JP2022071845A - Adhesive tape - Google Patents

Abstract

To provide an adhesive tape having excellent repeated impact resistance.SOLUTION: An adhesive tape has an adhesive layer on at least one side of a foam substrate. The foam substrate has at least one peak in each of the 50-100°C range and the -100°C-10°C range in DSC measurement at a temperature increase rate of 10°C/min, in the temperature range of -100°C to 200°C, and at one cycle number.SELECTED DRAWING: None

Description

The present invention relates to an adhesive tape.

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

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

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

As the adhesive tape having excellent flexibility and impact resistance, an adhesive tape using a foam base material obtained by foaming a polyolefin resin is known. On the other hand, in recent years, portable electronic devices, in-vehicle electronic devices, and the like are required to withstand repeated impacts due to harshness and diversification of usage conditions. However, with the conventional adhesive tape, even if it is not peeled off by a single impact, it may be peeled off or the adherend may be damaged when a continuous drop impact is applied.

It is an object of the present invention to provide an adhesive tape having excellent repeated impact resistance.

The present invention is an adhesive tape having an adhesive layer on at least one surface of a foam substrate.
The foam substrate has a temperature rise rate of 10 ° C./min, a temperature range of -100 ° C. to 200 ° C., and a region of 50 to 100 ° C. and -100 ° C. to 10 when DSC measurement is performed with one cycle count. An adhesive tape characterized by having at least one peak in each of the ° C. regions.
The present invention will be described in detail below.

The adhesive tape of the present invention has an adhesive layer on at least one surface of the foam substrate.
By using the foam base material, the adhesive tape of the present invention can exhibit excellent flexibility and impact resistance. The foam base material may have an open cell structure or a closed cell structure, but is preferably a closed cell structure. The foam base material may have a single-layer structure or a multi-layer structure.

The foam substrate has a temperature range of 50 to 100 ° C. when DSC (differential scanning calorimetry) measurement is performed under the conditions of a temperature rise rate of 10 ° C./min, a temperature range of -100 ° C. to 200 ° C., and one cycle cycle. And each has at least one peak in the region of -100 ° C to 10 ° C.
When the foam has at least one peak in the region of 50 to 100 ° C. and the region of 10 ° C. or lower when DSC measurement is performed, the foam has a rigid structure (hereinafter, also referred to as a hard portion). ) And a flexible structure (hereinafter, also referred to as a soft moiety) to construct a phase-separated structure by a copolymer. The phase-separated structure is a structure in which the aggregated hard parts are scattered like islands in the sea of the soft parts due to the aggregation of the hard parts (sea island structure). In such a phase-separated structure, it is considered that rubber elasticity is imparted to the copolymer by the islands formed by the hard portions as pseudo-crosslinking points, and high repeated impact resistance can be imparted to the obtained adhesive tape. .. Since the repeated impact resistance is further improved, the foam base material has a temperature range of -100 ° C to 200 ° C and 50 to 100 ° C when DSC (differential scanning calorimetry) measurement is performed under the condition of one cycle. It is preferable to have at least one peak in each of the region of -100 ° C to 0 ° C. The peak region can be adjusted by the type of monomer used for the hard site and the soft site.
For the above DSC measurement, a differential scanning calorimeter (for example, trade name "220C" manufactured by Seiko Instruments Inc.) is used, and the temperature rise rate in the atmosphere is 10 ° C./min and the temperature range is -100 ° C. to 100 mg of the foam. Perform under the conditions of 200 ° C. and one cycle.

The foam base material preferably has an island structure having a maximum major axis of 60 nm or less.
The island structure is an island-like structure formed by agglomeration of the above-mentioned hard parts. Since the maximum major axis of the island structure is small, that is, the sea island structure is finely formed, the impact resistance can be further improved. It is not clear why the finely formed sea-island structure improves the impact resistance repeatedly, but the finer sea-island structure increases the interface area between the island structure and the sea structure, and disperses the impact more. It is thought that it can be absorbed. The maximum major axis can be calculated based on a TEM (transmission electron microscope) observation and the TEM image. More specifically, first, TEM observation is performed at a magnification of 5000 times, and an observation image for a region of 4.3 μm × 4.3 μm is acquired. Next, the acquired image is automatically binarized using image analysis software (for example, Aviso, ver2019.4, Thermo Fisher Scientific Co., Ltd., etc.). From the binarized image, the major axis of each island structure (dark part) is measured, and the arithmetic mean value of these is taken as the maximum major axis. For details of the above automatic binarization method, see the known literature (“Automatic threshold selection method based on discrimination and minimum squared criteria”, Nobuyuki Otsu, IEICE Transactions D, Vol. J63-D, No. .4, pp.349-356).

The maximum major axis is more preferably 55 nm or less, further preferably 50 nm or less, further preferably 40 nm or less, and particularly preferably 30 nm or less. In particular, it is preferable that the maximum major axis is so small that the sea-island structure cannot be visually confirmed when the TEM observation is performed. By constructing a sea-island structure that is so fine that it cannot be confirmed by the above TEM observation, the impact resistance can be further improved. Even if the sea-island structure cannot be confirmed with the naked eye from the TEM image, at least one peak is formed in the region of 50 to 100 ° C and the region of -100 ° C to 10 ° C when the DSC measurement is performed. If it has, it can be confirmed that a fine sea-island structure is constructed because it has a phase-separated structure. The lower limit of the maximum major axis is not particularly limited, and the smaller the peak in the region when the DSC measurement is performed, the smaller the lower limit, and the maximum major axis may be, for example, 0.5 nm or more. preferable. The maximum major axis can be adjusted by the content of the hard moiety in the copolymer.

