double-sided adhesive film

Abstract

To provide a double-sided adhesive film having almost equal rates of elongation in the XY (longitudinal and lateral) directions, more preferably in the thickness direction while preventing the occurrence of squeezing-out of an adhesive agent, and adhesive burr, improving adhesive force and holding force compared to the same adhesive one-layer article, and adaptable to an adherend having elasticity and flexibility.SOLUTION: A double-sided adhesive film is a substrate-less double-sided adhesive film which is composed of a center layer formed from a resin adhesive agent, and an adhesive agent layer laminated on the surface and rear face of the center layer and formed from resin the same or the same system as the resin forming the center layer, and in which a weight average molecular weight or a degree of cross-linking of the resin forming the center layer is larger than a weight average molecular weight or a degree of cross-linking of the resin forming the adhesive agent layer. A tolerance between a rate of elongation in the longitudinal direction and a rate of elongation in the lateral direction is ±20% or less to the one rate of elongation, and more preferably, the rates of elongation in the longitudinal direction and the lateral direction are equal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a substrate-less double-sided adhesive film.

[0002] In the present invention, the term "film" includes any of tape, sheet, and film forms. [Background technology]

[0003] Conventionally, adhesive films have been used in which an adhesive layer made of an adhesive (in this specification, "adhesive" refers to an adhesive that has viscoelasticity at room temperature and in a solvent-free state, and flows when pressure is applied to it to achieve the required adhesive strength; the same applies hereinafter) is formed on one or both sides of a substrate (substrate layer) made of polyethylene terephthalate (PET), nonwoven fabric, etc. (See Patent Document 1, columns

[0002] and

[0003] ). Note that such adhesive films are subjected to various processes, such as cutting into predetermined sizes and shapes by punching, slitting, etc., depending on the purpose.

[0004] However, conventional double-sided adhesive films using the above-mentioned substrates have had problems such as the inability to make the film thin and poor die-cutting properties.

[0005] In particular, there were problems such as difficulty in stretching the film uniformly to fit the shape of the substrate because the mechanical properties (physical properties) of the base layer and the adhesive layer were significantly different, and there were also problems with poor workability, such as stress being placed only on the adhesive layer when the film was cut, causing the adhesive layer to wrinkle or develop glue burrs.

[0006] For example, a double-sided adhesive tape is provided in which a biaxially oriented PET film with excellent dimensional stability is used as the base layer, and the above-mentioned pressure-sensitive adhesive layer is formed on both sides of the base layer, and the difference in shear strength between the base layer and the pressure-sensitive adhesive layer in this configuration is 180:1 (base layer: pressure-sensitive adhesive layer) when the base layer thickness is 5 μm and the pressure-sensitive adhesive thickness is 25 μm, as shown in Table 1 below. Furthermore, when the thickness of the base layer is 25 μm (see Table 2), the difference is 400:1 (base layer: pressure-sensitive adhesive layer).

[0007] Furthermore, as shown in Table 1, the difference in longitudinal elongation rate between the base layer and the adhesive layer is 142% for the biaxially oriented PET film (thickness 5 μm) of the base layer, while that of the adhesive layer is over 400%, a difference of more than 2.8 times (base layer:adhesive layer = 1:2.81).

[0008] Similarly, the ratio of the lateral elongation rate of the base layer to that of the adhesive layer is 118% for the biaxially oriented PET film (thickness 5 μm) of the base layer, while that of the adhesive layer is over 400%, a difference of more than 3.3 times (base layer:adhesive layer = 1:3.38).

[0009] In addition, the thermal shrinkage of biaxially stretched PET film in the longitudinal and transverse directions when heated to 150°C for 3 minutes is 1.4%, which is 7 times the shrinkage in the longitudinal direction compared to 0.2% in the transverse direction (anisotropy).

[0010] On the other hand, when wet rayon nonwoven fabric is used for the base layer, according to Table 1, the thermal shrinkage of wet rayon nonwoven fabric is 0.15% in the longitudinal direction and 0.5% in the transverse direction, demonstrating its dimensional stability compared to the biaxially oriented PET film. However, because the directionality of the water flow cannot be avoided during the manufacturing process, the shear strength of wet rayon nonwoven fabric is 9.7 N in the longitudinal direction and 1.3 N, about 1 / 7 of that in the transverse direction (anisotropy).

[0011] As mentioned above, referring to Table 1, in terms of shear strength, the biaxially oriented PET film is 180 to 400 times stronger than the adhesive in the longitudinal direction, and even in the longitudinal direction of the wet rayon nonwoven fabric, the difference is about 90 times greater. On the other hand, the opposite is true for elongation, with the adhesive having an elongation of over 400%, while the wet rayon nonwoven fabric is 1 / 133 of this in the longitudinal direction, and the biaxially oriented PET film is about 1 / 3 of this in the longitudinal direction. In any case, there is a large difference in mechanical strength (physical properties) between the base layer and the adhesive layer.

[0012] Furthermore, the biaxially stretched PET film and the wet-laid rayon nonwoven fabric have different mechanical strengths (physical properties) in the longitudinal and transverse directions (anisotropy).

[0013] [Table 1]

[0014] [Table 2]

[0015] Due to the large differences in the physical properties of the base layer and adhesive layer mentioned above, and the different orientation (anisotropy) of the base layer, where the physical properties differ in the vertical and horizontal directions, the finished double-sided adhesive film as a whole lacks uniformity in plastic deformation, so when adherends are bonded together, wrinkles and other problems are likely to occur, and when used in handle sensors, pressure sensors, etc., this can easily cause undesigned error signals.

[0016] Furthermore, when double-sided adhesive film is used in products that require high precision, such as for bonding electronic components in communication devices such as sensors, the film is subjected to fine cutting, which may result in bending of the cut edges after cutting, transfer of glue burrs to the mounted components, or the electronic components being lifted by the glue burrs, which may result in the film not performing the desired function and causing product defects.

