JP7236466B2 - Foam adhesive tape for flexible display and flexible display laminate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a foam adhesive tape for flexible displays and a flexible display laminate.

Adhesive tapes are widely used in the production of electronic equipment such as OA equipment and home electric appliances because of their excellent workability and high adhesion reliability. In recent years, electronic devices, especially portable electronic terminals such as personal computers, digital video cameras, electronic notebooks, mobile phones, PHS, smartphones, game machines, and electronic books, are required to be smaller and thinner. Also, adhesive tapes and the like constituting the portable electronic terminals are required to be thinner.

Display devices such as those described above generally use a so-called rigid display in which display elements are formed on a glass substrate. In many cases, an adhesive tape having a cushioning foam layer is attached to the back surface of the display (see Patent Document 1).

As an adhesive tape having a foam layer, for example, air bubbles can be quickly removed from the interface with the adherend, air bubbles can be prevented from remaining at the interface, and excellent adhesion and cushioning properties can be obtained at a low cost. A thin adhesive tape has also been proposed (see Patent Document 2).

On the other hand, in recent years, by forming a display element on a flexible resin substrate, there is an increasing demand for a flexible display that can be deformed into various shapes, and extensive development is being carried out.

However, since rigid displays and flexible displays differ in flexibility, the characteristics of adhesive tapes suitable for flexible displays are still unknown, and there is a strong demand for adhesive tapes with characteristics suitable for flexible displays. is the current situation.

Japanese Patent Application Laid-Open No. 2004-309699 WO2018/116845

An object of the present invention is to solve the above-mentioned conventional problems and to achieve the following objects. That is, an object of the present invention is to provide a flexible display foam pressure-sensitive adhesive tape having properties suitable for a flexible display, and a flexible display laminate having the foam pressure-sensitive adhesive tape for a flexible display.

Means for solving the above problems are as follows. Namely
<1> A foam adhesive tape for use in a flexible display having an adhesive layer (B) on at least one side of the foam layer (A),
The 25% compression strength of the foam adhesive tape is 100 kPa or more,
The foam pressure-sensitive adhesive tape for a flexible display is characterized in that the foam pressure-sensitive adhesive tape has a point impact absorption rate calculated by the following formula (1) of 35% or more.
Point impact absorption rate (%)={(f _p0 −f _p1 )/f _p0 }×100 Equation (1)
In the above formula (1), f _p1 is the pressure when the foam adhesive tape is placed on a load cell and a steel ball with a diameter of 12.5 mm is dropped on the foam layer (A) surface of the foam adhesive tape. is the impact load,
f _p0 is the impact load when the steel ball is dropped without placing the foam adhesive tape on the load cell.
<2> A flexible display laminate comprising: a flexible display having a light emitting surface; and the flexible display foam adhesive tape according to <1> arranged on the back side of the light emitting surface. .

ADVANTAGE OF THE INVENTION According to this invention, the above-mentioned various problems in the past can be solved, the said objective can be achieved, and it has the foam adhesive tape for flexible displays which has the characteristic suitable for a flexible display, and the said foam adhesive tape for flexible displays. A flexible display laminate can be provided.

FIG. 1 is a schematic illustration of a point impact absorption test using a falling ball tester. FIG. 2 is a schematic illustration of the polyimide substrate 7 provided with the copper wiring 8 used in the evaluation of the ball falling onto the polyimide substrate in Test Example 1. As shown in FIG. FIG. 3 is a schematic diagram showing an example of a method for producing the foam layer (A) in the foam pressure-sensitive adhesive tape for flexible display of the present invention. FIG. 4 is a graph showing the relationship between the 25% compressive strength [kPa] and the point impact absorption rate [%] of foam adhesive tapes of Examples and Comparative Examples. In the graph, "●" indicates an example, and "▲" indicates a comparative example. FIG. 5 shows the arithmetic mean value (n = 5) is a graph showing.

(Foam adhesive tape for flexible displays)
The foam pressure-sensitive adhesive tape for flexible displays of the present invention (hereinafter sometimes simply referred to as "foam pressure-sensitive adhesive tape") has a pressure-sensitive adhesive layer (B) on at least one side of the foam layer (A). and, if necessary, other layers.

In this specification, the term "flexible display" means a flexible display device. Therefore, the "flexible display" includes a "bendable display" that can be repeatedly bent, a "foldable display" that can be folded, a "rollable display" that can be rolled, It can also be regarded as a "curved display" that can be bent or a "stretchable display" that can be stretched, and refers to a display that encompasses these.

- 25% compression strength of foam adhesive tape -
The 25% compression strength of the foam adhesive tape is not particularly limited as long as it is 100 kPa or more, and can be appropriately selected according to the purpose. preferable. When the 25% compressive strength of the foam adhesive tape is 100 kPa or more, when an impact is applied to the display side of the flexible display, the foam adhesive tape itself deforms and absorbs the impact. can be kept small. Therefore, it is possible to absorb impact while suppressing deformation of the substrate used in the flexible display, which is advantageous in terms of excellent protection performance of the display element in the flexible display. Although there is no particular upper limit for the 25% compression strength of the foam adhesive tape, it is preferably 1,000 kPa or less. On the other hand, when the 25% compressive strength of the foam adhesive tape is less than 100 kPa, the substrate of the flexible display deforms when an impact is applied to the display side of the flexible display even if the impact is sufficiently absorbed, The display element in the flexible display cannot be protected.

The 25% compressive strength of the foam adhesive tape refers to a value measured according to JIS K 6767. Specifically, a laminate is obtained by stacking foamed pressure-sensitive adhesive tapes cut into 25 mm squares (length 25 mm, width 25 mm) to a thickness of about 10 mm. The laminate is sandwiched between two stainless steel plates having a larger area than the laminate, and the laminate is tested at a speed of 10 mm/min at 23° C. using a dual column desktop universal testing machine Model 5966 (manufactured by Instron). is compressed to about 7.5 mm (75% of the original thickness).
In addition, when the foam adhesive tape has the other layers, the foam adhesive tape used for measuring the 25% compression strength is the foam layer obtained by removing the release liner layer (D) described later. (A), the pressure-sensitive adhesive layer (B), and a layer other than the release liner layer (D).

-Point impact absorption rate of foam adhesive tape-
The point impact absorption rate of the foamed pressure-sensitive adhesive tape is not particularly limited as long as it is 35% or more, and can be appropriately selected depending on the purpose, but is preferably 37% or more. When the foam pressure-sensitive adhesive tape has a point impact absorption rate of 35% or more, deformation of the substrate used in the flexible display can be suppressed, which is advantageous in terms of excellent protection performance of the display element in the flexible display. If the point impact absorption rate of the adhesive tape is less than 35%, when an impact is applied to the display side of the flexible display, the impact is not dispersed and high pressure is applied at pinpoints, resulting in deformation of the substrate of the flexible display. However, the display element in the flexible display cannot be protected.

In the present specification, the point impact absorption rate is measured using the falling ball tester shown in FIG. is attached, a steel ball 2 weighing 8.3 g (diameter 12.5 mm) is held on the electromagnet 1, and the steel ball 2 is attached to the foam layer (A) from a height of 20 cm from the surface 3 of the foam layer (A). It refers to the value calculated by the following formula (1) from the value of the impact load measured by free-falling on three surfaces.
Point impact absorption rate (%)={(f _p0 −f _p1 )/f _p0 }×100 Equation (1)
In the above formula (1), f _p1 is the pressure when the foam adhesive tape is placed on a load cell and a steel ball with a diameter of 12.5 mm is dropped on the foam layer (A) surface of the foam adhesive tape. is the impact load,
f _p0 is the impact load when the steel ball is dropped without placing the foam adhesive tape on the load cell.
In addition, when the foam adhesive tape has the other layers, the foam adhesive tape for measuring the point impact absorption rate is the foam layer obtained by removing the release liner layer (D) described later. (A), the pressure-sensitive adhesive layer (B), and a layer other than the release liner layer (D).

<Foam layer (A)>
The raw material for the foam constituting the foam layer (A) is not particularly limited as long as it does not impair the effects of the present invention, and can be appropriately selected from known foam raw materials. It preferably contains a foaming agent and a cross-linking agent, and may contain other additives.

<<resin emulsion>>
The resin emulsion contains at least a resin and a dispersion medium, and further contains other components as necessary.

The resin is preferably a water-dispersible resin. The resin emulsion dispersed in the dispersion medium is not particularly limited as long as it is an emulsion capable of forming a foam by a known method, and can be appropriately selected according to the purpose. Emulsions, urethane emulsions, ethylene-vinyl acetate copolymer resin emulsions, vinyl chloride emulsions, epoxy emulsions, and the like. These may be used individually by 1 type, and may use 2 or more types together. Among these, acrylic emulsions are preferred.

The method for preparing the acrylic emulsion (acrylic resin dispersion) is not particularly limited and can be appropriately selected according to the purpose. , a polymerizable monomer and, if necessary, a mixture of another polymerizable monomer copolymerizable with the polymerizable monomer. Two or more acrylic emulsions may be used in combination.

Examples of the polymerizable monomer that can be used for preparing the acrylic emulsion include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. , hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, octadecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, (meth)acrylic acid Nonyl, dodecyl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, etc. (meth) ) acrylic acid ester-based monomer; acrylic acid, methacrylic acid, β-carboxyethyl (meth)acrylate, 2-(meth)acryloylpropionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, itaconic acid half ester, Unsaturated bond-containing monomers having a carboxyl group such as maleic acid half ester, maleic anhydride, and itaconic anhydride; glycidyl group-containing polymerizable monomers such as glycidyl (meth)acrylate and allyl glycidyl ether; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl acrylate, polyethylene glycol mono (meth) acrylate, glycerol mono (meth) acrylate and other hydroxyl group-containing polymerizable monomers; ethylene glycol di (meth) Acrylates, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, diallyl phthalate , divinylbenzene, allyl (meth)acrylate, and the like. These may be used individually by 1 type, and may use 2 or more types together.

The polymerization initiator, emulsifier, and dispersion stabilizer are not particularly limited and can be appropriately selected from known ones.