Here, the sea island structure will be described. A photograph of TEM observation of the foam substrate of the present invention is shown in FIG. As shown in FIGS. 1 (a) and 1 (b), in the copolymer having a hard part and a soft part, since the hard part and the soft part are difficult to be compatible with each other, the sea of the soft part (the bright part in the photograph). ) Has a non-uniform phase-separated structure (sea island structure) in which islands of hard parts (black parts in the photograph) are scattered. In FIG. 1A, it can be confirmed that the major axis of each island structure is about several nm. On the other hand, in FIG. 1 (b), the major axis of the island structure extends to several tens of nm.

The material constituting the foam substrate is not particularly limited as long as it is a copolymer having a peak in the region when the DSC measurement is performed, that is, having a hard portion and a soft moiety, and for example, the block co-weight. Examples thereof include coalescing, graft polymers, and random copolymers. Among them, block copolymers are preferable because they can impart high flexibility and impact resistance to the obtained adhesive tape and are also excellent in repeated impact resistance. Examples of the block copolymer include a diblock copolymer, a triblock copolymer, a graft copolymer and the like. Among them, from the viewpoint of phase separation formation, the copolymer is preferably a diblock copolymer or a triblock copolymer, and a bird having a structure in which a block composed of the soft moiety is sandwiched between blocks composed of the hard moiety. Block copolymers are more preferred.

The hard portion is not particularly limited as long as it has a rigid structure. When the copolymer is a block copolymer, the hard moiety may be a polymer of a monomer having a single rigid structure, or a copolymer composed of a plurality of monomers including a monomer having a rigid structure. It may be a polymer. Examples of the monomer having a rigid structure include a vinyl aromatic compound, a compound having a cyclic structure, and a compound having a short side chain substituent. Above all, it is more preferable that the copolymer has a structure derived from a vinyl aromatic compound monomer as the hard moiety because the impact resistance is further improved. Examples of the vinyl aromatic compound monomer include styrene, alphamethylstyrene, paramethylstyrene, chlorostyrene and the like. Of these, styrene is preferable because it further improves impact resistance. In the present specification, the structure derived from the vinyl aromatic compound monomer refers to the structure represented by the following general formulas (1) and (2).

式（１）、（２）中Ｒ^１は芳香環を有する置換基を表す。置換基Ｒ^１としては、フェニル基、メチルフェニル基、クロロフェニル基等が挙げられる。

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

When the copolymer has a structure derived from the vinyl aromatic compound monomer, the content of the structure derived from the vinyl aromatic compound monomer in the copolymer is 0.5% by weight or more and 30% by weight or less. Is preferable.
When the content of the structure derived from the vinyl aromatic compound monomer is within the above range, a sea-island type phase-separated structure can be formed, and the flexibility, impact resistance and repeated impact resistance can be further improved. Can be done. A more preferable lower limit of the content of the structure derived from the vinyl aromatic compound monomer is 0.5% by weight, a further preferable lower limit is 1% by weight, a particularly preferable lower limit is 2% by weight, and a particularly preferable lower limit is 2.5% by weight. A more preferable upper limit is 19% by weight, a further preferable upper limit is 16% by weight, a particularly preferable upper limit is 8% by weight, and a particularly preferable upper limit is 5% by weight.

The hard moiety preferably has a structure derived from a monomer having a crosslinkable functional group.
When the hard moiety has a crosslinkable functional group, the rubber elasticity of the copolymer is increased by the crosslinking, so that the flexibility and impact resistance can be further improved. The crosslinkable functional group may or may not be crosslinked, and even if the structure remains uncrosslinked, the cohesive force of the hard site is improved by the interaction between the functional groups and the flexibility is improved. And impact resistance is improved, but it is more preferable that it is crosslinked. In the present specification, the structure derived from the monomer having a crosslinkable functional group refers to the structure represented by the following general formulas (3) and (4).

ここで、Ｒ^２は少なくとも１つの官能基を含む置換基を表す。
官能基としては、例えばカルボキシル基、水酸基、エポキシ基、二重結合、三重結合、アミノ基、アミド基、ニトリル基等が挙げられる。なお置換基Ｒ^２は、その構成要素としてアルキル基やエーテル基、カルボニル基、エステル基、カーボネート基、アミド基、ウレタン基などを含んでいてもよい。