[0017] Furthermore, with conventional adhesive films that use a substrate, glue burrs that are generated by shearing the adhesive layer during punching can adhere to the cutting blades of the shearing machine, drills, slitters, and other processing tools, which can interfere with subsequent processes when shearing in a continuous process and cause the production line to be interrupted.Therefore, for example, when punching or pressing is performed, high-intensity inspection is required to check whether adhesive burrs have been transferred to the processed product and whether the adhesive film has been completely removed.Furthermore, glue burrs that have adhered to the blades must be removed approximately every 40,000 shots, which creates the problem of complicating the manufacturing process.

[0018] In addition, in conventional adhesive films that are made by laminating an adhesive layer onto a base layer, one of the reasons why glue burrs occur when shearing processes such as punching and drilling are performed is because there is an interface between the base layer and the adhesive layer that has different elongation rates.It is thought that most glue burrs are caused by the adhesive that makes up the adhesive layer peeling off from the base material due to the breakdown of this interface. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] Japanese Patent Application Publication No. 9-208907 [Patent Document 2] Japanese Patent Application Publication No. 63-268784 Summary of the Invention [Problem to be solved by the invention]

[0020] In order to solve the problems associated with conventional adhesive films using the above-mentioned substrates, a substrate-less double-sided adhesive film, that is, a double-sided adhesive film consisting only of an adhesive layer, has been proposed.

[0021] However, conventional substrate-less double-sided adhesive films have the following problems.

[0022] (1) Double-sided adhesive films without a substrate are prone to blocking, making it impossible to increase tack. For example, with conventional double-sided adhesive films without a substrate, the adhesive layer tends to protrude during storage, and when the adhesive protrudes in this way, blocking occurs when the adhesive tape is rewound, making it unusable.

[0023] (2) Without a substrate, the adhesive may not be held firmly in place, causing the adhesive layer to be pulled out by the slitter when slitting (the occurrence of glue burrs).

[0024] The occurrence of glue burrs is a particular problem when precision is required, such as when gluing electronic parts. The presence of glue burrs can cause glued electronic components to lift up, resulting in defective products.

[0025] With conventional adhesive films without substrates, adhesive burrs are unavoidable due to the adhesive's tendency to adhere and stretch, and because the adhesive burrs have an adhesive function, they tend to grow easily, causing even more problems.

[0026] To address this issue, one option is to increase the molecular weight of the adhesive to 800,000 to 1,000,000 or more, or to formulate it as a highly cross-linked type, but this tends to reduce tack, potentially sacrificing adhesion at room temperature, and also increases Tg, making it likely to sacrifice adhesion at low temperatures.

[0027] (3) Furthermore, in an adhesive film consisting only of an adhesive layer, it is difficult to change the adhesiveness of the front and back surfaces of the film. For example, Japanese Patent Application Laid-Open No. 63-268784 discloses a substrate-less adhesive film consisting of a photo-crosslinkable adhesive layer (one layer) containing an acrylic copolymer as a component, and having a difference in adhesive strength on the front and back surfaces of the adhesive layer due to the difference in the degree of crosslinking.

[0028] In the double-sided adhesive film of the above-mentioned Patent Publication No. 268784 / 1988, an attempt is made to change the adhesiveness between the front and back surfaces, but because such double-sided adhesive films change their adhesiveness only by the presence or absence of crosslinking in one adhesive layer, a sufficient difference in adhesiveness is not necessarily obtained, and problems such as blocking and adhesive overflow, as mentioned above, still remain.

[0029] (4) Furthermore, the inventors have found through careful investigation that when bonding to soft materials such as steering wheel sensors in automobiles or the surface heating sheets in automobile seats, unless the material has a specified adhesive strength, thin thickness, and approximately uniform non-orientation and stress relaxation (elasticity) in both the vertical and horizontal directions, it will not be able to follow the plastic deformation of the substrate, resulting in distortion such as lifting.

[0030] Similarly, for applications requiring stress relaxation (stretchability) and flexibility, such as connected cars, sensors, and soft actuators, conventional substrate-less double-sided adhesive films were not suitable because they had insufficient adhesive strength and also had problems such as distortion and breakage due to differences in elongation rate, thermal shrinkage rate, etc. in the length and width directions (anisotropy). Furthermore, if residual distortion remains in the double-sided adhesive film, it can cause pressure-sensitive sensors to malfunction, which in turn can interfere with the sensor's sensing function.

[0031] In addition to the above, there are other inconveniences such as the adhesive layer overflowing and peeling off, and conventional double-sided adhesive films or single-layer adhesive films have the problem that it is difficult to meet the multiple requirements mentioned above at once, since the performance of the entire film is determined by the properties of the adhesive used.

[0032] In view of the above-mentioned problems, the present invention aims to provide a double-sided adhesive film that has a substantially uniform elongation rate in the XY (length and width) directions, and more preferably in the Z (thickness) direction, while preventing the adhesive from overflowing or the occurrence of adhesive burrs, and further has adhesive strength and holding power that are 1.5 to 3 times greater in both the length and width directions compared to the same single-layer adhesive product (comparable to viscoelastic adhesion), and that can be used on stretchy and flexible adherends. [Means for solving the problem]

[0033] In order to achieve the above object, the double-sided pressure-sensitive adhesive film of the present invention is methacrylic acid ester consists of A central layer formed from an acrylic emulsion resin adhesive; An alkyl acrylate-vinyl acetate copolymer that is laminated on the front and back surfaces of the central layer and forms the central layer consists of It consists of an adhesive layer made of acrylic resin, A substrateless double-sided pressure-sensitive adhesive film, wherein the weight average molecular weight and crosslinking degree of the resin forming the central layer are greater than the weight average molecular weight and crosslinking degree of the resin forming the pressure-sensitive adhesive layer, The adhesive layer has a structure that generates a gradient in molecular weight and crosslinking degree in the interfacial region between the central layer and the adhesive layer, and Both the longitudinal and transverse elongation rates 36~37 % range and The tolerance between the longitudinal elongation rate and the transverse elongation rate is ± 1 %, and more preferably, the elongation rate is equal in both the longitudinal and transverse directions (claim 1).