The viscosity of the acrylic emulsion is not particularly limited and can be appropriately selected according to the purpose. ,000 mPa·s is more preferable. When the viscosity of the acrylic emulsion is 5,000 mPa·s or more, the bubble holding power during molding becomes sufficient, finer cells can be molded, and adhesive strength tends to be higher. In addition, when the viscosity of the acrylic emulsion is 20,000 mPa·s or less, the shearing force applied to the raw material of the foam during molding can be reduced, so that the molding of distorted cells can be prevented. Sufficient adhesive strength can be obtained.
In addition, the viscosity of the said acrylic emulsion points out the value measured with the Brookfield viscometer at 25 degreeC.

The glass transition temperature of the acrylic emulsion is not particularly limited and can be appropriately selected according to the purpose. It is preferably -10°C or lower.
In addition, the glass transition temperature of the said acrylic emulsion points out the value measured based on JISK7198. Specifically, using a dynamic viscoelasticity apparatus (model “MCR302”, manufactured by Anton Paar), the temperature was raised from −80° C. to 150° C. at 5° C./1 minute, and the tan δ measured under the condition of a frequency of 1 Hz. Let the temperature which shows a peak value be a glass transition temperature.

The amount of the water-dispersible resin (solid content) blended in the dispersion medium is not particularly limited and can be appropriately selected according to the purpose. ~80 parts by weight is preferred. When the blending amount of the water-dispersible resin (solid content) is within the preferred range, a stable foam can be formed.

In the present specification, the components constituting the "solid content" of the emulsion are the components excluding the dispersion medium from the emulsion. Specifically, in addition to the resin, it contains other components such as surfactants and fillers.

The amount of the resin emulsion to be blended in the foam raw material is not particularly limited and can be appropriately selected according to the purpose. parts) is preferably more than 10 parts by weight and 90 parts by weight or less, more preferably 20 parts by weight or more and 80 parts by weight or less, and even more preferably 30 parts by weight or more and 75 parts by weight or less. In general, the solid content of the resin emulsion is 30 to 80 parts by weight, preferably 40 to 70 parts by weight, more preferably 45 to 60 parts by weight.

<<dispersion medium>>
The dispersion medium preferably contains water, and may be a mixture of water and a water-soluble solvent.
The water-soluble solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, butyl polar solvents such as pyrrolidone; These may be used individually by 1 type, and may use 2 or more types together.

The amount of the dispersion medium used in the foam raw material is not particularly limited, and can be appropriately selected according to the application.

<< Foaming agent >>
The foaming agent is not particularly limited and can be appropriately selected depending on the intended purpose. Examples thereof include anionic surfactants and amphoteric surfactants. These may be used individually by 1 type, and may use 2 or more types together.

When the anionic surfactant and the amphoteric surfactant are used in combination, the air bubbles are fine and uniform. In addition, while the charge of the hydrophilic groups of the anionic surfactant molecules repels each other and the anionic surfactant molecules maintain a certain distance, the electrically neutral double-sided active agent becomes anionic. By entering between the molecules of the system surfactant, the bubbles can be made more stable and the size of the bubbles can be reduced. Therefore, the delamination strength can be improved. Therefore, it is preferable to use both an anionic surfactant and an amphoteric surfactant.

Specific examples of the anionic surfactant include sodium laurate, sodium myristate, sodium stearate, ammonium stearate, sodium oleate, potassium oleate soap, potassium castor oil soap, potassium coconut oil soap, sodium lauroyl sarcosinate. , sodium myristoyl sarcosinate, sodium oleyl sarcosinate, sodium cocoyl sarcosinate, sodium coconut oil alcohol sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium alkylsulfosuccinate, sodium lauryl sulfoacetate, sodium alkylbenzenesulfonate, sodium α-olefin sulfonate, etc. is mentioned. Among these, ammonium stearate, sodium alkylsulfuccinate and the like are preferred.

The HLB of the anionic surfactant is not particularly limited and can be appropriately selected depending on the intended purpose. It is more preferable to be 1, and 30 or more is even more preferable.

The amount of the anionic surfactant blended in the foam raw material is not particularly limited and can be appropriately selected according to the purpose. 100 parts by weight), preferably 1.0 to 10 parts by weight, more preferably 3 to 10 parts by weight. When the blending amount of the anionic surfactant in the foam raw material is within the preferred range, appropriate foaming can be easily achieved and a fine cell structure can be formed.

The amphoteric surfactant is not particularly limited and can be appropriately selected depending on the intended purpose. Examples thereof include amphoteric surfactants such as amino acid type, betaine type and amine oxide type.

The HLB of the amphoteric surfactant is not particularly limited and can be appropriately selected depending on the purpose. ~12 are preferred.

Specific examples of the amino acid type amphoteric surfactants include N-alkyl or alkenyl amino acids or salts thereof. An N-alkyl or alkenyl amino acid has an alkyl group or alkenyl group bonded to a nitrogen atom, and further has one or two "-R-COOH" (wherein R represents a divalent hydrocarbon group, preferably It is an alkylene group, and preferably has 1 to 2 carbon atoms.) is bonded. In a compound in which one "--R--COOH" is bound, a hydrogen atom is further bound to the nitrogen atom. A compound having one "-R-COOH" is called a mono-form, and a compound having two "-R-COOH" is called a di-form. As the amphoteric surfactant, both mono-isomer and di-isomer can be used. In N-alkyl or alkenyl amino acids, the alkyl group and alkenyl group may be linear or branched. More specifically, amino acid-type amphoteric surfactants include sodium lauryldiaminoethylglycinate, sodium trimethylglycinate, sodium cocoyl taurate, sodium cocoyl methyl taurate, sodium lauroyl glutamate, potassium lauroyl glutamate, lauroylmethyl-β-alanine, and the like. mentioned.

Specific examples of the betaine type amphoteric surfactant include alkylbetaine, imidazolinium betaine, carbobetaine, amidocarbobetaine, amidobetaine, alkylamidobetaine, sulfobetaine, amidosulfobetaine, and phosphobetaine. More specifically, the betaine-type amphoteric surfactants include lauryl betaine, stearyl betaine, lauryldimethylamino betaine, stearyldimethylamino betaine, lauramidopropyldimethylamino betaine, and isostearamide ethyldimethylaminoacetic acid. Betaine, betaine isostearamide propyl dimethylaminoacetate, betaine isostearamide ethyl diethylaminoacetate, betaine isostearamide propyl diethylaminoacetate, betaine isostearamide ethyl dimethylaminohydroxysulfobetaine, isostearamide propyl dimethylaminohydroxysulfobetaine, isostearamide Ethyldiethylaminohydroxysulfobetaine, isostearamidopropyl diethylaminohydroxysulfobetaine, N-lauryl-N,N-dimethylammonium-N-propylsulfobetaine, N-lauryl-N,N-dimethylammonium-N-(2-hydroxypropyl ) sulfobetaine, N-lauryl-N,N-dimethyl-N-(2-hydroxy-1-sulfopropyl)ammonium sulfobetaine, lauryl hydroxysulfobetaine, dodecylaminomethyldimethylsulfopropylbetaine, octadecylaminomethyldimethylsulfopropylbetaine , 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine (2-lauryl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine 2-stearyl-N-carboxymethyl-N-hydroxyethylimidazolinium linium betaine, etc.), coconut oil fatty acid amidopropyl betaine, coconut oil fatty acid amidopropyl hydroxysultaine, and the like.

Specific examples of the amine oxide type amphoteric surfactant include lauryldimethylamine-N-oxide and oleyldimethylamine-N-oxide.

Among the above amphoteric surfactants, it is preferable to use betaine type amphoteric surfactants, and among betaine types, alkylbetaine, imidazolinium betaine, and carbobetaine are particularly preferred.

The content of the amphoteric surfactant in the foam raw material is not particularly limited and can be appropriately selected according to the purpose. 100 parts by weight), preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight. When the amount of the amphoteric surfactant compounded in the foam raw material is within the preferred range, appropriate foaming can be easily achieved and a fine cell structure can be formed.

<<crosslinking agent (curing agent)>>
The use of a cross-linking agent as a raw material of the foam is preferable in that the strength of the foam can be improved.

The cross-linking agent is not particularly limited and can be appropriately selected from known cross-linking agents. An agent or the like can be used in an appropriate amount depending on the type and amount of functional groups contained in the resin compounding system used. These may be used individually by 1 type, and may use 2 or more types together. Among these, epoxy-based cross-linking agents and isocyanate-based cross-linking agents are preferred because they can improve adhesive strength, tack strength, and delamination strength. The isocyanate-based cross-linking agent and the epoxy-based cross-linking agent can prevent material destruction of the adherend and the porous foam by increasing material strength. Among these, aliphatic isocyanates are more preferred.

The amount of the cross-linking agent to be added to the foam raw material is not particularly limited, and can be appropriately selected according to the application. The cross-linking method using the cross-linking agent includes, for example, physical cross-linking, ionic cross-linking, chemical cross-linking, etc., and can be selected according to the type of resin emulsion.

The amount of the cross-linking agent blended in the raw material for the foam is not particularly limited and can be appropriately selected according to the purpose. The resin emulsion] is preferably 0.01 to 0.12, more preferably 0.025 to 0.05. When the weight ratio [the cross-linking agent/the resin emulsion] is within the preferred range, a foam having a small residual compression strain can be molded.

<<Other Additives>>
The other additives are not particularly limited and can be appropriately selected from known additives. Examples include ultraviolet absorbers, antioxidants, organic and inorganic fillers, colorants, and foaming agents. and other surfactants. These may be used individually by 1 type, and may use 2 or more types together.

Examples of surfactants other than the foaming agent include surfactants for dispersing the resin (sometimes referred to as "water-dispersible resin-dispersing surfactants"). Unlike the anionic surfactant, the surfactant for dispersing the dispersible resin may not have an effect as a foaming agent, and can be appropriately selected according to the selected resin.