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

The monomer having a crosslinkable functional group is not particularly limited, and for example, a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an epoxy group-containing monomer, a double bond-containing monomer, a triple bond-containing monomer, an amino group-containing monomer, and an amide group-containing monomer. , A nitrile group-containing monomer and the like. Among them, since the flexibility and impact resistance are further improved, it is selected from the group consisting of a hydroxyl group-containing monomer, a carboxyl group-containing monomer, an epoxy group-containing monomer, an amide group-containing monomer, a double bond-containing monomer and a triple bond-containing monomer. It is preferable that it is at least one kind. Examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate. Examples of the carboxyl group-containing monomer include (meth) acrylic acid. Examples of the epoxy group-containing monomer include glycidyl (meth) acrylate and the like. Examples of the amide group-containing monomer include (meth) acrylamide and the like. Examples of the double bond-containing monomer include allyl (meth) acrylate and hexanediol di (meth) acrylate. Examples of the triple bond-containing monomer include propargyl (meth) acrylate and the like. Among these, a carboxyl group-containing monomer and a hydroxyl group-containing monomer are preferable because the adhesive tape can impart excellent flexibility and impact resistance, and a carboxyl group-containing (meth) acrylic acid-based monomer and a hydroxyl group-containing meta) acrylic acid are preferable. Acrylic acid, 4-hydroxybutyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate are more preferable.

When the hard moiety is a copolymer of the monomer having the rigid structure and the monomer having the crosslinkable functional group, the hard moiety has a structure derived from the monomer having the crosslinkable functional group by 0.1 weight. It is preferably contained in an amount of% or more and 30% by weight or less.
When the content of the structure derived from the monomer having the crosslinkable functional group in the hard moiety is in the above range, the flexibility and the impact resistance can be further improved. A more preferable lower limit of the content of the structure derived from the monomer having a crosslinkable functional group is 0.5% by weight, a further preferable lower limit is 1% by weight, a more preferable upper limit is 25% by weight, and a further preferable upper limit is 20% by weight. be.

The soft moiety constituting the copolymer is not particularly limited as long as it has flexibility to exhibit rubber elasticity, but it is preferable to have a structure derived from a (meth) acrylic monomer.
Since the soft part is composed of a (meth) acrylic monomer, heat resistance can be imparted to the obtained adhesive tape, and the adhesive tape can be deformed or peeled even when exposed to high temperature for a long period of time. It can be suppressed. The (meth) acrylic monomer may be a single monomer, or a plurality of monomers may be used. Further, a monomer other than the (meth) acrylic monomer may be used as long as the effect of the present invention is not lost. In the present specification, the structure derived from the (meth) acrylic monomer refers to the structure represented by the following general formulas (5) and (6).

ここでＲ^３は側鎖を表す。側鎖Ｒ^３としては、メチル基、エチル基、プロピル基、ブチル基、ペンチル基、ヘキシル基、ヘプチル基、オクチル基、２－エチルへキシル基、ノニル基、デシル基、ドデシル基、ラウリル基、イソステアリル基等が挙げられる。

Here, R ³ represents a side chain. The side chain R ³ includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, a dodecyl group and a lauryl group. Examples thereof include an isostearyl group.

Examples of the (meth) acrylic monomer used as a raw material for the soft portion include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, and hexyl (meth). Meta) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, Examples thereof include isostearyl (meth) acrylate. Of these, methyl acrylate, ethyl acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate are preferable because they can easily achieve both heat resistance and flexibility, and methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethyl. Hexyl acrylate is more preferred.

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

As the (meth) acrylic monomer used as a raw material for the soft portion, it is preferable to use a (meth) acrylic monomer having 2 or less side chain carbon atoms. When a (meth) acrylic monomer having 2 or less carbon atoms in the side chain is used, the entanglement between the obtained polymer chains increases and the cohesive force is improved, so that the heat resistance and impact resistance can be further improved. can. Examples of the (meth) acrylic monomer having 2 or less side chain carbon atoms include methyl (meth) acrylate and ethyl (meth) acrylate, and methyl acrylate and ethyl acrylate are particularly preferable.

The preferable lower limit of the content of the (meth) acrylic monomer having 2 or less side chain carbon atoms in the soft moiety is 5% by weight. By including this lower limit amount, the above-mentioned cohesive force improving effect is likely to be exhibited. A more preferable lower limit is 10% by weight, a further preferable lower limit is 20% by weight, a particularly preferable lower limit is 25% by weight, and a particularly preferable lower limit is 30% by weight. The preferable upper limit of the content of the (meth) acrylic monomer having 2 or less side chain carbon atoms in the soft moiety is 90% by weight. When it is not more than this upper limit, the cohesive force does not become too high, and the flexibility as an adhesive tape can be further enhanced. A more preferred upper limit is 85%, a more preferred upper limit is 80% by weight, a particularly preferred upper limit is 75% by weight, and a particularly preferred upper limit is 70% by weight.

The copolymer preferably contains the hard portion in an amount of 1% by weight or more and 40% by weight or less. By setting the content of the hard portion in the above range, it is possible to form a foam base material having excellent flexibility, impact resistance and repeated impact resistance. From the viewpoint of further enhancing flexibility, impact resistance and heat resistance, the more preferable lower limit of the content of the hard portion is 2% by weight, the more preferable lower limit is 2.5% by weight, and the particularly preferable lower limit is 3% by weight, more preferable. The upper limit is 30% by weight, the more preferable upper limit is 26% by weight, the more preferable upper limit is 20% by weight, the further preferable upper limit is 17% by weight, the particularly preferable upper limit is 8% by weight, and the particularly preferable upper limit is 5% by weight.