[0035] The total thickness of the double-sided adhesive film is preferably 5 to 300 μm (see claim 2 ).

[0036] It is also preferable that the ratio of the elongation rate of the resin forming the central layer to the elongation rate of the resin forming the adhesive layer is 1:1 to 1:20 (see claim 3 ).

[0037] It is also preferable that the central layer and the adhesive layer are non-oriented (see claim 4 ).

[0038] Furthermore, it is preferable that the molecules in the resin forming the central layer and the molecules in the resin forming the adhesive layer are crosslinked in the interface region between the central layer and the adhesive layer (see claim 5 ).

[0039] It has been found that it is more preferable that the tolerance of each of the elongation rates in the machine direction, the transverse direction and the thickness direction is ±20% or less with respect to each of the elongation rates in the other two directions (see claim 6 ).

[0041] Furthermore, the adhesive layer (first adhesive layer) laminated on the surface of the central layer and the adhesive layer (second adhesive layer) laminated on the back surface of the central layer may be formed from resins having different adhesive strengths (see claim 7 ).

[0042] A conductive material may be added to the double-sided adhesive film of the present invention (see claims 8 ).

[0043] Furthermore, a thermally conductive material may be added to the double-sided adhesive film of the present invention (see claims). 9 ).

[0044] The central layer may have fiber pieces dispersed therein (see claim 10 ). [Effects of the Invention]

[0045] In the double-sided adhesive film of the present invention having the above configuration, the center layer and the adhesive layer are both made of adhesive resin and have similar resin compositions, which allows for good interlayer compatibility between the center layer and the adhesive layer, and the resin of the adhesive layer can penetrate almost completely into the recesses of the fine irregularities on the outer surface of the center layer (eliminating gaps between the adhesive layer and the center layer). This not only results in high intermolecular forces, but also creates a gradient in molecular weight distribution or crosslinking degree from the center to the outside (front and back sides) in the thickness direction of the film, eliminating or softening the interface between the center layer and the adhesive layer. This creates a gradient in elongation in the thickness direction, creates a strong bond between the layers, makes delamination less likely, and provides excellent stress relaxation throughout the film, preventing creases and extrusion when cut, resulting in good workability. Furthermore, problems such as blocking and adhesive extrusion, which are common with substrate-less double-sided adhesive films, are also eliminated.

[0046] Furthermore, the double-sided adhesive film of the present invention has a substantially uniform elongation rate in both the longitudinal and transverse directions, which, combined with the above-mentioned effects, allows it to be uniformly stretched and attached to the shape of the adherend, and can easily undergo plastic deformation (follow) regardless of the shape, movement, or deformation of the adherend. Moreover, because the plastic deformation is not lacking in uniformity, and because the molecular weight distribution gradient and molecular entanglement in the interlayer region between the center layer and the adhesive layer provide an excellent stress relaxation effect, it is possible to prevent distortion or breakage of the film after application.

[0047] As described above, the double-sided adhesive film of the present invention can be freely designed to have various functionalities, thicknesses, and material properties depending on the application, such as industrial or medical use, and the finished product has uniform stretch in both the vertical and horizontal directions, so the range of applications can be expanded to include lamination of temperature sensors, pressure sensors, connected cars, soft actuators, etc.

[0048] It is more preferable that both the central layer and the adhesive layer are non-oriented.

[0049] Furthermore, since the double-sided adhesive film of the present invention can form adhesive layers with different adhesive strengths on the front and back of the film, alignment can be easily achieved by attaching or peeling off the side with weaker adhesive strength to the substrate when applying the film.

[0050] Furthermore, by adding functional materials such as conductivity and heat dissipation properties to the double-sided adhesive tape layer to form a three-layer structure or more, a gradient in the composition of the functional materials can be obtained, and as a result, the expression of the functional materials and the adhesive strength can be controlled. [Brief explanation of the drawings]

[0051] [Figure 1] FIG. 2 is a diagram showing the elongation in the thickness direction of the double-sided pressure-sensitive adhesive film of the present invention. [Figure 2] FIG. 2 shows the results of a 90-degree peel test on the double-sided pressure-sensitive adhesive film of the present invention. [Figure 3] FIG. 1 shows the results of a 90-degree peel test on a conventional double-sided tape with a nonwoven fabric substrate. DETAILED DESCRIPTION OF THE INVENTION

[0052] The double-sided adhesive film of the present invention is a substrate-less double-sided adhesive film consisting of a central layer formed from an adhesive and adhesive layers laminated on the front and back surfaces of the central layer (for convenience, in the following specification, the adhesive layer formed on the front surface of the central layer will be referred to as the first adhesive layer, and the adhesive layer formed on the back surface of the central layer will be referred to as the second adhesive layer).

[0053] [Central layer] The central layer is composed of a resin typically used as an adhesive, molded into a film of the desired thickness. Examples of such resins include, but are not limited to, natural rubber, synthetic rubber, acrylic resin, olefin resin, silicone resin, urethane resin, and polyester resin. Examples of such synthetic rubbers include, but are not limited to, styrene-butadiene, polyisobutylene, and isoprene-based synthetic rubbers. Examples of such acrylic resins include, but are not limited to, polymers of 2-ethylhexyl acrylate, butyl acrylate, and ethyl acrylate. Examples of such olefin resins include, but are not limited to, polystyrene-ethylene / butylene copolymers, ethylene-vinyl acetate copolymers, polyethylene (e.g., polyethylene with polar groups introduced), and polystyrene-ethylene-propylene copolymers. Examples of such silicone resins include, but are not limited to, vinyl polydimethylsiloxane copolymers and vinyl trichlorosilane-alkoxysilane copolymers. Examples of such urethane resins include, but are not limited to, those obtained by reacting polyisocyanate with the following polyols (polyester polyols, polyester polyols, polylactone polyols, etc.). Examples of the polyester resin include saturated polyester resin and unsaturated polyester resin, but are not limited to these.

