a further preferable upper limit is 8% by weight.

It is preferable that the block copolymer further has a structure derived from a monomer having a crosslinkable functional group.
When the block copolymer has a crosslinkable functional group, the rubber elasticity of the copolymer is increased by crosslinking, so that the impact absorption of the adhesive tape is further improved. Further, even if the block copolymer remains in a non-crosslinked structure, the cohesive force in the hard block or the soft block (particularly, the hard block) is improved by the interaction between the functional groups. , The shock absorption of the adhesive tape is further improved. In the present specification, the structure derived from the monomer having a crosslinkable functional group refers to the structure represented by the following general formulas (3) and (4).

In the general formulas (3) and (4), R ² represents a substituent containing at least one functional group. Examples of the functional group include a carboxyl group, a hydroxyl group, an epoxy group, a double bond, a triple bond, an amino group, an amide group, a nitrile group and the like. The substituent ^R2 containing at least one functional group may contain an alkyl group, an ether group, a carbonyl group, an ester group, a carbonate group, an amide group, a urethane group and the like as its constituent elements.

The monomer having a crosslinkable functional group is not particularly limited, and for example, a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an epoxy group-containing monomer, a double bond-containing monomer, a triple bond-containing monomer, an amino group-containing monomer, and an amide group-containing monomer. , A nitrile group-containing monomer and the like. These crosslinkable functional groups may be used alone or in combination of two or more. Among them, since the impact absorption of the adhesive tape is further improved, it is selected from the group consisting of a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an epoxy group-containing monomer, a double bond-containing monomer, a triple bond-containing monomer and an amide group-containing monomer. At least one type is preferable.
Examples of the carboxyl group-containing monomer include (meth) acrylic acid-based monomers such as (meth) acrylic acid. Examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate. Examples of the epoxy group-containing monomer include glycidyl (meth) acrylate and the like. Examples of the double bond-containing monomer include allyl (meth) acrylate and hexanediol di (meth) acrylate. Examples of the triple bond-containing monomer include propargyl (meth) acrylate and the like. Examples of the amide group-containing monomer include (meth) acrylamide and the like. Of these, a carboxyl group-containing monomer and a hydroxyl group-containing monomer are preferable because the impact absorption of the adhesive tape is further improved. As the carboxyl group-containing monomer, a (meth) acrylic acid-based monomer is more preferable, and acrylic acid is further preferable. As the hydroxyl group-containing monomer, 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate are preferable.

The content of the structure derived from the monomer having a crosslinkable functional group in the block copolymer is not particularly limited, but is preferably 0.1% by weight or more and 30% by weight or less. When the content of the structure derived from the monomer having a crosslinkable functional group is in the above range, the impact absorption of the adhesive tape is further improved. A more preferable lower limit of the content of the structure derived from the monomer having a crosslinkable functional group is 0.5% by weight, a further preferable lower limit is 1% by weight, a more preferable upper limit is 25% by weight, and a further preferable upper limit is 20% by weight. be.

The (meth) acrylic monomer may be a single monomer or may use a plurality of monomers. In the present specification, the structure derived from the (meth) acrylic monomer refers to the structure represented by the following general formulas (5) and (6).

In the general formulas (5) and (6), R ³ represents a side chain. The side chain R ³ includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, a dodecyl group and a lauryl group. Examples thereof include an isostearyl group and a methoxyethyl group.

Examples of the (meth) acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, and heptyl (meth). Meta) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, isostearyl (meth) acrylate , Methoxyethyl (meth) acrylate and the like. These (meth) acrylic monomers may be used alone or in combination of two or more. Of these, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate are preferable, and methyl acrylate and ethyl are preferable because the impact absorption of the adhesive tape is further improved. Acrylate, butyl acrylate, 2-ethylhexyl acrylate and methoxyethyl acrylate are more preferable.

Further, as the (meth) acrylic monomer, it is preferable to use a (meth) acrylic monomer having 2 or less side chain carbon atoms. When the (meth) acrylic monomer having 2 or less side chains is used, the entanglement between the obtained copolymer chains is increased, the cohesive force is improved, and the impact absorption of the adhesive tape is further improved. Heat resistance is also improved.
Examples of the (meth) acrylic monomer having 2 or less side chain carbon atoms include methyl (meth) acrylate and ethyl (meth) acrylate, and methyl acrylate and ethyl acrylate are particularly preferable.

Further, as the (meth) acrylic monomer, it is preferable to use a (meth) acrylic monomer having a glass transition temperature Tg of the homopolymer of −50 ° C. or lower. When a (meth) acrylic monomer having a glass transition temperature Tg of −50 ° C. or lower of the homopolymer is used, the loss tangent tan δ in the frequency range at 23 ° C. and the elongation at break X are adjusted to the above ranges. This makes it easier and the shock absorption of the adhesive tape is further improved.
Examples of the (meth) acrylic monomer having a glass transition temperature Tg of −50 ° C. or lower of the homopolymer include methoxyethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Of these, methoxyethyl acrylate and 2-ethylhexyl acrylate are preferable.