-Thickness of foam layer (A)-
The thickness of the foam layer (A) is not particularly limited and can be appropriately selected depending on the application and design requirements, but it is preferably 5 μm or more and 500 μm or less. If the thickness of the foam layer (A) is too thin, the cells may not be dispersed uniformly, or the impact absorption performance may be insufficient. On the other hand, if the foam layer (A) is too thick, it may not fit in the limited space of a space-saving electronic/electrical device. Therefore, the lower limit of the thickness of the foam layer (A) is preferably 60 µm, more preferably 70 µm, and still more preferably 80 µm. The upper limit of the foam layer (A) is preferably 400 µm, more preferably 300 µm, and still more preferably 200 µm.

- Density of foam layer (A) -
The density (apparent density) of the foam layer (A) is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.40 g/cm ³ or more and 1.00 g/cm ³ or less. The apparent density is a measure of the cell inclusion rate of the foam. If the apparent density is too low, the foam has too many cells, resulting in low impact absorption performance. In particular, the point impact absorption performance is remarkably lowered. On the other hand, if the apparent density is too high, the number of cells in the foam is too small, resulting in a decrease in impact absorption performance. Therefore, the lower limit of the apparent density is preferably 0.41 g/cm ³ , more preferably 0.42 g/cm ³ and even more preferably 0.43 g/cm ³ . Moreover, the upper limit of the apparent density is preferably 0.99 g/cm ³ , more preferably 0.98 g/cm ³ , and still more preferably 0.97 g/cm ³ .
In addition, the said density refers to the value measured by calculating from the weight per unit volume based on JISK7222.

-Loss tangent tan δ of foam layer (A)-
The loss tangent tan δ based on the dynamic viscoelastic spectrum measured at a frequency of 1 Hz of the foam layer (A) is not particularly limited and can be appropriately selected depending on the purpose, but is 0.4 or more. is preferred, and 0.5 or more is more preferred. When the loss tangent tan δ of the foam layer (A) is within the preferred range, the foam layer (A) becomes relatively elastic, resulting in a decrease in point impact absorption. For example, when the impact is applied at a high speed, such as when electronic or electrical equipment is dropped, the viscoelastic properties of the foam are measured in terms of temperature and time conversion (TT conversion) of the viscoelastic body. Based on this, the characteristics of the temperature range on the lower temperature side are shown. That is, the elastic behavior becomes relatively strong, and the point impact absorption performance is lowered. Therefore, the greater the loss tangent (tan δ) at 23° C., the higher the point impact absorption performance.

The loss tangent tan δ is a value measured according to JIS K7198. Specifically, using a dynamic viscoelasticity device (model “MCR302”, manufactured by Anton Paar), the temperature was raised from −80° C. to 150° C. at a rate of 5° C./1 minute, and the measurement was performed under the conditions of a frequency of 1 Hz. The storage elastic modulus (G′) and loss elastic modulus (G″) at 23° C. are measured, and the value calculated by the following formula (2) is defined as the loss tangent tan δ of the foam layer (A).
Loss tangent tan δ=G″/G′ Equation (2)

The storage elastic modulus is a parameter representing the elastic term of the foam, which is a viscoelastic body, and represents the ability to store applied deformation energy or the like as elastic energy. On the other hand, the loss modulus is a parameter that represents the viscosity term of the foam, which is a viscoelastic body, and represents the ability to dissipate the applied deformation energy or the like by internal friction or the like inside the foam. Also, the loss tangent is calculated by the above formula (2) and is an index of whether the foam is relatively viscous. Thus, the high loss tangent foam will be relatively viscous and the low loss tangent foam will be relatively non-viscous or elastic.

-Glass transition temperature of foam layer (A)-
The glass transition temperature (Tg) of the foam layer (A) is not particularly limited and may be appropriately selected depending on the purpose, but is preferably 5°C or higher and 40°C or lower. When the glass transition temperature (Tg) of the foam layer (A) is within the preferred range, good point impact absorption is obtained. On the other hand, if the glass transition temperature is less than 5°C, the point impact absorption may decrease due to relatively excessive viscosity. In some cases, the point impact absorption is significantly reduced due to excessive elasticity.
The glass transition temperature refers to the temperature showing the peak value of the loss tangent tan δ measured according to JIS K 7198.

Examples of the method for controlling the glass transition temperature of the foam layer (A) include a method of mixing a plurality of resin emulsions in the foam raw material. At this time, the glass transition temperature of a plurality of mixed resin emulsions is determined by measuring the glass transition temperatures of homopolymers of various copolymerization monomers, and measuring the glass transition temperatures of these homopolymers, The reciprocal of the glass transition temperature is obtained by dividing the weight fraction and summing the divisors of the individual comonomers to be mixed. Here, the various copolymerizable monomers mentioned above specifically include styrene, vinyl acetate, butyl acrylate, 2-ethylhexyl acrylate, ethyl acrylate, hexyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, and the like. mentioned.

<<Method for Forming Foam Layer (A)>>
The method for forming the foam layer (A) is not particularly limited and can be appropriately selected from known methods. and the like, and may further include other steps.

-Foam raw material preparation process-
The foam raw material preparation step is a step of mixing the foam raw materials to prepare a resin emulsion composition that is a mixture of the foam raw materials.
The method for mixing the foam raw material is not particularly limited and can be appropriately selected according to the purpose. A method of mixing and the like can be mentioned.

- Foaming process -
In the foaming step, a predetermined foaming gas is added to the resin emulsion composition obtained in the foam raw material preparation step, and these are sufficiently mixed to form a state in which many bubbles are present in the resin emulsion composition. (sometimes referred to as "foaming emulsion composition", "gas-liquid mixture", etc.).
The foaming step is usually carried out by sufficiently mixing the foam raw material mixture of the liquid porous foam obtained in the foam raw material preparation step and the foaming gas with a mixing device such as a mixing head. be.

Air is mainly used as the type of the foaming gas, but inert gases such as nitrogen, carbon dioxide, helium, and argon can also be used.

The foaming gas forms cells in the foam, and the foaming ratio and density of the resulting foam are determined by the amount of the foaming gas mixed therein. In order to adjust the density of the porous foam, from the desired density of the porous foam and the volume of the raw material of the porous foam (for example, the internal volume of the mold into which the raw material of the porous foam is injected), The weight of the necessary raw material for the porous foam is calculated, and the amount of the foaming gas is determined so that the desired volume can be obtained with this weight.

Examples of a method for foaming in the foaming step include a mechanical floss (mechanical foaming) method. The mechanical froth method is a method of stirring the resin emulsion composition with a stirring blade or the like to mix the foaming gas into the resin emulsion composition to foam the resin emulsion composition.

The device used for the stirring is not particularly limited, and a stirring device commonly used in the mechanical froth method can be used. Examples thereof include homogenizers, dissolvers, and mechanical froth foamers.

According to the mechanical froth method, by adjusting the mixing ratio of the resin emulsion composition and the foaming gas, a porous foam having a density suitable for various uses can be obtained. It is possible to use other foaming methods in combination, but when foaming methods using chemical foaming agents are used in combination, the percentage of closed cells increases, resulting in an increase in density and loss of flexibility of the porous foam. Therefore, it is not preferable.

The mixing time of the resin emulsion composition and the foaming gas is not particularly limited and can be appropriately selected depending on the intended purpose. more preferred.

The temperature at which the resin emulsion composition and the foaming gas are mixed is not particularly limited and can be appropriately selected depending on the intended purpose, but it is usually room temperature.

The stirring speed for mixing the resin emulsion composition and the foaming gas is not particularly limited and can be appropriately selected according to the purpose. 500 rpm or more is more preferable. Moreover, the stirring speed is preferably 2,000 rpm or less, more preferably 800 rpm or less, in order to smoothly discharge the foam from the foaming machine.

The resin emulsion composition foamed as described above (sometimes referred to as "foamed emulsion composition", "gas-liquid mixture", etc.) is prepared by known means such as a roll coater, doctor knife, doctor roll, etc. It is formed into a foam such as a sheet having a desired thickness.

When the foamed resin emulsion composition was formed into a sheet, the upper side of the foamed resin emulsion composition was treated with release paper or a release treatment different from the release liner layer (D) described later. A resin film may be supplied. By supplying such a release paper or a resin film that has been subjected to a release treatment, it is easy to adjust the thickness of the uncured layer composed of the foamed resin emulsion composition, and the thickness of the foam layer obtained after heat treatment. A skin layer can be formed on the surface (the surface in contact with the release paper or the resin film treated for release).

-Curing process-
The curing step is a step of curing the foamed emulsion composition.
A method for curing the foamed emulsion composition is not particularly limited, and a known method can be used. The foamed emulsion composition can be self-crosslinked, but the foam may be cured by applying energy to crosslink the resin constituting the emulsion via a crosslinking agent. The step of applying the energy is not particularly limited, and examples thereof include a heating step (thermal cross-linking).

In the heating step, the dispersion medium in the molded foamed emulsion composition is evaporated. The drying method in this case is not particularly limited, and examples thereof include a hot air drying method and a far-infrared heating method.
The drying temperature and time are also not particularly limited, and can be appropriately selected according to the drying method.

In the heating step, the dispersion medium evaporates from the foamed emulsion composition, and the passage through which this vapor escapes communicates from the inside to the outside of the porous foam. Therefore, in the foam in the foam layer (A), since the passages through which the water vapor escapes remain as open cells, at least some of the cells existing in the porous foam become open cells. Here, when the foaming gas mixed in the foaming step remains as it is, it forms closed cells in the obtained porous foam, and the mixed foaming gas is converted into steam in the heating step. If they are communicated when they are pulled out, they become open cells in the resulting porous foam. That is, the porous foam has a structure in which some of the cells in the porous foam are open cells and the remaining cells are closed cells, resulting in a semi-open cell structure in which open cells and closed cells are mixed.

When a cross-linking agent is added in the curing step, the heating step advances and completes the cross-linking (curing) reaction of the foam raw material. Specifically, the foam raw materials are cross-linked by the cross-linking agent to form a cured porous foam. The heating means at this time is not particularly limited as long as it can sufficiently heat the foam raw material to crosslink (harden) the foam raw material, and examples thereof include a tunnel heating furnace. Also, the heating temperature and heating time are not particularly limited as long as the temperature and time are such that the foam raw material can be crosslinked (cured). It should be to some extent.