[0054] The central layer may also be formed from a blend of multiple resins listed above. Furthermore, the central layer may also be formed from a mixture of resins other than those listed above, such as a mixture of acrylic resin and vinyl acetate resin, as long as the mixture exhibits adhesive strength due to the inclusion of the resins listed above.

[0055] The central layer is preferably formed from an acrylic resin. The acrylic resin may be obtained by polymerizing one or more of the following monomers by solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, or the like. Examples of the monomer include, but are not limited to, acrylic acid, methacrylic acid, alkyl acrylates or alkyl methacrylates having 1 to 20 carbon atoms with unsubstituted or substituted alkyl groups (e.g., methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, methyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and dimethylaminoethyl methacrylate), acrylonitrile, acrylamide, methylolacrylamide, and glycidyl methacrylate. The acrylic resin may also be a copolymer of the above-mentioned acrylic acid monomer with, for example, vinyl acetate, vinylidene chloride, styrene, itaconic acid, or maleic anhydride.

[0056] The central layer may also be formed from a water-based acrylic emulsion resin.

[0057] It is preferable to use the core layer by forming the above-mentioned resin into a non-oriented film without performing orientation treatment such as stretching during the manufacturing process, so that the physical properties of the film do not vary significantly depending on the direction, and are uniform or similar in all directions.

[0058] The thickness of the central layer differs depending on the application and the resin material (adhesive material) used, but is preferably 1 to 150 μm, and more preferably 10 to 50 μm.

[0059] To form the central layer, one or more raw material monomers or polymers are mixed with additives such as crosslinking agents as desired, and polymerized by, for example, solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc., and used as the raw material.

[0060] Examples of the crosslinking agent that can be used include epoxy resin, isocyanate, melamine resin, urea resin, etherified amino resin, metal chelate, etc. The resin that forms the central layer may be crosslinked by incorporating the crosslinking agent during polymerization.

[0061] In addition, examples of the additives other than the crosslinking agent include anti-aging agents, thermally conductive materials, flame retardants, heat shrinkage prevention agents, conductive materials, and the like.

[0062] The method for forming (forming) the central layer can be performed using the above-mentioned raw materials by extrusion methods such as the T-die method and the inflation method, a roll coater, a casting method, etc., but it is also possible to form three layers simultaneously, including the front and back surfaces that will become the adhesive layers described below.

[0063] It is also acceptable for the central layer to contain fiber fragments as pseudo-crosslinks. Specifically, pseudo-crosslinks formed by the entanglement of fiber fragments within the layer can reduce the fluidity of the layer and make it physically hard.

[0064] The fiber pieces may be made of, for example, acrylic, polyester, nylon, olefin, rayon, glass, etc., and have a denier of 5d or less, preferably 2d or less, and a length of 5mm or less.

[0065] The amount of the fiber pieces to be blended is 3 to 40 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of the adhesive solid content.

[0066] [Adhesive layer] The resin used to form the adhesive layer laminated on the front and back surfaces of the above-mentioned central layer can be any of various known resins that can normally be used as adhesives.

[0067] Examples of the resin include, but are not limited to, natural rubber, synthetic rubber, acrylic resin, olefin resin, silicone resin, and urethane resin. Examples of the synthetic rubber include, but are not limited to, styrene-butadiene, polyisobutylene, and isoprene-based synthetic rubbers. Examples of the acrylic resin include, but are not limited to, methyl (meth)acrylate, ethyl (methyl)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of the olefin resin include, but are not limited to, polyethylene (e.g., with polar groups introduced), polypropylene, and the like. Examples of the silicone resin include, but are not limited to, siloxane trichlorosilane, alkoxysilane, and the like. Examples of the urethane resin include, but are not limited to, polyester polyol, polycarbonate, polyethylene polyol, and polyalkylene polyol.

[0068] The adhesive layer may be formed by blending multiple resins described above. Furthermore, the adhesive layer may be formed by mixing resins other than those described above, as long as the adhesive layer exhibits adhesive strength by including the resins described above.

[0069] The adhesive layer is preferably formed from an acrylic resin, which may be obtained by polymerizing one or more of the monomers listed above for the central layer by, for example, solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, or the like.

[0070] The first adhesive layer and the second adhesive layer may be formed from different resins. However, it is preferable that the first adhesive layer and the second adhesive layer are formed from the same or similar resin as the resin forming the central layer. The term "similar" means that the side chain functional groups in the unit structures or parts of the main skeletons in the unit structures are different, but the main skeletons of the unit structures partially overlap, and so on, and have similar chemical structures.

[0071] Furthermore, it is preferable that the pressure-sensitive adhesive layer be formed from the above-mentioned resin into a non-oriented film before use.

[0072] The thickness of the adhesive layer is preferably 1 to 100 μm, more preferably 10 to 50 μm, on one side of the central layer.

[0073] Furthermore, the adhesive layer may contain additives such as tackifiers, softeners, fillers, antioxidants, crosslinking agents, thermally conductive materials, and electrically conductive materials, if desired.

[0074] The tackifier may be, for example, rosin-based (e.g., rosin, gum rosin, modified rosin, rosin ester); terpene-phenolic resin; terpene resin; synthetic petroleum resin (e.g., copolymers of isoprene, cyclopentadiene, 1,3-pentadiene, 1-pentene, copolymers of 2-pentene, dicyclopentadiene, 1,3-pentadiene-based resins, copolymers of indene, styrene, methylindene, α-methylstyrene); phenolic resin; xylene resin; alicyclic petroleum resin; coumarone-indene resin; styrene-based resin; dicyclopentadiene resin.