The content of the structure derived from the (meth) acrylic monomer in the block copolymer is not particularly limited, and the effect of the present invention may be exhibited, but it is 30% by weight or more and 99% by weight or less. Is preferable. The content of the structure derived from the (meth) acrylic monomer is more preferably 40% by weight or more and 98% by weight or less, and further preferably 50% by weight or more and 97% by weight or less.

Further, in the block copolymer, the content of the structure derived from the (meth) acrylic monomer having 2 or less side chain carbon atoms is not particularly limited, but the preferable lower limit is 2% by weight and the preferable upper limit is 40% by weight. Is. When the content of the structure derived from the (meth) acrylic monomer having 2 or less side chain carbon atoms is 2% by weight or more, the effect of improving the cohesive force is likely to be exhibited. If the content of the structure derived from the (meth) acrylic monomer having 2 or less side chain carbon atoms is 40% by weight or less, the cohesive force becomes too high and the flexibility becomes low, and the flexibility as an adhesive tape Can be prevented from being lost. A more preferable lower limit of the content of the structure derived from the (meth) acrylic monomer having 2 or less side chain carbon atoms is 3% by weight, a further preferable lower limit is 4% by weight, and a further preferable lower limit is 5% by weight. A more preferable upper limit is 30% by weight, a further preferable upper limit is 25% by weight, and a further preferable upper limit is 20% by weight.

Further, in the soft block of the block copolymer, the content of the structure derived from the (meth) acrylic monomer having a glass transition temperature Tg of −50 ° C. or lower of the homopolymer is not particularly limited, but the preferable lower limit is 80. % By weight. When the content of the structure derived from the (meth) acrylic monomer having a glass transition temperature Tg of −50 ° C. or lower of the homopolymer is 80% by weight or more, the shock absorption of the adhesive tape is further improved. A more preferable lower limit of the content of the structure derived from the (meth) acrylic monomer having a glass transition temperature Tg of −50 ° C. or lower of the homopolymer is 85% by weight, and a further preferable lower limit is 90% by weight.
The glass transition temperature Tg of the homopolymer of the (meth) acrylic monomer can be measured using a differential scanning calorimeter (for example, DSC 2920 manufactured by TA Instruments). More specifically, the glass transition temperature Tg can be measured under the conditions of a temperature range of −100 to 200 ° C., a heating rate of 10 ° C./min, and one cycle count.

The hard block is not particularly limited as long as it has a rigid structure, and in addition to the structure derived from the vinyl aromatic monomer, for example, a compound having a cyclic structure, a compound having a short side chain substituent, or the like can be used. It may have a derived structure. The soft block may have a structure derived from a monomer other than the (meth) acrylic monomer as long as the effect of the present invention is not lost.

The block copolymer may have any structure such as a diblock structure or a triblock structure, but since the impact absorption of the adhesive tape is further improved, the soft block is placed between the hard blocks. It is preferable to have a tri-block structure having the same.
Further, the block copolymer may be a graft copolymer in which the hard block and the soft block are separated into a main chain and a side chain. Examples of the graft copolymer include a styrene macromer- (meth) acrylic monomer copolymer and the like.

The content of the hard block in the block copolymer is not particularly limited, but is preferably 1% by weight or more and 40% by weight or less. When the content of the hard block is in the above range, the impact absorption of the adhesive tape is further improved and the heat resistance is also improved. From the viewpoint of further enhancing shock absorption and heat resistance, the more preferable lower limit of the content of the hard block is 2% by weight, the more preferable lower limit is 2.5% by weight, and the particularly preferable lower limit is 3% by weight. A more preferable upper limit of the content of the hard block is 35% by weight, a further preferable upper limit is 30% by weight, a further preferable upper limit is 26% by weight, a further preferable upper limit is 20% by weight, and a particularly preferable upper limit is 17% by weight, particularly preferable. The upper limit is 8% by weight.

The weight average molecular weight (Mw) of the block copolymer is not particularly limited, but is preferably 200,000 or more and 1.2 million or less. When the weight average molecular weight is in the above range, the impact absorption of the adhesive tape is further improved and the heat resistance is also improved. The more preferable lower limit of the weight average molecular weight is 400,000, and the more preferable upper limit is 1 million.
The weight average molecular weight can be determined, for example, by a GPC (Gel Permeation Chromatography) method in terms of standard polystyrene. More specifically, for example, "2690 Separations Module" manufactured by Water Co., Ltd., "GPC KF-806L" manufactured by Showa Denko Co., Ltd. as a column, and ethyl acetate as a solvent are used as a measuring device, a sample flow rate of 1 mL / min, and a column temperature of 40 ° C. It can be measured under the conditions of.

To obtain the block copolymer, the hard block and the raw material monomers of the soft block are radically reacted in the presence of a polymerization initiator to obtain the hard block and the soft block, and then the two are reacted. It may be allowed to or copolymerize. Further, after obtaining the hard block, the raw material monomer of the soft block may be continuously added and copolymerized. In order to obtain the above random copolymer, a solution mixed with the raw material monomers may be subjected to a radical reaction in the presence of a polymerization initiator.
As the method for causing the radical reaction, that is, the 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.

Even if the shock absorbing sheet contains additives such as antistatic agents, mold release agents, antioxidants, weathering agents, and crystal nucleating agents, and resin modifiers such as polyolefins, polyesters, polyamides, and elastomers. good.