The polymerization average molecular weight of the copolymer is preferably 50,000 to 800,000.
When the weight average molecular weight of the copolymer is in the above range, flexibility, impact resistance and heat resistance can be further enhanced. The more preferable lower limit of the polymerization average molecular weight of the copolymer is 75,000, and the more preferable upper limit is 600,000. The weight average molecular weight can be measured by, for example, the GPC method, and a sample is used using "2690 Separations Model" manufactured by Water Co., Ltd. as a measuring device and "GPC KF-806L" manufactured by Showa Denko Co., Ltd. as a solvent and ethyl acetate as a column. It can be measured under the conditions of a flow rate of 1 mL / min and a column temperature of 40 ° C.

The method for producing the above-mentioned copolymer is not particularly limited. For example, when the copolymer is a block copolymer, in order to obtain the block copolymer, the raw material monomers of the hard moiety and the soft moiety are subjected to radical reaction in the presence of a polymerization initiator, respectively, to obtain the hard moiety. And after obtaining the soft part, both may be reacted. Alternatively, after obtaining the hard moiety by the above method, the raw material monomer of the soft moiety may be continuously added and copolymerized. When the above-mentioned copolymer is a random copolymer, a solution obtained by mixing a raw material monomer of a hard moiety and a soft moiety and, if necessary, another monomer may be radically reacted in the presence of a polymerization initiator. .. As the method for causing the radical reaction, that is, the polymerization method, a conventionally known method is used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.

The foam base material contains additives such as antistatic agents, mold release agents, antioxidants, weathering agents, and crystal nucleating agents, and resin modifiers such as polyolefins, polyesters, polyamides, and elastomers. May be good.

The foam substrate preferably has an apparent density of 0.3 g / cm ³ or more and 0.75 g / cm ³ or less.
By setting the apparent density of the foam base material within the above range, it is possible to obtain an adhesive tape having higher flexibility and impact resistance while maintaining strength. From the viewpoint of further enhancing the strength, flexibility and impact resistance of the adhesive tape, the more preferable lower limit of the foam base material is 0.33 g / cm ³ , the more preferable upper limit is 0.73 g / cm ³ , and the more preferable lower limit is 0.73 g / cm 3. Is 0.35 g / cm ³ , and a more preferable upper limit is 0.71 g / cm ³ .
The apparent density can be measured using an electronic hydrometer (for example, "ED120T" manufactured by Mirage Co., Ltd.) in accordance with JIS K 7222.

The foam substrate preferably has a gel fraction of 95% or less.
When the gel fraction of the foam base material is within the above range, the impact resistance of the obtained adhesive tape can be further enhanced. From the viewpoint of further enhancing the impact resistance of the adhesive tape, the more preferable upper limit of the gel fraction is 90%, and the more preferable upper limit is 85%. The lower limit of the gel fraction is not particularly limited, but is, for example, 10% or more, particularly 20% or more, and particularly 35% or more. The gel fraction can be adjusted by cross-linking at least one of the hard and soft sites. The gel fraction can be measured by the following method.
Only 0.1 g of the foam base material is taken out from the obtained adhesive tape, immersed in 50 ml of ethyl acetate, and shaken with a shaker at a temperature of 23 ° C. and 120 rpm for 24 hours. After shaking, a metal mesh (opening # 200 mesh) is used to absorb ethyl acetate and ethyl acetate and separate the swollen foam substrate. The separated foam substrate is dried under the condition of 110 ° C. for 1 hour. The weight of the foam base material including the dried metal mesh is measured, and the gel fraction of the foam base material is calculated using the following formula.
Gel fraction (% by weight) = 100 x (W1-W2) / W0
(W0: weight of initial foam base material, W1: weight of foam base material including dried metal mesh, W2: initial weight of metal mesh)

It is preferable that the foam base material has a cross-linked structure formed between the main chains of the resin constituting the foam base material by adding a cross-linking agent. By forming a crosslinked structure between the main chains of the resin constituting the foam base material, the peeling stress applied intermittently can be dispersed, and the heat resistance and impact resistance of the adhesive tape can be further improved. can. The cross-linking agent is not particularly limited, and can be appropriately selected depending on the functional group of the resin constituting the foam base material. Specific examples thereof include isocyanate-based cross-linking agents, aziridine-based cross-linking agents, epoxy-based cross-linking agents, and metal chelate-type cross-linking agents. Among them, an epoxy-based cross-linking agent or an isocyanate-based cross-linking agent is preferable because a resin having an alcoholic hydroxyl group or a carboxyl group that can further improve flexibility and impact resistance can be cross-linked. The isocyanate-based cross-linking agent cross-links between the alcoholic hydroxyl group or carboxyl group in the resin constituting the foam base material and the isocyanate group of the cross-linking agent. Further, the epoxy-based cross-linking agent cross-links between the carboxyl group in the resin constituting the foam base material and the epoxy group of the cross-linking agent.
The amount of the cross-linking agent added is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, based on 100 parts by weight of the resin as the main component of the foam base material.