[0075] The crosslinking agent can be selected from those listed as crosslinking agents to be added to the central layer.

[0076] Furthermore, fiber pieces may be dispersed in the adhesive layer. The type, denier, and length of the fiber pieces are as explained above for the central layer.

[0077] However, when fiber pieces are dispersed in the adhesive layer to ensure the adhesive strength of the adhesive layer, the density of the fiber pieces per unit volume is made relatively lower than that of the central layer, and the fluidity is made relatively higher than that of the central layer.

[0078] [Combination of central layer and adhesive layer] After extensive research, the inventors have found that glue burrs that occur during slitting and cutting are caused by the adhesive phenomenon of low-molecular-weight, uncrosslinked components inherent to adhesives and the failure of adhesive components when stretched. They have noticed that solving this problem requires not only the longitudinal and lateral elongation rates but also the thickness direction elongation rate, and have found that by exhibiting one or all of the following at the interface between one side of the adhesive layer and the front and back surfaces of the core layer: proximity or gradient of elongation rate, proximity or gradient of molecular weight, and proximity or gradient of crosslinking, the elongation of the adhesive layer at the interface between the core layer and the adhesive layer can be brought closer to that of the core layer, making it possible to balance the elongation rates in the XYZ [longitudinal, transverse, thickness] directions of the entire film, thereby achieving the desired performance without sacrificing adhesive strength.

[0079] As described above, in the double-sided pressure-sensitive adhesive film of the present invention, in order to obtain a gradient between the interface of the layers due to stress relaxation, the resin forming the central layer is the same as or similar to the resin forming the first pressure-sensitive adhesive layer and the resin forming the second pressure-sensitive adhesive layer, preferably formed from a resin polymerized from monomers of the same composition, and the resin forming the central layer is preferably made of a resin with a larger molecular weight (weight-average molecular weight) than the resin forming the first pressure-sensitive adhesive layer and the resin forming the second pressure-sensitive adhesive layer. The weight-average molecular weight of the resin forming the central layer is, for example, 2,000 to 1,500,000, preferably 5,000 to 500,000, and particularly 200,000 to 300,000.

[0080] Alternatively, in order to obtain a gradient between the interface of the layers due to stress relaxation, the resin forming the central layer is preferably the same or similar resin as the resin forming the first adhesive layer and the resin forming the second adhesive layer, preferably a resin polymerized from monomers of the same composition, and it is preferable that the resin of the central layer be a resin with a higher degree of cross-linking than the resin of the adhesive layers.

[0081] By configuring the double-sided adhesive film of the present invention as described above, the center layer and adhesive layer are both made of adhesive resin, and because the resin compositions are similar, the layers fit together easily and the resin of the adhesive layer can penetrate almost completely into the depths of the fine concaves and convexes on the outer surface of the center layer (there are no gaps between the adhesive layer and the center layer).This not only results in high intermolecular forces, but also creates a gradient in molecular weight or degree of crosslinking from the center of the film thickness direction to the outside (front and back sides), and the interface between the center layer and the adhesive layer disappears or is relaxed.As a result, a gradient in elongation also occurs in the thickness direction, and high bonding strength is created between the layers, making interlayer delamination less likely to occur.The entire film has excellent stress relaxation, and furthermore, glue burrs are less likely to occur even during continuous die-cutting processing.

[0082] In general, if the molecular weight or degree of cross-linking of the resin is large, the fluidity related to adhesive strength decreases, but the shape retention improves, and if the molecular weight or degree of cross-linking of the resin is large, the elongation rate decreases.

[0083] In addition, in order to further strengthen the prevention of delamination between the core layer and the adhesive layer, it is effective to mitigate the differences in composition between the resin that makes up the core layer and the resin that makes up the adhesive layer, such as by exerting functions such as intermolecular crosslinking at the interface region between the core layer and the adhesive layer, and to make the phases of the interface between the two as similar as possible.

[0084] Like the double-sided adhesive film of the present invention, the adhesive layers (first adhesive layer and second adhesive layer) are made of resins with a relatively low molecular weight or low degree of crosslinking in order to exert their adhesive properties, whereas the central layer is made of resins with a relatively high degree of crosslinking or high molecular weight in order to give the adhesive film shape retention and strength, etc., and by making all or part of the composition of each resin common, covalent bonding (crosslinking) reactions between functional groups contained in the components of the resins forming these adhesive layers and the resins forming the central layer, and by using crosslinking agents such as epoxy and isocyanate in the central layer, the crosslinking of the crosslinking agent in the central layer can be prevented. Some of the crosslinking agent bleeds out into the adhesive layer, causing the uncrosslinked components of the crosslinking agent to undergo a crosslinking reaction at the interface between the central layer and the adhesive layer in an attempt to achieve equilibrium, resulting in some of the molecules of the adhesive layer being absorbed (crosslinked / bonded) by the molecules of the central layer, resulting in a more effective gradient in molecular weight or degree of crosslinking at the interface.Furthermore, if the resin forming the central layer and the resin forming the adhesive layer have different compositions, a gradient in molecular composition will occur at the interface (mitigating the difference in composition between the resin forming the central layer and the resin forming the adhesive layer), which is thought to effectively eliminate or mitigate the interface between the central layer and the adhesive layer.

[0085] Furthermore, by creating a gradient in molecular weight distribution, degree of crosslinking, and molecular composition in the interfacial region between the central layer and the adhesive layer, the interface between the central layer and the adhesive layer disappears or is relaxed, meaning that the central layer and the adhesive layer attempt to balance each other in the interfacial region, which also creates a gradient in elongation in the thickness direction, allowing for excellent absorption and dispersion of stress in the XYZ [length, width, thickness] directions and conformability to the adherend, resulting in improved adhesive performance, reduced interlayer peeling, and less thermal shrinkage and warping of the adhesive film when heated. It also has excellent parting properties during blade die-cutting, is less likely to produce glue burrs during continuous die-cutting, and is excellent for slitter processing.