The shock absorbing sheet may have a single-layer structure or a multi-layer structure.
The shock absorbing sheet is preferably a foam. Since the impact absorbing sheet is the foam, the loss tangent tan δ in the frequency range at 23 ° C., the breaking elongation X and the above (Y / X) (breaking strength / breaking elongation) × 100 values. Can be easily adjusted to the above range, and the impact absorption of the adhesive tape is further improved. The foam may have an open cell structure or a closed cell structure, but it is preferable to have a closed cell structure.

When the shock absorbing sheet is a foam, the foaming ratio is not particularly limited, but the preferable lower limit is 1.0 and the preferable upper limit is 1.33. When the foaming ratio is in the above range, the balance between the strength and the flexibility of the shock absorbing sheet can be further improved, so that the shock absorbing property of the adhesive tape is further improved. From the viewpoint of further enhancing the shock absorption, the more preferable lower limit of the foaming ratio is 1.05, the more preferable upper limit is 1.3, the further preferable lower limit is 1.1, and the further preferable upper limit is 1.25.
The foaming ratio of the shock absorbing sheet is a numerical value calculated by cutting the shock absorbing sheet into 30 mm × 30 mm and dividing the weight measured using an electronic hydrometer (for example, ED120T manufactured by Mirage Co., Ltd.) by the volume. Represents the reciprocal.

When the shock absorbing sheet is a foam, the apparent density is not particularly limited, but the preferred lower limit is 0.75 g / cm ³ and the preferred upper limit is 1.10 g / cm ³ . When the apparent density is in the above range, the balance between the strength and the flexibility of the shock absorbing sheet can be further improved, so that the shock absorbing property of the adhesive tape is further improved. From the viewpoint of further enhancing the shock absorption, the more preferable lower limit of the apparent density is 0.80 g / cm ³ , the more preferable upper limit is 1.07 g / cm ³ , and the more preferable lower limit is 0.88 g / cm ³ , still more preferable. The upper limit is 1.05 g / cm ³ .
The apparent density of the shock absorbing sheet is the weight measured by cutting the shock absorbing sheet into 30 mm × 30 mm and using an electronic hydrometer (for example, ED120T manufactured by Mirage Co., Ltd.) in accordance with JIS K 7222. Can be calculated by dividing.

When the shock absorbing sheet is a foam, the average cell diameter is not particularly limited, but is preferably 80 μm or less. When the average cell diameter is 80 μm or less, the balance between the strength and flexibility of the shock absorbing sheet can be further improved, so that the shock absorbing property of the adhesive tape is further improved. The average bubble diameter is more preferably 60 μm or less, and further preferably 55 μm or less.
The lower limit of the average bubble diameter is not particularly limited, but from the viewpoint of ensuring the flexibility of the shock absorbing sheet, it is preferably 20 μm or more, and more preferably 30 μm or more.
The average bubble diameter of the shock absorbing sheet can be measured by the following method. First, the shock absorbing sheet is cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, and then cut on a surface perpendicular to the thickness direction of the shock absorbing sheet using a razor blade. Then, using a digital microscope (for example, "VHX-900" manufactured by KEYENCE Corporation), a magnified photograph of the cut surface was taken at a magnification of 200 times, and the most bubbles existing in the range of thickness × 2 mm were taken. Measure a long bubble diameter (bubble diameter). This operation is repeated 5 times, and the average bubble diameter is calculated by averaging all the obtained bubble diameters.

The impact absorbing sheet preferably has a gel fraction of 50% by weight or less from the viewpoint of further enhancing the impact absorption of the adhesive tape.
A more preferable upper limit of the gel fraction is 40% by weight, and a more preferable upper limit is 30% by weight. The lower limit of the gel fraction is not particularly limited. The gel fraction can be adjusted by cross-linking the resin constituting the shock absorbing sheet.
The gel fraction of the shock absorbing sheet can be measured by the following method. Remove 0.1 g of the shock absorbing sheet from the adhesive tape, immerse it in 50 mL of ethyl acetate, and shake it with a shaker at a temperature of 23 ° C. and 120 rpm for 24 hours. After shaking, a metal mesh (opening # 200 mesh) is used to absorb ethyl acetate and ethyl acetate and separate the swollen shock absorbing sheet. The separated shock absorbing sheet is dried under the condition of 110 ° C. for 1 hour. The weight of the shock absorbing sheet including the dried metal mesh is measured, and the gel fraction of the shock absorbing sheet is calculated using the following formula.
Gel fraction (% by weight) = 100 x (W ₁ -W ₂ ) / W ₀
(W ₀ : weight of initial shock absorbing sheet, W ₁ : weight of shock absorbing sheet including dried metal mesh, W ₂ : initial weight of metal mesh)

It is preferable that the shock absorbing sheet has a crosslinked structure formed between the main chains of the resin constituting the shock absorbing sheet by adding a crosslinking agent.
By forming a crosslinked structure between the main chains of the resin constituting the shock absorbing sheet, the cohesive force of the adhesive tape is further improved and the heat resistance is also improved.