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

The thickness of the foam base material is not particularly limited, but the preferred lower limit is 40 μm and the preferred upper limit is 2900 μm. By setting the thickness of the foam base material within the above range, the adhesive tape of the present invention can be suitably used for fixing portable electronic device parts, in-vehicle electronic device parts, and the like. From the viewpoint that it can be more preferably used for fixing the parts and the like, the more preferable lower limit of the thickness of the foam base material is 60 μm, the more preferable upper limit is 1900 μm, the further preferable lower limit is 80 μm, the further preferable upper limit is 1400 μm, and the particularly preferable lower limit. Is 100 μm, and a particularly preferable upper limit is 1000 μm.

The foam base material may have a bubble structure, and the production method is not particularly limited. Examples of the manufacturing method include a method of manufacturing the foam base material by the action of a foaming gas and a method of manufacturing by blending hollow spheres in a raw material matrix. Among them, the foam produced by the latter method is called syntactic foam, and is more excellent in impact resistance and heat resistance. Therefore, the foam base material is preferably syntactic foam. By using syntactic foam as the foam base material, a closed cell type foam having a uniform size distribution of foam bubbles can be obtained, so that the density of the entire foam base material becomes more constant and the impact resistance is further improved. Can be enhanced. In addition, syntactic foam exhibits higher heat resistance than other foams because it is less prone to irreversible disintegration under high temperatures and pressures. Some syntactic foams have a foamed structure made of hollow inorganic particles and some have a foamed structure made of hollow organic particles. From the viewpoint of flexibility, syntactic foam having a foamed structure made of hollow organic particles is used. preferable.

Examples of the hollow organic fine particles include Expancel DU series (manufactured by Nippon Philite Co., Ltd.), Advancel EM series (manufactured by Sekisui Chemical Co., Ltd.) and the like. In particular, since it is easy to design the cell diameter after foaming in a region with higher effect, expand cell 461-20 (average cell diameter after foaming 20 μm under optimum conditions) and expand cell 461-40 (under optimum conditions). The average cell diameter after foaming is 40 μm), expand cell 043-80 (average cell diameter after foaming under optimum conditions 80 μm), and Advancell EML101 (average cell diameter after foaming 50 μm under optimum conditions) are preferable.

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

The pressure-sensitive adhesive layer is not particularly limited, and examples thereof include an acrylic pressure-sensitive adhesive layer, a rubber-based pressure-sensitive adhesive layer, a urethane pressure-sensitive adhesive layer, and a silicone-based pressure-sensitive adhesive layer. Among them, an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer is preferable because it has excellent heat resistance and can be adhered to a wide variety of adherends.

The acrylic copolymer constituting the acrylic pressure-sensitive adhesive layer contains a monomer mixture containing butyl acrylate and / or 2-ethylhexyl acrylate from the viewpoint of improving the initial tack and making it easy to attach at low temperature. It is preferably obtained by polymerization. Above all, it is more preferable to obtain it by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate.
The preferable lower limit of the content of the butyl acrylate in the total monomer mixture is 40% by weight, and the preferable upper limit is 80% by weight. By setting the content of the butyl acrylate in the above range, both high adhesive strength and tackiness can be achieved at the same time.
The preferable lower limit of the content of the 2-ethylhexyl acrylate in the total monomer mixture is 10% by weight, the preferable upper limit is 100% by weight, the more preferable lower limit is 30% by weight, the more preferable upper limit is 80% by weight, and the further preferable lower limit is 50% by weight. %, A more preferred upper limit is 60% by weight. By setting the content of the 2-ethylhexyl acrylate in the above range, high adhesive strength can be exhibited.

The monomer mixture may contain other copolymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate, if necessary. Examples of the other copolymerizable monomer include a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 3 carbon atoms and a (meth) acrylic acid alkyl ester having an alkyl group having 13 to 18 carbon atoms. Examples include functional monomers.
Examples of the (meth) acrylic acid alkyl ester having 1 to 3 carbon atoms in the alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and (meth) acrylic acid. Examples include isopropyl. Examples of the (meth) acrylic acid alkyl ester having 13 to 18 carbon atoms in the alkyl group include tridecylic methacrylic acid and stearyl (meth) acrylic acid. Examples of the functional monomer include (meth) acrylic acid hydroxyalkyl, glycerin dimethacrylate, (meth) glycidyl acrylate, 2-methacryloyloxyethyl isocyanate, (meth) acrylic acid, itaconic acid, maleic anhydride, and crotonic acid. Maleic acid, fumaric acid and the like can be mentioned.

In order to copolymerize the monomer mixture to obtain the acrylic copolymer, the monomer mixture may be subjected to a radical reaction in the presence of a polymerization initiator. As a method of radically reacting the monomer mixture, that is, a polymerization method, a conventionally known method is used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.

The weight average molecular weight (Mw) of the acrylic copolymer has a preferable lower limit of 400,000 and a preferable upper limit of 1.5 million. By setting the weight average molecular weight of the acrylic copolymer in the above range, high adhesive strength can be exhibited. From the viewpoint of further improving the adhesive strength, the more preferable lower limit of the weight average molecular weight is 500,000, and the more preferable upper limit is 1.4 million.
The weight average molecular weight (Mw) is a standard polystyrene-equivalent weight average molecular weight by GPC (Gel Permeation Chromatography).