[0086] The total thickness (center layer+first adhesive layer+second adhesive layer) of the double-sided adhesive film of the present invention is preferably 5 to 300 μm, and particularly preferably 40 to 160 μm.

[0087] Regarding the elongation percentage, the elongation percentage in both the longitudinal and transverse directions of the resin forming the core layer is preferably 10 to 300%, more preferably 20 to 200%, and particularly preferably 80 to 150%. In this specification, "elongation percentage" refers to the "elongation" defined in JIS Z 0237 1991-.

[0088] Furthermore, with regard to the elongation rate of the adhesive layer, it is preferable that the elongation rate of the resin forming the central layer is similar to the elongation rate of the resin forming the adhesive layer; for example, the ratio of the elongation rate of the resin forming the central layer to the elongation rate of the resin forming the first and second adhesive layers is preferably 1:1 to 1:20, more preferably 1:1 to 1:10, and particularly preferably 1:1.5 to 1:2.5 (= 2:3 to 2:5), in both the vertical and horizontal directions.

[0089] As mentioned above, in the double-sided adhesive film of the present invention, a gradient in molecular weight, degree of crosslinking, and molecular composition occurs in the interfacial region between the central layer and the adhesive layer, causing the interface between the central layer and the adhesive layer to disappear or be relaxed, in other words, the central layer and the adhesive layer attempt to equilibrate (balance) with each other in the interfacial region, resulting in a gradient in elongation in the thickness direction. Figure 1 is a graph illustrating how the double-sided adhesive film of the present invention (A in the figure) has a gradient in elongation in the thickness direction (the elongation changes gradually in the interfacial region), while the double-sided adhesive film using a conventional PET base material (B in the figure) does not have a gradient in elongation (the elongation changes suddenly at the interface).

[0090] In this way, since the double-sided adhesive film of the present invention has a gradient of elongation in the interface region, it can be used effectively even when the ratio of the elongation of the resin forming the central layer to the elongation of the resin forming the first and second adhesive layers is 1:20 in either the vertical or horizontal direction.

[0091] The elongation of the three layers or the entire layer when further laminated to three layers in the finished double-sided pressure-sensitive adhesive film of the present invention is 300% or less in both the longitudinal and transverse directions, preferably 20 to 300%, and preferably 250% or less from the viewpoint of punching processability. The tolerance between the longitudinal and transverse elongation rates is ±20% or less relative to one of the elongation rates, and it is particularly preferable that the longitudinal and transverse elongation rates are equal.

[0092] As a result of extensive research, the inventors have found that, like the double-sided adhesive film of the present invention, a film has a structure that generates a gradient in molecular weight, degree of crosslinking, and molecular composition in the interface region between the central layer and the adhesive layer, and by making the tolerance between the longitudinal elongation rate and the lateral elongation rate less than ±20% of one of the elongation rates, it can be stretched uniformly to fit the shape of the adherend and adhered, and further, it can easily undergo plastic deformation (conform) regardless of the shape, movement, and deformation of the adherend, and because the plastic deformation is not lacking in uniformity, it exhibits an excellent stress relaxation effect and can prevent distortion or breakage of the film after application.

[0093] It was also found that it is more preferable for the elongation rates in the longitudinal, transverse and thickness directions to have a tolerance of ±20% or less relative to each other and to the elongation rates in the other two directions.

[0094] In order to obtain the above-mentioned interlayer interface gradient due to stress relaxation, it is preferable that the central layer be formed from a resin having a Tg (glass transition temperature) close to that of the resins forming the first and second pressure-sensitive adhesive layers. For example, the difference between the Tg of the resin forming the first and / or second pressure-sensitive adhesive layers and the Tg of the resin forming the central layer is 1 to 80, preferably 1 to 50, and particularly 1 to 20.

[0095] Furthermore, when the double-sided pressure-sensitive adhesive film of the present invention is required to be conductive, a conductive material such as conductive carbon, zinc oxide, or tin oxide can be dispersed in the pressure-sensitive adhesive layer and the core layer. The particle size of the conductive material is preferably 0.01 to 30 μm, more preferably 0.01 to 0.02 μm. Organic conductive agents such as polypyrrole and polyaniline may also be used in combination.

[0096] The amount of the conductive material is preferably 20 to 40% by weight (20 to 40 parts by weight) of the amount of resin (100 parts by weight) forming the central layer and the adhesive layer, respectively.Furthermore, it is preferable to control the balance between conductivity and adhesive strength by, for example, using a gradient part number such that the conductive material is 40 parts by weight for the central layer relative to 100 parts by weight of the resin forming the central layer, and 20 parts by weight for the adhesive layers on the front and back sides (first adhesive layer, second adhesive layer) relative to 100 parts by weight of the resin forming the adhesive layers (there is a gradient in the number of parts of the conductive material in the thickness direction from the central layer to the first adhesive layer and the second adhesive layer).

[0097] When heat dissipation properties are required for the double-sided pressure-sensitive adhesive film of the present invention, a thermally conductive material such as carbon fiber pieces, aluminum nitride, zinc oxide, nickel, or tin oxide can be dispersed in the adhesive layer and the central layer. The particle size of the thermally conductive material is preferably 0.01 to 30 μm, more preferably 0.1 to 2 μm. The amount of the thermally conductive material is preferably 20 to 60% by weight (20 to 60 parts by weight) of the amount of resin (100 parts by weight) forming the central layer and the adhesive layer. Furthermore, it is preferable to control the balance between thermal conductivity and adhesive strength by, for example, using 50 parts by weight of the thermally conductive material in the central layer relative to 100 parts by weight of the resin forming the central layer, and 20 parts by weight of the thermally conductive material in the adhesive layers on the front and back surfaces relative to 100 parts by weight of the resin forming the adhesive layer (a gradient in the amount of the thermally conductive material in the thickness direction from the central layer to the first adhesive layer and the second adhesive layer).