The cross-linking agent is not particularly limited, and can be appropriately selected depending on the functional group of the resin constituting the shock absorbing sheet. Specific examples thereof include isocyanate-based cross-linking agents, aziridine-based cross-linking agents, epoxy-based cross-linking agents, and metal chelate-type cross-linking agents. Among them, an epoxy-based cross-linking agent or an isocyanate-based cross-linking agent is preferable because a resin having an alcoholic hydroxyl group or a carboxyl group that can further improve flexibility can be cross-linked. When the isocyanate-based cross-linking agent is used, the alcoholic hydroxyl group or carboxyl group in the resin constituting the shock absorbing sheet is crosslinked with the isocyanate group of the isocyanate-based cross-linking agent. Further, when the epoxy-based cross-linking agent is used, the carboxyl group in the resin constituting the shock absorbing sheet and the epoxy group of the epoxy-based cross-linking agent are cross-linked. The amount of the cross-linking agent added is not particularly limited.

The thickness of the shock absorbing sheet is not particularly limited, but the preferred lower limit is 40 μm and the preferred upper limit is 2900 μm. By setting the thickness of the shock absorbing sheet within the above range, it is possible to obtain an adhesive tape having excellent flexibility, shock absorption, heat resistance, handleability, etc., and the adhesive tape can be used as a portable electronic device component or an in-vehicle electronic device. It can be suitably used for fixing electronic device parts such as device parts. From the viewpoint that it can be more preferably used for fixing the above parts and the like, the more preferable lower limit of the thickness of the shock absorbing sheet is 60 μm, the more preferable upper limit is 1900 μm, the further preferable lower limit is 80 μm, the further preferable upper limit is 1400 μm, and the particularly preferable lower limit is. 100 μm, a particularly preferred upper limit is 1000 μm.

The method for manufacturing the shock absorbing sheet is not particularly limited. Among the shock absorbing sheets, examples of the method for producing a foam include a method of producing by the action of foaming gas and a method of producing by blending hollow spheres in a raw material matrix. Among them, the shock absorbing sheet produced by the latter method is called syntactic foam, and is excellent in strength, flexibility and heat resistance. Therefore, the shock absorbing sheet is preferably syntactic foam.

Since the shock absorbing sheet is syntactic foam, it becomes a closed cell type foam having a uniform size distribution, so that the density of the entire shock absorbing sheet becomes more constant, and the strength, flexibility and heat resistance become higher. improves. In addition, syntactic foam exhibits higher heat resistance than other foams because it is less likely to cause irreversible disintegration under high temperature and high pressure. Syntactic foam includes those having a foamed structure made of hollow inorganic particles and those having a foamed structure made of hollow organic particles. From the viewpoint of flexibility, syntactic foam having a foamed structure made of hollow organic particles. Foam is preferred.

Examples of the hollow organic particles include Expancel DU series (manufactured by Nippon Philite Co., Ltd.), Advancel EM series (manufactured by Sekisui Chemical Co., Ltd.) and the like. Among them, since it is easy to design the bubble diameter after foaming in a region with higher effect, Expandel 461-20 (average bubble diameter after foaming under optimum conditions 20 μm) and Expandel 461-40 (optimum conditions). The average cell diameter after foaming in the above 40 μm), Expandel 043-80 (average cell diameter after foaming under optimum conditions 80 μm), and Advansel EML101 (average cell diameter after foaming under optimum conditions 50 μm) are preferable.
The content of the hollow organic particles is not particularly limited, but from the viewpoint of further improving the impact absorption of the adhesive tape, the preferable lower limit is 0.2 parts by weight and the preferable upper limit is 0.2 parts by weight with respect to 100 parts by weight of the resin constituting the impact absorbing sheet. It is 1.5 parts by weight, the more preferable lower limit is 0.4 parts by weight, and the more preferable upper limit is 1.2 parts by weight.

When the shock absorbing sheet is made of a foam other than the syntactic foam, the foaming agent is not particularly limited, and a conventionally known foaming agent such as a pyrolytic foaming agent can be used.

The pressure-sensitive adhesive layer may be laminated on only one surface of the shock absorbing sheet, or may be laminated on both sides. When the pressure-sensitive adhesive layer is laminated on both sides of the shock absorbing sheet, the pressure-sensitive adhesive layers on both sides may have the same composition and physical properties, or may have different compositions and physical properties.
The pressure-sensitive adhesive layer is not particularly limited, and examples thereof include an acrylic pressure-sensitive adhesive layer, a rubber-based pressure-sensitive adhesive layer, a urethane pressure-sensitive adhesive layer, and a silicone-based pressure-sensitive adhesive layer. Among them, an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer is preferable because it has excellent heat resistance and can be adhered to a wide variety of adherends.

The acrylic copolymer can be obtained by copolymerizing a monomer mixture containing butyl acrylate and / or 2-ethylhexyl acrylate from the viewpoint of improving the initial tack and making it easy to attach at low temperature. preferable. Above all, it is more preferable to obtain it by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate.
The preferable lower limit of the content of the butyl acrylate in the total monomer mixture is 10% by weight, and the preferable upper limit is 80% by weight. By setting the content of the butyl acrylate in the above range, both high adhesive strength and tackiness can be achieved at the same time.
The preferable lower limit of the content of the 2-ethylhexyl acrylate in the total monomer mixture is 10% by weight, the preferable upper limit is 100% by weight, the more preferable lower limit is 20% by weight, and the more preferable upper limit is 80% by weight. By setting the content of the 2-ethylhexyl acrylate in the above range, high adhesive strength can be exhibited.