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

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

The content of the tackifier resin is not particularly limited, but the preferable lower limit is 10 parts by weight and the preferable upper limit is 60 parts by weight with respect to 100 parts by weight of the resin (for example, acrylic copolymer) which is the main component of the pressure-sensitive adhesive layer. .. When the content of the pressure-sensitive adhesive resin is 10 parts by weight or more, it is possible to suppress a decrease in the adhesive strength of the pressure-sensitive adhesive layer. When the content of the pressure-sensitive adhesive resin is 60 parts by weight or less, it is possible to suppress a decrease in adhesive strength or tackiness due to the hardening of the pressure-sensitive adhesive layer.

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

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

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

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but a preferable lower limit is 0.01 mm and a preferable upper limit is 0.1 mm. By setting the thickness of the pressure-sensitive adhesive layer within the above range, the pressure-sensitive adhesive tape of the present invention can be suitably used for fixing portable electronic device parts, vehicle-mounted electronic device parts, and the like. From the viewpoint that the parts and the like can be more preferably used, the more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 0.015 mm, and the more preferable upper limit is 0.09 mm.

The adhesive tape of the present invention preferably has a resin layer on at least one surface of the foam base material.
By having the resin layer between the foam base material and the pressure-sensitive adhesive layer, the strength of the obtained adhesive tape is improved, so that the impact resistance can be further enhanced, and particularly when the impact is repeatedly applied. Durability (tumble property) can be increased. The resin layer may be formed on one side of the foam base material or on both sides, but is preferably formed on one side of the foam base material.

The resin constituting the resin layer preferably has heat resistance. Examples of the resin constituting the heat-resistant resin layer include polyester resins such as polyethylene terephthalate, acrylic resins, silicone resins, phenol resins, polyimides, and polycarbonates. Among them, acrylic resin and polyester resin are preferable, and polyethylene terephthalate is more preferable, because an adhesive tape having excellent flexibility can be obtained.

The resin layer may be colored. By coloring the resin layer, it is possible to impart light-shielding properties to the adhesive tape.
The method of coloring the resin layer is not particularly limited, and for example, a method of kneading particles such as carbon black or titanium oxide or fine bubbles into the resin constituting the resin layer, or applying ink to the surface of the resin layer. The method and the like can be mentioned.

The resin layer may contain conventionally known fine particles and additives such as inorganic fine particles, conductive fine particles, plasticizers, tackifiers, ultraviolet absorbers, antioxidants, foaming agents, organic fillers, and inorganic fillers, as required. May be contained.

The thickness of the resin layer is not particularly limited, but the preferred lower limit is 5 μm and the preferred upper limit is 100 μm. By setting the thickness of the resin layer within the above range, it is possible to achieve both handleability and impact resistance of the adhesive tape. From the viewpoint of further achieving both handleability and impact resistance, the more preferable lower limit of the thickness of the resin layer is 10 μm, and the more preferable upper limit is 70 μm.

The adhesive tape of the present invention may have a layer other than the foam base material, the pressure-sensitive adhesive layer and the resin layer, if necessary.

The pressure-sensitive adhesive tape of the present invention preferably has a ratio of the thickness of the pressure-sensitive adhesive layer to the thickness of the foam base material (adhesive layer thickness / foam base material thickness) of 0.1 or more and 2 or less. When the ratio of the thickness of the pressure-sensitive adhesive layer to the foam base material is within the above range, the strength of the entire obtained pressure-sensitive adhesive tape is improved, so that the impact resistance can be further improved. The ratio of the thickness of the pressure-sensitive adhesive layer to the thickness of the foam base material is more preferably 0.15 or more, and more preferably 1.2 or less. The thickness of the pressure-sensitive adhesive layer refers to the total thickness of the pressure-sensitive adhesive layers on both sides.

The thickness of the adhesive tape of the present invention is not particularly limited, but a preferable lower limit is 0.04 mm, a more preferable lower limit is 0.05 mm, a preferable upper limit is 2 mm, and a more preferable upper limit is 1.5 mm. By setting the thickness of the adhesive tape of the present invention within the above range, it is possible to obtain an adhesive tape having excellent handleability.

The method for producing the adhesive tape of the present invention is not particularly limited, and examples thereof include the following methods. First, a pressure-sensitive adhesive solution is applied to a release film and dried to form a pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer is formed in the same manner. Next, the unfoamed base material is manufactured by the above method, and the resin layer is laminated on the unfoamed base material to form a laminated body. Then, the obtained adhesive layers are bonded to both sides of the obtained laminate and heated to foam the unfoamed base material to produce an adhesive tape.

The shape of the adhesive tape of the present invention is not particularly limited, and examples thereof include a rectangular shape, a frame shape, a circular shape, an elliptical shape, and a donut shape.

The use of the adhesive tape of the present invention is not particularly limited, but since it is excellent in flexibility, repeated impact resistance and heat resistance, it is used for fixing electronic parts such as portable electronic device parts and in-vehicle electronic device parts. It can be suitably used as a sex adhesive tape.

According to the present invention, it is possible to provide an adhesive tape having excellent repeated impact resistance.

It is a photograph of the TEM observation of the foam base material of the present invention.