[0098] In addition, in order for the double-sided pressure-sensitive adhesive film of the present invention to meet the requirements for compliance with the longitudinal and transverse expansion and flexibility of the adherend, the measurement method and measurement values ​​for these requirements conform to JIS-Z-1528 (:2009). However, although the longitudinal and transverse peel angle can be 180 degrees, a 90 degree angle is preferable in order to measure the interlayer stress of the adhesive. This is because, while the peel value at the adherend interface is important, the interlayer stress of the adhesive is also extremely important in adhesive bonding to the adherend as in the present invention, due to the ability to conform to the expansion and contraction of the adherend, including the protection of various sensor functions. In addition, a peel speed of 20 to 200 mm / min is preferable in the 90-degree peel test.

[0099] Below, a 90-degree peel test was carried out on a conventional double-sided tape with a nonwoven fabric substrate and the double-sided pressure-sensitive adhesive film (tape-like) of the present invention, and the results are shown as examples.

[0100] The double-sided adhesive film used in this test was configured as follows: a central layer (weight average molecular weight: approximately 800,000) made of acrylic resin, with a first adhesive layer (weight average molecular weight: approximately 400,000) made of acrylic resin laminated on the surface, and a second adhesive layer (weight average molecular weight: approximately 400,000) made of acrylic resin laminated on the back surface of the central layer.

[0101] The test method was to first cut each evaluation sample to a width of 25 mm. Next, the cut sample was attached to SUS and pressed back and forth with a 2 kg roll. The test piece was then left at room temperature (23°C) for 1 hour. The adhesive strength was then measured by peeling it off in a 90° direction at a peel speed of 50 mm / min.

[0102] FIG. 2 shows the results of a 90-degree peel test on the double-sided pressure-sensitive adhesive film of the present invention, and FIG. 3 shows the results of a 90-degree peel test on a conventional double-sided tape with a nonwoven fabric substrate.

[0103] In a 90-degree peel test, which is a measurement method that evaluates interlayer stress as well, the double-sided adhesive film of the present invention exhibits a gradient of approximately 200% between the load cell start value for peel measurement (approximately 20 N) and the maximum measurement value after load cell measurement (approximately 40 N), as shown in Figure 2 (here, the minimum and maximum peel values ​​are used as the method for evaluating the stress absorption (expansion) characteristics), resulting in a peel value that is approximately 1.5 to 2 times higher than that of conventional double-sided tapes with a nonwoven fabric base.

[0104] [Method for manufacturing double-sided adhesive film] The double-sided adhesive film of the present invention is produced, for example, by the following method.

[0105] The adhesive or its solution is applied to the release paper using a kiss roll coater, gravure coater, knife coater, reverse roll coater, etc. so that the thickness when dried is 10 to 100 μm, and then dried at a temperature of 60 to 120°C.

[0106] The central layer is then laminated onto this, dried at a temperature of 60 to 120°C, and rolled up.

[0107] Furthermore, while rewinding the film, an adhesive or its solution is applied to the central layer using a kiss roll coater, gravure coater, knife coater, reverse roll coater, etc. so that the thickness when dried is 10 to 100 μm, and the film is dried at a temperature of 60 to 120°C and rolled up.

[0108] The double-sided adhesive film of the present invention can be wrapped up into a tape shape with one or both sides covered with a release material. In this case, the above-mentioned wrapping step is followed by a step of slitting the film to the desired tape width.

[0109] Furthermore, the double-sided adhesive film of the present invention can be formed into a sheet shape by covering both sides with a release material. In this case, following the above-mentioned winding process, cutting into any appropriate shape or size is carried out. The formed sheet can then be cut or punched into the desired shape when used.

[0110] The release material may be, for example, paper anchor coated with resin, or a highly peelable resin sheet made of polyethylene, polypropylene, etc., with a release agent such as a silicone-based material applied to the surface if desired.

[0111] Furthermore, in addition to the above, the method for producing the double-sided adhesive film of the present invention may also be a method for simultaneously forming three layers, namely, the central layer, the first adhesive layer, and the second adhesive layer.

[0112] For example, simultaneous three-layer formation using the three-layer T-die method is achieved by placing the raw materials for the center layer, first adhesive layer, and second adhesive layer in an extruder, heating and melting them, then extruding them from a T-die, casting them onto the double-sided silicone release paper surface of a take-up roll, and cooling them.

[0113] When simultaneously forming three layers using the three-layer T-die method, thermoplastic SIS (styrene-isoprene-styrene), SBS (styrene-butadiene-styrene), acrylic, or other random or block copolymer adhesives are preferably used.

[0114] In the case of solvent-based simultaneous three-layer formation, the three-layer T-die and double-sided release paper are the same as those mentioned above, but after casting in the T-die, the film is dried and cooled in a heated dryer.

[0115] In solvent-based simultaneous three-layer formation, the central layer, first adhesive layer, and second adhesive layer are preferably made of acrylic resin, silicone resin, urethane resin, or thermoplastic SIS (styrene-isoprene-styrene), SBS (styrene-butadiene-styrene) adhesives, etc.

[0116] In the case of UV (ultraviolet) reactive solventless simultaneous three-layer formation, the aforementioned three-layer T-die and double-sided release paper are the same, but after casting with the T-die, oxygen is blocked by nitrogen purging and UV irradiation is performed. Note that oxygen can also be blocked by attaching a transparent, UV-transmitting stretched PET film with a thickness of 5 to 200 μm, one-sided release silicone treated product, with the release silicone surface attached to the above-mentioned three-layer formation and irradiating it with UV.