The monomer mixture may contain other copolymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate, if necessary. Examples of the other copolymerizable monomer include (meth) acrylic acid alkyl esters having 1 to 18 carbon atoms in the alkyl group, functional monomers and the like.
Examples of the (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl group include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, n-propyl (meth) acrylic acid, and (meth) acrylic acid. Examples thereof include isopropyl, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, tridecyl methacrylate, and stearyl (meth) acrylate. Examples of the functional monomer include hydroxyalkyl (meth) acrylate, alkoxyalkyl (meth) acrylate, glycerin dimethacrylate, glycidyl (meth) acrylate, 2-methacryloyloxyethyl isocyanate, (meth) acrylic acid, and 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 subjected to a radical reaction in the presence of a polymerization initiator. As a method of radically reacting 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 weight average molecular weight (Mw) of the acrylic copolymer is not particularly limited, but the preferred lower limit is 400,000 and the preferred upper limit is 1.5 million. By setting the weight average molecular weight of the acrylic copolymer in the above range, high adhesive strength can be exhibited. From the viewpoint of further improving the adhesive strength, the more preferable lower limit of the weight average molecular weight is 500,000, and the more preferable upper limit is 1.4 million.

The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic copolymer is preferably 10.0. When Mw / Mn is 10.0 or less, the ratio of the small molecule component is suppressed, the pressure-sensitive adhesive layer is softened at a high temperature, the bulk strength is lowered, and the adhesive strength is suppressed. From the same viewpoint, the more preferable upper limit of Mw / Mn is 5.0, and the more preferable upper limit is 3.0.

The pressure-sensitive adhesive layer may contain a pressure-sensitive adhesive resin.
Examples of the tackifier resin include rosin ester resin, hydrogenated rosin resin, terpene resin, terpene phenol resin, Kumaron inden resin, alicyclic saturated hydrocarbon resin, C5 petroleum resin, and C9 resin. Examples thereof include petroleum resins and C5-C9 copolymerized petroleum resins. These tackifier 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 with respect to 100 parts by weight of the resin (for example, acrylic copolymer) which is the main component of the pressure-sensitive adhesive layer. .. When the content of the pressure-sensitive adhesive resin is 10 parts by weight or more, the pressure-sensitive adhesive layer can exhibit high adhesive strength. When the content of the pressure-sensitive adhesive resin is 60 parts by weight or less, it is possible to suppress a decrease in adhesive strength or tackiness due to the hardening of the pressure-sensitive adhesive layer.

The pressure-sensitive adhesive layer has a cross-linked structure formed between the main chains of the resin (for example, the acrylic copolymer, the pressure-sensitive adhesive resin, etc.) constituting the pressure-sensitive adhesive layer by adding a cross-linking agent. Is preferable.
The above-mentioned cross-linking agent is not particularly limited, and examples thereof include an isocyanate-based cross-linking agent, an aziridine-based cross-linking agent, an epoxy-based cross-linking agent, and a metal chelate-type cross-linking agent. Of these, isocyanate-based cross-linking agents are preferable. By adding an isocyanate-based cross-linking agent to the pressure-sensitive adhesive layer, the isocyanate group of the isocyanate-based cross-linking agent and the alcohol in the resin constituting the pressure-sensitive adhesive layer (for example, the acrylic copolymer, the pressure-sensitive adhesive resin, etc.) The pressure-sensitive adhesive layer is crosslinked by reacting with the sex hydroxylate. By forming a crosslinked structure between the main chains of the resin constituting the pressure-sensitive adhesive layer, it is possible to disperse the stress applied intermittently, and the impact absorption of the pressure-sensitive adhesive tape is further improved and the heat resistance is also improved. do.
The amount of the cross-linking agent added is preferably 0.01 to 10 parts by weight, preferably 0.1 to 7 parts by weight, based on 100 parts by weight of the resin (for example, the acrylic copolymer) which is the main component of the pressure-sensitive adhesive layer. Is more preferable.

The pressure-sensitive adhesive layer may contain a silane coupling agent for the purpose of improving the pressure-sensitive adhesive strength. The silane coupling agent is not particularly limited, and examples thereof include epoxysilanes, acrylicsilanes, methacrylsilanes, aminosilanes, and isocyanatesilanes.

The pressure-sensitive adhesive layer may contain a coloring material for the purpose of imparting light-shielding properties. The coloring material is not particularly limited, and examples thereof include carbon black, aniline black, and titanium oxide. Of these, carbon black is preferable because it is relatively inexpensive and chemically stable.
The pressure-sensitive adhesive layer may contain conventionally known particles and additives such as inorganic particles, conductive particles, antioxidants, foaming agents, organic fillers, and inorganic fillers, if necessary.