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

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

87 g of styrene (St), 12 g of acrylic acid (AA), 1 g of 2-hydroxyethyl acrylate (HEA), 2.5 g of RAFT agent, and 2,2'-azobis (2-methylbutyronitrile) (ABN-). E) 0.3 g was put into a two-necked flask, and the temperature was raised to 85 ° C. while replacing the inside of the flask with nitrogen gas. Then, the polymerization reaction was carried out by stirring at 85 ° C. for 6 hours (first step reaction).
After completion of the reaction, 4000 g of n-hexane was put into the flask and stirred to precipitate the reaction product, then the unreacted monomer and RAFT agent were filtered, and the reaction product was dried under reduced pressure at 70 ° C. and co-weighted. A coalescence (hard part) was obtained.

A mixture containing 49.5 g of butyl acrylate (BA), 49.5 g of methyl acrylate (MA), 1 g of acrylic acid, 0.058 g of ABN-E, and 50 g of ethyl acetate, and the copolymer (hard moiety) obtained above. ) And was put into a two-necked flask, and the temperature was raised to 85 ° C. while replacing the inside of the flask with nitrogen gas. Then, the polymerization reaction was carried out by stirring at 85 ° C. for 6 hours (second step reaction) to obtain a reaction solution containing a block copolymer formed from a hard moiety and a soft moiety. The blending amount of the mixture (soft moiety) and the hard moiety was set so that the content of the hard moiety in the obtained block copolymer was 3% by weight.
A part of the reaction solution was collected, 4000 g of n-hexane was added thereto, and the mixture was stirred to precipitate the reaction product. Then, the unreacted monomer and the solvent were filtered, and the reaction product was dried under reduced pressure at 70 ° C. The block copolymer (base resin) was taken out from the reaction solution. The weight average molecular weight of the obtained block copolymer was measured by the GPC method and found to be 398,000. "2690 Separations Module" manufactured by Water Co., Ltd. was used as a measuring instrument, and "GPC KF-806L" manufactured by Showa Denko Co., Ltd. was used as a solvent, and ethyl acetate was used as a solvent, and the measurement was performed under the conditions of a sample flow rate of 1 mL / min and a column temperature of 40 ° C.

The obtained block copolymer was dissolved in ethyl acetate so that the solid content ratio became 35%, and Expancel 461-DU-40 (manufactured by Nippon Philite Co., Ltd.) was used as a foaming agent for 100 parts by weight of the block copolymer A. , 461 DU40 in the table) 3.3 parts by weight and 0.12 parts by weight of Tetrad C (manufactured by Mitsubishi Gas Chemicals, Inc.) as a cross-linking agent were added and further sufficiently stirred to obtain a substrate solution. An unfoamed base material was obtained by applying the obtained base material solution on the corona-treated surface of a 23 μm polyethylene terephthalate (PET) film having one side treated with corona and drying at 90 ° C. for 7 minutes. The thickness of the unfoamed substrate was adjusted to 127 μm when the unfoamed substrate was allowed to stand in an environment of 40 ° C. for 48 hours and then heated at 130 ° C. for 1 minute.

(2) Preparation of pressure-sensitive adhesive solution 52 parts by weight of ethyl acetate was placed in a reactor equipped with a thermometer, a stirrer, and a cooling tube, and after nitrogen substitution, the reactor was heated to start reflux. Thirty minutes after the ethyl acetate boiled, 0.08 part by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 70 parts by weight of butyl acrylate, 27 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 0.2 parts by weight of 2-hydroxyethyl acrylate was added dropwise thereto evenly and gradually over 1 hour and 30 minutes. It was reacted. Thirty minutes after the completion of the dropping, 0.1 part by weight of azobisisobutyronitrile was added, and the polymerization reaction was further carried out for 5 hours. Ethyl acetate was added to the reactor and cooled while diluting to obtain a solid content of 40% by weight. A solution of acrylic random copolymer was obtained.
The weight average molecular weight of the obtained acrylic random copolymer was 710,000 as a result of measuring the weight average molecular weight by the GPC method using "2690 Separations Model" manufactured by Water Co., Ltd. as a column. The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) was 5.5.
With respect to 100 parts by weight of the solid content of the obtained acrylic random copolymer, 15 parts by weight of a polymerized rosin ester having a softening point of 150 ° C., 10 parts by weight of terpene phenol having a softening point of 145 ° C., and 10 parts by weight of a rosin ester having a softening point of 70 ° C. Parts were added. Further, 30 parts by weight of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.) and 3.0 parts by weight of an isocyanate-based cross-linking agent (Coronate L45 manufactured by Tosoh Co., Ltd.) were added and stirred to obtain a pressure-sensitive adhesive solution.

(3) Manufacture of Adhesive Tape On the release-treated surface of a 50 μm polyethylene terephthalate (PET) film with a mold release treatment on one side, a doctor puts the obtained adhesive solution on the dry film so that the thickness of the dry film is 75 μm. The coating was applied with a knife and heated at 110 ° C. for 5 minutes to dry the coating solution to obtain an adhesive layer. Then, another pressure-sensitive adhesive layer was produced by the same operation to obtain two pressure-sensitive adhesive layers. Then, the two adhesive layers obtained above were laminated on both sides of the non-foamed substrate obtained above, and allowed to stand in an environment of 40 ° C. for 48 hours. After 48 hours, the substrate was removed from the environment at 40 ° C. and heated at 130 ° C. for 1 minute to foam the substrate to obtain an adhesive tape.