As a method for laminating the foam layer (A) and the pressure-sensitive adhesive layer (B), for example, the foam emulsion composition is applied onto the release liner layer (D) described later, and the curing step is performed. For example, after curing, the release liner layer (D) is peeled off and laminated on the pressure-sensitive adhesive layer (B).
Moreover, the foam layer (A) may be formed on a resin film layer (C) described later. As a method for forming the foam layer (A) on the resin film layer (C), for example, the foam emulsion composition is directly applied on the resin film layer (C), and the foam layer ( A) and the said resin film layer (C) are laminated|stacked on the said adhesive layer (B) as it is, etc., for example.
Alternatively, a laminate in which the resin film layer (C) and the adhesive layer (B) are arranged in this order is formed in advance, and the adhesive layer (B) of the resin film layer (C) is The foam (A) may be laminated on the side opposite to the side on which is present.

<Adhesive layer (B)>
The pressure-sensitive adhesive layer (B) contains at least a pressure-sensitive adhesive and, if necessary, further contains other components.

<<Adhesive>>
The adhesive is not particularly limited and can be appropriately selected from known adhesives. For example, acrylic adhesive resin, acrylic adhesive, rubber adhesive, silicone adhesive, urethane adhesive Adhesives, polyester-based adhesives, styrene-diene block copolymer-based adhesives, vinyl alkyl ether-based adhesives, polyamide-based adhesives, fluorine-based adhesives, creep property-improved adhesives, radiation-curable adhesives, etc. is mentioned. These may be used individually by 1 type, and may use 2 or more types together. Among these adhesives, an acrylic adhesive is preferable because of its excellent adhesion reliability.

--Acrylic adhesive--
The acrylic pressure-sensitive adhesive resin is not particularly limited and can be appropriately selected depending on the intended purpose. etc.

As the acrylic polymer, for example, one obtained by polymerizing a monomer mixture containing a (meth)acrylic monomer can be used.

Examples of the (meth)acrylic monomer include monomers having a carboxyl group such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid and isocrotonic acid, or anhydrides thereof; sodium vinyl sulfonate; a monomer having a sulfonic acid group; a monomer having a cyano group such as acrylonitrile; a monomer having an amide group such as acrylamide, methacrylamide, N-vinylpyrrolidone, N,N-dimethyl (meth)acrylamide; Monomers having a hydroxyl group such as hydroxyalkyl (meth)acrylate and glycerol dimethacrylate; monomers having an amino group such as aminoethyl (meth)acrylate and acryloylmorpholine (meth); cyclohexylmaleimide, isopropylmaleimide and the like Monomers having an imide group; monomers having an epoxy group such as glycidyl (meth) acrylate and methyl glycidyl (meth) acrylate; monomers having an isocyanate group such as 2-methacryloyloxyethyl isocyanate; methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, triethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, ethylene glycol di (meth) acrylate, tetra Ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa (Meth)acrylates, divinylbenzene, (meth)acrylic acid alkyl esters, and the like. These may be used individually by 1 type, and may use 2 or more types together. Among these, (meth)acrylic acid alkyl esters are preferable.

Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylate, ) isobutyl acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate , 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, (meth)acrylic acid Undecyl, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate , nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These may be used individually by 1 type, and may use 2 or more types together. Among these, as the (meth)acrylic acid alkyl ester, it is preferable to use a (meth)acrylic acid alkyl ester having the alkyl group having 1 to 20 carbon atoms, and the alkyl group having 4 carbon atoms. It is more preferred to use -18 (meth)acrylic acid alkyl esters. Examples of the alkyl group include linear or branched alkyl groups.

As the (meth)acrylic acid alkyl ester having 4 to 18 carbon atoms for the acrylic group, use of butyl (meth)acrylate can easily prevent changes over time and can maintain good adhesive strength. It is preferable for obtaining a foam pressure-sensitive adhesive tape.

In addition to the (meth)acrylic monomers, the monomers include aromatic vinyl compounds such as styrene and substituted styrene; olefins such as ethylene, propylene and butadiene; vinyl esters such as vinyl acetate; Vinyl chloride or the like can also be used.

The method for producing the acrylic polymer is not particularly limited, and can be appropriately selected from known methods according to the purpose. A method of polymerizing by a polymerization method such as a turbidity polymerization method or an emulsion polymerization method can be used. Among these, the acrylic polymer is preferably produced by a solution polymerization method in order to improve production efficiency of the acrylic polymer.

Examples of the solution polymerization method include a method of mixing and stirring the monomers, a polymerization initiator, and an organic solvent at a temperature of preferably 40° C. to 90° C. to carry out radical polymerization.

Examples of the polymerization initiator include peroxides such as benzoyl peroxide and lauryl peroxide, azo thermal polymerization initiators such as azobisisobutylnitrile, acetophenone photopolymerization initiators, benzoin ether photopolymerization initiators, Examples include benzyl ketal photopolymerization initiators, acylphosphine oxide photopolymerization initiators, benzoin photopolymerization initiators, benzophenone photopolymerization initiators, and the like. These may be used individually by 1 type, and may use 2 or more types together.

The acrylic polymer obtained by the above method may be dissolved or dispersed in an organic solvent, for example, if it is produced by a solution polymerization method.

The weight average molecular weight of the acrylic polymer obtained by the above method is preferably 300,000 to 1,200,000, more preferably 400,000 to 1,100,000, and more preferably 500,000 to 1,100,000. It is preferable to use one of 1,000,000 in order to obtain a foam pressure-sensitive adhesive tape having even better adhesion even if it is thin.

The weight average molecular weight is measured by gel permeation chromatography (GPC) and refers to a value calculated in terms of standard polystyrene. Specifically, the weight average molecular weight is a standard polystyrene conversion value measured using a PC device (HLC-8329GPC, manufactured by Tosoh Corporation) under the following measurement conditions.
[Measurement condition]
・ Sample concentration: 0.5% by weight (tetrahydrofuran (THF) solution)
・ Sample injection volume: 100 μL
・ Eluent: THF
・ Flow rate: 1.0 mL / minute ・ Measurement temperature: 40 ° C
・ Main column: TSKgel GMHHR-H (20) 2 ・ Guard column: TSKgel HXL-H
・ Detector: Differential refractometer ・ Standard polystyrene molecular weight: 10,000 to 20 million (manufactured by Tosoh Corporation)

As the pressure-sensitive adhesive, it is preferable to use one containing a tackifying resin in order to form a pressure-sensitive adhesive layer (B) having even better adhesive strength, tensile strength and tensile strength at break.

The tackifying resin is not particularly limited and can be appropriately selected depending on the intended purpose. Tackifier resin, stabilized rosin ester tackifier resin, disproportionated rosin ester tackifier resin, hydrogenated rosin ester tackifier resin, terpene tackifier resin, terpene phenol tackifier resin, styrene tackifier resin, etc. and petroleum resin-based tackifying resins. These may be used individually by 1 type, and may use 2 or more types together.

As the tackifying resin, the combination of the rosin-based tackifying resin and the petroleum resin-based tackifying resin is used in order to obtain a foamed pressure-sensitive adhesive tape having even better adhesion even if it is thin. preferable. The rosin-based tackifying resin and the petroleum resin-based tackifying resin are preferably used in combination with the acrylic polymer, and the acrylic polymer obtained by polymerizing the monomer containing butyl (meth)acrylate. It is preferable to use it in combination with a polymer in order to obtain a foam pressure-sensitive adhesive tape having even better adhesion even if it is thin.

Moreover, as the tackifying resin, it is preferable to use a tackifying resin that is liquid at room temperature in order to further improve the initial adhesive strength of the pressure-sensitive adhesive. Examples of tackifier resins that are liquid at room temperature include process oils, polyester plasticizers, low molecular weight liquid rubbers such as polybutene, and terpene phenol resins. These may be used individually by 1 type, and may use 2 or more types together. Commercially available products of the terpene phenol resin include, for example, the product name "YP-90L" (manufactured by Yasuhara Chemical Co., Ltd.).

The amount of the tackifying resin to be used is not particularly limited, and can be appropriately selected according to the purpose. is preferred, and use in the range of 30 parts by weight to 55 parts by weight is more preferred for obtaining a foam pressure-sensitive adhesive tape with even better adhesion.

<<Other Ingredients>>
Examples of the other components in the pressure-sensitive adhesive layer (B) include polymer components other than the pressure-sensitive adhesive resin, cross-linking agents, anti-aging agents, colorants, ultraviolet absorbers, fillers, polymerization inhibitors, and surface modifiers. , antistatic agents, antifoaming agents, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, antioxidants, leveling agents, organic pigments, inorganic pigments, pigment dispersants, plasticizers, softeners, flame retardants , metal deactivators, silica beads, organic beads; inorganic fillers such as silicon oxide, aluminum oxide, titanium oxide, zirconia, antimony pentoxide; These may be used individually by 1 type, and may use 2 or more types together. Among these, the use of the cross-linking agent can adjust the gel fraction of the pressure-sensitive adhesive layer (B) to a suitable range, and as a result, it is easy to prevent the pressure-sensitive adhesive from changing over time. , is preferable because a foam pressure-sensitive adhesive tape having excellent adhesion can be obtained.
The content of the other components in the pressure-sensitive adhesive layer (B) can be appropriately selected within a range that does not impair the properties of the foam pressure-sensitive adhesive tape.

The cross-linking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include isocyanate cross-linking agents, epoxy cross-linking agents, metal chelate cross-linking agents, aziridine cross-linking agents and the like. These may be used individually by 1 type, and may use 2 or more types together. Among these, the cross-linking agent is preferably a cross-linking agent of the type that is mixed after the production of the acrylic polymer to promote the cross-linking reaction, and an isocyanate-based cross-linking agent or an epoxy-based cross-linking agent that is highly reactive with the acrylic polymer is used. is more preferable.