In the pressure-sensitive adhesive layer, the preferable lower limit of the gel fraction is 5% by weight, and the preferable upper limit is 90% by weight. When the gel fraction is within the above range, the impact absorption of the adhesive tape is further improved. The more preferable lower limit of the gel fraction is 10% by weight, the more preferable upper limit is 80% by weight, the particularly preferable lower limit is 20% by weight, and the particularly preferable upper limit is 60% by weight.
The gel fraction of the pressure-sensitive adhesive layer can be measured by the same method as the gel fraction of the shock absorbing sheet.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but a preferable lower limit is 0.01 mm, a preferable upper limit is 0.1 mm, a more preferable lower limit is 0.015 mm, and a more preferable upper limit is 0.09 mm. By setting the thickness of the adhesive layer within the above range, it is possible to obtain an adhesive tape having excellent flexibility, shock absorption, heat resistance, handleability, etc., and the adhesive tape can be used as a portable electronic device component or an in-vehicle electronic device. It can be suitably used for fixing electronic device parts such as device parts.

The thickness of the entire adhesive tape of the present invention is not particularly limited, but a preferable lower limit is 0.06 mm, a more preferable lower limit is 0.08 mm, a preferable upper limit is 2 mm, and a more preferable upper limit is 1.5 mm. By setting the thickness of the entire adhesive tape of the present invention within the above range, it is possible to obtain an adhesive tape having excellent flexibility, shock absorption, heat resistance, handleability and the like.
The shape of the adhesive tape of the present invention is not particularly limited, and examples thereof include a rectangular shape, a frame shape, a circular shape, an elliptical shape, and a donut shape.

The method for producing the adhesive tape of the present invention is not particularly limited, and examples thereof include the following methods. First, an unfoamed shock absorbing sheet is manufactured and heated and foamed to obtain a shock absorbing sheet (foam). Next, a pressure-sensitive adhesive solution is applied to the release film and dried to form a pressure-sensitive adhesive layer. After that, an adhesive layer is attached to both sides of the shock absorbing sheet (foam) to manufacture an adhesive tape.

The use of the adhesive tape of the present invention is not particularly limited, but it is preferably used for assembling or fixing electronic device parts such as portable electronic device parts and in-vehicle electronic device parts because of its excellent shock absorption.

According to the present invention, it is possible to provide an adhesive tape having excellent shock absorption.

It is a figure which shows typically the evaluation method of the shock absorption of an adhesive tape.

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

(Example 1)
(1) Production of shock absorbing sheet 0.902 g of 1,6-hexanedithiol, 1.83 g of carbon disulfide, and 11 mL of dimethylformamide were put into a two-necked flask and stirred at 25 ° C. To this, 2.49 g of triethylamine was added dropwise over 15 minutes, and the mixture was stirred at 25 ° C. for 3 hours. Then, 2.75 g of methyl-α-bromophenylacetic acid was added dropwise over 15 minutes, and the mixture was stirred at 25 ° C. for 4 hours. Then, 100 mL of an extraction solvent (n-hexane: ethyl acetate = 50: 50) and 50 mL of water were added to the reaction solution for liquid-liquid extraction. The organic layers obtained by the first and second liquid separation extractions were mixed and washed in order with 50 mL of 1 M hydrochloric acid, 50 mL of water and 50 mL of saturated brine. Sodium sulfate was added to the washed organic layer and dried, and then the sodium sulfate was filtered, and the filtrate was concentrated with an evaporator to remove the organic solvent. The obtained concentrate was purified by silica gel column chromatography to obtain a RAFT agent.

87 parts by weight of styrene (St), 12 parts by weight of acrylic acid (AAc), 1 part by weight of hydroxyethyl acrylate (HEA), 2.8 parts by weight of RAFT agent, and 2,2'-azobis (2-methylbuty). 0.35 part by weight of bnitrile) (ABN-E) was put into a two-port flask, and the temperature was raised to 85 ° C. while replacing the inside of the flask with nitrogen gas. Then, the polymerization reaction was carried out by stirring at 85 ° C. for 6 hours (first step reaction).
After completion of the reaction, 4000 parts by weight of n-hexane was placed in the flask and stirred to precipitate the reaction product, and then the unreacted monomers (St, AAc, HEA) and RAFT agent were filtered to obtain 70 parts of the reaction product. A copolymer (hard block) was obtained by drying under reduced pressure at ° C.

A mixture containing 10 parts by weight of methyl acrylate (MA), 85 parts by weight of methoxyethyl acrylate (MOEA), 5 parts by weight of 4-hydroxybutyl acrylate (4HBA), 0.058 parts by weight of ABN-E and 50 parts by weight of ethyl acetate, and the above. The copolymer (hard block) obtained in 1 above was put into a two-necked flask. The temperature was raised to 85 ° C. while replacing the inside of the flask with nitrogen gas. Then, the polymerization reaction was carried out by stirring at 85 ° C. for 6 hours (second step reaction) to obtain a reaction solution containing a block copolymer formed from a hard block and a soft block. The blending amount of the mixture was adjusted so that the content of the hard block in the obtained block copolymer was 6% by weight and the content of the soft block was 94% by weight.
A part of the reaction solution is collected, 4000 parts by weight of n-hexane is added thereto, and the mixture is stirred to precipitate the reaction product, and then the unreacted monomers (MA, MOEA, 4HBA) and the solvent are filtered to react. The product was dried under reduced pressure at 70 ° C. to obtain a block copolymer.
The weight average molecular weight of the obtained block copolymer was measured by the GPC method and found to be 800,000. Using "2690 Separations Module" manufactured by Water Co., Ltd. as a measuring device, "GPC KF-806L" manufactured by Showa Denko Co., Ltd. as a column, and ethyl acetate as a solvent, the measurement was performed under the conditions of a sample flow rate of 1 mL / min and a column temperature of 40 ° C.