[0117] In UV (ultraviolet) reactive, solvent-free simultaneous three-layer formation, the central layer, first adhesive layer, and second adhesive layer are preferably selected from acrylic resin, silicone resin, urethane resin, or thermoplastic SIS (styrene-isoprene-styrene), SBS (styrene-butadiene-styrene) adhesives, etc., along with a UV initiator. [Example]

[0118] Example 1 [Manufacturing of the central layer] Acrylic emulsion resin (methacrylic ester consists of (weight average molecular weight 600,000, DM772, manufactured by Hoechst Chemical Co., Ltd.) was cast using a casting device (comma coater, OPP film 25 μm thick) and dried at 100°C to form a central layer (film) with a thickness of 10 μm.

[0119] The longitudinal and transverse elongation rates of the obtained central layer were both 180%, and the Tg was 180°C.

[0120] [Preparation of Adhesive Solution A] The adhesive solution for forming the first adhesive layer is an acrylic resin: acrylic acid alkyl ester-vinyl acetate copolymer. consists of An adhesive solution A was prepared using an adhesive (weight average molecular weight: approximately 400,000), for example, SK Dyne 1717 (trademark) manufactured by Soken Chemical Industries, Ltd.

[0121] [Preparation of Adhesive Solution B] As an adhesive solution for forming a second adhesive layer, adhesive solution B was prepared by mixing 100 parts by weight of adhesive solution A with 0.5 parts by weight of tolylene diisocyanate (solid content 45%) as a crosslinking agent.

[0122] [Production of double-sided adhesive film] The adhesive solution A prepared as described above was applied to a release paper using a gravure coater in an amount such that the thickness when dried would be 30 μm, and the paper was dried at 100°C to form a first adhesive layer on the release paper, which was then rolled up.

[0123] While unwinding this, the central layer prepared as described above was laminated on the first adhesive layer, dried at 100°C, and then wound up.

[0124] While rewinding this, adhesive solution B was applied to the central layer formed as described above using a gravure coater in an amount such that the thickness when dried would be 30 μm, and this was dried at 100°C to form a second adhesive layer on the central layer, which was then rolled up.

[0125] The elongation percentages of the first adhesive layer formed as described above in both the longitudinal and lateral directions were 270%, and the elongation percentages of the second adhesive layer in both the longitudinal and lateral directions were 240%.

[0126] [Performance of double-sided adhesive film] The double-sided adhesive film of this example, which was completed through the above-described manufacturing process, had a longitudinal elongation rate of 36% and a lateral elongation rate of 37%.

[0127] The elongation rate of the double-sided adhesive film of this example is reduced to approximately 1 / 10 compared to conventional substrate-less double-sided adhesive films, which reduces the flow of the adhesive film during die cutting or after application to the substrate, and also provides dimensional stability.

[0128] Furthermore, the double-sided adhesive film of this embodiment has improved breaking strength (approximately three times that of conventional substrate-less double-sided adhesive films), and is not brittle as an adhesive film.

[0129] Furthermore, when the obtained double-sided adhesive film was slit into a width of 25 mm using a slitter, no excess adhesive was observed during slitting.

[0130] Furthermore, when the double-sided adhesive film manufactured as described above was attached to an LLDPE (low-pressure polyethylene) film and cut into a 100 mm x 100 mm piece, and then the piece was attached to a sphere (curved surface) with a spherical diameter equivalent to 300 mm (diameter of the sphere), it could be attached without distortion in either the vertical or horizontal directions.

[0131] Furthermore, when the double-sided adhesive tape or sheet manufactured as described above was stored for 7 days in an environment of 80°C and 80% humidity, no defects such as adhesive overflow were observed.

Claims

1. A central layer formed from an adhesive of an acrylic emulsion resin made from a methacrylic acid ester; and pressure-sensitive adhesive layers laminated on the front and back surfaces of the central layer and formed from an acrylic resin consisting of an acrylic acid alkyl ester-vinyl acetate copolymer; A substrateless double-sided PSA film, wherein the weight average molecular weight and crosslinking degree of the resin forming the central layer are greater than the weight average molecular weight and crosslinking degree of the resin forming the PSA layer, The adhesive layer has a structure that generates a gradient in molecular weight and crosslinking degree in the interfacial region between the central layer and the adhesive layer, and The elongation rate in both the longitudinal and transverse directions is within the range of 36 to 37%. A double-sided adhesive film characterized in that the tolerance between the longitudinal elongation rate and the transverse elongation rate is ±1% or less relative to one of the elongation rates.

2. 2. The double-sided pressure-sensitive adhesive film according to claim 1, having a total thickness of 5 to 300 μm.

3. 3. The double-sided adhesive film according to claim 1, wherein the ratio of the elongation percentage of the resin forming the central layer to the elongation percentage of the resin forming the adhesive layer is 1:1 to 1:

20.

4. 4. The double-sided pressure-sensitive adhesive film according to claim 1, wherein the central layer and the pressure-sensitive adhesive layer are non-oriented.

5. The double-sided adhesive film according to any one of claims 1 to 4, characterized in that, in the interfacial region between the central layer and the adhesive layer, molecules in the resin forming the central layer and molecules in the resin forming the adhesive layer are crosslinked.

6. A double-sided pressure-sensitive adhesive film according to any one of claims 1 to 5, characterized in that the elongation percentages in the longitudinal, transverse and thickness directions have tolerances of ±20% or less relative to the elongation percentages in the other two directions.

7. The double-sided adhesive film according to any one of claims 1 to 6, characterized in that the adhesive layer laminated on the surface of the core layer and the adhesive layer laminated on the back surface of the core layer are formed from resins having different adhesive strengths.

8. 8. The double-sided pressure-sensitive adhesive film according to claim 1, wherein a conductive material is added to the central layer and the pressure-sensitive adhesive layer.

9. 9. The double-sided pressure-sensitive adhesive film according to claim 1, wherein a thermally conductive material is added to the core layer and the pressure-sensitive adhesive layer.

10. The double-sided pressure-sensitive adhesive film according to any one of claims 1 to 9, characterized in that fiber pieces are dispersed in the central layer.

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