Examples of the isocyanate-based crosslinking agent include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and trimethylolpropane-modified tolylene diisocyanate. These may be used individually by 1 type, and may use 2 or more types together. Among these, toluene diisocyanate adducts such as tolylene diisocyanate and trimethylolpropane-modified tolylene diisocyanate are preferably used. The toluene diisocyanate adduct has a structure derived from toluene diisocyanate in the molecule, and commercially available products include, for example, the product name "Coronate L" (manufactured by Nippon Polyurethane Industry Co., Ltd.).

When using the isocyanate-based cross-linking agent, it is preferable to use an acrylic polymer having a hydroxyl group as the acrylic polymer. Examples of monomers used in the production of the acrylic polymer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. etc. can be used, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are more preferably used.

Examples of the epoxy-based cross-linking agent include trade name "Tetrad X" and trade name "Tetrad C" (both manufactured by Mitsubishi Gas Chemical Company, Inc.) and E-05X (manufactured by Soken Chemical Co., Ltd.). can be used.

When using the epoxy cross-linking agent, it is preferable to use an acrylic polymer having an acid group as the acrylic polymer. For the acrylic polymer having an acid group, it is preferable to use, for example, (meth)acrylic acid, acrylic acid dimer, itaconic acid, crotonic acid, maleic acid, maleic anhydride, etc. as the monomers used for its production. , (meth)acrylic acid is more preferably used.

It is preferable to use the pressure-sensitive adhesive that contains a solvent as necessary. The viscosity of the pressure-sensitive adhesive is not particularly limited, and can be appropriately selected according to the purpose. It is more preferable to use one adjusted to the range of 1 mPa·s to 200 mPa·s, and more preferably to use the one adjusted to the range of 10 mPa·s to 100 mPa·s.

-Gel fraction of adhesive layer (B)-
The gel fraction of the pressure-sensitive adhesive layer (B) is not particularly limited and can be appropriately selected depending on the intended purpose. It is preferable to use one having a gel fraction of 20% to 55% by weight, and it is more preferable to use one having a gel fraction of 30% to 50% by weight. It is more preferable because it is easy to prevent such a change, and it is possible to more effectively prevent deterioration of performance such as thermal conductivity (heat dissipation), heat resistance, and adhesive strength.

In addition, the said gel fraction points out the value measured by the method shown below.
(1) On the release-treated surface of the release liner, the pressure-sensitive adhesive and, if necessary, the other components are applied so that the thickness after drying is 50 µm, and the adhesive is applied in an environment of 100°C. After drying for 3 minutes, the adhesive layer (B) is formed by aging in an environment of 40° C. for 2 days.
(2) A test piece is obtained by cutting the adhesive layer (B) into a square having a length of 50 mm and a width of 50 mm.
(3) After measuring the weight (G1) of the test piece, the test piece is immersed in toluene for 24 hours in an environment of 23°C.
(4) After the immersion, the mixture of the test piece and toluene is separated by filtration using a 300-mesh wire mesh to extract components insoluble in toluene. The weight (G2) of the insoluble component dried in an environment of 110° C. for 1 hour is measured.
(5) Based on the weight (G1) and the weight (G2), the gel fraction can be calculated by the following formula (3).
Gel fraction (% by weight)=(G2/G1)×100 Formula (3)

-Dynamic viscoelasticity of adhesive layer (B)-
The peak temperature of the loss tangent based on the dynamic viscoelastic spectrum measured at a frequency of 1 Hz of the pressure-sensitive adhesive layer (B) is not particularly limited and can be appropriately selected depending on the purpose. It is preferably -20 ° C., more preferably -20 ° C. to 10 ° C., and -10 ° C. to 5 ° C. can maintain good adhesive strength, thermal conductivity (heat dissipation) and heat resistance. It is more preferable because deterioration of properties such as properties and adhesive strength can be more effectively prevented.

In the dynamic viscoelasticity, a viscoelasticity tester (trade name "Ares 2KSTD", manufactured by Rheometrics Co., Ltd.) is used, a test piece is sandwiched between parallel discs that are the measurement part of the tester, and stored at a frequency of 1 Hz. The elastic modulus (G') and loss elastic modulus (G'') are measured. The loss tangent is calculated by the following formula (2). The above peak temperature refers to the peak temperature confirmed in the tan δ spectrum for the measured temperature range (-50°C to 150°C).
Loss tangent tan δ=G″/G′ Equation (2)

As the test piece, an adhesive layer (B) having a thickness of 0.05 mm to 2.5 mm formed using the adhesive used for forming the adhesive layer (B) can be used. The test piece may have a thickness of 0.05 mm to 2.5 mm by laminating a plurality of adhesive layers (B) formed. Further, as the test piece, among those obtained by laminating a plurality of foamed adhesive tapes, one having a total thickness of the adhesive layer (B) of 0.05 mm to 2.5 mm can be used. When test pieces with different configurations are used, the tan δ value changes, but when the total thickness of the pressure-sensitive adhesive layer (B) in the test piece is the same, the peak temperature is substantially It does not change. Therefore, any test piece may be used in the measurement of the peak temperature.

-Thickness of adhesive layer (B)-
The thickness of the pressure-sensitive adhesive layer (B) is not particularly limited and can be appropriately selected depending on the purpose. This is more preferable because it is possible to more effectively prevent deterioration of performance such as thermal conductivity, heat resistance, and adhesive strength of the foamed pressure-sensitive adhesive tape.

<<Method for Forming Adhesive Layer (B)>>
The method for forming the pressure-sensitive adhesive layer (B) is not particularly limited, and can be appropriately selected from known methods according to the purpose. A stretching method, a sequential secondary stretching method, a simultaneous biaxial stretching method, an inflation method, a tube method, a calendering method, a solution method, and the like can be mentioned. Among these, the solution method is preferred.

Examples of the solution method include a method of applying a solution containing the pressure-sensitive adhesive and, if necessary, the other components onto the release liner using a roll coater or the like.

The pressure-sensitive adhesive layer (B) is not particularly limited as long as it is arranged on at least one side of the foam layer (A), and can be appropriately selected depending on the purpose of use. It may be arranged only on one side of the layer (A), or may be arranged on both sides of the foam layer (A).
When the foam adhesive tape has the adhesive layer (B) on both sides of the foam layer (A), the adhesive layers (B) arranged on both sides have the same composition and gel content. different compositions or gel fractions.

The adhesive layer (B) may be formed on the entirety of the foam adhesive tape, and when the foam adhesive tape is observed from one surface side of the foam layer (A), approximately It may be configured to have an adhesive part in a shape such as a square, a rectangle, a trapezoid, a rhombus, or any other shape; a substantially hexagonal shape; or a substantially circular shape. When the pressure-sensitive adhesive layer (B) has the pressure-sensitive adhesive portion, air bubbles can be easily released from the interface with the adherend (air release property), and good adhesive strength can be maintained.
Examples of the adhesive portion having the shape include those described in International Publication No. 2018/116845.

<Other layers>
The other layers are not particularly limited as long as they do not impair the effects of the present invention, and can be appropriately selected depending on the purpose. is preferred. It may also have a primer layer, an antistatic layer, an incombustible layer, a decorative layer, a conductive layer, a heat conductive layer, a release layer, and the like.

<<resin film layer (C)>>
The foam pressure-sensitive adhesive tape may have the resin film layer (C) between the foam layer (A) and the pressure-sensitive adhesive layer (B) to give strength to the foam pressure-sensitive adhesive tape. It is preferable in that it can be done.

The resin film layer (C) is not particularly limited, and can be appropriately selected from known resin films. Examples thereof include polyester film, polyimide film, polyolefin film, polyamide film, and polyurethane film. These may be used individually by 1 type, and may use 2 or more types together. Among these, polyethylene terephthalate film is preferable because it is excellent in heat resistance and strength and is low in cost.

The thickness of the resin film layer (C) is not particularly limited and can be appropriately selected according to the purpose. A thickness of 0.5 μm to 6 μm is more preferable because it is thin and does not reduce the cushioning properties.

The method for forming the resin film layer (C) is not particularly limited and can be appropriately selected from known methods. For example, the resin film layer (C ), and affixing them using a laminator.

<<Release liner layer (D)>>
The foam pressure-sensitive adhesive tape further includes the release liner layer (D) to prevent damage to the foam layer (A) and the pressure-sensitive adhesive layer (B) during transportation and before use. point is preferable. The release liner layer (D) is removed when the foam adhesive tape is used.

The material constituting the release liner layer (D) is not particularly limited and can be appropriately selected depending on the intended purpose. Resin films such as polyethylene, polypropylene (biaxially oriented polypropylene (OPP), uniaxially oriented polypropylene (CPP)), polyethylene terephthalate (PET); and laminated paper obtained by laminating the above paper and a resin film. The paper may be treated with clay, polyvinyl alcohol, or the like, and the material may be surface-treated with a known release agent such as silicone resin.

The thickness of the resin film in the release liner layer (D) is not particularly limited and can be appropriately selected depending on the intended purpose. When the thickness of the resin film is within the preferred range, it is advantageous in that unevenness in the foam layer (A) hardly occurs when the foam layer (A) is formed.

The release agent in the release liner layer (D) is not particularly limited and can be appropriately selected depending on the intended purpose. Silicone-based release agents are preferable because the release force can be easily adjusted.

The order in which the release liner layer (D) is arranged is not particularly limited and can be appropriately selected according to the purpose, and the adhesive layer (B) is arranged on one side of the foam adhesive tape. In the case, the configuration ([foam layer (A) / adhesive layer (B) / release liner layer (D)]) or a configuration arranged on the surface of the foam layer (A) opposite to the side having the adhesive layer (B) ([release liner layer (D) / foam layer (A)/adhesive layer (B)]), and a configuration in which both the adhesive layer (B) and the foam layer (A) are adjacent to the release liner layer (D) ([release liner layer ( D)/foam layer (A)/adhesive layer (B)/release liner layer (D)]).
Further, when the adhesive layer (B) is arranged on both sides of the foam adhesive tape, [adhesive layer (B) / foam layer (A) / adhesive layer (B) / release liner layer (D)], [Release liner layer (D) / Adhesive layer (B) / Foam layer (A) / Adhesive layer (B)], [Release liner layer (D) / Adhesive A configuration such as an adhesive layer (B)/foam layer (A)/adhesive layer (B)/release liner layer (D)] may be mentioned.