The obtained block copolymer was dissolved in ethyl acetate so that the solid content was 35%, and the expander 461-40 (461DU40) was used as a foaming agent (foaming particles) with respect to 100 parts by weight of the block copolymer. (Manufactured by Nippon Philite Co., Ltd.) 0.5 parts by weight was added and further sufficiently stirred to obtain a solution for an unfoamed shock absorbing sheet. The obtained solution for unfoamed shock absorbing sheet is applied on the mold-released surface of a 50 μm polyethylene terephthalate (PET) film that has been mold-released on one side, and dried at 90 ° C. for 7 minutes to absorb unfoamed shock. A sheet was prepared and heated at 130 ° C. for 1 minute to obtain a shock absorbing sheet (foam, thickness 120 μm).

(2) Production of Adhesive Tape 52 parts by weight of ethyl acetate was placed in a reactor equipped with a thermometer, a stirrer, and a cooling tube, and after nitrogen substitution, the reactor was heated to start reflux. Thirty minutes after the ethyl acetate boiled, 0.08 part by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 17 parts by weight of butyl acrylate, 80 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 0.1 part by weight of 2-hydroxyethyl acrylate was added dropwise thereto evenly and gradually over 1 hour and 30 minutes. It was reacted. Thirty minutes after the completion of the dropping, 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 40% by weight. A solution of an acrylic copolymer (random copolymer) was obtained.
The weight average molecular weight of the obtained acrylic copolymer was measured by the GPC method using "2690 Separations Model" manufactured by Water Co., Ltd. as a column, and it was 650,000. The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) was 5.8.
With respect to 100 parts by weight of the solid content of the obtained acrylic copolymer, 15 parts by weight of the polymerized rosin ester having a softening point of 150 ° C., 10 parts by weight of terpene phenol having a softening point of 145 ° C., and 10 parts by weight of a rosin ester having a softening point of 100 ° C. Was added. Further, 30 parts by weight of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.) and 2.0 parts by weight of an isocyanate-based cross-linking agent (Coronate L45 manufactured by Tosoh Co., Ltd.) were added and stirred to obtain a pressure-sensitive adhesive solution.
On the release-treated surface of a 50 μm polyethylene terephthalate (PET) film with a mold release treatment on one side, the obtained adhesive solution was applied with a doctor knife so that the thickness of the dry film was 40 μm, and 110 The coating solution was dried by heating at ° C. for 5 minutes to obtain a pressure-sensitive adhesive layer. Another pressure-sensitive adhesive layer was manufactured by the same operation. After that, the release film is peeled off from the shock absorbing sheet obtained above, two adhesive layers are attached to both sides of the shock absorbing sheet, and the adhesive tape is left to stand in an environment of 40 ° C. for 48 hours to attach the adhesive tape. Obtained.

(3) Measurement of the apparent density of the shock absorbing sheet The shock absorbing sheet is cut into 30 mm × 30 mm, and the weight measured using an electronic hydrometer (“ED120T” manufactured by Mirage) in accordance with JIS K 7222 is divided by the volume. The apparent density of the shock absorbing sheet was determined.

(4) Measurement of loss tangent tan δ of shock absorbing sheet at 23 ° C. Using a viscoelastic spectrometer (DVA-200 manufactured by IT Measurement Control Co., Ltd.), a shock absorbing sheet cut to 5 mm × 30 mm was cut at a chuck interval of 15 mm. After fixing, the tensile viscoelasticity was measured under the conditions of a heating rate of 5 ° C./min and a temperature rise rate of −40 to 140 ° C. Then, a master curve was synthesized at a reference temperature of 23 ° C., and a loss tangent tan δ at a frequency of 1.0 × 10 ^3.5 to 1.0 × 10 ⁴ Hz of the shock absorbing sheet at 23 ° C. was obtained. The table shows the minimum value of the loss tangent tan δ at frequencies of 1.0 × 10 ^3.5 to 1.0 × 10 ⁴ Hz.

(5) Measurement of breaking elongation X and breaking strength Y of impact absorbing sheet Using a desktop precision universal testing machine (manufactured by Shimadzu Corporation, Autograph AGS-X series) in accordance with JIS K 7161, the length The breaking elongation X and breaking strength Y of the impact absorbing sheet were measured by pulling a test piece having a width of 20 mm, a width of 10 mm and a thickness of 1 mm at a speed of 500 mm / min in an environment of −20 ° C. From the obtained breaking elongation X and breaking strength Y, a value of (Y / X) × 100 was obtained.

(Examples 2 to 16, Comparative Examples 1 to 7)
An adhesive tape was obtained in the same manner as in Example 1 except that the shock absorbing sheet was changed as shown in Tables 1 and 2. In Examples 6, 12 to 14, and Comparative Examples 3 and 5, the solution for the unfoamed shock absorbing sheet did not contain a foaming agent (foaming particles), so that the shock absorbing sheet remained as an unfoamed material even after heating at 130 ° C. for 1 minute. there were. In Comparative Example 6, a polyethylene foam having the physical characteristics shown in the table was used, and in Comparative Example 7, a urethane foam having the physical characteristics shown in the table was used as the shock absorbing sheet. The raw materials in the table are as follows.