(4) DSC measurement A measurement sample of only the foam substrate was prepared by the above method. The obtained measurement sample was measured using a differential scanning calorimeter (manufactured by Seiko Instruments, 220C) under the conditions of a heating rate of 10 ° C / min, a temperature range of -100 ° C to 200 ° C, and one cycle. The number of peaks in the region of 50 to 100 ° C., −100 ° C. to 0 ° C. and −100 ° C. to 10 ° C. was measured.

(5) Transmission electron microscope (TEM) measurement Only the foam base material was prepared by the above method. Small pieces trimmed from the foamed substrate are dyed with a 2% osmium acid aqueous solution at 60 ° C. for 12 hours and then washed, and the small piece temperature is -100 by cryomicrotome (ULTRACUT FC7 manufactured by LEICA) in the thickness direction of the foamed substrate. A section having a thickness of less than 100 nm was cut out at ° C. and placed on a sheet mesh covered with a support film to prepare a measurement sample.
The obtained measurement sample was observed using a transmission electron microscope (JEM-2100, manufactured by JEOL Ltd.) in a region of 4.3 μm × 4.3 μm (square) at a magnification of 5000 times. The image observed by the transmission electron microscope was automatically binarized using image analysis software Aviso (ver2019.4, manufactured by Thermo Fisher Scientific). In the binarized image, the major axis of each island structure (dark part) was measured, and the maximum major axis of the island structure was calculated from these arithmetic mean values.

(6) Measurement of Gel Fragment of Foam Base Material Only 0.1 g of the foam base material was taken out from the obtained adhesive tape, immersed in 50 ml of ethyl acetate, and shaken at a temperature of 23 ° C. and 120 rpm. Shake for 24 hours. After shaking, a metal mesh (opening # 200 mesh) was used to absorb ethyl acetate and ethyl acetate, and the swollen foam substrate was separated. The separated foam substrate was dried under the condition of 110 ° C. for 1 hour. The weight of the foam base material including the dried metal mesh was measured, and the gel fraction of the foam base material was calculated using the following formula.
Gel fraction (% by weight) = 100 x (W1-W2) / W0
(W0: weight of initial foam base material, W1: weight of foam base material including dried metal mesh, W2: initial weight of metal mesh)

(Examples 2 to 5, Comparative Examples 1 and 2)
An adhesive tape was obtained in the same manner as in Example 1 except that the composition of the hard portion and the soft portion and the blending amount of the foamed fine particles were as shown in Table 1. Each measurement of the obtained adhesive tape was carried out in the same manner as in Example 1. The AS-6S (manufactured by Toa Synthetic Co., Ltd., styrene macromonomer solution (50% toluene solution)) used in Example 5 was used after adjusting the solid amount of the styrene macromonomer to the value shown in Table 1. board. Further, although the foamed fine particles were not blended in Comparative Example 2, heating was performed at 130 ° C. for 1 minute in the same manner as in other examples in order to make the heat history uniform.

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

(Evaluation of tumble property)
Two adhesive tapes cut out to 1 mm × 70 mm were prepared. Next, an adhesive tape was attached to each short side of a polycarbonate plate having a length of 72 mm, a width of 135 mm, and a thickness of 1 mm. Then, the surface to which the adhesive tape of the polycarbonate plate is attached and the polycarbonate plate having a length of 77 mm, a width of 150 mm, and a thickness of 4 mm are overlapped so that the short sides of the two polycarbonate plates face each other and the long sides face each other. Two polycarbonate plates were bonded by pressurizing at 7 MPa for 15 seconds. Then, a test sample was obtained by allowing it to stand at 23 ° C. for 24 hours. The obtained test sample is placed in a TD-1000A drum type rotary drop tester (manufactured by Shinei Denshi Keiki Co., Ltd.) and rotated at a speed of 12 rpm while maintaining a room temperature environment at 23 ° C. for measurement. The sample was repeatedly dropped from a height of 1 m. The tumble property was evaluated as "◯" when the number of drops when the polycarbonate plate was peeled off was more than 1000 times and "x" when the number of drops was 1000 times or less.

According to the present invention, it is possible to provide an adhesive tape having excellent repeated impact resistance.

Claims (4)

An adhesive tape having an adhesive layer on at least one surface of a foam substrate.
The foam substrate has a temperature rise rate of 10 ° C./min, a temperature range of -100 ° C. to 200 ° C., and a region of 50 to 100 ° C. and -100 ° C. to 10 when DSC measurement is performed with one cycle count. Adhesive tape with at least one peak in each ° C region. The adhesive tape according to claim 1, wherein the foam base material has an island structure having a maximum major axis of 60 nm or less. The adhesive tape according to claim 1 or 2, wherein the foam base material contains a copolymer having a structure derived from a vinyl aromatic compound monomer and a structure derived from a (meth) acrylic monomer. The adhesive tape according to any one of claims 1 to 3, which has a resin layer on at least one surface of the foam base material.

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