The method for forming the release liner layer (D) is not particularly limited, and can be appropriately selected from known methods. In the case of a structure arranged on the side opposite to the side having the foam layer (A), a method of forming the pressure-sensitive adhesive layer (B) directly on the release liner layer (D), and the pressure-sensitive adhesive A method of disposing the release liner layer on the layer (B) and laminating it by a known method such as pressing can be used.

-Thickness of foam adhesive tape-
The thickness of the foam adhesive tape is not particularly limited, and can be appropriately selected according to the purpose. Although the thickness can be appropriately selected depending on the thickness, etc., it is preferably 6 μm to 520 μm.

The thickness of each layer in the foam adhesive tape can be measured by observing a cross section of the foam adhesive tape in the thickness direction with an electron microscope. Specifically, after immersing the foam adhesive tape in liquid nitrogen for 1 minute, the foam adhesive tape is folded and split in the liquid nitrogen using tweezers in the width direction of the foam adhesive tape. A slice for observing the fractured surface in the thickness direction is prepared. After the section was returned to room temperature in a desiccator, it was fixed on a sample stage so that the electron beam was incident perpendicularly to the fractured surface, and an electron microscope (Miniscope (registered trademark) TM3030Plus, manufactured by Hitachi High Technology Co., Ltd.) was used. is used to observe the fractured surface. Based on the scale of the electron microscope, the thickness of each layer of the foam adhesive tape is measured at 10 points, and the arithmetic mean value is taken as the thickness of each layer.

-Structure of foam adhesive tape-
The structure of the foam adhesive tape is not particularly limited as long as it has an adhesive layer (B) on at least one surface side of the foam layer (A), and each layer may be provided in multiple layers. good. For example, it may have a configuration of [foam layer (A)/adhesive layer (B)/foam layer (A)/adhesive layer (B)], or [release liner layer (D)/foam layer (A)/Resin film layer (C)/Adhesive layer (B)/Release liner layer (D)] and [Release liner layer (D)/Adhesive layer (B)/Resin film layer (C) /Foam layer (A)/Resin film layer (C)/Adhesive layer (B)/Release liner layer (D)].

<Method for producing foam adhesive tape for flexible display>
The method for producing the foam adhesive tape for a flexible display is not particularly limited as long as it has the foam layer (A) and the adhesive layer (B), and can be appropriately selected from known methods. However, it is preferable to include a step of forming a foam layer (A) and a step of forming an adhesive layer (B), and if necessary, a step of forming a resin film layer (C) and a release liner layer (D). It includes other layer forming steps such as steps. Alternatively, the foam layer (A) forming step and the pressure-sensitive adhesive layer (B) forming step may be simultaneously formed by a multi-layer simultaneous forming step.

<<Foam layer (A) forming step>>
The foam layer (A) forming step is not particularly limited as long as the foam layer (A) can be formed, and can be appropriately selected according to the purpose. Formation method of layer (A)>>”, and preferred embodiments are also the same.

<<Adhesive layer (B) forming step>>
The pressure-sensitive adhesive layer (B) forming step is not particularly limited as long as the pressure-sensitive adhesive layer (B) can be formed, and can be appropriately selected according to the purpose. Formation method of layer (B)>>”, and preferred embodiments are also the same.

<<Resin film layer forming process>>
The resin film layer (C) forming step is not particularly limited as long as the resin film layer (C) can be formed, and can be appropriately selected according to the purpose. Layer (C) >>” and the same method as the method for forming the resin film layer (C), and preferred embodiments are also the same.

<<Release liner layer (D) forming step>>
The release liner layer (D) forming step is not particularly limited as long as the release liner layer (D) can be formed, and can be appropriately selected according to the purpose. Layer (D) >>” and the same method as the method for forming the release liner layer (D), and preferred embodiments are also the same.

The foamed pressure-sensitive adhesive tape can effectively protect the flexible display device by suppressing deformation of the display element caused by an impact on the display surface and the accompanying defects such as circuit breakage.

(flexible display laminate)
The flexible display laminate of the present invention has at least a flexible display having a light-emitting surface and the flexible display foam adhesive tape of the present invention arranged on the back side of the light-emitting surface, and if necessary, It also has other elements.
The flexible display is not particularly limited as long as it has known elements such as a flexible substrate and a circuit that normally function as a flexible display, and can be appropriately selected according to the purpose.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

(Preparation Example 1-1: Preparation of foam raw material 1)
Resin emulsion b (acrylic copolymer, solid content 45%, trade name “Boncoat ED-85E”, manufactured by DIC Corporation) 80 parts by weight and resin emulsion c (acrylic copolymer, solid content 60%, trade name “Boncoat AC-501", manufactured by DIC Corporation) 20 parts by weight is used as the main agent, and the total amount of the resin emulsion is used as a basis (the total of the solid content and non-solid content is 100 parts by weight), and surfactant 1 (stearin ammonium acid, 30% solids) 3 parts by weight, Surfactant 2 (sodium alkyl sulfuccinate, 35% solids) 3 parts by weight, Surfactant 3 (alkylbetaine, 30% solids) 1 part by weight, and A foam raw material 1 was prepared by mixing 2 parts by weight of a crosslinking agent (hydrophobic HDI isocyanurate (functional group number: 3.5), solid content: 100%).

(Preparation Example 1-2: Preparation of foam raw material 2)
In the preparation of foam raw material 1 of Preparation Example 1-1, the main agent was prepared from 80 parts by weight of resin emulsion b and 20 parts by weight of resin emulsion c to 60 parts by weight of resin emulsion b and resin emulsion d (acrylic copolymer, solid content 60%, trade name "Boncoat S-5", manufactured by DIC Corporation) 40 parts by weight, in the same manner as in Preparation Example 1-1, to prepare foam raw material 2 of Preparation Example 1-2. bottom.

(Preparation Example 1-3: Preparation of foam raw material 3)
In the preparation of foam raw material 1 of Preparation Example 1-1, the main agent was prepared from 80 parts by weight of resin emulsion b and 20 parts by weight of resin emulsion c, resin emulsion a (acrylic copolymer, solid content 55%, trade name "ACOUSTICRYL AV1331” manufactured by Dow Chemical Co.) was changed to 100 parts by weight, in the same manner as in Preparation Example 1-1, to prepare Foam Raw Material 3 of Preparation Example 1-3.

(Preparation Example 1-4: Preparation of foam raw material 4)
In the preparation of foam raw material 1 of Preparation Example 1-1, the main agent was prepared from 80 parts by weight of resin emulsion b and 20 parts by weight of resin emulsion c, to 50 parts by weight of resin emulsion a and resin emulsion e (acrylic copolymer, solid content 60%, trade name "Boncoat R-510-E", manufactured by DIC Corporation) 50 parts by weight of the foam raw material 4 of Preparation Example 1-4 in the same manner as in Preparation Example 1-1 was prepared.

(Preparation Example 1-5: Preparation of foam raw material 5)
In the preparation of foam raw material 1 of Preparation Example 1-1, the main agent was prepared from 80 parts by weight of resin emulsion b and 20 parts by weight of resin emulsion c, resin emulsion f (polyether carbonate-based urethane emulsion, solid content 60%, trade name "Implaneal (registered trademark)" manufactured by Sumika Covestro Urethane Co., Ltd.) was changed to 100 parts by weight, and the foam raw material 5 of Preparation Example 1-5 was prepared in the same manner as in Preparation Example 1-1. prepared.

(Preparation Example 2: Preparation of adhesive b)
97.98 parts by weight of n-butyl acrylate, 2 parts by weight of acrylic acid, 0.02 parts by weight of 4-hydroxybutyl acrylate, 0.2 parts by weight of azobisisobutyronitrile as a polymerization initiator, ethyl acetate An acrylic polymer having a weight average molecular weight of 900,000 was obtained by solution polymerization at 80° C. for 8 hours in the solution.
Based on 100 parts by weight of the acrylic polymer, 5 parts by weight of polymerized rosin ester (trade name "D-135", manufactured by Arakawa Chemical Industries, Ltd.) and disproportionated rosin ester (trade name "KE-100", Arakawa Chemical Industry Co., Ltd.) 20 parts by weight and petroleum resin (trade name “FTR (registered trademark) 6100”, Mitsui Chemicals, Inc.) 25 parts by weight were mixed, and ethyl acetate was added to obtain a solid content of 40% by weight. A pressure-sensitive adhesive solution adjusted to
The pressure-sensitive adhesive solution and 2.0 parts by weight of an isocyanate cross-linking agent (trade name “NC40” manufactured by DIC Corporation) were mixed and stirred to obtain pressure-sensitive adhesive b.

(Example 1: Production of foam adhesive tape 1)
<Preparation of adhesive layer (B)>
The pressure-sensitive adhesive b of Preparation Example 2 was applied to a release liner (grade “J0”, release load 50 mN/50 mm width, manufactured by Nippa Co., Ltd.) having a silicone-based release treatment surface on the surface of a polyester film having a thickness of 50 μm using a roll coater. and dried at 100° C. for 1 minute to obtain a laminate a consisting of a 2 μm-thick pressure-sensitive adhesive layer (B) and a release liner layer (D).