-Additive E-5C (Tetrad C, cross-linking agent, manufactured by Mitsubishi Gas Chemical Company)

・ Monomer BA (butyl acrylate), which is a raw material for shock absorbing sheets
2EHA (2-ethylhexyl acrylate)

<Evaluation>
The following evaluations were performed on the adhesive tapes obtained in Examples and Comparative Examples. The results are shown in Tables 1 and 2.

(1) Evaluation of Impact Absorption FIG. 1 shows a diagram schematically showing an evaluation method of impact absorption of an adhesive tape.
(1-1) Preparation of Test Device As shown in FIG. 1 (a), the adhesive tape was punched into an outer diameter of 24 mm × 24 mm and an inner diameter of 20 mm × 20 mm to prepare a frame-shaped test piece 2 having a width of 2 mm. A test piece 1 from which the release film was peeled off was attached to a SUS plate 1 having a thickness of 2 mm and a square hole of 20 mm × 20 mm in the central portion so that the square hole was located substantially in the center. From the upper surface of the test piece 1, a polycarbonate plate 3 having a thickness of 27 mm × 27 mm and a thickness of 2 mm was attached so that the test piece 1 was located substantially in the center, and the test apparatus was assembled. A pressure of 5 kgf was applied from the polycarbonate plate 3 side located on the upper surface of the test device for 10 seconds to crimp the polycarbonate plate 3 and the SUS plate 1 located above and below, and left at room temperature for 72 hours.

(1-2) Measurement of Impact Absorption Energy (E) Impact absorption energy (E) was measured using an Instron Ceast 9340 drop weight impact tester (manufactured by Instron).
As shown in FIG. 1 (b), the prepared test apparatus was turned over and fixed to a support base, and a 5 kg weight 4 having a size passing through the square hole was dropped from a height of 50 mm so as to pass through the square hole. .. The passing speed of the weight 4 was adjusted to be a constant speed of 1 m / s. Measure the transition of the impact force for each 0.005 mm section with respect to the displacement amount D from the contact of the weight 4 with the polycarbonate plate 3 until the test piece 2 and the polycarbonate plate 3 are peeled off by the impact applied by the drop of the weight 4. bottom. The product of the displacement amount and the impact force was calculated in each 0.005 mm section of the displacement amount D, and the sum of the total sections was calculated as the impact absorption energy (E).
The case where the impact absorption energy (E) was 0.65 J or more was evaluated as ◯, and the case where the impact absorption energy (E) was less than 0.65 J was evaluated as x. When the shock absorption energy (E) is 0.65J or more, when the adhesive tape is used for assembling or fixing electronic device parts such as smartphones, it falls when the electronic device is dropped while sitting. It is possible to sufficiently absorb the energy of the impact caused by.

According to the present invention, it is possible to provide an adhesive tape having excellent shock absorption.

1 SUS plate 2 Test piece (adhesive tape)
3 Polycarbonate plate 4 Weight

Claims (12)

An adhesive tape having a shock absorbing sheet and an adhesive layer laminated on at least one surface of the shock absorbing sheet.
The shock absorbing sheet has a loss tangent tan δ of 0.8 or more at a frequency of 1.0 × 10 ^3.5 to 1.0 × 10 ⁴ Hz at 23 ° C., and has a breaking elongation of X (%) in tensile measurement. , X ≧ 400 and (Y / X) × 100 ≧ 0.1, where the breaking strength is Y (MPa). The adhesive tape according to claim 1, wherein the shock absorbing sheet has an apparent density of 0.75 g / cm ³ or more and 1.10 g / cm ³ or less. The adhesive tape according to claim 1 or 2, wherein the shock absorbing sheet is a foam. The adhesive tape according to claim 1, 2 or 3, wherein the shock absorbing sheet contains a block copolymer having a hard block and a soft block. The adhesive tape according to claim 4, wherein the block copolymer has a hard block content of 1% by weight or more and 40% by weight or less. The adhesive tape according to claim 4 or 5, wherein the hard block has a structure derived from a vinyl aromatic monomer. The adhesive tape according to claim 6, wherein the block copolymer has a structure derived from the vinyl aromatic monomer in an amount of 1% by weight or more and 30% by weight or less. The adhesive tape according to claim 4, 5, 6 or 7, wherein the soft block has a structure derived from a (meth) acrylic monomer. The adhesive tape according to claim 8, wherein the soft block has a structure derived from a (meth) acrylic monomer having a glass transition temperature Tg of −50 ° C. or less of a homopolymer of 80% by weight or more. .. The adhesive tape according to claim 8 or 9, wherein the block copolymer has a structure derived from the (meth) acrylic monomer in an amount of 30% by weight or more and 99% by weight or less. The block copolymer further has a structure derived from a monomer having a crosslinkable functional group, and the content of the structure derived from the monomer having a crosslinkable functional group is 0.1% by weight or more and 30% by weight. The adhesive tape according to claim 4, 5, 6, 7, 8, 9 or 10, wherein the adhesive tape is as follows. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, which is used for assembling or fixing electronic device parts.

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