-Measurement of gel fraction of adhesive layer (B)-
The adhesive b was applied to the release-treated surface of the release liner so that the thickness after drying was 50 μm, dried at 100° C. for 3 minutes, and then kept at 40° C. for 2 days. A pressure-sensitive adhesive layer (B) was formed by aging. A test piece was prepared by cutting the pressure-sensitive adhesive layer (B) into a square having a length of 50 mm and a width of 50 mm.
After measuring the weight (G1) of the test piece, the test piece was immersed in toluene for 24 hours in an environment of 23°C. After the immersion, the mixture of the test piece and toluene was filtered using a 300-mesh wire mesh to extract components insoluble in toluene. The weight (G2) of the insoluble component dried in an environment of 110° C. for 1 hour was measured.
The gel fraction of the adhesive layer (B) calculated by the following formula (3) was 40% by weight.
Gel fraction (% by weight)=(G2/G1)×100 Formula (3)

-Measurement of dynamic viscoelasticity of adhesive layer (B)-
The adhesive b was applied to the release-treated surface of the release liner so that the thickness after drying was 50 μm, dried at 100° C. for 3 minutes, and then dried at 40° C. for 2 minutes. A pressure-sensitive adhesive layer (B) was formed by aging for days. A test piece was prepared by stacking the adhesive layers (B) until the total thickness was 2 mm.
Next, using a viscoelasticity tester (trade name “Ares 2KSTD”, manufactured by Rheometrics Co., Ltd.), the test piece was sandwiched between parallel disk-shaped measurement units with a diameter of 7.9 mm, and the frequency was 1 Hz and the heating time was 1 ° C./ Storage modulus (G') and loss modulus (G'') were measured from -50°C to 150°C under conditions of 1 minute.
The peak temperature of the loss tangent tan δ of the pressure-sensitive adhesive layer (B) calculated by the following formula (2) was 0°C.
Loss tangent tan δ=G″/G′ Equation (2)
to obtain an adhesive layer (B) having a thickness of 2 μm.

<Production of laminate b>
A 2 μm polyester film (trade name “K100-2.0W”, manufactured by Mitsubishi Plastics Co., Ltd.) as a resin film layer (C) is overlaid on the adhesive layer (B) side of the laminate a, and is laminated using a laminator. It was attached at a linear pressure of 3 N/mm to obtain a laminate b. This laminate b was cured at 40° C. for 2 days.

<Production of foam layer (A) 1>
As shown in FIG. 3, the foam raw material 1 prepared in Preparation Example 1-1 was charged into a chamber 9 provided in an Oaks mixer. At the same time, nitrogen gas was injected so that the foam layer had a density of 700 kg/m ³ . Next, in the chamber 9 , the foam raw material 1 and nitrogen gas were stirred to prepare a foamed gas-liquid mixture 13 .
On the resin film layer (C) in the laminate b12 consisting of the release liner layer (D), the pressure-sensitive adhesive layer (B), and the resin film layer (C) delivered at a speed of 5 m/min Then, the gas-liquid mixture 13 is supplied, and the surface of the drooling gas-liquid mixture is peeled from the upper side (the side opposite to the side in contact with the resin film layer (C)) at the same speed as the laminate b12. Paper 14 (trade name “Sumirease SL-70S (U2)”, manufactured by Sumika Kakoshi Co., Ltd.) is supplied, and the thickness of the gas-liquid mixture 13 is adjusted by a roll coater 10 to 100 μm. An uncured layer of liquid mixture 13 was formed.
A laminate c comprising the release liner layer (D), the adhesive layer (B), the resin film layer (C), the uncured layer, and the release paper was heated to 150°C by a far infrared heater. and heated for 1 minute to obtain a foam layer A1.
Next, the release paper 14 is peeled off from the laminate c, and the release liner layer (D), the adhesive layer (B), the resin film layer (C), and the foam layer (A) 1 are separated. A joined foam adhesive tape 1 was obtained.

(Example 2: Production of foam adhesive tape 2)
A foam pressure-sensitive adhesive tape was produced in the same manner as in Example 1, except that <Preparation of foam layer (A) 1> in Example 1 was changed to <Preparation of foam layer (A) 2> below. got 2.

<Production of foam layer (A) 2>
In <Preparation of foam layer (A) 1> of Example 1, foam layer (A) 2 was obtained by changing foam raw material 1 to foam raw material 2 prepared in Preparation Example 1-2. Except for the above, the release liner layer (D), the pressure-sensitive adhesive layer (B), and the resin film layer (C) are formed in the same manner as in <Preparation of the foam layer (A) 1> of Example 1. , to obtain a foam adhesive tape 2 to which the foam layer (A) 2 was bonded.

(Comparative Example 1: Production of Foam Adhesive Tape 3)
Foam adhesive tape was produced in the same manner as in Example 1, except that <Preparation of foam layer (A) 1> in Example 1 was changed to <Preparation of foam layer (A) 3> below. got 3.

<Production of foam layer (A) 3>
In <Production of foam layer (A) 1> of Example 1, foam layer (A) 3 was obtained by changing foam raw material 1 to foam raw material 3 prepared in Preparation Example 1-3. Except for the above, the release liner layer (D), the pressure-sensitive adhesive layer (B), and the resin film layer (C) are formed in the same manner as in <Preparation of the foam layer (A) 1> of Example 1. , to obtain a foam adhesive tape 3 to which the foam layer (A) 3 was bonded.

(Comparative Example 2: Production of Foam Adhesive Tape 4)
Foam adhesive tape was produced in the same manner as in Example 1, except that <Preparation of foam layer (A) 1> in Example 1 was changed to <Preparation of foam layer (A) 4> below. Got 4.

<Production of foam layer (A) 4>
In <Production of foam layer (A) 1> of Example 1, foam layer (A) 4 was obtained by changing foam raw material 1 to foam raw material 4 prepared in Preparation Example 1-4. Except for the above, the release liner layer (D), the pressure-sensitive adhesive layer (B), and the resin film layer (C) are formed in the same manner as in <Preparation of the foam layer (A) 1> of Example 1. , to obtain a foam adhesive tape 4 to which the foam layer (A) 4 was bonded.

(Comparative Example 3: Production of Foam Adhesive Tape 5)
Foam pressure-sensitive adhesive tape was produced in the same manner as in Example 1, except that <Preparation of foam layer (A) 1> in Example 1 was changed to <Preparation of foam layer (A) 5> below. Got 5.

<Production of foam layer (A) 5>
In <Preparation of foam layer (A) 1> of Example 1, the foam raw material 1 was changed to the foam raw material 5 prepared in Preparation Example 1-5, and the nitrogen gas injection conditions were adjusted to the density of the foam layer. Since nitrogen gas was injected so that the density of the foam layer was 700 kg/m ³ , the foam layer (A) 5 was obtained by injecting nitrogen gas so that the density of the foam layer was 400 kg/m ³ . Except for the above, the release liner layer (D), the pressure-sensitive adhesive layer (B), and the resin film layer (C) are formed in the same manner as in <Preparation of the foam layer (A) 1> of Example 1. , to obtain a foam adhesive tape 5 to which the foam layer (A) 5 is bonded.

The following physical properties of the foam adhesive tapes 1 to 5 and foam layers (A) 1 to (A) 5 of Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the methods shown below. .

-Measurement of thickness of each layer-
After removing the release liner layer (D) from each of the foam adhesive tapes 1 to 5 and immersing them in liquid nitrogen for 1 minute, each foam adhesive tape was folded in the liquid nitrogen using tweezers along the width direction. It was split by hand to prepare a slice for observation of the split surface in the thickness direction of each of the foamed pressure-sensitive adhesive tapes. After the section was returned to room temperature in a desiccator, it was fixed on a sample stage so that the electron beam was incident perpendicularly to the fractured surface, and an electron microscope (Miniscope (registered trademark) TM3030Plus, manufactured by Hitachi High Technology Co., Ltd.) was used. was used to observe the fractured surface. Based on the scale of the electron microscope, the thickness of each layer of foam adhesive tapes 1 to 5 was measured at 10 points, and the arithmetic average value was taken as the thickness of each layer. The results are shown in Table 1 below.

- Measurement of density of foam layer (A) -
The densities of the foam layers (A) 1 to (A) 5 in the foam adhesive tapes 1 to 5 were measured according to JIS K 7222 and calculated from the weight per unit volume. The results are shown in Table 1 below.

-Measurement of loss tangent Tanδ and glass transition temperature Tg of foam layer (A)-
The dynamic viscoelasticity of the foam layers (A)1 to (A)5 in the foam adhesive tapes 1 to 5 was measured according to JIS K7198. Specifically, using a dynamic viscoelasticity device (model “MCR302”, manufactured by Anton Paar), the temperature was raised from −80° C. to 150° C. at a rate of 5° C./1 minute, and the measurement was performed under the conditions of a frequency of 1 Hz. Storage modulus and loss modulus at 23°C were measured. As in the above formula (2), the value obtained by dividing the loss elastic modulus by the storage elastic modulus was defined as the loss tangent tan δ of the foam layer (A). The temperature at which the tan δ peak value was taken as the glass transition temperature Tg of the foam layer (A). The results are shown in Table 1 below.

-Measurement of 25% compressive strength of foam adhesive tape-
The 25% compressive strength of foam adhesive tapes 1 to 5 was measured according to JIS K 6767. Specifically, the release liner layer (D) was removed from each foam pressure-sensitive adhesive tape cut into 25 mm squares (length 25 mm, width 25 mm), and the tapes were laminated to a thickness of about 10 mm to form a laminate. The laminate is sandwiched between two stainless steel plates having a larger area than the laminate, and the laminate is tested at a speed of 10 mm/min at 23° C. using a dual column desktop universal testing machine Model 5966 (manufactured by Instron). was compressed to about 7.5 mm (75% of the original thickness). The results are shown in Table 1 below and FIG.

-Measurement of point impact absorption rate of foam adhesive tape-
The point impact absorption rate of foam pressure-sensitive adhesive tapes 1 to 5 was measured by the following point impact absorption test using the falling ball tester shown in FIG. Specifically, the release liner layer (D) was removed from each adhesive foam tape, and the adhesive layer (B) 4 side was attached to the SUS sample stage 5 placed on the load cell 6 . Next, a steel ball 2 weighing 8.3 g and having a diameter of 12.5 mm was held on the electromagnet 1, and the steel ball 2 was placed on the foam layer (A) 3 from a height of 20 cm from the surface of the foam layer (A) 3. It was allowed to fall freely on a surface and the impact load was measured. The point impact absorption rate of the foam pressure-sensitive adhesive tape was calculated by the following formula (1) from the value of the impact load. The results are shown in Table 1 below and FIG. In the graph of FIG. 4, "●" indicates an example, and "▲" indicates a comparative example.
Point impact absorption rate (%)={(f _p0 −f _p1 )/f _p0 }×100 Equation (1)
In the above formula (1), f _p1 is the pressure when the foam adhesive tape is placed on a load cell and a steel ball with a diameter of 12.5 mm is dropped on the foam layer (A) surface of the foam adhesive tape. is the impact load,
f _p0 is the impact load when the steel ball is dropped without placing the foam adhesive tape on the load cell.

(Test Example 1: Evaluation of falling ball on polyimide substrate)
As shown in FIG. 2, on one side of a 125 μm-thick polyimide film substrate (trade name “Kapton (registered trademark) 500H”, manufactured by DuPont-Toray Co., Ltd.), a 300 nm-thick, 100 μm wiring width, and 400 μm wiring spacing was applied to one side of the substrate 7 . A polyimide substrate provided with copper wiring 8 in a grid pattern was produced.
The release liner layer (D) was removed from the foamed adhesive tapes 1 to 5 of Examples 1 and 2 and Comparative Examples 1 to 3, respectively, and wiring was provided between the adhesive layer (B) surface and the polyimide substrate. A polyimide substrate laminate was produced by bonding the two surfaces together.
A 5 cm square (length 5 cm, width 5 cm) cut from the polyimide substrate laminate was placed on a tempered glass plate with a thickness of 10 mm with the copper wiring side facing up, and the point impact absorption rate was measured. Similarly, a steel ball weighing 8.3 g and having a diameter of 12.5 mm was allowed to freely fall from a height of 20 cm from the copper wiring surface of the polyimide substrate onto the surface of the copper wiring side.
Using a white light interferometer (VertScan (registered trademark) 2.0 R3300G Lite, manufactured by Ryoka System Co., Ltd.), the dents produced on the polyimide substrate laminate by the falling ball were observed from directly above, and the dents were centered. The three-dimensional height was measured. Next, using analysis software (VS-Viewer, manufactured by Ryoka System Co., Ltd.), the difference between the height of the dent center and the height of an arbitrary point on a circle with a radius of 3 mm from the dent center is calculated. The depth of the dent on the polyimide substrate was used. This falling ball evaluation was performed on five polyimide substrate laminates, and the arithmetic mean values calculated from the depths of dents on the polyimide substrate laminates in the five polyimide substrate laminates are shown in Table 1 below and FIG.

In addition, the copper wiring side of the polyimide substrate laminate after the falling ball was observed with an optical microscope, and the presence or absence of breakage of the copper wiring was visually evaluated.
[Disconnection evaluation]
○: There was no breakage of the copper wiring on the polyimide substrate ×: There was one or more breaks in the copper wiring on the polyimide substrate

(Test Example 2: Evaluation of falling ball to glass substrate)
In the same manner as in Test Example 1, copper wiring 8 was provided in a grid pattern with a thickness of 300 nm, a wiring width of 100 μm, and a wiring interval of 400 μm on one side of a 1 mm thick, 50 mm square (50 mm long, 50 mm wide) glass substrate. A glass substrate was produced.
The release liner layer (D) was removed from the foamed adhesive tapes 1 to 5 of Examples 1 and 2 and Comparative Examples 1 to 3, respectively, and wiring was provided between the adhesive layer (B) surface and the glass substrate. A glass substrate laminate was produced by bonding the non-bonded surfaces together.
The glass substrate laminate was placed on a tempered glass plate with a thickness of 10 mm with the copper wiring side facing upward, and a steel ball weighing 8.3 g (diameter 12 .5 mm) was freely dropped from a height of 20 cm (potential energy of 16.3 mJ) from the copper wiring surface of the glass substrate to the copper wiring side surface.

The cracks of the glass substrates in the glass substrate laminate after the falling ball were visually confirmed, and the results of evaluation based on the following evaluation criteria are shown in Table 1 below.
[Crack evaluation]
○: There was no crack in the glass substrate ×: There was a crack in the glass substrate

In addition, the copper wiring side of the glass substrate laminate after the falling ball was observed with an optical microscope to visually evaluate whether or not the copper wiring was broken.
[Disconnection evaluation]
○: There was no breakage of the copper wiring on the glass substrate ×: There was one or more breaks in the copper wiring on the glass substrate

実施例１及び２の発泡体粘着テープをフレキシブルな基板に使用した場合、該発泡体粘

When the foam adhesive tapes of Examples 1 and 2 were used for flexible substrates, the foam adhesive

The 25% compressive strength of the adhesive tape is 100 kPa or more, and the point impact absorption rate of the foam adhesive tape is 35% or more, so that even if a point impact with a momentary high impact force is applied. However, it was found that the flexible substrate was not deformed and the accompanying wire breakage occurred even when the substrate was deformed, and the protection performance against impact was excellent.
On the other hand, when the foamed pressure-sensitive adhesive tapes of Comparative Examples 1 to 3 were used on a flexible substrate, deformation of the flexible substrate and accompanying disconnection occurred when a point impact with a momentary high impact force was applied. and the protection performance against impact was insufficient.
However, when the foamed pressure-sensitive adhesive tapes of Examples 1 and 2 and Comparative Examples 1-3 were used on a glass substrate, even if a point impact with a momentary high impact force was applied, both There was no cracking of the glass substrate or disconnection of the copper wiring, and it had sufficient protective performance against impact.

While rigid displays use a hard glass substrate and cover glass, flexible displays have a structure in which light-emitting elements (circuits, light-emitting cells) are formed on a highly flexible substrate such as a polyimide substrate, and covered with a cover film. becomes.
From the results of Test Examples 1 and 2 above, when an impact is applied to the display side of the display, the impact force is dispersed by the glass in the rigid display and a weak impact force is applied to the entire display element, whereas the impact is dispersed in the flexible display. It was found that pinpoint high pressure was applied because the pressure was not applied.
Therefore, even if the impact does not pose a problem for rigid displays, the deformation of the substrate causes disconnection of the circuit in flexible displays. It has been found that having a certain point impact absorption rate and a certain compressive strength is important from a display protection point of view.

Embodiments of the present invention include, for example, the following.
<1> A foam adhesive tape for use in a flexible display having an adhesive layer (B) on at least one side of the foam layer (A),
The 25% compression strength of the foam adhesive tape is 100 kPa or more,
The foam pressure-sensitive adhesive tape for a flexible display is characterized in that the foam pressure-sensitive adhesive tape has a point impact absorption rate calculated by the following formula (1) of 35% or more.
Point impact absorption rate (%)={(f _p0 −f _p1 )/f _p0 }×100 Equation (1)
In the above formula (1), f _p1 is the pressure when the foam adhesive tape is placed on a load cell and a steel ball with a diameter of 12.5 mm is dropped on the foam layer (A) surface of the foam adhesive tape. is the impact load,
f _p0 is the impact load when the steel ball is dropped without placing the foam adhesive tape on the load cell.
<2> The foam adhesive tape for a flexible display according to <1>, further comprising a resin film layer (C) between the foam layer (A) and the adhesive layer (B).
<3> The foam pressure-sensitive adhesive tape for a flexible display according to any one of <1> to <2>, further comprising a release liner layer (D).
<4> A flexible display having a light-emitting surface, and the flexible display foam adhesive tape according to any one of <1> to <3> arranged on the back side of the light-emitting surface It is a flexible display laminate that

INDUSTRIAL APPLICABILITY According to the present invention, a flexible display foam adhesive that can effectively protect a flexible display device by suppressing the deformation of the display element caused by the impact on the display surface and the accompanying defects such as circuit breakage. A tape and a flexible display laminate having the foam adhesive tape for a flexible display can be provided.

1 electromagnet 2 steel ball 3 foam layer (A)
4 adhesive layer (B)
5 SUS sample stage 6 load cell 7 substrate 8 copper wiring 9 chamber 10 roll coater 11 heating furnace 12 laminate b of resin film (C), adhesive layer (B) and release liner layer (D)
13 gas-liquid mixture 14 release paper

Claims (5)

A foam adhesive tape having an adhesive layer (B) on at least one surface side of a foam layer (A) and arranged on the back side of the light emitting surface of a flexible display having a light emitting surface,
The foam layer (A) is formed by foaming an acrylic emulsion,
The foam layer (A) has a thickness of 5 μm or more and 400 μm or less,
The foam layer (A) has a density of 0.40 g/cm ³ or more and 1.00 g/cm ³ or less,
The foam layer (A) has a glass transition temperature of 5° C. or higher and 40° C. or lower,
The pressure-sensitive adhesive layer (B) is made of a composition containing an acrylic polymer, a rosin ester-based resin, and an isocyanate-based cross-linking agent,
The 25% compression strength of the foam adhesive tape is 100 kPa or more,
A foam pressure-sensitive adhesive tape for a flexible display, wherein the foam pressure-sensitive adhesive tape has a point impact absorption rate calculated by the following formula (1) of 35% or more and 44% or less .
Point impact absorption rate (%)={(f _p0 −f _p1 )/f _p0 }×100 Equation (1)
In the above formula (1), f _p1 is obtained by placing the foam adhesive tape on a load cell and placing it on the foam layer (A) surface of the foam adhesive tape from a height of 20 cm with a weight of 8.3 g and a diameter of 12 is the impact load when a 5mm steel ball is dropped,
f _p0 is the impact load when the steel ball is dropped without placing the foam adhesive tape on the load cell. 2. The foam adhesive tape for a flexible display according to claim 1, wherein the adhesive layer (B) has a gel fraction of 10% by weight to 60% by weight. 3. The foam pressure-sensitive adhesive tape for a flexible display according to claim 1, further comprising a resin film layer (C) between the foam layer (A) and the pressure-sensitive adhesive layer (B). 4. The foam pressure-sensitive adhesive tape for a flexible display according to any one of claims 1 to 3, further comprising a release liner layer (D). A flexible display laminate comprising: a flexible display having a light emitting surface; and the foam adhesive tape for a flexible display according to any one of claims 1 to 4 arranged on the back side of the light emitting surface.

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